The National Nuclear Regulator's (NNR) mandate is to protect the people, property and environment from radiological damage. NNR is currently involved in projects to establish the radioactivity of drinking water in the vicinity of authorised sites. It is important that before this, preliminary reference levels which will be used to assess the radioactivity levels in collected samples are established. These reference levels will inform whether the water resource from which the samples were collected poses a radiological threat to human health if ingested. The study seeks to derive preliminary reference levels based on international best practices. Annual Limit on Intake (ALI) was calculated making use of the principles of the World Health Organisation (WHO) which is considered to be international best practice. The calculations factored in different age groups and made use of dose conversion factors provided by the International Atomic Energy Agency (IAEA) in the General Safety Regulations (GSR Part 3). Calculated ALI values for infant, child and adult age groups are presented. The results suggest an insignificant (orders of magnitude) difference in calculated ALI values across ages. Therefore it is recommended that the NNR use calculated ALI for adults as preliminary reference levels. These can be used in assessing the radioactivity status of baseline data that is currently being collected.
Keywords: Drinking water, radioactivity, reference levels
The iThemba LABS fast neutron beam facility (D-line vault) is an international niche facility that can provide ns-pulsed quasi-monoenergetic neutron beams in the energy range of 30 to 200 MeV. Available neutron beam facilities with energy range similar to this facility are described in details by the EURADOS (European Radiation Dosimetry) Report [1]. The facility has remained practically unchanged since it was first built more than 30 years ago and over the years, a number of problems associated with low energy neutron backgrounds in the vault and the stability of the proton beam on target were identified [2].
As a plan going forward and motivation for the vault development, the National Metrology Institute of South Africa (NMISA) designated iThemba LABS facility as an entity responsible for providing traceability for the medium and high-energy neutron measurements in South Africa. This resulted in a formal collaboration between iThemba LABS, University of Cape Town, together with international partners Institute de Radioprotection et Sûreté Nucléaire (IRSN in France), National Physical Laboratory (NPL in UK) and Physikalisch-Technische Bundesanstalt (PTB in Germany) to upgrade the facility in order to achieve ISO/IEC 17025 accreditation status for the medium and high-energy neutron region. We present the status on the progress of the D-line vault upgrade, including results from previous measurements of the neutron background from the original configuration of the vault. Results from these measurements, together with results from Monte-Carlo simulations, were used to reconfigure the physical infrastructure of the D-line vault.
References
[1] Pomp S. et al., “High-energy quasi-monoenergetic neutron fields: existing facilities and future needs”, EURADOS, Braunschweig, Germany, EURADOS Rep. 2013-02 (May 2013).
[2] Mosconi M. et al., "Characterisation of the High-energy Neutron Beam at iThemba LABS", Radiation Measurements 45, 1342-1345 (2010).
Despite advances in cancer treatment, lung cancer remains one of the leading causes of cancer deaths worldwide. Lung cancer can spread through the blood and lymphatic systems, as well as infiltrate healthy tissues underlying the lung, resulting in both distant and local metastasis. The most common causes of death are cancer metastasis and the threat of secondary tumours. The ability of cells to invade, which is largely controlled by cell motility, is an essential aspect of metastases. Photodynamic therapy (PDT), a minimally invasive cancer treatment, is based on the concept of light stimulation of a photosensitizing agent at a certain wavelength, which, combined with an optimum energy density of light activation, induces the photosensitizer (PS) to reach their triplet state, where oxidants causing tumour cell death can form in the presence of molecular oxygen. Due to their physicochemical and optical properties, gold nanoparticles have been shown to improve the effectivity of PDT by increasing the loading potential of the PS within cancer cells, are biocompatible and non-toxic, and give improved permeability and retention. The use of gold nanoparticles in nano-mediated PDT has been shown to cause lung cancer cell death. Several physiological studies, including migration, cell cycle analysis and the extracellular matrix cell invasion assay were carried out in this study to determine whether PDT using a gold nano sensitizer inhibits lung cancer migration and invasion. The results show that nano mediated PDT treatment of lung cancer inhibits lung cancer migration and invasion, causes cell cycle arrest, and reduces lung cancer proliferative abilities, elaborating on the efficacy of nano mediated PDT treatment of lung cancer.
Mitogen Activated Protein Kinase (MAPK) signalling is one of the best characterised signal transduction pathways in cell biology and is involved in wound healing processes. Photobiomodulation (PBM) has been used to induce physiological changes and has been shown to improve wound healing processes, however underlying molecular and cellular mechanisms of action remain largely unexplained. The purpose of this study was to determine the effect of PBM at 660 nm on nuclear translocation of MAPK and release of basic fibroblast growth factor (b-FGF) in diabetic wounded fibroblast cells in vitro. This was evaluated by irradiating cells at a wavelength of 660 nm with 5 J/cm2 and incubating them for 24 and 48 h. Non-irradiated cells (0 J/cm2) served as controls. b-FGF was measured by the Enzyme Linked Immunosorbent Assay (ELISA) and translocation of phosphorylated MAPK was assessed by immunofluorescence. PBM of diabetic wounded cells showed an increased release of b-FGF and translocation of MAPK in irradiated cells at 24 and 48 h as compared to non-irradiated cells. The findings of this study showed that PBM is capable of facilitating the releasing of b-FGF and activation of MAPK in diabetic wound cells in vitro, thus facilitating wound healing under diabetic conditions.
The central nervous system (CNS) of mammals is limited in its repair and regeneration in the event of injury due to trauma or neurodegeneration, therefore, optimization of its regeneration capabilities is necessary. Studies have shown that this issue may be addressed through the transdifferentiation of adipose-derived mesenchymal stem cells (ADMSCs) into neuronal cells. This process has not been efficiently achieved with chemical and biological inducers; this study explored possible optimization through the addition of photobiomodulation (PBM). PBM uses low intensity light to stimulate intracellular processes and has been known to increase cell proliferation and aid in stem cell differentiation. This in vitro research aimed to differentiate ADMSCs with growth factors and chemical inducers and subsequently measure the optimization effects that PBM had on differentiation. PBM was applied as single use at a low energy density, at visible and near-infrared (NIR) wavelengths. Characterization of immortalized ADMSCs (iADMSCs) with ELISA, immunofluorescence microscopy, and flow cytometry was used in identifying specific transcription factors and neuronal markers. After this, biochemical analysis was performed to observe reactive oxygen species (ROS) production, cytotoxicity, migration abilities for homing, morphology, proliferation, and the mitochondrial membrane potential (MMP). Probable results will be effective ADMSC transdifferentiation to neuronal cells through induction with growth factors and PBM support. Moreover, an optimized protocol for in vitro differentiation of ADMSCs will be established for subsequent use in clinical application and regenerative therapy in the event of damage to the CNS.
Metastatic Melanoma (MM) is highly aggressive and is among cancers causing major global deaths annually. It is imperative to find therapies that can eliminate MM and has become a major concern due to the potential for cancer relapse and metastasis, as well as the disease being accounted to be resistant to multiple forms of therapy. This in vitro study explores the effect of Photodynamic Therapy (PDT) using an Aluminium Phthalocyanine Photosensitizer (AlPcS4Cl) at 673 nm and a fluency of 5 J/cm2, in targeting Melanoma cells (A375). Dose dependent response of AlPcS4Cl was studied on both A375 and fibroblast (WS1) cell lines and the IC50 calculated from this. Significant post-irradiation signs of cell death were detected using microscopy and biochemical assays. Cell viability testing showed increased damaged cells taking up Trypan Blue Dye. A decrease in cell proliferation was observed through the measurement of Adenosine Triphosphate (ATP) content. An increased release of Lactate Dehydrogenase (LDH) content due to cytotoxicity with increasing doses of AlPcS4Cl was measured. The study suggested an effective treatment against Melanoma cells. Enhanced capabilities of PDT for MM could possibly be achieved through gold nanoparticle (AuNP) activated increased uptake of AlPcS4Cl photosensitizer, targeting their quiescent cancer stem cells.
Abstract. Colorectal cancer (CRC) is a fatal malignancy with limited therapeutic options and its incidence is on the rise in recent years. Photodynamic therapy (PDT) has emerged as a promising minimally invasive therapeutic modality that employs three fundamentals to induce tumour damage: a photosensitizer (PS), light of a specific wavelength and molecular oxygen. However, PDT has shown undesirable lack of specificity for tumour cells. The aim of this study was to develop a targeted PDT multicomponent nanoparticle-antibody (ZnPcS4 – AuNP-PEG5000-SH-NH2 - Anti-GCC Ab) based system that is capable of enhanced and targeted ZnPcS4 PS delivery within in vitro cultured CRC cells (CaCo-2) for improved PDT treatment. The final conjugate was successfully synthesized and characterized to confirm the efficient binding of the antibody and PS to functionalized gold nanoparticle surfaces. Immunofluorescent results noted that the final actively targeted PS nanoconjugate was able to actively and specifically localize in target CRC cells only. Thus, the increased bioavailability of ZnPcS4 PS in CaCo-2 cells elicited significant cytotoxic responses, suggesting that through nano active targeting the enhanced PDT treatment of CRC can be achieved.
Cancer is a global emergency that needs instant intervention. Breast cancer is the second most common cancer after Lung, and the first most common cancer amongst women. Current treatments are linked with adverse side effects, treatment failure and cancer relapse. Photodynamic therapy (PDT) is one of the emerging cancer treatment options that is highly selective and specific towards cancer cells. Consequently, the use of gold nanoparticles (AuNP) further enhances the efficacy of PDT. In this study, gold-nanoparticle (AuNP) conjugated Hypericin (Hyp) mediated PDT was used for the treatment of MCF-7 human breast cancer cells by inducing cell death, in vitro. Cellular responses after treatment at 12 and 24 h incubation post PDT, and at different laser fluencies was observed. The morphological changes, viability, cytotoxicity and cell death analysis by Annexin V/PI staining was performed. The results showed activation of the apoptotic pathway with characteristic features of dying cells observed in their morphology and biochemical responses. Hence this study provided an insight into the application of advanced PDT in breast cancer treatment by actively targeting the apoptotic cell death pathway in vitro.
Speaker: Benjamin Hlope, Director of Technology Operations at Kutleng Engineering Technologies
Speaker: Dominque Adams, Project manager at Data Convergence
Speaker: Rinae Nnduvheni, Intelligence and Insights Lead at EY Consulting
Structuring materials to exhibit phenomena such as negative refractive indices and near-zero indices has given rise to an exciting class of materials, known as metamaterials and their 2D counterparts, metasurfaces. Due to these unique properties and the ability to control the size, shape, density and orientations of these materials, one is able to have unprecedented control of their impact on light striking these structures. Controlling light with subwavelength-designed metasurfaces (MSs) has thus allowed for the arbitrary creation of structured light by precisely engineering both the material and composite structures formed from them. With structured light modes such as those carrying orbital angular momentum (OAM) taking hold in many fields from communications, cryptography and optical trapping to metrology, it follows that arbitrary generational control and easily employed devices such as these can form an important part in helping develop these fields.
As such, we characterize both the purity and conversion efficiency of such MSs, designed to generate hybrid twisted light modes, which exemplify the versatility of the imparted properties that are possible. Here we used a recently reported method to design and fabricate meta-surfaces that exploit generalized spin-orbit coupling and propagation phase to produce vector OAM or twisted states with asymmetric superpositions; this allowing for one to break the symmetrical restrictions imposed by previous classes of such devices. Here, the symmetrical restrictions are broken both in the input spin states required for the modal patterning as well as the OAM values paired in each device. For example, asymmetrical charges of 1 and 5 are coupled to linear and circular polarization states in addition to fractional vector OAM states with charges of 3.5 and 6.5 being generated on the same device. The common symmetrical conjugate spin and OAM of 1 is also demonstrated as reported in previously restricted spin-orbit coupling devices. The generated structures of the resulting beams are quantitatively studied here, by exploiting the reciprocal nature of light. We thus establish both the purity and conversion efficiency with conversion efficiencies exceeding 75% and purities in excess of 95%, yielding good modal quality.
The class of R2T2X intermetallics (R = rare earth, T = transition metal, X = main group) have a geometrically frustrated R-lattice which forms layers arranged in a Shastry-Sutherland lattice. In addition, due to the basic triangular motif in the frustrated structure, stabilization of different nearest-neighbor J values leads to complex low-temperature magnetic behavior. In this work, we have synthesized the Pr2Pd2In compound by arc-melting technique. The powder X-ray diffraction spectrum with a full-profile refinement confirms that Pr2Pd2In crystallizes in the layered Mo2B2Fe-type tetragonal structure, where planes of R = Pr ions lie on a triangular network. Dc-magnetic susceptibility shows that the Pr ions are in the magnetic trivalent state. Field-dependent magnetization shows metamagnetic behavior in the compound with the critical field of 1.5 T at 2 K. The antiferromagnetic order is unstable in applied magnetic fields, becoming ferromagnetic beyond a field value of 1.5 T. The magnetic entropy from our heat capacity studies revealed that the magnetic ground state is a well-isolated doublet. The electronic heat capacity coefficient value estimated from C4f data indicated that the compound belongs to the heavy-fermion family. The variety of magnetic properties such as para- ferro- and antiferromagnetic behavior including metamagnetic transition is observed due to the magnetic frustration from distorted triangles of Pr-atoms in Pr2Pd2In. This study may contribute towards a better understanding of the physics in Shastry-Sutherland structure compounds since in a frustrated lattice system such as this there are strict constraints imposed upon the magnetic order parameter.
Multiferroic rare-earth composites in thin-film format have shown promising results towards the attainment of strong coupling of ferroic orders (ferroelasticity, ferromagnetism, ferroelectricity, and ferrotoroidicity) at room temperature, which is a key parameter to the realization of low-energy dissipating devices such as solid-state refrigerators, spintronic memory storage, etc. In this work, we have synthesized Tb-MnO based thin films on (001) Si at ambient temperature using radio frequency magnetron (RF) sputtering at 50 W and investigated their elastic and magnetic properties. The elastic properties of the films have been measured by surface Brillouin scattering (SBS) at ambient temperature, optimized, and fitted with data simulated using surface Elastodynamic Green’s function for discrete phonon dispersion in the k//d range of 0–5. By least-squares fitting approach, the measurement uncertainties have been obtained from the Taylor series expansion of the phonon phase velocity dependence on the primary elastic constants (C11 and C44), yielding the optimum values as; C11 = 180 +/- 4.90 GPa and C44 = 43 +/- 0.89 GPa. On the other hand, the magnetic properties of the films have been studied by vibrating sample magnetometry (VSM). The films have been noted to attain ferromagnetic ordering at T<150 K. Spin-glass-like behaviour associated with competing ferromagnetic and antiferromagnetic magnetic ordering has also been observed at T~50 K.
Keywords: Multiferroics, thin-film, elastic constants, ferromagnetism, spin-glass
Impact of Helium (He) in the migration of strontium implanted 6H-SiC
T.F. Mokgadi$^1$, T.T. Hlatshwayo$^1$, M. Msimanga$^2$, V.A. Skuratov$^3$
$^1$ Physics Department, University of Pretoria, Pretoria, South Africa.
$^2$ Physics Department, Tshwane University of Technology, P Bag X680, Pretoria 0001, South Africa
$^3$ Joint Institute for Nuclear Research, Dubna, Russia
Silicon carbide (SiC) is regarded as the main candidate material for nuclear energy application, such as a structural material in future fusion reactors and as fuel cladding in future generation fission reactors, based on its low neutron capture cross-section, outstanding chemical and thermal stability. In fission reactors such as the PBMR, the fuel particle (TRISO particle) where SiC is the main diffusion barrier of fission products (FPs), is able to retain most of the radiologically important FPs with the exception of strontium ($^{90}$Sr), Europium (Eu) and silver (Ag). $^{90}$Sr is an isotope of naturally occurring nontoxic and nonradioactive strontium, it is also a by-product of fission reactions in nuclear reactors with yields of about 5.7% and 6.6% from U-235 and U-233, respectively. It has a half-life of about 29 years and undergoes a beta decay into yttrium-90 ($^{90}$Y) accompanied by a decay energy of about 0.55 MeV. This, is the more reason why it is important to investigate the retention of Sr in the TRISO particle, specifically SiC. Simultaneous to the release of FPs in fission reactions is the release of alpha-particles. Alpha-particles/helium ions (He$^+$) are a product of nuclear reactions with generation rates of about 2.5 appm He/dpa and have been reported to form bubbles in SiC which in the long run compromises its structural integrity. Therefore, in the nuclear reactor environment SiC will be exposed to high dose, temperature irradiation, and He$^+$ generation. We will be presenting the results of a study that looks into the dual implantation of Sr and He at room temperature and the impact of He bubbles in the Sr migration in SiC at high temperatures.
Demands for higher performance of solar cells have led researchers to non-sophisticated, low temperature crystal-growth processes like spray pyrolysis and sol-gel spin coating as the future of efficient solar cells technology as stability remains challenge. This project seeks investigation of Beta-Gallium Trioxide (β-Ga2O3) for solar cells passivation to improve their stability and PCE, insulating barrier in light junctions, gas sensors, luminescent phosphors and dielectric coating for solar cells. In spray pyrolysis, precursor Tetrahydroxogallate (III) Ammonium from Gallium Nitrate with 32% concentrated ammonium hydroxide was deposited on 1cm2-Sapphire substrate at 3200C and 2.4kPa. In spin coating, precursor viscosity was improved by the addition of Monoethanolamine. Monocrystalline β-Ga2O3 was obtained by post annealing films at 7500C and investigated using XRD to determine crystallite size and orientation, Raman spectroscopy, EDX to determine percentage of elements composition and SEM to image film morphology. Film thicknesses were determined by profilometry, transmittance and absorbance were determined by UV-Vis spectroscopy and used to determine optical band gaps by Tauc technique. Spin coated films had orientation along (-201) with thickness range 165nm-354nm having 16.08nm grain size and optical band gap range 4.59eV-4.99eV. Films from spray pyrolysis had (-201) orientation with thickness range 158-255nm, grain size of 15.52nm and band gap 4.60eV-4.93eV that showed a broad emission in UV-blue region originating from oxygen and gallium vacancies in lattice; an essential component for good photodetectors and vital for solar cells passivation since dielectric coating with β-Ga2O3 will reduce refractive index between air and solar cells, hence improve solar energy absorption.
A series of undoped mixed phase BaAl2O4/CaAl4O7 (hereafter called BC) and doped BC:x% Eu3+ (0 < x ≤ 5.5) mixed phases nanophosphors were successfully prepared by the citrate sol-gel technique. The structure, morphology and optical properties of the nanophosphors were studied in details by the X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and Photoluminescence (PL) spectroscopy. XRD and SEM showed that all the BC:x% Eu3+ samples consists of the crystalline structure of the mixed phases of both the BaAl2O4 and CaAl4O7 materials. The structure resembles more of the BaAl2O4 than the CaAl4O7 phase. The TEM results suggest that crystallite sizes are in the nanometer scale with rods-like particles. PL results showed multiple emission peaks located at 436, 590, 616, 656 and 703 nm, which were assigned to the intrinsic defects within the BC matrix, 5D0 → 7F1, 5D0 → 7F2, 5D0 → 7F3 and 5D0 → 7F4 transitions of Eu3+, respectively. The decay curves evidently showed that the nanophosphors have persistent luminescence. The Commission International de l’Eclairage (CIE) analysis revealed that BC emits a blue colour while the Eu3+-doped BC phosphors emit in the orange-red region. The results indicate that the Eu3+-doped samples can potentially be used in the orange/red-emitting phosphors.
Open quantum walks (OQWs) have been introduced as a type of quantum walks which are entirely driven by the dissipative interaction with external environments and are defined in terms of discrete completely positive trace-preserving maps on graphs [1]. Recently, a quantum optical scheme for the experimental realization of OQWs was proposed [2]. In the proposed scheme, a two-level atom plays the role of the "walker" and the Fock states of the cavity mode correspond to the lattice sites of the OQW. Using the small unitary rotations approach and rotating wave approximation the effective dynamics of the system is shown to be an OQW. The presence of spontaneous emission in the system was an essential ingredient for obtaining an OQW. In this contribution, we solve this OQW analytically using generating functions. We used the obtained solution to construct the moments of this quantum walk explicitly. The dynamics of the observables (mean, variance) are presented for various parameters.
Keywords: Open quantum walks; quantum optics; quantum dynamics engineering.
References:
[1] S. Attal, F. Petruccione, C. Sabot and I. Sinayskiy, J. Stat. Phys. 147 (2012), 832.
[2] I. Sinayskiy and F. Petruccione, Int. J. Quantum Inform. 12 (2014), 1461010.
Emerging quantum technologies rely principally on quantum phenomena such as superposition and entanglement for their unique capabilities. To this end, it is essential to develop well-defined and efficient protocols to produce and further exercise control over states of quantum bits that exhibit desired quantum mechanical traits. From a pure separable multipartite state, a control sequence, which includes rotation, spin squeezing via one-axis twisting, quantum measurement and post-selection, generates a highly entangled multipartite state, which we refer to as a Projected Squeezed ($PS$) state. Through an optimization method, we then identify parameters required to maximize the overlap fidelity of the $PS$ state with the maximally entangled Greenberger-Horne-Zeilinger ($GHZ$) state. The method leads to an appreciable decrease in the state preparation time of $n$-qubit $GHZ$ states when compared to preparation through unitary evolution. The efficiency of the $PS$ state protocol is studied in non-ideal experimentally relevant settings by simulating decoherence channels using numerical methods.
The theoretical framework behind modern-day quantum optics has been successful in explaining a number of interesting phenomena. However, since it is traditionally formulated using ordinary quantum mechanics and Fourier optics, it cannot account for relativistic notions such as different reference frames (including non-inertial ones) or curved classical gravitational backgrounds. In an attempt to understand the quantum imaging process within a more complete quantum field theory (QFT) framework, a novel analogy is proposed: so-called Unruh-DeWitt (UDW) detectors can be used to model both the object one wishes to image as well as the pixelated imaging device itself. As an example, after coupling a QFT version of a biphoton state created via spontaneous parametric down-conversion (which is one of the principal processes used to create entangled photons in the laboratory) with arrays of Unruh-DeWitt detectors, we investigate quantum ghost imaging under both inertial and accelerating conditions. Given that the reconstructed images can be discerned better than a pure guess, the formalism appears capable of describing the quantum imaging process in non-trivial reference frames.
Traditionally, quantum key distribution (QKD) is used for sharing secret key between two distant authorized participants with unconditional security. Here, we extend the reach of QKD by proposing a reference frame independent quantum key distribution (RFI-QKD) which allows three legitimate parties to share the common secret keys without any alignment of reference frames in their quantum channels. Furthermore, we relax the assumption of perfect state preparation by employing loss tolerant technique proposed by Tamaki et al. [Phys. Rev. A 90, 052314 (2014)] in our security proof, which makes the proposed protocol suitable for practical applications. In addition, we derive bounds of the proposed RFI-QKD protocol by considering finite-size key security analysis against general attacks in the presence of statistical fluctuations. The simulation results show that the performance of RFI-QKD with an imperfect source is comparable to that of RFI-QKD with a perfect source. Also, we investigated the impact of reference frame misalignment on the stability of our protocol for drifting of reference frames by angles 𝛽 = 𝜋/4, 𝜋/6 and 𝛽 = 𝜋/8. Remarkably, our results demonstrate that our proposed protocol is not heavily affected by an increase in misalignment of reference frames as the achievable transmission distances are still comparable to the case where there is no misalignment in reference frames (when 𝛽 = 0). The proposed protocol has immediate application in quantum network scenarios such as web conferences and online courses, where there are more than two users who need to share keys.
In this contribution, we present the results of calculations for the ground state energy of H2+ employing Sinc functions as a basis set as discussed for a number of
examples in [1]. The modifications required to the basis functions to make them suitable for calculating the ground state energy of H2+ as well as the application of the cusp factor formulism [2] are outlined. Finally the resulting energies are investigated as a function of the number of basis functions and double-logarithmic fits are performed. It is found that they converge with an order of at least six.
[1] Proceedings of 64th SAIP Conference 2019, ISBN: 978-0-620-88875-2, edited by Prof. Makaiko Chithambo, p 347
[2] Eur. Phys. J. B. (2019) 92: 230
Molecular machines, known as motor proteins, walk along configurations of filamentous proteins which make up the cytoskeleton of a cell. These motor proteins, for example kinesins, are responsible for transporting a variety of cargoes within the cell. The arrival of the cargoes at specific locations within the cell are imperative for the successful execution of various cellular processes, including cell division. Although much detail is known about the different proteins that are able to transport certain cargoes, the exact processes that influence the distribution of these cargoes throughout the cell are still unclear. Whilst theoretical models may provide further insights into intracellular processes, there is an absence of such models describing the dynamics and diffusion of motor proteins throughout the interior of cells. In light of this, the aim of this talk is to explore possibilities for analytical modelling of the motion of motor proteins within the context of a cell. To begin this exploration, the Langevin dynamics of a single motor protein transporting a cargo as it progresses along different configurations of a single filament will be considered. The mathematical challenge posed by modelling this process in a similar manner for more intricate filament configurations will then be addressed through a combination of a dynamical field theoretical formalism with a networking theory employed in polymer physics (see e.g. [1]). The talk will be concluded with a glimpse of how the formalism may allow for the extension of the model to describe transport over a density of filaments that one might expect to find within a cell.
[1] S. F. Edwards, “A field theory formulation of polymer networks,” J. Phys. Fr., vol. 49,
pp. 1673–1682, 1988.
In December 2017, the Executive Board of the SA-CERN Consortium approved an investment in the local research infrastructure at the University of Zululand. As a result, an Electronics Research Laboratory was developed and completed in 2019. The laboratory host state of the art electronics test equipment and it was enhanced when the Centre for High Performance Computing (CHPC) in Cape Town deployed a High Performance Cluster (HPC) to the institution. While it services members of the ATLAS team in South Africa who are heavily involved in the TileCal Instrumentation upgrades at CERN, the laboratory goes beyond just the ATLAS group to accommodate other research groups. This presentation focuses on possible projects that can be dealt with in this laboratory. It is to create an awareness to the Physics community, especially the Nuclear and High Energy Particle Physics groups, on what the laboratory offers.
Key words: Electronics Research Laboratory, State of the Art Test Equipment, High Performance Computing.
This study presents the results of irradiation tests used to qualify the End-of-Substructure (EoS) card for operation within the ATLAS Inner Tracker (ITk) at the High Luminosity Large Hadron Collider (HL-LHC). The EoS card is responsible for interfacing the data, command, and power signals between on and off-detector electronics. The radiation environment within the ITk poses a challenge for electronics as energized particles are capable of upsetting the logic, referred to as Single Event Upsets (SEU), of the constituent components, resulting in corrupted data. The irradiation test setup at the University of Cape Town is outlined and the steps taken in the experiments are discussed. The results found indicate that one of the primary ASICs on the EoS card is susceptible to SEUs under experimental conditions.
Four major experiments for the High Luminosity Large Hardron Collider (HL-LHC) are upgraded to accommodate an increase in luminosity. ATLAS (A Toroidal LHC ApparatuS) is part of these four major experiments and it is upgraded to investigate a wide range of physics. The detector is divided into long barrel and two extended barrels. The Tile Calorimeter (TileCal) is part of the ATLAS detector and is the central hadronic calorimeter. The main aim of the TileCal Phase-II upgrade is to completely redesign the on- and off-detector electronics. The Tile PreProcessor (TilePPr) is part of the off-detector electronics and it is responsible for storing the detector data with a total data bandwidth of 40 Tbps. University of the Witwatersrand is contributing 24 % to the total design and production of boards toward the TilePPr. The TilePPr is made up of numerous components and University of the Witwatersrand is responsible for Tile GbE Switch and TileCoM components.
In the beginning of 2025, the Large Hadron Collider (LHC) will be shutdown in order for the final upgrades to the High Luminosity LHC (HL-LHC) to commence. This will almost quadruple the amount of collisions in the LHC, increasing the amount of data the detectors will have to deal with. Since the detectors were not designed to operate at these levels, they will also need an upgrade to deal with the increased radiation, data rates and amount of particles travelling through the detectors. One of the most extensive upgrades to the ATLAS detector will be the replacement of the current Inner Detector (ID) with an all silicon semiconductor based Inner Tracker (ITk). However, not only will the actual detector be upgraded, but the simulation of the detector will also need to be updated to match this new version. An accurate simulation of the detector is important since this is what is used to convert the outputs of the theoretical calculations (be it Standard Model (SM) or Beyond the Standard Model (BSM)) into a format that can be directly compared with the data coming from the experiment. Presented is some of the work behind updating the simulation of the strip detector in the ITk, from the sensors to the support structures and shielding components.
Power Electronics used in high-energy physics experiments at the Large Hadron
Collider (LHC) more specifically the ATLAS detector, which are custom built and have to work reliably in the presence of ionizing radiation and an ever present magnetic field. In many such applications, owing to cost constraints, Commercial Off-The-Shelf (COTS) components are often used instead of components that are radiation-hard by design. Moreover, design complexity, verification effort, and scalability issues in centralized structures can impede performance improvement in monolithic designs. This talk presents the steps followed for upgrading and re-designing a radiation tolerant low voltage power supply for a large scale operation and the considerations made for such a design. This includes measurements taken at component level, system level, and radiation tests done using the newly upgraded low voltage power supply
The start of the operation of the High Luminosity LHC (HL-LHC) is planned
for the year 2027. The planned increase in luminosity provides the opportunity for further
scientific discoveries within the field of particle physics as well as many technical challenges
associated with the new HL-LHC environment. Due to these environmental changes the ATLAS
Tile-Calorimeter (TileCal) is to undergo its Phase-II upgrade in 2025 in order to ensure peak
performance in the coming years. To this end the University of the Witwatersrand Institute for
Collider Particle Physics, iThemba Labs, and SA-CERN, in collaboration with the University of
Texas at Arlington, are currently undertaking the development and production of approximately
2300 Low-Voltage Power Supply (LVPS) Bricks. In order to ensure the reliable operation of
these Bricks on-detector an extensive quality control procedure is to be implemented. This
procedure is two-pronged in its approach. Firstly, initial testing is undertaken to ensure
various performance metrics such as the Bricks output voltage are met. After which, the
Bricks undergo Burn-in testing which functions to improve the reliability of the components via
accelerated aging. Both of these processes require custom test apparatus which take the form
of the Initial and Burn-in test stations. This presentation will provide an overview of these test
stations including their hardware, software, and the certification of the Bricks before installation
within TileCal.
Electric Field Induced Second Harmonic (EFISH) generation is a technique to probe the structure of and charge transfer across buried interfaces. It is particularly suitable to study the Si/SiO2 interfaces that are crucial in electronics undergoing continuous miniaturization. This makes it important to investigate the interaction of the front and rear Si/SiO2 interfaces of thin silicon membranes. EFISH signals typically increase quadratically with both the pump beam intensity and the quasi-static electric field that builds up over the interface due to photo-induced charge transfer.
The EFISH signals from the front and rear Si/SiO2 interfaces of thin silicon membranes (10-30 micron thick, slightly p-doped) were generated by a laser beam (Ti:sapphire laser tuned to 800 nm, 90 fs pulse duration at 80 MHz repetition rate) transmitted through the membrane. Detailed measurements on samples with different thicknesses have confirmed counter-intuitive results that for thin samples the EFISH signal generated at the rear interface is stronger than that at the front interface in spite of attenuation of the incident beam. These results lead to a hypothesis that the quasi-static electric field at the rear interface consists of two counteracting components and the degree of interaction between the front and rear interfaces varies significantly with thickness over the 10-30 micron range. It is also shown that the effective third order susceptibility for the EFISH-active layers at the rear interface is larger than that at the front interface which paves the way for future theoretical modelling.
Light sheet fluorescence microscopy is a powerful tool within the field of microscopy. The inherent advantages over other fluorescence microscopy techniques inclue high sectioning capabilities, reduced photo-damage in the sample and short data acquisition times.
In this presentation, the development of a light sheet microscope is described. The system relies on the use of a thin sheet of light to illuminate a fluorescent sample. The light sheet can be generated using a cylindrical lens or by rapidly scanning a circular beam using a galvonometer. Two dimensional images are acquired perpendicular the the illumination path. The sample can be translated through the light sheet, acquiring images at different depths in the sample. The images are then used to reconstruct a three dimentional fluorescence image of the sample.
The light sheet microscope system is developed to allow for the incorporation of various light sheet generation techniques, allowing for the parameters of the light sheet to be tailored for various applications. The implementation of the scanned beams to generate light sheets allow for the use of non-diffracting beams. A comparison of the results for various light sheet generation techniques are presented. Using the microscope, images are acquired and analysed to demonstrate the systems capabilities and limitations. Image restoration is implemented by the deconvolution of the point spread function and the images. Using the deconvolved images, three dimensional fluorescence images of the sample are obtained. The result is a multi-purpose light sheet microscope for use in biological imaging.
Optical tweezers have found countless applications in the fields of physics and biology ever since its advent in 1986 by Arthur Ashkin. Using only focused light, optical tweezers are able to trap and manipulate microscopic particles. In this work, we investigate the possibility of combining the optical tweezer with fluorescence spectroscopy to develop an ultra-sensitive analytical instrument. We specifically focus on the feasibility of quantum dot nanoparticles used in conjunction with optical tweezers. In this work, we report on the synthesis of L-cysteine capped CdSe/ZnS quantum dots (QDs) and the coupling thereof to commercial carboxyl-modified beads. The QD-tagged beads which are two µm in diameter can be trapped with the optical tweezers and will be used as the fluorescence probe. A setup of an optical tweezer with a 532 nm laser was employed with which trapping of particles was demonstrated. The detection of fluorescence emission from the QDs that are covalently bonded to the beads was also demonstrated with the optical tweezer. This research, therefore, serves as a proof of concept for a sensitive analytical method that makes use of an optical tweezer in combination with fluorescent QDs.
We investigate Mie scattering from particles in an optical trap. Optical tweezers and counter propagating optical traps allow micron sized particles to be optically trapped and investigated by scattering white light off the particles. In optical tweezers, a high numerical aperture microscope objective is used to focus a laser beam and create an optical trap for microscopic particles, such as polystyrene beads or biological cells suspended in water. The trapped particle has a higher refractive index than the medium which surrounds the particle. The light refracts through the particle and due to conservation of momentum, a net force pushes the particle towards the focus of the beam. In a counter propagating optical trap, microscope objectives with a longer working distance can be used. Using two high numerical aperture microscope objectives, two counter propagating beams create a trap where the two foci overlap in space. The design and construction of the counter propagating optical trap will be discussed. In this work, the ultimate aim is to trap microscopic water droplets suspended in air. Once trapped, the droplet’s morphology can be studied using whispering gallery modes, also known as morphologically dependent resonances, formed within the particle when it is illuminated with white light. Specific wavelengths resonate within the spherical cavity due to total internal reflection of the light. These resonances can be seen on the measured spectrum of the Mie scattered light from the particle. By comparing the spectrum of the scattered light to that predicted by Mie Theory one can precisely determine the particle’s diameter and/or its refractive index. Mie scattering theory and simulations will be briefly discussed to illustrate this.
Any image of a point source in a diffraction-limited system will result in a blurred pattern, the point spread function (PSF). In the case of fluorescence microscopy, incoherent imaging modality can be described by a convolution of the object with the PSF, a common approach to improve the image quality tries to undo this convolution. A successful deconvolution requires a good model of the PSF [1,2]. A practical way to obtain a PSF is by measuring it experimentally and averaging over images of multiple fluorescent beads with diameters far below the diffraction limit of the system, but the photon noise and small depth of field in the region of interest can limit its use [3]. Studies have been conducted for computing PSFs. Each technique has its own pros and cons. In this work, we present novel approaches for computing PSFs and we aim to validate the models experimentally.
Important parameters of the imaging system such as it satisfying the aplanatic condition and a possible refractive index mismatch are included in our theoretical PSF models. Aberrated PSFs with varying spherical aberration are measured by varying the refractive index of the embedding medium of the bead sample and/or the immersion medium. A high fidelity of a theoretical PSF model to represent the imaging system corresponds to the normalized cross-correlation (NCC) to the ground truth, which is the experimental PSF, being close to one. The accuracy of the PSF models are also tested by using them in image reconstruction. To this aim, we image a spherical sample object of diameter four times higher than the diffraction limit and retrieve the most accurate representation of the object by deconvolving the recorded image of the object with the theoretical aberrated PSFs and the experimental PSF. The accuracy of each PSF model is deduced from the NCC between the deconvolved image and the ground truth, which corresponds to our input sample object.
As a result, PSF models, which uses Fourier transform as a mathematical operator deviate significantly from the ground truth at higher depth if the window size of the image is too small. A combination of adjusted windows sizes and using the Chirp-Z transform prevents this large error but ads computational costs. This experimental validation and comparisons with respect to the precision and accuracy of each PSF technique under a given condition are discussed in depth in this presentation.
[1] Griffa A, Garin N, Sage D. Comparison of deconvolution software in 3D microscopy: a user point of view—part 1. GIT Imaging & Microscopy. 2010;12(ARTICLE):43-5.
[2] Griffa A, Garin N, Sage D. Comparison of deconvolution software: a user point of view—part 2. GIT Imaging & Microscopy. 2010;12(ARTICLE):41-3.
[3] Diaz Zamboni JE, Casco VH. Estimation Methods of the Point Spread Function Axial Position: A Comparative Computational Study. Journal of Imaging. 2017 Mar;3(1):7.
[4] Ghosh S, Preza C. Fluorescence microscopy point spread function model accounting for aberrations due to refractive index variability within a specimen. Journal of biomedical optics. 2015 Jul;20(7):075003.
Resonance Ionization Spectroscopy (RIS) is a spectroscopic technique that relies on the resonant excitation of an atom using lasers. The process involves series of atomic excitations, with at least one resonant transition, and ends when the atom is ionized. The RIS process can be applied in the production and study of rare and exotic nuclei via radioactive ion beams at accelerator facilities such as ISOLDE at CERN or LERIB at iThemba LABS. RIS can also be used to enhance the production and quality of isotopes used for medical applications.
The main aim of this project is to improve and optimize an existing RIS setup for the study of the various stable isotopes of tin. Tin is an important element in the study of nucleus structure as it has a high stability due to completely filled proton shells, and therefore a large number of isotopes. In this presentation, we report on the different methods applied at the RIS facility at CERN while highlighting key differences, advantages, and disadvantages of the methods used. We also report on the progress made at the RIS lab at Stellenbosch University and the future plans for applications.
The electron transport model is one of the consensus models currently used to teach DC circuits worldwide. The model explains current in terms of the flow of electrons. Regardless of its frequent use in high schools to explain DC circuits, the model was ineffective in helping students to understand the topic of DC qualitatively. The electron transport model also fail to provide a complete and coherent account of how electrons are involved in the transportation and distribution of energy around the circuit. As an alternative to the electron transport model, the field model was used during intervention to teach DC circuits to pre-service teachers at the University of Johannesburg. The current study reports the impact of the field model on preservice students’ qualitative understanding of DC circuits as measured by the international DIRECT concept test instrument.
The Force Concept Inventory (FCI) can be used as an assessment tool to measure the gains in a cohort of students. In this study it was given to first year mechanics students pre- and post-mechanics lectures, for students at the University of Johannesburg. From these results we examine of the change from traditional classes to online classes, as imposed by the COVID-19 lockdown. Overall gains and student perspectives indicate no appreciable difference of gain, when bench-marked against previous studies using this assessment tool. When compared with 2019 grades, the 2020 semester grades do not appear to be greatly affected. Furthermore, initial statistical analyses also indicate a gender difference in mean gains in favour of females at the 95% significance level. A survey given to students also appeared to indicate that most students were aware of their conceptual performance in physics, and the main constraint to their studies was due to difficulties associated with being online. As such, the change in pedagogy and the stresses of lockdown were found to not be suggestive of a depreciation of FCI gains and grades.
In South Africa, only 22% of households have a computer, and 10% have an internet connection at home. This disparity has exacerbated education inequalities during the COVID-19 pandemic; school closures and limited online schooling saw learners struggling to catch up – especially in crucial subjects like Science and Mathematics. The iNethi project seeks to solve the lack of access or affordable access to the Internet and locally relevant content in low-income communities. The iNethi platform allows communities to quickly bootstrap a community owned network to provide affordable Internet access and host a local cloud server that allows communities to interact with fast free local content easily. The local cloud service currently provide free access to a local file storage platform, a local chat server, and a video streaming platform and education-focused resources such as Physics Education Technology (PhET) simulations, Wikipedia, Khan Academy and TED talks. iNethi also provides a mechanism to automatically synchronise content uploaded to a global server from anywhere in the world to a server running in a local community. iNethi has been deployed in Ocean View, Cape Town and during COVID-19 it allowed teachers to stay in contact with high school learners. The learners downloaded free teaching videos from nine hot spots around Ocean View; these videos were recorded by the high-school teachers, uploaded to the global platform and then synchronised to the server in Ocean View. The “Essential Skills” Physics Videos and resources created by the UniZulu Science Centre have also recently been uploaded to the platform to enrich the learning experience of matric students. These videos will also be available for free from any iNethi hotspots in Ocean View. In this work, we will describe the architecture of iNethi, its current impact and the potential of iNethi to provide public access to high-value digital resources in low-income communities throughout South Africa.
Manghweni village in Limpopo as any rural area does not have enough job opportunities for its inhabitants. Community projects might be initiated and developed to provide community residents with opportunities to either start their own small businesses or work for part-time jobs under the municipality or the local leadership. This would contribute to the socio-economical survival. In the past 10 years, many community led project have been found failing and abandoned. The need to palliate the root causes of community project deliverables failure and abandonment and the necessity to set and successfully implement appropriate remedial strategies in Manghweni prompted this paper. The physics reasoning behind the grey rationale analysis methodology has been employed in this qualitative study where structured questionnaires were administered in a semi-structured interviews. Secondary data from recorded municipality information center were also used. Findings identified failure root causes as expressed by the Pareto diagrams. Based on the above, strategies for sustainability of future community led projects in Manghweni are discussed while the most suitable outcome alternatives are derived from the grey rationale analysis on the above.
We present an approach to outreach that is based on developing scientist communicators, more than it is focused the audience and the contents. Indeed, outreach has three aspects - both the people carrying it out and the audience, and the content itself. While there has been a lot of work on outreach content creation and audience engagement, the relatability and role modelling of the ambassadors of the field who carry out the outreach have been less of a focus. In the Cascade Outreach model, we emphasise the development of relatable role models and stimulate a cascading effect of the outreach, similar to near-peer mentoring. While doing so, we explicitly ensure that the scientist communicators themselves are empowered and gain in communication and teaching skills, as well as confidence to navigate their professional environment. Challenges that are faced by scientist communicators often relate to their professional situation and personal exposure. This has so far not been seen as priority in outreach, but is a natural area of concern when focusing on the scientist communicators. We discuss how we approach this, especially in the context of social media.
Physics is a foundational science that lays the groundwork for scientific thinking and problem solving. South Africa has a strong Physics community in experimental and theoretical physics, but our graduates are not always given the chance to appreciate how broadly applicable physics principles and tools are. At the University of the Western Cape, we are setting up a Science for Development course to equip our graduates with a broad physics perspective on development challenges of all kinds. In this paper, we describe the UWC Honours programme's origins and the efforts to adapt it to the needs of our students, our research capacity and pressing issues of our country. We then describe the syllabus for this Science for Development module, how it fits into a university physics curriculum and how we hope it will broaden our physics graduates' thinking.
Heavy transition metals are frequently used as electrodes and substrates in scanning tunneling microscopy experiments. In the constricted low dimensional systems that occur in such experiments, typically under conditions of non-zero bias voltage, spin-imbalance may develop even in non-magnetic atomic- and nano-systems. This phenomenon arises as a result of spin selective effects mediated by spin-orbit coupling. It is important to not only understand the emergence of the spin imbalance, but also to model associated properties such as spin-polarized electron transport in these systems. Conventional theoretical approaches cannot model these effects because they usually neglect spin-orbit coupling. Therefore, to model spin-imbalance in the electronic transport of constricted nano-systems, such as in atomically sharp transition metal electrode tips or surfaces, as well as in organic molecules bridging the electrode tips, we have implemented spin-orbit coupling as a post-self-consistent correction in atomic orbital basis density functional theory within the non-equilibrium Green’s function formalism. Our method takes advantage of optimized Gaussian orbital basis sets and effective core potentials and one-shot transport calculations with steady convergence and charge transfer properties compared to other similar approaches. We apply this method to a selected number of sample constricted low dimensional systems where spin-imbalance is important by performing density functional transport calculations. This permits us to demonstrate that incorporation of spin-orbit coupling is essential to understanding emergent spin-imbalance in molecular electronics, while in certain instances, the consideration of the applied bias is also important to the manifestation of spin imbalance phenomena in heavy transition metal electrodes and substrates.
In this study, the phase stability of B2 and B19 Ti50Pt43.75-xCoxTa6.25 structures using ab initio density functional theory approach was investigated. Their structural, vibrational and mechanical properties were determined to show their stability. The supercell approach was employed to substitute Pt with Ta on the TiPtCo and evaluate the stability of the structures. The calculated heats of formation predicted Ti50Pt37.50Co6.25Ta6.25 to be the most stable structures as compared to other concentrations for both B2 and B19 systems. The calculated elastic properties show that TiPtCoTa is mechanically stable at different concentrations of Co. Moreover, the temperature dependence was also calculated to predict the possible transformation.
The comparison study on adsorption of normal butyl xanthate (PNBX), mono butyl dithiocarbamate (BDTC) and dibutyl dithiophosphate (DBDTP) on sperrylite mineral forms a basis in understanding the floatability improvement and paves a way for design of collectors that may impact a wide range of arsenide minerals. This study used a computational density functional theory (DFT) and experimental microcalorimetry approach to determine the adsorption energies of NBX, BDTC and BDTP collectors onto sperrylite mineral surface. For computational aspect, we considered the most stable surface plane of (100) surface, which had been found to give the lowest surface energy as compared to the other surface planes. We observed that the NBX, BDTC and BDTP preferred to bridge on the As and Pt atoms through the S atoms. These finding showed that the collector adsorb on the surface through both Pt and As atoms and indicated that the As atoms were significantly active in the adsorptions. The computational calculated adsorption energies were in the order: BDTC (–376.93 kJ/mol) > NBX (–369.47 kJ/mol) > BDTP (–350.97 kJ/mol), indicating that the dithiocarbamate had strong exothermic adsorption. From the microcalorimetry test we also found that the BDTC was more exothermic than the BDTP and the PNBX and the adsorption energies were in the order: BDTC (–473.50 kJ/mol) > BDTP (–392.56 kJ/mol) > NBX (–331.13 kJ/mol). These results showed that nitrogen atom in the BDTC collector had a great influence in the adsorption strength of the collector on the mineral surface. These results paved a way for design of novel collector for sperrylite and other chalcogenide minerals and suggested that nitrogen in a collector may significantly improve the affinity of the collector for better recovery.
Aluminium oxide (α-Al2O3) emerged as a potential surface coating material for Li-ion batteries because it has proved to improve the electrochemical performance and capacity upon cycling. It was also considered due to its high thermal conductivity, resistance against extreme temperatures and excellent electric insulation. Despite the intense studies on the surface coating with α-Al2O3, there remains a lack of deep understanding of its reactivity towards the electrolyte content. Herein, we report the adsorption of organic solvent, ethylene carbonate (EC) on the major α-Al2O3 (0001) surface using density functional theory calculations. During the single EC adsorption, it was found that the molecule prefers to binds with the surface when placed parallel interacting through the carbonyl oxygen. The adsorption energy per EC molecule (Eads/EC) was found to increases for parallel interactions and decrease for perpendicular. Upon increasing the surface coverage, we have noted a decrease in surface free energy, thus a decrease in surface stability. Furthermore, it has been observed a decrease in electronic charge transfer as we increase the EC coverage.
One of the major limitations associated with spinel LiMn2O4 despite its superior properties such as high voltage, great cycling performance, being environmentally friendly and cost-effective is the impact of the stress it endures through strain during the process of cycling. For that reason, this study seeks to understand the implications that come with stress-strain and how it affects the mechanical properties of a battery material; and eventually come with a better nanoporous structure that can withstand these harsh conditions.
Herein, the amorphisation and recrystallisation technique were used to simulate the Li-Mn-O nanoporous structures of different lattice sizes at 75, 69 and 67 Å and varying lithium concentrations, (Li1+XMn2O4, 0 ≤ X ≤ 1) using the DL_POLY code. Recrystallisation of the nanoporous structures resulted in single and multiple grained materials with microstructures that shows a profusion of point defects. Furthermore, the microstructures capture the spinel layered composites which are also validated by the X-ray diffraction patterns of these structures. The stress and strain analysis shows that nanoporous 69 Å has the highest yield strength compared to its nanoporous counterparts. This, therefore, implies that nanoporous 69 Å is more robust and can be a better candidate to help restrict battery hazards in the future as far as fracture is concerned.
Titanium can be produced as both a metal and in powder form. It finds applications in various industries such as in medical and aerospace, where the fabrication of components with excellent corrosion and high-temperature performance are significant. The titanium metal also plays a significant role in the titanium production process due to its desirable physical and chemical properties. Also, this process occurs in the presence of alkali metal and alkali earth metal salt mediums. Recent experimental studies are on testing the lithiothermic part of the titanium formation process, however, the small titanium clusters are thermodynamically unstable. In this study, classical molecular dynamic calculations were performed to understand the growth/evolution of the small titanium Ti5 cluster after interactions with LiCl medium. The DL_POLY code was used to evaluate the temperature dependence of the structure. Furthermore, the stability of the cluster was evaluated using the CASTEP code. It was found that the cluster maintains its trigonal bipyramid geometry at the temperature range of 100 K – 2000 K. Moreover, the cluster was observed to show growth patterns, indicated by the absence of bonding between atoms. The results of this study might give us more insight into the growth/evolution of titanium in salt mediums.
We present our latest findings on the status of factorization in heavy ion collisions. In the first microsecond of the universe, space was filled with deconfined nuclear matter at a temperature of a trillion degrees. These conditions are recreated thousands of times a second at experiments in the US and Europe in which large nuclei such as gold and lead are collided at nearly the speed of light. Very high momentum particles that propagate through the fireballs generated in these heavy ion collisions form one of the essential probes of the properties of the quark-gluon plasma (QGP) that permeated the early universe. In order for these high momentum particles to be a well-calibrated probe, we must ensure that the quantitative predictions for their behavior are well-controlled. The rigorous language for this control is known as factorization, which implies that the production and hadronization processes are independent of the interaction of the probe with the QGP medium. We show how previous energy loss calculations diagrammatically fail at factorization and point to a way forward for future progress.
We present predictions for the suppression and angular distribution of B and D mesons in $\sqrt{s}=5.5$ TeV Pb+Pb collisions at the LHC for central, semi-central and peripheral collisions. Ultrarelativistic heavy-ion collisions produce an enormous amount of energy, resulting in the formation of a quark-gluon plasma (QGP). Studying the behaviour of particles (e.g. heavy quarks) propagating through the QGP enables us to probe the physics of the QGP and the many-body dynamics of QCD. B and D mesons are the decay products of heavy quarks i.e. bottom and charm respectively and their large mass implies that they are produced very early in the collision and act as ideal probes, since they navigate the whole evolution of the QGP medium. The suppression of heavy mesons is a result of interactions with the produced QGP medium and the angular distribution is due to the initial geometric asymmetry during the collision. These heavy flavour energy loss studies are crucial for understanding the properties of nuclear matter and we provide these predictions for comparison to future LHC measurements.
We study the relic density and astrophysical constraints of an effective model featuring top-philic scalar dark matter and a heavy T-channel mediator. The addition of a dimension-five contact term which is common to BSM scenarios modifies the available parameter space, and the model features interplay between the associated Wilson coefficient and Yukawa parameter in producing the correct relic density. We present an analytical fit to the relic density, considering co-annihilations when relevant, and discuss the detection constraints.
One of the biggest problems in particle physics today, is understanding the nature of dark matter. If dark mesons exist, their evolution and hadronization procedure are currently little constrained. They could decay promptly and result in a very SM QCD like jet structure, even though the original decaying particles are dark sector ones; they could behave as semi-visible jets; or they could behave as completely detector-stable hadrons, in which case the final state is just the missing transverse momentum. In a recent work, we have shown that the dark sector can potentially be probed with jet-substructure observables, however, the modelling of these scenarios is somewhat an unexplored area, owing to the existence of only Pythia Hidden Valley dark shower module. An alternate dark shower model is becoming more necessary, in order to gauge the theory systematics and the extent of model dependence. In this talk, I will cover the proposed idea of having a Herwig hidden valley dark shower and hadronisation module, as well as our published work on jet-substructure studies for semi-visible jets.
In an era where high energy particle physics is having to transition from a theory-driven to a data-driven approach, the traditional method of performing specific searches off of theory models may be inefficient. Contur (Constraints On New Theories Using Rivet) was designed as a means to quickly exclude BSM models based off the many LHC measurements currently contained in Rivet. Focusing on track based measurements, the sensitivity of Contur to some Dark Matter models was explored. The exclusion potential of soft unclustered energy patterns (SUEP) and different dark sector jets scenarios will be presented.
Random numbers are used extensively in both cryptography and simulation, but are difficult to generate reliably using classical methods. We investigate random number generation on the ibmq_16_melbourne quantum processor, a 15-qubit superconducting quantum computer. By applying simple post-processing techniques to the random bits generated, we were able to extract a sample of random bits which passed the NIST Statistical Test Suite. This shows that, with some post-processing, solid-state quantum computers such as IBM quantum processors can be used to generate random numbers of sufficient quality for cryptographic applications.
A functional material of carbon nano-composite is investigated to be utilised as a Thermal Interface Material (TIM) in the Low Voltage Power Supply (LVPS) bricks as part of the upgrade of the large Hardron Collider (LHC) accelerator at CERN. The TIM is a composite in a pasty form, based on carbon nanomaterials (CNMs) and Silicone heat transfer compound. The goal behind the implementation of the carbon nano-material in the TIM was to increase the thermal transfer from the electronics to the heat sink by the intermediary of the aluminium oxide (Al2O3) posts. The temperature of the thermal posts was aquisite by the means of an automated test stand built in house and monitored hourly with a Labview interface. The composite of CNMs and silicone compound were dissolved in acetone, then annealed at high temperatures in atmospheric air in order to achieve a homogeneous mixture. The CNMs investigated in this research work are Carbon Nanotubes (CNTs) and Carbon Nanospheres (CNSs) which were synthesised by Chemical Vapor Deposition. Also, the study included the investigation of the weighting of the CNMs in the nano-composite.
The Vacuum Arc Thruster (VAT) is an unconventional plasma propulsion system with unique advantages for small satellite applications. The relevant literature and figures of merit were presented. An inductive energy storage pulsed power circuit was built which delivered triangular submillisecond current pulses to a coaxial VAT. The dense copper plasma, the expansion of the macroparticle plume, high velocity luminous micro-droplets and cathode ablation were documented among other plasma phenomena. A pulse forming network was built to deliver square pulses with higher current to the VAT. Thruster performance differences between the two circuits are discussed. The fractal and explosive ecton models of the arc are considered. The retrograde motion of the cathode spots is discussed with special attention given to the balance of plasma and magnetic pressure. Finally, ion current density measurements are presented.
The DC discharge microthruster concept is a simple, energy efficient plasma micropropulsion system that operates using an ionisation-acceleration coupling mechanism. This system was developed in the hopes of addressing some of the shortcomings of many state-of-the art electric micropropulsion systems. Preliminary studies have been conducted on the thruster from which the stable operating parameters were deduced. Plasma plume diagnostic measurements, including the ion current density and ion energy distribution and the influence of changes in the operating parameters (applied voltage, discharge current etc.) on these measured quantities will be presented. The estimated thrust-to power-ratio of the system and its overall feasibility as a micropropulsion mechanism will also be discussed.
Measuring phase differences between orthogonal polarisations has become a common industry practice. In food and drug production the circular birefringence exhibited by chiral molecules has been used to identify and measure the concentrations of enantiomers, while linear birefringence has been used in stress and biological imaging. Conventional techniques regularly rely on stressing photo-elastic materials to produce birefringence in order to measure the same phenomenon. We demonstrate how holographic phase shifting induced by a digital micro-mirror device (DMD) can be used to acquire spatially resolved arbitrary birefringence measurements. Linear and circular birefringence in both static and dynamic liquid crystal optics, metasurfaces as well as chiral sugar solutions were measured through maximum-likelihood estimation fitting. The acquired images have resolutions dependent purely on the camera used and the entire measurement process involves no moving parts. The polarisation and wavelength independence of DMDs as well as high refresh rates and relative low cost makes the technique a promising digital candidate for applications in industry.
The gold industry in South Africa, mainly based on the metal extraction through cyanide leaching and the use of microorganisms, has been among the top 10% country's main source of income. This results in a strong economy, emergence of new towns and new financial structures. The use of cyanide as a lixiviant raises serious environmental concerns as it negatively impacts on the biodiversity, humans, soil, water, air and surrounding flora. Additionally, gold extraction operational costs continue to grow because of the ore falling grades, increased mining depth in the reserves, and a drop in the gold price on the market, resulting in a gradual drop in gold production. As a result, enhanced productivity is crucial to the gold industry's sustainability in South Africa. In the search of alternative solutions, thiosulphate (copper ammonia system) is studied as a potential substitute to cyanide for the recovery of gold from its minerals. The paper discusses the kinetics of gold dissolution in a thiosulphate aqueous solution as lixiviant concentration is varied from 0.5 M to 3M and the contact time in the leaching vessel is maintained in the range between 30 minutes and 6 hours. The shrinking core model as well as the solution diffusion model exploiting the double layer concept elucidate the outcomes of the work justifying the kinetics models observed.
Kimberlite rock has been activated with a high energy photon beam, following which high energy resolution spectra have been acquired in time differential mode. This enables a lifetime analysis of the isotopes that have been activated. An isotope identification is then performed using the dual information of characteristic gamma rays and lifetimes. This enables an unambiguous assignment of the isotope identification. The results have been made quantitative by the Monte Carlo modelling of the activation process to extract the product of the effective radiation field and integrate this over the energy dependence of the cross-section. The results are compared to the known composition of kimberlite as follows: The time differential activation code, FISPACT, is used to perform a pathway analysis to establish the various activation pathways, given the mixed radiation field and the ENDF / TENDL cross sections for the various nuclear reactions. The pathway analysis is then used to attribute the measured activity to specific parent isotope composition, and hence to the elemental analysis of the kimberlite. The experimental work was performed using the Aarhus 100 MeV electron microtron. The results have two roles. In the first place, they establish the radiological significance of the activation process of the MinPET method in sorting diamondiferous from barren kimberlite rock. In the second place, this is an interesting analysis technique capable of nuclear analysis of light elements (carbon and oxygen) and also differentiating various PET isotopes.
Jets in blazars are an excellent forum for studying acceleration at relativistic
MHD shocks, since this process is likely to spawn the highly-variable emission
seen across the electromagnetic spectrum from radio to gamma-rays. Our recent
work on combining time-dependent multi-wavelength leptonic emission models with
complete simulated thermal + non-thermal particle distributions from shock
acceleration theory has resulted in new insights into plasma conditions in
AGN jets. This has demonstrated the ability to infer the plasma density, and
suggested the interpretation that turbulence levels decline with remoteness from
jet shocks, with a significant role for non-gyroresonant diffusion. Using our
time-dependent two-zone construction, we are able to model together both extended,
enhanced emission states from larger radiative regions, and prompt flare events
in select Fermi-LAT and TeV blazars. In this contribution, I present recent
applications of this simulation framework to AstroSAT and multi-wavelength
observations of the prototypical VHE gamma-ray blazar 1ES 1959+650 and
NuSTAR and multi-wavelength observations of the high-redshift FSRQ PKS 0537-286.
A prime goal is to ascertain whether such flares are truly associated with prompt
shock acceleration activity in relatively confined regions. The results illustrate
how parametric degeneracies in shock acceleration conditions can lead to refined
determinations of the plasma density and particle diffusion character in blazar jets.
The spectral energy distributions (SEDs) of some blazars exhibit an ultraviolet (UV) and/or soft Xray excess, which can be modelled with different radiation mechanisms. Polarization measurements of the UV/X-ray emission from blazars may provide new and unique information about the astrophysical environment of blazar jets and could thus help to distinguish between different emission scenarios. I will present a new Monte-Carlo code – MAPPIES (Monte-Carlo Applications for Partially Polarized Inverse External-Compton Scattering) – for polarization-dependent Compton scattering. I will present the code by showing results of the polarization signatures in a model where the UV/soft X-ray excess arises from the bulk Compton process. Predictions of the expected polarization signatures of Compton emission from the soft X-ray excess in the SED of AO 0235+164, and the UV excess in the SED of 3C 279 are made for upcoming and proposed polarimetry missions.
The radio through optical/UV/X-ray emission from blazars is dominated by highly polarised synchrotron emission from relativistic electrons in their jets. The total degree of polarisation is a composition of the polarised non-thermal synchrotron emission and thermal unpolarised emission components from the dusty torus, host galaxy, emission lines from the broad line region (BLR) and accretion disk. For some blazars the accretion disk is not directly observed as it is outshone by synchrotron emission. However, it reveals its presence through a decrease of the optical polarisation degree towards higher frequencies in spectropolarimetry observations, where the disk is diluting the synchrotron polarisation. Considering a leptonic model, the high-energy X-ray and gamma-ray emission can be modelled as polarised synchrotron self-Compton radiation which is diluted by Compton up-scattering of unpolarised external radiation fields of the BLR and accretion disk. A model is constructed that simultaneously fits spectral energy distributions and multi-wavelength polarisation of blazars. A target-of-opportunity, Large Science program "Observing the Transient Universe" from the Southern African Large Telescope, provides spectropolarimetry data for flaring blazars in the optical-UV regime. This program includes co-ordinated multi-wavelength observations from the Las Cumbres Observatory, the Swift-XRT and the Fermi-LAT. We present results for the flat spectrum radio quasar 4C+01.02 ($z=2.1$), for which we constrained its black hole mass as $4 \times 10^8 \; M_{\odot}$ and obtained a scaling factor that is indicative of the degree of order of the magnetic field (and dependent on line-of-sight) in the emission region.
In this talk we present an investigation into the nature of
multi-wavelength variability of blazars from a purely numerical approach.
We use a time-dependent one-zone leptonic blazar emission model to
simulate multi-wavelength variability by introducing stochastic parameter
variations in the emission region. These stochastic parameter variations
are generated by Monte Carlo methods and have a characteristic power law
index, $\alpha=-2$ in their power spectral densities (PSDs). We include
representative blazar test cases for a flat spectrum radio quasar (FSRQ)
and a high synchrotron peaked BL Lacertae object (HBL) for which the high
energy component of the Spectral Energy Distribution (SED) is dominated by
external Compton (EC) or synchrotron self-Compton (SSC) emission
respectively. The simulated variability is analyzed in order to
characterise the distinctions between the two blazar cases and the type of
progenitor variations. We show that the variability's power spectrum is
closely related to underlying progenitor variations for both cases.
Distinct differences between the different progenitor variations are
present in the multi-wavelength cross-correlation functions.
We analyse medium resolution optical spectra of six Active Galactic Nuclei (AGN), with strong iron emission spectra and characteristics associated with the class referred to as Narrow-Line Seyfert 1 (NLS1) galaxies. These were observed using the 1.9 m telescope at the South African Astronomical Observatory in Sutherland. The objects are among the brighter sources of that description accessible from the southern hemisphere: Fairall 265, NPM1G $-$15.0297, CTS J03.19, EUVE 0414$-$596, A 644-1, and HE 2116$-$3609. For each target we performed multiple integrations totalling between 1 and 2.5 hours, yielding spectra in the range $\sim$ 3700-6000 A with relatively high signal-to-noise ratios. This enabled us to locate multiple spectral emission features, including the strong Fe II bands in the range 4000-5400 A as well as other prominent emission lines associated with the Balmer series, Helium and the [O III] nebular doublet. Our measurements include the flux, the width and peak wavelength shifts of the lines, which sometimes displayed multiple components. We describe the properties of our sample, compare these to other representatives of the NLS1 class and interpret their physical mechanism in the context of AGN theory.
Much of the evolution of galaxies takes place in groups that occupy the interesting intermediate-mass range, where feedback has the greatest impact on galaxy formation and evolution. By using multi-band data (FUV, Mid-IR, Radio, CO, and X-rays), and an optically selected, statistically complete sample of 53 groups (< 80 Mpc; CLoGS sample) the galaxy evolution and star-formation activity of the central group dominant early-type galaxies is examined in relation to their gas content, AGN activity and local environment. The majority of the group dominant galaxies (87%; 41/47) are found to be passive systems without any significant star-forming activity, with the rest of the highest star-forming systems found to present significant cold gas detections, residing in X-ray faint groups (X-ray halo <65 kpc) and none hosting a powerful radio source (P1.4GHz>10^23 W/Hz). As galaxy groups are a favorable environment for both cooling flows and gas-rich galaxy mergers and interactions, the significant role of both processes on the origin of cold gas and the fuelling of an AGN or star-formation will be discussed along with results on the properties of the highest star-forming systems and the implications on AGN feedback in galaxy groups.
The study present the measurement of the contribution, purity, of $Z + \gamma$ and $Z+$ jet background events in the search for high-mass $Z\gamma$ resonances. The study uses events were the $Z$ boson decays into a pairs of oppositely charged electrons or muons. The events used consist of 139 fb${}^{-1}$ of proton-proton, $pp$, collisions data at $\sqrt{s} = 13$ TeV, recorded by the ATLAS detector at the CERN Large Hadron Collider.
The measured purity of $Z+\gamma$ background events depends on the parameter $R$ that gives the correlation between the isolation and identification criteria for jets faking photons in $Z+$ jet events. A data-driven method that uses $\gamma\gamma$ events collected in the same detector conditions as the $Z\gamma$ events is used to determine $R$ in various bins of the photon transverse momentum or the invariant mass bins. The results are compared against results that are obtained using the $R$ computed using a $Z+$jet Monte Carlo sample and a data-driven method that uses $Z+\gamma$ events to estimate $R$.
One indication that the Standard Model of particle physics is incomplete lies in the unanswered question of neutrino mass generation. Most popular among the possible explanations of this mystery is the see-saw mechanism which postulates that small neutrino masses arise from the exchange of heavy force-carriers. Additionally, a framework for this mechanism is the so-called Left-Right Symmetric Model (LRSM) which is favoured since it offers a number of advantages such as explanations for violation of parity in the Standard Model, generation of mass in both heavy and light neutrinos, and accounts for parity symmetry at high energies. This model can be analysed through studying lepton-number violation, of which the Keung-Senjanovi\'c process is a culprit. The search herein investigates the decay of a heavy right-handed gauge boson $W_R$ into a heavy neutrino $N_R$ via the aforementioned process, with keen focus on regions where the gauge boson $W_R$ is much heavier than the boosted neutrino $N_R$. The basis of the search is Run 2 data collected during the years 2015 to 2018, from the ATLAS detector at the Large Hadron Collider (LHC). For such a search, muon and electron channels result in different topologies; in the former, a unique method of large-radius jets containing electrons is employed.
Search for the presence of a new heavy resonance, produced via gluon-gluon fusion and decaying to the four-lepton ($4\ell$) final state, in association with missing transverse energy ($E^{\text{miss}}_{\text{T}}$), with $\ell$ = $e$, $\mu$. The search uses 2015–2018 proton–proton collision data at $\sqrt{s}$ = 13 TeV, corresponding to an integrated luminosity of 139 fb$^{-1}$, collected by the ATLAS detector at the Large Hadron Collider at CERN. The data is interpreted in terms of two models, firstly the $R\rightarrow SH \rightarrow 4\ell+ E^{\text{miss}}_{\text{T}}$, where $R$ is a scalar boson, which decays to two lighter scalar bosons ($S$ and $H$). The $S$ decays to a pair of neutrinos ($E^{\text{miss}}_{\text{T}}$) and the $H$ decays into $4\ell$, through $ZZ$ bosons. The second model is the $A\rightarrow ZH \rightarrow 4\ell + E^{\text{miss}}_{\text{T}}$, where $A$ is considered to be a CP-odd scalar which decays to a CP-even scalar $H$, and the $Z$ boson. The $Z$ boson decays to a pair of neutrinos, and the $H$ decays to the $4\ell$ final state.
Several astronomical observations have revealed the existence of larger matter quantities which are thought to occupy 27% of the universe. Many hypotheses exist about the nature of these elusive dark matter particles. One of these hypotheses predicts the existence of a hypothetical dark photon. The unique signature of this particle can be searched for at the Large Hadron Collider (LHC) at CERN. A study is performed to determine the feasibility of this search in ATLAS. A theoretical model containing a vector-like quark is considered which decays into a top quark and a dark photon. The focus will be on the decay channel containing a leptonic top consisting of either an electron or muon. Signal and several background distributions for some key variables of this decay mode will also be presented. This proposed search could lead to detectable dark matter whilst simultaneously expanding our limited understanding thereof.
Recent studies in particle physics have shown that there are myriad possibilities for strong dark sector studies at the LHC. One signature is the case of semi-visible jets, where parton evolution includes dark sector emissions, resulting in jets overlapping with missing transverse energy. Owing to the unusual MET-along-the-jet event topology, this is yet an unexplored domain within ATLAS. In this talk, I will discuss my ongoing ATLAS search, focussing on the performance and optimisation challenges associated with such a unique final state, specifically looking at the angle difference between the hardest jet and the missing transverse energy, and targeting a cut-and-count strategy.
The recent anomalous magnetic moment of the muon (muon g-2) result presents a pattern of deviation from the standard model prediction in the interaction of muons with a surrounding magnetic field. A similar deviation from the standard model prediction is seen in the LHCb results on rare B-meson decay. Plausible explanations of these anomalies are leptoquarks. Leptoquarks when coupled with a chirality flip interaction to a heavy quark can boost the muon's anomalous magnetic moment. This study presents a search for leptoquark in single production in ATLAS, with the leptoquark decaying into a one-light jet (b-tagged) and one lepton accompanied by an oppositely charged lepton in the final state.
Photonics and Lasers have become the centre of several modern day technologies such as the internet, additive manufacturing, remote sensors and even entertainment. They have revolutionized how we view Physics opening the door to a plethora of applications and new Photonics phenomena. In this non-specialist lecture we will take you on a trip through the development of lasers and the concept of structured laser beams and its impressive advances in Photonics.
It is well understood that structured light becomes distorted after propagating through the atmosphere. These distortions are the result of random refractive index fluctuations, themselves a product of atmospheric turbulence. In particular, these distortions have been realised as modal crosstalk in beams carrying orbital angular momentum. Such beams are ubiquitously used in free space optical communication applications. Commonly, the atmosphere is treated as a phase-only effect that induces this modal scattering. However, this approach offers little insight as it does not focus on the gain or loss of OAM that the beam experiences from interacting with the atmosphere. We ask the question: from where did the OAM come? We develop an alternate, novel model to provide generalised explanations to the sometimes-contested effects of atmospheric turbulence on light.
High dimensional entangled quantum systems are important in various applications such as quantum teleportation, secure quantum key distribution and cryptography. Such applications require a method to characterize the state density matrix. Conventional methods such a Quantum State Tomography work, however, can become computationally cumbersome if the dimension becomes too great. The method outlined, which is an extension of a proven method that uses isotropic states as model states, makes use of Werner states instead. Minimization techniques are used to extract key parameters that determine the state, rather than to necessarily reconstruct the state itself. Werner states are mixed entangled states and are good representations of bipartite quantum entangled systems. They consist of different weightings of projectors onto anti-symmetric and symmetric subspaces. The process involves using analyser matrices to probe Hilbert space. Chi-squared minimization using visibility calculations leads to the extraction of a symmetric weighting value and the dimensionality.
Structured light beams from the Laguerre-Hermite-Gaussian mode families with scalar or vector polarization structures have found applications in many diverse areas, particularly in high dimensional quantum communication, optical particle trapping and super-resolution microscopy. However, only a small subset of these structured beams, namely, the radially and azimuthally polarized annular modes, have been applied in the laser materials processing industry. The full spectrum of scalar and vector polarized structured light modes are easily accessible through devices such as the Spatial Light Modulator (SLM's) and Digital Micromirror Devices (DMD's), but due to their low-power handlining ability, direct generation at high power (>100W) is not possible. We propose a system that performs beam shaping (Gaussian -> Structured Mode) at low power with subsequent amplification to high-power using the Master Oscillator Power Amplifier (MOPA) strategy while preserving the complex spatial, phase and polarization properties of the beam. In this work, we explore amplification of vector and scalar polarized structured beams selected with a spatial light modulator using a detailed analytical model developed for double-pass end-pumped MOPA architecture. We demonstrate stable output power from the amplifier system and confirm the preservation of the beam characteristics using the modal decomposition and vector quality factor characterization techniques. This novel work will form part of an intermediate step towards the realization of Killo-watt level structured light beams for application in industrial laser material processing.
Hermite-Gaussian laser modes are a complete set of solutions to the free-space paraxial wave equation in Cartesian coordinates. They are often referred to as transverse electromagnetic modes and represent a close approximation to physically realizable laser cavity modes. Their applications ranges from enhancing optical communications information capacity to description of optical fields as well as in achieving high resolution imaging in microscopy. This study will propose and implement atmospheric turbulence effects on hermite Gaussian laser modes with orbital angular momentum.
The influence of Location and Gender on Shaping Student Performance in Physics.
Oluseye Folasayo Sadare¹, Thasmai Dhurumraj2&Awelani V. Mudau3
1. Department of Science and Technology Education, University of South Africa.
2. Department of Science and Technology Education, University of Johannesburg
3. Department of Science and Technology Education, University of South Africa.
Email: sadareoluseye@gmail.com1,tdhurumraj@uj.ac.za2, , mudauav@unisa.ac.za
Abstract
The poor enrolment of females in Science subjects creates gender inequalities. This study sought to explore how location and gender shape student performance in Physics. A qualitative approach was adopted for this study that randomly selected four co-educational public secondary schools, two schools from urban areas and rural areas respectively in Nigeria. Ethical considerations were accounted for by gaining permissions from the relevant departments to conduct the study. Pseudo names have been used for all participants. Data was collected through interviews, classroom observations, and document analysis. Data was analyzed deductively. The findings revealed that the gender of the students affect their performance in Physics with male students performing better than female students. Also, urban students perform better than rural students in physics. This study will assist government in the distribution of amenities to various towns and communities and also develop the interest of female students in Physics.
Experience and other studies show that students come to our Science Centres with pre-existing ideas of how the world works (often called prior-, naïve- or mis-conceptions). When confronted with conflicting ideas from science they are forced to make a “border crossing” (Aikenhead, 1999) from the familiar territory of their cherished beliefs into the “unknown country” of science. How difficult this crossing is and how comfortable a student feels to remain in this new country depends on many factors both internal and external to the student. The challenge for our Science Centres is to assist students to cross these borders more easily and to remain in their new country without feeling threatened. An example will be given of student prior conceptions with regard to sound and waves: a brief literature survey will outline pre-existent conceptions noted around the world. The 4 level framework of (Grayson et al, 2001) is used to classify these conceptions and modify them in the light of data gathered. Student responses to a questionnaire provide multiple mode (MCQ, written and drawings) feedback into this process. The result is a modified table of local students’ prior conceptions with regard to sound and waves. This is a useful resource when designing (and improving) science shows, exhibits and other programme materials in this area. While the specific example of sound and waves will be the focus of this presentation, suggestions will be made of how this resource can be used in other subject areas.
One of the challenges facing Physics Education worldwide is the improvement of learning outcomes. These have been intensified by the known attitudes of many, towards this subject. The Global Corona Pandemic also added fire to the challenge by shifting the teaching and learning from face-to-face to online. Based on this radical change to online teaching and learning platforms, it is necessary to assess if students’ attitude towards their learning of Physics has changed or not. To achieve this an attitude test called Epistemological Beliefs about Physical Sciences was deployed. The current study reports preliminary results of the EBAPS questionnaire administered at UJ to first-year extended and pre-service teachers’ students.
In May 2019 a very significant event in the world of metrology occurred whereby all seven of the SI base units were refined in reference to seven “defining” constants. Among them are fundamental constants of nature such as the Planck constant and the speed of light, and thus the definitions are based on and represent our present understanding of the laws of physics. The new self-consistent approach offers a unique opportunity to make useful impact on physics education both at high school and university level.
The present project is developing a set of teaching materials for use by educators and students which introduce the fundamentals of measurement and uncertainty in ways which are aligned to the ISO-recommended framework for measurement 1.
The work is being informed both by our research into students’ understanding of measurement [2], and our experience in teaching measurement and uncertainty to university students [3]. It has been shown [4] that students are able to develop a more robust understanding of the nature of scientific measurement when the measurement result is understood to be a statement of knowledge. Uncertainty is then associated with the quality of this knowledge.
We present the development of posters which are freely available for download [3], and progress towards a set of worksheet-based materials which are aimed to be distributed to schools and universities throughout South Africa and beyond. The teaching materials will be designed to be used within a wide range of contexts, with few additional resources, and will also introduce the new definitions of the SI base units in a way which promotes an improved philosophy of scientific measurement.
1 BIPM, IEC, IFCC, ISO, IUPAC, IUPAP and OIML (1995) Guide to the Expression of Uncertainty in Measurement (GUM) (Geneva: ISO)
[2] A. Buffler et al. (2001) Int. J. Sci. Educ. 23, 1137.
[3] [http://www.measure.uct.ac.za/msr/education]1
[4] A. Pillay et al. (2008) Eur. J. of Phys. 29, 647.
The Major Project has been an important component of the 3rd Year Physics curriculum at WITS for many decades. It has proven very popular with students, and has allowed academic staff to identify students with research potential as early as final year undergraduate level. In the original model each student chose a project offered by a member of the academic staff, and completed the work required during one of the first three quarters of the academic year. In 2015 the student numbers increased dramatically from approximately 25 students to approximately 50 students, and it became increasingly difficult to run the projects in their existing form. In 2018 the major project underwent a transformation, and since then students have completed an Independent Research Essay (IRE) under supervision of a member of the academic staff, with a student teaching assistant acting as a mentor for a small group of students. This presentation will provide a description of the evolution of the Major Project, paying particular attention to the components of the IRE as it is at present. In particular, it will be shown how the IRE may be used to inculcate or enhance essential skills for budding scientists.
Ion beam induced sputtering in matter is of interest for fundamental ion-atom interaction studies. It is also important for practical applications such as ion beam materials analysis techniques like Secondary Ion Mass Spectrometry at MeV ion energies (MeV SIMS). Theoretical descriptions of nuclear sputtering yields due to keV projectile ions are generally in good agreement with experimental data, but this is not the case for electronic sputtering yields using heavy projectile ions There is thus a need for experimental data to improve existing theoretical models that describe electronic sputtering due to MeV ions. This work presents results of thin film sputtering yield measurements carried out using the Elastic Recoil Detection Analysis technique (ERDA). Measurements were carried out to determine the electronic sputtering yield in Indium Tin Oxide (ITO) due to 29 Cu q+ and 79 Au q+ MeV ion beams at an ion velocity range of 0.1 MeV/u - 0.6 MeV/u. The UV-Vis characterization technique was also used to determine the changes in the optical properties of the conducting oxide films due to heavy-ion beam irradiation. Results show that reduction in thickness of the ITO film is attributed to the preferential sputtering of oxygen from the surface. The measured sputtering yield data were found to decrease with increasing ion fluence in the ITO target material for both Au and Cu ion beams. The optical band gap was found to decrease only slightly from 3.99 eV (for pristine) to 3.93 eV with increasing ion fluence. The results, in general, indicate that heavy ion beams irradiation can be used as an effective tool to induce surface modifications in thin films by dense electronic excitation.
In this study, polyaniline thin films with thickness of approximately 100 nm were spin-coated on a silicon substrate. The films were then irradiated at normal incidence and room temperature by 150 keV Ar+ ions to fluences ranging from 1 × 10^12 to 5 × 10^16 ions/cm2. According to the Monte Carlo simulation code, Stopping and Range of Ions in Matter (SRIM), the approximate penetration depth of the Ar+ ions in the thin films was found to be 279 nm. The surface morphology and roughness of the irradiated films was investigated by atomic force microscopy (AFM), while the optical properties and bandgap determination of the thin films were investigated by ultraviolet-visible spectrophotometry (UV–Vis). Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA) were used to study the effects of irradiation on the film thickness and compositional changes. AFM analysis showed that the roughness of the films decreases from about 33 nm to 19 nm as the ion fluence increases. The optical band gap of PANI film also decreased from 1,9 eV at 1 × 10^12 ions/cm2 to 1,4 eV at 5 × 10^16 ions/cm2 signifying the presence of new defect states within the bandgap as fluence increases. RBS results showed that there is a decrease of the thickness with increasing fluence while ERDA showed a decrease in hydrogen atoms of the film.
Ion Beam Analysis (IBA) is a suite of techniques used to determine elemental composition and depth profiles of thin film materials. Ion beam induced damage in soft insulating materials like polymers can be a limiting factor to the accuracy of IBA especially when using heavy ions. The usability of Heavy Ion Elastic Recoil Detection Analysis (ERDA) at iThemba LABS for analysis of polymeric films is presented in this work. The primary aim of the work was to optimize the applicability of the technique towards depth profiling ion implanted species in polymer films using different heavy ions of Au7+ and Cu5+. The films were implanted with different ion fluences of 80 keV Ti+ ions ranging from 5 x 1015 to 5 x 1016 ions/cm2 at liquid nitrogen temperature. Effects of ion implantation on the optical properties of polymers were investigated using Ultraviolet-Visible (UV-Vis) spectroscopy. Comparative Rutherford Backscattering Spectroscopy (RBS) analysis confirmed the implanted ion doses and increase in carbon concentration in the polymers. Ion implantation induced loss of hydrogen in the near surface of the polymers has been observed using Time of Flight-ERDA. The analysis efficacy of and ion beam induced damages due to Au7+ and Cu5+ beams have been investigated comparatively. UV-Vis analysis shows an increase in absorption intensity and a decrease in optical energy band gap as the ion fluence increases. The observed changes in UV-Vis have been correlated with RBS and Time of Flight-ERDA results. Possible ways of minimizing beam induced damage while improving efficacy of the analysis have been suggested.
Ion implantation is a technique of choice for inducing disorder in semiconducting materials such as crystalline GaAs. Interestingly, the properties of these amorphous materials such as the medium-range order (MRO) and small range order (SRO) depend heavily on the material of interest and its implantation conditions. Understanding the crystalline to amorphous phase transformations is vital for the continued use of GaAs in optoelectronic applications. In the present work, the configuration of the disordered layer in GaAs is generated using Ar$^+$ and Si$^+$ ions at different energies and different fluences, and the elastic properties are investigated. Raman spectroscopy was used to determine the structural configurations and phonon confinement of the damage layers after ion implantation. The crystal structure and the physical properties were determined using GIXRD and XRR for phonon dispersion simulations. The dynamics of acoustic propagation of the disordered layer are investigated using surface Brillouin scattering in the backscattering geometry. The derived phonon dispersion curves are fitted using surface elastodynamic Green's function to yield the elastic constants of the disordered layers on (001) GaAs substrate.
A suite of electronic and magnetic property studies were conducted on a Pr0.5La0.5Pt4Ge12 (Skutterudite) polycrystalline sample with an objective of investigating its superconducting state. The two parent compounds PrPt4Ge12 (Tc= 8K) and LaPt4Ge12 (Tc= 7.8K) both form in the filled-cage cubic Skutterudite structure and both have a superconducting ground state. However, their superconducting order parameters differ: PrPt4Ge12 has been characterized in the literature as an unconventional, multi-band superconductor and furthermore with evidence for time reversal symmetry breaking in its superconducting state. The isostructural compound LaPt4Ge12 on the other hand is a conventional superconductor. In this work we report the results of magnetization, magnetic susceptibility and heat capacity as functions of temperature and applied magnetic field in order to study the entanglement of the two types of superconductivity, and in an attempt to search for evidence of time-reversal symmetry breaking that may result from an internal magnetic field generated in the superconducting state.
A polycrystalline sample with the nominal composition RhFe3C was synthesized and its properties were investigated using powder x-ray diffraction (XRD), transmission Mössbauer spectroscopy and heat capacity Cp(T) measurements. The XRD data shows that RhFe3C has a cubic structure with a lattice parameter of 5.8907(3) Å. The room temperature Mössbauer spectrum of RhFe3C exhibits magnetic structure with three spectral components assigned to three different iron sites. The site assignments will be discussed in detail. The Cp(T) data show a distinct behavior and can be fitted with the Debye model with an additional Einstein term. The extracted fitted value of the Debye temperature was determined as 371(1) K. The results obtained from the different experiments will be discussed and compared with literature.
In this work, a brief review of a new form of scalar-tensor theories of gravity, known as gravitational scalar-tensor theories (GST) in which the action is composed of the Ricci scalar and its first and second derivatives is made. Some of the cosmological applications that have been investigated in these new theories are discussed considering different models corresponding to the first non-trivial extensions of general relativity possessing 2 + 2 degrees of freedom. We show that the resulting cosmological behavior is in agreement with observations.
The accelerated expansion of the universe and the rotational dynamics of galaxies have become part of the mysteries of the physical world and have had theorists working tirelessy for the past years. There is no consensus on what is causing these observable effects: whether it is the the unknown dark energy and dark matter or it is the breaking down of our currently accepted theory of gravity, General Relativity, at larger scales. In this work we study the dynamics of a cosmological model described by the Bianchi Type V spacetime in f(R) gravity using the dynamical system analysis. We derive the field equations for a general Bianchi model in the context of f(R) gravity using the tetrad formalism and then specialize in the Type V model. Qualitative description and exact solutions are given for f(R) = R (General Relativity) and for f(R) = R^n. We find no accelerating solutions in the case of General Relativity with an exception when darkn energy is considered where we find one accelerating solution. In the case of Rn-gravity we find 2 possible accelerating solutions depending on the value of n.
The quasinormal modes (QNMs) of a black hole (BH) may be identified as a class of damped, classical oscillations in spacetime, emergent as part of the late-stage response to a perturbation of the compact body. In the weak-field limit, the radial behaviour of these oscillations can be modelled as a wave equation whose potential varies to represent different fields. The choice of computational method applied to solve these QNMs must accommodate the specifics of the BH spacetime and wave equation dependencies, as a certain approach may fail under conditions where another proves more accurate. Through a novel exploitation of the null geodesics of spherically-symmetric BHs, Dolan and Ottewill recently constructed an inverse multipolar expansion method that allows for the efficient computation of BH quasinormal frequencies (QNFs). In a previous work, we have seen that this method is well suited to the exploration of the large angular momentum regime of QNFs of various spin for Schwarzschild, Reissner-Nordström, and Schwarzschild de Sitter BHs. Here, we extend this method to the computation of the QNM wavefunctions within a Schwarzschild BH spacetime, and subject the resulting expressions to the asymptotic limit of $\ell \rightarrow \infty$.
Previously, we have discussed Bell correlations in a relativistic setting and the possibility of using these to detect weak forces between particles. Now a theoretical description of quantum entanglement in terms of relativistic quantum mechanics is presented. Essentially, in non-relativistic quantum mechanics, entanglement leads to a non-local correlation between 2 particles. This was shown by John Bell in 1964 when he derived an inequality that should hold for all possible correlations that could be described by classical local realism. However, it turns out that the predictions of quantum mechanics can violate this inequality and these predictions have subsequently been confirmed experimentally, hence these correlations must be non-local. Bell’s original calculation was only done for non-relativistic quantum mechanics but there have been some recent authors who have tried to do the calculation for relativistic quantum mechanics. What they have found is that the Bell correlations in relativistic quantum mechanics are altered slightly from the non-relativistic case. For example, the measurement of the Bell correlations from a lab frame in a Lorentz boost perpendicular to the centre of momentum frame produces a correlation that differs from the maximum violation by the Wigner angle (i.e. the angle produced by combining 2 Lorentz boosts in special relativity). While at first sight, it appears as the the correlation is weakened, one can in fact recover the maximal violation of the Bell inequality by adjusting the directions of measurement relative to each other by this Wigner angle. So in fact, the maximal violation of Bell’s inequality is preserved but in different directions. This effect was the centrepiece of our previous work published in SAIP conference proceedings because we showed that if there were accelerations between the entangled particles (probably due to forces between the particles), it could potentially produce a measurable effect. Now we’re putting this work on a more theoretical footing, by calculating the effect in the language of relativistic quantum mechanics by making use of Dirac spinors and the Schwinger-Tomonaga equation.
Inspired by the dual correspondence between measurement and preparation procedures, we discuss inequalities for observables of local realistic models which are violated according to the predictions of quantum mechanics, thus demonstrating the inability of classical physics to reproduce all quantum predictions (Bell's theorem). Such Bell inequalities test the statistical correlation between different state preparations that lead to the same measurement result rather than vice versa as in previous Bell tests. The different perspective on quantum foundations leads to a new QKD protocol and hopefully paves the way to other applications of quantum mechanics.
The recent paper by google [1] claiming to achieve quantum supremacy in quantum computing has risen a lot of interest. While there seems to be lot of questions regarding the validity of their claims of achieving quantum supremacy and comparison with the classical time frames in calculating the same quantity, it seems that there is little doubt they indeed perform computation using quantum operations. But the question still remains “after operating the random quantum gates on the input state and making measurement, with just the output data available, how do we classify the data as quantum or classical?” I.e, The inputs sate has indeed has gone through a series of quantum operations (that operate on more than 2 qubits at a time) to produce the available data. This due to the fact that the data supporting supremacy is not verified. To address this question we propose a modified verification scheme to test the output data which can tell us whether data available is generated from a quantum computer or not along with the fidelity and number of qubits in the quantum computer.
References:
[1] Frank Arute etal. Quantum supremacy using a programmable superconducting processor, Nature, Vol574, 24 October 2019, 505.
During the early high-level lockdown linked to the COVID-19 pandemic in 2020 much of the South African industrial and economic sectors ground to a halt. This provided an opportunity to identify the role human activities have on the local contribution to aerosol emissions in Gauteng by comparing the 2020 atmospheric turbidity during that time of the year with the levels observed in prior years. We examine Council for Scientific and Industrial Research solar spectral irradiance, broadband irradiance and weather data for the period in question together with corresponding data from an earlier year. We categorise days and months according to the measured degree of turbidity for the period April-July for 2018 and 2020 through analysis of the relationship between the measured irradiance and the solar zenith angle on cloud-free days. Spectral data also allows an insight into the aerosol type and particle size. We discuss whether the solar irradiance data provides evidence of lower aerosol concentrations due to the COVID-19 lockdown.
Food drying is an energy-intensive operation that results in the removal or reduction of the moisture content of different foods for storage, quality retention, and enhancement purposes. In developing countries, open solar drying is one of the major methods adopted for the preservation of agricultural products due to the availability of solar energy at little or no cost, especially in Africa. Open sun drying is not as effective as solar drying using a solar collector in terms of the quality of the product, and the reduced drying period, thus different types of solar dryers have been developed in recent years. The absence of solar energy at night and cloudy periods has led to the development of thermal energy storage (TES) for solar dryers. This stored solar thermal energy can be utilized for drying at night and cloudy periods. The aim of this article is to review various thermal energy storage systems used in solar dryers with a particular emphasis on numerical models aimed at enhancing the efficiency and cost of TES. Different types of models and numerical results of TES systems for solar dryers will be presented. These models include finite difference, computational fluid dynamics (CFD), and artificial neural network (ANN) models.
Keywords: Modelling, Thermal Energy Storage (TES), Solar Food Dryer
Abstract.
In this work, thin films of dip coated CuO nanoparticles were prepared on fluorine-doped tin oxide (FTO) substrates and the film’s processing parameters which includes the withdrawal rate, film thickness and annealing temperature were optimized for photoelectrochemical (PEC) water splitting. CuO films were prepared at withdrawal speeds ranging from 50-200 mm/min, with thicknesses of 158-627 nm and annealed at 400-650 °C for 1 hr. X-ray diffraction (XRD) and Raman spectroscopy studies confirmed the preparation of crystallized CuO films of high purity. The estimated crystal sizes for the films increases with withdrawal rate and annealing temperature, producing the highest value for films withdrawn and annealed at 150 mm/min and 600°C respectively. The CuO films indicated strong optical absorptions in the visible region and their absorbance increases with increasing film thickness. The band gaps of all samples ranged from 1.69 to 2.08 eV. Linear Sweep Voltammetry (LSV) measurements yielded the highest photocurrent densities of 2, 2.6 and 2.9 mA/cm2 at 0.37 V vs RHE for films prepared at withdrawal speed of 150 mm/min, deposited with 7 layers and annealed at 600°C. The high photocurrent obtained for the films was due to the optimized film thickness, enhanced crystallization and the decrease in charge transfer resistance at solid/liquid interface achieved for the films. The least photocurrent was observed for films annealed at 400°C due to poor crystallization and high charge transfer resistance obtained. This study emphasized the importance of optimizing processing parameters such as withdrawal speed, film thickness and annealing temperature in the preparation of CuO films for photocatalytic applications.
Keywords: CuO photocathodes, PEC water-splitting, withdrawal speed, film thickness, annealing temperature.
In this paper, a combined solar cooker with a sunflower oil storage tank is presented. The solar cooker consists of a 1.8 m parabolic dish that has an oil circulating copper spiral coil receiver embedded to a metallic cooking plate. The receiver is connected to a 50 L sunflower oil storage tank for the dual purpose of heat storage and cooking. A DC pump is used to circulate the oil during charging and discharging. The receiver has a circular metallic plate for cooking, while the copper coil is embedded below the plate to circulate sunflower oil that is heated up and stored during the cooking (charging) experiments. During charging, 1.5 L of water is boiled in a cooking pot with storage tank temperatures above 100 oC being achieved. During discharging, the pump is reversed and 1.5 L of water is heated up with the stored heat, however, heat transfer is poor with the water temperature only achieving temperatures just above 50 oC. Preliminary experiments are presented, and the charging process is seen to be more efficient than the discharging process with the charging pump reversed. The system can be used to cook food as well as provide heat for indirect cooking using insulated bag slow cookers. However, cooking food directly on the cooking plate using the reverse discharging progress is not efficient, and heat transfer should be enhanced to make the process more efficient and viable.
Keywords; Combined solar cooking and storage; Sunflower oil; Receiver; Thermal performance
Hydra A is a type I Fanaroff-Riley radio galaxy which hosts a pair of 300-kiloparsec diameter radio lobes that are being powered by the previous powerful AGN outburst. Radio observations provide us with an excellent probe for the study of high energy particles residing in the lobes. The MeerKAT radio telescope carried out observations of Hydra A, from which we obtained radio maps at several frequencies. A spatial analysis of the radio maps reveals a pair of inner lobes and a pair of outer lobes. Using these observations, we computed the radiative flux densities and combined them with previous results from low frequency VLA observations at 74MHz and 327 MHz. We found that the spectrum in the MeerKAT frequency range is well described by a power law. We set constraints on the magnetic field strength and the age of the outer radio lobes through electron spectrum modelling which includes electron ageing.
The Madala model was introduced to explain several anomalies observed at the Large Hadron Collider. This model introduces a dark matter candidate through the extension of the standard model’s Higgs-sector, i.e. heavier scalar bosons are introduced, which can couple to dark matter. The cosmic ray spectra and galactic centre's gamma-ray flux excesses have been observed in the AMS-02 and Fermi-LAT experiments, respectively. Assuming the Madala model can explain these excesses, the aim is to make synchrotron emission predictions for MeerKAT observations. The region of interest for the predictions is the nearby satellite Reticulum II. The MeerKAT predictions will instigate the validation of our assumption and otherwise allow us to constrain the particle properties of the Madala model from an astrophysical standpoint. In essence we are able to describe the multi-lepton anomalies at the LHC and the anomalies in astrophysics simultaneously.
The nature of the cold dark matter (CDM) can be understood by looking for light scalar candidates such as axion-like particles (ALPs). The coupling between ALPs and photons allows for the spontaneous decay of ALPs into pairs of photons. However, the rate of this process is believed to be small enough to be ignored on cosmological timescales. Furthermore, it has been claimed in several recent works that ALPs can gravitationally thermalize and form macroscopic condensates. The stimulated decay of the ALP condensates is also possible with a significantly high rate. Consequently, the photon occupation number can receive Bose enhancement and grows exponentially. This can lead to radio emissions produced from this process and could be observed by the forthcoming radio telescopes. In this work, we investigate the detectability of such a radio signature from some astrophysical targets using the MeerKAT radio telescopes. This might provide indirect evidence for the existence of the CDM ALPs.
Generally, one expects to find accretion disks around massive objects since their gravity is able to pull in surrounding gas, dust, etc. toward themselves. Such astrophysical objects include black holes and their binaries. However, as of yet, no circumbinary disks have been found around inspiralling stellar-mass black hole binaries related to LIGO events. Our aim is to try find a mechanism to explain why this is the case. We start by assuming that these binaries do indeed possess a circumbinary disk initially but that they, through some as yet-to-be-determined mechanism, lose their disk by the time the LIGO-observable inspiral begins. We perform a computational study of a Kerr binary black hole system, for masses in the LIGO regime. We do this to derive some properties of the circumbinary accretion disk. This is possible using a novel approach to numerical relativity calculations where the disk dynamics are studied with the help of recently developed analytical spacetime models. In this talk we discuss two types of analytical models which may be used to study the geodesics relating to two different metrics. That is, we compare asymptotic patching vs. asymptotic matching, which is used to build a global metric from subdivided metric pieces. We discuss preliminary results.
We present the evolutionary constraints of shear-free cosmological solutions in the presence of a dark fluid. After describing the general evolution and constraint equations for quasi-Newtonian and anti-Newtonian spacetimes, we derive, at the level of linear perturbations, the conditions for the existence and consistent evolution of such spacetimes when they are endowed with the Chaplygin gas which mimics a unified description of dark matter and dark energy.
Previous calculations of diffuse radio emissions from dark matter annihilations have made use of Green’s function approximations to solve the diffusive cosmic ray transport equation. Some notable astrophysical code packages, including GALPROP and DRAGON, take a numerical approach to this calculation that involves the use of the Crank-Nicolson finite-differencing scheme. In this work we analyse the physical accuracy of the analytic approximations and directly compare the computational efficiency of the two solution methods. We also incorporate full spatial dependence into the diffusion and energy-loss coefficients, and compare this to the approach of using spatially-averaged values of the magnetic field strength and thermal electron population.
A search for a heavy resonance pseudo-scalar, A, decaying into a $Z$ boson and another heavy scalar boson, $H$, is carried out at the LHC using a data sample corresponding to an integrated luminosity of 139 fb$^{-1}$ from proton-proton collisions at $\sqrt{s}$ = 13 TeV. In these studies, the scalars $H$ will decay to two scalars $S$ or an $S$ and a Standard Model Higgs boson $H$ via an effective model. The $A \rightarrow Z(\rightarrow \ell\ell) $ and $ H (H\rightarrow SS $ or $Sh)$ production in at least four leptons final state will be examined in this search.
In this work, Stokes polarimetery is used to extract the polarization structure of optical fields from only four measurements as opposed to the usual six measurements. Here, instead of using static polarization optics, we develop an all-digital technique by implementing a Polarization Grating (PG) which projects a mode into left- and right-circular states which are subsequently directed to a Digital Micromirror Device (DMD) which imparts a phase retardance for full polarization acquisition. We apply our approach in real-time to reconstruct the State of Polarization (SoP) and intra-modal phase of optical modes.
Optical fields can often show unexpected effects when interference effects are used. Examples of these are angularly accelerating beams. In this work we present a novel structure of light that exhibits State-of-Polarization (SoP) structures that rotate with acceleration and deceleration when propagating in free space. We achieve this by creating a superposition of beams with accelerated transport of intensity in different polarization components, in such a way that the intensity profile remains constant, but each polarization projection changes differently. The Stokes vector for each point of the transverse profile exhibits a circular trajectory in the Poincaré sphere, showing an accelerated rotation around the axis of the generating polarization basis. We hope that this vector field with non-trivial structures can be used to study the interaction of vector light with matter.
Vector beams have inhomogeneous polarisation distributions that introduce a new degree of freedom that can be used to structure light. Pure vector beams have spatial and polarisation components that are non-separable affording them various interesting properties. Common examples include cylindrical vector vortex modes, Poincaré beams and vector beams on the Higher Order Poincaré Sphere. These beams are created using orthogonal modes from the same mode set, on two orthogonal polarisation bases. Vector modes have been studied in atmospheric turbulence and have displayed no specific advantage over scalar modes. Interestingly, it has recently been shown that different modal bases experience turbulence differently- can we use this to improve the robustness of a vector mode in turbulence by creating a “hybrid mode vector beam” that makes use of orthogonal component modes from the Hermite-Gaussian and Laguerre-Gaussian bases? Here we present an analysis of experimentally generated hybrid mode vector beams by determining the state of polarisation through Stokes’ polarimetry and by calculating the vector quality factor.
The study of the spatial properties of light has been rapidly evolving in the past decades. One of many applications of studying spatial light can be found in the field of quantum optics and quantum information. In these fields of study, it has become increasingly important to shape beams in experiments. This is done in order to achieve a desired output, such as increasing the entanglement amongst photons for example. This can be achieved in theory by investigating the degree of entanglement of two correlated photons created by the process of spontaneous parametric down-conversion of an input photon whose transverse probability distribution is given by the field known as a pump field. Manipulation of the pump beam in order to attain a specified correlation between the two output beams is what is known as pump shaping. Here we aim for an arbitrary decomposition of the output beams in two bases (Hermite-Gaussian or Laguerre-Gaussian transverse modes), depending on the desired properties that wish to be explored. One noteworthy result is the generation of high dimensional maximally entangled states with no post-selection.
Light affords a convenient avenue for transmitting, encoding, computing and filtering information where structuring the spatial degree of freedom allows us to perform operations at the speed of light and transfer a large range of information simultaneously in both the classical and quantum realms of physics. For example, exploiting the spatial structure of light provides a notable increase in the rate of transmission in both free-space and optical fiber transmissions. Applying this to photons also extends quantum protocols, entangling experiments into multidimensionality.
Accordingly, these schemes rely on the ability to detect and distinguish the structures holding the information encoded. Hermite-Gaussian (HG) or Laguerre-Gaussian (LG) modes are two examples of spatial modes that form an orthogonal basis and thus allows one to identify, extract and thus retrieve the entirety of the states being carried by the beam by projecting onto the individual states.
Traditionally, this is done by unitary transformations whereby the light is passed through linear elements such as a spatial light modulator. Here we demonstrate that this idea is not confined to this, but can also be extended into the non-linear regime by utilizing sum-frequency generation (SFG). By co-linearly directing the beam one would like to analyze into a χ^2 crystal with another beam carrying the basis mode one would like to project onto, one can detect the associated information in the resulting color-converted or SFG beam due to the conservation of momentum. Not only is non-linear optics shown to be a viable method for detecting spatial structures, changing the color of the light being detected offers additional flexibility in the detection hardware required as well as encryption schemes, such as high dimensional teleportation.
Quantum information processing beyond the traditional 2-dimensional qubit states has recently become topical, benefiting numerous applications such as quantum computing, quantum ghost imaging, quantum cryptography and quantum teleportation with high information capacities. The need to accurately characterize key performance parameters, such as the dimensionality of the encoding basis or the purity of an entangled state, is an essential step towards deploying any quantum protocol that uses high dimensional entanglement as a resource. Quantum state tomography takes far too long as the measurements scale to the fourth power with increasing dimensions while a simple spectral decomposition is not sufficient to confirm entanglement. Here, we present a simple to implement approach that scales linearly with dimensions and returns the purity and dimensionality of a quantum state accurately. In our approach a set of conditional measurements return visibilities that can be used in a simple fitting procedure to infer the purity and dimensions of the system. Our technique advances the toolbox for accurate characterisation of entangled quantum states. We demonstrate the technique in the orbital angular momentum and pixel (coordinate) basis using photons generated from spontaneous parametric down conversion.
Microprocessors and controllers are used everywhere: in microwave ovens, televisions, computers, cell phones, motor cars, traffic lights, satellites, etc. Therefore, Physics students need to gain basic knowledge about it, at least of how it works and can be used. The introductory physics laboratory is an appropriate environment and the Arduino a suitable tool to learn about it.
An Arduino contains a microcontroller and components that aid inputs and outputs of data. Digital and analog pins may be interfaced to breadboards with circuits and electronic components as well as sensors and actuators. Open-source software (mostly programmed in C++) is available for numerous applications.
Using the Arduino combines knowledge about electronics, control and programming. In the physics laboratory, it allows for student experimentation (e.g. Ohm’s law and Hooke’s law) with low cost instruments (e.g. for measuring temperature, pH, pressure, etc). Real world controlled systems can be planned, constructed and tested (e.g. alarm systems, cranes and robots). Additional educational advantages are the learning of scientific problem solving, critical thinking and collaboration.
This study explored South African Grade 11 Physical Sciences learners’ perceptions of scientific inquiry within the context of science classrooms. The study adopted a mixed method approach as part of an exploratory descriptive survey design and involved 50 purposively selected Grade 11 physical sciences learners from 3 South African township schools. The empirical investigation is underpinned by inquiry in school science as the underlying theoretical framework. Quantitative data was collected by administering a validated Learner Perceptions of Classroom Inquiry (LPCI) instrument with the participants. Qualitative data was collected through semi-structured interviews. The study revealed that the learners held mixed conceptions about the nature of scientific inquiry. A substantial number of learners held naïve and incoherent views about the nature of scientific inquiry. Lack of practical laboratory lessons, lack of well-equipped science laboratories, inadequate teacher professional competence when conducting scientific investigations, and limited opportunities for meaningful engagement in inquiry-based learning activities were perceived to be contextual factors that serve to hinder meaningful enactment of scientific inquiry in science classrooms. The findings have profound implications for meaningful enactment of contemporary pedagogic approaches such as inquiry-based learning in diverse contexts. Theoretical implications for coherent development of scientific literacy through meaningful enactment of scientific inquiry within the broader South African educational context are discussed.
Peer-reviewed publications are the basis of the body of scientific knowledge and of acknowledgement of contributions to science. In many countries, authorship is also used in the evaluation of individual performance and institutional achievement, and has become a part of hiring and promotion practices. As the participation of women in physics changes, it is of interest to understand whether a gender gap exists in publication. A Joint Data-backed Study of Publication Patterns was undertaken as a task within the Gender Gap in Science Project initiated through the International Science Council. This global project was a collaboration of eight scientific unions (mathematics, chemistry, physics, astronomy, industrial and applied mathematics, biosciences, history and philosophy of science, and computing machinery) together with three international organisations (UNESCO, GenderInSITE, and the Organisation of Women in Science for the Developing World). The bibliometric study of gender patterns was based on metadata available through publication databases, which allow inference of author gender from name strings using services that provide access to databases of names. Five such services were benchmarked. Results have been made available in an interactive online tool, from which the data available from South Africa have been drawn. Within the NASA Astrophysics Data System, the rise in South African publications in the field can be observed, together with the evolution of the proportion of authorships by women. Global results on fractional authorships by women in high-impact journals in theoretical physics shows average percentages of women near 10%, with little or no tendency to rise since 1999, while top journals in astrophysics and astronomy show steadily rising fractional authorships by women which have approximately doubled since 1999 [Mihalević and Santamaría, chapter in Roy, Guillopé and Cesa, eds., A Global Approach to the Gender Gap in Mathematical, Computing, and Natural Sciences, Int. Mathematical Union, Berlin 2020].
Artificial Intelligence (AI) and Quantum Machine Learning (QML) have become the most promising significant tools for addressing the challenges of the Fourth Industrial Revolution (4IR). Besides its use in understanding physical and complex systems, these tools have demonstrated unmatched potential applications in numerous research disciplines and sectors such as banking, finance, social networks, cybersecurity, and health. Most importantly, recently, they play a critical role in addressing challenges related to the Covid-19 pandemic. While these developments are remarkable, Africa has been lagging. Therefore, this paper aims to identify opportunities behind the challenges of implementing AI and MLA in addressing this technology gap, especially in the sectors mentioned above, and to participate in the 4IR fully. While the “quantum difference” presents various opportunities, especially for industries and stakeholders, we examine which challenges can be addressed by these intelligent tools. Thus, this will allow the proper application of these techniques to provide solutions to Africa’s long-standing problems.
Unizulu Science Centre (USC) has been running face to face matric workshops for 25 years, presenting practicals and sharpening skills for over 200 000 matric science students. The 2020 lockdown presented a dilemma: matrics needed assistance more than ever, but schools were closed and large gatherings impossible. Many SC’s around the world went online, making digital content available through the internet. Very few of the schools in which USC works have reliable internet and almost none of the homes, so this route was not possible. USC worked to convert a 4 hour contact workshop into 8 one-hour videos, highlighting the essential skills for Matric Science Paper 1 – the physics paper. While these videos were made available on the internet for download or streaming, they were physically distributed on memory sticks to teachers, along with an accompanying 48-page workbook. Local industry funding saw provision for the King Cetshwayo district (5500 students in 180 schools) and further SAIP funding (with support from Allan Gray) saw a further 20 000 booklets printed and 500 memory sticks manufactured. These were distributed to schools in 3 other provinces and used as the basis for teacher training.
Now, in 2021, the Physics booklet and videos have been extensively rewritten and refilmed, adding about 50 % more content and updating with 2020 exams. In addition, projects are underway to make a video series for Life Science and Chemistry. Evaluation has been conducted to try to measure the effectiveness of this method and for further improvement. Valuable lessons learnt in the process will be shared.
The first quantum revolution started in the early 1900s and was characterized by the exploration of physics at the sub-atomic level. This was followed by a second revolution around the 1970s, which witnessed the application of quantum physics to develop quantum technologies. Currently, quantum technology is gaining traction in most parts of the world. However, besides having a history of innovation in quantum physics, Africa has fallen behind in each quantum revolution. Therefore, this paper addresses challenges relating to quantum technologies and points to the opportunities that quantum technologies present to close the gap and drive economic growth and development in Africa. The latter can be achieved through capacitation and the democratization of quantum technology knowledge. This initiative will, in turn, ensure that Africa is adequately represented in the second quantum revolution. Finally, in this paper, we introduce a new development framework, namely quantum technology for development (QT4D), and explore how Africa could deploy this framework to advance the adoption and use of quantum technology and become part of mainstream computing landscape. This will allow Africa to apply these technologies in space communications, finance, drug
development, and material science, thus solving some everyday challenges and opening new opportunities for industries leading to economic growth and development.
The cathode materials that can exhibits a capacity of >270 mAh/g with little or no capacity fade are the most promising next-generation cathode active materials for Li-ion batteries. Hence, the layered oxides relative to the stoichiometry Li1+yMn1-yO2 can deliver discharge capacities of >250 mAh/g after they have been activated by charging first to a voltage of 4.6–4.9 V in a Li-cell. However, the structural inherent complexity of Li-rich oxides causes deficiencies, and the ways to illuminate them have not yet established. In the present work, we investigate the structures of the pure and Li-rich, LiMnO2 and Li1.2Mn0.8O2 at the nanoscale to shorten the path length of lithium-ion transportation, in an attempt to improve the rate performance of the systems. High-temperature molecular dynamics simulations running a DL_POLY code was utilized to carry out the amorphization and recrystallization technique under a microcanonical ensemble (NVE) and a canonical ensemble (NVT) respectively. The microstructure snapshots confirm the two defective phase composites of Li2MnO3/LiMnO2 with crystallographic defects within the nanostructures; dominated mainly by Li and Mn ions mixing layers and grain boundaries. Furthermore, the calculated XRD patterns confirm the single-phase formation of orthorhombic LiMnO2 in the pure structure and formation of the two-phase together with a spinel-type Li2Mn2O4 in the Li-rich nanoparticles. The findings of the current study will provide a better understanding of the Li-rich structures.
Due to the outstanding chemical stability against high voltage electrode, the oxide garnet with tetragonal structure Li7La3Zr2O12 (LLZO), is one of the most promising solid-state electrolytes for li-ion batteries. However, it has low ionic conductivity (~10-6 S.cm-1) at room temperature, which limits its practical application. Doping with a supervalent cation such as Ta on the Zr site of LLZO is an effective way to improve Li+ conductivity and further stabilize the tetragonal phase. To this end, the fundamental aspects regarding stability of most stable structural configuration of Ta-doped LLZO structures are still not entirely clear.
In this study, we have combined the first-principle calculations within the generalised gradient approximation (GGA) by determining the structural and thermodynamic properties of pure and doped t-LLZO for high ionic conductivity. The negative energy of formation in pure t-LLZO shows that the structure is thermodynamically stable. We further employed the substitutional search (SS) module to identify all possible structures and provide a better understanding of doped supervalent cation Ta on the octahedral 16c Zr site of LLZO. The substitutional search was used to replace a fraction of Zr atoms with Ta atoms, so that it can enable excess Li to occupy the disordered octahedral sites (occupied by Zr atoms), which could facilitate better li-ion transport and increase ionic conductivity. Furthermore, the substitutional search generated 3 new multi-component structures (monoclinic Li28La12Zr7TaO48, orthorhombic Li14La6Zr3TaO24 and triclinic Li28La12Zr7TaO48) of Ta doped LLZO. The calculated lattice parameters of doped LLZO are smaller than that of pure t-LLZO. The results show that the distance between Li-Li in doped Ta-LLZO is smaller than in pure t-LLZO, which indicates that the smaller the difference between the dopant ionic radius and the critical dopant radius, the higher the conductivity. Therefore, the structural properties of tantalum-doped structures are shown to improve, due to the smooth decrease in calculated lattice parameters. Hence, it is important to understand the stability of Ta doped LLZO for the development of all solid-state Li batteries.
The demand for lithium-ion batteries has increased in the last decades due to their broad applicability as power storage systems. However, their energy density is too low for high-power applications such as electric vehicles and renewable energy storage grids. The most substantial electroactive component of a battery is the cathode and thus much research has been devoted to improving them. In this regard, lithium-rich layered oxide Li2MnO3 has been considered as a promising cathode material for lithium-ion batteries due to their high theoretical specific capacity of 459 mA h/g, environmental friendliness and a high operating voltage. Therefore, it is necessary to investigate its properties to gain a better understating of the system. In the current study, density functional theory calculations with Hubbard Hamiltonian (DFT+U) were employed to explore stability, structural and electronic properties of bulk Li2MnO3. The calculated lattice parameters were found to be in good agreement with the experimental data, validating the approach employed. Furthermore, the negative heats of formation suggest that the structure is thermodynamically stable. The density of states revealed the presence of a bandgap at the Fermi level, implying that pristine Li2MnO3 is semiconducting, this agrees with what was found in literature. The system was found to mechanically unstable due to negative C25 and C46 elastic constants. There were no soft modes observed in the phonon dispersion curves, suggesting vibrational stability. These findings gave an insight into the bulk properties and stability of Li2MnO3.
The realisation of advanced lithium-ion battery (LIB) technologies has been hindered by the slow progress in discovering high capacity cathodes. Considerable research is focused on the lithium-rich layered Li2MnO3 owing to its ability to reversibly intercalate more lithium. However, the cycling of this material results in capacity degradation due to complex phenomena such as the irreversible oxygen loss and phase transformation caused by lattice reconstruction. Herein, a series of nanostructured Li2MnO3 models have been generated via the simulated amorphisation and recrystallisation (A+R) technique and their internal microstructures interrogated during the cycling process. The charging process involved the concurrent removal of lithium (Li) and oxygen (O) ions to restrain the release of oxygen and resulted in Li2-xMnO3-x composites. Detailed analysis of these composites reveals that the models crystallised into multiple grains which increased with decreasing Li/O content along with stacking faults and vacancies thus leading to Mn ions migrating to the Li layers. The internal microstructures display a wealth of defects leading to the emergence of distorted cubic spinel LiMn2O4, Li2MnO3 and LiMnO2 polymorphs. Characterisation of the x-ray diffraction patterns revealed peak broadening along with the growing of 2Θ~18-25 and 2Θ~29⁰ peaks associated with the spinel-like phase. These results shed insights on the mechanism that takes place during the cycling of the Li2MnO3 with complex structures and will help guide the optimisation of high-capacity energy storages.
Li-Mn-O layered-spinel composites are among the promising and economically viable, high energy density cathode materials for improving the performance of lithium ion batteries. A number of studies have focused on the specific capacity of these composite materials. However, the complex internal structural changes affecting their performance during the discharge process (lithiation) are not yet fully understood. As such, we perform the spin polarised density functional theory DFT calculations using the CASTEP (traditional DFT) and the ONETEP (linear-scaling DFT) codes to elucidate the effect of lithiation on the electronic structure of spinel LixMn2O4 (0 ≤ x ≤ 2). The electronic structure calculations were performed under the generalized gradient approximation (GGA). Electronic structure analysis depicted semiconducting properties for delithiated-Mn2O4 with a band gap of ~0.65 eV whilst, LiMn2O4 and lithiated-LiMn2O4 were found to be conductors. Furthermore, it was found that less amount of energy is required for electrons to occupy the eg orbitals of LiMn2O4 than of the eg orbitals of the delithiated-Mn2O4. This indicates that lithiation favours Mn3+ which is in line with what was observed experimentally. The LiMn2O4 Density of States (DoS) calculated with ONETEP clearly distinguish the dx2-y2 and dz2 orbitals. The dx2-y2 orbital is filled and the dz2 orbital is empty, which is consistent with the dual-existence of Mn4+ and Mn3+. We also performed a scaling test with ONETEP on supercells of LiMn2O4 spinel structure and the best performance was achieved by ensuring that the product of MPI processes and OMPI_THREADS are equivalent to the requested number of cores in the Lengau cluster. Our current findings forms a basis for moving from traditional DFT to linear-scaling DFT which will enable the study of the electronic properties of Li-Mn-O layered-spinel nanoarchitectures.
A novel cavity type solar receiver for solar trough thermal plants was developed. Previously, the theory for such a receiver was developed, and a simulation written based on it. Some results from the simulation were compared to an indoors experiment to encouraging agreement. In this talk, I present a version that was developed for a ~20kW solar plant and is tested in the open using an in-house designed solar setup. Engineering and economic aspects of the solar plant will be discussed as well as some results related to the thermal properties.
The determination of the dark electrical characteristics of each cell within a PV module enables the simulation of the complete PV modules electrical performance when in operation. It is, therefore, possible to estimate the power output of a PV module in operation. In a previous study, a method was developed that used injection dependent Electroluminescence (EL) images to characterise individual cells within a module. However, this method has specific weaknesses. The first major weakness is that when the cells are not luminescing, the cell voltages cannot be determined. The second weakness is that if the module has parallel string, the assumption that all cell currents are equal, is not valid. The method developed in the current work proposes that individual cell voltages can be determined using dark IR imaging only. When combined with the previous method, the proposed method allows for the individual cell characterisation in modules with parallel strings. This paper discusses the method employed and presents results for various modules, including modules with parallel strings.
Thin-film photovoltaic (PV) technology has been around for quite some time with varying performance for the different technologies. A major shortcoming of thin-film PV modules compared to crystalline PV technology is their shorter guaranteed operational lifespan as they degrade faster. In this study, the performance of thin-film technology operating in an outdoor environment is monitored and analysed.
An embedded generation network has been established by the PV Research group at Nelson Mandela University. The network is currently based at the PV Outdoor Research Facility (ORF) on the Nelson Mandela University, South Campus in Port Elizabeth. This embedded generation network contains three kW-scale grid-connected PV arrays comprising of various thin-film technologies. These technologies are Cadmium Telluride (CdTe), Copper Indium diselenide (CIS) and amorphous Silicon (a-Si). Custom designed and built data loggers were used to acquire AC and DC data for the various PV systems, as well as relevant meteorological data. a LabVIEW program was developed and used to process the respective datasets and for analysis. This paper presents and discusses the performance data of these three arrays over an extended period of time. A thorough comparison of the energy production is given, together with preliminary performance loss and degradation. From the data acquired, it is observed that the CIS and CdTe systems have higher performance ratios of the order of 85 %, while the performance ratio of the a-Si system consistently below 80 %.
Key words: PV systems, Thin-film technology, embedded generation, performance monitoring, PV modules
Carbon based nanostructures have a long history, dating back to the 30ies and 40ies of the 20th century. They got a strong boost with the discovery of the fullerenes and nanotubes, and they were crowned by the research on graphene. The investigations on these nanostructures are of both fundamental and technological interest due to the interesting electronic and physical properties intrinsically associated with their low dimensionality and quantum confinement effects. With the successful synthesis of graphene nanoribbons and functionalization of graphene layers some shortcoming of 2D graphene could be overcome, opening extremely promising applications in the future nanoscale electronic devices. The intrinsic physical and chemical properties of such modified graphene based systems, will be discussed in comparison with graphene. Especially, the electronic, magnetic and mechanical properties of such structures in terms of their functionalization will be discussed on the basis of theoretical investigations.
Diphenylaniline dyes are important sets of organic dyes that has stirred many research interest as photosensitizers in TiO2 semiconductor based dye sensitized solar cells (DSSCs). The advantages of organic dyes over metal based complexes are higher extinction coefficient, low cost, good environmental compatibility and electrochemical properties. The diphenylaniline organic dyes with basic configuration of donor-π-acceptor are relatively cheap, easy to synthesize and possess chemical structures that can easily be altered to optimize their photocatalytic properties. The enormous interest in dipheylaniline dyes as photosensitizers is due to their fascinating spectral properties which include visible light to near infra-red light absorption. In this work, density functional theory approach via GPAW, Avogadro and ASE were employed to study the effect of the methoxy functionalized group on the spectral properties of diphenylaniline dyes to improve their photocatalytic properties to harness more near infrared photons. Our results shows that the two dyes with pure phenyl groups D5 and D7 shows maximum absorption peaks at 750 nm and 850 nm, while D9 and D11 with methoxy group shows maximum absorption peak at 800 nm and 900 nm respectively. The highest absorption wavelength is notable for D9 and D11 containing methoxy groups. Also D9 and D11 dyes with the methoxy group shows lower energy gap of 0.98 and 0.85 respectively than the corresponding D5 and D7 dyes with energy gap of 1.32 and 1.08. The analysis of their electron injection kinetics ∆Ginject into the band gap of TiO2 shows that D9 and D11 with the methoxy group has higher electron injection kinetics of -2.070 and -2.030 than the corresponding pure phenyl dyes with ∆Ginject values of -2.820 and -2.130 respectively. Our findings suggest that the photocatalytic properties of organic chromophores with donor-π-acceptor configuration can be enhanced by the addition of functionalized groups.
Recently, carbonaceous nanomaterials such as carbon nanotubes and two-dimensional graphene have attracted the attention of the scientific community in probe to improve energy conversion and storage technologies. The graphene sheet is more preferred due to its large specific area, flexible structure, high transparency, excellent mobility of charge carriers and is expected to be able to slow the charge recombination. Graphene/Transition metal oxides nanocomposite study has become much of a wide interest recently with metal oxides like TiO2 and ZnO. These metal oxides are used as thin films in photovoltaic technology to harness energy. The final composite embodies both the transport properties of the former and the semiconducting properties of the latter species. This work describes an analysis of the electronic and optical properties of graphene/TiO2 studied using the Density Functional Theory (DFT) in application to dye-sensitized solar cells (DSSCs).
More than half of all galaxies within the local Universe are found within group environments. Therefore, galaxy groups are excellent laboratories for studying galaxy evolution in the local Universe. The Complete Local Volume Groups Sample (CLoGS) is the first statistically complete galaxy group survey in the optical, X-ray and radio bands, consisting of 53 galaxy groups and 1427 member galaxies in total. The basic properties of the member galaxies, such as their morphologies, star formation rates, stellar masses and radio emission have been determined and studied with regards to their unique group environments. Exciting statistical relations between the properties of the member galaxies and their group environments have been found; such as trends in star formation that relate to each group's dynamical age, X-ray halo and radio emission from their brightest group ellipticals (BGEs). As a continuation of this study, a detailed optical spectroscopic study of these BGEs using data obtained on SALT (Southern African Large Telescope) is currently underway. The determined statistical relations and latest spectroscopy results will be presented.
Large, state-of-the-art cosmological simulations allow us to follow the evolution of various galaxies, and since it contains detailed knowledge of e.g. the metal content of the stars in each galaxy, it can be used to compare to galaxies in the real Universe. In our work, we are improving the implementations of the stellar feedback model within the GIZMO-Mufasa cosmological simulation. This particular simulation is the merged product of GIZMO's public available code and Mufasa/SIMBA to create realistic large-scale enviroments. Specifically, we are improving the current simplistic instantaneous recycling of the metals model, with a more accurate Cosmic Chemical Enrichment model developed by Kobayashi et al (2007) and updated in Kobayashi et al (2020). This will improve the time delay due to the star's evolution and the time delay for the local enrichment to occur, as well as add new metals to the evolutionary tracks of stars tracked by simulations. We added a probability distribution to determine if a specific region will be enriched (rather than a fixed distance distribution) into the mechanical feedback process. This distribution can be found in the thermal feedback process in the main GIZMO simulation. This will lead to more realistic black hole seedings. Ultimately, we can compare the new model to the old simplistic model using various different well-tested scenarios (e.g Mass-Metallicity relation) and interpret any differences.
In 2015, the massive protostellar cluster NGC6334I-MM1 flared in various maser species detected by long term monitoring at HartRAO. Followup infrared, millimetre and centimetre observations confirmed that a massive protostar MM1B (M ~ $6.7 M_\odot$) inside the cluster underwent a period of high mass gain, an accretion burst. To probe the effects of such a transient event on the native protostellar environment, multi-wavelength, multi-epoch and multi-scale observations are required. We present high-resolution relative proper motion observations of highly variable water masers in NGC6334I during the onset of the accretion burst. High veloctiy ($\bar{v} = 85$ kms$^{-1}$) proper motions were detected in five regions, CM2-W2, MM1-W1, MM1-W3, UCHII-W1 and UCHII-W3. Using velocity variance and covariance analysis, we calculated the position angle of the major axis of motions to be -79.4$^\circ$ centred on MM1B, showing the axis of the jet driving the CM2-W2 shock. The axis traced by water maser motion correspond to an outflow previously detected in CO emission. Complex motions in MM1-W1 indicate possible turbulent interactions between multiple outflows centred on MM1. Unpublished high resolution water maser maps of the period before, during and after the accretion burst will also be presented, showing the large effects of these bursts on protostellar environments.
Astronomical maser emission occurs in various astrophysical environments and can be used to infer the physical properties of the regions where they are excited. An import part of interpreting the presence of maser emission associated with a specific astrophysical environment is knowing what the pumping mechanism (radiative or collisional) for a particular maser is. Based on calculations using the online RADEX facility, Baan et al (2017) recently concluded that the extragalactic $4.8$GHz formaldehyde megamasers are radiatively pumped. This is contrary to the conclusion of van der Walt (2014) that formaldehyde masers associated with high mass star forming regions are collisionally pumped. Since much of the interpretation of the maser emission depends on pumping mechanism, we revisited the pumping of the formaldehyde masers (1) to try to understand the results obtained by Baan et al (2017) using the RADEX facility and (2) to extend the calculations of van der Walt (2014) to also include parts of parameter space considered by Baan et al (2017) but not by van der Walt (2014). Some preliminary results, which suggest that the formaldehyde masers are indeed collisionally pumped, are presented.
Hyper-runaways are stars moving at supersonic speeds through the interstellar medium; they can be thought of as a subset of runaway stars but moving with velocities that are comparable to the Galactic escape velocity $(\sim 500\,$km/s). Because of the strong stellar winds and high space velocities, we expect massive (hyper)runaway stars to produce bow shocks. We use PLUTO, a magneto-hydrodynamics grid code, to simulate these bow shocks, performing axi-symmetric hydrodynamic simulations in 3-dimensions while including thermal conduction and detailed radiative cooling processes. In this talk we will present our results for a range of stellar velocities ($100 \leq v_{\rm star} \leq 500\,$km/s) and discuss the implications for potentially observing hyper-runaways.
Capture-recapture has been identified as a possible use case for estimating the underlying size of astrophysical transient and variable populations. We present a series of exploratory analyses using capture-recapture methods from biostatistics. Several estimators were tested for their applicability. We implemented two different capture-recapture approaches: a statistically closed population and a robust design, a mixture of closed and open population modelling.
In the first approach, we used simulations of the X-ray lightcurves of high mass X-ray binaries (HMXBs) to probe the convergence to the input population for several estimators as a function of the number of observations. The cadence played a crucial role in the rate of convergence to the underlying population with respect to the number of observations relative to the underlying period distribution of the recurrent source outbursts. The cadence and threshold discrimination of sources between outburst and quiescent states affect the capture probability of sources. Capture probability was demonstrated to be a key factor for population estimation, categorised into 'behavioural', 'temporal', and 'heterogeneous' effects. The simulations were extended to a real data application for HMXBs in the Small Magellanic Cloud using the OGLE-IV XROM survey. The observations were grouped into a fixed number of samples, and the optical characteristics included large variation in quiescent flux that creates heterogeneous population capture probability. The estimation was notably limited by the observational flux threshold in this instance.
The robust design investigated a population of Dwarf Nova identified from the OGLE-II, -III, and -IV phases. New individuals were added to the monitoring sample between phases, which the robust design accounts for in its modelling, and abundances were estimated within phases and for the entire study.
These investigations have opened a course for population estimation of transients and variable stars alongside population synthesis simulations. The generation of capture histories remain non-trivial through the choice of observation grouping, brightness scale, and imposed flux threshold. Recommendations are made for further exploration of the topic.
The connection between the multi-lepton anomalies at the Large Hadron Collider and astrophysics can be described by a two Higgs doublet model with an additional singlet scalar (2HDM+S). We make studies on the interaction mechanism of singlet S to dark matter. This is achieved from the annihilation of Dark Matter (DM). We demonstrate that using this model we could also describe the excesses in gamma-ray flux from the galactic centre and the cosmic-ray spectra from AMS-02. Moreover, this study provides indirect searches for new bosons that have never been performed before at the LHC, namely the search for H→SS,S→invisible and S decaying into other particles.
In this presentation an account of the multi-lepton (electrons and muons) anomalies at the LHC will be given. These include the excess production of opposite sign leptons with and without $b$-quarks, including a corner of the phase-space with a full hadronic jet veto; same sign leptons with and without b-quarks; three leptons with and without $b$-quarks, including also the presence of a $Z$. Excesses emerge in corners of the phase space where a range of SM processes dominate, indicating that the potential mismodeling of a particular SM process is unlikely to explain them. A procedure is implemented that avoids parameter tuning or scanning the phase-space in order to nullify potential look-else-where effects or selection biases. The internal consistency of these anomalies and their interpretation in the framework of a simplified model will be presented. Implications on the SM Higgs boson measurements, the muon g-2, astrophysics and other potential deviations from the Standard Model will be discussed.
As a branch of Physics, Astronomy has put significant effort and resources into using all aspects of the field to stimulate global development. This talk will reflect on the first decade of the International Astronomical Union's Office of Astronomy for Development (OAD). Established in April 2011, the OAD is a partnership between the IAU and the South African National Research Foundation, mandated to use astronomy to stimulate development globally. Over the past decade the OAD has established 11 regional offices and language centres and funded over 200 projects targeting audiences in over 100 countries, which includes 43 COVID-related projects. We will discuss the OAD's activities, challenges and impact over the years, as well as plans for the future.
The standard of engagement in science classes is fundamental for effective learning. Creating an active learning environment is essential for engaging learners. However, implementing engagement is one of the most important problems facing teachers. Furthermore, there are different engagement strategies and teachers often do not know what strategy to use, or only use one of them. This paper attends to the factors that could influence the choice of an appropriate engagement strategy.
In a research study we set out to explore music, context-based inquiry, and computer simulation as engagement strategies as well as the impact of these strategies on the four components (behavioural, emotional, cognitive, and authentic) of engagement. The application of mixed methods comprised of a pre-test and post-test questionnaire (quantitative), video recording and semi-structural interviews (qualitative). The general results that follow from this research is that the choice of an appropriate engagement strategy does not only depend on the topic to be taught, but also on other factors namely teachers' acquaintance with the strategy, the learning environment, the background of the learners, the engagement components that need attention as well as the amount of time available. A combination of the three engagement strategies has proven to enhance engagement.
Embracing 4IR in the education system has become mandatory more than before considering the current global pandemic. Teacher beliefs influence their practices. It has also been found that sometimes there is a mismatch between teachers’ beliefs about the affordances of technology and the actual practices in the classrooms due to contextual factors. Many countries have embraced 4IR in their education system and South Africa is part of the change. Because this is a ‘revolution’ many science teachers have been caught off guard and they harbour mixed feelings regarding their roles and what the future has in store for them. The current study sought to establish newly qualified science teachers’ perspectives on their roles due to the call to embrace 4IR tools in their classrooms. The qualitative study was guided by the research question: What are teachers’ beliefs about their roles in science classrooms where 4IR is embraced? The participants were ideal considering their relative young age which is coined as ‘the digital age’. An online questionnaire was administered to 60 teachers who had just qualified to teach science. The questionnaire specifically sought science teachers’ levels of preparedness in terms of competencies, resource availability and management, and future professional prospects. Data was subjected to content analysis and three themes emerged. 1. Teachers believed that the government and the Department of Basic Education’s stance to embrace 4IR is a vehicle that promotes unequal education opportunities for science learners. The teachers’ argument was that whilst it is a welcome development, there has not been parity in resource distribution in schools because learners come from diverse socioeconomic backgrounds. Those from disadvantaged backgrounds even struggled with acquisition of simple calculators in which case the acquisition of electronic gadgets could even be out of reach for many. 2. Most of the science teachers showed lack of confidence as they believed they were not technologically prepared to embrace 4IR tools such as AI, coding and robotics. As such, they expressed fears and insecurities when it comes to their competencies to deliver technology led classroom teaching and learning of science. 3. The science teachers believed that too much utilisation of technology in a science classroom will demean the actual teaching and learning of scientific concepts. In this case the teachers questioned the effectiveness of technology in providing meaningful learning of science. The findings of this study contribute towards the need to change the status quo on the disparities between urban, rural as well as township and suburban schools in terms of resource distribution; and teacher professional development on the need for continued technological knowledge and skills development.
Key words: Classroom practices, science teacher beliefs, 4IR.
The COVID-19 pandemic has impacted teaching and learning at the University of the Western Cape, in particularly the first year students from high schools. These students who traditionally received their teaching and learning through face-to-face teaching and learning method now receive their teaching and learning via online (electronic teaching and learning) because the university has decided to make online teaching and learning the core method to deliver the curriculum during the pandemic.
After the first term of online teaching and learning, an online survey was conducted to investigate the perception of online teaching and learning among the first year main stream physics students in the department of Physics and Astronomy at the University of the Western Cape. In this presentation the results of the survey will be presented and discussed.
The pandemic year represented a challenging time for educators, a time where the classical way of teaching change from contact to remote learning. While contact lectures can be replaced by videos or video conferences, the laboratory can be replaced with simulations or by instructing the students to buy and build ad hoc systems by supplying the essential instructions. A remote assisted experiment requires to be conducted safely, the components readily available, and possibly low-cost. Technical High Schools and universities teach the logic gates and how to assemble a circuit to solve a specific function. Several licensed and free software are available for simulation, and for a hypothetical real experiment, it is necessary to supply the students with several components and tools. This project proposes performing several digital electronics experiments by using a building block, a logic gate emulator. This device can be modified according to the teacher's needs and sent to the students to do remote experiments.
In line with current realities and best practices across the world, preparing physics students and graduates is beyond the usual physics career bracket. Preparation of Physics students in the now is beyond the standard model, where preparation now include working well in teams, understanding how science and technology are used in real-world settings, writing, and speaking well, and understanding the context in which work is now done; where use and value of knowledge and graduate skills go beyond the knowledge of physics is often engaged. These concerns led the researchers to draw on various education theories in to order to understand, investigate and relate how preparedness in terms of graduate skills will benefit physics graduates. In this study, the researchers will focus on the Benchmark Statement on BSc Physics and BSc (Hons) Physics programs in South Africa as articulated by SAIP, graduate attributes (transferable skills and citizen skills) in the context of Physics Graduate Attributes (PGAs), the physics curriculum from a progressive university in South Africa in answering “How are intended physics graduate attributes (as specified by SAIP and Charter of graduate attributes) embedded in the BSc and BSc (Hons) physics curriculum?”. The study will assess the stand of SAIP regarding how Universities adopt the Benchmark Statement and recommend suggestions for further oversight by SAIP.
In this investigation, air plasma spraying was used to coat two sets of geometrically different Ti-6Al-4V alloy substrates with hydroxyapatite (HAp). The two sets of samples were then immersed in simulated body fluid (SBF), a fluid whose ionic composition resembles that of the human fluid, to determine the biofunctional performance of the coatings. Immersion was done for varying time periods (0, 7, 28 and 56 days) under physiological conditions. Samples where then analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM) in order to compare coatings deposited on the two geometrically different substrates before and after immersion. XRD technique was used to investigate the effect of the simulated body fluid on the thermal products formed, the degree of crystallinity and the residual stresses of the coating for both substrate geometries. SEM was used to study the surface morphology and microstructure of both samples after coating and immersion. Previous investigations conducted on these coatings indicated that immersion in SBF has an effect on the morphology and chemical composition of the samples.
Iron doped (FE:5Ti) sodium and (FE:10Ti) potassium titanates were prepared by the Pechini sol-gel method and calcined at 800 . X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission Electron Microscopy (TEM), Energy Dispersive X-ray spectrometry (EDS), FTIR and Raman spectroscopy were used to characterize the titanate nanomaterials. A quantitative XRD analysis using Rietveld refinement of the titanates confirmed the powders to consist of crystalline phases with the Na2Ti7O15 and K2Ti8O17 phases predominant for the sodium and potassium titanate, respectively. This was further confirmed using selected area electron diffraction (SAED) in the TEM. SEM analysis indicated the titanates consistent with a nanostructured material exhibiting rod like morphology. The elemental compositions of the titanites were examined by SEM-EDS and TEM-EDS and found to agree well with the targeted Fe to Ti ratio from synthesis. Limited evidence for the segregation of iron in the titanate regions were found indicating the iron to be incorporated within the titanate lattice. Electron energy loss spectroscopy (EELS) fine-structure analysis of the Fe L2,3 core-loss edge was successfully used to match the Fe to a 3+ or 4+ valence state. Finally, Fourier transform infrared spectroscopy (FTIR) was used to classify the stretching and bending vibration modes of the functional group of sodium and potassium titanates along with Raman spectroscopy.
Mixed phases of Tb3+ doped CaAl2O4/Ca1.02Sr1.98Al2O4/SrAl2O4/SrO/Al2O3 (CCSSA:x%Tb3+ (0 ≤ x ≤ 2)) nanophosphors were successfully prepared using sol-gel method. X-ray diffraction (XRD) patterns revealed that all the annealed samples resembled the mixed phases of monoclinic (CaAl2O4 and SrAl2O4), cubic (Ca1.02Sr1.98Al2O4 and SrO) and hexagonal (Al2O3) crystal structures, which were not influenced by variation the Tb3+ concentration. Scanning electron microscopy (SEM) images showed that the morphological features of the prepared nanophosphors were influenced by the Tb3+ concentration. Transmission electron microscopy (TEM) confirmed that the prepared materials were on the nanoscale region. Ultraviolet–visible (UV–vis) diffuse reflection spectroscopy showed that the band gap energy can be tuned in the range 4.90- 5.35 eV. Photoluminescence (PL) results showed four emission peaks located at around 490, 544, 583 and 622 nm and they were respectively ascribed to 5D4 → 7F6, 5D4 → 7F5, 5D4 → 7F4 and 5D4 → 7F3 transitions of Tb3+ ions.
Citrate sol-gel method was used to successfully prepare mixed phases of strontium and barium aluminate powders doped with 0.1% Tb3+. All powders were annealed at 1000 oC while varying the annealing time (AT) from 0.5 – 4 hours (h). The X-ray powder diffraction (XRD) results revealed that the prepared powders is the mixture of phases consisting of cubic (Sr3Al2O6, Ba3Al2H12O12), monoclinic (SrAl2O4, SrAl4O7), hexagonal (Ba0.6Sr0.4Al2O4, SrO, BaAl2O4) and orthorhombic (BaH4O3) crystal structures. Tb3+ did not influence the structure of mixed phases of BaAl2O4/BaH4O3/Ba3Al2H12O12/Ba0.6Sr0.4Al2O4/SrAl2O4,SrAl4O7/ Sr3Al2O6/SrO (BBBBSSSS). The energy dispersive X-ray spectroscopy (EDS) mapping showed homogeneous distribution of elements on the surface. The scanning electron microscopy (SEM) images showed that as the AT increases the particle becomes more agglomerated and smoother. Transition electron microscopy (TEM) images suggested that the particle sizes were not influenced by the AT. Ultraviolet–visible (UV–vis) diffuse reflection spectroscopy confirmed that AT influenced the energy band gap (Eg) of the prepared nanophosphor. The Eg can be tuned between 5.1 and 5.7 eV. Photoluminescence (PL) results showed four emission peaks located around 489, 546, 589 and 618 nm which are attributed to 5D4 →7F6, 5D4 →7F5, 5D4 →7F4, and 5D4 →7F3 transitions of Tb3+ ions, respectively.
Rechargeable sodium-ion batteries (SIBs) have attracted great attention for large-scale electric energy storage applications and smart grid owing to the abundance of Na resources and comparable performance with lithium-ion batteries. The use of organic electrode materials enables a sodium storage system with high energy/power density, metal-free, environmental friendliness, flexibility, lightweight, and cost-effectiveness, in this study Density functional theory (DFT) has been used to study the electronic (band structure & TDOS), Elastic properties and intercalation voltage of NaMnO2 doped with Ni.The generalized gradient approximation (GGA) was used in the scheme of Perdew-Burke Ernzerhof to describe the exchange -correlation function as implemented in the CASTEP package in material studio of BIOVIA. Our findings show that NaMnO2 possess high voltage window and a good reversible capacity. The elastic properties shows that NaMnO2 doped with Ni is stable, while the electronic properties shows that metallicity of NaMnO2 gradually increases during Na extraction
The University of the Witwatersrand will be producing over 1200 Low Voltage Power Supplies (LVPS) to power the on-detector electronics of the Tile Calorimeter (TileCal) ATLAS detector in preparation for the Phase II upgrade. Two burn-in type test stations are currently being developed in the high-throughput electronics laboratory. The Load readout board is used to read and control/adjust parameters of four channels electronic dummy load board, and several parameters. In this talk, we discuss how different commands for each PIC micro-controller are written and used to shift bits into the register of the Digital to Analog converter (DAC) contained on the dummy load to control the load current. A hexadecimal source file is thus generated and typically used by programmable logic devices which provides general information of the configured functions.
With University of the Witwatersrand responsible for producing 50% of the Low Voltage Power Supplies (LVPS) bricks for powering on-detector electronics of the Handronic Tile Calorimeter (TileCal). The Burn-in testing station is used to detect early failures in components of the LVPS bricks, thereby increasing component reliability, detect early failures in components. The LVPS bricks that passes this test are then shipped to CERN, for installation on the detector. Here we describe the significance and functionality of the brick interface board on the burn-in station, and the process to programme PIC16f883 microcontroller, which is used to send commands and act as a multiplexer to main board, brick interface boards on the burn-in test station and enables the LabView software programme to interface with the hardware of the Burn-in to successfully carryout its functions.
Time coincidence detection of annihilation photon pairs is used to determine the instantaneous position of point-like particles used as flow following tracers in dynamic systems. Locations are calculated by a minimisation approach applied to a small number of reconstructed pairs assuming a fixed signal to noise ratio. Consecutive locations define the particle trajectory, and hence the dynamic parameters of particle motion, from which the global system behaviour is inferred. The measurement precision depends upon the positron range and annihilation physics, the spatial resolution and geometry of the detector array, and the amount of photon scattering and absorbing material within the field of view. Statistical processes further limit the precision, with high activity tracers (100s MBq) and high event rates (MHz) preferred. However, deadtime, pulse pileup, and the increased contribution of random coincidences reduce the signal to noise ratio in these conditions.
At PEPT Cape Town large arrays of position sensitive detectors are used to track particles with diameters down to 50 um to within 1 mm in 3D. Typically particles moving at speeds up to 10 m/s can be reliably tracked, by measuring locations many thousands of times per second. In an effort to observe flow phenomena on the micro-scale we have investigated the use of small scale pixelated semiconductor detectors with superior energy resolution. An analysis of the factors contributing to spatial resolution in PEPT measurements in both scenarios is presented.
Instrumental neutron activation analysis (INAA) is a non-destructive technique used for qualitative and quantitative elemental analysis in a range of contexts, including the food, coal and minerals processing industries, and the detection of contraband. Broadly, INAA requires the irradiation of a sample in a neutron field, and the neutron interactions within the sample to produce radioactive isotopes with characteristic gamma ray emissions. These characteristic gamma ray emissions are then detected using a gamma ray spectrometer and further analysed to determine elemental composition.
In 2017, the UCT Department of Physics commissioned the n-lab, a fast neutron laboratory centred around a Thermo MP-320 deuterium-tritium sealed tube neutron generator (STNG) and a 220 GBq Americium-Beryllium (Am-Be) radioisotopic source. The aims of this project are to characterise the n-lab as an INAA facility, and to develop standardised analysis protocols for the elemental analysis of bulk materials. Fundamental to INAA is knowledge of the number and energy distribution of neutrons incident upon the sample of interest. The process of determining the neutron flux by the activation of foils is presented, in addition to the recent results from the activation of copper and aluminium samples by the STNG. The next stages of this project are discussed with respect to measurement and radiation transport simulations, with a particular focus on the use of pulsed 14.1 MeV neutron beams produced by the STNG.
The Positron Emission Particle Tracking (PEPT) technique enables the tracking of a moving
radioactive tracer particle at high spatial and temporal resolution, from which its trajectory can
be accurately reconstructed. The uncertainty budget is complex and poorly understood,
particularly for derived quantities such as momenta, energies, and forces, which are typically
calculated using numerical differentiation techniques.
We report a filtering and data processing method based on a local polynomial least squares
fitting approach known as the Savitzky-Golay filter. The method is adapted to incorporate the
propagation of measurement uncertainties, maintaining them within useful bounds. The
method is benchmarked against several systems of known particle motion, including constant
velocity and constant acceleration, to place confidence limits on the results. Across all tested
regimes the Savitzky-Golay filter resolves higher precision than existing methods, providing
notable improvements to the uncertainty budget in PEPT analysis. We demonstrate tracking of
a particle moving up to 3 m/s with location precision within its diameter, and a 60% and 40%
average reduction in uncertainty bounds for velocity and acceleration respectively.
These results have motivated development of a high-resolution detector array for PEPT,
enabling measurements on the micro-scale by making immediate use of the improvements in
precision. Successful implementation will allow the meaningful application of PEPT to identified
problems in diagnostic medicine and in the study of micro-fluidic devices.
In 2015 the advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO) detected the first ever gravitational
event, gravitational wave event GW150914, with multiple new gravitational wave events, originating from both
binary neutron stars and binary black hole (BBH) mergers, detected in subsequent years. In light of these detections,
we simulate the dynamics of ambient test particles in the gravitational potential well of a BBH system close to its
inspiral phase with the goal of simulating the associated electromagnetic radiation and resulting spectral energy
density distribution of such a BBH system. This could shed light on possible detection ranges of electromagnetic
counterparts to BBH mergers. The potentials are numerically calculated using finite difference methods, under the
assumption of non-rotating black holes with the post-Newtonian Paczynski-Wiita potential approximation in tandem
with retarded time concepts analogous to electrodynamics. We find that the frequencies of potential electromagnetic
radiation produced by these systems (possibly reaching earth), range between a few kHz to a few 100kHz. The bulk
of radiation is distributed at frequencies below 100kHz.
Keywords: Binary black hole merger, binary black hole, binary black hole merger simulation, particle acceleration,
gravity.
Neutral Hydrogen (HI) Intensity Mapping (IM) promises to open a new window for cosmology, probing Large Scales Structures (LSS) in the Universe over a wide range of redshifts. Unfortunately, HI IM is contaminated by several effects, one of these is the emission from artificial satellites. We aim to simulate the Radio Frequency Interference (RFI) emitted from the Global Navigation Satellite System (GNSS) for the MeerKAT Single Dish HI IM observations, focusing on the 1000-1500 MHz frequency range. We fit our satellite model to data taken using the MeerKAT telescope and study the impact of the residual contamination in the supposedly RFI free regions.
Recent detections of the Crab, Vela, Geminga pulsar as well as PSR B1706-44 by ground-based Cherenkov telescopes have created exciting prospects of many more such discoveries by the upcoming Cherenkov Telescope Array. Pulsed photons with energies in excess of 1 TeV detected from the Crab and Vela pulsars severely constrain the particle energetics, emission mechanisms, as well as spatial aspects of the dissipation regions within the pulsar magnetosphere. Within an extended slot-gap framework, we model the broad-band pulsar spectrum invoking force-free-like fields and multiple emission components, including synchro-curvature, synchrotron self-Compton (SSC) and inverse Compton (IC) radiation by both primary particles and pairs. IOn particular, we predict two TeV components: (i) SSC from pairs and (ii) IC from particles accelerated in the current sheet upscattering pair synchrotron radiation. We fit our predictions to available broadband data, indicating that it may now be possible to directly measure the maximum particle energy in pulsars.
The wealth of multiwavelength pulsar data has stimulated the development of emission models that predict light curves (LCs) over multiple wavebands, most notably radio and gamma-ray. Using established statistical methods to fit these model LCs to data can prove ineffectual if the data from one waveband are substantially more precise. This waveband—typically radio—dominates the fit and biases inferred parameters. We re-examine the use of Pearson's chi-squared statistic for joint fits, and introduce a new, derived statistic. The core insight that this statistic encodes is that the component single-band chi-squared values implicitly express goodness of fit in units of the respective LC uncertainties. The resulting implicit weighting the dual-band chi-squared carries is eliminated by expressing these values in a shared unit before calculating their sum, derived by effectively standardizing the scaled pulsar-associated flux across the two wavebands. Importantly, chi-squared and our new statistic converge to the same constraints as the precision disparity dissipates. As a first test, we fit two amalgamated dual-band models to 23 Fermi LAT pulsars and compare the resulting constraints to earlier results derived using the same data and similar models. Our fits consistently show no radio dominance, and our constraints more strongly correlate with those derived by eye.
The Neutron star Interior Composition Explorer (NICER) was installed aboard the International Space Station (ISS) in 2017 with the major aim of a better understanding of the extreme nature and composition of neutron stars (NSs). With its exceptional sensitivity, it hopes to constrain the equation of state for these compact objects to high precision. Modelling thermal X-ray light curves (LCs) of pulsars can also provide us insights into the magnetic field structure of NS which further helps in understanding the morphology of the surface hot spots.
Recently, works by Miller et al. (2019) and Riley et al. (2019) suggested strong evidence for a multipolar magnetic field of the millisecond pulsar PSR J0030+0451, constraining its mass and radius with unprecedented accuracy. Kalapotharakos et al. (2021) constrained the parameter space for an offset-dipole plus quadrupole field configuration, by calculating polar caps which accurately produce the NICER X-ray LC (and inferred surface hotspots) of J0030 making use of Markov chain Monte Carlo (MCMC) methods. This approach indicates field degeneracies for offset static vacuum and force-free configurations, meaning different configurations adequately describe the same observed LCs. Exploring the same configuration to fit the gamma-ray LCs measured by Fermi data breaks the field degeneracies – giving a more constrained model solution.
We are extending the above study by changing the static vacuum field configuration to a more realistic retarded field in terms of a multipole expansion, where we include higher multipoles, i.e. beyond quadrupole, and then including general relativistic effects and an offset configuration. Exploring the field parameter space by using MCMC for this configuration to fit the X-ray LCs and corresponding Fermi gamma-ray LCs would help us constrain the field structure, and eventually the stellar mass and radii, more robustly. In the talk, the impact of this work and future implications would be discussed.
Marsh et al.~(2016) detected radio/optical/UV pulsations from the binary system AR Scorpii (AR Sco) mainly at the beat period of $118$~s. This system, with an orbital period of $3.55$h, is composed of a cool, low-mass star and a white dwarf with a spin period of $117$~s. More recent observations also showed X-ray pulsations from this source (Takata et al. 2018). Buckley et al.~(2017) found that the polarimetric emission from the white dwarf is strongly linearly polarised (up to $\sim 40\%$) with periodically changing intensities. This emission is thought to be powered by the highly magnetised ($5\times10^{8}$~G) white dwarf that is spinning down. We fitted a standard rotating vector model to these polarisation position angle data, and found a magnetic inclination angle $\alpha\sim90^{\circ}$ and an observer angle $\zeta\sim60^{\circ}$, similar to independent constraints found by others. Previously we determined that synchrotron radiation dominates other radiation mechanisms for producing the optical emission as long as the pitch angles of the particles can be maintained; otherwise curvature radiation would dominate. We applied our model to the orbitally phase-resolved polarisation position angle data from Potter and Buckley (2018b) and present these results on the evolution of $\alpha$ and $\zeta$ vs. orbital phase. Additionally, we investigate the evolution of the linear-flux light curves binned independently at the spin and beat frequency independently vs. orbital phase. Finally we include a Lomb$-$Scargle periodogram for the different regions of the orbital phase thereby constraining any potential signature of precession in the system.
A search for $tWZ$ production using events containing three leptons from Run 2 ATLAS proton-proton collision data with a centre of mass energy of 13 TeV will be presented. An event selection scheme was developed using simulation to select $tWZ$ events and to broadly suppress background events. Events were then separated into mutually-exclusive regions of phase space to increase the amount of $tWZ$ events compared to background events, and to calibrate the modelling of the background production processes. Background events were further suppressed through the use of Gradient Boosted Decision Tree (GBDT) machine learning algorithms. First, a GBDT was trained to identify hadronically-decaying $W$ bosons since these are a characteristic feature of $tWZ$ events and help distinguish between $tWZ$ and one of the major background processes, $WZ$. Then, this GBDT and other event information was used to train an event-level GBDT used to distinguish between $tWZ$ and all backgrounds. Using the output of the event-level GBDT, a maximum likelihood fit was used to estimate the signal strength, $\mu$, of $tWZ$ production, where nuisance parameters were assigned to theoretical and experimental systematic uncertainties. A signal strength of $\mu = 1.80^{+1.88}_{-1.83}$ was determined with an expected significance of $0.55\sigma$, and an expected upper limit on $\mu$ of $3.6^{+3.1}_{-1.7}$ was also determined. The preliminary blinded results show that the search has the potential to put the strongest ever constraint on tWZ production, but does not have the potential to observe tWZ production as predicted by the Standard Model. These constraints are limited by statistical uncertainties, therefore an outlook on future measurements of $tWZ$ within ATLAS will be discussed.
This paper presents the search for the Higgs boson, with mass 125GeV, decaying to two new intermediate states and then into four lepton final states, H → ZdZd → 4l together with the search for a double Zd1 and Zd2 hypothesis. The analysis is conducted using the Run II data set from pp collisions collected with the ATLAS detector corresponding to a total integrated luminosity of 140fb−1 at a centre of mass energy of √s = 13TeV. A study on modifying the signal region has also been conducted, assuming a broader width on the Zd. Based on the signal and background models, the total number of expected events is 14, while 19 events were observed in the modified signal region. The results are compatible with Standard Model predictions. The search for the double hypothesized Zd1 and Zd2 is performed in the medium signal region. For this study, clustering algorithms and azimuthal integration are used to find the hypothesized Zd1 and Zd2 vector boson masses. Particular emphasis is also given to the limit setting procedure used in this analysis. In addition, the procedure used to port the limit setting code from CPU to GPU is reviewed together with the performance of the modified machinery.
A search for the non-resonant production of a pair of the Standard Model Higgs boson $h$ via gluon-fusion, $gg\rightarrow hh$, is performed. Each Higgs boson decays to either $W^+W^-W^+W^-$, $ZZZZ$ or $ZZW^+W^-$ leading to $4\ell+X$ in the final state. The $\ell$ could be an electron or a muon, and $X$ is missing transverse energy or jets. The b-tagged as jets is vetoed in this analysis. The search uses the data at a centre-of-mass energy of 13 TeV collected by the ATLAS detector between 2015-2018 at the Large Hadron Collider. Cut-based and multivariate analyses are used to exploit the signal.
Studies towards a measurement of the leptonic charge asymmetry in top quark pair production in association with a W boson($t\bar{t}W^{\pm} $) at 13 TeV with the ATLAS experiment are presented. Previous measurements of the $t\bar{t}W^{\pm} $ cross-section have been shown to be higher than that predicted by the standard model indicating a potential discrepancy in the modeling of the $t\bar{t}W^{\pm} $ process. This analysis aimed to study the leptonic charge asymmetry of $t\bar{t}W^{\pm} $ as it provides an independent method of verifying the modeling of the process and has never been measured before in $t\bar{t}W^{\pm} $. The full run II data(139 $fb^{-1}$) was utilized in these studies. An event selection scheme was put in place to optimally select for $t\bar{t}W^{\pm} $ events in the three-lepton final state while suppressing background events. The leptonic charge asymmetry is calculated using the $\eta$ of the top and anti-top leptons. As such a machine learning algorithm was implemented to optimally select the pair of leptons decaying from the top quarks from the total three leptons in the event. Finally, the extraction of the leptonic charge asymmetry was implemented using a method known as template morphing. This analysis has remained blinded as it forms the basis of an official ATLAS analysis. Several sources of error have been considered namely: cross-sections, lepton trigger efficiencies, and b-tagging efficiencies. The main source of uncertainty in these studies is the limited statistics. With this in place a leptonic charge asymmetry of $A_{C}^{\ell} $ = $-0.08^{ +0.29}_{-0.31}$ was extracted using Asimov data. This analysis does not have sufficient statistics to observe the leptonic charge asymmetry at the level predicted by the standard model. However, novel constraints on effective field theories may be possible and are being investigated.
We search for a heavy resonance decaying into diphoton in association with at least one b jet. The search uses Run II proton-proton collision data with an integrated luminosity of 139~fb^{−1} recorded by the ATLAS experiment at a centre-of-mass energy of \sqrt{s} = 13~TeV during 2015 to 2018 at the Large Hadron Collider. Three models are tested in this final state. A Higgs boson like heavy scalar X produced with top quarks, b quarks or Z boson decaying into b\bar{b} are examined. In this Analysis, we setup limits on production cross-section times branching ratio on these models for the resonance mass ranging from 180~GeV–1.5~TeV.
Presented are the studies of the production of the Standard Model Higgs boson in association with a $W$ or $Z$ boson, where the Higgs decays to $b\bar{b}$ and the $W/Z$ bosons decay leptonically. The $H\rightarrow b\bar{b}$ decay has a branching fraction of $\sim58\%$, so this study allows the probing of the dominant Higgs decay mode, as well as providing the best sensitivity to the $WH$ and $ZH$ production modes and allowing the study of the Higgs at high transverse momentum. These points are important for the interpretation of the Higgs measurements in Effective Field Theories (EFTs). Since $b$-hadrons are the only down-type hadrons that can be effectively tagged, this decay mode also allows the study of the Yukawa coupling of the Higgs boson to the down-type quarks.\
The full Run-2 dataset, corresponding to 139 fb$^{-1}$ of instantaneous luminosity, was collected in proton-proton collisions with the ATLAS detector at a centre of mass energy of $\sqrt{s}=13$ TeV. The cross-sections of this process were measured using the Simplified Template Cross Section (STXS) method. Here, the cross sections are measured as a function of the $W/Z$ boson transverse momentum in different fiducial volumes based on kinematic cuts. Results of both the resolved (where each $b$-jet is reconstructed as a separate jet) and the boosted (where the two $b$-jets are reconstructed as one fat jet) analyses are shown, as well as the future prospects of the combination of these two different methods.
There seems to be problems in South African schools regarding Science and Mathematics at the GET and FET phases in parts of Cape Flats where crime and other vices thrive. The security, social and economic effect cannot be overemphasized as whatever choice learners make in school regarding mathematics and the sciences impact the very society they live in. This problem will have economic implications in the long run if South Africa wants to be a global player in the 4th Industrial Revolution. That is because, South Africa will need to produce students who can follow careers in the Sciences, Technology, Engineering and Mathematics (STEM) stream, to foster skills relating to the 4th Industrial Revolution and to lead life in the global village. For the STEM career paths, learners with good foundation in Mathematics will always be needed and will always be in short supply. The North High School is a technical school with great potential of meeting a small portion of the supply chain for learners that are needed for the STEM field in South Africa and it stands to develop individuals to attain their full potentials in life. The pass rate for grades 8 and 9 mathematics for 2017/2018 was about 10% respectively, thus the need for this intervention. The overall goal of the intervention is at the community level with high schools is to ensure significant growth and improvement in learners’ achievement, learners’ interest and learners’ participation in Mathematics. The study sought to identify factors that encourages learners’ retention in such programme.
Since the birth of quantum computing around 1982, when Richard Feynman envisioned a quantum computer that could mimic quantum physics using quantum mechanics laws to work and function, quantum computers have offered numerous powerful possibilities in solving complex problems. In particular, quantum computers take advantage of quantum mechanical properties such as entanglement and superposition to provide massive computational power for simulations of complex quantum systems. Quantum computing can outperform any modern supercomputer in terms of computational capability, raising the interest of both the computer science industry and academics to create the world's first quantum computer. Quantum computing has demonstrated numerous applications in the 4.0 industry, such as artificial intelligence and machine learning, computational chemistry, cybersecurity and cryptography, drug design and development, financial modelling, and weather forecasting. However, in all these technologies and applications, Africa has not been fully participating. Considering that technology is potentially a potent tool for economic development, this work unveils the challenges and opportunities faced by African research institutions and industries in using AI and ML techniques in Industry 4.0. Moreover, we review the progress in these areas especially relating to Africa and provide instances where these techniques have been applied. Lastly, we provide a roadmap on how these techniques can be used by stakeholders such as start-ups, research institutions, and industries for economic development.
This paper reports events and impact of a two-day Physics Without Frontiers (PWF)
quantum computing School that took place on the 14th and 15th of November 2020 at the National University of Lesotho (NUL). Sponsored by the International Centre for Theoretical Physics (ICTP) and aimed to run annually, the School was intended to introduce quantum computing; using existing open-source quantum computing platforms, to undergraduate students in Lesotho as well as to highlight how quantum computing can be used as a driver for the Fourth Industrial Revolution (4IR). The School was also intended to encourage students to consider furthering their study in quantum computing and related disciplines. This (hoped-to-be annual) event will potentially unite the NUL, the Lesotho government and the ICTP in a long-term relationship; to the benefit of young Basotho scientists and students. The November 2020 event was, in and of itself, a success on several response measures including good and consistent attendance over the two days, as well as being influential based on several students’ requests for postgraduate reference letters following this event. The outreach approach used here can be replicated elsewhere, especially in Africa, in order to capacitate students with quantum computing skills. Challenges encountered in this event will also be discussed in the paper.
Intense domestic resources utilisation might have been heavy weighing toward an increased electricity and water consumptions during the COVID-19 related lockdowns and people movement restrictions, while the routine energy consumption by technical instrumentations, and electronic and electrical appliance at institutions of higher learning would have been slightly reduced. Closely monitored access to laboratories by student groups and academic and technical staff compounded with a reduced frequency might be the root causes. Energy and resources utilisation are also tools used in the performance assessment of a tertiary programme or an academic department sustainability. The effective and efficient laboratory usages during the lockdowns imposed online learning and teaching activities have been assessed for the period between March 2020 to April 2021. Five laboratories (mineral processing, analytical techniques laboratory, heat treatment laboratory, wet chemistry laboratory, and coal processing laboratory) of a metallurgical engineering department at a local university were used. Bill of materials, water and related energy consumed were benchmarked with respect to the average consumption within the country while laboratory access by students and student to staff ratio during the above-mentioned period served as supporting additional component into the sustainability criteria of the studied academic department. The paper discusses the modelling of the sustainability of the studied academic department using the Grey rationale analysis optimisation methodology. Multiple alternatives as sustainability pointers are discussed and the most desirable outcomes elucidated.
The IAU Office of Astronomy for Development (OAD) and DARA Big Data (Development in Africa through Radio Astronomy), in partnership with the Inter-University Institute For Data Intensive Astronomy (IDIA) is implementing a number of Big Data Hackathons in Africa in order to promote data-intensive research skills development ahead of the Fourth Industrial Revolution (4IR). These hackathons are part of a multi-year programme that aims to provide data science and machine learning exposure through interesting real-world projects that are astronomy or development related. We present the programme initiatives thus far, as well as a preliminary impact analysis and future model implementations.
Structure light beams that are tailored in the polarisation and transverse spatial degrees of freedom are ubiquitous to numerous applications and emerging technologies ranging from laser cutting, particle tracking, to high dimensional classical and quantum secure communication. Imperfections in optical elements or perturbations in a propagation medium can degrade the quality of spatial modes therefore limiting the performance of structure light beams in practical applications. For vector beams, where the spatial and polarisation components are coupled in a nonseparable way, spatially dependent perturbations can also indirectly distort the polarisation vector fields. Remarkably, vector beams possess intriguing features such as the ability to behave like quantum entangled particles, where the nonseparable correlations exist between the internal degrees of freedom (polarisation and spatial). Here we show that vector beams can be used to characterise the nonseparability, or equivalently entanglement, between the spatial and polarisation components of modes within the same subspace. By exploiting the parallelism between nonseparability in vector beams and quantum entanglement, we invoke a unique feature inherent to entangled states, namely channel state duality, to map the nonseparability of any spatial mode using a single vector beam. We demonstrate this principle through turbulence and apply it to different mode sets. This method advances the use of nonseparable states of light for the analysis of spatial mode decay through an optical medium.
This study examined changes in the properties of poly-crystalline hexagonal boron nitride (h-BN) samples implanted with light ions (He+, Li+, B+, and Ne+) at 150 keV and at a fluence of 1x1015 ions/cm2. We have previously reported the production of cubic boron nitride nanoparticles in a subsurface layer, accompanied by a measurable hardening. The GIXRD findings show a new peak at 46.45° characteristic of c-BN (111) on the XRD spectra of implanted samples. The as-grown h-BN lattice parameter, as determined from XRD, was 2.499 Å and the lattice parameters of samples implanted with He+, Li+, B+ and Ne+ ions were 2.581 Å, 2.514 Å, 2.508 Å and 2.509 Å, respectively. There is a transition to lower angles and expansion in the peak position, this is due to the residual stress caused by ion implantation since there is a difference in the lattice parameter ratios, i.e., one lattice parameter is shorter, the other is longer (a and c lattice parameters, respectively). This could mean a hexagonal stress-related phase change to cubic nanoparticles (nc-BN). The increase in hardness affects the attenuation of X-ray photons because the density of the material on the implanted surface is affected and the X-ray photons penetrate deep into the sample. The Scherrer equation was used to calculate the particle size of the induced nc-BN particles.
Abstract
At nanoscale, the electrical, optical, and catalytic properties of metal nanoparticles depend on shape and size. In this study, gold nanoparticles (AuNPs) were synthesized using the seed-mediated growth method. Au nanospheres, nanoprisms and nanorods with average sizes of 6 and 68 nm, (70 nm length, 40 nm width) and grain sizes of 14, 20 and 130 nm, respectively; obtained by SEM and TEM. The plasmon absorption bands of Au seeds, nanospheres, nanoprisms were observed to be 395, 511, 543 and 528-629 nm, respectively, using UV-Vis spectroscopy. As the AuNPs shape changed, size increased and the wavelength increased, hence a red-shift was observed. From Raman spectrum, strong and sharp Raman peaks for the three shapes were observed. The XRD patterns confirmed AuNPs with the face-centered cubic (fcc) of gold and crystalline. The crystallite sizes of Au nanorods and Au nanoprisms obtained from XRD studies were 14.65 and 11.44 nm, respectively. The lattice constants of Au nanorods and Au nano-prisms were 4.15 and 4.10 Å, respectively. The structural and optical properties of shape dependent AuNPs were studied. The obtained nanoparticles, Au nanoprisms, nanospheres and nanorods have good applications in organic solar cells, photothermal therapy, sensing and imaging. Therefore, the results indicate that the sizes and shapes of AuNPs can be controlled by using different reducing agents.
Keywords: Gold nanoparticles; Plasmonic effect; synthesis; Au nanorods; Au nanoprisms
PEPT Cape Town has established the development of Gallium-68 based tracer particle analogues for use in positron emission particle tracking studies of granular and multiphase systems. The accuracy of the measured data relies strongly on how representative the tracer particle analogue is to the media of interest in these dynamic systems. The ability to control and manipulate the tracer particle properties expands the range of applications and systems suitable for investigation with PEPT. The density of the material represented by the analogue is often a critical parameter of the system under study. Tracer production methods developed at PEPT Cape Town rely on multiple layers of coatings on tracers created by radiolabelling ion exchange resin beads. The layers include the radioactive core, a density-controlled region and may include an additional coating used to control the surface chemistry of the particle. The current available densities range between 1.00 and 2.85 g cm-3 with final particle diameters as small as 450 microns. We report on our methods for creating density-modified tracer particles and illustrate their application in PEPT measurements from an industrial system designed to separate higher density minerals from lower density gangue.
Positron Emission Particle Tracking (PEPT) is a radioactive tracer technique used to determine the trajectory of a positron emitting macroscopic particle used as a flow follower. The nearly collinear 511 keV gamma ray pairs resulting from positron annihilation are detected in dedicated arrays. The tracking efficiency and performance is dependent on the physical properties of the tracer, particularly the achievable positron activity. The primary application of PEPT is to study dynamic flow systems under varying conditions; including a wide range of particle size distributions, physical, and chemical properties (e.g. densities, shapes, surface chemistry, friction coefficients, etc.), with applications across the science disciplines.
We are developing tracer particles for PEPT applications based on the radioisotope 18F. Radiochemical and physical methods are being explored to produce tracer particles representative of the system under study with respect to size, density and shape. In radiochemical tracer particle production, we extract 18F from commercially available 18-fluorodeoxyglucose (18FDG) and implement ion-exchange techniques to label small phase-representative resin particles (diameter < 1mm). For physical activation we utilise the novel reaction 16O(alpha,pn)18F using 100 MeV alpha particles produced by the iThemba LABS separated sector cyclotron (SSC) to produce 18F in-situ for larger particles (>5mm diameter).
This work will develop iThemba LABS specific tracer particle production mechanisms using 18F for the first time. The effects of tracer particle properties in PEPT applications, including optimisation of the PEPT technique and enhanced tracer production mechanisms, will be discussed.
Fast neutron fields are found in a wide variety of contexts, for example at accelerator and medical radiation facilities, around nuclear power plants, in aviation and space flight. The essence of neutron metrology is to quantify both the fluence and energy of these fields, which is complicated by the large range of energies, intensities and directional characteristics in each unique scenario [1]. Neutron metrology and spectrometry communities are beginning to adopt modern digital pulse processing systems to complement, and eventually replace, the existing analogue data acquisition systems [1,2]. Digital pulse processing electronics offer several distinct advantages over the existing analogue systems, with a need to rigorously benchmark against the current metrology standards prior to deployment [3].
The standard analogue data acquisition system at the AMANDE fast neutron metrology facility [5] at the IRSN, is compared to a new digital system comprised of a CAEN DT5730 digitizer and the open source QtDAQ software [4]. Measurements were made using a BC-501A scintillator detector for neutron fields with energies between 1.2 MeV and 20.0 MeV over the full range of available beam currents at AMANDE. Uncertainty budgets were constructed and compared for the measurements of energy dependent neutron fluence. The results of the comparison are presented along with recommendations for measurements with a fully digital acquisition system in contexts where metrological considerations are critical.
The top quark is the heaviest particle in the standard model and reducing the uncertainty of the top quark mass directly speaks to/ affects precision tests of the consistency of the standard model, where breaks from this consistency would point to the existence of more massive particles. Since the top quark decays before hadronizing, either the kinematic properties of the decay products or measurements of the rate of the top quark production have been used to measure the mass of the top quark. The majority of measurements consider various decay modes of the W boson with no specification on the decay of the b-quark when utilizing the kinematic properties of the decay products. These measurements are predominantly limited by uncertainties related to the reconstruction of jets. However, there is a top quark decay mode which are largely independent of the aforementioned uncertainty but require large amounts of data due to their low production rate. This decay mode includes a $J/\psi$ meson originating from a b-hadron and a semi-leptonic decay of the W boson. The invariant mass of the $J/\psi$ meson and lepton is sensitive to the top quark mass. This paper describes a maximum likelihood approach to extract the top quark mass from a probability density function, pdf, while studying the impact of the correlations between each of the pdf parameters.
Classifying a jet initiated from quarks or gluons based on its substructure is one of the most challenging problems at the LHC. The difference in the color structure of quarks and gluons can reflect in the amount of energy loss or the pattern of radiated energy of a jet originated from quarks or gluons. The low-level detector output can be used to identify parton jets using Machine learning techniques. Here we will present the performance of the existing quark versus gluon jet tagger in the ATLAS experiment for RUN 2 data with a 60% efficiency for selecting a quark-initiated jet. We will also present preliminary studies for a new forward tagger using the ATLAS calorimeter where the granularity is coarse.
In this project, ideas for the implementation of a data-quality early warning system (DQEWS) are explored. The DQEWS project aims to use supervised machine learning (ML) methods to evaluate data-quality from the ATLAS detector for each sequential luminosity-block over the course of a run. The idea is to then
make use of feature extraction from the results of the classification procedure in order to determine which of these features in the data-sets can reliably indicate problems in the detector, while accounting for expected differences in distributions as the beam intensity reduces over the course of a run. In principle, it is these features which may point experts to issues further down in the DAQ process which may be resulting in this drift during a run of the detector. This is, in essence, an exploration of an idea for a data-quality monitoring
system for the ATLAS detector. Within the scope of this project thus far, the following have been shown. Firstly, the use of gradient boosted decision trees (GBDTs) are preferable to deep neural networks (DNNs). This is due to DNNs requiring more computational power than GBDTs to backpropagate through the trained
models’ internal weights in order to rank the features used in classification. Secondly, differences in datasets have been shown with the training of the GBDTs, and are shown to increase with comparisons of LB data further apart from the initiation of a run of the detector.
Unlike supervised learning which is known to assume a full knowledge of the underlying model, semi-supervised learning, weak supervision in particular allows with partial knowledge to extract new information from the data. The objective of this study is to set up the search for heavy resonances at the electroweak scale with topological requirements. These resonances could be produced with different production mechanisms. In this case we will be focusing on the searches for new resonances in the Zγ final state using weak supervised learning approach. This will then be compared to the performance of the full supervision approach.
We propose a new approach to search for new resonances beyond the Standard Model (SM) of particle physics in topological configurations using Machine Learning techniques. This involves a novel classification procedure based on a combination of weak-supervision and full-supervision in conjunction with Deep Neural Network algorithms. The performance of this strategy is evaluated on the production of SM Higgs boson decaying to a pair of photons inclusively and exclusive regions of phase space, for specific production modes at the Large Hadron Collider (LHC), namely through the gluon-gluon fusion, the fusion of weak vector bosons, in associated production with a weak vector boson, or in association with a pair of top quarks. After verifying the ability of the methodology to extract different Higgs signal mechanisms, a search for new phenomena in high-mass diphoton final states is setup for the LHC.
When utilizing semi-supervised techniques in training machine learning models in the search for bosons at ATLAS, the overtraining of the model must be investigated. In particle physics internal fluctuations of the phase space and bias in training can cause semi-supervised models to label false signals within the phase space due to overfitting. The issue of false signal generation in semi-supervised models has not been fully analyzed and therefore utilizing a toy Monte Carlo model, the probability of such situations occurring can be quantified. This investigation of Zgamma resonances is performed using a pure background Monte Carlo sample. Through unique pure background samples extracted to mimic ATLAS data in a background-plus-signal region, multiple runs enable the probability of these fake signals occurring due to overtraining to be thoroughly investigated.
In 2024, for the first time in the 100 year history of the International Astronomical Union (IAU), the General Assembly will take place on the African continent! The capacity to host a General Assembly is a result of exciting infrastructure and human capital development projects on the continent, and also shows that Africa is no longer just peripheral to the global scientific endeavour. In this presentation, we share the vision for the 2024 General Assembly of the IAU through the lenses of research, people, infrastructure and legacy. We hope to stimulate collaborations that can shape the future of astronomy and physics both on the African continent, and globally.
The design of initiatives for reducing the gender gap should be based on evidence. The resolution on which the International Union of Pure and Applied Physics (IUPAP) Working Group on Women in Physics was founded was to “to survey the situation of women physicists in IUPAP member countries, to analyze and report the data collected along with suggestions on how to improve the situation…”. A major step in this direction was the Global Survey of Physicists of 2010 [Ivie and Tesfaye, Physics Today 65 47-50, 2012]. However, changes occur in the global academic, scientific and social environment, and in 2016 a successful application was made to the International Science Council for the project “A Global Approach to the Gender Gap in Mathematical, Computing, and Natural Sciences: How to Measure It, How to Reduce It?”. The project was proposed by IUPAP, and involved seven additional international unions: mathematics, chemistry, astronomy, industrial and applied mathematics, biosciences, history and philosophy of science, and computing machinery, together with three international organisations: UNESCO, GenderInSITE, and the Organisation of Women in Science for the Developing World. The project undertook three tasks: a global survey to which there were 32 346 respondents, a data-backed study of publication patterns, and the collection of initiatives known to have successfully addressed the gender gap in science. When a statistically significant difference is seen between the responses of men and women in a multivariate model that includes discipline, geographic region, country development level, and employment sector, then it is likely that the difference in the men’s and women’s responses is due to gender and not to any other factors. The most significant difference was seen in reporting on sexual harassment, with 29% of women and 2% of men in physics indicating that they personally encountered sexual harassment at school or work. In this short paper the focus will be on fair treatment at work. In physics there is a statistically significant gap in response to the statement “My employer treats everyone fairly”, with which 62% of women and 73% agree. Recommendations will be offered.
This study examines the origin of the sources and the effect of the change in water isotope composition isotopic constituent of hydrogen (2H), oxygen (18O) and radioactive tritium (3H). The rare stable isotopes of hydrogen and oxygen (2H, 18O) which are the constituents of the water molecule (H2O) itself and the radioactive tritium (3H ) are the classical tools of isotope hydrology. The aim of this study was to determine the water isotope composition in the North West Province of South Africa. About forty borehole water samples from selected villages in the Northwest Province of South Africa was collected to investigate the relationship between stable isotopes (δ 18O and δ 2H), climate, and topography from underground water aquifers. A cavity ring-down spectroscopy analyser with laser-current-tuned cavity resonance a Picarro L2130-i was used to measure high-precision triple water-isotope ratios at the Center for Applied Radiation Science and Technology. Results show that a plot of δ2H vs δ 18O (y = 8.2423x + 13.185) gives a line which is very close to IAEA Global Meteoric Water Line, defined by the IAEA to represent global meteoric water line. The study of the origin of groundwater and groundwater recharge In hydrogeology, is often described by the composition of δ18O and δ2H. This composition in local meteoric water can be applied to trace local relative humidity, study local climate and used as a tracer of climate change.
Astronomy for development is making great strides in Namibia. As a country renowned for its dark and pristine skies, Namibia offers the perfect landscape for the construction of ground-based observatories. The benefits of developing astrophysics infrastructure are not only limited to solving the mysteries of the Universe, however. Numerous research has shown that astronomy projects around the world lead to many other benefits – societal, cultural, economic, and environmental.
The High Energy Stereoscopic System (H.E.S.S.) is so far the first and only large-scale telescope to arrive in Namibia, in operation since 2002. Plans of building more telescopes in the country, such as the African Millimetre Telescope (AMT) and a part of the African Very Long Baseline Interferometry Network (AVN) of telescopes are currently underway.
The AMT will bring with it many more opportunities for capacity-building, and our multi-disciplinary collaboration is working on a Social Impact Plan to maximise the societal benefits brought about by the future observatory. This Plan takes a multi-disciplinary approach to setting the scene for astronomy and sustainable development in Namibia. Looking at education more closely, we outline plans for the Mobile Planetarium; the materials we will create for schools; teacher training; bringing international astronomy training programmes to Namibia; mentorship, scholarship, and fellowship programmes; and the inclusion of indigenous knowledge. In all, sustainability is our utmost priority and by incorporating these different efforts we hope to inspire a new generation of scientists in Namibia.
The rapid transition to online teaching necessitated by the coronavirus pandemic has been a good opportunity to rethink our approach to teaching. Moving to an online format suggests that many activities that have traditionally been synchronous and instructor-paced, can be made asynchronous and self-paced. What may have seemed like a challenge, is a great opportunity to improve the quality of education.
High entropy alloys (HEA) containing Co, Ni, Fe have recently enjoyed considerable attention in the material sciences due to their interesting mechanical and magnetic properties that are further enhanced by the additive manufacturing technique often used to process them.
HEAs are theoretically difficult to describe as they often form amorphous structures and the Bloch theorem is not applicable. In this article the method of the effective medium is used and the corresponding many body problem is solved selfconsistently within the coherent potential approximation. The mixing entropy of HEAs and their phase stability are explained using an optimization approach. The complex micro- and multi phase structure are due to many body effects that are discussed from a calculation of the quasiparticle density of states. It turns out that these many body effects are most significant if the components of the alloy are present at about equal proportions. Applications to Kondo insulators and superparamagnetism are investigated where the interaction between magnetic moments is of indirect type and mediated by the free electrons of the conduction band (RKKY interaction). In the strong coupling limit it is shown that the susceptibility has a maximum at the blocking temperature indicating a phase transition from ferromagnetism to superparamagnetism. Using alternatively a lattice gas model to represent the disordered alloy the existence of the second order phase transition is confirmed and the blocking temperature is calculated. It is shown that the results of the two model calculations are in qualitative agreement with one another and must thus be regarded as good and reliable.
Perovskite-based solar cells (PSC) is the rapidly emerging solar technology up to the present since its introduction in 2009, hence invigorating the photovoltaic (PV) zone. To reach the maximum potential of hybrid perovskite solar cell performance, analyses of the dominant mechanisms in a perovskite material, together with interfacial properties of contact materials and their impact on the performance and stability of the device become imperative. Understanding the interface properties of the contact materials is the primary strategy for harnessing the full potential of perovskite-based solar cells. In this study, we focused on the charge transfer process and interfacial recombination within solar cell devices with n–i–p architecture. The motivation for this paper is to investigate the impact of recombination mechanisms that exist within the interface in order to quantify their effects on the performance and stability.
To achieve our objective, we firstly provide a rationale for the photoluminescence and UV-vis measurements on perovskite thin film to allow for disentangling of different recombination pathways. Secondly, we use ideality factor measurements (I-V curve) and impedance spectroscopy to access information about recombination mechanisms in full device. Our findings suggest that charge loss in PSC is dependent mainly on the configuration of the cell and morphology of the layer, with insignificant dependence on the material preparation of the perovskite itself. This is based on result of the individual analyses of the perovskite film and device, which suggest that major recombination losses are most likely located at the interface.
ERDA and RBS analysis of hydrogenated Pd-Ti-Pd multilayer stacked film prepared on CT-Ti and Ti6Al4V substrates using an electron beam evaporator were conducted in this investigation. The hydrogenation of the samples was achieved by flowing pure H2 (100%) and H2(15%)/Ar(85%) gas mixture while annealing samples at 550oC. The stability of the multilayer stack system at 550 °C was also investigated using RBS for the investigation of possible intermixing of layers and XRD for crystal structure and any possible new phase formation due to elevated temperatures. SEM was used for surface topography investigation. ERDA revealed an average H content of ~ 3.5 at.% in CP-Ti and ~6.2 at.% in Ti6Al4V for samples annealed under H2(15%)/Ar(85%) gas mixture. We recorded a hydrogen content of ~19.5 at.% in CP-Ti annealed under pure H2 while ~25.5 at.% was found in Ti6Al4V annealed under the same conditions. Rutherford backscattering spectrometry (RBS) revealed intermixing of layers as evidenced by the diffusion of Pd toward the bulk, while XRD indicated the formation of the PdTi2 phase in the samples annealed under vacuum and H/Ar gas mixture atmosphere. In-situ, real-time RBS showed that the annealing under pure H2 preserves the integrity of the Pd catalyst. No indication of the PdTi2 formation in the pure H2 annealed samples was observed; instead only the TiH2 phase appeared, indicating the absorption of H into the system. These results indicated the sensitivity of such a system to the H2(15%)/Ar(85%) gas mixture.
In this study, 4H-silicon carbide samples were bombarded with 167 MeV Xe ions to a fluence of 1×108 cm-2 at 300 K prior to the fabrication of Schottky contacts. The samples were also annealed at approximately 900 °C before thermal fabrication of the contacts. When compared current-voltage results with the as-grown device, generation-recombination occurred in the implanted samples. The presence of four deep level defects (0.10, 0.12, 0.16 and 0.65 eV) were observed in as-grown devices when characterized by deep level transient spectroscopy. In addition, two deep level defects with activation energies of 0.40 and 0.69 eV below the conduction band minimum were induced as a result of implantation. These two induced-defects have similar signatures to other defects observed by MeV electron irradiation. It was observed that the two defects induced were annealed out at 400 °C which indicated the instability of the defects after annealing the implanted sample.
Limestone is a calcareous rock and is among the common hydrocarbon reservoirs (others being dolostone, sandstone and unconsolidated sands). Carbonate reservoirs hold a significant percentage of the world's oil and gas reserves. This study explores the nanopore structure of calcitic and dolomitic limestone by virtue of them being abundant in the chosen area of study. The difference between these two types of limestones is their magnesium carbonate content, calcitic limestone has about 5% of magnesium carbonate while dolomitic limestone has about 40%. By characterizing the nanopore structure, the intent is to determine the fluid transport capabilities of the limestones under study. The results of the study will be beneficial to the energy resources exploration and add on to the understanding of pore systems in limestone.
A reservoir, body of porous rock that contains fluids (water and/or hydrocarbons) and in which these fluids can migrate, is controlled by two key properties, which are porosity and permeability. These properties are further influenced by other parameters such as pore size, pore diameter, pore throat radius, pore coordination number and pore size distribution.
This presentation gives an account of sample preparation of the limestones for analysis using small angle scattering (SAS) techniques, small angle light scattering (SALS) and small angle x-ray scattering (SAXS) in particular. SALS can structurally characterize materials with pore diameters in the sub-micron range and SAXS is effective in characterizing nano-range structured materials.
The paper presents the data analysis of Aerosol Optical Depth (AOD) measured from a CIMEL Sun-photometer at CSIR-Defence and Security in Pretoria, South Africa. This Aeronet instrument has been recording data since 2011 till 2018 for use in the calibration and validation process of space sensors such as earth observation satellites in space. These sensors encounter challenges while capturing information about the earth surface since the presence of aerosols in the atmosphere inhibit the target image and degrade information about the area. The purpose of ground truth instruments such as the CIMEL Sunphotometer is to generate aerosol measurements specifically the AOD, and requires analysis of the data to ensure stability and quality before any calibration or validation of the Satellite sensor. The study will provide an overview of the AOD behaviour during warm and dry seasons of the 2017 data.
The solar modulation of Helium isotopes (Helium-3 and Helium-4) is studied and compared to observations at the Earth. This is done from the period of minimum solar activity from 2006 to 2011, up to the period of solar maximum activity from 2012 to 2015. Computed spectra are compared to the precise measurements of Helium-3 and Helium-4 fluxes measured by the PAMELA and AMS-02 space missions between July 2006 and December 2015, spanning time frames that include the solar magnetic field reversal epoch. Insight gained from this comprehensive modeling, with a three-dimensional drift model, about the relative roles of the four main modulation processes over the mentioned period will be shown and discussed.
Radiation exposure during commercial flights remains one of the dominating and inevitable factors relevant to flight personnel and passengers' health and safety. At aviation altitudes, the radiation environment that the flight personnel are exposed to, during their day-to-day occupational activities, differs significantly from terrestrial radiation received by the general population on the ground. Currently, there are no dosimetric services in South Africa that collects data of the flight personnel's exposure during their occupational activities. The North-West University, in conjunction with scientists from the Christian-Albrechts-Universität zu Kiel, have assembled an active (battery powered) dosimeter (known as the RPiRENA) to measure the flight personnel and passengers' exposure during commercial flight cruises. Here we introduce this device, discuss its calibration, and show initial results during long-haul flights.
keyword(s): Radiation dosimetry, Active dosimeters, Cosmic-rays
Large amplitude nonlinear soliton and supersoliton structures are investigated in three-component magnetized plasma models, consisting of inertial adiabatic ions and two-temperature electrons. We determine the existence of nonlinear structures which are propagating obliquely relative to the ambient magnetic field using the Sagdeev pseudopotential formalism in which an energy integral is derived, under the assumption of quasineutrality. We will test the plasma composition and parameter range to establish whether the system supports the existence of supersolitons. The electric fields of such structures have a characteristic wiggled appearance in comparison with regular solitons. We consider first Boltzmann distributions for the cool and hot electrons and then study the effect of nonthermal Cairns and kappa distributions for the hot electrons
Charged particles and plasma waves occur throughout the solar system. These particles can move slowly relative to the plasma or be accelerated to relativistic speeds by reconnection events such as solar flares. The types of waves depend on whether one considers the plasma in the solar chromosphere, solar corona, solar wind or the planetary magnetospheres. In this study we investigate the amount of energy that becomes available when the charged particles interact with the plasma waves through the mechanism of Landau damping. The linearised Vlasov equation is solved, from which we obtain an expression for the total amount of energy available for transfer through the Landau mechanism. The interactions with Alfven, slow and fast magnetosonic, as well as ion-cyclotron waves are obtained. In each case the energy deposited into the plasma is calculated, which is then available to do work in the form of heating or acceleration of the local plasma. The final expressions are presented in terms of Stokes parameters.
Observations of solar coronal loops with the Atmospheric Imaging Assembly (AIA) instrument of SDO have revealed the existence of a low amplitude decay-less regime of transverse oscillations. These appear to be like the well understood large amplitude and rapidly decaying fast kink-mode oscillations observed in loops, but their means of excitation and exact nature are still debated. Addressing these two questions is essential for using the former as diagnostic tools in coronal seismology, as well as determining their potential role in wave heating of the solar corona. In this talk, results from a number of 3D numerical magnetohydrodynamic studies will be presented, in which we have studied loops undergoing decay-less oscillations. The different proposed interpretations and excitation mechanisms of these waves will be presented, alongside our results on the spatial evolution of these oscillating loops. Wave energy dissipation in the case of decay-less oscillations will also be discussed, alongside some of our recent findings supporting the idea that the dissipated energy can potentially overcome of the radiative losses for the Quiet Sun.