Quantum condensation of alpha particles is believed to occur in cluster states of the self-conjugate alpha nuclei 12C and 16O. This phenomenon is similar to the Bose-Einstein condensation observed through the laser cooling of atoms such as Rb or Na. A state of this nature, which must be of 0+ character, is expected to exist just above the 5 alpha decay threshold in 20Ne. In this region,...
A symmetrized and dynamical density matrix renormalization group is used to study 1-dimensional extended Peierls-Hubbard model at half-filling. We have investigated the optical conductivity spectrum and electro-absorption spectrum for low-lying optical exciton with strong, intermediate and weak coupling parameter sets for the on-site and neighbor interactions. We were able to capture the...
High concentration photovoltaic (CPV) systems utilize non-imaging optics to concentrate and distribute the solar flux uniformly onto a solar receiver to achieve maximum performance and power output from a CPV module. However, in many cases due to mechanical misalignment, tracker error and imperfections in the optical material, the optimum performance of the module is compromised. A LabVIEW...
A dielectric barrier discharge CO2 TEA laser excited by a thyratron driven power supply has been developed and characterized. Laser output was observed at frequencies up to 25 Hz for an electrode separation of 10 mm with 1.8 mm Suprasil glass covering the electrodes. At this gap separation, pulsed power output of about 9 W was detected for gas pressures between 100 and 400 mbar. Changing...
This study explores learners’ knowledge of measuring instruments (Ammeter and Voltmeter) in a direct current resistive circuit. It investigates learners’ understanding of how instruments should be connected and why they have to be connected in a particular way. Ammeter and voltmeter are used to determine the behavior of a circuit by indicating the readings of current and voltage,...
Following the repair of the SALT optics in late 2010, the telescope has reentered the commissioning phase with its principal scientific instruments, SALTICAM and RSS. Both these instruments have undergone major refurbishments in their own right, and their current status and that of the telescope will be described, together with an update on its performance.
Covellite copper monosulphide (CuS) is a representative I–VI chalcogenide semiconductor with the unique photoelectricity transformation characteristic. Due to quantum confinement effect, CuS nanoparticles exhibit optical and electrical properties as compared to the bulk materials. CuS is an indirect semiconductor with a bandgap around 1.7 eV. At high temperature CuS exhibits fast ion...
Motivated by several theoretical cluster calculations that predict the existence of the 06+ state in 16O located at 15.1 MeV as a very good candidate for the equivalence of the Hoyle state in 12C, a high resolution measurement of 16O spectrum in coincidence with the 16O decay products was proposed using a (p,t) reaction at...
A method of experimentally decomposing a field within an apertured plano-concave resonator cavity into a forward propagating field (plane to concave) and a backward propagating field (concave to plane) is presented. The use of an intra-cavity aperture which is a simple method of laser beam shaping is a means of mode selection as higher-order modes are actively discriminated. This apertured...
Mathematics is an essential tool in studying physics, i.e., it will be difficult to study Physics without the sound basics of Mathematics. It is even called the “language of physics” (Redish, 2005). Physicists blend conceptual physics with mathematical skills and use them to solve and interpret equations and graphs. For instance, in kinematics, different aspects from mathematics such as...
Efficient thermal management of low concentrator photovoltaic (LCPV) modules ensures that the maximum power capabilities of the LCPV system are harnessed, and may substantially prolong the operating lifetime of the photovoltaic (PV) cells. A general understanding of the thermal transfer properties of PV modules is thus necessary to effectively design, construct, and implement viable LCPV...
The advent of international wideband communication by optical fibre has produced a revolution in communications and the use of the internet. Many African countries are now connected to undersea fibre linking them to other African countries and to other continents. Previously international communication was by microwave links through geostationary satellites. These are becoming redundant...
An Investigation of students’ expectations when they are accepted to study at the University of Pretoria, how they study for physics and their reactions after the first semester test. We find that most students are shocked after their first semester test, because they expected to obtain high marks and don’t, or the other way around.
The adsorption of Sb on the (111) plane of noble metals surfaces such as copper and silver has long been of practical interest in the fields of surface science and technology. The electronic properties of such surface alloys are important for several surface and interface related applications like metal-metal or semiconductor-metal heteroepitaxy, heterogeneous catalysis, sensors and...
The benefit of concentrating sunlight onto solar cells is that expensive solar cell material can be reduced and replaced with relatively inexpensive optical elements, which has the potential to reduce the cost of solar energy. In low concentration photovoltaics (LCPV), solar cells are subjected to higher irradiance levels. The electrical output, and hence efficiency of a LCPV module is...
Passively Q-switched Nd:YAG lasers with Cr4+:YAG as a saturable absorber that can operate with pulse repetition frequencies(PRF) in the hundreds of kilohertz typically have problems with pulse to pulse fluctuations of pulse energy and width and the associated timing jitter as well as drift in PRF. One technique for stabilizing the PRF and reducing fluctuations is modulation of pump power....
In our experiments devoted to studying of a new ternary decay of low excited heavy nuclei called “collinear cluster tri-partition” (CCT) a specific CCT mode was observed based on double magic 132Sn cluster. Pre-scission configuration which presumably gives rise to the mode under discussion can be obtained. The Sn cluster can "move" as a whole along the cylinder-like configuration that...
Long afterglow calcium aluminate phosphors doped with Eu2+ and co-doped with Nd3+ /or Dy3+ (CaAl2O4:Eu2+, Nd3+, Dy3+) were fabricated by urea-nitrate solution – combustion method at 500 °C. The effects of varying concentrations of Ca:Al and co-dopants molar ratio (Nd3+:Dy3+) on the...
We have previously demonstrated a novel laser pulse energy control system based on two analog controllers to control a Q-switched Nd:YLF laser. We now present the improved technique based on a custom-designed high-speed FPGA (field programmable gate array) digital logic controller, together with experimental results from controlling a high-energy Ho:YLF ring laser. Laser pulses of...
Understanding the magnetic effects of ultra-dense, cold nuclear matter is of particular importance when investigating the magnetic properties of dense matter systems such as neutron stars. One property that we are interested in is the possibility of generating a magnetic field in nuclear matter as the central density increases. We investigate this possibility by employing a relativistic,...
Recent developments in electricity regulatory environment and the possible inclusion of small, kW-scale, photovoltaic (PV) systems in the feed-in tariff framework has led to an increased interest in these systems. In South Africa, grid reliability issues are not fully mitigated by employing a straight grid-tie PV system, with users sometimes wanting some battery backup for load-shed...
The purpose of this study was to investigate the pre-knowledge of the Physics I students on vectors. The study was conducted on 234 Physics I students from the University of Limpopo (Medunsa campus). The sample was divided into four groups, where the first group (n = 119) did their grade 12 in 2010, the second group (n = 46) did their grade 12 prior 2010, the third group (n = 42) did...
Cluster-like structures in the shell-model description of the ground state of nuclei can be conveniently studied by means of knockout reactions. Of these the (p, p alpha) reaction is perhaps the simplest, especially from the viewpoint of the tractability of theoretical calculations used to interpret experimental results. The distorted wave impulse approximation (DWIA) is a versatile theory...
Most properties of polycrystalline materials are controlled by the structure and interfaces they possess – e.g., grain boundaries. When a Cu surface is alloyed with antimony, the Sb atoms appear to diffuse to the growth surface and continuing to act as a surfactant throughout the growth process. Copper alloys are important commercial materials, which are often used at temperatures where...
ThunderKAT is one of ten accepted MeerKAT Large Survey Projects. ThunderKAT will study all aspects of transient radio emission associated with accretion and explosive events. Through a comprehensive and complementary programme of monitoring Galactic synchrotron transients (across a range of compact accretors and a range of other explosive phenomena) and exploring distinct populations of...
Lasers and amplifiers emitting 2µm single-frequency pulses are used for spectroscopy, remote sensing, and defence applications. The laser sources group at the CSIR National Laser Centre has developed a number of 2µm lasers and amplifiers over the course of five years. We report on three of these, all of which achieved record breaking output energies. To generate the high energy 2µm...
The theory of continuous measurement provides a tool to monitor the evolution of the wave function of a single quantum system in real time. We derive the master equation in the non-selective regime for the dynamics of the wave function of a particle in an external potential which is subject to continuous measurement of position. In the derivation we view continuous measurement as the limit...
The magnetic and electrical properties of nitrogen doped carbon nanospheres can be probed using Electron Magnetic Resonance (EMR) techniques. Previous Raman spectroscopy studies show that both the pristine and doped spheres are graphitic in character. However, XRD measurement showed that these spheres consist of graphitic crystallites embedded in an amorphous phase. Previous ESR...
We carried out ab initio self-consistent calculations to study the modification of the band offsets by polar layers. We considered a double line of C in a monolayer of hexagonal BN, also known as Boronitrene. This effectively introduces a line of dipoles at the interface. We considered BN/C zigzag and armchair configurations. The BN/C zigzag-short is found to be energetically most...
With the birth of the new generation ground-based gamma-ray imaging atmospheric Cherenkov telescope arrays (such as H.E.S.S., MAGIC and VERITAS), there is a growing need to probe X-ray binary stars for very high energy gamma-ray emissions. Since the discovery of the first extra-solar X-ray binary (XRB), namely the Scorpius X-1 in 1962, XRBs are now well-established systems in the realm of...
In heavy ion reactions the emission of Intermediate Mass Fragments (IMFs) at forward angles is dominated by the direct break-up process. To improve our understanding of this process in the reaction mechanisms involving the interaction of light projectiles with light to heavy target nuclei, a coincidence measurement was performed at iThemba LABS. Standard ΔE-E detector telescopes were used...
A simple pinhole camera was used to demonstrate to students that light travels in a straight line. The one to one correspondence between a point on the object and a point on the image was used to explain why the image was upside down and reversed from left to right.
Optically pumped molecular lasers are attractive alternatives to generate high energy pulses in the mid-infrared wavelength range, compared to non-linear conversion that can suffer from optical damage. One such laser is based on HBr, for which it has been experimentally demonstrated to emit laser light in the 4 µm wavelength range when pumped at 1.3 µm or at 2 µm. Prior to the work...
Black chromium-chromium (III) oxide cermet (Ceramic-Metal) nano-composites exhibit attractive solar absorbance characteristics. They are used widely as selective solar heat thermal collector nano-coatings. These black chromium-chromium (III) oxide selective solar absorbers are produced by various physical vapor deposition techniques such as DC and RF reactive sputtering, pulsed sputtering...
We consider a solar trough system in which cylindrical parabolic mirrors focus the sun’s radiation onto a receiver pipe, heating it. Conventionally, the pipe is enclosed in a glass cover under vacuum and the dominant radiation losses are reduced by the use of a selective coating on the receiver pipe. We study the suitability of applying a ‘hot mirror’ coating on the glass cover instead,...
The investigation reflects on the causes of unsatisfactory students’ performance on the section involving forces during tests. It has been realized that more often than not students tend to be excited after undertaking a test on forces. However, subsequent feedback usually paints a different picture and this has become a worrying trend. The results of the investigation in this regard seem...
The fusion evaporation reaction is mainly used to populate high spin states in atomic nuclei. Using stable beams, a large number of β + unstable nuclei were studied i.e. those nuclei on the neutron deficient side of the valley of stability. A plethora of experimental data is available in a wide range of mass A ∼ 20 to A ∼ 250 and was used to test the statistical model codes such as PACE,...
Laser pyrolysis has been used to synthesize tungsten oxide (WO3-x) nanostructures, and here we report on the production of six-sided nanostars. The proposed mechanism used to explain the growth of the stars is the concentration difference and gradient mechanism which speculates that a high local concentration of one reactant mixed with a low concentration of another reactant under ambient...
We investigate the scattering of a wave-packet off a soliton in the (1+1) dimensional kink model. We solve the classical, time-dependent field equation numerically subject to the initial condition that the wave-packet is widely separated from the kink soliton at very early times and propagates towards the soliton. After some time the wave-packet interacts with the static soliton and...
The Fermi Large Area Telescope (LAT) has revolutionized high-energy (HE) astronomy, and is making enormous contributions particularly to gamma-ray pulsar science. As a result of the many new pulsar discoveries, the gamma-ray pulsar population is now approaching 100. Some very famous millisecond pulsars (MSPs) have also been detected: J1939+2134 (a.k.a. B1937+21), the first MSP ever...
Since the launch of the Large Area Telescope (LAT) on board the Fermi spacecraft in June 2008, the number of observed gamma-ray pulsars has increased dramatically. A large number of these are also observed at radio frequencies. Weltevrede et al. (2010) derived constraints on the viewing geometries of 6 gamma-ray pulsars exhibiting single-peaked gamma-ray profiles using high-quality radio...
To our knowledge, we have demonstrated the first optically pumped tunable HBr oscillator lasing on both the P- and the R-branches. Through the implementation of an intra-cavity diffractive grating, we could tune the wavelength over a range of 538 nm from 3872 nm to 4410 nm. A single-frequency Ho:YLF ring laser and amplifier system was used as pump source. The oscillator was pumped in a...
Carbon nanoparticles embedded in thin NiO layers have shown an increasing interest for application in spectrally selective solar absorbers that can be used for low temperature photothermal applications. It is expected that the size and shape of carbon nanoparticles in the NiO matrix is extremely important in tuning the selectivity of the coatings. In this work, multiwall carbon nanotubes...
Quantum walks of particles obeying bose statistics are introduced. In such a quantum walks the conditional shift operation is performed with the single coin tossing for the whole lattice. An explicit form for the transition probabilities in a single step is derived. This allow to describe the evolution of an arbitrary state and an arbitrary number of steps. This model easily embrace the...
Control of diameter, length and level of nitrogen doping in synthesis of nitrogen doped carbon nanotubes (N-CNTs) can be achieved by careful selection of catalyst, precursor mixture and chemical vapour deposition (CVD) synthesis temperature. Solutions of ethanol and acetonitrile (20% acetonitrile) were pyrolysed over a Fe/Al/MgO catalyst in a CVD reactor at temperatures from 700 OC to 1000...
Nanocomposite materials have wide range of applications in solar energy conversion. In this work, C-NiO nanocomposite coatings are prepared using sol-gel synthesis and deposited on aluminium substrates using a spin coater. The coatings are prepared from alcoholic sols based on Ni-acetate using diethalonamine as a chelating agent and polyethylene glycol (PEG) as organic template. Sucrose is...
GEANT 4 is a C++ library developed by CERN to simulate particle physics experiments. However, GEANT 4 can be also be used for other applications that need not have anything to do with particle or high-energy physics. Here we discuss an application of GEANT 4 that simulates the EMU Spectrometer for Muon Spin Relaxation measurements at the ISIS facility in the Rutherford Appleton Laboratory....
The preparedness of matriculants for university studies has been a subject of intense debate and interrogation at various levels of public discourse. In addition, the standardization of Grade 12 assessment marks in various subjects by the Quality Assurance Body (Umalusi) has of late become a highly contentious issue. It is in recognition of these considerations that we undertook to...
Si, C and SiC are very well known technologically important materials. They have been extensively studied in their multitude of structures and polytypes, but there is a surprising dearth of information for off-50:50 compounds involving Si and C. What are the possible stable structures for such compounds? Using ab initio techniques, we investigate two proposed structures for...
The spectrum of a carbon nanotube in a strong enough magnetic field (>50T for a 3nm nanotube) revealed an almost dispersionless band at the Fermi energy. The formation of Landau levels has been theoretically and experimentally investigated. In experimental studies the existence of Landau levels is indirectly derived from longitudinal conductance measurements. We will show that a more direct...
Saldanha Bay on the West Coast of South Africa is surrounded by various nature reserves and protected areas which amongst other includes heritage sites like the West Coast Fossil Park. Large parts of these sensitive areas were however exposed to anthropogenic activities, which includes farming and mining as well as training and preparation for war. This article investigates the prospect...
Science, Engineering and Technology (SET) have become essential in the development of the country in all its facets. It has been observed over the past few years that students entering university for degree studies in their respective fields experience considerable level of difficulty. Inadequate understanding of basic mathematics and physics concepts has been identified as a critical...
This paper presents results of long term temperature monitoring in an energy efficient solar house at the University of Fort Hare, South Africa. Measured data was stored by a datalogger every 10 minutes. Formulas for predicting the daily indoor maximum, average and minimum temperatures were developed on the basis of outdoor climatic parameters. Passive solar housing aims to raise and lower...
Copper based interconnect are widely used in the electronic industry. They provide the conductive path required to achieve connection from one circuit element to another. However, the application of copper based interconnect is often limited by the oxidation behaviour of copper. At elevated temperature and humidity, the bonding strength of copper interconnect deteriorates due to copper...
Cerium-based ternary compounds demonstrate different and interesting phenomena depending on the valence of the Ce ion. The hybridization between Ce-4f electrons and the neighbouring conduction electrons is responsible for the anomolous properties observed in different systems. Depending on the strength of the f-ligand hybridization, one observes in these compounds phenomena such as magnetic...
Active learning techniques were used for the first time in the Statistical Physics module presented to third year students at the University of the Witwatersrand in the first semester of 2009. The reaction of the students, recorded in a formal Student Assessment of Lecturer Performance, administered by the Centre for Teaching and Learning Development at the University, was overwhelmingly...
Few options are apparent for achieving a benign, sustainable energy future except those relying on the utilization of solar energy in one way or another. Experience with fossil and nuclear sources has revealed an array of unsolved problems of increasing concern as more evidence and understanding emerges. Africa has the world’s best solar resources. Several countries have exploited solar...
We report on the electrical transport properties of graphene oxide (GO) and GO reduced using an organic acid (RGO). Two terminal GO and RGO devices were assembled via dielectrophoresis. The current-voltage characteristics of these devices were studied at low temperatures (77 K to 300 K) using a micromanipulated probe station. The I-V characteristics for RGO devices were found to be almost...
The highly transient novalike variable AE Aqr is perhaps an ideal laboratory to study accretion related astrophysical fluid dynamics. It consists of a fast spinning highly magnetic white dwarf (WD) orbiting, and accreting mass, from a low-mass main sequence companion. The system emits, and has been detected in almost all wavelengths. AE Aqr is in a propeller state, and most of its emission...
Highly crystalline nano-spherical Fe-Pt systems were produced by 248 nm laser irradiation of liquid precursor at different laser fluence ranging from 100 – 375 mJ/cm2. The influence of laser intensity on the particle size, iron composition and vibrational properties was systematically investigated. The study reveals that the larger particles have higher iron content. The prepared precursor...
Ab initio density functional calculations within the generalised gradient approximation (GGA) have been carried out on a wide range of phases and stoichiometries for the platinum-titanium (Pt-Ti) and iridium-titanium (Ir-Ti) alloy systems, using the Vienna Ab Initio Simulation Package (VASP). The elastic constants and elastic moduli are calculated and the electronic structure and density...
Nanostructured materials are used to develop lithium-ion batteries with high energy, high-rate capability and excellent cycling stability due to their huge surface area, short distance for mass and charge transport and freedom for volume change. They are capable of reversibly accommodating large amount of Li, on intercalation mesoporous β-MnO2 can accommodate Li/Mn = 0.92:1 with...
Alq3 is widely used in organic light emitting diodes (OLEDs) as emission and electron transport layer. During the fabrication of OLEDs the current trend is to use solution-processing; however, Alq3 must be vacuum deposited. One possible way to overcome this problem is to use different polymers containing the Alq3. In this study blended thin films of Alq3...
Some eclipsing contact binary stars of the W UMa-type are known to undergo changes in orbital period. These changes can be as a result of the light travel time effect if the contact binary is a member of a multiple stellar system or due to some intrinsic phenomena that are poorly understood at this stage. Analysing systems that appear to be undergoing changes in orbital period may shed...
The transient absorption of Zinc phthalocyanine (ZnPc) has been studied by femtosecond pump-probe spectroscopy. We present results on the ultrafast spectroscopy of ZnPc, specifically identifying three ultrafast components observed. These are the inertial solvation dynamics (~1.8 ps), the dielectric solvation dynamics (~39 ps) and vibrational relaxation (~2.7 ps) in the electronic excited...
This study examines the effect on the learning experiences of students of changes to the running of laboratory and tutorial sessions of the first year auxiliary physics course at the University of the Witwatersrand, between 2001 and 2010. This research is underpinned by the principles of indirect interactive instructional skills and experiential learning. Two concerns drove this study: the...
Electrostatic ion propulsion systems resist miniaturization due to constraints imposed by the size of the discharge chamber. We introduce a thruster concept where the same field is responsible for both ionization of the neutrals and acceleration of the ions, by letting the neutral propellant gas escape into a high field region through a thin, hollow needle at high electric potential. The...
Reactions involving four particles, either in the entrance or final channel, are quite involved when computing observables in comparison to three-body reactions. Yet these reactions are of interest in studying reactions of astrophysical interest, such as hep process, which is essential for describing the quantitative solar model. At lower solar energies, it is difficult to measure the...
The goal of any measurement and data-analysis technique should always be to minimize uncertainties, whether it is statistical or systematic. Although uncertainties are unavoidable, one can find ways to reduce them depending on the circumstances. High-precision measurements play a crucial role in constraining various quantities. Recently a new inorganic scintillation detector has become...
Understanding molecular dynamics on potential energy surfaces has been at the heart of ultrafast transient absorption in the recent years [Philipp K, etal., 2005],[Karel G, etal., 2008]. Based on the on-going experiment at our ultrafast laboratory, we ran density functional calculations on metal dithizonates, starting with their kernel molecule, formaldimine, to validate what we observe...
Kazarovets et al. (1999) gave General Catalogue of Variable Star (GCVS) designations to 3157 variable stars that had been identified from observations made using the Hipparcos satellite. The variables were classified into standard GCVS categories according to their photometric light curves, but no other parameters of the variables were documented. V-band photometric data for many of the...
Crystals of LiFePO4 and related materials have recently received a lot of attention due to their promising use as cathodes in rechargeable lithium ion batteries. These compounds have been known for good stability and low cost. The Co based compound LiCoPO4, has rapidly become of particular interest as recent measurements found a potential of 4.8 V, while the Mn based...
The discovery of the giant magnetocaloric effect (MCE) in Gd5Si2Ge2, a member of the substitution series Gd5Si4-xGex has generated significant interest into MCE phenomena in rare earth intermetalic compounds. Much recent effort has gone into determining how the MCE in such systems is influenced by the many salient features...
The investigation of low voltage electron induced cathodoluminescence (CL) degradation of Zn3(PO4)2:Tb phosphor has been extended for possible application in low voltage field emission displays (FED). There are two important reasons for studying phosphate based phosphors. These are their chemical, thermal stability and variation in emission colour, which is influenced by the site occupied...
Pigulski and Kolaczkowski (2002, A&A 388, 88) announced the first discovery of Beta Cephei (BCep) pulsators in the LMC. This was a remarkable discovery, since theoretical analyses of pulsational stability had previously predicted that early B main-sequence stars with metallicities lower than Z = 0.01 should not pulsate at all (e.g. Pamyatnykh 1999, Acta Astron 49, 199). Following this...
The Nobel prize winning technology involving a mode-locked femtosecond laser frequency comb (FLFC) has been at the epi-centre of a scientific revolution over the last two or so decades. Even though originally designed to count cycles in optical clocks, it has had a profound impact on other research areas, with a range of applications including spectroscopy, trace gas detection, signal...
Radiopharmaceuticals is compounds labelled with a radioactive isotope that are used for studying different organs in the human body. Technetium-99m (99mTc) labelled iminodiacetic acid (IDA) derivatives are commonly used as hepatobiliary imaging agents. Radiopharmaceuticals used for hepatobiliary imaging are divided into two groups based on the physiologic function of the liver they are...
High Voltage Direct Current (HVDC) overhead power transmission trends are currently advancing toward high system voltages over very long distances in a bid to viably tap from remotely located renewable energy sources. Corona effect plays a very crucial role in the design of overhead power transmission systems. Through corona, part of the energy carried on the transmission line is expended...
Quantum Cryptography, one aspect of which is Quantum Key Distri- bution (QKD), provides the only physically secure and proven method for the transmission of a secret key between two distant parties, Alice and Bob. The goal of QKD is to guarantee that a possible eavesdropper (Eve), with access to the communication channel is unable to obtain useful information about the message. The...
I adapt a recent work by Zahn et al. on the shape of rapidly rotating stars to explore the degree of oblateness for uniform, differential and shellular rotation of the star. I also discuss the relation of these results to the classical Roche limit.
Ground-state properties of three-nucleon systems consisting of one and two hyperons are studied with the integro-differential equations approach. The Hamiltonian of the systems is constructed with semi-realistic nucleon-nucleon interactions and phenomenological nucleon-hyperon interactions. The results obtained for the ground-state energies and root-mean-square radii are compared with the...
Over the past dozen years we have produced some of the most widely used interactive computer-based curricular materials for the teaching of introductory and advanced physics courses. These materials are now hosted on and distributed from the Open Source Physics (OSP) Collection of the ComPADRE National Science Digital Library. This talk outlines the tripartite integration of ComPADRE with...
Ab-intio Density Fuctional Theory has been employed to investigate the stabilities of Li< sub >2< /sub >O, Li< sub >2< /sub >S, Li< sub >2< /sub >O< sub >2< /sub > and Li< sub >2< /sub >S< sub >2< /sub > systems. Calculations were carried out utilizing Plane-wave Pseudopotential method within GGA-PBE using VASP CODE. We found good agreement between predicted data and experimental data of...
Planewave pseudopotential calculations were conducted to predict the phase stability of Pt-Cr binary alloys. The heats of formation are determined for five different phases, L12, A15, DOC, DO'C and tP16 of Pt3Cr and PtCr3. We observed that the cubic L12 Pt3Cr is the most stable structure in agreement with the experiments. The results for PtCr3 indicate the negative heat of formation for the...
The system ZrO2-xSxx is limited by the cases ZrO2 and ZrS2 (x = 0, 2). Physical properties of such systems for 0 < x < 2 are of great interest, but difficult to obtain from first principles calculation. A recently suggested approach, i.e virtual crystal approximation, allows simulation for changes in composition, while retaining a small unit...
In order to investigate the diffusion of indium (In) when an In thin film is coated with a copper (Cu) thin film, thin In/Cu films were grown on a silicon dioxide (SiO2) substrate. Both the In and the Cu layers were grown by electron beam evaporation. The temperature during evaporation of the films ranged between 27 and 38 oC. The In films (500 Å) were coated with Cu...
The behaviour of iodine implanted in highly oriented pyrolytic graphite (HOPG) has been investigated using Rutherford backscattering spectrometry (RBS), scanning electron microscopy (SEM) and x-ray diffraction (XRD). Iodine ions were implanted into HOPG using an energy of 360 keV and a dose of 1×1015 atoms cm-2 at room temperature. The implanted samples were annealed in vacuum at 900 0C,...
Preparation of Er3+, Ho3+ and Tm3+ ions co-doped SiO2 nanoparticle phosphor powders by sol gel method is reported. The morphology and the particle size of the SiO2 host matrix were confirmed by field emission scanning electron microscopy (FESEM). Ultraviolet, visible (UV/VIS) and cathodoluminescence measurements were carried out in order to investigate the optical properties of our powder...
We have investigated the electronic, structural and optical properties of the PtAs< sub >< /sub>2 and PtAsS structures using the density functional theory in the framework of Vienna Ab initio Simulation Package (VASP) code within the generalized gradient approximations of Perdew, Burke and Erzenhof (GGA-PBE) . The total energy calculation of PtAs < sub >< /sub>2 and PtAsS have been...
We investigate the transformation from hematite to ilmenite structure by solid solution approach using ab initio quantum-mechanical simulation technique. The method uses the Density functional theory with the plane-wave (PW) pseudopotential method within the CASTEP code. We performed full structural relaxation allowing lattice parameters and cell violume to change to their mechanical...
Rutile and anatase structured tin dioxide ceramics have been intensively studied in recent years because of their potential in sensing and fuel cells.The present work uses classical molecular dynamics simulations focused on the structure and possible transformation from anatase to rutile tin dioxide.The empirical Buckingham potential has been used to describe the interatomic interactions in...
Rutile and anatase structured tin dioxide ceramics have been intensively studied in recent years because of their potential in sensing and fuel cells. The present work uses classical molecular dynamics simulations focused on the structure and possible transformation from anatase to rutile tin dioxide. The empirical Buckingham potential has been used to describe the interatomic interactions...
The effects of side chain size and spacing on the mobility of the PEO backbone have been studied using molecular dynamics (MD) in Forcite code of Materials studio. The systems investigated contain a PEO chain of 186 ethylene oxide (EO) monomers to which side chains of 5, 6, 7, 8 and 9 PDMS monomers have been attached. The separations of the side chains used are 5, 10, 15, 20 and 50 EO...
Cobalt pentlandite (Co9S8)is the major source of cobalt. Of the several cobalt minerals, cobalt pentlandite is the most abundant and has the widest geographical distribution. This presentation looks at the computer simulation of Co9S8 structure using different computer simulation techniques, i.e. METADISE, VASP. These techniques have been employed...
CeCuGe is one of the few compounds to order ferromagnetically at low temperatures. The compound has been observed to exhibit paramagnetic-ferromagnetic (PM-FM) magnetic transition, TC = 10 K This magnetic ordering has been observed from specific heat (Cp), magnetization, (M(T,B)) and resistivity data. Isothermal magnetization of a hexagonal, highly ordered CeCuGe were measured in order to...
Within the confines of the standard model of rare earth magnetism, the high temperature magnetic properties of rare earth ions in a crystalline environment are identical to the magnetic behaviour of free tri-positive rare earth ions. At low temperatures deviations from free-ion behaviour occur due to the action of an anisotropic crystalline electric field (CEF). For Pr3+-ions...
Graphene characterization and device fabrication often require extensive use of the scanning electron microscopy (SEM) and tunneling electron microscopy (TEM). These techniques involve electron beam irradiation that usually causes defects in materials under investigation. The radiation induced defects may lead to significant damage to the material which may alter its properties, normally an...
Short range biaxial and hydrostatic strains in quantum dots caused by spacer layers affect the aspect ratio to a great extent, leading to variations in the conduction and valence band energy levels. This paper aims to study the effect of the indium mole fraction and thickness of the spacer layer on the size and shape of multi-stack quantum dots grown by metalorganic vapour phase epitaxy....
Amorphous and nanocrystalline silicon carbide thin films were deposited on corning glass 7059 and c-Si (100) substrates using the Hot Wire Chemical Vapor Deposition (HWCVD) and Magnetron Sputtering (MS) techniques. Samples were prepared at low substrate temperatures below 300 degrees celsius and a gas mixture of SiH4/CH4/H2 was used in case of HWCVD. For MS, the temperature of the substrate...
Silicon carbide (SiC) materials have attracted a lot of attention because of their good optical and electrical properties. In recent years there has been an intense focus in research on controlling the optical and electrical properties of amorphous SiC thin films deposited at low temperature of the substrate. SiC has a wide bandgap which can be tuned by varying the carbon content in the...
Hydroxyapatite coating (HAp, Ca10(PO4)6OH2), produced by air plasma spraying, was investigated for depth profiling behavior of phase composition, crystallinity and residual stress using diffractometry techniques. Probing was carried out using conventional 8 keV laboratory X-rays, 11 keV and 100 keV radiations from 2nd and 3rd synchrotron facilities, respectively. The latter employed...
Titania is a cheap and nontoxic polymorphic material of current interest for a variety of technological applications like in gas sensing and photovoltaic cells. Generally, TiO2, with a band gap of 3.2 eV, can only be excited by a small UV fraction of solar light, which accounts for only 3-5% of the solar energy. Various strategies have been pursued including doping with metallic elements...
Ce doped silica has potential applications for a luminescent material as phosphors for cathodoluminescence, scintillators and detectors. Ce ions can occur in a trivalent or a tetravalent state: only the trivalent Ce3+ state with a single 4f electron is optically active, while the tetravalent Ce4+ ion is non-luminescent. X-ray photoelectron spectroscopy (XPS) is a...
MgxZn1-xO films were grown on c-plane sapphire substrates by metal organic chemical vapour deposition. The effects of growth rate and low temperature (280ºC) ZnO buffer layer thickness on the incorporation efficiency of Mg as well as the optical and structural properties of the MgxZn1-xO films were investigated. Low growth rates enhance the segregation of Mg, leading to a magnesium rich...
Fe2O3 nanostructures were synthesized for various pH values on Corning glass substrates by aqueous chemical growth (ACG) using a solution of ferric chloride (FeCl3). It was found that increasing the pH from 1.16 to 5.0 of the solution significantly leads to a modification of the Fe2O3 morphology or orientation from randomly parallel needle shaped rod-like to randomly perpendicular...
Palladium (Pd) and ruthenium (Ru) Schottky barrier diodes were fabricated on (100) Sb-doped n-type germanium using resistive evaporation and electron beam deposition systems, respectively. Electrical characterization of these diodes using current-voltage (I-V) measurements was performed under various annealing conditions. The morphological evolution of the surface was analysed using the...
The AlxGa1-xN materials system is important for realising tuneable LED and laser sources and short wavelength photodetectors. While AlxGa1-xN (x = 0) is fairly known, there is interest in studying the effects of an increasing Al fraction on properties of devices. In particular, on the properties of a bi-metal Ni\ Au Schottky contact. We utilise Current-Voltage (I-V) and the forward...
We investigate the electrical parameters of n- GaN irradiated at room temperature with 5.4 MeV alpha-particles from an americium-241 (Am-241) radio-nuclide source under dark conditions. The radiation damage was studied using current–voltage (I–V) and capacitance –voltage (C–V) characteristics for a total irradiation time of 14 hours at a dose rate of and the corresponding dose range of ....
Measurements of X-rays diffraction (XRD), electrical resistivity (T), magnetic susceptibility (T), and magnetization (µ0H) are repeated for the pseudo-ternary alloy (Ce1xTbx) Pt2Si2. XRD results for all the compositions of (Ce1xTbx) Pt2Si2 system indicate a tetragonal CaBe2Ge2-type structure. (T) results indicate evolution from coherent Kondo lattice to incoherent single ion Kondo...
The Cr-Re alloy system was chosen in order to investigate a previous observation of the co-existence of superconductivity and antiferromagnetism, as well as the possibility of a quantum critical point (QCP) in this alloy system. For the initial studies a Cr86Re14 mother alloy was doped with V in order to decrease the electron to atom ratio, resulting in a decrease in...
The main aim of this project is to synthesize, isolate, identify and characterize graphene, defined as a one-atom layer of hexagonally bonded carbon atoms using mechanical exfoliation method. Moreover, this technique is based on pulling apart the layers of a piece of highly oriented pyrolytic graphite(HOPG) and transfer layers from the graphite onto a SiO2 substrate. Graphene is the first...
The effects of annealing temperature and time on glassy carbon implanted with 360 keV strontium ions at room and high temperatures are reported. The samples were implanted with strontium ions to a fluence of 2 x 1016 ions/cm2 at room temperatures, 350ºC and 600ºC. The room temperature implanted samples were isochronally vacuum annealed at temperatures from 200ºC to...
Hydrogen is the lightest element and it has the highest energy content per unit of weight of any known element and thus, it can be used as a source of clean energy. Previous research studies on hydrogen storage show that storing hydrogen as a solid hydride is preferred compared to liquid and gas because of the very high pressures and low temperatures needed to maintain the system. Hydrogen...
Optical selection rules for the intervalley scattering for direct and indirect transitions are investigated. The non-zero matrix elements of the scattering tensors are derived by the method of vector coupling coefficients. These coefficients are needed for the understanding of Gunn effect.
Noble gas ion sputtering combined with Auger analysis has been applied extensively to determine the elemental composition as function of sputtering depth. Data from these depth profiles have been used to determine the sputter yield coefficients (S) of elements that are of fundamental interests in many fields, such as in: sample preparations particularly were the sputter ion source is...
ZnO and PVP capped ZnO nanoparticles were synthesised using the sol-gel method at low temperature with ethanol as a solvent, zinc acetate as a precursor and methanol as the cleaning agent. The influence of temperature on the morphology, structure and the optical properties of the ZnO nanoparticles were investigated. The effect of addition different molar masses of the PVP during the...
A wet chemistry route is an essential method used today to synthesize high quality ZnO nanoparticles and nanorods. It is a novel low cost method to produce nanoparticles and nanorods with relatively high dispersivity. In this study optical properties and morphology of the nanoparticles and nanorods were investigated. The X-ray diffraction (XRD) patterns of both nanoparticles and nanorods...
The existence of the ternary intermetallic compound CeRh2Sn2 has been known since the crystallographic report of Selsane et al on the CeM2Sn2 family of compounds in which M is a d–electron element. The crystal structure is well ordered and the sole magnetic species, Ce, occupies a unique symmetry site in the unit cell. Subsequent studies into...
The novel ternary intermetallic compound Ce6Pd12In5 forms in a well-defined atomic stoichiometry with a hexagonal crystal structure (space group P63/mcm) and a unique atom in each of the crystallographic sites available in this space group. The bonding lengths are comparatively short and suggest strong interaction especially between Ce and Pd...
We present specific heat, electrical resistivity, susceptibility, and thermopower measurements on the two novel intermetallic compounds CeFe2Al8 and CeCo2Al8. They form in an orthorhombic crystal structure of space group Pbam. In the unit cell representation Ce atom occupies only one lattice site,having Ce-Ce interatomic distance of 4.03Å....
Recent measurements on an antiferromagnetic (AFM) Cr0.978Al0.022 alloy single crystal suggest that the triple point (TP) on the magnetic phase diagram (MPD) might be a special type of critical point. This suggestion is further investigated here through electrical resistivity and specific heat measurements on a series of Cr1-xAlx alloy single...
Traditionally magnetic forces are supposed to act on moving electric scalar charges and the hitherto undetected Dirac’s magnetic (scalar) charges, and that work done by such forces is always zero. Any possible evidence to the contrary is vehemently denied in order to justify this long held myth. Following our recently developed and validated concept of magnetic vector charges as sources of...
The optical and structural properties of ZnO grown with a mixture of oxygen and nitric oxide as oxidants are investigated. With R defined as the ratio of oxygen to nitric oxide molar flow rates, samples grown with R ≥ 1 (i.e. a higher low rate of oxygen compared to nitric oxide) reveal a 3D growth mode with columns perpendicular to the substrate, while for R < 1 a preferential 2D growth...
SrGa2S4:Ce3+ thin films are promising for full colour thin-film electroluminescent (EL) and field emission displays (FED’s) because of its good optical properties. These films were previously prepared using several different techniques such as sputtering (RF), molecular beam epitaxy (MBE), reactive multi-source deposition (MSD), metal-organic chemical vapour...
Surface mapping of quantum well structures using photoluminescence measurements is ideal for determining the overall behaviour of such samples with regard to their chemical composition and well-width fluctuations. In some areas where the structural variations are large over a sample, photoluminescence mapping can yield information which would otherwise require several samples to be grown....
Nano-pahsed structures based on metal-dielectric composites also called cermets (Ceramic-Metal) are considered among the most effective spectrally selective solar absorbers. For high temperature applications (stable up to 650°C) noble metals nanoparticles and refractory oxide host matrices are ideal as per their high temperature chemical inertness and stability: Pt/Al2O3 cermet...
ZrN films were deposited on Si<100> substrates, Al and brass strips by DC magnetron sputtering under varying conditions of power, pressure, argon and nitrogen gas flow rates as well as temperature and characterized by SEM, AFM, RBS, resonant RBS, and XRD. The films are transparent and semiconducting. They tend to absorb oxygen. The films were found to adhere well to the substrates. The...
CaTiO3 exhibits a Perovskite structures that has an ABO3 stochiometry where A and B represent metal cations with a combined charge of 6+ valency and O with 6- valency, and thus bring about charge neutrality to the compound. Upon introducing Pr3+ ions in the site of Ca2+ ions, charge imbalance occurs by introducing a 7+ valency, and this force the material to compensate for this effect by...
There has been a growing demand for quantum cutting and upconverting efficient nano luminescent materials during the last decades. Wide band gap luminescent materials, specially the fluoride, are one of the major role players. Due to a number of advantages such as the excellent transparency in theinfrared (IR) to far ultraviolet (UV) range and low-energy phonons as well as low toxicity...
Previous studies in our laboratory on the (Cr100-xAlx)95Mo5 alloy system through electrical resistivity and magnetoelastic measurements suggest that spin-density-wave (SDW) antiferromagnetism is fully suppressed down to 4 K in the concentration range 2.0 ≤ x ≤ 5.0 at.% Al. The current interest in quantum criticality in Cr and Cr alloy systems...
Zinc-oxide nanoparticles are well known for their novel optical and electronic properties for applications in various fields such as solar cells, ultra violet shielding, gas sensors, paint and heat mirrors. We report on the relation between the structure and optical properties of ZnO nanoparticles synthesized via the sol-gel technique, with specific emphasis on the effect of growth and...
Porphyrins are macro-cycles often organized into nano-scale structures which perform many of the essential light-harvesting-, electron- and energy-transfer functions in various natural and synthetic systems. In addition to the sub-picosecond charge generation and transfer, they exhibit various shapes and functional properties that make them useful for the construction of ultrafast...
Presently Ca AlxOy:Tb green phosphors are mainly prepared by the solid-state process which is more feasible than others in terms of operation and large-scale production. However, the raw materials are usually not mixed well and very high temperature is needed to synthesize the final powder using the solid-state process. In order to solve these problems, Terbium ion...
Crystalline lead sulfide (PbS) nanorods were synthesized by chemical bath deposition (CBD) method using the mixed aqueous solutions of lead acetate, thiourea and ammonium solution. The lead acetate concentrations were varied in the deposition process to determine the effect thereof. The temperature of the bath was maintained at 80ºC. The final yields were characterized for structural,...
Cobalt sulphide nanoparticles are one of the most complex and challenging particles to synthesize due to strongly reducibility of the cobalt ion and the oxidizable nature of the sulphide ion. Cobalt sulphide therefore exist in various phases with different compositions including Co4S3, Co9S8, CoS, Co1-xS, Co3S4, Co2S3 and CoS2. Herein, we describe the synthesis of CoxSy nanoparticles;...
Rare earth oxysulfide materials exhibit high luminescence efficiency as well as excellent chemical stability. These materials are widely used as luminescent host materials of several commercially available red emitting phosphors. However, there still remain issues affecting the operational parameters such as luminescence efficiency, stability against temperature, high color purity and long...
Tb3+-activated calcium silicate (CaxSyyOz:Tb3+) nanophosphors have been synthesized by means of simple and low temperatures (500°C) using the solution-combustion of corresponding metal nitrate, TEOS and urea solution mixtures. The structural evolution of the phosphor was studied by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and the luminescence properties of the...
Tb3+-doped SrZnAl2O4 nanocrystalline phosphor with good crystallinity were successfully prepared by a combustion method at a relatively low temperature (500o-C), using urea as fuel and metal nitrates as precursors. The effects of Sr and Zn concentrations on the structure and luminescent properties of the material were investigated. In addition,...
Barium-substituted phosphor powders of (Ba1-xSrx)Al2O4:Eu2+ ;Nd3+ composition were prepared by combustion method at an initiating temperature of 5000C, using urea as reducer. The powders were then annealed at higher temperatures of 8000C and 10000C for 3 hours. Their crystallinity and phase...
The study of annealing effects on platinum binary systems has both the fundamental and applied aspects. It is due to the fact that the formation of ordered domains increases the strength and surface hardness and could also have an impact on surface activity and chemical properties. The changes of mechanical, physical and chemical properties caused by annealing could be of significant...
Pr3+-Tb3+, and Pr3+-Eu3+ ion pairs co-doped in SiO2 matrix were prepared by a sol-gel method. The photoluminescence (PL) measurements revealed the red and green emissions centred at 614 nm (5D0-7F2) and 541 nm (5D4→7F5) for single doped Eu3+ and Tb3+ ions in SiO2, respectively. Co-doping of Eu3+ and Tb3+ ions with Pr3+ in SiO2 showed that the energy transfer between Pr3+ and nearest Eu3+...
The concentration of any dopant in a semiconductor can usually easily and readily be established using the plasma resonance minimum. Infrared reflectance spectroscopy was used to assess the doping of SiC wafers by phosphor implantation. However, results obtained did not match the theoretical predictions. The problem was investigated, including an assessment of the applicable theory. ...
The magnetocaloric effect (MCE) may become strongly enhanced in systems exhibiting a second order magnetic phase transition due to critical behaviour of the order parameter in close proximity of the transition region. Recently it has been shown that, analogous to the order parameter, the MCE shows scaling behaviour with the applied magnetic field along the critical isotherm. It has been...
The importance of gold for scientific use is of fundamental importance to research and technology developments. The bulk gold shows reluctance to participate in chemical reactions, the effect which has been corrected by the change in the size towards nanoclusters and, this makes the study of temperature effects on gold very important. We have performed molecular dynamics simulations on...
The interaction of Pd and SiC samples during thermal annealing were investigated using x-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS) as well as Scanning Electron Microscopy (SEM). Two sample configuration were used (1) the palladium (50nm) was deposited onto a degreased 6H-SiC substrate and (2) palladium ions were implanted into the 6H-SiC substrate at room...
There is a general misunderstanding regarding the creation of Frenkel pairs in the vicinity of the observed critical temperature Tc in superionic materials. The measured conductivity increases sharply at a temperature coinciding with the deviation of temperature-dependent lattice constant from 6.2086 A. Frenkel pairs responsible for superionic conduction are gradually generated well below...
Previous experimental investigations have only shown, without explanation, that the pre-exponential factor (D0), in the diffusion coefficient of Sb segregating in Cu, is dependent on the surface orientation of a crystal. In this study, the surface concentration of Sb in a Sb doped Cu(111/110) bi-crystal was measured using a method combining AES and linear temperature heating. ...
The binary compound CeCu5 is an archetypal heavy-fermion Kondo lattice with an antiferromagnetic ground state. Strong hybridization effects between the localized 4f-electron moment and conduction electrons result in incoherent spin scattering in the electronic transport at high temperatures, but with an effective magnetic moment nearly equal to that of the free-ion...
Since the first report of the anomalous magnetic and electronic phenomena in CeRu2Al10 this intermetallic class of compounds, incorporating also members with elements Os and Fe in the place of Ru, have attracted considerable interest. N spite of large interatomic distances antiferromagnetic order sets in at TN =27 K in the ru and Os derivatives, with simultaneous...
It is evident that the Eu2+ ion acts as a luminescent centre emitting in the blue (λmax ~ 440 nm) spectral region for CaAl2O4:Eu2+. The R3+ ion is believed to act as a trap or somehow modify the trap properties in these phosphors. Despite a large number of research on the phenomenon the mechanism of the persistent luminescence of the...
Polycrystalline diamond (PCD) cylindrical cutters used in oil well drilling are susceptible to fracture due to the hostile environment of randomly occurring high impact loads. These cutters commonly consist of a PCD layer sintered onto a cobalt-tungsten carbide (Co-WC) substrate. The fact that the cutters fail after repeated use gives rise to the possibility of fatigue type processes in...
Vanadium dioxide falls into the category of smart thermochromic materials, one where the property of the material changes due to the effect of temperature. High quality pure thermochromic thin films of vanadium dioxide were prepared by using two physical methods, Rf-reactive sputtering and pulsed laser deposition methods. These deposition methods were used to study the effect of deposition...
Different compositions of Ti-Pt were varied within the B2 region i.e. 45-55 at% Pt using solid solution method employed in CASTEP code. The Ti50Pt50 structure was found to be more stable as compared with other different compositions with the heats of formation of -0.8584 eV. We also observed that the more we increase the Ti and decrease the Pt composition, the change...
We report on the characterization of commercially terbium doped gadolinium oxysulfide (Gd2O2S:Tb) phosphor and the degradation of the Gd2O2S:Tb green phosphor for its application in CRT screens. As a result, degradation of the cathodoluminescence (CL) intensity during irradiation of the powder with 2 keV electrons in an oxygen pressure of 1 x 10-6 Torr was studied. The ESSCR mechanisms was...
Recent studies have employed manganese dioxide (MnO2) catalysts to improve the efficiency of Li-air batteries, while other studies have revealed that the Li/O2 cell can be recharged with high efficiency without a catalyst using an appropriate porous carbon electrode. Interestingly, charge voltages of these cells are similar to those of the MnO2, while both...
Models with extra spacial dimensions offer a new way to address outstanding problems in and beyond the standard model. In such models the Planck scale in the bulk can be of the order of the electro-weak symmetry breaking scale. This allows the coupling strength of gravity to increase to a size similar to the other interactions, opening the way to the unification of gravity and the gauge...
The cosmic microwave background (CMB) carries information from the last scattering surface that puts constraints on the multitude of proposed cosmological models and the gravity theories they are based on. Amongst such theories are the f(R) theories of gravity which have become an interesting endeavour to correct for the degeneracies of the concordance model. We present a description of...
Semiconductors are important because of their numerous technological applications. As such, there have been a number of investigations on the recrystallization of amorphous GaAs. We present results of the isochronal annealing of an ̴ 140nm amorphous layer of GaAs on a crystalline substrate produced by bombarding with 100 KeV argon ions with a fluence of 5×1015 ions/cm2. Raman measurements...
Lightning has in recent times wreaked havoc during the rainy season in several parts of South Africa and this prompted the physics community under the auspices of the South African Institute of Physics (SAIP) to devise meaningful strategies for promoting public awareness. In response to this call, first year physics students at the University of Johannesburg responded to a carefully...
This work is part of a program based on the electro-production of baryonic resonances. In part, the physics goals are to assess the relevant degrees of freedom appropriate to describe high momentum transfer exclusive reactions. In particular, the interest is in the region where the four – momentum transfer squared, t ~ Q2 varies beyond the validity of the constituent quark model (CQM),...
N=4 SYM theory has been extensively studied in the planar limit. A very significant result of this study is a map from the planar dilatation operator to the Hamiltonian of an integrable spin chain. In this talk we consider a large N (but not planar) limit of the theory. This is a considerably more complicated problem since non-planar corrections need to be summed. This summation is...
Laguerre-Gaussian (LG) beams possess many interesting properties, one of which is that they carry orbital angular momentum, an extrinsic component of angular momentum, when the electric field or mode has an azimuthal angular dependence of exp(il), where l is the azimuthal mode index. These beams are easily generated using spatial light modulators (SLMs), where a Gaussian beam incident on...
In recent years student satisfaction surveys have become increasingly popular in universities. Whether this gain in popularity is because students themselves know best when they are learning, or whether it is because universities merely wish to ensure that they have satisfied customers, is still a matter of debate. Nevertheless, the importance of student satisfaction surveys in universities...
The direct evidence for the acceleration of hadronic cosmic rays at supernova remnants underlined the need for a 3D time dependent treatment of the propagation of Galactic Cosmic Rays (CRs). Full 3D time dependent calculations of the propagation of CRs have shown that if CRs indeed originate from supernova remnants, transient point-like sources, the flux of the CR primary component measured...
The measurement of the isolated di-photon cross-section at the LHC is crucial as these events constitute an irreducible background to new physics processes, such as a Higgs boson or graviton decaying to two photons. These events also provide important information for the understanding of QCD processes. The di-photon cross-section has been measured in ATLAS using the full 2010 data sample,...
ABJM theory is an N=6 Superconformal Chern-Simons theory with gauge group U(N)XU(N). This gauge theory has been extensively studied in the planar limit. Motivated by similar results for N=4 SYM, the planar dilatation operator of ABJM theory has been mapped to the Hamiltonian of an integrable system. Recently, it has been argued that there are large N (but not planar) limits of N=4 SYM...
The dispersion relation of surface acoustic waves in TiC thin hard films of various thicknesses on silicon and silicon carbide substrate is studied using Surface Brillouin scattering. Simulations of surface Brillouin scattering (SBS) spectra of TiC thin hard films on silicon and SiC substrates have been carried out over a range of film thickness from 5nm to 1000nm. The simulations are based...
In this work we propose an implementation of a new intra–cavity beam shaping technique to vary the intensity distribution of the fundamental mode in a resonator cavity while maintaining a constant intensity distribution at the output. This method can be useful for fitting a transversal intensity profile of the required mode with a pump beam profile in the region of the active medium to...
A two-dimensional hydrodynamic numerical model is extended and applied to simulate the interaction between stellar winds and the interstellar medium (ISM). In particular, the stellar wind evolution of O-and B-type stars is calculated. First, the evolution of a stellar wind into the ISM and also a more dense molecular cloud are considered for the case of no relative motion between the star...
Optical Coherence tomography (OCT) is a non-invasive imaging technique that is known to be used to monitor changes and differences in different types of materials. In the field of Biophysics/Biophotonics OCT can be used to non-invasively detect changes occurring in tissue. This study will look at using OCT to detect skin cancer. Similar work has been done by other groups, however the...
The H -> ZZ(*) -> 4leptons channel is one of the most promising channels for a low-mass Higgs boson, as it has both a clean signature and a large branching fraction for Higgs mass below a few hundred GeV. The ATLAS experiment has explored this channel using the LHC collisions data at a center-of-mass energy of 7 TeV, using data-driven background estimation techniques. Some Abelian Hidden...
It is well known that neutron stars have very strong magnetic fields and that these fields impact the behaviour of the star. The focus of our research is on the interaction between the magnetic field and the constituent matter in the neutron star’s interior. In particular we investigate the possibility of a ferromagnetic phase in the neutron star interior being the source of the star’s...
Experiments at the Large Hadron Collider (LHC) aim to address fundamental questions in particle physics such as the origin of mass for elementary particles, the matter/anti-matter asymmetry in the universe, the nature of Dark Matter, the state of matter in the early universe, etc. The ATLAS detector is one of the four major detectors being exploited at the LHC to shed some light on the...
The Faculty of Military Science of Stellenbosch University presents an Algebra-based Physics course to first year students. The practical component comprises of a range of experiments that differ significantly in characteristics. Questionnaires are yearly completed by the students to evaluate the theoretical and practical components of this course. This paper will explore some of the...
In this work, we report on the fabrication of multiwall carbon nanotubes (MWCNT)/NiO nanocomposite thin films by the pulsed laser deposition technique on to aluminium substrates. Samples were prepared with different MWCNT content, and varying substrate temperatures. Structural and optical properties were investigated by scanning electron microscopy, x-ray diffraction, Raman spectroscopy,...
In order to apply light treatment to skin, the absorption through the outer layers of the skin needs to be considered. Human skin is a highly scattering medium and the melanin in the epidermal layer of the skin is a major absorber of light in the visible and near infrared wavelengths. Darker skin has a higher concentration of melanin in the epidermis and absorbs more light than fair skin....
A new correspondence between type IIA string theory on AdS4×CP3 and an N=6 Super Chern-Simons-matter theory was proposed by Aharony, Bergman, Jafferis and Maldacena (ABJM) in 2008. We construct the D4-brane giant graviton, extended and moving in the complex projective space, which is dual to a subdeterminant operator in ABJM theory. This dynamically stable configuration factorizes at...
We outline an approach for the calculation of the mean focal length of an aberrated lens, and provide closed form solutions that show that the focal length of the lens is dependent on the presence of defocus, x-astigmatism and spherical aberration. The results are applicable to Gaussian beams in the presence of arbitrary sized apertures. The theoretical results are confirmed experimentally,...
Rare–earths (Tb3+ or Ce3+) doped zinc aluminate (ZnAl2O4) nanocrystals were successfully prepared by a modified combustion method using urea (CH4N2O, 99–99.5%) as fuel and characterized to investigate down-converted emission by energy transfer from Ce3+ to Tb3+ . The post-preparation annealing of the...
N=4 SYM theory has been extensively studied in the planar limit. An important result is that the planar dilatation operator can be mapped to the Hamiltonian of an integrable system. In this talk we study certain large N (but not planar) limits of the theory. We argue that the dilatation operator remains integrable: it reduces to a set of decoupled harmonic oscillators. This challenges...
In his work on superfluid helium, Feynman gave both qualitative and quantitative descriptions of the excitation spectrum of superfluid helium. I briefly review Feynman's approach to superfluid helium and assess the applicability of this theory to neutron star interiors.
Due to their self-renewal and pluripotency characteristics, stem cells possess the potential to dramatically advance current therapies in tissue regeneration and engineering. Nonetheless, there still remains a pressing necessity to answer the biological questions concerning how stem cell renewal and differentiation programs are operated and regulated at the genetic level. Genetic...
Traditional lecturing of Physics in a preaching pattern to a multitude stduent masses in a large lecture theatre, has not succeeded in attracting more number into Physics further than second year. University of Pretoria Physics Education Research Group (UPPERG) has introduced "Interactive-Inquiry Learning" Teaching where Masters and Doctoral students are guided to lecture groups of 40 BSc4Y...
Since its inception, optical trapping has found its place in the field of physics, biology and recently in micro-fluidics. To a physicist, this technique opens up avenues to carry out force measurement with utmost accuracy and precision on the micro-scale level. This is attained by measuring the magnitude of the trapping force required to restrain a trapped particle to its equilibrium...
The advent of the MeerKAT and SKA radio telescope projects will allow for vastly improved precision in the measurement of pulsar radio frequency emissions. Thus, the propagation of a pulsar’s conical radio beam through the strong gravitational field region in the vicinity of a compact object, i.e. black-hole or another neutron star, will probe the metric of spacetime in the high-field...
An entangled bipartite Gaussian state is coupled to two thermal reservoirs, one for each particle. A harmonic oscillation is allowed between the two particles. The reservoirs are assumed to have different temperatures and to be coupled to the particles with different coupling strengths. This allows for a realistic situation where a bipartite state may be shared between two parties who...
Recent theoretical work has suggested that some nuclei in the rare earth region might exhibit tetrahderal deformations. Several nuclei have been studied at iThemba LABS, resulting in evidence against the possibility of low-lying tetrahedrally deformed bands. In a continued study of the region, further gamma-ray spectroscopy experiments have been performed at iThemba LABS, populating low...
With modern liquid crystal devices it is possible to implement digital holograms for the modulation in amplitude and phase of light: so called 'structured light'. In this non-specialist talk, we will introduce the concept of complex amplitude modulation, and show how light can be tailored to have interesting properties: defying diffraction, twisted like a spring in intensity and phase, and...
The current-voltage (I-V) characteristics of sulphur passivated n-GaSb have been studied in the temperature range 80 K - 330 K using Au Schottky barrier diodes (SBDs). The forward I-V characteristics have been analysed assuming that thermionic emission is the dominant current transport mechanism and that the barrier height patchiness takes on a Gaussian distribution. It has been found that...
An introduction to the new development project on the implementation of a radioactive ion beam (RIB) facility at iThemba LABS will be presented. In particular with relation to the uses of the RIB for the application of research in condense matter and materials research. Some leading examples by international laboratories using radioactive nuclei as probes to enhance the understanding of...
Premature withdrawal from university due to academic failure has the potential to present problems to both students and educators. The demand from industry for a larger pool of science and engineering graduates in South Africa is in line with international norms. This state of affairs is compounded by a shrinking pool of good quality school leavers. For the desired growth in graduate...
Applying the quantisation of action variables to a theory of gravitation one derives discrete values for planetary distances from the sun. The calculated values agree with the observed values of all the planets. The derived equation also applies to the exoplanets. The application is similar to that of the Wilson-Sommerfeld rule for atomic orbits.
Decoherence indicates the process that a quantum system undergoes through the interaction with an external environment. The central issue and one of the greatest challenges in Nanotechnology and Quantum Information Processing is the way to control or delay the destructive effect of the environment on qubit coherence. For this reason, a qubit interacting with a reservoir of bosons...
Energetic stability of magnetically ordering dopants in diamond holds the prospect of achieving a diamond based diluted magnetic semiconductor which, in addition to diamond’s extreme properties may successfully be considered for spintronic device applications. However, one of the problems to be addressed is that of predicting the most energetically stable lattice configurations or charge...
Diabetes mellitus (DM) is a chronic disease characterized by impeded glucose metabolism and preceded by diabetic ulcers which are chronic due to deteriorated healing process. Hypoxia, decreased fibroblast proliferation and impaired growth factors are amongst root factors that contribute to impaired healing. Photostimulation is a non-invasive treatment that utilizes low intensity laser...
During the past decades there has been an increasing interest in alternative conceptions in physics. An alternative conception in science refers to a conception which in some aspects is contradictory to or inconsistent with the concept as intended by the scientists. Research in this domain tries to answer questions such as which misconceptions occur, what are their origins, how extensive...
We studied charge injection and transport mechanisms in blends of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methylester (PCBM), by analysing dark, temperature dependent current-voltage characteristics of the P3HT:PCBM blend thin films sandwiched between aluminium electrodes in a MIM configuration. We present a general method of interpreting Fowler - Nordheim plots of...
The nuclei 158,15968Er are classic examples of many phenomena in the study of nuclei at high spin. However, although the multi-quasi particle structures of 158,15968Er are well established, there is not much spectroscopic information on the vibrational structures in 158Er or how these couple to the odd neutron in 159Er. Additionally, there are several bands where the spins and/or parities...
Perturbation theory uses Lagrangian techniques that require vector fields to be compared at finitely separated points. This method can be generalised to the strong gravitational field regime in one of two ways, using either covariant or Lie derivatives. In this paper, I argue that those methods based on the Lie derivative are more useful. The Lie derivative provides a clear picture of how...
The transfer of energy and information in quantum networks plays an important role in both quantum communication and quantum computation. The quantum system inevitably interacts with the surrounding environment, and such interaction leads to dissipation and decoherence, which are processes typically associated with a destruction of quantum coherence in the system. However, recently evidence...
The study investigated the effects of low intensity laser radiation (LILI) and epidermal growth factor (EGF) on adult adipose derived stem cells (hADSCs) isolated from human adipose tissue. Isolated cells were cultured in complete Dulbeco’s Modified Eagle Medium (DMEM) containing 10% featal bovine serum (FBS), EGF and antibiotics and incubated at 37°C in 85% humidified atmosphere of 5%...
Crystalline thin solid films of WO3 have been prepared on Corning glass, FTO and Si through the low temperature, wet chemistry method of Aqueous Chemical Growth. SEM images of the thin films produced show that the surface morphology of the films is influenced by the kind of substrate used for the synthesis. While nanoplatelet-containing flower-like structures were consistently obtained on...
Negative-parity side bands in nuclei localized in the vicinity of N = 90 are known to have strong electric dipole transitions from each level to the ground-state band, with weak or unseen E2 transitions (E2s) in the medium (~15h) to low-spin region. These structures have always been regarded as octupole vibrational bands. On the other hand, Dudek et al. recently proposed that these...
In this work we investigate the behavior of an instantaneous Poynting vector for different types of cylindrical symmetric beams such Gaussian beams, Bessel beams and so on. In most investigations for energy flow in real laser beams, the oscillation component of the Poynting vector is not considered. However this component of the Poynting vector carries useful information regarding beam...
Silica is a basic material of technological importance for optics, microelectronics, photonics and fibre optics. Its high absorption edge energy makes its particularly useful for UV applications and it has been used as a host material for a variety of luminescent lanthanide ions due to its chemical stability and non-hygroscopic nature. For lanthanide ions the 4f electron energy levels are...
Educational technology in the form of classroom response systems (clickers)have become a tool in classroom instruction. In the classroom the clickers are used to promote interactive student engagement and immediate assessment of student understanding. The paper reports on a study using clickers as well as flash cards (a low tech version of the clicker) as a tool to enhance interactive...
Since the invention of the laser, its application in the health sector has been studied and in an attempt to discover effective alternative treatments, Low Level Laser Therapy (LLLT), commonly known as biostimulation or photo-biostimulation, has emerged. This therapy has been successfully used both in in vitro and in vivo studies in wound healing. Although this therapy is in use worldwide,...
Every year over a hundred people die unnecessarily from lighting in South Africa. Recent reporting and correspondence in the media clearly indicated a total lack of knowledge on the part of the public, from Ministerial level down, about the causes and effects of lightning. Much work has been done by organizations such as the CSIR and SA Weather Bureau, and there are several commercial...
Quantum Random Walks have been introduced almost 20 years by Y. Aharonov et al. [Phys. Rev. A, 48(2):1687–1690, 1993] and have found wide applications in quantum computing. As is often the case in quantum theory, Quantum Walks differ strongly from classical random walks. In joint work of S. Attal, C. Sabot, F. Petruccione and I. Sinayskiy the concept of Open Quantum Random Walks was...
To understand the formation of stars one must be able to identify young objects. RCW 34 is a star forming region in the constellation of Vela. A study was conducted in the near-infrared where it was found that a large number of stars surrounding the nebula shows NIR characteristics of lower mass pre-main sequence stars. To prove the suspicions a follow-up study was conducted in the optical....
Europium (Eu2+) and gadolinium (Gd3+) doped BaAl2O4 powder phosphors were prepared by combustion method at different initiating temperatures (400-1000 oC), using urea as a comburent. The powders were annealed at different temperatures in the range of 400-1000 oC for 3 hours. X-ray diffraction data show that the crystallinity of the BaAl2O4 structure greatly improved as the annealing...
Nuclei near N=90 are considered transitional, since they lie between nuclei that display vibrational spectra and nuclei that display rotational spectra. The structure of these transitional nulei, in particular the nature of the low-lying first excited states |0+2> still pose a great challenge with various theoretical models competing. A new perspective to the understanding of the structure...
Graphene is a two-dimensional crystal of carbon atoms arranged in a honeycomb lattice. It is a zero band gap semimetal with very unique electronic optical and mechanical properties which make it useful for many applications such as ultra-high-speed field-effect transistors, p-n junction diodes, terahertz oscillators, and low-noise electronic, NEMS and optical sensors. The high quality mass...
The Coulomb excitation of light nuclei can provide unique information on the matrix elements for excited states. This contribution will discuss experiments to measure such excitation as well as ab initio large shell model calculations calculations that can be tested by these measurements.
The successful incorporation of ZnO nanoparticles and Ce3+ ions in Pr3+ doped SiO2 using a sol-gel process is reported. SiO2:Pr3+ gels, with or without ZnO and Ce3+, were dried at room temperature and annealed at 600 oC. The Field Emission Scanning Electron Microscopy (FESEM) indicated clustered SiO2 nanoparticles with with particle size diameter ranging between 20 to 120 nm while the high...
We find non-local but non-signaling probabilities satisfying the 'nonlocality without inequality’ arguments for multiple two-level systems. Maximum probability of success of these arguments are obtained in the framework of a generalized nonlocal theory. Interestingly, for two two-level systems, the probability of success of these arguments converge to a common maximum in this framework....
Photovoltaic cell devices constructed from organic materials are becoming increasingly efficient because of the discovery of the bulk heterojunction concept. Today, organic photovoltaic cell (OPVC) devices fabricated from the blends of poly(3-hyxylthiopene) (P3HT) and [6,6] –phenyl C61-butyric acid methyl ester (PCBM) are the most widely studied bulk heterojunction systems because of their...
The phase measurements of a Shack-Hartmann wavefront sensor are calibrated. The process involves creating holograms of known amounts of individual phase aberrations on a spatial light modulator and reflects an aberration free laser beam off of the modulator’s liquid crystal display thereby giving the beam that aberration. The beam is then relayed onto the sensor for direct measurement. The...
We use the HI velocity profiles of The HI Nearby Galaxy Survey (THINGS) to study the phase structure of the ISM and its relation to galaxy properties and morphology. To construct high S/N profiles, we use a method analogous to the stacking method sometimes used in high redshift HI observations. We call these high S/N profiles super profiles. By decomposing the super profiles into Gaussian...
Many nascent proteins, including nearly all membrane and secreted proteins, must traverse a membrane-bound protein-conducting channel prior to their full maturation. This channel, the Sec translocon, is found in all domains of life and possesses the novel ability to direct nascent proteins to the membrane or to the extracellular space, depending on their sequences, often concomitant with...
In this project data from The HI Nearby Galaxy Survey (THINGS) and from the HERA CO Extragalactic Line Survey (HERACLES) is being used to compare the HI (neutral hydrogen) and CO dispersions in nearby galaxies in order to see if they are related. This is important in improving star formation laws (as they currently only use HI dispersions, but stars form from molecular gas) and to better...
The notion of mirror symmetry is well-established for nuclei on or near the valley of stability, and this has its roots in the (largely) charge independent nature of the nuclear force. We have applied this assumption to nuclei near or beyond the drip lines, in particular, the mass-15 system for 15F and 15C. Using information on the bound states in 15C we predicted states in 15F in 2006...
Some results from applying nuclear and related analytical techniques in medical, environmental and industrial biotechnologies are presented. In the biomedical experiments biomass from the blue-green alga Spirulina platensis has been used as a matrix for the development of pharmaceutical substances containing such essential trace elements as selenium, chromium and iodine. The feasibility of...
Ground-state properties of three-nucleon and four-nucleon systems are studied with the angular-momentum-projected and parity-projected antisymmetrized molecular dynamics. The Hamiltonian of the systems is constructed with semi-realistic nucleon-nucleon interactions. The results obtained for the ground-state energies, root-mean-square radii and magnetic dipole moments are compared with the...
Europium-doped barium magnesium aluminate (BaMgAlx0y:Eu) phosphors were obtained at low temperatures (500˚C) using the solution - combustion of corresponding metal nitrate–urea solution mixtures. The particle size and morphology and the structural and luminescent properties of the as-synthesized phosphors were examined by means of scanning electron microscopy (SEM), X-ray diffraction (XRD),...
Zinc oxide is a direct, wide bandgap semiconductor material with many promising properties for blue/UV optoelectronics, transparent electronics, spintronic devices and sensor applications. ZnO has been commonly used in its polycrystalline form in a wide range of applications such as sunscreens, catalysts, piezoelectric transducers, varistors, and as transparent conducting electrodes. ZnO...
The aim of this project is to study the stellar populations, and thereby evolution and star formation histories of brightest cluster galaxies (BCGs). In particular, I will determine if a Single Stellar Populations (SSP) or Composite Stellar Populations (CSP) provides the most significant fit for the BCGs using high signal-to-noise ratio (S/N), long-slit spectra, obtained on the Gemini and...
The angular-momentum-projected and parity-projected antisymmetrized molecular dynamics is used to analyse the charge and magnetic form factors of the three-nucleon systems. Non-relativistic nuclear charge and current operators with relativistic corrections are employed. The Hamiltonian of the nuclear systems is described with a semi-realistic nucleon-nucleon potential. The results...
Diamond tools are generally made of sintered polycrystalline diamond (PCD) on a hard metal tungsten carbide (WC-Co) substrate during the High Pressure High Temperature (HPHT) process. The diamond tools are used widely as cutting and drilling tools due to their unique combination of superior properties. However, there are several issues that need to be resolved about the diamond tools. At...
Nitrilase and amidase enzymes catalyse the conversion of nitriles and amides to their corresponding acid and ammonia - chemistry which is useful in synthesis of drug compounds and fine chemicals. The conversion of cyanide, a nitrile, to ammonia and formic acid is useful in detoxification of contaminated wastewater. The cyanide dihydratase from Bacillus pumilus (CynDpum) catalyses this...
During the last 15 years there has been considerable interest in density matrix based methods for electronic structure calculations. The “difficult” problem of ensuring idempotency conservation of the density matrix through an appropriate purification scheme as well as the use of the “nearsightedness” and associated sparsity of the density matrix to achieve linear scaling with system size...
We use density functional theory to investigate the structural, elastic properties and energetic stabilities of Zr, Nb and its alloys in the alpha and beta phases, employing pseudopotential plane wave methods within the Pardew-Burke-Ernzerhof Generalized Gradient Approximation (PBE-GGA). The structures were fully optimized in a non-magnetic state, allowing atomic positions, cell volume and...
The transition from intermediate valence (IV) behaviour in CeNi2Si2 to magnetically ordered Kondo lattice behaviour in CeAu2Si2 is investigated through measurements of X-ray diffraction (XRD), electrical resistivity &rho(T), magnetization &sigma(µ0H) and magnetic susceptibility &chi(T) on the polycrystalline...
A feasibility to develop a radioactive beam facility at iThemba LABS has commenced. The proposal envisages the addition of a new cyclotron, a k70 negative-ion accelerator. Such an accelerator can supply two beams simultaneously, one to be used for isotope production and neutron therapy, the other to create radioactive ions. These can be post accelerated by the existing SSC accelerator to...
Time-domain terahertz (TD-THz) spectroscopy has emerged as a valuable tool for studying material properties in the THz region of the electromagnetic spectrum. Many classes of materials exhibit characteristic absorption signatures in this previously unstudied portion of the electromagnetic spectrum. This opens up the possibility for non-destructive and non-invasive testing and analysis of...
The amidases catalyse the conversion of amides to the corresponding carboxylic acid and ammonia. We have visualized the structure of the amidase (MW= 30 kDa) from a bacterium, Nesterenkonia sp. at atomic resolution by X-ray crystallography. The primary components of the active site are two negatively charged carboxylates (E1 and E2) arising from two conserved glutamate side chains, a...
The formation energy of self-interstitial defects in silicon was studied. The 〈110〉split site was found to be the lowest energy position for the silicon self-interstitial at neutral charge state, as well as singly and doubly negative charged state. The tetrahedral site is found to be the lowest energy site for the singly and doubly charged positive states. The energy barriers for diffusion...
We observe ultrafast structural dynamics in crystals. For that, we use the 'Pump Probe Technique': The 'Pump' triggers a fast process, the 'Probe' takes a snapshot of it at a specific time. We are interested in observing processes, which happen on a picosecond timescale. That means, the duration of our 'Probe' must be in the order of ~ 100 fs. The only source of a 100 fs short signal,...
The use of tetrahedral amorphous carbon thin films in bolometers depends strongly on the ability to tune its optical properties. This can be achieved by controlling the density of dangling bond defects and the disorder in the material. The pi-orbital axis vector theory is used in this study to investigate the phenomenon of rehybridization of the carbon bonding in tetrahedral amorphous...
Obtaining single shot electron diffraction patterns is highly desirable when dealing with samples that are either destroyed or display irreversible structural changes upon photo-excitation. Such single shot measurements demand highly charged pulses that contain in the order of 105 – 106 electrons. Maintaining femtosecond pulse duration in the presence of the inevitably...
A number of solutions to the dark energy problem have been proposed in literature, the simplest is the cosmological constant Λ. But the cosmological constant lacks theoretical explanation for its extremely small value, thus dark energy is more generally modeled as quintessence scalar field rolling down a flat potential. For the quintessence scalar field to be evolving on cosmological...
Microcrystalline germanium-carbide formation was studied in germanium substrate using perturbed gamma-gamma angular correlation (PAC) method. Information about the lattice location of carbon atoms, in the host matrix, can be obtained via the interaction between carbon and unstable probe nucleus (111In). At high dose carbon implantation, in crystal germanium substrate, two defect complexes...
Physics is one of the most digitally-intensive areas of modern research and has traditionally led the development of tools to increase the efficiency and capability of research activities. The integration of the tools necessary for today's competitive physics research projects, from HPC centres to data resources, metadata catalogues, and services to enable collaboration in virtual...
In materials’ manufacturing, evaluation and/or characterization is a key final stage in the production process. This quality assurance tests whether the product meets an industry norm or specified standard required by the customer. The evaluation is also required on machinery / plant parts that are already in operation. The parts are periodically ‘tested’ to ascertain as to whether they...
We will present submillimeter (submm) polarized imaging of the nearby star-forming galaxies M82 and NGC253. The data, obtained with the Caltech Submillimeter Observatory in Hawaii, probe the emission from dust grains aligned by magnetic fields in these galaxies, and thus fields in relatively dense regions of the galaxies.
A mathematical model for temperature control in a continuously stirred tank reactor is developed. The startegy used involves a coil immersed in a coolant which proves to provide sufficient heat removal by controlling the coolant flow rate in exponential mode. The approach shows that specific ranges of exponents for the coolant flow rate must be used for the reactor to operate optimally.
Several previous studies, including one using early Sanae radar data, have found examples of high speed ionospheric plasma flows on the nightside, mapping to the magnetospheric tail, during periods which were magnetically quiet. These high speed flows were interpreted to be associated with the release of energy from a rapid reconfiguration of tail magnetic field lines due to reconnection....
Media generated by random mixing of hot and cold gases can be of great importance for laser beam propagation. However, it is not always possible to represent the media’s behaviour using simple formulation. This opens the door for the use of numerical methods. We show that, for aerodynamic media, we can use computational fluid dynamics (CFD) software to acquire density distribution data to...
We have analysed broad-band global solar irradiation measurements collected at the Soweto campus of the University of Johannesburg over the two-year period 1998-1999. We estimate the direct and diffuse irradiation using radiation models, and utilise the results to determine the atmospheric turbidity for all cloud-free days. From this we calculate aerosol densities and the solar radiation...
The atomic physics relevant to gaseous nebulae is critically examined using modeling software with particular emphasis on recombination spectral lines that occur in the radio regime. The spectral line intensities that we observe from nebulae can be deduced if we know the population structure of the bound electrons in the gas under non-thermal equilibrium conditions. The population structure...
Biogas from anaerobic digestion can be a solution to current and future energy needs in South Africa. One option for improving biogas yield of anaerobic digestion of organic matter is co-digestion. Cow dung and donkey manure were co-digested together at different mixing ratios. Total Solids (TS) and volatile solids (VS), ammonia-nitrogen, pH, alkalinity, volatile fatty acids (VFA) and...
The supply of adequate clean water to communities is a problem in many countries, especially in Africa where the rural population depend on water from rivers, dams and streams for domestic use. Such water contains many chemical substances and microorganisms that affect the health of human beings and animals. Use of simple water purification systems, like filters, by households, is a...
Classical molecular dynamics simulations were used to study the modification of some carbon forms. The type of carbons that were used is diamond and nanocarbon. Carbon is unique among other elements in its ability to form strong chemical bonds with a variety of coordination numbers. The simulations predict that the behaviour of diamond and nanocarbon are similar although the nanotube has...
Nonlinear effects are easily observed in single mode optical fibres because of the fibre small spot size and extreme low loss. At high optical intensities in fibres the refractive index becomes a function of the intensity of the optical signal. This refractive index is known as the Kerr nonlinearity. This leads to the optical Kerr effect where the nonlinear phase shift induced by an intense...
We will show the changes and improvements made to the Ultrafast Electron Diffraction setup which led us to doing the first time-resolved experiments. We have implemented beam tracking and correction systems in both the pump and probe beams, ensuring that we keep spatial overlap during a measurement. By using a different cathode and metal coating we were able to improve the electron...
Very Low Frequency (VLF) radio waves travel with little attenuation in the Earth-ionosphere waveguide. The waveguide propagation conditions are determined by a variety of factors including the surface of the Earth and the free electron density profile. Perturbations of the lower ionosphere modify the waveguide and the propagation conditions in it. A model based on Wait's mode theory is...
Nuclear reactions employed in the production of neutron-rich radioactive beams often produce many species simultaneously. To extract these beams, they must not only be ionized, but ionized selectively, so that only the desired species is extracted. We are developing the laser resonant ionization technique to fulfil these requirements. The method makes use of high power pulsed lasers,...
A magneto optical trap (MOT) is capable of trapping a vapor cloud consisting of atoms cooled down to the micro Kelvin range. Three orthogonal pairs of counter-propagating laser beams of the correct circular polarisation form an optical molasses which facilitates the cooling of neutral atoms. Additionally a spatially non-uniform magnetic field produced by two current carrying coils in a...
This paper gives the details of a photovoltaic water heating system and the effects of direct water cooling on the performance of a photovoltaic module. The SW 80 polcrystalline modules were used in the investigation. They wehre both fixed next toe ach other on a north facing rack located on roof top. One of the modules had a batch water cooling container and the other module had no...
Carbon modified titanium dioxide nanoparticles (C:TiO2 NPs) have been synthesized by ultrasonic nebulizer spray pyrolysis (USP) and pneumatic spray pyrolysis (PSP) techniques using titanium tetraethoxide as the precursor solution. High resolution transmission electron microscopy on the NPs shows difference in lattice spacing in the NP structures prepared by the two methods – 2.02 Å for the...
We present measurements of the slope efficiency of a Tm3+ -doped silica triple-clad fiber laser emitting at 2.02 µm using different cooling techniques. The maximum slope efficiency of 53.6 % was obtained at a temperature of 25o C with a maximum output power of 5 W for 19 W of absorbed power at the pump wavelength of 800 nm and 9.9 W threshold. In a slightly different setup, the output power...
A harmonious formulation of the inverse–square laws for fields shows that elemental sources are rightfully represented as scalars for both gravitational and electric fields, but as vectors for magnetic fields. This permits an effective simple illustration that, unlike the gravitational or electric flux, the magnetic flux out of any closed surface is zero irrespective of whether the enclosed...
Hydrogen production from biomass holds the greatest promise, since biomass is abundantly available everywhere in the world. However, hydrogen from biomass has major challenges. The yield of hydrogen is low from biomass since the hydrogen content in biomass is low to begin with (approximately 6%) and the energy content is low due to the 40% oxygen content of biomass. A novel gasification...
In order to examine the effect of Cr on the microstructure and hardness behaviour of WC cermet, coatings have been obtained by laser surface alloying technique. WC-9Co-4Cr particulate was injected into the surface of AISI 304L stainless steel under different processing variables. The morphologies and microstructures of the composite coatings were investigated using optical microscopy and...
We present pulse characterization of various amplified shaped pulses, using second harmonic autocorrelation, frequency resolved optical gating (FROG), as well as their analogue techniques using only the pulse shaper and no moving parts in the experimental setup. This involves creating double pulse seperations using the pulse shaper only and recording the resulting SHG autocorrelation and...
We explore a method in the selection of a specific higher-order mode through judicious shaping of the pump light to create a high modal overlap with the desired mode. To demonstrate this principle, we create a donut-shaped pump profile in the focal plane of a converging lens by use of a beam shaping element. This pump profile is used to longitudinally pump a monolithic microchip laser and a...
Recently, I . Kanter et al, developed an Ultra fast random bit generator, based on a semiconductor laser, having time delayed self-feedback, which operates reliably at rate up to 300 GB/s. The method uses a high derivative of the digitized laser intensity and generates the random sequence by retaining a number of the least significant bits of the high derivative value. The generator is...
In the context of activation studies, in order to uniquely identify an isotope via gamma spectroscopy, both the lifetime and the energy of the emitted gamma rays are required. Traditional detectors collect only integral data, losing information about the timing of individual events. This makes lifetime analysis a manually intensive task, as data points must be obtained by cycling the target...
The most abundant and efficient light harvesting, energy transfer and transduction systems are found in nature within the process of photosynthesis. Although the processing sequences of an absorbed solar photon in the photosynthetic apparatus have been deciphered, the underlying physical basis of photosynthesis is not well understood yet. Our research aims to contribute to this...
It is well understood that the fundamental mode of a cavity may be selected by suitable choice of intra-cavity amplitude or phase elements. If one wishes to dynamically control the mode, for example, to manage thermal aberrations, then intra-cavity elements that are controllable are required. Two such elements are adaptive mirrors and spatial light modulators (SLMs). In this poster we...
HF propagation involves transmission and reception of radio signals within a frequency range of 3 − 30 MHz. It finds applications in a number of communication fields such as international short wave broadcasting, mobile telephone systems, radio navigation and operation of radar systems. However, it depends on the ionosphere which is constantly varying mainly due changes in the neutral...
Metal nanoparticles (MNP) were synthesized by room temperature ion implantation of high fluences (from 6x1016 to 5x1017 cm-2) of 150 keV Ag and 15 -22 MeV Au ions into Al2O3 and MgO single crystals. Optical absorption (OA) spectra show surface plasmon resonance (SPR) bands characteristic of the implanted metal ions. Upon annealing...
Ionospheric storms represent large global disturbances in the ionospheric F2 region electron density in response to geomagnetic storms. The mechanisms for generation of negative storms are well understood and accepted. In contrast, positive storms show different characteristics and have not been fully understood. In this study, we investigate the ionospheric response during the geomagnetic...
Studying pulsating stars in Eclipsing binaries has the potential to be an exacting test of theoretical stellar models as a result of the large number of constraints physically that can be imposed on individual components in the binary system. In this particular example, Kpl Rumple, the measurement of the large number of frequencies in the star of precisely known mass and radius from binary...
The experimental demonstration of Bose-Einstein Condensation (BEC) is one of the most exciting developments of recent years. It has enabled researchers to study a macroscopic quantum object with well controllable parameters. This has sparked a lasting flurry of experiments covering an enormous range of fields, which have made significant contributions to our understanding of atomic and...
Optimization of power output from ducted wind turbines has been the focus of many researchers in recent years. However many have dwelt much on diffusers than concentrators (nozzles) . Diffusers are characterized by flow separation due to deceleration of the fluid and this leads to energy dissipation. On the other hand a concentrator is accompanied by a favourable pressure gradient which...
Metal contacts on clean, hydrogenated and oxygenated diamond surfaces have been studied using ab initio Density Functional Theory. Five metals, i.e., gold, titanium, tantalum, vanadium and palladium on the three surfaces were considered. Gold and palladium were found to form weak bonds on clean, hydrogenated or oxygenated diamond (111) surfaces compared to the other three metals. Bulk...
Micromachining of single-mode telecommunication fibres (SMF28) was accomplished with a Nd:YAG laser at a wavelength of 532 nm. The goal of the micromachining process is to machine miniature Fabry-Perot interferometers in the fiber to manufacture fast temperature sensors. To produce micro features by direct machining the laser beam is focused to spot sizes of 30 µm and below. The different...
Stars are believed to be formed from massive stable gas clouds, which under enough perturbation will collapse to form a protostar. The protostar evolves to form a star by accreting matter until the fusion is initiated in the dense core. Surrounding these protostars are ionized hydrogen (HII) regions and molecule species where masing occurs. MASER is an acronym for Microwave Amplification by...
Biomass gasification for electricity generation has attracted much attention over the past few years. This is due to the fact that biomass is a renewable resource, which is also considered to be carbon neutral. However electricity generation using biomass gasifiers can only be technically and economically achieved at small scale using downdraft gasifier systems, which produce gas that has...
The principal source and loss mechanisms in the Earth's radiation belts are currently not completely understood. Loss rates are important since they determine the duration of exposure of satellites to enhanced radiation conditions during a geomagnetic storm. The dominant loss process is relativistic electron precipitation via resonant interactions with a variety of wave modes. These...
Quantum Key Distribution employs the laws of quantum mechanics for the purpose of cryptography. Two parties, called Alice and Bob, are able to create a random key which is used to encrypt a message. QKD is a provably secure method for cryptography because any eavesdropper attempting to anonymously retrieve the key must make measurements, thereby disturbing the system. Using this principle,...
Ion Beam Applications (IBA) commercial cyclotron (IBA Cyclone 70) with capability of accelerating protons up to 70MeV and 350µA of current is to be constructed at iThemba Labs to increase the capacity of the current facility. The two opposite simultaneous extraction of beams using the Carbon foil stripper, enable for the concurrent production of radioactive ion beam (RIB) for nuclear...
Radon is a naturally occurring radioactive inert gas in the decay chain of uranium-238. High radon levels in houses have been linked to the occurrence of lung cancer via the deposition of radon progeny in the lungs. The radon activity in houses depends on the concentration of radium in the soil below the house and the diffusion of radon into the house. Another pathway is the...
Metal Au, Ni and Ni/Au contacts on n-GaN were studied for metal contacts for the fabrication of Shottky barrier ultraviolet photodetectors. AES, RBS and current-voltage measurements were used to study the samples. Figure 2 shows the current voltage mechanism of Au, Ni and Ni/Au transparent contacts onto GaN. The Schottky barrier heights of Au contacts were averaged at 0.84 ± 0.02 eV and the...
In the large mass region, the dominant decay mode of the Higgs boson is to two W bosons, where the Higgs can be produced via either gluon fusion or vector boson fusion. Of the possible W decay modes, the current analyses focus on the W(->l nu)W(->l nu) decay channels where the lepton is either an electron or muon. At a center of mass energy of 7 TeV, the results from the ATLAS detector are...
Investigation of the First-year students' abilities to use mathematical concepts of straight line equation and graph to analyse Physics properties with particular references to a Simple Pendulum motion experiment.
Chorus emissions are whistler mode waves propagating through the Earth’s magnetosphere in two distinct frequency bands, typically in the range of 0.1-0.8 fce, where fce is the equatorial electron gyro-frequency. Chorus consists of discrete elements, which are normally rising tones, each of which lasts for a few tenths of a second. Chorus is predominantly observed during the onset of the...
This study investigates the Pencil Proton Beam scanning technique to determine the dosage obtained during clinical treatments due to secondary radiation. Simulations in MCNPX and GEANT4/GATE are of particular interest in this study. The study is based on a variation of the traditional Hogstrom Pencil beam model for electron beams to provide a description of clinical proton beams. This new...
Space weather describes the conditions in space that affect both Earth- and Space bound technological and biological systems. It is a consequence of the behavior of the Sun, the nature of the Earth’s magnetic field and atmosphere, and our location in the solar system. Space weather is one of the principal threats to modern technology. With the increase in technological systems the need for...
The spectral response measurement system is an important tool for optimization of solar cells. Its measurement permit an examination of how photons of different wavelength contribute to the cell generated current at zero bias voltage. In this study photovoltaic (PV) and photochemical (PC) solar cells were used and their spectral responses were measured. The aim is to use the spectral...
We determine the stellar mass of star forming galaxies in the X-ray luminous cluster MS 0451.6-0305 at z ∼ 0.54. The stellar masses are estimated from fitting model spectral energy distributions (SEDs) to deep, optical UBRIz observations obtained from WIYN 3.5m telescope and public NIR K-band image from Palomar Observatory telescope. The model SEDs are based on the stellar population...
Apart from the presence of an active AGN, very young and massive super star clusters (SSCs) are likely to be found in local starbursts and interacting luminous infrared galaxies. SSCs are responsible of a high star formation rate (SFR) of the host galaxy. From an on-going deep NIR AO imaging survey, we were able to observe some SSCs hidden by the dusty central regions. To better...
The proposed dependence of atmospheric electrical properties on the ionizing influence of cosmic rays has resulted in numerous attempts to obtain convincing correlations. While most of the studies remain largely theoretical, a few results (e.g. Stozhkov, 2003) indicate that there is a plausible link between lightning activity and the cosmic ray ionization rate measured at specific locations...
An energy efficient passive solar house was designed, constructed and its natural ventilation efficiency monitored. Carbon tracer test was used to measure the ventilation efficiency of each ventilation component. Windows were found to have higher impact on the ventilation rate than doors. The correct operation of the ventilation components was found to be the main contribution factor in...
The purpose of this work was to study the dose enhancement factor (DEF) by high-Z material in water phantom, irradiated by photon beams. Two energies, 6 and 15 MeV generated by Varian linear accelerator were used. Monte Carlo technique (EGSnrc code) was used in this study. The source model was validated against measured data. The effect of photon beam quality, atomic number (Z) and the...
On the 4 August 2010, chorus was observed at Marion Island from 03:00 - 07:00 UT (06:00 - 10:00 LT). Marion Island (46.9°S/37.1°E, L = 2.62) is within the plasmasphere during periods of low geomagnetic disturbance, making the observation of chorus there a rare occurrence. On the 4 August, a moderate geomagnetic storm occurred, with a maximum Kp of 6+, and a minumum DST of -70nT. These...
A sequel to representing elemental sources of magnetic fields as elemental magnetic vector charges is realizing that electric and magnetic dipole moments are different classes of moments. The distinction between monopolar and dipolar moments becomes clearer when any distribution of electric scalar charge or magnetic vector charge is depicted as one or more pairs of charges with equal...
Digital thermal neutron imaging (radiography and tomography) is a powerful non-destructive analytical tool and has demonstrated its importance in industrial and research application world-wide. However, standards through test samples, methods and procedures, which are essential when the technique is to be applied in the national and international industrial and research environment, do not...
During the onset of a substorm, a burst of energetic (10-100 keV) electrons is injected into the inner magnetosphere. The subsequent motion of these electrons is dictated by their energy, pitch angle and the Earth's magnetic field geometry. More specifically, if the Earth's magnetic field is not varying rapidly then the three adiabatic invariants associated with each of the electrons'...
D149 Dye has proven to be an effective photo-absorber for use in dye sensitized solar cells. Pump-probe measurements were conducted on D149 dye as well as D149 adsorbed to Zinc Oxide semi-conducting particles. Ultrafast dynamics on a sub-ps time scale, easily resolved by the current experimental setup at the LRI, were observed in both samples. Significant quenching of the excited state...
For many Galactic black hole binaries, there exists kinematic data that constrain the black hole masses to be within the stellar-mass regime. However, due to their extragalactic distances, ultraluminous X-ray sources (ULXs) have no such available dynamical information. Hence, in order to constrain the system parameters, we must use indirect methods. We present an analysis of recent...
Examples of novel coating technologies towards Infrared solar radiation regulation/modulation in smart glass windows for the satellite sector include electrochromic and thermochromic based high vacuum manufactured dynamic coatings. The latter two technologies are solar radiations control oriented technologies in the visible and infrared radiation respectively. The thermochromic smart coated...
Star formation constitutes one of the basic problems of astrophysics due to the fact that stars are fundamental objects of astronomy. Shu et al. (1987) reviews the theory of low mass star formation from the molecular cloud via accretion disk-outflow. The formation of high mass stars is still not well understood. They may also be formed through accretion disk plus outflow (Shu et al. 1987)...
The highly transient multi-wavelength system AE Aqr consists of a fast rotating highly magnetic WD, accreting mass from a K3-5 secondary companion. This magnetic CV has a characteristic orbital period of 9.88 h, and is in a propeller state. The turbulent interaction between the fast spinning WD magnetosphere and the accretion flow is believed to play a crucial role in the multi-wavelength...
Defects introduced by 300 keV Eu ions in HVPE grown Si-doped GaN were investigated by means of deep level transient spectroscopy (DLTS). After implantation, the samples were annealed at 1000 °C and Ti/Al/Ni/Au ohmic and Ni/Au Schottky contacts were deposited. The Schottky contacts were found to be of high quality, with leakage current at 1 V reverse bias of below 10 8 A. Two peaks in the...
An ionospheric eight year study (2001-2008) over South Africa (SA) was conducted using ionosonde data observed by DPS-4 digisondes with a time resolution of 10, 15 and 30 minutes from Madimbo, Grahamstown and Louisvale. Spread F (SF) characterized by ionograms is observed when the pulses returned from the F region of the ionosphere are of longer duration than the transmitted signals....
Block copolymers can self-assemble into lamellar and cylindrical phases with a fundamental period of 10-100nm. These nanoscopic phases are a basis for a great range of applications in nanotechnology. We describe how electric fields can be utilized to tune the lamellar period of copolymers that consist of liquid-crystal sub-units. Copolymers that are swollen in liquid-crystals have...
With the current success of physics and astronomy and their technological support bases in South Africa, there is a need to identify and nurture talent in physics. It is clear that the current South African schooling system has little chance of doing this, and thus it becomes imperative that alternative means are found to grow local talent. This need was identified by the International...
The South African Neutron Radiography (SANRAD) facility hosts a neutron/x-ray tomography system which is extensively being utilized in non-destructive examination experiments where it is necessary to characterize and determine the properties (e.g. size, porosity, permeability and morphology) of samples. Sometimes, quantitative information is needed about the type elemental composition of...
There have been tremendous inputs into improving the efficiencies of nanostructure solar cells by extending their absorption wavelength to the near-infrared. This can potentially be achieved by using colloidal nanocrystal quantum dots as the light-harvesting material, as their optical band gap can be tuned to a desired range. Copper selenide is an interesting semiconductor with a bulk band...
The quaternary compound semiconductor Cu(In,Ga)Se2 is one of the most attractive materials for high efficiency solar cells due to its tunable band gap to match well the solar spectrum. In this study, semiconducting Cu(In,Ga)Se2 thin films were prepared by a classical two-step growth process, which involves the selenization and/or sulfurization of In/Cu-Ga precursor. During the precursor...
This talk forms part of the author’s Masters investigation into perceptions of Physics in school visitors to Unizul Science Centre. Visitors typically fall into three distinct groups with very different needs and responses. Those coming from: rural schools, township schools and urban schools. In this study, pupils were exposed to an interactive Science Show: Good Vibrations, presenting the...
The world is experiencing an ever-growing demand for energy. This coupled with the demand to decrease the carbon-footprint have led to a reconsideration of nuclear power as an alternative to fossil fuel power stations. Many countries have either started again to build nuclear power plants while others, like South Africa, are planning to build ones in the near future. One of the most...
The importance of calibrating satellite imagers has been explained in literature such as K Arai (2007) and K J Thome (2001). Calibration of satellite sensors (imagers) is crucial for data consistency, reliability and comparability. To perform a meaningful analysis of a satellite image, the Digital Numbers (DNs) of the image are first converted to absolute radiance by using the...
A survey of the fine structure phenomenon of the Isovector Giant Dipole Resonance (IVGDR) was investigated, using the newly commissioned Zero-degree Facility of the K = 600 magnetic spectrometer of iThemba LABS. Measurements were performed for inelastic proton scattering at an incident energy of 200 MeV for targets ranging from 27Al to 208Pb. Targets of areal density...
Problems involving bound states of few particles can be solved exactly since the number of degrees of freedom are small. Several methods in this direction exist. One of these is the Integro-differential equation approximation method (IDEA). These few-body methods have been succesfully applied to obtained bound and scattering states for three- and four-body problems for nuclear and molecular...
Covalently bonded solids based on boron, carbon, or nitrogen are the hardest materials, and B4C is the third hardest after diamond and cubic boron nitride. Thin films of boron carbide were formed by pulsed laser deposition at room temperature and at higher temperatures up to 800 o C using a sintered B4C target. Whilst the nature of the particulates embedded in the films and the composition...
Quantum key distribution (QKD) is a secure method of transferring encryption keys between two distant parties. It provides a physical layer of security rather than a mathematical algorithm used in conventional encryption systems. As QKD is of paramount importance in the future ICT landscape, various innovative solutions have been developed and tested to expand the spatial coverage of these...
We look at the use of Positron Emission Tomography to detect light organic elements in two different contexts, namely to locate diamonds within partially crushed kimberlite (Mineral PET), and to locate buried land mines. Light organic elements such as carbon have traditionally proved difficult to locate, and currently mines crush rock down to a fine size, and then employ manual sorting...
This paper addresses what has been done in the Science Faculty at the University of the Western Cape (UWC). The Extended Curriculum Programme (ECP) Physics at UWC centers its focus on giving students access to the studies of the Physical Sciences and improving their success. The paper notes that the incoming students enter university with educational disadvantage backgrounds. For this...
A systematic experimental investigation of the phenomenon of fine structure, with emphasis on the region of the Isoscalar Giant Quadrupole Resonance (ISGQR), in nuclei across stable even-even neodymium isotopes has been performed. Measurements were made using the K600 Magnetic Spectrometer of iThemba Laboratory for Accelerator Based Sciences, a facility which is situated at Faure near Cape...
Around 70 million tones of coal are burned annually in power stations whilst around 50 million tones of coal are converted to chemicals in the petrochemical sector in the same period of time. Researchers, nationally and internationally, aim to optimize the processes to extract the most energy from the limited coal reserves. One such petrochemical process that is of significance to South...
A circular electric current, perpendicularly bisected by a field plane, was modelled as a continuum of pairs of distinct Cartesian component elemental magnetic vector charges normal and parallel to the field plane. The Cartesian elemental magnetic vector charges normal to the field plane pair up into Cartesian elemental magnetic dipoles with intra-dipolar displacements parallel to the...
Iron oxide-based nanomagnets, such as maghemite (Fe2O3) and magnetite (Fe3O4), have attracted a great deal of attention in nanomedicine over the past decade. On the nanoscale, superparamagnetic iron oxide nanoparticles can only be magnetized in the presence of an external magnetic field. This property makes these nanoparticles capable of forming stable colloids in a physio-biological...
Analytical equations of motion, in the form dxi ⁄ dt = fi(x,t), are derived for a damped harmonically driven triple plane pendulum. This form of the equations clearly displays the nature of the non-linear coupling and provides a basis for physical interpretation. The equations also facilitate the derivation of the Jacobian...
Satellites have to operate in a hostile space environment that poses numerous threats from radiation, charged particles, residual atmosphere, micrometeoritic impacts, space debris and other operational and defunct satellites. The region of outer space around the Earth is becoming polluted from anthropogenic space system junk and fragments. Currently, according to US Space Surveillance...
The orbital angular momentum (OAM) state of light has been the object of much interest within the quantum information community lately mainly because it can be used to implement higher dimensional entanglement. Unfortunately, the OAM cannot be used for quantum communication through optical fibers in use today because these fibers support only modes with zero OAM values. One can...
The proverb “seeing is believing” is generally applied in science education today. Many of the contemporary teaching strategies engage the learners in activities that guide them in making their own observations. Still, problems regarding the learning of physics, especially the prevalence of alternative conceptions, remain a head-ache in physics education research. A variety of causes...
Carbon nanospheres were produced using two different sets of apparatus in the School of Chemistry at the University of the Witwatersrand. Nitrogen was introduced into the samples using a several sources of nitrogen, including pyridine. Electron magnetic resonance (EMR) was used to characterize a range of samples of varying concentrations of nitrogen at room temperature. The spheres doped...
Efficient and reliable methods to solve effective three dimensional Schroedinger equations are an important ingredient for both density functional as well as Hartree Fock methods used to calculate the properties of molecules and solids. In order to judge the accuracy of popular methods such as using Gaussian basis functions or smooth pseudo potentials it is desirable to use a method that...
A magnetized dusty plasma composed of an adiabatic negatively charged dust fluid, Boltzmann ions and Boltzmann electrons is considered for which coupled nonlinear dust-acoustic and dust-cyclotron waves hav- ing sinusoidal, sawtooth or spiky electric field waveforms are found to be supported when charge neutrality is assumed (Maharaj et al, 2008). The focus of this investigation is to...
A review of our last results on the phase dynamics of a stack of coupled Josephson junctions in layered superconductors is presented. The current voltage characteristics (CVC) of intrinsic Josephson junctions (IJJ) are numerically calculated in capacitively coupled Josephson junction model (CCJJ model) and CCJJ model with diffusion current (CCJJ+DC model). We discuss the features of the...
The concept of radiation, in the scientific and analytical environment is normally not understood and has being neglected and not considered as analytical probe due to the lack of knowledge of the general public and researchers about its potential as analytical probe, the misunderstanding of the possible “danger’ in the utilization thereof and the “unavailability” of facilities in South...
We simulate real-time quantum state estimation due to a sequence of so-called "unsharp" measurements applied to a two-level system undergoing Rabi oscillations. These measurements allow an experimentalist to extract information about the system without destroying the quantum state. They can be realized physically through the use of auxilary quantum states in addition to the quantum state...
We study the generation of Pc3 geomagnetic pulsations (22 – 100 mHz) measured at Tihany, Hungary during intervals of very low solar wind (SW) proton density (low density events - LDE’s) when Np ~ 1/cc. We know the main SW based drivers of Pc3's are SW velocity and interplanetary magnetic field (IMF) direction. However, it is observed that under very low SW density pulsation activity...
The temperature dependence of the 35Cl quadrupolar resonance frequency has been measured in a high purity sample of mercuric chloride (HgCl2) over the temperature range 4 K - 460 K. The results allow the temperature dependence of the electric field gradient (efg) at the two inequivalent sites of the chlorine atoms to be determined. Several models were considered to...
I will present three unrelated examples in which efficient computer simulations have been employed to address soft matter properties. The first example will deal with the dynamics of polymers near surfaces. Despite the significant progress within the last decade, in particular on the structure and thermodynamic properties in confinement, their dynamics remained an active field of research....
P-LABS at Necsa consists of two linear particle accelerator facilities; a Van de Graaff with terminal potential up to 4 MV and two radio frequency quadrapole (RFQ) accelerator systems that can accelerate D+ ions to 3.7 - 5.1 MeV (or protons to 1.8 – 2.5 MeV). Depending on the beam target used these accelerators can produce fast neutrons (and associated gamma rays) at a rate of 10^6 - 10^12...
For several years an on-going study has examined student performance in relation to the types of assessment task encountered in first year physics examinations. The typology used recognises four basic task types: routine operations, novel problems, interpretive questions and bookwork. Thus far it appears that average student performance is strongest for routine operations, variable for...
We devise a hierarchy of computational algorithms to enumerate the microstates of a system comprising N independent, distinguishable particles. An important challenge is to cope with integers that increase exponentially with system size, and which very quickly become too large to be addressed by the computer. A related problem is that the computational time for the most obvious brute-force...
In 1958, Eugene Parker predicted that the outer parts of the Sun's atmosphere, the solar corona, must be expanding in the form of a supersonic solar wind. This was confirmed by the Mariner 2 spacecraft in 1962. On 16 December 2004, the Voyager 1 spacecraft crossed the heliospheric termination shock, where the flow becomes subsonic, and began exploring the heliosheath. In August 2007,...
One of the striking features of particle production at high beam energies is the near equal abundance of matter and antimatter in the central rapidity region. In this paper we would like to study how this symmetry is reached as the beam energy is increased. In particular we quantify explicitly the energy dependence of the approach to matter/antimatter symmetry. Expectations are...
Graphite composite comprising of 64 wt% of natural graphite, 16 wt% of synthetic graphite and 20 wt% of phenolic resin binder heat treated at 1800 0C have been used to encapsulate the TRISO coated fuel particles in the PBMR and considered to serve in the initial state of neutron moderation as well as heat conduction. The structural and thermal properties of the pristine and irradiated...
The International Astronomical Union (IAU), in recognition of the immense use of astronomy to stimulate development, has developed a decadal strategic plan entitled "Astronomy for the Developing World". At the heart of the implementation of this plan is the Global Office of Astronomy for Development. South Africa bid in 2010 to host this office and was selected as the host country, with the...
The growing social concern for environmental protection and human health has driven widespread interest in analysis of heavy metals in the various environmental compartments including soil. Soil is unanimously considered as one of the recipients of heavy metals released by several human activities. Rapid analysis of heavy metals in soil is an important factor in modelling the effect of...
iThemba LABS was requested by the Institut für Kernphysik at Forschungszentrum Jülich, Germany, to design and calculate a magnet system for a proposed non-destructive Ionization Beam Profile Monitor (IBPM) that can measure beam profiles using the secondary ions produced in the rest gas, planned to be implemented with the FAIR-GSI project in Darmstadt Apart from the geometrical...
This study investigates the principle and capabilities of Dual Energy X-Ray Radiography/Tomography when applied on nuclear and related materials. The dual-energy X-ray technique is a significant improvement to X-ray imaging systems and gives additional information on the composition of the object being imaged. Within this technique, two radiographs are obtained at two distinct X-ray...
In recent years the need to produce low charge state ion beams with good beam quality and ion sources with good gas efficiency are on an increasing demand. The various applications of these specific ion beams are ranging from radioactive ion beam production to high energy ion implanters. The Accelerator Physics Department at iThemba LABS has developed a prototype microwave ion source. The...
We investigate cosmic-ray intensities as measured by neutron monitors as function of the corresponding heliospheric current sheet tilt angle. Three solar cycles with three changes in solar magnetic polarity are examined. The results are compared to predictions of cosmic-ray modulation models that include drift effects. The intensity-tilt plots produce open loops with clockwise rotations for...
A systematic strategy for the algebraic calculation of density functionals consists in coding information about the density and the energy into polynomials of the degrees of freedom of the wave functions. Density functionals and Kohn-Sham potentials are then obtained by standard elimination procedures of such degrees of freedom between the polynomials. Numerical examples illustrate the formalism.
Solutions of General Relativity Theory (GRT) pertaining to space geodesy are weak field, slow motion approximations. These approximations are valid as the gravitational field in which the solutions are performed has a potential of small magnitude and the velocities involved for any of the satellites are much smaller than the velocity of light. The basic effects of GRT on space geodetic...
Maintaining, monitoring and safeguarding South Africa’s oceans and dams is a multifaceted project requiring the skills and expertise from several scientific domains-.The radiometric study and spectral characterization through in situ measurements of these water systems is critical to such a project. The objective is to develop and subsequently test 2 prototype radiometers for their...
Heavy ion beams at iThemba LABS have been produced in a 10GHz Minimafos electron cyclotron resonance ion source (ECRIS) for the past two decades. The typical values for the injection and extraction coil current are in the range of 1000A. The operating pressure is about 10-6 mbar depending of the ion produced. The Minimafios ECRIS allow the use of supporting gas like helium, oxygen etc. It...
An understanding of the types of defects produced during the doping/implantation of diamond remains essential for the optimization of high-temperature, high-power electronic applications. Thus this study focuses on investigating the nature of the radiation damage produced during the multi-implantation of carbon ions in synthetic type Ib and natural diamonds, according to the CIRA...
We present results on the synthesis of precise and thickness controlled carbon structures using ion implantation into thin films of a typical metal catalyst, for Schottky contacts and spintronic applications. Thin films of FeCr on a silicon substrate was prepared using magnetron sputtering and then implanted with carbon ions at controlled thicknesses close to the surface at elevated...
Light Detection and Ranging (LIDAR) studies on particulate matter (Aerosols) and pollutants; elucidate their distribution and concentration in the atmosphere. Particulate matter plays a key role in atmospheric physical and chemical processes from local to global scale. The complexity of these processes have been largely reviewed in literatures and LIDAR measurements have mostly...
Lightning induced whistler waves are one of the primary causes of energetic electron loss from the Earth's radiation belts. This is mainly due to the pitch angle scattering of the particles by whistler mode waves, leading to precipitation. The detailed spatial and temporal influence of lightning on precipitation losses is, however, not well known. The World Wide Lightning Location Network...
The synthesis of the c-BN (cubic boron nitride) has developed great interest due to its excellent physico-electrochemical properties. These include; high hardness values (73 GPa) second after diamond, wide band gap (6.4 eV), optical transparency in a wide region of the electromagnetic spectrum, high temperature stability (1200 oC) and chemical inertness. These properties enable c-BN to be...
The present observational data strongly suggest that Einstein's gravity must be modified, one of the popular modifications being provided by superstring ideas. In view of the mathematical problems of the string theory, other, much simpler, modifications of gravity that affect only the gravitational sector (not touching other interactions) are also popular. One of them is based on...
The OMNI-2 data set enables a correlation study of solar wind and geomagnetic parameters, allowing the stream Interfaces events (SIs) to be examined. A superposed epoch analysis of these events was performed to determine the threshold levels of IMF Bz and other geophysical parameters. Based on energy, temporal and spatial characteristics, statistical analysis of electron flux data from...
A short resume about the nature of EPs followed by a discussion about their ubiquitous occurrence in a great variety of physical problems. EPs feature in quantum phase transition, quantum chaos, they produce dramatic effects in multichannel scattering, specific time dependence and more. In nuclear physics they are associated with instabilities and affect approximation schemes. EPs could...
Markarian 926 (= MCG-2-58-22) is one of the earliest Seyfert galaxies identified. At discovery it was one of the most luminous nearby active galactic nuclei (AGN), with strong, wide broad lines. In the late 1980's it started fading, eventually settling at barely ~10% of its recorded peak luminosity. The luminosity decrease was accompanied by significant spectral changes, with the broad-line...
