Conveners
Poster2: NPRP, Theoretical, APSS, LOS, Education
- Patrick Woudt (Department of Astronomy, University of Cape Town)
- Frederik Vorster (NMMU)
- Frederik Scholtz (National Institute for Theoretical Physics)
- Erich Rohwer (University of Stellenbosch)
- Sam Ramaila (University of Johannesburg)
- Simon Mullins (iThemba LABS (Gauteng))
- Andrew Collier (Hermanus Magnetic Observatory)
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...
Photovoltaic thermal heating system have gained momentum in the recent years with many investigations be been done on how to maximize the heat harnessing mechanisms. In some case copper tubes fixed on the back part of the module, are used to circulate forced water around them by external driving force e.g. pumps and, in the process extract heat from the module and provide the cooling...
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...
