Browsing Research articles (Dept of Physics) by Title
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King, J.G.; Williams, W. (American Geophysical Union. http://www.agu.org/journals/jd/, NaN, NaN)[more][less]
Abstract: Although several studies have recommended removal of secondary components of magnetic remanence by zero-field cycling from room temperature to a temperature much lower than the low temperature transition for magnetite (about 120 K), the method has not become a standard routine technique. This is partly due to the poor understanding of the behavior of magnetite particles at the low-temperature transition zone. Previous experiments by other researchers have used magnetite powders. In such powders it is always possible to attribute any discrepancy between the results observed and theory to possible existence of magnetostatic interaction effects or existence of elongated particles in samples presumed to contain only equant particles. Such factors need to be eliminated in order to have a better understanding of the low temperature behavior of magnetite particles. Low-temperature magnetic properties of lithographically produced arrays of both interacting and noninteracting cubic magnetite particles as well as those from powder particles have been measured as part of this study. A gradual increase in the amount of saturation isothermal remanent magnetization (SIRM) lost at the Verwey transition Tv with increasing particle size in the pseudo-single-domain size range has been observed. This behavior is consistent with the vortex state domain structure. The grain size dependence of the amount of SIRM lost at Tv is most probably what previous researchers reported as a magnetic memory particle-size-dependent trend. Magnetic memory measured during the cooling and warming process is shown to be a stress-related phenomenon. Such measurements could be useful in assessing the nature of stress in a magnetite sample. URI: http://hdl.handle.net/10311/347 Files in this item: 1
King_JGR_2000.pdf (2.594Mb) -
Nijegorodov, N.; Mabbs, R. (Elsevier Science BV; www.elsevier.com/locate/saa, January 15, 2002)[more][less]
Abstract: [Please note that the mathematical symbols have not transposed into this abstact].The luminescent and laser properties of heteroaromatic and aromatic compounds are reviewed and discussed on the basis of all possible mutual arrangements of singlet and triplet states. All heteroaromatic compounds are divided into five classes. It is shown that a heteroaromatic compound can only be an effective laser dye if it belongs to class V (a situation where the Tn_* level lies at higher energy than the S__* 1 level). Moreover, it is shown that the energy interval between the Tn_* and S__* 1 states must be no less than 1000 cmâ 1 since the rate constant of the non-radiative process S__*1 _Tn_*_T__1 is usually 100 times greater than the fluorescence rate constant. The classification is extended to compounds with orbitals of _l,_*, _,__* and _l,__* nature. Pure aromatic compounds, the spectral-luminescent properties of which are solely determined by transitions of _-electrons (_ _ _*), are also divided into five classes, depending on the mutual arrangement of the Sp(1La), S_(1Lb), Tp(3La) and T_(3Bb) states. It is found that only aromatic compounds of classes IV and V can be effective scintillators and laser dyes. It is also shown that the energy interval S_â Sp (for class IV) and T_â Sp (for class V) must be no less than 1000 cmâ 1. To illustrate the classifications for heteroaromatic and aromatic compounds, 12 specifically chosen compounds were studied experimentally and quantum chemically. The quantum yields, _ and decay times, _f of fluorescence in aerated and non-deaerated ethanol or cyclohexane solutions were measured. The oscillator strength, fe, fluorescence rate constant, kf, natural lifetimes, _0 T and intersystem crossing rate constants, kST are calculated. The laser ability of each of the compounds studied is tested. The suggested classification schemes can be extremely useful in the quest for effective scintillators and laser dyes among hypothetical heteroaromatic and aromatic molecules, enabling evaluation of these properties for a particular compound using only quantum chemical simulations. URI: http://hdl.handle.net/10311/136 Files in this item: 2
license.txt (1.998Kb)nijegorodov_sa_2002.pdf (1.811Mb) -
Muxworthy, A.R.; King, J.G.; Odling, N. (AGU and the Geochemical Society. http://www.agu.org/journals/gc/index.shtml, NaN, 2006)[more][less]
Abstract: The magnetic hysteresis properties for well-defined micron-sized magnetite samples produced by electron beam lithography (EBL) are presented. In addition to measuring standard hysteresis parameters, first-order reversal curve (FORC) diagrams are also reported. EBL produces samples that consist of particles with very tightly constrained size distributions, and spatial distributions that govern the degree of intergrain magnetostatic interactions are accurately controlled and known. Thus EBL samples are significantly better characterized compared to powdered samples, which are conventionally used to characterize the size dependency of magnetic hysteresis properties of naturally occurring magnetic minerals. Compared with the hysteresis properties of powdered samples of the same nominal sizes, EBL samples display more multidomain-like (MD) behavior. The influence of magnetostatic interactions fields on hysteresis properties is analyzed. When magnetostatic interactions are effectively in only one direction, the hysteresis properties become more single domain-like, and if the interactions are in more than one direction, hysteresis becomes more MD-like, in agreement with numerical models. URI: http://hdl.handle.net/10311/360 Files in this item: 1
Muxworthy_GGG_2006.pdf (1.589Mb) -
King, J G; Ranganai, RT (BOSHASTED, NaN, 2000)[more][less]
Abstract: Emissions of vehicles represent a significant contribution to environmental pollution along roads. Pollutants from cars include gases such as (NOx, CO, CO2), solid components such as sort particles from exhaust system, abrasion products from the brakes and engine etc (Leven et al., 1999). Aerosols pollutants can reduce significantly the quality of the environment and seriously affect human health e.g. by contributing to high rates of allergies or diseases of the respiratory system. In this study, samples were collected at various distances from a busy road, Gaborone-Tlokweng road near Game store. Non-magnetic adhesive paper pieces were used as sample collectors. Magnetic properties of the aerosols collected were measured using a highly sensitive magnetometer (AGM-Micromag). Magnetic properties measured include total magnetic moment, hysteresis loops and associated parameters such as coercivity. In general, observed hysteresis loops are typical for magnetite. URI: http://hdl.handle.net/10311/406 Files in this item: 1
King_BOSHASTED_2000.pdf (159.1Kb) -
Simon, R.E.; Wright, C.; Kwadiba, M.T.O.; Kgaswane, E.M. (Elsevier Science Ltd. www.elsevier.com/locate/lithos, NaN, 2003)[more][less]
Abstract: Average one-dimensional P and S wavespeed models from the surface to depths of 800 km were derived for the southern African region using travel times and waveforms from earthquakes recorded at stations of the Kaapvaal and South African seismic networks. The Herglotz–Wiechert method combined with ray tracing was used to derive a preliminary P wavespeed model, followed by refinements using phase-weighted stacking and synthetic seismograms to yield the final model. Travel times combined with ray tracing were used to derive the S wavespeed model, which was also refined using phase-weighted stacking and synthetic seismograms. The presence of a high wavespeed upper mantle lid in the S model overlying a low wavespeed zone (LWZ) around 210- to - 345-km depth that is not observed in the P wavespeed model was inferred. The 410-km discontinuity shows similar characteristics to that in other continental regions, but occurs slightly deeper at 420 km. Depletion of iron and/or enrichment in aluminium relative to other regions are the preferred explanation, since the P wavespeeds throughout the transition zone are slightly higher than average. The average S wavespeed structure beneath southern Africa within and below the transition zone is similar to that of the IASP91 model. There is no evidence for discontinuity at 520-km depth. The 660-km discontinuity also appears to be slightly deeper than average (668 km), although the estimated thickness of the transition zone is 248 km, similar to the global average of 241 km. The small size of the 660-km discontinuity for P waves, compared with many other regions, suggests that interpretation of the discontinuity as the transformation of spinel to perovskite and magnesiowu¨ stite may require modification. Alternative explanations include the presence of garnetite-rich material or ilmenite-forming phase transformations above the 660-km discontinuity, and the garnet– perovskite transformation as the discontinuity. URI: http://hdl.handle.net/10311/265 Files in this item: 1
Simon_L71_2003.pdf (2.274Mb) -
Cao, Y.; Allameh, S.; Sethiaraj, S. (Elsevier, NaN, 2006)[more][less]
Abstract: This paper presents the results of nanoindentation experimental studies of the contact-induced deformation in Au and Ag thin films. The paper examines the effects of film thickness and substrate deformation restraint on the mechanical properties of electron beam (e-beam) deposited Au and Ag films. Following a brief description of film microstructure, surface topography, and contact-induced pile-up deformation, film mechanical properties (hardness and Young’s modulus) were determined using nanoindentation techniques. The indentation size effects (ISE) observed in films with different thicknesses were explained using a mechanism-based strain gradient (MSG) theory. The intrinsic film yield strengths and hardnesses extracted from the MSG theory are shown to exhibit classical Hall–Petch dependence on the inverse square root of the average film grain size. Displacement bursts were also found to occur in Ag films at indentation load levels of 100 N. These were attributed to the initial onset of dislocation slip activity, when the shear stress exceeds the estimated theoretical shear strengths of the materials. URI: http://hdl.handle.net/10311/537 Files in this item: 1
Nanoindentation measurements.pdf (1.173Mb) -
Murty, V.R.K.; Karunakara, N. (Elsevier, www.elsevier.com/locate/radmeas, NaN, 2008)[more][less]
Abstract: Studies on concentrations of primordial radionuclides in soil samples of Botswana were carried out. Measurements were made by gamma spectrometry employing a 41% relative efficiency HPGe detector. The activity of 226Ra was found to vary in the range 6.1–97.4 Bq kg 1 with a mean value of 34.8 Bq kg 1, 232Th in 7.4–110.0 Bq kg 1 with a mean value of 41.8 Bq kg 1 and that of 40K between 33.5 and 1085.7 Bq kg 1 with a mean value of 432.7 Bq kg 1 in surface soils. Existence of strong correlations in the distributions of these radionuclides indicates that an individual result for any one of the radionuclide is a good predictor of the concentration of the other. The mean value of effective dose, due to the 238U series, 232Th series and 40K in soil, was 0.07 mSV. The results of the present study are compared with the literature values reported for other normal background regions of the world and discussed. URI: http://hdl.handle.net/10311/493 Files in this item: 1
Murty2008SoilSamples.pdf (782.0Kb) -
Kumar, P.; Sathiaraj, T.S.; Thangaraj, R. (Taylor & Francis, NaN, 2010)[more][less]
Abstract: The measurements and analysis of optical transmission and far-infrared (IR) reflectivity spectra of thermally evaporated Sb2Se3:Sn films are reported. The refractive index and film thickness have been determined from the upper and lower envelopes of the transmission spectra (Swanepoel’s standard envelope method), measured at normal incidence, in the spectral range from 800 to 2500 nm. Values of the refractive index fit well to Cauchy’s dispersion relation. The optical gap decreases with an increase in the Sn content, while a maximum in the tailing parameter and Urbach’s energy occurs with only a small amount ( 1 at %) of this additive. Characteristic vibrational bands for SbSe3 structural units are revealed in the far-IR spectrum with no additional ones arising from the Sn additive. The Kramers–Kronig analysis has been used to calculate the dielectric constants and hence the longitudinal optic and transverse optic splitting for various compositions. The inclusion of Sn as a charged entity along with the Coulomb interactions which serve to polarize the glass medium is found to be responsible for these results. URI: http://hdl.handle.net/10311/547 Files in this item: 1
Optical properties.pdf (1.116Mb) -
Ringrose, S.; Kampunzu, A.B.; Vink, B.W.; Matheson, W.; Downey, W.S. (John Wiley & Sons, Ltd. http://www3.interscience.wiley.com/journal/117935722/grouphome/home.html, NaN, 2002)[more][less]
Abstract: Quaternary sedimentation in the Moshaweng dry valley of southeastern Botswana is evaluated on the basis of geomorphological evolution and sedimentological analyses. Stratigraphic evidence reveals an 'upper surface (1095 m) containing abundant sil-calcrete, an intermediate surface (1085 m) in which sil-calcrete underlies nodular calcrete and lower (1075 m) surface in which sil-calcrete and nodular calcrete are interbedded. This subdivision is reflected in the geochemical composition of the sediments which show an overall trend of decreasing Si02 content (and increasing CaC03 content) with depth from the highest to the lowest surface levels. The calcretes and sil-calcretes represent modifications of pre-existing detrital Kalahari Group sand and basal Kalahari pebbles which thinned over a Karoo bedrock high. Modification took place during wet periods when abundant Ca++ -rich groundwater flowed along the structurally aligned valley system. With the onset of drier conditions, water table fluctuations led to the precipitation of nodular calcretes in the phreatic layer to a depth of about 20 m. A major geochemical change resulted in the preferential silicification of the nodular calcrete deposits. Conditions for silica mobilization may be related to drying-induced salinity and in situ geochemical differentiation brought about by pebble dissociation towards the top of the sediment pile. As calcretization and valley formation progressed to lower levels, silica release took place on a diminishing scale. Thermoluminescence dating infers a mid-Pleistocene age for sil-calcrete formation suggesting that valley evolution and original calcrete precipitation are much older. Late st~ge dissolution of CaC03 from pre-existing surface calcretes or sil-calcretes led to the formation of pedogenic case-hardened deposits during a time of reduced flow through the Moshaweng system possibly during the upper or late Pleistocene. URI: http://hdl.handle.net/10311/310 Files in this item: 1
Ringrose_ESPL_2002.pdf (3.095Mb) -
Kumar, J.; Ahmad, M.; Chander, R.; Thangaraj, R.; Sathiaraj, T.S. (EDP Sciences, NaN, 2008)[more][less]
Abstract: Effect of Pb substitution on the amorphous-crystalline transformation temperature, optical band gap and crystalline structure of Ge2Sb2Te5 has been studied. In Pb:GeSbTe chalcogenide films prepared by thermal evaporation, an amorphous to crystallization transition is observed at 124, 129, 136 and 138 ◦C in Pb0Ge20Sb24Te56, Pb1.6Ge19Sb26Te54, Pb3Ge17Sb28Te53 and Pb5Ge12Sb28Te55 respectively. XRD investigations of annealed samples reveal that Pb substitution retains NaCl type crystalline structure of GST but expands the lattice due to large atomic radii. The increase in amorphous-crystalline transformation temperature is followed with the increase in phase segregation. The optical gap shows marginal variations with composition. URI: http://hdl.handle.net/10311/531 Files in this item: 1
Phase segregation.pdf (573.5Kb) -
Kumar, J.; Ahmad, M.; Chander, R.; Thangaraj, R.; Sathiaraj, T.S. (EDP Sciences. http://www.epjap.org/, NaN, 2008)[more][less]
Abstract: Effect of Pb substitution on the amorphous-crystalline transformation temperature, optical band gap and crystalline structure of Ge2Sb2Te5 has been studied. In Pb:GeSbTe chalcogenide films prepared by thermal evaporation, an amorphous to crystallization transition is observed at 124, 129, 136 and 138 ◦C in Pb0Ge20Sb24Te56, Pb1.6Ge19Sb26Te54, Pb3Ge17Sb28Te53 and Pb5Ge12Sb28Te55 respectively. XRD investigations of annealed samples reveal that Pb substitution retains NaCl type crystalline structure of GST but expands the lattice due to large atomic radii. The increase in amorphous-crystalline transformation temperature is followed with the increase in phase segregation. The optical gap shows marginal variations with composition. URI: http://hdl.handle.net/10311/278 Files in this item: 1
Kumar_EPJAP41_2008.pdf (796.1Kb) -
Nijegorodov, N.; Zvolinski, V.; Luhanga, P.V.C.; Mabbs, R.; Ahmad, J. (Elsevier Ltd. www.elsevier.com/locate/saa, NaN, 2006)[more][less]
Abstract: The multi-banded fluorescence and laser properties of 11 new amino- and tosylamino derivatives of 2,5-di(phenyl)-1,3,4-oxadiazole and oxadiazole in various solvents at 293 K are reported. All the compounds investigated possess intra-molecular hydrogen quasi-bond (IHB) of 4.6-5.2 kcal mol-1 in the ground state. In the excited state they can undergo protolytic dissociation or intra-molecular photon-initiated transfer of proton and reveal anomalous fluorescence which cannot be explained within the framework of the Kasha and Kasha-Vavilov rules. Depending upon the excitation wavelength, solvent, concentration and pH of the medium, the compounds studied show a single, double, triple or even a four-banded fluorescence, which has not been reported earlier. The nature of multi-banded fluorescence is explained in terms of the possible photochromic processes in excited states. Quantum yields and decay times of the different fluorescence bands are reported. Anomalous dependence of quantum yield upon concentration of the solution is observed. Laser properties of the compounds studied are carefully tested. Laser action based on the fluorescence of the so-called bi-radical molecules is reported. Various possible arrangements of singlet and triplet levels of compounds investigated are discussed. URI: http://hdl.handle.net/10311/176 Files in this item: 2
license.txt (1.998Kb) -
Nijegorodov, N; Zvolinski, V; Luhanga, P V C; Mabbs, R; Ahmad, J (Elsevier Science Ltd. www.elsevier.com/locate/saa, NaN, 2006)[more][less]
Abstract: The multi-banded fluorescence and laser properties of 11 new amino- and tosylamino derivatives of 2,5-di(phenyl)-1,3,4-oxadiazole and oxadiazole in various solvents at 293K are reported. All the compounds investigated possess intra-molecular hydrogen quasi-bond (IHB) of 4.6–5.2 kcal mol−1 in the ground state. In the excited state they can undergo protolytic dissociation or intra-molecular photon-initiated transfer of proton and reveal anomalous fluorescence which cannot be explained within the framework of the Kasha and Kasha–Vavilov rules. Depending upon the excitation wavelength, solvent, concentration and pH of the medium, the compounds studied show a single, double, triple or even a four-banded fluorescence, which has not been reported earlier. The nature of multi-banded fluorescence is explained in terms of the possible photochromic processes in excited states. Quantum yields and decay times of the different fluorescence bands are reported. Anomalous dependence of quantum yield upon concentration of the solution is observed. Laser properties of the compounds studied are carefully tested. Laser action based on the fluorescence of the so-called bi-radical molecules is reported. Various possible arrangements of singlet and triplet levels of compounds investigated are discussed. URI: http://hdl.handle.net/10311/247 Files in this item: 2
license.txt (1.998Kb)Nijegorodov_SAa65_2006.pdf (2.225Mb) -
Murty, V.R.K.; Devan, K.R.S. (Elsevier Science Ltd. www.elsevier.com/locate/radphyschem, NaN, 2004)[more][less]
Abstract: The interaction of photons with matter has been extensively studied over the past several decades in view of its importance in basic radiation physics research, medical, industrial and other applied fields. Large amounts of data have been complied on photon cross sections mostly in tabular and graphical forms (Hubbell, 1999, 1994; Berger and Hubbell, 1987). A careful survey of the latest bibliography (Hubbell, 1994) of experimental investigations shows gaps in the cross section data, especially in certain low-Z elements. These are mainly attributed to the difficulty in procuring thin absorbers in suitable form for low energy experiments. It was also evident from the bibliography that the cross section data was sparse for elements Mg and V, especially, using high resolution solid state detectors in the photon energy region below 100 keV. URI: http://hdl.handle.net/10311/266 Files in this item: 1
Murty_RPC_2004.pdf (191.6Kb) -
Nijegorodov, N.; Zvolinsky, V.; Luhanga, P.V.C. (Elsevier Science Ltd. www.elsevier.com/locate/jphotochem, NaN, 2008)[more][less]
Abstract: Intramolecular processes and fluorescence properties of 32 specially chosen aromatic molecules, different in degrees of planarity and rigidity, but family related in -structure are experimentally and theoretically (using the PPP-method) studied at room temperature (293 K). The quantum yields of fluorescence , and decay times τf, of deaerated and non-deaerated cyclohexane solutions are measured. The oscillator strength fe, the fluorescence rate constants kf, the natural lifetimes τT o , and the intersystem crossing rate constants kST, are calculated. The investigations showed the following differences in the behaviour of the fluorescence parameters in transition from the non-planar molecule to the planar and more rigid-type: the value of the symmetry line wave-number υ00 (the frequency of the S0→S1 * transition) and the Stokes shift υST, decrease. The oscillator strength and fluorescence constant, normally decrease. The change in the quantum yield of the fluorescence depends upon the changes in the kf and kST values. Furthermore, the intersystem crossing rate constant generally decreases, sometimes very significantly. However, there are some interesting exceptions. For example, the kST value of the non-planar molecule of 9,10-diphenylanthracene is less than the kST value of the planar and very rigid molecule of anthracene. This important phenomenon is explained. The differences of the intramolecular processes of planar and non-planar molecules are discussed. The photochemical stability of planar and non-planar molecules is studied. The effect of planarity, rigidity and molecular symmetry upon laser properties is also traced. URI: http://hdl.handle.net/10311/367 Files in this item: 1
Nijegorodov_JPPaC196_2008.pdf (1.901Mb) -
Mphale, K.M.; Heron, M.L. (Elsevier Science Ltd. www.elsevier.com/locate/jastp, NaN, 2007)[more][less]
Abstract: The flames of wildfires are weakly ionized gas. The ionization is mainly due to omnipresent alkali and alkaline earth metal species that are emitted from thermally decomposing plant structure into the flame during a wildfire. The amount of ionization in flames with alkali impurities is a factor of both the temperature and the quantity of the emitted alkali species in vegetation. Assuming a Maxwellian velocity distribution of flame particles and collision frequencies much higher than plasma frequencies, the propagation of radio waves through wildfires is predicted to have attenuation and phase shift. A theoretical model has been developed to predict propagation characteristics of HF–VHF radio signals at normal incidence to a high intensity wildfire fuel–flame interface. At the interface, the flame medium is modelled by a series of mini-slabs, each with a different but fixed electron density and dielectric permittivity governed by the Rayleigh distribution of temperature. Electron density in each mini-slab is calculated from thermal ionization of alkali species assuming the existence of thermal equilibrium. The model predicts average electron densities ranging from 10¹4 to 10¹7m–³ for fuel–flame interfaces with maximum temperatures from 900 to 1200 K. Specific attenuation and phase shift for propagation in the ionized gas are calculated from the predicted average electron density and collision frequency. At collision frequency of 10¹¹ s–¹, radio signal specific attenuation for the simulated grassfires range from 0.001 to 0.49 dBm–¹ while specific phase shift ranged from 0.0002 to 152°m–¹ for the maximum temperature range of 900–1150 K. URI: http://hdl.handle.net/10311/269 Files in this item: 1
Mphale_JASTP69_2007.pdf (2.265Mb) -
Kwadiba, M.T.O.G.; Wright, C.; Kgaswane, E.M.; Simon, R.E.; Nguuri, T.K. (Elsevier Science Ltd. www.elsevier.com/locate/lithos, NaN, 2003)[more][less]
Abstract: Pn arrivals from mining-induced earthquakes on the edge of the Witwatersrand basin show that the P wavespeeds in the uppermost mantle are almost constant throughout most of the Kaapvaal craton. The presence of only small wavespeed variations allows the use of a simple method of estimating crustal thicknesses below the stations of the Kaapvaal broad-band network using Pn times that has been compared with results from receiver functions. One thousand three hundred thirty-seven Pn arrivals were used to derive crustal thicknesses at 46 stations on the Kaapvaal craton. The average crustal thicknesses for 19 centrally located stations on each of the northern and southern regions of the craton that yielded well-constrained thicknesses were 50.52 ± 0.88 km and 38.07 ± 0.85 km, respectively. In contrast, the corresponding average thicknesses determined from receiver functions were 43.58 ± 0.57 km and 37.58 ± 0.70 km, respectively. The systematically lower values for receiver functions in the northern part of the Kaapvaal craton that was affected by the Bushveld magmatism at 2.05 Ga, suggest that the receiver functions do not enable the petrological crust mantle boundary to be reliably resolved due to variations in composition and metamorphic grade in a mafic lower crust. The Pn times also suggest pervasive azimuthal anisotropy with maximum wavespeeds of about 8.40 km/s at azimuths of about 15° and 217° in the northern and southern regions of the craton, respectively, and minimum wavespeeds of about 8.25 km/s. URI: http://hdl.handle.net/10311/281 Files in this item: 1
Kwadiba_L71_2003.pdf (2.747Mb) -
Jain, P.K.; Lungu, E.M.; Mogotsi, B. (Elsevier Science Ltd. http://www.sciencedirect.com/science/journal/09601481, January NaN, 2002)[more][less]
Abstract: Lack of trained manpower for repair and maintenance of solar energy devices in Botswana has resulted in failure of devices, loss of revenue, and dwindling of consumer faith in solar technologies. The government of Botswana commissioned a study to assess the needs for trained manpower in New and Renewable Sources of Energy (NRSE) technologies, to identify the required training programs and their levels, and the facilities that need to be upgraded and/or created for the implementation of such training programs at the existing technical and educational institutions within the country. The paper presents the findings of the study, and the recommendations made. The study proposed seven training programs at progressively increasing skills and expertise levels that include two certificate courses in each of the solar water heating and photovoltaic technologies for maintenance personnel, a national craft certificate program in solar energy technologies, a higher diploma in energy technologies for supervisory personnel, and a short course for upper management personnel in decision-making positions in order to raise their skills in the procurement of equipment and services, and to provide overall effective leadership. A short course to upgrade the skills of the present maintenance personnel to alleviate the immediate problems is also proposed. Required upgrading of existing technical training facilities, the creation of new facilities and estimated budgetary requirements constitute some of the recommendations. The recommendations have gone through various channels of discussions, and have been accepted in principle. The report is currently under consideration for implementation by relevant government departments. URI: http://hdl.handle.net/10311/137 Files in this item: 2
license.txt (1.998Kb) -
Masale, M. (Elsevier Science Ltd. http://www.elsevier.com/locate/physb, NaN, 2004)[more][less]
Abstract: The energy spectrum of an electron confined near a current-carrying core is obtained as a function of the azimuthal applied magnetic field within the effective-mass approximation. The double degeneracy of the non-zero electron's axial wave number (kz) states is lifted by the current-induced magnetic field while that of the non-zero azimuthal quantum number (m) states is preserved. A further analysis is the evaluations of the oscillator strengths for optical transitions involving the lowest-order pair of the electron's energy subbands within the dipole approximation. The radiation field is taken as that of elliptically polarized light incident along the core axis. In this polarization and within the dipole approximation, the allowed transitions are only those governed by the following specific selection rules. The azimuthal quantum numbers of the initial and final states must differ by unity while the electron's axial wave number is conserved. The azimuthal magnetic field is also found to lift the multiple degeneracies of the kz=0 interaction integrals as well as those of the oscillator strengths for optical transitions. URI: http://hdl.handle.net/10311/244 Files in this item: 2
license.txt (1.998Kb)Masale_PB_2004.pdf (1.197Mb) -
Wright, C.; Kgaswane, E.M.; Kwadiba, M.T.O.; Simon, R.E.; Nguuri, T.K.; McRae-Samuel, R. (Elsevier Science Ltd. www.elsevier.com/locate/lithos, NaN, 2003)[more][less]
Abstract: Events induced by deep gold-mining activity on the edge of the Witwatersrand basin dominate the seismicity of South Africa. The deployment of 54 broad-band seismic stations at 84 separate locations across southern Africa between April 1997 and April 1999 (Kaapvaal network) enabled the seismicity of South Africa to be better defined over a 2-year period. Seismic events located by the South African national network, and by localized seismic networks deployed in mines or across goldmining areas, were used to evaluate earthquake location procedures and to show that the Kaapvaal network locates mininginduced tremors with an average error of 1.56 ± 0.10 km compared with 9.50 ± 0.36 km for the South African network. Travel times of seismic events from the mines recorded at the Kaapvaal network indicate regional variations in the thickness of the crust but no clearly resolved variations in seismic wavespeeds in the uppermost mantle. Greater average crustal thicknesses (48–50 km compared with 41–43 km) are observed in the northern parts of the Kaapvaal craton that were affected by the Bushveld magmatism at 2.05 Ga. Estimates of average crustal thickness for the southern part of the Kaapvaal craton from receiver functions (38 km) agree well with those from refracted arrivals from mining-induced earthquakes if the crustal thicknesses below the sources are assumed to be 40–43 km. In contrast, the average crustal thickness inferred from refracted arrivals for the northern part of the Kaapvaal craton is larger by about 7 km (51 km) than that inferred from receiver functions (44 km), suggesting a thick mafic lower crust of variable seismic properties due to variations in composition and metamorphic grade. Pn wavespeeds are high (8.3–8.4 km/s), indicating the presence of highly depleted magnesium-rich peridotite throughout the uppermost mantle of the craton. Seismic Pg and Sg phases indicate that the upper crust around the Witwatersrand basin is comparatively uniform in composition when averaged over several kilometres. URI: http://hdl.handle.net/10311/280 Files in this item: 1
Wright_L71_2003.pdf (3.483Mb)