Browsing Physics by Title
-
King, J.G.; Ranganai, R.T. (Botswana Geoscientists Association, NaN, 2001)[more][less]
Abstract: The Hopkinson effect is the increase of magnetic susceptibility with temperature from near room temperature to near the Curie point. Although this effect has been known for more than a century, it has not been effectively utilised as an analysing tool in palaeo, rock and environmental magnetic studies. This is partly due to the poor understanding of the influence of magnetite (Fe,O.)grain parameters on the Hopkinson effect. In an attempt to study the effects of grain size on the Hopkinson effect, magnetite samples with well-defined grain sizes have been used. it was found that in general, magnetic susceptibility enhancement factor (SEF) obtained by heating the sample in a non-oxidising environment, increase with decreasing grain size. The relation of SEF to grain size is linear when plotted on a log-log scale. This relation has been used to infer grain sizes (hence magnetic domains) for some selected Botswana rocks. The inferred magnetic domains are consistent with independent predictions from hysteresis measurements for the same samples. URI: http://hdl.handle.net/10311/338 Files in this item: 1
King_BJES_2001.pdf (625.5Kb) -
Sathiaraj, T.S. (Elsevier Ltd, NaN, 2008)[more][less]
Abstract: Indium tin oxide (ITO) thin films were prepared by RF sputtering of ceramic ITO target in pure argon atmosphere at a high base pressure of 3 10 4mbar without substrate heating and oxygen admittance. The use of pure argon during deposition resulted in films with high transparency (80–85%) in the visible and IR wavelength region. The films were subsequently annealed in air in the temperature range 100–400 1C. The annealed films show decreased transmittance in the IR region and decreased resistivity. The films were characterized by electron microscopy, spectrophotometry and XRD. The predominant orientation of the films is (2 2 2) instead of (4 0 0). The transmission and reflection spectra in the wavelength range 300–2500 nm are used to study the optical behaviour of the films. The optical transmittance and reflectance spectra of the films were simultaneously simulated with different dielectric function models. The best fit of the spectrophotometric data was obtained using the frequency-dependent damping constant in the Drude model coupled with the Bruggeman effective medium theory for the surface roughness. It has been found that the sputtering power and the chamber residual pressure play a key role in the resulting optical properties. This paper presents the refractive index profile, the structure determined from the XRD and the electrical properties of ITO films. It has been found from the electrical measurement that films sputtered at 200W power and subsequently annealed at 400 1C have a sheet resistance of 80O/& and resistivity of 1.9 10 3Ocm. Description: Some mathematical symbols may not come as they are in the abstract. URI: http://hdl.handle.net/10311/690 Files in this item: 1
Effect of annealing.pdf (1.308Mb) -
Sathiaraj, T.S. (Elsevier Science Ltd. http://www.elsevier.com/locate/mejo, NaN, 2008)[more][less]
Abstract: Indium tin oxide (ITO) thin films were prepared by RF sputtering of ceramic ITO target in pure argon atmosphere at a high base pressure of 3×10−4 mbar without substrate heating and oxygen admittance. The use of pure argon during deposition resulted in films with high transparency (80–85%) in the visible and IR wavelength region. The films were subsequently annealed in air in the temperature range 100–400 °C. The annealed films show decreased transmittance in the IR region and decreased resistivity. The films were characterized by electron microscopy, spectrophotometry and XRD. The predominant orientation of the films is (2 2 2) instead of (4 0 0). The transmission and reflection spectra in the wavelength range 300–2500 nm are used to study the optical behaviour of the films. The optical transmittance and reflectance spectra of the films were simultaneously simulated with different dielectric function models. The best fit of the spectrophotometric data was obtained using the frequency-dependent damping constant in the Drude model coupled with the Bruggeman effective medium theory for the surface roughness. It has been found that the sputtering power and the chamber residual pressure play a key role in the resulting optical properties. This paper presents the refractive index profile, the structure determined from the XRD and the electrical properties of ITO films. It has been found from the electrical measurement that films sputtered at 200 W power and subsequently annealed at 400 °C have a sheet resistance of 80 Ω/□ and resistivity of 1.9×10−3 Ωcm. URI: http://hdl.handle.net/10311/631 Files in this item: 1
Sathiaraj_MJ_2008.pdf (763.9Kb) -
Kumar, J.; Kumar, P.; Suri, N.; Ahmad, M.; Thangaraj, R.; Sathiaraj, T.S. ( NaN, 2008)[more][less]
Abstract: Optical properties of Pb doped ternary Ge-Sb-Te chalcognide films prepared by thermal evaporation have been studied in the visible and near-infrared spectral regions. The straightforward analysis proposed by Swanepoel has been successfully employed and it has allowed us to accurately determine the refractive index and extinction coefficient of the films. The refractive index has been determined from the upper and lower envelopes of the transmission spectra. The absorption coefficient and extinction coefficient have been determined from the transmission spectra in the strong-absorption region. The dispersion of the refractive index is discussed in terms of the Wemple–DiDomenico single oscillator model. URI: http://hdl.handle.net/10311/544 Files in this item: 1
Effect of composition.pdf (950.3Kb) -
Murty, V.R.K. (Elsevier Science Ltd. www.elsevier.com/locate/radphyschem, NaN, 2004)[more][less]
Abstract: The study of interaction of photons with matter finds wide application in areas such as industry, medical radiation dosimetry and radiation shielding. A careful review of these measurements indicates that the studies are exhaustive in respect of pure elements. However, measurements on photon attenuation in alloys are meagre. This is mainly due to the difficulty in procuring targets in suitable form for experimentation. Such studies play a prominent role in selecting alternative shielding materials on the cost-effective basis. URI: http://hdl.handle.net/10311/268 Files in this item: 1
Murty_RPC71_2004.pdf (223.2Kb) -
Masale, M. (Elsevier Science Ltd. http://www.elsevier.com/wps/find/journaldescription.cws_home/622948/description#description, NaN, 2008)[more][less]
Abstract: A calculation is presented on the scattering rates of electrons via the bulk spectrum of longitudinal optical phonons near a current-carrying core of radius R employing the Frohlich interaction Hamiltonian. The electrons are mainly confined near the core by an electric potential and are also under the influence of the current-induced spatially inhomogeneous static azimuthal magnetic field. The external magnetic field lifts the double degeneracy of the non-zero electron's axial wave number (kz ) states, while that of the nonzero azimuthal quantum number (m) states is preserved. In fact, the kz < 0 electron's energy subbands are found to be characterized by minima in their variations with the field. The intrasubband scattering rates show a remarkable behavior in their variations with the field. First, for weak electric potential of the nanosystem, these exhibit a strong, nonetheless inharmonic, oscillatory behavior in their variations with the field. The oscillations are, however, smoothed out as the strength of the electrical potential is increased, commencing at lower values of the field, within the same range of values of the field used. Second, for the same strength of the electric potential, there arise phase variations of the scattering rates in their variations with the field, resulting from the variation in the electron's axial wave number. URI: http://hdl.handle.net/10311/232 Files in this item: 2
license.txt (1.998Kb)Masale_SM_2008.pdf (1.267Mb) -
King, J.G.; Garegae, M.; Ngwisanyi, T.H.; Ranganai, R. (Botswana Geoscientists Association, December NaN, 2005)[more][less]
Abstract: Fault-plane solutions of an earthquake can provide information about the type of fault. We report on the calculation of the fault-plane solutions of the earthquake that occurred on the morning of 18 May 2001 and was felt in the southern parts of Botswana and the North West Province of South Africa. The fact that there were few seismic stations in the vicinity of these areas meant that standard programs such as FOCMEC would produce a large number of possible fault-plane solutions. In this study a semi-manual method of determining fault-plane solution was utilized to obtain the most likely solution from a SEISAN program. The results obtained from these two methods shows that the focal mechanism for this earthquake was normal faulting. The two methods used compliment each other. Other information obtained includes epicenter at coordinates (longitude 26.0E, latitude 25.6S), magnitude of about 4.6 ML and origin time of 9:14.10.52 UTC. URI: http://hdl.handle.net/10311/337 Files in this item: 1
King_BJES_2005.pdf (143.0Kb) -
Mabbs, R.; Nijegorodov, N.; Downey, W.S. (Elsevier Science Ltd. www.elsevier.com/locate/saa, NaN, 2003)[more][less]
-
Ranganai, R.T.; Whaler, K.A.; Ebinger, C.J. (Elsevier Science Ltd. www.elsevier.com/locate/jafrearsci, NaN, 2008)[more][less]
Abstract: The granite-greenstone terrain of south-central Zimbabwe, encompassing the Belingwe (Mberengwa) greenstone belt and sections of the Great Dyke, provides important constraints on models for the evolution of the Zimbabwe craton and the Archaean crust in general. In this paper we enhance and model existing and recently acquired gravity data from the region and correlate the anomalies and their derivatives with the known basement geology to evaluate models for greenstone belt development. We also study the spatial gneiss-granite- greenstone association in general, and the geologic implications of models of the anomaly patterns in particular. Although the Belingwe greenstone belt has been mapped, its subsurface geometry is poorly known. Similarly, the Great Dyke is well studied, but no systematic study of the extent and cross-cutting relations of other mafic dykes in the Archaean crust has been undertaken. The regional gravity field shows no evidence for crustal thickness variations in the area and the gravity anomalies can be explained by lateral density variations of the supracrustal rocks. Prominent gravity highs are observed over the high density (≤ 3000 kg/m3) volcanosedimentary piles (greenstone belts) and ultramafic complexes. Well-defined elongate, sub-oval/elliptical gravity lows are associated with intrusive granitic plutons. The granite-greenstone contacts are marked by steep gravity gradients of up to 5 mGal/km that imply steeply dipping or near-vertical contacts for the anomalous bodies. This is tested and confirmed by 2½D modelling of gravity profiles across the Belingwe and Fort Rixon greenstone belts, constrained by measured densities and observed geological data. The modelling also indicates that these belts, and possibly all the belts in the study area (based on comparable densities and anomaly amplitudes), have limited depth extents in the range of 3–5 km. This is comparable to thicknesses obtained elsewhere from deep seismic reflection data and geoelectrical studies, but mapped stratigraphic thicknesses give a maximum depth extent of about 9.5 km. Present studies and previous work support the idea that the volcanics were extruded within rift zones and laid on older granitic crust, followed by subsidence and rapid deposition of sediments that were sourced from the adjacent basement terrains. The volcano-sedimentary sequences were subsequently deformed by intruding younger plutons and affected by late-stage strike-slip activity producing cross-cutting structures. URI: http://hdl.handle.net/10311/276 Files in this item: 1
Ranganai_JAES_2008.pdf (4.603Mb) -
Ranganai, R.T.; Kampunzu, A.B.; Atekwana, E.A.; Paya, B.K.; King, J.G.; Koosimile, D.I.; Stettler, E.H. (Royal Astronomical Society. http://www.wiley.com/bw/journal.asp?ref=0956-540X&site=1, NaN, 2002)[more][less]
Abstract: The Limpopo Belt of southern Africa is a Neoarchean orogenic belt located between two older Archean provinces, the Zimbabwe craton to the north and the Kaapvaal craton to the south. Previous studies considered the Limpopo Belt to be a linearly trending east-northeast belt with a width of ~250 km and ~600 km long. We provide evidence from gravity data constrained by seismic and geochronologic data suggesting that the Limpopo Belt is much larger than previously assumed and includes the Shashe Belt in Botswana, thus defining a southward convex orogenic arc sandwiched between the two cratons. The 2 Ga Magondi orogenic belt truncates the Limpopo–Shahse Belt to the west. The northern marginal, central and southern marginal tectonic zones define a single gravity anomaly on upward continued maps, indicating that they had the same exhumation history. This interpretation requires a tectonic model involving convergence between the Kaapvaal and Zimbabwe cratons during a Neoarchean orogeny that preserved the thick cratonic keel that has been imaged in tomographic models. URI: http://hdl.handle.net/10311/326 Files in this item: 1
Ranganai_GJI_2002.pdf (1.361Mb) -
Ahmad, M.; Thangaraj, R.; Sathiaraj, T.S. (Springer, NaN, 2010)[more][less]
Abstract: Bulk samples of Sn10Sb20-xBixSe70 (0 B x B 8) chalcogenide alloys were prepared by the conventional melt quenching technique. Thin films were prepared on wellcleaned glass substrates by thermal evaporation technique. X-ray diffraction studies revealed that the alloys with x = 0 and 2 at.% of Bi were amorphous, whereas the alloys with x = 4, 6, 8 at.% were crystalline. The crystalline phases are identified as due to the formation of Bi2Se3 and BiSe2 phases. The microstructural and differential scanning calorimetric studies show the presence of these phases. A simple, straight forward procedure suggested by Swanepoel has been used to calculate the optical parameters, refractive index, and extinction coefficient. The optical gap for all the samples has been obtained from the Tauc plots. The variation in optical parameters for different Bi concentration has been explained on the basis of presence of defect states and the change in stoichiometry with the change in Bi concentration. Description: some symbols on the abstract may not appear as they are on the text. URI: http://hdl.handle.net/10311/752 Files in this item: 1
Heterogeneous crystallization.pdf (777.8Kb) -
Nijegorodov, N.; Winkoun, D.P.; Nkoma, J.S. (Elsevier Science Ltd http:www.elsevier.com/locate/saa, NaN, 2003)[more][less]
Abstract: Please refer to the attached article for an ABSTRACT. The abstract was not uploaded here due to formula appearance problem in UBRISA. URI: http://hdl.handle.net/10311/403 Files in this item: 1
Nijegorodov_SAa60_2004.pdf (1.056Mb) -
Nijegorodov, N.; Winkoun, D.P.; Nkoma, J.S. (Elsevier Science Ltd. www.elsevier.com/locate/saa, NaN, 2004)[more][less]
Abstract: The fluorescence and laser properties of seven specially chosen aromatic compounds are studied at 293 ◦C. The quantum yield of fluorescence, γ, decay times, τf , of the deaerated and non-deaerated solutions are measured. The oscillator strength, fe, fluorescence rate constants, kf , natural lifetimes, τT 0 , and intersystem crossing rate constants, kST, are calculated. Some laser parameters are calculated or measured experimentally. It is found that the position of the T level plays an important role in the fluorescence and laser properties of aromatic compounds. If the T level is situated below the Sp level, it decreases the quantum yield of fluorescence and the decay time and increases the threshold of laser action. If, due to some structural changes of a molecule, the T level is situated higher than the Sp level, then the quantum yield of fluorescence and the decay times are increasing and the threshold of laser action is decreasing. Such influence of the position of the T level upon fluorescence and laser properties of aromatic compound is explained by the fact that the Sp level mixes with the T level more readily than with other τ ∗ levels. URI: http://hdl.handle.net/10311/366 Files in this item: 1
Nijegorodov_SAa60_2004.pdf (1.056Mb) -
Nijegorodov, N.; Mabbs, R.; Winkoun, D.P. (Elsevier Science Ltd. www.elsevier.com/locate/saa, NaN, 2003)[more][less]
Abstract: Please refer to the attached article for an ABSTRACT. The abstract was not uploaded here due to formula appearance problem in UBRISA. URI: http://hdl.handle.net/10311/402 Files in this item: 1
Nijegorodov_SAa59-2003.pdf (1.367Mb) -
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)