Browsing Faculty of Science by Author "King, J.G."
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Nijegorodov, N.; Luhanga, P.V.C.; King, J.G. (Regional Energy Resources Information Center (RERIC) Asian Institute of Technology. http://www.rericjournal.ait.ac.th/index.php/reric/index, December NaN, 2005)[more][less]
Abstract: Please refer to the attached article for the ABSTRACT. Due to technical problems with some scientific formulae it was not possible to upload the abstract HERE. URI: http://hdl.handle.net/10311/408 Files in this item: 1
Nijegorodov_IEJ_2005.pdf (2.539Mb) -
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) -
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) -
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) -
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) -
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)
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