Browsing Faculty of Science by Title
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Dikinya, O.; Hinz, C.; Aylmore, G. (Elsevier http://www.linkinghub.elsevier.com/retrieve/pii/S0016706108001365, NaN, 2008)[more][less]
Abstract: The dynamics of the process of self-filtration in soil columns have been evaluated for two soils with different structural cohesion (Balkuling agricultural soil and a mining residue) by carrying out experiments focusing on microscopic particle behaviour during filtration. Soil column experiments were set up to simultaneously measure changes in hydraulic gradients (ΔH/ΔL) along the columns and outflow particle sizes and concentrations during pressure leaching with solutions of 100, 10 and 1 mmol/L NaCl and deionised water. The lowest ionic strength has resulted in more reduced hydraulic conductivity and relatively more release of colloids associated with hydrodynamic shear and dispersion. Steady increases in hydraulic gradient (ΔH/ΔL) and corresponding decreases in relative saturated hydraulic conductivity (K/Ko) with time were observed for both soils and follow similar trends at all column depths. The most severe increases in ΔH/ΔL and decreases in K/Ko always occurred near the inlet to the columns and the decline gradually decreased along the column. The decrease in K/Ko and increase in ΔH/ΔL were clearly influenced by the size as well as the concentration of migrating particles in the porous medium. The finer mobile particles in the mining residue were clearly more readily self-filtered at the lower concentration than the larger Balkuling soil particles producing more rapid increases in ΔH/ΔL and decreases in K/Ko. This was attributable to more effective self-filtration and more pore clogging probably due to increased development of the diffuse double layer, swelling and dispersion within the soil matrix at these concentrations. URI: http://hdl.handle.net/10311/488 Files in this item: 1
Dikinya_Geoderma_2008.pdf (1.429Mb) -
Daka, P.S.; Obuseng, V.C.; Torto, N.; Huntsman-Mapila, P. (Water SA Pretoria; Water Research Commission; http://www.wrc.org.za/, October NaN, 2006)[more][less]
Abstract: Deltamethrin concentrations were determined in 35 sediment samples collected from three different habitats: channel, lagoon and pool sites from Xakanaxa in the Okavango Delta, NW Botswana. The samples were Soxhlet-extracted in acetone to extract deltamethrin residues and subsequently cleaned-up with silica gel 60. The final determination was carried out with a gas chromatograph equipped with an electron capture detector (GC-ECD). The sample work-up and determination gave deltamethrin recoveries of 54 to 97%, and detection limits of 0.004 mg/kg dw. The concentration of deltamethrin residues in the sediment samples collected from the three sprayed areas in the Okavango delta ranged between 0.013 and 0.291 mg/kg dw, with the highest concentrations observed in samples obtained from the pool sites. Analysis of samples for organic matter content showed percentage total organic carbon (% TOC) ranging between 0.19% and 8.21%, with samples collected from the pool having the highest total organic carbon. The concentrations of deltamethrin residues and the % TOC in sediment samples showed a similar trend with the highest levels recorded in the pool samples. These data confirmed that a simple method based on GC-ECD, after Soxhlet extraction, was robust enough to enable quantification of deltamethrin in the sediments, because comparable results were obtained with a more sophisticated system consisting of a GC coupled to a mass spectrometer with a time of flight (TOF) analyser. URI: http://hdl.handle.net/10311/140 Files in this item: 2
dakaetal.pdf (463.1Kb)license.txt (1.998Kb) -
Bernard, T.; Moetapele, N. (Elsevier http://www.doi:10.1016/j.jaridenv.2005.02.001, NaN, 2005)[more][less]
Abstract: For at least 200 years, Gomoti River people and their neighbours lived interactively with the Okavango flood pulse system, travelling widely in dugout canoes, practicing flood recession agriculture, fishing, hunting, and collecting wild foods. Today they are wetlanders without wetlands. A major outflow channel of the eastern Okavango Delta in the 1930s, the Gomoti River rarely flows these days. This paper explores the Gomoti’s demise, through the lenses first of science and second of Gomoti basin residents. Models developed over the past 20 years attribute the Gomoti’s drying to a complex set of bio-hydrologic processes and feedback loops that begin with sedimentation and conclude with channel switching, peat fires, and purging of toxic salts. Such models essentially omit the long history of human habitation and ecological interaction with the delta. Local people, on the other hand, tell of deliberate and systematic management of channels and floodplains, and they argue this management kept the river healthy and flowing. The picture is confounded by colonial era interventions and by Botswana government policies partitioning the Gomoti and restricting access to its headwaters. We conclude with a model combining meso-scale scientific explanation with micro-scale indigenous constructions as a context for new thinking about Okavango Delta resource management. URI: http://hdl.handle.net/10311/467 Files in this item: 1
Bernard_JAE_2005.pdf (2.556Mb) -
Mpoloka, S.W.; Kgotlele, T.; Wally, A. (Academic Journals, www.academicjournals.org, April 17, 2008)[more][less]
Abstract: Allele frequencies for nine short tandem repeat (STR) loci from the AmpFlSTR® Profiler Plus PCR Amplification Kit were determined in five subpopulations across Botswana and tested for suitability for use in individual identification. DNA was extracted from whole blood samples collected from 150 unrelated individuals. Targeted regions of DNA (vWA, FGA, D3S1358, D5S818, D7S820, D8S1179, D13S317, D18S51, D21S11 and the sex determining locus Amelogenin) were amplified using multiplexed PCR. The alleles showed a high degree of polymorphism, with heterozygosity above 67%, indicating that there is no significant inbreeding within the subpopulations. Matching probability was below 0.2 hence power of discrimination was high, indicating that the alleles from the five subpopulations can be used in human identifications. The present study is the first reported attempt at determining allele frequencies of subpopulations in Botswana and could possibly be used in developing a national DNA database. URI: http://hdl.handle.net/10311/1010 Files in this item: 1
mpoloka ajb paper.pdf (292.5Kb) -
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) -
Ngadjui, B.; Dongo, E.; Abegaz, B.; Fotso, S.; Tamboue, H. (Elsevier Science Ltd. www.elsevier.com/locate/phytochem, NaN, 2002)[more][less]
Abstract: Three prenylated flavonoids, dinklagins A, B and C identified, respectively, as ( )-6-(3,3-dimethylallyl)-7-hydroxy-6000, 6000-dimethylchromeno-( 40,30,2000,3000)-flavanone, (+)-5,40,500x-trihydroxy-600,600-dimethylchromano-(7,6,200,300)-flavone and (+)6-(2x-hydroxy- 3-methyl-3-butenyl)-5,7,40-trihydroxyflavone were isolated from the twigs of Dorstenia dinklagei together with the known 6-prenylapigenin, 4-hydroxylonchocarpin, stipulin and 5,40-dihydroxy-600,600-dimethylchromano-(7,6,200,300)-flavone. Their structures were determined on the basis of spectral data and by comparison with data reported in the literature and with authentic specimens for known compounds. URI: http://hdl.handle.net/10311/262 Files in this item: 2
license.txt (1.998Kb) -
Ngameni, B.; Ngadjui, B.; Folefoc, G.; Watchueng, J.; Abegaz, B. (Elsevier Ltd; www.elsevier.com/locate/phytochem, NaN, 2003)[more][less]
Abstract: The twigs of Dorstenia barteri var. subtriangularis yielded three diprenylated chalcones: ( )-3-(3,3-dimethylallyl)-50-(2-hydroxy-3- methylbut-3-enyl)-4,20,40-trihydroxychalcone, (+)-3-(3,3-dimethylallyl)-40,50-[2000-(1-hydroxy-1-methylethyl)-dihydrofurano]-4,20- dihydroxychalcone and 3,4-(600,600-dimethyldihydropyrano)-40,50-[2000,-(1-hydroxy-1-methylethyl)-dihydrofurano]-20-hydroxychalcone for which the names bartericins A, B and C, respectively, are proposed. Stipulin, b-sitosterol and its 3-b-D-glucopyranosyl derivative were also isolated. The structures of these secondary metabolites were determined on the basis of spectroscopic analysis, especially, NMR spectra in conjunction with 2D experiments, COSY, HMQC and HMBC. The structural relationship of bartericins B and C was further established by the chemical cyclization of one to the other. URI: http://hdl.handle.net/10311/258 Files in this item: 2
Diprenylated chalcones and other.pdf (3.479Mb)license.txt (1.998Kb) -
Ngadjui, B.T.; Abegaz, B.M.; Keumedjio, F.; Folefoc, G.N.; Kapchec, G.W.F. (Elsevier Science Ltd. www.elsevier.com/locate/phytochem, NaN, 2002)[more][less]
Abstract: Three clerodane diterpenoids, crotozambefurans A, B and C were isolated from the stem bark of Croton zambesicus together with the known clerodane crotocorylifuran and two trachylobanes: 7b-acetoxytrachyloban-18-oic acid and trachyloban-7b, 18-diol. Betulinol, lupeol, sitosterol and its 3b-glucopyranosyl derivative were also obtained. The structures of crotozambefurans A, B and C were determined, respectively, as: 15,16-epoxy-1,3,13(16),14-clerodatetraen-20,12-olide-18,19-dioic acid dimethylester, 15,16-epoxy- 1,3,13(16),14-clerodatetraen-18,19,20-trioic acid trimethylester and 15,16-epoxy-3,13(16),14-clerodatrien-19,1a:20,12-diolide-18-oic acid methylester, using spectroscopic analysis, especially, NMR spectra in conjunction with 2D experiments, COSY, HSQC, HMBC and TOCSY. URI: http://hdl.handle.net/10311/251 Files in this item: 2
Diterpenoids from the stem bark.pdf (2.493Mb)license.txt (1.998Kb) -
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) -
Chaturvedi, P.; George, S.; Milinganyo, M.; Tripathi, Y.B. (John Wiley & Sons, Ltd, http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1099-1573, NaN, 2004)[more][less]
Abstract: In this study, the methanol extract of Momordica charantia fruit extract was administered to diabetic rats to assess the long term effect of the extract on the lipid profile and the oral glucose tolerance test. Treatment for 30 days showed a significant decrease in triglyceride, low density lipoprotein and a significant increase in high density lipoprotein level. A significant effect on oral glucose tolerance was also noted. Chronic administration showed an improvement in the oral glucose tolerance curve. The effect was more pronounced when the test was done in rats fed the extract on the day of the test compared with tests done in rats which were not fed the extract on the same day. URI: http://hdl.handle.net/10311/1017 Files in this item: 1
Chaturvedi_PR_2004.pdf (258.2Kb) -
Moseki, B.; Dintwe, K. (Global Science Books, http://www.globalsciencebooks.info/, NaN, 2011)[more][less]
Abstract: The effects of water stress on the photosynthetic characteristics of two locally-cultivated sorghum cultivars (‘Segaolane’ and ‘Town’) were investigated over a period of weeks. Water stress was imposed on 1-week-old plants by withholding water. Measurements of chlorophyll fluorescence were used to determine changes in the efficiency of light utilization for electron transport, the occurrence of photoinhibition of photosystem II photochemistry on the sorghum cultivars. Drought treatment significantly decreased leaf area in all species, an important factor in drought-induced decreases in photosynthetic productivity. Water-stressed ‘Town’ exhibited a decrease in maximum photochemical efficiency of PSII (estimated from dark-adapted Fν⁄Fм ratio) with increasing period of withholding water. Light-adapted Fν’⁄Fм’ estimated the efficiency of excitation energy transfer to open PSII centres. Water-stressed ‘Town’ displayed a decrease in the efficiency of excitation energy transfer to open PSII reaction centres throughout the entire study period. The quantum yield of PSII electron transport (фPSII), which represents electron flow beyond PSII, decreased markedly in water-stressed ‘Town’ compared with that of water-stressed ‘Segaolane’. These initial findings indicate that ‘Town’ is more prone to photoinhibition than ‘Segaolane’. URI: http://hdl.handle.net/10311/962 Files in this item: 1
Moseki_AJPSB_2011.pdf (96.03Kb) -
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) -
Chaturvedi, P.; Segale, M. (Academic Journals http://www.academicjournals.org/SRE/index.htm, NaN, 2007)[more][less]
Abstract: Four types of extracts were prepared from Melia azedarach fruits. These were methanol extract and three types of water decoctions; urine treated water decoction (UE), milk treated water decoction (ME) and plain water decoction (WE). Different doses of these four extracts were tried in normal rats to estimate the hypoglycemic activity of these extracts against glucose induced hyperglycemia. Most potent doses of all the extracts were assessed for their effects on lipid peroxidation, toxic effects on liver and reduced glutathione which is considered as first line of defense against free radicals in normal rats after 10 days of oral administration. All the extracts were found to posses hypoglycemic properties. Methanol extract showed toxic effects on the liver as indicated by high activities of Serum glutamate oxaloacetate (SGOT) and serum glutamate pyruvate tranasaminase (SGPT). It also indicated high rate of lipid peroxidation and depleted reduced glutathione levels of plasma. On the other hand three water decoctions showed very low activities of SGOT, SGPT, very low rates of lipid peroxidation and high levels of reduced glutathione. Extract prepared by the Ayurvedic method reduce blood glucose in glucose induced hyperglycemic rats and impart no toxicity. URI: http://hdl.handle.net/10311/181 Files in this item: 2
Effects of different types of water.pdf (836.9Kb)license.txt (1.998Kb) -
Mpoloka, S.W. (Academic Journals. http://www.academicjournals.org/AJB, NaN, 2008)[more][less]
Abstract: Over the past few decades, there has been a depletion of the stratospheric ozone layer due to emissions of halogen-containing compounds of anthropogenic origin. This has resulted in a concomitant increase in solar ultraviolet-B radiation. High levels of UV-B radiation are responsible for multiple biologically harmful effects in both plants and animals. In plants, these effects include DNA damage, which often causes heritable mutations affecting various physiological processes, including the photosynthetic apparatus, protein destruction and signal transduction via UV-B photoreceptors. High UV-B levels introduce a number of different lesions, predominantly cyclobutane pyrimidine dimmers (CPDs) and pyrimidine (6-4) pyrimidinone products [(6-4) PPs] in the genome. These could adversely affect plant growth, development and morphology, especially the productivity of sensitive crop species. This paper reviews the genetic effects of long-term UV-B exposure in plants. URI: http://hdl.handle.net/10311/491 Files in this item: 1
Effects of prolonged.pdf (2.345Mb) -
Siele, M.P.; Mubyana-John, T.; Bonyongo, M.C. (Global Science Books http://www.globalsciencebooks.com/index.php?page=shop.product_details&category_id=1&flypage=shop.flypage&product_id=5&option=com_virtuemart&Itemid=56&vmcchk=1&Itemid=56, NaN, 2008)[more][less]
Abstract: Soil cover influences soil biological and chemical processes in various ways. The effects of soil cover (bare soil without litter, litter cover, Mopane tree canopy and grass cover) on soil respiration and microbial population at four sites in the Mopane woodland of north western Botswana were investigated. Soil respiration rates were measured using an infrared gas analyzer. Nitrifying bacterial populations were quantified by MPN on ammonium and nitrite calcium carbonate media, oligotrophs on 1% nutrient agar, actinomycetes on starch casein agar, bacteriovorous protozoans by MPN on sodium chloride agar baited with Enterobacter, and fungal biomass carbon using buried slides were also determined. Soil respiration in different habitats was significantly influenced by type of cover, diurnal temperature variations and soil moisture. Soils under cover showed significantly higher soil respiration than the bare soils. Autochthonous bacterial populations in the Mopane woodland soils consisted mostly of oligotrophs which varied insignificantly between seasons. Fungi were the most dominant microorganisms in all the Mopane woodland soils, with biomass of 162.05 to 282.14 μg C/g soil in the wet season and 11.84 to 44.16 μg C/g soil in the dry season. Microscopic observation of buried slides revealed that fungi play a vital role in holding soil particles together in these soils. The results showed a strong positive relationship between changes in fungal biomass and fluctuation of soil respiration. However, no clear correlation was observed between the variation of soil respiration and other microbial populations (oligotrophic bacteria, actinomycetes, and nitrifying bacteria). Overall these results indicate that in soils under Mopane tree canopy, fungi contribute significantly to soil structure and soil respiration. Other microbial populations consist mostly of oligotrophs which show minimal seasonal variations. Soil moisture significantly influences seasonal fluctuation in soil respiration. URI: http://hdl.handle.net/10311/292 Files in this item: 1
The Effects of Soil Cover.pdf (6.625Mb) -
Toteng, E.N. (Routledge http://dx.doi.org/10.1080/02508060802475415, NaN, 2008)[more][less]
Abstract: This article examines the adverse effects of a fragmented water management framework and the role of domestic water users on water conservation in Gaborone, the rapidly growing capital city of Botswana. There was a major drought in Botswana in 2004, which recurred in 2007. The drought seriously affected water availability in Gaborone, re-igniting the water conservation debate. Most urban households prior to 2004 did not practise water conservation, except in cases of enforced temporary measures, such as water restrictions and increased water tariffs imposed by the Water Utilities Corporation. From secondary evidence, the situation had not changed much in 2007. URI: http://hdl.handle.net/10311/363 Files in this item: 1
Toteng_WI_2008.pdf (851.6Kb) -
Mazimba, O.; Masesane, I.B.; Majinda, R.R. (Elsevier Science Ltd, http://www.elsevier.com/locate/tetlet, NaN, 2011)[more][less]
Abstract: An efficient total synthesis of flavans from the reactions of salicylaldehyde and acetophenone derivatives is reported. The synthesis involves preparation of chalcones through an aldol reaction followed by reduction of both the double bond and the ketone using NaBH4 and an acetic acid mediated cyclization. Methoxy groups on the aromatic rings did not affect significantly the yields of the procedure. URI: http://hdl.handle.net/10311/1027 Files in this item: 1
Mazimba_TL_2011.pdf (204.0Kb) -
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)