Browsing Faculty of Science by Title
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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) -
Goodwin, J.W.; Hughes, R.W.; Kwaambwa, H.M.; Reynolds, P.A. (Elseview Science B.V. www.elsevier.nl/locate/colsurfa, NaN, 2000)[more][less]
Abstract: A series of well characterised cis-polyisoprene polymers have been added to dispersions of PHS coated PMMA particles in dodecane. At a molecular weight of 8000 g mol−1 and above, these systems showed phase separation at low particle volume fractions and above a critical polymer concentration. The rate of separation has been shown to be influenced by the viscosity of the polymer. At high polymer and particle volume fractions long lived metastable phases occurred. Above a critical concentration these were viscoelastic indicating an appreciable change in diffusion dynamics with two relaxation processes present. A significant Bingham yield stress was also observed. The Asakura Oosawa potential was not able to describe the observed rheological properties. At a molecular weight of 1000 g mol−1 no phase separation was observed. At high particle concentrations the yield stress was found to reduce with the addition of polymer. This was due to the polymer acting as a ‘solvent’ and penetrating the stabilising layer on the particles. URI: http://hdl.handle.net/10311/329 Files in this item: 1
Phase separation behaviour.pdf (2.723Mb) -
Munkombwe N.M. (Elsevier Ltd. www.elsevier.com/locate/phytochem, NaN, 2003)[more][less]
Abstract: Two phenylpropanoid glucosides, 2-O-b-d-glucosyloxy-4-methoxybenzenepropanoic acid and its methyl ester, together with syringin and adicardin were isolated from the stem of Gnidia polycephala and characterized by physical and spectroscopic data. URI: http://hdl.handle.net/10311/275 Files in this item: 2
Phenylpropanoid glycosides.pdf (2.288Mb)Phenylpropanoid glycosides of Gnidia.pdf (155.6Kb) -
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) -
Meck, M.L.; Atlhopheng, J.; Masamba, W.R.L.; Ringrose, S. (Elsevier Science Ltd, http://www.elsevier.com/locate/pce, NaN, 2010)[more][less]
Abstract: The study set out to determine the weathering and dissolution of metal hosting minerals at Dorowa for purposes of deducing pollution potential to the nearby Save River. Phosphate rock is mined at Dorowa for the production of phosphate fertilizer. The major minerals found in the ring complex are feldspars, pyroxenes, apatite, magnetite and calcite. Chemical analysis established that the rocks are associated with metals that include copper, lead, zinc, cobalt, nickel, tin and cadmium. Among the many minerals present apatite and calcite host metals more than the other minerals due to their crystal structure. This study investigated the weathering and dissolution of these two minerals. Both apatite and calcite dissolve in natural environmental conditions prevalent at Dorowa. From the analysis the study concludes that the potential availability of metals trapped in the calcite and apatite structures is high. The understanding of weathering and dissolution of metal hosting minerals is important in predicting quality of water around the study area, because most villagers use the Save River as their primary drinking water source. URI: http://hdl.handle.net/10311/1021 Files in this item: 1
Atlhopheng_PCE_2010.pdf (758.1Kb) -
Gwebu, T.D. (Springer http://www.springerlink.com/index/3NU5AFH2F999FM9P.pdf -, NaN, 2003)[more][less]
Abstract: Based on government and other relevant documentation, this paper explores the conceptual linkage between population, development, and waste management in Botswana and the implications of this relationship for global climate change. Population is increasing, albeit at a decreasing rate. Spatially, the population is becoming more and more concentrated as the rates and level of urbanization increase. Economic growth has remained consistently high. The combined effect of population dynamics and economic development are having a noticeable imprint on the environment in the form of increased waste generation. Poor waste management poses a real threat to environmental sustainability in general and climate change in particular because of inadequate technology, weak institutional mechanisms to enforce regulations, and low levels of sensitization among the public to deal with the problem. Mitigation measures are suggested to minimize the negative effects of waste management on climate change. URI: http://hdl.handle.net/10311/478 Files in this item: 1
Gwebu_EM_2003.pdf (459.8Kb) -
Kapche, G.D.W.F.; Fozing, C.D.; Donfack, J.H.; Fotso, G.W.; Amadou, D.; Tchana, A.N.; Bezabih, M.; Moundipa, P F; Ngadjui, B.N.; Abegaz, B.M. (Elsevier Ltd. www.elsevier.com/locate/phytochem, NaN, 2008)[more][less]
Abstract: Five prenylated arylbenzofurans, moracins Q–U, were isolated from Morus mesozygia (Moraceae). Their structures were elucidated on the basis of spectroscopic evidence. Along with these compounds, 3b-acetoxyurs- 12-en-11-one, marsformoxide, moracin C, moracin M, moracin K, artocarpesin, cycloartocarpesin, morachalcone A were also isolated. Four of the five compounds, (moracins R–U) displayed potent antioxidant activity. URI: http://hdl.handle.net/10311/315 Files in this item: 1
Prenylated arylbenzofuran.pdf (3.853Mb) -
Ngadjui, B.; Watchueng, J.; Keumedjio, F.; Ngameni, B.; Simo, I.; Abegaz, B. (Elsevier Ltd. www.elsevier.com/locate/phytochem, NaN, 2004)[more][less]
Abstract: The twigs of Dorstenia angusticornis and Dorstenia barteri var. subtriangularis yielded 16 compounds. Two novel diprenylated chalcones: 3,50-di-(2-hydroxy-3-methylbut-3-enyl)-4,20,40-trihydroxychalcone, 3, 4-(2,2-dimethylpyrano)-30-(2-hydroxy-3-methylbut- 3-enyl)-20,40-dihydroxychalcone and the known stipulin were isolated from both species. 3-(2-Hydroxy-3-methylbut-3-enyl)- 50-(3,3-dimethylallyl)-4,20,40-trihydroxychalcone and the known compounds: 4-hydroxylonchocarpin, kanzonol B, bartericins A, B, C and 30-(2-hydroxy -3-methylbut-3-enyl)-4,20,40-trihydroxychalcone were isolated from D. barteri while the known compounds: gancaonin Q, paratocarpins C, F, and lupeol were obtained from Dorstenia angusticornis. b-Sitosterol and its b-D-glucopyranoside were isolated from both species. Structures of these secondary metabolites were established using spectroscopic analysis, especially, NMR spectra in conjunction with 2D experiments, COSY, HMQC and HMBC. URI: http://hdl.handle.net/10311/253 Files in this item: 2
license.txt (1.998Kb)Prenylated chalcones, flavone.pdf (3.563Mb) -
Simo, I.K.; Ngadjui, B.T.; Abegaz, B.M. (Elsevier Ltd. www.elsevier.com/locate/biochemsyseco, June 18, 2005)[more][less]
Abstract: Dorstenia (Moraceae) is a mainly tropical genus of some 170 species (Mabberley, 1987). There are 23 species in Cameroon where a decoction of the leaves is administered for the treatment of cough, headache and stomach pain (Bouquet, 1969). The genus is made up largely of herbaceous perennials with succulent and non-succulent scrambling rhizomes (Berg et al., 1989). The twigs of Dorstenia angusticornis were collected in February 2002 from Kumba South West Province of Cameroon. Voucher specimen (No 28165/sfcam) is deposited at the National Herbarium Yaounde, Cameroon. URI: http://hdl.handle.net/10311/255 Files in this item: 1
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Abegaz, B.M.; Ngadjui, B.T.; Folefoc, G.N.; Fotso, S.; Ambassa, P.; Bezabih, M.; Dongo, E.; Rise, F.; Petersen, D. (Elsevier Ltd. www.elsevier.com/locate/phytochem, NaN, 2003)[more][less]
Abstract: A monoprenylated flavan and two monoterpenoid substituted furanocoumarins were isolated from the twigs of Dorstenia elliptica along with 3-(3,3-dimethylallyl)-4,20,40-trihydroxylchalcone, psoralen, bergapten, O-[3-(2,2-dimethyl-3-oxo-2H-furan-5-yl)butyl] bergaptol, b-sitosterol and its b-d-glucopyranoside. The structure of the flavan was determined as 6(1,1-dimethylallyl)-7,40- dihydroxylflavan and the monoterpenoid substituted furanocoumarins were assigned as O-[3-(2,2-dimethyl-3-oxo-2H-furan-5-yl)-3- hydroxybutyl]-bergaptol and O-[2-(5-hydroxy-2,6,6-trimethyl-3-oxo-2H-pyran-2-yl)ethyl]bergaptol, respectively, using spectroscopic analysis, especially, 2D NMR spectra. URI: http://hdl.handle.net/10311/286 Files in this item: 1
Prenylated flavonoids,.pdf (3.692Mb) -
Morobe, I.C.; Obi, C.L.; Nyila, M.A.; Gashe, B.A.; Matsheka, M.I. (Academic Journals, http://www.academicjournals.org/AJB, NaN, 2009)[more][less]
Abstract: Listeria monocytogenes is known to cause epidemic and sporadic cases of listeriosis. The present study investigated the occurrence, antibiograms and molecular serotypes of the organism in various retail outlets in Gaborone, Botswana. Food samples were obtained randomly from selected supermarkets and street vendors in 5 geographical areas of Gaborone from May, 2007 to September 2007. L. monocytogenes was isolated and positively identified by using morphological and biochemical tests. From a total of 1324 food samples tested 57(4.3 %) were positive for L. monocytogenes. Out of the 57 isolates of L. monocytogenes 7 (12.3%), 3 (5.3%), 0 (0%), 27 (47.4%) and 20 (35.1%) were isolated from cheese, raw milk, meat (biltong), frozen cabbage and salad (coleslaw), respectively. From the 5 geographical areas selected for sampling in this study, Gaborone South recorded the highest number 19 (33.3%) of L. monocytogenes isolates while Gaborone West recorded the least, 7 (12.3%). The findings in this study reveal the presence of L. monocytogenes serotypes 1/2a and 1/2b in ready to eat food and highlight the need for education and training programmes in food safety in Gaborone, Botswana. URI: http://hdl.handle.net/10311/996 Files in this item: 1
Morobe_AJB_2009.pdf (86.64Kb) -
Chaturvedi, P.; George, S.; John, A. (British Journal of Biomedical Science. http://www.ibms.org/index.cfm?method=publications.british_journal, NaN, 2007)[more][less]
Abstract: In the present study, preventive and protective effects of Ocimum gratissimum in ethanol-induced hepatotoxicity are assessed in albino rats. A methanol extract of O. gratissimum leaves is prepared, with a yield of 3.5% (w/w) of the dry weight of leaves. Graded doses of the extract (10, 20, 40 and 80 mg/kg body weight), together with ethanol (5 gm/kg body weight) are administered orally to experimental groups for 30 days. Normal control rats receive distilled water only, while rats in an alcohol control group (AC) receive ethanol only for 30 days. O. gratissimum reduced the level of thiobarbituric acid reactive substance in all experimental groups (E1â E4). Alanine transaminase and aspartate transaminase levels fell in all experimental groups (E1â E4), but this reduction was significant only in groups E3 and E4 (P<0.05), indicating inhibition of lipid peroxidation by free radicals generated after ethanol metabolism. Levels of antioxidants also increased. Ascorbic acid and glutathione levels increased in all experimental groups (E1â E4; P<0.05 and P<0.01, respectively). A significant increase in catalase (P<0.05) was noted only in group E4, although an upward trend was noted in all experimental groups. This study shows that O. gratissimum prevents free radical damage to the liver and thus protects the organ from oxidative stress. URI: http://hdl.handle.net/10311/309 Files in this item: 1
Preventive and pro.pdf (2.493Mb) -
Mbaiwa, J.E.; Toteng, E.N.; Moswete, N. (Taylor & Francis (Routledge), http://www.informaworld.com/smpp/title~content=t713413745, December NaN, 2007)[more][less]
Abstract: This paper draws on the tourism system framework to examine the problems and prospects of urban tourism in Gaborone and Maun, Botswana. These are young centres that have a growing number of tourist attractions, facilities and services that could promote urban tourism. The findings of this study, based on both secondary and primary data sources, indicate that urban tourism in Botswana is relatively undeveloped because there is no substantial domestic market, tourist attractions in urban centres are poorly developed and marketed, and city development plans and the national tourism policy are not integrated. The study concludes that, for tourism to become a viable economic sector in the country, urban tourism should be integrated into Botswana’s tourism policy and city planning. URI: http://hdl.handle.net/10311/1020 Files in this item: 1
Mbaiwa_DSA_2007.pdf (1.060Mb) -
Abegaz, B.M. (Chemical Society of Ethiopia. http://www.aau.edu.et/faculties/sc/CSE/home.html, NaN, 1996)[more][less]
URI: http://hdl.handle.net/10311/345 Files in this item: 1
progress in the chemistry of.pdf (922.3Kb) -
Ketshajwang, K.K.; Holmback, J.; Yeboah, S.O. (AOCS Press. http://www.springerlink.com/content/120382/, NaN, 1998)[more][less]
Abstract: Seed oils were extracted with n-hexane from three edible Leguminosae seeds: Tylosema esculentum, Xanthocercis zambesiaca, and Bauhinia petersiana, giving yields of 48.2, 17.6, and 20.8% (w/w), respectively. Some physical and chemical parameters were determined to ascertain the general characteristics of the oils. The saponification and iodine values indicated that all three oil samples could be classified among the olive group of oils. This inference was supported by the results of the detailed fatty acid composition of the oils as determined by capillary gas chromatography. The ratio of total unsaturated to total saturated fatty acids in all three oil samples was approximately 70:30, with either oleic or linoleic acid being the dominant fatty acid. These results were in agreement with a proton nuclear magnetic resonance analysis of the fatty acid classes in the seed oils. Thus, the analysis served to justify the use of the three Leguminosae seed oils in food preparations. The work has further indicated that, with their attractive properties, the seed oils from T. esculentum, X. zambesiaca, and B. petersiana are good candidates for further studies to evaluate their future commercial prospects in the Southern African region. URI: http://hdl.handle.net/10311/304 Files in this item: 1
quality and compositional.pdf (1.683Mb)