Browsing Faculty of Science by Title
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Abegaz, B.M.; Bezabih, M.; Msuta, T.; Brun, R.; Menche, D.; Muhlbacher, J.; Bringmann, G. (American Chemical Society. http://pubs.acs.org/jnp/, NaN, 2002)[more][less]
Abstract: The novel phenylanthraquinones 4'-O-demethylknipholone-4'-O-β-D-glucopyranoside (2) and gaboroquinones A (3) and B (4) were isolated from the African medicinal plant Bulbine frutescens. Biaryl 2 represents the first phenylanthraquinone glucoside, while 3 and 4 are the first side-chain-hydroxylated phenylanthraquinones. Their constitutions were determined by spectroscopic analysis, in particular by HMBC, HMQC, and ROESY NMR investigations, and by chemical transformations. The axial configurations were elucidated chemically, by deglucosylation of 2 and by side-chain deoxygenation of 3 and 4 to give the known phenylanthraquinones 4'-O-demethylknipholone (5), isoknipholone (6), and knipholone (1), respectively, and chiroptically, by CD investigations. Compounds 2, 3, and 4 showed moderate to good antiplasmodial and antitrypanosomal activities in vitro. URI: http://hdl.handle.net/10311/346 Files in this item: 1
Gaboroquinones.pdf (407.3Kb) -
Motshegwe, S.M.; Holmback, J.; Yeboah, S.O. (AOCS Press. http://www.springerlink.com/content/0003-021X, NaN, 1998)[more][less]
Abstract: A preliminary investigation of the bulk properties of the oil from the edible mophane caterpillar (phane), Imbrasia belina, showed a significant difference in the iodine values of the oils from mature and young phane. Detailed analysis of the fatty acid composition of the two oil samples was thus carried out by capillary gas chromatography (GC) and complemented with 1H and 13C nuclear magnetic resonance (NMR) studies to investigate the degree of unstauration in the two oil samples. While these studies showed that the oil samples from the mature and young mophane caterpillar were much the same in fatty acid composition, the data revealed a significant divergence from a literature report on phane oil. This earlier report puts the ratio of total saturated to total unsaturated fatty acids at approximately 1:1 (48.2:48.8, in percentages) and estimates the fatty acid composition for the major fatty acids as 16:0 (31.9%), 18:0 (15.2%), 18:1 (20.4%), 18:2 (9.9%), and 18:3 (19%). The data collected from the present work, however, showed the fatty acid composition for total saturated and total unsaturated fatty acids to be 40.5 and 57.0%, respectively. This work estimated the fatty acid composition for the major fatty acids as 16:0 (27.2%), 18:0 (12.3%), 18:1 (16.1%), 18.2 (10.7%), and 18:3 (29.0%). Thus, linolenic acid was the most abundant fatty acid in the phane oil. The GC results of the present analysis were largely corroborated by studies of the composition of fatty acid classes in the phane oil estimated from integrals of 1H and 13C NMR signals. Oils from other edible Lepidoptera larvae are also known to be much richer in unsaturated than saturated fatty acids. URI: http://hdl.handle.net/10311/307 Files in this item: 1
General properties.pdf (1.906Mb) -
Cailteux, J.L.H.; Kampunzu, A.B.; Lerouge, C.; Kaputo, A.K.; Milesi, J.P. (Elsevier www.elsevier.com/locate/jafrearsci, NaN, 2005)[more][less]
Abstract: The Neoproterozoic central African Copperbelt is one of the greatest sediment-hosted stratiform Cu–Co provinces in the world, totalling 140 Mt copper and 6 Mt cobalt and including several world-class deposits (P10 Mt copper). The origin of Cu–Co mineralisation in this province remains speculative, with the debate centred around syngenetic–diagenetic and hydrothermal-diagenetic hypotheses. The regional distribution of metals indicates that most of the cobalt-rich copper deposits are hosted in dolomites and dolomitic shales forming allochthonous units exposed in Congo and known as Congolese facies of the Katangan sedimentary succession (average Co:Cu = 1:13). The highest Co:Cu ratio (up to 3:1) occurs in ore deposits located along the southern structural block of the Lufilian Arc. The predominantly siliciclastic Zambian facies, exposed in Zambia and in SE Congo, forms para-autochthonous sedimentary units hosting ore deposits characterized by lower a Co:Cu ratio (average 1:57). Transitional lithofacies in Zambia (e.g. Baluba, Mindola) and in Congo (e.g. Lubembe) indicate a gradual transition in the Katangan basin during the deposition of laterally correlative clastic and carbonate sedimentary rocks exposed in Zambia and in Congo, and are marked by Co:Cu ratios in the range 1:15. The main Cu–Co orebodies occur at the base of the Mines/Musoshi Subgroup, which is characterized by evaporitic intertidal–supratidal sedimentary rocks. All additional lenticular orebodies known in the upper part of the Mines/Musoshi Subgroup are hosted in similar sedimentary rocks, suggesting highly favourable conditions for the ore genesis in particular sedimentary environments. Prelithification sedimentary structures affecting disseminated sulphides indicate that metals were deposited before compaction and consolidation of the host sediment. The ore parageneses indicate several generations of sulphides marking syngenetic, early diagenetic and late diagenetic processes. Sulphur isotopic data on sulphides suggest the derivation of sulphur essentially from the bacterial reduction of seawater sulphates. The mineralizing brines were generated from sea water in sabkhas or hypersaline lagoons during the deposition of the host rocks. Changes of Eh–pH and salinity probably were critical for concentrating copper–cobalt and nickel mineralisation. Compressional tectonic and related metamorphic processes and supergene enrichment have played variable roles in the remobilisation and upgrading of the primary mineralisation. There is no evidence to support models assuming that metals originated from: (1) Katangan igneous rocks and related hydrothermal processes or; (2) leaching of red beds underlying the orebodies. The metal sources are pre-Katangan continental rocks, especially the Palaeoproterozoic low-grade porphyry copper deposits known in the Bangweulu block and subsidiary Cu–Co–Ni deposits/occurrences in the Archaean rocks of the Zimbabwe craton. These two sources contain low grade ore deposits portraying the peculiar metal association (Cu, Co, Ni, U, Cr, Au, Ag, PGE) recorded in the Katangan sediment-hosted ore deposits. Metals were transported into the basin dissolved in water. The stratiform deposits of Congo and Zambia display features indicating that syngenetic and early diagenetic processes controlled the formation of the Neoproterozoic Copperbelt of central Africa. URI: http://hdl.handle.net/10311/387 Files in this item: 1
Kampunzu2005GenesisSediment.pdf (2.837Mb) -
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) -
Mbongwe, B.; Mmereki, B.T.; Magashula, A. (Elsevier Ltd. http://www.elsevier.com/wps/find/journaldescription.cws_home/404/description#description, March 12, 2007)[more][less]
Abstract: Healthcare waste management continues to present an array of challenges for developing countries, and Botswana is no exception. The possible impact of healthcare waste on public health and the environment has received a lot of attention such that Waste Management dedicated a special issue to the management of healthcare waste (Healthcare Wastes Management, 2005. Waste Management 25(6) 567-665). As the demand for more healthcare facilities increases, there is also an increase on waste generation from these facilities. This situation requires an organised system of healthcare waste management to curb public health risks as well as occupational hazards among healthcare workers as a result of poor waste management. This paper reviews current waste management practices at the healthcare facility level and proposes possible options for improvement in Botswana. URI: http://hdl.handle.net/10311/223 Files in this item: 2
license.txt (1.998Kb) -
Chaturvedi, P.; Pipedi-Tshekiso, M.; Moseki, B.; Kwape, P.E. (Academic Journals, http://www.academicjournals.org/SRE, NaN, 2011)[more][less]
Abstract: Bark of Bauhinia purpurea tree was collected and both the water and methanol extracts were prepared. Both extracts were tested for free radical scavenging activities and phenol content. Water extract was then tested for its protective potentials against alcohol induced toxicity. For this experiment, twenty rats were randomly divided into four groups, alcohol control group, normal control and two experimental groups. The rats in alcohol control group received alcohol (5 g/kg), rats in normal control were given water. Rats in two experimental groups were administered two doses of methanol extract (50 and 100 mg/kg respectively) plus alcohol (5 g/kg) for 30 days. At the end of the experiment, rats were killed after ether anesthesia. Liver and blood samples were collected for biochemical measurements. Parameters measured were thiobarbituric acid reactive substances, serum glutamate oxaloacetate transaminase, serum glutamate pyruvate transaminase, reduced glutathione, glutathione peroxidase, superoxide dismutase, catalase and ascorbic acid. Results showed that both methanol and water extracts scavenged free radicals equivalent to gallic acid scavenging and were found rich in total phenol content. Results of in vivo experiments showed that the water extract inhibited lipid peroxidation, protected the experimental animals from hepatic toxicity and maintained the levels of antioxidants in dose dependent manner. URI: http://hdl.handle.net/10311/1018 Files in this item: 1
Chaturvedi_SRE_2011.pdf (207.7Kb) -
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) -
Mutanyatta, J.; Matapa, B.; Shushu, D.; Abegaz, B. (Elsevier Ltd. www.elsevier.com/locate/phytochem, NaN, 2002)[more][less]
Abstract: Eleven homoisoflavonoids and two xanthones were isolated and characterized from the bulbs of Ledebouria graminifolia. Five of the homoisoflavonoids are new compounds and were identified as: 5-hydroxy-7-methoxy-3-(40-hydroxybenzyl)-4-chromanone, 5-hydroxy-6,7-dimethoxy-3-(40-hydroxybenzyl)-4-chromanone, 5,7,8-trimethoxy-3-(40-hydroxybenzyl)-4-chromanone, 5-hydroxy- 30,40,7-trimethoxyspiro{2H-1-benzopyran-70-bicyclo[4.2.0]octa[1,3,5]-trien}-4-one, 5,7-dihydroxy-30,40-dimethoxyspiro{2H-1-benzopyran- 70-bicyclo[4.2.0]octa[1,3,5]-trien}-4-one. Structures were elucidated by extensive 1D, and 2D NMR spectroscopy and HRMS. A method for tissue culture was developed and the bulbs of mature plants were found to contain all the compounds isolated from the wild specimens of L. graminifolia. URI: http://hdl.handle.net/10311/249 Files in this item: 2
license.txt (1.998Kb) -
Gatsinzi, J-B. (International Press; http://www.intlpress.com/HHA/, NaN, 2004)[more][less]
Abstract: In this paper, we show that the rational homotopy Lie algebra of classifying spaces for certain types of hyperbolic coformal 2-cones is not nilpotent. Description: Copyright of International Press. http://www.intlpress.com/ URI: http://hdl.handle.net/10311/183 Files in this item: 2
license.txt (1.998Kb)Microsoft Word - Gatsinzi 2004.pdf (611.5Kb) -
Onibere, E.A.; Morgan, S.; Busang, E.M.; Mpoeleng, D. (Elsevier Science Ltd, www.elsevier.com/locate/intcom, NaN, 2001)[more][less]
Abstract: This paper reports on research carried out to determine whether a localised interface is preferred by users in a multi-cultural and multi-lingual country where a non-local language is nationally used,. We attempted to discover whether local symbols are more acceptable to users as icons and also whether the current phrases used in menus and icon descriptions are clearly understood by the various communities. A survey was conducted nation-wide among computer end-users in Botswana. The results indicate an overwhelming desire from users for a localised interface. However, there appears to be little need for localised icons and no agreement as to which language to use for text-based interfaces. URI: http://hdl.handle.net/10311/887 Files in this item: 1
Mpoeleng_IC_2001.pdf (1.247Mb) -
Nkoane, B.B.M.; Sawula, G.M.; Wibetoe, G.; Lund, W. (Elsevier www.elsevier.com/locate/jgeoexp, NaN, 2005)[more][less]
Abstract: Plant species that accumulate high levels of metals in proportion to the metal content in the soil are of considerable interest in biogeochemical and biogeobotanical prospecting. This study was aimed at investigating copper and nickel accumulation in the plants Helichrysum candolleanum and Blepharis diversispina, to assess their potential use as mineral indicators in biogeochemical prospecting. Soils and plants were collected from copper–nickel mineralised areas in Botswana. Analyses of the soils and the respective plant parts (roots, stem, leaves and flowers) were carried out using ultrasonic slurry sampling electrothermal atomic absorption spectrometry (ETAAS), which allowed rapid determination of copper and nickel in small amounts of the samples. The metal concentration in the soil was in the range c40 Ag/g–4% (w/w) for Cu and c60 Ag/g–0.3% (w/w) for Ni. The concentration ranges of the elements in the plant parts were c6 Ag/g–0.2% Cu and c3–210 Ag/g Ni. At high soil metal content (greater than 2.5% (w/w) Cu and 0.1% (w/w) Ni), high levels of both nickel and copper were found in the shoots (leaves and flowers) of H. candolleanum. Concentrations as high as 0.2% (w/w) Cu were found in the leaves and flowers of H. candolleanum, indicating hyperaccumulation for this plant. For B. diversispina, the metal concentrations did not exceed 100 Ag/ g for any plant part, for both metals. Both plant species tolerate high concentrations of metals and should therefore be categorized as metallophytes. In order to evaluate metal translocation from the soil to the shoots, metal leaf transfer coefficients (ratio of metal concentration in the leaf to metal concentration in the soil) were calculated. Our data suggest that the two plant species have different metal uptake and transport mechanisms, which needs to be investigated further. The present work also suggests that H. candolleanum may be used as a copper/nickel indicator plant in biogeochemical or biogeobotanical prospecting. URI: http://hdl.handle.net/10311/527 Files in this item: 1
NKOANE2005Indicatorplants.pdf (1.835Mb) -
Ali, M.M.; Kaelo, P. (Elsevier Ltd. www.elevier.com/locate/amc, NaN, 2008)[more][less]
Abstract: Particle swarm optimization algorithm has recently gained much attention in the global optimization research community. As a result, a few variants of the algorithm have been suggested. In this paper, we study the efficiency and robustness of a number of particle swarm optimization algorithms and identify the cause for their slow convergence. We then propose some modifications in the position update rule of particle swarm optimization algorithm in order to make the convergence faster. These modifications result in two new versions of the particle swarm optimization algorithm. A numerical study is carried out using a set of 54 test problems some of which are inspired by practical applications. Results show that the new algorithms are much more robust and efficient than some existing particle swarm optimization algorithms. A comparison of the new algorithms with the differential evolution algorithm is also made. URI: http://hdl.handle.net/10311/178 Files in this item: 2
Ali_Kaelo_AMC_2008.pdf (3.814Mb)license.txt (1.998Kb) -
Ogwu, F.J.; Talib, M.; Aderounmu, G.A. (Science Publications, http://www.scipub.org/scipub/c4p.php?j_id=JCS, NaN, 2007)[more][less]
Abstract: This study presents a technique for improving the quality of service (QoS) guarantee in an ATM network. In the proposed model, it was assumed that high priority traffic have been allocated a switch resource to guarantee a given QoS and low priority cells are allowed to enter the buffer, to improve the exploitation of reserved resources. The proposed technique was backed up with an exact analytical model for evaluating the cell loss probability of high and low priority cells. The performance of the proposed model was evaluated using C++ programming language. The results of the simulation shows that the loss probability of both high and low cells reduces as the buffer capacity increase and that the performance of high priority cell is better than that of low priority cell. URI: http://hdl.handle.net/10311/818 Files in this item: 1
Ogwu_JCS11_2007.pdf (556.8Kb) -
Banda, A.; Mubyana-John, T.; Taylor, J.E. (Global Science Books, http://www.globalsciencebooks.info/, NaN, 2011)[more][less]
Abstract: The influence of burning on soil microbial dehydrogenase activity, nitrogen content and fungal population along the Boro route in the Okavango Delta was assessed in the flood and dry seasons. Soil samples from the burnt plots and the adjacent control un-burnt plots were cultured on agar plates using dilution methods. Fusarium spp. were dominant while Aspergillus species were low in burnt plots. The other fungi such as Drechslera sp., Exophiala jeanselmmei, Penicillium compactum and Chrysosporium merdarium were only in the burnt plots as compared to unburnt control plots. However, fungal diversity and soil dehydrogenase activity reduced after 6 months of burning showing significant increase in Chrysosporium merdarium in almost all the burnt plots. The influence of burning on soil nitrogen was insignificant instead flooding had a stronger influence on nitrogen content than burning. The results indicate that burning increased fungal diversity and biomass, however, reduces overall microbial enzyme activity after burning without influencing soil nitrogen and pH. URI: http://hdl.handle.net/10311/919 Files in this item: 1
Mbuyana_AJPSB_2011.pdf (220.0Kb) -
Mubyana, T.; Krah, M.; Totolo, O.; Bonyongo, M. (Journal of Arid Environments. http://www.elsevier.com/wps/find/journaldescription.cws_home/622855/description#description, NaN, 2003)[more][less]
Abstract: The effect of flooding on soil total nitrogen, phosphorus and microbial population in different vegetation zones (floodplain, island and woodland) and profile depth (0?1, 0?5, 2?0, 3?0, 4?0 and 5?0m) of the Okavango Delta was studied from February to July 1999. Total nitrogen significantly differed with soil profile depth, moisture regime and months. In the woodlands, insignificant total nitrogen was detected at all depths except at 0?1m, where 0?03% and 1?17% were detected in February and March, respectively. In the island samples, only 0?05% was detected at 4m in February. Nitrogen in the floodplain samples was concentrated in the A1 horizon where 0?12%, 0?61% and 0?03% were detected in February, March, and May, respectively. Organic phosphorus significantly differed with vegetation zone but not with months and depth. Although organic phosphorus was low (0?02–0?52%) at all sites, it was liberally distributed throughout the profiles. On the island, actinomycetes were only detected up to 2m in February and up to 3m in July. Fungi concentrated in the top 0?5m (103–105). In both the floodplain and island samples, bacteria concentrated in the upper 3m. However, after May, populations decreased significantly. In the floodplain, significant actinomycetes populations were only detected in the upper 0?5m. Generally, organic phosphorus showed positive correlations with fungal populations. This study indicates that these soils are low in total nitrogen and phosphorus. URI: http://hdl.handle.net/10311/293 Files in this item: 1
Influence of seasonal flooding.pdf (3.953Mb) -
Dikinya, O.; Hinz, C.; Aylmore, L.G. (Csiro, http://www.publish.csiro.au/nid/84.htm, NaN, 2007)[more][less]
Abstract: The paper examines the effects of electrolyte concentration and sodium adsorption ration (SAR) on the relative saturated hydraulic conductivity (RHC) and the ionic behaviour of calcium (Ca) and sodium (Na) ions in the Na-Ca echange complex. Batch binary exchange and saturated column transport experiments were carried out to quantify these effects using agricultural Balkuling soil and mining residue. Generally, RHC has been found to decrease with time, with increasing SAR and with decreasing electrolyte concentration. The more rapid decrease in RHC in the mining residue, particularly at the lowest concentration (1 mmol/L), was consistent at all SAR values. The decreases in RHC were likely to be caused by partial blocking of pores by dispersed clay particles, as evidenced by the appearance of suspended clay particles in the effluent during leaching. Significant differences in RHC were abserved in the passage of fronts of decreasing electrolyte concentration for CaCl2 and SAR 15 solutions through the soil columns. These differences were attributable to structural alterations (slaking) of the media and the nature of the particles released and mobilised within the porous structure at a given point in the column. Measurements at the critical threshold concentration and turbidity increase in SAR to 15 is initially accompained by erractic RHC, presumably due to the break up of soilaggregates under the increased swelling forces. The less coherent mining residue soil was substantially more vulnerable to blockage of pores than the Balkuling soil in which clay particles are likely to be more readily mobilised, and hence available to re-deposit and occlude the matrix pores. URI: http://hdl.handle.net/10311/312 Files in this item: 1
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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)