Browsing by Author "Mabbs, R."
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Comprehensive study of solar conditions in Mozambique: the effect of trade winds on solar componentsNijegorodov, N.I.; Devan, K.R.S.; Simao, H.; Mabbs, R. (Elsevier Science Ltd. www.elsevier.com/locate/renene, NaN, 2003)[more][less]
Abstract: A new algorithm to simulate all solar components and optimum slopes, Bopt, based on new models for direct normal beam and diffuse radiation and an analytical model to predict Bopt, developed at the University of Botswana is applied for complete study of solar conditions in Mozambique. The components of solar radiation depend to a large extent on the number of h of sunshine. However, it is obvious that cloud-cover is determined mainly by the prevailing trade winds, which carry moisture and rain clouds. This is of especial concern in coastal areas. In the current work, hourly, I, daily, H and monthly mean, H¯ components of solar radiation and the optimum slopes of a north-south aligned collector are simulated and analyzed for 21 synoptic stations in Mozambique. Monthly mean daily direct normal, H¯ bn solar radiation maps are plotted for December and June and discussed. It is found that, to a great extent, isoinsolation curves are determined by the prevailing trade winds, mountain chains and coastal conditions. Plotted maps of annual mean daily direct normal and global solar radiation also show tremendous dependence on the prevailing winds. Several special locations in Mozambique with quite high or very low solar radiation components are pointed out and the reasons explained. URI: http://hdl.handle.net/10311/267 Files in this item: 1
Nijegorodov_RE28_2003.pdf (2.514Mb) -
Mabbs, R.; Nijegorodov, N.; Downey, W.S. (Elsevier Science Ltd. www.elsevier.com/locate/saa, NaN, 2003)[more][less]
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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) -
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) -
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)
Now showing items 1-5 of 5