Showing papers by "Banaras Hindu University published in 1982"

Semiconductor Photoelectrochemical Solar Cells

Abstract: The total band bending or potential drop at the electrode-electrolyte interface is across the space charge layer in the semiconductor plus that across the Helmoltz layer in the electrolyte. The latter is negligible. The band bending at the electrode-electrolyte interface changes on illumination, as for p-n junctions, and can be used for constructing solar cells. Such solar cells are termed 'photoelectrochemical solar cells'. The charge transfer from semiconductor to electrolyte can take place such that under different conditions it can either reduce or oxidise the species in the electrolyte depending upon the redox reaction (Esub(F, redox)) energy value with respect to Esub(c) and Esub(v) at the edge. Generally, the enhanced charge transfer under illumination results in a voltage. However, if the redox species is H/sub 2/O/O/sub 2/, the electrolysis of water takes place. Such cells are known as photoelectrolysis cells. These cells have low efficiency of approx. equal to 1% and hence not economically viable at present. However, an efficiency approx. equal to 10 to 14% has been attained in electrochemical photovoltaic solar cells within four years since the first report by Gerischer. This seems encouraging and competitive to conventional photovoltaic solar cells.

Silicide Precipitation in Alloy Ti-6AI-5Zr-0.5Mo-0.25Si

Abstract: Silicide precipitation in the titanium alloy containing by wt pct 6Al-5Zr-0.5Mo-0.25Si (Alloy 685) has been investigated using electron diffraction. The solutionizing temperature for this alloy is 1323 K. It is observed that no resolvable silicide precipitates are present in the alloy as received, furnace cooled from 1323 K and aged at 823 K, or oil quenched from 1323 K and aged at 823 K. Specimen solutionized at 1323 K for 30 minutes followed by water quenching and aging at 923 K for 24 hours shows fine precipitates at boundaries of α′ platelets. Diffraction analysis shows that the fine precipitates belong to two different types of identifiable hexagonal silicides similar to those observed by Floweret al in the ternary Ti-5Zr-0.5Si alloy to be (TiZr)5Si3 and another of unknown stoichiometry. However, aging of the water quenched specimens for 24 hours at higher temperatures, 973 K and 1073 K, results in the precipitation of a silicide similar to the latter one. It is analyzed that this silicide has lattice parameters a = 0.702 nm and c = 0.368 nm. Since aging at 973 K and 1073 K gives rise to precipitation of the same silicide, it is concluded that this is the stable silicide in Alloy 685 in the temperature range investigated.

Conservation of the 93D puff of Drosophila melanogaster in different species of Drosophila

Abstract: Temperature shock (TS) results in activation of a specific set of puffs in polytene nuclei of D. melanogaster. Earlier studies in this species from several laboratories revealed certain unique features of the major TS puff at 93D locus, which is also specifically induced by benzamide (BM) and by incubation of glands in heat shocked glands' homogenate (HSGH). We have now extended studies on TS response to several other species of Drosophila to ascertain whether loci homologous to 93D puff of D. melanogaster are present in other species. In polytene nuclei of two closely related (D. ananassae, D. kikkawai) and in two distantly related species (D. hydei, D. nasuta), six to nine puffs are induced by TS. Interestingly, in each species one of the major TS puffs, viz., 2L-2C in D. ananassae, E-11BC in D. kikkawai, 2R-48A in D. nasuta and 2-48C in D. hydei, is also specifically induced by BM, autologous species' HSGH and vitamine-B6 (vit-B6) treatment. HSGH of a different species fails to induce these puffs. These puffs thus resemble the 93D locus of D. melanogaster, although the 93D puff does not respond to vit-B6. These observations are discussed in relation to the conservation of 93D puff locus in different species of Drosophila.

Effect of ozone and sulphur dioxide pollutants separately and in mixture on chlorophyll and carotenoid pigments ofOryza sativa

Abstract: Exposure of rice plants to low concentrations of O3 and SO2 singly and in combination showed foliar injury of different levels. The maximum leaf injury was noted in case of O3+SO2 treated plants and the minimum in O3 treated ones. Also the reductions in chlorophylla,b and total chlorophyll and carotenoid contents in leaves exposed to O3+SO2 mixtures were higher than the reduction noted in case of each individual pollutant. Thus the results suggest a synergism existing between O3 and SO2 regarding plant injury, especially with respect to chlorophyll and carotenoid contents of rice (Oryza sativa).

Absence of novel translation products in relation to induced activity of the 93D puff in Drosophila melanogaster.

Abstract: Salivary glands of Drosophila larvae were treated in vitro with benzamide or with a homogenate of heat shocked glands to specifically induce high transcriptional activity of the 93D puff. The newly synthesized 14C-amino acids labelled polypeptides in the treated and sister control glands were analysed by polyacrylamide gel electrophoresis, followed by gel autoradiography. The protein synthesis patterns in the treated glands in either case remain the same as in control glands. No novel polypeptide was seen which could be correlated with the high induced transcriptional activity of the 93D puff. This suggests that the 93D transcript/s is/are probably not translated.

Lime-enhanced hydrogen reduction of molybdenite

Abstract: Kinetics of the direct hydrogen reduction of a high-grade (59 pct Mo) molybdenite (MoS2) concentrate was investigated in the presence of lime as a function of the quantity of lime in the charge, hydrogen flow rate, temperature, and time of reduction. Lime was found to enhance tremendously the reduction rate of MoS2 and drastically reduce H2S emission into the off gas to negligible levels. Successful application of the lime-hydrogen reduction technique was found to depend on the employment of low hydrogen flow rate and moderate temperatures of reduction. In these laboratory studies, best results were obtained with a lime addition ≥ three times the theoretical requirement and at 1173 K in 3.6 ks employing a hydrogen flow rate of 3.33 cm3s-1. The results were tested for the treatment of a low-grade (41 pct Mo) molybdenite concentrate. In this latter case, the procedure consisted of upgrading the concentrate by acid leaching (with dil HC1+HF) followed by lime-hydrogen reduction. The influence of quantity of acids, temperature, and time of leaching were investigated to optimize the conditions required for upgrading the MoS2 concentrate. The molybdenum powders obtained from the highgrade as well as upgraded molybdenite concentrates had 96 to 97 pct purity and could be further refined to 99.9 pct by electron-beam melting. Based on this lime-enhanced hydrogen reduction concept, a new ‘Leach-Reduction-Melting’ approach has been suggested as an alternative to the traditional methods of molybdenum extraction.

X‐ray diffraction study of the 2H to 3C solid state transformation in vapour grown single crystals of ZnS

Abstract: An X-ray diffraction study is made of the 2H 3C solid-state structural transformation in ZnS. Single crystals of 2H ZnS (wurtzite), grown from the vapour phase above 1100 °C in the presence of H2S2, are annealed in vacuum at different temperatures ranging from 300 to 650 °C. The transformation is found to commence with a statistical insertion of stacking faults as revealed by the intensification of the diffuse streaks along reciprocal lattice rows parallel to c*. Diffraction spots characteristic of the 3C structure appear on the streaks at a later stage and the end product is invariably a disordered, twinned 3C structure. The rate of transformation is found to depend on the annealing temperature as well as the perfection of the initial crystal. No change in the external shape of the crystals is observed. To determine the nature of stacking faults involved in the transformation the broadening of the X-ray diffraction maxima are investigated produced by annealing 2H ZnS crystals. The point intensity distribution along the 10.L reciprocal lattice row of a slightly faulted 2H crystal is recorded on a four-circle single-crystal diffractometer in steps of ΔL = 0.01. It is found that the half widths of the L even and L odd reflections are equal, indicating that the stacking faults introduced during annealing are predominantly deformation faults. The observed and calculated intensity profiles of different individual reflections are found to be in good agreement. A slight discrepancy observed is attributed to the non-random insertion of stacking faults during transformation. Es werden Bontgenbeugungsuntersuchungen an den 2H-3C-Festkorper-Strukturubergangen in ZnS durchgefuhrt. 2H-ZnS (Wurtzit)-Einkristalle, aus der Dampfphase oberhalb 1100 °C in H2S- Atmosphare gezuchtet, werden im Vakuum bei verschiedenen Temperaturen im Bereich von 300 bis 650 °C getempert. Es wird gefunden, das der ubergang mit dem statistischen Einsetzen von Stapelfehlern ubereinstimmt, wie aus der Vermehrung der diffusen Streifen langs der Reihen parallel zu c* im reziproken Gitter gefunden wird. Fur die 3C-Struktur charakteristische Beugungs punkte erscheinen auf den Streuen in einem spateren Zustand, und das Endprodukt ist invariabel eine fehlgeordnete verzwillingte 3C-Struktur. Die Transformationsrate hangt sowohl von der Temperungstemperatur als auch von der Perfektion des Ausgangskristalls ab. In der auseren Form des Kristalls wird keine anderung beobachtet. Um die Art der bei dem ubergang beteiligten Stapelfehler zu bestimmen, wird die Verbreiterung der Rontgenbeugungsmaxima infolge der Temperung der 2H-ZnS-Kristalle untersucht. Die Punktintensitatsverteilung in Richtung der 10.L-Reihe des reziproken Gitters eines schwach fehlerhaften 2H-Kristalls wird mit einem Vier- Kreis-Einkristall-Diffraktometer in Stufen von ΔL = 0.01 aufgezeichnet. Es wird gefunden, das die Halbwertsbreiten der geraden und ungeraden Reflexionen gleich sind, was darauf hinweist, das die wahrend der Temperung eingebrachten Stapelfehler uberwiegend Deformationsstapelfehler sind. Die beobachteten und berechneten Intensitatsprofile von verschiedenen individuellen Reflexionen befinden sich in guter ubereinstimmung. Eine leichte Diskrepanz, die beobachtet wird, wird der nichtstatistischen Einfuhrung der Stapelfehler wahrend der Transformation zugeordnet.

MHD free-convection flow in the Stokes problem for a porous vertical plate.

Abstract: The effect of a uniform transverse magnetic field on the free-convection flow of an electrically-conducting fluid past an infinite, vertical, porous plate for both classes of impulsive as well as uniformly-accelerated motion of the plate is discussed. The magnetic lines of force are assumed to be fixed relative to the plate. Expressions for the velocity field and skin friction for both cases are obtained by the Laplace transform technique. The influence of the various parameters, entering into the problem, on the velocity field and skin-friction is extensively discussed with the help of graphs and tables.

Influence of stacking faults on the spiral growth of polytype structures in mica

Abstract: A systematic theoretical deduction of polytype structures of mica that can result by the spiral growth mechanism operating in faulted 1M, 2M1 and 3T basic matrices is reported. As a prerequisite, all possible intrinsic and extrinsic stacking fault configurations in each of the basic matrices have been worked out and their stacking fault energy (SFE) estimated. The deduction of polytype structures on the basis of the “faulted-matrix model” takes into account (i) the introduction of each of the low energy fault configurations in the exposed ledge of the screw dislocations, (ii) the change in the layer-position of the fault within the exposed ledge and (iii) the variation of the strength of the generating screw dislocation. At each stage, the spirally-grown polytypes are deduced for each basic structure. The most probable structures are predicted on the basis of the lowest SFE for the same strength of the screw dislocation and are then compared with the polytype structures reported in the literature. It was found that the faulted matrix model accounts successfully for the origin of all the polytype structures in mica. Furthermore, it may provide a basis for limiting the number of trial structures for determining the structures of long period polytypes.

The Archean Craton of Southern India: Metamorphic evolution and P-T conditions

Abstract: The Archaean craton of southern India is characterized by a highly complicated and not yet fully understood geological history comprizing several cycles of sedimentation and volcanism, deformation and metamorphism in the span between about 3400 and 2500 m. y. The large scale regional variation in metamorphic grade observed today is essentially related to a metamorphic event at about 2600 m. y. ago which affected an older migmatite, gneiss-greenstone terrain (2900–3400 m. y.).

Persistence of chromosomal polymorphism in various strains of Drosophila ananassae

Abstract: Strains of Drosophila ananassae, each descended from a single inseminated female collected in nature, were maintained in laboratory cultures for 10 to nearly 50 generations. The chromosomal analysis of these strains was made immediately after their capture and chromosomal inversions were detected. The same strains were re-examined and it was found that all the strains remained polymorphic during the course of time. Although some of the strains did not show the same chromosomes which were ascertained at the original examination, they failed to become homozygous in all the chromosomes. Some old strains maintained for more than 100 generations but not established by the author were also examined and showed a persistence of inversion polymorphism.

Evaluation of radiation-induced chromosomal aberrations in human peripheral blood lymphocytes in vitro: result of an IAEA-coordinated programme.

Abstract: The results of an IAEA coordinated programme on radiation induced chromosomal aberrations in human peripheral blood lymphocytes in vitro are presented. In a master experiment, a whole blood sample from one donor was irradiated with 200 R of X-rays. Different fixation times from 46 to 82 h were used. The progression of cells into mitosis was monitored by BrdUrd incorporation. 14 investigators took part in the scoring of chromosomal aberrations. The main conclusions of this study are: (1) The mean frequencies of aberrations changed with fixation time. (2) The number of cells scored as aberrant by different laboratories was very similar, but there was variability in the number of aberrations scored per aberrant cell. (3) The differences in the frequencies of aberrations between laboratories were minimal when the scoring was restricted to the first major peak of mitotic activity and sufficient cells were scored. It is concluded that using controlled experimental conditions, human peripheral blood lymphocytes can effectively be used as a reliable biological dosimeter for absorbed radiation dose.

Amino acid nutrition in the blue‐green alga nostoc muscorum

Abstract: SUMMARY The L-isomers of 21 amino acids have been screened for their ability to serve as carbon or nitrogen sources for growth of the het+ nif−11 heterocystous and non-nitrogen fixing mutant strain of the blue-green alga Nostoc muscorum by a simple test system combining the use of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) (an inhibitor of photosynthetic assimilation of CO2) and the auxotrophic (non-nitrogen fixing) characteristic of the mutant. The amino acids glutamate, alanine, tyrosine and cysteine were toxic; glutamine, histidine, asparagine, tryptophan and serine were utilized as nitrogen sources; arginine, proline and phenylalanine were utilized as carbon sources; leucine, isoleucine, lysine, methionine, valine and citrulline were utilized as sources of both carbon and nitrogen; aspartate, threonine and glycine served neither as carbon nor nitrogen sources.

Differential rates of fetal growth in two successive pregnancies in the emballonurid bat, Taphozous longimanus Hardwicke.

Abstract: Tapbozou.s longimanus breeds twice per year in quick succession. The first pregnancy has a duration of 105 days and the second 86 days. This variation in length appears to be due to differences in the rate of fetal growth in successive pregnancies.

Gibberella indica: the perfect state of Fusarium udum

Abstract: (1982). Gibberella Indica: The Perfect State of Fusarium Udum. Mycologia: Vol. 74, No. 2, pp. 343-346.

Effects of nutrients present in bold's basal medium on the green alga Stigeoclonium pascheri.

Abstract: The effects of varying concentrations of nutrients present in Bold’s basal medium on the extent of colony formation from vegetative fragments, sporulation and spore germination of the green algaStigeoclonium poscheri were studied. A decrease of colony formation was observed in media deficient in MgSO4, NaNO3, phosphates, and containing a 10-fold increase of H3BO3. Sporulation decreased in the same media. However, sporulation was greater in an increasing order in media containing 2- to 10-fold increase in MgSO4. There was a decrease in spore germination in media deficient in phosphates, MgSO4, containing 5- or 10-fold MgSO4, or containing 2- to 10-fold of CaCl2, H3BO3 or microelements. Spore germination increased in media containing 2-fold MgSO4, deficient in H3BO3 or microelements or containing none of the three micronutrient solutions.

Stannous‐Stannic Equilibrium in Molten Binary Alkali Silicate and Ternary Silicate Glasses

Abstract: The stannous-stannic equilibrium in binary alkali silicate and ternary silicate glasses was studied by equilibrating glassmelts with air at 1400°C. The Sn2+-Sn4+ equilibrium shifts more toward the oxidized state with increasing ionic radii of the alkali ions or with increasing concentration of the alkali ions in the same series of glasses. The slope of the straight lines obtained on plotting log (Sn4+)/(Sn2+)(pO2)n/2 vs mol% R2O increased in the order Li→Na→K. In ternary silicate glasses having the base glass composition 20Na2O·10RO·70SiO2, the Sn2+-Sn4+ equilibrium shifts more toward the reduced state, with increasing bond strength between the divalent cations and the nonbridging oxygens. With increasing temperature, the equilibrium shifts more toward the reduced state.