Showing papers by "Banaras Hindu University published in 1981"

Phycology and heavy-metal pollution

Abstract: Summary 1. All heavy metals, including those that are essential micronutrients (e.g. copper, zinc, etc.), are toxic to algae at high concentrations. 2. One characteristic feature of heavy-metal toxicity is the poisoning and inactivation of enzyme systems. Many of the physiological and biochemical processes, viz., photosynthesis, respiration, protein synthesis and chlorophyll synthesis, etc., are severely affected at high metal concentrations. 3. Some algae inhabit waters chronically polluted with heavy-metal-laden wastes from mining and smelting operations; Nodularia sp., Oscillatoria sp., Cladophora sp., Hormidium sp., Fucus sp. and Laminaria sp., etc., occur in metal-rich waters. These algal forms are probably more capable of combating the toxic levels of heavy metals and this attribute is a result of physiological and/or genetic adaptations. The sensitivity or tolerance to heavy metals varies amongst different algae. The phenomena of multiple tolerance and co-tolerance may be exhibited by some algae. 4. Heavy-metal pollution causes reduction in species diversity leading to the dominance of a few tolerant algal forms. The primary productivity also decreases after metal supplementation. 5. The uptake and accumulation of heavy metals can be active (energy-dependent), passive (energy-independent), or both. 6. Heavy metals can be safely stored as intranuclear complexes by some algae. Notwithstanding this, some changes in the cell wall can enable the algae to tolerate heavy metals by checking the entry of the metals (exclusion mechanism). 7. The metal content of algae growing in a waterbody may yield valuable information for simulating heavy metal pollution: several species of Cladophora and Fucus have been extensively used for this purpose. 8. Several factors affect and determine toxicity of heavy metals to algae. At low pH, the availability of heavy metals to algae is greatly increased, as a consequence of which pronounced toxicity is evident. Hard waters decrease metal toxicity. Some ions, e.g., calcium, magnesium and phosphorus, can alleviate toxicity of metals. 9. The presence of other metals can influence toxicity of a heavy metal through simple additive effect or by synergistic and antagonistic interactions. Similarly, other pollutants can influence heavy-metal toxicity. 10. The toxicity of heavy metals depends upon their chemical speciation. Various ionic forms of a metal characterized by different valency states, may be differentially toxic to a test alga. 11. Amino acids, organic matter, humic acids, fulvic acid, EDTA, NTA, etc. can complex with heavy metals and render them unavailable. This may eventually lead to less toxicity. 12. Heavy-metal toxicity largely depends upon algal population density: the denser the population the more numerous the cellular sites available, leading to decreased toxicity.

The three activation energies with isothermal transformations: applications to metallic glasses

Abstract: In crystallization or precipitation, the activation energy for nucleation of particles,En, for growth of particles,Eg, and for the total process,Ec, can all be determined independently by experiment. Formulae relating these three values are developed. Cases of linear and parabolic growth are included for different nucleation rates and morphologies. The formulae are tested experimentally on amorphous alloys (metallic glasses) based on Fe-Ni. The agreement between the theory and the experiments is very satisfactory.

Estimation of complex concentration in a regular associated solution

Abstract: Novel procedures have been developed to estimate the concentration ofApB –type clusters in liquid alloys with the aid of regular associated solution model utilizing activity coefficients of the components at infinite dilution and activity data at any one other composition. The equilibrium constant for the dissociation of clusters as well as the nature and magnitude of pairwise interaction energies between unassociated atoms and clusters have been evaluated without making any assumptions whatsoever. These enable estimation of thermodynamic properties of the liquid alloys at any other desired composition. The utility of the procedures has been demonstrated with respect to the thermodynamics of association in molten Mg-Sn and In-Sb alloys. The calculated activities, enthalpies and free energies are shown to be in excellent agreement with experimental values.

Alkaloid constituents of Sida acuta, S. humilis, S. rhombifolia and S. spinosa.

Abstract: Three types of alkaloidal constituents, viz., beta-phenethylamines, quinazolines and carboxylated tryptamines, in addition to choline and betaine have been isolated from Sida acuta Burm., S. humilis Willd., S. rhombifolia L., and S. spinosa L. and characterized by their physical and spectral properties, and by chemical transformations. The qualitative and quantitative variations in the alkaloidal constituents of roots and aerial portions at different stages of growth were also noted. Elaboration of the quinazoline alkaloids seems to be a characteristic feature of this genus. The favourable combination of sympathomimetic amines and vasicinone in these species would account for their major therapeutic uses in the Indian system of medicine.

Cast aluminium alloy composites containing copper-coated ground mica particles

Abstract: An electroless method of coating copper on ground mica particles using copper sulphate solution is described. The effects of time of sensitization, PdCl2 concentration and time of stirring the activated particles in electroless solution, on the extent of copper coating on mica particles are reported. Using this method it is possible to deposit up to about 35 wt% copper on mica particles. A process for making cast aluminium alloy-mica particle composite alloys using these coated particles is also described. The process involves stirring the copper-coated mica particles into liquid alloys using an impeller, and casting the melts containing suspended mica particles in suitable permanent moulds. Coating of copper on mica particles makes possible the dispersion of ground mica particles in molten aluminium alloys with high recoveries which is otherwise difficult, even when magnesium is added to the surface of the melts. Copper coating on ground mica particles masks the basal planes, and apparently increases their wettability with aluminium alloy melts. Recoveries of ground mica particles in composite castings made using copper-coated mica particles are as high as 80%, which is three times higher than the corresponding recoveries in the castings made using uncoated particles. The mechanical properties of cast aluminium mica composites made using copper-coated ground mica powders are adequate for a variety of bearing and antifriction applications.

Electronic behaviour of SnS2 crystals

Abstract: Electronic band gaps of various polytypes of SnS2, are estimated from the measurements of the variation of conductivity with temperature. It is found that for hexagonal polytypes, the band gap decreases as the polytype periodicity increases, as for instance the band gap values for the basic polytype 2H and the long period polytype 50H are 2.18 and 0.81 eV, respectively. The band gap of the other basic polytype 18R is found to be higher than that of 2H. However, a decrease in the band gap values for other long period polytypes based on 18R again is found to occur. The band gap variations of SnS2, polytypes are explained based on calculations of one-dimensional band structures. Yet another curious electronic characteristic of SnS2, crystals observed in the present investigation is the occurrence of current controlled negative resistance and the accompanying switching behaviour. CCNR and switching are broadly polytype independent and occur when the crystals are imparted special annealing treatments. Les bandes interdites de plusieurs polytypes de SnS2, ont ete estimees a partir des mesures de la variation de la conductivite en fonction de la temperature. On a decouvert que pour des polytypes hexagonaux, le bande interdite diminue quand la periodicite du polytype augmente: ainsi, les valeurs du bande interdite pour le polytype de base 2H et le polytype de longue periode 50H sont respectivement de 2,18 et de 0,81 eV. On a decouvert que le bande interdite de l'autre polytype de base 18R etait supbrieur a celui de 2H. Cependant on a a nouveau constate qu'il se produisait une diminution dans les valeurs du bande interdite pour d'autres polytypes de longue periodicite bases sur 18R. Les variations du bande interdite de polytypes SnS2, ont ete expliquees a partir des calculs faits sur des structures de bande a, une dimension. Cependant, une autre curieuse caracterestique electronique des cristaux de SnS2, observee dans la presente etude est l'existence dune resistance negative controlee par le courant et le effet interrupteur que l'accompagne. CCNR et le effet interrupteur sont en gros des polytypes et apparaissent quand les cristaux sont l'objet de traitments speciaux sous I'effet de la chaleur.

Genetic analysis of adult plant resistance to powdery mildew in pea (Pisum sativum L.)

Abstract: An analysis of adult plant resistance of powdery mildew in 15 F1, F2 and F3 populations of pea derived from crossing 15 diverse and susceptible lines with one resistant line revealed that resistance to powdery mildew is controlled by duplicate recessive genes The genes were designated as er1 and er2 Disease reaction showed independent segregation with three known markers in the resistant parent, namely, af (afila, chromosome 1), st (stipule reduced, chromosome 3) and tl (clavicula, chromosome 7)

Photoperiodic control of seasonal reproduction in tropical weaver bird

Abstract: Experiments were performed in order to provide information on the extent of involvement of daylength, if any, in the control of seasonal breeding in the tropical weaver bird. The reproductive cycle was completely abolished in both short and long photoperiods. The cycle was suppressed in short photoperiods, and in long photoperiods gonads were maintained in a stimulated state indefinitely. These results indicated a definite photoperiodic requirement for gonadal development in the weaver bird. the photoperiodic response threshold was found to be 11 hours daily. Gonads in a period of 12L/12D exhibited cyclicity, though at a low level, indicating that a light period of 12 hours daily allows gonadal regression which is abolished in longer photoperiods. On correlating these laboratory observations with the natural reproductive cycle, it seems that the annual timing of reproduction in the weaver bird may coincide with the time in the spring when the increasing day length reaches the photoperiodic response threshold.

Circadian periodicity and the initiation of gonadal growth in male blackheaded buntings (Emberiza melanocephala)

Abstract: Photosensitive male blackheaded buntings were held under six different light cycles consisting of a 6-hour main photophase coupled with scotophases of various durations (6L/6 (2 n+1) D). Testicular growth was stimulated in buntings by cycle lengths of 12-(6L∶6D), 36-(6L∶30D) and 60-hours (6L∶54D), but not by cycles of 24-(6L∶18D), 48-(6L∶42D) and 72-hours (6L∶66D). These results are consistent with the Bunning hypothesis and indicate that an endogenous rhythm with a period of approximately 24 hours plays a role in the initiation of testicular growth in this bird.

Densification of Alumina and Silica in the Presence of a Liquid Phase

Abstract: Alumina and silica powders were sintered at 1250° to 1460°C in the presence of liquid phases containing CaO, A12O3, and SiO2. The data were analyzed using the equation D = K log t +C and the Arrhenius equation. The activation energy for sintering decreases with increasing amounts of liquid phase.

Justicisaponin-I, a New Triterpenoid Saponin from Justicia simplex

Abstract: A new triterpenoid saponin, named justicisaponin-I, has been isolated from Justicia simplex D. Don. (Acanthaceae). It has been assigned oleanolic acid-3-O-beta-D-glucopyranosyl-4'-O-ferulate structure (1) on the basis of chemical transformation and comprehensive spectral evidence. Justicisaponin-I has produced significant sperm acrosomal membrane stabilizing action and may prove to be a potent antifertility agent.

Culture media and species-related variations in the requirement of 5-bromodeoxyuridine for differential sister-chromatic staining

Abstract: Various concentrations of 5-bromodeoxyuridine (BrdU) ranging from 0.01 to 10.0 μg/ml were tried for finding the minimal concentration required for differential staining of sister chromatids in lymphocytes of man, muntjac and cattle grown in three commonly used culture media, namely TC 199, Dulbecco's MEM and Ham's F-10. The lymphocytes grown in TC 199 required the lowest concentration of BrdU whereas it was highest for the lymphocytes grown in F-10. The minimal concentration varied for the 3 species studied, and it was not related to their DNA content. The differing amounts of thymidine and folic acid present in the various culture media seemed to account for the difference in the quantity of BrdU required for eliciting differential staining. Staining may also have depended on the intracellular nucleotide pool and/or on the difference in the substitutable dT sites of the genomes.

Paragenetic relations in gedrite-cordierite-staurolite-biotite sillimanite-kyanite gneisses at Ajitpura, Rajasthan, India

Abstract: Aluminous parageneses containing gedrite, cordierite, garnet, staurolite, biotite, sillimanite, kyanite, quartz or spinel plus corundum are found as dark colored lenses in the polymetamorphic, multideformed Archean complex at Ajitpura in northwest peninsular India. Staurolite, like kyanite, is a relict phase of earlier metamorphism and is excluded as a paragenetic mineral in view of its incompatibility with quartz and gedrite and its lower X Mg values than for garnet of the assemblage. Its stability here is attributed to zinc content of up to 3 wt%. The XMg in other ferromagnesian minerals decreases in the order: cordierite, biotite, gedrite, garnet, as found elsewhere in high grade rocks. The textural criteria and systematic partitioning of Fe and Mg in the ferromagnesian phases, excluding staurolite, indicate attainment of equilibrium during the second metamorphism. From tie line configurations in the phase diagrams, X Mg ratios in the constituent minerals, and other petrographic criteria, it is suggested that gedrite — cordierite-garnet — sillimanite — biotite assemblage has been produced by the reactions: Biotite+Sillimanite+Quartz = Cordierite+Garnet+K-feldspar+Vapor (1) and Biotite+Sillimanite+Quartz = Cordierite +Gedrite+K-feldspar+Vapor (2) which occurred during partial melting of the rocks at fixed P and T conditions. By isothermal P-X(Fe-Mg) sections it has been demonstrated that release of FeO, SiO2 and other components modified the composition of the reactant biotite presumably by the substitution FeSi⇄2 Al, whereby reaction 1 was replaced by reaction 2. Cordierite with higher X Mg was produced with gedrite instead of with garnet, whose X Mg is less than X Mg of gedrite. Reaction 2 has been tentatively located in T-P space from the intersection of some continuous loops in the P-X(Fe-Mg) diagram at 700°C and also by other constraints. The discontinuous reaction 2 is located about 1–2 kilobars higher than reaction 1, which implies that it is difficult to distinguish between effects of pressure and those of melting on the X Mg ratios of the reaction phases. The P-T calibrations of garnet — cordierite, garnet — biotite and garnet — plagioclase equilibria and the calibrations from other dehydration curves give temperatures near 700°C and pressure (assuming $$P_{H_2 O} = P_{total}$$ ) about 6 kilobars.