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Showing papers by "Indian Institute of Science published in 1981"


Journal ArticleDOI
TL;DR: In this paper, a simple method of calculating the elemental stoichiometric coefficient, φe has been developed, which can easily be applied to multicomponent fuel-oxidizer compositions.

1,062 citations


Journal ArticleDOI
TL;DR: In this article, the two-impurity Kondo problem is studied by using perturbative scaling techniques and the physics are determined by the interplay between the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between the two impurity spins and the Kondo effect.
Abstract: The two-impurity Kondo problem is studied by use of perturbative scaling techniques. The physics is determined by the interplay between the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between the two impurity spins and the Kondo effect. In particular, for a strong ferromagnetic RKKY interaction the susceptibility exhibits three structures as the temperature is lowered, corresponding to the ferromagnetic locking together of the two impurity spins followed by a two-stage freezing out of their local moments by the conduction electrons due to the Kondo effect.

213 citations


Book ChapterDOI
TL;DR: This chapter highlights physiological and metabolic effects on enzyme activities of vanadium, affecting the transition state of phosphate, which seems to have an affinity for the binding sites on these enzymes.
Abstract: Publisher Summary This chapter highlights physiological and metabolic effects on enzyme activities. Vanadium, a group V element, belongs to the first transition series and can form compounds mainly in valence states 3+, 4+, and 5+, both anionic and cationic species. Several criteria of essentiality of an element are satisfied by the properties of vanadium such as low molecular weight, excellent catalytic activity, appropriate atomic structure, its position as a transition metal, ability to form chelates potentially with biologically active compounds, ubiquity in the geosphere and possibly in the biosphere, homeostatic regulation by controlled accumulation and rapid excretion, deficiency in animals and plants showing characteristic symptoms, and low toxicity on oral intake. At least three significant enzymes of the plasma membrane are affected by vanadate—Na, K-ATPase is inhibited in nanomolar concentrations and adenylate cyclase and NADH oxidase are activated in micro-molar to milli-molar concentrations. These enzymes are interrelated. ATP is the substrate for the first two, and both substrates are nucleotides. Vanadate, affecting the transition state of phosphate, seems to have an affinity for the binding sites on these enzymes.

157 citations


Journal ArticleDOI
01 Jul 1981
TL;DR: In this article, the authors studied the asymptotic behavior of the eigenvalues and the Eigenvectors when the number of holes in the domain increases to infinity.
Abstract: In this paper, we treat some eigenvalue problems in periodically perforated domains and study the asymptotic behaviour of the eigenvalues and the eigenvectors when the number of holes in the domain increases to infinity Using the method of asymptotic expansion, we give explicit formula for the homogenized coefficients and expansion for eigenvalues and eigenvectors. If we denote by e the size of each hole in the domain, then we obtain the following aysmptotic expansion for the eigenvalues: Dirichlet: λe = e−2 λ + λ0 +O (e), Stekloff: λe = eλ1 +O (e2), Neumann: λe = λ0 + eλ1 +O (e2).Using the method of energy, we prove a theorem of convergence in each case considered here. We briefly study correctors in the case of Neumann eigenvalue problem.

119 citations


Journal ArticleDOI
TL;DR: The rate of NADH oxidation with oxygen as the acceptor is very low in mouse liver plasma membrane and erythrocyte membrane, but when vanadate is added, this rate is stimulated 10- to 20-fold, indicating that oxygen is the electron acceptor and the reaction is mediated by superoxide.

106 citations


Journal ArticleDOI
TL;DR: The stable A conformation observed in the crystal may have some structural relevance to promoter regions where the T-A-T-A sequence is frequently found and the R factors are 31% for 1 and 28% for 2 at the present stage of refinement.
Abstract: An A-DNA type double helical conformation was observed in the single crystal X-ray structure of the octamer d(G-G-T-A-T-A-C-C), 1, and its 5-bromouracil-containing analogue, 2. The structure of the isomorphous crystals (space group P6$_{1}$) was solved by a search technique based on packing criteria and R-factor calculations, with use of only low order data. At the present stage of refinement the R factors are 31% for 1 and 28% for 2 at a resolution of 2.25 angstrom (0.225 nm). The molecules interact through their minor grooves by hydrogen bonding and base to sugar van der Waals contacts. The stable A conformation observed in the crystal may have some structural relevance to promoter regions where the T-A-T-A sequence is frequently found.

98 citations


Journal ArticleDOI
TL;DR: In this paper, a direct method of preparing cast aluminium alloy-graphite particle composites using uncoated graphite particles is reported, and the method consists of introducing and dispersing un-coated but suitably pretreated graphite particle in aluminium alloy melts, and casting the resulting composite melts in suitable permanent moulds.
Abstract: A direct method of preparing cast aluminium alloy-graphite particle composites using uncoated graphite particles is reported. The method consists of introducing and dispersing uncoated but suitably pretreated graphite particles in aluminium alloy melts, and casting the resulting composite melts in suitable permanent moulds. The optical pretreatment required for the dispersion of the uncoated graphite particles in aluminium alloy melts consists of heating the graphite particles to 400° C in air for 1 h just prior to their dispersion in the melts. The effects of alloying elements such as Si, Cu and Mg on the dispersability of pretreated graphite in molten aluminium have also been reported. It was found that additions of about 0.5% Mg or 5% Si significantly improve the dispersability of graphite particles in aluminium alloy melts as indicated by the high recoveries of graphite in the castings of these composites. It was also possible to disperse upto 3% graphite in LM 13 alloy melts and retain the graphite particles in a well distributed fashion in the castings using the pre-heat-treated graphite particles. The observations in this study have been related to the information presently available on wetting between graphite and molten aluminium in the presence of different elements and our own thermogravimetric analysis studies on graphite particles. Physical and mechanical properties of LM 13-3% graphite composite made using pre-heat-treated graphite powder, were found to be adequate for many applications, including pistons which have been successfully used in internal combustion engines.

95 citations


Journal ArticleDOI
TL;DR: In this article, the eigenvalues and eigenfunctions corresponding to the three-dimensional equations for the linear elastic equilibrium of a clamped plate of thickness 2 ϵ, are shown to converge (in a specific sense) to the 2-dimensional biharmonic operator of plate theory, as ϵ approaches zero.

92 citations


Journal ArticleDOI
01 Jan 1981-Nature
TL;DR: In this paper, it was shown that the commercially important zeolite-Y may be chemically stabilized against electron irradiation damage by the simple expedient of incorporating uranyl (UO2+2) ions into the structure beforehand.
Abstract: The aluminosilicate framework of synthetic ‘zeolites’ of type A (Na+-form) and ZSM-5, as well as the Na+-forms of faujasite (Fig. 1) in their so-called X- and Y-variants (fuller structural descriptions are given in ref s 1 and 2) have recently been imaged at near-atomic scale by high-resolution electron microscopy (HREM)3–5. However, the as-prepared synthetic and naturally occurring zeolites, all of which contain alkali metal and alkaline-earth exhangeable cations and much constitutional, intracrys-tallite water, are converted within minutes into an amorphous state on examination in an electron beam of the intensity required to yield high-resolution images. The specimen has to withstand 106 electrons A−2 bombardment within a few minutes. To extract further information from HREM about the local atomic structure, and, in particular, to identify the siting of the various cations that may be accomodated in these catalytically important and shape-selective materials, methods have to be developed which retain the structural integrity of the zeolite for a reasonable time under electron irradiation in vacuo. It has been shown3 that dehydration of the zeolite before observation significantly increases its lifetime in an electron beam. Here we show that the commercially important4 zeolite-Y may be chemically stabilized against electron irradiation damage by the simple expedient of incorporating uranyl (UO2+2) ions into the structure beforehand. Beam sensitivities are decreased by factors of 10–100 in this way, but appropriate heat-treatment of the UO2-exchanged zeolite is required to achieve this stability and hence to locate these heavy cations.

87 citations


Journal ArticleDOI
TL;DR: In this paper, an intrinsic effective stress is attributed to chemical bonds, which can influence the shear strength behavior of soils subjected to repeated wetting and drying in the laboratory, which results in greater shears strength and in a stiffer stress-strain response.
Abstract: Climatic changes, such as repeated wetting and drying over geological ages, lead to the degeneration of the parent rock to form soil. Simultaneously these actions can also cause some aggregation of soil particles and the production of bonds, called desiccation bonds, which impart an intrinsic effective stress to the soil. This intrinsic effective stress can influence the shear strength behavior of soils subjected to such climatic actions. When a soil is subjected to repeated wetting and drying in the laboratory, an intrinsic effective stress is imparted to it which results in greater shear strength and in a stiffer stress-strain response. This intrinsic effective stress may be attributed to chemical bonds.

76 citations


Journal ArticleDOI
15 May 1981-Wear
TL;DR: In this article, the dry wear characteristics of the Al-(2.7% −5.7%) graphite particle composite were found to deteriorate with the addition of graphite, load and sliding distance.

Journal ArticleDOI
TL;DR: This work uses an approach based on multiobjective phased-mission analysis to evaluate the effectiveness of a distributed avionics architecture used in a transport aircraft and views the computing system as a multistate s-coherent structure.
Abstract: Effectiveness evaluation of aerospace fault-tolerant computing systems used in a phased-mission environment is rather tricky and difficult because of the interaction of its several degraded performance levels with the multiple objectives of the mission and the use environment. Part I uses an approach based on multiobjective phased-mission analysis to evaluate the effectiveness of a distributed avionics architecture used in a transport aircraft. Part II views the computing system as a multistate s-coherent structure. Lower bounds on the probabilities of accomplishing various levels of performance are evaluated.

Journal ArticleDOI
TL;DR: In this article, the nucleation growth model of electrochemical phase formation is analyzed for the linear potential sweep input, and a distinction is made between adsorption and phase transition, which seems useful for understanding the nature of ECPF phenomena.

Journal ArticleDOI
TL;DR: In this article, a historical account of the discovery of the Raman Effect is given, starting from Raman's voyage to Europe through the Mediterranean Sea in the summer of 1921 to the observation of modified lines in benzene when illuminated by the 435.8 nm radiations of mercury, through a direct vision spectroscope, on 28 February 1928.
Abstract: The paper gives a historical account of the discovery of the Raman Effect, starting from Raman's voyage to Europe through the Mediterranean Sea in the summer of 1921 to the observation of modified lines in benzene when illuminated by the 435.8 nm radiations of mercury, through a direct vision spectroscope, on 28 February 1928. The important contributions of Raman and his students during the period which form the progressive stages in the road to discovery have been briefly touched upon. The work of the French group, the Russian group and the theoretical work of Smekal are narrated in sequence

Book ChapterDOI
TL;DR: It is recognized that one of the typical properties of the epithelial cells is that they undergo constant in situ regeneration, therefore it follows that vitamin A is required for their controlled division and differentiation.
Abstract: Publisher Summary This chapter reviews the effects of vitamin A deficiency. Vitamin A is essential for several physiological functions in animals—namely, (1) vision, (2) growth, (3) reproduction, and (4) proper maintenance of the integrity of epithelial cells. The chapter also discusses the requirement of vitamin A in specific biological events, such as in the regeneration of the liver cells in an adult rat after partial hepatectomy and in the estrogen-induced development of chick oviduct. The effects of vitamin A deprivation on biosynthesis of RNA and proteins and on glycosylation of proteins are described. The chapter examines the transport, delivery, and mode of action of steroid hormones and the transport and delivery of retinol. An overview of the similarities between the mode of action of retinol and steroid hormones is presented. The chapter concludes that the most pronounced and characteristic effects are invariably on the epithelial cells. It is recognized that one of the typical properties of the epithelial cells is that they undergo constant in situ regeneration. Therefore it follows that vitamin A is required for their controlled division and differentiation. The chapter also focuses on the fact that the steroid hormones circulate in blood bound to proteins, from which they are removed by specific receptor proteins present in the target cells. The steroid–receptor complex in the target cells is translocated into the cell nucleus, where it binds to the chromatin and induces characteristic gene expression.

Journal ArticleDOI
TL;DR: In this article, the authors reported the total synthesis of alamethicin I by solution phase methods, which was achieved by coupling Z-Ail+PrhAib-OH and Boc-Ala-AibAiwMe as shown in Fig. 2.

Journal ArticleDOI
TL;DR: It is concluded that, if allowed to accumulate within the tissue, trehalose may be potentially toxic or inhibitory to higher plants in general.
Abstract: A toxic effect of α,α-trehalose in an angiospermic plant, Cuscuta reflexa (dodder), is described. This disaccharide and its analogs, 2-aminotrehalose and 4-aminotrehalose, induced a rapid blackening of the terminal region of the vine which is involved in elongation growth. From the results of in vitro growth of several angiospermic plants and determination of trehalase activity in them, it is concluded that the toxic effect of trehalose in Cuscuta is because of the very low trehalase activity in the vine. As a result, trehalose accumulates in the vine and interferes with some process closely associated with growth. The growth potential of Lemna (a duckweed) in a medium containing trehalose as the carbon source was irreversibly lost upon addition of trehalosamine, an inhibitor of trehalase activity. It is concluded that, if allowed to accumulate within the tissue, trehalose may be potentially toxic or inhibitory to higher plants in general. The presence of trehalase activity in plants, where its substrate has not been found to occur, is envisaged to relieve the plant from the toxic effects of trehalose which it may encounter in soil or during association with fungi or insects.

Journal ArticleDOI
TL;DR: In this article, it was shown that Cr(VI and Cr(V) decreases with increase in Cr content of the calcined catalysts and the proportion of V(VI) decreases as the Cr content increases.

Journal ArticleDOI
TL;DR: In this article, a systematic derivation of the approximate coupled amplitude equations governing the propagation of a quasi-monochromatic Rayleigh surface wave on an isotropic solid is presented, starting from the nonlinear governing differential equations and the non-linear free-surface boundary conditions, using the method of mulitple scales.

Journal ArticleDOI
01 Sep 1981-Biomass
TL;DR: In this article, simple expressions have been derived for the carrying capacity of the ecosystem with respect to cereal crops, the pasture land-crop land ratio, the number of draught animal pairs, the human to draught-animal pair ratio and the human-to-cattle ratio.

Journal ArticleDOI
TL;DR: In this paper, a method employing two liquid crystals of opposite diamagnetic anisotropies to determine chemical shift anisotropy without using any reference compound is described, and individual values of the direct and indirect spin-spin coupling constants between heteronuclei are reported.

Journal ArticleDOI
TL;DR: The degree of consanguinity of the progeny, the number of live-borns and number of living children were determined in 3350 marriages in Bangalore, Karnataka and the coefficient of inbreeding was higher than in comparable, urban populations in other South Indian states.
Abstract: The degree of consanguinity of the progeny, the number of live-borns and number of living children were determined in 3350 marriages in Bangalore, Karnataka. The coefficient of inbreeding (F) was 0-02308, higher than in comparable, urban populations in other South Indian states. No significant differences were found between the consanguineous and nonconsanguineous groups in numbers of live-born or living children nor was there any consanguinity-related trend with respect to these parameters.

Journal ArticleDOI
26 Feb 1981-Nature
TL;DR: The X-ray structure analysis of the synthetic analogue of the antibiotic triostin A, TANDEM, is reported, which binds preferentially to alternating adenine-thymine sequences7 and suggests possible models for the binding of other members of the quinoxaline series.
Abstract: Quinoxaline antibiotics (Fig. 1a, b) form a useful group of compounds for the study of drug–nucleic acid interactions1,2. They consist of a cross-bridged cyclic octadepsipeptide, variously modified, bearing two quinoxaline chromophores. These antibiotics intercalate bifunctionally into DNA2,3 probably via the narrow groove, forming a complex in which, most probably, two base pairs are sandwiched between the chromophores4,5. Depending on the nature of their sulphur-containing cross-bridge and modifications to their amino acid side chains, they display characteristic patterns of nucleotide sequence selectivity when binding to DNAs of different base composition and to synthetic polydeoxynucleotides4,6,7. This specificity has been tentatively ascribed to specific hydrogen-bonding interactions between functional groups in the DNA and complementary moieties on the peptide ring2,4,5. Variations in selectivity have been attributed both to changes in the conformation of the peptide backbone6 and no modifications of the cross-bridge7. These suggestions were made, however, in the absence of firm knowledge about the three-dimensional structure and conformation of the antibiotic molecules. We now report the X-ray structure analysis of the synthetic analogue of the antibiotic triostin A, TANDEM (des-N-tetramethyl triostin A) (Fig. 1c), which binds preferentially to alternating adenine-thymine sequences7. The X-ray structure provides a starting point for exploring the origin of this specificity and suggests possible models for the binding of other members of the quinoxaline series.

Journal ArticleDOI
TL;DR: In this paper, the tetrapeptide Z-{(Aib-Pro)}_2-OMe was synthesized using dicyclohexylcarbodiimide.
Abstract: The synthesis of the tetrapeptide $benzyloxycarbonyl{(\alpha-aminoisobutyryl-L-prolyl)}_2-methyl ester$ $(Z-{(Aib-Pro)}_2-OMe)$ and an analysis of its conformation in solution and the solid state are reported. Stepwise synthesis using dicyclohexylcarbodiimide leads to racemization at Pro(2). Evidence for the presence of diastereomeric tetrapeptides is obtained from 270-${MHz}^1H-nmr$ and 67.89-MHz 13C-nmr. The all-L tetrapeptide is obtained by fractional crystallization from ethyl acetate. The NH of Aib(3) is shown to be involved in an intramolecular hydrogen bond by variable-temperature 1H-nmr and the solvent dependence of NH chemical shifts. The results are consistent with a \beta-turn conformation with Aib(1) and Pro(2) at the corners stabilized by a 4 \rightarrow 1 hydrogen bond. The molecule crystallizes in the space group ${P2}_12_12_1$, with a = 8.839, b = 14.938, and c = 22.015 A. The structure has been refined to an R value of 0.051. The peptide backbone is all-trans, and a 4 \rightarrow 1 hydrogen bond, between the CO group of the urethane moiety and Aib(3) NH, is observed. Aib(1) and Pro(2) occupy the corner positions of a type I \beta-turn with \phi = -55.4 deg, \psi = -31.3 deg for Aib(1) and \phi = -71.6 deg, \psi = -38 deg for Pro(2). The tertiary amide unit linking Pro(2) and Aib(3) is significantly distorted from planarity (${\Delta}_{\omega}$ = 14.3 deg).

Journal ArticleDOI
TL;DR: In this paper, a novel type of magnesium-air primary cell has been evolved which employs non-polluting and abundantly available materials, and the cell is based on the scheme Mg/Mg(NO3)2, NaNO2, H20/Q(C).
Abstract: A novel type of magnesium-air primary cell has been evolved which employs non-polluting and abundantly available materials. The cell is based on the scheme Mg/Mg(NO3)2, NaNO2, H20/Q(C). The magnesium anode utilization is about 90% at a current density of 20 mAcm -2. The anode has been shown to exhibit a low open-circuit corrosion, a relatively uniform pattern of corrosion and a low negative difference effect in the electrolyte developed above as compared to the conventional halide or perchlorate electrolytes. In the usual air-depolarized mode of operation, the cell has been found to be capable of continuous discharge over several months at a constant cell voltage of about 1 V and a current density of 1 mAcm -2 at the cathode. The long service-life capability arises from the formation of a protective film on the porous carbon cathode and fast sedimentation of the anodic product (magnesium hydroxide) in the electrolyte. The cell has a shelf-life in the activated state of about a year due to the low open-circuit corrosion of the anode. These favourable features suggest the practical feasibility of developing economical, long-life, non-reserve magnesium-air ceils for diverse applications using magnesium anodes with a high surface area and porous carbon-air electrodes.

Journal ArticleDOI
TL;DR: In this article, a method for the conversion of electron rich benzylic hydrocarbons to carbonyl compounds is described, which is a convenient method for converting carbonyls.

Journal ArticleDOI
TL;DR: In this paper, the properties of rare earth transition metal sulfides are discussed in terms of their structures and the electronic configurations of the transition metal ions, including vanadium and chromium sulfides.

Journal ArticleDOI
TL;DR: For the first time, the pathway of proline metabolism in plants is established by way of detection of the activities of all the enzymes involved and the role of these enzymes in proline accumulation during water stress is highlighted.
Abstract: Free proline content in Ragi (Eleusine coracana) leaves increased markedly (6 to 85 fold) as the degree of water stress, created by polyethylene gylcol treatment, was prolonged There was also a marginal increase in soluble proteins in the stressed leaves as compared to that in the controls. Water stress stimulated the activities of ornithine aminotransferase and pyrroline-5-carboxylate reductase, the enzymes of proline biosynthesis and markedly inhibited the enzymes involved in proline degradation viz., proline oxidase and pyrroline-5-carboxylate dehydrogenase. These results suggest that increase in free proline content of Ragi leaves could be due to enhanced activities of the enzymes synthesizing proline but more importantly due to severe inhibition of the enzymes degrading proline. These observations establish for the first time, the pathway of proline metabolism in plants by way of detection of the activities of all the enzymes involved and also highlight the role of these enzymes in proline accumulation during water stress.

Journal ArticleDOI
TL;DR: In this paper, the minimum energy required for the formation of conjugate pair of charged defects is found to be approximately equal to the experimental activation energy for d.c. conductivity in a number of amorphous chalcoganides and pnictides.

Journal ArticleDOI
TL;DR: In this paper, the synthesis of the octapeptide, benzyloxycarbonyl-(-aminoisobutyryl-L-prolyl)4-methyl ester [Z-(Aib-Pro) 4-OMe] and an analysis of its solution conformation is reported.
Abstract: The synthesis of the octapeptide, benzyloxycarbonyl-(-aminoisobutyryl-L-prolyl)4-methyl ester [Z-(Aib-Pro)4-OMe] and an analysis of its solution conformation is reported. The octapeptide is shown to possess three strong intramolecular hydrogen bonds on the basis of studies of the solvent and temperature dependence of NH chemical shifts and rates of hydrogen-deuterium exchange. 13C studies are consistent with a structure involving only trans Aib-Pro bonds, while ir experiments support a hydrogen-bonded conformation. The Aib 3, 5, and 7 NH groups are shown to participate in hydrogen bonding. A 310 helical conformation compatible with the spectroscopic data is suggested. The proposed conformation consists of three type III -turns with Aib and Pro at the corners and stabilized by 4 1 intramolecular hydrogen bonds.