Showing papers by "Indian Association for the Cultivation of Science published in 1993"
TL;DR: In this paper, the miscibility of copolymer compositions has been studied by a film clarity test, Tg and cloud-point (Tp) studies, and the phase diagrams of the blends were determined.
237 citations
TL;DR: The coercivity values for different heat-treated samples were found to be in the range 20−95 Oe, which are significantly larger than that for samples having grain sizes of the order of a few microns as mentioned in this paper.
154 citations
TL;DR: In this article, two ground-state rotamers with distinct excitation and emission spectra and lifetimes have been identified using steady-state and time-resolved emission spectroscopy and semi-empirical quantum-chemical methods.
112 citations
TL;DR: Study reported herein strongly suggest that the tumoricidal effect of MG is mediated at least in part through the inhibition of mitochondrial respiration and inactivation of GA3PD, and this enzyme may play an important role in the high glycolytic capacity of the malignant cells.
Abstract: The effect of methylglyoxal (MG) on the aerobic glycolysis of Ehrlich ascites carcinoma (EAC) cells has been tested. Methylglyoxal inhibited glucose utilization and glucose 6-phosphate (G6P) and L-lactate formation in whole EAC cells. Methylglyoxal strongly inactivated glyceraldehyde 3-phosphate dehydrogenase (GA3PD) of the malignant cells, whereas MG has little inactivating effect on this enzyme from several normal sources. Methylglyoxal also inactivated only the participate hexominase of the EAC cells, but this inactivation was less pronounced than the effect on GA3PD. Methylglyoxal has little inactivating effect on glucose 6-phosphate dehydrogenase (G6PD), and no effect on L-lactate dehydrogenase (LDH) of the malignant cells. Glucose-dependent L-lactic acid formation of EAC-cell-free homogenate was strongly inhibited by MG, but when GA3PD of normal cells was added to this homogenate, significant lactate formation was observed even in the presence of MG. Methylglyoxal also inhibited the respiration of EAC-cell mitochondria. Respiration of mitochondria isolated from liver and kidney of normal mice, however, remained unaffected. As a consequence of the inhibition of glycolysis and mitochondrial respiration, the ATp level of the EAC cells was drastically reduced. Studies reported herein strongly suggest that the tumoricidal effect of MG is mediated at least in part through the inhibition of mitochondrial respiration and inactivation of GA3PD, and this enzyme may play an important role in the high glycolytic capacity of the malignant cells.
62 citations
TL;DR: In this article, a polycrystalline, 10μm size magnesium silicide was prepared by alloying 99.9% purity poly crystalstalline silicon obtained from rice husk ash and high-purity magnesium powder.
Abstract: Polycrystalline, 10μm size magnesium silicide was prepared by alloying 99.9% purity polycrystalline silicon obtained from rice husk ash and high-purity magnesium powder. The material in sintered pellet form was characterized for its structural, electrical, thermal, thermoelectric and other properties. A typical sintered pellet exhibited a room-temperature (30°C) thermoelectric power of 565 μV K−1 and an electrical resistivity of 35 Ω cm. On the other hand, the material was found to be thermally quite stable up to 650°C with a room-temperature thermal conductivity of 6.3×10−3cals−1cm−1K−1 (2.6 J s−1 m−1 K−1). These properties of the material indicate that the material can find potential applications as a thermoelectric generator and in other semiconductor devices. Furthermore, an indigenous technology for large-scale production of silanes (SiH4) can be developed using this Mg2Si which could be prepared in large quantities by a simple and low-cost process.
61 citations
TL;DR: In this article, the reaction of Ru(PPh 3 ) 3 X 2 (X Cl, Br) with the Schiff base condensate of 4-substituted benzaldehyde (RC 6 H 4 CHO) and 2-aminophenol under aerobic conditions affords the complexes Ru III (RL)(PPH 3 ) 2 X in which RL is the Schiffbase ligand bound to the metal centre at the phenolic oxygen (deprotonated azomethine nitrogen and an ortho carbon atom (deprobated) of the benzaldehyde fragment
55 citations
TL;DR: In this article, a facile and general synthesis of quinolines and 2,3-dihydro-4(1H)-quinolones was accomplished, through palladium catalysed reaction of o-iodoanilides with acetylenic carbinols.
52 citations
TL;DR: At high temperatures, Mott's model of phonon-assisted small-polaron hopping between nearest neighbors is consistent with the data, while at low temperatures the variable-range-hopping model appears to be valid.
Abstract: Measurements are reported for the electrical conductivity of different compositions of silicate glasses containing copper and vanadium in the temperature range 200\char21{}500 K. The experimental results for the two systems are found to be very similar and are analyzed with respect to theoretical models existing in the literature. At high temperatures, Mott's model of phonon-assisted small-polaron hopping between nearest neighbors is consistent with the data, while at low temperatures the variable-range-hopping model appears to be valid. The generalized polaron-hopping model of Schnakenberg and the percolation model applied to the small-polaron-hopping regime of Triberis and Friedman can also predict the temperature dependence of the conductivity data. The various model parameters obtained from the best fits are found to be consistent with the glass compositions.
43 citations
TL;DR: In this paper, it was shown that hydroxyl compounds readily add to dihydropyran in presence of a catalytic amount of ceric ammonium nitrate to give high yield of tetrahydropyranyl ethers.
43 citations
TL;DR: The formalism is a natural nonperturbative analog of the thermodynamic perturbation theory by showing that a perturbative solution of the thermal-cluster-cumulant equations generates a variation of the Bloch-Balian-de Dominicis theory.
Abstract: We present in this paper a systematic nonperturbative cluster-cumulant method for deriving thermal averages of operators in quantum many-body systems. The method combines the advantages of the cumulant expansion scheme of thermodynamic perturbation theory, the approach of thermofield dynamics as a finite-temperature field theory, and the time-dependent coupled-cluster theory extended to "imaginary time". We have generalized the concepts of cumulants in a nonperturbative manner and have posited on the statistical operator an exponential-like ansatz containing connected, size-extensive operators in the exponent. These latter cumulantlike operators have been termed "cluster cumulants" by us. For a compact treatment, we have derived an alternative thermal field theory in which a time-ordered product is expanded in terms of "thermal normal products" of operators and thermal contractions-leading to a "thermal Wick's theorem". The thermal normal products are the finite-temperature analogs of the ordinary normal products and have zero thermal averages. Operators in these products commute (anticommute) under permutations for bosons (fermions). This thermal representation is shown to be unitarily related to the traditional thermofield dynamics formulation, but has the advantage of using only the physical variables. The imaginary-time evolution of the statistical operator is treated by our recently formulated time-dependent cluster-cumulant theory. The partition function is evaluated as an exponential of a connected quantity. As an illustrative example, we have computed the partition function of an anharmonic oscillator with equally weighted cubic and quartic perturbation for a wide range of coupling, extending to the strongly nonperturbative regime. We study the behavior of free energy in the low-temperature limit and verify numerically the validity of the Kohn-Luttinger theorem [Phys. Rev. 118, 41 (1960)] for this system. We also show that our formalism is a natural nonperturbative analog of the thermodynamic perturbative theory by showing that a perturbative solution of the thermal-cluster-cumulant equations generates a variation of the Bloch-Balian-de Dominicis theory.
37 citations
TL;DR: In this article, a highly stereocontrolled synthesis of furofuran lignans, Paulownin (1a) and Isogmelinol (1b) is described involving intramolecular radical cyclisation as a key step.
TL;DR: In this article, a time-correlated single-photon counting technique is used to determine the fluorescence lifetimes in some hydrocarbon solvents at room temperature, and it is suggested that the proton transfer in 4-methyl-2,6-diformyl phenol (MFOH) can have only one ground state conformation, except in benzene and toluene.
TL;DR: In this article, a local grid method is proposed for computing the bound state eigenvalues and eigenvectors of multidimensional systems and the connection of the proposed methods with the one-dimensional Fourier grid Hamiltonian method is clarified.
TL;DR: In this article, a glass-metal nanocomposites involving copper and nickel, respectively, have been synthesized in bulk form by hot pressing sol-gel derived silica-metal nanoparticle composite powders.
Abstract: Glass-metal nanocomposites involving copper and nickel, respectively, have been synthesized in bulk form by hot pressing sol-gel derived silica-metal nanoparticle composite powders. The particle diameters range from 9 to 17.5 nm. The specimens exhibit the characteristic behavior of the metallic species in their nanocrystalline forms.
TL;DR: The results of a comprehensive study of localization and electron-electron interaction effects in doped polypyrrole films show the conductivity when temperature T>10 K can be explained by Mott's variable-range hopping model and the density of states and hopping distance can be calculated from these data.
Abstract: We report the results of a comprehensive study of localization and electron-electron interaction effects in doped polypyrrole films. We have measured the electrical conductivity and magnetoconductivity within the temperature range 1.8 K≤T≤300 K. The observed temperature dependence of dc conductivity cannot be explained either by the band-conduction model or by assuming a temperature-dependent energy gap. However, the conductivity when temperature T>10 K can be explained by Mott's variable-range hopping model and the density of states and hopping distance can be calculated from these data
TL;DR: Clean and efficient Michael addition of silyl enol ethers to methyl vinyl ketone has been achieved through a simple solvent-free reaction on the surfac as mentioned in this paper, which has been shown to be solvent free.
TL;DR: Raman spectroscopic studies of three isomeric pyridinic carboxylic acids, viz. picolinic, nicotinic and iso-nicotinic acid in solid state, in aqueous solution and in silver hydrosol, in the frequency range 900-1750 cm −1, have been made.
TL;DR: In this article, a highly correlated scheme for implementing a Fockspace multireference coupled-cluster theory for computing directly ionization potentials (IPs) is proposed. But it is not shown that the computed IP values from their scheme are correct at least up to fourth order.
TL;DR: It is interesting to note that with the introduction of appropriate nonlinearity a micromaser can be made to approach towards a number state with a low number of photons.
Abstract: A micromaser containing a Kerr medium in its cavity has been investigated. We have presented an exact solution to the model Hamiltonian, which, apart from the usual Jaynes-Cummings terms, contains a Kerr term (${\mathit{a}}^{\mathrm{\ifmmode^\circ\else\textdegree\fi{}}2}$${\mathit{a}}^{2}$). We have shown that the Kerr cavity nonlinearity significantly modifies the photon statistics of the micromaser field. Particularly, it is interesting to note that with the introduction of appropriate nonlinearity a micromaser can be made to approach towards a number state with a low number of photons.
TL;DR: In this article, the grain boundary potential, the density of trap states and the carrier concentration of the films can be obtained by measuring reflectances of the film deposited on non-absorbing substrates.
TL;DR: In this article, the authors present a review of the electron transfer reactions of dodecatungstocobaltate(II/III) and dodecamolybdocerate(IV) with peroxodisulphate and periodate.
TL;DR: A number of 5-substituted uracils, eg [ E-5-(2-acylvinyl)uracils 8a–8g, were found to have cytotoxic activities against CCRF-CEM human lymphoblastoid cells, HT-29 colon carcinoma cells and L1210/0 mouse leukemia cells and to inhibit thymidylate synthase.
TL;DR: In this article, the ground state conformers of 4-methyl-2,6-diformyl phenol (MFOH) in two proton-accepting solvents (dimethylsulphoxide (DMSO) and N,N -dimethylformamide (DMF)) were identified.
Abstract: From a detailed study of the fluorescence spectra, excitation spectra and time-resolved kinetics, two ground state conformers of 4-methyl-2,6-diformyl phenol (MFOH) in two proton-accepting solvents (dimethylsulphoxide (DMSO) and N,N -dimethylformamide (DMF)) were identified: the 4-methyl-2,6-diformyl phenolate (MFO − ) anion and the hydrogen-bonded closed conformer. The yellow—green and blue emissions at 520 and 460 nm are assigned to MFO − and the hydrogen-bonded open conformer respectively. At 77 K the fluorescence due to the open conformer is markedly suppressed, showing that this conformer is less stable than (MFO − )*. At this low temperature the fluorescence spectrum is shown to be contaminated by phosphorescence. Fluorescence decay times were measured for both species. Experimental evidence is in favour of an equilibrium between two conformers in both the ground and excited states. It is shown that the short- to long-wavelength fluorescence intensity ratio is dependent on the excitation energy.
TL;DR: In this paper, the effect of a magnetic field on the luminescence of unlinked as well as linked exciplex systems has been discussed and a complex interplay between spin evolution, radical pair recombination and diffusion determine the magnitude and nature of the magnetic field effect (MFE).
TL;DR: In this paper, the variations in ultrasonic velocity and attenuation with temperature have been explained by a model assuming an asymmetric double-well potential having distributions of both the barrier height and the asymmetry parameter.
Abstract: The ultrasonic velocity and attenuation in four different samples of the (V2O5)x−(GeO2)1−x glass system (x = 0.5321,0.5816,0.6635 and 0.7132) have been measured at temperatures between 77 and 300 K using the ultrasonic pulse echo technique at 8 MHz. The elastic moduli and Debye temperatures have been calculated from the velocity data for each composition. The variations in ultrasonic velocity and attenuation with temperature have been explained by a model assuming an asymmetric double-well potential having distributions of both the barrier height and the asymmetry parameter.
TL;DR: It is shown that the now established coupled-cluster-based linear-response theory can be viewed as an approximate version of the consistent propagator theory, which furnishes the same poles as the latter but nonconsistent residues.
Abstract: We develop in this paper a consistent superoperator-resolvent-based propagator theory using the extended coupled-cluster (CC) parametrization [Phys. Rev. A 36, 2519 (1987); Ann. Phys. 151, 311 (1983)] of the ground state. The method exploits the underlying non-Hermitian nature of the transformed Hamiltonian appearing in the extended coupled-cluster method. In this method, we obtain finite expressions in powers of cluster coefficients for both the transition amplitudes as the residues and the elements of the effective matrix contributing to the poles of the propagator. There is a natural ``resolution of identity'' involving consistent basis constructed by us, which leads to the biorthogonal sets of ket and bra functions used in the representation of the intermediate states in the inner projection of the propagator. The manifold of operators generating these states satisfies the ``vacuum-annihilation condition'' on the ground state and is thus consistent. There is a natural decoupling of the forward and backward components of the propagator even under the uneven truncation of the CC expansion of the ground state and the operator basis, which should be convenient for practical applications. We have discussed in detail the realization of the consistent representation of the ionized or excited states by taking as illustrative examples the case of one-electron and polarization propagators and have suggested practical truncation schemes for their implementation. An order-by-order perturbative analysis has been made to indicate the relation of our formalism to some of the more recent theories. We have also shown that the now established coupled-cluster-based linear-response theory can be viewed as an approximate version of the consistent propagator theory, which furnishes the same poles as the latter but nonconsistent residues.
TL;DR: A convenient route to the vicinally substituted cyclopentanones 4,8 have been developed via rearrangement of oxabicyclo[3.2.0]heptanes obtained through intramolecular [2+2] photocycloaddition in dienes derived from ketones 1, 7.
TL;DR: In this article, the hexadentate ligands RN(O)NNHC6H4S(CH2)3SC6H 4NHN(O)(NR (H2L1: R Me; H2L2 : R ǫ > g|) and their nickel(II) complexes were synthesized.
TL;DR: In this article, the aldol reaction of trimethyl silyl enol ethers with aldehydes on the solid surface of neutral alumina under sonication without any solvent is found to proceed providing cross aldolic products with anti selectivity.
TL;DR: Dendritic growth has been observed in glasses containing nanometer-sized metal particles of either bismuth or aluminum, and the fractal dimension of all the electrodeposits appears to increase as the length scale is reduced.
Abstract: Silver electrodeposits have been grown within a wide range of oxide glass sytems. The latter are first of all subjected to an alkali-metal\char21{}silver-ion exchange reaction. The experimental configuration ensures two-dimensional growth. The fractal dimension of the electrodeposits has been estimated for each sample. Glasses having lithium ions (in the original composition) show a fractal dimension around 1.85 whereas those containing sodium ions give a fractal dimension of 1.68 for their respective silver deposits. Dendritic growth has been observed in glasses containing nanometer-sized metal particles of either bismuth or aluminum. The fractal dimension of all the electrodeposits appears to increase as the length scale is reduced.