Showing papers by "Government College published in 1993"

A finite element analysis of plane strain dynamic crack growth in materials displaying the Bauschinger effect

Abstract: In this paper dynamic crack growth in an elastic-plastic material is analyzed under mode I plane strain small-scale yielding conditions using a finite element procedure. The main objective of this paper is to investigate the influence of anisotropic strain hardening on the material resistance to rapid crack growth. To this end, materials that obey an incremental plasticity theory with linear isotropic or kinematic hardening are considered. A detailed study of the near-tip stress and deformation fields is conducted for various crack speeds. The results demonstrate that kinematic hardening does not oppose the role of inertia in decreasing the plastic strains and stresses near the crack tip with increase in crack speed to the same extent as isotropic strain hardening. A ductile crack growth criterion based on the attainment of a critical crack opening displacement at a small micro-structural distance behind the tip is used to obtain the dependence of the theoretical dynamic fracture toughness with crack speed. It is found that for any given level of strain hardening, the dynamic fracture toughness displays a much more steep increase with crack speed over the quasi-static toughness for the kinematic hardening material as compared to the isotropic hardening case.

Investigation of the activation parameters of low-temperature slip in anthracene single crystals

Abstract: In 1990 Kojima and Okada reported their observations on the temperature dependence of the yield-stress and of the activation-volume in anthracene single crystals for (001) [010] and (001) [110] slip systems in the range 80 to 370 K. Their data have been examined within the framework of the kink-pair nucleation model of plastic flow, which was originally proposed by Fletham for body-centred cubic metals, and has recently been improved and further developed by Butt. The observed interdependences of yield stress, activation volume and temperature for anthracene single crystals in the range 80 to 200 K are found to be fully explicable in terms of the model referred to, in which slip is considered to be induced by stress-assisted thermally activated formation of arcs of screw dislocations trapped in Peierls troughs.

Microhardness studies on some alum crystals

Abstract: Microhardness studies were carried out using four alums. The hardness of these crystals was found to be more than alkali halides but was comparable with alkaline earth nitrates. The load variation of hardness has been discussed. Hardness results on these alums have been analysed taking into account the structure. It was observed that hardness varied witha−4, wherea is the lattice constant. Preliminary results on dislocation etching are reported.

Energetic Band Location of Rhenium‐doped MoSe2 Single Crystals to Assess their Usefulness in PEC Solar Cell Fabrication

Abstract: Single crystals of MoSe 2 and rhenium-doped MoSe 2 have been grown by direct vapour transport technique and characterized by optical and electrochemical studies. The transmission spectra show the crystals of MoSe 2 and rhenium-doped MoSe 2 to be direct band gap semiconductors with band gap 1.6 eV and 1.2 eV, respectively. Mott-Schottky plots have been drawn to determine the type of semiconductor and its parameters, N D , E C and E V

Structure-activity relationship studies of 4-substituted-2-guanidinothiazoles: reversible inhibitors of gastric (H+/K+)-ATPase.

Abstract: The role of physicochemical factors, electronic and hydrophobic, and a hydrogen donor index in the inhibition of gastric (H+/K+)-ATPase by 4-phenyl-2-guanidinothiazoles and the 4-indolyl-2-guanidinothiazoles has been quantitatively analysed. For the first congeneric series, the resonance effect of the ortho- and para-substituents and hydrogen donor property of the meta-substituent in the phenyl ring play crucial role, whereas for 4-indolyl analogues, the hydrophobicity and electron withdrawing effect of X-substituents in the indolyl ring are shown to be important decisive factors. Also the substitution of the guanidine moiety, e.g. by benzyl, raises the activity of proton pump inhibitors. The substitution at 5-position of thiazole ring does not enhance the potency.

X-ray K-Absorption Near Edge Structure Studies of Some Mixed Ligand Cobalt (II) complexes

Abstract: X-ray absorption near edge structure (XANES) measurements have been made on the K-edges of cobalt in the five oximinoacetone thiosemicarbazone (oatsc) complexes of cobalt viz., [(Co(oatsc)2(oAc)2]; [Co(oatsc)2(Br)2]; [Co(oatsc)2(Cl)2]; [Co(oatsc)2(ClO4)2] and [Co(oatsc)2(NO3)2]. These complexes are important from the pharmacological point of view. The present XANES studies reveal that as far as the structure is concerned, the four complexes with (oAc)2, Br2, Cl2 and (ClO4)2 ligands are similar and these ligands are part of the first coordination sphere. In [Co(oatsc)2(NO3)2] we find that one nitrate group is inside the coordination sphere, whereas one nitrate group is out-side the coordination sphere. Our studies establish the relative ionic character in the order [Co(oatsc)2(NO3)2] > [Co(oatsc)2(ClO4)2] > [Co(oatsc)2(Cl)2]> [Co(oatsc)2(Br)2] > [Co(oatsc)2(oAc)2]. The average metal-ligand bond distance have been estimated and explained on the basis of the structures of the complexes.

Oxadiazolylimidazobenzodiazepines as novel partial agonists with the benzodiazepine receptor: a QSAR analysis.

Abstract: This communication reports a QSAR analysis of two series of oxadiazolylimidazobenzodiazepines, which were recently reported by Watjen et al. (1989) to possess partial agonist activity with the benzodiazepine receptor, BZR

Fluorine‐Containing Bioactive Benzimidazoles.

Abstract: Benzimidazole derivatives are important in the field of biochemistry and medicine. Although several reviews exist on benzimidazoles and some of the well-known fluorinated derivatives like astemizole, pimozide, benperidol and droperidol, there is nothing comprehensive on the fluorinated derivatives. In this article, we have tried to cover the synthesis and biological activity (where reported) of all types of fluorinated benzimidazoles. The text has been classified on the basis of the position of fluorine or of fluorinated groups on the benzimidazole system, as follows: I On a nitrogen atom (a) On one nitrogen (b) On both the nitrogens II On imidazolyl carbon III On the benzene ring (a) At one position (b) At more than one position IV On more than one atom (a) On the benzene ring and on the nitrogen atom (b) On the benzene ring and on imidazolyl carbon (c) On the imidazolyl carbon and nitrogen atom (d) On the benzene ring, nitrogen atom and imidazolyl carbon (e) On two benzimidazole rings