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991.
Bishambhar Dayal Saksena Krishna Gopal Srivastava 《Proceedings Mathematical Sciences》1948,28(5):437-446
The method of finding the piezo-electric constants with the help of the variations of bond distances and bond angles on strain has been utilised in finding the variations of the piezo-electric constants ε11 and ε41 of α-quartz with temperature. It is found that the variations of ε11 with temperature can be explained on the basis of the change of co-ordinates with temperature. At 558° C. the silicon atoms are found to occupy the same positions as they do in β-quartz. As the transition temperature is reached, the longitudinal coefficient ε11 drops to zero, while the transverse coefficient ε41 decreases by only 15%. The piezo-electric constant of β-quartz has been similarly determined and its value comes out to be 1·05×104 for a non-ionic crystal (k=·724) and 1·45×104 for an ionic crystal (k=1). 相似文献
992.
N. Ananda Krishna 《Journal of Quantitative Spectroscopy & Radiative Transfer》2006,102(3):432-440
Application of the discrete transfer method (DTM) has been extended to the analysis of radiative heat transfer in a variable refractive index participating medium. To validate the DTM formulation, radiative heat transfer in an absorbing, emitting and isotropically scattering planar medium was considered. The participating medium was assumed to be in radiative equilibrium. For both constant and variable refractive indices of the medium, the DTM results were compared with those available in the literature. The DTM was found to provide accurate results. 相似文献
993.
R. Krishna Kumar 《Tetrahedron》2006,62(18):4528-4534
It is demonstrated that solid support containing a novel universal linker could be efficiently used to synthesize both phosphorothioate oligodeoxyribonucleotides and second-generation 2′-O-methoxyethyloligoribonucleotides with high yield and quality as judged by ion-pair-liquid chromatography-electrospray mass spectroscopy, 31P NMR and reversed phase HPLC. Analysis of oligonucleotides shows quality being superior to that produced with standard succinyl-linker solid supports, without contamination of materials resulting from linker or support backbone decomposition. 相似文献
994.
Triquinanes and their oxygenated congeners, oxa- and dioxa-triquinanes, exhibit versatile biological activities in conjunction with synthetically challenging molecular architecture. Owing to these properties, several new strategies have been developed to accomplish the synthesis of these sesquiterpenes. Among the new strategies, cascade radical cyclization strategy has been broadly explored and well studied. Herein, we report our efforts in detail for the synthesis of dioxa-triquinanes using a domino enyne/RCM strategy as the key step. Carbohydrate based synthesis not only allows the use of inexpensive and optically pure starting materials, but also the furanose derivatives, which already possess one of the requisite dihydro-furan moieties in the desired dioxa-triquinane. The other two five-membered rings were constructed simultaneously by the cascade enyne/RCM reaction using the Grubbs' second-generation catalyst. During the course of our synthesis it was observed that the acetonide protection hinders the RCM reaction, after the initial enyne metathesis reaction. The reaction underwent smoothly under argon atmosphere, whilst use of ethylene atmosphere was found to hinder the formation of the tandem enyne/RCM product. The effect of substitution on the key reaction is described here. 相似文献
995.
Palakodety Radha Krishna P.V. Narasimha Reddy M. Uday Kiran 《Tetrahedron letters》2007,48(37):6466-6470
The Baylis-Hillman reaction of acyclic sugar-derived aldehydes is invoked as an attractive synthetic strategy for ready access to higher-carbon sugars. 相似文献
996.
Vivek Kumar Gupta D.S. Shankar Rao Chethan V. Lobo S. Krishna Prasad Uma S. Hiremath Channabasaveshwara V. Yelamaggad 《Thermochimica Acta》2006,440(2):205-211
High pressure investigations have been carried out on the photo-stimulated phase transition exhibited by a guest–host system, where the host is a non-photoactive liquid crystal. As guest molecules we chose successive homologues of a dimeric photoactive azobenzene liquid crystalline molecule to understand the influence of the length and parity of the alkylene spacer on such a transition. Our studies show that application of pressure as well as the parity of the spacer has a drastic influence both on the static and dynamic characters of the photo-stimulated phase transition. 相似文献
997.
The complete set of non-vanishing third-order elastic constants of the semiconductors ZnS and ZnSe is obtained theoretically. The strain energy density is estimated using finite strain elasticity theory by considering the interactions up to two nearest neighbours of each atom in the unit cell of these compounds. This energy density is compared with the strain dependent lattice energy density from the continuum model approximation. The second-order parameter of the potential function φ is obtained from the measured principal axis Cij. The third-order potential parameter is estimated by assuming a Lennard-Jones type of interatomic potential. The interlattice displacements as well as the second-order elastic constants are evaluated along with the six third-order elastic constants of ZnS and ZnSe. Using these second- and third-order elastic constants of ZnS, the pressure derivatives of second-order elastic constants are evaluated. The second- and third-order elastic constants of ZnSe are compared with the available experimental values. The third-order elastic constants show anisotropy in different directions. 相似文献
998.
999.
G.V.M. Sharma J. Janardhan Reddy P. Sree Lakshmi P. Radha Krishna 《Tetrahedron letters》2005,46(36):6119-6121
A versatile and efficient route to 4-substituted coumarins via a Pechmann reaction using ZrCl4 as the catalyst (10 mol %) is described. This method provides several advantages over alternative procedures such as mild, solvent-free conditions at ambient temperature, and direct isolation of the products in high yields. 相似文献
1000.
Janmanchi Damodar Srinivasulu Reddy Krishna Mohan Srinivasulu Reddy Jayarama Reddy 《Electrochemistry communications》2001,3(12):5741
Electrochemical carboxylation of benzylchlorides catalysed by Pd(II) complex afforded 2-arylpropionic acids in good yields under atmospheric pressure of carbon dioxide at constant current of 10 mA cm−2. Mechanistic and electrochemical studies revealed the cooperative role of reduced palladium species in the activation of carbon dioxide. 相似文献