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1.
C. V. Yelamaggad Manoj Mathews Uma Hiremath Geetha Nair D. S. Shankar Rao S. Krishna Prasad 《Liquid crystals》2003,30(8):899-908
A series of symmetrical dimers consisting of salicylaldimine moieties connected by flexible alkylene central spacer via ether linkages has been synthesized. In order to validate the empirical rule suggested by Date et al. to account for the smectic behaviour of such dimers, the chain length of the terminal alkoxy chain has been kept constant (C8) while the number of methylene units in the central spacer was varied from C3 to C11. Another aim of the present investigation was to understand structure-property relationship in these dimers in which the salicylaldimine mesogenic segment has been used for the first time in dimers. The mesomorphic behaviour of these dimers was evaluated using optical microscopy and differential scanning calorimetry and the structure of some of the mesophases has been further investigated with the help of X-ray diffraction. Our studies reveal that the dimers consisting of 3 to 8 methylene units in the flexible spacer show only smectic (smectic C and smectic A) phases. For the dimers containing 4, 6 and 8 methylene units in the central spacer, a unique filament growth pattern has been observed in the smectic A phase while cooling from the isotropic phase. The dimers containing of C9 to C11 methylene groups exhibit the nematic phase in addition to smectic modifications. This observation indicates that when the terminal chains are shorter than the spacer, the tendency to form smectic phases is not fully extinguished but is perhaps reduced. 相似文献
2.
G. Date T. R. Govindarajan P. Sankaran R. Shankar 《Communications in Mathematical Physics》1990,132(2):293-313
We compute the homotopy groups
0 and
1 of the classical configuration space of anO(3) invariant field theory on
×, where
is a compact two dimensional manifold for arbitrary genusg and- denotes the time coordinate. We also present the finite dimensional, unitary, irreducible, inequivalent representations of the appropriate fundamental groups and comment on some of their implications. 相似文献
3.
4.
We consider the Lie-Backlund symmetries and conservation laws of a perturbed KdV equation and NLS equation. The arbitrary coefficients of the perturbing terms can be related to the condition of existence of nontrivial LB symmetry generator. When the perturbed KdV equation is subjected to Painlevé analysisa la Weiss, it is found that the resonance position changes compared to the unperturbed one. We prove the compatibility of the overdetermined set of equations obtained at the different stages of recursion relations, at least for one branch. All other branches are also indicated and difficulties associated them are discussed considering the perturbation parameter to be small. We determine the Lax pair for the aforesaid branch through the use of Schwarzian derivative. For the perturbed NLS equation we determine the conservation laws following the approach of Chen and Liu. From the recurrence of these conservation laws a Lax pair is constructed. But the Painlevé analysis does not produce a positive answer for the perturbed NLS equation. So here we have two contrasting examples of perturbed nonlinear equations: one passes the Painlevé test and its Lax pair can be found from the analysis itself, but the other equation does not meet the criterion of the Painlevé test, though its Lax pair is found in another way. 相似文献
5.
Here we report the synthesis of a novel PNA based neocuproine.Zn RNA cleaving agent; we demonstrate that such agents sequence specifically cleave a synthetic RNA target and in particular the RNA component of human telomerase. 相似文献
6.
Shankar Kumar John M. Rosenberg Djamal Bouzida Robert H. Swendsen Peter A. Kollman 《Journal of computational chemistry》1992,13(8):1011-1021
The Weighted Histogram Analysis Method (WHAM), an extension of Ferrenberg and Swendsen's Multiple Histogram Technique, has been applied for the first time on complex biomolecular Hamiltonians. The method is presented here as an extension of the Umbrella Sampling method for free-energy and Potential of Mean Force calculations. This algorithm possesses the following advantages over methods that are currently employed: (1) It provides a built-in estimate of sampling errors thereby yielding objective estimates of the optimal location and length of additional simulations needed to achieve a desired level of precision; (2) it yields the “best” value of free energies by taking into account all the simulations so as to minimize the statistical errors; (3) in addition to optimizing the links between simulations, it also allows multiple overlaps of probability distributions for obtaining better estimates of the free-energy differences. By recasting the Ferrenberg–Swendsen Multiple Histogram equations in a form suitable for molecular mechanics type Hamiltonians, we have demonstrated the feasibility and robustness of this method by applying it to a test problem of the generation of the Potential of Mean Force profile of the pseudorotation phase angle of the sugar ring in deoxyadenosine. © 1992 by John Wiley & Sons, Inc. 相似文献
7.
J.S. Yadav B.V. Subba Reddy A.K. Basak A.V. Narsaiah A. Prabhakar B. Jagadeesh 《Tetrahedron letters》2005,46(4):639-641
Baylis-Hillman acetates undergo SN2′ allylic substitution with indoles in the presence of 20 mol % of indium tribromide under mild conditions to afford a new class of substituted indoles in high yields with (E)-stereoselectivity. The stereochemistry of the products was assigned by various NMR experiments. 相似文献
8.
Crude extracellular invertase fromSclerotium rolfsii, when coupled to glutaraldehyde activated Indion 48-R, retained 70–80% activity of the soluble enzyme. Immobilization resulted
in a decrease in the pH and temperature optima but it increased the temperature stability. Km and Vmax also increased as a result of immobilization. Both soluble and immobilized invertase showed inhibition at high substrate
concentrations. The bound enzyme showed excellent stability to repeated use and retained approx 90% of its initial activity
after 8 cycles of use. 相似文献
9.
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