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41.
42.
By observing trends in the folding kinetics of experimental 2-state proteins at their transition midpoints, and by observing trends in the barrier heights of numerous simulations of coarse-grained, C(alpha) model Go proteins, we show that folding rates correlate with the degree of heterogeneity in the formation of native contacts. Statistically significant correlations are observed between folding rates and measures of heterogeneity inherent in the native topology, as well as between rates and the variance in the distribution of either experimentally measured or simulated phi values. 相似文献
43.
Viswanathan R Prabhakaran EN Plotkin MA Johnston JN 《Journal of the American Chemical Society》2003,125(1):163-168
The scope of aryl radical additions to the nitrogen of azomethines is described. Aryl, trifluoromethyl alkyl, and alpha,beta-unsaturated ketimines engage in regioselective aryl-nitrogen bond formation via 5-exo cyclizations of an aryl radical to azomethine nitrogen. Selectivity for carbon-nitrogen over carbon-carbon bond formation is generally high (>95:5) and competes only with direct aryl radical reduction by stannane (0-10%). Alpha-ketoimines are a promising new class of carbon radical acceptors for which no competitive aryl radical reduction is observed. The reaction conditions are pH-neutral and are therefore among the mildest methods available for amination of an aromatic ring. The ketimines examined did not suffer from competitive reduction by stannane, offering an advantage over the use of diazo and azide functional groups as nitrogen sources for carbon radicals. The free radical-mediated aryl amination was sequenced with the O'Donnell phase transfer-catalyzed enantioselective alkylation strategy of glycinyl imine to provide either enantiomer of indoline alpha-amino acids with high ee. These new constrained phenyl alanine derivatives are now readily available for evaluation across a variety of applications. 相似文献
44.
V. V. Plotkin 《Radiophysics and Quantum Electronics》1992,35(11-12):575-583
Low-frequency electric-mode excitation in the earth-ionosphere cavity is considered with the aid of Maxwellequation vector mode transformation with allowance for field penetration into the ionosphere and magnetosphere. It is shown that for atmospheric current generators, the ionosphere can exhibit the properties of a conductor or an insulator, depending, on frequency. The penetration of atmospheric electric fields from the earth into the ionosphere can cause corresponding unitary variatary variations of geophysical parameters. 相似文献
45.
46.
In this paper we study the notion of knowledge from the positions of universal algebra and algebraic logic. We consider first
order knowledge which is based on first order logic. We define categories of knowledge and knowledge base models. These notions
are defined for the fixed subject of knowledge. The key notion of informational equivalence of two knowledge base models is
introduced. We use the idea of equivalence of categories in this definition. We prove that for finite models there is a clear
way to determine whether the knowledge base models are informationally equivalent. 相似文献
47.
A Soibel SS Banerjee Y Myasoedov ML Rapparort E Zeldov S Ooi T Tamegai 《Pramana》2002,58(5-6):893-898
Using a novel differential magneto-optical imaging technique we investigate the phenomenon of vortex lattice melting in crystals
of Bi2Sr2CaCu2O8 (BSCCO). The images of melting reveal complex patterns in the formation and evolution of the vortex solid-liquid interface
with varying field (H)/temperature (T). We believe that the complex melting patterns are due to a random distribution of material disorder/inhomogeneities across
the sample, which create fluctuations in the local melting temperature or field value. To study the fluctuations in the local
melting temperature/field, we have constructed maps of the melting landscape T
m(H, r), viz., the melting temperature (T
m) at a given location (r) in the sample at a given field (H). A study of these melting landscapes reveals an unexpected feature: the melting landscape is not fixed, but changes rather
dramatically with varying field and temperature along the melting line. It is concluded that the changes in both the scale
and shape of the landscape result from the competing contributions of different types of quenched disorder which have opposite
effects on the local melting transition. 相似文献
48.
The aim of this work is to study the notions of elementarily equivalent and isotypic knowledge bases. We prove that isotypic knowledge bases are informationally equivalent. 相似文献
49.
50.