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61.
The preliminary results presented in this work show that an enantiomer purification approach based on SDE via sublimation can be extended to non-volatile liquid compounds such as α-(phenyl)ethylamine and its β-fluoro-derivatives by way of their rational modification with a sublimation enabling tag. 3,3,3-Trifluoro-2-(trifluoromethyl)-2-methyl-propanoic acid was found to perfectly serve the role of such a modifying tag. Thus, the corresponding amides derived from the amines and the fluorinated propanoic acid were highly crystalline and reasonably volatile compounds allowing for their sublimation at room temperature under normal pressure. All of these derivatives showed substantial self-disproportionation of enantiomers (SDEs) via sublimation under kinetic conditions (on a Petri dish in the open air). These preliminary results serve as a proof of a new principle that may extend the generality of enantiomer purification via sublimation to various organic compounds with physico-chemical properties of which render them otherwise unsuitable for a sublimation procedure. In particular, the very attractive cost structure of sublimation procedure renders this approach of potentially high practical and economic efficiency. 相似文献
62.
63.
We present a solution to this problem in the form of a fast algorithm with computational complexity that scales as N log N , where N is the number of spatial measurements of the scattered field. 相似文献
64.
65.
We consider the nonlinear Schrodinger equation with the nonlinearity management which describes Bose-Einstein condensates under Feshbach resonance. By using an averaging theory, we derive the Hamiltonian averaged equation and compare it with other averaging methods developed for this problem. The averaged equation is used for analytical approximations of nonlinearity-managed solitons. 相似文献
66.
We study a type Ia supernova explosion using three-dimensional numerical simulations based on reactive fluid dynamics. We consider a delayed-detonation model that assumes a deflagration-to-detonation transition. In contrast with the pure deflagration model, the delayed-detonation model releases enough energy to account for a healthy explosion, and does not leave carbon, oxygen, and intermediate-mass elements in central parts of a white dwarf. This removes the key disagreement between simulations and observations, and makes a delayed detonation the mostly likely mechanism for type Ia supernovae. 相似文献
67.
We report what we believe to be the first rigorous numerical solution of the two-dimensional Maxwell equations for optical propagation within, and scattering by, a random medium of macroscopic dimensions. Our solution is based on the pseudospectral time-domain technique, which provides essentially exact results for electromagnetic field spatial modes sampled at the Nyquist rate or better. The results point toward the emerging feasibility of direct, exact Maxwell equations modeling of light propagation through many millimeters of biological tissues. More generally, our results have a wider implication: Namely, the study of electromagnetic wave propagation within random media is moving toward exact rather than approximate solutions of Maxwell's equations. 相似文献
68.
Coherent backscattering (CBS) of light in random media has been previously investigated by use of coherent light sources. Here we report a novel method of CBS measurement that combines low spatial coherence, broadband illumination, and spectrally resolved detection. We show that low spatial coherence illumination leads to an anomalously broad CBS peak and a dramatic speckle reduction; the latter is further facilitated by low temporal coherence detection. Thus CBS can be observed in biological tissue and other media that previously were beyond the reach of conventional CBS measurements. We also demonstrate, for the first time to our knowledge, spectroscopic analysis of CBS. CBS spectroscopy may find important applications in probing random media such as biological tissue in which depth-selective measurements are crucial. 相似文献
69.
Kessler VG 《Chemical communications (Cambridge, England)》2003,(11):1213-1222
General principles of formation and stability of the heterometallic alkoxides existing due to Lewis Acid-Base interaction, isomorphous substitution and heterometallic metal-metal bonds are discussed. The molecular structure design approach based on the choice of a proper molecular structure type and completing it with the ligands, providing both the necessary number of donor atoms and the sterical protection of the metaloxygen core, is presented. Its applications in prediction of the composition and structure of single source precursors of inorganic materials are demonstrated for such classes of compounds as oxoalkoxides, alkoxide beta-diketonates, alkoxide carboxylates, derivatives of functional alcohols, metallatranes and metallasiloxanes. 相似文献
70.
The stable set problem is to find in a simple graph a maximum subset of pairwise non-adjacent vertices. The problem is known to be NP-hard in general and can be solved in polynomial time on some special classes, like cographs or claw-free graphs. Usually, efficient algorithms assume membership of a given graph in a special class. Robust algorithms apply to any graph G and either solve the problem for G or find in it special forbidden configurations. In the present paper we describe several efficient robust algorithms, extending some known results. 相似文献