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981.
The evolution of 2-D disturbances in hypersonic boundary layer with Mach number 6,8, and 10 was investigated numerically by
three different numerical schemes. At the entrance, second mode T-S waves with different amplitudes were introduced, and the
relation between the Mach number and the amplitude of the disturbance when shocklets started to appear was investigated. By
comparing the disturbance velocity profiles with those provided by linear stability theory, the effects of shocklets on flow
structures were also investigated. 相似文献
982.
Piaoping Yang Zhenlü Wang JianFeng Yu Qingsheng Liu Tonghao Wu 《Reaction Kinetics and Catalysis Letters》2004,83(1):129-136
A kinetic model is proposed to account for the effect of oxygen during catalyst premodification on the rate and enantioselectivity in hydrogenation of methyl pyruvate over cinchonidine modified platinum catalysts.This revised version was published online in December 2005 with corrections to the Cover Date. 相似文献
983.
Titanium pyrrolyl complexes are effective catalysts for the synthesis of alpha,beta-unsaturated imines, which can be further functionalized using Rh-catalyzed alkene or alkyne insertion into the beta-C-H bond. 相似文献
984.
In this paper we have demonstrated that the crystallization method of amorphous colloids is convenient and feasible in the large-scale production of one-dimensional (1D) nanostructures. For the crystals with highly anisotropic structures, such as orthorhombic, trigonal, and hexagonal crystals, the crystallization generally tends to occur along the (001) axis. The preparation of orthorhombic bismuth sulfide (Bi2S3) nanorods and trigonal selenium ( t-Se) nanowires by the crystallization route was used as typical examples to illustrate the process and mechanism of crystallization. The as-prepared products were characterized with transmission electron microscopy, field-emission scanning electron microscopy, X-ray diffraction, and selected area electron diffraction. Additionally, the detailed crystal growth processes involved in the crystallization of amorphous Bi2S3 colloid were investigated by studying the morphology and structure of intermediates. It demonstrates that the growth of the nanorods is through two key steps: (1) the formation of multiple activated sites on the surface of spherical Bi2S3 colloid and (2) the subsequent preferential growth along these sites. 相似文献
985.
Cao XY Liu XH Zhou XH Zhang Y Jiang Y Cao Y Cui YX Pei J 《The Journal of organic chemistry》2004,69(18):6050-6058
This paper reports the facile synthetic strategy of a series of novel pi-conjugated dendrimers (G0 and G1) based on 10,15-dihydro-5H-diindeno[1,2-a;1',2'-c]fluorene (truxene) in which the benzene cores are generated "in-situ" from acetyl aromatics by the acid-promoted cyclotrimerizations. The unique NMR behaviors, physical properties, and electroluminescence device applications are also presented. Besides the purity, the structure, and the confirmation of the successful formation and isolation of desired compounds by clear assignments of every molecule by (1)H and (13)C and 2D NMR characterizations, several astonishing NMR behaviors have been observed in various solvents. For 1, chemical shift values belonging to H-2' of hexyl substituents move to the most upfield; however, such chemical shift values move from 0.48 to 0.85 ppm when pyridine-d(5) or benzene-d(6) is used as solvent. Our dendrimers as the emissive layers in organic light-emitting diodes gave blue-green light with an external quantum efficiency up to 0.16% both for G0 and for G1 in nitrogen, respectively, which exhibit unique electroluminescence spectra in comparison with their corresponding photoluminescence ones. 相似文献
986.
The Markov moment problem is to characterize sequences admitting the representation sn=01xnf(x)dx, where f(x) is a probability density on [0,1] and 0f(x)c for almost all x. There are well-known characterizations through complex systems of non-linear inequalities on {sn}. Necessary and sufficient linear conditions are the following: s0=1, and for all and . Here, is the forward difference operator. This result is due to Hausdorff. We give a new proof with some ancillary results, for example, characterizing monotone densities. Then we make the connection to de Finettis theorem, with characterizations of the mixing measure.in final form: 18 June 2003 相似文献
987.
Magnetic-field- and temperature-dependent Raman scattering studies of Ca3Ru2O7 reveal dramatic field-dependent properties arising from transitions between various complex orbital and magnetic phases, including a field-induced orbital-ordered to orbital-disordered transition (H(o) // hard axis), and a reentrant orbital-ordered to orbital-disordered to orbital-ordered transition (H(o) // easy axis). We find that the dramatic magnetic-field properties are most prevalent in a "mixed"-magnetic and -orbital phase regime, providing evidence for a strong connection between orbital phase inhomogeneity and "colossal" field effects in the ruthenates. 相似文献
988.
We applied a finite-difference time domain algorithm to the study of field and intensity correlations in random media. Close to the onset of Anderson localization, we observe deviations of the correlation functions, in both shape and magnitude, from those predicted by the diffusion theory. Physical implications of the observed phenomena are discussed. 相似文献
989.
The relaxor based ferroelectric (1-x)Pb(Zn(1/3)Nb(2/3))O(3)-xPbTiO(3) and (1-x)Pb(Mg(1/3)Nb(2/3))O(3)-xPbTiO(3) single crystals provided new challenges in property characterization because their extraordinarily large piezoelectric coefficients and electromechanical coupling coefficients. Large errors may occur in some of the derived material constants using conventional characterization techniques. This paper will analyze the inadequacy of the traditional characterization methods and provide some basic guidelines for properly characterizing piezoelectric materials with extremely high piezoelectric and electromechanical coupling coefficients. 相似文献
990.
Zhong-Peng Yang Chong-guang Cao Xiao-Min Tang 《Journal of Applied Mathematics and Computing》2003,13(1-2):117-123
For ann x n real matrixX, let ?(X)=X ο (X ?1) T , where ο stands for the Hadamard (entrywise) product. SupposeA, B, C andD aren x n real nonsingular matrices, and among them there are at least one solutions to the equation ?(X)=1/nJ n . An equivalent condition which enable $M = \left( {\begin{array}{*{20}c} A & B \\ C & D \\ \end{array} } \right)$ become a real solution to the equation ?(X)=1/2nJ 2n , is given. As applications, we get new real solutions to the matrix equation ?(X)-1/2nJ 2n by applying the results of Zhang, Yang and Cao [SIAM. J. Matrix Anal. Appl, 21 (1999), pp: 642–645] and Chen [SIAM. J. Matrix Anal. Appl, 22 (2001), pp:965–970]. At the same time, all solutions of the matrix equation ?(X)=1/4J 4 are also given. 相似文献