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71.
Laura Pop Pierrik Lassalas László Csaba Bencze Monica Ioana Toşa Botond Nagy Florin Dan Irimie Christophe Hoarau 《Tetrahedron: Asymmetry》2012,23(6-7):474-481
Stereoselective preparative enzymatic acylation and hydrolysis/methanolysis of various C-substituted rac-thiazol-2-yl-methanols were achieved for the preparation of enantiopure or enantiomerically enriched, naturally occurring 2-hydroxymethylthiazoles. The absolute configurations of the resulting secondary alcohols were determined by a detailed 1H NMR study of Mosher’s derivatives. 相似文献
72.
RUAN Zhen-Kui JIANG Xian XU Yi-DeState Key Laboratory of CatalysisDalian Institute of Chemical Physics Academia SinicaDalian. Liaoning To whom correspondence should he addressed 《天然气化学杂志》1995,(3)
The reaction product distributions from the reactions of n-C6 and MCP over different Pt-catalysts at different temperatures were studied. It is shown that the product distributions depended on the reaction temperatures The influences of the zeolite channel functioned only at high temperature. The activity and selectivity of aromatization of n-C6 over Pt/AIPO4-5 were lower than those over Pt/L zeolite catalysts. A1PO4-5 is a non-basic support and its product distribution and reaction mechanism were different from that of basic-support catalysts such as Pt/KL and Pt/RbL. 相似文献
73.
Correction of a coherent image during KrF excimer laser ablation using a mask projection 总被引:1,自引:1,他引:0
Dong Sig Shin Jae Hoon Lee Jeong Suh To Hoon Kim 《Optics and Lasers in Engineering》2006,44(6):615-622
Using masks for laser ablation has proven useful in the fabrication of prototypes for the manufacturing of micro-fluidic devices. In this work, an excimer laser was used to engrave microscopic channels on the surface of polyethylene terephthalate (PET), which showed a high absorption ratio for an excimer laser beam with a wavelength of 248 nm. When 50 μm wide rectangular microscopic channels were made using a 500×500 μm square mask and a magnification ratio of 1/10, ditch-shaped defects were found at both corners. The calculation of the laser beam intensity showed that a coherent image in the PET specimen caused the defects. An analysis based on the Fourier diffraction theory enabled the prediction of a coherent shape at the image plane, as well as a diffracted beam between the mask and the image plane. The analysis also showed that the diameter of the aperture was a predominant factor toward the elimination of ditch-shaped defects in the rectangular microscopic channels on the PET produced by an excimer laser ablation. 相似文献
74.
5. Conclusion Chaplygin’s method is not convenient for the application in analytical form. However, the discretization of this method can
be made successfully. The method of discretization described in this work is easy for the program-ming and, in some cases,
gives better results than the Runge—Kutta method. Specifically, this happens when the steph is relatively small. It is highly un-likely that more than 6 iterations are necessary to achieve full accuracy, with 3 iterations
being the most usual case.
The fact that the upper and lower Chaplygin’s boundary functions be-come almost identical after several iterations (in the
sense of the floating point representation of their values on the grid) did not produce noticeable problems, even though it
means evident departure from the assumptions of Chaplygin’s Theorem (specifically, the solution of the differential equation
ceases to be bounded by the lower and upper functions). Nevertheless, the definite conclusion on this subject requires further
theoretical investigation. 相似文献
75.
76.
An explicit combinatorial formula for the number of Kekulé structures of a hexagon-shaped benzencid system is deduced. Thus, the validity of the previously proposed, but hitherto unproved formulas of Everett (from 195'1), Woodger (from 1951), and Cyvin from 1986) is confirmed. The proof is based on the application of the John-Sachs theorem. 相似文献
77.
Quang Huy To Yong Rok Lee Sung Hong Kim 《Monatshefte für Chemie / Chemical Monthly》2012,14(2):1421-1426
Abstract
A simple and efficient method to synthesize a variety of tetrahydroquinolinones was successfully achieved by reacting various β-enaminones with several α,β-unsaturated aldehydes. This strategy can be viewed as a Br?nsted acid-mediated formal [3+3] cycloaddition. 相似文献78.
Ratko Tošić 《Discrete Mathematics》1983,46(3):295-298
We consider the problem of ascertaining the minimum number of weighings which suffice to determine the counterfeit (heavier) coins in a set of n coins of the same appearance, given a balance scale and the information that there are exactly two heavier coins present. An optimal procedure is constructed for infinitely many n's, and for all other n's a lower bound and an upper bound for the maximum number of steps of an optimal precedure are determined which differ by just one unit. Some results of Cairns are improved, and his conjecture at the end of [3] is proved in a slightly modified form. 相似文献
79.
单点金刚石车削技术被广泛应用于光学表面的超精密加工。然而,车削表面固有的周期性残留刀痕结构将增强表面散射效应,恶化元件光学性能。为了抑制散射以获得高质量光学表面,采用气囊抛光技术主动改变车削表面周期性刀痕结构。基于Taguchi正交试验,以表面粗糙度及功率谱密度的改善率为设计指标,分析获得了最优抛光参数。采用该最优参数对一精车表面进行了抛光试验,抛光后表面粗糙度Ra由3.81 nm降到1.42 nm,各空间频率功率谱密度大幅降低,同时表面的衍射条纹消失。试验结果验证了所采用的抛光及相应优化方法的有效性,具有重要的工程应用价值。 相似文献
80.