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951.
Hcp-icosahedron structural transformation induced by the change in Ag concentration during the freezing of (CoAg)561 clusters 下载免费PDF全文
The synergy effect of alloy elements in bimetallic clusters can be used to tune the chemical and physical properties. Research on the influences of alloy concentration and distribution on the frozen structure of bimetallic clusters plays a key rolc in exploring new structural materials. In this paper, we study the influence of Ag concentration on the frozen structure of the (AgCo)561 cluster by using molecular dynamics simulation with a general embedded atom method. The results indicate that tt~e structure and chemical ordering of the (AgCo)561 cluster are strongly related to Ag concentration. Hcp-icosahedron structural transformation in the frozen (CoAg)561 cluster can be induced by changing Ag concentration. The chemical ordering also transforms to Janus-like Co Ag from core-shell Co-Ag. 相似文献
952.
大尺度三维几何尺寸立体视觉测量系统实现 总被引:17,自引:2,他引:15
基于立体视觉的大尺度三维几何尺寸测量技术是对外形不规则的大型物体进行几何量测量的有效方法。与传统的视觉测量技术不同,大尺度视觉测量的精度随测量距离的增加而迅速下降,同时大尺度空间下照明条件难以控制,也使得测量变得不稳定。因此如何在大测量尺度的前提下提高测量精度成为这一领域的研究难点。从立体视觉测量系统的原理出发,分析了影响系统精度的各种因素,将相位一致性变换与极线约束条件引入结构光光条中心提取之中,显著提高了图像分析的精度。研制了测量系统的样机并给出了实验结果,现场测试表明该系统可以有效地保证大尺度条件下的测量精度。 相似文献
953.
G. H. Cao R. Schaarschuch C.‐G. Oertel W. Skrotzki 《Crystal Research and Technology》2012,47(1):13-18
Polycrystalline YCu specimens with a CsCl‐type B2 structure made by induction melting were investigated by transmission electron microscopy (TEM). TEM studies show that an orthorhombic YCu B27 martensite with FeB‐type structure having lattice parameters a = 0.71 nm, b = 0.45 nm and c = 0.54 nm forms during deformation at ambient temperature. (101) twins are observed in the YCu B27 phase. The orientation relationship of B27 with B2 matrix is (001)[1 0]B27 ‖ (112)[1 0]B2. Effects of B27 phase formation on the ductility of YCu alloy are discussed. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
954.
955.
Xiao LiuRidao Chen Dan XieMei Mei Jianhua ZouXiaoguang Chen Jungui Dai 《Tetrahedron》2012,68(47):9539-9549
Microbial transformation of two taxadienes (1, 2) was individually investigated with two filamentous fungi, Cunninghamella echinulata CGMCC 3.3400 and Aspergillus niger CGMCC 3.1858, and two actinomycete stains, Streptomyces griseus CACC 200300 and Nocardia purpurea CGMCC 4.1182. A total of 21 products were obtained, 13 of which were new compounds. The reactions that occurred exhibited diversity, including selective hydroxylation, epoxidation, oxidation, demethylation, acetylation, deacetylation, and O-alkylation, and we have proposed plausible bioconversion routes. The results of a pharmacological evaluation showed that compound 15 displayed significant reversal of activity toward multi-drug resistant (MDR) tumor cell line A549/taxol when co-administered with paclitaxel at 10 μM. This investigation provided a useful approach to prepare new active taxane derivatives that were difficult to access by chemical means. 相似文献
956.
Pushyamitra MishraHardesh K. Maurya Brijesh KumarVishnu K. Tandon Vishnu Ji Ram 《Tetrahedron letters》2012,53(9):1056-1059
An efficient and concise one pot synthesis of highly functionalized thiophenes and pyranone fused thiophenes has been delineated through base induced ring transformation of suitably functionalized 2H-pyran-2-ones by ethyl thioglycolate by inter and intramolecular C-S and C-C bond formation. 相似文献
957.
《Analytical letters》2012,45(11):2252-2270
Abstract A novel adsorptive fast Fourier transform cyclic voltammetry (AFFTCV) technique for the fast determination of tramadol in flow‐injection systems has been introduced in this work. The potential waveform, consisting of the potential steps for cleaning, stripping, and potential ramp, was continuously applied on an Au disk microelectrode (with a 12.5 µm in radius). The proposed detection method has some advantages, the greatest of which are as follows: first, it is no more necessary to remove oxygen from the analyte solution and second, it is a very fast and appropriate technique for determination of the drug compound in a wide variety of chromatographic analysis methods. The influences of pH of eluent, accumulation potential, sweep rate, and accumulation time on the determination of the tramadol were considered. The method was linear over the concentration range of 1.5–900,000 pg/ml (r=0.9968) with a limit of detection and quantitation 0.32 and 1.5 pg/ml, respectively. The method has the requisite accuracy, sensitivity, precision, and selectivity to assay tramadol in tablets and in biological fluids. 相似文献
958.
A new synthetic approach for the preparation of block copolymers by mechanistic transformation from atom transfer radical polymerization (ATRP) to visible light‐induced free radical promoted cationic polymerization is described. A series of halide end‐functionalized polystyrenes with different molecular weights synthesized by ATRP were utilized as macro‐coinitiators in dimanganese decacarbonyl [Mn2(CO)10] mediated free radical promoted cationic photopolymerization of cyclohexene oxide or isobutyl vinyl ether. Precursor polymers and corresponding block copolymers were characterized by spectral, chromatographic, and thermal analyses. 相似文献
959.
《Analytical letters》2012,45(4):747-762
Abstract In this work a novel method for the determination of piroxicam in flow‐injection systems has been developed. A system using fast Fourier transform continuous cyclic voltammetry (FFTCV), at a gold microelectrode in flowing solution, was used for determining piroxicam in its pharmaceutical formulations. The developed technique is very simple, precise, accurate, time saving, and economical, compared to all of the previously reported methods. The effects of various parameters on the sensitivity of the method were investigated. The best performance was obtained with a pH value of 2, scan rate value of 40 V/s, accumulation potential of (400) mV, and accumulation time of 0.4 s. The proposed method has some advantages over other reported methods, such as, no need for the removal of oxygen from the test solution, a picomolar detection limit, and finally that the method is fast enough for the determination of any such compound, in a wide variety of chromatographic methods. To obtain a sensitive determination, the integration range of currents was set for all the potential scan ranges, including oxidation and reduction of the Au surface electrode, while performing the measurements. The potential waveform, consisting of the potential steps for cleaning, accumulation, and potential ramp of analyte, was applied on an Au disk microelectrode (with a 12.5 µm in radius) in a continuous way. The method was linear over the concentration range of 1.5–364000 pg/ml (r=0.998) with a limit of detection and quantitation of 0.33 and 1.5 pg/ml, respectively. The method has the requisite accuracy, sensitivity, precision, and selectivity to assay piroxicam in tablets. 相似文献
960.
A few years back T. Vértesi et al. (J Phys Chem A 2005, 109, 3476) gave an elegant procedure to derive the adiabatic‐to‐diabatic transformation angle (ADT‐angle) for lowest two states, γ12, in presence of their interaction with the higher states. In this article, we explicitly solved the coupled differential equations involving the ADT‐angles describing the mixing of four interacting states for the first time to get all the ADT‐angles, γij's (including the γ12) associated with well‐defined topological phases. In application to a suitable configuration space (CS) of a molecular system, we have demonstrated well‐defined Berry phases (Berry M. V., R Soc London Ser A 1984, 45, 392) for an isolated system with as many as four strongly interacting states. © 2012 Wiley Periodicals, Inc. 相似文献