排序方式: 共有33条查询结果,搜索用时 15 毫秒
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Guoliang Li Ioan Silaghi-Dumitrescu R. Bruce King Henry F. Schaefer III 《Journal of organometallic chemistry》2010,695(6):804-808
Density functional theory studies on a series of Cp2Co2E2 derivatives (E = S and PX; X = H, Cl, OH, OMe, NH2, NMe2) predict global minimum butterfly structures with one Co-Co bond for the “body” of the butterfly and four Co-E bonds at the edges of the “wings” of the butterfly. Tetrahedrane structures with both Co-Co and E-E bonds are higher in energy for Cp2Co2S2 and Cp2Co2(PH)2 and are not found in the other systems. This differs from the corresponding Fe2(CO)6S2 and Fe2(CO)6(PX)2 derivatives where tetrahedrane structures are predicted to be the lowest energy structures for all cases except X = NR2 and OH and such a tetrahedrane structure is found experimentally for Fe2(CO)6S2. The butterfly structures for the Cp2Co2E2 derivatives are of two types. For Cp2Co2(PX)2 (X = H, OH, OMe, NH2, NMe2) the lowest energy structures are unsymmetrical butterflies Cp2Co2(P)(PX2) with two X groups on one phosphorus atom and a lone pair on the other (naked) phosphorus atom. Related low-energy unsymmetrical butterfly Fe2(CO)6(P)(PX2) structures, not observed in previous theoretical studies, are now found for the corresponding Fe2(CO)6(PX)2 derivatives. Symmetrical butterfly singlet diradical structures with one X group on each phosphorus atom in relative cis or trans positions are also found for the Cp2Co2(PX)2 derivatives and are the global minima for Cp2Co2(PCl)2 as well as Cp2Co2S2. In all cases the cis structures are of lower energy than the corresponding trans structures. Rhombus structures having neither Co-Co nor E-E bonds are also found for all of the Cp2Co2(PX)2 derivatives but always at higher energies than the butterfly structures, ranging from 17 to 29 kcal/mol above the global minima. 相似文献
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A. Emin Tatar 《Advances in Mathematics》2011,(1):62
We define a tricategory T[−2,0] of length 3 complexes of abelian sheaves, whose hom-bigroupoids consist of weak morphisms of such complexes. We also define a 3-category 2Pic(S) of Picard 2-stacks, whose hom-2-groupoids consist of additive 2-functors. We prove that these categories are triequivalent as tricategories. As a consequence we obtain a generalization of Deligne's analogous result about Picard stacks in SGA4, Exposé XVIII (Deligne (1973) [11]). 相似文献
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Anotida Madzvamuse Andrew J. Wathen Philip K. Maini 《Journal of computational physics》2003,190(2):478-500
Many problems in biology involve growth. In numerical simulations it can therefore be very convenient to employ a moving computational grid on a continuously deforming domain. In this paper we present a novel application of the moving grid finite element method to compute solutions of reaction–diffusion systems in two-dimensional continuously deforming Euclidean domains. A numerical software package has been developed as a result of this research that is capable of solving generalised Turing models for morphogenesis. 相似文献
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Mark Tygert 《Journal of computational physics》2010,229(18):6181-6192
We accelerate the computation of spherical harmonic transforms, using what is known as the butterfly scheme. This provides a convenient alternative to the approach taken in the second paper from this series on “Fast algorithms for spherical harmonic expansions”. The requisite precomputations become manageable when organized as a “depth-first traversal” of the program’s control-flow graph, rather than as the perhaps more natural “breadth-first traversal” that processes one-by-one each level of the multilevel procedure. We illustrate the results via several numerical examples. 相似文献
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采用扫描电子显微镜(SEM)观察了双带闪蝶(Morpho Achilles)翅膀表面的微观形貌, 通过样品的表观接触角表征了其浸润性, 采用高敏感性微电力学天平比较了水滴在蝴蝶翅膀表面不同方向运动时受到的黏附力. 实验结果表明, 水滴沿着干燥的蝴蝶翅膀鳞片堆叠方向运动时受到的黏附力要明显小于其它方向运动时受到的力, 且受力较稳定; 当蝴蝶翅膀被水滴浸润后, 水滴沿着湿润的蝴蝶翅膀鳞片堆叠方向运动时受到的黏附力接近甚至大于逆着鳞片堆叠方向运动时受到的力. 相似文献
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Paul D. Manuel Mostafa I. Abd-El-Barr Indra Rajasingh Bharati Rajan 《Journal of Discrete Algorithms》2008,6(1):11-19
The most popular bounded-degree derivative network of the hypercube is the butterfly network. The Benes network consists of back-to-back butterflies. There exist a number of topological representations that are used to describe butterfly—like architectures. We identify a new topological representation of butterfly and Benes networks.The minimum metric dimension problem is to find a minimum set of vertices of a graph G(V,E) such that for every pair of vertices u and v of G, there exists a vertex w with the condition that the length of a shortest path from u to w is different from the length of a shortest path from v to w. It is NP-hard in the general sense. We show that it remains NP-hard for bipartite graphs. The algorithmic complexity status of this NP-hard problem is not known for butterfly and Benes networks, which are subclasses of bipartite graphs. By using the proposed new representations, we solve the minimum metric dimension problem for butterfly and Benes networks. The minimum metric dimension problem is important in areas such as robot navigation in space applications. 相似文献
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HE Liming 《Chinese Journal of Lasers》1994,3(3):275-282
ButterflyinterconnectionnetworksandtheirapplicationsinWalsh-Hadamardtransform-basedinformationprocessingandopticalcomputingHE... 相似文献
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This paper describes high fidelity modeling and analysis of the opening and closing processes of butterfly valves driven by solenoid actuators using multiphysics models. The equations are derived and solved numerically. The variable of primary interest is the butterfly valve rotation angle. The coupled model for electromagnetics, fluid dynamics and mechanical dynamics are derived by making some simplifying assumptions. It is shown that the behavior of hydrodynamic torque plays an important role in the closing and opening processes. A discussion is presented with an explanation of the results and a comparison has been made for both the processes. 相似文献