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991.
为了在弹性波波导中实现缺陷态的调控,该文基于相位失配原理设计了一种周期性平板波导结构。以正弦边界弹性波导为例,通过连接具有不同相位的两段波导结构,形成了弹性板中不同程度的缺陷,并分析了其谱带特性和能量局域化特征。结果表明,禁带中存在两个不同模式的缺陷态,其以透射峰形式出现并随着相位的改变产生频移。与此同时,两个缺陷态在空间上对应的应力场和位移场分布也具有不同的模态特征。该文提出的复合弹性波导缺陷态调控方法,不仅为研究弹性波与结构之间的内在联系提供了关键的理论支持,也为实际弹性波探测器件的设计提供重要参考。 相似文献
992.
993.
994.
We consider the problem of laminar mixed convection flow between parallel, vertical and uniformly heated plates where the governing dimensionless parameters are the Prandtl, Rayleigh and Reynolds numbers. Using the method based on the centre manifold theorem which was derived from the general theory of dynamical systems, we reduce a three-dimensional simplified model of ordinary differential amplitude equations emanating from the original Navier-Stokes system of the problem in the vicinity of a trivial stationary solution. We have found that when the forcing parameter, the Rayleigh number, increases beyond the critical value Ras, the stationary solution is a pitchfork bifurcation point of the system. 相似文献
995.
The conductivity or bulk modulus of an isotropic composite consisting of two well-ordered isotropic phases is situated between the lower and upper bounds of Hashin and Shtrikman. This work is concerned with the construction of two new microstructures capable of realizing every conductivity or bulk modulus comprised between these bounds. The two microstructures obtained, appearing to be simpler than those presented in the literature to achieve the same purpose, have the property that the variation of the corresponding conductivity or bulk modulus is strictly monotone with respect to the geometric parameter characterizing them. To cite this article: Q.-C. He, H.L. Quang, C. R. Mecanique 333 (2005). 相似文献
996.
This paper develops a theoretical analysis of a Bingham fluid in slipping squeeze flow. The flow field decomposition consists
in combining a central extensional flow zone in the plane of symmetry and shear flow zones near the plates. It is also considered
that the slipping zone is located around a central sticking zone as previously shown from experiments. It is assumed that
the shear stress at the plates is constant in the slipping zone and equals a fixed friction yield value. The squeeze force
required to compress a Bingham fluid under the slipping behaviour as well as the radial evolution of the transition point
between both sticking and slipping zones are finally determined. 相似文献
997.
This work is concerned with a two-phase material consisting of an elastoplastic matrix reinforced by linearly elastic fibres. It is first shown that uniform strain fields can be generated in this heterogeneous material. A return-mapping based algorithm is then proposed and used to find uniform strain loading paths. With the help of uniform strain fields, exact results, independent of the transverse geometry and arrangement of the fibres, are derived for the effective elastic properties and for the effective initial and current yield surfaces. To cite this article: Q.-C. He, H. Le Quang, C. R. Mecanique 332 (2004). 相似文献
998.
本文在长波假定下用流体力学线性稳定性理论对大动脉中血液流动求出了一种中性扰动。结果表明,心室或瓣引起的扰动在一定条件下有可能量一种中性扰动,它可以沿着动脉管无变形地传播到动脉远端。这说明也许有可能提供一种通过在远离心脏的某些浅表动脉部位检测这种中性成动以了解心脏的某些功能的新方法。 相似文献
999.
Prof. Ibon Alkorta Dr. Christophe Dardonville Prof. José Elguero 《Angewandte Chemie (International ed. in English)》2015,54(13):3997-4000
The first example in the literature of a compound showing anisochronous 15N atoms resulting from diastereotopicity is described. Racemic 1,3‐dimethyl‐2‐phenyloctahydro‐1H‐benzimidazole was prepared and studied by 1H, 13C and 15N NMR spectroscopy. If convenient conditions were used (monitored by theoretical calculations of 2JN‐H spin–spin coupling constants), two 15N NMR signals were observed and corresponded to the diastereotopic atoms. GIAO/density‐functional calculations of chemical shifts were not only in good agreement with the experimental values but also served as prediction tools. This study suggests that 15N NMR spectroscopy could be used to probe chirality. 相似文献
1000.
Organocatalyzed Asymmetric Conjugate Addition of Heteroaryl and Aryl Trifluoroborates: a Synthetic Strategy for Discoipyrrole D
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Jiun‐Le Shih Thien S. Nguyen Prof. Jeremy A. May 《Angewandte Chemie (International ed. in English)》2015,54(34):9931-9935
Bis‐heteroaryl or bis‐aryl stereocenters were formed by an organocatalytic enantioselective conjugate addition using the respective trifluoroborate salts as nucleophiles. Control studies suggested that fluoride dissociation is necessary in the anhydrous conditions. This strategy is applicable to the synthesis of discoipyrrole D, an inhibitor of BR5 fibroblast migration. 相似文献