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911.
912.
本文从三维弹性理论出发,用特征函数法研究多层横观各向同性圆柱壳的轴对称问题.把位移和应力分量的齐次解表达成特征函数展开式,并把特解部分用Fourier级数表示.以多层圆柱壳的内、外柱面作为齐次边界,同时考虑层间的连续条件,推导出问题的特征方程并用Muller法求解.文中运用传递矩阵技术处理多层问题,并用边界型最小二乘配点法处理端部边界条件.作为实例,对双层圆柱壳作了数值计算. 相似文献
913.
This paper reports the results of an investigation into the characteristics of wave propagation in carbon nanotubes embedded
in an elastic matrix, based on an exact shell model. Each of the concentric tubes of multi-walled carbon nanotubes is considered
as an individual elastic shell and coupled together through the van der Waals forces between two adjacent tubes. The matrix
surrounding carbon nanotubes is described as a spring element defined by the Winkler model. The effects of rotatory inertia
and elastic matrix on the wave velocity, the critical frequency, and the amplitude ratio between two adjacent tubes are described
and discussed through numerical examples. The results obtained show that wave propagation in carbon nanotubes may appear in
a critical frequency at which the wave velocity changes suddenly; the elastic matrix surrounding carbon nanotubes debases
the critical frequency and the wave velocity, and changes the vibration modes between two adjacent tubes; the rotatory inertia
based on an exact shell model obviously influences the wave velocity at some wave modes. Finally, a comparison of dispersion
solutions from different shell models is given. The present work may serve as a useful reference for the application and the
design of nano-electronic and nano-drive devices, nano-oscillators, and nano-sensors, in which carbon nanotubes act as basic
elements. 相似文献
914.
在遗传算法或神经网络方法识别结构损伤位置和程度时,都是基于少量的在线测量的损伤结构振动响应数据和大量的模型仿真数据来实现的,因而建立高效和精确的损伤结构动力学有限元模型,以便仿真获得损伤结构的大量动力学响应数据是十分重要的基础前提工作。本文针对ANSYS结构分析软件在建立结构小损伤有限元动力学模型存在两个关键问题,结构损伤处直接网格划分的计算结果误差和网格节省问题,以结构损伤振动检测的实际需要为出发点,提出了建立含小损伤结构的ANSYS动力学建模技术,研究了结构局部小损伤及其位置与所在处单元刚度矩阵变化的数量关系。 相似文献
915.
高温磨损中合金组成体的作用及其相互依赖 总被引:5,自引:2,他引:5
作者用其自制的高温磨损试验机考察了不同含碳量的Fe-Cr及Fe-Cr-Mn合金的高温耐磨性。通过数据分析及磨损面和亚表层之结构和组织的观察,论述了共晶碳化物及金属基体在高温磨损条件下对材料耐磨性的贡献和相互依赖性。作者指出,高硬度共晶碳化物在高温磨损过程中能够发挥一定的抵抗磨料的作用而使合金的耐磨性提高;基体组织在高温时的塑性变形是影响合金高温耐磨性的一个重要因素,它直接影响共晶碳化物发挥抵抗磨料作用的程度;Fe-Cr-Mn合金中由于Mn的加入改善了基体组织的性能,使其硬度和高温耐磨性均比Fe-Cr合金的高。 相似文献
916.
917.
918.
High‐temperature superconductivity and long‐range order in strongly correlated electronic systems
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Lawrence J. Dunne 《International journal of quantum chemistry》2015,115(20):1443-1458
A selective review of the question of how repulsive electron correlations might give rise to off‐diagonal long‐range order (ODLRO) in high‐temperature superconductors is presented. The article makes detailed explanations of the relevance to superconductivity of reduced electronic density matrices and how these can be used to understand whether ODLRO might arise from Coulombic repulsions in strongly correlated electronic systems. Time‐reversed electron pairs on alternant Cuprate and the iron‐based pnictide and chalcogenide lattices may have a weak long‐range attractive tail and much stronger short‐range repulsive Coulomb interaction. The long‐range attractive tail may find its origin in one of the many suggested proposals for high‐Tc superconductivity and thus has an uncertain origin. A phenomenological Hamiltonian is invoked whose model parameters are obtained by fitting to experimental data. A detailed summary is given of the arguments that such interacting electrons can cooperate to produce a superconducting state in which time‐reversed pairs of electrons effectively avoid the repulsive hard‐core of the Coulomb interaction but reside on average in the attractive well of the long‐range potential. Thus, the pairing of electrons itself provides an enhanced screening mechanism. The alternant lattice structure is the key to achieving robust high‐temperature superconductivity with dx2‐y2 or sign alternating s‐wave or s± condensate symmetries in cuprates and iron‐based compounds. Some attention is also given to the question first raised by Leggett as to where the Coulombic energy is saved in the superconducting transition in cuprates. A mean‐field‐type model in which the condensate density serves as an order parameter is discussed. Many of the observed trends in the thermal properties of cuprate superconductors are reproduced giving strong support for the proposed model for high‐temperature superconductivity in such strongly correlated electronic systems. © 2015 Wiley Periodicals, Inc. 相似文献
919.
In this study, we investigated the influence of relative humidity (RH) and loading rate on the energy response of PA6.6 matrix specimens. The latter were subjected to oligocyclic tensile-tensile tests at 3 different RH and 2 loading rates. Infrared thermography was used to obtain a direct estimate of heat sources using the heat diffusion equation. Using the mechanical and thermal responses discussed in the first part of this work, complete energy rate balances were drawn up. In particular, the time courses of deformation, and dissipated and stored energy rates are discussed. The strong influence of the loading frequency and RH on the energy storage mechanisms is also highlighted. 相似文献
920.
Synthesis and application of mesoporous molecular sieve for miniaturized matrix solid‐phase dispersion extraction of bioactive flavonoids from toothpaste,plant, and saliva
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Wan Cao Jun Cao Li‐Hong Ye Jing‐Jing Xu Shuai‐Shuai Hu Li‐Qing Peng 《Electrophoresis》2015,36(23):2951-2960
This article describes the use of the mesoporous molecular sieve KIT‐6 as a sorbent in miniaturized matrix solid‐phase dispersion (MSPD) in combination with ultra‐performance LC for the determination of bioactive flavonoids in toothpaste, Scutellariae Radix, and saliva. In this study, for the first time, KIT‐6 was used as a sorbent material for this mode of extraction. Compared with common silica‐based sorbents (C18 and activated silica gel), the proposed KIT‐6 dispersant with a three‐dimensional cubic Ia3d structure and highly ordered arrays of mesoporous channels exhibits excellent adsorption capability of the tested compounds. In addition, several experimental variables, such as the mass ratio of sample to dispersant, grinding time, and elution solvent, were optimized to maximize the extraction efficiency. The proposed analytical method is simple, fast, and entails low consumption of samples, dispersants and elution solvents, thereby meeting “green chemistry” requirements. Under the optimized conditions, the recoveries of three bioactive flavonoids obtained by analyzing the spiked samples were from 89.22 to 101.17%. Also, the LODs and LOQs for determining the analytes were in the range of 0.02–0.04 μg/mL and 0.07–0.13 μg/mL, respectively. Finally, the miniaturized matrix solid‐phase dispersion method was successfully applied to the analysis of target solutes in real samples, and satisfactory results were obtained. 相似文献