Stress Analysis And Geometrical Configuration Selection for Multilayer Piezoelectric Displacement Actuator

Multilayer piezoelectric ceramic displacement actuators are susceptible to cracking in the region near the edge of the internal electrode, which may cause system damage or failure. In this paper, the stress distribution of a multilayer piezoelectric composite is investigated in a working environment and the optimized geometrical con?guration of the piezoelectric layer is obtained. The stress distribution in the structure and the stress concentration near the edge of th…     

Verma modules for twisted Yangians

Abstract

A sufficient and necessary condition for the reducibility of the Verma modules over the twisted Yangians of rank one is given.     

A DAMAGE MECHANICS MODEL FOR TWISTED CARBON NANOTUBE FIBERS

Carbon nanotube fibers can be fabricated by the chemical vapor deposition spinning process. They are promising for a wide range of applications such as the building blocks of high-performance composite materials and micro-electrochemical sensors. Mechanical twisting is an effective means of enhancing the mechanical properties of carbon nanotube fibers during fabrication or by post processing. However, the effects of twisting on the mechanical properties remain an unsolved issue. In this paper, we present a two-scale damage mechanics model to quantitatively investigate the effects of twisting on the mechanical properties of carbon nanotube fibers. The numerical results demonstrate that the developed damage mechanics model can effectively describe the elastic and the plastic-like behaviors of carbon nanotube fibers during the tension process. A definite range of twisting which can effectively enhance the mechanical properties of carbon nanotube fiber is given. The results can be used to guide the mechanical twisting of carbon nanotube fibers to improve their properties and help optimize the mechanical performance of carbon nanotube-based materials.     

无理数e的统计估计法

本文通过著名的“匹配试验”构造出了无理数ｅ的统计估计公式，并讨论了该估计的性质．     

Automatic evaluation of photoelastic fringe constant by the nonlinear least-squares method

A nonlinear least-squares method was applied to determine the photoelastic fringe constant from isochromatic phase field obtained by digital phase-shifting photoelasticity. To perform automatic evaluation, not only the photoelastic fringe constant but the center coordinates of a disk under diametral compression are also determined simultaneously using the nonlinear least-squares method. A set of over-determined nonlinear equations is obtained to estimate the unknown parameters by an iterative procedure based on Newton–Raphson method. Simulation and experimental results show that the parameters are evaluated accurately from the isochromatic phase field obtained from the phase-shifting photoelasticity. The photoelastic fringe constant and the disk center coordinates can be evaluated easily, simply and automatically by the technique.     

异质双材料界面端部应力奇异性的实验分析

用高灵敏度的云纹干涉实验方法测量了弯曲载荷作用下异质结构的位移场，并采用局部混合法对实验结果进行处理，根据结果对界面端部区域的应力分布规律进行了讨论；求出了应力奇异性阶数λ和应力强度因子Ｋ，并将这一结果与Ｂｏｇｙ￣［１］等人用理论分析的方法所预期的结果和有限元计算结果进行了比较。本文的工作从实验的角度证实了异质双材料结构界面端部区域的应力状态可以用表达式：σ＿（ｉｊ）（ｒ，θ）＝ｋ·ｒ￣（－λ）ｆ＿（ｉｊ）（θ）来描述。     

Jahn–Teller Disproportionation Induced Exfoliation of Unit-Cell Scale ϵ-MnO2

Exfoliation of non-layered (structurally) bulk materials at the nanoscale is challenging because of the strong chemical bonds in the lattice, as opposed to the weak van der Waals (vdW) interactions in layered materials. We propose a top-down method to exfoliate ϵ-MnO₂ nanosheets in a family of charge-ordered La_1−xAE_xMnO₃ (AE=Ca, Sr, Ba) perovskites, taking advantage of the Jahn–Teller disproportionation effect of Mn³⁺ and bond-strength differences. ϵ-MnO₂ crystallized into a nickel arsenide (NiAs) structure, with a thickness of 0.91 nm, displays thermal metastability and superior water oxidation activity compared to other manganese oxides. The exfoliation mechanism involves a synergistic proton-induced Mn³⁺ disproportionation and structural reconstruction. The synthetic method could also be potentially extended to the exfoliation of other two-dimensional nanosheet materials with non-layered structures.     

A BRIEF REVIEW AND PROSPECT OF EXPERIMENTAL SOLID MECHANICS IN CHINA

In this review, acritical look at the research progress ofexperimentalsolid mechanics in China for the past years is presented. Issues are discussed of the discovery and development of new fundamental methods and techniques versus performance benchmarking for many of their applications. Included herein are photoelasticity and various forms of modern photomechanics, acoustical techniques, image processing and videometrics, radial and spectrum techniques, and experimental mechanics on micro/nano scale. It is also noticed that both the ever developed instrumentation and specialized synthetical techniques have played important roles in advancing experimental mechanics in scientific researches and industrial applications. Finally, an attempt is made to look into the future of experimental solid mechanics with personal opinions offered on what the future trends will be for the researches in the field.     

Expression,Purification, and Characterization of Hepatitis B Virus Surface Antigens (HBsAg) in Yeast <Emphasis Type="Italic">Pichia Pastoris</Emphasis>

Prevention of the prevalence of HB depends upon the development of efficient diagnostic reagent and preventive vaccine. Pichia pastoris offers many advantages over the other expression systems in the production of recombinant HBsAg. In this study, we reported that the recombinant P. pastoris strains were cultured in shake flasks and then scaled up in a 5.0-l bioreactor: approximately 27 mg/l of the protein and the maximal cell OD at 600 nm of 310 were achieved in the bioreactor. The recombinant HBsAg was purified by three steps of purification procedures. SDS-PAGE showed that the purified recombinant HBsAg constituted only one homogeneous band of ~24 kDa. CsCl density gradient ultracentrifugation assay indicated that the density of the HBsAg was 1.2 mg/ml, which was in agreement with the natural HBsAg, the HBsAg expressed in Saccharomyces cerevisiae and in mammalian cells. Electron microscope observation revealed that the purified recombinant HBsAg was homogeneous 22-nm particles, suggesting the HBsAg expressed in P. pastoris was self-assembled to virus-like structures. Competitive ELISA indicated that P. pastoris-derived HBsAg possessed the excellent immunoreaction with anti-HBsAg. Animal immunization showed that the immunogenicity of P. pastoris-derived HBsAg was superior to that of S. cerevisiae-derived HBsAg. Together, our results demonstrated that the recombinant HBsAg expressed in P. pastoris could provide promising, inexpensive, and large-scale materials for the diagnostic reagent and vaccine to prevent HBV infection. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Rushi Liu and Qinlu Lin contributed equally to this work.