Axisymmetric wave propagation in a layered transversely isotropic medium

Summary In this paper, the method of numerical integration along bicharacteristics is generalized to the case of layered transversely isotropic medium for analysing the axisymmetric stress wave propagation. The stability of the present scheme is studied. The advantages and limitations of the method are discussed. Received 12 June 1996; accepted for publication 6 May 1997     

预载对高温超导磁悬浮系统中横向运动引起的悬浮力衰减行为的影响

预载是一种有效抑制高温超导磁悬浮系统中由横向运动引起的悬浮力衰减的方法,但目前研究仅停留在概念验证阶段,尚未对影响预载效果的一些因素进行详细地分析和研究.利用高温超导磁悬浮测试系统,本文通过改变块材的冷却条件(场冷和零场冷)、悬浮高度以及轨道磁场结构、材料性能等实验研究了不同预载高度下YB-CO块材的悬浮力随横向运动次数的变化关系,得到这些因素对预载条件下悬浮力随横向运动变化情况影响的规律.结果表明,预载高度越低,由横向运动引起的悬浮力变化越快地趋于稳定,但悬浮力的稳定值也越小,并且这一现象不随冷却条件、悬浮高度、轨道磁场结构和材料性能等因素的改变而变化.     

横向加热石墨炉原子吸收法测定蘑菇、茶叶中的铬和铍

采用横向加热石墨炉原子吸收法测定蘑菇、茶叶中的铬和铍。以MgNO3 作为基体改进剂 ,提高了测定铍的灰化温度和灵敏度 ,很好消除了基体干扰。方法简便、快速、准确度高。铬和铍的线性范围分别为0～ 80、0～ 8μg/L ;特征量分别为 5 .3× 10 -12 g和 1.9× 10 -12 g ;相对标准偏差分别为 3.0 %～ 17.3%和 4 .3%～ 11.6 % ;回收率分别为 98%～ 10 3%和 98%～ 10 6 % ;检出限分别为 6 6和 4 .8ng/ g。     

Stress state of a piezoceramic body with a plane crack opened by a rigid inclusion

The paper establishes a relationship between the solutions for cracks located in the isotropy plane of a transversely isotropic piezoceramic medium and opened (without friction) by rigid inclusions and the solutions for cracks in a purely elastic medium. This makes it possible to calculate the stress intensity factor (SIF) for cracks in an electroelastic medium from the SIF for an elastic isotropic material, without the need to solve the electroelastic problem. The use of the approach is exemplified by a penny-shaped crack opened by either a disk-shaped rigid inclusion of constant thickness or a rigid oblate spheroidal inclusion in an electroelastic medium __________ Translated from Prikladnaya Mekhanika, Vol. 44, No. 7, pp. 47–60, July 2008.     

The 3-D stress intensity factor for a half plane crack in a transversely isotropic solid due to the motion of loads on the crack faces

Three-dimensional analysis of a half plane crack in a transversely isotropic solid is performed. The crack is subjected to a pair of normal point loads moving in a direction perpendicular to the crack edge on its faces. Transform methods are used to reduce the boundary value problem to a single integral equation that can be solved by the Wiener-Hopf technique. The Cagniard-de Hoop method is employed to invert the transforms. An exact expression is derived for the mode I stress intensity factor as a function of time and position along the crack edge. Some features of the solution are discussed through numerical results. The project supported by the Guangdong Provincial Natural Science Foundation and the Science Foundation of Shantou University     

Penny-shaped and half-plane cracks in a transversely isotropic piezoelectric solid under arbitrary loading

Summary The problem of a penny-shaped crack in a transversely isotropic piezoelectric material loaded by both normal and tangential tractions and by electric charges is analyzed. Closed-form solutions are obtained for the full electroelastic fields as well as for the stress and electric displacement intensity factors. Solutions are also obtained for the (non-trivial) limiting case of a half-plane crack. The results are illustrated on the example of piezoceramics PZT-6B. Received 12 July 1999; accepted for publication 20 July 1999     

Transverse oscillations for tissue motion estimation

This paper gives an overview of the methods developed for tissue motion estimation using transverse oscillation images (TO). TO images are specific radiofrequency ultrasound images featuring oscillations in both spatial directions. The initial studies on TO were published in the late 1990s. This paper reviews the main ideas and applications behind this motion estimation approach. First the origin and motivation of TO is briefly reviewed. Then the beamforming methods that lead to TO images are given, detailing the receive-only approach and the transmit-and-receive approach using synthetic aperture data. The different medical applications where TO has been used are discussed (blood flow, elastography and echocardiography), showing how it can improve motion estimation. Finally, the future perspectives of TO are outlined.     

Energy dependence of pion interferometry scales in ultra-relativistic heavy ion collisions

A study of energy behavior of the pion spectra and interferometry scales is carried out for the top SPS, RHIC and LHC energies within the hydrokinetic approach. The latter allows one to describe evolution of quark–gluon and hadron matter as well as continuous particle emission from the fluid in agreement with the underlying kinetic equations. The main mechanisms that lead to the paradoxical, at first sight, behavior of the interferometry scales, are exposed. In particular, a slow decrease and apparent saturation of Rout/Rside$R_{\text{<italic>out</italic>}}/R_{\text{<italic>side</italic>}}$ ratio with an energy growth happens due to a strengthening of positive correlations between space and time positions of pions emitted at the radial periphery of the system. Such en effect is a consequence of the two factors: a developing of the pre-thermal collective transverse flows and an increase of the initial energy density in the fireball.     

一种用于层状结构模型的先进计算方法

提出一种针对层状结构模型的先进计算方法。研究的层状结构通常为水平层状板或者层状半空间,结构由横观各向同性（TI）材料组成,材料对称轴指向分层方向。本文方法可以考虑材料的多场耦合特性,即热弹性、多孔弹性和磁电弹性耦合。基于最近提出的傅立叶-贝塞尔级数（FBS）向量函数系和双变量/位置（DVP）方法,建立了本文的先进计算方法。DVP能够无条件稳定地将层矩阵从一层传播到下一层。FBS向量函数系具有以下特点,（1）反映了具有明确类型的广义变形/波,（2）将展开系数预先计算为Love数,然后将其用于涉及问题的模拟。层状地球中的断层（或位错）作用、土-结构相互作用以及近地表地球剖面中的瞬态波等三个典型算例,证明了提出方法的准确性和有效性。     

页岩储层各向异性对水平井坍塌压力的影响

为揭示层理页岩强度各向异性对水平井井壁坍塌压力的影响规律,对取自四川盆地龙马溪组页岩钻井不同层理角度的岩芯,通过岩芯观测、偏光显微镜、扫描电镜试验分别从宏观和微观角度研究了页岩层理特征,并基于单轴抗压强度研究了页岩强度各向异性特征.层理结构发育导致页岩呈现出显著的各向异性特征,粗略地将页岩视为各向同性体及简单采用Mohr-Coulomb准则作为破坏判据,使得预测的维持井壁稳定的坍塌压力不能满足安全钻井的需要.该文在研究层理地层岩石力学特性的基础上,采用横观各向同性地层井周应力分析模型,研究了弹性模量及地应力各向异性比对井周应力的影响;并结合考虑中间主应力的Mogi-Coulomb判据,分析了井壁坍塌压力对弹性模量E和Poisson(泊松)比ν各向异性比值变化的敏感性.实例分析结果表明:弹性模量和水平地应力各向异性比值的变化会对井周应力产生较大影响;Poisson比各向异性对井壁坍塌压力没有明显影响,而弹性模量比值的变化对井壁坍塌压力影响较大;横观各向同性地层中井壁坍塌压力与储层水平和垂直方向的硬脆性强弱关系有关,弹性力学参数各向异性既有可能利于井壁稳定,也可能更易导致井壁的剪切破坏;在实际工程中应根据储层岩石水平和垂直方向的硬脆性强弱关系,确定安全钻井液密度窗口.该结果对现场施工具有很好的指导意义.