基于移动端多天线系统的无线衰落信道模型

根据当前无线移动通信对多天线移动接收端性能仿真的要求，讨论并建立了适于空时信号处理的移动端矢量信道模型。通过分析无线移动信道特点。研究了影响接收信号幅度相位的诸多因素，建立了相应的数学模型。并对随机参数选取进行了探讨。其中考虑到移动端接收信号到达角扩散的特点，采用GBSB椭圆模型产生了适于移动端接收信号仿真的随机角度，改进了一种瑞利衰落生成算法。最后信道的数值仿真结果符合理论和经验。同时，通过TD-SCDMA系统链路级仿真，也证明了该信道模型的有效性。     

Stress Concentration Factors for a Circular Hole in Curved Beams Under Bending Loads

Abstract: As a contribution to the field of stress concentration studies, the case of circular hole in curved bar elements under bending is hereby studied. Trend values of stress concentration factors (SCF) are presented based on selected variables of the problem for two critical hole locations. The results will help to identify an SCF law for practical use by applying the statistical method of regression analysis. Two approximations obtained by means of computational methods are compared with those obtained by photoelastic experimental method.     

Asymptotic stress intensity factor density profiles for smeared-tip method for cohesive fracture

The paper presents a computational approach and numerical data which facilitate the use of the smeared-tip method for cohesive fracture in large enough structures. In the recently developed K-version of the smeared tip method, the large-size asymptotic profile of the stress intensity factor density along a cohesive crack is considered as a material characteristic, which is uniquely related to the softening stress-displacement law of the cohesive crack. After reviewing the K-version, an accurate and efficient numerical algorithm for the computation of this asymptotic profile is presented. The algorithm is based on solving a singular Abel's integral equation. The profiles corresponding to various typical softening stress-displacement laws of the cohesive crack model are computed, tabulated and plotted. The profiles for a certain range of other typical softening laws can be approximately obtained by interpolation from the tables. Knowing the profile, one can obtain with the smeared-tip method an analytical expression for the large-size solution to fracture problems, including the first two asymptotic terms of the size effect law. Consequently, numerical solutions of the integral equations of the cohesive crack model as well as finite element simulations of the cohesive crack are made superfluous. However, when the fracture process zone is attached to a notch or to the body surface and the cohesive zone ends with a stress jump, the solution is expected to be accurate only for large-enough structures.     

On the specific reactivity of platinum segregated layers on Pt80X20 (111) (X= Ni,Co, Fe) alloys

The influence of alloying of Pt with 20 at.% of Ni, Co and Fe has been studied in the hydrogenation of 1,3 butadiene. Iron induces the more important modifications, with both higher activity and selectivity. The results are discussed in terms of the surface segregation, the local order in surface and the electronic properties measured by photoemission of core levels.     

Effects of α‐form or β‐form nuclei on polymorphic crystalline morphology of poly(butylene adipate)

The effects of α‐form and β‐form nuclei on polymorphic morphology of poly(butylene adipate) (PBA) upon recrystallization from the molten state up to various T_max values were examined by differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD) and polarized light microscopy (PLM). In this study, PBA with complex melting and polymorphism behaviour was used as a model for examining different types and extents of residual nuclei. As the PBA initially containing the sole α‐crystal was brought to a molten state of various T_max, the extents of trace α‐form crystal nuclei varied and were dependent on T_max. Furthermore, it did not matter whether, initially, the PBA contained α‐ or β‐form crystals (or both) because only a single type of α‐nuclei could be left upon treatment to the molten liquid state at T_max. Therefore, only the α‐crystal in PBA had ‘memory capacity’ in the molten liquid state while the β‐crystal did not. This was so because the latter had been completely transformed into the solid state prior to being heated into a liquid. PBA crystallized before α‐nuclei could be packed into α‐crystal, regardless of the crystallization temperature (T_c). For recrystallization from molten PBA without any nuclei, the crystalline polymorphism was correspondingly influenced by T_c. Copyright © 2005 Society of Chemical Industry     

自成像列阵共振腔的分析——Ⅰ.Talbot共振腔

利用自成像效应进行半导体列阵激光器锁相是一种重要的外腔锁相技术,所构成的共振腔可分为Talbot腔和带相位补偿板的Lau腔。我们用Fox-Li方法计算了共振模式。本文给出了Talbot腔的计算结果和分析,表明同相和反相模的损耗随腔长变化存在临界点。     

一种用于强振环境的转速传感器

该文介绍一种简单、可靠、小巧的转速传感器。它的特点是在强振环境下仍具有很高的可靠,可用于坦克底盘、重型工程机械,燃气轮机组等机械作为转速监测。     

Spatiotemporal aspects of jerky flow in Al–Mg alloys, in relation with the Mg content

The spatiotemporal aspects of the Portevin–Le Chatelier effect in Al–Mg alloys are investigated using direct observations of the sample surface with a digital camera. Optical measurements of the surface profile using a white light interferometer allow the estimation of the local strain and strain rate associated with the bands. The effect of Mg content on instability characteristics is analyzed. The reloading time is shown to depend on the Mg content only at the strain and strain rates where type C bands are observed.     

一种控制盐层段井眼闭合率的钻井液密度新公式

针对钻井过程中钻遇的盐层段井眼蠕变缩径问题,利用弹塑性力学理论,蠕变本构方程采用Heard蠕变方程,在平面应变和均匀地应力假设下,推导出控制井眼收缩的钻井液密度新公式,该公式与前人推导的公式不同。通过理论分析,指出产生差异的根本原因在于蠕变应力差(极坐标下表示的径向应力与切向应力之差)公式的推导上,用有限元法计算结果对理论公式进行检验,证明是可行的。对文中的力学模型采用有限元法建模、求解,利用求解结果对各应力差公式进行验证,得出:根据文中公式计算结果与有限元法计算结果完全一致,而据前人公式计算结果偏离有限元计算值较大,从而间接证明了该钻井液密度新公式的推导更严密,更准确。     

NUMERICAL STUDY ON SORET-EFFECT AND DUFOUR-EFFECT FOR DOUBLE-DIFFUSIVE NATURAL CONVECTION IN POROUS ENCLOSURE

The influences of Soret effect and Dufour effect on the natural convection and heat and mass transfer for a porous enclosure were investigated by means of the penalty finite element method. Numerical results indicate that the Soret and Dufour effects have significant influences on heat and mass transfer in the presence of large temperature gradient and concentration gradient.