Representation surfaces of Young''s modulus and Poisson''s ratio for BCC transition metals

 The general expressions for the compliance , Young's modulus E(h k l) and Poisson's ratio υ(h k l) along an arbitrary direction [h k l] are given for cubic crystals. The representation surfaces, for which the length of the radius vector in the [h k l] direction equals to E(h k l) or υ(h k l), are constructed for seven BCC transition metals Cr, Fe, Mo, Nb, Ta, V and W. Neglecting W, which is isotropic, both representation surfaces of Young's modulus and Poisson's ratio are spherical surfaces. The remaining BCC transition metals may be grouped into two classes. In the first group (Cr, Mo, Nb and V) with negative values of s_A, Young's modulus surface has eight depressed corners and six rounded protuberances at the centers of the faces. In the second group (Fe and Ta) with positive values of s_A, on the contrary, Young's modulus surface has eight rounded protuberance corners and six depressions at the centers of the faces. The contrary conclusions are obtained for Poisson's ratio.     

稀薄气体二维外部柱体绕流特性研究

本文采用直接模拟蒙特卡罗方法对稀薄气体二维外部柱体绕流问题进行了数值模拟。结果表明:外部绕流问题,在特定情况下会产生激波,激波的产生,不仅与气体的稀薄程度有关,还与来流马赫数有关。而气流与壁面之间的换热,随来流马赫数增加而增加,随气体稀薄程度增加而减小。     

Multiplicity results for positive solutions of some semi-positone three-point boundary value problems

In this paper, some multiplicity results for positive solutions of some singular semi-positone three-point boundary value problem be obtained by using the fixed point index method.     

Ab-initio molecular dynamics simulation on nano-system under external pressure

A new constant-pressure molecular dynamics (MD) method is developed to simulate the dynamic behavior and structure transition of finite system under external pressure. In this method, no artificial parameter is introduced and the computation overheads are very small. As an application, a hard-soft transition of single wall carbon nanotube (SWCNT) under external pressure is found, which is in agreement with the experiments.

     

互补型自适应滤波器在心磁信号处理中的应用

将心磁信号从干扰噪声中加以提取并有效地消除噪声干扰是心磁信号处理中尤为重要的环节 .从改进算法的角度出发，提出互补型自适应滤波器结构以实现心磁信号的消噪处理.该滤波器针对心磁这类非平稳信号进行设计，有效地解决了常规自适应滤波器应用于心磁信号处理时收敛速度和稳态误差的矛盾.通过仿真实验和心磁实验结果表明，该算法能有效地消除心磁信号的背景噪声和工频干扰噪声.同时该算法也可用于其他非平稳信号的消噪处理. 关键词： 自适应滤波 心磁图 最小均方误差     

A New Cytotoxic Acetogenin from the Seeds of Annona squamosa

A New Annonaceous acetogenin,squamostolide(1),was isolated from the seeds of Annona squamosa.Its structure was elucidated based on spectroscopic methods and comparison with known compounds.It is the first example of Annonaceous acetogenin with each of the two ends of the aliphatic chain bearing a γ-lactone.Thenew compound exhibited cytotoxic activity in vitro against bel-7402 and CNE2 human tumor cell lines.     

Analytical study of a flattened Gaussian beam through multi-apertured optical imaging systems of B = 0

By using the methods of the matrix decomposition and expansion of the hard-edged aperture function into a finite sum of complex Gaussian functions, the recurrence propagation expressions for a flattened Gaussian beam (FGB) through multi-apertured optical imaging systems of B = 0 are derived and illustrated with numerical examples. Comparisons with the straightforward numerical integration of the Collins formula and with the previous work are made. It is shown that the main advantages of our methods and results are the more accuracy and great reduction of computer time.     

压缩偶相干态的制备及其非经典特性

通过保持非耗散介观LC电路的固有频率不变，而使电路参数作阶跃函数变化，就可将介观LC电路由初始的偶相干态制备到压缩偶相干态；在压缩偶相干态下，介观电路系统不仅有非经典的量子压缩效应，而且有非经典的反聚束效应. 关键词： 介观LC电路 单位阶跃函数 压缩算符 压缩偶相干态     

MgO在Mg-hBN体系中对合成cBN晶体的影响

 以金属镁粉为触媒，以六角氮化硼为原料，其中加入适量比例的氧化镁，在国产六面顶压机上，在约5.0 GPa压力、1 500～1 800 K温度条件下，合成出了颜色均匀、晶形完整的黄色立方氮化硼单晶体。实验结果表明，在Mg-hBN体系中，氧化镁对合成cBN晶体的颜色及合成温度有很大的影响。