动量相关作用对两体耗散同位旋效应的重要性

利用同位旋相关的量子分子动力学,研究了中能重离子碰撞中动量相关的状态方程对原子核阻止基于两体耗散的同位旋效应的影响.计算结果表明原子核阻止对同位旋相关和同位旋无关的核子–核子碰撞截面(两体耗散)的差值强烈地依赖于动量相关势,即在有动量相关势的情况下原子核阻止对同位旋相关和同位旋无关的核子–核子碰撞截面的差值大于没有动量相关势的情况.这就意味着动量相关作用明显地提高了原子核阻止对于核子–核子碰撞截面的灵敏性.因此,在考虑动量相关势的情况下,原子核阻止可以更准确地作为提取同位旋相关的核子–核子碰撞截面的一个探针.     

Viable improvement of the full potential linearized augmented plane wave (FLAPW) method

A characteristic feature of the Full Potential Linearized Augmented Plane Wave (FLAPW)-method consists in the spatial subdivision of the charge density analogous to that of the one-particle wavefunctions, i.e. into a portion that is expanded in terms of spherical harmonics Y_lm inside the muffin-tin spheres and into a plane wave expansion of the interstitial charge density. To obtain the Hartree potential inside the spheres one is hence forced to solve a boundary value problem at the sphere surface. In addition, in all non-equivalent spheres each (l,m)-component of the charge density is mapped onto 300-400 radial grid points. To ensure an accelerated convergence of the calculation, the pertinent schemes require this rather large data set to be stored and mixed within 3-6 iteration steps. We show and illustrate for the example of a spin-polarized Ni-film with and without an oxygen overlayer and for bulk Si that this data set can be compressed by at least two orders of magnitude if one partitions the charge density in a different way so that the relevant portion determining the interatomic bonding can be Fourier expanded throughout the lattice cell. One thereby arrives at a modified FLAPW-scheme that combines favorable features of the original method with virtues of the pseudopotential method which consist in the simple construction of the Hartree potential and the efficient way of achieving self-consistency. These advantages can be exploited to the fullest by using Fast Fourier Transform. Moreover, forces that atoms experience in off-equilibrium positions attain a particularly simple form in terms of the charge density expansion coefficients. Received: 31 May 1997 / Revised: 12 December 1997 / Accepted: 18 December 1997     

多径衰落短波信道中SFH／MFSK通信系统的性能

分析研究了慢跳频／Ｍ进制频率键控（ＳＦＨ／ＭＦＳＫ）通信系统在存在瑞利（Ｒａｙｌｅｉｇｈ）衰落和莱斯（Ｒｉｃｉａｎ）衰落的多径延时短波信道上的性能，导出了其准确的比特差错率的表达式，表明多径干扰数及其强度对系统性能的影响．同时给出了它们的数值结果和性能曲线．     

频率模型与一个考古问题

本文给出了式样流行的几何频率模型 ,并用该数学模型解决了考古学中确定发掘物先后历史年代的问题 .     

Optimum design of vibrating cantilevers: A classical probem revisited

Optimum design of vibrating cantilevers is a classical problem widely used in the literature and textbooks in structural optimization. The problem, originally formulated and solved by Karihalloo and Niordson (Ref. 5), was to find the optimal beam shape that will maximize the fundamental vibration frequency of a cantilever. Upon reexamination of the problem, it has been found that the original analysis and solution procedure can be simplified and improved substantially. Specifically, the time-consuming inner loop devised for solving the Lagrange multiplier in the original work has been proved to be tolally unnecessary and thus should not be considered in the problem solution. This conclusion has led to a new set of simplified equations for the construction of iteration schemes. New asymptotic expressions for the optimum design solution have been obtained and verified by numerical results. Numerical analysis has shown a significant improvement in convergence rate by the proposed new procedure. Also some obvious numerical errors in the original paper have been identified and corrected.This work was suppoted in part by the University of Arizona Foundation and the Office of the Vice President for Research. The author is grateful to the reviewers for their valuable comments.     

Inducing superconductivity and structural transformations by fluorination of reduced YBCO

Bulk superconductivity with T_c up to 94 K has been induced by fluorination of non-superconducting YBa₂Cu₃O_6.11 using XeF₂ as a fluorination agent. Strong changes on X-ray patterns were found after fluorination of reduced YBCO. High resolution electron microscopy of superconducting samples showed the presence of a new phase with c ≈ 13 Å which exists as noticeable areas included within a matrix of the 123 structure or which occurs as isolated defects with a limited extension. All fluorinated compounds exhibited a strong disorder along the c-direction resulting in a ‘loss’ of c-parameter on X-ray patterns. The present results demonstrate that fluorine indeed enters the YBCO structure with a significant structural rearrangement for the high level of fluorination. The structure of the fully fluorinated YBa₂Cu₃O₆F₂ phase, possibly responsible for superconductivity, has been deduced from high resolution electron microscopy.     

重复频率激光辐照涂层金属材料的温升

 测量了重复频率YAG激光辐照涂层金属材料(30CrMnSiA钢和LF6M铝金壳体)的前后表面温度, 分析了不同频率激光辐照涂层壳体材料的温升特性。实验结果表明:在相同平均功率的条件下, 激光脉冲频率越高, 对材料的加热效率越明显, 重复频率激光对材料的加热优于连续激光。     

两能级原子在激光衰波场中的共振反射

在共振情况下求解两能级原子在激光衰波场中的薛定谔方程，得到了基态原子反射率Ｒｇ、激发态原子反射率Ｒｅ以及原子总反射率Ｒｔ的解析表达式。然后通过数值计算，详细讨论了Ｒｇ、Ｒｅ，Ｒｔ与拉比频率，原子垂直于靶面方向运动的动能的依赖关系，得到一些有意义的结果。     

中心集体流对带电粒子关联函数的影响

讨论了中心集体流对带电粒子关联函数的影响,采用蒙特卡罗方法研究了热源发射出的单粒子能谱与双粒子关联谱受中心集体流的影响. 利用QMD模型计算了100MeV/u的Ni+Ni系统在b=0fm条件下的双质子关联函数. 在计算中发展了一种交换粒子计算方法并证实了在100MeV/u Ni+Ni的中心碰撞中存在中心集体流. 计算结果表明,在中重系统中关联函数对中心集体流是灵敏的,为在100MeV/u以上能区研究中重系统中心碰撞形成的中心集体流提供了一种可行的方法.     

基于经典控制理论的控制系统计算机辅助设计软件

频率法和根轨迹法是经典控制理论的两个基本的控制系统设计与分析方法。本文主要介绍的两个计算机辅助设计（ＣＡＤ）软件，分别建立在频率法和根轨迹法的基础上。通过这两个ＣＡＮ软件，可以根据给定的单输入单输出（ＳＩＳＯ）控制系统数学模型，进行各种计算，从而得到我们所需要的结果．