Two local operators and the BLUE

For a given matrix A, a matrix P such that PA = A is said to be a local identity, and such that P²A = PA is said to be a local idempotent. In the paper, some simple properties of such operators are presented. Their relation to the best linear unbiased estimation in the general Gauss-Markov model is also demonstrated.     

Numerical study of chaotic oscillations in the electron beam with virtual cathode in the external non-uniform magnetic fields

In this Letter the results of theoretical investigations of the chaotic microwave oscillator based on the electron beam with a virtual cathode are presented. Nonlinear non-stationary processes in these electron systems are studied by means of numerical analysis of 2.5D model. It was discovered that the non-uniform external magnetic field value controls the dynamical regime of oscillations in the virtual cathode oscillator. The processes of the chaotization of output microwave radiation are described and interpreted from the point of view of the formation and interaction of electron structures (bunches) in the electron beams. The numerical results have shown that the investigated electron system with virtual cathode could be considered as a promising controlled source of wideband chaotic oscillations in the microwave range.     

Searching for a near neighbor particle in DSMC cells using pseudo-subcells

LeBeau et al. (2003) [4] introduced the ‘virtual-subcell’ (VSC) method of finding a collision partner for a given DSMC particle in a cell; all potential collision partners in the cell are examined to find the nearest neighbor, which becomes the collision partner. Here I propose a modification of the VSC method, the ‘pseudo-subcell’ (PSC) method, whereby the search for a collision partner stops whenever a ‘near-enough’ particle is found, i.e. whenever another particle is found within the ‘pseudo-subcell’ of radius δ centered on the first particle. The radius of the pseudo-subcell is given by δ = Fd_n, where d_n is the expected distance to the nearest neighbor and F is a constant which can be adjusted to give a desired trade-off between CPU time and accuracy as measured by a small mean collision separation (MCS). For 3D orthogonal cells, of various aspect ratios, d_n/L ≈ 0.746/N^0.383 where N is the number of particles in the cell and L is the cube root of the cell volume. There is a good chance that a particle will be found in the pseudo-subcell and there is a good chance that such a particle is in fact the nearest neighbor. If no particle is found within the pseudo-subcell the closest particle becomes the collision partner.     

互联网中身份管理应对策略思考

随着Web2.0的出现,互联网进入第三个高速发展阶段,互联网已经成为日常生活中的重要组成部分,同时互联网上的个人隐私泄露与保护问题也日益凸显。因此,建立以身份管理为核心的信息网络基础设施,用于规范个人信息管理,提升政府的监管能力,促进ICT网络的融合与发展。本文从互联网典型身份管理技术方案分析入手,继而分析互联网中身份管理相关问题,提出身份管理作为信息网络重要基础设施的应对策略以及下一步的研究建议。     

虚拟机在多媒体教室管理中的应用探讨

虚拟机技术的发展近年来已经越来越成熟,并在教学中得到了广泛的应用.结合实际的工作经验,就虚拟机在多媒体教室计算机系统管理中的应用作了探讨性的研究,分析研究了虚拟机的特点及利用虚拟机软件解决多媒体教室计算机系统管理中的若干问题.     

一次性口令认证重同步方法的研究

重同步问题是一次性口令（One—Time Password,OTP）系统中的关键环节。传统的身份认证采用静态口令,但是静态口令一旦被截获,就会被他人利用。针对静态口令的缺点,一种常见的解决方法就是采用一次性口令来实现身份认证。目前流行的一次性口令系统是S／KEY结构。在S／KEY体系结构中,任何一个密码不能被重复使用。同时,已经使用过的密码序列不能为新生成的密码提供任何有用的信息。文中在分析一次性口令重同步原理的基础上,提出了一种基于一次性口令之间无相关性的重同步方法。实验表明,该方法可以在安全、高效的前提下很好地解决一次性口令的重同步问题。     

基于主机标识的访问控制模型研究

身份认证和访问控制是Internet应用的重要方面,传统的实施方案通常针对于特定的应用,也不能用于普适计算环境下的移动终端。文中提出了一个新的访问控制模型,利用了由IETF定义的主机标识协议（HIP）,并扩展了HIP基本交换过程来实现对用户的认证,并通过客户端主机标识和用户标识的绑定认证来建立主机和用户的绑定关系,从而实现对用户访问请求的判断。     

基于VLAN的策略路由的应用

简单介绍虚拟局域网(VLAN)及策略路由的概念,详细介绍在Linux下VLAN及策略路由的实现.根据具体问题并结合实例详细介绍在Linux下如何将二者结合解决实际问题.     

Enumeration formulas for standard Young tableaux of nearly hollow rectangular shapes

This paper considers the enumeration problem of a generalization of standard Young tableau (SYT) of truncated shape. Let $\lambda ?\mu |\left\{(i_0,j_0)\right\}$ be the SYT of shape $\lambda$ truncated by $\mu$ whose upper left cell is $(i_0,j_0)$, where $\lambda$ and $\mu$ are partitions of integers. The summation representation of the number of SYT of the truncated shape $(n+k+2,{(n+2)}^{m+1})?\left(n^m\right)|\left\{(2,2)\right\}$ is derived. Consequently, three closed formulas for SYT of hollow shapes are obtained, including the cases of (i). $m=n=1$, (ii). $k=0$, and (iii). $k=1,m=n$. Finally, an open problem is posed.