Incidence of apparent restricted diffusion in three different models of cerebral infarction

High speed magnetic resonance imaging (MRI) and short diffusion times are used to investigate the appearance of restricted diffusion in three different models of cerebral infarction. The models are: the middle cerebral artery occlusion (MCAO) model in the rat, the carotid occlusion model in the gerbil, and the Rose Bengal microvascular occlusion model in the rat. All three were investigated for 16 b-values equally spaced between 10 and 1510 s/mm² using two distinct experiments. In the ct (constant time) experiment, the diffusion time was held constant at 11.7 ms while the b-value was varied with the gradient strength. In the cg (constant gradient) experiment, the gradient strength was held constant and the b-value increased by varying the diffusion time from 4.4 to 11.7 ms. A monoexponential decay of the signal intensity with b-value in the ct experiment accompanied by nonmonoexponential (NME) decay in the cg experiment is indicative of restricted diffusion. As this phenomenon is detectable only at short diffusion times, it cannot be due to restriction by impermeable membranes, and we have thus termed this apparent restriction. For the MCAO model and the carotid occlusion model, apparent restriction was found both inside the infarct territory and in some regions outside it. No definite evidence for restriction was found for the Rose Bengal model, which was, however, only studied from 24 h post-insult.     

The annular twist mapping of the restricted three-body problem

This paper presents a new derivation of the twist mapping in the planar restricted problem. It differs from other treatments in the use of a novel canonical transformation which allows for the utilization of symplectic reduction techniques.     

Hypergraph list coloring and Euclidean Ramsey theory

A hypergraph is simple if it has no two edges sharing more than a single vertex. It is s‐list colorable (or s‐choosable) if for any assignment of a list of s colors to each of its vertices, there is a vertex coloring assigning to each vertex a color from its list, so that no edge is monochromatic. We prove that for every positive integer r, there is a function d_r(s) such that no r‐uniform simple hypergraph with average degree at least d_r(s) is s‐list‐colorable. This extends a similar result for graphs, due to the first author, but does not give as good estimates of d_r(s) as are known for d₂(s), since our proof only shows that for each fixed r ≥ 2, d_r(s) ≤ 2 We use the result to prove that for any finite set of points X in the plane, and for any finite integer s, one can assign a list of s distinct colors to each point of the plane so that any coloring of the plane that colors each point by a color from its list contains a monochromatic isometric copy of X. © 2011 Wiley Periodicals, Inc. Random Struct. Alg., 2011     

大口径光学非球面轮廓测量过程可视化研究

研究了大口径非球面光学元件表面轮廓测量过程可视化,并设计、开发了基于双向链接边表的软件系统。提出一种改进的双向链接边表数据结构完成三维模型加载方法,建立数据结构及其相关图形元作为软件的基础层。计算非球面曲面方程获得表面轮廓的数据生成图形场景节点,并自动生成曲面测量轨迹。在非接触检测平台上进行测试,对测量数据进行平滑处理,拟合出测量获得的非球面面形,完成面形精度和表面粗糙度的评价。实验结果表明,该可视化系统技术路线正确高效、稳定性好,为非球面检测数据及其综合分析仿真提供直观的可视化平台。     

Parametric study of ship maneuverability in laterally restricted waters: Stochastic control approach

A stochastic control approach is used in a parametric study of ship maneuverability in a restricted channel of prescribed geometry. A realistic method, based on some empirical data, is used for the mathematical modelling of the ship motion in deep water.The authors are grateful to Mr. Lodewyk Wessels, Department of Electrical and Electronic Engineering, University of Pretoria, for generating the plots in this article.     

Why Restricted Additive Schwarz Converges Faster than Additive Schwarz

Recently a variant of the additive Schwarz (AS) preconditioner, the restricted additive Schwarz (RAS) preconditioner has been introduced, and numerical experiments showed that RAS converges faster and requires less communication than AS. We show in this paper how RAS, which is defined at the matrix level, can be interpreted as an iteration at the continuous level of the underlying problem. This interpretation reveals why RAS converges faster than classical AS.This revised version was published online in October 2005 with corrections to the Cover Date.     

算法的发现(IV)——论组合优化的特性清单

组合优化问题的定义［１］是定义１问题ＸＹＺ是指：对于每一个π（１）－集合Ｓ，从其诸π（２）－子集合中找出π（３）－（优）集合Ｓ＊．本文直接从它出发，§§２－５讨论诸π（ｉ）－集合（ｉ＝１，２，３）的某基本特性（ｐｒｏｐｅｒｔｙ），公理（ｐｏｓ－ｔｕｌａｔｅ），或者特殊情形（ｐａｒｔｉｃｕｌａｒｃａｓｅ）．列出了一个清单ＰＰＰ，叫做特性清单．它远非完善，但已经可以用来讨论不少问题．§６起简单地讨论若干个子清单，所对应的问题类，并讨论求解它们的一些方法．     

关于Tuza和Voigt的(Dm,m)-可选择性刻画定理

给出一个不属于Non-D的图,但该图却不是(Dm,m)-可选择的.这表明在Tuza Zs和Voigt M的Non-D定义和(Dm,m)-可选择图的特征化定理中存在一定的冲突.针对如上冲突,对Tuza Zs和Voigh M所给出的Non-D的定义,以及(Dm,m)-可选择图的特征化定理的证明进行了修正.     

ON A CLASS OF SIMPLE TABLE ALGEBRAS

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Implementing the ALGOL 68 heap

The implications of the heap, reference variables and global generators in ALGOL 68 are examined and some notes on possible implementation mechanisms are presented. In particular the use or simulation of hardware with segment addressing facilities is discussed.