Improved Lower Bounds for the Critical Probability of Oriented Bond Percolation in Two Dimensions

We present a coupled decreasing sequence of random walks on Z that dominate the edge process of oriented bond percolation in two dimensions. Using the concept of random walk in a strip, we describe an algorithm that generates an increasing sequence of lower bounds that converges to the critical probability of oriented percolation p_c. From the 7th term on, these lower bounds improve upon 0.6298, the best rigorous lower bound at present, establishing 0.63328 as a rigorous lower bound for p_c. Finally, a Monte Carlo simulation technique is presented; the use thereof establishes 0.64450 as a non-rigorous five-digit-precision (lower) estimate for p_c. Mathematics Subject Classification (1991): 60K35 Supported by CNPq (grant N.301637/91-1). Supported by a grant from CNPq.     

一类六参数非协调任意凸四边形单元

本文构造了一类六参数非协调四边形单元,证明由此产生的有限元对任意四边形网格通过Irons分片检查,其收敛效果同Wilson元相当且形状函数的选择不依赖于单元本身。类Wilson元及改进的Wilson任意四边形单元是其中的特例。     

关于参数型copula函数的拟合检验

在金融和保险中,copula函数是一种构造多元相关分布函数的有力工具．然而,怎样选择一个适当的copula函数用于拟合数据,并没有找到统一的方法．因此,基于copula函数的经验分布,我们提出了一种用于检验具有某种特定参数结构的copula函数拟合数据优良性的方法,并得到了此检验的渐近性质．由于该检验统计量的极限分布依赖未知参数,我们采用非参数蒙特卡罗方法确定临界值．我们做了一个简单的模拟来验证本文提出的检验方法的功效．     

扁平绕带式低温高压容器绝热性能分析和计算

扁平绕带式低温高压容器是一种新型低温液体贮存设备 ,由内外两层容器组成 ,内筒体的外壁焊有液氮预冷夹套。平均蒸发率是衡量扁平绕带式低温高压容器绝热性能的重要指标。文中在分析其传热过程和壁厚温差影响因素的基础上 ,提出了一种计算其蒸发率的工程方法 ,并结合1 0 m3液氢储罐设计实例进行了计算。结果表明扁平绕带式低温高压容器具有良好的绝热性能 ,适用于重要介质的低温贮运     

Preliminary Design of ITER Test Blanket Module HC-SB Structure

The helium cooled solid breeder blanket that represents the main stream in relevant blanket concepts. It is considered as one of the main options for the fusion reactor. This concept have advantage as follows： （ 1 ） structure simpleness and stability, （ 2 ） no effect of MHD, （ 3 ） a good compatibility in different materials.     

Test sets for integer programs

In this paper I discuss various properties of the simplicial complex of maximal lattice free bodies associated with a matrixA. If the matrix satisfies some mild conditions, and isgeneric, the edges of the complex form the minimal test set for the family of integer programs obtained by selecting a particular row ofA as the objective function, and using the remaining rows to impose constraints on the integer variables.     

Trapping efficiencies of various collection solvents after supercritical fluid extraction

A polarity test mix consisting of acetophenone, N, N-dimethylaniline, naphthalene, decanoic acid, 2-naphthol, and n-tetracosane was spiked onto sand, and extracted with supercritical carbon dioxide, to evaluate the collection efficiency of various solvents and solvent mixtures. Nine single collection solvent systems and four mixed collection solvent systems were studied. When one-component collection solvents were employed, quantitative (above 90%) recovery of all analytes was not possible. With mixed collection solvents, recoveries of 90% or better with all analytes studied were possible.     

Dynamic behavior of two parallel symmetric permeable cracks in a piezoelectric strip

The dynamic behavior of two parallel symmetric cracks in a piezoelectric strip under harmonic anti-plane shear waves is studied using the Schmidt method for permeable crack surface conditions. The cracks are parallel to the edge of the strip. By means of the Fourier transform, the problem can be solved with the help of two pairs of dual integral equations. These equations are solved using the schmidt method. The results show that the stress and the electric displacement intensity factors depend on the geometry of the cracks, the frequency of incident waves, the distance between cracks and the thickness of the strip. It is also found that the electric displacement intensity factors for the permeable crack surface conditions are much smaller than those for the impermeable crack surface conditions. Project supported by the Post Doctoral Science Foundation of Heilongjiang Province, the Natural Science Foundation of Heilongjiang Province, the National Science Foundation with the Excellent Young Investigator Award (No. 19725209) and the Scientific Research Foundation of Harbin Institute of Technology (HIT.2000.30).