多孔介质中可压缩可混溶驱动问题的有限体积元法

有界区域上多孔介质中可压缩可混溶驱动问题由两个非线性抛物型方程耦合而成：压力方程和饱和度方程均是抛物型方程．运用有限体积元法对两个方程进行数值分析,给出了全离散有限体积元格式,并通过详细的理论分析,得到了近似解与原问题真解的最优H^1模误差估计。     

多孔介质中不可压缩流体的可混溶驱动问题的配置法

有了以上准备之后,我们给出有限元剖分,以h_c,h_p分别表示饱和度方程和压力方程的空间剖分步长,Δt_c,Δt_p分别表示饱和度方程和压力方程的时间剖分步长,且使:     

三维两相渗流驱动问题迎风区域分裂显隐差分法

对三维两相渗流驱动问题提出了两种迎风区域分裂显隐差分格式．压力方程采用了七点差分格式,为了能达到实际并行计算的要求,对饱和度方程采用了迎风区域分裂差分法,内边界处和各子区域分别对应显隐格式．得到了离散l2模收敛性分析,最后给出数值试验,支撑了理论分析结果．     

关于求解二相渗流的平面问题的一类新方法

本文提出一类求解二相平面渗流问题的新方法:用有限元法求解关于压力分布的椭圆型方程,然后利用所得的对压力梯度的半解析解,根据已有的饱和度沿流线传播的精确公式求得饱和度场.其主要特点和优点是能克服通常的数值模拟方法所具有的数值弥散,给出准确清晰的水驱油前沿饱和度间断面的位置,并且完全避免了通常必须与压力方程联立求解或交替求解的饱和度方程,从而使计算工作量大大减少.     

可压缩可混溶驱动问题的有限元配置法

多孔介质中可压缩可混溶驱动问题是非线性抛物系统,压力方程和饱和度方程用有限元配置方法来求解,证明了配置解的存在唯一性,最后得到了最优阶的误差估计．     

油藏数值模拟中动边值问题的迎风差分格式

考虑了三维油藏数值模拟中的动边值问题,对压力方程,给出中心差分格式;对饱和度方程给出隐式迎风差分格式及修正的迎风差分格式,并证明了格式的收敛性。数值算例与理论结果是一致的。     

两相渗流问题特征混合元数值模拟方法

本文提出求解两相渗流问题的一类克服数值弥散的特征混合元方法,用混合元法求解压力方程,利用后退特征线方法导出饱和度沿流线的移动;证明了格式的L_∞稳定性和收敛性,并给出最优阶的误差估计。     

服从OldroydB型微分模型的粘弹性流体问题的数值解法

本文对服从OldroydB型微分模型的粘弹性流体问题给出了一种数值逼近算法．该算法对压力方程采用标准混合有限元方法,对速度方程采用并行非重叠区域分解方法和特征线法．这种并行算法在子区域上用Galerkin方法,通过积分平均方法显式地给出内边界的数值流．在本文最后还给出了该算法的最优L^2。一误差估计．     

多孔介质中两相不可压缩不易混溶渗流问题的特征配置法

多孔介质中两相不可压缩不易混溶渗流问题是非线性偏微分方程的耦合系统,其中压力方程是椭圆的用配置法逼近,而饱和度方程是对流占优的抛物方程,用特征配置法来逼近,并且证明了数值解的存在唯一性,最后得到了最优的误差估计.     

油水驱动半正定问题迎风混合元格式及其数值分析

研究了不可压缩油水两相渗透流驱动问题.在扩散矩阵仅是半正定的假设条件下,提出了迎风混合元方法.混合元方法近似压力方程,饱和度方程的对流项用Godunov迎风格式来处理,扩散项则用推广的混合元来逼进,并推导出格式的误差估计.此种格式的优越性表现在两个方面:首先是饱和度方程的扩散矩阵仅是半正定的;二是摒弃了特征格式所限制的周期性条件,更适用于实际问题.     

Distribution of rational numbers in short intervals

A simplified proof for a well-distribution property for rational numbers is given and a connection with Riemann’s Hypothesis is pointed out. More precisely, we consider rational numbers with denominators of a given order of magnitude and show that the number of such numbers lying in a short interval of given length is normally close to its expectation in a mean square sense. The proof is elementary, using only Fourier series and Ramanujan sums. At the end of the paper, a variant of the circle method is discussed as an application.      

Quadrangles inscribed in an ellipse

Necessary and sufficient conditions are given under which a quadrangle similar to a given one can be inscribed in a given ellipse. The class of quadrangles for which this problem is solvable is described. Bibliography: 2 titles. Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 246, 1997, pp. 130–140. Translated by S. Yu. Pilyugin.     

Controlled selection a technique in random sampling

Summary The paper gives a method of constructing a random sampling design corresponding to a given population and a given sample sizen by means of which the probability of drawing a non-preferred combination of units can be reduced up to a certain level. Appropriate methods of analysing the data obtained from samples selected by this procedure are also given. A numerical example is given to illustrate the method developed in the paper.     

On the Jordan form in a unitary space

A method is given, which determines an orthonormal part of a basis with reto which a given transformation is in Jordan canonical form.     

Asymptotic normality in random graphs with given vertex degrees

We consider random graphs with a given degree sequence and show, under weak technical conditions, asymptotic normality of the number of components isomorphic to a given tree, first for the random multigraph given by the configuration model and then, by a conditioning argument, for the simple uniform random graph with the given degree sequence. Such conditioning is standard for convergence in probability, but much less straightforward for convergence in distribution as here. The proof uses the method of moments, and is based on a new estimate of mixed cumulants in a case of weakly dependent variables. The result on small components is applied to give a new proof of a recent result by Barbour and Röllin on asymptotic normality of the size of the giant component in the random multigraph; moreover, we extend this to the random simple graph.     

Continuous Subsonic-Sonic Flows in a Convergent Nozzle

This paper concerns continuous subsonic-sonic potential flows in a two-dimensional convergent nozzle. It is shown that for a given nozzle which is a perturbation of a straight one, a given point on its wall where the curvature is zero, and a given inlet which is a perturbation of an arc centered at the vertex, there exists uniquely a continuous subsonic-sonic flow whose velocity vector is along the normal direction at the inlet and the sonic curve, which satisfies the slip conditions on the nozzle walls and whose sonic curve intersects the upper wall at the given point. Furthermore, the sonic curve of this flow is a free boundary, where the flow is singular in the sense that the speed is only C^1/2 Hölder continuous and the acceleration blows up. The perturbation problem is solved in the potential plane, where the flow is governed by a free boundary problem of a degenerate elliptic equation with two free boundaries and two nonlocal boundary conditions, and the equation is degenerate at one free boundary.     

半平面中解析函数的零点

对在半平面中属于加权Hardy空间,不恒为零且在某一固定点列上为零的解析函数的存在性给出了充分必要条件。     

Axiomatization of identity-free equations valid in relation algebras

A finite axiom set for the identity-free equations valid in relation algebras is given. This is a simplification of the one given by Jónsson, and confirms a conjecture of Tarski. An axiom set for the identity-free equations valid in the representable relation algebras is given, too. We show that in the class of representable relation algebras, both the operation of taking converse and the identity constant are finitely axiomatizable (over the rest of the operations).Dedicated to the memory of Alan DayPresented by J. Sichler.     

Notes on equivalent stationary policies in Markov decision processes with total rewards

We construct examples of Markov Decision Processes for which, for a given initial state and for a given nonstationary transient policy, there is no equivalent (randomized) stationary policy, i.e. there is no stationary policy which occupation measure is equal to the occupation measure of a given policy. We also investigate the relation between the existence of equivalent stationary policies in special models and the existence of equivalent strategies in various classes of nonstationary policies in general models.     

Clustering Methods in Microarrays

Summary DCT Given a finite set of points in an Euclidean space the \emph{spanning tree} is a tree of minimal length having the given points as vertices. The length of the tree is the sum of the distances of all connected point pairs of the tree. The clustering tree with a given length of a given finite set of points is the spanning tree of an appropriately chosen other set of points approximating the given set of points with minimal sum of square distances among all spanning trees with the given length. DCM A matrix of real numbers is said to be column monotone orderable if there exists an ordering of columns of the matrix such that all rows of the matrix become monotone after ordering. The {\emph{monotone sum of squares of a matrix}} is the minimum of sum of squares of differences of the elements of the matrix and a column monotone orderable matrix where the minimum is taken on the set of all column monotone orderable matrices. Decomposition clusters of monotone orderings of a matrix is a clustering ofthe rows of the matrix into given number of clusters such that thesum of monotone sum of squares of the matrices formed by the rowsof the same cluster is minimal.DCP A matrix of real numbers is said to be column partitionable if there exists a partition of the columns such that the elements belonging to the same subset of the partition are equal in each row. Given a partition of the columns of a matrix the partition sum of squares of the matrix is the minimum of the sum of square of differences of the elements of the matrix and a column partitionable matrix where the minimum is taken on the set of all column partitionable matrices. Decomposition of the rows of a matrix into clusters of partitions is the minimization of the corresponding partition sum of squares given the number of clusters and the sizes of the subsets of the partitions.