Approximation of Sobolev Classes by Their Finite-Dimensional Sections

We consider relative widths characterizing the best approximation of a fixed set by its sections of given dimension. For Sobolev classes of periodic functions of a single variable with constraints inL _∞ orL ₁ on higher-order derivatives, we present the exact orders of such widths in the spaces L _q.     

一类微分从属性及其应用

记△={|z|<1}.设函数(?):C~2×△→C在区域D(?)C中解析,G是△中的单叶解析函数.若△中的解析函数p(z)满足微分从属关系(?)(p(z),zp’(z);z)(?)G(z),z∈△,则可确定(?)和G的某些条件使之Re p(z)>p(z∈△),并且给出这些结果的某些应用.     

幺半群的内射类及投射类刻画

类比于一般环上模的内射类,定义了幺半群上的S-系的内射类和投射类,并利用它们刻画了几类特殊的幺半群．证明了完全内射幺半群和完全拟内射幺半群是等价的．并且证明了对于标致幺半群S,它是完全投射的当且仅当它是完全拟投射的当且仅当它上面的投射S-系构成了一个投射类．     

Approximation of Sobolev Classes by Their Sections of Finite Dimension

For Sobolev classes of periodic functions of one variable with restrictions on higher derivatives in L ₂, we determine the exact orders of relative widths characterizing the best approximation of a fixed set by its sections of given dimension in the spaces L _q.     

I-Radicals,Their Lattices,and Some Classes of Rings

We describe some I-radicals in the categories of modules over semilocal rings. We give a characterization of rings over which the set of I-radicals coincides with the set of hereditary idempotent radicals. We prove that the lattices of I-radicals in the categories of modules over Morita-equivalent rings are isomorphic.     

狄氏型及其在数学物理中的应用

简介狄氏型理论。该理论已成为紧密联系解析位势论与马氏过程理论的强有力数学工具,并因此在数学与物理中有许多应用。     

Schur Convexity for Two Classes of Symmetric Functions and Their Applications

For x =(x1, x2, ···, xn) ∈ Rn+∪ Rn-, the symmetric functions Fn(x, r) and Gn(x, r) are defined by r1 + xFij n(x, r) = Fn(x1, x2, ···, xn; r) =x1≤iij1i2···ir ≤n j=1and r1- xGij n(x, r) = Gn(x1, x2, ···, xn; r) =,x1≤i1i2···ir ≤n j=1ij respectively, where r = 1, 2, ···, n, and i1, i2, ···, in are positive integers. In this paper,the Schur convexity of Fn(x, r) and Gn(x, r) are discussed. As applications, by a bijective transformation of independent variable for a Schur convex function, the authors obtain Schur convexity for some other symmetric functions, which subsumes the main results in recent literature; and by use of the theory of majorization establish some inequalities. In particular, the authors derive from the results of this paper the Weierstrass inequalities and the Ky Fan's inequality, and give a generalization of Safta's conjecture in the n-dimensional space and others.     

Gevrey函数类和超分布中的Paley—Wiener型定理及其应用

众所周知,Paley-Wiener定理深刻地刻画了具紧支集的无穷可微函数及具紧支集的分布同它们的Fourier-Laplace变换之间的关系,建立了具紧支集的无穷可微函数或分布同指数型整函数之间的关系。正因为如此,Paley-Wiener定理在数学中、特别是在偏微分方程的C~∞理论中起着相当重要的作用。本文在具紧支集的Gevrey函数类及具紧支集的超分布中考虑同样类型的定理,称之为Paley-Wiener型定理。     

Hyperbolic Mapping Classes and Their Lifts on the Bers Fiber Space

Let S be a Riemann surface with genus p and n punctures. Assume that 3p - 3 n ＞ 0 and n ≥ 1. Let a be a puncture of S and let (～S) = S ∪ {a}. Then all mapping classes in the mapping class group Mods that fixes the puncture a can be projected to mapping classes of Mod(～S) under the forgetful map. In this paper the author studies the mapping classes in Mods that can be projected to a given hyperbolic mapping class in Mod(～S).     

How Students Use Physics to Reason About Calculus Tasks

The present research study investigates how undergraduate students in an integrated calculus and physics class use physics to help them solve calculus problems. Using Zandieh's (2000) framework for analyzing student understanding of derivative as a starting point, this study adds detail to her “paradigmatic physical” context and begins to address the need for a theoretical basis for investigating learning and teaching in integrated mathematics and science classrooms. A case study design was used to investigate the different ways students use physics ideas as they worked through calculus tasks. Data were gathered through four individual interviews with each of 8 ICP students, classroom participant‐observation, and triangulation of the data through student homework and exams. The main result of this study is the Physics Use Classification Scheme, a tool consisting of four categories used to characterize students' uses of physics on tasks involving average rate of change, derivative, and integral concepts. Two of the categories from the Physics Use Classification Scheme are elucidated with contrasting student cases in this paper.     

两类重要p-群及其自同构群的阶

In the paper we obtain two infinite classes of p-groups,calculate the orders of their automorphism groups and correct a mistake(perhaps misprinted)of Rodney James'paper in 1980.     

Pseudo-Anosov Mapping Classes and Their Representations by Products of Two Dehn Twists

Let S be a Riemann surface of analytically finite type （p, n） with 3p-3＋n 〉 0. Let a ∈ S and S = S - {a}. In this article, the author studies those pseudo-Anosov maps on S that are isotopic to the identity on S and can be represented by products of Dehn twists. It is also proved that for any pseudo-Anosov map f of S isotopic to the identity on S, there are infinitely many pseudo-Anosov maps F on S - {b} = S - {a, b}, where b is a point on S, such that F is isotopic to f on S as b is filled in.     

State constraints in the linear regulator problem: Case study

In this paper, we consider the problem of minimum-norm control of the double integrator with bilateral inequality constraints for the output. We approximate the constraints by piecewise linear functions and prove that the Langrange multipliers associated with the state constraints of the approximating problem are discrete measures, concentrated in at most two points in every interval of discretization. This allows us to reduce the problem to a convex finite-dimensional optimization problem. An algorithm based on this reduction is proposed and its convergence is examined. Numerical examples illustrate our approach. We also discuss regularity properties of the optimal control for a higher-dimensional state-constrained linear regulator problem.The first author was supported by the National Science Foundation, Grant No. DMS-9404431. The second author was supported by a François-Xavier Bagnoud Doctoral Fellowship and by NSF Grants DMS-9404431 and MSS-9114630.     

Mathematical Problem-Solving Processes of Elementary Male and Female Students

This study examined the problem solving behavior of young elementary school students. Ninety second-and third-grade students were observed and interviewed as they solved three problems. Conclusions included that the children readily attempted unfamiliar problems and that they used systematic solution processes. No significant gender differences were observed.