A note on bifurcation points for index-1 differential-algebraic problems

The arclength continuation method is proposed for index-1 DAEs with singular points. In particular, the cusp points, the tangency points and equilibrium points are investigated. The numerical iterative matrix is studied at a singular point. The numerical examples are given to illustrate the robustness of the continuation method.     

二阶多项式系统固定奇点附近解的解析展开

研究二阶多项式系统所确定的通过固定奇点的解．利用牛顿图法研究了这种解在固定奇点处的幂级数展开式,给出有无穷多个解通过固定奇点的判据,并在只有有限个解通过固定奇点的情况下,给出了过固定奇点的解个数的上界．     

Some new monotonicity formulas and the singular set in the lower dimensional obstacle problem

We construct two new one-parameter families of monotonicity formulas to study the free boundary points in the lower dimensional obstacle problem. The first one is a family of Weiss type formulas geared for points of any given homogeneity and the second one is a family of Monneau type formulas suited for the study of singular points. We show the uniqueness and continuous dependence of the blowups at singular points of given homogeneity. This allows to prove a structural theorem for the singular set. Our approach works both for zero and smooth non-zero lower dimensional obstacles. The study in the latter case is based on a generalization of Almgren’s frequency formula, first established by Caffarelli, Salsa, and Silvestre. N. Garofalo is supported in part by NSF grant DMS-0701001. A. Petrosyan is supported in part by NSF grant DMS-0701015.     

Partial regularity of suitable weak solutions to the four‐dimensional incompressible magneto‐hydrodynamic equations

In this paper, we study the partial regularity of suitable weak solutions to the incompressible magneto‐hydrodynamic equations in dimension four by borrowing and improving the arguments given by Caffarelli, Kohn, and Nirenberg for incompressible Navier–Stokes equations. The so‐called ε‐regularity criteria are established for suitable weak solutions. As an application, an estimate on Hausdorff dimension of the possible singular points set for a suitable weak solution is given. Finally, we present further information on distribution of the possible singular points if the given initial data decay sufficiently rapidly or are not too singular at the origin, in some sense. Copyright © 2012 John Wiley & Sons, Ltd.     

有限元奇性问题的自适应处理

§1.引言 有限元奇性问题(包括凹角域问题以及方程本身的奇性等问题),由于奇点的存在,致使奇点附近收敛速度明显减慢。处理这一问题的有效方法是构作可靠实用的后验估计量来寻找收敛慢的坏单元,进行局部加密剖分,从而以最快的速度提高整体精度,但工作量最小。 本文的特点在于:1.对剖分条件限制较弱,只要求正规剖分(regular meshes)即     

Solution of boundary value problems for Laplace’s equation in a piecewise homogeneous plane with a parabolic crack (screen)

Boundary value problems for Laplace’s equation are considered in a piecewise homogeneous plane divided into two zones by a strongly permeable crack or a weakly permeable screen in the form of a parabola. The desired potentials have prescribed singular points (sources, sinks, etc.). Formulas are derived expressing the potentials in terms of harmonic functions that have the given singular points and describe similar processes in a homogeneous plane.     

Some examples of singular fluid flows

We show, by an explicit construction, the existence of solutions to the Stokes system in dimension three that are singular on a fractal set. The singular points are understood in the sense given by Caffarelli, Kohn and Nirenberg [2]. As an application, we show the existence of suitable weak solutions to the Navier-Stokes equations, driven by rough forces, that are singular on a fractal set.     

The approximation of generalized turning points by projection methods with superconvergence to the critical parameter

Summary A procedure is given that generates characterizations of singular manifolds for mildly nonlinear mappings between Banach spaces. This characterization is used to develop a method for determining generalized turning points by using projection methods as a discretization. Applications are given to parameter dependent two-point boundary value problems. In particular, collocation at Gauss points is shown to achieve superconvergence in approximating the parameter at simple turning points.     

Singular Points of Real Sextic Curves I

A complete classification of the individual types of singular points is given for irreducible real sextic curves. This classification is derived by using the computer algebra system Maple. There are 191 types of singular points for real irreducible sextic curves. We clarify that the classification is based on computing just enough of the Puiseux expansion to separate the branches. A significant portion of the proof consists of a sequence of large symbolic computations that can be done nicely using Maple.     

Invariant subspaces of a lightguide with periodic boundary

A waveguide operator is defined. It is proved that its spectrum coincides with the spectrum of a lightguide. The classification of singular points of the continuous spectrum is given. Invariant subspaces of the waveguide operator are distinguished that are related to an interval of the continuous spectrum without singular points. Bibliography: 9 titles. Translated fromProblemy Matematicheskogo Analiza, No. 14, 1995, pp. 51–62.     

Construction of a Fuchs equation with four singular points and with given reducible 2 × 2 monodromy matrices on the complex projective line

On the complex projective line, we construct a Fuchs equation with four singular points and with given reducible 2 × 2 monodromy matrices such that the fundamental solution matrix of this equation realizes a given homomorphism.     

Construction of a Fuchs Equation with Four Given Finite Singular Points and Given Reducible 2 × 2 Monodromy Matrices

On the complex projective line, we construct a Fuchs equation with four given finite singular points and with fundamental solution matrix that has given reducible 2×2 monodromy matrices in the nonresonance case.     

用新的逼近空间求解奇性问题

用新的逼近空间求解奇性问题梁国平，孔林，何江衡（中国科学院数学研究所）ＡＮＥＷＦＩＮＩＴＥＥＬＥＭＥＮＴＳＰＡＣＥＦＯＲＳＩＮＧＵＬＡＲＩＴＹＰＲＯＢＬＥＭＳ￥ＬｉａｎｇＧｕｏ－ｐｉｎｇ；ＫｏｎｇＬｉｎ；ＨｅＪｉａｎｇ－ｈｅｎｇ（Ｉｎｓｔｉｔｕｔｅｏ...     

The Haar condition and multiplicity of zeros

Summary In this paper the problem is investigated of how to take the (possibly noninteger) multiplicity of zeros into account in the Haar condition for a linear function space on a given interval. Therefore, a distinction is made between regular and singular points of the interval, and a notion of geometric multiplicity, which always is a positive integer, is introduced. It is pointed out that, for regular zeros (i.e., zeros situate at regular points), aq-fold zero (in the sense that its geometric multiplicity equalsq), counts forq distinct zeros in the Haar condition. For singular zeros (i.e., zeros situated at singular points), this geometric multiplicity has to be diminished by some well-determinable integer.     

关于血红蛋白(或变构酶)的一组动力学方程的定性分析

本文对文献[1]提出的血红蛋血的基本动力学方程组(三维自治系统)做以下定性分析:1.指出有意义的解应在一空间闭四面体内,证明四面体的四个面是无切面,积分曲线进入此体即永不复出.2.找到全部奇点,并证明其中两个奇点分别在四面体的一对不相邻的棱上(相应的棱是积分曲线),其余奇点一般都在四面体外无实际意义.3.证明在方程的7个物理参数中,仅参数b的符号决定奇点的性质.4.澄清该模型与MWC模型的关系.分析表明,该方程组较好地反映了变构酶的动力学性质.     

Some properties of the isolated invariant set of a flow

In this paper, several results involving m-chain are proved. At the same time, a criterion for the existence of trajectories joining singular points is given.     

Multiple positive solutions for a semilinear equation with prescribed singularity

Variational methods are used to prove the existence of multiple positive solutions for a semilinear equation with prescribed finitely many singular points. Some exact local behavior for positive solutions are also given.     

Notes on pedal and contrapedal curves of fronts in the Euclidean plane

A pedal curve (a contrapedal curve) of a regular plane curve is the locus of the feet of the perpendiculars from a point to the tangents (normals) to the curve. These curves can be parametrized by using the Frenet frame of the curve. Yet provided that the curve has some singular points, the Frenet frame at these singular points is not well‐defined. Thus, we cannot use the Frenet frame to examine pedal or contrapedal curves. In this paper, pedal and contrapedal curves of plane curves, which have singular points, are investigated. By using the Legendrian Frenet frame along a front, the pedal and contrapedal curves of a front are introduced and properties of these curves are given. Then, the condition for a pedal (and a contrapedal) curve of a front to be a frontal is obtained. Furthermore, by considering the definitions of the evolute, the involute, and the offset of a front, some relationships are given. Finally, some illustrated examples are presented.     

闭曲面上的C^0流的几类局部结构

本文提出了闭曲面上的Ｃ＾０流的几类轨道（包括准吸引及准排斥的奇点及周期轨道，以及较广义的鞍点，等等）的定义，并讨论了这几类轨道的邻域的结构。     

一类具有13个参数的7次系统的极限环分支

研究了一类具有幂零奇点的7次多项式微分系统的极限环分支与中心问题.借助于数学软件MATHEMATICA,推导出系统在原点的前14个拟Lyapunov常数,从而得到了系统的原点为中心的充要条件,证明了系统在3阶幂零奇点处可以分支出14个极限环,给出了7次李雅谱诺夫系统在3阶幂零奇点处的环性数的下界.