Singular Points Near an X_0-breaking Double Singular Fold Point in Z_2-symmetric Nonlinear Equations

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Double $S$-Breaking Cubic Turning Points and Their Computation

1.Introducti0nManynaturalphen0menapossessm0reorlessexactsymmetries,whicharelikelytobereflectedinanysensiblemathematicalm0del.Idealizationssuchasperiodicboundaryconditi0nscanproduceadditionaJsymmetries.Phen0menawhosemodelsexhibitbothsymmetryandnonlinearityleadtopr0blemswhicharechallengingandrichinc0mplexity.Problemswithsymmetriescanshowarichbifurcationbehavi0ur.Theoccurrenceofmultiplesteadystatebifurcationismostlyduetounderlyingsymmetries.Thisgivesrisetothedifficultiestonumericalcomputation-H…     

On the Number of Unbounded Solution Branches in a Neighborhood of an Asymptotic Bifurcation Point

We suggest a method for studying asymptotically linear vector fields with a parameter. The method permits one to prove theorems on asymptotic bifurcation points (bifurcation points at infinity) for the case of double degeneration of the principal linear part. We single out a class of fields that have more than two unbounded branches of singular points in a neighborhood of a bifurcation point. Some applications of the general theorems to bifurcations of periodic solutions and subharmonics as well as to the two-point boundary value problem are given.     

BIFURCATION ANALYSIS AND COMPUTATION OF DOUBLE TAKENS-BOGDANOV POINT IN Z2-EQUIVARIABLE NONLINEAR EQUATIONS

The paper deals with the computation and bifurcation analysis of double Takens-Bogdanov point (u~0, Λ~0) (in short, DTB point) in the Z_2-equivariable nonlinear equation f(u,Λ)=0,f:U×R~4→ V, where U and V are Banach spaces, parameters A∈R~4. At (u~0,Λ~0) , the null space of f_u~0 has geometric multiplicity 2 and algebraic multiplicity 4. Firstly a regular extended system for computing DTB point is proposed. Secondly, it is proved that there arc four branches of singular points bifurcated from DTB point: two paths of STB points, two paths of TB-Hopf points. Finally, the numerical results of one dimensional Brusselator equations are given to show the effectiveness of our theory and method.     

A Berger-Green type inequality for compact Lorentzian manifolds

We give a Lorentzian metric on the null congruence associated with a timelike conformal vector field. A Liouville type theorem is proved and a boundedness for the volume of the null congruence, analogous to a well-known Berger-Green theorem in the Riemannian case, will be derived by studying conjugate points along null geodesics. As a consequence, several classification results on certain compact Lorentzian manifolds without conjugate points on its null geodesics are obtained. Finally, several properties of null geodesics of a natural Lorentzian metric on each odd-dimensional sphere have been found.

     

Qualification of optimal strategies and singular surfaces of a class of differential games

At each point of a regular region, there exist two tangent cones which are complementary to each other. The two vectograms defined by the pair of optimal strategies must be contained separately in the two tangent cones. The velocity vector resulting from the selection of the optimal strategies consequently must represent a semipermeable direction. These conditions, which reveal a fundamental separating property of the optimal velocity vector, are weaker than that of Isaacs' main equation. However, they hold even on singular surfaces. A singular surface arises only when the resulting velocity vector of the previous optimal strategies cannot continuously represent a semipermeable direction after the optimal path crosses over the surface. This observation yields a necessary condition for a singular surface to occur. The localization of singular surfaces is then possible. Finally, a smooth condition with respect to optimal paths is given.The author expresses his deep gratitude to his thesis advisor, Professor R. Isaacs, Johns Hopkins University, for his very stimulating of this research. This research was supported in part by the Center for Naval Analyses, University of Rochester, Rochester, New York.     

A FORMULA FOR INDEX OF A SINGULAR POINT OF POLYNOMIAL DIFFERENTIAL SYSTEMS IN THE PLANE

1IntroductionandConclllsionIntheplallalrPolynomialdifferentialsystem$~p.(x,y) of(x,y)=X(x,y),Z~q.(x,Y) '()(x,y)~I'(x,y)(l)wherep.(x,y),q.(x,y)arehomogenouspolynomialsinigyofthedegreen>1,(x,y)ER',withq:(x,7/) p:(x,y)/0,andof(x,y),,of(x,]j)arepolynomialinx,…     

Center conditions and bifurcation of limit cycles at degenerate singular points in a quintic polynomial differential system

The center problem and bifurcation of limit cycles for degenerate singular points are far to be solved in general. In this paper, we study center conditions and bifurcation of limit cycles at the degenerate singular point in a class of quintic polynomial vector field with a small parameter and eight normal parameters. We deduce a recursion formula for singular point quantities at the degenerate singular points in this system and reach with relative ease an expression of the first five quantities at the degenerate singular point. The center conditions for the degenerate singular point of this system are derived. Consequently, we construct a quintic system, which can bifurcates 5 limit cycles in the neighborhood of the degenerate singular point. The positions of these limit cycles can be pointed out exactly without constructing Poincaré cycle fields. The technique employed in this work is essentially different from more usual ones. The recursion formula we present in this paper for the calculation of singular point quantities at degenerate singular point is linear and then avoids complex integrating operations.     

Maximal and extremal singular graphs

A graph G is singular if the nullspace of its adjacency matrix is nontrivial. Such a graph contains induced subgraphs called singular configurations of nullity 1. We present two algorithms. One is for the construction of a maximal singular nontrivial graph G containing an induced subgraph, which is a singular configuration with the support of a vector in its nullspace as in that of G. The second is for the construction of a nut graph, a graph of nullity one whose null vector has no zero entries. An extremal singular graph of a given order, with the maximal nullity and support, has a nut graph as a maximal singular configuration.     

赋范线性空间集合的严有效点

本文引入一个新的有效点概念一严有效点,它是Borwein超有效点的推广.此外还讨论了严有效点的基本性质:存在性条件、纯量化特征、稠密性定理以及与Borwein超有效点的关系.     

Characterizations of strictly convex sets by the uniqueness of support points

Abstract

This short paper characterizes strictly convex sets by the uniqueness of support points (such points are called unique support points or exposed points) under appropriate assumptions. A class of so-called regular sets, for which every extreme point is a unique support point, is introduced. Closed strictly convex sets and their intersections with some other sets are shown to belong to this class. The obtained characterizations are then applied to set-valued maps and to the separation of a convex set and a strictly convex set. Under suitable assumptions, so-called set-valued maps with path property are characterized by strictly convex images of the considered set-valued map.     

Normal forms and invariants for 2-dimensional almost-Riemannian structures

2-Dimensional almost-Riemannian structures are generalized Riemannian structures on surfaces for which a local orthonormal frame is given by a Lie bracket generating pair of vector fields that can become collinear. Generically, there are three types of points: Riemannian points where the two vector fields are linearly independent, Grushin points where the two vector fields are collinear but their Lie bracket is not, and tangency points where the two vector fields and their Lie bracket are collinear and the missing direction is obtained with one more bracket.In this paper we consider the problem of finding normal forms and functional invariants at each type of point. We also require that functional invariants are “complete” in the sense that they permit to recognize locally isometric structures.The problem happens to be equivalent to the one of finding a smooth canonical parameterized curve passing through the point and being transversal to the distribution.For Riemannian points such that the gradient of the Gaussian curvature K is different from zero, we use the level set of K as support of the parameterized curve. For Riemannian points such that the gradient of the curvature vanishes (and under additional generic conditions), we use a curve which is found by looking for crests and valleys of the curvature. For Grushin points we use the set where the vector fields are parallel.Tangency points are the most complicated to deal with. The cut locus from the tangency point is not a good candidate as canonical parameterized curve since it is known to be non-smooth. Thus, we analyse the cut locus from the singular set and we prove that it is not smooth either. A good candidate appears to be a curve which is found by looking for crests and valleys of the Gaussian curvature. We prove that the support of such a curve is uniquely determined and has a canonical parametrization.     

Hopf bifurcation near a double singular point

The nonlinear equation f(x,λ,) = 0, f:X × R²→X, where X is a Banach space and f satisfies a Z₂-symmetry relation is considered. Interest centres on a certain type of double singular point, where the solution x is symmetric and f_x has a double zero eigenvalue, with one eigenvector symmetric and one antisymmetric.

We show that under certain nondegeneracy conditions, which are stated both algebraically and geometrically, there exists a path of Hopf bifurcations or imaginary Hopf bifurcations passing through the double singular point, and for which x is not symmetric except at the double singular point. An easy geometrical test is found to decide which type of phenomenon occurs. A biproduct of the analysis is that explicit expressions are obtained for quantities which help to provide a reliable numerical method to compute these paths. A pseudo-spectral method was used to obtain numerical results for the Brusselator equations to illustrate the theory.     

在有限部分具有四个奇点二次系统的无穷远奇点

为了研究具有四个奇点二次系统的结构,本文研究了这类系统的无穷远奇点。 一般来说,二次系统的无穷远奇点是比较复杂的。但是在有限范围内具有四个奇点的次系统,它的无穷远奇点则具有某些特殊性质。为了方便,下面以E_2~4表示这种系统。     

Periodic orbits and chaos in fast-slow systems with Bogdanov-Takens type fold points

The existence of stable periodic orbits and chaotic invariant sets of singularly perturbed problems of fast-slow type having Bogdanov-Takens bifurcation points in its fast subsystem is proved by means of the geometric singular perturbation method and the blow-up method. In particular, the blow-up method is effectively used for analyzing the flow near the Bogdanov-Takens type fold point in order to show that a slow manifold near the fold point is extended along the Boutroux's tritronquée solution of the first Painlevé equation in the blow-up space.     

Bifurcation and Isochronicity at Infinity in a Class of Cubic Polynomial Vector Fields

In this paper, we study the appearance of limit cycles from the equator and isochronicity of infinity in polynomial vector fields with no singular points at infinity. We give a recursive formula to compute the singular point quantities of a class of cubic polynomial systems, which is used to calculate the first seven singular point quantities. Further, we prove that such a cubic vector field can have maximal seven limit cycles in the neighborhood of infinity. We actually and construct a system that has seven limit cycles. The positions of these limit cycles can be given exactly without constructing the Poincare cycle fields. The technique employed in this work is essentially different from the previously widely used ones. Finally, the isochronous center conditions at infinity are given.     

On vector optimization problems and vector variational inequalities using convexificators

In this paper, we establish some results which exhibit an application of convexificators in vector optimization problems (VOPs) and vector variational inequaities involving locally Lipschitz functions. We formulate vector variational inequalities of Stampacchia and Minty type in terms of convexificators and use these vector variational inequalities as a tool to find out necessary and sufficient conditions for a point to be a vector minimal point of the VOP. We also consider the corresponding weak versions of the vector variational inequalities and establish several results to find out weak vector minimal points.     

Existence of efficient solutions for vector maximization problems

The vector maximization problem arises when more than one objective function is to be maximized over a given feasibility region. The concept of efficiency has played a useful role in analyzing this problem. In order to exclude efficient solutions of a certain anomalous type, the concept of proper efficiency has also been utilized. In this paper, an examination of the existence of efficient and properly efficient solutions for the vector maximization problem is undertaken. Given a feasible solution for the vector maximization problem, a related single-objective mathematical programming problem is investigated. Any optimal solution to this program, if one exists, yields an efficient solution for the vector maximization problem. In many cases, the unboundedness of this problem shows that no properly efficient solutions exist. Conditions are pointed out under which the latter conclusion implies that the set of efficient solutions is null. As a byproduct of our results, conditions are derived which guarantee that the outcome of any improperly efficient point is the limit of the outcomes of some sequence of properly efficient points. Examples are provided to illustrate these results.The author would like to thank Professor T. L. Morin for his helpful comments. Thanks also go to an anonymous reviewer for his useful comments concerning an earlier version of this paper.The author would like to acknowledge a useful discussion with Professor G. Bitran which helped in motivating Example 4.1.     

Kinematische Erzeugung der Schiebrömerflächen im Flaggenraum

Algebraic surfaces of fourth order containing three double lines with a common point are called Steiner-surfaces. These surfaces contain a two-parameter set of conics lying in the tangent planes of . According to WUNDERLICH [17] a Steiner-surface can be generated by translation of a parabola along a parabola if and only if two or three of the double lines coincide. If such a special double line, the tangent plane along it und the singular point lying on it are choosen to represent the absolute line, plane and point respectivly of a flag space F³, the conies of are circles in the sense of F³. An infinite set of oneparameter motions generating as path of a circle is given. Among these motions exist Darboux-motions, whereby the points move along congruent circles.     

Asymptotic expansions using blow-up

The method of matched asymptotic expansions and geometric singular perturbation theory are the most common and successful approaches to singular perturbation problems. In this work we establish a connection between the two approaches in the context of the simple fold problem. Using the blow-up technique [5], [12] and the tools of geometric singular perturbation theory we derive asymptotic expansions of slow manifolds continued beyond the fold point. Our analysis explains the structure of the expansion and gives an algorithm for computing its coefficients.