A note on the existence, uniqueness and symmetry of par-balanced realizations

We give a proof of the realization theorem of N.J. Young which states that analytic functions which are symbols of bounded Hankel operators admit par-balanced realizations. The main tool used in this proof is the induced Hilbert spaces and a lifting lemma of Kreîn-Reid-Lax-Dieudonné. Alternatively one can use the Loewner inequality. A short proof of the uniqueness of par-balanced realizations is included. As an application, it is proved that par-balanced realizations of real symmetric transfer functions areJ-self-adjoint.Research supported in part by the Romanian Academy grant GAR-6645/1996.This research was supported in part by NSF grant DMS-9501223.     

On the existence and uniqueness of limit cycles in planar continuous piecewise linear systems without symmetry

Some techniques to show the existence and uniqueness of limit cycles, typically stated for smooth vector fields, are extended to continuous piecewise-linear differential systems.New results are obtained for systems with three linearity zones without symmetry and having one equilibrium point in the central region. We also revisit the case of systems with only two linear zones giving shorter proofs of known results.A relevant application to the McKean piecewise linear model of a single neuron activity is included.     

Global existence without uniqueness

Summary In this paper we investigate the extendability of solutions of ordinary differential equations on [to, ∞) with the use of Liapunov functions. The results extend to non-unique systems the work done by Conti and Strauss, as well as establishing an equivalence between two properties of a Liapunov function. This work is part of the author's doctoral thesis under the direction of ProfessorA. Strauss at the University of Maryland. This research was supported in part by the National Science Foundation under Grant GP-6167. Entrata in Redazione il 20 febbraio 1970.     

On the multiple values and uniqueness of algebroid functions on annuli

In this paper, we discuss the influence of multiple values and Valiron deficiencies on the uniqueness problem of algebroid functions on annuli, we get the several uniqueness theorems of algebroid functions on annuli, and also we extend the Nevanlinna value distribution theory for algebroid functions on annuli.     

On existence and uniqueness in incremental thermoelasticity

Summary Existence and uniqueness of solutions to the evolution equations which govern small thermoelastic deformations superposed on a general non-linear thermomechanical deformation is investigated. The problem is solved by means of the semigroup theory applied to the abstract temporally inhomogeneous equation arising in this case.

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Résumé On étudie l'existence et l'unicité des solutions des équations qui gouvernent les petites déformations thermoélastiques superposés à un procés thermomécanique non linéaire général. Le problème est résolu à l'aide de la théorie des semigroupes apliquée à l'équation abstraite non homogène.

     

First order difference system- existence and uniqueness

In this paper, the general solution of the homogeneous matrix difference system is constructed in terms of two fundamental matrix solutions. The general solution of the inhomogeneous matrix difference system is established by the variation of parameters formula. A unique solution of the two-point boundary value problem associated with the matrix difference system is constructed by applying the QR-algorithm and the Bartels-Stewart algorithm.

     

Positivity,symmetry and uniqueness for minimizers of second-order Sobolev inequalities

We prove that minimizers for subcritical second-order Sobolev embeddings in the unit ball are unique, positive and radially symmetric. Since the proofs of the corresponding first-order results cannot be extended to the present situation, we apply new and recently developed techniques.     

A uniqueness theorem in symmetry classes

In this paper we prove a uniqueness theorem concerning irreducible sums of decomposable elements in a symmetry class of tensors.     

Generic existence and uniqueness of positive eigenvalues and eigenvectors

We consider a closed cone of positive operators on an ordered Banach space and prove that a generic element of this cone has a unique positive eigenvalue and a unique (up to a positive multiple) positive eigenvector. Moreover, the normalized iterations of such a generic element converge to its unique eigenvector.     

General economic equilibrium and variational inequalities: existence,uniqueness and sensitivity

In this paper we use the theory of variational inequalities to study the general economic equilibrium problem with production. The variational inequality is defined on a bounded set. Existence, uniqueness and sensitivity of the equilibrium point (pair of price vector and activity vector) are discussed through studying this variational inequality.     

Radial symmetry and uniqueness for an overdetermined problem

Consider a function u, harmonic in a ring‐shaped domain and taking two constant (distinct) values on the two connected components of the boundary. If we know in advance that one of the components is a sphere, and that u satisfies some overdetermined condition on the other one, can we conclude that u is radial? This paper answers this question for certain overdetermined conditions on the gradient of u, generalizing some previous results. Conditions depending on the principal curvatures of the boundary are also investigated. Existence and uniqueness of a radial solution to the overdetermined problem are discussed. Some extensions to ellipsoidal domains, as well as to quasilinear elliptic equations, are carried out. Copyright © 2001 John Wiley & Sons, Ltd.     

非线性方程极限环的存在惟一性及惟二性

考虑非线性方程 x=(y) - h(y) F(x) ,y=- g(x)的极限环问题 .通过考察方程轨线的走向及比较沿闭轨线的发散量积分 ,给出了极限环的存在惟一性及惟二性的若干组充分条件 ,推广了已有文献的相应结果     

The existence and uniqueness of strong kings in tournaments

A king x in a tournament T is a player who beats any other player y directly (i.e., x→y) or indirectly through a third player z (i.e., x→z and z→y). For x,y∈V(T), let b(x,y) denote the number of third players through which x beats y indirectly. Then, a king x is strong if the following condition is fulfilled: b(x,y)>b(y,x) whenever y→x. In this paper, a result shows that for a tournament on n players there exist exactly k strong kings, 1?k?n, with the following exceptions: k=n-1 when n is odd and k=n when n is even. Moreover, we completely determine the uniqueness of tournaments.