Riccati Equations for the Bolza Problem Arising in Boundary/Point Control Problems Governed by <Emphasis Type="Italic">C</Emphasis><Subscript>0</Subscript> Semigroups Satisfying a Singular Estimate

We establish solvability of Riccati equations and optimal feedback synthesis in the context of Bolza control problem for a special class of control systems referred to in the literature as control systems with singular estimate. Boundary/point control problems governed by analytic semigroups constitute a very special subcategory of this class which was motivated by and encompasses many PDE control systems with both boundary and point controls that involve interactions of different types of dynamics (parabolic and hyperbolic) on an interface. We also discuss two examples from thermoelasticity and structure acoustics. Research partially supported by NSF Grant DMS 0104305.     

Structural properties of Markov chains with weak and strong interactions

Markov chains have been frequently used to characterize uncertainty in many real-world problems. Quite often, these Markov chains can be decomposed into a vector consisting of fast and slow components; these components are coupled through weak and strong interactions. The main goal of this work is to study the structural properties of such Markov chains. Under mild conditions, it is proved that the underlying Markov chain can be approximated in the weak topology of L² by an aggregated process. Moreover, the aggregated process is shown to converge in distribution to a Markov chain as the rate of fast transitions tends to infinity. Under an additional Lipschitz condition, error bounds of the approximation sequences are obtained.     

The Schrödinger equation with a moving point interaction in three dimensions

In the case of a single point interaction we improve, by using different methods, the existence theorem for the unitary evolution generated by a Schrödinger operator with moving point interactions obtained by Dell'Antonio, Figari and Teta.

     

Lower bound for the spectrum and the presence of pure point spectrum of a singular discrete Hamiltonian system

In this paper, criteria for limit-point (n) case of a singular discrete Hamiltonian system are established. Furthermore, the lower bound of the essential spectrum is obtained and the present of pure point spectrum is discussed for such system by using the spectral theory of self-adjoint operators in a Hilbert space.     

Equifocality of a singular Riemannian foliation

A singular foliation on a complete Riemannian manifold is said to be Riemannian if each geodesic that is perpendicular to a leaf at one point remains perpendicular to every leaf it meets. We prove that the regular leaves are equifocal, i.e., the end point map of a normal foliated vector field has constant rank. This implies that we can reconstruct the singular foliation by taking all parallel submanifolds of a regular leaf with trivial holonomy. In addition, the end point map of a normal foliated vector field on a leaf with trivial holonomy is a covering map. These results generalize previous results of the authors on singular Riemannian foliations with sections.

     

On the existence of bubble-type solutions of nonlinear singular problems

Considered in this paper is a class of singular boundary value&nbsp;problem, arising&nbsp;in hydrodynamics and nonlinear field theory, when centrally bubble-type solutions are&nbsp;sought: \((p(t)u0)0 = c(t)p(t)f(u); u0(0) = 0; u(+1) = L &gt; 0\) in the half-line \([0;+1)\), where \(p(0) = 0\). We are interested in strictly increasing solutions&nbsp;of this problem in \([0;1)\) having just one zero in \((0;+1) \)and finite limit at zero, which has&nbsp;great importance in applications or pure and applied mathematics. Su&plusmn;cient conditions&nbsp;of the existence of such solutions are obtained by applying the critical point theory and&nbsp;by using shooting argument [9,10] to better analysis the properties of certain solutions&nbsp;associated with the singular di&reg;erential equation. To the authors' knowledge, for the first&nbsp;time, the above problem is dealt with when f satis&macr;es non-Lipschitz condition. Recent&nbsp;results in the literature are generalized and signi&macr;cantly improved.     

A continuous model for the theory of organizational structure

We investigate a general class of linear models of dyadic interactions with a constant discrete time delay. We prove that the changes in stability of the stationary states occur for various intervals of the parameters that determine the strength and nature of emotional interactions between the partners. The dynamics of interactions depend on both reactivity of partners to their own emotional states as well as to the partner's states. The results suggest that reactivity to the partner's states has greater impact on the dynamics of the relationship than the reactivity to one's own states. Moreover, the results underscore the importance of deliberation in maintaining the stability of the relationship. Moreover, we have found that multiple stability switches are only possible when one of the partners reacts with delay to their own emotional states. We also propose a generalization to triadic interactions.     

粒子的相互作用、极限环和相变

从各种相互作用的规范理论出发,讨论了规范场方程的某些新的解,并引入了势,然后探讨了它们与极限环、各种奇异点的关系,最后论述了这些结果可能具有的粒子性质和相变等物理意义．     

Smoothness of transition maps in singular perturbation problems with one fast variable

This paper deals with the smoothness of the transition map between two sections transverse to the fast flow of a singularly perturbed vector field (one fast, multiple slow directions). Orbits connecting both sections are canard orbits, i.e. they first move rapidly towards the attracting part of a critical surface, then travel a distance near this critical surface, even beyond the point where the orbit enters the repelling part of the critical surface, and finally repel away from the surface. We prove that the transition map is smooth. In a transcritical situation however, where orbits from an attracting part of one critical manifold follow the repelling part of another critical manifold, the smoothness of the transition map may be limited, due to resonance phenomena that are revealed by blowing up the turning point! We present a polynomial example in R³.     

一类四阶边值问题的分析

该文考虑的四阶边值问题，可用于描述飞机、轮船及建筑物的结构模型。由经典的分析方法，如辅助的截断函数，Schauder不动点定理，作者首先提出一种改进的上、下解方法；然后，利用二阶齐次边值问题的第一特征函数，构造出具体的上解，同时取0为相应下解，在更一般的假设下得到正解的存在性； 最后探讨了右端项f(x,y,z)在y=0奇异的情形。     

非线性奇异扩散方程解的存在性与唯一性

本文讨论奇异扩散方程Ｃａｕｃｈｙ问题解的存在性与唯一性,得到的主要结果是：存在唯一的正则解。     

奇异半正二阶脉冲Dirichlet边值问题的正解

该文利用锥不动点定理讨论了奇异半正二阶脉冲Dirichlet边值问题正解的存在性.     

On approximations of rank one -perturbations

Approximations of rank one -perturbations of self-adjoint operators by operators with regular rank one perturbations are discussed. It is proven that in the case of arbitrary not semibounded operators such approximations in the norm resolvent sense can be constructed without any renormalization of the coupling constant. Approximations of semibounded operators are constructed using rank one non-symmetric regular perturbations.

     

Spectral Asymptotics for Schrödinger Operators with Periodic Point Interactions

Spectrum of the second-order differential operator with periodic point interactions in L₂(R) is investigated. Classes of unitary equivalent operators of this type are described. Spectral asymptotics for the whole family of periodic operators are calculated. It is proven that the first several terms in the asymptotics determine the class of equivalent operators uniquely. It is proven that the spectrum of the operators with anomalous spectral asymptotics (when the ratio between the lengths of the bands and gaps tends to zero at infinity) can be approximated by standard periodic “weighted” operators with step-wise density functions. It is shown that this sequence of periodic weighted operators converges in the norm resolvent sense to the formal (generalized) resolvent of the periodic “Schrödinger operator” with certain energy-dependent boundary conditions. The operator acting in an extended Hilbert space such that its resolvent restricted to L₂(R) coincides with the formal resolvent is constructed explicitly.     

一类具对流项的奇异扩散方程解的逼近性质

讨论了一类带对流项的奇异扩散方.程的Neumann边值问题,证明了整体解的存在唯一性;讨论了带对流项非线性间题解的线性逼近,得到了逼近的显式表示式;同时还对││u-(u)││L2(0,1)进行了估计,得到了解关于时间t充分大时的渐近性态,其中(u)＝∫o/1udx.     

Dynamics of an integrable Kadomtsev–Petviashvili-based system

Kadomtsev–Petviashvili (KP)-type equations are seen in fluid mechanics, plasma physics, and gas dynamics. Hereby we consider an integrable KP-based system. With the Hirota method, symbolic computation and truncated Painlevé expansion, we obtain bright one- and two-soliton solutions. Figures are plotted to help us understand the dynamics of regular and resonant interactions, and we find that the regular interaction of solitons is completely elastic. Based on the asymptotic and graphical behavior of the two-soliton solutions, we analyze two kinds of resonance between the solitons, both of which are non-completely elastic. A triple structure, a periodic resonant structure in the procedure of interactions and a high wave hump in the vicinity of the crossing point, can be observed. Through the linear stability analysis, instability condition for the soliton solutions can be given, which might be useful, e.g., for the ship traffic on the surface of water.     

Cluster Algorithms for Spatial Point Processes with Symmetric and Shift Invariant Interactions

Abstract

In this article, Swendsen–Wang–Wolff algorithms are extended to simulate spatial point processes with symmetric and stationary interactions. Convergence of these algorithms is considered. Some further generalizations of the algorithms are discussed. The ideas presented in this article can also be useful in handling some large and complicated systems.     

Singular perturbation problems for time-reversible systems

In this paper singularly perturbed reversible vector fields defined in without normal hyperbolicity conditions are discussed. The main results give conditions for the existence of infinitely many periodic orbits and heteroclinic cycles converging to singular orbits with respect to the Hausdorff distance.

     

A CLASS OF SINGULAR PERTURBATIONS FOR SECOND ORDER QUASI－LINEAR BOUNDARY VALUE PROBLEMS ON INFINITE INTERVAL

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Singular quasilinear elliptic systems involving gradient terms

In this paper we establish the existence of at least one smooth positive solution for a singular quasilinear elliptic system involving gradient terms. The approach combines the sub-supersolutions method and Schauder’s fixed point theorem.