一类具有非线性阻尼的梁系统的整体吸引子

利用经典的算子半群理论,研究了一类具有非线性阻尼和非线性外力项的梁方程的初边值问题,证明了系统解的存在唯一性,然后引入一个算子半群;利用经典的算子半群分解方法,证明了系统存在整体吸引子.     

对边简支矩形薄板方程的算子半群方法

考虑弹性理论中对边简支矩形薄板方程,用算子半群方法求解问题.首先,将方程转换成抽象Cauchy问题.其次,构造空间框架并证明对应的算子矩阵生成压缩半群.最后,经Fourier变换,采用一致连续半群做逼近,进而给出对边简支矩形薄板方程的解析解.该方法自然蕴含着解的存在唯一性.     

广义分布半群与退化发展方程的分布解

在Banach空间中引进了由有界线性算子引导的广义分布半群的新概念,并讨论了它的有关性质.在我们的方法中,广义分布半群的生成元可以不是稠定的.此外,还引进了退化发展方程在Laplace变换意义下的分布解,应用广义分布半群给出了退化发展方程分布解的构造性表达式.     

板几何中一类具完全反射边界条件的奇异迁移算子的谱

在L1空间上研究了板几何中一类具完全反射边界条件下各向异性、连续能量、均匀介质的奇异迁移方程.证明了这类方程相应的奇异迁移算子产生C0半群和该半群的Dyson-Phillips展开式的二阶余项是弱紧的,从而得到了该迁移算子的谱在区域Γ中仅由至多有限个具有限代数重数的离散本征值组成等结果.     

带强阻尼的Kirchhoff型吊桥方程指数吸引子的存在性

利用算子半群分解技巧,本文研究Kirchhoff型吊桥方程长时间动力学行为.在较弱的非线性条件下,首先验证解半群在两个空间中的渐近紧性;其次运用算子分解技巧,得到带有强阻尼的Kirchhoff型吊桥方程指数吸引子的存在性.     

全正则子半群构成链的正则半群(英文)

本文考虑全正则子半群构成链的正则半群,得到了正则半群具有全正则子半群构成链的一个充分必要条件,这推广了Jones关于具有全正则子半群构成链的逆半群的结果.特别地,建立了具有全正则子半群构成链的完全0-单半群的结构.     

半线性抛物方程在L2p空间中全局吸引子的存在性

本文研究了半线性抛物方程所生成的半群{S（t）}t≥0的吸引子的存在性.利用文献[1]中证明吸引子正则性的思想,分别得到半群{S（t）}t≥0在L^2p（Ω）空间中具有一个有界吸收集和一个全局吸引子.     

一类双曲型方程的Hamilton算子半群方法

将一类双曲型方程混合问题转换成一阶抽象Cauchy问题,证明所得Hamilton算子矩阵H在相应空间中生成压缩半群,并借助Fourier变换,采用一致连续半群做逼近的方法,得到H所生成的压缩半群,进而给出了问题的古典解.     

Euler-Bernoulli梁方程基于边界分数阶导数反馈控制的镇定

研究具有边界控制的Euler-Bernoulli梁方程基于边界分数阶导数反馈控制的镇定问题.首先,给出开环系统在Salamon意义下的适定性;其次,运用半群方法和LaSalle不变原理,证明了闭环系统生成C_0-半群并且闭环系统是渐近稳定的;最后,设计了一个未知输入类型的状态观测器,其观测器状态渐近收敛于原系统的状态.     

积分双半群与抽象动力方程的可解性

本文从一类抽象积分微分方程的可解性，引人积分双半群的概念，并讨论了积分双半群的一些性质．利用积分双半群，说明了一类抽象动力方程的可解性，特别是抽象动力方程边值问题的可解性．     

Determination of Lagrangians from Equations of Motion and Commutator Brackets

The question as to whether a given set of equations, which govern the dynamical evolution of a system, determine a Lagrangian is considered. This problem, which has come to be known as the inverse problem of the calculus of variations, is reviewed and theorems which contain systems of partial differential equations which determine a type of self-adjointness are developed. It is shown that, given a reasonable form for the classical correspondence, the usual quantum commutator brackets can be expressed in terms of classical quantities which satisfy a particular form of these equations.     

Almost diagonal systems of linear difference equations

Linear homogeneous difference systems of equations on an infinite interval are considered. Conditions are given which allow to represent a fundamental solution as a product of two square matrices. The product is made of a diagonal matrix and a matrix which is a perturbation of the identity. The diagonal matrix being on the left in the proposed product rather than on the right as it has been traditionally represented. A self contained theorem of asymptotic approximation is provided which is applied to a special family of difference systems. A theorem, utilizing a linear transformation, which is best possible in a certain sense, is also given.     

Cycles of covers

We initially consider an example of Flynn and Redmond, which gives an infinite family of curves to which Chabauty’s Theorem is not applicable, and which even resist solution by one application of a certain bielliptic covering technique. In this article, we shall consider a general context, of which this family is a special case, and in this general situation we shall prove that repeated application of bielliptic covers always results in a sequence of genus 2 curves which cycle after a finite number of repetitions. We shall also give an example which is resistant to repeated applications of the technique.     

Cycles of covers

We initially consider an example of Flynn and Redmond, which gives an infinite family of curves to which Chabauty’s Theorem is not applicable, and which even resist solution by one application of a certain bielliptic covering technique. In this article, we shall consider a general context, of which this family is a special case, and in this general situation we shall prove that repeated application of bielliptic covers always results in a sequence of genus 2 curves which cycle after a finite number of repetitions. We shall also give an example which is resistant to repeated applications of the technique. E. V. Flynn thanks the International Center for Transdisciplinary Studies at Jacobs University Bremen for its hospitality during July 2007, and thanks EPSRC for support: grant number EP/F060661/1.     

On the optimal control of the growth of a forest in a special case

In Ref. 1, the author considered the following large-scale forest management problem. There is a system consisting of several factories which all use, as raw material, wood obtained from a large forest region. This forest is divided into a large number of subforests, each of which is felled after it has reached a given age, after which a new forest is immediately planted. The instants in time at which each subforest is felled are assumed to form a stationary point process. In Ref. 1, it was demonstrated how the parameters of the system must be chosen in order to achieve a flow of raw material such that the probability that a shortage will occur is less than a preset value. In the present paper, we consider the problem of maximizing the yield of a single subforest.     

一类非线性染病年龄结构模型渐近性态

研究一类具有非线性染病年龄结构SIS流行病传播数学模型动力学性态,得到疾病绝灭和持续生存的阈值--基本再生数.当基本再生数小于或等于1时,仅存在无病平衡点,且在其小于1的情况下,无病平衡点全局渐近稳定,疾病将逐渐消除;当基本再生数大于1时,存在不稳定的无病平衡点和唯一的局部渐近稳定的地方病平衡点,疾病将持续存在.     

Control of mechanical systems with uncertain parameters by means of small forces

An approach to the construction of a feedback control for non-linear Lagrange mechanical systems with uncertain parameters is developed. A Lagrange mechanical system with uncertain parameters, which is subject to the action of potential forces, control forces and unknown perturbations is considered is considered. It is assumed that the potential forces can be considerably greater than the control forces which, in their turn, are greater than the perturbations. An approach to the construction of a control, is proposed which enables one to bring a system from an arbitrary initial state to a specified final state in a finite time using a bounded control. A procedure, in which the specified nominal trajectory of the motion is tracked, is used. Initially, the trajectory, joining the specified initial and final states of the system, is constructed for a certain dynamical system which is close to the initial system but with completely known parameters. Then, using deviation equations, a control is constructed which brings the initial system onto this nominal trajectory in a finite time and subsequently forces the system to move along this nominal trajectory up to the final state. The control law used in tracking the nominal trajectory is based on a linear feedback, the gains of which depends on the discrepancy between the real trajectory and the nominal trajectory. The gain increase and tend to infinity as the discrepancies tend to zero but the control forces remain bounded and satisfy the conditions imposed on them. The results of numerical modelling of the controlled motions of a plane double pendulum are presented as an illustration.     

Expansion of a wedge of non-ideal gas into vacuum

We study the problem of expansion of a wedge of non-ideal gas into vacuum in a two-dimensional bounded domain. The non-ideal gas is characterized by a van der Waals type equation of state. The problem is modeled by standard Euler equations of compressible flow, which are simplified by a transformation to similarity variables and then to hodograph transformation to arrive at a second order quasilinear partial differential equation in phase space; this, using Riemann variants, can be expressed as a non-homogeneous linearly degenerate system provided that the flow is supersonic. For the solution of the governing system, we study the interaction of two-dimensional planar rarefaction waves, which is a two-dimensional Riemann problem with piecewise constant data in the self-similar plane. The real gas effects, which significantly influence the flow regions and boundaries and which do not show-up in the ideal gas model, are elucidated; this aspect of the problem has not been considered until now.     

Uniform Convergence of Spectral Expansions in the Terms of Root Functions of a Spectral Problem for the Equation of a Vibrating Beam

In this paper we consider a spectral problem which describes bending vibrations of a homogeneous rod, in cross-sections of which the longitudinal force acts, the left end of which is fixed rigidly and on the right end is concentrated an elastically fixed load. We study the uniform convergence of spectral expansions in terms of root functions of this problem.     

A contribution to the statistical theory of linear graduation

Moving (weighted) average techniques provide a flexible tool for the graduation (smoothing) of vital rates. As is shown in the present paper, one may construct linear graduation methods which are superior with respect to some formal evaluation criteria, but such ‘improved’ methods lack an important robustness property which the moving average graduation techniques possess and which is a main motivation for their use.A linear graduation technique is an estimation method, and an important consideration in the evaluation of its properties is the class for which it is unbiased, i.e., the class of functions which it reproduces unchanged. A classical test usually said to be a chi-square test of the goodness-of-fit of a graduation is revealed to be a test of the hypothesis that the graduation method is indeed unbiased for the set of theoretical rates actually estimated, and its properties are investigated along with those of alternative chi-square tests.