On delay-dependent stability for a class of nonlinear stochastic delay-differential equations

Global asymptotic stability conditions for nonlinear stochastic systems with state delay are obtained based on the convergence theorem for semimartingale inequalities, without assuming the Lipschitz conditions for nonlinear drift functions. The Lyapunov–Krasovskii and degenerate functionals techniques are used. The derived stability conditions are directly expressed in terms of the system coefficients. Nontrivial examples of nonlinear systems satisfying the obtained stability conditions are given.     

估计时变幅值复线性调频信号的循环平稳方法及其统计性能分析

本文分析了利用循环平稳方法估计离散时间变幅值复线性调频（ＬＦＭ）信号参数的渐近统计性能，表明所得的时变幅值ＬＦＭ信号参数估计的均方差与相应的Ｃｒａｍｅｒ－Ｒａｏ界关于Ｔ的收敛性具有相同的数量级。模拟结果验证了所得结果的正确性。     

Reliability analysis—a review and some perspectives

Theory and methods of structural reliability are briefly summarized and reviewed, both in original and standard space. Some extreme examples demonstrate where and why these methods do not work. Importance sampling schemes for updating approximate probability estimates are described. Algorithmic problems are addressed. Some new fields of potential application are outlined. Most urgent is the development of suitable optimization procedures for structures. Finally, the question of acceptability is discussed and a concept for assessing acceptability limits is described.     

电磁场分析中大型稀疏对称线性方程组的一种改进解法

针对电磁场分析中的大型稀疏对称线性方程组 ,提出一种新的改进ICCG法 (不完全乔列斯基分解的共轭梯度法 )。此方法是通过引进一个控制参数来减少不完全乔列斯基分解的元素的个数 ,从而减少不完全分解和共轭梯度法每一迭代步的计算时间 ;通过理论分析 ,适当选取控制参数不仅不影响收敛速度 ,有时还会加快收敛。数值例子表明 ,该方法可比常规ICCG法(或PCBCG ,即预处理复双共轭梯度法 )减少 30 %～ 50 %的计算时间。     

Asymptotic stabilization via control by interconnection of port-Hamiltonian systems

We study the asymptotic properties of control by interconnection, a passivity-based controller design methodology for stabilization of port-Hamiltonian systems. It is well-known that the method, in its basic form, imposes some unnatural controller initialization to yield asymptotic stability of the desired equilibrium. We propose two different ways to overcome this restriction, one based on adaptation ideas, and the other one adding an extra damping injection to the controller. The analysis and design principles are illustrated through an academic example.     

Large sample properties of spectral estimators for a class of stationary nonlinear processes

Abstract. We consider the standard spectral estimators based on a sample from a class of strictly stationary nonlinear processes which include, in particular, the bilinear and Volterra processes. It is shown that these estimators, under certain mild regularity conditions are both consistent and asymptotically normal.     

Plane-strain propagation of a fluid-driven fracture during injection and shut-in: Asymptotics of large toughness

This paper considers the problem of plane-strain fluid-driven fracture propagating in an impermeable elastic medium under condition of large toughness or, equivalently, of low fracturing fluid viscosity. We construct an explicit solution for a fracture propagating in the toughness-dominated regime when the energy dissipated in the viscous fluid flow inside the fracture is negligibly small compared to the energy expended in fracturing the solid medium. The next order corrections in viscosity to this limiting solution are then derived, allowing the range of problem parameters corresponding to the toughness-dominated regime to be established. The first-order small viscosity (large toughness) solution is shown to provide an excellent approximation of the solution for the crack length in the wide range of the viscosity parameter. Furthermore, this solution, when combined with the first-order small-toughness solution of Garagash and Detournay [Journal of Applied Mechanics, 2005], provides a simple analytical approximation of the crack length solution in practically the entire range of viscosity (toughness). It is also shown that the established method of asymptotic expansion in small parameter is equally applicable to study other small effects (e.g., fluid inertia) on the otherwise toughness-dominated solution. A solution for the fracture evolution during shut-in (i.e., after fluid injection rate is suddenly stopped) is also obtained. This solution, which corresponds to a slowing fracture evolving towards the toughness-dominated steady state, draws attention to the possibility of substantial fracture growth after fluid injection is ceased especially under conditions when the fracture propagation during injection phase is dominated by viscous dissipation.     

Coating flows of non-Newtonian fluids: weakly and strongly elastic limits

This paper presents an asymptotic analysis of the thickness of the liquid film that coats a smooth solid substrate when it is withdrawn from a bath of non-Newtonian fluid, and compares the results with experimental measurements. The film thickness is, to a good approximation, uniform above the point where the film is withdrawn from the fluid bath, and depends on the rotation rate, the fluid properties and the substrate geometry. Theoretical predictions of the film thickness for a number of different substrate geometries (an inclined plate, roller and fiber) are presented, and are compared with experimental measurements in a single roller geometry. Results are obtained for two different limits of the Criminale–Ericksen–Filbey constitutive equation in which the fluid rheology is either weakly elastic and dominated by shear thinning, or strongly elastic and dominated by elastic stresses. A lubrication analysis yields a thin-film equation which characterizes the film thickness as a function of spatial position. The rheological properties of the test fluids are measured independently using steady and oscillatory shearing deformations. The viscometric parameters are then used, in conjunction with the governing thin-film equation, which is solved using matched asymptotics, to give a quantitative prediction of the thickness of the fluid coating. The onset of an instability which causes the film thickness to vary with axial position along the roller is also observed experimentally.     

Lyapunov stability analysis for nonlinear delay systems

Sufficient conditions ensuring that a nonlinear system with disturbances having a delay is globally asymptotically stable independent of delay are given. The proof carried out relies extensively on a characterization of the stability property in terms of Lyapunov function. The result is applied to some biological systems and neural networks. A stabilizing memoryless controller for a second-order system with state-delay is also proposed.     

The derivation and application of a semi-infinite flat and rounded asymptotic frictionless contact

The solution is found for the contact pressure distribution between a semi-infinite flat and rounded, frictionless, elastic punch pressed onto an elastically similar half-plane. This is used to obtain an asymptotic form of wide-ranging applicability, for finding the near-edge contact pressure in a contact which is nearly complete in character, and this is illustrated by example.