Long-Time Behaviour of Heat Flow: Global Estimates and Exact Asymptotics

We obtain global upper and lower bounds on the heat kernel of an elliptic second-order differential operator, which become sharp in certain long-time and large-space asymptotics. We prove a generalization of Aronson's Gaussian bounds which identifies correctly an effective drift for heat flow. In the case of periodic coefficients we give variational characterizations of the effective conductivity, which is then made to appear in heat kernel bounds. These results are for heat kernels with measurable coefficients. For differentiable coefficients we prove tighter estimates, in which the rate of homogenization is known to be optimal. (Accepted May 20, 1996)     

Sharp Interface Limits for Non-Local Anisotropic Interactions

We prove a convexity property of the surface tension corresponding to a non-local, anisotropic free-energy functional of van der Waals type which implies that the Wulff shape is strictly convex and smooth. We also prove that the transport coefficients of the limiting anisotropic motion by mean curvature obtained in [33] are strictly positive and equal to the stiffness parameters determined by the surface tension.     

Convergence Results for Forchheimer’s Equations for Fluid Flow in Porous Media

The Forchheimer equations for non-slow flow in a saturated porous medium are studied. We prove the convergence results for both the first and the second Forchheimer coefficients.     

Some results on homogenization of convection-diffusion equations

We consider some models of degenerate convection-diffusion equations with oscillating coefficients. We prove that the homogenization process produces non-local and memory effects when the diffusion is longitudinal. When the diffusion is transverse we obtain a stability result. We also examine parametrized families of diffusion equations involving non-local terms.     

Renormalized Solutions to the Vlasov Equation with Coefficients of Bounded Variation

We prove that weak bounded solutions to the Vlasov equation with BV coefficients have the renormalization property, and we show that when the renormalization property holds for a general transport equation, it also holds for only Lipschitz nonlinearities. Accepted December 1, 2000?Published online March 7, 2001     

Structure of Solutions of Multidimensional Conservation Laws with Discontinuous Flux and Applications to Uniqueness

We investigate the structure of solutions of conservation laws with discontinuous flux under quite general assumption on the flux. We show that any entropy solution admits traces on the discontinuity set of the coefficients and we use this to prove the validity of a generalized Kato inequality for any pair of solutions. Applications to uniqueness of solutions are then given.     

Exponential decay in a thermoelastic mixture of solids

In this paper, we investigate the asymptotic behaviour of solutions to the initial boundary value problem for a one-dimensional mixture of thermoelastic solids. Our main result is to establish a necessary and sufficient condition over the coefficients of the system to get the exponential stability of the corresponding semigroup. We also prove the impossibility of time localization of solutions.     

Torsion of an elastic rod whose cross-section is a parallelogram,trapezoid, or triangle,or has an arbitrary shape by the method of transformation to a rectangular domain

A coordinate transformation is used to take the domain of the rod cross-section to a rectangular domain for which the spectra of eigenfunctions and eigenvalues are known. The torsion function is represented as a generalized Fourier series to reduce the problem to solving a closed linear system of algebraic equations for the expansion coefficients. It is shown that these Fourier series converge absolutely, because the expansion coefficients decrease by a cubic law depending on the term number. We prove that the approximate solution in the form of a finite sum of the Fourier series converges to the exact solution. This theorem is generalized to the case of a rod cross-section of arbitrary shape.     

Well-Posedness of the Ericksen–Leslie System

We prove the local well-posedness of the Ericksen–Leslie system, and the global well-posedness for small initial data under a physical constraint condition on the Leslie coefficients, which ensures that the energy of the system is dissipated. Instead of the Ginzburg–Landau approximation, we construct an approximate system with the dissipated energy based on a new formulation of the system.     

Exponential Dichotomy and Mild Solutions of Nonautonomous Equations in Banach Spaces

We prove that the exponential dichotomy of a strongly continuous evolution family on a Banach space is equivalent to the existence and uniqueness of continuous bounded mild solutions of the corresponding inhomogeneous equation. This result addresses nonautonomous abstract Cauchy problems with unbounded coefficients. The technique used involves evolution semigroups. Some applications are given to evolution families on scales of Banach spaces arising in center manifolds theory.     

Calculation of Transport‐Equation Eigenvalues

The eigenvalue problem for the transport equation with variable coefficients in an arbitrary domain with a smooth boundary is considered. A saturationfree numerical algorithm is constructed. Examples of numerical calculations are given, which prove the effectiveness of the proposed procedure.     

Factorization of Transport Coefficients in Macroporous Media

We prove the fundamental theorem about factorization of the phenomenological coefficients for transport in macroporous media. By factorization we mean the representation of the transport coefficients as products of geometric parameters of the porous medium and the parameters characteristic of the multicomponent fluid saturating the porous space. The two permeabilities of the porous medium, the convective and the diffusional ones, are separated. A similarity between the diffusional permeability and the porosity–tortuosity factor of the Kozeny–Carman theory is demonstrated. We do not make any specific assumption about stochastic or deterministic structure of the porous medium. The fluxes in fluid on the pore level are described by general relations of the non-equilibrium thermodynamics.     

Heat transfer coefficients during quenching of steels

Heat transfer coefficients for quenching in water have been measured as a function of temperature using steel probes for a variety of iron alloys. The coefficients were derived from measured cooling curves combined with calculated heat-capacities. The resulting data were then used to calculate cooling curves using the finite volume method for a large steel sample and these curves have been demonstrated to be consistent with measured values for the large sample. Furthermore, by combining the estimated cooling curves with time-temperature-transformation (TTT) diagrams it has been possible to predict the variation of hardness as a function of distance via the quench factor analysis. The work should prove useful in the heat treatment of the steels studied, some of which are in the development stage.     

Analyticity of Homogenized Coefficients Under Bernoulli Perturbations and the Clausius–Mossotti Formulas

This paper is concerned with the behavior of the homogenized coefficients associated with some random stationary ergodic medium under a Bernoulli perturbation. Introducing a new family of energy estimates that combine probability and physical spaces, we prove the analyticity of the perturbed homogenized coefficients with respect to the Bernoulli parameter. Our approach holds under the minimal assumptions of stationarity and ergodicity, both in the scalar and vector cases, and gives analytical formulas for each derivative that essentially coincide with the so-called cluster expansion used by physicists. In particular, the first term yields the celebrated (electric and elastic) Clausius–Mossotti formulas for isotropic spherical random inclusions in an isotropic reference medium. This work constitutes the first general proof of these formulas in the case of random inclusions.     

The effect of a dipolar structure on the Hölder stability in Green–Naghdi thermoelasticity

This study is concerned with the mixed initial boundary value problem for a dipolar body in the context of the thermoelastic theory proposed by Green and Naghdi. For the solutions of this problem we prove a result of Hölder’s-type stability on the supply terms. We impose middle restrictions on the thermoelastic coefficients, which are common in continuum mechanics. For the same conditions we propose a continuous dependence result with regard to the initial data.     

Multipoint problem for higher-order parabolic equations in a parallelepiped

We study the well-posedness of a problem for a Petrovskii-parabolic equation with coefficients depending on the space coordinates and with multipoint conditions with respect to the time variable. We establish conditions for the existence and uniqueness of the classical solution of the problem. For the proof of the existence of a solution of the problem, the method of divided differences is used. We prove a metric-type theorem on lower bounds for the small denominators that appear in the construction of the solution.     

Elastic perfectly plastic structures with temperature dependent elastic coefficients

We study the evolution of elastic perfectly plastic structures where the elastic coefficients depend on temperature, as they are subjected to classical loading and given variation of the temperature field. We prove variational theorems for the instantaneous fields of velocities and stress rates, and establish the generalized differential equation for the evolution of the stress field. To cite this article: B. Halphen, C. R. Mecanique 333 (2005).     

加速度计的全组合标定方法

阐述了在重力场上用全组合法标定单加速度计的方法,并且推导了加速度计全组合标定法测试原理。这种方法剔出了测试设备的确定性角位置误差对加速度计误差模型系数标定精度的影响,提高了加速度计的标定精度。结合上述的理论分析,对某型号加速度计进行了实际测试和误差分析,实验结果证明本方法对于提高加速度计标定精度是非常有效的。     

Two-Phase Problems for Linear Elliptic Operators with Variable Coefficients: Lipschitz Free Boundaries are <Emphasis Type="Italic">C</Emphasis><Superscript><Emphasis Type="Italic">1,γ</Emphasis></Superscript>

We prove C ^1, regularity of Lipschitz free boundaries of two-phase problems for linear elliptic operators with Hölder continuous coefficients.     

On the <Emphasis Type="Italic">L</Emphasis><Subscript><Emphasis Type="Italic">p</Emphasis></Subscript>-Solvability of Higher Order Parabolic and Elliptic Systems with BMO Coefficients

We prove the solvability in Sobolev spaces for both divergence and non-divergence form higher order parabolic and elliptic systems in the whole space, on a half space, and on a bounded domain. The leading coefficients are assumed to be merely measurable only in the time variable and have small mean oscillations with respect to the spatial variables in small balls or cylinders. For the proof, we develop a set of new techniques to produce mean oscillation estimates for systems on a half space.