The fundamental solution on manifolds with time-dependent metrics

In this article we prove the existence of a fundamental solution for the linear parabolic operator L(u) = (Δ − ∂/∂t − h)u, on a compact n-dimensional manifold M with a time-parameterized family of smooth Riemannian metrics g(t). Δ is the time-dependent Laplacian based on g(t), and h(x, t) is smooth. Uniqueness, positivity, the adjoint property, and the semigroup property hold. We further derive a Harnack inequality for positive solutions of L(u) = 0 on (M, g(t) on a time interval depending on curvature bounds and the dimension of M, and in the special case of Ricci flow, use it to find lower bounds on the fundamental solution of the heat operator in terms of geometric data and an explicit Euclidean type heat kernel.     

各项异性椭圆方程基本解的存在性

证明了右端可测的各项异性椭圆方程基本解的存在性,其中应用了各项异性Sobolev空间和Lebesgue空间.首先得到近似方程的解,然后通过对这些解的子列取极限,得到原方程的解.关键是要有一个近似函数空间以及近似方程的先验估计.最后运用Vitali定理证明了原方程基本解的存在性,推广和改进了已有方程.     

Rellich type inequalities related to Grushin type operator and Greiner type operator

We prove some sharp Hardy inequality associated with the gradient ? _?? = (? _x ,|x| ^?? ? _y ) by a direct and simple approach. Moreover, similar method is applied to obtain some weighted sharp Rellich inequality related to the Grushin operator in the setting of L ^p . We also get some weighted Hardy and Rellich type inequalities related to a class of Greiner type operators.     

Towards the Keldysh Tauberian Theorem

New versions of the Tauberian theorem of Keldysh are proved. We give examples to show the sharpness of the conditions of these theorems. Among auxiliary results, new cases of inversion of the de l'Hospital rule are obtained. Bibliography: 14 titles. __________ Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 315, 2004, pp. 63–89.     

On the approximate solution of operator equations

Numerische Mathematik - Prolongations and restrictions are used to derive error estimates when linear operator equations of the second kind are solved by discretisation methods.     

The Fefferman-Stein type inequality for the Kakeya maximal operator

Let , , be the Kakeya maximal operator defined as the supremum of averages over tubes of the eccentricity . We shall prove the so-called Fefferman-Stein type inequality for ,

in the range , , with some constants and independent of and the weight .

     

The evolution operator solution of the Cauchy problem for the Hamilton-Jacobi equation

The theory of nonlinear evolution equations in a Banach space is used to prove the existence of global weak solutions of the Cauchy problem for the general time and space-dependent Hamilton-Jacobi equation.     

Fundamental solution of a higher step Grushin type operator

We examine a class of Grushin type operators _Pk$P_k$ where k∈_N0$k\in {\mathbb{N}}_0$ defined in (1.1). The operators _Pk$P_k$ are non-elliptic and degenerate on a sub-manifold of R^N+?${\mathbb{R}}^{N+?}$. Geometrically they arise via a submersion from a sub-Laplace operator on a nilpotent Lie group of step k+1$k+1$. We explain the geometric framework and prove some analytic properties such as essential self-adjointness. The main purpose of the paper is to give an explicit expression of the fundamental solution of _Pk$P_k$. Our methods rely on an appropriate change of coordinates and involve the theory of Bessel and modified Bessel functions together with Weber's second exponential integral.     

On approximate solution for operator equations of Hammerstein type

The aim of this paper is to investigate a method of approximating a solution of the operator equation of Hammerstein type x + KF(x) = f by solutions of similar finite-dimensional problems which contain operators better than K and F. Conditions of convergence and convergence rate are given and an iteration method to solve the approximative equation is proposed and applied to a concrete example.     

The fundamental solution of the space-time fractional advection-dispersion equation

A space-time fractional advection-dispersion equation (ADE) is a generalization of the classical ADE in which the first-order time derivative is replaced with Caputo derivative of order α ∈ (0, 1], and the second-order space derivative is replaced with a Riesz-Feller derivative of order β ∈ (0, 2]. We derive the solution of its Cauchy problem in terms of the Green functions and the representations of the Green function by applying its Fourier-Laplace transforms. The Green function also can be interpreted as a spatial probability density function (pdf) evolving in time. We do the same on another kind of space-time fractional advection-dispersion equation whose space and time derivatives both replacing with Caputo derivatives.     

Explicit solution of the operator equation

In this paper we find the explicit solution of the equation

A^*X+X^*A=B