Theta Characteristics in Trigonal Curves

Some spaces of trigonal curves having a theta characteristic with many sections are described.     

Inverse spectral problems for Sturm-Liouville operators with singular potentials. Part III: Reconstruction by three spectra

We solve the inverse spectral problem of recovering the singular potential from W⁻¹₂(0,1) of a Sturm-Liouville operator by its spectra on the three intervals [0,1], [0,a], and [a,1] for some a∈(0,1). Necessary and sufficient conditions on the spectral data are derived, and uniqueness of the solution is analyzed.     

Inverse Spectral Problems in Rectangular Domains

We consider the Schrödinger operator ? Δ + q in domains of the form R = {x ∈ ? ⁿ : 0 ≤ x _i  ≤ a _i , i = 1,…, n} with either Dirichlet or Neumann boundary conditions on the faces of R, and study the constraints on q imposed by fixing the spectrum of ? Δ + q with these boundary conditions. We work in the space of potentials, q, which become real-analytic on ? ⁿ when they are extended evenly across the coordinate planes and then periodically. Our results have the corollary that there are no continuous isospectral deformations for these operators within that class of potentials. This work is based on new formulas for the trace of the wave group in this setting. In addition to the inverse spectral results these formulas lead to asymptotic expansions for the traces of the wave and heat kernels on rectangular domains.     

Spectral Theory for Slowly Oscillating Potentials II. Schrödinger Operators

This paper continues the investigation about the singularity theory in dual rich quasi–Banach spaces given in T. Runst [Ru 2]. The abstract results are applied to the study of the solution structure of semilinear elliptic boundary value problems in spaces of Besov – Triebel – Lizorkin type.     

边界条件含特征参数的奇异不连续Sturm-Liouville算子的渐近特征

研究有限区间内一类边界条件含特征参数的不连续奇异Sturm-Liouville问题.利用函数论和算子理论的方法,证明该问题的自伴性,得到其特征值的相关性质,基本解及其特征值的渐近公式.     

Elliptic Equations with Multi-Singular Inverse-Square Potentials and Critical Nonlinearity

ABSTRACT

This article deals with a class of nonlinear elliptic equations involving a critical power-nonlinearity as well as a potential featuring multiple inverse square singularities. We show that existence of solutions heavily depends on the strength and the location of the singularities. We associate to the problem the corresponding Rayleigh quotient and give both sufficient and necessary conditions on masses and location of singularities for the minimum to be achieved. Both the cases of whole ? ^N and bounded domains are taken into account.     

Construction of Equilibrium Magnetic Vector Potentials

In [9] we introduced the notion of equilibrium surface current JdS_x on the closed C smooth surfaces in R ³ as a generalization of electric solenoid, and proved their existence. We here show an algorithm for JdS_x starting from a given surface current J dS_x on .     

N维向量Sturm-Liouville算子的正则迹及其在反谱问题中的应用

研究了赋予一般分离型边界条件的N维向量Sturm-Liouville方程的特征值问题,获得了该系统的一个正则迹公式.迹公式不仅形式美观,而且它在反谱理论中具有重要的作用.     

Riesz Spherical Potentials with External Fields and Minimal Energy Points Separation

In this paper we consider the minimal energy problem on the sphere S ^d for Riesz potentials with external fields. Fundamental existence, uniqueness, and characterization results are derived about the associated equilibrium measure. The discrete problem and the corresponding weighted Fekete points are investigated. As an application we obtain the separation of the minimal s-energy points for d – 2 < s < d. The explicit form of the separation constant is new even for the classical case of s = d – 1. Research supported, in part, by a National Science Foundation Research grant DMS 0532154.     

Wannier Functions for Quasiperiodic Finite-Gap Potentials

We consider Wannier functions of quasiperiodic g-gap (g ≥ 1) potentials and investigate their main properties. In particular, we discuss the problem of averaging that underlies the definition of the Wannier functions for both periodic and quasiperiodic potentials and express Bloch functions and quasimomenta in terms of hyperelliptic σ-functions. Using this approach, we derive a power series for the Wannier function for quasiperiodic potentials valid for |x| ≃ 0 and an asymptotic expansion valid at large distances. These functions are important in a number of applied problems. __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 144, No. 2, pp. 234–256, August, 2005.     

一个特征值问题的迹公式

本文利用逼近理论的方法,分别提出了一个特征值问题在周期条件下以及在无穷衰减条件下的迹公式。     

On Two-Dimensional Finite-Gap Potential Schroedinger and Dirac Operators with Singular Spectral Curves

We describe a wide class of two-dimensional potential Schroedinger and Dirac operators which are finite-gap at the zero energy level and whose spectral curves at this level are singular, in particular may have n-multiple points with n3.     

Perturbation of Harmonic Spaces by Differences of Bounded Potentials

This paper is devoted to a study of perturbation of harmonic (Bauer) spaces by local differences of bounded potentials. In particular, for a local difference M of bounded potentials that are locally less then 1 or that are countable sum of continuous potentials it turns out that the perturbed space is again a Bauer space if and only if M is continuous (i.e., the difference is continuous, but not necessarily each potential.     

Inversion of Bessel Potentials with the Aid of Weighted Wavelet Transforms

A special type of weighted wavelet transforms is introduced and the relevant Calderón reproducing formula for functions f ∈ L^p(ℝⁿ ) is proved. By making use of these wavelet‐type transforms a new inversion formula of the classical Bessel potentials is obtained.     

On the Convergence of Backward Differentiation Formulas for Stiff Initial Value Problems

The influence of a time-dependent transformation to a numerical method is studied. Thus convergence results of backward differentiation formulas applied to the non-autonomous stiff system y = A(t)y + (t) are given. The approach is based on a special decomposition of the companion matrix.This revised version was published online in October 2005 with corrections to the Cover Date.     

Inverse problems for the Sturm-Liouville equation with the discontinuous coefficient

In this study we derive the Gelfand-Levitan-Marchenko type main integral equation of the inverse problem for the boundary value problem $L$ and prove the uniquely solvability of the main integral equation. Further, we give the solution of the inverse problem by the spectral data and by two spectrum.     

An Inverse Problem for the Matrix Schrödinger Equation

By modifying and generalizing some old techniques of N. Levinson, a uniqueness theorem is established for an inverse problem related to periodic and Sturm-Liouville boundary value problems for the matrix Schrödinger equation.     

Wolff's Inequality for Radially Nonincreasing Kernels and Applications to Trace Inequalities

We extend Th. Wolff's inequality to a general class of radially decreasing convolution kernels. As an application we obtain characterizations of nonnegative Borel measures on R ⁿ such that the trace inequality holds for every f in L ^p (dx).     

Inversion of Trace Formulas for a Sturm-Liouville Operator

This paper revisits the classical problem “Can we hear the density of a string?”, which can be formulated as an inverse spectral problem for a Sturm-Liouville operator. Instead of inverting the map from density to spectral data directly, we propose a novel method to reconstruct the density based on inverting a sequence of trace formulas which bridge the density and its spectral data clearly in terms of a series of nonlinear integral equations. Numerical experiments are presented to verify the validity and effectiveness of the proposed numerical algorithm. The impact of different parameters involved in the algorithm is also discussed.