Rellich type identities for eigenvalue problems and application to the Pompeiu problem

For classical Neumann eigenvalue, buckling eigenvalue and clamped plate eigenvalue, we give the corresponding Rellich type identities. As an application of these results, then, we obtain a new necessary and sufficient condition for a domain without the Pompeiu property.     

A Wiener-Tauberian and a Pompeiu type theorems on the Laguerre hypergroup

A Wiener-Tauberian theorem is proven on the Laguerre hypergroup [M.M. Nessibi, K. Trimèche, Inversion of the Radon transform on the Laguerre hypergroup by using generalized wavelets, J. Math. Anal. Appl. 208 (1997) 337-363]. As consequence of this theorem we establish a Pompeiu type-theorem and we study some of its applications.     

Fourier transform, null variety, and Laplacian's eigenvalues

We consider a quantity κ(Ω)—the distance to the origin from the null variety of the Fourier transform of the characteristic function of Ω. We conjecture, firstly, that κ(Ω) is maximised, among all convex balanced domains Ω⊂Rd of a fixed volume, by a ball, and also that κ(Ω) is bounded above by the square root of the second Dirichlet eigenvalue of Ω. We prove some weaker versions of these conjectures in dimension two, as well as their validity for domains asymptotically close to a disk, and also discuss further links between κ(Ω) and the eigenvalues of the Laplacians.     

The Generalized Pompeiu Metric in the Isometry Problem for Hyperspaces

The isometries of the hyperspace of a compact subset of the real line endowed with the generalized Pompeiu metric are considered. It is proved that any such an isometry is generated by an isometry of the base space.__________Translated from Matematicheskie Zametki, vol. 78, no. 2, 2005, pp. 163–170.Original Russian Text Copyright © 2005 by V. V. Aseev, A. V. Tetenov, A. P. Maksimova.     

Boundary regularity for a family of overdetermined problems for the Helmholtz equation

If a nonconstant solution u of the Helmholtz equation exists on a bounded domain with u satisfying overdetermined boundary conditions (u and its normal derivative both required to be constant on the boundary), then under certain assumptions the boundary of the domain is proved to be real-analytic. Under weaker assumptions, if a real-analytic portion of the boundary has a real-analytic extension, then that extension must also be part of the boundary. Also, an explicit formula for u is given and a condition (which does not involve u) is given for a bounded domain to have such a solution u defined on it. Both of these last results involve acoustic single- and double-layer potentials.     

A new result on the problem of Zarankiewicz

Zarankiewicz (Colloq. Math.2 (1951), 301) raised the following problem: Determine the least positive integer z(m, n, j, k) such that each 0–1-matrix with m rows and n columns containing z(m, n, j, k) ones has a submatrix with j rows and k columns consisting entirely of ones. This paper improves a result of Hylten-Cavallius (Colloq. Math.6 (1958), 59–65) who proved: $\text{[}\text{k}\text{2}\text{]}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{?}\text{lim}{}_{\mathrm{n\to \infty }}\text{inf}\text{z(n, n, 2, k)n}{}^{\mathrm{<mtext>?</mtext><mtext>3</mtext><mtext>2</mtext>}}\text{?}\text{lim}{}_{\mathrm{n\to \infty }}\text{sup}\text{z(n, n, 2, k)n}{}^{\mathrm{<mtext>?</mtext><mtext>3</mtext><mtext>2</mtext>}}\text{? (k ? 1)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$. We prove that $\text{lim}{}_{\mathrm{n\to \infty }}\text{z(n, n, 2, k)n}{}^{\mathrm{<mtext>?</mtext><mtext>3</mtext><mtext>2</mtext>}}$ exists and is equal to $\text{(k ? 1)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$. For the special case where k = 2 resp. k = 3 this result was proved earlier by Kövari, Sos and Turan (Colloq. Math.3 (1954), 50–57) resp. Hylten-Cavallius.     

A partial solution of the Pompeiu problem

A nonempty bounded open subset D of ⁿ is said to have the Pompeiu property if and only if for every continuous complex-valued function f on ⁿ which does not vanish identically there is a rigid motion of ⁿ onto itself — taking D onto (D) — such that the integral of f over (D) is not zero. This article gives a partial solution of the Pompeiu problem, the problem of finding all sets D with the Pompeiu property.In the special case that D is the interior of a homeomorphic image of an(n–1)-dimensional sphere, the main result states that if D has a portion of an(n–1)-dimensional real analytic surface on its boundary, then either D has the Pompeiu property or any connected real analytic extension of the surface also lies on the boundary of D. Thus, for example, any such region D having a portion of a hyperplane as part of its boundary must have the Pompeiu property, since the entire hyperplane cannot lie in the boundary of the bounded set D.The research for this paper was done in part while on sabbatical at the Courant Institute of Mathematical Sciences, New York University.     

Extremal cases of the Pompeiu problem

The Pompeiu problem is studied for functions defined on a ballB ⁿ and having zero integrals over all sets congruent to a given compact setK B. The problem of finding the least radiusr=r(K) ofB for whichK is a Pompeiu set is considered. The solution is obtained for the cases in whichK is a cube or a hemisphere.Translated fromMatematicheskie Zametki, Vol. 59, No. 5, pp. 671–680, May, 1996.     

扇形域上高阶Schwarz边值问题

本文主要讨论一类角度为θ=π/α,α≥1/2的扇形域上高阶多解析方程的Schwarz边值问题.通过构造适当的高阶-Schwarz算子和Pompeiu算子,我们给出了详细的解表达式.本文把边值问题进一步推广到高阶情形,丰富了扇形域上边值问题的发展.     

A blow-up result in a Cauchy viscoelastic problem

In this work we consider a Cauchy problem for a nonlinear viscoelastic equation. Under suitable conditions on the initial data and the relaxation function, we prove a finite-time blow-up result.     

Additional results of Zalcman's Pompeiu problem

Summary In this article we continue our study of the following problem posed by Lawrence Zalcman in 1972. LetS be the closed unit square. For eachz in the interior,S ⁰, ofS letS(z) be the largest closed square inS with centroidz, and for each in the interval (0, 1] letS _(z) be the square homothetic toS(z) with linear ratio . Iff is a continuous function such that its integral overS _(z) vanishes for allz in S⁰, is f =0? We show that the answer is yes if 3/4 < 1.     

On the Pompeiu problem and its generalizations

Functions are investigated whose integrals over a given collection of sets are zero. Pompeiu sets are described in terms of the approximation of their indicators by linear combinations of the indicators of balls with special radii.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 45, No. 10, pp. 1444–1448, October, 1993.     

A higher dimensional fractional Borel‐Pompeiu formula and a related hypercomplex fractional operator calculus

In this paper, we develop a fractional integro‐differential operator calculus for Clifford algebra‐valued functions. To do that, we introduce fractional analogues of the Teodorescu and Cauchy‐Bitsadze operators, and we investigate some of their mapping properties. As a main result, we prove a fractional Borel‐Pompeiu formula based on a fractional Stokes formula. This tool in hand allows us to present a Hodge‐type decomposition for the fractional Dirac operator. Our results exhibit an amazing duality relation between left and right operators and between Caputo and Riemann‐Liouville fractional derivatives. We round off this paper by presenting a direct application to the resolution of boundary value problems related to Laplace operators of fractional order.     

A stability result concerning the obstacle problem for a plate

It is proposed here to study the free boundary of the obstacle problem in the case of an elastic plate. Under a nondegeneracy assumption, we prove a stability theorem which relates the variations of the contact zone to the variations the external forces. The statement of this result obtained and the steps in the proof are very close to those given by D.G. Schaeffer in 1975, except for the very important fact that the present study deals with the biharmonic operator.     

A new approach to Cagniard's problem

Cagniard problem refers to the class of linear reflection and transmission problem for pulsed line and point sources, which have solution methods leading to exact algebraic representations of the wave fields. All previous methods have relied heavily on integral or differential transforms. We present in this paper a new and direct approach to the problem which involves only the wave equation and its associated characteristic equation. We illustrate the new method by applying it to the problem of the reflection and transmission of acoustic waves radiating from a line source in the vicinity of a plane boundary separating two uniform acoustic media.     

A new upper bound for the bipartite Ramsey problem

We consider the following question: how large does n have to be to guarantee that in any two‐coloring of the edges of the complete graph K_n,n there is a monochromatic K_k,k? In the late 1970s, Irving showed that it was sufficient, for k large, that n ≥ 2^{k ? 1} (k ? 1) ? 1. Here we improve upon this bound, showing that it is sufficient to take where the log is taken to the base 2. © 2008 Wiley Periodicals, Inc. J Graph Theory 58: 351–356, 2008