On the existence of periodic solutions in the thermistor problem with degenerate thermal conductivity

Abstract This paper deals with the existence of weak periodic solutions for a parabolic-elliptic system proposed as a model for a time dependent thermistor with degenerate thermal conductivity. Applying the maximal monotone mappings theory, we prove an existence result for weak periodic solutions. Keywords: Nonlinear parabolic-elliptic system of degenerate type, Periodic solutions, Thermistor problem Mathematics Subject Classification (2000): 35B10, 35J60, 35K65     

A residual–based error estimator for BEM–discretizations of contact problems

Summary. We develop an a posteriori error estimate for boundary element solutions of static contact problems without friction. The presented result is based on an error estimate for linear pseudodifferential equations and on a certain commutator property for pseudodifferential operators. A heuristic extension of the obtained error estimate to frictional contact problems is presented, too. Numerical examples indicate a good performance of the error estimator for both the frictionless and the frictional problem. Mathematics Subject Classification (1991):35J85, 65N38, 73T05Dedicated to Hans Grabmüller on the occasion of his 60th birthday     

A direct uniqueness proof for equations involving the p-Laplace operator

 We provide a simple convexity argument for some known uniqueness theorems. Previous proofs were more technical and had to pay attention to the behaviour of solutions near the boundary. Received: 3 May 2002 Mathematics Subject Classification (2000): 35J20, 35J70, 49R05     

Existence and multiplicity of nontrivial solutions for an elliptic equation on ℝ<Superscript><Emphasis Type="Italic">N</Emphasis></Superscript> with indefinite linear part

 Via the Linking Theorem and Pseudo-index theory, we consider the existence and multiplicity of nontrivial solutions for a class of elliptic problems in all of ℝ ^N with indefinite linear part involving resonance and non-resonance at any eigenvalue. Received: 9 September 2002 / Revised version: 14 February 2003 Published online: 24 April 2003 Mathematics Subject Classification (2000): 35J20, 35J70     

On blow-up solutions for systems of semilinear heat equations with quadratic nonlinearities

This article deals with blow-up solutions of the Cauchy–Dirichlet problem for system of semilinear heat equations with quadratic non-linearities. Sufficient conditions for the existence of blow-up solutions are established. Sets of initial values for these solutions as well as upper bounds for corresponding blow-up time are determined. Furthermore, an application to the Lotka-Volterra system with diffusion is also discussed. The result of this article may be considered as a continuation and a generalization of the results obtained in (Baris, J., Baris, P. and Ruchlewicz, B., 2006, On blow-up solutions of nonautonomous quadratic differential systems. Differential Equations, 42, 320–326; Baris, J., Baris, P. and Wawiórko, E., 2006, Asymptotic behaviour of solutions of Lotka-Volterra systems. Nonlinear Analysis: Real World Applications, 7, 610–618; Baris, J., Baris, P. and Ruchlewicz, B., 2006, On blow-up solutions of quadratic systems of differential equations. Sovremennaya Matematika. Fundamentalnye Napravleniya, 15, 29–35 (in Russian); Baris, J. and Wawiórko, E., On blow-up solutions of polynomial Kolmogorov systems. Nonlinear Analysis: Real World Applications, to appear).     

Low regularity solutions for the wave map equation into the 2-D sphere

A class of weak wave map solutions with initial data in Sobolev space of order s<1 is studied. A non uniqueness result is proved for the case, when the target manifold is a two dimensional sphere. Using an equivariant wave map ansatz a family of self - similar solutions is constructed. This construction enables one to show ill - posedness of the inhomogeneous Cauchy problem for wave maps.Mathematics Subject Classification (2000): 35L70, 58J45.in final form: 17 January 2003     

Boundedness of the gradient of a solution and Wiener test of order one for the biharmonic equation

The behavior of solutions to the biharmonic equation is well-understood in smooth domains. In the past two decades substantial progress has also been made for the polyhedral domains and domains with Lipschitz boundaries. However, very little is known about higher order elliptic equations in the general setting. In this paper we introduce new integral identities that allow to investigate the solutions to the biharmonic equation in an arbitrary domain. We establish: (1) boundedness of the gradient of a solution in any three-dimensional domain; (2) pointwise estimates on the derivatives of the biharmonic Green function; (3) Wiener-type necessary and sufficient conditions for continuity of the gradient of a solution. Mathematics Subject Classification (2000)  35J40, 35J30, 35B65     

On a periodic Schrödinger equation with nonlocal superlinear part

We consider the Choquard-Pekar equation and focus on the case of periodic potential V. For a large class of even functions W we show existence and multiplicity of solutions. Essentially the conditions are that 0 is not in the spectrum of the linear part –+V and that W does not change sign. Our results carry over to more general nonlinear terms in arbitrary space dimension N2.Mathematics Subject Classification (2000):35Q55, 35Q40, 35J10, 35J20, 35J60, 46N50, 49J35, 81V70in final form: 14 November 2003     

Sharp Gradient Estimate and Yau's Liouville Theorem for the Heat Equation on Noncompact Manifolds

We derive a sharp, localized version of elliptic type gradientestimates for positive solutions (bounded or not) to the heatequation. These estimates are related to the Cheng–Yauestimate for the Laplace equation and Hamilton's estimate forbounded solutions to the heat equation on compact manifolds.As applications, we generalize Yau's celebrated Liouville theoremfor positive harmonic functions to positive ancient (includingeternal) solutions of the heat equation, under certain growthconditions. Surprisingly this Liouville theorem for the heatequation does not hold even in Rⁿ without such a condition.We also prove a sharpened long-time gradient estimate for thelog of the heat kernel on noncompact manifolds. 2000 MathematicsSubject Classification 35K05, 58J35.     

Partial regularity results for evolutional p-Laplacian systems with natural growth

 We study a regularity for evolutional p-Laplacian systems with natural growth on the gradient. It is shown that weak solutions of small image and their gradients are partial H?lder continuous and the size of the exceptional set for regularity is estimated in terms of Hausdorff measure. The main ingredient is to improve the Gehring inequality, which implies the higher integrability of the gradient and was first developed by Kinnunen and Lewis, so as to be well-worked in our perturbation estimate. We also use a refinement of the perturbation argument and make a device for H?lder estimates of the gradient. Received: 4 March 2002 Mathematics Subject Classification (2000): Primary 35D10, 35B65, 35K65     

Heat escape

We study non-uniqueness of nonnegative solutions of the Cauchy or Dirichlet problem for parabolic equations on domains which are not relatively compact in Riemannian manifolds. By introducing the notion of heat escape, we give a general and sharp sufficient condition for the non-uniqueness: If there is a heat escape, then the Cauchy problem (or Dirichlet problem) has a positive solution with zero initial value (or zero initial-boundary value). We also show, under a general and sharp condition, uniqueness of nonnegative solutions to the Dirichlet problem for parabolic equations. Mathematics Subject Classification (1991):31C12, 35K20, 35J25, 35K15, 58G11, 58G03, 31C05     

Gradient estimates for solutions to the conductivity problem

In this paper we derive very precise gradient estimates for solutions to the conductivity problem in the case where two circular conductivity inclusions are very close but not touching. The novelty of these estimates is that they give very specific information about the blow up of the gradient as the conductivities of the inclusions degenerate.Mathematics Subject Classification (2000): 35J25, 73C40     

Semicontinuity of the solution mappings to weak generalized parametric Ky Fan inequality problems with trifunctions

In this article, we discuss the lower semicontinuity of solution maps without the condition of C-strict monotonicity for two classes of weak generalized parametric Ky Fan inequalities under the case that the f-solution set be a general set-valued one. Our results extend the recent ones in the literature (e.g. Cheng, Y.H., Zhu, D.L.: Global stability results for the weak vector variational inequality. J. Glob. Optim. 32, 543–550 (2005); C.R. Chen and S.J. Li, On the solution continuity of parametric generalized systems, Pac. J. Optim. 6 (2010), pp. 141–151; Gong, X.H., Yao, J.C.: Lower semicontinuity of the set of efficient solutions for generalized systems. J. Optim. Theory Appl. 138, 197–205 (2008); Gong, X.H.: Continuity of the solution set to parametric weak vector equilibrium problems. J. Optim. Theory Appl. 139, 35–46 (2008)). Several examples are given for the illustration of our results.     

Constructing convex solutions via Perron’s method

Abstract In this paper we construct convex solutions for certain elliptic boundary value problems via Perron’s method. The solutions constructed are weak solutions in the viscosity sense, and our construction follows work of Ishii (Duke Math. J., 55 (2) 369–384, 1987). The same general approach appears in work of Andrews and Feldman (J. Differential Equations, 182 (2) 298–343, 2002) in which they show existence for a weak nonlocal parabolic flow of convex curves. The time independent special case of their work leads to a one dimensional elliptic result which we extend to two dimensions. Similar results are required to extend their theory of nonlocal geometric flows to surfaces. The two dimensional case is essentially different from the one dimensional case and involves a regularity result (cf. Theorem 3.1), which has independent interest. Roughly speaking, given an arbitrary convex function (which is not smooth) supported at one point by a smooth function of prescribed Hessian (which is not convex), one must construct a third function that is both convex and smooth and appropriately approximates both of the given functions. Keywords: Viscosity solutions, Elliptic partial differential equations, Perron procedure, Convexity, Regularity, Fully nonlinear, Monge-Ampere Mathematics Subject Classification (2000:) 35J60, 53A05, 52A15, 26B05     

Nonlinear evolutions with Carathéodory forcing

Let A be an m-accretive operator in a real Banach space X and f : J x X X a function of Carathéodory type, where $ J = [0, a] \subset \mathbb{R} $. This paper investigates the existence of mild solutions of the evolution system satisfying additional time-dependent constraints $ u(t) \in K(t) $ on J for a given tube K(·). Main emphasis is on existence results that are valid under minimal assumptions on f, K and X.AMS Subject Classification: Primary: 47J35, 35K90, Secondary: 34G25, 47H20.     

Pairs of positive solutions for nonlinear elliptic equations with the <Emphasis Type="Italic">p</Emphasis>-Laplacian and a nonsmooth potential

In this paper we examine a nonlinear elliptic problem driven by the p-Laplacian differential operator and with a potential function which is only locally Lipschitz, not necessarily C¹ (hemivariational inequality). Using the nonsmooth critical point theory of Chang, we obtain two strictly positive solutions. One solution is obtained by minimization of a suitable modification of the energy functional. The second solution is obtained by generalizing a result of Brezis-Nirenberg about the local C¹₀-minimizers versus the local H¹₀-minimizers of a C¹-functional. Mathematics Subject Classification (2000) 35J50, 35J85, 35R70     

Heat kernel estimates and Riesz transforms on some Riemannian covering manifolds

Consider a Riemannian manifold M which is a Galois covering of a compact manifold, with nilpotent deck transformation group G. For the Laplace operator on M, we prove a precise estimate for the gradient of the heat kernel, and show that the Riesz transforms are bounded in L^p(M), 1 < p < . We also obtain estimates for discrete oscillations of the heat kernel, and boundedness of discrete Riesz transform operators, which are defined using the action of G on M.Mathematics Subject Classification (2000): 58J35, 35B65, 42B20in final form: 8 August 2003     

Nonlinear elliptic equations with large supercritical exponents

The paper deals with the existence of positive solutions of the problem -Δ u=u^p in Ω, u=0 on ∂Ω, where Ω is a bounded domain of , n≥ 3, and p>2. We describe new concentration phenomena, which arise as p→ +∞ and can be exploited in order to construct, for p large enough, positive solutions that concentrate, as p→ +∞, near submanifolds of codimension 2. In this paper we consider, in particular, domains with axial symmetry and obtain positive solutions concentrating near (n-2)-dimensional spheres, which approach the boundary of Ω as p→ +∞. The existence and multiplicity results we state allow us to find positive solutions, for large p, also in domains which can be contractible and even arbitrarily close to starshaped domains (while no solution can exist if Ω is starshaped and , as a consequence of the Pohožaev's identity). Mathematics Subject Classification (2000) 35J20, 35J60, 35J65     

On <Emphasis Type="Italic">L</Emphasis><Superscript><Emphasis Type="Italic">1</Emphasis></Superscript>-summability and asymptotic profiles for smooth solutions to Navier–Stokes equations in a 3D exterior domain

The exterior nonstationary problem is studied for the 3D Navier-Stokes equations. The L ¹ -summability is proved for smooth solutions which correspond to initial data satisfying certain symmetry and moment conditions. The result is then applied to show that such solutions decay in time more rapidly than observed in general. Furthermore, an asymptotic expansion is deduced and a lower bound estimate is given for the rates of decay in time. Mathematics Subject Classifications (1991): 35Q30, 76D05.On leave of absence from Institute of Applied Mathematics, Academy of Mathematics and System Sciences. Academia Sinica, Beijing 100080, Peoples Republic of China. Supported by JSPS     

Homoclinic solutions for a semilinear elliptic equation with an asymptotically linear nonlinearity

We study the following semilinear elliptic equation where b is periodic and f is assumed to be asymptotically linear. The purpose of this paper is to establish the existence of infinitely many homoclinic type solutions for this class of nonlinearities.Received: 30 December 2002, Accepted: 26 August 2003, Published online: 15 October 2003Mathematics Subject Classification (2000): 35J60,35B05, 58E05