Sign-changing and constant-sign solutions for p-Laplacian problems with jumping nonlinearities

By variational methods, we prove the existence of a sign-changing solution for the p-Laplacian equation under Dirichlet boundary condition with jumping nonlinearity having relation to the Fu?ík spectrum of p-Laplacian. We also provide the multiple existence results for the p-Laplacian problems.     

On the second best constant in logarithmic Sobolev inequalities on complete Riemannian manifolds

We study the second best constant problem for logarithmic Sobolev inequalities on complete Riemannian manifolds and investigate its relationship with optimal heat kernel bounds and the existence of extremal functions.     

Monotonicity constraints and supercritical Neumann problems

We prove the existence of a positive and radially increasing solution for a semilinear Neumann problem on a ball. No growth conditions are imposed on the nonlinearity. The method introduces monotonicity constraints which simplify the existence of a minimizer for the associated functional. Special care must be employed to establish the validity of the Euler equation.     

Positive solutions of semilinear biharmonic equations with critical Sobolev exponents

In this paper we study the critical growth biharmonic problem with a parameter λ and establish uniform lower bounds for Λ, which is the supremum of the set of λ, related to the existence of positive solutions of the biharmonic problem.     

Two solutions for inhomogeneous nonlinear elliptic equations at critical growth

The existence of two nontrivial solutions for a class of fully nonlinear problems at critical growth with perturbations of lower order is proved. The first solution is obtained via a local minimization argument while the second solution follows by a non-smooth mountain pass theorem.     

Multiple bifurcation branches for variational inequalities

We prove the existence of two bifurcation branches for a variational inequality in a case when the corresponding asymptotic problem is nonsymmetric. We use a nonsmooth variational framework and a blow-up argument which allows to find multiple critical points possibly at the same level. An application to plates with obstacle is presented.     

Solutions to a gradient system with resonance at both zero and infinity

In this paper, we study the existence and multiplicity of nontrivial solutions for a gradient system with resonance at both zero and infinity via Morse theory.     

Existence of solutions on weak vector equilibrium problems

Weak vector equilibrium problems with bi-variable mappings from product space of two bounded complete locally convex Hausdorff topological vector spaces to another topological vector space are studied. The existence theorems of solutions are proved by the FKKM fixed point theorem. Viscosity principle of vector equilibrium problems is dealt with. The relations between solutions of the vector equilibrium problem and those of its perturbation problem are presented.     

Symmetric boundary values for the Dirichlet problem for harmonic maps from the disc into the 2-sphere

Let Aut(D) denote the group of biholomorphic diffeormorphisms from the unit disc D onto itself and O(3) the group of orthogonal transformations of the unit sphere S ². The existence of multiple solutions to the Dirichlet problem for harmonic maps from D into S ² is related to the symmetries (if any) of the boundary value γ : ∂D → S ², by invariance of the Dirichlet energy under the action of Aut(D) × O(3). In this paper, we classify the stabilizers in Aut(D) × O(3) of boundary values in H ^1/2(S ¹, S ²) and . We give two applications to the Dirichlet problem for harmonic maps. This work was partially supported by the CMLA, Ecole Normale Supérieure de Cachan, Cachan, France.     

Doubly resonant semilinear elliptic problems via nonsmooth critical point theory

We consider the existence of weak solutions for classical doubly resonant semilinear elliptic problems. We show how the main technical assumptions can be used to define appropriate metrics on the underlying function space, so that extensions of the results already known in the literature can be obtained using only basic facts from critical point theory for continuous functionals on complete metric spaces.     

Sharp Nash inequalities on the unit sphere: The influence of symmetries

In this paper both we establish the best constants for the Nash inequalities on the standard unit sphere Sⁿ of Rⁿ⁺¹, n≥3 and we give answers on the existence of extremal functions on the corresponding problems. Also we study the problem of the best constants in the case where the data are invariant under the action of the group G=O(k)×O(m), k+m=n+1 and we find the best constants.     

The Landau-Lifshitz equation of the ferromagnetic spin chain and harmonic maps

We prove a global existence of solutions for the Landau-Lifshitz equation of the ferromagnetic spin chain from am-dimensional manifoldM into the unit sphereS ² of ³ and establish some new links between harmonic maps and the solutions of the Landau-Lifshitz equation.     

The use of factors to discover potential systems or linearizations

Factors of a given system of PDEs are solutions of an adjoint system of PDEs related to the system's Fréchet derivative. In this paper, we introduce the notion of potential conservation laws, arising from specific types of factors, which lead to useful potential systems. Point symmetries of a potential system could yield nonlocal symmetries of the given system and its linearization by a noninvertible mapping.We also introduce the notion of linearizing factors to determine necessary conditions for the existence of a linearization of a given system of PDEs.     

Existence of critical points in a general setting

The paper proves the existence of critical points for a general locally Lipschitz functional usually arising in nonlinear elliptic problems. It extends and unifies various results in the critical point theory. The applications treat new situations involving discontinuous elliptic equations containing both sublinear and superlinear terms, integro-differential equations and nonlinear elliptic systems.     

Splitting theorem, Poincaré-Hopf theorem and jumping nonlinear problems

In this paper, we establish a Gromoll-Meyer splitting theorem and a shifting theorem for J∈C^2-0(E,R) and by using the finite-dimensional approximation, mollifiers and Morse theory we generalize the Poincaré-Hopf theorem to J∈C¹(E,R) case. By combining the Poincaré-Hopf theorem and the splitting theorem, we study the existence of multiple solutions for jumping nonlinear elliptic equations.     

Existence results for semilinear elliptical hemivariational inequalities

We are interested in studying the existence of solutions to an elliptical hemivariational inequality, depending on a real parameter λ$\lambda$. The main tool in the proof of our results is a critical point theorem recently established. We obtain the existence of solution through a direct method, both with a changing sign nonlinearity of the kind p(x)f(ξ)$p\left(x\right)f\left(\xi \right)$ and in the classical one P(x,ξ)$P(x,\xi )$ too.     

An optimal partition problem related to nonlinear eigenvalues

We extend to the case of many competing densities the results of the paper (Ann. Inst. H. Poincaré 6 (2002)). More precisely, we are concerned with an optimal partition problem in N-dimensional domains related to the method of nonlinear eigenvalues introduced by Nehari, (Acta Math. 105 (1961)). We prove existence of the minimal partition and some extremality conditions. Moreover, in the case of two-dimensional domains we give an asymptotic formula near the multiple intersection points. Finally, we show some connections between the variational problem and the behavior of competing species systems with large interaction.     

Cantor families of periodic solutions for wave equations via a variational principle

We prove existence of small amplitude periodic solutions of completely resonant wave equations with frequencies in a Cantor set of asymptotically full measure, via a variational principle. A Lyapunov-Schmidt decomposition reduces the problem to a finite dimensional bifurcation equation—variational in nature—defined on a Cantor set of non-resonant parameters. The Cantor gaps are due to “small divisors” phenomena. To solve the bifurcation equation we develop a suitable variational method. In particular, we do not require the typical “Arnold non-degeneracy condition” of the known theory on the nonlinear terms. As a consequence our existence results hold for new generic sets of nonlinearities.