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26. CMB 2007 (vol 50 pp. 356)

Filippakis, Michael E.; Papageorgiou, Nikolaos S.
 Existence of Positive Solutions for Nonlinear Noncoercive Hemivariational Inequalities In this paper we investigate the existence of positive solutions for nonlinear elliptic problems driven by the $p$-Laplacian with a nonsmooth potential (hemivariational inequality). Under asymptotic conditions that make the Euler functional indefinite and incorporate in our framework the asymptotically linear problems, using a variational approach based on nonsmooth critical point theory, we obtain positive smooth solutions. Our analysis also leads naturally to multiplicity results. Keywords:$p$-Laplacian, locally Lipschitz potential, nonsmooth critical point theory, principal eigenvalue, positive solutions, nonsmooth Mountain Pass TheoremCategories:35J20, 35J60, 35J85

27. CMB 2007 (vol 50 pp. 35)

Duyckaerts, Thomas
 A Singular Critical Potential for the SchrÃ¶dinger Operator Consider a real potential $V$ on $\RR^d$, $d\geq 2$, and the Schr\"odinger equation: $$\tag{LS} \label{LS1} i\partial_t u +\Delta u -Vu=0,\quad u_{\restriction t=0}=u_0\in L^2.$$ In this paper, we investigate the minimal local regularity of $V$ needed to get local in time dispersive estimates (such as local in time Strichartz estimates or local smoothing effect with gain of $1/2$ derivative) on solutions of \eqref{LS1}. Prior works show some dispersive properties when $V$ (small at infinity) is in $L^{d/2}$ or in spaces just a little larger but with a smallness condition on $V$ (or at least on its negative part). In this work, we prove the critical character of these results by constructing a positive potential $V$ which has compact support, bounded outside $0$ and of the order $(\log|x|)^2/|x|^2$ near $0$. The lack of dispersiveness comes from the existence of a sequence of quasimodes for the operator $P:=-\Delta+V$. The elementary construction of $V$ consists in sticking together concentrated, truncated potential wells near $0$. This yields a potential oscillating with infinite speed and amplitude at $0$, such that the operator $P$ admits a sequence of quasi-modes of polynomial order whose support concentrates on the pole. Categories:35B65, 35L05, 35Q40, 35Q55

28. CMB 2006 (vol 49 pp. 358)

Khalil, Abdelouahed El; Manouni, Said El; Ouanan, Mohammed
 On the Principal Eigencurve of the $p$-Laplacian: Stability Phenomena We show that each point of the principal eigencurve of the nonlinear problem $$-\Delta_{p}u-\lambda m(x)|u|^{p-2}u=\mu|u|^{p-2}u \quad \text{in } \Omega,$$ is stable (continuous) with respect to the exponent $p$ varying in $(1,\infty)$; we also prove some convergence results of the principal eigenfunctions corresponding. Keywords:$p$-Laplacian with indefinite weight, principal eigencurve, principal eigenvalue, principal eigenfunction, stabilityCategories:35P30, 35P60, 35J70

29. CMB 2006 (vol 49 pp. 226)

Engman, Martin
 The Spectrum and Isometric Embeddings of Surfaces of Revolution A sharp upper bound on the first $S^{1}$ invariant eigenvalue of the Laplacian for $S^1$ invariant metrics on $S^2$ is used to find obstructions to the existence of $S^1$ equivariant isometric embeddings of such metrics in $(\R^3,\can)$. As a corollary we prove: If the first four distinct eigenvalues have even multiplicities then the metric cannot be equivariantly, isometrically embedded in $(\R^3,\can)$. This leads to generalizations of some classical results in the theory of surfaces. Categories:58J50, 58J53, 53C20, 35P15

30. CMB 2006 (vol 49 pp. 144)

Taylor, Michael
 Scattering Length and the Spectrum of $-\Delta+V$ Given a non-negative, locally integrable function $V$ on $\RR^n$, we give a necessary and sufficient condition that $-\Delta+V$ have purely discrete spectrum, in terms of the scattering length of $V$ restricted to boxes. Category:35J10

31. CMB 2005 (vol 48 pp. 405)

Froese, Richard
 Liouville's Theorem in the Radially Symmetric Case We present a very short proof of Liouville's theorem for solutions to a non-uniformly elliptic radially symmetric equation. The proof uses the Ricatti equation satisfied by the Dirichlet to Neumann map. Categories:35B05, 34A30

32. CMB 2005 (vol 48 pp. 3)

Burq, N.
 Quantum Ergodicity of Boundary Values of Eigenfunctions: A Control Theory Approach Consider $M$, a bounded domain in ${\mathbb R}^d$, which is a Riemanian manifold with piecewise smooth boundary and suppose that the billiard associated to the geodesic flow reflecting on the boundary according to the laws of geometric optics is ergodic. We prove that the boundary value of the eigenfunctions of the Laplace operator with reasonable boundary conditions are asymptotically equidistributed in the boundary, extending previous results by G\'erard and Leichtnam as well as Hassell and Zelditch, obtained under the additional assumption of the convexity of~$M$. Categories:35Q55, 35BXX, 37K05, 37L50, 81Q20

33. CMB 2004 (vol 47 pp. 515)

Frigon, M.
 Remarques sur l'enlacement en thÃ©orie des points critiques pour des fonctionnelles continues Dans cet article, \a partir de la notion d'enlacement introduite dans ~\cite{F} entre des paires d'ensembles $(B,A)$ et $(Q,P)$, nous \'etablissons l'existence d'un point critique d'une fonctionnelle continue sur un espace m\'etrique lorsqu'une de ces paires enlace l'autre. Des renseignements sur la localisation du point critique sont aussi obtenus. Ces r\'esultats conduisent \a une g\'en\'eralisation du th\'eor\eme des trois points critiques. Finalement, des applications \a des probl\emes aux limites pour une \'equation quasi-lin\'eaire elliptique sont pr\'esent\'ees. Categories:58E05, 35J20

34. CMB 2004 (vol 47 pp. 504)

Cardoso, Fernando; Vodev, Georgi
 High Frequency Resolvent Estimates and Energy Decay of Solutions to the Wave Equation We prove an uniform H\"older continuity of the resolvent of the Laplace-Beltrami operator on the real axis for a class of asymptotically Euclidean Riemannian manifolds. As an application we extend a result of Burq on the behaviour of the local energy of solutions to the wave equation. Categories:35B37, 35J15, 47F05

35. CMB 2004 (vol 47 pp. 407)

Nedelec, L.
 Multiplicity of Resonances in Black Box Scattering We apply the method of complex scaling to give a natural proof of a formula relating the multiplicity of a resonance to the multiplicity of a pole of the scattering matrix. Category:35P25

36. CMB 2004 (vol 47 pp. 417)

Niu, Pengcheng; Han, Yanwu; Han, Junqiang
 A Hopf Type Lemma and a CR Type Inversion for the Generalized Greiner Operator In this paper we establish a Hopf type lemma and a CR type inversion for the generalized Greiner operator. Some nonlinear Keywords:Hopf type lemma, CR inversion, Liouville type, theorem generalized Greiner operator

37. CMB 2003 (vol 46 pp. 323)

Chamberland, Marc
 Characterizing Two-Dimensional Maps Whose Jacobians Have Constant Eigenvalues Recent papers have shown that $C^1$ maps $F\colon \mathbb{R}^2 \rightarrow \mathbb{R}^2$ whose Jacobians have constant eigenvalues can be completely characterized if either the eigenvalues are equal or $F$ is a polynomial. Specifically, $F=(u,v)$ must take the form \begin{gather*} u = ax + by + \beta \phi(\alpha x + \beta y) + e \\ v = cx + dy - \alpha \phi(\alpha x + \beta y) + f \end{gather*} for some constants $a$, $b$, $c$, $d$, $e$, $f$, $\alpha$, $\beta$ and a $C^1$ function $\phi$ in one variable. If, in addition, the function $\phi$ is not affine, then $$\alpha\beta (d-a) + b\alpha^2 - c\beta^2 = 0.$$ This paper shows how these theorems cannot be extended by constructing a real-analytic map whose Jacobian eigenvalues are $\pm 1/2$ and does not fit the previous form. This example is also used to construct non-obvious solutions to nonlinear PDEs, including the Monge--Amp\ere equation. Keywords:Jacobian Conjecture, injectivity, Monge--AmpÃ¨re equationCategories:26B10, 14R15, 35L70

38. CMB 2001 (vol 44 pp. 346)

Wang, Wei
 Positive Solution of a Subelliptic Nonlinear Equation on the Heisenberg Group In this paper, we establish the existence of positive solution of a nonlinear subelliptic equation involving the critical Sobolev exponent on the Heisenberg group, which generalizes a result of Brezis and Nirenberg in the Euclidean case. Keywords:Heisenberg group, subLapacian, critical Sobolev exponent, extremalsCategories:35J20, 35J60

39. CMB 2001 (vol 44 pp. 210)

Leung, Man Chun
 Growth Estimates on Positive Solutions of the Equation $\Delta u+K u^{\frac{n+2}{n-2}}=0$ in $\R^n$ We construct unbounded positive $C^2$-solutions of the equation $\Delta u + K u^{(n + 2)/(n - 2)} = 0$ in $\R^n$ (equipped with Euclidean metric $g_o$) such that $K$ is bounded between two positive numbers in $\R^n$, the conformal metric $g=u^{4/(n-2)}g_o$ is complete, and the volume growth of $g$ can be arbitrarily fast or reasonably slow according to the constructions. By imposing natural conditions on $u$, we obtain growth estimate on the $L^{2n/(n-2)}$-norm of the solution and show that it has slow decay. Keywords:positive solution, conformal scalar curvature equation, growth estimateCategories:35J60, 58G03

40. CMB 2000 (vol 43 pp. 477)

Ward, Michael J.
 The Dynamics of Localized Solutions of Nonlocal Reaction-Diffusion Equations Many classes of singularly perturbed reaction-diffusion equations possess localized solutions where the gradient of the solution is large only in the vicinity of certain points or interfaces in the domain. The problems of this type that are considered are an interface propagation model from materials science and an activator-inhibitor model of morphogenesis. These two models are formulated as nonlocal partial differential equations. Results concerning the existence of equilibria, their stability, and the dynamical behavior of localized structures in the interior and on the boundary of the domain are surveyed for these two models. By examining the spectrum associated with the linearization of these problems around certain canonical solutions, it is shown that the nonlocal term can lead to the existence of an exponentially small principal eigenvalue for the linearized problem. This eigenvalue is then responsible for an exponentially slow, or metastable, motion of the localized structure. Categories:35Q35, 35C20, 35K60

41. CMB 2000 (vol 43 pp. 51)

Edward, Julian
 Eigenfunction Decay For the Neumann Laplacian on Horn-Like Domains The growth properties at infinity for eigenfunctions corresponding to embedded eigenvalues of the Neumann Laplacian on horn-like domains are studied. For domains that pinch at polynomial rate, it is shown that the eigenfunctions vanish at infinity faster than the reciprocal of any polynomial. For a class of domains that pinch at an exponential rate, weaker, $L^2$ bounds are proven. A corollary is that eigenvalues can accumulate only at zero or infinity. Keywords:Neumann Laplacian, horn-like domain, spectrumCategories:35P25, 58G25

42. CMB 1999 (vol 42 pp. 169)

Ding, Hongming
 Heat Kernels of Lorentz Cones We obtain an explicit formula for heat kernels of Lorentz cones, a family of classical symmetric cones. By this formula, the heat kernel of a Lorentz cone is expressed by a function of time $t$ and two eigenvalues of an element in the cone. We obtain also upper and lower bounds for the heat kernels of Lorentz cones. Keywords:Lorentz cone, symmetric cone, Jordan algebra, heat kernel, heat equation, Laplace-Beltrami operator, eigenvaluesCategories:35K05, 43A85, 35K15, 80A20

43. CMB 1997 (vol 40 pp. 464)

Kuo, Chung-Cheng
 On the solvability of a Neumann boundary value problem at resonance We study the existence of solutions of the semilinear equations (1) $\triangle u + g(x,u)=h$, ${\partial u \over \partial n} = 0$ on $\partial \Omega$ in which the non-linearity $g$ may grow superlinearly in $u$ in one of directions $u \to \infty$ and $u \to -\infty$, and (2) $-\triangle u + g(x,u)=h$, ${\partial u \over \partial n} = 0$ on $\partial \Omega$ in which the nonlinear term $g$ may grow superlinearly in $u$ as $|u| \to \infty$. The purpose of this paper is to obtain solvability theorems for (1) and (2) when the Landesman-Lazer condition does not hold. More precisely, we require that $h$ may satisfy $\int g^\delta_- (x) \, dx < \int h(x) \, dx = 0< \int g^\gamma_+ (x)\,dx$, where $\gamma, \delta$ are arbitrarily nonnegative constants, $g^\gamma_+ (x) = \lim_{u \to \infty} \inf g(x,u) |u|^\gamma$ and $g^\delta_- (x)=\lim_{u \to -\infty} \sup g(x,u)|u|^\delta$. The proofs are based upon degree theoretic arguments. Keywords:Landesman-Lazer condition, Leray Schauder degreeCategories:35J65, 47H11, 47H15

44. CMB 1997 (vol 40 pp. 174)

Hungerbühler, Norbert
 Non-uniqueness for the $p$-harmonic flow If $f_0\colon\Omega\subset \R^m\to S^n$ is a weakly $p$-harmonic map from a bounded smooth domain $\Omega$ in $\R^m$ (with $2 Categories:35K40, 35K55, 35K65 45. CMB 1997 (vol 40 pp. 244) Naito, Yūki; Usami, Hiroyuki  Nonexistence results of positive entire solutions for quasilinear elliptic inequalities This paper treats the quasilinear elliptic inequality $$\div (|Du|^{m-2}Du) \geq p(x)u^{\sigma}, \quad x \in \Rs^N,$$ where$N \geq 2$,$m > 1$,$ \sigma > m - 1$, and$p \colon \Rs^N \rightarrow (0, \infty)$is continuous. Sufficient conditions are given for this inequality to have no positive entire solutions. When$p$has radial symmetry, the existence of positive entire solutions can be characterized by our results and some known results. Categories:35J70, 35B05 46. CMB 1997 (vol 40 pp. 60) Khavinson, Dmitry  Cauchy's problem for harmonic functions with entire data on a sphere We give an elementary potential-theoretic proof of a theorem of G.~Johnsson: all solutions of Cauchy's problems for the Laplace equations with an entire data on a sphere extend harmonically to the whole space${\bf R}^N\$ except, perhaps, for the center of the sphere. Keywords:harmonic functions, Cauchy's problem, homogeneous harmonicsCategories:35B60, 31B20
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