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In this paper we shall investigate the nonexistence of positive solutions for the following nonlinear parabolic partial differential equation:\[ \begin{cases} \frac{\partial u}{\partial t}= \Delta_{\mathbb{G},p}u+V(x)u^{p-1} & \text{in}\quad \Omega \times (0, T), \quad 1<p<2, u(x,0)=u_{0}(x)\geq 0 & \text{in} \quad\Omega, u(x,t)=0 & \text{on}\quad \partial\Omega\times (0, T) \end{cases} \] where $ \Delta_{\mathbb{G},p}$ is the $p$-sub-Laplacian on Carnot group $ \mathbb{G}$ and $V\in L_{\text{loc}}^1(\Omega)$. | The Hardy inequality and Nonlinear parabolic equations on Carnot groups | 11,300 |
Using the framework of Colombeau algebras of generalized functions, we prove the existence and uniqueness results for global generalized solvability of semilinear hyperbolic systems with nonlinear nonlocal boundary conditions. We admit strong singularities in the differential equations as well as in the initial and boundary conditions. Our analysis covers the case of non-Lipshitz nonlinearities both in the differential equations and in the boundary conditions. | Generalized Solutions to Hyperbolic Systems with Nonlinear Conditions
and Strongly Singular Data | 11,301 |
We consider nondecreasing entropy solutions to 1-d scalar conservation laws and show that the spatial derivatives of such solutions satisfy a contraction property with respect to the Wasserstein distance of any order. This result extends the L^1-contraction property shown by Kruzkov. | Contractive metrics for scalar conservation laws | 11,302 |
We give a necessary and sufficient condition on the cost function so that the map solution of Monge's optimal transportation problem is continuous for arbitrary smooth positive data. This condition was first introduced by Ma, Trudinger and Wang \cite{MTW, TW} for a priori estimates of the corresponding Monge-Amp\`ere equation. It is expressed by a so-called {\em cost-sectional curvature} being non-negative. We show that when the cost function is the squared distance of a Riemannian manifold, the cost-sectional curvature yields the sectional curvature. As a consequence, if the manifold does not have non-negative sectional curvature everywhere, the optimal transport map {\em can not be continuous} for arbitrary smooth positive data. The non-negativity of the cost-sectional curvature is shown to be equivalent to the connectedness of the contact set between any cost-convex function (the proper generalization of a convex function) and any of its supporting functions. When the cost-sectional curvature is uniformly positive, we obtain that optimal maps are continuous or H\"older continuous under quite weak assumptions on the data, compared to what is needed in the Euclidean case. This case includes the reflector antenna problem and the squared Riemannian distance on the sphere. | On the regularity of maps solutions of optimal transportation problems | 11,303 |
This work gathers new results concerning the semi-geostrophic equations: existence and stability of measure valued solutions, existence and uniqueness of solutions under certain continuity conditions for the density, convergence to the incompressible Euler equations. Meanwhile, a general technique to prove uniqueness of sufficiently smooth solutions to non-linearly coupled system is introduced, using optimal transportation. | A fully non-linear version of the Euler incompressible equations: the
semi-geostrophic system | 11,304 |
We consider in this paper a plasma subject to a strong deterministic magnetic field and we investigate the effect on this plasma of a stochastic electric field. We show that the limit behavior, which corresponds to the transfer of energy from the electric wave to the particles (Landau phenomena), is described by a Spherical Harmonics Expansion (SHE) model. | Electric turbulence in a plasma subject to a strong magnetic field | 11,305 |
In this note, we show uniqueness of weak solutions to the Vlasov-Poisson system on the only condition that the macroscopic density $\rho$ defined by $\rho(t,x) = \int_{\Rd} f(t,x,\xi)d\xi$ is bounded in $\Linf$. Our proof is based on optimal transportation. | Uniqueness of the solution to the Vlasov-Poisson system with bounded
density | 11,306 |
We will show in this paper that if $\lambda$ is very close to 1, then $$I(M,\lambda,m)= \sup_{u\in H^{1,n}_0(M) ,\int_M|\nabla u|^ndV=1}\int_\Omega (e^{\alpha_n |u|^\frac{n}{n-1}}-\lambda\sum\limits_{k=1}^m\frac{|\alpha_nu^\frac{n}{n-1}|^k} {k!})dV,$$ can be attained, where $M$ is a compact manifold with boundary. This result gives a counter example to the conjecture of de Figueiredo, do \'o, and Ruf in their paper titled "On a inequality by N.Trudinger and J.Moser and related elliptic equations" (Comm. Pure. Appl. Math.,{\bf 55}:135-152, 2002). | Remarks on the Extremal Functions for the Moser-Trudinger Inequalities | 11,307 |
We study Maxwell's equations in time domain in an anisotropic medium. The goal of the paper is to solve an inverse boundary value problem for anisotropies characterized by scalar impedance $\alpha$. This means that the material is conformal, i.e., the electric permittivity $\epsilon$ and magnetic permeability $\mu$ are tensors satisfying $\mu =\alpha^2\epsilon$. This condition is equivalent to a single propagation speed of waves with different polarizations which uniquely defines an underlying Riemannian structure. The analysis is based on an invariant formulation of the system of electrodynamics as a Dirac type first order system on a Riemannian $3-$manifold with an additional structure of the wave impedance, $(M,g,\alpha)$, where $g$ is the travel-time metric. We study the properties of this system in the first part of the paper. In the second part we consider the inverse problem, that is, the determination of $(M,g,\alpha)$ from measurements done only on an open part of the boundary and on a finite time interval. As an application, in the isotropic case with $M\subset \R^3$, we prove that the boundary data given only on an open part of the boundary determine uniquely the domain $M$ and the coefficients $\epsilon$ and $\mu$. | Maxwell's Equations with Scalar Impedance: Inverse Problems with data
given on a part of the boundary | 11,308 |
We consider the reaction-diffusion equation \[ T_t = T_{xx} + f(T) \] on $\bbR$ with $T_0(x) \equiv \chi_{[-L,L]} (x)$ and $f(0)=f(1)=0$. In 1964 Kanel' proved that if $f$ is an ignition non-linearity, then $T\to 0$ as $t\to\infty$ when $L<L_0$, and $T\to 1$ when $L>L_1$. We answer the open question of relation of $L_0$ and $L_1$ by showing that $L_0=L_1$. We also determine the large time limit of $T$ in the critical case $L=L_0$, thus providing the phase portrait for the above PDE with respect to a 1-parameter family of initial data. Analogous results for combustion and bistable non-linearities are proved as well. | Sharp Transition Between Extinction and Propagation of Reaction | 11,309 |
In this paper we construct a global, continuous flow of solutions to the Camassa-Holm equation on the entire space $H^1$. Our solutions are conservative, in the sense that the total energy $\int (u^2+u_x^2) dx$ remains a.e. constant in time. Our new approach is based on a distance functional $J(u,v)$, defined in terms of an optimal transportation problem, which satisfies ${d\over dt} J(u(t), v(t))\leq \kappa\cdot J(u(t),v(t))$ for every couple of solutions. Using this new distance functional, we can construct arbitrary solutions as the uniform limit of multi-peakon solutions, and prove a general uniqueness result. | An Optimal Transportation Metric for Solutions of the Camassa-Holm
Equation | 11,310 |
The aim of this thesis is to derive new gradient estimates for parabolic equations. The gradient estimates found are independent of the regularity of the initial data. This allows us to prove the existence of solutions to problems that have non-smooth, continuous initial data. We include existence proofs for problems with both Neumann and Dirichlet boundary data. The class of equations studied is modelled on mean curvature flow for graphs. It includes anisotropic mean curvature flow, and other operators that have no uniform non-degeneracy bound. We arrive at similar estimates by three different paths: a 'double coordinate' approach, an approach examining the intersections of a solution and a given barrier, and a classical geometric approach. | Parabolic equations with continuous initial data | 11,311 |
For the Schr\"odinger flow from $R^2 \times R^+$ to the 2-sphere $S^2$, it is not known if finite energy solutions can blow up in finite time. We study equivariant solutions whose energy is near the energy of the family of equivariant harmonic maps. We prove that such solutions remain close to the harmonic maps until the blow up time (if any), and that they blow up if and only if the length scale of the nearest harmonic map goes to zero. | Schrodinger Flow Near Harmonic Maps | 11,312 |
We derive the high frequency limit of the Helmholtz equation with source term when the source is the sum of two point sources. We study it in terms of Wigner measures (quadratic observables). We prove that the Wigner measure associated with the solution satisfies a Liouville equation with, as source term, the sum of the source terms that would be created by each of the two point sources taken separately. The first step, and main difficulty, in our study is the obtention of uniform estimates on the solution. Then, from these bounds, we derive the source term in the Liouville equation together with the radiation condition at infinity satisfied by the Wigner measure. | High frequency analysis of Helmholtz equations: case of two point
sources | 11,313 |
We establish several results related to existence, nonexistence or bifurcation of positive solutions for a Dirichlet boundary value problem with in a smooth bounded domain. The main feature of this paper consists in the presence of a singular nonlinearity, combined with a convection term. Our approach takes into account both the sign of the potential and the decay rate around the origin of the singular nonlinearity. The proofs are based on various techniques related to the maximum principle for elliptic equations. | On a class of sublinear singular elliptic problems with convection term | 11,314 |
Let $\sigma(x,\xi) $ be a sufficiently regular function defined on $R^d \times R^d.$ The pseudo-differential operator with symbol $\sigma$ is defined on the Schwartz class by the formula: \[f\to\sigma f(x)=\int_{R^d} \sigma(x,\xi) \hat{f}(\xi)e^{2\pi ix\xi}d\xi, \] where $\hat{f}(\xi)=\int_{R^d} f(x)e^{-2\pi ix\xi}dx$ is the Fourier transform of $f.$ In this paper, we shall consider the regularity of the following type : \begin{description} \item[(a)] $| \partial_{\xi}^{\alpha}\sigma(x,\xi) | \leq A_{\alpha}(1+| \xi|) ^{-| \alpha|},$ \item[(b)] $| \partial_{\xi}^{\alpha}\sigma(x+y,\xi) -\partial_{\xi}^{\alpha}\sigma(x,\xi) | \leq A_{\alpha}\omega(| y|) (1+| \xi|) ^{-| \alpha|},$ \end{description} % | Multipliers spaces and pseudo-differential operators | 11,315 |
We present some new regularity criteria for ``suitable weak solutions'' of the Navier-Stokes equations near the boundary in dimension three. We prove that suitable weak solutions are H\"older continuous up to the boundary provided that the scaled mixed norm $L^{p,q}_{x,t}$ with $3/p+2/q\leq 2, 2<q\le \infty$, $(p,q) \not = (3/2,\infty)$, is small near the boundary. Our methods yield new results in the interior case as well. Partial regularity of weak solutions is also analyzed under some conditions of the Prodi-Serrin type. | Regularity criteria for suitable weak solutions of the Navier-Stokes
equations near the boundary | 11,316 |
For a non-cooperative differential game, the value functions of the various players satisfy a system of Hamilton-Jacobi equations. In the present paper, we consider a class of infinite-horizon games with nonlinear costs exponentially discounted in time. By the analysis of the value functions, we establish the existence of Nash equilibrium solutions in feedback form and provide results and counterexamples on their uniqueness and stability. | Infinite Horizon Noncooperative Differential Games | 11,317 |
We settle the issue of well-posedness for the Dirichlet problem for a higher order elliptic system ${\mathcal L}(x,D_x)$ with complex-valued, bounded, measurable coefficients in a Lipschitz domain $\Omega$, with boundary data in Besov spaces. The main hypothesis under which our principal result is established is in the nature of best possible and requires that, at small scales, the mean oscillations of the unit normal to $\partial\Omega$ and of the coefficients of the differential operator ${\mathcal L}(x,D_x)$ are not too large. | The Dirichlet problem in Lipschitz domains with boundary data in Besov
spaces for higher order elliptic systems with rough coefficients | 11,318 |
This paper was removed by arXiv admin because it plagiarizes the electronic article HYKE 2005-010 (http://www.hyke.org/preprint/index.php), by Jose-A. Carrillo and Lucas C.f. Ferreira, entitled "Self-similar solutions and large time asymptotics for the dissipative quasi-geostrophic equations". | Quasi-geostrophic equations with initial data in Banach spaces of local
measures | 11,319 |
We present a modification of the BC-method in the inverse hyperbolic problems. The main novelty is the study of the restrictions of the solutions to the characteristic surfaces instead of the fixed time hyperplanes. The main result is that the time-dependent Dirichlet-to-Neumann operator prescribed on a part of the boundary uniquely determines the coefficients of the self-adjoint hyperbolic operator up to a diffeomorphism and a gauge transformation. In this paper we prove the crucial local step. The global step of the proof will be presented in the forthcoming paper. | A new approach to hyperbolic inverse problems | 11,320 |
The Fourier transforms of the products of two respectively three solutions of the free Schroedinger equation in one space dimension are estimated in mixed and, in the first case weighted, L^p - norms. Inserted into an appropriate variant of the Fourier restriction norm method, these estimates serve to prove local well-posedness of the Cauchy problem for the cubic nonlinear Schroedinger (NLS) equation with data u_0 in the function space ^L^r:=^H^r_0, where for s \in R the spaces ^H^r_s are defined by the norms ||u_0||_{^H^r_s}:=||^u_0||_{L^r'_\xi}, 1/r + 1/r'=1. Similar arguments, combined with a gauge transform, lead to local well-posedness of the Cauchy problem for the derivative nonlinear Schroedinger (DNLS) equation with data u_0 \in ^H^r_{1/2}. In the local result on cubic NLS the parameter r is allowed in the whole subcritical range 1<r<\infty, while for DNLS we assume 1<r \le 2. In the special case r=2 both results coincide with the optimal ones on the H^s - scale. Furthermore, concerning the cubic NLS equation, it is shown by a decomposition argument that the local solution extends globally, provided 2 \ge r > 5/3. | Bi- and trilinear Schroedinger estimates in one space dimension with
applications to cubic NLS and DNLS | 11,321 |
We consider the mixed problem for the Laplace operator in a class of Lipschitz graph domains in two dimensions with Lipschitz constant at most 1. The boundary of the domain is decomposed into two disjoint sets D and N. We suppose the Dirichlet data, f_D has one derivative in L^p(D) of the boundary and the Neumann data is in L^p(N). We find conditions on the domain and the sets D and N so that there is a p_0>1 so that for p in the interval (1,p_0), we may find a unique solution to the mixed problem and the gradient of the solution lies in L^p. | The mixed problem in L^p for some two-dimensional Lipschitz domains | 11,322 |
We establish a general criterion which ensures exponential mixing of parabolic Stochastic Partial Differential Equations (SPDE) driven by a non additive noise which is white in time and smooth in space. We apply this criterion on two representative examples: 2D Navier-Stokes (NS) equations and Complex Ginzburg-Landau (CGL) equation with a locally Lipschitz noise. Due to the possible degeneracy of the noise, Doob theorem cannot be applied. Hence a coupling method is used in the spirit of [EMS], [KS3] and [Matt]. Previous results require assumptions on the covariance of the noise which might seem restrictive and artificial. For instance, for NS and CGL, the covariance operator is supposed to be diagonal in the eigenbasis of the Laplacian and not depending on the high modes of the solutions. The method developped in the present paper gets rid of such assumptions and only requires that the range of the covariance operator contains the low modes. | Exponential Mixing for Stochastic PDEs: The Non-Additive Case | 11,323 |
We study the inverse boundary value problems for the Schr\"{o}dinger equations with Yang-Mills potentials in a bounded domain $\Omega_0\subset\R^n$ containing finite number of smooth obstacles $\Omega_j,1\leq j \leq r$. We prove that the Dirichlet-to-Neumann operator on $\partial\Omega_0$ determines the gauge equivalence class of the Yang-Mills potentials. We also prove that the metric tensor can be recovered up to a diffeomorphism that is identity on $\partial\Omega_0$. | Inverse problems for Schrodinger equations with Yang-Mills potentials in
domains with obstacles and the Aharonov-Bohm effect | 11,324 |
We analyze a second order, linear, elliptic PDE with mixed boundary conditions. This problem arose as a limiting case of a Markov-modulated queueing model for data handling switches in communications networks. We use singular perturbation methods to analyze the problem. In particular we use the ray method to solve the PDE in the limit where convection dominates diffusion. We show that there are both interior and boundary caustics, as well as a cusp point where two caustics meet, an internal layer, boundary layers and a corner layer. Our analysis leads to approximate formulas for the queue length (or buffer content) distribution at the switch. | Ray solution of a singularly perturbed elliptic PDE with applications to
communications networks | 11,325 |
It is shown that large classes of nonlinear systems of PDEs, with possibly associated initial and/or boundary value problems, can be solved by the method of order completion. The solutions obtained can be assimilated with Hausdorff continuous functions. The usual Navier-Stokes equations, as well as their various modifications aiming at a realistic modelling are included as particular cases. The same holds for the critically important constitutive relations in various branches of Continuum Mechanics. The solution method does not involve functional analysis, nor various Sobolev or other spaces of distributions or generalized functions. The general and type independent existence and regularity results regarding solutions presented here are a first in the literature. | Solving large classes of nonlinear systems of PDEs | 11,326 |
We consider 1D completely resonant nonlinear wave equations of the type v_{tt}-v_{xx}=-v^3+O(v^4) with spatial periodic boundary conditions. We prove the existence of a new type of quasi-periodic small amplitude solutions with two frequencies, for more general nonlinearities. These solutions turn out to be, at the first order, the superposition of a traveling wave and a modulation of long period, depending only on time. | Quasi-periodic solutions of the equation v_{tt}-v_{xx}+v^3=f(v) | 11,327 |
We establish the uniqueness of the positive solution for equations of the form $-\Delta u=au-b(x)f(u)$ in $\Omega$, $u|\_{\partial\Omega}=\infty$. The special feature is to consider nonlinearities $f$ whose variation at infinity is \emph{not regular} (e.g., $\exp(u)-1$, $\sinh(u)$, $\cosh(u)-1$, $\exp(u)\log(u+1)$, $u^\beta \exp(u^\gamma)$, $\beta\in {\mathbb R}$, $\gamma>0$ or $\exp(\exp(u))-e$) and functions $b\geq 0$ in $\Omega$ vanishing on $\partial\Omega$. The main innovation consists of using Karamata's theory not only in the statement/proof of the main result but also to link the non-regular variation of $f$ at infinity with the blow-up rate of the solution near $\partial\Omega$. | Boundary blow-up in nonlinear elliptic equations of
Bieberbach--Rademacher type | 11,328 |
We study the uniqueness and expansion properties of the positive solution of the logistic equation $\Delta u+au=b(x)f(u)$ in a smooth bounded domain $\Omega$, subject to the singular boundary condition $u=+\infty$ on $\partial\Omega$. The absorption term $f$ is a positive function satisfying the Keller--Osserman condition and such that the mapping $f(u)/u$ is increasing on $(0,+\infty)$. We assume that $b$ is non-negative, while the values of the real parameter $a$ are related to an appropriate semilinear eigenvalue problem. Our analysis is based on the Karamata regular variation theory. | Nonlinear problems with boundary blow-up: a Karamata regular variation
theory approach | 11,329 |
We consider a system of weakly coupled singularly perturbed semilinear elliptic equations. First, we obtain a Lipschitz regularity result for the associated ground energy function $\Sigma$ as well as representation formulas for the left and the right derivatives. Then, we show that the concentration points of the solutions locate close to the critical points of $\Sigma$ in the sense of subdifferential calculus. | Locating the peaks of semilinear elliptic systems | 11,330 |
This article is devoted to obtain the $\Gamma$-limit, as $\epsilon$ tends to zero, of the family of functionals $$F_{\epsilon}(u)=\int_{\Omega}f\Bigl(x,\frac{x}{\epsilon},..., \frac{x}{\epsilon^n},\nabla u(x)\Bigr)dx$$, where $f=f(x,y^1,...,y^n,z)$ is periodic in $y^1,...,y^n$, convex in $z$ and satisfies a very weak regularity assumption with respect to $x,y^1,...,y^n$. We approach the problem using the multiscale Young measures. | Multiscale homogenization of convex functionals with discontinuous
integrand | 11,331 |
Investigating for interior regularity of viscosity solutions to the fully nonlinear elliptic equation $$F(x,u,\triangledown u,\triangledown ^2 u)=0,$$ we establish the interior $C^{1+1}$ continuity under the assumptions that $F$ is uniformly elliptic, H$\ddot o$lder continuous and satisfies the natural structure conditions of fractional order, but without the concavity assumption of $F$. These assumptions are weaker and the result is stronger than that of Caffarelli and Wang[1], Chen[2]. | The Second Order Estimate for Fully Nonlinear Uniformly Elliptic
Equations without Concavity Assumption | 11,332 |
This paper deals with a class of nonlinear elliptic equations involving a critical power-nonlinearity as well as a potential featuring multiple inverse square singularities. When the poles form a symmetric structure, it is natural we wonder how the symmetry affects such mutual interaction. The present paper means to study this aspect from the point of view of the existence of solutions inheriting the same symmetry properties as the set of singularities. | Nonlinear Schrodinger equations with symmetric multi-polar potentials | 11,333 |
We study the homogenization of a diffusion process which takes place in a binary structure formed by an ambiental connected phase surrounding a suspension of very small spheres distributed in an $\veps$-periodic network. The asymptotic distribution of the concentration is determined for both phases, as $\veps\to 0$, assuming that the suspension has mass of unity order and vanishing volume. Three cases are distinguished according to the values of a certain limit capacity. When it is positive and finite, the macroscopic system involves a two-concentration system, coupled through a term accounting for the non local effects. In the other two cases, where the capacity is either infinite or going to zero, although the form of the system is much simpler, some peculiar effects still account for the presence of the suspension. | Homogenization of a diffusion process in a rarefied binary structure | 11,334 |
We develop the existence, uniqueness, continuity, stability, and scattering theory for energy-critical nonlinear Schr\"odinger equations in dimensions $n \geq 3$, for solutions which have large, but finite, energy and large, but finite, Strichartz norms. For dimensions $n \leq 6$, this theory is a standard extension of the small data well-posedness theory based on iteration in Strichartz spaces. However, in dimensions $n > 6$ there is an obstruction to this approach because of the subquadratic nature of the nonlinearity (which makes the derivative of the nonlinearity non-Lipschitz). We resolve this by iterating in exotic Strichartz spaces instead. The theory developed here will be applied in a subsequent paper of the second author, to establish global well-posedness and scattering for the defocusing energy-critical equation for large energy data. | Stability of energy-critical nonlinear Schrödinger equations in high
dimensions | 11,335 |
In this note we consider a free discontinuity problem for a scalar function, whose energy depends also on the size of the jump. We prove that the gradient of every smooth local minimizer never exceeds a constant, determined only by the data of the problem. | Gradient bounds for minimizers of free discontinuity problems related to
cohesive zone models in fracture mechanics | 11,336 |
We study a class of elastic systems described by a (hyperbolic) partial differential equation. Our working example is the equation of a vibrating string subject to linear disturbance. The main goal is to establish conditions for stabilization and asymptotic stabilization by applying a fast oscillating control to the string. In the first situation studied we assume that system is subject to a damping force; next we consider the system without damping. We extend the tools of high-order averaging and of chronological calculus for studying stability of this distributed parameter system. | On stability and stabilization of elastic systems by time-variant
feedback | 11,337 |
We prove local well-posedness of the initial-boundary value problem for the Korteweg-de Vries equation on the right half-line, left half-line, and line segment, in the low regularity setting. This is accomplished by introducing an analytic family of boundary forcing operators, extending the techniques of Colliander-Kenig (2002). | The initial-boundary value problem for the Korteweg-de Vries equation | 11,338 |
We study solvability of the {\it generalized Possio integral equation} - a tool in analysis of a boundary value problem in 2D subsonic aeroelasticity with the Kutta-Joukowski condition - {\it "zero pressure discontinuity"} - $\psi(x,0,t)=0$ on the complement of a finite interval in the whole real line $\R$. The corresponding problem with boundary condition on finite intervals adjacent to the "chord" was considered in \cite{P}. | Solvability of the generalized Possio equation in 2D subsonic
aeroelasticity | 11,339 |
The extended principle of minimal action is described in the presence of prescribed source and sink points. Under the assumption of zero net flux, it leads to an optimal Monge-Kantorovich transport problem of metric type. We concentrate on action corresponding to a mecahnical Lagrangian. The optimal solution turns out to be a measure supprted on a graph composed of geodesic arcs connecting pairs of sources and sinks. | Extended least action principle for steady flows under a prescribed flux | 11,340 |
We show that the celebrated 1956 Lax-Richtmyer linear theorem in Numerical Analysis - often called the Fundamental Theorem of Numerical Analysis - is in fact wrong. Here "wrong" does not mean that its statement is false mathematically, but that it has a limited practical relevance as it misrepresents what actually goes on in the numerical analysis of partial differential equations. Namely, the assumptions used in that theorem are excessive to the extent of being unrealistic from practical point of view. The two facts which the mentioned theorem gets wrong from practical point of view are : - the relationship between the convergence and stability of numerical methods for linear PDEs, - the effect of the propagation of round-off errors in such numerical methods. The mentioned theorem leads to a result for PDEs which is unrealistically better than the well known best possible similar result in the numerical analysis of ODEs. Strangely enough, this fact seems not to be known well enough in the literature. Once one becomes aware of the above, new avenues of both practical and theoretical interest can open up in the numerical analysis of PDEs. | What is wrong with the Lax-Richtmyer fundamental theorem of linear
numerical analysis ? | 11,341 |
We prove a regularity result for the unstable elliptic free boundary problem $\Delta u = -\chi_{\{u>0\}}$ related to traveling waves in a problem arising in solid combustion. The maximal solution and every local minimizer of the energy are regular, that is, $\{u=0\}$ is locally an analytic surface and $u|_{\bar{\{u>0\}}}, u|_{\bar{\{u<0\}}}$ are locally analytic functions. Moreover we prove a partial regularity result for solutions that are non-degenerate of second order: here $\{u=0\}$ is analytic up to a closed set of Hausdorff dimension $n-2$. We discuss possible singularities. | An Unstable Elliptic Free Boundary Problem arising in Solid Combustion | 11,342 |
We derive upper bounds for the number of asymptotic degrees (determining modes and nodes) of freedom for the two-dimensional Navier--Stokes system and Navier-Stokes system with damping. In the first case we obtain the previously known estimates in an explicit form, which are larger than the fractal dimension of the global attractor. However, for the Navier--Stokes system with damping our estimates for the number of the determining modes and nodes are comparable to the sharp estimates for the fractal dimension of the global attractor. Our investigation of the damped-driven 2D Navier--Stokes system is inspired by the Stommel--Charney barotropic model of ocean circulation where the damping represents the Rayleigh friction. We remark that our results equally apply to the Stommel--Charney model. | Sharp estimates for the number of degrees of freedom for the
damped-driven 2D Navier--Stokes equations | 11,343 |
A new mathematical model for the dynamics of prion proliferation involving an ordinary differential equation coupled with a partial integro-differential equation is analyzed, continuing earlier work. We show the well-posedness of this problem in a natural phase space, i.e. there is a unique global semiflow in the phase space associated to the problem. A theorem of threshold type is derived for this model which is typical for mathematical epidemics. If a certain combination of kinetic parameters is below or at the threshold, there is a unique steady state, the disease-free equilibrium, which is globally asymptotically stable; above the threshold it is unstable, and there is another unique steady state, the disease equilibrium, which inherits that property. | Analysis of a model for the dynamics of prions II | 11,344 |
The L^2 -critical defocusing nonlinear Schrodinger initial value problem on R^d is known to be locally well-posed for initial data in L^2. Hamiltonian conservation and the pseudoconformal transformation show that global well-posedness holds for initial data u_0 in Sobolev H^1 and for data in the weighted space (1+|x|) u_0 in L^2. For the d=2 problem, it is known that global existence holds for data in H^s and also for data in the weighted space (1+|x|)^{\sigma} u_0 in L^2 for certain s, \sigma < 1. We prove: If global well-posedness holds in H^s then global existence and scattering holds for initial data in the weighted space with \sigma = s. | Global well-posedness in Sobolev space implies global existence for
weighted L^2 initial data for L^2 -critical NLS | 11,345 |
We prove two new results about the Cauchy problem for nonlinear Schroedinger equations on four-dimensional compact manifolds. The first one concerns global wellposedness for Hartree-type nonlinearities and includes approximations of cubic NLS on the sphere. The second one provides local wellposedness for quadratic nonlinearities in the case of zonal data on the sphere. Both results are based on new multilinear Strichartz-type estimates for the Schroedinger group. | Nonlinear Schrödinger equation on four-dimensional compact manifolds | 11,346 |
We consider the $2 \times 2$ parabolic systems \begin{equation*} u^{\epsilon}_t + A(u^{\epsilon}) u^{\epsilon}_x = \epsilon u^{\epsilon}_{xx} \end{equation*} on a domain $(t, x) \in ]0, + \infty[ \times ]0, l[$ with Dirichlet boundary conditions imposed at $x=0$ and at $x=l$. The matrix $A$ is assumed to be in triangular form and strictly hyperbolic, and the boundary is not characteristic, i.e. the eigenvalues of $A$ are different from 0. We show that, if the initial and boundary data have sufficiently small total variation, then the solution $u^{\epsilon}$ exists for all $t \geq 0$ and depends Lipschitz continuously in $L^1$ on the initial and boundary data. Moreover, as $\epsilon \to 0^+$, the solutions $u^{\epsilon}(t)$ converge in $L^1$ to a unique limit $u(t)$, which can be seen as the vanishing viscosity solution of the quasilinear hyperbolic system \begin{equation*} u_t + A(u)u_x = 0, \quad x \in ]0, l[. \end{equation*} This solution $u(t)$ depends Lipschitz continuously in $L^1$ w.r.t the initial and boundary data. We also characterize precisely in which sense the boundary data are assumed by the solution of the hyperbolic system. 2000 Mathematics Subject Classification: 35L65. Key words: Hyperbolic systems, conservation laws, initial boundary value problems, viscous approximations. | Vanishing viscosity solutions of a $2 \times 2$ triangular hyperbolic
system with Dirichlet conditions on two boundaries | 11,347 |
We consider the inverse problem for the second order self-adjoint hyperbolic equation in a bounded domain in $\R^n$ with lower order terms depending analytically on the time variable. We prove that, assuming the BLR condition, the time-dependent Dirichlet-to-Neumann operator prescribed on a part of the boundary uniquely determines the coefficients of the hyperbolic equation up to a diffeomorphism and a gauge transformation. As a by-product we prove a similar result for the nonself-adjoint hyperbolic operator with time-independent coefficients. | Inverse hyperbolic problems with time-dependent coefficients | 11,348 |
We investigate singular and degenerate behavior of solutions of the unstable free boundary problem $$\Delta u = -\chi_{\{u>0\}} .$$ First, we construct a solution that is not of class $C^{1,1}$ and whose free boundary consists of four arcs meeting in a {\em cross}-shaped singularity. This solution is completely unstable/repulsive from above and below which would make it hard to get by the usual methods, and even numerics is non-trivial. We also show existence of a degenerate solution. This answers two of the open questions in a recent paper by R. Monneau-G.S. Weiss. | Cross-shaped and Degenerate Singularities in an Unstable Elliptic Free
Boundary Problem | 11,349 |
We establish that the quadratic non-linear Schr\"odinger equation $$ iu_t + u_{xx} = u^2$$ where $u: \R \times \R \to \C$, is locally well-posed in $H^s(\R)$ when $s \geq -1$ and ill-posed when $s < -1$. Previous work of Kenig, Ponce and Vega had established local well-posedness for $s > -3/4$. The local well-posedness is achieved by an iteration using a modification of the standard $X^{s,b}$ spaces. The ill-posedness uses an abstract and general argument relying on the high-to-low frequency cascade present in the non-linearity, and a computation of the first non-linear iterate. | Sharp well-posedness and ill-posedness results for a quadratic
non-linear Schrödinger equation | 11,350 |
This note is a continuation of the previous paper math.AP/0411383 by the same authors. Its purpose is to extend the results of math.AP/0411383 to the context of root systems with even multiplicities. Under the even multiplicity assumption, we prove a local Paley-Wiener theorem for the Jacobi transform and the strong Huygens' principle for the wave equation associated with the modified compact Laplace operator. | The Paley-Wiener Theorem for the Jacobi Transform and the Local Huygens'
Principle for Root Systems with Even Multiplicities | 11,351 |
We solve variationally certain equations of stellar dynamics of the form $-\sum_i\partial_{ii} u(x) =\frac{|u|^{p-2}u(x)}{{\rm dist} (x,{\mathcal A} )^s}$ in a domain $\Omega$ of $\rn$, where ${\mathcal A} $ is a proper linear subspace of $\rn$. Existence problems are related to the question of attainability of the best constant in the following recent inequality of Badiale-Tarantello [1]: $$0<\mu_{s,\P}(\Omega)=\inf{\int_{\Omega}|\nabla u|^2 dx; u\in \huno \hbox{and}\int_{\Omega}\frac{|u(x)|^{\crit(s)}}{|\pi(x)|^s} dx=1}$$ where $0<s<2$, $\crit(s)=\frac{2(n-s)}{n-2}$ and where $\pi$ is the orthogonal projection on a linear space $\P$, where $\hbox{dim}_{\rr}\P \geq 2$. We investigate this question and how it depends on the relative position of the subspace $\Porth$, the orthogonal of $\P$, with respect to the domain $\Omega$ as well as on the curvature of the boundary $\partial\Omega$ at its points of intersection with $\Porth $. | Elliptic Equations with Critical Growth and a Large Set of Boundary
Singularities | 11,352 |
We use a new variational method --based on the theory of anti-selfdual Lagrangians developed in [2] and [3]-- to establish the existence of solutions of convex Hamiltonian systems that connect two given Lagrangian submanifolds in $\R^{2N}$. We also consider the case where the Hamiltonian is only semi-convex. A variational principle is also used to establish existence for the corresponding Cauchy problem. The case of periodic solutions will be considered in a forthcoming paper [5]. | On the existence of Hamiltonian paths connecting Lagrangian submanifolds | 11,353 |
Radiant spherical suspensions have an $\veps$-periodic distribution in a tridimensional incompressible viscous fluid governed by the Stokes-Boussinesq system. We perform the homogenization procedure when the radius of the solid spheres is of order $\veps^3$ (the critical size of perforations for the Navier-Stokes system) and when the ratio of the fluid/solid conductivities is of order $\veps^6$, the order of the total volume of suspensions. Adapting the methods used in the study of small inclusions, we prove that the macroscopic behavior is described by a Brinkman-Boussinesq type law and two coupled heat equations, where certain capacities of the suspensions and of the radiant sources appear. | Asymptotics of a thermal flow with highly conductive and radiant
suspensions | 11,354 |
We give a condition for the periodic, three dimensional, incompressible Navier-Stokes equations to be globally wellposed. This condition is not a smallness condition on the initial data, as the data is allowed to be arbitrarily large in the scale invariant space $ B^{-1}\_{\infty,\infty}$, which contains all the known spaces in which there is a global solution for small data. The smallness condition is rather a nonlinear type condition on the initial data; an explicit example of such initial data is constructed, which is arbitrarily large and yet gives rise to a global, smooth solution. | On the global wellposedness of the 3-D Navier-Stokes equations with
large initial data | 11,355 |
Answering a question left open in \cite{MZ2}, we show for general symmetric hyperbolic boundary problems with constant coefficients, including in particular systems with characteristics of variable multiplicity, that the uniform Lopatinski condition implies strong $L^2$ well-posedness, with no further structural assumptions. The result applies, more generally, to any system that is strongly $L^2$ well-posed for at least one boundary condition. The proof is completely elementary, avoiding reference to Kreiss symmetrizers or other specific techniques. On the other hand, it is specific to the constant-coefficient case; at least, it does not translate in an obvious way to the variable-coefficient case. The result in the hyperbolic case is derived from a more general principle that can be applied, for example, to parabolic or partially parabolic problems like the Navier-Stokes or viscous MHD equations linearized about a constant state or even a viscous shock. | Uniform stability estimates for constant-coefficient symmetric
hyperbolic boundary value problems | 11,356 |
We consider the spectral semi-Galerkin method applied to the nonhomogeneous Navier-Stokes equations. Under certain conditions it is known that the approximate solutions constructed through this method converge to a global strong solution of these equations. Here, we derive an optimal uniform in time error estimate in the $H^1$ norm for the velocity. We also derive an error estimate for the density in some spaces $L^r$. | Error bounds for semi-Galerkin approximations of nonhomogeneous
incompressible fluids | 11,357 |
This expository article is intended to give an overview about recently achieved results on asymptotic properties of solutions to the Cauchy problem $u_{tt}-\Delta u+b(t)u_t =0,\qquad u(0,\cdot)=u_1,\quad \mathrm{D}_tu(0,\cdot)=u_2$ for a wave equation with time-dependent dissipation term. The results are based on structural properties of the Fourier multipliers representing its solution. The article explains the general philosophy behind the approach. | $L^p$--$L^q$ decay estimates for wave equations with monotone
time-dependent dissipation | 11,358 |
Refining previous work in \cite{Z.3, MaZ.3, Ra, HZ, HR}, we derive sharp pointwise bounds on behavior of perturbed viscous shock profiles for large-amplitude Lax or overcompressive type shocks and physical viscosity. These extend well-known results of Liu \cite{Liu97} obtained by somewhat different techniques for small-amplitude Lax type shocks and artificial viscosity, completing a program set out in \cite{ZH}. As pointed out in \cite{Liu91, Liu97}, the key to obtaining sharp bounds is to take account of cancellation associated with the property that the solution decays faster along characteristic than in other directions. Thus, we must here estimate characteristic derivatives for the entire nonlinear perturbation, rather than judicially chosen parts as in \cite{Ra, HR}. a requirement that greatly complicates the analysis. | Sharp pointwise bounds for perturbed viscous shock waves | 11,359 |
We study local bifurcation from an eigenvalue with multiplicity greater than one for a class of semilinear elliptic equations. We evaluate the exact number of bifurcation branches of non trivial solutions and we compute the Morse index of the solutions in those branches. | On the exact number of bifurcation branches from a multiple eigenvalue | 11,360 |
We study the heat equation associated to a multiplicity function on a root system, where the corresponding Laplace operator has been defined by Heckman and Opdam. In particular, we describe the image of the associated Segal-Bargmann transform as a space of holomorphic functions. In the case where the multiplicity function corresponds to a Riemannian symmetric space G/K of noncompact type, we obtain a description of the image of the space of K-invariant L^2-function on G/K under the Segal-Bargmann transform associated to the heat equation on G/K, thus generalizing (and reproving) a result of B. Hall for spaces of complex type. | The Segal-Bargmann transform for the heat equation associated with root
systems | 11,361 |
We prove existence of solutions for the Benjamin-Ono equation with data in $H^s(\R)$, $s>0$. Thanks to conservation laws, this yields global solutions for $H^\frac 1 2(\R)$ data, which is the natural ``finite energy'' class. Moreover, inconditional uniqueness is obtained in $L^\infty_t(H^\frac 1 2(\R))$, which includes weak solutions, while for $s>\frac 3 {20}$, uniqueness holds in a natural space which includes the obtained solutions. | On well-posedness for the Benjamin-Ono equation | 11,362 |
We study uniqueness properties of solutions of Schr\"odinger equations. The aim is to obtain sufficient conditions on the decay behavior of the difference of two solution $u_1-u_2$ of the equation at two different times $t_0=0$ and $t_1=1$ which guarantee the uniqueness of the solution, i.e. that $u_1\equiv u_2$. | On unique continuation of solutions of Schrödinger equations | 11,363 |
We consider solutions to linear parabolic equations with initial data decaying at spatial infinity. For a class of advection-diffusion equations with a spatially dependent velocity field, we study the behavior of solutions as time tends to infinity. We characterize velocity fields, so that positive solutions decay or lift-off at spatial infinity as time tends to infinity. This addresses the question of stability of the zero solution for decaying perturbations. | Decay at infinity for parabolic equations | 11,364 |
A bilinear estimate in Fourier restriction norm spaces with applications to the Cauchy problem associated to u_t - |D|^{\alpha}u_x + uu_x =0 is proved, for 1< \alpha <2. As a consequence, local well-posedness in H^s(\R) \cap \dot{H}^{-\omega}(\R) follows for s >-{3/4}(\alpha-1) and \omega=1/\alpha-1/2. This extends to global well-posedness for all s \geq 0. | An improved bilinear estimate for Benjamin-Ono type equations | 11,365 |
We establish the variational principle of Kolmogorov-Petrovsky-Piskunov (KPP) front speeds in temporally random shear flows inside an infinite cylinder, under suitable assumptions of the shear field. A key quantity in the variational principle is the almost sure Lyapunov exponent of a heat operator with random potential. The variational principle then allows us to bound and compute the front speeds. We show the linear and quadratic laws of speed enhancement as well as a resonance-like dependence of front speed on the temporal shear correlation length. To prove the variational principle, we use the comparison principle of solutions, the path integral representation of solutions, and large deviation estimates of the associated stochastic flows. | Variational Principle of KPP Front Speeds in Temporally Random Shear
Flows | 11,366 |
We study the convergence of a Finite Volume scheme for the linear advection equation with a Lipschitz divergence-free speed in $\R^d$. We prove a $h^{1/2}$-error estimate in the $L^\infty(0,t;L^1)$-norm for $BV$ data. This result was expected from numerical experiments and is optimal. | Error estimate for the Finite Volume Scheme applied to the advection
equation | 11,367 |
We investigate nonlinear dynamics near an unstable constant equilibrium in the classical Keller-Segel model. Given any general perturbation of magnitude $\delta$, we prove that its nonlinear evolution is dominated by the corresponding linear dynamics along a fixed finite number of fastest growing modes, over a time period of $ln(1/\delta)$. Our result can be interpreted as a rigourous mathematical characterization for early pattern formation in the Keller-Segel model. | Pattern formation (I): The Keller-Segel Model | 11,368 |
We prove global, scale invariant Strichartz estimates for the linear magnetic Schr\"odinger equation with small time dependent magnetic field. This is done by constructing an appropriate parametrix. As an application, we show a global regularity type result for Schr\"odinger maps in dimensions $n\geq 6$. | Strichartz estimates for the magnetic Schrödinger equation | 11,369 |
In this paper, we prove almost global existence of solutions to certain quasilinear wave equations with quadratic nonlinearities in infinite homogeneous waveguides with Neumann boundary conditions. We use a Galerkin method to expand the Laplacian of the compact base in terms of its eigenfunctions. For those terms corresponding to zero modes, we obtain decay using analogs of estimates of Klainerman and Sideris. For the nonzero modes, estimates for Klein-Gordon equations, which provide better decay, are available. | Almost global existence for quasilinear wave equations in waveguides
with Neumann boundary conditions | 11,370 |
In this work we study the asymptotic behavior of viscous incompressible 2D flow in the exterior of a small material obstacle. We fix the initial vorticity $\omega_0$ and the circulation $\gamma$ of the initial flow around the obstacle. We prove that, if $\gamma$ is sufficiently small, the limit flow satisfies the full-plane Navier-Stokes system, with initial vorticity $\omega_0 + \gamma \delta$, where $\delta$ is the standard Dirac measure. The result should be contrasted with the corresponding inviscid result obtained by the authors in [Comm P.D.E. 28 (2003) 349-379], where the effect of the small obstacle appears in the coefficients of the PDE and not only on the initial data. The main ingredients of the proof are $L^p-L^q$ estimates for the Stokes operator in an exterior domain, a priori estimates inspired on Kato's fixed point method, energy estimates, renormalization and interpolation. | Two-dimensional incompressible viscous flow around a small obstacle | 11,371 |
We study nonlinear dispersive wave systems described by hyperbolic PDE's in R^{d} and difference equations on the lattice Z^{d}. The systems involve two small parameters: one is the ratio of the slow and the fast time scales, and another one is the ratio of the small and the large space scales. We show that a wide class of such systems, including nonlinear Schrodinger and Maxwell equations, Fermi-Pasta-Ulam model and many other not completely integrable systems, satisfy a superposition principle. The principle essentially states that if a nonlinear evolution of a wave starts initially as a sum of generic wavepackets (defined as almost monochromatic waves), then this wave with a high accuracy remains a sum of separate wavepacket waves undergoing independent nonlinear evolution. The time intervals for which the evolution is considered are long enough to observe fully developed nonlinear phenomena for involved wavepackets. In particular, our approach provides a simple justification for numerically observed effect of almost non-interaction of solitons passing through each other without any recourse to the complete integrability. Our analysis does not rely on any ansatz or common asymptotic expansions with respect to the two small parameters but it uses rather explicit and constructive representation for solutions as functions of the initial data in the form of functional analytic series. | Linear superposition in nonlinear wave dynamics | 11,372 |
It is shown that a function $u$ satisfying, $|\Delta u+\partial_tu|\le M(|u|+|\nabla u|)$, $|u(x,t)|\le Me^{M|x|^2}$ in $\R^n\times [0,T]$ and $|u(x,0)|\le C_ke^{-k|x|^2}$ in $\R^n$ and for all $k\ge 1$, must vanish identically in $\R^n\times [0,T]$. | Decay at infinity of caloric functions within characteristic hyperplanes | 11,373 |
We study local in time Strichartz estimates for the Schroedinger equation associated to long range perturbations of the flat Laplacian on the euclidean space. We prove that in such a geometric situation, outside of a large ball centered at the origin, the solutions of the Schroedinger equation enjoy the same Strichartz estimates as in the non perturbed situation. The proof is based on the Isozaki-Kitada parametrix construction. If in addition the metric is non trapping, we prove that the Strichartz estimates hold in the whole space. | Strichartz estimates for long range perturbations | 11,374 |
Selfdual variational principles are introduced in order to construct solutions for Hamiltonian and other dynamical systems which satisfy a variety of linear and nonlinear boundary conditions including many of the standard ones. These principles lead to new variational proofs of the existence of parabolic flows with prescribed initial conditions, as well as periodic, anti-periodic and skew-periodic orbits of Hamiltonian systems. They are based on the theory of anti-selfdual Lagrangians introduced and developed recently in [3], [4] and [5]. | Selfdual Variational Principles for Periodic Solutions of Hamiltonian
and Other Dynamical Systems | 11,375 |
We analyze the nonlinear elliptic problem $\Delta u=\frac{\lambda f(x)}{(1+u)^2}$ on a bounded domain $\Omega$ of $\R^N$ with Dirichlet boundary conditions. This equation models a simple electrostatic Micro-Electromechanical System (MEMS) device consisting of a thin dielectric elastic membrane with boundary supported at 0 above a rigid ground plate located at -1. When a voltage --represented here by $\lambda$-- is applied, the membrane deflects towards the ground plate and a snap-through may occur when it exceeds a certain critical value $\lambda^*$ (pull-in voltage). This creates a so-called "pull-in instability" which greatly affects the design of many devices. The mathematical model lends to a nonlinear parabolic problem for the dynamic deflection of the elastic membrane which will be considered in forthcoming papers \cite{GG2} and \cite{GG3}. For now, we focus on the stationary equation where the challenge is to estimate $\lambda^*$ in terms of material properties of the membrane, which can be fabricated with a spatially varying dielectric permittivity profile $f$. Applying analytical and numerical techniques, the existence of $\lambda^*$ is established together with rigorous bounds. We show the existence of at least one steady-state when $\lambda < \lambda^*$ (and when $\lambda=\lambda^*$ in dimension $N< 8$) while none is possible for $\lambda>\lambda^*$. More refined properties of steady states --such as regularity, stability, uniqueness, multiplicity, energy estimates and comparison results-- are shown to depend on the dimension of the ambient space and on the permittivity profile. | On the Partial Differential Equations of Electrostatic MEMS Devices:
Stationary Case | 11,376 |
We prove almost optimal local well-posedness for the coupled Dirac-Klein-Gordon (DKG) system of equations in 1+3 dimensions. The proof relies on the null structure of the system, combined with bilinear spacetime estimates of Klainerman-Machedon type. It has been known for some time that the Klein-Gordon part of the system has a null structure; here we uncover an additional null structure in the Dirac equation, which cannot be seen directly, but appears after a duality argument. | Null structure and almost optimal local well-posedness of the
Dirac-Klein-Gordon system | 11,377 |
We study the homogeneous elliptic systems of order $2\ell$ with real constant coefficients on Lipschitz domains in $R^n$, $n\ge 4$. For any fixed $p>2$, we show that a reverse H\"older condition with exponent $p$ is necessary and sufficient for the solvability of the Dirichlet problem with boundary data in $L^p$. We also obtain a simple sufficient condition. As a consequence, we establish the solvability of the $L^p$ Dirichlet problem for $n\ge 4$ and $2-\e< p<\frac{2(n-1)}{n-3} +\e$. The range of $p$ is known to be sharp if $\ell\ge 2$ and $4\le n\le 2\ell +1$. For the polyharmonic equation, the sharp range of $p$ is also found in the case $n=6$, 7 if $\ell=2$, and $n=2\ell+2$ if $\ell\ge 3$. | Necessary and Sufficient Conditions for the Solvability of the $L^p$
Dirichlet Problem On Lipschitz Domains | 11,378 |
We study enhancement of diffusive mixing on a compact Riemannian manifold by a fast incompressible flow. Our main result is a sharp description of the class of flows that make the deviation of the solution from its average arbitrarily small in an arbitrarily short time, provided that the flow amplitude is large enough. The necessary and sufficient condition on such flows is expressed naturally in terms of the spectral properties of the dynamical system associated with the flow. In particular, we find that weakly mixing flows always enhance dissipation in this sense. The proofs are based on a general criterion for the decay of the semigroup generated by an operator of the form G+iAL with a negative unbounded self-adjoint operator G, a self-adjoint operator L, and parameter A >> 1. In particular, they employ the RAGE theorem describing evolution of a quantum state belonging to the continuous spectral subspace of the hamiltonian (related to a classical theorem of Wiener on Fourier transforms of measures). Applications to quenching in reaction-diffusion equations are also considered. | Diffusion and Mixing in Fluid Flow | 11,379 |
We study analytically and numerically a model describing front propagation of a KPP reaction in a fluid flow. The model consists of coupled one-dimensional reaction-diffusion equations with different drift coefficients. The main rigorous results give lower bounds for the speed of propagation that are linear in the drift coefficient, which agrees very well with the numerical observations. In addition, we find the optimal constant in a functional inequality of independent interest used in the proof. | Enhancement of combustion by drift in a coupled reaction-diffusion model | 11,380 |
We consider the Schroedinger operator in R^3 with N point interactions placed at Y=(y_1, ... ,y_N), y_j in R^3, of strength a=(a_1, ... ,a_N). Exploiting the spectral theorem and the rather explicit expression for the resolvent we prove a (weighted) dispersive estimate for the corresponding Schroedinger flow. In the special case N=1 the proof is directly obtained from the unitary group which is known in closed form. | Dispersive estimate for the Schroedinger equation with point
interactions | 11,381 |
Using Maz'ya type integral identities with power weights, we obtain new boundary estimates for biharmonic functions on Lipschitz and convex domains in $R^n$. For $n\ge 8$, combined with a result in \cite{S2}, these estimates lead to the solvability of the $L^p$ Dirichlet problem for the biharmonic equation on Lipschitz domains for a new range of $p$. In the case of convex domains, the estimates allow us to show that the $L^p$ Dirichlet problem is uniquely solvable for any $2-\e<p<\infty$ and $n\ge 4$. | On Estimates of Biharmonic Functions on Lipschitz and Convex Domains | 11,382 |
Let $u_t-u_{xx}=h(t)$ in $0\leq x \leq \pi, t\geq 0.$ Assume that $u(0,t)=v(t)$, $u(\pi,t)=0$, and $u(x,0)=g(t)$. The problem is: {\it what extra data determine the three unknown functions $\{h, v, g\}$ uniquely?}. This question is answered and an analytical method for recovery of the above three functions is proposed. | Inverse problems for parabolic equations 2 | 11,383 |
In this note we prove that any $W^{1,2}$ mapping $u$ in the plane that minimizes an appropriate quasiconvex energy functional subject to the Jacobian constraint ${\rm det} \na u=1$ a.e., are necessarily Lipschitz. Furthermore we show that the minimizers corresponding to uniformly convex energy are affine and give an example of non-affine minimizers subject to affine boundary data corresponding to a convex energy. We also discuss the regularity issues in dimension greater than or equal to 3. | A note on the smoothness of energy-minimizing incompressible
deformations | 11,384 |
With derive sharp spectral asymptotics (with the remainder estimate $O(\mu ^{-1}h^{1-d}+\mu ^{\frac{d} {2}-1}h^{1-\frac{d}{2}})$ for $d$-dimensional Schr\"odinger operator with a strong magnetic field; here $h$ and $\mu$ are Plank and binding constants respectively and magnetic intensity matrix has full rank at each point. In comparison with version 1 of 4.5 year ago this version contains more results (we also study some degenerations), improvements and some minor corrections. | Sharp Spectral Asymptotics for Operators with Irregular Coefficients.
IV. Multidimensional Schroedinger operator with a strong magnetic field.
Full-rank case | 11,385 |
This paper provides an extension for a function $u \in BV_H(\Omega)$ to a function $u_0 \in BV_H(G)$ when $\Omega$ is ``H-admissible,'' and G is a step 2 Carnot group. It is shown that H-admissible domains include non-characteristic domains and domains in groups of Heisenberg type which have a partial symmetry about characteristic points. An example is given of a domain that is $C^{1,\alpha}$, $\alpha <1$, that is not H-admissible. Further, when $\Omega$ is H-admissible a trace theorem is proved for $u \in BV_H(\Omega)$. | An extension and trace theorem for functions of H-bounded variation in
Carnot groups of step 2 | 11,386 |
Given two elliptic operators L and M in nondivergence form, with coefficients A_L(x), A_M(x) and drift terms b_L(x), b_M(x), respectively, satisfying a Carleson measure disagreement condition in a Lipschitz domain Omega in R^{n+1}, then their harmonic measures are mutually absolutely continuous. As an application of this, a new approximation argument and known results we obtain necessary and sufficient conditions for a single operator L (in divergence or nondivergence form) to have regular harmonic measure with respect to Lebesgue measure. The results are sharp in all cases. | The Dirichlet problem for elliptic equations in divergence and
nondivergence form with singular drift term | 11,387 |
We consider the classical Turing instability in a reaction-diffusion system as the secend part of our study on pattern formation. We prove that nonlinear dynamics of a general perturbation of the Turing instability is determined by the finite number of linear growing modes over a time scale of $ln(1/\delta)$, where &\delta$ is the strength of the initial perturbation. | Pattern formation (II): The Turing Instability | 11,388 |
We generalize work of Oh & Zumbrun and Serre on spectral stability of spatially periodic traveling waves of systems of viscous conservation laws from the one-dimensional to the multi-dimensional setting. Specifically, we extend to multi-dimensions the connection observed by Serre between the linearized dispersion relation near zero frequency of the linearized equations about the wave and the homogenized system obtained by slow modulation (WKB) approximation. This may be regarded as partial justification of the WKB expansion; an immediate consequence is that hyperbolicity of the multi-dimensional homogenized system is a necessary condition for stability of the wave. As pointed out by Oh & Zumbrun in one dimension, description of the low-frequency dispersion relation is also a first step in the determination of time-asymptotic behavior. | Low-frequency stability analysis of periodic traveling-wave solutions of
viscous conservation laws in several dimensions | 11,389 |
Let $(M,g)$ be a 2-dimensional compact Riemannian manifold. In this paper, we use the method of blowing up analysis to prove several Moser-Trdinger type inequalities for vector bundle over $(M,g)$. We also derive an upper bound of such inequalities under the assumption that blowing up occur. | Moser-Trudinger inequalities of vector bundle over a compact Riemannian
manifold of dimension 2 | 11,390 |
We prove the stability of a large class of unilateral minimality properties which arise naturally in the theory of crack propagation proposed by Francfort and Marigo in [Revisiting brittle fractures as an energy minimization problem. J. Mech. Phys. Solids, 46 (1998), 1319-1342]. Then we give an application to the quasistatic evolution of cracks in composite materials. | A $Γ$-convergence approach to stability of unilateral minimality
properties | 11,391 |
We obtain an estimate for the H\"older continuity exponent for weak solutions to the following elliptic equation in divergence form: \[ \mathrm{div}(A(x)\nabla u)=0 \qquad\mathrm{in\}\Omega, \] where $\Omega$ is a bounded open subset of $\R^2$ and, for every $x\in\Omega$, $A(x)$ is a matrix with bounded measurable coefficients. Such an estimate "interpolates" between the well-known estimate of Piccinini and Spagnolo in the isotropic case $A(x)=a(x)I$, where $a$ is a bounded measurable function, and our previous result in the unit determinant case $\det A(x)\equiv1$. Furthermore, we show that our estimate is sharp. Indeed, for every $\tau\in[0,1]$ we construct coefficient matrices $A_\tau$ such that $A_0$ is isotropic and $A_1$ has unit determinant, and such that our estimate for $A_\tau$ reduces to an equality, for every $\tau\in[0,1]$. | On the best Hoelder exponent for two dimensional elliptic equations in
divergence form | 11,392 |
In this paper we investigate the critical exponents of two families of Pucci's extremal operators. The notion of critical exponent that we have chosen for these fully nonlinear operators whihc are not variational is that of threshold betweeen existence and nonexistence of the solutions for semilinear equations with pure power nonlinearities. Interesting new exponents appear in this context. | Large critical exponents for some second order uniformly elliptic
operators | 11,393 |
We give a short proof of asymptotic completeness and global existence for the cubic Nonlinear Klein-Gordon equation in one dimension. Our approach to dealing with the long range behavior of the asymptotic solution is by reducing it, in hyperbolic coordinates to the study of an ODE. Similar arguments extend to higher dimensions and other long range type nonlinear problems. | A remark on asymptotic completeness for the critical nonlinear
Klein-Gordon equation | 11,394 |
Let $\Omega$ be a domain in $\mathbb{R}^d$, $d\geq 2$, and $1<p<\infty$. Fix $V\in L_{\mathrm{loc}}^\infty(\Omega)$. Consider the functional $Q$ and its G\^{a}teaux derivative $Q^\prime$ given by $$Q(u):=\int_\Omega (|\nabla u|^p+V|u|^p)\dx, \frac{1}{p}Q^\prime (u):=-\nabla\cdot(|\nabla u|^{p-2}\nabla u)+V|u|^{p-2}u.$$ If $Q\ge 0$ on $C_0^{\infty}(\Omega)$, then either there is a positive continuous function $W$ such that $\int W|u|^p \mathrm{d}x\leq Q(u)$ for all $u\in C_0^{\infty}(\Omega)$, or there is a sequence $u_k\in C_0^{\infty}(\Omega)$ and a function $v>0$ satisfying $Q^\prime (v)=0$, such that $Q(u_k)\to 0$, and $u_k\to v$ in $L^p_\mathrm{loc}(\Omega$). In the latter case, $v$ is (up to a multiplicative constant) the unique positive supersolution of the equation $Q^\prime (u)=0$ in $\Omega$, and one has for $Q$ an inequality of Poincar\'e type: there exists a positive continuous function $W$ such that for every $\psi\in C_0^\infty(\Omega)$ satisfying $\int \psi v \mathrm{d}x \neq 0$ there exists a constant $C>0$ such that $C^{-1}\int W|u|^p \mathrm{d}x\le Q(u)+C|\int u \psi \mathrm{d}x|^p$ for all $u\in C_0^\infty(\Omega)$. As a consequence, we prove positivity properties for the quasilinear operator $Q^\prime$ that are known to hold for general subcritical resp. critical second-order linear elliptic operators. | Ground state alternative for p-Laplacian with potential term | 11,395 |
We prove new velocity averaging results for second-order multidimensional equations of the general form, $\op(\nabla_x,v)f(x,v)=g(x,v)$ where $\op(\nabla_x,v):=\bba(v)\cdot\nabla_x-\nabla_x^\top\cdot\bbb(v)\nabla_x$. These results quantify the Sobolev regularity of the averages, $\int_vf(x,v)\phi(v)dv$, in terms of the non-degeneracy of the set $\{v: |\op(\ixi,v)|\leq \delta\}$ and the mere integrability of the data, $(f,g)\in (L^p_{x,v},L^q_{x,v})$. Velocity averaging is then used to study the \emph{regularizing effect} in quasilinear second-order equations, $\op(\nabla_x,\rho)\rho=S(\rho)$ using their underlying kinetic formulations, $\op(\nabla_x,v)\chi_\rho=g_{{}_S}$. In particular, we improve previous regularity statements for nonlinear conservation laws, and we derive completely new regularity results for convection-diffusion and elliptic equations driven by degenerate, non-isotropic diffusion. | The Averaging lemma and regularizing effect | 11,396 |
We undertake a comprehensive study of the nonlinear Schr\"odinger equation $$ i u_t +\Delta u = \lambda_1|u|^{p_1} u+ \lambda_2 |u|^{p_2} u, $$ where $u(t,x)$ is a complex-valued function in spacetime $\R_t\times\R^n_x$, $\lambda_1$ and $\lambda_2$ are nonzero real constants, and $0<p_1<p_2\le \frac 4{n-2}$. We address questions related to local and global well-posedness, finite time blowup, and asymptotic behaviour. Scattering is considered both in the energy space $H^1(\R^n)$ and in the pseudoconformal space $\Sigma:=\{f\in H^1(\R^n); xf\in L^2(\R^n)\}$. Of particular interest is the case when both nonlinearities are defocusing and correspond to the $L_x^2$-critical, respectively $\dot H^1_x$-critical NLS, that is, $\lambda_1, \lambda_2>0$ and $p_1=\frac{4}{n}$, $p_2=\frac{4}{n-2}$. The results at the endpoint $p_1 = \frac{4}{n}$ are conditional on a conjectured global existence and spacetime estimate for the $L^2_x$-critical nonlinear Schr\"odinger equation. As an off-shoot of our analysis, we also obtain a new, simpler proof of scattering in $H^1_x$ for solutions to the nonlinear Schr\"odinger equation $$ i u_t +\Delta u = |u|^{p} u, $$ with $\frac{4}{n}<p<\frac{4}{n-2}$, which was first obtained by J. Ginibre and G. Velo, \cite{gv:scatter}. | The nonlinear Schrödinger equation with combined power-type
nonlinearities | 11,397 |
This paper concerns the derivation of a Fokker-Planck equation for the correlation of two high frequency wave fields propagating in two different random media. The mismatch between the random media need be small, on the order of the wavelength, and their correlation length need be large relative to the wavelength. The loss of correlation caused by the mismatch in the random media is quantified and the limit process for the phase difference is obtained. The derivation is based on a random Liouville equation to model high frequency correlations and on the method of characteristics to characterize mixing in the random Liouville equation. Applications of such correlation loss include the monitoring in time of random media and the analysis of time reversed waves in changing heterogeneous domains. | Wave field correlations in weakly mismatched random media | 11,398 |
We prove uniform existence results for the full Navier-Stokes equations for time intervals which are independent of the Mach number, the Reynolds number and the P\'eclet number. We consider general equations of state and we give an application for the low Mach number limit combustion problem introduced by Majda. | Low Mach number flows, and combustion | 11,399 |
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