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1078-0947

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## Discrete & Continuous Dynamical Systems - A

December 2015 , Volume 35 , Issue 12

Special issue on contemporary PDEs between theory and applications

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2015, 35(12): i-i
doi: 10.3934/dcds.2015.35.12i

*+*[Abstract](1185)*+*[PDF](72.5KB)**Abstract:**

This special issue of Discrete and Continuous Dynamical Systems is devoted to some recent developments in some important fields of partial differential equations.

The aim is to bring together several contributions in different fields that range from classical to modern topics with the intent to present new research perspectives, innovative methods and challenging applications.

Though it was of course impossible to take into account all the possible lines of research in PDEs, we tried to present a wide spectrum, hoping to capture the interest of both the general mathematical audience and the specialized mathematicians that work in differential equations and related fields.

We think that the Authors put a great effort to write their contributions in the clearest possible language. We are indeed grateful to all the Authors that contributed to this special issue, donating beautiful pieces of mathematics to the community and promoting further developments in the field.

We also thank the Managing Editor for his kind invitation to act as an editor of this special issue.

Also, we express our gratitude to all the Referees who kindly agreed to devote their time and efforts to read and check all the papers carefully, providing useful comments and recommendations. Indeed, each paper was submitted to the meticulous inspection of two independent and anonymous Experts, whose observations were fundamental to the final outcome of this special issue.

Finally, we would like to wish a `Happy reading!' to the Reader. This volume is for Her (or Him), after all.

2015, 35(12): 5555-5607
doi: 10.3934/dcds.2015.35.5555

*+*[Abstract](1598)*+*[PDF](661.7KB)**Abstract:**

We present a notion of weak solution for the Dirichlet problem driven by the fractional Laplacian, following the Stampacchia theory. Then, we study semilinear problems of the form $$ \left\lbrace\begin{array}{ll} (-\triangle)^s u = \pm\,f(x,u) & \hbox{ in }\Omega \\ u=g & \hbox{ in }\mathbb{R}^n\setminus\overline{\Omega}\\ Eu=h & \hbox{ on }\partial\Omega \end{array}\right. $$ when the nonlinearity $f$ and the boundary data $g,h$ are positive, but allowing the right-hand side to be both positive or negative and looking for solutions that blow up at the boundary. The operator $E$ is a weighted limit to the boundary: for example, if $\Omega$ is the ball $B$, there exists a constant $C(n,s)>0$ such that $$ Eu(\theta) = C(n,s) \lim_{x \to \theta}_{x\in B} u(x) {dist(x,\partial B)}^{1-s}, \hbox{ for all } \theta \in \partial B. $$ Our starting observation is the existence of $s$-harmonic functions which explode at the boundary: these will be used both as supersolutions in the case of negative right-hand side and as subsolutions in the positive case.

2015, 35(12): 5609-5629
doi: 10.3934/dcds.2015.35.5609

*+*[Abstract](1113)*+*[PDF](432.2KB)**Abstract:**

We characterize the set of harmonic functions with Dirichlet boundary conditions in unbounded domains which are union of two different chambers. We analyse the asymptotic behavior of the solutions in connection with the changes in the domain's geometry; we classify all (possibly sign-changing) infinite energy solutions having given asymptotic frequency at the infinite ends of the domain; finally we sketch the case of several different chambers.

2015, 35(12): 5631-5663
doi: 10.3934/dcds.2015.35.5631

*+*[Abstract](1151)*+*[PDF](716.8KB)**Abstract:**

We extend the Caffarelli--Córdoba estimates to the vector case (L. Caffarelli and A. Córdoba, Uniform Convergence of a singular perturbation problem,

*Comm. Pure Appl. Math.*

**48**(1995)). In particular, we establish lower codimension density estimates. These are useful for studying the hierarchical structure of minimal solutions. We also give applications.

2015, 35(12): 5665-5688
doi: 10.3934/dcds.2015.35.5665

*+*[Abstract](1336)*+*[PDF](458.1KB)**Abstract:**

We establish a variational parabolic capacity in a context of degenerate parabolic equations of $p$-Laplace type, and show that this capacity is equivalent to the nonlinear parabolic capacity. As an application, we estimate the capacities of several explicit sets.

2015, 35(12): 5689-5709
doi: 10.3934/dcds.2015.35.5689

*+*[Abstract](1470)*+*[PDF](466.7KB)**Abstract:**

This paper provides an elementary proof of the classical limit of the Schrödinger equation with WKB type initial data and over arbitrary long finite time intervals. We use only the stationary phase method and the Laptev-Sigal simple and elegant construction of a parametrix for Schrödinger type equations [A. Laptev, I. Sigal, Review of Math. Phys.

**12**(2000), 749--766]. We also explain in detail how the phase shifts across caustics obtained when using the Laptev-Sigal parametrix are related to the Maslov index.

2015, 35(12): 5711-5723
doi: 10.3934/dcds.2015.35.5711

*+*[Abstract](1197)*+*[PDF](406.8KB)**Abstract:**

We show that the parabolic minimal surface equation has an eventual regularization effect, that is, the solution becomes smooth after a strictly positive finite time.

2015, 35(12): 5725-5767
doi: 10.3934/dcds.2015.35.5725

*+*[Abstract](1743)*+*[PDF](703.0KB)**Abstract:**

We consider nonlinear diffusive evolution equations posed on bounded space domains, governed by fractional Laplace-type operators, and involving porous medium type nonlinearities. We establish existence and uniqueness results in a suitable class of solutions using the theory of maximal monotone operators on dual spaces. Then we describe the long-time asymptotics in terms of separate-variables solutions of the friendly giant type. As a by-product, we obtain an existence and uniqueness result for semilinear elliptic non local equations with sub-linear nonlinearities. The Appendix contains a review of the theory of fractional Sobolev spaces and of the interpolation theory that are used in the rest of the paper.

2015, 35(12): 5769-5786
doi: 10.3934/dcds.2015.35.5769

*+*[Abstract](1346)*+*[PDF](426.4KB)**Abstract:**

In this brief note we study how the fractional mean curvature of order $s \in (0, 1)$ varies with respect to $C^{1, \alpha}$ diffeomorphisms. We prove that, if $\alpha > s$, then the variation under a $C^{1, \alpha}$ diffeomorphism $\Psi$ of the $s$-mean curvature of a set $E$ is controlled by the $C^{0, \alpha}$ norm of the Jacobian of $\Psi$. When $\alpha = 1$ we discuss the stability of these estimates as $s \rightarrow 1^-$ and comment on the consistency of our result with the classical framework.

2015, 35(12): 5787-5798
doi: 10.3934/dcds.2015.35.5787

*+*[Abstract](1211)*+*[PDF](334.3KB)**Abstract:**

Given a compact three--manifold together with a Riemannian metric, we prove the short--time existence of a solution to the renormalization group flow, truncated at the second order term, under a suitable hypothesis on the sectional curvature of the initial metric.

2015, 35(12): 5799-5825
doi: 10.3934/dcds.2015.35.5799

*+*[Abstract](1227)*+*[PDF](470.7KB)**Abstract:**

We prove the existence of extremal domains with small prescribed volume for the first eigenvalue of the Laplace-Beltrami operator in any compact Riemannian manifold. This result generalizes a results of F. Pacard and the second author where the existence of a nondegenerate critical point of the scalar curvature of the Riemannian manifold was required.

2015, 35(12): 5827-5867
doi: 10.3934/dcds.2015.35.5827

*+*[Abstract](1514)*+*[PDF](644.7KB)**Abstract:**

Asymptotics of solutions to relativistic fractional elliptic equations with Hardy type potentials is established in this paper. As a consequence, unique continuation properties are obtained.

2015, 35(12): 5869-5877
doi: 10.3934/dcds.2015.35.5869

*+*[Abstract](1365)*+*[PDF](356.5KB)**Abstract:**

We prove the symmetry of components and some Liouville-type theorems for, possibly sign changing, entire distributional solutions to a family of nonlinear elliptic systems encompassing models arising in Bose-Einstein condensation and in nonlinear optics. For these models we also provide precise classification results for non-negative solutions. The sharpness of our results is also discussed.

2015, 35(12): 5879-5908
doi: 10.3934/dcds.2015.35.5879

*+*[Abstract](1538)*+*[PDF](699.8KB)**Abstract:**

A plate model describing the statics and dynamics of a suspension bridge is suggested. A partially hinged plate subject to nonlinear restoring hangers is considered. The whole theory from linear problems, through nonlinear stationary equations, ending with the full hyperbolic evolution equation is studied. This paper aims to be the starting point for more refined models.

2015, 35(12): 5909-5926
doi: 10.3934/dcds.2015.35.5909

*+*[Abstract](1296)*+*[PDF](456.1KB)**Abstract:**

We prove Harnack type inequalities for a wide class of parabolic doubly nonlinear equations including $u_t=$ ${ div}(|u|^{m-1}|Du|^{p-2}Du)$. We will distinguish between the

*supercritical*range $3 - \frac {p} {N} < p+m < 3$ and the

*subcritical*$2 < p+m \le 3 - \frac {p} {N}$ range. Our results extend similar estimates holding for general equations having the same structure as the parabolic $p$-Laplace or the porous medium equation and recently collected in [6].

2015, 35(12): 5927-5962
doi: 10.3934/dcds.2015.35.5927

*+*[Abstract](1268)*+*[PDF](654.6KB)**Abstract:**

We are concerned with the long time behaviour of solutions to the fractional porous medium equation with a variable spatial density. We prove that if the density decays slowly at infinity, then the solution approaches the Barenblatt-type solution of a proper singular fractional problem. If, on the contrary, the density decays rapidly at infinity, we show that the minimal solution multiplied by a suitable power of the time variable converges to the minimal solution of a certain fractional sublinear elliptic equation.

2015, 35(12): 5963-5976
doi: 10.3934/dcds.2015.35.5963

*+*[Abstract](1069)*+*[PDF](406.8KB)**Abstract:**

We consider a class of scalar field equations with anisotropic nonlocal nonlinearities. We obtain a suitable extension of the well-known compactness lemma of Benci and Cerami to this variable exponent setting, and use it to prove that the Palais-Smale condition holds at all level below a certain threshold. We deduce the existence of a ground state when the variable exponent slowly approaches the limit at infinity from below.

2015, 35(12): 5977-5998
doi: 10.3934/dcds.2015.35.5977

*+*[Abstract](1843)*+*[PDF](454.5KB)**Abstract:**

We prove optimal pointwise Schauder estimates in the spatial variables for solutions of linear parabolic integro-differential equations. Optimal Hölder estimates in space-time for those spatial derivatives are also obtained.

2015, 35(12): 5999-6013
doi: 10.3934/dcds.2015.35.5999

*+*[Abstract](1229)*+*[PDF](412.3KB)**Abstract:**

A rate-independent model for the quasistatic evolution of a magnetoelastic plate is advanced and analyzed. Starting from the three-dimensional setting, we present an evolutionary $\Gamma$-convergence argument in order to pass to the limit in one of the material dimensions. By taking into account both conservative and dissipative actions, a nonlinear evolution system of rate-independent type is obtained. The existence of so-called

*energetic solutions*to such system is proved via approximation.

2015, 35(12): 6015-6030
doi: 10.3934/dcds.2015.35.6015

*+*[Abstract](1010)*+*[PDF](428.6KB)**Abstract:**

Smoothness of a function $f:\mathbb{R}^n\to\mathbb{R}$ can be measured in terms of the rate of convergence of $f*\rho_{\epsilon}$ to $f$, where $\rho$ is an appropriate mollifier. In the framework of fractional Sobolev spaces, we characterize the "appropriate" mollifiers. We also obtain sufficient conditions, close to being necessary, which ensure that $\rho$ is adapted to a given scale of spaces. Finally, we examine in detail the case where $\rho$ is a characteristic function.

2015, 35(12): 6031-6068
doi: 10.3934/dcds.2015.35.6031

*+*[Abstract](2393)*+*[PDF](475.5KB)**Abstract:**

In this work we consider the problems $$ \left\{\begin{array}{rcll} \mathcal{L \,} u&=&f &\hbox{ in } \Omega,\\ u&=&0 &\hbox{ in } \mathbb{R}^N\setminus\Omega, \end{array} \right. $$ and $$ \left\{\begin{array}{rcll} u_t +\mathcal{L \,} u&=&f &\hbox{ in } Q_{T}\equiv\Omega\times (0, T),\\ u (x,t) &=&0 &\hbox{ in } \big(\mathbb{R}^N\setminus\Omega\big) \times (0, T),\\ u(x,0)&=&0 &\hbox{ in } \Omega, \end{array} \right. $$ where $\mathcal{L \,}$ is a nonlocal differential operator and $\Omega$ is a bounded domain in $\mathbb{R}^N$, with Lipschitz boundary.

The main goal of this work is to study existence, uniqueness and summability of the solution $u$ with respect to the summability of the datum $f$. In the process we establish an $L^p$-theory, for $p \geq 1$, associated to these problems and we prove some useful inequalities for the applications.

2015, 35(12): 6069-6084
doi: 10.3934/dcds.2015.35.6069

*+*[Abstract](1405)*+*[PDF](405.6KB)**Abstract:**

In this paper, we study the regularity of convex solutions to the Dirichlet problem of the homogeneous Monge-Ampère equation $\det D^2 u=0$. We prove that if the domain is a strip region and the boundary functions are locally uniformly convex and $C^{k+2,\alpha}$ smooth, then the solution is $C^{k+2,\alpha}$ smooth up to boundary. By an example, we show the solution may fail to be $C^{2}$ smooth if boundary functions are not locally uniformly convex. Similar results have also been obtained for the Dirichlet problem on bounded convex domains.

2015, 35(12): 6085-6112
doi: 10.3934/dcds.2015.35.6085

*+*[Abstract](1462)*+*[PDF](546.0KB)**Abstract:**

For the cubic Schrödinger system with trapping potentials in $\mathbb{R}^N$, $N\leq3$, or in bounded domains, we investigate the existence and the orbital stability of standing waves having components with prescribed $L^2$-mass. We provide a variational characterization of such solutions, which gives information on the stability through a condition of Grillakis-Shatah-Strauss type. As an application, we show existence of conditionally orbitally stable solitary waves when: a) the masses are small, for almost every scattering lengths, and b) in the defocusing, weakly interacting case, for any masses.

2015, 35(12): 6113-6132
doi: 10.3934/dcds.2015.35.6113

*+*[Abstract](1131)*+*[PDF](418.7KB)**Abstract:**

This paper slightly improves a classical result by Gangbo and McCann (1996) about the structure of optimal transport plans for costs that are strictly concave and increasing functions of the Euclidean distance. Since the main difficulty for proving the existence of an optimal map comes from the possible singularity of the cost at $0$, everything is quite easy if the supports of the two measures are disjoint; Gangbo and McCann proved the result under the assumption $\mu(supp(\mathbf{v}))=0$; in this paper we replace this assumption with the fact that the two measures are singular to each other. In this case it is possible to prove the existence of an optimal transport map, provided the starting measure $\mu$ does not give mass to small sets (i.e. $(d\!-\!1)-$rectifiable sets). When the measures are not singular the optimal transport plan decomposes into two parts, one concentrated on the diagonal and the other being a transport map between mutually singular measures.

2015, 35(12): 6133-6153
doi: 10.3934/dcds.2015.35.6133

*+*[Abstract](1321)*+*[PDF](701.1KB)**Abstract:**

We consider the homogeneous wave equation on a bounded open connected subset $\Omega$ of $\mathbb{R}^n$. Some initial data being specified, we consider the problem of determining a measurable subset $\omega$ of $\Omega$ maximizing the $L^2$-norm of the restriction of the corresponding solution to $\omega$ over a time interval $[0,T]$, over all possible subsets of $\Omega$ having a certain prescribed measure. We prove that this problem always has at least one solution and that, if the initial data satisfy some analyticity assumptions, then the optimal set is unique and moreover has a finite number of connected components. In contrast, we construct smooth but not analytic initial conditions for which the optimal set is of Cantor type and in particular has an infinite number of connected components.

2015, 35(12): 6155-6163
doi: 10.3934/dcds.2015.35.6155

*+*[Abstract](1223)*+*[PDF](323.5KB)**Abstract:**

We show that the quotient of a harmonic function and a positive harmonic function, both vanishing on the boundary of a $C^{k,\alpha}$ domain is of class $C^{k,\alpha}$ up to the boundary.

2015, 35(12): 6165-6179
doi: 10.3934/dcds.2015.35.6165

*+*[Abstract](1384)*+*[PDF](401.8KB)**Abstract:**

The Hessian Sobolev inequality of X.-J. Wang, and the Hessian Poincaré inequalities of Trudinger and Wang are fundamental to differential and conformal geometry, and geometric PDE. These remarkable inequalities were originally established via gradient flow methods. In this paper, direct elliptic proofs are given, and extensions to trace inequalities with general measures in place of Lebesgue measure are obtained. The new techniques rely on global estimates of solutions to Hessian equations in terms of Wolff's potentials, and duality arguments making use of a non-commutative inner product on the cone of $k$-convex functions.

2018 Impact Factor: 1.143

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