Abstract: Abstract
The basic existence theory of Kato and Majda enables us to obtain local-in-time classical solutions to generally quasilinear hyperbolic systems in the framework of Sobolev spaces (in x) with higher regularity. However, it remains a challenging open problem whether classical solutions still preserve well-posedness in the case of critical regularity. This paper is concerned with partially dissipative hyperbolic system of balance laws. Under the entropy dissipative assumption, we establish the local well-posedness and blow-up criterion of classical solutions in the framework of Besov spaces with critical regularity with the aid of the standard iteration argument and Friedrichs’ regularization method. Then we explore the theory of function spaces and develop an elementary fact that indicates the relation between homogeneous and inhomogeneous Chemin–Lerner spaces (mixed space-time Besov spaces). This fact allows us to capture the dissipation rates generated from the partial dissipative source term and further obtain the global well-posedness and stability by assuming at all times the Shizuta–Kawashima algebraic condition. As a direct application, the corresponding well-posedness and stability of classical solutions to the compressible Euler equations with damping are also obtained. PubDate: 2014-02-01

Abstract: Abstract
The evolution problem for a membrane based model of an electrostatically actuated microelectromechanical system is studied. The model describes the dynamics of the membrane displacement and the electric potential. The latter is a harmonic function in an angular domain, the deformable membrane being a part of the boundary. The former solves a heat equation with a right-hand side that depends on the square of the trace of the gradient of the electric potential on the membrane. The resulting free boundary problem is shown to be well-posed locally in time. Furthermore, solutions corresponding to small voltage values exist globally in time, while global existence is shown not to hold for high voltage values. It is also proven that, for small voltage values, there is an asymptotically stable steady-state solution. Finally, the small aspect ratio limit is rigorously justified. PubDate: 2014-02-01

Abstract: Abstract
This paper is a first step toward understanding the effect of toroidal geometry on the rigorous stability theory of plasmas. We consider a collisionless plasma inside a torus, modeled by the relativistic Vlasov–Maxwell system. The surface of the torus is perfectly conducting and it reflects the particles specularly. We provide sharp criteria for the stability of equilibria under the assumption that the particle distributions and the electromagnetic fields depend only on the cross-sectional variables of the torus. PubDate: 2014-02-01

Abstract: Abstract
We give a general monotonicity formula for local minimizers of free discontinuity problems which have a critical deviation from minimality, of order d − 1. This result allows us to prove partial regularity results (that is closure and density estimates for the jump set) for a large class of free discontinuity problems involving general energies associated to the jump set, as for example free boundary problems with Robin conditions. In particular, we give a short proof to the De Giorgi–Carriero–Leaci result for the Mumford–Shah functional. PubDate: 2014-02-01

Abstract: Abstract
In this paper, we study real solutions of the nonlinear Helmholtz equation
$$- \Delta u - k^2 u = f(x,u),\quad x\in \mathbb{R}^N$$
satisfying the asymptotic conditions
$$u(x)=O\left( x ^{\frac{1-N}{2}}\right) \quad {\rm and} \quad \frac{\partial^2 u}{\partial r^2}(x)+k^2u(x)=o\left( x ^{\frac{1-N}{2}}\right) \quad {\rm as}\, r= x \to\infty.$$
We develop the variational framework to prove the existence of nontrivial solutions for compactly supported nonlinearities without any symmetry assumptions. In addition, we consider the radial case in which, for a larger class of nonlinearities, infinitely many solutions are shown to exist. Our results give rise to the existence of standing wave solutions of corresponding nonlinear Klein–Gordon equations with arbitrarily large frequency. PubDate: 2014-02-01

Abstract: Abstract
In this paper, we study the orbital stability of the periodic peaked solitons of the generalized μ-Camassa–Holm equation with nonlocal cubic and quadratic nonlinearities. The equation is a μ-version of a linear combination of the Camassa–Holm equation and the modified Camassa–Holm equation. It is also integrable with the Lax-pair and bi-Hamiltonian structure and admits the single peakons and multi-peakons. By constructing an inequality related to the maximum and minimum of solutions with the conservation laws, we prove that, even in the case that the Camassa–Holm energy counteracts in part the modified Camassa–Holm energy, the shapes of periodic peakons are still orbitally stable under small perturbations in the energy space. PubDate: 2014-02-01

Abstract: Abstract
This paper deals with an initial-boundary value problem for the system
$$\left\{ \begin{array}{llll} n_t + u\cdot\nabla n &=& \Delta n -\nabla \cdot (n\chi(c)\nabla c), \quad\quad & x\in\Omega, \, t > 0,\\ c_t + u\cdot\nabla c &=& \Delta c-nf(c), \quad\quad & x\in\Omega, \, t > 0,\\
u_t + \kappa (u\cdot \nabla) u &=& \Delta u + \nabla P + n \nabla\phi, \qquad & x\in\Omega, \, t > 0,\\
\nabla \cdot u &=& 0, \qquad & x\in\Omega, \, t > 0,\end{array} \right.$$
which has been proposed as a model for the spatio-temporal evolution of populations of swimming aerobic bacteria. It is known that in bounded convex domains
${\Omega \subset \mathbb{R}^2}$
and under appropriate assumptions on the parameter functions χ, f and ϕ, for each
${\kappa\in\mathbb{R}}$
and all sufficiently smooth initial data this problem possesses a unique global-in-time classical solution. The present work asserts that this solution stabilizes to the spatially uniform equilibrium
${(\overline{n_0},0,0)}$
, where
${\overline{n_0}:=\frac{1}{ \Omega } \int_\Omega n(x,0)\,{\rm d}x}$
, in the sense that as t→∞,
$$n(\cdot,t) \to \overline{n_0}, \qquad c(\cdot,t) \to 0 \qquad \text{and}\qquad u(\cdot,t) \to 0$$
hold with respect to the norm in
${L^\infty(\Omega)}$
. PubDate: 2014-02-01

Abstract: Abstract
We introduce the notions of viscosity super- and subsolutions suitable for singular diffusion equations of non-divergence type with a general spatially inhomogeneous driving term. In particular, the viscosity super- and subsolutions support facets and allow a possible facet bending. We prove a comparison principle by a modified doubling variables technique. Finally, we present examples of viscosity solutions. Our results apply to a general crystalline curvature flow with a spatially inhomogeneous driving term for a graph-like curve. PubDate: 2014-02-01

Abstract: Abstract
Consider the scaling
${\varepsilon^{1/2}(x-Vt) \to x, \varepsilon^{3/2}t \to t}$
in the Euler–Poisson system for ion-acoustic waves (1). We establish that as
${\varepsilon \to 0}$
, the solutions to such Euler–Poisson systems converge globally in time to the solutions of the Korteweg–de Vries equation. PubDate: 2014-02-01

Abstract: Abstract
This paper focuses on the mathematical analysis of biaxial loading experiments in martensite, more particularly on how hysteresis relates to metastability. These experiments were carried out by Chu and James and their mathematical treatment was initiated by Ball, Chu and James. Experimentally it is observed that a homogeneous deformation y
1 is the stable state for “small” loads while y
2 is stable for “large” loads. A model was proposed by Ball, Chu and James which, for a certain intermediate range of loads, predicts crucially that y
1 remains metastable (that is, a local—as opposed to global—minimiser of the energy). This result explains convincingly the hysteresis that is observed experimentally. It is easy to get an upper bound on the load at which metastability finishes. However, it was also noticed that this bound (the Schmid Law) may not be sharp, though this required some geometric conditions on the sample. In this research, we rigorously justify the Ball–Chu–James model by means of De Giorgi’s Γ-convergence, establish some properties of local minimisers of the (limiting) energy and prove the metastability result mentioned above. An important part of the paper is then devoted to establishing which geometric conditions are necessary and sufficient for the counter-example to the Schmid Law to apply, namely, the presence of sharp corners in the sample. PubDate: 2014-02-01

Abstract: Abstract
Gradient boundedness up to the boundary for solutions to Dirichlet and Neumann problems for elliptic systems with Uhlenbeck type structure is established. Nonlinearities of possibly non-polynomial type are allowed, and minimal regularity on the data and on the boundary of the domain is assumed. The case of arbitrary bounded convex domains is also included. PubDate: 2014-01-23

Abstract: Abstract
In the present paper, we prove the a priori estimates of Sobolev norms for a free boundary problem of the incompressible inviscid magnetohydrodynamics equations in all physical spatial dimensions n = 2 and 3 by adopting a geometrical point of view used in Christodoulou and Lindblad (Commun Pure Appl Math 53:1536–1602, 2000), and estimating quantities such as the second fundamental form and the velocity of the free surface. We identify the well-posedness condition that the outer normal derivative of the total pressure including the fluid and magnetic pressures is negative on the free boundary, which is similar to the physical condition (Taylor sign condition) for the incompressible Euler equations of fluids. PubDate: 2014-01-15

Abstract: Abstract
Models of tumor growth, now commonly used, present several levels of complexity, both in terms of the biomedical ingredients and the mathematical description. Our first goal here is to formulate a free boundary model of Hele–Shaw type, a variant including growth terms, starting from the description at the cell level and passing to the stiff limit in the pressure law of state. In contrast with the classical Hele–Shaw problem, here the geometric motion governed by the pressure is not sufficient to completely describe the dynamics. A complete description requires the equation on the cell number density. We then go on to consider a more complex model including the supply of nutrients through vasculature, and we study the stiff limit for the involved coupled system. PubDate: 2014-01-14

Abstract: This is the second in a series of papers in which we derive a Γ-expansion for the two-dimensional non-local Ginzburg–Landau energy with Coulomb repulsion known as the Ohta–Kawasaki model in connection with diblock copolymer systems. In this model, two phases appear, which interact via a nonlocal Coulomb type energy. Here we focus on the sharp interface version of this energy in the regime where one of the phases has very small volume fraction, thus creating small “droplets” of the minority phase in a “sea” of the majority phase. In our previous paper, we computed the Γ-limit of the leading order energy, which yields the averaged behavior for almost minimizers, namely that the density of droplets should be uniform. Here we go to the next order and derive a next order Γ-limit energy, which is exactly the Coulombian renormalized energy obtained by Sandier and Serfaty as a limiting interaction energy for vortices in the magnetic Ginzburg–Landau model. The derivation is based on the abstract scheme of Sandier-Serfaty that serves to obtain lower bounds for 2-scale energies and express them through some probabilities on patterns via the multiparameter ergodic theorem. Thus, without appealing to the Euler–Lagrange equation, we establish for all configurations which have “almost minimal energy” the asymptotic roundness and radius of the droplets, and the fact that they asymptotically shrink to points whose arrangement minimizes the renormalized energy in some averaged sense. Via a kind of Γ-equivalence, the obtained results also yield an expansion of the minimal energy and a characterization of the zero super-level sets of the minimizers for the original Ohta–Kawasaki energy. This leads to the expectation of seeing triangular lattices of droplets as energy minimizers. PubDate: 2014-01-14

Abstract: Abstract
We analyse a nonlinear Schrödinger equation for the time-evolution of the wave function of an electron beam, interacting selfconsistently through a Hartree–Fock nonlinearity and through the repulsive Coulomb interaction of an atomic nucleus. The electrons are supposed to move under the action of a time dependent, rapidly periodically oscillating electromagnetic potential. This can be considered a simplified effective single particle model for an X-ray free electron laser. We prove the existence and uniqueness for the Cauchy problem and the convergence of wave-functions to corresponding solutions of a Schrödinger equation with a time-averaged Coulomb potential in the high frequency limit for the oscillations of the electromagnetic potential. PubDate: 2014-01-14

Abstract: Abstract
In (Comm Pure Appl Math 62(4):502–564, 2009), Hou and Lei proposed a 3D model for the axisymmetric incompressible Euler and Navier–Stokes equations with swirl. This model shares a number of properties of the 3D incompressible Euler and Navier–Stokes equations. In this paper, we prove that the 3D inviscid model with an appropriate Neumann-Robin or Dirichlet-Robin boundary condition will develop a finite time singularity in an axisymmetric domain. We also provide numerical confirmation for our finite time blowup results. We further demonstrate that the energy of the blowup solution is bounded up to the singularity time, and the blowup mechanism for the mixed Dirichlet-Robin boundary condition is essentially the same as that for the energy conserving homogeneous Dirichlet boundary condition. Finally, we prove that the 3D inviscid model has globally smooth solutions for a class of large smooth initial data with some appropriate boundary condition. Both the analysis and the results we obtain here improve the previous work in a rectangular domain by Hou et al. (Adv Math 230:607–641, 2012) in several respects. PubDate: 2014-01-09

Abstract: Abstract
We prove various decay bounds on solutions (f
n
: n > 0) of the discrete and continuous Smoluchowski equations with diffusion. More precisely, we establish pointwise upper bounds on n
ℓ
f
n
in terms of a suitable average of the moments of the initial data for every positive ℓ. As a consequence, we can formulate sufficient conditions on the initial data to guarantee the finiteness of
${L^p(\mathbb{R}^d \times [0, T])}$
norms of the moments
${X_a(x, t) := \sum_{m\in\mathbb{N}}m^a f_m(x, t)}$
, (
${\int_0^{\infty} m^a f_m(x, t)dm}$
in the case of continuous Smoluchowski’s equation) for every
${p \in [1, \infty]}$
. In previous papers [11] and [5] we proved similar results for all weak solutions to the Smoluchowski’s equation provided that the diffusion coefficient d(n) is non-increasing as a function of the mass. In this paper we apply a new method to treat general diffusion coefficients and our bounds are expressed in terms of an auxiliary function
${\phi(n)}$
that is closely related to the total increase of the diffusion coefficient in the interval (0, n]. PubDate: 2014-01-09

Abstract: Abstract
We study the following nonlinear Stefan problem
$$\left\{\begin{aligned}\!\!&u_t\,-\,d\Delta u = g(u) & &\quad{\rm for}\,x\,\in\,\Omega(t), t > 0, \\ & u = 0 \, {\rm and} u_t = \mu \nabla_{x} u ^{2} &&\quad {\rm for}\,x\,\in\,\Gamma(t), t > 0, \\ &u(0, x) = u_{0}(x) &&\quad {\rm for}\,x\,\in\,\Omega_0,\end{aligned} \right.$$
where
${\Omega(t) \subset \mathbb{R}^{n}}$
(
${n \geqq 2}$
) is bounded by the free boundary
${\Gamma(t)}$
, with
${\Omega(0) = \Omega_0}$
, μ and d are given positive constants. The initial function u
0 is positive in
${\Omega_0}$
and vanishes on
${\partial \Omega_0}$
. The class of nonlinear functions g(u) includes the standard monostable, bistable and combustion type nonlinearities. We show that the free boundary
${\Gamma(t)}$
is smooth outside the closed convex hull of
${\Omega_0}$
, and as
${t \to \infty}$
, either
${\Omega(t)}$
expands to the entire
${\mathbb{R}^n}$
, or it stays bounded. Moreover, in the former case,
${\Gamma(t)}$
converges to the unit sphere when normalized, and in the latter case,
${u \to 0}$
uniformly. When
${g(u) = au - bu^2}$
, we further prove that in the case
${\Omega(t)}$
expands to
${{\mathbb R}^n}$
,
${u \to a/b}$
as
${t \to \infty}$
, and the spreading speed of the free boundary converges to a positive constant; moreover, there exists
${\mu^* \geqq 0}$
such that
${\Omega(t)}$
expands to
${{\mathbb{R}}^n}$
exactly when
${\mu > \mu^*}$
. PubDate: 2014-01-08

Abstract: Abstract
We prove some interior regularity results for potential functions of optimal transportation problems with power costs. The main point is that our problem is equivalent to a new optimal transportation problem whose cost function is a sufficiently small perturbation of the quadratic cost, but it does not satisfy the well known condition (A.3) guaranteeing regularity. The proof consists in a perturbation argument from the standard Monge–Ampère equation in order to obtain, first, interior C1,1 estimates for the potential and, second, interior Hölder estimates for second derivatives. In particular, we take a close look at the geometry of optimal transportation when the cost function is close to quadratic in order to understand how the equation degenerates near the boundary. PubDate: 2014-01-08

Abstract: Abstract
This note studies families of isothermal Navier–Stokes–Allen–Cahn systems that are parameterized by temperature. It shows that under natural assumptions, the possibility of traveling waves corresponding to phase boundaries arises during a phase transition at a critical temperature. Below that temperature, besides pairs of “Maxwell” states connected by waves with zero net mass flux, there exist also interfaces across which particles undergo a phase transformation. PubDate: 2014-01-01