We study the Strang splitting scheme for quasilinear Schrodinger equations. We establish the convergence of the scheme for solutions with small initial data. We analyze the linear instability of the numerical scheme, which explains the numerical blow-up of large data solutions and connects to analytical breakdown of regularity of solutions to quasilinear Schrodinger equations. Numerical tests are performed for a modified version of the superfluid thin film equation.

In [C. De Lellis and L. Szekelyhidi, Ann. of Math. 170, 1417-1436m 2009] C. De Lellis and L. Szekelyhidi Jr. constructed wild solutions of the incompressible Euler equations using a reformulation of the Euler equations as a differential inclusion together with convex integration. In this article we adapt their construction to the system consisting of adding the transport of a passive scalar to the two-dimensional incompressible Euler equations.

We aim to present a relaxation model that can be used in real simulations of dilute multicomponent reacting gases. The kinetic framework is the semi-classical approach with only one variable for the internal energy modes. The relaxation times for the internal energy modes are assumed to be smaller than the chemistry characteristic times. The strategy is the same as in [S. Brull, J. Schneider, Comm. Math. Sci. to appear]. That is a sum of operators for respectively the mechanical and chemical processes. The mechanical operator(s) is the "natural" extension to polyatomic gases of the method of moment relaxations presented in [S. Brull, J. Schneider, Cont. Mech. Thermodyn. 20, 63-74, 2008] and [S. Brull, V. Pavan and J. Schnieder, Eur. J. Mech. (B-Fluids) 33, 74-86, 2012]. The derivation of the chemical model lies on the chemical processes at thermal equilibria. It is shown that this BGK approach features the same properties as the Boltzmann equation: conservations and entropy production. Moreover null entropy production states are characterized by vanishing chemical production rates. We also study the hydrodynamic limit in the slow chemistry regime. Finally we show that the whole set of parameters that are used in the derivation of the model can be calculated by softwares such as EGlib or STANJAN.

Epitaxially grown heterogeneous nanowires present dislocations at the interface between the phases if their radius is big. We consider a corresponding variational discrete model with quadratic pairwise atomic interaction energy. By employing the notion of Gamma-convergence and a geometric rigidity estimate, we perform a discrete to continuum limit and a dimension reduction to a one-dimensional system. Moreover, we compare a defect-free model and models with dislocations at the interface and show that the latter are energetically convenient if the thickness of the wire is sufficiently large.

We investigate the time evolution of spin densities in a two-dimensional electron gas subjected to Rashba spin-orbit coupling on the basis of the quantum drift-diffusive model derived in [L. barletti and F. Mehats, J. Math. Phys. 51, 053304, 2010]. This model assumes the electrons to be in a quantum equilibrium state in the form of a Maxwellian operator. The resulting quantum drift-diffusion equations for spin-up and spin-down densities are coupled in a non-local manner via two spin chemical potentials (Lagrange multipliers) and via off-diagonal elements of the equilibrium spin density and spin current matrices, respectively. We present two space-time discretizations of the model, one semi-implicit and one explicit, which comprise also the Poisson equation in order to account for electron-electron interactions. In a first step pure time discretization is applied in order to prove the well-posedness of the two schemes, both of which are based on a functional formalism to treat the non-local relations between spin densities. We then use the fully space-time discrete schemes to simulate the time evolution of a Rashba electron gas confined in a bounded domain and subjected to spin-dependent external potentials. Finite difference approximations are first order in time and second order in space. The discrete functionals introduced are minimized with the help of a conjugate gradient-based algorithm, where the Newton method is applied in order to find the respective line minima. The numerical convergence in the long-time limit of a Gaussian initial condition towards the solution of the corresponding stationary Schr\"odinger-Poisson problem is demonstrated for different values of the parameters $\eps$ (semiclassical parameter), $\alpha$ (Rashba coupling parameter), $\Delta x$ (grid spacing) and $\Delta t$ (time step). Moreover, the performances of the semi-implicit and the explicit scheme are compared.

In this paper, we address the issue of designing a theoretically well- motivated and computationally efficient method ensuring topology preservation on image-registration-related deformation elds. The model is motivated by a mathematical characterization of topology preservation for a deformation eld mapping two subsets of Z^2, namely, positivity of the four approximations to the Jacobian determinant of the deformation on a square patch. The first step of the proposed algorithm thus consists in correcting the gradient vector field of the deformation (that does not comply with the topology preservation criteria) at the discrete level in order to fulfill this positivity condition. Once this step is achieved, it thus remains to reconstruct the deformation field, given its full set of discrete gradient vectors. We propose to decompose the reconstruction problem into independent problems of smaller dimensions, yielding a natural parallelization of the computations and enabling us to reduce drastically the computational time (up to 80 in some applications). For each subdomain, a functional minimization problem under Lagrange interpolation constraints is introduced and its well-posedness is studied: existence/uniqueness of the solution, characterization of the solution, convergence of the method when the number of data increases to infinity, discretization with the Finite Element Method and discussion on the properties of the matrix involved in the linear system. Numerical simulations based on OpenMP parallelization and MKL multi-threading demonstrating the ability of the model to handle large deformations (contrary to classical methods) and the interest of having decomposed the problem into smaller ones are provided.

We study orbital stability of solitary wave of the least energy for a nonlinear 2D Benney-Luke model of higher order related with long water waves with small amplitude in the presence of strong surface tension. We follow a variational approach which includes the characterization of the ground state solution set associated with solitary waves. We use the Hamiltonian structure of this model to establish the existence of an energy functional conserved in time for the modulated equation associated with this Benney-Luke type model. For wave speed near to zero or one, and in the regime of strong surface tension, we prove the orbital stability result by following a variational approach.

We study a system of self-propelled particles which interact with their neighbors via alignment and repulsion. The particle velocities result from self-propulsion and repulsion by close neighbors. The direction of self-propulsion is continuously aligned to that of the neighbors, up to some noise. A continuum model is derived starting from a mean-field kinetic description of the particle system. It leads to a set of non conservative hydrodynamic equations. We provide a numerical validation of the continuum model by comparison with the particle model. We also provide comparisons with other self-propelled particle models with alignment and repulsion.

In this paper an optimal control problem for a large system of interacting agents is considered using a kinetic perspective. As a prototype model we analyze a microscopic model of opinion formation under constraints. For this problem a Boltzmann type equation based on a model predictive control formulation is introduced and discussed. In particular, the receding horizon strategy permits to embed the minimization of suitable cost functional into binary particle interactions. The corresponding Fokker-Planck asymptotic limit is also derived and explicit expressions of stationary solutions are given. Several numerical results showing the robustness of the present approach are finally reported.

Owing to the Rosenau argument [Phys. Rev. A 46, 12-15, 1992], originally proposed to obtain a regularized version of the Chapman-Enskog expansion of hydrodynamics, we introduce a non-local linear kinetic equation which approximates a fractional diffusion equation. We then show that the solution to this approximation, apart of a rapidly vanishing in time perturbation, approaches the fundamental solution of the fractional diffusion (a Levy stable law) at large times.

We study a non-local parabolic Lotka-Volterra type equation describing a population struc- tured by a space variable x\in R^d and a phenotypical trait \theta \in {\Cal \Theta}. Considering diffusion, mu- tations and space-local competition between the individuals, we analyze the asymptotic (long time/longreal phase WKB ansatz, we prove that the propagation of the population in space can be de- scribed by a Hamilton-Jacobi equation with obstacle which is independent of \theta. The effective Hamiltonian is derived from an eigenvalue problem. The main difficulties are the lack of regularity estimates in the space variable, and the lack of comparison principle due to the non-local term.

In this paper, we study the asymptotic behavior of a state-based multiscale heterogeneous peridynamic model. The model involves nonlocal interaction forces with highly oscillatory perturbations representing the presence of heterogeneities on a finer spatial length scale. The two-scale convergence theory is established for a steady state variational problem associated with the multiscale linear model. We also examine the regularity of the limit nonlocal equation and present the strong approximation to the solution of the peridyanmic model via a suitably scaled two-scale limit.

This paper deals with the derivation of macroscopic equations from the underlying mesoscopic description that is suitable to capture the main features of pedestrian crowd dynamics. The interactions are modeled by means of theoretical tools of game theory, while the macroscopic equations are derived from asymptotic limits.

This paper concentrates on a (1+1)-dimensional nonlinear Dirac (NLD) equation with a general self-interaction, being a linear combination of the scalar, pseudoscalar, vector and axial vector self-interactions to the power of the integer k+1. The solitary wave solutions to the NLD equation are analytically derived, and the upper bounds of the hump number in the charge, energy and momentum densities for the solitary waves are proved analytically in theory. The results show that: (1) for a given integer k, the hump number in the charge density is not bigger than 4, while that in the energy density is not bigger than 3; (2) those upper bounds can only be achieved in the situation of higher nonlinearity, namely k\in {5,6,7, ...} for the charge density and k \in {3,5,7 ...} for the energy density; (3) the momentum density has the same multi-hump structure as the energy density; (4) more than two humps (resp. one hump) in the charge (resp. energy) density can only happen under the linear combination of the pseudoscalar self-interaction and at least one of the scalar and vector (or axial vector) self-interactions. Our results on the multi-hump structure will be interesting in the interaction dynamics for the NLD solitary waves.

We consider a diffuse interface model for phase separation of an isothermal incompressible binary fluid in a Brinkman porous medium. The coupled system consists of a convective Cahn-Hilliard equation for the phase field \phi, i.e., the difference of the (relative) concentrations of the two phases, coupled with a modified Darcy equation proposed by H.C. Brinkman in 1947 for the fluid velocity u. This equation incorporates a diffuse interface surface force proportional to \phi \nabla \mu, where \mu where 5 is the so-called chemical potential. We analyze the well-posedness of the resulting Cahn-Hilliard-Brinkman (CHB) system for (\phi, u). Then we establish the existence of a global attractor and the convergence of a given (weak) solution to a single equilibrium via Lojasiewicz-Simon inequality. Furthermore, we study the behavior of the solutions as the viscosity goes to zero, that is, when the CHB system approaches the Cahn-Hilliard-Hele-Shaw (CHHS) system. We first prove the existence of a weak solution to the CHHS system as limit of CHB solutions. Then, in dimension two, we estimate the difference of the solutions to CHB and CHHS systems in terms of the viscosity constant appearing in CHB.

This paper deals with the long time behavior of solutions to a "fractional Fokker-Planck" equation of the form \partial_t f= I[f] + \div(xf) where the operator I stands for a fractional Laplacian. We prove an exponential in time convergence towards equilibrium in new spaces. Indeed, such a result was already obtained in a L^2 space with a weight prescribed by the equilibrium in [Gentil, I. and ]Imbert, C., Asymp. Anal. 59, 3-4 (2008), 125-138] . We improve this result obtaining the convergence in a L^1 space with a polynomial weight. To do that, we take advantage of the recent paper [Gualdani, M.P., Mischler, S. and Mouhot, C., http://hal.archives-ouvertes.fr/ccsd-0049578 (2010).] in which an abstract theory of enlargement of the functional space of the semigroup decay is developed.

We study pathwise entropy solutions for scalar conservation laws with inhomogeneous fluxes and quasilinear multiplicative rough path dependence. This extends the previous work of Lions, Perthame and Souganidis who considered spatially independent and inhomogeneous fluxes with multiple paths and a single driving singular path respectively. The approach is motivated by the theory of stochastic viscosity solutions which relies on special test functions constructed by inverting locally the flow of the stochastic characteristics. For conservation laws this is best implemented at the level of the kinetic formulation which we follow here.

Selective image segmentation is the task of extracting one object of interest from an image,
based on minimal user input. Recent level-set based variational models have shown to
be effective and reliable, although they can be sensitive to initialization due to the minimization problems being nonconvex. This sometimes means that successful segmentation
relies too heavily on user input or a solution found is only a local minimizer, i.e. not the
correct solution. The same principle applies to variational models that extract all objects
in an image (global segmentation); however, in recent years, some have been successfully
reformulated as convex optimization problems, allowing global minimizers to be found.

There are, however, problems associated with extending the convex formulation to the
current selective models, which provides the motivation for the proposal of
a new selective
model. In this paper we propose a new selective segmentation model combining ideas from
global segmentation that can be reformulated as convex such that a global minimizer can
be found independent of initialization. Numerical results are given that demonstrate its
reliability in terms of removing the sensitivity to initialization present in previous models,
and its robustness to user input.

The present paper is devoted to the study of the Cauchy problem for the magnetic-curvature-driven electromagnetic fluid equation with random effects in a bounded domain of R^3. We first obtain a crucial property of the solution to O.U. process, thanks to the lemma, the local well-posedness of the equation with the initial and boundary value is established by the contraction mapping argument. Finally, by virtue of a priori estimates, the existence and uniqueness of global solution to the stochastic plasma equation is proved.

This paper addresses the problem of global well-posedness of a cou- pled system of Korteweg-de Vries equations, derived by Majda and Biello in the context of nonlinear resonant interaction of Rossby waves, in a periodic setting in homogeneous Sobolev spaces H^s, for s\ge 0. Our approach is based on a sussessive time-averaging method developed by Babin, Ilyin and Titi [A.V. Babin, A.A. Ilyin and E.S. Titi, Comm. Pure Appl. Math. 64, 591-648, 2011].

We study the large time behavior of solutions near a constant equilibrium state to the compressible Euler-Maxwell system in R^3. We first refine the global existence of solutions by assuming that the initial data is small in the H^3 norm but its higher order derivatives could be large. If further the initial data belongs to H^{-s} (0\le s \le 3/2) or B^{-s}_{2, \infty} (0\le s \le 3/2), then we obtain the various time decay rates of the solution and its higher order derivatives. As an immediate byproduct the L^p-L^2 (1\le p \le 2) type of the decay rates follows without requiring the smallness for L^p norm of the initial data. So far, our decay results are most comprehensive ones for the bipolar Euler-Maxwell system in R^3.

The main objective of this article is to study the order-disorder phase transition and pattern formation for systems with long-range repulsive interactions. The main focus is on a Cahn-Hilliard model with a nonlocal term in the corresponding energy functional, representing certain long-range repulsive interaction. We show that as soon as the trivial steady state loses its linear stability, the system always undergoes a dynamic transition to one of the three types-- continuous, catastrophic, or random-- forming different patterns/structures, such as lamellae, hexagonally packed cylinders, rectangles, and spheres. The types of transitions are dictated by a non-dimensional parameter, measuring the interactions between the long-range repulsive term and the quadratic and cubic nonlinearities in the model. In particular, the hexagonal pattern is unique to this long-range interaction, and it is captured by the corresponding two-dimensional reduced equations on the center manifold, which involve (degenerate) quadratic terms and non-degenerate cubic terms. Explicit information on the metastability and basins of attraction of different ordered states, corresponding to different patterns, are derived as well.

We study a general Ericksen-Leslie system with non-constant density, which describes the flow of nematic liquid crystal. In particular the model investigated here is associated with Parodi's relation. We prove that: in two dimension, the solutions are globally regular with general data; in three dimension, the solutions are globally regular with small initial data, or for short time with large data. Moreover, a weak-strong type of uniqueness result is obtained.

In recent work, Li et al. (Comm.\ Math.\ Sci., 7:81-107, 2009) developed a diffuse-domain method (DDM) for solving partial differential equations in complex, dynamic geometries with Dirichlet, Neumann, and Robin boundary conditions. The diffuse-domain method uses an implicit representation of the geometry where the sharp boundary is replaced by a diffuse layer with thickness $\epsilon$ that is typically proportional to the minimum grid size. The original equations are reformulated on a larger regular domain and the boundary conditions are incorporated via singular source terms. The resulting equations can be solved with standard finite difference and finite element software packages. Here, we present a matched asymptotic analysis of general diffuse-domain methods for Neumann and Robin boundary conditions. Our analysis shows that for certain choices of the boundary condition approximations, the DDM is second-order accurate in $\epsilon$. However, for other choices the DDM is only first-order accurate. This helps to explain why the choice of boundary-condition approximation is important for rapid global convergence and high accuracy. Our analysis also suggests correction terms that may be added to yield more accurate diffuse-domain methods. Simple modifications of first-order boundary condition approximations are proposed to achieve asymptotically second-order accurate schemes. Our analytic results are confirmed numerically in the $L^2$ and $L^\infty$ norms for selected test problems.

Global geometrical optics method is a new semi-classical approach for the high frequency linear waves proposed by the author in [Commun. Math. Sci., 11(1), 105-140, 2013]. In this paper, we rederive it in a more concise way. It is shown that the right candidate of solution ansatz for the high frequency wave equations is the extended WKB function, other than the WKB function used in the classical geometrical optics approximation. A new and main contribution of this paper is an interface analysis for the Helmholtz equation when the incident wave is of extended WKB-type. We derive asymptotic expressions for the reflected and/or transmitted propagating waves in the general case. These expressions are valid even when the incident rays include caustic points.

MUSCL extensions (Monotone Upstream-centered Schemes for Conservation Laws) of the Godunov numerical scheme for scalar conservation laws are shown to admit a rather simple reformulation when recast in the formalism of the Harr multi-resolution analysis of L^2(R). By pursuing this wavelet reformulation, a seeimingly new MUSCI-WB scheme is derived for advection-reaction equations which is stable for a Courant number up to 1 (instead of roughly 1/2). However these high-order reconstructions aren't likely to improve the handling of delication nonlinear wave interactions in the involved case of systems of Conservation/Balance laws.

We study the Godunov scheme for a nonlinear Maxwell model arising in nonlinear optics, the Kerr model. This is a hyperbolic system of conservation laws with some eigenvalues of variable multiplicity, neither genuinely nonlinear nor linearly degenerate. The solution of the Riemann problem for the full-vector 6\times 6 system is constrcuted and proved to exist for all data. This solution is comprated to the one of the reduced Transverse Magnetic model. The scheme is implemented in one and two space dimensions. The results are very close to the ones obtained with a Kerr-Debye relaxation approximation.

A real option model is built upon a stochastic process for some real investment decision making in incomplete markets. Typically, optimal consumption level is obtained under logarithm utility constraint, and a partial integro-dierential equation (PIDE) of the real option is deduced by martingale methods. Analytical formulation of the PIDE is solved by Fourier transformation. Two types of decision making strategies, i.e.: option price and IRP (inner risk primium) comparisons, are provided. Monte Carlo simulation and numerical computation are provided at last to verify the conclusion.

Kohn-Sham density functional theory is one of the most widely used electronic structure theories. The recently developed adaptive local basis functions form an accurate and systematically improvable basis set for solving Kohn-Sham density functional theory using discontinuous Galerkin methods, requiring a small number of basis functions per atom. In this paper we develop residual-based a posteriori error estimates for the adaptive local basis approach, which can be used to guide non-uniform basis refinement for highly inhomogeneous systems such as surfaces and large molecules. The adaptive local basis functions are non-polynomial basis functions, and standard a posteriori error estimates for hp-refinement using polynomial basis functions do not directly apply. We generalize the error estimates for hp-refinement to non-polynomial basis functions. We demonstrate the practical use of the a posteriori error estimator in performing three-dimensional Kohn-Sham density functional theory calculations for quasi-2D aluminum surfaces and a single-layer graphene oxide system in water.

We prove the existence of global-in-time weak solutions to a model of chemically reacting mixture. We consider a coupling between the compressible Navier-Stokes system and the reaction diusion equations for chemical species when the thermal eects are neglected. We rst prove the existence of weak solutions to the semi-discretization in time. Based of this, the existence of solutions to the evolutionary system is proved.

The compressible Navier{Stokes{Poisson equations driven by a time{periodic external force are considered in this paper. The system takes into account the eect of self{gravitation. We establish the existence of weak time{periodic solutions on condition that the adiabatic constant satisfices \gamma>5/3.

We study the Kuramoto model for coupled oscillators. For the case of identical natural frequencies, we give a new proof of the complete frequency synchronization for all initial data; extending this result to the continuous version of the model, we manage to prove the complete phase synchronization for any non-atomic measure-valued initial datum. We also discuss the relation between the boundedness of the entropy and the convergence to an incoherent state, for the case of non identical natural frequencies.

In underwater acoustic waveguides a pressure field can be decomposed over three kinds of modes: the propagating modes, the radiating modes and the evanescent modes. In this paper, we analyze the effects produced by a randomly perturbed free surface and an uneven bottom topography on the coupling mechanism between these three kinds of modes. Using an asymptotic analysis based on a separation of scales technique we derive the asymptotic form of the distribution of the forward mode amplitudes. We show that the surface and bottom fluctuations affect the propagating-mode amplitudes mainly in the same way. We observe an effective amplitude attenuation which is mainly due to the coupling between the propagating modes themselves. However, for the highest propagating modes this mechanism is stronger and due to an efficient coupling with the radiating modes.

We address the weighted decay for the solution of the surface quasi-geostrophic (SQG) equation. The first moment decay was obtained by M. and T. Schonbek. Here we obtain new decay rates of the first moment and the rate of increase of this quantity under natural assumption on the initial data.

In this paper, we study the existence and uniqueness of subsonic potential flows in general smooth bounded domains when the normal component of the momentum on the boundary is prescribed. It is showed that if the Bernoulli constant is given larger than a critical number, there exists a unique subsonic potential flow. Moreover, as the Bernoulli constants decrease to the critical number, the subsonic flows converge to a subsonic-sonic flow.

In this paper, we consider the well-posedness of the compressible nematic liquid crystal flow with the cylinder symmetry in R^n. By establishing a uniform point-wise positive lower and upper bounds of the density, we derive the global existence and uniqueness of strong solution and show the long time behavior of the global solution. Our results do not need the smallness of the initial data. Furthermore, a regularity result of global strong solution is given as well.

We propose a convex variational principle to find sparse representation of low-lying eigenspace of symmetric metrices in the context of electronic structure calculation, this corresponds to a sparse density matrix minimization algorithm with l_1 regularization. The minimization problem can be efficiently solved by a split Bregman iteration type algorithm. We further prove that from any initial condition, the algorithm converges to a minimizer of the variational principle.

Here we develop a model of smectic-C liquid crystals by forming their hydrostatic and hydrodynamic theories, which are motivated by the work of W. E [Arch. Rational Mech. Anal., 137(1997)]. A simplied model is also presented. In order to prove the rationality of the model, we establish the energy dissipative relation of the new model. Meanwhile, we verify that the system can also be obtained using asymptotic analysis when both the fluid and layers are incompressible.

Sparsity plays a central role in recent developments in signal processing, linear algebra, statistics, optimization, and other fields. In these developments, sparsity is promoted through the addition of an L^1 norm (or related quantity) as a constraint or penalty in a variational principle. We apply this approach to partial differential equations that come from a variational quantity, either by minimization (to obtain an elliptic PDE) or by gradientfl ow (to obtain a parabolic PDE). Also, we show that some PDEs can be rewritten in an L^1 form, such as the divisible sandlile problem and signum-Gordon. Addition of an L^1 term in the variational principle leads to a modied PDE where a subgradient term appears. It is known that modified PDEs of this form will often have solutions with compact support, which corresponds to the discrete solution being sparse. We show that this is advantageous numerically through the use of efficient algorithms for solving L^1 based problems.

We characterize interior transmission eigenvalues of penetrable anisotropic acoustic scattering objects by a technique known as inside-outside duality. This method has recently been identified to be able to link interior eigenvalues of the penetrable scatterer with the behavior of the eigenvalues of the far field operator for the corresponding exterior time-harmonic scattering problem. A basic ingredient for the resulting connection is a suitable self-adjoint factorization of the far field operator based on wave number-dependent function spaces. Under certain conditions on the anisotropic material coeffi cients of the scatterer, the inside-outside duality allows to rigorously characterize interior transmission eigenvalues from multi-frequency far field data. This theoretical characterization moreover allows to derive a simple numerical algorithm for the approximation of interior transmission eigenvalues. Since it is merely based on far field data, the resulting eigenvalue solver does not require knowledge on the scatterer or its material coefficient; several numerical examples show its feasibility and accuracy for noisy data.

Mean field type models have been recently introduced and analyzed by Lasry and Lions. They describe a limiting behavior of stochastic dierential games as the number of players tends to infinity. Numerical methods for the approximation of such models have been developed by Achdou, Camilli, Capuzzo-Dolcetta, Gueant, and others. Efficient algorithms for such problems require special efforts and so far all methods introduced have been first order accurate. In this manuscript we design a second order accurate numerical method for time dependent Mean Field Games. The discretization is based on central schemes which are widely used in hyperbolic conservation laws.

We consider two-phase Navier-Stokes flow with a Boussinesq-Scriven surface fluid. In such a fluid the rheological behaviour at the interface includes surface viscosity effects, in addition to the classical surface tension effects. We introduce and analyze parametric finite element approximations, and show, in particular, stability results for semidiscrete versions of the methods, by demonstrating that a free energy inequality also holds on the discrete level. We perform several numerical simulations for various scenarios in two and three dimensions, which illustrate the effects of the surface viscosity.

In order to validate theoretically a dynamic model adaptation method, we propose to consider a simple case where the model error can be thoroughly analyzed. The dynamic model adaptation consists in detecting at each time step the region where a given fine model can be replaced by a corresponding coarse model in an automatic way, without deteriorating the accuracy of the result, and to couple the two models, each being computed on its respective region. Our fine model is 2 \times 2 system which involves a small time scale and setting this time scale to 0 leads to a classical conservation law, the coarse model, with a flux which depends on the unknown and on space and time. The adaptation method provides an intermediate adapted solution which results from the coupling of both models at each time step. In order to obtain sharp and rigorous error estimates for the model adaptation procedure, a simple fine model is investigated and smooth transitions between fine and coarse models are considered. We refine existing stability results for conservation laws with respect to the flux function which enables us to know how to balance the time step, the threshold for the domain decomposition and the size of the transition zone. Numerical results are presented at the end and show that our estimate is optimal.

The present paper concerns the derivation of finite volume methods to approximate weak solutions of Ten-Moments equations with source terms. These equations model compressible anisotropic flows. A relaxation type scheme is proposed to approximate such flows. Both robustness and stability conditions of the suggested finite volume methods are established. To prove discrete entropy inequalities, we derive a new strategy based on local minimum entropy principle and never use some approximate PDE's auxiliary model as usually recommended. Moreover, numerical simulations in 1D and in 2D illustrate our approach.

The paper introduces a new way to construct dissipative solutions to a second order variational wave equation. By a variable transformation, from the nonlinear PDE one obtains a semilinear hyperbolic system with sources. In contrast with the conservative case, here the source terms are discontinuous and the discontinuities are not always crossed transversally. Solutions to the semilinear system are obtained by an approximation argument, relying on Kolmogorov's compactness theorem. Reverting to the original variables, one recovers a solution to the nonlinear wave equation where the total energy is a monotone decreasing function of time.

We study a model of magnetization switching driven by a spin current: the magnetization reversal can be induced without applying an external magnetic field. We first write our one dimensional model in an adimensionalized form, using a small parameter $\epsilon$. We then explain the various time and space scales involved in the studied phenomena. Taking into account these scales, we first construct an appropriate numerical scheme, that allows us to recover numerically various results of physical experiments. We then perform a formal asymptotic study as $\epsilon$ tends to 0, using a multiscale approach and asymptotic expansions. We thus obtain approximate limit models that we compare with the original model via numerical simulation.

Bi-Jacobi fields are generalized Jacobi fields, and are used to efficiently compute approximations to Riemannian cubic splines in a Riemannian manifold M. Calculating bi-Jacobi fields is straightforward when M is a symmetric space such as bi-invariant SO(3), but not for Lie groups whose Riemannian metric is only left-invariant. Because left-invariant Riemannian metrics occur naturally in applications, there is also a need to calculate bi-Jacobi fields in such cases. The present paper investigates bi-Jacobi fields for left-invariant Riemannian metrics on SO(3), reducing calculations to quadratures of Jacobi fields. Then left Lie-reductions are used to give an easily implemented numerical method for calculating bi-Jacobi fields along geodesics in SO(3), and an example is given of a nearly geodesic approximate Riemannan cubic.

In this paper, we study the large time behavior of entropy solutions to the one-dimensional unipolar hydrodynamic model for semiconductors in the form of Euler-Poisson equations. First of all, a large time behavior framework for the time-increasing entropy solutions is given. In this framework, the global entropy solutions (which increase with time not very fast) are proved to decay exponentially fast to the corresponding stationary solutions. Then, for an application purpose, the existence and time-increasing-rate of the global entropy solutions with large initial data is considered by using a modified fractional step Lax-Friedrichs scheme and the theory of compensated compactness. By using the large time behavior framework, the global entropy solutions are proved to decay exponentially fast to the stationary solutions when the adiabatic index $\G>3$, without any assumption on smallness or regularity for the initial data.

The incorporation of priors [H. Owhadi, C. Scovel and T.J. Sullivan,
arXiv:1304.6772, 2013] in the Optimal Uncertainty Quantication (OUQ)
framework [H. Owhardi, C. Scovel, T.J. Sullican, M. McKerns, and
M. Ortiz, SIAM Review 2013]
reveals brittleness in Bayesian inference; a model may share an arbitrarily
large number of finite-dimensional marginals with, or be arbitrarily close
(in Prokhorov
or total variation metrics) to, the data-generating distribution and still make the largest
possible prediction error after conditioning on an arbitrarily large number of samples.
The initial purpose of this paper is to unwrap this brittleness mechanism by providing
(i) a quantitative version of the Brittleness Theorem of [H. Owhadi, C. Scovel and T.J. Sullivan,
arXiv:1304.6772, 2013]
and (ii) a detailed and
comprehensive analysis of its application to the revealing example of estimating the
mean of a random variable on the unit interval [0,1] using priors
that exactly capture
the distribution of an arbitrarily large number of Hausdor moments.

However, in doing so, we discovered that the free parameter associated with Markov and Krein's
canonical representations of truncated Hausdor moments generates
reproducing kernel identities corresponding to reproducing kernel Hilbert spaces of polynomials. Furthermore, these reproducing identities lead to biorthogonal systems of Selberg
integral formulas.

This process of discovery appears to be generic: whereas Karlin and Shapley used
Selberg's integral formula to first compute the volume of the Hausdor moment space
(the polytope defined by the first
n
moments of a probability measure on the interval
[0, 1],
we observe that the computation of that volume along with higher order
moments of the uniform measure on the moment space, using different
finite-dimensional
representations of subsets of the infinite-dimensional set of probability measures on [0,1] representing the first
n
moments, leads to families of equalities corresponding to classical
and new Selberg identities.

This work considers the numerical approximation of the shallow-water equations. In this context, one faces three important issues related to the well-balanced, positivity and entropy preserving properties, as well as the ability to consider vacuum states. We propose a Godunov-type method based on the design of a three-wave Approximate Riemann Solver (ARS) which satisfies the first two properties and a weak form of the last one together. Regarding the entropy, the solver satisfies a discrete non-conservative entropy inequality. From a numerical point of view, we also investigate the validity of a conservative entropy inequality.

In this article, we study a one-dimensional hyperbolic quasilinear model of chemotaxis with a non-linear pressure and we consider its stationary solutions, in particular with vacuum regions. We study both cases of the system set on the whole line R and on a bounded interval with no- ux boundary conditions. In the case of the whole line R, we nd only one stationary solution, up to a translation, formed by a positive density region (called bump) surrounded by two regions of vacuum. However, in the case of a bounded interval, an innite of stationary solutions exists, where the number of bumps is limited by the length of the interval. We are able to compare the value of an energy of the system for these stationary solutions. Finally, we study the stability of these stationary solutions through numerical simulations.

The convergence to the equilibrium of the solution of a quantum Kac grazing limit model for Bose-Einstein identical particles is studied. Using the relative en-tropy method and a detailed analysis of the entropy production, the exponential decay rate is obtained under suitable assumptions on the mass and energy of the initial data. These theoretical results are further illustrated by numerical simulations.

An optimization based algorithm is proposed for solving elliptic problems with highly oscillatory coeffcients that do not exhibit scale separation in a subregion of the physical domain. The given method, written as a constrained minimization problem couples a numerical homogenization method in the subregion of the physical domain with scale separation with a ne scale solver in subregions without scale separation. The unknown boundary conditions of both problems in the overlap region are determined by minimizing the discrepancy of the corresponding solutions in this overlap.

In this note we provide new non-uniqueness examples for the continuity equation by constructing infinitely many weak solutions with prescribed energy.

We study the "one and one-half" dimensional Vlasov-Maxwell-Fokker-Planck system and obtain the first results concerning well-posedness of solutions. Specifically, we prove the global-in-time existence and uniqueness in the large of classical solutions to the Cauchy problem and a gain in regularity of the distribution function in its momentum argument.

In this paper, we investigate the zero Mach number limit for the three-dimensional compressible Navier-Stokes-Korteweg equations in the regime of smooth solutions. Based on the local existence theory of the compressible Navier-Stokes-Korteweg equations, we establish a convergence-stability principle. Then we show that, when the Mach number is sufficiently small, the initial value problem of the compressible Navier-Stokes-Korteweg equations has a unique smooth solution in the time interval where the corresponding incompressible Navier-Stokes equations have a smooth solution. It is important to remark that when the incompressible Navier-Stokes equations have a global smooth solution, the existence time of the solution for the compressible Navier-Stokes-Korteweg equations tends to infinity as the Mach number goes to zero. Moreover, we obtain the convergence of smooth solutions for the compressible Navier-Stokes-Korteweg equations towards those for the incompressible Navier-Stokes equations with a convergence rate. As we know, it is the first result about zero Mach number limit of the compressible Navier-Stokes-Korteweg equation.

We construct a mean-field variational model to study how the dependence of dielectric coeectric coefficient (i.e., relative permittivity) on local ionic concentrations affects the electrostatic interaction in an ionic solution near a charged surface. The electrostatic free-energy functional of ionic concentrations, which is the key object in our model, consists mainly of the electrostatic potential energy and the ionic ideal-gas entropy. The electrostatic potential is determined by Poisson's equation in which the dielectric coefficient depends on the sum of concentrations of individual ionic species. This dependence is assumed to be qualitatively the same as that on the salt concentration for which experimental data are available and analytical forms can be obtained by the data fitting. We derive the first and second variations of the free-energy functional, obtain the generalized Boltzmann distributions, and show that the free-energy functional is in general nonconvex. To validate our mathematical analysis, we numerically minimize our electrostatic free-energy functional for a radially symmetric charged system. Our extensive computations reveal several features that are signicantly different from a system modeled with a dielectric coefficient independent of ionic concentration. These include the non-monotonicity of ionic concentrations, the ionic depletion near a charged surface that has been previously predicted by a one-dimensional model, and the enhancement of such depletion due to the increase of surface charges or bulk ionic concentrations.

We present a BGK approximation of a kinetic Boltzmann model for a mixture of polyatomic gases, in which non-translational degrees of freedom of each gas are represented by means of a set of discrete internal energy levels. We deal also with situations in which even chemical reactions implying transfer of mass may occur. The consistency of the proposed BGK model is proved in both inert and reactive frames, and numerical simulations in space homogeneous settings are presented.

We study a stochastic fractional complex Ginzburg-Landau equation with multiplicative noise in three spatial dimensions with particular interest in the asymptotic behavior of its solutions. We first transform our equation into a random equation whose solutions generate a random dynamical system. A priori estimates are derived when the nonlinearity satisfies certain growth conditions. Applying the estimates for far-field values of solutions and a cut-off technique, asymptotic compactness is proved. Furthermore, the existence of a random attractorin H^1(R^3) of the random dynamical system is established.

In this paper, we study the long-time behavior of a fluid particle immersed in a turbulent fluid driven by a diffusion with jumps, that is, a Feller process associated with a non-local operator. We derive the law of large numbers and central limit theorem for the evolution process of the tracked fluid particle in the cases when the driving process: (i) has periodic coeffcients, (ii) is ergodic or (iii) is a class of well-known results for fluid flows driven by elliptic diffusion processes.

It is believed that social preference, economic disparity, and heterogeneous environments are mechanisms for segregation. However, it is difficult to unravel the exact role of each mechanism in such a complex system. We introduce a versatile, simple and intuitive particle-interaction model that allows to easily examine the effect of each of these factors. It is amenable to numerical simulations, and allows for the derivation of the macroscopic equations. As the population size and number of groups with different economic status approach infinity, we derive various local and non-local system of PDEs for the population density. Through the analysis of the continuous limiting equations, we conclude that social preference is a necessary but not always sufficient mechanism for segregation. On the other hand, when combined with the environment and economic disparity (which on the their own also do not cause segregation), social preference does enhance segregation.

In this paper, we first present the derivation of the anisotropic Lagrangian averaged gyrowaterbag continuum (LAGWB-alpha) equations. The gyrowaterbag (nickname for gyrokinetic-waterbag) continuum can be viewed as a special class of exact weak solution of the gyrokinetic-Vlasov equation, allowing to reduce this latter into an infinite dimensional set of hydrodynamic equations while keeping its kinetic features such as Landau damping. In order to obtain the LAGWBC-alpha equations from the gyrowaterbag continuum we use an Eulerian variational principle and Lagrangian averaging techniques introduced by Holm, Marsden and Ratiu, Marsden and Shkoller, for the mean motion of ideal incompressible flows, extended to barotropic compressible flows by Bhat et. al. and some supplementary approximations for the electrical potential uctuations. Regarding to the original gyrowaterbag continuum, the LAGWBC-alpha equations show some additional properties and several advantages from the mathematical and physical viewpoints, which make this model a good candidate for describing accurately gyrokinetic turbulence in magnetically confined plasma. In the second part of this paper we prove local-in-time well-posedness of an approximated version of the anisotropic LAGWBC-alpha equations, that we call the anisotropic" LAGWBC-alpha equations, by using quasilinear PDE type methods and elliptic regularity estimates for several operators.

A new class of high-order accuracy numerical methods for the BGK model of the Boltzmann equation is presented. The schemes are based on a semi-Lagrangian formulation of the BGK equation; time integration is dealt with DIRK (Diagonally Implicit Runge Kutta) and BDF methods; the latter turn out to be accurate and computationally less expensive than the former. Numerical results and examples show that the schemes are reliable and efficient for the investigation of both rarefied and fluid regimes in gasdynamics.

In this paper, we investigate the effects of environment fuctuations on the disease's
dynamics through studying the stochastic dynamics of an SIS model incorporating media coverage.
The value of this study lies in two aspects: Mathematically, we show that the disease dynamics the
SDE model can be governed by its related basic reproduction number R_0^S:
if R_0^S \le 1, the disease will die out stochastically, while R_0^S>1,
the disease will break out with probability one. Epidemiologically, we partially provide the effects of the environment fuctuations affect the disease spreading
incorporating media coverage. First, noise can suppress the disease outbreak. Notice that R_0^S

We construct small-amplitude steady periodic gravity water waves arising as the free surface of water flows that contain stagnation points and possess a discontinuous distribution of vorticity in the sense that the flows consists of two layers of constant but different vorticities. We also describe the streamline pattern in the moving frame for the constructed flows.