We study numerically the semiclassical limit for the nonlinearSchrödinger equation thanks to a modification of the Madelungtransform due to Grenier. This approach allows for the presence ofvacuum. Even if the mesh size and the time step do not depend on the Planck constant, we recover the position and current densities in thesemiclassical limit, with a numerical rate of convergence inaccordance with the theoreticalresults, before shocks appear in the limiting Eulerequation. By using simple projections, the mass and the momentum ofthe solution are well preserved by the numerical scheme,while the variation of the energy is not negligiblenumerically. Experiments suggest that beyond the critical time for theEuler equation, Grenier's approach yields smooth but highlyoscillatory terms.

This paper deals with the mathematical and numerical analysis of asimplified two-dimensional model for the interaction between the windand a sail. The wind is modeled as a steady irrotational plane flow pastthe sail, satisfying the Kutta-Joukowski condition. This conditionguarantees that the flow is not singular at the trailing edge of thesail. Although for the present analysis the position of the sail istaken as data, the final aim of this research is to develop tools tocompute the sail shape under the aerodynamic pressure exerted by thewind. This is the reason why we propose a fictitious domain formulationof the problem, involving the wind velocity stream function and aLagrange multiplier; the latter allows computing the force densityexerted by the wind on the sail. The Kutta-Joukowski condition isimposed in integral form as an additional constraint. The resultingproblem is proved to be well posed under mild assumptions. For thenumerical solution, we propose a finite element method based onpiecewise linear continuous elements to approximate the stream functionand piecewise constant ones for the Lagrange multiplier. Error estimatesare proved for both quantities and a couple of numerical testsconfirming the theoretical results are reported. Finally the method isused to determine the sail shape under the action of the wind.

We study the linearized water-wave problem in a bounded domain (e.g. afinite pond of water) of ${\mathbb R}^3$, having a cuspidal boundary irregularity created by a submerged body. In earlier publications the authors discovered thatin this situation the spectrum of the problem may contain a continuous component in spite of the boundedness of the domain. Here, we proceed to impose and study radiation conditions at a point ${\mathcal O}$ of the water surface, wherea submerged body touches the surface (see Fig. 1). The radiation conditions emerge from the requirement thatthe linear operator associated to the problem be Fredholm of index zeroin relevant weighted function spaces with separated asymptotics.The classification of incoming and outgoing (seen from ${\mathcal O}$) waves and the unitary scattering matrix are introduced.

It is well known that transcritical flow past an obstacle may generate undular bores propagating away from the obstacle. This flow has been successfully modelled in the framework of the forced Korteweg–de Vries equation, where numerical simulations and asymptotic analyses have shown that the unsteady undular bores are connected by a locally steady solution over the obstacle. In this paper we present an overview of the underlying theory, together with some recent work on the case where the obstacle has a large width.

High tuberculosis (TB) prevalence in Papua New Guinea (PNG) is a serious public health concern. The epidemic in this region is exacerbated by the presence of drug-resistant TB strains as well as HIV infection. This presents a public health threat not only locally but also to Australia due to the high potential for cross-border transmission between PNG’s Western Province and the Australian Torres Strait Islands. We present two mathematical models of TB in the Western Province: a simple model of the underlying TB dynamics, and a detailed model which accounts for the additional effects of HIV and drug resistance. The detailed model is used to make quantitative predictions about the impact of expanding the TB case detection rate under the Directly Observed Treatment, Short-course treatment regimen. This paper provides a framework for future investigation into the economic costs and public health benefits of potential TB interventions in this region, with the eventual aim of providing recommendations to guide policy makers in both PNG and Australia.

The Exp-function method is applied to construct a new type of solution of the coupled (2+1)-dimensional nonlinear system of Schrödinger equations. It is shown that the method provides a powerful mathematical tool for solving nonlinear evolution equations in mathematical physics.


In this paper, a dynamic viscoelastic problem is numerically studied. The variationalproblem is written in terms of the velocity field and it leads to a parabolic linearvariational equation. A fully discrete scheme is introduced by using thefinite element method to approximate the spatial variable andan Euler scheme to discretize time derivatives. An a priori error estimatesresult is recalled, from which the linear convergence is derived under suitableregularity conditions. Then, an a posteriorierror analysis is provided, extending some preliminary resultsobtained in the study of the heat equation and quasistatic viscoelastic problems.Upper and lower error bounds are obtained. Finally, some two-dimensionalnumerical simulations are presented to show the behavior of the error estimators.

This paper examines an antiplane crack problem for a functionally graded anisotropic elastic material in which the elastic moduli vary quadratically with the spatial coordinates. A solution to the crack problem is obtained in terms of a pair of integral equations. An iterative solution to the integral equations is used to examine the effect of the anisotropy and varying elastic moduli on the crack tip stress intensity factors and the crack displacement.

A boundary-value problem for cell growth leads to an eigenvalue problem. In this paper some properties of the eigenfunctions are studied. The first eigenfunction is a probability density function and is of importance in the cell growth model. We sharpen an earlier uniqueness result and show that the distribution is unimodal. We then show that the higher eigenfunctions have nested zeros. We show that the eigenfunctions are not mutually orthogonal, but that there are certain orthogonality relations that effectively partition the set of eigenfunctions into two sets.

We study a microfluidic flow model where the movement of several charged species is coupled with electric field and the motion of ambient fluid. The main numerical difficulty in this model is the net charge neutrality assumption which makes the system essentially overdetermined. Hence we propose to use the involutive and the associated augmented form of the system in numerical computations. Numerical experiments on electrophoresis and stacking show that the completed system significantly improves electroneutrality constraint conservation and recovers analytical results while a direct implementation of the initial model fails.

We consider the problem of approximating a probability measure defined on a metric spaceby a measure supported on a finite number of points. More specifically we seek theasymptotic behavior of the minimal Wasserstein distance to an approximation when thenumber of points goes to infinity. The main result gives an equivalent when the space is aRiemannian manifold and the approximated measure is absolutely continuous and compactlysupported.

We aim at characterizing viability, invariance and some reachability properties of controlled piecewise deterministic Markov processes (PDMPs). Using analytical methods from the theory of viscosity solutions, we establish criteria for viability and invariance in terms of the first order normal cone. We also investigate reachability of arbitrary open sets. The method is based on viscosity techniques and duality for some associated linearized problem. The theoretical results are applied to general On/Off systems, Cook’s model for haploinsufficiency, and a stochastic model for bacteriophage λ.

We consider chained systems that model various systems of mechanical or biologicalorigin. It is known according to Brockett that this class of systems, which arecontrollable, is not stabilizable by continuous stationary feedback (i.e.independent of time). Various approaches have been proposed to remedy thisproblem, especially instationary or discontinuous feedbacks. Here, we look at anotherstabilization strategy (by continuous stationary or discontinuous feedbacks) to ensure theasymptotic stability even in finite time for some variables, while other variables doconverge, and not necessarily toward equilibrium. Furthermore, we build feedbacks thatpermit to vanish the two first components of the Brockett integrator in finite time, whileensuring the convergence of the last one. The considering feedbacks are continuous anddiscontinuous and regular outside zero.

The Aviles Giga functional is a well known second order functional that forms a model forblistering and in a certain regime liquid crystals, a related functional models thinmagnetized films. Given Lipschitz domain Ω ⊂ ℝ2 the functionalis \hbox{$I_{\ep}(u)=\frac{1}{2}\int_{\Omega}\ep^{-1}\lt|1-\lt|Du\rt|^2\rt|^2+\ep\lt|D^2 u\rt|^2 {\rm d}z$}${\mathit{I}}_{\mathit{ϵ}}\mathrm{\left(}\mathit{u}\mathrm{\right)}\mathrm{=}\frac{\mathrm{1}}{\mathrm{2}}{{}^{\mathrm{\int }}}_{\mathit{\Omega }}{\mathit{ϵ}}^{-1}{\left|\mathrm{1}\mathrm{-}{\left|\mathit{Du}\right|}^{\mathrm{2}}\right|}^{\mathrm{2}}\mathrm{+}\mathit{ϵ}{\left|{\mathit{D}}^{\mathrm{2}}\mathit{u}\right|}^{\mathrm{2}}\mathrm{d}\mathit{z}$ whereu belongs to the subset of functions in\hbox{$W^{2,2}_{0}(\Omega)$}${\mathit{W}}_{\mathrm{0}}^{\mathrm{2}\mathit{,}\mathrm{2}}\mathrm{\left(}\mathit{\Omega }\mathrm{\right)}$ whose gradient (in thesense of trace) satisfiesDu(x)·ηx = 1where ηx is the inward pointing unit normalto ∂Ω at x. In [Ann. Sc. Norm. Super. Pisa Cl.Sci. 1 (2002) 187–202] Jabin et al. characterizeda class of functions which includes all limits of sequences\hbox{$u_n\in W^{2,2}_0(\Omega)$}${\mathit{u}}_{\mathit{n}}\mathrm{\in }{\mathit{W}}_{\mathrm{0}}^{\mathrm{2}\mathit{,}\mathrm{2}}\mathrm{\left(}\mathit{\Omega }\mathrm{\right)}$ withIϵn(un) → 0as ϵn → 0. A corollary to their work is thatif there exists such a sequence (un) for abounded domain Ω, then Ω must be a ball and (up tochange of sign)u: = limn → ∞un = dist(·,∂Ω).Recently [Lorent, Ann. Sc. Norm. Super. Pisa Cl. Sci. (submitted),http://arxiv.org/abs/0902.0154v1] we provided a quantitative generalizationof this corollary over the space of convex domains using ‘compensated compactness’inspired calculations of DeSimone et al. [Proc. Soc. Edinb. Sect.A 131 (2001) 833–844]. In this note we use methods of regularitytheory and ODE to provide a sharper estimate and a much simpler proof for the case whereΩ = B1(0) without the requiring the tracecondition on Du.

We derive an optimal lower bound of theinterpolation error for linear finite elements on a bounded two-dimensionaldomain. Using the supercloseness between the linear interpolantof the true solution of an elliptic problem and its finite elementsolution on uniform partitions, we furtherobtain two-sided a priori bounds of the discretization error by means of theinterpolation error. Two-sided bounds for bilinear finite elementsare given as well. Numerical tests illustrate our theoreticalanalysis.

A preconditioned iterative method for the two-dimensional Helmholtz equation with Robbins boundary conditions is discussed. Using a finite-difference method to discretize the Helmholtz equation leads to a sparse system of equations which is too large to solve directly. The approach taken in this paper is to precondition this linear system with a sine transform based preconditioner and then solve it using the generalized minimum residual method (GMRES). An analytical formula for the eigenvalues of the preconditioned matrix is derived and it is shown that the eigenvalues are clustered around 1 except for some outliers. Numerical results are reported to demonstrate the effectiveness of the proposed method.

We investigate natural convection cooling of the fluid in a drink can placed in a refrigerator by simulating the full combined boundary layer system on the can wall. The cylindrical can is filled with water at initial nondimensional temperature 0, and located within a larger cylindrical container filled with air at initial temperature −1. The outer container walls are maintained at constant temperature −1. Initially both fluids are at rest. Two configurations are examined: the first has the inner can placed vertically in the middle of the outer container with no contact with the outer container walls, and the second has the inner can placed vertically at the bottom of the outer container. The results are compared to those obtained by assuming that the inner can walls are maintained at a constant temperature, showing similar basic flow features and scaling relations, but with very different proportionality constants.