437 research outputs found
Remarks on the Rayleigh-Benard Convection on Spherical Shells
The main objective of this article is to study the effect of spherical
geometry on dynamic transitions and pattern formation for the Rayleigh-Benard
convection. The study is mainly motivated by the importance of spherical
geometry and convection in geophysical flows. It is shown in particular that
the system always undergoes a continuous (Type-I) transition to a
-dimensional sphere , where lc is the critical wave length
corresponding to the critical Rayleigh number. Furthermore, it has shown in
[12] that it is critical to add nonisotropic turbulent friction terms in the
momentum equation to capture the large-scale atmospheric and oceanic
circulation patterns. We show in particular that the system with turbulent
friction terms added undergoes the same type of dynamic transition, and obtain
an explicit formula linking the critical wave number (pattern selection), the
aspect ratio, and the ratio between the horizontal and vertical turbulent
friction coefficients
Random data Cauchy theory for supercritical wave equations II : A global existence result
We prove that the subquartic wave equation on the three dimensional ball
, with Dirichlet boundary conditions admits global strong solutions for
a large set of random supercritical initial data in .
We obtain this result as a consequence of a general random data Cauchy theory
for supercritical wave equations developed in our previous work \cite{BT2} and
invariant measure considerations which allow us to obtain also precise large
time dynamical informations on our solutions
On the approximate controllability for some explosive parabolic problems
We consider in this paper distributed systems governed by parabolic evolution equations which can blow up in finite time and which are controlled by initial conditions. We study here the following question : Can one choose the initial condition in such a way that the solution does not blow up before a given time T and which is, at time T, as close as we wish from a given state ? Some general results along these lines are presented here for semilinear second order parabolic equations as well as for a non local nonlinear problem. We also give some results proving that "the more the system will blow up" the "cheaper" it will be the control
Homogenization of nonlinear stochastic partial differential equations in a general ergodic environment
In this paper, we show that the concept of sigma-convergence associated to
stochastic processes can tackle the homogenization of stochastic partial
differential equations. In this regard, the homogenization problem for a
stochastic nonlinear partial differential equation is studied. Using some deep
compactness results such as the Prokhorov and Skorokhod theorems, we prove that
the sequence of solutions of this problem converges in probability towards the
solution of an equation of the same type. To proceed with, we use a suitable
version of sigma-convergence method, the sigma-convergence for stochastic
processes, which takes into account both the deterministic and random
behaviours of the solutions of the problem. We apply the homogenization result
to some concrete physical situations such as the periodicity, the almost
periodicity, the weak almost periodicity, and others.Comment: To appear in: Stochastic Analysis and Application
A geometric condition implying energy equality for solutions of 3D Navier-Stokes equation
We prove that every weak solution to the 3D Navier-Stokes equation that
belongs to the class and \n u belongs to localy
away from a 1/2-H\"{o}lder continuous curve in time satisfies the generalized
energy equality. In particular every such solution is suitable.Comment: 10 page
Mathematical results for some models of turbulence with critical and subcritical regularizations
In this paper, we establish the existence of a unique "regular" weak solution
to turbulent flows governed by a general family of models with
critical regularizations. In particular this family contains the simplified
Bardina model and the modified Leray- model. When the regularizations
are subcritical, we prove the existence of weak solutions and we establish an
upper bound on the Hausdorff dimension of the time singular set of those weak
solutions. The result is an interpolation between the bound proved by Scheffer
for the Navier-Stokes equations and the regularity result in the critical case
On thin plate spline interpolation
We present a simple, PDE-based proof of the result [M. Johnson, 2001] that
the error estimates of [J. Duchon, 1978] for thin plate spline interpolation
can be improved by . We illustrate that -matrix
techniques can successfully be employed to solve very large thin plate spline
interpolation problem
Blow up criterion for compressible nematic liquid crystal flows in dimension three
In this paper, we consider the short time strong solution to a simplified
hydrodynamic flow modeling the compressible, nematic liquid crystal materials
in dimension three. We establish a criterion for possible breakdown of such
solutions at finite time in terms of the temporal integral of both the maximum
norm of the deformation tensor of velocity gradient and the square of maximum
norm of gradient of liquid crystal director field.Comment: 22 page
Distributed optimal control of a nonstandard system of phase field equations
We investigate a distributed optimal control problem for a phase field model
of Cahn-Hilliard type. The model describes two-species phase segregation on an
atomic lattice under the presence of diffusion; it has been recently introduced
by the same authors in arXiv:1103.4585v1 [math.AP] and consists of a system of
two highly nonlinearly coupled PDEs. For this reason, standard arguments of
optimal control theory do not apply directly, although the control constraints
and the cost functional are of standard type. We show that the problem admits a
solution, and we derive the first-order necessary conditions of optimality.Comment: Key words: distributed optimal control, nonlinear phase field
systems, first-order necessary optimality condition
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