Topological singularities in W S,P ( S N , S 1)

We are interested in the location of the singularities of maps u ∈ W ^s,p (S ^N , S ¹) when 1 ≤ sp and 1 < sp < 2. To this end, we consider the distributional Jacobian. We show that the range of this operator on W ^s,p (S ^N , S ¹) is the closure in W ^s−2,p ⋂ W ^−1,sp of the set of N − 2-currents defined as the integration on smooth oriented N − 2-dimensional boundaryless submanifolds.     

Study of a class of control problems for the stationary Navier-Stokes equations with mixed boundary conditions

Under study are extremal problems for the stationary Navier-Stokes equations with mixed boundary conditions on velocity. Some new a priori estimates are deduced for solutions to the extremal problems under consideration. These yield some local theorems on the uniqueness and stability of solutions for the particular quality functionals that depend on the total pressure.     

The Luzin approximation of functions from classes Wαp on metric spaces with measure

In this paper we prove an analog of the Luzin theorem on correction for spaces of the Sobolev type on an arbitrary metric space with a measure, satisfying the doubling condition. The correcting function belongs to the H?lder class and approximates a given function in the metrics of the initial space. Dimensions of exceptional sets are evaluated in terms of Hausdorff capacities and volumes. Original Russian Text ? V.G. Krotov and M.A. Prokhorovich, 2008, published in Izvestiya Vysshikh Uchebnykh Zavedenii. Matematika, 2008, No. 5, pp. 55–66. Dedicated to the memory of Petr Lavrent’evich Ul’yanov     

Density of smooth maps in Wk, p(M, N) for a close to critical domain dimension

Assuming m − 1 < kp < m, we prove that the space C ^∞(M, N) of smooth mappings between compact Riemannian manifolds M, N (m = dim M) is dense in the Sobolev space W ^k,p (M, N) if and only if π _m−1(N) = {0}. If π _m−1(N) ≠ {0}, then every mapping in W ^k,p (M, N) can still be approximated by mappings M → N which are smooth except in finitely many points.     

Existence, uniqueness and stability of C m solutions of iterative functional equations

In this paper we discuss a relatively general kind of iterative functional equation G(x,f(x), ...,f ⁿ (x)) = 0 (for allx ∈J), whereJ is a connected closed subset of the real number axis ℝ,G∈C ^m (J ⁿ⁺¹, ℝ) andn ≥ 2. Using the method of approximating fixed points by small shift of maps, choosing suitable metrics on functional spaces and finding a relation between uniqueness and stability of fixed points of maps of general spaces, we prove the existence, uniqueness and stability ofCm solutions of the above equation for any integer m ≥ 0 under relatively weak conditions, and generalize related results in reference in different aspects.     

A refined mixed finite-element method for the stationary Navier Stokes equations with mixed boundary conditions

Serge Nicaise ^{This paper is concerned with the mixed formulation of the Navier–Stokesequations with mixed boundary conditions in 2D polygonal domainsand its numerical approximation. We first describe the regularityof any solution. The problem is then approximated by a mixedfinite-element method where the strain tensor and the antisymmetricgradient tensor, quantities of practical importance, are introducedas new unknowns. An existence result for the finite-elementsolution and convergence results are proved near a nonsingularsolution. Quasi-optimal error estimates are finally presented.}     

On the boundary regularity of suitable weak solutions to the Navier-Stokes equations

We consider suitable weak solutions to an incompressible viscous Newtonian fluid governed by the Navier-Stokes equations in the half space \({\mathbb {R}^3_+}\). Our main result is a direct proof of the partial regularity up to the flat boundary based on a new decay estimate, which implies the regularity in the cylinder \({Q_\rho ^+(x_0, t_0)}\) provided

$\limsup_{R\to 0}\frac {1} {R}\int\limits_{Q_R^+(x_0, t_0)} |{\rm rot}\,\mathbf u|^2 dxdt \,\leq\, \varepsilon _0$

with ε ₀ sufficiently small. In addition, we get a new condition for the local regularity beyond Serrin’s class which involves the L ²-norm of ?u and the L ^3/2-norm of the pressure.

     

Numerical stabilization of unstable solutions to Navier-Stokes equations from the domain boundary

In order to stabilize an unstable solution to Navier-Stokes equations with the help of boundary conditions, a discrete analogue of the algorithm proposed by A. V. Fursikov in the differential case is constructed. A Quette flow between rotating cylinders is taken as an unstable solution. A complete calculation cycle of stabilization is performed and the obtained results are discussed     

Global strong solutions of Navier-Stokes equations with interface boundary in three-dimensional thin domains

In this article, we study the spectrum of the Stokes operator in a 3D two layer domain with interface, obtain the asymptotic estimates on the spectrum of the Stokes operator as thickness ε goes to zero. Based on the spectral decomposition of the Stokes operator, a new average-like operator is introduced and applied to the study of Navier-Stokes equation in the two layer thin domains under interface boundary condition. We prove the global existence of strong solutions to the 3D Navier-Stokes equations when the initial data and external forces are in large sets as the thickness of the domain is small. This article is a continuation of our study on the Stokes operator under Navier friction boundary condition. Due to the viscosity distinction between the two layers, the Stokes operator displays radically different spectral structure from that under Navier friction boundary condition, then causes great difficulty to the analysis.     

Determination of the solutions of boundary value problems for stationary stokes and Navier-Stokes equations having an unbounded Dirichlet integral

In unbounded domains Ω of the three-dimensional Euclidean space, having several outlets Ω _i i=1,...,N, at infinity, one investigates the time-dependent solutions of the Stokes and Navier-Stokes system of equations for incompressible fluids, equal to zero at the boundary of the domain Ω and having arbitrary flows ∝ _i through each of the outlets Ω_i (the numbers ∝ _i satisfy only the necessary condition: \(\sum\limits_{i = 1}^N {\alpha _i } = 0\) ). For these solutions one establishes Phragmén-Lindelöf and Saint-Venant type theorems characterizing the growth of solutions at infinity. On their basis, one formulates well-posed boundary value problems for the above indicated systems and domain Ω and one proves their solvability for any quantities ∝ _i . One investigates various properties of these solutions and one gives sufficient conditions for uniqueness theorems. In particular, when Ω is a pipe with cylindrical ends, then our solutions approach the Poiseuille flows with a given flow ∝ _i , for any in the case of the Stokes system and for ∝ _i smaller in absolute value than some critical value ∝ _i ^* , in the case of the Navier-Stokes system.     

On some properties of solutions of Navier-Stokes equations with oscillating data

We prove statements on asymptotic estimates of solutions of nonstationary Navier-Stokes equations with periodic data rapidly oscillating with respect to the spatial variables when the oscillations are zero in mean. A viscosity coefficient is also considered as a positive parameter in the equations. In the general case, the proved estimates are realistic whenever the viscosity coefficient is not too small in comparison with some power of the parameter specifying the period of data oscillations. In particular, such estimates are valid for Kolmogorov flow with Reynolds number not too large. We formulate conditions under which the asymptotics for velocity fields can contain rapidly oscillating terms. __________ Translated from Trudy Seminara imeni I. G. Petrovskogo, No. 26, pp. 309–322, 2007.     

A generalization of adjoint crystals for the quantized affine algebras of type An(1) , Cn(1) and Dn+1(2)

We generalize Benkart-Frenkel-Kang-Lee’s adjoint crystals and describe their crystal structure for type A _n ⁽¹⁾, C _n ⁽¹⁾ and D _n+1⁽²⁾.