Weighted estimates for stationary Navier-Stokes equations

We show Morrey-type estimates for the weak solution of the periodic Navier-Stokes equations in dimensionN, 5 <N < 10. ForN < 8, we prove the existence of a maximum solution.     

Attractors for parabolic equations with dynamic boundary conditions

In this paper we prove existence of global solutions and (L²(Ω)×L²(Γ),(H¹(Ω)∩L^p(Ω))×L^p(Γ))$(L^2\left(\Omega \right)\times L^2\left(\Gamma \right),(H^1\left(\Omega \right)\cap L^p\left(\Omega \right))\times L^p\left(\Gamma \right))$-global attractors for semilinear parabolic equations with dynamic boundary conditions in bounded domains with a smooth boundary, where there is no other restriction on p(≥2)$p(\ge 2)$.     

A priori estimates for solutions to systems of nonlinear parabolic equations

A class of nondiagonal systems of nonlinear parabolic equations that can be reduced to a scalar parabolic equation in the phase space of a larger dimension is described. In view of such a reduction, it is possible to state the maximum principle for solutions to systems of nonlinear parabolic equations and derive a priori C^2+α-estimates for a solution to the Cauchy problem. Bibliography: 19 titles. Translated fromProblemy Matematicheskogo Analiza, No. 16. 1997, pp. 41–67.     

Attractors for a class of semi-linear degenerate parabolic equations

We consider degenerate parabolic equations of the form $$\left. \begin{array}{ll}\,\,\, \partial_t u = \Delta_\lambda u + f(u) \\u|_{\partial\Omega} = 0, u|_{t=0} = u_0\end{array}\right.$$ in a bounded domain ${\Omega\subset\mathbb{R}^N}$ , where Δ_λ is a subelliptic operator of the type $$\quad \Delta_\lambda:= \sum_{i=1}^{N} \partial_{x_i}(\lambda_{i}^{2} \partial_{x_i}),\qquad \lambda = (\lambda_1,\ldots, \lambda_N).$$ We prove global existence of solutions and characterize their longtime behavior. In particular, we show the existence and finite fractal dimension of the global attractor of the generated semigroup and the convergence of solutions to an equilibrium solution when time tends to infinity.     

Global estimates for nonlinear parabolic equations

We consider nonlinear parabolic equations of the type $$u_t - {\rm div}a(x, t, Du)= f(x, t) \quad {\rm on}\quad \Omega_T =\Omega\times (-T,0),$$ under standard growth conditions on a, with f only assumed to be integrable. We prove general decay estimates up to the boundary for level sets of the solutions u and the gradient Du which imply very general estimates in Lebesgue and Lorentz spaces. Assuming only that the involved domains satisfy a mild exterior capacity density condition, we provide global regularity results.     

Attractors for quasilinear second-order parabolic equations of the general form

The question of the existence of compact minimal global B-attractors and their properties is investigated for quasilinear second-order parabolic equations of the general form in bounded domains under the Dirichlet condition.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova Akad. Nauk SSSR, Vol. 171, pp. 163–173, 1989.     

Consistent two-sided estimates for the solutions of quasilinear parabolic equations and their approximations

For a linearized finite-difference scheme approximating the Dirichlet problem for a multidimensional quasilinear parabolic equation with unbounded nonlinearity, we establish pointwise two-sided solution estimates consistent with similar estimates for the differential problem. These estimates are used to prove the convergence of finite-difference schemes in the grid L ₂ norm.     

Attractors for nonautonomous 2D Navier-Stokes equations with less regular symbols

We introduce a new class of functions satisfying normal Condition (C*), denoted by , which are translation bounded but not translation compact — in particular, which are more general than normal functions (see [S.S. Lu, H.Q. Wu, C.K. Zhong, Attractors for nonautonomous 2D Navier-Stokes equations with normal external forces, Discrete Contin. Dyn. Syst., 13 (2005) 701-719] for the definition), denoted by . Furthermore, we prove the existence of uniform attractors for 2D Navier-Stokes equations with external forces belonging to in .     

Gradient estimates for doubly nonlinear parabolic equations

Local gradient estimates for weak solutions of the equation

Attractors for nonautonomous 2D Navier-Stokes equations with less regular normal forces

First, the existence and structure of uniform attractors in H is proved for nonautonomous 2D Navier-Stokes equations on bounded domain with a new class of distribution forces, termed normal in (see Definition 3.1), which are translation bounded but not translation compact in . Then, the properties of the kernel section are investigated. Last, the fractal dimension is estimated for the kernel sections of the uniform attractors obtained.     

Partial Schauder estimates for second-order elliptic and parabolic equations

We establish Schauder estimates for both divergence and non-divergence form second-order elliptic and parabolic equations involving H?lder semi-norms not with respect to all, but only with respect to some of the independent variables.     

Refined a priori estimates for the axisymmetric Navier-Stokes equations

In this paper, we consider the axisymmetric Navier-Stokes equations, and provide a refined a priori estimate for the swirl component of the vorticity. This extends Theorem 2 of [D. Chae, J. Lee, On the regularity of the axisymmetric solutions of the Navier-Stokes equations, Math. Z., 239 (2002), 645--671].     

Wiener estimates at boundary points for parabolic equations

Summary We prove an estimate on the modulus of continuity at a boundary point (Wiener estimate) for the weak solutions of parabolic equations.

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Sunto Si prova una stima per il modulo di continuità in un punto di frontiera (stima di Wiener) per soluzioni deboli di equazioni paraboliche.

     

Bilinear estimates in BMO and the Navier-Stokes equations

We prove that the BMO norm of the velocity and the vorticity controls the blow-up phenomena of smooth solutions to the Navier-Stokes equations. Our result is applied to the criterion on uniqueness and regularity of weak solutions in the marginal class. Received February 15, 1999; in final form October 11, 1999 / Published online July 3, 2000     

A priori estimates for quasilinear degenerate parabolic equations

We prove some maximum and gradient estimates for classical solutions to a wide class of quasilinear degenerate parabolic equations, including first order ones. The proof is elementary and exploits the smallness of the domain in the time direction.

     

Harnack estimates for quasi-linear degenerate parabolic differential equations

We establish the intrinsic Harnack inequality for non-negative solutions of a class of degenerate, quasilinear, parabolic equations, including equations of the p-Laplacian and porous medium type. It is shown that the classical Harnack estimate, while failing for degenerate parabolic equations, it continues to hold in a space-time geometry intrinsic to the degeneracy. The proof uses only measure-theoretical arguments, it reproduces the classical Moser theory, for non-degenerate equations, and it is novel even in that context. Hölder estimates are derived as a consequence of the Harnack inequality. The results solve a long standing problem in the theory of degenerate parabolic equations.     

Error estimates for semi-discrete gauge methods for the Navier-Stokes equations

The gauge formulation of the Navier-Stokes equations for incompressible fluids is a new projection method. It splits the velocity in terms of auxiliary (nonphysical) variables and and replaces the momentum equation by a heat-like equation for and the incompressibility constraint by a diffusion equation for . This paper studies two time-discrete algorithms based on this splitting and the backward Euler method for with explicit boundary conditions and shows their stability and rates of convergence for both velocity and pressure. The analyses are variational and hinge on realistic regularity requirements on the exact solution and data. Both Neumann and Dirichlet boundary conditions are, in principle, admissible for but a compatibility restriction for the latter is uncovered which limits its applicability.