We study the Kolmogorov’s entropy of uniform attractors for non-autonomous dissipative PDEs. The main attention is payed to the case where the external forces are not translation-compact. We present a new general scheme which allows us to give the upper bounds of this entropy for various classes of external forces through the entropy of proper projections of their hulls to the space of translation-compact functions. This result generalizes well known estimates of Vishik and Chepyzhov for the translation-compact case. The obtained results are applied to three model problems: sub-quintic 3D damped wave equation with Dirichlet boundary conditions, quintic 3D wave equation with periodic boundary conditions and 2D Navier-Stokes system in a bounded domain. The examples of finite-dimensional uniform attractors for some special external forces which are not translation-compact are also given.

We study the dimensions of the attractors for the fractional Navier-Stokes-Voigt equations. These equations, which include a fractional order of the Stokes operator applied to the time derivative, serve as natural extensions and regularizations of the classical Navier-Stokes equations. We give a comprehensive analysis of the upper bounds for the fractal dimensions of the attractor in terms of the relevant physical parameters based on the advanced spectral inequalities such as Lieb-Thirring and Cwikel-Lieb-Rozenblum inequalities. These results extend previous works on the classical Navier-Stokes-Voigt system to the fractional setting and give an essential improvement of the estimates known before for the non-fractional case as well.

We give explicit estimates of order gamma(-d) (with logarithmic correction in the 1D case) for the fractal dimension of the attractor of the damped hyperbolic equation (or system) in a bounded domain ohm subset of R-d, d >= 1, with linear damping coefficient gamma > 0. The key ingredient in the proof for d >= 3 is Lieb's bound for the Lp-norms of systems with orthonormal gradients based on the Cwikel-Lieb-Rozenblum (CLR) inequality for negative eigenvalues of the Schro & uml;dinger operator. The case d = 1 is simpler, but contains a logarithmic correction term that seems to be inevitable. The 2D case is more difficult and is strongly based on the Strichartz-type estimates for the linear equation. Lower bounds of the same order for the dimension of the attractor are also obtained for a damped hyperbolic system with non-linearity containing a small non-gradient perturbation term, meaning that in this case our estimates are optimal for d >= 2 and contain a logarithmic discrepancy for d = 1. Estimates for the various dimensions (Hausdorff, fractal, Lyapunov) of the attractor in purely gradient case are also given. We show, in particular, that the Lyapunov dimension of a non-trivial attractor is of the order gamma(-1) in all spatial dimensions d >= 1.

The Voigt regularization of the Navier–Stokes system is studied in a bounded domain and on the torus. In the 3D case we obtain new explicit bounds for the attractor dimension improving the previously known results. In the 2D case we show that the estimates so obtained converge to the known estimates for the attractor of the Navier–Stokes system as the regularization parameter tends to zero both for the Dirichlet and the periodic boundary conditions.

The Navier–Stokes–Voigt system on the entire four-dimensional space ℝ^4 is considered. Although we do not know any physical reason to consider this system in the four-dimensional space, the attractors theory for this case becomes especially simple and elegant and nothing similar happens when the space dimension is not four. In the present note, we develop this theory, including well-posedness, dissipativity, existence of a global attractor, and estimates for its dimension.

The Navier--Stokes--Voigt system in the whole four-dimensional space is considered. Although we do not know any physical reasons to consider this system in space dimension four, the attractors theory for this case becomes especially simple and elegant and nothing similar happens when the space dimension is different than four. These notes are devoted to developing this theory, including well-posedness, dissipativity, existence of a global attractor and estimates for its dimension.

The paper is devoted to a comprehensive study of smoothness of inertial manifolds for abstract semilinear parabolic problems. It is well known that in general we cannot expect more than $C^{1,\varepsilon}$-regularity for such manifolds (for some positive, but small $\varepsilon$). Nevertheless, as shown in the paper, under the natural assumptions, the obstacles to the existence of a $C^n$-smooth inertial manifold (where $n\in\mathbb N$ is any given number) can be removed by increasing the dimension and by modifying properly the nonlinearity outside of the global attractor (or even outside the $C^{1,\varepsilon}$-smooth IM of a minimal dimension). The proof is strongly based on the Whitney extension theorem.

For 2D Navier–Stokes equations in a bounded smooth domain, we construct a system of determining functionals which consists of N linear continuous functionals which depend on pressure p only and of one extra functional which is given by the value of vorticity at a fixed point x_0∈∂Ω.

A new method for obtaining lower bounds for the dimension of attractors for the Navier–Stokes equations is presented, which does not use Kolmogorov flows. By applying this method, exact estimates of the dimension are obtained for the case of equations on a plane with Ekman damping. Similar estimates were previously known only for the case of periodic boundary conditions. In addition, similar lower bounds are obtained for the classical Navier–Stokes system in a two-dimensional bounded domain with Dirichlet boundary conditions.

Reaction-diffusion systems with mass dissipation are known to possess blow-up solutions in high dimensions when the nonlinearities have super quadratic growth rates. In dimension one, it has been shown recently that one can have global existence of bounded solutions if nonlinearities are at most cubic. For the cubic intermediate sum condition, i.e. nonlinearities might have arbitrarily high growth rates, an additional entropy inequality had to be imposed. In this article, we remove this extra entropy assumption completely and obtain global boundedness for reaction-diffusion systems with cubic intermediate sum condition. The novel idea is to show a non-concentration phenomenon for mass dissipating systems, that is the mass dissipation implies a dissipation in a Morrey space $\mathsf{M}^{1,\delta}(\Omega)$ for some $\delta>0$. As far as we are concerned, it is the first time such a bound is derived for mass dissipating reaction-diffusion systems. The results are then applied to obtain global existence and boundedness of solutions to an oscillatory Belousov-Zhabotinsky system, which satisfies cubic intermediate sum condition but does not fulfill the entropy assumption. Extensions include global existence mass controlled systems with slightly-super cubic intermediate sum condition.

For each natural number n and any bounded, convex domain 2 C Rn we characterize the sharp constant C(n, 2) in the Poincare ' inequal-ity 11f - f over bar omega 11Loo(omega;R) < C(n, 2)11Vf11Loo(omega;R). Here, f over bar omega denotes the mean value of f over 2. In the case that 2 is a ball Br of radius r in Rn, we calculate C(n, Br) = C(n)r explicitly in terms of n and a ratio of the vol-umes of the unit balls in R2n-1 and Rn. More generally, we prove that C(n, Br(omega)) < C(n, 2) < nn+1 diam(2), where Br(omega) is a ball in Rn with the same n-dimensional Lebesgue measure as 2. Both bounds are sharp, and the lower bound can be interpreted as saying that, among convex domains of equal measure, balls have the best, i.e. smallest, Poincare ' constant.

This survey is dedicated to the 100th anniversary of Mark Iosifovich Vishik and is based on a number of mini-courses taught by the author at the University of Surrey (UK) and Lanzhou University (China). It discusses the classical and modern results of the theory of attractors for dissipative PDEs, including attractors for autonomous and non-autonomous equations, dynamical systems in general topological spaces, various types of trajectory, pullback and random attractors, exponential attractors, determining functionals and inertial manifolds, as well as the dimension theory for the classes of attractors mentioned above. The theoretical results are illustrated by a number of clarifying examples and counterexamples. Bibliography: 248 titles.

We formulate an effective numerical scheme that can readily, and accurately, calculate the dynamics of weakly interacting multi-pulse solutions of the quintic complex Ginzburg-Landau equation (QCGLE) in one space dimension. The scheme is based on a global centre-manifold reduction where one considers the solution of the QCGLE as the composition of individual pulses plus a remainder function, which is orthogonal to the adjoint eigenfunctions of the linearised operator about a single pulse. This centre-manifold projection overcomes the difficulties of other, more orthodox, numerical schemes, by yielding a fast-slow system describing 'slow' ordinary differential equations for the locations and phases of the individual pulses, and a 'fast' partial differential equation for the remainder function. With small parameter $\epsilon=e^{-\lambda_r d}$ where $\lambda_r$ is a constant and $d>0$ is the pulse separation distance, we write the fast-slow system in terms of first-order and second-order correction terms only, a formulation which is solved more efficiently than the full system. This fast-slow system is integrated numerically using adaptive time-stepping. Results are presented here for two- and three-pulse interactions. For the two-pulse problem, cells of periodic behaviour, separated by an infinite set of heteroclinic orbits, are shown to 'split' under perturbation creating complex spiral behaviour. For the case of three pulse interaction a range of dynamics, including chaotic pulse interaction, are found. While results are presented for pulse interaction in the QCGLE, the numerical scheme can also be applied to a wider class of parabolic PDEs.

Детально изучена динамика слабо диссипативных волновых уравнений в ограниченных трехмерных областях в случае, когда коэффициент диссипации явно зависит от времени и может менять знак. Показано, что в случае нелинейностей, растущих быстрее чем линейно, рассматриваемые уравнения остаются диссипативными, если некоторое весовое среднее коэффициента диссипации положительно, также продемонстрирована недостаточность подобного рода условий в случае линейных уравнений. Рассмотрены два принципиально различных случая. В первом случае, когда упомянутое выше среднее является равномерным (что соответствует случаю детерминистской диссипации), показано, что рассматриваемая динамическая система обладает гладким равномерным аттрактором, а также неавтономным экспоненциальным аттрактором конечной фрактальной размерности. Во втором случае, когда среднее диссипации не является равномерным (что соответствует случайной диссипации, например, порождаемой схемой Бернулли), построен случайный аттрактор умеренного роста. В отличие от стандартной ситуации, этот аттрактор видимо может иметь бесконечную хаусдорфову и фрактальную размерность. Упрощенный модельный пример, демонстрирующий бесконечномерность случайного аттрактора, также приведен. Библиография: 66 наименований.

Доказываются оценки $L^p$ норм систем функций и систем бездивергентных вектор-функций, которые ортонормированы в пространстве Соболева $H^1$ на двумерной сфере. Как следствие получены оптимальные по скорости роста постоянные в неравенствах Гальярдо-Ниренберга для вложения $H^1\hookrightarrow L^q$, $q<\infty$. Библиография: 25 названий.

We give a comprehensive study of the 3D Navier-Stokes-Brinkman-Forchheimer equations in a bounded domain endowed with the Dirichlet boundary conditions and non-autonomous external forces. This study includes the questions related with the regularity of weak solutions, their dissipativity in higher energy spaces and the existence of the corresponding uniform attractors

We develop the attractors theory for the semigroups with multidimensional time belonging to some closed cone in an Euclidean space and apply the obtained general results to partial differential equations (PDEs) in unbounded domains. The main attention is payed to elliptic boundary problems in general unbounded domains. In contrast to the previous works in this direction our theory does not require the underlying domain to be cylindrical or cone-like or to be shift semi-invariant with respect to some direction. In particular, the theory is applicable to the exterior domains.

We prove estimates for the $L^p$-norms of systems of functions and divergence-free vector functions that are orthonormal in the Sobolev space $H^1$ on the 2D sphere. As a corollary, order sharp constants for the embedding $H^1\hookrightarrow L^q$, $q<\infty$, are obtained in the Gagliardo-Nirenberg interpolation inequalities. Bibliography: 25 titles.

We study the properties of linear and non-linear determining functionals for dissipative dynamical systems generated by PDEs. The main attention is payed to the lower bounds for the number of such functionals. In contradiction to the common paradigm, it is shown that the optimal number of determining functionals (the so-called determining dimension) is strongly related to the proper dimension of the set of equilibria of the considered dynamical system rather than to the dimensions of the global attractors and the complexity of the dynamics on it. In particular, in the generic case where the set of equilibria is finite, the determining dimension equals to one (in complete agreement with the Takens delayed embedding theorem) no matter how complex the underlying dynamics is. The obtained results are illustrated by a number of explicit examples.

We prove the existence of an Inertial Manifold for 3D complex Ginzburg-Landau equation with periodic boundary conditions as well as for more general cross-diffusion system assuming that the dispersive exponent is not vanishing. The result is obtained under the assumption that the parameters of the equation is chosen in such a way that the finite-time blow up of smooth solutions does not take place. For the proof of this result we utilize the recently suggested method of spatio-temporal averaging.