The genuinely nonlinear Graetz—Nusselt ultraparabolic equation

We study a second-order quasilinear ultraparabolic equation whose matrix of the coefficients of the second derivatives is nonnegative, depends on the time and spatial variables, and can change rank in the case when it is diagonal and the coefficients of the first derivatives can be discontinuous. We prove that if the equation is a priori known to enjoy the maximum principle and satisfies the additional “genuine nonlinearity” condition then the Cauchy problem with arbitrary bounded initial data has at least one entropy solution and every uniformly bounded set of entropy solutions is relatively compact in L _loc ¹ . The proofs are based on introduction and systematic study of the kinetic formulation of the equation in question and application of the modification of the Tartar H-measures proposed by E. Yu. Panov.     

ONE DIMENSIONAL FILTRATION PROBLEM IN PARTIALLY SATURATED LAYERED POROUS MEDIA

ＯＮＥＤＩＭＥＮＳＩＯＮＡＬＦＩＬＴＲＡＴＩＯＮＰＲＯＢＬＥＭＩＮＰＡＲＴＩＡＬＬＹＳＡＴＵＲＡＴＥＤＬＡＹＥＲＥＤＰＯＲＯＵＳＭＥＤＩＡ￥ＸＩＡＯＳＨＵＴＩＥ（萧树铁）（ＤｅｐａｒｔｍｅｎｔｏｆＡｐｐｌｉｅｄＭａｔｈｅｍａｔｉｃｓ，Ｔｓｉｎｇｈｕａ...     

Explicit analytical solutions of the anisotropic Brinkman model for the natural convection in porous media

Some algebraically explicit analytical solutions are derived for the anisotropic Brinkman model-an improved Darcy model-describing the natural convection in porous media. Besides their important theoretical meaning (for example, to analyze the non-Darcy and anisotropic effects on the convection), such analytical solutions can be the benchmark solutions to promoting the development of computational heat and mass transfer. For instance, we can use them to check the accuracy, convergence and effectiveness of various numerical computational methods and to improve numerical calculation skills such as differential schemes and grid generation ways.     

Approximate self-similar solutions for the boundary value problem arising in modeling of gas flow in porous media with pressure dependent permeability

The flow of a gas through porous medium is considered in the case of pressure dependent permeability and viscosity. Approximate self-similar solutions of the boundary-value problems are found.     

Existence and nonexistence of global solutions to the Cauchy problem for a nonlinear beam equation

The paper studies the existence and nonexistence of global solutions to the Cauchy problem for a nonlinear beam equation arising in the model in variational form for the neo–Hookean elastomer rod where k₁, k₂>0 are real numbers, g(s) is a given nonlinear function. When g(s)=sⁿ (where n?2 is an integer), by using the Fourier transform method we prove that for any T>0, the Cauchy problem admits a unique global smooth solution u∈C^∞((0, T]; H^∞( R ))∩C([0, T]; H³( R ))∩C¹([0, T]; H^?1( R )) as long as initial data u₀∈W^{4, 1}( R )∩H³( R ), u₁∈L¹( R )∩H^?1( R ). Moreover, when (u₀, u₁)∈H²( R ) × L²( R ), g∈C²( R ) satisfy certain conditions, the Cauchy problem has no global solution in space C([0, T]; H²( R ))∩C¹([0, T]; L²( R ))∩H¹(0, T; H²( R )). Copyright © 2009 John Wiley & Sons, Ltd.     

Periodic Solutions of Porous Medium Equations with Weakly Nonlinear Sources

§ 1.Ｉｎｔｒｏｄｕｃｔｉｏｎ　ＴｈｉｓｐａｐｅｒｉｓｃｏｎｃｅｒｎｅｄｗｉｔｈｔｈｅｔｉｍｅｐｅｒｉｏｄｉｃｓｏｌｕｔｉｏｎｓｏｆｔｈｅｐｏｒｏｕｓｍｅｄｉｕｍｅｑｕａｔｉｏｎｓｗｉｔｈｗｅａｋｌｙｎｏｎｌｉｎｅａｒｓｏｕｒｃｅｓａｎｄｗｉｔｈｔｈｅＤｉｒｉｃｈｌｅｔｂｏｕｎｄａｒｙｖａｌｕｅｃｏｎｄｉｔｉｏｎ ,ｎａｍｅｌｙ ,ｔｈｅｐｒｏｂｌｅｍ ｕ ｔ =Δ(｜ｕ｜ｍ- 1ｕ) +Ｂ(ｘ ,ｔ,ｕ) +ｆ(ｘ ,ｔ)　ｉｎΩ×Ｒ ,(1 .1 )ｕ(ｘ ,ｔ) =0　ｏｎ Ω×Ｒ , (1 .2 )ｕ(ｘ ,ｔ+ω) =ｕ(ｘ ,ｔ)　ｉｎ Ω×Ｒ ,…     

Entropy Solutions to a Second Order Forward-Backward Parabolic Differential Equation

We prove that the first boundary value problem for a second order forward-backward parabolic differential equation in a bounded domain G _T ^d+1, where d 2, has a unique entropy solution in the sense of F. Otto. Under some natural restrictions on the boundary values this solution is constructed as the limit with respect to a small parameter of a sequence of solutions to Dirichlet problems for an elliptic differential equation. We also show that the entropy solution is stable in the metric of L ₁(G _T ) with respect to perturbations of the boundary values in the metric of L ₁(G _T ).Original Russian Text Copyright © 2005 Kuznetsov I. V.The author was supported by the Russian Foundation for Basic Research (Grant 03-01-00829).__________Translated from Sibirskii Matematicheskii Zhurnal, Vol. 46, No. 3, pp. 594–619, May–June, 2005.     

Asymptotic simplification for a reaction-diffusion problem with a nonlinear boundary condition

We study non-negative solutions of the porous medium equationwith a source and a nonlinear flux boundary condition, u_t =(u^m)_xx + u^p in (0, ), x (0, T); – (u^m)_x (0, t) = u^q (0,t) for t (0, T); u (x, 0) = u₀ (x) in (0, ), where m > 1,p, q > 0 are parameters. For every fixed m we prove thatthere are two critical curves in the (p, q-plane: (i) the criticalexistence curve, separating the region where every solutionis global from the region where there exist blowing-up solutions,and (ii) the Fujita curve, separating a region of parametersin which all solutions blow up from a region where both globalin time solutions and blowing-up solutions exist. In the caseof blow up we find the blow-up rates, the blow-up sets and theblow-up profiles, showing that there is a phenomenon of asymptoticsimplification. If 2q < p + m the asymptotics are governedby the source term. On the other hand, if 2q > p + m theevolution close to blow up is ruled by the boundary flux. If2q = p + m both terms are of the same order.     

Regularity for anisotropic solutions to some nonlinear elliptic system

This paper deals with anisotropic solutions u∈W1,(pi)(Ω,?N) to the nonlinear elliptic system −Σi=1nDi(aiα(χ,Du(χ)))=−Σi=1nDiFiα(χ), α=1,2,...,N, We present a monotonicity inequality for the matrix a=(aiα)∈?N×n,whichguarantees global pointwise bounds for anisotropic solutionsu.     

Singular limit of solutions of the porous medium equation with absorption

We prove that as the solutions of , , , , , , , converges in to the solution of the ODE , , where , , satisfies in for some function , , satisfying whenever for a.e. , for and for , where is a constant and is any measurable subset of .

     

Martingale solutions and Markov selections for stochastic partial differential equations

We present a general framework for solving stochastic porous medium equations and stochastic Navier–Stokes equations in the sense of martingale solutions. Following Krylov [N.V. Krylov, The selection of a Markov process from a Markov system of processes, and the construction of quasidiffusion processes, Izv. Akad. Nauk SSSR Ser. Mat. 37 (1973) 691–708] and Flandoli–Romito [F. Flandoli, N. Romito, Markov selections for the 3D stochastic Navier–Stokes equations, Probab. Theory Related Fields 140 (2008) 407–458], we also study the existence of Markov selections for stochastic evolution equations in the absence of uniqueness.     

Viscosity solutions to a Cauchy problem of a phase-field model for solid-solid phase transitions

We investigate a partial differential equation which models solid-solid phase transitions. This model is for martensitic phase transitions driven by configurational force and its counterpart is for interface motion by mean curvature. Mathematically, this equation is a second-order nonlinear degenerate parabolic equation. And in multidimensional case, its principal part cannot be written into divergence form . We prove the existence and uniqueness of viscosity solution to a Cauchy problem for this model.     

Solitary and periodic solutions of the generalized Kuramoto-Sivashinsky equation

The generalized Kuramoto-Sivashinsky equation in the case of the power nonlinearity with arbitrary degree is considered. New exact solutions of this equation are presented.      

Homoclinic solutions of a class of periodic difference equations with asymptotically linear nonlinearities

By using critical point theory and periodic approximations, new sufficient conditions are obtained on the existence and nonexistence of homoclinic solutions for a class of discrete nonlinear periodic equations with asymptotically linear nonlinearities. These results partially answer an open problem proposed by Pankov (2006) [2] under rather weaker conditions and greatly improve the related results before.     

Fundamental Solution of the Anisotropic Porous Medium Equation

We establish the existence of fundamental solutions for the anisotropic porous medium equation, ut = ∑n i=1（u^mi）xixi in R^n × （O,∞）, where m1,m2,..., and mn, are positive constants satisfying min1≤i≤n{mi}≤ 1, ∑i^n=1 mi 〉 n - 2, and max1≤i≤n{mi} ≤1/n（2 ＋ ∑i^n=1 mi）.     

Bifurcations and exact solutions of nonlinear Schrodinger equation with an anti-cubic nonlinearity

In this paper, we consider the nonlinear Schr\"{o}dinger equation with an anti-cubic nonlinearity. By using the method of dynamical systems, we obtain bifurcations of the phase portraits of the corresponding planar dynamical system under different parameter conditions. Corresponding to different level curves defined by the Hamiltonian, we derive all exact explicit parametric representations of the bounded solutions (including periodic peakon solutions, periodic solutions, homoclinic solutions, heteroclinic solutions and compacton solutions).     

On the structure of positive solutions to an elliptic problem arising in thin film equations

We consider the structure of positive radial solutions of

     

Entropy solutions for linearly degenerate hyperbolic systems of rich type

Consider a linearly degenerate hyperbolic system of rich type. Assuming that each eigenvalue of the system has a constant multiplicity, we construct a representation formula of entropy solutions in L^∞ to the Cauchy problem. This formula depends on the solution of an autonomous system of ordinary differential equations taking x as parameter. We prove that for smooth initial data, the Cauchy problem for such an autonomous system admits a unique global solution. By using this formula together with classical compactness arguments, we give a very simple proof on the global existence of entropy solutions. Moreover, in a particular case of the system, we obtain an another explicit expression and the uniqueness of the entropy solution. Applications include the one-dimensional Born–Infeld system and linear Lagrangian systems.