On the existence of square-integrable solutions for systems with weak nonlinearity

The paper considers the problem of structural stability of systems under disturbance of coefficients having small L ²(ℝ)-norm. We derive conditions which guarantee that for every solution of the perturbed system there exists a solution of the original system which is close to the former in L ²(ℝ)-norm.     

On the global existence of weak solutions for the Cucker-Smale-Navier-Stokes system with shear thickening

We study the large-time dynamics of Cucker-Smale (C-S) flocking particles interacting with non-Newtonian incompressible fluids. Dynamics of particles and fluids were modeled using the kinetic Cucker-Smale equation for particles and non-Newtonian Navier-Stokes system for fluids, respectively and these two systems are coupled via the drag force, which is the main flocking (alignment) mechanism between particles and fluids. We present a global existence theory for weak solutions to the coupled Cucker-Smale-Navier-Stokes system with shear thickening. We also use a Lyapunov functional approach to show that sufficiently regular solutions approach flocking states exponentially fast in time.     

ON THE EXISTENCE OF GLOBAL GENERAL SOLUTIONS OF POLYNOMIAL SYSTEMS

ＯＮＴＨＥＥＸＩＳＴＥＮＣＥＯＦＧＬＯＢＡＬＧＥＮＥＲＡＬＳＯＬＵＴＩＯＮＳＯＦ　ＰＯＬＹＮＯＭＩＡＬＳＹＳＴＥＭＳＺＨＡＯＸＩＡＯＱＩＡＮＧ（赵晓强）（ＩｎｓｔｉｔｕｔｅｏｆＡｐｐｌｉｅｄＭａｔｈｅｍａｔｉｃｓ，ｔｈｅＣｈｉｎｅｓｅＡｃａｄｅｍｙｏ...     

On global existence for semilinear parabolic systems

We present some results on global existence of classical solutions of certain semilinear parabolic systems with homogeneous Dirichlet boundary conditions in bounded domains with a smooth boundary, relaxing the usual monotonicity assumptions on the nonlinearities.     

On existence of weak solutions for one-dimensional forward-backward diffusion equations

We establish the existence of infinitely many weak solutions for the general one-dimensional forward-backward diffusion equation u_t=σ(u_x)_x under the homogeneous Neumann boundary condition by rephrasing it as a first-order differential inclusion problem.     

On the existence of weak solutions of semilinear elliptic equations and systems with Hardy potentials

Let $\mathrm{\Omega }?{\mathbb{R}}^N$ ($N\ge 3$) be a bounded $C^2$ domain and $\delta (x)=\mathrm{dist}(x,?\mathrm{\Omega })$. Put $L_{\mu }=\mathrm{\Delta }+\frac{\mu }{{\delta }^2}$ with $\mu >0$. In this paper, we provide various necessary and sufficient conditions for the existence of weak solutions to

$?L_{\mu }u=u^p+\tau \text{in }\mathrm{\Omega },u=\nu \text{on }?\mathrm{\Omega },$

where $\mu >0$, $p>0$, τ and ν are measures on Ω and ?Ω respectively. We then establish existence results for the system

$\{\begin{array}{cc}\hfill & ?L_{\mu }u=?v^p+\tau \text{in }\mathrm{\Omega },\hfill \\ \hfill & ?L_{\mu }v=?u^{\stackrel{?}{p}}+\stackrel{?}{\tau }\text{in }\mathrm{\Omega },\hfill \\ \hfill & u=\nu ,v=\stackrel{?}{\nu }\text{on }?\mathrm{\Omega },\hfill \end{array}$

where $?=\pm 1$, $p>0$, $\stackrel{?}{p}>0$, τ and $\stackrel{?}{\tau }$ are measures on Ω, ν and $\stackrel{?}{\nu }$ are measures on ?Ω. We also deal with elliptic systems where the nonlinearities are more general.     

On the existence of periodic solutions for large-scale systems

In recent ten years or more, many scholars have engaged in the investigation concerning the stability of large-scale systems, but up to the present, the problem on the existence of periodic solutions for large-scale systems has yet been seldomly touched upon in the literature.In this paper, by means of the method of constructing Lyapunov function. We study the problem on the existence of periodic solutions for linear and nonlinear large-scale systems, and obtain several sufficient conditions which guarantee the existence of periodic solutions.     

On the existence of global weak solutions to the Navier–Stokes equations for viscous compressible and heat conducting fluids

The purpose of this work is to investigate the problem of global in time existence of sequences of weak solutions to the Navier–Stokes equations for viscous compressible and heat conducting fluids. A class of density and temperature dependent viscosity and conductivity coefficients is considered. This result extends P.-L. Lions' work in 1993 [P.-L. Lions, Compacité des solutions des équations de Navier–Stokes compressibles isentropiques, C. R. Acad. Sci. Paris, Sér. I 317 (1993) 115–120] restricted to barotropic flows, and provides weak solutions “à la Leray” to the full compressible model that includes internal energy evolution equation with thermal conduction effects. A partial answer is therefore given to this currently widely open problem, described for instance in P.-L. Lions' book [P.-L. Lions, Mathematical Topics in Fluid Dynamics, vol. 2, Compressible Models, Oxford Science Publication, Oxford, 1998]. The proof uses the generalization to the temperature dependent case, of a new mathematical entropy equality derived by the authors in [D. Bresch, B. Desjardins, Some diffusive capillary models of Korteweg type, C. R. Acad. Sci., Paris, Section Mécanique 332 (11) (2004) 881–886]. The construction scheme of approximate solutions, using on additional regularizing effects such as capillarity, is provided in [D. Bresch, B. Desjardins, On the construction of approximate solutions for 2D viscous shallow water model and for compressible Navier–Stokes models, J. Math. Pures Appl. 86 (4) (2006) 362–368], and allows to use the stability arguments of this paper.     

椭圆方程组径向非负解的存在性

应用锥不动点定理证明了圆环中半线性椭圆方程径向非负解的存在性.     

On the global existence of solutions to the Prandtl's system

In this paper we establish a global existence of weak solutions to the two-dimensional Prandtl's system for unsteady boundary layers in the class considered by Oleinik (J. Appl. Math. Mech. 30 (1966) 951) provided that the pressure is favourable. This generalizes the local well-posedness results due to Oleinik (1966; Mathematical Models in Boundary Layer Theory, Chapman & Hall, London, 1999). For the proof, we introduce a viscous splitting method so that the asymptotic behaviour of the solution near the boundary can be estimated more accurately by methods applicable to the degenerate parabolic equations.     

On the existence of weak solutions of anisotropic generally restrained plates

This paper presents investigations of free vibration of anisotropic plates of different geometrical shapes and generally restrained boundaries. The existence and uniqueness of weak solutions of boundary value problems and eigenvalue problems which correspond to the statical and dynamical behaviour of the mentioned plates is demonstrated. It is determined that when the plates have corner points formed by the intersection of edges free or elastically restrained against translation, the corresponding bilinear forms maintain the V – ellipticity property.     

On existence of solutions for some hyperbolic-parabolic-type chemotaxis systems

In this paper, we discuss the local and global existence ofweak solutions for some hyperbolic–parabolic systems modellingchemotaxis.     

A remark on global existence of solutions of shadow systems

Let ?? be an open, bounded domain in ${\mathbb{R}^n\;(n \in \mathbb{N})}$ with smooth boundary ???. Let p, q, r, d ₁, ?? be positive real numbers and s be a non-negative number which satisfies ${0 < \frac{p-1}{r} < \frac{q}{s+1}}$ . We consider the shadow system of the well-known Gierer?CMeinhardt system: $$ \left \{ \begin{array}{l@{\quad}l} \displaystyle{u_t = d_1\Delta u - u + \frac{u^p}{\xi^q}}, & \quad {\rm in}\;\Omega \times (0,T), \\ \displaystyle{\tau \xi_t = -\xi + \frac{1}{|\Omega|} \int\nolimits_\Omega\frac{u^r}{\xi^s} {\rm d}x}, & \quad {\rm in}\;(0,T), \\ \displaystyle{\frac{\partial u}{\partial \nu} =0}, & \quad {\rm on}\;\partial \Omega \times (0,T), \\ \displaystyle{\xi(0) = \xi_0 >0 , \quad u(\cdot,0) = u_0(\cdot)} \geq 0 & \quad {\rm in}\;\Omega. \end{array} \right. $$ We prove that solutions of this system exist globally in time under some conditions on the coefficients. Our results are based on a priori estimates of the solutions and improve the global existence results of Li and Ni in [4].     

A remark on global existence of solutions of shadow systems

Let Ω be an open, bounded domain in \mathbbRⁿ  (n ? \mathbbN){\mathbb{R}^n\;(n \in \mathbb{N})} with smooth boundary ∂Ω. Let p, q, r, d ₁, τ be positive real numbers and s be a non-negative number which satisfies 0 < \fracp-1r < \fracqs+1{0 < \frac{p-1}{r} < \frac{q}{s+1}}. We consider the shadow system of the well-known Gierer–Meinhardt system:

On the global existence of solutions to an aggregation model

In this paper we consider a reaction-diffusion-chemotaxis aggregation model of Keller-Segel type with a nonlinear, degenerate diffusion. Assuming that the diffusion function f(n) takes values sufficiently large, i.e. takes values greater than the values of a power function with sufficiently high power (f(n)?δnp for all n>0, where δ>0 is a constant), we prove global-in-time existence of weak solutions. Since one of the main features of Keller-Segel type models is the possibility of blow-up of solutions in finite time, we will derive the uniform-in-time boundedness, which prevents the explosion of solutions. The uniqueness of solutions is proved provided that some higher regularity condition on solutions is known a priori. Finally, computational simulation results showing the effect of three different types of diffusion function are presented.