We study the existence of positive solutions for a class of semilinear ellipcic systems in general domains via the blow up argument and degree theory. The main idea can be used to establish the existence of positive solutions for the Navier problems of polyharmonic semilinear equations in general domains.

In this paper, we consider Muskat problem with surface tension at the free boundary. Under the natural conditions, we prove tbe existence of classical solution locally in time by Schauder fixed point theorem.

The existence of global solution of initial-value problem for one class of system of nonlinear evolution equation is proved, we also study the asymptotic behavior and “blow up” of the solution.

To following boundary value problem a(t)\overline{Φ^+(t)} + b(t)Φ^+[α(t)] + c(t)\overline{Φ^-(t)} + d(t)Φ^-[a(t)] = f(t) this paper has given out the number of linearly independent solutions and the conditions of solvability, so as to deepen the study of the problem to the same level as that of following problem a(t)\overline{Φ^+(t)} + b(t)Φ^+(t) + c(t)\overline{Φ^-(t)} + d(t)Φ^-(t) = f(t)

In this paper, we study the general difference schemes of the boundary value problem for the nonlinear parabolic systems with two and three space dimensions. To solve the nonlinear difference schemes, we construct an iterative sequence from the solutions or the linearized difference schemes. We shall prove the convergence of the difference solutions for the iterative difference schemes to the solution of the original boundary value problem or the nonlinear parabolic systems.

M. Bertsch & R. Dal Passo proved the existence and uniqueness of the Cauchy problem for u_t = (φ(u),ψ(u_x))_x, where φ > 0, ψ is a strictly increasing function with lim_{s → ∞}ψ(s) = ψ_∞ < ∞. The regularity of the solution has been obtained under the condition φ" < 0 or φ = const. In the present paper, under the condition φ" ≤ 0, we give some regularity results. We show that the solution can be classical after a finite time. Further, under the condition φ" ≤ -α_0 (where -α_0 is a constant), we prove the gradient of the solution converges to zero uniformly with respect to x as t → +∞.

We prove the well-posedness of the Cauchy problem for strictly hyperbolic equations and systems with Log-Lipschitz coefficients in the time variable.