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Uniqueness of positive solutions of nonlinear second order systems.

Robert Dalmasso (1995)

Revista Matemática Iberoamericana

In this paper we discuss the uniqueness of positive solutions of the nonlinear second order system -u'' = g(v), -v'' = f(u) in (-R,R), u(±R) = v(±R) = 0 where f and g satisfy some appropriate conditions. Our result applies, in particular, to g(v) = v, f(u) = up, p > 1, or f(u) = λu + a1up1 + ... + akupk, with pj > 1, aj > 0 for j = 1, ..., k and 0 ≤ λ < μ12 where μ1 = π2/4R2.

Uniqueness of very singular self-similar solution of a quasilinear degenerate parabolic equation with absorption.

Jesús Ildefonso Díaz, José Evaristo Saa (1992)

Publicacions Matemàtiques

We show the uniqueness of the very singular self-similar solution of the equationut - Δ pum + uq = 0.The result is carried out by studying the stationary associate equation and by introducing a suitable change of unknown. That allows to assume the zero-order perturbation term in the new equation to be monotone increasing. A careful study of the behaviour of solutions near the boundary of their support is also used in order to prove the main result.

Upper and lower solutions satisfying the inverse inequality

Irena Rachůnková (1997)

Annales Polonici Mathematici

We consider multipoint and two-point BVPs for second order ordinary differential equations with a Carathéodory right hand side. We prove the existence of solutions provided there exist upper and lower solutions of the BVP and the upper solution is less than the lower one.

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