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• A review on solving nonlinear hyperbolic systems of PDEs containing Dirac δ measures. • A review on α -product applications to some nonlinear models arising in mathematical physics. • Under certain conditions, δ waves in the Klein-Gordon equation behave like classical solitons in the sine-Gordon equation. The present paper studies the interaction of Dirac δ -waves in models ruled by the nonlinear Klein-Gordon equation u t t − c 2 u x x = ϕ (u) , where c > 0 is a real number and ϕ is an entire function taking real values on the real axis. Such study is made using a product of distributions that both extends the meaning of ϕ (u) for certain distributions u and allows the definition of a solution concept consistent with the classical solution concept. From such study, it emerges that in several nonlinear Klein-Gordon equations Dirac δ -waves behave like classical solitons in the sine-Gordon equation. As particular cases, this work examines the phi-four equation and the sine-Gordon equation. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we study the stability of the nonlinear wave structure caused by the attack of an incident shock on an interface of two different kinds of media. The attack will produce a reflected wave and a refracted wave, and also let the interface deflected. In this paper we will mainly study the case, when the reflected wave is a shock, and the flow between the reflected wave and the refracted shock is relatively subsonic. Our result indicates that the wave structure and the flow field for the reflection–refraction problem in this case is conditionally stable. To describe the motion of the fluid we use the inviscid Euler system as the mathematical model. The reflection–refraction problem can be reduced to a free boundary value problem, where the unknown reflected shock and refracted shock are free boundaries, and the deflected interface is also to be determined. In the proof of the existence and the stability of the corresponding wave structure we apply the Lagrange transformation to fix the interface and the decoupling technique to decouple the elliptic–hyperbolic composite system in its principal part. Meanwhile, some efficient weighted Sobolev estimates are established to derive the existence for corresponding nonlinear problems. [Copyright &y& Elsevier]

Abstract: The first half of this paper is concerning with the nonlinear drift-diffusion semiconductor model in d () dimensional space. The global estimate is achieved on the evolution of support of solution and the finite speed of propagation. The proof is based on the estimate of the weighted norm with special designed weight functions. In the second half, we prove the quasineutral limit locally for 1-dimensional standard drift-diffusion model with discontinuous, sign-changing doping profile. [Copyright &y& Elsevier]