Uniqueness and existence results for ordinary differential equations

We establish some uniqueness and existence results for first-order ordinary differential equations with constant-signed discontinuous nonlinear parts. Several examples are given to illustrate the applicability of our work.     

Multiple homoclinic solutions for singular differential equations

The homoclinic bifurcations of ordinary differential equation under singular perturbations are considered. We use exponential dichotomy, Fredholm alternative and scales of Banach spaces to obtain various bifurcation manifolds with finite codimension in an appropriate infinite-dimensional space. When the perturbative term is taken from these bifurcation manifolds, the perturbed system has various coexistence of homoclinic solutions which are linearly independent.     

Uniqueness of bounded solutions for some abstract differential equations

Summary For some differential equations in Hilbert space we prove uniqueness of bounded solutions in the Stepanoff norm.

---

Riassunto Si dimostra l’unicità delle soluzioniS ²-limitate per alcune equazioni differenziali astratte.

---

---

This research is supported by a grant of the N.R.C. of Canada.     

Uniqueness for algebraically regular solutions to pathological differential equations

A uniqueness theorem is proved for algebraically regular solutions to the unbounded initial value problem P′ = AP, P(0) = diag(1, 1, 1,…) in the real Banach algebra of infinite matrices $\text{M}$ with standard norm. It is not assumed that $\text{A}$ ∈ $\text{M}$, but it is required that A have an inverse in $\text{M}$, a property which is seen to be implied quite naturally by certain divergent or pathological systems. The conditions for the theorem are motivated by a particular system, previously considered by Hille and Feller, which arises from a divergent, purebirth, time dependent stochastic process, although no restriction requiring the solution matrix to be either stochastic or substochastic is necessary.The theorem may be easily generalized to any Banach algebra with identity.     

Uniqueness results for a class of hamilton-jacobi equations with singular coefficients

We establish uniqueness or comparison results for a class of Hamilton-Jacobi equations and give characterizations of maximal solutions of Hamilton-Jacobi equations. The results are applied to characterizing value functions of exit time problems in optimal control.     

Uniqueness of bounded weak solutions for some abstract differential equations

Riassunto Si dà un teorema di unicità per soluzioni deboli limitate di alcune equazioni differenziali astratte.

---

---

This research is supported by of the N.R.C. of Canada.     

Periodic solutions for second order singular damped differential equations

We study the existence of positive periodic solutions for second order singular damped differential equations by combining the analysis of the sign of Green?s functions for the linear damped equation, together with a nonlinear alternative principle of Leray–Schauder. Recent results in the literature are generalized and significantly improved.     

Uniqueness and non-uniqueness of bounded solutions to singular nonlinear parabolic equations

We investigate well-posedness of initial-boundary value problems for a class of nonlinear parabolic equations with variable density. At some part of the boundary, called singular boundary, the density can either vanish or diverge or not need to have a limit. We provide simple conditions for uniqueness or non-uniqueness of bounded solutions, depending on the behaviour of the density near the singular boundary.     

Impulsive periodic solutions of first-order singular differential equations

In this work, we study the impulsive periodic solutions of first-ordersingular ordinary differential equations. The proof is basedon a nonlinear alternative principle of Leray–Schauder,together with a truncation technique. Some recent results inthe literature are generalized and improved.     

Existence of positive solutions for the singular fractional differential equations

In this paper, we consider the following two-point fractional boundary value problem. We provide sufficient conditions for the existence of multiple positive solutions for the following boundary value problems that the nonlinear terms contain i-order derivative where n?1<α≤n is a real number, n is natural number and n≥2, α?i>1, i∈N and 0≤i≤n?1. ${}^{c}D_{0^{+}}^{\alpha}$ is the standard Caputo derivative. f(t,x ₀,x ₁,…,x _i ) may be singular at t=0.     

Uniqueness and continuous dependence of weak solutions in compressible magnetohydrodynamics

We prove uniqueness and continuous dependence on initial data of weak solutions of the equations of compressible magnetohydrodynamics. The solutions we consider may exhibit discontinuities in density and in the gradients of velocity, temperature, and magnetic field. Continuous dependence is deduced by duality from existence and regularity of solutions of the adjoint of the first variation system. The analysis is complicated by the absence of strict parabolicity, the strong nonlinear coupling in the highest-order terms, and the lack of regularity in the coefficients of the adjoint system.Research supported in part by the NSF under Grant DMS-0305072.Received: May 5, 2004     

Uniqueness and continuous dependence of weak solutions in compressible magnetohydrodynamics

We prove uniqueness and continuous dependence on initial data of weak solutions of the equations of compressible magnetohydrodynamics. The solutions we consider may exhibit discontinuities in density and in the gradients of velocity, temperature, and magnetic field. Continuous dependence is deduced by duality from existence and regularity of solutions of the adjoint of the first variation system. The analysis is complicated by the absence of strict parabolicity, the strong nonlinear coupling in the highest-order terms, and the lack of regularity in the coefficients of the adjoint system.     

Formal and convergent solutions of singular partial differential equations

We consider the problem of the existence of convergent series solutions for partial differential operators of the form . We give first conditions for P such that the linear equation Pu=f has an analytic solution, then we solve nonlinear equations of the form Pu=F(x,u). For applications we treat also cases with parameters and give a proof of a theorem of S. Kaplan [5]. In the last section we consider a case where small denominators occur.