MATHEMATICA BOHEMICA, Vol. 131, No. 4, pp. 393-409, 2006

Strong singularities in mixed boundary
value problems

Irena Rachunkova

Irena Rachunkova, Department of Mathematics, Palacky University, Tomkova 40, 779 00 Olomouc, Czech Republic, e-mail: rachunko@inf.upol.cz

Abstract: We study singular boundary value problems with mixed boundary conditions of the form
(p(t)u')'+ p(t)f(t,u,p(t)u')=0, \quad\lim_{t\to0+}p(t)u'(t)=0, \quad u(T)=0,
where $[0,T]\subset\R.$ We assume that $\D\subset\R^2,$ $f$ satisfies the Caratheodory conditions on $(0,T)\times\D,$ $p\in C[0,T]$ and ${1/p}$ need not be integrable on $[0,T].$ Here $f$ can have time singularities at $t=0$ and/or $t=T$ and a space singularity at $x=0$. Moreover, $f$ can change its sign. Provided $f$ is nonnegative it can have even a space singularity at $y=0.$ We present conditions for the existence of solutions positive on $[0,T).$

Keywords: singular mixed boundary value problem, positive solution, lower function, upper function, convergence of approximate regular problems

Classification (MSC 2000): 34B16, 34B18


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