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          | The question of blow-up of solutions to nonlinear parabolic equations and systems has received considerable attention in the recent literature.In practical situations one would like to know among other things whether the solution blows up
 and, if so, at which time blow-up occurs.  When the solution does blow up at some  finite time T, this time can seldom be determined explicitly, so much effort has been devoted to the calculation of estimates for T. Most of the methods 
 used until recently have yielded  only estimates from above for  T, so that in particular problems  in which blow-up has to be avoided, they are of little value.  We are mainly interested in estimates from below. In particular, 
we investigate the question of blow-up for nonnegative classical solutions of some nonlinear parabolic problems  defined in  bounded domains. Under conditions on data and geometry of the spatial domain,  explicit
estimates  from below  for the blow-up time are derived. |  |