  We study the melting of a double stranded DNA in the presence of stretching
forces, via 3D Monte-Carlo simulations, exactly solvable models and heuristic
arguments. The resulting force-temperature phase diagram is dramatically
different for the cases where the force is applied to only one strand or to
both. Different assumptions on the monomer size of single and double stranded
DNA lead to opposite conclusions as to whether DNA melts or not as it
overstretches.
