Question: A plot fail problem

Hi guys, my Maple version is 15.01, when I want to do the following plots, the Maple pops up this failure "Kernal Connenction Lost":

Here're the corresponding input commands:

J := u -> evalf(Int(1/(sqrt(x^2+u^2)*(exp(sqrt(x^2+u^2))+1)), x = 0 .. infinity));

plot(exp(-2*J(Delta/(.4))), Delta = 0 .. 1);

Does anyone encouter the same problem if you try the commands? I wonder how to fix it, thank you.

 

Dust you are, to dust you shall return.

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