Author 
Comment/Response 
jf

05/23/13 11:00am
The problem is upstream from Plot. Look at DR for a typical value of T,
In[8]:= DR[0.12, 1, 1, 0.08, 0.05]
Out[8]=
1.*Log[(63.98528749321458*ˆ)/2.718281828459045^(4.8540672474690165*ˆ)]
The exponent has a number times a caret symbol.
I converted the inputs to simpler formatting (Cell menu  ConvertTo  RawInputForm) and saw an oddity.
B[Alpha_, Gamma_, Sigma_, t_, T_] := ((2*(Exp[Eta[Alpha, Sigma]*(T  t)]  1))/
((Alpha + Eta[Alpha, Sigma])*(Exp[Eta[Alpha, Sigma]*(T  t)]  1) +
2*Eta[Alpha, Sigma]))*ˆ*(2*Alpha*(Gamma/Sigma^2));
Note "..Sigma]))*ˆ*(2*Alpha.."  the caret is treated as a separate symbol. Function A has a similar glitch.
The thing that you are using as a caret (^) is different than the shorthand for Power. I suggest retyping that character. The standard caret on most American keyboards is a Shift6.
Since DR is not giving just a number, Plot cannot plot it.
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