x = J/(0.69502*T)
y= J2/(0.69502*T)
top=6*exp(x-y)+6+30*exp(2*x)
bot=3*exp(x-y)+exp(-x)+3+5*exp(2*x)
chi=0.375*g*g*top/bot/(T-TH)/3
chi=chi*(1-ro)+0.375*g*g*ro*3.5/T/3+TIP