The nucleon mass shift is calculated using chiral counting arguments and a virial expansion, without and with the $Delta$. At all temperatures, the mass shift and damping rate are dominated by the $Delta$. Our results are compared with the empirical analysis of Leutwyler and Smilga, as well as results from heavy baryon chiral perturbation theory in the large $N_{c}$ (number of color) limit. We show that unitarity implies that the concepts of thermal shifts are process dependent.
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