Entropy in some simple one-dimensional configurations

Continuing the discussion on negative entropy in Casimir-effect like configurations, we consider two simple one-dimensional examples. One is the s-wave contribution to a plasma sphere and the other a single delta function potential. Some information on generic background potential is gained applying Levinson's theorem. For the first example we find negative entropy. The one-dimensional examples are especially interesting as these do not require the subtraction of contributions growing with temperature faster than the classical limit.