  Given a zero-one matrix A we consider certain one-parameter groups of
automorphisms of the Cuntz-Krieger algebra O_A, generalizing the usual gauge
group, and depending on a positive continuous function H defined on the Markov
space \Sigma_A. The main result consists of an application of Ruelle's
Perron-Frobenius Theorem to show that these automorphism groups admit a single
KMS state.
