One may expect that the observables connected with nonequilibrium processes will show abrupt changes if a substance undergoes a secondhyphen;order phase transition, since the equilibrium thermodynamic quantities appear to do so. In order to study these phenomena in a connected way the assumption is made that the longhyphen;range order parameter and the shorthyphen;range order parameter can be treated as fluxes and forces in the sense of Onsager's theory of irreversible thermodynamics. Actual calculations are performed for two cases: an ordermdash;disorder system with shorthyphen; and longhyphen;range order and a system with two modes of longhyphen;range order (antiferromagnet). The absorption of sound is calculated and its behavior near the critical temperature is analyzed. The function is continuous with a discontinuity in the slope provided the phenomenological constants are smooth functions of the temperature.
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