title: Single-order-parameter description of glass-forming liquids: a one-frequency test.
abstract: Thermoviscoelastic linear-response functions are calculated from the master equation describing viscous liquid inherent dynamics. From the imaginary parts of the frequency-dependent isobaric specific heat, isothermal compressibility, and isobaric thermal expansion coefficient, we define a "linear dynamic Prigogine-Defay ratio" LambdaTp(omega) with the property that if LambdaTp(omega)=1 at one frequency, then LambdaTp(omega) is unity at all frequencies. This happens if and only if there is a single-order-parameter description of the thermoviscoelastic linear responses via an order parameter (which may be nonexponential in time). Generalizations to other cases of thermodynamic control parameters than temperature and pressure are also presented.
authors.affiliation: DNRF Centre Glass and Time, IMFUFA (27), Department of Sciences, Roskilde University, Postbox 260, DK-4000 Roskilde, Denmark.
authors.forename: Niels L
authors.initials: NL
authors.lastname: Ellegaard
authors.forename: Tage
authors.initials: T
authors.lastname: Christensen
authors.forename: Peder Voetmann
authors.initials: PV
authors.lastname: Christiansen
authors.forename: Niels Boye
authors.initials: NB
authors.lastname: Olsen
authors.forename: Ulf R
authors.initials: UR
authors.lastname: Pedersen
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Schrøder
authors.forename: Jeppe C
authors.initials: JC
authors.lastname: Dyre