in Wiley InterScience (www.interscience.wiley.com).Three activity coefficient models for electrolyte solutions were evaluated and compared. The activity coefficient models are: The electrolyte NRTL model (ElecNRTL) by Aspentech, the mixed solvent electrolyte model (MSE) by OLI Systems, and the Extended UNIQUAC model from the Technical University of Denmark (DTU). Test systems containing a single salt (NaCl), multiple salts, and mixed solvent aqueous electrolyte solutions were chosen. The performance of the activity coefficient models were compared regarding the accuracy of solid-liquid and vapor-liquid equilibrium calculations for the test systems. V

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Abstract. We reelaborate on a general method for obtaining effective Hamiltonians that describe different nonlinear optical processes. The method exploits the existence of a nonlinear deformation of the su(2) algebra that arises as the dynamical symmetry of the original model. When some physical parameter (usually related to the dispersive limit) becomes small, we immediately get a diagonal effective Hamiltonian that represents correctly the dynamics for arbitrary states and long times. We apply the same technique to obtain how the noise terms in the original model transform under this scheme, providing a systematic way of including damping effects in processes described in terms of effective Hamiltonians.

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For a pure substance, the spinodal curve is defined as the locus where thermodynamic quantities such as the thermal expansion coefficient a,, the isothermal compressibility KT, and the isobaric heat capacity C, are expected to diverge. Its location is of particular importance from both practical and theoretical points of view, since it represents the limit beyond which a particular state of matter, in our case the liquid state, can exist or not. In this work, several predictions of the spinodal curve have been tested, compared, and discussed for 2,3-dimethylbutane. Thecomparison with results found in the literature reveals that some conclusions established here could be of general application.