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Note: / The purpose of this study was to develop and evaluate a numerical model for simulating the influence of seasonal snow cover on the ground thermal regime.The physical processes occurring within the snow pack and underlying ground, as well as at the surface, are reviewed from the viewpoint of their eventual inclusion in a practical numerical model. A finite difference heat conduction model suitable for long-term studies of the snow-ground thermal interaction is presented. This model incorporates a numerical prediction of density and temperature profiles within an evolving snow cover. Phase change within the ground is treated by a new numerical method which has important computational advantages over older methods.[...] / Cette etude avait pour but Ie developpement et l'evaluation d'un modele numerique pour la simulation de l'influence du manteau neigeux saisonier sur Ie regime thermique du sol.Les processus physiques rencontres dans Ie manteau neigeux et Ie sol sous-jacent ainsi quIa l'interface air-surface sont discutes et passes en revue dans l'optique restreinte de leur eventuelle inclusion dans un modele numerique. On presente ensuite un modele a conduction en differences finies qui convient pour les etudes de l'interaction thermique neige-sol a long terme. Le modele inclut un calcul numerique de l'evolution temporelle des profiles de densite et de temperature du manteau neigeux. Les changements de phase dans Ie sol sont traites par une nouvelle technique numerique avantageuse pour Ie calcul.[...]

Relative densities and relative massic heat capacities have been measured for aqueous solutions of triflic acid (CF3SO3H), sodium triflate (NaCF3SO3), gadolinium triflate (Gd(CF3SO3)3), dysprosium triflate (Dy(CF3SO3)3), neodymium triflate (Nd(CF3SO3)3), erbium triflate (Er(CF3SO3)3), ytterbium triflate (Yb(CF3SO3)3), and yttrium triflate (Y(CF3SO3)3) at T = (288.15, 298.15, 313.15, and 328.15) K and p = 0.1 MPa. The resulting densities and massic heat capacities have been used to calculate out apparent molar volume and apparent molar heat capacity data for each of the investigated aqueous systems. The concentration dependencies of the apparent molar volumes and apparent molar heat capacities have been modeled using Pitzer-ion interaction equations. Single ion volumes and heat capacities have been calculated using estimates of the apparent molar properties at infinite dilution obtained from the Pitzer-ion interaction equations. These single ion values have, where possible, been compared with those previously reported in the literature. Also, relative densities have been measured for aqueous solutions of CF3SO3H, Gd(CF3SO3)3, Nd(CF3SO3)3, and Yb(CF3SO3)3 at T = (323.15, 348.15, 373.15, and 423.15) K and p = (5.00, 10.00, and 15.00) MPa. The resulting densities have been used to calculate apparent molar volumes. The concentration dependences of these properties have also been modeled using Pitzer-ion interaction equations. The apparent molar volumes have been used to calculate single ion volumes which, in turn, have been compared with those previously reported in the literature. This thesis also attempts to model the temperature, pressure, and concentration dependencies of the reported apparent molar properties of each system investigated using an equation of state commonly referred to as the density model. Where possible, the results of this model have been compared with those results from models previously reported in the literature. / xiv, 148 leaves ; 29 cm.

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