Abstract. The volumes of the pure synthetic pyrope, spessartine and uvarovite garnets have been determined by powder x-ray diffraction as a function of pressure up to 25 GPa in a diamond anvil cell at room temperature. Experiments in different pressui'e transmitting media have been systematically carried out to determine the effects of anisotropic stress components, which were found to be substantial and have been taken into account. Assuming that the bulk moduli determined from ultrasonic experiments have the lowest uncertainties, the following values for the pressure derivatives of the bulk modulus of uvarovite, spessartine and pyrope were respectively obtained: 4.7_+ 0.7, 7-7.3 _+ 1 and 3.4_+ 1. The value for pyrope can be attributed to the small size of the Mg z+ cation in its dodecahedral site.

ElsevierRedon Climent, A.; Navarro-Peris, E.; M. Pitarch; José Gonzálvez-Maciá; José M. Corberán (2014). Analysis and optimization of subcritical two-stage vapor injection heat pump systems. Applied Energy. 124:231-240. Analysis and optimization of subcritical two-stage vapor injection heat pump systems AbstractTwo of the major problems of heat pump systems working in extreme conditions are the loss of efficiency of the system and the high compressor discharge temperatures which can even impede the correct performance of the machine. One possibility in order to overcome these issues is to perform the compression in two stages. In this frame the use of vapor injection two stage cycles represent an economic and effective solution. The results of using this kind of cycles are the reduction of the pressure ratio of each compression stage, the reduction of the discharge temperature due to the cooling effect provided by the intermediate cooling and the increase of theoretical cycle efficiency. This study analyzes two vapor injection cycles, in terms of the injection conditions for three different refrigerants (R407C, R290 and R22). The work considers the efficiencies of each component and their sensibility to the working conditions. From all the analysis, guidelines for the optimum design and control of such systems are obtained in terms of capacity, COP and discharge temperature criteria.Keywords: Heat pump, vapor injection, efficiency, simulation, Two-stage.

The properties of the ferroelectric IV-VI semiconductor GeTe have been studied as a function of pressure up to 25 GPa at room temperature, by powder X-ray diffraction in a diamond anvil cell. In a truly hydrostatic medium, the transition from the rhombohedral to cubic NaCl-type structure was not observed up to 8 GPa while it occurred below 5 GPa in a solid pressure transmitting medium. In both cases, no discontinuity could be observed in the lattice parameter. However, the transformation probably remains of the first order, as at normal pressure, but with a very small volume discontinuity. The presence of small anisotropic stress components has a large effect on the equilibrium pressure of the transition and possibly on its mechanism. In addition, a transition to an orthorhombic structure takes place in the same pressure range; no cubic CsCl-type structure was evident below 25 GPa.

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