Sn is a classical superconductor on the border between type I and type II with critical temperature of 3.7 K. We show that its critical parameters can be dramatically increased if it is brought in the form of loosely bound bundles of thin nanowires. The specific heat displays a pronounced double phase transition at 3.7 K and 5.5 K, which we attribute to the inner ‘bulk’ contribution of the nanowires and to the surface contribution, respectively. The latter is visible only because of the large volume fraction of the surface layer in relation to the bulk volume. The upper transition coincides with the onset of the resistive transition, while zero resistance is gradually approached below the lower transition. In contrast to the low critical field Hc = 0.03 T of Sn in its bulk form, a magnetic field of more than 3 T is required to fully restore the normal state.
Considerable cold energy embodied in liquefied natural gas (LNG) can be recycled in LNG regasification, which can not only save energy but also avoid cold pollution within the low-temperature fluid emission. Review on both domestic and overseas is conducted on the recycling of LNG cold energy in different applications. Against the single purpose utilization of LNG cold energy with a large amount of energy loss, the cascade recycling strategy is proposed for highly-efficient utilization of LNG cold energy. Based on the defined cold exergy efficiency, the exergy analysis is performed for some different recycling applications of LNG cold energy. The system exergy rate method is used to compare the superiority of modes in which the LNG is converted into NG under normal temperature. The results show that the exergy efficiency of a LNG cold energy cascade recycling system is higher than that of a single utilization system. Apart from the improved efficiency, the cascade recycling strategy can expand the applicable temperature range of LNG cold energy compared with the single utilization. Finally, the entropy and entransy for evaluating the LNG cold energy transport process are compared and discussed, from which it is indicated that entransy is more appropriate for the heat transfer process with low-temperature or large temperature difference, as is the case for LNG cold energy recycling.
Phase behaviors in fluid state of systems of purely repulsive potentials (PRPs) are investigated with a recently proposed 3rd-order thermodynamic perturbation theory (TPT) (Phys. Rev. E. 2006, 74, 031119). It is found that a usual gas-liquid transition (GLT) always happen to several investigate PRPs, whose perturbation part as a function of particle separation holds a discontinuous point, or an indifferentiable point, or is differentiable, but with an additional length scale besides the hard sphere diameter. Other findings to include that 1: a longer range of the repulsive perturbation tail, or a bigger jump of the repulsive perturbation tail at an interrupted point, can stabilize the GLT more easily; 2: all of the GLTs resulting from the investigated PRPs is accompanied with a density anomaly, in contrast to the traditional GLTs due to a hard core plus an attractive tail. Finally, contrary to the previous findings in literature due to conventional 1st-order TPT, and 2nd-order TPT based on a macroscopic compressibility approximation (MCA), the present investigation does not discover for a square shoulder (SS) potential in any periodic phase behavior of critical temperature as a function of the repulsive step radius and high density liquid-low density liquid transition (HDL-LDL). A convergence analysis of the 3rd-order TPT indicates that the previously found SS potential phenomenology (Phys. Rev. E. 2003, 67, 010201(R); Phys. Rev. E. 2006, 74, 041201), should be an artifact originating from the insufficiency of the employed 1st-order TPT and 2nd-order MCA-TPT. The counter examples are found to a liquid-liquid transition hypothesis (Nature, 1992, 360, 324) of the density anomaly.
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