Thermodynamic and Pseudo Binary Phase Diagram of REBa2Cu3O7-x-"Ba2Cu5O7" systems

In this work the effect of oxygen pressure on the primary crystallisation fields for REBa₂Cu₃O_7-x(RE=Nd, Sm, and Eu) has been studied. A DTA apparatus has been modified in order to carry out analyses under gas pressure, so the trend of temperatures of peritectic decomposition of the REBa₂Cu₃O_7-xphases and of the eutectic equilibrium involving REBa₂Cu₃O_7-x phases and flux mixture "Ba₂Cu₅O₇" have been studied at oxygen pressures of 0.21, 1, and 10 atm. This showed that primary crystallisation fields spread at the increase of the oxygen pressure and allowed us to calculate the enthalpies of reactions of REBa₂Cu₃O_7-xphases too. This revised version was published online in July 2006 with corrections to the Cover Date.     

Quiesent Crystallization Kinetics of Nucleated Metallocene and ZN Isotactic Polypropylenes

Crystallization kinetics and thermodynamic properties of nucleated isotactic polypropylene (PP) are analyzed using Hoffman—Lauritzen crystallization theory to determine the mechanistic effects of the nucleators. Calorimetric data provides quantitative comparisons between nucleating efficiences of the (Millad) and (NJSTAR) nucleator in Metallocene (M) and Ziegler—Natta (ZN) PP. The two types of PP without nucleators showed similar crystallization behavior though the T°_m for ZN-iPP was about 10°C higher than M-iPP. Both nucleators show significant improvement in crystallization rate in both types of PP. In addition, Millad outperforms NJSTAR. The magnitude of the kinetic response is,however, different and both the nucleators appear to function better in ZN than in Metallocene PP. nucleated PP shows predominantly the form. The amount of the form is thermal history dependent and changes with supercooling (T=T°_m–T_c). Similar equilibrium melting temperature (T°_m) in the nucleated and control PPs indicates the lack of any thermodynamic effect of the nucleator. All nucleated PPs show a much lower secondary nucleation rate constant, K_g.This revised version was published online in November 2005 with corrections to the Cover Date.     

Linear response and relaxation in quantum lattice systems

For spin-lattice systems, the Kubo formula, expressing the relaxation function in terms of the linear response function, is found to be exact in the thermodynamic limit. In addition, analyticity properties are obtained.     

Determination of activity coefficients for ammonium chloride at 25°C

Precise values of the activity coefficients of aqueous ammonium chloride solutions at 25°C determined from emf measurements of cells with transference are reported for the concentration range 0 to 0.2m. The results show no anomalous behavior with respect to the Debye-Hückel limiting law. An interpretation of excess thermodynamic functions of potassium and ammonium chloride solutions is made in terms of ionic influences on solvent structure. The relative order of activity coefficients for the R ₄ NCl series up to 0.1m is shown to be (NH ₄ Cl)>(Me ₄ NCl)>(Et ₄ NCl)>(n-Bu ₄ NCl).     

Thermodynamic Equilibrium in the System of Chaotic Quantized Vortices in a Weakly Imperfect Bose Gas

In the example of a weakly imperfect Bose gas, we discuss the mechanism of establishing thermodynamic equilibrium for a chaotic set of quantum vortex filaments. We assume that the dynamics of the Bose condensate is described by the Gross–Pitaevsky equation with an additional noise satisfying the fluctuation–dissipation theorem. In considering a vortex filament as the intersection line of surfaces on which the real and imaginary parts of the order parameter (x,t) vanish, we obtain an equation of the Langevin type for elements of the vortex filament with an appropriately transformed random force. The Fokker–Planck equation for the probability density has a solution given by the Gibbs distribution at the temperature of the Bose condensate. In other words, when the Bose condensate is in thermal equilibrium and no other random actions exist, the system of vortices is also in thermal equilibrium.     

Effect of H/D-isotope substitution on the solubility and solvation thermodynamics of krypton in methanol solutions of carbamide

The solubility of gaseous krypton in CO(NH₂)₂—CH₃OH (CD₃OH) and CO(ND₂)₂—CH₃OD solutions with carbamide concentrations of up to 1.5 solvomolality units (0.026 mole fractions) was measured at 278, 288, 298, 308, and 318 K and at a partial gas pressure of 101325 Pa. The thermodynamic functions of dissolution (solvation) of krypton and the standard Setchenov coefficients were calculated. The solvation of Kr molecules increases upon deuterium substitution and with an increase in the temperature and carbamide concentration. In these solutions, specific contacts between the carbamide and methanol molecules play the predominant role.     

Determining Liquid Structure from the Tail of the Direct Correlation Function

In important early work, Stell showed that one can determine the pair correlation function h(r) of the hard-sphere fluid for all distances r by specifying only the tail of the direct correlation function c(r) at separations greater than the hard-core diameter. We extend this idea in a very natural way to potentials with a soft repulsive core of finite extent and a weaker and longer ranged tail. We introduce a new continuous function T(r) which reduces exactly to the tail of c(r) outside the (soft) core region and show that both h(r) and c(r) depend only on the out projection of T(r): i.e., the product of the Boltzmann factor of the repulsive core potential times T(r). Standard integral equation closures can thus be reinterpreted and assessed in terms of their predictions for the tail of c(r) and simple approximations for its form suggest new closures. A new and very efficient variational method is proposed for solving the Ornstein–Zernike equation given an approximation for the tail of c. Initial applications of these ideas to the Lennard-Jones and the hard-core Yukawa fluid are discussed.     

Taub-NUT时空视界附近自旋场的热力学量

利用Wentzel-Kramers-Brillouin近似计算了Taub-NUT时空事件视界附近自旋为1/2，1，3/2，2等无质量场的熵密度、压强和能量密度.结果表明，自旋场附近的热力学量不仅具有与平直时空相同的主导项，还多了两项自旋依赖的附加项. 关键词： Taub-NUT时空 自旋场 热力学量     

弱磁场中弱相互作用费米气体的有限粒子数效应(英文)

由弱磁场中弱相互作用费米气体的配分函数,导出有限粒子数条件下系统的配分函数G(β,N ).在此基础上,运用统计平均方法求解有限粒子数弱相互作用费米气体热力学量的解析表达式,给出各种温度条件下的热力学性质.研究结果表明,有限粒子数效应使各个热力学量都产生了一个修正项,除温度趋于0外,粒子数对化学势的修正项有直接影响,对内能和热容量的修正项并不产生直接影响.并且有限粒子数效应总是降低化学势,从而使化学势的0点向低温漂移,粒子数增大,会削弱这种效应,粒子间的相互排斥会加强这种效应.