环形装置中三维MHD平衡与稳定性的计算机模拟

一、引 言 在聚变研究中,环形等离子体的磁约束起着重要作用。目前托卡马克研究的进展令人鼓舞,其理论与实验比较符合,定标关系清楚。但是无论从聚变的最终目标来看,还是从实验的安排考虑,完全轴对称的几何形状给各方面部带来许多不便。人们希望知道如果把环形几何中加进直线段,或者把圆环改成不具有对称性的环形,会对等离子体约束产生何种影响?     

Hydrothermal phase equilibria in Ln2O3-H2O systems

Hydrothermal phase equilibria studies have been carried out in the Ln₂O₃-H₂O systems (Ln = La, Pr, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) and the stability fields of the phases Ln(OH)₃ LnOOH and Ln₂O₃-C have been established in the pressure-temperature range of 25000 psi and 900° C. The sequioxides Ln₂O₃-C are stable only in the last four systems of Er to Lu along with the Ln(OH)₃ and LnOOH. The systems from Nd to Ho have only Ln(OH)₃ and LnOOH as stable phases and those from La to Pr have only Ln(OH)₃ as the stable phase. The unit cell parameters of trihydroxides deviate from the values reported in the literature and this is attributed to the contamination of CO₂ in the starting material.     

Extraction Equilibria between Benzene and Water of Uni- and Bivalent Metal Picrates with Lariat 16-Crown-5: Effect of the Side Arms on the Extraction Ability and Selectivity

The overall extraction constants (K_ex) of uni- andbivalent metal picrates with 15-(2,5-dioxahexyl)-15-methyl-16-crown-5(L16C5) were determined between benzene and water at 25°C. TheK_ex values were analyzed into the constituent equilibriumconstants, i.e., the extraction constant of picric acid, the distributionconstant of the crown ether, the stability constant of the metalion–crown ether complex in water, and the ion-pair extraction constantof the complex cation with the picrate anion. The K_ex valuedecreases in the orders Ag⁺ > Na⁺ >Tl⁺ > K⁺ > Li⁺ andPb²⁺ > Ba²⁺ > Sr²⁺ for theuni- and bivalent metals, respectively, which are the same as those observedfor 16C5. The extraction selectivity was found to be governed by theselectivity of the ion-pair extraction of the L16C5–metal picratecomplex rather than by that of the complex formation in water. Theextraction ability of L16C5 is smaller for all the metals than that of 16C5,which is mostly attributed to the higher lipophilicity of L16C5. Differencesin the extraction selectivity between L16C5 and 16C5 were observed for thebivalent metals but little for the univalent metals. The side-arm effect onthe extraction selectivity was interpreted on the basis of the negativecorrelation between the effect on the complex stability constant in waterand that on the ion-pair extraction constant.     

Computational study of keto–enol equilibria of tropolone in gas and aqueous solution phase

Density functional theory calculations employing the B3LYP exchange-correlation functional, as well as Hartree–Fock computations, were performed on 2-hydroxy-2,4,6-cycloheptatrien-1-one (tropolone) and 3,5- and 3,6-cycloheptadiene-1,2-dione in gas and aqueous solution phases in order to determine the equilibrium constant for keto to enol interconversion of the isomers of C₇H₆O₂. Two standard basis sets were used throughout, namely 6-311++G^∗∗ and aug-cc-pVDZ. Solvent effects were modelled using two different self-consistent reaction field approaches – the Onsager dipole and the polarizable continuum models (PCM). In addition, the G3 method was used for calculations on species in the gas phase. Molecular geometries were fully optimized at each model chemistry, and it was found that the two keto isomers are always higher in energy than the enol form. From the results of B3LYP/6-311++G^∗∗ calculations of the difference in Gibbs free energy in the gas phase and using PCM, the relative pK values for the 2-hydroxy-2,4,6-cycloheptatrien-1-one ? 3,5- and 3,6-cycloheptadiene-1,2-dione system are 13.75 (g), 15.78 (g) and 13.05 (aq) and 13.45 (aq), respectively. That equilibrium is tilted almost exclusively in the direction of tropolone is due to resonance stabilization of the enol as a result of aromaticity, and is most easily understood on the basis of elementary Hückel theory.     

On the limitation of the van der Waals-Platteeuw-based thermodynamic models for hydrates with multiple occupancy of cavities

Thermodynamic models based on the van der Waals–Platteeuw statistical theory (Adv. Chem. Phys. 2, 1 (1959)) can be very accurate in describing hydrate equilibrium conditions, even for some occasions when multiple cavity occupancy occurs. These are cases outside the range of assumptions used for the development of the original statistical theory. However, during multiple cavity occupancy such models can perform poorly when calculating the cavity occupancies. This paper reports novel Grand Canonical Monte Carlo molecular simulations for the case of pure structure II N₂ hydrate and compares the calculated cavity occupancies with experimental data and observe reasonable agreement. Also examined are the van der Waals–Platteeuw-based modifications that retained the single-occupancy assumption of the original theory and how they perform when predicting cavity occupancies and hydrate equilibrium pressures.     

无水坝抽水蓄能系统高压溶气问题研究

无水坝抽水蓄能系统利用封闭容器内的高压气体构建虚拟水坝,是兼具压缩空气储能和抽水蓄能优点的新型储能系统。但该系统的封闭容器内水和气在高压状态共存有可能造成水中溶气,从而对水轮机造成汽蚀等破坏。本文采用实际气体状态方程及分子动力学模拟方法,研究了宽广的压力、温度范围下气体在水中的溶解及扩散规律,揭示了水中气体溶解量随时间和水深的变化规律。研究结果表明释能结束后保证水-气共容舱内剩余水的高度大于0.5 m时,高压溶气不会对水轮机产生危害,该结论对系统的工程应用及推广具有指导意义。     

On stochastic auctions in risk-averse electricity markets with uncertain supply

This paper studies risk in a stochastic auction which facilitates the integration of renewable generation in electricity markets. We model market participants who are risk averse and reflect their risk aversion through coherent risk measures. We uncover a closed form characterization of a risk-averse generator’s optimal pre-commitment behaviour for a given real-time policy, both with and without risk trading.     

全国平均每百户居民私家车拥有量预测

为了对全国平均每百户居民私家车拥有量进行预测，建立了可分离变量微分方程的数学模型，采用最小二乘法，借助Excel作为计算工具，得到了微分方程近似解的参数值，并用微分方程的近似解估计了最大拥有量以及2010年以后某些年的拥有量．     

Vapor–liquid equilibria of some binary mixtures formed by methylethylketone at 94.7 kPa

Bubble temperatures at 94.7?kPa, for the binary mixtures formed by methylethylketone (MEK) with cyclo-hexanone, tetrahydrofuran, ortho- and meta-xylenes, bromobenzene, chlorobenzene, epichlorohydrin, nitrobenzene, and iso- and tert-butanols have been measured by means of a Swietoslawski-type ebulliometer. The data could be represented well by the Wilson model.