The Rate of Spontaneous Formation of Microscopic Nuclei in Supersaturated Vapor

The equilibrium nucleus-size distribution determined by the method of statistical physics has been analyzed. The analysis has shown that nuclei composed of 1000 or fewer molecules are microscopic objects. They are described by partition functions and cannot be described by thermodynamic methods. An approach has been proposed that makes it possible to determine a partition function over internal degrees of freedom of a nucleus and express the aforementioned distribution via commonly accepted thermodynamic parameters. The solution of the problem is reduced to the determination of the evaporation rate of clusters by extrapolating the evaporation rate, which has been calculated for a macroscopic droplet of an incompressible liquid in terms of thermodynamic concepts with allowance for fluctuations, to the sizes of nuclei. As a result, a theory has been formulated for homogeneous stationary nucleation. The comparison of the proposed theory with experimental data has shown that the calculated sizes of critical nuclei coincide with the measured ones and that the theoretical nucleation rates either coincide with the measured rates or agree with them within one or two decimal orders of magnitude.     

Experimental Determination of the Surface Energy of Critical Nuclei During the Nucleation of Supersaturated Vapor

Theoretical substantiation of the empirical method for determining the surface (or excess) energy of critical nuclei was performed within the framework of thermodynamic approach. Characteristics of critical nuclei were determined based on the studies of the nucleation of supersaturated vapors of glycerol in the vicinity of its melting point and the critical temperature of carrier gas. The effect of the specific features of physicochemical parameters of the studied substance and carrier gas on the parameters of critical nuclei was revealed. Experimental values of the surface energy of critical nuclei were compared with those calculated by the droplet model. The necessity for the allowance for the temperature dependence of the surface energy of critical nuclei was demonstrated. It was noted that the largest deviation from the predictions of droplet model arises at small (about 10) numbers of molecules in a critical nucleus; as the size of a nucleus increases, the surface energy, in the limiting case, tends to physically correct value.     

On the Problem of Nucleation in a Supersaturated Vapor in the Presence of Heterogeneous Centers of Different Natures

The rules for constructing the analytical approximation are formulated for the law of the accumulation of the condensing substance by droplets that have emerged at centers of different natures. The accuracy of the suggested approximation is tested for the limiting cases of homogeneous nucleation and nucleation at centers of the same type. A general algorithm is constructed for describing the nucleation stage at centers of different natures after instantaneous creation of vapor supersaturation. Numerical calculations are conducted for the numbers of droplets formed at positively and negatively charged univalent ions in water vapors.     

Study of Relaxation in Micellar Solution by the Numerical Experiment

A numerical simulation of the relaxation process of surfactant micellar solution to a new equilibrium state is performed using model analytical representations for the main characteristics of micellar aggregates. Relaxation stages of molecular aggregate size distribution in the typical regions of aggregation number variations predicted by the analytical theory in two-flux approximation are revealed. Good agreement between the predicted values of the relaxation times of micellar solution and those obtained in numerical simulation is disclosed within the domain of applicability of two-flux approximation. Numerical algorithm proposed in this work makes it possible to study the relaxation process of micellar solution even in the case when two-flux approximation becomes inapplicable. The realization of numerical algorithm can be considered as a kind of experiment for studying the relaxation process of a model micellar solution.     

Spatial Electron Relaxation: Comparison of Monte Carlo and Boltzmann Equation Results

In former investigations on the spatial relaxation of the electron component of weakly ionized plasmas a considerable spectrum of distinct spatial structures has been found in the velocity distribution function as well as in various macroscopic quantities of the electrons. These results have been mainly obtained by solving the spatially inhomogeneous electron Boltzmann equation considering the action of uniform electric fields and the impact of elastic and inelastic collisions of the electrons with the gas atoms. To verify these partly unexpected results on the complex structure formation, analogous Monte Carlo simulations were performed now for a helium plasma at various reduced electric field strengths. Detailed comparisons were made between the results of the two independent kinetic approaches with respect to the spatial evolution of the velocity distribution function as well as of associated macroscopic quantities. Good agreement was generally found, thus confirming the earlier results on the complex spatial relaxation structures.     

Computer Simulation of Charge Separation in Vapor–Gas Mixtures

The interaction between counterions in water vapor is modeled by the Monte-Carlo method. A material contact of a system with vapor is modeled using a large canonical statistical ensemble. A powerful minimum, which forms in the medium-strength interaction potential at the expense of pulling molecules into the ion–ion gap, leads to separation of charges and stabilization of ions at distances that are much greater than the thickness of hydration shells of the ions. Spatial charge separation dramatically inhibits recombination and leads to accumulation of nonrecombined ion pairs. The discovered effect is of universal nature and explains some important atmospheric phenomena and results of electrometric laboratory experiments in moist air.     

Structural Analysis of the Condensation Products of Xylan with Organotin Halides

Physical characterization of the products resulting from condensation of xylan with organostannanes halides is consistent with a tin-modified product. Results from elemental analysis shows the presence of tin consistent with the presence of the tin moiety. Results from control reactions are consistent with the product containing portions derived from both reactants. The presence of the Sn–O–R ether linkage is found by infrared spectroscopy. The presence of portions derived from both reactants is indicated by mass and infrared spectral results.     

色质联用研究柴油蒸汽的可燃性

用色质联用的方法分析不同温度下柴油蒸汽的组成，确定正烷烃在油蒸汽中的分布；并结合勒夏特列原理计算出各个温度下的蒸汽可燃性指数，计算结果接近于实际情况。     

Numerical Study of Vibrational Energy Relaxation of O-H Bending inLiquid H2O

The relaxation of O-H bending of water molecule H2O in the liquid phase was studied with the molecular dynamics simulation approach. Both rigid and fexible solvents were used to identify the di?erent channels for the vibrational energy relaxation. It was observed that the relaxation time for the O-H bend overtone is 174 fs in the rigid solvent while it is 115 fs in the fexible solvent. The main pathway of the O-H bend overtone is transition to the bend fundamental. The relaxation time of the O-H bend fundamental was calculated as 204 fs which is comparable to the experimental value 170 fs.     

分子动力学模拟纳米尺寸限制体系下氩溶液中I2的振动能量弛豫

利用平衡态分子动力学方法(EMD)模拟了纳米尺寸限制球壳内I2在Ar溶液中的振动能量转移.计算并讨论了I2振动能量弛豫时间T1随球壳半径、溶剂密度的变化规律.通过分子间相互作用分析,在原子、分子水平上,揭示了随着球壳半径的减小,T1呈逐渐增大趋势的原因.结果表明,球壳的几何限制效应和表面作用对受限溶液密度分布的影响较大,从而导致溶质振动弛豫的显著变化.此外,非限制体系模拟显示,非平衡态分子动力学(NEMD)方法可以得到与平衡态分子动力学方法较一致的振动能量弛豫时间T1.     

质子交换膜燃料电池输出性能的数值模拟

运用COMSOL软件模拟分析3种流道下的质子交换膜燃料电池输出性能. 在相同的操作条件下,比较了单蛇形流道、交指流道以及混合流道之间的性能差异,详细说明了3种流道下质子交换膜燃料电池输出性能差异的原因. 由模拟结果分析得出,混合流道输出性能最好,交指流道输出性能其次,单蛇形流道输出性能最差;混合流道的排水能力最好,氧气浓度分布的最均匀;混合流道阴极进出口氧气浓度差最小. 模拟结果对质子交换膜燃料电池结构的优化和设计具有重要的指导意义.     

一种基于数值分析的矩形离子阱仿真优化方法

提出了一种对矩形离子阱进行仿真设计和优化的方法。该方法以数值分析为基础,对离子在矩形离子阱中的运动进行分析,得到相应的离子运动二阶微分方程。然后使用数值分析的Runge-Kutta法,对此二阶微分方程进行求解,可以得到理想状态下离子在离子阱中稳定的条件,从而完成对矩形离子阱的设计和优化。采用本方法,设计并优化了一种矩形离子阱,质量范围最大为260 amu/e,使用乙醇作为目标样品,紫外灯源作为离子源,法拉第筒作为检测器,对该矩形离子阱进行了质谱实验,成功得到了质谱结果,验证了所提出的数值分析仿真优化方法的实用性和正确性。本方法简单易行,便于修改,针对性强,可对多个参数使用循环遍历的方式来寻找最优值,特别适用于对未知结构或参数的探索研究。以此方法为基础可开发离子运动仿真软件,有很好的应用前景。     

过饱和MgSO4溶液结构的X射线衍射研究

用X射线衍射法研究了过饱和MgSO₄溶液298 K的水合结构.用经验黄金规则r=0.618λ/sin θ推断实验衍射曲线的结构信息,而另一个r=0.618×4π/s阐述结构函数曲线的峰.结构模型的计算表明,过饱和溶液中存在着水共享离子对和接触离子对.接触离子对的Mg-S特征距离为0.328 nm,表明硫酸根离子大多是以单齿形式配位到镁离子.Mg²⁺与硫酸根氧原子Mg-O_S(1)距离为0.205 nm,与Mg-H₂O是等价的;Mg-O_S(2)和Mg-O_S(3)很接近,大约为0.355 nm; Mg-O_S(4)距离为0.456 nm.随着浓度增加,接触离子对明显增加.水共享离子对Mg-S距离被确定在0.492 nm,并同时与接触离子对共存.硫酸根配合物的形成,降低了硫酸根水合结构的对称性.     

稀土在土壤中运移数值模拟研究

９种不同性质土壤Ｃｅ和Ｎｄ吸附和度达５０％时，用同位素示踪法和数值模拟法对ＲＥ运移进行比较，发现两者对极大多数土壤有较好的拟合性。说明该数值模拟程序对预测稀土长期在土壤中运移具有一定的可靠性。预测结果表明，在自然降雨量情况下，ＲＥ吸附饱和度１０％时，在吸附容量小的酸性土壤中，ＲＥ下移约每年１ｃｍ，吸附容量中等的中性、策酸性土壤，每两年约下移１ｃｍ而吸附容量较大的碱性土壤，ＲＥ很难被雨水运移。     

数值误差对能斯特方程计算结果的影响

电势和浓度通过能斯特方程相互计算时,计算结果受对方数值误差的影响。本文通过误差传递和实例研究了这种影响。结果表明,浓度误差对电势计算值的影响小,而电势误差对浓度计算值的影响大;这种现象在电子转移数较多、电势较大时更加显著。浓度为计算目标时需要重视数值误差的影响,所以代入能斯特方程的电势值应该有足够精度,或者避免使用能斯特方程,而是通过平衡常数进行计算。电势为计算目标时,浓度误差的影响较小,因此可以通过近似手段估算浓度,然后代入能斯特方程,既简化计算,又保证精度。     

化学弛豫法进行催化动力学分析的探索

化学弛豫动力学是研究快速反应的一种重要手段［１］,特别适合于研究复杂的生物化学体系［２］．若某一反应体系在固定的外界条件下先期达到平衡,然后给该体系一个外（或内）参量跃变的扰动,使体系偏离平衡,体系经弛豫过程将达到新的平衡,用不同的检测方法可求出弛豫...     

Simulation of the Radiation-Chemical Conversion of Mercury Vapor in Power-Plant Flue Gases in the Presence of Hydrogen Chloride

The effect of HCl on the conversion of mercury vapor in the electron-beam treatment of power-plant flue gases for removing nitrogen and sulfur oxides was investigated. A kinetic scheme for the process consists of the liquid-phase oxidation of Hg by O₃molecules and OH radicals followed by the adsorption of liquid-phase oxidation products on soot particles, which are removed from the gas flow using filters. It was found that almost complete removal of mercury vapor is attained at typical radiation doses and process temperatures at soot concentrations higher than 100 g/m³(STP). At a soot concentration lower than 100 g/m³(STP) and an HCl concentration higher than 50 mg/m³(STP) in the gas phase, biologically active HgCl₂is formed in considerable amounts.