非平衡相变的临界标度理论及普适性

综述了作者近年来在非平衡相变临界（ Ｎ Ｐ Ｃ） 标度理论及普适性研究的进展。主要包括一般 Ｎ Ｐ Ｃ 系统规格化模型,局域序参量的概率分布,广义势的临界渐近形式,空时有关函数及其临界奇异行为。论证了 Ｎ Ｐ Ｃ 系统的临界可标度性,导出了一组普适的 Ｎ Ｐ Ｃ 标度关系,由之计算出的４ 种 Ｎ Ｐ Ｃ 普适类的临界指数与目前已知的实验及理论结果吻合得非常好。此外,还讨论了非平衡相变临界标度理论的普适性,将平衡相变临界标度理论作为一种特殊极限情况含于同一理论体系中。     

非平衡相变的临界标度理论及普适性

综述了作者近年来在非平衡相变临界（ Ｎ Ｐ Ｃ） 标度理论及普适性研究的进展。主要包括一般 Ｎ Ｐ Ｃ 系统规格化模型,局域序参量的概率分布,广义势的临界渐近形式,空时有关函数及其临界奇异行为。论证了 Ｎ Ｐ Ｃ 系统的临界可标度性,导出了一组普适的 Ｎ Ｐ Ｃ 标度关系,由之计算出的４ 种 Ｎ Ｐ Ｃ 普适类的临界指数与目前已知的实验及理论结果吻合得非常好。此外,还讨论了非平衡相变临界标度理论的普适性,将平衡相变临界标度理论作为一种特殊极限情况含于同一理论体系中。     

Spinodal decomposition of two-dimensional fluid mixtures: A spectral analysis of droplet growth

The spinodal decomposition of two-dimensional fluid mixture is studied by numerical simulation. For the high viscous fluid mixture it has not been evident whether the interfacial tension is relevant to the droplet growth or not. A length scale R defined by the structure function extracting the effect of the long wavelength mode justifies a rapid growth close to R approximately t, but the length scale energetically defined reveals a much slower growth R approximately t(0.5), where t is time. This discrepancy represents the violation of the dynamical scaling with single length scale. The slow gowth of the length scale is attributed to the accumulation of the number of isolated droplets in phase separating state, whereas the rapid growth represents the relevance of the surface tension as the driving force in two dimensions. For a low viscous fluid mixture the dynamical scaling is a good assumption with the growth law R approximately t(2/3) up to a very large Reynolds number Re approximately 1500, which is the limit in the present simulation.     

Analytical study of the changes in the color of daylight due to sulfate droplets and soot grains in the atmosphere

Absorption of daylight by an atmospheric layer that comprises non-interacting water and sulfate droplets, interstitial soot grains, and composite sulfate-soot particles is determined by use of exact theories of Mie or extended-Mie scattering from all types of suspended particles. Interest is in the color of the sky, as observed from the ground underneath a light-absorbing atmospheric layer which has been synthesized as above. The end-result of the theory presented in this paper is the spectral radiant power distribution and the colorimetric features of daylight at ground level. The numerical application manifests that microlensing by sulfate droplets gives rise to enhanced absorption by soot grains, which results in attenuation and redshifts of daylight. An investigation is made of the changes in the color of the sky, as observed from the ground, due to pollution of the air by sulfuric acid and carbon.     

Stochastic theories and scaling relations for early-stage surface growth

Recent theories for the surface growth are reviewed, which describe the nucleation kinetics of binary alloys in the first layer and the nucleation on top of islands in the second layer. In the first part, describing the submonolayer regime, scaling relations for the number density of stable islands in dependence of the growth parameters are derived from an extension of the classical rate equation approach to binary systems. In the second part a general stochastic theory is presented that allows one to predict whether thin films become smooth or rough under non-equilibrium growth conditions.     

Coalescence of spreading droplets on a wettable substrate

We investigate experimentally and theoretically the coalescence dynamics of two spreading droplets on a highly wettable substrate. Upon contact, surface tension drives a rapid motion perpendicular to the line of centers that joins the drops and lowers the total surface area. We find that the width of the growing meniscus bridge between the two droplets exhibits power-law behavior, growing at early times as t1/2. Moreover, the growth rate is highly sensitive to both the radii and heights of the droplets at contact, scaling as ho3/2/Ro. This size dependence differs significantly from the behavior of freely suspended droplets, in which the coalescence growth rate depends only weakly on the droplet size. We demonstrate that the scaling behavior is consistent with a model in which the growth of the meniscus bridge is governed by the viscously hindered flux from the droplets.     

落管中Al4Mn合金的形核研究

用1.2米长的落管对Al₄Mn合金进行了形核与过冷的研究.在落管底部收集到的样品中得到了正交Al₆Mn,β-Mn,两个十次准晶相关相、一个二十面体五次准晶相关相和十次准晶畴.发现这些相的含量与样品的尺寸大小有关,根据传统的形核理论对相含量与样品尺寸大小之间的关系作了定性的分析和讨论. 关键词：     

Raman and Rayleigh spectroscopy and molecular motions

Raman and Rayleigh scattering experiments on HCl, DCl, HBr and DBr molecules (pure liquid or isotopically diluted) have been carried out at room temperature. Results are discussed in the light of the existing theories on molecular motions in the liquid phase. The comparison of Rayleigh and Raman scattering results shows that reorientational processes are not sufficient to explain completely the profile of anisotropic Raman scattering. According to a recent theory due to Bratos, the rotational correlation function can be obtained only after elimination of the vibrational correlation function determined from the isotropic Raman scattering. In this last case broadening may arise from three causes: translational motion, resonance broadening and vibration-rotation coupling. A comparative study of the band profile of anisotropic Rayleigh and Raman scattering shows that the wings in both cases come from essentially the same origin while a band moment analysis is consistent with Gordon's theory according to which they are of reorientational origin.     

Multi-phase field simulation of grain growth in multiple phase transformations of a binary alloy

This work establishes a temperature-controlled sequence function, and a new multi-phase-field model, for liquid–solid–solid multi-phase transformation by coupling the liquid–solid phase transformation model with the solid–solid phase transformation model. Taking an Fe–C alloy as an example, the continuous evolution of a multi-phase transformation is simulated by using this new model. In addition, the growth of grains affected by the grain orientation of the parent phase(generated in liquid–solid phase transformation) in the solid–solid phase transformation is studied. The results show that the morphology of ferrite grains which nucleate at the boundaries of the austenite grains is influenced by the orientation of the parent austenite grains. The growth rate of ferrite grains which nucleate at small-angle austenite grain boundaries is faster than those that nucleate at large-angle austenite grain boundaries. The difference of the growth rate of ferrites grains in different parent phase that nucleate at large-angle austenite grain boundaries, on both sides of the boundaries, is greater than that of ferrites nucleating at small-angle austenite grain boundaries.     

非晶态Cu12.5Ni10Zr41Ti14Be22.5合金相分离的动力学标度

利用实时小角中子散射实验研究了非晶态Cu_12.5Ni₁₀Zr₄₁Ti₁₄Be_22.5合金相分离的动力学标度性质．通过对相分离过程中实时小角中子散射谱进行详细的标度分析，揭示出散射函数S（q，t）（q为散射波矢，t为时间）在相分离的早期即达到动力学标度态，从而证明动力学标度假设也适用于描述深过冷液态的相分离过程 关键词：     

Fast and accurate radiance calculations using truncation approximation for anisotropic scattering phase functions

The phase function for solar light scattering by large particles such as cloud droplets is strongly anisotropic due to very strong peaking in the forward direction. This creates numerical difficulties when attempting to calculate accurate reflected and transmitted radiances, which are important for remote sensing of atmospheric and surface properties. A popular approach uses the delta function to approximate the forward-scattering peak in a fraction of energy and a limited number of polynomial terms or a geometrically truncated function for the remaining fraction (so-called truncation approximations). This article compares and discusses several methods for fast and accurate calculations using truncation approximations. When using a single truncation approximation for all scattering orders, large biases appear in directions near the solar and anti-solar points. As shown here, high accuracy can be obtained using different truncation approximations depending on the order of scattering. Of particular importance is the use of phase functions close to the exact phase functions for the first few orders of scattering. Applying the method in combination with the Monte Carlo (MC) method, in which the truncation fraction for a scattering order depends on the scattering angle at the previous scattering event, obtains accurate radiance calculations under almost all geometrical and optical conditions, including in directions near the solar point. Because the method also reduces computational noise due to the MC sampling of radiance, it is useful for fast and accurate radiance calculations for cloudy atmospheres.     

The scattering of line radiation—I. A generalized redistribution function

The theory of the frequency redistribution of radiation during scattering is re-investigated with the aim of producing a generalized frequency redistribution function. The assumption, commonly made, that the atom performing the scattering of the radiation has a constant velocity for the duration of the scattering event is not made in the present investigation. As a result a formal theory is developed which does indeed lead to a generalized redistribution function. Two limiting cases are discussed: in one of the limits, we reconsider the case where the velocity of the atom is constant during the scattering event; the other limiting case describes the situation which occurs when the velocity at absorption, of the atom performing the scattering, is completely uncorrelated with its velocity at emission. This latter case is then more fully discussed with a view to overcoming one of the major difficulties encountered with the existing theories of frequency redistribution, i.e. that complete redistribution in the radiation scattered from an atmosphere being viewed by a distant observer can not be predicted.     

Geometrical scaling at inelastic threshold

The possibility of geometrical scaling being a low energy phenomenon is investigated using phase shift data. For exotic reactions, in particular in K⁺p scattering, scaling is observed and the high energy (NAL-ISR)GS curve agrees with phase shift inelasticity η down to the inelastic threshold. For reactions with resonances the high energy curves average the phase shift inelasticities. The consequences of these results are discussed and predictions for ππ and Kπ scattering are presented.     

Cluster description of water-in-oil microemulsions near the critical and percolation points

The three-component ionic microemulsion system consisting of AOT/water/decane shows an unusual phase behavior in the vicinity of room temperature. The phase diagram in the temperature-volume fraction (of the dispersed phase) plane exhibits a lower consolute critical point at about 40 degrees centigrades and 10% volume fraction. A percolation line, starting from the vicinity of the critical point, cuts across the plane, extending to high volume fraction side at progressively lower temperatures. In this paper we review the evidence that allows to interpret the phase behavior of our system in terms of interacting spherical droplets. We also investigate the dynamics of droplets, below and approaching the critical point by dynamic light scattering. The first cumulant and time evolution of the droplet density correlation function can be quantitatively calculated by assuming the existence of polydispersed fractal clusters formed by the microemulsion droplets due to attraction. The relaxation phenomena observed in an extensive set of measurements of electrical conductivity and permittivity close to percolation is also reviewed and interpreted through the same cluster-forming mechanism, which reproduces the most relevant features of the frequency-dependent complex dielectric constant of this system. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Growth of rough surfaces

The growth of objects with rough surfaces is a common phenomenon. We describe several models used in the study of the temporal evolution of fluctuating interfaces and then we explain the dynamical scaling in this class of growth models with self-affine surfaces. The recent progress in this field is reviewed. Much emphasis is put on roughness properties and in particular on a possible kinetic roughening transition — a nonequilibrium analog of the thermal roughening transition. Both analytical and numerical results for scaling exponents are summarized and indications of a phase transition in some models are discussed.     

Computer simulation study of phase separation in a binary mixture with a glass-forming component

We present a computer simulation study of spinodal decomposition with one of the two phases freezing in a glassy state during phase separation. As a model we used the Cahn-Hilliard equation with a concentration-dependent mobility coefficient which decreases rapidly with increasing concentration of the glass-forming component. We solved the Cahn-Hilliard equation numerically for two dimensions. The domain growth depends crucially on the volume fraction of the glassy phase. For high volume fractions, when the glassy phase forms a percolating matrix, a novel coarsening mechanism is discovered, which arises from the migration and coalescence of liquid droplets within the glassy matrix. Various quantities characterizing the time-dependent domain pattern, like droplet size distribution, one- and two-point distribution function and structure factor of the concentration field, are computed. We checked the validity of the dynamic scaling hypothesis.     

One more hydrodynamic scenario of ultrarelativistic nuclear collisions

A new hydrodynamic scenario of ultrarelativistic nuclear collisions is discussed. It includes two stages: one-dimensional scaling expansion and break-up of a hydrodynamic system into separate spherical droplets. The correlation between the average transverse momentum and multiplicity (sensitive to the quark-hadron phase transition) is calculated.     

相态对冰水混合云微观特性反演的影响研究

当云层的温度在－40℃~0℃之间时, 云层中会存在冰和水两种相态的云滴, 其散射特性与纯水云以及纯冰云特性有较大差异, 因此遥感反演混合相云层的微观和宏观物理特性具有重要的意义。本文采用冰水双层球模型模拟了冰水混合云中的云滴, 利用Mie理论计算了纯水、纯冰和冰水颗粒的单次散射特性, 分析了单次散射相函数, 不对称因子, 单次散射反照率等随着有效半径、相态、内外半径比等的变化特性。利用离散纵标法(DISORT)计算了水云和冰云对0.75 μm、2.16 μm和3.3 μm的双向反射函数, 讨论了利用纯水滴和纯冰滴反演冰水混合云滴的误差。分析结果表明, 利用0.75 μm和2.16 μm的太阳光反演冰水混合云的光学厚度和有效半径时, 光学厚度误差较大, 有效半径误差较小; 结合0.75 μm和3.3 μm的太阳光反演冰水混合云的光学厚度和有效半径时, 光学厚度误差较小, 有效半径误差较大, 其会高估其有效半径; 另外结合0.75 μm和3.3 μm这两个波长的反射函数反演冰水云的冰水混合比更为有效。     

Homogeneous nucleation and growth of droplets in vapours

The theory of homogeneous nucleation of liquid drops in supersaturated vapours is reviewed. A new kinetic treatment which accounts for the heating of the growing clusters due to the latent heat of condensation is presented, and the irreversible thermodynamics of non-isothermal nucleation discussed. It is found that growing clusters are generally colder than the surrounding vapour during their sub-critical growth period.

Time dependent nucleation is discussed and a simple estimate for the time-lag in establishing the steady state is given. The nucleation in cloud chambers expanding with constant speed is discussed in detail, and the number of droplets formed and their final mean size is calculated as a function of the terminal expansion ratio. Re-evaporation of nucleated clusters is discussed. Numerical results are given for a number of typical situations in experiments on water-vapour. These results for the nucleation rate as corrected by Lothe and Pound predict much lower ‘critical’ expansion ratios than indicated by the limited experimental data available, even when the non-isothermal theory is used.

To restore agreement between theory and experiments the surface tension for small droplets (?100 molecules) could be increased some 15% above that of the bulk liquid, or the pre-exponential in the nucleation rate could be decreased by some 10^?15. This latter expedient roughly corresponds to use of the ‘classical’ instead of the Lothe-Pound nucleation rate. These two alterations would, however, affect the theoretical curves in different manners and careful experiments could possibly distinguish between them.