Determination of the Order Parameter in Binary Fluid Mixtures

We propose a microscopic approach to the study of phase transitions in fluid mixtures. It is based on the collective variables method with a reference system. The problem of definition of the order parameter in a two-component fluid system is considered in detail. This system is described with two sets of collective variables: _k and _k. It is shown that the CV connected with the order parameter is _k=0 in the case of a gas–liquid critical point as well as in the case of a mixing–demixing phase transition. The relations between the microscopic parameters, temperature, density and concentration which determine the particular form of ₀ for each of these phenomena are obtained. Based on these results we will be able to construct an effective Ginsburg–Landau–Wilson Hamiltonian.     

Dielectric investigation on some binary mixtures of hockey-stick-shaped liquid crystal and octyloxy-cyanobiphenyl

We report the measurement of temperature-dependent dielectric parameters in some binary liquid crystal mixtures comprising of a hockey-stick-shaped mesogen 4-(3-decyloxyphenyliminomethyl) phenyl-4-decyloxycinnamate (SF7) and calamitic compound 4′-octyloxy-4-cyanobiphenyl (8OCB). All the investigated mixtures possess a large positive dielectric anisotropy (Δε), although a noticeable reduction has been found by increasing the diverse-shaped dopant concentration. Investigation on the pretransitional behavior in the vicinity of isotropic to nematic (I–N) phase transition suggesting a tricritical character for all the studied mixtures. Parameterization of dielectric permittivity close to the nematic to smectic-A (N–Sm-A) phase transition exhibits non-universal values of the critical exponents describing a second-order nature of the transition. Systematic variation of critical exponents against dopant concentration and McMillan ratio reveals a well consistency with those obtained from the high-resolution optical birefringence measurements.     

Sound velocity in binary liquid mixtures and the statistical mechanical theories

Sound velocity in three binary liquid mixtures benzene+cyclohexane (I), cyclohexane+carbontetrachloride (II) and benzene+carbontetrachloride (III) has been measured. Significant structure and Flory — Patterson theories have been employed to evaluate ultrasonic velocity in the systems. The values are in good agreement with the experimental ones. A comparative study of significant structure theory and Flory-Patterson Theory has been made. Both the theories give satisfactory results for the three liquid mixtures.     

Theoretical calculation of acoustic non-linearity parameter B/A of binary mixtures

Acoustic non-linearity parameter B/A is calculated for five binary liquid mixtures using Tong and Dong equation along with the Flory’s statistical theory. Similar to other excess thermodynamical quantities an excess non-linearity parameter (B/A)^E is defined for binary liquid mixtures. The interactions in the liquid mixtures are explained on the basis of the excess non-linearity parameter.     

Temperature-dependent sound velocities,attenuation and elastic moduli anomalies in Pr1− x Sr x MnO3 perovskite manganite materials at 0.28 ≤ X ≤ 0.41

Pr_{1? x} Sr _x MnO₃ perovskite manganite materials with different compositions of x (x?=?0.28, 0.33, 0.35, 0.38 and 0.41) have been prepared using solid-state reaction technique. The ultrasonic longitudinal and shear velocities and longitudinal attenuation have been measured employing through transmission method operated at a fundamental frequency of 5?MHz over a wide range of temperatures. In all the compositions, the temperature-dependent sound velocities, attenuation and elastic constants show interesting anomalies at Curie temperature (T _C) and Neel temperature (T _N). The observed anomalies at T _C and T _N have been discussed in terms of phase transition, strength of linear magnetostriction effect and competition between paramagnetism and ferromagnetism.     

Anomalies in the velocity of longitudinal ultrasonic waves in cesium under the pressure up to 5 GPa

Abstract

The velocity of longitudinal ultrasonic waves, ν₁,(P), in polycrystalline cesium was measured at 293 ±1K in the pressure interval 0–5 GPa. v ₁(P) alterations at BCC-FCC phase transition at 2.3 GPa and at the electronic-structure transformation at 4.3 GPa were obtained. Decrease of v ₁(P) to 4.3 GPa after a maximum at ～3.8 GPa were found, that gave evidence to the appearance of a corresponding soft mode in the FCC-Cs phonon spectrum. The peculiarities of dependence v ₁(P) correlate with s-conduction electrons promotion to the empty d-band in accordance with the theoretically predicted continuous electronic s-d transformation in Cs.     

Non-linearity parameter B/A of binary liquid mixtures at elevated pressures

When sound waves of high amplitude propagate, several non-linear effects occur. Ultrasonic studies in liquid mixtures provide valuable information about structure and interaction in such systems. The present investigation comprises of theoretical evaluation of the acoustic non-linearity parameter B/A of four binary liquid mixtures using Tong and Dong equation at high pressures and T=303.15 K. Thermodynamic method has also been used to calculate the non-linearity parameter after making certain approximations.     

超声波在液体中相速与群速的测量

简要叙述了相速与群速的定义,并用实验测量了超声波在不同液体中的相速与群速.     

Binary nonadditive hard-sphere mixtures at high dimension

At high spatial dimension, a suitably scaled classical system of interacting particles truncates at second virial terms. A binary mixture of nonadditive hard spheres with sufficiently repulsive interaction between unlike particles decomposes at sufficiently high density into two coexisting phases. The region around the critical density behaves classically.     

Ultrasonic measurement of the elastic properties of benzoyl glycine single crystals

Certain organic crystals are found to possess high non-linear optical coefficients, often one to two orders of magnitude higher than those of the well-known inorganic non-linear optical materials. Benzoyl glycine is one such crystal whose optical second-harmonic generation efficiency is much higher than that of potassium dihydrogen phosphate. Single crystals of benzoyl glycine are grown by solvent evaporation technique usingN, N-dimethyl formamide as the solvent. All the nine second-order elastic stiffness constants of this orthorhombic crystal are determined from ultrasonic wave velocity measurements employing the pulse echo overlap technique. The anisotropy of elastic wave propagation in this crystal is demonstrated by plotting the phase velocity, slowness, Young’s modulus and linear compressibility surfaces along symmetry planes. The volume compressibility, bulk modulus and relevant Poisson’s ratios are also determined. Variation of the diagonal elastic stiffness constants with temperature over a limited range are measured and reported.     

描述混合物固液相变的两个近似模型

提出了描述混合物固液相变的两个近似模型：混合相模型和等效物质模型。通过对304钢的计算和比较表明,由两个模型计算得到的结果与直接利用304钢的材料参数计算得到的结果相符合。     

Optical Inverse Perfect Shuffle Interconnection and Its Application to Polynomial Evaluation

An optoelectronic implementation of polynomial evaluation has been presented which uses a recirculating inverse perfect shuffle interconnection (IPS). The IPS interconnection is formed by a binary phase grating which permits a high density of interconnection; it can be utilized in a high order of polynomial evaluation processing system.     

LaCoO3中自旋态转变现象的超声研究

测量了LaCoO₃单相多晶样品的纵波与横波超声声速和衰减随温度的变化关系, 在材料的自 旋态转变温度附近（≈90K）,纵波声速出现明显的软化并伴随一个尖锐的衰减峰,但是在 横波的测量中却没有出现类似的超声异常,分析认为LaCoO₃在90K附近的自旋态 转变是由于Co³⁺离子是从低自旋态(LS,t⁶_2ge⁰ _g)转变到中等自旋态(IS,t⁵ _2ge¹_g ),而不是高等自旋态(HS,t⁴_2ge²_g).随着温度的升高,在 200K附近纵波和横波测量上都观察到一个伴随着微小声速软化的宽大的衰减峰,这可能是随 机分布的IS态Co³⁺离子的Jahn-Teller效应导致的局域晶格扭曲所造成的.关键词：超声声速与衰减自旋态转变Jahn-Teller效应     

Thermodynamic properties of molecular fluid mixtures of hard ellipsoids

Thermodynamic properties of molecular fluid mixtures of hard ellipsoids are calculated. Numerical results are given for equation of state and excess-free energy of the binary mixture of both additive and non-additive hard ellipsoids. It is found that the equation of state and free energy of mixtures increase with increase of anisotropy parameterx ₀.     

Elasticity of the B2 phase and the effect of the B1–B2 phase transition on the elasticity of MgO

A study of the high-pressure anisotropy of MgO was conducted using first-principles calculations based on density functional theory within the generalized gradient approximations. The pressure dependence of the elastic stiffness coefficients and the anisotropy parameters, in both B1 and B2 phases, shows that for high-hydrostatic compression the easiest deformation is the shear along (100) plane and the the material's response to deformation and to shearing strains is quite the same. According to the calculations of the velocities of propagation of elastic waves, we deduced that MgO develop an elastic anisotropy, especially, in the B1 phase. We present the B2 phase elastic properties which are not already studied under high pressure.     

Lattice models for hydrogen-bonded solvents

A class of lattice models for a binary mixture is defined by assuming that one of the components may form bonds to neighboring molecules of the same species. It is assumed that the fugacity of a molecule depends on the number of bonds which connect the molecule to other molecules. If no molecule is allowed to be connected by more than two bonds to other molecules, then no phase transition occurs, while phase transition can occur if more than two bonds are allowed. If only two or no bonds are allowed, then the model can be solved rigorously for certain planar lattices by transforming it to a dimer covering problem; this model shows behavior similar to the Ising model in zero magnetic field.Work supported by National Science Foundation grant GP-26526.On leave of absence from Corpus Christi College, Cambridge, England.On leave from the University of Copenhagen.