RESEARCH NOTE WCA repulsive and attractive contributions to the thermodynamic properties at the vapour-liquid equilibrium

The Lennard-Jones attractive and repulsive contributions of intermolecular forces (as separated in the Weeks-Chandler-Andersen (WCA) theory) to the pressure and chemical potential of coexisting vapour and liquid phases are obtained by using an equation of state recently proposed by us. Some comments are given about the computer simulation results obtained by Plackov and Sadus (1997, Fluid Phase Equilib., 134, 77) using the McQuarrie-Katz separation of the intermolecular potential.     

The evaluation of some integrals that arise in the perturbation theory of liquids

ABSTRACT

The venerable, but still very useful, perturbation theory of liquids of Barker and Henderson involves some integrals that must be obtained numerically. There is no avoiding this for potentials such as the Lennard–Jones potential. However, to obtain the pressure, Barker and Henderson also obtained the necessary density derivatives numerically. This is cumbersome and care must be used to avoid excessive error. In this paper, it is noted that the earlier and less successful perturbation theory of Frisch et al. employed an alternative method, all but forgotten, for the evaluation of similar integrals. Their method still requires numerical integration. However, it allows an investigator to obtain the integrals for the pressure by analytical differentiation. The resultant integrals must still be evaluated numerically, but the extra step and annoyance of numerical differentiation is avoided. It is noted here that this method of using density derivatives can be incorporated into the Barker–Henderson theory.     

Probe diagnostics of strongly ionized inert-gas plasmas at atmospheric pressure

The technique of probe measurements (experiment and theory) is applied in a dense, strongly ionized inert-gas plasma at atmospheric pressure. The measurements are performed in a high-current (250–550 A) free-burning argon arc with a thermionic cathode. As a control technique we used spectroscopic measurements. Comparison of calculation with experiment reveals good agreement. The possibility of determining the plasma potential from the measured floating-probe potential is demonstrated. Zh. Tekh. Fiz. 68, 51–55 (June 1998)     

Lattice Dynamics of Some Fcc F-Shell Metals

A model pseudopotential depending on an effective core radius but otherwise parameter free is used to study the binding energy, equation of state, ion-ion interaction, phonon dispersion curves (q-space and r-space analysis), phonon density of states, Debye temperature, mode Grüneisen parameters, dynamical elastic constants, Debye-Waller factor, mean-square displacement, Debye-Waller temperature parameter and propagation velocities of elastic waves of some fcc f-shell metals La, Yb, Ce, and Th. The contribution of the s-like electrons is calculated in the second-order perturbation theory for the model potential while d- and f-like electron is taken into account by introduction of repulsive short-range Born-Mayer term. Very recently proposed screening function due to Sarkar et al. has been used to obtain the screened form factor. The parameter of the potential is evaluated by zero pressure condition. Which is independent of any fitting procedure. An excellent agreement between theoretical investigations and experimental findings prove the ability of the potential for d- and f-shell metals exclusively.     

High-pressure study of the non-Fermi liquid material U 2 Pt 2 In

The effect of hydrostatic pressure ( p ? 1.8 GPa) on the non-Fermi liquid state of U₂Pt₂In is investigated by electrical resistivity measurements in the temperature interval 0.3-300 K. The experiments were carried out on single-crystals with the current along ( I || c ) and perpendicular ( I || a ) to the tetragonal axis. The pressure effect is strongly current-direction dependent. For I || a we observe a rapid recovery of the Fermi-liquid T²-term with pressure. A comparison of the data with the magnetotransport theory of Rosch provides evidence for the location of U₂Pt₂In at an antiferromagnetic quantum critical point. For I || c the resistivity increases under pressure, indicating the enhancement of an additional scattering mechanism. Received 2 March 2001 and Received in final form 29 June 2001     

Predicting phase transition possibility pressure in solids: A semi-classical possibility

Abstract

This is a short review of the physical ideas, algorithm for calculations of the phase transition pressure, and some results of a semi-classical theory of the behavior of materials under high pressure proposed by Savi? and Ka[sbreve]anin. It is based on the Coulomb interaction, supplemented by a microscopic selection rule and a set of experimentally founded postulates. The theory hasbeen applied to cases ranging from DAC experiments to the calculation of models of planetary internal structure.     

A theory of probes in high-pressure strongly-ionized plasmas

A theory is developed for a probe in a strongly ionized high-pressure plasma. The situation discussed is typical of high-pressure plasmas, where the plasma occupying most of the near-probe layer is in a state of local ionization equilibrium with a common temperature for electrons and heavy particles. The possibility of determining the parameters of the unperturbed plasma by analyzing the probe characteristics on its ion saturation segment, transient segment, and for a floating probe potential is discussed. The calculations are carried out for the example of a strongly ionized xenon plasma at atmospheric pressure. Zh. Tekh. Fiz. 67, 16–20 (December 1997)     

Structural,elastic, thermodynamic and electronic properties of LuX (X = N,Bi and Sb) compounds: first principles calculations

ABSTRACT

The structural, electronic, elastic and thermodynamic properties of LuX (X = N, Bi and Sb) based on rare earth into phases, Rocksalt (B1) and CsCl (B2) have been investigated using full-potential linearized muffin-tin orbital method (FP-LMTO) within density functional theory. Local density approximation (LDA) for exchange-correlation potential and local spin density approximation (LSDA) are employed. The structural parameters as lattice parameters a₀, bulk modulus B, its pressure derivate B’ and cut-off energy (E_c) within LDA and LSDA are presented. The elastic constants were derived from the stress–strain relation at 0 K. The thermodynamic properties for LuX using the quasi-harmonic Debye model are studied. The temperature and pressure variation of volume, bulk modulus, thermal expansion coefficient, heat capacities, Debye temperature and Gibbs free energy at different pressures (0–50 GPa) and temperatures (0–1600 K) are predicted. The calculated results are in accordance with other data.     

Magneto-optical studies of CdTe/CdMnTe semimagnetic semiconductor superlattices under high pressure

Abstract

The photoluminescence (PL) of a CdTe/CdMnTe superlattice has been studied at pressures up to 4.1GPa, where the phase transition occurs. PL is observed up to this pressure, and it moves to higher energy with pressure at 66meV/GPa. This result is consistent with theory. Magnetic fields decrease the band-gap of the semimagnetic CdMnTe barriers and this reduces the PL energy. The pressure dependence of this effect is expected to provide a stringent test of the theory of semimagnetic materials and of superlattices.     

Resistivity of positive-J spin glasses: Study ofLaGd under hydrostatic pressure

Results of a new calculation of the resistivity in the noise model of spin glasses, based on the –J S interaction forpositive J, are compared with measurements of the resistivity in an fcc La-8at% Gd alloy under hydrostatic pressures up to 12 kbar, the first positive-J resistivity investigations under pressure. A positive value ofJ that decreases with increasing pressure, in accord with other experiments, leads to quantitative agreement between theory and experiment if one uses a large electronic density of states at the Fermi energy, in accord with specific heat measurements and electronic band structure calculations in fcc La. Impurity potential scattering is found to contribute significantly to the resistivity. Its size and pressure variation is determined.This work is supported in part by the Deutsche Forschungs-gemeinschaft.     

Measurements of compressibility of solids and powder compacts by a strain gauge technique at hydrostatic pressure up to 9GPa

Abstract

An experimental technique is described which enables one to measure the pressure-volume (P-V) relationship of solids and powder compacts and the linear compressibility of anisotropic single crystals by means of the resistive strain gauges at hydrostatic pressure up to 9 GPa. The potential of this technique is demostrated for solids possessing pressure induced phase transitions (PbTe, SmSe) and anisotropic crystals (Sb). For the first time P-V relationship is measured for highly compressible powder compact at increase and decrease of pressure.     

A Theory of Non-Linear Elasticity Compatible With the Murnaghan Equation of State

We present an equation of state for a cubic non-linear elastic material in a general state of finite strain. For hydrostatic pressure, the predictions closely follow Murnaghan's well-known equation of state. At 170 kbar, our model differs from Murnaghan's equation by only 1.3%, which contrasts with the currently accepted non-linear elasticity theory that differs by 10% at this pressure. The theory is based on expressing the variation of the elastic constants as a linear function of stress rather than strain. We define a different set of third-order elastic constants, which involve a derivative with respect to stress, and relate these to the conventional third-order elastic constants. We apply the model to GaAs under hydrostatic pressure and we compare the predictions of the conventional non-linear theory with those of the model we present.     

Changes in chemical and microbiological characteristics of goat cheese made from raw,pasteurized or high-pressure-treated milk

Abstract

High-pressure treatment offers to the dairy industry a new technique for food preservation. Very little research is available on the use of high pressure and its potential for cheesemaking. The use of high-pressure treated milk to produce goat cheese has been studied. The effect of high pressure on the ripening process of goat cheese, including the microbiological quality of goat milk and cheese has been included.     

High pressures: Recent trends in materials science

Abstract

Pressure was developed during the 20th century. The most important illustration of the use of high pressure in Materials Science was the synthesis of diamond at the beginning of the fifties.

This contribution will describe the main scientific research axis developed these last years and based on high pressure (synthesis of new materials, stabilization of specific structures, crystal-growth, preparation of finely divided materials…).

In parallel some industrial developments will be analyzed.

In conclusion, the potential of high pressure will be sketched for the near future.     

Self-diffusion and inter-diffusion coefficients of liquid lithium isotopes

Experimental data on ⁶Li and ⁷Li diffusivities, as determined by Feinauer et al. [A. Feinauer, G. Majer and A. Seeger, J. Phys. Condensed Matter 6 L355 (1994)], are discussed in the framework of a theory previously developed by Omini [M. Omini, Phil. Mag. A 54 561 (1986)]. The scattering processes responsible for diffusion are described in terms of a Fourier-transformable pair potential through which the diffusing atom interacts with the atoms of the surrounding liquid. Two main improvements are introduced into the theory with respect to its original formulation: the first is represented by a more reliable form of trial function in the variational procedure used to solve the transport equation; the second consists of a reinterpretation of the long wavelength part of the potential, i.e. the part connected with collective modes of vibration. The theory provides an explanation of the dynamic isotope effects observed in self-diffusion and inter-diffusion coefficients.     

A theoretical study of the structures and stabilities of N4O2 isomers

Five N₄O₂ isomers and their possible decomposition pathways were investigated with Møller–Plesset perturbation theory (MP2) and density functional theory (DFT). The most stable isomer is the open-chain C_2v structure, which has not been reported before. For all five N₄O₂ isomers, dissociation energies and eight transition states were studied in the present paper. The open-chain isomer 1 and the planar (C_2h) isomer 3 could be potential candidates for high energy density materials (HEDM) due to their large dissociation energy and moderate dissociation barrier.     

Structural Properties of Anthracene Under High Pressure

The aim of our studies is to investigate the nature of intermolecular interactions in crystals based on aromatic molecules. For this purpose we carry out angle dispersive (ADXD) as well as energy dispersive (EDXD) X-ray diffraction experiments under pressure in combination with Rietveld refinement. The other approach is density functional theory (DFT), where our calculations are based on the experimentally obtained lattice parameters. In the present work we focus on anthracene C 14 H 10 (monoclinic space group P2 1 /a) as a representative for the herringbone structure that is common for rigid rod-like molecules. We discuss its structural properties as a function of pressure and find very good agreement between experiment and theory.     

DFT/TDDFT investigation on the photophysical properties of a series of phosphorescent cyclometalated complexes based on the benchmark complex FIrpic

The photophysical properties of four Ir(III) complexes have been investigated by means of the density functional theory/time-dependent density functional theory (DFT/TDDFT). The effect of the electron-withdrawing and electron-donating substituents on charge injection, transport, absorption and phosphorescent properties has been studied. The theoretical calculation shows that the lowest-lying singlet absorptions for complexes 1–4 are located at 387, 385, 418 and 386 nm, respectively. For 1–4, the phosphorescence at 465, 485, 494 and 478 nm is mainly attributed to the LUMO → HOMO and LUMO → HOMO-1 transition configurations characteristics. In addition, ionisation potential (IP), electron affinities (EAs) and reorganisation energy have been investigated to evaluate the charge transfer and balance properties between hole and electron. The balance of the reorganisation energies for complex 3 is better than others. The difference between hole transport and electron transport for complex 3 is the smallest among these complexes, which is beneficial to achieve the hole and electron transfer balance in emitting layer.     

Radiation,pair creation,and semiclassical QED in crystals

Abstract

The surface potential on pure and doped sodium chloride single crystals fits conventional defect theory, but the potential on grain boundaries in bicrystals is difficult to explain. The electrical width of the grain boundary is also an uncertain quantity that needs further investigation.