Light scattering in monatomic dense gases from a kinetic model of the Enskog equation

The light scattering spectra of dense monatomic gases are determined from a kinetic model of the Enskog equation in which the reference distribution function is a function of the gradients of velocity and temperature. A good agreement between the theoretical and experimental light scattering spectra is found for values of the pressure going from 0.022 to 10 atm, which correspond to the free molecular and hydrodynamic regimes, respectively.     

NaCl的Gruneisen参数及其随压力变化的计算

 本文利用刚性离子模型计算了NaCl的Gruneisen参数及其随压力的变化。计算中，使用了我们以前成功地计算了状态方程的离子势：对最近邻排斥势分别使用了两种形式的修正的Born-Mayer势，并利用电子气理论的计算结果处理了次近邻排斥势和关联势的影响。所得到的结果与实验符合的程度是令人满意的。     

Interaction induced Raman light scattering as a probe of the local density structure of binary supercritical solutions

Interaction induced Raman light scattering is presented as a unique tool for the understanding of solvation processes from the solute's point of view in weakly interacting solute-solvent systems. A review of pertinent literature shows that this technique should be useful at least in single-phase binary mixtures such as supercritical solutions. Methane is used here as a probe molecule at 10mol% concentration (as the solute) and 90mol% CO and CO₂ are the solvents. The light scattering results, i.e., the dependence of the anisotropic intensities divided by density (I/d) on the density, are interpreted by use of the Duh-Haymet-Henderson closure (bridge) function of the Ornstein-Zernike integral equation. These data, together, are examined in the context of known supercritical solution thermodynamics and statistical mechanical results. It is shown that the light scattering I/d data versus density yield maxima in both attractive and repulsive solute-solvent systems. The local number density maxima were found near these same densities by the integral equation calculations for both methane + carbon monoxide or carbon dioxide using only Lennard-Jones single-centre parameters as input. The methane + carbon monoxide system is identified as weakly attractive (augmenting), whereas the methane + carbon dioxide system is identified as repulsive (avoidance).     

中能重离子碰撞中K介子产生动力学研究(英文)

基于兰州量子分子动力学(LQMD)模型研究了阈能附近K介子(K0和K+)产生动力学机制。LQMD模型能够较好地描述中能重离子碰撞中K介子产额分布。通过拟合K介子动能谱分布,计算中采用了排斥的K-核子相互作用势。该光学势增强了高动量K介子产生,而降低了K介子总产额。结合实验数据比较,在高密区域给出了较软的对称核物质状态方程。对称能的软硬对K0/K+比值起着重要作用,特别是在阈下区域。而K介子光学势对K0/K+比值激发函数影响不明显。     

Testing Dirac-Brueckner models in collective flow of heavy-ion collisions

We investigate differential in-plane and out-of-plane flow observables in heavy-ion reactions at intermediate energies from 0.2-2 AGeV within the framework of relativistic BUU transport calculations. The mean field is based on microscopic Dirac-Brueckner-Hartree-Fock (DB) calculations. We apply two different sets of DB predictions, those of ter Haar and Malfliet and more recent ones from the Tübingen group, which are similar in general but differ in details. The latter DB calculations exclude spurious contributions from the negative-energy sector to the mean field which results in a slightly softer equation of state and a less repulsive momentum dependence of the nucleon-nucleus potential at high densities and high momenta. For the application to heavy-ion collisions in both cases non-equilibrium features of the phase space are taken into account on the level of the effective interaction. The systematic comparison to experimental data favours the less repulsive and softer model. Relative to non-relativistic approaches one obtains larger values of the effective nucleon mass. This produces a sufficient amount of repulsion to describe the differential flow data reasonably well. Received: 8 January 2001 / Accepted: 12 November 2001     

650nm光在Intralipid-10%中分布的测量和分析

本文提出一种用光纤测定光在生物组织模型Iitralipid内部光分布的方法并测定了650nm激光在Iitralipid 10%中的分布,该方法与各向同性球形光纤探头探测组织内光分布是一种互补的方法。实验结果揭示了在生物组织模型中不同方向散射光的分布规律,表明了不同的组织光学参数和不同直径的入射光束与光分布之间的关系;采用外推边界条件的漫射方程解拟合前向散射光的测量数据确定了组织模型的散射系数和吸收系数并得到较好的结果,所测量的光学参数与公开发表的结果比较其差别在2 35%以内。     

The effect of steepness of soft-core square-well potential model on some fluid properties

The effect of repulsive steepness of the soft-core square well (SCSW) potential model on the second virial coefficient, critical behaviour (two- phase region and the position of critical point), and coordination number are investigated. The soft-core thermodynamic perturbation theory (TPT) presented by Weeks-Chandler-Anderson (WCA) recently developed by Ben-Amotz and Stell (BAS) has been used for the reference system, and the Barker-Henderson TPT for the perturbed system. The Barker-Henderson macroscopic compressibility approximation has been used for all order perturbation terms in which the second-order one is improved by assuming that the molecules in every two neighbouring shells are correlated upon the original assumption. By using the hard-sphere isothermal compressibility consistency for the radial distribution function (RDF), an analytical closed expression has been derived for the Helmholtz free energy function contained effective hard-sphere diameter. The accuracy of the model has been examined for the hard-core system, and an appropriate range found for the attractive width of the potential well (R), then the effect of steepness parameter on the critical quantities, coordination number, and the inversion temperature of the second virial coefficient, has been investigated qualitatively. The predicted results are in good agreement with the computer simulation data for the critical constants, and coordination number at the limit of the hard-core square-well potential model at least qualitatively, and for the attractive range 1.55 ≤ R ≤ 1.7, quantitatively. It was found that the steepness of the potential model has a marginal effect on the critical behaviour, and also every thermodynamic quantity at low and medium temperatures for which the molecular penetration is negligible, but since the penetration at high temperatures is significant, the role of the steepness of potential on the inversion temperature of the second virial coefficient and coordination number is highlighted.     

The influence of pressure on freezing in molecular liquids

We present the results of experimental investigation of some liquid alkanes PVT behaviour. Their molecular structure was investigated by MoK X-ray scattering method. The obtained data allow suggesting the equation of state and determination of the relation of these equation parameters to molecular characteristics such as molecular mass and exponents of the potential of molecular interaction.     

Anomalous light scattering on polaritons in the region of phase transition in α-LiJO3 single-crystals

The experimental investigation of the temperature dependence of spectra of spontaneous Raman light scattering on polaritons in α-LiJO₃ crystal has been carried out. An anomalous broadening of the frequency-angular spectrum of scattered radiation was found in the region of phase transition α→γ→β at 256°C. It is assumed that this phenomenon is due to an anomalous increase of non-linearity of the third order and, hence, of the probability of the four-particle scattering process at which a pumping photon is decayed into a photon and two polaritons during a common act.     

New gap equation for strongly correlated metals

Assuming a phenomenological self-energy ImΣ(ω)|ω|^β, (β=1), which becomes gapped below T_c, we derived a new gap equation. The new gap equation contains the effect of the kinetic energy gain upon developing a superconducting order parameter. However, this new kinetic energy gain mechanism works only for a repulsive pairing potential leading to a s-wave state. In this case, compared to the usual potential energy gain in the superconducting state as in the BCS gap equation, the kinetic energy gain is more effective to easily achieve a high critical temperature T_c, since it is naturally Fermi energy scale. In view of the experimental evidences of a d-wave pairing state in the hole-doped copper-oxide high-T_c superconductors, we discuss the implications of our results.     

Equation of state and thermodynamics of fcc transition metals: A pseudopotential approach

A simple pseudopotential model is used for the calculation of the phonon spectra at the equilibrium volume and under pressure. The model is based on the secondorder perturbation theory with the local pseudopotential acting on thes electrons while thed electrons contribution is simulated by the repulsive Born-Mayer interatomic potential. Pressure influence on the lattice properties was studied for small compressions (mode Grüneisen parameters) as well as for ultrahigh pressure (equation of state up to 1 TPa). Results of the lattice dynamics calculations were used for determining temperature dependence of the lattice heat capacity and of the macroscopic Grüneisen parameter. The Kohn anomaly at the small wave vectors obtained previously in palladium, platinum and rhodium affects strongly the temperature dependence at low temperature.     

Spectral line shapes of collision-induced light scattering (CILS) and collision-induced absorption (CIA) using isotropic intermolecular potential for H2–Ar

Quantum mechanical line shapes of collision-induced light scattering at room temperature (295 K) and collision-induced absorption at T = 195 K are computed for gaseous mixtures of molecular hydrogen and argon using theoretical values for pair-polarisability trace and anisotropy and induced dipole moments as input. Comparison with other theoretical spectra of isotropic and anisotropic light scattering and measured spectra of absorption shows satisfactory agreement, for which the uncertainty in measurement of its spectral moments is seen to be large. Ab initio models of the trace and anisotropy polarisability which reproduce the recent spectra of scattering are given. Empirical model of the dipole moment which reproduce the experimental spectra and the first three spectral moments more closely than the fundamental theory are also given. Good agreement between computed and/or experimental line shapes of both absorption and scattering is obtained when the potential model which is constructed from the transport and thermo-physical properties is used.     

Theoretical studies of local structure and high-pressure shifts of the spin-orbit levels of Co in KZnF3

The local crystal structure of a Co²⁺ dopant ion in KZnF₃ has been determined on the basis of the experimental optical spectra, electron paramagnetic resonance parameter g, the approximately equivalent molecular orbital model, and the μ kα model. The results show that when a Co²⁺ ion occupies a Zn²⁺ site, the bond length changes by about 6%. Using the experimental high-pressure shifts of the spin-orbit levels, the state equation and the pressure dependence of the g-factor are obtained. The good agreement between theory and experimental findings shows that the method is reasonable. The state equation and the pressure dependence of the g-factor await further experimental tests.     

Raman scattering in Europium chalcogenides near magnetic phase transitions

The inelastic light scattering spectra of the europium chalcogenides are analyzed in terms of a one phonon-one spin Raman process. Calculations are presented for the temperature dependence of the integrated intensity of the “spin-disorder” spectrum of EuS and compared with experiment. The observed temperature dependence of the Raman spectrum of EuSe in the two-sublattice antiferromagnetic phase is presented and examined in terms of the one phonon-one spin mechanism. Experiments are suggested in which the Raman spectra can be used to measure the magnetic field dependence of the order parameter exponent β in EuTe.     

Phonon Spectrum and Structural Transformations at High Pressures in Vanadyl IV Phthalocyanine Crystals

The Raman scattering spectra and crystalline structure of vanadyl IV phthalocyanine (VOPc) at normal and high pressures has been studied. According to the X-ray diffraction data, the initial microcrystalline powder represented a mixture of the triclinic α phase (79%) and the monoclinic β phase (21%) possessing P$$\bar {1}$$ and P21/c symmetry, respectively. Raman spectra of the two phases are similar, but the phonon modes of the β phase are shifted toward higher frequencies (energies). The pressure dependence of the spectra of the α phase has been determined and it is established that the interval of 2.3–3.4 GPa reveals reversible pressure-dependent variations: above 3 GPa, some phonon modes exhibit splitting and the coefficients of pressure-induced (baric) shift for almost all modes show a decrease. A high-pressure feature observed in the Raman spectra can be related to changes in intermolecular interactions in crystalline structure of the α phase. The pressure dependence of the α phase unit cell volume measured at pressures increasing up to 4 GPa is a smooth monotonic function that can be well described by the Murnaghan equation of state. The obtained data were used to calculate the Grüneisen parameters of VOPc phonon modes.     

Asymmetric phase diagram and coverage dependent effective pair interactions for hydrogen on close-packed metal surfaces

The asymmetry in the phase diagram of the H/Ru(001) system is studied by assuming a lattice gas model for the chemisorbed hydrogen and using the cluster variation method. Ground state analysis of the ordered structures shows that the effective pair interaction for the next-nearest neighbors has to be repulsive. We also found that the order-disorder transition temperatures and hence the phase diagram are very sensitive to v₃, the ratio of the effective next-nearest to nearest neighbor interactions of H adatoms. The asymmetry in the phase diagram, which cannot be accounted for by the adsorbate relaxation model by Persson [Surf. Sci. 258 (1991) 451], is attributed to the coverage dependence of the effective pair interactions. By assuming a simple piecewise linear dependence of v₃ on the chemical potential, we constructed an asymmetric phase diagram which is in excellent agreement with the experimental data. The model studied can be applied to the H/Pd(111) system directly and can be easily generalized for other close-packed metal surfaces.     

Spin fluctuations in intermetallics

A review is given of investigations of the quasiparticle spectra and of the magnetic fluctuations spectra of metals with strong longitudinal magnetic susceptibilities which were performed by means of the de Haas-van Alphen effect and inelastic neutron scattering. Among the systems investigated are the incipient ferromagnets Ni₃Ga and TiBe₂, the low temperature ferromagnets Ni₃Al, YNi₃, ZrZn₂ and MnSi, the light rare earth metals including PrCu₂ which are close to antiferromagnetic instabilities at low temperatures, and the actinide heavy fermion superconductors UPt₃ and UBe₁₃. The strong renormalisation of the quasiparticle masses and the temperature dependence of the heat capacity and of the magnetic equation of state of these systems are discussed in terms of a quantitative model based on the relaxation frequency of very low lying spin fluctuations.     

Weitere Messungen zur Anisotropie der intermolekularen Wechselwirkung durch Streuung von Molekülen in definiertem Quantenzustand

In a previous paper the anisotropy parameter of the attractive part of the intermolecular potential has been determined from total cross sections measured by scattering of TlF-molecules in selected rotational states by rare gases. In this series of papers, further measurements on the systems TlF-He, Ne, Ar, Xe, CH₄, and CsF-He, Ar will be described. In the case of CsF-He, it has been possible to determine the anisotropy parameter of the repulsive part of the potential additionally, by comparing cross sections related to different rotational states over a large velocity range and by using the high energy approximation. The determination of the anisotropy parameter for the repulsive potential requires knowledge of the parameters of the angle averaged potential. Part I describes the determination of these parameters for a Lennard-Jones-potential from measurements of the velocity dependence and the absolute value of the total cross section by scattering of not state selected CsF-molecules by He and Ar. Since these systems show no glory undulations in the experimentally accessible velocity range, they require an evaluation procedure, which is independent of the appearance of such undulations. The procedure described below only uses the velocity dependence of the cross section itself by fitting of quantum mechanically calculated cross sections. The finite resolving power of the apparatus and the influence of velocity distributions are taken into account. The results are communicated, the parallel evaluation of an experiment on K-Ar serves as a test for the procedure described.     

Nucleon-nucleon interaction with tensor forces in the quark compound bag model

A model forN-N interaction proposed earlier by two of us (VSB and VKG), has been extended to incorporate the tensor component of the nuclear force. Based on the quark compound bag model (QCB), the nucleon-nucleon potential has a short range repulsive core which is non-local and has a characteristic energy dependence and is expressed in terms of the parameters relating to the six-quark compound bag. To account for the low energy properties, this repulsive core interaction is supplemented by a phenomenological non-local potential containing both central (S-wave) and tensor components and operates only outside the QCB. Using this model, we analyse and compare the results with the experimental data for the electromagnetic form factors of the deuteron, theD-state observables, such as the quadrupole moment, theD-state probability, and theD/S ratio along with then-p scattering phase shifts up to about 400 MeV.     

Low-frequency Raman scattering study of the ferroelectric phase transition in the DKDP crystal

The low-frequency Raman scattering spectra of the DKDP ferroelectric crystal are studied in the temperature range 30–393 K. At temperatures above 150 K, the Raman spectra exhibit a central peak which reflects the lattice relaxation susceptibility. The width and integrated intensity of the central peak are derived from the experimental spectra. The critical slowing down of the relaxation response predicted by the Ginzburg-Landau-Devonshire theory is observed throughout the temperature range in which the central peak persists. Its integrated intensity does not, however, follow the predictions of the theory and reveals a strong temperature dependence in the ferroelectric phase and a weaker dependence in the paraphase. It is shown that the thermal activation law describes well the temperature dependence of the intensity of the central peak. An interpretation is proposed according to which the intensity of order parameter fluctuations is related to the activation barrier whose height is proportional to the deviation from the phase transition temperature.