Experimental gravity induced coexistence curve of methyl fluoride near the critical point

Abstract

The top part of the coexistence curve of methyl fluoride in the critical region has been determined first by direct observation of the disappearance of the meniscus of the fluid situated in a high-pressure light scattering cell and subsequently from the measured maximum depolarization ratio of an appreciable number of isochores close to the critical point. The experimental data obtained from direct observations yield a coexistence curve which nearly coincides with that found recently from pVT measurements. However, the data obtained from light scattering experiments describe a gravity induced coexistence curve which lies above the previous one and which shows a minimum at the critical point. The complete experimental data have been used to evaluate the critical parameters p_c, ρ_c and T_c and the critical exponent β.     

A Langevin equation for the rates of currency exchange based on the Markov analysis

We propose a method for analyzing the data for the rates of exchange of various currencies versus the U.S. dollar. The method analyzes the return time series of the data as a Markov process, and develops an effective equation which reconstructs it. We find that the Markov time scale, i.e., the time scale over which the data are Markov-correlated, is one day for the majority of the daily exchange rates that we analyze. We derive an effective Langevin equation to describe the fluctuations in the rates. The equation contains two quantities, D⁽¹⁾ and D⁽²⁾, representing the drift and diffusion coefficients, respectively. We demonstrate how the two coefficients are estimated directly from the data, without using any assumptions or models for the underlying stochastic time series that represent the daily rates of exchange of various currencies versus the U.S. dollar.     

Hyperthermal cluster-surface scattering

Using molecular-dynamics simulation, we study the processes occurring after impact of clusters on a rigid wall. Comparing the impact of model clusters consisting of 13 atoms, or of 13 diatomic molecules with varied bond strength, the systematics in the results of the collision process are investigated. Four regimes of impact-induced cluster fragmentation are identified: intact reflection, shattering into large fragments, complete fragmentation, and molecule dissociation. The effect of the number of degrees of freedom activated in the collision on the translational and internal energies of the reflected fragments is discussed in detail. As a rule, with increasing number of degrees of freedom which can be activated in the collision, the translational energy sinks. On the other hand, for weak intramolecular bonding, intramolecular vibrations are easily excited at small impact energies, reducing the resulting translational energy. The presence of even a very weak attractive well epsilon_w at the surface has a major influence on the sticking behavior of the clusters — and hence also on the absolute reflected energies — even at impact energies E₀ ≫ epsilon_w.     

Diffusion in flashing periodic potentials

The one-dimensional overdamped Brownian motion in a symmetric periodic potential modulated by external time-reversible noise is analyzed. The calculation of the effective diffusion coefficient is reduced to the mean first passage time problem. We derive general equations to calculate the effective diffusion coefficient of Brownian particles moving in arbitrary supersymmetric potential modulated by: (i) an external white Gaussian noise and (ii) a Markovian dichotomous noise. For both cases the exact expressions for the effective diffusion coefficient are derived. We obtain acceleration of diffusion in comparison with the free diffusion case for fast fluctuating potentials with arbitrary profile and for sawtooth potential in case (ii). In this case the parameter region where this effect can be observed is given. We obtain also a finite net diffusion in the absence of thermal noise. For rectangular potential the diffusion slows down, for all parameters of noise and of potential, in comparison with the case when particles diffuse freely.     

Quantum Brownian motion and the second law of thermodynamics

We consider a single harmonic oscillator coupled to a bath at zero temperature. As is well-known, the oscillator then has a higher average energy than that given by its ground state. Here we show analytically that for a damping model with arbitrarily discrete distribution of bath modes and damping models with continuous distributions of bath modes with cut-off frequencies, this excess energy is less than the work needed to couple the system to the bath, therefore, the quantum second law is not violated. On the other hand, the second law may be violated for bath modes without cut-off frequencies, which are, however, physically unrealistic models. An erratum to this article is available at .     

First principle study of the magnetism of Sr2CoMoO6-δ (δ = 0, 1/2) double perovskites

We investigate the electronic structure of bulk Sr₂CoMoO_6-δ double perovskites using the ab initio Full Potential Linearized Augmented Plane Wave method in order to study their magnetic properties within the GGA and GGA+U methods. We discuss the relative stability of ferromagnetic (FM) and antiferromagnetic (AFM) orders (i) without and with taking into account the observed tilting of the oxygen octahedra and (ii) by introducing oxygen vacancies. We show that a very good agreement with experimental results — AFM order for δ= 0 and FM order for δ= 1/2 — is obtained only when the tilting of the oxygen tetrahedra is taking into account and when the GGA+U method is used.     

Energy transport in the inductively coupled plasma

Time- and space-resolved electron density measurements, made both above the load coil and in the load coil region of a pulsed inductively coupled plasma, are presented. These data, coupled with argon and calcium emission data, give values for the rates of both radial and vertical transport in the plasma. The data indicate that analyte emission behavior is governed primarily by the rate at which the central channel can be heated through radial transport processes. The electron densities measured in the load coil region agree well with electron densities calculated by models assuming local thermodynamic equilibrium, but agree poorly with non-equilibrium models. Some of the timedependent emission behavior observed in previous work with modulated plasmas is explained by non-uniform heating of argon in the load coil region.Presented in part at the 1989 European Winter Conference on Plasma Spectrochemistry, Reutte, Austria     

分数布朗运动和反常扩散

本文评述了分数布朗运动和反常扩散现象及描写它们的几种数学方式。报告了我们在弹道扩散的产生条件、起源和长时间效应方面的工作。     

Spiral tip meandering induced by excitability modulation

In this work, we introduce a spatiotemporal modulation for excitability into an excitable medium, the Barkley model. The modulation can make the spiral wave tip meandering. Various types of periodic spiral and quasiperiodic meandering spiral motions can be observed numerically by varying the modulation. And the theoretical analysis for the conditions of Hopf bifurcation, based on an ordinary-differential-equation (ODE) model, is applied to well explain the rich behaviors of numerical simulations.     

Time-Resolved Reflectance of an Optical Pulse in Adult Heads Based on the Finite Difference Time Domain (FDTD) Analysis

Time-resolved reflectance of an optical pulse in adult head models including non-scattering cerebrospinal fluid (CSF) has been analyzed by the finite difference time domain (FDTD) analysis formulated by the authors. Averaged light intensity and mean time of flight dependences on the source-detector separations calculated by the FDTD analysis are in good agreement with previous experiments, hybrid finite element method (FEM) and Monte Carlo calculations, which justify the FDTD analysis. Based on the analysis, time-resolved reflectance sensitivities to detect optical property changes in brain have been analyzed. As a result, it has been become clear that the sensitivities to detect absorption changes of brain are enhanced in time-resolved reflectance compared to the sensitivities in averaged light intensity, whereas the sensitivities to detect scattering property changes of brain are almost the same in time-resolved reflectance and in averaged light intensity. © 2005 The Optical Society of Japan