Kinetic theory of fluctuations near a convective instability

The kinetic theory of density and velocity fluctuations below and above the first convective instability in a Benard cell is presented. Results are given in a form valid for all fluid densities. In particular, the singular behavior near the instability point is computed and a detailed comparison with that near a critical point is made. Mode coupling effects, involving the viscous and the heat mode, that determine the singular behavior of the thermal conductivity near the critical point, are also responsible for the singular behavior of the pair correlation function and in particular the density-density correlation function near the instability point. The anomalous density fluctuations could be measured directly by microwave scattering experiments, while the velocity fluctuation could be measured by laser Doppler velocimetry.     

Vibrational phase relaxation along the critical isochore of nitrogen: the role of local density fluctuations in the rate enhancement

Vibrational dephasing of the nitrogen molecule is known to show highly interesting anomalies near its gas-liquid critical point. Here we present theoretical and computational studies of the Raman linewidth of nitrogen along the critical isochore. The linewidth is found to have a lambda-shaped temperature dependence near the critical point. As observed in experimental studies, the calculated line shape becomes Gaussian as the critical temperature (T(c)) is approached. Both the present simulation and a mode coupling theory analysis show that the slow decay of the enhanced density fluctuations near the critical point, probed at the subpicosecond time scales by vibrational frequency modulation, along with an enhanced vibration-rotation coupling, are the main causes of the observed anomalies.     

新的适用于整个热力面的1,1,1,2-四氟乙烷(R134a)跨接状态方程

1前言作者建立了一个新型的符合临界重整化群理论的跨接状态方程，能够描述物质的整个区域热力性质山。鉴于R134a是R12的新的主要替代制冷剂，为了计算其整个区域的热力性质，本文将新跨接状态方程应用于R134a，以便提供一个能在整个区域计算R134a热力性质的状态方程。2新跨接状态方程作者建立了以下型式的新跨接状态方程l‘］：上式中，西方一r一IDZ户一p巾c；，一DI—TD；T—To／T；产为密度；pc为临界密度；T为温度；To为临界温度；矿对比过余Helmholtz自由能；A是Helmholtz自由能。新函数中，a。一30，a，一10；0—0．325和西一…     

Field-theoretic approach to critical dynamics far from equilibrium

The field-theoretic approach to critical phenomena is extended to deal with critical dynamics far from equilibrium. In particular, the macroscopic evolution equation for the average order parameter is derived in a manner parallel to the derivation of the equation of state. The method is illustrated by deriving the scaled macroscopic equation of motion for the timedependent Ginzburg-Landau model near the critical point for dimensionality near four.     

Cavity correlation and bridge functions at high density and near the critical point: a test of second-order Percus–Yevick theory

ABSTRACT

Cavity correlation functions, pair correlation functions, and bridge functions for the Lennard-Jones fluid are calculated from first Percus–Yevick (PY) theory and second-order Percus– Yevick (PY2) theory, molecular dynamics, and grand canonical Monte Carlo techniques. We find that the PY2 theory is significantly more accurate than the PY theory, especially at high density and near the critical point. The pair correlation function near the critical point has the expected slowly decaying long-range behaviour. However, we do not observe any long-range behaviour in the bridge function for the state points near the critical point we have simulated. However, we do note that the bridge function, which is usually negative near r = 0, becomes positive as r → 0. This behaviour is seen for the bridge functions computed from both PY2 and molecular dynamics, but not from PY.     

Cold and supercooled water: A novel supercritical-fluid solvent

Peculiar properties of fluid mixtures in the vicinity of the critical point of the pure solvent are commonly used in supercritical-fluid technologies, such as fluid extraction, enhanced oil recovery, supercritical chromatography, and micronization. These properties are linked to critical-point anomalies, in particular, very large compressibility and very low interfacial tension. Water, near its vapor-liquid critical point, as a supercritical solvent, is well studied, in contrast to supercooled water. However, more recently, many scientists have started to believe that deep in supercooled region, not directly accessible to bulk-water experiments, there exists a critical point of liquid-liquid separation (“liquid water polyamorphism”). If the water liquid-liquid critical point exists, the addition of a solute will generate critical lines emanating from the pure-water critical point. The phenomenon would be conceptually similar to what is known near the vapor-liquid critical point and what is commonly exploited in supercritical-fluid science and technology. This new idea has not yet been elaborated. The investigation of aqueous systems below the freezing temperature of pure water would not only shed light on the nature of plausible water polyamorphism, but also could open the way for utilizing cold water as a novel and unusual supercritical-fluid solvent.     

A new interpretation of the critical behavior in NH4Cl and ND4Cl

It is proposed that the first order transition of NH₄Cl and ND₄Cl is not located near a tricritical point but near a critical point of type 4. Good agreement between the measured and calculated values of the critical exponent β and α′ is obtained.     

Signature of Critical Point in Momentum Profile of Trapped Ultracold Bose Gases

We present a new method to identify the critical point for the Bose-Einstein condensation(BEC) of a trapped Bose gas.We calculate the momentum distribution of an interacting Bose gas near the critical temperature,and find that it deviates significantly from the Gaussian profile as the temperature approaches the critical point.More importantly,the standard deviation between the calculated momentum spectrum and the Gaussian profile at the same temperature shows a turning point at the critical point,which can be used to determine the critical temperature.These predictions are aiso confirmed by our BEC experiment for magnetically trapped ~(87)Rb gases.     

Nonasymptotic critical thermodynamical behavior of fluids

The paper is concerned with some theoretical and empirical attempts to obtain a unified equation for the thermodynamic properties of fluids that incorporates the nonclassical scaling laws near the critical point and crosses over to a classical analytic equation far away from the critical point. Specifically we investigate to what extent the various proposed crossover models agree with the known theoretical predictions for the universal ratios among the asymptotic and correction-to-scaling amplitudes in the power-law expansions of the thermodynamic properties around the critical point.     

Anomalous properties and coexistence of antiferromagnetism and superconductivity near a quantum critical point in rare-earth intermetallides

Mechanisms of the appearance of anomalous properties experimentally observed at the transition through the quantum critical point in rare-earth intermetallides have been studied. Quantum phase transitions are induced by the external pressure and are manifested as the destruction of the long-range antiferromagnetic order at zero temperature. The suppression of the long-range order is accompanied by an increase in the area of the Fermi surface, and the effective electron mass is strongly renormalized near the quantum critical point. It has been shown that such a renormalization is due to the reconstruction of the quasiparticle band, which is responsible for the formation of heavy fermions. It has been established that these features hold when the coexistence phase of antiferromagnetism and superconductivity is implemented near the quantum critical point.     

Canonical Entropy and Phase Transition of Rotating Black Hole

Recently, the Hawking radiation of a black hole has been studied using the tunnel effect method. The radiation spectrum of a black hole is derived. By discussing the correction to spectrum of the rotating black hole, we obtain the canonical entropy. The derived canonical entropy is equal to the sum of Bekenstein-Havcking entropy and correction term. The correction term near the critical point is different from the one near others. This difference plays an important role in studying the phase transition of the black hole. The black hole thermal capacity diverges at the critical point. However, the canonical entropy is not a complex number at this point. Thus we think that the phase transition created by this critical point is the second order phase transition. The discussed black hole is a five-dimensional Kerr-AdS black hole. We provide a basis for discussing thermodynamic properties of a higher-dimensional rotating black hole.     

Undressing the Kondo effect near the antiferromagnetic quantum critical point

The problem of a spin-1/2 magnetic impurity near an antiferromagnetic transition of the host lattice is shown to transform to a multichannel problem. A variety of fixed points is discovered asymptotically near the antiferromagnetic critical point. Among these is a new variety of stable fixed point of a multichannel Kondo problem which does not require channel isotropy. At this point Kondo screening disappears but coupling to spin fluctuations remains. In addition to its intrinsic interest, the problem is an essential ingredient in the problem of quantum critical points in heavy fermions.     

Critical exponents of a three-component ethanol-water-chloroform mixture

The measured renormalized critical exponents for the ethanol-water-chloroform mixture near its plait point show first evidence of the nonzero critical exponent η in a three-component fluid system, demonstrate the critical-exponent renormalization, and verify the scaling relations.     

Phantom Accretion onto the Schwarzschild Anti de-Sitter Black Hole

In this paper we study phantom energy accretion onto the Schwarzschild anti de-Sitter black hole. We obtain critical point where the speed of flow is equal speed of sound. We find that the critical point is near the black hole horizon.     

Critical Casimir forces and anomalous wetting

We present a review of critical Casimir forces in connection with successive experiments on wetting near the critical point of helium mixtures.     

Experimental evidence of the vapor recoil mechanism in the boiling crisis

Boiling crisis experiments are carried out in the vicinity of the liquid-gas critical point of H2. A magnetic gravity compensation setup is used to enable nucleate boiling at near critical pressure. The measurements of the critical heat flux that defines the threshold for the boiling crisis are carried out as a function of the distance from the critical point. The obtained power law behavior and the boiling crisis dynamics agree with the predictions of the vapor recoil mechanism and disagree with the classical vapor column mechanism.     

Topological jamming and the glass transition in a frustrated system

The relationship between extended structures, glassy dynamics and an underlying critical point is examined in the context of a lattice model of fluctuating lines. Monte Carlo simulations are used to construct an effective, coarse-grained dynamics for the “order parameter” near the critical point. Analysis of the effective dynamics reveals that the critical point is associated with diverging barriers leading to the observed Vogel-Fulcher divergence of the relaxation times. A direct connection is established between the presence of extended structures and the activated dynamics. Received 15 March 2002     

Renormalization of the 1/N expansion and critical behaviour of (2+1)-dimensional supersymmetric non-linear sigma-models

Renormalized 1/N expansion in both high-and low-temperature phases as well as of the critical theory of three-dimensional supersymmetric generalized non-linear sigma-models is constructed and scaling laws for the Green's functions near the critical point with only two independent critical exponents are established.     

Neutron enhancement from laser interaction with a critical fluid

We discuss experimentally and theoretically neutron production from the laser driven explosion of gas clusters prepared near the liquid-gas critical point. We let deuterated methane that was prepared very close to its critical temperature and pressure expand through a conical nozzle to create clusters, and then irradiated those clusters with a high intensity pulse from the Texas Petawatt Laser. After ionization, the clusters explode producing energetic ions, some of which fuse with resultant neutron emission. We show that the critical fluctuations present in the nozzle before the expansion influence the dynamics of neutron production. Neutron production near the critical point follows a power law, which is a signature of a second order phase transition and it is consistent with the Fisher model. This result might be relevant for energy production from fusion reactions.     

Osmotic compressibility and correlation range of the system polystyrene-diethyl malonate very near its critical point

The angular dependence of the scattered light intensity was measured by use of a capillary cell for the system polystyrene-diethyl malonate very near its critical point. Multiple scattering was well eliminated and reliable light scattering data in the critical region were obtained.