Ultrasound propagation near the critical mixing point of sodium-ammonia solutions

Ultrasonic absorption and dispersion measurements near the critical mixing point of sodium-ammonia solutions are reported. The results are interpreted in terms of a coupling of the ultrasonic wave and mass diffusional modes. The critical behavior of sound propagation shows features not observed in organic binary mixtures.     

The equation of state of metastable liquid xenon near the critical point

This paper presents the results of measurements of xenon density near the critical liquid-vapour point in stable and metastable states. The spinodal has been approximated. The equation of state of metastable liquid is discussed.     

Non-newtonian effect near the critical point

In the presence of a shear flow the order parameter fluctuations are distorted and suppressed by the shear and there appears a new correlation length independent of temperature sufficiently near the critical point.     

Ultrasound absorption in polystyrene solutions near the miscibility coexistence curve and critical point

Ultrasound absorption is reported for solutions of a monodisperse polystyrene. These solutions were studied above the miscibility coexistence curve, for concentrations near and above the critical value. An excess absorption of the Kawasaki-type multiple relaxation was observed. The absorption exhibited a phase-separation, but not a critical-point, anomaly.     

Some features of the perturbing effects of gravity near the gas liquid critical point

The effect of gravity on various thermodynamic properties near the gas-liquid critical point has been calculated. Using a simple equation satisfying scaling requirements, an analytic expression for density profile is obtained, using which the effect on different thermodynamic properties can be easily calculated.     

Properties of the adsorption layer in a binary liquid mixture near the critical point

A method for the determination of parameters of the surface layer (thickness and refraction index) at the liquid-vapor interface in binary liquid mixtures was developed. The parameters of the surface layer for the C₇H₁₄-C₇F₁₄ liquid mixture in the vicinity of the critical point, which was studied by means of ellipsometry in [1], were calculated using the proposed method. The temperature dependences of the thickness and refraction index that were determined in the homogeneous isotropic layer approximation at the interface liquid-vapor, show structural peculiarities that were not observed earlier. Their appearance is explained by the possible influence of hydrodynamic processes at the boundary.     

Xenon-131 surface sensitive imaging of aerogels in liquid xenon near the critical point

In recent years, optically pumped xenon-129 has received a great deal of attention as a contrast agent in gas-phase imaging. This report is about the other NMR active xenon isotope (i.e., xenon-131, S = 32) which exhibits distinctive features for imaging applications in material sciences that are not obtainable from xenon-129 (S = (1/2)). The spin dynamics of xenon-131 in gas and liquid phases is largely determined by quadrupolar interactions which depend strongly on the surface of the surrounding materials. This leads to a surface dependent dispersion of relaxation rates, which can be substantial for this isotope. The dephasing of the coherence due to quadrupolar interactions may be used to yield surface specific contrast for imaging. Although optical pumping is not practical for this isotope because of its fast quadrupolar relaxation, a high spin density of liquid xenon close to the critical point (289 K) overcomes the sensitivity problems of xenon-131. We report the first xenon-131 magnetic resonance images and have tested this technique on various meso-porous aerogels as host structures. Aerogels of different densities and changing levels of hydration can clearly be distinguished from the images obtained.     

Two-scale-factor universality near the critical point of fluids

Experimental evidence is presented in support of the validity of the hypothesis of two-scale-factor universality for the correlation function of fluids near the gas-liquid critical point. For Xe, SF₆, and CO₂, the dimensionless quantity $\text{R = ξ}{}_0\text{(}\text{B}{}^2\text{P}{}_{\mathrm{c}}\text{Γk}{}_{\mathrm{B}}\text{T}{}_{\mathrm{c}}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$ is universal within the experimental accuracy of 10% and agrees with the value predicted by theory.     

Sign of kurtosis near the QCD critical point

We point out that the quartic cumulant (and kurtosis) of the order parameter fluctuations is universally negative when the critical point is approached on the crossover side of the phase separation line. As a consequence, the kurtosis of a fluctuating observable, such as, e.g., proton multiplicity, may become smaller than the value given by independent Poisson statistics. We discuss implications for the beam energy scan program at RHIC at BNL.     

A scaling equation of state near the critical point and the stability boundary of a liquid

A new scaling equation of state is proposed to describe the equilibrium thermodynamic properties of liquids near the critical point. In distinction from the existing scaling equations, which are parametric, the new equation is nonparametric and is expressed directly in terms of the physical quantities (pressure, temperature, and so on). It creates a number of advantages for the traditional representation and data processing. The equation gives rise to a binodal, spinodal, and a curve of thermal capacity divergence (pseudospinodal). The equation is expressed in terms of reduced variables (the ratio of the deviation of a thermodynamic variable from its critical value to the critical value) and contains 3 system-dependent adjustable constants. With the help of this equation, we conducted an approximation of the experimental PVT data in the critical region of ⁴He, C₂H₄, and H₂O with a pressure error of 0.4% and carried out a calculation of the C _v ⁴He thermal capacity with no more than 4% error using a three-system constant determined from the PVT data.     

Nucleation in turbulent fluids near the critical point

Effects of turbulence on nucleation are investigated in classical fluids near the critical point. Turbulence can suppress the onset of nucleation, enhance the coagulation of droplets, and break up droplets. The final characteristic droplet size strongly depends on the temperature difference T_c − T and the Reynolds number Re.     

Sigma mesonic mode near the QCD critical point

Properties of the QCD critical point, an endpoint of the first order boundary line in the temperature T–baryochemical potential μ _B plane, are discussed with the Nambu–Jona-Lasinio model. It is demonstrated that the softening of the sigma mesonic mode is inherent to the crossover transition of the chiral symmetry while the spectral enhancement of the particle–hole mode near zero frequency is associated with the QCD critical point. Phenomenological implications in heavy-ion experiments are mentioned briefly.     

Contraction and reswelling of a polymer chain near the critical point of a binary liquid mixture

We have studied the conformation change of a flexible linear polymer chain near the critical point of a binary liquid mixture using fluorescence correlation spectroscopy, which measured the hydrodynamic radius of the chains. Our results indicate that as the critical temperature (Tc) is approached, the chain size decreases. The polymer attains its most compact conformation when the correlation length of the critical fluctuations becomes comparable to the coil size. At very close to Tc, the polymer reexpands dramatically. To our knowledge, this is the first experimental evidence supporting the prediction of Brochard and de Gennes that a polymer chain will collapse and subsequently reswell on approaching Tc.     

Growth rate of critical nuclei near the critical point of a fluid

The growth rate of critical nuclei for a fluid near its critical point is discussed on the basis of the stochastic equation for the probability distribution function of the local order parameter, which was derived previously by the author. The growth rate was found to depend on , the range of correlation of the order parameter fluctuation, andR, the radius of critical nuclei, as ⁰ R ^–3, in conformity with dynamical scaling. The rate of nucleation at the liquid-gas transition near the critical point is also discussed on the basis of this result.     

Magnetization of lutetium iron garnet near the critical point

A study has been made of the critical magnetic properties of lutetium iron garnet. Values of the critical exponents, β, δ and λ were seen to fulfill the scaling relation, β(δ?1)=λ, within the limits of experimental error. The critical temperature, obtained from the kink-point plot of applied magnetic field vs break-point temperature, was reaffirmed through utilization of the Kouvel-Fisher analysis.