Scaling in superconductor-insulator mixtures

We present a scaling theory for mixtures of insulator and superconductor. The theory agrees with existing experiments on Hg_x Xe_1?x and predicts some relations at low temperatures near the percolation concentration which can be tested.     

Precursors in gas-liquid mixtures

Two types of precursors propagating at the speed of sound in a pure liquid have been revealed in the experiments on the evolution of pressure pulses in a gas-liquid mixture; at the same time, the main pressure pulse propagates at a low equilibrium speed of sound and its evolution is described by the Burgers-Korteweg-de Vries equation. The first high-frequency precursor is a complete analog of a classical Sommerfeld precursor, because the resonance dispersion equation for a bubble mixture coincides with that for insulators in the Lorentz model, and oscillates at a frequency close to the “plasma frequency.” The second low-frequency precursor has been revealed in this work. The frequency of the low-frequency precursor is close to the resonance frequency of pulsations of bubbles, which is almost an order of magnitude lower than the frequency of the high-frequency precursor. The low-frequency precursor has a much larger amplitude of pulsations and smaller damping and is not described within the homogeneous model of the gas-liquid mixture. The observed phenomenon of low-frequency precursors has been explained within a simple heterogeneous model of a bubble liquid.     

Flow birefringence in gaseous mixtures

In an earlier paper, an alignment of the rotational angular momenta of gas molecules produced by a gradient in the stream velocity has been shown to cause a measurable birefringence in the gas. The present paper reports an extension of these measurements to mixtures, specifically N₂ and HD with He, Ne and Ar. The concentration dependence found in these experiments can be well interpreted in terms of a kinetic theory, based on the Waldmann-Snider equation, employing data obtained from other experiments, such as the Senftleben-Beenakker effect and depolarized Rayleigh scattering.     

Copolymer-homopolymer mixtures in a nanopore

We have performed the cell dynamics simulation with the time-dependent Ginzburg-Landau theory to study the selfassembled morphology of A-B diblock copolymers and C homopolymers in a neutral nanopore. The nanopore diameter and length are systematically varied to examine their effects on the structures of various morphologies and their phase transition. From the simulation, it is observed that the equilibrium morphology of the confined system is sensitive to pore diameter D and pore length Lpore , the phase behavior in neutral nanopores is due to an interplay of two factors: the surface effect and the extension effect. When the nanopore length and the lamellae spacing are not commensurate, the surface effect prevails at small nanopores (small diameters or short lengths), the extension effect takes over at larger nanopores (large diameters or long lengths). When the nanopore length and the lamellae spacing are commensurate, the surface effect dominates. Furthermore, the interactions between different monomers are also discussed and we obtain a transition from a tilted pancakes/cylinder structure (L⊥tilted ) to a concentric cylindrical structure with defects and to a concentric cylindrical structure (L|| ). We also investigate the effect of the relative concentrations of diblock copolymer-homopolymer and obtain a transition in which the position of the C blocks changes from the outer of the cylinder to the middle of the cylinder and then to the inner of the cylinder with the concentration of the C blocks decreasing.     

Magnetoelectricity in two-dimensional statistical mixtures

The concentration and frequency dependences of the effective physical constants are investigated for two-dimensional “ferrite-piezoelectric ceramic” composites in the form of a statistical mixture in which the components are randomly arranged elongated cylinders with a circular cross section and axes identically oriented in the z direction. The effective physical constants are calculated using the self-consistent effective-medium method. It is revealed that the concentration dependences of the magnetoelectric permeability and the permittivity exhibit a nonmonotonic behavior, whereas the corresponding dependences of the piezomagnetic and piezoelectric moduli are monotonic in character. A deep non-Debye relaxation of the piezomagnetic and piezoelectric coefficients is observed for some concentration of components.     

Maxwell stress in fluid mixtures

We examine the structure of Maxwell stress in binary fluid mixtures under an external electric field and discuss its consequence. In particular, we show that, in immiscible blends, it is intimately related to the statistics of domain structure. This leads to a compact formula, which may be useful in the investigation of electrorheological effects in such systems. The stress tensor calculated in a phase separated fluid under a steady electric field is in a good agreement with recent experiments.     

Bose-Fermi mixtures in optical lattices

Using mean field theory, we have studied Bose-Fermi mixtures in a one-dimensional optical lattice in the case of an attractive boson-fermion interaction. We consider that the fermions are in the degenerate regime and that the laser intensities are such that quantum coherence across the condensate is ensured. We discuss the effect of the optical lattice on the critical rotational frequency for vortex line creation in the Bose-Einstein condensate, as well as how it affects the stability of the boson-fermion mixture. A reduction of the critical frequency for nucleating a vortex is observed as the strength of the applied laser is increased. The onset of instability of the mixture occurs for a sizably lower number of fermions in the presence of a deep optical lattice.     

Dielectric losses in statistical mixtures

The specific features of the dielectric spectra of statistical mixtures in the form of heterogeneous systems with spherical particles chaotically arranged in the space have been investigated. The distribution function of relaxation times f(τ) has been restored. It has been established that the relaxation times are continuously distributed within a wide interval [τ₁, τ₂]. Different methods for broadening the relaxation time distribution interval and approximating the relaxation time distribution function f(τ) have been analyzed. It has been demonstrated that f(τ) is a nonmonotonic function with two maxima at the boundaries and a minimum in the vicinity of the midpoint of the interval [τ₁, τ₂]. These features of the relaxation time distribution function are responsible for the large difference between the average relaxation frequencies of the permittivity and the dielectric loss (electrical conductivity).     

Gravity-induced gradients in critical mixtures

We report experimental measurement of gravitationally induced concentration gradients in a binary critical mixture. Measurements are performed for the first time with a non-perturbative optical technique upon entire size of the cell. In this way, both the shape of the gradients as a function of the height and their time evolution can be detected and analysed.     

Instabilities in thin-film binary mixtures

Binary mixtures of ultra-thin films are subject to both height and concentration fluctuations, either of which, under the appropriate conditions, can become unstable. We investigate a simple general thermodynamic model which shows that, due to the constraint imposed upon coupling between these fluctuations, a thin-film binary mixture will be less stable than if either height or concentration fluctuations are considered in isolation. We investigate the height dependence of the stability condition, discuss equilibrium conditions when higher-order contributions to the free energy are negligible, and predict the scaling behaviour.Received: 18 June 2004, Published online: 20 July 2004PACS: 68.55.-a Thin film structure and morphology - 83.80.Tc Polymer blends     

Percolation processes in monomer-polyatomic mixtures

In this paper, the percolation of mixtures of monomers and polyatomic species (k$k$-mers) on a square lattice is studied. By means of a finite-size scaling analysis, the critical exponents and the scaling collapsing of the fraction of percolating lattices are found. A phase diagram separating a percolating from a non-percolating region is determined. The main features of the phase diagram are discussed in order to predict its evolution for larger k$k$-mer sizes.     

Muonium radicals in benzene-styrene mixtures

Muonium radicals were observed through theirSR precession frequencies in high transverse magnetic fields in pure benzene, pure styrene and their mixtures, all as liquids at room temperature. In benzene-styrene mixtures, the radicals obtained in each pure liquid are both present, so no slow (10^–9–10^–5 s) intermolecular exchange occurs; but strong selectivity was found with the formation of the radical from styrene being about eight-times more probable than the radical from benzene.     

Shear instabilities in granular mixtures

Dynamical instabilities in fluid mechanics are responsible for a variety of important common phenomena, such as waves on the sea surface or Taylor vortices in Couette flow. In granular media dynamical instabilities have just begun to be discovered. Here we show by means of molecular dynamics simulation the existence of a new dynamical instability of a granular mixture under oscillating horizontal shear, which leads to the formation of a striped pattern where the components are segregated. We investigate the properties of such a Kelvin-Helmholtz-like instability and show how it is connected to pattern formation in granular flow and segregation.     

Space solitons in gas mixtures

Evidences that there are incoherent space solitons at discharges in gas mixtures at normal conditions are presented. A new mechanism of optical quadratic nonlinearity responsible for an increase in the refraction index of gas mixture is considered. It is shown that an intense light produced at a discharge in a gas mixture is instable and optical incoherent spatial solitons appear in a form of thin spherical layers where an intense white light circulates in all possible directions and provides concentration of the mixture molecules with maximal refraction index.     

Pink afterglow in nitrogen-argon mixtures

The nitrogen pink afterglow was studied by optical emission spectroscopy in the DC flowing regime at a total gas pressure of 700 Pa and at the discharge current of 120 mA. The discharge was created in a Pyrex tube of 13 mm i.d. using nitrogen and argon of 99.999% purity with additional purification by Oxiclear columns and liquid nitrogen traps. The area ±3 cm around the observation point had to be cooled down to liquid nitrogen wall temperature in order to allow the study of the reactor wall temperature effect on the post-discharge. The maximum pink afterglow emission in pure nitrogen at ambient wall temperature was observed at a decay time of 6 ms. When the argon percentage in the gas mixture was increased the pink emission maximum was shifted to the later decay times. Simultaneously, the intensity of the pink afterglow decreased and at a 1:1 nitrogen-argon ratio the effect disappeared. Similar effects were also observed when the discharge tube wall around the observation point was cooled down to liquid nitrogen temperature. The argon atomic lines were only observed during the post-discharge at the highest argon concentration at a low wall temperature. The kinetic model showed that the pink afterglow quenching was connected to the decrease of the and pooling processes efficiency.