The solution of the Martynov-Sarkisov closure (MS) of the Ornstein-Zernike equation has to satisfy the condition for the mean force potential w≥-1. It is shown both for one-component soft-sphere fluids and for two-component hard-sphere mixtures that densities at which this condition becomes broken are close to the freezing densities provided by computer simulation (CS). For pressure data, the agreement between MS and CS is rather poor. In particular, for hard-sphere mixtures, MS exhibits only the spindle-type diagram while CS presents also azeotropic and eutectic forms.

We have detected a slow ion-acoustic wave propagating obliquely to the equilibrium magnetic field in a low-density, weakly ionized helium plasma produced by rf power in the linear mirror machine LISA. When an upper hybrid wave is launched perpendicular to the ambient magnetic field, we have observed that the upper hybrid wave decays parametrically into another upper hybrid wave and a slow ion-acoustic wave.

The integral equations applied to a hydrogen plasma by Yan, Tsai, and Ichimaru [Phys. Rev. A 43, 3057 (1991)] are shown to become inappropriate when the plasma begins to have a bound state which brings about a low degree of ionization: the bound-state contribution to forming an ion should be taken in the form needed to induce changes in the bare ion-ion and electron-ion interactions. Moreover, their definition of a degree of ionization shows an abrupt change when a bound state disappears, and this discontinuity is associated with a phase transition. However, this discontinuity in the ionization may not be a real one, since it is possible to define a degree of ionization, which remains continuous in the change from a bound to a continuum state.

It is shown that a closed V-type, three-level system, which is incoherently pumped on the transition at which lasing occurs and coherently pumped on the other transition, exhibits lasing without population inversion in any atomic state basis. The same system can be also made to exhibit lasing without population inversion in the bare atomic state basis but with population inversion in the dressed-state basis.

Classical potentials giving the same spectrum as the q-deformed anharmonic oscillators having the symmetries ${\mathrm{U}}_{\mathit{q}}$(2)⊃O(2) and ${\mathrm{SU}}_{\mathit{q}}$(1,1), which have been used for the description of vibrational spectra of diatomic molecules, are determined in analytic form. The potentials found here are somewhat wider than the corresponding classical anharmonic potentials obtained in the limit q→1, while their Taylor expansions are similar to the expansion of the modified Pöschl-Teller potential, which is connected to the Morse potential through a known transformation.

Differential cross sections for single and double ionization for p+He collisions at 0.3, 0.7, and 1 MeV are calculated using the Glauber approximation. The angular dependence of the fraction of double ionization shows a sharp peak at a scattering angle of 0.8 mrad, which is slightly smaller than the experimental finding. The peak values decrease slowly with increasing collision energies, in accordance with the experiment, but the absolute values are about twice as large. The analysis of the present result shows that the peak of the fraction is caused mainly by the structure of the single-ionization cross section rather than the double-ionization cross section.

We investigate theoretically laser cooling with broadband ${\mathrm{\sigma }}_{+\mathrm{-}}$${\mathrm{\sigma }}_{\mathrm{-}}$ lasers acting on J=0→J=1 and J=1→J=2 transitions. For cross-correlated laser fluctuations an instability in the friction force at zero velocity is predicted for red laser detunings. The dependence of this instability on the cross-correlation and spectral line shape is investigated.

The scaling behavior of self-avoiding (SA) fluid membranes in three dimensions subject to a bending rigidity κ is studied by Monte Carlo simulation. For κ=0, open and closed membranes behave like SA branched polymers at large length scales. For arbitrary κ, scaling functions of the combination y==${\mathit{N}}^{1/2}$/κ are found to describe the shape variables of closed membranes. The transition from a rigid phase at small y to a SA branched polymer phase at large y is smooth for closed membranes.

We have carried out large-scale computer simulations of experimentally motivated (1+1)-dimensional models of kinetic surface roughening with power-law-distributed amplitudes of uncorrelated noise. The appropriately normalized qth-order correlation function of the height differences ${\mathit{c}}_{\mathit{q}}$(x)=〈‖h(x+x’)-h(x’)${\mathrm{\Vert }}^{\mathit{q}}$〉 shows strong multifractal scaling behavior up to a crossover length depending on the system size, i.e., ${\mathit{c}}_{\mathit{q}}$(x)∼${\mathit{x}}_{\mathit{q}}^{\mathit{q}\mathit{H}}$, where ${\mathit{H}}_{\mathit{q}}$ is a continuously changing nontrivial function. Beyond the crossover length, conventional scaling is found.

We study both numerically and analytically the steady-state flux of particles in a finite one-dimensional Sinai-type disordered system (with no global bias). We show that the steady flux is proportional to ${\mathit{N}}^{\mathrm{-}1/2}$, where N is chain length, i.e., it has a much slower dependence on N than the Fickian flux.

The effect of external periodic driving forces in the tunneling process of a two-level system is studied within the Floquet formalism and perturbation theory. Coherent tunneling can be increased or decreased depending on the external forces parameters. In particular, the model is able to account accurately for the tunneling suppression phenomenon recently discovered [Grossman et al., Phys. Rev. Lett. 67, 516 (1991)] in a quartic bistable potential.

In this paper we present numerical results for the transverse fluctuations 〈${\mathit{x}}^2$(t)〉 of a directed polymer in a random potential field on fractal substrates. Because of the randomness of the potential these mean-squared displacements are shown to be enhanced with respect to the regular random-walk behavior on fractals. The enhancement enters in a subordinated way 〈${\mathit{x}}^2$(t)〉∼${\mathit{t}}^{\mathrm{\alpha }}$, with α=(2/${\mathit{d}}_{\mathit{W}}$)ν, where ${\mathit{d}}_{\mathit{w}}$ is the walk exponent for fractals and ν is the enhancement factor. The minimal energy fluctuations are also calculated and show a similar behavior, ΔE∼${\mathit{t}}_{\mathit{w}}^{(2/\mathit{d}}$)β. On the Sierpinski gaskets studied up to the numerical accuracy ν and β appear to concur with the values 4/3 and 1/3, correspondingly, independent of the embedding Euclidean dimension.

A criterion for the freezing of a liquid is investigated through an analysis of the contribution of multiparticle correlations to the statistical entropy. Molecular-dynamics results are presented for a Lennard-Jones system at two subcritical isotherms in a range of densities across the freezing line.

The existence of polar electro-optic effect induced by a surface polarization of a nematic liquid crystal is proved using a simultaneous action of vertical dc and high-frequency ac electric fields on the homeotropically aligned nematic liquid crystal with positive dielectric anisotropy. The proposed method enables us to measure the surface electric polarization and the anchoring energy in the course of the same experiment. The evaluated surface polarization for the pentylcyanobiphenyl–silicone elastomere interface is 1 order of magnitude larger than the nematic flexoelectric constant.

We present simulations of Poiseuille flow in standard models of two-dimensional porous media for a variety of viscosity ratios. These simulations show definite crossover from initial diffusion-limited-aggregationlike fractal growth (m∝${\mathit{R}}^{1.7}$) to compact growth (m∝${\mathit{R}}^2$) on a length scale ${\mathit{R}}_{\mathit{c}}$, which increases as approximately the 1/3 power of the viscosity ratio. There appears to be an intermediate regime of denser-than-compact growth.

We report the numerical observation of temporally linear domain growth in a phenomenological model of segregating fluids. Our observation is facilitated by the use of computationally efficient cell dynamical system models.

We demonstrate a plastically deformable coupling of liquid-crystal molecules to a rubbed polymer surface, showing that the large electric-field-induced torques available in ferroelectric liquid crystals can overwhelm the intrinsic surface anisotropy to produce new stable surface orientations.

The multifractal structure of the growth probability distribution on the perimeter of a pit in the diffusion-limited pitting corrosion is derived by making use of the Monte Carlo estimation of the hitting probabilities by successive launching of a large number of random walkers. The multifractal spectrum α-f(α) is determined, and compared with that of the diffusion-limited aggregation. It is found that the scaling exponent β of width w of the corrosion pit (w≊${\mathit{n}}^{\mathrm{\beta }}$, where n is the particle number removed from metal) is given by β=${\mathit{D}}_{\mathit{n}}$(1) where ${\mathit{D}}_{\mathit{n}}$(1) is the information dimension. It is also shown that the scaling exponent β is related to the maximum growth probability ${\mathit{p}}_{\max }$ at the edge of the corrosion pit and approximately given by β=1-${\mathit{D}}_{\mathit{n}}$(∞).

We show how the Casimir force between dielectrics can be calculated in terms of source fields, with no explicit reference to zero-point-field energy. Using Feynman’s interpretation of the Lamb shift, the commutativity of equal-time electron and field operators, and a relation between a Green function and a vacuum-field-correlation function, we show why the theories of Lifshitz, van Kampen, and Schwinger produce identical results, even though they appear to be based on very different physical premises. We suggest the possibility of modifying van der Waals-Casimir forces with any external field having some degree of spatial coherence.