We investigated the temperature dependence of the optical Fréedericksz threshold in nematic liquid crystals doped with anthraquinone dyes. In the presence of these dyes, the Fréedericksz threshold is anomalously low and exhibits an unusual temperature dependence. A microscopic model is proposed, according to which the anisotropic orientational distribution and the rotational dynamics of the excited dye molecules play an important role in the observed phenomena.

The aging of a liquid surface is made evident through the surface-mass-density variation with time. By using the surface-mass conservation law together with the solution of the diffusion equation, we find, for dilute solutions, that surface-mass changes with time following a Volterra integro-differential equation of the second kind. The solution of this equation, for a semi-infinite fluid, together with the two-dimensional equation of state for a dilute gas, allows us to find the surface-tension variation with time. The result is compared with a recent experimental dynamic measurement of the liquid-vapor interfacial tension for aqueous solutions of a nonionic detergent.

We derive the interfacial-curvature free energy for a simple fluid from density-functional theory, and find a form matching that for a two-dimensional shearless elastic media. The fourth moment of the direct correlation function and the density gradient determine the bending moduli κ and κ¯, while the spontaneous curvature ${\mathit{c}}_0$ is given by asymmetry in the density. We obtain the critical indices of these quantities and corrections to the Laplace equation for curved interfaces.

The present paper was motivated by an attempt to understand the transition from a nonionic to an ionic micelle from both the experimental and theoretical points of view. Small-angle neutron-scattering experiments were performed on mixed micelles of nonionic-ionic surfactants as the charge was increased in steps. Evidence for the charge condensation on the surface of the micelles is obtained. An extension of the sticky-hard-sphere model to include the Coulomb potentials is presented and used to analyze experimental results on two systems. It is concluded that this model is more appropriate than the currently used models.

Growth features of aggregates including surface-diffusion processes are studied by Monte Carlo simulations on a two-dimensional square lattice. A dendritic pattern with thick branches changes its anisotropy from the 〈10〉 direction to 〈11〉 depending on the surface-diffusion mechanism. A homogeneous diffusion-limited-aggregation (DLA) pattern with a fractal dimension of ${\mathit{d}}_{\mathit{f}}$=1.716±0.003 grows in the crossover domain between two anisotropies. Results indicate that a random tip-splitting process arising from noise is necessary to hold its homogeneity and self-similarity. Such processes in other DLA patterns and in a dense radial-like pattern obtained from altered simulations are also investigated.

A diagnostic method for laser-imploded targets, particularly plastic shells, is described. It is based on the observation of a peak in the continuum x-ray spectrum emitted from the target. The peak is the result of the high absorption of low-energy x rays from the implosion core by the cooler, compressed shell surrounding the core. In glass targets, where the shell absorption is typically dominated by bound-free transitions (photoionization), the position of this peak in the spectrum depends on the shell ρ Δr. In plastic targets, where the shell absorption is due mainly to free-free transitions (inverse bremsstrahlung), the position of the peak depends on the ${\mathrm{\rho }}^2$ Δr/${\mathit{T}}^{1/2}$ for the shell. We study the relationship between the position of the peak and these two quantities, both analytically as well as with a simulation code.

In this paper we analyze the dynamics of a free-electron laser in the strong-signal regime, drawing a parallel with that of a conventional laser. A simple model of gain saturation is developed and a scaling relation of the gain versus the intracavity laser intensity is derived.

We analyze the parameters present in the Morse potential and van Zandt potential to describe the hydrogen bonds in DNA using the quasicontinuum model applied to the low-frequency vibrational modes.

In a recent article, Berdichevsky, Kunin, and Hussain [Phys. Rev. A 43, 2050 (1991)] claim to have ‘‘resolved’’ the ‘‘paradox of negative temperatures of point vortices’’ by means of a redefinition of entropy, following an early speculation of Gibbs. It is suggested here that there is no paradox to resolve, and doubt is expressed that the redefinition of temperature sheds light on the high-energy behavior of ideal line-vortex systems.

We respond to the main points in the preeeding Comment [D. Montgomery, Phys. Rev. A 44, 8437 (1991)], which are the following: (a) For spatially inhomogeneous configurations of point vortices in a box, negative temperature occurs and is not a paradox to be resolved. (b) ‘‘A redefinition of temperature following early speculation of Gibbs’’ does not shed light on the high-energy behavior of point vortices.

We point out publications that preceded a recent paper by Shi, Seinfeld, and Okuyama [Phys. Rev. A 41, 2101 (1990)] and contained some of its main results. We also discuss their interpretation of the transient critical flux value as the nucleation rate and present the result for the supercritical flux time dependence.

The results obtained in our previous paper [Phys. Rev. A 41, 2101 (1990)] are extended to obtain N(${\mathit{g}}_{\mathit{d}}$,t), the total accumulated number concentration of nucleated clusters at the detectable size, ${\mathit{g}}_{\mathit{d}}$. It is shown that N(${\mathit{g}}_{\mathit{d}}$,t) obtained by Shneidman [preceding Comment, Phys. Rev. A 44, 8441 (1991)] is incorrect since the time lag associated with N(${\mathit{g}}_{\mathit{d}}$,t) suffers a singularity at ln(-1).

The definition of the direct correlation functions (DCF) used by Tanaka, Yan, and Ichimaru [Phys. Rev. A 41, 5616 (1990)] is a semiclassical one, even though the functional derivative is performed taking account of the quantum effect. As a consequence, the Ornstein-Zernike relations, the electron-screened ion-ion interaction, the electron-screened ion-ion DCF, and the compressibility cannot be derived in correct forms for an electron-proton mixture, where the electrons behave as a quantum fluid.

It is shown that the direct correlation functions in the preceding Comment [Chihara, Phys. Rev. A 44, 8446 (1991)] and the static local-field corrections used in the article being commented upon [Tanaka, Yan, and Ichimaru, Phys. Rev. A 41, 5616 (1990)] are defined in the same way and that both involve a static and therefore classical approximation to the correlations in a quantum fluid. Remarks are made on the derivation of the Ornstein-Zernike relation and on the compressibility sum rule.

High-precision variational calculations using multiple basis sets in Hylleraas coordinates are presented for the 1${\mathit{s}}^2$2s ${}_{}{}^2{}_{}{}^{}$S state of lithium. The variational bound of -7.478 060 326(10) a.u. for the nonrelativistic energy is in good agreement with our revised experimental value of -7.47 806 034(20) a.u., thereby resolving a long-standing disrepancy. Two-electron calculations of the QED corrections are extended to three-electron systems and compared with other results. The comparison for Li-like ions up to ${\mathrm{U}}^{89+}$ suggests a simple interpretation for the ‘‘screening of the Lamb shift’’ recently calculated by Cheng, Johnson, and Sapirstein [Phys. Rev. Lett. 66, 2960 (1991)].

Measurements of the total photoionization cross section of lead in the energy range between the 6${\mathit{s}}^2$6p${(}^2$${\mathit{P}}_{1/2}$) ionization threshold at 59 819 ${\mathrm{cm}}^{\mathrm{-}1}$ and the 6${\mathit{s}}^2$6p${(}^2$${\mathit{P}}_{3/2}$) threshold at 73 900 ${\mathrm{cm}}^{\mathrm{-}1}$ are reported. Just above the ionization threshold the cross section is dominated by broad window resonances, members of the 6pnd and 6pns Rydberg series converging to the 6${\mathit{s}}^2$6p${(}^2$${\mathit{P}}_{3/2}$) threshold. The Rydberg series are perturbed by a very broad and intense autoionizing resonance near the threshold. The resonance energy, width, and shape parameter of this resonance are determined. Close to the 6${\mathit{s}}^2$6p${(}^2$${\mathit{P}}_{3/2}$) series limit the data indicate the presence of a further broad-window-type resonance.

Cross sections for ionization of two electrons in helium by high-energy photons have been evaluated using many-body perturbation theory. All lowest-order amplitudes [from the effects of shakeoff, ground-state correlation, and the absorption of a photon by one electron, which then hits another electron (two-step 1)] are included. At a photon energy of 2.8 keV our calculated ratio of double- to single-ionzation cross sections is 1.6%, in agreement with a very recently observed value of 1.6±0.3%.

Anomalous features in the resonantly excited 2p autoionization spectrum of Mg are attributed to overlapping shake transitions of the excited bound (spectator) electron. Universal features of the shake spectrum are displayed and related to the post-collision interaction.

Dielectronic satellite spectra of the Fe xxv Kα resonance line observed from tokamak fusion test reactor plasmas have been compared with recent explicit calculations for the n=3–8 dielectronic satellites as well as the earlier theoretical predictions, which were based on the 1/${\mathit{n}}^3$ scaling law for n>4 satellites. The analysis has been performed by least-squares fits of synthetic spectra to the experimental data. The synthetic spectra constructed from both theories are in good agreement with the observed data. However, the electron-temperature values obtained from the fit of the present explicit calculations are in better agreement with independent measurements.

We report a quantitative study of spectral diffusion in a solid-state system by measuring the stimulated echo relaxation. The spectral diffusion process in ${\mathrm{Pr}}^{3+}$:${\mathrm{YAlO}}_3$ at low temperatures (2.0 K) is found to be dominated by the relaxation of the ‘‘frozen core’’ of nearest neighboring Al spins. The decay of the echo signal is found to be fully described by a simple spin-flip diffusion model and by a first-principle calculation. The complete understanding of the spectral diffusion process in this simple model system establishes a quantitative basis for using coherent optical techniques to study slow dynamics in complex systems.