We discuss the linearization of the kinetic-variational theory (KVT) II equation for mixtures around absolute equilibrium for a family of pair potentials with hard core and soft tail. In the case of a continuous soft tail, the linear equation reduces to that of Sung and Dahler [J. Chem. Phys. 80, 3025 (1984)], which in turn generalizes to mixtures, the short-time result of Lebowitz, Percus, and Sykes [Phys. Rev. 188, 487 (1969)] that had subsequently been obtained by others using different means. Our equation also represents a generalization of the linearized revised Enskog theory to potentials with attractive tails. Hence, at this level of theory the application of the fundamental technique in the kinetic-variational approach, maximization of entropy subject to constraints, is equivalent to the approaches used by others. However, this technique appears to be more amenable to the production of more general theories. Analysis of the structure of the KVT II theory reveals the necessity of relaxation mechanisms for fluid equilibration that are absent in the various linear theories. These include a mechanism for mixing kinetic and potential energies and a temperature associated with the relaxation of the fluid structure. Various options for these are described and compared. A consistent set of mechanisms provided by a more general class of kinetic-variational theories (KVT III) is discussed. These should serve as a useful guide in improving the alternative approaches that are equivalent to linearized KVT II.

We study the complex, disordered structure of clusters formed by several kinetic aggregation processes. By expanding the structure factor into spherical harmonics, detailed information about both the structure and anisotropy of the clusters at all length scales is obtained. The scaling of the expansion terms with cluster mass and order of the expansion is investigated. For cluster-cluster aggregates, we find that the fractal dimension, which reflects the scaling of the orientationally averaged structure, also describes the scaling of the spherical harmonics, which reflect the anisotropies of the structure. By contrast, clusters formed by single-particle diffusion-limited aggregation do not appear to exhibit the same degree of scale invariance. Cluster-cluster aggregates are found to exhibit considerably more anisotropy than those formed by single-particle diffusion. The consequences of the anisotropies for quasielastic light scattering experiments are discussed.

We study the problem of arranging p self-avoiding flexible chains of molecular weight M on a hypercubic lattice of N sites with lattice coordination number z using a field-theoretic approach. The thermodynamic limit of pM becoming infinite, with the packing fraction f=pM/N ranging from zero to 1, is considered. Hence the dimer, the Hamiltonian walk, and the single self-avoiding walk problems are included as particular cases. Mean-field theory is of the Flory type and it becomes exact at z=∞. Systematic corrections in powers of $z^{\mathrm{-}1}$ can be evaluated. We calculate the weight- and volume-fraction-dependent connectivity constant and site entropy to second order in $z^{\mathrm{-}1}$ and compare it with known results in two and three dimensions. The site entropy, which vanishes at f=0, is a convex function of f (for any M) with a maximum at f≳0.6 that moves towards higher f as either M or z increases. We also discuss the most efficient packing of M-mers at a given volume fraction and dimensionality.

A three-dimensional model of an α helix is built applying a molecular-mechanics approach. The potential-energy function describing the system is based on empirical data and implemented in the molecular-dynamics computer program charmm. The time evolution of amide-I vibrations has been examined numerically. In order to examine the coupling mechanism of an amide-I oscillator to other amide-I oscillators along the backbone as well as along the so-called spines, a simple analytical model has been set up. From this model the coupling along the backbone is estimated to be more than 50% stronger than the coupling along the spines.

We present a Landau theory for transitions among tilted hexatic phases in liquid-crystal films. Using the renormalization group, we then derive phase diagrams with four tilted hexatic phases: the hexatic-I and hexatic-F phases, an intermediate hexatic-L phase, and an unlocked phase. If the films are crystalline rather than hexatic, all these phases except the unlocked phase still exist. These results are consistent with recent experiments on thermotropic and lyotropic liquid crystals. We also study the five-armed ‘‘star’’ defect close to the hexatic-to-hexatic transitions. Near the first-order transition from hexatic-I to hexatic-F, the thickness of the arms increases as ‖T-$T_{\mathrm{IF}}$${\Vert }^{\mathrm{-}1/3}$ through a process similar to wetting. This thickening should be observable in thin tilted hexatic films.

High-resolution heat capacity measurements have been made on six mixtures of 40.8 and 60.8, the butyl and hexyl homologs of alkoxybenzylidene octylaniline. The nematic (N)–smectic-A (Sm-A) transition becomes tricritical close to X=0.35, where X is the mole fraction of 60.8. The $C_p$ data for a mixture with X=0.35 are well described by the tricritical exponent α=0.5 and an amplitude ratio $A^{\mathrm{-}}$/$A^{+}$=1.6, which is not a universal quantity for tricritical measurements over the accessible range of reduced temperatures. The small value of $A^{\mathrm{-}}$/$A^{+}$ means that N–Sm-A tricriticality is further from classical Landau tricritical behavior than is the ${}_{}{}^3{}_{}{}^{}\mathrm{-}_{}^4{}_{}{}^{}$He system. Analysis of $C_p$ data over an extended range shows the importance of several correction terms to the leading singularity. In particular, there seems to be a small step discontinuity at $T_c$, which does not violate scaling at a tricritical point as it would for a second-order critical point.

We study the decay of magnetically trapped doubly spin-polarized atomic hydrogen in the density and temperature regime of the Bose-Einstein phase transition and calculate the temperature and magnetic field dependence of all relevant relaxation rate constants $G_{\mathrm{dd}\to \kappa \lambda }$. At the transition temperature $T_c$ the rate constants have a discontinuous second derivative with respect to T. Below $T_c$ they show a pronounced decrease relative to the extrapolated above-$T_c$ values, the observation of which is a clear signal for the experimental realization of Bose-Einstein condensation.

The statistical characteristics of the free-energy fluctuations in a one-dimensional random-bond Ising model are investigated by using the fluctuation-spectrum theory developed for the global characterization of fluctuations. As illustrations the characteristic function, the order-q free energy, and the fluctuation spectrum are calculated by generating the random coupling through chaotic dynamics.

We calculate the far-infrared absorption of a specific form of DNA polymer—the B conformation, poly(dA)⋅poly(dT)—using eigenvectors from a lattice dynamical model refined with inelastic neutron scattering data. Our various calculations include the isolated helix, the addition of counterions, and the addition of a ‘‘spine of hydration’’ in the minor groove. We find agreement with experimental infrared data except for one mode. We then attempt to model a coupling between two helices and show some evidence that this mode is interhelical.

An exact solvable model for the growth of breath figures in the intermediate time regime is presented. The model is based on the individual-droplet-growth power law $t^{\alpha }$, and a pattern of self-similarity. A relationship between this growth model and ultradynamics is proposed. The scaling behavior of ultradynamics accounts for the various observed features of breath-figure growth, such as the constant surface-area coverage and polydispersity as well as the average-growth power law $t^{3\alpha }$. The resulting distribution function of the droplet radius is in qualitative agreement with recent computer simulation results.

The model of noise-reduced diffusion-limited aggregation is analyzed in detail using classical methods of conformal mappings. It is shown that there are two phases of growth, compact and fractal, and the transition between them depends only weakly on the level of noise reduction. Detailed descriptions of the rate of growth, mass-to-size scaling, mass distribution, and shape of the clusters in both the compact and the fractal phases are presented. The results of the theoretical analysis are compared to extensive numerical simulations, and agreement down to fine details is reported.

We show that in the Jaynes-Cummings model with the intensity-dependent coupling interacting with the Holstein-Primakoff SU(1,1) coherent state the revivals of the radiation squeezing are strictly periodical for any value of initial squeezing. The expression for the atomic population inversion exhibiting the exact periodicity of the population revivals is obtained.

Formulas of x-ray absorption cross sections for unpolarized x rays combined with circularly and linearly polarized laser beams and also for polarized x-ray and laser beams of parallel states of polarization valid for moderate laser intensities are deduced. The hindering effect of the ponderomotive potential of the intense laser field on the laser-assisted x-ray absorption near the absorption edge is predicted.

We discuss the manifestation of Berry’s phase in the degenerate parametric amplifier of quantum optics. Mainly we derive the Berry phase in the simplest case when the phase of the classical pump field varies adiabatically. Also we show that the effect of the phase may be discerned at all times in the photon-counting statistics of the output field.

We compute numerically the cellular shape expected for the directional solidification of ${\mathrm{CBr}}_4$, at velocities far above the threshold for the Mullins-Sekerka instability. Our cell has a smooth tip plunging to a deep narrow channel which ends with a small liquid bubble. Our results are compared to the experimental findings of S. de Cheveigne, C. Guthmann, and M. M. Lebrun [J. Phys. (Paris) 47, 2095 (1986)].

In this paper we demonstrate how the squeezed-pump-laser model of Marte and Walls [Phys. Rev. A 37, 1235 (1988)] may be realized in practice. We consider a three-level atomic medium interacting with two cavity modes pumped with squeezed light. We show that this pumping mechanism both achieves atomic inversion and squeezes the fluctuations on the lasing transition.

Phase transitions in the thermodynamic description of the intermittent systems of Manneville are studied in connection to the non-Gaussian fluctuations. The universal critical behavior is derived exactly, with the critical exponent depending only on the characteristic exponent z of the map. Two types of behavior are classified according to z<2 or z≥2.

In this paper we derive the Bethe-Salpeter equation for a bound state consisting of a spin-0 particle and a spin-(3/2 particle in the general case. For the electromagnetic bound state, in the ladder approximation, a Wick-Cutkosky-type equation and its solution for an S-wave state are obtained. Using this relativistic Bethe-Salpeter amplitude, we calculate the probabilities of production, the disintegration, and decay rate of the (${\pi }^{+}$${\Omega }^{\mathrm{-}}$) atom.

The static electric dipole polarizability of small spherical metallic clusters is calculated using density-functional theory. We study systematically corrections to the local-density approximation which are particularly important when the spatial extension of the induced charge at the surface of the cluster becomes comparable to the size of the exchange hole. Additional corrections to the polarizability arising from the actual atomic structure of the metal cluster in comparison to a spherical jellium model are discussed.

A preliminary discussion of the calculation of nonrelativistic bremsstrahlung cross sections, the photon energy differential, and electron recoil angle differentials is given for incident-electron kinetic energy $T_1$=50 keV, based on a numerical calculation in a partial-wave formulation. Our results show that angular distributions of recoiled electrons for high-atomic-number (Z) elements are not smoothly varying functions of the electron recoil angle and present peaks and dips, unlike in the low-Z cases. The screening effect is important in the high-Z cases.