We use the 800-MeV LAMPF ${\mathrm{H}}^{\mathrm{-}}$ beam to Doppler-shift the energies of photons from a Nd:YAG laser (where YAG denotes yttrium aluminum garnet) up to the 10–13-eV range. Using these Doppler-shifted photons and calibrating our apparatus by observing the Lyman resonances in ${\mathrm{H}}^0$, we find that the energy of the first Feshbach resonance below n=2 in the ${\mathrm{H}}^{\mathrm{-}}$ ion is 10.9264(6) eV. This energy is in good agreement with predictions and appears to indicate that the one-electron reduced-mass rydberg, rather than the infinite-mass rydberg, is appropriate to use for this Feshbach resonance.

The concentration and temperature dependences of the Cotton-Mouton coefficient C for the binary mixture cesium perfluoro-octanoate and water close to a nearly-second-order nematic-isotropic transition are reported. It was found that (T-$T^{\mathrm{*}}$)C is a weakly decreasing function of concentration, indicating a significant concentration dependence of the micelle structure.

We have numerically investigated period-doubling bifurcations in four-dimensional symplectic maps. Our study indicates the existence of a universally self-similar period-doubling sequence. Unlike the two-dimensional case, the fixed-point map has two unstable directions under the period-doubling operator with two relevant eigenvalues 8.721 097 2 and -15.0786. The four orbital scaling factors along and across the dominant symmetry surface are, respectively, 16.1449, -4.018 07, 16.36, and -7.5393.

The finger of fluid formed during the displacement of a more viscous fluid is a well-known example of nonequilibrium pattern formation. Previous efforts claimed that the steady-state solution discovered by Saffman and Taylor was linearly unstable, in contradiction with experimental observations. In this work, we present a new stability analysis which demonstrates stability and resolves the aforementioned conflict. We describe how this lends support to a new paradigm governing interfacial pattern-forming systems, that of ‘‘microscopic solvability.’’

Subtle difficulties encountered with non-Markovian first-crossing problems are emphasized and illustrated by an exact study of a non-Markovian flow driven by exponentially correlated telegraphic noise. The connection with approximative schemes is made and a general inequality is derived. The relationship with the escape rate at a low noise level is clarified and the Markovian limits to white shot noise and white Gaussian noise are presented.

Extensive high-resolution heat-capacity measurements have been carried out near the smectic-A–hexatic-B transition of various compounds in the homologous series of n-alkyl-4’-n-alkoxybiphenyl-4-carboxylate. In contrast with the nematic–smectic-A and smectic-A–smectic-C (or chiral-smectic-C) transitions, the critical exponent α characterizing the smectic-A–hexatic-B heat-capacity anomaly is found to be large and does not vary monotonically with the size of the disordered-phase (i.e., smectic-A) temperature range.

Measurements of the thermal conductivity of mixtures of methane and ethane reveal an enhancement in the mixture critical region apparently contradicting theoretical predictions. The anomaly is similar in size and temperature dependence to that found for pure fluids.

The electromagnetic force on a magnetic monopole in matter is shown to be F=g(H-v×E/c) when there is only one magnetic monopole in matter. The relation between this force and the conservation law of momentum is discussed. The case in which a macroscopic number of magnetic monopoles exist in matter is also discussed.

Two dynamical models, proposed by Hopfield and Little to account for the collective behavior of neural networks, are analyzed. The long-time behavior of these models is governed by the statistical mechanics of infinite-range Ising spin-glass Hamiltonians. Certain configurations of the spin system, chosen at random, which serve as memories, are stored in the quenched random couplings. The present analysis is restricted to the case of a finite number p of memorized spin configurations, in the thermodynamic limit. We show that the long-time behavior of the two models is identical, for all temperatures below a transition temperature $T_c$. The structure of the stable and metastable states is displayed. Below $T_c$, these systems have 2p ground states of the Mattis type: Each one of them is fully correlated with one of the stored patterns. Below T∼0.46$T_c$, additional dynamically stable states appear. These metastable states correspond to specific mixings of the embedded patterns. The thermodynamic and dynamic properties of the system in the cases of more general distributions of random memories are discussed.

We develop and discuss a Taylor-series expansion of the addition theorem for screened spherical waves, $i^l$$h_l$(kr)$Y_{\mathrm{lm}}$(r^). The expansion is designed for orderly progression in the addition of curved–wave-front corrections to multiple scattering of electrons in solids, but it applies to any wave-scattering problem based on the addition theorem for spherical waves. We relate one of the expansion indices to a magnetic quantum number in a coordinate system rotated to align the quantization and translation axes.

The rapid fragmentation of two-dimensional high-pressure disks of Lennard-Jones fluid was studied using molecular dynamics. The free expansion of 169-, 721-, 2611-, and 14 491-particle systems was studied for several sound-traversal times. The breakup into fragments (or clusters) can be roughly described by Grady’s model, which balances the surface energy with the comoving (dilational) kinetic energy of the fragments. The model predicts that the number of fragments varies as the cube root of the system population and the 2D/3 power of the initial pressure where D (2 or 3) is the dimensionality of the system. The molecular-dynamics results confirm these predictions within about ±0.1 and thereby rule out three other fragmentation models. The relatively high monomer temperatures and relatively uniform fragment temperatures found here correspond to temperatures found in recent three-dimensional Lennard-Jones simulations by Vicentini, Jacucci, and Pandharipande.

This paper reports a comprehensive x-ray diffraction study of the structure and the restacking transitions which occur within the crystalline-B phases of N-[4-(n-heptyl)oxybenzylidene]-4’-(n-heptyl)aniline (7O.7). Between 63 °C and 59 °C, this system exhibits a rich structural behavior with a series of three transitions involving restacking and subtle changes in the intralayer packing. In order of decreasing temperature, the structures are hexagonal close packed (69–63 °C), orthorhombic F (63–60.1 °C), monoclinic C (60.1–59.75 °C), and simple hexagonal (59.75–55 °C). In the last three phases, there is also a long-wavelength modulation (λ∼100 Å) in which the smectic layers are displaced along their normals. The wave vector of the modulation lies in the plane of the smectic layers directed along a reciprocal-lattice vector and exhibits a weak (∼20%) temperature variation. Both low-resolution (rotating-anode) and high-resolution (synchrotron) measurements of the structures and of the diffuse scattering are reported.

Use is made of the macroscopic cold-fluid Poisson equations to investigate the electrostatic stability properties of nonrelativistic, non-neutral electron flow in a cylindrical diode with applied magnetic field $B_0$e${^}_z$. The cathode is located at r=a and the anode is located at r=b. Space-charge-limited flow with $E_r^0$(r=a)=0 is assumed. Detailed stability properties are investigated analytically and numerically for electrostatic flute perturbations with ∂/∂z=0. Particular emphasis is placed on the influence of the neutral anode plasma on stability behavior assuming uniform cathode electron density (n${^}_b$) extending from the cathode (r=a) to r=$r_b$, and uniform anode plasma density (n${^}_e$=$Z_i$n${^}_i$) extending from r=$r_p$ to the anode (r=b). Depending on the cathode electron density (as measured by $s_b$=ω^ ${}_{\mathrm{pb}}{}^2{}_{}{}^{}$/${\omega }_{\mathrm{ce}}^2$), the anode plasma density (as measured by $s_e$=ω^ ${}_{\mathrm{pe}}{}^2{}_{}{}^{}$/${\omega }_{\mathrm{ce}}^2$), the diode aspect ratio, etc., it is found that there can be a strong coupling of the anode plasma to the cathode electrons, and a concomitant large influence on detailed stability behavior for both the high-frequency (electron-driven) and low-frequency (ion-driven) branches. Detailed stability properties are investigated over a wide range of cathode electron density, anode plasma density, diode aspect ratio, etc.

The objective of this paper is to present a simple time-dependent calculation of the light-absorption cross section for a strongly coupled partially degenerate plasma so as to transcend the usual single-particle picture. This is achieved within the density-functional theory (DFT) of plasmas by generalizing the method given by Zangwill and Soven [Phys. Rev. A 21, 1561 (1980)] for atomic calculations at zero temperature. The essential feature of the time-dependent DFT is the correct treatment of the relaxation of the system under the external field. Exploratory calculations for an Fe plasma at 100 eV show new features in the absorption cross section which are absent in the usual single-particle theory. These arise from intershell correlations, and channel-mixing and self-energy effects. These many-body effects introduce significant modifications to the radiative properties of plasmas and are shown to be efficiently calculable by this time-dependent density-functional theory.

We consider diffusion on a lattice governed by a master equation in which the bond transition rates fluctuate dynamically between two different values with a relaxation time τ. The effective-medium bond transition rate in the Laplace domain is ψ(z+1/τ), where ψ(z) is the known solution in the static limit τ→∞. This solution exhibits no percolation transition for any finite τ, but it interpolates smoothly between the static solution and the solution in the limit of rapid fluctuations (τ=0).

The change in the bifurcation structure of a quadratic map due to the introduction of linear time dependence of the bifurcation parameter is investigated. Although nontrivial fixed points do not exist for this system, a bifurcation diagram can be constructed provided the sweep rate is not too large. The characteristic scaling features and hysteresis effects exhibited in this diagram are studied. Since studies of bifurcation points are often carried out by such parameter variations, the results should provide guides for the interpretation of experimental data.

A kinetic model has been formulated based on the generalized Enskog equations for a binary mixture of hard-sphere fluids. The resulting description is an improvement over an existing model based on the linearized Boltzmann equations for Maxwell molecules in that effects of thermal diffusion and nonideality corrections are taken into account. It is shown that the present model gives results for density fluctuations in quantitative agreement with light-scattering spectra of Xe-He mixtures.

The stability of magnetically insulated electron flow is studied for wavelengths longer than gyrolengths and frequencies lower than gyrofrequencies. This is done by using a general theory that allows for a distribution of electrons of different canonical momentum and total energy. The stability theory leads to a set of integro-differential equations for the eigenfunctions of the potentials. The integral portion of the equations relates positions across the flow that are connected by the finite size of the electron orbits. A general stability criterion is found. The stability of the flow is determined by the distribution of the electrons in canonical-momentum–total-energy space. The criterion can be stated roughly as depending upon whether the distribution function increases or decreases with drift velocity. If it increases, the flow is unstable.

We study the electromagnetic fields in layered-inhomogeneous uniaxial planar structures using the geometrical-optics approximation (GOA). Explicit expressions for the fields in the higher- (first-) order GOA are obtained. We also obtain the validation criterion for the zeroth-order GOA. There results are important for studying the true significance of the geometrical-optics approximation and the extension of its usefulness. The GOA solution shows that when total internal reflection occurs in the medium, the field amplitudes become zero and the angle of refraction becomes π/2. The azimuthal dependence of the ray direction and total internal reflection is discussed. The results are applied to a wave propagation in a hybrid oriented uniaxial nematic liquid crystal in an external field.

This paper deals with recent advances in search for possible types of regularities and systematic trends in the Stark broadening and shift parameters. The emphasis is (i) on the Stark parameters’ dependence on the ionization potential from the upper level of a corresponding transition (which, after being established, is used for the theoretical prediction of these parameters for the spectral lines where not available) and (ii) on the experimental determination of the Stark line broadening and shift parameters of group-IV and -V homologous singly charged ions. The data set obtained in such a way, together with existing experimental and theoretical data, are used to demonstrate the existence of several other types of common regularities in the Stark widths and shifts of the lines originating from the same type of transition of neutral atoms and singly charged ions of the elements along the periodic system.