Two recent studies of Lennard-Jones liquid-phase triple-point heat conductivity suggested very different nonlinear dependences of conductivity on field strength. This difference appeared to be paradoxical because the two calculations used very similar driving forces to generate heat flows. Here we analyze two sets of model calculations parallel to the Lennard-Jones work. The calculations describe a simple relaxation-time model for field-induced diffusive flow in a low-density gas of two hard disks. The nonlinearities found in the simple model suggest that the difference between the two Lennard-Jones conductivity calculations mainly reflects a difference in the comparable strengths of the currents studied.

A wide class of deterministic integer maps exhibit transient behavior which can be described in universal fashion. For the cases which in the continuum limit correspond to bifurcations, transients consist of two regimes, sharply separated by a crossover point which displays universal scaling with the size of the set. Moreover, their average lengths display power-law dependence on the accuracy of their measurement. This scaling behavior persists away from neutrally stable points but with logarithmic dependence on the size of the set.

We show that it is not always possible to describe a vapor by a Doppler-free model when several beams create a grating inside the vapor. This result, which is even true in the nonresonant case, is due to inelastic processes (collision, spontaneous emission). We show that it can be important to separate the adiabatic and inelastic contributions to the atomic polarizability, which have different time constants.

The fine structure of 1$s^2$2snl states with high angular momentum l has been measured for the first time in a high-Z four-electron system by studying the n=6-7 transition in the ${\mathrm{S}}^{12+}$ ion. Strong perturbations by 1$s^2$2pn’l’ states are observed and are interpreted using results of new multiconfiguration Dirac-Fock calculations. Implications for the spectroscopy of highly ionized atoms and the determination of high-Z atomic core polarizabilities are discussed.

Generalized oscillator strengths (GOS’s) are calculated from accurate five-state close-coupling differential cross sections for the resonance transition in Mg ii at electron impact energies 15, 50, 60, and 100 eV. Curves of the GOS versus momentum transfer squared, $K^2$, remain separate down to zero scattering angle, with the 50, 60, and 100 eV curves showing maxima close to $K^2$=0. We interpret the new phenomenon, maxima at small scattering angles, as a manifestation of the inadequacy of the Lassettre et al. formula to represent the GOS at small $K^2$ for intermediate energies. At 50 eV our GOS’s compare well with those deduced from measurement.

The attractive interaction between an atom and an electron or positron is described as a complex single-particle self-energy in which the effects of recoil and finite velocity are treated exactly. In addition to the well-known expansion for the potential in powers of the inverse separation distance 1/R with nonadiabatic corrections, we obtain a contribution due to the recoil of the electron as it exchanges virtual quanta with the atom.

The theoretical (e,2e) reaction cross sections for ${\mathrm{H}}_2$ in the plane-wave impulse approximation are calculated by use of the very highly electron correlated ground-state wave function of ${\mathrm{H}}_2$ (this wave function gives 98% of molecular binding energy) and the exact Born-Oppenheimer wave functions of ${\mathrm{H}}_2$${\mathrm{}}^{+}$ for the various electronic states. The theoretical value for the n=2 to n=1 cross-section ratio for q≃0.3 a.u. is in good agreement with the experiment, where n is the principal molecular-ion quantum number and q is the recoil momentum. However, the disagreement of 34% for q≃0.7 a.u. remains unresolved. The separate calculated cross sections for transitions to the n=2 final states remain in total disagreement with two sets of experimental data. As a result of the large disagreement, the first-order distorted-wave impulse approximation may not be able to explain such a large discrepancy. It is argued that the disagreement, as large as 10 times in the separate energy spectrum expecially for the peak observed around 30 eV assigned to 2p${\sigma }_u$, may be due to the involvement of an autoionization process of ${\mathrm{H}}_2$. This resembles the energetic proton spectrum reported for ${\mathrm{H}}_2$ by electron impact.

The angular distribution of electrons from above-threshold multiphoton ionization (photon energy 1.17 eV) was measured. Photoelectrons are preferentially ejected along the direction of the laser’s linear polarization; the distributions become narrower with increasing number of absorbed photons.

Measurements of a.c. Stark shifts and broadening have been made on several two-photon resonant rovibronic levels in nitric oxide, with use of resonance multiphoton spectroscopy with a calibrated proportional-counter system. Contrary to a similar study recently published [Li, Porter, and Johnson, Phys. Rev. Lett. 53, 1336 (1984)], a.c. Stark effects are found to be independent of pressure. However, we find that space-charge effects in ionization detectors can strongly influence observed line shape at high target gas density and high laser intensities.

Off-resonant core excitation is shown to be a highly sensitive spectroscopic method for the investigation of bound Rydberg states. Several applications are discussed, which include the precision measurement of effective quantum numbers without knowledge of the ionization limit and the ‘‘Rydberg filter,’’ a laser-based state-selective detection method for highly excited states.

Torsional-rotational levels of methanol are analyzed statistically. Nearest-neighbor-spacing distributions, considered separately for each symmetry as well as together, point towards a Poisson distribution. However, ${\Delta }_3$ statistics and the correlation coefficients for each of the symmetries show strong deviations from Poisson statistics.

Spectroscopy of photoelectrons produced by strontium atoms irradiated by strong picosecond laser pulses reveals excited states of ${\mathrm{Sr}}^{+}$ and, for the first time, electrons from stepwise double ionization. Different threshold behaviors are observed for these transitions.

We have observed optical phase-sensitive noise in homodyne detection of a cw light beam which has propagated through sodium vapor near the D lines. Although at present the minimum noise is at or above the vacuum-state quantum limit due to zero-point fluctuations, nevertheless its phase behavior is like that of a squeezed state. Our observations are consistent both with the predictions of the quantum-mechanical theory of degenerate four-wave mixing and the theory of multiatom resonance fluorescence in the forward direction.

We analyze a set of small-angle neutron scattering (SANS) data of micellar solutions using a re- scaled mean spherical approximation (MSA). The rescaling is shown to overcome the inaccuracy of MSA for the cases of dilute and strongly coupled solutions. The theory is in excellent agreement with SANS data for dilute as well as concentrated solutions. The counter-ion size effect is explicitly taken into account and the extracted renormalized micellar charges are reasonable but smaller, compared to that from the rescaled one-component macro-ion approximation.

The stationary spatial correlations of the director field of a nematic liquid crystal near the Freedericksz transition in a magnetic field with a time-dependent random component are studied by means of a stochastic dynamical model. A correlation length is shown to diverge at a shifted instability point.

Zinc-metal ‘‘trees’’ are grown two dimensionally from a line electrode by electrodeposition. The deposits, which consist of trees of all sizes, bear close resemblance to the patterns of two-dimensional (d=2) diffusion-limited deposition on a one-dimensional ($d_b$=1) substrate computer simulated first by Meakin. The fractal nature of the deposits is confirmed with the fractal dimension $d_f$(2,1)=0.70±0.06. The number of deposits (trees) of size s is also found to scale as $n_s$∼$s^{\mathrm{-}\tau }$ with τapeq21.54. These values are in excellent agreement with the theoretical values calculated for the case of the diffusion-limited deposition with d=2 and $d_b$=1 and with the large-scale computer-simulation results.

The first-order prewetting transition that has been predicted to occur at the interface between a fluid and a single wall is investigated for the case of a fluid confined between two walls. Prewetting is found to be in competition with capillary condensation of the undersaturated gas to a liquid. The results of density-functional calculations suggest that only for wall separation H>$H_{\mathrm{triple}\left(\mathrm{T}\right)}$ will prewetting occur at larger undersaturations than condensation. For H<$H_{\mathrm{triple}\left(\mathrm{T}\right)}$ coexistence between stable thick and thin films will not be observed. Since $H_{\mathrm{triple}}$ is typically 100 molecular diameters or more, this places restrictions on those adsorption experiments and computer simulations that search for prewetting.

Theoretical calculations are presented which account for the development of the step observed on the leading edge of the current pulse in a negative point-plane corona (Trichel pulse). The theory explains the step in terms of independent photon and ion secondary processes at the cathode. It is applied specifically to describe the shape of an experimentally determined corona current pulse from a 2-mm-diam negative point located 20 mm from a positive plane in oxygen at 6.67 kPa. The secondary-emission coefficients are determined to be ${\gamma }_p$=2×${10}^{\mathrm{-}4}$ (photon secondaries) and ${\gamma }_i$=0.12 (ion secondaries).

The evolution of the surface of two-dimensional Eden deposits grown in a strip of width L is related to the dynamics of a set of ‘‘normal modes’’ of wave number q. Monte Carlo simulations show striking similarities with critical phenomena. The amplitude squared of the modes relax in the long-time limit (t→∞) to a value S(q)∼$q^{\mathrm{-}2}$, and the relaxation towards the steady state is dominated by a relaxation time scaling as τ(q)∼$q^{\mathrm{-}z}$ with z=1.55±0.15. This implies that the surface width has the scaling from ξ(t,L)∼$L^{1/2}$G(t/$L^z$) with G(x)→G(∞)≠0 as x→∞ and G(x)∼$x^{1/\left(2z\right)}$ for x→0.