We have performed polarized Bragg-scattering measurements from the cholesteric blue phases (BP) of a mixture of cholesteryl oleyl carbonate (COC) and 4-cyano-4’-(n-hexyl)biphenyl (6CB). Our data, which are reported in the form of a temperature-dependent Mueller scattering matrix, confirm the previous results obtained in a more complicated mixture by Flack, Crooker, and Svoboda. The scattering is dominated, in both BP I and BP II, by the m=-2 order-parameter coefficient, and we observe no change in the Mueller matrix at the BP I–BP II transition despite a discontinuous step in the Bragg wavelength. The structural implications of the results are discussed within the context of the theory of Grebel, Hornreich, and Shtrikman.

An expression for the ponderomotive Hamiltonian for a relativistic particle gyrating in a quasistatic magnetic field and in the presence of two interacting electromagnetic waves is derived. The frequencies of the waves are of the order of the gyrofrequency meaning that an average is performed over the gyration and the rapid oscillations of the waves leading to the ponderomotive Hamiltonian which contains only quasistatic and slow oscillatory terms. The derivation is systematic and allows for arbitrary kρ, v/c, $E_{\mathrm{para}}$/$E_{\perp }$, polarizations, and for slowly growing and spatially modulated waves. Nonuniformities in the background magnetic and electric fields are also included.

We investigate the diffraction (Heisenberg) as well as the symmetry (Pauli) correction to the high-frequency component of the thermal microfield in a dense quasiclassical electron plasma. We consider both neutral and singly charged points. The diffraction effects are considered in a much larger ($n_e$,$T_e$) domain than previously. The symmetry correction leads to a larger perturbation to the microfield distribution H(β), with a peak markedly enhanced and shifted toward smaller β (=E/$E_0$) values. Numerical data are supplied in tables and figures for β up to 100.

The role played by thermally generated positive molecular ions in the density dependence of the electronic properties of hot, dense fluids is examined. It is shown that the cohesion within such ions dominates the density dependence of the activation energy for electronic conduction in fluids such as Cs, Rb, and Hg. The model is shown to account for the observed electrical conductivity in the insulating regime. Also, the evolution to semimetallic behavior with increasing atomic density is obtained correctly.

The mode-coupling theory of the glass transition recently presented by Leutheusser is generalized so that some of the important wave-number dependence neglected in his theory is taken into account. As a consequence the correlation functions which appear in the theory presented here involve a continuous range of relaxation times rather than the single relaxation time obtained by Leutheusser. However, the important exponents describing the divergence in the shear viscosity and the vanishing of the self-diffusion coefficient are very similar in the two theories.

The relation between different thermodynamic ensembles is studied, the finiteness of the systems being explicitly taken into account. Especially, equilibrium fluctuations of thermodynamic parameters (temperature, pressure, chemical potential) are considered. Several discrepancies occur in the literature. Interpreting the pressure in a concrete way makes it possible to evaluate the solutions proposed in the literature. These considerations are then applied to the special case of computer experiments.

The propagation of electromagnetic waves in weakly nonlinear, relativistic electron-positron plasmas is investigated. It is shown that the resulting waves can have a solitonic envelope, both for linearly and circularly polarized waves. A dispersion relation is derived, and the results for the linearly polarized case are used to check a recent suggestion of possible self-modulational formation of pulsar microstructure.

The chemical potential of a fluid can be determined in a Monte Carlo simulation by gradually turning on or off the interaction of one particle with the other particles. This method, which can be employed at densities where a direct use of the Widom formula is impractical, has been tested on a two-dimensional fluid of particles with a Lennard-Jones pair interaction.

Molecular-dynamics simulations of dense Lennard-Jones gases at 297 K have been carried out for number density (a) n=0.0138 Å ${}_{}{}^{\mathrm{-}3}{}_{}{}^{}$ and (b) n=0.0106 Å ${}_{}{}^{\mathrm{-}3}{}_{}{}^{}$ to obtain the static pair correlation function g(r) and the second and fourth frequency sum rules of longitudinal and transverse current correlation functions. The results for the fourth frequency sum rule are compared with those obtained using the superposition approximation (SA) for the static triplet correlation function $g_3$(r→,r→ ’) appearing in the molecular expression of the sum rule. It is found that errors involved due to the use of SA in the calculation of sum rules are not of much significance. The triplet contribution is found to be the largest near the triple point for wave number q<(3/4)$q_0$, where $q_0$ is the position of the first peak in S(q), and decreases at lower densities.

We have used the frequency-moment sum rules and a viscoelastic model for the relaxation kernels appearing in the continued-fraction representation of the generalized Langevin equation to calculate the dynamical structure factor of dense Lennard-Jones gases. Shear viscosity and diffusion coefficients have also been calculated. These results when compared with molecular-dynamics data and neutron scattering experiments show an overall good agreement for both of the density states considered.

The density-functional theory of plasmas is used to investigate the changes in the electronic structure of an iron atom immersed in plasmas of various atomic numbers, but all having the same average electron density and temperature. We have calculated the radial distribution functions for ions and electrons around the iron atom and also the Kohn-Sham eigenfunctions, phase shifts, etc., for the electrons. The increase of positive charge around the Fe atom when the plasma ions become lighter induces more bound states and increases electronic binding. The resulting changes in photoeffect cross sections, free-free absorption coefficient, and average opacities are calculated in the case of H, He, Be, C, Ne, and Fe plasmas.

The diffusion coefficient D has been measured for ${}_{}{}^{133}{}_{}{}^{}\mathrm{Xe}$ atoms diffusing through 12 liquid n-alkanes, n-pentane through n-hexadecane, at 20.0 °C. The dependence of D (${\mathrm{cm}}^2$/sec) on the viscosity η (P) was found to be D=(1.26±0.06)×${10}^{\mathrm{-}6}$${\eta }^{\mathrm{-}0}$ ${}_{}{}^{686\pm 0.011}{}_{}{}^{}$ where ${\eta }_{20.0}$ ${}_{°\mathrm{C}}{}^{}{}_{}{}^{}$ varies monotonically in these solvents from 0.235 cP (for n-${\mathrm{C}}_5$${\mathrm{H}}_{12}$) to 3.48 cP (for n-${\mathrm{C}}_{16}$${\mathrm{H}}_{34}$). The observation that D is proportional to η to a negative power of magnitude near (2/3) is in agreement with other work on several different solute-solvent systems. Some ramifications of this dependence are suggested.

Our previous studies of the growing interface of two-dimensional clusters produced by the Eden process and by diffusion-limited aggregation are expanded and extended to d=3 dimension. Growth is described in terms of the motion of an active zone defined as the region of the clusters where the probability of collecting new particles is nonzero. If the description is limited to spherically averaged properties then this active region can be characterized by the probability P(r,N)dr that the Nth particle is deposited a distance r from the center of mass of the existing cluster. As in our previous Monte Carlo simulations of the d=X2 case, we find that, for large N, P(r,N)=(√2π ${\xi }_N$${)}^{\mathrm{-}1}$exp[-(r-r${¯}_N$${)}^2$/ 2${\xi }_N^2$] with r${¯}_N$∼$N^{\nu }$∼$N^{1/D}$, where D is the fractal dimension of the infinite cluster and ${\xi }_N$∼$N^{\nu ¯}$ where ν¯<ν, indicating the presence of a second diverging length in these growth processes. We also study the center-of-mass motion of growing clusters. We find that one has to be especially careful with simulations of diffusion-limited aggregation because discarding particles which wander too far away from the cluster generates an effective force on the center of mass, resulting in a motion which can obscure the intrinsic structure of the clusters.

The classical theory of thermal noise of mechanical systems and the effects of feedback is reinvestigated. Previous developments which set a limit to the noise reduction by feedback when a given measuring time is assumed have ignored the situation where the system is acting as an unchanging mechanical reference. A precision rotor clock is one such system. The present work uses the galvanometer as the general model and includes this situation. It explicates the nature of the limit when it exists by treating it without assuming any particular measuring optimization method.

The hypothesis is tested that ground-state potential-energy curves for neutral, bound diatomic molecules are universal scaled versions of one another in the sense of Ferrante, Smith, and Rose [Phys. Rev. Lett. 50, 1385 (1983)]. Let ε=[E(R)-E(∞)]/$D_e$ and s=(R-$R_e$)/$R_e$ be reduced energy and displacement variables, where $R_e$ and $D_e$ are the equilibrium distance and dissociation energy. The hypothesis is that ε=F(κs), where F(t) is a universal function and κ is a species-dependent parameter. By analysis of the data for 150 molecules the hypothesis is shown to be only moderately well satisfied if F(t) is taken to be a different characteristic function for each pair of columns in the Periodic Table, less well satisfied with F(t) completely universal. If F(t) is taken to be a single-parameter function, a much improved fit of almost all data is obtained. The second derivative at t=0, F’’(0), may be taken equal to 2 without loss of generality. Values of the third and fourth derivatives at t=0, F’’’(0) and $F^{\mathrm{iv}\mathrm{}\left(0\right)\mathrm{}}$, are given for the various cases. The standard formula for κ is ($k_e$$R_e^2$/2$D_e$${)}^{1/2}$.

State-changing collisions of Ca(4s6s ${}^1$$S_0$) with the rare gases are studied by pulsed laser excitation and time- and wavelength-resolved detection. The total depletion rates of the 4s6s ${}^1$$S_0$ state with different rare gases vary by over a factor 10, with the lighter rare gases being markedly more efficient than the heavier ones. Relative branching ratios to the specific near-resonant, energy-transfer product states, 4p4p ${}^1$$D_2$ (ΔE=-29 ${\mathrm{cm}}^{\mathrm{-}1}$), 3d4p ${}^1$$F_3$ (ΔE=152 ${\mathrm{cm}}^{\mathrm{-}1}$), and 4s6s ${}^3$$S_1$ (ΔE=216 ${\mathrm{cm}}^{\mathrm{-}1}$), are measured for ${}_{}{}^3{}_{}{}^{}\mathrm{He}$, ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, Ne, and Xe. Transfer to the ${}_{}{}^1{}_{}{}^{}\mathrm{D}_2^{}{}_{}{}^{}$ state is always the major relaxation pathway. The rate constant for ${}_{}{}^3{}_{}{}^{}\mathrm{S}_1^{}{}_{}{}^{}$ production is immeasurably small, implying a small spin-orbit matrix element for curve crossing that leads to a spin change. The results for 4p4p ${}^1$$D_2$ production are compared with simple theoretical calculations based on established models for near-resonant energy transfer between states which are coupled at large internuclear distance. These models successfully explain the dominant transfer to the 4p4p ${}^1$$D_2$ state and the trends with rare gas, which are attributed largely to enhancement of the near-resonant-transfer process with increasing velocity. The effects of wave-function mixing in the isolated atom (e.g., spin mixing) on the general outcome of state-changing collisions in two-electron atoms are discussed. Two-electron atoms offer numerous possibilities for further testing of theories of near-resonant energy transfer.

The perturbative variational method is used to analyze electron excitation. We formulate a time-dependent variational theory for the Dirac Hamiltonian. Fluctuations in the variation parameters and deviation from the mean variational field are taken into account. The calculated positron spectrum compares well with experiment.

Integrated moments of the transition matrix elements for proton-electron Coulomb collisions in strong (B≳${10}^{12}$ G) magnetic fields are calculated numerically. Calculations are carried out for various energies and incident angles. Excitations of the electrons to the first excited Landau level are included. Analytic results are also presented for comparison. These calculations should be applicable to detailed models for the x-ray emission from accreting, magnetized neutron stars.

M-shell x-ray production cross sections in thick targets of Ir, Pt, and Pb have been measured for ${}_{}{}^4{}_{}{}^{}\mathrm{He}_{}^{+}{}_{}{}^{}$ ions of energy from 0.4 to 2.2 MeV in steps of 0.1 MeV. The cross sections are compared with plane-wave Born approximation (PWBA) calculations and with perturbed-stationary-state calculations with energy-loss, Coulomb deflection, and relativistic corrections (ECPSSR). The present measurements, in general, agree well with the PWBA predictions at all energies, but agree with the ECPSSR theory only at projectile energies ≥1.5 MeV. The M-subshell x-ray cross sections are also calculated by a nonlinear (iterative) least-squares-fitting algorithm by extracting the relative line intensities of the experimentally observed spectra obtained with a Si(Li) detector. The subshell cross sections are compared with the scaled cross sections based on PWBA calculations. Good agreement is obtained for the case of $M_1$, $M_2$, and $M_4$, and a larger deviation is found for $M_3$ and $M_5$. The double nodal structure of the 3s-electron wave functions is confirmed, and the single inflection associated with the 3$p_{3/2}$-electron wave functions is not clearly visible in our data. The M-subshell cross-section ratios for $M_1$/($M_2$+$M_3$), $M_1$/($M_4$+$M_5$), and ($M_2$+$M_3$)/($M_4$+$M_5$) are also calcu- lated, compared with the PWBA and ECPSSR theories, and discussed.

Results are presented of five-state close-coupling and distorted-wave calculations for electron-impact excitation of Li ii from the ground state to the four n=2 states (2 ${}^3$S, 2 ${}^1$S, 2 ${}^3$$P^o$, 2 ${}^1$$P^o$) for energies below the ionization threshold. Sensitivity of the results to scattering approximation, target wave functions, and resonance effects is examined. The spin-allowed transitions are found to be much more sensitive to scattering approximation and to the choice of target wave functions than are the spin-forbidden transitions. Resonances contribute noticeably to both spin-allowed and spin-forbidden transitions, but rather more strongly to the latter. Good quantitative agreement is obtained with measurements of the 1 ${}^1$S→2 ${}^3$$P^o$ cross section, and of the positions of the lowest 1s3l3l’ resonances.