Polarized Bragg-scattering measurements using visible light have been used to determine the structure of the blue phases of cholesteric liquid crystals. Observations of the third Bragg peak (in order of decreasing wavelength) in CB15-E9 mixtures [chiral 4-cyano-4′-(2-methyl)butylbiphenyl (CB15) and a proprietary mixture of nematic biphenyl compounds (E9) from British Drug House] reveal that, for these mixtures, blue phase II has a body-centered-cubic structure.

We have derived an exact analytic solution for the electric field and time dependence of the survival fraction in the one-dimensional trapping problem. The intermediate- and long-time behavior is discussed below and above a threshold region of the electric field strength. The mean decay rate is given as a function of trap concentration and electric field strength.

Proposed here is an exactly soluble model for the field-free motion of a quantum particle interacting with a heat bath. The heat-bath interaction includes a fluctuating random force and a frictional force of Langevin type. The momentum and position distributions obtained in the model have a close relation to the corresponding solutions of the Fokker-Planck equation of a free classical particle.

The scaling variational method recently discussed by Fernández and Castro is given a formulation based on the dynamical group SO(2,1).

I discuss the flow of excitation probability along a multistate chain of resonant excitations as driven by coherent photoexcitation, in particular the gated interruption of this probability flow caused by a strongly coupled side branch. If the side branch is itself a chain, not a single transition, then flow inhibition occurs if the number of branch transitions is odd, but no inhibition occurs if the number is even. The inhibition provides a limiting bound on the intensity of amplified stimulated emission.

Recently Cardimona and Stroud emphasized that, when the energy levels of an atom are degenerate or nearly so, there can exist a strong radiative interaction between different spontaneous transitions of the atom. This interaction is described by the generalized damping terms and generalized frequency-shift terms in the equation of motion for the atomic density matrix. We here point out that the generalized damping terms can play an important role in the absence of degeneracy for systems other than atoms, and cite the harmonic oscillator as an example. Specifically, we show that these terms are needed for a proper classical limit of radiation damping, and that a small anharmonicity can have a very large effect on the radiative decay rate of the oscillator's amplitude.

Ab initio calculations of cross sections for simultaneous rotational and vibrational excitation of HCl by low-energy electrons have been made in the multipole-extracted adiabatic-nuclei approximation. These calculations employed a free-electron-gas model of the exchange interaction, and represent the first application of a new parameter-free model of the correlation-polarization interaction to vibrational excitation. The cross sections increase by an order of magnitude with the inclusion of this interaction, which is much more important for vibrationally inelastic than elastic collisions.

Hartree-Fock calculations of the photoionization of the Cs $6d$ excited-state cross section are presented which quantitatively revise previous central-field estimates and bring the results into agreement with experiment.

Using a high-power dye laser, the $2S_{\frac{1}{2}}-2\mathrm{}{P}_{\frac{3}{2}}$ transition [$E=2.895\mathrm{}50\left(61\right)\mathrm{}$ eV] was induced in a metastable ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}_{}^{15+}{}_{}{}^{}$ beam, leading to a deduced value of the Lamb shift of 104.22(66) × ${10}^{-3\mathrm{}}$ eV or 25.20(16) THz.

Quasibound NaNe molecules are shown to contribute strongly to the spin relaxation of Na optically pumped in the presence of Ne. Molecules formed in two-body (tunneling) collisions are distinguished from those formed in three-body collisions. The cross section for the collisional breakup of the quasibound complexes has been measured to be 3 ′ ${10}^{-13\mathrm{}}$ ${\mathrm{cm}}^2$.

Molecular-dynamics simulations of dense Lennard-Jones-like fluids show new evidence for the existence of sound waves with wavelengths comparable to the size of the atoms. The sound frequency vanishes for a small but finite region of wavelengths as predicted by kinetic theory, and appears to depend mainly on the repulsive part of the interaction potential.

By use of a suitable target geometry, self-absorption of x-ray lines has been evidenced and measured in a laser-created aluminum plasma. Solution of the radiative-transfer equation allows inference of optical depth and electron density from plasma-expansion data.

We consider the structure and fractal dimension of aggregates formed by cluster-cluster diffusional encounters. Both the fractal dimensions and symmetry properties of these aggregates are found to differ significantly from those found in the case of a single aggregating cluster. We find for the fractal dimension $D\left(d\right)=\frac{d(4d+3)\mathrm{}}{\mathrm{}(9d-2)\mathrm{}}$ for $d<\mathrm{}{d}_c=8\mathrm{}$ and $D\left(d\right)=\frac{d}{2}$ for $d>\mathrm{}{d}_c$.