We show that cholesteric liquid crystals with a sufficiently short pitch, when put in an electric field, can exhibit undulations, the analog of mechanical undulations or of thermal undulations obtained when an external pressure or a temperature gradient is applied, respectively. As the pitch is increased a competition between the electric-field-induced undulations and the electrohydrodynamic instability arises. We give numerical estimates for both instabilities in this system, which represents another example of a competition between a constrained pattern-forming equilibrium system (electric-field-induced undulations) and a nonequilibrium (electrohydrodynamic) instability.

A recent theory of the initial density dependences of both viscosity and thermal conductivity has been extended to include lower reduced temperatures. New data on the second viscosity virial coefficients of some organic vapors are found to be in substantial agreement with the theory even at the lowest temperatures. We present in tabular form the numerical values for both transport virial coefficients in the reduced temperature range 0.5≤$T^{\mathrm{*}}$≤100 and include values for the constituent two-monomer, three-monomer, and monomer-dimer contributions. A brief discussion of the theoretical approach and calculational methods is also given.

It is pointed out that the spin-1 Hamiltonian H=-J ${\mathcal{J}}_{〈\mathrm{ij}〉}$ $S_i$$S_j$-K ${\mathcal{J}}_{〈\mathrm{ij}〉}$ $S_i^2$$S_j^2$-C ${\mathcal{J}}_{〈\mathrm{ij}〉}$ ($S_i^2$$S_j$+$S_i$$S_J^2$)+Δ ${\mathcal{J}}_i$ $S_i^2$ with staggered field C represents the Widom-type lattice mixture of bifunctional molecules ab and AA with finite interactions. The structure of the mean-field phase behavior of the model micellar solution is provided partially by that of the symmetrical section of Griffiths’s three-component model.

We present experimental and theoretical studies of the $m_l$=1 photoionization channel of H(n=2,$m_l$=0) blue and red parabolic states in strong external electric fields in the energy region between the classical ionization threshold at E=-2 √F and the isolated-atom photoionization threshold at E=0. Our results indicate that the ionization from the rapidly ionizing channels is concentrated away from but between the two thresholds. We also find that the fractions of the nuclear charge $Z_1$=0, (1/2, and 1 define two regions that classify the properties of the states. These results are in contrast to our previous results for the $m_l$=0 channels where the ionization is concentrated at the two thresholds and the fractions $Z_1$=0, (1/4, (1/2, (3/4, and 1 define four quarters that classify the properties of these channels.

For nondilation analytic potentials the applicability of the complex coordinate method (CCM) depends on the representation. In particular, it was shown by Colbert, Mashorfer, and Certain that the CCM fails for the Natanzon potential. Analytic expressions for the resonances for this problem were given by Ginocchio and by Alhassid, Iachello, and Levine. It is shown here that the resonances can be obtained by an analytic transformation rather than analytic dilation of the potential.

The integral-transform (generator-coordinate) method has been applied to calculate the binding energies of the lowest S states of a set of muonic molecules. The wave functions obtained are both compact and accurate, as indicated by energy eigenvalues. The calculated values of the energies of ddμ, ttμ, and tt${\mu }^{\mathrm{*}}$ are the lowest reported so far, and they lead to a new estimation of the corresponding asymptotic values for a saturated basis set.

In a cw laser spectroscopic experiment using a collimated atomic beam of barium we have excited the 5dnf J=4 and 5 autoionizing series. In transitions from the metastable 5$d^2$ ${\mathrm{}}^1$$G_4$ level inherently narrow autoionization linewidths, down to a Doppler-limited value of 10 MHz, have been observed. Assignment of all observed 5dnf transitions has been made.

The charge-state distribution of neon recoil ions produced by ion-atom collisions has been investigated with ${\mathrm{Ni}}^{\mathrm{p}+}$, ${\mathrm{Cu}}^{\mathrm{p}+}$, and ${\mathrm{N}}^{2+}$ projectiles. The dependence of recoil-ion production on the ionization state of the primary ions has been investigated for two projectile energies in an intermediate velocity range not previously studied. Absolute net-ionization and charge-specific cross sections have been determined and are compared with other experiments and with theoretical predictions.

In double ionization at very high collision velocities Becker has pointed out that so-called direct mechanism obeys the dipole selection rule while the rearrangement mechanism is a monopole transition, and since s and p waves cannot interfere in total cross sections, interference between these mechanisms is forbidden. It is shown here that interference is possible due to dipole-forbidden contributions to the direct mechanism or rearrangement process.

Using an analytically solvable model we investigate the dependence of the above-threshold electron ejection spectra on the angular momentum of the initial state, on the polarization, and on the intensity of the laser field.

The time dependence of the vibrational angular momentum in the resonant Henon-Heiles Hamiltonian is approximated in closed form using Birkhoff-Gustavson perturbation theory. An energy threshold is found to separate two drastically differing regimes.

With reference to recent numerical calculations, it is argued that the classical exponent describing the singularity close to a surface spinodal is independent of the nature of the intermolecular forces, and different from the force-dependent exponents associated with complete wetting.

It is shown that a hot magnetized plasma can support a new short-wavelength aperiodic electrostatic flute mode. In an equilibrium plasma, the electric field spectrum of the latter can cause the cross-field electron transport which is comparable to that arising from thermally excited convective cells.

As a novel application of the hypervirial theorem, a new recursion relation for the calculation of any operator two-center integral, in the most general case of arbitrary potential eigenfunctions, is presented. The proposed formula, in addition to reducing properly to the recurrence relation for the calculation of one-center matrix elements that come from the second hypervirial theorem, allows us to obtain a generalization of the Ta-You Wu equation for the calculation of Franck-Condon factors.

We analyze the recent work by Halsey et al. [Phys. Rev. A 33, 1141 (1986)] on the characterization of certain singular measures in dynamical systems in terms of algebraic singularities of strength α and their dimensions f(α). Analytic study of the two-scale Cantor set suggests that these singularities are only virtual in nature and f(α), which has previously been interpreted as the fractal dimension for the subset of singularities of strength α, is not so. Modified interpretation of f(α) is provided.

We report the first observation of Autler-Townes splitting in multiphoton ionization of molecules and its application to measure vibronic transition moments between excited electronic states. The effect was observed in the two-color, four-photon ionization of ${\mathrm{H}}_2$ via the resonant levels $E$, $F{{}_{}{}^1{}_{}{}^{}\Sigma _g^{}{}_{}{}^{}}^{+}$, $v=6\mathrm{}$, $J=1\mathrm{}$ and $D{}_{}{}^1{}_{}{}^{}\Pi _u^{}{}_{}{}^{}$, $v=2\mathrm{}$, $J=2\mathrm{}$. Calculations give good fits to the observed spectra. They yield a vibronic transition moment of 2.0±0.5 a.u. between the above excited states, in agreement with the ab initio value 1.97 a.u. calculated by Huo and Jaffe.

The energy spectra of electrons produced in strong-field above-threshold ionization are shown to be shifted and broadened when very short laser pulses are used. The shifts crucially depend on the ratio of the pulse duration to the lapse of time spent by the electron to escape from the focal spot. Red shifts up to 0.9 eV were measured with 30-ps pulses at 1064 nm and found to vary linearly with the light intensity. A theoretical model, based on a classical description of the electron behavior in strong fields, accounts for most of the experimental data.

We report on an interferometric frequency measurement of a ${}_{}{}^{130}{}_{}{}^{}\mathrm{Te}_2^{}{}_{}{}^{}$ absorption line which can be used as a reference in Doppler-free two-photon spectroscopy of the muonium $1S-2S$ transition. The frequency of this 488-nm ${}_{}{}^{130}{}_{}{}^{}\mathrm{Te}_2^{}{}_{}{}^{}$ transition is determined with a precision of 1 part in ${10}^9$ by comparison with a previously calibrated ${}_{}{}^{130}{}_{}{}^{}\mathrm{Te}_2^{}{}_{}{}^{}$ line near 486 nm.

In this paper we describe a method for calculating the nonlinear shear viscosity at arbitrarily small strain rates. Although these calculations are consistent with previously observed enhanced long-time tail behavior at higher strain rates, they also show that in small periodic systems classical Burnett behavior is the ultimate small-field nonlinear response.

We study the selection of the shape and growth velocity of three-dimensional dendritic crystals in cubically anisotropic materials. We demonstrate that aside from minor additional complexities due to the lack of axisymmetry, the recently discovered mechanism of "microscopic solvability" can be extended to these systems and used to find a unique needle-crystal solution of the equations of thermal diffusion-controlled solidification. For 1% crystal anisotropy our calculation yields a dimensionless growth rate ${\gamma }_0={\sigma }^{*}{p}^2$, for Peclet number $p$, with ${\sigma }^{*}=0.0195\mathrm{}$.