The stability of Taylor-Couette flow is studied as a function of the angular velocities of the inner and outer cylinders, ${\mathrm{\Omega }}_1$ and ${\mathrm{\Omega }}_2$=ε${\mathrm{\Omega }}_1$ cos(ωt), respectively. Contrary to the theoretical prediction, outer cylinder modulation stabilizes the flow. The critical Reynolds number, ${\mathrm{Re}}_{1\mathrm{c}}$, is a function of the dimensionless frequency, γ=(ω${\mathrm{d}}^2$/2ν${)}^{1/2}$, where d is the gap size and ν is the kinematic viscosity, and a monotonically increasing function of ε over the range examined: 0.3≤ε≤2.0. At larger ε stabilization is spectacular, ${\mathrm{Re}}_{1\mathrm{c}}$ reaching a value nearly double the value for stationary outer cylinder.

An electrode with a positive dc bias inserted into a Maxwellian plasma is observed to generate coherent high-frequency oscillations at the sheath-plasma antiresonance frequency (ω≲${\omega }_{\mathrm{pe}}$). The phenomenon is explained by a negative resistance associated with the finite electron transit time through the sheath. Harmonics of the fundamental are radiated as electromagnetic waves but are clearly shown not to be caused by electron orbital instabilities.

The anisotropic interfacial tension of a simple-cubic Ising model is calculated for the first time by use of extensive Monte Carlo studies with a tilted interface for a wide range of lattice size L and temperature T. The size dependence of the step free energy is used to probe the correlation length near the roughening transition and confirms the expected square-root T dependence. Finite-size scaling implies that the step free energy varies as 1/L in the rough phase, and thus the applicability of a capillary-wave Hamiltonian to describe interfaces of lattice models may be limited.

Using renormalization-group methods we have obtained the first analytical predictions for the winding-angle distribution of a self-avoiding walk, which can be used to describe the extent to which a long-chain polymer with short-range repulsive interaction wraps around a long straight rod. We find that moments of the winding angle scale asymptotically with the square root of the logarithm of the number of steps in the walk. This is consistent with the numerical results of Fisher, Privman, and Redner and differs qualitatively from the known behavior of the ordinary walk.

Tight-binding electronic band-structure calculations were combined with a free-energy expression from a statistical mechanical method called the cluster-variation method. The effective pair interactions used in the cluster-variation calculation were evaluated by the generalized perturbation method. Only d orbitals were included and the numbers of d electrons per atom were taken to be three for the pure A element and eight for the pure B. A phase diagram was constructed incorporating, for the first time, both fcc and bcc lattices and their simple-ordered superstructures. The calculated diagram agreed reasonably well with those determined empirically for Ti-Rh or Ti-Ir.

Nonperturbative contributions are shown to produce anomalously slow relaxation in dilute ferromagnets (or antiferromagnets), both in the paramagnetic and ‘‘Griffiths’’ phases. In the paramagnetic phase, the pseudoscaling form C(t)∼exp{-${\mathit{t}}^{\mathit{d}/(\mathit{d}+\mathit{z})}$f(t/${\xi }_{\mathit{p}}^{\mathit{d}+\mathit{z}}$)} is predicted for the spin autocorrelation function, with ${\xi }_{\mathit{p}}$ the correlation length of the nondilute system. In the Griffiths phase, C(t)∼exp{-A1nt${)}^{\mathit{d}/\left(\mathit{d}\mathrm{-}1\right)}$} and exp{-(Bt${)}^{1/2}$} are predicted for Ising Heisenberg systems, respectively, for t≫${\xi }_{\mathit{p}}^{\mathit{d}+\mathit{z}}$.

The heat capacity of ${\mathrm{La}}_{2\mathrm{-}\mathrm{x}}$${\mathrm{Ba}}_{\mathrm{x}}$${\mathrm{CuO}}_4$ was investigated between 0.8 and 10 K. The linear temperature term γT of the heat capacity is absent in the antiferromagnetic-ordered region of x≤0.02. γ increases abruptly from x=0.02 to x=0.04 where the system is still insulating at low temperature, and seems to saturate at the order of 5 mJ/mol ${\mathrm{K}}^2$ in the superconducting region of x≥0.05. The correlation between magnetic order and vanishing γT term and the existence of a finite γT term for Ba doping give support to the resonating-valence-bond picture.

Spin splitting of subband states in semiconductor heterostructures at B=0 is ascribed to the inversion asymmetry–induced bulk ${\mathrm{k}}^3$ term, which dominates in large-gap materials, and to the interface spin-orbit or Rashba term, which becomes important in narrow-gap systems. We show for AlGaAs/GaAs heterostructures how this finite spin splitting at B=0 evolves from the Zeeman splitting for B≠0 and predict a vanishing spin splitting at a finite -magnetic- field —, which depends on the electron concentration in the inversion layer.

We report observation of spin-pair excitations in ${\mathrm{Ba}}_2$${\mathrm{YCu}}_3$${\mathrm{O}}_{6+\mathrm{\delta }}$, with δ in the range 0.0–0.9. The frequency of the excitations, and hence the value of the exchange constant, J=950 ${\mathrm{cm}}^{\mathrm{-}1}$, is similar to that reported recently for (nonsuperconducting) ${\mathrm{La}}_2$${\mathrm{CuO}}_4$. The present observation of magnetic excitations in a superconducting material, and of their evolution as a function of δ, demonstrate a large influence of carrier concentration on the spin-fluctuation dynamics.

We present for the first time an exact decomposition procedure for the current spectral density in the presence of generation-recombination mechanisms. The correct microscopic analysis shows that the cross correlation between velocity and number fluctuations plays an essential role in the noise properties of semiconductors. This, in turn, yields a generalization of the Nyquist-Einstein relationship in the presence of an applied electric field when statistical generation and recombination mechanisms are active.

The energy of one and two holes in a Hubbard antiferromagnet for nonzero exchange, J, in the Ising limit is calculated within the Brinkman-Rice approximation. Only the p- and d-symmetry states bind with an energy of order J. The implications for superconductivity and antiferromagnetism of doped Hubbard insulators is discussed.

X-ray diffraction patterns of superconducting ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$ particles which have typical dimensions D<5 μm and do not levitate in an inhomogeneous magnetic field at T<$T_c$ show marked evidence of particle alignment when powder specimens are subjected to a 0.5-T field at T<$T_c$, but reveal random orientation for T>$T_c$. A majority of the particles align preferentially with their antiphase twin boundary planes and a-b planes along the applied field, but a minority align with their b axes along the field.

It is argued that, in fundamental string theories, as one traces the universe back in time a point is reached when the expansion rate is so fast that the rate of string creation due to quantum effects balances the dilution of the string density due to the expansion. One is therefore led into a phase of constant string density and an exponentially expanding universe. Fundamental strings therefore seem to lead naturally to inflation.

The lack of systematic band crossings at high spin in ${}_{}{}^{159}{}_{}{}^{}$,160Er and the selectivity of the single observed neutron band crossing at ħω>0.37 MeV in ${}_{}{}^{159}{}_{}{}^{}\mathrm{Er}$ (i) indicate that static neutron-pair correlations are too weak for the excitation of a pair of quasineutrons, and (ii) can be explained in terms of the expected spectrum of single-neutron states in the absence of static pair correlations.

The process of nuclear fission induced by nonlinear radiative coupling to atomic electrons is considered. For 248-nm radiation at an intensity of ≃${10}^{21}$ W/${\mathrm{cm}}^2$, highly relativistic currents are produced which can couple to the fission mode of nuclear decay. With irradiation for a time of ≃100 fs the results indicate a fission probability of ≃${10}^{\mathrm{-}5}$ for ${}_{{\mathrm{}}^2{\mathrm{}}_{92}^{38}}{}^{}{}_{}{}^{}\mathrm{U}$ nuclei located at the surface of a solid target, a value several orders of magnitude above the limit of detection.

A new method has been developed for determining the correlation of a product molecule with the partner product molecule formed in the same chemical event. Doppler-shift measurements are used in conjunction with level-specific detection of scattered photofragments by laser-induced fluorescence. The technique is demonstrated in the photodissociation of ${\mathrm{H}}_2$${\mathrm{O}}_2$ where Doppler profiles of OH absorption lines are used to determine the mean rotational state of the OH partner molecule coincidently formed in the same fragmentation process.

Seven-photon ionization of xenon is investigated for the first time with 100-fs, very intense (1.7×${10}^{14}$ W ${\mathrm{cm}}^{\mathrm{-}2}$) pulses. The electron spectra show a large number of peaks due to above-threshold ionization. Because of the short pulse duration, large threshold shifts (up to 5.6 eV) are directly observable in the electron spectra. The magnitude of the ionization signal reveals that the ionization probability is much lower than expected at such a high intensity. By a linking of the observed shift to the laser intensity, the latter can be obtained with high accuracy.

We report here the first experimental observation of nonsymmetrical N=2 solitonlike pulses. These solitons are produced by a passively mode-locked dye laser. The evolution of the pulse spectrum has been recorded and compared with theoretical predictions of the nonlinear Schrodinger equation.

Fully relativistic, two-center, coupled-channels calculations for atomic collisions of high-Z ions at arbitrary impact parameters have been performed for the first time. With the use of a set of twenty atomic Dirac basis states, detailed predictions for state-to-state excitation and charge-transfer cross sections in ${\mathrm{U}}^{92+}$+${\mathrm{U}}^{91+}$ collisions at 1 and 0.5 GeV/u are presented. It is shown that relativistically induced magnetic effects give rise to unusual long-range couplings which affect certain excitation cross sections.

Electron density perturbations produced by sawtooth oscillations in the interior of the Texas Experimental Tokamak are measured with a high-resolution, multichannel, far-infrared interferometer. Abel inversion over the sawtooth perturbation indicates a space-time evolution which is diffusive in character. The diffusion coefficient is determined from a density-pulse–propagation model and found to be appreciably larger than equilibrium values.