We report direct quantitative measurements of the light-induced drift velocity in Na–noble-gas mixtures under well-defined conditions. Results are in excellent agreement with predictions from a realistic numerical model incorporating the multilevel structure of the Na atom. The effect of optical hyperfine pumping on light-induced drift is investigated. Limiting values for the drift velocity are predicted.

A simple Fokker-Planck model of rf heating is presented which includes quasilinear velocity diffusion, collisions, and particle transport by radial collisional diffusion and direct-drift losses. In addition, the influence of the incident-wave electric-field spatial profile on the velocity-space structure of the quasilinear operator and, in turn, the effect of the nonlinear distribution function on the wave field are included. Application is made to electron-cyclotron heating in the Elmo bumpy torus.

Recent experimental and theoretical developments, including an electric field diagnostic based on optogalvanic detection of Rydberg atoms, an analytic treatment of ion transport in the cathode fall, and a null collision Monte Carlo technique, are combined to determine the current balance at the surface of a cold cathode in a He glow discharge. The ratio of the ion current to the electron current is measured and calculated over a range of current densities from a near normal to a highly abnormal glow discharge.

Growth rates of the Rayleigh-Taylor instability in foils accelerated with a laser beam smoothed by induced spatial incoherence were measured and compared with hydrodynamic code simulations. Modes with 150- and 100-μm wavelengths grew at predicted rates. However, no growth was experimentally observed at a 50-μm wavelength. Code simulations suggest that induced spatial incoherence can influence the 50-μm Rayleigh-Taylor mode by delaying the start of its growth.

We consider a system of randomly cross-linked, interacting macromolecules, within the framework of replica field theory. We find that above a critical number of cross links, translational and replica symmetry are simultaneously broken, thus showing that the system is an equilibrium amorphous solid, with many pure phases unrelated by global symmetry. We argue that each symmetry-unrelated pure phase describes a separate realization of the topology of the network.

We have observed that ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ atoms, besides adsorbing onto the surface of graphite, can penetrate through the surface even at temperatures well below 1 K. The penetration process is well described by the tunneling model first proposed to explain the anomalous properties of glasses.

We have grown epitaxial films of the ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$ compound on ${\mathrm{SrTiO}}_3$ substrates. The superconducting critical current in these films at 77 K is in excess of ${10}^5$ A/${\mathrm{cm}}^2$ and at 4.2 K in excess of ${10}^6$ A/${\mathrm{cm}}^2$.

We report direct observation of the anisotropic electronic behavior of the high-temperature superconductor ${\mathrm{Y}}_1$${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$. Critical-field and critical-current measurements performed on single crystals show anisotropies of 10 and greater. Critical supercurrent densities in favorable directions in single crystals are 3×${10}^6$ A/${\mathrm{cm}}^2$ in low fields at 4.5 K and remain above ${10}^6$ A/${\mathrm{cm}}^2$ to beyond 40 kG.

An analysis of the resistivity above ${\mathrm{T}}_{\mathrm{c}}$ in the oxide superconductors shows that the inelastic-scattering rate is several times kT. This inelastic scattering yields pair breaking which suppresses ${\mathrm{T}}_{\mathrm{c}}$ relative to the energy gap. The large energy scale in the problem suggests an electronic pairing mechanism, which we believe leads to d-wave pairing. The inelastic scattering has contributions from electron-phonon and from electron-electron scattering in a two-dimensional square lattice near half filling. In the latter case, the pair breaking can be reduced in a more three-dimensional structure.

The temperature and magnetic field dependence of the magnetization and susceptibility of single-crystal decamethylferrocenium tetracyanoethenide (DMeFc TCNE) demonstrate that this material is the first molecular compound with a ferromagnetic ground state. A spontaneous magnetization is observed for T<4.8 K. The results are consistent with a crossover from a dominance of one-dimensional ferromagnetic exchange interaction to a 3D mean-field-like interaction at ∼16 K. The critical exponents are in accord with mean-field behavior. A generalized Hubbard model is proposed to account for the unusual ferromagnetic exchange interactions in this system.

Nuclear Bragg scattering of synchrotron radiation from isotopically enriched ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}_2^{}{}_{}{}^{}$${\mathrm{O}}_3$ has been observed at a signal-to-noise ratio of 100:1 without delayed-coincidence techniques. The use of a high-resolution premonochromator providing a 5-meV energy spread and 0.4’’ collimation allows for high-resolution studies of dynamical diffraction effects. In particular, the observed intensity of the pure nuclear (7,7,7) reflection implies a dramatic decrease of the effective lifetime due to coherent scattering.

In order to compare linear spin-wave theory with the effects of nonlinear excitations in spin-1/2 Ising-Heisenberg ferromagnetic chains, we have studied the differential susceptibility of (${\mathrm{C}}_6$${\mathrm{H}}_{11}$${\mathrm{NH}}_3$)${\mathrm{CuCl}}_3$ in the region 4.2 K<T<40 K, in fields of 0, 1, 2, and 3 T. The data are analyzed in terms of linear spin-wave theory and a nonlinear theory which includes bound-magnon effects. Our analysis shows that linear spin-wave theory cannot describe the data, and that the susceptibility is dominated by the bound-magnon contribution. The correspondence between bound magnons and solitons is discussed.

It is shown that intra-atomic Coulomb correlation causes the f electrons in heavy-fermion materials to propagate like polarons in insulators and semiconductors. The effective mass of the quasiparticles is enhanced, and at finite temperatures the quasiparticles are damped so that the polaron effect may be a contributing factor to the crossover from coherent behavior at low temperatures to single-site behavior at high temperatures.

Transient photoconductivity experiments have been carried out on single crystals of polydiacetylene-(bis p-toluene sulfonate), PDA-TS. The low–electric-field photocurrent decay consists of a temperature-independent fast (picosecond) initial component and a longer-time (nanosecond) component with magnitude that is strongly temperature dependent. Using very small spacings between electrodes on the sample, we have succeeded in achieving sweepout for the longer-lived carriers; the data yield a mobility of ≊5 ${\mathrm{cm}}^2$/V⋅s at room temperature in the nanosecond regime. These results demonstrate that the Onsager geminate recombination model, previously used extensively for the polydiacetylenes, is not applicable to PDA-TS.

Electron-capture spectroscopy is used to study the long-ranged surface ferromagnetic order of Gd in the neighborhood of the bulk Curie temperature ${\mathrm{T}}_{\mathrm{C}{}^{\mathrm{bulk}}}$ at which, unlike bulk ferromagnetic order, it does not vanish. The surface magnetization, together with its first temperature derivative, is found to be a continuous function of temperature at ${\mathrm{T}}_{\mathrm{C}{}^{\mathrm{bulk}}}$ and, as temperature is varied, the surface magnetization is found to depart linearly from the nonzero value it assumes at ${\mathrm{T}}_{\mathrm{C}{}^{\mathrm{bulk}}}$, with critical exponents ${\mathrm{x}}_{+}$=1.00±0.03 (T>${\mathrm{T}}_{\mathrm{C}{}^{\mathrm{bulk}}}$) and ${\mathrm{x}}_{\mathrm{-}}$=1.00 ±0.01 (T<${\mathrm{T}}_{\mathrm{C}{}^{\mathrm{bulk}}}$). These findings are discussed in the light of recent theoretical studies.

Cahn’s scheme for simulating the morphology of isotropic spinodal decomposition is adapted to a mathematical model of bicontinuous partitioning of space by interfacial pairs that may be useful for problems of microdispersed and microporous systems distinguished by a morphology with a well defined length scale, including surfactant films in microemulsions and coatings in porous media. Real-space and scattering properties are analyzed, and qualitatively the model accounts for the principal features of recent contrast variation small-angle neutron-scattering experiments on Winsor III type microemulsions.

We analyzed the neutrino burst from the supernova 1987A detected by the Kamiokande II collaboration, and obtained the following results. (1) The total energy of antineutrinos is about 4.8×${10}^{52}$ ergs, which is consistent with theoretical predictions. If we take Wilson’s group simulation as the theoretical model, it corresponds to the models with the progenitor mass 15$M_{\odot }$. (2) The first two neutrino events cannot correspond to the predicted initial neutronization burst from the energetics and the duration time. (3) The duration time of the burst suggests that the electron-neutrino mass <26 eV. We also discussed implications on the explosion mechanism of the supernova.

We investigate the correspondence between a ${\mathrm{Z}}_2$ orbifold string and a torus string model which have the same vacuum amplitudes when they take particular radii. We show that ground states of the twisted sector of ${\mathrm{Z}}_2$ orbifold can be easily described by the torus string. In our formalism, we obtain the same amplitudes as those of Hamidi and Vafa, and of Dixon, Friedan, Martinec, and Shenker.

We present results for the low-lying energies of pure SU(2) gauge theory in a cubic volume up to a size of five inverse glueball masses, based on an analytic-variational continuum calculation. We observe as lowest mass a ${\mathrm{T}}_2$${(2\mathrm{}}^{+}$) state, roughly half the mass of the almost degenerate ${\mathrm{A}}_1$${(0\mathrm{}}^{+}$) and E${(2\mathrm{}}^{+}$) states. The ${\mathrm{A}}_1$${(0\mathrm{}}^{\mathrm{-}}$) state shows a pronounced volume dependence. There is fair agreement with existing finite-volume Monte Carlo results.

Finite-temperature behavior of quantum chromodynamics with two light dynamical flavors is studied by Langevin simulation on a $8^3$×4 lattice with the Kogut-Susskind quark action. It is found that the chiral transition strengthens as the quark mass $m_q$ decreases towards zero, changing from a continuous crossover at $m_q$a=0.2 to a first-order transition at $m_q$a=0.1. The critical coupling at $m_q$=0 is estimated to be ${\beta }_c$=6/$g_c^2$=5.29–5.32, and the physical scale of $T_c$≃(0.19–0.24)$m_{\rho }$. .AE