We present a novel ab initio approach to piezoelectricity. The piezoelectric tensor is given by the stress induced by a homogeneous electric field. The perturbation is treated self-consistently by linear response, thus avoiding both supercells and numerical differentiation. We calculate the piezoelectric constants of none III-V semiconductors: as a by-product we also provide the first systematic study of zone-center phonons, internal strain parameters, effective charges, and dielectric constants. Our results agree very well with experiments where available, and allow predictions where they are not.

Within a thermally activated flux-motion model we derive an exact inversion scheme which makes it possible to calculate the distribution m(${\mathrm{E}}^{\mathrm{*}}$) of activation energies ${\mathrm{E}}^{\mathrm{*}}$ for flux motion from experimental magnetic relaxation data M(t,T). The distributions determined from relaxation data for polycrystalline and single-crystalline ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ strongly resemble a log-normal distribution function. The results show that within this model existing data imply that structural disorder is present in both ceramic and single-crystalline samples.

We report high-resolution nonlinear laser-spectroscopy studies of the n=1 heavy-hole exciton in GaAs multiple quantum wells. Using a new method of cw frequency-domain four-wave mixing, we first show that the excitation relaxation consists of both fast and slow components. We then show that the contribution of well-width fluctuations to inhomogeneous broadening can be elimiated enabling us to obtain a direct measure of the intrinsic exciton line shape. Under certain conditions, this line shape is non-Lorentzian and cannot be explained on the basis of simple excited-state relaxation dynamics.

Anticrossing of two Raman lines, that of a donor-electron spin flip and that of an intra-${\mathrm{Fe}}^{++}$-ion excitation, has been observed in ${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Fe}}_{\mathrm{x}}$Se, a Van Vleck–type semimagnetic semiconductor. A new model of a bound magnetic polaron (BMP) is reported, which accounts for the experimental data. At zero magnetic field, this BMP is characterized by a finite local spin polarization at its center, 〈${\mathrm{S}}^{\mathrm{x}}$〉=0.06, and by an exchange energy shift of its ground state of Δ${\mathrm{E}}_{\mathrm{p}}$=-0.26 ${\mathrm{cm}}^{\mathrm{-}1}$ for x=0.018, despite the fact that the spin-flip energy of the donor electron is strictly zero.

Ion channeling along the c axis in ${\mathrm{ErBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ reveals a normal (Debye-type) temperature dependence for thermal vibrations of the Er and Ba atoms between 40 and 300 K. In contrast, a substantially stronger than normal temperature dependence is found for the Cu-O atom vibrations, and a large, anomalous change (∼30%) is seen at the superconducting transition. The large magnitude of the vibrational changes found for the Cu-O rows across ${\mathrm{T}}_{\mathrm{c}}$ suggests that the atoms in these rows become strongly coupled in the superconducting state.

We propose an effective theory of superconductivity based on a microscopic theory of the T- and P-breaking spin-liquid state. There are two independent gauge invariances broken by two separate condensates. The theory may be useful for phenomenological calculations. In particular, we find that ${\mathrm{H}}_{\mathrm{c}1}$ are different for magnetic fields with opposite orientations. We also find that the polarization of an electromagnetic wave is rotated after reflection from these T- and P-breaking superconductors.

The dynamics of long chain macromolecules in field-inversion gel electrophoresis is studied by Monte Carlo simulation using a reptation model which includes tube length fluctuations. A sharp minimum in chain mobility is observed as the pulse duration is varied, occurring at longer pulse periods for larger chains. Detailed examination of the dynamics shows that the reduced mobility results from the chain being trapped in long-lived compact configurations which have no net translational motion.

We have discovered a temperature-driven unbinding transition of fluid membranes in samples of digalactosyldiacylglycerol (DGDG) swollen in 0.1M NaCl aqueous solution. Single bilayers were observed by phase contrast light microscopy. The transition is reversible and without apparent hysteresis. Its temperature is only a few °C lower for the single membranes of two vesicles than for multilayer systems, but it varies strongly among samples. The bending rigidity of DGDG bilayers was also measured and found to be (0.12–0.21)×${10}^{\mathrm{-}12}$ erg.

We construct extended Higgs-boson models of soft CP-invariance violation arising from scalar-pseudoscalar mixing. Using the electric dipole moment of neutron as input, we find that the charged-lepton electric dipole moments scale as (mass${)}^3$. They are estimated to be 2.1×${10}^{\mathrm{-}28}$, 4.4×${10}^{\mathrm{-}22}$, and 1.8×${10}^{\mathrm{-}19}$ e cm for electron, muon, and τ, respectively. An important test of this source of CP violation lies in the longitudinal polarizations of muon in η→μμ¯ and $K_L^0$→μμ¯, which we estimate to be of the order of ${10}^{\mathrm{-}2}$ and ${10}^{\mathrm{-}1}$, respectively.

One decade ago evidence for the formation of diproton resonances was first reported in the mass range of 2140 to 2220 MeV. Recently structures at much higher mass region (2700 to 2900 MeV) were found in various measurements. A new Δ${\sigma }_L$ measurement revealing bumps and a dip is reported here in this mass region and the nature of the structure is discussed.

We report on the measurements of electron pair production in p-Be collisions at 1.0, 2.1, and 4.9 GeV beam kinetic energies. The invariant-mass and transverse-momentum spectra are presented, along with the total cross sections. A rapid decrease in the integrated cross section is observed as the beam energy is reduced. Comparison of the excitation function for dielectron ($e^{+}$$e^{\mathrm{-}}$) and dipion (${\pi }^{+}$${\pi }^{\mathrm{-}}$) production suggests that the dominant production mechanism at beam kinetic energies 2.1 and 4.9 GeV may be ${\pi }^{+}$${\pi }^{\mathrm{-}}$ annihilation.

We report on high-resolution, state-selective dielectronic-recombination measurements for metastable, He-like ${\mathrm{O}}^{6+}$ ions. The measurements were performed with a merged-beams configuration in an electron cooler. The energy resolution was found to be as low as 0.135 eV. Dielectronic recombination associated with excitations of the 1s2s${(}^1$S) and 1s2s${(}^3$S) cores are reported. The data demonstrate strong effects of configuration interaction between different intermediate states with almost identical energy.

Measurements of electric-field–induced second-harmonic generation are presented which show that the hyperpolarizability (γ) of the Ne atom decreases with increasing frequency at infrared frequencies. Such negative dispersion of γ at frequencies far below the first resonance is unprecedented. The new data, when combined with the results of ab initio calculations indicate that the electron-correlation contribution is 40% of ${\gamma }_{\mathrm{Ne}}$. This raises the question of the adequacy of Hartree-Fock calculations of the nonlinear optical properties of other atoms and molecules.

Results from a quasioptical gyrotron experiment with a 20–28-cm mirror separation are presented showing operation from 95–130 GHz at powers up to 148 kW and output efficiencies up to 12%. The output coupling could be varied from 0.4%–3% by changing the mirror separation and operating frequency. Efficiency optimization by variation of output coupling and by tapering the magnetic field has been demonstrated and regions of single-mode operation at powers up to 125 kW have been characterized.

We report measurements of the temporal autocorrelation function g(t) of light scattered from critical binary liquid mixtures which are being continuously and turbulently stirred. The functional form of g(t) changes dramatically when the turbulent shear is changed from weak to strong. In the strong shear regime g(t) becomes a stretched exponential function, with an exponent that decreases as the temperature approaches the critical temperature. This stretched exponential behavior is associated with spatially intermittent suppression of critical fluctuations produced by the turbulence.

A novel multipole wiggler and an associated beam line have been installed in the accumulation ring for the TRISTAN project at the National Laboratory for High Energy Physics (KEK). An intense source of circularly polarized synchrotron radiation in the energy ranging 40 to 80 keV has been achieved for the first time. A degree of circular polarization, ${\mathrm{P}}_{\mathrm{c}}$≃0.7, at 60 keV of photon energy was in good agreement with a theoretical prediction in the 6-GeV operation of the accumulation ring.

Results of short-pulse, low–duty-cycle hf-heating experiments are shown to agree with predictions of a model of correlated, localized cavitons which undergo cycles of nucleation, collapse, and burnout. Predicted ‘‘free-mode’’ spectral features associated with the radiation of Langmuir waves from collapsing cavitons are observed. Single radar pulse data provide evidence that temporal correlations between caviton events are present at early times following the onset of heating.

We have derived analytic expressions, in terms of Airy functions, for the reflection and mode-conversion coefficients of Langmuir and electromagnetic waves in an inhomogeneous, unmagnetized plasma. The reflection coefficient for the ‘‘direct’’ problem (incident electromagnetic wave) is equal in magnitude to that for the ‘‘inverse’’ problem (incident electrostatic wave) and the corresponding mode-conversion coefficients satisfy energy conservation. Our results, which are valid in the limit of nonrelativistic electron temperature, T/${\mathrm{mc}}^2$≪1, agree with earlier numerical calculations.

Simulations show that for shock waves propagating obliquely to a magnetic field (angles from 55° to 80° for the parameters run), a double layer forms at the shock front and plays an important role in the shock dynamics. Electrons are strongly accelerated through the double layer and scattered off ion and magnetic field fluctuations behind the shock. Some ions are reflected by the double layer and the jump in magnetic field. For these investigations, electron heating is the major dissipation.

The Fokker-Planck equation for electrons in two spatial dimensions in the diffusive approximation is solved by the alternating direction implicit method. The ions are modeled hydrodynamically. We discuss simulations of short-pulse (3.4 psec) experiments at a wavelength of (1/4 μm. We find substantial departures from Spitzer heat flow in both magnitude and direction. As a result we find that, even for 10-μm-diam laser spots, the heat flow into the target is not strongly reduced by energy escaping along the target surface.