In the four-momentum-transfer range 0.05≤${\mathit{q}}_{\nu }^2$≤0.27 (GeV/c${)}^2$, longitudinal and transverse response functions have been determined by performing a Rosenbluth separation of ${}_{}{}^2{}_{}{}^{}\mathrm{H}$(e,e’p) coincidence cross sections measured in parallel kinematics. The results are compared to nonrelativistic calculations that include the effects of final-state interaction, meson-exchange currents, and isobar configurations, and to relativistic calculations that include the effects of final-state interaction. The ratios of the response functions agree with both calculations; the absolute values are (16±3±8)% larger than predicted.

We have made precision wavelength measurements on the 1s2s ${}_{}{}^3{}_{}{}^{}$${\mathit{S}}_1$–1s2p ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_{0,1,2}$° transitions in heliumlike boron using fast-beam laser excitation. These measurements are accurate to 2 parts in ${10}^7$ of the transition energy and test the most recent calculations at a level of 0.1% of the Lamb shift. The relatively high Z of boron, in comparison to helium, makes the transition energies sensitive to higher powers of αZ in the calculations, and our measurements show discrepancies which may be due to these uncalculated higher-order terms.

Evidence for a dynamical symmetry describing the electronic states in the first series of hydride diatomic molecules is presented. The symmetry applies to the energy spectra of the whole set of molecules with small rms deviations. This is the first instance of a dynamical symmetry in electronic molecular spectra.

Amplitude noise on the light from a semiconductor laser produced a photocurrent fluctuation spectrum that was a maximum of 85% (-8.3 dB) below the shot-noise limit. Squeezing in semiconductor lasers is not limited by the overall quantum, or current transfer, efficiency from the laser injection current to the detector photocurrent. Current leakage away from the lasing junction does not introduce Poissonian partition noise.

The characteristics of so-called ideal ‘‘quasimodes’’ or ‘‘collective modes’’ are investigated in the framework of linearized, compressible and resistive magnetohydrodynamics. It is shown that ideal quasimodes correspond to weakly damped eigenmodes of the resistive-MHD differential operator. The damping of these modes becomes independent of the plasma resistivity in the limit of vanishing η. Hence, for the first time in the range of the Alfvén continuum, resistive eigenmodes have been found that converge to their ideal-MHD transforms as η→0.

Toroidally rotating saturated 2/1 and 3/1 tearing modes in a tokamak plasma have been locked by current in an external resonant helical coil. This has allowed, for the first time, the stabilizing effect of the wall boundary condition to be varied in a controlled manner. The edge 3/1 mode can cause a minor disruption as a result of the coil-induced locking but the 2/1 mode is unaffected, remaining benign over several energy confinement times before precipitating a major disruption. Control measures taken during the locked phase lead to avoidance of the disruption.

A heuristic criterion is introduced and applied for derivation of percolation thresholds in continuum systems. The criterion is comprehensive in the sense that it applies to systems with diverse bonding criteria as well as to systems with a correlated distribution of sites. Its usefulness is manifested by the excellent quantitative agreement between the values obtained and available Monte Carlo data.

The effective exponents characterizing the orientational order parameter at the nematic-to-isotropic transition in discotic micellar solutions obtained on dissolution of either cesium pentadecafluoro-octanoate or ammonium pentadecafluoro-octanoate in water have been measured and found to have the value 0.34±0.02 over a wide range of concentrations. Thus, within experimental error, these exponents appear to be universal to a remarkably high degree. It is argued that, as for second-order phase transitions, these exponents characterize the fluctuations near the transition and can presumably be associated with some inaccessible fixed point of the renormalization-group flow.

We show that the hydrodynamics in nematic polymer solutions (NPS) is substantially different from that in nematics of low-molecular-weight molecules (NLMM). In NPS, the diffusive splay-bend wave in NLMM is replaced by a propagating second sound that has only been known to exist in spatially ordered liquid crystals. This property is caused by two combined effects in NPS: (a) the coupling between the nematic director and the polymer concentration; (b) the additional solvent component. Recent experimental results suggest that the second sound can be measured in NPS.

A macroscopic study of chiral smectic-${\mathit{O}}^{\mathrm{*}}$ films, which float at the free surface of isotropic droplets of 1(methyl)-heptyl-terephtalidene-bis-amino cinnamate, is presented. It allows us to directly prove antiferroelectricity with in-plane polarization in the smectic-${\mathit{O}}^{\mathrm{*}}$ phase, and to confirm the herringbone structure of this original phase. The bulk antiferroelectric polarization is measured to be about 0.1 D per molecule.

We have measured the relaxation of energy and polarization m in transiently polarized liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$. From these measurements we deduce the value of the magnetic field necessary to stabilize m. This field is shown to be higher than the extrapolation of the low-field regime, and amounts to 200 T at m=0.6, T=70 mK, P=26 bars.

We extend a continuum model recently proposed by Villain [J. Phys. I (France) 1, 19 (1991)] to study equilibrium and nonequilibrium diffusion on a high-symmetry surface under a fluctuating particle beam. Exponents characterizing dynamic scaling in various regimes are derived explicitly in all dimensions, as well as the relevant lengths which separate these regimes. Different surface morphologies are correlated with experimentally accessible parameters such as substrate temperature and deposition rate.

We describe anomalous strain relaxation in graded SiGe superlattices and thin films. This relaxation is characterized by the presence of dislocations in the Si substrate, as well as in the lower part of the film or superlattice, and results in a dislocation-free top layer. This challenges the basic assumption, dating back to Van der Merwe, that the substrate does not participate in the strain-relief process. We show that this phenomenon is due to the paucity of nucleation sites, and controlled by the specific Ge concentration profile in the film. Relaxed, defect-free ${\mathrm{Si}}_{\mathit{x}}$${\mathrm{Ge}}_{1\mathrm{-}\mathit{x}}$ films containing up to 60% Ge have been grown in this manner.

High resistivities associated with a reduced density of states and a very low effective number of carriers are measured in high-structural-quality AlCuFe icosahedral phases. These properties vary strongly with composition close to ${\mathrm{Al}}_{63}$${\mathrm{Cu}}_{25}$${\mathrm{Fe}}_{12}$ and suggest that insulating quasicrystals could exist. We also show evidence for quantum interference effects in the measured transport properties and diamagnetic susceptibility.

Synchrotron-x-ray powder-diffraction and differential-scanning-calorimetry measurements on solid ${\mathrm{C}}_{60}$ reveal a first-order phase transition from a low-temperature simple-cubic structure with a four-molecule basis to a face-centered-cubic structure at 249 K. The free-energy change at the transition is approximately 6.7 J/g. Model fits to the diffraction intensities are consistent with complete orientational disorder at room temperature, and with the development of orientational order rather than molecular displacements or distortions at low temperature.

Starting with a view of condensed matter as a neutral assembly of electrons and nuclei, with mutual Coulomb interactions, a coherent-state functional-integral approach gives a first-principles theory of pairing phases that requires no adiabatic separation of time scales. For electrons and protons, both fermions, we show that an interdependent pairing of electrons and of protons can arise at low temperature with effective pairing interactions. A critical point for this system is identified, which is discussed in the light of recent experiments on dense hydrogen.

The phase diagram for the Anderson transition of a two-dimensional disordered system with variable impurity concentration and a perpendicular magnetic field is investigated. A phase boundary is found, separating localized from extended states. It is calculated by means of a finite-size-scaling approach. The shape of the phase boundary and the change in the magnetoresistance are explained in terms of quantum interference effects, i.e., weak localization. A critical exponent for the correlation length and the onset of the delocalized phase are determined.

The longitudinal component of the zero-field-cooled (${\mathit{M}}_{\mathrm{ZFC}}$) and field-cooled (${\mathit{M}}_{\mathrm{FC}}$) magnetization of dilute Cu:Mn has been measured in magnetic fields between 2 G and 30 kG. The difference, Δ${\mathit{M}}_{\mathrm{irr}}$=${\mathit{M}}_{\mathrm{FC}}$-${\mathit{M}}_{\mathrm{ZFC}}$, is taken to be the irreversible magnetization. Above ≊500 G, a weak irreversibility and a strong irreversibility are observed. The onset temperature of the former, or weak irreversibility, follows the Gabay-Toulouse H-T relation with a coefficient close to the mean-field value for a Heisenberg system. The onset temperature of the latter is found to have quantitative agreement with the mean-field d’Almeida-Thouless–like H-T crossover relation for longitudinal freezing in a Heisenberg system.

Recent experimental measurements of the resistive transition in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$/${\mathrm{PrBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ superlattices show a dramatic suppression in the resistive transition temperature ${\mathit{T}}_{\mathit{c}}$ as the thickness of the Pr layer increases while the thickness of the Y layer decreases. We show that the qualitative features of these experiments (and in particular most of the suppression in ${\mathit{T}}_{\mathit{c}}$) can be accounted for within the Kosterlitz-Thouless theory. A small further suppression in ${\mathit{T}}_{\mathit{c}}$ is shown to occur due to charge transfer from Y to the Pr layers.

We study both classical and quantum vortex creep in disordered thin-film superconductors in an applied magnetic field. Quantum tunneling of vortices leads to a variable-range-hopping resistivity with a non-Arrhenius temperature dependence at low T. Mott’s 1/3 law is modified by long-range vortex interactions, and a numerical analysis enables us to estimate a temperature exponent between roughly 2/3 and 4/5. At higher T, a classical hopping regime is expected with a current-density scale for nonlinearities varying (roughly) as ${\mathit{T}}^3$.