It is shown that the properties of high-${\mathrm{T}}_{\mathrm{c}}$ oxide superconductors are consistent with a model in which the charge carriers are holes in the O(2p) states and the pairing is mediated by strong coupling to local spin configurations on the Cu sites.

We have observed anomalous voltage excursions as a function of temperature and magnetic field in samples of Y-Ba-Cu-O above 100 K. These transient voltages are attributed to flux jumps which are characteristic of granular superconductors. The field dependence of the effect strongly supports this interpretation. We conclude that there exists grains in the sample with superconducting transition temperatures at least as high as 160 K.

Powder neutron diffraction studies of undoped ${\mathrm{La}}_2$${\mathrm{CuO}}_{4\mathrm{-}\mathrm{y}}$ have revealed new superlattice peaks below ∼220 K. The absence of corresponding x-ray superlattice lines and an observed susceptibility anomaly near 220 K suggest the occurrence of antiferromagnetism. From the magnetic peak intensities we deduce a structure consisting of ferromagnetic sheets of Cu spins alternating along the [100] orthorhombic axis, with the spins aligned along the [001] orthorhombic axis, The low-temperature magnetic moment is approximately 0.5${\mathrm{\mu }}_{\mathrm{B}}$/(Cu atom). The tetragonal-orthorhombic transition at 505 K has also been studied.

Branch imbalance has been a valuable probe of nonequilibrium superconductivity for many years, and is presumed to be well understood. However, measurements on bulk niobium samples show existing pictures to be inadequate in two ways. In a single-crystal sample, an excitation with an anomalously long diffusion length is detected; and the magnitude and decay length of the branch imbalance signal in the mixed state tend to increase with increasing magnetic field strength, in contradistinction to all previous expectations and interpretations.

uv-photoemission spectra of ${\mathrm{CeSi}}_2$ have been measured with a resolution of 18 meV in the temperature range 15 K<T≤300 K. The spectral analysis has been performed within the Anderson single-impurity model using the noncrossing approximation and including 4f-spin-orbit and crystal-field splittings. It accounts perfectly for the observed flattening of the fine structures in the spectra when the temperature increases. This study confirms indisputably the many-body nature of the low-lying excitations around ${\mathrm{E}}_{\mathrm{F}}$ observed with photoemission.

We have observed the Aharonov-Bohm effect in the magnetoresistance of doubly connected geometries fabricated in high-mobility GaAs/AlGaAs heterostructures. Periodic oscillations in the resistance associated with the flux’s penetrating the annulus are suppressed above ${\omega }_c$τ≊5, where ${\omega }_c$ is the cyclotron frequency and τ is the scattering time, while fluctuations in the resistance as a function of magnetic field are observed for 0<${\omega }_c$τ<300, superimposed upon Shubnikov-deHaas oscillations.

A cellular-automaton-type stochastic process is introduced in order to simulate the fractal distribution of galaxies. The rules of the model are constructed to approximate the explosive-galaxy-formation scenario. For a range of the single parameter the model depends on, the fractal dimension corresponding to the power-law density correlation function is found to be D≊1.2, in good agreement with the observations. The multiplicity function n(s) is shown to scale as n(s)∼${\mathrm{s}}^{\mathrm{-}\mathrm{\tau }}$, with τ≊1.9, where s is the cluster size.

We show that a duality transformation (connecting integrable Hamiltonian systems) recently discovered by Hietarinta and co-workers in two dimensions at a classical level can be directly established in N dimensions from a quantum formulation of the problem. Further, we show duality to be valid for a much larger class of dynamical systems and to be not necessarily unique. We speculate that this nonuniqueness could be a characteristic of separable systems.

A new perturbative computational scheme for solving quantum field theory is proposed. The interaction term in the Lagrangean is expanded about a free-theory form, the expansion involving powers of logarithms of the fields. The resulting perturbation series appears to have a finite radius of convergence and numerical results for simple models are good.

We consider two models of discretized string theories with an action which depends on the extrinsic curvature and prove that the string tension vanishes as the coupling strength of the extrinsic curvature tends to infinity. We discuss the physical properties of the models and argue that they possess a nontrivial scaling limit.

Flavor chirality is combined with genuine left-right symmetry in a unified SU(5${)}_{\mathrm{L}}$⊗SU(5${)}_{\mathrm{R}}$ manner. An SU(2${)}_{\mathrm{L}}$⊗SU(2${)}_{\mathrm{R}}$-singlet fermionic companion to each quark and lepton is predicted; the associated seesaw mechanism is examined in the light of proton stability. The evolution of ${\sin }^2$${\mathrm{\theta }}_{\mathrm{W}}$ exhibits distinctive features: (i) It starts at (3/16 and rises, and (ii) it is N dependent (N being the total number of generations). N=3,4 dictates an intermediate mass scale ∼${10}^7$ GeV, marking the breakdown of SU(5${)}_{\mathrm{R}}$.

The production of strange baryons ${\Sigma }^{\pm }$ (1385) and ${\Xi }^{\mathrm{-}}$ has been observed in $e^{+}$$e^{\mathrm{-}}$ annihilations at 29 GeV center-of-mass energy, by use of data obtained with the High Resolution Spectrometer at the SLAC storage ring PEP. The total mean multiplicities are measured to be 〈$n_{\Sigma }^{\pm }$(1385)〉=0.033±0.006±0.005 and &〉=0.016±0.004 ±0.004 per hadronic event. The results are in good agreement with the Lund string model.

This Letter describes a new technique for obtaining level positions, linewidths, autoionizing times, and oscillator strengths of core-excited levels and transitions. The technique uses a tunable laser to deplete the population of a radiating core-excited level, as other levels within the core-excited manifold are accessed. Level positions and linewidths are ascertained to within 1.0 ${\mathrm{cm}}^{\mathrm{-}1}$ accuracy, and autoionizing times whose Lorentzian linewidths lie beneath the combined Doppler-hyperfine structure are measured.

A simple theory is presented for the electron affinity of a small cluster of polar molecules (${\mathrm{NH}}_3$${)}_{\mathrm{n}}$. We obtain that the excess electron is bound inside the cluster essentially by the electric field resulting from the polarization of the molecular dipole moments. In agreement with experiment we obtain a sharp transition from unstable (${\mathrm{NH}}_3$${)}_{\mathrm{n}}$${\mathrm{}}^{\mathrm{-}}$ to stable (${\mathrm{NH}}_3$${)}_{\mathrm{n}+1\mathrm{}}$${\mathrm{}}^{\mathrm{-}}$ with a large barrier against dissociation for a critical cluster size n of about 30.

New phenomena observed in the shakeup satellite electron spectrum Ne 1s are discussed. It is shown that for satellites lying above the shakeoff threshold, the structures observed correspond to autoionizing resonances. By use of high-resolution x-ray photoelectron spectroscopy the Fano profile of the 2s-3s lower shakeup satellite line is resolved for the first time. The Fano parameters for this line are determined to q=-2.2(2) and ${\mathrm{\rho }}^2$=0.35(5). The width of the resonance is 0.57(7) eV, i.e., almost a factor of 2 larger than the unperturbed linewidth.

We report the measurement of state-to-state differential cross sections for rotationally inelastic electron-${\mathrm{Na}}_2$ collisions for impact energies from 150 to 300 eV. The data demonstrate for the first time large rotational transitions (0≤Δj≤30) for backward scattering. The most surprising result is the observation of pronounced rotational rainbows. These structures are expected to be general features in high-energy electron-molecule scattering.

It has recently been shown theoretically that correlations between fluctuations of the source distribution at different source points can produce red shifts or blue shifts of emitted spectral lines. To facilitate experimental demonstration of this effect a simple example is analyzed. It involves only two small appropriately correlated sources and brings out the essential physical features of this new phenomenon.

Wolf has recently shown that the spectrum of radiation from an extended source changes on propagation unless a certain scaling condition is obeyed by the degree of spectral coherence across the source. For a large class of source-coherence functions, the change may be such as to produce red shifts or blue shifts of spectral lines. We have performed an acoustic experiment with two small partially correlated sources and demonstrated Wolf’s prediction of frequency shifts of spectral lines by this mechanism.

Spatial patterns in temporal chaotic regimes of Rayleigh-Bénard convection have been experimentally studied with a measuring technique able to resolve in time the gradient of the temperature field. We find two different time-dependent regimes, one characterized by oscillations localized in space and the other consisting of traveling waves. The transition between these two regimes is also analyzed.

The channel capacity C of a light-wave communication system based on photoevent point process observations cannot be increased by use of photon-number–squeezed light. Under a constraint of maximum photon rate ${\lambda }_{\max }$, the channel capacity C=${\lambda }_{\max /\mathrm{e}}$ is achieved with a Poisson process. On the other hand, the channel capacity of a communication system based on photon counting can be increased by use of photon-number–squeezed light. The improvement vanishes in the limit of very small mean counts.