By applying the perturbed-γ-ray distribution method following heavy-ion reactions we have observed nonmagnetic behavior for Mo and Tc ions in Pd, but a high local susceptibility for Ru in Pd consistent with the formation of a giant 4d moment. These trends agree with local-spin-density calculations, yielding a magnetic moment for Ru in Pd and a strong ferromagnetic host-d-spin polarization if Ru, Rh, and Pd ions in Pd are locally magnetized by a small magnetic field. We suggest that the occurrence of magnetism and the spin-fluctuation temperatures for 4d and 3d ions in Pd are strongly correlated with the sign and strength of the induced host-d-spin polarization.

We have measured and calculated the dependence of the Raman phonon intensities of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ on laser frequency. The local-density approximation and the linear muffin-tin-orbital method were used for the calculations. We find good agreement not only in the absolute phonon intensities in zz or xx/yy polarization but also in the shape of the resonance profiles. These results indicate that the local-density approximation gives an essentially correct description of the band structure and of the electron-phonon interaction ±2 eV around the Fermi energy. We interpret our data in terms of specific interband transitions and estimate the mode mixing.

Measurements of the transverse sound attenuation and velocity in a ceramic ${\mathrm{Bi}}_{1.6}$${\mathrm{Pb}}_{0.4}$${\mathrm{Sr}}_2$${\mathrm{Ca}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{\mathit{y}}$ superconductor (${\mathit{T}}_{\mathit{c}}$=110 K) were performed with and without a magnetic field. Pronounced peaks in the field-induced attenuation and an increase of the velocity at low temperatures were observed. These effects can be attributed to the transition of a rigidly pinned flux-line lattice into a depinned state. A quantitative explanation is presented within the framework of thermally assisted flux flow and without any adjustable parameter.

We have performed high-resolution angle-resolved-photoemission experiments on ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_{8+\mathrm{\delta }}$ single crystals with different annealing histories. By depositing a small amount of Au on the surface, we were able to distinguish electronic states associated with the Bi-O surface layer. We found that the Bi-O atomic surface layer is metallic and superconducting for samples that were high-temperature annealed in oxygen but not for as-grown samples. The Cu-O plane is found to be superconducting in all samples.

It is shown that recent data of Murray et al. on spatial correlations in flux lattices of Bi-Sr-Ca-Cu-O (BSCCO) may be explained if one assumes that 1% of oxygen atoms in ${\mathrm{CuO}}_2$ layers are missing. This estimate, being in remarkable agreement with that deduced by Kes and van der Beek from ac-susceptibility measurements, provides strong confidence that oxygen vacancies are the major source of pinning in BSCCO.

We have found the presence of at least one family of stable periodic orbits in the system H=1/2(${\mathit{p}}_{\mathit{x}}^2$+${\mathit{p}}_{\mathit{y}}^2$+${\mathit{x}}^2$${\mathit{y}}^2$). This counterproves earlier claims that the ${\mathit{x}}^2$${\mathit{y}}^2$ potential gives fully ergodic motion.

I have recently proposed that both H i regions of the Galaxy and Lyman-α clouds are mainly ionized by decaying dark matter. Here I point out that to avoid an excessive metagalactic ionizing flux F, the energy ${\mathit{E}}_{\gamma }$ of the decay photons must be severely constrained. It then follows that the mass ${\mathit{m}}_1$ and lifetime τ of the decaying particles, the flux F, the density ρ and age ${\mathit{t}}_{\mathit{U}}$ of the Universe, Ω (=ρ/${\mathrm{\rho }}_{\mathrm{crit}}$), and the Hubble constant H also have to be severely constrained. The validity of our theory requires that ${\mathit{E}}_{\gamma }$=14.4±0.5 eV, ${\mathit{m}}_1$=28.9±1.1 eV, τ=(2+1)×${10}^{23}$ sec, F=(3.8±2.2)×${10}^5$ ${\mathrm{cm}}^{\mathrm{-}2}$ ${\sec }^{\mathrm{-}1}$, ρ=(6.14±0.26×${10}^{\mathrm{-}30}$ g ${\mathrm{cm}}^{\mathrm{-}3}$, ${\mathit{t}}_{\mathit{U}}$∼1.2×${10}^{10}$yr, Ω∼1, and H=55±1 km ${\sec }^{\mathrm{-}1}$ ${\mathrm{Mpc}}^{\mathrm{-}1}$.

We report a measurement of Λ polarization in the two-body decay ${\mathrm{\Lambda }}_{\mathit{c}}^{+}$→Λ${\mathrm{\pi }}^{+}$, in nonresonant ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ interactions from data taken with the CLEO detector. Using these data we have determined the parity-violating asymmetry decay parameter ${\mathrm{\alpha }}_{\mathrm{\Lambda }\mathit{c}}$ to be -1.$0_{\mathrm{-}0.0}^{+0.4\mathrm{}}$. We see no evidence for significant ${\mathrm{\Lambda }}_{\mathit{c}}^{+}$ polarization.

The total cross section for the reaction pp→pp${\mathrm{\pi }}^0$ was measured at nine center-of-mass energies from 1.5 to 23 MeV above threshold. The experiment was carried out with the Indiana Cooler, a recently constructed storage ring. The experimental advantages of an electron-cooled proton beam were utilized. The data cover an energy range where only the lowest possible angular momentum state contributes in the exit channel. The measured energy dependence of the total cross section is not compatible with that predicted by models of s-wave pion production and rescattering.

Recent observations of the giant dipole resonance in states at high angular momentum and temperature have shown an effective narrowing of the resonance. It is pointed out that this may be interpreted as a signature of rotation of the nucleus about a symmetry axis. In this limit, the giant dipole orientation freezes in the plane of rotation, the analog of the Foucault pendulum positioned at the North Pole. All effects of rotation, other than those of pure deformation, cease to be present. In this region it is thus possible to probe the nuclear shape directly, uncontaminated by rotational effects.

The purity of intrinsic states of nuclei with respect to a proton-neutron boson symmetry (F spin) is shown to be largely determined by the difference between proton and neutron deformations and not by whether the Hamiltonian is an F-spin scalar. Upper and lower bounds on F-spin mixing in the ground-state band of ${}_{}{}^{165}{}_{}{}^{}\mathrm{Ho}$ are estimated using recent pion single-charge-exchange data.

It has been suggested to measure ratios of atomic parity-nonconservation observables in strings of isotopes to cancel atomic-structure effects. Nuclear-structure-effects nevertheless play a significant role in extracting weak-interaction parameters. Uncertainties in nuclear structure, especially in the neutron distribution, severely limit the precision of extracting the weak-interaction parameters. On the other hand, the sensitivity to the neutron distribution could provide a unique method for accurately determining rms radii of neutron distributions.

A comparison is made between the cross section ${\mathrm{\sigma }}_{\mathit{e}}^{+}$ for electron-impact ionization of singly charged ions and the ratio ${\mathrm{\sigma }}^{2+}$/${\mathrm{\sigma }}_{\mathit{t}}$(abs) of double photoionization to the total photoionization cross section for N, O, and Ne. The photon- and electron-impact data were found to be proportional to each other to within about 9% for the first 70 eV above threshold. A study of the literature data shows that this proportionality between photon- and electron-impact data is a general phenomenon. The limits of the proportionality are unknown.

The nonlinear dynamics of dissipative trapped-ion convective cells in broadband turbulence is analyzed. Saturation is achieved by both local and nonlocal transfer of spectral energy from unstable long-wavelength trapped-ion fluctuations to shear-damped moderate-wavelength trapped-electron modes. In particular, contrary to previous studies, it is shown conclusively that no long-wavelength condensation of fluctuation energy is possible. The transport level associated with these structures is therefore moderate and not catastrophic (Bohm-like), as conventionally believed.

Measurements on the TFTR tokamak of the electron-temperature-profile evolution and soft-x-ray emissivity on a fast (10-μsec) time scale during a sawtooth crash show that significant heat is deposited beyond the mixing (or reconnection) radius within 200 μsec following a sawtooth crash. This extended region in which electron heat is redistributed during the sawtooth crash substantially complicates the determination of heat transport properties from the subsequent heat pulse propagation. It is shown that the relaxation of this extended perturbation is consistent with the power-balance estimates of the local thermal diffusivity.

The nonlinear saturated state of the radiative thermal-condensation instability responsible for the phenomenon of multifaceted asymmetric radiation observed in tokamak edge plasmas has been investigated. The essential problem to study two-dimensional thermal equilibria where perpendicular and parallel heat conduction balances the radiated power and heat flux to the limiter. In certain reasonable limits, the nonlinear Poisson’s equation can be solved exactly to display many features of the observed detached plasma transition. Numerical results taking realistic temperature dependences for thermal-conductivity coefficients and a common coronal radiation model are also presented.

Experiments on the TEXT tokamak show that the temporal evolution of a single helicity tearing mode is dominated by the Rutherford regime. Further analysis of the Mirnov signal and sawtooth activity combined with numerical simulation emphasizes the global characteristics of the tearing mode.

Molecular-dynamics simulations of highly nonspherical rodlike and platelike molecules reveal that one of the two diffusion coefficients in the nematic-liquid-crystal phase increases with density, reaches a maximum, and decreases, while the other coefficient decreases monotonically in the usual way. This effect seems to be associated with the density variation of the nematic order parameter near the phase transition. A kinetic theory based on isolated binary collisions significantly underestimates the diffusion coefficients, but partially accounts for the enhancement effect.

We model the dynamics of a molecular network with two distinct energy scales ${\mathit{E}}_1$≪${\mathit{E}}_2$. A novel critical bond dynamics is shown to arise due to screening. We identify an order parameter and determine the related exponent at the critical temperature ${\mathit{T}}_{\mathit{c}}$. Above ${\mathit{T}}_{\mathit{c}}$, the dynamics is characterized by a power-law distribution of bond lifetimes with an exponential cutoff at a time that diverges at ${\mathit{T}}_{\mathit{c}}$. Our picture is applied ot liquid water.

Initial chemical-interdiffusion coefficients in a simple cubic, random, binary alloy, Ising model have been determined analytically and by Monte Carlo simulations, using chemical rate equations for atomic exchanges. The results, obtained as a function of the composition gradient, enthalpy of mixing, and temperature, show that the chemical enhancement of the diffusion coefficients saturates and is considerably lower than predicted by Darken’s equation. The discrepancy is due to the inadequacy of the mean-field theory and linear-response approximation at high enthalpies of mixing.