We demonstrate the existence of nonequilibrium between electrons and holes in the semiconductor GaAs under the influence of high electric fields. Hot-electron distributions in the presence of a cool majority hole plasma are observed. The measurement of the electron-energy-loss rate under these conditions allows the first experimental determination of the energy transfer by electron-hole Coulomb scattering in a semiconductor.

It is demonstrated for the first time that hydrogen can passivate shallow-donor impurities in n-type single-crystal silicon, and a novel chemical-bonding model is proposed to explain the phenomenon. Phosphorus greatly slows the bulk diffusion of hydrogen at ∼150 °C. Conductivity and Hall measurements show that the room-temperature electron density is decreased by hydrogenation, but the mobility is increased, so that compensation is ruled out. Total-energy calculations predict an energy minimum for H at the antibonding site of a silicon nearest neighbor of substitutional P. Known solubilities imply ∼1-eV binding for atomic H in pure silicon.

Nuclear magnetic resonance of the stable ${}_{}{}^{55}{}_{}{}^{}\mathrm{Mn}$ nuclei in antiferromagnetic ${\mathrm{MnCl}}_2$⋅${4\mathrm{H}}_2$O has been detected by observation of the nuclear orientation of ${}_{}{}^{54}{}_{}{}^{}\mathrm{Mn}$ nuclei doped into the sample. The technique allows the detection of NMR under conditions in which NMR from oriented nuclei cannot be observed. Also the NMR linewidths of the concentrated ${}_{}{}^{55}{}_{}{}^{}\mathrm{Mn}$ spins and the dilute system of ${}_{}{}^{54}{}_{}{}^{}\mathrm{Mn}$ spins can be compared.

The influence of charge-carrier concentration on the magnetic properties of the semimagnetic semiconductor [(PbTe${)}_{1\mathrm{-}\mathrm{x}}$(SnTe${)}_{\mathrm{x}}$${]}_{1\mathrm{-}\mathrm{y}}$[MnTe] ${}_{\mathrm{y}}{}^{}{}_{}{}^{}$ (x=0.72, y=0.03) is reported. Magnetization, magnetic susceptibility, and specific heat have been measured. For carrier concentrations below p=3×${10}^{20}$ ${\mathrm{cm}}^{\mathrm{-}3}$ the alloy is paramagnetic. For p≥3×${10}^{20}$ ${\mathrm{cm}}^{\mathrm{-}3}$ an abrupt transition to a ferromagnetic phase is observed at helium temperatures. The ferromagnetic transition temperature increases with increasing p. This is the first demonstration of the effect of carrier concentration on the magnetic properties of semimagnetic semiconductors.

It is shown that chiral symmetry and chiral anomaly are inherent to the incommensurability of a quasi one-dimensional charge-density-wave system. The chiral anomaly induced by the applied electric field is interpreted as an acceleration mechanism of the sliding charge-density wave and is connected with the Thomas-Fermi screening effect. The explicit breaking of chiral symmetry due to the external potential is proved to have sinusoidal dependence on the phase order parameter. Possible observable effects are also discussed.

We present a fractal analysis of severe convective storms using data collected during a recent hail suppression experiment ‘‘Grossversuch IV’’ in Switzerland. For larger clouds, a fractal shape is observed and from an analysis of the perimeter-to-area relation the fractal (i.e., Hausdorff) dimension is found to be ${\mathrm{D}}_{\mathrm{s}}$=1.36±0.1 in agreement with the value 1.35 from the theory of relative turbulent diffusion and an earlier analysis of cloud shapes. Moreover, a particle drift, present in strong lateral winds as well as in the center of hail clouds, is presumably responsible for a rather sharp crossover to a smooth behavior (${\mathrm{D}}_{\mathrm{s}}$=1) showing the existence of an apparent characteristic length.

The limiting distribution P(s) of quasienergy-level spacings is investigated for a quantum model which is stochastic in the classical limit. The numerical results show that in the case of a strong perturbation, the distribution P(s) corresponds closely to the Wigner-Dyson distribution. The relations between the limiting distribution P(s) and the symmetries of both the unperturbed and perturbed motions are independently investigated.

The formula for the fractal dimensionality of the perimeter (hull) of a percolation cluster, ${\mathrm{d}}_{\mathrm{f}}^{\mathcal{’}}$=1+1/ν, proposed recently by Sapoval, Rosso, and Gouyet, is shown to imply for the perimeter scaling exponents τ’=1+2ν/(1+ν), σ’=1/(1+ν), and γ’=2. Monte Carlo simulations of very large perimeter-generating walks yield τ’=2.143±0.002 and ${\mathrm{d}}_{\mathrm{f}}^{\mathcal{’}}$=1.751±0.002, consistent with these predictions (on the assumption that ν=(4/3)). The walks are also used to determine ${\mathrm{p}}_{\mathrm{c}}$=0.5927 5±0.0000 3 for site percolation on a square lattice.

Using the ARGUS detector at the DORIS II $e^{+}$$e^{\mathrm{-}}$ storage ring at DESY, we have obtained evidence for a new charmed resonance which decays into $D^{\mathrm{*}\pm }$(2010)${\pi }^{\mp }$. The observed mass and width are 2420±6 MeV/$c^2$ and 70±21 MeV/$c^2$, respectively. The fragmentation function is found to be hard, as expected for a state containing a leading charm quark produced by nonresonant $e^{+}$$e^{\mathrm{-}}$ annihilation.

The first result of a monopole-search experiment in at the Akeno Air Shower Observatory with helium proportional counters is presented. The aperture of the detector is 130 ${\mathrm{m}}^2$ sr including upward and downward directions. In 4154 h of operation no monopole candidate is observed, giving the flux upper limit as 1.2×${10}^{\mathrm{-}13}$ ${\mathrm{cm}}^{\mathrm{-}2}$ ${\sec }^{\mathrm{-}1}$ ${\mathrm{Sr}}^{\mathrm{-}1}$ (90% confidence level) for a monopole velocity larger than 7×${10}^{\mathrm{-}4}$c.

Superstring models with an intermediate mass scale possess a novel mechanism for generating the baryon asymmetry in the Universe. It involves the out-of-equilibrium decay of heavy particles at temperatures close to the electroweak scale. The gravitino problem encountered in many supergravity models is automatically resolved.

We propose a new mechanism for understanding small neutrino masses in supersymmetric theories without unnatural fine tuning of parameters. This idea may be useful for superstring ${\mathrm{E}}_6$ models, where the conventional mechanism is not available for suppressing neutrino masses.

We discuss the problem of neutrino mass, which arises in the low-energy limit of superstring theories. We propose a new mechanism, where the higher-dimensional terms in the Lagrangian can generate a small mass for the physical neutrinos.

Nuclear resonance fluorescence measurements with linearly polarized bremsstrahlung were performed to determine parities of bound dipole transitions in ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$. A new $1^{+}$ level at 5800 keV was found, which has almost the same strength as the isoscalar M1 transition in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$. Twenty-four further dipole states in ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$ below 7.6 MeV possess negative parity.

Quasielastic nucleon-transfer cross sections have been mea- sured at energies ≊35% above the Coulomb barrier for ${}_{}{}^{58}{}_{}{}^{}$,64Ni ${+\mathrm{}}^{112}$,116,120,124Sn. The systematic trends were studied over the range of systems, which span a factor of 2 in neutron excess N-Z. The observed magnitude of the cross sections and their surface localization suggest that quasielastic processes play an important role in the average nucleus-nucleus potential, a quantity of considerable recent interest in near-barrier collisions of heavy systems.

We report on a first precise measurement of the 1S-2S energy interval in atomic hydrogen. Observing the 1S-2S transition in an atomic beam by pulsed Doppler-free two-photon spectroscopy and using an interferometrically calibrated absorption line of ${}_{}{}^{130}{}_{}{}^{}\mathrm{Te}_2^{}{}_{}{}^{}$ at 486 nm as the reference, we measure the frequency f(1S-2S)=2 466 061 395.6(4.8) MHz. Using the calculated 1S Lamb shift, we obtain a value for the Rydberg constant, ${\mathrm{R}}_{\mathrm{\infty }}$=109 737.314 92(22) ${\mathrm{cm}}^{\mathrm{-}1}$, which is not in good agreement with the most recent previous measurement.

The 1${\mathrm{S}}_{1/2}$-2${\mathrm{S}}_{1/2}$ transition frequency in atomic hydrogen has been interferometrically measured by comparison with a reference line in ${}_{}{}^{130}{}_{}{}^{}\mathrm{Te}_2^{}{}_{}{}^{}$ by Doppler-free two-photon laser spectroscopy. The measured 1${\mathrm{S}}_{1/2}$-2${\mathrm{S}}_{1/2}$ transition frequency of 2 466 061 397(25) MHz is in good agreement with the theoretical predictions of Erickson modified to take account of recent measurements of the Rydberg constant. This measurement can be used to deduce a value for the ground-state Lamb shift and gives the result of 8182(25) MHz which compares with a value of 8173.248(81) MHz predicted by Erickson.

The argon 3${\mathrm{s}}^{\mathrm{-}1}$ photoelectron, spectrum has been measured with tunable synchrotron radiation (80–130 eV). The intensity of the 3${\mathrm{s}}^2$3${\mathrm{p}}^4$3d${(\mathrm{}}^2$S) satellite at 38.6 eV, relative to the main 3s3${\mathrm{p}}^6$${(\mathrm{}}^2$S) line at 29.3 eV, increases with increase in photon energy contrary to recent theoretical predictions. The intensity ratio increases towards the value given by electron momentum [binary (e,2e)] spectroscopy.

New experimental results on muon-catalyzed d-t fusion are reported. Unexpected target-density effects have been discovered both in dtμ molecular formation in tμ+${\mathrm{D}}_2$ collisions and in the effective sticking probability. The dtμ formation rate is significantly enhanced at high density, presumably because of a strong three-body contribution. The origin of the observed reduction of the sticking probability at high density remains unclear. Both effects increase the number of fusions per muon that can be achieved; 150±4(stat.)±20(syst.) fusions per muon have been observed.

Two distinct autodetachment channels are observed in the electron energy spectra of ${\mathrm{He}}_2$${\mathrm{}}^{\mathrm{-}}$ formed by double charge exchange of energetic ${\mathrm{He}}_2$${\mathrm{}}^{+}$ (30–65 keV) in lithium vapor. A single narrow peak has a center-of-mass energy of 11.5±2.6 meV, and is attributed to vibrational autodetachment [e.g., ${\mathrm{He}}_2$${\mathrm{}}^{\mathrm{-}}$${(}^4$${\mathrm{\Pi }}_{\mathrm{g}}$${)}_{\mathrm{v}=1\mathrm{}}$ →${\mathrm{He}}_2$${\mathrm{}}^0$ (a ${}^3$${\Sigma }_{\mathrm{u}}^{+}$${)}_{v=0\mathrm{}}$+e]. A second broad peak has a center-of-mass energy of 15.78±0.13 eV and results from autodetachment of ${\mathrm{He}}_2$${\mathrm{}}^{\mathrm{-}}$ into the ${\mathrm{He}}_2$(X ${\mathrm{}}^1$${\mathrm{\Sigma }}_{\mathrm{g}{}^{+})+\mathrm{e}}$ repulsive continuum. An electron affinity of 0.175±0.032 eV was determined for the ${}_{}{}^4{}_{}{}^{}\mathrm{He}_2^{}{}_{}{}^{}$(a ${\mathrm{}}^3$${\mathrm{\Sigma }}_{{\mathrm{u}}^{+}}$) state by comparison of the ${}_{}{}^3{}_{}{}^{}\mathrm{He}_2^{}{}_{}{}^{}$${\mathrm{}}^{\mathrm{-}}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}_2^{}{}_{}{}^{}$${\mathrm{}}^{\mathrm{-}}$ autodetachment spectra.