The resistivity of single-crystal ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$ has been found to be anisotropic, with magnitude and temperature dependence similar to ceramic samples in directions parallel to the Cu-O planes, and with a 30 times larger room-temperature value and a much smaller temperature dependence in the orthogonal direction. The Hall coefficient, with a magnetic field applied parallel to the Cu-O planes, is negative (electronlike) and essentially temperature independent in these crystals, in direct contrast to the behavior of other types of samples.

The spectra of conductance fluctuations caused by fluctuating interference terms in the scattering of disordered materials at low temperature are calculated. When the net magnitude of the temporal fluctuation approaches the ‘‘universal’’ value, the form of the spectrum is found to change from that obtained from the bare spectrum of the time-varying scatterers. Anomalous fluctuation statistics occur in the same regime. Remnants of such effects for high-temperature 1/f noise are discussed.

An even-denominator rational quantum number has been observed in the Hall resistance of a two-dimensional electron system. At partial filling of the second Landau level ν=2+(1/2= 5) / 2 and at temperatures below 100 mK, a fractional Hall plateau develops at ${\mathrm{\rho }}_{\mathrm{xy}}$=(h/${\mathrm{e}}^2$)/(5/2 defined to better than 0.5%. Equivalent even-denominator quantization is absent in the lowest Landau level under comparable conditions.

We have investigated static and dynamic properties of wet-spun DNA fibers in their C, A, and B conformations using the thermal neutron scattering. Over-damped and underdamped longitudinal acoustic umklapp phonons are observed in the vicinity of a hydration-dependent two-dimensional sheet of diffuse scattering perpendicular to the helix axis. A quantitative analysis of this mode is presented for the B-DNA sample in terms of a harmonic one-dimensional liquid, i.e., taking into account all orders of fluctuations. The resulting effective dispersion does not extrapolate to zero frequency at the position of the sheet.

Motion of the earth through the cosmic neutrino background, or through certain kinds of vacuum states, produces a term of the form gσ⋅v in the energy of an electron. To search for such a term a cryogenic torsion pendulum carrying a transversely polarized magnet was used. Superconducting shields reduced magnetic torques. A σ⋅v term would produce a sinusoidal oscillation of the pendulum with a period of one sidereal day. Such an oscillation was not detected, and a new limit of 8.5×${10}^{\mathrm{-}18}$ eV for the splitting of the spin states of an electron at rest on the Earth has been set.

Leggett and Garg have argued that the phenomenon of quantum flux tunneling oscillations will, according to the predictions of quantum mechanics, contradict the pair of assumptions ‘‘macroscopic realism’’ and ‘‘noninvasive measurability.’’ It is argued here that there can be no contradiction of realism in such a case, and that the contradiction is between quantum mechanics and noninvasive measurability.

The interrelation between random matrices and physical matrix Hamiltonians is established by introduction of a construction scheme whereby a single matrix is projected onto a subensemble of smaller matrices. Exact analytical results are obtained for random matrices and compared with numerical calculations on a model Hamiltonian.

A recent study by Zaslavskii et al. demonstrates that under certain conditions a charged particle may be accelerated by an arbitrarily small electrostatic wave packet in a magnetic field to arbitrary energy by the process of Arnol’d diffusion in 1(1/2 dimensions. A relativistic calculation shows, however, that the particles can only be accelerated up to a critical energy by a wave packet above a critical amplitude.

The case of a domain wall of finite thickness is examined by use of two different expressions for the energy-stress tensor of domain walls but no symmetry condition. It is found that the equations of general relativity show that such walls cannot be in static equilibrium, and further even nonequilibrium walls can be consistent with Einstein’s equations only under very special circumstances.

The fundamental soliton solution of the O(3) nonlinear σ model in two space dimensions is examined. It is pointed out that the classical soliton is associated with an infinite moment of inertia and infinite moment of dilation, and argued that the quantum soliton is as well. It follows that the spin of the soliton is undefined, contrary to recent claims that it be fractional.

This paper points out some implications of the possibility that electric-charge nonconservation may occur in nature via an interaction that changes an electron to a positron (i.e., ΔQ=2).

We combine measurements of the chiral-symmetry–restoration transition temperature and hadron masses in lattice QCD with two flavors of light quarks to estimate the transition temperature in megaelectronvolts. We compare this estimate to results of ‘‘quenched’’ QCD to estimate the effects of our large lattice spacing on the results. We find that the dynamical quarks lower the temperature of the phase transition relative to the pure gauge theory.

A superlight (of mass ∼$M_W^2$$M_{\mathrm{Pl}{}^{\mathrm{-}1}}$) gravitino may have observable consequences for high-energy reactions at the teraelectronvolt scale. Tree-level unitarity is shown to break down there for two-photon production of a pair of longitudinally polarized gravitinos. The cross section rises fast with energy and should be measurable at around 100 GeV. A double-tag search for eē→eē+‘‘nothing’’ will push up the lower bound on the gravitino mass or detect a superlight gravitino.

B decays to charmless inclusive final states are discussed. The generic process is the loop-induced b→${\mathrm{sg}}^{\mathrm{*}}$, $g^{\mathrm{*}}$ being an on-shell or off-shell gluon. We include the cases when the gluon momentum is lightlike, timelike, and spacelike. The timelike case includes $g^{\mathrm{*}}$→qq¯ and gg splitup. Our findings are as follows: (1) B(b→${\mathrm{sg}}^{\mathrm{*}}$)≃1% for three generations; (2) an experimental observation of charmless branching ratio ≥5% would (conservatively) imply the possibility of a fourth generation; and (3) charmless branching ratio >20% would be difficult to accomodate in the standard model even with four families.

The remarkably large value of ρ=Ref/Imf at √s =546 GeV found recently in an experiment at the CERN Spp¯S collider is shown to have dramatic consequences.

The decay τ→ρν is studied in τ pair production by $e^{+}$$e^{\mathrm{-}}$ annihilation at √s =3.77 GeV, 0.20 GeV above ττ threshold. The branching fraction is measured to be B(τ→ρν)=(23.0±1.3±1.7)%. The measured distribution of the helicity angle of the charged pion from the ρ decay agrees with the theoretical prediction.

We report on the observation of a narrow resonance at a mass of 2459 MeV/$c^2$ in the final states Λ$K^{\mathrm{-}}$${\pi }^{+}$${\pi }^{+}$ and ${\Sigma }^0$$K^{\mathrm{-}}$${\pi }^{+}$${\pi }^{+}$. The mass, width, lifetime, and decay modes support the interpretation of a hadronically produced charmed strange baryon, the ${\Xi }_c^{+}$. We present our measurements of the lifetime, cross section, and relative branching fractions, and the A, $x_f$, and $p_t$ dependence of the state.

The differential cross section in free n-p forward elastic scattering has been measured for incident neutron energies of 378, 481, 582, 683, 784, 884, and 1085 MeV and for momentum transfer 0.01<‖t‖<0.08 (GeV/c${)}^2$. The experiment used a recoil-detector ionization chamber which served at the same time as a gas target. Special care has been taken to obtain a precise absolute normalization.

The ${}_{}{}^3{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ charge and magnetic form factors have been extracted from cross-section measurements in the region 0.3≲Q≲2.9 ${\mathrm{fm}}^{\mathrm{-}1}$. The measurements have random uncertainties of about 2% and systematic uncertainties of about 2% for ${}_{}{}^3{}_{}{}^{}\mathrm{H}$ and 1.5% for ${}_{}{}^3{}_{}{}^{}\mathrm{He}$. The small systematic uncertainties allow accurate determination of the isoscalar and isovector trinucleon form factors. The isoscalar charge and isovector magnetic form factors are in reasonable agreement with current theoretical models, whereas the isovector charge and isoscalar magnetic form factors show significant deviations from the models.

It is shown, by use of the O(6) limit of the interacting-boson model, that the γ-unstable state can be generated from the rigid triaxial intrinsic state with γ=30°. This equivalence between the two descriptions holds under a certain condition on the number of bosons, which is satisfied in realistic cases. The β-γ deformation potential calculated from this triaxial intrinsic state has a minimum also at γ=30°, though quite shallow. The validity of the potential and the triaxial intrinsic state, which has been questioned because of the shallow minimum, is thus confirmed.