We have determined ${\mathit{m}}_{\mathit{W}}$=79.91±0.39 GeV/${\mathit{c}}^2$ from an analysis of W→eν and W→μν data from the Collider Detector at Fermilab in p¯p collisions at a c.m. energy of √s =1.8 TeV. This result, together with the world-average Z mass, determines the weak mixing angle to be ${\sin }^2$${\mathrm{\theta }}_{\mathit{W}}$=0.232±0.008. Bounds on the top-quark mass are discussed.

The influence of inelastic nuclear scattering on atomic charge transfer in asymmetric ion-atom collisions is described within a new theory, combining a two-channel model for the nuclear reaction with the impulse approximation for electron capture by the projectile. Test calculations of the capture probability during the reaction ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$(p,α${)}^{15}$N indicate that inelastic nuclear reactions are a more transparent probe for the atomic transition amplitudes than elastic resonances.

Mode competition in a far-infrared, free-electron laser operating in the quasi-cw regime has been investigated by means of direct spectral measurement with a heterodyne receiver system. About 30% of the spectra had a single longitudinal mode. The observed data compare reasonably well with theory. It is found that even in a regime of multimode operation the laser signals are only weakly modulated in time, as observed with a video detector. Such an observation is consistent with a phase locking of multiple modes, as predicted by theory.

Measurements of the spatial structure of the transport coefficients of ${\mathrm{He}}^{2+}$ on the Tokamak Fusion Test Reactor is reported. ${\mathrm{He}}^{2+}$ profiles were measured using charge-exchange spectroscopy after a helium puff into corotating L-mode plasmas. Modeling shows that the ${\mathrm{He}}^{2+}$ diffusivity is about 10 ${\mathrm{m}}^2$/s near the plasma edge and drops to below 1 ${\mathrm{m}}^2$/s inside of the q=1 surface. The convective velocity ranges from 1–3 m/s near q=1 to 20–40 m/s near the edge. The helium diffusivity is on the order of the ion momentum and thermal diffusivity and is greater than the electron thermal diffusivity.

Relaxation dynamics of metastable RNS folding are modeled by means of a master equation for the distribution of folded-state occupancies. The underlying primary sequence is considered to be random and uncorrelated. The model is tested vis-a`-vis a Monte Carlo simulation of kinetically governed refolding events. The validity of a random energy model is established.

The thermodynamics and dynamics of the spin-boson model are formulated in terms of the exact formal solutions. The low-temperature features of the free energy, the static susceptibility, and the equilibrium correlation function are presented for Ohmic and super-Ohmic dissipation, and various universal properties are deduced. In the Ohmic case the Wilson ratio and the spectral properties at low frequencies (Shiba’s relation) are calculation in the range 0<α<1 of the coupling strength. The corresponding universal relations are determined also for super-Ohmic dissipation.

Experiments on the formation of faults in a laboratory model of the Earth’s crust are presented; they respect its vertical rheological stratification, a brittle layer on top of ductile layers. As a result of the competition between the different nature of the brittle and ductile-layer deformations, complex fractal patterns of faults are formed with fractal dimension 1.70±0.05 independent of the fault densities associated with different brittle-ductile coupling. We propose a kinematic formulation of the mechanical problem which suggests an analogy with previously studied fractal-growth problems.

An atomic-force microscope was used to measure the surface forces between a sharp tungsten tip and several different types of molecularly thin organic films on a silicon substrate. The forces are dramatically influenced by the molecular films covering the surfaces. The films investigated fall into three categories: liquid for unbound films of perfluoropolyether, intermediate for bonded films of perfluoropolyether, and soft solid for multilayers of cadmium arachidate. Molecular-level origins of these forces are discussed.

The nucleation of thin-film amorphous silicon (a-Si), sputter deposited on oxidized c-Si, is investigated by real-time spectroscopic ellipsometry from 1.5 to 4.5 eV with a resolution of 3 s and a repetition period of 15 s. Analysis of real-time spectra provides unprecedented sensitivity and quantitative information on the microstructural evolution. Under preparation conditions resulting in a-Si of the highest bulk Si-Si bond-packing density, an abrupt transition representing the onset of bulk film growth can be identified unambiguously when nuclei reach a thickness of 13±1 Å.

We show how the intensity enhancement of angle-resolved x-ray photoelectrons along the emitter-scatterer internuclear directions can be used to monitor layer-by-layer growth of Co on Cu(111). Specifically, we show how the technique can distinguish between fcc or hcp growth and determine precisely the thickness at which the fcc stacking switches to hcp. We also show how the interference patterns around each forward-focusing direction can be used to produce real-space images of nearest-neighbor atoms in the atomic plane above the emitting atom.

Fourier-transform photoluminescence spectroscopy has been used to obtain detailed and unequivocal information on the two major transitions involving the deep EL2 level in semi-insulating gallium arsenide. We report the first observation of a shallow, hydrogenic state of neutral EL2, which leads to sharp structure in the luminescence spectrum. This new fine structure should prove extremely useful in perturbation studies of the EL2 defect. These new transitions also locate the energy position of neutral EL2 within the band gap with unprecedented precision.

Through the field dependence of its linewidth, the ${\mathit{s}}_0$ local mode at 83 ${\mathrm{cm}}^{\mathrm{-}1}$ associated with a ${\mathrm{V}}^{2+}$ impurity in ${\mathrm{FeF}}_2$ is used as a novel probe of impurity shell modes, host magnon density of states, and the phonon mixing of the magnon branches at the magnon–acoustic-phonon level crossings. This is the first observation of individual shell modes. ${\mathit{S}}_{\mathit{z}}$-nonconserving and direct exchange interactions contribute to the ${\mathit{s}}_0$-local-mode relaxation. The method has general applicability to antiferromagnets.

Electronic properties of the itinerant electron antiferromagnet ${\mathrm{NpSn}}_3$ were studied by ${}_{}{}^{237}{}_{}{}^{}\mathrm{Np}$ Mössbauer spectroscopy under pressures up to ∼6.2 GPa. These measurements revealed totally unexpected results: With reduced volume the hyperfine field changes very slightly, but the Néel temperature increases strongly. Such a behavior is typical for localized 5f electrons. We propose that ${\mathrm{NpSn}}_3$ should be viewed as a concentrated Kondo system, similar to ${\mathrm{CeAl}}_2$.

We studied elastic constants, ultrasonic attenuation, and ac susceptibility in a high-quality single crystal of ${\mathrm{UPt}}_3$ in the superconducting phase. We investigated the coupling of strain and order parameter for the different elastic modes. A detailed B-T phase diagram for the superconducting phases obtained from elastic-constant measurements is given and compared with theoretical predictions.

We present measurements of longitudinal ultrasonic velocity on single crystals of the heavy-fermion superconductor ${\mathrm{UPt}}_3$. The measurements show clear signatures of second-order phase transitions in the superconducting state, with the velocity anomalies well accounted for by Ginzburg-Landau theory. From these signatures we construct a phase diagram for ${\mathrm{UPt}}_3$ that reveals all the boundary lines that have been identified as possible phase transitions. We are able to track the phase transition lines to a tetracritical point, located on the upper-critical-field curve, to within the width of the normal-superconducting transition.

The response of rf-biased Josephson junctions to special aperiodic driving forces is studied through theory and numerical simulation. It is shown that aperiodic driving forces of very small amplitude can transform the junction from a stationary state into the rotation state. In addition, it can be shown that the resulting dynamics is not chaotic, in contrast to the generic dynamics resulting from a sinusoidal driving force. We discuss possible experimental applications.

In a recent Letter we argued that the existence of an upper Hubbard band necessarily would lead to Luttinger liquid (Z=0) properties for a strongly interacting electron gas, as opposed to Fermi liquid. In this paper we identify the singular-scattering diagrams and make a hypothesis about the form of the ground state of the 2D Hubbard model.

The critical exponents for the charge, spin, electron, and superconducting correlation functions of the one-dimensional t-J model at t=J are obtained for arbitrary band filling. Our method is based on the Bethe-ansatz solution and the finite-size scaling analysis in conformal field theory. The long-distance behavior of the model belongs to the same universality class as the repulsive Hubbard model. Near half-filling the exponents take the values expected in the strong-correlation limit of the Hubbard model. In the low-density limit the exponents are those of the noninteracting system.

Statistical mechanics is applied to estimate the maximal information capacity per synapse (${\mathrm{\alpha }}_{\mathit{c}}$) of a multilayered feedforward neural network, functioning as a parity machine. For a large number of hidden units, K, the replica-symmetric solution overestimates dramatically the capacity, ${\mathrm{\alpha }}_{\mathit{c}}$∝${\mathit{K}}^2$. However, a one-step replica-symmetry breaking gives ${\mathrm{\alpha }}_{\mathit{c}}$∼lnK/ln2, which coincides with a theoretical upper bound. It is suggested that this asymptotic behavior is exact. Results for finite K are also discussed.

We propose a new method for evaluating the decay rates of time correlations in chaotic dynamical systems, based on averaging over periodic orbits. We use a cycle expansion of a Fredholm determinant which is in practice superior to the corresponding expansion for the Ruelle ζ function. The method is tested in one-dimensional expanding maps with the resulting decay rates compared to those obtained in two other independent ways: By a perturbative calculation of the spectrum of the transfer operator and by direct numerical computations of time correlations. Moreover, we show that in general the decay rates are not simply related to generalized Lyapunov exponents.