We show that Bayesian Physical inference, like that used in statistical mechanics, can guide the systematic construction of Fourier dark-field methods for localizing periodicity in near-field (e.g., scanning tunneling and electron phase contrast) images. For crystals in an aperiodic field, the Fourier coefficient ${\mathrm{Ze}}^{\mathrm{icphi}}$ combines with a prior estimate for background amplitude B to predict background phase (β) values distributed with a probability p(β-φ‖Z,φ,B) inversely proportional to amplitude P of the signal of interest, when the latter is treated as an unknown translation scaled to B.

We have measured surface stresses on clean Si(111) 7×7 by comparing this surface to a reference surface on which gallium atoms are adsorbed under UHV conditions. Stresses are determined by optically measuring the macroscopic strain induced in thin samples. We find a surface stress of 2.37 eV/(1×1 cell) for Si(111) 7×7, and a stress in the range 0.90–1.09 eV/(1×1 cell) for the Si(Ga) (111) superlattice associated with one monolayer Ga coverage. Comparison with theory suggests that our technique will be a powerful tool to measure equilibrium stresses in atomically clean surfaces.

We have studied stresses in thin Ge growing on Si(001), in situ and in real time, with submonolayer sensitivity. As a result of the 4.3% lattice mismatch, Ge films develop a compressive stress in the 2D growth regime, which saturates when 3D growth sets in. These measurements give new insight in the interatomic forces that play a dominant role in establishing growth mode and the generation of defects, and provide a new test for state-of-the-art total-energy calculations.

The relaxation of electric birefringence in dilute solutions of a polyelectrolyte is shown to be consistent with a stretched-exponential form, exp[-(t/τ${)}^{\alpha }$]. The exponent α depends on polymer length L and solvent ionic strength only through the ratio x==L/$L_p$, where $L_p$ is the persistence length, and crosses over from α≃1 for stiff chains (x≃1) to α≃0.44±0.02 in the self-avoiding-walk regime x≫1, the latter in accord with a simple scaling theory of polymer statistics and dynamics.

The $L_2$,3 emission spectrum of c-Si, excited by monochromatized synchrotron radiation, has been recorded with a 5-m Rowland spectrometer. Dramatic spectral changes are observed as the excitation energy is varied from the 2p binding energy up to 144 eV. It is proposed that a spectator electron, close to the bottom of the conduction band, influences the emission spectrum. The observations suggest that intraband shakeup is important in the excitation process, and that a population of low-lying levels, via initial-state shakeup, influences the high-energy-excited Si L emission spectrum.

The local potential created by photoexcited electron-hole pairs at the surface of clean and partially oxidized Si(111)-(7×7) surfaces is probed with a scanning tunneling microscope. Strong reductions in the surface photovoltage on the 15–20-Å length scale are observed due to localized surface recombination centers. The dependence of the local photovoltage on illumination intensity allows recombination effects to be distinguished from band bending. Virtually all defects on Si(111)-(7×7) increase the combination rate by destroying the two-dimensional order and increasing the coupling between surface and bulk states.

Photoluminescence has been observed in the energy range 0.7 to 0.9 eV in short-period Si/Ge strained-layer superlattices grown on Si(100) and Ge(100) substrates. The luminescence is strongly influenced by period, layer-thickness ratio, and strain distribution. The experimental results are in good agreement with the expected fundamental energy gaps of the superlattices as calculated with a Kronig-Penney–type model.

We have explored the relationship between epitaxial growth and magnetism in the case of ultrathin fcc-Co films by means of a multitechnique approach. For high-quality fcc-Co films less than 3 monolayers thick the Curie temperatures ${\mathrm{T}}_{\mathrm{C}}$ are dramatically lower than ${\mathrm{T}}_{\mathrm{C}}^{\mathrm{B}}$ of bulk fcc-Co and decease distinctly with film thickness. In contrast to previous claims, ${\mathrm{T}}_{\mathrm{C}}$ of a single monolayer appears to be far below 300 K. Substrate topology is found to strongly influence the structural perfection of the films which in turn determines their magnetic properties (Curie temperature, coercive field, and anisotropies).

In layered superconductors with very weak coupling between the layers the concept of a flux-line lattice breaks down when the field is oriented parallel to the superconducting planes. For an arbitrary field orientation we propose that the formation of an Abrikosov lattice is only related to the perpendicular field component. The parallel field component penetrates as if the superconducting planes were completely decoupled. This model explains recent experiments which have questioned the driving mechanism for dissipation in the superconducting phase of the high-temperature oxide superconductors.

Reflectance spectra of polycrystalline n-type ceramic superconductors ${\mathrm{Nd}}_{1.85}$${\mathrm{R}}_{0.15}$${\mathrm{CuO}}_{4\mathrm{-}\mathit{y}}$(R=Ce and Th) were measured over the range from 2 to 300 K from 20 to 10 000 ${\mathrm{cm}}^{\mathrm{-}1}$. The spectra and reflectance ratios show a number of prominent features. Those which show no significant temperature dependence over this temperature range are assigned to lattice vibrations of free-carrier excitations. Increases in reflectivity below about 50 ${\mathrm{cm}}^{\mathrm{-}1}$ occur on the transition into the superconducting state. Energy gaps inferred from them for excitations along the c axis are in the range predicted by BCS theory.

The forward-backward asymmetry of quarks produced in $e^{+}$$e^{\mathrm{-}}$ annihilations, summed over all flavors, is measured at √s between 50 and 60.8 GeV. Methods of determining the charge direction of jet pairs are discussed. The asymmetry is found to agree with the five-flavor standard model.

We measured the differential jet-multiplicity distribution in $e^{+}$$e^{\mathrm{-}}$ annihilation with the Mark II detector. This distribution is compared with the second-order QCD prediction and ${\alpha }_s$ is determined to be 0.123±0.009±0.005 at √s≊${\mathit{M}}_{\mathit{Z}}$ (at the SLAC Linear Collider) and 0.149±0.002±0.007 at √s=29 GeV (at the SLAC storage ring PEP). The running of ${\mathrm{\alpha }}_{\mathit{s}}$ between these two center-of-mass energies is consistent with the QCD prediction.

The yields and the transverse-momentum distributions of pions, kaons, and antiprotons produced in the central region of p¯p collisions at √s =1.8 TeV at the Fermilab Tevatron collider have been measured up to a charged-particle pseudorapidity density of approximately 20. The average transverse momentum 〈$p_t$〉 as a function of 〈${\mathrm{dN}}_c$/dη〉 for all three types of particles is presented.

Data are presented for the left-right asymmetry in inclusive production of ${\pi }^{+}$, ${\pi }^{\mathrm{-}}$, and p with proton beams (polarized normal to the scattering plane) of 13.3 and 18.5 GeV/c incident on a ${\mathrm{LH}}_2$ target. At both energies the asymmetry in ${\pi }^{+}$ production grows steadily to about 25% near the kinematic limit, whereas the ${\pi }^{\mathrm{-}}$ and p asymmetries are consistent with zero over the measured range of $p_t$, 1.1–2.2 GeV/c.

The recent measurements of Z decay at the SLAC Linear Collider and the CERN $e^{+}$$e^{\mathrm{-}}$ collider LEP, when combined with nonaccelerator experiments, rule out various weakly-interacting-massive-particle (WIMP) candidates for dark matter including Dirac neutrinos, and strongly constrain all others. I discuss this, along with other implications of current Z measurements for the discovery of WIMP’s in the laboratory.

We consider the effect of disorder on coherent tunneling of electrons through a double-barrier structure. When the disorder potential is treated in leading order we obtain a result with transparent physical consequences. The effect of interface roughness on resonant tunneling is shown to depend qualitatively on the location of the rough interface. Our results may help to explain the often observed asymmetry in the current-voltage characteristics of double-barrier structures.

Certain subsystems of nonlinear, chaotic systems can be made to synchronize by linking them with common signals. The criterion for this is the sign of the sub-Lyapunov exponents. We apply these ideas to a real set of synchronizing chaotic circuits.

A recent experiment reporting an anomalous weight reduction for a spinning gyroscope weighed on a pan balance has been repeated in our laboratory. We find no anomalous weight changes of the magnitude reported that depend on rotor speed and/or rotational sense about the vertical axis.

We outline the construction of D=4 type-I superstrings in the fermionic formulation. Two models are presented as examples, one of which is space-time supersymmetric and finite at the one-loop level.

We discuss a natural generalization of the McClain-Roth-O’Brien-Tan theorem in the context of interacting bosonic strings at finite temperature and explain a discrepancy between the Polyakov path-integral approach and the multiloop operator formalism in the calculation of the string free energy at higher genus.