Superheavy particles near the unification threshold introduce modifications to precise grand-unified-theory (GUT) predictions. We establish a very useful and general theorem valid in a class of models possessing the custodial symmetry SU(2${)}_{\mathit{L}}$×SU(2${)}_{\mathit{R}}$×SU(4${)}_{\mathit{C}}$×P at the highest intermediate scale, according to which the one-loop GUT-threshold contribution to ${\sin }^2$${\mathrm{\theta }}_{\mathit{W}}$ by every class of superheavy particles (gauge bosons, Higgs scalars, and additional fermions) vanishes. The result also applies with supersymmetry, infinite towers, or higher-dimensional operators, and is independent of other intermediate symmetries at lower scales.

We have computed analytically within the framework of perturbative QCD the O(${\mathrm{\alpha }}_{\mathit{s}}^3$) corrections to the Bjorken sum rule for deep-inelastic neutrino-nucleon scattering. For five active flavors the correction is about -8.49 (${\mathrm{\alpha }}_{\mathit{s}}$/π${)}^3$ times the zeroth-order contribution within the modified minimal-subtraction scheme.

Fermilab experiment 711 has investigated proton-nucleus collisions in which two high-transverse-momentum hadrons are produced forming high-mass ++, +-, and -- charged states, using an 800-GeV/c proton beam on targets of beryllium, aluminum, iron, and tungsten. Our data cover the range in dihadron mass from 6 to 15 GeV/${\mathit{c}}^2$. We show here that the dependence of the cross section on atomic weight A can be parametrized as ${\mathit{A}}^{\mathrm{\alpha }}$ where α=1.043±0.011(stat)±0.025 (syst), and is independent of the charge state of the dihadron system.

A microscopic model for estimating ${\mathit{n}}_0$, the initial number of degrees of freedom used in calculating pre-equilibrium nucleon emission from heavy-ion reactions, is presented. The model follows the evolution of the geometrical and phase spaces during the process of the gradual fusioning of the target and the projectile. A good agreement is found between the calculated values of ${\mathit{n}}_0$ and the empirical values extracted from fits to nucleon spectra.

High-energy photon and neutron emission has been measured in coincidence with fission fragments in α${+}^{232}$ Th reactions at 170 MeV. From measurements parallel and perpendicular to the fission plane, anisotropies relative to the reaction plane were determined. The in-plane/out-of-plane intensity ratio is 0.72(7) for photons with energies above 20 MeV and 11(3) for neutrons at 35 MeV. The result for high-energy photons can be explained by nucleon-nucleon bremsstrahlung if the initial flow of nucleons has a correlation to the reaction plane similar to the one observed for fast neutrons.

Using parity projection and the generator-coordinate method we investigate the left-right-asymmetric softness of the superdeformed minimum of ${}_{}{}^{194}{}_{}{}^{}\mathrm{Pb}$. The collective wave functions exhibit large octupole dipsersions. Our calculation suggests that above the ground-state superdeformed band there should exist a negative-parity band of similar quadrupole deformation with an excitation energy close to 2 MeV.

A perturbation theory for determining the electron-nuclear coupling corrections to the adiabatic expectation values of operators of molecular systems is developed and applied to the hyperfine Hamiltonian of the hydrogen molecular ion. The expectation values of the Fermi contact parameter for the rotation-vibration states N=1, v=4–8 are compared with experimental results. Previous adiabatic expectation values differ from the empirical values by about 600 kHz. Inclusion of the first-order corrections reduces the discrepancies to less than 9 kHz.

A new high-resolution measurement of the C 1s near-edge photoabsorption spectrum of the ethylene molecule is reported. An analysis of the vibrational structure in the C 1s-${\mathrm{\pi }}^{\mathrm{*}}$ band indicates strong excitation of non-totally-symmetry modes and the importance of vibronic coupling. The latter phenomenon provides a mechanism for core-hole localization in the final state.

We observed the change in fluorescence lifetime from a molecular dye embedded in a colloidal suspension of polystyrene spheres when the mean separation between spheres remains less than the wavelength of emission. At high densities of colloidal particles the spontaneous emission is inhibited, while as the density of colloidal particles is lowered the spontaneous emission is enhanced. This phenomenon is interpreted in terms of coherent interference from the electric field radiated by the molecular dipole and the reradiated field from the dielectric spheres.

Combining methods and ideas of dynamical systems theory with the usual stability analysis for extended hydrodynamic systems we show that defect-mediated turbulence is a generic consequence of a set of physical properties which are shared by many systems. We show how the interplay between broken continuous symmetries and the dynamics of patterns leads to a universal scenario for the onset of this type of turbulence.

The conformal-invariance approach is extended to two-dimensional critical systems with mixed ab boundary conditions. The profiles 〈φ(r)${\mathrm{〉}}_{\mathit{a}\mathit{b}}$ of the magnetization and the energy density in Ising and Q-state Potts strips with +- and fixed-free boundary conditions are derived. The profile of an arbritrary operator degenerate at level 2 is expressed in terms of hypergeometric functions. The universal amplitudes ${\mathit{A}}_{\mathit{a}\mathit{b}}$${\mathit{B}}_{\mathit{a}\mathit{b}}$ of the Casimir force and the Fisher–de Gennes distant-wall correction to the profile satisfy ${\mathit{B}}_{\mathit{a}\mathit{b}}$=-4π${\mathit{x}}_{\mathrm{\phi }}$${\mathit{c}}^{\mathrm{-}1}$${\mathit{A}}_{\mathit{a}\mathit{b}}$. Here ${\mathit{x}}_{\mathrm{\phi }}$ is the scaling dimension of φ(r) and c is the central charge.

We study adsorption-desorption kinetics of polymer chains at a solid surface. Protio polystyrene, adsorbed from cyclohexane to a single surface of oxidized silicon, was displaced by deuterio poly- styrene. A single time constant, ${\mathrm{\tau }}_{\mathrm{off}}$, described displacement for a significant time (1–2 h). An aging effect, in which ${\mathrm{\tau }}_{\mathrm{off}}$ continued to increase even after mass adsorbed had equilibrated, implied surprisingly slow rearrangements of adsorbed chains in the direction of conformational equilibrium. After equilibration, ${\mathrm{\tau }}_{\mathrm{off}}$ increased exponentially with length of adsorbed chains.

Small- and wide-angle x-ray-diffraction measurements on the ${\mathrm{P}}_{\mathrm{\beta }\prime }$ phase of fully hydrated DL-β,γ-dipalmitoyl-α-phosphatidylcholine were performed in highly oriented lipid-water multibilayer samples. The data extend previous results on the ripple structure of this phase, as obtained by x-ray diffraction and scanning tunneling microscopy, and for the first time provide evidence that ${\mathrm{theL}}_{\mathrm{\beta }\prime }$→${\mathrm{P}}_{\mathrm{\beta }\prime }$ phase transition is characterized by a change in hydrocarbon-chain tilt direction, from the ortorhombic binto the a direction.© 1991 The American Physical Society

A chiral four-state clock-step model is introduced to describe the deconstruction and roughening of missing-row-reconstructed (110) facets of fcc crystals. Unlike simple cubic (110) facets, a reconstructed rough phase is absent. Roughening induces a simultaneous deconstruction transition, which at zero chirality has central charge c=1.5 and both Ising and conventional roughening critical exponents. Pt(110) and Au(110) are suggested as realizations of this at small chirality, where this transition has the character of an incommensurate melting transition into a rough incommensurate missing-row fluid.

We present extensive molecular-dynamics simulations of small gold particles of N=100–900 atoms. We use a many-body interatomic potential of proven accuracy for gold surfaces. Structural properties are determined with various annealing strategies. Our results provide for the first time a microscopic description of the melting transition of metal clusters, revealing in particular the formation of a liquid skin as precursor effect for N>350. The experimentally observed sharp decrease of the melting temperature with decreasing size is recovered. Implications for larger sizes, as well as for other metals, are discussed.

We present a formulation for calculating entropy based on the application of classical transition-rate theory to quantum-mechanical energy surfaces. Using this approach, which avoids difficulties due to anharmonicity and large energy barriers, we calculate the entropy of concerted exchange (CE) in Si and find it to be 3.3k in the high-temperature regime. The relatively high entropy of CE is traced to multiple equivalent exchange paths and to a a combination of a stiff mode at the equilibrium and a soft mode at the saddle-point configurations. Comparison to harmonic-approximation results shows substantial differences, in both the low- and in the high-temperature limits.

Inelastic-neutron-scattering techniques have been used to measure the generalized phonon density of states in superconducting ${\mathrm{Nd}}_{1.85}$${\mathrm{Ce}}_{0.15}$${\mathrm{CuO}}_4$. There is reasonable agreement at low energies between our measurements and recent point-contact-tunneling density-of-states measurements reported by Huang et al., which suggests that phonons play a major role in pairing in the electron-superconductor systems. The correspondence at higher energies, however, is not particularly good, but probably reflects the difficulty in obtaining quantitative tunneling data.

Giant transport anomalies in (Fe,Ru)-Cu-Al quasicrystals can be explained by an internal structural model based on two large building blocks, one icosahedral and one layered. The model explains a wide variety of electronic and structural regularities.

Below a critical filling factor (${\nu }_{\mathit{c}}$=0.28) and critical temperature (${\mathit{T}}_{\mathit{c}}$=1.4 K at 26 T) an additional line has been observed in the luminescence spectrum of a GaAs-${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As heterojunction; it grows in intensity with decreasing ν, dominating the spectrum at ν<1/11. Its appearance is accompanied by a strong reduction in overall integrated intensity, while its relative intensity decreases sharply at ν=1/5, 1/7, and 1/9. The lack of correlation between ${\nu }_{\mathit{c}}$ and the disorder-related properties of the system indicates the intrinsic nature of the line which we propose signals the formation of a pinned Wigner solid.

Many features found in the resistance of a junction between quasi-one-dimensional wires have been recently attributed to classical ballistic effects. Using experiments and calculations, we show that at low temperature, electron confinement and coherent scattering from the leads and impurities give rise to sharp minima in the resistance of a bend, associated with subband thresholds. These minima are interpreted as a feature of the average resistance, unlike conductance fluctuations in disordered wires.