The conventional left-right gauge model based on the group SU(3)×SU(2${)}_{\mathrm{L}}$×SU(2${)}_{\mathrm{R}}$×U(1) is extended to include singlet quarks and leptons but the usual Higgs-boson doublet-doublet is replaced by two doublet-singlets and two singlet-doublets. As a result, realistic radiative masses for light quarks and leptons can be obtained. Neutrino masses are further suppressed by the seesaw mechanism. There is no need for any assumed discrete symmetry.

A novel form of the free-string field action is proposed for both the closed bosonic string and the heterotic string.

Measurements of the β anisotropy of the mirror nuclei ${}_{}{}^{15}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{17}{}_{}{}^{}\mathrm{F}$, using on-line isotope separation and low-temperature nuclear orientation, are reported for the first time. Results of this novel approach are discussed in connection with the study of weak interactions in nuclei.

‘‘Complete’’ valence photoelectron spectra of neon and argon have been measured at several photon energies between 50 and 150 eV. Besides a symmetric shake-off energy spectrum as anticipated theoretically many unexpected electron lines with fixed kinetic energy were observed, particularly in the low-energy part of the spectra. These lines are identified as due to participator Auger transitions from inner-valence satellite states. The consequence of the measured strengths of the valence Auger transitions regarding the common interpretation of valence double-ionization rates in terns of shake-off processes is discussed.

The role of multiphoton resonances in the above-threshold ionization of helium at intensities above ${10}^{14}$ W/${\mathrm{cm}}^{\mathrm{-}2}$ is investigated by both theory and experiment from 280 to 297 nm. Strong enhancement is observed in above-threshold ionization electron spectra and is attributed to five- and six-photon resonances to the 1s2p and 1s3d, respectively. Numerical solution of the time-dependent Schrödinger equation predicts asymmetric resonance profiles with positions and ionization rates which are in good agreement with experiment.

Harmonic absolute instability in the ${\mathrm{TE}}_{21}$ mode is found to cause mode competition in a new millimeter-wave gyrotron traveling-wave experiment designed for high stability in the ${\mathrm{TE}}_{11}$ mode. Complete suppression of this instability by the application of the ${\mathrm{TE}}_{11}$ drive has been observed with beam current up to at least 6 times the instability threshold, which results in high amplified power (∼25 kW) at high efficiency (∼23%). The study is significant in that it demonstrates that cyclotron-maser amplifiers may operate at a current well above oscillation threshold without degradation in saturated performance.

A new nonclassical model is proposed for the radiation from electrons skimming over and colliding at grazing incidence with a conducting diffraction grating. Radiation originating from induced surface currents and bremsstrahlung is amplified as it passes through spatially modulated wave functions above the grating. The predicted magnitude and dependence on electron beam thickness agree with experiments at visible wavelengths and suggest the possibility of a compact x-ray laser.

Using light scattering, we have studied the effect of shear on nucleation in the binary-fluid mixture 2,6-lutidine + water. The experimental method differs from traditional ones, in that the measurements were made in the steady state: droplets which formed in the quenched mixture were constantly being ruptured by the continuous shear. The shear was produced by the spinning of a stirrer magnet inside the sample. It was found that when the stirring frequency f exceeds, by a very small amount, some critical value ${\mathrm{f}}_{\mathrm{c}}$ (for a fixed quench depth δT), the scattering changes by orders of magnitude. Our results are compared with a simple theory of Onuki and Takesue.

We present a molecular-dynamics study of a system of end-grafted polymers between parallel surfaces. We find that the forces between the surfaces as a function of their separation can be described both by scaling and self-consistent field theories and agree with the experiments of Taunton et al. We quantify the amount of interpenetration of the two brushes and describe it with a simple scaling form. Overall monomer density profiles as well as the contribution from each brush are also presented.

We consider the rate at which bubbles form when a negative pressure is applied to liquid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. We show that at a critical pressure ${\mathrm{P}}_{\mathrm{c}}$ of about -9 bars, the liquid becomes macroscopically unstable and the barrier against nucleation of bubbles becomes zero. The tensile strength of liquid helium is calculated as a function of temperature allowing for these effects.

Structural phase transitions in amorphous solids associated with vanishing bulk modulus K or shear modulus μ are considered. We find that the transition (realized in gels) at K=0, though of second order, does not exhibit true scaling behavior of density fluctuations. An isotropic state with vanishing μ is unstable to the formation of an anisotropic glassy phase that has a phonon spectrum exhibiting soft directions in momentum space similar to those in liquid crystals. The effects of internal random stresses are studied.

Direct observation of the removal of the ‘‘missing row’’ reconstruction of the clean Pt(110) surface under the influence of CO adsorption by scanning tunneling microscopy revealed that at 300 K this process is initiated by homogeneous nucleation of small characteristic 1×1 patches. Their further growth is limited by thermal activation; migration of Pt atoms is restricted to a few lattice sites. At higher temperatures, correlated jumps cause the lateral displacement of longer chains, and the enhanced surface mobility leads to the formation of larger, strongly anisotropic 1×1 islands.

Employing first-principles calculations, we have studied the behavior of hydrogen in crystalline silicon under compression and tension. The stable site for hydrogen is found to depend critically on both the pressure and on the hydrogen charge state. In particular, as a function of pressure, hydrogen undergoes a transition from an energy minimum at the tetrahedral interstitial site to one at the bond-center site. This results has implications for the behavior of hydrogen in the stress fields of dislocations, grain boundaries, and crack tips.

We present a novel first-principles calculation of the microscopic and macroscopic capture cross sections due to acoustic-phonon processes. The role of excited levels in determining the recombination is naturally included and found to be of main importance at increasing lattice temperatures. Numerical results compare favorable with available experiments.

We have measured activation energies for fractional-quantum-Hall-effect (FQHE) states with a magnetic field added in the plane of the two-dimensional electron gas. Our data are incompatible with calculations of the expected finite-size corrections due to the added parallel field. Instead, the activation energies for some FQHE states depend linearly on the total magnetic field; others depend only on the perpendicular magnetic field. These dependencies indicate that spin-flip excitations are important for certain FQHE gaps.

A large exchange enhancement of the spin-splitting of a two-dimensional electron gas in GaAs has been determined from optical spectroscopy. When the Fermi energy is located between the spin-split electron states (ν=1), we observe a striking temperature dependence in the optical absorption of interband transitions associated with both spin levels. The absorption intensity of the transitions monitors the occupations of the spin-split levels. Analysis of the temperature dependence reveals an exchange enhancement of the electron g factor of ≊9. .AE

The thermal fluctuation of the vortex positions in type-II superconductors with large Ginzburg-Landau parameter κ and weak pinning is drastically increased when calculated from the correct nonlocal elasticity of the vortex lattice. As compared to the usual (local) elastic result, the mean-square shear strain and vortex displacements increase by a factor of ≊(B¯/${\mathit{B}}_{\mathit{c}1}$${)}^{1/2}$/(1-B¯/${\mathit{B}}_{\mathit{c}2}$${)}^{1/2}$ (B¯ is the flux density, $B_{c1}$ and $B_{c2}$ are the lower and upper critical fields). The melting temperature of the vortex lattice is reduced by the same factor.

We prove a theorem on the O(3) nonlinear σ model with the topological θ term which states that the grround-state energy at θ=π is always higher than the ground-state energy at θ=0, for the same value of the coupling constant g. Provided that the nonlinear σ model gives the correct description for the Heisenberg spin chains in the large-s limit, this theorem makes a definite prediction relating the ground-state energies of the half-integer- and the integer-spin chains. The ground-state energies obtained from the exact Bethe Ansatz solution for the spin-(1/2 chain and the numerical diagonalizaton on the spin-1,- (3/2, and -2 chains support this prediction.

We reconsider the high-frequency susceptibility of partially magnetized uniaxial ferrimagnets. For a demagnetized sample, effective-medium theory reproduces the exact result. Spontaneous resonances appear in a band of frequencies, in which the susceptibility follows a universal behavior. A new effect is found; a weak magnetization m ‘‘digs a hole’’ in this resonant band, of width proportional to m. The formula we propose agree with experimental data, from which microscopic parameters can be obtained. These also apply to the resistivity of a 2D conductor in a random magnetic field.

We calculate the spin-spin relaxation function for a two-dimensional quantum antiferromagnet of arbitrary spin at low temperature from first principles. The calculation justifies the picture of the excitations of the system as a weakly interacting Bose gas of spin waves.