The opening of a new channel of excitative Penning ionization by a collision-complex absorption of laser light has been observed in the system Ar*(${}_{}{}^3{}_{}{}^{}P$) + Ca. Two relatively broad resonances at 5958 and 5990 Å were found, corresponding to the production of ${\mathrm{Ca}}^{+}$($5p{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$) and ${\mathrm{Ca}}^{+}$($5p{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$), respectively. The data indicate that the laser-assisted Penning-ionization cross section to these states exceeds that of the field-free ionization to ${\mathrm{Ca}}^{+}$($4p{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$).

A homogeneously broadened two-mode ring laser has two metastable states in which one or the other mode intensity is zero. Quantum fluctuations cause the system to switch spontaneously, and at random times, between these states. The probability distribution of the light intensity of one laser mode has been measured, and found to exhibit two completely resolved peaks at zero and nonzero intensities, as predicted. This confirms the existence of a first-order laser phase transition.

Sufficiently long population decay times and sufficiently short dipole decay times in a single-mode laser with saturable absorber permit passive $Q$ switching in the form of a hard-mode sustained relaxation oscillation.

If an extraordinary wave is normally incident on a large volume magnetoplasma, then below the second gyroharmonic, conversion into short-wavelength Bernstein waves is observed near the upper-hybrid layer. Significant conversion efficiency is attained in the optimum conditions. For high power incidence, considerable electron heating due to the converted wave is found to be localized in the mode-conversion region.

By injecting rf power $P_{\mathrm{rf}}$ near the lower hybrid frequency into an Ohmically heated plasma near the end of tokamak discharge in the WT-2, an rf-driven current-sustained plasma is produced and continues to exist during the rf injection period, the toroidal current ($I_p\sim 10$ kA) being generated by the lower hybrid wave only without the Ohmic power. The efficiency of rf-driven current generation is high and attains $\frac{I_p}{P_{\mathrm{rf}}}\approx 0.9$ kA/kW at the plasma density $n_e\simeq 1.4\times {10}^{12}$ ${\mathrm{cm}}^{-3\mathrm{}}$, with somewhat lower efficiency at higher density.

The phonon transmission from solid to liquid helium has been measured at temperatures in the range 0.1 to 0.5 K. The results support the theory of Marchenko and Parshin in which the phonon transmission occurs because of capillary effects at the interface.

Based on pseudopotential local spin-density calculations, it is proposed that the minimum-energy Si(111) nonbuckled surface is stable against 2×1 buckling distortions. A 2×1 antiferromagnetic spin-density wave, localized on the surface, enhances the stability of this structure.

Several qualitatively different structural models have been examined in a critical evaluation of spectroscopic and other data for the Si(111)-(2×1) surface. Within the one-electron theory, only a novel $\pi$-bonded chain model with a covalent surface, and not the generally accepted buckled model with an ionic surface, is consistent with the data.

Recent x-ray data on the angles and 2-theta shifts in the smectic-$C$ phase of a binary liquid-crystal mixture were analyzed via a mean-field theory. We demonstrated that the smectic-$A$-smectic-$C$ transitions ($\mathrm{AC}$) are mean-field-like. This conclusion is consistent with recent heat-capacity data along the $\mathrm{AC}$ transition line. Furthermore, the nematic-smectic-$A$-smectic-$C$ point in this binary mixture is found to be in the vicinity of the tricritical point along the $\mathrm{AC}$ and nematic-smectic-$C$ transition line.

By use of the new technique of electroreflectance in the infrared frequency range, a low-lying unoccupied surface state on the (100) single-crystal surface of Ag has been detected. Another absorption feature, due to excitation into a higher surface state, has been seen around 3.1 eV. The positions of the two surface states are in good agreement with the calculated values. A study of the Stark shift of these states has revealed that the electric field near the metal surface has a much more complex structure than hitherto recognized.

The exchange-interaction parameters $J_1$ and $J_2$ determine the type of magnetic ordering in ${\mathrm{Eu}}_x{\mathrm{Sr}}_{1-x}{\mathrm{S}}_y{\mathrm{Se}}_{1-y}$. The ratio $\frac{J_2}{J_1}=-1\mathrm{}$, which holds at a concentration $y=0.1\mathrm{}$, appears as a critical point in the magnetic phase diagram. Close to this point mictomagnetism is observed in samples with Eu concentration high but lower than a critical value.

The dispersion equation of injected surface-plasma waves that propagate on thin metal films has been solved as a function of the film thickness, and splitting of the modes into two branches is observed. For one branch the imaginary part of the propagation constant goes to zero as the thickness of the metal decreases. Reflectivity calculations agree with this result, which predicts that one can obtain propagation distances that are more than 1 order of magnitude larger than observed before.

The pinning force $F_p$ in amorphous ${\mathrm{Nb}}_3$Ge films with $T_c\sim 4$ K has been measured as a function of perpendicular field, temperature, and thickness of the samples. As a result of the large $\kappa$ and low $J_c$ characteristic of amorphous superconductors the pinning force for the first time is found to be in good agreement with the theory of Larkin and Ovchinnikov for collective pinning extended to the two-dimensional case. Pinning-mediated renormalization of the shear modulus leads to a sharp peak in $F_p$ near the upper critical field.

$\mathrm{SU}\mathrm{}\left(N\right)\mathrm{}\otimes \mathrm{SU}\mathrm{}\left(N\right)\mathrm{}$ spin systems in two dimensions are studied for $N=2, 3, \mathrm{and} 4$ on 10×10, 20×20, and 30×30 lattices with use of Monte Carlo methods. Variant forms of the action are considered. In addition to crossover phenomena, unexpected first-order transitions in multidimensional phase diagrams are discovered. These transitions are related to the presence of $Z_N$ vortices which experience short-range interactions. Contrasts with $\mathrm{SU}\mathrm{}\left(N\right)\mathrm{}$ gauge theories in four dimensions are drawn.

A nontrivial family of $d$-dimensional scale-invariant fractal lattices is described, on which statistical mechanics and conductivity problems are exactly solvable for every $d$. These fractals are finitely ramified but not quasi one dimensional, and hence can be used to model the important geometrical features of the percolating cluster's backbone. Critical exponents calculated for this model agree with those of "real" systems at low dimensionalities.

A generally applicable gauge-invariant renormalization transformation is proposed for the study of lattice gauge theories. Practical calculations can be carried out with use of Monte Carlo computer simulations. The power and efficiency of this approach is demonstrated by explicit calculations for the $Z\mathrm{}\left(2\right)\mathrm{}$ lattice gauge theory in three dimensions.

In the tagged-photon beam at Fermilab, differential cross sections were measured for the elastic scattering of photons on a liquid-hydrogen target. The diffractive forward peak was measured for photon energies between 50 and 130 GeV and $\left|t\right|$ values between 0.07 and 1.20 ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$. The shape of the diffraction peak is similar to that seen in $\pi -p$ scattering. The magnitude is that predicted by the optical theorem.

A study of quasielastic $\omega$ photoproduction where the $\omega$ was detected in its ${\pi }^0\gamma$ decay mode is reported. The recoil proton's angle was detected with a nonmagnetic spectrometer allowing a full reconstruction of the final state. Differential cross sections for $0.1<\left|t\right|<\mathrm{}1.2\mathrm{}$ ${\mathrm{GeV}}^2$ are presented, providing a test of the vector-meson dominance model over an extensive energy and momentum transfer range. The shape of the differential cross section agrees with that seen in both elastic $\gamma p$ and $\pi p$ scattering as expected from this model.

Naturalness arguments are presented vis-á-vis the chiral symmetry of the lightest fermionic generation, in support of Glashow's Ansatz on the proportionality between the mass matrices of the charge-$\frac{2}{3}$ quarks and of the leptons, leading to a prediction on the top mass.

An electroweak gauge model is discussed, where generations are associated with separate gauge groups with different couplings. The observed $\mu -e$ universality is the result of a mass-scale inequality, ${\nu }_{03}\ll {\nu }_{12}$, in much the same way as strong isospin is the result of $m_u$, $m_d\ll 1$ GeV. However, in contrast to the standard model, it is now possible to have (1) a longer $\tau$ lifetime, (2) an observable $B^0-{\overline{B}}^0$ mixing, and (3) many gauge bosons $W_i$,$Z_i$ in place of $W$,$Z$ with $M_{W_i}>M_W$ and $M_{Z_i}>M_Z$.