The qualitative form of the predictions of Light and Szöke for an optical collision involving the $\lambda =460.7\mathrm{}$-nm transition in strontium perturbed by argon has been verified. In the presence of linearly polarized laser light the $m_J=0\mathrm{}$ to $m_J=0\mathrm{}$ is "switched off" at large field intensities (≳ 50 MW/${\mathrm{cm}}^2$) whereas the $m_J=0\mathrm{}$ to $m_J=\pm 1$ transition is not observed to saturate. The consequences for the study of laser-induced phenomena is discussed.

Time-dependent free convective flow phenomena are investigated in slender vertical containers heated from below. Power-density spectra are calculated from time-dependent thermocouple signals. The range of oscillatory convective flow yields periodic, quasiperiodic, or stochastic structures. After stochastic flow, quasiperiodic and periodic oscillations reappear with increasing temperature difference. Finally, at even higher Rayleigh numbers, a stationary flow pattern develops.

Measurements of the divertor-region plasma characteristics and argon exhaust efficiencies of the expanded-boundary divertor are reported. High plasma and neutral-hydrogen densities (∼${10}^{14}$/${\mathrm{cm}}^{-3\mathrm{}}$) are observed in the divertor region, and the exhaust efficiency for injected argon exceeds 95%. A simple model based on electron heat conduction parallel to the diverted field lines and frictional force due to proton-argon collisions in the divertor region accurately describes the experimental observations.

It is shown that the upper hybrid mode can collapse into thin magnetic-field-aligned filaments as a result of coupling to the electrostatic ion-cyclotron mode.

A continuum of $\theta$-parametrized gauge transformations is used to relate the order-parameter correlation function, $G_{\theta }(\overrightarrow{\mathrm{x}}, 0)$, in gauge $\theta$ to that in the transverse gauge ($\theta =\frac{\pi }{2}$). The exponent ${\eta }_{\theta }$ depends continuously on $\theta$ at an isotropic critical point. In the physical gauge ($\theta =0\mathrm{}$) in three dimensions ($d=3\mathrm{}$), Caillé's results for reduced temperature $t<\mathrm{}0\mathrm{}$, and a finite susceptibility at $t=0\mathrm{}$ at an isotropic critical point are found. For $t=0\mathrm{}$ and $d=3\mathrm{}$, the correlation lengths obtained from $G_0$ differ from those obtained from $G_{\frac{\pi }{2}}$ and satisfy ${{\xi }_{\parallel }}^{\mathrm{x}}\sim \frac{{\left({{\xi }_{\perp }}^{\mathrm{x}}\right)}^2}{\ln {{\xi }_{\perp }}^{\mathrm{x}}}$.

It is shown that the ESR modes observed in Cu: Mn alloys can be explained in terms of an Edwards-Anderson-type theory for a spin-glass when an anisotropy energy is included. Unlike other theories, the present one involves the conventional form for this anisotropy, $U_K=K{sin}^2\theta$, where $\theta$ is the angle the local microscopic magnetization makes with the symmetry rather than equilibrium direction. The present theory is distinguished by a predicted, but as yet unobserved, angular dependence of single-crystal samples with axial symmetry.

Measurements of the magnetoresistance are reported for a series of granular aluminum specimens on the metal side of the metal-insulator transition. A clear separation can be made between the effects of localization and those of electron-electron interactions. Sufficiently far on the metal side localization effects dominate. At high fields, interactions account for the observed dependences on resistivity and temperature, both of which are absent in the localization theory.

The effects of two-dimensional electron localization have been studied by measuring thermopower and resistivity of thin (18-25 Å) films of palladium. "Metallic" samples have a small thermopower which tends to zero as $T\to 0$. Insulating samples have large thermopower which increases as $T\to 0$. The metal-insulator transition in Pd films thus involves the opening of a gap at the Fermi energy. With use of the thermopower to define the metal-insulator transition a critical resistivity of ∼ 30 kΩ/□ is found.

Monte Carlo simulations show that for a system of Ruderman-Kittel-Kasuya-Yosida-coupled classical spins there exists an energy below which the system remains trapped near a single energy minimum. Provided that a small amount of anisotropy is introduced the system then exhibits, in the neighborhood of this energy, (a) a spin-glass-like peak in the susceptibility $\chi$, (b) a well-marked maximum at $\frac{d^2\chi }{d{H}^2}$, and (c) evidence for spin freezing at lower energies. Without anisotropy these effects are absent.

A new Monte Carlo approach applicable to systems with fermion and boson degrees of freedom is proposed. The main advantage of the method is its speed: For systems in one space and one time dimension (1 + 1) the calculation reduces to doing Monte Carlo computations on a two-dimensional classical system with local interactions. Here the potential of the method is illustrated by application to various (1 + 1)-dimensional systems.

The first measurements of the second-overtone absorption spectrum of solid $n$-${\mathrm{H}}_2$ are reported. The observed frequencies and line strengths are not predicted from the known high-pressure gas data, but the trend is consistent with similar data for the fundamental band. The observation of this very weak optical absorption provides important data for reexamination and extension of theoretical treatment of this important molecular solid.

A magnetic-field-induced optical linear dichroism has been observed in photolyzed $\beta$-hemoglobin at temperatures below 20 K. Nonadiabatic reaction rate theory for spinforbidden processes predicts a magnetic modulation of the tunneling rate which may account for the signal observed. The effect observed should be sensitive to crystal-field energy-level splittings for the iron atom in the heme group.

The generalized $H$ theorem, ${(-\frac{d}{\mathrm{dt}})}^{n}H>~0$, is verified for $n<~30$ for the Bobylev-Krook-Wu solution of the Boltzmann equation, and for $d$-dimensional generalizations of that solution, $1<~d<~6$.

A self-consistent effective-medium approximation is presented for the problem of diffusion and ac conductivity on a lattice characterized by random values of transfer rates between pairs of nearest-neighbor sites. The approximation is applied to a percolation model in which only a fraction of the bonds are assigned a finite transfer rate. The results reflect the existence of a percolation threshold in the system, and are consistent with the properties of clusters of bonds in the critical region.

An exact algorithm is formulated to calculate the expected walk length $〈n〉$ for a walker (atom, molecule) undergoing random displacements on a finite or infinite (periodic) $d$-dimensional lattice with traps (reactive sites). The method is illustrated for the case of a single deep trap surrounded by shallow traps and the calculated value of $〈n〉$ agrees to within 0.3% of the Monte Carlo result for all lattices considered. The theory introduced is capable of generalization to many new classes of problems in lattice statistics.

The statistics of pure quantum states of the harmonic oscillator is separated into a quantum mechanical and a classical part by associating a classical analog with each quantum state. Several types of states are considered and it is shown that all pure states of the same average energy are equally close to their classical analogs.

The result of a search for nucleon decay using a 300-ton water Čerenkov detector located in the Homestake gold mine is reported. The nucleon total lifetime is found to be $T_N>3\mathrm{}\times {10}^{31}{B}_{\mu }$ yr, where $B_{\mu }$ is the model-dependent probability for production and detection of a decaying muon following a nucleon decay event. In the SU(5) grand unified model, published calculations of $B_{\mu }$ vary from 5% to 10%, thereby yielding nucleon total lifetime limits in the range (1.5-3)×${10}^{30}$ yr.

Phenomenologically acceptable quark and lepton masses result if the known light fermions are coupled to heavy fermions and bosons (mass order ${10}^{15}$ GeV) with SU(2) ⊗ U(1)- breaking mass mixing of order 100 GeV. It is argued that adequate mixing may be obtained in a hypercolor theory which has a nontrivial fixed point. This is illustrated in a toy model based on SU(5) ⊗ SU(2).

The levels in ${}_{}{}^{74,76}{}_{}{}^{}\mathrm{Kr}$ were studied with in-beam $\gamma$-spectroscopy techniques and the ${\beta }^{+}$ decay of ${}_{}{}^{76}{}_{}{}^{}\mathrm{Rb}$. The energies of the $2_1^{+}$ states in ${}_{}{}^{74,76}{}_{}{}^{}\mathrm{Kr}$ deviate from smooth behavior compared with the higher spin levels. The yrast cascade $B\left(E2\mathrm{}\right)\mathrm{}$'s are highly collective. The ${}_{}{}^{74,76}{}_{}{}^{}\mathrm{Kr}$ ground states have unusually large deformation. The origin of this deformation and of shape coexistence in this region is described in terms of the protons driving the deformation.

Neutron spectra from ${}_{}{}^{37}{}_{}{}^{}\mathrm{Cl}$($p$,$n$)${}_{}{}^{37}{}_{}{}^{}\mathrm{Ar}$ at $E_p=120\mathrm{}$ MeV are measured in the angular range 0°-30°. Neutron groups characterized with $L=0\mathrm{}$ transfer are obtained up to approximately 12-MeV excitation energy in ${}_{}{}^{37}{}_{}{}^{}\mathrm{Ar}$. From the observed 0° cross section the Gamow-Teller strengths for ${}_{}{}^{37}{}_{}{}^{}\mathrm{Cl}$→${}_{}{}^{37}{}_{}{}^{}\mathrm{Ar}$ transitions are obtained which are directly related to neutrino absorption by ${}_{}{}^{37}{}_{}{}^{}\mathrm{Cl}$. The cross section for ${}_{}{}^8{}_{}{}^{}\mathrm{B}$ solar neutrinos incident on ${}_{}{}^{37}{}_{}{}^{}\mathrm{Cl}$ is reported.