The predicted metastable ${}_{}{}^4{}_{}{}^{}\mathrm{S}_{3/2}^{\mathrm{e}}{}_{}{}^{}$ ${\mathrm{Ar}}^{\mathrm{-}}$ ion has been observed for the first time. It was produced from an ${\mathrm{Ar}}^{+}$ beam by two-step electron capture in Cs vapor. Decay-rate measurements favor the existence of only one state with a lifetime of 350±150 ns.

Rydberg states of ${\mathrm{H}}_2$ with n=10, L=3–6, formed in charge-capture collisions of (11 KeV) ${\mathrm{H}}_2$${\mathrm{}}^{+}$ ions, are resolved spectroscopically by laser excitation of the 10→27 electronic transition, detected by Stark ionization of the upper state. Measured level positions are in good agreement with a priori predictions. The Rydberg spectrum identifies participating ${\mathrm{H}}_2$${\mathrm{}}^{+}$ core states as ν=0 (only) and R=0–3, but relative line intensities appear anomalous.

Large-orbit, nonthermal ${\mathrm{d}}^{+}$ migma plasma with ${\mathrm{P}}_{\mathrm{\theta }}$∼0 and ${\mathrm{E}}_{\mathrm{ion}=0.7\mathrm{}}$ MeV was formed in the center of a simple mirror with densities n${=10\mathrm{}}^9$–${10}^{10}$ ${\mathrm{cm}}^{\mathrm{-}3}$. Confinement time was 20–45 s. Flute, negative-mass, and ion-cyclotron instabilities, found in other mirrors at several orders-of-magnitude lower n, were not observed. An instability was suppressed by an electric field. Confinement parameters are ${\mathrm{E}}_{\mathrm{i}}$${\mathrm{n}}_{\mathrm{c}}$τ∼${10}^{14}$ keV ${\mathrm{cm}}^{\mathrm{-}3}$ s, ${\mathrm{n}}_{\mathrm{c}}$τ∼${10}^{11}$ ${\mathrm{cm}}^{\mathrm{-}3}$ s, luminosity ∼${10}^{29}$ ${\mathrm{cm}}^{\mathrm{-}2}$ ${\mathrm{s}}^{\mathrm{-}1}$.

High-resolution spectral measurements of electron plasma-frequency emission from alcator C tokamak reveal a level of coherence indicative of maser activity (Δω/ω=6×${10}^{\mathrm{-}6}$). A full-wave theoretical analysis yields the complete mode structure of the electromagnetic fields as well as the dispersion relation. This analysis shows that for wave frequencies near the central plasma frequency the waves are highly localized and thereby the plasma forms a high-Q cavity for these waves.

Plasmon wave packets are shown to be nucleated in narrow density holes which are the remnants of previous generations of ‘‘burnt out’’ cavitons. The proximity of the nucleation length scales to those of dissipation precludes the possibility of a self-similar inertial range for wide range of parameters. The nucleation mechanism may also arise in other contexts.

We propose a theory that a new type of magnetic reconnection, nonlinear driven reconnection, is triggered during the nonlinear development of an m=1 helical kink-mode instability. This reconnection process can well explain nonlinear reconnection observed in the previous simulation and can be a candidate for the self-reversal mechanism in the reversed-field pinch.

An inhibition of long-range three-dimensional order at low temperatures in nearly commensurate Cs-graphite (stages 2 and 3) is reported. We interpret this as the result of a competition between local in-plane ordering at domain walls and interlayer interactions which in stage 3 favor a simple hcp intercalant stacking. Computer modeling shows evidence for two stable rotated domain-wall configurations.

A new c(4×2) structure for the Si(100) surface is proposed in which the second-layer atoms are dimerized and the top-layer atoms form π-bonded chains. Pseudopotential total-energy calculations indicate that this c(4×2) dime-plus-chain structure has a lower energy’than the (2×1) dimerized surface. The bond topology of the structure explains the streaking and weakness of the (1/4)-order diffraction spots observed in low-energy electron and He-atom diffraction.

An anlysis is reported of earlier light-scattering measurements by Wong and Knobler on a liquid mixture undergoing phase separation. When the system was quenched into the two-phase region to a temperature near the cloud point, the growth of intensity with time displayed two characteristic regions: an initial rapid rise followed by a sharp crossover to slower growth. It is shown that such behavior is consistent with the predictions of the Langer-Schwartz description of the homogeneous nucleation and growth of droplets.

It is shown that the intramolecular Fermi doublet {${\nu }_1$,2${\nu }_2$} in crystalline ${\mathrm{CO}}_2$ arising from resonant anharmonic coupling between a single-phonon state and a quasibound two-phonon state can be coherently driven and its dynamics determined by time-resolved nonlinear optical techniques. Coherence relaxation times for both components of the doublet are measured between 9 K and the fusion point (217 K). A mechanism for loss of coherence is proposed which involves modulation by low-lying intermolecular modes.

The atomic structure at the interface of a 180° rotated single-crystal ${\mathrm{NiSi}}_2$ film on Si(111) has been determined by a new thin-film ion-channeling method, using ultrahigh depth resolution. The Ni atoms at the interface are found to be sevenfold coordinated. The bonds across the interface are slightly contracted.

The localization in two-dimensional disordered electron systems in strong magnetic fields is investigated by the finite-size scaling method. The scaling function numerically obtained for macroscopically long systems shows that the single-parameter scaling is invalid. The inverse localization length is found to have a novel critical behavior near the center of the Landau band, in which the Landau-index–dependent critical exponent determines the behavior of conductivity.

Monochromatization of synchrotron radiation down to about ${10}^{\mathrm{-}8}$ eV at an energy of 14.4 keV has been achieved by double nuclear Bragg diffraction from ${}_{}{}^{57}{}_{}{}^{}\mathrm{yttrium}$ iron garnet single-crystal films set for the electronically forbidden {200} reflection. The monochromatized γ quanta have been analyzed with respect to time delay and capabiltiy of resonance absorption. By setting of appropriate energy and time windows a pure beam of resonant γ quanta at a rate of about 1 Hz is available.

For a general class of ferromagnetic models of one-component spins it is rigorously shown that (i) the phase transition, at zero magnetic field, occurs directly from the high-temperature phase to the low-temperature regime; (ii) the critical exponent β is bounded by its mean-field value, β≤1/2; (iii) the critical temperature can be rigorously estimated to any desired accuracy, by finite-size calculations; and (iv) ${\mathrm{T}}_{\mathrm{c}}$ depends continuously on the model—in domains over which the models satisfy uniformly a new regularity condition.

We have performed polarized- and unpolarized-neutron scattering measurements on amorphous MnSi. The results are consistent with bulk susceptibility data for the same sample, and show that a-MnSi behaves like the classical, dilute-moment spin-glass, CuMn. Relative to the spin-glass transition temperature, the energy scale for spin fluctuations is much larger in this material than in other concentrated spin-glasses.

It is shown that in a collision between any two aggregates of particles the points of stationary phase for the scattering amplitude lie on the hypersurface determined by the condition that the potential energy of the interaction betwen the two aggregates vanishes.

We show the near-universal existence of a second invariant that is polynomial in the momenta for integrable Hamiltonian systems in two dimensions. Specifically, Hietarinta's three "counterexamples" are converted to polynomial form.

We report a new type of anomalous diffusion in chaotic systems with periodic symmetry. It is characterized by mean square displacements diverging faster than linearly in time. By a comparison of power spectra we conclude that the phenomenon has occurred in a recent observation of $\frac{1}{f}$ noise in Josephson junctions.

The critical dimension of string theories in which the background metric is a product of Minkowski space and an $\mathrm{SU}\mathrm{}\left(N\right)\mathrm{}$ or $\mathrm{SO}\mathrm{}\left(N\right)\mathrm{}$ group manifold is derived. A consistent string theory can be constructed only in the presence of a Wess-Zumino term associated with the compactified dimension. This implies that the compactified radius is quantized in units of the string tension. A generalization to the supersymmetric case is discussed.

We report a measurement of the branching ratios for two decay modes of the $\tau$ lepton: $R_B({\tau }^{\pm }\to K^{\pm }{K}^{\mp }{\pi }^{\pm }{\nu }_{\tau })=\left({0.22}_{-0.11\mathrm{}}^{+0.17\mathrm{}}\right)\%$ and $R_B({\tau }^{\pm }\to K^{\pm }{\pi }^{\mp }{\pi }^{\pm }({\pi }^0\left){\nu }_{\tau }\right)=\left({0.22}_{-0.13\mathrm{}}^{+0.16\mathrm{}}\right)\%$. The separation of these channels is accomplished in the DELCO detector by use of a gas Čerenkov counter to identify fast kaons. The invariant-mass distribution of the $K^{\pm }{K}^{\mp }{\pi }^{\pm }$ system has been used to set an upper bound on the $\tau$ neutrino mass of 157 MeV at 95% confidence limit.