New results have been obtained, by field-ion microscopy, relating to the atomic structure of clean {001}W. The evidence supports a reconstruction model with periodic displacements of atoms having vertical components. The reconstructed atomic configuration prevails over the entire temperature range of this investigation (∼ 15-460 K), suggesting that no phase transition may be needed to account for the structural features of {001}W.

Five principal transitions, three of which from the first excited state, have been measured in absorption for the ${F_2}^{+}$ center in KF. With one significant exception, these data are in essential agreement with predictions of the simple ${\mathrm{H}}_2^{+}$ molecular-ion model. The measurements were made by way of a novel optical pumping technique, which allows for direct, accurate determination of band strengths and shapes, even in the presence of strong overlapping absorptions by other species.

Intravalley exchange and correlation are found to induce a first-order transition at low densities in the inversion layer, lowering the valley degeneracy. For the $n$ channel on Si(100) surface, the reduction from two valleys to one occurs roughly below 3×${10}^{11}$ ${\mathrm{cm}}^{-2\mathrm{}}$. The one-valley phase with domain structure yields activated conductivity and other observed low-density behavior.

EPR and dc conductivity measurements in pristine and acceptor-doped cis-${\left(\mathrm{CH}\right)}_x$ and pristine trans-${\left(\mathrm{CH}\right)}_x$ are reported. At dopant concentrations of 0.7% and 0.9% As${\mathrm{F}}_5$, the cis isomer shows a Pauli susceptibility and a conductivity that seem to arise from randomly distributed, highly conducting regions—a sign of dopant aggregation. There in no need to invoke charged solitons. Comparison with previous experimental results suggests that they do not support the existence of charged solitons in the doped trans isomer; neutral solitons in the undoped trans isomer are also questioned.

We report on the attenuation of ballistic phonons generated in bulk GaAs and propagating through epitaxial layers of ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ containing up to ${10}^{18}$ Sn or Te donors per cubic centimeter. The latter donors are known to form a complex with an unidentified defect (DX center) whose occupation is changed by photoexcitation. The symmetry of the ionized DX center is shown to be trigonal in the case of Sn and most likely orthorhombic in the case of Te donors.

No energy dependence of the velocities of neutrinos or antineutrinos is observed within the statistical and systematic errors over the energy range 30 to 200 GeV. The velocity differences (95% confidence level) are $|{\beta }_{\nu }-{\beta }_{\overline{\nu }}|<\mathrm{}0.7\mathrm{}\times {10}^{-4\mathrm{}}$, $|{\beta }_{{\nu }_K}-{\beta }_{{\nu }_{\pi }}|<\mathrm{}0.5\mathrm{}\times {10}^{-4\mathrm{}}$, and $|{\beta }_{\nu \left(\overline{\nu }\right)}-{\beta }_{\mu }(\mathrm{corrected}\left)\right|=|\mathrm{}{\beta }_{\nu \left(\overline{\nu }\right)}-1|<\mathrm{}0.4\mathrm{}\times {10}^{-4\mathrm{}}$, where $\beta =\frac{v}{c}$.

Grand unified models of elementary particle interactions contain stable superheavy magnetic monopoles. The density of such monopoles in the early universe is estimated to be unacceptably large. Cosmological monopole production may be suppressed if the phase transition at the grand unification mass scale is strongly first order.

The decay of the giant-resonance region in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ has been studied in a ${\alpha }^{\prime }-\gamma$ angular correlation experiment via the reaction chain ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$($\alpha$, ${\alpha }^{\prime }$)${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ ${}_{}{}^{\mathrm{GR}}{}_{}{}^{}\mathrm{}\left(n\right)\mathrm{}$${}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}$*($\gamma$)${}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}$. The correlation functions are in agreement with the assumption of predominant $E2\mathrm{}$ strength for the resonance around $E_x=10.9\mathrm{}$ MeV, but require considerable strengths of excitation modes higher than $E0\mathrm{}$ for the resonance around $E_x=13.7\mathrm{}$ MeV. The coincident $\alpha$-particle spectra show significant fine structure in the giant-resonance region.

We compare total reaction cross sections found in proton and composite-projectile ($d$ and $\alpha$) collisions with ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ target nuclei at incident energies between 5 and 600 MeV/nucleon. The energy dependence of the composite-projectile ${\sigma }_R$ values is found to be as large as or larger than for protons. A simple semiclassical analysis suggests that, at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}/\mathrm{nucleon}$ of approximately 250 MeV, composite-projectile collisions are, in effect, more transparent than proton collisions with the same target nucleus.

The nuclear spins of the very neutron-deficient ${}_{}{}^{191m-185m}{}_{}{}^{}\mathrm{Hg}$ isomers were measured on line at the mass separator ISO LIDE at CERN using pulsed-laser excitation and observation of the time-resolved quantum beats from selected hyperfine-structure states. The spins of these isomers are with $I=\frac{13}{2}$ equal to those of the long-lived isomers ${}_{}{}^{199m-193m}{}_{}{}^{}\mathrm{Hg}$ already known. The persistence of this spin value for eight isomers is explained by the model of rotation-aligned coupling.

A previously presented narrow-bandwidth theory is used to interpret recent data on the four-photon ionization of Cs near the $6F$ resonance. The theory is based on treating the amplitude of the radiation field as a constant relative to its rapid phase oscillations. The ionization rate adiabatically follows a pulsed amplitude leading to maximum ionization for times at which the pulse develops sufficient intensity to shift the $6S\to 6F$ transition into resonance.

Photoelectron spectra from atomic barium were recorded following excitation with synchrotron radiation at selected autoionization resonance energies. The greatly enhanced intensities of peaks arising from certain levels in ${\mathrm{Ba}}^{+}$ elucidate the structures of the autoionizing levels and implicate Auger decay as the dominant mode for their interaction with the continuum. Resonance photoelectron spectroscopy shows promise of wide applicability.

Comparative rates for simultaneous capture of zero, one, two, and three electrons into bound states measured in coincidence with an electron capture to continuum states, have been determined for 7-9-a.u. velocity ${\mathrm{C}}^{6+}$ and ${\mathrm{O}}^{8+}$ ions in Ar. Estimates based on the high correlations observed lead to the conclusion that traditionally measured cross sections for single and multiple bound-state capture have often been inappropriately compared with pure bound-state capture theories, tacitly ignoring an important unseen channel.

The modification of the trajectory of a focused resonance cone as a result of the ponderomotive force is investigated experimentally in a cylindrical plasma column. The new trajectory is seen to be in good agreement with recent theory.

The flux-conserving tokamak model suggested that rapid heating would yield equilibria with high relative energy density ($\beta =\frac{2p}{B^2}$) while nonetheless allowing control over $q$, the so-called safety factor for instability within the ideal magnetohydrodynamic plasma model. In this study, we show that this is adequate to provide stability to $\beta$ values of 10%, if there is a superconducting metal shell in the vicinity of the plasma.

This paper describes examination of certain linear and nonlinear properties of macroscopic tearing modes driven by anomalous electron viscosity effects associated with magnetic braiding. It is shown that strong linear growth of $m=1, 2$ tearing modes (respectively proportional to ${\mu }^{\frac{1}{5}}$ and ${\mu }^{\frac{1}{3}}$ can occur for rather modest values of $\mu$. In the nonlinear phase, the island width grows in time as $t^{\frac{1}{3}}$. Some speculations regarding the disruptive instability in tokamaks are also investigated.

In a beautiful recent experiment Sakagami et al. have recorded, on magnetic tape, the spatial field distribution produced in laser-plasma interaction. The standard infinite-plane theory of magnetic field produced by resonance absorption is unable to explain their experimental observations. This Letter proposes that finite geometry effects in resonance absorption produce a new magnetic field contribution which is responsible for their results.

Instabilities and double-layer formation are systematically investigated on a bounded collisionless system with electron beam penetrating through a plasma. The Buneman instability is observed at low beam currents. Above a critical current, there appears a sudden nonoscillatory potential drop due to the Pierce instability, which traps ions in the potential well. This collisionless ion trapping provides a new formation mechanism of the double layer, which is controlled by changing the speed of the potential drop.

Positron lifetime and angular correlation measurements have been made on the plastic crystal succinonitrile. They confirm the phase transition at 234 ± 1 K. In the plastic phase the average orthopositronium lifetime increases with temperature and saturates at the highest temperatures. This is interpreted as orthopositronium trapping in thermally created defects, probably vacancies. A defect formation energy of 0.36 ± 0.1 eV is deduced. This is lower than predicted values of the vacancy formation energy.

The classical criterion for the stability of cubic crystals under constant hydrostatic pressure is distinguished from the notional criterion of stability introduced by Born. Although the latter has been widely used in the literature, theoretical computations demonstrate appreciable quantitative and qualitative divergences between the criteria. The computations are made within the framework of a crystal model that is both mathematically tractable and sufficiently realistic for the intended purpose.