A multilayer sample of Dy(47 Å)/Y(40 Å), produced by molecular-beam-epitaxy techniques, is shown to order magnetically in an incommensurate helix that is coherent over several multilayer periods. The magnetic satellite peak has harmonics resulting from the multilayer modulation. The dc magnetic properties are suggestive of a metamagnet.

If our galactic halo is composed of heavy (several gigaelectron- volts), weakly interacting particles, pair annihilation into a heavy-quark–antiquark bound state plus a monochromatic photon can produce potentially observable sharp peaks in the diffuse cosmic-γ-ray background.

An approach to string theory in curved space is investigated. We use only fermionic dynamical variables. An essential role is played by a noncompact group in order that the observed space-time structure be incorporated. Frenkel-Kac realization of the current algebra obtained from the noncompact group is also investigated.

Evidence is presented for a narrow state, called ξ, in the decay modes J/ψ→γξ, ξ→$K^{+}$$K^{\mathrm{-}}$, and ξ→$K_S^0$$K_S^0$. In the $K^{+}$$K^{\mathrm{-}}$ mode, the ξ has a mass of 2.230±0.006±0.014 GeV/$c^2$, a width of Γ${=0.026\mathrm{}}_{\mathrm{-}0.016}^{+0.020\mathrm{}}$± 0.017 GeV/$c^2$, a product branching ratio of ${(4.2\mathrm{}}_{\mathrm{-}1.4}^{+1.7\mathrm{}}$±0.8)×10 ${}_{}{}^{\mathrm{-}5}{}_{}{}^{}$, and a statistical significance of ∼4.5 standard deviations. In the $K_S^0$$K_S^0$ mode, it has a mass of 2.232±0.007±0.007 GeV/$c^2$, a width of Γ${=0.018\mathrm{}}_{\mathrm{-}0.015}^{+0.023\mathrm{}}$± 0.010 GeV/$c^2$, a product branching ratio of ${(3.1\mathrm{}}_{\mathrm{-}1.3}^{+1.6\mathrm{}}$±0.7)×10 ${}_{}{}^{\mathrm{-}5}{}_{}{}^{}$, and a statistical significance of ∼3.6 standard deviations. Limits on ξ decay to other final states are presented.

We present the first results obtained from the sixteen-processor version of the parallel supercomputer being built at Columbia. The color-deconfining phase transition has been studied fo pure SU(3) gauge theory on lattices with a spatial volume of ${16}^3$ sites and temporal sizes of 10, 12, and 14 sites. The values found for the critical coupling are 6.07, 6.26, and 6.36, respectively. These results are in agreement with the perturbative predictions of the renormalization group, suggesting that lattice QCD calculations with the parameter β at least as large as 6.07 may approximate the continuum limit.

A Monte Carlo simulation of SU(3) lattice gauge theory at finite temperature which includes the effect of all purely timelike quark loops indicates that there is no deconfining phase transition for realistic quark masses. The results are in agreement with predictions based on effective-spin models of the deconfining transition.

We argue that existing Σ-hypernuclear data do not unambiguously determine the Σ-nuclear spin-orbit splitting ${\epsilon }_p$, and suggest that the reactions ${}_{}{}^7{}_{}{}^{}(K^{\mathrm{-}}$,${\pi }^{+}$${)}_{\Sigma }^7$H, ${}_{}{}^{13}{}_{}{}^{}(K^{\mathrm{-}}$,${\pi }^{+}$${)}_{\Sigma }^{13}$ Be, and ${}_{}{}^{13}{}_{}{}^{}(K^{\mathrm{-}}$,${\pi }^{\mathrm{-}}$${)}_{\Sigma }^{13}$ C are well suited for a unique determination of ${\epsilon }_p$.

The laser-induced atomic collision process Na(3S)+Ar+ħω→Na(3${\mathrm{P}}_{1/2}$)+ Ar has been studied by use of an intense, off-resonant laser pulse whose duration is shorter than the collision duration. It has been found that at fixed laser intensity the efficiency for exciting the Na(3${\mathrm{P}}_{1/2}$) state is higher for these ultrashort pulses than for pulses with duration longer than the collision duration. This effect is caused by a time-dependent modification of the collision potentials by the intense laser field. A theoretical calculation is in qualitative agreement with the results.

The effects of state mixing by extrinsic fields in the collision region have been investigated for the dielectronic recombination process ${\mathrm{Mg}}^{+}$(3s)+e→Mg(3p,nl)→Mg(3s ,nl)+hν. By field ionization of the Rydberg atoms produced, cross sections σ($n_f$) have been measured. The observed large changes of σ($n_f$) with alteration of the extrinsic field provide the first incontrovertible experimental evidence that dielectronic recombination can be changed by external fields.

Photoelectron spectroscopy and photoion-photoion coincidence technique are combined for the first time to show, in a molecule, the selectivity of electronic decay channels of resonances near a core edge. Tetramethylsilane is studied near the ${\mathrm{L}}_{\mathrm{I}\mathrm{I},\mathrm{I}\mathrm{I}\mathrm{I}}$ level of silicon, by use of monochromatized synchrotron radiation in the 100–120-eV range. Autoionization and simple and double-resonant Auger processes explain the formation of one-hole and multiple-hole excited configurations of the final ionic states.

We report the first observation of the modulational instability of light waves in dielectric material using a neodymium-doped yttrium aluminum garnet laser operated at 1.319 μm and single-mode optical fibers with anomalous group-velocity dispersion. The observed results are in good agreement with the theoretical predictions. The relationship between the modulation instability and parametric four-wave mixing and the interplay with stimulated Raman and Brillouin scatterings are also presented.

By combination of the benefits of magnetic and inertial confinements, a new fusion scheme is introduced with a plasma density of ≳${10}^{21}$ ${\mathrm{cm}}^{\mathrm{-}3}$ whose pressure is confined by inertia of a metallic container of a cannonball type while its heat is insulated by a self-generated magnetic field of ≳100 T.

The stability problem for strongly inhomogeneous plasma equilibria is treated by the method of relaxation under constraints. By use of statistical mechanics, a thermodynamic potential is derived for two-dimensional plasma configurations. As a consequence of a suitable constraint the plasma carries a nonvanishing electrical current. The state variables include the average electromagnetic fields. With the aid of the second law of thermodynamics the thermodynamic potential provides a necessary and sufficient stability criterion.

It is shown that for electrons trapped in a static potential a finite-amplitude frequency-modulated wave induces stochastic motions (and diffusion) in electron orbits over a significantly larger area of phase space than a single frequency wave of the same amplitude. The wavelength of the frequency-modulated fields is unimportant if it is greater than twice the width of the static potential. It is proposed that this be used for pumping of mirror trapped electrons to enhance the confining potential in a tandem mirror cell.

The intensity of the Fe xviii forbidden line at 975 Å (2$s^2$2$p^5$ ${}^2$$P_{1/2}$→2$s^2$2$p^5$ ${}^2$$P_{3/2}$) relative to that of an allowed line at 94 Å (2s2$p^6$ ${}^2$$S_{1/2}$→2$s^2$2$p^5$ ${}^2$$P_{3/2}$) was measured during ion-Bernstein-wave heating in tokamak discharges. The results at low electron densities ($n_e$<3×${10}^{13}$ ${\mathrm{cm}}^{\mathrm{-}3}$) indicated a noticeable effect of proton collisions on the intensity of the forbidden line. Calculation also shows the importance of proton collision to the Fe xviii forbidden-line intensity.

Molecular-dynamics simulations and in situ experimental observations of the melting and equilibrium structure of the crystalline Si(100)-melt interface are described. The equilibrium interface is structured, exhibiting facets established on (111) planes.

We have studied by neutron spectroscopy the concentration (1.5×${10}^{\mathrm{-}4}$≤x≤1.1×${10}^{\mathrm{-}2}$) and temperature dependence (0.5 K≤T≤10 K) of H tunneling in Nb(OH${)}_{\mathrm{x}}$. For T<5 K a narrow inelastic line is observed for x=1.5×${10}^{\mathrm{-}4}$ which changes into a broad peak at higher concentrations. This shows that interactions between the defects lead to a distribution of both the asymmetry of the potentials and the matrix element. Between 5 and 10 K the data reveal a renormalization of the matrix element and an increased damping due to a Korringa-type coupling of the tunnel system with conduction electrons.

Infrared-absorption measurements to a peak pressure of 93 GPa document the pressure-induced closure of the band gap of CsI to about 4450 ${\mathrm{cm}}^{\mathrm{-}1}$ (0.55 eV). In accord with previous spectroscopic measurements to 60 GPa, our data show that the band gap of CsI decreases continuously with pressure, and metallization (complete closure of the gap) is expected to occur above 100 GPa. A recent claim that CsI becomes metallic at 65±5 GPa is therefore spurious.

Measurements of the specific heat on two single crystals of ${\mathrm{ErRh}}_4$${\mathrm{B}}_4$ indicate that the origin of the hysteresis at the reentrant temperature is due to superheating effects. An analysis of the superheating behavior indicates the minimum free-energy difference between the ferromagnetic and coexistence state to be 0.325 and 0.375 J/mole for the two samples.

Mössbauer-effect measurements on ${\mathrm{Al}}_{86}$${(}^{57}$${\mathrm{Fe}}_{0.02}$${\mathrm{Mn}}_{0.}$ 98)>14 in the icosahedral phase indicate a distribution of quadrupole-splitting magnitudes at the iron sites. This distribution strongly indicates the existence of more than two inequivalent Mn sites. It can be fitted at least as well with a continuous distribution of sites of the form suggested by an amorphous analog as with a discrete set.