X-ray spectra of He-like argon (${\mathrm{Ar}}^{+16\mathrm{}}$) have been obtained for the transitions 1snp→1$s^2$, with 3≤n<∞, from Alcator-C tokamak plasmas. In the periphery of the plasma, the n=9 and 10 and 15<n≤40 levels are observed to be predominantly populated by charge transfer between ${\mathrm{Ar}}^{+17\mathrm{}}$ and intrinsic neutral hydrogen in the ground and first few excited states. Neutral hydrogen density pro- files are deduced from these measurements. The first experimental observations of the reactions ${\mathrm{Ar}}^{+17\mathrm{}}$(1s ${\mathrm{}}^2$S)+${\mathrm{H}}_0^{\mathrm{*}}$(n=2,3) →${\mathrm{Ar}}^{+16\mathrm{}\mathrm{*}}$(1snp ${\mathrm{}}^1$P)+${\mathrm{H}}^{+}$ are presented and their cross sections are estimated.

A new model based on the linear combination of atomic orbitals molecular-orbital wave functions is proposed to explain the reduction of the relative intensity of the fluorine ${\mathrm{KL}}^1$ satellite line in covalent fluorine compounds. Values of a reduction factor r of the ${\mathrm{KL}}^1$ line intensity are calculated and compared with experimental ones. Agreement is found for the size of the factor, but problems are found in use of the Pauling crystal ionicity to characterize molecular orbits. In addition, it is shown that the same effects are expected for direct and shakeoff multiple ionization in application of the sudden approximation method to molecular wave functions.

In the process of spontaneous parametric down-conversion a signal and an idler photon are created simultaneously. By use of the photoelectric detection of the signal photon as a gate, a good approximation to the ideal localized one-photon state can be achieved. This has been confirmed by direct photon-counting measurements.

We present experimental results for the initial decay rate ${\mathrm{\Gamma }}_1$ of concentration fluctuations in solutions of linear polymers, for various molecular weights, concentrations, and wave vector q, in two rather different solvents. We find that under all conditions explored the dimensionless decay rate 6π${\mathrm{\eta }}_0$${\mathrm{\Gamma }}_1$/(${\mathrm{k}}_{\mathrm{B}{\mathrm{Tq}}^3}$) is a function only of the scaled wave vector q${\xi }_{\mathrm{H}}$. Here ${\mathrm{\eta }}_0$ is the solvent viscosity, and ${\xi }_{\mathrm{H}}$ is the length scale defined by ${\xi }_{\mathrm{H}}^{\mathrm{-}1}$≡${\lim }_{\mathrm{q}\to 0}$6π${\mathrm{\eta }}_0$Γ 1/(${\mathrm{k}}_{\mathrm{B}}$${\mathrm{Tq}}^2$).

The early stages of formation of thin layers of IrSi and IrGe on Ir surfaces have been studied. Distinctive stages of growth have been observed. In the earliest stage on Ir(001), atomically resolved images show a structure resembling the c(2×2) of the substrate, which we believe to have the (011) Ir-layer structure of the IrSi and IrGe crystals. In the second stage, the (2×1) image structure on Ir(011) is identified to be the Ir layer of the IrSi(001) fundamental plane.

We have observed that the motion of a vibrating-wire resonator in superfluid ${}_{}{}^3{}_{}{}^{}\mathit{B}$ at temperatures below ${\mathrm{T}}_{\mathrm{c}}$/8 is associated with a sharp critical velocity, ${\mathrm{v}}_{\mathrm{c}}$, above which very high dissipation sets in. We identify this velocity with the Landau critical velocity for pair breaking. That the observed value of ${\mathrm{v}}_{\mathrm{c}}$ is a factor of 2 lower than the critical velocity expected from the BCS value of the gap we take as evidence that the gap is suppressed by about 50% of its bulk value near a moving boundary.

The effect of perturbative infrared singularities on the finite-temperature effective potential in the standard model with a light Higgs boson is investigated. Together with the Coleman-Weinberg term, it promotes the full gauge-symmetry breaking. The transition to the U(1) vacuum via quantum tunneling is expected to occur at some temperature ∼100 MeV. However, without knowledge of dynamical details, one cannot conclusively decide whether the chiral or the (full) gauge symmetry breaks first.

A pronounced triangular background, observed near the specular beam with He diffraction from Ni(100)-c(2×2)O, is explained by hard-wall calculations as originating from a random distribution of ≃15% empty oxygen sites in good agreement with Auger calibration. Lateral adatom relaxations of ≃0.25 Å away from the empty sites fit both the background shape and intensity. This is the first application of He scattering for defect characterization at high coverages.

In addition to bulk viscosities that diverge as 1/ω, Mazenko, Ramaswamy, and Toner have predicted that smectic-A liquid crystals will have shear viscosities with (1) divergent real parts—implying no flow below a minimum yield stress—and (2) divergent imaginary parts—implying glassy behavior. In this Letter it is shown that smectic-A liquid crystals are neither ‘‘Bingham plastics’’ nor ‘‘glasses.’’ The finiteness of ${\mathrm{\eta }}_2$ to all orders of perturbation theory is proven, and the relevant cancellations to one-loop order are displayed.

Electronic structure calculations on Al and Al-Mn clusters of icosahedral (${\mathrm{I}}_{\mathrm{h}}$) symmetry show important differences compared with such calculations on clusters of cubic (${\mathrm{O}}_{\mathrm{h}}$) symmetry. Anomalously high state densities at ${\mathrm{E}}_{\mathrm{F}}$ and energy dependence proportional to ${\mathrm{E}}^{\mathrm{n}}$, n≥1, characterize the ${\mathrm{I}}_{\mathrm{h}}$ clusters. Highly symmetric molecular-orbital topologies make icosahedral clusters appear like large quasiatoms. Central Mn atoms destabilize ${\mathrm{I}}_{\mathrm{h}}$ clusters.

Quantization of the Hall effect and concomitantly vanishing magnetoresistance are observed in a GaAs/(AlGa)As superlattice structure whose electronic spectrum exhibits dispersion in all three spatial dimensions.

Drastic increases of resonance frequency (factor of 7) and damping (factor of >500) of a superconducting reed is observed when a longitudinal magnetic field is applied. The frequency change is much larger than expected from the pole effect (${10}^5$ times) or from the flux-line-tilt modulus (20 times). We give a quantitative explanation with no adjustable parameter. Unpinning of flux lines leads to frequency corrections and to damping. This allows novel precision measurements of extremely weak pinning in amorphous alloys. First experiments demonstrate the feasibility of this method.

Presumably the simplest model of chemical turbulence is proposed, for which the spatial degree of freedom plays an important role. The concentration, as well as space and time, is discretized. As in the real experiment a turbulent phase is found sandwiched by two ordered phases. In addition, the model predicts a solitonlike phase. Thus the model can exhibit a variety of behaviors encountered in partial differential equation systems. It is also closely related to cellular automata.

The spontaneous symmetry breaking in higher-dimensional unified field theories is discussed in a general setting. A purely geometric symmetry-breaking mechanism involving no free parameters is presented, in which the symmetry is broken by the higher-dimensional metric through Einstein’s equation.

We define maximal CP nonconservation to occur when a unique convention-independent parameter t, a quartic function of the Kobayashi-Maskawa matrix V, is maximized. The maximum value is much greater than the experimental upper limit, and so the observed CP nonconservation is much less than maximal. Maximal CP nonconservation corresponds to maximum mixing of the quark generations, just as maximal parity nonconservation corresponds to maximum mixing of the vector and axial-vector interactions.

We estimate the $B_d$-B${¯}_d$ and $B_s$-B${¯}_s$ mixing effects using computed production cross sections for $B_q$B${¯}_q$, $B_q$B${¯}_q^{\mathrm{*}}$+c.c., $B_q^{\mathrm{*}}$B${¯}_q^{\mathrm{*}}$ (q=d,s) in the region from Υ(4S) to Υ(7S). It is shown that the mixing signal of same-sign leptons will peak at Υ(5S) under the assumption of standard model estimates, and if the total integrated luminosity of 1000 ${\mathrm{pb}}^{\mathrm{-}1}$ is achieved, it will be observable.

The first observation of transitions between bound electronic states of neutral helium hydride is reported. Excited molecules were produced by electron transfer to the corresponding molecular ions. Emission spectra in the visible were obtained. Five electronic bands could be identified for three isotopic mixtures. Molecular constants confirming recent calculations of potential curves were derived for the first time. Predissociation of the upper state occurs for ${}_{}{}^4{}_{}{}^{}\mathrm{HeH}$ in contrast to ${}_{}{}^3{}_{}{}^{}\mathrm{HeD}$. Also NeH spectra could be obtained by the same method.

We present the first experimental study of shear-flow–induced behavior in a two-dimensional anisotropic fluid: circular, freely suspended films of smectic-C liquid crystals. Depending on the topology of the in-plane director configuration, we observe either a phase winding state, where Φ, the phase defining the director orientation relative to the velocity field, winds up in the center of the film, or, a flow alignment state, where Φ is constant.

Coexistence between moderately polarized ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ liquid and solid at pressures substantially below the melting curve persists for several minutes in high magnetic fields at low temperatures. This work, together with observations made in other laboratories, reveals that the relaxation time of the depression is strongly magnetic-field and temperature dependent. Analysis of the 8-T depression in which the cell-averaged polarization is near 65% favors an interpretation with equal polarizations for the liquid and solid rather than a model in which the equivalent fields for the two phases are equal.

This Letter discusses the time development of a system in which small spheres of a stable phase grow out of a supersaturated melt. A study of the growth of pairs of particles in an effective background accounts for two-particle correlations. These correlations broaden the distribution of particle sizes, even for relatively dilute systems, in accord with experiment.