An off-shell isobar model for πN→πN, πN→ηN, and ηN→ηN t matrices is presented. The πN, ηN, and πΔ+(ππN) channels are treated in a coupled-channel formalism. We are able to determine various vertex functions of the model by using only πN (complex) phase shifts in $S_{11}$, $P_{11}$, $D_{13}$, and $P_{33}$ partial waves. The model gives good predictions for ${\pi }^{\mathrm{-}}$p→ηn cross sections. It also predicts an attractive S-wave ηN interaction.

We have studied the decays of the low-lying gluonic excitations of mesons (hybrids) predicted by a flux-tube model for chromodynamics. The probable reason for the absence to date of signals for such states is immediately explained: The lowest-lying hybrids decay preferentially to final states with one excited meson [e.g., B(1235)π, ${\mathrm{A}}_2$(1320)π, ${\mathrm{K}}^{\mathrm{*}}$(1420)K¯, π(1300)pi,. . .] rather than to two ground-state mesons (e.g., ππ, ρπ, ${\mathrm{K}}^{\mathrm{*}}$K¯,. . .). We make specific predictions of decay channels which will contain ${\mathrm{J}}^{\mathrm{PC}}$ exotic hybrid resonance signals and suggest some possibly fruitful production mechanisms.

The relationship between instantons and the index-theory analysis of anomalies is examined in odd-dimensional gauge theories. Consistency of the anomalous production of fermions associated with nontrivial spectral flows of Dirac Hamiltonians and the absence of odd-dimensional anomalies in continuous symmetries is clarified. A new structure of three-dimensional matter is suggested.

The differenctial cross section and the transverse spin-flip probability have been measured for the dominant transitions in ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$(p,n${)\mathrm{}}^{13}$N and ${}_{}{}^{15}{}_{}{}^{}$N(p,n${)\mathrm{}}^{15}$O at ${\mathrm{E}}_{\mathrm{p}}$=160 MeV. The Gamow-Teller transition strengths deduced from the data show that the major ${\mathrm{}(1/2)\mathrm{}}^{\mathrm{-}}$→${\mathrm{}(3/2)\mathrm{}}^{\mathrm{-}}$ transitions are strongly quenched relative to the ${\mathrm{}(1/2)\mathrm{}}^{\mathrm{-}}$→${\mathrm{}(1/2)\mathrm{}}^{\mathrm{-}}$ mirror transitions, in strong disagreement with simple shell-model expectations.

It is shown that additional information from the (p,p’) reaction can provide an important test of the nature of the M1 excitations recently observed in deformed nuclei via electromagnetic studies and interpreted to be collective current excitations.

A photoionization experiment on free oriented molecules in the gas phase has been performed. ${\mathrm{CH}}_3$I molecules in a supersonic beam have been oriented with respect to the molecular axis parallel to an external field by use of an electric hexapole. The photoelectrons ejected by vacuum ultraviolet radiation in a region of a very weak field from the lone-pair orbital located at the iodine atom show a pronounced asymmetry depending on whether electrons are emitted parallel or antiparallel to the molecular axis.

A high-gain, high–extraction-efficiency, linearly polarized free-electron laser amplifier has been operated at 34.6 GHz. At low signal levels, exponential gain of 13.4 dB/m has been measured. With a 3-=kW input signal, saturation was observed with an 80-MW output and a 5% extraction efficiency. The results are in good agreement with linear models at small signal levels and nonlinear models at large signal levels.

Recent experiments exploring the use of transition radiation as an intense source of tunable, coherent x rays included a measurement of the energy spectra and angular distribution of transition radiation in the soft x-ray energy range. The radiation was produced when 25-MeV electrons penetrated a stack of eighteen 1-μm-thick beryllium foils. The most striking result is the demonstration of coherence of the photons emitted at the two surfaces of a single foil.

The circuit equations for current drive are derived by the finding of appropriate response functions in the presence of an electric field. The effect of arbitrary wave-induced fluxes on runaway production and current generation can then be determined. An interpretation of recent remarkable experiments is now possible, and the favorable results appear to scale to reactor-grade devices.

We show that the recently measured kinetic energy of atoms in solid helium is substantially larger than expected for even a moderately anharmonic solid. The large kinetic energy is rather an explicit measure of the highly anharmonic nature of solid helium. An explanation is proposed here in terms of the anharmonic one-phonon response functions which have large, high-frequency tails that contribute significantly to the kinetic energy.

A combination of x-ray diffraction and extended x-ray-absorption fine-structure analyses were used to show that an order-disorder structural transition from zinc blende-to-diamond occurs in metastable (GaSb${)}_{1\mathrm{-}\mathrm{x}}$(${\mathrm{Ge}}_2$${)}_{\mathrm{x}}$ alloys at a critical composition ${\mathrm{x}}_{\mathrm{c}}$ even though the short-range order remains perfect throughout; i.e., there is no evidence for Ga-Ga or Sb-Sb bonds in either the zinc-blende or the diamond structure. However, the critical composition ${\mathrm{x}}_{\mathrm{c}}$ was found to depend upon the film growth conditions and a model is presented which explains this result on the basis of morphological effects on film growth kinetics.

The inelastic scattering of neutrons by liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ at 0.2 K and saturated vapor pressure has been measured for momentum transfers in the range 10 A${\mathrm{̊}}^{\mathrm{-}1}$${\mathrm{̊}}^{\mathrm{-}1}$. The observed scattering function is well described, within statistical uncertainties, by a Gaussian centered at the recoil energy. The average kinetic energy per atom, obtained from the width of the scattering function, is ${8.1}_{\mathrm{-}1.3}^{+1.7\mathrm{}}$ K.

Measurements have been made of electrical conductivity and Young’s modulus of a set of sintered, submicron, silver-powder beams with occupied volume fractions (f) in the range 0.1 to 0.3. The results show clear evidence for a percolation threshold at ${\mathrm{f}}_{\mathrm{c}}$=0.062±0.01. The conductivity and elasticity critical exponents, measured in the range 0.6≤(f-${\mathrm{f}}_{\mathrm{c}}$)/${\mathrm{f}}_{\mathrm{c}}$≤4, were t=2.15±0.25 and τ=3.8±0.5, in agreement with recent theories and numerical simulations that show τ>t, 1.65<t<2.2, and τ>3.55 in three dimensions.

We report the first observation of a hydrogen-induced strain modulation in a metal superlattice due to interstitially dissolved atomic hydrogen. The intensities of the x-ray satellites from this strained Nb-Ta superlattice depend on temperature. This leads to a Curie-Weiss behavior for a H concentration modulation and can be explained in terms of a simple modulated lattice-gas model. In addition, we have found that the solubility of H in these thin Nb-Ta films is dramatically increased from what would be expected for bulk Nb or Ta.

The temperature dependence of the square of the smectic order parameter, ‖Ψ${\mathrm{\Vert }}^2$, was determined from the integrated x-ray scattering intensity. The data are described very well by the form I(t)/I(0)=1∓${\mathrm{A}}^{(\pm )}$‖t${\mathrm{\Vert }}^{\mathrm{x}}$, where t=(T-${\mathrm{T}}_{\mathrm{NA}}$)/${\mathrm{T}}_{\mathrm{NA}}$. The determined values for x do not agree with the theoretically expected value x=1-α, where α is the heat-capacity exponent. This disagreement raises questions concerning the quantitative validity of the Landau–de Gennes free energy.

The three-dimensional Ising spin-glass in zero field with nearest-neighbor interactions having ±J distribution is studied by Monte Carlo simulations for samples of linear dimension L with 3≤L≤20. Results for the probability distribution, ${\mathrm{P}}_{\mathrm{L}}$(q), of the spin-glass order parameter are analyzed by finite-size scaling. Data for T≥1.2 are consistent with a conventional phase transition at ${\mathrm{T}}_{\mathrm{c}}$${=1.2\mathrm{}}_{\mathrm{-}0.2}^{+0.1\mathrm{}}$, with exponents ν=1.3±0.3 and η=-0.3±0.2. However, results at lower temperature indicate marginal behavior and suggest that the lower critical dimensional is close to three.

First results of massive Monte Carlo simulations of the d=3 Ising spin-glass with ±J bond distribution, performed on a fast special purpose computer, are presented. A qualitative change in the behavior of the system and best fits for the spin-glass correlation length and relaxation time favor equilibrium phase transition at ${\mathrm{T}}_{\mathrm{c}}$/J≊1.2. .AE

Spin- and angle-resolved photoemission spectra calculated in a bulk tight-binding formalism for bcc iron clusters with varying local exchange fields strongly depend on the assumed degree of magnetic order. Comparison with experimental data implies that iron has a short-range magnetic order of at least 4 Å in the vicinity of the Curie temperature.

Near-edge x-ray absorption fine-structure studies above the C and O K edges for CO on Pt(111) reveal a 4-eV shift of the σ shape resonance when Na(0.2 monolayer) is coabsorbed. This allows determination of a Na-induced (0.12±0.03)-Å expansion of the C-O bond. Na does not affect the vertical molecular orientation on the surface. Reduction and broadening of the 1s→2${\mathrm{\pi }}^{\mathrm{*}}$ resonance and the CO bond lengthening in the presence of Na signifies substantially increased metal to CO backbonding.

Forward light scattering by the thermally excited acoustic eigenmodes of an optical fiber produce numerous narrow lines not predicted by the bulk-interaction theory of Brillouin scattering. Optical heterodyne detection has been used to resolve the scattering spectrum which begins at about 20 MHz and extends to the detection limit.