We examine the behavior of the connected n-point function in a zero-dimensional scalar theory (scrL=-1/2${\mathit{m}}^2$${\mathrm{\phi }}^2$-1/4λ${\mathrm{\phi }}^4$). The problematic n!(√λ ${)}^{\mathit{n}}$ behavior for large n, previously found for tree graphs in scalar field theory, is again obtained in saddle-point approximation in this model. However, a similar behavior, n![f(λ)${]}^{\mathit{n}}$, persists in the full theory, where f∼ √λ for λ→0, f∼${\lambda }^{\mathrm{-}1/4}$ for λ≫1. This behavior can be traced to the existence of zeros in the complex J plane of the generating functional Z(J), which in turn is controlled by the asymptotic behavior in ‖J‖ of Z(J) calculated in saddle-point approximation. The application of these results to field theory is discussed.

The effects of instanton-induced interactions on the H-dibaryon mass are studied. It is found that a strong three-body repulsion will result in a weakly bound or unbound H dibaryon with binding energy ≲10 MeV.

Exchange currents in nuclei are derived from chiral Lagrangians, and a justification is offered for the ‘‘chiral filter hypothesis’’ which seems to be supported by all presently available experimental data.

Cross sections, pion momentum spectra, and angular distributions for the reactions ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(${\mathrm{\pi }}^{\mathrm{-}}$,${\mathrm{\pi }}^{+}$${\mathrm{\pi }}^{\mathrm{-}}$) and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(${\mathrm{\pi }}^{\mathrm{-}}$,2${\mathrm{\pi }}^{\mathrm{-}}$) at a bombarding energy of 292 MeV were measured wth a 360° spectrometer. An enhancement of the cross-section ratio of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(${\mathrm{\pi }}^{\mathrm{-}}$,2${\mathrm{\pi }}^{\mathrm{-}}$) to ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(${\mathrm{\pi }}^{\mathrm{-}}$,${\mathrm{\pi }}^{+}$${\mathrm{\pi }}^{\mathrm{-}}$) relative to that of the elementary cross sections was observed, and is discussed in terms of various nuclear-medium effects including a double-Δ production channel.

Inclusive electron-scattering cross sections have been measured for ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$ in the quasielastic region at electron energies between 0.9 and 4.3 GeV, at scattering angles of 15° and 85°. Longitudinal and transverse response functions at a q of 1.14 GeV/c have been extracted using a Rosenbluth separation. The experimental Coulomb sum has been obtained with aid of an extrapolation. The longitudinal response function, after correction for Coulomb distortion, is lower than quasifree-scattering-model predictions at the quasielastic peak and on the high-ω side.

The cross section of the isovector giant dipole resonance (GDR) excited by inelastic scattering of 120-MeV α particles for 0°≤Θα’≤3° has been measured using the ${}_{}{}^{116,124}{}_{}{}^{}\mathrm{Sn}$(α,α’${\gamma }_0$) and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$(α,α’${\gamma }_0$) reactions. The results are compared with distorted-wave Born-approximation calculations with a GDR form factor depending on the relative difference of proton and neutron radii (Δ${\mathit{R}}_{\mathit{p}\mathit{n}}$/${\mathit{R}}_0$). Within the model used, the Δ${\mathit{R}}_{\mathit{p}\mathit{n}}$/${\mathit{R}}_0$ values for ${}_{}{}^{116}{}_{}{}^{}\mathrm{Sn}$, ${}_{}{}^{124}{}_{}{}^{}\mathrm{Sn}$, and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ deduced from the comparison of measured and calculated cross sections are (0.$7_{\mathrm{-}0.7}^{+2.3\mathrm{}}$)%, (4.$1_{\mathrm{-}2.5}^{+2.1\mathrm{}}$)%, and (3.0±1.3)%, respectively.

Nuclei with Z up to 82 emitted in the ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$${+}^{197}$Au reaction at ${\mathit{E}}_{\mathrm{lab}}$=29 MeV per nucleon have been measured as a function of the associated neutron multiplicity. The data reveal the presence of strong correlations between character of a collision and neutron multiplicity. The trends suggest a disassembly of the nuclear system into a large number of nucleons and small fragments in the events with the highest neutron multiplicity. In such events, approximately one-third of the neturons are released from the system and fragment yields decrease in an exponential fashion with increasing mass.

Molecular-dynamics simulations were used to calculate the photodissociation yield of ${\mathrm{F}}_2$ in solid Kr as a function of proton energy at 12 K. The calculations used pairwise interactions including empirical gas-phase F${(}^2$${\mathit{P}}_{3/2}$)/Kr potentials. Excellent agreement was found with recent experimental data, showing the quantitative accuracy of molecular-dynamics simulations using pairwise reagent solvent potentials, in describing a chemical condensed-matter reaction.

We have performed the first direct search for orthopositronium decay into two photons in order to determine if this decay, forbidden by space-rotational invariance, is the cause of the reported discrepancy in the orthopositronium decay rate. A high-resolution measurement of the photon-energy spectrum by a germanium detector was used to discriminate the expected sharp peak of the two-photon decay from the broader peak of the pickoff annihilations, the magnitude of which was minimized by selecting a target of low-density silica powder and by placing it in vacuum. No evidence of such decay is observed, resulting in an upper limit on the branching ratio of 3.5×${10}^{\mathrm{-}4}$, a factor of 6 below the level that could explain the decay-rate discrepancy.

A direct search for γ rays from the forbidden decay o-Ps→2γ has been performed using the same apparatus that recently measured an anomalously high o-Ps decay rate. Using a high-resolution Ge γ-ray detector, a 233-ppm limit is set on the branching ratio to a pair of 511-keV γ rays, and a 200-ppm limit is set on the branching ratio pair of unequal-energy γ rays that sum to 1022 keV. Hence, these 2γ modes cannot be responsible for the o-Ps decay-rate discrepancy between theory and experiment of 1400±230 ppm.

High-resolution photoionization studies of He have revealed more than 50 states below the N=2–7 thresholds of ${\mathrm{He}}^{+}$, including sixteen (sp,2n+) and five (sp,2n-) states in the N=2 series. With a resolving power of E/ΔE≃10 000, states as narrow as 0.1 meV could be observed and linewidths were determined with an accuracy up to ±0.5 meV. Interchannel interferences, evident through effects on positions, shapes, and intensities of Rydberg lines, were interpreted within the framework of the multichannel quantum-defect theory.

We use an iterative process to get an analytical solution for a screened Thomas-Fermi (Yukawa) potential. The analytical solution is not exact, but the result agrees with the best variational and numerical integration results. The critical Thomas-Fermi wave vector ${\mathit{q}}_{\mathit{c}}$ above which there is no bound state is obtained within 0.03% accuracy. We also show that the critical effective charge vanishes.

The propagation of target waves in the presence of walls and windows is considered. It is shown that in a finite system, for sufficiently small passages no target waves are triggered. Propagation through a large opening can inhibit the onset of waves from smaller windows.

Scanning-tunneling-microscope images of ${\mathrm{NbSe}}_3$ at 4.2 K show that all three pairs of chains in the unit cell carry a strong charge-density-wave (CDW) modulation. The high-temperature CDW is strongly localized on one pair of chains, consistent with previous conclusions. The low-temperature CDW forms on the remaining two pairs of chains in disagreement with previous results and analysis which concluded that only one pair of chains participated in the low-temperature CDW formation.

Thermal and structural studies have been performed on thin films of n-heptyl-4’-n-pentyloxylbiphenyl-4-carboxylate (75OBC). Similar to 65OBC, a surface hexatic phase is observed for films greater than four molecular layers in thickness. Four- and three-layer films display a single, two-dimensional liquid-hexatic transition. The four-layer heat-capacity anomaly is described well by a divergent power-law expression. The three-layer heat-capacity anomaly is qualitatively the same, although its size is greatly reduced. Also, a surface crystal-E phase is observed immediately below the liquid-hexatic transition(s).

The spinodal decomposition of mixtures of poly(ethylenepropylene) (PEP) and perdeuterated poly-(ethylenepropylene) has been studied near the surface using forward-recoil spectrometry. Instead of the composition waves with randomly oriented wave vectors (and random phases) found in the bulk, we observe composition waves with wave vectors normal to, and which propagate inwards from, the surface, maintaining coherence for several wavelengths. We argue that these surface-directed spinodal decomposition waves are caused by the preferential attraction of the d-PEP to the surface.

We present the results of a Monte Carlo study of the surfaces (or ‘‘hulls’’) of percolation clusters in three dimensions. The hulls were generated using a novel growing self-avoiding surface. Our results strongly suggest that the surface and bulk of the infinite cluster have the same fractal dimension at the percolation threshold, and that the other bulk and hull critical exponents are identical as well. These conclusions are supported by heuristic scaling arguments.

We report a light-scattering observation of β relaxation in [Ca(${\mathrm{NO}}_3$${)}_2$${]}_{0.4}$-(${\mathrm{KNO}}_3$${)}_{0.6}$ in the vicinity of the liquid-glass transition. The spectra exhibit self-similarity with I(ω)=A/${\mathrm{\omega }}^{1\mathrm{-}\mathit{a}}$ over a spectral range of nearly 3 orders of magnitude in both the liquid and glass phases. This result agrees with predictions of mode-coupling theories of the glass transition. However, the value of a is strongly temperature dependent, a result not predicted by the theory. The spectra are strongly depolarized with a depolarization ratio of ∼0.75.

We report the structural and electronic properties of Cs adsorbed on room-temperature GaAs and InSb (110) surfaces as observed with scanning tunneling microscopy. Cs initially forms long one-dimensional (1D) zigzag chains on both surfaces. Additional Cs adsorption on GaAs(110) results in the formation of a 2D overlayer consisting of five-atom Cs polygons arranged in c(4×4) superlattice. The tunneling gap measured over these insulating structures narrows with the transition from 1D to 2D, with metallic characteristics observed following saturation with a second Cs overlayer.

A microwave-pumped spin-wave-instability experiment is used to demonstrate that chaos can be controlled by a small periodic perturbation of an available system parameter, as recently proposed by Ott, Grebogi, and Yorke. The experiment is performed in an yttrium-iron-garnet sphere in the subsidiary-resonance configuration with a small modulation in the applied magnetic field. Observation of the Fourier spectrum of the low-frequency auto-oscillations and measurment of the attractor dimension and metric entropy demonstrate clearly that the chaotic attractor becomes periodic when the modulation frequency and amplitude are carefully chosen.