Two-level resistance fluctuations have been observed in clean metallic constrictions of sizes 40-8000 ${\mathrm{nm}}^3$. At low temperatures the measured values for the activation energies, attempt frequencies, and scattering cross-section changes of such two-level fluctuations suggest that we are observing defects moving between metastable configurations. The strength of observed interactions between fluctuations has been estimated. At high temperatures interactions dominate the noise dynamics, causing complex fluctuations that evolve slowly in time to produce a $\frac{1}{f}$ noise spectrum.

We report the observation of a novel phase transition in dilute aqueous suspensions of polystyrene particles as a function of ionic impurity concentration $C$. The suspension phase separates into dense and rare phases only for a restricted range of $C$ which depends on particle concentration $n$. The dense phase has liquidlike or crystalline order depending on $n$ and $C$. Free energies of the homogeneous and the phase-separated states are calculated with an effective interparticle potential. The calculated phase diagram is in qualitative agreement with the present experimental results.

Nonperturbative quantum gravitational effects can act as a damping mechanism in primordial inflation. It is shown that this effect can reduce the value of $\frac{\delta \rho }{\rho }$ to an acceptable value of ∼${10}^{-4\mathrm{}}$ in primordial inflation. The same effect reduces the gravitational-wave background by a factor ${10}^{-6\mathrm{}}$, making the primordial inflation viable.

A nonsingular classical magnetic-monopole solution is obtained in a theory with Wilson-loop symmetry breaking. The solution is used to elucidate the quantization rules governing the magnetic charge, which are more restrictive than those for Higgs monopoles.

An improved Monte Carlo renormalization-group method is used to determine the $\beta$ function of the two-dimensional O(4) $\sigma$ model. While for (inverse) couplings $\beta \gtrsim 2.2$ one obtains agreement with asymptotic scaling according to asymptotic freedom, one can see deviations from it at smaller couplings. They are, however, consistent with the behavior of the correlation length, indicating "scaling" according to the full $\beta$ function. These results contradict recent claims that the model has a critical point at finite coupling.

The decays $\frac{J}{\psi }\to \gamma K^{+}{K}^{-}$ and $\gamma K_S^0{K}_S^0$ have been studied by use of 8.6×${10}^6$ $\frac{J}{\psi }\text{'}\mathrm{s}$ produced in the DM2 detector. Clean and well-separated signals of $f_2^{\prime }\mathrm{}\left(1525\right)\mathrm{}$ and $f_2\mathrm{}\left(1720\right)\mathrm{}$ are observed in both channels and the measured product branching ratios are given. In neither channel is the $\xi \mathrm{}\left(2230\right)\mathrm{}$ seen; upper limits are given. Last, an as-yet-unexplained production of events is observed in the $K_S^0{K}_S^0$ mass spectrum between 2.0 and 2.5 GeV/${\mathit{c}}^2$.

We present the results of a search for resonantlike structures in the two-photon decay channel of the $e^{+}-e^{-}$ system at energies corresponding to the anomalous peaks seen at Gesellschaft für Schwerionen-forschung in heavy-ion reactions. Within our sensitivity, no evidence for resonances at the 3% level was found. This enables us to exclude the existence of a Wong-Becker-type particle and to set an upper limit on the ratio $\frac{{\Gamma }_{\gamma \gamma }}{{\Gamma }_{e^{+}{e}^{-}}}\le 0.7$ at 810 keV.

We have studied the $\beta$ decays of ${}_{}{}^{60}{}_{}{}^{}\mathrm{Co}$ at times $\lesssim {10}^{-4\mathrm{}}{t}_{\frac{1}{2}}$ and those of ${}_{}{}^{56}{}_{}{}^{}\mathrm{Mn}$ over the interval $0.3t_{\frac{1}{2}}\le t\le 45t_{\frac{1}{2}}$ to search for proposed deviations from the exponential decay law at short and long times, respectively. Over all time periods examined, our data are consistent with purely exponential behavior. From these measurements, stringent limits are derived on the amplitudes of possible deviations from the exponential decay law.

The theoretical estimates of the $P$-conserving $T$-invariance violation in neutron transmission are reexamined. It is shown that the previously omitted factors of dynamical enhancement caused by the $T$-nonconserving interaction of the two closely lying resonances might sum up to an overall amplification of the effect by 3-5 orders of magnitude.

It is shown within the Hartree-Fock method with the Skyrme force that the quadrupole-quadrupole neutron-proton interaction gives the leading term in the nuclear deformation energy. The quadrupole-quadrupole coupling constants are derived and shown to agree with those obtained within the simple harmonic-oscillator model.

Using a thin stack of glass detectors to measure $\frac{Z}{\beta }$ of forward-projected fast fragments from interactions of 900-MeV/nucleon ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ nuclei, we measure a cross section of 35 ± 8 mb for charge pickup ($\Delta Z=+1\mathrm{}$) from Au to Hg, and we infer a mean velocity downshift $\delta \beta \approx -0.004\mathrm{}$ and a mean momentum downshift $\delta p_{\parallel }\approx -6\mathrm{}$ GeV/c for Au to Hg, 2 orders of magnitude larger than observed for charge pickup by light nuclei. Implications of this result are discussed.

In deformed Hartree-Fock calculations with Skyrme interactions, a near degeneracy of the intrinsic state energies of $n$-particle, $n$-hole ($n\mathrm{p}-n\mathrm{h}$) deformed states with differing $n$ has been obtained. For example, in ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ the 8p-8h intrinsic state energy is close to but even lower than that of the 4p-4h deformed state. Whether there is an underlying symmetry to explain this near degeneracy has yet to be determined.

A single-mode laser with a saturable absorber exhibits spontaneous pulsation in the output (passive $Q$ switching). Period-doubling bifurcation and chaotic passive $Q$ switching which are predicted on the basis of the recently proposed model of the laser system have been observed by use of a C${\mathrm{O}}_2$ laser with a formic acid absorber. This is the first experimental evidence of deterministic chaos in a single-mode laser system with a saturable absorber.

Numerical simulations of two-dimensional model equations show that a coupling between amplitude and vertical-vorticity fields allows chaotic flows near the onset of Rayleigh-Bénard convection in large-aspect-ratio domains. In cylindrical cells, mean flows arising from this coupling lead to a chaotic nucleation of dislocations that is remarkably similar to recent observations in convection experiments.

A simple Lagrangean extrapolation scheme for modeling of the nonlinear development of the Rayleigh-Taylor instability is suggested. The model incorporates Whitham's small-amplitude formulas, given up to the cube of the wave amplitude, and extends them such that multivalued contours are obtained after a while and a bubble eventually detaches itself from the fluid. The initial stages of the bubble evolution found in this way are very similar to those recently obtained numerically by other authors.

A new model of $L$- to $H$-mode transition in tokamak plasmas is presented. Nonambipolar particle losses determine the consistent radial electric field near plasma periphery. A "cusp-type catastrophe" among the radial electric field, particle flux, and edge gradients is found. At the transition, plasma loss can take multiple values for one profile of density and temperature near the edge. A critical edge condition for the transition is obtained.

Localized vibrational modes have been identified in a number of computer-generated models of amorphous silicon. Networks containing coordination defects give rise to extra resonant states at low frequencies. The densities of states, and dynamic structure factors for localized, resonant, and extented modes, are discussed and compared with recent neutron-scattering data.

An ionic model has been used in conjunction with classical constant-pressure molecular-dynamics calculations to explore the properties of possible high-pressure phases of ice. Around 100 GPa, the model is found to convert from the symmetric hydrogen-bonded cuprite structure (ice X) to a fully ordered antifluorite structure. On heating, the new phase, ice XI, becomes a fast-ion proton conductor.

Bonding in the near-surface region is strongly influenced by the truncation of the lattice at the surface. This many-body effect is examined quantitatively by use of the embedded-atom method on low-index transition-metal surfaces. An unreconstructed metal surface is found to have a tensile strain of several percent. This many-body surface strain is an important factor in the energetics of surface structure, serving as a parameter combining surface stress and nonlinear elastic effects. In particular, it is demonstrated that the surface strain drives surface reconstruction, and also produces asymmetry in the stability properties of thin mismatched epitaxial overlayers.

We have performed precise measurements of the energy spectrum of bremsstrahlung from a single crystal. The results are compared with the theory of coherent bremsstrahlung and found to be sensitive to the choice of the functional form of the atomic form factor. The Si data agree with the theoretical curve which is obtained with the form factor based on the Hartree-Fock model within a systematic error of 2%. It is pointed out that measurements sensitive to the atomic form factor to the 0.5% level will become feasible for various materials by improvement of the present method.