Previous work on bifurcations and chaos in ferromagnetic resonance has singled out only the most unstable pair of spin waves for consideration, even though in general an entire manifold of spin wave is elegible for instability. This serious defect is removed here, and, as the result, we are able to calculate analytically the frequency of the limit cycle and its accompanying distinctive spatial correlation patterns.

The transition from Cs to ${\mathrm{Cs}}_{11}$${\mathrm{O}}_3$ leads to a twofold increase of the intensity of electron emission from the valence band (and to a substantial decrease of the emission from the $\mathrm{Cs} 5p$-core levels) as probed by metastable deexcitation spectroscopy, although the concentration of conduction electrons is reduced by about 50%. This phenomenon is attributed to a quantum size effect of the conduction electrons as proposed in a theory by Burt and Heine.

A rotationally invariant translation-generating functional for the continuum model of a ferromagnetic chain is found, resolving a long-standing paradox. The condition of rotational invariance leads to a topological quantization in the continuum classical model that corresponds to spin quantization in the equivalent discrete quantum model. The relation between the classical continuum model and the discrete quantum models is made precise.

We show that in the low-velocity limit extreme Reissner-Nordstrom black holes describe approximate geodesic motion on a $3N$-dimensional parameter space. We discuss the metric and the motions in the limits that one hole is much smaller than the others and also where the holes are well separated. We also consider the quantum mechanics of these solutions.

The effect of an unstable continuum on the time evolution of an embedded state is examined. It is found that the decay law remains exponential, but that the lifetime is modified. Under suitable conditions, the initial state may survive longer than would be the case if the continuum were stable.

The average lifetime of a chaotic transient versus a system parameter is studied for the case wherein a chaotic attractor is converted into a chaotic transient upon collision with its basin boundary (a crisis). Typically the average lifetime $T$ depends upon the system parameter $p$ via $T\sim {|p-p_c|}^{-\gamma }$, where $p_c$ denotes the value of $p$ at the crisis and we call $\gamma$ the critical exponent of the chaotic transient. A theory determining $\gamma$ for two-dimensional maps is developed and compared with numerical experiments. The theory also applies to critical behavior at interior crises.

We present results for the $0^{++}$ glueball mass ($m_G$) and the string tension ($\sigma$) in pure gauge lattice QCD with a four-parameter improved action. We suggest and confirm that previous estimates for $\frac{m_G}{\sqrt{\sigma }}$ have been too low because of the influence of the unphysical and nonuniversal phase structure in the fundamental-adjoint coupling plane. We find that $m_G\approx 1200-1400$ MeV using $\sqrt{\sigma }=420\mathrm{}$ MeV.

We analyze the strong-coupling limit of lattice $\mathrm{SU}\mathrm{}\left(N\right)\mathrm{}$ QCD at finite chemical potential. Using a dimer approach and mean-field techniques we predict the existence of a chiral-symmetry-restoring first-order phase transition for $N>~3$. We conclude that recent nonstandard results discussed in the literature may be due to numerical problems.

High-statistics data on the reaction ${\pi }^{-}p\to \eta {\pi }^{+}{\pi }^{-}n$ at 8.06 GeV/c were obtained. An isobarmodel partial-wave analysis was performed for the $\eta \pi \pi$ system. The $\eta \mathrm{}\left(1275\right)\mathrm{}$ meson was confirmed as a narrow $I{J}^{\mathrm{PC}}={00}^{-+}$ resonance. It decays through both $\delta \pi$ and $\epsilon \eta$. A narrow state with $I{J}^{\mathrm{PC}}={00}^{-+}$ was found in an $\eta \pi \pi$ decay channel at 1.42 GeV. It has a prominent peak in a $\delta \pi$ decay mode. No significant $E\left(1420\right)\mathrm{}$ signal with $I{J}^{\mathrm{PC}}={01}^{++}$ was found near the mass region of 1.42 GeV.

We report on the observation of novel Ramsey-type resonances due to collisional velocity diffusion in atomic samarium vapor in the presence of rare-gas perturbers. The experimental technique uses counterpropagating laser fields and relies on coherent resonance Raman processes to optically excite and detect sublevel coherence within the Doppler-broadened ${}_{}{}^{154}{}_{}{}^{}\mathrm{Sm}$ $\lambda =570.68\mathrm{}$-nm ${}_{}{}^7{}_{}{}^{}F_1^{}{}_{}{}^{}-{}_{}{}^7{}_{}{}^{}F_0^{}{}_{}{}^{}$ transition. The experimental findings are in good agreement with theoretical predictions based on a Fokker-Planck equation; time constants for the collisional thermalization of Sm in He and Ne atmospheres are derived from our data.

First experimental evidence of a radiative wave propagating ahead of a supercritical shock is given. An aluminum piston driven by laser light at wavelengths of 1.06 and 0.35 μm induces the shock wave in xenon gas. The plane piston velocity ranges from 2.5 × ${10}^6$ to 1.2 × ${10}^7$ cm·${\mathrm{s}}^{-1\mathrm{}}$ and the gas pressure is up to 6 bars. Experimental results are in good agreement with a simple analytical model of the propagation of a radiative wave in front of a supercritical shock wave when the approximation of radiation heat conduction is assumed.

Results from simulations of Ni, Al, ${\mathrm{Ni}}_3$Al, and NiAl show long-range, oscillatory surface relaxations that decay exponentially into the bulk. Pure fcc Ni and Al have oscillation periods that are close to the nearest-neighbor distance, independent of crystal face. This is shown to be due to surface smoothing and steric effects. In ${\mathrm{Ni}}_3$Al and NiAl, the surface planes are rippled, with the Ni-Ni and Al-Al interlayer spacings oscillating 180° out of phase. Very good agreement between our results and experimentally measured atomic relaxations is obtained.

Mutual-diffusion and tracer-diffusion coefficients, $D$ and $D^{*}$, are measured in the miscible polymer blend system polystyrene + poly (2,6-dimethyl-1,4-phenyleneoxide) by forward recoil spectrometry. We find $D$ to be much larger than $D^{*}$, an increase that is predicted quantitatively by a theory which includes the entire chemical-potential driving force for interdiffusion.

The structural environment of Bi incorporated in Ge chalcogenide glasses has been found from extended x-ray absorption fine-structure data to consist of threefold coordination. An increase by a factor of 2 in the Debye-Waller factor occurs as the carrier type changes from $p$ to $n$. A mechanism involving the suppression of positively charged structural defects, and the consequent unpinning of the Fermi level, by the formation of partially ionic Bi-chalcogen bonds is proposed to account for the doping effect.

The Su-Schrieffer-Heeger model for the coupled electron-phonon system in polyacetylene has been extended to include phonons. Two localized IR-active vibrational states are found. We also find significant mixing between the Goldstone mode of the soliton and the lower-frequency modes in the acoustic phonon branch, creating for a charged soliton an "infrared-active acoustic phonon branch." The IR oscillator strengths are calculated for the bound and acoustic modes of interest and their effect on the structure and shape of the "pinned" mode is discussed.

Ultrasonic experiments performed on a three-dimensional percolating system made from sintered copper powder show a rapid increase in the attenuation, corresponding to a sudden decrease in the localization length for vibrations, at wavelengths approaching the percolation correlation length. The data support recent theoretical predictions of a crossover from extended phonon excitations to localized fracton excitations at a length scale below which the structure has the self-similarity of a fractal system.

The method of molecular-dynamics simulation for an assembly of 6480 soft spheres is used to investigate the layerwise structure of a {111} solid-liquid interface for an fcc crystal. A heterogeneous two-phase structure in each layer is suggested by a 2D Voronoi polygonal analysis but this is not supported by various order parameters. The distribution of angular correlation, positional correlation, and free volume all suggest a rather homogeneous, though nonhexatic, structure within each layer. The free volume per particle increases across the interface little more than does the total volume.

We report the observation of a (5×5) reconstruction on the pure Si (111) surface, which is induced and stabilized by a tensile strain. The stabilization is so strong that the reconstruction survives extended exposure to air and the formation of a native oxide layer. Modeling of experimental high-resolution transmission-electron-microscope profile images indicates that the native oxide is ordered. The (5×5) reconstruction can also be induced at an initially unreconstructed Si-oxide interface by application of tension and appropriate annealing.

Critical slowing down poses a major obstacle to reaching the steady-state distribution in large-scale numerical simulations. We demonstrate how to alleviate this problem by means of Fourier acceleration, a method consisting of updating in $k$ space with a $k$-dependent time step. The method is general and applicable to a wide range of problems. We demonstrate its use by numerical experiments on random resistor networks at the percolation threshold.

Certain close packings of disks around rhomboidal seeds contain deterministic fractal defect structures. The defects, in the form of stacking faults, grow and bifurcate by deterministic rules. We derive the fractal dimension of the defect structure, a universal function independent of all variables except the acute angle of the rhomboidal seed.