It is pointed out that in fluorescent and Raman scattering by molecules in or near a small particle, large enhancements in the scattered signals are obtained when both the incident and the fluorescent frequencies coincide with eigenfrequencies of the particle. Numerical results are presented for spherical particles with a refractive index $2.2+0.409\times {10}^{-2\mathrm{}}i$ uniformly filled with fluorescent scatterers. The effects are found to be substantial.

Observations are reported of current oscillations with frequency proportional to current in the nonlinear conduction region in ${\mathrm{NbSe}}_3$. At high electric field strengths the amplitude of the oscillations decreases with increasing charge-density-wave current. It is suggested that this behavior is due to the periodic motion of the charge-density wave as it slides through pinning potential, and good agreement is found when the potential is evaluated from the frequency-dependent conductivity. The same theory is used to estimate the stability of the pinned charge-density wave.

The exact thermodynamic equations of the Kondo model are solved in the scaling regime and the impurity magnetization, susceptibility, and specific-heat curves are obtained as functions of the temperature for different magnetic fields. This is done for the case where the impurity has spin ½, 1 and $\frac{3}{2}$.

A thermally induced change in the vibrational properties of a coadsorbed oxygen-water overlayer on Ru(001) is attributed to the formation of a local O-${\mathrm{H}}_2$O complex. An O-H stretching mode of this complex is observed in electron-energy-loss data, but not in infrared reflection-absorption data available from another laboratory. This provides the first direct experimental evidence of a case in which the surface dipolar selection rule applies in an infrared but not in an energy-loss measurement.

The Eguchi-Kawai model is studied by using the Monte Carlo technique with the gauge groups $\mathrm{SU}\mathrm{}\left(N\right)\mathrm{}$, $N=2, 3, 4, 5, \mathrm{and} 10$. Clear evidence of spontaneous breaking of the $Z_N$ symmetry is observed in the weak-coupling region for $N=10\mathrm{}$.

The charged multiplicity has been measured at the $\Upsilon \mathrm{}\left(4S\right)\mathrm{}$ and a value of 5.75±0.1±0.2 has been obtained for the mean charged multiplicity in $B$-meson decay. Combining this result with the measurement of prompt leptons from $B$ decay, the values 4.1±0.35±0.2 and 6.3±0.2±0.2 are found for the semileptonic and nonleptonic charged multiplicities, respectively. If $b\to c$ dominance is assumed for the weak decay of the $B$ meson, then the semileptonic multiplicity is consistent with the recoil mass determined from the lepton momentum spectrum.

First measurements of 40-500-MeV $\gamma$ rays from collisions of 2-GeV/amu Ne and Ar with Ca and Pb targets are presented. Implications with regard to production of bremsstrahlung photons and of ${\pi }^0$, $\eta$, and $\Delta \mathrm{}\left(1232\right)\mathrm{}$ particles are discussed.

The threshold law for electron-atom ionization is derived on the basis of the Coulomb-dipole theory. The result is a modulated quasilinear law for the yield: $2\propto E{\left(\ln E\right)}^{-2\mathrm{}}[1+Csin(\alpha \ln E+\mu \left)\right]$. The derivation depends on a more accurate description of the dipole moment seen by the outer electron as the distance of the inner electron from the nucleus. The derivation also implies $C\cong {\alpha }^{-1\mathrm{}}$, and it also suggests that $\alpha$ is large. The same law also applies to positron-atom impact ionization.

Spectral power and phase measurements are presented which demonstrate the existence of a wavy Taylor vortex-flow state with a mode number $m=\frac{3}{2}$. The mode is periodically continued around the annulus by a phase anomaly which is stationary in the laboratory frame. It is also shown that wavy Taylor vortex flow results in an increase (decrease) of the Taylor vortex-pair width near the center (ends) of the apparatus.

Stimulated Raman backscatter from long-scale-length, magnetically confined, underdense plasma has been studied for incident C${\mathrm{O}}_2$ laser intensities up to 2.5×${10}^{11}$ W/${\mathrm{cm}}^2$. Above an incident threshold of 4×${10}^{10}$ W/${\mathrm{cm}}^2$ the reflectivity rapidly rises to a saturated value of 0.7%. The measurements are in good agreement with a theoretical model of absolute instability which includes both collisional and Landau damping due to hot-electron production.

An abrupt decrease in the acoustic loss $Q^{-1\mathrm{}}$ has been observed in flexural modes of polycrystalline Nb disk samples on cooling through the superconducting transition temperature $T_c$. High-resolution measurements on a 1.6-kHz mode of one sample showed a 30% decrease in $Q^{-1\mathrm{}}$ in a 20-mK temperature interval. It is shown that these results are clearly identifiable with the reduction of the thermoelastic contribution to the acoustic loss in the superconducting state.

The detailed NMR line of ${}_{}{}^{195}{}_{}{}^{}\mathrm{Pt}$ atoms in the surface layer of small particles of Pt metal on which CO has been chemisorbed has been observed. The surface ${}_{}{}^{195}{}_{}{}^{}\mathrm{Pt}$ are resolved from the ${}_{}{}^{195}{}_{}{}^{}\mathrm{Pt}$ resonances of atoms deeper in the particle by spin-echo double resonance between ${}_{}{}^{195}{}_{}{}^{}\mathrm{Pt}$ and ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$. The ${}_{}{}^{195}{}_{}{}^{}\mathrm{Pt}$ resonance position and ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$-${}_{}{}^{195}{}_{}{}^{}\mathrm{Pt}$ indirect spin coupling are found to be very similar to those in diamagnetic Pt-carbonyl molecules. The results show that CO bonds via the C atom and verify that concepts deduced from studies of large single crystals are valid for the small particles.

Resonantly excited desorption of pyridine molecules adsorbed on silver surfaces at 95 K has been observed. The strong dependence of the laser-induced desorption on the laser wavelength and the polarization of the incident radiation clearly show that molecular vibrational activation plays a major role in the observed desorption phenomenon. The desorption yields per laser pulse are also determined from the thermal desorption spectra and the x-ray photoemission-spectroscopy intensity analyses.

The dynamical behavior of the two-dimensional Ising-like antiferromagnet ${\mathrm{Rb}}_2$${\mathrm{CoF}}_4$, which is expected to provide a real system within the $n=1\mathrm{}$, $d=2\mathrm{}$, universality class, has been investigated near $T_N=102.96\mathrm{}$ K with high-resolution inelastic neutron scattering. Measurement of the characteristic frequency of the longitudinal susceptibility fluctuations yields a dynamic critical exponent $z=1.69\mathrm{}\pm 0.05$. This is close to the conventional theoretical value $z=\gamma =1.75\mathrm{}$.

Measurements are reported, for the first time, for detection of nonequilibrium phonons emitted from the inhomogeneous gap states of a nonequilibrium superconductor by means of a phonon transmission technique. The observed phonon signal exhibits a clear spatial structure with a certain periodicity. The connection between the $I-V$ characteristic and the phonon signal is discussed.

Donor-donor and donor-acceptor dynamics in ${\mathrm{La}}_{1-x}{\mathrm{P}}_5{\mathrm{O}}_{14}:{{\mathrm{Nd}}_x}^{3+}$ are measured directly with a high-resolution, near-ir laser system. Time-resolved fluorescence line-narrowing measurements show an absence of rapid donor-donor transfer below 20 K and an onset of spectral diffusion at ≈ 20 K for an $x=0.75\mathrm{}$ sample. The linear concentration quenching and exponential decay in the absence of fast diffusion are explained with existing energy-transfer theories and are consistent with room-temperature studies.

Persistent nonphotochemical spectral holes have been burnt at low laser intensity in the vibrational absorption line of a spherical-top molecule in alkali halide crystals. These observations complement earlier studies on electronic transitions in organic crystals and glasses and demonstrate that persistent hole burning is a general solid-state phenomenon.

The effect of quantum fluctuations of the phonon field on the ground-state character of one-dimensional electron-phonon systems is studied with a numerical simulation technique. Two different electron-phonon models are studied, both for spinless and spin-½ electrons, in the half-filled-band case. In both models, it is found that in the spinless case quantum fluctuations destroy the long-range dimerization order for small electron-phonon coupling constant $\lambda$. For the spin-½ case, the results are consistent with the Peierls transition occurring at $\lambda =0\mathrm{}$.

The Hall conductance of a two-dimensional electron gas has been studied in a uniform magnetic field and a periodic substrate potential $U$. The Kubo formula is written in a form that makes apparent the quantization when the Fermi energy lies in a gap. Explicit expressions have been obtained for the Hall conductance for both large and small $\frac{U}{\hslash {\omega }_c}$.

A simple model of a classical spin-glass with weakly correlated disorder is presented. It includes both randomness and frustration, and is exactly soluble, but its solution can be obtained without replicas. Among the several phases of the model a mixed phase is found where spin-glass and ferromagnetism coexist. In addition the characteristic S shape of the spin-glass magnetization is reproduced.