Classical light-scattering studies of colloidal silica gels show that they have a fractal structure for length scales shorter than a concentration-dependent crossover length $\xi$, and behave like a collection of nearly randomly distributed scattering centers for length scales greater than $\xi$. Our data show that $\xi$ has a power-law concentration dependence, $\xi \propto c^{-1.17\mathrm{}\pm 0.1}$.

The maximum-entropy formalism is used to characterize the fluctuations in transition strengths for a bound quantum-mechanical system. In the chaotic limit only one, ever present, sum rule is required as a constraint. The resulting distribution is that of Porter and Thomas, which can also be derived from random-matrix theory. For nonchaotic systems the distribution of transition strengths has a lower entropy. A possible additional constraint, operative during the onset of chaos, is proposed. The distribution of maximal entropy subject to both constraints accords with computed intensities in a system of two degrees of freedom.

Classical Kolmogorov-Arnol'd-Moser tori and cantori are found to act as barriers in the quantum dynamics of a kicked rotator. In their vicinity the asymptotic distribution decays exponentially. The penetration depth of a Kolmogorov-Arnol'd-Moser torus scales as ${\hslash }^{0.66}$ and the penetration probability as ${\hslash }^{2.5}$. Cantori can inhibit the diffusive growth of mean square displacements and thus act as barriers more drastically than in classical systems.

Our formalism for describing quantum measurements is generalized to the multitime case and used to derive rigorous time-energy uncertainty relations. For a free particle, we find that $T\delta H\ge \frac{1}{2}$, where $\delta H$ is the dispersion in energy and $T$ is the measurement duration as given by an external clock of arbitrarily high accuracy. Moreover, any system used as a clock obeys $\delta t\delta H\ge \frac{1}{2}$, where $\delta t$ is the dispersion in the values of time as measured by the system.

We apply a formalism for the description of multitime measurements to the derivation of the quantum limit on the precision with which a pair of successive position measurements can be performed on a free mass under conditions that would be optimal for detecting very weak forces. The result depends on the position resolution of the measuring device as well as on the time interval between the two measurements, and it spans a range of values which include a presently controversial result known as the standard quantum limit; any controversy is thereby resolved.

The transport coefficients in quarkless QCD are presented by Kubo-type formulas. A comparison with the results from kinetic theory is made. Estimates for these coefficients in the high-temperature phase from weak-coupling perturbation theory and in the low-temperature phase from the strong-coupling expansion on the lattice are given.

We have located 3886 neutrino interactions in the fiducial volume of a hybrid emulsion spectrometer installed in the Fermilab wide-band neutrino beam. A search for ${\tau }^{-}$ decays yielded no candidate, resulting in an upper limit of 0.002 (0.073) for direct coupling of ${\nu }_{\mu } \left({\nu }_e\right)$ to ${\tau }^{-}$. The ${\nu }_{\mu } \left({\nu }_e\right)$ to ${\nu }_{\tau }$ limits to mass differences and mixing angles ($\alpha$) between the neutrinos are at maximum mixing $\Delta M^2<0.9\mathrm{} \mathrm{}\left(9.0\right)\mathrm{}$ ${\mathrm{eV}}^2$, and at maximum sensitivity ${sin}^2\left(2\mathrm{}\alpha \right)<\mathrm{}0.004\mathrm{} \mathrm{}\left(0.12\right)\mathrm{}$. The direct-coupling limits are also used to show that most ${\tau }^{-}$ decays must contain a neutral lepton other than ${\nu }_{\mu }$ or ${\nu }_e$.

Particle emission from a spatially static nucleus at finite temperature is studied by means of a computer simulation. In particular, the two-particle correlation function at small relative momentum is constructed from the analysis of 20000 emission events. The apparent size of the emitting region is found to decrease with increasing energy of the emitted particles, as has been observed experimentally. In the simulations, the large apparent source size associated with slow particles arises because of the longer average emission time of these particles, which tends to wash out the correlations.

Coincidences between fragments ($Z=8\mathrm{}-36,\theta =3\mathrm{}°-30°$) emitted in the Kr+Au reaction at 35 and 44 MeV/u have been measured. On the basis of final-state interactions, the coincidence events can be divided into two distinct groups. In one group, products with near beam velocity are identified with the remaining part of the projectile; they are detected in coincidence with much slower fragments emitted by the target or by a hot zone common to the projectile and the target. The fragments of the second group have intermediate velocity and may be emitted by a much slowed-down projectile.

High-energy $\gamma$ rays observed by Stevenson et al. in the reaction of 20-, 30-, and 40-MeV/nucleon ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$+C and Pb are calculated from the Boltzmann master equation. The production of $\gamma$ rays is included via a semiclassical $\mathrm{np}$ bremsstrahlung calculation. Good agreement is found in shape and magnitude between calculated and experimental results.

There is mounting evidence that the nuclear rotational motion is damped at modest (≅0.5 MeV) temperatures, which reduces correlations between the energies of $\gamma$ rays emitted in a rotational cascade. We observe such reduction to be strongest at the highest spins and to be larger than previously thought. Preliminary calculation shows that shape fluctuations are most likely responsible for the increased size.

Properties of deformed light nuclei are calculated within a relativistic mean-field theory with use of an axially symmetric space lattice. The axial results are in good agreement with the results of previous calculations for spherical nuclei. For deformed nuclei, parameters fitted to describe spherical nuclei fail to reproduce energies and deformations.

In infrared photodepletion spectroscopy of molecular beams of $\mathrm{S}{\mathrm{F}}_6-{\mathrm{Ar}}_n$ clusters, a shifting and broadening of the ${\nu }_3$ band of S${\mathrm{F}}_6$ was observed by Gough, Knight, and Scoles for a narrow range of experimental conditions. A Monte Carlo simulation of those spectra based on an instantaneous dipoleinduced dipole model reproduces them semiquantitatively and shows that such broadening can be caused by phase coexistence. However, cluster-size distribution effects make it nuclear whether this is the source of the broadening observed in the existing data.

Spectra of very highly charged ions of Au, Pb, Bi, Th, and U have been observed in laser-produced plasmas generated by the OMEGA laser. Line identifications in the region 9-110 Å were made for ions in the Fe, Co, Cu, and Zn isoelectronic sequences. Comparison of the measured wavelengths of the Cu-like ions with values calculated with and without QED corrections shows that the inclusion of QED corrections greatly improves the accuracy of the calculated $4s-4p$ wavelengths. However, significant differences between the observed and calculated values remain.

We report a value of 70.4 ± 8.3 eV for the one-electron Lamb shift in uranium, in agreement with the theoretical value of 75.3 ± 0.4 eV. We extract our Lamb shift from a beam-foil time-of-flight measurement of the (54.4 ± 3.4)-ps lifetime of the $1s2p_{\frac{1}{2}}{}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$ state of heliumlike uranium.

A method has been developed to calculate the spectrum over the $l$- and $n$-mixing regimes of an arbitrary nonhydrogenic system in an external laboratory-strength magnetic field. The original experimental results on Sr and Ba are explained in detail for the first time. The importance of quadratic Zeeman spectroscopy in the quantitative study of atomic structure is made clear.

The effect of finite geometry on the competition between traveling waves and standing waves in systems with a Hopf bifurcation to a state with spatial structure is considered in the linear and weakly nonlinear regimes. The spatial structure observed by Kolodner et al. in binary-fluid convection is explained in terms of the reflection of the linear traveling waves. The reflection coefficient is calculated, and is found to go to zero as the frequency of the waves becomes small. The pattern expected in a saturated nonlinear state is discussed.

We report the observation of gain in a new type of short-wavelength laser system at 108.9 nm. Soft x rays from a laser-produced plasma photoeject an inner-shell electron from xenon, and a population inversion is created by subsequent Auger decay to particular excited states. A model for this system is described, spectroscopic data are presented, and gain limitations due to parasitic amplified spontaneous emission are discussed. A maximum gain of 0.8 ${\mathrm{cm}}^{-1\mathrm{}}$ over a length of 9 cm is reported.

We observe magnetic ordering of the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ spins at the surface of exfoliated graphite. In very low applied magnetic fields (≤3 G) we find new modes in the NMR resonance spectrum with the amplitude of these lines increasing sharply below 0.8 mK. We interpret our results in terms of a ferromagnetically aligned spin system, and conclude that there must be an anisotropy in the graphite planes.

Surface-phonon dispersion curves have been measured by He-atom inelastic scattering for in situ cleaved Si(111) (2×1). A mode with a flat dispersion curve at 10.5 meV has been observed which can be shown experimentally to be intrinsic to the reconstructed surface. This finding explains the anomaly in the temperature dependence of the optical excitation of electronic surface states but is in contradiction to lattice-dynamical calculations based on the $\pi$-bonded-chain model.