The E-802 spectrometer at the Brookhaven Alternating Gradient Synchrotron, enhanced by a trigger for selection of events with one or more specified particles, has been used to measure the momentum-space correlation between pairs of ${\mathit{K}}^{+}$’s emitted in central Si+Au collisions at 14.6 A GeV/c. This correlation has been projected onto the Lorentz-invariant relative four-momentum axis. Fits to this correlation function yield a size for the kaon source that is comparable to that found using ${\mathrm{\pi }}^{+}$ pairs from a similar rapidity range, once a transformation from the particle-pair frames to a single source frame is made.

General exact projection formulas at finite temperature for one-body statistical operators with broken symmetries are derived and applied to the calculation of angular momentum projected average energies and level densities in the static path approximation. The method is illustrated for ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ using a quadrupole interaction and compared with exact shell model results.

A rotational band based on the proton ${\mathit{h}}_{11/2}$ orbital has been observed to high spin (79/2ħ) and high rotational frequency (ħω≃1.0 meV) in the nucleus ${}_{51}{}^{113}{}_{}{}^{}\mathrm{Sb}$. The measured transition quadrupole moment is ${\mathit{Q}}_0$=4.4±0.6 e b, consistent with an axial prolate deformation of ${\mathrm{\beta }}_2$≃0.32. A large interaction strength (360±60 keV) has been measured for the rotational alignment of ${\mathit{h}}_{11/2}$ neutrons which, together with a considerable delay in the crossing frequency (Δħω≃0.09 MeV), is construed as the first direct evidence of a large high-j proton-neutron interaction.

Connections between the superdeformed and normal-deformed states in ${}_{}{}^{143}{}_{}{}^{}\mathrm{Eu}$ have been established by measuring energy sums of two consecutive γ-ray transitions in the linking cascade. Six decay paths have been observed connecting discrete states in the two potential wells. The absolute excitation energy and the most likely spin of the superdeformed band have been determined directly for the first time.

We have measured x-ray emission from the neutralization of slow ${\mathrm{U}}^{\mathit{q}+}$ ions with charge states q=61–73 and energies of 7×q keV on a Be foil. We were able to resolve M-satellite groups and found an expected increase in M x-ray intensity with increasing number of M-shell vacancies in the incident ions. However, for charge states with no M-shell vacancies, we also observed a significant intensity of M x rays. We take this observation as evidence of an internal dielectronic excitation process occurring during the neutralization of the ions.

Molecular bond-softening and above-threshold dissociation of ${\mathrm{H}}_2^{+}$ and ${\mathrm{D}}_2^{+}$ in intense laser fields is reexamined using 160 fs pulses of 769 nm light. At intensities greater than ∼${10}^{13}$ W/${\mathrm{cm}}^2$ new features appear in the dissociation spectrum. These are consistent with the formation of trapped population in light-induced vibrational states, formed in the adiabatic potential near the three-photon resonance between the 1s${\mathrm{\sigma }}_{\mathit{g}}$ and 2p${\mathrm{\sigma }}_{\mathit{u}}$ states. Rovibrational structure of such light-induced states appears in the kinetic energy spectra of the ion fragments detected after multiphoton ionization.

We show that the autoionization line shape can be modified by the choice of two laser intensities and the relative phase. Under well specified conditions, proper choice of the phase can lead to selective cancellation of the transition to the discrete or the continuum part of the state. Application of the idea to a multichannel problem in the rare gases also provides significant effects.

Molecular left-right asymmetry is an origin of nonvanishing even-order optical nonlinear susceptibilities of nonracemic solutions of chiral molecules. Though second harmonic generation (SHG) due to quadratic dipolar nonlinearity is still symmetry forbidden in optically active liquids yet we have succeeded in experimental observation, for the first time, of noncollinear SHG due to a five-wave mixing process according to a scheme 2ω=3ω-ω, governed by a fourth-order susceptibility tensor ${\mathrm{\chi }}^{\mathrm{}\left(4\right)\mathrm{}\mathit{D}}$. The SHG signal is found to be well collimated and quasi-phase-matched; it shows theoretically predicted polarization, intensity, spectral, and temporal properties.

The deformed Gaussian orthogonal ensemble introduced earlier is developed here for large dimensional matrices. Both the spacing and eigenvector distributions are studied and compared to other ones suggested for the chaos-order transition problem. The concept of a universal lower entropy with respect to the Gaussian orthogonal ensemble entropy is proved very useful.

We report for the first time quantum calculations for the so-called bouncer model, the classical analog of which is well known to manifest a chaotic behavior. Three versions of our model are fully tractable quantum mechanically and are potentially a rich source of data for establishing properties of a quantum system of which the classical mechanics can be chaotic. Among the results presented here, consequences of the varying bandwidth of infinite-dimensional transition matrices on the use of the correspondence between classical chaos and non-Poissonian quasienergy statistics are discussed.

Accumulated photon-echo experiments in pumped Er-doped fibers are reported. The echoes were observed to decrease and disappear as the fiber was pumped to transparency, and then to increase again as the system was inverted. Coherent saturation between the pulses unbalanced the initially identical excitation pulses. We describe a simple frequency domain model that explains all the observed features.

We develop a large-N method for the problem of homogeneous turbulence. The spherical (N→∞) limit yields Kraichnan’s direct interaction approximation equations. Implications for real turbulence (N=1) are discussed. In particular, we argue that the renormalization-group results obtained by setting the expansion parameter y=4 are incorrect, and that the Kolmogorov exponent ζ has a nontrivial dependence on N, with ζ(N→∞)=3/2. This value is remarkably close to the experimental result ζ≃5/3, which must therefore result from higher-order corrections in powers of 1/N.

An integral formulation is presented taking into account ion dynamics in the Pierce diode problem. Earlier restrictions on the ion drift velocity are lifted and generalized to an arbitrary ion injection velocity. An analysis of equilibrium solutions reveals a new quality of the diode as the number of nonuniform solutions is finite and reduces pairwise when the ion beam control parameter μ^≡${\mathit{m}}_{\mathit{e}}$${\mathit{v}}_{0\mathit{e}}^2$/${\mathit{m}}_{\mathit{i}}$${\mathit{v}}_{0\mathit{i}}^2$ is increased. Beyond μ^=0.2172 no solution exists. The consequences on the ballistic ion beam transport in the ion-beam neutralization problem are discussed.

Spatiotemporally resolved plasma induced emission spectroscopy in a symmetric 13.56 MHz rf discharge in helium is applied to investigate the existence of fast secondary electrons. The time evolution of the excitation is monitored in the emission of the He 6678 Å and Heii 4686 Å lines. Time development is resolved using the single photon counting technique.

We propose a rapid new iterative scheme for accurately reconstructing the relative positions of source and scatterers directly from the data of a monoenergetic point-source diffraction pattern. It takes account of the squared object-wave terms neglected in traditional holographic algorithms, does not suffer from a twin-image problem, and even identifies the chemical species of the scattering atoms.

The atomic and electronic structure of various Si-based layered structures is calculated using pseudopotential density-functional theory and a self-energy approach. A silicon-hydrogen compound, consisting of a stacking in the [111] direction of double layers of Si terminated with H, is found to have an almost direct band gap of 2.75 eV. Substituting OH groups for H atoms leads to the compound siloxene, which is found to have a direct band gap of ∼1.7 eV. Investigations of the band-edge states and calculations of matrix elements show that these direct transitions are very strong.

Crystal to glass transitions are simulated using molecular dynamics for an fcc binary random solid solution with varying atomic size ratios and concentrations. The transition occurs at a critical supersaturated solute concentration with a sufficiently large solute-solvent atomic size difference. Close to the amorphization, the shear elastic moduli become dramatically softened, accompanied by a Martensite-like structural change. Large strain fluctuations and small enthalpy and volume changes at the transition indicate that it is triggered by a mechanical instability reached in the metastable crystal.

We introduce a generalization of the directed polymer model, where the energies of the bonds building the paths are not random variables, but solutions of Kirchhoff’s equations for a network of random resistors. This applies exactly to a hydrodynamic dispersion problem, namely, finding the first arrival time of a tracer convected by a fluid through a porous medium at high Peclet numbers. Our model may also have some relevance to fracture of heterogeneous media. It is shown to be in the same universality class as the directed polymer, but corrections to scaling are generated in two dimensions by the nonlocality of the Laplace field.

We have measured the difference in vibrational entropy of ${\mathrm{Ni}}_3$Al in two states of chemical order: as a disordered fcc solid solution, and as the equilibrium L$1_2$ ordered structure. Data were obtained from three independent methods: low-temperature calorimetry, temperature-dependent x-ray diffractometry, and temperature-dependent extended electron energy loss fine structure spectrometry. We estimate that at high temperatures, the vibrational entropy of chemically disordered ${\mathrm{Ni}}_3$Al is 0.3${\mathit{k}}_{\mathit{B}}$/atom greater than for ordered ${\mathrm{Ni}}_3$Al.

A renormalizable field theory is developed for (multi)critical roughening of interacting interfaces in systems of dimension d<3. There is an infinite hierarchy of universality classes that mirrors the series of multicritical points in Ising systems. The relevant operator algebra of these theories is built up by local scaling fields that are singular distributions of the basic field variable. Critical indices, e.g., the exponent α, of the specific heat, are obtained analytically in an ɛ expansion. The extension of our results to d=3 is discussed.