A new analysis of yrast energies in collective medium and heavy even-even nuclei shows two startling results. First, although these nuclei exhibit widely varying structure [the ratio E($4_1^{+}$)/E($2_1^{+}$) ranges from ∼2.0 to ∼3.33], they show a universal behavior of an anharmonic vibrator with nearly constant anharmonicity in which the multiphonon interactions are independent of the internal structure of the vibration. Second, the transition from anharmonic vibrator to rotor can be described by critical phase transitional behavior. These results suggest a reexamination of very basic ideas of structural evolution in finite-body nuclear systems.

A ridge structure consisting of stretched E2 transitions and extending from ħω≃0.6 to 0.75 MeV has been found in a proton-selected γ-γ matrix in the reaction ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$${(}^{37}$Cl, xn${)}^{152,153}$Dy at 187 MeV. The ridge spacing corresponds to a dynamic moment of inertia, ${\mathit{scrI}}^{\mathrm{}\left(2\right)\mathrm{}}$, of about 130${\mathrm{ħ}}^2$ ${\mathrm{MeV}}^{\mathrm{-}1}$ and suggests the existence of a hyperdeformed prolate shape with a quadrupole deformation ${\mathrm{\beta }}_2$≥0.9. Furthermore, a cascade of 10 discrete transitions with an average energy spacing of 30±3 keV has been found. This result is consistent with calculations indicating conditions favorable to hyperdeformed structures.

We report the first measurements of a rank 4 state multipole for He($3^1$D) excitation by electron impact with a polarized photon-photon coincidence technique. Our results allow, for the first time, the extraction of partial cross sections ${\mathrm{\sigma }}_{\mathit{m}}$ for He($3^1$${\mathit{D}}_{\mathit{m}}$) excitation (m=0, ±1, ±2) which are not otherwise available. The present results put stringent tests on existing theories and, for example, point in the theoretical calculations to an overestimation of the partial cross section ${\mathrm{\sigma }}_2$.

The single-band description of Bloch electrons in magnetic fields (e.g., by Harper’s equation) leads to classically integrable Hamiltonians and thus fails for lateral surface superlattices (LSSLs) where chaotic trajectories prevail near the classical limit. We derive a new model [Eq. (18)], which is reminescent of Harper’s equation, but is exact under the most general conditions and exhibits chaos in the classical limit. A matrix continued fraction expansion allows us to study the influence of classical chaos on the fractal spectrum known as Hofstadter’s butterfly and to make predictions on its observability in LSSLs.

A new type of phase matching based on the ring-shaped pump beam for efficient harmonic generation is studied theoretically and experimentally. The ring-shaped pump beam is shown to provide self-organized phase-matching conditions for a wide range of vapor density/refractive index variation. Because of symmetry self-phase matching may automatically compensate the phase mismatch created by the optical Kerr effect, as well as the negative influence of nonuniform spatiotemporal pump beam distribution. Self-phase matching is expected to be very efficient for frequency tripling of broadband and/or ultrashort pulses, as well as for high order harmonic generation. A factor of 4–5 improvement in the conversion efficiency of 1.06μ radiation tripling in Rb, Na vapor is obtained, when a disk-shaped beam is replaced by a ring-shaped beam. The high conversion efficiency ∼1.5% for a very short interaction length (l∼4 cm) is achieved.

We extend the Gross-Pitaevskii equation for neutral superflows to a model with a roton minimum in the dispersion curve. The flow around an obstacle shows dramatic differences compared to the case without roton minimum: a stationary modulation pattern bifurcates supercritically and transforms continuously into a Čerenkov cone when the speed at infinity exceeds the Landau critical speed for the rotons. This yields a Čerenkov-like drag. An analytical approach to the problem is sketched in the weak amplitude limit.

The holographic principle is used to invert experimental photoelectron diffraction spectra to reveal the surface structure of Si(111)(√3 × √3 )-Al. The photon-energy dependence for the Al 2p emission intensity is measured for a set of emission angles. A new transformation method is applied to measured scanned-photon-energy photoemission spectra. The results of each inversion are summed over the set of angles giving images which clearly show the local geometry near the emitting atom, Al. Images are also obtained by theoretical simulation and agree well with experiment. The results demonstrate the technique as a direct, model-independent structural method, yielding bond distances and directions.

We study a reversible phase transition of one monolayer of Pb on a Ge(111) surface with a tunneling microscope over a temperature range from below to above the transition (∼175 °C). The controversial high temperature phase is actually a simple Pb-terminated 1×1 structure. Below the transition temperature, Pb atoms are displaced from their ${\mathit{T}}_1$ positions and form trimers with √3 × √3 periodicity. A fluctuating structure with patches of trimers can be resolved slightly above the transition temperature. The important effects of boundaries and domain size on the phase transformation are discussed.

The behavior of quantized vortex filaments subject to flow through an idealized orifice is investigated. Small loops nucleated at the wall are entrained and stretched by the diverging flow of the orifice, leading to individual phase-slip events. A macroscopic remanent vortex, however, can repeatedly give rise to a cascade of phase slips draining large amounts of energy from the flow field.

We have deposited cesium with monolayer thickness resolution on to the surfaces of a low-temperature quartz microbalance. By controlling the cesium thickness in the range from 1 to 25 monolayers, we have been able to continuously tune the substrate adsorption potential and observe its effect on the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ prewetting phase diagram. The wetting temperature can be conveniently adjusted in the range between 1 and 2 K. Features in both the frequency shift and the dissipation of the microbalance were used to map out the superfluid-normal boundary in the prewetting phase diagram. The transition from thin normal to thick superfluid occurs without the dissipation peak characteristic of a Kosterlitz-Thouless transition.

Quantum simulation studies have been performed on metal-ammonia solutions for a wide range of concentrations using a model consisting of excess electrons in a molecular solvent. At low electron concentrations, the electron density is localized, and the electrons pair to form peanut-shaped bipolarons. At higher electron concentrations, the bipolarons exhibit a tendency to cluster. Eventually, at yet higher concentrations, the electron density becomes delocalized and spans the system indicating that the system has become metallic.

The phase diagram of spinless fermions with repulsive interaction on a hypercubic lattice is calculated analytically in infinite dimensions. For 0<T<0.183 the susceptibility χ(k) diverges for incommensurate values of k thus masking a region of phase separation including a tricritical point. In this region a new phase must exist. Its structure is still unknown in spite of the simplicity of the model. We compare our finding to results for other interacting fermion systems and discuss its possible relation to superconductivity.

A novel hierarchy of the one-dimensional SU(N) electron models with 1/${\mathit{r}}^2$ interaction is proposed and solved by the asymptotic Bethe ansatz both for the continuum and lattice cases. The construction of the hierarchy is closely related to that for the fractional quantum Hall effect (FQHE) of the filling factor ${\nu }_{\mathit{c}}$=1/[${\mathit{p}}_1$-1/(${\mathit{p}}_2$-...-1/${\mathit{p}}_{\mathit{N}}$)...]. Under the chiral constraint the model describes the essential properties of the edge states for the FQHE with the above filling fraction. Furthermore the matrix deduced from the excitation spectrum characterizes the topological order of the FQHE state.

We investigate equilibrium electron currents and magnetization in an ideal two-dimensional disk of radius R placed in a strong magnetic field H. The most striking results emerge when the conditions for the existence of edge and bulk states are met, namely, R≫${\mathit{a}}_{\mathit{H}}$=(ħc/eH${)}^{1/2}$. When the Fermi energy is locked on a Landau level, the current as a function of electron density is quantized in units of (e/h)ħ${\mathrm{\omega }}_{\mathit{c}}$/2, where ${\mathrm{\omega }}_{\mathit{c}}$ is the cyclotron frequency. We argue that this effect survives against weak disorder. It is also shown that the persistent current has an approximately periodic dependence on 1/H.

The copper and oxygen isotope effects were investigated in ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_4$ for x=0.15 and x=0.125. It is found that the partial isotope exponents ${\mathrm{\alpha }}_{\mathrm{Cu}}$ and ${\mathrm{\alpha }}_{\mathrm{O}}$ are close to each other. For x=0.15 we find ${\mathrm{\alpha }}_{\mathrm{Cu}}$=0.15 and ${\mathrm{\alpha }}_{\mathrm{O}}$=0.11, while for x=0.125 anomalously large isotope exponents of ${\mathrm{\alpha }}_{\mathrm{Cu}}$=0.93 and ${\mathrm{\alpha }}_{\mathrm{O}}$=0.91 are found. The results show that large parts of the phonon spectrum influence the superconducting transition temperature.

We show that, in the fast collision approximation, the scattering operator for resonant x-ray scattering can be expressed in terms of simple spin-orbital moment operators ${\mathit{M}}^{\left(\mathit{k}\right)}$(l,s) of the valence shell involved in the resonance. This theory is applicable to the analysis of a broad range of resonant x-ray elestic and inelastic scattering and absorption experiments involving rare earth, actinide, and transition elements.

Characteristic variations in the total electron yield γ as a function of crystal azimuthal orientation are reported for slow ${\mathrm{N}}^{2+}$, ${\mathrm{N}}^{5+}$, and ${\mathrm{N}}^{6+}$ ions incident on a AU(011) single crystal. These variations allow the direct separation of kinetic and potential electron emission, and allow, for the first time, an analysis of the neutralization dynamics of multicharged ions interacting with a metal surface, above the kinetic emission threshold. Electron emission resulting from below-surface Auger transitions is shown to be the dominant potential emission mechanism.

Measurement of the phase velocities of guided modes in optical waveguides yields information about the optical parameters of the waveguide and the medium surrounding it. Application of this technique to a planar waveguide upon which proteins are allowed to adsorb from solution has yielded the first experimental data accurate enough to be able to test analytical expressions for the kinetics of random sequential deposition in two dimensions. The equation of Schaaf and Talbot for intermediate coverages is found to describe the measured kinetics with good accuracy. The rate of deposition should scale linearly with bulk protein concentration, but this was found to be the case only at very low values (≳/20 μg/${\mathrm{cm}}^3$); at higher concentrations a very marked deviation occurs. A concomitant deviation occurs at the jamming limit coverage, which attains about 76% at a concentration of 400 μg/${\mathrm{cm}}^3$.

The path integral for the propagator is expanded into a perturbation series, which can be exactly summed in the case of δ-function perturbations giving a closed expression for the (energy-dependent) Green function. Making the strength of the δ-function perturbation infinite repulsive produces a totally reflecting boundary, hence giving a path integral solution in half spaces in terms of the corresponding Green function. The example of the Wood-Saxon potential serves by an appropriate limiting procedure to obtain the Green function for the step potential and the finite potential well in the half space, respectively.

We study roughening interfaces that become self-organized critical by a rule similar to that of invasion percolation. We demonstrate that there is a fundamental difference between transient and critical dynamical exponents. The exponents break the Galilean invariance and temporal multiscaling is observed. We show that the activity along the interface exhibits nontrivial power law correlations in both space and time even though only quenched Gaussian noise is applied. The results are compared with simulations where spatial power law correlated noise is used as input.