The potential-energy-surface concept of the generalized collective model is given a shell-model interpretation. For deformation less than the equilibrium value, $\beta <{\beta }_0$, the shape of the potential is related to intrashell dynamics while the sharp rise for $\beta >{\beta }_0$ is shown to be an intershell phenomenon that depends on competition between major shell excitation energies and the binding energy of the residual interaction. The exclusion principle plays an essential role in the argument. Results for ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ illustrate the necessity of an open-shell picture.

In the reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}(e, e^{\prime }d){}_{}{}^{10}{}_{}{}^{}\mathrm{B}$ the lowest-lying $T=1\mathrm{}$ state in ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$ is found to be as strongly excited as the $T=0\mathrm{}$ ground state of ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$, although the transition to the $T=1\mathrm{}$ state is isospin forbidden for direct deuteron knockout. A mechanism integration of a $p-n$ pair in a relative $T=1\mathrm{}$ state into a deuteron is proposed to explain this result. This new proposed mechanism is consistent with both the observed purely transverse character of the transition and the momentum-transfer dependence of the cross section.

A simple experimental arrangement demonstrates back-action evasion of noise in a quantum measurement of an optical field. Correlation between the photocurrents from a measured signal beam and a measurement readout beam is 0.6 dB below the shot-noise limit. The measurement is accomplished by use of a single-pass parametric down-conversion process.

Weak new features in the absorption spectrum of solid hydrogen were observed by high-resolution infrared spectroscopy, and assigned as transitions with total change in angular momentum of $\Delta J=6\mathrm{}$. The tetrahexacontapole (64-pole)-induced rotational transition $W_0\mathrm{}\left(0\right)\mathrm{}$ was studied with a difference frequency laser spectrometer and found to be very narrow, with a linewidth of 0.003 ${\mathrm{cm}}^{-1\mathrm{}}$ HWHM in 99.8% parahydrogen. Frequencies, linewidths, and integrated absorption strengths were measured for several pure rotational and rotation-vibration transitions from 1800 to 7000 ${\mathrm{cm}}^{-1\mathrm{}}$, and the tetrahexacontapole moment was determined.

Angle-resolved photoion spectroscopy has been applied for the first time to molecular fragments emitted after Auger decay following photoexcitation of the ${\mathrm{N}}_2$ $K$ shell in the gas phase. Considerable angular distribution asymmetries of photofragments have been observed not only at the ${\pi }^{*}$ discrete resonance but also across the ${\sigma }^{*}$ shape resonance.

We have investigated the distribution of avalanches which occur when the slope of a sandpile exceeds the metastable slope given by the angle of repose. In contradiction to recent models by Bak, Tang, and Wiesenfeld for the dynamics of granular systems, we do not observe power-law distributions. We also find that the slope of a sandpile decays as $log\mathrm{}\left(t\right)\mathrm{}$ when vibrations are introduced. We propose a simple model for this effect.

When a bead heap is submitted to low-frequency ($\frac{\omega }{2\pi }=10-1000\mathrm{}$ Hz) vertical vibrations at a large enough amplitude $a$, its horizontal free surface becomes unstable and a stationary state is reached. This one is characterized firstly by a free surface which is inclined within an angle $\theta$ to the horizontal, secondly by a continuous flow of particles rolling down the free surface, and thirdly by a convective transport inside the material which refills the top of the heap with new beads. We demonstrate that a control parameter is the vibration acceleration $\gamma =a{\omega }^2$.

We study the propagation of light through a semi-infinite medium with transverse disorder (that is, disorder in two directions only). We show that such a system exhibits strong two-dimensional localization by demonstrating that on propagation a beam expands until the transverse localization length is reached.

We investigate the conditions of the vanishing cosmological constant and the presence of gravity and vector gauge fields in a $D$-dimensional non-Abelian Kaluza-Klein theory based on a dimensionally continued $2N$-dimensional Euler-form action. It is shown that these conditions can be satisfied only for $D=2N+3\mathrm{}$.

For those electrons whose Larmor radius is less then the Debye length, by averaging over binary collisions with ions and using a guiding-center approximation, a simple collision operator has been obtained which reproduces accurately the moments obtained from the existing more complex operators.

Small-angle neutron-scattering studies have been carried out on solutions of the conjugated polymer poly-3-butylthiophene. At room temperature positive interchain interactions occur even at concentration as low as 0.1 g/1. At $T=65\mathrm{}°$C the statistical length $b=55\mathrm{}$ Å of isolated neutral chains has been measured. Upon doping of the polymer chains, a large conformational transition occurs. In the dilute regime, the charged polymer chains are in a rodlike state. Doped-conjugated-polymer solutions do not behave like common polyelectrolytes.

The resolution of individual atoms in scanning-tunneling-microscopy (STM) images of Al(111) is demonstrated. From results of gap-width and energy-dependent measurements the corrugation observed in the STM images cannot reflect the electronic structure of the Al surface near $E_F$, as usually assumed for such images, but must be due to tip-surface interactions. On the basis of an investigation of the process of tip preparation, an elastic deformation of the frontmost end of the tip mediated by adhesive tip-surface interactions is proposed as the predominant factor for atomic-resolution STM imaging of such metal surfaces.

We present energy-resolved He-scattering data on the thermal behavior of the clean Cu(110) surface. At variance with a recent x-ray study we have observed no evidence for a proliferation of steps, i.e., for thermal roughening, up to $T=900\mathrm{}$ K. The analysis points to an anomalous increase of the mean-square displacement of the surface atoms at temperatures $T\ge 550$ K which might be ascribed to an enhanced surface anharmonicity.

The acoustic-phonon velocities of a single crystal of BaTi${\mathrm{O}}_3$ have been measured as a function of pressure up to 8 GPa, including the transition pressure $p_c=2.35\mathrm{}$ GPa, by means of Brillouin scattering technique. Only one elastic eigenmode shows an anomalous decrease on approaching $p_c$ and the elastic anisotropy increases. The elastic anomaly of cubic BaTi${\mathrm{O}}_3$ is interpreted well by introducing a new tensorial order parameter which describes the anisotropy. The cubic-to-tetragonal phase transition in BaTi${\mathrm{O}}_3$ is shown to be triggered by the fluctuation of the anisotropy, not the polarization itself.

We present photoemission spectra from the $3p$ level of Cu(100) obtained in coincidence with the $M_3\mathrm{VV}$ Auger line. The $3p$ level is narrowed from its 2.2-eV core-lifetime-broadened width to 1.0 eV, representing the intrinsic width of the ${}_{}{}^1{}_{}{}^{}G$ Auger final state. The core line changes its energy within the 2.2-eV envelope as the Auger coincidence energy is changed, conserving the sum of Auger-electron and photoelectron kinetic energies.

A laser beam irradiating a semiconductor in its transparency region induces a splitting of the exciton line through the dependence of the optical Stark effect on the different transition matrix elements. The splitting is observed in bulk and multiple-quantum-well GaAs, by femtosecond time-resolved spectroscopy for various polarization configurations. Experimental results are in good agreement with theory.

The mixing interaction in the Anderson model of local moments in metals $V_{\mathrm{k}\sigma ,m}$ depends on the orbital state $m$ of the local electron. We have taken into account this anisotropy and find that, quite aside from other mechanisms, e.g., crystalline electric fields, the mixing alone can account for the magnitudes of the splitting and linewidths of the local $f$ states observed in Kondo-type systems, e.g., heavy-fermion and mixed-valence compounds.

From a sample of 332000 $B\overline{B}$ pairs produced in $e^{+}{e}^{-}$ annihilations at the $\Upsilon \mathrm{}\left(4S\right)\mathrm{}$ resonance we derive upper limits for the branching fractions for the decays $B^{-}\to p\overline{p}{\pi }^{-}$ and ${\overline{B}}^0\to p\overline{p}{\pi }^{+}{\pi }^{-}$ in several final-state momentum configurations. The results do not confirm recently reported observations of charmless $B$ decays.

Starting directly from the microscopic Hamiltonian, we derive a field-theory model for the fractional quantum Hall effect. By considering an approximate coarse-grained version of the same model, we construct a Landau-Ginzburg theory similar to that of Girvin. The partition function of the model exhibits cusps as a function of density and the Hall conductance is quantized at filling factors $\nu ={\mathrm{}(2k-1)\mathrm{}}^{-1\mathrm{}}$ with $k$ an arbitrary integer. At these fractions the ground state is incompressible, and the quasiparticles and quasiholes have fractional charge and obey fractional statistics. Finally, we show that the collective density fluctuations are massive.

A new order parameter with a novel broken symmetry is proposed for the fractional quantum Hall effect, with the Laughlin state as the mean-field ground state. The classical Ginzburg-Landau theory of Girvin is derived microscopically from this starting point and exhibits all the phenomenology of the fractional quantum Hall effect.