We calculate the charge response to an electromagnetic field for a homogeneous system of nucleons and pions in the functional framework. This requires dealing with the pion propagation in the medium within the random-phase-approximation scheme. A quenching of the response is obtained in line with the experimental findings. Remarkably, the quenching takes place mainly in the isoscalar channel.

This Letter reports the first measurements of the angular distribution of Auger electrons emitted from the decay of the (1s2s2${\mathit{p}}^2$${)}^3$D ${\mathrm{O}}^{4+\mathrm{*}\mathrm{*}}$ doubly excited state formed predominantly through resonant transfer and excitation (RTE) in collisions of 13-MeV ${\mathrm{O}}^{5+}$ projectiles with He. The (1s2s2${\mathit{p}}^2$${)}^3$D angular distribution is strongly peaked along the beam direction, in agreement with recent calculations of the RTE angle-dependent impulse approximation. Furthermore, interference effects between the RTE and the elastic target direct-ionization channels are observed.

A microcavity technique is adopted to investigate, we believe for the first time, the process of transverse interatom quantum correlations taking place after photon emission, according to the plane-wave QED photon-delocalization model. We find that the QED model is indeed verified, but that it is generally limited by the nonideal cavity properties. The concept introduced here of ‘‘transverse quantum-correlation length’’ is of fundamental relevance to all kinds of Casimir-type vacuum-confinement processes, including ‘‘anomalous’’ QED effects in spontaneous emission. It also sets a fundamental limitation on the performance of the ‘‘thresholdless laser,’’ a device of actual scientific and technological interest.

We use beams of polarized electrons and polarized hydrogen atoms to measure the ionization-rate asymmetry, ${\mathrm{\Delta }}_{\mathit{I}}$=[R(↑↓)-R(↑↑)]/[R(↑↓)+R(↑↑)], in the near-threshold region, where R(↑↓) and R(↑↑) are the ionization rates when the electron spin is antiparallel and parallel, respectively, to the atomic spins. Within 1.7 eV above threshold, our results reveal the presence of structure, which heretofore has not been predicted by any conventional theoretical calculation.

61 vibronic states of CaF in the region 41 930–45 905 ${\mathrm{cm}}^{\mathrm{-}1}$ are observed by optical-optical double resonance, rovibronically assigned, and shown to belong to 37 Rydberg electronic states. These states are organized into six core-penetrating (l≤2), mixed-l Rydberg series, from which we obtain an improved value of the CaF ionization potential, 47 005±20 ${\mathrm{cm}}^{\mathrm{-}1}$. All previously observed low Rydberg and valence states of CaF fit smoothly into these six Rydberg series, which form the complete set of l≤2 series. Using this information, absolute quantum defects have been determined and the series are assigned nominally (i.e., dominant l character) as d (Δ, Π, and Σ), p (Π and Σ), and s (Σ).

We have used a laser-induced resonance Raman transition between the ground-state hyperfine sublevels in a sodium atomic beam to excite individual dressed states of the microwave-spin hyperfine transition. In addition, we have used the microwave interaction to excite the Raman trapped state. Extension of this technique to mm waves or to the far infrared may lead to applications such as mm-wave-beam steering and holographic image conversion.

The temporal instabilities of a linear array of vortices are studied experimentally; a short-wavelength instability is observed. The results are compared to a one-dimensional model of coupled nonlinear oscillators, leading to excellent agreement.

A one-dimensional theory of dynamical hysteresis in periodically switched bistable systems is formulated. The predictions of the theory are tested and verified by experiments on a bistable semiconductor laser. We find that the increase of the area of the hysteresis loop scales as the two-thirds power of the switching frequency. From this, we deduce a law for the increase in input power necessary to maintain repetitive switching of the bistable system as the driving frequency is increased.

Inhibition of the radiative decay of dye molecules embedded in an ordered aqueous suspension of polystyrene spheres has been measured using picosecond pump-probe techniques. The inhibition is interpreted in terms of excluded vacuum modes and compared with results based on the Wigner-Weisskopf formalism and a three-dimensional scattering model for the fcc colloidal structures.

Trapping of femtosecond optical solitons has been observed for the first time in an erbium-doped fiber amplifier operating at 1.55 μm. The pulse width of the trapped soliton is adiabatically narrowed by the moderate optical gain. By further increasing the gain, the trap is broken and the carrier wavelength of the soliton starts to move toward longer wavelengths by the soliton self-frequency shift.

We use the pressure generated by a small-amplitude oscillatory flow to probe the dynamics of moving contact lines. By measuring the Fourier amplitude at harmonics of the applied frequency as a function of the steady-state velocity, we are able to determine the velocity dependence of the excess dissipation caused by the moving contact line. We find that the pressure drop associated with this dissipation scales as a power of the contact-line velocity V as ${\mathit{P}}_{\mathrm{cap}}$∝${\mathit{V}}^{\mathit{x}}$, with x=0.40±0.05. We discuss these results in terms of recent theoretical models.

The nonlinear properties of ion acoustic waves produced by a strong ponderomotive force have been analyzed in the regime where the amplitude of ponderomotive potential is comparable to the plasma thermal energy density. Analytical solutions of the nonlinear fluid equations predict formation of the periodic sequence of shock waves. These solutions compare well with the results of numerical simulations of the full set of the hydrodynamical and Maxwell equations, which also reveal the oscillatory structure of the shock. These results are applied to the analysis of stimulated Brillouin scattering.

A model low-molecular-weight polymer mixture was studied as a function of temperature near the critical point by small-angle neutron scattering (SANS) and dynamic light scattering (DLS). SANS measurements reveal a crossover in the static susceptibility from mean-field to non-mean-field behavior at ${\mathit{T}}_{\mathit{x}}$≃${\mathit{T}}_{\mathit{c}}$+30 °C, in quantitative agreement with the Ginzburg criterion. This crossover behavior is also reflected in the DLS experiments, which reveal mode-coupled critical dynamics far into the mean-field regime.

The wetting behavior of two-phase systems confined inside cylindrical pores is studied theoretically. The confined geometry gives rise to wetting configurations, or microstructures, which have no analog in the well-studied planar case. Many features observed in experiments on binary liquid mixtures in porous media, previously interpreted in terms of random fields, are shown to be consistent with wetting in a confined geometry with no randomness.

We present experimental evidence that a critical point, also reported by Hemley and Mao, exists for the hydrogen-A phase line at a pressure of 173(4) GPa and 151(15) K. We give an interpretation of this critical point in terms of its relationship to a low-pressure disordered insulating phase and a possible metallic phase at high pressure. We interpret the temeprature dependence of the vibron frequency of the H-A phase as a measure of one of the two order parameters characterizing this phase.

The radial distribution function obtained by neutron diffraction on amorphous carbon films is compared to recent theoretical models. The first-neighbor peak is found to be quite broad for an amorphous semiconductor, in qualitative agreement with the predictions of molecular dynamics. However, the detailed shape of the first two peaks, including contributions in the minimum region, differs from all current models. Although the areas of the first two peaks indicate predominant threefold bonding, no evidence for a distinct peak associated with graphitelike, intrahexagon, third neighbors is observed. This distinguishes amorphous carbon from local two-dimensionally ordered graphitelike materials.

We present a new defect model for the reconstructed Si(001) surface. Ab initio molecular-dynamics simulations at finite temperature show the existence of interstitial dimers which are recessed from the surface. These dimers and adjacent on-surface dimers are both symmetric. The possibility that missing dimer vacancies observed by scanning tunneling microscopy contain these new surface defects is pointed out.

Scanning-tunneling-microscopy images of vicinal Si(001) with an equilibrium distribution of steps and kinks have been analyzed to determine the distribution of kink separations and kink lengths. From these distributions, step and kink energies have been directly determined.

Tunneling images of the ideal Si(111):H-1×1 surface exhibit features and electronic structure consistent with a simple termination of the surface dangling bonds by atomic hydrogen. Bombardment of the surface with low-energy (2–10 eV) electrons desorbs the hydrogen, converting the 1×1 surface phase to the 2×1 π-bonded chain. The efficiency of this process versus electron kinetic energy indicates that the desorption is mediated by promoting electrons from the σ to the ${\mathrm{\sigma }}^{\mathrm{*}}$ band. The resultant increase in surface free energy drives a spontaneous phase transition to the 2×1. Individual 2×1 regions as small as ten surface sites have been created in this fashion.

The cross-relaxation time ${\mathrm{\tau }}_{\mathit{x}}$ between the Zeeman temperatures of the ${}_{}{}^{107}{}_{}{}^{}\mathrm{Ag}$ and ${}_{}{}^{109}{}_{}{}^{}\mathrm{Ag}$ spin species in silver metal has been measured over five decades at low nanokelvin temperatures as a function of the external magnetic field B. Besides increasing with B, ${\mathrm{\tau }}_{\mathit{x}}$ decreases with spin polarization. From the data, the strength of the Ruderman-Kittel interaction between the nuclei is determined. These experiments demonstrate that thermal equilibrium is not reached via mutual flips of unlike spins, but in much slower processes involving single spin flips, caused by the dipolar interaction.