We measured free exciton splitting and Faraday rotation of the diluted magnetic semiconductor ${\mathrm{Zn}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Cr}}_{\mathit{x}}$Se (x<0.005) and found valence band splitting which is reversed relative to the materials with Mn, Co, or Fe. This fact indicates a ferromagnetic p-d exchange, observed for the first time in II-VI diluted magnetic semiconductors.

At room temperature a large magnetoresistance, ΔR/R(H=0), of 60% has been observed in thin magnetic films of perovskitelike La-Ba-Mn-O. The films were grown epitaxially on ${\mathrm{SrTiO}}_3$ substrates by off-axis laser deposition. In the as-deposited state, the Curie temperature and the saturation magnetization were considerably lower compared to bulk samples, but were increased by a subsequent heat treatment. The samples show a drop in the resistivity at the magnetic transition, and the existence of magnetic polarons seems to dominate the electric transport in this region.

We report the first observation of a large (more than 10%) reflectance anisotropy on a Ag(110) single crystal. We reproduce the experimental data fairly well by use of a theoretical model, based on the quasistatic approximation, which takes into account both the actual geometry of the crystal surface and the interband and intraband transitions. This demonstrates that the main effect is the screened surface local-field effect on resonant dipolar oscillation localized near the surface.

Typically surface core-level shifts (SCLS) of clean surfaces are explained in the initial-state model, thus ignoring the screening of the photon-induced hole. We will show that this approach is not valid for the (001) surfaces of Si and Ge. Using ab initio density-functional theory we calculate the SCLS from differences of total energies of slabs containing excited atoms at different positions at the surface and in the bulk. Comparison with initial-state results reveals an enhanced screening at the surface, which is even remarkably different for the two atoms forming the surface dimer.

We present measurements of the thinning velocity of circular horizontal soap films made from dilute surfactant solutions (around the critical micellar concentration). We have solved numerically the hydrodynamic equations for the drainage process. After data fitting, we deduce the values of the elasticities of the surfactant monolayer that stabilizes the soap film. These elasticity values have been compared to elasticities obtained independently from the study of waves at the surface of the solution. The comparison reveals the importance of surface convection in the drainage process and demonstrates the important role of surface elasticity.

A semiclassical method is discussed for propagating wave packets that incorporates nonlinear classical dynamical information through the use of multiple reference trajectories. We apply the theory to obtain an analytic approximation for the autocorrelation function in the Coulomb potential which is extremely accurate in many circumstances in spite of the Coulomb singularity. All the detailed quantum behavior is reproduced including the long time revivals and the spectrum. The evolving phase space structure of the classical analog reveals how well a particular case will be approximated.

We use heavy element nucleosynthesis from supernovae to probe the mixing of ${\nu }_{\mathit{e}}$ with ${\nu }_{\mathrm{\tau }}$ (or ${\nu }_{\mathrm{\mu }}$) possessing cosmologically significant masses (1 to 100 eV). We conclude that the ${\nu }_{\mathrm{\tau }}$(${\nu }_{\mathrm{\mu }}$)-${\nu }_{\mathit{e}}$ vacuum mixing angle must satisfy ${\sin }^2$2θ<${10}^{\mathrm{-}5}$, in order to ensure that r-process heavy elements can be produced in neutrino-heated supernova ejecta. Mixing at a level exceeding this limit precludes r-process nucleosynthesis in this site.

We construct a lattice model of compact (2+1)-dimensional Maxwell-Chern-Simons theory, starting from its formulation in terms of gauge invariant quantities proposed by Deser and Jackiw. We thereby identify the topological excitations and their interactions. These consist of monopole-antimonopole pairs bounded by strings carrying both magnetic flux and electric charge. The electric charge renders the Dirac strings observable and endows them with a finite energy per unit length, which results in a linearly confining string tension. Additionally, the strings interact via an imaginary, topological term measuring the (self-)linking number of closed strings.

Using data from CLEO II at the Cornell Electron Storage Ring we provide a new measurement of the branching fraction for ${\mathit{D}}^0$→${\mathrm{\pi }}^{+}$${\mathrm{\pi }}^{\mathrm{-}}$, and we present the first measurements of ${\mathit{D}}^0$→${\mathrm{\pi }}^0$${\mathrm{\pi }}^0$ and of ${\mathit{D}}^{+}$→${\mathrm{\pi }}^{+}$${\mathrm{\pi }}^0$, which is due to an isospin changing ΔI=3/2 transition. From these data we extract the ratio of isospin amplitudes ‖${\mathit{A}}_2$/${\mathit{A}}_0$‖, and the cosine of the relative phase δ=${\mathrm{\delta }}_2$-${\mathrm{\delta }}_0$ between these amplitudes, for D→ππ decays. Unlike the situation in kaon decay where ${\mathit{A}}_2$ is strongly suppressed, we find ‖${\mathit{A}}_2$/${\mathit{A}}_0$‖=0.72±0.13±0.11 and cosδ=0.14±0.13±0.09.

We investigate πρ scattering in the pseudoscalar (π) and axial-vector (${\mathit{A}}_1$) channel. Our model based on s- as well as t-channel meson exchange can resolve apparent discrepancies occurring in the analysis of the axial-vector ${\mathit{A}}_1$ meson. Furthermore, it leads to an appreciable softening of the πNN form factor in agreement with information from other sources. This strong contribution in the pionic channel substantiates earlier claims that inclusion of correlated πρ exchange might allow the use of a soft πNN form factor in NN potential models and thus could resolve a long-standing puzzle.

Measurements have been made of Δ${\mathrm{\sigma }}_{\mathit{T}}$ for polarized neutrons incident on a polarized-proton target from 3.65 to 11.60 MeV. In the energy range near 10 MeV, Δ${\mathrm{\sigma }}_{\mathit{T}}$ is very sensitive to the nucleon-nucleon tensor interaction. Comparison of the data to potential-model predictions indicate that the tensor interaction is weak, resulting in values of the ${}_{}{}^3{}_{}{}^{}$${\mathit{S}}_1$${\mathrm{-}}^3$${\mathit{D}}_1$ mixing parameter ${\mathrm{\epsilon }}_1$ which are smaller than predicted by any nucleon-nucleon potential model. A smaller tensor force will bring the predictions of local potential models for the triton binding energy into closer agreement with the experimental value.

The disappearance of collective flow in nucleus-nucleus collisions occurs at an incident energy (${\mathit{E}}_{\mathrm{bal}}$) where the attractive scattering dominant at low energies balances the repulsive scattering dominant at high energies. We have performed the first systematic study of the entrance-channel mass dependence of the disappearance of flow and hence ${\mathit{E}}_{\mathrm{bal}}$. The new data presented for the C+C, Ne+Al, Ar+Sc, and Kr+Nb systems show that ${\mathit{E}}_{\mathrm{bal}}$ scales as ${\mathit{A}}^{\mathrm{-}1/3}$ where A is the mass of the combined system. Boltzmann-Uehling-Uehlenbeck model calculations show trends which are in qualitative agreement with these new results.

E3 matrix elements have been determined for transitions between states up to ${\mathit{I}}^{\mathrm{\pi }}$=${13}^{\mathrm{-}}$ in ${}_{}{}^{148}{}_{}{}^{}\mathrm{Nd}$, providing direct evidence for strong octupole collectivity in a rotational band. These values, as well as the corresponding E1 and E2 matrix elements, were obtained from Coulomb excitation data using ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ and ${}_{}{}^{92}{}_{}{}^{}\mathrm{Mo}$ ions, projectile excitation using a ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ target, and from recoil distance lifetime measurements. The results are consistent with collective model predictions for ${}_{}{}^{148}{}_{}{}^{}\mathrm{Nd}$ assuming intrinsic quadrupole and octupole moments of ${\mathit{Q}}_{20}$≊400 e ${\mathrm{fm}}^2$ and ${\mathit{Q}}_{30}$≊1500 e ${\mathrm{fm}}^3$. The E3 strength coupling the negative-parity states to the β band is found to be appreciable.

During strong-field multiphoton ionization, a wave packet is formed each time the laser field passes its maximum value. Within the first laser period after ionization there is a significant probability that the electron will return to the vicinity of the ion with very high kinetic energy. High-harmonic generation, multiphoton two-electron ejection, and very high energy above-threshold-ionization electrons are all conssequences of this electron-ion interaction. One important parameter which determines the strength of these effects is the rate at which the wave packet spreads in the direction perpendicular to the laser electric field; another is the polarization of the laser. It will be essential for experimentalists to be aware of these crucial parameters in future experiments.

We compare the cyclotron frequency of two single ions in a Penning trap to obtain their mass ratio with a relative uncertainty close to 1×${10}^{\mathrm{-}10}$. We have developed methods, based on a classical implementation of the separated oscillatory fields technique, that extend this precision to mass ratios far from unity (nondoublets). This allows direct determination of the atomic mass of any ion by comparison to a ${\mathrm{C}}^{+}$ ion. Using isotopically selected methane ions, we obtain the masses of H, D, and the neutron with up to 40 times improved precision over accepted values. We have checked our technique with known nondoublet ratios such as M[${\mathrm{N}}_2^{+}$]/M[${\mathrm{N}}^{+}$].

Two configurations involving high quantum efficiency photodetectors and light emitting diodes have been investigated. A light beam was detected with a photodetector and its photocurrent was used to measure the incoming beam. Simultaneously, the photocurrent was used, with and without amplification, to regenerate the absorbed beam. With these schemes photon number amplification, duplication, and information tapping without introducing any significant noise to the downstream propagating beam could be experimentally realized.

We describe an amplifying system using a photodiode and a light emitting diode, which is able to measure and to ‘‘recreate’’ the quantum statistics of the intensity of a light beam. This system acts therefore as a nonclassical ‘‘quantum optical repeater.’’ The overall information transfer is improved by a factor of 1.8 compared to a classical device, while the ideal quantum value would be 2, and the correlation between the signal and meter outputs is 1.2 dB below the shot-noise limit. We also demonstrate the use of this device for both detecting and recreating an input squeezed state.

We introduce models incorporating an adaptive self-regulatory feedback mechanism on an extended chaotic lattice. Numerical experiments show that our system gives rise to a host of novel spatiotemporal phenomena characterized by a rich variety of ‘‘phases’’ in parameter space. Moreover, interestingly, certain phases exhibit distinct scaling properties and 1/f noise.

A self-consistent many-body approach to quantum noise is presented. Many-photon polarization effects produce system-size scaling in quantum dissipative systems. The role of system-size quantum noise on the dynamics near the bifurcation point in an optical parametric oscillator is investigated, and nonlinear spectra are presented in the nonadiabatic limit.

Experimental results of the first efficient operation of a long pulse cyclotron autoresonance maser oscillator are presented. Output power of 1.9 MW for a beam energy of 450 keV and current of 80 A, corresponding to an efficiency of 5.2%, has been measured at 27.8 GHz in the ${\mathrm{TE}}_{11}$ mode of a Bragg resonator. The observed frequency of the cyclotron autoresonance maser emission corresponds to a Doppler unshifted frequency of 2.9 times the relativistic cyclotron frequency. A significant mode competition between the ${\mathrm{TE}}_{11}$ and a ${\mathrm{TM}}_{01}$ mode is present.