Direct experimental evidence is obtained for the occurrence of fusion in collisions between two ${\mathrm{C}}_{60}$ molecules at collision energies of 200 to 500 eV in the center-of-mass frame of reference. The ${\mathrm{C}}_{120}^{+}$ formed at 200 and 250 eV collision energy has a lifetime of more than 70 μs with high internal energy. Results are in good qualitative agreement with recent molecular dynamics simulations combined with density functional theory.

We demonstrate experimentally that a type-II pulsed optical parametric amplifier can duplicate (or, clone) a signal in the quadrature it amplifies. Although this device is an amplifier with large gain, it meets the quantitative criteria for quantum nondemolition measurements and, thus, operates in the nonclassical regime. It can be used as a noiseless amplifying optical tap which, at the same time, can overcome the noise introduced downstream by propagation and detection losses.

We have realized a system which is able to read out information encoded on the amplitude of a laser beam without degrading the signal-to-noise ratio of the carrier. This has been implemented using the two-photon cross-phase-modulation effect of a three-level system in a sodium atomic beam located in a doubly resonant optical cavity. We have achieved an improvement by a factor of 1.35 of the overall information transer compared to any classical optical tap, where a perfect quantum duplicator would reach the ideal value of 2.

We observe that high-stretch tails of finite-time Lyapunov exponent distributions associated with interfaces evolving under a class of nonturbulent chaotic flows can range from essentially Gaussian tails to nearly exponential tails, and show that the non-Gaussian deviations can have a significant effect on interfacial evolution. This observation motivates new insight into stretch processes under chaotic flows.

On-off intermittency is an aperiodic switching between static, or laminar, behavior and chaotic bursts of oscillation. It can be generated by systems having an unstable invariant (or quasi-invariant) manifold, within which is found a suitable attractor. We clarify the roles of such attractors in producing intermittency, provide examples, and relate them to previous work.

Starting from an assumption of universality in turbulence and building upon the work in Y. G. Sinai and V. Yakhot, Phys. Rev. Lett. 63, 1962 (1989), we construct a closed-form expression for the probability density function of temperature fluctuations. This result is found to be in good correspondence to experimental data obtained at Chicago and Yale. By extending this method, we obtain a similar expression for the probability density function of temperature differences between two times. Again the result is checked to hold very well, except for very short time separations.

We present the first direct measurements of the local velocity of a sheared polymer melt within the first 100 nm from the solid-liquid interface. For high enough shear rates we observe a sharp transition between weak and strong slip (i.e., a nonzero boundary fluid velocity) in the case of weak polymer-surface interactions [polydimethylsiloxane (PDMS) on silanated silica surfaces]. For strong polymer surface interactions the slip is strongly reduced. These results are compared to a theoretical model recently proposed by Brochard and de Gennes.

A multimode nonlinear particle simulation code is used to find the saturated efficiency for power transfer into modes of a cylindrical waveguide carrying a spatiotemporally modulated gyrating electron beam. For A ${\mathrm{TE}}_{51}$-mode fifth harmonic 94-GHz harmonic converter using a 150-kV, 6.7-A cold beam, this code predicts a conversion efficiency of 57% when a linearly tapered guide magnetic field is used, and 70% when a nonlinear taper is used. Efficiency in the linear taper case is shown to be insensitive to beam axial velocity spread, while both cases show negligible power flow into competing modes.

Observation of the ion resonance instability in a pure electron plasma trap contaminated with a small population of ions is reported. The ion population is maintained by ionization of the background gas. The instability causes the plasma to move steadily off-center while undergoing l=1 diocotron oscillations. The observed scaling of the maximum growth point is presented, and the growth rate and its dependence on ion density are discussed. Several aspects of the observed behavior are not in agreement with previous theory but derive from the transitory nature of the ion population.

We present an experimental method for stabilization of stored self-colliding ions at density 30 times greater than the space-charge limit (SCL) density. Previously, instabilities have prevented stable storage of ions in excess of the SCD density. Electrons were made to oscillate through the ions; the electron frequency was a critical stabilization parameter and varied by an open-loop (nonfeedback) application of an external field. The observations are compatible with a nonlinear stabilization effect not hitherto used in particle systems.

Chaos generated by the interaction between charged particles and electrostatic plasma waves has been observed in a linear magnetized plasma. The macroscopic wave properties, the kinetic ion dielectric response, and the microscopic heating mechanisms have been investigated via optical diagnostic techniques based on laser-induced fluorescence. Observations of test-particle dynamical evolution indicate an exponential separation of initially close ion trajectories.

Surface segregation in thin films of symmetric polyolefin diblock copolymers containing a lamellar microstructure, cast on a variety of substrates, has been investigated. In all cases, the conformationally smaller block preferentially segregated to both the solid and air interfaces even though the surface energy of the solid substrate always exceeded that of the block copolymer. These results indicate an entropically driven surface segregation effect that we attribute to block conformational asymmetry.

By a combination of high-resolution imaging and grazing-incidence x-ray diffraction at the GaAs(001)-CdTe(111) heterostructure we solve the atomic structure at the interface. We measure a √2 (2×9) reconstructed unit cell and show that only three monolayers are involved in the interface relaxation. We deduce the first nearest neighbors of each atomic species at the interface and describe how they differ from the initial adsorbed layer on a bare GaAs(001) surface. This structure is compatible with two electrons per bond at any atom.

The structure of the √3 × √3 R30° overlayer formed by CO molecules adsorbed on a Ru(0001) was analyzed by low energy electron diffraction. Anisotropic atomic motions under the influence of thermal excitation were taken into account by adopting the concept of split positions. Apart from considerable improvement in the structural refinement this technique provides information about dynamic processes. In particular, the molecular axis of the CO molecules was found to be tilted on the average by (12±3° at 150 K, which is attributed to excitation of the bending mode vibration (i.e., frustrated translation).

A new regime is obtained in semiconductor heterostructures with constituents of nearly identical band gaps. Previously, it has been shown that even extremely shallow quantum wells (SHQWs) exhibit excitonic and electroabsorption properties typical of a 2D system, but 3D transport features. We show that, surprisingly, even when carriers are two-dimensionally confined in SHQWs, the hole spin relaxation is extremely fast (∼400 fsec) as in the bulk (3D) limit and that a 2D-3D transition in the hole spin dynamics in GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As SHQWs takes place at x∼5%.

We consider the optical absorption and emission spectra of excitons in two-dimensional semiconductors disordered through interface fluctuations. These spectra show a universal behavior exemplified by the fact that the offset of the spectral peaks (the Stokes shift) is proportinal to their linewidths over a range of at least 2 orders of magnitude. We introduce a topographical theory of the exciton spectra which models such behavior in terms of statistical properties of a Gaussian random function. The coefficient of proportionality between the Stokes shift and the exciton absorption linewidth is found to be γ=2/ √6π ln2 =0.553 by analysis and 0.6 by experiment.

We observe nonequidistant oscillations in the correlation trace of the nonlinear signal in a four-wave mixing experiment when exciting the upper polariton branch between the ${\mathit{A}}_{\mathit{n}=1\mathrm{}}$ and the ${\mathit{A}}_{\mathit{n}=2\mathrm{}}$ excitons in CdSe. The quantum beats are described qualitatively and quantitatively taking into account propagation interference effects on the third-order nonlinear polarization, and the homogeneous dampings of the exciton polaritons are determined.

Experiments are described which show that, in charge-density-wave (CDW) conduction in ${\mathrm{NbSe}}_3$, phase slip occurs in regions extending for substantial distances from the current terminals. Contrary to the assumptions of previous discussions, most of the excess voltage associated with phase slip comes from the reduction of Frohlich current in these regions, and not from the voltage needed to nucleate CDW dislocation loops. An explanation is suggested, in terms of dislocation motion in the strain field due to terminals on the side of the specimen.

Using a variational quantum Monte Carlo method, we study the two-dimensional Wigner crystal induced by a strong magnetic field in the fractional quantum Hall effect regime. Effects of exchange, intra-Landau-level correlation, and inter-Landau-level mixing on the total energy and their dependence on the carrier mass and magnetic field strength are calculated. Our results support that the recently observed reentrant behavior to an insulating phase around ν=1/3 in p-doped GaAs/AlGaAs is a consequence of an increased stability of the Wigner crystal due to the effects of Landau-level mixing.

At finite magnetic field and fixed filling factor ν, as the particle density decreases, the fractional quantum Hall state will at some point give way to the Wigner solid. We calculate the ground-state energy of a Laughlin-like variational wave function at finite magnetic field and density by a quantum Monte Carlo method and compare the results with a calculation of the Wigner solid energy to get an estimate of the zero temperature finite density phase boundary.