We demonstrate that the attractive interaction measured between like-charged colloidal spheres near a wall can be accounted for by a nonequilibrium hydrodynamic effect. We present both analytical results and Brownian dynamics simulations which quantitatively capture the one-wall experiments of Larsen and Grier [Nature (London) 385, 230 (1997)], using a single unmeasured parameter.

We have studied experimentally the rheological behavior of concentrated suspensions of soft deformable microgels below the yield point. We have found history-dependent effects which are interpreted in terms of aging and rejuvenation phenomena, analogous to those existing in glassy systems. The stress amplitude controls the long-time memory and determines the slow evolution of the suspensions.

Cosmological data suggest that we live in an interesting period in the history of the universe when ${\rho }_{\Lambda }\sim {\rho }_M\sim {\rho }_R$. The occurrence of any epoch with such a “triple coincidence” is puzzling, while the question of why we happen to live during this special epoch is the “Why now?” problem. We introduce a framework which makes the triple coincidence inevitable; furthermore, the “Why now?” problem is transformed and greatly ameliorated. The framework assumes that the only relevant mass scales are the electroweak scale $M_{\mathrm{EW}}$, and the Planck scale $M_{\mathrm{Pl}}$ and requires ${\rho }_{\Lambda }^{1/4}\sim M_{\mathrm{EW}}^2/M_{\mathrm{Pl}}$ parametrically. Assuming that the true vacuum energy vanishes, we present a simple model, where a false vacuum energy yields a cosmological constant of this form.

We have observed the spontaneous evolution of a dense sample of Rydberg atoms into an ultracold plasma, in spite of the fact that each of the atoms may initially be bound by up to $100{\mathrm{cm}}^{-1\mathrm{}}$. When the atoms are initially bound by $70{\mathrm{cm}}^{-1\mathrm{}}$, this evolution occurs when most of the atoms are translationally cold, $<1\mathrm{mK}$, but a small fraction, $\sim 1\%$, is at room temperature. Ionizing collisions between hot and cold Rydberg atoms and blackbody photoionization produce an essentially stationary cloud of cold ions, which traps electrons produced later. The trapped electrons rapidly collisionally ionize the remaining cold Rydberg atoms to form a cold plasma.

We show that the crystal growth rate of a very long-chain $n$-alkane $\mathrm{C}{}_{198}\mathrm{H}{}_{398}$ from solution can decrease with increasing supersaturation and follow strongly negative order kinetics. The experimental behavior can be well represented by a theoretical model which allows the molecule to attach and detach as either extended or folded in two. The obstruction of extended-chain growth by unstable folded depositions increases disproportionately with increasing concentration. As a consequence of this abnormal kinetics, a “dilution wave” can propagate and trigger a folded-to-extended-chain transformation on its way.

We present a scheme for creating quantum entangled atomic states through the coherent spin-exchange collision of a spinor Bose-Einstein condensate. The state generated possesses macroscopic Einstein-Podolsky-Rosen correlation and the fluctuation in one of its quasispin components vanishes. We show that an elongated condensate with large aspect ratio is most suitable for creating such a state.

We propose and analyze a scheme for generating entangled atomic beams out of a Bose-Einstein condensate using spin-exchanging collisions. In particular, we show how to create both atomic squeezed states and entangled states of pairs of atoms.

We describe a simple experimental technique which allows us to store a small and deterministic number of neutral atoms in an optical dipole trap. The desired atom number is prepared in a magneto-optical trap overlapped with a single focused Nd:YAG laser beam. Dipole trap loading efficiency of $100\%$ and storage times of about one minute have been achieved. We have also prepared atoms in a certain hyperfine state and demonstrated the feasibility of a state-selective detection via resonance fluorescence at the level of a few neutral atoms. A spin relaxation time of the polarized sample of $4.2\pm 0.7\mathrm{s}$ has been measured. Possible applications are briefly discussed.

Exploiting the energetic interaction of intense femtosecond laser pulses with deuterium clusters, it is possible to create conditions in which nuclear fusion results from explosions of these clusters. We have conducted high-resolution neutron time-of-flight spectroscopy on these plasmas and show that they yield fast bursts of nearly monochromatic fusion neutrons with temporal duration as short as a few hundred picoseconds. Such a short, nearly pointlike source now opens up the unique possibility of using these bright neutron pulses, either as a pump or a probe, to conduct ultrafast studies with neutrons.

We have measured the spectrum of velocity fluctuations in a granular system confined to a vertical plane and driven into a homogeneous, steady state by strong vertical vibration. The distribution of horizontal velocities is not Maxwell-Boltzmann and is given by $P\left(v\right)=C\exp [-\beta (|v|/\sigma {)}^{\alpha }]$ where $\alpha =1.55\mathrm{}\pm 0.1$ at all frequencies and amplitudes investigated, and also for varying boundary conditions. The deviation from Maxwell-Boltzmann statistics occurs in the absence of spatial clustering and does not result from an inhomogeneous average over regions of varying local density. Surprisingly, $P\left(v\right)$ has the same shape over a wide range of densities.

Experimental observations of time-delay-induced amplitude death in two coupled nonlinear electronic circuits that are individually capable of exhibiting limit-cycle oscillations are described. The existence of multiply connected death islands in the parameter space of coupling strength and time delay for coupled identical oscillators is established. The existence of such regions was predicted earlier on theoretical grounds [Phys. Rev. Lett. 80, 5109 (1998); Physica (Amsterdam) 129D, 15 (1999)]. The experiments also reveal the occurrence of multiple frequency states, frequency suppression of oscillations with increased time delay, and the onset of both in-phase and antiphase collective oscillations.

A quantitative study of the long-range interaction between single copper adatoms on Cu(111) mediated by the electrons in the two-dimensional surface-state band is presented. The interaction potential was determined by evaluating the distance distribution of two adatoms from a series of scanning tunneling microscopy images taken at temperatures of 9–21 K. The long-range interaction is oscillatory with a period of half the Fermi wavelength and decays for larger distances $d$ as $1/d^2$. Five potential minima were identified for separations of up to 70 Å. The interaction significantly changes the growth of Cu/Cu(111) at low temperatures.

We have demonstrated experimentally that polar molecules revolve around the inner electrode of a charged cylindrical capacitor in helical trajectories that result from a superposition of a translational motion along and an orbital motion around the cylinder axis. In this way molecular beams can be guided over any given distance. The results have been obtained for nozzle beams of NaCl, NaBr, and NaI seeded in Kr. The capacitor bent into a toroid may be used as a storage ring for polar molecules in high field seeking rotational states.

Scanning probe microscopy (SPM) can be expanded to volume imaging. As an example, the core of a dislocation within the three-dimensional (3D) spatial microdomain structure of poly(styrene-block-butadiene-block-styrene) was imaged with $\approx 10\mathrm{nm}$ resolution. The specimen was eroded step by step and its chemical composition in layers beneath the original surface was imaged with SPM. Similar to computed tomography, the 3D distribution of polystyrene and polybutadiene was reconstructed from a series of images. This approach might provide a simple means for real-space volume imaging with nanometer and even atomic resolution of various materials and physical properties.

The fact that the melting points of nanoparticles are always lower than those of the corresponding bulk material is a paradigm supported by extensive experimental data for a large number of systems and by numerous calculations. Here we demonstrate that tin cluster ions with 10–30 atoms remain solid at $\sim 50$ K above the melting point of bulk tin. This behavior is possibly related to the fact that the structure of the clusters is completely different from that of the bulk element.

A molecular beam consisting of small helium clusters is diffracted from a 100 nm period transmission grating. The relative dimer intensities have been measured out to the 7th order and are used to determine the reduction of the effective slit width resulting from the finite size of the dimer. From a theoretical analysis of the data which also takes into account the van der Waals interaction with the grating bars, the bond length (mean internuclear distance) and the binding energy are found to be $〈r〉=52\mathrm{}\pm 4Å$ and $|E_b|=1.1+0.3\mathrm{}/-0.2\mathrm{}$ mK.

Matter between contiguous crystallites is assimilated to a thin elastic plate immersed in a different elastic medium. It is shown that a shear stress exceeding a critical value should corrugate the boundary and induce periodic normal stress fields in the two adjacent crystal surfaces, which cause motion of vacancies in closed loops between the two crystals. The consequent cyclic transport of atoms in the opposite sense determines crystal sliding at a temperature dependent relative speed. Most of the phenomenology of superplastic allows follows in a quantitative manner.

We have succeeded in observing nuclear excitation by electron transition (NEET) in ${}^{197}\mathrm{Au}$ by a new method. Monochromatic x-rays of synchrotron radiation were used to ionize the $K$ shell of gold atoms in a target foil. The internal-conversion electrons emitted from excited nuclei were detected with a silicon avalanche photodiode. At a photon energy of 80.989 keV, the NEET probability in ${}^{197}\mathrm{Au}$ was determined to be $(5.0\pm 0.6)\times {10}^{-8\mathrm{}}$ from a comparison of the event number per photon between NEET and the nuclear resonance at 77.351 keV.

Resonant formation of $d\mu t$ molecules in collisions of muonic tritium ( $\mu t$) on ${\mathrm{D}}_2$ was investigated using a beam of $\mu t$ atoms, demonstrating a new direct approach in muon catalyzed fusion studies. Strong epithermal resonances in $d\mu t$ formation were directly revealed for the first time. From the time-of-flight analysis of $2036\pm 116$ $\mathrm{dt}$ fusion events, a formation rate consistent with $0.73\pm (0.16{)}_{\mathrm{meas}}\pm (0.09{)}_{\mathrm{model}}$ times the theoretical prediction was obtained. For the largest peak at a resonance energy of $0.423\pm 0.037\mathrm{eV}$, this corresponds to a rate of $(7.1\pm 1.8)\times {10}^9{\mathrm{s}}^{-1\mathrm{}}$, more than an order of magnitude larger than those at low energies.

In situ high-temperature, high resolution transmission electron microscopy (HRTEM) was performed on an Al-Cu-Co decagonal quasicrystal, to investigate thermal fluctuation of phasons. A tiling pattern constructed from the HRTEM image was analyzed in the framework of the strip-projection method. Transitions between two local tile arrangements were observed at high temperature for the first time, and were shown to correspond to a thermal phason fluctuation.