We show that a dilute two-species gas of Fermi-Dirac alkali-metal atoms in a periodic optical lattice may exhibit fractionalization of the particle number when the two components are coupled via a coherent electromagnetic field with a topologically nontrivial phase profile. This results in fractional eigenvalues of the spin operator with vanishing fluctuations. The fractional part can be accurately controlled by modifying the effective detuning of the electromagnetic field.

Nonionized media subject to strong fields can become locally ionized by penetration of finger-shaped streamers. We study negative streamers between planar electrodes in a simple deterministic continuum approximation. We observe that, for sufficiently large fields, the streamer tip can split. This happens close to the limit of “ideal conductivity.” Qualitatively, the tip splitting is due to a Laplacian instability quite like that in viscous fingering. For future quantitative analytical progress, our stability analysis of planar fronts identifies the screening length as a regularization mechanism.

We measured the strength of the $0_{\mathrm{gs}}^{+}\to 2_1^{+}$ excitations in the radioactive mirror nuclei ${}^{32}\mathrm{Ar}$ and ${}^{32}\mathrm{Si}$ using the techniques of intermediate-energy Coulomb excitation for ${}^{32}\mathrm{Ar}$ and inelastic proton scattering in inverse kinematics for ${}^{32}\mathrm{Si}$. The ${}^{32}\mathrm{Ar}$ measurement, taken together with previously existing Coulomb excitation data for ${}^{32}\mathrm{Si}$, yields the isoscalar and isovector multipole matrix elements for the $0_1^{+}\to 2_1^{+}$ transition between $T=2\mathrm{}$ states in the $A=32\mathrm{}$ system. The proton scattering measurement for ${}^{32}\mathrm{Si}$, when combined with the Coulomb excitation data for this nucleus, yields a ratio of neutron and proton matrix elements, $M_n{/M}_p$, for ${}^{32}\mathrm{Si}$.

We investigate electronic transport through two types of conjugated molecules. Mechanically controlled break junctions are used to couple thiol end groups of single molecules to two gold electrodes. Current-voltage characteristics ( $\mathrm{IV}$s) of the metal-molecule-metal system are observed. These $\mathrm{IV}$s reproduce the spatial symmetry of the molecules with respect to the direction of current flow. We hereby unambiguously detect an intrinsic property of the molecule and are able to distinguish the influence of both the molecule and the contact to the metal electrodes on the transport properties of the compound system.

On the basis of high pressure diamond-anvil compression studies for the precious metals Ru, Ir, and Os we report the surprising discovery that metallic osmium has a lower compressibility than covalently bonded diamond. We also find that Ir and Ru are as incompressible as Re. In addition, we have performed first principles calculations that confirm the trend in the measured transition metal compressibilities.

The behavior of DNA molecules is observed in a nanofluidic device near the interface of two regions that produce different configuration entropies. An electric field is applied to drive the molecules partway across the interface. Upon removal of the field, the molecules recoil to the higher-entropy region with a profile characteristic of a force localized to the interface and independent of length. This is consistent with a confinement-mediated entropic force, distinct from the well-known entropic elasticity common to all polymers. An estimate of the hydrodynamic drag is used to produce a lower bound for the force. The phenomenon can be exploited to separate long-strand polyelectrolytes according to length.

We measured the long term spontaneous electrical activity of neuronal networks with different sizes, grown on lithographically prepared substrates and recorded with multi-electrode-array technology. The time sequences of synchronized bursting events were used to characterize network dynamics. All networks exhibit scale-invariant Lévy distributions and long-range correlations. These observations suggest that different-size networks self-organize to adjust their activities over many time scales. As predictions of current models differ from our observations, this calls for revised models.

The vacuum Einstein equations in five dimensions are shown to admit a solution describing a stationary asymptotically flat spacetime regular on and outside an event horizon of topology $S^1\times S^2$. It describes a rotating “black ring.” This is the first example of a stationary asymptotically flat vacuum solution with an event horizon of nonspherical topology. The existence of this solution implies that the uniqueness theorems valid in four dimensions do not have simple five-dimensional generalizations. It is suggested that increasing the spin of a spherical black hole beyond a critical value results in a transition to a black ring, which can have an arbitrarily large angular momentum for a given mass.

Neutron scattering has been used to measure the charge and spin structure in the highly underdoped superconductor ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6.35}$. Incommensurate static charge ordering is found that remains at high temperatures. The magnetic pattern is complex with a resonance and incommensurate structure observed at low temperatures. The results clarify the role of striped phases in ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6+x}$ superconductors.

We address the problem of heat conduction in 1D nonlinear chains; we show that, acting on the parameter which controls the strength of the on-site potential inside a segment of the chain, we induce a transition from conducting to insulating behavior in the whole system. Quite remarkably, the same transition can be observed by increasing the temperatures of the thermal baths at both ends of the chain by the same amount. The control of heat conduction by nonlinearity opens the possibility to propose new devices such as a thermal rectifier.

The fast, irregular, fluctuations of the state of polarization of light output from an erbium doper fiber ring laser are used to communicate digital information. The experiments illustrate the application of a dynamical encoding and information recovery scheme that is robust to perturbations of the communication channel, a standard single mode fiber. A fiber-optic polarization analyzer was used to measure and visualize the polarization dynamics at nanosecond time scales on the Poincaré sphere.

In atom lithography with optical masks, deposition of an atomic beam on a given substrate is controlled by a standing light-wave field. The lateral intensity distribution of the light field is transferred to the substrate with nanometer scale. We have tailored a complex pattern of this intensity distribution through diffraction of a laser beam from a hologram that is stored in a photorefractive crystal. This method can be extended to superpose 1000 or more laser beams. The method is furthermore applicable during growth processes and thus allows full 3D structuring of suitable materials with periodic and nonperiodic patterns at nanometer scales.

Electromagnetic bursts of substantial energy on a nuclear time scale of ${10}^{-21\mathrm{}}–{10}^{-22\mathrm{}}\mathrm{s}$ [zeptosecond (zs) to sub-zs] can theoretically be generated by a perawatt or multiterawatt laser beam focused on a subwavelength-size solid particle or thin wire. Terawatt laser in a similar setup could be instrumental in reaching the subattosecond domain. The system may also generate a half-cycle pulse magnetic field on astrophysical scale up to $\sim {10}^6\mathrm{T}$.

Crumpled sheets have a surprisingly large resistance to further compression. We have studied the crumpling of thin sheets of Mylar under different loading conditions. When placed under a fixed compressive force, the size of a crumpled material decreases logarithmically in time for periods up to three weeks. We also find hysteretic behavior when measuring the compression as a function of applied force. By using a pretreating protocol, we control this hysteresis and find reproducible scaling behavior for the size of the crumpled material as a function of the applied force.

A method, by which periodic two-dimensional arrays of identical metal clusters of nanometer size and spacing could be spontaneously obtained by taking advantage of surface mediated clustering, is reported. The versatility of the method is demonstrated for a broad range of metals on $\mathrm{Si}\left(111\right)-(7\times 7)$ substrates. In situ scanning tunneling microscopy analysis of In clusters, combined with first-principles total energy calculations, unveils unique initial-stage atomic structures of the surface-supported clusters and the vital steps that lead to the success of this method. A strong interaction between the clusters and the surface holds the key to the observed cluster sizes.

The retraction energy of a multiwalled carbon nanotube with an extruded core causes the core to oscillate with respect to its fully retracted position where the van der Waals potential energy is minimized. This phenomenon, together with the available nanotechnology, leads to the creation of nanomechanical systems of operating frequency up to several gigahertz.

Ultrahigh energy cosmic rays create black holes in scenarios with extra dimensions and TeV-scale gravity. In particular, cosmic neutrinos will produce black holes deep in the atmosphere, initiating quasihorizontal showers far above the standard model rate. At the Auger Observatory, hundreds of black hole events may be observed, providing evidence for extra dimensions and the first opportunity for experimental study of microscopic black holes. If no black holes are found, the fundamental Planck scale must be above 2 TeV for any number of extra dimensions.

We report the observation of 3D linear or branched chains of polymer-blend microspheres generated from liquid droplets of solution where the modified surface structure of the polymer composite results in highly robust interparticle bonds. Using a linear quadrupole to precisely position particles in space, we are able to take advantage of this novel material property to actively assemble particles in programmable three-dimensional architectures. The robust interlocking nature of interparticle linkage gives rise to strongly coupled morphology-dependent resonances in bisphere and trisphere systems, suggesting the possibility of three-dimensional photonic “molecules” and microscale optical manipulation applications.

Transverse momentum spectra for charged hadrons and for neutral pions in the range $1\mathrm{GeV}/c<\mathrm{}{p}_T<5\mathrm{}\mathrm{GeV}/c$ have been measured by the PHENIX experiment at RHIC in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=130\mathrm{}\mathrm{GeV}$. At high $p_T$ the spectra from peripheral nuclear collisions are consistent with scaling the spectra from $p+p$ collisions by the average number of binary nucleon-nucleon collisions. The spectra from central collisions are significantly suppressed when compared to the binary-scaled $p+p$ expectation, and also when compared to similarly binary-scaled peripheral collisions, indicating a novel nuclear-medium effect in central nuclear collisions at RHIC energies.

We have found an oscillating instability of fast-running cracks in thin rubber sheets. A well defined transition from straight to wavy cracks occurs as the amount of biaxial strain increases. Measurements of the amplitude and wavelength of the oscillation near the onset of this instability indicate that the instability is a Hopf bifurcation.