We provide the first evidence that stochastic resonance within the human brain can enhance behavioral responses to weak sensory inputs. We asked subjects to adjust handgrip force to a slowly changing, subthreshold gray level signal presented to their right eye. Behavioral responses were optimized by presenting randomly changing gray levels separately to the left eye. The results indicate that observed behavioral stochastic resonance was mediated by neural activity within the human brain where the information from both eyes converges.

Simultaneous observations of the solar atmosphere from its surface to the corona obtained with the Solar and Heliospheric Observatory (SOHO) and Transition Region and Coronal Explorer (TRACE) show a ubiquitous sequence of events that start from cancellation of photospheric magnetic fields, pass through shock formation, and result in transition region supersonic jets and microflares. These results support a novel view of the energy buildup in the solar atmosphere associated with a cascade of shock waves produced by interacting network magnetic elements in the photosphere and provide insight into the origin of the solar transition region. The findings account for the general mechanisms of energy production, transfer, and release throughout the Sun’s and stellar atmospheres.

The perpendicular critical fields of a superconducting film have been strongly enhanced by using a nanoengineered lattice of magnetic dots (dipoles) on top of the film. Magnetic-field-induced superconductivity is observed in these hybrid superconductor/ferromagnet systems due to the compensation of the applied field between the dots by the stray field of the dipole array. By switching between different magnetic states of the nanoengineered field compensator, the critical parameters of the superconductor can be effectively controlled.

We report on craters formed by balls dropped into dry, noncohesive, granular media. By explicit variation of ball density ${\rho }_b$, diameter $D_b$, and drop height $H$, the crater diameter is confirmed to scale as the $1/4$ power of the energy of the ball at impact: $D_c\sim ({\rho }_b{D}_b^{3}H{)}^{1/4}$. Against expectation, a different scaling law is discovered for the crater depth: $d\sim ({\rho }_b^{3/2}{D}_b^{2}H{)}^{1/3}$. The scaling with properties of the medium is also established. The crater depth has significance for granular mechanics in that it relates to the stopping force on the ball.

We observe experimentally that particle systems that would otherwise mix can be made to segregate and vice versa simply by adding moisture. Using a newly developed theoretical approach, we generate phase diagrams that exhibit both mixed and segregated phases and show how the location of phase boundaries may be manipulated via modifying the mechanical and surface properties of the particles. These results have implications for industrial mixing/separation processes as well as novel particle production methods (e.g., engineered agglomerates with precisely prescribed compositions).

A near contact atomic force microscope operated at low-temperature is used for vertical manipulation of selected single atoms from the $\mathrm{S}\mathrm{i}(111)\mathrm{\text{−}}(7\times 7)$ surface. The strong repulsive short-range chemical force interaction between the closest atoms of both tip apex and surface during a soft nanoindentation leads to the removal of a selected silicon atom from its equilibrium position at the surface without additional perturbation of the $(7\times 7)$ unit cell. Deposition of a single atom on a created vacancy at the surface is achieved as well. These manipulation processes are purely mechanical, since neither bias voltage nor voltage pulse is applied between probe and sample. Differences in the mechanical response of the two nonequivalent adatoms of the $\mathrm{S}\mathrm{i}(111)\mathrm{\text{−}}(7\times 7)$ with the load applied is also detected.

The atomic level structure of the element fermium was investigated for the first time using a sample of $2.7\times {10}^{10}$ atoms of the isotope ${}^{255}\mathrm{F}\mathrm{m}$ with a half-life of 20.1 h. The atoms were evaporated from a filament and stored in the argon buffer gas of an optical cell. Atomic levels were sought by the method of resonance ionization spectroscopy using an excimer-dye-laser combination. Two atomic levels were found at wave numbers $(25099.8\pm 0.2)$ and $(25111.8\pm 0.2){\mathrm{c}\mathrm{m}}^{-1}$. Partial transition rates to the $5f^{12}7s^2$ ${}^{3}H_6^e$ ground state have been determined from their saturation characteristics. Multiconfiguration Dirac-Fock calculations suggest that the leading orders of these levels could be the $5f^{12}7s7p$ ${}^{5}I_6^o$ and $5f^{12}7s7p$ ${}^{5}G_5^o$ terms.

We present a theoretical foundation for the beaming of light displayed by a single subwavelength aperture in an appropriately corrugated metal film [H. J. Lezec et al., Science 297, 820 (2002)]. Good agreement is found between calculations and experimental data. We show that beaming is due to the formation of electromagnetic surface resonances and that the beam direction, width, and wavelength at which it occurs can be selected by tuning geometrical parameters of the structure.

We propose a scheme to observe strongly correlated fermionic phenomena with bosonic atoms in optical lattices. For different values of the sign and strength of the scattering lengths, it is possible to reach either a “superconducting” regime, where the system exhibits atomic pairing, or a Luttinger liquid behavior. We identify the range of parameters where these phenomena appear, illustrate our predictions with numerical calculations, and show how to detect the presence of pairing.

We show that the band structure of a carbon nanotube (NT) can be dramatically altered by mechanical strain. We employ an atomic force microscope tip to simultaneously vary the NT strain and to electrostatically gate the tube. We show that strain can open a band gap in a metallic NT and modify the band gap in a semiconducting NT. Theoretical work predicts that band gap changes can range between $\pm 100\mathrm{m}\mathrm{e}\mathrm{V}$ per $1\%$ stretch, depending on NT chirality, and our measurements are consistent with this predicted range.

We report on a new class of electromagnetically driven fluid interface instability. Using the optical radiation pressure of a cw laser to bend a very soft near-critical liquid-liquid interface, we show that it becomes unstable for sufficiently large beam power $P$, leading to the formation of a stationary beam-centered liquid microjet. We explore the behavior of the instability onset by tuning the interface softness with temperature and varying the size of the exciting beam. The instability mechanism is experimentally demonstrated. It simply relies on total reflection of light at the deformed interface whose condition provides the universal scaling relation for the onset $P_S$ of the instability.

We demonstrate all-optical quantum interference injection and control of a ballistic pure spin current (without an accompanying charge current) in $\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ quantum wells, consisting of spin-up electrons traveling in one direction and spin-down electrons traveling in the opposite direction. This current is generated through quantum interference of one- and two-photon absorption of $\sim 100\mathrm{f}\mathrm{s}$ phase-locked pulses that have orthogonal linear polarizations. We use a spatially resolved pump-probe technique to measure carrier movement of $\sim 10\mathrm{n}\mathrm{m}$. Results agree with recent theoretical predictions.

Inelastic neutron scattering measurements on several Tl filled skutterudites (${\mathrm{T}\mathrm{l}}_{0.5}{\mathrm{C}\mathrm{o}}_{3.5}{\mathrm{F}\mathrm{e}}_{0.5}{\mathrm{S}\mathrm{b}}_{12}$, ${\mathrm{T}\mathrm{l}}_{0.8}{\mathrm{C}\mathrm{o}}_3\mathrm{F}\mathrm{e}{\mathrm{S}\mathrm{b}}_{12}$, and ${\mathrm{T}\mathrm{l}}_{0.8}{\mathrm{C}\mathrm{o}}_4{\mathrm{S}\mathrm{b}}_{11}\mathrm{S}\mathrm{n}$) all show a sharp peak in the vibrational density of states at $57\pm 2\mathrm{K}$, which is absent in the unfilled skutterudite ${\mathrm{C}\mathrm{o}\mathrm{S}\mathrm{b}}_3$. Heat capacity measurements on ${\mathrm{T}\mathrm{l}}_{0.8}{\mathrm{C}\mathrm{o}}_4{\mathrm{S}\mathrm{b}}_{11}\mathrm{S}\mathrm{n}$ as compared to ${\mathrm{C}\mathrm{o}\mathrm{S}\mathrm{b}}_3$ are consistent with the presence of a localized vibrational mode associated with the “rattling” thallium atoms in this filled skutterudite compound. Both results are well described by a localized Einstein mode model with an Einstein temperature ${\Theta }_E$ of $53\pm 1\mathrm{K}$. These data provide perhaps the clearest example of local mode behavior in a concentrated metallic system.

We describe how twist could play an essential role in stabilizing 20 nm diameter sickle hemoglobin fibers. Our theory successfully reproduces the observed variation of helical pitch length with fiber diameter. With no remaining adjustable parameters it also yields a prediction for the torsional rigidity of sickle hemoglobin fibers that is in good agreement with experiment and hence retains the striking feature that such fibers can be highly mechanically anisotropic, even with a ratio of bending to torsional rigidity of about 50. We discuss how our study might be relevant to the development of treatment strategies.

Bloch-like surface waves associated with a quasiperiodic structure are observed in a classic wave propagation experiment which consists of pulse propagation with a shallow fluid covering a quasiperiodically drilled bottom. We show that a transversal pulse propagates as a plane wave with quasiperiodic modulation, displaying the characteristic undulatory propagation in this quasiperiodic system and reinforcing the idea that analogous concepts to Bloch functions can be applied to quasicrystals under certain circumstances.

A new technology for generating steady state, brilliant, broadband, coherent, far-infrared (FIR) radiation in electron storage rings is presented, suitable for FIR spectroscopy. An FIR power increase of up to 100 000 compared to the normal, incoherent synchrotron radiation in the range of $\sim 5$ to $\sim 40{\mathrm{c}\mathrm{m}}^{-1}$ could be achieved. The source is up to 1000 times more brillant compared to a standard Hg arc lamp. The coherent synchrotron radiation is produced in a “low alpha” optics mode of the synchrotron light source BESSY, by bunch shortening and non-Gaussian bunch deformation.

We report in situ atomic force microscopy experiments which reveal the presence of nanoscale damage cavities ahead of a stress-corrosion crack tip in glass. Their presence might explain the departure from linear elasticity observed in the vicinity of a crack tip in glass. Such a ductile fracture mechanism, widely observed in the case of metallic materials at the micrometer scale, might be also at the origin of the striking similarity of the morphologies of fracture surfaces of glass and metallic alloys at different length scales.

The wrinkling of thin elastic sheets occurs over a range of length scales, from the fine scale patterns in substrates on which cells crawl to the coarse wrinkles seen in clothes. Motivated by the wrinkling of a stretched elastic sheet, we deduce a general theory of wrinkling, valid far from the onset of the instability, using elementary geometry and the physics of bending and stretching. Our main result is a set of simple scaling laws; the wavelength of the wrinkles $\lambda \sim K^{-1/4}$, where $K$ is the stiffness due to an “elastic substrate” effect with a multitude of origins, and the amplitude of the wrinkle $A\sim \lambda$. These could form the basis of a highly sensitive quantitative wrinkling assay for the mechanical characterization of thin solid membranes.

A shadow is an exact solution to a chaotic system of equations that remains close to a numerically computed solution for a long time. Using a variable-order, variable–time-step integrator, we numerically compute solutions to a gravitational $N$-body problem in which many particles move and interact in a fixed potential. We then search for shadows of these solutions with the longest possible duration. We find that in “softened” potentials, shadow durations are sufficiently long for significant evolution to occur. However, in unsoftened potentials, shadow durations are typically very short.

We theoretically study the mechanical interaction between radiation and a semiconductor nanoparticle, based on a microscopic model of confined excitons. The exerted force is calculated by using the Maxwell stress tensor expressed in terms of the microscopic response field. The numerical demonstrations clarify the following: (1) The enhancement of the force by using electronic resonance is remarkable for a particle with a radius of less than 100 nm for semiconductor materials. (2) The spectral peak position of the exerted force is considerably sensitive to nanoscale-size changes which would be useful for highly accurate size-selective manipulation.