Great expectations: Specific lexical anticipation influences the processing of spoken language

Background  

Recently several studies have shown that people use contextual information to make predictions about the rest of the sentence or story as the text unfolds. Using event related potentials (ERPs) we tested whether these on-line predictions are based on a message-level representation of the discourse or on simple automatic activation by individual words. Subjects heard short stories that were highly constraining for one specific noun, or stories that were not specifically predictive but contained the same prime words as the predictive stories. To test whether listeners make specific predictions critical nouns were preceded by an adjective that was inflected according to, or in contrast with, the gender of the expected noun.     

Nitride band-structure model in a quantum well laser simulator

The two-dimensional quantum well laser simulator Visible Laser Simulator (VLS) has been extended to simulate III–V nitride based lasers. In this paper, we present details about the laser simulator and focus on the six band k.p solver used to calculate the electronic band structure. The effect of strain on bulk and quantum well electronic dispersion is analyzed, and the influence of the built-in polarization charges on the band diagram is likewise considered.     

Breakdown limits on Gigavolt-per-meter electron-beam-driven wakefields in dielectric structures

First measurements of the breakdown threshold in a dielectric subjected to GV/m wakefields produced by short (30-330 fs), 28.5 GeV electron bunches have been made. Fused silica tubes of 100 microm inner diameter were exposed to a range of bunch lengths, allowing surface dielectric fields up to 27 GV/m to be generated. The onset of breakdown, detected through light emission from the tube ends, is observed to occur when the peak electric field at the dielectric surface reaches 13.8+/-0.7 GV/m. The correlation of structure damage to beam-induced breakdown is established using an array of postexposure inspection techniques.     

Wideband time-reversal imaging of an elastic target in an acoustic waveguide

Time-reversal is addressed for imaging elastic targets situated in an acoustic waveguide. It is assumed that the target-sensor range is large relative to the channel depth. We investigate the theory of wideband time-reversal imaging of an extended elastic target, for which the target dimensions are large relative to the principal wavelengths. When performing time-reversal imaging one requires a forward model for propagation through the channel, and the quality of the resulting image may be used as a measure of the match between the modeled and actual (measured) channel parameters. It is demonstrated that the channel parameters associated with a given measurement may be determined via a genetic-algorithm (GA) search in parameter space, employing a cost function based on the time-reversal image quality. Example GA channel-parameter-inversion results and imagery are presented for measured at-sea data.     

Anomalous atomic hydrogen shock pattern in a supersonic plasma Jet

A two-photon laser-induced fluorescence study on the transport of ground-state atomic hydrogen in a supersonic plasma jet, generated from an Ar-H (2) mixture, reveals an unexpected shock pattern. Whereas both the axial-velocity profile and the temperature profile of hydrogen atoms along the jet centerline can be interpreted in terms of a supersonic expansion of an Ar-H gas mixture, the H-atom density profiles do not satisfy the well established Rankine-Hugoniot relation leading to a nonconservation of the forward flux. The experimental results show that H atoms escape from the supersonic expansion by a diffusion process due to strong density gradients between the core of the jet and its vicinity.     

Alignment dependent chemisorption of vibrationally excited CH4(ν3) on Ni(100), Ni(110), and Ni(111)

We present a stereodynamics study of the dissociative chemisorption of vibrationally excited methane on the (100), (110), and (111) planes of a nickel single crystal surface. Using linearly polarized infrared excitation of the antisymmetric C-H stretch normal mode vibration (ν(3)), we aligned the angular momentum and C-H stretch amplitude of CH(4)(ν(3)) in the laboratory frame and measured the alignment dependence of state-resolved reactivity of CH(4) for the ν(3) = 1, J = 0-3 quantum states over a range of incident translational energies. For all three surfaces studied, in-plane alignment of the C-H stretch results in the highest dissociation probability and alignment along the surface normal in the lowest reactivity. The largest alignment contrast between the maximum and minimum reactivity is observed for Ni(110), which has its surface atoms arranged in close-packed rows separated by one layer deep troughs. For Ni(110), we also probed for alignment effects relative to the direction of the Ni rows. In-plane C-H stretch alignment perpendicular to the surface rows results in higher reactivity than parallel to the surface rows. The alignment effects on Ni(110) and Ni(100) are independent of incident translational energy between 10 and 50 kJ/mol. Quantum state-resolved reaction probabilities are reported for CH(4)(ν(3)) on Ni(110) for translational energies between 10 and 50 kJ/mol.     

Quantifying desorption of saturated hydrocarbons from silicon with quantum calculations and scanning tunneling microscopy

Electron stimulated desorption of cyclopentene from the Si(100)-(2 x 1) surface is studied experimentally with cryogenic UHV STM and theoretically with transport, electronic structure, and dynamical calculations. Unexpectedly for a saturated hydrocarbon on silicon, desorption is observed at bias magnitudes as low as 2.5 V, albeit the desorption yields are a factor of 500 to 1000 lower than previously reported for unsaturated molecules on silicon. The low threshold voltage for desorption is attributed to hybridization of the molecule with the silicon surface, which results in low-lying ionic resonances within 2-3 eV of the Fermi level. These resonances are long-lived, spatially localized, and displaced in equilibrium with respect to the neutral state. This study highlights the importance of nuclear dynamics in silicon-based molecular electronics and suggests new guidelines for the control of such dynamics.