Motion of a rigid punch at a low velocity along the boundary of a viscoelastic half-plane

The contact problem of the interaction of a rigid punch with a viscoelastic half-plane is considered. The dependence of the displacement of the boundary of half-plane on the normal load applied to it is determined, and the integral equation for determining the contact pressure is derived and solved by the method of “small λ”. Distributions of contact pressures under the punch are graphically represented.     

The input impedance of the dielectric resonator antenna

Dielectric cylinders of very high permittivity have been used in the past as resonant cavities, but since the structure is not enclosed by metallic walls, electromagnetic fields do exist beyond the geometrical boundaries of the structure and part of the power is radiated. Through the proper choice of geometry and permittivity this radiation can become the dominant feature of the structure and become an efficient antenna for use at millimeter wave frequencies. Both experimental and theoretical investigations of a variety of these dielectric resonator antennas have been undertaken. In particular, the input impedance of a probe-fed cylindrical structure was examined in detail and a comparison of theoretical and experimental results was made.     

Improved limits on the mass of the tau neutrino

Several methods to determine (or set an upper bound on) the mass of the tau neutrino are described. The decay spectrum of \(\tau \to e\bar \nu _e \nu _\tau \) near the high center-of-mass electron-energy end is particularly sensitive to the tau-neutrino mass. It is shown that an upper bound of 20 MeV or lower may be feasible. In addition, improved limits on the mass and mixing angle of a heavy component of the tau-neutrino may be readily obtained. We also discuss the purely leptonic decays of theD andF mesons, and show how measurements of the ratiosB(D→τν_τ/B(D→μν_μ,B(F→τν_τ/B(D→μν_μ can be sensitive to tau-neutrino masses of 30 MeV or greater.     

The enhancement effect: evidence for adaptation of inhibition using a binaural centering task

The enhancement effect is consistently shown when simultaneously masked stimuli are preceded by the masker alone, with a reduction in the amount of masking relative to when that precursor is absent. One explanation for this effect proposed by Viemeister and Bacon [(1982). J. Acoust. Soc. Am. 71, 1502-1507] is the adaptation of inhibition, which predicts that an enhanced component (the "target") will be effectively more intense within the auditory system than one that has not been enhanced. Forward masking studies have indicated this effect of increased gain; however, other explanations of the enhancement effect have also been suggested. In order to provide an alternative measure of the amount of effective gain for an enhanced target, a subjective binaural centering task was used in which listeners matched the intensities of enhanced and unenhanced 2-kHz tones presented to opposite ears to produce a centered stimulus. The results showed that the enhancement effect produces an effective 4-5 dB increase in the level of the enhanced target. The enhancement effect was also measured using other enhancement paradigms which yielded similar results over a range of levels for the target, supporting an account based on adaptation of inhibition.     

Discrimination of temporally asymmetric modulation with triangular envelopes on a broadband-noise carrier (L)

Highly detectable, time-reversed triangular amplitude modulation, with linear increases and decreases in amplitude, was used in an adaptive task to measure just-noticeable differences for changes in the direction of envelope temporal asymmetry for different modulation depths (m = 1.0 and 0.5) and rates (8, 16, and 32 Hz). Thresholds were analyzed using three different measures of the modulator's shape based on (1) the change in the position of the peak within a cycle, (2) the change in the slope of the modulator's increasing amplitude portion, and (3) the change in slope measured in units of amplitude per unit cycle rather than amplitude per unit time. The amplitude per unit cycle measure resulted in the best fit to all the data, and predicted additional data that were gathered with roved modulation frequency. The results suggest that a time normalization process may be involved in the perception and discrimination of envelope shape.     

Ab initio prediction of conduction band spin splitting in zinc blende semiconductors

We use a recently developed self-consistent GW approximation to present systematic ab initio calculations of the conduction band spin splitting in III-V and II-VI zinc blende semiconductors. The spin-orbit interaction is taken into account as a perturbation to the scalar relativistic Hamiltonian. These are the first calculations of conduction band spin splittings based on a quasiparticle approach; and because the self-consistent GW scheme accurately reproduces the relevant band parameters, it is expected to be a reliable predictor of spin splittings. The results are compared to the few available experimental data and a previous calculation based on a model one-particle potential. We also briefly address the widely used k x p parametrization in the context of these results.     

Synchrotron X‐ray footprinting on tour

Synchrotron footprinting is a valuable technique in structural biology for understanding macromolecular solution‐state structure and dynamics of proteins and nucleic acids. Although an extremely powerful tool, there is currently only a single facility in the USA, the X28C beamline at the National Synchrotron Light Source (NSLS), dedicated to providing infrastructure, technology development and support for these studies. The high flux density of the focused white beam and variety of specialized exposure environments available at X28C enables footprinting of highly complex biological systems; however, it is likely that a significant fraction of interesting experiments could be performed at unspecialized facilities. In an effort to investigate the viability of a beamline‐flexible footprinting program, a standard sample was taken on tour around the nation to be exposed at several US synchrotrons. This work describes how a relatively simple and transportable apparatus can allow beamlines at the NSLS, CHESS, APS and ALS to be used for synchrotron footprinting in a general user mode that can provide useful results.