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We report on the analysis of 34 years of photometric observations of the pulsating helium atmosphere white dwarf GD358. The complete data set includes archival data from 1982-2006, and 1195.2 hours of new observations from 2007- 2016. From this data set, we extract 15 frequencies representing g-mode pulsation modes, adding 4 modes to the 11 modes known previously. We present evidence that these 15 modes are ell = 1 modes, 13 of which belong to a consecutive sequence in radial overtone k. We perform a detailed asteroseismic analysis using models that include parameterized, complex carbon and oxygen core composition profiles to fit the periods. Recent spectroscopic analyses place GD358 near the red edge of the DBV instability strip, at 24,000 plus or minus 500 K and a log g of 7.8 plus or minus 0.08 dex. The surface gravity translates to a mass range of 0.455 to 0.540 solar masses. Our best fit model has a temperature of 23,650 K and a mass of 0.5706 solar masses. That is slightly more massive than suggested by most the recent spectroscopy. We find a pure helium layer mass of 10^-5.50, consistent with the result of previous studies and the outward diffusion of helium over time., Comment: 94 pages, 14 figures, 7 tables, Accepted for publication in the ApJ

The desorption of Na+ under electron irradiation at low energies (

Purpose: Gradual drifting of baseline signal intensity is common in functional MRI (fMRI) time course data. Methods for dealing with this effect are studied. Method: Simulations and fMRI data are used to study three statistical models that account for baseline drift. A method is proposed in which the time course data are linear least-squares fit to a reference function that includes the slope of the baseline drift as a free parameter. Results: It is shown that the least-squares method is equivalent to cross-correlation with Gram-Schmidt orthogonalization. Additionally, it is shown that certain paradigm designs improve the sensitivity of statistical tests when using any of the drift correction methods commonly employed. The least-squares method results in a variety of useful parameters such as activation amplitude, with a well characterized error. Conclusion: Very simple techniques can effectively account for observed drifts. It is important to design paradigms that are symmetric about the midpoint of the time series. In calculating confidence levels, a proper statistical model that accounts for baseline drifts is necessary to ensure accurate confidence level assessment. Index Terms: Magnetic resonance imaging, functional-Time series analysis.

The heat treatment of the Caribbean steel drum has been found to involve strain ageing and is especially prominent in drum steels containing 0.03–0.04 wt% C. The optimum strain-ageing conditions appear to be about 350 °C for 10 min, and either water quenching or air cooling produce similar ageing effects (hardness increases) ranging from about 5 to 20%. The strain ageing combined with the strain hardening applied to the drum-head sinking and note-fabrication processes, produces a requisite elastic–plastic interaction, which allows for multiharmonic tuning and the creation of the unique chromatic tones and harmonic overtones that are a characteristic of the various instruments. These unique features of note vibrations were illustrated by comparing dynamic impact hardness profiles with corresponding, static Vickers hardness measurements for actual, tuned notes and the same, corresponding notes extracted from the drum head, respectively. Elastic–plastic and plastic-hardness profiles were compared in unique colour maps. Microstructural analyses by light metallography and transmission electron microscopy illustrate corresponding dislocation substructures and carbide precipitation. Finally, the analysis and comparison of acoustic spectra for specific steel-drum note zones illustrates their complex, non-linear behaviour, and the role that deformation-induced defects play in acoustic dispersion and multiharmonic signal production.

Steel-drum fabrication, especially the sinking of the drum head (also referred to as the “pan”) by hand with a hammer, has been examined in detail utilizing light metallography (LM) and transmission electron microscopy (TEM) to characterize residual microstructures corresponding to reductions in thickness of up to 50 % at the bottom of the drum head. Dislocation densities in the low-carbon (0.01–0.05 wt % C), ferritic steels can exceed 1010 cm-2. Simulations of simple, ideal, free circular notes utilizing 316 stainless-steel plates (0.05 wt % C), cold rolled to reductions up to 40%, revealed that deformation (per cent cold reduction) has an important effect on the acoustic spectrum, especially harmonic spectra. Harmonic-node splitting was observed for thin circular plates (0.076 cm thick); the frequency difference was 60 Hz at 20% cold reduction and 160 Hz at 40% cold reduction. These dispersion effects, due to deformation-induced microstructures, as well as irregularities in the note geometries and thicknesses, point to the complex and non-linear acoustic features that contribute to the unique sounds of the Caribbean steel drum.

A Monte Carlo random walk model was used to study the creation and dynamics of F- and H-centers induced by electron irradiation in alkali-halide single crystals. The purpose of the study was to observe the effects of depth dependent electron energy deposition near the surface region using beam energies of 500 eV or less and relatively low currents (< 100 μA/cm2). The calculations were carried out using the parameters appropriate for an FCC LiF single crystal at room temperature. Depth dependent dynamics of F- and H-centers are also presented as well as F—H center recombination rates, and thermal and non-thermal halogen production rates at the surface. The model demonstrates that F—H center recombination dramatically affects the F-center distribution. F-center distributions are found to be peaked at the surface and do not reflect the initial energy deposition profile.

In initial observations during Auger studies of NaCl, we have observed stable, clearly resolved Auger peaks. With time, however, some of the Auger spectra reveal the occurrence of strong negative charging. This charging appears to be a result of irradiation-induced accumulation of sodium metal on the sample surface. We report the dependence of the strong negatively charged state on temperature. The results are consistent with the above model; the strongly negatively charged surface cannot be maintained at temperatures sufficiently high that sodium metal evaporation occurs.

We study temperature programmed desorption of sodium and chlorine from an electron irradiated sodium chloride (100) surface. In this experiment, the sodium chloride crystal is irradiated with 500 eV electrons. After the electron beam is turned off, the crystal is heated and desorption of the alkali atoms is observed. This delayed desorption of sodium is analyzed using fractional order desorption equations. The results clearly show that the desorption is not a first order process. The data are interpreted in terms of a thick layer of sodium forming on the surface.

The distributions of quarks in the pion and nucleon are extracted from measurements of the reaction ${\ensuremath{\pi}}^{\ensuremath{-}}N\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}X$ at 253 GeV/c in a naive Drell-Yan analysis, as well as QCD-corrected analyses at leading-log and next-to-leading-log order. As ${x}_{\ensuremath{\pi}}\ensuremath{\rightarrow}1$ the pion structure function shows a term that varies as $\frac{1}{{m}_{\ensuremath{\mu}\ensuremath{\mu}}^{4}}$, which we interpret as a higher-twist effect. Additionally, the angular distribution of the ${\ensuremath{\mu}}^{+}$ in the muon-pair rest frame tends towards ${sin}^{2}\ensuremath{\theta}$ as ${x}_{\ensuremath{\pi}}\ensuremath{\rightarrow}1$ and as ${m}_{\ensuremath{\mu}\ensuremath{\mu}}\ensuremath{\rightarrow}0$ in a manner consistent with higher-twist effects. When the strongly mass-dependent higher-twist effects are included as part of the pion structure function, the nucleon structure function agrees well with leading-twist results from deeply inelastic lepton-hadron scattering. A significant advance of the present work is the extension of the analysis to low masses by the subtraction of the $\frac{J}{\ensuremath{\psi}}$ and ${\ensuremath{\psi}}^{\ensuremath{'}}$ resonances from the continuum. Our analysis covers the kinematic range $0.4l{x}_{\ensuremath{\pi}}l1.0$ and $0.02l{x}_{N}l0.33$ with $3.0l{m}_{\ensuremath{\mu}\ensuremath{\mu}}l8.55$ GeV/${\mathit{c}}^{2}$. Cross sections for ${\ensuremath{\psi}}^{\ensuremath{'}}$ production are presented in an appendix.

We have compared the data resulting from magnetoencephalography (MEG) and functional MRI (fMRI) mapping of the same subjects under the same stimulus conditions in an evoked motor response paradigm. The goals of this study were threefold: 1) to compare the activation foci revealed by each modality as a cross-validation check; 2) to compare the quantitative aspects of the signal yielded by each modality, in this case parametric changes in signal strength as a function of stimulus intensity; and 3) to lay a foundation for future work in which results from both modalities will be combined in such a way as to enhance the information content of both.

In binocular rivalry, a subject views two incongruent stimuli through each eye but consciously perceives only one stimulus at a time, with a switch in perceptual dominance every few seconds. To investigate the neural correlates of perceptual dominance in humans, seven subjects were recorded with a 148-channel magnetoencephalography array while experiencing binocular rivalry. A red vertical grating flickering at one frequency was presented to one eye through a red filter and a blue horizontal grating flickering at a different frequency was presented to the other eye through a blue filter. Steady-state neuromagnetic responses at the two frequencies were used as tags for the two stimuli and analyzed with high-resolution power spectra. It was found that a large number of channels showed peaks at both frequencies, arranged in a horseshoe pattern from posterior to anterior regions, whether or not the subject was consciously perceiving the corresponding stimulus. However, the amount of power at the stimulus frequency was modulated in relation to perceptual dominance, being lower in many channels by 50–85% when the subject was not conscious of that stimulus. Such modulation by perceptual dominance, although not global, was distributed to a large subset of regions showing stimulus-related responses, including regions outside visual cortex. The results demonstrate a correlation between the conscious perception of a visual stimulus and the synchronous activity of large populations of neurons as reflected by steady-state neuromagnetic responses.

In this study we observe that the positions of Auger signals shift from slightly below (∼10 eV) the tabulated values to well above (>150 eV). The observed shifts can be understood by a simple model of surface charging based on the change in the secondary electron emission of the damaged region.

A schematic model is described for taking into account the effect of potential pockets (motivated by positron experiments at GSI) on sub-Coulomb nucleon transfer cross sections. Results for single-neutron transfer in 238U-238U collisions bear a remarkable resemblance to data for some bombarding energies.

The rate of radiated photons per electron passing through a helium-filled \ifmmode \hat{C}\else \^{C}\fi{}erenkov counter is observed to oscillate as a function of the gas pressure when a weak, static magnetic field is applied. The data agree well with an analysis which treats \ifmmode \hat{C}\else \^{C}\fi{}erenkov and synchrotron radiation as limiting manifestations of a unified process.

Presents a theoretical analysis of a hexapole magnet used for state selection and focusing of the F=1, mF=0 hyperfine state in hydrogen masers. The analysis determines the relative importance of the magnet properties and the geometry of the beam system in providing state selection and focusing. This in turn shows how the system may be optimised for minimum hydrogen flow at a given level of maser oscillation, thereby improving frequency stability (via reduction of the spin exchange interaction) and increasing operating time for a given volume of hydrogen gas.

Two problems are discussed, both related to the suggestion that HI interaction potentials contain minima or pockets which cause “sticking” and time delays in sub-Coulomb collisions.