Scattering fidelity in elastodynamics

The recent introduction of the concept of scattering fidelity, causes us to revisit the experiment by Lobkis and Weaver [Phys. Rev. Lett. 90, 254302 (2003)]. There, the ``distortion'' of the coda of an acoustic signal is measured under temperature changes. This quantity is in fact the negative logarithm of scattering fidelity. We re-analyse their experimental data for two samples, and we find good agreement with random matrix predictions for the standard fidelity. Usually, one may expect such an agreement for chaotic systems only. While the first sample, may indeed be assumed chaotic, for the second sample, a perfect cuboid, such an agreement is more surprising. For the first sample, the random matrix analysis yields a perturbation strength compatible with semiclassical predictions. For the cuboid the measured perturbation strength is much larger than expected, but with the fitted values for this strength, the experimental data are well reproduced.Comment: 4 page

Thermal analysis of submicron nanocrystalline diamond films

The thermal properties of sub-μm nanocrystalline diamond films in the range of 0.37–1.1 μm grown by hot filament CVD, initiated by bias enhanced nucleation on a nm-thin Si-nucleation layer on various substrates, have been characterized by scanning thermal microscopy. After coalescence, the films have been outgrown with a columnar grain structure. The results indicate that even in the sub-μm range, the average thermal conductivity of these NCD films approaches 400 W m− 1 K− 1. By patterning the films into membranes and step-like mesas, the lateral component and the vertical component of the thermal conductivity, k<sub>lateral</sub> and k<sub>vertical</sub>, have been isolated showing an anisotropy between vertical conduction along the columns, with k<sub>vertical</sub> ≈ 1000 W m− 1 K− 1, and a weaker lateral conduction across the columns, with k<sub>lateral</sub> ≈ 300 W m− 1 K− 1

Role of oxygen in the electron-doped superconducting cuprates

We report on resistivity and Hall measurements in thin films of the electron-doped superconducting cuprate Pr$_{2-x}$Ce$_{x}$CuO$_{4\pm\delta}$. Comparisons between x = 0.17 samples subjected to either ion-irradiation or oxygenation demonstrate that changing the oxygen content has two separable effects: 1) a doping effect similar to that of cerium, and 2) a disorder effect. These results are consistent with prior speculations that apical oxygen removal is necessary to achieve superconductivity in this compound.Comment: 5 pages, 5 figure

The complex morphology of the young disk MWC 758: Spirals and dust clumps around a large cavity

We present Atacama Large Millimeter Array (ALMA) observations at an angular resolution of 0.1-0.2" of the disk surrounding the young Herbig Ae star MWC 758. The data consist of images of the dust continuum emission recorded at 0.88 millimeter, as well as images of the 13CO and C18O J = 3-2 emission lines. The dust continuum emission is characterized by a large cavity of roughly 40 au in radius which might contain a mildly inner warped disk. The outer disk features two bright emission clumps at radii of about 47 and 82 au that present azimuthal extensions and form a double-ring structure. The comparison with radiative transfer models indicates that these two maxima of emission correspond to local increases in the dust surface density of about a factor 2.5 and 6.5 for the south and north clumps, respectively. The optically thick 13CO peak emission, which traces the temperature, and the dust continuum emission, which probes the disk midplane, additionally reveal two spirals previously detected in near-IR at the disk surface. The spirals seen in the dust continuum emission present, however, a slight shift of a few au towards larger radii and one of the spirals crosses the south dust clump. Finally, we present different scenarios in order to explain the complex structure of the disk.Comment: 15 pages, 11 figures. The paper has been published in ApJ. References added and typos correcte

Observed transition from Richtmyer-Meshkov jet formation through feedout oscillations to Rayleigh-Taylor instability in a laser target

Experimental study of hydrodynamic perturbation evolution triggered by a laser-driven shock wave breakout at the free rippled rear surface of a plastic target is reported. At sub-megabar shock pressure, planar jets manifesting the development of the Richtmyer-Meshkov-type instability in a non-accelerated target are observed. As the shock pressure exceeds 1 Mbar, an oscillatory rippled expansion wave is observed, followed by the "feedout" of the rear-surface perturbations to the ablation front and the development of the Rayleigh-Taylor instability, which breaks up the accelerated target.Comment: 12 pages, 4 figure

ASCA Observations of the Starburst-Driven Superwind Galaxy NGC 2146: Broad Band (0.6 - 9 keV) Spectral Properties

We report ASCA GIS and SIS observations of the nearby (D = 11.6 Mpc), nearly edge-on, starburst galaxy NGC 2146. These X-ray spectral data complement ROSAT PSPC and HRI imaging discussed by Armus et al., 1995. The broad band (0.6-9 keV) X-ray spectrum of NGC 2146 is best described by a two component model: the soft X-ray emission with a Raymond-Smith thermal plasma model having a temperature of kT $\sim 0.8$ keV; the hard X-ray emission with a thermal plasma model having kT $\sim 8$ keV or a power-law model having a photon index of $\sim 1.7$. We do not find compelling evidence of substantial excess absorption above the Galactic value. The soft (hard) thermal component provides about 30% (70%) of the total luminosity in the 0.5 - 2.0 keV energy band, while in the 2-10 keV energy range only the hard component plays a major role. The spectral results allow us to set tighter constraints on the starburst-driven superwind model, which we show can satisfactorily account for the luminosity, mass, and energy content represented by the soft X-ray spectral component. We estimate that the mass outflow rate ($\sim$ 9 M$_{\odot}$ per year) is about an order of magnitude greater than the predicted rate at which supernovae and stellar winds return mass into the interstellar medium and, therefore, argue that the flow is strongly "mass-loaded" with material in and around the starburst. The estimated outflow velocity of the hot gas is close to the escape velocity from the galaxy, so the fate of the gas is not clear. We suggest that the hard X-ray spectral component is due to the combined emission of X-ray binaries and/or young supernovae remnants associated with the starburst.Comment: 26 pages plus 4 figures, LaTex manuscript, Accepted for publication in the Astrophysical Journa

Are the Nuclei of Seyfert 2 Galaxies Viewed Face-On?

We show from modeling the Fe Kalpha line in the ASCA spectra of four X-ray bright narrow emission line galaxies (Seyfert types 1.9 and 2) that two equally viable physical models can describe the observed line profile. The first is discussed by Turner et al. (1998) and consists of emission from a nearly pole-on accretion disk. The second, which is statistically preferred, is a superposition of emission from an accretion disk viewed at an intermediate inclination of about 48 degrees and a distinct, unresolved feature that presumably originates some distance from the galaxy nucleus. The intermediate inclination is entirely consistent with unified schemes and our findings challenge recent assertions that Seyfert 2 galaxies are preferentially viewed with their inner regions face-on. We derive mean equivalent widths for the narrow and disk lines of =60 eV and = 213 eV, respectively. The X-ray data are well described by a geometry in which our view of the active nucleus intersects and is blocked by the outer edges of the obscuring torus, and therefore do not require severe misalignments between the accretion disk and the torus.Comment: 19 pages, 3 postscript figures. Accepted for publication in ApJ

The Southern Galactic Plane Survey: The Test Region

The Southern Galactic Plane Survey (SGPS) is a project to image the HI line emission and 1.4 GHz continuum in the fourth quadrant of the Milky Way at high resolution using the Australia Telescope Compact Array (ATCA) and the Parkes Radio Telescope. In this paper we describe the survey details and goals, present lambda 21-cm continuum data, and discuss HI absorption and emission characteristics of the SGPS Test Region (325.5 deg < l < 333.5 deg; -0.5 deg < b < +3.5 deg). We explore the effects of massive stars on the interstellar medium (ISM) through a study of HI shells and the HI environments of HII regions and supernova remnants. We find an HI shell surrounding the HII region RCW 94 which indicates that the region is embedded in a molecular cloud. We give lower limits for the kinematic distances to SNRs G327.4+0.4 and G330.2+1.0 of 4.3 kpc and 4.9 kpc, respectively. We find evidence of interaction with the surrounding HI for both of these remnants. We also present images of a possible new SNR G328.6-0.0. Additionally, we have discovered two small HI shells with no counterparts in continuum emission.Comment: 17 pages, 7 embedded EPS figures, 10 low-res jpeg figures, uses emulateapj5.sty. Accepted for publication in the Astrophysical Journal. Version with all full resolution figures embedded is available at http://www.astro.umn.edu/~naomi/sgps/papers/SGPS.ps.g

Spitzer observations of the asteroid-comet transition object and potential spacecraft target 107P (4015) Wilson-Harrington

Context. Near-Earth asteroid-comet transition object 107P/ (4015) Wilson-Harrington is a possible target of the joint European Space Agency (ESA) and Japanese Aerospace Exploration Agency (JAXA) Marco Polo sample return mission. Physical studies of this object are relevant to this mission, and also to understanding its asteroidal or cometary nature. Aims. Our aim is to obtain significant new constraints on the surface thermal properties of this object. Methods. We present mid-infrared photometry in two filters (16 and 22 microns) obtained with NASA's Spitzer Space Telescope on February 12, 2007, and results from the application of the Near Earth Asteroid Thermal Model (NEATM).We obtained high S/N in two mid-IR bands allowing accurate measurements of its thermal emission. Results. We obtain a well constrained beaming parameter (eta = 1.39 +/- 0.26) and obtain a diameter and geometric albedo of D = 3.46 +/- 0.32 km, and pV = 0.059 +/- 0.011. We also obtain similar results when we apply this best-fitting thermal model to single-band mid-IR photometry reported by Campins et al. (1995), Kraemer et al. (2005) and Reach et al. (2007). Conclusions. The albedo of 4015 Wilson-Harrington is low, consistent with those of comet nuclei and primitive C-, P-, D-type asteorids. We establish a rough lower limit for the thermal inertia of W-H of 60 Jm^-2s^(-0.5)K^-1 when it is at r=1AU, which is slightly over the limit of 30 Jm^-2s^(-0.5)K-1 derived by Groussin et al. (2009) for the thermal inertia of the nucleus of comet 22P/Kopff.Comment: 4 pages, 1 figure and 3 tables. Paper accepted for publicatio