788 research outputs found
Shock formation and the ideal shape of ramp compression waves
We derive expressions for shock formation based on the local curvature of the
flow characteristics during dynamic compression. Given a specific ramp adiabat,
calculated for instance from the equation of state for a substance, the ideal
nonlinear shape for an applied ramp loading history can be determined. We
discuss the region affected by lateral release, which can be presented in
compact form for the ideal loading history. Example calculations are given for
representative metals and plastic ablators. Continuum dynamics (hydrocode)
simulations were in good agreement with the algebraic forms. Example
applications are presented for several classes of laser-loading experiment,
identifying conditions where shocks are desired but not formed, and where long
duration ramps are desired
Efficacy of a Manualized and Workbook-Driven Individual Treatment for Social Anxiety Disorder
Social anxiety disorder is a prevalent and impairing disorder for which viable cognitive-behavioral therapies exist. However, these treatments have not been easily packaged for dissemination and may be underutilized as a result. The current study reports on the findings of a randomized controlled trial of a manualized and workbook-driven individual cognitive-behavioral treatment for social anxiety disorder (Hope, Heimberg, Juster, & Turk, 2000; Hope, Heimberg, & Turk, 2006). This treatment package was derived from an empirically supported group treatment for social anxiety disorder and intended for broad dissemination, but it has not previously been subjected to empirical examination on its own. As a first step in that examination, 38 clients seeking treatment for social anxiety disorder at either the Adult Anxiety Clinic of Temple University or the Anxiety Disorders Clinic of the University of Nebraska–Lincoln were randomly assigned to receive either immediate treatment with this cognitive-behavioral treatment package or treatment delayed for 20 weeks. Evaluation at the posttreatment/postdelay period revealed substantially greater improvements among immediate treatment clients on interviewer-rated and self-report measures of social anxiety and impairment. Three-month follow-up assessment revealed maintenance of gains. Clinical implications and directions for future research are discussed
Dissolved methane distributions and air-sea flux in the plume of a massive seep field, Coal Oil Point, California
Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 34 (2007): L22603, doi:10.1029/2007GL031344.Large quantities of natural gas are emitted from the seafloor into the stratified coastal ocean near Coal Oil Point, Santa Barbara Channel, California. Methane was quantified in the down current surface water at 79 stations in a 280 km2 study area. The methane plume spread over an area of ~70 km2 and emitted on the order of 5 × 104 mol d−1 to the atmosphere. A monthly time series at 14 stations showed variable methane concentrations which were correlated with changing sub-mesoscale surface currents. Air-sea fluxes estimated from the time series indicate that the air-sea flux derived for the 280 km2 area is representative of the daily mean flux from this area. Only 1% of the dissolved methane originating from Coal Oil Point enters the atmosphere within the study area. Most of it appears to be transported below the surface and oxidized by microbial activity.The research was supported by the University
of California Energy Institute and the National Science Foundation (OCE
0447395)
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The characteristics of cognitive neuroscience tests in a schizophrenia cognition clinical trial: Psychometric properties and correlations with standard measures.
In comparison to batteries of standard neuropsychological tests, cognitive neuroscience tests may offer a more specific assessment of discrete neurobiological processes that may be aberrant in schizophrenia. However, more information regarding psychometric properties and correlations with standard neuropsychological tests and functional measures is warranted to establish their validity as treatment outcome measures. The N-back and AX-Continuous Performance Task (AX-CPT) are two promising cognitive neuroscience tests designed to measure specific components of working memory and contextual processing respectively. In the current study, we report the psychometric properties of multiple outcome measures from these two tests as well as their correlations with standard neuropsychological measures and functional capacity measures. The results suggest that while the AX-CPT and N-back display favorable psychometric properties, they do not exhibit greater sensitivity or specificity with functional measures than standard neurocognitive tests
Angular momentum and an invariant quasilocal energy in general relativity
Owing to its transformation property under local boosts, the Brown-York
quasilocal energy surface density is the analogue of E in the special
relativity formula: E^2-p^2=m^2. In this paper I will motivate the general
relativistic version of this formula, and thereby arrive at a geometrically
natural definition of an `invariant quasilocal energy', or IQE. In analogy with
the invariant mass m, the IQE is invariant under local boosts of the set of
observers on a given two-surface S in spacetime. A reference energy subtraction
procedure is required, but in contrast to the Brown-York procedure, S is
isometrically embedded into a four-dimensional reference spacetime. This
virtually eliminates the embeddability problem inherent in the use of a
three-dimensional reference space, but introduces a new one: such embeddings
are not unique, leading to an ambiguity in the reference IQE. However, in this
codimension-two setting there are two curvatures associated with S: the
curvatures of its tangent and normal bundles. Taking advantage of this fact, I
will suggest a possible way to resolve the embedding ambiguity, which at the
same time will be seen to incorporate angular momentum into the energy at the
quasilocal level. I will analyze the IQE in the following cases: both the
spatial and future null infinity limits of a large sphere in asymptotically
flat spacetimes; a small sphere shrinking toward a point along either spatial
or null directions; and finally, in asymptotically anti-de Sitter spacetimes.
The last case reveals a striking similarity between the reference IQE and a
certain counterterm energy recently proposed in the context of the conjectured
AdS/CFT correspondence.Comment: 54 pages LaTeX, no figures, includes brief summary of results,
submitted to Physical Review
The TEMPO Survey I: Predicting Yields of the Transiting Exosatellites, Moons, and Planets from a 30-day Survey of Orion with the Nancy Grace Roman Space Telescope
We present design considerations for the Transiting Exosatellites, Moons, and
Planets in Orion (TEMPO) Survey with the Nancy Grace Roman Space Telescope.
This proposed 30-day survey is designed to detect a population of transiting
extrasolar satellites, moons, and planets in the Orion Nebula Cluster (ONC).
The young (1-3 Myr), densely-populated ONC harbors about a thousand bright
brown dwarfs (BDs) and free-floating planetary-mass objects (FFPs). TEMPO
offers sufficient photometric precision to monitor FFPs with for transiting satellites. The survey is also capable of detecting
FFPs down to sub-Saturn masses via direct imaging, although follow-up
confirmation will be challenging. TEMPO yield estimates include 14 (3-22)
exomoons/satellites transiting FFPs and 54 (8-100) satellites transiting BDs.
Of this population, approximately of companions would be "super-Titans"
(Titan to Earth mass). Yield estimates also include approximately
exoplanets transiting young Orion stars, of which will orbit
mid-to-late M dwarfs and approximately ten will be proto-habitable zone,
terrestrial () exoplanets. TEMPO would
provide the first census demographics of small exosatellites orbiting FFPs and
BDs, while simultaneously offering insights into exoplanet evolution at the
earliest stages. This detected exosatellite population is likely to be markedly
different from the current census of exoplanets with similar masses (e.g.,
Earth-mass exosatellites that still possess H/He envelopes). Although our yield
estimates are highly uncertain, as there are no known exoplanets or exomoons
analogous to these satellites, the TEMPO survey would test the prevailing
theories of exosatellite formation and evolution, which limit the certainty
surrounding detection yields.Comment: Submitted to PAS
The Sensitivity of Convection Zone Depth to Stellar Abundances: An Absolute Stellar Abundance Scale from Asteroseismology
The base of the convection zone is a source of acoustic glitches in the
asteroseismic frequency spectra of solar-like oscillators, allowing one to
precisely measure the acoustic depth to the feature. We examine the sensitivity
of the depth of the convection zone to mass, stellar abundances, and input
physics, and in particular, the use of a measurement of the acoustic depth to
the CZ as an atmosphere-independent, absolute measure of stellar metallicities.
We find that for low mass stars on the main sequence with , the acoustic depth to the base of the convection zone,
normalized by the acoustic depth to the center of the star, , is
both a strong function of mass, and varies at the 0.5-1% per 0.1 dex level in
[Z/X], and is therefore also a sensitive probe of the composition. We estimate
the theoretical uncertainties in the stellar models, and show that combined
with reasonable observational uncertainties, we can expect measure the the
metallicity to within 0.15 - 0.3 dex for solar-like stars. We discuss the
applications of this work to rotational mixing, particularly in the context of
the observed mid F star Li dip, and to distguishing between different mixtures
of heavy elements.Comment: 37 pages, 12 figures, 2 tables, submitted to ApJ. For a brief video
explaining the key result of this paper, see
http://www.youtube.com/user/OSUAstronom
Reproducibility of in-vivo OCT measured three-dimensional human lamina cribrosa microarchitecture
Purpose: To determine the reproducibility of automated segmentation of the three-dimensional (3D) lamina cribrosa (LC) microarchitecture scanned in-vivo using optical coherence tomography (OCT). Methods: Thirty-nine eyes (8 healthy, 19 glaucoma suspects and 12 glaucoma) from 49 subjects were scanned twice using swept-source (SS-) OCT in a 3.5x3.5x3.64 mm (400x400x896 pixels) volume centered on the optic nerve head, with the focus readjusted after each scan. The LC was automatically segmented and analyzed for microarchitectural parameters, including pore diameter, pore diameter standard deviation (SD), pore aspect ratio, pore area, beam thickness, beam thickness SD, and beam thickness to pore diameter ratio. Reproducibility of the parameters was assessed by computing the imprecision of the parameters between the scans. Results: The automated segmentation demonstrated excellent reproducibility. All LC microarchitecture parameters had an imprecision of less or equal to 4.2%. There was little variability in imprecision with respect to diagnostic category, although the method tends to show higher imprecision amongst healthy subjects. Conclusion: The proposed automated segmentation of the LC demonstrated high reproducibility for 3D LC parameters. This segmentation analysis tool will be useful for in-vivo studies of the LC. © 2014 Wang et al
High-resolution Infrared Imaging and Spectroscopy of the Z Canis Majoris System during Quiescence and Outburst
We present adaptive optics photometry and spectra in the JHKL bands along with high spectral resolution K-band spectroscopy for each component of the Z Canis Majoris system. Our high angular resolution photometry of this very young (≾1 Myr) binary, comprised of an FU Ori object and a Herbig Ae/Be star, was gathered shortly after the 2008 outburst while our high-resolution spectroscopy was gathered during a quiescent phase. Our photometry conclusively determines that the outburst was due solely to the embedded Herbig Ae/Be member, supporting results from earlier works, and that the optically visible FU Ori component decreased slightly (~30%) in luminosity during the same period, consistent with previous works on the variability of FU Ori type systems. Further, our high-resolution K-band spectra definitively demonstrate that the 2.294 μm CO absorption feature seen in composite spectra of the system is due solely to the FU Ori component, while a prominent CO emission feature at the same wavelength, long suspected to be associated with the innermost regions of a circumstellar accretion disk, can be assigned to the Herbig Ae/Be member. These findings clarify previous analyses of the origin of the CO emission in this complex system
Omega and Antiomega production in central Pb+Pb collisions at 40 and 158 AGeV
Results are presented on Omega production in central Pb+Pb collisions at 40
and 158 AGeV beam energy. Given are transverse-mass spectra, rapidity
distributions, and total yields for the sum Omega+Antiomega at 40 AGeV and for
Omega and Antiomega separately at 158 AGeV. The yields are strongly
under-predicted by the string-hadronic UrQMD model and are in better agreement
with predictions from a hadron gas models.Comment: 5 papes, 4 figures, 1 table, updated figure 4 and table 1. Final
version, including some editorial changes, as published in PR
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