1,920 research outputs found
Thermal photon production in high-energy nuclear collisions
We use a boost-invariant one-dimensional (cylindrically symmetric) fluid
dynamics code to calculate thermal photon production in the central rapidity
region of S+Au and Pb+Pb collisions at SPS energy ( GeV/nucleon).
We assume that the hot matter is in thermal equilibrium throughout the
expansion, but consider deviations from chemical equilibrium in the high
temperature (deconfined) phase. We use equations of state with a first-order
phase transition between a massless pion gas and quark gluon plasma, with
transition temperatures in the range MeV.Comment: revised, now includes a_1 contribution. revtex, 10 pages plus 4
figures (uuencoded postscript
Mortality of Vertebrates and Invertebrates on an Athens County, Ohio, Highway
Author Institution: Department of Zoological and Biomedical Sciences, Ohio UniversityAlthough previous road-kill surveys have tallied the number and kinds of vertebrates that were victims of vehicular traffic (mostly birds and mammals), none has recorded invertebrate mortality. A 14-month survey on foot of each side of a 1.6 km (1 mi) stretch of dual lane highway provided 188 vertebrate and 1,162 invertebrate victims. Finding rare and unusual species of invertebrates suggests that this technique be used as a supplementary faunal survey
Secondary phi meson peak as an indicator of QCD phase transition in ultrarelativistic heavy ion collisions
In a previous paper, we have shown that a double phi peak structure appears
in the dilepton invariant mass spectrum if a first order QCD phase transition
occurs in ultrarelativistic heavy ion collisions. Furthermore, the transition
temperature can be determined from the transverse momentum distribution of the
low mass phi peak. In this work, we extend the study to the case that a smooth
crossover occurs in the quark-gluon plasma to the hadronic matter transition.
We find that the double phi peak structure still exists in the dilepton
spectrum and thus remains a viable signal for the formation of the quark-gluon
plasma in ultrarelativistic heavy ion collisions.Comment: 8 pages, 9 uuencoded postscript figures included, Latex, LBL-3572
Morphology of ledge patterns during step flow growth of metal surfaces vicinal to fcc(001)
The morphological development of step edge patterns in the presence of
meandering instability during step flow growth is studied by simulations and
numerical integration of a continuum model. It is demonstrated that the kink
Ehrlich-Schwoebel barrier responsible for the instability leads to an invariant
shape of the step profiles. The step morphologies change with increasing
coverage from a somewhat triangular shape to a more flat, invariant steady
state form. The average pattern shape extracted from the simulations is shown
to be in good agreement with that obtained from numerical integration of the
continuum theory.Comment: 4 pages, 4 figures, RevTeX 3, submitted to Phys. Rev.
Constructing a WISE High Resolution Galaxy Atlas
After eight months of continuous observations, the Wide-field Infrared Survey
Explorer (WISE) mapped the entire sky at 3.4 {\mu}m, 4.6 {\mu}m, 12 {\mu}m and
22 {\mu}m. We have begun a dedicated WISE High Resolution Galaxy Atlas (WHRGA)
project to fully characterize large, nearby galaxies and produce a legacy image
atlas and source catalogue. Here we summarize the deconvolution technique used
to significantly improve the spatial resolution of WISE imaging, specifically
designed to study the internal anatomy of nearby galaxies. As a case study, we
present results for the galaxy NGC 1566, comparing the WISE super-resolution
image processing to that of Spitzer, GALEX and ground-based imaging. The is the
first paper in a two part series; results for a much larger sample of nearby
galaxies is presented in the second paper.Comment: Published in the AJ (2012, AJ, 144, 68
Towards a more secure border control with 3D face recognition
Biometric data have been integrated in all ICAO compliant passports, since the ICAO members started to implement the ePassport standard. The additional use of three-dimensional models promises significant performance enhancements for border control points. By combining the geometry- and texture-channel information of the face, 3D face recognition systems show an improved robustness while processing variations in poses and problematic lighting conditions when taking the photo. This even holds in a hybrid scenario, when a 3D face scan is compared to a 2D reference image. To assess the potential of three-dimensional face recognition, the 3D Face project was initiated. This paper outlines the approach and research results of this project: The objective was not only to increase the recognition rate but also to develop a new, fake resistant capture device. In addition, methods for protection of the biometric template were researched and the second generation of the international standard ISO/IEC 19794-5:2011 was inspired by the project results
Diffusion processes and growth on stepped metal surfaces
We study the dynamics of adatoms in a model of vicinal (11m) fcc metal
surfaces. We examine the role of different diffusion mechanisms and their
implications to surface growth. In particular, we study the effect of steps and
kinks on adatom dynamics. We show that the existence of kinks is crucially
important for adatom motion along and across steps. Our results are in
agreement with recent experiments on Cu(100) and Cu(1,1,19) surfaces. The
results also suggest that for some metals exotic diffusion mechanisms may be
important for mass transport across the steps.Comment: 3 pages, revtex, complete file available from
ftp://rock.helsinki.fi/pub/preprints/tft/ or at
http://www.physics.helsinki.fi/tft/tft_preprints.html (to appear in Phys.
Rev. B Rapid Comm.
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AAPM medical physics practice guideline 10.a.: Scope of practice for clinical medical physics.
The American Association of Physicists in Medicine (AAPM) is a nonprofit professional society whose primary purposes are to advance the science, education, and professional practice of medical physics. The AAPM has more than 8000 members and is the principal organization of medical physicists in the United States. The AAPM will periodically define new practice guidelines for medical physics practice to help advance the science of medical physics and to improve the quality of service to patients throughout the United States. Existing medical physics practice guidelines will be reviewed for the purpose of revision or renewal, as appropriate, on their fifth anniversary or sooner. Each medical physics practice guideline (MPPG) represents a policy statement by the AAPM, has undergone a thorough consensus process in which it has been subjected to extensive review, and requires the approval of the Professional Council. The medical physics practice guidelines recognize that the safe and effective use of diagnostic and therapeutic radiation requires specific training, skills, and techniques as described in each document. As the review of the previous version of AAPM Professional Policy (PP)-17 (Scope of Practice) progressed, the writing group focused on one of the main goals: to have this document accepted by regulatory and accrediting bodies. After much discussion, it was decided that this goal would be better served through a MPPG. To further advance this goal, the text was updated to reflect the rationale and processes by which the activities in the scope of practice were identified and categorized. Lastly, the AAPM Professional Council believes that this document has benefitted from public comment which is part of the MPPG process but not the AAPM Professional Policy approval process. The following terms are used in the AAPM's MPPGs: Must and Must Not: Used to indicate that adherence to the recommendation is considered necessary to conform to this practice guideline. Should and Should Not: Used to indicate a prudent practice to which exceptions may occasionally be made in appropriate circumstances
The Longitudinal Polarimeter at HERA
The design, construction and operation of a Compton back-scattering laser
polarimeter at the HERA storage ring at DESY are described. The device measures
the longitudinal polarization of the electron beam between the spin rotators at
the HERMES experiment with a fractional systematic uncertainty of 1.6%. A
measurement of the beam polarization to an absolute statistical precision of
0.01 requires typically one minute when the device is operated in the
multi-photon mode. The polarimeter also measures the polarization of each
individual electron bunch to an absolute statistical precision of 0.06 in
approximately five minutes. It was found that colliding and non-colliding
bunches can have substantially different polarizations. This information is
important to the collider experiments H1 and ZEUS for their future
longitudinally polarized electron program because those experiments use the
colliding bunches only.Comment: 21 pages (Latex), 14 figures (EPS
Extinction law variations and dust excitation in the spiral galaxy NGC 300
We investigate the origin of the strong radial gradient in the
ultraviolet-to-infrared ratio in the spiral galaxy NGC 300, and emphasize the
importance of local variations in the interstellar medium geometry, concluding
that they cannot be neglected with respect to metallicity effects. This
analysis is based upon a combination of maps from GALEX and Spitzer, and from
the ground (UBVRI, Halpha and Hbeta). We select ionizing stellar clusters
associated with HII regions of widely varying morphologies, and derive their
fundamental parameters from population synthesis fitting of their spectral
energy distributions, measured to eliminate local backgrounds accurately. From
these fits, we conclude that the stellar extinction law is highly variable in
the line of sight of young clusters of similar ages. In the particular model
geometry that we consider most appropriate to the sampled regions, we checked
that our findings are not significantly altered by the correct treatment of
radiative transfer effects. The variations are systematic in nature: extinction
laws of the Milky Way or LMC type are associated with compact HII regions (the
compacity being quantified in two different ways), while clusters surrounded by
diffuse HII regions follow extinction laws of the 30 Doradus or SMC type. The
Calzetti starburst attenuation law, although most often degenerate with the 30
Doradus extinction law, overpredicts ionizing photon fluxes by large amounts.
We also find that the extinction law variations are correlated with the column
density of dust species emitting in the near- and mid-infrared. Finally, we
briefly discuss the nebular to stellar extinction ratios, and the excitation of
aromatic band carriers, invalidating their claimed association with cold dust.Comment: accepted for publication in ApJ -- figure 6 abridged her
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