3,322 research outputs found
Experimental study on a metal hydride based hydrogen compressor
This is the post-print version of the final paper published in Journal of Alloys and Compounds. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2008 Elsevier B.V.A three-stage metal hydride based hydrogen compressor prototype was built. It has been designed for a hydrogen production facility using a low-pressure alkaline electrolyser. The compression system should transfer heat recovered from the electrolyser into the hydride beds to allow hydrogen desorption flow. The three-stage compressor achieves a compression ratio of 20:1 atm. It performs a thermal cycling of three AB5 hydrides between 20 and 80 °C. Its flow rate, for 25 g of each hydride bed, reaches about 20 l (NTP) of hydrogen per hour. The prototype is now operational. Some improvements in the heat transfer management system are also carried out before proceeding to the interconnection with the electrolyser and to the extent that the hydrogen produced satisfies the high purity requirement of the hydrides used in the compressor.Natural Resources Canada(NRCan), Ministère des Ressources Naturelles
et de la Faune du Québec (MRNF), and Natural Sciences and Engineering Research Council of Canada
Nonperturbative structure of the quark-gluon vertex
The complete tensor structure of the quark--gluon vertex in Landau gauge is
determined at two kinematical points (`asymmetric' and `symmetric') from
lattice QCD in the quenched approximation. The simulations are carried out at
beta=6.0, using a mean-field improved Sheikholeslami-Wohlert fermion action,
with two quark masses ~ 60 and 115 MeV. We find substantial deviations from the
abelian form at the asymmetric point. The mass dependence is found to be
negligible. At the symmetric point, the form factor related to the
chromomagnetic moment is determined and found to contribute significantly to
the infrared interaction strength.Comment: 16 pages, 11 figures, JHEP3.cl
Primordial magnetic fields and the HI signal from the epoch of reionization
The implication of primordial magnetic-field-induced structure formation for
the HI signal from the epoch of reionization is studied. Using semi-analytic
models, we compute both the density and ionization inhomogeneities in this
scenario. We show that: (a) The global HI signal can only be seen in emission,
unlike in the standard CDM models, (b) the density perturbations
induced by primordial fields, leave distinctive signatures of the magnetic
field Jeans' length on the HI two-point correlation function, (c) the length
scale of ionization inhomogeneities is \la 1 \rm Mpc. We find that the peak
expected signal (two-point correlation function) is in
the range of scales for magnetic field strength in the
range . We also discuss the
detectability of the HI signal. The angular resolution of the on-going and
planned radio interferometers allows one to probe only the largest magnetic
field strengths that we consider. They have the sensitivity to detect the
magnetic field-induced features. We show that thefuture SKA has both the
angular resolution and the sensitivity to detect the magnetic field-induced
signal in the entire range of magnetic field values we consider, in an
integration time of one week.Comment: 19 pages, 5 figures, to appear in JCA
Specification and Verification of Media Constraints using UPPAAL
We present the formal specification and verification of a multimedia stream. The stream is described in a timed automata notation. We verify that the stream satisfies certain quality of service properties, in particular, throughput and end-to-end latency. The verification tool used is the real-time model checker UPPAAL
NASA Constellation Distributed Simulation Middleware Trade Study
This paper presents the results of a trade study designed to assess three distributed simulation middleware technologies for support of the NASA Constellation Distributed Space Exploration Simulation (DSES) project and Test and Verification Distributed System Integration Laboratory (DSIL). The technologies are the High Level Architecture (HLA), the Test and Training Enabling Architecture (TENA), and an XML-based variant of Distributed Interactive Simulation (DIS-XML) coupled with the Extensible Messaging and Presence Protocol (XMPP). According to the criteria and weights determined in this study, HLA scores better than the other two for DSES as well as the DSIL
An Overview of the Distributed Space Exploration Simulation (DSES) Project
This paper describes the Distributed Space Exploration Simulation (DSES) Project, a research and development collaboration between NASA centers which investigates technologies, and processes related to integrated, distributed simulation of complex space systems in support of NASA's Exploration Initiative. In particular, it describes the three major components of DSES: network infrastructure, software infrastructure and simulation development. With regard to network infrastructure, DSES is developing a Distributed Simulation Network for use by all NASA centers. With regard to software, DSES is developing software models, tools and procedures that streamline distributed simulation development and provide an interoperable infrastructure for agency-wide integrated simulation. Finally, with regard to simulation development, DSES is developing an integrated end-to-end simulation capability to support NASA development of new exploration spacecraft and missions. This paper presents the current status and plans for these three areas, including examples of specific simulations
The Distributed Space Exploration Simulation (DSES)
The paper describes the Distributed Space Exploration Simulation (DSES) Project, a research and development collaboration between NASA centers which focuses on the investigation and development of technologies, processes and integrated simulations related to the collaborative distributed simulation of complex space systems in support of NASA's Exploration Initiative. This paper describes the three major components of DSES: network infrastructure, software infrastructure and simulation development. In the network work area, DSES is developing a Distributed Simulation Network that will provide agency wide support for distributed simulation between all NASA centers. In the software work area, DSES is developing a collection of software models, tool and procedures that ease the burden of developing distributed simulations and provides a consistent interoperability infrastructure for agency wide participation in integrated simulation. Finally, for simulation development, DSES is developing an integrated end-to-end simulation capability to support NASA development of new exploration spacecraft and missions. This paper will present current status and plans for each of these work areas with specific examples of simulations that support NASA's exploration initiatives
Measuring Dust Attenuation Curves of SINGS/KINGFISH Galaxies Using Swift/UVOT Photometry
We present Swift/Ultraviolet Optical Telescope (UVOT) integrated light
photometry of the Spitzer Infrared Nearby Galaxies Survey (SINGS) and the Key
Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel (KINGFISH)
samples of nearby galaxies. Combining the Swift/UVOT data with archival
photometry, we investigate a variety of dust attenuation curves derived using
MCSED, a flexible spectral energy distribution fitting code. We fit the
panchromatic data using three different star formation history (SFH)
parameterizations: a decaying exponential, a double power law, and a piecewise
function with breaks at physically motivated ages. We find that the average
attenuation law of the sample changes slightly based on the SFH assumed.
Specifically, the exponential SFH leads to the shallowest attenuation curves.
Using simulated data, we also find the exponential SFH fails to outperform the
more complex SFHs. Finally, we find a systematic offset in the derived bump
strength between SED fits with and without UVOT data, where the inclusion of
UVOT data leads to smaller bump strengths, highlighting the importance of the
UVOT data. This discrepancy is not seen in fits to mock photometry.
Understanding dust attenuation in the local universe is key to understanding
high redshift objects where rest-frame far-infrared data is unavailable.Comment: 30 pages, 13 figures, accepted for publication in Ap
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