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An experimental study of polymer electrolyte fuel cell operation at sub-freezing temperatures
The ability of polymer electrolyte fuel cells (PEFCs) to startup at subfreezing temperatures is governed by whether it is able to overcome the freezing point (0°C) before product ice prevents the electrochemical reactions. In this work, we experimentally investigated the coulombs of charge Qc transferred in PEFCs under subfreezing operation before the output voltage drops to 0.0V. PEFCs with various membranes and catalyst-layer thicknesses, ionomer-carbon ratios, operating current density, and initial hydration of PEFCs were studied, and their influences on cold-start performance and coulombs of charge were experimentally measured. We find that subfreezing temperature, ionomer-catalyst ratio, and catalyst-layer thickness, significantly affect the amount of charge transferred before operational failure, whereas the membrane thickness and initial hydration level have limited effect for the considered cases. © 2013 The Electrochemical Society
The economics of garbage collection
This paper argues that economic theory can improve our understanding of memory management. We introduce the allocation curve, as an analogue of the demand curve from microeconomics. An allocation curve for a program characterises how the amount of garbage collection activity required during its execution varies in relation to the heap size associated with that program. The standard treatment of microeconomic demand curves (shifts and elasticity) can be applied directly and intuitively to our new allocation curves. As an application of this new theory, we show how allocation elasticity can be used to control the heap growth rate for variable sized heaps in Jikes RVM
Use of neural networks for the identification of new z>=3.6 QSOs from FIRST-SDSS DR5
We aim to obtain a complete sample of redshift > 3.6 radio QSOs from FIRST
sources having star-like counterparts in the SDSS DR5 photometric survey
(r<=20.2). We found that simple supervised neural networks, trained on sources
with SDSS spectra, and using optical photometry and radio data, are very
effective for identifying high-z QSOs without spectra. The technique yields a
completeness of 96 per cent and an efficiency of 62 per cent. Applying the
trained networks to 4415 sources without DR5 spectra we found 58 z>=3.6 QSO
candidates. We obtained spectra of 27 of them, and 17 are confirmed as high-z
QSOs. Spectra of 13 additional candidates from the literature and from SDSS DR6
revealed 7 more z>=3.6 QSOs, giving and overall efficiency of 60 per cent. None
of the non-candidates with spectra from NED or DR6 is a z>=3.6 QSO,
consistently with a high completeness. The initial sample of z>=3.6 QSOs is
increased from 52 to 76, i.e. by a factor 1.46. From the new identifications
and candidates we estimate an incompleteness of SDSS for the spectroscopic
classification of FIRST 3.6<=z<=4.6 QSOs of 15 percent for r<=20.2.Comment: 16 pages, 9 figures accepted for publication in MNRA
Home Page: The Mode of Transport through the Information Superhighway
The purpose of the project with the Aeroacoustics Branch was to create and submit a home page for the internet about branch information. In order to do this, one must also become familiar with the way that the internet operates. Learning HyperText Markup Language (HTML), and the ability to create a document using this language was the final objective in order to place a home page on the internet (World Wide Web). A manual of instructions regarding maintenance of the home page, and how to keep it up to date was also necessary in order to provide branch members with the opportunity to make any pertinent changes
Solving the solar neutrino problem with kamLAND and BOREXINO
We analyze the expected signals of two future neutrino experiments, kamLAND
and BOREXINO. We show that with just these experiments, we will hopefully be
able to determine which of the existing solutions to the solar neutrino problem
is the real solution. We also analyze existing solar neutrino data and
determine the best-fit points in the oscillation-parameter space finding that
with the inclusion of SNO-charged current, the global-rates analysis gives a
favored LMA solution with a goodness of fit (g.o.f) of just 32.63%, whereas the
g.o.f of the SMA solution is 9.83%. Nonetheless, maximal and quasi-maximal
mixing is not favored. If we include the Superkamiokande spectrum in our \chi^2
analysis, we obtain a LMA solution with a g.o.f. of 84.38%.Comment: 4 pages, 5 figures, Talk given at 37th Rencontres de Moriond on
Electroweak Interactions and Unified Theories, Les Arcs, France, 9-16 Mar
200
The solar neutrino puzzle: present situation and future scenarios
We present a short review of the existing evidence in favor of neutrino mass
and neutrino oscillations which come from different kinds of experiments. We
focus our attention in particular on solar neutrinos, presenting a global
updated phenomenological analysis of all the available data and we comment on
different possible future scenarios.Comment: 22 pp. Expanded version of the contribution to appear in the
Proceedings of ``Les Rencontres de Physique de la Vallee d'Aoste'', February
200
After Sno and Before Kamland: Present and Future of Solar and Reactor Neutrino Physics
We present a short review of the existing evidence in favor of neutrino mass
and neutrino oscillations which come from different kinds of experiments. We
focus our attention in particular on solar neutrinos, presenting a review of
some recent analysis of all available neutrino oscillation evidence in Solar
experiments including the recent and data. We present in detail
the power of the reactor experiment KamLAND for discriminating existing
solutions to the SNP and giving accurate information on neutrino masses and
mixing angles.Comment: Expanded version of the contribution to appear in the Proceedings of
''Third Tropical Workshop on Particle Physics and Cosmology: Neutrinos,
Branes and Cosmology (Puerto Rico, August 2002)'
A model for fermion masses and lepton mixing in SO(10) x A4
The discrete flavor symmetry A4 explains very well neutrino data at low
energy, but it seems difficult to extend it to grand unified models since in
general left-handed and right-handed fields belong to different A4
representations. Recently it has been proposed a model where all the fermions
equally transform under A4. We study here a concrete SO(10) realization of such
a model providing small neutrino masses through the seesaw mechanism. We fit at
tree level the charged fermion masses run up to the unification scale. Some
fermion masses properties come from the SO(10) symmetry while lepton mixing
angles are consequence of the A4 properties. Moreover, our model predicts the
absolute value of the neutrino masses, these ones are in the range .Comment: 15 pages. V2: Final version to appear in the journa
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