330 research outputs found
Oxygen Generation from Carbon Dioxide for Advanced Life Support
The partial electrochemical reduction of CO2 using ceramic oxygen generators (COGs) is well known and has been studied. Conventional COGs use yttria-stabilized zirconia (YSZ) electrolytes and operate at temperatures greater than 700 C (1, 2). Operating at a lower temperature has the advantage of reducing the mass of the ancillary components such as insulation. Moreover, complete reduction of metabolically produced CO2 (into carbon and oxygen) has the potential of reducing oxygen storage weight if the oxygen can be recovered. Recently, the University of Florida developed ceramic oxygen generators employing a bilayer electrolyte of gadolinia-doped ceria and erbia-stabilized bismuth oxide (ESB) for NASA s future exploration of Mars (3). The results showed that oxygen could be reliably produced from CO2 at temperatures as low as 400 C. These results indicate that this technology could be adapted to CO2 removal from a spacesuit and other applications in which CO2 removal is an issue. This strategy for CO2 removal in advanced life support systems employs a catalytic layer combined with a COG so that the CO2 is reduced completely to solid carbon and oxygen. First, to reduce the COG operating temperature, a thin, bilayer electrolyte was employed. Second, to promote full CO2 reduction while avoiding the problem of carbon deposition on the COG cathode, a catalytic carbon deposition layer was designed and the cathode utilized materials shown to be coke resistant. Third, a composite anode was used consisting of bismuth ruthenate (BRO) and ESB that has been shown to have high performance (4). The inset of figure 1 shows the conceptual design of the tubular COG and the rest of the figure shows schematically the test apparatus. Figure 2 shows the microstructure of a COG tube prior to testing. During testing, current is applied across the cell and initially CuO is reduced to copper metal by electrochemical pumping. Then the oxygen source becomes the CO/CO2. This presentation details the results of testing the COG
Contributions from SUSY-FCNC couplings to the interpretation of the HyperCP events for the decay \Sigma^+ \to p \mu^+ \mu^-
The observation of three events for the decay
with a dimuon invariant mass of MeV by the HyperCP collaboration
imply that a new particle X may be needed to explain the observed dimuon
invariant mass distribution. We show that there are regions in the SUSY-FCNC
parameter space where the in the NMSSM can be used to explain the
HyperCP events without contradicting all the existing constraints from the
measurements of the kaon decays, and the constraints from the
mixing are automatically satisfied once the constraints from kaon decays are
satisfied.Comment: 18 pages, 7 figure
Light Neutralinos in B-Decays
We consider the decays of a -meson into a pair of lightest
supersymmetric particles (LSP) in the minimal supersymmetric standard model. It
is found that the parameter space for light LSP's in the range of 1 GeV can be
appreciably constrained by looking for such decays.Comment: 9 pages, LaTex, 2 figures (hard copies of the figures available from
the Authors on request
Sparticle Mass Spectra from SO(10) Grand Unified Models with Yukawa Coupling Unification
We examine the spectrum of superparticles obtained from the minimal SO(10)
grand unified model, where it is assumed the gauge symmetry breaking yields the
Minimal Supersymmetric Standard Model (MSSM) as the effective theory at
GeV. In this model, unification of Yukawa
couplings implies a value of . At such high values of
, assuming universality of scalar masses, the usual mechanism of
radiative electroweak symmetry breaking breaks down. We show that a set of weak
scale sparticle masses consistent with radiative electroweak symmetry breaking
can be generated by imposing non-universal GUT scale scalar masses consistent
with universality within SO(10) plus extra -term contributions associated
with the reduction in rank of the gauge symmetry group when SO(10)
spontaneously breaks to . We comment upon the
consequences of the sparticle mass spectrum for collider searches for
supersymmetry. One implication of SO(10) unification is that the light bottom
squark can be by far the lightest of the squarks. This motivates a dedicated
search for bottom squark pair production at and colliders.Comment: 12 page REVTEX file including 3 PS figures; revised manuscript
includes minor changes to coincide with published versio
Constraining the CKM Parameters using CP Violation in semi-leptonic B Decays
We discuss the usefulness of the CP violating semi-leptonic asymmetry a_{SL}
not only as a signal of new physics, but also as a tool in constraining the CKM
parameters. We show that this technique could yield useful results in the first
years of running at the B factories. We present the analysis graphically in
terms of M_{12}, the dispersive part of the B-Bbar mixing amplitude. This is
complementary to the usual unitarity triangle representation and often allows a
cleaner interpretation of the data.Comment: 15 pages REVTEX, 7 figure
Sparticle Spectrum Constraints
The supersymmetric standard model with supergravity-inspired soft breaking
terms predicts a rich pectrum of sparticles to be discovered at the SSC, LHC
and NLC. Because there are more supersymmetric particles than unknown
parameters, one can write down sum rules relating their masses. We discuss the
pectrum of sparticles from this point of view. Some of the sum rules do not
depend on the input parameters and can be used to test the consistency of the
model, while others are useful in determining the input parameters of the
theory. If supersymmetry is discovered but the sum rules turn out to be
violated, it will be evidence of new physics beyond the minimal supersymmetric
standard model with universal soft supersymmetry-breaking terms.Comment: 25 pages. NUB-3067-93TH, UFIFT-HEP-93-16, SSCL-Preprint-439, June
199
Sneutrino-induced like sign dilepton signal with conserved R-parity
Lepton number violation could be manifest in the sneutrino sector of
supersymmetric extensions of the standard model with conserved R-parity. Then
sneutrinos decay partly into the ``wrong sign charged lepton'' final state, if
kinematically accessible. In sneutrino pair production or associated single
sneutrino production, the signal then is a like sign dilepton final state.
Under favourable circumstances, such a signal could be visible at the LHC or a
next generation linear collider for a relative sneutrino mass-splitting of
order and sneutrino width of order (1 GeV). On the
other hand, the like sign dilepton event rate at the TEVATRON is probably too
small to be observable.Comment: 19 pages, 14 Figures. Section about LSD at LHC and TEVATRON added.
Previous Title "Single sneutrino production and the wrong charged lepton
signal
Re-calibrated Generalized-Scidar measurements at Cerro Paranal (VLT's site)
Generalized Scidar (GS) measurements taken at the Paranal Observatory in
November/December 2007 in the context of a site qualification for the future
European Extremely Large Telescope E-ELT are re-calibrated to overcome the bias
induced on the CN2 profiles by a not correct normalization of the
autocorrelation of the scintillation maps that has been recently identified in
the GS technique. A complete analysis of the GS corrected measurements as well
as of the corrected errors is performed statistically as well as on individual
nights and for each time during all nights. The relative errors of the CN2
profiles can reach up to 60% in some narrow temporal windows and some vertical
slabs, the total seeing up to 12% and the total integrated turbulence J up to
21%. However, the statistic analysis tells us that the absolute errors of the
median values of the total seeing is 0.06 arcsec (relative error 5.6%), for the
boundary seeing 0.05 arcsec (relative error 5.6%) and for the seeing in the
free atmosphere 0.04 arcsec (relative error 9%). We find that, in spite of the
fact that the relative error increases with the height, the boundary and the
free atmosphere seeing contribute in an equivalent way to the error on the
total seeing in absolute terms. Besides, we find that there are no correlations
between the relative errors and the value of the correspondent seeing. The
absolute error of the median value of the isoplanatic angle is 0.13 arcsec
(relative error 6.9%).Comment: 22 figures, MNRAS accepte
Eternal annihilations of light photinos
In a class of low-energy supersymmetry models the photino is a natural dark
matter candidate. We investigate the effects of post-freeze-out photino
annihilations which can generate electromognetic cascades and lead to
photo-destruction of He and subsequent overproduction of D and He. We
also generalize our analysis to a generic dark matter component whose relic
abundance is {\it not} determined by the cross section of the
self-annihilations giving rise to electromagnetic showers.Comment: 13 page LaTeX file (no figures
LIGHT PHOTINOS AS DARK MATTER
There are good reasons to consider models of low-energy supersymmetry with
very light photinos and gluinos. In a wide class of models the lightest
-odd, color-singlet state containing a gluino, the , has a mass in the
1-2 GeV range and the slightly lighter photino, \pho, would survive as the
relic -odd species. For the light photino masses considered here, previous
calculations resulted in an unacceptable photino relic abundance. But we point
out that processes other than photino self-annihilation determine the relic
abundance when the photino and are close in mass. Including
\r0\longleftrightarrow\pho processes, we find that the photino relic
abundance is most sensitive to the -to-\pho mass ratio, and within model
uncertainties, a critical density in photinos may be obtained for an
-to-\pho mass ratio in the range 1.2 to 2.2. We propose photinos in the
mass range of 500 MeV to 1.6 GeV as a dark matter candidate, and discuss a
strategy to test the hypothesis.Comment: uuencoded compressed tar file containing 32 page LaTeX file and eight
postscript figure
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