205 research outputs found
Reducing variability in the cost of energy of ocean energy arrays
Variability in the predicted cost of energy of an ocean energy converter array is more substantial than for other forms of energy generation, due to the combined stochastic action of weather conditions and failures. If the variability is great enough, then this may influence future financial decisions. This paper provides the unique contribution of quantifying variability in the predicted cost of energy and introduces a framework for investigating reduction of variability through investment in components. Following review of existing methodologies for parametric analysis of ocean energy array design, the development of the DTOcean software tool is presented. DTOcean can quantify variability by simulating the design, deployment and operation of arrays with higher complexity than previous models, designing sub-systems at component level. A case study of a theoretical floating wave energy converter array is used to demonstrate that the variability in levelised cost of energy (LCOE) can be greatest for the smallest arrays and that investment in improved component reliability can reduce both the variability and most likely value of LCOE. A hypothetical study of improved electrical cables and connectors shows reductions in LCOE up to 2.51% and reductions in the variability of LCOE of over 50%; these minima occur for different combinations of components.The research leading to this publication is part of the DTOceanPlus project which has received funding from the EuropeanUnion's Horizon 2020 research and innovation programme under grant agreement No 785921. Funding was also received from the European Community's Seventh Framework Programme for the DTOcean Project (grant agreement No. 608597). The contribution of Sandia National Laboratories was funded by the U.S. Department of Energy's Water Power Technologies Office. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government. The image of the RM3 device, in Fig. 7, was reproduced with the permission of Sandia National Laboratorie
Organic nitrate aerosol formation via NOÂł + biogenic volatile organic compounds in the southeastern United States
Gas- and aerosol-phase measurements of oxidants, biogenic volatile organic compounds (BVOCs) and organic nitrates made during the Southern Oxidant and Aerosol Study (SOAS campaign, Summer 2013) in central Alabama show that a nitrate radical (NOâ) reaction with monoterpenes leads to significant secondary aerosol formation. Cumulative losses of NOâ to terpenes are correlated with increase in gasand aerosol-organic nitrate concentrations made during the campaign. Correlation of NOâ radical consumption to organic nitrate aerosol formation as measured by aerosol mass spectrometry and thermal dissociation laser-induced fluorescence suggests a molar yield of aerosol-phase monoterpene nitrates of 23â44 %. Compounds observed via chemical ionization mass spectrometry (CIMS) are correlated to predicted nitrate loss to BVOCs and show CââHââNOâ
, likely a hydroperoxy nitrate, is a major nitrate-oxidized terpene product being incorporated into aerosols. The comparable isoprene product Câ
HâNOâ
was observed to contribute less than 1% of the total organic nitrate in the aerosol phase and correlations show that it is principally a gas-phase product from nitrate oxidation of isoprene. Organic nitrates comprise between 30 and 45% of the NOy budget during SOAS. Inorganic nitrates were also monitored and showed that during incidents of increased coarse-mode mineral dust, HNOâ uptake produced nitrate aerosol mass loading at a rate comparable to that of organic nitrate produced via NOâ CBVOCs
The Ekpyrotic Universe: Colliding Branes and the Origin of the Hot Big Bang
We propose a cosmological scenario in which the hot big bang universe is
produced by the collision of a brane in the bulk space with a bounding orbifold
plane, beginning from an otherwise cold, vacuous, static universe. The model
addresses the cosmological horizon, flatness and monopole problems and
generates a nearly scale-invariant spectrum of density perturbations without
invoking superluminal expansion (inflation). The scenario relies, instead, on
physical phenomena that arise naturally in theories based on extra dimensions
and branes. As an example, we present our scenario predominantly within the
context of heterotic M-theory. A prediction that distinguishes this scenario
from standard inflationary cosmology is a strongly blue gravitational wave
spectrum, which has consequences for microwave background polarization
experiments and gravitational wave detectors.Comment: 67 pages, 4 figures. v2,v3: minor corrections, references adde
Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV
A search for a Higgs boson decaying into two photons is described. The
analysis is performed using a dataset recorded by the CMS experiment at the LHC
from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an
integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross
section of the standard model Higgs boson decaying to two photons. The expected
exclusion limit at 95% confidence level is between 1.4 and 2.4 times the
standard model cross section in the mass range between 110 and 150 GeV. The
analysis of the data excludes, at 95% confidence level, the standard model
Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The
largest excess of events above the expected standard model background is
observed for a Higgs boson mass hypothesis of 124 GeV with a local significance
of 3.1 sigma. The global significance of observing an excess with a local
significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is
estimated to be 1.8 sigma. More data are required to ascertain the origin of
this excess.Comment: Submitted to Physics Letters
Measurement of isolated photon production in pp and PbPb collisions at sqrt(sNN) = 2.76 TeV
Isolated photon production is measured in proton-proton and lead-lead
collisions at nucleon-nucleon centre-of-mass energies of 2.76 TeV in the
pseudorapidity range |eta|<1.44 and transverse energies ET between 20 and 80
GeV with the CMS detector at the LHC. The measured ET spectra are found to be
in good agreement with next-to-leading-order perturbative QCD predictions. The
ratio of PbPb to pp isolated photon ET-differential yields, scaled by the
number of incoherent nucleon-nucleon collisions, is consistent with unity for
all PbPb reaction centralities.Comment: Submitted to Physics Letters
Closed-Form transformation between geodetic and ellipsoidal coordinates
We present formulas for direct closed-form transformation between geodetic coordinates(Ό, Ν, h) and ellipsoidal coordinates (β, Ν, u) for any oblate ellipsoid of revolution.These will be useful for those dealing with ellipsoidal representations of the Earth's gravityfield or other oblate ellipsoidal figures. The numerical stability of the transformations for nearpolarand near-equatorial regions is also considered
Oscillatory activity in prefrontal and posterior regions during implicit letter-location binding.
Many cognitive abilities involve the integration of information from different modalities, a process referred to as âbinding.â It remains less clear, however, whether the creation of bound representations occurs in an involuntary manner, and whether the links between the constituent features of an object are symmetrical. We used magnetoencephalography to investigate whether oscillatory brain activity related to binding processes would be observed in conditions in which participants maintain one feature only (involuntary binding); and whether this activity varies as a function of the feature attended to by participants (binding asymmetry). Participants performed two probe recognition tasks that were identical in terms of their perceptual characteristics and only differed with respect to the instructions given (to memorize either consonants or locations). MEG data were reconstructed using a current source distribution estimation in the classical frequency bands. We observed implicit verbalâspatial binding only when participants successfully maintained the identity of consonants, which was associated with a selective increase in oscillatory activity over prefrontal regions in all frequency bands during the first half of the retention period and accompanied by increased activity in posterior brain regions. The increase in oscillatory activity in prefrontal areas was only observed during the verbal task, which suggests that this activity might be signaling neural processes specifically involved in cross-code binding. Current results are in agreement with proposals suggesting that the prefrontal cortex function as a âpointerâ which indexes the features that belong together within an object
Tides in colliding galaxies
Long tails and streams of stars are the most noticeable upshots of galaxy
collisions. Their origin as gravitational, tidal, disturbances has however been
recognized only less than fifty years ago and more than ten years after their
first observations. This Review describes how the idea of galactic tides
emerged, in particular thanks to the advances in numerical simulations, from
the first ones that included tens of particles to the most sophisticated ones
with tens of millions of them and state-of-the-art hydrodynamical
prescriptions. Theoretical aspects pertaining to the formation of tidal tails
are then presented. The third part of the review turns to observations and
underlines the need for collecting deep multi-wavelength data to tackle the
variety of physical processes exhibited by collisional debris. Tidal tails are
not just stellar structures, but turn out to contain all the components usually
found in galactic disks, in particular atomic / molecular gas and dust. They
host star-forming complexes and are able to form star-clusters or even
second-generation dwarf galaxies. The final part of the review discusses what
tidal tails can tell us (or not) about the structure and content of present-day
galaxies, including their dark components, and explains how tidal tails may be
used to probe the past evolution of galaxies and their mass assembly history.
On-going deep wide-field surveys disclose many new low-surface brightness
structures in the nearby Universe, offering great opportunities for attempting
galactic archeology with tidal tails.Comment: 46 pages, 13 figures, Review to be published in "Tidal effects in
Astronomy and Astrophysics", Lecture Notes in Physics. Comments are most
welcom
Studies of jet quenching using isolated-photon + jet correlations in PbPb and pp collisions at sqrt(s[NN]) = 2.76 TeV
Results from the first study of isolated-photon + jet correlations in
relativistic heavy ion collisions are reported. The analysis uses data from
PbPb collisions at a centre-of-mass energy of 2.76 TeV per nucleon pair
corresponding to an integrated luminosity of 150 inverse microbarns recorded by
the CMS experiment at the LHC. For events containing an isolated photon with
transverse momentum pt(gamma) > 60 GeV and an associated jet with pt(Jet) > 30
GeV, the photon + jet pt imbalance is studied as a function of collision
centrality and compared to pp data and PYTHIA calculations at the same
collision energy. Using the pt(gamma) of the isolated photon as an estimate of
the momentum of the associated parton at production, this measurement allows an
unbiased characterisation of the in-medium parton energy loss. For more central
PbPb collisions, a significant decrease in the ratio pt(Jet)/pt(gamma) relative
to that in the PYTHIA reference is observed. Furthermore, significantly more
pt(gamma) > 60 GeV photons in PbPb are observed not to have an associated
pt(Jet) > 30 GeV jet, compared to the reference. However, no significant
broadening of the photon + jet azimuthal correlation is observed.Comment: Submitted to Physics Letters
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