788 research outputs found
Herschel-ATLAS: Dust temperature and redshift distribution of SPIRE and PACS detected sources using submillimetre colours
We present colourâcolour diagrams of detected sources in the Herschel-ATLAS science demonstration field from 100 to 500 ÎŒm using both PACS and SPIRE. We fit isothermal modified black bodies to the spectral energy distribution (SED) to extract the dust temperature of sources with counterparts in Galaxy And Mass Assembly (GAMA) or SDSS surveys with either a spectroscopic or a photometric redshift. For a subsample of 330 sources detected in at least three FIR bands with a significance greater than 3Ï, we find an average dust temperature of (28±8) K. For sources with no known redshift, we populate the colourâcolour diagram with a large number of SEDs generated with a broad range of dust temperatures and emissivity parameters, and compare to colours of observed sources to establish the redshift distribution of this sample. For another subsample of 1686 sources with fluxes above 35 mJy at 350 ÎŒm and detected at 250 and 500 ÎŒm with a significance greater than 3Ï, we find an average redshift of 2.2 ± 0.6
Lensing and Supernovae: Quantifying The Bias on the Dark Energy Equation of State
The gravitational magnification and demagnification of Type Ia supernovae
(SNe) modify their positions on the Hubble diagram, shifting the distance
estimates from the underlying luminosity-distance relation. This can introduce
a systematic uncertainty in the dark energy equation of state (EOS) estimated
from SNe, although this systematic is expected to average away for sufficiently
large data sets. Using mock SN samples over the redshift range
we quantify the lensing bias. We find that the bias on the dark energy EOS is
less than half a percent for large datasets ( 2,000 SNe). However, if
highly magnified events (SNe deviating by more than 2.5) are
systematically removed from the analysis, the bias increases to 0.8%.
Given that the EOS parameters measured from such a sample have a 1
uncertainty of 10%, the systematic bias related to lensing in SN data out to can be safely ignored in future cosmological measurements.Comment: 5 pages, 4 figures; one figure and references added; minor
modifications to text; reflects version accepted for publication in Ap
Hétérotrophie algale : effets de la gentamycine et de la cycloheximide sur les activités hétérotrophes et photosynthétiques des bacteries et des algues
Afin de tenter de dĂ©terminer les parts respectives des activitĂ©s bactĂ©rienne et algale, nous avons testĂ© d'une part, l'action d'une substance antibactĂ©rienne (la gentamycine), et d'autre part, l'action d'un inhibiteur mĂ©tabolique des cellules eucaryotes (la cycloheximide) sur des cultures d'algues et de bactĂ©ries et sur des Ă©chantillons provenant du milieu naturel et soumis Ă des filtrations diffĂ©rentielles. Les effets de ces inhibiteurs ont Ă©tĂ© testĂ©s au niveau des activitĂ©s hĂ©tĂ©rotrophe et photosynthĂ©tique globales, mais Ă©galement au niveau de l'incorporation des marqueurs radioactifs lors de la synthĂšse des macromolĂ©cules et des composĂ©s de faible poids molĂ©culaire.Les rĂ©sultats obtenus laissent apparaĂźtre que l'inhibition de l'activitĂ© bactĂ©rienne par la gentamyclne est significative mais non complĂšte (pourcentage d'inhibition moyen = 67 %). De plus, l'efficacitĂ© de la gentamycine augmente avec la durĂ©e d'incubation. Par ailleurs, les effets secondaires de la gentamycine sur les activitĂ©s hĂ©tĂ©rotrophe et photosynthĂ©tique d'une culture de Melosira italica subsp. subarctica sont acceptables seulement pour des incubations de courte durĂ©e (< 4 heures).En revanche, l'emploi de la cycloheximide s'est rĂ©vĂ©lĂ© sans aucun effet significatif sur les activitĂ©s photosynthĂ©tique et hĂ©rĂ©rotrophe de la culture de Melosira, mĂȘme aprĂšs 24 h d'incubation.A partir des Ă©chantillons prĂ©levĂ©s en milieu naturel, l'emploi de la gentamycine a permis de rĂ©duire l'interfĂ©rence bactĂ©rienne dans les mesures d'activitĂ© hĂ©tĂ©rotrophe algale. Enfin, nous avons pu constater que la gentamycine modifie l'allocation des marqueurs radioactifs dans les macromolĂ©cules.The ability of many planktonic algae to use particulate and/or dissolved organic carbon directly by phagotrophy or osmotrophy in laboratory cultures is well documented (DROOP, 1974; NEILSON and LEWIN, 1974; HELLEBUST and LEWIN, 1977; BIRD and KALFF, 1986). In axenic cultures, numerous microalgae grow in the dark with micromolar concentrations of diverse organic nutrients as their sole sources of carbon and energy (RIVKIN and PUTT, 1987). However, to demonstrate algal heterotrophy in the field, it is necessary to differentiate between bacterial and algal activities. In the course of this study, we tested the effect of an antibacterial substance (gentamycin) and of a metabolic inhibitor of eukaryotic cells (cycloheximide) on algal and bacterial cultures, and also on lake water samples submitted to differential filtration. The effect of these inhibitors was tested both at the overall heterotrophic and photosynthetic activities level and the level of the incorporation of radiolabeled tracers in macromolecules and low molecular weight compounds.Gentamycin was tested on bacteria and on an axenic culture of the diatom Melosira italica subsp. subarctica, the dominant species of the spring phyto-planktonic bloom of many temperate lakes. Bacterial culture was obtained by filtration of a senescent culture of Melosira through a 0.45 ”m pore-size membrane. During exponential growth, gentamycin (40 ”g.ml-1) was added to different flasks containing 100 ml of culture, 30 mn after gentamycin addition, Na H14CO3 (12”Ci/100 ml) was introduced into the flasks. In each case, two replicates were incubated in the light and two in the dark for 0.5, 1, 2, 4, 6, 8, 12 and 24 hours. After incubation, aliquots were collected on a filtration membrane (0.45 ”m) and the radioactivity was measured using an LKB liquid scintillation counter to estimate photosynthetic activity. Incorporation of inorganic carbon into macromolecules was measured using the procedure described by LANCELOT and MATHOT (1985), which allows the separation of lipids, polysaccharides, proteins and low molecular weight compounds (e.g. amino acids, organic acids and monosaccharides) by virtue of their relative solubilities in different extraction solvents :- lipids were extracted with a 2/1 (v/v) chloroform-methanol mixture;- low molecular weight compounds were extracted with hot ethanol;- proteins were precipated with TCA at elevated temperature; this also separated them from polysaccharides. Nucleic acids were recovered with the polysaccharides fraction. Results are given as a percentage of total radioactivity. The same method, as that described for photosynthetic incorporation, was used to measure incorporation of glucose 3H (19 nmoles.l-1) and for the allocation of radioactive marker in macromolecules. To assess the effect of cycloheximide, the same procedure as that described for gentamycin was used. However, due to the lack of references, three cycloheximide concentrations were tested = 50, 100 and 150 ”g.ml-1, and aliquots were collected on a 0.2 ”m pore-size membrane.Field samples were taken in Lake Pavin, an oligomesotrophic French lake, during the sedimentation of Melosira italica subsp. subarctica, the prevailing species of the spring bloom. The effects of gentamycin on photosynthetic and heterotrophic incorporations were tested with the came procedure as that described for cultures. However, radioactivity was measured for different size tractions : 0.2-0.45 ”m, 0.45-5 ”m and 5-160 ”m, after incubations for 0.5, 1, 3, 6, 12 and 24 hours. Phytoplanktonic cells were counted on a Wild M40 inverted microscope and bacterial enumeration was realized in epifluorescence microscopy after staining with acridine orange (HOBBIE el al., 1977).Results show that gentamycin used at 40 ”g.ml-1 inhibits significantly but not completely the activity of the bacterial culture (mean inhibition percent = 67 %). Gentamycin efficiency increases with incubation time, the inhibition reaching 81 % after 24 h. At the same time, the secondary effects of gentamycin on heterotrophic and photosynthetic activities of Melosira italica subsp. subarctica in culture were only tolerable with short incubation times (< 4 h), when the percents of inhibition were respectively 13.6 and 12.2%. On the other band, cycloheximide produced no significant effect on photosynthetic and heterotrophic activities of Melosira italica in culture, the percent of inhibition always remaining below 6.5 %.The use of gentamycin in natural samples reduced bacterial interference with algal heterotrophic activily measurements. The percent of inhibition caused by gentamycin was high (< 76 %) In the small-size fraction where the bacterial biomass predominate on the phytoplanktonic one.Lastly, in all samples, we could demonstrate that gentamycin modifies the allocation of inorganic carbon and radioactivity in macromolecules. The incorporation in proteins is significantly reduced essentially to benefit of the incorporation in low molecular weight compounds
Nonequilibrium phase transition in the coevolution of networks and opinions
Models of the convergence of opinion in social systems have been the subject
of a considerable amount of recent attention in the physics literature. These
models divide into two classes, those in which individuals form their beliefs
based on the opinions of their neighbors in a social network of personal
acquaintances, and those in which, conversely, network connections form between
individuals of similar beliefs. While both of these processes can give rise to
realistic levels of agreement between acquaintances, practical experience
suggests that opinion formation in the real world is not a result of one
process or the other, but a combination of the two. Here we present a simple
model of this combination, with a single parameter controlling the balance of
the two processes. We find that the model undergoes a continuous phase
transition as this parameter is varied, from a regime in which opinions are
arbitrarily diverse to one in which most individuals hold the same opinion. We
characterize the static and dynamical properties of this transition
CMB Constraints on Primordial non-Gaussianity from the Bispectrum (f_{NL}) and Trispectrum (g_{NL} and \tau_{NL}) and a New Consistency Test of Single-Field Inflation
We outline the expected constraints on non-Gaussianity from the cosmic
microwave background (CMB) with current and future experiments, focusing on
both the third (f_{NL}) and fourth-order (g_{NL} and \tau_{NL}) amplitudes of
the local configuration or non-Gaussianity. The experimental focus is the
skewness (two-to-one) and kurtosis (two-to-two and three-to-one) power spectra
from weighted maps. In adition to a measurement of \tau_{NL} and g_{NL} with
WMAP 5-year data, our study provides the first forecasts for future constraints
on g_{NL}. We describe how these statistics can be corrected for the mask and
cut-sky through a window function, bypassing the need to compute linear terms
that were introduced for the previous-generation non-Gaussianity statistics,
such as the skewness estimator. We discus the ratio A_{NL} =
\tau_{NL}/(6f_{NL}/5)^2 as an additional test of single-field inflationary
models and discuss the physical significance of each statistic. Using these
estimators with WMAP 5-Year V+W-band data out to l_{max}=600 we constrain the
cubic order non-Gaussianity parameters \tau_{NL}, and g_{NL} and find -7.4 <
g_{NL}/10^5 < 8.2 and -0.6 < \tau_{NL}/10^4 < 3.3 improving the previous
COBE-based limit on \tau_{NL} < 10^8 nearly four orders of magnitude with WMAP.Comment: 15 pages. 14 figure
Amplitudes of thermal and kinetic Sunyaev-Zel'dovich signals from small-scale CMB anisotropies
While the arcminute-scale Cosmic Microwave Background (CMB) anisotropies are
due to secondary effects, point sources dominate the total anisotropy power
spectrum. At high frequencies the point sources are primarily in the form of
dusty, star-forming galaxies. Both Herschel and Planck have recently measured
the anisotropy power spectrum of cosmic infrared background (CIB) generated by
dusty, star-forming galaxies from degree to sub-arcminute angular scales,
including the non-linear clustering of these galaxies at multipoles of 3000 to
6000 relevant to CMB secondary anisotropy studies. We scale the CIB angular
power spectra to CMB frequencies and interpret the combined WMAP-7 year and
arcminute-scale Atacama Cosmology Telescope (ACT) and South Pole Telescope
(SPT) CMB power spectra measurements to constrain the Sunyaev-Zel'dovich (SZ)
effects. Allowing the CIB clustering amplitude to vary, we constrain the
amplitudes of thermal and kinetic SZ power spectra at 150 GHz.Comment: 8 pages, 3 figures, 2 table
CLC, a promising concept with challenging development issues
Chemical Looping Combustion (CLC) is a promising technique to achieve fuel combustion in a nitrogen free atmosphere, therefore giving the possibility to separate and store or use CO2. Several potential applications are considered in the field of power generation with gas, liquid and solid fuels. In the Carbon Capture, Storage and Utilization (CCSU) context, energy penalty is reduced compared to other routes. In addition, other applications of Chemical Looping are considered in the field of H2 production or gasification for instance.
In the past years, a huge effort has been conducted worldwide to investigate CLC materials and process issues. In 2008, IFPEN and Total have started an ambitious collaboration to develop CLC applications. Nowadays, the CLC concept is well demonstrated at the pilot scale. The next step is to demonstrate the technology over time at larger scale. However, for further developments, the challenges are numerous and will be discussed, both on market and technical aspects. Short term market is limited. Uncertainties around CO2 emission market and storage issues are related to CO2 policy and public acceptance of storage which still must evolve in the right direction... Financing of demonstration units in this context is challenging and other applications of CLC have to be investigated. The industrial use of synthetic metal oxides or natural ores at large scale generates a lot of issues related to availability, price, waste disposal, health and safety, additionally to chemical and mechanical stability over time, reactivity, and oxygen transfer capacity. Chemical looping reactor and process technology concepts have to be explored, developed, modeled and scaled-up in order to ensure adequate power production together with good gas solid contact and reaction requirement, controlled circulation of mixtures of particle (oxygen carrier, ash, solid fuel for instance). All these points should be considered at very large scale for CCS applications in order to minimize energy penalty and cost in severe operating conditions (temperatures above 800°C and intense solid circulation).
Technical challenges remain to be solved and proven with large demonstration over long periods of time. In this context, research in the field of fluidization technology is essential and we will address a couple of key points already investigated at IFPEN and related to control of solid circulation, oxygen carrier attrition, conceptual design of CLC reactors and process performance
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