| 1. |
- Pierre, M., et al.
(författare)
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The XXL survey : First results and future
- 2017
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Ingår i: Astronomical Notes - Astronomische Nachrichten. - : Wiley-VCH Verlagsgesellschaft. - 0004-6337 .- 1521-3994. ; 338:2-3, s. 334-341
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Tidskriftsartikel (refereegranskat)abstract
- The XXL survey currently covers two 25 deg(2) patches with XMM observations of similar to 10 ks. We summarize the scientific results associated with the first release of the XXL dataset, which occurred in mid-2016. We review several arguments for increasing the survey depth to 40 ks during the next decade of XMM operations. X-ray (z < 2) cluster, (z < 4) active galactic nuclei (AGN), and cosmic background survey science will then benefit from an extraordinary data reservoir. This, combined with deep multi-lambda observations, will lead to solid standalone cosmological constraints and provide a wealth of information on the formation and evolution of AGN, clusters, and the X-ray background. In particular, it will offer a unique opportunity to pinpoint the z > 1 cluster density. It will eventually constitute a reference study and an ideal calibration field for the upcoming eROSITA and Euclid missions.
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| 2. |
- Farahi, A., et al.
(författare)
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Mass variance from archival X-ray properties of Dark Energy Survey Year-1 galaxy clusters
- 2019
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Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966. ; 490:3, s. 3341-3354
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Tidskriftsartikel (refereegranskat)abstract
- Using archival X-ray observations and a lognormal population model, we estimate constraints on the intrinsic scatter in halo mass at fixed optical richness for a galaxy cluster sample identified in Dark Energy Survey Year-One (DES-Y1) data with the redMaPPer algorithm. We examine the scaling behaviour of X-ray temperatures, T-X, with optical richness, lambda(RM), for clusters in the redshift range 0.2 < z < 0.7. X-ray temperatures are obtained from Chandra and XMM observations for 58 and 110 redMaPPer systems, respectively. Despite non-uniform sky coverage, the T-X measurements are > 50 per cent complete for clusters with lambda(RM) > 130. Regression analysis on the two samples produces consistent posterior scaling parameters, from which we derive a combined constraint on the residual scatter, sigma(ln) (T) (vertical bar) (lambda) = 0.275 +/- 0.019. Joined with constraints for T-X scaling with halo mass from the Weighing the Giants program and richness-temperature covariance estimates from the LoCuSS sample, we derive the richness-conditioned scatter in mass, sigma(ln) (M) (vertical bar) (lambda) = 0.30 +/- 0.04((stat)) +/- 0.09((sys)), at an optical richness of approximately 100. Uncertainties in external parameters, particularly the slope and variance of the T-X-mass relation and the covariance of T-X and lambda(RM) at fixed mass, dominate the systematic error. The 95 per cent confidence region from joint sample analysis is relatively broad, sigma(ln) (M) (vertical bar) (lambda) is an element of [0.14, 0.55], or a factor 10 in variance.
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| 3. |
- Zhang, Y., et al.
(författare)
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Dark Energy Surveyed Year 1 results : calibration of cluster mis-centring in the redMaPPer catalogues
- 2019
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Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966. ; 487:2, s. 2578-2593
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Tidskriftsartikel (refereegranskat)abstract
- The centre determination of a galaxy cluster from an optical cluster finding algorithm can be offset from theoretical prescriptions or N-body definitions of its host halo centre. These offsets impact the recovered cluster statistics, affecting both richness measurements and the weak lensing shear profile around the clusters. This paper models the centring performance of the redMaPPer cluster finding algorithm using archival X-ray observations of redMaPPer-selected clusters. Assuming the X-ray emission peaks as the fiducial halo centres, and through analysing their offsets to the redMaPPer centres, we find that similar to 75 +/- 8 per cent of the redMaPPer clusters are well centred and the mis-centred offset follows a Gamma distribution in normalized, projected distance. These mis-centring offsets cause a systematic underestimation of cluster richness relative to the well-centred clusters, for which we propose a descriptive model. Our results enable the DES Y1 cluster cosmology analysis by characterizing the necessary corrections to both the weak lensing and richness abundance functions of the DES Y1 redMaPPer cluster catalogue.
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| 4. |
- Pierre, M., et al.
(författare)
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The XXL Survey I. Scientific motivations - XMM-Newton observing plan - Follow-up observations and simulation programme
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 592
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Tidskriftsartikel (refereegranskat)abstract
- Context. The quest for the cosmological parameters that describe our universe continues to motivate the scientific community to undertake very large survey initiatives across the electromagnetic spectrum. Over the past two decades, the Chandra and XMM-Newton observatories have supported numerous studies of X-ray-selected clusters of galaxies, active galactic nuclei (AGNs), and the X-ray background. The present paper is the first in a series reporting results of the XXL-XMM survey; it comes at a time when the Planck mission results are being finalised. Aims. We present the XXL Survey, the largest XMM programme totaling some 6.9 Ms to date and involving an international consortium of roughly 100 members. The XXL Survey covers two extragalactic areas of 25 deg(2) each at a point-source sensitivity of similar to 5 x 10(-15) erg s(-1) cm(-2) in the [0.5-2] keV band (completeness limit). The survey's main goals are to provide constraints on the dark energy equation of state from the space-time distribution of clusters of galaxies and to serve as a pathfinder for future, wide-area X-ray missions. We review science objectives, including cluster studies, AGN evolution, and large-scale structure, that are being conducted with the support of approximately 30 follow-up programmes. Methods. We describe the 542 XMM observations along with the associated multi-lambda and numerical simulation programmes. We give a detailed account of the X-ray processing steps and describe innovative tools being developed for the cosmological analysis. Results. The paper provides a thorough evaluation of the X-ray data, including quality controls, photon statistics, exposure and background maps, and sky coverage. Source catalogue construction and multi-lambda associations are briefly described. This material will be the basis for the calculation of the cluster and AGN selection functions, critical elements of the cosmological and science analyses. Conclusions. The XXL multi-lambda data set will have a unique lasting legacy value for cosmological and extragalactic studies and will serve as a calibration resource for future dark energy studies with clusters and other X-ray selected sources. With the present article, we release the XMM XXL photon and smoothed images along with the corresponding exposure maps.
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| 5. |
- Abazajian, Kevork, et al.
(författare)
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CMB-S4 : Forecasting Constraints on Primordial Gravitational Waves
- 2022
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 926:1
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Tidskriftsartikel (refereegranskat)abstract
- CMB-S4—the next-generation ground-based cosmic microwave background (CMB) experiment—is set to significantly advance the sensitivity of CMB measurements and enhance our understanding of the origin and evolution of the universe. Among the science cases pursued with CMB-S4, the quest for detecting primordial gravitational waves is a central driver of the experimental design. This work details the development of a forecasting framework that includes a power-spectrum-based semianalytic projection tool, targeted explicitly toward optimizing constraints on the tensor-to-scalar ratio, r, in the presence of Galactic foregrounds and gravitational lensing of the CMB. This framework is unique in its direct use of information from the achieved performance of current Stage 2–3 CMB experiments to robustly forecast the science reach of upcoming CMB-polarization endeavors. The methodology allows for rapid iteration over experimental configurations and offers a flexible way to optimize the design of future experiments, given a desired scientific goal. To form a closed-loop process, we couple this semianalytic tool with map-based validation studies, which allow for the injection of additional complexity and verification of our forecasts with several independent analysis methods. We document multiple rounds of forecasts for CMB-S4 using this process and the resulting establishment of the current reference design of the primordial gravitational-wave component of the Stage-4 experiment, optimized to achieve our science goals of detecting primordial gravitational waves for r > 0.003 at greater than 5σ, or in the absence of a detection, of reaching an upper limit of r < 0.001 at 95% CL.
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| 6. |
- Beale, S. B., et al.
(författare)
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Combined two-phase co-flow and counter-flow in a gas channel/porous transport layer assembly
- 2020. - 9
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Ingår i: PRiME 2020 : Polymer Electrolyte Fuel Cells and Electrolyzers 20 (PEFC and E 20) - Polymer Electrolyte Fuel Cells and Electrolyzers 20 (PEFC and E 20). - : The Electrochemical Society. - 1938-5862 .- 1938-6737. - 9781607685395 ; 98:9, s. 305-315
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Konferensbidrag (refereegranskat)abstract
- This paper considers a detailed numerical analysis of combined liquid-gas co-flow in a gas channel, with liquid-gas counter-flow in a porous transport layer, as is typically found on the cathode side of a polymer electrolyte fuel cell. The geometry is obtained by digital reconstruction of nano-computer tomography images. From this, the domain is tessellated with an unstructured castellated or octree mesh, upon which the equations of mass and momentum are solved by means of a volume of fluid method. Liquid water is produced from an electrode where gaseous oxygen is simultaneously consumed by electrochemical reduction; Liquid-gas counter flow in the porous transport layer results in liquid drops being entrained in co-flow in the gas channels and convected by the gas downstream.
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| 7. |
- Andersson, M., et al.
(författare)
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Coupling of lattice boltzmann and volume of fluid approaches to study the droplet behavior at the gas diffusion layer/gas channel interface
- 2018. - 13
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Ingår i: ECS Transactions. - : The Electrochemical Society. - 1938-6737 .- 1938-5862. - 9781607688600 ; 86, s. 329-336
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Konferensbidrag (refereegranskat)abstract
- A typical polymer electrolyte fuel cell (PEFC) flow field consists of micro/minichannels. The continues removal of liquid water from the cathode channels is a critical topic, as water droplets forming in the channels may block the transport of gaseous oxygen to the active sites, which not only gives an uneven current distribution and substantial loss of performance, but also, increases degradation rates and unstable operation. Water generated by the electrochemical reactions condenses, depending on temperature mainly, into liquid form, potentially flooding various part of the PEFC. The aim of this work is to obtain an increased understanding of the droplet behavior at the gas diffusion layer (GDL) interface with the gas channels in PEFCs by the coupling of Lattice Boltzmann (LB) and Volume of Fluid (VOF) approaches. A multiscale environment is established with input parameters in the VOF model being extracted from in-house LB calculations. It is clear that the contact angle as well as the size of the liquid droplet vary with positions at the GDL surface, depending on the stochastic GDL geometry. A VOF model describing one straight channel with one gas inlet, one liquid inlet (at the GDL surface) and one two-phase outlet is employed.
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| 8. |
- Zhang, Shidong, et al.
(författare)
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Simple and complex polymer electrolyte fuel cell stack models : A comparison
- 2018. - 13
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Ingår i: ECS Transactions. - : The Electrochemical Society. - 1938-6737 .- 1938-5862. - 9781607685395 ; 86, s. 287-300
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Konferensbidrag (refereegranskat)abstract
- In this paper, two distinct polymer electrolyte fuel cell stack models are constructed: a detailed numerical model (DNM) employing a fine-scale computational mesh and a coarse-mesh approach based on a distributed resistance analogy (DRA) where diffusion terms in the transport equations are replaced by rate terms. Both methods are applied to a 5-cell, high-temperature polymer electrolyte fuel cell stack with an active area of 200 cm2 per cell. The polarization curve and local current density distributions from both the DRA and DNM are compared with experimental data, finding good agreement. Temperature, pressure, Nernst potential, and species distributions are also exhibited. The DNM displays details of fine-scale local extrema not captured by the DRA; however, the latter requires orders of magnitude less computer processor power and memory for execution. Both methods provide much finer-scale results than present experimental techniques.
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| 9. |
- Mantz, A. B., et al.
(författare)
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The XXL Survey. V. Detection of the Sunyaev-Zel'Dovich Effect of the Redshift 1.9 Galaxy Cluster XLSSU J021744.1-034536 With Carma
- 2014
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 794:2
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Tidskriftsartikel (refereegranskat)abstract
- We report the detection of the Sunyaev-Zel'dovich (SZ) effect of galaxy cluster XLSSU J021744.1-034536, using 30 GHz Combined Array for Research in Millimeter-wave Astronomy (CARMA) data. This cluster was discovered via its extended X-ray emission in the XMM-Newton Large Scale Structure survey, the precursor to the XXL survey. It has a photometrically determined redshift z = 1.91(-0.21)(+0.19), making it among the most distant clusters known, and nominally the most distant for which the SZ effect has been measured. The spherically integrated Comptonization is Y-500 = (3.0 +/- 0.4) x 10(-12), a measurement that is relatively insensitive to assumptions regarding the size and redshift of the cluster, as well as the background cosmology. Using a variety of locally calibrated cluster scaling relations extrapolated to z similar to 2, we estimate a mass M-500 similar to (1-2) x 10(14) M-circle dot from the X-ray flux and SZ signal. The measured properties of this cluster are in good agreement with the extrapolation of an X-ray luminosity-SZ effect scaling relation calibrated from clusters discovered by the South Pole Telescope at higher masses and lower redshifts. The full XXL-CARMA sample will provide a more complete, multi-wavelength census of distant clusters in order to robustly extend the calibration of cluster scaling relations to these high redshifts.
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| 10. |
- Rich, Rebecca L., et al.
(författare)
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A global benchmark study using affinity-based biosensors
- 2009
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Ingår i: Analytical Biochemistry. - : Elsevier BV. - 0003-2697 .- 1096-0309. ; 386:2, s. 194-216
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Tidskriftsartikel (refereegranskat)abstract
- To explore the variability in biosensor studies, 150 participants from 20 countries were given the same protein samples and asked to determine kinetic rate constants for the interaction. We chose a protein system that was amenable to analysis using different biosensor platforms as well as by users of different expertise levels. The two proteins (a 50-kDa Fab and a 60-kDa glutathione S-transferase [GST] antigen) form a relatively high-affinity complex, so participants needed to optimize several experimental parameters, including ligand immobilization and regeneration conditions as well as analyte concentrations and injection/dissociation times. Although most participants collected binding responses that could be fit to yield kinetic parameters, the quality of a few data sets could have been improved by optimizing the assay design. Once these outliers were removed, the average reported affinity across the remaining panel of participants was 620 pM with a standard deviation of 980 pM. These results demonstrate that when this biosensor assay was designed and executed appropriately, the reported rate constants were consistent, and independent of which protein was immobilized and which biosensor was used.
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