1,806 research outputs found
Optimizing weak lensing mass estimates for cluster profile uncertainty
Weak lensing measurements of cluster masses are necessary for calibrating
mass-observable relations (MORs) to investigate the growth of structure and the
properties of dark energy. However, the measured cluster shear signal varies at
fixed mass M_200m due to inherent ellipticity of background galaxies,
intervening structures along the line of sight, and variations in the cluster
structure due to scatter in concentrations, asphericity and substructure. We
use N-body simulated halos to derive and evaluate a weak lensing circular
aperture mass measurement M_ap that minimizes the mass estimate variance <(M_ap
- M_200m)^2> in the presence of all these forms of variability. Depending on
halo mass and observational conditions, the resulting mass estimator improves
on M_ap filters optimized for circular NFW-profile clusters in the presence of
uncorrelated large scale structure (LSS) about as much as the latter improve on
an estimator that only minimizes the influence of shape noise. Optimizing for
uncorrelated LSS while ignoring the variation of internal cluster structure
puts too much weight on the profile near the cores of halos, and under some
circumstances can even be worse than not accounting for LSS at all. We briefly
discuss the impact of variability in cluster structure and correlated
structures on the design and performance of weak lensing surveys intended to
calibrate cluster MORs.Comment: 11 pages, 5 figures; accepted by MNRA
Characterization and correction of charge-induced pixel shifts in DECam
Interaction of charges in CCDs with the already accumulated charge
distribution causes both a flux dependence of the point-spread function (an
increase of observed size with flux, also known as the brighter/fatter effect)
and pixel-to-pixel correlations of the Poissonian noise in flat fields. We
describe these effects in the Dark Energy Camera (DECam) with charge dependent
shifts of effective pixel borders, i.e. the Antilogus et al. (2014) model,
which we fit to measurements of flat-field Poissonian noise correlations. The
latter fall off approximately as a power-law r^-2.5 with pixel separation r,
are isotropic except for an asymmetry in the direct neighbors along rows and
columns, are stable in time, and are weakly dependent on wavelength. They show
variations from chip to chip at the 20% level that correlate with the silicon
resistivity. The charge shifts predicted by the model cause biased shape
measurements, primarily due to their effect on bright stars, at levels
exceeding weak lensing science requirements. We measure the flux dependence of
star images and show that the effect can be mitigated by applying the reverse
charge shifts at the pixel level during image processing. Differences in
stellar size, however, remain significant due to residuals at larger distance
from the centroid.Comment: typo and formatting fixes, matches version published in JINS
Environment-based selection effects of Planck clusters
We investigate whether the large scale structure environment of galaxy
clusters imprints a selection bias on Sunyaev Zel'dovich (SZ) catalogs. Such a
selection effect might be caused by line of sight (LoS) structures that add to
the SZ signal or contain point sources that disturb the signal extraction in
the SZ survey. We use the Planck PSZ1 union catalog (Planck Collab- oration et
al. 2013a) in the SDSS region as our sample of SZ selected clusters. We
calculate the angular two-point correlation function (2pcf) for physically
correlated, foreground and background structure in the RedMaPPer SDSS DR8
catalog with respect to each cluster. We compare our results with an optically
selected comparison cluster sample and with theoretical predictions. In
contrast to the hypothesis of no environment-based selection, we find a mean
2pcf for background structures of -0.049 on scales of ,
significantly non-zero at , which means that Planck clusters are
more likely to be detected in regions of low background density. We hypothesize
this effect arises either from background estimation in the SZ survey or from
radio sources in the background. We estimate the defect in SZ signal caused by
this effect to be negligibly small, of the order of of the
signal of a typical Planck detection. Analogously, there are no implications on
X-ray mass measurements. However, the environ- mental dependence has important
consequences for weak lensing follow up of Planck galaxy clusters: we predict
that projection effects account for half of the mass contained within a 15'
radius of Planck galaxy clusters. We did not detect a background underdensity
of CMASS LRGs, which also leaves a spatially varying redshift dependence of the
Planck SZ selection function as a possible cause for our findings.Comment: 14 pages, 9 figure
MC: Subaru and Hubble Space Telescope Weak-Lensing Analysis of the Double Radio Relic Galaxy Cluster PLCK G287.0+32.9
The second most significant detection of the Planck Sunyaev Zel'dovich
survey, PLCK~G287.0+32.9 () boasts two similarly bright radio relics
and a radio halo. One radio relic is located kpc northwest of the
X-ray peak and the other Mpc to the southeast. This large difference
suggests that a complex merging scenario is required. A key missing puzzle for
the merging scenario reconstruction is the underlying dark matter distribution
in high resolution. We present a joint Subaru Telescope and {\it Hubble Space
Telescope} weak-lensing analysis of the cluster. Our analysis shows that the
mass distribution features four significant substructures. Of the
substructures, a primary cluster of mass
$M_{200\text{c}}=1.59^{+0.25}_{-0.22}\times 10^{15} \ h^{-1}_{70} \
\text{M}_{\odot}M_{200\text{c}}=1.16^{+0.15}_{-0.13}\times 10^{14} \ h^{-1}_{70} \
\text{M}_{\odot}\sim 400\sim 2M_{200\text{c}}=1.68^{+0.22}_{-0.20}\times
10^{14} \ h^{-1}_{70} \ \text{M}_{\odot}M_{200\text{c}}=1.87^{+0.24}_{-0.22}\times 10^{14} \ h^{-1}_{70} \
\text{M}_{\odot}$, is northwest of the X-ray peak and beyond the NW radio
relic.Comment: 19 pages, 14 figures; Accepted to Ap
Patients with diffuse idiopathic skeletal hyperostosis do not have increased peripheral bone mineral density and geometry
Objectives. Recent studies have suggested that areal BMD (aBMD) measured by DXA is elevated in patients with DISH. We used peripheral QCT (pQCT) to assess volumetric BMD (vBMD) and bone geometry of the radius, tibia and the third metacarpal bone. Methods. Patients with established DISH and a control group of healthy individuals were recruited. pQCT measurements were performed at the distal epiphyses and mid-shafts of the radius, the tibia and the third metacarpal bone. At the epiphyses cross-sectional area (CSA), total BMD and trabecular BMD were measured. At the shafts, total bone CSA, cortical CSA, cortical wall thickness and cortical BMD were determined. In addition, muscle and fat CSA of the forearm and lower leg were assessed. Bone parameters were compared between the two groups using independent t-tests. Results. Thirty DISH patients and 30 controls comparable with regard to age and height were included in this study. None of the measured bone parameters differed between groups. Conclusions. In contrast to suggestions based on DXA, pQCT revealed that DISH patients do not have increased vBMD and bone geometry in the appendicular skeleton. Ossification at tendon or ligament insertion sites may lead to overestimation of aBMD if assessed by DX
On-Orbit Ephemeris Determination with Radio Doppler Validation
Multiple CubeSats are often released from the same host spacecraft into virtually the same orbit at nearly the same time. A satellite team needs the ability to identify and track its own satellites as soon as possible. However, this can be a difficult and confusing task with a large number of satellites. Los Alamos National Laboratory encountered this issue during a launch of LANL-designed CubeSats that were released with more than 20 other objects. A simple radio Doppler method used shortly after launch by the Los Alamos team to select its satellites of interest from the list of available tracked ephemerides is described. This method can also be used for automated real time ephemeris validation. For future efforts, each LANL-designed CubeSat will automatically perform orbit determination from the position, velocity, and covariance estimates provided by an added on-board GPS receiver. This self-determined ephemeris will be automatically downlinked by ground stations for mission planning, antenna tracking, Doppler-pre-correction, etc. A simple algorithm based on established theory and well suited for embedded on-board processing is presented. The trades examined in selecting the algorithm components and data formats are briefly discussed, as is the expected performance
Attitudes Concerning Postmortem Organ Donation : A Multicenter Survey in Various German Cohorts
BACKGROUND
The aim of this study was to characterize postmortem organ donation attitudes in various German cohorts.
MATERIAL AND METHODS
Employees of 2 German cities and 2 German university hospitals, employees of a German automobile enterprise, and members of a German Medical Society were administered a questionnaire about postmortem organ and tissue donation attitudes. Demographic data and general attitudes were questioned and focused on: I) willingness to donate organs, II) holding a donor card, and III) having discussed the topic with the family.
RESULTS
Of 5291 participants, 65.2% reported favoring postmortem organ donation. Missing negative experiences, the idea that donation is helpful, a non-medical professional environment, excellent general health, gender, agreement with the brain-death paradigm, and age significantly influenced the participants’ attitudes. Participants were more likely to possess donor cards and had discussed more often with family members if they agreed with the brain-death paradigm and considered donation to be helpful. Males and older participants were the most likely to neglect donor cards, and Catholics, Protestants, and participants with poor health were the least likely to donate organs. Interest in receiving more information was expressed by 38.1% and 50.6% of participants refusing donation of all or of specific organs, respectively, and suggested the internet (60.0%) and family doctors (35.0%) as preferred sources of information.
CONCLUSIONS
Public campaigns in Germany should focus on males and older people as regards donor cards, and females, younger, and religiously affiliated persons as regards the general willingness to donate organs postmortem
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