11,093 research outputs found
Implementation of robust image artifact removal in SWarp through clipped mean stacking
We implement an algorithm for detecting and removing artifacts from
astronomical images by means of outlier rejection during stacking. Our method
is capable of addressing both small, highly significant artifacts such as
cosmic rays and, by applying a filtering technique to generate single frame
masks, larger area but lower surface brightness features such as secondary
(ghost) images of bright stars. In contrast to the common method of building a
median stack, the clipped or outlier-filtered mean stacked point-spread
function (PSF) is a linear combination of the single frame PSFs as long as the
latter are moderately homogeneous, a property of great importance for weak
lensing shape measurement or model fitting photometry. In addition, it has
superior noise properties, allowing a significant reduction in exposure time
compared to median stacking. We make publicly available a modified version of
SWarp that implements clipped mean stacking and software to generate single
frame masks from the list of outlier pixels.Comment: PASP accepted; software for download at
http://www.usm.uni-muenchen.de/~dgruen
The Actual Harm Requirement and the Federal Trademark Dilution Act: Ringling Brothers-Barnum & Bailey Combined Shows, Inc. v. Utah Division of Travel Development
The sizes of galaxy halos in galaxy cluster Abell 1689
The multiple images observed in galaxy cluster Abell 1689 provide strong
constraints not only on the mass distribution of the cluster but also on the
ensemble properties of the cluster galaxies. Using parametric strong lensing
models for the cluster, and by assuming well motivated scaling laws between the
truncation radius s and the velocity dispersion sigma of a cluster galaxy we
are able to derive sizes of the dark matter halos of cluster galaxies.
For the scaling law expected for galaxies in the cluster environment (s
propto sigma), we obtain s = 64^{+15}_{-14} (sigma / 220 km/s) kpc. For the
scaling law used for galaxies in the field with s propto sigma^2 we find s =
66^{+18}_{-16} (sigma / 220 km/s)^2 kpc. Compared to halos of field galaxies,
the cluster galaxy halos in Abell 1689 are strongly truncated.Comment: 12 pages, 4 figures. Accepted for publication in the Ap
A Comparison of Simple Mass Estimators for Galaxy Clusters
High-resolution N-body simulations are used to investigate systematic trends
in the mass profiles and total masses of clusters as derived from 3 simple
estimators: (1) the weak gravitational lensing shear field under the assumption
of an isothermal cluster potential, (2) the dynamical mass obtained from the
measured velocity dispersion under the assumption of an isothermal cluster
potential, and (3) the classical virial estimator. The clusters consist of
order 2.5e+05 particles of mass m_p \simeq 10^{10} \Msun, have triaxial mass
distributions, and significant substructure exists within their virial radii.
Not surprisingly, the level of agreement between the mass profiles obtained
from the various estimators and the actual mass profiles is found to be
scale-dependent.
The virial estimator yields a good measurement of the total cluster mass,
though it is systematically underestimated by of order 10%. This result
suggests that, at least in the limit of ideal data, the virial estimator is
quite robust to deviations from pure spherical symmetry and the presence of
substructure. The dynamical mass estimate based upon a measurement of the
cluster velocity dispersion and an assumption of an isothermal potential yields
a poor measurement of the total mass. The weak lensing estimate yields a very
good measurement of the total mass, provided the mean shear used to determine
the equivalent cluster velocity dispersion is computed from an average of the
lensing signal over the entire cluster (i.e. the mean shear is computed
interior to the virial radius). [abridged]Comment: Accepted for publication in The Astrophysical Journal. Complete
paper, including 3 large colour figures can also be obtained from
http://bu-ast.bu.edu/~brainerd/preprints
Direction, Not Destination: Institutional Work Practices in the Face of Field-Level Uncertainty
Though field-level uncertainty represents a common challenge, research seldom addresses how institutional work that aims to influence institutional change occurs in the face of uncertainty. We study institutional work practices in a field beset with high uncertainty. Focusing on a field-configuring event in the semiconductor industry, we show how institutional work is possible through practices of dealing with uncertainty that do not eliminate the basic uncertainty but nevertheless configure the field and institutionalize a common direction without specifying a final destination. We find evidence of the open-endedness and collectiveness of institutional work and we contribute to the microfoundations of institutional theory conceptualizing a set of four practices of dealing with field-level uncertainty purposively but not purposefully, i.e., bootstrapping, roadmapping, leader-picking, and issue-bracketing. We highlight the reciprocal relationship between practices and uncertainty, focus on the coordination of institutionalization, and distinguish between events in fields marked by high versus low uncertainty.1. Introduction 2. Theoretical background and aims 3. Research setting and methods 4. Findings 5. Discussion and theory development 6. Limitations and outlook Acknowledgements Reference
Performance evaluation of novel SiPM for medical imaging applications
Silicon Photomultiplier (SiPM) detectors are investigated
world-wide as a suitable replacement for the conventional
vacuum based PhotoMultiplier Tube (PMT) and are enabling
applications otherwise not possible with PMT detectors. Progress
in recent years has been substantial with SiPM detectors pushing
the boundaries in energy and time resolution as well as photon
detection efficiency and active surface area. In this paper we
report on the performance of a gamma detector comprising latest
generation SiPM detectors from SensL coupled to novel Cerium
doped Gd3Al2Ga3O12 (GAGG) scintillators from Furukawa,
Japan. Both 3mm�3mm N-on-P and P-on-N SiPM detectors have
been optically coupled to 3mm�3mm�30mm crystals. An energy
resolution (662 keV Cs-137) of 9.4% has been measured for
GAGG crystal coupled to a 3mm�3mm N-on-P SiPM detector
Species- and organ-specificity of secretory proteins derived from human prostate and seminal vesicles
Polyclonal antibodies against semenogelin (SG) isolated from human seminal vesicle secretion and acid phosphatase (PAP), βâmicroseminoprotein (βâMSP), and ProstateâSpecific Antigen (PSA) derived from human prostatic fluid, as well as a monoclonal antibody against βâMSP were used for immunocytochemical detection of the respective antigens in different organs from different species. SG immunoreactivity was detected in the epithelium of the pubertal and adult human and in monkey seminal vesicle, ampulla of the vas deferens, and ejaculatory duct. PAP, βâMSP, and PSA immunoreactivities were detected in the pubertal and adult human prostate and the cranial and caudal monkey prostate. With the exception of a weak PSA immunoreactivity in the proximal portions of the ejaculatory duct, none of the latter antisera reacted with seminal vesicle, ampullary, and ejaculatory duct epithelium. Among the nonâprimate species studied (dog, bull, rat, guinea pig) only the canine prostatic epithelium displayed a definite immunoreactivity with the PAP antibody and a moderate reaction with the PSA antibody. No immunoreaction was seen in bull and rat seminal vesicle and canine ampulla of the vas deferens with the SG antibody. The same was true for the (ventral) prostate of rat, bull, and dog for βâMSP. The epithelium of the rat dorsal prostate showed a slight crossâreactivity with the monoclonal antibody against βâMSP and one polyclonal antibody against PSA. The findings indicate a rather strict speciesâdependent expression of human seminal proteins which show some similarities in primates, but only marginal relationship to species with different physiology of seminal fluid
Weak Lensing Analysis of the z~0.8 cluster CL 0152-1357 with the Advanced Camera for Surveys
We present a weak lensing analysis of the X-ray luminous cluster CL 0152-1357
at z~0.84 using HST/ACS observations. The unparalleled resolution and
sensitivity of ACS enable us to measure weakly distorted, faint background
galaxies to the extent that the number density reaches ~175 arcmin^-2. The PSF
of ACS has a complicated shape that also varies across the field. We construct
a PSF model for ACS from an extensive investigation of 47 Tuc stars in a
modestly crowded region. We show that this model PSF excellently describes the
PSF variation pattern in the cluster observation when a slight adjustment of
ellipticity is applied. The high number density of source galaxies and the
accurate removal of the PSF effect through moment-based deconvolution allow us
to restore the dark matter distribution of the cluster in great detail. The
direct comparison of the mass map with the X-ray morphology from Chandra
observations shows that the two peaks of intracluster medium traced by X-ray
emission are lagging behind the corresponding dark matter clumps, indicative of
an on-going merger. The overall mass profile of the cluster can be well
described by an NFW profile with a scale radius of r_s =309+-45 kpc and a
concentration parameter of c=3.7+-0.5. The mass estimates from the lensing
analysis are consistent with those from X-ray and Sunyaev-Zeldovich analyses.
The predicted velocity dispersion is also in good agreement with the
spectroscopic measurement from VLT observations. In the adopted WMAP cosmology,
the total projected mass and the mass-to-light ratio within 1 Mpc are estimated
to be 4.92+-0.44 10^14 solar mass and 95+-8 solar mass/solar luminosity,
respectively.Comment: Accepted for publication in Astrophysical Journal. 58 pages, 26
figures. Figures have been degraded to meet size limit; a higher resolution
version available at http://acs.pha.jhu.edu/~mkjee/ms_cl0152.pd
Reconstruction methods â P‾ANDA focussing-light guide disc DIRC
The Focussing-Lightguide Disc DIRC will provide crucial Particle Identification (PID) information for the P‾ANDA experiment at FAIR, GSI. This detector presents a challenging environment for reconstruction due to the complexity of the expected hit patterns and the operating conditions of the P‾ANDA experiment. A discussion of possible methods to reconstruct PID from this detector is given here. Reconstruction software is currently under development
- âŚ