5,131 research outputs found
Demonstrating the negligible contribution of optical ACS/HST galaxies to source-subtracted cosmic infrared background fluctuations in deep IRAC/Spitzer images
We study the possible contribution of optical galaxies detected with the {\it
Hubble} ACS instrument to the near-IR cosmic infrared (CIB) fluctuations in
deep {\it Spitzer} images. The {\it Spitzer} data used in this analysis are
obtained in the course of the GOODS project from which we select four
independent regions observed at both 3.6 and 4.5
\um. ACS source catalogs for all of these areas are used to construct maps
containing only their emissions in the ACS -bands. We find that
deep Spitzer data exhibit CIB fluctuations remaining after removal of
foreground galaxies of a very different clustering pattern at both 3.6 and 4.5
\um than the ACS galaxies could contribute. We also find that there are very
good correlations between the ACS galaxies and the {\it removed} galaxies in
the Spitzer maps, but practically no correlations remain with the residual
Spitzer maps used to identify the CIB fluctuations. These contributions become
negligible on larger scales used to probe the CIB fluctuations arising from
clustering. This means that the ACS galaxies cannot contribute to the
large-scale CIB fluctuations found in the residual Spitzer data. The absence of
their contributions also means that the CIB fluctuations arise at z\gsim 7.5
as the Lyman break of their sources must be redshifted past the longest ACS
band, or the fluctuations have to originate in the more local but extremely low
luminosity galaxies.Comment: Ap.J.Letters, in press. Minor revisions to mathc the accepted versio
An Electronic Mach-Zehnder Quantum Eraser
We propose an electronic quantum eraser in which the electrons are injected
into a mesoscopic conductor at the quantum Hall regime. The conductor is
composed of a two-path interferometer which is an electronic analogue of the
optical Mach-Zehnder interferometer, and a quantum point contact detector
capacitively coupled to the interferometer. While the interference of the
output current at the interferometer is shown to be suppressed by the
which-path information, we show that the which-path information is erased by
the zero-frequency cross correlation measurement between the interferometer and
the detector output leads. We also investigate a modified setup in which the
detector is replaced by a two-path interferometer.We show that the path
distinguishability and the visibility of the joint detection can be controlled
in a continuous manner, and satisfy a complementarity relation for the
entangled electrons.Comment: 5 pages, 2 figure
Calibrating Array Detectors
The development of sensitive large format imaging arrays for the infrared
promises to provide revolutionary capabilities for space astronomy. For
example, the Infrared Array Camera (IRAC) on SIRTF will use four 256 x 256
arrays to provide background limited high spatial resolution images of the sky
in the 3 to 8 micron spectral region. In order to reach the performance limits
possible with this generation of sensitive detectors, calibration procedures
must be developed so that uncertainties in detector calibration will always be
dominated by photon statistics from the dark sky as a major system noise
source. In the near infrared, where the faint extragalactic sky is observed
through the scattered and reemitted zodiacal light from our solar system,
calibration is particularly important. Faint sources must be detected on this
brighter local foreground.
We present a procedure for calibrating imaging systems and analyzing such
data. In our approach, by proper choice of observing strategy, information
about detector parameters is encoded in the sky measurements. Proper analysis
allows us to simultaneously solve for sky brightness and detector parameters,
and provides accurate formal error estimates.
This approach allows us to extract the calibration from the observations
themselves; little or no additional information is necessary to allow full
interpretation of the data. Further, this approach allows refinement and
verification of detector parameters during the mission, and thus does not
depend on a priori knowledge of the system or ground calibration for
interpretation of images.Comment: Scheduled for ApJS, June 2000 (16 pages, 3 JPEG figures
Development of a general purpose airborne simulator
Variable stability system development for General Purpose Airborne Simulator /GPAS
New measurements of cosmic infrared background fluctuations from early epochs
Cosmic infrared background fluctuations may contain measurable contribution
from objects inaccessible to current telescopic studies, such as the first
stars and other luminous objects in the first Gyr of the Universe's evolution.
In an attempt to uncover this contribution we have analyzed the GOODS data
obtained with the Spitzer IRAC instrument, which are deeper and cover larger
scales than the Spitzer data we have previously analyzed. Here we report these
new measurements of the cosmic infrared background (CIB) fluctuations remaining
after removing cosmic sources to fainter levels than before. The remaining
anisotropies on scales > 0.5 arcmin have a significant clustering component
with a low shot-noise contribution. We show that these fluctuations cannot be
accounted for by instrumental effects, nor by the Solar system and Galactic
foreground emissions and must arise from extragalactic sources.Comment: Ap.J.Letters, in pres
Reflection high-energy electron diffraction experimental analysis of polycrystalline MgO films with grain size and orientation distributions
Analysis of biaxial texture of MgO films grown by ion-beam-assisted deposition (IBAD) has been performed using a quantitative reflection high-energy electron diffraction (RHEED) based method. MgO biaxial texture is determined by analysis of diffraction spot shapes from single RHEED images, and by measuring the width of RHEED in-plane rocking curves for MgO films grown on amorphous Si3N4 by IBAD using 750 eV Ar+ ions, at 45° incidence angle, and MgO e-beam evaporation. RHEED-based biaxial texture measurement accuracy is verified by comparison with in-plane and out-of-plane orientation distribution measurements made using transmission electron microscopy and x-ray rocking curves. In situ RHEED measurements also enable the analysis of the evolution of the biaxial texture which narrows with increasing film thickness. RHEED-based measurements of IBAD MgO biaxial texture show that the minimum in-plane orientation distribution depends on the out-of-plane orientation distribution, and indicates that the minimum obtainable in-plane orientation on distribution is 2°
Implementing New Elements into an Existing PSM System
PresentationThis paper will present an approach for successfully implementing a new element(s) into a site or company’s existing process safety management (PSM) system. This approach includes steps for: (1) developing a new element (2) integrating new element activities into existing elements (3) implementing new Risk Based Process Safety (RBPS) elements, and (4) monitoring new elements or activities. Specific examples for implementing RBPS elements such as Process Safety Culture, Compliance with Standards, Process Safety Competency, Stakeholder Outreach, Conduct of Operations, Measurement and Metrics, and/or Management Review and Continuous Improvement will be provided. This approach and the examples presented will be drawn from Guidelines for Implementing Process Safety Management, 2nd Edition (CCPS), which is due for publication in the summer of 2015
Reconstructing emission from pre-reionization sources with cosmic infrared background fluctuation measurements by the JWST
We present new methodology to use cosmic infrared background (CIB)
fluctuations to probe sources at 10<z<30 from a JWST/NIRCam configuration that
will isolate known galaxies to 28 AB mag at 0.5--5 micron. At present
significant mutually consistent source-subtracted CIB fluctuations have been
identified in the Spitzer and Akari data at 2--5 micron, but we demonstrate
internal inconsistencies at shorter wavelengths in the recent CIBER data. We
evaluate CIB contributions from remaining galaxies and show that the bulk of
the high-z sources will be in the confusion noise of the NIRCam beam, requiring
CIB studies. The accurate measurement of the angular spectrum of the
fluctuations and probing the dependence of its clustering component on the
remaining shot noise power would discriminate between the various currently
proposed models for their origin and probe the flux distribution of its
sources. We show that the contribution to CIB fluctuations from remaining
galaxies is large at visible wavelengths for the current instruments precluding
probing the putative Lyman-break of the CIB fluctuations. We demonstrate that
with the proposed JWST configuration such measurements will enable probing the
Lyman break. We develop a Lyman-break tomography method to use the NIRCam
wavelength coverage to identify or constrain, via the adjacent two-band
subtraction, the history of emissions over 10<z<30 as the Universe comes out of
the 'Dark Ages'. We apply the proposed tomography to the current Spitzer/IRAC
measurements at 3.6 and 4.5 micron, to find that it already leads to
interestingly low upper limit on emissions at z>30.Comment: ApJ, in press. Minor revisions/additions to match the version in
proof
Evidence for Halo Kinematics among Cool Carbon-Rich Dwarfs
This paper reports preliminary yet compelling kinematical inferences for N ~
600 carbon-rich dwarf stars that demonstrate around 30% to 60% are members of
the Galactic halo. The study uses a spectroscopically and non-kinematically
selected sample of stars from the SDSS, and cross-correlates these data with
three proper motion catalogs based on Gaia DR1 astrometry to generate estimates
of their 3-D space velocities. The fraction of stars with halo-like kinematics
is roughly 30% for distances based on a limited number of parallax
measurements, with the remainder dominated by the thick disk, but close to 60%
of the sample lie below an old, metal-poor disk isochrone in reduced proper
motion. An ancient population is consistent with an extrinsic origin for C/O >1
in cool dwarfs, where a fixed mass of carbon pollution more readily surmounts
lower oxygen abundances, and with a lack of detectable ultraviolet-blue flux
from younger white dwarf companions. For an initial stellar mass function that
favors low-mass stars as in the Galactic disk, the dC stars are likely to be
the dominant source of carbon-enhanced, metal-poor stars in the Galaxy.Comment: 7 pages, 1 table, and 3 figures. Accepted to MNRA
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