542 research outputs found
Construction and Measurements of an Improved Vacuum-Swing-Adsorption Radon-Mitigation System
In order to reduce backgrounds from radon-daughter plate-out onto detector
surfaces, an ultra-low-radon cleanroom is being commissioned at the South
Dakota School of Mines and Technology. An improved vacuum-swing-adsorption
radon mitigation system and cleanroom build upon a previous design implemented
at Syracuse University that achieved radon levels of
0.2Bqm. This improved system will employ a better pump and
larger carbon beds feeding a redesigned cleanroom with an internal HVAC unit
and aged water for humidification. With the rebuilt (original) radon mitigation
system, the new low-radon cleanroom has already achieved a 300
reduction from an input activity of Bqm to a
cleanroom activity of Bqm.Comment: 5 pages, 4 figures, Proceedings of Low Radioactivity Techniques (LRT)
2015, Seattle, WA, March 18-20, 201
Predator-specific inducible morphological defenses of a water flea against two freshwater predators
How well does wind speed predict air-sea gas transfer in the sea ice zone? A synthesis of radon deficit profiles in the upper water column of the Arctic Ocean
Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 122 (2017): 3696â3714, doi:10.1002/2016JC012460.We present 34 profiles of radon-deficit from the ice-ocean boundary layer of the Beaufort Sea. Including these 34, there are presently 58 published radon-deficit estimates of air-sea gas transfer velocity (k) in the Arctic Ocean; 52 of these estimates were derived from water covered by 10% sea ice or more. The average value of k collected since 2011 is 4.0â±â1.2 m dâ1. This exceeds the quadratic wind speed prediction of weighted kwsâ=â2.85 m dâ1 with mean-weighted wind speed of 6.4 m sâ1. We show how ice cover changes the mixed-layer radon budget, and yields an âeffective gas transfer velocity.â We use these 58 estimates to statistically evaluate the suitability of a wind speed parameterization for k, when the ocean surface is ice covered. Whereas the six profiles taken from the open ocean indicate a statistically good fit to wind speed parameterizations, the same parameterizations could not reproduce k from the sea ice zone. We conclude that techniques for estimating k in the open ocean cannot be similarly applied to determine k in the presence of sea ice. The magnitude of k through gaps in the ice may reach high values as ice cover increases, possibly as a result of focused turbulence dissipation at openings in the free surface. These 58 profiles are presently the most complete set of estimates of k across seasons and variable ice cover; as dissolved tracer budgets they reflect air-sea gas exchange with no impact from air-ice gas exchange.NSF Arctic Natural Sciences program Grant Number: 12035582017-11-0
Imaging Jupiter's radiation belts down to 127 MHz with LOFAR
Context. Observing Jupiter's synchrotron emission from the Earth remains
today the sole method to scrutinize the distribution and dynamical behavior of
the ultra energetic electrons magnetically trapped around the planet (because
in-situ particle data are limited in the inner magnetosphere). Aims. We perform
the first resolved and low-frequency imaging of the synchrotron emission with
LOFAR at 127 MHz. The radiation comes from low energy electrons (~1-30 MeV)
which map a broad region of Jupiter's inner magnetosphere. Methods (see article
for complete abstract) Results. The first resolved images of Jupiter's
radiation belts at 127-172 MHz are obtained along with total integrated flux
densities. They are compared with previous observations at higher frequencies
and show a larger extent of the synchrotron emission source (>=4 ). The
asymmetry and the dynamic of east-west emission peaks are measured and the
presence of a hot spot at lambda_III=230 {\deg} 25 {\deg}. Spectral flux
density measurements are on the low side of previous (unresolved) ones,
suggesting a low-frequency turnover and/or time variations of the emission
spectrum. Conclusions. LOFAR is a powerful and flexible planetary imager. The
observations at 127 MHz depict an extended emission up to ~4-5 planetary radii.
The similarities with high frequency results reinforce the conclusion that: i)
the magnetic field morphology primarily shapes the brightness distribution of
the emission and ii) the radiating electrons are likely radially and
latitudinally distributed inside about 2 . Nonetheless, the larger extent
of the brightness combined with the overall lower flux density, yields new
information on Jupiter's electron distribution, that may shed light on the
origin and mode of transport of these particles.Comment: 10 pages, 12 figures, accepted for publication in A&A (27/11/2015) -
abstract edited because of limited character
Weak ferromagnetism with very large canting in a chiral lattice: (pyrimidine)2FeCl2
The transition metal coordination compound (pyrimidine)2FeCl2 crystallizes in
a chiral lattice, space group I 4_1 2 2 (or I4_3 2 2). Combined magnetization,
Mossbauer spectroscopy and powder neutron diffraction studies reveal that it is
a canted antiferromagnet below T_N = 6.4 K with an unusually large canting of
the magnetic moments of 14 deg. from their general antiferromagnetic alignment,
one of the largest reported to date. This results in weak ferromagnetism with a
ferromagnetic component of 1 mu_B. The large canting is due to the interplay
between the antiferromagnetic exchange interaction and the local single-ion
anisotropy in the chiral lattice. The magnetically ordered structure of
(pyrimidine)2FeCl2, however, is not chiral. The implications of these findings
for the search of molecule based materials exhibiting chiral magnetic ordering
is discussed.Comment: 6 pages, 5 figure
The Nature of Starbursts : II. The Duration of Starbursts in Dwarf Galaxies
The starburst phenomenon can shape the evolution of the host galaxy and the
surrounding intergalactic medium. The extent of the evolutionary impact is
partly determined by the duration of the starburst, which has a direct
correlation with both the amount of stellar feedback and the development of
galactic winds, particularly for smaller mass dwarf systems. We measure the
duration of starbursts in twenty nearby, ongoing, and "fossil" starbursts in
dwarf galaxies based on the recent star formation histories derived from
resolved stellar population data obtained with the Hubble Space Telescope.
Contrary to the shorter times of 3-10 Myr often cited, the starburst durations
we measure range from 450 - 650 Myr in fifteen of the dwarf galaxies and up to
1.3 Gyr in four galaxies; these longer durations are comparable to or longer
than the dynamical timescales for each system. The same feedback from massive
stars that may quench the flickering SF does not disrupt the overall burst
event in our sample of galaxies. While five galaxies present fossil bursts,
fifteen galaxies show ongoing bursts and thus the final durations may be longer
than we report here for these systems. One galaxy shows a burst that has been
ongoing for only 20 Myr; we are likely seeing the beginning of a burst event in
this system. Using the duration of the starbursts, we calculate that the bursts
deposited 10^(53.9)-10^(57.2) ergs of energy into the interstellar medium
through stellar winds and supernovae and produced 3%-26% of the host galaxy's
mass.Comment: 28 pages, 4 figure
Optimized Trigger for Ultra-High-Energy Cosmic-Ray and Neutrino Observations with the Low Frequency Radio Array
When an ultra-high energy neutrino or cosmic ray strikes the Lunar surface a
radio-frequency pulse is emitted. We plan to use the LOFAR radio telescope to
detect these pulses. In this work we propose an efficient trigger
implementation for LOFAR optimized for the observation of short radio pulses.Comment: Submitted to Nuclear Instruments and Methods in Physics Research
Section
Apertif 1.4 GHz continuum observations of the Bo\"otes field and their combined view with LOFAR
We present a new image of a 26.5 square degree region in the Bo\"otes
constellation obtained at 1.4 GHz using the Aperture Tile in Focus (Apertif)
system on the Westerbork Synthesis Radio Telescope. We use a newly developed
processing pipeline which includes direction-dependent self-calibration which
provides a significant improvement of the quality of the images compared to
those released as part of the Apertif first data release. For the Bo\"otes
region, we mosaic 187 Apertif images and extract a source catalog. The mosaic
image has an angular resolution of 2711.5 arcseconds and a median
background noise of 40 Jy/beam. The catalog has 8994 sources and is
complete down to the 0.3 mJy level. We combine the Apertif image with LOFAR
images of the Bo\"otes field at 54 and 150 MHz to study spectral properties of
the sources. We find a spectral flattening towards low flux density sources.
Using the spectral index limits from Apertif non-detections we derive that up
to 9 percent of the sources have ultra-steep spectra with a slope steeper than
-1.2. Steepening of the spectral index with increasing redshift is also seen in
the data showing a different dependency for the low-frequency spectral index
and the high frequency one. This can be explained by a population of sources
having concave radio spectra with a turnover frequency around the LOFAR band.
Additionally, we discuss cases of individual extended sources with an
interesting resolved spectral structure. With the improved pipeline, we aim to
continue processing data from the Apertif wide-area surveys and release the
improved 1.4 GHz images of several famous fields.Comment: 13 pages, 9 figures; to be published in A&
Detectors for the James Webb Space Telescope Near-Infrared Spectrograph I: Readout Mode, Noise Model, and Calibration Considerations
We describe how the James Webb Space Telescope (JWST) Near-Infrared
Spectrograph's (NIRSpec's) detectors will be read out, and present a model of
how noise scales with the number of multiple non-destructive reads
sampling-up-the-ramp. We believe that this noise model, which is validated
using real and simulated test data, is applicable to most astronomical
near-infrared instruments. We describe some non-ideal behaviors that have been
observed in engineering grade NIRSpec detectors, and demonstrate that they are
unlikely to affect NIRSpec sensitivity, operations, or calibration. These
include a HAWAII-2RG reset anomaly and random telegraph noise (RTN). Using real
test data, we show that the reset anomaly is: (1) very nearly noiseless and (2)
can be easily calibrated out. Likewise, we show that large-amplitude RTN
affects only a small and fixed population of pixels. It can therefore be
tracked using standard pixel operability maps.Comment: 55 pages, 10 figure
Real-time selective sequencing using nanopore technology
The Oxford Nanopore Technologies MinION sequencer enables the selection of specific DNA molecules for sequencing by reversing the driving voltage across individual nanopores. To directly select molecules for sequencing, we used dynamic time warping to match reads to reference sequences. We demonstrate our open-source Read Until software in real-time selective sequencing of regions within small genomes, individual amplicon enrichment and normalization of an amplicon set
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