1,555 research outputs found
Jetstream: A national science & engineering cloud. Globus World Lightning Talk.
Presentation highlighting the capabilities and purpose for the upcoming Jetstream system.Jetstream and related material to its operation are funded by the National Science Foundation under grant No. ACI-1445604
Modeling the Radio Background from the First Black Holes at Cosmic Dawn: Implications for the 21 cm Absorption Amplitude
We estimate the 21 cm Radio Background from accretion onto the first
intermediate-mass Black Holes between and .
Combining potentially optimistic, but plausible, scenarios for black hole
formation and growth with empirical correlations between luminosity and
radio-emission observed in low-redshift active galactic nuclei, we find that a
model of black holes forming in molecular cooling halos is able to produce a 21
cm background that exceeds the Cosmic Microwave Background (CMB) at though models involving larger halo masses are not entirely excluded. Such
a background could explain the surprisingly large amplitude of the 21 cm
absorption feature recently reported by the EDGES collaboration. Such black
holes would also produce significant X-ray emission and contribute to the
keV soft X-ray background at the level of
erg sec cm deg, consistent with existing constraints. In
order to avoid heating the IGM over the EDGES trough, these black holes would
need to be obscured by Hydrogen column depths of . Such black holes would avoid violating contraints on
the CMB optical depth from Planck if their UV photon escape fractions were
below , which would be a natural result of
imposed by an unheated IGM.Comment: 10 pages, 7 figures, accepted to ApJ, replacement to match submitted
versio
A Low Noise Thermometer Readout for Ruthenium Oxide Resistors
The thermometer and thermal control system, for the Absolute Radiometer for
Cosmology, Astrophysics, and Diffuse Emission (ARCADE) experiment, is
described, including the design, testing, and results from the first flight of
ARCADE. The noise is equivalent to about 1 Omega or 0.15 mK in a second for the
RuO_2 resistive thermometers at 2.7 K. The average power dissipation in each
thermometer is 1 nW. The control system can take full advantage of the
thermometers to maintain stable temperatures. Systematic effects are still
under investigation, but the measured precision and accuracy are sufficient to
allow measurement of the cosmic background spectrum.
Journal-ref: Review of Scientific Instruments Vol 73 #10 (Oct 2002)Comment: 5 pages text 7 figure
A Model Rock Biofilm Growing in Percolation Columns
Sub-aerial biofilms (SAB) are ubiquitous, self-sufficient microbial ecosystems
found on mineral surfaces at all altitudes and latitudes. SABs, which are the
principal causes of weathering on exposed terrestrial surfaces, are
characterized by patchy growth dominated by associations of algae,
cyanobacteria, fungi and heterotrophic bacteria. A recently developed in vitro
system to study colonization of rocks exposed to air included two key SAB
participants - the rock-inhabiting ascomycete Knufia petricola (CBS 123872)
and the phototrophic cyanobacterium Nostoc punctiforme ATCC29133. Both
partners are genetically tractable and we used them here to study weathering
of granite, K-feldspar and plagioclase. Small fragments of the various rocks
or minerals (1â6 mm) were packed into flow-through columns and incubated with
0.1% glucose and 10 ÎŒM thiamine-hydrochloride (90 ÎŒL minâ1) to compare
weathering with and without biofilms. Dissolution of the minerals was followed
by: (i) analysing the degradation products in the effluent from the columns
via Inductively Coupled Plasma Spectroscopy and (ii) by studying polished
sections of the incubated mineral fragments/grains using scanning electron
microscopy, transmission electron microscopy and energy dispersive X-ray
analyses. K. petricola/N. punctiforme stimulated release of Ca, Na, Mg and Mn.
Analyses of the polished sections confirmed depletion of Ca, Na and K near the
surface of the fragments. The abrupt decrease in Ca concentration observed in
peripheral areas of plagioclase fragments favored a dissolution-
reprecipitation mechanism. Percolation columns in combination with a model
biofilm can thus be used to study weathering in closed systems. Columns can
easily be filled with different minerals and biofilms, the effluent as well as
grains can be collected after long-term exposure under axenic conditions and
easily analyzed
A Spin Modulated Telescope to Make Two Dimensional CMB Maps
We describe the HEMT Advanced Cosmic Microwave Explorer (HACME), a balloon
borne experiment designed to measure sub-degree scale Cosmic Microwave
Background anisotropy over hundreds of square degrees, using a unique two
dimensional scanning strategy. A spinning flat mirror that is canted relative
to its spin axis modulates the direction of beam response in a nearly
elliptical path on the sky. The experiment was successfully flown in February
of 1996, achieving near laboratory performance for several hours at float
altitude. A map free of instrumental systematic effects is produced for a 3.5
hour observation of 630 square degrees, resulting in a flat band power upper
limit of (l(l+1)C_l/2 pi)^0.5 < 77 microK at l = 38 (95% confidence). The
experiment design, flight operations and data, including atmospheric effects
and noise performance, are discussed.Comment: 4 pages, 3 figure
Pulmonary effects of inhalation of spark-generated silver nanoparticles in Brown-Norway and Sprague-Dawley rats
The increasing use of silver nanoparticles (AgNPs) in consumer products is concerning. We examined the potential toxic effects when inhaled in Brown-Norway (BN) rats with a pre-inflammatory state compared to Sprague-Dawley (SD) rats.We determined the effect of AgNPs generated from a spark generator (mass concentration: 600-800Â ÎŒg/mm(3); mean diameter: 13-16Â nm; total lung doses: 8 [Low] and 26-28 [High] ÎŒg) inhaled by the nasal route in both rat strains. Rats were sacrificed at day 1 and day 7 after exposure and measurement of lung function.In both strains, there was an increase in neutrophils in bronchoalveolar lavage (BAL) fluid at 24Â h at the high dose, with concomitant eosinophilia in BN rats. While BAL inflammatory cells were mostly normalised by Day 7, lung inflammation scores remained increased although not the tissue eosinophil scores. Total protein levels were elevated at both lung doses in both strains. There was an increase in BAL IL-1ÎČ, KC, IL-17, CCL2 and CCL3 levels in both strains at Day 1, mostly at high dose. Phospholipid levels were increased at the high dose in SD rats at Day 1 and 7, while in BN rats, this was only seen at Day 1; surfactant protein D levels decreased at day 7 at the high dose in SD rats, but was increased at Day 1 at the low dose in BN rats. There was a transient increase in central airway resistance and in tissue elastance in BN rats at Day 1 but not in SD rats. Positive silver-staining was seen particularly in lung tissue macrophages in a dose and time-dependent response in both strains, maximal by day 7. Lung silver levels were relatively higher in BN rat and present at day 7 in both strains.Presence of cellular inflammation and increasing silver-positive macrophages in lungs at day 7, associated with significant levels of lung silver indicate that lung toxicity is persistent even with the absence of airway luminal inflammation at that time-point. The higher levels and persistence of lung silver in BN rats may be due to the pre-existing inflammatory state of the lungs
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