118 research outputs found
Market Conditions and Political Forces: Charter School Restarts in Washington, DC
Charter schools provide public education choices to educational consumers, school-aged children and their families. As independently run and publicly funded schools of choice, charter schools straddle the line between government and private enterprise and are held accountable by a combination of market mechanisms and bureaucratic accountability. Schools that fail to satisfy public standards or consumers may close, causing disruption to students and families. Recently, some charter school closures have resulted in charter restarts, the acquisition of the assets of a closed school by a new, proven or promising school operator serving substantially the same student population. This qualitative case study examines eight charter school closures and five charter school restarts in Washington, DC between 2013 and 2016. The study aims to answer three exploratory research questions: Why are some schools restarted and others closed outright? Who decides which charter schools are closed and which are restarted? How do they make these decisions? The study finds that numerous actors are involved in decisions about charter school restarts, including the boards of closing schools, the authorizer, other government entities, and various private actors. Communities and families, however, lack proactive roles in the decision-making process. Decisions are made based on a varied combination of market and political forces, though there is often more of an illusion of process than an actual one. The study also finds that market factors, a complex set of political interactions and conditions, including varying levels of social capital among actors, and issues of race are all at work in determining why some schools close and others restart
Census of the Local Universe (CLU) Narrow-Band Survey I: Galaxy Catalogs from Preliminary Fields
We present the Census of the Local Universe (CLU) narrow-band survey to
search for emission-line (\ha) galaxies. CLU-\ha~has imaged 3 of
the sky (26,470~deg) with 4 narrow-band filters that probe a distance out
to 200~Mpc. We have obtained spectroscopic follow-up for galaxy candidates in
14 preliminary fields (101.6~deg) to characterize the limits and
completeness of the survey. In these preliminary fields, CLU can identify
emission lines down to an \ha~flux limit of
~ at 90\% completeness, and recovers 83\%
(67\%) of the \ha~flux from catalogued galaxies in our search volume at the
=2.5 (=5) color excess levels. The contamination from galaxies
with no emission lines is 61\% (12\%) for =2.5 (=5). Also, in
the regions of overlap between our preliminary fields and previous
emission-line surveys, we recover the majority of the galaxies found in
previous surveys and identify an additional 300 galaxies. In total, we
find 90 galaxies with no previous distance information, several of which are
interesting objects: 7 blue compact dwarfs, 1 green pea, and a Seyfert galaxy;
we also identified a known planetary nebula. These objects show that the
CLU-\ha~survey can be a discovery machine for objects in our own Galaxy and
extreme galaxies out to intermediate redshifts. However, the majority of the
CLU-\ha~galaxies identified in this work show properties consistent with normal
star-forming galaxies. CLU-\ha~galaxies with new redshifts will be added to
existing galaxy catalogs to focus the search for the electromagnetic
counterpart to gravitational wave events.Comment: 28 pages, 22 figures, 4 tables (Accepted to ApJ
Myo/Nog cell regulation of bone morphogenetic protein signaling in the blastocyst is essential for normal morphogenesis and striated muscle lineage specification
AbstractCells that express MyoD mRNA, the G8 antigen and the bone morphogenetic protein (BMP) inhibitor noggin (Nog) are present in the epiblast before gastrulation. Ablation of “Myo/Nog” cells in the blastocyst results in an expansion of canonical BMP signaling and prevents the expression of noggin and follistatin before and after the onset of gastrulation. Once eliminated in the epiblast, they are neither replaced nor compensated for as development progresses. Older embryos lacking Myo/Nog cells exhibit severe axial malformations. Although Wnts and Sonic hedgehog are expressed in ablated embryos, skeletal muscle progenitors expressing Pax3 are missing in the somites. Pax3+ cells do emerge adjacent to Wnt3a+ cells in vitro; however, few undergo skeletal myogenesis. Ablation of Myo/Nog cells also results in ectopically placed cardiac progenitors and cardiomyocytes in the somites. Reintroduction of Myo/Nog cells into the epiblast of ablated embryos restores normal patterns of BMP signaling, morphogenesis and skeletal myogenesis, and inhibits the expression of cardiac markers in the somites. This study demonstrates that Myo/Nog cells are essential regulators of BMP signaling in the early epiblast and are indispensable for normal morphogenesis and striated muscle lineage specification
Identification of microorganisms by a rapid PCR panel from positive blood cultures leads to faster optimal antimicrobial therapy - a before-after study
BACKGROUND
The BioFire® FilmArray® Blood Culture Identification Panel 1 (BF-FA-BCIP) detects microorganisms with high accuracy in positive blood cultures (BC) - a key step in the management of patients with suspected bacteraemia. We aimed to compare the time to optimal antimicrobial therapy (OAT) for the BF-FA-BCIP vs. standard culture-based identification.
METHODS
In this retrospective single-centre study with a before-after design, 386 positive BC cases with identification by BF-FA-BCIP were compared to 414 controls with culture-based identification. The primary endpoint was the time from BC sampling to OAT. Secondary endpoints were time to effective therapy, length of stay, (re-)admission to ICU, in-hospital and 30-day mortality. Outcomes were assessed using Cox proportional hazard models and logistic regressions.
RESULTS
Baseline characteristics of included adult inpatients were comparable. Main sources of bacteraemia were urinary tract and intra-abdominal infection (19.2% vs. 22.0% and 16.8% vs. 15.7%, for cases and controls, respectively). Median (95%CI) time to OAT was 25.5 (21.0-31.2) hours with BF-FA-BCIP compared to 45.7 (37.7-51.4) hours with culture-based identification. We observed no significant difference for secondary outcomes.
CONCLUSIONS
Rapid microorganism identification by BF-FA-BCIP was associated with a median 20-h earlier initiation of OAT in patients with positive BC. No impact on length of stay and mortality was noted.
TRIAL REGISTRATION
Clinicaltrials.gov, NCT04156633, registered on November 5, 2019
Radial Star Formation Histories in 32 Nearby Galaxies
The spatially resolved star formation histories are studied for 32 normal
star-forming galaxies drawn from the the Spitzer Extended Disk Galaxy
Exploration Science survey. At surface brightness sensitivities fainter than 28
mag arcsec, the new optical photometry is deep enough to complement
archival ultraviolet and infrared imaging and to explore the properties of the
emission well beyond the traditional optical extents of these nearby galaxies.
Fits to the spectral energy distributions using a delayed star formation
history model indicate a subtle but interesting average radial trend for the
spiral galaxies: the inner stellar systems decrease in age with increasing
radius, consistent with inside-out disk formation, but the trend reverses in
the outermost regions with the stellar age nearly as old as the innermost
stars. These results suggest an old stellar outer disk population formed
through radial migration and/or the cumulative history of minor mergers and
accretions of satellite dwarf galaxies. The subset of S0 galaxies studied here
show the opposite trend compared to what is inferred for spirals:
characteristic stellar ages that are increasingly older with radius for the
inner portions of the galaxies, and increasingly younger stellar ages for the
outer portions. This result suggests that either S0 galaxies are not well
modeled by a delayed- model, and/or that S0 galaxies have a more
complicated formation history than spiral galaxies.Comment: Accepted for publication in the Astronomical Journal. arXiv admin
note: text overlap with arXiv:1511.0328
Using [C II] 158 μm Emission from Isolated ISM Phases as a Star Formation Rate Indicator
The brightest observed emission line in many star-forming galaxies is the [C II] 158 μm line, making it detectable up to z ~ 7. In order to better understand and quantify the [C II] emission as a tracer of star formation, the theoretical ratio between the [N II] 205 μm emission and the [C II] 158 μm emission has been employed to empirically determine the fraction of [C II] emission that originates from the ionized and neutral phases of the interstellar medium (ISM). Sub-kiloparsec measurements of the [C II] 158 μm and [N II] 205 μm lines in nearby galaxies have recently become available as part of the Key Insights in Nearby Galaxies: a Far Infrared Survey with Herschel (KINGFISH) and Beyond the Peak programs. With the information from these two far-infrared lines along with the multi-wavelength suite of KINGFISH data, a calibration of the [C II] emission line as a star formation rate (SFR) indicator and a better understanding of the [C II] deficit are pursued. [C II] emission is also compared to polycyclic aromatic hydrocarbon (PAH) emission in these regions to compare photoelectric heating from PAH molecules to cooling by [C II] in the neutral and ionized phases of the ISM. We find that the [C II] emission originating in the neutral phase of the ISM does not exhibit a deficit with respect to the infrared luminosity and is therefore preferred over the [C II] emission originating in the ionized phase of the ISM as an SFR indicator for the normal star-forming galaxies included in this sample
PHANGS-JWST: Data-processing Pipeline and First Full Public Data Release
The exquisite angular resolution and sensitivity of JWST are opening a new window for our understanding of the Universe. In nearby galaxies, JWST observations are revolutionizing our understanding of the first phases of star formation and the dusty interstellar medium. Nineteen local galaxies spanning a range of properties and morphologies across the star-forming main sequence have been observed as part of the PHANGS-JWST Cycle 1 Treasury program at spatial scales of ∼5–50 pc. Here, we describe pjpipe, an image-processing pipeline developed for the PHANGS-JWST program that wraps around and extends the official JWST pipeline. We release this pipeline to the community as it contains a number of tools generally useful for JWST NIRCam and MIRI observations. Particularly for extended sources, pjpipe products provide significant improvements over mosaics from the MAST archive in terms of removing instrumental noise in NIRCam data, background flux matching, and calibration of relative and absolute astrometry. We show that slightly smoothing F2100W MIRI data to 0.″9 (degrading the resolution by about 30%) reduces the noise by a factor of ≈3. We also present the first public release (DR1.1.0) of the pjpipe processed eight-band 2–21 μm imaging for all 19 galaxies in the PHANGS-JWST Cycle 1 Treasury program. An additional 55 galaxies will soon follow from a new PHANGS-JWST Cycle 2 Treasury program
Calibrating mid-infrared emission as a tracer of obscured star formation on HII-region scales in the era of JWST
Measurements of the star formation activity on cloud scales are fundamental
to uncovering the physics of the molecular cloud, star formation, and stellar
feedback cycle in galaxies. Infrared (IR) emission from small dust grains and
polycyclic aromatic hydrocarbons (PAHs) are widely used to trace the obscured
component of star formation. However, the relation between these emission
features and dust attenuation is complicated by the combined effects of dust
heating from old stellar populations and an uncertain dust geometry with
respect to heating sources. We use images obtained with NIRCam and MIRI as part
of the PHANGS--JWST survey to calibrate dust emission at 21, and the
emission in the PAH-tracing bands at 3.3, 7.7, 10, and 11.3 as
tracers of obscured star formation. We analyse 20000 optically selected
HII regions across 19 nearby star-forming galaxies, and benchmark their IR
emission against dust attenuation measured from the Balmer decrement. We model
the extinction-corrected H flux as the sum of the observed H
emission and a term proportional to the IR emission, with as the
proportionality coefficient. A constant leads to extinction-corrected
H estimates which agree with those obtained with the Balmer decrement
with a scatter of 0.1 dex for all bands considered. Among these bands,
21 emission is demonstrated to be the best tracer of dust
attenuation. The PAH-tracing bands underestimate the correction for bright HII
regions, since in these environments the ratio of PAH-tracing bands to 21 decreases, signalling destruction of the PAH molecules. For fainter HII
regions all bands suffer from an increasing contamination from the diffuse
infrared background.Comment: accepted for publication in A&
PHANGS-ML: Dissecting Multiphase Gas and Dust in Nearby Galaxies Using Machine Learning
The PHANGS survey uses Atacama Large Millimeter/submillimeter Array, Hubble Space Telescope, Very Large Telescope, and JWST to obtain an unprecedented high-resolution view of nearby galaxies, covering millions of spatially independent regions. The high dimensionality of such a diverse multiwavelength data set makes it challenging to identify new trends, particularly when they connect observables from different wavelengths. Here, we use unsupervised machine-learning algorithms to mine this information-rich data set to identify novel patterns. We focus on three of the PHANGS-JWST galaxies, for which we extract properties pertaining to their stellar populations; warm ionized and cold molecular gas; and polycyclic aromatic hydrocarbons (PAHs), as measured over 150 pc scale regions. We show that we can divide the regions into groups with distinct multiphase gas and PAH properties. In the process, we identify previously unknown galaxy-wide correlations between PAH band and optical line ratios and use our identified groups to interpret them. The correlations we measure can be naturally explained in a scenario where the PAHs and the ionized gas are exposed to different parts of the same radiation field that varies spatially across the galaxies. This scenario has several implications for nearby galaxies: (i) The uniform PAH ionized fraction on 150 pc scales suggests significant self-regulation in the interstellar medium, (ii) the PAH 11.3/7.7 μm band ratio may be used to constrain the shape of the non-ionizing far-ultraviolet to optical part of the radiation field, and (iii) the varying radiation field affects line ratios that are commonly used as PAH size diagnostics. Neglecting this effect leads to incorrect or biased PAH sizes
PHANGS-ML: dissecting multiphase gas and dust in nearby galaxies using machine learning
The PHANGS survey uses ALMA, HST, VLT, and JWST to obtain an unprecedented
high-resolution view of nearby galaxies, covering millions of spatially
independent regions. The high dimensionality of such a diverse multi-wavelength
dataset makes it challenging to identify new trends, particularly when they
connect observables from different wavelengths. Here we use unsupervised
machine learning algorithms to mine this information-rich dataset to identify
novel patterns. We focus on three of the PHANGS-JWST galaxies, for which we
extract properties pertaining to their stellar populations; warm ionized and
cold molecular gas; and Polycyclic Aromatic Hydrocarbons (PAHs), as measured
over 150 pc-scale regions. We show that we can divide the regions into groups
with distinct multiphase gas and PAH properties. In the process, we identify
previously-unknown galaxy-wide correlations between PAH band and optical line
ratios and use our identified groups to interpret them. The correlations we
measure can be naturally explained in a scenario where the PAHs and the ionized
gas are exposed to different parts of the same radiation field that varies
spatially across the galaxies. This scenario has several implications for
nearby galaxies: (i) The uniform PAH ionized fraction on 150 pc scales suggests
significant self-regulation in the ISM, (ii) the PAH 11.3/7.7 \mic~ band ratio
may be used to constrain the shape of the non-ionizing far-ultraviolet to
optical part of the radiation field, and (iii) the varying radiation field
affects line ratios that are commonly used as PAH size diagnostics. Neglecting
this effect leads to incorrect or biased PAH sizes.Comment: Main results in figures 6 and 12. Submitted to ApJ, and comments are
welcome
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