1,008 research outputs found
CHANG-ES XI: Circular Polarization in the Cores of Nearby Galaxies
We detect 5 galaxies in the CHANG-ES (Continuum Halos in Nearby Galaxies --
an EVLA Survey) sample that show circular polarization (CP) at L-band in our
high resolution data sets. Two of the galaxies (NGC~4388 and NGC~4845) show
strong Stokes \%, two (NGC~660 and NGC~3628) have
values of \%, and NGC~3079 is a marginal detection at \%. The two strongest galaxies also have the most luminous X-ray
cores and the strongest internal absorption in X-rays. We have expanded on our
previous Faraday conversion interpretation and analysis and provide analytical
expressions for the expected signal for a general case in which the cosmic
ray electron energy spectral index can take on any value. We provide examples
as to how such expressions could be used to estimate magnetic field strengths
and the lower energy cutoff for CR electrons. Four out of our detections are
{\it resolved}, showing unique structures, including a {\it jet} in NGC~4388
and a CP `conversion disk' in NGC~4845. The conversion disk is inclined to the
galactic disk but is perpendicular to a possible outflow direction. Such CP
structures have never before been seen in any galaxy to our knowledge. None of
the galaxy cores show linear polarization at L-band. Thus CP may provide a
unique probe of physical conditions deep into radio AGNs.Comment: 30 pages, 4 figures, accepted to MNRA
An examination of the long-term CO records from MOPITT and IASI: comparison of retrieval methodology
International audienceCarbon monoxide (CO) is a key atmospheric compound that can be remotely sensed by satellite on the global scale. Fifteen years of continuous observations are now available from the MOPITT/Terra mission (2000 to present). Another fifteen and more years of observations will be provided by the IASI/MetOp instrument series (2007–2023>). In order to study long term variability and trends, a homogeneous record is required, which is not straightforward as the retrieved products are instrument and processing dependent. The present study aims at evaluating the consistency between the CO products derived from the MOPITT and IASI missions, both for total columns and vertical profiles, during a six year overlap period (2008–2013). The analysis is performed by first comparing the available 2013 versions of the retrieval algorithms, and second using a dedicated reprocessing of MOPITT CO profiles and columns based on the IASI a priori constraints. MOPITT v5T total columns are generally slightly higher over land (bias ranging from 0 to 13%) than IASI v20100815 data. When IASI and MOPITT data are retrieved with the same a priori constraints, correlation coefficients are slightly improved. Large discrepancies (total column bias over 15%) observed in the Northern Hemisphere during the winter months are reduced by a factor of 2 to 2.5. The detailed analysis of retrieved vertical profiles compared with collocated aircraft data from the MOZAIC-IAGOS network, illustrates the advantages and disadvantages of a constant vs. a variable a priori. On one hand, MOPITT agrees better with the aircraft profiles for observations with persisting high levels of CO throughout the year due to pollution or seasonal fire activity (because the climatology-based a priori is supposed to be closer to the real atmospheric state). On the other hand, IASI performs better when unexpected events leading to high levels of CO occur, due to the less constrained variance-covariance matrix
Gas phase characterization of the noncovalent quaternary structure of Cholera toxin and the Cholera toxin B subunit pentamer
Cholera toxin (CTx) is an AB5 cytotonic protein that has medical relevance in cholera and as a novel mucosal adjuvant. Here, we report an analysis of the noncovalent homopentameric complex of CTx B chain (CTx B5) using electrospray ionization triple quadrupole mass spectrometry and tandem mass spectrometry and the analysis of the noncovalent hexameric holotoxin usingelectrospray ionization time-of-flight mass spectrometry over a range of pH values that correlate with those encountered by this toxin after cellular uptake. We show that noncovalent interactions within the toxin assemblies were maintained under both acidic and neutral conditions in the gas phase. However, unlike the related Escherichia coli Shiga-like toxin B5 pentamer (SLTx B), the CTx B5 pentamer was stable at low pH, indicating that additional interactions must be present within the latter. Structural comparison of the CTx B monomer interface reveals an additional α-helix that is absent in the SLTx B monomer. In silico energy calculations support interactions between this helix and the adjacent monomer. These data provide insight into the apparent stabilization of CTx B relative to SLTx B
Influence of baryons on the orbital structure of dark matter haloes
We explore the dynamical signatures imprinted by baryons on dark matter
haloes during the formation process using the OverWhelmingly Large Simulations
(OWLS), a set of state-of-the-art high-resolution cosmological hydrodynamical
simulations. We present a detailed study of the effects of the implemented
feedback prescriptions on the orbits of dark matter particles, stellar
particles and subhaloes, analysing runs with no feedback, with stellar feedback
and with feedback from supermassive black holes. We focus on the central
regions (0.25 r_{200}) of haloes with virial masses ~ 6 x 10^{13} (~ 7 x
10^{11}) Msun/h at z = 0(2). We also investigate how the orbital content
(relative fractions of the different orbital types) of these haloes depends on
several key parameters such as their mass, redshift and dynamical state. The
results of spectral analyses of the orbital content of these simulations are
compared, and the change in fraction of box, tube and irregular orbits is
quantified. Box orbits are found to dominate the orbital structure of dark
matter haloes in cosmological simulations. There is a strong anticorrelation
between the fraction of box orbits and the central baryon fraction. While
radiative cooling acts to reduce the fraction of box orbits, strong feedback
implementations result in a similar orbital distribution to that of the dark
matter only case. The orbital content described by the stellar particles is
found to be remarkably similar to that drawn from the orbits of dark matter
particles, suggesting that either they have forgotten their dynamical history,
or that subhaloes bringing in stars are not biased significantly with respect
to the main distribution. The orbital content of the subhaloes is in broad
agreement with that seen in the outer regions of the particle distributions.Comment: 18 pages, 13 figures, 3 tables. Accepted for publication in MNRA
A Brightest Cluster Galaxy with an Extremely Large Flat Core
Hubble Space Telescope images of the galaxy cluster Abell 2261, obtained as
part of the Cluster Lensing And Supernova survey with Hubble, show that the
brightest galaxy in the cluster, A2261-BCG, has the largest core yet detected
in any galaxy. The cusp radius of A2261-BCG is 3.2 kpc, twice as big as the
next largest core known, and ~3x bigger than those typically seen in the most
luminous BCGs. The morphology of the core in A2261-BCG is also unusual, having
a flat or even slightly-depressed interior surface brightness profile, rather
than the typical shallow cusp. This implies that the galaxy has a core with
constant or even centrally decreasing stellar density. Interpretation of the
core as an end product of the "scouring" action of a binary supermassive black
hole implies a total black hole mass ~1E+10 M_sun from the extrapolation of
most relationships between core structure and black hole mass. The core falls
1-sigma above the cusp-radius versus galaxy luminosity relation. Its large size
in real terms, and the extremely large black hole mass required to generate it,
raise the possibility that the core has been enlarged by additional processes,
such as the ejection of the black holes that originally generated the core. The
flat central stellar density profile is consistent with this hypothesis. The
core is also displaced by 0.7 kpc from the center of the surrounding envelope,
consistent with a local dynamical perturbation of the core.Comment: 11 pages, 7 figures, accepted for publication in the Astrophysical
Journa
Effective modeling for integrated water resource management: a guide to contextual practices by phases and steps and future opportunities
The effectiveness of Integrated Water Resource Management (IWRM) modeling hinges on the quality of practices employed through the process, starting from early problem definition all the way through to using the model in a way that serves its intended purpose. The adoption and implementation of effective modeling practices need to be guided by a practical understanding of the variety of decisions that modelers make, and the information considered in making these choices. There is still limited documented knowledge on the modeling workflow, and the role of contextual factors in determining this workflow and which practices to employ. This paper attempts to contribute to this knowledge gap by providing systematic guidance of the modeling practices through the phases (Planning, Development, Application, and Perpetuation) and steps that comprise the modeling process, positing questions that should be addressed. Practice-focused guidance helps explain the detailed process of conducting IWRM modeling, including the role of contextual factors in shaping practices. We draw on findings from literature and the authors’ collective experience to articulate what and how contextual factors play out in employing those practices. In order to accelerate our learning about how to improve IWRM modeling, the paper concludes with five key areas for future practice-related research: knowledge sharing, overcoming data limitations, informed stakeholder involvement, social equity and uncertainty management. © 2019 Elsevier Lt
Ongoing Assembly of Massive Galaxies by Major Merging in Large Groups and Clusters from the SDSS
We investigate the incidence of major mergers creating >10e11 Msun galaxies
in present-day groups and clusters more massive than 2.5e13 Msun. We identify
38 pairs of massive galaxies with mutual tidal interaction signatures selected
from >5000 galaxies with >5e10 Msun that reside in 845 such groups. We fit the
images of each galaxy pair as the line-of-sight projection of symmetric models
and identify mergers by the presence of residual asymmetries around each
progenitor, such as off-center isophotes, broad tidal tails, and dynamical
friction wakes. At the resolution and sensitivity of the SDSS, such mergers are
found in 16% of high-mass, galaxy-galaxy pairs with magnitude differences of
<1.5 and <30 kpc projected separations. We find that 90% of these mergers have
nearly equal-mass progenitors with red-sequence colors and
centrally-concentrated morphologies, the hallmarks of dissipationless merger
simulations. Mergers at group centers are more common than between 2
satellites, but both are morphologically indistinguishable and we tentatively
conclude that the latter are likely located at the dynamical centers of
recently accreted subhalos. The frequency of central and satellite merging
diminishes with group mass consistent with dynamical friction expectations.
Based on reasonable assumptions, the centers of these massive halos are growing
in stellar mass by 1-9% per Gyr, on average. Compared to all LRG-LRG mergers,
we find a 2-9 times higher rate for their merging when restricted to these
dense environments. Our results imply that the massive end of the galaxy
population continues to evolve hierarchically at a measurable level, and that
the centers of massive groups are the preferred environment for merger-driven
galaxy assembly. (abridged)Comment: 48 pages, 21 figures. Submitted for publication in MNRAS. Version
with full resolution figures at
http://www.astro.umass.edu/~dmac/Preprints/mergers.hires.pd
Distribution of Mycobacterium ulcerans in Buruli Ulcer Endemic and Non-Endemic Aquatic Sites in Ghana
Mycobacterium ulcerans, the causative agent of Buruli ulcer, is an emerging environmental bacterium in Australia and West Africa. The primary risk factor associated with Buruli ulcer is proximity to slow moving water. Environmental constraints for disease are shown by the absence of infection in arid regions of infected countries. A particularly mysterious aspect of Buruli ulcer is the fact that endemic and non-endemic villages may be only a few kilometers apart within the same watershed. Recent studies suggest that aquatic invertebrate species may serve as reservoirs for M. ulcerans, although transmission pathways remain unknown. Systematic studies of the distribution of M. ulcerans in the environment using standard ecological methods have not been reported. Here we present results from the first study based on random sampling of endemic and non-endemic sites. In this study PCR-based methods, along with biofilm collections, have been used to map the presence of M. ulcerans within 26 aquatic sites in Ghana. Results suggest that M. ulcerans is present in both endemic and non-endemic sites and that variable number tandem repeat (VNTR) profiling can be used to follow chains of transmission from the environment to humans. Our results suggesting that the distribution of M. ulcerans is far broader than the distribution of human disease is characteristic of environmental pathogens. These findings imply that focal demography, along with patterns of human water contact, may play a major role in transmission of Buruli ulcer
The Restyled Federal Rules of Evidence
A lightly edited transcript of the Symposium held at the William & Mary School of Law on October 28, 2011
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