2,951 research outputs found
EVLA Observations of OH Masers in ON 1
This Letter reports on initial Expanded Very Large Array (EVLA) observations
of the 6035 MHz masers in ON 1. The EVLA data are of good quality, lending
confidence in the new receiver system. Nineteen maser features, including six
Zeeman pairs, are detected. The overall distribution of 6035 MHz OH masers is
similar to that of the 1665 MHz OH masers. The spatial resolution is sufficient
to unambiguously determine that the magnetic field is strong (~ -10 mG) at the
location of the blueshifted masers in the north, consistent with Zeeman
splitting detected in 13441 MHz OH masers in the same velocity range. Left and
right circularly polarized ground-state features dominate in different regions
in the north of the source, which may be due to a combination of magnetic field
and velocity gradients. The combined distribution of all OH masers toward the
south is suggestive of a shock structure of the sort previously seen in W3(OH).Comment: 4 pages using emulateapj.cls including 2 tables and 2 color figure
Disparity in the natural cycles of Borrelia burgdorferi and the agent of human granulocytic ehrlichiosis.
We studied the prevalence of Borrelia burgdorferi and the agent of human granulocytic ehrlichiosis (HGE) among questing nymphal and adult Ixodes scapularis ticks of the same generation and the infectivity of wild white-footed mice for ticks feeding on them. The prevalence of B. burgdorferi infection in host-seeking ticks increased less than twofold from nymphal (31% to 33%) to adult (52% to 56%) stage, and 52% of white-footed mice were infected. Prevalence of the agent of HGE increased 4.5- to 10.6-fold from nymphal (1.5% to 1.8%) to adult stage (7.6% to 19.0%), while only 18% of mice were infectious to ticks. B. burgdorferi infection was more common in mouse-fed ticks than in ticks collected from vegetation, whereas the agent of HGE was half as common in mouse-fed ticks as in ticks collected from vegetation. The different prevalence in nature of these pathogens in ticks suggests that their maintenance cycles are also different
Relative Astrometry of Compact Flaring Structures in Sgr A* with Polarimetric VLBI
We demonstrate that polarimetric interferometry can be used to extract
precise spatial information about compact polarized flares of Sgr A*. We show
that, for a faint dynamical component, a single interferometric baseline
suffices to determine both its polarization and projected displacement from the
quiescent intensity centroid. A second baseline enables two-dimensional
reconstruction of the displacement, and additional baselines can self-calibrate
using the flare, enhancing synthesis imaging of the quiescent emission. We
apply this technique to simulated 1.3-mm wavelength observations of a "hot
spot" embedded in a radiatively inefficient accretion disk around Sgr A*. Our
results indicate that, even with current sensitivities, polarimetric
interferometry with the Event Horizon Telescope can achieve ~5 microarcsecond
relative astrometry of compact flaring structures near Sgr A* on timescales of
minutes.Comment: 9 Pages, 4 Figures, accepted for publication in Ap
Changing the HTS Paradigm: AI-Driven Iterative Screening for Hit Finding
Iterative screening is a process in which screening is done in batches, with each batch filled by using machine learning to select the most promising compounds from the library based on the previous results. We believe iterative screening is poised to enhance the screening process by improving hit finding while at the same time reducing the number of compounds screened. In addition, we see this process as a key enabler of next-generation high-throughput screening (HTS), which uses more complex assays that better describe the biology but demand more resource per screened compound. To demonstrate the utility of these methods, we retrospectively analyze HTS data from PubChem with a focus on machine learning-based screening strategies that can be readily implemented in practice. Our results show that over a variety of HTS experimental paradigms, an iterative screening setup that screens a total of 35% of the screening collection over as few as three iterations has a median return rate of approximately 70% of the active compounds. Increasing the portion of the library screened to 50% yields median returns of approximately 80% of actives. Using six iterations increases these return rates to 78% and 90%, respectively. The best results were achieved with machine learning models that can be run on a standard desktop. By demonstrating that the utility of iterative screening holds true even with a small number of iterations, and without requiring significant computational resources, we provide a roadmap for the practical implementation of these techniques in hit finding
Noether's second theorem in a general setting. Reducible gauge theories
We prove Noether's direct and inverse second theorems for Lagrangian systems
on fiber bundles in the case of gauge symmetries depending on derivatives of
dynamic variables of an arbitrary order. The appropriate notions of reducible
gauge symmetries and Noether's identities are formulated, and their equivalence
by means of certain intertwining operator is proved.Comment: 20 pages, to be published in J. Phys. A (2005
Effelsberg Observations of Excited-State (6.0 GHz) OH in Supernova Remnants and W3(OH)
While masers in the 1720 MHz transition of OH are detected toward many
supernova remnants (SNRs), no other OH transition is seen as a maser in SNRs.
We present a search for masers at 6049 MHz, which has recently been predicted
to produce masers by pure collisional excitation at conditions similar to that
required for 1720 MHz masing. The Effelsberg 100 m telescope was used to
observe the excited-state 6016, 6030, 6035, and 6049 MHz lines of OH toward
selected SNRs, most of which have previously-detected bright 1720 MHz masers.
No excited-state masers are found toward SNRs, consistent with previous
observations of the 6049 MHz and other excited-state transitions. We do not see
clear evidence of absorption toward SNR target positions, although we do see
evidence of absorption in the molecular cloud at +50 km/s near Sgr A East. Weak
absorption is detected at 6016 MHz toward W3(OH), while stronger, narrower
emission is seen at 6049 MHz, suggesting that the 6049 MHz emission is a
low-gain maser. We conclude that conditions in SNRs are not conducive to
excited-state maser emission, especially in excited-state satellite lines.Comment: 4 pages using emulateapj.cls including 2 tables and 1 figure,
accepted to ApJ
Imaging an Event Horizon: Mitigation of Source Variability of Sagittarius A*
The black hole in the center of the Galaxy, associated with the compact
source Sagittarius A* (Sgr A*), is predicted to cast a shadow upon the emission
of the surrounding plasma flow, which encodes the influence of general
relativity in the strong-field regime. The Event Horizon Telescope (EHT) is a
Very Long Baseline Interferometry (VLBI) network with a goal of imaging nearby
supermassive black holes (in particular Sgr A* and M87) with angular resolution
sufficient to observe strong gravity effects near the event horizon. General
relativistic magnetohydrodynamic (GRMHD) simulations show that radio emission
from Sgr A* exhibits vari- ability on timescales of minutes, much shorter than
the duration of a typical VLBI imaging experiment, which usually takes several
hours. A changing source structure during the observations, however, violates
one of the basic assumptions needed for aperture synthesis in radio
interferometry imaging to work. By simulating realistic EHT observations of a
model movie of Sgr A*, we demonstrate that an image of the average quiescent
emission, featuring the characteristic black hole shadow and photon ring
predicted by general relativity, can nonetheless be obtained by observing over
multiple days and subsequent processing of the visibilities (scaling,
averaging, and smoothing) before imaging. Moreover, it is shown that this
procedure can be combined with an existing method to mitigate the effects of
interstellar scattering. Taken together, these techniques allow the black hole
shadow in the Galactic center to be recovered on the reconstructed image.Comment: 10 pages, 12figures, accepted for publication in Ap
Interpretation and the Constraints on International Courts
This paper argues that methodologies of interpretation do not do what they promise â they do not constrain interpretation by providing neutral steps that one can follow in finding out a meaning of a text â but nevertheless do their constraining work by being part of what can be described as the legal practice
Observing---and Imaging---Active Galactic Nuclei with the Event Horizon Telescope
Originally developed to image the shadow region of the central black hole in
Sagittarius A* and in the nearby galaxy M87, the Event Horizon Telescope (EHT)
provides deep, very high angular resolution data on other AGN sources too. The
challenges of working with EHT data have spurred the development of new image
reconstruction algorithms. This work briefly reviews the status of the EHT and
its utility for observing AGN sources, with emphasis on novel imaging
techniques that offer the promise of better reconstructions at 1.3 mm and other
wavelengths.Comment: 10 pages, proceedings contribution for Blazars through Sharp
Multi-Wavelength Eyes, submitted to Galaxie
Full-Polarization Observations of OH Masers in Massive Star-Forming Regions: I. Data
We present full-polarization VLBA maps of the ground-state, main-line, 2 Pi
3/2, J = 3/2 OH masers in 18 Galactic massive star-forming regions. This is the
first large polarization survey of interstellar hydroxyl masers at VLBI
resolution. A total of 184 Zeeman pairs are identified, and the corresponding
magnetic field strengths are indicated. We also present spectra of the NH3
emission or absorption in these star-forming regions. Analysis of these data
will be presented in a companion paper.Comment: 111 pages, including 42 figures and 21 tables, to appear in ApJ
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