757 research outputs found
Exploratory ASCA Observations of Broad Absorption Line Quasi-Stellar Objects
We present the analysis and interpretation of a sample of eight ASCA
observations of Broad Absorption Line Quasi-Stellar Objects (BALQSOs). This is
the first moderate-sized sample of sensitive BALQSO observations above 2 keV,
and the BALQSOs in our sample are among the optically brightest known
(B=14.5-18.5). Despite the ability of 2-10 keV X-rays to penetrate large column
densities, we find BALQSOs to be extremely weak sources above 2 keV, and we are
only able to add two new 2-10 keV detections (0226-104 and IRAS 07598+6508) to
those previously reported. By comparison with non-BALQSOs of similar optical
continuum magnitudes, we derive the column densities needed to suppress the
expected X-ray fluxes of our BALQSOs. In several cases we derive column
densities > 5x10^{23} cm^{-2} for a neutral absorber with solar abundances.
These are the largest X-ray column densities yet inferred for BALQSOs, and they
exceed ROSAT lower limits by about an order of magnitude. Optical brightness
does not appear to be a good predictor of 2-10 keV brightness for BALQSOs, but
our data do suggest that the BALQSOs with high optical continuum polarizations
may be the X-ray brighter members of the class. For example, the highly
polarized object PHL 5200 appears to be unusually X-ray bright for a BALQSO
given its optical magnitude. We discuss the implications of our results for
future observations with AXAF and XMM. If the objects in our sample are
representative of the BALQSO population, precision X-ray spectroscopy of most
BALQSOs will unfortunately prove difficult in the near future.Comment: 19 pages, ApJ in press, also available from
http://www.astro.psu.edu/users/niel/papers/papers.htm
Detectability of low energy X-ray spectral components in type 1 AGN
In this paper we examine the percentage of type 1 AGN which require the
inclusion of a soft excess component and/or significant cold absorption in the
modelling of their X-ray spectra obtained by XMM-Newton. We do this by
simulating spectra which mimic typical spectral shapes in order to find the
maximum detectability expected at different count levels. We then apply a
correction to the observed percentages found for the Scott et al. (2011) sample
of 761 sources. We estimate the true percentage of AGN with a soft excess
component to be 75+/-23%, suggesting that soft excesses are ubiquitous in the
X-ray spectra of type 1 AGN. By carrying out joint fits on groups of low count
spectra in narrow z bins in which additional spectral components were not
originally detected, we show that the soft excess feature is recovered with a
mean temperature kT and blackbody to power-law normalisation ratio consistent
with those of components detected in individual high count spectra. Cold
absorption with nH values broadly consistent with those reported in individual
spectra are also recovered. We suggest such intrinsic cold absorption is found
in a minimum of ~5% of type 1 AGN and may be present in up to ~10%.Comment: 10 pages, 6 figures, 4 tables. Accepted for publication in MNRA
A new species of the fish louse genus Dipteropeltis Calman, 1912 (Crustacea: Branchiura) from Peru
Dipteropeltis es un género poco descrito de piojo de los peces endémico de Sudamérica. En una pequeña región de aguas negras en Loreto, Perú, se observaron y recolectaron 13 especímenes adultos y juveniles de una especie no identificada de Dipteropeltis Calman, 1912, así como un espécimen adulto de D. hirundo Calman, 1912. Se adquirieron micrografías electrónicas y ópticas de barrido para examinar y medir características clave de estos especímenes. Las diferencias morfológicas con las dos especies conocidas de Dipteropeltis, D. hirundo y D. Dipteropeltis Neethling et al., 2014, indican que los especímenes recogidos representan una nueva especie. Dipteropeltis longicaudatus sp. nov. se distingue por sus lóbulos abdominales alargados, un caparazón en forma de cresta y unos maxilares de forma única. Un espécimen representa el branquiuro más largo documentado hasta la fecha, con 31,5 mm. Además, se proporcionan los primeros datos de secuencia para este género utilizando códigos de barras de ADN, lo que corrobora la designación de una nueva especie. También se grabaron vídeos que documentan comportamientos como la fijación al hospedero, la pulsación de los lóbulos abdominales, el "desplazamiento" del disco de succión y la natación. Los hallazgos tienen implicaciones para sus hospederos teleósteos, Triportheus albus Cope, 1872 y Brycon amazonicus Spix & Agassiz, 1829, siendo este último una especie crítica para la acuicultura y la pesca comercial en la Amazonia.Revisión por pares
The QUIET Instrument
The Q/U Imaging ExperimenT (QUIET) is designed to measure polarization in the
Cosmic Microwave Background, targeting the imprint of inflationary
gravitational waves at large angular scales (~ 1 degree). Between 2008 October
and 2010 December, two independent receiver arrays were deployed sequentially
on a 1.4 m side-fed Dragonian telescope. The polarimeters which form the focal
planes use a highly compact design based on High Electron Mobility Transistors
(HEMTs) that provides simultaneous measurements of the Stokes parameters Q, U,
and I in a single module. The 17-element Q-band polarimeter array, with a
central frequency of 43.1 GHz, has the best sensitivity (69 uK sqrt(s)) and the
lowest instrumental systematic errors ever achieved in this band, contributing
to the tensor-to-scalar ratio at r < 0.1. The 84-element W-band polarimeter
array has a sensitivity of 87 uK sqrt(s) at a central frequency of 94.5 GHz. It
has the lowest systematic errors to date, contributing at r < 0.01. The two
arrays together cover multipoles in the range l= 25-975. These are the largest
HEMT-based arrays deployed to date. This article describes the design,
calibration, performance of, and sources of systematic error for the
instrument
First Season QUIET Observations: Measurements of CMB Polarization Power Spectra at 43 GHz in the Multipole Range 25 <= ell <= 475
The Q/U Imaging ExperimenT (QUIET) employs coherent receivers at 43GHz and
95GHz, operating on the Chajnantor plateau in the Atacama Desert in Chile, to
measure the anisotropy in the polarization of the CMB. QUIET primarily targets
the B modes from primordial gravitational waves. The combination of these
frequencies gives sensitivity to foreground contributions from diffuse Galactic
synchrotron radiation. Between 2008 October and 2010 December, >10,000hours of
data were collected, first with the 19-element 43GHz array (3458hours) and then
with the 90-element 95GHz array. Each array observes the same four fields,
selected for low foregrounds, together covering ~1000deg^2. This paper reports
initial results from the 43GHz receiver which has an array sensitivity to CMB
fluctuations of 69uK sqrt(s). The data were extensively studied with a large
suite of null tests before the power spectra, determined with two independent
pipelines, were examined. Analysis choices, including data selection, were
modified until the null tests passed. Cross correlating maps with different
telescope pointings is used to eliminate a bias. This paper reports the EE, BB
and EB power spectra in the multipole range ell=25-475. With the exception of
the lowest multipole bin for one of the fields, where a polarized foreground,
consistent with Galactic synchrotron radiation, is detected with 3sigma
significance, the E-mode spectrum is consistent with the LCDM model, confirming
the only previous detection of the first acoustic peak. The B-mode spectrum is
consistent with zero, leading to a measurement of the tensor-to-scalar ratio of
r=0.35+1.06-0.87. The combination of a new time-stream double-demodulation
technique, Mizuguchi-Dragone optics, natural sky rotation, and frequent
boresight rotation leads to the lowest level of systematic contamination in the
B-mode power so far reported, below the level of r=0.1Comment: 19 pages, 14 figures, higher quality figures are available at
http://quiet.uchicago.edu/results/index.html; Fixed a typo and corrected
statistical error values used as a reference in Figure 14, showing our
systematic uncertainties (unchanged) vs. multipole; Revision to ApJ accepted
version, this paper should be cited as "QUIET Collaboration et al. (2011)
Systems Analysis of miRNA Biomarkers to Inform Drug Safety
microRNAs (miRNAs or miRs) are short non-coding RNA molecules which have been shown to be dysregulated and released into the extracellular milieu as a result of many drug and non-drug-induced pathologies in different organ systems. Consequently, circulating miRs have been proposed as useful biomarkers of many disease states, including drug-induced tissue injury. miRs have shown potential to support or even replace the existing traditional biomarkers of drug-induced toxicity in terms of sensitivity and specificity, and there is some evidence for their improved diagnostic and prognostic value. However, several pre-analytical and analytical challenges, mainly associated with assay standardization, require solutions before circulating miRs can be successfully translated into the clinic. This review will consider the value and potential for the use of circulating miRs in drug-safety assessment and describe a systems approach to the analysis of the miRNAome in the discovery setting, as well as highlighting standardization issues that at this stage prevent their clinical use as biomarkers. Highlighting these challenges will hopefully drive future research into finding appropriate solutions, and eventually circulating miRs may be translated to the clinic where their undoubted biomarker potential can be used to benefit patients in rapid, easy to use, point-of-care test systems
Phylogenomics reveals the history of host use in mosquitoes
Mosquitoes have profoundly affected human history and continue to threaten human health through the transmission of a diverse array of pathogens. The phylogeny of mosquitoes has remained poorly characterized due to difficulty in taxonomic sampling and limited availability of genomic data beyond the most important vector species. Here, we used phylogenomic analysis of 709 single copy ortholog groups from 256 mosquito species to produce a strongly supported phylogeny that resolves the position of the major disease vector species and the major mosquito lineages. Our analyses support an origin of mosquitoes in the early Triassic (217 MYA [highest posterior density region: 188–250 MYA]), considerably older than previous estimates. Moreover, we utilize an extensive database of host associations for mosquitoes to show that mosquitoes have shifted to feeding upon the blood of mammals numerous times, and that mosquito diversification and host-use patterns within major lineages appear to coincide in earth history both with major continental drift events and with the diversification of vertebrate classes. © 2023, Springer Nature Limited
COMAP Early Science: II. Pathfinder Instrument
Line intensity mapping (LIM) is a new technique for tracing the global
properties of galaxies over cosmic time. Detection of the very faint signals
from redshifted carbon monoxide (CO), a tracer of star formation, pushes the
limits of what is feasible with a total-power instrument. The CO Mapping
Project (COMAP) Pathfinder is a first-generation instrument aiming to prove the
concept and develop the technology for future experiments, as well as
delivering early science products. With 19 receiver channels in a hexagonal
focal plane arrangement on a 10.4 m antenna, and an instantaneous 26-34 GHz
frequency range with 2 MHz resolution, it is ideally suited to measuring
CO(=1-0) from . In this paper we discuss strategies for designing
and building the Pathfinder and the challenges that were encountered. The
design of the instrument prioritized LIM requirements over those of ancillary
science. After a couple of years of operation, the instrument is well
understood, and the first year of data is already yielding useful science
results. Experience with this Pathfinder will drive the design of the next
generations of experiments.Comment: Paper 2 of 7 in series. 27 pages, 28 figures, submitted to Ap
Second Season QUIET Observations: Measurements of the CMB Polarization Power Spectrum at 95 GHz
The Q/U Imaging ExperimenT (QUIET) has observed the cosmic microwave
background (CMB) at 43 and 95GHz. The 43-GHz results have been published in
QUIET Collaboration et al. (2011), and here we report the measurement of CMB
polarization power spectra using the 95-GHz data. This data set comprises 5337
hours of observations recorded by an array of 84 polarized coherent receivers
with a total array sensitivity of 87 uK sqrt(s). Four low-foreground fields
were observed, covering a total of ~1000 square degrees with an effective
angular resolution of 12.8', allowing for constraints on primordial
gravitational waves and high-signal-to-noise measurements of the E-modes across
three acoustic peaks. The data reduction was performed using two independent
analysis pipelines, one based on a pseudo-Cl (PCL) cross-correlation approach,
and the other on a maximum-likelihood (ML) approach. All data selection
criteria and filters were modified until a predefined set of null tests had
been satisfied before inspecting any non-null power spectrum. The results
derived by the two pipelines are in good agreement. We characterize the EE, EB
and BB power spectra between l=25 and 975 and find that the EE spectrum is
consistent with LCDM, while the BB power spectrum is consistent with zero.
Based on these measurements, we constrain the tensor-to-scalar ratio to
r=1.1+0.9-0.8 (r<2.8 at 95% C.L.) as derived by the ML pipeline, and
r=1.2+0.9-0.8 (r<2.7 at 95% C.L.) as derived by the PCL pipeline. In one of the
fields, we find a correlation with the dust component of the Planck Sky Model,
though the corresponding excess power is small compared to statistical errors.
Finally, we derive limits on all known systematic errors, and demonstrate that
these correspond to a tensor-to-scalar ratio smaller than r=0.01, the lowest
level yet reported in the literature.Comment: 10 pages, 6 figures, 3 tables, submitted to ApJ, This paper should be
cited as "QUIET Collaboration (2012)." v2: updated to reflect published
versio
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