238 research outputs found
Probable detection of starlight reflected from the giant exoplanet orbiting tau Bootis
Giant planets orbiting stars other than the Sun are clearly detectable
through precise radial-velocity measurements of the orbital reflex motion of
the parent star. In the four years since the discovery of the companion to the
star 51 Peg, similar low-amplitude ``Doppler star wobbles'' have revealed the
presence of some 20 planets orbiting nearby solar-type stars. Several of these
newly-discovered planets are very close to their parent stars, in orbits with
periods of only a few days. Being an indirect technique, however, the
reflex-velocity method has little to say about the sizes or compositions of the
planets, and can only place lower limits on their masses. Here we report the
use of high-resolution optical spectroscopy to achieve a probable detection of
the Doppler-shifted signature of starlight reflected from one of these objects,
the giant exoplanet orbiting the star tau Bootis. Our data give the planet's
orbital inclination i=29 degrees, indicating that its mass is some 8 times that
of Jupiter, and suggest strongly that the planet has the size and reflectivity
expected for a gas-giant planet.Comment: 15 pages, 4 figures. (Fig 1 and equation for epsilon on p1 para 2
revised; changed from double to single spacing
Recovery of 29-s Oscillations in HST/FOS Eclipse Observations of the Cataclysmic Variable UX Ursae Majoris
[abridged abstract]
Low amplitude (~=0.5%) 29-s oscillations have been detected in HST/FOS
eclipse observations of the nova-like cataclysmic variable UX UMa. These are
the same dwarf nova-type oscillations that were originally discovered in this
system by Warner & Nather in 1972. The oscillations are sinusoidal to within
the small observational errors and undergo an approximately -360 degree phase
shift during eclipses. Their amplitudes are highest at pre-eclipse orbital
phases and exhibit a rather gradual eclipse whose shape is roughly similar to
UX~UMa's overall light curve. Oscillation spectra derived from pre-eclipse data
segments are extremely blue, whereas mid-eclipse oscillation spectra are much
redder.
We suggest that the ultimate source of the oscillations is a hot, compact
region near disk center, but that a significant fraction of the observed,
modulated flux is due to reprocessing of the light emitted by this source in
the accretion disk atmosphere. The compact source is occulted at orbital phases
near mid-eclipse, leaving only part of the more extended reprocessing region(s)
to produce the weak oscillations that persist even at conjunction.
The highly sinusoidal oscillation pulse shape does not permit the
identification of the compact component in this model with emission produced by
a rotating disturbance in the inner disk or in an equatorial boundary layer,
and a standard intermediate polar model can also be ruled out. A model invoking
magnetically controlled accretion onto differentially rotating WD surface
layers may be viable, but needs more theoretical work.Comment: 28 pages, including 9 figures; to appear in the ApJ (Vol. 499
Reverberation Mapping of the Seyfert 1 Galaxy NGC 7469
A large reverberation mapping study of the Seyfert 1 galaxy NGC 7469 has
yielded emission-line lags for Hbeta 4861 and He II 4686 and a central black
hole mass measurement of about 10 million solar masses, consistent with
previous measurements. A very low level of variability during the monitoring
campaign precluded meeting our original goal of recovering velocity-delay maps
from the data, but with the new Hbeta measurement, NGC 7469 is no longer an
outlier in the relationship between the size of the Hbeta-emitting broad-line
region and the AGN luminosity. It was necessary to detrend the continuum and
Hbeta and He II 4686 line light curves and those from archival UV data for
different time-series analysis methods to yield consistent results.Comment: 9 Pages, 7 figures, 6 tables. Accepted for publication in The
Astrophysical Journa
Observations and modelling of pulsed radio emission from CU Virginis
We present 13 cm and 20 cm radio observations of the magnetic chemically
peculiar star CU Virginis taken with the Australia Telescope Compact Array. We
detect two circularly polarised radio pulses every rotation period which
confirm previous detections. In the first pulse, the lower frequency emission
arrives before the higher frequency emission and the ordering reverses in the
second pulse. In order to explain the frequency dependence of the time between
the two pulses, we construct a geometric model of the magnetosphere of CU
Virginis, and consider various emission angles relative to the magnetic field
lines. A simple electron cyclotron maser emission model, in which the emission
is perpendicular to the magnetic field lines, is not consistent with our data.
A model in which the emission is refracted through cold plasma in the
magnetosphere is shown to have the correct pulse arrival time frequency
dependence.Comment: Accepted by MNRA
Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb carbonate geochronology: strategies, progress, and limitations
Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb geochronology of carbonate minerals, calcite in particular, is rapidly gaining popularity as an absolute dating method. The high spatial resolution of LA-ICP-MS U–Pb carbonate geochronology has benefits over traditional isotope dilution methods, particularly for diagenetic and hydrothermal calcite, because uranium and lead are heterogeneously distributed on the sub-millimetre scale. At the same time, this can provide limitations to the method, as locating zones of radiogenic lead can be time-consuming and “hit or miss”. Here, we present strategies for dating carbonates with in situ techniques, through imaging and petrographic techniques to data interpretation; our examples are drawn from the dating of fracture-filling calcite, but our discussion is relevant to all carbonate applications. We review several limitations to the method, including open-system behaviour, variable initial-lead compositions, and U–daughter disequilibrium. We also discuss two approaches to data collection: traditional spot analyses guided by petrographic and elemental imaging and image-based dating that utilises LA-ICP-MS elemental and isotopic map data
Absent expansion of AXIN2+ hepatocytes and altered physiology in Axin2CreERT2 mice challenges the role of pericentral hepatocytes in homeostatic liver regeneration
Background & Aims:
Mouse models of lineage tracing have helped to describe the important subpopulations of hepatocytes responsible for liver regeneration. However, conflicting results have been obtained from different models. Herein, we aimed to reconcile these conflicting reports by repeating a key lineage-tracing study from pericentral hepatocytes and characterising this Axin2CreERT2 model in detail.
Methods:
We performed detailed characterisation of the labelled population in the Axin2CreERT2 model. We lineage traced this cell population, quantifying the labelled population over 1 year and performed in-depth phenotypic comparisons, including transcriptomics, metabolomics and analysis of proteins through immunohistochemistry, of Axin2CreERT2 mice to WT counterparts.
Results:
We found that after careful definition of a baseline population, there are marked differences in labelling between male and female mice. Upon induced lineage tracing there was no expansion of the labelled hepatocyte population in Axin2CreERT2 mice. We found substantial evidence of disrupted homeostasis in Axin2CreERT2 mice. Offspring are born with sub-Mendelian ratios and adult mice have perturbations of hepatic Wnt/β-catenin signalling and related metabolomic disturbance.
Conclusions:
We find no evidence of predominant expansion of the pericentral hepatocyte population during liver homeostatic regeneration. Our data highlight the importance of detailed preclinical model characterisation and the pitfalls which may occur when comparing across sexes and backgrounds of mice and the effects of genetic insertion into native loci.
Impact and implications:
Understanding the source of cells which regenerate the liver is crucial to harness their potential to regrow injured livers. Herein, we show that cells which were previously thought to repopulate the liver play only a limited role in physiological regeneration. Our data helps to reconcile differing conclusions drawn from results from a number of prior studies and highlights methodological challenges which are relevant to preclinical models more generally
Ultrasound evaluation of the abductor hallucis muscle: Reliability study
© 2008 Cameron et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution Licens
Genomic, Pathway Network, and Immunologic Features Distinguishing Squamous Carcinomas
This integrated, multiplatform PanCancer Atlas study co-mapped and identified distinguishing
molecular features of squamous cell carcinomas (SCCs) from five sites associated with smokin
Pan-Cancer Analysis of lncRNA Regulation Supports Their Targeting of Cancer Genes in Each Tumor Context
Long noncoding RNAs (lncRNAs) are commonly dys-regulated in tumors, but only a handful are known toplay pathophysiological roles in cancer. We inferredlncRNAs that dysregulate cancer pathways, onco-genes, and tumor suppressors (cancer genes) bymodeling their effects on the activity of transcriptionfactors, RNA-binding proteins, and microRNAs in5,185 TCGA tumors and 1,019 ENCODE assays.Our predictions included hundreds of candidateonco- and tumor-suppressor lncRNAs (cancerlncRNAs) whose somatic alterations account for thedysregulation of dozens of cancer genes and path-ways in each of 14 tumor contexts. To demonstrateproof of concept, we showed that perturbations tar-geting OIP5-AS1 (an inferred tumor suppressor) andTUG1 and WT1-AS (inferred onco-lncRNAs) dysre-gulated cancer genes and altered proliferation ofbreast and gynecologic cancer cells. Our analysis in-dicates that, although most lncRNAs are dysregu-lated in a tumor-specific manner, some, includingOIP5-AS1, TUG1, NEAT1, MEG3, and TSIX, synergis-tically dysregulate cancer pathways in multiple tumorcontexts
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