2,775 research outputs found
Precision radial velocities with CSHELL
Radial velocity identification of extrasolar planets has historically been
dominated by optical surveys. Interest in expanding exoplanet searches to M
dwarfs and young stars, however, has motivated a push to improve the precision
of near infrared radial velocity techniques. We present our methodology for
achieving 58 m/s precision in the K band on the M0 dwarf GJ 281 using the
CSHELL spectrograph at the 3-meter NASA IRTF. We also demonstrate our ability
to recover the known 4 Mjup exoplanet Gl 86 b and discuss the implications for
success in detecting planets around 1-3 Myr old T Tauri stars.Comment: 31 pages, 3 figures, 2 tables, accepted for publication in Ap
Starspot-induced optical and infrared radial velocity variability in T Tauri star Hubble 4
We report optical (6150 Ang) and K-band (2.3 micron) radial velocities
obtained over two years for the pre-main sequence weak-lined T Tauri star
Hubble I 4. We detect periodic and near-sinusoidal radial velocity variations
at both wavelengths, with a semi-amplitude of 1395\pm94 m/s in the optical and
365\pm80 m/s in the infrared. The lower velocity amplitude at the longer
wavelength, combined with bisector analysis and spot modeling, indicates that
there are large, cool spots on the stellar surface that are causing the radial
velocity modulation. The radial velocities maintain phase coherence over
hundreds of days suggesting that the starspots are long-lived. This is one of
the first active stars where the spot-induced velocity modulation has been
resolved in the infrared.Comment: Accepted for publication in The Astrophysical Journa
The Antarctic Submillimeter Telescope and Remote Observatory (AST/RO)
AST/RO, a 1.7 m diameter telescope for astronomy and aeronomy studies at
wavelengths between 200 and 2000 microns, was installed at the South Pole
during the 1994-1995 Austral summer. The telescope operates continuously
through the Austral winter, and is being used primarily for spectroscopic
studies of neutral atomic carbon and carbon monoxide in the interstellar medium
of the Milky Way and the Magellanic Clouds. The South Pole environment is
unique among observatory sites for unusually low wind speeds, low absolute
humidity, and the consistent clarity of the submillimeter sky. Four heterodyne
receivers, an array receiver, three acousto-optical spectrometers, and an array
spectrometer are installed. A Fabry-Perot spectrometer using a bolometric array
and a Terahertz receiver are in development. Telescope pointing, focus, and
calibration methods as well as the unique working environment and logistical
requirements of the South Pole are described.Comment: 57 pages, 15 figures. Submitted to PAS
Two-Way Regulation of MmpL3 Expression Identifies and Validates Inhibitors of MmpL3 Function in Mycobacterium tuberculosis
MmpL3, an essential mycolate transporter in the inner membrane of Mycobacterium tuberculosis (Mtb), has been identified as a target of multiple, chemically diverse antitubercular drugs. However, several of these molecules seem to have secondary targets and inhibit bacterial growth by more than one mechanism. Here, we describe a cell-based assay that utilizes two-way regulation of MmpL3 expression to readily identify MmpL3-specific inhibitors. We successfully used this assay to identify a novel guanidine-based MmpL3 inhibitor from a library of 220 compounds that inhibit growth of Mtb by largely unknown mechanisms. We furthermore identified inhibitors of cytochrome bc1-aa3 oxidase as one class of off-target hits in whole-cell screens for MmpL3 inhibitors and report a novel sulfanylacetamide as a potential QcrB inhibitor
Reconstructing Single Field Inflationary Actions From CMBR Data
This paper describes a general program for deriving the action of single
field inflation models with nonstandard kinetic energy terms using CMBR power
spectrum data. This method assumes that an action depends on a set of
undetermined functions, each of which is a function of either the inflaton wave
function or its time derivative. The scalar, tensor and non-gaussianity of the
curvature perturbation spectrum are used to derive a set of reconstruction
equations whose solution set can specify up to three of the undetermined
functions. The method is then used to find the undetermined functions in
various types of actions assuming power law type scalar and tensor spectra. In
actions that contain only two unknown functions, the third reconstruction
equation implies a consistency relation between the non-gaussianty, sound speed
and slow roll parameters. In particular we focus on reconstructing a
generalized DBI action with an unknown potential and warp factor. We find that
for realistic scalar and tensor spectra, the reconstructed warp factor and
potential are very similar to the theoretically derived result. Furthermore,
physical consistency of the reconstructed warp factor and potential imposes
strict constraints on the scalar and tensor spectral indices.Comment: 33 pages, 3 figures: v3 - References adde
High resolution sequencing of hepatitis C virus reveals limited intra-hepatic compartmentalization in end-stage liver disease
Background & Aims
The high replication and mutation rate of hepatitis C virus (HCV) results in a heterogeneous population of viral sequences in vivo. HCV replicates in the liver and infected hepatocytes occur as foci surrounded by uninfected cells that may promote compartmentalization of viral variants. Given recent reports showing interferon stimulated gene (ISG) expression in chronic hepatitis C, we hypothesized that local interferon responses may limit HCV replication and evolution.
Methods
To investigate the spatial influence of liver architecture on viral replication we measured HCV RNA and ISG mRNA from each of the 8 Couinaud segments of the liver from 21 patients undergoing liver transplant.
Results
HCV RNA and ISG mRNA levels were comparable across all sites from an individual liver but showed up to 500-fold difference between patients. Importantly, there was no association between ISG and HCV RNA expression across all sites in the liver or plasma. Deep sequencing of HCV RNA isolated from the 8 hepatic sites from two subjects showed a similar distribution of viral quasispecies across the liver and uniform sequence diversity. Single genome amplification of HCV E1E2-envelope clones from 6 selected patients at 2 hepatic sites supported these data and showed no evidence for HCV compartmentalization.
Conclusions
We found no differences between the hepatic and plasma viral quasispecies in all patients sampled. We conclude that in end-stage liver disease HCV RNA levels and the genetic pool of HCV envelope sequences are indistinguishable between distant sites in the liver and plasma, arguing against viral compartmentalization
A search for giant planet companions to t tauri stars
We present results from an ongoing multiwavelength radial velocity (RV) survey of the Taurus–Auriga star-forming
region as part of our effort to identify pre-main-sequence giant planet hosts. These 1–3 Myr old T Tauri stars present
significant challenges to traditional RV surveys. The presence of strong magnetic fields gives rise to large, cool
star spots. These spots introduce significant RV jitter which can mimic the velocity modulation from a planet-mass
companion. To distinguish between spot-induced and planet-induced RV modulation, we conduct observations at
∼6700Åand∼2.3μmand measure thewavelength dependence (if any) in theRVamplitude. CSHELL observations
of the known exoplanet host Gl 86 demonstrate our ability to detect not only hot Jupiters in the near-infrared but
also secular trends from more distant companions. Observations of nine very young stars reveal a typical reduction
in RV amplitude at the longer wavelengths by a factor of ∼2–3. While we cannot confirm the presence of planets
in this sample, three targets show different periodicities in the two wavelength regions. This suggests different
physical mechanisms underlying the optical and the K-band variability
Evaluation of antithrombotic use and COVID-19 outcomes in a nationwide atrial fibrillation cohort
OBJECTIVE: To evaluate antithrombotic (AT) use in individuals with atrial fibrillation (AF) and at high risk of stroke (CHA2DS2-VASc score ≥2) and investigate whether pre-existing AT use may improve COVID-19 outcomes. METHODS: Individuals with AF and CHA2DS2-VASc score ≥2 on 1 January 2020 were identified using electronic health records for 56 million people in England and were followed up until 1 May 2021. Factors associated with pre-existing AT use were analysed using logistic regression. Differences in COVID-19-related hospitalisation and death were analysed using logistic and Cox regression in individuals with pre-existing AT use versus no AT use, anticoagulants (AC) versus antiplatelets (AP), and direct oral anticoagulants (DOACs) versus warfarin. RESULTS: From 972 971 individuals with AF (age 79 (±9.3), female 46.2%) and CHA2DS2-VASc score ≥2, 88.0% (n=856 336) had pre-existing AT use, 3.8% (n=37 418) had a COVID-19 hospitalisation and 2.2% (n=21 116) died, followed up to 1 May 2021. Factors associated with no AT use included comorbidities that may contraindicate AT use (liver disease and history of falls) and demographics (socioeconomic status and ethnicity). Pre-existing AT use was associated with lower odds of death (OR=0.92, 95% CI 0.87 to 0.96), but higher odds of hospitalisation (OR=1.20, 95% CI 1.15 to 1.26). AC versus AP was associated with lower odds of death (OR=0.93, 95% CI 0.87 to 0.98) and higher hospitalisation (OR=1.17, 95% CI 1.11 to 1.24). For DOACs versus warfarin, lower odds were observed for hospitalisation (OR=0.86, 95% CI 0.82 to 0.89) but not for death (OR=1.00, 95% CI 0.95 to 1.05). CONCLUSIONS: Pre-existing AT use may be associated with lower odds of COVID-19 death and, while not evidence of causality, provides further incentive to improve AT coverage for eligible individuals with AF
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