1,048 research outputs found
Seeking celestial Positronium with an OH-suppressed diffraction-limited spectrograph
Celestially, Positronium (Ps), has only been observed through gamma-ray
emission produced by its annihilation. However, in its triplet state, a Ps atom
has a mean lifetime long enough for electronic transitions to occur between
quantum states. This produces a recombination spectrum observable in principle
at near IR wavelengths, where angular resolution greatly exceeding that of the
gamma-ray observations is possible. However, the background in the NIR is
dominated by extremely bright atmospheric hydroxyl (OH) emission lines. In this
paper we present the design of a diffraction-limited spectroscopic system using
novel photonic components - a photonic lantern, OH Fiber Bragg Grating filters,
and a photonic TIGER 2-dimensional pseudo-slit - to observe the Ps Balmer alpha
line at 1.3122 microns for the first time.Comment: 6 pages, 9 Figures, 2 Tables. Accepted to Applied Optics feature
issue on Astrophotonic
Empirical Verification of the Fe II Oscillator Strengths in the FUSE Bandpass
We report empirical determinations of atomic oscillator strengths, or
f-values, for 11 ground-state transitions of Fe II in the wavelength range 1050
to 1150 Ang. We use ultraviolet absorption line observations of interstellar
material towards stars in the Galaxy and the Magellanic Clouds taken with
Copernicus, the Goddard High Resolution Spectrograph on-board the Hubble Space
Telescope, and the Far Ultraviolet Spectroscopic Explorer. We derive absolute
oscillator strengths by a combination of the apparent optical depth, component
fitting, and curve-of-growth fitting techniques. Our derived oscillator
strengths are generally in excellent agreement with recent theoretical
calculations by Raassen & Uylings using the orthogonal operator technique.
However, we identify three of the eleven transitions studied here whose
f-values seem to be incompatible with these calculations, by as much as a
factor of two. We suggest revisions to these f-values based upon our analysis.Comment: To appear in the Astrophysical Journal. 31 pages, including 8
embedded tables and 10 embedded figures. Also available at
http://fuse.pha.jhu.edu/~howk/Papers
Nonparametric Bayesian inference for perturbed and orthologous gene regulatory networks
Motivation: The generation of time series transcriptomic datasets collected under multiple experimental conditions has proven to be a powerful approach for disentangling complex biological processes, allowing for the reverse engineering of gene regulatory networks (GRNs). Most methods for reverse engineering GRNs from multiple datasets assume that each of the time series were generated from networks with identical topology. In this study, we outline a hierarchical, non-parametric Bayesian approach for reverse engineering GRNs using multiple time series that can be applied in a number of novel situations including: (i) where different, but overlapping sets of transcription factors are expected to bind in the different experimental conditions; that is, where switching events could potentially arise under the different treatments and (ii) for inference in evolutionary related species in which orthologous GRNs exist. More generally, the method can be used to identify context-specific regulation by leveraging time series gene expression data alongside methods that can identify putative lists of transcription factors or transcription factor targets.
Results: The hierarchical inference outperforms related (but non-hierarchical) approaches when the networks used to generate the data were identical, and performs comparably even when the networks used to generate data were independent. The method was subsequently used alongside yeast one hybrid and microarray time series data to infer potential transcriptional switches in Arabidopsis thaliana response to stress. The results confirm previous biological studies and allow for additional insights into gene regulation under various abiotic stresses.
Availability: The methods outlined in this article have been implemented in Matlab and are available on request
GNOSIS: the first instrument to use fibre Bragg gratings for OH suppression
GNOSIS is a prototype astrophotonic instrument that utilizes OH suppression
fibres consisting of fibre Bragg gratings and photonic lanterns to suppress the
103 brightest atmospheric emission doublets between 1.47-1.7 microns. GNOSIS
was commissioned at the 3.9-meter Anglo-Australian Telescope with the IRIS2
spectrograph to demonstrate the potential of OH suppression fibres, but may be
potentially used with any telescope and spectrograph combination. Unlike
previous atmospheric suppression techniques GNOSIS suppresses the lines before
dispersion and in a manner that depends purely on wavelength. We present the
instrument design and report the results of laboratory and on-sky tests from
commissioning. While these tests demonstrated high throughput and excellent
suppression of the skylines by the OH suppression fibres, surprisingly GNOSIS
produced no significant reduction in the interline background and the
sensitivity of GNOSIS and IRIS2 is about the same as IRIS2. It is unclear
whether the lack of reduction in the interline background is due to physical
sources or systematic errors as the observations are detector noise-dominated.
OH suppression fibres could potentially impact ground-based astronomy at the
level of adaptive optics or greater. However, until a clear reduction in the
interline background and the corresponding increasing in sensitivity is
demonstrated optimized OH suppression fibres paired with a fibre-fed
spectrograph will at least provide a real benefits at low resolving powers.Comment: 15 pages, 13 figures, accepted to A
STRING 8--a global view on proteins and their functional interactions in 630 organisms
International audienceno abstrac
Dolores Keane in concert (poster)
Poster for the concert held on Saturday 27 February 1999 at Wembley Conference Centre, organised by The Irish Chaplaincy
The Peculiar SN 2005hk: Do Some Type Ia Supernovae Explode as Deflagrations?
We present extensive u'g'r'i'BVRIYJHKs photometry and optical spectroscopy of
SN 2005hk. These data reveal that SN 2005hk was nearly identical in its
observed properties to SN 2002cx, which has been called ``the most peculiar
known type Ia supernova.'' Both supernovae exhibited high ionization SN
1991T-like pre-maximum spectra, yet low peak luminosities like SN 1991bg. The
spectra reveal that SN 2005hk, like SN 2002cx, exhibited expansion velocities
that were roughly half those of typical type Ia supernovae. The R and I light
curves of both supernovae were also peculiar in not displaying the secondary
maximum observed for normal type Ia supernovae. Our YJH photometry of SN 2005hk
reveals the same peculiarity in the near-infrared. By combining our optical and
near-infrared photometry of SN 2005hk with published ultraviolet light curves
obtained with the Swift satellite, we are able to construct a bolometric light
curve from ~10 days before to ~60 days after B maximum. The shape and unusually
low peak luminosity of this light curve, plus the low expansion velocities and
absence of a secondary maximum at red and near-infrared wavelengths, are all in
reasonable agreement with model calculations of a 3D deflagration which
produces ~0.25 M_sun of 56Ni.Comment: Accepted by PASP, to appear in April 2007 issue, 63 pages, 16
figures, 11 table
Carnegie Supernova Project-II: Extending the Near-Infrared Hubble Diagram for Type Ia Supernovae to
The Carnegie Supernova Project-II (CSP-II) was an NSF-funded, four-year
program to obtain optical and near-infrared observations of a "Cosmology"
sample of Type Ia supernovae located in the smooth Hubble flow (). Light curves were also obtained of a "Physics"
sample composed of 90 nearby Type Ia supernovae at selected for
near-infrared spectroscopic time-series observations. The primary emphasis of
the CSP-II is to use the combination of optical and near-infrared photometry to
achieve a distance precision of better than 5%. In this paper, details of the
supernova sample, the observational strategy, and the characteristics of the
photometric data are provided. In a companion paper, the near-infrared
spectroscopy component of the project is presented.Comment: 43 pages, 10 figures, accepted for publication in PAS
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