762 research outputs found
A new method for the inversion of atmospheric parameters of A/Am stars
We present an automated procedure that derives simultaneously the effective
temperature , the surface gravity logg, the metallicity [Fe/H], and
the equatorial projected rotational velocity vsini for "normal" A and Am stars.
The procedure is based on the principal component analysis inversion method of
Paletou et al. (2015a). A sample of 322 high resolution spectra of F0-B9 stars,
retrieved from the Polarbase, SOPHIE, and ELODIE databases, were used to test
this technique with real data. We have selected the spectral region from
4400-5000\AA\ as it contains many metallic lines and the Balmer H line.
Using 3 datasets at resolving powers of R=42000, 65000 and 76000, about
6.6x synthetic spectra were calculated to build a large learning
database. The Online Power Iteration algorithm was applied to these learning
datasets to estimate the principal components (PC). The projection of spectra
onto the few PCs offered an efficient comparison metric in a low dimensional
space. The spectra of the well known A0- and A1-type stars, Vega and Sirius A,
were used as control spectra in the three databases. Spectra of other well
known A-type stars were also employed in order to characterize the accuracy of
the inversion technique. All observational spectra were inverted and
atmospheric parameters derived. After removal of a few outliers, the
PCA-inversion method appears to be very efficient in determining ,
[Fe/H], and vsini for A/Am stars. The derived parameters agree very well with
previous determinations. Using a statistical approach, deviations of around 150
K, 0.35 dex, 0.15 dex, and 2 km/s were found for , logg, [Fe/H], and
vsini with respect to literature values for A-type stars. The PCA-inversion
proves to be a very fast, practical, and reliable tool for estimating stellar
parameters of FGK and A stars, and deriving effective temperatures of M stars.Comment: 16 pages, 9 figures. Accepted in A&
The z=0.0912 and z=0.2212 Damped Lyman Alpha Galaxies Along the Sight-Line Toward the Quasar OI 363
New optical and infrared observations along the sight-line toward the quasar
OI 363 (0738+313) are presented and discussed. Excluding systems which lack
confirming UV spectroscopic observations of the actual Lyman alpha line, this
sight-line presently contains the two lowest-redshift classical damped Lyman
alpha (DLA) quasar absorption line systems known (i.e. with N(HI) \ge 2 x
10^{20} atoms cm^{-2}), one at z(abs)=0.0912 and the other at z(abs)=0.2212.
The z=0.09 DLA galaxy appears to be an extended low surface brightness galaxy
which is easily visible only in infrared images and shows rich morphological
structure. Subtraction of the quasar nuclear and host light yields L_K \approx
0.08L_K* at z=0.09. The impact parameter between the galaxy and quasar
sight-line is very small, b<3.6 kpc (<2 arcsec), which makes measurements
difficult. The z=0.22 DLA galaxy is an early-type dwarf with a K-band
luminosity of L_K \approx 0.1L_K* at impact parameter b=20 kpc. In general,
these results serve to support mounting evidence that DLA galaxies are drawn
from a wide variety of gas-rich galaxy types. (Abridged)Comment: 27 pages, 6 figures, 2 in color. Submitted to Ap
The ESO UVES Advanced Data Products Quasar Sample - VI. Sub-Damped Lyman- Metallicity Measurements and the Circum-Galactic Medium
The Circum-Galactic Medium (CGM) can be probed through the analysis of
absorbing systems in the line-of-sight to bright background quasars. We present
measurements of the metallicity of a new sample of 15 sub-damped Lyman-
absorbers (sub-DLAs, defined as absorbers with 19.0 < log N(H I) < 20.3) with
redshift 0.584 < < 3.104 from the ESO Ultra-Violet Echelle
Spectrograph (UVES) Advanced Data Products Quasar Sample (EUADP). We combine
these results with other measurements from the literature to produce a
compilation of metallicity measurements for 92 sub-DLAs as well as a sample of
362 DLAs. We apply a multi-element analysis to quantify the amount of dust in
these two classes of systems. We find that either the element depletion
patterns in these systems differ from the Galactic depletion patterns or they
have a different nucleosynthetic history than our own Galaxy. We propose a new
method to derive the velocity width of absorption profiles, using the modeled
Voigt profile features. The correlation between the velocity width delta_V90 of
the absorption profile and the metallicity is found to be tighter for DLAs than
for sub-DLAs. We report hints of a bimodal distribution in the [Fe/H]
metallicity of low redshift (z < 1.25) sub-DLAs, which is unseen at higher
redshifts. This feature can be interpreted as a signature from the metal-poor,
accreting gas and the metal-rich, outflowing gas, both being traced by sub-DLAs
at low redshifts.Comment: 64 pages, 31 figures, 27 tables. Submitted to MNRA
The feed-in tariff in the UK : a case study focus on domestic photovoltaic systems
This paper explores the photovoltaic (PV) industry in the United Kingdom (UK) as experienced by those who are working with it directly and with consideration of current standards, module efficiencies and future environmental trends. The government's consultation on the comprehensive review for solar PV tariffs, proposes a reduction of the generation tariff for PV installations in the UK of more than 50%. The introduction of the Feed-In Tariffs scheme (FITs) has rapidly increased deployment of PV technologies at small scale since its introduction in April 2010. The central principle of FIT policies is to offer guaranteed prices for fixed periods to enable greater number of investors. A financial analysis was performed on two real-life installations in Cornwall, UK to determine the impact of proposed cuts to the FIT will make to a typical domestic PV system under 4 kW. The results show that a healthy Return on Investment (ROI) can still be made but that future installations should focus on off-setting electricity required from the national grid as a long term push for true sustainability rather than subsidised schemes. The profitability of future installations will have to be featured within in-service and end-of-service considerations such as the feed-in tariff, module efficiencies and the implications of costs associated with end-of-life disposal
Flux front penetration in disordered superconductors
We investigate flux front penetration in a disordered type II superconductor
by molecular dynamics (MD) simulations of interacting vortices and find scaling
laws for the front position and the density profile. The scaling can be
understood performing a coarse graining of the system and writing a disordered
non-linear diffusion equation. Integrating numerically the equation, we observe
a crossover from flat to fractal front penetration as the system parameters are
varied. The value of the fractal dimension indicates that the invasion process
is described by gradient percolation.Comment: 5 pages, 4 figures, to appear in Phys. Rev. Let
Host-derived viral transporter protein for nitrogen uptake in infected marine phytoplankton
This is the author's accepted manuscriptFinal version available from NAS via the DOI in this recordPhytoplankton community structure is shaped by both bottom–up factors, such as nutrient availability, and top–down processes, such as predation. Here we show that marine viruses can blur these distinctions, being able to amend how host cells acquire nutrients from their environment while also predating and lysing their algal hosts. Viral genomes often encode genes derived from their host. These genes may allow the virus to manipulate host metabolism to improve viral fitness. We identify in the genome of a phytoplankton virus, which infects the small green alga Ostreococcus tauri, a host-derived ammonium transporter. This gene is transcribed during infection and when expressed in yeast mutants the viral protein is located to the plasma membrane and rescues growth when cultured with ammonium as the sole nitrogen source. We also show that viral infection alters the nature of nitrogen compound uptake of host cells, by both increasing substrate affinity and allowing the host to access diverse nitrogen sources. This is important because the availability of nitrogen often limits phytoplankton growth. Collectively, these data show that a virus can acquire genes encoding nutrient transporters from a host genome and that expression of the viral gene can alter the nutrient uptake behavior of host cells. These results have implications for understanding how viruses manipulate the physiology and ecology of phytoplankton, influence marine nutrient cycles, and act as vectors for horizontal gene transfer.A.M. and T.A.R. are funded by the Royal Society, through Newton and University Research fellowships, respectively. This work is supported in part by research grants from The Gordon and Betty Moore Foundation (GBMF5514), Leverhulme Trust (PLP-2014-147), and the University of Exeter. The University of Exeter OmniLog facility is supported by a Wellcome Trust Institutional Strategic Support Award WT105618MA. Phylogenetic reconstructions were computed on the Data Intensive Academic Grid (National Science Foundation, MRI-R2 Project DBI-0959894)
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