1,510 research outputs found
From "community" to "commercial" FLOSS: The case of moodle
This is the post-print version of the final published article that is available from the link below. Copyright © 2010 ACM, Inc.This paper documents the evolution of Moodle, an advanced Content Management System, and its transition from a purely volunteer-based project to one driven by commercial interests and stakeholders. The study of its evolution provides evidence of the sustainability of its process: increasing amounts of provided effort by developers correspond to similarly increasing produced outputs to the Moodle system. It is also evident how this OSS system, apart from achieving the transition to a successful multisite, collaborative and community-based OSS project, depends more on its community than its commercial partners
Secretion and assembly of functional mini-cellulosomes from synthetic chromosomal operons in Clostridium acetobutylicum ATCC 824.
Background: Consolidated bioprocessing (CBP) is reliant on the simultaneous enzyme production, saccharification of biomass, and fermentation of released sugars into valuable products such as butanol. Clostridial species that produce butanol are, however, unable to grow on crystalline cellulose. In contrast, those saccharolytic species that produce predominantly ethanol, such as Clostridium thermocellum and Clostridium cellulolyticum, degrade crystalline cellulose with high efficiency due to their possession of a multienzyme complex termed the cellulosome. This has led to studies directed at endowing butanol-producing species with the genetic potential to produce a cellulosome, albeit by localising the necessary transgenes to unstable autonomous plasmids. Here we have explored the potential of our previously described Allele-Coupled Exchange (ACE) technology for creating strains of the butanol producing species Clostridium acetobutylicum in which the genes encoding the various cellulosome components are stably integrated into the genome. Results: We used BioBrick2 (BB2) standardised parts to assemble a range of synthetic genes encoding C. thermocellum cellulosomal scaffoldin proteins (CipA variants) and glycoside hydrolases (GHs, Cel8A, Cel9B, Cel48S and Cel9K) as well as synthetic cellulosomal operons that direct the synthesis of Cel8A, Cel9B and a truncated form of CipA. All synthetic genes and operons were integrated into the C. acetobutylicum genome using the recently developed ACE technology. Heterologous protein expression levels and mini-cellulosome self-assembly were assayed by western blot and native PAGE analysis. Conclusions: We demonstrate the successful expression, secretion and self-assembly of cellulosomal subunits by the recombinant C. acetobutylicum strains, providing a platform for the construction of novel cellulosomes. © 2013 Kovács et al.; licensee BioMed Central Ltd
F stars, metallicity, and the ages of red galaxies at z > 1
We explore whether the rest-frame near-UV spectral region, observable in
high-redshift galaxies via optical spectroscopy, contains sufficient
information to allow the degeneracy between age and metallicity to be lifted.
We do this by testing the ability of evolutionary synthesis models to reclaim
the correct metallicity when fitted to the near-UV spectra of F stars of known
(sub-solar and super-solar) metallicity. F stars are of particular interest
because the rest-frame near-UV spectra of the oldest known elliptical galaxies
at z > 1 appear to be dominated by F stars near to the main-sequence turnoff.
We find that, in the case of the F stars, where the HST ultraviolet spectra
have high signal:noise, model-fitting with metallicity allowed to vary as a
free parameter is rather successful at deriving the correct metallicity. As a
result, the estimated turnoff ages of these stars yielded by the model fitting
are well constrained. Encouraged by this we have fitted these same variable-
metallicity models to the deep, optical spectra of the z \simeq 1.5 mJy radio
galaxies 53W091 and 53W069 obtained with the Keck telescope. While the
age-metallicity degeneracy is not so easily lifted for these galaxies, we find
that even when metallicity is allowed as a free parameter, the best estimates
of their ages are still \geq 3 Gyr, with ages younger than 2 Gyr now strongly
excluded. Furthermore, we find that a search of the entire parameter space of
metallicity and star formation history using MOPED (Heavens et al., 2000) leads
to the same conclusion. Our results therefore continue to argue strongly
against an Einstein-de Sitter universe, and favour a lambda-dominated universe
in which star formation in at least these particular elliptical galaxies was
completed somewhere in the redshift range z = 3 - 5.Comment: 10 pages, LaTeX, uses MNRAS style file, incorporates 14 postscript
figures, submitted to MNRAS. Changes include: inclusion of single stellar
atmosphere model fits; more rigorous calculation of confidence regions; some
re-structurin
All-Sky spectrally matched UBVRI-ZY and u'g'r'i'z' magnitudes for stars in the Tycho2 catalog
We present fitted UBVRI-ZY and u'g'r'i'z' magnitudes, spectral types and
distances for 2.4M stars, derived from synthetic photometry of a library
spectrum that best matches the Tycho2 BtVt, NOMAD Rn and 2MASS JHK_{2/S}
catalog magnitudes. We present similarly synthesized multi-filter magnitudes,
types and distances for 4.8M stars with 2MASS and SDSS photometry to g<16
within the Sloan survey region, for Landolt and Sloan primary standards, and
for Sloan Northern (PT) and Southern secondary standards.
The synthetic magnitude zeropoints for BtVt, UBVRI, ZvYv, JHK_{2/S},
JHK_{MKO}, Stromgren uvby, Sloan u'g'r'i'z' and ugriz are calibrated on 20
calspec spectrophotometric standards. The UBVRI and ugriz zeropoints have
dispersions of 1--3%, for standards covering a range of color from -0.3 < V-I <
4.6; those for other filters are in the range 2--5%.
The spectrally matched fits to Tycho2 stars provide estimated 1-sigma errors
per star of ~0.2, 0.15, 0.12, 0.10 and 0.08 mags respectively in either UBVRI
or u'g'r'i'z'; those for at least 70% of the SDSS survey region to g<16 have
estimated 1-sigma errors per star of ~0.2, 0.06, 0.04, 0.04, 0.05 in u'g'r'i'z'
or UBVRI.
The density of Tycho2 stars, averaging about 60 stars per square degree,
provides sufficient stars to enable automatic flux calibrations for most
digital images with fields of view of 0.5 degree or more. Using several such
standards per field, automatic flux calibration can be achieved to a few
percent in any filter, at any airmass, in most workable observing conditions,
to facilitate inter-comparison of data from different sites, telescopes and
instruments.Comment: 36 pages, 30 figures, 3 printed tables, several electronic tables,
accepted PASP Dec 201
Fundamental Properties of O-Type Stars
We present a comprehensive analysis of high-resolution, far-UV HST/STIS,
FUSE, and optical spectra of 17 O stars in the SMC. Our analysis is based on
NLTE metal line-blanketed model atmospheres calculated with our NLTE code
TLUSTY. We systematically explore the sensitivity of various UV and optical
lines to different stellar parameters. We have obtained consistent fits of the
UV and the optical spectrum to derive the effective temperature, surface
gravity, surface composition, and microturbulent velocity of each star. Stellar
radii, masses, luminosities and ages then follow. Similarly to more limited
recent studies, we derive cooler temperatures than the standard Teff
calibration of O stars. We propose a new calibration between the spectral type
and effective temperature based on our results from UV metal lines as well as
optical hydrogen and helium lines. For stars of the same spectral subtype, we
find a general good agreement between Teff determinations obtained with TLUSTY,
CMFGEN, and FASTWIND models. We derive ionizing luminosities that are smaller
by a factor of 3 compared to luminosities inferred from previous standard
calibrations. The chemical composition analysis reveals that the surface of
about 3/4 of the program stars is moderately to strongly enriched in nitrogen,
while showing the original helium, carbon, and oxygen abundances. Our results
support the new stellar evolution models that predict that the surface of fast
rotating stars becomes N-rich during the main sequence phase because of
rotationally-induced mixing. Most stars exhibit the ``mass discrepancy''
problem. This discrepancy too is a result of fast rotation which lowers the
measured effective gravity. Our study thus emphasizes the importance of
rotation in our understanding of the properties of massive stars. (abridged)Comment: Submitted to Astrophysical Journal; 69 page
What makes for prize-winning television?
We investigate the determinants of success in four international television awards festivals between 1994 and 2012. We find that countries with larger markets and greater expenditure on public broadcasting tend to win more awards, but that the degree of concentration in the market for television and rates of penetration of pay-per-view television are unrelated to success. These findings are consistent with general industrial organisation literature on quality and market size, and with media policy literature on public service broadcasting acting as a force for quality. However, we also find that ‘home countries’ enjoy a strong advantage in these festivals, which is not consistent with festival success acting as a pure proxy for television quality
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