1,033 research outputs found
An optimization model for metabolic pathways
This article is available open access through the publisher’s website through the link below. Copyright @ The Author 2009.Motivation: Different mathematical methods have emerged in the post-genomic era to determine metabolic pathways. These methods can be divided into stoichiometric methods and path finding methods. In this paper we detail a novel optimization model, based upon integer linear programming, to determine metabolic pathways. Our model links reaction stoichiometry with path finding in a single approach. We test the ability of our model to determine 40 annotated Escherichia coli metabolic pathways. We show that our model is able to determine 36 of these 40 pathways in a computationally effective manner.
Contact: [email protected]
Supplementary information: Supplementary data are available at Bioinformatics online (http://bioinformatics.oxfordjournals.org/cgi/content/full/btp441/DC1)
Progress in Measurements of the Gravitational Bending of Radio Waves Using the VLBA
We have used the Very Long Baseline Array (VLBA) at 43, 23 and 15 GHz to
measure the solar gravitational deflection of radio waves among four radio
sources during an 18-day period in October 2005. Using phase-referenced radio
interferometry to fit the measured phase delay to the propagation equation of
the parameterized post-Newtonian (PPN) formalism, we have determined the
deflection parameter gamma = 0.9998 +/- 0.0003$ (68% confidence level), in
agreement with General Relativity. The results come mainly from 43 GHz
observations where the refraction effects of the solar corona were negligible
beyond 3 degrees from the sun. The purpose of this experiment is three-fold: to
improve on the previous results in the gravitational bending experiments near
the solar limb; to examine and evaluate the accuracy limits of terrestrial VLBI
techniques; and to determine the prospects and outcomes of future experiments.
Our conclusion is that a series of improved designed experiments with the VLBA
could increase the presented accuracy by at least a factor of 4.Comment: 22 pages, 3 figure
The catalogue of positions of optically bright extragalactic radio sources OBRS-1
It is expected that the European Space Agency mission Gaia will make possible
to determine coordinates in the optical domain of more than 500000 quasars. In
2006, a radio astrometry project was launched with the overall goal to make
comparison of coordinate systems derived from future space-born astrometry
instruments with the coordinate system constructed from analysis of the global
very long baseline interferometry (VLBI) more robust. Investigation of their
rotation, zonal errors, and the non-alignment of the radio and optical
positions caused by both radio and optical structures are important for
validation of both techniques. In order to support these studies, the
densification of the list of compact extragalactic objects that are bright in
both radio and optical ranges is desirable. A set of 105 objects from the list
of 398 compact extragalactic radio sources with declination > -10 deg was
observed with the VLBA+EVN with the primary goal of producing their images with
milliarcsecond resolution. These sources are brighter than 18 magnitude at V
band, and they were previously detected at the European VLBI network. In this
paper coordinates of observed sources have been derived with milliarcsecond
accuracies from analysis of these VLBI observations following the method of
absolute astrometry. The catalogue of positions of 105 target sources is
presented. The accuracies of sources coordinates are in the range of 0.3 to 7
mas, with the median 1.1 mas.Comment: 6 pages, 1 figure, accepted by the Astronomical Journal, ID:
AJ-10606. Electronic table 2 with the catalogue is available in the source
code of this submissio
A Method for Providing High-volume Interprofessional Simulation Encounters in Physical and Occupational Therapy Education Programs
With an increasing emphasis on interprofessional education within the allied health professions, simulation has potential for being a useful teaching modality for providing collaborative learning experiences for occupational and physical therapist students. However, there are many challenges associated with conducting simulations with large numbers of students. We describe the design, planning, cost, and support staff time required for conducting an interprofessional simulation of the intensive care setting, including a methodology for maximizing resources and student opportunities for participation for 64 physical and occupational therapy students over a 4-hour time period. Qualitative analyses of student experiences are also presented
Age and mass studies for young star clusters in M31 from SEDs-fit
In this paper, we present photometry for young star clusters in M31, which
are selected from Caldwell et al. These star clusters have been observed as
part of the Beijing--Arizona--Taiwan--Connecticut (BATC) Multicolor Sky Survey
from 1995 February to 2008 March. The BATC images including these star clusters
are taken with 15 intermediate-band filters covering 3000--10000 \AA. Combined
with photometry in the {\sl GALEX} far- and near-ultraviolet, broad-band
, SDSS , and infrared of Two Micron All Sky Survey,
we obtain their accurate spectral energy distributions (SEDs) from 1538-20000
\AA. We derive these star clusters' ages and masses by comparing their SEDs
with stellar population synthesis models. Our results are in good agreement
with previous determinations. The mean value of age and mass of young clusters
( Gyr) is about 385 Myr and , respectively. There
are two distinct peaks in the age distribution, a highest peak at age 60
Myr and a secondary peak around 250 Myr, while the mass distribution shows a
single peak around . A few young star clusters have two-body
relaxation times greater than their ages, indicating that those clusters have
not been well dynamically relaxed and therefore have not established the
thermal equilibrium. There are several regions showing aggregations of young
star clusters around the 10 kpc ring and the outer ring, indicating that the
distribution of the young star clusters is well correlated with M31's
star-forming regions. The young massive star clusters (age Myr and
mass ) show apparent concentration around the ring
splitting region, suggesting a recent passage of a satellite galaxy (M32)
through M31 disk.Comment: Accepted for Publication in AJ, 15 pages, 14 figures and 4 table
Precise absolute astrometry from the VLBA imaging and polarimetry survey at 5 GHz
We present in this paper accurate positions of 857 sources derived from the
astrometric analysis of 16 eleven-hour experiments from the Very Long Baseline
Array imaging and polarimetry survey at 5 GHz (VIPS). Among observed sources,
positions of 430 objects were not determined before at a milliarcsecond level
of accuracy. For 95% of the sources the uncertainty of their positions range
from 0.3 to 0.9 mas, with the median value of 0.5 mas. This estimate of
accuracy is substantiated by the comparison of positions of 386 sources that
were previously observed in astrometric programs simultaneously at 2.3/8.6 GHz.
Surprisingly, the ionosphere contribution to group delay was adequately modeled
with the use of the total electron contents maps derived from GPS observations
and only marginally affected estimates of source coordinates.Comment: Accepted for publication by the Astronomical Journal. 7 pages, 2
tables, 4 figures. Submission contains an ascii file with the catalogue. You
can get the catalogue by downloading the source of this paper and extracting
file table2.tx
Age and structure parameters of a remote M31 globular cluster B514 based on HST, 2MASS, GALEX and BATC observations
B514 is a remote M31 globular cluster which locating at a projected distance
of R_p~55 kpc. Deep observations with the Advanced Camera for Surveys (ACS) on
the Hubble Space Telescope (HST) are used to provide the accurate integrated
light and star counts of B514. By coupling analysis of the distribution of the
integrated light with star counts, we are able to reliably follow the profile
of the cluster out to ~40". Based on the combined profile, we study in detail
its surface brightness distribution in F606W and F814W filters, and determine
its structural parameters by fitting a single-mass isotropic King model. The
results showed that, the surface brightness distribution departs from the
best-fit King model for r>10". B514 is quite flatted in the inner region, and
has a larger half-light radius than majority of normal globular clusters of the
same luminosity. It is interesting that, in the M_V versus log R_h plane, B514
lies nearly on the threshold for ordinary globular clusters as defined by
Mackey & van den Bergh. In addition, B514 was observed as part of the
Beijing-Arizona-Taiwan-Connecticut (BATC) Multicolor Sky Survey, using 13
intermediate-band filters covering a wavelength range of 3000--8500 \AA. Based
on aperture photometry, we obtain its SEDs as defined by the 13 BATC filters.
We determine the cluster's age and mass by comparing its SEDs (from 2267 to
20000{\AA}, comprising photometric data in the near-ultraviolet of GALEX, 5
SDSS bands, 13 BATC intermediate-band, and 2MASS near-infrared JHKs} filters)
with theoretical stellar population synthesis models, resulting in age of
Gyr. This age confirms the previous suggestion that B514 is an old
GC in M31. B514 has a mass of , and is a
medium-mass globular cluster in M31.Comment: Accepted for Publication in AJ, 18 pages, 6 figures and 9 table
A SAURON study of dwarf elliptical galaxies in the Virgo Cluster: kinematics and stellar populations
Dwarf elliptical galaxies (dEs) are the most common galaxy type in nearby
galaxy clusters; even so, many of their basic properties have yet to be
quantified. Here we present the results of our study of 4 Virgo dwarf
ellipticals obtained with the SAURON integral field unit on the William
Herschel Telescope (La Palma, Spain). While traditional long-slit observations
are likely to miss more complicated kinematic features, with SAURON we are able
to study both kinematics and stellar populations in two dimensions, obtaining a
much more detailed view of the mass distribution and star formation histories.
What is visible even in such a small sample is that dEs are not a uniform
group, not only morphologically, but also as far as their kinematic and stellar
population properties are concerned. We find the presence of substructures,
varying degrees of flattening and of rotation, as well as differences in age
and metallicity gradients. We confirm that two of our galaxies are
significantly flattened, yet non-rotating objects, which makes them likely
triaxial systems. The comparison between the dwarf and the giant groups shows
that dEs could be a low-mass extension of Es in the sense that they do seem to
follow the same trends with mass. However, dEs as progenitors of Es seem less
likely as we have seen that dEs have much lower abundance ratios.Comment: 8 pages, 6 figures; to appear in the proceedings of the JENAM 2010
Symposium on Dwarf Galaxies (Lisbon, September 9-10, 2010); minor edits and
references adde
Characterizing Operations Preserving Separability Measures via Linear Preserver Problems
We use classical results from the theory of linear preserver problems to
characterize operators that send the set of pure states with Schmidt rank no
greater than k back into itself, extending known results characterizing
operators that send separable pure states to separable pure states. We also
provide a new proof of an analogous statement in the multipartite setting. We
use these results to develop a bipartite version of a classical result about
the structure of maps that preserve rank-1 operators and then characterize the
isometries for two families of norms that have recently been studied in quantum
information theory. We see in particular that for k at least 2 the operator
norms induced by states with Schmidt rank k are invariant only under local
unitaries, the swap operator and the transpose map. However, in the k = 1 case
there is an additional isometry: the partial transpose map.Comment: 16 pages, typos corrected, references added, proof of Theorem 4.3
simplified and clarifie
Sub one per cent mass fractions of young stars in red massive galaxies
Early-type galaxies are considered to be the end products of massive galaxy formation1. Optical spectroscopic studies reveal that massive early-type galaxies formed the bulk of their stars over short timescales (≲≲1 Gyr) and at high redshift (z ≳≳ 2), followed by passive evolution to the present2. However, their optical spectra are unable to constrain small episodes of recent star formation, since they are dominated by old stars. Fortunately, this problem can be tackled in the ultraviolet range. While recent studies that make use of ultraviolet absorption lines have suggested the presence of young stars in a few early-type galaxies3, the age and mass fractions of young stars and their dependence on galaxy mass are unknown. Here we report a detailed study of these young stellar populations, from high-quality stacked spectra of 28,663 galaxies from the BOSS survey4, analysing optical and ultraviolet absorption lines simultaneously. We find that residual star formation is ubiquitous in massive early-type galaxies, measuring average mass fractions of 0.5% in young stars in the last 2 Gyr of their evolution. This fraction shows a decreasing trend with galaxy stellar mass, consistent with a downsizing scenario5. We also find that synthetic galaxies from state-of-the-art cosmological numerical simulations6 substantially overproduce both intermediate and young stellar populations. Therefore, our results pose stringent constraints on numerical simulations of galaxy formation6,7
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