95 research outputs found
The stellar metallicity distribution in intermediate latitude fields with BATC and SDSS data
Based on the Beijing-Arizona-Taiwan-Connecticut (BATC) and Sloan Digital Sky
Survey (SDSS) photometric data, we adopt SEDs fitting Method to evaluate the
metallicity distribution for \sim40,000 main-sequence stars in the Galaxy.
According to the derived photometric metallicities of these sample stars, we
find that the metallicity distribution shift from metal-rich to metal-poor with
the increase of distance from the Galactic center. The mean metallicity is
about of 1.5 \pm 0.2dex in the outer halo and 1.3 \pm 0.1 dex in the inner
halo. The mean metallicity smoothly decreases from -0.4 to -0.8 in interval 0 <
r \leq 5 kpc. The fluctuation in the mean metallicity with Galactic longitude
can be found in interval 4 < r \leq 8 kpc. There is a vertical abundance
gradients d[Fe/H]/dz\sim -0.21 \pm 0.05 dex kpc-1 for the thin disk (z \leq 2
kpc). At distance 2 < z \leq 5 kpc, where the thick disk stars are dominated,
the gradients are about of -0.16 \pm0.06 dex kpc-1, it can be interpreted as a
mixture of stellar population with different mean metallicities at all z
levels. The vertical metallicity gradient is - 0.05 \pm0.04 dex kpc-1 for the
halo (z > 5 kpc). So there is little or no metallicity gradient in the halo
THE HIGH CADENCE TRANSIENT SURVEY (HITS). I. SURVEY DESIGN AND SUPERNOVA SHOCK BREAKOUT CONSTRAINTS
Indexación: Web of Science; Scopus.We present the first results of the High Cadence Transient Survey (HiTS), a survey for which the objective is to detect and follow-up optical transients with characteristic timescales from hours to days, especially the earliest hours of supernova (SN) explosions. HiTS uses the Dark Energy Camera and a custom pipeline for image subtraction, candidate filtering and candidate visualization, which runs in real-time to be able to react rapidly to the new transients. We discuss the survey design, the technical challenges associated with the real-time analysis of these large volumes of data and our first results. In our 2013, 2014, and 2015 campaigns, we detected more than 120 young SN candidates, but we did not find a clear signature from the short-lived SN shock breakouts (SBOs) originating after the core collapse of red supergiant stars, which was the initial science aim of this survey. Using the empirical distribution of limiting magnitudes from our observational campaigns, we measured the expected recovery fraction of randomly injected SN light curves, which included SBO optical peaks produced with models from Tominaga et al. (2011) and Nakar & Sari (2010). From this analysis, we cannot rule out the models from Tominaga et al. (2011) under any reasonable distributions of progenitor masses, but we can marginally rule out the brighter and longer-lived SBO models from Nakar & Sari (2010) under our best-guess distribution of progenitor masses. Finally, we highlight the implications of this work for future massive data sets produced by astronomical observatories, such as LSST.http://iopscience.iop.org/article/10.3847/0004-637X/832/2/155/meta;jsessionid=76BDFFFE378003616F6DBA56A9225673.c4.iopscience.cld.iop.or
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Variable Stars in the Giant Satellite Galaxy Antlia 2
We report 350 pulsating variable stars found in four DECam fields (
sq. deg.) covering the Antlia 2 satellite galaxy. The sample of variables
includes 318 RR Lyrae stars and eight anomalous Cepheids in the galaxy.
Reclassification of several objects designated previously to be RR Lyrae as
Anomalous Cepheids gets rid of the satellite's stars intervening along the line
of sight. This in turn removes the need for prolific tidal disruption of the
dwarf, in agreement with the recently updated proper motion and peri-centre
measurements based on Gaia EDR3. There are also several bright foreground RR
Lyrae stars in the field, and two distant background variables located kpc behind Antlia 2. We found RR Lyrae stars over the full search area,
suggesting that the galaxy is very large and likely extends beyond our observed
area. The mean period of the RRab in Antlia 2 is 0.599 days, while the RRc have
a mean period of 0.368 days, indicating the galaxy is an
Oosterhoff-intermediate system. The distance to Antlia 2 based on the RR Lyrae
stars is kpc () with a dispersion of kpc. We
measured a clear distance gradient along the semi-major axis of the galaxy,
with the South-East side of Antlia 2 being kpc farther away from the
North-West side. This elongation along the line of sight is likely due to the
ongoing tidal disruption of Ant 2
Sustainable development of a GCP-compliant clinical trials platform in Africa: the Malaria Clinical Trials Alliance perspective
BACKGROUND: The Malaria Clinical Trials Alliance (MCTA), a programme of INDEPTH network of demographic surveillance centres, was launched in 2006 with two broad objectives: to facilitate the timely development of a network of centres in Africa with the capacity to conduct clinical trials of malaria vaccines and drugs under conditions of good clinical practice (GCP); and to support, strengthen and mentor the centres in the network to facilitate their progression towards self-sustaining clinical research centres. CASE DESCRIPTION: Sixteen research centres in 10 African malaria-endemic countries were selected that were already working with the Malaria Vaccine Initiative (MVI) or the Medicines for Malaria Venture (MMV). All centres were visited to assess their requirements for research capacity development through infrastructure strengthening and training. Support provided by MCTA included: laboratory and facility refurbishment; workshops on GCP, malaria diagnosis, strategic management and media training; and training to support staff to undertake accreditation examinations of the Association of Clinical Research Professionals (ACRP). Short attachments to other network centres were also supported to facilitate sharing practices within the Alliance. MCTA also played a key role in the creation of the African Media & Malaria Research Network (AMMREN), which aims to promote interaction between researchers and the media for appropriate publicity and media reporting of research and developments on malaria, including drug and vaccine trials. CONCLUSION: In three years, MCTA strengthened 13 centres to perform GCP-compliant drug and vaccine trials, including 11 centres that form the backbone of a large phase III malaria vaccine trial. MCTA activities have demonstrated that centres can be brought up to GCP compliance on this time scale, but the costs are substantial and there is a need for further support of other centres to meet the growing demand for clinical trial capacity. The MCTA experience also indicates that capacity development in clinical trials is best carried out in the context of preparation for specific trials. In this regard MCTA centres involved in the phase III malaria vaccine trial were, on average, more successful at consolidating the training and infrastructure support than those centres focussing only on drug trials
Phenolic and furanic compounds of Portuguese chestnut and French, American and Portuguese oak wood chips
Botanical species used on aging process must
be wisely and judiciously chosen, and for this selection, a
basic knowledge of the chemical composition of woods is
warranted. Aiming to contribute to extend the knowledge
of the chemical composition of several wood species useful
for enological purposes, we have focused our studies on
Portuguese chestnut and French, American and Portuguese
oak chips. The profile of low molecular weight phenolic
composition of these chips was achieved, using an optimized
extraction method based on pressurized liquid
extraction, followed by the quantification of phenolic acids,
phenolic aldehydes and furanic derivatives by high-performance
liquid chromatography (HPLC-DAD). The
identification of those compounds was also confirmed by
LC-DAD/ESI-MS. This study allowed the determination of
the low molecular phenolic composition of Portuguese
chestnut and French, American and Portuguese oak wood.
According to our results, the influence of the botanical
species seems to be more relevant than the geographic
origin of the wood species
Evaluating cloud deployment scenarios based on security and privacy requirements
Migrating organisational services, data and application on the Cloud is an important strategic decision for organisations due to the large number of benefits introduced by the usage of cloud computing, such as cost reduction and on demand resources. Despite, however, of the many benefits, there are challenges and risks for cloud adaption related to (amongst others) data leakage, insecure APIs, and shared technology vulnerabilities. These challenges need to be understood and analysed in the context of an organisation relevant cloud computing deployment models. Although, the literature provides a large number of references to works that consider cloud computing security issues, no work has been provided, to our knowledge, which supports the elicitation of security and privacy requirements and the selection of an appropriate cloud deployment model based on such requirements. This work contributes towards this gap. In particular, we propose a requirements engineering framework to support the elicitation of security and privacy requirements and the selection of an appropriate deployment model based on the elicited requirements. Our framework provides a modelling language that builds on concepts from requirements, security, privacy and cloud engineering and a systematic process. We use a real case study, based on the Greek National Gazette, to demonstrate the applicability of our work
The stellar halo of the Galaxy
Stellar halos may hold some of the best preserved fossils of the formation
history of galaxies. They are a natural product of the merging processes that
probably take place during the assembly of a galaxy, and hence may well be the
most ubiquitous component of galaxies, independently of their Hubble type. This
review focuses on our current understanding of the spatial structure, the
kinematics and chemistry of halo stars in the Milky Way. In recent years, we
have experienced a change in paradigm thanks to the discovery of large amounts
of substructure, especially in the outer halo. I discuss the implications of
the currently available observational constraints and fold them into several
possible formation scenarios. Unraveling the formation of the Galactic halo
will be possible in the near future through a combination of large wide field
photometric and spectroscopic surveys, and especially in the era of Gaia.Comment: 46 pages, 16 figures. References updated and some minor changes.
Full-resolution version available at
http://www.astro.rug.nl/~ahelmi/stellar-halo-review.pd
Phenolic and furanic compounds of Portuguese chestnut and French, American and Portuguese oak wood chips
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