625 research outputs found
Classification methods for noise transients in advanced gravitational-wave detectors II: performance tests on Advanced LIGO data
The data taken by the advanced LIGO and Virgo gravitational-wave detectors contains short duration noise transients that limit the significance of astrophysical detections and reduce the duty cycle of the instruments. As the advanced detectors are reaching sensitivity levels that allow for multiple detections of astrophysical gravitational-wave sources it is crucial to achieve a fast and accurate characterization of non-astrophysical transient noise shortly after it occurs in the detectors. Previously we presented three methods for the classification of transient noise sources. They are Principal Component Analysis for Transients (PCAT), Principal Component LALInference Burst (PC-LIB) and Wavelet Detection Filter with Machine Learning (WDF-ML). In this study we carry out the first performance tests of these algorithms on gravitational-wave data from the Advanced LIGO detectors. We use the data taken between the 3rd of June 2015 and the 14th of June 2015 during the 7th engineering run (ER7), and outline the improvements made to increase the performance and lower the latency of the algorithms on real data. This work provides an important test for understanding the performance of these methods on real, non stationary data in preparation for the second advanced gravitational-wave detector observation run, planned for later this year. We show that all methods can classify transients in non stationary data with a high level of accuracy and show the benefits of using multiple classifiers
The metallicity distribution of the halo and the satellites of the Milky way in the hierarchical merging paradigm
To account for the observed differential metallicity distribution (DMD) of
the Milky Way halo, a semi-analytical model is presented in the framework of
the hierarchical merging paradigm for structure formation. It is assumed that
the Milky Way halo is composed of a number of sub-haloes with properties either
as observed in the dwarf satellite galaxies of the Local group (shape of
metallicity distribution, effective yield) or derived from calculations of
structure formation (sub-halo distribution function). With reasonable
assumptions for the parameters involved, we find that the overall shape and
effective yield of the Galactic halo DMD can be reproduced in the framework of
such a simple model. The low metallicity tail of the DMD presents a defficiency
of stars with respect to the simple model predictions (akin to the G-dwarf
problem in the solar neighborhood); it is suggested that an early infall phase
can account for that problem, as well as for the observed DMDs of dwarf
satellite galaxies.Accretion of galaxies similar (but not identical) to the
progenitors of present day dwarf satellites of the Milky Way may well have
formed the Galactic halo.Comment: 10 pages, 6 fig. to appear in Astronomy and Astrophysic
Cherry-picking participation: explaining the fate of proposals from participatory processesÂ
What happens to the proposals generated by participatory processes? One of the key aspects of research on public participation that has been the subject of rare systematic analysis and comparison is the fate of the output from participatory processes: their proposals. Which specific factors explain whether proposals are accepted, rejected or transformed by public authorities? This paper contributes to this gap in our understanding in two steps. First, we identify contextual, process and proposal related factors that are likely to affect the prospect of proposals being implemented, generating a set of testable hypotheses. Second, we test the explanatory power of these hypotheses through multilevel analysis on a diverse set of 571 policy proposals. Our findings offer evidence that while there is no effect for contextual factors, both process and proposal related variables have significant explanatory power. The design of participatory processes affects the degree of implementation, with participatory budgeting and higher quality processes being particularly effective. But most significant for explaining implementation are proposal level economic and political factors: a proposal's cost, the extent to which it challenges existing policy and the degree of support it has within the municipality all strongly affect the chance of implementation.
H-alpha kinematics of S4G spiral galaxies-II. Data description and non-circular motions
We present a kinematical study of 29 spiral galaxies included in the Spitzer
Survey of Stellar Structure in Galaxies, using Halpha Fabry-Perot data obtained
with the Galaxy Halpha Fabry-Perot System instrument at the William Herschel
Telescope in La Palma, complemented with images in the R-band and in Halpha.
The primary goal is to study the evolution and properties of the main
structural components of galaxies through the kinematical analysis of the FP
data, complemented with studies of morphology, star formation and mass
distribution. In this paper we describe how the FP data have been obtained,
processed and analysed. We present the resulting moment maps, rotation curves,
velocity model maps and residual maps. Images are available in FITS format
through the NASA/IPAC Extragalactic Database and the Centre de Donn\'ees
Stellaires. With these data products we study the non-circular motions, in
particular those found along the bars and spiral arms. The data indicate that
the amplitude of the non-circular motions created by the bar does not correlate
with the bar strength indicators. The amplitude of those non-circular motions
in the spiral arms does not correlate with either arm class or star formation
rate along the spiral arms. This implies that the presence and the magnitude of
the streaming motions in the arms is a local phenomenon.Comment: 23 pages, 14 figures, without appendices, accepted to be published in
MNRA
Chemical abundances of distant extremely metal-poor unevolved stars
Aims: The purpose of our study is to determine the chemical composition of a
sample of 16 candidate Extremely Metal-Poor (EMP) dwarf stars, extracted from
the Sloan Digital Sky Survey (SDSS). There are two main purposes: in the first
place to verify the reliability of the metallicity estimates derived from the
SDSS spectra; in the second place to see if the abundance trends found for the
brighter nearer stars studied previously also hold for this sample of fainter,
more distant stars. Methods: We used the UVES at the VLT to obtain
high-resolution spectra of the programme stars. The abundances were determined
by an automatic analysis with the MyGIsFOS code, with the exception of lithium,
for which the abundances were determined from the measured equivalent widths of
the Li I resonance doublet. Results: All candidates are confirmed to be EMP
stars, with [Fe/H]<= -3.0. The chemical composition of the sample of stars is
similar to that of brighter and nearer samples. We measured the lithium
abundance for 12 stars and provide stringent upper limits for three other
stars, for a fourth star the upper limit is not significant, owing to the low
signal-to noise ratio of the spectrum. The "meltdown" of the Spite plateau is
confirmed, but some of the lowest metallicity stars of the sample lie on the
plateau. Conclusions: The concordance of the metallicities derived from
high-resolution spectra and those estimated from the SDSS spectra suggests that
the latter may be used to study the metallicity distribution of the halo. The
abundance pattern suggests that the halo was well mixed for all probed
metallicities and distances. The fact that at the lowest metallicities we find
stars on the Spite plateau suggests that the meltdown depends on at least
another parameter, besides metallicity. (abridged)Comment: A&A in pres
The U.S. Arctic Observing Viewer: A Web-Mapping Application for Enhancing Environmental Observation of the Changing Arctic
Although much progress has been made with various Arctic Observing efforts, assessing that progress can be difficult. What data collection efforts are established or underway? Where? By whom? To help meet the strategic needs of programs such as the U.S. Study of Environmental Arctic Change (SEARCH), the Arctic Observing Network (AON), Sustaining Arctic Observing Networks (SAON) and related initiatives, an update has been released for the Arctic Observing Viewer (AOV; http://ArcticObservingViewer.org). This web mapping application and information system has begun to compile the who, what, where, and when for thousands of data collection sites (such as boreholes, ship tracks, buoys, towers, sampling stations, sensor networks, vegetation sites, stream gauges, and observatories) wherever marine, terrestrial, or atmospheric data are collected. Contributing partners for this collaborative resource include the U.S. NSF, ACADIS, ADIwg, AOOS, a2dc, AON, ARMAP, BAID, CAFF, IASOA, INTERACT, and others. While focusing on U.S. activities, the AOV welcomes information exchange with international groups for mutual benefit. Users can visualize, navigate, select, search, draw, print, and more. AOV is founded on principles of interoperability, with open metadata and web service standards, so that agencies and organizations can use AOV tools and services for their own purposes. In this way, AOV will reinforce and complement other distributed yet interoperable cyber-resources and will help science planners, funding agencies, researchers, data specialists, and others to assess status, identify overlap, fill gaps, optimize sampling design, refine network performance, clarify directions, access data, coordinate logistics, collaborate, and more in order to meet Arctic Observing goals.MalgrĂ© les progrĂšs rĂ©alisĂ©s dans le cadre de nombreux efforts dâobservation de lâArctique, les progrĂšs peuvent ĂȘtre difficiles Ă Ă©valuer. Quelles initiatives de collecte de donnĂ©es sont en cours ou sont Ă©tablies? Ă quel endroit? Et qui gĂšre ces initiatives? Pour aider Ă rĂ©pondre aux besoins stratĂ©giques de programmes comme ceux de lâorganisme amĂ©ricain Study of Environmental Arctic Change (SEARCH), du rĂ©seau Arctic Observing Network (AON), des rĂ©seaux Sustaining Arctic Observing Networks (SAON) et dâautres programmes connexes, on a procĂ©dĂ© Ă la mise Ă jour de lâArctic Observing Viewer (AOV; http://ArcticObservingViewer.org). Ce systĂšme dâinformation jumelĂ© Ă une application de mappage sur le Web a amorcĂ© la compilation des coordonnĂ©es et des renseignements se rapportant Ă des milliers de sites de collecte de donnĂ©es (comme les trous de forage, les trajets de navires, les bouĂ©es, les tours, les stations dâĂ©chantillonnage, les rĂ©seaux de capteurs, les sites de vĂ©gĂ©tation, les fluviomĂštres et les observatoires) oĂč des donnĂ©es marines, terrestres ou atmosphĂ©riques sont prĂ©levĂ©es. Parmi les partenaires qui collaborent Ă cette ressource, notons U.S. NSF, ACADIS, ADIwg, AOOS, a2dc, AON, ARMAP, BAID, CAFF, IASOA, INTERACT et dâautres encore. Bien que lâAOV se concentre sur les activitĂ©s amĂ©ricaines, il accepte lâĂ©change dâinformation avec des groupes internationaux lorsquâil existe des avantages mutuels. Les utilisateurs peuvent visualiser les donnĂ©es, naviguer dans le systĂšme, faire des sĂ©lections et des recherches, dessiner, imprimer et ainsi de suite. LâAOV fonctionne moyennant des principes dâinteropĂ©rabilitĂ©, avec des mĂ©tadonnĂ©es ouvertes et des normes de service sur le Web afin que les organismes et les organisations puissent utiliser les outils et les services de lâAOV pour leurs propres fins. De cette façon, lâAOV sera en mesure de consolider et de complĂ©ter dâautres cyberressources Ă la fois rĂ©parties et interopĂ©rables, en plus dâaider les planificateurs de la science, les bailleurs de fonds, les chercheurs, les spĂ©cialistes des donnĂ©es et dâautres encore Ă Ă©valuer les statuts, Ă repĂ©rer les dĂ©doublements, Ă combler les Ă©carts, Ă optimiser les plans dâĂ©chantillonnage, Ă raffiner le rendement des rĂ©seaux, Ă clarifier les consignes, Ă accĂ©der aux donnĂ©es, Ă coordonner la logistique, Ă collaborer et ainsi de suite afin de rĂ©pondre aux objectifs dâobservation de lâArctique
An HST/ACS investigation of the spatial and chemical structure and sub-structure of NGC 891, a Milky Way analogue
We present a structural analysis of NGC891, an edge-on galaxy that has long
been considered to be an analogue of the Milky Way. Using starcounts derived
from deep HST/ACS images, we detect the presence of a thick disk component in
this galaxy with vertical scale height 1.44+/-0.03 kpc and radial scale length
4.8+/-0.1 kpc, only slightly longer than that of the thin disk. A stellar
spheroid with a de Vaucouleurs-like profile is detected from a radial distance
of 0.5 kpc to the edge of the survey at 25 kpc; the structure appears to become
more flattened with distance, reaching q = 0.50 in the outermost halo region
probed. The halo inside of 15 kpc is moderately metal-rich (median [Fe/H] ~
-1.1) and approximately uniform in median metallicity. Beyond that distance a
modest chemical gradient is detected, with the median reaching [Fe/H] ~ -1.3 at
20 kpc. We find evidence for subtle, but very significant, small-scale
variations in the median colour and density over the halo survey area. We argue
that the colour variations are unlikely to be due to internal extinction or
foreground extinction, and reflect instead variations in the stellar
metallicity. Their presence suggests a startling conclusion: that the halo of
this galaxy is composed of a large number of incompletely-mixed
sub-populations, testifying to its origin in a deluge of small accretions.Comment: 21 pages, 16 figures, accepted for publication in MNRA
Strategy for signal classiïŹcation to improve data quality for Advanced Detectors gravitational-wave searches
Noise of non-astrophysical origin contaminates science data taken by the Advanced Laser Interferometer Gravitational-wave Observatory and Advanced Virgo gravitational-wave detectors. Characterization of instrumental and environmental noise transients has proven critical in identifying false positives in the ïŹrst aLIGO observing run O1. In this talk, we present three algorithms designed for the automatic classiïŹcation of non-astrophysical transients in advanced detectors. Principal Component Analysis for Transients (PCAT) and an adaptation of LALInference Burst (PC-LIB) are based on Principal Component Analysis. The third algorithm is a combination of a glitch ïŹnder called Wavelet Detection Filter (WDF) and unsupervised machine learning techniques for classiïŹcation
Psychomotor impairments and therapeutic implications revealed by a mutation associated with infantile Parkinsonism-Dystonia
Parkinson disease (PD) is a progressive, neurodegenerative disorder affecting over 6.1 million people worldwide. Although the cause of PD remains unclear, studies of highly penetrant mutations identified in early-onset familial parkinsonism have contributed to our understanding of the molecular mechanisms underlying disease pathology. Dopamine (DA) transporter (DAT) deficiency syndrome (DTDS) is a distinct type of infantile parkinsonism-dystonia that shares key clinical features with PD, including motor deficits (progressive bradykinesia, tremor, hypomimia) and altered DA neurotransmission. Here, we define structural, functional, and behavioral consequences of a Cys substitution at R445 in human DAT (hDAT R445C), identified in a patient with DTDS. We found that this R445 substitution disrupts a phylogenetically conserved intracellular (IC) network of interactions that compromise the hDAT IC gate. This is demonstrated by both Rosetta molecular modeling and fine-grained simulations using hDAT R445C, as well as EPR analysis and X-ray crystallography of the bacterial homolog leucine transporter. Notably, the disruption of this IC network of interactions supported a channel-like intermediate of hDAT and compromised hDAT function. We demonstrate that Drosophila melanogaster expressing hDAT R445C show impaired hDAT activity, which is associated with DA dysfunction in isolated brains and with abnormal behaviors monitored at high-speed time resolution. We show that hDAT R445C Drosophila exhibit motor deficits, lack of motor coordination (i.e. flight coordination) and phenotypic heterogeneity in these behaviors that is typically associated with DTDS and PD. These behaviors are linked with altered dopaminergic signaling stemming from loss of DA neurons and decreased DA availability. We rescued flight coordination with chloroquine, a lysosomal inhibitor that enhanced DAT expression in a heterologous expression system. Together, these studies shed some light on how a DTDS-linked DAT mutation underlies DA dysfunction and, possibly, clinical phenotypes shared by DTDS and PD
Exploring the Universe with Metal-Poor Stars
The early chemical evolution of the Galaxy and the Universe is vital to our
understanding of a host of astrophysical phenomena. Since the most metal-poor
Galactic stars (with metallicities down to [Fe/H]\sim-5.5) are relics from the
high-redshift Universe, they probe the chemical and dynamical conditions of the
Milky Way and the origin and evolution of the elements through nucleosynthesis.
They also provide constraints on the nature of the first stars, their
associated supernovae and initial mass function, and early star and galaxy
formation. The Milky Way's dwarf satellites contain a large fraction (~30%) of
the known most metal-poor stars that have chemical abundances that closely
resemble those of equivalent halo stars. This suggests that chemical evolution
may be universal, at least at early times, and that it is driven by massive,
energetic SNe. Some of these surviving, ultra-faint systems may show the
signature of just one such PopIII star; they may even be surviving first
galaxies. Early analogs of the surviving dwarfs may thus have played an
important role in the assembly of the old Galactic halo whose formation can now
be studied with stellar chemistry. Following the cosmic evolution of small
halos in simulations of structure formation enables tracing the cosmological
origin of the most metal-poor stars in the halo and dwarf galaxies. Together
with future observations and additional modeling, many of these issues,
including the reionization history of the Milky Way, may be constrained this
way. The chapter concludes with an outlook about upcoming observational
challenges and ways forward is to use metal-poor stars to constrain theoretical
studies.Comment: 34 pages, 11 figures. Book chapter to appear in "The First Galaxies -
Theoretical Predictions and Observational Clues", 2012 by Springer, eds. V.
Bromm, B. Mobasher, T. Wiklin
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