108 research outputs found
Idiomatic Persistence and Querying for the W3C Web Annotation Data Model
Abstract. W3C Web annotations are a powerful way to support metadata information about digital resources. The Web Annotation Data Model proposes standardised RDF structures that express this by implementing a hierarchical annotation structure. Those annotations are designed to be shared, linked, tracked back as well as searched and discovered across different peers. However, non-Semantic Web experts may struggle to produce the corresponding RDF data or SPARQL queries. Therefore, we propose Anno4j, a Java-based library that gives developers the possibility to create and consume Web Annotations by using plain old Java objects. Anno4j follows natural Object-oriented idioms including inheritance, polymorphism, and composition to facilitate the development with Web Annotations. An extensible and modular architecture supports enhancements and use-case specific model alterations, while the plugin functionality of Anno4j allows to enrich querying by adding custom function evaluators
Plug-and-Play SLAM: A Unified SLAM Architecture for Modularity and Ease of Use
Nowadays, SLAM (Simultaneous Localization and Mapping) is considered by the
Robotics community to be a mature field. Currently, there are many open-source
systems that are able to deliver fast and accurate estimation in typical
real-world scenarios. Still, all these systems often provide an ad-hoc
implementation that entailed to predefined sensor configurations. In this work,
we tackle this issue, proposing a novel SLAM architecture specifically designed
to address heterogeneous sensors' configuration and to standardize SLAM
solutions. Thanks to its modularity and to specific design patterns, the
presented architecture is easy to extend, enhancing code reuse and efficiency.
Finally, adopting our solution, we conducted comparative experiments for a
variety of sensor configurations, showing competitive results that confirm
state-of-the-art performance
Estimating Black Hole Masses in Active Galactic Nuclei Using the MgII 2800 Emission Line
We investigate the relationship between the linewidths of broad Mg II
\lambda2800 and Hbeta in active galactic nuclei (AGNs) to refine them as tools
to estimate black hole (BH) masses. We perform a detailed spectral analysis of
a large sample of AGNs at intermediate redshifts selected from the Sloan
Digital Sky Survey, along with a smaller sample of archival ultraviolet spectra
for nearby sources monitored with reverberation mapping. Careful attention is
devoted to accurate spectral decomposition, especially in the treatment of
narrow-line blending and Fe II contamination. We show that, contrary to popular
belief, the velocity width of Mg II tends to be smaller than that of Hbeta,
suggesting that the two species are not cospatial in the broad-line region.
Using these findings and recently updated BH mass measurements from
reverberation mapping, we present a new calibration of the empirical
prescriptions for estimating virial BH masses for AGNs using the broad Mg II
and Hbeta lines. We show that the BH masses derived from our new formalisms
show subtle but important differences compared to some of the mass estimators
currently used in the literature.Comment: Matches version to appear in ApJ, preliminarily 706:1-13, 2009; a
minor error corrected (in Table 2 only
Drivers of Change in Arctic Fjord Socio-ecological Systems: Examples from the European Arctic
Fjord systems are transition zones between land and sea, resulting in complex and dynamic environments. They are of particular interest in the Arctic as they harbour ecosystems inhabited by a rich range of species and provide many societal benefits. The key drivers of change in the European Arctic (i.e., Greenland, Svalbard, and Northern Norway) fjord socio-ecological systems are reviewed here, structured into five categories: cryosphere (sea ice, glacier mass balance, and glacial and riverine discharge), physics (seawater temperature, salinity, and light), chemistry (carbonate system, nutrients), biology (primary production, biomass, and species richness), and social (governance, tourism, and fisheries). The data available for the past and present state of these drivers, as well as future model projections, are analysed in a companion paper. Changes to the two drivers at the base of most interactions within fjords, seawater temperature and glacier mass balance, will have the most significant and profound consequences on the future of European Arctic fjords. This is because even though governance may be effective at mitigating/adapting to local disruptions caused by the changing climate, there is possibly nothing that can be done to halt the melting of glaciers, the warming of fjord waters, and all of the downstream consequences that these two changes will have. This review provides the first transdisciplinary synthesis of the interactions between the drivers of change within Arctic fjord socio-ecological systems. Knowledge of what these drivers of change are, and how they interact with one another, should provide more expedient focus for future research on the needs of adapting to the changing Arctic
Broad-line Balmer Decrements in Blue Active Galactic Nuclei
We have investigated the broad-line Balmer decrements (Halpha/Hbeta) for a
large, homogeneous sample of Seyfert 1 galaxies and QSOs using spectroscopic
data obtained in the Sloan Digital Sky Survey. The sample, drawn from the
Fourth Data Release, comprises 446 low redshift (z < 0.35) active galactic
nuclei (AGN) that have blue optical continua as indicated by the spectral
slopes in order to minimize the effect of dust extinction. We find that (i) the
distribution of the intrinsic broad-line Halpha/Hbeta ratio can be well
described by log-Gaussian, with a peak at Halpha/Hbeta=3.06 and a standard
deviation of about 0.03 dex only; (ii) the Balmer decrement does not correlate
with AGN properties such as luminosity, accretion rate, and continuum slope,
etc.; (iii) on average, the Balmer decrements are found to be only slightly
larger in radio-loud sources (3.37) and sources having double-peaked
emission-line profiles (3.27) compared to the rest of the sample. We therefore
suggest that the broad-line Halpha/Hbeta ratio can be used as a good indicator
for dust extinction in the AGN broad-line region; this is especially true for
radio-quiet AGN with regular emission-line profiles, which constitute the vast
majority of the AGN population.Comment: To appear in MNRAS. The data and the fitted parameters for the
decomposed spectral components (continuum, FeII and other emission lines) of
the 446 blue AGNs are available at
http://staff.ustc.edu.cn/~xbdong/Data_Release/blueAGN_DR4
The DESI Sky Continuum Monitor System
The Dark Energy Spectroscopic Instrument (DESI) is an ongoing spectroscopic
survey to measure the dark energy equation of state to unprecedented precision.
We describe the DESI Sky Continuum Monitor System, which tracks the night sky
brightness as part of a system that dynamically adjusts the spectroscopic
exposure time to produce more uniform data quality and to maximize observing
efficiency. The DESI dynamic exposure time calculator (ETC) will combine sky
brightness measurements from the Sky Monitor with data from the guider system
to calculate the exposure time to achieve uniform signal-to-noise ratio (SNR)
in the spectra under various observing conditions. The DESI design includes 20
sky fibers, and these are split between two identical Sky Monitor units to
provide redundancy. Each Sky Monitor unit uses an SBIG STXL-6303e CCD camera
and supports an eight-position filter wheel. Both units have been completed and
delivered to the Mayall Telescope at the Kitt Peak National Observatory.
Commissioning results show that the Sky Monitor delivers the required
performance necessary for the ETC.Comment: 9 pages, 7 figures, 1 tabl
SDSS-IV/MaNGA: Spectrophotometric Calibration Technique
Mapping Nearby Galaxies at Apache Point Observatory (MaNGA), one of three core programs in the Sloan Digital Sky Survey-IV, is an integral-field spectroscopic survey of roughly 10,000 nearby galaxies. It employs dithered observations using 17 hexagonal bundles of 2'' fibers to obtain resolved spectroscopy over a wide wavelength range of 3600â10300 Ă
. To map the internal variations within each galaxy, we need to perform accurate spectral surface photometry, which is to calibrate the specific intensity at every spatial location sampled by each individual aperture element of the integral field unit. The calibration must correct only for the flux loss due to atmospheric throughput and the instrument response, but not for losses due to the finite geometry of the fiber aperture. This requires the use of standard star measurements to strictly separate these two flux loss factors (throughput versus geometry), a difficult challenge with standard single-fiber spectroscopy techniques due to various practical limitations. Therefore, we developed a technique for spectral surface photometry using multiple small fiber-bundles targeting standard stars simultaneously with galaxy observations. We discuss the principles of our approach and how they compare to previous efforts, and we demonstrate the precision and accuracy achieved. MaNGA's relative calibration between the wavelengths of Hα and HÎČ has an rms of 1.7%, while that between [N ii] λ6583 and [O ii] λ3727 has an rms of 4.7%. Using extinction-corrected star formation rates and gas-phase metallicities as an illustration, this level of precision guarantees that flux calibration errors will be sub-dominant when estimating these quantities. The absolute calibration is better than 5% for more than 89% of MaNGA's wavelength range
The Fourteenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the extended Baryon Oscillation Spectroscopic Survey and from the second phase of the Apache Point Observatory Galactic Evolution Experiment
The fourth generation of the Sloan Digital Sky Survey (SDSS-IV) has been in
operation since July 2014. This paper describes the second data release from
this phase, and the fourteenth from SDSS overall (making this, Data Release
Fourteen or DR14). This release makes public data taken by SDSS-IV in its first
two years of operation (July 2014-2016). Like all previous SDSS releases, DR14
is cumulative, including the most recent reductions and calibrations of all
data taken by SDSS since the first phase began operations in 2000. New in DR14
is the first public release of data from the extended Baryon Oscillation
Spectroscopic Survey (eBOSS); the first data from the second phase of the
Apache Point Observatory (APO) Galactic Evolution Experiment (APOGEE-2),
including stellar parameter estimates from an innovative data driven machine
learning algorithm known as "The Cannon"; and almost twice as many data cubes
from the Mapping Nearby Galaxies at APO (MaNGA) survey as were in the previous
release (N = 2812 in total). This paper describes the location and format of
the publicly available data from SDSS-IV surveys. We provide references to the
important technical papers describing how these data have been taken (both
targeting and observation details) and processed for scientific use. The SDSS
website (www.sdss.org) has been updated for this release, and provides links to
data downloads, as well as tutorials and examples of data use. SDSS-IV is
planning to continue to collect astronomical data until 2020, and will be
followed by SDSS-V.Comment: SDSS-IV collaboration alphabetical author data release paper. DR14
happened on 31st July 2017. 19 pages, 5 figures. Accepted by ApJS on 28th Nov
2017 (this is the "post-print" and "post-proofs" version; minor corrections
only from v1, and most of errors found in proofs corrected
Deficiency of Vasodilator-Stimulated Phosphoprotein (VASP) Increases Blood-Brain-Barrier Damage and Edema Formation after Ischemic Stroke in Mice
Background: Stroke-induced brain edema formation is a frequent cause of secondary infarct growth and deterioration of neurological function. The molecular mechanisms underlying edema formation after stroke are largely unknown. Vasodilator-stimulated phosphoprotein (VASP) is an important regulator of actin dynamics and stabilizes endothelial barriers through interaction with cell-cell contacts and focal adhesion sites. Hypoxia has been shown to foster vascular leakage by downregulation of VASP in vitro but the significance of VASP for regulating vascular permeability in the hypoxic brain in vivo awaits clarification. Methodology/Principal Findings: Focal cerebral ischemia was induced in Vasp2/2 mice and wild-type (WT) littermates by transient middle cerebral artery occlusion (tMCAO). Evanâs Blue tracer was applied to visualize the extent of blood-brainbarrier (BBB) damage. Brain edema formation and infarct volumes were calculated from 2,3,5-triphenyltetrazolium chloride (TTC)-stained brain slices. Both mouse groups were carefully controlled for anatomical and physiological parameters relevant for edema formation and stroke outcome. BBB damage (p,0.05) and edema volumes (1.7 mm360.5 mm3 versus 0.8 mm360.4 mm3; p,0.0001) were significantly enhanced in Vasp2/2 mice compared to controls on day 1 after tMCAO. This was accompanied by a significant increase in infarct size (56.1 mm3617.3 mm3 versus 39.3 mm3610.7 mm3, respectively; p,0.01) and a non significant trend (p.0.05) towards worse neurological outcomes. Conclusion: Our study identifies VASP as critical regulator of BBB maintenance during acute ischemic stroke. Therapeutic modulation of VASP or VASP-dependent signalling pathways could become a novel strategy to combat excessive edema formation in ischemic brain damage
- âŠ