184 research outputs found
Sub-percent Photometry: Faint DA White Dwarf Spectophotometric Standards for Astrophysical Observatories
We have established a network of 19 faint (16.5 mag 19 mag) northern
and equatorial DA white dwarfs as spectrophotometric standards for present and
future wide-field observatories. Our analysis infers SED models for the stars
that are tied to the three CALSPEC primary standards. Our SED models are
consistent with panchromatic Hubble Space Telescope () photometry to
better than 1%. The excellent agreement between observations and models
validates the use of non-local-thermodynamic-equilibrium (NLTE) DA white dwarf
atmospheres extinguished by interstellar dust as accurate spectrophotometric
references. Our standards are accessible from both hemispheres and suitable for
ground and space-based observatories covering the ultraviolet to the near
infrared. The high-precision of these faint sources make our network of
standards ideally suited for any experiment that has very stringent
requirements on flux calibration, such as studies of dark energy using the
Large Synoptic Survey Telescope (LSST) and the Wide-Field Infrared Survey
Telescope ().Comment: 46 pages, 23 figures, 8 tables, accepted for publication in ApJ
All Weather Calibration of Wide Field Optical and NIR Surveys
The science goals for ground-based large-area surveys, such as the Dark
Energy Survey, Pan-STARRS, and the Large Synoptic Survey Telescope, require
calibration of broadband photometry that is stable in time and uniform over the
sky to precisions of a per cent or better. This performance will need to be
achieved with data taken over the course of many years, and often in less than
ideal conditions. This paper describes a strategy to achieve precise internal
calibration of imaging survey data taken in less than photometric conditions,
and reports results of an observational study of the techniques needed to
implement this strategy. We find that images of celestial fields used in this
case study with stellar densities of order one per arcmin-squared and taken
through cloudless skies can be calibrated with relative precision of 0.5 per
cent (reproducibility). We report measurements of spatial structure functions
of cloud absorption observed over a range of atmospheric conditions, and find
it possible to achieve photometric measurements that are reproducible to 1 per
cent in images that were taken through cloud layers that transmit as little as
25 per cent of the incident optical flux (1.5 magnitudes of extinction). We
find, however, that photometric precision below 1 per cent is impeded by the
thinnest detectable cloud layers. We comment on implications of these results
for the observing strategies of future surveys.Comment: Accepted for publication in The Astronomical Journal (AJ
Structure of the first representative of Pfam family PF04016 (DUF364) reveals enolase and Rossmann-like folds that combine to form a unique active site with a possible role in heavy-metal chelation.
The crystal structure of Dhaf4260 from Desulfitobacterium hafniense DCB-2 was determined by single-wavelength anomalous diffraction (SAD) to a resolution of 2.01â
Ă
using the semi-automated high-throughput pipeline of the Joint Center for Structural Genomics (JCSG) as part of the NIGMS Protein Structure Initiative (PSI). This protein structure is the first representative of the PF04016 (DUF364) Pfam family and reveals a novel combination of two well known domains (an enolase N-terminal-like fold followed by a Rossmann-like domain). Structural and bioinformatic analyses reveal partial similarities to Rossmann-like methyltransferases, with residues from the enolase-like fold combining to form a unique active site that is likely to be involved in the condensation or hydrolysis of molecules implicated in the synthesis of flavins, pterins or other siderophores. The genome context of Dhaf4260 and homologs additionally supports a role in heavy-metal chelation
The structure of BVU2987 from Bacteroides vulgatus reveals a superfamily of bacterial periplasmic proteins with possible inhibitory function.
Proteins that contain the DUF2874 domain constitute a new Pfam family PF11396. Members of this family have predominantly been identified in microbes found in the human gut and oral cavity. The crystal structure of one member of this family, BVU2987 from Bacteroides vulgatus, has been determined, revealing a ÎČ-lactamase inhibitor protein-like structure with a tandem repeat of domains. Sequence analysis and structural comparisons reveal that BVU2987 and other DUF2874 proteins are related to ÎČ-lactamase inhibitor protein, PepSY and SmpA_OmlA proteins and hence are likely to function as inhibitory proteins
Structure of a putative NTP pyrophosphohydrolase: YP_001813558.1 from Exiguobacterium sibiricum 255-15.
The crystal structure of a putative NTPase, YP_001813558.1 from Exiguobacterium sibiricum 255-15 (PF09934, DUF2166) was determined to 1.78â
Ă
resolution. YP_001813558.1 and its homologs (dimeric dUTPases, MazG proteins and HisE-encoded phosphoribosyl ATP pyrophosphohydrolases) form a superfamily of all-α-helical NTP pyrophosphatases. In dimeric dUTPase-like proteins, a central four-helix bundle forms the active site. However, in YP_001813558.1, an unexpected intertwined swapping of two of the helices that compose the conserved helix bundle results in a `linked dimer' that has not previously been observed for this family. Interestingly, despite this novel mode of dimerization, the metal-binding site for divalent cations, such as magnesium, that are essential for NTPase activity is still conserved. Furthermore, the active-site residues that are involved in sugar binding of the NTPs are also conserved when compared with other α-helical NTPases, but those that recognize the nucleotide bases are not conserved, suggesting a different substrate specificity
Defecting or not defecting: how to "read" human behavior during cooperative games by EEG measurements
Understanding the neural mechanisms responsible for human social interactions
is difficult, since the brain activities of two or more individuals have to be
examined simultaneously and correlated with the observed social patterns. We
introduce the concept of hyper-brain network, a connectivity pattern
representing at once the information flow among the cortical regions of a
single brain as well as the relations among the areas of two distinct brains.
Graph analysis of hyper-brain networks constructed from the EEG scanning of 26
couples of individuals playing the Iterated Prisoner's Dilemma reveals the
possibility to predict non-cooperative interactions during the decision-making
phase. The hyper-brain networks of two-defector couples have significantly less
inter-brain links and overall higher modularity - i.e. the tendency to form two
separate subgraphs - than couples playing cooperative or tit-for-tat
strategies. The decision to defect can be "read" in advance by evaluating the
changes of connectivity pattern in the hyper-brain network
LSST Science Book, Version 2.0
A survey that can cover the sky in optical bands over wide fields to faint
magnitudes with a fast cadence will enable many of the exciting science
opportunities of the next decade. The Large Synoptic Survey Telescope (LSST)
will have an effective aperture of 6.7 meters and an imaging camera with field
of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over
20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with
fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a
total point-source depth of r~27.5. The LSST Science Book describes the basic
parameters of the LSST hardware, software, and observing plans. The book
discusses educational and outreach opportunities, then goes on to describe a
broad range of science that LSST will revolutionize: mapping the inner and
outer Solar System, stellar populations in the Milky Way and nearby galaxies,
the structure of the Milky Way disk and halo and other objects in the Local
Volume, transient and variable objects both at low and high redshift, and the
properties of normal and active galaxies at low and high redshift. It then
turns to far-field cosmological topics, exploring properties of supernovae to
z~1, strong and weak lensing, the large-scale distribution of galaxies and
baryon oscillations, and how these different probes may be combined to
constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at
http://www.lsst.org/lsst/sciboo
LSST: from Science Drivers to Reference Design and Anticipated Data Products
(Abridged) We describe here the most ambitious survey currently planned in
the optical, the Large Synoptic Survey Telescope (LSST). A vast array of
science will be enabled by a single wide-deep-fast sky survey, and LSST will
have unique survey capability in the faint time domain. The LSST design is
driven by four main science themes: probing dark energy and dark matter, taking
an inventory of the Solar System, exploring the transient optical sky, and
mapping the Milky Way. LSST will be a wide-field ground-based system sited at
Cerro Pach\'{o}n in northern Chile. The telescope will have an 8.4 m (6.5 m
effective) primary mirror, a 9.6 deg field of view, and a 3.2 Gigapixel
camera. The standard observing sequence will consist of pairs of 15-second
exposures in a given field, with two such visits in each pointing in a given
night. With these repeats, the LSST system is capable of imaging about 10,000
square degrees of sky in a single filter in three nights. The typical 5
point-source depth in a single visit in will be (AB). The
project is in the construction phase and will begin regular survey operations
by 2022. The survey area will be contained within 30,000 deg with
, and will be imaged multiple times in six bands, ,
covering the wavelength range 320--1050 nm. About 90\% of the observing time
will be devoted to a deep-wide-fast survey mode which will uniformly observe a
18,000 deg region about 800 times (summed over all six bands) during the
anticipated 10 years of operations, and yield a coadded map to . The
remaining 10\% of the observing time will be allocated to projects such as a
Very Deep and Fast time domain survey. The goal is to make LSST data products,
including a relational database of about 32 trillion observations of 40 billion
objects, available to the public and scientists around the world.Comment: 57 pages, 32 color figures, version with high-resolution figures
available from https://www.lsst.org/overvie
The structure of SSO2064, the first representative of Pfam family PF01796, reveals a novel two-domain zinc-ribbon OB-fold architecture with a potential acyl-CoA-binding role
The crystal structure of SSO2064, the first structural representative of Pfam family PF01796 (DUF35), reveals a two-domain architecture comprising an N-terminal zinc-ribbon domain and a C-terminal OB-fold domain. Analysis of the domain architecture, operon organization and bacterial orthologs combined with the structural features of SSO2064 suggests a role involving acyl-CoA binding for this family of proteins
Structure of an essential bacterial protein YeaZ (TM0874) from Thermotoga maritima at 2.5â Ă resolution
The crystal structure of an essential bacterial protein, YeaZ, from T. maritima identifies an interface that potentially mediates proteinâprotein interaction
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