195 research outputs found
SL(2,R)-geometric phase space and (2+2)-dimensions
We propose an alternative geometric mathematical structure for arbitrary
phase space. The main guide in our approach is the hidden SL(2,R)-symmetry
which acts on the phase space changing coordinates by momenta and vice versa.
We show that the SL(2,R)-symmetry is implicit in any symplectic structure. We
also prove that in any sensible physical theory based on the SL(2,R)-symmetry
the signature of the flat target "spacetime" must be associated with either
one-time and one-space or at least two-time and two-space coordinates. We
discuss the consequences as well as possible applications of our approach on
different physical scenarios.Comment: 17 pages, no figure
Oriented Matroids -- Combinatorial Structures Underlying Loop Quantum Gravity
We analyze combinatorial structures which play a central role in determining
spectral properties of the volume operator in loop quantum gravity (LQG). These
structures encode geometrical information of the embedding of arbitrary valence
vertices of a graph in 3-dimensional Riemannian space, and can be represented
by sign strings containing relative orientations of embedded edges. We
demonstrate that these signature factors are a special representation of the
general mathematical concept of an oriented matroid. Moreover, we show that
oriented matroids can also be used to describe the topology (connectedness) of
directed graphs. Hence the mathematical methods developed for oriented matroids
can be applied to the difficult combinatorics of embedded graphs underlying the
construction of LQG. As a first application we revisit the analysis of [4-5],
and find that enumeration of all possible sign configurations used there is
equivalent to enumerating all realizable oriented matroids of rank 3, and thus
can be greatly simplified. We find that for 7-valent vertices having no
coplanar triples of edge tangents, the smallest non-zero eigenvalue of the
volume spectrum does not grow as one increases the maximum spin \jmax at the
vertex, for any orientation of the edge tangents. This indicates that, in
contrast to the area operator, considering large \jmax does not necessarily
imply large volume eigenvalues. In addition we give an outlook to possible
starting points for rewriting the combinatorics of LQG in terms of oriented
matroids.Comment: 43 pages, 26 figures, LaTeX. Version published in CQG. Typos
corrected, presentation slightly extende
Tidal Interaction of M32 and NGC 205 with M31: Surface Photometry and Numerical Simulations
We investigate the interaction history of the M31 sub-group of galaxies by
comparing surface photometry of its two nearest satellites, M32 and NGC 205,
with N-body simulations of satellite destruction. The recent discovery of a
giant stream in M31's outer halo, apparently pointed towards M32 and NGC 205,
makes such an investigation particularly relevant. The observational component
of this study is based on 1.7 x 5.0 degree B- and I- band CCD mosaic images
centered on M31 and covering both satellites. The simulation component of this
project is based on the analysis of single-component, spherical model
satellites that are tidally disrupted through interactions with their parent
galaxy. Generic features of the simulations include an excess in the surface
brightness profile at large radii, a depletion zone at intermediate radii, and
isophotal elongation and twists that are coincident with breaks in the
brightness profile. The satellites M32 and NGC 205 display most of these
features consistently across the B and I bands, strongly suggestive of tidal
interaction and probable stripping by M31. We discuss what these observed
features can tell us about the satellites' orbital parameters and histories.
Specifically, M32 is found to be on a highly eccentric orbit and away from
pericenter. Investigating M32's unusual combination of high surface brightness
and low luminosity (the hallmark of compact ellipticals), we conclude on
empirical grounds that M32 is not likely to be the residual core of a
tidally-stripped normal elliptical galaxy as has been suggested, but rather
that its precursor was intrinsically compact.Comment: 43 pages, including 16 figures, and 2 tables; accepted for
publication in AJ; minor changes made to the tex
An Imaging Survey of Early-Type Barred Galaxies
This paper presents the results of a high-resolution imaging survey, using
both ground-based and Hubble Space Telescope images, of a complete sample of
nearby barred S0--Sa galaxies in the field, with a particular emphasis on
identifying and measuring central structures within the bars: secondary bars,
inner disks, nuclear rings and spirals, and off-plane dust. A discussion of the
frequency and statistical properties of the various types of inner structures
has already been published. Here, we present the data for the individual
galaxies and measurements of their bars and inner structures. We set out the
methods we use to find and measure these structures, and how we discriminate
between them. In particular, we discuss some of the deficiencies of ellipse
fitting of the isophotes, which by itself cannot always distinguish between
bars, rings, spirals, and dust, and which can produce erroneous measurements of
bar sizes and orientations.Comment: LaTeX, 66 pages (including 42 figures, 36 in color). To appear in The
Astrophysical Journal Supplement. Full-resolution and text-only versions
available at http://www.iac.es/galeria/erwin/research
The TeV Sun Rises: Discovery of Gamma rays from the Quiescent Sun with HAWC
We report the first detection of a TeV gamma-ray flux from the solar disk
(6.3), based on 6.1 years of data from the High Altitude Water
Cherenkov (HAWC) observatory. The 0.5--2.6 TeV spectrum is well fit by a power
law, dN/dE = , with TeV cm s and . The flux
shows a strong indication of anticorrelation with solar activity. These results
extend the bright, hard GeV emission from the disk observed with Fermi-LAT,
seemingly due to hadronic Galactic cosmic rays showering on nuclei in the solar
atmosphere. However, current theoretical models are unable to explain the
details of how solar magnetic fields shape these interactions. HAWC's TeV
detection thus deepens the mysteries of the solar-disk emission.Comment: 15 pages, 8 figures including supplementary material. Accepted for
publication in Physical Review Letter
International longitudinal registry of patients with atrial fibrillation and treated with rivaroxaban: RIVaroxaban Evaluation in Real life setting (RIVER)
Background
Real-world data on non-vitamin K oral anticoagulants (NOACs) are essential in determining whether evidence from randomised controlled clinical trials translate into meaningful clinical benefits for patients in everyday practice. RIVER (RIVaroxaban Evaluation in Real life setting) is an ongoing international, prospective registry of patients with newly diagnosed non-valvular atrial fibrillation (NVAF) and at least one investigator-determined risk factor for stroke who received rivaroxaban as an initial treatment for the prevention of thromboembolic stroke. The aim of this paper is to describe the design of the RIVER registry and baseline characteristics of patients with newly diagnosed NVAF who received rivaroxaban as an initial treatment.
Methods and results
Between January 2014 and June 2017, RIVER investigators recruited 5072 patients at 309 centres in 17 countries. The aim was to enroll consecutive patients at sites where rivaroxaban was already routinely prescribed for stroke prevention. Each patient is being followed up prospectively for a minimum of 2-years. The registry will capture data on the rate and nature of all thromboembolic events (stroke / systemic embolism), bleeding complications, all-cause mortality and other major cardiovascular events as they occur. Data quality is assured through a combination of remote electronic monitoring and onsite monitoring (including source data verification in 10% of cases). Patients were mostly enrolled by cardiologists (n = 3776, 74.6%), by internal medicine specialists 14.2% (n = 718) and by primary care/general practice physicians 8.2% (n = 417). The mean (SD) age of the population was 69.5 (11.0) years, 44.3% were women. Mean (SD) CHADS2 score was 1.9 (1.2) and CHA2DS2-VASc scores was 3.2 (1.6). Almost all patients (98.5%) were prescribed with once daily dose of rivaroxaban, most commonly 20 mg (76.5%) and 15 mg (20.0%) as their initial treatment; 17.9% of patients received concomitant antiplatelet therapy. Most patients enrolled in RIVER met the recommended threshold for AC therapy (86.6% for 2012 ESC Guidelines, and 79.8% of patients according to 2016 ESC Guidelines).
Conclusions
The RIVER prospective registry will expand our knowledge of how rivaroxaban is prescribed in everyday practice and whether evidence from clinical trials can be translated to the broader cross-section of patients in the real world
- …