2,554 research outputs found
Resolved Kinematics of Runaway and Field OB Stars in the Small Magellanic Cloud
We use GAIA DR2 proper motions of the RIOTS4 field OB stars in the Small
Magellanic Cloud (SMC) to study the kinematics of runaway stars. The data
reveal that the SMC Wing has a systemic peculiar motion relative to the SMC Bar
of (v_RA, v_Dec) = (62 +/-7, -18+/-5) km/s and relative radial velocity +4.5
+/- 5.0 km/s. This unambiguously demonstrates that these two regions are
kinematically distinct: the Wing is moving away from the Bar, and towards the
Large Magellanic Cloud with a 3-D velocity of 64 +/- 10 km/s. This is
consistent with models for a recent, direct collision between the Clouds. We
present transverse velocity distributions for our field OB stars, confirming
that unbound runaways comprise on the order of half our sample, possibly more.
Using eclipsing binaries and double-lined spectroscopic binaries as tracers of
dynamically ejected runaways, and high-mass X-ray binaries (HMXBs) as tracers
of runaways accelerated by supernova kicks, we find significant contributions
from both populations. The data suggest that HMXBs have lower velocity
dispersion relative to dynamically ejected binaries, consistent with the former
corresponding to less energetic supernova kicks that failed to unbind the
components. Evidence suggests that our fast runaways are dominated by
dynamical, rather than supernova, ejections.Comment: Accepted to ApJ Letters. 10 pages, 4 figure
Dynamical mechanism of atrial fibrillation: a topological approach
While spiral wave breakup has been implicated in the emergence of atrial
fibrillation, its role in maintaining this complex type of cardiac arrhythmia
is less clear. We used the Karma model of cardiac excitation to investigate the
dynamical mechanisms that sustain atrial fibrillation once it has been
established. The results of our numerical study show that spatiotemporally
chaotic dynamics in this regime can be described as a dynamical equilibrium
between topologically distinct types of transitions that increase or decrease
the number of wavelets, in general agreement with the multiple wavelets
hypothesis. Surprisingly, we found that the process of continuous excitation
waves breaking up into discontinuous pieces plays no role whatsoever in
maintaining spatiotemporal complexity. Instead this complexity is maintained as
a dynamical balance between wave coalescence -- a unique, previously
unidentified, topological process that increases the number of wavelets -- and
wave collapse -- a different topological process that decreases their number.Comment: 15 pages, 14 figure
A New Class of Majoron-Emitting Double-Beta Decays
Motivated by the excess events that have recently been found near the
endpoints of the double beta decay spectra of several elements, we re-examine
models in which double beta decay can proceed through the neutrinoless emission
of massless Nambu-Goldstone bosons (majorons). Noting that models proposed to
date for this process must fine-tune either a scalar mass or a VEV to be less
than 10 keV, we introduce a new kind of majoron which avoids this difficulty by
carrying lepton number . We analyze in detail the requirements that
models of both the conventional and our new type must satisfy if they are to
account for the observed excess events. We find: (1) the electron sum-energy
spectrum can be used to distinguish the two classes of models from one another;
(2) the decay rate for the new models depends on different nuclear matrix
elements than for ordinary majorons; and (3) all models require a (pseudo)
Dirac neutrino, having a mass of a several hundred MeV, which mixes with
.Comment: 43 pages, 10 figures (included), [figure captions are now included
Mathematical retroreflectors
Retroreflectors are optical devices that reverse the direction of incident
beams of light. Here we present a collection of billiard type retroreflectors
consisting of four objects; three of them are asymptotically perfect
retroreflectors, and the fourth one is a retroreflector which is very close to
perfect. Three objects of the collection have recently been discovered and
published or submitted for publication. The fourth object - notched angle - is
a new one; a proof of its retroreflectivity is given.Comment: 32 pages, 19 figure
Face-to-face: Social work and evil
The concept of evil continues to feature in public discourses and has been reinvigorated in some academic disciplines and caring professions. This article navigates social workers through the controversy surrounding evil so that they are better equipped to acknowledge, reframe or repudiate attributions of evil in respect of themselves, their service users or the societal contexts impinging upon both. A tour of the landscape of evil brings us face-to-face with moral, administrative, societal and metaphysical evils, although it terminates in an exhortation to cultivate a more metaphorical language. The implications for social work ethics, practice and education are also discussed
Influence of silicon doping on vacancies and optical properties of AlxGa1-xN thin films
The authors have used positron annihilation spectroscopy and photoluminescence measurements to study the influence of silicon doping on vacancy formation in AlGaN:Si structures. The results show a correlation between the Doppler broadening measurements and the intensity from 510nm photoluminescence transition. The reduction in the W parameter when the [Si]∕[Al+Ga] fraction in the gas phase is above 3×10exp−4 indicates that the positrons annihilate in an environment where less Ga 3d electrons are present, i.e., they are trapped in group-III vacancies. The observation of vacancies at these silicon concentrations coincides with the onset of the photoluminescence transition at 510 nm.Peer reviewe
Determinants of long-term economic growth redux: A Measurement Error Model Averaging (MEMA) approach
This paper estimates determinants of long-run growth rates of GDP per capita in a cross section of countries. We propose a novel Measurement Error Model Averaging (MEMA) approach that accounts for measurement error in international income data as well as model uncertainty. Estimating the model using eight vintages of the Penn World Tables (PWT) together with other proposed growth determinants, we identify 18 variables related to economic growth. In addition, the results are robust to allowing for outliers in the form of heteroscedastic model errors
2-year outcomes for transcatheter repair in patients with functional mitral regurgitation from the CLASP study
Background: Transcatheter mitral valve repair has emerged as a favourable option in patient care for treating functional mitral regurgitation (FMR) with a need for longer term data. We herein report two-year outcomes from the FMR group of the multicentre, prospective, single arm CLASP study with the PASCAL transcatheter valve repair system.
Methods: Patients with symptomatic, clinically significant FMR ≥3+ as evaluated by the core laboratory and deemed candidates for transcatheter repair by the local heart team were eligible for the study. Follow-up was conducted at 30 days, one year, and two years with echocardiographic outcomes evaluated by the core laboratory at all timepoints and major adverse events (MAEs) evaluated by an independent clinical events committee to one year (site-reported thereafter).
Results: Eighty-five FMR patients were treated with mean age 72 years, 55% male, 65% in NYHA Class III-IVa, 37% LVEF, and 100% MR grade ≥3+. Successful implantation was achieved in 96% of patients. MAEs included one cardiovascular mortality (1.2%) and one conversion tomitral valve replacement surgery (1.2%) at 30 days, and two reinterventions between 30 days and two years. Kaplan-Meier (KM) estimates for survival were 88% at one year and 72% at two years. Freedom from heart failure (HF) rehospitalization KM estimates were 81% at one year and 78% for two years. The reduction in annualized HF hospitalization rate was 81% at two years (p\u3c0.001). MR ≤1+ was achieved in 73% of patients at 30 days, 75% at one year, and 84% at two years; MR ≤2+ was achieved in 96% of patients at 30 days, 100% at one year, and 95% two years (all p\u3c0.001). Mean LVEDV of 199 mL at baseline decreased by 9 mL at 30 days (p=0.039), 29 mL at one year (p\u3c0.001), and 31 mL at two years (p\u3c0.001). NYHA class I/II was achieved in 87% of patients at 30 days, 86% at one year, and 88% at two years (all p\u3c0.001). Six-minute walk distance (6MWD) improved by 22 m at 30 days (p=0.004) and 40 m at one year (p=0.003). Kansas City Cardiomyopathy Questionnaire (KCCQ) score improved by 16 points at 30 days and one year (all p\u3c0.001).
Conclusions: In the CLASP study, the PASCAL transcatheter valve repair system demonstrated sustained favourable outcomes at two years in patients with FMR. Results showed a high survival rate of 72% and freedom from HF rehospitalization of 78% at two years. An 81% reduction in annualized HF hospitalization rate was observed. At two years, sustained MR reduction of MR ≤2+ was achieved in 95% andMR ≤1+ in 84% of patients, with evidence of left ventricular reverse remodelling. Improvements in functional status were significant and sustained at two years. The CLASP IIF randomized pivotal trial is ongoing
A Generic Tool for Tracing Executions Back to a DSML's Operational Semantics
International audienceThe increasing complexity of software development requires rigorously defined domain specific modeling languages (DSML). Model-driven engineering (\mde) allows users to define a DSML's syntax in terms of metamodels. The behaviour of a language can also be described, either operationally, or via transformations to other languages (e.g., by code generation). If the first approach requires to redefine analysis tools for each DSML (simulator, model-checker...), the second approach allows to reuse existing tools in the targeted language. However, the second approach (also called translational semantics) imply that the results (e.g., a program crash log, or a counterexample returned by a model checker) may not be straightforward to interpret by the users of a DSML. We propose in this paper a generic tool for formally tracing such analysis/execution results back to the original DSML's syntax and operational semantics, and we illustrate it on xSPEM, a timed process modeling language
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