2,424 research outputs found
Fast Neural Network Predictions from Constrained Aerodynamics Datasets
Incorporating computational fluid dynamics in the design process of jets,
spacecraft, or gas turbine engines is often challenged by the required
computational resources and simulation time, which depend on the chosen
physics-based computational models and grid resolutions. An ongoing problem in
the field is how to simulate these systems faster but with sufficient accuracy.
While many approaches involve simplified models of the underlying physics,
others are model-free and make predictions based only on existing simulation
data. We present a novel model-free approach in which we reformulate the
simulation problem to effectively increase the size of constrained pre-computed
datasets and introduce a novel neural network architecture (called a cluster
network) with an inductive bias well-suited to highly nonlinear computational
fluid dynamics solutions. Compared to the state-of-the-art in model-based
approximations, we show that our approach is nearly as accurate, an order of
magnitude faster, and easier to apply. Furthermore, we show that our method
outperforms other model-free approaches
Free field realization of the exceptional current superalgebra \hat{D(2,1;\a)}_k
The free-field representations of the D(2,1;\a) current superalgebra and
the corresponding energy-momentum tensor are constructed. The related screening
currents of the first kind are also presented.Comment: Latex file, 10 page
Influence of an external magnetic field on the decoherence of a central spin coupled to an antiferromagnetic environment
Using the spin wave approximation, we study the decoherence dynamics of a
central spin coupled to an antiferromagnetic environment under the application
of an external global magnetic field. The external magnetic field affects the
decoherence process through its effect on the antiferromagnetic environment. It
is shown explicitly that the decoherence factor which displays a Gaussian decay
with time depends on the strength of the external magnetic field and the
crystal anisotropy field in the antiferromagnetic environment. When the values
of the external magnetic field is increased to the critical field point at
which the spin-flop transition (a first-order quantum phase transition) happens
in the antiferromagnetic environment, the decoherence of the central spin
reaches its highest point. This result is consistent with several recent
quantum phase transition witness studies. The influences of the environmental
temperature on the decoherence behavior of the central spin are also
investigated.Comment: 29 preprint pages, 4 figures, to appear in New Journal of Physic
Dynamics of localized structures in vector waves
Dynamical properties of topological defects in a twodimensional complex
vector field are considered. These objects naturally arise in the study of
polarized transverse light waves. Dynamics is modeled by a Vector Complex
Ginzburg-Landau Equation with parameter values appropriate for linearly
polarized laser emission. Creation and annihilation processes, and
selforganization of defects in lattice structures, are described. We find
"glassy" configurations dominated by vectorial defects and a melting process
associated to topological-charge unbinding.Comment: 4 pages, 5 figures included in the text. To appear in Phys. Rev.
Lett. (2000). Related material at http://www.imedea.uib.es/Nonlinear and
http://www.imedea.uib.es/Photonics . In this new version, Fig. 3 has been
replaced by a better on
Targeting Current and Future Threats: Recent Methodological Trends in Environmental Antimicrobial Resistance Research and Their Relationships to Risk Assessment
Antimicrobial resistance (AMR) is a growing public health threat. Improved surveillance of AMR\u27s genetic indicators in environmental reservoirs should lead to a more comprehensive understanding of the problem at a global scale, as with SARS-CoV-2 monitoring in sewage. However, the “best” monitoring approach is unclear. Some scientific works have emphasized monitoring for the abundance of already-known antimicrobial resistance genes (ARGs); others have emphasized monitoring for the potential of new ARGs to arise. The goal of this study was to examine which methods were employed by highly-cited papers studying AMR in environmental engineering and agricultural systems, thus providing insight into current and future methodological trends for monitoring ARGs. We searched recent (2018–2020) literature documenting AMR in five environmental matrices: wastewater, surface water, drinking water, stormwater, and livestock manure. We selected the most highly-cited papers across these matrices (89 papers from 17809 initial results) and categorized them as using targeted methods (e.g., qPCR), non-targeted methods (e.g., shotgun metagenomics), or both. More than 80% of papers employed targeted methods. Only 33% employed non-targeted methods, and the use of targeted versus non-targeted methods varied by environmental matrix. We posit that improving AMR surveillance in environmental reservoirs requires assessing risk, and that different monitoring approaches imply different objectives for risk assessment. Targeted methods are appropriate for quantifying known threats, particularly in environmental matrices where direct human exposure is likely (e.g., drinking water). However, long-term studies employing non-targeted methods are needed to provide an understanding of how frequently new threats (i.e., novel ARGs) arise
Differences in Respiratory Symptoms and Lung Structure Between Hispanic and Non-Hispanic White Smokers: A Comparative Study
Background: Prior studies have demonstrated that U.S. Hispanic
smokers have a lower risk of decline in lung function and
chronic obstructive pulmonary disease (COPD) compared with
non-Hispanic whites (NHW). This suggests there might be
racial-ethnic differences in susceptibility in cigarette
smoke-induced respiratory symptoms, lung parenchymal
destruction, and airway and vascular disease, as well as in
extra-pulmonary manifestations of COPD. Therefore, we aimed to
explore respiratory symptoms, lung function, and pulmonary and
extra-pulmonary structural changes in Hispanic and NHW smokers.
Methods: We compared respiratory symptoms, lung function, and
computed tomography (CT) measures of emphysema-like tissue,
airway disease, the branching generation number (BGN) to reach a
2-mm-lumen-diameter airway, and vascular pruning as well as
muscle and fat mass between 39 Hispanic and 39 sex-, age- and
smoking exposure-matched NHW smokers. Results: Hispanic smokers
had higher odds of dyspnea than NHW after adjustment for COPD
and asthma statuses (odds ratio[OR] = 2.96; 95% confidence
interval [CI] 1.09-8.04), but no significant differences were
found in lung function and CT measurements. Conclusions: While
lung function and CT measures of the lung structure were
similar, dyspnea is reported more frequently by Hispanic than
matched-NHW smokers. It seems to be an impossible puzzle but
it's easy to solve a Rubik' Cube using a few algorithms
A Kato type Theorem for the inviscid limit of the Navier-Stokes equations with a moving rigid body
The issue of the inviscid limit for the incompressible Navier-Stokes
equations when a no-slip condition is prescribed on the boundary is a famous
open problem. A result by Tosio Kato says that convergence to the Euler
equations holds true in the energy space if and only if the energy dissipation
rate of the viscous flow in a boundary layer of width proportional to the
viscosity vanishes. Of course, if one considers the motion of a solid body in
an incompressible fluid, with a no-slip condition at the interface, the issue
of the inviscid limit is as least as difficult. However it is not clear if the
additional difficulties linked to the body's dynamic make this issue more
difficult or not. In this paper we consider the motion of a rigid body in an
incompressible fluid occupying the complementary set in the space and we prove
that a Kato type condition implies the convergence of the fluid velocity and of
the body velocity as well, what seems to indicate that an answer in the case of
a fixed boundary could also bring an answer to the case where there is a moving
body in the fluid
Integration of a Spanish-to-LSE machine translation system into an e-learning platform
The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-642-21657-2_61This paper presents the first results of the integration of a Spanish-to-LSE Machine Translation (MT) system into an e-learning platform. Most e-learning platforms provide speech-based contents, which makes them inaccessible to the Deaf. To solve this issue, we have developed a MT system that translates Spanish speech-based contents into LSE.
To test our MT system, we have integrated it into an e-learning tool. The e-learning tool sends the audio to our platform. The platform sends back the subtitles and a video stream with the signed translation to the e-learning tool.
Preliminary results, evaluating the sign language synthesis module, show an isolated sign recognition accuracy of 97%. The sentence recognition accuracy was of 93%.Authors would like to acknowledge the FPU-UAM grant program
for its financial support. Authors are grateful to the FCNSE linguistic department for sharing their knowledge in LSE and performing the evaluations. Many thanks go to María Chulvi and Benjamín Nogal for providing help during the imple-mentation of this system. This work was partially supported by the Telefónica Móviles España S.A. project number 10-047158-TE-Ed-01-1
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