4,562 research outputs found
Extended Bargmann supergravity from a Lie algebra expansion
In this paper we show how the method of Lie algebra expansions may be used to
obtain, in a simple way, both the extended Bargmann Lie superalgebra and the
Chern-Simons action associated to it in three dimensions, starting from ,
superPoincar\'e and its corresponding Chern-Simons
supergravity.Comment: 17 page
Optimization of Nanoparticle-Based SERS Substrates through Large-Scale Realistic Simulations
Surface-enhanced Raman scattering (SERS) has
become a widely used spectroscopic technique for chemical
identification, providing unbeaten sensitivity down to the singlemolecule
level. The amplification of the optical near field
produced by collective electron excitations plasmons in
nanostructured metal surfaces gives rise to a dramatic increase
by many orders of magnitude in the Raman scattering intensities
from neighboring molecules. This effect strongly depends on
the detailed geometry and composition of the plasmonsupporting
metallic structures. However, the search for
optimized SERS substrates has largely relied on empirical
data, due in part to the complexity of the structures, whose
simulation becomes prohibitively demanding. In this work, we
use state-of-the-art electromagnetic computation techniques to
produce predictive simulations for a wide range of nanoparticle-based SERS substrates, including realistic configurations
consisting of random arrangements of hundreds of nanoparticles with various morphologies. This allows us to derive rules of
thumb for the influence of particle anisotropy and substrate coverage on the obtained SERS enhancement and optimum spectral
ranges of operation. Our results provide a solid background to understand and design optimized SERS substrates.Peer ReviewedPostprint (published version
An overdetermined eigenvalue problem and the Critical Catenoid conjecture
We consider the eigenvalue problem in
and along , being the
complement of a disjoint and finite union of smooth and bounded simply
connected regions in the two-sphere . Imposing that is locally constant along and that has infinitely
many maximum points, we are able to classify positive solutions as the
rotationally symmetric ones. As a consequence, we obtain a characterization of
the critical catenoid as the only embedded free boundary minimal annulus in the
unit ball whose support function has infinitely many critical points
Using AOP to Automatically Provide Distribution, Fault Tolerance, and Load Balancing to the CORBA-LC Component Model
Mejora y evaluación de un cuestionario de creencias de matemáticas en función de nacionalidad, edad y sexo
Este artÃculo describe la adaptación al contexto educativo español e inglés del cuestionario de creencias de matemáticas (Mathematics-Related Beliefs Questionnaire MRBQ), desarrollado en la Universidad de Lovaina (Op’t Eynde y De Corte, 2003). El instrumento original, evaluado con estudiantes flamencos, dio como resultado cuatro escalas de las que sólo dos resultaron fiables. En este trabajo mostramos cómo el cuestionario ha sido mejorado, obteniendo cuatro escalas y diez subescalas fiables, con estudiantes de secundaria. Los resultados muestran la eficacia del instrumento ya revisado para evaluar sistemas de creencias entre estudiantes de diferente nacionalidad, edad y sexo
A Detailed Identification of Classificatory Variables in Ship Accidents: A Spanish Case Study
[Abstract] The present paper shows an original study of more than 163 ship accidents in Spain showing which of the usually employed variables are related to each type of vessel accident due to the lack of information in this region. To this end, research was carried out based on the Spanish Commission for Investigation of Maritime Accidents and Incidents (CIAIM) reports. Detailed combinatory ANOVA analysis and Bayesian networks results showed a good agreement with studies of other regions but with some particularities per each type of accident analyzed. In particular, ship length was defined as the more relevant variable at the time to differentiate types of accidents. At the same time, both the year of build and the fact that the ship meets the minimum crew members required were excellent variables to model ship accidents. Despite this, the particularities of the Spanish Search and Rescue (SAR) region were defined at the time to identify accidents. In this sense, although variables like visibility and sea conditions were employed in different previous studies as variables related to accidents occurrences, they were the worst variables to define accidents for this region. Finally, different models to relate variables were obtained being the base of deterministic dynamic analysis. Furthermore, to improve the accuracy of the developed work some indications were obtained; revision of CIAIM accidents scales, identification of redundant variables, and the need for an agreement at the time to define the classification limits of each identification variable.This research was funded by the Sustainability Specialization Campus of the University of A Coruña grant number 6310G49279- 541A- 64900
Hierarchical improvement of foreground segmentation masks in background subtraction
A plethora of algorithms have been defined for foreground
segmentation, a fundamental stage for many computer
vision applications. In this work, we propose a post-processing
framework to improve foreground segmentation performance of
background subtraction algorithms. We define a hierarchical
framework for extending segmented foreground pixels to undetected
foreground object areas and for removing erroneously
segmented foreground. Firstly, we create a motion-aware hierarchical
image segmentation of each frame that prevents merging
foreground and background image regions. Then, we estimate
the quality of the foreground mask through the fitness of the
binary regions in the mask and the hierarchy of segmented
regions. Finally, the improved foreground mask is obtained as
an optimal labeling by jointly exploiting foreground quality and
spatial color relations in a pixel-wise fully-connected Conditional
Random Field. Experiments are conducted over four large and
heterogeneous datasets with varied challenges (CDNET2014,
LASIESTA, SABS and BMC) demonstrating the capability of the
proposed framework to improve background subtraction resultsThis work was partially supported by the Spanish Government
(HAVideo, TEC2014-53176-R
Low temperature dielectric relaxation in ordinary perovskite ferroelectrics: enlightenment from high-energy x-ray diffraction
Ordinary ferroelectrics exhibit a second order phase transition that is characterized by a sharp peak in the dielectric permittivity at a frequency-independent temperature. Furthermore, these materials show a low temperature dielectric relaxation that appears to be a common behavior of perovskite systems. Tetragonal lead zirconate titanate is used here as a model system in order to explore the origin of such an anomaly, since there is no consensus about the physical phenomenon involved in it. Crystallographic and domain structure studies are performed from temperature dependent synchrotron x-ray diffraction measurement. Results indicate that the dielectric relaxation cannot be associated with crystallographic or domain configuration changes. The relaxation process is then parameterized by using the Vogel–Fulcher–Tammann phenomenological equation. Results allow us to hypothesize that the observed phenomenon is due to changes in the dynamic behavior of the ferroelectric domains related to the fluctuation of the local polarization.Postprint (author's final draft
- …