572 research outputs found
Tunneling and Metastability of continuous time Markov chains
We propose a new definition of metastability of Markov processes on countable
state spaces. We obtain sufficient conditions for a sequence of processes to be
metastable. In the reversible case these conditions are expressed in terms of
the capacity and of the stationary measure of the metastable states
Fast building – increasing the geometrical freedom of textile reinforced concrete systems
Apresentação efetuada na 9th International Conference Mechanics and Materials in Design - Theory, Experiments and Applications in Engineering (M2D2021), no Funchal, Portugal, 2022[Excerpt] Introduction
Textile technology is highly innovative, and several techniques are already being used to act as building parts for fast
building, interior design, architectural details and offshore structures. However, such potential still fails when complex
geometrical structures or multifunctionality are required.Fundação para a Ciência e a Tecnologia - grant SFRH/BD/144201/2019European Regional Development Fund (FEDER), Operational Program for Competitiveness Factors
(COMPETE) POCI-01-0247-312 FEDER-03973
Non-Perturbative Effects in Matrix Models and D-branes
The large order growth of string perturbation theory in conformal
field theory coupled to world sheet gravity implies the presence of
non-perturbative effects, whose leading behavior can be
calculated in the matrix model approach. Recently it was proposed that the same
effects should be reproduced by studying certain localized D-branes in
Liouville Field Theory, which were constructed by A. and Al. Zamolodchikov. We
discuss this correspondence in a number of different cases: unitary minimal
models coupled to Liouville, where we compare the continuum analysis to the
matrix model results of Eynard and Zinn-Justin, and compact c=1 CFT coupled to
Liouville in the presence of a condensate of winding modes, where we derive the
matrix model prediction and compare it to Liouville theory. In both cases we
find agreement between the two approaches. The c=1 analysis also leads to
predictions about properties of D-branes localized in the vicinity of the tip
of the cigar in SL(2)/U(1) CFT with c=26.Comment: 27 pages, lanlmac; minor change
Topology Control in Cooperative Ad Hoc Wireless Networks
AbstractCooperative communication (CC) is a technique that exploits spatial diversity allowing multiple nodes to cooperatively relay signals to the receiver so that it can combine the received signals to obtain the original message. CC can be combined with topology control to increase connectivity at the cost of a small increase in energy consumption. This work focuses on exploring CC to improve the connectivity with a sink node in ad hoc wireless networks. More precisely, this work proposes a new technique, named CoopSink, that combines CC and topology control techniques to increase connectivity to a sink node while ensuring energy-efficient routes. Simulation results show that connectivity and routing to the sink cost can be improved up to 6.8 and 2.3 times, respectively, when compared with other similar strategies
Report of the 2006 ICCAT workshop for bluefin tuna direct ageing
This report provides the presentations, discussions and conclusions from the ICCAT bluefin
tuna workshop for direct ageing held in Santander, Spain, in April 2006. The report
summarizes the ageing criteria used in the past and the agreements on future age determination
based on otoliths, vertebrae and spines. Advantages and disadvantages of each calcified
structure for ageing and border interpretation were discussed. It was considered that bluefin
tuna age interpretation becomes very difficult from age ten onwards using the whole vertebra
and the spine sections methods, but this last technique continues to be useful for older ages.
Otolith sections can be used for the whole age range. Participants agreed that none of these
three structures could be excluded from routine ageing because otoliths are not easily
available. Age estimations within the same structure and between different structures of the
same specimen were compared for several readers. Better precision was found between spine
readers compared to vertebra and otolith readers. Good age agreement was also achieved
between readers of spines and vertebrae from the same bluefin for ages less than 12 years.
Preliminary results from radiocarbon assays on otoliths were presented at the workshop and
gave promising outcomes for bluefin tuna age validation. Also, these suggested that bluefin
tuna can live longer than had previously been established and that a review is needed of the
currently used asymptotic size and growth rate for both stocks. Another important contribution
of the workshop was a manual for age interpretation.Le présent rapport recueille les présentations, discussions et conclusions de l’Atelier de
l’ICCAT chargé de la détermination directe de l’âge du thon rouge, tenu à Santander
(Espagne) au mois d’avril 2006. Le rapport résume les critères employés par le passé pour
interpréter l’âge et les accords pour la détermination future de l’âge à partir des otolithes,
vertèbres et épines. L’Atelier a discuté des avantages et des inconvénients de chaque structure
calcifiée pour déterminer l’âge et l’interprétation du type de bord. On a abordé la difficulté de
l’interprétation de l’âge des thons de plus de 10 ans au moyen de la vertèbre entière et des
sections des épines, bien que cette dernière méthode continue d’être utile pour les âges
avancés. Les sections d’otolithes peuvent être employées pour toute la gamme d’âges. Les
participants ont convenu qu’aucune de ces trois structures ne doit être exclue pour
l’interprétation de l’âge parce qu’il n’est pas toujours possible d’obtenir des otolithes. On a
comparé les lectures de l’âge à l’intérieur de la même structure et entre différentes structures
du même exemplaire pour divers lecteurs. On a obtenu une plus grande précision parmi les
lecteurs d’épines que parmi les lecteurs de vertèbres et d’otolithes. On a également obtenu un
bon accord entre les lecteurs d’épines et de vertèbres originaires du même exemplaire pour les
âges inférieurs à 12 ans. Les résultats préliminaires des essais de radiocarbone dans les
otolithes ont été présentés à l’Atelier, offrant de bonnes perspectives pour son utilisation dans la validation de l’âge. Ces résultats indiquent aussi que le thon rouge a une plus grande
longévité que ce qui avait été auparavant établi et qu’il est nécessaire de réviser la longueur
asymptotique et le taux de croissance actuellement utilisés. L’élaboration d’un manuel aux fins
de l’interprétation de l’âge a constitué une autre contribution importante de l’Atelier.Este informe recoge las presentaciones, discusiones y conclusiones del congreso de ICCAT
para la determinación directa de la edad de atún rojo, celebrado en Santander, España, en
abril de 2006. El informe resume los criterios empleados en el pasado para interpretar la edad
y los acuerdos para la determinación futura de la edad a partir de otolitos, vértebras y espinas.
Se discutieron las ventajas y los inconvenientes de cada estructura calcificada para determinar
la edad y la interpretación del tipo borde. Se planteó la dificultad en la interpretación de la
edad de atunes mayores de 10 años utilizando la vértebra entera y las secciones de espinas, no
obstante este último método continúa siendo útil para edades mayores. Las secciones de
otolitos pueden ser empleadas para todo el rango de edades. Los participantes acordaron que
ninguna de estas tres estructuras deben excluirse para la interpretación de la edad porque no
siempre es posible obtener los otolitos. Se compararon las lecturas de edad dentro de la misma
estructura y entre diferentes estructuras del mismo ejemplar para varios lectores. Se obtuvo
una mayor precisión entre lectores de espinas comparada con las obtenidas por los lectores de
vértebras y otolitos. También se obtuvo un buen acuerdo entre lectores de espinas y vértebras
procedentes del mismo ejemplar para edades menores de 12 años. Los resultados preliminares
de las pruebas de radiocarbono en otolitos fueron presentados en el congreso, proporcionando
buenas expectativas para su uso en la validación de la edad. Estos resultados también indican
que el atún rojo es más longevo de lo que se consideraba y que es necesaria una revisión de la
longitud asintótica y de la tasa de crecimiento empleadas actualmente. Otra importante
contribución del congreso fue la elaboración de un manual para la interpretación de la edad
Demagnetization via Nucleation of the Nonequilibrium Metastable Phase in a Model of Disorder
We study both analytically and numerically metastability and nucleation in a
two-dimensional nonequilibrium Ising ferromagnet. Canonical equilibrium is
dynamically impeded by a weak random perturbation which models homogeneous
disorder of undetermined source. We present a simple theoretical description,
in perfect agreement with Monte Carlo simulations, assuming that the decay of
the nonequilibrium metastable state is due, as in equilibrium, to the
competition between the surface and the bulk. This suggests one to accept a
nonequilibrium "free-energy" at a mesoscopic/cluster level, and it ensues a
nonequilibrium "surface tension" with some peculiar low-T behavior. We
illustrate the occurrence of intriguing nonequilibrium phenomena, including:
(i) Noise-enhanced stabilization of nonequilibrium metastable states; (ii)
reentrance of the limit of metastability under strong nonequilibrium
conditions; and (iii) resonant propagation of domain walls. The cooperative
behavior of our system may also be understood in terms of a Langevin equation
with additive and multiplicative noises. We also studied metastability in the
case of open boundaries as it may correspond to a magnetic nanoparticle. We
then observe burst-like relaxation at low T, triggered by the additional
surface randomness, with scale-free avalanches which closely resemble the type
of relaxation reported for many complex systems. We show that this results from
the superposition of many demagnetization events, each with a well- defined
scale which is determined by the curvature of the domain wall at which it
originates. This is an example of (apparent) scale invariance in a
nonequilibrium setting which is not to be associated with any familiar kind of
criticality.Comment: 26 pages, 22 figure
Occurrence and Quantification of Antimicrobial Resistance Genes in the Gastrointestinal Microbiome of Two Wild Seabird Species With Contrasting Behaviors
Indexación ScopusAntimicrobial resistance genes (ARGs) are environmental pollutants and anthropization indicators. We evaluated human interference in the marine ecosystem through the ocurrence and quantification (real-time PCRs) of 21 plasmid-mediated ARGs in enema samples of 25 wild seabirds, upon admission into rehabilitation: kelp gull (Larus dominicanus, n = 14) and Magellanic penguin (Spheniscus magellanicus, n = 11). Overall, higher resistance values were observed in kelp gulls (non-migratory coastal synanthropic) in comparison with Magellanic penguins (migratory pelagic non-synanthropic). There were significant differences between species (respectively, kelp gull and Magellanic penguin): ARGs occurrence (blaTEM [p = 0.032]; tetM [p = 0.015]; tetA [p = 0.003]; and sulII [p = 0.007]), mean number of ARGs per sample (p = 0.031), ARGs mean load percentage (aadA [p = 0.045], tetA [p = 0.031], tetM [p = 0.016], blaTEM [p = 0.032], sulII [p = 0.008]), percentage of genes conferring resistance to an antimicrobial class (betalactams [p = 0.036] and sulfonamides [p = 0.033]), mean number of genes conferring resistance to one or more antimicrobial classes (p = 0.024]), percentage of multiresistant microbiomes (p = 0.032), and clustering (p = 0.006). These differences are likely due to these species' contrasting biology and ecology - key factors in the epidemiology of ARGs in seabirds. Additionally, this is the first report of mecA in seabirds in the Americas. Further studies are necessary to clarify the occurrence and diversity of ARGs in seabirds, and their role as potential sources of infection and dispersal within the One Health chain of ARGs. © Copyright © 2021 Ewbank, Esperón, Sacristán, Sacristán, Neves, Costa-Silva, Antonelli, Rocha Lorenço, Kolesnikovas and Catão-Dias.https://www.frontiersin.org/articles/10.3389/fvets.2021.651781/ful
Measurements of high-energy neutron-induced fission of (nat)Pb and (209)Bi
This is an Open Access article distributed under the terms of the Creative Commons Attribution-Noncommercial License 3.0, which permits unrestricted use, distribution, and reproduction in any noncommercial medium, provided the original work is properly citedThe CERN Neutron Time-Of-Flight (n_TOF) facility is well suited to measure low cross sections as those of neutron-induced fission in subactinides. The cross section ratios of (nat)Pb and (209)Bi relative to (235)U and (238)U were measured using PPAC detectors and a fragment coincidence method that allows us to identify the fission events. The present experiment provides first results for neutron-induced fission up to 1 GeV. Good agreement is found with previous experimental data below 200 MeV. The comparison with proton-induced fission indicates that the limiting regime where neutron-induced and proton-induced fission reach equal cross sections is close to 1 GeV
Resonance capture cross section of 207Pb
The radiative neutron capture cross section of 207Pb has been measured at the
CERN neutron time of flight installation n_TOF using the pulse height weighting
technique in the resolved energy region. The measurement has been performed
with an optimized setup of two C6D6 scintillation detectors, which allowed us
to reduce scattered neutron backgrounds down to a negligible level. Resonance
parameters and radiative kernels have been determined for 16 resonances by
means of an R-matrix analysis in the neutron energy range from 3 keV to 320
keV. Good agreement with previous measurements was found at low neutron
energies, whereas substantial discrepancies appear beyond 45 keV. With the
present results, we obtain an s-process contribution of 77(8)% to the solar
abundance of 207Pb. This corresponds to an r-process component of 23(8)%, which
is important for deriving the U/Th ages of metal poor halo stars.Comment: 7 pages, 3 figures, to be published in Phys. Rev.
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