5,544 research outputs found
Revealing hidden symmetries and gauge invariance of the massive Carroll-Field-Jackiw model
In this paper we have analyzed the improved version of the Gauge Unfixing
(GU) formalism of the massive Carroll-Field-Jackiw model, which breaks both the
Lorentz and gauge invariances, to disclose hidden symmetries to obtain gauge
invariance, the key stone of the Standard Model. In this process, as usual, we
have converted this second-class system into a first-class one and we have
obtained two gauge invariant models. We have verified that the Poisson brackets
involving the gauge invariant variables, obtained through the GU formalism,
coincide with the Dirac brackets between the original second-class variables of
the phase space. Finally, we have obtained two gauge invariant Lagrangians
where one of them represents the Stueckelberg form.Comment: revised version. To appear in Europhysics Letter
Unipolar resistive switching in metal oxide/organic semiconductor non-volatile memories as a critical phenomenon
Diodes incorporating a bilayer of an organic semiconductor and a wide bandgap metal oxide can show unipolar, non-volatile memory behavior after electroforming. The prolonged bias voltage stress induces defects in the metal oxide with an areal density exceeding 10(17) m(-2). We explain the electrical bistability by the coexistence of two thermodynamically stable phases at the interface between an organic semiconductor and metal oxide. One phase contains mainly ionized defects and has a low work function, while the other phase has mainly neutral defects and a high work function. In the diodes, domains of the phase with a low work function constitute current filaments. The phase composition and critical temperature are derived from a 2D Ising model as a function of chemical potential. The model predicts filamentary conduction exhibiting a negative differential resistance and nonvolatile memory behavior. The model is expected to be generally applicable to any bilayer system that shows unipolar resistive switching. (C) 2015 Author(s).Dutch Polymer Institute (DPI), BISTABLE [704]; Fundacao para Ciencia e Tecnologia (FCT) through the research Instituto de Telecommunicacoes (IT-Lx); project Memristor based Adaptive Neuronal Networks (MemBrAiNN) [PTDC/CTM-NAN/122868/2010]; European Community Seventh Framework Programme FP7', ONE-P [212311]; Dutch Ministry of Education, Culture and Science (Gravity Program) [024.001.035]info:eu-repo/semantics/publishedVersio
Mean-field analysis of the majority-vote model broken-ergodicity steady state
We study analytically a variant of the one-dimensional majority-vote model in
which the individual retains its opinion in case there is a tie among the
neighbors' opinions. The individuals are fixed in the sites of a ring of size
and can interact with their nearest neighbors only. The interesting feature
of this model is that it exhibits an infinity of spatially heterogeneous
absorbing configurations for whose statistical properties we
probe analytically using a mean-field framework based on the decomposition of
the -site joint probability distribution into the -contiguous-site joint
distributions, the so-called -site approximation. To describe the
broken-ergodicity steady state of the model we solve analytically the
mean-field dynamic equations for arbitrary time in the cases n=3 and 4. The
asymptotic limit reveals the mapping between the statistical
properties of the random initial configurations and those of the final
absorbing configurations. For the pair approximation () we derive that
mapping using a trick that avoids solving the full dynamics. Most remarkably,
we find that the predictions of the 4-site approximation reduce to those of the
3-site in the case of expectations involving three contiguous sites. In
addition, those expectations fit the Monte Carlo data perfectly and so we
conjecture that they are in fact the exact expectations for the one-dimensional
majority-vote model
Decomposition of stochastic flows with automorphism of subbundles component
We show that given a -structure on a differentiable manifold , if
the group of automorphisms of is big enough, then there exists the
quotient of an stochastic flows by , in the sense that where , the remainder has
derivative which is vertical but transversal to the fibre of . This
geometrical context generalizes previous results where is a Riemannian
manifold and is decomposed with an isometric component, see Liao
\cite{Liao1} and Ruffino \cite{Ruffino}, which in our context corresponds to
the particular case of an SO(n)-structure on .Comment: To appear in Stochastics and Dynamics, 201
Modelling of friction stir welding and its influence on the structural behaviour of aluminium stiffened panels
This work deals with the modelling and numerical simulation of aluminium stiffened panels, assembled by means of friction stir welding (FSW) operations, and subjected to compressive loads that can catastrophically induce buckling (global or local) unstable modes and, subsequently, overall failure. Due to their geometrical complexity, added to localized thermo-mechanical effects that typically come from joining by welding, approximation methods such as the Finite Element Method are typically used in such nonlinear analyses, having proved to be useful to designers focused on the prediction of the behaviour (before and post buckling) of such structures. Being grounded on previous contributions from the authors, the present paper aims to bring a number of innovative aspects to the current state of the art by considering in the developed models the simultaneous influence of residual stress fields, material softening effects and geometrical imperfections. Doing so, it is possible to infer about the singular and combined influence of these effects in the overall structural performance of stiffened panels, building up a useful and comprehensive methodology for design stages
Numerical simulation of the buckling behaviour of stiffened panels: Benchmarks for assessment of distinct modelling strategies
This work deals with the effective modelling and simulation of the behavior of stiffened panels, when subjected to compressive (buckling) loads. Within the Finite Element Method, two numerical strategies are compared, namely the Riks method and the displacement incremental control method, including damping effects. The capabilities and limitations of both approaches are explored for two distinct benchmarks: a panel with a blade stiffener, and a panel with a T shaped stiffener. In both cases, material (plasticity) and geometrical (large displacements) nonlinearities are considered, together with a modelling strategy based on shell elements. Following previous works of the authors, each panel accounts for initial geometric imperfections coming from friction stir welding joining operations. The paper shows a number of considerations that must be undertaken when choosing between one of the two modelling strategies. Both benchmarks involve a number of challenges from the point of view of modelling unstable structural behaviors, and therefore the proposed benchmarks can represent a valid set of case studies in the understanding of the capabilities of current numerical simulation codes
Hidrogenionic potential (pH) of the attractant, trap density and control threshold for Ceratitis capitata (Diptera: tephritidae) on Hamlin oranges in São Paulo central region, Brazil
This study evaluated the effect of initial pH values of 4.5, 6.5 and 8.5 of the attractant
(protein bait) Milhocina® and borax (sodium borate) in the feld, on the capture of fruit flies in McPhail
traps, using 1, 2, 4 and 8 traps per hectare, in order to estimate control thresholds in a Hamlin orange grove
in the central region of the state of São Paulo. The most abundant fruit fly species was Ceratitis capitata,
comprising almost 99% of the fruit flies captured, of which 80% were females. The largest captures of C.
capitata were found in traps baited with Milhocina® and borax at pH 8.5. Captures per trap for the four
densities were similar, indicating that the population can be estimated with one trap per hectare in areas
with high populations. It was found positive relationships between captures of C. capitata and the number
of Hamlin oranges damaged, 2 and 3 weeks after capture. It was obtained equations that correlate captures
and damage levels which can be used to estimate control thresholds. The average loss caused in Hamlin
orange fruits by C. capitata was 2.5 tons per hectare or 7.5% of production.Esta pesquisa teve como objetivos: avaliar o efeito do pH inicial, 4.5; 6.5 e 8.5, do atrativo
proteico Milhocina® e bórax (tetraborato de sódio) na captura de moscas-das-frutas em armadilhas McPhail;
estudar densidades de armadilhas, 1; 2; 4 e 8 por hectare, para estimar níveis de controle em laranja cv.
Hamlin, na região central de São Paulo. A espécie predominante, com 99% das moscas-das-frutas capturadas,
foi Ceratitis capitata, sendo 80% de fêmeas. As maiores capturas de C. capitata ocorreram nas armadilhas
com Milhocina® e bórax em pH 8.5. As capturas, nas 4 densidades, foram semelhantes, indicando que a
população pode ser estimada com uma armadilha por hectare em áreas de altas populações. Houve relações
positivas entre capturas de C. capitata e o número de frutos danificados, 2 e 3 semanas após a captura. Assim,
foram obtidas equações que relacionam a captura e o dano, possibilitando estimar níveis de controle desse
inseto. As perdas médias causadas por C. capitata em laranja cv. Hamlin chegaram a 2,5 toneladas de frutos
por hectare ou 7,5% da produção.info:eu-repo/semantics/publishedVersio
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