37,557 research outputs found
VSR symmetries in the DKP algebra: the interplay between Dirac and Elko spinor fields
VSR symmetries are here naturally incorporated in the DKP algebra on the
spin-0 and the spin-1 DKP sectors. We show that the Elko (dark) spinor fields
structure plays an essential role on accomplishing this aim, unravelling hidden
symmetries on the bosonic DKP fields under the action of discrete symmetries.Comment: 17 page
Flag-Dipole Spinor Fields in ESK Gravities
We consider the Riemann-Cartan geometry as a basis for the
Einstein-Sciama-Kibble theory coupled to spinor fields: we focus on and
conformal gravities, regarding the flag-dipole spinor fields, type-(4) spinor
fields under the Lounesto classification. We study such theories in specific
cases given for instance by cosmological scenarios: we find that in such
background the Dirac equation admits solutions that are not Dirac spinor
fields, but in fact the aforementioned flag-dipoles ones. These solutions are
important from a theoretical perspective, as they evince that spinor fields are
not necessarily determined by their dynamics, but also a discussion on their
structural (algebraic) properties must be carried off. Furthermore, the
phenomenological point of view is shown to be also relevant, since for
isotropic Universes they circumvent the question whether spinor fields do
undergo the Cosmological Principle.Comment: 18 pages, improved versio
Information entropy of classical versus explosive percolation
We study the Shannon entropy of the cluster size distribution in classical as
well as explosive percolation, in order to estimate the uncertainty in the
sizes of randomly chosen clusters. At the critical point the cluster size
distribution is a power-law, i.e. there are clusters of all sizes, so one
expects the information entropy to attain a maximum. As expected, our results
show that the entropy attains a maximum at this point for classical
percolation. Surprisingly, for explosive percolation the maximum entropy does
not match the critical point. Moreover, we show that it is possible determine
the critical point without using the conventional order parameter, just
analysing the entropy's derivatives.Comment: 6 pages, 6 figure
Dynamical Lorentz and CPT symmetry breaking in a 4D four-fermion model
In a 4D chiral Thirring model we analyse the possibility that radiative
corrections may produce spontaneous breaking of Lorentz and CPT symmetry. By
studying the effective potential, we verified that the chiral current
may assume a nonzero vacuum expectation
value which triggers the Lorentz and CPT violations. Furthermore, by making
fluctuations on the minimum of the potential we dynamically induce a bumblebee
like model containing a Chern-Simons term.Comment: Small modifications in the text and new references added, 12 pages, 4
figures, revtex4. To appear in Phys. Rev.
Seismic vulnerability assessment of the old city centre of Seixal, Portugal
The seismic vulnerability assessment of old traditional masonry building stocks, in a seismic risk mitigation perspective, is truly essential not only for buildings with recognized historical and patrimonial value, but also, in relation to regular buildings. In this sense, this paper approaches the issue of the seismic vulnerability assessment of masonry buildings through the application of a simplified methodology to building stock of the old city centre of Seixal, Portugal. This methodology is based on a vulnerability index, suitable in the evaluation of damage and in the creation of large scale loss scenarios (economical and human). Over 500 buildings were evaluated in accordance with the referred methodology and the results obtained were then integrated into a Geographical Information System tool. The integration of this kind of vulnerability and loss results into a GIS tool allows that city councils or regional authorities make their decisions based on a global view of the site under analysis, which led to more accurate and faster decisions either in terms of risk mitigation strategies or rehabilitation plans. This tool can also assumes great importance in the construction of safety and rescue plans
Vulnerability assessment of urban building stock: a hierarchic approach
In the last decades the evaluation of the seismic risk are of rising concern, considered essential in the activity and
definition of strategy planning and urban management. The evaluation of the seismic vulnerability of the existent building stock
in the perspective of the seismic risk mitigation should not be placed only in relation to the isolated buildings of relevant
historical and cultural importance, but also, in relation to the agglomerate of buildings in urban centres. The chronological
construction process frequently results in characteristic heterogeneity of masonry and wall connection quality. In addition,
buildings do not constitute independent units given that they share the mid-walls with adjacent buildings and the façade walls are
aligned. This way, as post-seismic observations proved, buildings do not have an independent structural behaviour, but they
interact amongst themselves, mainly for horizontal actions and so the structural performance should be studied at the level of the
aggregate and not only for each isolated building. In most cases, for masonry structures there is no need for sophisticated
dynamic analyses for seismic resistance verification or vulnerability assessment. This is even more relevant when an assessment
at the level of a city centre is pursued. In this work, the results of evaluation of the vulnerability will be presented in accordance
to three proposed methodologies based on a vulnerability index that consequently allows the evaluation of damage and creation
of loss scenarios (economical and human) not only at the level of the building and its façade walls but also at the level of the
aggregates. It will be discussed and evaluated the application of the referred methodologies and its integration in an SIG
platform
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