4,692 research outputs found
Universality class for bootstrap percolation with on the cubic lattice
We study the bootstrap percolation model on a cubic lattice, using
Monte Carlo simulation and finite-size scaling techniques. In bootstrap
percolation, sites on a lattice are considered occupied (present) or vacant
(absent) with probability or , respectively. Occupied sites with less
than occupied first-neighbours are then rendered unoccupied; this culling
process is repeated until a stable configuration is reached. We evaluate the
percolation critical probability, , and both scaling powers, and
, and, contrarily to previous calculations, our results indicate that the
model belongs to the same universality class as usual percolation (i.e.,
). The critical spanning probability, , is also numerically
studied, for systems with linear sizes ranging from L=32 up to L=480: the value
we found, , is the same as for usual percolation with
free boundary conditions.Comment: 11 pages; 4 figures; to appear in Int. J. Mod. Phys.
Group-theoretic restrictions on generation of CP-violation in multi-Higgs-doublet models
It has been known since decades that imposing a symmetry group G on the
scalar sector of multi-Higgs-doublet models has consequences for CP-violation.
In all examples of two- and three-Higgs-doublet models equipped with
symmetries, one observes the following intriguing property: if G prevents
explicit CP-violation (CPV), at least in the neutral Higgs sector, then it also
prevents spontaneous CPV, and if G allows explicit CPV, then it allows for
spontaneous CPV. One is led to conjecture that this is a general phenomenon. In
this paper, we prove this conjecture for any rephasing symmetry group G and any
number of doublets.Comment: 16 page
Spontaneous melanotic lesions in axillary seabream, Pagellus acarne (Risso)
In this paper, we describe spontaneous melanotic lesions in the skin of axillary seabream, Pagellus acarne (Risso) from a defined area of the Portuguese Coast, located in Cabo da Roca and Foz do Arelho. The lesions corresponded to black pigmentation spots on the skin of the head, fins, lips and conjunctiva and, additionally, black nodules on the skin of the head and lips. In some specimens, the nodular formations in the head changed their anatomical conformation. Histologically, there were melanophores scattered along the basement membrane or forming aggregates in the dermis, infiltrating the subcutaneous tissue but not invading the adjacent muscle tissue. The aim of this study was to characterize the macroscopic and microscopic features of the pigmented lesions. These fish show sessile hyperpigmented lesions (spots) that correspond to proliferative lesions of melanophores in the dermis and nodular lesions that correspond to neoplastic lesions, melanophoromas. The melanophores in such lesions showed high concentration of melanin in the cytoplasm, moderate pleomorphism and compact distribution throughout all of the dermis
Mechanical characterization of timber in structural sizes: bending and compression tests
This paper presents the results obtained in a series of tests on Pinus Pinaster Ait. timber specimens, using the prEN408:2000, to estimate the local and global Young’s modulus and strength both in bending and compression parallel to the grain. The results obtained are compared with the values presented in the Portuguese Nationally Determined Parameters of Eurocode 5, for the quality classes assign by Portuguese Standard NP4305:1994 by visual grading
Discrete and continuous symmetries in multi-Higgs-doublet models
We consider the Higgs sector of multi-Higgs-doublet models in the presence of
simple symmetries relating the various fields. We construct basis invariant
observables which may in principle be used to detect these symmetries for any
number of doublets. A categorization of the symmetries into classes is
required, which we perform in detail for the case of two and three Higgs
doublets.Comment: 13 pages, RevTex, references adde
Behaviour of traditional Portuguese timber roof structures
The aim of this paper is to present the results of a structural analysis of common trusses traditionally used in roof construction in Portugal. The study includes the results of a preliminary survey intending to assess the geometry, materials and on site pathologies, as well as a twodimensional linear elastic static and dynamic analysis. The trusses behaviour under symmetric and non-symmetric loads, the king post/tie-beam connection, the stiffness of the joints and the incorrect positioning of the purlins, were some of the structural aspects that have been investigated
Experimental analysis of original and strengthened traditional timber connections
Tests on full-scale unstrengthened connections were performed under monotonic and cyclic loading. Attention has been principally focused on the birdsmouth joint, because of its common use in practice. Different strengthening solutions with metal elements have been evaluated
Modelling of timber joints in traditional structures
Original unstrengthened timber connections and the effects of different strengthening techniques
have been evaluated experimentally with tests on full-scale birdsmouth joints. Experimental results
show that structural response of traditional timber connections under cyclic loading cannot be
represented by common constraint models, like perfect hinges or rigid joints, but should be using
semi-rigid and friction based models. A research program has investigated the behaviour of old
timber joints and examined strengthening criteria. The main parameters affecting the mechanical
behaviour of the connection have been singled out. A synthetic model of cyclic behaviour has been
adapted on the basis of experimental results
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