7,050 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.
A Statistical Model to Explain the Mendel--Fisher Controversy
In 1866 Gregor Mendel published a seminal paper containing the foundations of
modern genetics. In 1936 Ronald Fisher published a statistical analysis of
Mendel's data concluding that "the data of most, if not all, of the experiments
have been falsified so as to agree closely with Mendel's expectations." The
accusation gave rise to a controversy which has reached the present time. There
are reasonable grounds to assume that a certain unconscious bias was
systematically introduced in Mendel's experimentation. Based on this
assumption, a probability model that fits Mendel's data and does not offend
Fisher's analysis is given. This reconciliation model may well be the end of
the Mendel--Fisher controversy.Comment: Published in at http://dx.doi.org/10.1214/10-STS342 the Statistical
Science (http://www.imstat.org/sts/) by the Institute of Mathematical
Statistics (http://www.imstat.org
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
Unitarity Triangles and the Search for New Physics
Assuming that the Kobayashi-Maskawa mechanism gives the dominant contribution
to CP violation at low energies, we propose a novel way of testing the flavour
sector of the Standard Model which has the potencial for discovering New
Physics. Using 3 x 3 unitarity of the V_{CKM} matrix and choosing a complete
set of rephasing invariant phases, we derive a set of exact relations in terms
of measurable quantities, namely moduli of V_{CKM} and arguments of rephasing
invariant quartets. These tests complement the usual analysis in the \rho, \eta
plane and, if there is New Physics, may reveal its source.Comment: 20 pages, 7 figures, uses tcilate
Flavour Physics and CP Violation in the Standard Model and Beyond
We present the invited lectures given at the Third IDPASC School which took
place in Santiago de Compostela in January 2013. The students attending the
school had very different backgrounds, some of them were doing their Ph.D. in
experimental particle physics, others in theory. As a result, and in order to
make the lectures useful for most of the students, we focused on basic topics
of broad interest, avoiding the more technical aspects of Flavour Physics and
CP Violation. We make a brief review of the Standard Model, paying special
attention to the generation of fermion masses and mixing, as well as to CP
violation. We describe some of the simplest extensions of the SM, emphasising
novel flavour aspects which arise in their framework.Comment: Invited talk at the Third IDPASC School 2013, January 21st - February
2nd 2013, Santiago de Compostela, Galiza, Spain; 36 pages, 8 figures, 2
tables; version with few misprints correcte
New Physics and Evidence for a Complex CKM
We carefully analyse the present experimental evidence for a complex CKM
matrix, even allowing for New Physics contributions to ,
, , , and the piece of and . We emphasize the crucial r\^
ole played by the angle in both providing irrefutable evidence for a
complex CKM matrix and placing constraints on the size of NP contributions. It
is shown that even if one allows for New Physics a real CKM matrix is excluded
at a 99.92% C.L., and the probability for the phase to be in the
interval is 99.7%.Comment: 24 pages, 15 figures. Revised version, analyses extended to more
general New Physics; C.L. of exclusion of a real CKM matrix include
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
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
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