12,108 research outputs found
Avaliação do impacto das degradações no ruído pneu-pavimento
O ruído pneu-pavimento é a principal fonte de ruído nos veículos a velocidades superiores a 40 km/h, sendo de forma indireta um grande contribuinte para o ruído ambiental. Como as degradações existentes na superfície dos pavimentos provocam alterações nas suas características, torna-se importante o estudo da influência destas no ruído pneu-pavimento. Assim, neste estudo, recorrendo ao método da proximidade imediata (CPX) e a uma técnica de Data Mining, designada de Máquinas de Vetores de Suporte, para a modelação do ruído, avaliou-se a importância de degradações tais como o fendilhamento, a pele de corocodilo e a desagregação na geração do ruído pneu-pavimento. Confirmou-se assim que as patologias têm uma contribuição relevante para o ruído pneu-pavimento, o que justifica ter em conta o estado de degradação do pavimento quando se pretende estimar os níveis de ruído pneu-pavimento.Este artigo foi elaborado com o apoio da FCT – Fundação para a Ciência e Tecnologia e contém
informação proveniente do projeto PEst-OE/ECI/UI4047/2014, financiado no âmbito do Programa
Operacional Temático Fatores de Competitividade (COMPETE) e comparticipado pelo Fundo
Comunitário Europeu FEDER. Também foi parcialmente financiado pelos fundos FEDER através do
Programa Operacional Temático Fatores de Competitividade - COMPETE e por fundos nacionais
através da FCT - Fundação para a Ciência e Tecnologia no âmbito do projeto POCI-01-0145-FEDER-
007633.info:eu-repo/semantics/publishedVersio
Gravitational fields as generalized string models
We show that Einstein's main equations for stationary axisymmetric fields in
vacuum are equivalent to the motion equations for bosonic strings moving on a
special nonflat background. This new representation is based on the analysis of
generalized harmonic maps in which the metric of the target space explicitly
depends on the parametrization of the base space. It is shown that this
representation is valid for any gravitational field which possesses two
commuting Killing vector fields. We introduce the concept of dimensional
extension which allows us to consider this type of gravitational fields as
strings embedded in D-dimensional nonflat backgrounds, even in the limiting
case where the Killing vector fields are hypersurface orthogonal.Comment: latex, 25 page
Spanning avalanches in the three-dimensional Gaussian Random Field Ising Model with metastable dynamics: field dependence and geometrical properties
Spanning avalanches in the 3D Gaussian Random Field Ising Model (3D-GRFIM)
with metastable dynamics at T=0 have been studied. Statistical analysis of the
field values for which avalanches occur has enabled a Finite-Size Scaling (FSS)
study of the avalanche density to be performed. Furthermore, direct measurement
of the geometrical properties of the avalanches has confirmed an earlier
hypothesis that several kinds of spanning avalanches with two different fractal
dimensions coexist at the critical point. We finally compare the phase diagram
of the 3D-GRFIM with metastable dynamics with the same model in equilibrium at
T=0.Comment: 16 pages, 17 figure
NUMERICAL SIMULATION OF THE IMPACT OF WATER-AIR FRONTS ON RADIONUCLIDE PLUMES IN HETEROGENEOUS MEDIA
The goal of this paper is to investigate the interaction of water-air fronts with radionuclide plumes in unsaturated heterogeneous porous media. This problem is modeled by a system of equations that describes both water-air flow and radionuclide transport. The water-air flow problem is solved numerically by a mixed finite element combined with a non-oscillatory central difference scheme. For the radionuclide transport equation we use the Modified Method of Characteristics (MMOC).We present results of numerical simulations for heterogeneous permeability fields taking into account sorption effects
Exactly Solvable Interacting Spin-Ice Vertex Model
A special family of solvable five-vertex model is introduced on a square
lattice. In addition to the usual nearest neighbor interactions, the vertices
defining the model also interact alongone of the diagonals of the lattice. Such
family of models includes in a special limit the standard six-vertex model. The
exact solution of these models gives the first application of the matrix
product ansatz introduced recently and applied successfully in the solution of
quantum chains. The phase diagram and the free energy of the models are
calculated in the thermodynamic limit. The models exhibit massless phases and
our analyticaland numerical analysis indicate that such phases are governed by
a conformal field theory with central charge and continuosly varying
critical exponents.Comment: 14 pages, 11 figure
Universal integrals for superintegrable systems on N-dimensional spaces of constant curvature
An infinite family of classical superintegrable Hamiltonians defined on the
N-dimensional spherical, Euclidean and hyperbolic spaces are shown to have a
common set of (2N-3) functionally independent constants of the motion. Among
them, two different subsets of N integrals in involution (including the
Hamiltonian) can always be explicitly identified. As particular cases, we
recover in a straightforward way most of the superintegrability properties of
the Smorodinsky-Winternitz and generalized Kepler-Coulomb systems on spaces of
constant curvature and we introduce as well new classes of (quasi-maximally)
superintegrable potentials on these spaces. Results here presented are a
consequence of the sl(2) Poisson coalgebra symmetry of all the Hamiltonians,
together with an appropriate use of the phase spaces associated to Poincare and
Beltrami coordinates.Comment: 12 page
Soliton pinning by long-range order in aperiodic systems
We investigate propagation of a kink soliton along inhomogeneous chains with
two different constituents, arranged either periodically, aperiodically, or
randomly. For the discrete sine-Gordon equation and the Fibonacci and
Thue-Morse chains taken as examples, we have found that the phenomenology of
aperiodic systems is very peculiar: On the one hand, they exhibit soliton
pinning as in the random chain, although the depinning forces are clearly
smaller. In addition, solitons are seen to propagate differently in the
aperiodic chains than on periodic chains with large unit cells, given by
approximations to the full aperiodic sequence. We show that most of these
phenomena can be understood by means of simple collective coordinate arguments,
with the exception of long range order effects. In the conclusion we comment on
the interesting implications that our work could bring about in the field of
solitons in molecular (e.g., DNA) chains.Comment: 4 pages, REVTeX 3.0 + epsf, 3 figures in accompanying PostScript file
(Submitted to Phys Rev E Rapid Comm
Maximal superintegrability on N-dimensional curved spaces
A unified algebraic construction of the classical Smorodinsky-Winternitz
systems on the ND sphere, Euclidean and hyperbolic spaces through the Lie
groups SO(N+1), ISO(N), and SO(N,1) is presented. Firstly, general expressions
for the Hamiltonian and its integrals of motion are given in a linear ambient
space , and secondly they are expressed in terms of two geodesic
coordinate systems on the ND spaces themselves, with an explicit dependence on
the curvature as a parameter. On the sphere, the potential is interpreted as a
superposition of N+1 oscillators. Furthermore each Lie algebra generator
provides an integral of motion and a set of 2N-1 functionally independent ones
are explicitly given. In this way the maximal superintegrability of the ND
Euclidean Smorodinsky-Winternitz system is shown for any value of the
curvature.Comment: 8 pages, LaTe
Conformal compactification and cycle-preserving symmetries of spacetimes
The cycle-preserving symmetries for the nine two-dimensional real spaces of
constant curvature are collectively obtained within a Cayley-Klein framework.
This approach affords a unified and global study of the conformal structure of
the three classical Riemannian spaces as well as of the six relativistic and
non-relativistic spacetimes (Minkowskian, de Sitter, anti-de Sitter, both
Newton-Hooke and Galilean), and gives rise to general expressions holding
simultaneously for all of them. Their metric structure and cycles (lines with
constant geodesic curvature that include geodesics and circles) are explicitly
characterized. The corresponding cyclic (Mobius-like) Lie groups together with
the differential realizations of their algebras are then deduced; this
derivation is new and much simpler than the usual ones and applies to any
homogeneous space in the Cayley-Klein family, whether flat or curved and with
any signature. Laplace and wave-type differential equations with conformal
algebra symmetry are constructed. Furthermore, the conformal groups are
realized as matrix groups acting as globally defined linear transformations in
a four-dimensional "conformal ambient space", which in turn leads to an
explicit description of the "conformal completion" or compactification of the
nine spaces.Comment: 43 pages, LaTe
- …