12,117 research outputs found
Stability properties and asymptotics for N non-minimally coupled scalar fields cosmology
We consider here the dynamics of some homogeneous and isotropic cosmological
models with interacting classical scalar fields non-minimally coupled to
the spacetime curvature, as an attempt to generalize some recent results
obtained for one and two scalar fields. We show that a Lyapunov function can be
constructed under certain conditions for a large class of models, suggesting
that chaotic behavior is ruled out for them. Typical solutions tend generically
to the empty de Sitter (or Minkowski) fixed points, and the previous asymptotic
results obtained for the one field model remain valid. In particular, we
confirm that, for large times and a vanishing cosmological constant, even in
the presence of the extra scalar fields, the universe tends to an infinite
diluted matter dominated era.Comment: 10 page
k-deformed Poincare algebras and quantum Clifford-Hopf algebras
The Minkowski spacetime quantum Clifford algebra structure associated with
the conformal group and the Clifford-Hopf alternative k-deformed quantum
Poincare algebra is investigated in the Atiyah-Bott-Shapiro mod 8 theorem
context. The resulting algebra is equivalent to the deformed anti-de Sitter
algebra U_q(so(3,2)), when the associated Clifford-Hopf algebra is taken into
account, together with the associated quantum Clifford algebra and a (not
braided) deformation of the periodicity Atiyah-Bott-Shapiro theorem.Comment: 10 pages, RevTeX, one Section and references added, improved content
Superinflation, quintessence, and the avoidance of the initial singularity
We consider the dynamics of a spatially flat universe dominated by a
self-interacting nonminimally coupled scalar field. The structure of the phase
space and complete phase portraits for the conformal coupling case are given.
It is shown that the non-minimal coupling modifies drastically the dynamics of
the universe. New cosmological behaviors are identified, including
superinflation (), avoidance of big bang singularities through
classical birth of the universe from empty Minkowski space, and spontaneous
entry into and exit from inflation. The relevance of this model to the
description of quintessence is discussed.Comment: RevTex, 10 pages, 4 figures, To appear in the proceedings of the 5th
Peyresq meetin
Fitness profiles of elite Portuguese rugby union players
The aim of this study was to describe the fitness profiles of senior elite Portuguese rugby players. Forty-six
senior Portuguese rugby players, classified as backs (n=22; age 26.2±2.8) and forwards (n=24; age 26.7±2.9) were
assessed during physical testing sessions carried out for the Portuguese National rugby team. The body composition,
maximum strength and anaerobic capacity of players are hypothesized to be important physical characteristics as
successful performance in rugby is predicated on the ability to undertake skilled behaviours both quickly and whilst
withstanding large forces when in contact situations. No absolute differences were found between the backs and
forwards for the speed performance variables although positional differences were found across all speeds when assessed
relative to body mass since the forwards were significantly heavier. Coaches and the management team can use this
information for monitoring progressive improvements in the physiological capacities of rugby players. These physical
characteristics of elite rugby players provide normative profiles for specific positions and should form the basis of
developmental programmes for adolescents
Bloqueio Epidural Torácico em Cirurgia de Nuss: Caso de Sucesso
Os autores descrevem o caso c1ínico de um adolescente com o diagnóstico de pectus excavatum grave, submetido a cirurgia de Nuss sob controlo toracoscópico. Realizou-se anestesia combinada, com cateter epidural torácico que permitiu um periodo intra e pós-operatório estável, sem intercorrências e sem necessidade de suplementação analgésica
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