Repositório Colecção:
http://hdl.handle.net/10198/419
Sat, 12 Jul 2014 14:02:11 GMT2014-07-12T14:02:11ZAngular momentum transport by internal waves in the solar interior
http://hdl.handle.net/10198/8290
Título: Angular momentum transport by internal waves in the solar interior
Autor: Zahn, Jean-Paul; Talon, Suzanne; Matias, José
Resumo: The internal gravity waves of low frequency which
are emitted at the base of the solar convection zone are able
to extract angular momentum from the radiative interior. We
evaluate this transport with some simplifying assumptions: we
ignore the Coriolis force, approximate the spectrum of turbulent
convection by the Kolmogorov law, and couple this turbulence
to the internal waves through their pressure fluctuations, following
Press (1981) and Garc´ıa L´opez & Spruit (1991). The
local frequency of an internal wave varies with depth in a differentially
rotating star, and it can vanish at some location, thus
leading to enhanced damping (Goldreich & Nicholson 1989). It
is this dissipation mechanism only that we take into account in
the exchange of momentum between waves and stellar rotation.
The flux of angular momentum is then an implicit function of
depth, involving the local rotation rate and an integral representing
the cumulative effect of radiative dissipation. We find that
the efficiency of this transport process is rather high: it operates
on a timescale of 107 years, and is probably responsible for the
flat rotation profile which has been detected through helioseismology.Wed, 01 Jan 1997 00:00:00 GMThttp://hdl.handle.net/10198/82901997-01-01T00:00:00ZInterior point filter method for semi-infinite programming problems
http://hdl.handle.net/10198/7531
Título: Interior point filter method for semi-infinite programming problems
Autor: Pereira, Ana I.; Costa, M. Fernanda; Fernandes, Edite M.G.P.
Resumo: Semi-infinite programming (SIP) problems can be efficiently solved by reduction-type methods. Here, we present a new reduction method for SIP, where the multi-local optimization is carried out with a stretched simulated annealing algorithm, the reduced (finite) problem is approximately solved
by a Newton’s primal–dual interior point method that uses a novel twodimensional
filter line search strategy to guarantee the convergence to a KKT point that is a minimizer, and the global convergence of the overall reduction method is promoted through the implementation of a classical two-dimensional filter line search. Numerical experiments with a set of well-known problems are shown.Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10198/75312011-01-01T00:00:00ZAsymmetry of red blood cell motions in a microchannel with a diverging and converging bifurcation
http://hdl.handle.net/10198/7003
Título: Asymmetry of red blood cell motions in a microchannel with a diverging and converging bifurcation
Autor: Leble, Vladimir; Lima, R.; Dias, Ricardo P.; Fernandes, Carla S.; Ishikawa, Takuji; Imai, Yohsuke; Yamaguchi, Takami
Resumo: In microcirculation, red blood cells (RBCs) flowing through bifurcations may deform considerably due to combination of different phenomena that happen at the micro-scale level, such as: attraction effect, high shear and extensional stress, all of which may influence the rheological properties and flow behavior of blood. Thus, it is important to investigate in detail the behavior of blood flow occurring at both bifurcations and confluences. In the present paper, by using a micro-PTV system, we investigated the variations of velocity profiles of two working fluids flowing through diverging and converging bifurcations - human red blood cells suspended in dextran 40 with about 14% of haematocrit level (14Hct) and pure water seeded with fluorescent trace particles. All the measurements were performed in the center plane of rectangular microchannels using a constant flow rate of about 3.0×10-12 m3/s. Moreover, the experimental data was compared with numerical results obtained for Newtonian incompressible fluid. The behavior of RBCs was asymmetric at the divergent and convergent side of the geometry, whereas the velocities of tracer particles suspended in pure water were symmetric and well described by numerical simulation. The formation of a red cell-depleted zone immediately downstream of the apex of the converging bifurcation was observed and its effect on velocity profiles of RBCs flow has been investigated. Conversely, a cell-depleted region was not formed around the apex of the diverging bifurcation and as a result the adhesion of RBCs to the wall surface was enhanced in this region.Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10198/70032011-01-01T00:00:00ZOn the relative solvability of certain inverse monoids
http://hdl.handle.net/10198/6341
Título: On the relative solvability of certain inverse monoids
Autor: Cordeiro, Edite; Delgado, Manuel
Resumo: The notion of kernel of a finite monoid relative to a pseudovariety of groups can be used to define relative solvability of monoids in a similar way to the manner in which the notion of derived subgroup can be used to define solvable group. In this paper we study the solvability of certain inverse monoids relative to pseudovarieties of abelian groups.Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/10198/63412010-01-01T00:00:00Z