23,010 research outputs found
Compact stars with a small electric charge: the limiting radius to mass relation and the maximum mass for incompressible matter
One of the stiffest equations of state for matter in a compact star is
constant energy density and this generates the interior Schwarzschild radius to
mass relation and the Misner maximum mass for relativistic compact stars. If
dark matter populates the interior of stars, and this matter is supersymmetric
or of some other type, some of it possessing a tiny electric charge, there is
the possibility that highly compact stars can trap a small but non-negligible
electric charge. In this case the radius to mass relation for such compact
stars should get modifications. We use an analytical scheme to investigate the
limiting radius to mass relation and the maximum mass of relativistic stars
made of an incompressible fluid with a small electric charge. The investigation
is carried out by using the hydrostatic equilibrium equation, i.e., the
Tolman-Oppenheimer-Volkoff (TOV) equation, together with the other equations of
structure, with the further hypothesis that the charge distribution is
proportional to the energy density. The approach relies on Volkoff and Misner's
method to solve the TOV equation. For zero charge one gets the interior
Schwarzschild limit, and supposing incompressible boson or fermion matter with
constituents with masses of the order of the neutron mass one gets that the
maximum mass is the Misner mass. For a small electric charge, our analytical
approximating scheme valid in first order in the star's electric charge, shows
that the maximum mass increases relatively to the uncharged case, whereas the
minimum possible radius decreases, an expected effect since the new field is
repulsive aiding the pressure to sustain the star against gravitational
collapse.Comment: 23 pages, no figure
Declining autonomy at work in the EU and its effect on civic behaviour
The aim of this paper is to show that social benefits may accrue from work environments that support autonomous forms of work. Based on social psychology, economics and philosophy
approaches, we argue that autonomy is a basic human need which, when satisfied, enhances
civic behavior. Using individual data from the EWCS, we find evidence of the positive effect of work autonomy on volunteer work and political/trade union activities. Overall, work autonomy has decreased over the last fifteen years for all skill levels in the EU, though there are
substantial differences between countries. Organizational practices that promote autonomy should be deliberately stimulated if civic participation is to be furthered.FC
Vanishing Viscosity Limits and Boundary Layers for Circularly Symmetric 2D Flows
We continue the work of Lopes Filho, Mazzucato and Nussenzveig Lopes [LMN],
on the vanishing viscosity limit of circularly symmetric viscous flow in a disk
with rotating boundary, shown there to converge to the inviscid limit in
-norm as long as the prescribed angular velocity of the
boundary has bounded total variation. Here we establish convergence in stronger
and -Sobolev spaces, allow for more singular angular velocities
, and address the issue of analyzing the behavior of the boundary
layer. This includes an analysis of concentration of vorticity in the vanishing
viscosity limit. We also consider such flows on an annulus, whose two boundary
components rotate independently.
[LMN] Lopes Filho, M. C., Mazzucato, A. L. and Nussenzveig Lopes, H. J.,
Vanishing viscosity limit for incompressible flow inside a rotating circle,
preprint 2006
Eigenfunctions of the Laplacian and associated Ruelle operator
Let be a co-compact Fuchsian group of isometries on the Poincar\'e
disk \DD and the corresponding hyperbolic Laplace operator. Any
smooth eigenfunction of , equivariant by with real
eigenvalue , where , admits an integral
representation by a distribution \dd_{f,s} (the Helgason distribution) which
is equivariant by and supported at infinity \partial\DD=\SS^1. The
geodesic flow on the compact surface \DD/\Gamma is conjugate to a suspension
over a natural extension of a piecewise analytic map T:\SS^1\to\SS^1, the
so-called Bowen-Series transformation. Let be the complex Ruelle
transfer operator associated to the jacobian . M. Pollicott showed
that \dd_{f,s} is an eigenfunction of the dual operator for the
eigenvalue 1. Here we show the existence of a (nonzero) piecewise real analytic
eigenfunction of for the eigenvalue 1, given by an
integral formula \psi_{f,s} (\xi)=\int \frac{J(\xi,\eta)}{|\xi-\eta|^{2s}}
\dd_{f,s} (d\eta), \noindent where is a -valued
piecewise constant function whose definition depends upon the geometry of the
Dirichlet fundamental domain representing the surface \DD/\Gamma
Nuno Portas and the Spanish influence on the definition of housing policies in Portugal in the period of democratic transition
Taking the housing crisis and the SAAL program as a central interest point of architects and
sociologists in the aftermath of the Portuguese revolution, this chapter tracks the influence of
Spanish architecture in Portugal and the relations of Portuguese and Spanish architects, signaling the
main role of Nuno Portas. It begins by introducing the background of the architecture exchange
between Portugal and Spain, since the 1960’s, through the diffusion and interchange activities of
Nuno Portas (section 2). It continues to discuss the role of architects on urban change during the
revolutionary process from the viewpoint Joan Antonio Solans experiences and writings (Section 3).
Then it takes on the social movements debate with Manuel Castells reflections and writings about
the new housing policies and experiences (Section 4). Finally, a short reflection on the interchange of
ideas and experiences between Portugal and Spain in presented in the conclusion (Section 5).info:eu-repo/semantics/submittedVersio
Chiral Zeromodes on Vortex-type Intersecting Heterotic Five-branes
We solve the gaugino Dirac equation on a smeared intersecting five-brane
solution in E_8\times E_8 heterotic string theory to search for localized
chiral zeromodes on the intersection. The background is chosen to depend on the
full two-dimensional overall transverse coordinates to the branes. Under some
appropriate boundary conditions, we compute the complete spectrum of zeromodes
to find that, among infinite towers of Fourier modes, there exist only three
localized normalizable zeromodes, one of which has opposite chirality to the
other two. This agrees with the result previously obtained in the domain-wall
type solution, supporting the claim that there exists one net chiral zeromode
localized on the heterotic five-brane system.Comment: 10 pages, 2 figure
Chelas Zone J revisited: Urban morphology and change in a recovering neighbourhood
Among new council housing areas from 1960s Lisbon is the Chelas Valley, by then overwhelmingly agrarian. Although an integral urbanization plan - the Plano de Urbanização de Chelas (PUC) – was prepared until 1964, the area was divided into six zones, urbanized in different periods, with great deviances from the original plan.
Upon construction, Chelas was challenged by social problems. One of the zones, Zone J, has been particularly associated with this negative image. The architectural designs by Tomás Taveira and Victor Consiglieri introduced changes to the urban plan by Francisco Silva Dias and José Lobo de Carvalho. After construction, several municipal initiatives tried to improve living conditions in Zone J, ranging from façade changes to demolitions. All along, it has been accepted that the urban form of Zone J was a determinant factor of its failure as a habitat.
Here, we revisit the original Zone J Plan. How was it implemented, and how has it changed since? What has been the input of the residents in the territory they inhabit? Can it contribute to make Lisbon a more sustainable city? This presentation aims to answer these questions while trying to identify parallels with other urban areas in a crisis that share morphological characteristics with Chelas Zone J.info:eu-repo/semantics/publishedVersio
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