332 research outputs found
An Efficient Implementation of Flux Formulae in Multidimensional Relativistic Hydrodynamical Codes
We derive and analyze a simplified formulation of the numerical viscosity
terms appearing in the expression of the numerical fluxes associated to several
High-Resolution Shock-Capturing schemes. After some algebraic pre-processing,
we give explicit expressions for the numerical viscosity terms of two of the
most widely used flux formulae, which implementation saves computational time
in multidimensional simulations of relativistic flows. Additionally, such
treatment explicitely cancells and factorizes a number of terms helping to
amortiguate the growing of round-off errors. We have checked the performance of
our formulation running a 3D relativistic hydrodynamical code to solve a
standard test-bed problem and found that the improvement in efficiency is of
high practical interest in numerical simulations of relativistic flows in
Astrophysics.Comment: 10 pages, accepted for publication in Computer Physics Communication
A virtual laboratory designed for teaching diffractive lenses
[EN] We present a virtual laboratory generated in Matlab GuiQc (Graphical User Interface) for its use in Optics courses as an informatic tool for teaching the focusing properties of a diffractive lens. This Gui allows the students to learn easily and rapidly about the influence on the focal volume of the lens construction parameters. As an example in this work we analyze fractal diffractive lenses because we found that fractal geometry is a highly motivating topic for students since it is related to a wide range of scientific and technological phenomena.[ES] En este trabajo presentamos un laboratorio virtual desarrollado en Matlab GuiQc (Interfaz Gráfica con el Usuario) para su uso en los cursos de Ă“ptica como herramienta informática para la enseñanza de las propiedades de focalizaciĂłn de las lentes difractivas. Esta interfaz GUI permite a los estudiantes aprender fácil y rápidamente la influencia de los parámetros constructivos de la lente en el volumen focal. A modo de ejemplo analizamos en este trabajo lentes difractivas fractales porque hemos encontrado que la geometrĂa fractal es un tema muy motivador para los estudiantes ya que está relacionado con un gran nĂşmero de fenĂłmenos cientĂficos y tecnolĂłgicos.GimĂ©nez, F.; Monsoriu, J.; Furlan, W.; Pons, A. (2010). A virtual laboratory designed for teaching diffractive lenses. Modelling in Science Education and Learning. 3:29-37. doi:10.4995/msel.2010.3108SWORD2937
On the equivalence of the Einstein-Hilbert and the Einstein-Palatini formulations of general relativity for an arbitrary connection
In the framework of the Einstein-Palatini formalism, even though the
projective transformation connecting the arbitrary connection with the Levi
Civita connection has been floating in the literature for a long time and
perhaps the result was implicitly known in the affine gravity community, yet as
far as we know Julia and Silva were the first to realise its gauge character.
We rederive this result by using the Rosenfeld-Dirac-Bergmann approach to
constrained Hamiltonian systems and do a comprehensive self contained analysis
establishing the equivalence of the Einstein-Palatini and the metric
formulations without having to impose the gauge choice that the connection is
symmetric. We also make contact with the the Einstein-Cartan theory when the
matter Lagrangian has fermions.Comment: 18 pages. Slight change in the title and wording of some sections to
emphasize the main results. References added. Matches published versio
Stability of the lattice formed in first-order phase transitions to matter containing strangeness in protoneutron stars
Well into the deleptonization phase of a core collapse supernova, a
first-order phase transition to matter with macroscopic strangeness content is
assumed to occur and lead to a structured lattice defined by negatively charged
strange droplets. The lattice is shown to crystallize for expected droplet
charges and separations at temperatures typically obtained during the
protoneutronstar evolution. The melting curve of the lattice for small
spherical droplets is presented. The one-component plasma model proves to be an
adequate description for the lattice in its solid phase with deformation modes
freezing out around the melting temperature. The mechanical stability against
shear stresses is such that velocities predicted for convective phenomena and
differential rotation during the Kelvin-Helmholtz cooling phase might prevent
the crystallization of the phase transition lattice. A solid lattice might be
fractured by transient convection, which could result in anisotropic neutrino
transport. The melting curve of the lattice is relevant for the mechanical
evolution of the protoneutronstar and therefore should be included in future
hydrodynamics simulations.Comment: accepted for publication in Physical Review
AnĂ lisi espacio-temporal de la lĂnia de costa i del foredune del sistema dunar de Sa Canova d’ArtĂ (Mallorca)
[cat] Els sistemes platja-duna, sĂłn una de les morfologies sedimentĂ ries mĂ©s abundants a les Illes Balears. Aquests es troben composats per diferents subsistemes, els quals presenten diferents nivells de dinamisme. Des d’aquest punt de vista, la foredune Ă©s el sector mĂ©s dinĂ mic de la part emergida del sistema i en la qual la vegetaciĂł tĂ© un paper clau per al desenvolupament de la resta del sistema. Tots i cada un dels sistemes existents a la comunitat autònoma i a la resta del mĂłn disposa d’una condicions/caracterĂstiques que el fan peculiar i diferent a la resta; a part de les pròpies condicions fĂsiques intrĂnseques al propi medi, a dia d’avui els sistemes han de fer front a tota una sèrie de pressions d’origen antròpic, destacant especialment l’activitat turĂstica en el cas Balear. El cas d’estudi, Ă©s Sa Canova, situada al terme municipal d’ArtĂ (NE de l’illa de Mallorca); aquest sistema tampoc n’és una excepciĂł, al llarg del perĂode d’estudi (1956-2012), ha sofert variacions, tant d’origen natural, com antròpic, les quals han tingut com a conseqüència el sistema dunar actualment existent.[eng] The beach-dune systems, are one of the most abundant sedimentary morphologies in the Balearic Islands. These are composed of different subsystems, which present different levels of dynamism. From this point of view, Foredune is the most dynamic sector of the emerging part of the system and in which vegetation plays a key role for the development of the rest of the system. Each and every one of the existing systems in the autonomous community and the rest of the world has conditions / characteristics that make it peculiar and different from the rest; Apart from the intrinsic physical conditions inherent in their own environment, today, systems have to deal with a whole series of pressures of anthropogenic origin, with special emphasis on tourism in the Balearic Islands. The case study is Sa Canova, located in the municipality of ArtĂ (NE of the island of Mallorca); This system is not an exception either, during the period of study (1956-2012), it has undergone variations, both of natural origin and anthropic, which have resulted in the current dune system
Are Post-Newtonian templates faithful and effectual in detecting gravitational signals from neutron star binaries?
We compute the overlap function between Post-Newtonian (PN) templates and
gravitational signals emitted by binary systems composed of one neutron star
and one point mass, obtained by a perturbative approach. The calculations are
performed for different stellar models and for different detectors, to estimate
how effectual and faithful the PN templates are, and to establish whether
effects related to the internal structure of neutron stars may possibly be
extracted by the matched filtering technique.Comment: 14 pages, 3 figures, accepted for publication in Phys. Rev.
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