Determinació abreujada del cost de les construccions rurals

Peer Reviewe

El fons còsmic de microones i l'origen de l'Univers

Datat 13.700 milions d'anys enrere, l'origen de l'Univers pot semblar difícil d'investigar després d'haver passat tant de temps. Però el treball de Mather i Smoot sobre el fons còsmic de radiació de microones -gràcies al qual han guanyat el premi Nobel de física del 2006- ha proporcionat noves evidències sobre el que va passar en èpoques tan remotes

The work process from the perspectives of situated activity and soeially distributed knowledge

[Resumen]: La diversidad de procesos y estrategias empresariales de producción que se vienen desarrollando en las últimas décadas tienen su origen y se suelen definir a partir de los cambios en la organización y funcionamiento interno y de los factores técnicos. En este sentido hablamos de cambios y transformaciones de los procesos de producción. El interés de este artículo se centra en introducir en el análisis de los procesos de trabajo los factores contextuales, sociales y organizativos de la empresa y sus consecuencias mediante una redefinición del concepto de proceso de trabajo, que permita analizarlo en su situación real. Para analizar dichos cambios y sus consecuencias, teniendo en cuenta los supuestos macro y microsociológicos que intervienen, creemos que es indicado entender el Proceso de Trabajo (PT) desde las aproximaciones propias de la Actividad Situada (AS) y del Conocimiento Socialmente Distribuido (CSD).[Abstract]: The diversity of processes and strategies of production carried on by companies in the latter decades has its origin and its rationale in the changes in their organization and internal operative and in technical factors. In this sense we speak of changes and transformations in the process of production. The interest of this article lies in the objective of introducing he companies’ contextual, social and organizational factors and their consequences in the analysis of the work process by means of a re-definition of the concept of work process allowing an analysis in real conditions. We think the way of doing so is to understand the work process using the approaches characteristic of Situated Activity and Socially Distributed Knowledge; by this it is possible analyzing the above mentioned changes and their consequences taking into account the intervening macro and micosociological conditions

Efficient implementation of finite volume methods in Numerical Relativity

Centered finite volume methods are considered in the context of Numerical Relativity. A specific formulation is presented, in which third-order space accuracy is reached by using a piecewise-linear reconstruction. This formulation can be interpreted as an 'adaptive viscosity' modification of centered finite difference algorithms. These points are fully confirmed by 1D black-hole simulations. In the 3D case, evidence is found that the use of a conformal decomposition is a key ingredient for the robustness of black hole numerical codes.Comment: Revised version, 10 pages, 6 figures. To appear in Phys. Rev.

A Simflowny-based high-performance 3D code for the generalized induction equation

In the interior of neutron stars, the induction equation regulates the long-term evolution of the magnetic fields by means of resistivity, Hall dynamics and ambipolar diffusion. Despite the apparent simplicity and compactness of the equation, the dynamics it describes is not trivial and its understanding relies on accurate numerical simulations. While a few works in 2D have reached a mature stage and a consensus on the general dynamics at least for some simple initial data, only few attempts have been performed in 3D, due to the computational costs and the need for a proper numerical treatment of the intrinsic non-linearity of the equation. Here, we carefully analyze the general induction equation, studying its characteristic structure, and we present a new Cartesian 3D code, generated by the user-friendly, publicly available {\em Simflowny} platform. The code uses high-order numerical schemes for the time and spatial discretization, and relies on the highly-scalable {\em SAMRAI} architecture for the adaptive mesh refinement. We present the application of the code to several benchmark tests, showing the high order of convergence and accuracy achieved and the capabilities in terms of magnetic shock resolution and three-dimensionality. This paper paves the way for the applications to a realistic, 3D long-term evolution of neutron stars interior and, possibly, of other astrophysical sources.Comment: 23 pages, 13 figures. In pres

Global high-order numerical schemes for the time evolution of the general relativistic radiation magneto-hydrodynamics equations

Modeling correctly the transport of neutrinos is crucial in some astrophysical scenarios such as core-collapse supernovae and binary neutron star mergers. In this paper, we focus on the truncated-moment formalism, considering only the first two moments (M1 scheme) within the grey approximation, which reduces Boltzmann seven-dimensional equation to a system of $3+1$ equations closely resembling the hydrodynamic ones. Solving the M1 scheme is still mathematically challenging, since it is necessary to model the radiation-matter interaction in regimes where the evolution equations become stiff and behave as an advection-diffusion problem. Here, we present different global, high-order time integration schemes based on Implicit-Explicit Runge-Kutta (IMEX) methods designed to overcome the time-step restriction caused by such behavior while allowing us to use the explicit RK commonly employed for the MHD and Einstein equations. Finally, we analyze their performance in several numerical tests.Comment: 18 + 6. Updated manuscript matching published version + additional appendix "Comparing the convergence order of IMEX and semi-implicit schemes

New Formalism for Numerical Relativity

We present a new formulation of the Einstein equations that casts them in an explicitly first order, flux-conservative, hyperbolic form. We show that this now can be done for a wide class of time slicing conditions, including maximal slicing, making it potentially very useful for numerical relativity. This development permits the application to the Einstein equations of advanced numerical methods developed to solve the fluid dynamic equations, {\em without} overly restricting the time slicing, for the first time. The full set of characteristic fields and speeds is explicitly given.Comment: uucompresed PS file. 4 pages including 1 figure. Revised version adds a figure showing a comparison between the standard ADM approach and the new formulation. Also available at http://jean-luc.ncsa.uiuc.edu/Papers/ Appeared in Physical Review Letters 75, 600 (1995