Two-fluid dust and gas mixtures in smoothed particle hydrodynamics II: an improved semi-implicit approach

We present an improved version of the Loren-Aguilar & Bate (2014) method to integrate the two-fluid dust/gas equations that correctly captures the limiting velocity of small grains in the presence of net differences (excluding the drag force) between the accelerations of the dust and the gas. A series of accelerated DUSTYBOX tests and a simulation of dust-settling in a protoplanetary disc are performed comparing the performance of the new and old methods. The modified method can accurately capture the correct limiting velocity while preserving all the conservation properties of the original method.Comment: Accepted for publication in MNRA

Two fluid dust and gas mixtures in SPH: A semi-implicit approach

A method to avoid the explicit time integration of small dust grains in the two fluid gas/dust smoothed particle hydrodynamics (SPH) approach is proposed. By assuming a very simple exponential decay model for the relative velocity between the gas and dust components, all the effective characteristics of the drag force can be reproduced. A series of tests has been performed to compare the accuracy of the method with analytical and explicit integration results. We find that the method performs well on a wide range of tests, and can provide large speed ups over explicit integration when the dust stopping time is small. We have also found that the method is much less dissipative than conventional explicit or implicit two-fluid SPH approaches when modelling dusty shocks.Comment: 20 pages, 14 figures. Accepted for publication in MNRA

Toroidal vortices as a solution to the dust migration problem

In an earlier letter, we reported that dust settling in protoplanetary discs may lead to a dynamical dust-gas instability that produces global toroidal vortices. In this letter, we investigate the evolution of a dusty protoplanetary disc with two different dust species (1 mm and 50 cm dust grains), under the presence of the instability. We show how toroidal vortices, triggered by the interaction of mm grains with the gas, stop the radial migration of metre-sized dust, potentially offering a natural and efficient solution to the dust migration problem.Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letter

Consumption recovery in 2021: an analysis drawing on consumer expectations

Artículo de revistaConsumers’ expectations of economic developments are a fundamental determinant of their spending decisions. This article estimates, using simple expectation formation rules in the context of a general equilibrium model, the degree of persistence that households assign to the economic impact of the pandemic. The findings show that households have perceived that the COVID-19 shock has a lower degree of persistence than other previous negative shocks. According to the model used, this would signal an uptick in private consumption, once the health crisis is over, that would tend to offset the decline observed during the pandemic

Derechos de participación y derecho a participar

La participación en la Constitución de 2008 es un elemento fundamental de la organización estatal, pero los instrumentos participativos no son suficientes para concretarla. No se toma en cuenta que el espacio participativo no puede nacer desde las leyes sino a partir de formas de acción política que modifiquen los esquemas tradicionales de toma de decisiones. Se confunde el espacio de lo público con el estatal, la estructura participativa no es otra cosa que aparato de estado. La experiencia: participación vigente en el papel; temas de interés colectivo pasan por la representación o la protesta (casos de trampolín político); nuevas leyes con la falta de participación; y fortalecimiento de un poder personal y autoritario, que no deja espacio para ejercicios democráticos o participativos

Information frictions and policy in DSGE models

150 p.Esta tesis presenta un análisis de las implicaciones de las principales hipótesis de los modelos de equilibrio general, ampliamente usados tanto en los ámbitos de investigación económica como en las decisiones de políticas macroeconómicas, desde un aspecto teórico como práctico, permitiendo cuantificar el impacto de estas y estableciendo recomendaciones en el uso de modelos de equilibrio general. La primera parte de la tesis, capítulos I y II se centran en la alternativa de expectativas de aprendizaje respecto a la hipótesis estándar de expectativas racionales. El primer capítulo muestra como la alternativa de expectativas adaptativas permite una caracterización a través de reglas sencillas del proceso de formación de expectativas por parte de los agentes económicos, con el resultado de una mejor caracterización del ciclo económico. El segundo capítulo utiliza esta representación de las expectativas para medir el impacto de cambios en la política económica, permitiendo cuantificar el impacto tanto en la duración del aprendizaje de esta nueva regla por parte de los agentes como el coste económico asociado a este, ejercicio que en los modelos tradicionales no sería posible. El tercer capítulo se centra en la naturaleza de los datos, en tiempo real o revisados, en el análisis macroeconómico, mostrando que existen revisiones importantes en los datos iniciales y proponiendo una metodología para acomodar este hecho en los modelos que usen datos en tiempo real. El capítulo IV, y último, se centra en el diseño y calibración de herramientas de política macroprudencial en los modelos macrofinancieros de equilibrio general

Weaving a fabric of socially aware agents

The expansion of web-enabled social interaction has shed light on social aspects of intelligence that have not been typically studied within the AI paradigm so far. In this context, our aim is to understand what constitutes intelligent social behaviour and to build computational systems that support it. We argue that social intelligence involves socially aware, autonomous individuals that agree on how to accomplish a common endeavour, and then enact such agreements. In particular, we provide a framework with the essential elements for such agreements to be achieved and executed by individuals that meet in an open environment. Such framework sets the foundations to build a computational infrastructure that enables socially aware autonomy.This work has been supported by the projects EVE(TIN2009-14702-C02-01) and AT (CSD2007-0022)Peer Reviewe

Detonations in white dwarf dynamical interactions

In old, dense stellar systems collisions of white dwarfs are a rather frequent phenomenon. Here we present the results of a comprehensive set of Smoothed Particle Hydrodynamics simulations of close encounters of white dwarfs aimed to explore the outcome of the interaction and the nature of the final remnants for different initial conditions. Depending on the initial conditions and the white dwarf masses, three different outcomes are possible. Specifically, the outcome of the interaction can be either a direct or a lateral collision or the interaction can result in the formation of an eccentric binary system. In those cases in which a collision occurs, the infalling material is compressed and heated such that the physical conditions for a detonation may be reached during the most violent phases of the merger. While we find that detonations occur in a significant number of our simulations, in some of them the temperature increase in the shocked region rapidly lifts degeneracy, leading to the quenching of the burning. We thus characterize under which circumstances a detonation is likely to occur as a result of the impact of the disrupted star on the surface of the more massive white dwarf. Finally, we also study which interactions result in bound systems, and in which ones the more massive white dwarf is also disrupted as a consequence of the dynamical interaction. The sizable number of simulations performed in this work allows to find how the outcome of the interaction depends on the distance at closest approach, and on the masses of the colliding white dwarfs, and which is the chemical pattern of the nuclearly processed material. Finally, we also discuss the influence of the masses and core chemical compositions of the interacting white dwarfs and the different kinds of impact in the properties of the remnants.Comment: 18 pages, 6 figures. Accepted for publication in MNRA