Black Holes, Cosmological Solutions, Future Singularities, and Their Thermodynamical Properties in Modified Gravity Theorie

54 p.

Double layers in gravity theories

Gravitational double layers, unlike their classical electromagnetic counterparts, are thought to be forbidden in gravity theories. It has been recently shown, however, that they are feasible in, for instance, gravity theories with a Lagrangian quadratic in the curvature. This is surprising with many potential consequences and the possibility of new physical behaviours. While a clear interpretation seems elusive, several lines of research are open. I present the field equations for double layers, the new physical quantities arising, and several explicit examples

Methods for Measuring Aggregate Costs of Conflict

This paper reviews the methods for measuring the economic cost of conflict. Estimating the economic costs of conflict requires a counterfactual calculation, which makes this a very difficult task. Social researchers have resorted to different estimation methods depending on the particular effect in question. The method used in each case depends on the units being analyzed (firms, sectors, regions or countries), the outcome variable under study (aggregate output, market valuation of firms, market shares, etc.) and data availability (a single cross-section, time series or panel data). This paper reviews existing methods used in the literature to assess the economic impact of conflict: cost accounting, cross-section methods, time series methods, panel data methods, gravity models, event studies, natural experiments and comparative case studies. The paper ends with a discussion of cost estimates and directions for further research.

Parámetros de contaminación y normativa en colectores urbanos

[ES] La contaminación por aguas residuales urbanas es uno de los problemas de mayor importancia para mantener un nivel de calidad aceptable del agua, debido al número elevado de fuentes, a la participación de la contaminación difusa y a la elevada concentración de materia orgánica. La normativa legal plantea unos límites eflDidos, pero no se han realizado campañas de seguimiento de forma suficiente para su comprobación, particularmente en estiaje. El problema se complica por la diversidad apreciable que se observa y la necesidad de dar significación estadística a las conclusiones. En este trabajo, junto a un análisis del seguimiento de una docena de parámetros en diversos colectores de aguas residuales de una zona urbana, se pretende eparar/advertir la dificultad que presenta cada uno de eUos para el cumplimiento legal en relación con las caraterísticas de las fuentes de procedencia y la situación estacional durante el análisis. Además, se pretende buscar de una forma incial las posibles relaciones que se presentan entre las variaciones simultáneas de dichos parámetros. Algunos de eUos muestran una relación clara por lo que podría establecerse alguna dependencia funcional, mientras que en otros casos el problema resulta excesivamente complejo por la necesidad de disponer de más información para Uegar a establecer alguna relación.

Is General Relativity a simplified theory?

IARD 8th Biennial Conference on Classical and Quantum Relativistic Dynamics of Particles and Fields - Galileo Galilei Inst Theoret Phys (GGI), Florence, ITALY - MAY 29-JUN 01, 2012. Edited by:Horowitz, LP

Possible antigravity regions in F (R) theory?

We construct an F(R) gravity theory corresponding to the Weyl invariant two scalar field theory. We investigate whether such F (R) gravity can have the antigravity regions where the Weyl curvature invariant does not diverge at the Big Bang and Big Crunch singularities. It is revealed that the divergence cannot be evaded completely but can be much milder than that in the original Weyl invariant two scalar field theory. (C) 2014 The Authors. Published by Elsevier B.V.