Birkhoff's Theorem in Higher Derivative Theories of Gravity

In this paper we present a class of higher derivative theories of gravity which admit Birkhoff's theorem. In particular, we explicitly show that in this class of theories, although generically the field equations are of fourth order, under spherical (plane or hyperbolic) symmetry, all the field equations reduce to second order and have exactly the same or similar structure to those of Lovelock theories, depending on the spacetime dimensions and the order of the Lagrangian.Comment: 7 pages, no figures. v1: This version received an Honorable Mention from the Gravity Research Foundation - 2011 Awards for Essays on Gravitation. v2: Expanded version. To appear in CQ

Post-Katrina New Orleans. Dalla ricostruzione alla resilienza

Attraverso lo studio di un\u2019esperienza emblematica come quella di New Orleans e della sua pianificazione post-Katrina, ci si propone di avviare una riflessione sulle opportunit\ue0 generate dalla crisi ambientale, nello specifico scaturite da un evento estremo e distruttivo (tanto da far identificare una citt\ue0 \u201cpre-\u201d e una citt\ue0 \u201cpost-\u201d); opportunit\ue0 rese visibili e derivanti dall\u2019applicazione di un approccio basato sulla resilienza. Tale approccio non ha caratterizzato la pianificazione post-Katrina fin dall\u2019inizio, ma, al contrario, \ue8 possibile osservare un\u2019evoluzione degli strumenti adottati, che, in un decennio, ha visto la graduale, ma esplicita, integrazione della resilienza nella pianificazione della citt\ue0

Resilienza e adattamento: definizioni, modelli e sfide progettuali

Il concetto di 'citt\ue0 resiliente' \ue8 emerso negli ultimi decenni in risposta alle nuove sfide che le citt\ue0 sono chiamate ad affrontare, sfide poste dalla crisi economica e sociale, dalla scarsit\ue0 delle risorse, dal rischio ambientale, dai cambiamenti climatici. Ma una citt\ue0 resiliente, prima ancora che reagire ai mutamenti climatici, sociali o economici, \ue8 in grado di prevenire le crisi, o di sfruttarle come 'opportunit\ue0'. Il contributo intende indagare i campi d\u2019azione e gli strumenti della resilienza urbana a partire dai significati che emergono dalla letteratura e dal dibattito disciplinare, e fornire una prima analisi di alcune esperienze di formazione di strategie e piani di adattamento fondati sulla resilienza in atto in Italia: il progetto BLUE AP (Bologna Local Urban Environment Adaptation Plan for a Resilient City) di Bologna, tra le citt\ue0 firmatarie dell\u2019iniziativa europea 'Mayors Adapt', e l\u2019adesione delle citt\ue0 di Roma e Milano al programma '100 Resilient Cities\u2019 della Rockefeller Foundation. Presentando le prime riflessioni frutto dell\u2019avvio della ricerca di dottorato dell\u2019autore, con un approccio aperto e sperimentale, in formazione, il paper vuole contribuire alla riflessione sul tema proposto, sostenendo l\u2019importanza di una dimensione proattiva, e non solo di prevenzione dei rischi, offrendo un punto di vista che interpreta la resilienza come un possibile nuovo paradigma per la pianificazione e la progettazione urbana

Exact Hairy Black Holes and their Modification to the Universal Law of Gravitation

In this paper two things are done. First, it is pointed out the existence of exact asymptotically flat, spherically symmetric black holes when a self interacting, minimally coupled scalar field is the source of the energy momentum of the Einstein equations in four dimensions. The scalar field potential is the recently found to be compatible with the hairy generalization of the Plebanski-Demianski solution of general relativity. This paper describes the spherically symmetric solutions that smoothly connect the Schwarzschild black hole with its hairy counterpart. The geometry and scalar field are everywhere regular except at the usual Schwarzschild like singularity inside the black hole. The scalar field energy momentum tensor satisfies the null energy condition in the static region of the spacetime. The first law holds when the parameters of the scalar field potential are fixed under thermodynamical variation. Secondly, it is shown that an extra, dimensionless parameter, present in the hairy solution, allows to modify the gravitational field of a spherically symmetric black hole in a remarkable way. When the dimensionless parameter is increased, the scalar field generates a flat gravitational potential, that however asymptotically matches the Schwarzschild gravitational field. Finally, it is shown that a positive cosmological constant can render the scalar field potential convex if the parameters are within a specific rank.Comment: Two new references, 10 pages, 2 figure

A type system for Continuation Calculus

Continuation Calculus (CC), introduced by Geron and Geuvers, is a simple foundational model for functional computation. It is closely related to lambda calculus and term rewriting, but it has no variable binding and no pattern matching. It is Turing complete and evaluation is deterministic. Notions like "call-by-value" and "call-by-name" computation are available by choosing appropriate function definitions: e.g. there is a call-by-value and a call-by-name addition function. In the present paper we extend CC with types, to be able to define data types in a canonical way, and functions over these data types, defined by iteration. Data type definitions follow the so-called "Scott encoding" of data, as opposed to the more familiar "Church encoding". The iteration scheme comes in two flavors: a call-by-value and a call-by-name iteration scheme. The call-by-value variant is a double negation variant of call-by-name iteration. The double negation translation allows to move between call-by-name and call-by-value.Comment: In Proceedings CL&C 2014, arXiv:1409.259

Zastosowanie programu gwarancji dla zdrowia jamy ustnej w opiece nad kobietą w ciąży w rodzinnym centrum zdrowia w Concepción, Chile, w latach 2014–2015

Indexación: Scopus.Background. Oral health plays a crucial role in general health, quality of life and well-being of pregnant women and their newborns. In Chile, pregnant women have dental care guaranteed by law. However, due to the lack of previous epidemiological studies on the benefits of this guarantee, it is necessary to describe this situation and evaluate the need to change the methods of providing dental services. Objectives. The objective of this study was to describe the pattern of providing dental benefits resulting from the Explicit Health Guarantee – Integral Oral Health in Pregnant Women (GES-SOIE) program to pregnant women attending the Juan Soto Fernández Family Health Center, Concepción, Chile, in 2014–2015. Material and methods. A cross-sectional study of the electronic dental records of patients admitted to GES-SOIE was conducted. The variables studied were sociodemographic data, dental chair hours, non-attendance, treatment completion, and the type of referral to secondary healthcare (SHC). Results. Of 233 pregnant women, 65.2% were registered for non-attendance, 21.2% required referral to SHC and 76.4% completed their treatment. When performing logistic regression, it was found that for each non-attendance the chance of not completing the treatment increased 1.4 times. Conclusions. The level of non-attendance and opting out of the treatment in pregnant women is high, which hinders the proper functioning and effectiveness of GES-SOIE. © 2018 by Wroclaw Medical University and Polish Dental Society.http://www.dmp.umed.wroc.pl/en/article/2018/55/2/179

Implementación de un Sistema RV Multiusuario en la División de Estudios para Graduados de la Facultad de Arquitectura y Diseño de la Universidad del Zulia

The present article describes the implementation of a VR multi-user system, in the computer laboratories of the Graduate School of Architecture and Design in the University of Zulia, Maracaibo, Venezuela, and the technical and operational features that have to be considered in this kind of project.El presente artículo describe la implementación de un sistema RV Multiusuario en los laboratorios de computación del Postgrado de la Facultad de Arquitectura y Diseño de la Universidad del Zulia, Maracaibo, Venezuela, y las consideraciones de tipo técnico y operativo que este proyecto implica para su uso con fines académicos

Exact solutions for the Einstein-Gauss-Bonnet theory in five dimensions: Black holes, wormholes and spacetime horns

An exhaustive classification of certain class of static solutions for the five-dimensional Einstein-Gauss-Bonnet theory in vacuum is presented. The class of metrics under consideration is such that the spacelike section is a warped product of the real line with a nontrivial base manifold. It is shown that for generic values of the coupling constants the base manifold must be necessarily of constant curvature, and the solution reduces to the topological extension of the Boulware-Deser metric. It is also shown that the base manifold admits a wider class of geometries for the special case when the Gauss-Bonnet coupling is properly tuned in terms of the cosmological and Newton constants. This freedom in the metric at the boundary, which determines the base manifold, allows the existence of three main branches of geometries in the bulk. For negative cosmological constant, if the boundary metric is such that the base manifold is arbitrary, but fixed, the solution describes black holes whose horizon geometry inherits the metric of the base manifold. If the base manifold possesses a negative constant Ricci scalar, two different kinds of wormholes in vacuum are obtained. For base manifolds with vanishing Ricci scalar, a different class of solutions appears resembling "spacetime horns". There is also a special case for which, if the base manifold is of constant curvature, due to certain class of degeneration of the field equations, the metric admits an arbitrary redshift function. For wormholes and spacetime horns, there are regions for which the gravitational and centrifugal forces point towards the same direction. All these solutions have finite Euclidean action, which reduces to the free energy in the case of black holes, and vanishes in the other cases. Their mass is also obtained from a surface integral.Comment: 31 pages, 1 figure, minor changes and references added. Final version to be published in PR