Covariant Charges in Chern-Simons AdS_3 Gravity

We try to give hereafter an answer to some open questions about the definition of conserved quantities in Chern-Simons theory, with particular reference to Chern-Simons AdS_3 Gravity. Our attention is focused on the problem of global covariance and gauge invariance of the variation of Noether charges. A theory which satisfies the principle of covariance on each step of its construction is developed, starting from a gauge invariant Chern-Simons Lagrangian and using a recipe developed in gr-qc/0110104 and gr-qc/0107074 to calculate the variation of conserved quantities. The problem to give a mathematical well-defined expression for the infinitesimal generators of symmetries is pointed out and it is shown that the generalized Kosmann lift of spacetime vector fields leads to the expected numerical values for the conserved quantities when the solution corresponds to the BTZ black hole. The fist law of black holes mechanics for the BTZ solution is then proved and the transition between the variation of conserved quantities in Chern-Simons AdS_3 Gravity theory and the variation of conserved quantities in General Relativity is analysed in detail.Comment: 30 pages, no figures. References adde

The long-term optical spectral variability of BL Lacertae

We present the results from a study of the long-term optical spectral variations of BL Lacertae, using the long and well-sampled B and R-band light curves of the Whole Earth Blazar Telescope (WEBT) collaboration, binned on time intervals of 1 day. The relation between spectral slope and flux (the spectrum gets bluer as the source flux increases) is well described by a power-law model, although there is significant scatter around the best-fitting model line. To some extent, this is due to the spectral evolution of the source (along well-defined loop-like structures) during low-amplitude events, which are superimposed on the major optical flares, and evolve on time scales of a few days. The "bluer-when-brighter" mild chromatism of the long-term variations of the source can be explained if the flux increases/decreases faster in the B than in the R band. The B and R-band variations are well correlated, with no significant, measurable delays larger than a few days. On the other hand, we find that the spectral variations lead those in the flux light curves by ~ 4 days. Our results can be explained in terms of Doppler factor variations due to changes in the viewing angle of a curved and inhomogeneous emitting jet.Comment: 7 pages, 5 figures, accepted for publication in A&

Comunit\ue0 locali, servizi sociali e diritti: una prospettiva teorica

La produzione delle politiche tende ad una sottoutilizzazione delle forme giuridiche (che presuppongono l\u2019implementazione) che favorisce l\u2019uso della pianificazione, ossia di strumenti non necessariamente giuridico-normativi. L\u2019assunzione del punto di vista della legittimit\ue0 dell\u2019azione discrezionale dell\u2019amministrazione riguardo all\u2019individuazione del significato da assegnare al testo normativo si risolve quindi in una presa d\u2019atto del superamento della pretesa neutralit\ue0 del diritto, utilizzato per strutturare i processi decisionali in modo da favorire la condivisione degli esiti allocativi delle politiche non solo da parte dei destinatari di queste ultime ma anche, e forse soprattutto, dei soggetti esclusi. Tale scenario prelude alla comprensione di processi regolativi in cui rileva la dimensione locale, intesa come l\u2019insieme delle specificit\ue0 dei contesti geografici, storici e culturali, dell\u2019individuazione di preesistenti meccanismi regolativi sociali e delle condizioni di attivazione di tali meccanismi. Cos\uec all\u2019origine dell\u2019inclusione del welfare nella comprensiva idea di police power dello Stato vi \ue8 l\u2019obiettivo di proteggere gli interessi del resto della societ\ue0 perseguito da una legislazione sulla povert\ue0 risalente, ma al tempo stesso moderna, in ragione del suo carattere \u201cpubblico\u201d, mentre in Inghilterra la trasformazione della funzione assistenziale in una funzione pubblica \ue8 stata paradossalmente favorita dallo smantellamento del modello assistenziale ecclesiastico a seguito della Riforma protestante. Le politiche sociali contemporanee sono declinate in termini di pretese esigibili, ossia di diritti ed obbligazioni a prestazioni positive da parte dello Stato e delle sue articolazioni territoriali: si tratta di \uabdiritti sociali\ubb che richiedono l\u2019erogazione di prestazioni e servizi da parte dell\u2019amministrazione, e rispetto ai quali la legge non si limita a circoscrivere e definire la dimensione pubblica e privata, ma si occupa dell\u2019organizzazione delle strutture amministrative e della previsione delle spese necessarie per realizzare l\u2019effettivit\ue0 del diritto sociale. Al centro di tale impostazione si colloca il tema della \u2018giustiziabilit\ue0\u2019 dei diritti sociali, strettamente, ma anche problematicamente, connesso a quello della loro costituzionalizzazione e si riflette sulle tecniche di riconoscimento di tali diritti adottate nei documenti costituzionali, che nel saggio sono discusse in modo critico

Postille sulla produzione di dati mediante indagini di vittimizzazione

Il saggio propone una lettura critica della relazione tra dimensioni delle forze dell’ordine e criminalità mediata dalla precauzione adottata dalle vittime potenziali esaminata da due studiosi olandesi, Vollaard e Koning, nella prospettiva della law and economics alla luce del confronto tra dati rilevati dai rapporti delle forze dell’ordine e dati prodotti mediante indagini di vittimizzazione. La questione più controversa riguarda l’adozione di un modello sincronico, che viene fortemente messa in discussione sottolineandone limiti e paradossi che ne derivano. Viceversa l’autrice mostra i vantaggi connessi all’adozione di un modello ricorsivo, caratterizzato da un gap temporale tra aumento della criminalità, del contingente di forze dell’ordine e dei livelli di precauzione adottati dalle vittime potenziali che evidenzia la capacità di retroagire di ciascuna variabile, contribuendo in tal modo alla corretta individuazione dei nessi causali. Cet essai donne un aperçu critique du lien entre la proportion des forces de police et le taux de criminalité, faisant intervenir aussi les précautions prises par les victimes potentielles, examinées par deux chercheurs néerlandais, Vollaard et Koning, du point de vue «du droit et de l’économie » (law and economics) ; ce lien a été analysé sur la base de la comparaison entre les données recueillies à partir des rapports de police et les données provenant des enquêtes de victimisation. La question la plus controversée dans la recherche néerlandaise concerne le choix d’un modèle synchrone qui est ici vigoureusement contesté, en soulignant ses problématiques et ses paradoxes. L’auteure montre au contraire les avantages de l’adoption d’un modèle récursif, caractérisé par un écart de temps entre l’accroissement du niveau des précautions prises par les victimes potentielles, la recrudescence de la criminalité et l’accroissement des forces de police ; ce modèle récursif peut représenter la capacité de feed-back de chaque variable, contribuant ainsi à une identification correcte des liens de causalité. This essay puts forward a critical review of the relationship between the size of the police force and crime rate mediated by the precaution taken by potential victims. It has been examined by two Dutch scholars, Vollaard and Koning, from the law and economics point of view and is a comparison between data collected from police reports and data generated through victimization surveys. The matter concerns the acceptance of the synchronous model scrutinised, which is being strongly questioned underlining the limits and paradoxes that may occur. Conversely, the author outlines the advantages of assuming a recursive model, characterised by a time gap between increases in crime rate, size of the police force and precautions taken by potential victims that will be able to highlight the strength of each variable to fight back, thus contributing to the correct detection of causal links

The nature of optical and near-infrared variability of BL Lacertae

Since 1997, BL Lacertae has undergone a phase of high optical activity, with the occurrence of several prominent outbursts. Starting from 1999, the Whole Earth Blazar Telescope (WEBT) consortium has organized various multifrequency campaigns on this blazar, collecting tens of thousands of data points. One of the main issues in the analysis of this huge dataset has been the study of colour variability. The massive amount of optical and near-infrared data collected during the campaigns enables us to perform a deep analysis of multiband data, with the aim of understanding the flux variability mechanisms. We use a new approach for the analysis of these data, focusing on the source spectral evolution. We show that the overall behaviour of the BL Lacertae light and colour curves can be explained in terms of changing viewing angle of a moving, discrete emitting region, which causes variable Doppler boosting of the corresponding radiation. A fractal helical structure is suggested to be at the origin of the different time scales of variability.Comment: 6 pages, 8 figures, accepted by A&

Polarization measurements and their perspectives: PVLAS Phase II

We sketch the proposal for a "PVLAS-Phase II" experiment. The main physics goal is to achieve the first direct observation of non-linear effects in electromagnetism predicted by QED and the measurement of the photon-photon scattering cross section at low energies (1-2 eV). Physical processes such as ALP and MCP production in a magnetic field could also be accessible if sensitive enough operation is reached. The short term experimental strategy is to compact as much as possible the dimensions of the apparatus in order to bring noise sources under control and to attain a sufficient sensitivity. We will also briefly mention future pespectives, such as a scheme to implement the resonant regeneration principle for the detection of ALPs.Comment: Paper submitted to the proceedings of the "4th Patras Workshop on Axions, WIMPs and WISPs", DESY, Hamburg Site /Germany, 18-21 June 200

Reactive Force Field for Proton Diffusion in BaZrO3 using an empirical valence bond approach

A new reactive force field to describe proton diffusion within the solid-oxide fuel cell material BaZrO3 has been derived. Using a quantum mechanical potential energy surface, the parameters of an interatomic potential model to describe hydroxyl groups within both pure and yttrium-doped BaZrO3 have been determined. Reactivity is then incorporated through the use of the empirical valence bond model. Molecular dynamics simulations (EVB-MD) have been performed to explore the diffusion of hydrogen using a stochastic thermostat and barostat whose equations are extended to the isostress-isothermal ensemble. In the low concentration limit, the presence of yttrium is found not to significantly influence the diffusivity of hydrogen, despite the proton having a longer residence time at oxygen adjacent to the dopant. This lack of influence is due to the fact that trapping occurs infrequently, even when the proton diffuses through octahedra adjacent to the dopant. The activation energy for diffusion is found to be 0.42 eV, in good agreement with experimental values, though the prefactor is slightly underestimated.Comment: Corrected titl