Simple model of the slingshot effect

We present a detailed quantitative description of the recently proposed "slingshot effect" [Fiore, Fedele, De angelis 2014]. Namely, we determine a broad range of conditions under which the impact of a very short and intense laser pulse normally onto a low-density plasma (or matter to be locally completely ionized into a plasma by the pulse) causes the expulsion of a bunch of surface electrons in the direction opposite to the one of propagation of the pulse, and the detailed, ready-for-experiments features of the expelled electrons (energy spectrum, collimation, etc). The effect is due to the combined actions of the ponderomotive force and the huge longitudinal field arising from charge separation. Our predictions are based on estimating 3D corrections to a simple, yet powerful plane magnetohydrodynamic (MHD) model where the equations to be solved are reduced to a system of Hamilton equations in one dimension (or a collection of) which become autonomous after the pulse has overcome the electrons. Experimental tests seem to be at hand. If confirmed by the latter, the effect would provide a new extraction and acceleration mechanism for electrons, alternative to traditional radio-frequency-based or Laser-Wake-Field ones.Comment: Revtex4.1 file, 14 pages, 10 figures, one table. Final version to appear in Phys. Rev. Acc. Beams. The title has slightly changed to match to the one decided by the edito

A "slingshot" laser-driven acceleration mechanism of plasma electrons

We briefly report on the recently proposed [G. Fiore, R. Fedele, U. de Angelis, Phys. Plasmas 21 (2014), 113105], [G. Fiore, S. De Nicola, arXiv:1509.04656] electron acceleration mechanism named "slingshot effect": under suitable conditions the impact of an ultra-short and ultra-intense laser pulse against the surface of a low-density plasma is expected to cause the expulsion of a bunch of superficial electrons with high energy in the direction opposite to that of the pulse propagation; this is due to the interplay of the huge ponderomotive force, huge longitudinal field arising from charge separation, and the finite size of the laser spot.Comment: 6 pages, 6 figures, one table. Talk held at the 2nd European Advanced Accelerator Concepts (EAAC) Workshop, 13-19 September 2015 La Biodola, Isola d'Elba. To appear in the proceedings, in Nucl. Instr. Meth. Phys. Res.

Monads in Double Categories

We extend the basic concepts of Street's formal theory of monads from the setting of 2-categories to that of double categories. In particular, we introduce the double category Mnd(C) of monads in a double category C and define what it means for a double category to admit the construction of free monads. Our main theorem shows that, under some mild conditions, a double category that is a framed bicategory admits the construction of free monads if its horizontal 2-category does. We apply this result to obtain double adjunctions which extend the adjunction between graphs and categories and the adjunction between polynomial endofunctors and polynomial monads.Comment: 30 pages; v2: accepted for publication in the Journal of Pure and Applied Algebra; added hypothesis in Theorem 3.7 that source and target functors preserve equalizers; on page 18, bottom, in the statement concerning the existence of a left adjoint, "if and only if" was replaced by "a sufficient condition"; acknowledgements expande

Double Adjunctions and Free Monads

We characterize double adjunctions in terms of presheaves and universal squares, and then apply these characterizations to free monads and Eilenberg--Moore objects in double categories. We improve upon our earlier result in "Monads in Double Categories", JPAA 215:6, pages 1174-1197, 2011, to conclude: if a double category with cofolding admits the construction of free monads in its horizontal 2-category, then it also admits the construction of free monads as a double category. We also prove that a double category admits Eilenberg--Moore objects if and only if a certain parameterized presheaf is representable. Along the way, we develop parameterized presheaves on double categories and prove a double-categorical Yoneda Lemma.Comment: 52 page

The interaction-driven starburst contribution to the cosmic star formation rate density

An increasing amount of observational evidence supports the notion that there are two modes of star formation: a quiescent mode in disk-like galaxies, and a starburst mode, which is generally interpreted as driven by merging. Using a semi-analytic model of galaxy formation, we derive the relative contribution to the cosmic star formation rate density of quiescently starforming and starburst galaxies, predicted under the assumption that starburst events are triggered by galaxy encounters (merging and fly-by kind) during their merging histories. We show that, within this framework, quiescently starforming galaxies dominate the cosmic star formation rate density at all redshifts. The contribution of the burst-dominated starforming galaxies increases with redshift, rising from <5% at low redshift (z5. We estimated that the fraction of the final (z=0) galaxy stellar mass which is formed through the burst component of star formation is ~10% for 10^10 M_\odot<M_*<10^11.5 M_\odot. Starburst galaxies, selected according to their distance from the galaxy main sequence, account for ~10% of the star formation rate density in the redshift interval 1.5<z<2.5, i.e. at the cosmic peak of the star formation activity.Comment: 11 pages, 8 figures. Accepted for publication in A&

The lifewatch approach to the exploration of distributed species information

© 2014 Daniel Fuentes, Nicola Fiore. This paper introduces a new method of automatically extracting, integrating and presenting information regarding species from the most relevant online taxonomic resources. First, the information is extracted and joined using data wrappers and integration solutions. Ten, an analytical tool is used to provide a visual representation of the data. Te information is then integrated into a user friendly content management system. Te proposal has been implemented using data from the Global Biodiversity Information Facility (GBIF), the Catalogue of Life (CoL), the World Register of Marine Species (WoRMS), the Integrated Taxonomic Information System (ITIS) and the Global Names Index (GNI). Te approach improves data quality, avoiding taxonomic and nomenclature errors whilst increasing the availability and accessibility of the information.Peer Reviewe

The Building Up of the Black Hole Mass - Stellar Mass Relation

We derive the growth of SMBHs relative to the stellar content of their host galaxy predicted under the assumption of BH accretion triggered by galaxy encounters occurring during their merging histories. We show that, within this framework, the ratio Gamma=(M_BH/M_*)(z)/(M_BH/M_*)(z=0) between the Black Hole mass and the galactic stellar mass (normalized to the local value) depends on both BH mass and redshift. While the average value and the spread of Gamma(z) increase with z, such an effect is larger for massive BHs, reaching values Gamma=5 for massive Black Holes (M>10^9 M_{\odot}) at z>4, in agreement with recent observations of high-redshift QSOs; this is due to the effectiveness of interactions in triggering BH accretion in high-density environments at high redshifts. To test such a model against observations, we worked out specific predictions for sub-samples of the simulated galaxies corresponding to the different observational samples for which measurements of Gamma have been obtained. We found that for Broad Line AGNs at 1<z<2 values of Gamma=2 are expected, with a mild trend toward larger value for increasing BH mass. Instead, when we select from our Monte Carlo simulations only extremely gas rich, rapidly star forming galaxies at 2<z<3, we find low values 0.3<Gamma<1.5, consistent with recent observational findings on samples of sub-mm galaxies; in the framework of our model, these objects end up at z=0 in low-to-intermediate mass BHs (M<10^9 M_{\odot}), and they do not represent typical paths leading to local massive galaxies. The latter have formed preferentially through paths passing above the local M_*-M_BH relation. We discuss how the global picture emerging from the model is consistent with a downsizing scenario, where massive BHs accrete a larger fraction of their final mass at high redshifts z>4.Comment: 13 pages, 9 figures. Accepted to MNRA

X-Ray Evolution of Active Galactic Nuclei and Hierarchical Galaxy Formation

We have incorporated the description of the X-ray properties of Active Galactic Nuclei (AGNs) into a semi-analytic model of galaxy formation, adopting physically motivated scaling laws for accretion triggered by galaxy encounters. Our model reproduces the level of the cosmic X-ray background at 30 keV; we predict that the largest contribution (around 2/3) comes from sources with intermediate X-ray luminosity 10^{43.5}< L_X/erg/s <10^{44.5}, with 50 % of the total specific intensity produced at z<2. The predicted number density of luminous X-ray AGNs (L_X>10^{44.5} erg/s in the 2-10 keV band) peaks at z around 2 with a decline of around 3 dex to z=0; for the low luminosity sources (10^{43}<L_X/erg/s <10^{44}) it has a broaderand less pronounced maximum around z 1.5. The comparison with the data shows a generally good agreement. The model predictions slightly exceed the observed number of low-luminosity AGNs at z around 1.5, with the discrepancy progressively extending to intermediate-luminosity objects at higher redshifts; we discuss possible origins for the mismatch. Finally, we predict the source counts and the flux distribution at different redshifts in the hard (20-100 keV) X-ray band for the sources contributing to the X- ray background.Comment: 27 pages, accepted for publication in Ap

Un contributo alla valutazione del rischio incendio di hangar metallici con i metodi della Fire Safety Engineering nell’ambito del quadro normativo attuale

La tesi di dottorato svolge un approfondimento sulla valutazione del rischio di incendio delle strutture metalliche di grande luce, con particolare riferimento alle strutture per hangar dell’Aeronautica Militare, nell’ambito del moderno approccio della Fire Safety Engineering e dell’attuale quadro normativo. L’attività svolta si è quindi articolata nella definizione degli scenari di incendio per la tipologia hangar dell’Aeronautica Militare, nell'analisi dei campi di temperatura all'interno dell'hangar e nell’analisi termo-meccanica delle strutture con modelli di calcolo avanzati che tengono conto degli effetti iperstatici indotti dalle dilatazioni termiche contrastate e del comportamento non lineare meccanico e geometrico. Gli hangar oggetto di studio sono rappresentativi di differenti destinazioni d’uso e possibili scenari di incendio, quali aviorimessa di velivoli militari e stoccaggio di materiali di varia natura. Per le analisi termofluidodinamiche sono stati utilizzati software specifici e di comprovata affidabilità, quali Ozone, CFast e FDS, mentre per le analisi termo-strutturali è stato utilizzato il codice di calcolo SAFIR, che consente analisi con modelli di calcolo avanzati in campo non lineare. In particolare, il sono stati approfonditi anzitutto gli argomenti relativi allo sviluppo del fenomeno fisico dell'incendio in hangar tipo, simulando il comportamento termofluidodinamico di differenti scenari di incendio in hangar, cercando di cogliere la distribuzione dei gradienti di temperatura ai quali sono sottoposte le strutture dell’hangar in caso di incendio, nonché le temperature ed i flussi termici ai quali sono soggetti i vari elementi strutturali. La definizione degli scenari di incendio e dei modelli di incendio nell’hangar tipo è stata sviluppata attraverso analisi accurate dei materiali presenti e delle loro composizioni (ad es. razioni di cibo, velivoli militari, articoli farmaceutici, autoveicoli, pallet di legno, tende per uso militare), nonchè delle loro possibili distribuzioni all’interno dell’hangar tipo. Ciò ha consentito di definire curve di incendio naturali, che caratterizzino con buona affidabilità i possibili scenari di incendio ai fini delle analisi necessarie per la valutazione della sicurezza strutturale con l’approccio ingegneristico. Sono stati quindi implementati modelli di calcolo termostrutturale dell’hangar tipo in grado di tener conto della della riduzione di rigidezza e di resistenza dei materiali strutturali in funzione della temperatura, degli effetti non lineari geometrici e meccanici e degli effetti delle dilatazioni termiche sul comportamento strutturale. Per approfondire gli aspetti di verifica di resistenza di elementi strutturali soggetti ad incendio, è stato anche sviluppato dall’autore un software specifico per il calcolo del dominio di resistenza di sezioni di acciaio, calcestruzzo armato e composte acciaio-calcestruzzo, che utilizza i legami costitutivi dei materiali in condizioni di incendio forniti dagli Eurocodici. La definizione dei possibili scenari di incendio, le corrispondenti analisi termofluidodinamiche e le analisi termo-meccaniche effettuate per la verifica di sicurezza delle strutture dell’hangar tipo nell’ambito dei criteri della Fire Safety Engineering (FSE) hanno consentito di individuare gli scenari di incendio più pericolosi in termini di distribuzione delle temperature e di sicurezza strutturale sotto incendio di hangar tipici dell’Aeronautica Militare. Il confronto tra i risultati ottenuti applicando i criteri della FSE e quelli del classico approccio prescrittivo ha poi fornito importanti indicazioni che evidenziano l’utilità di valutare la sicurezza strutturale antincendio di edifici di importanza strategica, quali gli hangar dell’Aeronautica Militare, mediante l’approccio della FSE, in generale più completo ed affidabile. In particolare questi metodi sono in grado di delineare le vulnerabilità strutturali e consentono una progettazione efficace ed ottimale degli interventi, su strutture esistenti e nuove, considerate le prestazioni attese per profili di rischio corrispondenti a strutture strategich

Will the Proliferation of 5G Base Stations Increase the Radio-Frequency "Pollution"?

A common concern among the population is that installing new 5G Base Stations (BSs) over a given geographic region may result in an uncontrollable increase of Radio-Frequency "Pollution" (RFP). To face this dispute in a way that can be understood by the layman, we develop a very simple model, which evaluates the RFP at selected distances between the user and the 5G BS locations. We then obtain closed-form expressions to quantify the RFP increase/decrease when comparing a pair of alternative 5G deployments. Results show that a dense 5G deployment is beneficial to the users living in proximity to the 5G BSs, with an abrupt decrease of RFP (up to three orders of magnitude) compared to a sparse deployment. We also analyze scenarios where the user equipment minimum detectable signal threshold is increased, showing that in such cases a (slight) increase of RFP may be experienced.Comment: Cite as: Luca Chiaraviglio, Giuseppe Bianchi, Nicola Blefari-Melazzi, Marco Fiore, Will the Proliferation of 5G Base Stations Increase the Radio-Frequency "Pollution"?, IEEE 91st Vehicular Technology Conference (VTC-Spring), Antwerp, Belgium, May 202