Steps toward a classifier for the Virtual Observatory. I. Classifying the SDSS photometric archive

Modern photometric multiband digital surveys produce large amounts of data that, in order to be effectively exploited, need automatic tools capable to extract from photometric data an objective classification. We present here a new method for classifying objects in large multi-parametric photometric data bases, consisting of a combination of a clustering algorithm and a cluster agglomeration tool. The generalization capabilities and the potentialities of this approach are tested against the complexity of the Sloan Digital Sky Survey archive, for which an example of application is reported.Comment: To appear in the Proceedings of the "1st Workshop of Astronomy and Astrophysics for Students" - Naples, 19-20 April 200

WATCAT: a tale of wide-angle tailed radio galaxies

We present a catalog of 47 wide-angle tailed radio galaxies (WATs), the WATCAT; these galaxies were selected by combining observations from the National Radio Astronomy Observatory/Very Large Array Sky Survey (NVSS), the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST), and the Sloan Digital Sky Survey (SDSS), and mainly built including a radio morphological classification. We included in the catalog only radio sources showing two-sided jets with two clear "warmspots" (i.e., jet knots as bright as 20% of the nucleus) lying on the opposite side of the radio core, and having classical extended emission resembling a plume beyond them. The catalog is limited to redshifts z $\leq$ 0.15, and lists only sources with radio emission extended beyond 30 kpc from the host galaxy. We found that host galaxies of WATCAT sources are all luminous (-20.5 $\gtrsim$ Mr $\gtrsim$ -23.7), red early-type galaxies with black hole masses in the range $10^8\lesssim$ M$_{\rm BH} \lesssim 10^9$ M$_\odot$. The spectroscopic classification indicates that they are all low-excitation galaxies (LEGs). Comparing WAT multifrequency properties with those of FRI and FRII radio galaxies at the same redshifts, we conclude that WATs show multifrequency properties remarkably similar to FRI radio galaxies, having radio power of typical FRIIs

A nearly zero-energy microgrid testbed laboratory: Centralized control strategy based on SCADA system

Currently, despite the use of renewable energy sources (RESs), distribution networks are facing problems, such as complexity and low productivity. Emerging microgrids (MGs) with RESs based on supervisory control and data acquisition (SCADA) are an effective solution to control, manage, and finally deal with these challenges. The development and success of MGs is highly dependent on the use of power electronic interfaces. The use of these interfaces is directly related to the progress of SCADA systems and communication infrastructures. The use of SCADA systems for the control and operation of MGs and active distribution networks promotes productivity and efficiency. This paper presents a real MG case study called the LAMBDA MG testbed laboratory, which has been implemented in the electrical department of the Sapienza University of Rome with a centralized energy management system (CEMS). The real-time results of the SCADA system show that a CEMS can create proper energy balance in a LAMBDA MG testbed and, consequently, minimize the exchange power of the LAMBDA MG and main grid

Probing BH mass and accretion through X-ray variability in the CDFS

Recent work on nearby AGNs has shown that X-ray variability is correlated with the mass and accretion rate onto the central SMBH. Here we present the application of the variability-luminosity relation to high redshift AGNs in the CDFS, making use of XMM-Newton observations. We use Monte Carlo simulations in order to properly account for bias and uncertainties introduced by the sparse sampling and the very low statistics. Our preliminary results indicate that BH masses span over the range from 10^5 to 10^9 solar mass while accretion rates range from 10^-3 up to values greater than 1, in unit of Eddington accretion rate.Comment: 2 pages, 2 figures,in press in the X-ray 2009 Conference Proceedings (Bologna, 7-11 September 2009

Estimation of signal parameters in the frequency domain in the presence of harmonic interference: a comparative analysis

In this paper, a novel method for the estimation of the parameters of the spectral components of a signal, also in the case of harmonic interference, is characterized and compared to other methods proposed in literature. The comparison criteria include the evaluation of residual errors and uncertainties on estimated parameters for different multicomponent signals

Prevalence of X-ray variability in the Chandra Deep Field South

We studied the X-ray variability of sources detected in the Chandra Deep Field South (Giacconi et al. 2002), nearly all of which are low to moderate z AGN (Tozzi et al. 2001). We find that 45% of the sources with >100 counts exhibit significant variability on timescales ranging from a day up to a year. The fraction of sources found to be variable increases with observed flux, suggesting that >90% of all AGNs possess intrinsic variability. We also find that the fraction of variable sources appears to decrease with increasing intrinsic absorption; a lack of variability in hard, absorbed AGNs could be due to an increased contribution of reflected X-rays to the total flux. We do not detect significant spectral variability in the majority (~70%) of our sources. In half of the remaining 30%, the hardness ratio is anti-correlated with flux, mimicking the high/soft-low/hard states of galactic sources. The X-ray variability appears anti-correlated with the luminosity of the sources, in agreement with previous studies. High redshift sources, however, have larger variability amplitudes than expected from extrapolations of their low-z counterparts, suggesting a possible evolution in the accretion rate and/or size of the X-ray emitting region. Finally, we discuss some effects that may produce the observed decrease in the fraction of variable sources from z=0.5 out to z=2.Comment: 24 pages, including 15 figures and 1 table. In press on Ap

Probing the Low Mass X-ray Binaries/Globular Cluster connection in NGC1399

We present a wide field study of the Globular Clusters/Low Mass X-ray Binaries connection in the cD elliptical NGC1399, combining HST/ACS and Chandra high resolution data. We find evidence that LMXB formation likelihood is influenced by GCs structural parameters, in addition to the well known effects of mass and metallicity, independently from galactocentric distance.Comment: in press in the Proceedings of the X-ray 2009 Conference, 7-11 September 2009, Bologna, Ital

Globular Cluster Scale Sizes in Giant Galaxies: Orbital Anisotropy and Tidally Under-filling Clusters in M87, NGC 1399, and NGC 5128

We investigate the shallow increase in globular cluster half-light radii with projected galactocentric distance $R_{gc}$ observed in the giant galaxies M87, NGC 1399, and NGC 5128. To model the trend in each galaxy, we explore the effects of orbital anisotropy and tidally under-filling clusters. While a strong degeneracy exists between the two parameters, we use kinematic studies to help constrain the distance $R_\beta$ beyond which cluster orbits become anisotropic, as well as the distance $R_{f\alpha}$ beyond which clusters are tidally under-filling. For M87 we find $R_\beta > 27$ kpc and $20 < R_{f\alpha} 13$ kpc and $10 < R_{f\alpha} < 30$ kpc. The connection of $R_{f\alpha}$ with each galaxy's mass profile indicates the relationship between size and $R_{gc}$ may be imposed at formation, with only inner clusters being tidally affected. The best fitted models suggest the dynamical histories of brightest cluster galaxies yield similar present-day distributions of cluster properties. For NGC 5128, the central giant in a small galaxy group, we find $R_\beta > 5$ kpc and $R_{f\alpha} > 30$ kpc. While we cannot rule out a dependence on $R_{gc}$, NGC 5128 is well fitted by a tidally filling cluster population with an isotropic distribution of orbits, suggesting it may have formed via an initial fast accretion phase. Perturbations from the surrounding environment may also affect a galaxy's orbital anisotropy profile, as outer clusters in M87 and NGC 1399 have primarily radial orbits while outer NGC 5128 clusters remain isotropic.Comment: 16 pages, 7 figures, 4 tables, Accepted for publication in MNRA

The XMM deep survey in the CDF-S. X. X-ray variability of bright sources

We aim to study the variability properties of bright hard X-ray selected Active Galactic Nuclei (AGN) with redshift between 0.3 and 1.6 detected in the Chandra Deep Field South (XMM-CDFS) by a long XMM observation. Taking advantage of the good count statistics in the XMM CDFS we search for flux and spectral variability using the hardness ratio techniques. We also investigated spectral variability of different spectral components. The spectra were merged in six epochs (defined as adjacent observations) and in high and low flux states to understand whether the flux transitions are accompanied by spectral changes. The flux variability is significant in all the sources investigated. The hardness ratios in general are not as variable as the fluxes. Only one source displays a variable HR, anti-correlated with the flux (source 337). The spectral analysis in the available epochs confirms the steeper when brighter trend consistent with Comptonisation models only in this source. Finding this trend in one out of seven unabsorbed sources is consistent, within the statistical limits, with the 15 % of unabsorbed AGN in previous deep surveys. No significant variability in the column densities, nor in the Compton reflection component, has been detected across the epochs considered. The high and low states display in general different normalisations but consistent spectral properties. X-ray flux fluctuations are ubiquitous in AGN. In general, the significant flux variations are not associated with a spectral variability: photon index and column densities are not significantly variable in nine out of the ten AGN over long timescales (from 3 to 6.5 years). The photon index variability is found only in one source (which is steeper when brighter) out of seven unabsorbed AGN. These results are consistent with previous deep samples.Comment: 14 pages, 11 figures. Accepted in A&

Improving Safety at Work: the Role of Climates

La letteratura sulla sicurezza nei luoghi di lavoro ha da sempre principalmente riguardato il concetto di clima di sicurezza - definito come l\u2019insieme delle percezioni riguardanti politiche, pratiche e procedure relative alla sicurezza che influenzano il benessere dei lavoratori - e i comportamenti di sicurezza, rappresentati in termini di comportamenti di compliance \u2013 ossia tutti i comportamenti che riguardano l'adesione e il rispetto delle procedure, e pi\uf9 in generale il lavorare in modo sicuro - e i comportamenti di partecipazione alla sicurezza, cio\ue8 quei comportamenti volontari che il lavoratore agisce per migliorare la sicurezza nella propria organizzazione. La letteratura sul tema suggerisce inoltre come la tendenza principale della ricerca in questo settore sia stata e sia ancora la capacit\ue0 del clima di sicurezza di predire i comportamenti di sicurezza, tralasciando una serie di elementi importanti e rappresentativi di nuove prospettive di sviluppo per la ricerca in questo settore. La sfida principale che \ue8 emersa da una pi\uf9 ampia review della letteratura riguarda soprattutto l'influenza di altre variabili legate al contesto organizzativo che possono influenzare la performance di sicurezza; in particolare, accanto al clima di sicurezza non si pu\uf2 ignorare l\u2019esistenza nei contesti lavorativi di molteplici climi organizzativi operanti in simultanea, ciascuno con diversi effetti che vanno ad interagire (sommandosi, annullandosi, moltiplicandosi), e con ricadute - ancora poco esplorate - sui comportamenti organizzativi e di conseguenza anche su quelli legati alla sicurezza. Pertanto la finalit\ue0 principale di questo lavoro di tesi \ue8 stata quella di utilizzare un approccio pi\uf9 ampio nello studio delle dinamiche organizzative relative alla sicurezza, e in particolar modo di verificare se altre tipologie di clima organizzativo - oltre al clima di sicurezza - possano avere un impatto sui comportamenti sicuri messi in atto dai lavoratori e sul numero di infortuni sul lavoro nel settore metalmeccanico. Nello specifico, la crescente diversit\ue0 della forza lavoro nei contesti organizzativi attuali richiede di essere presa in considerazione quando si studia il rapporto tra clima sicurezza e prestazioni di sicurezza; le aziende che desiderino stare al passo con i costanti processi di trasformazione e diversificazione dei mercati odierni, dovranno assumere, coordinare, e sviluppare un'ampia variet\ue0 di risorse umane, con conseguenze importanti per le organizzazioni, anche in materia di gestione della sicurezza. Per tale ragione il primo studio del presente lavoro di tesi \ue8 focalizzato sulla verifica delle propriet\ue0 psicometriche della scala sul clima di diversit\ue0 sviluppata da Mor Barak, Cherin e Berkman (1998), adattata al contesto italiano. In particolare tale studio rappresenta il primo tentativo di validazione di uno strumento per la valutazione del clima di diversit\ue0 in un contesto europeo. I risultati mostrano una soluzione tri-fattoriale per il campione italiano e un minor numero di items rispetto alla scala originale; inoltre lo strumento sembra funzionare in modo equivalente sia per gli uomini che per le donne e dimostra buone validit\ue0 di criterio e discriminante. Pertanto, questo primo studio ci ha consentito di adattare tale strumento al contesto italiano al fine di utilizzarlo negli studi successivi per valutare la relazione tra clima di diversit\ue0 e comportamenti di sicurezza. Nel secondo studio il costrutto di clima di diversit\ue0 \ue8 stato utilizzato insieme a quello di clima per l'inclusione al fine di verificare il rispettivo impatto sui comportamenti partecipativi di sicurezza a livello individuale, ipotizzando un ruolo di mediazione svolto dalla motivazione del lavoratore a promuovere attivamente la sicurezza sul lavoro. L\u2019innovazione rappresentata da tale studio risiede nel fatto che la letteratura precedente sul tema si era limitata a investigare la relazione tra specifiche e oggettive tipologie di diversit\ue0 (e.g. differenze nelle caratteristiche sociali e demografiche) dei lavoratori e il loro effetto sull\u2019incidenza di infortuni, senza tenere in considerazione il ruolo giocato dalle percezioni relative alla diversit\ue0 e a come questa venga gestita in azienda. La scelta di prendere in considerazione anche il costrutto di clima per l\u2019inclusione risiede nel fatto che tale costrutto si fonda sul coinvolgimento attivo e sulla partecipazione dei lavoratori ad attivit\ue0 formali e informali cruciali per l\u2019organizzazione, con ricadute ampiamente dimostrate in termini di qualit\ue0 del lavoro svolto e benessere dei lavoratori; pertanto \ue8 stato ipotizzato che un clima di questo tipo possa avere conseguenze positive anche sui comportamenti di partecipazione alla sicurezza. I risultati dimostrano che il clima di diversit\ue0 e il clima per l'inclusione sono costrutti differenti ma correlati, e che risultano legati alla sicurezza in modo diverso; infatti il clima di diversit\ue0 sembra predire i comportamenti di partecipazione alla sicurezza attraverso la mediazione totale svolta dalla motivazione alla partecipazione alla sicurezza, mentre tale motivazione risulta mediare solo parzialmente la relazione tra clima per l\u2019inclusione e gli stessi comportamenti partecipativi nei confronti della sicurezza. Il terzo scopo della presente tesi \ue8 stato quello di ampliare l\u2019indagine relativa all\u2019influenza che molteplici climi organizzativi operanti simultaneamente hanno sugli infortuni lavorativi, analizzando i dati a livello di gruppo e utilizzando una tecnica statistica \u2013 l\u2019analisi delle corrispondenze multiple \u2013 ancora poco considerata nella ricerca sulla sicurezza e pi\uf9 in generale nella letteratura sui climi organizzativi. Oltre al clima di diversit\ue0 e a quello per l'inclusione, nel presente studio sono stati utilizzati anche i costrutti di clima di sicurezza (e.g., Zohar, 1980; 2000) e clima di comunicazione (Smidts, Pruyn & van Riel, 2001), dal momento che precedenti ricerche hanno sottolineato come prestazione sicure siano strettamente dipendenti dalla qualit\ue0 della comunicazione e degli scambi sociali tra i lavoratori e i loro supervisori e colleghi. I risultati mostrano la presenza di quattro patterns o configurazioni diverse di climi; tuttavia, la distribuzione degli infortuni non sembra seguire in modo coerente i patterns climatici rilevati; possibili interpretazioni dei risultati riscontrati si rifanno all\u2019effetto alone (Wells, 1907 Thorndike , 1920) e alla letteratura sul "reporting climate" (Probst & Estrada 2010, p. 1443). Riassumendo i risultati dei tre studi \ue8 possibile concludere che essi rappresentano un contributo estremamente innovativo alla letteratura sul clima organizzativo e, relativamente alla questione della sicurezza sul lavoro, esplorano percorsi di ricerca non considerati in precedenza.Main organizational and psychological factors considered by literature about safety concerned the concept of safety climate - defined as individual perceptions about the policies, practices, and procedures related to safety issues affecting well-being at work - and that one of safety behaviors, represented in a dichotomy that comprises both safety compliance and safety participation behaviors. Literature review suggested that the main trend of research in that field has been the focus on the ability of safety climate to predict safety behaviors, not considering some important challenges for research development in this area. The main challenge concerns the influence of other variables related to the social context on safety issues; for instance, the existence of multiple simultaneous organizational climates with different effects on the same safety outcomes. Therefore, the first aim of this PhD thesis was to consider a broader approach when studying organizational dynamics pertaining to safety and to test whether other dimensions of organizational climate can be strictly relevant for safety even if they are not specific to safety. In particular, the increasing presence of diverse workforce in the organizations requires to be taken into account when studying the relationship between safety climate and safety performance; indeed, if companies want to take the most from today\u2019s ever-diversifying markets, they will have to hire, coordinate, and retain a broad base of human resources, with consequences for organizational and group performance, even specifically that one pertaining to safety. For that reason, the first study of the present dissertation has been focused on developing an Italian validation of a useful instrument to measure Diversity Climate, by adapting the Mor Barak, Cherin and Berkman (1998) Diversity Perceptions Scale, the most widely used questionnaire to assess diversity climate, considering the lack of any validated measure of diversity climate in the European context. Results interestingly showed a different factorial solution for the Italian sample using a shorter version than the original scale; moreover the scale seemed to be invariant for both men and women and to show good discriminant and criterion validities. Therefore, this first study allowed us to make this instrument suitable for the Italian context, in order to use it for evaluating whether diversity climate could specifically affect some safety outcomes in the subsequent studies. In the second study the diversity climate measure was used together with a measure of climate for inclusion (Mor Barak, 2005) to test their impact on safety participative behaviors at the individual level and for the first time, by hypothesizing a mediating role performed by the motivation to actively promote safety at work. The choice to consider also the construct of inclusion climate as linked to safety is due to the particular kind of social empowerment and involvement \u2013 regardless of workers\u2019 diversities - which form this kind of climate; moreover it has been already demonstrated to influence work quality and behaviors, so we hypothesized that it could also have positive consequences for workers\u2019 involvement and commitment to safety and their safety performance. Results showed that diversity climate and climate for inclusion are different constructs which have different and important impacts on safety; specifically safety participation motivation revealed to fully mediate the relationship between diversity climate and safety participation behaviors, whereas it only partially mediated the relationship between inclusion climate and safety participation behaviors. The third aim of the present dissertation was to enlarge the effort of investigating the impact of distinct facet-specific climates on specific safety behaviors, by exploring the possible influence of multiple existing climates on injury rates at the unit-level and with a qualitative statistical technique - multi-correspondence analysis. In addition to diversity climate and inclusion climate, safety climate (e.g., Zohar, 1980; 2000) and communication climate (Smidts, Pruyn & van Riel, 2001) measures were also used for this purpose, as previous research stressed how safety performance is strictly dependent on the supervisors\u2019 and coworkers\u2019 communication and quality of social exchange. Results showed the presence of four differentiated patterns of climates; however, injury\u2019s distribution did not seem to be coherent with the climates\u2019 patterns, and references to the halo effect (Wells, 1907; Thorndike, 1920) and to the injury \u201creporting climate\u201d (Probst & Estrada, 2010, p. 1443) have been made to explain those findings. Summarizing the results of the three studies, it is possible to conclude that they represents very innovative contributions to the organizational climate literature, and with regard to the safety area, they explore research avenues not addressed before