The MEXSAS2 Sample and the Ensemble X-ray Variability of Quasars

We present the second Multi-Epoch X-ray Serendipitous AGN Sample (MEXSAS2), extracted from the 6th release of the XMM Serendipitous Source Catalogue (XMMSSC-DR6), cross-matched with Sloan Digital Sky Survey quasar catalogues DR7Q and DR12Q. Our sample also includes the available measurements for masses, bolometric luminosities, and Eddington ratios. Analyses of the ensemble structure function and spectral variability are presented, together with their dependences on such parameters. We confirm a decrease of the structure function with the X-ray luminosity, and find a weak dependence on the black hole mass. We introduce a new spectral variability estimator, taking errors on both fluxes and spectral indices into account. We confirm an ensemble softer when brighter trend, with no dependence of such estimator on black hole mass, Eddington ratio, redshift, X-ray and bolometric luminosity.Comment: 6 pages, 3 figures, to appear in Frontiers in Astronomy and Space Science

Ensemble spectral variability study of Active Galactic Nuclei from the XMM-Newton serendipitous source catalogue

The variability of the X-ray spectra of active galactic nuclei (AGN) usually includes a change of the spectral slope. This has been investigated for a small sample of local AGNs by Sobolewska and Papadakis, who found that slope variations are well correlated with flux variations, and that spectra are typically steeper in the bright phase (softer when brighter behaviour). Not much information is available for the spectral variability of high-luminosity AGNs and quasars. In order to investigate this phenomenon, we use data from the XMM-Newton Serendipitous Source Catalogue, Data Release 5, which contains X-ray observations for a large number of active galactic nuclei in a wide luminosity and redshift range, for several different epochs. This allows to perform an ensemble analysis of the spectral variability for a large sample of quasars. We quantify the spectral variability through the spectral variability parameter $\beta$, defined as the ratio between the change in spectral slope and the corresponding logarithmic flux variation. We find that the spectral variability of quasars has a softer when brighter behaviour, similarly to local AGNs.Comment: 5 pages, 2 figures. Prepared for the proceedings of the 6th Young Researchers Meeting, L'Aquil

New mobile visualities and the social communication of photography : Instagram as a case study

This research intends to show how visuality, through the mobility of Instagram (a social media platform designed for photo sharing), is modifying individuals’ perception of the world and their mediated lives. It examines how Instagram transforms individuals’ perception of interpersonal relationships, marketing, privacy and surveillance, identity and memory, and communication. It attempts a critical re-reading of the combined interrelations between the concept of mobility (smart mobile devices) and the thematic areas mentioned above. Conducting an empirical examination, it delineates the changing dynamics that digitality determines within the contemporary experience of visual communication. In order to understand visual practices it is important to consider how relationships develop among individuals, visual technologies, practices and images, society and culture (Pink, 2007: 35). A qualitative research method informed by netnography, computer-mediated interviews and visual analysis (Rose, 2007) is employed in this study. Findings show that the ubiquitous use of smart mobile devices guides us towards the development of new forms and conceptions of mobile mediated visualities.The critical analysis of the (embedded) multiple-case study presents the innovative transformations that the mediation and mobility of Instagram bring into everyday relations between human-technologies. Findings show that now that daily life is experienced as a succession of photo opportunities that allow the creation of social networks but do not replace physical relationships. Images figure as a fair means of communication although they cannot fulfil verbal ones. However, the connections that images establish become a valuable part of new social media marketing strategies. With the widespread use of the platform, companies start to monitor users and influence their online behaviour without causing concern in relation to privacy and surveillance issues. The protection of personal information instead is related to the visibility that the contents of images acquire within the virality of the Internet. Within this, the voyeuristic spirit that animates the platform affects individuals’ interest in disclosing self-identity through visual metaphors. The disclosure of visual narrations of the self, at the same time, models the sharing of new networked archives of personal and collective memories.The ephemerality of digital culture is embraced by smart mobile technologies considering the importance that individuals give to the act of producing multimedia contents more than the content itself. Smart mobile devices represent the element of mediation in social instances and they strongly represent the foundation of a new mobile visualities aesthetic. Societies produce peculiar forms of expression and communication that are shaped by the co-presence of individual demands and the current typology of means of communication. Every alteration in the structure of societies has influence on individuals and on means of expression. This thesis shows that in contemporary life visualities have crucial functions in different environments such as business, leisure, and surveillance. Lastly, the triangulation of mediation-mobility-visuality produces a snapshot aesthetic, which radically transforms traditional functions of photography

Culture, Policies and Labor Market Outcomes

We study whether cultural attitudes towards gender, the young, and leisure are significant determinants of the evolution over time of the employment rates of women and of the young, and of hours worked in OECD countries. Beyond controlling for a larger menu of policies, institutions and structural characteristics of the economy than has been done so far, our analysis improves upon existing studies of the role of "culture" for labor market outcomes by dealing explicitly with the endogeneity of attitudes, policies and institutions, and by allowing for the persistent nature of labor market outcomes. When we do all this we find that culture still matters for women employment rates and for hours worked. However, policies and other institutional or structural characteristics are also important. Attitudes towards youth independence, however, do not appear to be important in explaining the employment rate of the young. In the case of women employment rates, the policy variable that is significant along with attitudes, is the OECD index of employment protection legislation. For hours worked the policy variables that play a role, along with attitudes, are the tax wedge and unemployment benefits. The quantitative impact of these policy variables is such that changes in policies have at least the potential to undo the effect of variations in cultural traits on labor market outcomes.culture, policies, institutions, employment, hours

“Good” Firms, Worker Flows, and Local Productivity

This paper is the first to present direct evidence showing how localized knowledge spillovers arise from workers changing jobs within the same local labor market. Using a unique data set combining Social Security earnings records and balance sheet information for the Veneto region of Italy, I first identify a set of highly productive firms, then show that hiring workers with experience at these firms significantly increases the productivity of other firms. My findings imply that worker flows explain around 10% of the productivity gains experienced by incumbent firms when new highly productive firms are added to a local labor market

A method for narrow-band searches of continuous gravitational wave signals

Targeted searches of continuous waves from spinning neutron stars normally assume that the frequency of the gravitational wave signal is at a given known ratio with respect to the rotational frequency of the source, e.g. twice for an asymmetric neutron star rotating around a principal axis of inertia. In fact this assumption may well be invalid if, for instance, the gravitational wave signal is due to a solid core rotating at a slightly different rate with respect to the star crust. In this paper we present a method for {\it narrow-band} searches of continuous gravitational wave signals from known pulsars in the data of interferometric detectors. This method assumes source position is known to high accuracy, while a small frequency and spin-down range around the electromagnetic-inferred values is explored. Barycentric and spin-down corrections are done with an efficient time-domain procedure. Sensitivity and computational efficiency estimates are given and results of tests done using simulated data are also discussed.Comment: 13 pages; 6 figures; accepted in PR

Good Firms, Worker Flows and Productivity

I present direct evidence on the role of firm-to-firm labor mobility in enhancing the productivity of firms located near highly productive firms. Using matched employer-employee and balance sheet data for the Veneto region of Italy, I identify a set of high-wage firms (HWF) and show they are more productive than other firms. I then show that hiring a worker with HWF experience increases the productivity of other (non-HWF) firms. A simulation indicates that worker flows explain 10-15 percent of the productivity gains experienced by other firms when HWFs in the same industry are added to a local labor market

X-ray spectral variability of Active Galactic Nuclei from XMM-Newton data

The X-ray spectral variability of Active Galactic Nuclei typically follows a “softer when brighter” trend, which is believed to be originated mainly from the superposition of different spectral components, varying independently from each other, although some intrinsic variations of the continuum are also possible. We analyzed the MEXSAS sample, made up by more than 7800 observations from 2700 quasars from the fifth release of the XMM-Newton Serendipitous Source Catalogue (3XMM-SSC), cross-matched with two quasar catalogues, SDSS-DR7Q and SDSS-DR12Q. We developed a technique that is able to compute estimates of the photon index from approximate spectral fits, using the fluxes in the catalogue. Following Trevese & Vagnetti (2002), we quantify the spectral variability using β = −∆Γ/∆ log F. We find an ensemble softer when brighter trend, extending therefore this result to quasars, and the same result is found for eight single sources extracted from the catalogue, plus one (PG 1114+445) discarded because of the presence of a prominent warm absorber, although with different extent. To investigate the reason for this range of different values of beta, we investigated a sample of X-ray bright sources taken from the samples of Sobolewska & Papadakis (2009), plus M81, for which it is possible to obtain accurate photon indices. We compute both the accurate and approximate photon indices and we confront β obtained with both methods. Finally, we studied the spectra of 13 observations of PG 1114+445, finding multiple absorbers, one possibly being a highly ionized, ultra-fast outflow, with velocity of about 15% of the speed of light, which is observable in four observations

Good Firms, Worker Flows and Productivity

I present direct evidence on the role of firm-to-firm labor mobility in enhancing the productivity of firms located near highly productive firms. Using matched employer-employee and balance sheet data for the Veneto region of Italy, I identify a set of high-wage firms (HWF) and show they are more productive than other firms. I then show that hiring a worker with HWF experience increases the productivity of other (non-HWF) firms. A simulation indicates that worker flows explain 10-15 percent of the productivity gains experienced by other firms when HWFs in the same industry are added to a local labor market