4,914 research outputs found

    Temperature structure of the intergalactic medium within seven nearby and bright clusters of galaxies observed with XMM-Newton

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    Aims. We map the temperature structure of the intra-cluster medium (ICM) within a nearly complete X-ray flux limited sample of galaxy clusters in the redshift range z=[0.045,0.096]. Our sample contains seven bright clusters of galaxies observed with XMM-Newton: Abell 399, Abell 401, Abell 478, Abell 1795, Abell 2029, Abell 2065, Abell 2256. Methods. We use a multi-scale spectral mapping algorithm especially designed to map spectroscopic observables from X-ray extended emission of the ICM. Derived from a former algorithm using Haar wavelets, our algorithm is now implemented with B-spline wavelets in order to perform a more regular analysis of the signal. Results. For the four clusters in our sample that are major mergers, we find a complex thermal structure with strong thermal variations consistent with their dynamics. For two of them, A2065 and A2256, we perform a 3-d analysis of cold front features evidenced from the gas temperature and brightness maps. Furthermore, we detect a significant non-radial thermal structure outside the cool core region of the other 3 more "regular" clusters, with relative amplitudes of about about 10%. We investigate possible implications of this structure on the mass estimates of the "regular" clusters A1795 and A2029, by extracting surface brightness and temperature profiles from sectors correspondings to the hottest and coldest regions in the maps. While compensating with surface brightness for A2029, leading to consistent mass profiles, the temperature structure leads to significant mass discrepancies in the innermost region of A1795.Comment: published in A&

    Comparing the temperatures of galaxy clusters from hydro-N-body simulations to Chandra and XMM-Newton observations

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    Theoretical studies of the physical processes guiding the formation and evolution of galaxies and galaxy clusters in the X-ray are mainly based on the results of numerical hydrodynamical N-body simulations, which in turn are often directly compared to X-ray observations. Although trivial in principle, these comparisons are not always simple. We demonstrate that the projected spectroscopic temperature of thermally complex clusters obtained from X-ray observations is always lower than the emission-weighed temperature, which is widely used in the analysis of numerical simulations. We show that this temperature bias is mainly related to the fact that the emission-weighted temperature does not reflect the actual spectral properties of the observed source. This has important implications for the study of thermal structures in clusters, especially when strong temperature gradients, like shock fronts, are present. Because of this bias, in real observations shock fronts appear much weaker than what is predicted by emission-weighted temperature maps, and may even not be detected. This may explain why, although numerical simulations predict that shock fronts are a quite common feature in clusters of galaxies, to date there are very few observations of objects in which they are clearly seen. To fix this problem we propose a new formula, the spectroscopic-like temperature function, and show that, for temperature larger than 3 keV, it approximates the spectroscopic temperature better than few per cent, making simulations more directly comparable to observations.Comment: Submitted for publication in MNRAS; 15 pages, 10 color figures and 13 BW figures,mn2e.cls. High resolution figures available here: http://people.roma2.infn.it/~mazzotta/preprints/mazzotta.pd

    Foreign exchange option and returns based correlation forecasts: evaluation and two applications

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    We compare option-implied correlation forecasts from a dataset consisting of over 10 years of daily data on over-the-counter (OTC) currency option prices to a set of return-based correlation measures and assess the relative quality of the correlation forecasts. We find that while the predictive power of implied correlation is not always superior to that of returns based correlations measures, it tends to provide the most consistent results across currencies. Predictions that use both implied and returns-based correlations generate the highest adjusted R2s, explaining up to 42 per cent of the realised correlations. We then apply the correlation forecasts to two policyrelevant topics, to produce scenario analyses for the euro effective exchange rate index, and to analyse the impact on cross-currency co-movement of interventions on the JPY/USD exchange rate. JEL Classification: F31, F37, G15Correlation forecasts, currency options data, effective exchange rate

    Bivariate Probit Models for Analysing how “Knowledge” Affects Innovation and Performance in Small and Medium Sized Firms

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    This paper examines the determinants of innovation and its effects on small- and medium-sized firms We use the data from the OPIS databank, which provides a survey on a representative sample of firms from a province of the Southern Italy. We want to study whether small and medium sized firms can have a competitive advantage using their innovative capabilities, regardless of their sectoral and size limits. The main factor influencing the likelihood of innovation is knowledge, which is acquired through different ways. The econometric methodology consists of two bivariate models in order to estimate the probability of increased sales conditioned to the probability of innovation. We found that knowledge positively influences the probability of innovation; at the same time, knowledge has also a positive indirect effect on the increase of sales through innovation.innovation; small and medium sized firms; human capital; networks; bivariate probit

    The Choice of Search Methods: Some Empirical Evidence from Italy

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    In labour market part of the coordination process involves the matching between job skills and vacancies requiring specific skills. On the side of unemployed workers, the process requires a searching activity based on the gathering of information on available vacancies, the related wages and skills. The distinction among search methods plays a significant role as to the success of individual job search. The factors characterising the methods and the individuals searching for a job influence their choice. The specific aim of this empirical analysis is to understand how individual look for a job and, thus, how they decide to choose the search methods drawn from the set of search actions as specified in the 1993 Bank of Italy Survey.labour supply; unemployment; models and job search

    Jon Search Methods:The Choice Between the Public and the Private Sector

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    It is well known that the lack of information often leads to the difficulty of decentralised decision units solving coordination problems through market functioning. In labour market the lack of information is often characterised by asymmetric information on heterogeneous labour skills and the related productive capabilities [Spence, 1973] and coordination mainly concerns the matching of vacant jobs with unemployed individuals, which results from a costly and time-consuming process. Coordination involves also the matching between job skills and vacancies requiring specific skills. This process is characterised by the existence of uncertainty as unemployed individuals know the general features of wage distribution in an area but ignore which firms are offering each wage. Accordingly, coordination on the side of unemployed workers involves a searching activity based on the gathering of information on available vacancies, the related wage and skill, whereas on the side of firms the gathering of information on the characteristics of individuals willing to fill the vacancies like their skills. As to unemployed workers, the distinction among search methods plays a significant role in the final result of their job search.labour supply; unemployment; job search

    Youth Unemployment and Youth Employment Policies in Italy

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    The labour market in Italy is characterised by the following structurally specific features: 1) Regional differentials. In 1996 the unemployment rate was between 7% and 10% in Central and Northern regions, while it was over 21% in the South where, moreover, the participation rate was also low, especially for women (37% in the North and Centre, 28% in the South);2) Unemployment is highest for young people. In 1996 the unemployment rate of the 15-29 year old labour force (25.8%), in Italy, was more than double that of the total working age population and the youth problem is much greater in the South where the unemployment rate of 15-29 year olds rises to 45.3%; 3) The low rate of employment is mainly due to the lower female rate of employment (36.2%) that is far inferior than the EU average rate of employment (49.7%). Why is the youth unemployment rate so high?-