Variability of the soft X-ray excess in IRAS 13224-3809

We study the soft excess variability of the narrow line Seyfert 1 galaxy IRAS 13224-3809. We considered all five archival XMM-Newton observations, and we applied the 'flux-flux plot' (FFP) method. We found that the flux-flux plots were highly affected by the choice of the light curves' time bin size, most probably because of the fast and large amplitude variations, and the intrinsic non-linear flux--flux relations in this source. Therefore, we recommend that the smallest bin-size should be used in such cases. Hence, We constructed FFPs in 11 energy bands below 1.7 keV, and we considered the 1.7-3 keV band, as being representative of the primary emission. The FFPs are reasonably well fitted by a 'power-law plus a constant' model. We detected significant positive constants in three out of five observations. The best-fit slopes are flatter than unity at energies below $\sim 0.9$ keV, where the soft excess is strongest. This suggests the presence of intrinsic spectral variability. A power-law-like primary component, which is variable in flux and spectral slope (as $\Gamma\propto N_{\rm PL}^{0.1}$) and a soft-excess component, which varies with the primary continuum (as $F_{\rm excess}\propto F_{\rm primary}^{0.46}$), can broadly explain the FFPs. In fact, this can create positive `constants', even when a stable spectral component does not exist. Nevertheless, the possibility of a stable, soft--band constant component cannot be ruled out, but its contribution to the observed 0.2-1 keV band flux should be less than $\sim 15$ %. The model constants in the FFPs were consistent with zero in one observation, and negative at energies below 1 keV in another. It is hard to explain these results in the context of any spectral variability scenario, but they may signify the presence of a variable, warm absorber in the source.Comment: Accepted for publication in A&A, 10 pages, 7 figure

Angioplastie coronaire percutanée chez la femme : particularités cliniques, procédurales et pronostiques

AbstractX Les résultats de l´angioplastie transluminale (ATL) des coronaires chez la femme ont été pendant de nombreuses années controversés et longtemps considérés comme moins favorable que chez l´homme. Le but de notre travail était d’évaluer les caractéristiques de l’angioplastie coronaire chez la femme, ainsi que les résultats immédiats et à moyen terme et de les comparer à ceux chez l’homme. Nous avons comparé 200 patients dont 100 femmes, ayant bénéficié d’une angioplastie coronaire, colligés au service de cardiologie de l’hôpital Hédi Chaker de Sfax entre 2002 et 2007. Les femmes étaient significativement plus âgées que les hommes. La comparaison de la fréquence des facteurs de risque d’athérosclérose chez les deux sexes, a permis de noter une co-morbidité franchement plus importante chez la femme, avec une différence statiquement significative. L’ATL a été plus motivée chez la femme devant un angor stable sévère (p<0,05) et un SCA ST- (p=NS). Les femmes avaient plus d’atteinte polytronculaire (p<0,05), d’atteintes des segments moyens et distaux (p<0,05) et plus des lésions serrées (p=NS), longues et calcifiées (p<0,05). 259 stents ont été déployés, un stenting direct était plus fréquent dans la population féminine (p<0,05). Le diamètre des artères féminines, assimilé à celui du stent et/ou ballon utilisé, a été significativement moins important que celui des hommes. La longueur des stents et/ou ballon utilisés, ainsi que les pressions de larguage des stents ont été plus importantes chez la population féminine (p<0,05). Le succès angiographique global a été obtenu chez 94% de la population générale, sans différence significative entre les deux sexes. Les évènements cardiaques majeurs (MACE) hospitaliers ont été plus fréquents chez la femme (p=0,05). Après un suivi moyen de 31 mois, le taux de MACE global a été significativement plus important chez la femme (39% vs. 28%, p<0,05), portant surtout sur la mortalité globale (13% vs. 3%, p<0,05). Le taux de resténose a été comparable chez les deux sexes. L’angioplastie coronaire constitue actuellement un moyen thérapeutique efficace et sur chez la femme, au prix de complications plus fréquentes.Key words: Angioplastie coronaire percutanée, syndrome coronarien aigu, sexes, mortalité, Tunisi

Asymptotic Analysis of RZF in Large-Scale MU-MIMO Systems over Rician Channels

In this paper, we focus on the downlink ergodic sum rate of a single-cell large-scale multiuser MIMO system in which the base station employs $N$ antennas to communicate with $K$ single-antenna user equipments (UEs). A regularized zero-forcing (RZF) scheme is used for precoding under the assumption that each UE uses a specific power and each link forms a spatially correlated MIMO Rician fading channel. The analysis is conducted assuming that $N$ and $K$ grow large with a given ratio and perfect channel state information is available at the base station. New results from random matrix theory and large system analysis are used to compute an asymptotic expression of the signal-to-interference-plus-noise ratio as a function of system parameters, spatial correlation matrix, and Rician factor. Numerical results are used to validate the accuracy of asymptotic approximations in the finite system regime and to evaluate the performance under different operating conditions. It turns out that the asymptotic expressions provide accurate approximations even for relatively small values of $N$ and $K$

Do financial professionals behave according to prospect theory? An experimental study

Prospect theory is increasingly used to explain deviations from the traditional paradigm of rational agents. Empirical support for prospect theory comes mainly from laboratory experiments using student samples. It is obviously important to know whether and to what extent this support generalizes to more naturally occurring circumstances. This article explores this question and measures prospect theory for a sample of private bankers and fund managers. We obtained clear support for prospect theory. Our financial professionals behaved according to prospect theory and violated expected utility maximization. They were risk averse for gains and risk seeking for losses and their utility was concave for gains and (slightly) convex for losses. They were also averse to losses, but less so than commonly observed in laboratory studies and assumed in behavioral finance. A substantial minority focused on gains and largely ignored losses, behavior reminiscent of what caused the current financial crisis