1,721,005 research outputs found
Myocarditis in the Athlete: Arrhythmogenic Substrates, Clinical Manifestations, Management, and Eligibility Decisions
No full textMyocarditis is as an important cause of sudden cardiac death (SCD) among athletes. The incidence of SCD ascribed to myocarditis did not change after the introduction of pre-participation screening in Italy, due to the transient nature of the disease and problems in the differential diagnosis with the athlete’s heart. The arrhythmic burden and the underlying mechanisms differ between the acute and chronic setting, depending on the relative impact of acute inflammation versus post-inflammatory myocardial fibrosis. In the acute phase, ventricular arrhythmias vary from isolated ventricular ectopic beats to complex tachycardias that can lead to SCD. Atrioventricular blocks are typical of specific forms of myocarditis, and supraventricular arrhythmias may be observed in case of atrial inflammation. Athletes with acute myocarditis should be temporarily restricted from physical exercise, until complete recovery. However, ventricular tachycardia may also occur in the chronic phase in the context of post-inflammatory myocardial scar
ON THE RELATIONSHIP BETWEEN THE OPTICAL AND X-RAY LUMINOSITIES OF QUASARS
No full textWe address the question of the relationship between X-ray and optical luminosities for both optically and X-ray selected quasar samples. We apply a generalized regression algorithm for the case of samples involving censored data, with errors on both the dependent and the independent variable. Contrary to some previous results, we find that such relationship is consistent with being a linear one (L(x) proportional to L(o)). We argue that previous reports of non-linear relationships (i.e. L(x) proportional to L(o)(e) with e < 1) are due to the neglect of the influence of the photometric errors, the precise knowledge of which strongly influences the reliability of the results. Further progresses in the determination of the L(o) - L(x) relationship can be achieved with ROSAT observations of the new generation of large bright quasar surveys
Probability density estimation in astronomy
No full textIn this paper we consider three empirical estimators (Kernel, adaptive Kernel and parametrizing families of Johnson) of the probability density function, which are alternatives to the classical Histogram. By means of numerical simulations the superiority of such estimators is shown in the context of some typical astronomical problems. Given the simplicity of implementation and the efficiency of calculation, the use of these methods is recommended. Indication for the implementation is provided
The Shapes of Galaxy Groups
No full textThe shape of groups of galaxies has been since now a disregarded topic in the literature, mainly due to the fact that individual ellipticity estimates of poor systems are strongly biased toward higher values. Such a bias turns out to depend on both the ellipticity itself and on the richness of the group. In this paper we have devised a modified version of the classical Lucy's iterative method, which is able to perform a statistical rectification of the observed ellipticity distribution of groups. Since this method needs an estimate of the average radial profile of the groups, we have faced also this problem.
Our analysis has been applied to a sample of 54 groups belonging to the Tully (1987) catalog. The sample is selected in order to reduce the well-known, distance-dependent observational biases, which are present in all available group catalogs (Pisani et al. 1992). We found statistical evidence that galaxy groups share a common law for the radial distribution of members. This law can be quite satisfactorily represented by a simple Gaussian model, whereas a de Vaucouleurs profile (for instance) is definitely not consistent with the data. It is important to stress that the rectified distribution of apparent ellipticities looks very different from the original (unrectified) one. This implies that any statistical analysis which does not take into account the above mentioned bias, has to give meaningless results.
The final aim of the paper is to produce the distribution of intrinsic ellipticities of groups, by deprojection of their apparent (rectified) ellipticity distribution. To do this we have to assume a biaxial (oblate or prolate) intrinsic shape of the groups are some model for their spatial orientation. Because of this reason, before the deprojection, we have searched for possible alignments of the group major axes along the supergalactic plane or toward the Local Supercluster center. We found a weak indication in favor of the latter hypothesis, but more sizable samples are needed to give statistical significance to this conclusion. At this stage, we have been forced to perform the deprojection by assuming a random orientation of the groups in the space.
The apparent (rectified) ellipticity distribution which is obtained from our sample of galaxy groups, turned out to be consistent with both the oblate and the prolate intrinsic shapes. However, the oblate hypothesis should imply that a great fraction of groups has a very flattened, disklike structure. This circumstance is rather difficult to be explained within the available cosmological scenarios. Moreover, the convergence of the deprojection algorithm in the oblate case is hard-earned, and the final agreement with the data is less satisfactory than that obtained in the prolate case. All these facts led us to prefer the prolate solution with respect to the oblate one. Obviously a mixture of two different populations (oblate and prolate), as well as a triaxial solution, cannot be excluded
The Optical Variability of the Quasar 3C 446
No full textThe optical variability of the quasar 3C 446 is investigated using power spectrum and structure function analysis along with a new set of observations that extend the available data till 1989. No contradiction is found between the PS and SF analyses. The presence of the 1540-day periodicity is strengthened by the occurrence of the 1988 luminosity peak, suggesting that the next burst will occur in the northern spring of 1992. The time series of the quasar is nonstationary. The light variations are determined by a sequence of luminosity bursts, mostly regularly spaced in time and lasting up to 2 yr
Reply to the Editor—Mexiletine in myotonic dystrophy: Beware of ventricular arrhythmias!
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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