4,189 research outputs found
Gravitational signals emitted by a point mass orbiting a neutron star: a perturbative approach
No full textWe compute the energy spectra of the gravitational signals emitted when a pointlike mass moves on a closed orbit around a nonrotating neutron star, inducing a perturbation of its gravitational field and its internal structure. The Einstein equations and the hydrodynamical equations are perturbed and numerically integrated in the frequency domain. The results are compared with the energy spectra computed by the quadrupole formalism which assumes that both masses are pointlike, and accounts only for the radiation emitted because the orbital motion produces a time dependent quadrupole moment. The results of our perturbative approach show that, in general, the quadrupole formalism overestimates the amount of emitted radiation, especially when the two masses are close. However, if the pointlike mass is allowed to move on an orbit so tight that the Keplerian orbital frequency resonates with the frequency of the fundamental quasinormal mode of the star (2ωK=ωf), this mode can be excited and the emitted radiation can be considerably larger than that computed by the quadrupole approach
Le «buone letture». 2. Giovanni Casati
No full textIl saggio è costituito da due parti, la prima delle quali, dedicata alla fondazione della Federazione italiana delle biblioteche circolanti cattoliche, è stata pubblicata nel precedente numero dei «Nuovi Annali», XXVII (2013), pp. 137-163. In questa seconda parte viene delineata la figura intellettuale di Giovanni Casati, che diresse la «Rivista di letture» dal 1912 al 1944, trasformando il periodico della Federazione in una rivista impegnata nella divulgazione della cultura cattolica. A questo impegno militante Casati fece corrispondere un intenso programma editoriale, che trovò espressione nella pubblicazione di saggi letterari, di manuali e opere repertoriali.The study consists of two parts; the first is dedicated to the history of the Federazione italiana delle biblioteche circolanti cattoliche since its foundation (1904) up to 1912 and was published in the previous volume of the «Nuovi Annali », XXVII (2013), pp. 137-163. In this second part, the author outlines the intellectual figure of Giovanni Casati, who directed the «Rivista di letture» from 1912 to 1944, transforming the magazine of the Federation in a journal engaged in the spreading of Catholic culture. To this militant engagement Casati matched an intense publishing program, which found its expression in the publication of literary essays, manuals and reference works
Comico e tragico del diritto nella novellistica italiana: il novelliere di Giovanni Sercambi
No full textNelle novelle di età tardomedievale ed umanistica, a causa del loro carattere fortemente realistico, il diritto ha un posto importante, poiché rappresenta un elemento centrale e ineliminabile della vita della comunità. Il novelliere di Giovanni Sercambi da Lucca non fa eccezione, anche se l’autore non ha una cultura giuridica né s’interessa in modo specifico al diritto. Il presente saggio vuole analizzare sotto tale profilo queste novelle per verificare quale concezione del diritto emerge da esse e come la narrazione ne risulti arricchita.In the late medieval and humanistic novellas, owing to their very realistic character, the right is an important central and inevitable element in community life. Giovanni Sercambi’s novelliere is no exception even if the author lacks a legal culture, nor is specifically interested in right. This essay intends to analyze these novellas under this profile to verify what kind of right they consider and how the stories are enriched
Investigating the Complex X-Ray Spectrum of a Broad-Line 2MASS Red Quasar: XMM-Newton Observation of FTM 0830+3759
No full textBird presence vegetation complexity data in Melbourne, Australia. Data created in 2018 by Giovanni Carrabs.
No full textBird presence and vegetation complexity data from Melbourne, Australia. Data created for a university thesis project and publication in 2018. Author: Giovanni Carrabs.</p
Non-radial oscillation modes as a probe of density discontinuities in neutron stars
No full textA phase transition occurring in the inner core of a neutron star could be associated with a density discontinuity that would affect the frequency spectrum of the non-radial oscillation modes in two ways. First, it would produce a softening of the equation of state, leading to more compact equilibrium configurations and changing the frequency of the fundamental and pressure modes of the neutron star. Secondly, a new non-zero frequency g mode would appear, associated with each discontinuity. These discontinuity g modes have typical frequencies larger than those of g modes previously studied in the literature (thermal, core g modes or g modes caused by chemical inhomogeneities in the outer layers), and smaller than that of the fundamental mode; therefore they should be distinguishable from the other modes of non-radial oscillation. In this paper we investigate how high-density discontinuities change the frequency spectrum of the non-radial oscillations, within the framework of the general relativistic theory of stellar perturbations. Our purpose is to understand whether a gravitational signal, emitted at the frequencies of the quasi-normal modes, may give some clear information on the equation of state of the neutron star and, in particular, on the parameters that characterize the density discontinuity. We discuss some astrophysical processes that may be associated with the excitation of these modes, and estimate how much gravitational energy should the modes convey to produce a signal detectable by high-frequency gravitational detectors
Are post-Newtonian templates faithful and effectual in detecting gravitational signals from neutron star binaries?
No full textWe compute the overlap function between post-Newtonian (PN) templates and gravitational signals emitted by binary systems composed of one neutron star and one point mass, obtained by a perturbative approach. The calculations are performed for different stellar models and for different detectors, to estimate how effectual and faithful the PN templates are, and to establish whether effects related to the internal structure of neutron stars may possibly be extracted by the matched filtering technique. © 2002 The American Physical Society
Gravitational signals emitted by a point mass orbiting a neutron star: Effects of stellar structure
No full textThe effects that the structure of a neutron star would have on the gravitational emission of a binary system are studied in a perturbative regime, and in the frequency domain. Assuming that a neutron star is perturbed by a point mass moving on a close, circular orbit, we solve the equations of stellar perturbations in general relativity to evaluate the energy lost by the system in gravitational waves. We compare the energy output obtained for different stellar models with that found by assuming that the perturbed object is a black hole with the same mass, and we discuss the role played by the excitation of the stellar modes. Our results indicate that the stellar structure begins to affect the emitted power when the orbital velocity is vgreater than or similar to0.2 c (nu(GW)greater than or similar to185 Hz for a binary system composed of two 1.4M neutron stars). We show that the differences between different stellar models and a black hole are due mainly to the excitation of the quasinormal modes of the star. Finally, we discuss to what extent and up to which distance the perturbative approach can be used to describe the interaction of a star and a pointlike massive body
Chapter Atto biografo di Giovanni Gualberto
No full textThe paper examines the Vita s. Iohannis Gualberti by Atto, reconstructing its genesis and fortune. Probably the author wrote this hagiography when he was abbot and before becoming bishop of Pistoia. He re-elaborated the Life of the saint by Andrea of Strumi, adapting it to a changed historical and ecclesiastical context. The text was successful among the Vallombrosan Order and it was used by later hagiographers to create epitomes and rewritings of the Life of Giovanni Gualberto
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