1,721,129 research outputs found
Fourth Italian-Pakistani Workshop on Relativistic Astrophysics
No full textIl Workshop, tenutosi dal 15 al 17 febbraio 2013 presso il Rettorato della National University of Sciences and Technology, Islamabad, Pakistan ha visto la partecipazione di olltre sessantta scienziati da Italia, Pakistan, Uzbekistan, Russia, Svizzera, Germania, Iran. Gli atti sono in via di pubblicazione sul numero di luglio 2014 di Physica Scripta (Eds. F. De Paolis, A.A. Siddiqui, A. Qadir)
Second Italian-Pakistani Workshop on Relativistic Astrophysics
No full textIl Workshop, tenutosi dall'8 al 10 luglio 2009 al centro ICRANet di Pescara, ha visto la partecipazione di oltre quaranta scienziati da Italia, Pakistan, Svizzera, Nuova Zelanda, Corea del Sud, Messico, Russia, Brasile, Stati Uniti. Gli atti sono stati pubblicati in General Relativity and Gravitation, Vol. 43, pag. 929-1202, 2011 (Eds. F. De Paolis, G.F.R. Ellis, A. Qadir, R. Ruffini). Per ulteriori informazioni si veda il sito http://www.fisica.unisalento.it/iwra/2009
Radiation from fast rotating neutron stars
No full textThe radiation field of an arbitrarily fast rotating magnetic star is investigated, using the 4-vector formalism in the Deutsch analysis, for a two-fold purpose. The first is to verify that the radiation field of an arbitrarily fast rotating magnetic dipole, obtained by Belinsky et al, corresponds to a relativistically corrected expression for the Deutsch analysis. The second is to investigate the differences between the radiation fields of a fast rotating magnetic dipole and Deutsch star
Collapsed white dwarfs as gamma-ray bursts sources
No full textIt has been suggested by Usov (1992) that accreting white dwarfs, collapsing
to neutron stars may be the sources of the gamma-ray bursts observed at cosmological
distances, provided they rotate very fast and have enormously high magnetic fields. In this
model the burst's duration r is given by the ratio of pulsar kinetic energy and magneticdipole
luminosity, so that in order to account for the shortest (r ,,~ 0.1 s) bursts, the pulsars
must rotate very fast (with period P ,-~ 0.5 ms) and have magnetic fields of 1016 - 101T
G. Though the high pulsar frequency was anticipated (Qadir and Rafique, 1986) and has
been shown to be plausible (Abramowicz, 1990), the extremely high magnetic fields seem
anomalous as observed neutron stars have fields below ~ 1013 G.
The problem with Usov's proposal is reduced by incorporating the relativistic corrections
for fast rotating magnetic dipoles (Belinsky et al., 1994) or magnetic stars (De Paolis
and Qadir, 1994). These corrections substantially enhance the radiation efficiency due
to the existence of a magnetic synchrotron effect so that the magnetic field required for
the explanation of the shortest gamma-ray bursts is strongly reduced. As such the model
becomes much more plausible
Black Holes in Bulk Viscous Cosmology
No full textWe investigate the effects of the accretion of phantom energy with non-zero bulk viscosity onto a Schwarzschild black hole and show that black holes accreting viscous phantom energy will lose mass rapidly compared to the non-viscous case. When matter is incorporated along with the phantom energy, the black holes meet with the same fate as bulk viscous forces dominate matter accretion. If the phantom energy has large bulk viscosity, then the mass of the black hole will reduce faster than in the small viscosity case
The Multipole Expansion of the Radiation Field from a Relativistically Rotating Oblique Magnetic Dipole
No full textUsing the methods of Haxton and Ruffini the multipole expansion of the radiation field of an arbitrarily fast rotating magnetic dipole, with its axis inclined relative to the rotation axis, is obtained. This result is compared with the Fourier decomposition of the radiation emitted by the rotating dipole, obtained by Belinskyet al
Editorial on the special issue: Selected papers from the 2nd Joint Italian-Pakistani Workshop on Relativistic Astrophysics
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Going 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
A note on electromagnetic fields of a slowly rotating magnetized neutron star
No full textUsing the electromagnetic fields of an aligned rotating magnetic dipole in a Schwarzschild background, the fields and the surface and bulk charge densities had been computed for an obliquely rotating dipole by De Paolis, Qadir and Tarman (Nuovo Cimento B, 114 (1999) 11). Rezzolla, Ahmedov and Miller (Mon. Not. R. Astron. Soc., 322 (2001) 723) had argued that the analysis was not valid as the Kerr background should have been used. As such the charge density and fields obtained earlier needed to be recomputed using their analysis. This suggestion has been followed here
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