Istituto Universitario Di Studi Superiori Di Pavia

About: Istituto Universitario Di Studi Superiori Di Pavia is a education organization based out in Pavia, Italy. It is known for research contribution in the topics: Pulsar & Neutron star. The organization has 162 authors who have published 566 publications receiving 22605 citations.

Discovery of a compact companion to the hot subdwarf star bd +37° 442

Abstract: We report the results of the first X-ray observation of the luminous and helium-rich O-type subdwarf BD +37 Degree-Sign 442 carried out with the XMM-Newton satellite in 2011 August. X-ray emission is detected with a flux of about 3 Multiplication-Sign 10{sup -14} erg cm{sup -2} s{sup -1} (0.2-1 keV) and a very soft spectrum, well fit by the sum of a blackbody with temperature kT{sub BB} = 45{sup +11}{sub -9} eV, and a power law with a poorly constrained photon index. Significant pulsations with a period of 19.2 s are detected, indicating that the X-ray emission originates in a white dwarf or neutron star companion, most likely powered by accretion from the wind of BD +37 Degree-Sign 442.

Traffic, crowds, and swarms

Abstract: The interest in complex systems, namely systems of several individuals interacting in a nonlinear manner, has seen, in recent years, a remarkable increase. Their collective behavior is difficult to be understood and the model is based only on the description of the dynamics of a few individual entities. This interest is due to a raising awareness that many systems in nature are of this kind and that cannot be successfully modelled by traditional methods used for systems of the inert matter. Moreover, an increasing number of applications in technology, economy, and social sciences resemble such systems, given the high number of elements and the complex interactions among them. See for instance in fields such as transportation and communication networks, or social and economics interchanges. This special issue is devoted to modelling and simulation of the dynamics of crowds, swarms, and vehicular traffic on roads and networks of roads. The contributions are focused on the study of complex systems, where the overall dynamics is determined by individual interactions, while modelling of individual dynamics does not straightforwardly lead to the mathematical description of the collective dynamics. As known, different representations and related mathematical modelling approaches can be developed corresponding to the microscopic and macroscopic scales. Moreover, the statistical representation over the microscopic state delivered by suitable generalizations of the mathematical kinetic theory or by master equation methods for multi-agent systems are often used. It is also well understood that none of the above representations is fully appropriate considering that the number of interacting entities in crowds, swarms, and vehicular traffic is not large enough to justify either the continuum mechanics approximation, namely at the macroscopic scale, or the statistical representation

Fiber-Section Model with an Exact Shear Strain Profile for Two-Dimensional RC Frame Structures

Abstract: A fiber-section model for nonlinear analysis of shear-critical reinforced concrete frames is developed. The model incorporates a new procedure for the computation of an exact shear strain p...

X-ray emission from the luminous O-type subdwarf HD 49798 and its compact companion

Abstract: The X-ray source RX J0648.0-4418 is the only confirmed binary system in which a compact object, most likely a massive white dwarf, accretes from a hot subdwarf companion, the bright sdO star HD 49798. The X-ray emission from this system is characterized by two periodic modulations caused by an eclipse, at the orbital period of 1.55 d, and by the rotation of the compact object with a spin period of 13.2 s. In 2011 we obtained six short XMM-Newton observations centered at orbital phase 0.75, in order to study the system during the eclipse, and spaced at increasingly long time intervals in order to obtain an accurate measure of the spin-period evolution through phase-connected timing. The duration of the eclipse ingress and egress, 500 s, indicates the presence of an X-ray emitting region with dimensions of the order of a few 10^4 km, surrounding the pulsar and probably due to scattering in the companion's wind. We derived an upper limit on the spin-period derivative |Pdot|<6x10^-15 s/s, more than two orders of magnitude smaller than the previously available value. Significant X-ray emission is detected also during the 1.2 hours-long eclipse, with a luminosity of about 3x10^30 erg/s. The eclipse spectrum shows prominent emission lines of H- and He-like nitrogen, an overabundant element in HD 49798. These findings support the suggestion that the X-ray emission observed during the eclipse originates in HD 49798 and that the processes responsible for X-ray emission in the stellar winds of massive O stars are also at work in the much weaker winds of hot subdwarfs.