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Adaptive mesh refinement simulations of collisional ring galaxies: effects of the interaction geometry.
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Dynamics of massive stellar black holes in young star clusters and the displacement of ultra-luminous X-ray sources
No full textAdaptive mesh refinement simulations of collisional ring galaxies: effects of the interaction geometry
Full text linkCollisional ring galaxies are the outcome of nearly axisymmetric high-speed encounters between a disc and an intruder galaxy. We investigate the properties of collisional ring galaxies as a function of the impact parameter, the initial relative velocity and the inclination angle. We employ new adaptive mesh refinement simulations to trace the evolution with time of both stars and gas, taking into account star formation and supernova feedback. Axisymmetric encounters produce circular primary rings followed by smaller secondary rings, while off-centre interactions produce asymmetric rings with displaced nuclei. We propose an analytical treatment of the disc warping induced by an inclination angle greater than zero. The star formation history of our models is mainly influenced by the impact parameter: axisymmetric collisions induce impulsive short-lived starburst episodes, whereas off-centre encounters produce long-lived star formation. We compute synthetic colour maps of our models and we find that rings have a B - V colour typically ˜0.2 mag bluer than the inner and outer disc, in agreement with observations
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
The Detection of Gravitational Waves
No full textThe detection of gravitational waves is challenging researchers since half a century. The relative precision required, , is difficult to imagine, this is the diameter of a proton over several km, using masses of tens of kg, or picometers over millions of km. A theoretical description of gravitational radiation and of its effects on matter, all consequence of the General theory of Relativity, is given. Then the astrophysical phenomena that are candidates for gravitational wave emission are discussed, considering also amplitudes and rates. The binary neutron star system PSR1913+16, which provided in 1975 the first evidence for energy loss by gravitational radiation, is briefly discussed. Then comes a description of the experimental developments, starting with ground based interferometers, their working principles and their most important sources of noise. The Earth wide network that is being built describes how these instruments will be used in the observation era. Several other detection techniques, space interferometry, pulsar timing arrays and resonant detectors, covering different bands of the gravitational wave frequency spectrum complete these lectures
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