Star Formation and Dynamics in the Galactic Centre

The centre of our Galaxy is one of the most studied and yet enigmatic places in the Universe. At a distance of about 8 kpc from our Sun, the Galactic centre (GC) is the ideal environment to study the extreme processes that take place in the vicinity of a supermassive black hole (SMBH). Despite the hostile environment, several tens of early-type stars populate the central parsec of our Galaxy. A fraction of them lie in a thin ring with mild eccentricity and inner radius ~0.04 pc, while the S-stars, i.e. the ~30 stars closest to the SMBH (<0.04 pc), have randomly oriented and highly eccentric orbits. The formation of such early-type stars has been a puzzle for a long time: molecular clouds should be tidally disrupted by the SMBH before they can fragment into stars. We review the main scenarios proposed to explain the formation and the dynamical evolution of the early-type stars in the GC. In particular, we discuss the most popular in situ scenarios (accretion disc fragmentation and molecular cloud disruption) and migration scenarios (star cluster inspiral and Hills mechanism). We focus on the most pressing challenges that must be faced to shed light on the process of star formation in the vicinity of a SMBH.Comment: 68 pages, 35 figures; invited review chapter, to be published in expanded form in Haardt, F., Gorini, V., Moschella, U. and Treves, A., 'Astrophysical Black Holes'. Lecture Notes in Physics. Springer 201

Immediate postoperative retention of visual discriminations following selective cortical lesions in the cat

Cats were trained preoperatively for brightness discrimination and 7 pattern and form discriminations and then retested for preoperative retention. Cortical lesions were then placed in Areas 17 and 18 in Group 1 (4 cats); in Areas 17, 18, and 19 in Group 2 (3 cats); and in the suprasylvian cortex in Group 3 (4 cats). Results are also reported for Group 4 with extensive suprasylvian lesions and an unintended undercutting of Areas 17 and 18 (4 cats). Ss in Group 1 behaved as though they could immediately recognize the discriminative stimuli as efficiently as before. Group 2 Ss showed a substantial postoperative loss of all discriminations. In Group 3, postoperative retention was also generally impaired, but the reacquisition of efficient performance was superior to that of the previous group. Lesions suffered by Group 4 proved disruptive for all discriminative capacities, both in retention and in relearning. The excellent retention of all discriminations following Areas 17 and 18 lesions shows that these areas are not essential for complex vision in the cat. Results also indicate that the high-level visual capacities of destriate cats are not due to reorganization of readaptation processes occurring in extrastriate areas after a 17/18 removal. The retention deficits that were present in cats with cortical lesions more extensive than Areas 17 and 18 or outside of the latter areas prove the essential participation of extrastriate cortical areas in visual discrimination. (42 ref) (PsycLIT Database Copyright 1986 American Psychological Assn, all rights reserved

Management of contamination risks in rose cultures using recycled effluents

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Les bases du recyclage : maitrise du risque pathologique

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Fleurs coupées : la désinfection des solutions nutritives un effet positif

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La désinfection des eaux de drainage

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Recyclage des eaux de drainage en culture hors-sol : prise en compte du risque pathologique

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