Collège de France

About: Collège de France is a education organization based out in Paris, France. It is known for research contribution in the topics: Population & Dopamine. The organization has 6541 authors who have published 11983 publications receiving 648742 citations. The organization is also known as: College de France.

ALMA observations of molecular tori around massive black holes

Abstract: We report Atacama Large Millimeter/submillimeter Array (ALMA) observations of CO(3-2) emission in a sample of seven Seyfert/LINER galaxies at the unprecedented spatial resolution of 0 .″ 1 = 4-8 pc. Our aim is to explore the close environment of active galactic nuclei (AGN), and the dynamical structures leading to their fueling, through the morphology and kinematics of the gas inside the sphere of influence of the black hole. The selected galaxies host low-luminosity AGN and have a wide range of activity types (Seyferts 1 to 2, LINERs), and barred or ringed morphologies. The observed maps reveal the existence of circumnuclear disk structures, defined by their morphology and decoupled kinematics, in most of the sample. We call these structures molecular tori, even though they often appear as disks without holes in the center. They have varying orientations along the line of sight, unaligned with the host galaxy orientation. The radius of the tori ranges from 6 to 27 pc, and their mass from 0.7 × 10 7 to 3.9 × 10 7 M · . The most edge-on orientations of the torus correspond to obscured Seyferts. In only one case (NGC 1365), the AGN is centered on the central gas hole of the torus. On a larger scale, the gas is always piled up in a few resonant rings 100 pc in scale that play the role of a reservoir to fuel the nucleus. In some cases, a trailing spiral is observed inside the ring, providing evidence for feeding processes. More frequently, the torus and the AGN are slightly off-centered with respect to the bar-resonant ring position, implying that the black hole is wandering by a few 10 pc amplitude around the center of mass of the galaxy. Our spatial resolution allows us to measure gas velocities inside the sphere of influence of the central black holes. By fitting the observations with different simulated cubes, varying the torus inclination and the black hole mass, it is possible to estimate the mass of the central black hole, which is in general difficult for such late-type galaxies, with only a pseudo-bulge. In some cases, AGN feedback is revealed through a molecular outflow, which will be studied in detail in a subsequent article.

Control of arterial branching morphogenesis in embryogenesis: go with the flow.

Abstract: Formation of a properly branched vascular system during embryogenesis is crucial for embryo survival. Here we review the regulation of the morphogenesis of the arterial and venous system during embryogenesis. We show that in addition to deterministic patterning mechanisms and plasticity of endothelial cells, arterial-venous differentiation and branching morphogenesis involves a prominent role for blood flow. Based on in vivo observations of developing arteries, we identified a novel morphological event crucial for the morphogenesis of the arterial tree, disconnection of small side branches. This disconnection of side branches occurs exactly at the point of bifurcation. The rate of disconnection of side branches depends on flow velocity and branching angle. The balance between disconnection and maintenance of arterial side branches determines the number of side branches connected to a large artery. Based on these observations, we postulate that the number of pre-existing collaterals connected to a large artery is a function of the disconnection process and can be regulated by hemodynamics. We furthermore show that embryonic arteries already adapt their lumen diameter to the amount of flow carried. Taken together, we suggest that hemodynamics plays a pivotal role in shaping the arterial system. We suggest that flow-evoked remodeling processes determine the number of preexisting collaterals during critical periods of embryo-fetal development. Insight into these basic principles of arterial growth and branching during embryogenesis may aid to understanding the observed variability in the capacity to establish a collateral circulation in patients with ischemic diseases and finding new strategies for therapeutic arteriogenesis.

The cohomological equation for Roth-type interval exchange maps

Abstract: 0. Introduction 0.1. Interval exchange maps 0.2. The cohomological equation 0.3. Summary of the contents 1. The continued fraction algorithm for interval exchange maps 1.1. Interval exchange maps 1.2. The continued fraction algorithm 1.3. Roth-type interval exchange maps 2. The cohomological equation 2.1. The theorem of Gottschalk and Hedlund 2.2. Special Birkhoff sums 2.3. Estimates for functions of bounded variation 2.4. Primitives of functions of bounded variation 3. Suspensions of interval exchange maps 3.1. Suspension data 3.2. Construction of a Riemann surface 3.3. Compactification of M∗ ζ 3.4. The cohomological equation for higher smoothness 4. Proof of full measure for Roth type 4.1. The basic operation of the algorithm for suspensions 4.2. The Teichmuller flow 4.3. The absolutely continuous invariant measure 4.4. Integrability of log ‖Z(1)‖ 4.5. Conditions (b) and (c) have full measure 4.6. The main step 4.7. Condition (a) has full measure 4.8. Proof of the proposition Appendix A. Roth-type conditions in a concrete family of interval exchange maps Appendix B. A nonuniquely ergodic interval exchange map satisfying condition (a)