Phase-space structure analysis of self-gravitating collisionless spherical systems

In the mean field limit, isolated gravitational systems often evolve towards a steady state through a violent relaxation phase. One question is to understand the nature of this relaxation phase, in particular the role of radial instabilities in the establishment/destruction of the steady profile. Here, through a detailed phase-space analysis based both on a spherical Vlasov solver, a shell code and a $N$-body code, we revisit the evolution of collisionless self-gravitating spherical systems with initial power-law density profiles $\rho(r) \propto r^n$, $0 \leq n \leq -1.5$, and Gaussian velocity dispersion. Two sub-classes of models are considered, with initial virial ratios $\eta=0.5$ ("warm") and $\eta=0.1$ ("cool"). Thanks to the numerical techniques used and the high resolution of the simulations, our numerical analyses are able, for the first time, to show the clear separation between two or three well known dynamical phases: (i) the establishment of a spherical quasi-steady state through a violent relaxation phase during which the phase-space density displays a smooth spiral structure presenting a morphology consistent with predictions from self-similar dynamics, (ii) a quasi-steady state phase during which radial instabilities can take place at small scales and destroy the spiral structure but do not change quantitatively the properties of the phase-space distribution at the coarse grained level and (iii) relaxation to non spherical state due to radial orbit instabilities for $n \leq -1$ in the cool case.Comment: Accepted for publication in Astronomy and Astrophysics, 14 pages, 9 figure

mTOR-dependent translation amplifies microglia priming in aging mice.

peer reviewedMicroglia maintain homeostasis in the brain. However, with age, they become primed and respond more strongly to inflammatory stimuli. We show here that microglia from aged mice had upregulated mTOR complex 1 signaling controlling translation, as well as protein levels of inflammatory mediators. Genetic ablation of mTOR signaling showed a dual yet contrasting effect on microglia priming: it caused an NF-κB-dependent upregulation of priming genes at the mRNA level; however, mice displayed reduced cytokine protein levels, diminished microglia activation, and milder sickness behavior. The effect on translation was dependent on reduced phosphorylation of 4EBP1, resulting in decreased binding of eIF4E to eIF4G. Similar changes were present in aged human microglia and in damage-associated microglia, indicating that upregulation of mTOR-dependent translation is an essential aspect of microglia priming in aging and neurodegeneration

Stellar radial migration in discs: a quantification of churning and blurring

<p>Radial stellar migration in galactic discs has received much attention in studies of galactic dynamics and chemical evolution, but remains a dynamical phenomenon that needs to be fully quantified. We present results from Halle et al 2015 and extensions on the churning (change in angular momentum) and blurring (radial epicyclic oscillations) in simulations of bar-dominated discs, and we discuss the influence of radial migration on the dynamical heating of stellar discs.</p

Stellar Radial Migration In Galactic Discs

International audienceRadial migration in galactic discs has been more and more studied because of puzzling observations in the Milky Way or local galaxies. Numerical simulations show the migration depends on the parameters of non-axisymmetric patterns (bars or spiral arms). In particular, radial migration may not always be able to cause some observational features of the outer parts of discs. Its impact on the thickness of discs is also debated. We present some results of numerical simulations of isolated galactic discs. Radial migration is studied with respect to the location of the main resonances of the bar of these bar-dominated discs