Michel Agier, Aux bords du monde, les réfugiés

En 1950, il y avait dans le monde un million de réfugiés. Ils sont aujourd’hui cinquante millions de déportés, déplacés, refoulés, déguerpis, « victimes de déplacements forcés », selon la définition du Haut Comité aux réfugiés ; ils ont fui les nombreux conflits locaux au centre de l’actualité internationale depuis plusieurs décennies. La liste de ces populations meurtries semble ne jamais pouvoir se clore et ne fait même que s’allonger au fil du temps : Palestiniens, Somaliens, Soudanais, Tc..

Michel Agier, L’Invention de la ville. Banlieue, township, invasions et favelas

Depuis plusieurs décennies, les spécialistes du monde urbain, qu’ils soient acteurs ou chercheurs, constatent une dégradation persistante du tissu des relations sociales dans les villes des sociétés occidentalisées. D’un côté, la ségrégation et l’exclusion y prennent des formes de plus en plus marquées. De l’autre, la modernisation des moyens de transport et de communication mettent à mal les formes de convivialité dont la ville historique était supposée être le lieu privilégié. Quant aux agg..

Wiktor Stoczkowski, Des hommes, des dieux et des extraterrestres. Ethnologie d’une croyance moderne

Voici un ouvrage qui nous fait entrer de plain-pied dans une subculture contemporaine généralement perçue comme marginale et qui s’avère pourtant être d’une importance sociale considérable. Il s’agit de l’univers, exotique s’il en est, des parasciences et de la pensée occultiste. Le lecteur curieux y trouvera un ensemble de développements remarquablement bien documentés et ordonnés sur un certain nombre de sujets et de thèmes liés à cette pensée contemporaine dont les ramifications tentaculai..

Michel Agier, L’Invention de la ville. Banlieue, township, invasions et favelas

Depuis plusieurs décennies, les spécialistes du monde urbain, qu’ils soient acteurs ou chercheurs, constatent une dégradation persistante du tissu des relations sociales dans les villes des sociétés occidentalisées. D’un côté, la ségrégation et l’exclusion y prennent des formes de plus en plus marquées. De l’autre, la modernisation des moyens de transport et de communication mettent à mal les formes de convivialité dont la ville historique était supposée être le lieu privilégié. Quant aux agg..

Thermal Shadows and Compositional Structure in Comet Nuclei

We use a fully 3-dimensional thermal evolution model to examine the effects of a non-uniform surface albedo on the subsurface thermal structure of comets. Surface albedo markings cast "thermal shadows", with strong lateral thermal gradients. Corresponding compositional gradients can be strong, especially if the crystallization of amorphous water ice is triggered in the hottest regions. We show that the spatial extent of the structure depends mainly on the obliquity, ther- mal conductivity and heliocentric distance. In some circumstances, subsurface structure caused by the thermal shadows of surface features can be maintained for more than 10 Myr, the median transport time from the Kuiper Belt to the inner solar system. Non-uniform compositional structure can be an evolutionary product and does not necessarily imply that comets consist of building blocks accumulated in different regions of the protoplanetary disk.Comment: Accepted in Ap

Thermal processing of Jupiter Family Comets during their chaotic orbital evolution

Evidence for cometary activity beyond Jupiter and Saturn's orbits -- such as that observed for Centaurs and long period comets -- suggests that the thermal processing of comet nuclei starts long before they enter the inner Solar System, where they are typically observed and monitored. Such observations raise questions as to the depth of unprocessed material, and whether the activity of JFCs can be representative of any primitive material. Here we model the coupled thermal and dynamical evolution of Jupiter Family Comets (JFCs), from the moment they leave their outer Solar System reservoirs until their ejection into interstellar space. We apply a thermal evolution model to a sample of simulated JFCs obtained from dynamical simulations (arXiv:1706.07447) that successfully reproduce the orbital distribution of observed JFCs. We show that due to the stochastic nature of comet trajectories toward the inner solar system, all simulated JFCs undergo multiple heating episodes resulting in significant modifications of their initial volatile contents. A statistical analysis constrains the extent of such processing. We suggest that primordial condensed hypervolatile ices should be entirely lost from the layers that contribute to cometary activity observed today. Our results demonstrate that understanding the orbital (and thus, heating) history of JFCs is essential when putting observations in a broader context.Comment: 30 pages, 10 figures, to be published in Ap

The Sources of HCN and CH3OH and the Rotational Temperature in Comet 103P/Hartley 2 from Time-Resolved Millimeter Spectroscopy

One of the least understood properties of comets is the compositional structure of their nuclei, which can either be homogeneous or heterogeneous. The nucleus structure can be conveniently studied at millimeter wavelengths, using velocity-resolved spectral time series of the emission lines, obtained simultaneously for multiple molecules as the body rotates. Using this technique, we investigated the sources of CH3OH and HCN in comet 103P/Hartley 2, the target of NASA's EPOXI mission, which had an exceptionally favorable apparition in late 2010. Our monitoring with the IRAM 30 m telescope shows short-term variability of the spectral lines caused by nucleus rotation. The varying production rates generate changes in brightness by a factor of 4 for HCN and by a factor of 2 for CH3OH, and they are remarkably well correlated in time. With the addition of the velocity information from the line profiles, we identify the main sources of outgassing: two jets, oppositely directed in a radial sense, and icy grains, injected into the coma primarily through one of the jets. The mixing ratio of CH3OH and HCN is dramatically different in the two jets, which evidently shows large-scale chemical heterogeneity of the nucleus. We propose a network of identities linking the two jets with morphological features reported elsewhere, and postulate that the chemical heterogeneity may result from thermal evolution. The model-dependent average production rates are 3.5x10**26 molec/s for CH3OH and 1.25x10**25 molec/s for HCN, and their ratio of 28 is rather high but not abnormal. The rotational temperature from CH3OH varied strongly, presumably due to nucleus rotation, with the average value being 47 K.Comment: Published in ApJ 756, 80 (2012). Supplementary materials available at http://www.its.caltech.edu/~mdrahus/103p_paperII.htm

Pediatric Pneumococcal Serotypes in 4 European Countries

TOC Summary: Non–heptavalent pneumococcal conjugate vaccine serotypes have increased in Spain, France, Belgium, and England and Wales

Limits to Ice on Asteroids (24) Themis and (65) Cybele

We present optical spectra of (24) Themis and (65) Cybele, two large main-belt asteroids on which exposed water ice has recently been reported. No emission lines, expected from resonance fluorescence in gas sublimated from the ice, were detected. Derived limits to the production rates of water are < 400 kg/s (5{\sigma}), for each object, assuming a cometary H2O/CN ratio. We rule out models in which a large fraction of the surface is occupied by high albedo ("fresh") water ice because the measured albedos of Themis and Cybele are low (0.05 - 0.07). We also rule out models in which a large fraction of the surface is occupied by low albedo ("dirty") water ice because dirty ice would be warm, and would sublimate strongly enough for gaseous products to have been detected. If ice exists on these bodies it must be relatively clean (albedo >0.3) and confined to a fraction of the Earth-facing surface <10%. By analogy with impacted asteroid (596) Scheila, we propose an impact excavation scenario, in which 10 m scale projectiles have exposed buried ice. If the ice is even more reflective (albedo >0.6) then the timescale for sublimation of an optically thick layer can rival the 10^3 yr interval between impacts with bodies this size. In this sense, exposure by impact may be a quasi steady-state feature of ice-containing asteroids at 3 AU

The Active Asteroids

Some asteroids eject dust, unexpectedly producing transient, comet-like comae and tails. First ascribed to the sublimation of near-surface water ice, mass losing asteroids (also called "main-belt comets") can in fact be driven by a surprising diversity of mechanisms. In this paper, we consider eleven dynamical asteroids losing mass, in nine of which the ejected material is spatially resolved. We address mechanisms for producing mass loss including rotational instability, impact ejection, electrostatic repulsion, radiation pressure sweeping, dehydration stresses and thermal fracture, in addition to the sublimation of ice. In two objects (133P and 238P) the repetitive nature of the observed activity leaves ice sublimation as the only reasonable explanation while, in a third ((596) Scheila), a recent impact is the cause. Another impact may account for activity in P/2010 A2 but this tiny object can also be explained as having shed mass after reaching rotational instability. Mass loss from (3200) Phaethon is probably due to cracking or dehydration at extreme (~1000 K) perihelion temperatures, perhaps aided by radiation pressure sweeping. For the other bodies, the mass loss mechanisms remain unidentified, pending the acquisition of more and better data. While the active asteroid sample size remains small, the evidence for an astonishing diversity of mass loss processes in these bodies is clear.Comment: 42, pages, 9 figures, The Astronomical Journal, in pres