A ~6 Mpc overdensity at z = 2.7 detected along a pair of quasar sight lines: filament or protocluster?

Simulations predict that gas in the intergalactic medium (IGM) is distributed in filamentary structures that connect dense galaxy clusters and form the cosmic web. These structures of predominantly ionized hydrogen are difficult to observe directly due to their lack of emitting regions. We serendipitously detected an overdensity of log N(HI) > 18.0 absorbers at z = 2.69 along the lines of sight toward a pair of background quasars. Three main absorption regions spanning ~2000 km/s (corresponding to 6.4 (h_70)^(-1) Mpc proper) are coincident in the two lines of sight, which are separated by ~90 (h_70)^(-1) kpc transverse proper distance. Two regions have [Fe/H] < -1.9 and correspond to mild overdensities in the IGM gas. The third region is a sub-DLA with [Fe/H] = -1.1 that is probably associated with a galaxy. We discuss the possibility that the lines of sight probe along the length of a filament or intercept a galaxy protocluster

Hypothesis: A Role for Fragile X Mental Retardation Protein in Mediating and Relieving MicroRNA-Guided Translational Repression?

MicroRNA (miRNA)-guided messenger RNA (mRNA) translational repression is believed to be mediated by effector miRNA-containing ribonucleoprotein (miRNP) complexes harboring fragile X mental retardation protein (FMRP). Recent studies documented the nucleic acid chaperone properties of FMRP and characterized its role and importance in RNA silencing in mammalian cells. We propose a model in which FMRP could facilitate miRNA assembly on target mRNAs in a process involving recognition of G quartet structures. Functioning within a duplex miRNP, FMRP may also mediate mRNA targeting through a strand exchange mechanism, in which the miRNA* of the duplex is swapped for the mRNA. Furthermore, FMRP may contribute to the relief of miRNA-guided mRNA repression through a reverse strand exchange reaction, possibly initiated by a specific cellular signal, that would liberate the mRNA for translation. Suboptimal utilization of miRNAs may thus account for some of the molecular defects in patients with the fragile X syndrome

Extended Lyα\alpha emission around quasars with eclipsing damped Lyα\alpha systems

We present spectroscopic observations of six high redshift ($z_{\rm em}$ $>$ 2) quasars, which have been selected for their Lyman $\alpha$ (Ly$\alpha$) emission region being only partially covered by a strong proximate ($z_{\rm abs}$ $\sim$ $z_{\rm em}$) coronagraphic damped Ly$\alpha$ system (DLA). We detected spatially extended Ly$\alpha$ emission envelopes surrounding these six quasars, with projected spatial extent in the range 26 $\le$ $d_{\rm Ly\alpha}$ $\le$ 51 kpc. No correlation is found between the quasar ionizing luminosity and the Ly$\alpha$ luminosity of their extended envelopes. This could be related to the limited covering factor of the extended gas and/or due to the AGN being obscured in other directions than towards the observer. Indeed, we find a strong correlation between the luminosity of the envelope and its spatial extent, which suggests that the envelopes are probably ionized by the AGN. The metallicity of the coronagraphic DLAs is low and varies in the range $-$1.75 $<$ [Si/H] $<$ $-$0.63. Highly ionized gas is observed to be associated with most of these DLAs, probably indicating ionization by the central AGN. One of these DLAs has the highest AlIII/SiII ratio ever reported for any intervening and/or proximate DLA. Most of these DLAs are redshifted with respect to the quasar, implying that they might represent infalling gas probably accreted onto the quasar host galaxies through filaments.Comment: Accepted for publication in MNRAS, 27 pages, 19 figures, 6 table

Les approches de la vulnérabilité alimentaire dans le sud de Madagascar

La vulnérabilité alimentaire peut être définie comme la probabilité pour un individu ou un groupe de voir sa sécurité alimentaire menacée par la survenue d'un événement climatique ou économique (sécheresse, chute des prix agricoles etc.) Les individus les plus vulnérables sont ceux qui ont une structure des capacités faible ou peu diversifiée. Cette analyse s'appuie sur une étude empirique de la région du Grand Sud de Madagascar, dont une partie est confrontée régulièrement à des difficultés alimentaires. L'objectif est de comparer les systèmes d'information actuellement en place dans la zone et leur apport dans l'approche par les capabilités. Les niveaux d'observation sont différents selon les méthodologies mises en oeuvre : on passe ainsi du niveau individuel (enquêtes ménages sur les observatoires ruraux) qui permet une approche micro-économique à une approche méso-économique à l'échelle de la commune ou de la région (système d'alerte précoce et enquête communautaire). L'analyse de l'articulation entre les différents niveaux permet de mettre en évidence les synergies et les complémentarités entre les différents systèmes d'information actuellement en place et qui sont destinés à améliorer l'efficacité des interventions de développement et la réduction de la vulnérabilité alimentaire. Food vulnerability can be defined as the probability an individual (or a household) of seeing a decreas its food security when faced with an event such drought. People who are most vulnerable are those who do not have enough capabilities to the risk of falling into chronic food insecurity. This paper describes an empirical analysis of food vulnerability in the South of Madagascar. This area is often facing drought and food security problems. Our aim is to compare three different surveys and their contribution to food vulnerability analysis, using the capability approach. Each survey has a different level of observation, corresponding to its own methodology. The ROR (rural observatories network) survey, which is a household survey can provide individual information allowing micro-economic approach. It is thus well adapted to capability approach. The SAP (early warning system) survey, which is a community survey, provides data on small geographical units, such as village or district. It is also suited for capability approach but better used for understanding social opportunities. In the end, one can see complementarity between different information systems for food vulnerability analysis capability approach, as in this study. (Full text in french)

Revue sur l’état actuel des connaissances des procédés utilisés pour l’élimination des cyanobactéries et cyanotoxines lors de la potabilisation des eaux

Les toxines cyanobactériennes sont des contaminants importants des écosystèmes aquatiques et constituent un risque pour la santé humaine. Les cyanobactéries peuvent libérer des toxines dans l’eau, particulièrement lors de la lyse des cellules qui se produit souvent au moment de leur passage à travers la filière conventionnelle de potabilisation des eaux. Dans cet article de revue de la littérature, les normes sur la qualité de l’eau concernant les toxines ainsi que les principales méthodes de détection des toxines sont d’abord présentées. Les méthodes d’élimination des cyanobactéries et des cyanotoxines sont ensuite décrites et leur performance discutée. Les procédés conventionnels présentés sont la coagulation/floculation, la clarification, la filtration sur sable, l’utilisation du charbon actif ainsi que l’oxydation chimique par chloration ou par le permanganate de potassium. Les méthodes alternatives présentement en développement pour optimiser les systèmes actuels de potabilisation des eaux ou remplacer les technologies conventionnelles trop peu efficaces pour l’élimination des polluants émergents (par ex., les procédés d’oxydation avancée et la filtration membranaire) sont également présentées. Des procédés conventionnels tels que la chloration peuvent s’avérer inadéquats, notamment par leur manque de fiabilité pour l’oxydation des cyanotoxines et par le risque encouru suite à la formation de sous-produits toxiques (par ex., les organochlorés). Des méthodes alternatives telles que la combinaison d’ozone et de peroxyde d’hydrogène permettent une oxydation fiable des cyanotoxines en assurant un effet rémanent à la sortie du contacteur. Ce type de traitement peut être facilement mis en oeuvre dans les usines de potabilisation des eaux possédant déjà une unité d’ozonation. L’utilisation du charbon actif, notamment sous forme de poudre, peut être efficace lors de contaminations ponctuelles par les fleurs d’eau de cyanobactéries. Ce document fait ainsi une synthèse de ces procédés chimiques, physiques ou physico-chimiques contribuant à l’élimination des cyanotoxines et des cyanobactéries lors de la potabilisation des eaux.Cyanobacterial toxins are important contaminants of aquatic ecosystems and present a risk for human health. Cyanobacteria can release toxins in water, particularly following cell lysis, which often happens during their passage through a conventional water treatment plant. In this literature review, water quality guidelines for the elimination of cyanotoxins and major detection methods of cyanotoxins are briefly presented. The processes used for cyanobacteria and cyanotoxin removal from drinking water are then reviewed and their performance discussed. The conventional methods presented are: coagulation/flocculation, clarification, sand filtration, activated carbon and chemical oxidation with chlorination or potassium permanganate. Alternative methods that are presently developed to enhance existing treatment plants or to replace conventional technologies that are less effective in removing emergent pollutants (e.g., advanced oxidation processes and membrane filtration) are also presented. Conventional methods such as chlorination can be inappropriate, notably because of their inability to fully oxidize cyanotoxins and the associated risk of formation of toxic by-products (e.g., organochlorinated compounds). Alternative methods such as the combination of ozone and hydrogen peroxide are more reliable to eliminate cyanotoxins, with a residual effect downstream from the treatment contactor. In addition, this type of treatment can be easily implemented in water treatment plants that are already using ozonation. The use of activated carbon, notably in the form of powder, can be efficient in the case of point contamination by cyanobacterial blooms. This document aims to synthesize these chemical, physical and physico-chemical methods to eliminate cyanotoxins and cyanobacteria during the treatment of drinking water

Fano Resonances in Mid-Infrared Spectra of Single-Walled Carbon Nanotubes

This work revisits the physics giving rise to the carbon nanotubes phonon bands in the mid- infrared. Our measurements of doped and undoped samples of single-walled carbon nanotubes in Fourier transform infrared spectroscopy show that the phonon bands exhibit an asymmetric lineshape and that their effective cross-section is enhanced upon doping. We relate these observations to electron-phonon coupling or, more specifically, to a Fano resonance phenomenon. We note that only the dopant-induced intraband continuum couples to the phonon modes and that defects induced in the sidewall increase the resonance probabilities.Comment: 5 pages, 4 figures and 1 Supplementary Information File (in pdf