10 research outputs found
Tides in colliding galaxies
Long tails and streams of stars are the most noticeable upshots of galaxy
collisions. Their origin as gravitational, tidal, disturbances has however been
recognized only less than fifty years ago and more than ten years after their
first observations. This Review describes how the idea of galactic tides
emerged, in particular thanks to the advances in numerical simulations, from
the first ones that included tens of particles to the most sophisticated ones
with tens of millions of them and state-of-the-art hydrodynamical
prescriptions. Theoretical aspects pertaining to the formation of tidal tails
are then presented. The third part of the review turns to observations and
underlines the need for collecting deep multi-wavelength data to tackle the
variety of physical processes exhibited by collisional debris. Tidal tails are
not just stellar structures, but turn out to contain all the components usually
found in galactic disks, in particular atomic / molecular gas and dust. They
host star-forming complexes and are able to form star-clusters or even
second-generation dwarf galaxies. The final part of the review discusses what
tidal tails can tell us (or not) about the structure and content of present-day
galaxies, including their dark components, and explains how tidal tails may be
used to probe the past evolution of galaxies and their mass assembly history.
On-going deep wide-field surveys disclose many new low-surface brightness
structures in the nearby Universe, offering great opportunities for attempting
galactic archeology with tidal tails.Comment: 46 pages, 13 figures, Review to be published in "Tidal effects in
Astronomy and Astrophysics", Lecture Notes in Physics. Comments are most
welcom
GaNAsSb : How does it compare with other dilute III-V nitride alloys ?
International audienceGrowth and properties of GaNAsSb alloys are investigated and compared with those of other dilute III-N-V alloys. Similar properties are observed including very high bandgap bowing, carrier localization at low temperature, sensitivity to thermal annealing and passivation of N-related electronic states by hydrogen. On the other hand, we point out some features of this alloy system and evaluate its potential for device applications. Probably, GaNAsSb can achieve emission at longer wavelengths than GaInNAs alloys grown to date. Its conduction- and valence-band offsets can be independently tuned by adjusting the N and Sb composition, respectively. Since this compound has a single group III element, its electronic structure should be less dependent on alloy configuration than GaInNAs
De la ville a la megapole : essor ou declin des villes au XXIe siecle
SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : RP 14840 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
Acidentes quĂmicos ampliados: um desafio para a saĂșde pĂșblica The increase in chemical accidents: a challenge for public health
Os acidentes envolvendo substĂąncias perigosas nas atividades de transporte, armazenamento e produção industrial de produtos quĂmicos constituem um sĂ©rio risco Ă saĂșde e ao meio ambiente. Objetiva-se discutir, no Ăąmbito da saĂșde pĂșblica, alguns dos desafios que esses tipos de acidentes colocam, principalmente para os paĂses de economia perifĂ©rica. AtravĂ©s da combinação de informaçÔes quantitativas e qualitativas, foram definidos e caracterizados esses tipos de acidentes e seus diversos riscos. Esses acidentes tĂȘm se apresentado com a maior gravidade nos paĂses de economia perifĂ©rica, embora a maioria deles venha ocorrendo sem o adequado registro de informaçÔes bĂĄsicas para a avaliação e vigilĂąncia, como Ă© demonstrado no caso do Rio de Janeiro (Brasil). AlĂ©m da tarefa de se avaliar as conseqĂŒĂȘncias de eventos, por vezes extremamente complexos, coloca-se tambĂ©m, a de formular estratĂ©gias de controle e prevenção em realidades sociais que configuram um terreno fĂ©rtil para a ocorrĂȘncia e agravamento dos mesmos.<br>Chemical accidents involving explosions, large fires and leakages of hazardous substances occuring during transport, storage and industrial production of chemicals constitute a real challeng to health, environmental and industrial safety professionals. The aim of this article is to discuss the main questions that this kind of accident provokes, in terms of public helth, particularly in developing countries such as Brazil. The paper defines and characterises these accidents and the various health risk they involve excluding the leakages of hazardous substances during "normal" production in industry - through the combination of quantitative and qualitative information drawn from the international literature on the subject. From some examples of chemical accidents such as occurred in Bophal (Ăndia), Vila SocĂł (Brazil), SĂŁo Paulo (MĂ©xico) and data of the World Health Organization (WHO), the authors seek to show that these events present a worsening, in terms of immediate deaths and injuries, in developing countries. The statistics of chemical accidents which occurred during the last ten years (1984 to 1993) in the State of Rio de Janeiro are used taken as a frame reference for the purpose of bringing to light the great number of occurrences made with no registration of basic information regarding assessment or surveillance. The complexity of causes and consequences, together with the structural problems of developing countries, present public health professionals and institutions, with some important tasks especially those os health risk assessment and the formulation of strategies to prevent and control future major chemical accidents