Dynamics of dikes versus cone sheets in volcanic systems

International audienceIgneous sheet intrusions of various shapes, such as dikes and cone sheets, coexist as parts of complex volcanic plumbing systems likely fed by common sources. How they form is fundamental regarding volcanic hazards, yet no dynamic model simulates and predicts satisfactorily their diversity. Here we present scaled laboratory experiments that reproduced dikes and cone sheets under controlled conditions. Our models show that their formation is governed by a dimensionless ratio (Π1), which describes the geometry of the magma source, and a dynamic dimensionless ratio (Π2), which compares the viscous stresses in the flowing magma to the host rock strength. Plotting our experiments against these two numbers results in a phase diagram evidencing a dike and a cone sheet field, separated by a sharp transition that fits a power law. This result shows that dikes and cone sheets correspond to distinct physical regimes of magma emplacement in the crust. For a given host rock strength, cone sheets preferentially form when the source is shallow, relative to its lateral extent, orwhen the magma influx velocity (or viscosity) is high. Conversely, dikes form when the source is deep compared to its size, or when magma influx rate (or viscosity) is low. Both dikes and cone sheets may form fromthe same source, the shift fromone regime to the other being then controlled by magma dynamics, i.e., different values of Π2. The extrapolated empirical dike-to-cone sheet transition is in good agreement with the occurrence of dikes and cone sheets in various natural volcanic settings

Does turbulence affect the habitat choice of Atlantic salmon parr?

Habitat preferences of Atlantic salmon parr are commonly described using mean flow velocity, water depth, and substrate as habitat variables, and a variety of habitat models have been developed using these variables to predict habitat quality. However, Atlantic salmon parr live in highly turbulent streams and rivers, in which intense fluctuations of flow velocity occur. Habitat preferences that consider the high variability of flow velocity have not been studied, and this although it has been shown in laboratory experiments that turbulence may affect the behavior and energetics of fish. Consequently, we studied the use of turbulent flow by Atlantic salmon parr in Patapédia River, Québec, Canada using radio-telemetry. We analyzed summer habitat preferences of individual parr in relation to several dynamic hydraulic variables such as standard deviation of flow velocity, turbulent kinetic energy, Froude number, and shear stress, and compared them with the habitat availability within the river reach. Our results revealed that in a natural flow environment, parr display a high individual variability in habitat preferences in relation to flow turbulence. Such heterogeneous habitat preferences suggest that individuals are not constrained to single habitat types and exhibit flexible habitat use. Furthermore, no differences were observed in habitat preferences between the four daily periods (dawn, day, dusk, and night) within individual parr

The volcaniclastic series from the luang prabang basin, Laos: A witness of a triassic magmatic arc?

International audienceThe paleogeographic evolution of South East Asia (SEA) during the early Mesozoic is still poorly understood and a number of models have recently been put forward to account for the geodynamic evolution of SEA. The Luang Prabang Basin (north Laos), located in the core of a “paleogeographic jigsaw” in SEA, recorded a long lasting volcanism that spanned for ∼ 35 my from the earliest Triassic up to Late Triassic as evidenced by combined stratigraphic and geochronological (U-Pb/zircon) analyses performed on both volcanic and volcaniclastic series. The volcanic rocks are arc tholeiites and calk-alkaline andesites to dacites. The volcaniclastic rocks contain, in part, volcaniclasts produced contemporaneously with sedimentation. Both the volcanic and volcaniclastic series display geochemical features characteristic of a subduction related volcanism. Therefore, the Luang Prabang Basin documents a magmatic arc in a good agreement with the recent recognition of neighboring ophiolitic rocks in the Luang Prabang area. Following a passive margin setting that prevailed from the late Carboniferous to the late Permian, an active margin then initiated along the western margin of the Indochina Block. This active magmatic arc developed as the result of an east-dipping subduction below the Indochina Block during most of the Triassic, at least from ca. 250 to 215 Ma. Subsequently, this oceanic subduction episode must have been followed by a continental collision of the Indochina Block with the eastern Simao Block, at a period that remains to be defined

Covert Encryption and Document Authentication using Texture Coding

With the improvements in the quality of Commercial-Off-The-Shelf (COTS) printing and scanning devices, the ability to counterfeit documents has become a widespread problem. Consequently, there has been an increasing demand to develop digital watermarking techniques which can be applied to both electronic and printed images (and documents) that can be authenticated, prevent unauthorized copying and withstand abuse and degradation. In this paper , a new approach to digital watermarking is presented and a range of possible applications are considered. The process is defined by using concepts and techniques borrowed from Cryptography. It is based on computing a \u27scramble image\u27 by diffusing a watermark image with a noise field (a cipher). The cover image (covertext) is then introduced using a simple additive process (confusion). The watermark is subsequently recovered by removing the covertext and then correlating the output with the original (key dependent) noise field. For covert encryption, this approach provides the user with a method of hiding ciphertext (the scrambled image) in a host image before the transmission of the data. With regard to document authentication, a diffusion only or \u27texture coding\u27 approach that is robust to a wide variety of attacks including geometric attacks, crumpling and print/scan attacks are considered

Regime de metas de inflação e a continuidade da política monetária do Brasil em 2004 e em 2011

O Regime de Metas de Inflação tem guiado a política monetária brasileira nos últimos 18 anos. O objetivo deste trabalho é avaliar se houve uma continuidade na condução da política monetária em conformidade com este regime, mesmo com a mudança Presidencial e do presidente do Banco Central Brasileiro em 2011. Inicialmente o trabalho aborda uma investigação da evolução das diferentes teorias de política monetária, até chegar na elaboração do regime de metas inflacionárias como instrumento para a condução da política monetária. Em seguida, o estudo analisa o contexto macroeconômico do Brasil em 2004, ano em que a decisão de aumentar a taxa básica de juros mostrou a importância dada pelo Banco Central Brasileiro ao Regime de Metas de Inflação e seus fundamentos. Finalmente, para avaliar se houve continuidade na administração do regime monetário, o trabalho elabora um resumo da conjuntura macroeconômica do Brasil em 2011, após a mudança presidencial da República e do Banco Central Brasileiro. Em agosto de 2011, apesar das incertezas internas e externa, o Banco Central decide diminuir a taxa básica de juros, causando polêmica entre os economistas da época. O trabalho estabelece que esta decisão marca, na realidade, o início da implementação da Nova Matriz Macroeconômica, que se revelou uma ruptura na condução da política econômica e monetária deixando de guiar-se apenas pelo Regime de Metas de Inflação

Savoir-vivre et savoir être dans les romans de T. Trilby : éléments d’une stratégie éducative

L’œuvre de T. Trilby (1875-1962), auteur de romans pour la jeunesse publiés principalement dans la collection « Pour les jeunes » de Flammarion entre 1935 et 1961, dessine au fil des publications un monde cohérent à l’usage des enfants, destiné à transmettre des savoir-vivre et des savoir être plutôt que des savoirs scolaires. Ces romans initiatiques, qui ont connu un grand succès, sont représentatifs d’une conception normative de la littérature pour la jeunesse. Leur trame narrative reprend ainsi les éléments traditionnels d’une littérature éducative autoritaire, recueils d’exempla, catéchismes ou paraphrases des Évangiles. Ces livres destinés aux enfants s’insèrent donc dans une stratégie éducative plus large des familles de la bourgeoisie conservatrice et catholique, s’intégrant dans les processus familiaux de transmission informelle de savoirs, savoir-vivre et savoir être propres à une classe sociale. Ce faisant, ces lectures occupent, dans la formation des enfants, une place à la fois complémentaire et décalée par rapport à l’école, complétant d’une éducation morale l’instruction scolaire