Large-scale doming on Europa: A model of formation of Thera Macula.

International audienceSince Galileo spacecraft reveals Europa's surface at high and medium resolutions, deformation and processes affecting the relatively young surface have been more accurately defined. This work reports the observations carried out on a large-scale feature of the south hemisphere, Thera Macula. It is shown that Thera presents common points with many other features including small-scale domes, lenticulae and large-scale chaotic areas (disrupted ancient surfaces lying on a dark matrix), but remains singular through its asymmetric morphology. On the basis of observations, we propose a scenario for the setting of Thera Macula. It involves a large-scale doming (40–70km in radius) of the pre-existing surface associated with ductile deformations, and the consecutive collapse of the created megadome associated with brittle disruption of blocks and flow of low viscosity material over the surrounding ridged plains. The processes responsible for each stage of the proposed scenario have been investigated. Both cryomagmatic and diapiric origins are discussed and confronted by observations. Finally, comparison of similar features at various scales suggests that Thera Macula by its originalities (asymmetry, rounding bulge) may have preserved the intermediate stages of the formation of subcircular chaos at least up to about 50km in radius. A common evolution and endogenic origin for multi-scale hot spot features is proposed: (1) the doming stage, (2) the collapse and extrusion stage and (3) the relaxation stage

Shrinkage Function And Its Applications In Matrix Approximation

The shrinkage function is widely used in matrix low-rank approximation, compressive sensing, and statistical estimation. In this article, an elementary derivation of the shrinkage function is given. In addition, applications of the shrinkage function are demonstrated in solving several well-known problems, together with a new result in matrix approximation

Ni–W diffusion barrier: Its influence on the oxidation behaviour of a β-(Ni,Pt)Al coated fourth generation nickel-base superalloy

A Ni–W base diffusion barrier (DB) has been developed to limit interdiffusion between a fourth generation Ni-base superalloy (MCNG) and a Pt-modified nickel aluminide bondcoat. After long term oxidation, the DB layer permits to reduce the Al depletion in the coating and to delay the phase transformations in the coating. But despite this result, the oxidation behaviour of the system with DB is slightly worse than without the DB. This difference may be caused by the addition of S and/orWin the coating of the system with the DB. The DB layer also delays the Secondary Reaction Zone (SRZ) formation. Nevertheless, the propagation of the SRZ is similar in systems with and without a DB, with growth kinetics which are driven by interdiffusion

Les structures d'impact sur Europe : implications sur la rhéologie et la thermique de la croûte de glace. Impact features on Europa : rheological and thermal states of the icy crust.

texte intégral en français English abridged versionInternational audienceThe depth of the brittle/ductile transition has been estimated under each graben rounding two ancient impact basins on Europa, Callanish and Tyre. Surface thermal gradients have been computed and are respectively equal to 4.3 +/- 0.4 and 2.4 +/- 0.25 K/km. These results differ strongly from previous works obtained on other Europa's features. This can be explained by the variation of both the icy grain size and the chemical composition of the crust, but also by the variation of the local deformation rate

Fracturación asociada a pliegues en las calizas jurásicas de las cadenas del Sur del Rif (Marruecos)

The study of fractures affecting the Jurassic Ridges of Fert El Bir, Kefs and Outita from South Rifian Ridges, Northern Morocco, allowed us to propose a folding-fracturing model that summarizes the distribution of fractures within fault-propagation folds and the chronology of the different families of fractures occurring during the history of Miocene and Quaternary shortening phases, oriented NE-SW. At the beginning of compressional phase, sedimentary series corresponding mainly to limestones are deformed by layer parallel shortening (LPS) accompanied by pure shear causing thickening with the occurrence of oblique and transverse fractures. Following the establishment of the ramp fold, existing fractures are locally affected by simple shear within the two flanks of the fold and axial fractures are developed as a response of the accommodation of the surface foldingA partir del estudio de la fracturación en los materiales jurásicos de las estribaciones del sur de las cadenas rifeñas (norte de Marruecos), se propone un modelo de plegamiento y fracturación que explica la distribución de fracturas en pliegues de propagación de fallas, así como la cronología de las distintas familias de fracturas formadas durante la historia deformacional del Mioceno y Cuaternario (compresión NE-SW). Al comienzo de la etapa compresiva, las secuencias sedimentarias sufrieron una deformación por acortamiento paralelo a las capas (layer-parallel shortening, LPS), acompañada de cizalla pura que trajo como resultado el engrosamiento de las capas y la aparición de fracturas oblicuas y transversas. Después del emplazamiento del pliegue asociado a la falla, las fracturas sufrieron desplazamientos en los dos flancos del pliegue, y se formaron nuevas fracturas como resultado de la acomodación a la superficie de plegamient

Sedimentation/erosion balance in the lake of Grand-Lieu (France, Loire-Atlantique): implications for natural environment management

The lake of Grand-Lieu (2000 ha) is a part of a large wetland of Western France. The surface and depth of this lake recently increased. This erosive crisis began around thirty years ago as the consequence of an imbalance between sediment input (0.15 to 0.5 kg/m2/year of allochthonous TSS and 0.03 to 0.1 kg/m2/year of autochthonous organic matter) and sediment export. The export of sediment is about 1.5 to 2 times higher than inputs ; this situation is exceptional in lake systems. Ultimately, conservation of certain natural environments could be compromised. In this paper, first we present erosion processes that are related to the extensive resuspension of sediments, and then show how, among other factors, the current water management promotes the export of sediment and how it is possible to adapt it in order to reduce the sediment exportLe lac de Grand-Lieu, partie lacustre (2000 ha) d'une vaste zone humide de l'Ouest de la France, a vu sa surface et sa profondeur augmenter récemment. Cette crise érosive a débuté depuis une trentaine d'années et résulte d'un déséquilibre entre l'apport sédimentaire (de 0,15 à 0,5 kg/m2/an de MES allochtone et de 0,03 à 0,1 kg/m2/an de MO autochtone) et l'exportation qui est environ 1,5 à 2 fois plus importante ; ce qui est exceptionnel dans les systèmes lacustres. À terme, la conservation de certains milieux naturels peut être compromise. Nous présentons les processus d'érosion qui sont liés à l'abondante remise en suspension des sédiments, puis nous montrons comment la gestion hydraulique actuelle, entre autres facteurs, favorise l'exportation de ces sédiments et comment il est possible de réduire l'impact de cette gestion

Is There an Economic Advantage to Planting Diverse Summer Annual Forage Mixtures?

This study examined economic implications of planting summer annual mixtures of grasses, legumes, and forbs at varying nitrogen rates. No differences in yield occurred between the three mixtures, indicating that mixtures with lowest seed cost will be most economical. Applying N resulted in yield increases of 12.26 lb DM per lb N applied. Although yield responses to N were positive, sensitivity analyses showed that applying N resulted in positive net returns only when hay prices were high and N prices were low. When utilization rates are accounted for, enterprise budgets determined grazing to be 18% cheaper to implement than haying

Geologic interpretation of the aeromagnetic survey in the Agourai area (Central Morocco)

Abstract The aim of this work is to interpret the geologic structures of the Agourai area (Paleozoic and Mesozoic structures) from processed magnetic maps. The detected magnetic anomalies from different standard methods used in aeromagnetism (Residual map, RTP map, horizontal gradient map) were compared to geologic structures and permit enhancing the mapping quality of some areas, and thus defining many geologic features. Existing geologic maps and geologic field studies allow interpreting some detected anomalies. It was thus possible to define the limits between the Paleozoic basement and the Mesozoic cover, to determine magnetic anomalies according to NE-SW trends compatible with the regional geologic structures and finally to detect a NE to SW-oriented fault system in the Mesozoic cover of the Agourai Plateau. Despite the reliability of this approach, some folded basaltic sills occurring in this region were not well detected, probably because of their reduced thickness