Enhanced and reduced transmission of acoustic waves with bubble meta-screens

We present a class of sonic meta-screens for manipulating air-borne acoustic waves at ultrasonic or audible frequencies. Our screens consist of periodic arrangements of air bubbles in water or possibly embedded in a soft elastic matrix. They can be used for soundproofing, but also for exalting transmission at an air/water interface or even to achieve enhanced absorption

Mineralogical Limitations for X-Ray Tomography of Crystalline Cumulate Rocks

The use of x-ray computed tomography (XRCT) on igneous rocks enables the visualisation and quantification of the 3D texture of the rock and of the crystal population as opposed to a more traditional 2D vision using thin sections and 3D stereological conversions. Although still in its infancy, the application of XRCT on igneous rocks provides a 3D map of the distribution of each mineral phase, the overall dimensional metrology of crystals (size, area volume, shape, orientation and geometry) and potentially their crystallographic orientation. The precision of crystal size distributions (CSD), which are often used for describing rocks and understanding igneous processes, is enhanced by the use of the 3D analysis of crystal size. XRCT shows promising results when applied to volcanic rocks but only limited applications with intrusive igneous rocks In this study, we compare the dimensional metrology of crystals in 2D and in 3D of a Tugtutoq peridotite sample using a thin section and 3D tomography data to investigate how different the 3D data is from the 2D to test the utility of using XRCT on a dense cumulate. The tomography data is processed in four steps: i) post-processing which includes filtering noise and correcting artefacts linked to the XRCT acquisition; ii) segmentation of the cumulus phase in the sample (in this case olivine); iii) separation of the segmented olivine into realistic and discrete crystals; and iv) the extraction of the data from the 3D-separated olivine crystals (size, location and distribution in the sample, shape, orientation, …). The results of the tomography scan of the peridotite sample are close to the thin section data but the error associated with the tomography data is difficult to quantify. That error is likely high due to the low contrast in attenuation coefficients between the crystal populations – linked to the similar densities of the mineral phases in the sample – and the close proximity and extensive contact between the olivine crystals. When applied to cumulate rocks, the method cannot be automated to produce reproducible and objective results, but we suggest the application of this method for processing tomography data with either volcanic rocks or cumulates solidified from a more permeable mush, where there is minimal contact between the crystals of interest and the density contrast between phenocrysts and groundmass is high

The permeability of magma mush

Models for the evolution of magma mush zones are of fundamental importance for understanding magma storage, differentiation in the crust, and melt extraction processes that prime eruptions. Mush mobilisation and melt segregation are predominant mechanisms that control mush evolution yet are to date still insufficiently understood and models for these are poorly constrained. These models are underpinned by calculations of the permeability of the evolving crystal frameworks in the mush, which controls the rate of melt movement relative to crystals. To date, no mush permeability model accounts for the shape of the crystals that form the crystal-framework in the mush. Herein, we assume that mush crystals are approximately cuboidal, and using that geometric approximation, we present new models for the permeability of mush in which crystal shape parameters are a key input. First, we present an extension of the Kozeny-Carman permeability law specifically for crystal packs at their maximum packing, for which the axis lengths of the crystals are the primary input. Second, we present a model for the evolution of magma mush permeability that is valid from maximum packing down to low melt fractions, ideal for simulating permeability as mush crystalises. In all cases we use a combination of numerical approaches to generate packs of cuboids for analysis, and experimental approaches to create digital 3D scans of anisotropic crystal shapes as an analogue for crystal mush. Using a combination of Avizo 3D image analysis, and a lattice-Boltzmann simulation technique, we constrain the permeability of both the numerical and experimental samples; these data then validate our models across a wide range of parameter space applicable to real magma mush. Furthermore, we propose and validate innovative solutions for permeability that can be found using only 2D data (for example, using a thin section scan), which is useful for common situations where full 3D information may not be available for analysis. In general, our results show that if we consider melt percolation in magma mush akin to fluid flow through porous media, the complexity and anisotropy are well represented by the specific surface area of the crystals. Knowledge of the crystal shape and size are essential variables in our proposed permeability model, unless the mush displays overgrowth textures at low melt fraction, in which case the effect of shape becomes less important. Our results have key implications for melt extraction timescales and cumulate textures as well as for crustal melt segregation processes and reactive flow on the scale of mush reservoirs

Autoroute A83, section 5 Oulmes : bilan général

L’année 1995 marque l’achèvement des travaux de terrain sur le périmètre actuellement défini. Le projet d’aménagement, dans son avant-dernière section, vient buter sur la RN 148 (Oulmes) par l’intermédiaire d’un barreau de raccordement destiné à être remplacé ultérieurement par la section établissant la liaison entre Oulmes et l’A10. Lors des deux avant-projets sommaires (1991 et 1993) présentant les projets de contournement de Niort, le dépouillement de la carte archéologique faisait état d’..

Optimized Adaptive Streaming Representations based on System Dynamics

Adaptive streaming addresses the increasing and heterogenous demand of multimedia content over the Internet by offering several encoded versions for each video sequence. Each version (or representation) has a different resolution and bit rate, aimed at a specific set of users, like TV or mobile phone clients. While most existing works on adaptive streaming deal with effective playout-control strategies at the client side, we take in this paper a providers' perspective and propose solutions to improve user satisfaction by optimizing the encoding rates of the video sequences. We formulate an integer linear program that maximizes users' average satisfaction, taking into account the network dynamics, the video content information, and the user population characteristics. The solution of the optimization is a set of encoding parameters that permit to create different streams to robustly satisfy users' requests over time. We simulate multiple adaptive streaming sessions characterized by realistic network connections models, where the proposed solution outperforms commonly used vendor recommendations, in terms of user satisfaction but also in terms of fairness and outage probability. The simulation results further show that video content information as well as network constraints and users' statistics play a crucial role in selecting proper encoding parameters to provide fairness a mong users and to reduce network resource usage. We finally propose a few practical guidelines that can be used to choose the encoding parameters based on the user base characteristics, the network capacity and the type of video content

Rapport d\u27activité 2014 - SCD Université de Bretagne Occidentale

Rapport d\u27activité du Service Commun de Documentation de l\u27Université de Bretagne Occidentale pour l\u27année 2014

Métiers des bibliothèques : guide des formations

Ce guide des formations aux métiers des bibliothèques propose deux entrées principales : -la préparation et l’accès aux métiers des bibliothèques qui revient sur les formations préparatoires, les organismes de préparation aux concours ainsi que les différents concours ; -la formation continue qui présente les organismes de formation ainsi que le plan régional de formation

Rapport d\u27activité 2016 - SCD Université de Bretagne Occidentale

Rapport d\u27activité du Service Commun de Documentation de l\u27Université de Bretagne Occidentale pour l\u27année 2016