The development of materials capable of operation in an oxidizing atmosphere for extended periods of time

An evaluation is presented of silicon carbide, zirconium diboride, and iridium-coated graphite as materials for construction of furnace cores which could operate under highly oxidizing conditions at temperatures of approximately 2,200 C in the presence of molten aluminum oxide. It was found that silicon carbide and zirconium diboride could not withstand oxidizing atmospheres in the presence of aluminum oxide at temperature 2,200 C. However, graphite furnace cores coated with iridium were found to be useful furnace cores at 2,200 C in an oxidizing atmosphere for reasonably extended periods of time

Le rôle du tourisme dans le développement du territoire

« Le rôle du tourisme dans le développement du territoire» (chapitre 5), in Violier Ph. (dir.), Le tourisme, un phénomène économique, Paris, La Documentation française, coll. Les Etudes, p. 163-206

Les grands hôtels, témoins de l'histoire du tourisme : le Royal et Splendid Hôtel à Saint-Gervais-les-Bains (Haute-Savoie)

Buildings offer an operational insight into the way territories are structured and redesigned. In a spatial approach to tourism, grand old hotels reveal a great deal about the establishment and construction of tourist resorts. The apparent unity of a building often conceals a long and complex history, which is worth deciphering.

A blind decision feedback equalizer incorporating fixed lag smoothing

Copyright © 2000 IEEEA new type of blind decision feedback equalizer (DFE) incorporating fixed lag smoothing is developed in this paper. The structure is motivated by the fact that if we make full use of the dependence of the observed data on a given transmitted symbol, delayed decisions may produce better estimates of that symbol. To this end, we use a hidden Markov model (HMM) suboptimal formulation that offers a good tradeoff between computational complexity and bit error rate (BER) performance. The proposed equalizer also provides estimates of the channel coefficients and operates adaptively (so that it can adapt to a fading channel for instance) by means of an online version of the expectation-maximization (EM) algorithm. The resulting equalizer structure takes the form of a linear feedback system including a quantizer, and hence, it is easily implemented. In fact, because of its feedback structure, the proposed equalizer shows some similarities with the well-known DFE. A full theoretical analysis of the initial version of the algorithm is not available, but a characterization of a simplified version is provided. We demonstrate that compared to the zero-forcing DFE (ZF-DFE), the algorithm yields many improvements. A large range of simulations on finite impulse response (FIR) channels and on typical fading GSM channel models illustrate the potential of the proposed equalizer.Sylvie Perreau, Langford B. White and Pierre Duhame

Tourisme et mondialisation

La croissance annoncée du tourisme international présage une croissance exponentielle pour les premières décennies du XXIe siècle, laquelle se combinera avec une croissance des mobilités touristiques nationales. De nos jours, tout se passe comme si s\u27opérait une transition touristique, avec le passage d\u27un régime d\u27habiter le monde non touristique à un autre, où le tourisme devient une composante de l\u27existence humaine. Dès lors, si l\u27on considère que la transition touristique se déploiera à l\u27égale de la transition urbaine (généralement, la transition urbaine s\u27achève avec des taux voisins à 80 % de la population vivant en ville), on pressent la marge de manœuvre qu\u27il reste à conquérir aux tourismes international et national. Nous serions au début d\u27un phénomène dont le développement et les implications restent à venir. Finalement, à l\u27exception des pays occidentaux, anciens foyers touristiques dont la démographie est limitée, le tourisme reste à construire ailleurs dans le monde pour plusieurs milliards d\u27individus.  Ce constat va de pair avec une nouvelle étape dans le développement du tourisme, qui est l\u27avènement d\u27un tourisme de masse mondialisé. Admettre que le tourisme est aujourd\u27hui un phénomène mondialisé n\u27est plus une originalité. Poser qu\u27il est mondialisé et mondialisant, c\u27est franchir un pas supplémentaire.  Face à cette mise en tourisme mondiale, survient une autre question, importante pour les destinations et les lieux touristiques : comment survivre face à la concurrence accrue ? Cette concurrence n\u27est pas forcément produite par une fréquentation réelle du monde touristique, mais est induite par l\u27évolution et l\u27amélioration de la connaissance des individus-touristes de ce qui se passe dans le monde.  Le tourisme, qui fut longtemps une affaire européenne puis occidentale, est aussi, depuis trente années, une affaire asiatique. Et il apparaît de plus en plus clairement aux chercheurs que les touristes asiatiques, au-delà des apparences, n\u27agiraient pas tout à fait comme les touristes occidentaux. Certes, ils se reposent, visitent, jouent et font du shopping, mais pas de la même façon que les touristes occidentaux…  La recherche scientifique a considérablement progressé ces dernières années en reconnaissance et en connaissance de ces écarts aux modèles praticiels. Par touches successives, d\u27autres attitudes émergent, des subtilités pointent au-delà des importantes différences.  Dès lors, nous vivons un autre moment important dans la constitution du monde touristique ; celui où, peut-être, d\u27autres modèles se forgent. Ainsi le refus de bronzer est-il temporaire ou définitif, instillant un nouveau rapport au soleil ? Si tel est le cas, comment cette posture évoluera-t-elle et influencera-t-elle les Occidentaux ? La question de la circulation des modèles est posée ; la réflexion sur la diffusion de la pratique est engagée. Le présent ouvrage privilégie trois thématiques qui croisent mondialisation des modèles et tourisme : le durable, la culture et la gastronomie.  Cet ouvrage collectif est issu des Troisièmes Rendez-vous Champlain sur le tourisme, qui se sont tenus en juin 2010 à Angers.

Al based alloys containing amorphous and nanostructured phases

Nanostructured or partially amorphous Al-based alloys are attractive candidates for advanced high-strength lightweight materials. The strength of such materials is often 2 - 3 times higher than the strength of commercial crystalline alloys. Further property improvements are achievable by designing multi-phase composite materials with optimized length scale and intrinsic properties of the constituent phases. Such alloys can be prepared by quenching from the melt or by powder metallurgy using mechanical attrition techniques. This paper focuses on mechanically attrited Al-based powders containing amorphous or nano-crystalline phases, Al-based MMCs containing metallic glass reinforcement and on their consolidation into bulk specimens. Selected examples of mechanical deformation behavior are presented, revealing that the properties can be tuned within a wide range of strength and ductility as a function of size and volume fraction of the different phases

Fast Fourier Optimization: Sparsity Matters

Many interesting and fundamentally practical optimization problems, ranging from optics, to signal processing, to radar and acoustics, involve constraints on the Fourier transform of a function. It is well-known that the {\em fast Fourier transform} (fft) is a recursive algorithm that can dramatically improve the efficiency for computing the discrete Fourier transform. However, because it is recursive, it is difficult to embed into a linear optimization problem. In this paper, we explain the main idea behind the fast Fourier transform and show how to adapt it in such a manner as to make it encodable as constraints in an optimization problem. We demonstrate a real-world problem from the field of high-contrast imaging. On this problem, dramatic improvements are translated to an ability to solve problems with a much finer grid of discretized points. As we shall show, in general, the "fast Fourier" version of the optimization constraints produces a larger but sparser constraint matrix and therefore one can think of the fast Fourier transform as a method of sparsifying the constraints in an optimization problem, which is usually a good thing.Comment: 16 pages, 8 figure

Dynamic response of railway tracks in tunnel

International audiencePeriodically supported beams subjected to a moving load are often used for modelling the railway dynamics and analytical solutions have been developed for such modelling [3, 4]. More complex models can be constructed by including supports with damping or non-linear stiffness elements. This study deals with the dynamical modelling of non-ballasted railways, especially railways in tunnels. The model is developed as a dynamical system of multi-degree of freedom. Under the periodic assumption on the reaction force of the supports, the equation of motion for a periodically supported beam subjected to a moving load has been written. Then the Fourier transform has been used to solve this equation in case of damped supports. Analytical solutions have been established for the motion of the wheel and rail and also for the reaction force of the supports. The analytical solutions have been compared with in situ experimental measurements. The comparison shows that the theoretical results agree well with the measured results if damped supports are included in the model