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Search Results: 1 - 10 of 5297 matches for " Bernard Lacaze "
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New Formulas for Irregular Sampling of Two-Bands Signals  [PDF]
Bernard Lacaze
Journal of Signal and Information Processing (JSIP) , 2011, DOI: 10.4236/jsip.2011.24035
Abstract: Many sampling formulas are available for processes in baseband (-a,a) at the Nyquist rate a/π. However signals of telecommunications have power spectra which occupate two bands or more. We know that PNS (periodic non-uniform sampling) allow an errorless reconstruction at rate smaller than the Nyquist one. For instance PNS2 can be used in the two-bands case (-a,-b)∪(b,a) at the Landau rate (a-b)/π We prove a set of formulas which are available in cases more general than the PNS2. They take into account two sampling sequences which can be periodic or not and with same mean rate or not.
Beams Propagation Modelled by Bi-filters
Bernard Lacaze
Physics , 2010,
Abstract: In acoustic, ultrasonic or electromagnetic propagation, crossed media are often modelled by linear filters with complex gains in accordance with the Beer-Lambert law. This paper addresses the problem of propagation in media where polarization has to be taken into account. Because waves are now bi-dimensional, an unique filter is not sufficient to represent the effects of the medium. We propose a model which uses four linear invariant filters, which allows to take into account exchanges between components of the field. We call it bi-filter because it has two inputs and two outputs. Such a circuit can be fitted to light devices like polarizers, rotators and compensators and to propagation in free space. We give a generalization of the Beer-Lambert law which can be reduced to the usual one in some cases and which justifies the proposed model for propagation of electromagnic beams in continuous media.
About the Bidimensional Beer-Lambert Law
Bernard Lacaze
Physics , 2012,
Abstract: In acoustics, ultrasonics and in electromagnetic wave propagation, the crossed medium can be often modelled by a linear invariant filter (LIF) which acts on a wide-sense stationary process. Its complex gain follows the Beer-Lambert law i.e is in the form exp [-\alphaz] where z is the thickness of the medium and \alpha depends on the frequency and on the medium properties. This paper addresses a generalization for electromagnetic waves when the beam polarization has to be taken into account. In this case, we have to study the evolution of both components of the electric field (assumed orthogonal to the trajectory). We assume that each component at z is a linear function of both components at 0. New results are obtained modelling each piece of medium by four LIF. They lead to a great choice of possibilities in the medium modelling. Particular cases can be deduced from works of R. C. Jones on deterministic monochromatic light. keywords: linear filtering, polarization, Beer-Lambert law, random processes.
Equivalent random propagation time for coaxial cables
Bernard Lacaze
Physics , 2012,
Abstract: Propagation of monochromatic electromagnetic waves in free space results in a widening of the spectral line. On the contrary, propagation preserves monochromaticity in the case of acoustic waves. In this case, the propagation can be modelled by a linear invariant filter leading to attenuations and phases changes. Due to the Beer-Lambert law, the associated transfer function is an exponential of power functions with frequency-dependent parameters. In recent papers, we have proved that the acoustic propagation time can be modelled as a random variable following a stable probability distribution. In this paper, we show that the same model can be applied to the propagation in coaxial cables.
Stable probability laws modeling random propagation times of waves crossing different media
Bernard Lacaze
Physics , 2014,
Abstract: In a communication scheme, there exist points at the transmitter and at the receiver where the wave is reduced to a finite set of functions of time which describe amplitudes and phases. For instance, the information is summarized in electrical cables which preceed or follow antennas. In many cases, a random propagation time is sufficient to explain changes induced by the medium. In this paper we study models based on stable probability laws which explain power spectra due to propagation of different kinds of waves in different media, for instance, acoustics in quiet or turbulent atmosphere, ultrasonics in liquids or tissues, or electromagnetic waves in free space or in cables. Physical examples show that a sub-class of probability laws appears in accordance with the causality property of linear filters.
TEM Study of High-Temperature Precipitation of Delta Phase in Inconel 718 Alloy
Moukrane Dehmas,Jacques Lacaze,Aliou Niang,Bernard Viguier
Advances in Materials Science and Engineering , 2011, DOI: 10.1155/2011/940634
Abstract: Inconel 718 is widely used because of its ability to retain strength at up to 650°C for long periods of time through coherent metastable Ni3Nb precipitation associated with a smaller volume fraction of Ni3Al precipitates. At very long ageing times at service temperature, decomposes to the stable Ni3Nb phase. This latter phase is also present above the solvus and is used for grain control during forging of alloy 718. While most works available on precipitation have been performed at temperatures below the solvus, it appeared of interest to also investigate the case where phase precipitates directly from the fcc matrix free of precipitates. This was studied by X-ray diffraction and transmission electron microscopy (TEM). TEM observations confirmed the presence of rotation-ordered domains in plates, and some unexpected contrast could be explained by double diffraction due to overlapping phases. 1. Introduction Alloy 718 is the most widely used material for turbine disks and it is selected for many other applications as a high-strength material for temperatures up to 650°C. This alloy was developed in the 60s when the former Fe-based superalloys evolved towards Ni-based superalloys. Alloy 718 contains both Fe and Ni alloyed with some Al and Ti, though the most important addition is the refractory element Nb. A typical composition of alloy 718 is reported in Table 1. It contains a small amount of carbon as well as very low levels of other species such as Si, Ta, Mn, Cu, S, B, P, and Mg, not listed in Table 1 but generally controlled. Table 1: Specification (wt.%) of alloy 718 [ 8] and composition of the alloys used in the present study [ 7, 9]. The strength of alloy 718 comes from coherent solid-state precipitates, which are for a small part -Ni3Al but mostly -Ni3Nb precipitates [1–6]. Both of these precipitates are ordered forms of the fcc-A1 Ni-rich matrix: L12 in the case of and DO22 in the case of . The solvus of these precipitates is at about 900–920°C as discussed previously [7]. Moreover, precipitates are metastable while the stable form of Ni3Nb is the so-called delta phase which is orthorhombic. Forging of 718 alloy is done at about 980°C slightly below the solvus of the delta phase, in such a way that this phase is sufficiently abundant to be effective in limiting grain growth but not too abundant to avoid significant Nb depletion in the matrix which would affect the subsequent strengthening by precipitation. This latter precipitation is generally obtained after two successive periods of isothermal ageing at 750°C and 650°C, respectively.
Consumos alimentarios sustentables en argentina: Una estimación de la disposición a pagar por alimentos orgánicos frescos y procesados por consumidores de la ciudad de Buenos Aires
Agroalimentaria , 2009,
Abstract: throughout these last years, organic agriculture has undergone an important expansion due, among other things, to a higher interest of consumers that involves food quality concerns and has been influenced by mass media diffusion. the objective of this paper is to calculate consumers′ willingness-to-pay for different organic food products. the estimations were made for consumers of medium-high or high socioeconomic level who live in buenos aires city. it is predictable that those argentinean consumers would be willing to pay higher prices to purchase organic products instead of conventional ones, because the first are perceived as free of harmful substances, healthier and of exclusive quality. data derive from a food consumer survey conducted in buenos aires city, argentina, in april 2005. binomial logit models were estimated for four selected products: leafy vegetables, whole wheat flour, fresh chicken and aromatics. the intention to buy each of the selected organic products is mainly explained by the habitual consumption of organic products; respondents′ desires of organics regular availability in the domestic market and respondents′ assessment of food labels information. also health risks perceptions linked to pesticide and hormone content in conventional leafy vegetables and fresh chicken, respectively, are mentioned as well.
Luana Lacaze Camargo Casella
Revista Brasileira de Ecoturismo , 2011,
Abstract: O ecoturismo nos parques, uma das categorias de unidades de conserva o - UC, além de ser um forte aliado para sua conserva o e preserva o, ao ser incorporado na oferta turística do seu entorno, quando n o é o motivador da viagem, proporciona novas oportunidades de atividades aos turistas, estimulando uma maior permanência na localidade, podendo atrair novos segmentos turísticos. Também favorece a gera o de renda e emprego nessas áreas que devem fornecer todos os servi os de apoio a estes turistas, como meios de hospedagem, alimenta o, transporte, entre outros, no antes e no pós visita, já que muitas destas atividades s o inapropriadas ou mesmo proibidas nas UC. Desta maneira, o ecoturismo é capaz de gerar benefícios socioambientais n o somente para os turistas, mas também para a popula o local do entorno da UC. No presente trabalho o objetivo foi identificar o conhecimento dos turistas de Itanhaém e Guarujá sobre o Parque Estadual da Serra do Mar-PESM e qual seria a aceita o, pelos mesmos, quanto à incorpora o desta UC na oferta turística local. Isso porque tanto o Guarujá como Itanhaém, estancias balneárias, tem no turismo uma das mais importantes fontes econ micas municipais, principalmente no segmento de sol e praia, o que confere um caráter sazonal à atividade turística. Entretanto, ambos os municípios est o muito próximos ao PESM, que nos seus mais de 300 mil hectares contém a maior área contínua de Mata Atlantica preservada no Brasil (IF, 2010), o que seria de grande interesse ao desenvolvimento do ecoturismo. Para tanto, em janeiro de 2010, nas praias dos Sonhos e do Tombo, em Itanhaém e Guarujá, respectivamente, aplicou-se, em cada praia, 30 questionários, com 14 quest es cada, entre abertas e fechadas, cujo objetivo foi identificar o perfil dos turistas, seus conhecimentos sobre UC e a existência do PESM, bem como identificar, nos visitantes, se há motiva es e quais s o elas para conhecerem uma UC. Como as entrevistas ocorreram na alta temporada de ver o, a maior parte dos entrevistados, em ambas as praias, eram provenientes principalmente da capital S o Paulo, o que conferiu uma forte proximidade em todas as respostas obtidas. Os turistas tinham como as principais motiva es da viagem o descanso, seguido da busca por um lazer diferente da rotina. Durante sua estada nas duas cidades, a maioria dos entrevistados vai à praia, dando a entender que é a única atividade realizada nas cidades. Observou-se que embora os turistas n o saibam o que seja uma UC e da existência do PESM, gostariam de conhecer e se sentiriam estimulados a freqüentá-l
Juan Manuel López-Mu oz, Sophie Marnette, Laurence Rosier, Diane Vincent (dir.). La circulation des discours
Grégoire LACAZE
E-rea : Revue électronique d’études sur le Monde Anglophone , 2012,
Abstract: Cet ouvrage collectif, dirigé par Juan Manuel López Mu oz, Sophie Marnette, Laurence Rosier et Diane Vincent et paru en 2009 aux éditions Nota Bene, est une publication qui fait suite au 3e colloque Ci-dit organisé à l’Université de Laval (Québec) du 5 au 7 octobre 2006. L’objet d’étude est le discours rapporté envisagé cette fois en tant que pratique de discours et pratique intersubjective et sociale (7).Lorsqu’un discours est produit par un locuteur origine, ce discours peut être ra...
Une analyse d’une production de discours rapporté : l’introduction des tours de parole dans “Hills Like White Elephants” d’Ernest Hemingway
Grégoire LACAZE
E-rea : Revue électronique d’études sur le Monde Anglophone , 2010, DOI: 10.4000/erea.1348
Abstract: Cette nouvelle d’Ernest Hemingway est construite principalement autour du report de paroles au discours direct des deux personnages principaux. Elle a déjà fait l’objet de nombreuses études critiques, notamment sur le style de son auteur. Nous nous intéressons ici à un aspect souvent négligé dans ces études, l’introduction du discours direct, car celle-ci nous semble relativement importante dans la réception1 de la nouvelle.à partir de cette production de discours rapporté, nous étudierons comment le narrateur choisit d’introduire les différents tours de parole. Cette réflexion, s’inscrivant dans une perspective énonciative, s’appuiera sur une étude grammaticale et sémantique prenant en compte les spécificités du genre de la nouvelle et leur influence sur les choix stylistiques de l’auteur. Une étude statistique sur la composition des structures d’introduction du discours des personnages viendra étayer l’analyse. Hemingway’s short story, “Hills Like White Elephants”, is largely built around a reported dialogue involving two main characters. Although many critical studies have been devoted to this short story, focusing especially on Hemingway’s style, this paper seeks to explore a relatively neglected theme, namely the introduction of direct speech, which acquires significant importance in the reception of the short story.Thanks to the dialogue that materializes as an occurrence of reported speech produced by a reporter, we will study how the narrator chooses to introduce the various turns constituting the dialogue. This analysis, inscribed within the framework of an enunciative approach, aims at pointing out the stylistic devices used by the author. Both linguistic and semantic aspects will be taken into account as well as the specificities induced by the genre of the short story and their influence on the stylistic choices made by the author. The analysis will be backed up with statistical data related to the composition of the various structures introducing the characters’ words.
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