Littérature scientifique sur le sujet « Banda larga - Diffusione »

Worldwide, governments and industries are pursuing the use of clean hydrogen to achieve zero emissions, especially for difficult to decarbonize sectors such as heavy-duty transportation, aviation, shipping and chemical manufacturing. Polymer electrolyte fuel cells (PEFCs) are an excellent candidate for heavy-duty vehicles (HDVs), particularly for their ability to scale range at a much smaller additional weight penalty1. However, initial system cost remains a significant challenge for large scale adoption mainly due to use of Platinum (Pt) electrocatalyst. Current approach to reduce initial cost by utilizing highly dispersed Pt nanoparticles (2-3 nm) adversely affects the system lifetime. The smaller nanoparticle size does result in improved Pt dispersion, which enhances performance and reduces Pt loading and cost. But smaller nanoparticles also tend to degrade faster due to higher surface energy, which negatively impacts durability1. During a HDV drive cycle, Pt nanoparticle surface undergoes repeated oxidation-reduction, which leads to dissolution of Pt ions causing loss in electrochemical surface area. The dissolved Pt ions can redeposit on nearby larger nanoparticles. This effect is known as electrochemical Ostwald ripening2. The Pt ions can also diffuse towards the anode and get reduced near the membrane-cathode interface by the crossover hydrogen to form a Pt band2. In addition, the Pt ions can leave the system via effluent water. The complex balance between cost, performance and durability of PEFCs makes understanding degradation mechanisms a priority. In this study, membrane electrode assemblies (MEAs) were subjected to accelerated stress tests (ASTs) to simulate heavy-duty lifetime. A simple method was developed to use micro-X-ray fluorescence spectroscopy to map identical locations of catalyst layer before and after the AST. The AST consisted of potential cycling between 0.6 V to 0.9 V (3s hold time each) for 90,000 cycles. Electrochemical characterization was performed at beginning of test, after 10k, 30k, 60k and 90k (end of test) AST cycles. The identical location maps revealed significant in-plane movement of Pt over the course of AST suggesting that electrochemical Ostwald ripening may not be a local effect. The in-plane movement of Pt led to development of local loading hotspots. A movement of Pt away from the cathode catalyst layer cracks was also observed. Such movement may be due to relative surface energy differences between the regions. A modified gas diffusion layer MEA was used to highlight the advantages and necessity of the method developed in this study. The modified MEA showed a ~13% change in/loss of Pt loading in the mapped region closer to the gas inlet. Identical location mapping allowed quantification of changes in the Pt loading caused by the AST. Lastly, identical location synchrotron micro-X-ray diffraction and florescence mapping was performed after the heavy-duty AST to identify correlation between Pt nanoparticle size growth and Pt loading. A direct correlation was observed, which developed only after the MEA was subjected to heavy-duty AST. References Cullen, D. A. et al. New roads and challenges for fuel cells in heavy-duty transportation. Nat. Energy 6, 462–474 (2021). Khedekar, K. et al. Probing Heterogeneous Degradation of Catalyst in PEM Fuel Cells under Realistic Automotive Conditions with Multi-Modal Techniques. Adv. Energy Mater. 11, (2021).

Abstract: This article explores the history of the Intercom Ontario field trial in which residents of 64 homes were offered a variety of digital communication services and access to digital content delivered over a symmetric high-bandwidth data network. Some insights gleaned from the trial are: novel services can be designed and successfully implemented at low cost by small, highly collaborative groups; broadband communication channels, such as two-way video, are likely to be exploited in ways not anticipated by the designers; people seek out a broader variety of content selections than traditional models predict; the value of a mailing list as a community-building tool extends to geographically based communities; the discrepancies between the ways in which the introduction of technological innovations are perceived by users, developers, and providers are significant, complex, and deserve further study. Résumé: Cet article explore l'histoire de recherches sur le terrain menées par Intercom Ontario au cours desquelles on a offert aux habitants de 64 maisons une variété de services de communication digitaux et l'accès à un contenu digital livré au moyen d'un réseau téléinformatique symétrique à haute largeur de bande. Parmi les observations recueillies grâce à ces recherches: de petits groupes capables de collaborer très étroitement peuvent concevoir et mettre en place des services inédits; on utilise les canaux de communication à large bande, comme les vidéos bidirectionnels, de façons que les concepteurs originaux n'auraient pas prédites; la valeur d'une liste de diffusion pour former des communautés s'étend à des communautés géographiques; les écarts entre les manières dont les créateurs, les fournisseurs et les utilisateurs d'innovations technologiques perçoivent l'introduction de celles-ci sont significatifs et complexes, et méritent d'être étudiés plus à fond.

Artivisme est un néologisme composé des mots art et activisme. Il concerne l’engagement social et politique d’artistes militants (Lemoine et Ouardi 2010) mais aussi l’art utilisé par des citoyen.ne.s comme moyen d’expression politique (Salzbrunn 2014, 2015 ; Malzacher 2014 : 14 ; Mouffe 2014). La distinction qui porte sur la formation initiale est davantage analytique qu’empirique dans la mesure où la définition d’artistes ou d’œuvres d’art en lien avec une formation institutionnelle (hautes écoles d’art) est aujourd’hui mise en question : Le succès planétaire d’artistes autodidactes engagés comme le photographe français JR montrent qu’on peut acquérir une reconnaissance en tant qu’artiste sans avoir été formé dans une école d’art. De plus, la différence entre l’engagement politique des artistes et leurs œuvres au sens propre est de plus en plus difficile à saisir (Roussel 2006 ; Dufournet et al. 2007). Sur le plan conceptuel, les recherches sur l’artivisme remettent en question la distinction entre l’art considéré comme travail et l’art pour l’art, discutée entre autres par Jacques Rancière dans « Le partage du sensible. Esthétique et politique » : « Produire unit à l’acte de fabriquer celui de mettre au jour, de définir un rapport nouveau entre le faire et le voir. L’art anticipe le travail parce qu’il en réalise le principe : la transformation de la matière sensible en présentation à soi de la communauté » (Rancière 2000 : 71). Les expressions artistiques couvrent un très large panel, allant de l’art plastique et mural, en passant par le graffiti, la bande dessinée, la musique, le flash mobs, le théâtre, à l’invention de nouvelles formes d’expression (Concept Store #3, 2010). L’artivisme actuel, notamment les performances, trouvent leurs racines dans d’autres courants artistiques expérimentaux développés dans les années 1960, notamment le théâtre de l’opprimé d’Agosto Boal, le situationnisme (Debord 1967), le fluxus (http://georgemaciunas.com/). Certains remontent encore plus loin vers le surréalisme et le dadaïsme auxquels l’Internationale situationniste (1958-1969) se réfère afin de pousser la création libre encore plus loin. Tout comme le mouvement situationniste cherchait à créer des situations (1967) pour changer la situation et déstabiliser le public (Lemoine et Ouardiri 2010), et que le théâtre de l’opprimé (Boal 1996) pratiquait le théâtre comme thérapie, l’artivisme contemporain vise à éveiller les consciences afin que les spectateurs sortent de leur « inertie supposée » et prennent position (Lemoine et Ouardi 2010 ; pour les transformations dans et de l’espace urbain voir aussi Schmitz 2015 ; Salzbrunn 2011). Ainsi, les mouvements politiques récents comme Occupy Wallstreet (Graeber 2012) ou La nuit debout (Les Temps Modernes, 2016/05, no. 691 ; Vacarme 2016/03, no. 76) ont occupé l’espace publique de façon créative, se servant de la mascarade et du détournement (de situations, notamment de l’état d’urgence et de l’interdiction de rassemblement), afin d’inciter les passants à s’exprimer et à participer (Bishop 2012). D’autres courants comme les Femen, mouvement féministe translocal, ont eu recours à des performances spectaculaires dans l’espace public ou faisant irruption au cours de rituels religieux ou politiques (Femen 2015). Si ces moyens d’action performatifs au sein du politique étaient largement employés par les courants politiques de gauche (Butler et Athanasiou 2013), l’extrême-droite les emploie également, comme le mouvement identitaire qui a protesté par des actions coup de poing contre les réfugiés dans les Alpes françaises en hiver 2018 (https://www.lemonde.fr/police-justice/article/2018/04/30/militants-identitaires-dans-les-alpes-les-autorites-denoncent-une-operation-de-communication_5292856_1653578.html). Les thèmes politiques abordés se situent néanmoins majoritairement à gauche de l’échiquier politique : mouvement zapatiste, LGBTqueer, lutte anti-capitaliste, antifasciste et pro-refugiés, (afro-/latino-) féminismes (de Lima Costa 2012), mouvement contre l’exclusion des personnes à mobilité réduite, protestation contre la gentrification et la dépossession de l’espace urbain qui s’opère en faveur des touristes et spéculateurs immobiliers et qui va à l’encontre des habitants (Youkhana 2014 ; Pisanello 2017), mouvement d’occupation d’espace, de squat et de centres sociaux auto-gérés, lutte créative en faveur de nouvelles formes de vie commune comme dans la ZAD (Zone à défendre) contre l’aéroport de Nantes etc. (Rancière 2017 : 65-73). Si ces luttes s’inscrivent dans une réflexion critique générale sur les conséquences de la glocalisation, elles se concentrent parfois sur l’amélioration de l’espace local, voire micro-local (Lindgaard 2005), par exemple en créant une convivialité (Caillé et al. 2013) ou des espaces de « guerilla gardening » (mouvement de jardinage urbain comme acte politique) au sein d’une ville. Les « commonistes » qui s’occupent de biens communs et développent les créations par soi-même (DIY – Do it yourself) à travers des FabLabs (laboratoires de fabrication) s’inscrivent également dans cette philosophie en mettant en question de façon créative le rapport entre production et consommation (Baier et al. 2013). Enfin, les mouvements actuels ont largement recours aux dernières technologies d’information et de diffusion, pendant le processus de création et pendant la circulation des œuvres, des images et des témoignages (Salzbrunn et al. 2015). Plus radicalement encore, les hacktivistes interviennent sur des sites web en les détournant et en les transformant. Dans certains endroits, l’humour occupe une place centrale au sein de ces activités artistiques, que ce soit dans le recours aux moyens de style carnavalesques (Cohen 1993), en réinventant le carnaval (Salzbrunn 2014) ou encore en cherchant à créer une ambiance politico-festive réenchantente, assurant un moment de joie et de partage heureux pour les participants. Betz (2016) a traité ce dernier aspect en analysant notamment des « Schnippeldiskos », discos organisés par le mouvement slow food jeunesse qui prennent la forme d’une séance joyeuse de coupage de légumes destinées à une soupe partagée, un moment de « protestation joyeuse », une « forme hybride de désobéissance collective ». Ces nouvelles formes d’interaction entre art, activisme et politique appellent au développement de méthodes de recherches anthropologiques inédites. Ainsi, l’ethnographie est devenue multi-sensorielle (Pink 2009), attentive au toucher, aux parfums, au goût, aux sensations des chercheur.e.s et des personnes impliquées dans l’action artivistique. L’observation participante devient plus radicale sous forme d’apprentissage (Downey et al. 2015). Enfin, les anthropologues qui travaillent sur l’artivisme ont non seulement recours à de nouvelles méthodes, mais aussi à de formes inédites de restitution de leurs recherches, visant notamment à dépasser le centrage sur le texte (Schneider et Wright 2006) en tournant des films documentaires, créant des bandes dessinées (www.erccomics.com), discutant avec les artivistes à travers blogs (www.erc-artivism.ch), ou interagissant à travers des performances comme « Rawson’s Boat », conduite par le Nigérian Jelili Akiku en mai 2018 au Musée d’Acquitaine de Bordeaux.

2011-2012
La banda larga è un fattore fondamentale per lo sviluppo della società dell’informazione. Nei paesi sviluppati si assiste ad una rapida crescita della larga banda, ma mentre il numero di nuovi sottoscrittori alla banda larga fissa si è quasi arrestato, quello relativo alla banda larga mobile sta crescendo molto rapidamente. In questo lavoro, utilizzando un panel di dati relativi ai 27 Stati membri dell’Unione europea, ha analizzato i fattori che determinano la diffusione della banda larga fissa e quelli che determinano la diffusione della banda larga mobile. Per quanto riguarda le variabili utilizzate per individuare i fattori che influenzano la diffusione della banda larga fissa, l’analisi econometrica mostra che il livello di prodotto pro-capite ha un impatto positivo, statisticamente significativo e quantitativamente rilevante sulla diffusione del servizio, mentre non risulta significativo il livello di istruzione. La quota di mercato dell’incumbent, usata come proxy della politica del unbundling del local loop, non è mai risultata significativa, a conferma la non elevata efficacia della concorrenza intramodale sulla diffusione della larga banda fissa. Invece, la variabile DSL che rappresenta la percentuale linee DSL sul totale delle linee a banda larga fissa attive, quali una proxy della concorrenza fra piattaforme, è invece risultata sempre significativa. Per quanto riguarda la variabile prezzo, i nostri risultati relativamente al prezzo del servizio di larga banda fissa sono conformi a molti lavori empirici che non trovano un’associazione negativa fra il prezzo e la diffusione della banda larga fissa. Per quanto riguarda la diffusione della banda larga mobile, le stime ottenute evidenziano la significatività di due variabili non considerate in molti lavori: la penetrazione della telefonia cellulare e la copertura 3G del territorio. Quindi, non è tanto la densità della popolazione, come a volte si sostiene, ad influire sulla diffusione della larga banda mobile quanto la copertura del territorio con tecnologie adeguate. La copertura con tecnologie adeguate – fattore che dipende dalle politiche seguite – è quindi una variabile molto più importante della densità della popolazione per quanto riguarda la diffusione della banda larga mobile. Infine, la non significatività del prezzo del servizio di banda larga fissa evidenzia che i due servizi di larga banda appartengono a due mercati differenti. Da questi risultati si può concludere in primo luogo che i due servizi a banda larga fissa e banda larga mobile si trovano in mercati differenti, in secondo luogo che la concorrenza fra piattaforme è più efficace della concorrenza politica all’interno della piattaforma per la diffusione della larga banda fissa. Infine, in particolare per quanto riguarda la banda larga mobile i risultati ottenuti indicano l’esigenza di attuare politiche a favore dell’educazione e politiche che incentivino gli investimenti nelle reti 4G e che possono incrementare la diffusione. [a cura dell'autore]
XI n.s.

Questa tesi introduce una classe di modelli epidemici di diffusione specificamente adattati alla descrizione e all'analisi delle tecnologie ICT, mediante la definizione di un mercato potenziale dinamico che dipende dalla dimensione della rete del numero di individui che hanno già adottato. Rispetto ai tradizionali prodotti “stand alone”, le tecnologie ICT hanno caratteristiche peculiari e differenti comportamenti di adozione che possono essere spiegati dagli effetti e dalle esternalità di rete. Dopo una panoramica dello stato dell'arte della letteratura sulla diffusione delle innovazioni e sulle reti (capitolo 1), viene presentato il lavoro teorico (capitolo 2). Qui, eseguiamo uno studio funzionale sistematico che conduce alla costruzione di una classe di nuovi modelli, alla loro parametrizzazione e analisi in statica comparata, e infine alla simulazione. Il modello di Bass, che assume un mercato potenziale fisso, è preso come riferimento per le comparazioni, oltre ad essere la struttura portante della nostra classe di modelli. Dalle simulazioni emerge che la nostra classe di modelli è in grado di descrivere gli effetti di rete (e le esternalità) e il loro ruolo nel plasmare la diffusione di tali tecnologie. Nel capitolo 3, testiamo la capacità di questa classe di modelli di spiegare empiricamente, con i dati di mercato, i percorsi storici di diffusione delle ICT, cercando di derivarne implicazioni utili per il policy maker (ad esempio, nel campo delle attuali agende digitali). Questo capitolo presenta la stima econometrica NLS dei modelli costruiti, prendendo come riferimento i percorsi di diffusione delle tecnologie a banda larga in alcuni paesi dell'UE: in particolare, ci concentriamo sulle serie storiche ITU di abbonamenti a banda larga fissa dei “cinque grandi” paesi europei. Le stime econometriche confermano che la nostra classe di modelli fornisce uno strumento analitico ed empirico originale per catturare e stilizzare i fenomeni di rete che dominano i percorsi di diffusione dei principali mercati delle telecomunicazioni e dei media, come la banda larga fissa. Come tale, consente anche una serie di esercizi di valutazione delle politiche future.
This thesis introduces a class of epidemic diffusion models specifically tailored to the description and analysis of ICT technologies, by defining a dynamic potential market that depends on the network size of the number of individuals who have already adopted. Compared to traditional “stand alone” products, ICT technologies have peculiar characteristics and different adoption behaviours that can be explained by network effects and externalities. After an overview of the state of the art of the literature on the diffusion of innovations and on networks (chapter 1), the theoretical work is presented (chapter 2). Here, we carry out a systematic functional study leading to the construction of a class of new models, to their parameterization and analysis in comparative statics, and finally simulation. The basic Bass model, which assumes a fixed potential market, is taken as a reference for comparisons, beside being the backbone of our class of models. From the simulations, it emerges that our class of models is able to describe the network effects (and externalities) and their role in shaping the diffusion of such technologies. In chapter 3, we test the capability of this class of models to explain empirically, with market data, the historical ICT diffusion paths, trying to derive useful implications for the policy-maker (for example, in the realm of contemporary digital agendas). This chapter features the NLS econometric estimation of the previous models, taking as a reference the real diffusion paths of broadband technologies in selected EU countries: in particular, we focus on the ITU time series of fixed broadband subscriptions of the "five big" European countries. The econometric estimates confirm that our class of models provides an original analytical and empirical instrument for capturing and stylizing the network phenomena that dominate the diffusion paths of the main telecommunications and media markets, such as fixed broadband. As such, it also enables a series of future policy evaluation exercises.

En zone de résonance, la réponse d’une cible radar à une onde électromagnétique large bande présente des singularités appelées pôles de résonance. Ces pôles de résonance sont intrinsèques à chaque objet et peuvent, par conséquent, être utilisés dans un processus d’identification. Sont étudiées dans cette thèse : une analyse du caractère résonant des objets à partir du facteur de qualité, une procédure de sélection des pôles de résonance qui suffisent pour caractériser un objet, la détermination des dimensions caractéristiques d’objets à partir des pôles de résonance, la caractérisation de cibles diélectriques, etc
In resonance region, the radar scattering response of any object can be modelled by poles of resonance. The mapping of these poles in the complex plane gives useful information for the discrimination of a radar target, as its general shape, its characteristic dimension and its constitution. This thesis presents several studies such as: an analysis of the resonant behaviour of targets with the quality factor, a procedure for selecting the poles that actually contribute to the scattering response, the determination of characteristic dimensions of targets with the resonance poles, the characterisation of dielectric targets, etc

Dans le cadre de ce travail de thèse plusieurs études seront exposées. La première aborde le problème de la conservation de l'information lors d'un processus d'amplification Brillouin. La seconde s'attache à la réalisation d'un amplificateur Brillouin possédant une large bande passante. Enfin la dernière porte sur la réalisation de lasers Brillouin de très grande cohérence. Une étude expérimentale de la transition entre le générateur Brillouin et l'amplificateur Brillouin dans un régime de saturation est effectuée. Elle met en évidence le transfert d'énergie du générateur vers la sonde amplifiée. Nous avons prouvés que même dans un régime où un générateur est puissant, les qualités spectrales de la sonde amplifiée sont préservées quand la résonance est atteinte. Les qualités de l'amplificateur Brillouin nous amènent dans une seconde partie à tenter d'augmenter sa bande passante car l'étroitesse de la bande de gain est une limite à de nombreuses applications, en particulier dans le domaine des télécommunications. Nous explorons la possibilité de travailler avec une pompe spectralement large et démontrons un élargissement spectral dépassant 10 GHz par l'application d'une pompe originellement large. Nous démontrons un laser monomode, d'une largeur spectrale inférieure au kHz, stable en fréquence et en intensité et dont le seuil est accessible par des diodes lasers DFB commerciales. Le montage est compact, robuste et le coût de revient relativement faible. La cavité peut également être utilisée séparément, c'est-à-dire sans pompe attribuée, pour des applications d'affinement spectral ou de filtrage. Enfin, l'application du dispositif à la caractérisation spectrale de lasers cohérents est démontrée et discutée
As part of this thesis several studies will be presented. The first presentes the problem of preservation of information in a Brillouin amplification process. The second focuses on the achievement of a Brillouin amplifier with a broad bandwidth. The last part concerns the achievement of Brillouin lasers of high coherence. An experimental study of the transition between Brillouin generator and Brillouin amplifier in a state of saturation is performed. It highlights the transfer of energy from the generator to the probe. We have proven that even in a regime of powerful generator, the spectral qualities of the probe are preserved when the resonance is reached. The qualities of the Brillouin amplifier lead us in a second part to try to increase its bandwidth as narrow band gain is a limitation for many applications, especially in the field of telecommunications. We explore the possibility of working with a large-band pump to achieve broad band amplification. We prove a bandwidth above 10 GHz. We demonstrate a monomode laser, with a spectral width below one kHz, stable in frequency and intensity, in which the threshold is reached by commercial DFB laser diodes. The set-up is compact, robust and cost effective. The cavity can also be used separately, ie without pump assigned, to applications of spectral narrowing or filtering. Finally, the application of the device to spectral characterization of coherent lasers is proved and discussed

Le disulfure de carbone a fait objet de plusieurs types d'études en optique non linéaire, durant plusieurs décennies. C'est à ce titre qu'il est considéré comme un corps de référence dans les liquides. La forte constante Kerr de ce milieu et son seuil de diffusion peu élevé ont fait de celui-ci un milieu difficile à cerner. Ainsi, les spectres émanant de ce corps ont été interprétés de différentes manières selon les auteurs, en fonction du régime d'excitation et des intensités laser. Nous proposons dans un premier temps une étude spectrale en fonction de l'énergie (de 3. 10⁻ ¹ à 10 GW/cm²) sur le faisceau rétrodiffusé par le disulfure de carbone dans le cas où nous l'excitons avec une seule onde intense, en régime picoseconde; nous montrons le rôle de l'autofocalisation, et de l'automodulation de phase dans le développement des instabilités liées aux processus de diffusion. Dans un second temps, nous étudions la rétrodiffusion ainsi produite dans une expérience pompe-sonde. Nous montrons que la présence de la sonde modifie la direction de la rétrodiffusion, son intensité et son spectre. Les expériences sont faites en fonction des paramètres géométriques et temporels. Nous essayons enfin par la suite une étude préliminaire d'amplification sur une sonde se situant dans la large bande spectrale révélée par les études à une onde dans le disulfure de carbone.

La tendance majeure dominant actuellement le marché des Technologies de l'Information et de la Communication (TIC) est la création d'un nouvel environnement dont les fonctionnalités permettraient aux utilisateurs d'avoir accès à une pluralité de services sans contrainte de lieu, de temps et de terminal. Les nouvelles générations de réseaux et systèmes ouvriront la voie en fournissant une plus grande accessibilité réseau et en créant un contexte d'inter-opérabilité aux systèmes hétérogènes. Ces réseaux hétérogènes trouvent leurs origines dans trois mondes: le monde des télécommunications, le monde des diffuseurs et le monde de l’Internet. Dans cet optique, nous proposons une architecture large-bande de réseau métropolitain sans-fil utilisant le flux DVB-T dans les configurations régénératives, ceci en vue de créer une infrastructure multi-services au sein de la bande UHF/VHF. Cette épine dorsale DVB-T permettra une inter-connection continue des réseaux d'accès multi-technologiques. Une approche reposant sur un système de management dynamique et interactif de la bande-passante est proposée, comprenant des fonctionnalités de prédiction et des techniques de fitrage adaptives pour la livraison optimale en simultanée de services IP et de TV numérique. Au niveau des services, le défi à relever concerne particulièrement l'accès omniprésent au service. Afin de réaliser ces concepts novateurs, une solution complète, constituée autour d'un middleware et reposant sur des outils orientés sur les meta-données (MPEG-21), est exposée. Celle-ci apportera une nouvelle vision aux plateformes de services de nouvelle génération directement dédiée à la création de services multimedia ambiants
The actual trend in the IT (Information Technology) market is to create a new environment that will enable end-users to access a variety of services (TV/Radio programs, Internet, Multimedia applications, Games. . . ), wherever they are, whenever they want and whatever terminal they use. The heterogeneous networks basically come from three worlds: the Telecommunication world, the Broadcasting world and the Internet world. This cross-industry synergy is jointly driven by the tremendous growing interest to Internet services and the planned adoption of the Digital SwitchOver (DSO) in UHF, enabling broadband terrestrial digital broadcasting infrastructures (e. G. DVB-T). To this end, we propose a broadband wireless metropolitan area network architecture that utilises the DVB-T stream in regenerative configurations for creating a multi-service capable infrastructure in the UHF/VHF band. Within this mixed context, an important issue arises concerning the management of resources between IP and DTV services. Towards this, we present an approach based on an interactive Dynamic Bandwidth Management System, with prediction functionalities and using adaptive filtering techniques for optimal provisioning of IP and Digital TV services

Ce travail concerne la caractérisation du fond marin au moyen d'un sonar très large bande à directivité constante. L'originalité de l'étude repose d'une part sur la mise en œuvre d'un système sonar expérimental capable d'émettre et de recevoir des signaux "chirp" (modulation linéaire de fréquence entre 20-140 kHz) et d'autre part sur le développement de méthodes de modélisation, d'identification et de classification adaptées à l'analyse des signaux rétrodiffusés par le fond marin. Dans une première partie, les signaux collectés sur 5 types de fonds différents sont analysés par la fonction d'ambiguïté pour laquelle on compare les performances des formulations large bande et bande étroite ainsi que les relations existant avec les représentations temps-fréquence. Dans une deuxième partie, la répartition de l'énergie rétrodiffusée par le fond est analysée dans le plan temps fréquence ce qui permet de rendre compte des phénomènes de diffusion de l'onde acoustique d'un point de vue spatial et fréquentiel. Afin d'améliorer la lisibilité des représentations temps-fréquence de type Wigner-Ville, nous avons proposé une représentation originale adaptée aux signaux "chirp" et la comparaison avec les autres représentations de la classe de Cohen montre l'amélioration apportée par notre méthode. Enfin, dans une 3ème partie, un modèle de rétrodiffusion par une surface rugueuse est développé. Nous montrons que ce modèle est la convolution entre la réponse impulsionnelle d'un fond plan et la densité de probabilité des rugosités. Une procédure d'estimation de la rugosité à partir des données expérimentales est proposée. Ce modèle est bien adapté aux fonds de sable, graviers et galets alors que le fond de vase nécessite un modèle prenant en compte la propagation de l'onde acoustique dans la couche sédimentaire. Dans chaque situation, les résultats des analyses des signaux sont confrontés aux analyses géotechniques réalisées durant l'étude
This work is concerned with the characterisation of the sea bottom by means of a constant beamwidth wideband sonar. The originality of this work is: firstly, the development of an experimental wideband sonar system which transmits linear chirp signal (20-140 kHz). Secondly, modelization, identification and classification methods adapted to the bottom backscattering signals have been developed. In the first part, backscattered signals from 5 types of bottoms have been analyzed by the ambiguity function. The performances of the wideband ambiguity function and the narrow band ambiguity function are compared for the chirp signal, and the relationship with the time-frequency representations is presented. In the second part, la distribution of the bottom backscattered energy is analyzed in the time-frequency plane which permits to consider the acoustic diffusion phenomena. In order to improve the comprehension of the Wigner time-frequency representation, we propose an original time-frequency representation adapted to chirp. The comparison with other Cohen's class representations shows the improvement given by our method. At last, in the third part, a rough surface backscattering model is developed. We have shown that the statistical average of the impulse response is a convolution between the impulse response of a plane and the probability density function of the roughness. A roughness estimation method is therefore proposed. This model is well adapted to sand, gravel, and pebbles bottoms. For the silt bottom, a volume backscattering model is developed. In each situation, the results of the estimation are compared with the geotechnical analysis

Nombre d'applications récentes reposent sur la capacité des systèmes de communication à délivrer des informations de localisation. Les propriétés de la technologie Ultra-Large Bande (ULB) peuvent alors être mises à profit: résolution, précision temporelle pour la mesure de temps de vol et la synchronisation. Les travaux présentés traitent du problème de localisation ULB dans les réseaux sans-fil, mettant en avant la diversité multi-trajets, la connaissance a priori ou les formes nouvelles de réseau (ad hoc). Nous modélisons les erreurs susceptibles d'affecter des temps (ou différences de temps) d'arrivée, qu'elles soient " indépendantes " de la couche physique ou directement imputables au canal de propagation. Nous évaluons les performances de détection de récepteurs ULB. Nous préconisons des stratégies de positionnement et de poursuite adaptées aux non-visibilités. Enfin, des résultats d'expérimentations conduites dans la bande basse illustrent certains des points abordés
Many recent applications rely on the capability of communication means in delivering location information. Hence, the properties of the Ultra Wideband (UWB) radio technology can be exploited: resolution, fine temporal precision enabling Time Of Flight estimation and synchronization. . . The proposed work addresses the UWB localization problem in wireless networks, emphasizing multipath diversity, modern network embodiments (ad hoc), or the a priori knowledge. The errors affecting times (or time differences) of arrival are modelled. These errors can be independent of the physical layer or can result from severe propagation conditions. The detection performance of low-complexity UWB receivers is also evaluated. Then, we recommend the use of positioning or tracking techniques adapted to non-line of sight situations. Finally, some experimental results obtained in the lower band are provided and allow us to illustrate some of the discussed points

Ce travail de thèse porte sur la diffusion des porteurs de charge en excès dans deux semiconducteurs à large bande interdite: l’alliage ZnMgO et le diamant 13C. Il est basé sur l’étude d’hétérostructures ZnMgO/ZnO/ZnMgO et 13C/12C/13C à puits de collecte ZnO ou 12C. Sur leurs sections transverses et avec la résolution nanométrique en excitation par cathodoluminescence (CL), nous avons étudié l’évolution de l’intensité de l’émission issue du puits en ZnO ou 12C en fonction de la distance entre l’impact de l’excitation et le puits. Cela nous a permis de mesurer directement les longueurs de diffusion effectives dans ZnMgO et le diamant.Dans ZnMgO, la valeur de 55 nm à 300 K, mesurée sur section transverse clivée, est proche de celle du matériau massif. Elle correspond à une diffusion mixte excitons/porteurs libres. Avec l’utilisation de lames minces érodées par faisceau d’ions, une diminution de a été observée jusqu’à 8 nm dans les parties les plus fines. Cet effet est attribué aux recombinaisons non radiatives de surface. Les lames minces apparaissent alors d’un grand intérêt pour améliorer la résolution spatiale des images CL.Dans le diamant, la diffusion excitonique à basse température montre une faible dépendance de avec l’énergie incidente des électrons. Cela indique que ≈ 15 µm à 20 K dans le diamant massif 13C. Une diminution de jusqu’à 3,3 µm à 118 K est observée en fonction de la température.Enfin, nous avons mis en évidence la formation de polyexcitons dans le diamant en augmentant la densité des paires électron-trou, soit par la puissance d’excitation, soit par le confinement spatial des excitons dans des puits de diamant 12C de faible épaisseurs
This work focuses on the determination of the carrier diffusion length in two wide bandgap semiconductors: the ternary alloy ZnMgO and diamond. This determination has been achieved by using of ZnMgO/ZnO/ZnMgO and 13C/12C/13C heterostructures containing ZnO or 12C collecting wells. Their transverse section was scanned by CL spectroscopy with a nanometer scale resolution in excitation. The effective excess carrier diffusion length is deduced from the evolution of the well emission intensity with the distance between the excitation impact and the well.In ZnMgO, the value at 300 K is 55 nm, obtained from a cleaved cross section. It is close to the bulk material diffusion and is attributed to a mixed diffusion of excitons/free carriers. A decrease of down to 8 nm is observed in the thinnest portions of cross sections shaped by focused ion beam (FIB). This effect is attributed to non-radiative surface recombinations. These thin slabs appear of great interest to enhance the spatial resolution of CL images.In diamond, the exciton diffusion at 20 K exhibits a slight dependence on the incident electron energy. This indicates that the exciton diffusion length is around 15 µm in 13C bulk diamond. The values decrease down to 3.3 µm at 118 K.Finally, we highlighted the formation of polyexcitons in diamond by increasing the electron-hole pairs density either by the excitation power, or by the spatial confinement of excitons in thin 12C wells

Les études réalisées ont été consacrées à la détermination de l'influence du vieillissement physique sur la nanostructure et les relaxations moléculaires de homopolymères et copolymères amorphes. Les techniques utilisées étaient les difussions Raman et de RX, les spectrospcopies diélectrique et mécanique, ainsi que la calorimétrie. On a constaté que la structure des homopolymères amorphes devient plus homogène par lissage du constraste de constante élastique à l'échelle nanométrique. Au contraire, la structure à l'échelle nanométrique des copolymères étudiés tend à être plus hétérogène par vieillissement. Cela est du à l'agrégation d'unités chimiques semblables à l'échelle de quelques nanaomètres. Les techniques utilisées pour la détection de la mobilité moléculaire ont permis d'observer une diminution du recouvrement des relaxations α et β pendant le vieillissement

The influence of institutional pressures on standards and standardization are readily apparent in their most direct form. For example, in the mid-1990s, both the European Union and the United States issued new wireless communications licenses in the 1.8-2.0 GHz band: the EU countries mandated use of their decade-old communications standard, while the U.S. authorized three competing standards not yet widely used in the U.S. (Mehrotra, 1994). However, institutional pressures can also shape standardization efforts in a less direct fashion. For example, in a regulated industry such as telecommunications, existing economic and political institutions constrain the diffusion of a new technology. Such diffusion mediates the impact of product compatibility standards upon society. If producers adopt standards for their goods and services, and if users adopt the products that incorporate such standards, only then such standards can have an economic or social effect upon society at large. Therefore, it is important to understand the impact of institutional pressures on diffusion of the innovation that incorporates a standard if we wish to explain the eventual success or failure of such a standard. Here a particular standards-based innovation, analog cellular telephone service, provides an opportunity to contrast the effects of institutions on diffusion and thus standardization. Over a four year period, three independent design centers deployed mutually incompatible standards in three continents. While the technical solutions were similar, differences in institutional context between the regions influenced both the nature of the respective standards and their corresponding diffusion. In particular, the systems were deployed in a period of shifting telecommunications competition policies and priorities for radio frequency allocation. Prior research has examined the causal links between standards and institutions, both the institutional context of standards development (e.g., Besen, 1990) and also how established standards themselves function as institutions (Kindleberger, 1983). But rarely do we have the opportunity to examine the diffusion of the same innovation in differing institutional contexts. This paper will focus on the most complex institutional context for the deployment of cellular telephone service, the United States, which despite having invented cellular technology, was the third region to deploy cellular service due to regulatory delays. The experience of Japan and Northern Europe are offered as contrasts to highlight the importance of the institutional context in the adoption of both standards and standardized products.

Chalcogenide thin films have attracted a great deal of attention for decades because of their unique properties. The recent developments on thin film-based supercapacitor applications were reported. As a result of sustained efforts, the experimental findings revealed remarkable properties with enhanced fabrication methods. The properties of perovskite solar cells were discussed in terms of crystal structure and phase transition, electronic structure, optical properties, and electrical properties. Perovskite solar cell has gained attention due to its high absorption coefficient with a sharp absorption edge, high photoluminescence quantum yield, long charge carrier diffusion lengths, large mobility, high defect tolerance, and low surface recombination velocity. The thin film-based gas sensors are used for equally the identification and quantification of gases, and hence should be both selective and sensitive to a required target gas in a mixture of gases. Metal chalcogenide materials are considered excellent absorber materials in photovoltaic cell applications. These materials exhibited excellent absorption coefficient and suitable band gap value to absorb the maximum number of photons from sun radiation. The photovoltaic parameters were strongly dependent on various experimental conditions.

Abstract Materials with fine-scale structures are recognized to exhibit technologically efficient mechanical or thermal properties. Thermal sprayed nanostructured media could also be interesting in the optical field thanks to the diffusion interaction between short wavelength radiations and submicron-sized pores. One difficulty of the Suspension Plasma Spray (SPS) technique is to provide a sufficiently thick coating and to maintain efficient mechanical properties when the coating is removed from the substrate. The aim of this study was to spray a reflective and diffusive self-supporting alumina bilayer. The first coating was obtained by Atmospheric Plasma Spraying of micron-sized powders in order to obtain a thick layer and the second coating was sprayed by SPS onto the first one with strong adhesion. An oxide ceramic material with high scattering reflectance in a large band of wavelengths was thus obtained.

Gas discharge excitation at 40.68 MHz (ISM frequency in the VHF-band) is proven to be efficient for non-wave-guide, diffusion-cooled, large area CO2 laser employing a novel type of resonator cavity referred to as split-wave hybrid (SWH) resonator [1]. SWH resonator approach represents a custom resonator concept in the design of sealed-off, high power, single mode CO2 lasers for industrial applications. Electrode walls in the SWH resonator act as wave-front-splitting mirrors similar to a Fresnel double mirror or Lloyd mirror interferometer [2].

As much as 25% self-diffraction has been observed at the surface of n-GaAs:Te when two pumps (and a weak probe) intersect with an internal angle of 0.15 rad in the Raman–Nath regime. The photoinduced gratings decayed in less than 100 ps. The diffraction efficiency was nearly independent of sample thickness (40 μm and 350 μm), and careful investigation has shown that the diffraction arose primarily at the surface and was resonant just below the band edge. It is proposed that band-bending at the surface states causes increased absorption and results in a sheet of optically induced charge. The faster diffusion of electrons relative to holes allows a transient charge separation to a distance of one diffusion length (1 μm). As a result, a space-charge field is formed (Dember field) that can cause an index change through the Franz–Keldysh effect. The resulting transient grating can cause the large observed diffraction. This new BEST effect has potential for optical-switching applications.

The phonon Boltzmann Transport Equation (BTE) is difficult to solve on account of the directional and spectral nature of the phonon intensity, which necessitates angular and spectral discretization, and ultimately results in a large number (typically few hundreds) of four-dimensional partial differential equations. In the ballistic (large Knudsen number) regime, the phonon intensity is highly anisotropic, and therefore, angular resolution is desirable. However, in the diffusive (small Knudsen number) regime, the intensity is fairly isotropic, and hence, angular discretization is wasteful. In such scenarios, the method of spherical harmonics may be effectively used to reduce the large number of directional BTEs to a few partial differential equations. Since the Knudsen number is frequency dependent, the decision to preserve or eliminate angular discretization may be made frequency by frequency based on whether the spectral Knudsen number is large or small. In this article, a hybrid method is proposed in which for some frequency intervals (bands), full angular discretization is used, while for others, the first order spherical harmonics (P1) is invoked to reduce the number of directional BTEs. The accuracy and efficiency of the hybrid method is tested by solving several steady state and transient nanoscale heat conduction problems in two and three-dimensional geometries. Silicon is used as the candidate material. It is found that hybridization is effective in significantly improving the efficiency of solution of the BTE — sometimes by a factor of three — without significant penalty on the accuracy.

Isolation and purification of antithrombin III (AT III) by affinity chromatography on immobilized heparin is a standard method for the large scale preparation of this protein from human or animal plasma. Hence, after AT III became available by gentechnological methods, we tried to adapt this procedure for the isolation of AT III from supernatants of mammalian- and yeast-cells. Indeed, it was possible to use this method also for the isolation of the recombinant gene products. Since, however, the cell growth media contain heterologous protein or peptide mixtures like fetal calf serum, the method had to be improved to avoid the adsorption of non human proteins or peptides. We are now able to purify AT III from CHO-cell-superna-tants to more than 95 % purity. The characterization of this AT III-product by double immuno diffusion revealed that it is immunologically totally identical with the authentic material from plasma. AT III antigen content, progressive inhibitor activity and heparin cofactor activity compare very well in the final product; hence, it is totally active compared to AT III from plasma.In polyacrylamidegel electrophoresis most of the material migrated differently to the authentic material showing 9 bands in equal distance to each other, instead four in the At III from plasma. After degradation with sialinidase from both AT III preparations identical cleavage products were obtained migrating predominantly as a single band. Hence, the electrophoretic heterogeneity seems to be due to a different degree of sialinyla-tion of the products.

Resonatorless absorptive switching and self-pulsing have been observed in bulk ZnSe when excited by square input pulses at 476.5 nm on a time scale from ~1 μs to >1 s. Beyond a critical intensity of ~7 kW/cm2 the material begins to switch repeatedly between a transmission of ≥60% and ≤5%. This switching and self-pulsing behavior is a local phenomenon (resonatorless). This bistable behavior is based upon band gap renormalization, band filling, and plasma screening. Through absorption there is an increase in the temperature. This results in a shifting of the band edge to longer wavelengths. This further increases the absorption. At some point the incident photons become completely absorbed and a switching to an “off” state results. At this point a relatively large number of electron-hole pairs are created. Depending on the thermal and electron-hole pair concentration dynamics, a filling of the available states eventually results and the absorption decreases. Thermal diffusion then allows for local cooling, the band gap shifts to shorter wavelengths, and a switching to the “on” state results. This modulation of the absorption continues, and one sees a sequence of pulses (self-pulsing) in the transmission.

The origin of optical nonlinearity in a semiconductor-doped glass at room temperature is studied using a pump-probe experimental technique. Glasses doped with semiconductor crystallites which are commercially known as sharp-cut color filters provide very interesting media for nonlinear signal processing because of their rapid response time (due to short carrier diffusion time) and large optical nonlinearity.1 The output of a nitrogen laser is used to pump a tunable dye laser (pump) and a dye cell (probe continuum). The pump-induced changes in transmission of the broadband probe are recorded with a combination of a spectrometer and an optical multichannel analyzer. A 100-Å blue shift of the band edge is observed in a selenium ruby glass (100–1000-Å microcrystallites of CdS1− x embedded in a borosilicate glass matrix, x = 0.7–0.9) with 4 μJ of the narrow bandwidth pump tuned to 5100 Å (band edge ≃ 5200 Å). Using a high energy continuum alone (2-μJ energy), a blue shift of ≃ 175 Å is observed. The blue shift of the band edge cannot arise from a pump-induced thermal effect that would instead bring about a red shift. The band-edge blue shift is evidence for efficient band filling by injected carriers. The measurement of the nonlinear index, using an interferometric technique, is under way.

Ultrasound imaging technique finds crucial application in clinical diagnosis of breast cancer. Presence of noise in ultrasound image due to different factor degrades the image quality and so the accuracy of diagnosis. Wavelet thresholding have been used from very beginning for de-noising of ultrasound image. Here in this paper we propose an intervention of anisotropic diffusion techniques in wavelet thresholding. In wavelet thresholding the thresholding operation usually applied after various feature extraction step, but in this study, we proposed to use a combinational approach. The approach reduces computational complexity of previous techniques. The proposed technique provides a Peak Signal to Noise Ratio of 28.46 and Mean Square Error of about 92.5537. The technique was practiced over large dataset of breast cancer images.

A beam-coupling gain of 19.1 cm−1 in InP:Fe has been achieved using near band edge photorefractive techniques. The conventional electro-optic photorefractive (EOPR) effect in semiconductors may be combined with the Franz–Keldysh electrorefractive photorefractive (ERPR) effect to produce large beam coupling gain coefficients. We have examined the effects using a tuneable Ti:sapphire laser in a pump/probe configuration and an applied electric field. Conventional EOPR creates a sinusoidal space-charge field (Esc) through carrier drift and diffusion, and the applied field (Edc) increases the magnitude of the applied space charge (Etot = Esc + Edc), as well as affecting the phase shift of Δn with respect to the intensity pattern. With appropriate temperature stabilization and ERPR, this phase shift can be maintained near ±90°, depending on the sign of Edc, determining the direction of energy transfer. We have characterized beam coupling gain, Γ, as a function of wavelength, intensity, temperature, grating spacing, and applied electric field and achieved a maximum Γ = 19.1 cm−1 at λ = 970 nm, T = 17 °C, Λ (grating wavelength) = 8.5 μm, IPump = 141 mW/cm2, and β (pump/probe ratio) ≈ 1000. Still higher gains have been seen using a moving grating technique, and the results will be presented at the conference.

Semiconductor multiple quantum well structures exhibit very large, room temperature, nonlinear refractive effects associated with resolvable excitonic features [1]. These nonlinearities may find use in all-optical devices if sufficient refractive index change can be achieved before the exciton completely saturates [2]. A unique aspect of band gap resonant optical, nonlinearities in quantum wells is the spatial confinement of the generated carriers within the layers. We have exploited the excitonic refractive nonlinearity in GaAs/AlGaAs multiple quantum wells in two separate degenerate four wave mixing configurations. These compare the intra-well and cross-well contributions to highly anisotropic carrier diffusion and also allow measurement of carrier relaxation rates and the saturation of the excitonic nonlinear refraction with increasing intensity.