Academic literature on the topic 'Matrix de réflexion'

Transmedia storytelling, as defined by Henry Jenkins in 2006 in his book Convergence Culture, highlights a production strategy that aims to augment the narration of a cultural work by scattering it across several media platforms—digital or non-digital. The term is certainly quite recent, but the practices are not new and allow us to understand the evolution of the cultural industries and the creation of a new media ecosystem. As Matthew Freeman states, transmedia storytelling always relies on industrial changes, the narration adapting itself to new media synergies and novelties to create engaging and coherent storyworlds.Producers of American TV shows, showrunners, and networks are more and more eager to develop narrative universes on other media platforms in order to target new audiences and to give food for thought to fans, as well as reward them for their intellectual and emotional investment. Ancillary content and tie-ins sometimes take the form of novelisations or comic books, highlighting the fact that strategies of transmedia storytelling can be deployed on non-digital platforms and still enhance the narrative aspects of the show. For example, Twin Peaks (1990) developed The Diary of Laura Palmer (1990), a journal written by the character Laura Palmer who gave insights on her life and details about her relationships with other characters before she was murdered at the beginning of the series. How I Met Your Mother (2005-2014) published The BroCode (2008), first seen on episode “The Goat” (season 3 episode 17), and The Playbook (2012), first seen in an episode entitled “The Playbook” (season 5 episode 8). They are bibles written by character Barney Stinson that contain rules or advice for picking up women. For instance, The BroCode contains 150 articles, a glossary of terms, a definition of “a bro,” history of the code, amendments, violations, and approved punishments, all invented by Barney; some of these components were talked about on the show, while others were original additions for the book.Another way to create transmedia storytelling around TV shows is by developing comic books. This article will explore this specific media form in relation to transmedia strategies and will try to underline how comic books can make a narrative richer by focusing on parts of the plot, characters, times, or locations. First, I will focus on the importance of seriality from a historical perspective, because seriality appears to be one of the main principles of transmedia storytelling. Yet, is this narrative continuity always coherent and always canon when it comes to the publication of comic books? I will then propose a typology of the narratives comic books exploit to augment the storytelling of a show. I will give examples to illustrate how comic books can enrich the narrative universe of a given show and how characters can smoothly move from one platform to the other.A Transmedia World: Television and Comic Books Hand in HandSeriality is one of the main pillars of transmedia storytelling, and, according to Jenkins, “it is about breaking things down into chapters which are satisfying on their own terms, but which motivate us to come back for more” (“Transmedia”). These characteristics are already present in the way TV series are written, produced, and broadcast, and in the way comic books are created. They rely on episodes for TV shows and on issues for comic books that usually end with suspense and a suspension in the narrative continuity, commonly known as a cliff-hanger. For comic books, this narrative continuity took root in the early comic strips of the 18th and 19th century (Maigret and Stefanelli), which played a huge part in what we now know as comic books. As Pagello explains:The extensive practice of narrative serialisation played a major role in this context: the creative process, the industrial production and distribution, the editorial practices and, finally, the experience of comics readers all underwent dramatic changes when comics started to develop an identity distinguished from satirical cartoons, illustrated books and the various forms of children’s picture stories.According to Derek Johnson, these evolutions, in terms of production and reception, are closely linked to the widespread use of the franchise model in media industries. Johnson explains thatcomic books, video games, and other markets once considered ancillary now play increasingly significant and recentered roles in the production and consumption of everyday film and television properties such as Heroes, Transformers, and the re-envisioned Star Trek in ways that only very few innovators (such as George Lucas and his carefully elaborated and expanded Star Wars empire) had previously conceived in the twentieth century.The creation of transmedia strategies that capitalize on narrative continuity and seriality call for some synergies between media and for a “gatekeeper” of the stories who will ensure that all is coherent in the storyworld. Thus, “in 2006, the management of Heroes, for example, became a job for a professional ‘Transmedia Team’ charged with implementing creative coordination across television, comics, and the Internet” (Johnson).Another principle of transmedia storytelling, closely linked to seriality and the essence of the definition, is the creation of a narrative universe, that is “world-building,” in which plots and characters develop, and which will lay the foundations for the story. These foundations will be written in what is called a Bible, a document containing all the narrative elements in order to ensure coherence. In the notion of world-building, a matrix of possibilities is deployed, since stories can potentially become threads to weave, and re-weave. This rhizomatic world can be extended to infinity in a canonical way (by the official production) and in a non-canonical one (by the creations of fans). For Mark Wolf, these narrative worlds work like dynamic entities, and are transformative, transmedial, and transauthorial, which are similar to the notions and possibilities of transmedia storytelling, and media and cultural convergence. Stories that cannot be contained within the “real” of a single medium will be expended and developed on another or several other ones, creating a rich storyworlds. Comic books can be one of these tie-in media.New Term, Old Creations: An Historical OverviewMatthew Freeman wrote in his latest book Historicising Transmedia Storytelling that these transmedia practices do have a past and existed long before the introduction of the term due to new technologies, production strategies, and reception tactics. Comic books were often an option to enrich storylines and further develop the characters. For example, L. Frank Baum created a storyworld around The Wizard of Oz made of mock newspapers, conferences, billboards, novels, musicals, and comic strips in order to “appeal to a migratory audience” (Jenkins, “I Have”) and to deepen the characters, introduce new ones, and discover the land of Oz as if it were a real location. The author used techniques of advertising to promote and above all to expand his storyworld. As newspaper comic strips were quite popular at the time, Baum created several tie-in extensions in the newspapers and in a novel format. As Jason Scott underlines, “serial narratology enhances the possibilities of advertising and exploitation through the established market for the second and subsequent instalment” (14). The series of comic strips entitled Queer Visitor from the Marvellous Land of Oz (1904-1905) picked up, in terms of narration, just after the end of the book, offering a new temporality and life for the characters. As Freeman notes, this choice follows an economic logic:The era’s newspaper comic strips and their institutional tendency to prioritize recurring characters as successful advertising mechanisms (as witnessed in the cross-media dispersion of Buster Brown) had in fact influenced Baum to return to the series’ more familiar faces of Dorothy, the Scarecrow, and the Tin Woodman (2371).Here, the beloved characters are moving from one medium to the next, giving new insights on their life after the end of the book, and enhancing their stories beyond its pages.A Typology of Comic Books and Tie-in Extensions of TV SeriesBefore diving into a tentative typology, I want to look at the definition of canon in a transmedia storyworld. There is a strong debate in academic discussions around the issues of canonicity, and here I understand canonicity as the production of official texts around a given cultural content. That is because of precisely what is qualified as an official text or an official extension, and what is not. In the book I co-edited with Benjamin W.L. Derhy Kurtz (Derhy Kurtz and Bourdaa), we respond by coining the term “transtexts,” which includes officially produced texts and fantexts in the same narrative universe. The dichotomy between both kinds of texts is thus diminished. Nonetheless, in production and transmedia strategies, canonicity is hard to evaluate because “few television series have attempted to create transmedia extensions that offer such a (high level of) canonic integration, with interwoven story events that must be consumed across media for full comprehension” (Mittell 298). He follows by proposing a typology of two possible transmedia extensions based on a canon perspective versus a non-canon one: “what is extensions” extend the storyworld canonically and in a coherent way, whereas “what if extensions” “pose(s) hypothetical possibilities rather than canonical certainties, inviting viewers to imagine alternate stories and approaches to storytelling that are distinctly not to be treated as potential canon” (Mittell 298). Mark Wolf refers to the term growth to qualify canonical materials which are going to expand a given storyworld and which nourish the stories. As argued by Gabriel et al., “Wolf’s definition of ‘growth’ makes it clear that, for him, a transmedial product can only be considered to contribute to a world’s growth if it adds new ‘canonical’ material, i.e. material that presents new pieces of information that are “true” for the fictional world” (Gabriel et al. 169). This notion of “truth” to the diegesis can be opposed in this context to the notion of alternate stories and alternate versions of the characters.My attempted typology lays its foundation upon this opposition between what is seen as an official extension and what is seen as an unofficial extension, but offers alternate perspectives to expand the storyworld using new characters, locations, or universes. The first category will look at canonical extensions and how they can deepen characters’ development and temporalities. The second category will deal with “canon divergent” (to use fans’ language) extensions and how they can offer new entries into the stories by creating new characters or presenting new locations.Canonical Extensions: CharactersTie-in extensions in the form of comic books help to deepen the characters, especially supporting characters, by delving into their motivations and psychology, or by giving them backstories and origin stories. According to Paolo Bertetti, “the transmedia character is a fictional hero whose adventures are told on several media platforms, each providing details about the character's life” (2344). Actually, motivated characters are the quintessential element of the narration of the classic Hollywood era, which was then reused in the narration of TV series, which were then penned into comic books. In her definition of transmedia superstructures, Marsha Kinder based her analysis on how characters moved from one medium to the next, making them the centre of the narrative universe and the element audiences would follow.For example, Fringe (2008), in a deal with DC comics, extended its stories and its characters in comic books, which were an integral part of the storyworld, and which included canon materials by offering Easter Eggs to fans and rewarding them for their investment in the narrative universe. Each issue of the second series dealt with a major or recurring character from the show, deepening them by giving them backgrounds. That way, audiences can discover the backstories of Agent Broyles, Nina Sharp, the CEO of Massive Dynamic, or even Gene, Walter’s cow, all of which are featured in the series but not well developed.Written by actor Tim Rozon (who plays Doc Holliday on the show) and author Beau Smith, Wynonna Earp Season Zero (2017) focuses on the past of main character Wynonna Earp when she was an outlaw and before she comes back to her hometown, Purgatory. The past comes to life on the pages, while it was only hinted at in the show. It is a good introduction to the main character before the show, since Wynonna comes back to Purgatory by bus at the beginning of the very first episode and there are no flashback episode relating her story earlier. Because the two authors of this comic book are part of the creative crew of the show, an actor and a writer, they ensure a sense of coherence in the extensions they write.In collaboration with Dynamite Entertainment, an American comic book company, NBC Universal launched a series of comic book issues entitled Origins (2008) as an ancillary text to Battlestar Galactica (2004). “Origin stories” are a specific genre related to superhero franchises. M.J. Clarke underlines that,the use of Origins Stories is influenced by the economic structure of the comic book industry, which continues to produce stories over years and decades. ... By remaining faithful to the Origins (which are frequently modified in their consistency), readers can discover a story without having to navigate in more than 400 numbers of commix. (54)The goal of these comic books is to create a "past" for the human characters that appeared in the series. The collection of comic books thus focuses on five main characters in 11 issues, spread out over a year: William Adama, Zarek, Gaius Baltar, Kara "Starbuck” Thrace, and Karl "Helo" Agathon. These issues are collected in an eponymous Omnibus. Likewise, Orphan Black (2011) also offered backstories for its “clone club” without disrupting the pace of the show. The stories, tied to the events of the series, focus on the opportunity to better understand the emotions, thoughts, and feelings that exemplify the characters of the show.It is interesting to note that the authors of these comic book extensions were in close contact with Ronald D. Moore and David Eick, showrunners of the Battlestar Galactica series, which guaranteed coherence and canonicity to the newly created material. In a personal interview, Robert Napton, writer of Origins, explained the creative process:so every week we would watch episodes and make sure our stories matched as closely as possible to what the television series was doing …we tried to make it feel like it was very much part of the series, so they were untold adventures and we tried to fit it into the continuity of the series as much as possible.Brandon Jerwa, writer for Battlestar Galactica comic book series Season Zero and Ghosts (2009), confirmed that, “It is my understanding that the comics were passed through Mr. Moore’s office, and they were certainly vetted by Syfy and Universal.” Jerwa also added an interesting input on perception of canonicity versus non-canonicity by fans who can be picky about the ancillary contents and added materials that extend a storyworld:Most comic tie-ins have a hard time being considered a legitimate part of the canon, and that is simply beyond the control of the creative team. I worked very hard to make sure that I was writing material that adhered to the continuity of the show as closely as humanly possible. I don’t believe in writing a licensed property in such a way as to put forward ‘my vision’ of the universe; I believe very firmly that it is my responsibility to serve the source material above all else.Canonical Extensions: TemporalitiesComic books as a licensed product can expand the temporalities of the show and tell stories before the beginning of the series and after it ended, as well as fill time voids and ellipses. For example, now in its 11th season in comic books, Joss Whedon managed to keep Buffy the Vampire Slayer (1997-2003) alive and to attract new fans without alienating its original fanbase. Blogger and web entrepreneur Keith McDuffee felt that reading Buffy as a comic book after seeing it on television for seven years was strange, but the new format was a good sign because: “the medium lets creativity go completely wild without budget worries.” The comic books focus on the famous characters and created a life for them after the end of the show, making them jump from the screen onto the pages. Sometimes, the comic books told original stories that might seem out-of-character, like the issue in which Buffy sleeps with a woman. That kind of storyline wasn’t explored in the TV show, and comics offer one way to go deeper into the characters’ backgrounds and psychology. Sometimes, the tie-ins do not strictly follow the continuity and become non-canon regarding the stories of the TV shows. For example, DC/Wildstorm presented comic book issues around The X-Files (1993-) that were set in continuity of the show but failed to refer to main plot events (for example, Scully’s pregnancy). “Rather than offering ‘additive comprehension’ to a pre-existing television and film narrative, Spotnitz chose to write licensed comics on their own terms” (Pillai 112).DC is familiar with offering new adventures for its superhero characters in the form of comic books (which are first published online), going back to the basics. Of course, in this case, the relationship between the comic book medium and the television medium is more intricate, as the TV series are based on comic book characters whose stories are then extended again in comic books, which are created specifically to extend the TV shows’ storyworlds. The creation of the comic book series The Flash Season Zero (2015) set the stories between the episodes of the first season of The Flash and focus on the struggles of Barry Allen as he juggles between his job as a CSI, his love for Iris West, his childhood sweetheart, and his new identity as a vigilante with superpowers. This allows viewers to better understand a part of Barry Allen’s life that was not well developed in the show, adding temporal layers to the stories. The Adventures of Supergirl vol. 1 (2016) also depict the battles of the girl of steel between episodes, as well as her life with her sister, Alex (who is also a new addition in the comic book), and her co-workers at the DEO. For Arrow,the digital tie-ins offer producers [opportunities] to explore side stories they are unable to cover on screen. In the case of Season 2.5, the 22-chapter comic enabled the producers to fill in the blanks in between the seasons, thus offering more opportunities to explore the dynamics of fan-favorite characters such as Felicity and Diggle. (Bourdaa and Chin 183)These DC comic books are examples of giving life to a TV show beyond the TV screen, enhancing the timeframe of the stories and providing new content. The characters pass through the screen to live new adventures in comic books. In some cases, the involvement of the series' actor and writer in comic book scripting confirms the desire for consistency in the extensions of the series, whatever the medium used and whatever the objectives.Canon Divergent Extensions or the Real PossibilitiesFinally, comic books can deploy stories that will display a new point of view on the canon: a “multiplicity” (Jenkins, “La Licorne”) or a “what-if story” (Mittell), which will explore new possibilities and new characters.The second series of Orphan Black comic book tie-ins entitled Helsinki (2016) dealt with clones in the capital of Finland. The readers discover the lives of other clones, how they deal with the discovery of their “condition,” and that they have a caretaker. The comics are written by John Fawcett, who is also a showrunner for the series. The narrative universe is stretched into new possibilities, seen with new eyes, and shown from the perspective of new clones. The introduction of new characters gives opportunities to tell new stories and diverge from the canonical content, especially in terms of the characters’ development and depth.Battlestar Galactica, after the show ended, partnered once again with Dynamite Entertainment, to publish a new set of comic books entitled BSG: Ghosts (2009), which tells the story of new characters surviving the Cylon genocide. Writer Brandon Jerwa asks in BSG: Ghosts: "And if a squadron of secret agents had also survived Cylon Attack?" For him, comic books are a good opportunity to relaunch the narrative universe by introducing new characters in a well-known storyworld.The comic books will definitely have to evolve in order to survive because at some point we will end up exhausting the interest of the readers on the narrative continuity. Projects like Ghosts are definitely a good way to test public reaction to new ideas in a familiar environment. (Jerwa)Conclusion: From One Medium to the Next, From Narrative Extensions to MarketingThis article offers an overview of how comic books are used as tie-in products to extend TV series’ narrative universe. The ambition was not to give an exhaustive panorama but to propose a typology with some examples. I showed that characters’ development, temporalities, and new points of view are narrative angles exploited in comic books to give depth to a storyworld. Of course, this raises issues of labour, authorship, and canon content, which are already discussed elsewhere (see, for example: Clarke, Pillai, Scott). Yet, comic books are an integral part of transmedia storytelling and capitalise on notions of seriality, offering readers new stories, continuity, depth, and character motivations in order to enrich storylines and make them live beyond the screen. However, Robert Napton, in our interview, underlines an interesting opposition between licensing and marketing: “Frankly, comic books are considered licensing and marketing, not official canon. The only TV comic that is canon is Buffy Season 8 and 9 because Joss Whedon says they are, but that is not the normal situation.” He clearly draws a line between what he considers to be a licensed product, in this article what I describe as canonical content, and a marketing product, which could be understood in this article as a canon divergent tie-in. The debate here is clearly on, since understandings of transmedia vary between the perspectives of production companies, which are trying to gain profit by providing new content, the perspectives of fans, who know the storyworlds and the characters extensively and could be very possessive of them, and the perspectives of extension authors, who “have very strict story guidelines” (Jerwa) and have to make their stories fit within the narrative universe as it is told onscreen.ReferencesBertetti, Paolo. “Towards a Typology of Transmedia Characters.” International Journal of Communication 8 (2014): 2344-2361.Boni, Marta. World Building: Transmedia, Fans, Industries. Amsterdam: Amsterdam UP, 2017.Bourdaa, Mélanie. “Transmedia Storytelling: Entre Narration Augmentée et Logiques Immersives.” InaGlobal (2012). 16 December 2017 <http://www.inaglobal.fr/numerique/article/le-transmedia-entre-narration-augmentee-et-logiques-immersives>.Bourdaa, Mélanie, and Bertha Chin. “World and Fandom Building: Extending the Universe of Arrow in Arrow 2.5.” Arrow and Superhero Television: Essays on Themes and Characters of the Series. Eds. James F. Iaccino, Cory Barker, and Myc Wiatrowski. Jefferson: MacFarland, 2017.Clarke, M.J. Transmedia Television: New Trends in Network Serial Production. New York: Continuum Publishing, 2013.Derhy Kurtz, WL Benjamin, and Mélanie Bourdaa. The Rise of Transtexts: Challenges and Opportunities. London: Routledge, 2016.Freeman, Matthew. Historicising Transmedia Storytelling: Early Twentieth-Century Transmedia Story Worlds. London: Routledge, 2017.Gabriel, Nicole, Bogna Kazur, and Kai Matuszkiewicz. “Reconsidering Transmedia(l) Worlds.” Convergence Culture Reconsidered: Media—Participation—Environments. Eds. Claudia Georgi and Brigitte Johanna Glaser. Göttingen: Universitätsverlag Göttingen, 2015.Gillan, Jennifer. Television and New Media: Must-Click TV. New York: Routledge, 2010.Jenkins, Henry. Convergence Culture: Where Old and New Media Collide. New York: NYU Press, 2006.Jenkins, Henry. “I Have Seen the Future of Entertainment… And It Works.” Confessions of an Aca-Fan, 2008. <http://henryjenkins.org/blog/2008/10/i_have_seen_the_futures_of_ent.html>.Jenkins, Henry. “Transmedia Education: The 7 Principles Revisited.” Confessions of an Aca-Fan, 2010. <http://henryjenkins.org/blog/2010/06/transmedia_education_the_7_pri.html>.Jenkins, Henry. “La Licorne Origami Contre-attaque: Réflexions Plus Poussées sur le transmedia storytelling.” Terminal 10-11 (2013): 11-28. <http://journals.openedition.org/terminal/455>.Jerwa, Brandon. Personal Correspondence. 2013.Johnson, Derek. “A History of Transmedia Entertainment.” Spreadable Media: Web Exclusive Essays. <http://spreadablemedia.org/essays/johnson/#.Wo6g24IiGgQ>.Maigret, Eric, and Matteo Stefanelli. La Bande Dessinée: Une Médiaculture. Paris: Armand Colin, 2012.McDuffee, Keith. Buffy the Vampire Slayer: The Long Way Home, Part 1. Season premiere. 2007. <http://www.aoltv.com/2007/03/16/buffy-the-vampire-slayer-the-long-way-home-season-premiere/.>.Mittell, Jason. Complex TV: The Poetics of Contemporary Television Storytelling. New York: NYU Press, 2015.Napton, Robert. Personal Correspondence. 2013.Pagello, Federico. “Before the Comics: On Seriality of Graphic Narratives during the Nineteenth Century.” Belphégor 14 (2016). <http://journals.openedition.org/belphegor/810>.Pillai, Nicolas. “What Am I Looking at Mulder?: Licensed Comics and Freedoms of Transmedia Storytelling.” Science Fiction and Television 6.1 (2013): 101-117.Scott, Jason. “The Character-Orientated Franchise: Promotion and Exploitation of Pre-Sold Characters in American Film, 1913–1950.” Scope: An Online Journal of Film and Television Studies (2009): 10–28.

Les techniques de microscopie interférométrique présentent une sensibilité aux aberrations qui limite leurs pouvoirs de résolution et de pénétration. Initialement développées en astronomie, des méthodes d'optique adaptative ont été transposées en microscopie afin de compenser les effets dues aux aberrations. Celles-ci reposent principalement sur la mesure du front d'onde et sur la correction en boucle fermée des aberrations à l'aide de dispositifs de contrôle du front d'onde. Ces méthodes sont toutefois limitées par les cadences de mesure et de correction, et ne peuvent compenser que des aberrations d'ordres peu élevés.L'objectif de cette thèse est de proposer une approche matricielle innovante reposant sur l'étude d'un nouvel opérateur, la matrice distorsion, permettant de quantifier localement les paramètres liés aux aberrations et à la diffusion, et de corriger les aberrations sur l'ensemble du champs de vision. En parallèle, nous présentons un formalisme mathématique permettant d'expliquer la manifestation des aberrations en OCT plein champ et étendons le champ d'application de la méthode matricielle à de vastes champs de vision au moyen d'un dispositif expérimental de mesure de la matrice de réflexion inspiré de cette technique d'imagerie
Interferometric techniques of microscopy display sensitivity to aberrations affecting both resolution and depth of imaging. Formerly introduced in astronomy, different methods of adaptive optics have been applied to microscopy in order to compensate for these effects. Most of them rely on the measurement of the wave front and on a close-loop correction of the aberrations using wave-front control devices. These methods are nevertheless limited by the rates of measurement and correction and can only compensate for low-order aberrations.The purpose of this thesis is to present an innovative matrix approach relying on the analysis of a new operator, the distorsion matrix, allowing to locally quantify the scattering and aberration parameters, and to compensate for the aberrations over the whole field of view. Besides, we introduce a mathematical formalism in order to describe the effects of aberrations in full-field OCT and we extend the scope of the matrix approach to very large fields of view thanks to an experimental setup of reflection matrix measurement inspired by this technique of imaging

Cette thèse se place dans le contexte général de la modélisation de réseaux d’antennes de grande taille, avec pour objectif d’atteindre un niveau de précision suffisamment élevé pour permettre une optimisation complète des performances et en particulier une amélioration de l’efficacité énergétique. Partant du constat que l’optimisation électromagnétique de grands réseaux représente un verrou si les couplages doivent être modélisés efficacement, cette thèse propose la mise en œuvre d’une méthode permettant la modélisation fine de grands réseaux d'antennes tout en réduisant les temps de calcul et en conservant un haut degré de précision. L'objectif est de montrer qu'une approche dérivée des formalismes périodiques infinis connus de la littérature permet d'obtenir une matrice [S] complète d'un réseau depuis l'étude d'une cellule unitaire. Après avoir présenté un état de l'art sur les réseaux d'antennes et leurs méthodes d'analyse, l'approche de modélisation proposée est détaillée. Des véhicules de test numériques et expérimentaux, permettant de valider cette méthode de modélisation, sont ensuite réalisés. L'approche est enfin utilisée avec succès pour deux types d'application
This thesis is organized in the general context of modeling a large antenna arrays with the aim of achieving a high level of precision. This modeling allows a complete optimization of the performances and an enhancement of the energy efficiency. Given that the electromagnetic optimization of large arrays still represents a challenge if the mutual coupling is not efficiently modeled. This work offers the implementation of a method allowing the precise modeling of large antenna arrays while reducing the computation time and maintaining a high degree of precision. The aim is to demonstrate that the derived approach from the infinite periodic formalisms makes it possible to obtain a full [S] matrix of an array based on the study of a unit cell. After presenting a state of the art of antenna arrays and their methods of analysis, the proposed modeling approach is explained. Numerical and Experimental demonstrators are then made for the validation. Finally, this method is successfully used for two types of applications

La structure des zones de faille a une directe implication sur l'évaluation des risques sismiques. Les techniques d'imagerie par réflexion, en particulier la migration, sont couramment utilisées pour imager le sous-sol. Un modèle de vitesse précis est souvent nécessaire pour localiser correctement les réflecteurs en profondeur. L'imagerie des zones de faille est un défi en raison de la distribution complexe de la vitesse des ondes de volume en leur sein. La plupart des techniques de réflexion imagent les zones de faille indirectement à partir de la discontinuité des couches géologiques. Les hétérogénéités à petite échelle, telles que les fissures et les fractures, sont généralement négligées. Dans cette thèse, nous proposons une approche d'imagerie matricielle pour l'exploration géophysique qui compense les variations de vitesse dans la croûte pour imager les hétérogénéités de cette dernière avec une résolution de l'ordre de la longueur d'onde autour des zones de faille.L'imagerie matricielle est inspirée de précédents travaux en imagerie ultrasonore et optique. D'une part, les corrélations du bruit ambiant sont utilisées pour construire la matrice de réflexion. La composante des ondes de volume dans cette matrice contient toute l'information disponible sur le milieu. D’autre part, l'approche présentée ne nécessite pas un modèle de vitesse détaillé du sous-sol.Dans une première application, nous utilisons des enregistrements de bruit ambiant dans la bande de fréquence [10 20] Hz provenant d'un réseau dense de géophones afin d'imager la faille de San Jacinto, Californie, à petite échelle. Les corrélations ZZ sont calculées et organisées en matrice 2D. En appliquant des lois de retard temporels sur les réponses impulsionnelles entre géophones, la matrice de réponse est projetée en profondeur, en se basant sur un modèle de vitesse homogène. Une matrice de réflexion focalisée est obtenue et contient les réponses impulsionnelles entre un ensemble de sources et récepteurs virtuels à chaque profondeur. A partir de cette matrice, l'image du milieu est construite et ses aberrations peuvent être quantifiées. La différence entre le modèle de vitesse considéré et la réalité entraînent des distorsions de phase, qui dégradent la résolution de l'image. Un processus de correction matricielle des aberrations permet de compenser ces distorsions en introduisant la matrice distorsion. Une image 3D des 4 premiers km de la croûte terrestre est obtenue avec une résolution huit fois plus fine que celle attendue en milieu homogène. Des différences de réflectivité sont observées entre le Nord-Ouest et le Sud-Est de la faille avec une zone de dommages intense et localisée dans le Sud-Est.Dans un deuxième cas d'étude, nous imageons la structure à grande échelle de la faille Nord Anatolienne en utilisant les corrélations horizontales [0.1 0.5] Hz calculées entre 73 paires de stations. Un modèle de vitesse multi-couches est considéré. Une correction locale des distorsions de phase est effectuée. La structure profonde des principaux blocs géologiques est révélée. Des différences dans la profondeur du Moho sont mises en lumière, avec un saut sous la branche nord. Une forte réflectivité est observée dans la région située le long de la branche Nord de la faille, coïncidant avec la limite des blocs lithosphériques. La diffusion dans le nord s'étend jusqu'à 60 km de profondeur, suggérant une zone de cisaillement qui pénètre dans le manteau supérieur sous la branche Nord.Dans la dernière partie de cette thèse, nous proposons une approche qui ouvre la voie à une tomographie passive 3D de la vitesse des ondes de volume. Enfin, toutes les applications présentées confirment l'efficacité de la matrice de réflexion pour révéler la distribution des hétérogénéités dans la croûte terrestre. Elle peut être appliquée sur n'importe quelle bande de fréquence, pourvu que l'échantillonnage spatial du réseau de géophones satisfasse au critère de Nyquist
Revealing the structure of fault zones provides insights required to assess seismic hazards. Reflection imaging methods, in particular migration, are commonly used to image the subsurface. An accurate velocity model is often needed to properly locate the reflectors in depth.Imaging fault zones is challenging due to the complex distribution of velocity. Also, most reflection techniques image fault zones indirectly from the discontinuity of geological layers. Wave diffraction by small-scale heterogeneities, such as cracks and fractures is generally neglected.In this thesis, we propose a matrix imaging approach for geophysical exploration that handles the velocity variation in the crust and allows to resolve heterogeneities of the order of the wavelength throughout the fault zone.The reflection matrix approach is inspired from previous studies in ultrasound and optical imaging of complex media. First, ambient noise cross-correlations are used to retrieve the reflection matrix associated with a dense array of geophones. The body wave components of this matrix contains all the information available on the medium. Second, the presented approach does not require a detailed velocity model of the subsurface. A set of matrix operation is applied to compensate for the mismatch between the actual wave velocity model and its approximate model.In a first application, we use ambient noise records in the frequency band [10 20] Hz from a dense array in order image the San Jacinto Fault, California, at small scale with an horizontal resolution of 80 m. ZZ cross-correlations are computed and arranged as 2D matrix. By applying time delays, the response matrix is projected to depth, using a homogeneous velocity model. A focused reflection matrix is obtained, that contains the impulse response between virtual sources and receivers at depth. From this matrix, the image of the medium is built and the resolution of the image can be quantified.Variations between the considered model and the reality result in phase distortions, i.e aberrations, that have detrimental effects on the image of the medium.We develop an aberration correction process that allows to compensate for these distortions by introducing a novel operator, the distortion matrix. 3D images of the first 4 km of the crust are retrieved. These images reveal the backscattered intensity generated by the heterogeneities in the medium. The location and reflectivity of scatterers are retrieved with a resolution 8 times better than the one in free space. Differences in the scattering between the Northwest and the Southeast of the fault were reported with an intense localized damage zone in the Southeast.In a second application, we image the large scale structure of North Anatolian Fault using [0.1 0.5] Hz horizontal cross-correlations computed between 73 pairs of stations. A multi-layered velocity model is considered. A local correction of the phase distortions is performed. The scattering structure of the crust and the upper mantle is revealed. Differences in the Moho depth are reported, with a step below the northern branch. Strong scattering is observed in the region lying along the northern strand of the fault, coinciding with the limit of the lithospheric blocks. The scattering in the North extends to 60 km depth, suggesting a shear zone that penetrates in the upper mantle beneath the northern strand. The scattering also reveals the deep structure of the main geological blocks.In the last part of this thesis, we propose an approach that paves the route towards a 3D passive tomography of the body wave velocity. Finally, all the presented applications confirm the efficiency of the reflection matrix approach in revealing the structure of the subsurface. It provides new insights into the scattering distribution in the Earth. It can be applied to any scale, scattering regime, and frequency bandwith, if the spatial sampling of the geophones' array satisfies the Nyquist criterion

Cette thèse propose un formalisme général pour modéliser la propagation des ondes acoustiques dans une multicouche composée de toute combinaison de couches liquides, solides élastiques isotropes et poro-élastiques isotropes, la méthode ayant la flexibilité d'être développée pour inclure d'autres natures de couches. Dans un premier lieu, un algorithme stable est développé, basé sur l'approche récursive de la matrice de rigidité, pour modéliser la propagation d'une onde plane incidente sur la multicouche en fonction de son angle d'incidence et de sa fréquence. Cet algorithme fusionne de manière récursive les matrices de rigidité des couches individuelles de la structure en une matrice de rigidité totale et permet ensuite le calcul des coefficients de réflexion et de transmission, ainsi que les composantes de déplacement et de contrainte à l'intérieur de la multicouche pour chaque direction d'incidence des ondes planes. Deuxièmement, pour modéliser la propagation d'un faisceau délimité d'ondes incidentes, la technique du spectre angulaire est utilisée, basée sur la décomposition de ce faisceau en un spectre d'ondes planes se propageant dans des directions différentes. Par la suite, le faisceau d'onde réfléchi dans le milieu d'incidence et le faisceau d'onde transmis dans le milieu de transmission, ainsi que la distribution des champs (composantes de déplacement et de contrainte) à l'intérieur de la multicouche sont obtenus en superposant la contribution de toutes les ondes planes se propageant dans les différentes directions. Comme application numérique, une tri-couche solide-poreuse-solide immergée dans l'eau est simulée. La réflexion et la transmission qui en résultent, ainsi que les composantes de déplacement et de contrainte dans la multicouche, correspondants à l’onde plane incidente et au faisceau limité incident, révèlent la stabilité du procédé et la continuité des déplacements et des contraintes aux interfaces
This thesis proposes a general formalism to model the acoustic wave propagation in a multilayer consisting of any combination of fluid, isotropic elastic solid, and isotropic poroelastic layers, the method having the flexibility to be extended to include other layer-natures. At a first stage, a stable algorithm is developed, based on the recursive stiffness matrix approach, to model the propagation of a plane wave incident on the multilayer as a function of its incidence angle and frequency. This algorithm merges recursively the structureindividual layers stiffness matrices into one total stiffness matrix and allows then the calculation of the reflection and transmission coefficients, as well as the displacement and stress components inside the multilayer for every incident plane wave direction. Secondly, to model the propagation of a bounded incident wave beam, the angular spectrum technique is used which is based on the decomposition of this beam into a spectrum of plane waves traveling in different directions. The corresponding reflected wave beam in the incidence medium, and the transmitted wave beam in the transmission medium, as well as the fields distributions (displacement and stress components) inside the multilayer are obtained by summing the contribution of all the plane waves traveling in different directions. As a numerical application, a three-layered solid-porous-solid structure immersed in water is simulated. The resulting reflection and transmission as well as the displacement and stress components in the multilayer corresponding to both, the incident plane wave in different directions and the incident bounded beam reveal the stability of the method and the continuity of the displacements and stresses at the interfaces

L'étude s'inscrit dans le cadre de la prévision des niveaux vibratoires induits par les chocs pyrotechniques lors de la phase de séparation des étages du lanceur Ariane 5, et plus particulièrement de la prévision des niveaux vibratoires dans la case a équipements. On développe une approche simplifiée permettant de déterminer la réponse dynamique de la structure à partir du calcul de matrices de rigidité dynamique exactes. Cette approche est réservée a des structures de type guides d'ondes dans lesquelles la direction de propagation des ondes est connue. On s'intéresse également a la prise en compte de liaisons entre structures ; on montre qu'il est possible de déterminer la matrice de rigidité dynamique des liaisons a partir de la connaissance des coefficients de réflexion et de transmission des ondes et des relations force-déplacement dans les éléments relies a la liaison.

Cette étude présente la mise en oeuvre dans le cas d'un champ acoustique multimodal des méthodes expérimentales pour la caractérisation d'une discontinuité à deux ports par mesure de sa matrice de diffusion et de transmission ainsi que sa dissipation acoustique, et d'une discontinuité à un port par mesure de sa matrice de réflexion. La méthode proposée est appliquée à la mesure de la matrice de diffusion d'un tronçon droit sans discontinuités et d'un tronçon réactif. Les matrices de réflexion et de transmission sont mesurées pour un tronçon droit couplé avec une terminaison ouverte du conduit. Avec le surdimensionnement sur le nombre des charges, les coefficients expérimentaux de la matrice de diffusion mesurés pour le tronçon droit montrent un très bon accord avec la théorie, sauf, à l'approche des fréquences de coupure des modes. Pour le tronçon réactif, une très bonne concordance entre l'expérience et la théorie est notée pour les coefficients de diffusion associés aux ondes incidentes du côté de la source. En revanche, pour les bandes de fréquences où le tronçon filtre un des modes, la méthode des charges ne peut être utilisée pour mesurer les coefficients de diffusion associés aux ondes incidentes du côté de la charge. Pour caractériser complètement un tronçon non symétrique, un essai supplémentaire après son inversion est donc nécessaire. Pour les matrices de transmission et de réflexion, le surdimensionnement sur le nombre des configurations de la source apporte une grande amélioration sur les résultats. D'un autre côté, et afin d'estimer la sensibilité des différentes méthodes aux imprécisions de mesure, une méthode de simulation analytique de l'expérience est développée
This study presents the development of experimental methods to characterise a two-port discontinuity by measurement of its scattering and transmission matrices and its power dissipation, and a one-port discontinuity by measurement of its reflection matrix in higher order modes propagation conditions. This method is applied to the measurement of a scattering matrix of a straight cylindrical duct and a reactive chamber. Reflection and transmission matrices are measured for an open end coupled with a straight duct. With the use of the overdetermination on the number of loads, a good agreement was found between analytical and experimental scattering-matrix coefficients measured for the straight duct except near of eut-off frequencies. The test with the reactive type muffler shows that the load method fails in determining the coefficients associated to the wave coming in the discontinuity from the open side because modes are filtered by the reactive chamber. To characterise completely an asymmetrical section, an additionnel test after its inversion is therefore necessary. Results of transmission and reflection matrices shows that the overdetermination procedure on the number of source configurations improves the results. Ln another side, and in order to estimite the sensitivity of various methods to measurement errors, an analytical procedure of simulation of the experience is developed

Cette thèse est consacrée à l'étude des représentations modulaires des algèbres d'Ariki-Koike, et des liens avec la théorie des cristaux et des bases canoniques de Kashiwara via le théorème de catégorification d'Ariki. Dans un premier temps, on étudie, grâce à des outils combinatoires, les matrices de décomposition de ces algèbres en généralisant les travaux de Geck et Jacon. On classifie entièrement les cas d'existence et de non-existence d'ensembles basiques, en construisant explicitement ces ensembles lorsqu'ils existent. On explicite ensuite les isomorphismes de cristaux pour les représentations de Fock de l'algèbre affine quantique de type A affine. On construit alors un isomorphisme particulier, dit canonique, qui permet entre autres une caractérisation non-récursive de n'importe quelle composante connexe du cristal. On souligne également les liens avec la combinatoire des mots sous-jacente à la structure cristalline des espaces de Fock, en décrivant notamment un analogue de la correspondance de Robinson-Schensted-Knuth pour le type A affine.

Le travail présenté ici repose sur l'étude de cristaux photoniques bidimensionnels et sur la mise en place des outils théoriques correspondants. La spécificité de notre travail repose sur deux aspects. Premièrement, nous avons eu recours à un programme général d'étude de multicouches, éventuellement rugueuses ou percées de trous, reposant sur une méthode de modes couplés et l'utilisation du formalisme de la matrice S. A partir de ce programme, nous avons cherché à obtenir un certain nombre de paramètres pertinents dans l'étude des systèmes optiques. Ces paramètres correspondent au calcul des coefficients de transmission et réflexion, dont on peut déduire les pertes en énergie. De plus, nous avons développé le calcul de cartes du champ proche et du champ dans le volume du système étudié, avec la possibilité, dans le cadre d'un problème de diffraction, de sélectionner certains ordres et certaines polarisations particulières. On peut y ajouter également la détermination, par l'étude directe des propriétés de la matrice S (entre autre de ses pôles), des modes propres du système étudié. Deuxièmement, le début de ce travail a coïncidé avec la publication en 1998 de résultats concernant l'étude expérimentale de cristaux photoniques bidimensionnels constitués d'une couche métallique percée de trous sublongueurs d'onde répartis selon un réseau à deux dimensions et déposée sur un substrat diélectrique. Aussi, nous avons tourné l'essentiel de notre travail vers l'analyse de ces expériences. Nous avons montré que, dans le cadre de ces expériences, la notion de modes propres associés à un système donné revêt un intérêt crucial. Plus particulièrement, nous avons soulevé l'importance de l'analyse des anomalies de Wood résonantes dans l'interprétation de ces expériences.

L'onde engendrée par le piston pendant la phase d'admission se propage dans le conduit d'air frais et revient au cylindre par réflexions. Les phénomènes acoustiques augmentent jusqu'à 30% la quantité d'air admise par le moteur. La propagation acoustique dans les conduits portant un écoulement moyen turbulent est modélisée en une et trois dimensions. L'impédance d'entrée calculée est comparée aux résultats d'un dispositif expérimental innovant. Une nouvelle méthode de mesure des matrices de transfert en absence d'écoulement est également mise au point. Un couplage non-linéaire de l'impédance d'entrée du circuit d'air avec la chambre de combustion permet le calcul du remplissage en air sur une plage étendue de régimes. L'évolution à plusieurs cylindres est envisagée par la construction de matrices d'impédance
The pressure wave generated by the moving of the piston during the intake stroke of an internal combustion engine propagates in the duct carrying cool gases and comes back to the cylinder by reflections. Acoustic phenomena can increase the amount of air trapped in the engine by 30% and so its performances. Acoustic propagation in ducts carrying a turbulent flow is modelled in one and three dimensions. The input impedance is calculated and compared to the results of a new measurement procedure with steady flows up to Mach number M=0. 15. A new method for measuring transfer matrices without flow has also been developed. Its results agree well with theory. The effect of acoustic properties of intake systems in the amount of air trapped in a one cylinder engine is modelled as a non-linear coupling of the combustion chamber with the input impedance, by a mechanical analogy. The acoustic pressures computed agree fairly well with the pressures measured in two different intake systems of a one-cylinder cold engine. The link between the acoustic properties of the intake duct expressed in the frequency domain alone and the volumetric efficiency of a cylinder has been quantified on a large range of running speed for the first time. In a multi-cylinder engine, the timing difference between intake strokes produces interferences in the intake system. The calculated impedance matrix and the study of phase explain a performance difference between cylinders that occurs in a turbocharged engine