Este trabalho trata do processo de digitação para violão da Ciaccona BWV 1004 (original para violino) de Johann Sebastian Bach (1685-1750). O objetivo foi desenvolver uma digitação de mão esquerda capaz de refletir as intenções musicais do presente autor. Para tal, foi estabelecido um modelo de análise, onde a textura musical é dividida e classificada, com base em referenciais teóricos, como: melódica, harmônica, motívica e polifônica. Ao analisar as digitações usadas em transcrições, e compará-las às desta pesquisa, concluímos que se pode ter autonomia para contestar uma digitação grafada, pois ela reflete nada mais que as decisões do seu autor, sejam musicais ou técnicas. A partir disto, podemos deduzir que elas se alteram conforme as nossas próprias decisões. / This work deals with the process of elaborating guitar fingerings for J. S. Bach’s Ciaccona BWV 1004 (original for violin). The aim was to develop a left hand fingering able to reflect the musical intentions of the present author. To this end, a model of analysis was established, in which the musical texture is divided and classified, based on theoretical references, into the following categories: melodic, harmonic, motivic and polyphonic. By analyzing the fingering used on transcriptions, and comparing it with the results of this research, we conclude that we can question a suggested fingering, because it reflects nothing more than the decisions of its author, whether musical or technical. From this we can deduce that they change according to our own decisions.

A capacidade de executar uma obra à primeira vista no violão é considerada por muitos uma tarefa de difícil execução. Um dos principais motivos para isto é o fato de uma mesma nota poder ser tocada em diferentes lugares da escala do violão, gerando diversas possibilidades de digitação para uma mesma passagem. A presente pesquisa investigou os procedimentos utilizados por 11 estudantes de graduação em violão durante a execução de uma tarefa de leitura à primeira vista. Os sujeitos da pesquisa foram filmados e entrevistados e os dados relativos ao histórico de cada sujeito foram acessados pela aplicação de questionário. Foram considerados como variáveis influentes na execução dessa tarefa fatores como as diferentes possibilidades de digitação para uma mesma passagem, o conhecimento das possibilidades expressivas do instrumento, e a habilidade motora. A digitação e a tonalidade apresentaram-se como as principais dificuldades. As questões expressivas foram deixadas em segundo plano, considerando a quantidade de decisões a serem tomadas no tempo de um minuto dado a leitura silenciosa. Assim, nem sempre a execução mais correta em termos de acertos de notas e tempo foi a de resultado mais expressivo. Evidenciou-se na pesquisa que nem sempre o tempo de estudo reflete no melhor resultado quando se trata da tarefa de leitura à primeira vista. Os sujeitos de melhores desempenhos na tarefa de leitura à primeira vista responderam em questionário que praticam música de câmara e/ou canto coral, mostrando que essas práticas podem influenciar positivamente o desenvolvimento da habilidade de leitura à primeira vista. Com relação ao teste de habilidade motora, os sujeitos com os melhores desempenhos na execução do teste de leitura à primeira vista (considerando fluência de tempo, evitando correções de notas e ritmos) ultrapassaram os sujeitos de menor desempenho em marcas metronômicas. / Sight-reading a piece on the guitar is often considered a difficult task. One reason for this may be the fact that the same note on the guitar may be played in different ways, thus generating various fingering possibilities for the same passage. The present study investigated the procedures adopted by 11 undergraduate guitar students in a sight-reading exercise. The subjects were filmed and interviewed and their background was taken from a written questionnaire. Distinct fingering possibilities for the same passage, knowledge of expressive possibilites of the guitar and mechanical dexterity were considered as influential variables in this study. Fingering and tonality proved to be the main difficulties. Expressive aspects were not considered the most important, considering the number of decisions to be made in the one minute allotted for silent reading before the sight-reading began. Thus, the best performances in terms of correct notes and tempo were not necessarily the most expressive. The best outcomes came from students who engage in choral or chamber music activities, therefore, these may have a positive influence on sight-reading. The mechanical ability exercise applied showed that the subjects that did better on the sight-reading passsage (considering tempo, correct notes and rhythm) surpassed those that had lower metronomical markings.

Die vorliegende Arbeit beschreibt eine experimentelle Untersuchung der Schichtbildung von nichtnewtonschen Flüssigkeiten im Tiefdruckverfahren auf nicht saugfähigen Substraten. Das fluiddynamisch bedingte „viscous fingering“ beim Farbspaltungsprozess soll mittels Hydrophobieren der Druckform gehemmt werden. Ziel ist es, möglichst homogene sowie wellenfreie Schichten zu erzeugen. Um ein direkt miteinander vergleichbares Druckergebnis zu erhalten, wird der Druckstoff parallel mit einer unbehandelten und hydrophobierten Form bedruckt. Als Druckstoff werden anstelle von Druckfarbe funktionale Materialien (vorzugsweise PEDOT:PSS) verwendet und variiert, wobei die elektrischen und geometrischen Schichteigenschaften, beispielsweise der elektrische Widerstand und die Rauheit, zur Ermittlung der gesetzten Ziele untersucht wurden. Hiermit und mittels Nutzung einer hydrophobierten Druckform kann eine deutliche Minderung der Wellenbildung (viscous fingering) bei vielen Druckstoffarten beobachtet werden. Die Minderung des viscous fingering im Farbspaltungsprozess und eine nahezu vollständige Leerung der hydrophobierten Tiefdruckform haben einen wesentlichen Nutzwert für den künftigen Einsatz nicht nur für die „gedruckte Elektronik“. / In this work is described experimental research about layer forming from non-Newtonian fluids in gravure printing on non-porous substrates. The viscous fingering, caused through fluid dynamics at splitting of printed material should be decreased by hydrophobic-surface modification of gravure printing form. The aim was to print wave-free homogenous layers. To achieve comparable results, modified and pure form were used simultaneously to print the same material. The printed material was mainly PEDOT:PSS and other, which is used in printed electronics. The properties (surface tension, viscosity) of printed materials were varied by additives. Printing conditions were varied too. The characteristic of printed layers were studied: resistivity, roughness, density, etc. The results shows decreasing of waviness, roughness and viscous fingering in final layer through use of hydrophobic gravure printing form, compared to print results with common printing form. This can be applied not only in the field of printed electronics.

Este trabalho trata da investigação dos princípios metodológicos necessários ao processo de digitação ao violão. Para tal, parâmetros digitacionais são convertidos em um protocolo de instâncias (exposição dos casos, aplicação dos comandos, avaliação das circunstâncias, gerenciamento das consequências e julgamento das condições), as quais são mediadas por princípios e circundadas por perspectivas, formando, assim, um cenário digitacional. Por meio de um processo de inferências, concluímos que a fluência sonora, independentemente de posicionamentos estéticos, é uma condição básica para uma execução satisfatória ao violão; por dedução, vimos que a capacidade de se tocar legato é o principal elemento desse ideal. Verificamos, também, que a digitação é, em termos, pessoal, pois todas as suas instâncias são de interação dialética entre sujeito e objeto; mas não completamente, pois cada instância é regida por princípios que não dizem respeito, exclusivamente, ao indivíduo. Observamos, por fim, que a construção de um cenário digitacional não é um meio de se encontrar a melhor digitação, mas sim, de buscá-la, pois o princípio básico em que ela se opera é a organização dos saberes que o executante mobiliza em seu processo. / This work deals with the investigation of the methodological principles necessary to the process of elaborating guitar fingerings. To this end, fingering parameters are converted into a protocol of instances (exposure of the cases, application of the commands, assessment of the circumstances, management of the consequences and judgment of the conditions), which are mediated by principles and surrounded by perspectives, thus forming a fingering scenario. Through a process of inference, we conclude that the sound fluency, independently of aesthetic positioning, is a basic condition for a satisfactory performance on guitar; by deduction, we have seen that the ability to play legato is the main element of this ideal. We also verified that fingering is, in terms, a matter of personal choice because all its instances are dialectical interaction between subject and object; but not completely so, because each instance is governed by principles which do not concern exclusively the individual. We note, finally, that the construction of a fingering scenario is not a way to find the best fingering, but, to seek it, because the basic principle on which it operates is the organization of acknowledgments that the performer mobilizes in his process. / Este trabajo se ocupa de la investigación de los principios metodológicos necesarios para el proceso de elaboración de la digitación en la guitarra. Con este fin, parámetros de digitación se convierten en un protocolo de instancias (la exposición de los casos, la aplicación de los comandos, la evaluación de las circunstancias, la administración de las consecuencias y el juicio de las condiciones), que están mediadas por principios y rodeadas de perspectivas, formando así un escenario de digitación. A través de un proceso de inferencia, llegamos a la conclusión de que la fluidez del sonido, independientemente de las posiciones estéticas, es una condición básica para una ejecución satisfactoria en la guitarra; por deducción, hemos visto que la capacidad de tocar legato es el elemento principal de este ideal. También verificamos que la digitación es, en términos, personal, porque todas las instancias son una interacción dialéctica entre el sujeto y el objeto; pero no completamente, porque cada instancia se rige por principios que no se refieren exclusivamente a la persona. Observamos, por último, que la construcción de un escenario de digitación no es una manera de encontrar la mejor digitación, sino buscarla, porque el principio básico en el que opera es la organización de los conocimientos que el intérprete moviliza en su proceso.

Este trabalho trata da investigação dos princípios metodológicos necessários ao processo de digitação ao violão. Para tal, parâmetros digitacionais são convertidos em um protocolo de instâncias (exposição dos casos, aplicação dos comandos, avaliação das circunstâncias, gerenciamento das consequências e julgamento das condições), as quais são mediadas por princípios e circundadas por perspectivas, formando, assim, um cenário digitacional. Por meio de um processo de inferências, concluímos que a fluência sonora, independentemente de posicionamentos estéticos, é uma condição básica para uma execução satisfatória ao violão; por dedução, vimos que a capacidade de se tocar legato é o principal elemento desse ideal. Verificamos, também, que a digitação é, em termos, pessoal, pois todas as suas instâncias são de interação dialética entre sujeito e objeto; mas não completamente, pois cada instância é regida por princípios que não dizem respeito, exclusivamente, ao indivíduo. Observamos, por fim, que a construção de um cenário digitacional não é um meio de se encontrar a melhor digitação, mas sim, de buscá-la, pois o princípio básico em que ela se opera é a organização dos saberes que o executante mobiliza em seu processo. / This work deals with the investigation of the methodological principles necessary to the process of elaborating guitar fingerings. To this end, fingering parameters are converted into a protocol of instances (exposure of the cases, application of the commands, assessment of the circumstances, management of the consequences and judgment of the conditions), which are mediated by principles and surrounded by perspectives, thus forming a fingering scenario. Through a process of inference, we conclude that the sound fluency, independently of aesthetic positioning, is a basic condition for a satisfactory performance on guitar; by deduction, we have seen that the ability to play legato is the main element of this ideal. We also verified that fingering is, in terms, a matter of personal choice because all its instances are dialectical interaction between subject and object; but not completely so, because each instance is governed by principles which do not concern exclusively the individual. We note, finally, that the construction of a fingering scenario is not a way to find the best fingering, but, to seek it, because the basic principle on which it operates is the organization of acknowledgments that the performer mobilizes in his process. / Este trabajo se ocupa de la investigación de los principios metodológicos necesarios para el proceso de elaboración de la digitación en la guitarra. Con este fin, parámetros de digitación se convierten en un protocolo de instancias (la exposición de los casos, la aplicación de los comandos, la evaluación de las circunstancias, la administración de las consecuencias y el juicio de las condiciones), que están mediadas por principios y rodeadas de perspectivas, formando así un escenario de digitación. A través de un proceso de inferencia, llegamos a la conclusión de que la fluidez del sonido, independientemente de las posiciones estéticas, es una condición básica para una ejecución satisfactoria en la guitarra; por deducción, hemos visto que la capacidad de tocar legato es el elemento principal de este ideal. También verificamos que la digitación es, en términos, personal, porque todas las instancias son una interacción dialéctica entre el sujeto y el objeto; pero no completamente, porque cada instancia se rige por principios que no se refieren exclusivamente a la persona. Observamos, por último, que la construcción de un escenario de digitación no es una manera de encontrar la mejor digitación, sino buscarla, porque el principio básico en el que opera es la organización de los conocimientos que el intérprete moviliza en su proceso.

Este trabalho trata da investigação dos princípios metodológicos necessários ao processo de digitação ao violão. Para tal, parâmetros digitacionais são convertidos em um protocolo de instâncias (exposição dos casos, aplicação dos comandos, avaliação das circunstâncias, gerenciamento das consequências e julgamento das condições), as quais são mediadas por princípios e circundadas por perspectivas, formando, assim, um cenário digitacional. Por meio de um processo de inferências, concluímos que a fluência sonora, independentemente de posicionamentos estéticos, é uma condição básica para uma execução satisfatória ao violão; por dedução, vimos que a capacidade de se tocar legato é o principal elemento desse ideal. Verificamos, também, que a digitação é, em termos, pessoal, pois todas as suas instâncias são de interação dialética entre sujeito e objeto; mas não completamente, pois cada instância é regida por princípios que não dizem respeito, exclusivamente, ao indivíduo. Observamos, por fim, que a construção de um cenário digitacional não é um meio de se encontrar a melhor digitação, mas sim, de buscá-la, pois o princípio básico em que ela se opera é a organização dos saberes que o executante mobiliza em seu processo. / This work deals with the investigation of the methodological principles necessary to the process of elaborating guitar fingerings. To this end, fingering parameters are converted into a protocol of instances (exposure of the cases, application of the commands, assessment of the circumstances, management of the consequences and judgment of the conditions), which are mediated by principles and surrounded by perspectives, thus forming a fingering scenario. Through a process of inference, we conclude that the sound fluency, independently of aesthetic positioning, is a basic condition for a satisfactory performance on guitar; by deduction, we have seen that the ability to play legato is the main element of this ideal. We also verified that fingering is, in terms, a matter of personal choice because all its instances are dialectical interaction between subject and object; but not completely so, because each instance is governed by principles which do not concern exclusively the individual. We note, finally, that the construction of a fingering scenario is not a way to find the best fingering, but, to seek it, because the basic principle on which it operates is the organization of acknowledgments that the performer mobilizes in his process. / Este trabajo se ocupa de la investigación de los principios metodológicos necesarios para el proceso de elaboración de la digitación en la guitarra. Con este fin, parámetros de digitación se convierten en un protocolo de instancias (la exposición de los casos, la aplicación de los comandos, la evaluación de las circunstancias, la administración de las consecuencias y el juicio de las condiciones), que están mediadas por principios y rodeadas de perspectivas, formando así un escenario de digitación. A través de un proceso de inferencia, llegamos a la conclusión de que la fluidez del sonido, independientemente de las posiciones estéticas, es una condición básica para una ejecución satisfactoria en la guitarra; por deducción, hemos visto que la capacidad de tocar legato es el elemento principal de este ideal. También verificamos que la digitación es, en términos, personal, porque todas las instancias son una interacción dialéctica entre el sujeto y el objeto; pero no completamente, porque cada instancia se rige por principios que no se refieren exclusivamente a la persona. Observamos, por último, que la construcción de un escenario de digitación no es una manera de encontrar la mejor digitación, sino buscarla, porque el principio básico en el que opera es la organización de los conocimientos que el intérprete moviliza en su proceso.

Die vorliegende Arbeit beschreibt eine experimentelle Untersuchung der Schichtbildung von nichtnewtonschen Flüssigkeiten im Tiefdruckverfahren auf nicht saugfähigen Substraten. Das fluiddynamisch bedingte „viscous fingering“ beim Farbspaltungsprozess soll mittels Hydrophobieren der Druckform gehemmt werden. Ziel ist es, möglichst homogene sowie wellenfreie Schichten zu erzeugen. Um ein direkt miteinander vergleichbares Druckergebnis zu erhalten, wird der Druckstoff parallel mit einer unbehandelten und hydrophobierten Form bedruckt. Als Druckstoff werden anstelle von Druckfarbe funktionale Materialien (vorzugsweise PEDOT:PSS) verwendet und variiert, wobei die elektrischen und geometrischen Schichteigenschaften, beispielsweise der elektrische Widerstand und die Rauheit, zur Ermittlung der gesetzten Ziele untersucht wurden. Hiermit und mittels Nutzung einer hydrophobierten Druckform kann eine deutliche Minderung der Wellenbildung (viscous fingering) bei vielen Druckstoffarten beobachtet werden. Die Minderung des viscous fingering im Farbspaltungsprozess und eine nahezu vollständige Leerung der hydrophobierten Tiefdruckform haben einen wesentlichen Nutzwert für den künftigen Einsatz nicht nur für die „gedruckte Elektronik“. / In this work is described experimental research about layer forming from non-Newtonian fluids in gravure printing on non-porous substrates. The viscous fingering, caused through fluid dynamics at splitting of printed material should be decreased by hydrophobic-surface modification of gravure printing form. The aim was to print wave-free homogenous layers. To achieve comparable results, modified and pure form were used simultaneously to print the same material. The printed material was mainly PEDOT:PSS and other, which is used in printed electronics. The properties (surface tension, viscosity) of printed materials were varied by additives. Printing conditions were varied too. The characteristic of printed layers were studied: resistivity, roughness, density, etc. The results shows decreasing of waviness, roughness and viscous fingering in final layer through use of hydrophobic gravure printing form, compared to print results with common printing form. This can be applied not only in the field of printed electronics.

This thesis focuses on two problems lying within the field of soft condensed matter: the viscous fingering or Saffman-Taylor instability and nematic liquid crystals in confinement. Whenever a low viscosity fluid displaces a high viscosity fluid in a porous medium, for example water pushing oil out of oil reservoirs, the interface between the two fluids is rendered unstable. Viscous fingers develop, grow and compete until a single finger spans all the way from inlet to outlet. Here, using a free energy lattice Boltzmann algorithm, we examine the Saffman-Taylor instability for two different wetting situations: (a) when neither of the two fluids wet the walls of the channel and (b) when the displacing fluids completely wets the walls. We demonstrate that curvature effects in the third dimension, which arise because of the wetting boundary conditions, can lead to a novel suppression of the instability. Recent experiments in microchannels using colloid-polymer mixtures support our findings. In the second part of the thesis we examine nematic liquid crystals confined in wedge-structured geometries. In these systems the final stable configuration of the liquid crystal system is controlled by the complex interplay between confinement, elasticity and surface anchoring. Varying the wedge opening angle this competition leads to a splay to bend transition mediated by a defect in the bulk of the wedge. Using a hybrid lattice Boltzmann algorithm we study the splay-bend transition and compare to recent experiments on {em fd} virus particles in microchannels. Our numerical results, in quantitative agreement with the experiments, enable us to predict the position of the defect as a function of opening angle, and elucidate its role in the change of director structure. This has relevance to novel energy saving, liquid crystal devices which rely on defect motion and pinning to create bistable director configurations.

Les mécanismes de fracture dans les matériaux solides ont été activement étudiés. Dans les fluides complexes, les fractures ont déjà été observées et sont jusqu'à présent beaucoup moins bien documentées. Nous avons choisi d'analyser les phénomènes de fracturation dans une classe particulière de fluides complexes : les gels transitoires auto-assemblés. Ces gels, viscoélastiques, possèdent la propriété de s'écouler aux temps longs et de se comporter de manière élastique aux temps courts. Nous avons axé cette thèse autour de trois systèmes modèles : des microémulsions connectées, des solutions de micelles géantes, ainsi qu'un système « hybride » constitué de solutions de micelles de morphologie contrôlable et connectées. Tous ces systèmes, qui sont à l'équilibre thermodynamique, se comportent comme des fluides de Maxwell, néanmoins leurs microstructures sont très différentes. Les microémulsions connectées sont formées de gouttelettes d'huile, stabilisées par des tensioactifs, dispersées dans de l'eau et connectées par des polymères téléchéliques. Les solutions de micelles géantes sont des agrégats allongés et semi-flexibles, enchevêtrés, résultant de l'auto-assemblage de tensioactifs en solution dans l'eau. Enfin, le système de micelles pontées est constitué d'agrégats de tensioactifs dont on peut contrôler la morphologie (sphères -> cylindres -> vers) et qui sont pontés par un polymère téléchélique. Ces trois systèmes ont été étudiés dans une géométrie confinée : une cellule de Hele-Shaw radiale. Elle est constituée de deux plaques de verre séparées par des espaceurs de taille contrôlée (500 µm) et percée d'un trou en son centre permettant l'injection de fluides.Nos expériences consistent en l'injection, à débit contrôlé, d'une huile faiblement visqueuse dans le gel. Le contraste de viscosité entre l'huile injectée et le gel étant important, l'interface huile/gel n'est pas stable. En fonction du débit d'injection d'huile, nous avons observé différents phénomènes. A bas débits d'injection, une instabilité visco-capillaire se développe : l'interface huile/gel se déforme et forme des motifs appelés doigts visqueux. Cette instabilité de Saffman-Taylor est bien connue pour des fluides visqueux. A plus haut débit en revanche, un autre type d'instabilité se développe, d'origine élasto-capillaire : les fractures.Nous avons quantifié les différences entre les deux types d'instabilité. En utilisant des techniques complémentaires, visualisation directe à l'aide d'une caméra rapide et vélocimétrie par corrélation d'images, nous avons montré qu'il existe une discontinuité entre la vitesse de l'interface huile/gel et la vitesse du gel à la pointe de fracture. Cette discontinuité est inexistante dans le cas de la digitation. Nous avons montré que la structure du gel influe sur la transition entre ces deux types d'instabilité. En étudiant les champs de déplacement des microémulsions connectées, nous avons caractérisé les déplacements du gel autour de la pointe, notamment la manière dont l'amplitude des déplacements du gel décroit quand on s'éloigne de la pointe de fracture. Quand la structure du gel peut se réorganiser sous écoulement, nous avons mesuré un signal de biréfringence associé à ces réorganisations. En étudiant ce signal, qui apparait à la pointe d'une fracture, nous avons pu réaliser une première mesure macroscopique de la taille d'une « zone de process ». Nous avons montré que cette zone est d'autant plus grande que la vitesse de la fracture est petite.Lors d'expériences consistant à injecter des solutions de micelles géantes dans elles-mêmes, nous avons découvert l'existence d'une instabilité d'écoulement inconnue jusqu'à aujourd'hui. Elle se caractérise par la perte transitoire de la symétrie radiale de l'écoulement et l'apparition de «branches » biréfringentes se propageant à de très hautes vitesses dans le gel et qui, au final, déforment l'interface air/gel. / Fracture mechanisms in solid materials have been extensively studied. Although cracks are also commonly seen in soft solids, the fracture process is still not very well understood for these materials. In this thesis we choose to study fracture on a particular class of materials: complex fluids. We will focus on one particular family of complex fluids which are self-assembled transient gels. These viscoelastic gels have the property to flow at long timescale while behaving as an elastic solid at short timescales. We have investigated three model systems: a bridged micro emulsion and a entangled solution of wormlike micelle, and a “hybrid” system made of bridged micelles of tunable morphology. These systems are at thermodynamic equilibrium and behave as Maxwell fluids but they differ in microscopic structures. Bridged micro emulsions are made of surfactant-stabilzed oil droplet dispersed in water and bridged by telechelic polymers. Wormlike micelles are long semi flexible aggregates made from the self-assembly of surfactant in a water solution. Lastly, bridged micelles are made of surfactant aggregates of controllable shape (sphere -> cylinder -> worm) in water bridged by telechelic polymers. We choose to study these different systems in a confined geometry: a radial Hele-Shaw cell. The Hele-Shaw cell is made of two glass plates separated by spacers of controllable thickness. A hole is pierced in the center of the cell for injecting the fluids. The experiments consist in the injection at a controlled rate of low viscosity oil inside the highly viscous gel. Because of the high viscosity contrast between the two fluids, the oil/gel interface is unstable. Depending of the injection rate, we observed different instabilities. At lowest rates, an instability of visco-capillary origins appears and the oil/gel interface is deformed leading to a viscous fingering pattern. This instability called Saffman Taylor instability is widely known and has been extensively studied for Newtonian fluids. At highest rates another instability patterns arise of elasto capillary origin where the patterns are vastly different from the previous one and are made of cracks propagating through the gel. We have quantified the difference between the two types of instability. By combining direct visualization using high speed imaging and digital image correlation techniques we have characterized the displacement field of the gel around the crack tip, and in particular how its amplitude decays away from the tip. For bridged microemulsion, we have also evidenced the existence of a velocity discontinuity between the crack velocity and the velocity of the gel near the crack tip whereas no discontinuity occurs in the case of viscous fingering. Using bridged micelles of tunable morphologies we have also shown that the transition between the two instabilities is controlled by the viscoelasticity of the gel. Finally, for gel that can reorient under flow we have measured a birefringence signal associated to these reorganization. By studying this signal at the crack tip we were able to perform a measurement of the size of the “process zone” which could be considered as the first macroscopic quantitative analysis of the ductility of a crack in complex fluids. During complementary experiments which consist of the injection of wormlike micelles in themselves we have reported a new kind of flow instability. This instability is characterized by the transient loss of the radial symmetry during flow and by the apparitions of typical “branches” which propagates at very high speed through the sample and finally distort the air/gel interface.

Les glissements de terrain se produisent dans toutes les chaînes de montagnes où la résistance de massifs rocheux est insuffisante pour contrer l’action de la gravité. Les terrains volcaniques sont particulièrement susceptibles de s’effondrer car les édifices sont composés des lithologies diverses et variées qui peuvent être fortement fracturées. En plus, la croissance rapide des édifices volcaniques favorise leur instabilité et leur effondrement. L’activité magmatique est un facteur additionnel responsable de la déformation des édifices, tandis que l’activité hydrothermale réduit la résistance des roches volcaniques. Pour ces raisons, l’évaluation des aléas liés à l’effondrement des édifices et à la formation des avalanches des débris volcaniques mérite une attention particulière. Les caractéristiques physiques des composants des avalanches des débris ont une influence directe sur la dynamique de ce type d'écoulement. Les dépôts des avalanches de débris présentent une morphologie de surface composée des nombreuses collines (hummocks), qui montrent fréquemment les séquences volcaniques initiales, ce qui suggère un mécanisme de mise en place proche de celui des glissements de terrain. Cependant, d’autres dépôts présentent des crêtes allongées (rides) dont le mécanisme de formation est encore méconnu. Le volcan Tutucapa (sud du Pérou) a été affecté récemment par deux avalanches de débris. La plus ancienne, « Azufre », est d’âge Holocène et résulte de l’effondrement d’un complexe des dômes et d’une séquence volcanique altérée (hydrothermalisée) sous-jacente. La deuxième avalanche, « Paipatja », a eu lieu il y a seulement 200-230 ans BP et est associée à une grande éruption explosive du Tutupaca. Les dépôts de cette avalanche présentent notamment de nombreuses rides. Les deux dépôts d’avalanche montrent deux unités différentes : une unité inférieure, caractérisée par la présence des blocs altérés (hydrothermalisés) provenant de l’édifice basal, tandis que l’unité supérieure est constituée par des blocs du complexe de dômes actifs. Le travail de terrain montre que les rides de l’avalanche « Paipatja » présentent une forte variation de granulométrie entre leur partie centrale (enrichie en blocs grossiers) et leurs parties latérales, ce qui suggère un processus de ségrégation granulaire. Des expériences analogiques montrent que des écoulements de mélanges de particules des différentes tailles subissent un processus de ségrégation et de digitation granulaire qui engendre des rides par jonction de levées statiques qui délimitent un chenal d’écoulement. Le processus de formation des rides est facilité par de faibles différence de taille des particules dans des mélanges bidisperses. Ces résultats suggèrent que les rides observées au Tutupaca résultent d’un écoulement granulaire. Les principales caractéristiques morphologiques des structures formées lors de ces expériences de laboratoire ont été comparées qualitativement avec les structures observées dans les dépôts du Tutupaca. Les structures observées au Tutupaca montrent que deux mécanismes de mise en place peuvent coexister dans les avalanches de débris volcaniques : le glissement de blocs plus ou moins cohérents, et l’écoulement semblable à celui d’un matériau granulaire. Cela dépend probablement de la nature des différents matériaux à la source des avalanches. Cette information doit être prise en compte pour l’évaluation des aléas liés aux avalanches des débris car des mécanismes d’écoulement différents peuvent induire des fortes variations de la distance parcourue par ces avalanches. / Landslides occur in all mountainous terrain, where the rock strength is unable to support topographic loading. Volcanic rocks are particularly landslide prone, as they mix strong and weak lithologies and are highly pre-fractured. Also, volcanoes themselves, are peculiar mountains, as they grow, thus creating their own topographic instability. Magmatic activity also deforms the edifice, and hydrothermal activity reduces strength. For all these reasons, volcanoes need close consideration for hazards, especially for the landslide-derived rock avalanches. The characteristics and properties of different debris avalanche components influence their behavior during motion. Deposits are generally hummocky, preserving original layering, which indicates a slide-type emplacement. However, some deposits have ridged morphology for which the formation mechanisms are not well understood. Two recent debris avalanches occurred at the Tutupaca volcano (S Peru). The first one, “Azufre” is Holocene and involved the collapse of active domes and underlying older hydrothermally altered rocks. The second debris avalanche, “Paipatja” occurred 200-230 y BP and is associated with a large explosive event and this deposit is ridged. The excellent conservation state of the deposits and surface structures allows a comprehensive analysis of the ridges. Both deposits have two contrasting units: a lower basal edifice-derived hydrothermally-rich subunit and an upper dome-derived block-rich unit. Detailed fieldwork has shown that Paipatja ridges have coarser core material and are finer in troughs, suggesting grain size segregation. Using analog experiments, the process that allow ridge formation are explored. We find that the mixtures undergo granular segregation and differential flow that create fingering that forms ridges by junction of static léeves defining a channel flow. Granular segregation and fingering are favored by small particle size contrast during bi-dispersed flow. The results suggest that the ridges observed at Tutupaca are product of a granular flow We extract the morphological characteristics of the deposits of granular flows generated in the laboratory and make a qualitative comparison with the Tutupaca deposits. The description of the different landslide and debris avalanche features at Tutupaca shows that two types of debris avalanche motion can occur in volcanic debris avalanches: the sliding of blocks more or less coherent and a flow similar to a granular material. This probably depends on source materials and the conditions of different parts of the initial landslide. Such information should be taken into account when estimating hazards at other volcanic landslide sites, as the different behaviors may result in different run outs.