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Dufresne, Anja. "Influence of runout path material on rock and debris avalanche mobility : field evidence and analogue modelling : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Geological Sciences/Hazard and Disaster Management, University of Canterbury, New Zealand /." Thesis, University of Canterbury. Geological Sciences, 2009. http://hdl.handle.net/10092/3076.
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Rock and debris avalanches result from sudden rock slope failure; they occur in a variety of materials and landscapes, and often have a catastrophic and lasting impact on the society, infrastructure, and landscape of the area. In order to fully understand these events, the factors leading to failure and those influencing the course of the event must be investigated. In recent years, increased attention has been given to numerous aspects of rock/debris avalanche emplacement: among these is the influence of runout path material on the behaviour of snow and ice avalanches, pyroclastic currents, debris flows, volcanic debris avalanches and non-volcanic rock avalanches. The fact that substrates are involved in rock avalanche emplacement has been known since Buss and Heim remarked on it in 1881, but few detailed studies on the effects of this involvement on avalanche emplacement exist. One popular hypothesis which has emerged is that the long runout of large rock avalanches can be explained by the basal friction reduction due to overrunning or failure of saturated substrate material. However, the present study shows that this is not the case. From analysis of nearly 400 rock and debris avalanche deposit descriptions it is evident that: (1) avalanches inevitably interact with their runout path material; (2) all large (> 10⁶ m³) rock and debris avalanche events have runout distances that exceed simple frictional model predictions regardless of type or degree of substrate interaction; (3) substrates only add complexities to the ‘long-runout’ avalanche events similar to topographic interference. The complexities resulting from substrate interaction include, for example, characteristic deposit surface features such as longitudinal ridges and flowbands, compressional faults and raised margins from rapid deceleration behind e.g. bulldozed substrates; shearing in a basal mixed zone and consequent changes in basal avalanche mechanical properties; volcanic edifice failure on weak underlying sediments with a change in volcano shape; transformation into more mobile debris flows through the entrainment of large quantities of water or water-bearing materials; and many others.
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Daerr, Adrian. "Dynamique des Avalanches." Phd thesis, Université Paris-Diderot - Paris VII, 2000. http://tel.archives-ouvertes.fr/tel-00003998.
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Un milieu granulaire peut rester au repos même avec une surface libre inclinée, et il ne se met spontanément en mouvement qu'au dessus d'un angle critique. Il apparaît alors un écoulement de surface dont l'amplitude et la dynamique sont régies par la mobilisation et le dépôt de grains à l'interface avec la phase statique. Malgré son importance pratique, la dynamique de cette transition demeure largement inconnue. Le manuscrit présente une étude expérimentale de ce problème dans deux géométries d'écoulements granulaires différentes. Dans la première expérience, l'équilibre d'une couche de sable déposée dynamiquement sur un plan rugueux est rendu métastable: après avoir augmenté l'inclinaison du plan, une perturbation locale déclenche une avalanche. La mesure du seuil de déclenchement montre que la transition entre équilibre statique et écoulement est sous-critique. La forme et la dynamique des avalanches résultent d'un échange permanent de matière avec la couche statique, mobilisant à l'avant et déposant des grains à l'arrière. De manière surprenante, une saturation de l'amplitude est observée, qui peut être attribuée à la présence du fond solide. Nous avons aussi mis en évidence l'existence de deux types d'avalanches, l'un où la couche n'est mobilisée qu'en aval du point de déclenchement et laissant une trace triangulaire, et l'autre où l'écoulement envahit tout le plan par un front de remontée. L'étude montre que des mécanismes de propagation différents interviennent dans ces deux cas. La deuxième expérience consiste à étudier l'écoulement transitoire à la formation d'un talus. Nous avons observé l'influence prépondérante de la préparation sur l'écoulement. Deux effets sont mis en évidence, l'un associé à la densité et l'autre à la «texture» anisotrope acquise pendant le remplissage. Dans la dernière partie, nous discutons de la validité des modèles existants pour décrire les avalanches sur le plan incliné. En guise de conclusion, nous développons un modèle continu décrivant la dynamique des écoulements granulaires de surface et prenant appui sur les résultats expérimentaux présentés.
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Jaeger, Paul. "Hysteresis and Avalanches." Thesis, KTH, Skolan för teknikvetenskap (SCI), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-154238.
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In this thesis crackling systems have been investigated. Applying an external force on these systems they respond with events of all sizes. The size distribution follows a power law of the form S¯
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Johnson, Benjamin Crane. "Remotely triggered slab avalanches." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/MQ64998.pdf.
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Courrech, du Pont Sylvain. "Avalanches granulaires en milieu fluide." Phd thesis, Université Paris Sud - Paris XI, 2003. http://tel.archives-ouvertes.fr/tel-00004216.
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Considérons une boite remplie de grains et inclinons la progressivement. Au-dessus d'un angle critique, un écoulement de surface se déclenche. Cette avalanche, d'amplitude et de durée finies, fait relaxer l'angle du tas de quelques degrés. Ce processus intervient fréquemment dans la nature, notamment sous la forme d'écoulements de débris qui se produisent aussi bien à la surface de la Terre que dans les fonds marins. Cependant, les écoulements denses de granulaires immergés dans un liquide ont été peu étudiés. Ainsi, le travail expérimental rapporté dans ce manuscrit s'attache à déterminer l'influence d'un fluide environnant, gaz ou liquide, sur l'amplitude et la dynamique des avalanches. Nous mettons en évidence trois régimes d'avalanches contrôlés par deux paramètres sans dimension : le rapport r entre la densité des grains et celle du fluide, et le nombre de Stokes St qui compare l'inertie d'un grain aux effets visqueux du fluide. Dans un gaz (grandes valeurs de r et de St), l'effet du fluide est négligeable. Dans les liquides (petites valeurs de r), l'amplitude des avalanches diminue tandis que leur durée augmente lorsque St diminue. Dans une deuxième partie, nous étudions l'effet d'un confinement du tas entre deux parois latérales sur sa stabilité. Maximale quand l'écart entre parois est minimum, la valeur des angles diminue sur une longueur caractéristique B lorsque l'écart entre parois augmente. Cet effet peut s'expliquer par la redirection d'une partie des contraintes internes au tas vers les parois, ce qui y induit des forces de frottement prévenant ou bloquant l'écoulement. Deux lois d'échelles dépendantes de la taille des grains sont mises en évidence pour la longueur B : l'effet des parois est géométrique pour les gros grains alors qu'un régime cohésif est observé pour les petits grains. Enfin, nous rapportons les résultats de premières expériences dans l'air où la vitesse des grains est mesurée et apparaÎt exponentiellement décroissante avec la profondeur.
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Scheiwiller, Thomas Scheiwiller T. "Dynamics of powder-snow avalanches /." [S.l.] : [s.n.], 1986. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=7951.
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Dunning, Stuart A. "Rock avalanches in high mountains." Thesis, University of Bedfordshire, 2004. http://hdl.handle.net/10547/322902.
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Rock avalanches are a high magnitude, low frequency catastrophic mass movement involving the failure of over 1 x 106 m3 of mountainside. Rock avalanches are considered a major hazard of the high mountains due to the excessive run-out often associated with them. To date the mechanism that allows for such excessive travel distance is unproven although several dozen possibilities have been proposed. Rock-avalanche deposits exhibit characteristic features such as sharp lateral margins, confinement to local topography, super-elevation on valley sides, intensely fragmented interiors and preserved stratigraphy relative to the source. However, there are few detailed studies of the internal sedimentology of rock-avalanche deposits. Such studies are a vital piece of evidence in the search for the mechanisms of motion as rock avalanches are rarely witnessed. This thesis examines the detailed sedimentology of five rock avalanche deposits of varied lithology and morphology. A novel methodology is developed to sample deposits for their grainsize distributions (GSD). The GSD's prove similar for deposits, with significant variation due to preserved lithological banding in the interior. This finding refutes the commonly held view that rock-avalanche deposits are simply inversely graded. Instead, a facies model is developed of a coarse Carapace facies forming the surface and near surface that overlies a highly fragmented Body facies that is in turn underlain by the Basal facies that is free to interact with the substrate. The sedimentology of the Body facies is considered in fine detail and is shown to be fractal in nature, that is, self-similar at all scales of observation. A predictive sedimentological plot is presented that allows generation of the grain-size distribution and descriptive statistics from a simple estimation of weight percent gravel at a rock avalanche exposure. The morphology of rock-avalanche deposits are examined and a classification presented of 'spread' 'two-phase' and 'stalled'. The hazard and features of each morphology is described in relation to the observed deposits.
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Cooperstein, Michael Stephen. "The effects of slope aspect on the formation of surface hoar and diurnally recrystalized near-surface faceted crystals." Thesis, Montana State University, 2008. http://etd.lib.montana.edu/etd/2008/cooperstein/CoopersteinM0508.pdf.
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This research was conducted to determine if slope aspect played a role in the formation, size and shape of surface hoar and near-surface faceted crystals and on the meteorological variables that are known to result in the formation of these two weak layers. No studies have specifically studied the effects of slope aspect on the size and shape of these crystals nor the effects of slope aspect on the meteorological variables which are known to result in differences in temperature and vapor pressure gradients and ultimately result in the formation of two weak layers.
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Chiu, Yu-ho, and 趙汝豪. "Design of barriers against recurrent debris flows." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2003. http://hub.hku.hk/bib/B30431669.
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Spigler, Stefano. "Les avalanches dans les systèmes vitreux." Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLET021/document.
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Beaucoup de systèmes qui ont un certain degré de désordre ont des similaritésdans leur structure: le paysage énergétique est aléatoire et il a plusieursminima locaux de l’énergie. Quand on ajoute une petite perturbation externeau système à basse temprature, il est raisonnable d’attendre que la dynamiqueconduira le système d’un minimum à l’autre, et ça donne lieu à une réponsealéatoire et saccadé. Les sautes discontinus que l’on observe sont appelésavalanches, et l’intérêt de ce travail est le calcul de leur distribution. Undes résultats est en effet le développement d’un cadre pour calculer cettedistribution dans des systèmes en dimension infinie qui peuvent être décritsavec le replica symmetry breaking. Nous appliquons les résultats à l’un desmodèles les plus simples des verres structuraux, c’est à dire les empilementsdenses de sphères molles avec répulsion harmonique, avec une déformation(shear strain) du volume comme perturbation. Nous soutenons que, quandla déformation est suffisamment petite, une portion de la distribution desavalanches devient une loi de puissance, dont l’exposant peut être directementlié au paramètre d’ordre de la brisure de symétrie de replica. Cet exposant estégalement lié à la distribution des forces de contact (au moins entre certainessphères), dont le comportement asymptotique on sais que ne dpends pasfortement de la dimension spatiale; pour cette raison nous comparons lesprdictions de champ moyen en dimension infinie avec des simulation du mêmesystème en dimension trois et, remarquablement, on trouve un bon accord.Dans le reste de la thèse nous discutons aussi les similarités avec des travauxprécédents et quelques consquences que la distribution des avalanches donnesur les propriétés élastiques de la matière granulaire denseMany systems that are somehow characterized by a degree of disorder sharea similar structure: the energy landscape has many sample-dependent localenergy minima. When a small external perturbation is applied to the systemat low temperature, it is reasonable to expect that the dynamics will leadthe system from a minimum to another, thus displaying a random and jerkyresponse. The discontinuous jumps that one observes are called avalanches,and the focus of this work is the computation of their distribution. Oneof the results is indeed the development of a framework that allows thecomputation of this distribution in infinite-dimensional systems that canbe described within a replica symmetry breaking ansatz. We apply theresults to one of the simplest models of structural glasses, namely densepackings of (harmonic) soft spheres, either at jamming or at larger densities,subject to a shear transformation that induces jumps both in the totalenergy and in the shear stress of the system. We argue that, when theshear strain is small enough, the avalanche distribution develops a power-lawbehavior, whose exponent can be directly related to the functional orderparameter of the replica symmetry breaking solution. This exponent is alsorelated to the distribution of contact forces (or at least of the contact forcesbetween some of the spheres), whose asymptotic behavior is known not todepend strongly on the spatial dimension; for this reason, we compare theinfinite-dimensional prediction with three dimensional simulations of thesame systems and, remarkably, we find a good agreement. In the rest of thethesis we compare our results with previous works, and we also discuss someof the consequences that the avalanche distribution lead to, concerning thestatistical elastic properties of dense granular media
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Hansen, Cassandra. "Synoptic scale weather patterns and large class V slab avalanches on Mt. Shasta, California." abstract and full text PDF (free order & download UNR users only), 2008. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1453585.
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Logan, Spencer Carl. "Temporal changes in the spatial patterns of weak layer shear strength and stability on uniform slopes." Thesis, Montana State University, 2005. http://etd.lib.montana.edu/etd/2005/logan/LoganS0805.pdf.
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Ricciardi, Francesco. "Automatic search of missing people in avalanches." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/15282/.
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One of the main source of danger for people practising activities in mountain environments is avalanches. In the early 70s has been commercialized the first model of avalanche beacon transceiver: a device, composed by a transmitter and a receiver, specialized to the purpose of finding people buried under the snow. Since 2013, project SHERPA is working to develop ground and aerial robots to support human in the search of missing people in avalanches.
The aim of this dissertation is to provide a way to interface an avalanche beacon receiver (ARTVA) with the autopilot module mounted on a quad-copter drone, and to study and realize a software implementation of two automatic search algorithms, with the intention of speeding up search operations with drones.
First we will focus on interfacing the ARTVA system with a quad-copter autopilot module, named Pixhawk. This module embed a software, named PX4, which runs on a real-time operating system (RTOS), and have several connection ports, among which there is the serial one that we will use for our purpose. Then we will analyse how to use the data coming from the ARTVA receiver to construct and implement the two search algorithms. The idea is to generate set-points, based on the information coming from the avalanche beacon receiver, and use them to feed the position controller which is implemented in the PX4 firmware. Finally, we will execute simulations, provide results, and investigate if a practical implementation is possible and what are the relative issues.
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Baillifard, Marc-André. "Interaction between snow avalanches and catching dams /." Zürich : ETH, 2007. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17301.
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Hughes, David W. "Avalanches, self organised networks and solar flares." Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.408384.
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Reznichenko, Natalya. "Rock Avalanches on Glaciers: Processes and Implications." Thesis, University of Canterbury. Geological Sciences, 2012. http://hdl.handle.net/10092/6524.
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This thesis examines the role of rock avalanches in tectonically active terrains including the effects of the deposits on glacier behaviour and their contribution to moraine formation. The chronologies of mountain glacier fluctuations, based on moraine ages, are widely used to infer regional climate change and are often correlated globally. In actively uplifting mountain ranges rock avalanches that travel onto the ablation zone of a glacier can reduce ice-surface melting by insulating the ice. This can cause buried ice to thicken due to slower ablation and can significantly alter the overall glacier mass balance. This glacier response to supraglacial rock avalanche deposits can confound apparent climatic signals extracted from moraine chronologies. This thesis investigates the processes through which rock avalanche deposits may affect glaciers and develops a new technique to identify the presence of rock avalanche debris in glacial moraines.
From laboratory experiments on the effects of debris on ice ablation it is demonstrated that the rate of underlying ice ablation is controlled by diurnal cyclicity and is amplified at high altitude and in lower latitudes. The relatively low permeability of rock avalanche sediment in comparison with non-rock avalanche supraglacial debris cover contributes to the suppression of ablation, at least partly because it greatly reduces the advection of heat from rain water to the underlying ice.
The laboratory findings are supplemented by field investigations of two recent rock avalanche deposits on glaciers in the Southern Alps of New Zealand. This work demonstrates that the rock avalanche deposits are very thick (10 m at Aoraki/Mt. Cook and 7m at Mt. Beatrice) and almost stopped the ablation of the overlying ice. This resulted in the formation of an ice-platform more than 30 m high. This led to a reduction of the existing negative mass balance of the affected Tasman and Hooker Glaciers. There was little noticeable alteration of the overall glacial regime due to the small scale of the debris covered area (4 and 1% of the ablation zones for the Tasman and Hooker Glaciers, respectively) but there is a significant contribution to supraglacial debris, which is passively transported toward the terminus. A conceptual model of the response of mountain valley glaciers to emplacement of extensive rock avalanche debris on the ablation zone has been proposed for the effect of this type of debris on terminal moraine formation based on enhanced ‘dumping’ of supraglacial sediments.
A new technique has been developed to distinguish rock-avalanche-derived sediment from sediment of glacial origin, based on the sedimentary characteristics of the finest fraction. Examination of rock avalanche sediment under the Scanning Electron Microscope showed that finer particles tend to form strong clumps, which comprise many smaller (down to nanometre-scale) clasts, named here ‘agglomerates’. These agglomerates are present in the fine fraction of all examined rock avalanche deposits and absent in known non-rock-avalanche-derived glacial sediments. The agglomerates are characteristics of sediment produced under the high-stress conditions of rock avalanche emplacement and contrast with lower-stress process sub- and en-glacial environments. It is demonstrated that these agglomerates are present in some moraines in the Southern Alps of New Zealand that have been attributed to climate fluctuation. Consequently, this technique has the potential to resolve long-standing arguments about the role of rock avalanches in moraine formation, and to enhance the use of moraines in palaeoclimatological studies.
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HaÌkonardoÌttir, Kristin Martha. "The interaction between snow avalanches and dams." Thesis, University of Bristol, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399862.
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Koehler, Anselm. "High resolution radar imaging of snow avalanches." Thesis, Durham University, 2018. http://etheses.dur.ac.uk/12556/.
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Snow avalanches are a complex type of gravity driven mass-movement phenomena and can exhibit very different flow dynamics. They may flow as a dilute and fast powder snow avalanche, or cohesive snow may cause a dense and slow gliding motion. The current knowledge and understanding of the processes involved are partly limited due to the lack of high-resolution spatial measurements of full-scale avalanches. The diversity of avalanches is known from point measurements and deposits, but only radar can connect those observation spatially. This thesis explores the newly developed radar sensor GEODAR. The radar signal can penetrate a powder cloud and measures reflections from the underlying denser flow structures. GEODAR allows us to track the evolution of flow features such as surges, flow regimes and transitions between them in time and space. In three chapters, I present interpretation of the GEODAR data and add greatly to the understanding of dynamic processes in snow avalanches. In particular, I identify typical avalanche signatures in the radar data and classify the variety of avalanches in terms of seven flow regimes. I investigate in detail the influence of surges on the intermittent regime which is uniquely found in large powder snow avalanches. And in a third study, I analyse transitions between cold and warm flow regimes and explain the occurrence with the temperature of the snow cover.
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Costa, Ariadne de Andrade. "Quasi-criticalidade auto-organizada em avalanches neuronais." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/59/59135/tde-17112011-204509/.
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Experimentos têm revelado que redes de neurônios, tanto in vitro como in vivo, mantêm atividade descrita por avalanches e se organizam em um estado crítico no qual essas avalanches são distribuídas de acordo com leis de potência. Mostramos no presente trabalho que um modelo de rede de elementos excitáveis com sinapses dinâ- micas é capaz de exibir criticalidade auto-organizada para ampla região do espaço de parâmetros. Nossos resultados estão de acordo com outros estudos que indicam que a depressão sináptica de curto prazo constitui mecanismo suciente para produzir criticalidade em avalanches neuronais. No entanto, segundo diversos pesquisadores, embora o ajuste de parâmetros seja grosso para que haja criticalidade no modelo, é mais preciso dizer que o sistema não apresenta criticalidade auto-organizada genu ína, mas sim quasi-criticalidade auto-organizada, como os demais modelos não conservativos presentes na literatura.Experiments have shown that neuronal networks, both in vitro and in vivo, maintain activity described by avalanches and they are organized into a critical state in which these avalanches are distributed according to power laws. We have demonstrated that a model based on a network of excitable elements with dynamical synapses is able to exhibit self-organized criticality for a wide range of the parameter\'s space. Our results are consistent with other studies that suggest short-term synaptic depression is enough to produce criticality in neuronal avalanches. However, according to several researchers, in spite of the tuning to be gross to ensure that there is criticality in the model, it is more accurate do not say that the system presents genuine self-organized criticality, but self-organized quasi-criticality as the other non-conservative models in the literature.
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El, Tannoury Claude. "Mécanismes de déclenchement des avalanches granulaires humides." Thesis, Rennes 1, 2018. http://www.theses.fr/2018REN1S125/document.
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La dynamique du déclenchement des avalanches dans un milieu granulaire lentement incliné passe par trois phases; (1) des petits réarrangements locaux et indépendants de grains (2) suivis de mouvements collectifs, successifs et quasi-périodiques, appelés 'précurseurs' (3) finissant par une avalanche. Cette dynamique peut dépendre de nombreux paramètres. Dans cette thèse, nous avons étudié, par des mesures optiques et acoustiques, la réponse du milieu granulaire soumis à une inclinaison lente de son container. Nous avons déterminé l'importance du choix de la puissance du signal acoustique sur nos mesures. Nous avons observé l'effet de l'état de surface des grains sur l'apparition des précurseurs et sur l'occurrence de l'avalanche. Nous avons réalisé des cycles d'inclinaison allant de -θ à +θ se terminant par une avalanche . Nous avons mis en évidence l'influence de l'angle du cycle θ sur les précurseurs et l'angle d'avalanche final. Nous avons aussi étudié des milieux granulaires soumis à des taux d'humidité comprises entre 40 et 96, par des mesures optiques surfaciques et latérales. Nous avons montré que les angles d'avalanche et l'apparition des premiers précurseurs dépendent de la taille des grains mais aussi de l'humidité. Cette dépendance est liée aux forces de cohésion qui sont relativement plus élevées à forte humidité et qui compensent la force de gravité pour des petits grains. Enfin, nous avons montré l'importance d'une diffusion homogène de l'humidité dans le milieu sur son comportement. L'impact de la mouillabilité des grains a été aussi abordéThe dynamics of avalanche triggering in a slowly inclined granular medium passes through three phases; (1) small local and independent rearrangements of grains (2) followed by collective, successive and quasi-periodic movements, called 'precursors' (3) ending in an avalanche. This dynamic can depend on many parameters. In this thesis, we have studied, by optical and acoustic measurements, the response of the granular medium subjected to a slow inclination of its container. We determined the importance of choosing the power of the acoustic signal on our measurements. We observed the effect of the grain surface condition on the occurrence of precursors and the occurrence of the avalanche. We performed tilted cycles ranging from -θ to +θ ending in an avalanche. We have demonstrated the influence of the θ cycle angle on the precursors and the final avalanche angle. We have also studied granular media with moisture contents between 40 and 96%, by surface and lateral optical measurements. We have shown that the avalanche angles and the appearance of the first precursors depend on the grain size but also the humidity. This dependence is related to cohesive forces that are relatively higher at high humidity and that compensate for the force of gravity for small grains. Finally, we have shown the importance of a homogeneous diffusion of moisture in the environment on its behavior. The impact of grain wettability was also discussed
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Bouchet, Alexi. "Etude expérimentale des avalanches denses de neige sèche." Université Joseph Fourier (Grenoble), 2003. http://www.theses.fr/2003GRE10095.
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Ash, M. "FMCW phased array radar for imaging snow avalanches." Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1383579/.
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Radar has emerged as a useful tool for measuring avalanches to improve our knowledge of their behaviour. These measurements are used to refine and validate mathematical models of avalanches which are employed in the calculation of avalanche risk zones. However, current radar measurements do not provide a true representation of an entire avalanche flow due to their inadequate range resolution and lack of cross-range resolution. This thesis describes the development of an FMCW phased-array radar for use as a research tool to enable 2-D field measurements of avalanches in unparalleled detail. The design of the radar is presented in detail based on a review of the current avalanche remote sensors and applicable radar literature. The radar operates at 5.3GHz to illuminate dense centimetre-size blocks of snow. It is shown that the developed radar has a range resolution of 1.3m following processing, a 19x gain over other avalanche radar, and is sensitive to snow movements beyond 2.5km, sufficient to measure an entire avalanche flow. Additionally, methods of processing the radar data are developed. These include MTI processing using an IIR filter, avalanche front detection using OS-CFAR, and cohering of the array using low-quality phase synchronising sources within the field-of-view of the radar. The radar is now deployed in a bunker at well-equipped avalanche test site in Switzerland where it automatically records naturally occurring avalanches. This thesis describes two avalanches which were recorded by the radar during the 2010/11 winter. The collected data has been processed using the aforementioned processing techniques. The processing outputs are presented including single channel range-time images, velocity measurements of the avalanche fronts, and detailed 2-D images of the avalanches showing unprecedented detail. It is shown that there is the potential to extract velocity measurements of individual blocks of snow comprising the avalanche.
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Valencia, Camilo Akimushkin. "Avalanches e redes complexas no modelo Kinouchi-Copelli." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-24102012-113159/.
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A capacidade de um sistema sensorial detectar estímulos eficientemente é tradicionalmente dimensionada pela faixa dinâmica, que é simplesmente uma medida da extensão do intervalo de intensidades de estímulo para as quais a rede é suficientemente sensível. Muitas vezes, sistemas biológicos exibem largas faixas dinâmicas, que abrangem diversas ordens de magnitude. A compreensão desse fenômeno não é trivial, haja vista que todos os neurônios apresentam janelas de sensibilidade muito estreitas. Tentativas de explicação baseadas em argumentos de recrutamento sequencial dos neurônios sensoriais, com efeitos essencialmente aditivos, simplesmente não são realísticas, haja vista que seria preciso que os limiares de ativação das unidades também apresentassem um escalonamento por várias ordens de magnitude, para cobrir a faixa dinâmica empiricamente observada em nível macroscópico. Notavelmente, o modelo Kinouchi-Copelli (KC), que carrega o nome de seus idealizadores, mostrou que aquele comportamento pode ser um efeito coletivo (não aditivo) do conjunto de neurônios sensoriais. O modelo KC é uma rede de unidades excitáveis com dinâmicas estocásticas e acoplados segundo uma topologia de grafo aleatório. Kinouchi e Copelli mostraram que a taxa espontânea de disparo dos neurônios (ou atividade média) sinaliza uma transição de fase fora do equilíbrio do tipo ordem-desordem, e que exatamente no ponto crítico desta transição (em termos de um parâmetro ligado às características estruturais da rede) a sensibilidade a estímulos externos é máxima, ou seja, a faixa dinâmica exibe uma otimização crítica. Neste trabalho, investigamos como o ponto crítico depende da topologia, utilizando os modelos mais comuns das chamadas redes complexas. Além disso, estudamos computacionalmente os padrões de atividade (avalanches neuronais) exibidos pelo modelo, com especial atenção às mudanças qualitativas de comportamento devido às mudanças de topologia. Comentaremos também a relação desses resultados com experimentos recentes de monitoramento de dinâmicas neurais.The capacity of a sensory system in efficiently detecting stimuli is usually given by the dynamic range, a simple measure of the range of stimulus intensity over which the network is sensible enough. Many times biological systems exhibit large dynamic ranges, covering many orders of magnitude. There is no easy explanation for that, since individual neurons present very short dynamic ranges isolatedly. Arguments based on sequential recruitment are doomed to failure since the corresponding arrangement of the limiar thresholds of the units over many orders of magnitude is unrealistic. Notably the so-called Kinouchi-Copelli (KC) model strongly suggested that large dynamic range should be a collective effect of the sensory neurons. The KC model is a network of stochastic excitable elements coupled as a random graph. KC showed the spontaneous activity of the network signals an order-disorder nonequilibrium phase transition and that the dynamic range exhibits an optimum precisely at the critical point (in terms of a control parameter related to structural properties of the network). In this work, we investigate how the critical point depends on the topology, considering the alternatives among the standard complex networks. We also study the burts of activity (neuronal avalanches) exhibited by the model, focusing on the qualitative changes due to alternative topologies. Finally we comment on possible connections among our results and recent observations of neural dynamics.
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Chianca, Cinthya Valeska. "Modelos computacionais para avalanches, fragmentação e séries temporais." Niterói, 2017. https://app.uff.br/riuff/handle/1/2931.
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Conselho Nacional de Desenvolvimento Científico e Tecnológico
Neste trabalho, estudamos sistemas com características diferentes mas que apresentam comportamento crítico. Na primeira parte, a partir de modelos que estudam avalanches usando blocos e molas e utilizando cadeias de bits simulamos estes sistemas de maneira simples e conseguimos obter resultados que são compatíveis com os já mostrados na literatura. A seguir, descrevemos um método para analisar séries temporais com tendências que serve para retirar tendências de baixas frequências da mesma. Finalmente, descrevemos a realização de uma experiência de fragmentação em gotas de mercúrio que repetimos para tentar obter melhores resultados.
In this work we study critical behaviour in systems with different characteristics. In the first part, beginning with block and spring models for avalanches, we use bit chains for simple simulations of these models and obtain results compatible with those published in the literature. Next, we describe a new method to analyse temporal series which is useful to extract the low frequency tendencies. Finally, we describe the realisation of an experiment using mercury drops, which we repeated to obtain bettes results.
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Porion, Patrice. "Frottement solide et avalanches dans les matériaux granulaires." Lille 1, 1994. http://www.theses.fr/1994LIL10050.
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Une etude des avalanches de materiaux granulaires secs a ete entreprise afin de mieux comprendre le mecanisme de ce mode de deformation de surface, de le comparer aux predictions theoriques des modeles physiques (bruit en 1/f) et aux resultats de la mecanique des sols. Pour une etude rigoureuse des effets lies a l'existence d'une surface libre, la densite des milieux etudies a ete systematiquement controlee; parallelement, les effets eventuels des forces de cohesion intergranulaire ont ete estimes grace a des experiences sous macro-gravite realisees a la centrifugeuse du laboratoire central des ponts et chaussees de nantes. Apres un rappel des methodes de la mecanique des sols et une presentation du concept de criticalite auto-organisee de p. Bak et al. - dont le modele propose est le tas de sable, et qui constitue une approche nouvelle des phenomenes critiques - nos resultats experimentaux sont exposes et analyses. Nous montrons en particulier que la cohesion intergranulaire et l'elasticite des grains peuvent etre negligees, que la taille des avalanches et la valeur de l'angle maximal de repos dependent de la densite initiale du tas, et que la surface du tas evolue spontanement vers un etat asymptotique apres quelques avalanches: cet etat est caracterise par l'inclinaison de sa surface libre par rapport a l'horizontale, egale a l'angle de frottement solide mesure a l'essai triaxial. Cependant, le frottement solide presente des fluctuations dont l'ampleur depend de la nature du materiau. Nos resultats presentent une bonne concordance avec ceux des essais triaxiaux classiques. Le parametre densite bien que pertinent, n'est pas le seul a controler le mecanisme d'avalanche. L'effet de taille finie a ete confirme, un comportement critique ayant pu etre mis en evidence sur les tas de petite taille.
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Bernard, Karine. "Quelques aspects sédimentaires des avalanches de débris volcaniques." Thesis, Clermont-Ferrand 2, 2015. http://www.theses.fr/2015CLF22624/document.
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La caractérisation granulaire de dépôts hétérométriques organisés en paquets glissés implique une démarche systématique afin d'optimiser l'extraction de données et de les rendre comparables. La quantification des rapports structures-fractions granulaires a permis de mettre en évidence des cinématiques localisées, inscrites dans des cinématiques d'ordre I. Les rides de Tutupaca, le lobe distal du Pichu-Pichu, l'effondrement du Misti au Pérou; la levée latérale du Cheix et le charriage distal de Perrier aux Mt Dore ; les transformations de Meager au Canada, de la Qda San Lazaro au Pérou, de Pardines en France ont été quantifiés. Héritage volcanique, ségrégations granulaires, cataclases syn-tectoniques sont des précurseurs aux modifications matricielles, à l'origine des transformations distales en lahars. Les données ainsi comparées permettent de proposer des classifications sédimentologiques distinguant les effondrements proximaux des transformations par les fluides ( hydrothermaux, eau). Seules quelques équations regroupent l'ensemble de ces dépôtsThe sedimentology of heterogeneous granular deposits, such as debris avalanches deposits require a systematic method to describe and compare data. The relationships between the localized structures and granular distributions show that the localized granular kinematics follow with the larger kinematic structural order. Structures and sedimentology are studied and quantified at the following debris avalanche deposits: the ridged avalanche units at Tutupaca (s. Peru), the distal lobe of the Pichu-Pichu debris avalanche (Arequipa, Peru), a lateral levee of a deposit at Cheix (Sancy volcano, France), a thrusted distal lobe at Perrier (Mt Dore, France). Debris avalanche - lahar transformations are studied at Mt Meager (Canada), Qda San Lazaro (Misti, Peru), Pardines (Mt Dore, France). The inherited granular distribution, the granular segregation, the syn-tectonic cataclasis are precursor stages to the distal matrix transformations. Sedimentological classifications are produced that differentiate the proximal collapse from later transformations caused by fluids (gas, water). Some equations are common for these heterogeneous deposits
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Lherminier, Sébastien. "Avalanches invariantes d’échelle dans un milieu granulaire modèle." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSE1229/document.
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Ce travail de thèse a pour objectif la reproduction et l'analyse du comportement invariant d'échelle, tel que l'on peut le trouver dans la nature et en particulier au niveau d'une faille tectonique. Pour cela, une expérience reproduisant la structure locale d'une faille par le cisaillement d'un milieu granulaire 2D a été montée et exploitée. L'utilisation de conditions aux limites périodiques dans cette expérience permet l'acquisition d'une statistique très riche, principal défaut des expériences présentes dans la littérature. Le suivi du système est effectué à la fois par des moyens optiques, mécaniques et acoustiques, ces derniers fournissant les informations les plus nombreuses et les plus précises. La dynamique a montré une invariance d'échelle compatible avec les lois statistiques existantes pour les tremblements de terre réels. Les corrélations entre les avalanches et entre les différents moyens de mesure sont analysées. Des expériences complémentaires ont été réalisées pour mieux comprendre les mécanismes à l'œuvre lors du déclenchement d'une avalanche et pendant son déroulement. La principale concerne la propagation d'une onde acoustique au sein d'un milieu granulaire, et a montré qu'une simple mesure de la vitesse de l'onde permet d'obtenir des informations sur la structure interne de l'empilement. L'utilisation d'un matériau photoélastique a permis, suite à une calibration adaptée, de sonder les forces locales au niveau des contacts entre grains et de voir l'évolution des réseaux de force dans le milieu au cours du cisaillementThe aim of this thesis is to reproduce and analyze the scale invariant behavior, as one can find in nature and in particular for a tectonic fault. Thus we set an experiment which reproduces the local structure of a fault thanks to a sheared 2D granular medium. The use of periodic boundaries in the experiment allows us to gain a very rich statistics, which was lacking in previous experiments presented in the literature. The system is monitored by three different methods: optical, mechanical and acoustics, which gives the most numerous and most precise informations. We observed scale invariant dynamics, consistent with statistical laws derived for real earthquakes. We also analyzed the correlations between avalanches and between the three monitoring methods. Additional experiments have been performed to better understand the mecanisms that take place at the triggering and during an avalanche. The main one focuses on sound wave propagation inside a granular pile, and we have shown that a mere velocity measure can give information about the internal structure of the pile. The use of a photoelastic material allows us (with appropriate calibration) to probe local forces at the edges and contacts of the grains and to see the evolution of force chains during the shear
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Peitzsch, Erich Hans. "Water movement in a stratified and inclined snowpack implications for wet slab avalanches /." Thesis, Montana State University, 2009. http://etd.lib.montana.edu/etd/2009/peitzsch/PeitzschE0509.pdf.
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Wet snow avalanches are dangerous and can be particularly difficult to predict. The rate of change from safe snow conditions to dangerous snow conditions occurs rapidly in a wet snowpack, often in response to water production and movement. This research focused on the relationship between snow stratigraphy and water movement in an inclined snowpack. Concentrating on transitions that impede water and flow finger formation within the snowpack, dye tracer was mixed with water and applied to a stratified snowpack to observe and measure the movement of water in various snow grain types, sizes, densities, and temperatures. There were two types of layer transitions that impeded water. Water was impeded at capillary boundaries caused by fine grains over coarse grains. It was also impeded at hydraulic conductivity boundaries, such as ice layers. In layer transitions that impeded water, the grain size of the layer above was significantly smaller than the layer below. The layer above a transition that impeded water was also significantly less dense than the layer below the transition. A qualitative analysis of grain type showed that there was no relationship between grain types in the layer above or below a transition and whether they will or will not impede water. A SnowMicroPen (SMP) was used to measure changes in structural element length to identify capillary boundaries. Results from SMP measurements indicate that microstructural analysis of the snowpack aids in characterizing capillary boundaries that impede water flow. The step change, rate of change, and percent increase were significantly larger in capillary boundaries than transitions that did not impede water for the entire dataset from all 8 sessions. When all transitions were ranked according to absolute change for each profile, capillary boundaries consistently ranked in the top two of all transitions evident within each SMP profile. The amount of water needed to produce flow fingers was highly variable. There was no significant relationship between the amount of water necessary to form flow fingers and snow density, snow grain size, snow temperature, or grain type. Layer transitions that impeded vertical water movement and flow finger formation may both play a large role in wet slab avalanche formation.
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Chan, Wai Yuen. "Probabilistic debris mobility modeling /." View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202009%20CHAN.
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Lins, Ribeiro Tiago. "Avalanches neuroniais durante o ciclo sono-vigília de ratos." Universidade Federal de Pernambuco, 2009. https://repositorio.ufpe.br/handle/123456789/6016.
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Previous issue date: 2009Conselho Nacional de Desenvolvimento Científico e Tecnológico
Avalanches neuronais são padrões espaço-temporais de atividade que ocorrem espontaneamente nas camadas superficiais do córtex mamífero sob várias condições experimentais. Estudos anteriores em fatias cerebrais e cultura de tecidos mostraram que a distribuição de tamanhos P(s) de avalanches neuronais obedece à uma relação de lei de potência: P(s) » s¡a , com expoente a '3=2. Isso é compatível com a idéia de que redes neuronais in vitro operam em regime crítico, mas pouco se sabe sobre as propriedades das avalanches neuronais in vivo. Nessa dissertação foi investigada a estatística das avalanches neuronais em registros extracelulares de potenciais de ação (disparos) obtidos de ratos cirurgicamente implantados com multi-eletrodos. Os animais foram continuamente registrados por várias horas ao longo do ciclo sono-vigília, antes, durante e depois de uma sessão de exploração de objetos novos. Também foram registrados animais sob efeito de anestesia. Em particular, procuramos assinaturas estatísticas nos registros in vivo que permitissem testar a hipótese de criticalidade no cérebro. Os dados foram divididos em bins temporais Dt. Uma avalanche foi definida como uma sequência de bins nos quais a atividade é não-nula. Realizamos análises estatísticas com respeito ao tamanho (número de disparos) s, a duração d e o intervalo t entre avalanches, para um dado Dt. Observamos que a estatística das avalanches neuronais varia de acordo com a fase do ciclo sono-vigília. Para qualquer fase, avalanches mais longas e maiores se tornam mais frequentes após a experiência de exploração. Encontramos distribuições de tamanhos que se assemelham à distribuição lognormal: P(s) » s¡1 exp[¡c(ln(s)¡b)2]. Estudamos um modelo de autômatos celulares excitáveis e mostramos que distribuições como essas podem ser obtidas em um sistema no ponto crítico quando há subamostragem. Ou seja, sistemas que exibem distribui ções de tamanhos do tipo lei de potência quando a medida das avalanches é realizada em todos os elementos da rede, apresentam distribuições que se assemelham à lognormal quando apenas uma pequena parte de seus elementos excitáveis é utilizada para fazer as medidas. Além disso, exploramos a dinâmica temporal e observamos que a família de distribuições de intervalos D(t ;sc) entre avalanches consecutivas com tamanho s ¸ sc obedecem a uma lei de escala: D(t ;sc) = R(sc)F(tR(sc)), onde R(sc) = ht i¡1 e F é uma função de escala. Os resultados são semelhantes às leis de escala encontradas em clarões solares (solar fiares), incêndios florestais, fraturas, terremotos e outros sistemas. A presença de lei de escala na dinâmica temporal do sistema é compatível com a idéia de criticalidade auto-organizada e foi encontrada nos mais diversos estados comportamentais, regiões do cérebro e períodos da experiência nos ratos estudados
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DORNELLES, Leonardo Dalla Porta. "Oscilações coletivas e avalanches em redes de neurônios estocásticos." Universidade Federal de Pernambuco, 2016. https://repositorio.ufpe.br/handle/123456789/18384.
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Avalanches neuronais, assim como oscilações e sincronização, são padrões de atividade espontânea observados em redes neuronais. O conceito de avalanches neuronais foi concebido na última década. Esse padrão de atividade tem distribuições de tamanhos P(s) e durações P(d) invariantes por escala, i.e., obedecem relações do tipo lei de potência P(s) ∼ s −τ, com expoente τ ≃ 3/2, e P(d) ∼ d−τt, com expoente τt ≃ 2, respectivamente. Essas propriedades são compatíveis com a ideia de que o cérebro opera em um regime crítico. A partir dessas constatações, muitos estudos teóricos e experimentais reportaram os potenciais benefícios de um cérebro operando na criticalidade, como por exemplo a máxima sensibilidade aos estímulos sensoriais, máxima capacidade de informação e transmissão e uma ótima capacidade computacional. Modelos da classe de universalidade de percolação direcionada (DP) têm sido amplamente utilizados para explicar a estatística invariante por escala das avalanches neuronais. Porém estes modelos não levam em consideração a dinâmica dos neurônios inibitórios e, além disso, como apresentam uma transição de fase entre um estado absorvente e uma fase ativa, torna-se difícil conciliar o modelo com correlações temporais de longo alcance que são observadas experimentalmente em diferentes escalas espaciais. Neste contexto, um novo modelo computacional (CROs, do original em inglês Critical Oscillations) surgiu na literatura (Poil et al., J. Neurosci., 32 9817, 2012), incluindo neurônios inibitórios e buscando conciliar correlações temporais com avalanches neuronais. Neste modelo não há uma fase absorvente, e uma suposta transição de fases ocorre entre uma fase ativa e outra com oscilações coletivas. Devido à ausência de uma fase absorvente, avalanches neuronais são definidas comparando-se a atividade instantânea da rede com um limiar que depende da mediana da atividade total. Justamente na linha crítica do espaço de parâmetros, quando há uma balanço entre excitação e inibição neuronal, avalanches neuronais invariantes por escala são observadas juntamente com correlações temporais de longo alcance (ruído 1/ f). No presente trabalho, um estudo mais profundo a respeito dos resultados reportados para o modelo CROs foi realizado. As oscilações neuronais mostraram-se robustas para diferentes tamanhos de rede, e observamos que a dinâmica local reflete a dinâmica oscilatória global da rede. Correlações temporais de longo alcance foram observadas (num intervalo de escalas temporais) através da técnica de Detrended Fluctuation Analysis, sendo robustas perante modificações no tamanho da rede. O resultado foi confirmado pela análise direta do espectro, que apresentou decaimento do tipo 1/ f numa determinada faixa de frequências. O diagrama de fases do modelo mostrou-se robusto em relação ao tamanho da rede, mantendo-se o alcance das interações locais. Entretanto, os resultados mostraram-se fortemente dependentes do limiar utilizado para detecção das avalanches neuronais. Por fim, mostramos que distribuições de durações de avalanches são do tipo lei de potência, com expoente τt ≃ 2. Este resultado é inédito e o valor encontrado coincide com o expoente crítico da classe de universalidade de DP na dimensão crítica superior. Em conjunto, nossos resultados fornecem mais evidências de que o modelo CROs de fato apresenta uma transição de fases.
Neuronal avalanches, as well as waves and synchronization, are types of spontaneous activity experimentally observed in neuronal networks. The concept of neuronal avalanches was conceived in the past decade. This pattern of activity has distributions of size P(s) and duration P(d) which are scale invariant, i.e., follow power-law relations P(s) ∼ s−τ, with exponent τ ≃ 3/2, and P(d) ∼ d−τd, with exponent τt ≃ 2, respectively. These properties are compatible with the idea that the brain operates in a critical regime. From these findings, many theoretical and experimental studies have reported the potential benefits of a brain operating at criticality, such as maximum sensitivity to sensory stimuli, maximum information capacity and transmission and an optimal computational capabilities. Models belonging to the directed percolation universality class (DP) have been widely used to explain the scale invariant statistic of neuronal avalanches. However, these models do not take into account the dynamics of inhibitory neurons and, since as they present a phase transition between an absorbing state and an active phase, it is difficult to reconcile the model with long-range temporal correlations that are observed experimentally at different spatial scales. In this context, a new computational model (CROs, Critical Oscillations) appeared in the literature (Poil et al., J. Neurosci., 32 9817, 2012), including inhibitory neurons and seeking to reconcile temporal correlations with neuronal avalanches. In this model there is no absorbing phase, and a supposed phase transition occurs between an active phase and another with collective oscillations. Due to the lack of an absorbing phase, neuronal avalanches are defined comparing by the instant network activity with a threshold that depends of the total activity median. Precisely at the critical line in parameter space, when a balance between neuronal excitation and inhibition occurs, scale invariant neuronal avalanches are observed with long-range temporal correlations (1/ f-like noise). In the present work, a deeper study about the results reported for the CROs model was performed. Neuronal oscillations have been shown to be robust to increasing network sizes, and it was observed that local dynamic reflects the oscillatory global dynamic of the network. Long-range temporal correlations were observed (in a range of time scales) via Detrended Fluctuation Analysis, being robust against changes in network size. The result was confirmed by direct analysis of the spectrum, which showed a decay like 1/ f in a given frequency band. The phase diagram of the model was robust with respect to the network size, as long as the range of local interactions was kept. However, the results were dependent of the threshold used to detect neuronal avalanches. Finally, we have shown that the distributions of avalanches duration follows a power-law with exponent τt ≃ 2. This result is unprecedented and the value obtained coincides with the critical exponent of the DP universality class in the upper critical dimension. Together, our results provide further evidence that in fact the CROs model presents a phase transition.
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Le, Priol Clément. "Long-range interactions in the avalanches of elastic interfaces." Thesis, Université Paris sciences et lettres, 2020. http://www.theses.fr/2020UPSLE008.
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Les systèmes désordonnés soumis à une contrainte lentement croissante présentent souvent une dynamique par sauts caractérisée par des poussées d’activité, appelées avalanches, qui sont la marque d’une transition de phase hors-équilibre. Cette thèse traite de la dynamique des interfaces élastiques au voisinage de la transition de dépiégeage, et plus spécialement de l’effet des interactions à longue-portée. Je dérive la forme d’échelle universelle des fonctions de corrélation du champ des vitesses locales. Cela permet de tester la classe d’universalité de la transition, ainsi que la portée des interactions. J’étudie aussi la statistique des clusters qui se forment en présence d’interactions à longue-portée et montre comment celle-ci est reliée à la statistique des avalanches globales. Enfin je présente des avancées analytiques vers la compréhension de la structure spatiale des avalanches dans un modèle de champ-moyen qui est le modèle de force brownienDisordered systems submitted to a slowly increasing external stress often reacts with a jerky dynamics characterized by bursts of activity, called avalanches, which are the manifestation of an out-of-equilibrium phase transition. This thesis focuses on the dynamics of elastic interfaces near the depinning transition, and more specially on the effect of long-range interactions. I derive the universal scaling form of the correlations functions of the local velocity field. It allows to test the universality class of the transition as well as the range of the interactions.I also study the statistics of the clusters that form in presence of long-range interactions and show how it relates to the statistics of the global avalanches. Finally I present analytical advances towards the understanding of the spatial structure of avalanches within a mean-field model, the Brownian Force Model
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Marco, Olivier. "Instrumentation d'un site avalancheux : de l'utilisation des propriétés acoustiques de la neige et des techniques d'imagerie pour la mesure de paramètres physiques d'une avalanche dense /." Saint-Martin-d'Hères : Centre national du machinisme agricole, du génie rural, des eaux et des forêts, Groupement de Grenoble, 1995. http://catalogue.bnf.fr/ark:/12148/cb35765325w.
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Valderrama, Murillo Patricio. "Origine et dynamique des avalanches des débris volcaniques : analyse des structures de surface au volcan Tutupaca (Pérou)." Thesis, Clermont-Ferrand 2, 2016. http://www.theses.fr/2016CLF22731/document.
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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 avalanchesLandslides 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
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Colgan, Timothy J. "Signal processing for the detection of snow avalanches using infrasound." Laramie, Wyo. : University of Wyoming, 2007. http://proquest.umi.com/pqdweb?did=1317343441&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.
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STEYER, ALEXANDRE. "La theorie des avalanches : physique sociale des phenomenes de propagation." Jouy-en Josas, HEC, 1993. http://www.theses.fr/1993EHEC0022.
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Pour tenir compte de l'effet du boucha a oreille et de l'imitation dans la diffusion des innovations, les chercheurs, a la suite de bass en 1969, utilisent des modeles formules de manieres differentielles, conduisant souvent a une croissance exponentielle des ventes en debut de cycle. La these propose une demarche alternative basee sur le concept d'avalanches. Un innovateur engendre a sa suite une "avalanche" d'achats modelisee par un processus stockastique multiplicatif de duree de vie aleatoire borne. La sommation renormalisee de ces avalanches conduit a la courbe de diffusion. Le modele est teste dans des situations empiriques sur le plan de la validite interne et externe. Il permet de faire des previsions a moyen terme beaucoup plus fiables, a nombre de parametres egal, que les modeles classiques. Le concept d'avalanche est ensuite generalise aux marches financiers ou il explique la diffusion fractale observee sur les actions et au cas de la propagation du sida, ou il explique la diffusion en loi de puissance observee alors que chacun pensait a une diffusion expotentielle de la maladieIn order to incorporate word of mouth effect in innovation diffusion models, researchears often use, like bass in 1969, a differential equation formulation, wich leads in general to an exponential growth of the sale in the begincing of the diffusion. We propose another approach based on the avalanche concept, as we can deduce it from consumer behaviou and social psychology studies. Each innovator give birth to an avalanche of sales modelised by a multiplicative. Stochastic process with a finite life duration the renormalised surn of all the avalanches leads to the diffusion curve. The model is validated on empirical data. It authorizes better forcasts than bass model with the same number of parameters. The avalanch concept is then used in two other fields. In the case of financial markets, it gives a explanation of the empirical observation of fractal motion for equities. In the case of aids spreading it explains why we observs a power law growth of the deasease instead of an exponential one
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Clément, Rastello Marie. "Etude de la dynamique des avalanches de neige en aérosol." Université Joseph Fourier (Grenoble), 2002. http://www.theses.fr/2002GRE10099.
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Les avalanches de neige en aérosol sont des bouffées de suspensions diluées de particules, très turbulentes qui descendent, de par leur poids, sur des pentes fortement inclinées. La motivation de la présente recherche était d'une part, d'améliorer notre connaissance de l'entraînement de neige du manteau neigeux par l'avalanche et d'autres part de développer un modèle théorique amélioré de la dynamique des avalanches. Le modèle théorique présenté dans cette thèse prend en compte les effets dus à la forte différence de densité entre l'avalanche et l'extérieur et démontre l'importance de l'entraînement de neige sur la vitesse de l'avalanche. Le modèle est en accord avec des mesures récentes de la vitesse de front d'une avalanche. Les paramètres du modèle (forme et croissance des bouffées) ont été déterminés à partir des expériences d'écoulements de laboratoire (d'eau salée ou de suspensions) dans un régime proche de celui des avalanches. Une extrapolation théorique de ces paramètres (obtenus en régime de Boussinesq) aux bouffées de fortes densité (avalanches) est proposée. Les expériences de laboratoire avec des bouffées entraînant des particules indiquent l'influence que l'entraînement de particules a sur la vitesse de l'avalanche. Une représentation en variables adimensionnelles des vitesses des avalanches et des bouffées de laboratoire montre clairement les ressemblances et différences entre les deux types d'écoulements.
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Santos, Carlos Alexandre Fernandes dos. "Simulação de avalanches de electrões em detectores gasosos de radiação." Master's thesis, Universidade de Aveiro, 2009. http://hdl.handle.net/10773/2618.
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Mestrado em Engenharia FísicaA Micro Hole & Strip Plate (MHSP) e a Gas Electron Multiplier (GEM) são detectores gasosos baseados em microestruturas (MPGD), que operam na região de proporcionalidade. Isto significa que a multiplicação de carga é obtida através de processos de avalanche. A Thick-MHSP e a Thick-GEM são microestruturas espessas que resultam do aumento das dimensões da MHSP e da GEM respectivamente. Detectores baseados em MHSP’s e GEM’s podem operar em modo normal de ionização, ou usando um fotocátodo semitransparente ou reflectivo. Além disso, as primeiras podem operar em modo normal ou em modo flipped-reversed (F-R) onde o objectivo é drenar os iões do meio em vez de promover a multiplicação de carga. Estudos no Garfield (programa de simulação de deriva de cargas em gases, baseado no método de Monte-Carlo) tais como a multiplicação de electrões, e eficiência de colecção são realizados para cada detector, para condições semelhantes às usadas experimentalmente, depois de simular os mapas de campo no Ansys® (programa baseado no método dos elementos finitos). A comparação de resultados entre estruturas, especialmente entre microestruturas normais e espessas, será um dos objectivos, assim como uma tentativa de comparação com os resultados experimentais. Resultados preliminares mostram que as simulações ajustam-se ao comportamento experimental dos detectores, ainda que os ganhos experimentais sejam sempre superiores no último caso. ABSTRACT: The Micro Hole and Strip Plate (MHSP) and the Gas Electron Multiplier (GEM) are Micropattern Gas Detectors (MPGD), that operate within the proportional region. This means that we obtain charge multiplication through an avalanche process. Thick-MHSP and Thick-GEM are thick microstructures that result from the increase in size of the MHSP and GEM respectively. MHSP and GEM based detectors can operate at normal ionization mode, or using a semitransparent or reflective photocathode. Besides that, the first ones can operate at normal mode, or at flipped-reversed (F-R) mode in which the purpose is to drain ions in spite of charge multiplication. Analysis in Garfield (Monte-Carlo method based software, which simulates charges drift in gases) such as electron multiplication, and collection efficiency are preformed at each detector, at similar conditions with experiments, after simulating their field map at Ansys® (finite element method based software). The comparison of results between structures, and especially between thick and normal microstructures will be preformed. Also, a comparison between simulations and experimental data will be tried Preliminary results show that the behavior of the simulations fits to the experimental detectors behavior, even having higher gains measured experimentally than the gains simulated.
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Caccamo, Paolo. "Experimental study of the influence of protection structures on avalanches and impact pressures." Thesis, Grenoble, 2012. http://www.theses.fr/2012GRENU043/document.
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L'auteur n'a pas fourni de résumé en françaisExperimental study of the influence of protection structures on avalanches and impact pressures Abstract: In the frame of snow avalanche protection, the optimisation of defence structure design depends on the understanding of the flow dynamics and on a exhaustive knowledge of the flow-obstacle interaction. The study presented here utilises a mainly experimental approach. Small-scale laboratory tests were combined with field measurements and observations. Dense snow avalanches are modelled by granular materials. Dry cohesionless and mono-dispersed glass beads are released down an inclined channel. Reference tests (with no obstacles) were carried out in order to characterise the flow dynamic properties, and an obstacle was then mounted and force measurements were taken. The geometry of two obstacles was tested: a large wall spanning the whole width of the flow and a narrower wall allowing lateral flows. Results showed that an influence zone forms uphill from the obstacle and plays an important role in the flow dynamics. An analysis of this zone was carried out, together with precise measurements of the flow depth (laser technique), surface velocity (PIV) and impact forces (force sensors). In relation to density currents, powder snow avalanches are modelled by a dyed salt solution flowing down an inclined channel immersed in a water tank. We investigated the influence of two different catching-dam-type obstacles on the flow behaviour with respect to reference conditions. The maximum flow height and its front and core velocity were measured by means of image processing and ultrasound Doppler velocimetry. Results mainly showed the higher effectiveness of a dam with vertical uphill face rather than inclined and underscored the importance of the velocity norm in the computation of the total incoming flow velocity. In-situ full-scale measurements complement small-scale laboratory tests. A new full-scale experimental site was implemented on the existing avalanche defence system of Taconnaz (Chamonix, France). Three breaking mounds were equipped with velocity and pressure sensors. The reference event, the rough site conditions, the need for data synchronization and remote access defined the design constraints. In December 2010, the first event was recorded, which proved that the conceived system works effectively and also provided the first set of data. Preliminary results showed very high pressure peaks with high impact pressures even for low velocity regimes and thus a drag coefficient which increases when the Froude number decreases. Isolated rocks or ice blocks struck the sensors, contributing significantly to the total energy released by the avalanche. This work provided effective inputs for numerical and analytical models and enhanced the current knowledge of avalanche dynamics in order to optimise the future design guidelines for avalanche protection structures. Keywords: Snow avalanches, impact pressure, laboratory experiments, dense avalanches, granular flows, influence zone, dead zone to granular jump transition, powder avalanches, density currents, ultrasound Doppler velocimetry, full-scale measurements
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Mahgoub, Abdelmagid. "Characteristics and mechanics of subaqueous debris flows /." Internet access available to MUN users only, 1998. http://collections.mun.ca/u?/theses,36691.
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Walker, David P. "Climatology of major avalanche events at two sites in the Sierra Nevada Range." abstract and full text PDF (free order & download UNR users only), 2007. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1446435.
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McCollister, Christopher Michael. "Geographic knowledge discovery techniques for exploring historical weather and avalanche data." Thesis, Montana State University, 2004. http://etd.lib.montana.edu/etd/2004/mccollister/McCollisterC0805.pdf.
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Chu, Wui-cheung Tommy. "Determination of design magnitude of debris flow hazard for mitigation measures in Hong Kong." Click to view the E-thesis via HKUTO, 2004. http://sunzi.lib.hku.hk/hkuto/record/B43895621.
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Rognon, Pierre. "Rhéologie des matériaux granulaires cohésifs. Application aux avalanches de neige dense." Phd thesis, Ecole des Ponts ParisTech, 2006. http://pastel.archives-ouvertes.fr/pastel-00002450.
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Le but de cette thèse est de mesurer le comportement rhélogique de la neige en écoulement et de comprendre les mécanismes physiques qui le contrôle. Pour répondre à cette double attente, deux approches complémentaires sont abordées : les écoulements expérimentaux de neige naturelle et les simulations numériques discrètes d'écoulements granulaires. La particularité des expériences est qu'elles se déroulent en haute montagne. Elles consistent à générer des écoulements de neige naturelle dans un canal à pente et débit contrôlés. Les mesures de profil de vitesse révèlent un comportement rhéologique atypique. Pour comprendre l'origine de ce comportement à l'échelle des grains de neige, nous avons simulé (méthode de dynamique moléculaire) des écoulements de grains cohésifs d'une part, et polydisperses d'autre part. Les géométries du cisaillement plan homogène et le plan incliné rugueux permettent d'identifier l'effet de la cohésion ou de la polydispersité sur le comportement rhéologique des grains, et de le comparer à celui de la neige.
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Pailha, Mickael. "Dynamique des avalanches granulaires immergées: rôle de la fraction volumique initiale." Phd thesis, Université de Provence - Aix-Marseille I, 2009. http://tel.archives-ouvertes.fr/tel-00433171.
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Le cadre général de cette thèse est d'obtenir une meilleure compréhension des écoulements géophysiques comme les glissements de terrains. Dans tous ces évènements, on sait que le couplage entre milieu granulaire et fluide interstitiel joue un rôle important. Lors du démarrage, la présence d'eau influe sur la déformation des sols; ainsi, des sols initialement différents se comportent différemment. Cette thèse présente une expérience et un modèle mettant en évidence les phénomènes physiques lors du déclenchement des avalanches immergées. Notamment, la dynamique de l'avalanche dépend fortement de la fraction volumique de l'empilement initial, le déclenchement étant fortement retardé lors d'une légère compaction initiale.
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Kohnhorst, K. "The geomorphic effect of snow avalanches in the Cairngorm Mountains, Scotland." Thesis, University of Edinburgh, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.653522.
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The thesis examines the evidence for geomorphic activity of avalanches in the Cairngorm Mountains, Scotland. A typical avalanche boulder tongue morphology is developed from the literature. The form will have the following characteristics: concave slope profile, the top of the form will be in exposed bedrock, the form will be fan shaped or road bank type tongue which extends beyond the main break of slope and is raised above the surrounding surface of the valley, debris will be strewn over the tongue especially in the deposition zone and microrelief features are present on different zones of the tongue (missing boulder hole, bump holes, debris tails, scratch marks and perched boulders). The field work shows that these features do occur in the study area and furthermore that two other types of avalanche modified forms are present. These are: avalanche swept slopes where the avalanche clears the slope of debris, depositing it at the furthest extent of the avalanche activity and avalanche plunge pools where the avalanche terminates in water and deposits debris in a crescentic shape, under water, at the outer limit of the avalanche's reach. From the evidence gathered in the field the typical avalanche modified slope for the Cairngorm area is developed, describing the morphology of each subtype of form found. Other minor forms are also found in the study area: avalanche garlands. These forms are small garlands of debris that are deposited at the base of a gully along the side of the slope. These are created by snow sluffs entraining debris a short distance down the slope and clearing the area immediately surrounding the gully. The thesis subsequently examines the variables that control the formation of these forms and statistical analysis is used to examine these variables and their importance in controlling the development of the form. This data is also used to calculate the probability of avalanche modified slopes forming in the study area.
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Rajna, Z. (Zalan). "Detection of activity avalanches and speeding up seek in MREG data." Master's thesis, University of Oulu, 2015. http://urn.fi/URN:NBN:fi:oulu-201509071960.
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Recent studies pinpoint visually cued networks of avalanches with MEG/EEG data, and hemodynamic fingerprints of neuronal avalanches as sudden high signal activity peaks in classical fMRI data. However, detection of neural avalanches faces the problem that the data contain a lot of physiological noise making the automatic analysis difficult. The aim of this study was to detect dynamic patterns of brain activity spreads with the use of ultrafast magnetic resonance encephalography (MREG). MREG achieves 10 Hz whole brain sampling, allowing the estimation of the spatial spread of an avalanche. A computational method was developed to separate neuronal avalanches from motion and physiological pulsations, and detect activity avalanches in human brain default mode network (DMN). Brain activity peaks could be identified from parts of the DMN, and normalized MREG data around each peak was extracted individually in order to show dynamic avalanche spreads as videos within the DMN. Individual avalanche videos of specific parts of the DMN were then averaged over a group of subjects. The results indicate that the detected peaks must be parts of activity avalanches, starting from (or crossing) the DMN. To support analyses on large fMRI data, like MREG recordings, also a method and implementation are presented to achieve a thousand fold speed-up for seeking in large compressed NIfTI neuroimaging data files. The method includes the creation of a novel index structure for the compressed data in order to achieve a speed-up of over hundred up to even five thousand, compared to the currently available implementations. By configuring the index structure, one can set an operating point which optimizes the efficiency as speed-up versus index size according to the requirements by the userUusimmat tutkimukset osoittavat, että MEG/EEG-datasta on visuaalisesti havaittavissa neuraalisia verkkoja joissa tapahtuu avalanssi-ilmiöitä. Lisäksi klassisessa fMRI-datassa on havaittu neuronaalisiin avalansseihin liittyviä hemodynaamisia jälkiä, jotka ilmenevät äkillisinä voimakkaina piikkeinä datassa. Neuraalisen avalanssin havaitsemisen automatisointi on kuitenkin hyvin haastavaa, koska data sisältää myös merkittäviä fysiologista kohinakomponentteja. Tämän tutkimuksen tavoitteena oli kehittää laskennallinen menetelmä havaita aivojen aktiviteetin leviämisen dynaamisia rakenteita hyödyntäen ultranopeaa magneettisen resonanssin enkefalografiaa (MREG). MREG kykenee saavuttamaan aivojen näytteistyksen 10 Hz taajuudella, mikä mahdollistaa neuraalisen avalanssin spatiaalisen leviämisen havaitsemisen. Työssä kehitettiin menetelmä erottaa neuraalinen avalanssi liikkeen ja fysiologisten pulsaatioiden tuottamista signaalikomponenteista, sekä havaita aktiviteettiavalanssi ihmisaivojen lepotilan aikaisessa neuraalisessa verkossa (default mode network, DMN). Menetelmä identifioi aivojen aktiviteettipiikkejä DMN-verkosta, normalisoi piikkien ympärillä olevan aktiviteettidatan yksilöllisesti ja lopulta esittää avalanssin leviämisen videona. Verkon toiminnan tutkimiseksi yksilölliset avalanssivideot määrätyistä DMN-verkon osista keskiarvoistettiin koehenkilöryhmän ylitse, jolloin ryhmäkäyttäytymisestä pääteltiin identifioitujen piikkien todella liittyvän DMN-verkosta alkaneisiin tai sen ylittäviin avalansseihin. Lisäksi työssä kehitettiin menetelmä nopeuttaa fMRI/MREG-datan käsittelyaikoja merkittävästi, mistä on suurta etua käsiteltäessä kompressoituja NIfTI-muodossa tallennettuja suuria neurokuvantamisen aineistoja. Menetelmä perustuu uudenlaiseen indeksointimenetelmään, jolla kompressoitua aineistoa voidaan selata nopeudella, joka ylittää monisatakertaisesti tai jopa monituhatkertaisesti perinteellisen menetelmän nopeuden. Konfiguroimalla indeksirakenne sopivasti voidaan asettaa toimintapiste menetelmälle siten, että haluttu kompromissi nopeuden ja indeksirakenteen viemän muistitilan kesken saavutetaan
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Rognon, Pierre Grégoire. "Rhéologie des matériaux granulaires cohésifs : application aux avalanches de neige denses." Marne-la-vallée, ENPC, 2006. https://pastel.archives-ouvertes.fr/pastel-00002450.
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Pailha, Mickaël. "Dynamique des avalanches granulaires immergées : rôle de la fraction volumique initiale." Aix-Marseille 1, 2009. https://tel.archives-ouvertes.fr/tel-00433171.
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Le cadre général de cette thèse est d'obtenir une meilleure compréhension des écoulements géophysiques comme les glissements de terrains. Dans tous ces évènements, on sait que le couplage entre milieu granulaire et uide interstitiel joue un rôle important. Lors du démarrage, la présence d'eau inue sur la déformation des sols ; ainsi, des sols initialement diérents se comportent diéremment. Cette thèse présente une expérience et un modèle mettant en évidence les phénomènes physiques lors du déclenchement des avalanches immergées. Notamment, la dynamique de l'avalanche dépend fortement de la fraction volumique de l'empilement initial, le déclenchement étant fortement retardé lors d'une légère compaction initialeInitiation of underwater granular avalanches : inuence of the inital volume fraction. The aim of this thesis is to obtain a better understanding of geophysical ows like landslides. In those events, the coupling between the granular material and the uid play an important role during the initiation. This thesis studies physical phenomenon during the initiation of underwater granular avalanches with an experiment and a model. The ow is shown to strongly depends on the initial volume fraction, its initiation being dramtically delayed by a slight
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Adjel, Ghall. "Méthodes statistiques pour la détermination de la distance d'arrêt des avalanches." Université Joseph Fourier (Grenoble), 1996. http://www.theses.fr/1996GRE10140.
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Des qu'un expert tente de prendre en compte le risque d'avalanche, son interet se porte avant tout sur l'emprise des avalanches. La difficulte de cette prise en compte a suscite le developpement de modeles. La variete des approches retenues atteste d'ailleurs de cette difficulte. Ainsi, des modeles physiques, dynamiques, symboliques et statistiques ont ete elabores pour tenter d'apporter un soutien a l'expert. Du point de vue statistique, on cherche a fournir des modeles pour la caracterisation de la distance d'arret des avalanches. Pour repondre a cet objectif, deux approches ont ete developpees dans cette etude: l'une qualifiee de spatiale parce qu'elle s'attache a fournir des modeles pour l'estimation de la distance d'arret maximale des avalanches, l'autre denommee spatio-temporelle car elle tente de definir un modele pour l'estimation de la distance d'arret des avalanches et de leurs periodes de retour. Dans l'approche spatiale, nous avons pu, a partir de deux methodes deja existantes, elaborer des modeles a l'aide d'un echantillon de sites avalancheux de haute-tarentaise (savoie). De plus, nous avons mis au point un protocole pour la comparaison de ces deux methodes. Dans l'approche spatio-temporelle, nous avons tente de definir un cadre methodologique pour l'estimation de la probabilite qu'un point d'un site soit atteint par les avalanches sur une periode de temps donnee. La difficulte a prendre en compte l'ensemble des parametres topographiques et a constituer un echantillon suffisant n'a cependant pas permis d'obtenir un modele completement operationnel. Neanmoins, cette voie semble offrir un cadre interessant pour la prise en compte des periodes de retour des avalanches. La fin du travail est consacree a une discussion des problemes a resoudre pour construire un systeme de cartographie des zones avalancheuses