Dissertations / Theses on the topic 'Fragmentation'

"Fragmentation" désigne une mise en rapport de la peinture, gravure et sérigraphie modulant une fascination pour Pinocchio. "A l'oeil", "à d'autres", "à l'oeuvre", et "au plaisir", ces quatre tomes précisent chacun un regard. A l'oeil. Peine perdue d'avance : comment taire le commentaire que les pièces provoquent ? A d'autres. Le centralisme de la personne n'est pas étranger aux rapports exacerbés aux maîtres, meurtriers et endettés, que des monstres indiquent. Puisque l'invention s'avère constituée d'emprunts, il faut substituer à "l'auteur" l'éloge de l'échange, beaux-arts et arts et métiers confondus. A l'oeuvre. "L’ergologie" (de l'unité d'enseignement et de recherche du langage à Rennes 2) interpelle le plasticien puisqu'elle vise à transposer analogiquement à l'art l'analyse propre au langage. A la réduction de l'activité aux moyens et aux fins auxquels correspondraient peinture, gravure, sérigraphie, dans le rapport à Pinocchio, il faut substituer la dualité des qualités et des quantités, et de deux manières : - par le fragmentant, non seulement il n'y a pas de "matière première", mais celle-ci est à prendre comme produit d'une élaboration- fragmentation en qualités utiles et en ustensiles; - par le fragmenté, en dissociant le fait de l'effet et le fabriqué de l'intention, pour reconnaître les potentialités créatrices des dispositifs impliqués, toujours déjà choisis et ordonnés en opération et appareillages. Au total, le rendement de la fragmentation réside dans l'interférence de pratiques "socio artistiquement" séparées puisqu'il n'y a pas de qualité ni de quantité qui n'y soit indifféremment productive. Au plaisir. Investissements de l'affectivité dans la conduite active plus que dans la conscience parlée, les dispositifs de fragmentation sont alors coupures et sutures. Face au vide de l'excision, le questionnement est module, entre la réticence d'un graveur et l'appétit effréné d'un peintre. Non plus "le sens" mais la perte à renouveler de l'image métamorphique de Pinocchio légitime diversement des iconoclasmes, dont la plastique, scandaleusement indifférente. Relier ainsi une plastique de la fragmentation à des visées différentes, c'est indiquer une mobilisation de l'art par des rapports conflictuels
"Fragmentation" designates the setting up of a relationship between painting, engraving and serigraphy, modulating a fascination for Pinocchio. "To the eye", "To others", "To the work", "To pleasure", each of these four volumes emphasizes a specific look. To the eye. To no avail : how to silence the comments that the works provoke? To others. The centering of the person is not alien to the exercerbated relationships, murdering and endebted to masters, that monsters indicate. Since invention proves to be made of borrowing, one must substitute for "the author" the praise of exchange, beaux-arts and arts and crafts taken together. To the work. Ergology (in the language and cultural sciences department of the University of Rennes 2) questions the graphic artist since it aims at transposing analogically the language analysis to art. To the reduction of activity to means and ends, to which would correspond painting, engraving and serigraphy-in relationship to Pinocchio - , one must substitute the duality of qualities and quantities in two ways : - through the "fragmenter" : not only is there no "raw material", but the latter is to be considered as a product of an elaboration-fragmenta- tion into useful qualities and utensils; - through the "fragmented" : in parting the fact from the effect, the fabricated from the intention, to recognize the creative potential of implied devices, always selected beforehand and arranged as to operations and tools. To sum up, the productivity of fragmentation lies in the interference of practices politically separated since quality and quantity are undifferentiately productive. To pleasure. Investments of affectivity in active conduct, more than in spoken conscious- ness, the fragmentation devices are therefore composed of ruptures and sutures. In the face of the emptiness of the excision, the questioning is modulated between the reticence of the engraver and the gluttony of the painter. No longer the "meaning", but the loss to be renewed of the metaphoric image of Pinocchio, diversely legitimates the iconoclasms, among which are graphic arts, scandalously indifferent. To link thus an esthetics of fragmentation to dif- ferent aims, is to stress a mobilisation of art through conflicting relationships

This thesis deals with fragmentation of complex molecular ions, especially biomolecules, in gas phase collision experiments. The aim is to investigate the relations between energy deposition and fragmentation and to shed light on the mechanisms behind energy and charge transfer processes in collisions involving the building blocks of life. Further, the question how a solvent environment influences the dissociation behavior is elucidated. In the first part of the thesis, results from different collision experiments with biomolecular ions are presented, focusing on electron capture induced dissociation of hydrated nucleotides and small peptides. The investigated processes may be relevant for the understanding of radiation damage and the optimization of sequencing methods used in protein research. Our results clearly demonstrate that effects due to surrounding solvent molecules are substantial. While the dissipation of internal energy by evaporation of the loosely bound solvent molecules may protect the biomolecule, the influence which this environment has on the electronic structure may lead to an enhancement or suppression of certain dissociation channels. The second part of the thesis focuses on recent instrumental developments. Here, the aim was to optimize and complement the techniques used in the experiments above and to have versatile tools available for different kinds of gas phase collision studies involving complex molecular ions. Therefore, we have constructed an electrospray ion source platform for the preparation of intense beams, with options of accumulation and cooling of mass selected ions, allowing for a large variety of experiments. This device is also intended to serve as an ion source for the new storage ring facility DESIREE (DoubleElectroStatic Ion Ring ExpEriment), which is currently under construction at Stockholm University. In these unique storage rings, oppositely charged ions may interact at very low relative velocities in a cryogenically cooled and ultrahigh vacuum environment.

The aim of my dissertation, as the title indicates, is to determine the relationship between modernism and fragmentation. The objective, however, is twofold. In addition to the argument through which I explicate the neglected discussion of the connection between modernism and fragmentation, this paper reveals the thought processes and artistic influences crucial to my own development as a painter. The majority of artists I discuss have informed my practice stylistically as well as aesthetically. The thesis therefore serves not only as a theoretical discussion but also as a partial justification of my personal conceptions regarding my work, on which I will elaborate in appendix. This paper demonstrates that the resolution of all things depends upon the collection, selection, arrangement and rearrangement of fragments, including my painting and this paper itself
Master of Arts

Findings through fragmentation Architecture is an obvious remnant of our collective past and gives us a fragment of a former life and a different time. This unique relationship between what’s new and old is a very powerful spatial opportunity. If memory is defined as ‘The faculty by which the mind stores and remembers information’ then the role of architecture comes to play is the prop for our collective and individual memories where it represents past events and people.  If we look closely at the definition of a fragment without it's context it will be read as ‘incomplete’ and subordinate to the completed it is extracted from. Architectural fragments have a power of resisting such expected unity and can be read into an alternative whole of none. By fragmenting industrial buildings that is going to b demolished, representing a time and a group of people in Lövholmen/Stockholm, I wish to embody memory and recall spaces that will be forever lost.
Rummet mellan det som är och det som har varit Arkitektur representerar vår historia och det kollektiva minnet.  Att minnas definieras som ‘förmågan att lagra erfarenheter och göra det möjligt att känna igen och lära’. Minnen placerar oss i förhållande till tid och rum vilket gör att platser och arkitektur kommer att spela en stor roll som bärare av vår kollektiva historia. Byggnader som bär spår av tid där de har varit grunden i en annan kontext kan utgöra ett unikt möte mellan det rum som existerar och det som har varit.  När vårt medvetna väljer ut och sorterar bland minnen fragmenteras det som vi upplevt och bara vissa delar finns kvar. Fragment kan definieras som en pusselbit som tillhört en helhet och blivit en spillra. Styrkan i arkitektonisk fragment är att de kan läsas på nya sätt efter att det isolerats från en helhet och antingen läsas in i en ny kontext eller ingen. Genom att fragmentera byggnader som representerar en specifik tid och grupp av människor som har använt dom vill jag förkroppsliga dessa rumsliga minnen innan de för alltid går förlorade.

The aim of my dissertation, as the title indicates, is to determine the relationship between modernism and fragmentation. The objective, however, is twofold. In addition to the argument through which I explicate the neglected discussion of the connection between modernism and fragmentation, this paper reveals the thought processes and artistic influences crucial to my own development as a painter. The majority of artists I discuss have informed my practice stylistically as well as aesthetically. The thesis therefore serves not only as a theoretical discussion but also as a partial justification of my personal conceptions regarding my work, on which I will elaborate in appendix. This paper demonstrates that the resolution of all things depends upon the collection, selection, arrangement and rearrangement of fragments, including my painting and this paper itself

The present thesis aims at the analysis of the fragmentation of rockfalls. The fragmentation is a complex phenomenon poorly understood with a lack of tools to reproduce it on rockfall simulators. The effect of fragmentation on the hazard assessment and mapping is significant and it may substantially modify the risk scenario. The analysis of the empirical data acquired in a series of inventoried natural rockfalls and real-scale drop tests, clearly suggests that fragmentation displays a fractal behavior. Based on these observations, a fractal fragmentation model is proposed heare, adapting the basics of Perfect (1997) to the specific case of rockfalls. An important development of the thesis presented is the procedure to characterize the rockfall mass before and after the fragmentation, which include the methodology to measure the block size distributions of the deposit, the use of Unmaned Aerial Vehicles (UAV) equipped with digital camera digital, and the photogrammetric analysis to reconstruct the detached block volumes based on 3D models and discrete joint characterization. The block size distributions before and after the fragmentation are related with the proposed model, using the real data to calibrate the model parameters by back analysis. The methodologies and the model proposed contribute to the understanding of the fragmentation phenomenon and have the capability to reproduce the entire block size distribution and the calculation of the number and volume of the fragments. They also allow the quantification of the areas of the fresh faces created due to breakage, which may be related to the required fragmentation energy. The final goal of the ongoing research is the implementation of fragmentation behavior on a rockfall simulator which is currently under developed within the Rockmodels project (https://rockmodels.upc.edu/es), and modify the criteria to calculate the probability of impact used in hazard mapping and in quantitative risk assessment studies. The results of the fragmentation model may also contribute to the analysis of the efficiency and to the design of the rockfall protection systems.
La present tesis es centra en el fenomen de la fragmentació en despreniments rocosos. La fragmentació és un fenomen complex de difícil caracterització i de la que ens manquen eines per a la seva modelació en programes de simulació de caiguda de blocs. Tanmateix, els efectes de la fragmentació sobre les prediccions i els conseqüents mapes de perill poden comportar modificacions en l’escenari de risc. A partir d’un conjunt de dades empíriques obtingudes mitjançant l’inventari de despreniments naturals, s’ha observat un clar comportament fractal. A partir d‘aquestes observacions, s’ha proposat un model de fragmentació fractal adaptant la descripció de Perfect (1997) al cas específic del despreniment rocós. Una part important del desenvolupament de la tesi són les metodologies utilitzades per a la caracterització de la massa rocosa abans i després de la fragmentació, des de metodologia per mesurar distribucions de volums de blocs al dipòsit, fins a la utilització de drons i fotogrametria digital per reconstruir el volums dels blocs abans de caure a partir de models 3D i de la caracterització discreta de les discontinuïtats del massís. Les distribucions de volums de blocs abans i després de la fragmentació és relaciones mitjançant el model de fragmentació proposat, utilitzant les dades reals per calibrar els paràmetres del model per retro anàlisis. La utilització de les metodologies proposades i del model de fragmentació ajuden a la comprensió del fenomen, permeten la reproducció de la distribució de blocs sencera amb una estimació del nombre de blocs i el seus volums. També permet una quantificació de la superfície nova creada en cares fresques degut a la ruptura, que es vincula amb l’energia dedicada a la fragmentació. L’objectiu final d’aquesta recerca és la implementació de la fragmentació en un simulador de caiguda de blocs que es troba en desenvolupament en el marc del projecte Rockmodels (https://rockmodels.upc.edu), així com modificar els criteris de càlcul de probabilitat d’arribada que s’utilitzen per elaborar els mapes de perill i els estudis quantitatius del risc. Les conclusions poden canviar la manera com es dissenyen els sistemes de protecció contra despreniments.
La presente tesis se centra en el fenómeno de la fragmentación en desprendimientos rocosos. La fragmentación es un fenómeno complejo de difícil caracterización y de la que nos faltan herramientas para su modelación en programas de simulación de caída de bloques. Sin embargo, los efectos de la fragmentación sobre las predicciones y los consecuentes mapas de peligro pueden conllevar modificaciones en el escenario de riesgo. A partir de un conjunto de datos empíricos obtenidos mediante el inventario de desprendimientos naturales, se ha observado un claro comportamiento fractal. A partir de estas observaciones, se ha propuesto un modelo de fragmentación fractal adaptando la descripción de Perfect (1997) en el caso específico del desprendimiento rocoso. Una parte importante del desarrollo de la tesis son las metodologías utilizadas para la caracterización de la masa rocosa antes y después de la fragmentación, desde metodología para medir distribuciones de volúmenes de bloques en el depósito, hasta la utilización de drones y fotogrametría digital para reconstruir el volúmenes de los bloques antes de caer a partir de modelos 3D y de la caracterización discreta de las discontinuidades del macizo. Las distribuciones de volúmenes de bloques antes y después de la fragmentación se relacionan mediante el modelo de fragmentación propuesto, utilizando los datos reales para calibrar los parámetros del modelo mediante retro análisis. La utilización de las metodologías propuestas y del modelo de fragmentación ayudan a la comprensión del fenómeno, permiten la reproducción de la distribución de bloques entera con una estimación del número de bloques y sus volúmenes. También permite una cuantificación de la superficie nueva creada en caras frescas debido a la ruptura, que se vincula con la energía dedicada a la fragmentación. El objetivo final de esta investigación es la implementación de la fragmentación en un simulador de caída de bloques que se encuentra en desarrollo en el marco del proyecto Rockmodels (https://rockmodels.upc.edu), así como modificar los criterios de cálculo de probabilidad de alcance que se utilizan para elaborar los mapas de peligro y los estudios cuantitativos del riesgo. Las conclusiones pueden cambiar la forma en que se diseñan los sistemas de protección contra desprendimientos.

Depuis 2014, l’Ukraine connait une fragmentation de son territoire national. A la suite du mouvement de protestations populaires de l’Euromaïdan (novembre 2013 – février 2014), l’Ukraine a vu émerger un conflit d’envergure nationale opposant les populations de l’Est et du Sud au gouvernement révolutionnaire soutenu par l’Ouest. Au printemps 2014, l’intervention de la Russie ancre cette fragmentation dans le territoire. La Crimée, au sud du pays, est annexée par Moscou en mars 2014. A l’est du pays, les deux républiques populaires sécessionnistes de Donetsk et Lougansk, sont proclamées par des groupes séparatistes soutenus par la Russie. A partir de 2014, le pouvoir russe met en place des stratégies d’appropriation territoriale distinctes dans ces deux espaces. Cette thèse se propose de montrer comment est structurée cette appropriation territoriale, en particulier en questionnant la place des réseaux de données dans cette appropriation. En effet, entre 2014 et 2020, l’évolution de la stratégie russe se reflète particulièrement au niveau de l’architecture des réseaux Internet. Indispensable au bon fonctionnement du réseau mondial, le routage des données numériques désigne les mécanismes qui permettent leur transit d’un point à l’autre du globe grâce à l’interconnexion de milliers de réseaux indépendants, les systèmes autonomes. En Ukraine, l’observation du routage permet de mettre en évidence la manière dont le réseau est d’une part un révélateur des stratégies de puissance russe dans le cyberespace, et d’autre part en quoi il constitue un outil d’appropriation et de maîtrise des territoires, qui reflète les pratiques russes dans le domaine géopolitique classique
Since 2014, Ukraine has experienced a fragmentation of its national territory. Following the Euromaidan protest movement (November 2013 - February 2014), Ukraine witnessed the emergence of a nationwide conflict pitting the populations of the East and South against the Western-backed revolutionary government. In the spring of 2014, Russia's intervention anchored this fragmentation in the territory. The southern peninsula of Crimea was annexed by Moscow in March 2014. In the east of the country, the two secessionist people's republics of Donetsk and Lugansk, are proclaimed by separatist groups supported by Russia. From 2014 onwards, Moscow has been setting up distinct strategies of territorial appropriation in these two regions. This thesis aims to show how this territorial appropriation is structured, in particular by questioning the place of digital networks in the process. Indeed, between 2014 and 2020, the evolution of Russia’s strategy is particularly reflected in the architecture of Internet networks. A core process of the global network, the routing of digital data refers to the mechanisms that allow their transit from one point to another of the globe through the interconnection of thousands of independent networks, called autonomous systems. In Ukraine, the observation of data routing allows us to highlight the way in which the network is on the one hand a revelation of Russian power strategies in cyberspace, and on the other hand how routing can be a tool of appropriation and control of territories, which reflects Russian practices in the classical geopolitical domain

The fragmentation process in rockfalls is a complex phenomenon that is not well understood and only a few rockfall simulation models consider it explicitly. Fragmentation significantly affects the evaluation of the hazard and therefore of the risk. This thesis aims to develop a rockfall propagation model that is capable of reproducing the fragmentation phenomenon in rockfalls and to assess its consequences in the risk analysis. Four real-scale tests in a quarry and one laboratory test were performed for a better understanding of the fragmentation process. During these tests, several remote sensing techniques were used to capture the motion of the blocks and the fragment size distributions of the resulting deposit. The analysis of the empirical data acquired confirmed that the mass distribution produced by the fragmentation of a single block can be adequately described using fractal theory. Moreover, it was observed that the envelope of the trajectories of the newly generated fragments adopted the shape of a cone. The knowledge gathered with these experiments led to the development of RockGIS, a stochastic program based on a lumped mass approach for the numerical simulation of rockfalls and their fragmentation using a fractal model. The model simulates the trajectories of the blocks using state-of-the-art methodologies and implements an innovative fragmentation module to consider block breakage using fractal theory. The code was developed within the framework of the Rockmodels project (https://rockmodels.upc.edu). In the simulation, the parameters that define the sizes of the fragments generated are computed at each impact according to the kinematic conditions. This approach allows different fragmentation patterns to be reproduced depending on the energy conditions of the impacts. The performance of the RockGIS code was verified and validated by the real-scale rockfall tests carried out and by reconstructing three inventoried natural rockfall events that took place in Spain: a 10,000 m³ rockfall near Vilanova de Banat (Eastern Pyrenees) in 2011, a 800 m³ rockfall in Monasterio de Piedra in 2017 (Zaragoza) and a 10 m³ rockfall on the Ma-10 road (Mallorca). For the calibration of the model different goodness-of-fit indicators were considered depending on the information available in each case study. Two main calibration criteria were used: the runout distance and the size distributions of all the fragments generated. Moreover, the fragment scattering along the slope, the number of blocks crossing a reference line, the position of the center of gravity of the whole deposit and other criteria were used in some scenarios to validate the simulation results. The parametric analysis showed that the model is highly sensitive to the parameters that control the fragmentation process. The performance of the fragmentation model developed is satisfactory and accomplishes the goal of representing the fragmentation process, as it is able to reproduce the field observations accurately. To use this approach for risk analysis and the design of protective measures, precise calibration is required to ensure the parameters are appropriate for each case study considered. Regarding the risk analysis, fragmentation has both a significant and a contrasting effect on the risk value and should not be ignored. The most significant effect is on the rockfall runout distance. Fragmentation may significantly reduce rockfall propagation if the slope is sufficiently gentle and long. In this case, the new fragments generated mobilize less energy and can be trapped by the topographic irregularities, obstacles and protection works. Conversely, a wide range of block sizes are able to reach corridors running below steep slopes. In such a situation, fragmentation facilitates the divergence of the blocks’ trajectories, which increases the probability of impact on people and vehicles and consequently the risk.
La fragmentació en despreniments rocosos és un fenomen complex, poc comprès i només alguns models de simulació de caigudes de roques la consideren explícitament. La fragmentació afecta l’avaluació del perill i conseqüentment l’avaluació del risc. L’objectiu d’aquesta tesi és desenvolupar un model de propagació de despreniments rocosos capaç de reproduir la fragmentació i avaluar les conseqüències de considerar-la en l'anàlisi del risc. Per millorar la comprensió del fenomen, s’han realitzat quatre assajos a escala real i un assaig al laboratori. L'anàlisi de les dades experimentals adquirides confirma que la distribució de volums produïda per un procés de fragmentació d'un bloc es pot descriure adequadament mitjançant la teoria del fractal. A més, han permès confirmar la hipòtesi que les trajectòries dels fragments que resulten de la fragmentació d’un bloc es mantenen dins d’un límit en forma de con. El coneixement recollit en aquestes campanyes experimentals ha permès el desenvolupament de RockGIS, un programa estocàstic basat en una aproximació puntual de la massa per a la simulació numèrica de despreniments rocosos i la fragmentació mitjançant un model fractal. El model simula les trajectòries dels blocs basant-se en les metodologies més recents i implementa un mòdul de fragmentació innovador que contempla la ruptura dels blocs gràcies a un model de fragmentació fractal desenvolupat en el marc del projecte Rockmodels (https://rockmodels.upc.edu). Segons les condicions cinemàtiques, a cada impacte es calculen els paràmetres del model de fragmentació que defineixen els volums dels nous fragments. Aquest enfocament permet reproduir diferents escenaris de fraccionament en funció de les condicions energètiques dels impactes. El funcionament del codi RockGIS ha estat verificat i validat per mitjà d’assajos a escala real i segons tres despreniments rocosos naturals inventariats que han tingut lloc a Espanya: un despreniment de 10.000 m³ a prop del poble de Vilanova de Banat (Pirineus orientals) el 2011, una caiguda de 800 m³ a Monasterio de Piedra el 2017 (Saragossa) i una caiguda de roca de 10 m³ a la carretera Ma-10 (Mallorca). Per calibrar el model es van considerar diferents indicadors de bondat d’ajust segons les dades disponibles en cada cas d’estudi. Es van utilitzar dos criteris principals de calibratge: l’abast, o distància recorreguda, dels fragments generats i la distribució de volums. A més, en alguns dels escenaris estudiats es van considerar criteris addicionals de calibratge com ara la dispersió lateral dels fragments al llarg del vessant, el nombre de fragments que traspassaven una línia de referència, la posició del centre de gravetat de tot el dipòsit, etc. Els resultats del model desenvolupat són satisfactoris i compleixen amb l’objectiu de representar la fragmentació en els despreniments rocosos, ja que és capaç de reproduir les observacions de camp de manera precisa. Per emprar la metodologia proposada en l’estimació del risc i el disseny de mesures de protecció, cal un calibratge precís per tal de garantir que els paràmetres seran adequats a cada cas d'estudi considerat. Pel que fa a l’anàlisi del risc, la fragmentació té un efecte significatiu i contrastat sobre el valor del risc i no s’ha d’ignorar. Principalment afecta al càlcul de l’abast màxim dels blocs. La fragmentació pot reduir significativament la propagació dels despreniments si el pendent és prou suau i llarg. En aquest cas, els nous fragments generats mobilitzen menys energia i poden quedar atrapats per les irregularitats topogràfiques, els obstacles i les obres de protecció. Per contra, una àmplia gamma de mides de blocs poden arribar als elements exposats que es troben sota de vessants amb inclinacions altes. En aquests casos, la fragmentació facilita la divergència de les trajectòries de blocs, cosa que augmenta la probabilitat d’impacte amb els elements exposats i el risc consegüent
La fragmentación en desprendimientos rocosos es un fenómeno complejo, poco comprendido y sólo algunos modelos de simulación de caídas de rocas la consideran explícitamente. La fragmentación afecta la evaluación del peligro, y consecuentemente la evaluación del riesgo. El objetivo de la presente tesis es desarrollar un modelo de propagación de desprendimientos rocosos capaz de reproducir la fragmentación y evaluar las consecuencias de considerarla en el análisis del riesgo. Para mejorar la comprensión del fenómeno, se realizaron cuatro ensayos a escala real y un ensayo en el laboratorio. El análisis de los datos experimentales adquiridas confirma que la distribución de volúmenes producida por un proceso de fragmentación de un bloque se puede describir adecuadamente mediante la teoría del fractal. Además, han permitido confirmar la hipótesis de que las trayectorias de los fragmentos resultantes de la fragmentación de un bloque se mantienen dentro de un límite en forma de cono. El conocimiento recogido en estas campañas experimentales ha permitido el desarrollo de Rock-GIS, un programa estocástico basado en una aproximación puntual de la masa para la simulación numérica de desprendimientos rocosos y su fragmentación mediante un modelo fractal. El modelo simula las trayectorias de los bloques basándose en las metodologías más recientes e implementa un módulo de fragmentación innovador que contempla la ruptura de los bloques gracias a un modelo de fragmentación fractal desarrollado en el marco del proyecto Rockmodels (https://rockmodels.upc.edu). Los parámetros del modelo de fragmentación que definen los volúmenes de los fragmentos generados utilizados en la simulación, se calculan en cada impacto según las condiciones cinemáticas. Este enfoque permite reproducir diferentes escenarios de fragmentación en función de las condiciones energéticas de los impactos. El funcionamiento del código RockGIS ha sido verificado y validado mediante ensayos a escala real y según tres desprendimientos rocosos naturales inventariados que han tenido lugar en España: uno de 10.000 m3 cerca de Vilanova de Banat (Pirineos orientales) el 2011, uno de 800 m3 en Monasterio de Piedra en 2017 (Zaragoza) y uno de 10 m3 en la carretera Ma-10(Mallorca). Para calibrar el modelo se consideraron diferentes indicadores de bondad de ajuste según los datos disponibles en cada caso de estudio. Se utilizaron dos criterios principales de calibración: el alcance, o distancia recorrida, de los fragmentos generados y su distribución de volúmenes. Además, en algunos casos se usaron criterios adicionales de calibración como la dispersión lateral de los fragmentos a lo largo de la vertiente, el número de fragmentos que traspasaban una línea de referencia, la posición del centro de gravedad de todo el depósito etc. Los resultados del modelo desarrollado son satisfactorios y cumplen con el objetivo de representar la fragmentación en los desprendimientos rocosos, ya que es capaz de reproducir las observaciones de campo de manera precisa. Para emplear la metodología propuesta en la estimación del riesgo y el diseño de medidas de protección, se requiere una calibración precisa para garantizar que los parámetros son adecuados a cada caso de estudio considerado. En cuanto al análisis del riesgo, la fragmentación tiene un efecto significativo y contrastado sobre el valor del riesgo y no se debe obviar. Principalmente afecta al cálculo del alcance máximo de los bloques. La fragmentación puede reducir significativamente la propagación de los desprendimientos si la pendiente es bastante suave y largo. En este caso, los nuevos fragmentos generados movilizan menos energía y pueden quedar atrapados por las irregularidades topográficas, los obstáculos y las obras de protección. Por el contrario, una amplia gama de tamaños de bloques puede llegar a los elementos expuestos que se encuentran debajo de laderas con inclinaciones altas. En estos casos, la fragmentación facilita la divergencia de las trayectorias de bloques, aumentando así la probabilidad de impacto con los elementos expuestos y el consecuente riesgo.

This thesis presents a study of three electrochemical methods applied to the fragmentation of proteins. Direct electrochemical oxidation at graphite electrodes, production of hydroxyl radicals on lead dioxide electrodes and electro-Fenton methods were each investigated as methods for fragmenting proteins. A key objective of this project was to achieve specific fragmentation, meaning that fragmentation would only occur at defined sites on each protein molecule and that this process may provide a new pathway to producing useful protein fragments. Protein fragments produced by electrochemical means were detected using mass spectroscopy and gel electrophoresis techniques. Direct electrochemical oxidation of the target proteins was studied at a graphite rod electrode in a solution containing acetonitrile, water and formic acid. β-lactoglobulin fragmentation was detected by mass spectroscopy, but fragmentation did not occur to an extent where fragments were observable by gel electrophoresis. It was evident that most of the electrolysis products appear to arise from non-cleavage oxidation reactions. The use of lead dioxide electrodes to generate hydroxyl radicals was thoroughly investigated in this work. For the first time, specific fragmentation of proteins has been achieved by direct electrochemical generation of hydroxyl radicals on the electrode surface. The pH and the chemical composition of the protein solutions were found have a strong influence on the extent of fragmentation. Electro-Fenton chemistry was conducted on a woven carbon fibre electrode. The electrode successfully reduced dissolved oxygen to produce hydrogen peroxide and regenerated Fe(II) from Fe(III). Cell conditions were optimized for applied current, method of oxygen delivery and cell division. The Fenton reaction between hydrogen peroxide and Fe(II) produced hydroxyl radicals that were able to specifically fragment proteins. It was not possible to increase the concentration of these protein fragments by increasing the hydrogen peroxide concentration, as the fragmentation products were also further fragmented. Electrochemical protein fragmentation was achieved in all three electrochemical systems, however the most promising results were achieved by electrochemical generation of hydroxyl radicals on a lead dioxide electrode. This work has the potential to become a fast and cost effective method for the fragmentation of proteins required for nutrition and medical purposes or for use in protein identification analysis with mass spectroscopy.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE EXCELENCIA ACADEMICA
Apresentamos um método computacional na GPU que lida com eventos de fragmentação dinâmica, simulados por meio de elementos de zona coesiva. O trabalho é dividido em duas partes. Na primeira parte, tratamos o pré-processamento de informações e a verificação de corretude e eficácia da inserção dinâmica de elementos coesivos em malhas grandes. Para tal, apresentamos uma simples estrutura de dados topológica composta de triângulos. Na segunda parte, o código explícito de dinâmica é apresentado, que implementa a formulação extrínsica de zona coesiva, onde os elementos são inseridos dinamicamente quando e onde forem necessários. O principal desafio da implementação na GPU, usando a formulação de zona coesiva extrínsica, é ser capaz de adaptar dinamicamente a malha de uma forma consistente, inserindo elementos coesivos nas facetas fraturadas. Para isso, a estrutura de dados convencional usada no código de elementos finitos (baseado na incidência de elementos) é estendida, armazenando, para cada elemento, referências para elementos adjacentes. Para evitar concorrência ao acessar entidades compartilhadas, uma estratégia convencional de coloração de grafos é adotada. Na fase de pré-processamento, cada nó do grafo (elementos na malha) é associado a uma cor diferente das cores de seus nós adjacentes. Desta maneira, elementos da mesma cor podem ser processados em paralelo sem concorrência. Todos os procedimentos necessários para a inserção de elementos coesivos nas facetas fraturadas e para computar propriedades de nós são feitas por threads associados a triângulos, invocando um kernel por cor. Computações em elementos coesivos existentes também são feitas baseadas nos elementos adjacentes.
A GPU-based computational framework is presented to deal with dynamic failure events simulated by means of cohesive zone elements. The work is divided into two parts. In the first part, we deal with pre-processing of the information and verify the effectiveness of dynamic insertion of cohesive elements in large meshes. To this effect, we employ a simplified topological data structured specialized for triangles. In the second part, we present an explicit dynamics code that implements an extrinsic cohesive zone formulation where the elements are inserted on-the-fly, when needed and where needed. The main challenge for implementing a GPU-based computational framework using extrinsic cohesive zone formulation resides on being able to dynamically adapt the mesh in a consistent way, inserting cohesive elements on fractured facets. In order to handle that, we extend the conventional data structure used in finite element code (based on element incidence) and store, for each element, references to the adjacent elements. To avoid concurrency on accessing shared entities, we employ the conventional strategy of graph coloring. In a pre-processing phase, each node of the dual graph (bulk element of the mesh) is assigned a color different to the colors assigned to adjacent nodes. In that way, elements of a same color can be processed in parallel without concurrency. All the procedures needed for the insertion of cohesive elements along fracture facets and for computing node properties are performed by threads assigned to triangles, invoking one kernel per color. Computations on existing cohesive elements are also performed based on adjacent bulk elements.

Drill and blast is a dominant technique in several surface and underground mines in the world. The purpose of this technique is to break rock mass into fragments, which can be handled by mining equipment. The identified major influencing factors in rock blasting are stress waves and gas pressurization. In underground mines, especially in sublevel caving mines, the blast is performed under confined conditions. Hence, one more category of mechanisms has to be taken into consideration which describes the behavior of granular materials. Several small-scale tests have been conducted in order to define parameters which affect fragmentation by blasting as well as to measure the burden behavior during blasting. The purpose of these tests was to investigate how firing pattern, confinement and inter-hole delay time influence the fragmentation. Additionally, an incremental relative distance sensor was developed to measure the burden movement during blasting. The results showed that the burden moved with a velocity of approximately 29 m/s. The V-shaped firing pattern gave coarser fragmentation compared with sequential firing pattern for both the blasted material and confining material.After the small-scale tests, a zero pillar test was conducted under confined conditions to evaluate and validate a newly developed measuring system. The purpose of this system was to measure the burden dynamics. The system was calibrated in laboratory conditions under dynamic loading. This system was based on a piston-like structure and it was equipped with accelerometers and a potentiometric distance sensor. In addition to the measuring system, several installation and initiation procedures have been developed. The results of the measuring system showed that the burden moved 0.98 m at a velocity of 17-18 m/s. All the procedures performed as well as expected and designed.In addition to the study of blasting related mechanisms, the results of a blast also have to be measured. Sieving is usually not an option for large scale operations due to high costs. The alternative way is to implement digital image analysis. This procedure does not interfere with the production of a mine. Several trials have been conducted at the Aitik open pit mine to investigate the influence of short inter-hole delay time (1 ms, 3 ms and 6 ms or 0.14 ms/m burden, 0.43 ms/m burden and 0.86 ms/m burden) on fragmentation. The examined mechanism was the interaction of stress waves between neighboring blastholes. The fragmentation results showed that the trial with 3 ms inter-hole delay time gave a finer fragmentation by 10 % compared with reference blasts and other trials. However, there was an indication that the large specific charge at the mine overshadows the stress wave interaction mechanisms.An additional set of trials was conducted at the Kiruna mine to investigate the gravity flow of broken material. The fragmentation measurements were done with SplitDesktop®. This is a digital image analysis software which calculates fragmentation based on a delineation process of the particles in an image. The aim of in these trials was to develop a procedure to minimize the image editing time. The application of ‘Unsharp Mask’ filter improved the image quality and enhanced the contrast between the particles combined with a quick rating system (developed by LKAB) so that the image processing time was significantly reduced from 2 hours to 10-15 minutes.
Godkänd; 2015; 20150831 (nikpet); Nedanstående person kommer att hålla licentiatseminarium för avläggande av teknologie licentiatexamen. Namn: Nikolaos Petropoulos Ämne: Gruv- och berganläggningsteknik/Mining and Rock Engineering Uppsats: Burden Dynamics and Fragmentation Examinator: Professor Erling Nordlund, Institutionen för samhällsbyggnad och naturresurser, Avd Geoteknologi, Luleå tekniska universitet Diskutant: Associate Professor Zongxian Zhang, The University Centre in Svalbard (UNIS), Longyearbyen, Norge Tid: Fredag 2 oktober 2015 kl 10.00 Plats: F1031, Luleå tekniska universitet

La regression de la vie pulsionnelle implique une interrogation de la relation infans-porte-parole. A travers les processus relationnels qui contribuent a l'engrammage et a la metabolisation d'informations au sein de la psyche, nous avons formule conjointement aux processus psychiques nes d'une interaction infans-monde exterieur un postulat impliquant le developpement de la vie pulsionnelle. A l'aide des travaux de p. Aulagnier et de s. Freud, nous avons tente d'interroger une pathologie complexe en formulant une hypothese donnant aux pulsions partielles une place et un role determinants. Nous avons interroge les concepts de regression, de fixation et de fragmentations. D'autre part, le concept de fragmentation lie de facon indelebile aux pulsions partielles, se trouve convoque au cours de ce travail puisque nous evoquons egalement une correlation etroite entre la vie pulsionnelle partielle et ce concept de fragmentation. Nous interrogeons la metapsychologie freudienne et nous postulons une combinaison ternaire : pulsions partiellespulsions de vie-pulsions de mort. Toutes les mises en relation impliquent a l'evidence pour le sujet fragmente un danger de perte des limites de soi dans la mesure ou les sollicitations de l'environnement exacerbent la problematique fragmentaire. Les personnes en contact avec les schizophrenes font l'experience de la fragmentation puisqu'elles doivent satisfaire des "besoins" partiels et ne peuvent etre investies la plupart du temps que comme sujets eux-memes fragmentes. Elles sont confrontees a la regression dans une double interaction
The regression of instructive life implicates an interrogation upon infrans-mother relationship. Through the different relational processes that contribute to the staring and to the metabolization of information inside the psyche, we have formulated joinly to psychic processes born from an interaction between infans and the external world a postulate implicating the developpement of instructive life. Thanks to p. Aulagnier's and s. Freud's works, we have tried to question a complex pathology, formulating an hypothesis giving to component instincts a deciding position and part. We have questionned unpon concepts of regression, of fixation and of fragmentation. On the other hand, the concept of fragmentation intimatly connected to component instincts is present in this study as we also evocate a narrow correlation between component instinctive life and this concept of fragmentation. We question freudian metasphychology and we postulate a ternary combination : component instincts - life instincts - death instincts. All these connections obviously implicate for the fragmented subject the danger of losing its self limits insofar as the sollicitations of the environnement exacerbates the fragmentary problematic. People in contact with schizophenics experience fragmentation because they have to satisfy partial needs and can be invested most of the time only as subject themselves fragmented. They are confronted to regression in a dual interaction

This thesis is written in relation to the current research at SIMLab in the field of impact engineering. An overall objective is to establish a general numerical model for predicting and simulating the fragmentation process of metallic materials during impact. Previously conducted experiments at SIMLab revealed that blunt nosed projectiles of hardened ARNE tool steel may be fragmented, when struck against thick target plates at certain velocities. Two preceding M.Sc. theses have been written at SIMLab on the same topic, and provided an experimental basis for evaluation of the present numerical results. Simulations were carried out using the nonlinear finite element codes IMPETUS Afea Solver and LS-DYNA. Series of 20 tensile tests were conducted for ARNE tool steel, hardened to nominally Rockwell C values of 40 and 52. A significant variation was found in the failure strain for both materials. Modified Johnson-Cook constitutive models were directly calibrated from the tests, in combination with stochastic failure models based on the Cockcroft-Latham criterion. Numerical simulations of the tensile tests were in good agreement with the experimental observations. Fractography unveiled fracture surfaces with both ductile and brittle characteristics in in the hardened projectiles. A brittle failure criterion was inversely calibrated based on previously conducted bending tests. Previously conducted Taylor tests, which induced fracture and fragmentation, were attempted simulated with the calibrated material models. The simulated plastic deformations in the unhardened projectiles were described in very good agreement with experimental observations. Both element erosion and node splitting have successively been used to model material failure. It became evident that a stochastic variation of the failure parameter can give good results, and seems necessary for capturing the fragmentation process in a brittle metallic material. Node splitting in combination with cubic 64-node elements seems to give good results when the problems are dominated by tension, while element erosion and small linear elements are more suitable for problems dominated by compressional stresses and shear fractures.

Microplastics are small piece of plastic debris < 5 mm in diameter, which arise and enter the environment either as a consequence of the direct release of small pieces of plastic debris or as a consequence of the fragmentation of larger items. They are widely distributed in the marine environment, on shorelines, at the sea surface, on the seabed. They are also ingested by a variety of marine organisms, and there is some evidence that this may cause adverse effects. This thesis investigates the potential sources, distribution and fate of this contaminant. Deterioration of plastics in a variety of environments was examined as a potential source of microplastics. Plastics were exposed in light and shade, in air, fresh water and sea water. Their deterioration was monitored over six hundred days. The fastest rate of deterioration, by far, was observed in air, and this was further accelerated by natural sunlight. Degradation in water was much slower and it was therefore concluded that plastic debris only fragments slowly into microplastics while they are in the water, and much faster when they are washed ashore and/or remain exposed to air, for example on a beach. A method to assess the contamination of beaches by microplastics' likely predecessors - small items of plastic debris - was therefore developed. High spatial variability, which can impede comparison between surveys undertaken by random sampling was overcome by assessing deliberately selected debris accumulations. An attempt to utilise citizen science using this rapid survey approach returned too much variability between volunteers to obtain consistent results. Nevertheless, the survey method was successfully used to identify narrow opening towards the sea, small tidal range and several weeks of high on-beach waves as predictors for high contamination. Evidence of harmful effects of microplastics on animals is primarily from laboratory studies and could be substantiated by exposure experiments \emph{in-situ}. Cockles were exposed to fluorescent plastic particles in an intertidal mudflat. After two weeks, particles were still present in the sediment. However, the test material could not be identified in the cockles with enough certainty to validate the method. The thesis concludes that fragmentation of larger items of debris on land is an important potential source of microplastics. Therefore, preventing plastics that are prone to deteriorate from entering the environment is likely the most effective way to prevent the generation of microplastics. Measuring the success of such preventive measures in the field returns highly variable results, as small plastic debris are elusive. Measuring effects in the environment demands large amounts of data, and highly specific methods are required to detect microplastics in animals. The shift of environmental plastic contamination towards small particles demands that plastic debris research adjusts to the elusiveness of these particles. Large volumes of variable data on plastics density and precise biological essays will be required.

In this paper, we first theoretically revise the traditional particle modeling (PM) by means of mathematical derivation in that, adopting of Lennard Jones (LJ) format equations, four conservative rules are satisfied in order to determine the four unknown in a LJ equation, such as the mass, the elastic energy, the Young's modulus and the tensile strength conservations in the PM and molecular dynamic (MD) models. This enables the new developed PM to uniquely define a material's properties to be studied and promisingly become a predictive tool in mining industries. A safe time increment scheme is also defined and a new modification to the model to avoid giving a pseudo-dynamic solution.
Consequently, we test this new PM by simulating fracture response of an elastic-brittle material---epoxy, with randomly distributed holes, in tension and then comparing the model results with the experiments.
Then, we use this developed PM to many applications, such as (i) simulating dynamic fragmentation of minerals encountered in comminution and blasting processes in the mining industry. In particular, we simulate single as well as multi-phase materials in two dimensions (2-D) and 3-D. We redefine the interactive particle relationship by which material impact-collision problems are realistically simulated and computational time is saved as well; (ii) investigating cracking propagation of a plate with crack-tip under mode-I loading.

Fragmentation processes describe phenomena of random splitting, with possibly infinite activity, according to certain rules that give rise to a close relation of these processes to branching processes and L´evy processes. In this thesis we study some asymptotic properties of fragmentation processes. More specifically, we prove certain strong laws of large numbers for self–similar fragmentations and we deal with the existence and uniqueness of solutions ofthe one–sided FKPP travelling wave equation for homogenous fragmentation processes. In addition to being concerned with standard fragmentation processes we also consider fragmentation processes with immigration, fragmentations stopped at a stopping line as well as killed fragmentation processes.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 215-245).
Run II at the LHC is pushing the energy and luminosity frontiers, and challenging the theory community to develop new tools both to increase the precision of our predictions and to expand their scope to match measurements of a more diverse set of observables. In this work, we describe the use of a new class of non-perturbative functions called Generalized Fragmentation Functions (GFFs) as a step towards these goals. This theoretical framework enables the calculation of a broad set of semi-inclusive jet observables. We explore known observables whose distributions can now be calculated using GFFs, and construct a new class of non-associative "fractal observables" which can be described with GFFs. As an important application, we calculate the spectrum of track-assisted mass, which can be measured experimentally with much better angular resolution than ordinary jet mass, including the effect of Soft-Drop grooming. In order to make connections to frameworks for describing Quantum Chromodynamics, we discuss the relationship between GFFs and the Generating Functional Approach (GFA).
by Benjamin T. Elder.
Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.
Includes bibliographical references (p. 165-167).
A novel technique (location-relaxed storage) of mixing products within warehouse storage bins is presented and evaluated. Analyses of warehouse operations, storage space efficiency, error sensitivity, and placement policies are presented and compared to traditional warehousing techniques. The major factors that drive the performance differences between traditional, highly organized storage and location-relaxed storage are shown to include the number of unique stock keeping units (SKUs) served by the warehouse and the picking lot size characteristic of demand. The analyses demonstrate traditional storage techniques have greater difficulty dealing with a large SKU base. Furthermore, location-relaxed storage is shown to have a lower sensitivity to operation errors and a greater opportunity for cost savings through optimization opportunities. Finally, a new placement strategy especially suited for location-relaxed storage is presented. As the popularity of Radio Frequency Identification (RFID) increases and the technical issues of widespread RFID implementation are addressed, new applications of RFID technology will change the way the world operates. An ongoing, industry-wide effort to implement RF-tags throughout the material goods supply chain has the support of manufacturers, retailers, and technology companies. RFID in the supply chain represents an enabling technology that will allow warehouse operations to break away from traditional methodologies and adopt revolutionary techniques, such as location-relaxed storage.
by Stephen Ho.
Ph.D.

The work contained in this thesis concerns the development, and the mathematical and numerical analysis, of a new class of hybrid discrete-continuous fragmentation model. The framework is introduced as a potential answer to the occurrence of 'shattering' mass loss, commonly observed in purely continuous fragmentation models. Initially, the study begins by introducing the model, which takes the form of an integro-differential equation, coupled with a system of ordinary differential equations. Once the model has been established, it is subjected to a rigorous mathematical analysis, using the theory and methods of operator semigroups and their generators. Most notably, by applying the theory relating to the Kato-Voigt perturbation theorem, honest substochastic semigroups and operator matrices, the existence of a unique, differentiable solution to the model is established. This solution is also shown to preserve non-negativity and conserve mass. Having determined the existence of a solution, the work continues with the development of a numerical scheme for the approximate solution of the modelling equations. Considering a truncated version of the equations, rewritten in an alternative conservative form, the scheme is built around a finite volume discretisation. Using a standard weak compactness argument, the approximations generated by the numerical scheme are shown to converge (weakly) to a weak solution of the truncated equations. By relating this weak solution to the strong solutions provided by the earlier semigroup analysis, the weak solution is found to be unique and as a consequence, differentiable, non-negative and mass-conserving. The theoretical study is completed with an examination of the effect of varying the truncation point. In particular, establishing that as the length of the truncated interval is increased, in the limit, the original solution to the full model is obtained. Finally, the thesis is completed with a numerical investigation, seeking to experimentally confirm the assertions of the earlier theoretical work and assess the performance of the numerical scheme for a suite of test models.

The complex and non-linear nature of blast fracturing have restricted common blast design mostly to empirical approaches. The code developed for this investigation avoids both empiricism and large memory requirement in order to simulate the pattern of interacting radial fractures from an array of shotholes, at various burdens and spacings, and in simultaneous and delayed modes. The resultant pattern is analyzed and a fragment size distribution calculated.

The rules governing the distribution of radial cracks and the way in which they interact are based on model scale experiments conducted by various investigators. Calculated fragment size- distribution agree with data from the field. Powder factor dependence of fragmentation results is also well described by the model.

The effect of discontinuities on rock fragmentation by blasting is also incorporated into the model. Discontinuities which are open and filled with air or soil-like material affect destructively the transmission of strain waves and propagation of cracks in the rock mass. These discontinuities can be incorporated into the simulation by inserting cracks to represent them. The cracks representing discontinuities will then terminate the cracks produced by blasting where they intersect. On the other hand, tight joints without filling material or with filling material but with a high bond strength and acoustic impedance close to that of the medium do not affect in a negative way the transmission of shock waves in the rock mass. A mathematical model was developed to treat these discontinuities which was based on principles from Linear Elastic Fracture Mechanics theory and Kuznetsov's equation which relates the mean fragment size obtained to the blast energy, hole size and rock characteristics.

Master of Science

Ce travail de these est une etude experimentale de certains aspects de la dynamique de materiaux granulaires modeles bidimensionnels. Il comporte trois parties. La premiere est l'etude de la decompaction granulaire sous vibration verticale. Nous mettons en evidence un mode de decompaction lie a des mouvements microscopiques de courtes durees (une fraction de la periode d'excitation). Ces micro-mouvements se produisent sous forme de fractures. En moyenne dans le temps, ils induisent des rouleaux de convection, des mises en tas et une dilatation de l'empilement qui decroit avec la profondeur dans le tas. Nous avons examine le role de la geometrie de l'empilement, du rapport hauteur/largeur de l'empilement et du frottement sur les parois laterales de la cellule. Par une modelisation theorique, testee experimentalement, nous definissons un parametre de decompaction sans dimension. La deuxieme etude concerne des ecoulements en chute verticale guidee. Nous mettons en evidence un mode de fragmentation du tas a partir du bas, genere par des fractures qui se propagent vers le haut. Nous montrons que l'apparition des fractures est liee a des fluctuations de force de contact provenant des irregularites de surface des parois laterales. En rapprochant nos resultats a des simulations numeriques, il apparait que cette fragmentation resulte de la formation et de la destruction successive de voutes prenant appui sur les parois laterales de la cellule. Cette etude montre aussi l'importance des couplages par rotation dans l'apparition de ces voutes. La troisieme etude concerne le phenomene de segregation sous vibration, selon la taille des particules. Deux regimes de segregation sont identifies : un regime genere par des mouvements de convection (pour de grandes accelerations) et un regime genere par des effets de voutes et des mouvements de fracturation de courtes durees (pour des accelerations proche de l'acceleration de la gravite). Dans ce dernier regime, la dynamique de segregation, entre un palet temoin et une assemblee de billes identiques, depend du rapport des tailles. Nous montrons l'existence d'une transition entre un regime de montee intermittente et un regime de montee continue. Cette transition est bien decrite par un modele geometrique simple.

Compreender os mecanismos físicos que são responsáveis pela formação e evolução das primeiras estrelas do universo, conhecidas como estrelas de população III (ou Pop II) é fundamental para compreendermos como evoluiu o universo até hoje. No modelo padrão da formação de estrelas de Pop III, a matéria bariónica é constituída principalmente por hidrogénio atómico na forma gasosa, e colapsa gravitacionalmente em mini-halos (pequenos halos) de matéria escura, dando origem à formação das estrelas. No entanto, muito pouco se sabe como a evolução dinâmica e química do gás primordial são afetadas pelas condições iniciais dos minihalos, em particular no que diz respeito ao efeito da rotação nos aglomerados estelares instáveis que se formam dentro dos mini-halos, ao impacto da turbulência, à formação de hidrogénio molecular, e ao impacto das variações cósmicas entre mini-halos. Neste trabalho usamos uma versão modificada do código Gadget-2, um programa de simulação hidrodinâmica baseado num algoritmo numérico conhecido por SPH (“smoothed particle hydrodynamics”), que permite seguir a evolução do gás durante o colapso, tanto no caso de mini-halos idealizados como em casos de mino-halos mais realistas. Em contraste com algumas simulações numéricas mais antigas, a implementação das partículas coletoras (“sink particles”) permite seguir a evolução do disco de acreção que se forma no centro dos fragmentos e dos mini-halos. Descobrimos que o processo de fragmentação depende do valor adotado para a taxa de formação (“three-body H2 formation rate”) de hidrogénio molecular (H2). Verificamos que o aumento da taxa de arrefecimento durante o período em que o hidrogénio atómico é convertido em hidrogénio molecular é compensado pelo aquecimento causado pela contração do gás. Propomos que o arrefecimento de H2, o aquecimento devido a formação de H2, e o aquecimento devido à compressão do gás, juntamente com a densidade e temperatura determinam a estrutura do disco que favorece a fragmentação. Também descobrimos que a rotação inicial da nuvem de gás tem um impacto muito relevante na evolução térmica e dinâmica do gás em colapso Nuvens com uma elevada rotação apresentam filamentos idênticos a braços espirais que se tornam gravitacionalmente instáveis, dando origem à fragmentação em várias escalas. Estes tipos de nuvens têm mais tendência a fragmentar e têm menores taxas de acreção em relação a nuvens com menor rotação. Adicionalmente, verificamos que a distribuição especifica de momento angular (L) do gás é descrita por uma relação de potência com a massa do gás capturado (M) dada pela expressão L = M1.125. Por sua vez o momento angular é controlado pelo torque gravitacional e pela pressão, embora não dependa dos valores de rotação e turbulência da nuvem inicial; Abstract: Understanding the physics of the very first stars in the universe, the so-called Population III (or Pop III) stars, is crucial in determining how the universe evolved into what we observe today. In the standard model of Pop III star formation, the baryonic matter, mainly atomic hydrogen, collapses gravitationally into small Dark Matter (DM) minihalos. However, so far there is little understanding on how the thermal, dynamical and chemical evolution of the primordial gas depend on the initial configuration of the minihalos (for example, rotation of the unstable clumps inside minihalos, turbulence, formation of molecular hydrogen and cosmic variance of the minihalos). We use the modified version of the Gadget-2 code, a three-dimensional smoothed particle hydrodynamics (SPH) simulations, to follow the evolution of the collapsing gas in both idealized as well as more realistic minihalos. Unlike some earlier cosmological calculations, the implementation of sink particles allows us to follow the evolution of the accretion disk that builds up in the centre of each minihalo and fragments. We find that the fragmentation behavior depends on the adopted choice of three-body H2 formation rate coefficient. The increasing cooling rate during rapid conversion of the atomic to molecular hydrogen is offset by the heating due to gas contraction. We propose that the H2 cooling, the heating due to H2 formation and compressional heating together set a density and temperature structure in the disk that favors fragmentation. We also find that the cloud’s initial degree of rotation has a significant effect on the thermal and dynamical evolution of the collapsing gas. Clouds with higher rotation exhibit spiral-arm-like structures that become gravitationally unstable to fragmentation on several scales. These type of clouds tend to fragment more and have lower accretion rates compared to their slowly rotating counterparts. In addition, we find that the distribution of specific angular momentum (L) of the gas follows a power-law relation with the enclosed gas mass (M), L ∝ M1.125, which is controlled by the gravitational and pressure torque, and does not depend on the cloud’s initial degree of rotation and turbulence.

Thesis (Ph. D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1997?
Includes copies of previously published articles. Includes bibliographical references (last 7 unnumbered leaves ).

Thesis (Ph. D.) -- University of Maryland, College Park, 2005.
Thesis research directed by: Government and Politics. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

La déstabilisation et la fragmentation de systèmes liquides en couches minces se rencontrent fréquemment dans la nature, ainsi que dans des contextes industriels. Cette éude expérimentale entreprend de décrire, comprendre et prévoir les mécanismes des instabilités et de formation des fragments liquides.

Une première étude concerne la brisure d'une fine bandelette liquide chutant librement dans une cellule de Hele-Shaw. Les lignes de contact mobiles introduisent des pressions différentes au niveau des interfaces et établissent un gradient de pression dans le fluide, favorisant ainsi sa déstabilisation. Une analyse de stabilité linéaire prédit correctement les taux de croissance et montre l'existence d'un plateau sur la relation de dispersion.

Une seconde étude analyse la déformation et la brisure d'une goutte liquide au sein d'un jet gazeux. Nous montrons que la d´eformation se produit à partir d'un certain nombre de Weber critique et nous proposons un modèle sur la formation et le gonflement du sac qui s'en suit, également appelé bag-breakup.

Une troisième étude concerne l'impact d'une goutte sur un solide de taille comparable. Nous montrons que la goutte se déorme pour former une nappe liquide entouré d'un bourrelet. Nous montrons que l'extension de la nappe déend du nombre de Weber contrairement à sa dynamique. Nous proposons également un modèle qui prédit correctement la taille de la nappe ainsi que la taille des fragments obtenus.

Une quatrième étude est dédiée au phénomène de vieillissement des mousses. Nous exposons un nouveau dispositif expérimental de soufflerie à mousse. Nous donnons une comparaison entre les systèmes expérimentaux classiques et notre dispositif. Nous montrant également une preuve expérimentale de la loi de von Neumann.

La thèse a porté sur l'étude de peptides et d'oligonucléotides par fragmentation dans la source électrospray d'un Quattro II (Micromass). L'instrument a d'abord été évalué en mode positif avec des peptides thioester modèles puis en mode négatif avec des oligodésoxynucléotides bromés dont la fragmentation de la base modifiée permet sa localisation dans la séquence. La fragmentation de peptides acétal et diol (aldéhyde hydraté) conduit à un même ion final cyclique. L'hydratation de peptides aldéhyde a été étudiée en solution par RMN et en phase gazeuse par fragmentation dans la source. Les informations issues de ce travail ont permis une meilleure compréhension du mécanisme de la réaction d'oximation.

Le dispositif expérimental original développé à Toulouse permet de contrôler les collisions entre un agrégat chargé, libre, thermalisé, sélectionné en masse et des molécules. Il permet d'étudier l'attachement de la molécule sur l'agrégat ou la fragmentation induite par collision. Afin de mieux comprendre les processus d'attachement d'une molécule sur un agrégat, nous avons mesuré les sections efficaces d'attachement de molécules d'alcool, méthanol et éthanol, sur des agrégats d'alcool. Nous avons pu observer un comportement similaire aux agrégats d'eau, c'est à dire des sections efficaces d'attachement inférieures à la section efficace géométrique aux petites tailles qui tendent vers cette section géométrique quand la taille augmente. Ce comportement avait été attribué pour l'eau à un effet dynamique. Ce modèle dynamique peut être étendu avec un bon accord qualitatif aux agrégats d'alcools. Les processus d'attachement et de fragmentation nous permettent de réaliser des expériences de nanocalorimétrie. Nous avons pu déterminer les capacités calorifiques et les températures de transition de phase dans des agrégats d'eau protonés (H2O)nH+, qui viennent compléter les mesures effectuées sur les agrégats déprotonés (H2O)n-1OH-. La nature de la transition est discutée. Un troisième volet de cette thèse concerne la fragmentation induite par collision de molécules d'intérêt biologique : l'uracile protoné, isolé ou hydraté. Nous avons observé les différentes voies de fragmentation de l'uracile protoné. L'influence du nombre de molécules d'eau hydratant la molécule d'uracile sur le spectre de fragmentation est liée à l'affinité protonique des constituants et à la structure de l'agrégat
The experimental set-up developed in Toulouse enables to control collisions between a charged thermalised mass-selected free cluster and molecules. Processes of attachement of the molecule onto the cluster and collision induced fragmentation can be studied. In order to better understand the process of attachment of a molecule onto a cluster, we have measured attachment cross-sections of alcohol molecules, methanol and ethanol, onto alcohol clusters. We have observed a similar behaviour as the one observed with water clusters, that is attachment cross-sections that are lower than the geometrical cross-section at small sizes and that converge to this geometrical cross-section at bigger sizes. This behaviour had been assigned to a dynamical effect in the case of water. This dynamical model can be extended with a good qualitative agreement to alcohol clusters. Processes of attachment and fragmentation enable to realise nanocalorimetry measurements. We have determined heat capacities and transition temperatures for protonated water clusters (H2O)nH+. They complete measurements already done for deprotonated water clusters (H2O)n-1OH-. The nature of the phase transition is discussed. The last part of this dissertation concerns collision induced fragmentation for molecules that has some biological interest : protonated uracil, bare or hydrated. Fragmentation pathways of the protonated uracil molecule has been observed. The influence of the number of water molecules on the fragmentation pattern of solvated uracil is linked to the proton affinity of the constituants and to the cluster structure

Collisions of positronium (Ps) with the noble gases helium, neon, argon, krypton and xenon are considered in a two stage approach. Firstly, 'target elastic' collisions, where the noble gas target does not change state, are dealt with within the Impulse approximation. Secondly, collisions where the atom does change state, 'target inelastic' collisions, are considered within the first Born approximation. In both cases it is the spectra of ejected positrons and electrons that is the focus. Finally, isomorphism of the dipositronium (Ps2 ) symmetry group with the point symmetry group D2d is shown. Projection operators are obtained for collisional calculations of Ps with Ps.

Results of a rock deformation study designed to investigate the energy budgets of glass fragmentation under triaxial conditions are presented. This work comprises a series of room-temperature experiments designed to explore the fundamental mechanical behaviour of natural (obsidian) and synthetic glasses (Pyrex) under confining pressures of 0.1 - 100 MPa and at displacement rates of 40μm/s. The results quantify the amount of energy stored in the samples prior to failure, and establish a relationship between grain-size distributions of experimental-products (D-values) and the stress drop at failure. The relationship found for compressive fragmentation is significantly different from the relationship between D-values and energy densities established by previous authors for decompressive fragmentation. Furthermore, I show that natural glasses have less potential to store elastic energy after fragmentation than synthetic glasses. However, the stress storage capacity of natural glass can be enhanced (approaching synthetic glasses) through heat-treatment. The evolution of the physical properties (strain, porosity, permeability and ultrasonic wave velocities) of conduit breccia deposits during compaction is addressed. Compaction produces strongly anisotropic materials, and the measured physical properties are controlled by this anisotropy. Measurements of permeability are up to two orders of magnitude higher and seismic wave velocities up to twice as fast along the direction of elongation. Measurements of physical properties are combined with models describing the timescales of porosity loss and from that, the timescales of permeability reduction and re-pressurization of the edifice are discussed.