Дисертації з теми "Dynamical domains"
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1
Comanici, Adela N. "Spiral waves on spherical domains: A dynamical systems approach." Thesis, University of Ottawa (Canada), 2004. http://hdl.handle.net/10393/29088.
Повний текст джерелаАнотація:
This thesis is concerned with the dynamics and bifurcations of spiral waves in excitable media with spherical or approximately spherical geometry (e.g. cardiac tissue).
First, we study parameter-dependent systems of reaction-diffusion partial differential equations on a sphere which are equivariant under the group SO(3) of all rigid rotations on a sphere. Two main types of spatial-temporal patterns that can appear in such systems are rotating waves (equilibrium in a co-rotating frame) and modulated rotating waves (periodic solution in a co-rotating frame). The transition from rotating waves to modulated rotating waves on spherical domains is explained via a supercritical Hopf bifurcation from a rotating wave and SO(3) symmetry. The Baker-Campbell-Haussdorff formula in the Lie algebra so(3) is used to get a formula for a primary frequency vector, as well as a formula for the periodic part associated to any modulated rotating wave obtained by a supercritical Hopf bifurcation from a rotating wave. In the resonant case, the primary frequency vector of the modulated rotating wave is generically orthogonal to the frequency vector of the initial rotating wave.
In the second part of the thesis, we study the effects of forced symmetry-breaking from SO(3) to SO(2) for a normally hyperbolic relative equilibrium. This is done by introducing a small SO(2)-equivariant perturbation into the above reaction-diffusion system. The relative equilibrium persists to a normally hyperbolic SO(2)-invariant manifold that is SO(2)-equivariant diffeomorphic to SO(3). The perturbed SO(2)-equivariant dynamics on this manifold are studied by using the projection onto the orbit space SO(3)/ SO(2). Depending on the frequency vectors of the rotating waves that form the relative equilibrium, these rotating waves (up to SO(2)) will give either SO(2)-orbits of rotating waves or SO(2)-orbits of modulated rotating waves (if some transversality conditions hold). The orbital stability of these solutions is established as well.
2
Belzil-Lacasse, Christian. "Study of Dissipative Spots In Three-Component Reaction-Difussion Systems on Two-Dimensional Domains." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/34257.
Повний текст джерелаАнотація:
Dissipative spots are found in physical experiments of many branches of natural science. In this thesis we use three-component reaction-diffusion systems on two-dimensional domains in order to generate these patterns. Using a dynamical system approach we proceed with a Fourier analysis on a linearized reaction-diffusion system in order to provide the bifurcation conditions for a given homogeneous state. We validate our results and establish it's limitations through numerical experiments. We report very interesting behavior during these simulations, notably hysteresis and multi-stability. We will then turn our attention to the relatively unexplored phenomenon of rotating spots. Based on previous work done for spiral waves, we investigate the effect of translational symmetry-breaking on a rotating spot mainly through careful numerical analysis.
3
Turhan, Nezihe. "Deterministic and Stochastic Bellman's Optimality Principles on Isolated Time Domains and Their Applications in Finance." TopSCHOLAR®, 2011. http://digitalcommons.wku.edu/theses/1045.
Повний текст джерелаАнотація:
The concept of dynamic programming was originally used in late 1949, mostly during the 1950s, by Richard Bellman to describe decision making problems. By 1952, he refined this to the modern meaning, referring specifically to nesting smaller decision problems inside larger decisions. Also, the Bellman equation, one of the basic concepts in dynamic programming, is named after him. Dynamic programming has become an important argument which was used in various fields; such as, economics, finance, bioinformatics, aerospace, information theory, etc. Since Richard Bellman's invention of dynamic programming, economists and mathematicians have formulated and solved a huge variety of sequential decision making problems both in deterministic and stochastic cases; either finite or infinite time horizon. This thesis is comprised of five chapters where the major objective is to study both deterministic and stochastic dynamic programming models in finance. In the first chapter, we give a brief history of dynamic programming and we introduce the essentials of theory. Unlike economists, who have analyzed the dynamic programming on discrete, that is, periodic and continuous time domains, we claim that trading is not a reasonably periodic or continuous act. Therefore, it is more accurate to demonstrate the dynamic programming on non-periodic time domains. In the second chapter we introduce time scales calculus. Moreover, since it is more realistic to analyze a decision maker’s behavior without risk aversion, we give basics of Stochastic Calculus in this chapter. After we introduce the necessary background, in the third chapter we construct the deterministic dynamic sequence problem on isolated time scales. Then we derive the corresponding Bellman equation for the sequence problem. We analyze the relation between solutions of the sequence problem and the Bellman equation through the principle of optimality. We give an example of the deterministic model in finance with all details of calculations by using guessing method, and we prove uniqueness and existence of the solution by using the Contraction Mapping Theorem. In the fourth chapter, we define the stochastic dynamic sequence problem on isolated time scales. Then we derive the corresponding stochastic Bellman equation. As in the deterministic case, we give an example in finance with the distributions of solutions.
4
Soler, Vila Paula 1989. "Multi-scale study of the genome architecture and its dynamical facets." Doctoral thesis, Universitat Pompeu Fabra, 2019. http://hdl.handle.net/10803/668229.
Повний текст джерелаАнотація:
High-throughput Chromosome Conformation Capture (3C) techniques have provided a comprehensive overview of the genome architecture. Hi-C, a derivative of 3C, has become a reference technique to study the 3D chromatin structure and its relationship with the functional state of the cell. However, several aspects of the analysis and interpretation of Hi-C data remain a challenge and may hide a potential yet to be unveiled.
In this thesis, we explore the structural landscape of multiple chromatin features. We developed an integrative approach combining in situ Hi-C data with nine additional omic layers and revealed a new dynamic and transitional genomic compartment enriched in poised and polycomb-repressed chromatin. This novel intermediate compartment plays an important role in the modulation of the genome during B cells differentiation and upon neoplastic transformation, specifically in chronic lymphocytic leukemia (CLL) or mantle cell lymphoma (MCL) patients.
We also developed TADpole, a computational tool designed to characterize the hierarchy of topologically-associated domains (TADs) using Hi-C interaction matrices. We demonstrated its technical and biological robustness, and its capacity to reveal topological differences in high-resolution capture Hi-C experiments.El desarrollo de métodos experimentales basados en la captura de la conformación cromosómica (3C) ha permitido tener una visión más detallada de la arquitectura genómica. El Hi-C, derivado del 3C, se ha convertido en una técnica de referencia para analizar la estructura tridimensional de la cromatina, así como su relación con el estado funcional celular. Sin embargo, varios aspectos del análisis y la interpretación de los datos de Hi-C siguen siendo un desafío, y pueden ocultar un potencial aún por descubrir. En esta tesis se exploran múltiples niveles de organización estructural de la cromatina. Hemos realizado un estudio integrativo combinando datos de in situ Hi-C con nueve capas epigenéticas y hemos revelado un nuevo compartimento genómico caracterizado por su dinámica y capacidad de transición, enriquecido en cromatina reprimida por polycomb. Este nuevo compartimento intermedio juega un papel importante en la modulación del genoma durante la diferenciación de células B y durante su transformación neoplásica, específicamente en pacientes con leucemia linfocítica crónica (CLL) o con linfoma de células del manto (MCL). Además, hemos desarrollado TADpole, un nuevo método computacional destinado a la detección de la jerarquía de dominios asociados topológicamente (TADs) empleando mapas de interacciones de Hi-C. Hemos demostrado su robustez ante una evaluación técnica y biológica, así como su capacidad de detectar diferencias topológicas en experimentos de capture Hi-C de alta resolución.
5
Feng, Libo. "Numerical investigation and application of fractional dynamical systems." Thesis, Queensland University of Technology, 2019. https://eprints.qut.edu.au/126980/1/Libo_Feng_Thesis.pdf.
Повний текст джерелаАнотація:
This thesis mainly concerns the numerical investigation and application of fractional dynamical systems. Two main problems are considered: fractional dynamical models involving the Riesz fractional operator, such as the time-space fractional Bloch-Torrey equation, and complex viscoelastic non-Newtonian Maxwell and Oldroyd-B fluid models. The two main contributions of the research are the treatment of the Riesz space fractional derivative on irregular convex domains and presenting a unified numerical scheme to solve a class of novel multi-term time fractional non-Newtonian fluid models. A rigorous stability and convergence analysis of the computational models is also established.
6
Pasa, Luca. "Linear Models and Deep Learning: Learning in Sequential Domains." Doctoral thesis, Università degli studi di Padova, 2017. http://hdl.handle.net/11577/3425865.
Повний текст джерелаАнотація:
With the diffusion of cheap sensors, sensor-equipped devices (e.g., drones), and sensor networks (such as Internet of Things), as well as the development of inexpensive human-machine interaction interfaces, the ability to quickly and effectively process sequential data is becoming more and more important. There are many tasks that may benefit from advancement in this field, ranging from monitoring and classification of human behavior to prediction of future events. Most of the above tasks require pattern recognition and machine learning capabilities.
There are many approaches that have been proposed in the past to learn in sequential domains, especially extensions in the field of Deep Learning. Deep Learning is based on highly nonlinear systems, which very often reach quite good classification/prediction performances, but at the expenses of a substantial computational burden.
Actually, when facing learning in a sequential, or more in general structured domain, it is common practice to readily resort to nonlinear systems. Not always, however, the task really requires a nonlinear system. So the risk is to run into difficult and computational expensive training procedures to eventually get a solution that improves of an epsilon (if not at all) the performances that can be reached by a simple linear dynamical system involving simpler training procedures and a much lower computational effort. The aim of this thesis is to discuss about the role that linear dynamical systems may have in learning in sequential domains. On one hand, we like to point out that a linear dynamical system (LDS) is able, in many cases, to already provide good performances at a relatively low computational cost. On the other hand, when a linear dynamical system is not enough to provide a reasonable solution, we show that it can be used as a building block to construct more complex and powerful models, or how to resort to it to design quite effective pre-training techniques for nonlinear dynamical systems, such as Echo State Networks (ESNs) and simple Recurrent Neural Networks (RNNs).
Specifically, in this thesis we consider the task of predicting the next event into a sequence of events. The datasets used to test various discussed models involve polyphonic music and contain quite long sequences. We start by introducing a simple state space LDS. Three different approaches to train the LDS are then considered. Then we introduce some brand new models that are inspired by the LDS and that have the aim to increase the prediction/classification capabilities of the simple linear models.
We then move to study the most common nonlinear models. From this point of view, we considered the RNN models, which are significantly more computationally demanding. We experimentally show that, at least for the addressed prediction task and the considered datasets, the introduction of pre-training approaches involving linear systems leads to quite large improvements in prediction performances. Specifically, we introduce pre-training via linear Autoencoder, and an alternative based on Hidden Markov Models (HMMs).
Experimental results suggest that linear models may play an important role for learning in sequential domains, both when used directly or indirectly (as basis for pre-training approaches): in fact, when used directly, linear models may by themselves return state-of-the-art performance, while requiring a much lower computational effort with respect to their nonlinear counterpart. Moreover, even when linear models do not perform well, it is always possible to successfully exploit them within pre-training approaches for nonlinear systems.Con la diffusione di dispositivi a basso costo, e reti di sensori (come ad esempio l'Internet of Things), nonché lo sviluppo di interfacce di interazione uomo-macchina a basso costo, la capacità di processare dati sequenziali in maniera veloce, e assicurando un basso consumo di risorse, è diventato sempre più importante. Molti sono i compiti che trarrebbero beneficio da un avanzamento in questo ambito, dal monitoraggio e classificazione di comportamenti umani fino alla predizioni di eventi futuri. Molti dei task citati richiedono l'uso di tecniche di pattern recognition e di abilità correlate con metodi tipici dell’apprendimento automatico. Molti sono gli approcci per eseguire apprendimento su domini sequenziali proposti nel recente passato, e molti sono basati su tecniche tipiche dell'ambito del Deep Learning. I metodi di Deep Learning sono tipicamente basati su sistemi fortemente non lineari, capaci di ottenere ottimi risultati in problemi di predizione/classificazione, ma che risultano anche essere molto costosi dal punto di vista computazionale. Quando si cerca di eseguire un compito di apprendimento su domini sequenziali, e più in generale su dati strutturati, tipicamente si ricorre all'utilizzo di sistemi non lineari. Non è però sempre vero che i task considerati richiedono modelli non lineari. Quindi il rischio è di andare ad utilizzare metodi troppo complessi, e computazionalmente costosi, per poi ottenere alla fine soluzioni che migliorano di un’epsilon (o anche no migliorano) i risultati ottenibili tramite l'utilizzo di sistemi lineari dinamici, che risultano essere molto meno costosi dal punto di vista dell'apprendimento, e del costo computazionale. L'obiettivo di questa tesi è di discutere del ruolo che i sistemi lineari dinamici possono avere nelle esecuzioni di compiti di apprendimento su dati strutturati. In questa tesi vogliamo mettere in luce le capacità dei sistemi lineari dinamici (LDS) di ottenere soluzioni molto buone ad un costo computazionale relativamente basso. Inoltre risulta interessante vedere come, nel caso in cui un sistema lineare non sia sufficiente per ottenere il risultato sperato, esso possa essere usato come base per costruire modelli più complessi, oppure possa essere utilizzato per eseguire la fase di pre-training per un modello non lineare, come ad esempio Echo State Networks (ESNs) e Recurrent Neural Networks (RNNs). Nello specifico in questa tesi è stato considerato un task di predizione dell'evento successivo, data una sequenza di eventi. I dataset usati per testare i vari modelli proposti nella tesi, contengono sequenze di musica polifonica, che risultano essere particolarmente lunghe e complesse. Nella prima parte della tesi viene proposto l'utilizzo del semplice modello LDS per affrontare il compito considerato. In particolare vengono considerati tre approcci diversi per eseguire l'apprendimento con questo modello. Viene poi introdotti nuovi modelli, ispirati al modello LDS, che hanno l'obiettivo di migliorare le prestazioni di quest'ultimo nei compiti di predizione/classificazione. Vengono poi considerati i più comuni modelli non lineari, in particolare il modello RNN il quale risulta essere significativamente più complesso e computazionalmente costoso da utilizzare. Viene quindi empiricamente dimostrato che, almeno per quanto riguarda il compito di predizione e i dataset considerati, l'introduzione di una fase di pre-training basati su sistemi lineari porta ad un significativo miglioramento delle prestazioni e della accuratezza nell'eseguire la predizione. In particolare 2 metodi di pre-training vengono proposti, il primo chiamato pre-training via Linear Autoencoder, ed il secondo basato su Hidden Markov Models (HMMs). I risultati sperimentali suggeriscono che i sistemi lineari possono giocare un ruolo importante per quanto riguarda il compito di apprendimento in domini sequenziali, sia che siano direttamente usati oppure siano usati indirettamente (come base per eseguire la fase di pre-training): infatti, usandoli direttamente, essi hanno permesso di raggiungere risultati che rappresentano lo stato dell'arte, andando però a richiedere uno sforzo computazionale molto limitato se confrontato con i più comuni modelli non lineari. Inoltre, anche quando le performance ottenute sono risultate non soddisfacenti, si è dimostrato che è possibile utilizzarli con successo per eseguire la fase di pre-training di sistemi non lineari.
7
Wuth, Clemens [Verfasser]. "Stochastic and coherent dynamics of individual magnetic domains and domain walls / Clemens Wuth." München : Verlag Dr. Hut, 2015. http://d-nb.info/1079768815/34.
Повний текст джерела
8
Richter, Kornel. "Study of the fast domain wall dynamics in thin magnetic wires." Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-01004612.
Повний текст джерелаАнотація:
The domain wall dynamics is used in many spintronic devices based on the uniaxial ferromagnetic wires to transport and store information. Therefore, the domain wall velocity is one of the main parameters that determine the operation speed of these devices. Recently, a big attention is being paid to amorphous glass-coated microwires due to the very high domain wall velocities that reach up to 20 km/s. In this work, the fast domain wall propagation in amorphous glass-coated microwires was found in the presence of two main factors: (i) relatively low magnetic anisotropy, (ii) complex geometry of magnetic anisotropies given by internal distribution of mechanical stresses. The domain wall dynamics was examined in amorphous glass-coated microwires of reduced diameter down to 1 μm. It was shown, that the domain wall dynamics in these wires is the same as in wires of bigger diameter. It proves that the high domain wall velocities in microwires are not the effect of microwire diameter value. The direct observation of the surface domain wall structure by use of MOKE microscope confirmed that the domain wall is inclined relatively to the main axis. A new method for magneto-optical observation of the samples with cylindrical geometry was proposed. The inclined structure of the domain wall was found to be partially responsible for the high apparent domain wall velocity measured by the Sixtus-Tonks method in microwires.
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Munz, Marton. "Computational studies of protein dynamics and dynamic similarity." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:2fb76765-3e43-409b-aad3-b5202f4668b3.
Повний текст джерелаАнотація:
At the time of writing this thesis, the complete genomes of more than 180 organisms have been sequenced and more than 80000 biological macromolecular structures are available in the Protein Data Bank (PDB). While the number of sequenced genomes and solved three-dimensional structures are rapidly increasing, the functional annotation of protein sequences and structures is a much slower process, mostly because the experimental de-termination of protein function is expensive and time-consuming. A major class of in silico methods used for protein function prediction aim to transfer annotations between proteins based on sequence or structural similarities. These approaches rely on the assumption that homologous proteins of similar primary sequences and three-dimensional structures also have similar functions. While in most cases this assumption appears to be valid, an increasing number of examples show that proteins of highly similar sequences and/or structures can have different biochemical functions. Thus the relationship between the divergence of protein sequence, structure and function is more complex than previously anticipated. On the other hand, there is mounting evidence suggesting that minor changes of the sequences and structures of proteins can cause large differences in their conformational dynamics. As the intrinsic fluctuations of many proteins are key to their biochemical functions, the fact that very similar (almost identical) sequences or structures can have entirely different dynamics might be important for understanding the link between sequence, structure and function. In other words, the dynamic similarity of proteins could often serve as a better indicator of functional similarity than the similarity of their sequences or structures alone. Currently, little is known about how proteins are distributed in the 'dynamics space' and how protein motions depend on structure and sequence. These problems are relevant in the field of protein design, studying protein evolution and to better understand the functional differences of proteins. To address these questions, one needs a precise definition of dynamic similarity, which is not trivial given the complexity of protein motions. This thesis is intended to explore the possibilities of describing the similarity of proteins in the 'dynamics space'. To this end, novel methods of characterizing and comparing protein motions based on molecular dynamics simulation data were introduced. The generally applicable approach was tested on the family of PDZ domains; these small protein-protein interaction domains play key roles in many signalling pathways. The methodology was successfully used to characterize the dynamic dissimilarities of PDZ domains and helped to explain differences of their functional properties (e.g. binding promiscuity) also relevant for drug design studies. The software tools developed to implement the analysis are also introduced in the thesis. Finally, a network analysis study is presented to reveal dynamics-mediated intramolecular signalling pathways in an allosteric PDZ domain.
10
Mayes, Katherine. "Dynamic domains in strongly driven ferromagnetic films." [S.l. : s.n.], 2002. http://elib.tu-darmstadt.de/diss/000302.
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Schwaiger, Christine S. "Dynamics of the voltage-sensor domain in voltage-gated ion channels : Studies on helical content and hydrophobic barriers within voltage-sensor domains." Licentiate thesis, KTH, Teoretisk fysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-33818.
Повний текст джерелаАнотація:
Voltage-gated ion channels play fundamental roles in neural excitability and thus dysfunctional channels can cause disease. Understanding how the voltage-sensor of these channels activate and inactivate could potentially be useful in future drug design of compounds targeting neuronal excitability. The opening and closing of the pore in voltage-gated ion channels is caused by the arginine-rich S4 helix of the voltage sensor domain (VSD) moving in response to an external potential. Exactly how this movement is accomplished is not yet fully known and an area of hot debate. In this thesis I study how the opening and closing in voltage-gated potassium (Kv) channels occurs. Recently, both experimental and computational results have pointed to the possibility of a secondary structure transition from α- to 3(10)-helix in S4 being an important part of the gating. First, I show that the 3(10)-helix structure in the S4 helix of a Kv1.2-2.1 chimera protein is significantly more favorable compared to the α-helix in terms of a lower free energy barrier during the gating motion. Additional I suggest a new gating model for S4, moving as sliding 310-helix. Interestingly, the single most conserved residue in voltage- gated ion channels is a phenylalanine located in the hydrophobic core and directly facing S4 causing a barrier for the gating charges. In a second study, I address the problem of the energy barrier and show that mutations of the phenylalanine directly alter the free energy barrier of the open to closed transition for S4. Mutations can either facilitate the relaxation of the voltage-sensor or increase the free energy barrier, depending on the size of the mutant. These results are confirmed by new experimental data that supports that a rigid, cyclic ring at the phenylalanine position is the determining rate-limiting factor for the voltage sensor gating process.QC 20110616
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Eitoku, Takeshi. "Photo-induced conformational dynamics of phototropin LOV domains." 京都大学 (Kyoto University), 2008. http://hdl.handle.net/2433/136904.
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13
Yusof, Mat Ikram. "Analysis and identification of nonlinear systems in the frequency domain." Thesis, University of Sheffield, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388690.
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Liu, Yuting. "Electric field control of magnetic domain wall dynamics." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS292/document.
Повний текст джерелаАнотація:
Contrôle électrique du champ magnétique dans les films ferromagnétiques minces a attiré de grandes attentions comme une caractéristique prometteuse qui pourrait conduire à des appareils électroniques rapides, ultra-bas et non volatils. La clé pour réaliser de tels dispositifs est de modifier efficacement l'anisotropie magnétique. Dans cette thèse, le contrôle de l'anisotropie magnétique et de la dynamique des parois de domaine a été étudié dans diverses structures basées sur des films minces CoFeB et Pt / Co. Les propriétés magnétiques et diélectriques des films minces CoFeB / MgO avec une couche de recouvrement différente (Ta, HfO2, Al2O3) ont d'abord été étudiées pour trouver le matériau optimal de l'effet de champ électrique. La couche de coiffage montre un effet non négligeable sur l'anisotropie magnétique du film CoFeB et une constante diélectrique élevée de 45 est obtenue dans une structure MgO / HfO2.Un liquide ionique [EMI] [TFSI] a été utilisé pour promouvoir l'effet de champ électrique dans les films magnétiques. L'effet du champ électrique a été étudié dans le liquide CoFeB / MgO / ionique et les structures liquides ioniques CoFeB / MgO / HfO2 / ioniques. L'efficacité du champ électrique sur l'anisotropie magnétique pour ces deux structures est de 60 fJ / Vm et 82 fJ / Vm, respectivement. En attendant, le liquide ionique CoFeB / MgO / HfO2 / ionique présente une plus grande stabilité contre l'environnement et la tension, ce qui permet une commutation facile à l'axe de l'avion dans un avion. En outre, l'effet de champ électrique dans la structure liquide Pt / Co / ionique a été étudié. Un effet important et non volatil peut être observéThis thesis focused on controlling magnetic anisotropy and domain wall dynamics in magnetic thin films. Thin CoFeB/MgO Ims with different capping layers were deposited to find suitable materials to fabricate a high performing E-field effect device. The E-field effect was studied in a Ta/CoFeB/MgO stack, a Ta/CoFeB/MgO/HfO2 stack and a Pt/Co/HfO2 stack assisted by ionic liquid gating. Large E-field effects on magnetic anisotropy were obtained and E-field effect on domain wall propagation, pining and depining were observed. The major conclusions of this thesis are listed below.Magnetic and dielectric properties of CoFeB/MgO/(Ta, HfO2 and Al2O3) havebeen studied.All studied samples show PMA with different values of HK. In as grown films,samples with Ta as protecting layer show the lowest HK. Highest HK is foundwhen capping with 30 nm HfO2 in 0.8nm (746 mT) and 1nm (218 mT) thickCoFeB films. After annealing at 290 degree, there is a general increase of HK. The largest HK of 1082 mT and 524 mT are found for 10 nm Al2O3 in 0.8 nmCoFeB samples and 1 nm CoFeB samples, respectively. HK can be varied up to 100 mT for 1 nm thick CoFeB samples and up to 220 mT for 0.8 nm thick CoFeB samples indicating a non-negligible effect of the capping layer on the surface magnetic anisotropy of thin films.A high dielectric constant of 45 is obtained in a MgO (2 nm)/HfO2 (30 nm) structure. The breakdown voltage increases with annealing temperature, however, there is a large decrease in the dielectric constant after annealing at 290 degrees. By decreasing the annealing temperature to 250 degree, the high dielectric constant can be preserved with an improved breakdown voltage. Aging effect on HK and -K2/K1 of samples with different capping layers has been studied. HK is not necessary decreasing, but inhomogeneities in the magnetic properties occur in aged samples. Aging increases -K2/K1 which could help the formation of an easy-cone state. Stability of a MgO (2 nm) layer incontact with an IL and ionic film has been studied. After recording HK for months, it has been found that a MgO/IL structure can not preserve a highmagnetic anisotropy but is able to remain relatively stable in a low anisotropy state. A MgO/ionic film structure is found to be stable since no sign of degradation was found. The stability of samples with a simple MgO (2 nm)/HfO2 structure has been tested. Ms of the sample covered with an IL and the one not covered with IL have been recorded for one month. It is found that the change is within 3% indicating a stable structure against ambient conditions and the IL.The E-field effect has been studied in the low and high PMA states of aTa/CoFeB/MgO/IL sample. PMA of the device evolves from a high PMA state to a low PMA state which can be linked to a potential increase in the oxygen content of MgO due to air exposure during fabrication and operation. In the high PMA state, domain wall velocities in the creep regime can be modulated by a factor of 4.2 and the coercive field increases by a factor of 1.3 when going from -0.8 V to 0.8V. In the low PMA state, a large modulation of the anisotropy field reaches 80 mT per V/nm with a low leakage current. The applied E-fields are seen to significantly influence DWs' pinning, depinning and nucleation processes. The results presented here show that a solid/liquid device structure based on CoFeB/MgO thin films can be an interesting approach to control magnetic properties with gate voltages below 1 V over large areas, allowing for potential parallel operation of pinning/nucleation units.The E-field effect has been studied in a Ta/CoFeB/MgO/HfO2/IL sample
15
Gao, Yiran. "Dynamic inter-domain distributed computing." Thesis, Queen Mary, University of London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.510898.
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Rowe, Michael C. (Michael Charles). "A Machine Learning Method Suitable for Dynamic Domains." Thesis, University of North Texas, 1996. https://digital.library.unt.edu/ark:/67531/metadc278720/.
Повний текст джерелаАнотація:
The efficacy of a machine learning technique is domain dependent. Some machine learning techniques work very well for certain domains but are ill-suited for other domains. One area that is of real-world concern is the flexibility with which machine learning techniques can adapt to dynamic domains. Currently, there are no known reports of any system that can learn dynamic domains, short of starting over (i.e., re-running the program). Starting over is neither time nor cost efficient for real-world production environments. This dissertation studied a method, referred to as Experience Based Learning (EBL), that attempts to deal with conditions related to learning dynamic domains. EBL is an extension of Instance Based Learning methods. The hypothesis of the study related to this research was that the EBL method would automatically adjust to domain changes and still provide classification accuracy similar to methods that require starting over. To test this hypothesis, twelve widely studied machine learning datasets were used. A dynamic domain was simulated by presenting these datasets in an uninterrupted cycle of train, test, and retrain. The order of the twelve datasets and the order of records within each dataset were randomized to control for order biases in each of ten runs. As a result, these methods provided datasets that represent extreme levels of domain change. Using the above datasets, EBL's mean classification accuracies for each dataset were compared to the published static domain results of other machine learning systems. The results indicated that the EBL's system performance was not statistically different (p>0.30) from the other machine learning methods. These results indicate that the EBL system is able to adjust to an extreme level of domain change and yet produce satisfactory results. This finding supports the use of the EBL method in real-world environments that incur rapid changes to both variables and values.
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Bedau, Daniel. "Domain wall dynamics in magnetic nanostructures." München Verl. Dr. Hut, 2008. http://d-nb.info/988229420/04.
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Wang, Suqin. "Magnetization dynamics of single domain nanomagnets /." Diss., Digital Dissertations Database. Restricted to UC campuses, 2007. http://uclibs.org/PID/11984.
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TOMASSETTI, GIUSEPPE. "Dynamics of domain walls in ferromagnets." Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2007. http://hdl.handle.net/2108/325.
Повний текст джерелаАнотація:
The Gilbert equation summarizes the standard model for the evolution of the magnetization m in rigid ferromagnetic bodies. Under common constitutive assumptions, it has the form of a parabolic PDE:
γ−1m˙ + μm×m˙ = m× (αΔm+ β(m· e)e + hs + he) .
Here m˙ and Δm denote, respectively, the time derivative and the Laplacian of m, and the symbol × denotes the cross product; γ is the gyromagnetic ratio, a negative constant; α, β, μ are positive constants; e is a unimodular vector (the easy axis); he is the external magnetic field and hs is the stray
field, the magnetic field generated by the body.1
In ferromagnetic bodies, it is possible to observe magnetic domains, i.e., regions where the orientation is nearly constant, separated by narrow transitions layers, the domain walls. The application of an external magnetic field induces re-orientation and growth of some domains at the expense of others.
Our intention is to picture the resulting domain-boundary displacement, accompanied by re-orientation changes in the magnetization, as a process in which domain walls are regarded as surfaces endowed with a mechanical structure, whose motion is ruled by dynamical laws deduced from the Gilbert equation.
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Sampoli, Benitez Benedetta A. "Structure and dynamics of EGF-like domains of thrombomodulin /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1999. http://wwwlib.umi.com/cr/ucsd/fullcit?p9935466.
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Bensaibi, Mahmoud. "Identification de la fonction de transfert d'une structure ou d'une sous-structure par méthodes fréquentielles et temporelles." Châtenay-Malabry, Ecole centrale de Paris, 1996. http://www.theses.fr/1996ECAP0468.
Повний текст джерелаАнотація:
Le présent mémoire comporte deux parties. La première partie approfondit la méthode d'identification ARMA appliquée aux structures. Une connaissance approfondie de cette technique est nécessaire si l'on veut être capable de régénérer de manière précise à partir d'une identification, les fonctions de transfert données par un analyseur. Pour cette raison nous avons mené une étude dans le domaine fréquentiel, afin d'avoir des élements de comparaison et une étude dans le domaine temporel, qui a nécessité des développements concernant la méthode ARMA. Un exemple expérimental a éte teste pour valider les techniques proposees dans les deux domaines temporel et frequentiel. En deuxieme partie, on a developpe tant en fréquentiel qu'en temporel une méthode d'identification de sous-structures in situ. Cette identification s'oppose au problème bien connu de synthèse modale. Au contraire de celle-ci, qui a pour but de reconstruire le comportement globale de la structure à partir de ses sous-structures, on cherche à partir du comportement global d'une structure, à identifier les caractéristiques dynamiques d'une sous-structure appartenant à cette structure totale. C'est donc un problème d'identification locale. Cette étude ayant pour objet une analyse expérimentale, le bruit de mesure est pris en considération. Des exemples numériques ont été présentés et ont montrés qu'on obtenait de bon resultats jusqu'à un niveau de bruit de 5% dans le domaine temporel et 2% dans le domaine frequentiel. Enfin, une validation expérimentale a été réalisée dont le but principal est de montrer l'efficacité de l'algorithme sur un cas réel. La régéneration de la fonction de transfert de la sous-structure à partir des paramètres identifiées est abordée également
22
Boden, E. P. "An adaptive gridding technique for conservation laws on complex domains." Thesis, Cranfield University, 1997. http://hdl.handle.net/1826/3398.
Повний текст джерелаАнотація:
Obtaining accurate solutions to flows that involve discontinuous features still re-
mains one of the most difficult tasks in computational fluid dynamics today. Some
discontinuous features, such as shear waves and material interfaces, are quite deli-
cate, yet they have a profound effect on the rest of the flow field. The accuracy of
the numerical scheme and the quality of the grid discretisation of the flow domain,
are both critical when computing multi-dimensional discontinuous solutions. Here,
the second order WAF scheme is used in conjuction with an adaptive grid algorithm,
which is able to automatically modify the grid in regions of discontinuous features
and solid boundaries. The grid algorithm is a combination of two successful ap-
proaches, namely Chimera and Cartesian grid Adaptive Mesh Refinement (AMR).
The Chimera approach is able to accurately represent non-Cartesian boundaries,
whilst the AMR approach yields significant savings in memory storage and cPu time.
The combined algorithm has been thoroughly validated for convection test problems
in gas dynamics. The computed solutions compare well with other numerical and
experimental results. These tests have also been used to assess the efficiency of the
grid adaption algorithms. Finally, the approach is applied to axi-symmetric, two-
dimensional, two-phase, reactive flows in the context of internal ballistics problems.
Again, the computed results are compared with other numerical and experimental
results.
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Yang, Jun. "A Smoothed Dissipative Particle Dynamics Methodology For Wall-Bounded Domains." Digital WPI, 2013. https://digitalcommons.wpi.edu/etd-dissertations/225.
Повний текст джерелаАнотація:
This work presents the mathematical and computational aspects of a smooth dissipative particle dynamics with dynamic virtual particle allocation method (SDPD-DV) for modeling and simulation of mesoscopic fluids in wall-bounded domains. The SDPD-DV method is realized with fluid particles, boundary particles and dynamically allocated virtual particles near solid boundaries. The physical domain in SDPD-DV contains external and internal solid boundaries, periodic inlets and outlets, and the fluid region. The solid boundaries of the domain are represented with boundary particles which have an assigned position, wall velocity, and temperature upon initialization. The fluid domain is discretized with fluid particles placed in a global index. The algorithm for nearest neighbor particle search is based on a combination of the linked-cell and Verlet-list approaches and utilizes large rectangular cells for computational efficiency. The density model of a fluid particle in the proximity of a solid boundary includes the contribution from the virtual particles in its truncated support domain. The thermodynamic properties of a virtual particle are identical to those of the corresponding fluid particle. A periodic boundary particle allocation method is used at periodic inlets and outlets. Models for the conservative and dissipative forces on a fluid particle in the proximity of a solid boundary are presented and include the contributions of the virtual particles in its truncated support domain. The integration of the fluid particle position and momentum equations is accomplished with an implementation of the velocity-Verlet algorithm. The integration is supplemented by a bounce-forward algorithm in cases where the virtual particle force model is not able to prevent particle penetration. The integration of the entropy equation is based on the Runge-Kutta scheme. In isothermal simulations, the pressure of a fluid particle is obtained by an artificial compressibility formulation for liquids and the ideal gas law for compressible fluids. Sampling methods used for particle properties and transport coefficients in SDPD-DV are presented. The self-diffusion coefficient is obtained by an implementation of the generalized Einstein and the Green-Kubo relations. Field properties are obtained by sampling SDPD-DV outputs on a post-processing grid that allows harnessing the particle information on desired spatio-temporal scales. The isothermal (without the entropy equation) SDPD-DV method is verified and validated with simulations in bounded and periodic domains that cover the hydrodynamic and mesoscopic regimes. Verification is achieved with SDPD-DV simulations of transient, Poiseuille, body-force driven flow of liquid water between plates separated. The velocity profiles from the SDPD-DV simulations are in very good agreement with analytical estimates and the field density fluctuation near solid boundaries is shown to be below 5%. Additional verification involves SDPD-DV simulations of transient, planar, Couette liquid water flow. The top plate is moving and separated from the bottom stationary plate. The numerical results are in very good agreement with the analytical solutions. Additional SDPD-DV verification is accomplished with the simulation of a body-force driven, low-Reynolds number flow of water over a cylinder of radius R=0.02m. The SDPD-DV field velocity and pressure are compared with those obtained by FLUENT. An extensive set of SDPD-DV simulations of liquid water and gaseous nitrogen in mesoscopic periodic domains is presented. For the SDPD-DV simulations of liquid water the mass of the fluid particles is varied between 1.24 and 3.3e-7 real molecular masses and their corresponding size is between 1.08 and 323 physical length scales. For SDPD-DV simulations of gaseous nitrogen the mass of the fluid particles is varied between 6.37e3and 6.37e6 real molecular masses and their corresponding size is between 2.2e2 and 2.2e3 physical length scales. The equilibrium states are obtained and show that the particle speeds scale inversely with particle mass (or size) and that the translational temperature is scale-free. The self-diffusion coefficient for liquid water is obtained through the mean-square displacement and the velocity auto-correlation methods for the range of fluid particle masses (or sizes) considered. Various analytical expressions for the self-diffusivity of the SDPD fluid are developed in analogy to the real fluid. The numerical results are in very good agreement with the SDPD-fluid analytical expressions. The numerical self-diffusivity is shown to be scale dependent. For fluid particles approaching asymptotically the mass of the real particle the self-diffusivity is shown to approach the experimental value. The Schmidt numbers obtained from the SDPD-DV simulations are within the range expected for liquid water. The SDPD-DV method (with entropy) is verified and validated with simulations with an extensive set of simulations of gaseous nitrogen in mesoscopic, periodic domains in equilibrium. The simulations of N2(g) are performed in rectangular domains. The self-diffusion coefficient for N2(g) at equilibrium states is obtained through the mean-square displacement for the range of fluid particle masses (or sizes) considered. The numerical self-diffusion is shown to be scale dependent. The simulations show that self-diffusion decreases with increasing mass ratio. For a given mass ratio, increasing the smoothing length, increases the self-diffusion coefficient. The shear viscosity obtained from SDPD-DV is shown to be scale free and in good agreement with the real value. We examine also the effects of timestep in SDPD-DV simulations by examining thermodynamic parameters at equilibrium. These results show that the time step can lead to a significant error depending on the fluid particle mass and smoothing length. Fluctuations in thermodynamic variables obtained from SDPD-DV are compared with analytical estimates. Additional verification involves SDPD-DV simulations of steady planar thermal Couette flow of N2(g). The top plate at temperature T1 =330K is moving at Vxw =30m/s and is separated by 10-4 m from the bottom stationary plate at T2=300K. The SDPD-DV velocity and temperature fields are in excellent agreement with those obtained by FLUENT.
24
Schartau, Pamela Jutta. "Investigations of stability, cooperativity and dynamics of homologous protein domains." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612742.
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Ashbee, T. L. "Dynamics and statistical mechanics of point vortices in bounded domains." Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1427632/.
Повний текст джерелаАнотація:
A general treatment of the dynamics and statistical mechanics of point vortices in bounded domains is introduced in Chapter 1. Chapter 2 then considers high positive energy statistical mechanics of 2D Euler vortices. In this case, the most-probable equilibrium dynamics are given by solutions of the sinh-Poisson equation and a particular heart-shaped domain is found in which below a critical energy the solution has a dipolar structure and above it a monopolar structure. Sinh-Poisson predictions are compared to long-time averages of dynamical simulations of the $N$ vortex system in the same domain. Chapter 3 introduces a new algorithm (VOR-MFS) for the solution of generalised point vortex dynamics in an arbitrary domain. The algorithm only requires knowledge of the free-space Green's function and utilises the exponentially convergent method of fundamental solutions to obtain an approximation to the vortex Hamiltonian by solution of an appropriate boundary value problem. A number of test cases are presented, including quasi-geostrophic shallow water (QGSW) point vortex motion (governed by a Bessel function). Chapter 4 concerns low energy (positive and negative) statistical mechanics of QGSW vortices in `Neumann oval' domains. In this case, the `vorticity fluctuation equation' -- analogous to the sinh-Poisson equation -- is derived and solved to give expressions for key thermodynamic quantities. These theoretical expressions are compared with results from direct sampling of the microcanonical ensemble, using VOR-MFS to calculate the energy of the QGSW system. Chapter 5 considers the distribution of 2D Euler vortices in a Neumann oval. At high energies, vortices of one sign cluster in one lobe of the domain and vortices of the other sign cluster in the other lobe. For long-time simulations, these clusters are found to switch lobes. This behaviour is verified using results from the microcanonical ensemble.
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Rink, Jochen C. "Rab-domain dynamics in endocytic membrane trafficking." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2005. http://nbn-resolving.de/urn:nbn:de:swb:14-1117095871452-66763.
Повний текст джерелаАнотація:
Eukaryotic cells depend on cargo uptake into the endocytic membrane system, which comprises a functionally interconnected network of endosomal compartments. The establishment and maintenance of such diverse compartments in face of the high rates of exchange between them, poses a major challenge for obtaining a molecular understanding of the endocytic system. Rab-GTPases have emerged as architectural key element thereof: Individual family members localize selectively to endosomal compartments, where they recruit a multitude of cytoplasmic effector proteins and coordinate them into membrane sub-domains. Such "Rab-domains" constitute modules of molecular membrane identity, which pattern the endocytic membrane system into a mosaic of Rab-domains. The main objective of this thesis research was to link such "static" mosaic-view with the highly dynamic nature of the endosomal system. The following questions were addressed: How are neighbouring Rab-domains coordinated? Are Rab-domains stable or can they undergo assembly and disassembly? Are the dynamics of Rab-domains utilized in cargo transport? The first part of this thesis research focused on the organization of Rab-domains in the recycling pathway. Utilizing Total Internal Reflection (TIRF) microscopy, Rab11-, but neither Rab4- nor Rab5-positive vesicles were observed to fuse with the plasma membrane. Rab4-positive membranes, however, could be induced to fuse in presence of Brefeldin A. Thus, these experiments complete the view of the recycling pathway by the following steps: a) Rab11-carriers likely mediate the return of recycling cargo to the surface; b) such carriers are presumably generated in an Arf-dependent fission reaction from Rab4-positive compartments. Rab11-chromatography was subsequently carried out in the hope of identifying Rab11-effectors functioning at the Rab4-Rab11 domain interface. An as yet uncharacterized ubiquitin ligase was identified, which selectively interacts with both Rab4 and Rab11. Contrary to expectations, however, the protein (termed RUL for *R*ab interacting *U*biquitin *L*igase) does not function in recycling,but appears to mediate trafficking between Golgi/TGN and endosomes instead.In order to address the dynamics of Rab-domains, fluorescently tagged Rab-GTPases were imaged during cargo transport reactions in living cells. Herefore high-speed/long-term imaging procedures and novel computational image analysis tools were developed. The application of such methodology to the analysis of Rab5-positive early endosomes showed that a) The amount of Rab5 associated with individual endosomes fluctuates strongly over time; b) such fluctuations can lead to the "catastrophic" loss of the Rab5-machinery from membranes; c) Rab5 catastrophe is part of a functional cycle of early endosomes, involving net centripetal motility, continuous growth and increase in Rab5 density. Next, the relevance of Rab5 catastrophe with respect to cargo transfer into either the recycling- or degradative pathway was examined. Recycling cargo (transferrin) could be observed to exit Rab5-positive early endosomes via the frequent budding of tubular exit carriers. Exit of degradative cargo (LDL) from Rab5-positive endosomes did not involve budding, but the rapid loss of Rab5 from the limiting membrane.Rab5-loss was further coordinated with the concomitant acquisition of Rab7, suggesting "Rab conversion" as mechanism of transport between early- and late endosomes.Altogether, this thesis research has shown that first, Rab-machineries can be acquired and lost from membranes. Second, such dynamics provide a molecular mechanism for cargo exchange between endosomal compartments. Jointly, these findings lead to the concept of Rab-domain dynamics modulation in /trans/ between neighbouring domains as mechanistic principle behind the dynamic organization of membrane trafficking pathways.
27
Richardson, Omar. "Large-scale multiscale particle models in inhomogeneous domains." Thesis, University of Technology Eindhoven, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-45862.
Повний текст джерелаАнотація:
In this thesis, we develop multiscale models for particle simulations in population dynamics. These models are characterised by prescribing particle motion on two spatial scales: microscopic and macroscopic.At the microscopic level, each particle has its own mass, position and velocity, while at the macroscopic level the particles are interpolated to a continuum quantity whose evolution is governed by a system of transport equations.This way, one can prescribe various types of interactions on a global scale, whilst still maintaining high simulation speed for a large number of particles. In addition, the interplay between particle motion and interaction is well tuned in both regions of low and high densities. We analyse links between models on these two scales and prove that under certain conditions, a system of interacting particles converges to a nonlinear coupled system of transport equations.We use this as a motivation to derive a model defined on both modelling scales and prescribe the intercommunication between them. Simulation takes place in inhomogeneous domains with arbitrary conditions at inflow and outflow boundaries. We realise this by modelling obstacles, sources and sinks.Integrating these aspects into the simulation requires a route planning algorithm for the particles. Several algorithms are considered and evaluated on accuracy, robustness and efficiency. All aspects mentioned above are combined in a novel open source prototyping simulation framework called Mercurial. This computational framework allows the design of geometries and is built for high performance when large numbers of particles are involved. Mercurial supports various types of inhomogeneities and global systems of equations. We apply our framework to simulate scenarios in crowd dynamics.We compare our results with test cases from literature to assess the quality of the simulations.Master Thesis in Industrial and Applied Mathematics
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Gomes, Reinaldo Cézar de Morais. "Inter domain negotiation." Universidade Federal de Pernambuco, 2010. https://repositorio.ufpe.br/handle/123456789/1775.
Повний текст джерелаАнотація:
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Previous issue date: 2010Universidade Federal de Campina Grande
Nos últimos anos diversas tecnologias foram desenvolvidas com o objetivo de facilitar a interação entre os usuários e seus dispositivos e melhorar a comunicação entre eles, necessitando da interoperabilidade entre essas tecnologias e, consequentemente, a necessidade de uma nova infraestrutura de rede que permita uma melhor adaptação aos novos requisitos criados por esta diversidade de tecnologias. O modelo de comunicação entre redes também está sendo modificado, uma vez que é esperado que elas sejam criadas dinamicamente para facilitar a utilização da rede pelos usuários e permitir que diversas operações sejam realizadas automaticamente (endereçamento, descoberta de serviços, etc.). Essas redes devem estar presentes em diversos cenários de comunicação e um dos seus principais desafios é permitir que diversos tipos de tecnologias cooperem em ambientes com alto dinamismo e heterogeneidade. Estas redes têm como objetivo interconectar diferentes tecnologias e domínios oferecendo uma comunicação que aparente ser homogêneo para os seus usuários. Para a criação dessas futuras redes dinâmicas pontos chaves são a interconexão e a cooperação entre as tecnologias envolvidas, o que exige o desenvolvimento de soluções para garantir que novos requisitos sejam suportados. Para permitir que novos requisitos sejam corretamente suportados, um conjunto de mecanismos para controlar a descoberta automática de recursos e realizar a sua configuração é proposto, permitindo que redes sejam criadas e adaptadas de maneira completamente automática. Também é proposto um mecanismo de negociação de políticas inter-domínio responsável por descobrir e negociar novos recursos que dever ser usados pelas redes, o que traz um novo modelo de comunicação baseado na criação oportunista de redes e ao mesmo tempo permite a criação de novos acordos de comunicação entre domínios administrativos de maneira dinâmica e sem a intervenção dos usuários ou dos administradores das redes
29
Al-Wasity, A. J. L. "Virtualized dynamic resource allocation algorithm for the internet DiffServ domains." Thesis, University of Salford, 2017. http://usir.salford.ac.uk/43695/.
Повний текст джерелаАнотація:
The Differentiated Services (DiffServ) architecture has been proposed for providing different levels of service to the Internet Protocol (IP) traffic. Current discussions in the DiffServ networks are focused on managing resources dynamically according to the traffic conditions of the DiffServ router (Per Hop Behaviour). Software Defined Networks (SDN) and Network Function Virtualisation (NFV) technologies have recently emerged in the research agenda to support researchers in managing network domains and to achieve better use of domain resources. This thesis introduces a new scheduling algorithm called “Dynamic Resource Allocation Management - Network Function Virtualization (DRAM-NFV)” to allocate the service classes resources in the proportional delay DiffServ domains. DRAM-NFV algorithm manages the resources among service classes within the edge routers of the DiffServ domains dynamically according to their traffic conditions and manages these resources between the DiffServ domains in the event of congestion based on their traffic conditions at the egress routers of the upstream domain and ingress routers of the downstream domain. The NFV executes the DRAM-NFV algorithm on a virtualized - Network as a Service (NaaS) - cloud infrastructure to manage the SDN controllers for the edge routers of the DiffServ domains through monitoring the traffic conditions in the service classes at the edge routers and reallocating the out-link resources of the edge routers among service classes. A number of test scenarios were conducted in this research in order to test the performance of the DRAM-NFV algorithm. The performance of DRAM-NFV algorithm is compared with the performance of the DWFQ algorithm by comparing the average End to End Delay for service classes traffic and links utilization. The DWFQ algorithm cannot manage resources between DiffServ domains but can manage the resources locally and dynamically for each DiffServ domain separately. The network simulator NS3 has been used to implement these test scenarios and to test the performance of the DRAM-NFV algorithm. The results show that with the DRAM-NFV algorithm, better balance for DiffServ domains resources can be achieved through monitoring the bandwidth hungry service class at the downstream domain and managing its resources at the upstream domains. As a consequence of this, the utilizations of some service classes traffic are improved and the average End to End Delay for overall traffic are also reduced. An example of the improvement that was achieved by managing resources between (upstream and downstream) DiffServ domains dynamically, in test scenario 3- Case Study 2, the average utilization for the highest priority class (SC1) for whole period of simulation at the destination end is increased by 0.175% and the average End to End Delay for overall traffic is also reduced by 800 msec. As a result of reducing the average End to End Delay for overall traffic and improving the utilizations of service classes traffic, the QoS of applications traffic can be improved during the congestion periods in DiffServ domains.
30
Galia, Antonio. "A Dynamic Homogenization Method for Nuclear Reactor Core Calculations." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASP042.
Повний текст джерелаАнотація:
Dans les calculs de réacteurs à trois dimensions, nombreuses techniques d'homogénéisation ont été développées pour l'utilisation du schéma de calcul classique à deux étapes, basé sur les sections efficaces homogénéisées au préalable et utilisées ensuite par interpolation pour un état physique donné.D'autre part, les schémas de calcul basées principalement sur les méthodes des caractéristiques, qui visent le calcul direct du réacteur sans homogénéisation, ont des performances encore limitées en raison des capacités des machines et font alors le recours à des solutions de transport simplifiées. Ce travail a pour objectif d'étudier une nouvelle approche dans laquelle l'homogénéisation dynamique est utilisée pourproduire le flux neutronique de pondération sur les modèles d'assemblage tridimensionnels. L'application de la méthode pour un calcul d'un REP en 3D est comparée aux résultats issus d'un calcul de référence numérique en transport 3D et d'un calcul classique à deux-étapes. La réalisation repose sur le calcul de haute performance et avec un haut niveau de parallélismeThree-dimensional deterministic core calculations are typically based on the classical two-step approach, where the homogenized cross sections of an assembly type are pre-calculated and then interpolated to the actual state in the reactor. The weighting flux used for cross-section homogenization is determined assuming the fundamental mode condition and using a critical-leakage modelthat does not account for the actual environment of an assembly. On the other hand, 3D direct transport calculations and the 2D/1D Fusion method, mostly based on the method of characteristics, have recently been applied showing excellent agreement with reference Monte-Carlo code, but still remaining computationally expensive for multiphysics applications and core depletioncalculations.In the present work, we propose a method of Dynamic Homogenization as an alternative technique for 3D core calculations, in the framework of domain decomposition method that can be massively parallelized. It consists of an iterative process between core and assembly calculationsthat preserves assembly exchanges. The main features of this approach are:i) cross-sections homogenization takes into account the environment of each assembly in the core;ii) the reflector can be homogenized with its realistic 2D geometry and its environment;iii) the method avoids expensive 3D transport calculations;iv) no “off-line” calculation and therefore v) no cross-section interpolation is required.The verification tests on 2D and 3D full core problems are presented applying several homogenization and equivalence techniques, comparing against direct 3D transport calculation. For this analysis, we solved the NEA “PWR MOX/UO2 Core Benchmark” problem, which is characterized by strong radial heterogeneities due to the presence of different types of UOx and MOx assemblies at different burnups. The obtained results show the advantages of the proposed method in terms of precision with respect to two-step and performances with respect to the direct approach
31
Ratcliffe, Colin Paul. "Dynamic structural modelling for time domain analysis." Thesis, University of Southampton, 1985. https://eprints.soton.ac.uk/52303/.
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32
Wang, Ruhuai. "Frequency domain fatigue analysis of dynamically sensitive structures." Thesis, University College London (University of London), 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264193.
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Chaves, Dayane de Souza. "Dynamique de parois chirales dans les multicouches magnétiques avec anisotropie perpendiculaire." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAY019/document.
Повний текст джерелаАнотація:
L'objectif de cette thèse a été d'étudier la dynamique de parois de domaines dans des couches minces magnétiques ayant anisotropie perpendiculaire, dans un empilement non-centrosymétrique. Dans ce type de système la compétition entre l'interaction d'échange de Heisenberg et un terme d'échange antisymétrique appelé interaction Dzyaloshinskii-Moriya interfaciale, favorise des textures magnétiques non colinéaires avec une chiralité définie, comme les parois de Néel chirales et les skyrmions. Dans ce travail nous nous sommes intéressés à la dynamique induite par un champ magnétique ou un courant électrique de parois Néel chirales dans une tricouches constituée d'une fine couche de cobalt déposée sur du platine, et recouverte par un oxyde.Nous avons démontré que la structure statique et la dynamique des parois est fortement impactée par la présence de la DMI. La DMI favorise une structure Néel avec une chiralité bien définie (plutôt que la structure de Bloch trouvé en général dans des systèmes symétriques). En comparant des parois dans Pt/Co/Pt (DMI=0) et Pt/Co/AlOx (DMI forte) nous avons montré que en la présence de DMI les parois de domaines peuvent être déplacées plus efficacement avec un champ magnétique. La stabilisation de la structure interne de la paroi par la DMI déplace le régime precessionnel à de plus hauts champs magnétiques et permet d'obtenir des vitesses importantes.En opposition à ce que prédisent les modèles 1D, nous montrons que en la présence de fort DMI la vitesse de paroi sature après le champ de Walker, et que la vitesse de saturation est proportionnelle au rapport entre la force de la DMI et l'aimantation à saturation (D/Ms). L'augmentation de la vitesse de saturation dans des systèmes avec faible Ms a été démontrée en comparant la dynamique de parois dans Pt/Co/GdOx et Pt/Co/Gd. Ceci implique aussi que en connaissant Ms, la mesure de la vitesse de saturation fournit une méthode originale pour quantifier l'interaction Dzyaloshinskii-Moriya interfaciale, comme nous montrons dans ce travail. Cette méthode a été utilisée pour mesurer la DMI dans des tricouches Pt/Co/AlOx avec oxydation variable de l'interface supérieure du Co. Nous montrons que en plus de la forte DMI de l'interface Pt/Co, l'interaction Co/oxyde contribue avec une DMI du même signe, la force de laquelle dépend du dégrée d'oxydation de l'interface. Nous observons aussi que cette DMI est proportionnelle à l'anisotropie magnétique perpendiculaire, ce qui suggère que les deux effets ont une origine commune. Pour finir, nous avons montré des résultats préliminaires de dynamique de parois induite par champ et courant dans des systèmes ferrimagnétiques GdCo. Si d'une part près de la compensation les parois de domaines dans des tricouches Pt/GdCo/Ta peuvent être déplacées seulement avec des champs très forts, d'autre part le courant est très efficace et les courants de dépiégeage très faibles. Nous avons attribué cet effet à la dépendance en 1/Ms du couple de spin-orbite qui agit sur l'aimantationThe aim of this thesis has been to study domain wall dynamics in magnetic thin films with perpendicular magnetic anisotropy embedded in a non centrosymmetric stack. In this kind of system the competition between the symmetric Heisenberg exchange and an antisymmetric exchange term, called the interfacial Dzyaloshinskii-Moriya interaction (DMI), favours non collinear magnetic textures with a fixed chirality, like chiral Néel domain walls and skyrmions. In this work we have been interested in the field and current-driven dynamics of chiral Néel walls in trilayer stacks, typically consisting of a thin Co film deposited on Pt and capped with an oxide.We have shown that the statics and dynamics of a domain wall (DW) is strongly affected by the DMI. The DMI favours Néel internal structure (rather than the Bloch structure usually found in symmetric systems) with a fixed chirality. By comparing DWs in Pt/Co/Pt (no DMI) and Pt/Co/AlOx (strong DMI), we have shown that in the presence of DMI, DWs can be moved more efficiently by a magnetic field. The stabilization of the internal DW structure by the DMI allows the precessional regime to be pushed to large magnetic fields and large velocities to be reached.Opposite to what is predicted by 1D models we show that in the presence of DMI, the DW velocity saturates after the Walker field, and that the saturation velocity is proportional to the ratio of the DMI strength and the saturation magnetization (D/Ms). The enhancement of the saturation velocity in systems with reduced Ms is shown by comparing DW dynamics in Pt/Co/GdOx and Pt/Co/Gd stacks. This also means that, knowing Ms, measuring the DW saturation velocity provides an original method to quantify the interfacial Dzyaloshinskii-Moriya interaction, as we show in this work.This method has been used to measure the DMI interaction in Pt/Co/AlOx trilayers in which the top Co interface presents a varying degree of oxidation. We show that besides the strong DMI at the Pt/Co interface, the Co/oxide interface also provides a DMI contribution of the same sign, whose strength depends on the degree of oxidation of the Co/AlOx interface. We also observe that this DMI scales with the perpendicular magnetic anisotropy, which suggest a common origin for the two effects. Finally we have shown preliminary results of field- and current-driven dynamics of DWs in a ferrimagnetic system (GdCo). While close to the compensation composition domain walls in Pt/GdCo/Ta trilayers can be moved to high velocities only by very high magnetic fields, the current driven dynamics is very efficient and depinning currents low. This effect is attributed to the 1/ Ms dependence of the spin-orbit torque acting on the DW magnetization
34
Marshall, Jonathan. "Function theory in multiply connected domains and applications to fluid dynamics." Thesis, Imperial College London, 2006. http://hdl.handle.net/10044/1/1258.
Повний текст джерелаАнотація:
In this thesis we shall be considering a variety of problems set in the complex plane whose common feature is that they involve domains of finite multiple connectivity. We choose to focus on a particular canonical class of domains, namely circular domains. We extend our results to more general domains using conformal mappings. Results are derived for these circular domains by using the theory of Schottky groups. Problems we consider include the construction of automorphic functions, Green’s functions, and conformal mappings from circular domains to other commonly studied canonical domains. The abstract function-theoretic results we derive are applied to a number of physical problems of fluid dynamics
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Van, der Ende Bryan. "Molecular dynamics simulations of wild-type and mutant neu transmembrane domains." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0030/MQ47371.pdf.
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Mizzi, Simon. "Extended macroscopic models for rarefied gas dynamics in micro-sized domains." Thesis, University of Strathclyde, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501879.
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Steffen, Peter. "Compiling a domain specific language for dynamic programming." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=983062382.
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Haghgou, Sanaz. "Domain Self-organization and Domain Wall Dynamics in the Ferromagnetic Semiconductor (Ga,Mn)(As,P)." Paris 6, 2012. http://www.theses.fr/2012PA066021.
Повний текст джерелаАнотація:
GaMnAs est un système modèle pour les semiconducteurs ferromagnétiques dilués. Le ferromagnétisme résulte de l'interaction d'échange entre les spins des porteurs et des électrons 3d de Mn avec une constante d'échange Jpd. L’alliage phosphoré de GaMnAs est utilisé comme une nouvelle technique pour ajuster l'anisotropie magnétique. On obtient des couches à anisotropie perpendiculaire très homogènes. La constante de raideur de spin A et la dynamique de paroi de domaine sont étudiées en utilisant la microscopie Kerr. Dans GaMnAsP, en raison de la faible densité de défauts, les domaines magnétiques forment un motif auto-organisé. De sa période la constante A et l’énergie d’échange entre premiers voisins JMnMn sont déterminées. JMnMn est plus grand que dans GaMnAs. Ce résultat ainsi que la raideur des ondes de spin dans GaMnAsP pourrait indiquer que Jpd est plus grand dans GaMnAsP que dans GaMnAs. La dépendance en température de A est comparée aux prédictions théoriques. La dynamique de paroi de domaine sous champ est étudiée dans GaMnAsP et GaMnAs. Les courbes de vitesse s'écartent du modèle 1D théorique, montrant des pics de vitesse. Les simulations micromagnétiques reproduisent un pic de vitesse lorsque l'épaisseur de l'échantillon est plus grande que la longueur d'échange. La paroi de domaine subit une flexion et le vecteur aimantation une torsion dans l’épaisseur de la couche. Les deux montrent une résonance au pic de vitesse. L’augmentation de vitesse résulte de l’effet du champ de fuite des domaines adjacents sur la torsion de l'aimantation de la paroi à cette résonance. Un comportement non-linéaire est observé dans l'évolution temporelle de la flexion et de la torsionGaMnAs is a model system for diluted ferromagnetic semiconductors. The origin of ferromagnetism is the exchange interaction between the carriers and the Mn 3d spins with exchange constant Jpd. The phosphorous alloying of GaMnAs is used as a novel practical technique to adjust the magnetic anisotropy. It provides layers with perpendicular anisotropy with high homogeneity. The spin-stiffness constant A is determined and the field-driven domain wall dynamics is investigated using Kerr microscopy. In GaMnAsP due to the low density of defects the magnetic domains form a self-organized pattern. From its period the spin-stiffness constant A and the first neighbor effective exchange energy JMnMn are determined. JMnMn is larger than in GaMnAs. This result along with the higher spin-wave stiffness in GaMnAsP might indicate that the Jpd value is higher in GaMnAsP than in GaMnAs. The temperature dependence of A is experimentally determined and compared to the theoretical predictions. The field-driven domain wall dynamics is studied in GaMnAsP and GaMnAs. The experimental velocity curves deviate from the theoretical 1D model, showing velocity peaks. Micromagnetic simulations indeed reproduce a velocity peak when the sample thickness is larger than the exchange length. The domain wall undergoes a flexion and the magnetization vector twists inside the domain wall. Both show a resonance at the velocity peak. The peak results from the effect of the stray field from the adjacent domains on the twisted magnetization of the wall. A non-linear behavior is observed in the temporal evolution of flexion and twist. The origin of this phenomenon calls for further analytical study
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Fall, Djiby. "Longtime dynamics of hyperbolic evolutionary equations in ubounded domains and lattice systems." [Tampa, Fla.] : University of South Florida, 2005. http://purl.fcla.edu/fcla/etd/SFE0001053.
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Gokce, Aytul. "The interfacial dynamics of Amari type neural field models on finite domains." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/48185/.
Повний текст джерелаАнотація:
Continuum neural field models mimic the large scale spatio-temporal dynamics of interacting neurons on a cortical surface. For smooth Mexican hat kernels, with short-range excitation and long-range inhibition, they support various localised structures as well as travelling waves similar to those seen in real cortex. These non-local models have been extensively studied, both analytically and numerically, yet there remain open challenges in their study. Here we provide new numerical and analytical treatments for the study of spatio-temporal pattern formation in neural field models. In this context, the description of spreading patterns with a well identified interface is of particular interest, as is their dependence on boundary conditions. This Thesis is dedicated to the analyses of one- and two-dimensional localised states as well as travelling waves in neural fields. Firstly we analyse the effects of Dirichlet boundary conditions on shaping and creating localised bumps in one- dimensional spatial models, and then on the development of labyrinthine structures in two spatial dimensions. Linear stability analysis is used to understand how spatially extended patterns may develop in the absence and presence of boundary conditions. For the case without boundary conditions we recover the results of Amari, namely the widest bump among two branches of solutions is stable. However, new stable solutions can arise with an imposed Dirichlet boundary condition. For a Heaviside non-linearity, the Amari model allows a description of solutions using an equivalent interface dynamics. We generalise this reduced, yet exact, description by deriving a normal velocity rule that can account for boundary conditions. We extend this approach to further treat neural field models with spike frequency adaptation. These can exhibit breathers and travelling waves. The latter can take the form of spiral waves, to which we devote particular attention. We further study neural fields on feature spaces in the primary visual cortex (V$1$), where cells respond preferentially to edges of a particular orientation. Considering a general form of the synaptic kernel which includes an orientation preference at each spatial point, we present the construction and stability of orientation bumps, as well as stripes. To date there has been surprisingly little analysis of spatio-temporal pattern formation in neural field equations described on curved surfaces. Finally, we study travelling fronts and pulses on non-flat geometries, where we consider the effects of inhomogeneities on the propagation velocity of these waves. In all sections, theoretical results for pattern formation are shown to be in excellent agreement with simulations of the full neural field models.
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Bennett, Elizabeth. "Modulating protein-protein interactions : Novel inhibitors of PDZ domains and tubulin dynamics." Thesis, University of Salford, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.502783.
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Houzeaux, G. (Guillaume). "A Geometrical Domain Decomposition Methods in Computational Fluid Dynamics." Doctoral thesis, Universitat Politècnica de Catalunya, 2002. http://hdl.handle.net/10803/6858.
Повний текст джерелаАнотація:
El método de descomposición de dominios (DD) que se propone en esta tesis pretende resolver flujos incompresibles alrededor de objetos en movimiento relativo. El algoritmo de DD está basado en un acoplamiento del tipo Dirichlet/Neumann(Robin) aplicado a subdominios con solapamiento, y es, por tanto, una extensión del método Dirichlet/Neumann(Robin) clásico con subdominios disjuntos. En realidad, el campo de aplicación de este estudio es mucho más amplio puesto que en el se propone un posible marco teórico para abordar la extensión a subdominios solapados de los métodos mixtos clásicos: métodos Dirichlet/Robin, Dirichlet/Neumann, Robin/Neumann y Robin/Robin. Se observa que los métodos mixtos propuestos heredan propiedades del método de Schwarz y al mismo tiempo conservan el comportamiento de sus equivalentes sin solapamiento cuando este tiende a cero. Se muestra como resultado principal que el solapamiento hace estos métodos más robustos que los métodos sin solapamiento. El método de DD que se estudia es geométrico y algorítmico. Es geométrico en el sentido de que la partición del dominio computacional se lleva a cabo antes del proceso de mallado y de acuerdo con el acoplamiento de DD que se prevé usar.
Es también algorítmico porque la solución en cada subdominio se obtiene en procesos diferentes y el intercambio de información entre subdominios se realiza mediante un código maestro. Tal estrategia es muy flexible puesto que requiere muy pocas modificaciones del código numérico original. Por consiguiente, sólo el código maestro necesita ser adaptado a los códigos y estrategias numéricos utilizados en cada subdominio.
Se presenta una descripción detallada de la implementación del método de DD propuesto en el contexto numérico de los elementos finitos. Presentamos técnicas de interpolación para los datos de tipo Dirichlet y Neumann y desarrollamos algoritmos de conservación. Una vez el acoplamiento de DD y las interpolaciones definidos, presentamos un método del tipo Chimera para la resolución de flujos alrededor de objetos en movimiento. En particular, definimos transformaciones tensoriales para transformar variables de un subdominio a otro.
Finalmente, el algoritmo de DD se aplica a un código implícito para la resolución de las ecuaciones de Navier-Stokes incompresibles y también a las ecuaciones de Navier-Stokes promediadas con un modelo de turbulencia de una ecuación.
The domain decomposition (DD) method we present in this work aims at solving incompressible flows around objects in relative motion. The DD algorithm is based on a Dirichlet/Neumann(Robin) coupling applied to overlapping subdomains. Hence, it is an extension of the classical Dirichlet/Neumann(Robin) method which uses disjoint subdomains.
Actually, the field of application of this work is wider as it proposes to set up a possible theoretical framework for studying the overlapping extensions of classical mixed methods: the Dirichlet/Robin, Dirichlet/Neumann, Robin/Neumann and Robin/Robin DD methods.
We observe that mixed DD methods inherit some properties of the Schwarz method while they keep the behavior of the classical mixed DD methods when the overlap tends to zero.
As a main result, we show that the overlap makes the proposed methods more robust than disjoint mixed DD methods.
The DD method we propose is geometric and algorithmic. It is geometric because the partition of the computational domain is performed before the meshing, and in accordance to the DD coupling. It is also algorithmic because the solution on each subdomain is obtained on separate processes and the exchange of information between the subdomains is carried out by a Master code. This strategy is very flexible as it requires almost no modification to the original numerical code. Therefore, only the Master code has to be adapted to the numerical codes and strategies used on each subdomain.
We present a detailed description of the implementation of the DD methods in the numerical framework of finite elements. We present interpolation techniques for Dirichlet and Neumann data as well as conservation algorithms.
Once the domain decomposition coupling and interpolation techniques are defined, we set up a Chimera method for the solution of the flow over objets in relative movements. Tensorial transformations are introduced to be able to express variables measures in one subdomain.
Finally, the DD algorithm is applied to an implicit finite element code for the solution of the Navier-Stokes equations and also of the Reynolds Averaged Navier-Stokes equations together with a one-equation turbulence model.
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Hu, Dunzhong. "Domain wall dynamics in ferroelectric ceramics under mechanical stress." Thesis, Queen Mary, University of London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417388.
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Andersson, Magnus. "Investigations of domain-wall motion using atomistic spin dynamics." Thesis, Uppsala universitet, Materialteori, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-247556.
Повний текст джерелаАнотація:
In this thesis, current driven domain-wall motion is studied using atomistic simulations with the exchange coupling modeled by the Heisenberg Hamiltonian under the nearest-neighbor approximation. The investigations may be divided into two parts, each concerned with how different aspects of the systems affect the domain-wall motion. The first part deals with domain-wall width dependence of the velocity in a three dimensional geometry with simple cubic crystal structure and uniaxial anisotropy. Results from this part showed that the velocity has a minor domain-wall width dependence. For a fixed current density, the velocity increased with domain-wall width, though only from 61.5 a/ns to 64.5 a/ns as the domain-wall width was increased from 3 to 25 atoms. The second part of the investigations deals with phenomena involving mixed cubic and uniaxial anisotropy, the non-adiabaticity parameter as well as the geometry of the system. The discussion includes an account of how the spin-transfer and cubic anisotropy torques contribute to the motion for different values of the non-adiabaticity parameter. In comparing a one dimensional atomic chain and a three dimensional system with simple cubic crystal structure, but otherwise with the same material properties, results showed a difference in how the two systems responded to currents. This difference is not accounted for by the micromagnetic theory, and its origin was unable to be determined.
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Gallagher, Thomas Robert Alexander. "The structure and dynamics of the p62-UBA domain." Thesis, University of Nottingham, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438269.
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46
Clark, Aileen. "The dynamics of dialogue in a restricted reference domain." Thesis, University of Glasgow, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385708.
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Viola, Giuseppe. "Domain switching dynamics in ferroelastic and ferroelastic/ferroelectric perovskites." Thesis, Queen Mary, University of London, 2010. http://qmro.qmul.ac.uk/xmlui/handle/123456789/382.
Повний текст джерелаАнотація:
A comprehensive study of domain switching process in different ferroelastic and ferroelastic/ferroelectric perovskite structured ceramics has been performed. The effects of thermal fluctuations on domain switching dynamics were investigated in the ferroelastic and in the ferroelectric case under static and dynamic electric and mechanical conditions. In the ferroelastic case, domain switching behaviour was investigated for different compositions, using different types of mechanical tests. Compression tests were carried out to characterize the ferroelastic properties, such as coercive stress, hysteresis loop and irreversible strain. Creep experiments were performed to study the domain switching time dependence at different stress levels. Domain switching kinetics during creep was characterized by implementing a rate model, based on thermal activation rate theory, which allowed the activation volume to be estimated. A Rayleigh-type analysis was performed to study the effects of stress amplitude, loading rate, temperature and composition on ferroelastic switching. Rayleigh-type relationships were proposed to fit the results and the rate model developed was applied to quantify the effect of the loading rate on the Rayleigh loops. Alternative methodologies were developed to assess the effects of rate and temperature on the coercive stress, providing original sets of data. A further application of the rate model provided an estimation of the activation parameters (volume and enthalpy). In PZT 5A at the coercive field the activation volume was calculated to be 2.44 nm3, with a reasonable consistency with the value obtained from creep tests (7.49 nm3). In the ferroelectric case, domain switching was studied by generating P-E and butterfly hysteresis loops and by analysing creep-relaxation curves. In creep experiments, the polarization and the strain were measured simultaneously, during the application of a constant electric field. An insight into the evolution of domain structure and on domain switching mechanisms was gained, highlighting analogies and differences with the ferroelastic case. Experiments at different frequencies, allowed the activation volume to be estimated at the coercive field (77 nm3). The relatively large value indicates small rate dependence and suggests a domain structure with broad and mobile domain walls, being the preferred sites for the nucleation.
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Albert, Maximilian. "Domain wall dynamics and resonant modes of magnetic nanostructures." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/413582/.
Повний текст джерелаАнотація:
In this work we present finite element-based simulations of magnetic nanostructures using the micromagnetic software packages Nmag and Finmag developed at the University of Southampton. As part of this work the package Finmag has been extended with the implementation of an eigenvalue-based method to compute resonant modes in magnetic nanosystems. The details of this implementation are discussed, including certain complications encountered in the context of a finite element discretisation scheme. The implementation is verified using results from an independently published study on eigenmodes of an elliptical nanodisc. We present two studies of domain walls in magnetic nanowires. The first one investigates field-driven domain wall motion in nanowires with edge roughness. A new roughness model is introduced which allows the systematic study of how edge roughness features influence the domain wall motion compared to the case of a smooth nanowire. While the large-scale behaviour, such as the asymptotic domain wall velocity, is largely unaffected by the roughness, it introduces marked local alterations to the domain wall trajectories and can lead to dynamic pinning, both below and above the Walker breakdown. It is shown that the effective pinning strength of the roughness features is strongest when their size is comparable to the size of the domain wall. The second domain wall study investigates different types of resonant modes (translational, breathing and twisting modes) of transverse domain walls pinned at notches in a magnetic nanowire. The different sensititivies of each mode type on the nanowire and notch geometry are investigated in detail. It is found that the translational and twisting mode respond relatively strongly to changes in the notch geometry, while the breathing mode is fairly robust to changes in the notches’ size, making it a promising candidate for applications. We finally present a study of resonant modes in an elliptical magnetic nanodisc representing the free layer of a spin-torque nano-oscillator. We demonstrate that the resonant frequencies and spatial mode profiles are altered in the presence of a magnetic nanoparticle. The dependence of the frequency shifts on the nanoparticle position and material parameters is studied systematically. It is shown that these frequency shifts exceed achievable linewidths in state-of-the-art spin-torque oscillators and that they can be maintained over large external field ranges (owing to to the fact that they are a direct response to the stray field of the nanoparticle and do not rely on changes to the magnetic ground state of the disc). This opens up promising applications for novel nano-sensing devices using frequency-based detection schemes.
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Bachy, Ismael. "Enrichissements de siegel." Thesis, Aix-Marseille 1, 2011. http://www.theses.fr/2011AIX10082.
Повний текст джерелаАнотація:
On s'intéresse dans ce travail à la description des enrichissements des disques de Siegel d'une fraction rationnelle f. Dans un premier temps nous étudions les enrichissements qui sont définis sur un ouvert de la grande orbite d'un disque de Siegel donné. Ce sont nécessairement des applications qui commutent à f là où les compositions ont un sens. Ce sont donc des applications linéaires en coordonnées linéarisantes. Le résultat principal de ce travail est que l'on peut obtenir toutes les applications linéaires en coordonnées linéarisantes définies sur un sous-disque du disque de Siegel de f. Pour démontrer ce résultat nous utilisons la compacité des applications linéarisantes normalisées, le théorème des fonctions implicites dans l'espace des fractions rationnelles de degré fixé et une étude du comportement du rayon d'univalence des applications linéarisantes. Nous identifions également les approches donnant lieu à des enrichissements définis ou à valeurs dans le disque de Siegel tout entier (enrichissements maximaux). Au passage nous généralisons aux limites avec ordre de contact fini par rapport au cercle unité un théorème de JC.Yoccoz sur le comportement du rayon d'univalence pour la famille quadratique lorsque le paramètre converge vers un nombre complexe de module un et d'argument un nombre de Brjuno.Ensuite, nous nous intéressons au cas où f a plusieurs cycles de disques de Siegel. Nous utilisons le théorème de transversalité d'A.Epstein pour décrire les enrichissements de f dans ce cas là. La linéarisabilité de f et la convergence des applications linéarisantes permet de transférer le problème de la description des enrichissements de Siegel de f à un problème de limite géométrique de sous-semigroupes de l'ensemble des nombres complexes non-nuls engendrés par un élément. Nous donnons dans ce travail un modèle topologique de l'adhérence de cet ensemble de sous-semigroupes. Nous déduisons de ces résultats une interprétation en terme de convergence géométrique de dynamiques de polynômes quadratiques et une description des points d'accumulation, pour la topologie de Hausdorff sur les compacts non-vides, des ensembles de Julia lorsque le paramètre tend vers un paramètre de SiegelIn this work we are interested in giving the description of Siegel discs enrichments of a rational map f. We first study the case of enrichments that are defined on an open subset of the grand orbit of a given Siegel disc. These maps commute with f where it makes sense. Thus they are linear in linearizing coordinates. The main result of this work is that we can obtain all linear maps in linearizing coordinates that are defined in a subdisc of the Siegel disc. For this we use the compactness of the set of normalized linearizing maps, the implicit functions theorem in the space of rational maps with fixed degree and a study on the behaviour on the univalent radius of the linearizing maps. We identify approaches giving enrichments that are defined or take values on the whole Siegel disc (maximal enrichments). We generalize to finite order of contact approaches with respect to the unit circle a theorem of JC.Yoccoz on the behaviour of the univalent radius for the quadratic family when the parameter converges to a complex number of modulus one with argument a Brjuno number.We then focus on the case where f has more than one Siegel disc. We make use of A.Epstein's transversality theorem to describe Siegel enrichments of f in this case. The linearisability of f and the convergence of the linearizing maps reduces the problem of Siegel enrichments description to a geometric limit problem on one generated closed sub-semigroups ofthe set of non zero complex numbers. We give in this work a topological model fot the closure of this set of sub-semigroups.We deduce from these results an interpretation in terms of geometric convergence of quadratic polynomial dynamics and we describe the accumulation points (for the Hausdorff topology on non empty compact subsets) of Julia sets when the parameter converges to a Siegel parameter
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Rydberg, David. "Dependence on pH of Structural and Dynamical Changes of a Calmodulin Domain Mutant." Thesis, Linköpings universitet, Institutionen för fysik, kemi och biologi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-121782.
Повний текст джерелаАнотація:
Calmodulin (CaM) is a highly conserved protein able to bind Ca2+. When Ca2+ is bound the protein can bind and activate further proteins with several individual functions. CaM switches to a more open conformation when Ca2+-bound and is able to do so at a high rate. Little is known about the conformational switches between apo and Ca2+-bound states. A hypothesis suggests that protonation/deprotonation of a histidine side-chain is part of the answer and thus the dynamics of CaM would be pH dependent. This was further investigated in this thesis. Methods to carry out the project included protein expression of isotope labelled CaM-TR2C E140Q, standard protein purification and protein adapted Nuclear Magnetic Resonance (NMR) spectroscopy. The results suggest that CaM-TR2C E140Q is likely to depend on pH and that histidine 107 (H107) may have a central role in the conformational changes observed. At lower pH it was also suggested that CaM-TR2C E140Q obtained a more open conformation with weakened intramolecular interactions and that the tertiary structure of CaM-TR2C E140Q may have been disrupted.Calmodulin (CaM) är ett, till hög grad konserverat protein med möjlighet att binda in Ca2+. Då Ca2+ är bundet kan proteinet binda och aktivera ytterligare protein med olika enskilda funktioner. CaM byter med hög hastighet till en mer öppen konformation då Ca2+ binder. Lite vetskap finns kring hur konformationsändringarna mellan apo-form och Ca2+-bunden form går till. En hypotes föreslår att protonering/deprotonering av en histidin-sidokedja kan vara en del av svaret och att CaMs dynamik därför bör vara beroende av pH. Detta undersöktes vidare i detta examensarbete. Metoder som användes för att genomföra projektet inkluderar proteinuttryck av isotopinmärkt CaM-TR2C E140Q, standardiserad proteinrening och proteinanpassad kärnmagnetisk resonans (NMR) spektroskopi. Resultaten föreslår att konformationsändringarna av CaM-TR2C E140Q troligen är pH-beroende och att histidin 107 (H107) kan ha en central roll vid dessa ändringar. Vid lägre pH föreslås att CaM-TR2C E140Q antar en mer öppen konformation med försvagade intramolekylära interaktioner och att tertiärstrukturen av CaM-TR2C E140Q kan ha blivit upplöst.