Дисертації: "Modes oscillatoire"

1

Anstie, James D. "A 50 K dual-mode sapphire oscillator and whispering spherical mode oscillators." University of Western Australia. School of Physics, 2007. http://theses.library.uwa.edu.au/adt-WU2007.0070.

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[Truncated abstract] This thesis is split into two parts. In part one; A 50 K dual mode oscillator, the aim of the project was to build a 50 K precision oscillator with frequency stability on the order of 1014 from 1 to 100 seconds. A dual-mode temperature compensation technique was used that relied on a turning point in the frequency-temperature relationship of the difference frequency between two orthogonal whispering gallery modes in a single sapphire crystal. A cylindrical sapphire loaded copper cavity resonator was designed, modelled and built with a turning point in the difference frequency between an E-mode and H-mode pair at approximately 52.5 K . . . The frequencies and Q-factors of whispering spherical modes in the 3-12 GHz range in the fused silica resonator are measured at 6, 77 and 300 K and the Q-factor is used to determine the loss tangent at these temperatures. The frequency and Q-factor temperature dependence of the TM2,1,2 whispering gallery mode at 5.18 GHZ is used to characterise the loss tangent and relative permittivity of the fused silica from 4-300 K. Below 22 K the frequency-temperature dependence of the resonator was found to be consistent with the combined effects of the thermal properties of the dielectric and the influence of an unknown paramagnetic impurity, with a spin resonance frequency at about 138 ± 31 GHz. Below 8 K the loss tangent exhibited a 9th order power law temperature dependence, which may be explained by Raman scattering of Phonons from the paramagnetic impurity ions. A spherical Bragg reflector resonator made from multiple concentric dielectric layers loaded in a spherical cavity that enables confinement of field in the centre of the resonator is described. A set of simultaneous equations is derived that allow the calculation of the required dimensions and resonance frequency for such a resonator and the solution is confirmed using finite element analysis. A spherical Bragg reflector resonator is constructed using Teflon and free-space as the dielectric materials. A Q-factor of 22,000 at 13.87 GHz was measured and found to compare well with the design values.

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2

Abdulhay, Enas. "Une nouvelle méthode non-invasive d'estimation cycle à cycle du volume d'éjection cardiaque dans le signal de plethysmographie respiratoire par inductance : algorithme de "double décomposition empirique"." Université Joseph Fourier (Grenoble ; 1971-2015), 2009. http://www.theses.fr/2009GRE10220.

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L'objectif principal qui guide les développements en traitement du signal de cette thèse est la mise au point d'un outil qui s'inscrit dans une démarche de physiologie intégrative où, à chaque échelle, le modèle des signaux peut être différent On cherche ici à restreindre le jeu d'hypothèses a priori à un ensemble de règles physiologiques qui régissent les interactions entre functions physiologiques en l'absence d'hypothèses fonnelles et: mathématiques sur les signaux. Nous avons appliqué cette démarche au problème de la détection des ondes cardiaques et: de l' estimation cycle à cycle du volume d'éjection dans le signal RIP (Respiratoty Inductive Plethysmography). L'approche par décomposition empirique se prête particulièrement à notre logique. Nous proposons ici la première version d'un algorithme basé sur une double décomposition empirique du signal RIP. La méthode choisie et: les outils correspondants ont été testés sur deux types de données, d'une part des signaux simulés, d'autre part des signaux enregistrés sur volontaires sains. Notre objectif est donc aussi de mettre au point un modèle cardiorespiratoire pouvant servir d'outil de simulation des signaux ventilatoires, cardiaques et: de RIP avec la simulation de l'effet de chaque système sur l'autre. Les résultats montrent que la méthode proposée est adaptée à l'analyse du signal RIP et: à l' estimation du volume d'éjection
The main objective that guides the signal processing approaches ofthis thesis is the development of a tool that oould be part of an integrative physiology approach where, at each scale, the model of signais may be different We seek here the restriction of asstnnptions a priori to a set: of rules goveming the physiological interactions between physiological functions in the absence of fannal and mathematical assumptions. We applied this approach to the problem of cardiac waves detection and estimation of cycle-to-cycle stroke volume in the RIP signal (Respiratory Inductive Plethysmography). The empirical decomposition approach seems to be particularly adapted to our logic. We propose here the first version of an algorithm based on RIP double decomposition. The method and its COITeSpül1ding tools have been tested on two types of data, simulated signais and real signais recorded at healthy volunteers. Our aim is also therefore to develop a cardio-respiratory model that can serve as a tool for ventilatory, cardiac and RIP signals simulation along with the simulation of the effect of each system on the other. The results show that the proposed method is suitable for RIP signal analysis and for stroke volume estimation

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3

JANIAUD, BEATRICE. "Instabilites de phase de modes oscillatoires." Paris 6, 1994. http://www.theses.fr/1994PA066156.

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Cette these est consacree a l'etude experimentale de la stabilite de modes oscillatoires non-lineaires. Comme dans le cas des structures dissipatives stationnaires, les instabilites se manifestent par des perturbations de phase ; toutefois leur nature oscillante fait apparaitre de nouveaux types de defauts localises. Nous avons etudie une structure unidimensionnelle, l'instabilite oscillatoire des rouleaux de convection de rayleigh-benard et une structure bidimensionnelle d'electro-convection d'un cristal liquide. La zone de stabilite du train d'onde unidimensionnel est limitee par l'instabilite d'eckhaus propagative, qui peut etre sur-critique. Par ailleurs nous avons mis en evidence des defauts localises, les trous de nozaki-bekki, qui sont une generalisation des dislocations spatio-temporelles. L'etude du mode optique de la structure bidimensionnelle a mis en evidence un couplage entre le reseau sous-jacent et le mode oscillatoire. Cette instabilite, correspondant a des deformations du reseau, conduit a l'apparition d'une structure localisee, en forme de cible. Pour chacune de ces trois instabilites, une comparaison quantitative avec l'equation complexe de landau-ginzburg et des simulations numeriques nous a permis de comprendre les mecanismes mis en jeu

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4

Mukherjee, Jayanta. "General non linear perturbation model of phase noise in LC oscillators." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1149061925.

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5

Barbagallo, Alexandre. "Model reduction and closed-loop control of oscillator and noise-amplifier flows." Palaiseau, Ecole polytechnique, 2011. https://pastel.hal.science/docs/00/65/49/30/PDF/Barbagallo_PhDThesis.pdf.

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This work deals with the closed-loop control of disturbances which develop linearly in laminar and incompressible flows. The control of both oscillator and amplifier flows is assessed. We consider a LQG control strategy in which the control law is computed using a reduced-order model of the flow. This reduced-order model is obtained by a Petrov-Galerkin projection. The first part is devoted to the stabilization of an open cavity flow which behaves as an oscillator. It is shown that the unstable subspace of the flow (the unstable global modes) and the input-output behaviour between the actuator and the sensor of the stable subspace must be captured by the reduced-order model to stabilize the system. Global modes, POD modes and BPOD modes are successively evaluated as projection bases to construct a reduced-order model of the stable part of the flow. It appears that global modes are not able to reproduce the input-output behaviour of the stable part of the flow and subsequently may only stabilize the flow if the instability is very weak (close to the criticality). On the contrary, reduced-order models based on POD modes and BPOD modes efficiently extract the input-output dynamic of the stable subspace and are successful to stabilize the flow. The second part of this work is dedicated to the reduction of the disturbances' amplification on a backward facing step. The influence of the sensor's location and of the cost functional on the performance of the compensator is studied. It is shown that the truncation of the reduced-order model may lead to an unstable closed-loop system. Finally, the possibility to control a non-linear simulation using a linear compensator is evaluated
Ce travail est consacré au contrôle en boucle fermée des perturbations se développant linéairement dans des écoulements laminaires et incompressibles de types oscillateurs et amplificateurs de bruit. La loi de contrôle, calculée selon la théorie du contrôle LQG, est basée sur un modèle d'ordre réduit de l'écoulement obtenu par projection de Petrov-Galerkin. La stabilisation d'un écoulement de cavité de type oscillateur est traitée dans une première partie. Il est montré que la totalité de la partie instable de l'écoulement (les modes globaux instables) ainsi que la relation entrée-sortie (action de l'actionneur sur le capteur) de la partie stable doivent être captées par le modèle réduit afin de stabiliser le système. Les modes globaux, modes POD et modes BPOD sont successivement évalués comme bases de projection pour modéliser la partie stable. Les modes globaux ne parviennent pas à reproduire le comportement entrée-sortie de la partie stable et par conséquent ne peuvent stabiliser l'écoulement que lorsque l'instabilité du système est initialement faible (nombre de Reynolds proche de la criticité). En revanche, les modes POD et plus particulièrement BPOD sont capable d'extraire la dynamique entrée-sortie stable et permettent de stabiliser efficacement l'écoulement. La seconde partie de ce travail est consacrée à la réduction de l'amplification des perturbations sur une marche descendante. L'influence de la localisation du capteur et de la fonctionnelle de coût sur la performance du compensateur est étudiée. Il est montré que la troncature du modèle réduit peut rendre le système bouclé instable. Finalement, la possibilité de contrôler une simulation non-linéaire avec un modèle linéaire est évaluée

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6

Ramirez, Avila Gonzalo. "Synchronization phenomena in light-controlled oscillators." Doctoral thesis, Universite Libre de Bruxelles, 2004. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/211169.

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Le but de cette thèse est d'étudier d'une façon expérimentale et théorique le comportement synchrone d'un groupe d'oscillateurs contrôlés par la lumière (LCOs). Ces LCOs sont très simples du point de vue électronique et ont la propriété d'imiter le comportement des lucioles puisqu'ils interagissent par des impulsions de lumière. En même temps, les LCOs sont une bonne approche pour étudier d'autres systèmes qui agissent comme des oscillateurs d'intégration et de tir car un LCO est un oscillateur de relaxation à deux échelles de temps :un long processus de charge alterné avec un très court processus de décharge. Une série d'expériences a été menée pour pouvoir comprendre le processus de synchronisation des LCOs. Nous avons trouvé que l'acquisition de la synchronisation est due aux effets de la perturbation à savoir: le raccourcissement de la charge et l'allongement de la décharge. Les mesures expérimentales ainsi que la physique liée aux LCOs nous ont permis de formuler un modèle qui a été utilisé pour trouver d'une façon analytique la courbe de réponse de phase (PRC) qui caractérise un LCO.

Le modèle a ensuite été validé en comparant les résultats expérimentaux et théoriques. Le modèle reproduit même, le phénomène de bifurcation qui apparaît lorsque trois LCOs sont couplés et disposés en ligne :deux états stables différents apparaissent selon les conditions initiales. L'accord trouvé entre théorie et expérience nous permet d'utiliser le modèle pour étudier d'autres situations qui ne sont pas facilement abordables du point de vue expérimental.

Nous avons étudié analytiquement deux LCOs identiques couplés. Même pour ce cas idéal, nous étions obligés de faire des simplifications pour pouvoir trouver des solutions exactes. On a trouvé pour ce système deux états possibles qui dépendent des conditions initiales, la synchronisation (stable) et l'anti-synchronisation (instable). Nous avons également montré que le temps de synchronisation augmente avec la distance entre LCOs. La construction des langues d'Arnold (régions de synchronisation) nous a permis de distinguer des régions de synchronisation pure d'ordre n:m et des régions de superposition synchronisation--modulation.

Nous avons travaillé numériquement avec des systèmes de LCOs affectés de bruits uniforme et Gaussien. Le comportement synchrone de ce système a été caractérisé en utilisant des paramètres statistiques simples tels que la moyenne de la différence de phase linéaire et la variance de la différence de phase cyclique. Nous avons démontré que le bruit, bien qu'il puisse perturber la synchronisation, peut aussi la favoriser entre deux LCOs qui ne se synchroniseraient pas en conditions normales, surtout quand le bruit est Gaussien et que les variances du bruit ne sont pas égales.

Nous avons étudié en termes statistiques la synchronisation de LCOs couplés localement et arrangés en ligne, en anneau et en réseau. Nous avons montré que la synchronisation totale se produit plus facilement pour des LCOs disposés en anneau. Concernant le temps de synchronisation, il est imprédictible. Les résultats analytiques et numériques suggèrent que la synchronisation totale est le phénomène le plus probable quand le nombre d'oscillateurs n'est pas très grand.

Finalement, nous avons étudié des LCOs statiques et mobiles couplés globalement. Dans les deux cas, nous avons trouvé que la synchronisation est moins probable quand le nombre d'oscillateurs augmente. Pour la condition statique, en considérant un couplage du type champ moyen, nous avons observé que le temps de synchronisation diminue avec le nombre de LCOs. Cependant, pour la situation plus réaliste dans laquelle l'interaction entre LCOs dépend de la distance les séparant, le temps de synchronisation devient à nouveau imprédictible. Enfin, nous avons étudié l'influence de la mobilité sur la synchronisation, problème qui est important en biologie et en robotique.

Notre système, de par ses caractéristiques et sa base expérimentale, est beaucoup plus proche de la réalité que ceux considérés d'habitude dans la littérature. Les résultats obtenus peuvent s'appliquer à des systèmes biologiques (lucioles, cellules cardiaques, neurones, …), mais également à la robotique, où la communication à longue portée par la lumière et l'émergence de patterns de synchronisation pourraient être très utiles dans le but d'effectuer des tâches spécifiques.
Doctorat en sciences, Spécialisation physique
info:eu-repo/semantics/nonPublished

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7

Parker, Julie. "A study of the phenylacetylene oxidative carbonylation reaction in oscillatory and non-oscillatory modes." Thesis, University of Newcastle upon Tyne, 2016. http://hdl.handle.net/10443/3281.

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The palladium-catalysed phenylacetylene oxidative carbonylation (PCPOC) reaction operates in both oscillatory and non-oscillatory modes. In oscillatory mode oscillations have been observed in pH, reaction heat (Qr), redox potential and gas uptake. This work documents the steps towards understanding the process and uncovering the reaction mechanism. An extensive experimental study was undertaken involving small-scale (25 mL) experiments on the catalytic system and large-scale (450 mL) experiments on the whole reaction system. The large-scale experiments on the whole system included studies at temperatures from 0-40 °C. The effect of increasing the concentration of water in the system by increasing the solvent volume ratio of water from 0% to 40% was also studied. Decreasing the reaction temperature is known to affect the period and amplitude of the pH oscillations but this work found that it also changes the selectivity of the reaction: the major product is dimethyl (2Z)-2-phenyl-2-butenedioate at 40 °C whereas at 0 °C the major product is 5,5-dimethoxy-3-phenyl-2(5H)-furanone. Increasing the concentration of water in the system affected product selectivity and the oscillatory pH behaviour. As the water concentration increased, pH behaviour changed: the regular shark fin waveform observed when no water was added to the system gradually became step-wise oscillatory behaviour. The small-scale experiments uncovered the link between the mono-carbonylation of phenylacetylene and the generation of H+. They also showed the autocatalytic nature of the reaction between the PdI2 catalyst and carbon monoxide as well as the involvement of water in H+ generation. Based on the experimental findings a tentative model was produced using BatchCAD which accounted for the key features of the observed pH behaviour. The modelling study showed the need for autocatalysis in the model producing the best fit when HI catalysed the reaction between PdI2, CO and H2O.

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8

Wedgwood, Kyle C. A., Kevin K. Lin, Ruediger Thul, and Stephen Coombes. "Phase-Amplitude Descriptions of Neural Oscillator Models." BioMed Central, 2013. http://hdl.handle.net/10150/610255.

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Phase oscillators are a common starting point for the reduced description of many single neuron models that exhibit a strongly attracting limit cycle. The framework for analysing such models in response to weak perturbations is now particularly well advanced, and has allowed for the development of a theory of weakly connected neural networks. However, the strong-attraction assumption may well not be the natural one for many neural oscillator models. For example, the popular conductance based Morris-Lecar model is known to respond to periodic pulsatile stimulation in a chaotic fashion that cannot be adequately described with a phase reduction. In this paper, we generalise the phase description that allows one to track the evolution of distance from the cycle as well as phase on cycle. We use a classical technique from the theory of ordinary differential equations that makes use of a moving coordinate system to analyse periodic orbits. The subsequent phase-amplitude description is shown to be very well suited to understanding the response of the oscillator to external stimuli (which are not necessarily weak). We consider a number of examples of neural oscillator models, ranging from planar through to high dimensional models, to illustrate the effectiveness of this approach in providing an improvement over the standard phase-reduction technique. As an explicit application of this phase-amplitude framework, we consider in some detail the response of a generic planar model where the strong-attraction assumption does not hold, and examine the response of the system to periodic pulsatile forcing. In addition, we explore how the presence of dynamical shear can lead to a chaotic response.

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9

Makarau, Amos, and Amos Makarau. "Intra-seasonal oscillatory modes of the southern Africa summer circulation." Doctoral thesis, University of Cape Town, 1995. http://hdl.handle.net/11427/23683.

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10

Tığrak, Ulaş Esra Pashaev Oktay. "Damping Oscillatory Models In General Theory of Relativity/." [s.l.]: [s.n.], 2007. http://library.iyte.edu.tr/tezler/master/matematik/T000667.pdf.

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11

Kurishina, Victoria. "Fluid nonlinearities for calibrated VIV wake oscillator models." Thesis, University of Aberdeen, 2018. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=237154.

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Onshore and offshore structures are subject of strict safety regulations, and acceptable design implies requirements for accurate models of potentially dangerous phenomena. The phenomenon of Vortex-Induced Vibrations (VIVs) develops when a slender structure interacts with a fluid flow. Vortices grow in the disturbed boundary layer and spread behind the structure, resulting in fluctuations of the fluid forces acting on the body. Slender structures are present almost everywhere in the form of tall buildings and skyscrapers, cranes, antennas, power lines, suspension bridges, umbilicals, risers and free spans of pipelines which deliver water, oil and gas. The deeper in the water and higher in the sky these structures are, more likely they can experience VIVs and the lock-in state due to the exposure to various flow profiles. The wake oscillator method allows to model fluid variables during VIV lock-in using self-excited and self-limited oscillators of Van der Pol or Rayleigh type. In this research, the capabilities of alternative nonlinear oscillators as fluid equations are considered for modelling elastically supported rigid structures with one and two degrees-of-freedom in uniform flow. For modelling two-dimensional flexible structures in uniform and sheared flows, new wake oscillator models are developed in this work and applied with alternative damping terms. The dynamics of the uniform flow model of flexible structure is investigated in detail with the focus on coexisting solutions of the displacement amplitudes. Empirical coefficients for wake oscillator models are calibrated in this study using constrained nonlinear minimization and experimental data available in the literature. The validation performed confirms the most successful results for the suite of models of 2DOF rigid structure for low mass ratio, where agreement with both in-line and cross-flow displacement records was obtained.

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12

Marquart, Chad A. "Sliding-mode amplitude control techniques for harmonic oscillators." Texas A&M University, 2003. http://hdl.handle.net/1969.1/5767.

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This thesis investigates both theoretical and implementation-level aspects of switching- feedback control strategies for the development of voltage-controlled oscillators. We use a modified sliding-mode compensation scheme based on various norms of the system state to achieve amplitude control for wide-tuning range oscillators. The proposed controller provides amplitude control at minimal cost in area and power consumption. Verification of our theory is achieved with the physical realization of an amplitude controlled negative-Gm LC oscillator. A wide-tuning range RF ring oscillator is developed and simulated, showing the effectiveness of our methods for high speed oscillators. The resulting ring oscillator produces an amplitude controlled sinusoidal signal operating at frequencies ranging from 170 MHz to 2.1 GHz. Total harmonic distortion is maintained below 0:8% for an oscillation amplitude of 2 Vpp over the entire tuning range. Phase noise is measured as -105.6 dBc/Hz at 1.135 GHz with a 1 MHz offset.

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13

Craig, Samantha L. "Rubidium Oscillator Error Model for Specific Force and Magnetic Field Susceptibility." Ohio University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1398126124.

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14

Ho, Wai-man, and 何慧敏. "A numerical study on turbulent oscillatory plane Couette flow." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2004. http://hub.hku.hk/bib/B2977083X.

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15

Luiz, Gustavo de Oliveira 1988. "Dynamics of coupled micro-oscillators = Dinâmica de micro-osciladores acoplados." [s.n.], 2017. http://repositorio.unicamp.br/jspui/handle/REPOSIP/325686.

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Orientador: Gustavo Silva Wiederhecker
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
Made available in DSpace on 2018-09-02T10:33:51Z (GMT). No. of bitstreams: 1 Luiz_GustavoDeOliveira_D.pdf: 5507367 bytes, checksum: 506db63a5a93a33d67a84dbb1f7b33ce (MD5) Previous issue date: 2017
Resumo: Nas últimas décadas a optomecânica de microcavidades chamou a atenção de cientistas e engenheiros, que encontraram na interação entre luz e ondas acústicas aplicações que variam de sensores de massa com resolução atômica, até a preparação de estados quânticos de osciladores harmônicos mesoscópicos, passando por simuladores quânticos, filtros ópticos controláveis opticamente, criação de estados topológicos para luz e fônons, apenas citando alguns exemplos. Apesar das diversas demonstrações de vários dispositivos, sendo discos e cristais fotônicos os formatos mais comuns, há ainda um grande esforço no sentido de aperfeiçoá-los reduzindo perdas ópticas e mecânicas e suprimindo outros fenômenos de óptica não-linear, como absorção de dois fótons, que podem impedir seu funcionamento apropriado. Como ressonadores ópticos e mecânicos tipicamente compartilham a mesma estrutura nestes dispositivos, seus projetos são acoplados, dificultando o aprimoramento independente de cada um. Nesta tese usamos dispositivos optomecânicos de campo próximo, cuja interação entre modos mecânicos e ópticos se dá através do campo evanescente do último, para desacoplar o projeto mecânico do óptico, o que nos permitiu estudar a otimização do ressonador mecânico sem qualquer efeito sobre a cavidade óptica. Com um ressonador mecânico de silício composto por dois osciladores acoplados, pudemos demonstrar que o correto equilíbrio das massas de cada oscilador é um método simples e eficiente para suprimir as perdas devido à radiação de energia mecânica para o substrato na escala de frequência de 50 MHz. Este processo permitiu que fatores de qualidade limitados por perdas relacionadas ao material e à superfície, da ordem de 10 mil à temperatura ambiente e de 50 mil a aproximadamente 25 K, fossem obtidos. Também observamos nestes dispositivos o fenômeno de auto-pulsação, que apresenta uma dinâmica própria tão interessante quanto a optomecânica, apesar de impedir a operação apropriada dos osciladores optomecânicos. Estudamos este fenômeno separadamente e demonstramos que estes pulsos, ocorrendo em duas cavidades ópticas acopladas por seus campos evanescentes, podem sincronizar com o campo óptico sendo o único intermediador. Ambas as demonstrações têm implicações importantes, abrindo caminho para o desenvolvimento de novas plataformas de interesse tanto científico quanto tecnológico, como estruturas para o estudo de estados topológicos para a luz e para ondas acústicas e geradores de sinal de radio-frequência de alto desempenho. Além disso, os dispositivos foram todos produzidos em uma fábrica comercial, o que também demonstra que sua fabricação está pronta para ser escalada para produção em massa
Abstract: Cavity optomechanics in the micro-scale has attracted the attention of scientists and engineers on the last few decades, who encountered applications to the interaction of light and acoustic waves ranging from atomic resolution mass sensors to the preparation of quantum states of mesoscopic harmonic oscillators, passing by quantum simulators, optically controllable optical filters, formation of topological states for both photons and phonons, just to mention a few examples. Although various devices have been demonstrated, with disks and photonics crystals being the most common designs, there is still a large effort to improve them by reducing optical and mechanical losses and suppressing other non-linear phenomena, such as two-photon absorption, that may affect their proper operation. Because optical and mechanical resonators typically share the same structure in these devices, their designs are coupled, which complicates the independent improvement of each one. In this thesis we used near-field optomechanical devices, whose mechanical modes interact with the optical through the latter¿s evanescent field, to decouple the mechanical design from the optical, what allowed us to focus all attention on the mechanical resonator. With a silicon mechanical resonator composed of two coupled oscillators, we could demonstrate that the correct balance of the masses of the oscillators is an efficient and simple way to suppress losses due to energy radiation to the substrate at the 50 MHz frequency range. This strategy led to material and surface limited quality factors close to 10k at room temperature and 50k at approximately 25 K. We also observed the phenomenon of self-pulsing in these devices, which presents dynamics as interesting as the optomechanical interactions do, in spite of being a problem for the proper operation of the optomechanical devices. We studied this phenomenon separately and demonstrated that these pulses, when occurring in two evanescently coupled optical cavities, may synchronize with the optical field being the sole intermediary. These two demonstrations have important implications, paving the way for new platforms of scientific and technological interest, such as structures for the study of topological states for both light and acoustic weaves as well as high efficiency radio-frequency signal generators. Moreover, these devices were all fabricated in a commercial foundry, which also demonstrates that the fabrication of such technology is ready to be scaled up to mass production
Doutorado
Física
Doutor em Ciências
153044/2013-6
CNPQ

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16

Caicedo-Casso, Angelica G. "Period Robustness Analysis of Minimal Models for Biochemical Oscillators." University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1427980229.

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17

Tavares, Pedro Ernesto Schiavinatti. "Consequências das excitações oscilatórias em condensados de Bose-Einstein." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-30052012-175444/.

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Neste trabalho, estudamos as consequências causadas em um condensado de Bose-Einstein de átomos de 87Rb quando sujeito a uma excitação oscilatória externa. Para a produção do condensado utilizamos técnicas de resfriamento atômico, como o resfriamento a laser e o resfriamento evaporativo, em átomos aprisionados em uma armadilha magnética harmônica. A excitação externa é produzida através de um campo magnético quadrupolar oscilatório que é sobreposto ao campo de aprisionamento. Para uma forma fixa dessa excitação, observamos que podemos excitar modos coletivos de oscilação na amostra de condensado, em especial analisamos os modos breathing, dipolar, quadrupolar e o scissor mode. Durante o movimento dipolar do condensado na armadilha magnética, identificamos que há um escoamento contrapropagante do condensado em relação à nuvem térmica que o permeia. Esse escoamento é analisado como um movimento de dois fluidos, onde o condensado desempenha o papel de um superfluido e a nuvem térmica o de um fluido normal. Irregularidades na superfície do condensado são observadas e seus comprimentos característicos crescem na região dos pontos de retorno do movimento dipolar do condensado. Nesses pontos, a forma das irregularidades sugerem estar relacionadas com o processo de geração de vórtices na amostra superfluida. Com base nestas análises, determinamos o valor da velocidade relativa dos fluidos e qual deve ser, tipicamente, o valor da velocidade relativa crítica para que as irregularidades se tornam maiores, possibilitando a geração de vórtices. As análises apresentadas neste trabalho são dedicadas a entender os mecanismos que possibilitaram, em nosso sistema, a observação de vórtices, turbulência quântica e a granulação do condensado, em 2009.
In this work we have studied the effects caused by an external oscillatory excitation in a Bose-Einstein condensate of 87Rb. The condensate is produced through by atomic laser cooling techniques, as laser cooling and evaporative cooling, for trapped atoms in a harmonic magnetic trap. The external excitation is generated by an oscillating magnetic quadrupole field superimposed to the trapping field. For a fixed type of excitation, we observe that collective modes of oscillation are excited in the condensate sample, particularly we analyze the dipole mode, quadrupole and scissor mode. During the motion of the condensate in dipolar mode inside the magnetic trap, we have identified a counterflow, i. e. a relative motion between the condensate and the thermal cloud. This flow is analyzed as a two fluids motion, where the condensate plays the role of a superfluid and the thermal cloud a normal fluid. Irregularities on the condensate surface are observed and their characteristic lengths grow in the turning point regions of this dipolar motion. At these points, the shape of this irregularities seems to be related to the vortices generation process in a superfluid sample. Based on this analysis, we determine the velocity of the counterflow and the critical velocity for the irregularities to become larger, allowing the generation of vortices. The analyses presented in this work are dedicated to understand the mechanisms that allowed in our system the observation of vortices, quantum turbulence and the condensate granulation, in 2009.

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18

Liljestrand, Charlotte. "Spatial mode engineering in mid-infrared optical parametric oscillators." Thesis, KTH, Laserfysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-42705.

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The purpose of this thesis was to investigate the possibilities of enhancing the temporal and spatial coherence of parametric devices in the mid-infrared spectrum by exploiting inherent coherence selection of Bessel beams. Several optical parametric oscillators (OPO) were constructed and characterized for various types of resonators and pump lasers. In the first part of this work an OPO was constructed out of a periodically poled KTP (PPKTP) crystal within a stable resonator. It was pumped by a Q-switched Nd:YAG laser in transversal and longitudinal single mode operation. The OPO was pumped at 1064 nm and operated at signal wavelength of 1595.9 nm with a bandwidth at FWHM of 0.2 nm and idler wavelength 3192.9 nm and bandwidth of 0.5nm at FWHM. The stable resonator was constructed out of a curved input coupler and a planar output coupler to generate a spatially coherent beam. The beam quality factor of the OPO was measured to M2=1.3 and M2=1.7 in the horizontal and the vertical direction respectively. In the second part of this work conical beams, and hence noncollinear phase matching, was used. This was done to improve and study the temporal and spatial coherence of the generated beam if the OPO is pumped by a laser operating in multiple transversal and longitudinal modes. Using noncollinear phase matching provides a possibility of generating a highly coherent signal (or idler) wave when using a pump laser which operates in multiple transversal and longitudinal modes. Usually, such pump laser makes it difficult to generate highly coherent beams since the properties, such as bandwidth and beam quality factor, of the pump laser are transferred to the generated waves. So called multimode lasers, which operate in multiple modes, can be considered inexpensive and reliable while providing high pulse energies, and they are therefore attractive as pump sources for nonlinear processes. Throughout this second part a Q-switched Nd:YAG laser operating in multiple transversal and longitudinal modes at a wavelength 1064 nm was used. Optical parametric generation (OPG) was used to compare the effects between pumping with a Gaussian wave, and collinear phase matching, and pumping with a conical, a Bessel beam and hence noncollinear phase matching. Thereafter, optical parametric oscillation was studied with collinear and noncollinear phase matching using a Fabry-Perot cavity. The OPO pumped by a Q-switched Gaussian beam, and hence using collinear phase matching had a signal wave at 1596.3 nm and a bandwidth at FWHM of 4 nm. The OPO pumped by a conical beam, hence a Bessel beam and noncollinear phase matching, had a signal wave at 1596.5 nm and a bandwidth at FWHM of 0.2 nm. Both OPOs had a beam quality factor M2~2 in horizontal and vertical direction.

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19

Francis, Benjamin Lane. "Information Geometry and Model Reduction in Oscillatory and Networked Systems." BYU ScholarsArchive, 2020. https://scholarsarchive.byu.edu/etd/8512.

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In this dissertation, I consider the problem of model reduction in both oscillatory and networked systems. Previously, the Manifold Boundary Approximation Method (MBAM) has been demonstrated as a data-driven tool for reducing the parametric complexity of so-called sloppy models. To be effective, MBAM requires the model manifold to have low curvature. I show that oscillatory models are characterized by model manifolds with high curvature in one or more directions. I propose methods for transforming the model manifolds of these models into ones with low curvature and demonstrate on a couple of test systems. I demonstrate MBAM as a tool for data-driven network reduction on a small model from power systems. I derive multiple effective networks for the model, each tailored to a specific choice of system observations. I find several important types of parameter reductions, including network reductions, which can be used in large power systems models. Finally, I consider the problem of piecemeal reduction of large systems. When a large system is split into pieces that are to be reduced separately using MBAM, there is no guarantee that the reduced pieces will be compatible for reassembly. I propose a strategy for reducing a system piecemeal while guaranteeing that the reduced pieces will be compatible. I demonstrate the reduction strategy on a small resistor network.

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20

Klocke, Benjamin. "Neurochemical Status and Cortical Oscillatory Activity in aGenetic Mouse Model." University of Dayton / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1596121308843991.

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21

Peron, Thomas Kauê Dal\'Maso. "Dynamics of Kuramoto oscillators in complex networks." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-21092017-100820/.

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Synchronization of an ensemble of oscillators is an emergent phenomenon present in several complex systems, ranging from biological and physical to social and technological systems. The most successful approach to describe how coherent behavior emerges in these complex systems is given by the paradigmatic Kuramoto model. For decades, this model has been traditionally studied in globally coupled topologies. However, besides being intrinsically dynamical, complex systems exhibit very heterogeneous structure, which can be represented as complex networks. This thesis is dedicated to the investigation of fundamental problems regarding the collective dynamics of Kuramoto oscillators coupled in complex networks. First, we address the effects on network dynamics caused by the presence of triangles, which are structural patterns that permeate real-world networks but are absent in random models. By extending the heterogeneous degree mean-field approach to a class of configuration model that generates random networks with variable clustering, we show that triangles weakly affect the onset of synchronization. Our results suggest that, at least in the low clustering regime, the dynamics of clustered networks are accurately described by tree-based theories. Secondly, we analyze the influence of inertia in the phases evolutions. More precisely, we substantially extend the mean-field calculations to second-order Kuramoto oscillators in uncorrelated networks. Thereby hysteretic transitions of the order parameter are predicted with good agreement with simulations. Effects of degree-degree correlations are also numerically scrutinized. In particular, we find an interesting dynamical equivalence between variations in assortativity and damping coefficients. Potential implications to real-world applications are discussed. Finally, we tackle the problem of two intertwined populations of stochastic oscillators subjected to asymmetric attractive and repulsive couplings. By employing the Gaussian approximation technique we derive a reduced set of ODEs whereby a thorough bifurcation analysis is performed revealing a rich phase diagram. Precisely, besides incoherence and partial synchronization, peculiar states are uncovered in which two clusters of oscillators emerge. If the phase lag between these clusters lies between zero and π, a spontaneous drift different from the natural rhythm of oscillation emerges. Similar dynamical patterns are found in chaotic oscillators under analogous couplings schemes.
Sincronização de conjuntos de osciladores é um fenômeno emergente que permeia sistemas complexos de diversas naturezas, como por exemplo, sistemas biológicos, físicos, naturais e tecnológicos. A abordagem mais bem sucedida na descrição da emergência de comportamento coletivo em sistemas complexos é fornecida pelo modelo de Kuramoto. Durante décadas, este modelo foi tradicionalmente estudado em topologias completamente conectadas. Entretanto, além de ser intrinsecamente dinâmicos, tais sistemas complexos possuem uma estrutura altamente heterogênea que pode ser apropriadamente representada por redes complexas. Esta tese é dedicada à investigação de problemas fundamentais da dinâmica coletiva de osciladores de Kuramoto acoplados em redes. Primeiramente, abordamos os efeitos sobre a dinâmica das redes causados pela presença de triângulos padrões que estão omnipresentes em redes reais mas estão ausentes em redes gerados por modelos aleatórios. Estendemos a abordagem via campo-médio para uma variação do modelo de configuração tradicional capaz de criar topologias com número variável de triângulos. Através desta abordagem, mostramos que tais padrões estruturais pouco influenciam a emergência de comportamento coletivo em redes, podendo a dinâmica destas ser descrita em termos de teorias desenvolvidas para redes com topologia local semelhante a grafos de tipo árvore. Em seguida, analisamos a influência de inércia na evolução das fases. Mais precisamente, generalizamos cálculos de campo-médio para osciladores de segunda-ordem acoplados em redes sem correlação de grau. Demonstramos que na presença de efeitos inerciais o parâmetro de ordem do sistema se comporta de forma histerética. Ademais, efeitos oriundos de correlações de grau são examinados. Em particular, verificamos uma interessante equivalência dinâmica entre variações nos coeficientes de assortatividade e amortecimento dos osciladores. Possíveis aplicações para situações reais são discutidas. Finalmente, abordamos o problema de duas populações de osciladores estocásticos sob a influência de acoplamentos atrativos e repulsivos. Através da aplicação da aproximação Gaussiana, derivamos um conjunto reduzido de EDOs através do qual as bifurcações do sistema foram analisadas. Além dos estados asíncrono e síncrono, verificamos a existência de padrões peculiares na dinâmica de tal sistema. Mais precisamente, observamos a formação de estados caracterizados pelo surgimento de dois aglomerados de osciladores. Caso a defasagem entre estes grupos é inferior a π, um novo ritmo de oscilação diferente da frequência natural dos vértices emerge. Comportamentos dinâmicos similares são observados em osciladores caóticos sujeitos a acoplamentos análogos.

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22

Urquiza, García José María Uriel. "Mathematical model in absolute units for the Arabidopsis circadian oscillator." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31132.

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The Earth’s oblique rotation results in changes in light and temperature across the day and time of year. Living organisms evolved rhythmic behaviours to anticipate these changes and execute appropriate responses at particular times. The current paradigm for the biological clocks in several branches of life is an underlying biochemical oscillator mainly composed by a network of repressive transcription factors. The slow decay in their activity is fundamental for generating anticipatory dynamics. Interestingly, these dynamics can be well appreciated when the biological system is left under constant environmental conditions, where oscillation of several physiological readouts persists with a period close to 24 hours, hence the term “circadian clocks”, circa=around dian=day. In plants the model species Arabidopsis thaliana has served as an invaluable tool for analysing the genetics, biochemical, developmental, and physiological effects of the oscillator. Many of these experimental results have been integrated in mechanistic and mathematical theories for the circadian oscillator. These models predict the timing of gene expression and protein presence in several genetic backgrounds and photoperiodic conditions. The aim of this work is the introduction of a correct mass scale for both the RNA transcript and protein variables of the clock models. The new mass scale is first introduced using published RNA data in absolute units, from qRT-PCR. This required reinterpreting several assumptions of an established clock model (P2011), resulting in an updated version named U2017. I evaluate the performance of the U2017 model in using data in absolute mass units, for the first time for this clock system. Introducing absolute units for the protein variables takes place by generating hypothetical protein data from the existing qRT-PCR data and comparing a data-driven model with western blot data from the literature. I explore the consequences of these predicted protein numbers for the model’s dynamics. The process required a meta-analysis of plant parameter values and genomic information, to interpret the biological relevance of the updated protein parameters. The predicted protein amounts justify, for example, the revised treatment of the Evening Complex in the U2017 model, compared to P2011. The difficulties of introducing absolute units for the protein components are discussed and components for experimental quantification are proposed. Validating the protein predictions required a new methodology for absolute quantification. The methodology is based on translational fusions with a luciferase reporter than has been little used in plants, NanoLUC. Firstly, the characterisation of NanoLUC as a new circadian reporter was explored using the clock gene BOA. The results show that this new system is a robust, sensitive and automatable approach for addressing quantitative biology questions. I selected five clock proteins CCA1, LHY, PRR7, TOC1 and LUX for absolute quantification using the new NanoLUC methodology. Functionality of translation fusions with NanoLUC was assessed by complementation experiments. The closest complementing line for each gene was selected to generate protein time series data. Absolute protein quantities were determined by generation of calibration curves using a recombinant NanoLUC standard. The developed methodology allows absolute quantification comparable to the calibrated qRT-PCR data. These experimental results test the predicted protein amounts and represent a technical resource to understand protein dynamics of Arabidopsis’ circadian oscillator quantitatively. The new experimental, meta-analysis and modelling results in absolute units allows future researchers to incorporate further, quantitative biochemical data.

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23

Bavisi, Amit. "Integrated multi-mode oscillators and filters for multi-band radios using liquid crystalline polymer based packaging technoloy." Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-04062006-131113/.

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Thesis (Ph. D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2006.
Swaminathan, Madhavan, Committee Chair ; Cressler, John D., Committee Co-Chair ; Kenney, Stevenson J., Committee Member ; Peterson, Andrew, Committee Member ; Durgin, Gregory, Committee Member ; Sitaraman, Suresh, Committee Member.

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24

Chenkosol, Pitak. "Spontaneous coherent pulsations in standing-wave laser oscillators : stability criteria." PDXScholar, 1992. https://pdxscholar.library.pdx.edu/open_access_etds/4211.

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The stability criteria for single-mode standing-wave laser oscillators in the strongly homogeneously broadened limit are reported for the first time. Two types of stability criteria are presented. The first type, called type 1, corresponds to the minimum value of threshold parameter for which an infinitesimal perturbation away from steady state grows into an oscillatory solution. Another type of stability criteria, called type 2, corresponds to the minimum value of threshold parameter for which large amplitude oscillatory solutions do not decay to the steady state solution. Undamped pulsations in single mode strongly homogeneously broadened standing-wave laser oscillators are found to occur at a much higher excitation level than that of ring-laser oscillators with the same type of line broadening. The effect of detuning on stability criteria is also investigated. We discovered that detuning tends to raise the type 1 instability threshold and to decrease the type 2 instability threshold.

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25

Rühl, Axel. "The normal dispersion regime in passively mode-locked fiber oscillators." Göttingen Cuvillier, 2008. http://d-nb.info/992263050/04.

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26

Awo, Founi Mesmin. "Modes interannnuels de la variabilité climatique de l'Atlantique tropical, dynamiques oscillatoires et signatures en salinité de surface de la mer." Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30171/document.

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Dans cette thèse, nous avons abordé plusieurs thématiques liées aux modes de variabilité climatique dans l'Atlantique tropical à l'échelle interannuelle. Les analyses statistiques nous ont permis dans un premier temps de mettre en évidence les deux principaux modes dominants de cette variabilité interannuelle: un mode équatorial et un mode méridien. Le mode équatorial est responsable d'anomalies de température de surface de la mer (SST) principalement dans le Golfe de Guinée et est identifié par des variations de la pente du niveau de la mer dans la bande équatoriale. Il est dû à des rétroactions dynamiques entre le vent, le niveau de la mer et la SST. Quant au mode méridien, il se manifeste par des fluctuations inter-hémisphériques de SST et est contrôlé par des rétroactions dynamiques et thermodynamiques entre le vent, l'évaporation et la SST. L'évaluation du couplage de ces variables clés du mode méridien nous a permis de proposer un modèle conceptuel pour expliquer les principaux mécanismes responsables des oscillations du mode méridien. Le modèle a montré que le mode méridien résulte de la superposition d'un mécanisme auto-entretenu basé sur les rétroactions positives et négatives générant des oscillations régulières de haute fréquence (2-3 ans) et d'un autre mécanisme d'oscillation basse fréquence (4-9 ans) lié à l'influence d'ENSO du Pacifique Est. Comme l'évolution de ces deux modes est fortement liée au déplacement méridien de la zone de convergence intertropicale (ITCZ) qui transporte les pluies, nous avons ensuite identifié la signature de ces modes sur la salinité de la surface de la mer à l'aide observations in situ et d'une simulation numérique régionale. Les processus océaniques et/ou atmosphériques responsables de la signature de chaque mode ont été également identifiés grâce à un bilan de sel dans la couche de mélange du modèle validé. Le bilan de sel a révélé que le forçage atmosphérique, lié à la migration de l'ITCZ, contrôle la région équatoriale tandis que l'advection, due à la modulation des courants, du gradient vertical et le mélange à la base de la couche de mélange, explique les variations de SSS dans les régions sous l'influence des panaches. [...]
In this thesis, we investigate several topics related to the interannual climatic modes in the tropical Atlantic. Statistical analyses allows us to extract the two main dominant modes of interannual variability: an equatorial mode and a meridional mode. The equatorial mode is responsible for Sea Surface Temperature (SST) anomalies mainly found in the Gulf of Guinea and is linked to variations of the sea-level slope in the equatorial band. It is due to dynamic feedbacks between zonal wind, sea level and SST. The meridional mode is characterised by inter-hemispheric SST fluctuations and is controlled by dynamic and thermodynamic feedbacks between the wind, evaporation and SST. After quantifying the coupling between key variables involved in the meridional mode, we develop a conceptual model to explain the main mechanisms responsible for meridional mode oscillations. The model shows that the meridional mode results from the superposition of a self-sustaining mechanism based on positive and negative feedbacks generating regular oscillations of high frequency (2-3 years) and another low frequency oscillation mechanism (4-9 years) related to the influence of ENSO. As the evolution of these two modes is strongly linked to the meridional shift of the Intertropical Convergence Zone (ITCZ) and associated rainfall maximum, we identify the signature of these modes on Sea Surface Salinity (SSS) using in situ observations and a regional numerical simulation. Oceanic and/or atmospheric processes responsible for the signature of each mode are also identified through a mixed-layer salt budget in the validated model. The salt balance reveals that the atmospheric forcing, related to the ITCZ migration, controls the equatorial region while the advection, due to the modulation of current dynamics, the vertical gradient and mixing at the base of the mixed layer, explains SSS variations in regions under the influence of plumes. Finally, we study the Equatorial Kelvin wave characteristics and influences on the density that are involved in the meridional and equatorial mode connection processes, using a very simplified model of gravity wave propagation along the equator. After a brief description of this model, which was initially constructed to study dynamics in the equatorial Pacific, we apply it to the specific case of the equatorial Atlantic by validating its analytical and numerical solutions under adiabatic conditions. [...]

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27

Hocepied, Gatien. "Détection précoce de crises d'épilepsie à l'aide d'une modélisation du comportement oscillatoire neuronal." Doctoral thesis, Universite Libre de Bruxelles, 2012. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209579.

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28

Chen, Tingsu. "Spin Torque Oscillator Modeling, CMOS Design and STO-CMOS Integration." Doctoral thesis, KTH, Integrerade komponenter och kretsar, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-176890.

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Spin torque oscillators (STOs) are microwave oscillators with an attractive blend of features, including a more-than-octave tunability, GHz operating frequencies, nanoscale size, nanosecond switching speed and full compatibility with CMOS technology. Over the past decade, STOs' physical phenomena have been explored to a greater extent, their performance has been further improved, and STOs have already shown great potential for a wide range of applications, from microwave sources and detectors to neuromorphic computing. This thesis is devoted to promoting the STO technology towards its applications, by means of implementing the STO's electrical model, dedicated CMOS integrated circuits (ICs), and STO-CMOS IC integration. An electrical model, which can capture magnetic tunnel junction (MTJ) STO's characteristics, while enabling system- and circuit-level designs and performance evaluations, is of great importance for the development of MTJ STO-based applications. A comprehensive and compact analytical model, which is based on macrospin approximations and can fulfill the aforementioned requirements, is proposed. This model is fully implemented in Verilog-A, and can be used for efficient simulations of various MTJ STOs. Moreover, an accurate phase noise generation approach, which ensures a reliable model, is proposed and successfully used in the Verilog-A model implementation. The model is experimentally validated by three different MTJ STOs under different bias conditions. CMOS circuits, which can enhance the limited output power of MTJ STOs to levels that are required in different applications, are proposed, implemented and tested. A novel balun-low noise amplifier (LNA), which can offer sufficient gain, bandwidth and linearity for MTJ STO-based magnetic field sensing applications, is proposed. Additionally, a wideband amplifier, which can be connected to an MTJ STO to form a highly-tunable microwave oscillator in a phase-locked loop (PLL), is also proposed. The measurement results demonstrate that the proposed circuits can be used to develop MTJ STO-based magnetic field sensing and microwave source applications. The investigation of possible STO-CMOS IC integration approaches demonstrates that the wire-bonding-based integration is the most suitable approach. Therefore, a giant magnetoresistance (GMR) STO is integrated with its dedicated CMOS IC, which provides the necessary functions, using the wire-bonding-based approach. The RF characterization of the integrated GMR STO-CMOS IC system under different magnetic fields and DC currents shows that such an integration can eliminate wave reflections. These findings open the possibility of using GMR STOs in magnetic field sensing and microwave source applications.

QC 20151112

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29

Chen, Bolun. "Dimensional Reduction for Identical Kuramoto Oscillators: A Geometric Perspective." Thesis, Boston College, 2017. http://hdl.handle.net/2345/bc-ir:107589.

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Thesis advisor: Jan R. Engelbrecht
Thesis advisor: Renato E. Mirollo
Many phenomena in nature that involve ordering in time can be understood as collective behavior of coupled oscillators. One paradigm for studying a population of self-sustained oscillators is the Kuramoto model, where each oscillator is described by a phase variable, and interacts with other oscillators through trigonometric functions of phase differences. This dissertation studies $N$ identical Kuramoto oscillators in a general form \[ \dot{\theta}_{j}=A+B\cos\theta_{j}+C\sin\theta_{j}\qquad j=1,\dots,N, \] where coefficients $A$, $B$, and $C$ are symmetric functions of all oscillators $(\theta_{1},\dots,\theta_{N})$. Dynamics of this model live in group orbits of M\"obius transformations, which are low-dimensional manifolds in the full state space. When the system is a phase model (invariant under a global phase shift), trajectories in a group orbit can be identified as flows in the unit disk with an intrinsic hyperbolic metric. A simple criterion for such system to be a gradient flow is found, which leads to new classes of models that can be described by potential or Hamiltonian functions while exhibiting a large number of constants of motions. A generalization to extended phase models with non-identical couplings gives rise to richer structures of fixed points and bifurcations. When the coupling weights sum to zero, the system is simultaneously gradient and Hamiltonian. The flows mimic field lines of a two-dimensional electrostatic system consisting of equal amounts of positive and negative charges. Bifurcations on a partially synchronized subspace are discussed as well
Thesis (PhD) — Boston College, 2017
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics

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30

Kazi, Ibrahim. "Low Power Current Mode Delta-SigmaADC using Ring Oscillator basedQuantizer." Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-119803.

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Low power ADCs have wide range of applications, from battery operated systems like biomedical devices to on chip power measurement systems. A more digital implementation is also desirable to take advantage of the technology scaling in digital CMOS technologies. This thesis explores the idea of a low power continuous time Delta-Sigma ADC using current mode signaling. It achieves a second order noise shaping by using a first order current filter, a digital dierence block and a current controlled ring oscillator. This type of ADC has a mostly digital implementation, as the main analog blocks are the current-mode filter and two op-amps which are used for biasing.The behavioral level ADC is implemented in VerilogA and the transistor level ADC is deisgned in CADENCE using UMC 180nm process. MonteCarlo simulations are also performed to ensure the proper operation of the current-mode filter in presence of mismatches, as log-domain filters are very sensitive to transistors mismatches. The ADC performance obtained from transistor level simulation is 7:3 Effective Number of Bits (ENOB) over 30KHz bandwidth and 5.3W power consumption.

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31

Ramos, Edmir Ravazzi Franco. "Oscillatory interaction in a Bose-Einstein condensate: collective and topological excitations." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-28052012-152412/.

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In this work, we theoretically analyze the behavior of a Bose-Einstein condensate when it is submitted to oscillatory interactions. For that, a homogeneous magnetic field is applied, tuned near a Feshbach resonance, and then it is set to oscillate in time. This variation of the magnetic field causes a scattering length oscillation, which oscillates to interatomic interaction. Thus, we study collective and topological excitations due this oscillation in the interaction. In addition, we have seen a coupling between collective modes as well a dynamical phase transition associated to topological excitation
Neste trabalho, analisamos teoricamente o comportamento de um condensado de Bose-Einstein quando submetido a interações oscilatórias. Para tal, é aplicado um campo magnético homogêneo, sintonizado próximo a uma ressonância de Feshbach e então colocado a oscilar no tempo. Esta variação do campo magnético faz com que o comprimento de espalhamento oscile, oscilando portanto a interação entre os átomos. Com isso, estudamos as excitações coletivas e topológicas provocadas devido a oscilação da interação. Além disso, vimos o acoplamento entre modos coletivos e uma transição de fase dinâmica associada a excitação topológica

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32

Hilder, Tamsyn A. "Modelling nanostructures as nano-oscillators for applications in nanomedicine." Access electronically, 2008. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20080918.101103/index.html.

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33

Khairi, Ahmad B. "Wide-Band Multi-Mode Voltage Tuning Oscillators utilizing Phase-Change Switches." Research Showcase @ CMU, 2016. http://repository.cmu.edu/dissertations/700.

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With the emergence of multi-standard and cognitive radios, the need for reconfigurable RF circuits increased. Such circuits require wide-band quadrature voltage controlled oscillators (QVCOs) to provide the local oscillator (LO) signal for up and down conversion. Wide-band QVCOs performance has lagged behind their narrowband VCO counterparts and numerous circuit techniques have been introduced to bridge the gap. This dissertation presents techniques that have been used to implement wide-band reconfigurable QVCOs with focus on dual-resonance based circuits. System and circuit analysis are performed to understand the tuning-range, phase noise, and power tradeoffs and to consider quadrature phase errors. An 8.8-15.0 GHz actively coupled QVCO and a 13.8-20GHz passively coupled QVCO are presented. Both oscillators employ dual-resonance to achieve extended tuning ranges. Impulse sensitivity functions were used to study the impact of different passive and active device noises on the overall phase noise performance of the dual-resonance oscillator and the actively and passively coupled quadrature oscillators. The quadrature phase error due to the different architecture parameters were investigated for the actively and passively coupled quadrature oscillators. The advantages of using switched capacitor tuning as a major part of passive tuning are identified, and the advantage of employing switches with large bandwidths, such as those associated with phase change materials, is mathematically quantified. Furthermore, a novel method for accurate off chip phase error measurement using discrete components and phase shifters that does not require calibration is introduced.

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34

Ramsden, Philip. "Mode-locking in heavily damped, periodically and quasiperiodically driven nonlinear oscillators." Thesis, Queen Mary, University of London, 2009. http://qmro.qmul.ac.uk/xmlui/handle/123456789/606.

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In the case of certain nonlinear oscillators, both elapsed time t and the system’s primary state variable θ may be thought of as periodic, meaning that the state space for the oscillator may be projected on to a torus. Each orbit may therefore be characterised by a winding number. Such systems exhibit a tendency to mode-lock: that is, to tend to orbits whose winding numbers are the sums of rational multiples of the driving frequencies. Mode-locking is influenced by the amplitudes of the components of such driving, and may be induced or suppressed by adjusting these. The phenomenon of strange nonchaotic attractors is associated with mode-locking, and its absence, in quasiperiodically driven oscillators. Various driving regimes, such as harmonic (i.e. sinusoidal) driving, biharmonic quasiperiodic driving (that is quasiperiodic driving consisting of superposition of two sinusoids), and biharmonic periodic driving, give rise to systems belonging to the same family, for which a general method of deploying second-order perturbation theory has been developed and applied. In all cases, the shape of regions in parameter space associated with mode-locking may be approximated using Bessel functions, or infinite sums that involve them. These results have been compared with numerical findings resulting from simple boundary location using interval bisection. Under certain conditions, all three of the types of driving exhibit “pinching”: regions in parameter space associated with mode-locking, themselves of positive measure, have zero width along certain paths. At such points, the behaviour of these non-integrable systems becomes surprisingly regular: in the case of periodic driving, for example, all orbits become, themselves, periodic (and not merely asymptotically so). Robust numerical evidence has been collected, using algorithms developed in Mathematica, for the reality of pinching in some important regions of parameter space, but the phenomenon is also very easy to break down (either by leaving such regions or through introducing certain kinds of harmonic).

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35

Becker-Weimann, Sabine. "Modeling feedback loops in the mammalian circadian oscillator." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2010. http://dx.doi.org/10.18452/16148.

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In den meisten Organismen tickt eine zirkadiane Uhr mit einer Periode von ungefähr 24 Stunden. Sie ermöglicht ihnen die Zeitmessung ohne äußere Signale. Viele physiologische und zelluläre Prozesse unterliegen zirkadianer Regulation. Die molekulare Uhr besteht aus gekoppelten intrazellulären Rückkopplungen: Die Produkte der Uhrgene regulieren ihre eigene Bildung direkt oder indirekt und erzeugen so molekulare Oszillationen. In dieser Arbeit werden bestehende und neue mathematische Modelle des zirkadianen Oszillators verwendet, um die Bedeutung struktureller Merkmale - insbesondere der Rückkopplungen - für grundlegende zirkadiane Eigenschaften zu untersuchen. In einem Modell (Goodwin-Modell), mit einer negativen Rückkopplung erleichtert sättigende Kinetik in einem Abbauterm, nicht aber in einem Produktionsterm, Oszillationen. Ein neues Modell mit zusätzlicher positiver Rückkopplung erzeugt korrekte Phasen zwischen den Komponenten. Es reproduziert die Phänotypen von zirkadianen Mutanten. Das Modell synchronisiert mit dem Licht/Dunkel-Rhythmus. Die positive Rückkopplung beeinflußt die Robustheit der Oszillationen gegenüber Parametervariationen nur gering. Dies erklärt den rhythmischen Phänotyp von Rev-erb alpha-/- Mäusen, die die positive Rückkopplung nicht besitzen. Die überraschende Wiederherstellung von zirkadianen Oszillationen in der Per2Brdm1/Cry2-/- Doppelmutante kann mit dem Modell erklärt werden. Die Wiederherstellung zirkadianer Oszillationen in der arhythmischen Per2Brdm1 Mutante durch zusätzliche Mutation von Rev-erb alpha-/- wird vorausgesagt. Durch das Einfügen von Rev-erb alpha in das Modell entsteht eine weitere Rückkopplung. Mit diesem neuen Modell koennen Phänotypen von Mutanten reproduziert werden. Zuletzt werden Modelle verschiedener molekularer Oszillatoren und allgemeine Modelle, die aus einer positiven oder negativen Rückkopplung unterschiedlicher Kettenlänge bestehen, bezüglich ihrer Robustheit bei Parametervariationen verglichen. Die strukturelle Anordnung und speziell die Art der Rückkopplung ist wichtig für die Robustheit der Modelle. Die weitere Untersuchung zirkadianer Eigenschaften mit diesen und anderen Modellen wird zum Verständnis der zugrundeliegenden Prinzipien des zirkadianen Oszillators beitragen.
In many organisms the circadian clock ticks with a period of approximately 24 hours, enabling the organisms to keep track of time without any environmental time cues. Many physiological and cellular processes underlie circadian regulation. The molecular clock is a network of intracellular feedback loops: The clock gene products directly or indirectly regulate their own transcription, which results in molecular oscillations. In this thesis, existing and new mathematical models of the circadian oscillator are used to investigate the meaning of structural features - in particular of the feedback loops - for fundamental circadian characteristics. In a simple model (Goodwin model) with one negative feedback loop, saturating kinetics in a degradation term, but not in a production term, support oscillations. A new model containing an additional positive feedback loop shows circadian oscillations with the correct phases between the clock components. The phenotype of several clock mutants can be reproduced. The model synchronizes with the light/dark cycle. Assuming restricted light-input (gating), its phase can be fixed to either light onset or light offset with varying day lengths. In this model, the positive feedback has only a minor influence on the robustness of the circadian oscillations towards parameter variations. This explains the rhythmic phenotype of Rev-erb alpha-/- mutant mice that lack a positive feedback. The model can also explain the unexpected regeneration of circadian oscillations in Per2Brdm1/ Cry2-/- double mutant mice. The regeneration of circadian oscillations in the arrhythmic Per2Brdm1 by additional mutation of Rev-erb alpha is predicted. By including Rev-erb alpha explicitly into the model, another negative feedback loop is added: This model reproduces the phenotypes of several clock mutants. Finally, models describing different molecular oscillators and general models with positive or negative feedback loops of varying chain length are compared with respect to their robustness towards parameter variation. The structural design and in particular the kind of feedback underlying the oscillator seems important for the robustness of the model. Further analysis of circadian features with these and other models will give insight into underlying principles of the circadian oscillator.

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36

Brown, Catherine Alicia. "Oscillatory behavior in an ocean general circulation model of the North Atlantic." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0004/MQ46006.pdf.

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37

Wong, Lok Haw. "A numerical model for vortex shedding from sharp wedges in oscillatory flow." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/28731.

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This thesis describes a numerical simulation and some flow visualization of vortex shedding from sharp edges in normal oscillatory flow. The modelling of vortex shedding from sharp edges has been done using a discrete vortex method; the separated shear layer issuing from the separation point is represented by a system of discrete two dimensional vortices. In Chapter Two, a finite wedge is modelled by considering the flow near the edge as the inner region of an oscillatory flow around an infinite wedge. This can be done if the Keulegan-Carpenter number is low, i.e. if the vortex hedding takes place mostly in the vicinity of the edge and is independent of shedding from any other edge(s). The mathematical formulation of this problem, although based on the combination of recent work of other researchers, represents a somewhat different approach when examined in detail. Each new vortex, called the nascent vortex, is introduced into the flow at a position not fixed in advance. Its position is dependent on the edge angle, the time step used in the numerical simulation and the influence of all the other vortices in the field. The expression describing the position of the nascent vortex can be derived as a natural development of the formulation. Therefore, it is not necessary to use empirical formulae to define the initial position of the nascent vortex and/or to fix this position for all time throughout the numerical simulation. Lamb vortices are used in the present study to delay the onset of instability in the numerical calculations. This results in very stable computations. Numerical modelling results concerning vortex induced forces are presented in Chapter Three. These results are then compared to those obtained numerically and experimentally by other researchers. Flow visualization experiments of vortex shedding from finite sharp wedges in an oscillatory flow are described in Chapter Four. The flow was produced using a sloshing tank, and visualized by hydrogen bubbles produced by the electrolysis of water. All results were recorded on video tape and photographs of flow visualizations have been produced through the use of a mirco-computer based frame grabber. The kinematics of the numerical modelling are compared to those obtained from flow visualizations. An application of the model to the roll decay of a simplified geometry of a single chine west coast trawler is presented in Chapter Five. No firm conclusions regarding the accuracy of the numerical prediction of roll decay can be drawn due to the gross simplification of the vessel section. However, the results do indicate that, with the absence of other forms of roll damping, vortex induced forces alone was able to cause roll extinction in the vessel. Therefore, it can be said that the prediction of roll extinction given by the present model is of an acceptable order of magnitude when compared to experimental roll decay results from previous work done in this department.
Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate

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38

Baldemir, Harun. "A mathematical study of complex oscillatory behaviour in an excitable cell model." Thesis, University of Exeter, 2018. http://hdl.handle.net/10871/34029.

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Inner hair cells (IHCs) are the actual sensory receptors in hearing. Immature IHCs generate spontaneous calcium-dependent action potentials. Changing the characteristic of the Ca2Å signals modulates the amplitude and duration of the action potentials in these cells. These spontaneous action potential firing patterns are thought to be important for the development of the auditory system. The aim of this thesis is to gain a deeper understanding of the electrical activity and calcium signalling during development of IHCs from a mathematical point of view. A numerical bifurcation analysis is performed to delineate the relative contributions of the model parameters to the asymptotic behaviour of the model. In particular, we investigate the pattern of periodic solutions including single (normal) spiking, pseudoplateau burstings and complex solutions using two-parameter sections of the parameter space. We also demonstrate that a simplified (three-dimensional) model can generate similar dynamics as the original (four-dimensional) IHC model. This reduced model could be characterised by two fast and one slow or one fast and two slow variables depending on the parameters’ choice. Hence, the mechanisms underlying the bursting dynamics and mixed mode oscillations in the model are studied applying 1-slow/2-fast and 2-slow/1-fast analysis, respectively.

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39

Favreau, John T. "Oscillatory wall strain reduction precedes arterial intimal hyperplasia in a murine model." Digital WPI, 2014. https://digitalcommons.wpi.edu/etd-dissertations/172.

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Cardiovascular diseases (CVD) remain the most common cause of death in the United States. Additionally, peripheral artery disease affects thousands of people each year. A major underlying cause of these diseases is the occlusion of the coronary or peripheral arteries due to arteriosclerosis. To overcome this, a number of vascular interventions have been developed including angioplasty, stenting, endarterectomies and bypass grafts. Although all of these methods are capable of restoring blood flow to the distal organ after occlusion, they are all plagued by unacceptably high restenosis rates. While the biological reactions that occur as a result of each of these methods differ, the initiating factor of both the primary atherosclerosis and subsequent failure of vascular interventions appears to be intimal hyperplasia (IH). Intimal hyperplasia is most simply defined as the expansion of multiple layers of cells internally to the internal elastic lamina of the blood vessel. This excessive cellular growth leads to arterial stenosis, plaque formation and inflammatory reactions. Despite extensive research the underlying factors that cause IH remain unclear. A quantity of research to date has implicated endothelial cell mechanosensation as the mechanism by which IH is initiated with evidence positively correlating wall shear stress with IH. Others, however, have demonstrated that changes in the stresses applied to the wall in vitro can modulate IH independent of hemodynamic shear stress. Thus, relations between wall tensile stress and IH in vivo may shed light on the underlying mechanisms of IH. Since noninvasive measurement of wall tensile stress in vivo is difficult, it is most feasible to measure oscillatory wall strain which is intimately related to wall tensile stress through the mechanical properties of the arterial wall. In this dissertation, we hypothesize that reductions in oscillatory wall strain precede the formation of intimal hyperplasia in a murine model. To test our hypothesis, we first developed a novel, high spatial and temporal resolution method to measure oscillatory wall strains in the murine common carotid artery. We validated this method both in vitro using an arterial phantom and in vivo using a murine model of abdominal aortic aneurysms. To assess relationships between strain and IH, we applied our strain measurement technique to a recently developed mouse model of IH. In this model, a suture is used to create a focal stenosis and reduce flow through the common carotid artery by 85%; resulting in proximal IH formation. Using this approach, we identified a relationship between oscillatory strain reductions and IH. Subsequent analysis demonstrated that early reductions in mechanical strain just 4 days after focal stenosis creation correlate with IH formation nearly 1 month later. Since IH is not expected to form by day 4 in this model, we went on to assess changes in gross vascular morphology at day 4. We discovered that, although strains are significantly reduced by day 4, no significant IH can be observed, suggesting that changes in wall structure are resulting in strain reductions. At day 4 post-op, we observed cellular proliferation and leukocyte recruitment to the wall without intimal hyperplasia. These studies suggest that early reductions in mechanical strain may be an important predictor of IH formation. Clinically, this relation could be important for the development of novel techniques for predicting IH formation before it becomes hemodynamically significant.

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40

Bharath, Ranjeetha. "Nonlinear observer design and synchronization analysis for classical models of neural oscillators." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/83684.

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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 37-38).
This thesis explores four nonlinear classical models of neural oscillators, the Hodgkin- Huxley model, the Fitzhugh-Nagumo model, the Morris-Lecar model, and the Hindmarsh-Rose model. Analysis techniques for nonlinear systems were used to develop a set of observers and perform synchronization analysis on the aforementioned neural systems. By using matrix analysis techniques, a study of biological background and motivation, and MATLAB simulation with mathematical computation, it was possible to do a preliminary contraction and nonlinear control systems structural study of these classical neural oscillator models. Neural oscillation and signaling models are based fundamentally on the biological function of the neuron, with behavior mediated through the channeling of ions across a cell membrane. The variable assumed to be measured for this study is the voltage or membrane potential, which could be measured empirically through the use of a neuronal force-clamp system. All other variables were estimated by using the partial state and full state observers developed here. Preliminary observer rate convergence analysis was done for the Fitzhugh-Nagumo system, and preliminary synchronization analysis was done for both the Fitzhugh-Nagumo and the Hodgkin- Huxley systems. It was found that by using a variety of techniques and mathematical matrix analyses methods (e.g. diagonal dominance or other norms), it was possible to develop a case-by-case nonlinear control systems approach to each particular system as a biomathematical entity.
by Ranjeetha Bharath.
S.B.

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41

Noble, Jeffrey Scott, and Jeffrey Scott Noble. "Laser Gyroscope based on Synchronously Pumped Bidirectional Fiber Optical Parametric Oscillator." Thesis, The University of Arizona, 2017. http://hdl.handle.net/10150/625701.

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This master thesis presents an experimental design of a laser gyroscope based on a stabilized fiber optical parametric oscillator frequency comb and the results of testing of the proposed design. Before going into the experimental details, a background for different types of gyroscopes is discussed. This new laser gyroscope design is made up of only polarization maintaining (PM) fiber and PM fiber components. By using only fiber and fiber components, we were able to minimize size, weight, and alignment issues that are typical in bulk optical designs for OPO's and gyroscopes. The fiber-based OPO produces counter propagating ultrafast pulses that overlap only twice in the cavity, resulting in a beatnote signal when combined outside of the laser cavity. A mode-locked laser is used as a pump source so the lock-in effect (or deadband region) is avoided for the experiment. The drift of this beatnote signal represents the rotation sensitivity of the experimental setup. Issues seen in past iterations, such as stability of mode-locked pump source and beatnote drift overtime due to environmental variables, have been reduced in this experiment. This has been done by comprising the entire pump source of PM components, and by placing the entire setup in an insulating box to minimize acoustic and temperature fluctuations. By creating a frequency comb and locking the laser gyroscope to an optical clock, this experiment can be used for very precise rotation sensing in comparison to other gyro designs currently available.

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42

Metka, Matthew. "Application of Fluidic Oscillator Separation Control to a Square-back Vehicle Model." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1439205355.

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43

Auroux, Vincent. "Application des lasers fibrés à verrouillage de modes à la génération très haute fréquence à haute pureté spectrale." Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30103/document.

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Le développement technologique dans le domaine des télécommunications, ainsi que des systèmes de détection, a accru ces dernières années la nécessité de signaux de référence présentant une très haute pureté spectrale. L'augmentation des débits, la saturation des bandes de fréquence ainsi que les performances imposées pour la détection radar ont ouvert la voie à la génération micro-onde par l'optique. Ces références de fréquence sont souvent issues d'oscillateurs optoélectroniques (OEO). Ces oscillateurs intègrent un élément de stockage de l'énergie au travers de résonateurs ou de longues lignes à retard fibrées afin d'augmenter leur facteur qualité et permettant ainsi d'atteindre des performances supérieures aux signaux multipliés à partir de sources basses fréquences ou directement à partir d'oscillateurs micro-ondes à résonateur diélectrique (DRO). Une topologie originale d'oscillateurs optoélectroniques a été proposée à la fin des années 1990 par une équipe américaine : il s'agit de remplacer le résonateur passif nécessitant un verrouillage du laser sur ce dernier par un résonateur actif, intégrant un amplificateur optique. Ce résonateur actif, un laser à blocage de modes, permet un couplage entre l'oscillation optique du laser et l'oscillation optoélectronique. On parle alors d'oscillateur optoélectronique couplé (COEO). Les performances du COEO sont étroitement liées à la pureté spectrale du signal issu du laser à blocage de modes. Ce travail de thèse traite de l'étude et de l'optimisation de ces systèmes. Une étude approfondie sur le bruit dans les amplificateurs optiques a tout d'abord été menée afin de déterminer quel type d'amplificateur choisir pour le COEO et sous quelles conditions l'amplification optique apporte un bruit de phase minimal. Ensuite, un COEO à 10 GHz a été réalisé, présentant un très faible bruit de phase atteignant - 132 dBc/Hz à 10 kHz de la porteuse. Un modèle a par ailleurs été implémenté, permettant de déterminer a posteriori l'efficacité du couplage et ainsi la bande de verrouillage entre l'oscillation optoélectronique et le laser à blocage de modes. Ce couplage interne dépend fortement de la dynamique du système. Cependant, les différents effets non linéaires qui ont lieu dans l'amplificateur à semiconducteur et les fibres ne permettent pas d'obtenir un modèle analytique. Un modèle itératif a alors été proposé afin d'obtenir les propriétés de l'enveloppe complexe lentement variable du peigne de fréquence généré en sortie du laser dont la photodétection conduit à la puissance RF générée par le COEO. Le COEO génère un peigne de fréquence suffisamment large pour produire des harmoniques RF supérieurs à la fréquence de répétition du laser à blocage de modes, si les modes longitudinaux espacés de plusieurs intervalles spectraux libres (ISL) sont en phase. Le modèle itératif développé permet, à partir des paramètres expérimentaux de déterminer le spectre optique ainsi que la distribution de phase à l'intérieur de celui-ci. Il est possible alors d'augmenter la puissance d'une harmonique en sortie de la photodiode par un ajout d'éléments dispersifs. Cette multiplication de fréquence permet la génération de signaux à haute pureté spectrale en bande millimétrique. Une démonstration expérimentale à 90 GHz a été proposée, basée sur un COEO fonctionnant à 30 GHz. Ces résultats sont prometteurs et une intégration du COEO dans un boîtier thermalisé ainsi qu'une gestion plus fine de la dispersion des fibres peut permettre des améliorations significatives sur le bruit de phase du système
The important rise of telecommunication systems in the past decades, together with the sensitivity improvement of radar systems, has increased the necessity for high spectral purity frequency references at high frequencies. The saturation of classical microwave bandwidths motivated the search of frequency references at higher frequencies, such as K-band. Frequency multiplication from highly stable sources, such as quartz sources, is limited by the increase of the noise floor, which is often prohibitive at millimeter wave frequencies. On the contrary, microwave generation using optics becomes a very efficient technique in this frequency range. Indeed, passive optical resonators or delay lines feature a high Q factor which can be used to stabilize the microwave frequency. The best phase noise performance is today obtained with long delay line oscillators. However, a spurious mode suppression technique has to be implemented in this type of OEOs. The use of an active optical resonator is a third solution, which avoids any locking technique between the laser and the passive resonator. The first architecture of this type has been proposed at the end of the 1990's. In such a system, a mode-locked laser is coupled to a microwave oscillator (COEO). COEO phase noise performances are strongly dependent on the spectral purity of the mode locked laser signal. This thesis work focus on the study and the optimization of this system. Optical amplifiers noise is firstly investigated, in order to determine the optimal conditions to minimize their phase noise contribution to the COEO. A 10 GHz SOA based COEO has been realized and features a low phase noise level reaching - 132 dBc/Hz at 10 kHz from the carrier. An analytical model has also been developed to obtain the locking range of the coupled oscillations. This frequency range is strongly dependent on the coupling efficiency between optical oscillation and the optoelectronic oscillation. This parameter cannot be calculated analytically and an iterative model has been proposed to determine the amplitude and phase of the optical spectrum. Therefore, one can calculate the RF power on the photodiode, on which the coupling efficiency is depending. Since COEO features a large optical frequency comb where each tooth of the comb is phase locked thanks to the mode locked laser, harmonic generation from COEO is possible. Wide frequency comb from high frequency COEO allow millimeter wave generation. The iterative model developed in this work enable to determine the RF power of one specified harmonic from experimental parameters. Harmonic selection can also be performed through the management of the chromatic dispersion. Such frequency multiplication has been implemented to generate a high purity 90 GHz signal from a 30 GHz COEO.These results are promising and an integration of the system in a thermalized box is under process

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44

Cao, Zhixin. "Non-oscillatory forward-in-time method for incompressible flows." Thesis, Loughborough University, 2018. https://dspace.lboro.ac.uk/2134/33265.

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This research extends the capabilities of Non-oscillatory Forward-in-Time (NFT) solvers operating on unstructured meshes to allow for accurate simulation of incompressible turbulent flows. This is achieved by the development of Large Eddy Simulation (LES) and Detached Eddy Simulation (DES) turbulent flow methodologies and the development of parallel option of the flow solver. The effective use of LES and DES requires a development of a subgrid-scale model. Several subgrid-scale models are implemented and studied, and their efficacy is assessed. The NFT solvers employed in this work are based on the Multidimensional Positive Definite Advection Transport Algorithm (MPDATA) that facilitates novel implicit Large Eddy Simulation (ILES) approach to treating turbulence. The flexibility and robustness of the new NFT MPDATA solver are studied and successfully validated using well established benchmarks and concentrate on a flow past a sphere. The flow statistics from the solutions are compared against the existing experimental and numerical data and fully confirm the validity of the approach. The parallel implementation of the flow solver is also documented and verified showing a substantial speedup of computations. The proposed method lays foundations for further studies and developments, especially for exploring the potential of MPDATA in the context of ILES and associated treatments of boundary conditions at solid boundaries.

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45

Waywell, M. N. "Predictions of wave and tidally induced oscillatory flows with Reynolds stress turbulence models." Thesis, University of Salford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308264.

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46

Kozhushko, A. P., and K. Riezva. "Comparison a running smoothness of a wheeled tractor with a semitrailer tank or unit while driving on asphalt-concrete surface." Thesis, Scientific Route, Estonia, 2019. http://repository.kpi.kharkov.ua/handle/KhPI-Press/46135.

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47

Dong, Zhi-wei. "Simulation study on mode-medium interaction in a Free Electron Laser oscillator." Kyoto University, 2001. http://hdl.handle.net/2433/150495.

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Kyoto University (京都大学)
0048
新制・課程博士
博士(エネルギー科学)
甲第9049号
エネ博第36号
新制||エネ||10(附属図書館)
UT51-2001-F379
京都大学大学院エネルギー科学研究科エネルギー変換科学専攻
(主査)教授吉川潔, 教授山嵜鉄夫, 教授若谷誠宏
学位規則第4条第1項該当

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48

Tönjes, Ralf. "Pattern formation through synchronization in systems of nonidentical autonomous oscillators." Phd thesis, Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1597/.

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Анотація:

This work is concerned with the spatio-temporal structures that emerge when non-identical, diffusively coupled oscillators synchronize. It contains analytical results and their confirmation through extensive computer simulations. We use the Kuramoto model which reduces general oscillatory systems to phase dynamics. The symmetry of the coupling plays an important role for the formation of patterns. We have studied the ordering influence of an asymmetry (non-isochronicity) in the phase coupling function on the phase profile in synchronization and the intricate interplay between this asymmetry and the frequency heterogeneity in the system. The thesis is divided into three main parts. Chapter 2 and 3 introduce the basic model of Kuramoto and conditions for stable synchronization. In Chapter 4 we characterize the phase profiles in synchronization for various special cases and in an exponential approximation of the phase coupling function, which allows for an analytical treatment. Finally, in the third part (Chapter 5) we study the influence of non-isochronicity on the synchronization frequency in continuous, reaction diffusion systems and discrete networks of oscillators.
Die vorliegende Arbeit beschäftigt sich in Theorie und Simulation mit den raum-zeitlichen Strukturen, die entstehen, wenn nicht-identische, diffusiv gekoppelte Oszillatoren synchronisieren. Wir greifen dabei auf die von Kuramoto hergeleiteten Phasengleichungen zurück. Eine entscheidene Rolle für die Musterbildung spielt die Symmetrie der Kopplung. Wir untersuchen den ordnenden Einfluss von Asymmetrie (Nichtisochronizität) in der Phasenkopplungsfunktion auf das Phasenprofil in Synchronisation und das Zusammenspiel zwischen dieser Asymmetrie und der Frequenzheterogenität im System. Die Arbeit gliedert sich in drei Hauptteile. Kapitel 2 und 3 beschäftigen sich mit den grundlegenden Gleichungen und den Bedingungen für stabile Synchronisation. Im Kapitel 4 charakterisieren wir die Phasenprofile in Synchronisation für verschiedene Spezialfälle sowie in der von uns eingeführten exponentiellen Approximation der Phasenkopplungsfunktion. Schliesslich untersuchen wir im dritten Teil (Kap.5) den Einfluss von Nichtisochronizität auf die Synchronisationsfrequenz in kontinuierlichen, oszillatorischen Reaktions-Diffusionssystemen und diskreten Netzwerken von Oszillatoren.

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49

Wang, Taige. "Mathematical Analysis on the PEC model for Thixotropic Fluids." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/70907.

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Анотація:

A lot of fluids are more complex than water: polymers, paints, gels, ketchup etc., because of big particles and their complicated microstructures, for instance, molecule entanglement. Due to this structure complexity, some material can display that it is still in yielded state when the imposed stress is released. This is referred to as thixotropy. This dissertation establishes mathematical analysis on a thixotropic yield stress fluid using a viscoelastic model under the limit that the ratio of retardation time versus relaxation time approaches zero. The differential equation model (the PEC model) describing the evolution of the conformation tensor is analyzed. We model the flow when simple shearing is imposed by prescribing a total stress. One part of this dissertation focuses on oscillatory shear stresses. In shear flow, different fluid states corresponding to yielded and unyielded phases occur. We use asymptotic analysis to study transition between these phases when slow oscillatory shearing is set up. Simulations will be used to illustrate and supplement the analysis. Another part of the dissertation focuses on planar Poiseuille flow. Since the flow is spatially inhomogeneous in this situation, shear bands are observed. The flow is driven by a homogeneous pressure gradient, leading to a variation of stress in the cross-stream direction. In this setting, the flow would yield in different time scales during the evolution. Formulas linking the yield locations, transition width, and yield time are obtained. When we introduce Korteweg stress in the transition, the yield location is shifted. An equal area rule is identified to fit the shifted locations.
Ph. D.

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50

El, Ati Ali. "Synchronization analysis of complex networks of nonlinear oscillators." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112362/document.

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Cette thèse porte sur l'analyse de la synchronisation des grands réseaux d'oscillateurs non linéaires et hétérogènes à l'aide d'outils et de méthodes issues de la théorie du contrôle. Nous considérons deux modèles de réseaux; à savoir, le modèle de Kuramoto qui considère seulement les coordonnées de phase des oscillateurs et des réseaux composés d'oscillateurs non linéaires de Stuart-Landau connectés par un couplage linéaire.Pour le modèle de Kuramoto nous construisons un système linéaire qui conserve les informations sur les fréquences naturelles et sur les gains d'interconnexion du modèle original de Kuramoto. Nous montrons en suite que l'existence de solutions à verrouillage de phase du modèle de Kuramoto est équivalente à l'existence d'un tel système linéaire avec certaines propriétés. Ce système est utilisé pour formuler les conditions d'existence de solutions à verrouillage de phase et de leur stabilité pour des structures particulières de l'interconnexion. Ensuite, cette analyse s'est étendue au cas où des interactions attractives et répulsives sont présentes dans le réseau. Nous considérons cette situation lorsque les gains d'interconnexion peuvent être à la fois positif et négatif. Dans le cadre de réseaux d'oscillateurs de Stuart-Landau, nous présentons une nouvelle transformation de coordonnées du réseau qui permet de réécrire le modèle du réseau en deux parties: une décrivant le comportement de l'oscillateur « moyenne » du réseau et la seconde partie présentant les dynamiques des erreurs de synchronisation par rapport à cet oscillateur « moyenne ». Cette transformation nous permet de caractériser les propriétés du réseau en termes de la stabilité des erreurs de synchronisation et du cycle limite de l'oscillateur « moyenne ». Pour ce faire, nous reformulons ce problème en un problème de stabilité de deux ensembles compacts et nous utilisons des outils issus de la stabilité de Lyapunov pour montrer la stabilité pratique de ces derniers pour des valeurs suffisamment grandes du gain d'interconnexion
This thesis is devoted to the analysis of synchronization in large networks of heterogeneous nonlinear oscillators using tools and methods issued from control theory. We consider two models of networks; namely, the Kuramoto model which takes into account only phase coordinates of the oscillators and networks composed of nonlinear Stuart-Landau oscillators interconnected by linear coupling. For the Kuramoto model we construct an auxiliary linear system that preserves information on the natural frequencies and interconnection gains of the original Kuramoto model. We show next that existence of phase locked solutions of the Kuramoto model is equivalent to the existence of such a linear system with certain properties. This system is used to formulate conditions that ensure existence of phase-locked solutions and their stability for particular structures of network interconnections. Next, this analysis is extended to the case where both attractive and repulsive interactions are present in the network that is we consider the situation where some of the interconnection gains are allowed to be negative. In the context of networks of Stuart-Landau oscillators, we present a new coordinate transformation of the network which allows to split the network model into two parts, one describing behaviour of an "averaged" network oscillator and the second one, describing dynamics of the synchronization errors relative to this "averaged" oscillator. This transformation allows us to characterize properties of the network in terms of stability of synchronization errors and limit cycle of the "averaged" oscillator. To do so, we recast this problem as a problem of stability of compact sets and use Lyapunov stability tools to ensure practical stability of both sets for sufficiently large values of the coupling strength

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