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Chen, Danjue. « Studies of traffic oscillations : a behavioral perspective ». Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/48975.
Texte intégralRésumé :
Traffic oscillations, or simply stop-and-go waves, are a common phenomenon arising in congested traffic but still not well understood. This phenomenon causes broad adverse impacts to safety risk, fuel efficiency and greenhouse emission. To eliminate or reduce those impacts, understanding the cause and propagation mechanism is essential. This dissertation studied driving behavior in traffic oscillations with the objective to uncover the formation and propagation mechanism of traffic oscillations. This study establishes a behavioral car-following model, the Asymmetric Behavioral model, based on empirical trajectory data that is able to reproduce the spontaneous formation and ensuing propagation of traffic oscillations in congested traffic. By analyzing individual drivers' car-following behavior throughout oscillation cycles it is found that this behavior is consistent across drivers and can be captured by a simple model. The statistical analysis of the model's parameters reveals that driver' behavior during oscillation (i.e., reaction to oscillation) is strongly correlated with driver behavior before oscillations and it varies with the development stage of the oscillation. Simulation of the model shows that it is able to produce characteristics of traffic oscillations consistently with empirical observations. This study also unveils the generation mechanism of the traffic hysteresis phenomenon arising in traffic oscillations using the Asymmetric Behavioral model. It is found that the occurrence of traffic hysteresis is closely correlated with driver behavior when experiencing traffic oscillations. In the growth and fully-developed stage of traffic oscillations, drivers behave differently, which results in different distribution of hysteresis patterns. This research makes it possible to unveil new management and control strategies of traffic oscillations to improve traffic operation and to quantify the environmental and safety impacts of traffic oscillations. For example, it can be used to estimate the increase of greenhouse emission and decrease of fuel efficiency imposed by traffic oscillations. It can also be used to study the increase of accident rate.
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Siegle, Joshua H. (Joshua Hangman). « Causal evidence for the behavioral impact of oscillations in neocortex and hippocampus ». Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/95857.
Texte intégralRésumé :
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Brain and Cognitive Sciences, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references.
Neuroscientists hold widely divergent opinions on the behavioral relevance of oscillatory brain states. Some consider them to be a side effect of anatomical connectivity, with little or no role in guiding action. Others view them as a fundamental feature of the network states that underlie perception and cognition. In this thesis, I take a systematic approach to studying two of the most prominent types of oscillations,'gamma rhythms in the neocortex (30-80 Hz) and theta rhythms in the hippocampus (4-12 Hz). In both cases, I use light-gated ion channels to manipulate spike activity on a cycle-by-cycle basis in awake, behaving mice. By rhythmically stimulating fast-spiking interneurons in somatosensory cortex, I can emulate the activity patterns that define gamma oscillations under natural conditions. Emulating gamma enhances the detection of threshold-level vibrissae deflections, analogous to the behavioral effects of shifting attention. By triggering stimulation of fast-spiking interneurons in the hippocampus on peaks and troughs of endogenous rhythms, I can reduce spike activity at specific phases of theta. In the context of a spatial navigation task, I find that the ability of inhibition to enhance decision-making accuracy depends on both the theta phase and the task segment in which it occurs. Both of these experiments provide novel causal evidence for the behavioral impact of oscillations, which offers a much more compelling argument for their utility than traditional correlative measures. Finally, I present a new platform for extracellular electrophysiology. This platform, called Open Ephys, makes the closed-loop experiments that are ideal for studying oscillations accessible to a wider audience.
by Joshua H. Siegle.
Ph. D.
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Cicchese, Joseph John. « Theta Oscillations Modulate Hippocampal Single-Unit Responses Across Subregions During Trace Eyeblink Classical Conditioning ». Miami University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=miami1466187297.
Texte intégral
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Hadzibegovic, Senka. « Behavioral, molecular and electrophysiological characterization of the learning and memory deficits induced in mouse models of Alzheimer’s disease ». Thesis, Bordeaux, 2015. http://www.theses.fr/2015BORD0151/document.
Texte intégralRésumé :
La maladie d’Alzheimer (MA) se caractérise par une perte des fonctions cognitives liée à une dégénérescence neuronale induite par l’accumulation de peptides amyloïdes-β (Aβs) dans des régions vulnérables du cerveau comme l’hippocampe. Au niveau moléculaire, les peptides Aβs se lient préférentiellement à la densité post-synaptique des synapses excitatrices, espace au niveau duquel la protéine d’échafaudage PSD-95 organise l’ancrage des récepteurs NMDA (RNMDAs) et régule leur mobilité membranaire. A l’aide d’une stratégie intégrative qui favorise des niveaux d’analyse verticaux (du phénotype aux événements moléculaires) et qui combine un ensemble d’approches corrélatives et invasives chez des souris double transgéniques APPswe/PS1dE9 modèles de la MA, nous avons mis en évidence que les peptides Aβs déstabilisent l’organisation synaptique (altération de l’expression de la PSD-95) et augmentent le pool extrasynaptique de sous-unités GluN2B des RNMDAs dans l’hippocampe. Cette réorganisation se traduit par une perturbation des fonctions mnésiques. Par ailleurs, il a été montré que certaines oscillations de l’activité hippocampique, comme les « sharp-wave ripples » (SWRs) générées pendant les périodes de sommeil, jouent un rôle crucial dans la formation de la mémoire. De façon surprenante, l’accumulation des peptides Aβs semble épargner la dynamique d’expression des SWRs durant les comportements de routine. Afin d’examiner l’effet potentiel des Aβs sur les SWRs chez des animaux confrontés à des challenges cognitifs, nous avons soumis des souris adultes injectées intracérébralement avec une solution d’Aβs à un test de reconnaissance spatiale. Alors qu’elles sont capables de former une mémoire à court terme, les souris Aβs montrent un oubli plus rapide, suggérant qu’elles encodent avec succès, mais qu’elles sont incapables de stabiliser et de rappeler une information acquise antérieurement. En l’absence d’une demande cognitive préalable, les propriétés des SWRs ne sont pas altérées par les Aβs. En revanche, lorsqu’elles doivent résoudre un test cognitif, les pics de SWRs normalement observés après encodage ou reconnaissance chez les souris témoins sont abolis chez les souris Aβs, indiquant une perturbation du traitement hippocampique de l’information spatiale. Pris dans leur ensemble, ces résultats identifient deux nouveaux mécanismes délétères sous-tendant les déficits de mémoire spatiale associés à la MACognitive impairments in Alzheimer’s disease (AD) are thought to be related to degenerative synaptic changes caused by the accumulation of amyloid-β peptides (Aβs) in vulnerable brain regions such as the hippocampus. At the molecular level, Aβs bind preferentially to the postsynaptic density of neuronal excitatory synapses, where the scaffolding post-synaptic protein-95 (PSD-95) organizes NMDA receptor (NMDAR) location as well as its downstream signaling. By using an integrative strategy which favoured vertical levels of analyses (from phenotype to molecular events) and combined a set of interrelated correlative and invasive approaches in a double transgenic mouse model of AD (APPswe/PS1dE9 mice), we were successful in establishing that Aβs destabilize the synaptic organization (reduction of expression of PSD-95) and increase the extrasynaptic pool of GluN2B-containing NMDAR in the hippocampus, a reorganization which translates into impaired memory functions. It is also well-known that hippocampal sharp wave-ripples (SWRs) generated during sleep periods are crucial for memory formation but accumulation of soluble Aβs, surprisingly seems to spare SWR dynamics during routine behavior. To unravel a potential effect of Aβs on SWRs in cognitively-challenged animals, we submitted vehicle- and Aβ-injected mice to spatial recognition memory testing. While capable of forming short-term memory, Aβ mice exhibited faster forgetting, suggesting successful encoding but an inability to adequately stabilize and/or retrieve previously acquired information. Without prior cognitive requirements, similar properties of SWRs were observed in both groups. In contrast, when cognitively challenged, the post-encoding and -recognition peaks in SWR occurrence observed in controls were abolished in Aβ mice, indicating impaired hippocampal processing of spatial information. Altogether these results identify two new disruptive mechanisms for the spatial memory deficits associated with AD
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Rabiller, Gratianne. « Contribution of hippocampal diaschisis to the memory deficits associated with focal cerebral ischemia in the rat : converging behavioral, electrophysiological and functional evidence ». Thesis, Bordeaux, 2015. http://www.theses.fr/2015BORD0461/document.
Texte intégralRésumé :
Les mécanismes impliqués dans les troubles cognitifs induits à la suite d’une ischémie cérébrale (IC) demeurent mal compris. En plus du cœur ischémique nécrosé et de la zone de pénombre entourant cette lésion, certaines régions éloignées de la zone ischémique peuvent être fonctionnellement affectées, un phénomène connu sous le nom de «diaschisis». Sachant qu’il existe de fortes interactions fonctionnelles entre l’hippocampe (HPC) et le cortex lors des processus mnésiques, nous avons émis la possibilité que les troubles mnésiques survenant après une IC focale qui préserve l’intégrité de l’HPC, auraient pour origine une perturbation de la connectivité cortico-hippocampique conduisant à un hypofonctionnement hippocampique induit par le phénomène de diaschisis. Afin d’éprouver cette hypothèse, nous avons utilisé le modèle d’occlusion permanente de l'artère cérébrale moyenne chez le rat (OPACM) qui reproduit l’ischémie cérébrale focale humaine. Dans ce modèle, le cortex somato-sensoriel (SS) est endommagé unilatéralement alors que l’intégrité de l’HPC est préservé. Les rats OPACM ont montré une diminution de l’expression du gène c-fos dans l’HPC lors de l'exploration d'un nouvel environnement, indiquant une hypoactivation neuronale. Les rats OPACM ont également présenté une perturbation des mémoires olfactive associative et spatiale lors des tests de transmission sociale de préférence alimentaire (TSPA) et du Barnes maze, respectivement. Afin de confirmer que l’hypofonctionnement hippocampique induit par l’IC résultait d’une réduction des afférences corticales («déactivation») provenant du cortex endommagé, nous avons réalisé des inactivations pharmacologiques spécifiques du cortex SS et ou de l’HPC par injection de lidocaïne ou de CNQX. Ces injections ont induit une hypoactivation hippocampique (réduction du nombre de noyaux Fos-positifs) associée à une perturbation mnésique dans le test de TSPA. L'activité hippocampique chez des rats anesthésiés pendant l’IC ou deux semaines après, ainsi que lors de l’inactivation pharmacologique du cortex SS, a également été examinée par une approche électrophysiologique. Les résultats ont montré une altération de la fréquence d’apparition des «sharp-wave ripples» hippocampiques et révélé une instabilité de la fréquence thêta hippocampique lors de la reperfusion ou deux semaines après IC, ainsi que lors de l’inactivation corticale, suggérant une altération de la dynamique d’interaction entre l’HPC et le cortex. Pris dans leur ensemble, ces résultats identifient le phénomène de diaschisis hippocampique comme un mécanisme crucial impliqué dans l’hypofonctionnement hippocampique et les déficits mnésiques observés après une ICThe cognitive consequences and the underlying mechanisms leading to cognitive impairments after cerebrovascular occlusive diseases are still unclear. In addition to the infarct zone that suffer the deadly consequence of ischemic stroke, the penumbra surrounding the lesion site and some brain regions more remote to the ischemic areas can be functionally affected by the insult. This phenomenon is referred to as diaschisis. In light of the importance of interactions between hippocampus and cortex during memory processing, we hypothesized that the cognitive impairments observed following focal ischemia could occur in the absence of direct hippocampal insult, possibly via impaired connectivity within cortico-hippocampal networks leading to diaschisis-induced hypofunctioning in specific hippocampal subregions. To examine this possibility, we used the distal middle cerebral artery occlusion (dMCAO) ischemic model in rats which induces restricted cortical infarct in the somatosensory (SS) cortex in the absence of direct hippocampal injury. dMCAO rats exhibited reduced expression of the activity-dependent gene c-fos in the hippocampus when exploring a novel environment, indicating neuronal hypoactivation. Ischemic rats also showed impaired associative olfactory and spatial memory when tested in the social transmission of food preference (STFP) task and the Barnes maze test, respectively. To confirm that the ischemic-induced hippocampal hypofunctioning resulted from reduced afferent inputs (i.e. deactivation) originating in the damaged cortex, we performed region-specific pharmacological inactivation of SS and/or HPC using lidocaine or CNQX. Fos imaging revealed that these treatments induced hippocampal hypoactivation and impaired memory performance as measured in the STFP task. We additionally performed electrophysiological recordings of hippocampal activity in anesthetized rats during acute stroke and two weeks later or after SS cortex inactivation. We found an alteration in the occurrence of sharp-wave ripples associated with instability of theta frequency during reperfusion after stroke and SS cortex inactivation, suggesting an alteration in the dynamics of hippocampal-cortical interactions. Taken collectively, these findings identify hippocampal diaschisis as a crucial mechanism for mediating stroke-induced hippocampal hypofunction and associated memory deficits
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Aravamuthan, Bhooma Rajagopalan. « Comparing the radiological anatomy, electrophysiology, and behavioral roles of the pedunculopontine and subthalamic nuclei in the normal and parkinsonian brain ». Thesis, University of Oxford, 2008. http://ora.ox.ac.uk/objects/uuid:9a735b39-c1fe-4d5f-b05f-3385f27e6e58.
Texte intégralRésumé :
Deep brain stimulation (DBS) of the subthalamic nucleus (STN) and DBS of the pedunculopontine nucleus (PPN) have been shown to be effective surgical therapies for Parkinson’s disease (PD). To better understand the PPN and STN as DBS targets for PD, this research compares the anatomy, electrophysiology, and motor control roles of these nuclei. PPN and STN connections were examined in vivo in human subjects and in the non-human primate using probabilistic diffusion tractography. Both the PPN and STN were connected with each other and with the motor cortex (M1) and basal ganglia. After studying these anatomical connections in primates, their functional significance was further explored in an anesthetized rat model of PD. Examination of the electrophysiological relationship between the PPN and basal ganglia in the presence of slow cortical oscillatory activity suggested that excitatory input from the STN may normally modulate PPN spike timing but that inhibitory oscillatory input from the basal ganglia output nuclei has a greater effect on PPN spike timing in the parkinsonian brain. To examine transmission and modulation of oscillatory activity between these structures at higher frequencies, LFP activity was recorded from the PPN and STN in PD patients performing simple voluntary movements. Movement-related modulation of oscillatory activity predominantly occurred in the α (8-12 Hz) and low β (12-20 Hz) frequencies in the STN but in the high β (20-35 Hz) frequencies in the PPN, supporting observations from rodent studies suggesting that oscillatory activity is not directly transmitted from the STN to the PPN in PD. Finally, to better understand the roles of the STN and PPN in large-scale movement, the effects of STN and PPN DBS on gait abnormalities in PD patients were studied. DBS of the STN appeared to improve gait by optimising executive gait control while DBS of the PPN appeared to restore autonomic gait control. These results have several implications for DBS patient selection, surgical targeting, and for understanding the mechanisms underlying DBS efficacy.
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Schumann, Michael. « Nonlinear dynamics in oscillating waterfalls ». PDXScholar, 1992. https://pdxscholar.library.pdx.edu/open_access_etds/4421.
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Zhang, Huihui. « Temporal dependence in perceptual decision-making : behavioural oscillations and sequential effects ». Thesis, The University of Sydney, 2019. http://hdl.handle.net/2123/20847.
Texte intégralRésumé :
Dynamic brain states influence perceptual decision making, especially when the immediate sensory evidence is noisy. In this thesis, I examine how perceptual decision making is shaped by two types of temporal contexts, one characterised by intrinsic temporal organisation of neural processing (i.e., neural oscillations) and one characterised by the recent history of perceptual, decisional, and motor experience (i.e., sequential effects). Chapter 2 examines rhythmic fluctuations of behavioural performance in visual orientation discrimination. The results indicate that sensitivity and response bias both modulate rhythmically over time: ~8 Hz for sensitivity, and ~10 Hz for response bias. Chapter 3 examines sequential effects in visual orientation discrimination. Analysing the data-set from chapter 2 shows that it’s the response, rather than the stimulus, that carries over to the next trial. Moreover, the one-trial back sequential effect shows individual differences (positive or negative). In a new experiment with a trial-by-trial random stimulus-response mapping, the choice effect was consistently positive and the motor effect was consistently repulsive, suggesting that the individual differences may be caused by different relative weightings of the perceptual decision and the motor response. Chapter 4 further examines sequential effects with auditory stimuli of different morph levels in two dimensions: gender, syllable (ba/da). Observers reported male or female and ba or da at the same time. For gender, decisions were biased towards the previous choice, and this bias was modulated by the similarity between previous and current stimuli – being stronger when the stimuli were similar. For syllable, the same bias towards previous choice was found, but the dependence was not modulated by similarity between temporally adjacent stimuli. To summarise, these findings reveal that both intrinsic neural oscillations and past history shape the current perceptual decision making.
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Iachello, Marco. « Nonlinear oscillations in high power systems ». Doctoral thesis, Università di Catania, 2015. http://hdl.handle.net/10761/3913.
Texte intégralRésumé :
The main topic of this work is to investigate on nonlinear phenomena affecting high power systems and on the strategies adopted to model them. In the first chapter the attention is focused on two big areas of high power systems: power electronics and systems/devices used to sustain plasma fusion. Although it is common that System Engineers tend to associate high power systems with power electronics, it is worth noting that power systems related to nuclear fusion represent a challenging area rich in nonlinearities. Specifically, while nonlinear oscillations in power electronics are due to oscillations of electrical nature, the ones present in nuclear fusion can also refer to other physical quantities. We will refer to the latter taking into account macroscopic plasma instabilities affecting JET plasmas, and proposing both theoretical approaches and experimental ones to describe their dynamic. The former rely on nonlinear mathematical equations able to mimic the nonlinear behavior of the system under certain conditions while the latter are based on a physical realization of the system starting from its mathematical model.
High power systems related to power electronics are investigated in Chapter 2 where the importance of thermal modeling for the power electronics modules is pointed out and a new modeling strategy which starts from a distributed parameter analysis to obtain a lumped parameter model is introduced.
In this case, the proposed methodology is based on the assumption that the heat transfer problem can be assumed to be linear and the thermal impedances approaches can be therefore used. In this relevant case study nonlinearities in modeling high power systems can also be neglected under certain conditions. In particular, concerning high power modules, it is well-known how the geometry of the device and the proper choice of the cooling system can play a key role for these simplifications.
A data-driven approach based on neural networks to model plasma instabilities is presented in Chapter 3. This approach is introduced because physical models often require a deep knowledge of the system parameters that sometimes is difficult to obtain.
In Chapter 4 considerations and results on new identification methodologies based on parallel identification models for discrete-time systems are presented.
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Feingold, Joseph. « Beta oscillations in frontal cortex and striatum represent post-processing of successful behavior ». Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/68453.
Texte intégralRésumé :
Thesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references.
Beta band (13-30 Hz) oscillations in sensorimotor cortex are associated with motor performance, but the nature of this relationship is not clear. Recently, excessive beta activity in cortico-basal ganglia circuits has been recognized as a hallmark of Parkinson's disease. Renewed interest in beta oscillations has since led to the suggestion that they might reflect the preservation of the current output or state of a given brain region. To investigate the potential role of beta activity in the brain, we recorded local field potentials in the frontal cortex and striatum of monkeys as they performed single and sequential arm movement tasks. To facilitate these experiments, we developed novel methods for recording simultaneously from independently moveable electrodes implanted chronically at over 100 sites in cortical and subcortical areas of the monkey brain. We found that, across tasks, beta oscillations occurred in brief, spatially localized bursts that were most prominent following task performance. Across brain regions, post-performance bursts were differentially modulated by the preceding task. In motor cortex they tracked the number of movements just performed. In contrast, striatal and prefrontal burst rates were proportional to the number of visual cues, or to a combination of the cues and movements, respectively, and were higher following correct, rewarded, trials than unrewarded errors. Pairs of striatal-prefrontal sites exhibited increased cross-covariance and coherence during post-trial beta bursts, suggesting that these bursts might be involved in communication or coordination across brain regions. Based on our results, we propose that beta oscillations may represent post-performance reinforcement of the network dynamics that led to the desired behavioral outcome obtained immediately prior.
by Joseph Feingold.
Ph.D.
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Piskun, Nikolay. « Auto-oscillation's behavior in YIG films from the stability point of view / ». The Ohio State University, 1999. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488193272066689.
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Kolomiyets, Yuriy V. « Asymptotic Behavior of Randomly Perturbed Dynamical Systems ». Kent State University / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=kent1164124028.
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Dong, Yan. « Performance and Oscillation Behavior of PBI-Phosphoric Acid based Higher-Temperature Vapor Feed Direct Methanol Fuel Cells ». Digital WPI, 2015. https://digitalcommons.wpi.edu/etd-theses/505.
Texte intégralRésumé :
Operation of a Direct Methanol Fuel Cell (DMFC) at high temperature with vapor feed can avoid many of the issues of conventional low temperatures DMFC, such as crossover, low efficiency and high catalyst loading. Here we investigate the behavior of a PBI-phosphoric acid membrane based DMFC. This project has two goals. The first goal is to investigate the effect of temperature and methanol concentration on the performance of Direct Methanol Fuel Cell (DMFC). The second goal is to investigate the effect of temperature and methanol on its oscillatory behavior under constant current or constant voltage operation. In this project, we use a commercial polybenzimidazole (PBI)-phosphoric acid based membrane electrode assembly (MEA), namely, Celtec-P 1100 from BASF. The Celtec-P 1100 MEA is actually designed for high temperature operation with referenced hydrogen. This kind of MEA operates at temperatures between 140℃ to 180℃, tolerating high concentrations of carbon monoxide and running independently of humidification. This study uses different vaporized concentration methanol instead of hydrogen at the anode and oxygen at the cathode. We tested in different conditions, the concentration of methanol from 1M to 10M and the operating temperature from 160℃ to 180℃. Results show that the performance of fuel cell increases with temperature up to 180℃ and the effect of methanol concentration is small. Further, oscillatory behavior is observed and reported for the first time. The oscillation is not significantly affected by the temperature and methanol concentration, current density or voltage. However, the oscillation is in special region in different condition.
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Mühlberg, Stefanie 1986. « Selective deployment of attention to time and modality and its impact upon behavior and brain oscillations ». Doctoral thesis, Universitat Pompeu Fabra, 2016. http://hdl.handle.net/10803/392142.
Texte intégralRésumé :
This thesis investigates the relationship between attention to time and modality at the levels of behavior and pre-stimulus brain oscillations, measured with EEG. Participants were presented with target stimuli from one of two possible modalities, which could appear at one of two different time points. The factors time and modality were interlaced with each other by the fact that each of the modalities was more likely to appear at a different point in time and additionally one of the modalities being more likely overall. We observed that attention to each modality followed its respective temporal likelihood, independently which combination of modalities was used, suggesting a general mechanism for cross-modal temporal decoupling in time. This result is in contrast with cross-modal attention in space, which occurs in a coupled way. At the physiological level, the decoupling effect in time also seems to modulate ongoing neural oscillations in different frequency bands. Based on the results obtained in the time-frequency analysis, we put forward the following tentative hypotheses: alpha oscillations appear to encode switches in modality expectation over sensory cortices, while the beta band might encode the expected modality of the next upcoming stimulus and for the effect of temporal attention itself.Esta tesis investiga la relación entre la atención al tiempo y a la modalidad al nivel de comportamiento y oscilaciones cerebrales pre-estímulo. En los estudios que se presentan aquí, los participantes debían responder a estímulos que se presentaban en una de dos modalidades distintas, y podían aparecer en uno de dos momentos distintos. Los factores de tiempo y modalidad fueron entrelazados el uno con el otro a través la manipulación de su probabilidad, según la cual una modalidad era más probable en un momento u otro y una de las modalidades era más probable en general. Los resultados mostraron que la atención a cada modalidad seguía su respectiva probabilidad temporal, independientemente de la combinación de modalidades, lo cual sugiere un mecanismo general para el desacoplamiento inter-sensorial en la atención temporal. Este resultado es interesante porque contrasta con la atención inter-sensorial en el dominio espacial, donde las distintas modalidades parecen funcionar de manera acoplada. El efecto de desacoplamiento en atención temporal también parece modular las oscilaciones cerebrales antes del momento en anticipación al estímulo, en bandas de frecuencia distintas. Según los resultados obtenidos mediante el registro de estas oscilaciones, elaboramos las siguientes hipótesis: las oscilaciones alfa parecen codificar expectativas sobre cambios de modalidad en las cortezas sensoriales, mientras que la banda beta parece codificar las expectativas sobre la modalidad del siguiente estímulo, y el efecto de atención temporal en sí.
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Fogelson, Noa. « Oscillations in the basal ganglia in Parkinson's disease patients and their influence on the cerebral cortex and behavioural performance ». Thesis, University College London (University of London), 2005. http://discovery.ucl.ac.uk/1445455/.
Texte intégralRésumé :
Synchronised bursting of the basal ganglia, specifically at frequencies below 30 Hz, has been implicated to have a major role in the pathophysiology of Parkinson's disease (PD). The aim of this thesis is to further investigate the pathological role of low frequency activities in the subthalamic nucleus. These activities are characterised through exploration of their interactions with oscillatory cortical activities as well as with subthalamic prokinetic high frequency activities and by determining their contribution to parkinsonian bradykinesia.
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Nakamura, Hideo. « The effect of beam oscillation rate on Al evaporation behavior in the electron beam melting process ». Thesis, University of British Columbia, 1989. http://hdl.handle.net/2429/27944.
Texte intégralRésumé :
Electron beam hearth melting process is widely used in producing superalloys, Ti and its alloys because of its excellent metallurgical characteristics. However, one of the disadvantages of the process is that alloying elements with high vapor pressure evaporate under the highly reduced operating pressure. This makes it very difficult to carry out an accurate chemical composition control. In order to prevent the excess evaporative loss by reducing the superheating of the molten pool, the beam scanning technique is employed in normal operation. Although the effect of this technique is well known empirically, few fundamental studies' have been made to date. The purpose of this study is, therefore, to clarify the quantitative effect of the beam oscillation rate on the evaporation behavior.
Small amounts of Ti-6Al-4V alloy were melted in an EB melting furnace. The temperature on the melt surface was measured in situ by an optical pyrometer during the melting period. The evaporation loss of both Ti and Al was also investigated.
On the basis of the experimental results, a two dimensional unsteady heat and mass transfer model was developed. (A one dimensional model was developed in the case of a stationary beam.) The model was used to investigate the effect of the beam oscillation rate on the evaporation behavior and also to discuss the optimum beam scanning rate. It was clearly shown that the evaporative loss of both Ti and Al could be suppressed by the increase of the beam oscillation rate. With the beam oscillation rate at more than 1.0 Hz, however, this effect could not be observed clearly anymore. It was also found that the beam scanning technique is useful not only in controlling Al concentration, wt%Al, but also in suppressing the total evaporative loss of both Ti and Al.Applied Science, Faculty of
Materials Engineering, Department of
Graduate
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Benz, Rafael Franzon. « Salicylate generates anxiety-like behavior and type 2 theta oscillation in the ventral hippocampus of mice ». PROGRAMA DE P?S-GRADUA??O EM NEUROCI?NCIAS, 2016. https://repositorio.ufrn.br/jspui/handle/123456789/22634.
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Salicilato, o principal composto de diversos medicamentos, como a Aspirina, ? conhecido por causar zumbido se consumido em altas doses ou de forma cr?nica (para o tratamento de osteoporose, por exemplo). Zumbido ? o ouvir ou a percep??o de um som quando nenhum est?mulo f?sico est? presente. O zumbido n?o ? uma doen?a em si, mas um sintoma presente em diversas doen?as, e est? associado ? ansiedade e outros dist?rbios de humor. Apesar de estar diretamente ligado ao sistema auditivo, o zumbido n?o ? gerado a partir de uma regi?o espec?fica do c?rebro. Al?m disso, alguns estudos mostraram que o salicilato afeta v?rias regi?es cerebrais al?m do sistema auditivo, como o estriado, amigdala e o hipocampo. Estudos iniciais atribu?ram uma fun??o unit?ria ao hipocampo: processamento de memorias declarativas. Entretanto, estudos mais recentes mostraram que o hipocampo n?o s? possui outras fun??es, como processamento emocional, mas tamb?m pode ser dividido em ventral e dorsal, e a parte ventral desempenha um papel essencial no processamento emocional. A oscila??o mais estudada do c?rebro ? o r?tmo teta, e ela pode ser encontrada em todo o hipocampo. Dois tipos de teta podem ser distinguidos: o teta tipo 1, que ? resistente a atropina, possui uma frequ?ncia mais alta (7 a 10 Hz) e est? relacionado com comportamentos de padr?o motor; e o teta tipo 2, que ? sens?vel a atropina, possui uma frequ?ncia mais baixa (4 to 7 Hz) e ocorre durante anestesia, estado de imobilidade vigilante e situa??es de alta ansiedade. O presente estudo investigou os efeitos eletrofisiol?gicos do salicilato no hipocampo ventral de camundongos em estado de comportamento. Atrav?s da inje??o de salicilato foi gerado teta tipo 2 no hipocampo ventral. Tamb?m foi encontrado que o salicilato leva a comportamentos de ansiedade.
Salicylate, the main compound of many medications as Aspirin, is known to cause tinnitus if consumed in high doses or in a chronic way (for the treatment of osteoporosis, for example). Tinnitus is the hearing or perception of a sound when no physical stimulus is present. Tinnitus is not a disease itself, but a symptom present in some diseases, and is associated with anxiety and other mood disorders. Despite being directly related with auditory system, tinnitus is not generated from one specific region of the brain. Additionally, some studies showed that salicylate affects various brain regions besides the auditory system, as the striatum, amygdala and the hippocampus. Early studies have ascribed a unitary function to the hippocampus: declarative memory processing. However, more recent studies showed that the hippocampus not only has other functions, as emotional processing, but also can be divided into ventral and dorsal, and the ventral part plays an essential role in emotional processing. The most studied oscillation of the brain is the theta rhythm, and it can be found in the entire hippocampus. Two types of theta can be distinguished: the type 1, that is atropine resistant, has a higher frequency (7 to 10 Hz) and is related with motor pattern behaviors; and the type 2 theta, that is atropine sensitive, has a lower frequency (4 to 7 Hz) and occur during anesthesia, alert immobility and high arousal situations. The present study investigated the electrophysiological effects of salicylate in the ventral hippocampus of behaving mice. Through salicylate injection we generated type 2 theta in the ventral hippocampus. We also found that salicylate led to anxietylike behavior
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Sharma, Arvindh R. « Liquid Jet in Oscillating Crossflow : Characterization of Near-Field and Far-Field Spray Behavior ». University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1439281517.
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Andersson, Jonathan. « Asymptotic behavior and effective boundaries forage-structured population models in aperiodically changing environment ». Thesis, Linköpings universitet, Matematik och tillämpad matematik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-133632.
Texte intégralRésumé :
Human activity and other events can cause environmental changes to the habitat of organisms. The environmental changes effect the vital rates for a population. In order to predict the impact of these environmental changes on populations, we use two different models for population dynamics. One simpler linear model that ignores environmental competition between individuals and another model that does not. Our population models take into consideration the age distribution of the population and thus takes into consideration the impact of demographics. This thesis generalize two theorems, one for each model, developed by Sonja Radosavljevic regarding long term upper and lower bounds of a population with periodic birth rate ; see [6] and [5]. The generalisation consist in including the case where the periodic part of the birth rate can be expressed with a finite Fourier series and also infinite Fourier series under some constraints. The old theorems only considers the case when the periodic part of the birth rate can be expressed with one cosine term. From the theorems we discover a connection between the frequency of oscillation and the effect on population growth. From this derived connection we conclude that periodical changing environments can have both positive and negative effects on the population.
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Felts, K. R. Chicone Carmen Charles. « Oscillators resonances and excitations / ». Diss., Columbia, Mo. : University of Missouri--Columbia, 2009. http://hdl.handle.net/10355/6147.
Texte intégralRésumé :
Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 11, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dissertation advisor: Dr. Carmen Chicone Vita. Includes bibliographical references.
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Mert, Raziye. « Qualitative Behavior Of Solutions Of Dynamic Equations On Time Scales ». Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/3/12611528/index.pdf.
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In this thesis, the asymptotic behavior and oscillation of solutions of dynamic equations on time scales are studied.
In the first part of the thesis, asymptotic equivalence and asymptotic equilibrium of dynamic systems are investigated. Sufficient conditions are established for the asymptotic equivalence of linear systems and linear and quasilinear systems, respectively, and for the asymptotic equilibrium of quasilinear systems by unifying and extending some known results for differential systems and difference systems to dynamic systems on arbitrary time scales. In particular, for the asymptotic equivalence of differential systems, the well-known theorems of Levinson and Yakubovich are improved and the well-known theorem of Wintner for the asymptotic equilibrium of linear differential systems is generalized to arbitrary time scales. Some of our results for asymptotic equilibrium are new even for difference systems. In the second part, the oscillation of solutions of a particular class of second order nonlinear delay dynamic equations and, more generally, two-dimensional nonlinear dynamic systems, including delay-dynamic systems, are discussed. Necessary and sufficient conditions are derived for the oscillation of solutions of nonlinear delay dynamic equations by extending some continuous results. Specifically, the classical theorems of Atkinson and Belohorec are generalized. Sufficient conditions are established for the oscillation of solutions of nonlinear dynamic systems by unifying and extending the corresponding continuous and discrete results. Particularly, the oscillation criteria of Atkinson, Belohorec, Waltman, and Hooker and Patula are generalized.
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Toyoda, Aru. « Studies on male mating strategy, reproductive success, and copulation related behaviors of stump-tailed macaques in Khao Krapuk Khao Taomor Non-Hunting Area, Thailand ». Kyoto University, 2018. http://hdl.handle.net/2433/235054.
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Carus-Cadavieco, Marta. « Coordination of innate behaviors by GABAergic cells in lateral hypothalamus ». Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/19135.
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Der laterale Hypothalamus (LH) reguliert angeborene Verhaltensweisen. Ob und wie die Koordination von hypothalamischen Neuronengruppen Verhaltensübergänge reguliert, blieb jedoch unbekannt. In dieser Arbeit wurde Optogenetik mit neuronalen Ableitungen in verhaltenden Mäusen kombiniert. LHVgat Neurone erhöhten ihre Aktivitätsrate während Übergängen vom NREM-Schlaf zum Wachzustand. LHVgat Zellen projizieren zum Nucleus reticularis des Thalamus (RTN). Optogenetische Aktivierung von Vgat Ausgängen im RTN führte eine starke, frequenzabhängige Inhibierung von RTN Zellen herbei und replizierte Verhaltenszustands-abhängige Aktivitätsraten in RTN Neuronen. Ableitungen von LH Neuronen während Umgebungserkundung ergaben, dass 65% der LH Neurone ihre Aktivitätsrate erhöhten, wenn das Tier began sich fortzubewegen. 'Top-down’ Vorderhirn Innervation des LH erfolgt größtenteils durch Signale ausgehend vom lateralen Septums (LS). Während spontaner Umgebungserkundung und freiem Zugang zu Futter wiesen der LH und das LS Gamma-Oszillationen (30-90 Hz) auf, welche neuronale Aktivität innerhalb und zwischen diesen beiden Gehirnregionen synchronisierten. Optogenetische Stimulation von Somatostatin-positiven GABAergen Projektionen zum LH mit Gamma-Frequenz förderte die Nahrungssuche und erhöhte die Wahrscheinlichkeit des Betretens der Nahrungszone. Inhibitorische Signale des LS bewirkten eine Unterteilung der LH Neurone: entsprechend ihrer Aktivität im Bezug zur Nahrungsstelle wurden sie während bestimmter Phasen der Gamma-Oszillation aktiviert. Dabei führte optogenetische Stimulation von LS-LH Neuronen mit Gamma-Frequenz keine Veränderung bei der Nahrungsaufnahme selbst herbei. Insgesamt liefert diese Arbeit neue Einsichten über die Funktion der neuronalen Netzwerke des LH, welche durch Signalgebung mit unterschiedlichen Zeitskalen über die Koordination mit vor- und nachgeschalteten neuronalen Netzwerken Übergange zwischen verschiedenen angeborenen Verhaltensweisen regeln.Lateral hypothalamus (LH) is crucial for regulation of innate behaviors. However, it remained unknown whether and how temporal coordination of hypothalamic neuronal populations regulates behavioral transitions. This work combined optogenetics with neuronal recordings in behaving mice. LHVgat cells were optogenetically identified. LHVgat neurons increased firing rates upon transitions from non-REM (NREM) sleep to wakefulness, and their optogenetic stimulation during NREM sleep induced a fast transition to wakefulness. LHVgat cells project to the reticular thalamic nucleus (RTN). Optogenetic activation of LHVgat terminals in the RTN exerted a strong frequency-dependent inhibition of RTN cells and replicated state-dependent changes in RTN neurons activity. Recordings of LH neurons during exploration revealed that 65% of LH neurons increased their activity upon the onset of locomotion. Top-down forebrain innervation of LH is provided, to a great extent, by inhibitory inputs from the lateral septum (LS). During spontaneous exploration in a free-feeding model, LS and LH displayed prominent gamma oscillations (30-90 Hz) which entrained neuronal activity within and across the two regions. Optogenetic gamma-frequency stimulation of somatostatin-positive GABAergic projections to LH facilitated food-seeking, and increased the probability of entering the food zone. LS inhibitory input enabled separate signaling by LH neurons according to their feeding-related activity, making them fire at distinct phases of the gamma oscillation. In contrast to increased food intake during optogenetic stimulation of LHVgat cells, food intake during gamma-rhythmic LS-LH stimulation was not changed. Overall this works provides new insight into the function of LH circuitry, that employs signalling at different time scales, which, in coordination with upstream and downstream circuits, regulates transitions between innate behaviors.
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Sokoliuk, Rodika. « From alpha to perception : investigating behavior and brain activity ». Toulouse 3, 2014. http://thesesups.ups-tlse.fr/2353/.
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Il a été proposé que la perception visuelle soit organisée de façon discrète, reposant sur l'activité cérébrale oscillatoire d'environ 10Hz. Bien qu'en condition normale notre perception visuelle nous paraisse continue, nous montrons dans une première expérience que cette continuité peut être interrompue lors de la perception d'un stimulus spécifique pourtant statique, révélant les cycles d'oscillations alpha (~10Hz) à la base de la perception visuelle. La 'Flickering Wheel Illusion' ('L'illusion de la roue qui clignote') génère un clignotement illusoire régulier, réapparaissant toutes les 100ms ce qui correspond à une phase du cycle alpha. Des études précédentes ont montré que certaines phases des oscillations alpha occipitales (tout comme des oscillations theta fronto-centrales) portent des propriétés 'inhibitrices' en vue du traitement visuel tandis que leurs phases opposées tendent à augmenter la probabilité de détecter des stimuli visuels. Dans une deuxième étude, nous avons analysé comment ce rapport phase-détection temporel est représenté au niveau spatial dans le cortex visuel. Pour cela, nous avons entraîné des oscillations alpha via le clignotement d'un disque à une certaine position spatiale du champ visuel, pendant que les participants avaient pour tâche de détecter des stimuli visuels de basse luminance pouvant apparaître à de multiples positions spatiales. Les oscillations entraînées modulaient la performance de détection à toutes les positions auxquelles des cibles pourraient apparaître montrant des maxima à différentes phases de l'oscillation. De façon intéressante, nous avons pu montrer que la phase des oscillations entraînées se propageait dans l'espace comme une onde progressive, une propriété qui pourrait impliquer des rôles fonctionnels spécifiques pour le traitement sensoriel. En plus de son influence sur les processus cognitives comme la perception visuelle, la phase des oscillations lentes peut aussi moduler l'amplitude d'une oscillation rapide ('phase-amplitude cross-frequency coupling' ; 'couplage phase-amplitude inter-fréquentiel' ;'PAC'). Dans une troisième expérience, nous avons révélé l'existence d'un PAC entre des oscillations alpha et gamma pendant l'état de repos (en l'absence de tâche cognitive spécifique) ce que nous avons assigné à de 'l'inhibition pulsative', un mécanisme de contrôle du traitement sensoriel porté par le rythme alpha. Selon cette théorie, les oscillations alpha mettraient donc à disposition des moments ou bien des phases spécifiques qui mènent à une augmentation d'amplitude d'oscillations gamma entrainant une augmentation du traitement sensoriel, tandis que des phases opposées inhiberaient le traitement sensoriel. En outre, nous avons observé un PAC robuste entre des oscillations theta et beta pendant l'état de repos ainsi que pendant une tâche de détection. Ce PAC pourrait aider à maintenir un état d'activité cérébrale de base. Finalement, nous avons pu révéler un PAC entre des oscillations theta et gamma principalement dans des régions fronto-centrales, influençant la perception visuelle avec emploi d'attention visuelle. Ce résultat est en continuité et complète des résultats précédents de notre groupe qui montraient l'influence de la phase des oscillations theta sur la perception visuelle. Le travail présenté dans cette thèse contribue aux connaissances du rôle important des oscillations spontanées pour la perception visuelle en utilisant plusieurs approches expérimentales et révèlent de nouvelles questions de ce champ de rechercheIt has been suggested that visual perception is organized in discrete snapshots relying on an oscillatory brain rhythm of about 10Hz. Even though, in normal conditions, our visual percept seems continuous to us, we show that a specific static stimulus pattern can lead to disruption of this continuity and uncover cycles of alpha oscillations (~10Hz) underlying visual perception. This 'Flickering Wheel Illusion' produces a regular illusory flicker recurring every ~100ms thus at one phase of the alpha cycle. According to previous work, specific phases of occipital alpha (and also fronto-central theta) oscillations are designated as 'inhibitory' for visual processing whereas opposite phases increase probability to detect visual stimuli. In a psychophysical experiment, we analyzed how this temporal phase-detection relationship is organized spatially in the visual cortex. We therefore entrained alpha oscillations with a specific spatial origin and probed visual detection of low-threshold targets at different spatial positions. Detection performance was modulated by the entrained oscillation at all target locations, showing maxima at different phases of the oscillation. We could show that the phase of the entrained alpha oscillations propagated over space like a traveling wave that could implicate important functional roles for sensory processing. Besides its influence on cognitive processes like visual perception, the phase of low frequency oscillations can also modulate the amplitude of fast oscillations (phase-amplitude cross-frequency coupling; PAC). In another experiment, we could reveal PAC between alpha and gamma oscillations during the resting state, what we referred to as pulsed inhibition, illustrating the alpha rhythm as a control mechanism of sensory processing. Alpha oscillations would thus provide specific moments, or phases that enhance gamma amplitude and thus sensory processing, whereas opposite phases would inhibit sensory processing. Moreover, we found a robust PAC between theta and beta oscillations which was also present during a visual detection task. This PAC could help maintaining a specific activity state of the brain. Finally, we could reveal PAC between theta and gamma oscillations in mainly fronto-central regions, influencing visual perception in the detection task but only within the focus of attention. This result is consistent with and complements previous findings of our group showing the influence of the phase of theta oscillations on visual perception. This work contributed to the findings of the important role of ongoing oscillations in visual perception, using multiple experimental approaches; yet our promising results uncovered new questions in this large field of research
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Samarbakhsh, Sina. « Investigation of the Lock-in behavior of an eccentrically rotating cylinder in regard to turbomachinery application ». Thesis, KTH, Kraft- och värmeteknologi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-154358.
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Interaction of fluctuating vortex shedding with blade vibration can lead to a new class of aeromechanical instability referred as Non-synchronous vibrations. Investigating a well-known case that shows similar NSV features such as a circular cylinder can develop the understanding of physics behind NSV. A common approach to further investigating the vortex induced vibration is to control the motion of the cylinder and allowing the response of the wake to the motion to be studied in isolation. It has been found very important to carefully match the experimental conditions between free and controlled vibration. Many of research in the field of vortex induced vibration apply a rigid cylinder mounted horizontally and moving transversely to the flow stream as a paradigm for understanding the physics behind this phenomenon. Regarding the difficulties of implementation of vertically moving cylinder in experimental study, vortex dynamic and lock-in behavior of eccentrically rotating cylinder is studied in this M.Sc. Thesis. The main focus of this research is to understand to what extend a general feature of free vortex-induced vibration can be observed in the case of eccentrically rotating cylinder. If the present case captures the essential characteristics of freely oscillating cylinder the results of the forced motion via eccentrically rotating cylinder can be applied to predict the motion of an elastically mounted body. To do so a CFD model is established to predict the response, vorticity structure in near wake, timing of vortex shedding and the range of lock-in region over specific parameter space of the introduced alternative case. A commercial CFD code, Ansys/CFX, was implemented to perform this numerical study. Existences of synchronization region, striking similarity in lift force coefficient and wake mode have been observed in the current study.
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Tremouilhac, Pierre. « Orientational behavior of the antimicrobial peptide PGLa in a lipid membrane environment studied by solid-state 2H-NMR spectroscopy Calibration of new flavor tagging algorithms using Bs oscillations / ». [S.l. : s.n.], 2007. http://digbib.ubka.uni-karlsruhe.de/volltexte/1000007219.
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Ahmed, Hafiz. « Modeling and synchronization of biological rhythms : from cells to oyster behavior ». Thesis, Lille 1, 2016. http://www.theses.fr/2016LIL10129/document.
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La modélisation, l’analyse et le contrôle des oscillations, notamment des rythmes biologiques ont été étudiés dans cette thèse. La thèse est divisée en deux parties. Dans la première partie, motivée par un problème pratique de la surveillance de l'environnement côtier, cette thèse considère les rythmes biologiques des huîtres. En utilisant les informations des rythmes biologiques, une solution de surveillance environnementale indirecte en utilisant les huîtres comme bio-capteur a été proposé. La solution proposée se base sur l'estimation de la perturbation par la modélisation du rythme biologique des huîtres par un oscillateur de Van der Pol. Une limite inhérente de cette approche est que celle-ci fonctionne uniquement grâce à la détection des comportements anormaux. Cependant les comportements anormaux ne sont pas tous liés à la pollution. Nous considérons donc la détection d'un type particulier de comportement oscillatoire anormal à savoir la ponte, qui est un phénomène naturel et non lié à la pollution. Le premier problème de la deuxième partie est la robustesse des oscillations dans la division cellulaire. Les oscillations persistent dans les oscillateurs génétiques après la division cellulaire. Dans cette thèse, nous fournissons des conditions d'analyse qui garantissent la synchronisation de phase après la division cellulaire. Enfin, nous considérons le problème de la synchronisation des systèmes multi-stables en utilisant l’Input-to-State Stability (ISS). En utilisant une généralisation récente de la théorie de l'ISS pour les systèmes multi-stables, nous proposons des conditions suffisantes pour la synchronisation des systèmes multi-stablesModeling, analysis and control of oscillations, notably biological rhythms have been studied in this thesis. The thesis is divided into two parts. In part-I, motivated by a practical problem of environmental monitoring of coastal environment, this thesis considers the biological rhythms of oysters. Using the information of biological rhythms, an indirect environmental monitoring solution using oysters as bio-sensor has been proposed. The proposed solution works on estimating the perturbation by modeling the biological rhythm of oysters through Van der Pol oscillator model. An inherent limit of this approach is that it works through detecting abnormal behavior only. However abnormal behaviors are not all related to pollution. So, we consider the detection of a particular type of abnormal oscillatory behavior i.e. spawning (behavior during reproduction) which is a natural phenomenon and not related to pollution. In part-II, oscillations are studied from a theoretical point of view. The first problem of this part is the robustness of oscillations under cell division. Oscillations persist in genetic oscillators after cell division. In this thesis, we provide analytical conditions that guarantee phase synchronization after cell division using Phase Response Curve (PRC) formalism. Finally we consider the problem of synchronization of multi-stable systems using Input-to-State (ISS) stability tool. Using a recent generalization of ISS theory for multi-stable systems, we propose sufficient conditions for the synchronization of multi-stable systems. As a side result, this work has been applied for the global synchronization of the Brockett oscillator
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Yusuf, Solieman Osama. « CAD-CAM ceramic veneers : tooth preparation status, accuracy of Intra Oral Scanner and mechanical behavior ». Thesis, Montpellier, 2018. http://www.theses.fr/2018MONTT044/document.
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Au cours des vingt dernières années, les facettes céramiques sont devenues une solution esthétique très répandue en raison de leur conception de préparation peu invasive, de leurs propriétés biocompatibles, de leur similitude avec la couleur naturelle des dents, ainsi que de leur translucidité et de leur résistance mécanique aux forces occlusales et à l’usure [1]. La définition des facettes dentaires est celle de « coquilles » très minces, faites sur mesure de matériaux de la couleur de la dent, conçues pour recouvrir la face avant ou la face supérieure des dents afin d' en améliorer l'esthétique et/ou corriger des problèmes occlusaux. Elles sont collées aux dents et pourront en modifier la couleur la forme, et le volume [2].Elles trouvent ainsi de multiples indications à différents endroits sur les arcades dentaires sur les faces vestibulaires des dents antérieures ou plus récemment pour restaurer les surfaces occlusales corriger une occlusion déficiente [3, 4].Ces restaurations modernes se sont développées avec l'arrivée de nouveaux matériaux de reconstructions et de collages, ainsi que de nouveaux modes de conception et fabrication répondant à des exigences de simplicité, de rapidité et de précision.Pour préparer la dent à recevoir une facette, l'oscillation d’inserts ultrasonores a été proposée pour améliorer la finition des lignes marginales et optimiser l’état de surface [5].Pour leur fabrication, outre les méthodes prothétiques classiques, la CFAO (conception assistée par ordinateur - fabrication assistée par ordinateur) au développement exponentiel [6, 7 permet de réaliser une prothèse restauratrice en une seule visite en clinique avec la précision que permettent l’optique (empreintes) et la robotique (fabrication de la facette) ;[8-14]. D’autre part l’apparition de nouvelles céramiques a permis d'améliorer leur esthétique et d'augmenter leur durabilité, qu'elle soit antérieure ou occlusale.Notre première étude portait sur de nouveaux outils permettant d'optimiser la procédure de préparation des facettes. L'utilisation ou non d‘inserts oscillants sur la qualité de l'état de surface de la dent traitées pour une telle préparation. Cette question importante et récurrente, [15] pose le problème de la qualité de l'état de surface destiné à recevoir par collage une pellicule de céramique de faible épaisseur. La pérennité de ce type de prothèse dépend essentiellement du collage avec les tissus dentinaires préparés [16, 17]. La littérature, atteste d’une meilleure qualité de collage entre des surfaces dentaires rugueuses et les matériaux de restauration [18-22]. Toutefois, une question se pose concernant la qualité de cette rugosité lorsqueThe first chapter of the thesis relieved the dentists from thinking a lot about the produced roughness regardless to the preparation tool. The roughness is a critical factor to the stability, to the retention, and eventually to the success of the ceramic veneers especially for the esthetic anterior veneers. This will speed up the procedure of achieving a fast treatment for the patients with the CAD-CAM systems. For the upcoming steps, an investigation is recommended to estimate the amount of the inquired roughness to achieve the minimum necessary adhesion value for the retention of the ceramic veneers, and vice versa, another investigation to evaluate the capability of the preparation tools in transferring the same roughness from the preparation tool grains to the target surface (dentin or enamel).152The second study had filled the gap of how to evaluate the IOS systems regardless to the recent common criteria, and the thesis created a novel measure (noise) to be used. The study asks the dentists to pay attention to other criteria to consider when buying an IOS system regardless to the criteria that already exists and had been directed by the producing companies. The thesis states that the noise increases when the direction of the IOS is changed. More attention should be paid at the transitional lines between the scanned surfaces while designing the digital model. An enhancement is demanded to compensate for (or if possible, to eliminate) this noise
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Vezenkov, Stoyan Raykov. « Pharmacological studies on the contribution of the neuropeptide proctolin to the cephalic control of singing behavior in grasshopper Chorthippus biguttulus (L. 1758) ». Doctoral thesis, [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=974032557.
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Darling, Ryan Daniel. « Single Cell Analysis of Hippocampal Neural Ensembles during Theta-Triggered Eyeblink Classical Conditioning in the Rabbit ». Miami University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=miami1225460517.
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Dolcemascolo, Axel. « Laser à semi-conducteur pour modéliser et contrôler des cellules et des réseaux excitables ». Thesis, Université Côte d'Azur (ComUE), 2018. http://www.theses.fr/2018AZUR4208/document.
Texte intégralRésumé :
Les systèmes « excitables » sont omniprésents dans la nature, le plus paradigmatique d'entre eux étant le neurone, qui répond de façon « tout ou rien » aux perturbations externes. Cette particularité étant clairement établie comme l'un des points clé pour le fonctionnement des systèmes nerveux, son analyse dans des systèmes modèles (mathématiques ou physiques) peut d'une part aider à la compréhension de la dynamique d'ensembles de neurones couplés et d'autre part ouvrir des voies pour un traitement neuromimétique de l'information. C'est dans cette logique que s'inscrit la préparation de cette thèse de doctorat. Dans ce mémoire, nous utilisons des systèmes basés sur des lasers à semiconducteur pour d'une part modéliser des systèmes excitables ou des ensembles de systèmes neuromimétiques couplés et d'autre part pour contrôler (grâce à l'optogénétique) des canaux ioniques impliqués dans l'émission de potentiels d'action par des neurones de mammifères. Le long du premier chapitre, nous présentons de manière synthétique les concepts dynamiques sur lesquels nous nous appuierons dans la suite du manuscrit. Par la suite, nous décrivons brièvement le contexte de ce travail du point de vue de la synchronisation, notamment de cellules excitables. Enfin, nous discutons le contexte applicatif potentiel de ces travaux, c’est-à-dire l'utilisation de systèmes photoniques dits « neuromimétiques » dans le but de traiter de l'information. Dans le chapitre 2, nous analysons tout d'abord du point de vue théorique et bibliographique le caractère excitable d'un laser à semiconducteur sous l'influence d'un forçage optique cohérent. Par la suite, nous détaillons nos travaux expérimentaux d'abord, puis numériques et théoriques, sur la réponse de ce système « neuromimétique » à des perturbations répétées dans le temps. Tandis que le modèle mathématique simplifié prévoit un comportement de type intégrateur en réponse a des perturbations répétées, nous montrons que le comportement est en fait souvent résonateur, ce qui confère à ce système la propriété étonnante d'émettre une impulsion seulement s'il reçoit deux perturbations séparées d'un intervalle de temps bien précis. Nous montrons également que ce système peut convertir des perturbations de différente intensité en une série d'impulsions toutes identiques mais dont le nombre dépend de l'intensité de la perturbation incidente. Dans le chapitre 3, nous analysons (de nouveau expérimentalement, puis numériquement et théoriquement) le comportement dynamique d'un réseau de lasers à semiconducteur couplés dans un régime de chaos lent-rapide. Nous nous basons sur une étude antérieure montrant qu'un seul de ces éléments peut présenter une dynamique neuromimétique (en particulier l'émission chaotique d'impulsions originant du phénomène de canard). De façon surprenante pour un système ayant un si grand nombre de degrés de liberté, nous observons une dynamique qui semble chaotique de basse dimension. Nous examinons l'impact des propriétés statistiques de la population considérée sur la dynamique et relions nos observations expérimentales et numériques à l'existence d'une variété critique calculable analytiquement pour le champ moyen et près duquel converge la dynamique grâce au caractère lent-rapide du système. Dans le chapitre 4 enfin, nous présentons une brève étude expérimentale de la réponse de cellules biologiques à des perturbations lumineuses. En effet, les techniques optogénétiques permettent de rendre des cellules (en particulier des neurones) sensibles à la lumière grâce au contrôle optique de l'ouverture et de la fermeture de canaux ioniques. Ainsi, après avoir étudié dans les chapitres précédents des systèmes optiques sur la base de considérations provenant de systèmes biologiques, nous amenons matériellement un système laser vers un système biologiqueExcitable systems are everywhere in Nature, and among them the neuron, which responds to an external stimulus with an all-or-none type of response, is often regarded as the most typical example. This excitability behaviour is clearly established as to be one of the underlying operating mechanisms of the nervous system and its analysis in model systems (being them mathematical of physical) can, from one hand, shed some light on the dynamics of neural networks, and from the other, open novel ways for a neuro-mimetic treatment of information. The work presented in this PhD thesis was realized in this perspective. In this dissertation we will consider systems based on semiconductor lasers both for modelling excitable systems or coupled neuromorphic networks and for controlling (in an optogenetic outlook) ionic channels that are involved in the emission of action potentials of neurons in mammals. During the first chapter, we will briefly present the dynamical concepts on which we will build our understanding for the rest of the manuscript. Thereafter, we will describe the context of this work from the point of view of synchronized systems, in particular excitable cells. Finally, we will discuss in this context the applications potential of this work, namely the possibility of using “neuromimetic” photonic systems as a was to treat information. In chapter 2 we will firstly analyse from a theoretical and bibliographical standpoint the excitable character of a laser with coherent injection. Later, we will firstly detail our results, firstly experimental and subsequently numerical and theoretical, on the response of this “neuromimetic” system to perturbations repeated in time. Whereas the simplified mathematical model envisions an integrator behaviour in response to repeated perturbations, we will show that the system often acts as a resonator, thus imparting the remarkable property of being able to emit a single pulse only if it receives two perturbations that are separated by a specific time interval. We will also illustrate how this system can convert perturbations of different intensity in a series of all identical pulses whose number depends on the intensity of the incoming perturbation. In the third chapter we will analyse, first experimentally and later numerically and theoretically, the dynamical behaviour of a network of coupled semiconductor lasers in a slow-fast chaotic regime. We will rely on a previous study documenting that a single such element can present a neuromimetic dynamics (in particular, the emission of chaotic pulses originating from a canard phenomenon). Surprisingly for a system having such a large number of degrees of freedom, we observe a dynamics which seems low dimensional chaotic. We will examine the impact of statistical properties of the selected population on the dynamics, and we will link our experimental and numerical observations to the existence of a slow manifold for the mean field, computable analytically, and towards whom the dynamics converges thanks to the slow-fact nature of the system. Finally, in chapter 4 we will present a short experimental study on the response of biological cells to light perturbations. Indeed, optogenetic techniques enables to render the cells (in particular neurons) sensitive to light due to the optical control of the opening and closing of ionic channels. Hence, after having studied in the previous chapters optical systems on the basis of observations derived from biological systems, we will physically transfer an optical system towards a biological one. Here we lay the groundwork of a photonic system which allows, with a moderate complexity, to realize cell measurements in response to spatially localized optical perturbations
32
Ossandon, Valdes Tomas. « A prefrontal-temporal network underlying state changes between Stimulus-Driven and Stimulus-Independent Cognition ». Phd thesis, Université Claude Bernard - Lyon I, 2010. http://tel.archives-ouvertes.fr/tel-00726306.
Texte intégralRésumé :
The brain displays moment-to-moment activity fluctuations that reflect various levels of engagement with the outside world. Processing external stimuli is not only associated with increased brain metabolism but also with prominent deactivation in specific structures, collectively known as the default-mode network (DMN). The role of the DMN remains enigmatic partly because its electrophysiological correlates and temporal dynamics are still poorly understood. Using unprecedented wide-spread depth recordings in epileptic patients, undergoing intracranial EEG during pre-surgical evaluation, we reveal that DMN neural populations display task-related suppressions of gamma (60-140 Hz) power and, critically, we show how millisecond temporal profile and amplitude of gamma deactivation tightly correlate with task demands and subject performance. The results show also that during an attentional task, sustained activations in the gamma band power are presented across large cortical networks, while transient activations are mostly specific to occipital and temporal regions. Our findings reveal a pivotal role for broadband gamma modulations in the interplay between activation and deactivation networks mediating efficient goal-directed behavior
33
Devlin, Adam Thomas. « On the variability of Pacific Ocean tides at seasonal to decadal time scales| Observed vs modelled ». Thesis, Portland State University, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10128376.
Texte intégralRésumé :
Ocean tides worldwide have exhibited secular changes in the past century, simultaneous with a global secular rise in mean sea level (MSL). The combination of these two factors contributes to higher water levels, and may increase threats to coastal regions and populations over the next century. Equally as important as these long-term changes are the short-term fluctuations in sea levels and tidal properties. These fluctuations may interact to yield locally extreme water level events, especially when combined with storm surge. This study, presented in three parts, examines the relationships between tidal anomalies and MSL anomalies on yearly and monthly timescales, with a goal of diagnosing dynamical factors that may influence the long-term evolution of tides in the Pacific Ocean. Correlations between yearly averaged properties are denoted tidal anomaly trends (TATs), and will be used to explore interannual behavior. Correlations of monthly averaged properties are denoted seasonal tidal anomaly trends (STATs), and are used to examine seasonal behavior. Four tidal constituents are analyzed: the two largest semidiurnal (twice daily) constituents, M2 and S2, and the two largest diurnal (once daily) constituents, K1 and O1.
Part I surveys TATs and STATs at 153 Pacific Ocean tide gauges, and discusses regional patterns within the entire Pacific Ocean. TATs with statistically significant relations between MSL and amplitudes (A-TATs) are seen at 89% of all gauges; 92 gauges for M2, 66 for S2, 82 for K1, and 59 for O1. TATs with statistically significant relations between tidal phase (the relative timing of high water of the tide) and MSL (P-TATs) are observed at 55 gauges for M2, 47 for S2, 42 for K1, and 61 for O1. Significant seasonal variations (STATs) are observed at about a third of all gauges, with the largest concentration in Southeast Asia. The effect of combined A-TATs was also considered. At selected stations, observed tidal sensitivity with MSL was extrapolated forward in time to the predicted sea level in 2100. Results suggest that stations with large positive combined A-TATs produce total water levels that are greater than those predicted by an increase in MSL alone, increasing the chances of high-water events.
Part II examines the mechanisms behind the yearly (TAT) variability in the Western Tropical Pacific Ocean. Significant amplitude TATs are found at more than half of 26 gauges for each of the two strongest tidal constituents, K1 (diurnal) and M2 (semidiurnal). For the lesser constituents analyzed (O1 and S2), significant trends are observed at ten gauges.
Part III analyzes the seasonal behavior of tides (STATs) at twenty tide gauges in the Southeast Asian waters, which exhibit variation by 10 – 30% of mean tidal amplitudes. A barotropic ocean tide model that considers the seasonal effects of MSL, stratification, and geostrophic and Ekman velocity is used to explain the observed seasonal variability in tides due to variations in monsoon-influenced climate forcing, with successful results at about half of all gauges. The observed changes in tides are best explained by the influence of non-tidal velocities (geostrophic and Ekman), though the effect of changing stratification is also an important secondary causative mechanism.
From the results of these surveys and investigations, it is concluded that short-term fluctuations in MSL and tidal properties at multiple time scales may be as important in determining the state of future water levels as the long-term trends. Global explanations for the observed tidal behavior have not been found in this study; however, significant regional explanations are found at the yearly time scale in the Solomon Sea, and at the seasonal time scale in Southeast Asia. It is likely that tidal sensitivity to annual and seasonal variations in MSL at other locations also are driven by locally specific processes, rather than factors with basin-wide coherence. (Abstract shortened by ProQuest.)
34
De, la Cruz Sanchez Carmen Mariella. « Utilisation de conduites de séchage oscillantes pour réduire les contraintes liées au retrait du bois ». Thesis, Paris, AgroParisTech, 2012. http://www.theses.fr/2012AGPT0068/document.
Texte intégralRésumé :
La maîtrise du procédé séchage, étape essentielle dans la transformation du bois, est devenue incontournable pour la filière bois. Cette thèse propose l'utilisation de conduites de séchage oscillantes pour réduire les contraintes de séchage liées au retrait par l'activation du fluage mécanosorptif. A ce jour, la meilleure façon d'appliquer les conduites oscillantes représente un défi pour la communauté scientifique. Dans ce travail, nous avons choisi comme matériel d'étude une essence feuillue fortement utilisée dans la filière et très susceptible aux déformations lors du séchage : le hêtre (Fagus sylvatica). L'effet des conduites oscillantes sur les contraintes de séchage est étudié par une approche expérimentale et par une approche théorique, articulées en trois parties : - Un premier volet expérimental sur un séchoir semi – industriel pour saisir l'effet global des conduites oscillantes à l'échelle d'une pile de planches. L'amélioration de la qualité du bois séché s'est avérée par : une meilleure homogénéité de la teneur en eau finale inter et intra-planche, la diminution des déformations globales et la diminution des contraintes résiduelles exprimées par le gap du « slicing test ». - Ensuite, nous avons développé un volet théorique sur la base de modélisations analytique et numérique pour étudier l'évolution des champs de teneur en eau et de contraintes mécaniques au sein d'une planche lorsque les conditions climatiques oscillent. Une formulation analytique simple, adaptée aux conduites oscillantes, est proposée pour les utilisateurs de séchoirs n'ayant pas accès à un outil numérique sophistiqué. L'approche numérique effectuée avec l'outil de simulation TransPore permet une étude plus réaliste du séchage oscillant. Ainsi, le module mécanique de TransPore a été utilisé pour dégager des configurations pertinentes de séchage permettant d'étudier l'effet des conduites oscillantes sur la relaxation des contraintes. - Enfin, un second volet expérimental a été réalisé sur un séchoir de laboratoire, à l'échelle d'une planche, pour tester les informations issues du volet théorique. Un dispositif de séchage dissymétrique (flying wood) et deux dispositifs de séchage sous charge (poutre cantilever et flexion trois points) ont été utilisés pour étudier l'effet des oscillations. Toutefois, ces essais ne permettent pas de montrer clairement l'effet des oscillations sur la relaxation des contraintes. La confrontation entre les résultats expérimentaux à l'échelle d'une planche et la simulation numérique a mis en évidence l'effet conséquent des oscillations parasites de faibles période et amplitude sur les résultats expérimentaux, provoquées par la régulation du séchoir. Des modifications du modèle de comportement mécanique différé ont été proposées en perspectives de ce travail afin de mieux saisir le comportement observé expérimentalementWood drying is an essential process in the wood industry. A perfect control of wood drying is nowadays very important for the wood industry. In this study, we propose the utilization of oscillating drying conditions to reduce the drying stresses induced by wood shrinkage by activating the mechanosorptive creep. The best way to apply this concept remains an open question in the scientific community. Beech wood (Fagus sylvatica), one of the most commonly used hardwood in France, was chosen for this study owing its elevated risk of drying defaults. The effect of oscillating conditions on drying stresses inside the boards was studied by both an experimental and a theoretical approach, structured in three parts: - A first experimental part realized with a semi – industrial kiln in order to study the global effect of oscillating conditions at the stack scale. Improvement of the quality of dried wood was showed by the best homogeneity of water content inside the board and among the boards and by the decrease of global deformations and residual stresses expressed by the gap measured by the slicing test. - The study was continued with a theoretical part based on analytical and numerical modeling to understand the development of internal heat and mass transfers inside the boards and the evolution of drying stresses during oscillating conditions. A simple analytical model adapted to the oscillating conditions was proposed, particularly for kiln users who don't have access to sophisticated numerical tools. The numerical approach used the simulation tool TransPore, able to simulate oscillating drying in more realistic conditions. Its mechanical module was used to set accurate drying schedules to study the effect of oscillating conditions on stresses relaxation. - Finally, a second experimental part was performed in a laboratory scale kiln, at the board scale, to test the information obtained theoretically. A non-symmetrical drying device (flying wood) and two different loaded drying devices (cantilever beam test and three points bending) were used to study the effect of oscillations. However, it is difficult to see the oscillating conditions effect on the stresses relaxation. The confrontation between experimental results at the board scale and the numerical simulation showed the significant effect produced on experimental results by parasite oscillations of small periods and intensities, originated by the kiln regulation. Further work should consider some modifications of the time dependent mechanical behavior model in order to capture the experimentally observed behavior
35
BENEDETTO, ALESSANDRO. « The temporal dynamics of vision for action and perception ». Doctoral thesis, 2017. http://hdl.handle.net/2158/1079075.
Texte intégralRésumé :
The aim of the present thesis is to investigate the mechanisms of sensorimotor integration, and - in particular - the role of oscillations in action and perception. In the first study, we considered the contrast sensitivity dynamics during the execution of free saccades. We tested the hypothesis that a voluntary eye movement could trigger behavioral oscillations, with the aim to study in depth the properties of these perceptual rhythmicity. The second study investigated the effect of saccades on the pupillary response. We studied the perceptual and the
pupillary dynamics at around the time of a saccade, looking for possible correlation between the perceptual response and the pupillary
constriction. In the third study, we moved to analyze the effect of a simple hand action (button press) over contrast sensitivity, investigating
also some possible modulatory effects of ambient luminance. Finally, in the fourth study (comprising three experiments), we enucleated the
modulatory effects of ambient luminance via an electrophysiological and psychophysical investigation. A general conclusion will sum up the
present findings shown here, suggesting possible future directions.
36
方柏元. « Digital-micro-fluid manipulation and oscillation behavior ». Thesis, 2008. http://ndltd.ncl.edu.tw/handle/75891862949732362574.
Texte intégral
37
Huang, Jyun Ming, et 黃俊銘. « Nonlinear Oscillation Behavior of a Gyrotron Traveling-Wave Amplifier ». Thesis, 2010. http://ndltd.ncl.edu.tw/handle/88296657578054426017.
Texte intégral
38
Devarakonda, Nagini. « Nonlinear Behavior of Longitudinal Waves in the Oscillations of Rijke Tube ». 2007. http://trace.tennessee.edu/utk_gradthes/278.
Texte intégralRésumé :
The Rijke tube device has been employed since its invention in 1859 in the experimental study of many examples of thermo-acoustic phenomena. The device exhibits generation of acoustic oscillations by heat energy supplied to the flow field in the fashion of a selfexcited oscillator. In recent times, the Rijke tube has proved to be a valuable tool in simulation of combustion instability phenomena in rockets and industrial burners. Despite the simplicity of the device, the Rijke tube simulates most important geometrical and physical features that lead to the growth of nonlinear pressure oscillations in combustion chambers. For example it provides a through-flow as in a rocket chamber and is fixed with an energy source that can cause unsteady combustion. The open ends and geometrical simplicity leads to easy accessibility for instrumentation to make measurements that would not be possible in actual combustion chambers. During operation, wave motions are generated by transfer of energy from a heated grid placed at a point within the chamber that can be related to theoretical models for the phenomenon by Rayleigh and other investigators. However, initially, there is exponential growth of these oscillations to high amplitude and transition to a nonlinear limit cycle at a nearly fixed amplitude (usually lasting several seconds) due to natural nonlinearities in the system. The hypothesis advanced in this thesis to explain this nonlinear limiting effect that is the wave steepening occurs in a manner analogous to similar generation of steep wave fronts in rocket motor chambers. The latter proposal is based on: 1) direct observation (using Schlieren techniques) of traveling shock-like waves in axial mode instability, 2) correlation of the observed waves with spectral components similar to that of sawtooth structure, and 3) theoretical calculations showing that the limit amplitude phenomenon is directly related to the cascade of energy from lower frequency standing acoustic modes to higher harmonics leading to characteristic spectrum similar to that of a traveling steep-fronted wave. In prior research, the ‘mechanism’ of initiation of instability in the system has been the main focus. The goal of the research described in this thesis is to measure and to characterize the signal produced during the high- amplitude (nearly steady state) oscillations at the limit cycle. The intent was to demonstrate in a very simple way that the gas motions produced during the limit cycle in the Rijke tube have the same characteristics observed in many years of rocket testing. The observations again verify the great utility of the Rijke tube in seeking better understanding of the analogous rocket instability.
39
Yang, Rong-Huei, et 楊榮輝. « Dynamic Behavior Study In Laser Syster From Chaos To Quasiperiodic Relaxation Oscillations ». Thesis, 2010. http://ndltd.ncl.edu.tw/handle/40100819131938472505.
Texte intégralRésumé :
碩士國立交通大學
理學院碩士在職專班應用科技學程
98
The purpose of this study is by experiments and observations to discover the output signal, it is produced by the plane-parallel resonator. The output time domain signal is continuous wave (CW) observed under the general oscilloscope (resolution 500MHz). The CW signal is parallel with X-axis (time axis). But when we observed the signal under the high speed oscilloscope (resolution 40GHz), there were still dynamic phenomena in the optical resonator. By means of changed the different factors, for examples, changed wedge-cut laser crystal and wedge-cut output coupler, we can clearly observe dynamic variations and fluctuations in different situations. Therefore, to advance experiments and discover that using the closed coupled cavity is to form the optical resonator. It may obtain not only a uniform periodic self pulsations signal but also a near perfect mode-locking output pattern. Besides the cavity can also offer a compact size resonator, easily modulate the length of the optical cavity, and obtain different repeating frequency。 Due to the higher laser output repeating frequencies、 sinusoidal-like pattern、 shortened the cavity and simple resonator structure characteristics, it can extremely get promising applications in industrial fields, such as applications in telecommunication systems.
40
Moreland, Heather L. « Determination of the Filippov solutions of the nonlinear oscillator with dry friction ». Thesis, 2001. http://hdl.handle.net/1957/32440.
Texte intégralRésumé :
In previous papers by Awrejcewicz in 1986 and Narayanan and Jayaraman in
1991, it was claimed that the nonlinear oscillator with dry friction exhibited chaos
for several forcing frequencies. The chaos determination was achieved using the
characteristic exponent of Lyapunov which requires the right-hand side of the differential
equation to be differentiable. With the addition of the dry friction term,
the right-hand side of the equation of motion is not continuous and therefore not
differentiable. Thus this approach cannot be used. The Filippov definition must
be employed to handle the discontinuity in the spatial variable. The behavior of the
nonlinear oscillator with dry friction is studied using a numerical solver which produces
the Filippov solution. The results show that the system is not chaotic; rather
it has a stable periodic limit cycle for at least one forcing frequency. Other forcing
frequencies produce results that do not clearly indicate the presence of chaotic
motion.Graduation date: 2002
41
Gottlieb, Oded. « Nonlinear oscillations, bifurcations and chaos in ocean mooring systems ». Thesis, 1991. http://hdl.handle.net/1957/36341.
Texte intégralRésumé :
Complex nonlinear and chaotic responses have been recently observed in various
compliant ocean systems. These systems are characterized by a nonlinear mooring
restoring force and a coupled fluid-structure interaction exciting force. A general class
of ocean mooring system models is formulated by incorporating a variable mooring
configuration and the exact form of the hydrodynamic excitation. The multi-degree of
freedom system, subjected to combined parametric and external excitation, is shown to
be complex, coupled and strongly nonlinear.
Stability analysis by a Liapunov function approach reveals global system
attraction which ensures that solutions remain bounded for small excitation.
Construction of the system's Poincare map and stability analysis of the map's fixed
points correspond to system stability of near resonance periodic orbits. Investigation of
nonresonant solutions is done by a local variational approach. Tangent and period
doubling bifurcations are identified by both local stability analysis techniques and are
further investigated to reveal global bifurcations. Application of Melnikov's method to
the perturbed averaged system provides an approximate criterion for the existence of
transverse homoclinic orbits resulting in chaotic system dynamics. Further stability
analysis of the subharmonic and ultraharmonic solutions reveals a cascade of period
doubling which is shown to evolve to a strange attractor.
Investigation of the bifurcation criteria obtained reveals a steady state
superstructure in the bifurcation set. This superstructure identifies a similar bifurcation
pattern of coexisting solutions in the sub, ultra and ultrasubharmonic domains. Within
this structure strange attractors appear when a period doubling sequence is infinite and
when abrupt changes in the size of an attractor occur near tangent bifurcations.
Parametric analysis of system instabilities reveals the influence of the convective inertial
force which can not be neglected for large response and the bias induced by the
quadratic viscous drag is found to be a controlling mechanism even for moderate sea
states.
Thus, stability analyses of a nonlinear ocean mooring system by semi-analytical
methods reveal the existence of bifurcations identifying complex periodic and aperiodic
nonlinear phenomena. The results obtained apply to a variety of nonlinear ocean
mooring and towing system configurations. Extensions and applications of this research
are discussed.Graduation date: 1992
42
Chen-HsuanFang et 方晨亘. « Studies on oscillation behavior of EIT-based light storage and retrieval ». Thesis, 2013. http://ndltd.ncl.edu.tw/handle/21176498166677129618.
Texte intégralRésumé :
碩士國立成功大學
物理學系碩博士班
101
We experimentally study on the oscillation behavior of light storage and retrieval due to the interference effect of multiple electromagnetically-induced-transparency systems in Zeeman degenerate states. The experiment is performed in cold Rubidium atoms with an optical density of about 20. We measure the oscillation frequency of the retrieved light as a function of the strength of the external magnetic field. Comparison between the experimental data and theoretical predictions shows good agreement. Moreover, we can reduce the residual magnetic field to below 1 mG with this method.
43
King, Paul E. « Deterministic and stochastic control of nonlinear oscillations in ocean structural systems ». Thesis, 2006. http://hdl.handle.net/1957/29586.
Texte intégralRésumé :
Complex oscillations including chaotic motions have been identified in
off-shore and submerged mooring systems characterized by nonlinear fluid-structure
interactions and restoring forces. In this paper, a means of controlling
these nonlinear oscillations is addressed. When applied, the controller is able to
drive the system to periodic oscillations of arbitrary periodicity. The controller
applies a perturbation to the nonlinear system at prescribed time intervals to guide
a trajectory towards a stable, periodic oscillatory state. The controller utilizes the
pole placement method, a state feedback rule designed to render the system
asymptotically stable. An outline of the proposed method is presented and
applied to the fluid-structure interaction system and several examples of the
controlled system are given. The effects of random noise in the excitation force
are also investigated and the subsequent influence on the controller identified. A
means of extending the controller design is explored to provide adequate control
in the presence of moderate noise levels. Meanwhile, in the presence of over
powering noise or system measurements that are not well defined, certain filtering
and estimation techniques are investigated for their applicability. In particular,
the Iterated Kalman Filter is investigated as a nonlinear state estimator of the
nonlinear oscillations in these off-shore compliant structures. It is seen that
although the inclusion of the nonlinearities is theoretically problematic, in
practice, by applying the estimator in a judicious manner and then implementing
the linear controllers outlined above, the system is able to estimate and control the
nonlinear systems over a wide area of pseudo-stochastic regimes.Graduation date: 2006
44
ZHAO, YOU-GUANG, et 趙有光. « Oscillation and asymptotic behavior of solutions of a second order nonlinear difference equation ». Thesis, 1990. http://ndltd.ncl.edu.tw/handle/30355723074142505151.
Texte intégral
45
Chang, Haw-Yuan, et 張浩元. « Nonlinear PI/ PID control straegies of bioreactor systems with self-oscillating behavior ». Thesis, 2004. http://ndltd.ncl.edu.tw/handle/33874777368548037248.
Texte intégralRésumé :
碩士國立雲林科技大學
工業化學與災害防治研究所
92
This article into three partly, to confer nonlinear PI/PID straegies recently to expand of bioreactor systems with self-oscillating behavior. Control law have a percentage, in-tegral and differential parameters in common with classic PID controller the base is second order differential equationis, both is convenient to make use of industry.The classic PID controller already had many methods to find the percentage、integral and differential parameters for optimum operation.This paper use a optimal control design to find the percentage, integral and differential parameters of nonlinear PID controller. The performance and robustness characteristics of developed control methodologies are evaluated through simulations.
46
KIVINDU, REUBEN MWANZA, et REUBEN MWANZA KIVINDU. « Flame Behavior and Thermal Structure of Combusting Non-premixed Plane Jets with and without Self-excited Transverse Oscillations ». Thesis, 2018. http://ndltd.ncl.edu.tw/handle/yn4gb2.
Texte intégralRésumé :
博士國立臺灣科技大學
機械工程系
106
The flame behavior and thermal structure of combusting non-premixed plane jets with and without self-excited transverse oscillations were investigated experimentally. The transversely-oscillating plane jet was generated by a specially designed fluidic oscillator. The flame behavior was studied using the instantaneous- and long-exposure photography techniques. Temperature and combustion-product concentration distributions were measured using a fine-wire type-R thermocouple and a gas analyzer, respectively. The results showed that the combusting transversely-oscillating plane jets had distributed blue flames with plaited-like edges, while the corresponding combusting non-excited plane jet had laminar blue-edged flames in the near field. The transversely-oscillating plane jet flames were categorized into three characteristic flame modes: attached flame, transitional flame, and lifted flame. The non-excited plane jet flames showed three flame modes, viz; momentum-deficit flame, transitional flame, and momentum-dominated flame. At high Reynolds number (Rej > 1204), the transversely-oscillating jet flames were significantly shorter and wider with shorter reaction-dominated zones than those of the non-oscillating plane jet flames. In addition, the transversely-oscillating combusting jets presented larger carbon dioxide and smaller unburned hydrocarbon concentrations, as well as portrayed characteristics of partially premixed flames. The non-oscillating combusting jets presented characteristics of diffusion flames. Generally, the transversely-oscillating jet flame had combustion performance characteristics that were superior to its non-oscillating plane jet flame counterpart. The improved combustion performance of the transversely-oscillating jet was due to the enhanced entrainment, mixing, and lateral spreading of the jet flow, which were induced by the vortical flow structure generated by lateral periodic jet oscillations, as well as the high turbulence created by the breakup of the vortices. The effects of co-flowing air streams and aspect ratios on the flame behavior and thermal structure of gaseous fuel jets issued from rectangular nozzles were additionally investigated and discussed.
47
LIU, SHIH-PEI, et 劉師沛. « Numeric investigation of the 3-D nonlinear resonant behaviors of gas oscillation of in a closed tube ». Thesis, 2011. http://ndltd.ncl.edu.tw/handle/j44s8y.
Texte intégralRésumé :
碩士國立臺灣科技大學
機械工程系
99
Traditionally, the study of standing wave resonance inside a closed tube is focussed on the low frequency resonance system (generally below 200 Hz), which is limited by the mechanical transmission mechanisms used. In order to reduce the space taken by the mechanical transmission mechanisms, high frequency resonance system is favored. In addition, it is very difficult to measure the variations of physical quantities inside the resonance tube with current technologies available. However, this presents no difficulties in using numerical simulation to monitor the variations of physical quantities inside the tube. In this work, the resonance behaviors inside a closed tube (0.0435 m in length, 0.026 m inside diameter) driven by a reciprocating piston at a frequency of 4000 Hz are studied. The tube is assumed to be axis-symmetric and the walls are assumed to be adiabatic. The effects of detuning and frequency multiplication on the nonlinear resonance are investigated. Closed to the exact resonance, the pressure waveforms are significantly distorted and become asymmetric. Formation of shock waves can be clearly observed. Due to the steep velocity gradient inside the velocity boundary layer, significant shear stresses occurs near the velocity boundary layer and kinetic energy is dissipated and converted into heat. This heat will accumulate inside the velocity boundary layer due to the adiabatic boundary conditions. This, in turn, will lead to the growth of thermal boundary layer and result in a very thick thermal boundary layer. The results of the simulations can provide the necessary guidelines for the selection of the proper locations of the stack plates inside a thermoacoustic resonance tube.
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Cheng-HanWu et 吳承翰. « Experimental Studies of Two Phase Flow Behaviors and Heat Transfer within Surface Modified Oscillating Heat Pipes ». Thesis, 2015. http://ndltd.ncl.edu.tw/handle/46780062686056620431.
Texte intégral
49
« The Effects of Nonlinear Damping on Post-flutter Behavior Using Geometrically Nonlinear Reduced Order Modeling ». Master's thesis, 2015. http://hdl.handle.net/2286/R.I.29759.
Texte intégralRésumé :
abstract: Recent studies of the occurrence of post-flutter limit cycle oscillations (LCO) of the F-16 have provided good support to the long-standing hypothesis that this phenomenon involves a nonlinear structural damping. A potential mechanism for the appearance of nonlinearity in the damping are the nonlinear geometric effects that arise when the deformations become large enough to exceed the linear regime. In this light, the focus of this investigation is first on extending nonlinear reduced order modeling (ROM) methods to include viscoelasticity which is introduced here through a linear Kelvin-Voigt model in the undeformed configuration. Proceeding with a Galerkin approach, the ROM governing equations of motion are obtained and are found to be of a generalized van der Pol-Duffing form with parameters depending on the structure and the chosen basis functions. An identification approach of the nonlinear damping parameters is next proposed which is applicable to structures modeled within commercial finite element software.
The effects of this nonlinear damping mechanism on the post-flutter response is next analyzed on the Goland wing through time-marching of the aeroelastic equations comprising a rational fraction approximation of the linear aerodynamic forces. It is indeed found that the nonlinearity in the damping can stabilize the unstable aerodynamics and lead to finite amplitude limit cycle oscillations even when the stiffness related nonlinear geometric effects are neglected. The incorporation of these latter effects in the model is found to further decrease the amplitude of LCO even though the dominant bending motions do not seem to stiffen as the level of displacements is increased in static analyses.Dissertation/Thesis
Masters Thesis Mechanical Engineering 2015
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Cheung, Shilin. « Interfacial Behavior of Immortalized Murine Hypothalamic Neurons Studied by an Acoustic Transverse Wave Biosensor ». Thesis, 2012. http://hdl.handle.net/1807/32683.
Texte intégralRésumé :
The objective of this thesis was to relate and link the physiological responses of the cells to the electrical responses or output obtained from the TSM acoustic wave sensor. In particular, the device was applied to the study of immortalized murine hypothalamic neurons (mHypoE-38 and -46 cell models) under a variety of conditions and stimuli. Cellular studies which lead to the production of detectable neuronal responses include neuronal deposition, adhesion and proliferation, alteration in the extent of specific cell-surface interactions, actin filament and microtubule cytoskeletal disruptions, effects of cell depolarization, solution tonicity, inhibition of the Na+-K+ pump via ouabain, effects of neuronal synchronization and the effects ligand-receptor interaction (glucagon). In addition, the introduction of drugs, neurotrophic factors (forskolin and beterferon), toxicity agents (NaOH, EtOH) and TiO2 nanoparticles were similarly investigated. A preliminary study conducted with mouse embryonic stem cells showed that not all cell lines are suitable for investigation with the TSM sensor at the current stage of sensor development.
It has been found that control studies conducted with water as the solvent and the bare sensor substrate is insufficient to model the behavior of the sensor in the absence of cells. When biological buffers are used in addition to protein coatings the sensor responses are altered in magnitude and direction.
To analyze the full range of cellular changes observed on the TSM sensor, the full impedance spectrum is required. As such in this thesis, the series and parallel resonant frequencies, the motional resistance, the maximum phase of the impedance and the static capacitance (fs, fp, Rm, θmax and Co were used to characterize the cellular responses observed. In the presence of cells fs shifts are largely influenced by the damping of the TSM resonator. The formation of cell-surface interactions and hence the increase in coupling and acoustic energy dissipation can be modeled as an additional resistor in the BVD model. Further sensor and cellular changes can be obtained by negating the effects of damping from fs with the use of Rm and θmax.