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Tsang, Chi Foon. "Dynamics of distributed feedback lasers." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320037.
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Graybill, Scott Jason. "Modelling nephron dynamics and tubuloglomerular feedback." Thesis, University of Canterbury. Centre for Bioengineering, 2010. http://hdl.handle.net/10092/4116.
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The kidneys are amazingly versatile organs that perform a wide range of vital bodily functions. This thesis provides an analysis into a range of mathematical models of the tubuloglomerular feedback (TGF) mechanism. The TGF mechanism is an autoregulatory mechanism unique to the kidney that maintains approximately constant blood flow to the organ despite wide fluctuations in pressure. Oscillations in pressure, flow, and sodium chloride concentration have been attributed to the action of the TGF mechanism through a number of experimental studies. These oscillations appear spontaneously or in response to a natural or artificial pressure step or microperfusion.
The reason for sustained oscillatory behaviour in nephrons is not immediately clear. Significant research has gone into experimentally determining the signal to the TGF mechanism, but the physiological significance is not mentioned in the literature. Considerable modelling of the oscillations attributed to the TGF mechanism has also been undertaken. However, this modelling uses models that are inherently oscillatory, such as a second-order differential equation or delay differential equations. While these models can be fitted to closely approximate the experimental results they do not address the physiological factors that contribute to sustained oscillations. This thesis aims to determine the contributing factors to the sustained oscillations. By understanding these factors a better hypothesis of the physiological role of the oscillations should be possible.
Chapter 3 presents a mathematical model by Holstein-Rathlou and Marsh [28] that uses a partial differential equation (PDE) model for the tubule and a second-order differential equation for the TGF feedback. The remainder of this chapter shows that oscillations occur without an inherently oscillatory second-order differential equation due to the delays in the system. Tubular compliance was also shown to be necessary for sustained oscillations. Sustained oscillations were not exhibited in the TGF model with a noncompliant tubule. Although damped oscillations were exhibited for a wide range of parameter space. Adding compliance to the tubule increased the delay around the loop of Henle. This additional delay elicited sustained oscillations.
The computationally expensive PDE model of 3 was simplified to an ordinary differential equation (ODE) model in Chapter 4 by assuming a spatial profile. This model exhibits much of the same qualitative behaviour as the PDE model including sustained oscillations for similar ranges of parameter space. Compliance was also found to be important in the generation of sustained oscillations in agreement with the PDE tubule model. This model is less computationally expensive than the PDE model and allows analysis that was unfeasible with the PDE model.
Significant natural and artificial blood pressure fluctuation occur in experimental rat models. Chapter 5 examines the effect of inlet pressure forcing on a nonoscillatory and an oscillatory model. The inherently nonoscillatory noncompliant model becomes oscillatory with a physiologically realistic pressure forcing. The oscillatory compliant model remains oscillatory with the addition of a inlet pressure forcing. Pressure fluctuations were hypothesised to contribute to sustained oscillations and could be validated experimentally.
Two extensions to the single nephron TGF models are presented in Chapter 6. A realistic juxtaglomerular delay is added to the single nephron models with both the ODE and PDE tubular models. Physiologically realistic juxtaglomerular delays induce sustained oscillations in the otherwise nonoscillatory noncompliant models. The remainder of this chapter presents a different model for a variable interstitial sodium chloride concentration profile. This model demonstrates experimentally observed function of the countercurrent mechanism by which a concentration gradient is set up and maintained in the interstitium.
Two single nephron models with ODE tubular models are coupled in Chapter 7. The coupling is modelled through the effect on the resistance of their neighbouring nephron's afferent arteriole resistance. The coupled nephron model exhibits entrainment as observed experimentally. Inhibiting the oscillation in one nephron reduces the amplitude of the oscillation in its neighbour. This result compares well with experiments where the TGF mechanism in one nephron is blocked by the administration of furosemide.
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Longo, Diane Marie. "The role of feedback in signaling dynamics." Diss., [La Jolla] : University of California, San Diego, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p3356134.
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Thesis (Ph. D.)--University of California, San Diego, 2009.Title from first page of PDF file (viewed June 15, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 99-107).
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Bhatia, Abhishek. "Multivariable Feedback Control of Unstable Aircraft Dynamics." University of Cincinnati / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1479809412341377.
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Pearson, Richard John. "Mass estimation, dynamics and feedback in galaxy groups." Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/5676/.
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Accurate mass estimates for galaxy groups and clusters are important for understanding the evolution of matter within the universe. In this thesis we first discuss methods of mass estimation currently used within the literature, and introduce a set of scaling relations for mass estimation in cases where literature methods are not applicable. We find that methods based on group richness provide the best (i.e. lowest scatter) mass estimator. Secondly, we study the impact of feedback on hot group gas for a sample of optically selected groups. We refine the group selection using their dynamical state, identified through substructure in the distribution of member galaxies. We find this sample to be underluminous compared to an X-ray selected sample. Furthermore, with two groups showing high 2σ lower limits on entropy, the population of high entropy groups predicted by hydrodynamical simulations may have been detected. Finally, we combine measures of dynamical state and mass estimation scaling relations to understand how the presence of substructure can impact upon the ability to reliably estimate group and cluster masses. We find that substructure introduced through poor group identification has the largest effect on the quality of the final mass estimates.
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Lu, Timothy K. (Timothy Kuan-Ta) 1981. "A feedback analysis of outer hair cell dynamics." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/29677.
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Thesis (M.Eng. and S.B.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.Includes bibliographical references (leaves 144-146).
Outer hair cells (OHCs) generate active forces in the mammalian cochlea. Acting as cochlear amplifiers, OHCs can counteract viscous drag, generating high gain at characteristic frequencies and allowing for the sharp frequency selectivity and sensitivity observed in mammals. Excitatory displacement of the basilar membrane causes depolarization of OHC membrane potentials which results in contraction. The motor protein prestin is driven by receptor potentials. However, low-pass filtering by the plasma membrane should severely attenuate the receptor potential at high frequencies (> 100 kHz) where mammalian hearing has been observed. Thus, an open question is how OHCs can respond at these high frequencies despite their low frequency cutoff. Inspired by the use of feedback in mechanical and electrical systems to accelerate slow poles, I demonstrate that negative feedback from the coupling of two mechanical modes of vibration can lead to a membrane time constant speedup and a sharpening of the mechanical response.
y Timothy K. Lu.
M.Eng.and S.B.
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Bauer, Stefan. "Nonlinear dynamics of semiconductor lasers with active optical feedback." Doctoral thesis, [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=973616423.
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Boulet, Jason. "The Effects of Delayed Visual Feedback on Postural Dynamics." Thesis, University of Ottawa (Canada), 2010. http://hdl.handle.net/10393/28594.
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We report on experiments and modeling of the interactions between delayed visual feedback and postural control in human quiet stance. A heuristic model is derived based on physiological and psychophysical parameters. The level of agreement found between the data and the model was found to be very good for power spectral densities, probability density functions and mean-squared displacements (or Hurst exponents). The stochastic delayed differential model identifies critical time scales of postural corrections. We also investigate properties of the model such as stability, small delay approximations and the power spectral density. Lastly, we use nonlinear time series techniques to investigate the temporal structure of the experimental postural dynamics. We propose the first dynamical model of visually assisted posture control.
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Rosino, Jeffery. "AUTONOMOUS ROBOTIC AUTOMATION SYSTEMWITH VISION FEEDBACK." Master's thesis, University of Central Florida, 2004. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2645.
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In this thesis, a full design, development and application of an autonomous robotic automation system using vision feedback is performed. To realize this system, a cylindrical manipulator configuration is implemented, using a personal computer (PC) based PID controller from National Instruments. Full autonomous control will be achieved via a programmable human machine interface (HMI) developed on a PC using Borland C++ Builder. The vision feedback position control is accomplished using an ordinary "off-the-shelf" web camera. The manuscript is organized as follows; After Chapter 1, an introduction to automation history and its role in the manufacturing industry, Chapter 2 discusses and outlines the development of the robotic kinematics and dynamics of the system. A control strategy is also developed and simulated in this chapter. Chapter 3 discusses color image processing and shows the development of the algorithm used for the vision feedback position control. Chapter 4 outlines the system development, which includes the hardware and software. Chapter 5 concludes with a summary, and improvement section. The process used as a basis for the design and development of this thesis of this thesis topic was constructed from a manual capacitor orientation check test station. A more detailed definition and objective is presented in the introduction.M.S.E.E.
Department of Electrical and Computer Engineering
Engineering and Computer Science
Electrical Engineering
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Neugebauer, Felix Sebastian. "Tayloring Brazil: a system dynamics model for monetary policy feedback." reponame:Repositório Institucional do FGV, 2011. http://hdl.handle.net/10438/9098.
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The thesis introduces a system dynamics Taylor rule model of new Keynesian nature for monetary policy feedback in Brazil. The nonlinear Taylor rule for interest rate changes con-siders gaps and dynamics of GDP growth and inflation. The model closely tracks the 2004 to 2011 business cycle and outlines the endogenous feedback between the real interest rate, GDP growth and inflation. The model identifies a high degree of endogenous feedback for monetary policy and inflation, while GDP growth remains highly exposed to exogenous eco-nomic conditions. The results also show that the majority of the monetary policy moves during the sample period was related to GDP growth, despite higher coefficients of inflation parameters in the Taylor rule. This observation challenges the intuition that inflation target-ing leads to a dominance of monetary policy moves with respect to inflation. Furthermore, the results suggest that backward looking price-setting with respect to GDP growth has been the dominant driver of inflation. Moreover, simulation exercises highlight the effects of the new BCB strategy initiated in August 2011 and also consider recession and inflation avoid-ance versions of the Taylor rule. In methodological terms, the Taylor rule model highlights the advantages of system dynamics with respect to nonlinear policies and to the stock-and-flow approach. In total, the strong historical fit and some counterintuitive observations of the Taylor rule model call for an application of the model to other economies.
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Henders, Michael G. "Nonlinear dynamics of the inverted pendulum under linear-feedback stabilization." Thesis, University of British Columbia, 1991. http://hdl.handle.net/2429/29971.
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Analysis is conducted on a linear control system used for the stabilization of an inverted pendulum, examining the behaviour of the system throughout its global state space. The dynamic equations of the inverted pendulum are obtained, and a linear state-feedback controller is designed, based on this system model, for its stabilization. The behaviour of the resulting closed-loop system is examined through simulation, in two stages.
In the first stage, the feedback controller is modified slightly to decouple the pendulum dynamics from those of its supporting cart, permitting examination of the pendulum dynamics in a two-dimensional state space, using phase plane analysis. In this way, a globally valid description of the pendulum dynamics is obtained, revealing the existence of two state attractors in this modified system. The feedback controller is seen to create a stable point attractor in the phase plane, as intended, but the basin of attraction of this point is of unusual shape and limited extent, due to the nonlinearity of the pendulum dynamics. All initial system states outside this basin are drawn to the second state attractor, which is a stable limit cycle.
As the second stage of analysis, the system is examined with its original controller; characterization of the overall dynamics then requires a four-dimensional state space. The continued existence of a point attractor at the state space origin is demonstrated, and the basin of attraction of this point is mapped numerically, using a state space sampling algorithm, which might readily be applied to the analysis of other dynamic systems. This basin is presented as a series of three-dimensional sections of the full four-dimensional region; taken together, these sections outline the entire basin map. The boundaries of the origin-bound basin are seen to be highly irregular, and potentially fractal in nature.
The existence of an infinite set of such four-dimensional stability regions is demonstrated, and complex, potentially chaotic, behaviour is observed outside the basins of attraction; it is not clear whether or not a four-dimensional counterpart of the limit cycle (from the first stage analysis) exists.Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate
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Hohl, Angela. "Dynamics of semiconductor laser systems with optical injection and external feedback." Diss., Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/29450.
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Ray, William Richard. "Stochastic and deterministic dynamics in a semiconductor laser with optical feedback." College Park, Md. : University of Maryland, 2006. http://hdl.handle.net/1903/4072.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2006.Thesis research directed by: Physics. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Fernandes, Cristina A. C. "Investigating the structure, dynamics and feedback processes of active galactic nuclei." Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.543552.
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Tomac, Mehmet Nazim. "Internal Fluid Dynamics and Frequency Characteristics of Feedback-Free Fluidic Oscillators." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1357142702.
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Tokuda, Hidekazu. "Dynamics of nonlinear dissipative traveling waves under feedback and external forcing." 京都大学 (Kyoto University), 2007. http://hdl.handle.net/2433/136751.
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Peil, Michael. "Dynamics and synchronization phenomena of semiconductor lasers with delayed optical feedback utilizing nonlinear dynamics for novel applications." Berlin Logos-Verl, 2006. http://deposit.ddb.de/cgi-bin/dokserv?id=2793060&prov=M&dok_var=1&dok_ext=htm.
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Elibiary, Khalid. "Utilization of force feedback for A poultry cutting application." Thesis, Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/17849.
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Theodosiou, Loukas [Verfasser]. "The role of the environment in eco-evolutionary feedback dynamics / Loukas Theodosiou." Kiel : Universitätsbibliothek Kiel, 2018. http://d-nb.info/1173703438/34.
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Furuyama, Jonathan Kiyoshi. "Contrast enhancement in MRI by non-linear dynamics using active feedback techniques." Diss., Restricted to subscribing institutions, 2009. http://proquest.umi.com/pqdweb?did=1835545411&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Friart, Gaetan. "Semiconductor laser dynamics: two polarization feedback, quantum cascade lasers, and ring lasers." Doctoral thesis, Universite Libre de Bruxelles, 2017. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/248835.
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Semiconductor lasers (Sls) are very sensitive to external perturbations which may destabilize their steady output. This is particularly striking when the SL is subject to optical feedback, i.e. when part of the light coming out of the laser is reinjected in the cavity after reflection from a distant mirror. For some applications, this is a nuisance that we wish to avoid. But optical feedback may also drive the laser into dynamical regimes which are useful for new applications. In this thesis, we study different problems where an SL is subject to a delayed feedback or to an injected signal. These problems are motivated by recent experiments, technological issues, or particular dynamical phenomena. Specifically, we combine analytical techniques, numerical simulations, and experiments to investigate the bifurcation mechanisms leading to a large variety of oscillatory outputs. The systems that we discuss are an edge-emitting laser with polarization-rotated optical feedback, a two-mode laser with optical injection, a quantum cascade laser with optical feedback, and a semiconductor ring laser with optical feedback. We show that the bifurcations from the steady-states are of primary importance. They not only delimit the stability boundaries of the laser output but they also form the backbone structure of many pulsating waveforms. We investigate these bifurcations in detail in order to find the best operating conditions to observe specific dynamical regimes. Our results highlight laser key parameters that allow their efficient control.Les lasers à semi-conducteur sont sensibles aux perturbations externes et celles-ci peuvent déstabiliser leur faisceau de sortie d’intensité constante. Ceci est particulièrement marquant quand le laser à semi-conducteur est sujet à un feedback optique, c’est-à-dire quand une partie de la lumière sortant du laser est réinjectée dans sa cavité après réflexion par un miroir distant. Pour certaines applications, cela représente une nuisance que l’on souhaite éviter. Mais le feedback optique peut aussi engendrer des régimes dynamiques utiles pour de nouvelles applications. Dans cette thèse, nous étudions différents problèmes où un laser à semi-conducteur est soumis à un feedback retardé ou à un signal injecté. Nos travaux sont motivés par de récentes expériences, des questions technologiques ou des phénomènes dynamiques particuliers. Nous combinons des techniques analytiques, des simulations numériques ainsi que des expériences afin d’analyser les mécanismes de bifurcation menant à une large variété de régimes oscillants.Nous étudions en premier lieu la dynamique d’un laser à semi-conducteur soumis à un feedback avec rotation de la polarisation. Nous examinons, à la fois théoriquement et expérimentalement, la séquence de bifurcations menant à des oscillations sous forme d’ondes carrées. Nous mettons en évidence une multistabilité entre différentes ondes carrées de périodes spécifiques. Nous introduisons alors un mécanisme de contrôle qui nous permet de sélectionner l’onde carrée désirée. Nous analysons ensuite les frontières de stabilité d’un laser à semi-conducteur à deux polarisations soumis à une injection optique. Nous montrons que si les gains des deux modes de polarisation sont suffisamment proches, un état stationnaire mixte stable peut exister. Nous explorons également les conditions permettant une bistabilité entre un état stationnaire pur et un état stationnaire mixte. Les lasers à cascade quantique sont de nouveaux lasers à semi-conducteur prometteurs qui possèdent une forte tolérance au feedback optique. Nous examinons de façon systématique leur stabilité dans la limite des grands retards. Nous montrons que des instabilités oscillantes sont cependant possibles pour de faibles valeurs du courant de pompe. Le dernier dispositif que nous étudions dans cette thèse est le laser à semi-conducteur en anneau soumis à un feedback optique. Nous identifions le mécanisme de bifurcation, appelé pont de bifurcation, responsable des instabilités oscillantes dans le faisceau de sortie du laser. Ces oscillations sont indésirables pour la plupart des applications impliquant de tels lasers. Nous montrons qu’elles peuvent être évitées en contrôlant la phase du feedback.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
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Mercier, Emeric. "High-frequency nonlinear dynamics of a laser diode with phase-conjugate feedback." Thesis, CentraleSupélec, 2016. http://www.theses.fr/2016SUPL0010/document.
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Nous étudions l’influence d’une rétroaction optique à conjugaison de phase dans une diode laser. Ce type de rétroaction a été peu étudié et nous montrons ici qu’il donne des résultats intéressants, permettant de débloquer du contenu à haute fréquence. Cela pourrait mener à de meilleures performances dans des systèmes de génération de nombres aléatoires utilisant du chaos optiqueWe study the influence of phase-conjugate feedback in a laser diode. This type of feedback has not been studied a lot and yet we show here that it can give interesting results. It unlocks oscillations at high frequencies. This could lead to an improvement in the performance of random number generators based on optical chaos
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TSURUOKA, SYUJI. "DYNAMICS AND FEEDBACK CONTROL OF CRYSTAL SIZE DISTRIBUTION IN A CONTINUOUS CRYSTALLIZER." Diss., The University of Arizona, 1986. http://hdl.handle.net/10150/183847.
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A simulation algorithm for crystal size distribution dynamics in a continuous crystallizer was developed using the method of lines. Dimensionless crystal sizes, in vector form, were used as state variables. Simulation results using this algorithm satisfied stability criteria for continuous crystallizers, which had been developed previously using different methods. The use of a state space representation of the algorithm permits the use of well-known theoretical and numerical approaches to the modeling of an experimental R-z crystallizer and for design of a proportional controller for a continuous crystallizer system. Boundary conditions defined by the nucleation/growth rate kinetics were separately written as an auxiliary function so that other kinetics can be substituted without any change of the main algorithm. This implies that the algorithm is applicable for any growth-type particulate system. CSD dynamics from an experimental crystallizer were satisfactorily modelled using this algorithm with reasonable parameters: e.g. the recycle ratios of the fines dissolver and the product classifier, crystal sizes at the upper cut size of the dissolver and at the lower cut size of the classifier, initial CSD, and the form of the upset. Algorithms for controller design using pole placement and optimization techniques were applied to develop a proportional matrix controller for an R-z crystallizer. It was evident that pole placement is a better method than optimization to design a controller for this crystallizer system. The system poles are concentrated at a point and it is necessary to assign the controller poles further apart to obtain appropriate control. To summarize controller design using the pole placement method, a schematic flow diagram of a system controller using the minimum order Luenberger observer was illustrated. In this example, only a few population densities need to be measured to drive the controller.
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Ushakov, Oleg. "Self-organization in semiconductor lasers with ultra-short optical feedback." Doctoral thesis, [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=985232145.
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Züllich, Gunda. "Migration and development in Senegal : a system dynamics analysis of the feedback relationships." Master's thesis, Universität Potsdam, 2011. http://opus.kobv.de/ubp/volltexte/2012/5783/.
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This thesis investigates the reciprocal relationship between migration and development in Senegal. Therewith, it contributes to the debate as to whether migration in developing countries enhances or rather impedes the development process. Even though extensive and controversial discussions can be found in the scientific literature regarding the impact of migration on development, research has scarcely examined the feedback relationships between migration and development. Science however agrees with both the fact that migration affects development as well as that the level of development in a country determines migration behaviour. Thus, both variables are neither dependent nor independent, but endogenous variables influencing each other and producing behavioural pattern that cannot be investigated using a static and unidirectional approach. On account of this, the thesis studies the feedback mechanisms existing between migration and development and the behavioural pattern generated by the high interdependence in order to be able to draw conclusions concerning the impact of changes in migration behaviour on the development process.
To explore these research questions, the study applies the computer simulation method ‘System Dynamics’ and amplifies the simulation model for national development planning called ‘Threshold 21’ (T21), representing development processes endogenously and integrating economic, social and environmental aspects, using a structure that portrays the reasons and consequences of migration. The model has been customised to Senegal, being an appropriate representative of the theoretical interesting universe of cases. The comparison of the model generated scenarios - in which the intensity of emigration, the loss and gain of education, the remittances or the level of dependence changes - facilitates the analysis.
The present study produces two important results. The first outcome is the development of an integrative framework representing migration and development in an endogenous way and incorporating several aspects of different theories. This model can be used as a starting point for further discussions and improvements and it is a fairly relevant and useful result against the background that migration is not integrated into most of the development planning tools despite its significant impact. The second outcome is the gained insights concerning the feedback relations between migration and development and the impact of changes in migration on development. To give two examples: It could be found that migration impacts development positively, indicated by HDI, but that the dominant behaviour of migration and development is a counteracting behaviour. That means that an increase in emigration leads to an improvement in development, while this in turn causes a decline in emigration, counterbalancing the initial increase. Another insight concerns the discovery that migration causes a decline in education in the short term, but leads to an increase in the long term, after approximately 25 years - a typical worse-before-better behaviour.
From these and further observations, important policy implications can be derived for the sending and receiving countries. Hence, by overcoming the unidirectional perspective, this study contributes to an improved understanding of the highly complex relationship between migration and development and their feedback relations.Die vorliegende Arbeit untersucht das wechselseitige Verhältnis zwischen Migration und Entwicklung im Senegal. Damit soll ein Beitrag zu der Debatte geleistet werden, ob Migration in Entwicklungsländern den Entwicklungsprozess eher fördert oder verhindert. Während die Frage nach der Auswirkung von Migration auf Entwicklung in der Literatur ausgiebig und kontrovers diskutiert wird, hat sich die Forschung bisher kaum den Rückkopplungen zwischen Migration und Entwicklung gewidmet, obwohl sich die Wissenschaft sowohl darüber einig ist, dass Migration den Entwicklungsprozess beeinflusst, als auch, dass der Entwicklungsstand eines Land das Migrationsverhalten bestimmt. Folglich sind beide Variablen weder abhängig, noch unabhängige, sondern endogene Variablen, die sich gegenseitig beeinflussen und damit Verhaltensweisen produzieren, deren Erforschung ein statischer, unidirektionaler Ansatz nicht gerecht wird. Deswegen fragt diese Arbeit nach den Rückwirkungsmechanismen, die zwischen Migration und Entwicklung existieren, und nach den Verhaltensweisen, die durch die hohe Interdependenz entstehen, um daraus Rückschlüsse auf die Frage ziehen zu können, welchen Einfluss Änderungen im Migrationsverhalten auf den Entwicklungsprozess haben. Um diese Forschungsfragen zu untersuchen wurde die Computersimulationsmethode System Dynamics genutzt und das Simulationsmodell zur nationalen Entwicklungsplanung, das ‚Threshold 21’ (T21), das die Entwicklungsprozesse endogen darstellt und soziale, ökonomische sowie ökologische Aspekte miteinander verknüpft, um eine Struktur erweitert, welche die Gründe und Konsequenzen von Migration abbildet. Dies wurde an den Senegal, ein angemessener Repräsentant der theoretisch interessanten Grundgesamtheit, angepasst. Der Vergleich der mit dem Modell generierten Szenarien, in denen die Intensität der Abwanderung, des Bildungsverlustes, des Bildungsgewinns, der Geldüberweisungen, oder der Abhängigkeit verändert wurden, ermöglichte die Analyse. Die Studie bringt zwei wichtige Ergebnisse hervor. Erstens entwickelt sie ein umfangreiches Modell, das Migration und Entwicklung endogen erklärt und verschiedene theoretische Ansatzpunkte enthält. Dies kann sowohl als Grundlage für weitere Diskussion und Verbesserungen genutzt werden, ist aber vor allem vor dem Hintergrund, dass Migration in den meisten Modellen zur Entwicklungsplanung trotz des relevanten Einflusses nicht integriert ist, ein wichtiges und nützliches Resultat. Zweitens konnte die Analyse des Verhaltens des Modells wichtige Erkenntnisse bezüglich der Rückwirkungsmechanismen zwischen Migration und Entwicklung und der Wirkung von Veränderungen in Migration auf Entwicklung erzielen. Um zwei Beispiele zu nennen, wurde herausgearbeitet, dass Migration sich positiv auf Entwicklung, gemessen am Human Development Index (HDI), auswirkt, dass es sich aber generell um ein sich ausgleichendes Verhalten handelt, da die positiven Einflüsse auf Entwicklung ihrerseits Migration verringern, wodurch die positiven Einflüsse wieder abnehmen. Ebenso konnte festgestellt werden, dass Migration für das Bildungsniveau zunächst eine Verschlechterung, später aber, nach ca. 25 Jahren, eine Verbesserung nach sich zieht. Aus diesen und weiteren Beobachtungen können wichtige Politikempfehlungen für die Sende- und Empfängerländer von Migration abgeleitet werden. Durch das Überwinden der unidirektionalen Betrachtungsweise trägt diese Arbeit somit zu einem besseren Verständnis des hoch komplexen und von Rückwirkungsmechanismen geprägten Verhältnisses zwischen Migration und Entwicklung bei.
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Vanreusel, Stephen. "Identification and multivariable feedback control of the vibration dynamics of an automobile suspension." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99119.
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This thesis considers the vibration control of an automobile suspension subject to road imperfections using multivariable feedback techniques.Frequency-domain system identification methods are applied to model the dynamic behaviour of the suspension system from experimental test data using a data analysis software tool called CIFER. Advanced features such as the Chirp-Z Transform and composite window techniques are used to extract high quality frequency responses. A linear multivariable state-space model is derived which matches the experimental frequency response data set in the frequency range 65Hz-240Hz.
Accurate uncertainty modeling on the nominal suspension is needed to design controllers achieving acceptable levels of robustness and performance. It is shown that modeling errors are best characterized using a combination of both additive and multiplicative uncertainty, as well as perturbations of the state-space model parameters.
Robust feedback control design techniques using H-infinity and mu-synthesis are presented. It is shown both through simulation and experiment that vibration attenuation over the frequency range 65Hz-120Hz is achieved without affecting the system dynamic behaviour outside this range.
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Wilson, Luke. "The influence of feedback connections on the dynamics of populations of spiking neurons /." Leeds : University of Leeds, School of Computer Studies, 2008. http://www.comp.leeds.ac.uk/fyproj/reports/0708/Wilson.pdf.
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Naknaimueang, Somprasong. "Control of spiral wave dynamics by feedback mechanism via a triangular sensory domain." [S.l.] : [s.n.], 2006. http://diglib.uni-magdeburg.de/Dissertationen/2006/somnaknaimueang.htm.
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Gary, Michael Shayne. "The dynamics of resource sharing in related diversification : a feedback simulation modelling approach." Thesis, London Business School (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325689.
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Puzyrev, Dmitry. "Dynamics of Localized Structures in Spatially Extended and Coupled Systems with Delayed Feedback." Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/19482.
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Systeme mit Zeitverzögerung sind von großem Interesse in Nichtlinearer Dynamik und allgegenwärtig in den Naturwissenschaften. Gegenstand dieser Doktorarbeit ist die raumzeitliche Dynamik räumlich-ausgedehnter, nichtlinearer Systeme mit Zeitverzögerung, mit besonderem Augenmerk auf deren lokalisierte Lösungen. Die betrachteten Systeme werden beschrieben durch partielle Differentialgleichungen und gekoppelte Systeme von gewöhnlichen Differentialgleichungen mit verzögerter Rückkopplung.
Hinsichtlich der partiellen Differentialgleichungen untersucht diese Arbeit die Existenz und Stabilität der ebenen Wellenlösungen ebenso, wie die Existenz und Stabilität der lokalisierten Lösungen der eindimensionalen, komplexen, kubischen und kubisch-quintischen Ginzburg-Landau Gleichung mit verzögerter, optischer Rückkopplung. Das erste Ergebnis dieser Arbeit ist die vollständige Beschreibung der Menge der ebenen Wellenlösungen und ihre Stabilität für lange Verzögerungszeiten. Aufgrund der Symmetrie der Ginzburg-Landau Gleichung bildet diese Menge eine eindimensionale Familie, die zum Auftreten einer „Tube“ in Parameter-Koordinaten führt.
Das zweite, neuartige Ergebnis ist die Beschreibung der Modulationsinstabilität dieser lokalisierten Strukturen. Diese Instabilität kann zu einer periodischen und chaotischen Zickzackbewegung der Lösung führen.
Das dritte Resultat ist die Charakterisierung gebundener Impulsfolgen in einem System von gekoppelten gewöhnlichen Differentialgleichungen mit Zeitverzögerung, das zur Beschreibung einer Anordnung von modengekoppelten Lasers herangezogen wird. In diesem Regime interagieren die modengekoppelten Impulse in verschiedenen Lasern lokal über die Balance von Abstoßung und Anziehung. Resultierend daraus entstehen Cluster von Impulsen, die in einzelnen modengekoppelten Lasern nicht möglich sind. Sämtliche genannte Phänomene wurden analytisch und numerisch behandelt.Systems with time-delay are ubiquitous in nature and attract significant interest in the field of nonlinear dynamics. The scope of this Thesis is the spatiotemporal dynamics in spatially extended nonlinear systems with time-delay, with a focus on the dynamics of localized structures. The systems under consideration are described by partial differential equations with delayed feedback and coupled systems of delay differential equations. For the partial differential equations, the existence and stability of plane wave solutions as well as localized structures are investigated in one-dimensional complex cubic and cubic-quintic Ginzburg-Landau equation with delayed feedback. The first result of this Thesis is the complete description of the set of plane wave solutions and their stability in the limit of large delay time. Due to the symmetry of Ginzburg-Landau equation, this set forms a one-dimensional family which leads to the appearance of the “tube” in parameter coordinates which is filled densely with plane wave solutions with the increase of the delay time. The second novel result is the description of modulational instability of localized structures in spatially extended systems with time-delay which can lead to periodic and chaotic zigzagging movement of the solution. The third result is the description of bound pulse trains in coupled delay systems depicting an array of mode-locked lasers. In this regime mode-locked pulses in different lasers interact locally via the balance of their repulsion and attraction. As a result, clusters of pulses emerge which can not exist in a solitary mode-locked laser. All of the aforementioned phenomena were described analytically and the results are supported by path continuation methods as well as direct numerical simulations with a specially designed software tool.
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Cadavid, Gomez Sandra. "Effects of dynamics and optical feedback on hybrid III-V/Si semiconductor lasers." Electronic Thesis or Diss., Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAT008.
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Les circuits intègres photoniques (PIC) sont devenus des éléments clés pour effectuer des fonctions de transmission et de réception à large bande dans les réseaux de communication optique. Cette thèse fournit des informations sur les lasers a semi-conducteurs hybrides (SCL) constitués d’une couche active de matériaux III-V sur un substrat de silicium sur isolant (SOI) pour exploser conjointement les propriétés d’émission des couches III-V et les nombreux avantages offerts par Si pour les applications sur chip. En raison des développements technologiques importants en électronique, cette approche hybride est bien positionnée pour répondre aux exigences de transmission et d’accès à courte distance à moindre cout. Cependant, plusieurs défis subsistent, comme le manque de sources lumineuses efficaces et de dispositif sans isolateur. Du point de vue de l’intégration monolithique d’une intégration hétérogène PIC, il est essential de s’assurer que les réflexions parasites qui peuvent provenir de plusieurs emplacement n’affectent pas la stabilité du laser. Plus précisément, les composants hybrides III-V sur Si semblent avoir de nombreuses sources potentielles de réflexions qui peuvent créer des centimètres de cavités externes en plus de celles naturellement produites à l’intérieur de la fibre de l’ordre de plusieurs mètres. Par conséquent, le travail présenté ici vise à comprendre le comportement des SCL III-V/Si lorsqu’ils sont soumis à une variation de réaction optique, explore les aspects fondamentaux de la dynamique chaotique et étudie les applications potentielles adaptées aux systèmes de télécommunications optiques dans une tentative de répondre aux exigences existantes en matière de haute vitessePhotonic Integrated Circuits (PIC) have become key elements to perform broadband transmission and reception functions in optical communication networks. This thesis provides information on hybrid semiconductor lasers (SCL) consisting of an active layer of III-V materials on a silicon-on-insulator (SOI) substrate to jointly explode the emitting properties of III-V layers and the numerous advantages offered by Si for on-chip applications. Due to the significant technological developments in electronics, this hybrid approach is well positioned to meet the high volume requirements for short distance transmission and access networks at a lower cost. However, several challengest still exist such as the lack of effective light sources and isolator-free devices. From a monolithic perspective of a PIC hetereogeneous integration, it is essential to ensure that the parasitic reflections that may stem from multiple locations do not affect the stability of the laser. Specifically, III-V hybrid components on Si appear to have many potential sources of reflections that can create centimeter external cavities in addition to those naturally produced inside the fiber in the order of several meters. Therefore, the work presented herein aims at understanding the behavior of III-V/Si SCLs when subjected to a variation of optical feedback, explores the basics aspects of chaotic dynamics, and investigates potential applications suitable for optical telecommunication systems in an attempt to meet the existing an emerging high speed requirements
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Al-Hosiny, Najm M. "Nonlinear dynamics of a distributed feedback laser subject to single and dual optical injection." Thesis, University of Essex, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.434393.
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Dickson, Scott M. "Stochastic neural network dynamics : synchronisation and control." Thesis, Loughborough University, 2014. https://dspace.lboro.ac.uk/2134/16508.
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Biological brains exhibit many interesting and complex behaviours. Understanding of the mechanisms behind brain behaviours is critical for continuing advancement in fields of research such as artificial intelligence and medicine. In particular, synchronisation of neuronal firing is associated with both improvements to and degeneration of the brain's performance; increased synchronisation can lead to enhanced information-processing or neurological disorders such as epilepsy and Parkinson's disease. As a result, it is desirable to research under which conditions synchronisation arises in neural networks and the possibility of controlling its prevalence. Stochastic ensembles of FitzHugh-Nagumo elements are used to model neural networks for numerical simulations and bifurcation analysis. The FitzHugh-Nagumo model is employed because of its realistic representation of the flow of sodium and potassium ions in addition to its advantageous property of allowing phase plane dynamics to be observed. Network characteristics such as connectivity, configuration and size are explored to determine their influences on global synchronisation generation in their respective systems. Oscillations in the mean-field are used to detect the presence of synchronisation over a range of coupling strength values. To ensure simulation efficiency, coupling strengths between neurons that are identical and fixed with time are investigated initially. Such networks where the interaction strengths are fixed are referred to as homogeneously coupled. The capacity of controlling and altering behaviours produced by homogeneously coupled networks is assessed through the application of weak and strong delayed feedback independently with various time delays. To imitate learning, the coupling strengths later deviate from one another and evolve with time in networks that are referred to as heterogeneously coupled. The intensity of coupling strength fluctuations and the rate at which coupling strengths converge to a desired mean value are studied to determine their impact upon synchronisation performance. The stochastic delay differential equations governing the numerically simulated networks are then converted into a finite set of deterministic cumulant equations by virtue of the Gaussian approximation method. Cumulant equations for maximal and sub-maximal connectivity are used to generate two-parameter bifurcation diagrams on the noise intensity and coupling strength plane, which provides qualitative agreement with numerical simulations. Analysis of artificial brain networks, in respect to biological brain networks, are discussed in light of recent research in sleep theory.
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Ooten, Erika Ann. "Command generation for flexible systems using numerator dynamics and sliding mode control." Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/18360.
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Nash, Christopher James. "Measurement and modelling of human sensory feedback in car driving." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/270641.
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With the growing complexity of vehicle control systems it is becoming increasingly important to understand the interaction between drivers and vehicles. Existing driver models do not adequately characterise limitations resulting from drivers’ physical systems. In particular, sensory dynamics limit the ability of drivers to perceive the states of real or simulated vehicles. Therefore, the aim of this thesis is to understand the impact of sensory dynamics on the control performance of a human driver in real and virtual environments. A new model of driver steering control is developed based on optimal control and state estimation theory, incorporating models of sensory dynamics, delays and noise. Some results are taken from published literature, however recent studies have shown that sensory delays and noise amplitudes may increase during an active control task such as driving. Therefore, a parameter identification procedure is used to fit the model predictions to measured steering responses of real drivers in a simulator. The model is found to fit measured results well under a variety of conditions. An initial experiment is designed with the physical motion of the simulator matching the motion of the virtual vehicle at full scale. However, during more realistic manoeuvres the physical motion must be scaled or filtered, introducing conflicts between measurements from different sensory systems. Drivers are found to adapt to simple conflicts such as scaled motion, but they have difficulty adapting to more complicated motion filters. The driver model is initially derived for linear vehicles with stochastic target and disturbance signals. In later chapters it is extended to account for transient targets and disturbances and vehicles with nonlinear tyres, and validated once again with experimental results. A series of simulations is used to demonstrate novel insights into how drivers use sensory information, and the resulting impact on control performance. The new model is also shown to predict difficulties real drivers have controlling unstable vehicles more reliably than existing driver models.
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Polston, James D. "DECENTRALIZED ADAPTIVE CONTROL FOR UNCERTAIN LINEAR SYSTEMS: TECHNIQUES WITH LOCAL FULL-STATE FEEDBACK OR LOCAL RELATIVE-DEGREE-ONE OUTPUT FEEDBACK." UKnowledge, 2013. http://uknowledge.uky.edu/me_etds/24.
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This thesis presents decentralized model reference adaptive control techniques for systems with full-state feedback and systems with output feedback. The controllers are strictly decentralized, that is, each local controller uses feedback from only local subsystems and no information is shared between local controllers.
The full-state feedback decentralized controller is effective for multi-input systems, where the dynamics matrix and control-input matrix are unknown. The decentralized controller achieves asymptotic stabilization and command following in the presence of sinusoidal disturbances with known spectrum. We present a construction technique of the reference-model dynamics such that the decentralized controller is effective for systems with arbitrarily large subsystem interconnections.
The output-feedback decentralized controller is effective for single-input single-output subsystems that are minimum phase and relative degree one. The decentralized controller achieves asymptotic stabilization and disturbance rejection in the presence of an unknown disturbance, which is generated by an unknown Lyapunov-stable linear system.
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Torrentino, Taciano. "Experimental and numerical study of the symbolic dynamics of modulated semiconductor lasers with optical feedback." Doctoral thesis, Universitat Politècnica de Catalunya, 2015. http://hdl.handle.net/10803/321354.
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The goal of this thesis is to investigate the influence of current modulation in the dynamics of the low-frequency fluctuations (LFF) regime induced by optical feedback in semiconductor lasers. In this regime the laser output exhibits apparently random and sudden dropouts that, in some statistical properties, are similar to excitable neuronal spikes. Long time series containing tens of thousands of LFF dropouts were experimentally acquired and simulated, using the Lang and Kobayashi model, under different conditions. By detecting the individual dropouts, the intensity time series were transformed in series of inter-spike intervals (ISI). We then analyzed the ISI sequences by using a symbolic method of analysis capable of unveil serial correlations in data sets, known as ordinal symbolic analysis. Our findings reveal the existence of a hierarchical and clustered organization of ordinal patterns in the ISI series.
When the laser is subject to periodical external forcing, through modulation of the injection current, we identify clear changes in the dynamics as the increase of the modulation amplitude induces deterministic-like behavior in the system. When the modulation frequency is varied, the change in the statistics of the various symbols is empirically shown to be related to specific changes in the ISI distribution, which arise due to different noisy phase-locking regimes.
We also investigated how the spike rate is affected by the modulation, for different parameters that determine the natural (without modulation) spike rate. When the intrinsic spike dynamics is slow, fast modulation can produce faster spikes. When the intrinsic dynamics is already fast, modulation cannot induce much faster spikes. Similar effects were observed in the spike correlations: we found that higher natural spike rates wash out the effects of the modulation in the spike correlations. Simulations of the Lang and Kobayashi model are shown to be in good agreement with the experimental observations.
The results reported in this thesis may be important to the use of semiconductor lasers as optical spiking neurons in information processing networks inspired by biological ones, and more generally, to the analysis of serial correlations in spiking excitable systems. Future work may include investigations of how correlations that encode an external signal spread in a small network of semiconductor lasers.El objetivo de esta tesis es investigar la influencia de la modulación de corriente sobre la dinámica de los láseres semiconductores con realimentación óptica en el regimen de fluctuaciones de baja frequencia (low-frequency fluctuations, o LFF) . En este regimen la intensidad de la salida del láser muestra caídas abruptas y aparentemente aleatorias que son similares, en algunas propiedades estadísticas, a los spikes neuronales excitables. Largas series temporales, que contienen decenas de estas caídas, fuerón adquiridas experimentalmente y simuladas usando el modelo de Lang y Kobayashi, bajo diferentes condiciones. Al detectar las caídas individuales, las series temporales son transformadas en series de intervalos entre caídas (inter-spike intervals, o ISI). Seguidamente, se analizan las secuencias de ISI mediante el uso de un método de análisis simbólico, conocidos como análisis simbólico ordinal, capaz de revelar correlaciones seriales en los conjuntos de datos. Nuestros resultados revelan la existencia de una organización jerárquica y agrupada de los patrones ordinales en las series de ISI. Cuando el láser está sujeto a forzamiento externo periódico, a través de la modulación de la corriente de inyección, identificamos cambios claros en la dinámica. El aumento de la amplitud de modulación induce comportamiento determinista en el sistema. Cuando la frecuencia de modulación es variada, se muestra empíricamente el cambio en las estadísticas de los distintos símbolos, que está relacionado a los cambios específicos en la distribución de los ISI. Estos cambios surgen debido a diferentes regímenes ruidosos en el bloqueo en fase. También se investigó cómo la frecuencia de aparicion de las caídas se ve afectada por la modulación, para los diferentes parámetros que determinan la frecuencia natural (sin modulación) de las caídas. Cuando la dinámica intrínseca de las caídas es lenta, la modulación rápida puede producir caídas más rápidas. Cuando la intrínseca dinámica ya es rápida, la modulación no puede inducir caídas mucho más rápidas. Efectos similares fueron observados en las correlaciones de las caídas: encontramos que mayores tasas de las caídas naturales acaban con los efectos de la modulación en las correlaciones. Las simulaciones de lo modelo de Lang y Kobayashi se muestran estar en buen acuerdo con las observaciones experimentales. Los resultados presentados en esta tesis pueden ser importantes para el uso de láseres semiconductores por ejemplo como neuronas ópticas en redes de procesamiento de información, inspiradas en las redes de neuronas biológicas, y más generalmente, para el análisis de las correlaciones seriales en sistemas excitables. El trabajo futuro podría incluir la investigación de cómo correlaciones que codifican una señal externa se propagan en una pequeña red de láseres semiconductores.
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Castillo, Martinez Guillermo Andres. "Design of Feedback Controllers for Biped Robots Based in Reinforcement Learning and Hybrid Zero Dynamics." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1555340995172442.
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Ramirez, Analiza Henedina M. "Dynamics of giant ragweed and common sunflower in Kansas: distribution, plant-soil feedback and demography." Diss., Kansas State University, 2010. http://hdl.handle.net/2097/7048.
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Doctor of PhilosophyDepartment of Agronomy
Johanna A. Dille
Success of plants depends largely on their environment. A survey, field and greenhouse studies were conducted from 2006 to 2010 to characterize the dynamics of giant ragweed (AMBTR) and common sunflower (HELAN) in KS through determining their distribution, plant-soil feedback response and demography. The survey revealed a distinct distribution pattern within the state with HELAN being more dominant than AMBTR. Populations of AMBTR and HELAN from KS could be grouped by their emergence characteristics. Plant-soil feedback response of AMBTR and HELAN varied across sites with HELAN having a consistent positive feedback response while AMBTR had negative feedback response in IL, KS, MI-a, MI-B, OR and SD but not in MT. Interaction coefficient analysis was neutral for IL, KS and MI-b while positive for OR and SD and negative for MI-a and MT. Plant-soil feedback response of KS-derived populations of AMBTR and HELAN indicated that both KS-AMBTR and KS-HELAN seemed to grow best in soil preconditioned by another species. Seed survivorship over winter and summer, emergence, and population growth rates of both weed species varied over three years with HELAN having higher growth rates that AMBTR. This study showed that demographic success of HELAN and AMBTR was greatly influenced by the climatic conditions more than any other factors. AMBTR from IL, if introduced to the state can adapt to KS conditions. Further studies including impacts of soil biota, nutrient dynamics and biochemical processes such as allelopathy are needed to better understand the mechanism behind the plant-soil feedback response of the two weed species and its contribution to the demographic success of AMBTR and HELAN.
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Skidmore, Gary R. "Experimental-theoretical study of velocity feedback damping of structural vibrations." Diss., Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/49788.
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Locquet, Alexandre Daniel. "Chaotic optical communications using delayed feedback systems." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10431.
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Chaotic dynamics produced by optical delay systems have interesting applications in telecommunications. Optical chaos can be used to transmit secretly, in real-time, a message between an emitter and a receiver. The noise-like appearance of chaos is used to conceal the message, and the synchronization of the receiver with the chaotic emitter is used to decode the message. This work focuses on the study of two crucial topics in the field of chaotic optical communications.
The first topic is the synchronization of chaotic external-cavity laser diodes, which are among the most promising chaotic emitters for secure communications. It is shown that, for edge-emitting lasers, two drastically different synchronization regimes are possible. The regimes differ in terms of the delay time in the synchronization and in terms of the robustness of the synchronization with respect to parameter mismatches between the emitter and the receiver. In vertical-cavity surface-emitting lasers, the two linearly-polarized components of the electric field also exhibit isochronous and anticipating synchronization when the coupling between the lasers is isotropic. When the coupling is polarized, the linearly-polarized component that is parallel to the injected polarization tends to synchronize isochronously with the injected optical field, while the other component tends to be suppressed, but it can also be antisynchronized.
The second topic is the analysis of time series produced by optical chaotic emitters subjected to a delayed feedback. First, we verify with experimental data that chaos produced by optical delay systems is highly complex. This high complexity is demonstrated by estimating chaos dimension and entropy from experimental time series and from models of optical delay systems. Second, by analyzing chaotic time series, it is shown that the value of the delay of a single-delay system can always be identified, independently of the type of system used and of its complexity. Unfortunately, an eavesdropper can use this information on the delay value to break the cryptosystem. We propose a new cryptosystem with two delayed feedback loops that increases the difficulty of the delay identification problem.
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Berry, Thomas D. "The emergence of a negative feedback bias as a product of supervisor and subordinate dynamics : consequences of opportunity-based supervision and performance variation /." Diss., This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06062008-164555/.
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Khan, Marryam. "Gender Dynamics from the Arab World: An Intercultural Service Encounter." Master's thesis, University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5960.
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Arab countries strive toward the modernization and feminization of the Arab culture; however, some of these countries (i.e., Saudi Arabia) are culturally and legally governed by “sharia law”, and have maintained cultural norms regarding segregation of the sexes. In order to have a better understanding of the Arab travelers to the U.S., this research focuses on the gender dynamics between the service providers and Arab customers during a service encounter. Specifically, this research examines how the same and opposite genders of service-provider and customer influence Arab customers' emotional response (comfort), consequently their service encounter evaluation (satisfaction), and behavioral intentions (feedback willingness). This research also examines how the employees' efforts to solicit feedback from Arab customers may intensify the effect of gender dynamics on Arab customers' responses.
Scenario-based online surveys are created and distributed to respondents of Arab descent in Saudi Arabia, Bahrain, and United Arab Emirates by using snowball sampling. The results based on 326 respondents show potential differences determined by gender interaction. Arab customers were more comfortable, more satisfied with the service encounter, and more willing to provide feedback, if the employee was the same gender as the customer, as opposed to the employee being the opposite gender from the customer. However, results showed that employee efforts to solicit feedback did not intensify the gender interaction effect. Additionally, through the service encounter, the Arab customers' comfort influenced their service encounter satisfaction and their willingness to provide feedback. The findings of this research provide valuable implications for hospitality managers to better cater to the needs of Arab customers by examining the dimensions of gender boundaries in an intercultural service encounter.M.S.
Masters
Hospitality Services
Hospitality Management
Hospitality and Tourism Management
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Aragoneses, Aguado Andrés. "Experimental study of feedback-induced dynamics in semiconductor lasers : from symbolic analysis to subwavelength position sensing." Doctoral thesis, Universitat Politècnica de Catalunya, 2014. http://hdl.handle.net/10803/277569.
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The aim of this thesis is the study of the dynamics induced by optical feedback in semiconductor lasers. This study aims, on the one hand, to improve our knowledge of stocahstic complex systems, and on the other hand, to use complex dynamics of semiconductor lasers to develop a protocol for subwavelength position sensing. The intensity of the light emitted by a semiconductor laser is stable, besides fluctuations due to spontaneous emission noise. When the light of the laser is reflected and part re-enters into the laser, the laser intensity can become unstable, displaying a broad range of dynamical behaviors. One of the dynamical regimes present in lasers with optical feedback is the low frequency fluctuations (LFF). This dynamics is characterized by sharp drops in the laser intensity (to almost switch the laser off), followed by gradual recoveries. The time intervals between two consecutive drops is irregular. The first part of this Thesis is focused on this dynamic regime, and a detailed experimental study has been performed to characterize it. A symbolic time series analysis has been used, based on the comparison of successive time intervals between dropouts. The dynamics of a semiconductor laser with feedback is governed by nonlinear light-matter interaction in the active medium of the laser, quantum noise due to spontaneous emission and time-delayed feedback. Therefore, the dropouts in the LFF regime can be noise-induced or triggered by deterministic processes. In this Thesis symbolic ordinal analysis has been used to statisticlly distinguish dropouts that can be noise-induced from those that have signatures of a deterministic origin. In this Thesis, the symbolic dynamics in the LFF regime has also been studied, and serial correlations have been found among several consecutive dropouts. It has been found a hierarchical and clustered structure of the symbolic dynamics. Moreover, a minimal iterative model has been found that, despite its simplicity, describes successfully the correlations found in the experiments.
Because of the importance of external forcing in dynamical systems, the effect of current modulation on the symbolic dynamics of the LFFs has been studied. These experiments have allowed to characterize the effect of the modulation in the symbolic dynamics. The clusters of ordinal patterns formed without forcing remain under external periodic forcing. The minimal model has been verified, as it reproduces satisfactorily the symbolic dynamics of the experimental data. Also, in this Thesis a technique has been developed to detect displacements of two independent objects at subwavelength resolution (λ/160). With this purpose, a setup has been developed with a semiconductor laser with dual feedback. In addition to the high resolution, this protocol offers the advantage of sensing two objects by just measuring one variable.El objetivo de esta tesis es el estudio de la dinámica inducida por realimentación óptica en láseres de semiconductor. Dicho estudio persigue, por un lado, profundizar en el conocimiento de aspectos generales de los sistemas complejos, y por otro lado, utilizar dicha dinámica para crear un protocolo para medir desplazamientos en dos dimensiones con una resolución mucho menor que la longitud de onda del láser utilizado. La intensidad de la luz emitida por un láser de semiconductor es estable salvo fluctuaciones debidas al ruido de emisión espontánea. Sin embargo, cuando la luz del láser se refleja en una superficie y parte de esta luz vuelve a entrar en el láser, la intensidad de la luz emitida se puede desestabilizar y mostrar una amplia gama de comportamientos dinámicos. Uno de los regímenes dinámicos presentes en láseres con realimentación óptica es el de fluctuaciones de baja frecuencia (LFF de sus siglas en inglés). Esta dinámica se caracteriza por caídas abruptas de la intensidad del láser (hasta casi apagarse), seguidas de recuperaciones graduales, siendo la separación temporal entre dos caídas consecutivas irregular. La primera parte de esta tesis está centrada en este régimen dinámico, habiéndose realizado un detallado estudio experimental para caracterizarlo. Se ha utilizado un análisis simbólico de series de datos basado en patrones ordinales, definidos mediante la comparación de tiempos consecutivos entre caídas. En la dinámica del láser de semiconductor con realimentación intervienen varios factores: la interacción no lineal entre luz y materia en el medio activo del láser, el ruido cuántico debido a la emisión espontánea y la señal retardada de la realimentación. Por ello las caídas en el régimen de LFFs pueden ser inducidas tanto por ruido como por procesos deterministas. En esta tesis, mediante el análisis simbólico se ha conseguido distinguir estadísticamente, qué caídas pueden ser inducidas por ruido y cuales presentan una estadística que muestra señales de determinismo. En esta tesis también se ha estudiado la dinámica simbólica del régimen de LFF y se han encontrado correlaciones entre varias caídas consecutivas. También se ha encontrado una estructura jerárquica en la dinámica simbólica que incluye emparejamientos de las probabilidades de los patrones simbólicos. Además se ha encontrado un modelo simple a tiempo discreto (mapa) que describe adecuadamente la dinámica simbólica del régimen de LFF. Debido a la importancia de forzamientos externos en sistemas dinámicos, se han realizado experimentos incorporando modulación en la corriente de inyección del láser. Estos experimentos han permitido caracterizar el efecto de la amplitud de la modulación en la dinámica simbólica, encontrando cambios claros en la estructura simbólica, inducidos por la modulación, pero que se conservan los emparejamientos observados sin modulación. El modelo simple ha sido verificado ya que reproduce satisfactoriamente la dinámica simbólica encontrada en los datos experimentales. Asimismo, en esta tesis se ha demostrado experimentalmente un protocolo que permite detectar desplazamientos de dos objetos independientes en una escala muy inferior a la longitud de onda de la luz empleada (Λ/160). Para ello se ha diseñado un experimento donde el láser está sometido a realimentación de dos espejos que se mueven de manera independiente. Además de la alta resolución, otra ventaja de este protocolo reside en que únicamente es preciso medir una variable para calcular los dos desplazamientos.
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Thompson, Christopher David. "An analytical and experimental investigation of respiratory dynamics using P/D control and carbon dioxide feedback." Thesis, Virginia Tech, 1988. http://hdl.handle.net/10919/43059.
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This thesis addresses the problem of defining the control law for human respiration.
Seven different drivers have been identified as possibly having an input to the
respiratory controller. These seven represent a combination of feedforward and feedback
inputs arising from neural and humoral mechanisms.
Using the assumption that carbon dioxide concentrations in the arterial blood have the
strongest effect, a control equation with proportional and derivative components based on
this driver was evaluated. The methodology for the evaluation was to create a model of
the respiratory system incorporating the P/D controller, obtain experimental data of one
test subject's respiratory response to exercise, then compare model generated output with
experimental data, and adjust the parameters in the control equation to yield optimal
model performance.
The usual practice of testing controller performance has been to apply single step loads
to a model and evaluate its response. A multi-step protocol was used here to provide a
better, more generalized test of controller performance. This thesis may represent the
first documented use of an approach of this type for evaluating respiratory controller
performance.
Application of a multi-step protocol revealed a non-linear controller was needed to keep
pace with system changes. Respiratory system operation was effectively managed using
a controller of the form:
VENTILATION = F(dCO2/dT,Q) + F(CO2,Q) + CONSTANT.Master of Science
46
Sarkar, Subhasis. "Recursive formulations of multibody systems in open loop configuration." Diss., Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/12414.
Full text
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Griffin, Stuart James. "Helicopter control law design using eigenstructure assignment." Thesis, University of York, 1997. http://etheses.whiterose.ac.uk/21041/.
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Al-nasur, Sadeq J. "New Models for Crowd Dynamics and Control." Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/30107.
Full textAbstract:
In recent years, there has been an increasing interest in modeling crowd and evacuation dynamics. Pedestrian models are based on macroscopic or microscopic behavior. In this work, we are interested in developing models that can be used for evacuation control strategies. Hence, we use macroscopic modeling approach, where pedestrians are treated in an aggregate way and detailed interactions are overlooked. In this dissertation, we developed two-dimensional space crowd dynamic models to allow bi-directional low by modifying and enhancing various features of existing traffic and fluid dynamic models. In this work, four models based on continuum theory are developed, and conservation laws such as the continuity and momentum equations are used. The first model uses a single hyperbolic partial differential equation with a velocity-density relationship, while the other three models are systems of hyperbolic partial differential equations. For one of the system models presented, we show how it can be derived independently from a microscopic crowd model. The models are nonlinear, time-varying, hyperbolic partial differential equations, and the numerical simulation results given for the four macroscopic models were based on computational fluid dynamics schemes.
We also started an initial control design that synthesizes the feedback linearization method for the one-dimensional traffic flow problem applied directly on the distributed parameter system. In addition, we suggest and discuss the information technology requirements for an evacuation system.
This research was supported in part from the National Science Foundation through grant no. CMS-0428196 with Dr. S. C. Liu as the Program Director. This support is gratefully acknowledged. Any opinion, findings, and conclusions or recommendations expressed in this study are those of the writer and do not necessarily reflect the views of the National Science Foundation.Ph. D.
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Morel, Yannick. "Applied Nonlinear Control of Unmanned Vehicles with Uncertain Dynamics." Diss., Virginia Tech, 2009. http://hdl.handle.net/10919/27426.
Full textAbstract:
The presented research concerns the control of unmanned vehicles. The results introduced
in this dissertation provide a solid control framework for a wide class of nonlinear uncertain
systems, with a special emphasis on issues related to implementation, such as control input
amplitude and rate saturation, or partial state measurements availability. More specifically,
an adaptive control framework, allowing to enforce amplitude and rate saturation of the
command, is developed. The motion control component of this framework, which works in
conjunction with a saturation algorithm, is then specialized to different types of vehicles.
Vertical take-off and landing aerial vehicles and a general class of autonomous marine vehicles
are considered. A nonlinear control algorithm addressing the tracking problem for a
class of underactuated, non-minimum phase marine vehicles is then introduced. This motion
controller is extended, using direct and indirect adaptive techniques, to handle parametric
uncertainties in the system model. Numerical simulations are used to illustrate the efficacy
of the algorithms. Next, the output feedback control problem is treated, for a large class of
nonlinear and uncertain systems. The proposed solution relies on a novel nonlinear observer
which uses output measurements and partial knowledge of the systemâ s dynamics to reconstruct
the entire state for a wide class of nonlinear systems. The observer is then extended
to operate in conjunction with a full state feedback control law and solve both the output
feedback control problem and the state observation problem simultaneously. The resulting
output feedback control algorithm is then adjusted to provide a high level of robustness to
both parametric and structural model uncertainties. Finally, in a natural extension of these
results from motion control of a single system to collaborative control of a group of vehicles,
a cooperative control framework addressing limited communication issues is introduced.Ph. D.
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Lee, Hyung-Chun. "Analysis, finite element approximation, and computation of optimal and feedback flow control problems." Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/37450.
Full textAbstract:
The analysis, finite element approximation, and numerical simulation of some control problems associated with fluid flows are considered.
First, we consider a coupled solid/fluid temperature control problem. This optimization problem is motivated by the desire to remove temperature peaks, i.e., "hot spots", along the bounding surface of containers of fluid flows. The heat equation of the solid container is coupled to the energy equation for the fluid. Control is effected by adjustments to the temperature of the fluid at the inflow boundary. We give a precise statement of the mathematical model, prove the existence and uniqueness of optimal solutions, and derive an optimality system. We study a finite element approximation and provide rigorous error estimates for the error in the approximate solution of the optimality system. We then develop and implement an iterative algorithm to compute the approximate solution.
Second, a computational study of the feedback control of the magnitude of the lift in flow around a cylinder is presented. The uncontrolled flow exhibits an unsymmetric Karman vortex street and a periodic lift coefficient. The size of the oscillations in the lift is reduced through an active feedback control system. The control used is the injection and suction of fluid through orifices on the cylinder; the amount of fluid injected or sucked is determined, through a simple feedback law, from pressure measurements at stations along the surface of the cylinder.
The results of some computational experiments are given; these indicate that the simple feedback law used is effective in reducing the size of the oscillations in the lift.
Finally, some boundary value problems which arise from a feedback control problem are considered. We give a precise statement of the mathematical problems and then prove the existence and uniqueness of solutions to the boundary value problems for the Laplace and Stokes equations by studying the boundary integral equation method.Ph. D.