Tesi sul tema "Oscillations"
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1
Kuzovkov, Vladimir, Guntars Zvejnieks, Olaf Kortlüke e Niessen Wolfgang von. "Forced oscillations in self-oscillating surface reaction models". Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-195406.
Testo completo
2
Kuzovkov, Vladimir, Guntars Zvejnieks, Olaf Kortlüke e Niessen Wolfgang von. "Forced oscillations in self-oscillating surface reaction models". Diffusion fundamentals 2 (2005) 27, S. 1-2, 2005. https://ul.qucosa.de/id/qucosa%3A14357.
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3
Andes, Derek. "Orbital oscillations". Thesis, University of Iowa, 2011. https://ir.uiowa.edu/etd/919.
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4
Fraser, Geoffrey Alan. "Nonradial oscillations in Spica". Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/24667.
Testo completoAbstract (sommario):
The absorption line profiles of Spica (α Virginis, HD116658, B1.5IV, m=0.97) show features, at about the 1% level, moving from the blue wavelengths towards the red wavelengths. A series of spectra were taken, at the 1.22 m telescope at the Dominion Astrophysical Observatory on three nights in April, 1982 and two nights in April, 1984, to study these moving features.
As Spica is a member of a binary system, the effect of the secondary had to be removed from the observations. This was done by subtracting a template spectrum which had been scaled, broadened and shifted to match the secondary, from each observation. The required shifts were determined using the orbital elements on blended nights and using the Fahlman-Glaspy small-shifts technique on unblended nights. An average of all the spectra was then subtracted from each observation. The resulting series of residuals clearly show the motion of the features seen in the line profiles.
The acceleration of the features was estimated to be between 0.0055 and 0.0068 kms⁻². Assuming the features are due to nonradial oscillations, this acceleration corresponds to waves moving slowly, about 5 to 20 kms⁻¹, in a prograde direction. The angular frequency of the oscillations, after accounting for the effects of rotation, would be about 3.4X10⁻⁵ rads⁻¹. A computer model that produces line profiles, under the assumption of a single nonradial oscillation, was used to produce profiles for comparison with observations. Using an [formula omitted]=8 and m=-8 mode, an intrinsic frequency of 3.4X10⁻⁵ rads⁻¹ and a stellar rotation rate of 190 kms⁻¹, the model produced profiles similar to those observed. The change in the model profiles with time was also similar to that observed.Science, Faculty of
Physics and Astronomy, Department of
Graduate
5
Rangavajhula, Krishna C. "Nonstationary oscillations through bifurcations". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq23875.pdf.
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6
Reid, Giles Adrian. "Neutrino Oscillations in Astrophysics". Thesis, University of Canterbury. Physics and Astronomy, 2010. http://hdl.handle.net/10092/4935.
Testo completoAbstract (sommario):
A survey of the theory of neutrino oscillations in dense matter and neutrino
backgrounds is presented. We discuss collective neutrino systems using the gyroscopic
pendulum analogy and describe the motion that results from self-induced
parametric resonances. The effects of dense matter on the
flavour oscillations
of neutrinos are also detailed. This theory is applied to the case of continuous
supernova neutrino spectra and explanations of the spectral swapping behaviour
seen in numerical studies are summarized.
The results of numerical simulations of supernova oscillations in turbulent
supernova backgrounds are presented and discussed. We study the motion of two
example supernova neutrino spectra and examine the differences in the dynamics
and
flavour evolution that results from adding turbulent
fluctuations to the
supernova matter background. We also investigate the effect that
fluctuations
in the neutrino density can have on the oscillation behaviour. We find that in
general the final neutrino spectra emerging from the inner supernova regions
are quite robust to
fluctuations in the backgrounds in our model, while the
intermediate dynamics can be very strongly altered. Some significant changes
in the final spectra are also found to occur when the neutrino background density
fluctuations are large.
We give a detailed review of the resonant matter effects that determine the
survival probabilities of atmospheric muon neutrinos. The differences between
various Earth density models are described, and these models are then used to
predict the flux of muon-type neutrino events in the Deep Core extension to the
IceCube detector. We use recent results from the detector collaboration and
build on previous work which considered the sensitivity of the detector to the
mass hierarchy, and show that uncertainties in the Earth's density can have a
significant influence on the event rates.
7
Pennequin, Denis. "Contrôle optimal et oscillations". Paris 1, 2000. http://www.theses.fr/2000PA010061.
Testo completoAbstract (sommario):
Dans cette thèse, nous nous sommes intéressés au problème du Contrôle Optimal des oscillations et à quelques applications économiques. Tout d'abord, on a mis en forme le formalisme de Percival liant une fonction quasi-périodique (=q. P. ) à sa génératrice sur le tore, avec un lien se comportant bien au niveau différentiel. Une étude du cas à paramètre, nécessaire pour traiter des équations autonomes, permet d'obtenir un théorème d'isomorphisme entre l'espace des fonctions presque- périodiques ( =p. P. ) à paramètres et un espace de fonctions p. P. à valeurs dans un Banach. Relativement au formalisme de Percival, nous introduisons des espaces du type de Sobolev où nous retrouvons l'absence de compacité, mais où l'étude ne nécessite pas d'hypothèses diophantiennes contrairement aux considérations plus géométriques de ces problèmes. Le formalisme de Percival transforme la recherche des solutions q. P. D'une équation différentielle en la recherche de solutions p. P. D'une E. D. P. Une notion de solution faible est introduite et comparée à l'usuelle, et l'on obtient pour celle-ci un théorème d'existence. L'absence de compacité implique une obligation de développer de nouvelles techniques, y compris dans les méthodes de régularisation, et l'on présente pour cela une nouvelle technique. Le cas discret est également traité (existence et structure), après avoir comparé différentes notions de suites p. P, courantes dans la littérature. On étudie alors les problèmes quasi-périodiques ; pour des problèmes autonomes linéaires-concaves, on démontre l'équivalence des problèmes p. P. , périodiques et statiques. Dans le cadre non nécessairement autonome, on obtient des théorèmes d'existence et de conditions nécessaire étendant ceux de Da-Prato et Ichikawa. Enfin, des applications économiques sont fournies.
8
Todd, Thomas. "Robust oscillations in cells". Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.685923.
Testo completoAbstract (sommario):
Oscillating chemical signals in cells play an essential role in biological processes. Understanding how to produce reliable oscillators using cellular machinery is useful for genetic engineering and is a key goal of synthetic biology. Motivated by an analysis of the robustness of a biological oscillator found in the cell cycle, a new technique is developed to evaluate the robustness of nonlinear models of oscillating genetic networks. This technique has been embedded in a software framework called INTRON which can be used by biologists seeking to design robust genetic oscillators or to understand the robustness of existing models. A set of case studies are presented in which INTRON is used to analyse the robustness of genetic oscillators.
9
Amon, Axelle. "Dynamique temporelle des oscillateurs paramétriques optiques continus : oscillations multimodes, oscillations en rafales et chaos". Phd thesis, Université des Sciences et Technologie de Lille - Lille I, 2003. http://tel.archives-ouvertes.fr/tel-00004477.
Testo completoAbstract (sommario):
Les oscillateurs paramétriques optiques (OPO) continus sont des sources de lumière cohérente largement accordables reposant sur l'interaction paramétrique de trois champs dans un cristal non-linéaire. Leur utilité est aussi bien liée à cette accordabilité (spectroscopie) qu'aux propriétés quantiques propres au système (génération d'états comprimés, photons jumeaux). D'autre part, en tant que systèmes non-linéaires, les OPO sont susceptibles de présenter une grande richesse de phénomènes dynamiques temporels et spatio-temporels. Nous présentons une étude expérimentale, théorique et numérique de différentes instabilités temporelles présentées par les intensités des champs à la sortie de la cavité de notre OPO. Nous caractérisons des oscillations de fréquence de 1 à 300MHz dont nous montrons expérimentalement qu'elles ont pour origine l'interaction entre plusieurs modes transverses. Ces oscillations rapides peuvent être couplées à des oscillations plus lentes d'origine thermique, menant à l'apparition d'instabilités du type oscillations en rafales. Un développement perturbatif multi-échelle permet d'obtenir des solutions analytiques pour les champs une fois les oscillations rapides moyennées. Nous avons d'autre part observé ce qui est à notre connaissance la première observation expérimentale de chaos déterministe dans ce système. Enfin nos travaux expérimentaux et théoriques ont permis d'améliorer notre compréhension de la sélection de modes dans les OPO.
10
Schwabedal, Justus Tilmann Caspar. "Phase dynamics of irregular oscillations". Phd thesis, Universität Potsdam, 2010. http://opus.kobv.de/ubp/volltexte/2011/5011/.
Testo completoAbstract (sommario):
In der vorliegenden Dissertation wird eine Beschreibung der Phasendynamik
irregulärer Oszillationen und deren Wechselwirkungen vorgestellt. Hierbei
werden chaotische und stochastische Oszillationen autonomer dissipativer Systeme
betrachtet. Für eine Phasenbeschreibung stochastischer Oszillationen müssen zum
einen unterschiedliche Werte der Phase zueinander in Beziehung gesetzt werden,
um ihre Dynamik unabhängig von der gewählten Parametrisierung der Oszillation
beschreiben zu können. Zum anderen müssen für stochastische und chaotische
Oszillationen diejenigen Systemzustände identifiziert werden, die sich in der
gleichen Phase befinden.
Im Rahmen dieser Dissertation werden die Werte der Phase über eine gemittelte
Phasengeschwindigkeitsfunktion miteinander in Beziehung gesetzt. Für
stochastische Oszillationen sind jedoch verschiedene Definitionen der mittleren
Geschwindigkeit möglich. Um die Unterschiede der Geschwindigkeitsdefinitionen
besser zu verstehen, werden auf ihrer Basis effektive deterministische Modelle
der Oszillationen konstruiert. Hierbei zeigt sich, dass die Modelle
unterschiedliche Oszillationseigenschaften, wie z. B. die mittlere Frequenz
oder die invariante Wahrscheinlichkeitsverteilung, nachahmen. Je nach Anwendung
stellt die effektive Phasengeschwindigkeitsfunktion eines speziellen Modells
eine zweckmäßige Phasenbeziehung her. Wie anhand einfacher Beispiele erklärt
wird, kann so die Theorie der effektiven Phasendynamik auch kontinuierlich und
pulsartig wechselwirkende stochastische Oszillationen beschreiben.
Weiterhin wird ein Kriterium für die invariante Identifikation von Zuständen
gleicher Phase irregulärer Oszillationen zu sogenannten generalisierten
Isophasen beschrieben: Die Zustände einer solchen Isophase sollen in ihrer
dynamischen Entwicklung ununterscheidbar werden. Für stochastische
Oszillationen wird dieses Kriterium in einem mittleren Sinne interpretiert. Wie
anhand von Beispielen demonstriert wird, lassen sich so verschiedene Typen
stochastischer Oszillationen in einheitlicher Weise auf eine stochastische
Phasendynamik reduzieren. Mit Hilfe eines numerischen Algorithmus zur Schätzung
der Isophasen aus Daten wird die Anwendbarkeit der Theorie anhand eines Signals
regelmäßiger Atmung gezeigt. Weiterhin zeigt sich, dass das Kriterium der
Phasenidentifikation für chaotische Oszillationen nur approximativ erfüllt
werden kann. Anhand des Rössleroszillators wird der tiefgreifende Zusammenhang
zwischen approximativen Isophasen, chaotischer Phasendiffusion und instabilen
periodischen Orbits dargelegt.
Gemeinsam ermöglichen die Theorien der effektiven Phasendynamik und der
generalisierten Isophasen eine umfassende und einheitliche Phasenbeschreibung
irregulärer Oszillationen.Many natural systems embedded in a complex surrounding show irregular oscillatory dynamics. The oscillations can be parameterized by a phase variable in order to obtain a simplified theoretical description of the dynamics. Importantly, a phase description can be easily extended to describe the interactions of the system with its surrounding. It is desirable to define an invariant phase that is independent of the observable or the arbitrary parameterization, in order to make, for example, the phase characteristics obtained from different experiments comparable. In this thesis, we present an invariant phase description of irregular oscillations and their interactions with the surrounding. The description is applicable to stochastic and chaotic irregular oscillations of autonomous dissipative systems. For this it is necessary to interrelate different phase values in order to allow for a parameterization-independent phase definition. On the other hand, a criterion is needed, that invariantly identifies the system states that are in the same phase. To allow for a parameterization-independent definition of phase, we interrelate different phase values by the phase velocity. However, the treatment of stochastic oscillations is complicated by the fact that different definitions of average velocity are possible. For a better understanding of their differences, we analyse effective deterministic phase models of the oscillations based upon the different velocity definitions. Dependent on the application, a certain effective velocity is suitable for a parameterization-independent phase description. In this way, continuous as well pulse-like interactions of stochastic oscillations can be described, as it is demonstrated with simple examples. On the other hand, an invariant criterion of identification is proposed that generalizes the concept of standard (Winfree) isophases. System states of the same phase are identified to belong to the same generalized isophase using the following invariant criterion: All states of an isophase shall become indistinguishable in the course of time. The criterion is interpreted in an average sense for stochastic oscillations. It allows for a unified treatment of different types of stochastic oscillations. Using a numerical estimation algorithm of isophases, the applicability of the theory is demonstrated by a signal of regular human respiration. For chaotic oscillations, generalized isophases can only be obtained up to a certain approximation. The intimate relationship between these approximate isophase, chaotic phase diffusion, and unstable periodic orbits is explained with the example of the chaotic roes oscillator. Together, the concept of generalized isophases and the effective phase theory allow for a unified, and invariant phase description of stochastic and chaotic irregular oscillations.
11
Jentsch, L., e D. Natroshvili. "Thermoelastic Oscillations of Anisotropic Bodies". Universitätsbibliothek Chemnitz, 1998. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-199800871.
Testo completoAbstract (sommario):
The generalized radiation conditions at infinity of Sommerfeld-Kupradze type are established in the theory of thermoelasticity of anisotropic bodies. Applying the potential method and the theory of pseudodifferential equations on manifolds the uniqueness and existence theorems of solutions to the basic three-dimensional exterior boundary value problems are proved and representation formulas of solutions by potential type integrals are obtained.
12
Rorrer, Ronald Alvin Lee. "Frictional oscillations in elastomeric sliding". Diss., This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-07282008-134509/.
Testo completo
13
Balmforth, N. J. "The theory of stellar oscillations". Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358576.
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14
Selbach, Arndt. "Flames with imposed air oscillations". Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326245.
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15
Roopun, Anita Kumari. "Cortical network oscillations in vitro". Thesis, University of Leeds, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426852.
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16
Colenso, Richard Arthur. "Simulations of neocortical columnar oscillations". Thesis, Open University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.412407.
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17
Fox, Sarah. "Oscillations memory and Alzheimer's disease". Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/oscillations-memory-and-alzheimers-disease(bbacb2f0-74f3-4071-b02f-19c0c5570227).html.
Testo completoAbstract (sommario):
Damage precipitating cognitive decline in Alzheimer's disease (AD) begins long before behavioural alterations become clinically apparent. At this prodromal stage, communication between networks of neurons connecting different brain regions starts to break down; setting in motion a chain of events leading to clinical AD. A significant challenge facing Alzheimer's researchers today is finding a cheap, easy-to-perform test capable of detecting prodromal AD. Such a test would afford significant benefits to patients, including a chance of early intervention. Perhaps, more importantly, it would also aid development and testing of novel therapies aimed at combating AD before it causes irreversible damage. Since oscillations in electrical field activity are important for facilitating connectivity across the brain and have been seen to alter in AD, this work studied how oscillations and regional connectivity are affected in the AD brain. Specifically, local field oscillations were recorded from the hippocampus and prelimbic cortex (regions implicated in memory formation and maintenance) in a double transgenic AD model - the TASTPM mouse. Here, periods of predominant theta activity were assessed both spontaneously, under urethane anaesthesia and following electrical induction through dorsal periaqueductal gray (dPAG) stimulation. From these recordings, spectral power and connectivity between regions was assessed using both a traditional measure of functional connectivity (inter-region correlation) and through a novel information theoretic approach measuring effective connectivity (transfer entropy).Perhaps the most prominent finding from this study was the observation that young TASTPM mice, at an age prior to overt cognitive decline or plaque deposition, showed significant alterations in measures of both functional and effective connectivity. This suggests that such measures may be used as biomarkers predictive of prodromal AD and, as such, may be used to aid development of drugs targeted towards treatment of prodromal AD.This study also uncovered a number of interesting observations concerning hippocampal/prelimbic connectivity. Firstly, although spectral power and inter-regional correlation peaked at ∼ 3Hz, information flow between these structures was strongest at ∼6Hz. This suggests that low and high-band theta activity may fulfil separate functions. Secondly, at theta frequencies, information flowed predominantly from the prelimbic cortex to the hippocampus. However, during lower frequency activity, information flowed predominantly in the opposite direction. Suggesting that separate frequency bands may be important for routing information flow between these structures. Finally, the strength of information transfer was seen to oscillate at approximately double the frequency of its carrier signal, perhaps suggesting locking of information transfer to certain phases of an underlying oscillation. Therefore, oscillations may structure information transfer by temporal windowing and frequency-locked routing; processes which can be studied using measures of effective connectivity such as transfer entropy.
18
Evesque, Stéphanie Marie-Noelle. "Adaptive control of combustion oscillations". Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620985.
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19
Granqvist, Emma. "Patterns of symbiotic calcium oscillations". Thesis, University of East Anglia, 2012. https://ueaeprints.uea.ac.uk/42339/.
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20
Keer, Lucy. "Neutron star oscillations from starquakes". Thesis, University of Southampton, 2014. https://eprints.soton.ac.uk/363269/.
Testo completoAbstract (sommario):
Glitches are sudden increases in the otherwise extremely regular spin rate of pulsars. One theory proposed to account for these glitches is the starquake model, in which the spinup is caused by a sudden rearrangement of the neutron star crust. Starquakes can be expected to excite some of the oscillation modes of the neutron star. These oscillations are of interest as a source of gravitational waves, and may also modify the pulsar radio emission. In this thesis we develop a toy model of the starquake and calculate which modes of the star are excited. We start by making some order-of-magnitude upper estimates on the energy made available by the starquake and the amplitude of the modes excited, before moving on to a more detailed calculation based on a speci�c model of the starquake in which all strain is lost instantaneously from the star at the glitch. To find out which modes are excited by the starquake, we construct initial data describing the change in the star at the glitch, and then project this against the basis of normal modes of the star. We first carry out this procedure for a simplified model in which the star has spun down to zero angular velocity before the starquake. We find that the majority of the energy released goes into a mode similar to the fundamental mode of a uid star. Finally, we describe the extension of this model to the more realistic case where the star is rotating before the glitch. We calculate the change in the normal modes of the star to first order in the rotation; these are no longer orthogonal, but we construct a scheme that still enables us to project our initial data against this set of modes, and discuss some preliminary results of the model.
21
Conrad, Emery David. "Mathematical Models of Biochemical Oscillations". Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/32781.
Testo completoAbstract (sommario):
The goal of this paper is to explain the mathematics involved in modeling biochemical oscillations. We first discuss several important biochemical concepts fundamental to the construction of descriptive mathematical models. We review the basic theory of differential equations and stability analysis as it relates to two-variable models exhibiting oscillatory behavior.
The importance of the Hopf Bifurcation will be discussed in detail for the central role it plays in limit cycle behavior and instability. Once we have exposed the necessary mathematical framework, we consider several specific models of biochemical oscillators in three or more variables. This will include a detailed analysis of Goodwin's equations and their modification first studied by Painter.
Additionally, we consider the consequences of introducing both distributed and discrete time delay into Goodwin's model. We will show that the presence of distributed time lag modifies Goodwin's model in no significant way.
The final section of the paper will discuss discrete time lag in the context of a minimal model of the circadian rhythm.
In the main, this paper will address mathematical, as opposed to biochemical, issues. Nevertheless, the significance of the mathematics to the biochemistry will be considered throughout.Master of Science
22
Allen, Sue. "Rapid oscillations in cataclysmic variables". Master's thesis, University of Cape Town, 1986. http://hdl.handle.net/11427/16374.
Testo completoAbstract (sommario):
Bibliography: pages 103-117.Coherent and quasi-periodic rapid oscillations have been seen in the optical and X-ray light curves of more than 30 cataclysmic variables to date. The observational characteristics of these oscillations are reviewed, and current models discussed. To put the observations in context, a detailed review is given of the canonical model of cataclysmic variables and the variations that give rise to its various sub-classes. Observations of two systems of particular interest are presented, and their contributions to the modelling of rapid oscillations are discussed. High-speed photometry of the very bright nova-like variable CPD-48°1577 (IX Velorum) is shown to reveal low-amplitude oscillations with periods between 24 and 31 seconds. The oscillations are present in more than half of the runs, making this variable an attractive target for simultaneous observations in different wavelength bands. The dwarf nova Z Cha is one of four cataclysmic variables which show rapid oscillations as well as primary eclipses. Photometry of z Cha, archived at the University of Cape Town over a period of ten years, is searched for rapid oscillations. Two runs show oscillations, with periods of 24 and 28 seconds. They exhibit eclipse-related phase changes which show qualitative repetition within a run, but significant long-term variation. This behaviour has not been seen in any other cataclysmic variable, and makes z Cha a potentially powerful discriminating tool for models of oscillation and superoutburst.
23
Nakagawa-Yoshikawa, Harunori. "Instabilités des interfaces sous oscillations". Paris 6, 2006. http://www.theses.fr/2006PA066303.
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24
Houbad, Mekki. "Oscillations, feuilletages, lois de Burger". Rennes 1, 2010. http://www.theses.fr/2010REN1S099.
Testo completoAbstract (sommario):
On présente dans ce mémoire de thèse quelques résultats nouveaux relevant du domaine de l’optique géométrique non linéaire sur-critique. Le cadre est fourni par les systèmes de type Burger en présence d’une contrainte de divergence nulle. On obtient dans ce contexte une classification complète de toutes les oscillations de grande amplitude qui sont localement solutions d’Euler incompressible (sans pression). Ces solutions sont principalement caractérisées par la nilpotence des matrices Jacobiennes associées. Notre approche repose sur une analyse BKW atypique dont un des ressorts est une bonne compréhension de la géométrie des phases portant les singularitésIn this work, we construct large amplitude oscillating waves which are local solutions on some open domain of the time-space of both the three dimensional Burger equations (without source term) and the incompressible Euler equations (without pressure). The solutions are mainly characterized by the fact that the corresponding Jacobian matrices are nilpotent. Our approach consists in performing some nonusual WKB analysis. The main difficulity is to understand what is the geometry of the phases brought into play
25
Rönnqvist, Kim. "Multimodal characterisation of sensorimotor oscillations". Thesis, Aston University, 2013. http://publications.aston.ac.uk/19564/.
Testo completoAbstract (sommario):
The studies in this project have investigated the ongoing neuronal network oscillatory activity found in the sensorimotor cortex using two modalities: magnetoencephalography (MEG) and in vitro slice recordings. The results have established that ongoing sensorimotor oscillations span the mu and beta frequency region both in vitro and in MEG recordings, with distinct frequency profiles for each recorded laminae in vitro, while MI and SI show less difference in humans. In addition, these studies show that connections between MI and SI modulate the ongoing neuronal network activity in these areas. The stimulation studies indicate that specific frequencies of stimulation affect the ongoing activity in the sensorimotor cortex. The continuous theta burst stimulation (cTBS) study demonstrates that cTBS predominantly enhances the power of the local ongoing activity. The stimulation studies in this project show limited comparison between modalities, which is informative of the role of connectivity in these effects. However, independently these studies provide novel information on the mechanisms on sensorimotor oscillatory interaction. The pharmacological studies reveal that GABAergic modulation with zolpidem changes the neuronal oscillatory network activity in both healthy and pathological MI. Zolpidem enhances the power of ongoing oscillatory activity in both sensorimotor laminae and in healthy subjects. In contrast, zolpidem attenuates the “abnormal” beta oscillatory activity in the affected hemisphere in Parkinsonian patients, while restoring the hemispheric beta power ratio and frequency variability and thereby improving motor symptomatology. Finally we show that independent signals from MI laminae can be integrated in silico to resemble the aggregate MEG MI oscillatory signals. This highlights the usefulness of combining these two methods when elucidating neuronal network oscillations in the sensorimotor cortex and any interventions.
26
Mönke, Gregor. "Stochastic oscillations in living cells". Doctoral thesis, Humboldt-Universität zu Berlin, Lebenswissenschaftliche Fakultät, 2015. http://dx.doi.org/10.18452/17211.
Testo completoAbstract (sommario):
In dieser Arbeit werden zwei intrazelluläre Signalwege, betreffend den Tumorsuppressor p53 und das Signalmolekül Ca2+ , diskutiert und modelliert. Einzelzellmessungen des Tumorsuppressors p53 zeigen pulsatile Antwor- ten nach Zufügung von DNA Doppelstrangbrüchen (DSBs). Außer für sehr hohe Schadensdosen, ist das zeitliche auftreten dieser Pulse unregelmäßig. Mithilfe eines Wavelet basierten Pulsdetektors werden die einzelzell Trajek- torien untersucht und die inter-Puls Intervall (IPI) Verteilungen extrahiert. Diese weisen auf nicht-oszillatorische Regime in den Daten hin. Die Theorie der anregbaren Systeme angewendet auf regulatorische Netzwerke ermöglicht dieses komplexe Verhalten mathematisch zu beschreiben. Die Kopplung von Schadens-Sensor-Kinase Dynamik mit dem kanonischen p53 negativen feedback loop, ergibt ein anregbares p53 Modell. Detaillier- te Bifurkationsanalysen zeigen ein robustes anregbares Regime, welches durch ein starkes Schadenssignal auch in Oszillationen überführt werden kann. Treibt man das p53 Modell mit einem stochastischen DNA-Schadens-Prozess, kann sowohl das oszillatorische Verhalten nach hohem Schaden, als auch das unregelmäßige pulsatile Verhalten ohne äußere Stimulation reproduziert werden. Intrazelluläre Ca 2+ Spikes entstehen durch eine hierarchische Kaskade stochastischer prozesse. Die Anwendung einer semi-markovschen Beschreibung führt zu praktischen analytischen Lösungen des erstpassagezeiten Problems. Eine hierbei entdeckte Zeitskalenseparation ermöglicht ein neues allgemeines Ca2+ -Modell. Dieses erklärt auf äußerst prägnante Weise viele wesentliche experimentelle Ergebnisse, insbesondere die Momentenbeziehungen der inter-Spike Intervall Verteilungen. Schließlich erlaubt die hier vorgestellte Theorie Berechnungen der Stimulus-Enkodierung, also die Adaption des Ca 2+ Signals auf veränderliche extrazelluläre Stimuli. Die Vorhersage einer fold change Enkodierung kann durch Experimente gestützt werden.In this work two signaling pathways, involving the tumor suppressor p53 and the second messenger Ca2+ , are to be discussed and modelled. The tumor suppressor p53 shows a pulsatile response in single cells after induction of DNA double strand breaks (DSBs). Except for very high amounts of damage, these pulses appear at irregular times. The concept of excitable systems is employed as a convenient way to model such observed dynamics. An application to biomolecular reaction networks shows the need for a positive feedback within the p53 regulatory network. Exploiting the reported ultrasensitive dynamics of the upstream damage sensor kinases, leads to a simplified excitable kinase-phosphatase model. Coupling that to the canonical negative feedback p53 regulatory loop, is the core idea behind the construction of the excitable p53 model. A detailed bifurcation analysis of the model establishes a robust excitable regime, which can be switched to oscillatory dynamics via a strong DNA damage signal. Driving the p53 model with a stochastic DSB process yields pulsatile dynamics which reflect different experimental scenarios. Intracellular Ca 2+ concentration spikes arise from a hierarchic cascade of stochastic events. An analytical solution strategy, employing a semi-Markovian description and involving Laplace transformations, is devised and successfully applied to a specific Ca2+ model. The new gained insights are then used, to construct a new generic Ca2+ model, which elegantly captures many known features of Ca2+ signaling. In particular the experimentally observed relations between the average and the standard deviation of the inter spike intervals (ISIs) can be explained in a concise way. Finally, the theoretical considerations allow to calculate the stimulus encoding relation, which governs the adaption of the Ca 2+ signals to varying extracellular stimuli. This is predicted to be a fold change response and new experimental results display a strong support of this idea.
27
Mirandés, Rivera Estefania de. "Bloch oscillations of ultracold atoms". Paris 6, 2006. http://www.theses.fr/2006PA066622.
Testo completo
28
Vidal, Alexandre. "Relaxation et oscillations en salves". Paris 6, 2007. http://www.theses.fr/2007PA066670.
Testo completoAbstract (sommario):
Les oscillations en salves apparaissent dans de nombreux systèmes biologiques, physiologiques et écologiques. Elles se caractérisent par l’alternance de phases dites silencieuses ou quiescentes séparées par des phases dites actives ou pulsatiles. Cette thèse est consacrée à l'analyse mathématique des systèmes dynamiques lents-rapides proposés pour la modélisation des oscillations en salves. Grâce à la théorie des bifurcations, la théorie des perturbations singulières et l’utilisation d’éclatements à paramètres, nous caractérisons les différents comportements de tels systèmes. En particulier, nous utilisons des développements asymptotiques pour les applications de transition entre phases d’évolution lentes et rapides. Nous montrons des résultats d’existence d’orbites périodiques non triviales, de convergence d’un continuum d’orbites vers un ensemble limite-périodique et d’apparition de « canards ».
29
Wilquet, Gaston. "Masses, mélange et oscillations de neutrinos". Doctoral thesis, Universite Libre de Bruxelles, 2005. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/211058.
Testo completoAbstract (sommario):
Une revue générale est faite de la situation expérimentale concernant la mesure des masses, du mélange et des oscillations de neutrinos, ainsi que de la phénoménologie sous-jacente. Mes contributions à travers le programme expérimental du CERN, CHARM-II, CHORUS et OPERA, font l'objet d'un développement particulier. Le dernier chapitre tente de mettre en perspective le programme expérimental à moyen et long terme.The experimental situation concerning the measurements of neutrinos masses, mixing and oscillation is reviewed, as well as of the underlying phenomenology. A particular attention is given to the CERN experimental program to which I took or take part, CHARM-II, CHORUS and OPERA. In the last chapter, I try to put into perspective the medium and long term experimental programme.
Agrégation de l'enseignement supérieur, Orientation sciences
info:eu-repo/semantics/nonPublished
30
Chang, Tien Fu. "Wave-induced oscillations in arbitrary harbours". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0006/MQ31552.pdf.
Testo completo
31
Dendis, Alexandros. "Oscillations of a multi-string pendulum". Thesis, Monterey, Calif. : Naval Postgraduate School, 2007. http://bosun.nps.edu/uhtbin/hyperion-image.exe/07Jun%5FDendis.pdf.
Testo completoAbstract (sommario):
Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, June 2007.Thesis Advisor(s): Fotis Papoulias. "June 2007." Description based on title screen as viewed on August 13, 2007. Includes bibliographical references (p. 133). Also available in print.
32
Bell, Nicole F. "Neutrino oscillations and the early universe /". Connect to thesis, 2000. http://eprints.unimelb.edu.au/archive/00000697.
Testo completo
33
Ugueto, Luis. "Experimental study of density waves oscillations". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-22654.
Testo completoAbstract (sommario):
Nowadays, systems based on convective boiling flows are found in a wide variety of industrial applications, such as boiling water reactors, boilers, thermosiphons, heat exchangers, condenser, chemical reactors and some other chemical process units. Such systems take advantage of the high heat transfer rates that a boiling fluid can reach at moderate temperature differences. However, those systems are unfortunately susceptible to thermally induced two-phase flow instabilities, such as Density Wave Oscillations. Thereby, the aim of present research is to perform an experimental investigation on Density Wave Oscillations, focusing on the analysis of the operational parameter effect in the system stability and characteristics of the oscillations. As a result of this investigation, the Ishii-Zuber plane is found to be appropriate to represent the system stability and that the Guido?s criteria cannot be used to estimate the instability threshold. Moreover, the oscillation amplitude monotonically increases by increasing the heat flux until it reaches an asymptote and the period is found to decrease when the amplitude is increased. Finally, a new dimensionless correlation based on amplitude ratio, is proposed as a result of the observed trends. It is found to be very useful, not only correlates well the collected data at the onset of Density Wave Oscillation, but also predicts the maximum amplitude for the given sets of operating conditions.
34
De, Zilwa Shane Ranel Noel. "Combustion oscillations in sudden-expansion flows". Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322706.
Testo completo
35
Robertson, David. "Transverse oscillations of interacting coronal loops". Thesis, University of Sheffield, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.538010.
Testo completo
36
Tullet, Peter Francis. "ULF oscillations in the terrestrial magnetosphere". Thesis, Lancaster University, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.543976.
Testo completo
37
Schwartzman, David John. "The Functional Role of Gamma Oscillations". Thesis, Oxford Brookes University, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.515265.
Testo completo
38
Wilsch, Anna. "Neural oscillations in auditory working memory". Doctoral thesis, Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-177313.
Testo completoAbstract (sommario):
The present thesis investigated memory load and memory decay in auditory working memory. Alpha power as a marker for memory load served as the primary indicator for load and decay fluctuations hypothetically reflecting functional inhibition of irrelevant information. Memory load was induced by presenting auditory signals (syllables and pure-tone sequences) in noise because speech-in-noise has been shown before to increase memory load. The aim of the thesis was to assess with magnetoencephalography whether a-priori temporal expectations for the onset-time of a to-be-remembered stimulus reduces memory load. It was reported previously that top-down modulations such as spatial expectations reduce memory load and improve memory performance. However, this effect has neither been investigated with temporal expectations nor in the auditory domain. The present thesis showed that temporal expectations for a syllable in noise reduced memory load. Reduced alpha power during stimulus maintenance as well as
improved performance indicated the decrease in memory load. Alpha power effects emerged from the right cingulo-opercular network, presumably reflecting a reduced need for functional inhibition. Critically, symbolic cues induced temporal expectations. This effect could not be replicated for clear speech. However, more implicit temporal expectations based on the passage of time elicited a similar decrease in alpha power for clear speech reflecting reduced memory load. Memory decay was assessed with variable delay phases in an auditory sensory memory task with pure-tone sequences. Similarly to memory performance, alpha power decreased with longer delay phases. Critically, temporal expectations counteracted memory decay and led to more sustained performance as well as alpha power across different delay phases. These alpha-power effects were localized to frontal and parietal attention networks as well as primary auditory and visual sensory areas. This implies the involvement of different brain regions relevant
for encoding and maintenance in auditory memory and questions a parsimonious functional inhibition explanation. A correlation of alpha power and behavioral performance underpinned the importance of alpha power for auditory working memory. Altogether, the results of the present thesis provide evidence for a beneficial effect of a-priori temporal expectations for an auditory signal on working memory. Moreover, alpha dynamics were shown to be a distinct marker for the neural efficiency of managing working memory limitations.
39
Elevant, Jessica. "CP-violation in Supernova Neutrino Oscillations". Thesis, Linköpings universitet, Teoretisk Fysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-109922.
Testo completoAbstract (sommario):
It is astonishing both how little and how much we know about neutrinos. On one hand, the neutrino is the second most abundant particle in our Universe. Neutrinos may be created in the Sun, core collapse supernovae, cosmic rays, geological background radiation, supernova remnants and in the Big Bang. On the other hand, they have unimaginably small masses and are unwilling to react with their surroundings. Because of their abundance and their inclination to show us physics beyond the standard model of particle physics, neutrinos are hoped to carry yet unknown information of the Universe. However, it will take some effort and time to persuade the neutrinos to tell us what they know. Among the things we do not yet know of the neutrinos, is the -phase in the neutrino mixing matrix. If is in fact non-zero, neutrino flavour oscillations violate CP-symmetry. Also, if neutrino masses are introduced in the standard model through the See-Saw mechanism and if leptogenesis is a valid theory, CP-violation in neutrino oscillations could help explain why our Universe has no antimatter even though equal amounts of matter and antimatter should have been created at the Big Bang. In this thesis, we investigate the flavour evolution of supernova neutrinos. We present the full Hamiltonian in the flavour basis for our system and identify how the different contributions affect the evolution and in which environment. We also present a theoretical motivation from [1, 2] as to how a non-zero -phase affects the flavour evolution and the final energy spectra. The analytical conclusion is that it has no impact under the assumptions made in our analysis. Thus, the -phase may not be measurable from supernova neutrinos.
40
Wilson, Sean Odell. "Nonlinear oscillations of a triatomic molecule". Thesis, Monterey California. Naval Postgraduate School, 2002. http://hdl.handle.net/10945/5664.
Testo completoAbstract (sommario):
Approved for public release; distribution is unlimitedude decreases if the difference of the frequency of the two modes is reduced. We consider the simplest case of a symmetric rectilinear molecule where the coupling has a cubic nonlinearity in addition to a linear restoring force. Approximate analytical results are in good agreement with numerical simulations of the exact equations of motion, although in some cases the actual behavior fundamentally deviates from the perturbative theory. Two physical demonstrations of the instability are described, where the apparatus are a system of gliders coupled by springs and magnets on an air track. Possible quantum mechanical implications are discussed. This work is a fundamental generalization of the parametric instability of two linearly coupled nonlinear oscillators that was reported in a previous investigation.
41
Jörg, David Josef. "Genetic Oscillations and Vertebrate Embryonic Development". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-159034.
Testo completoAbstract (sommario):
Recurrent processes are a general feature of living systems, from the cell cycle to circadian day-night rhythms to hibernation and flowering cycles. During development and life, numerous recurrent processes are controlled by genetic oscillators, a specific class of genetic regulatory networks that generates oscillations in the level of gene products. A vital mechanism controlled by genetic oscillators is the rhythmic and sequential segmentation of the elongating body axis of vertebrate embryos. During this process, a large collection of coupled genetic oscillators gives rise to spatio-temporal wave patterns of oscillating gene expression at tissue level, forming a dynamic prepattern for the precursors of the vertebrae. While such systems of genetic oscillators have been studied extensively over the past years, many fundamental questions about their collective behavior remain unanswered. In this thesis, we study the behavior and the properties of genetic oscillators from the single oscillator scale to the complex pattern forming system involved in vertebrate segmentation.
Genetic oscillators are subject to fluctuations because of the stochastic nature of gene expression. To study the effects of noisy biochemical coupling on genetic oscillators, we propose a theory in which both the internal dynamics of the oscillators as well as the coupling process are inherently stochastic. We find that stochastic coupling of oscillators profoundly affects their precision and synchronization properties, key features for their viability as biological pacemakers. Moreover, stochasticity introduces phenomena not known from deterministic systems, such as stochastic switching between different modes of synchrony.
During vertebrate segmentation, genetic oscillators play a key role in establishing a segmental prepattern on tissue scale. We study the spatio-temporal patterns of oscillating gene expression using a continuum theory of coupled phase oscillators. We investigate the effects of different biologically relevant factors such as delayed coupling due to complex signaling processes, local tissue growth, and tissue shortening on pattern formation and segmentation. We find that the decreasing tissue length induces a Doppler effect that contributes to the rate of segment formation in a hitherto unanticipated way. Comparison of our theoretical findings with experimental data reveals the occurrence of such a Doppler effect in vivo. To this end, we develop quantification methods for the spatio-temporal patterns of gene expression in developing zebrafish embryos.
On a cellular level, tissues have a discrete structure. To study the interplay of cellular processes like cell division and random cell movement with pattern formation, we go beyond the coarse-grained continuum theories and develop a three-dimensional cell-based model of vertebrate segmentation, in which the dynamics of the segmenting tissue emerges from the collective behavior of individual cells. We show that this model is able to describe tissue formation and segmentation in a self-organized way. It provides the first step of theoretically describing pattern formation and tissue dynamics during vertebrate segmentation in a unified framework involving a three-dimensional tissue with cells as distinct mechanical entities.
Finally, we study the synchronization dynamics of generic oscillator systems whose coupling is subject to phase shifts and time delays. Such phase shifts and time delays are induced by complex signaling processes as found, e.g., between genetic oscillators. We show how phase shifts and coupling delays can alter the synchronization dynamics while leaving the collective frequency of the synchronized oscillators invariant. We find that in globally coupled systems, fastest synchronization occurs for non-vanishing coupling delays while in spatially extended systems, fastest synchronization can occur on length scales larger than the coupling range, giving rise to novel synchronization scenarios. Beyond their potential relevance for biological systems, these results have implications for general oscillator systems, e.g., in physics and engineering.
In summary, we use discrete and continuous theories of genetic oscillators to study their dynamic behavior, comparing our theoretical results to experimental data where available. We cover a wide range of different topics, contributing to the general understanding of genetic oscillators and synchronization and revealing a hitherto unknown mechanism regulating the timing of embryonic pattern formation.
42
Lawrence, Yvonne Millicent. "Intracellular calcium oscillations in mouse oocytes". Thesis, University of Liverpool, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240642.
Testo completo
43
Grosart, Kirsty. "Oscillations and stability of rotating superfluids". Thesis, University of Southampton, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.433829.
Testo completo
44
Kohutova, Petra. "Magnetohydrodynamic oscillations in solar coronal rain". Thesis, University of Warwick, 2018. http://wrap.warwick.ac.uk/106944/.
Testo completoAbstract (sommario):
Coronal rain composed of cool plasma condensations falling from coronal heights along magnetic field lines is a phenomenon occurring in active region coronal loops. This work combines high-resolution observations and numerical simulations to understand the interplay between coronal rain and MHD oscillations. We analyse oscillations and kinematics of the coronal rain using high resolution observations. Two different regimes of transverse oscillations traced by the rain are detected: smallscale persistent oscillations driven by a continuously operating process and localized large-scale oscillations excited by a transient mechanism. The plasma condensations are found to move with accelerations largely below the free-fall rate. The observed evolution of the emission of the plasma at the loop top is found to exhibit clear signatures of a gradual cooling consistent with the limit cycle model and suggests the loop is going through a sequence of periodically repeating heating-condensation cycles. We further investigate the evolution and dynamics of coronal rain using 2.5D MHD simulations. We model the evolution of a cool plasma condensation in a gravitationally stratified coronal loop. The motion of plasma condensations is found to be strongly affected by the pressure of the coronal loop plasma. High coronal magnetic field or low condensation mass are found to lead to damped oscillatory motion of the condensations. The combined effect of plasma pressure gradients and magnetic tension force can therefore explain observed sub-ballistic motion and longitudinal oscillations of coronal rain. We finally address the possibility of excitation of loop oscillations by coronal rain. We carry out MHD simulations of a coronal loop containing a cool and dense condensation region near the loop apex. This is found to excite fundamental harmonic of a vertically polarised kink mode. As the condensations fall towards the loop footpoints, the fundamental mode period is found to decrease as a result of the change in distribution of mass along the loop. We also carry out simulations of a coronal loop with a siphon ow between the footpoints which is likely to arise in asymmetrically heated loops. The action of the centrifugal force associated with plasma moving along the curved axis of the loop is found to excite vertically polarised loop oscillations. We find that flows with realistic speeds are sufficient to excite oscillations with observable amplitudes. We therefore propose coronal rain as a possible excitation mechanism for transverse loop oscillations.
45
Yang, Qian. "Oscillations in stochastic multi-species interactions". Thesis, University of Bath, 2018. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.761013.
Testo completo
46
Händel, Chris. "Fluctuations and Oscillations in Cell Membranes". Doctoral thesis, Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-200703.
Testo completoAbstract (sommario):
Zellmembranen sind hochspezialisierte Mehrkomponentenlegierungen, welche sowohl die
Zelle selbst als auch ihre Organellen umgeben. Sie spielen eine entscheidende Rolle bei
vielen biologisch relevanten Prozessen wie die Signaltransduktion und die Zellbewegung.
Aus diesem Grund ist eine genaue Charakterisierung ihrer Eigenschaften der Schlüssel
zum Verständnis der Bausteine des Lebens sowie ihrer Erkrankungen. Besonders Krebs
steht im engen Zusammenhang mit Veränderungen der biomechanischen Eigenschaften
vom Gewebe, Zellen und ihren Organellen. Während Veränderungen des Zytoskeletts
von Krebszellen im Fokus vieler Biophysiker stehen, ist die Bedeutung der Biomechanik
von Zellmembran weitgehend unklar. Zellmembranen faszinieren Wissenschaftler jedoch
nicht nur wegen ihrer biomechanischen Eigenschaften. Sie sind auch Beispiele für eine
selbstorganisierte und heterogene Landschaft, in der Prozesse fernab des Gleichgewichtes,
wie z.B. räumliche und zeitliche Musterbildungen, auftreten. Die vorgelegte Dissertation
untersucht erstmals umfassend die zentrale Rolle der Zellmembran und ihrer molekularen
Architektur für die Signalübertragung, die Biomechanik und die Zellmigration. Hierfür
werden einfache Modellmembranen aber auch komplexere Vesikel und ganze Zellen
mittels etablierter physikalischer Methoden analysiert. Diese reichen von Fourier-
Analysen zur Charakterisierung von thermisch angeregten Membranundulationen über
Massenspektrometrie und ‘Optical Stretcher’ Messungen von ganzen Zellen bis hin
zur Filmwaagentechnik. Des Weiteren wird ein Modellsystem vorgestellt, welches
sowohl einen experimentellen als auch einen mathematischen Zugang zum ‘ME-switch’
ermöglicht. Die vorgelegte Dissertation bietet neue Einblicke in wichtige Funktionen
von Zellmembranen und zeigt neue therapeutische Perspektiven in der Membran- und
Krebsforschung auf.
47
Kuridze, D. "Magnetohydrodynamic oscillations in chromospheric fine structures". Thesis, Queen's University Belfast, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.678708.
Testo completoAbstract (sommario):
This thesis presents the study of magnetohydrodynamic (MHO) waves and oscillations in quiet Sun chromospheric fine structures near the solar disk center using multiwavelength, high temporal and spatial resolution observations. Transverse oscillations in chromospheric on-disk mottles that appear to be rooted in photospheric magnetic bright points are detected with great accuracy and interpreted in terms of MHO kink waves. Measured kink wave characteristiCs, such as periods (ranging from 70 to 280 s and peak at -165-s), phase speeds 40-120-km S·l, and transverse velocity amplitudes (2-18 km S-l), are similar to results found for limb spicules. An analysis of oscillation signals at different positions along the mottles provides evidence for upward and downward propagating and standing transverse waves. Wave characteristics including the maximum transverse velocity amplitude and the phase speed are measured as a function of distance along the structure's length. Solar magnetoseismology (SMS) is applied to these measured parameters to obtain diagnostic information on key plasma parameters (e.g., magnetic field, density, temperature, flow speed) of these localized waveguides. Using the SMS tool, the magnetic field strength of the mottle along the -2 Mm length is found to decrease by a factor of 12, while the local plasma density scale height is -280±80-km.
48
Andrews, David Jeremy. "Planetary-period oscillations in Saturn's magnetosphere". Thesis, University of Leicester, 2011. http://hdl.handle.net/2381/9995.
Testo completoAbstract (sommario):
This thesis is concerned with the study of near-planetary rotation period oscillations in Saturn’s magnetic field. Similar oscillations are present in a variety of other magnetospheric phenomena, most notably kilometre-wavelength radio emissions, and together they have a substantial influence throughout the Saturnian plasma environment. However, their origin remains poorly understood, despite more than a decade of study. Surprising new discoveries have been made regarding the seasonality of these oscillatory phenomena, and their intrinsic connection to the high-latitude upper atmosphere and ionosphere of the planet, though a complete theory of their origin remains to be developed. In this thesis, three detailed studies of this phenomenon are presented, each of which uses magnetic field data recently obtained by the Cassini spacecraft. The first consists of an extensive survey of near-equatorial field data during southern summer, from which the structure of the rotating oscillations is determined and the electrical currents flowing through the equatorial plane are calculated. The second study is prompted by the recent discovery of a north-south asymmetry in the period of related radio emissions, and consists of a survey of high-latitude magnetic field data in which evidence for a corresponding asymmetry in the magnetic field rotation period is found. Finally, the third study concerns the presence of long-termdrifts between the phase of the magnetic field oscillation and the Saturn kilometric radiation (SKR) modulation, which, through construction of a simple theoretical model, is shown to arise as a consequence of ‘rotational’ modulations in the SKR rather than the hitherto assumed ‘strobe-like’ modulations. These three studies substantially further our understanding of these phenomena, and in the case of the detection of a rotational modulation in the SKR overturn three decades of previous thought. Consequently, the results presented here elucidate characteristics of these phenomena that any theoretical understanding of their origin must serve to explain, and will therefore be of central importance in further development of this topic in the future. Before presenting these three studies, an introduction to the topics of space plasma physics and planetary magnetospheres is presented in Chapter 1. This is followed in Chapter 2 with a discussion of Saturn’s magnetosphere, and the topic of near-planetary period oscillations, and in Chapter 3 by descriptions of the instruments with which data used in this thesis have been obtained.
49
Burley, Jonathan Mark Anderson. "Magmatism and glacial cycles : coupled oscillations?" Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:c55a6d98-d222-46de-8500-1ad44d05be75.
Testo completoAbstract (sommario):
The Earth's climate system is driven by varying insolation from the Sun. The dominant variations in insolation are at 23 and 40 thousand year periods, yet for the past million years the Earth's climate has glacial cycles at approximately 100 kyr periodicity. These cycles are a coupled variation in temperature, ice volume, and atmospheric CO2. Somehow the Earth system's collective response to 23 and 40 kyr insolation forcing produces 100 kyr glacial-interglacial cycles. Generally it has been assumed that the causative mechanisms are a combination of ice dynamics (high ice reflectivity controlling temperature) and ocean circulation (changing carbon partitioning between the deep ocean and the atmosphere, and heat transport to the poles). However, these proposed mechanisms have not yet resulted in a compelling theory for all three variations, particularly CO2. This thesis explores the role of volcanic CO2 emissions in glacial cycles. I calculate that glacial-driven sea level change alters the pressure on mid-ocean ridges (MORs), changing their CO2 emissions by approximately 10%. This occurs because pressure affects the thermodynamics of melt generation. The delay between sea level change and the consequent change in MOR CO2 emissions is several tens-of-thousands-of-years, conceptually consistent with a coupled non-linear oscillation that could disrupt glacial cycles from a 40 kyr mode to a multiple of that period. I develop an Earth system model to investigate this possibility, running for approximately one million years and explicitly calculating global temperatures, ice sheet configuration, and CO2 concentration in the atmosphere. The model is driven by insolation, with all other components varying in response (and according to their own interactions). This model calculates that volcanism is capable of causing a transition to ̃100 kyr glacial cycles, however the required average volcanic CO2 emissions are barely within the 95% confidence interval. Therefore it is possible for volcanic systems and glacial cycles to form a 100 kyr coupled oscillation.
50
Smith, Thomas Charles Brannam. "Thermally driven oscillations in dynamic applications". Thesis, University of Cambridge, 2006. https://www.repository.cam.ac.uk/handle/1810/284059.
Testo completo