Дисертації з теми "Oscillating Mechanism"
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1
Calderon, Antonino M. "An experimental driving mechanism for a rigid oscillating foil propeller." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ62374.pdf.
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2
Мачача, Олександр Віталійович. "Розроблення та дослідження механізму третього класу основов’язальної машини". Магістерська робота, Київський національний університет технологій та дизайну, 2021. https://er.knutd.edu.ua/handle/123456789/19444.
Повний текст джерелаАнотація:
Робота присвячена аналізу та розробці механізму третього класу основов’язальної машини. Поставлені задачі аналізу механізму полягали в дослідженні призначення та галузі використання основов’язальної машини ОВ-7; дослідженні конструкції механізмів основов’язальної машини ОВ-7; кінематичному дослідженні механізму коливального руху вушкових голок основов’язальної машини ОВ-7. Поставлені задачі розробки механізму коливального руху вушкових голок основов’язальної машини полягали у геометричному синтезі механізму коливального руху вушкових голок основов’язальної машини нової конструкції, кінематичному дослідженні механізму коливального руху вушкових голок нової конструкції та силовому аналізу механізму коливального руху вушкових голок.The work is devoted to the analysis and development of the mechanism of the third class of the basic knitting machine. The tasks of the mechanism analysis were to study the purpose and field of use of the basic knitting machine OV-7; study of the design of the mechanisms of the basic knitting machine OV-7; kinematic study of the mechanism of oscillating motion of the eyelets of the basic knitting machine OV-7. The tasks of developing the mechanism of oscillating movement of the eyelets of the warp knitting machine were geometric synthesis of the mechanism of oscillating motion of the eyelets of the warp knitting machine of new design, kinematic study of the mechanism of oscillating motion of the eyelets of the new design and force analysis of the mechanism of oscillating motion of eyelets.
3
Jurisch, Martin. "On the mechanics of oscillating flames." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/61385.
Повний текст джерелаАнотація:
The major drive to advance the understanding of flames comes from industry as many technical devices propelled by flames are in constant need of design revisions and efficiency improvements. Lean-premixed combustion technology was one of such areas, which saw major advancements. Unfortunately, combustion devices operating in premixed mode often exhibit undesired flame oscillations, which may lead to damage or even failure of the combustor. The present work is dedicated to better understanding and predicting flame oscillation. A modelling framework based on high-order accurate Discontinuous Galerkin methods is presented to investigate the interaction of steadily propagating flames with pressure waves. The analysis of the results show that the time scale associated with the pressure wave incident upon the flame must be of the same order as the time scales in the primary reaction zone to lead to partial wave reflection and wave transmission at the flame. Hence providing a mechanism for initiating flame oscillation. The predictive capabilities of the Large Eddy Simulation technique in conjunction with the Probability Density Function model of the unresolved turbulence-chemistry interaction are demonstrated in the simulation of flame oscillation in industrially relevant combustors. Two test cases with increasing complexity are considered: a forced oscillating flame in a bluff-body stabilised combustor, and a self-excited flame oscillation in a swirl combustor with complex geometry. Good agreement between the measurements and the simulations is obtained. The flame dynamics are well captured by both simulations. The results obtained in the study of the bluff-body flame are used to identify suitable chemical markers which correlate well with the total heat release rate. The product of molecular oxygen and the ketenyl radical is found to correlate better with the total heat release rate than the commonly used formaldehyde-based markers in the investigated premixed fuel-lean ethylene-air flame. In the case of the swirl burner the predictions lead to the suggestion of a self-excited flame oscillation in the lateral direction as the result of an interaction of the flame with a vortex ring. The difference between the predicted and experimentally determined frequency of oscillation is 11 %.
4
Faiman, Jiří. "Tříválcový zážehový motor s excentrickým klikovým mechanismem pro osobní vozidla." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-231763.
Повний текст джерелаАнотація:
The first part of this thesis deals with the examination of the eccentricity of the crank mechanism for individual variables kinematics and dynamics of crank mechanism, analyticaly computed in Matlab. Then it compares the different possibilities of balancing moments of inertia forces and propose a specific design chosen for the value of eccentricity. In the second part is designed a model of crankshaft mechanism based on the investigated parameters. These parameters were carried out by structural analysis in Ansys.
5
Bradshaw, Joel. "Mathematical modelling of droplets climbing an oscillating plane." Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/33768/.
Повний текст джерелаАнотація:
Recent experiments [P. Brunet, J. Eggers, and R. Deegan, Phys. Rev. Lett. 99, 114501 (2007)] have shown that a liquid droplet on an inclined plane can be made to move uphill by sufficiently strong, vertical oscillations. In order to investigate this counterintuitive phenomenon we will derive three different models that qualitatively reproduce the main features of the experiment. For the first model the liquid's inertia and viscosity are assumed negligible, so that the motion of the droplet is dominated by the applied acceleration due to the oscillation of the plate, gravity and surface tension and that the droplet is thin. We explain how the leading order motion of the droplet can be separated into a spreading mode and a swaying mode. For a linear contact line law, the maximum rise velocity occurs when the frequencies of oscillation of the two modes are in phase. We show that, both with and without contact angle hysteresis, the droplet can climb uphill and also that, for certain contact line laws, the motion of the droplet can produce footprints similar to experimental results. We show that if the two modes are out of phase when there is no contact angle hysteresis, the inclusion of hysteresis can force them into phase. This in turn increases the rise velocity of the droplet and can, in some cases, cause a sliding droplet to climb. For the second model we use a two-dimensional flow where the Reynolds number is assumed large enough for viscosity to be neglected. We show that the leading order motion of the droplet can be separated into the same two modes and the net motion of the droplet is an oscillatory function of the frequency. For increasingly non-wetting droplets we discover that the rise velocity begins to oscillate very rapidly as a function of the static contact angle. What we also discover is that the change in the free surface of the droplet is actually a wave travelling travelling across the droplet, and the amount of modes present coincide with the rapid change in the rise velocity. Using a cubic contact line law and contact angle hysteresis we observe a droplet that can climb uphill for parameter values similar to that of the experiment. With the addition of a time dependent term within the contact line law we show that it is possible to obtain a multi-valued relationship between the velocity of the contact line and the respective contact angles, reproducing experimental observations seen for unsteady, moving contact lines. For the third model we again assume that the liquid's viscosity is negligible, similar to model 2, only now for a three-dimensional, thin droplet. For very small amplitudes the motion of the droplet is a combination of a swaying mode and a spreading mode that interact causing a net motion of the droplet. This motion is found to be an oscillatory function of the driving frequency and the magnitude of the peak rise velocity is proportional to one over the frequency squared. By examining the velocity of the centre of the droplet and the displacement of the contact line we see that the absolute maximums of both of these, over one period of oscillation, contain natural frequencies, which are evenly spaced with respect to the square root of the frequency of the oscillation.
6
Sekerli, Murat. "Mechanisms of oscillations in coupled neuromechanical systems." Thesis, Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/13421.
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7
Houara, Komba Eymard. "Reconstitution of tribological accommodation mechanisms for greased high loaded oscillating bearings." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEI018.
Повний текст джерелаАнотація:
Les roulements soumis à des mouvements oscillatoires et des charges élevées sont nécessaires pour le fonctionnement de nombreux mécanismes industriels (actionneurs, commandes d’avions, machines pour l’usinage, robots, chaînes d’assemblages, …). Ces roulements sont soumis à des pressions de contact locales extrêmement élevées avec des vitesses de roulement faibles qui ne permettent pas une lubrification adéquate des interfaces des premiers corps avec de l’huile. Les essais d’endurance sur les roulements ont permis la reconstitution des courbes de dégradation pendant la vie du roulement. Des analyses des surfaces, effectués à chaque phase de la vie du roulement ont permis aussi bien de suivre l’évolution de la topographie à l’interface entre les pistes et les éléments roulants. D’autre parte, des analyses numériques par éléments finis ont permis d’obtenir des informations sur les distributions des contraintes et des déformations. Le croisement des résultats expérimentaux et numériques a donc permis la reconstruction des mécanismes locaux d’accommodation. Dans le cas d’un roulement oscillant non graissé, les déplacements relatifs et les contraintes sont principalement accommodés aux interfaces des premiers corps en contact, ce qui accélère l’endommagement final du roulement. Dans le cas d’un roulement oscillant graissé, une partie des déplacements relatifs et contraintes est accommodée dans une sous couche qui se forme dans la peau des éléments roulants. Cette accommodation se manifeste par l’accumulation de déformations plastiques qui s’avèrent être aussi à l’origine de l’endommagement final du roulement. L’analyse des surfaces de contact des roulements oscillants graissés montre qu’il se forme, en présence de la graisse et très tôt dans la vie du roulement, une couche (troisième corps graisse/particule et TTS en surface de la piste) qui protège les surfaces en contact. D’autre part, une expertise de roulement ayant fonctionné sur un avion de de type A340 révèle une forte similarité entre ses faciès d’usure et ceux obtenus lors des essais d’endurance, et valide ainsi les mécanismes d’accommodation reconstitués. Enfin, des questions portant sur les effets de la quantité de graisse, du glissement des éléments roulants, et des pauses sur un essai donné sont aussi traitéesBearings subjected to oscillatory motions and high loads are necessary for the operation of several industrial mechanisms (actuators, aircraft controls, machining, robots, assembly lines, ...). These bearings are subjected to extremely high local contact pressures with low running speeds, which do not permit adequate lubrication of the interfaces of the first bodies with oil. Endurance tests perfomed on commercial bearings allowed at reconstructing the evolution of the degradation curves during the bearing life. Surface analyses carried out at each phase of the bearing life also allowed at following the evolution of the topography at the interface between the bearing raceways and the rolling elements. On the other hand, numerical analyses, by finite element method, have led to obtain information on the distributions of stresses and deformations. The dialogue between experimental and numerical results allowed the reconstruction of the local accomodation mechanisms. In the case of ungreased oscillating bearings, the relative displacements are mainly accommodated at the surfaces of the first bodies in contact, which accelerates the damage of the bearing. In the case of greased oscillating bearings, part of the relative displacements and stresses are accommodated at the subsurface of the rolling elements. This accommodation mechanism is manifested by the accumulation of plastic deformations which are at the origin of the final degradation of the bearing. The analysis of the contact surfaces of the raceways of the greased oscillating bearings shows as well that, in the presence of grease, a layer (third body mixture of grease and particles, and TTS on the track surface) protects the surfaces of the raceway and thus accommodates the other part of the displacements and stresses. On the other hand, the analysis of an airelon bearing, dismounted from an A340 type aircraft, revealed a strong similarity between its topographies and those obtained during the performed endurance tests, validateing the reconstructed accommodation mechanisms. Finally, questions about the effects of the amount of grease, sliding of the rolling elements, and pauses on a given test heve been discussed too
8
McCorquodale, Mark W. "Interaction between oscillating-grid turbulence and a solid impermeable boundary." Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/49971/.
Повний текст джерелаАнотація:
The interaction of a boundary with turbulence is a defining feature of many turbulent flows, resulting in a turbulent boundary layer which plays a prominent role in the production and dissipation of turbulence. Commonly, this interaction is dominated by the effects of mean shear. However, more subtle aspects of the interaction, such as effects associated with turbulent motions impinging onto the boundary, are still thought to play a key role in giving rise to the boundary layer structure. Unfortunately, these aspects of the interaction are currently poorly understood. A better understanding of these aspects of the interaction may be derived by isolating them from the effects of mean shear through the study of zero-mean-shear turbulence interacting with a boundary. This study reports experimental work investigating the interaction between oscillating-grid turbulence (OGT) and a solid impermeable boundary. OGT is a commonly used experimental tool that produces a turbulent flow which is approximately homogeneous and isotropic in planes parallel to the oscillating grid but which is inhomogeneous in planes perpendicular to the oscillating grid. Throughout this study, instantaneous velocity measurements of the flow are obtained by applying two-dimensional particle imaging velocimetry to the vertical plane through the centre of the oscillating grid. A detailed preliminary study to characterise the flow generated by the OGT apparatus is initially performed. Visualisation of the flow close to the oscillating grid indicates that large-scale circulations are induced in OGT by the merging of grid-induced jets close to the tank walls. The installation of an open-ended cuboidal `inner box' below the grid is shown to inhibit the merging of these jets, thereby resulting in a more regular jet structure close to the oscillating grid and a corresponding reduction in mean flow within the inner box. It is also found that, contrary to assumptions in the literature, this amendment to the standard OGT apparatus is most effective when the top of the inner box is located close to the oscillating grid. The reduction in mean flow intensity that results from the use of a correctly installed inner box brings about a turbulent flow in which the mean flow velocity components are small compared to velocity fluctuations, thereby enabling a meaningful comparison to be made with zero-mean-shear turbulence. Consequently, the interaction between OGT and a solid impermeable boundary is studied to derive insight into the mechanisms governing the interaction of zero-mean-shear turbulence with boundaries. Results indicate that a critical aspect of the interaction is the blocking of a boundary-normal flux of turbulent kinetic energy across the boundary-affected region, which acts to increase the magnitude of the boundary-tangential turbulent velocity components, relative to the far-field trend, but not the boundary-normal turbulent velocity component. This feature arises as a result of the anisotropic nature of the flow produced by OGT, whereby the turbulent fluctuations decay with distance normal to and away from the oscillating grid, and would not be present in a turbulent flow that was otherwise homogeneous above the boundary-affected region of the flow. This observation provides new insight into the validity of well-established models of the interaction of zero-mean-shear turbulence and a solid impermeable boundary and provides a physical mechanism that explains the disparity in previously reported measurements relating to this problem. The results reported are also in support of intercomponent energy transfer mechanisms previously proposed to govern the interaction of zero-mean-shear turbulence with boundaries, including viscous and `return-to-isotropy' mechanisms. That is, within a thin region adjacent to the boundary, approximately equal in thickness to the viscous sublayer, the data indicate that turbulent motions incident towards the boundary are more energetic than motions away, which are characteristics of an intercomponent energy transfer primarily driven by the viscous dissipation of turbulent kinetic energy. In addition, at the edge of the boundary-affected region, where the magnitude of the boundary-tangential turbulent velocity components exceeds the magnitude of the boundary-normal turbulent velocity component, results indicate that an intercomponent energy transfer occurs from the boundary-tangential turbulent velocity components to the boundary-normal turbulent velocity component in a so-called `return-to-isotropy' energy transfer. However, the data also indicate the presence of an additional intercomponent energy transfer, from the boundary-normal turbulent velocity component to the boundary-tangential turbulent velocity components over a thin region outside the viscous sublayer. Comparison to previously published results of related studies indicates that this mechanism is also prevalent in previous work, but is not captured within existing models of intercomponent energy transfer at the boundary. Results further indicate that the intercomponent energy transfer mechanisms are not independent of the blocking of the boundary-normal turbulent kinetic energy flux. That is, the blocking of the boundary-normal turbulent kinetic flux promotes anisotropy within the boundary-affected region of the flow and thereby induces a stronger `return-to-isotropy' energy transfer mechanism. Hence, the effect of a solid impermeable boundary on turbulent velocity components in zero-mean-shear turbulence depends critically on the nature of the original turbulent field (i.e. homogeneous or inhomogeneous turbulence).
9
Haslam, Michael C. "Mechanics of oscillating flow in tubes of elliptic cross-section." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/mq21043.pdf.
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Jia, XiaoJing 1977. "The mechanisms and the predictability of the Arctic oscillation and the North Atlantic oscillation /." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=103026.
Повний текст джерелаАнотація:
The Arctic Oscillation (AO) and the North Atlantic Oscillation (NAO) are the most pronounced modes of extratropical atmospheric wintertime variability in the Northern Hemisphere. This thesis investigates different aspects of the AO and NAO on the in traseasonal and seasonal time scales. First, the question of how the differences between the AO and NAO are influenced by the choice of the definitions of the NAO and to what extent the AO and NAO differ from each other is investigated using the daily NCEP/NCAR reanalysis data spanning 51 boreal winters. One AO index and four different NAO indices are used in this study. It is found that the AO and NAO are quite similar to each other when both are defined using pattern-based indices, while some notable differences are observed between them when the NAO is defined using a station/gridpoint-based index. Then the predictability of the AO and NAO is examined using a simple general circulation model (SGCM). Numerical experiments are performed to determine the sensitivity of the setup processes of the AO and NAO to the details of the initial conditions. The predictive skills for the AO and NAO are compared to each other. Finally, the potential role of tropical Pacific forcing in driving the seasonal variability of the AO is explored using both observations and the SGCM. The results indicate that a negative thermal forcing over the western tropical Pacific and a positive forcing north of the equatorial mid-Pacific play important roles in producing an AO-like atmospheric response.
11
Antonoudiou, Pantelis. "Cellular mechanisms and function of hippocampal gamma oscillations." Thesis, University of Oxford, 2018. http://ora.ox.ac.uk/objects/uuid:6ee54975-9e8e-46fd-8cbf-8ed16fb207c1.
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12
Drayton, Michael James. "Eulerian and Lagrangian studies of inhomogeneous turbulence generated by an oscillating grid." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318099.
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13
Stinson, Margaret Beverley. "An investigation into turbulence and the onset of separation in oscillating flow." Thesis, Queen's University Belfast, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296821.
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14
Lu, Chengbiao. "Cellular mechanism of age-dependent decline in hippocampal gamma oscillations." Thesis, University of Birmingham, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.532300.
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15
Aldridge, Christopher John. "Density-wave oscillations in two-phase flows." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260741.
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16
Amin, Norsarahaida. "Oscillation-induced mean flows and heat transfer." Thesis, University of East Anglia, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329339.
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Elwell, Lance Christopher. "Dynamics of stationary and obliquely oscillating free plane jets." Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/17371.
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18
Skrobot, Olivia Anna. "Mechanisms underlying spontaneous oscillations in the hippocampus in vitro." Thesis, University of Newcastle Upon Tyne, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.489300.
Повний текст джерелаАнотація:
In vivo oscillations, reflecting the coordinated activity ofneuronal ensembles, are observed spontaneously and through stimulus-driven experimentation, and have been suggested to be important for cognitive functions. This thesis has revealed the preservation of the hippocampus in the in vitro slice has sufficient endogenous drive and/or neuromodulatory substance release, to generate persistent spontaneous gamma-theta oscillations without the need for any external manipulations. In addition, hippocampal areas CAl and CA3 have the intrinsic capabilities to generate spontaneous oscillations without any external input. Spontaneous oscillations in area CA3 are inhibition-based rhythms. The time-dependent expressions of these rhythms were dependent upon NMDARs, with gamma frequency oscillation also reliant upon KAR, mGluR and AchRs. The stability ofestablished spontaneous beta and gamma frequency oscillations was reliant upon KAR, and mAchRs excitatory drives, holding some similarities to previous druginduced models. However, these spontaneous. oscillations required different excitatory transmitter systems in conjunction, suggesting they are unique in vitro hippocampal rhythms. Spontaneous theta oscillations also appeared to constitute a novel model of atropine-resistant theta rhythms, proposed to be generated via lacunosum-moleculare interneurons. A novel fmding showed the dependence of spontaneous oscillations on GlyR-mediated inhibition. In addition, this thesis discovered high concentrations of MK-801, SKF-1O,047 and PCP can induce gamma frequency oscillations in area CA3 de novo. MK-801-induced rhythmogenesis relied upon functional sigma-l receptors, but not functional NMDARs. The stability of the oscillations depended upon KAR excitatory and GABAAR inhibitory synaptic transmission, therefore exhibiting some similarities to the established spontaneous gamma frequency rhythms. In contrast, MK-801-induced gamma frequency rhythms were potentiated by mGluRI a antagonism and resistant to GlyR blockade, suggesting that, though similar, the mechanisms responsible for gamma rhythmogenesis with sigma receptor activation may be fundamentally different from those required to generate spontaneous rhythms in drug-free conditions.
19
Elgmati, Khalil. "Mechanisms of calcium oscillations in mouse and human eggs." Thesis, Cardiff University, 2013. http://orca.cf.ac.uk/50384/.
Повний текст джерелаАнотація:
Long lasting calcium (Ca2+) oscillations are necessary and sufficient for mammalian egg activation and early embryological development. In mammals, phospholipase C zeta (PLCζ) has been identified as the likely endogenous trigger of Ca2+ oscillations at fertilization. Some cases of male factor infertility have been associated with the absence / reduced or presence a mutant form of PLCζ. In these cases sperm fails to activate eggs after intra-cytoplasmic sperm injection (ICSI). Artificial egg activation is the potential way to trigger Ca2+ oscillations and egg activation. Strontium (Sr2+) is the main artificial agent for this purpose in rodent eggs. The work in this Thesis aims to examine the mechanism of PLCζ or Sr2+ ions to trigger Ca2+ oscillations in mammalian eggs. It was not clear how Sr2+ causes Ca2+ oscillations and why it is only effective in rodents but not human eggs or domestic animals. My studies show that Sr2+ is effective in causing Ca2+ oscillations in mouse eggs over a range of concentrations, but that its actions are influenced by the osmolarity of the medium. Low osmolarity enhances the ability of low concentrations of Sr2+ to cause Ca2+ oscillations. Further investigation revealed that Sr2+ influx is mainly through the reverse mode of the Na+/Ca2+ exchange protein (NCX) which can be controlled by the membrane potential and Na+ gradient across the plasma membrane. Preliminary studies investigated the ability of a modified Sr2+ media that maximizes reverse mode NCX to trigger Ca2+ changes in human eggs. In other studies, various PLCζ-luciferase cRNAs were injected into mouse and human eggs. PLCζ expression in mouse eggs was measured by imaging light due to luciferase iv activity, and Ca2+-oscillations were monitored with Ca2+ sensitive fluorescent dye. Aspects of the structure of PLCζ and the effects and the recent discovery of PLCζ sequence mutations were investigated. Preliminary studies were also carried out to test the ability of recombinant PLCζ protein to cause Ca2+ oscillations in mammalian eggs. It is hoped that these studies might open up new therapies for some male factor infertility couples that acconts 1-5% of failed ICSI.
20
Atobe, Yuta. "Mechanism of circadian oscillation of the mammalian core clock gene Per2." 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/199495.
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21
Tucher, Christopher A. "Steady-state oscillations of linear and nonlinear systems /." Online version of thesis, 1992. http://hdl.handle.net/1850/10990.
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22
Drbohlav, Hae-Kyung Lee. "Mechanism of the intraseasonal oscillation in the South Asian summer monsoon region." Thesis, University of Hawaii at Manoa, 2002. http://proquest.umi.com/pqdweb?index=0&did=765064431&SrchMode=1&sid=1&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1209149181&clientId=23440.
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Wallis, George J. "Selection mechanisms for working memory." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:1a9be8d6-9f8e-49af-8185-8be4c890010f.
Повний текст джерелаАнотація:
The experiments in this thesis investigated the mechanisms controlling input and output gating of working memory. In chapter 3, accuracy and reaction time data from a precision/capacity working memory task with prospective and retrospective cues were analysed. The results suggest that retrocues boost performance by facilitating output gating from working memory. In chapter 4, the role of perceptual cortex in mediating the cue benefits in this task was investigated with magnetoencephalography (MEG). The pattern of alpha (8-12Hz) power in visual cortex was modulated by cue direction following both precues and retrocues, but whilst this modulation was sustained following a precue (until presentation of the memory array) it was transient following a retrocue, suggesting that a memory representation was briefly retrieved or refreshed, but that there was not a sustained biasing of top-down input to visual cortex following retrocues. This argues against the standard model of working memory as sustained attention to internal representations, and in favour of a more dynamic view in which perceptual cortex is recruited transiently, and otherwise freed up for on-going processing. In chapter 5, the role of frontal networks in precueing and retrocueing was investigated. An fMRI meta-analysis identified control networks involved in preparatory and mnemonic selection: whilst the fronto-parietal network is recruited in both cases, the cingulo-opercular network is recruited only by retrocues. This spatial pattern was replicated with a source-space ROI analysis of MEG induced-responses. These data also characterised the time-course of control network activation shedding light on their functional roles. The fronto-parietal network was activated immediately following both precues and retrocues, consistent with a direct role in top-down influence over perceptual cortex. By contrast, the cingulo-opercular network was activated following retrocues only after the perceptual refreshing event was complete, suggesting a downstream role, perhaps in selecting representations to guide action. Chapter 6 investigated the role of reward associations in controlling access to working memory, testing behavioural predictions of two theories implicating the dopamine system and basal ganglia in control of working memory. The results supported a temporal gating account in which encountering reward associated items triggers a brief (<300ms) window in which there is a boost of encoding for WM. Chapter 7 discusses the implications of the current work and suggests some future directions.
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Strømsvåg, Dag. "Fundamental mechanisms of density wave oscillations and the effect of subcooling." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-12583.
Повний текст джерелаАнотація:
Boiling two-phase flow is found in many industrial applications such as boiling water reactors, two-phase flow heat exchangers and refrigeration systems. The physics of two-phase gas-liquid flow may lead to undesirable system instabilities, and in the literature density wave oscillations (DWO) is reported to be the most commonly observed instability phenomenon. However, the literature alsoprovides two opposing views on what the fundamental mechanism of DWO is. The so-called classical description of DWO focuses on the variation in mixture density as the governing mechanism, and the oscillation period will consequently be about one to two times the channel residence time. The findings presented in citet{Rizwan-Uddin1994} show that it is the variation in mixture velocity that hasthe dominating effect, and the oscillation period was reported to be closer to four times the channel residence time. citet{Ambrosini2000} united the two opposing views by stating that the governing mechanismdepends on the level of system subcooling. The classical description of DWO is based on a lower level of subcooling, while citet{Rizwan-Uddin1994} considered higher subcooling. Here, the fundamental mechanisms of DWO and the effect of system subcooling is investigated further by performing a numerical analysis using a one dimensional homogenous equilibrium flow model. The modeled system consists of a horizontal uniformlyheated boiling channel with an inlet- and exit restriction. The system is exposed to constant externally imposed pressure drop. The effect of system subcooling is investigated by comparing the self-sustained periodicoscillations which make out the modeled stability threshold. The flow model is validated by observing the above mentioned effects of subcooling on DWO. Further, it is found that the change from a density dominated exit restriction towards a velocity dominated exit restriction is a smooth transition for increased subcooling. The amplitude of the variations in exit mixture velocity increases continuously with subcooling, anddue to the squared relationship between the exit restriction pressure drop and the exit mixture velocity, velocity becomes the governing mechanism at high subcooling.The modeled stability threshold approaches a straight line at high subcooling. This line represents operating conditions which have the same mean boiling boundary location. However, the amplitude of the variations about this mean limit grows exponentially at high subcooling. The oscillation period of the observed DWO grows continuously with higher subcooling, and the period increases exponentially at high subcooling. In contrast, the mean boiling channel residence time approaches an upper mean limit at high subcooling. It is postulated that it is the transition towards a more mixture velocity dominated system that causes the oscillation period to evolve as it does with respect to the level of subcooling.
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AbuHassan, Kamal. "Modelling synaptic loss, compensation mechanisms and neural oscillations in Alzheimer's Disease." Thesis, Ulster University, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.591044.
Повний текст джерелаАнотація:
Alzheimer’s disease (AD) is a devastating brain disease that leads to a gradual loss of mental functions. The level of mental activity decline in AD is best correlated with the degree of synaptic loss. The latter is secondary to aggregations of two harmful proteins: neurofibrillary tangles (NFT) and beta-amyloid (Aβ) peptide. Such factors impair inter-neuronal communication thereby weakening the electrical activity of the brain. Non-invasive recording of the electrical activity along the brain scalp, known as Electroencephalography (EEG), reveals an overall power content shift towards the lower bands of the frequency domain in AD. Computational modelling studies have investigated biomarkers of EEG abnormalities in AD with the aim of a better understanding of altered neural processes in AD. The findings of these studies suggested that connectivity loss in the thalamocortical system, impaired production of the acetylcholine (ACh) neurotransmitter and deregulation of neuronal ionic channels are possible biomarkers of abnormal EEG activity in AD. This thesis presents a detailed investigation into the neural causes underpinning abnormal oscillatory activity in AD. The effects of excitatory neuronal death on beta band power (13-30 Hz) are assessed using a conductance-based network model of 200 neurons. Neurobiological studies have shown that cortical neuronal death is mediated by dysfunctional ionic behaviour. This work investigates the influence of deregulated negative feedback to the membrane potential of cortical neurons on the oscillatory activity of a cortical network model of 1000 neurons. Furthermore, a large-scale neuronal model with important characteristics is developed for the purpose of studying the interplay between various synaptic degeneration and compensation mechanisms. and abnormal oscillatory activity in AD. Finally, the influence of compensation mechanisms on the lesioned thalamocortical network is investigated with an improved neuronal model. The ultimate goal of the thesis is to provide insights for drug design in AD therapy and to contribute to the prevention measures of AD.
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Merrison-Hort, Robert. "Computational study of the mechanisms underlying oscillation in neuronal locomotor circuits." Thesis, University of Plymouth, 2014. http://hdl.handle.net/10026.1/3107.
Повний текст джерелаАнотація:
In this thesis we model two very different movement-related neuronal circuits, both of which produce oscillatory patterns of activity. In one case we study oscillatory activity in the basal ganglia under both normal and Parkinsonian conditions. First, we used a detailed Hodgkin-Huxley type spiking model to investigate the activity patterns that arise when oscillatory cortical input is transmitted to the globus pallidus via the subthalamic nucleus. Our model reproduced a result from rodent studies which shows that two anti-phase oscillatory groups of pallidal neurons appear under Parkinsonian conditions. Secondly, we used a population model of the basal ganglia to study whether oscillations could be locally generated. The basal ganglia are thought to be organised into multiple parallel channels. In our model, isolated channels could not generate oscillations, but if the lateral inhibition between channels is sufficiently strong then the network can act as a rhythm-generating ``pacemaker'' circuit. This was particularly true when we used a set of connection strength parameters that represent the basal ganglia under Parkinsonian conditions. Since many things are not known about the anatomy and electrophysiology of the basal ganglia, we also studied oscillatory activity in another, much simpler, movement-related neuronal system: the spinal cord of the Xenopus tadpole. We built a computational model of the spinal cord containing approximately 1,500 biologically realistic Hodgkin-Huxley neurons, with synaptic connectivity derived from a computational model of axon growth. The model produced physiological swimming behaviour and was used to investigate which aspects of axon growth and neuron dynamics are behaviourally important. We found that the oscillatory attractor associated with swimming was remarkably stable, which suggests that, surprisingly, many features of axonal growth and synapse formation are not necessary for swimming to emerge. We also studied how the same spinal cord network can generate a different oscillatory pattern in which neurons on both sides of the body fire synchronously. Our results here suggest that under normal conditions the synchronous state is unstable or weakly stable, but that even small increases in spike transmission delays act to stabilise it. Finally, we found that although the basal ganglia and the tadpole spinal cord are very different systems, the underlying mechanism by which they can produce oscillations may be remarkably similar. Insights from the tadpole model allow us to predict how the basal ganglia model may be capable of producing multiple patterns of oscillatory activity.
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Sanders, Jessica Rose. "Mechanisms of PLCζ induced Ca²⁺ oscillations in mouse eggs at fertilisation". Thesis, Cardiff University, 2017. http://orca.cf.ac.uk/103822/.
Повний текст джерелаАнотація:
All the events of egg activation in mammalian eggs are triggered physiologically by transient increases in cytosolic free Ca²⁺ referred to as Ca²⁺ioscillations. These oscillations are initiated by the sperm derived PLC isoform, PLCζ. PLCζ releases Ca²⁺ by hydrolysing its substrate PI(4,5)P₂ to produce IP₃, however, many of the mechanisms by which PLCζ elicits Ca²⁺release in eggs are poorly understood. The results of this thesis confirm that whilstPLCζ cRNA and recombinant protein is able to cause Ca²⁺ioscillations in mouse eggs the sperm derived protein PAWP does not cause any Ca²⁺ release in any circumstances. It is shown that EF hand domain and XY linker of PLCζ are important in determining its Ca²⁺i releasing ability by enabling PLCζ binding to its substrate PI(4,5)P₂ through electrostatic interactions. The C2 domain of PLCζ was also found to play a crucial role in the Ca²⁺ releasing ability of PLCζ, possibly by binding to lipids or proteins in the target membrane. The Ca²⁺releasing ability of eggs is acquired during oocyte maturation and a dramatic increase in PLCζ sensitivity of oocytes occurs after germinal vesicle breakdown. A variety of markers for PLCζ’s substrate PI(4,5)P₂ including fluorescent PI(4,5)P₂ and gelsolin based fluorescent probes suggests that this PI(4,5)P₂ is localised to intracellular vesicles that could derive from Golgi apparatus. Attempts are made to measure PI turnover in these intracellular compartments of eggs during PLCζ induced Ca²⁺i oscillations using several probes. The results of this thesis suggest that PLCζ releases Ca²⁺ by a novel IP₃ based signalling pathway that involves an intracellular source of PI(4,5)P₂.
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Goshawk, Jeffrey Alan. "Enhancement of the drainage of non-Newtonian liquid films by oscillation." Thesis, University of Liverpool, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333685.
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Qin, Xiang. "Controlling mechanism of basal myosin oscillation in epithelial cells during Drosophila tissue elongation." Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30006.
Повний текст джерелаАнотація:
La morphogenèse des tissus dans les organismes multicellulaires est très importante pour le développement et certaines pathologies. La morphogenèse tissulaire est dirigée par des forces bio-mécaniques générées par des moteurs moléculaires tels que la myosine et transmis via le cytosquelette et les structures d'adhésion à l'intérieur et entre les cellules. La contractilité de la myosine, souvent en mode oscillatoire, a été étudiée principalement au niveau du domaine apical des cellules épithéliales au cours du développement mais très peu au niveau de leur domaine basal. L'oscillation de la myosine basale est importante pour le contrôle de l'élongation du tissu durant l'oogenèse chez la Drosophile. Bien que la voie Rho1-ROCK-myosin-MBS soit connue pour contrôler l'activité de la myosine, le mécanisme précis de ce contrôle n'a pas été élucidé. Le but de mon projet de thèse est de répondre à deux questions : Quels sont les facteurs en amont de cette voie ? Comment cette voie de signalisation crée et maintient l'oscillation de la myosine ? 1) Contrairement à ce qui est déjà connu, Je me suis intéressé à l'effet des adhésions cellule-cellule et cellule-matrice dans le contrôle des voies de signalisation gouvernant l'oscillation de la myosine basale. Les adhésions cellule-matrice, mais pas les adhésions cellule-cellule, sont positivement corrélées avec l'intensité et la polarité dorso-ventrale de la myosine, indiquant que les adhésions cellule-matrice pourraient être les facteurs en amont de la voie Rho1-myosine. Les adhésions cellule-matrice régulent positivement l'activité de Rho1 près des jonctions et gouvernent les flux de ROCK et myosine à l'intérieur du domaine median, contrôlant ainsi l'élongation du tissu. D'une autre manière, les adhésions cellule-cellule affectent indirectement les flux de ROCK and myosine en contrôlant la distribution subcellulaire de ROCK et du réseau d'actomyosine. L'inhibition des adhésions cellule-cellule, qui a un effet mineur sur l'élongation du tissu, provoque la redistribution des adhésions cellule-matrice et des filaments F-actin entrainant le chargement de la myosine à différentes positions. 2) J'ai montré que l'oscillation de la myosine basale dépend peu de la tension corticale de l'actomyosine : l'inhibition du chargement de la myosine sur les filaments d'actine n'affecte pas le flux de myosine alors qu'il bloque fortement le cycle périodique des contractions/relaxations de la cellule indiquant que l'oscillation est principalement due à une réaction biochimique plutôt qu'à une tension corticale. Au cours de l'oscillation de la myosine, les protéines Rho1 et leur activité sont principalement distribuées et enrichies au niveau et près des jonctions basales, et le contrôle majeur de cette oscillation est le flux des signaux ROCK qui diffusent des jonctions basales au cortex medio-basal. Ce mouvement de ROCK est initié grâce à une interaction transitoire entre ROCK et Rho1 actif au niveau et près des jonctions basales, conduisant ainsi à l'ouverture et activation de la kinase ROCK. Au cours de ce mouvement, l'activation de ROCK permet l'accumulation et l'amplification des signaux ROCK; Cette amplification entraîne la phosphorylation de la myosine, qui ensuite génère la redistribution dynamique de la phosphatase MBS. Enfin, l'enrichissement des signaux MBS arrête les signaux ROCK et myosine. Dans ces deux études, nous avons construit un outil optogénétique confirmant les différentes étapes de l'oscillation de la myosine basale. L'ensemble de ces résultats démontrent que le mécanisme contrôlant l'oscillation de la myosine basale nécessite une réaction biochimique, et met en évidence deux contrôles diffèrent de cette oscillation par les adhésions cellule-cellule et les adhésions cellule-matriceTissue morphogenesis in multicellular organisms is very important in both development and human disease. Tissue morphogenesis is driven by bio-mechanic force that is normally generated by molecular motors such as myosin and transmitted via cytoskeleton and adhesion structures within and between cells. Myosin contractility, often as an oscillatory pattern, has been studied mainly in apical but less in basal domains of epithelial cells during development. Basal myosin oscillation is important in control of tissue elongation during Drosophila oogenesis. Although a signal cascade (Rho1-ROCK-myosin-MBS) has been known to regulate myosin activity, the detailed controlling mechanism is unclear. My project is aimed to address two questions: first, what is the upstream factor of this signal cascade? Second, how does this signal cascade create and maintain basal myosin oscillation? For this first question, I am interested in the effect of cell-cell and cell-matrix adhesion in control of this signal cascade governing basal myosin oscillation. Cell-matrix adhesion (Integrin and Talin), but not cell-cell adhesion (E-cadherin), is positively correlated with the intensity and Dorsal-ventral (DV) axis polarity of basal myosin oscillation, indicating that cell-matrix adhesion might be the upstream control of Rho1-myosin signal cascade. Cell-matrix adhesion positively regulates the Rho1 activity near junction and governs the pulsed ROCK and myosin signals within basal-medial domain, thus strongly controlling tissue elongation. Differently, cell-cell adhesion indirectly affects the ROCK and myosin pulses through controlling the subcellular distribution of ROCK and actomyosin network. Inhibition of cell-cell adhesion results in the redistribution of cell-matrix adhesion and F-actin filaments leading to different position of myosin loading, which plays minor effect on tissue elongation. For the second question, I unraveled that basal myosin oscillation is barely dependent on actomyosin cortical tension: inhibition of myosin loading to F-actin filament seems not to affect basal pulsatile myosin flows, while it strongly blocks the periodic cycle of cell contraction and relaxation at basal surface, thus indicating that oscillation is mainly from biochemical reaction rather than cortical tension. This observation highlighted that biochemical reaction is the main control of oscillation occurrence. During basal myosin oscillation, Rho1 proteins and Rho1 activity are mainly distributed and enriched at and near basal junction and the major control of basal myosin oscillation is the flow movement of oscillatory ROCK signals from basal junction to medio-basal cortex. This ROCK flow movement is initiated from the transient interaction of ROCK with active Rho1 at and near basal junction, thus leading to the opening and activation of ROCK kinase capability. During the membrane-medial flow movement, ROCK kinase activity mediates the accumulation and thus the amplification of ROCK signals; this positive signal amplification turns on the phosphorylation of myosin regulatory light chain (MRLC), which governs the dynamic redistribution of MBS. Finally, enriched MBS signals shut off both ROCK and myosin signals. In both study, an optogenetic tool named as LARIAT was built up in vivo to confirm the various status of basal myosin oscillation. Altogether, these results demonstrated two different controls of basal actomyosin signals by cell-matrix adhesion and cell-cell adhesion, and further demonstrated the underlying mechanism of basal myosin oscillation at the biochemical levels
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Liu, Chih-Hsing. "A finite element based dynamic modeling method for design analysis of flexible multibody systems." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/39605.
Повний текст джерелаАнотація:
This thesis develops a finite element based dynamic modeling method for design and analysis of compliant mechanisms which transfer input force, displacement and energy through elastic deformations. Most published analyses have largely based on quasi-static and lump-parameter models neglecting the effects of damping, torsion, complex geometry, and nonlinearity of deformable contacts. For applications such as handling of objects by the robotic hands with multiple high-damped compliant fingers, there is a need for a dynamic model capable of analyzing the flexible multibody system. This research begins with the formulation of the explicit dynamic finite element method (FEM) which takes into account the effects of damping, complex geometry and contact nonlinearity. The numerical stability is considered by evaluating the critical time step in terms of material properties and mesh quality. A general framework incorporating explicit dynamic FEM, topology optimization, modal analysis, and damping identification has been developed. Unlike previous studies commonly focusing on geometry optimization, this research considers both geometric and operating parameters for evaluation where the dynamic performance and trajectory of the multibody motion are particularly interested. The dynamic response and contact behavior of the rotating fingers acting on the fixed and moving objects are validated by comparing against published experimental results. The effectiveness of the dynamic modeling method, which relaxes the quasi-static assumption, has been demonstrated in the analyses of developing an automated transfer system involved grasping and handling objects by the compliant robotic hands. This FEM based dynamic model offers a more realistic simulation and a better understanding of the multibody motion for improving future design. It is expected that the method presented here can be applied to a spectrum of engineering applications where flexible multibody dynamics plays a significant role.
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Xu, Feng. "Self-excited oscillations of flexible-channel flow with fixed upstream flux." Thesis, University of Nottingham, 2014. http://eprints.nottingham.ac.uk/14135/.
Повний текст джерелаАнотація:
Self-excited oscillations in a collapsible-tube flow driven by fixed upstream flux have been observed by numerical and laboratory experiments. In this thesis we attempt to understand the mechanism of onset of these oscillations by focusing on a reduced physical model. We consider flow in a finite-length planar channel, where a segment of one wall is replaced by a membrane under longitudinal tension. The upstream flux and downstream pressure are prescribed and an external linear pressure distribution is applied to the membrane such that the system admits uniform Poiseuille flow as a steady solution. We describe the system using a one-dimensional model that accounts for viscous and fluid inertial effects. We perform linear stability analysis and weakly nonlinear analysis on the one-dimensional model, the resulting predictions are tested against two-dimensional Navier–Stokes numerical simulation. When the membrane has similar length to the rigid segment of channel downstream of the membrane, we find that in a narrow parameter regime we consider “mode-2” oscillations (i.e. membrane displacements with two extrema) are largely independent of the downstream segment but are driven by divergent instabilities of two non-uniform steady configurations of the membrane. When the downstream segment is much longer than the membrane, our analysis reveals how instability is promoted by a 1:1 resonant interaction between two modes, with the resulting oscillations described by a fourth-order amplitude equation. This predicts the existence of saturated sawtooth oscillations, which we reproduce in full Navier–Stokes simulations of the same system. In this case, our analysis shows some agreements with experimental observations, namely that increasing the length of the downstream tube reduces the frequency of oscillations but has little effect on the conditions for onset. We also use linear stability analysis to show that steady highly-collapsed solutions, constructed by utilizing matched asymptotic expansions, are very unstable, which allows the possibility that they are a precursor to slamming motion whereby the membrane becomes transiently constricted very close to the opposite rigid wall before rapidly recovering.
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Mikulovic, Sanja. "On the Mechanisms Behind Hippocampal Theta Oscillations : The role of OLMα2 interneurons". Doctoral thesis, Uppsala, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-282144.
Повний текст джерелаАнотація:
Theta activity is one of the most prominent rhythms in the brain and appears to be conserved among mammals. These 4-12 Hz oscillations have been predominantly studied in the dorsal hippocampus where they are correlated with a broad range of voluntary and exploratory behaviors. Theta activity has been also implicated in a number of mnemonic processes, long-term potentiation (LTP) induction and even acting as a global synchronizing mechanism. Moving along the dorso-ventral axis theta activity is reduced in power and desynchronized from the dorsal part. However, theta activity can also be generated in the ventral hippocampus itself during anxiety- and fear-related behaviors. Until now it was unknown which hippocampal cell population was capable to generate theta activity and it was controversial if its origin was local, in the hippocampus, or driven by other brain regions. In this thesis I present compelling in vitro and in vivo evidence that a subpopulation of OLM interneurons (defined by the Chrna2-cre line) distinctively enriched in the CA1 region of the ventral hippocampus is implicated in LTP function (paper I,II), information control (paper V) and the induction of theta activity that is under cholinergic control (paper IV). Importantly, a concomitant effect of the optogenetically induced theta activity is reduction in anxiety (Paper IV). Another innovation of this work was the development of a methodological approach to avoid artefactual signals when combining electrophysiology with light activation during optogenetic experiments (Paper III). In summary, the work presented in this thesis elucidates the role of a morphologically and electrophysiologially identified cell population, OLMα2 interneurons, first on the cellular, then on the circuit and ultimately on the behavioral level.
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Chadwick, Angus. "Hippocampal theta sequences : from phenomenology to circuit mechanisms." Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/22887.
Повний текст джерелаАнотація:
The hippocampus is a brain structure involved in episodic memory and spatial cognition. Neuronal activity within the hippocampus exhibits intricate temporal patterning, including oscillatory and sequential dynamics, which are believed to underlie these cognitive processes. In individual cells, a temporal activity pattern called phase precession occurs which leads to the organisation of neuronal populations into sequences. These sequences are hypothesised to form a substrate for episodic memory and the representation of spatial trajectories during navigation. In this thesis, I present a novel theory of the phenomenological properties of these neuronal activity sequences. In particular, I propose that the sequential organisation of population activity is governed by the independent phase precession of each cell. By comparison of models in which cells are independent and models in which cells exhibit coordinated activity against experimental data, I provide empirical evidence to support this hypothesis. Further, I show how independent coding affords a vast capacity for the generation of sequential activity patterns across distinct environments, allowing the representation of episodes and spatial experiences across a large number of contexts. This theory is then extended to account for grid cells, whose activity patterns form a hexagonal lattice over external space. By analysing simple forms of phase coding in populations of grid cells, I show how previously undocumented constraints on phase coding in two dimensional environments are imposed by the symmetries of grid cell firing fields. To overcome these constraints, I propose a more complex phenomenological model which can account for phase precession in both place cells and grid cells in two dimensional environments. Using insights from this theory, I then propose a biophysical circuit mechanism for hippocampal sequences. I show that this biophysical circuit model can account for the proposed phenomenological coding properties and provide experimentally testable predictions which can distinguish this model from existing models of phase precession. Finally, I outline a scheme by which this biophysical mechanism can implement supervised learning using spike time dependent plasticity in order to learn associations between events occurring on behavioural timescales. The models presented in this thesis challenge previous theories of hippocampal circuit function and suggest a much higher degree of flexibility and capacity for the generation of sequences than previously believed. This flexibility may underlie our ability to represent spatial experiences and store episodic memories across a seemingly unlimited number of distinct contexts.
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Pan, Linlin. "A study of dynamic mechanisms of annular modes." Thesis, University of Hawaii at Manoa, 2003. http://proquest.umi.com/pqdweb?index=0&did=765084681&SrchMode=2&sid=3&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1233249518&clientId=23440.
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Moon, Suk-Min. "Active damping control of a compliant base manipulator." Ohio : Ohio University, 1999. http://www.ohiolink.edu/etd/view.cgi?ohiou1175797025.
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Kooverji, Bavesh. "Pneumatic power measurement of an oscillating water column converter." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/86662.
Повний текст джерелаАнотація:
Thesis (MScEng)--Stellenbosch University, 2014.ENGLISH ABSTRACT: A measurement device was developed to accurately determine the pneumatic power performance of an Oscillating Water Column (OWC) model in a wave flume. The analysis of the pneumatic power is significant due to the wave-topneumatic energy being the primary energy conversion process and where the most energy losses can be expected. The aim of the research study is to address the accurate pneumatic power measurement of unsteady and bidirectional airflow in OWC model experiments. The two fundamental measurements required for the pneumatic power measurement are the pressure difference over an orifice on the OWC model and the volumetric flow rate of air through the outlet. The designed, constructed and assembled measurement device comprised of a venturi flow meter, containing a hot-film anemometer, which could measure the pressure drop and the volumetric flow rate in one device. The assembled pneumatic power measurement device was calibrated in a vertical wind tunnel at steady state. The results from the calibration tests showed that the volumetric flow rate measurements from the pneumatic power measurement device was accurate to within 3 % of the wind tunnel’s readings. The pneumatic power measurement device was incorporated onto a constructed Perspex physical model of a simple OWC device. This assembled system was used as the test unit in the wave flume at Stellenbosch University (SUN). The results from the experimental tests underwent comparative analysis with three analytical OWC air-flow models which were simulated as three scenarios using Matlab Simulink. These results showed that the measurement device has the ability to measure the pneumatic power but there is difficulty in modelling the complex air-flow system of the OWC device. This results in varying levels of agreement between the experimental and simulated pneumatic power results. The research study has revealed that there is difficulty in designing an accurate device for a wide range of test parameters due to the variance in output values. The unsteady and bidirectional nature of the air flow is also difficult to accurately simulate using a one-dimensional analytical model. Recommendations for further investigation are for CFD systems to be used for the analysis of the air-flow in an OWC system and to be used to validate future pneumatic power measurement devices.
AFRIKAANSE OPSOMMING: ‘n Meetinstrument was ontwikkel om die pneumatiese kraglewering van ‘n model van die Ossillerende Water Kolom (OWK) golfenergie omsetter in ‘n golf tenk akkuraat te meet. Dit is belangrik om die omskakeling van golf na pneumatiese energie te analiseer siende dat die grootste energieverlies in dié proses plaasvind. Die doel van hierdie navorsingsprojek was om die akkurate pneumatiese kragmeting van variërende en twee-rigting vloei van lug in ‘n OWK model na te vors. Die twee fundamentele metings wat benodig word vir die pneumatiese kragbepaling is die drukverskil oor die vloei vernouing en die volumetriese vloeitempo van lug deur die uitlaat van die toetstoestel. Die spesiaal ontwerpte meettoestel wat gebruik is in die eksperiment het bestaan uit ‘n venturi vloeimeter wat ‘n verhitte-film anemometer bevat het wat die drukverandering en die volumetriese vloeitempo kan meet in ‘n enkele instrument. Die pneumatiese kragmeting was gekalibreer in ‘n vertikale windtonnel waarin ‘n konstante vloei tempo geïnduseer was. Die kalibrasieproses het bevestig dat die meettoestel metings lewer met ‘n fout van minder as 3 % wanneer dit vergelyk word met die bekende konstante vloei tempo soos bepaal in die windtonnel. ‘n Fisiese model van ‘n vereenvoudigde OWK golfenergie omsetter was ontwerp en gebou uit Perspex om as toetstoestel te gebruik vir die evaluering van die ontwerpte pneumatiese kraglewering meettoestel. Die toetse was uitgevoer in ‘n golftenk by die Universiteit Stellenbosch (SUN). The toetsresultate was vergelyk met drie ander OWK lugvloei modelle wat gesimuleer was deur om die analitiese modelle op te stel en te simuleer in Matlab Simulink. Die vergelyking van modellering resultate het gewys dat die meettoestel die vermoë het om pneumatiese krag te meet. Daar was wel komplikasies met die modellering van die komplekse lugvloei in die OWK toestel, die resultate het geen definitiewe ooreenstemming gewys tussen die eksperimentele en gesimuleerde pneumatiese krag resultate nie. Die navorsingsprojek het gewys dat daar komplikasies is om ‘n enkel toestel te ontwerp wat oor ‘n wye bereik kan meet weens die variasie van die verskillende parameters. Die variërende en twee-rigting lugvloei is ook moeilik om akkuraat te simuleer met ‘n een-dimensionele analitiese simulasie model. Aanbevelings vir verdere navorsing sluit in om die lugvloei in die OWK stelsel te modelleer en te analiseer in ‘n drie-dimensionele model om die lesings van ‘n pneumatiese krag meettoestel te bevestig.
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Mills, Richard. "Anticipatory and Reactive Mechanisms of Postural Control in Children and Adolescents." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/37923.
Повний текст джерелаАнотація:
Maintaining postural control in standing requires the center of mass (COM) to be kept within the boundaries of the base of support (BOS). As the COM moves to a region outside the BOS, a step is often required, increasing the risk of falling, and therefore injury. All too often, humans are subjected to different perturbations while maintaining upright stance, and so to control the COM in these situations, postural activity through musculature at the ankle, knee, and hip are recruited according to demand associated with the level of perturbation. It is also believed that control of the head allows components of the visual and vestibular systems to contribute stable reference values.
In order to understand human response to, and in preparation for perturbation, researchers have employed a number of experimental techniques, including i) loading and subsequent unloading of body segments such as the arm or leg; ii) single discrete platform movements; and iii) continuous platform movements. While many studies have focussed on examining postural control mechanisms during discrete perturbations in children and adolescents, these mechanisms in response to continual perturbation have not been well documented in observable developmental stages of youth, nor have they been well documented in special populations. Therefore, the primary aim of this doctoral dissertation was to characterize the reactive and anticipatory postural control mechanisms in children and adolescents, as well as to examine and characterize them in the Cerebral Palsy population.
To achieve this overarching goal, three separate studies were performed. The first study characterized the anticipatory and reactive mechanisms of postural control in typically developing children aged 7 to 17 years. Specifically, postural muscle activity in the lower limbs, an index of head anchoring strategy, and body segment cross-correlations were characterized in response to, and in anticipation of, continuous platform oscillation movement at various frequencies. The second experiment characterized these same mechanisms in children of similar ages with cerebral palsy, and compared the results to those found in the first study. The results of these studies indicated a slight shift to anticipatory measures after repeated exposure to a specific frequency of platform oscillation, however, each transition to a greater platform speed resulted in more conservative measures of postural control. Furthermore, youth with cerebral palsy tended to control their posture much in the same way of typically developing children and adolescents under less challenging conditions however, with the increased difficulty associated with higher frequency oscillation were not able to generate adequate postural responses.
The final study in this dissertation investigated the effects of a one-week intensive virtual reality-based exercise programme. In this study, postural control mechanisms were observed before and after a one-week time period, during which half of the participants received the enhanced exercise while the remaining participants received no treatment at all. The results from this study indicated there was no effect of a 5-day VR-based intervention on postural control mechanisms used in response to oscillating platform perturbations.
Taken together, the results from these studies extend the current understanding of reactive and anticipatory mechanisms of postural control in children and adolescents, both typically developing and those with cerebral palsy.
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McCarthy, Michelle Marie. "Neocortical mechanisms mediating electroencephalographic oscillations a biomathematical analysis of anesthesia-induced paradoxical excitation /." Diss., Restricted to subscribing institutions, 2007. http://proquest.umi.com/pqdweb?did=1428839101&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Khamesian, Mahvand. "Mechanisms of High Sensitivity and Active Amplification in Sensory Hair Cells." Ohio University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou153243238506078.
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Piai, Maurizio. "Beyond the Standard Model: Topics on Chiral Gauge Anomalies and on Neutrino Oscillations." Doctoral thesis, SISSA, 2002. http://hdl.handle.net/20.500.11767/4301.
Повний текст джерелаАнотація:
Within the multi-folded research context of beyond the Standard Model physics,
the author of this Ph. D. Thesis works on several different research lines: the study
of low-energy Supersymmetry effects and of its underlying :flavor and GP-violating
structures at the B factories, the exploration of extra-dimension scenarios through
gravitational effects on ordinary matter and bulk fields, the development of anomaly
cancellation mechanisms for gauge theories in D dimensions, with the study of their
phenomenological implications, the discussion about new experimental facilities for
testing the structure of the neutrino mass matrix.
Not all of the material produced during the Ph. D. activity could be collected
here, but the results in two of these fields have been selected: topics related to the
cancellation of gauge anomalies and to the phenomenology of neutrino oscillations
from artificial sources.
As a result, this Thesis has a quite unusual structure: it is divided into two
separate parts, which share the effort of Particle Physics to go beyond the Standard
Model, but differ by the use of drastically different research techniques and
strategies.
Each of the two parts contains a brief introduction, which anticipates the main
lines of the research program developed and the results obtained, is divided in Chapters
and has a specific Bibliography.
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Gillies, Martin John. "Modulation of excitation as a mechanism of oscillation frequency transition in the hippocampus in vitro." Thesis, University of Leeds, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.403026.
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Faulkner, Howard John. "Disruption of fast oscillations in hippocampal networks in vitro : a common mechanism of anaesthetic drug action." Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322316.
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Moioli, Renan Cipriano. "Neuronal oscillations, information dynamics, and behaviour : an evolutionary robotics study." Thesis, University of Sussex, 2013. http://sro.sussex.ac.uk/id/eprint/45995/.
Повний текст джерелаАнотація:
Oscillatory neural activity is closely related to cognition and behaviour, with synchronisation mechanisms playing a key role in the integration and functional organization of different cortical areas. Nevertheless, its informational content and relationship with behaviour - and hence cognition - are still to be fully understood. This thesis is concerned with better understanding the role of neuronal oscillations and information dynamics towards the generation of embodied cognitive behaviours and with investigating the efficacy of such systems as practical robot controllers. To this end, we develop a novel model based on the Kuramoto model of coupled phase oscillators and perform three minimally cognitive evolutionary robotics experiments. The analyses focus both on a behavioural level description, investigating the robot's trajectories, and on a mechanism level description, exploring the variables' dynamics and the information transfer properties within and between the agent's body and the environment. The first experiment demonstrates that in an active categorical perception task under normal and inverted vision, networks with a definite, but not too strong, propensity for synchronisation are more able to reconfigure, to organise themselves functionally, and to adapt to different behavioural conditions. The second experiment relates assembly constitution and phase reorganisation dynamics to performance in supervised and unsupervised learning tasks. We demonstrate that assembly dynamics facilitate the evolutionary process, can account for varying degrees of stimuli modulation of the sensorimotor interactions, and can contribute to solving different tasks leaving aside other plasticity mechanisms. The third experiment explores an associative learning task considering a more realistic connectivity pattern between neurons. We demonstrate that networks with travelling waves as a default solution perform poorly compared to networks that are normally synchronised in the absence of stimuli. Overall, this thesis shows that neural synchronisation dynamics, when suitably flexible and reconfigurable, produce an asymmetric flow of information and can generate minimally cognitive embodied behaviours.
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Sebe, Joy Yoshiko. "Development, generation, and origin of synchronous oscillations in the brainstem respiratory network /." Thesis, Connect to this title online; UW restricted, 2006. http://hdl.handle.net/1773/10650.
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Tanugula, Rohit. "Effects of baffles on damping lateral fluid sloshing oscillations in tanker trucks." Morgantown, W. Va. : [West Virginia University Libraries], 2001. http://etd.wvu.edu/templates/showETD.cfm?recnum=2112.
Повний текст джерелаАнотація:
Thesis (M.S.)--West Virginia University, 2001.Title from document title page. Document formatted into pages; contains xiv, 97 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 90-92).
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Lawrence, Jason William. "Crane Oscillation Control: Nonlinear Elements and Educational Improvements." Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-07072006-175615/.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2007.William Singhose, Committee Chair ; Steven Danyluk, Committee Member ; Donna Llewellyn, Committee Member ; Nader Sadegh, Committee Member ; Neil Singer, Committee Member.
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Charifoullina, Elina. "Oscillatory motor discharges by brainstem neurons: functional mechanisms and consequences for cell survival." Doctoral thesis, SISSA, 2006. http://hdl.handle.net/20.500.11767/4671.
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MOORHEAD, ALEX PATTEN. "THE DAMPED OSCILLATIONS OF PASSIVE LIMBS AND THEIR ROLE IN HUMAN LOCOMOTION MECHANICS." Doctoral thesis, Università degli Studi di Milano, 2019. http://hdl.handle.net/2434/605781.
Повний текст джерелаАнотація:
The mechanics of locomotion classically take into account the work done by muscle force to raise and accelerate the body center of mass and to accelerate limbs with respect to it at each step. This last component, named Internal Work (W_INT), considers only the cost to overcome segment inertia, inherently assuming frictionless joints. Thus, the unavoidable damping opposing segmental oscillation due to anatomical structures within or around the pivoting centers has never been measured so far.
The frictional coefficient (b, N.m.s.rad-1) of such a biological rotational damper has been here assessed by sampling the time course of passive oscillation (with respect to the vertical axis) of upper and lower limbs and by analyzing its motion. This experiment (straight pendulum) was performed to assess joint energy dissipation during the swing phase of locomotion. A custom mathematical model, leading to a 2nd Order Non-Linear Ordinary Differential Equation, allowed to infer b values for upper (bUU = 0.39 ± 0.08) and lower (bUL = 2.24 ± 0.56 N.m.s.rad-1) limbs in 16 healthy males. Phase planes ensured that no muscle activity was involved. In the same population, the passive swing of a lower limb, behaving as an inverted pendulum after a push (body upside-down), was also sampled while loading the leg as to replicate the compressive stress to which the hip joint is exposed during stance phase. Loads ranged from 0 N (mass of leg only) to 118 N. Damper values (b) for the inverted swing of a loaded lower limb increased with the load and ranged from 4.89 ± 1.29 to 8.92 ± 1.74 N.m.s.rad-1.
The influence on locomotion mechanics has been here evaluated. In walking, for instance, each step includes 3 'passively' swinging, unloaded segments (2 upper limbs and the swinging lower limb with joints under tensile stress) and 1 'actively' oscillating, almost fully loaded segment (stance lower limb, joint under compressive stress). The actual experimental results have been combined to provide an estimate of the internal mechanical work due to tissue and joint damping. In walking that is comparable (and should be added) to the estimate obtained by means of a kinematics-based model (Minetti, 1998) and experimental data from the literature of the traditional ‘kinematic’ W_INT. In the discussion, the potential overestimation and underestimation of those two types of internal work are presented, together with the implications of the presented additional work (and its metabolic equivalent) to the energy balance and efficiency of human locomotion.
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Beton, Christopher William Hartley. "Application of the Boundary Element Method to the detachment, oscillation and interaction of gas bubbles in a fluid." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261660.
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Syyong, Harley Thomas Tan. "Mechanisms of asynchronous Ca²⁺ oscillations and their role in (mal)function of vascular smooth muscle." Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/24253.
Повний текст джерелаАнотація:
Contraction of vascular smooth muscle is regulated by fluctuations in the cytosolic concentration of Ca²⁺. The spatio-temporal regulation of Ca²⁺ relies on the subcellular architecture of the smooth muscle cell and the juxtaposition of the opposing plasmalemma, sarcoplasmic reticulum, and mitochondria. This thesis addresses two related aspects of Ca²⁺ signaling in vascular smooth muscle: 1) Reversal of the plasma membrane Na⁺/Ca²⁺ exchanger (NCX) during agonist-mediated stimulation in cultured rat aorta smooth muscle cells, and 2) the primary function of agonist-stimulated asynchronous Ca²⁺ waves and the signaling pathway(s) underlying them in the intact tissue.
Evidence for functional coupling of reverse-mode NCX with canonical transient receptor potential channels (TRPC), specifically TRPC6, was provided in rat aortic smooth muscle cells by demonstrating that NCX reversal was increased following stimulation with ATP and 1-Oleoyl-2-acetyl-sn-glycerol, a diacylglycerol analog. However, this was attenuated by blockade of non-selective cation channels with SKF-96365 and by activation of protein kinase C. These data are consistent with the known properties of TRPC6 and further support that functional coupling of TRPC6 and NCX occurs via a receptor-operated cascade.
A combination of wire myography and confocal microscopy determined that uridine 5’-triphosphate (UTP)-induced tonic contractions in rat basilar artery were associated with sustained repetitive oscillations in cytosolic Ca²⁺ which propagated along the length of the smooth muscle cells as Ca²⁺ waves. Pharmacological characterization of the mechanism of Ca²⁺ waves revealed that they are a result of repetitive cycles of sarcoplasmic reticulum (SR) Ca²⁺ release via inositol 1,4,5-trisphosphate-sensitive channels followed by the refilling of the SR. Plasmalemmal Ca²⁺ entry via the reverse-mode NCX coupled with the receptor-operated and L-type Ca²⁺ channels is involved in replenishing the SR and supporting the ongoing Ca²⁺ waves.
Finally, phenylephrine-stimulated vascular smooth muscle contraction in mesenteric arteries of a mouse model of Marfan syndrome was significantly inhibited and associated with reduced frequency of Ca²⁺ waves. In addition, endothelium-dependent and endothelium-independent vasodilation was impaired, and vessel stiffness was increased. Together, these vasomotor abnormalities in the resistance vessel may have a negative and detrimental impact on the overall cardiovascular function in Marfan syndrome.