To see the other types of publications on this topic, follow the link: Actin Waves.
Dissertations / Theses on the topic 'Actin Waves'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Actin Waves.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Dennis, Kadeem. "Mechanical Modification of Cells by Pressure Waves and Its Application to Traumatic Brain Injury." Thesis, Université d'Ottawa / University of Ottawa, 2015. http://hdl.handle.net/10393/34067.
Full textAbstract:
Recently there has been interest in determining what happens to the human brain during a traumatic brain injury (TBI). The blast wave created by explosive devices, such as landmines, is one of the most common causes of TBI. The purpose of this study is to investigate the link between an explosion and a cells reaction to a blast wave on a time scale of a few hours. Three different types of cells were tested by pressure waves exposure, fibroblasts (3T3), epithelial cervical cancer (HeLa), and canine epithelial kidney cells (MDCK). Fluorescent images of the cells before and after pressure wave exposure were used to determine how much damage cells have suffered. 3T3 cells showed the most cellular modification while HeLa and MDCK were more resilient. A simple scaling model is proposed to relate the cellular modification to the shock strength.
2
Iseppon, Federico. "Investigation on spatio-temporal dynamics of RhoGTPases and their role in neuronal growth cone and actin wave motility." Doctoral thesis, SISSA, 2016. http://hdl.handle.net/20.500.11767/4890.
Full textAbstract:
Neurons are highly polarised cells that migrate elongating their axon to reach distant synaptic targets. In the developing nervous system they travel along highly conserved trajectories defined by the molecules present in the surrounding environment, the so-called guidance cues. They can exert the function either at short range by direct contact or at long range, secreted by surrounding and target cells to create gradients that can be sensed by migrating axons.
During the PhD course I focused on investigating the spatio-temporal properties of neurons in response to chemical signals. I have studied in detail the morphology changes of Growth Cones (GC) upon local stimulation and the dynamics of signalling cascades regulating actin dynamics, with a particular attention on Rho-GTPases. Moreover I investigated the morphology, molecule composition of axonal Actin Waves (AWs), as well as the role of Rho-GTPases in their inception and movement kinetics. In these studies I adopted various techniques: from live-cell imaging of the actin dynamics in AWs to a combination of FRET imaging and optical manipulation to image the Rho-GTPases activation in GCs real time upon local chemical stimulus delivery.
The cellular module designed to perceive the guidance stimuli is the Growth Cone (GC), a specialised structure at the tip of the growing axon divided into three regions. The central region contains organelles and has a structural function, the transition region is formed by acto-myosin contractile arcs and the peripheral region, formed by thin filopodia and veil-like lamellipodia structures, that sustain dynamic protrusion and retraction cycles and express on the surface all the receptors to sense the presence of guidance molecules gradients.
The major component of these structures is actin, a molecule that polymerises to form filaments that can be arranged, with the cooperation of a wide variety of actin-binding molecules, into different architectures. Actin filaments are polarised structure with the “barbed” end oriented towards the leading edge and a “pointed” end towards the central region. Filaments undergo continuous cycles of polymerisation at the barbed end and depolymerisation at the pointed end, creating two dynamic behaviours called treadmilling and retrograde flow. The relative prominence of one process over the other is regulated by external signals that are sensed by receptors and initiate different intracellular signalling cascades. These pathways involve a lot of diverse proteins at various levels, but almost all of them pass through a “bottleneck” step: the Rho family of Guanosine Tri-Phosphatases (Rho-GTPases).
Rho-GTPases are molecular switches that cycle between activated, GTP-bound state and an inactivated, GDP-bound state. Their dynamics are modulated by upstream signals, and in turn they interact with downstream effectors to propagate the signal transduction to the actin cytoskeleton. A single Rho-GTPase can be regulated by many different molecules, called Guanosine Exchange Factors (GEFs), GTPase domain Activator Proteins (GAPs) and Guanine Nucleotide Dissociation Inhibitors (GDIs), and activate a wide range of cellular responses, depending on the cell type and the stimulus received. They are best known for their roles in the modulation of cytoskeleton rearrangements, cell motility and polarity and axon guidance. They exert their effect mainly by affecting actin dynamics, not only in the growth cone but also in the axon shaft.
A particular behaviour of the polarising neuronal cells is the extrusion of GC-like structures that travel along the neurite shaft towards the tip and fuses with the GC to promote elongation. These structures are called Actin Waves (AWs): they have a mean velocity of 2-3 µm/min and appear in a stochastic manner in all the growing neurites with a frequency of about 1-2 waves per hour. Their propagation is strongly dependent on the dynamic behaviour of the actin filaments, with the balance between barbed end polymerisation and pointed end de-polymerisation at its basis. Therefore all those proteins involved in the regulation of actin might have a prominent role in their structure and function, including the RhoGTPases.
The main achievements and findings of my PhD are the following:
1. I combined successfully for the first time FRET imaging with optical tweezers to provide a strong tool to study dynamics of intracellular signalling molecules upon local delivery of chemical attractants and repellants. The versatility of the optical tweezers, that have the possibility to exert both contact stimulation and local gradient delivery, along with the precision and high spatio-temporal resolution of the FRET, allowed us to highlight fine spatio-temporal dynamics of Rho-GTPases in live cells.
2. Local repulsive stimulation by semaphorin-3A triggers local retraction of the side of the growth cone facing the stimulus, with distinct RhoGTPases spatio-temporal dynamics:
a. I showed, in accordance to previous studies, that the stimulation triggers rapid activation of RhoA within 30 s in the central region of the growth cone, causing a delayed retraction (100-120 s from the stimulus application) that correlates with RhoA activation levels correlate with the induced morphological changes;
b. I demonstrated that semaphorin-3A local delivery causes a decrease in Cdc42 activity within 60 s from the stimulation. Activity levels vary in a wave-like retrograde manner that proceeds almost in synchrony with the retraction. In few cases the stimulation induced the formation of active Cdc42 waves that propagate in a region away from the local stimulus and promote the spawning of new filopodia and lamellipodia, suggesting a role of Cdc42 in travelling actin waves;
c. I showed that local stimulation with beads coated with semaphorin-3A induces the formation of active Cdc42 waves propagating from the GC edge to the central region with a mean period of 70 s. Same “travelling” waves have been found in some cases of spontaneous retraction in the neuronal cell culture, but they oscillate with a longer period (110 s).
These overall data show a more complex behaviour for Cdc42 than RhoA, and provide evidence for a higher degree of complexity in the Rho-GTPase signalling network.
3. Actin dynamics in neuronal actin waves are strongly dependent on Cdc42 and Rac1 activation dynamics. By means of immunofluorescence, STED nanoscopy and live cell imaging with inhibitors for different molecules, we showed that:
a. In accordance with previous studies, actin waves are growth cone-like structures that generate at the proximal segment of neurites and then propagate along the shaft towards the growth cone. When it reaches its vicinity, the growth cone retracts and the two structure fuse together to form a new, bigger and more dynamic growth cone that elongates again;
b. Myosin-IIB is localised at the rear of the propagating wave, suggesting a possible role of myosin in their dynamics. This role has been confirmed by further experiments in which myosin inhibition with 20 µM blebbistatin highlighted the disruption of the GC-like morphology of actin waves and the disappearing of the GC retraction upon wave incoming at the neurite tip, along with an effect on AW frequency and velocity;
c. Membrane tension has a role in maintenance of AW morphology and affects also AW initiation and propagation. Addition of 250 µM of β-cyclodextrin disrupted the GC-like morphology and decreased the AW area of more than 50%. Moreover the treatment decreased the velocity and significantly the frequency of AW initiation, suggesting a major role of the membrane in AW dynamicity;
d. Cdc42 and Rac1 have a strong impact on the initiation dynamics of the actin waves. The frequency of actin waves per hour is significantly reduced under 10 µM of both Cdc42 (ML141) and Rac1 (EHT1864) inhibition: from 2-3 waves per hour to about 0,5 and 1 wave per hour, respectively. Moreover, addition of a high concentration (30µM) of ML141 stopped the AW sprouting almost completely, demonstrating a prominent role of these Rho-GTPases in actin wave initiation at the initial segment of the neurite.
e. Cdc42 and Rac1 have a role also in the propagation dynamics of actin waves. Inhibition of both GTPases resulted in a significant decrease in the velocity of actin waves, from a mean of 2,2 µm/min to about 1,5 µm/min and 1,2 µm/min respectively. Moreover we observed a disruption of the GC-like morphology of AWs, as well as a reduction in the mean area of about 50%.
These results provide new insights for a prominent role of Rho-GTPases in the overall dynamics of the actin cytoskeleton within the travelling waves, in perfect accordance with previously reported data.
3
Iuliano, Olga. "Myosin1b controls the formation of the axon and the establishment of neuronal polarity by regulating actin waves." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066649.
Full textAbstract:
Les neurones sont des cellules polarisées qui présentent un seul axone et de nombreuses dendrites courtes. Les réarrangements du cytosquelette, l'augmentation du transport dépendant des microtubules et le couplage mécanique du cytosquelette d'actine à la membrane plasmique sont nécessaires pour établir cette polarité neuronale. Les Myosines 1 qui couplent le cytosquelette d'actine à la membrane plasmique sont des bons candidats pour réguler l'axonogenèse. La Myosine1b étant fortement exprimée dans le cerveau en développement, nous avons donc étudié son rôle dans l'axonogenèse. L'inhibition de l'expression de Myo1b dans les neurones corticaux retarde la différenciation neuronale et empêche l'axonogenèse et l'établissement de la polarité neuronale. La surexpression de Myo1b accélère le développement neuronal et induit la formation d'axones surnuméraires. L'activité motrice et l'interaction de Myo1b avec des phosphoinositides via son domaine PH est nécessaire pour ce processus. Myo1b est associée et contrôle la formation d'ondes d'actine antérogrades qui 'cross-talk" avec les microtubules pour diriger le transport de la kinésine1 sur les microtubules et conduire à la formation de l'axone. L'inhibition de Myo1b empêche la propagation des ondes d'actine et le mouvement de KIF5560 une version constitutivement active du moteur Kinésine 1 associé aux microtubules. L' activité motrice et le domaine PH de Myo1b sont nécessaire à la propagation des ondes d'actine. Nos résultats indiquent que la Myosine 1b contrôle la rupture de la symétrie axonale et la formation de l'axone en contrôllant l'orientation de la polymérisation d'actine à la membrane dans les ondes d'actine antérogradeNeurons are highly polarized cells, with a long axon and multiple short dendrites. Rearrangements of cytoskeleton, increased microtubule-based transport and coupling mechanically actin cytoskeleton to plasma membrane are required for the establishment of neuronal polarity. Class 1 Myosin, with the unique property to couple mechanically actin cytoskeleton to plasmamembrane are good candidate for regulatin axonogenesis. Myosin1b is highly expressed in developing brain where it was first identified. Thus, we investigated its role in axonogenesis. Depletion of endogenous Myo1b in cultured cortical neurons delays the neuronal differentiation and impairs the axonogenesis and the establishment of the neuronal polarity. The overexpression of Myosin1b rushes the neuronal development and promotes the formation of supernumerary axon-like structures. Myo1b requires its motor activity and its interaction with phosphoinositides via its PH motif to promote the axonogenesis. Myo1b associates and controls the formation of anterograde actin waves that cross-talk with microtubules to direct microtubules-bases transport of kinesin-1, and drive axon formation. Myo1b depletion impairs the propagation of actin waves and the translocation of KIF5560, a constitutively active version of the microtubules motor Kinesin-1. The motor activity and interaction with phosphoinositides of Myo1b are also required for the propagation of actin waves. Together our data indicate that myosin1b controls the neuronal symmetry breaking and the axogenesis by controlling the orientation of the actin polymerization to the membrane in the waves that drive the propagation of anterograde actin waves
4
Bernitt, Erik [Verfasser], Hans-Günther [Akademischer Betreuer] Döbereiner, and Karsten [Akademischer Betreuer] Kruse. "The Dynamics of Dorsal Actin Waves / Erik Bernitt. Betreuer: Hans-Günther Döbereiner. Gutachter: Hans-Günther Döbereiner ; Karsten Kruse." Bremen : Staats- und Universitätsbibliothek Bremen, 2015. http://d-nb.info/1082029785/34.
Full text
5
Gautier, Jérémie. "Rôle de la clathrine dans la formation des lamellipodes." Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00647325.
Full textAbstract:
Le complexe Scar/WAVE génère la formation des lamellipodes par l'intermédiaire du complexe Arp2/3 responsable de la polymérisation de réseaux d'actine branchés. Dans le but d'identifier de nouveaux régulateurs du complexe Scar/WAVE, nous avons conduit un crible en cellules de Drosophiles combinant une approche protéomique à une approche de génomique fonctionnelle. La chaîne lourde de la clathrine a été identifiée au cours de ce crible comme une protéine interagissant avec le complexe Scar/WAVE et dont la déplétion affecte la formation des lamellipodes. Ce rôle de la clathrine dans la formation des lamellipodes peut être découplé de son rôle classique dans le transport vésiculaire en utilisant différentes approches. De plus, la clathrine est localisée au lamellipode en l'absence d'adapteurs et des protéines accessoires de l'endocytose. La surexpression de la clathrine affecte le recrutement membranaire du complexe WAVE réduisant ainsi la vélocité des protrusions membranaire et la migration cellulaire. Par opposition, lorsque la clathrine est envoyée artificiellement à la membrane plasmique par une fusion à une séquence myristoylée, on observe une augmentation du recrutement membranaire du complexe Scar/WAVE, de la vélocité des protrusions membranaires et de la migration cellulaire. L'ensemble de ces résultats montrent que la clathrine envoie le complexe Scar/WAVE à la membrane plasmique et donc contrôle la formation des lamellipodes en plus de son rôle plus classique dans le traffic membranaire.
6
Tsimplis, Michael. "The attenuation of waves under the action of rain." Thesis, University of Southampton, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.277504.
Full text
7
York-Andersen, Anna Henrietta. "Investigating the calcium wave and actin dynamics at Drosophila egg activation." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/288873.
Full textAbstract:
Egg activation is a series of highly coordinated processes that prepare the mature oocyte for embryogenesis. Typically associated with fertilisation, egg activation results in the resumption of the cell cycle, expression of maternal mRNAs and cross-linking of the vitelline membrane. While some aspects of egg activation, such as initiation factors in mammals and environmental cues in sea animals, have been well-documented, the mechanics of egg activation in many animals are still not well understood. This is especially true for animals where fertilisation and egg activation are unlinked. In order to elucidate how egg activation is regulated independently of fertilisation, I use Drosophila melanogaster as a model system. This insect provides extensive genetic tools, ease of manipulation for experimentation and is amenable for imaging. Through visualisation of calcium, Processing bodies and meiotic spindles, I show that osmotic pressure acts as an initiation cue for the calcium wave and downstream processes, including the resumption of cell cycle and the dispersion of the translational repression sites. I further show that aquaporin channels, together with external sodium ions, play a role in coordinating swelling of the oocyte in response to the osmotic pressure. I proceed to identify the requirement of internal calcium sources together with a dynamic actin cytoskeleton for a calcium wave to occur. Through co-visualisation of calcium and actin, I provide the first evidence that the calcium wave is followed by a wavefront of non-cortical F-actin at egg activation, which requires the calcium wave. Genetic analysis supports a model where changes in osmotic pressure trigger the calcium wave via stretch sensitive calcium channels in the oocyte membrane and the calcium wave is relayed by nearby channels via the actin cytoskeleton. My work concludes that the mechanism of egg activation in Drosophila is more similar to plants, compared to most vertebrates.
8
Abou-Ghali, Majdouline. "Actin network architecture and dynamics studied in vitro and in vivo." Electronic Thesis or Diss., Sorbonne université, 2019. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2019SORUS012.pdf.
Full textAbstract:
Le changement de forme des cellules est primordial pour différents processus cellulaires tels que la motilité et division cellulaire, et certaines pathologies comme les métastases cancéreuses. La forme de la cellule est assurée par son cytosquelette. Un composant majeur du cytosquelette est l’actine. J’ai étudié le rôle de l’actine dans des systèmes in vitro et in vivo. In vitro, en utilisant un système reconstitué de l’assemblage de l’actine, j’examine le rôle de la protéine Ena/VASP. Mes résultats montrent que VASP est impliqué dans la polarisation de la croissance du réseau d’actine vers une surface en absence des protéines de coiffe, en induisant une augmentation de l’activité du complexe Arp2/3 à la surface formant un réseau d’actine polarisé. Je propose aussi un modèle de fonctionnement où la protéine VASP produit plus de filaments mère utilisés pour le branchement par Arp2/3. En utilisant le même système, j’ai identifié une nouvelle molécule qui inhibe l’activité du complexe Arp2/3 de manière contrôlée par la lumière. In vivo, j’ai commencé à explorer l’architecture de l’actine pendant la première division cellulaire de nématodes génétiquement différents de C. elegans. J’ai réduit le nombre d’outils pouvant être utilisés pour visualiser le réseau d’actine dans ces espèces. En somme, ces résultats montrent qu’en présence de Ena/VASP les protéines de coiffe ne sont pas nécessaires à la croissance polarisée du réseau, ni à sa motilité. Enfin, nous avons pu aider à identifier une molécule photoconvertible qui inhibe l’activité du complexe Arp2/3, qui peut être utilisée pour étudier le rôle du complexe dans des processus cellulaires de manière contrôléeCell shape changes are crucial for different cell processes such as cell motility, division, and are involved in pathologies like cancer. Cell shape is established by the cellular cytoskeleton. A key component of the cytoskeleton is actin. I studied actin network architecture and dynamics both in vitro and in vivo. For the in vitro part, I used a reconstituted system of actin assembly to examine the role of the barbed end elongation enhancement protein, Ena/VASP. I revealed the contribution of VASP in polarizing the growth of an actin network towards a surface in absence of capping protein, by promoting Arp2/3 complex activity at the surface that initiates actin network. I suggest a mode of action where VASP enhances Arp2/3 complex-based growth by providing mother filaments for Arp2/3 complex branch initiation. Using the same system and through a collaboration with chemists, we identified a new light controlled molecule based on CK-666, that inhibits Arp2/3 complex activity. In vivo, I started exploring actin architecture during the first cell division of nematode species that are genetically distant from C. elegans. I narrowed the window of tools that can be used to visualize the actin network in such nematodes. Overall these results demonstrate that capping protein was not necessary for polarized actin growth and motility in presence of VASP. VASP enhanced the activity of the Arp2/3 complex at the surface thus inducing a polarized growth of the network. I identified a photoswitchable Arp2/3 complex inhibitor, subsequent derivatives of which could be used to study the role of the Arp2/3 complex in cellular processes in a controlled manner
9
Bruce, Tom. "Violent wave action at seawalls and breakwaters." Thesis, University of Edinburgh, 2006. http://hdl.handle.net/1842/13135.
Full text
10
Salih, Barham A. "Probablistic properties of wave climates." Thesis, University of Liverpool, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.237665.
Full text
11
Cockrell, Deborah Jane. "Rural clinical placements for dental students : an action research study." Thesis, The University of Sydney, 2005. http://hdl.handle.net/2123/4662.
Full textAbstract:
Doctor of PhilosophyThis work was digitised and made available on open access by the University of Sydney, Faculty of Dentistry and Sydney eScholarship . It may only be used for the purposes of research and study. Where possible, the Faculty will try to notify the author of this work. If you have any inquiries or issues regarding this work being made available please contact the Sydney eScholarship Repository Coordinator - ses@library.usyd.edu.au
12
Cockrell, Deborah Jane. "Rural clinical placements for dental students : an action research study." University of Sydney, 2005. http://hdl.handle.net/2123/4662.
Full textAbstract:
Doctor of PhilosophyThis work was digitised and made available on open access by the University of Sydney, Faculty of Dentistry and Sydney eScholarship . It may only be used for the purposes of research and study. Where possible, the Faculty will try to notify the author of this work. If you have any inquiries or issues regarding this work being made available please contact the Sydney eScholarship Repository Coordinator - ses@library.usyd.edu.au
13
Gwyndaf, Robin. "Culture in action : studies in Welsh ethnology." Thesis, Bangor University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369399.
Full text
14
Mehidi, Mohamed El Amine. "Coordination spatio-temporelle des regulateurs du reseau branche d’actine dans les structures motiles." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0385/document.
Full textAbstract:
La motilité cellulaire est un processus intégré essentiel à de nombreux phénomènes physiologiques tels que la formation du cône de croissance et la plasticité synaptique. Des dérégulations de la motilité cellulaire peuvent être à l’origine de la formation de métastases ou de pathologies neuropsychiatriques comme la schizophrénie et l'autisme. La compréhension des mécanismes régulant la migration cellulaire est donc un enjeu majeur. La motilité cellulaire repose sur la formation de diverses structures constituées de réseaux d’actine branchés telles que le lamellipode. La formation du lamellipode nécessite l’intervention de protéines régulatrices de l’actine telles que Rac1 et les complexes Wave et Arp2/3. Grâce à l’utilisation de suivi de protéine unique, nous avons pu comprendre comment la coordination spatio-temporelle de ces régulateurs contrôle la formation et la morphologie des lamellipodes de cellules migrantes. Nous avons ainsi découvert que l’activation et la localisation du complexe Wave étaient régulées de manière enzymatique mais également mécanique. Dans une première étude, nous avons montré que la RhoGTPase Rac1 active le complexe Wave spécifiquement à l’extrémité du lamellipode. Dans une seconde étude, nous avons révélé que la localisation du complexe Wave est régulée par la dynamique des filaments des réseaux branchés d’actine. Ces données soulignent l’importance du complexe Wave dans la formation du lamellipode et révèlent l’existence d’une régulation mécanique de la localisation du complexe WaveCell motility is an integrated process involved in critical phenomena such as axonal pathfinding and synaptic plasticity. Dysregulation of cell motility can induce metastasis and abnormal spine shapes observed in neuropsychiatric disorders like autism and schizophrenia. Therefore it is essential to understand how cell motility is regulated. Cell motility requires the formation of branched actin networks propelled by actin polymerization that lead to the formation of membrane protrusions such as the lamellipodium. Several actin regulatory proteins are involved in this process, such as Rac1 and the WAVE and ARP2/3 complexes. Using single protein tracking, we revealed key phenomena concerning the spatio-temporal regulation of lamellipodium formation by actin regulatory proteins. We found that the localization and activation of the WAVE complex was enzymatically regulated, but also mechanically. First, we showed that the Rac1 RhoGTPase activates the WAVE complex specifically at the tip of the lamellipodium. We also showed that WAVE complex localization is regulated by the dynamics of branched-network actin filaments. This study confirms the crucial role of the WAVE complex in lamellipodium formation and reveals the existence of a mechanical regulation of the localization of this complex in the cell
15
Basquin, Cyril. "Les facteurs spécifiques de l’endocytose indépendante de la clathrine suivie par les récepteurs de cytokines." Thesis, Paris 11, 2013. http://www.theses.fr/2013PA112148.
Full textAbstract:
L’endocytose est le processus qui permet l’entrée spécifique et active dans la cellule du milieu extracellulaire et des substances qu’il contient. Ces dernières années, plusieurs mécanismes d’endocytose ont été identifiés, mais seule la voie impliquant la clathrine a été bien caractérisée. Il a été montré que certains récepteurs de cytokines comme celui de l’interleukine-2 (IL-2) empruntent une voie d’endocytose indépendante de la clathrine. Précédemment, mon laboratoire a identifié huit facteurs impliqués dans cette voie d’entrée dont l’actine et la dynamine. Nous savons notamment que l’activation de la RhoGTPase Rac1 permet l’induction des kinases Pak1 et Pak2 régulant ainsi la cortactine, le recrutement de N-WASP et la polymérisation d’actine nécessaire à l’internalisation de l’IL-2R. Cependant, les facteurs en amont de cette cascade Rac-Pak étaient inconnus et le rôle du cytosquelette d’actine restait mal défini. Les travaux que j’ai effectué durant mon doctorat ont mis en évidence que la PI3K en interagissant avec l’IL-2R, permettait la production locale de PI(3,4,5)P3 qui induisait le recrutement de Vav2; un facteur conduisant à l’activation de Rac1. De plus, j’ai montré que Rac1 activé était ensuite recruté par la PI3K, permettant ainsi l’activation locale de la cascade Rac/Pak lors de l’entrée de l’IL-2R. Ces données, qui ont fait l’objet d’une publication, ont montré que la PI3K n’était pas seulement impliquée dans la signalisation de l’IL-2, mais également dans son endocytose. Par la suite, la réalisation d’un crible par ARNi portant sur l’étude du rôle de 324 protéines humaines lors de l’entrée de l’IL-2R, a permis l’identification de 65 nouveaux facteurs impliqués dans ce mécanisme. Parmi ces protéines, j’ai étudié plus particulièrement le rôle du complexe WAVE connu pour être induit à la membrane plasmique par Rac1 et la PI3K. J’ai confirmé l’implication de ce complexe lors de l’entrée de l’IL-2R et mis en évidence qu’il interagissait avec le récepteur. De plus, cette étude a montré que le complexe WAVE était impliqué précocement dans ce mécanisme, probablement en permettant le recrutement du récepteur aux pieds de protrusions membranaires que le complexe pourrait induire. Cette localisation spécifique du récepteur suggère ainsi un nouveau mécanisme de formation des vésicules d’endocytose dont le puits s’initierait à partir des invaginations existantes à la base des protrusions membranairesEndocytosis is a basic and essential process used by eukaryotic cells to internalize, actively and specifically, a wide range of molecules. To date, several endocytic routes have been characterized, but the only well studied pathway is clathrin-dependent. This study focuses on a poorly characterized mechanism, the clathrin-independent endocytosis, used by several cytokine receptors such as the interleukin 2 receptors (IL-2R). Previously, my lab identified 8 factors in this process, most of them are related to actin polymerization and dynamin. We now know that the activation of the RhoGTPase Rac1 is required to induce Paks that regulate cortactin, N-WASP recruitment and actin polymerization essential for IL-2R uptake. However, upstream factors involved in the Rac-Pak cascade were unknown and the actin cytoskeleton function poorly characterised. During my PhD, I showed that IL-2R and the phosphatidylinositol 3-kinase (PI3K) interact, leading to the local production of phosphatidylinositol (3,4,5)-triphosphate (PIP3) and the recruitment by this lipid of the RacGEF Vav2, an activator of Rac1. In addition, I showed that activated Rac1 was able to interact with PI3K allowing the local activation of the Rac-Pak cascade during IL-2R entry. These published data highlight the dual role of PI3K as a regulator of both IL-2R endocytosis and IL-2 signaling. In an attempt to identify new actors involved in the endocytosis of IL-2R, I then performed a small interfering RNA (siRNA) screening, targeting 324 proteins involved mainly in membrane deformation. From this screening we identified 65 proteins and among them we found the WAVE complex as a new factor implicated in IL-2R uptake. Interestingly, to be recruited and activated at the plasma membrane, the WAVE complex required Rac1 and PI3K, two proteins essentials during IL-2R entry. First, I confirmed the results obtained from the screening and found that IL-2R can interact with the WAVE complex. In addition, I observed an early involvement of this complex during IL-2R uptake, which could be needed for the localization of the receptor at the basis of plasma membrane protrusions. These results reveal a new model for the formation of endocytic vesicles: IL-2R is recruited at the basis of WAVE-induced membrane protrusions initiating the pit and vesicle
16
Yuwono, Nur. "The stability of revetment blockwork under wave action." Thesis, University of Strathclyde, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292072.
Full text
17
Segal, Joseph. "STANDING WAVES OF SPATIALLY DISCRETE FITZHUGH-NAGUMO EQUATIONS." Master's thesis, University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3511.
Full textAbstract:
We study a system of spatially discrete FitzHugh-Nagumo equations, which are nonlinear differential-difference equations on an infinite one-dimensional lattice. These equations are used as a model of impulse propagation in nerve cells. We employ McKean's caricature of the cubic as our nonlinearity, which allows us to reduce the nonlinear problem into a linear inhomogeneous problem. We find exact solutions for standing waves, which are steady states of the system. We derive formulas for all 1-pulse solutions. We determine the range of parameter values that allow for the existence of standing waves. We use numerical methods to demonstrate the stability of our solutions and to investigate the relationship between the existence of standing waves and propagation failure of traveling waves.M.S.
Department of Mathematics
Sciences
Mathematical Science MS
18
Shih, Robert Wing Kin. "Wave induced uplift pressures acting on a horizontal platform." Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47655.
Full text
19
Mort, Richard Brian. "The effects of wave action on long sea outfalls." Thesis, University of Liverpool, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.253414.
Full text
20
Tomlinson, Bruce Nicholas. "Erosion studies of mixed sand beds under the combined action of waves and currents." Thesis, University of Southampton, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239502.
Full text
21
De, Man Pierre. "Contrôle actif du rayonnement acoustique des plaques: une approche à faible autorité." Doctoral thesis, Universite Libre de Bruxelles, 2004. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/211180.
Full textAbstract:
L'objectif de cette thèse consiste en l'étude d'une stratégie de contrôle actif à faible autorité avec comme application le contrôle actif du rayonnement acoustique d'une plaque. Depuis l'essor du contrôle actif, son application aux problèmes acoustiques et vibracoustiques a été investiguée par de nombreux chercheurs, exploitant soit la théorie du contrôle optimal, soit des approches originales basées plus particulièrement sur la physique. Des notions spécifiques au contrôle vibroacoustique ont été développées comme, par exemple, les modes radiatifs pouvant caractériser le rayonnement acoustique d'une plaque d'une manière adaptée au contrôle. Le contrôle actif à faible autorité, pour lequel le Laboratoire de Structures Actives a développé une expertise dans le domaine de l'amortissement et du contrôle actif des vibrations, est une solution attractive par sa simplicité de mise en oeuvre. Le plus souvent implémenté sous la forme d'un contrôle décentralisé constitué de boucles indépendantes, le contrôle à faible autorité bénéficie de certaines garanties de stabilité et de robustesse.
Bien que notre stratégie de contrôle puisse s'appliquer à n'importe quel type de plaque, l'application considérée dans ce travail a été motivée par le contexte socio-économique actuel en rapport avec les nuisances acoustiques. Il était en effet intéressant d'évaluer la stratégie de contrôle pour le problème de la transmission acoustique d'un vitrage. La stratégie de contrôle se divise en deux étapes. Tout d'abord le développement d'un capteur unique destiné à fournir une mesure représentative du bruit rayonné par une plaque en basse fréquence. Deux capteurs de vitesse volumétrique (l'un discret, l'autre distribué) ont ainsi été développés et évalués expérimentalement.
Ensuite, une procédure d'optimisation de l'emplacement d'un ensemble d'actionneurs pilotés en parallèle est proposée. L'objectif de cette phase d'optimisation est de forcer la réponse fréquentielle du système à posséder les propriétés d'un système colocalisé. La stratégie de contrôle est ensuite évaluée sur deux structures expérimentales.
/ This thesis is concerned with a low authority active control strategy applied to the sound radiation control of a baffled plate. Since the development of active control ,numerous researchers have studied its application to acoustical or vibroacoustical problems using either the modern control theory or other methods based rather on the understanding of the physics of the problem. Vibroacoustical active control has lead to the definition of radiation modes allowing to describe the radiated sound of a plate in an appropriate manner for active control purposes.
Low autorithy control (LAC), for which the Active Structures Laboratory has gained an expertise for active vibration control applications is an interesting solution for its implementation simplicity. Most of the time it consists of several decentralized control loops, and benefits from guaranteed stability and robustness properties. Although our control strategy can be applied to any kind of plates, the application considered here has been motivated by the present socio-economical context related to noise annoyances. The active control strategy has been applied the problem of the sound transmission loss of glass plates (windows). This strategy is in two steps :first a volume velocity sensor is developed as to give a measure representative of the radiated sound at low frequencies.
Two sensors have been developed (one discrete and one distributed) and experimentally tested. Next, an optimisation strategy is proposed which allow to locate on the plate a set of several actuators driven in parallel. The goal of this optimisation task is to obtain an open-loop frequency response which behave like a collocated system. The control strategy is finally evaluated on two plate structures.
Doctorat en sciences appliquées
info:eu-repo/semantics/nonPublished
22
Monaco, Marina. "Wave action on shallow water and applications to coastal hazard." Doctoral thesis, Universita degli studi di Salerno, 2010. http://hdl.handle.net/10556/127.
Full textAbstract:
2008-2009The mechanics of wave breaking in shallow water has been a major research field for many years, and a very large number of published results are available. No attempt is made here to review the whole literature. Some interesting – if somewhat outdated - descriptions of waves breaking on beaches are presented by Peregrine (1983), Battjes (1988) or Liberatore-Petti (1992). In fact, the most important process in the near coast zone of the shoreline motion is wave breaking. Some waves break in shallow water, some of them break at the water’s edge and in other circumstances waves do not break at all (with steep beach slopes, incident waves with low steepness - or long waves). In general, breaking in deep water is rarer than breaking in shallow water. The latter is triggered by the bottom and is more predictable, although the simple question ‘where breaking starts’ is far from having a unique answer, even in controlled physical experiments. The breaker types are, generally, classified as spilling (where the water spills down the front face), plunging (with a jet emanating from the front crest), surging (characterized by a rise in water surface before the breaking) and collapsing (between plunging and surging). The fluid dynamics of non-breaking waves can be described using potential theory in most of the flow field except near the bottom and near the free surface, where vorticity develops and is confined to a boundary layer. As long as the details near the free surface (e.g. necessary for wind–wave interaction) and/or near the bottom (e.g. necessary for sediment transport analysis) are not of interest, the potential theory approach is sufficient. After breaking, ‘waves’ and ‘eddies’, essentially a potential component and a rotational component of the flow field, are intimately mixed. The surf and swash zones are characterized by the complete transformation of the organized motion of the incident, sea-swell, waves into motions of different types and scales, including small-scale (less than a wave period) turbulence, and large-scale (much greater than the wave period) mean flows [Battjes, 1988]. It is obvious that [Stive and Wind, 1982; Lin and Liu, 1998a; Svendsen et al., 2000; Svendsen, 2005] contributions from terms which have traditionally been neglected in the traditional assumptions of hydrostatic pressure, depth uniform velocity profile, and negligible turbulence, are important and must be taken into full account in surf zone hydrodynamics. Non Linear Shallow Water equations (‘800) and Boussinesq models [Peregrine, 1967] have intrinsic limitations and can only simulate wave breaking and its evolution by assuming on semi-empirical ad hoc assumptions and threshold values to represent wave dissipation. Moreover, these models lack the capability to determine spatial distribution of the turbulent kinetic energy, which is of great importance for sediment transport studies [Lin and Liu, 1998b]. Given all this, it was only natural that the Navier-Stokes solvers now widely tested and developed in other fields of fluid mechanics, with less restricted assumptions involved, no wave theory assumed beforehand, and the capability to simulate complex turbulent processes, should soon become one of the main approaches to describe nearshore processes. Numerical modeling of three-dimensional breaking waves is extremely difficult. Several challenging tasks must be overcome. First of all, one must be able to track accurately the free surface location during the wave breaking process so that the near surface dynamics is captured. Secondly, one must properly model the physics of turbulence production, transport and dissipation throughout the entire wave breaking process. Thirdly, one needs to overcome the huge demand in computational resources. There have been some successful two-dimensional results. For instance, more recent is the treatment of the free surface within such an Eulerian framework with the marker and cell (MAC) method [e.g., Johnson et al.1994] and the volume of fluid method (VOF) [e.g., Ng and Kot 1992, Lin and Liu, 1998a]. The most common approach for simulating breaking waves is presently the application of 2D-Reynolds Averaged Navier-Stokes (RANS) equations with a Volume of Fluid (VOF) surface computation and a turbulence closure model. Such an approach, while being often tested for many years by many various Authors (see for instance Bovolin et al, 2004) only reached full maturity with a fundamental paper by Lin and Liu (1998a). This line of research has been going on successfully for many years to the point that reliable procedures now exist to simulate wave breaking, run up and interaction with structures. The next obvious step. i.e. the application of Large Eddy Simulation (LES) models has so far not been equally successful [Watanabe and Saeki, 1999; Christensen and Deigaard, 2001; Lubin et al, 2006; Christensen, 2006]. LES models necessarily require a fully three-dimensional solution and three-dimensional turbulence effects might be indeed important in the prediction of velocity within the surf zone, especially in the case of plunging breaker [Watanabe and Saeki, 1999]. Such models certainly are a promising tool in the study of surf zone hydrodynamics; however, the LES approach requires much finer grid resolution and a lager computational domain than the RANS approach, resulting in the very high demand on computational resource, at least for the time being. They are however a definite perspective for the future. Smoothed Particle Hydrodynamics (SPH) method, adapted from astrophysics into a number of fields, is a relatively new method for examining the propagation of highly nonlinear and breaking waves [Monaghan et al, 1977; Dalrymple et al, 2005; Viccione et al, 2007-2008]. SPH offers a variety of advantages for fluid modeling, particularly those with a free surface. The Lagrangian method is meshfree; the equivalents of mesh points are the fluid particles moving with the flow. The free surface requires no special approaches, such as the volume-of-fluid method or a Lagrangian surface tracking. Furthermore, the method can treat rotational flows with vorticity and turbulence. SPH is a technique based on computing the trajectories of particles of fluid, which interact according to the Navier–Stokes equations. Each of such particles carries scalar information, density, pressure, velocity components, etc. The work presented here is therefore mainly based on the application of the Eulerian 2-dimensional RANS/VOF equations to the study of surf zone processes on a beach. In particular the work is aimed at demonstrating the capability of RANS/VOF to improve the current modeling of surf zone hydrodynamics on sloping natural beach and in front of shallow water coastal structures , comparing its performance with laboratory observations and other theoretical and numerical results. [edited by author]
VIII n.s.
23
Abusbeaa, Abubaker Mohamed. "Maximum scour around cylinders induced by wave and current action." Thesis, University of British Columbia, 1986. http://hdl.handle.net/2429/26213.
Full textAbstract:
The maximum possible scour around cylindrical structures under the action of combined wave and current was investigated in this study. A review of the literature showed that there are no adequate theories or methods for predicting maximum possible scour depths around structures under the action of wave plus current. Development of such a scour prediction is of considerable economic importance for the design of offshore structures. The study started with experimental tests of the scour around cylindrical structures and a comparison was made between scour under steady currents alone, waves alone and combined wave and current conditions. Existing theories for scour and flow velocities under waves alone and currents alone were analyzed and sets of experiments were performed for the three flow conditions of waves alone, currents and waves plus currents using three sediment size ranges and five cylinder sizes. The dependence of maximum scour on both cylinder size and sediment size for the three flow cases was studied and graphical relationships were established. The maximum scour under combined wave and current at threshold conditions in the approaching flow was investigated in detail and the dependence of maximum scour on this critical threshold flow criterion was shown. The maximum scour depth can be roughly estimated using this study provided that the flow conditions, sediment properties and structure dimensions are defined.Applied Science, Faculty of
Civil Engineering, Department of
Graduate
24
Rose, Heather. "Issues in education : math curriculum and earnings, test score gaps, and affirmative action /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2001. http://wwwlib.umi.com/cr/ucsd/fullcit?p3015848.
Full text
25
Somero, John Ryan. "Structure and Persistence of Surface Ship Wakes." Thesis, Virginia Tech, 2021. http://hdl.handle.net/10919/101989.
Full textAbstract:
It has long been known that ship wakes are observable by synthetic aperture radar. However,
incomplete physical understanding has prevented the development of simulation tools
that can predict both the structure and persistence of wakes in the ocean environment.
It is the focus of this work to develop an end-to-end multi-scale modeling-and-simulation
methodology that captures the known physics between the source of disturbance and the
sensor. This includes turbulent hydrodynamics, free-surface effects, environmental forcing
through Langmuir-type circulations, generation of surface currents and redistribution of
surface-active substances, surface-roughness modification, and simulation of the signature
generated by reflection and scattering of electromagnetic waves from the ocean surface. The
end-to-end methodology is based upon several customized computational fluid dynamics
solvers and empirical models which are linked together. The unsteady Reynolds-averaged
Navier-Stokes equations, including models for the Craik-Leibovich vortex force and near surface
Reynolds-stress anisotropy, are solved at full-scale Reynolds and Froude numbers on
domains that extend tens of kilometers behind the ship. A parametric study is undertaken to
explore the effects of ship heading, ship propulsion, ocean-wave amplitude and wavelength,
and the relative importance of Langmuir-type circulations vs. near-surface Reynolds-stress
anisotropy on the generation of surface currents that are transverse to the wake centerline.
Due to the vortex force, the structure of the persistent wake is shown to be a function of
the relative angle between the ambient long-wavelength swell and the ship heading. Ships
operating in head seas observe 1-3 streaks, while ships operating in following seas observe
2 symmetric streaks. Ships operating in calm seas generate similar wakes to those in following
seas, but with reduced wake width and persistence. In addition to the structure of
the persistent wake, the far wake is shown to be dominated by ship-induced turbulence and
surface-current gradients generating a wide center wake. The redistribution of surface-active
substances by surface currents is simulated using a scalar-transport model on the ocean surface.
Simulation of surface-roughness modification is accomplished by solving a wave-action balance
model which accounts for the relative change in the ambient wave-spectrum by the
surface currents and the damping-effects of surface-active substances and turbulence. Simulated
returns from synthetic aperture radar are generated with two methods implemented.
The first method generates a perfect SAR image where the instrument and platform based
errors are neglected, but the impact of a randomized ocean field on the radar cross section
is considered. The second method simulates the full SAR process including signal detection
and processing. Comparisons are made to full-scale field experiments with good agreement
between the structure of the persistent wake and observed SAR imagery.1
It has long been known that ship wakes are observable by synthetic aperture radar. However, incomplete physical understanding has prevented the development of simulation tools that can predict both the structure and persistence of wakes in the ocean environment, which is critical to understanding both the design and operation of maritime remote sensors as well as providing tactically relevant operational guidance and awareness of the maritime domain. It is the focus of this work to develop an end-to-end multi-scale modeling-and simulation methodology that captures the known physics between the source of disturbance and the sensor. This includes turbulent hydrodynamics, free-surface effects, environmental forcing, generation of surface currents and redistribution of surface-active substances, surface-roughness modification, and simulation of the signature from the ocean surface. The end-to-end methodology is based upon several customized computational fluid dynamics solvers and empirical models. The unsteady Reynolds-averaged Navier-Stokes equations, including models to account for environmental effects and near-surface turbulence, are solved at full-scale on domains that extend tens of kilometers behind the ship. A parametric study is undertaken to explore the effects of ship heading, ship propulsion, ocean-wave amplitude and wavelength, and the relative importance of environmental forcing vs. near-surface turbulence on the generation of surface currents that are transverse to the wake centerline. Due to the environmental forcing, the structure of the persistent wake is shown to be a function of the relative angle between the ambient long-wavelength swell and the ship heading. Ships operating in head seas observe 1-3 streaks, while ships operating in following seas observe 2 symmetric streaks. Ships operating in calm seas generate similar wakes to those in following seas, but with reduced wake width and persistence. In addition to the structure of the persistent wake, the far wake is shown to be dominated by ship-induced turbulence and surface-current gradients generating a wide center wake. The redistribution of surface films by surface currents is simulated using a scalar-transport model on the ocean surface. Simulation of surface-roughness modification is accomplished by solving a wave-action-balance model which accounts for the relative change in the ambient surface profile by the surface currents and the damping-effects of surface-active substances and turbulence. Simulated returns from synthetic aperture radar are generated with two methods implemented. The first method generates a perfect SAR image where the instrument and platform based errors are neglected, but the impact of a randomized ocean field on the radar cross section is considered. The second method simulates the full SAR process including signal detection and processing. Comparisons are made to full-scale field experiments with good agreement between the structure of the persistent wake and observed SAR imagery.
26
Koble, Sean. "Acting the Role of Gods: Shinoda Masahiro's Cinematic Confrontations with the Absolute Image." Thesis, University of Oregon, 2014. http://hdl.handle.net/1794/18363.
Full textAbstract:
The narrative structure and formal style of the director Shinoda Masahiro's films reveal his ethical objective to encourage his viewer to engage with works of cinematic representation as the creative products of human agency that they are. Within his period films, Shinoda hopes to stimulate recognition of cinema's genealogical inheritance and reproduction of the absolutist propositions underlying traditional Japanese cultural forms. He posits that these have redirected essential human drives into masochistic self-effacement in tribute to a divine ideal imaged in the Imperial polity.
By disrupting the illusion of cinematic realism which simply serves to reinforce Japanese culture's existent intertextual networks, Shinoda seeks to reground cultural expressions in their material and human origins. This acts as the first step to imagining a Japanese subject outside of the limited definitions posed by nostalgic absolutism and its reactionary antithesis in the equally self-destructive mode of global capitalism.
27
Vithana, H. P. V. "The effect of stone protrusion on the incipient motion of rock armour under the action of regular waves." Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1388034/.
Full textAbstract:
Rock armour is often used to protect the seabed around offshore structures like oil platforms, wind farms, undersea cables etc. This thesis describes a laboratory study to investigate the effect of stone protrusion on threshold movement of rock armour under regular waves. Tests were carried out to investigate the incipient motion of light weight test spheres of differing density and diameter in the range, d = 9.5mm-31.8mm, resting on a rough bed of 19mm glass marbles in a wave flume. In past studies, researchers have used turbulence measurements, shear plate apparatus, hot film techniques etc., to quantify the bed shear stress. In the present study, shear stress was deduced from direct measurements of pressure on the surface of a 50mm spherical bed element. Advance flow measurement techniques such as Laser Doppler Velocimetry (LDV) and Volumetric Three-component Velocimetry (V3V) were also carried out for flow measurement and visualisation. It was found that the Shields critical shear stress increased when stone protrusion was gradually reduced following an exponential relationship. For each wave period a different Shields shear stress versus protrusion curve was obtained. When the wave period increased the curve shifted towards that for currents previously obtained by Fenton & Abbot (1977) and Chin & Chiew (1993) suggesting that for longer wave periods under the field conditions where high Reynolds/KC number flows exist, the curve obtained for currents is applicable. The method of rock armour placement crucially influences the stability of a bed protection. Significant reduction in bed damage can be achieved by placing stones to an optimum protrusion level of 0.2d above mean bed level. A model bed protection made of crushed natural rocks (anthracite) showed that the damage to a “levelled” bed is 50% less than in a randomly placed bed. This is because the fraction of the exposed stones increases when rocks are dumped from a barge or a side stone dumping vessel as opposed to reduced exposure observed in a levelled bed.
28
Brembu, Tore. "Genetic, molecular and functional studies of RAC GTPases and the WAVE-like regulatory protein complex in Arabidopsis thaliana." Doctoral thesis, Norwegian University of Science and Technology, Faculty of Natural Sciences and Technology, 2006. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-741.
Full textAbstract:
Small GTP-binding proteins are molecular switches that serve as important regulators of numerous cellular processes. In animal and plant cells, the Rho family of small GTPases participate in e.g. organisation of the actin cytoskeleton, production of reactive oxygen species through the NADPH oxidase complex, regulation of gene expression. The three most extensively studied subgroups of the Rho GTPase family are Cdc42, Rho and Rac. One of the mechanisms by which animal Rac and Cdc42 GTPases regulate actin filament organisation is through activation of the ARP2/3 complex, a multimeric protein complex which induces branching and nucleation/elongation/polymerisation of actin filaments. Activation of the ARP2/3 complex by Rac and Cdc42 is mediated through the proteins WAVE and WASP, respectively.
In a search for Ras-like GTPases in Arabidopsis, we identified a family of genes with similarity to Rac GTPases. Screens of cDNA and genomic libraries resulted in the finding of 11 genes named ARACs/AtRACs. Genes encoding Rho, Cdc42 or Ras homologues were not identified. Expression analysis of AtRAC1 to AtRAC5 indicated that AtRAC1, AtRAC3, AtRAC4 and AtRAC5 are expressed in all parts of the plant, whereas AtRAC2 is preferentially expressed in root, hypocotyl and stem.
The AtRAC gene family can be divided into two main groups based on sequence similarity, gene structure and post-translational modification. AtRAC group II genes contain an additional exon, caused by the insertion of an intron which disrupts the C-terminal geranylgeranylation motif. Instead, group II AtRACs contain a putative motif for palmitoylation. Phylogenetic analyses indicated that the division of plant RACs into group I and group II occurred before the split of monocotyledonous and dicotyledonous plants. Analyses of the genes neighbouring AtRAC genes revealed that several of the plant RAC genes have been created through duplications.
The restricted/tissue-specific expression pattern of AtRAC2 led us to do a more detailed expression analysis of this gene. A 1.3 kb fragment of the upstream (regulatory) sequence of AtRAC2 directed expression of GUS or GFP to developing primary xylem in root, hypocotyl, leaves and stem. In root tips, the onset GUS staining or GFP fluorescence regulated by the AtRAC2 promoter slighty preceded the appearance of secondary cell walls. In stems, GUS staining coincided with thickening of xylem cell walls. Transgenic plants expressing constitutively active AtRAC2 displayed defects in the polar growth of leaf epidermal cells, indicating that AtRAC2 may be able to regulate the actin cytoskeleton. Surprisingly, an AtRAC2 T-DNA insertion mutant did not show any observable phenotypes. GFP fusion proteins of wild type and constitutively active AtRAC2 were both localised to the plasma membrane. The data suggest that AtRAC2 is involved in development of xylem vessels, likely through regulation of the actin cytoskeleton or NADPH oxidase.
The role of RAC GTPases in regulation of the actin cytoskeleton in plants is well documented. However, although the ARP2/3 complex had been identified in plants/Arabidopsis, the mechanisms regulating this complex were unknown. Through database searches, we identified three Arabidopsis genes, AtBRK1, AtNAP and AtPIR, which encoded proteins with similarity to subunits of a protein complex shown to regulate the activity of WAVE1 in mammalian cells. T-DNA inactivation mutants of AtNAP and AtPIR displayed morphological defects on epidermal cells undergoing polar expansion, such as trichomes and leaf pavement cells. The phenotypes were similar to those observed for ARP2/3 complex mutants, suggesting that AtNAP and AtPIR act in the same pathway as the ARP2/3 complex in plants. The actin cytoskeleton in atnap and atpir mutants was less branched than in wild type plants; instead, actin filaments aggregated in thick actin bundles.
Finally, we have recently discovered a small gene family encoding putative WAVE homologues. In mammalian cells, Rac activates WAVE1 through binding to PIR121 or Sra1 (the mammalian homologues of AtPIR). The discovery of a putative WAVE regulatory complex as well as putative WAVE homologues in Arabidopsis suggests that plant RAC GTPases regulate organisation of the actin cytoskeleton during polar growth at least partly through the ARP2/3 complex, using an evolutionarily conserved mechanism.
29
Wang, Wei. "Manipulation of Lamb waves with elastic metamaterials." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS414.
Full textAbstract:
Nous développons des métamatériaux élastiques à piliers pour manipuler les ondes de Lamb. Dans un premier temps, les propriétés négatives associées aux résonances de flexion, de compression et de torsion dans deux structures constituées de piliers sur un seul côté d’une membrane sont examinées. Nous décrivons deux mécanismes différents des propriétés de double négativité. Le potentiel de ces structures pour la réfraction négative et le cloaking acoustique est démontré. Deuxièmement, nous présentons le transport protégé topologiquement des ondes de Lamb par analogie avec les effets Hall quantiques de spin et de vallée. En réorganisant les structures précédentes en un réseau en nid d'abeille, un cône de Dirac simple et un cône de Dirac double sont introduits. Nous discutons de l’apparition d’états de bord protégés topologiquement par une vallée dans une structure à piliers double face asymétrique. La propagation unidirectionnelle des états de bord est étudiée. De plus, nous considérons un système double face symétrique. Les états de bord protégés topologiquement sur le pseudospin et sur le pseudospin-vallée sont démontrés. Troisièmement, nous proposons une approche pour contrôler activement la transmission de l’onde de Lamb antisymétrique se propageant à travers une ligne infinie de piliers. Deux situations différentes avec les résonances de flexion et de compression respectivement séparées ou superposées sont étudiées. Une force de traction externe et une pression sont appliquées sur les piliers, ce qui permet de les coupler avec les vibrations de flexion et de compression. La transmission est étudiée en fonction de l’amplitude et de la phase relative des sources externesWe develop elastic pillared metamaterials to manipulate Lamb waves. Firstly, the negative properties associated with bending, compression and torsion resonances in two structures consisting of pillars on one side of a thin plate are examined. We describe in details two different mechanisms at the origin of doubly negative property. The potential of these structures for negative refraction of Lamb waves and acoustic cloaking is demonstrated numerically. Secondly, we present the topologically protected transport of Lamb waves by analogy with quantum spin and valley quantum Hall effects. By rearranging the previous structures into a honeycomb network, a single Dirac cone and a double Dirac cone are introduced. We discuss the appearance of topologically valley-protected edge states in an asymmetrical double-sided pillar structure. The unidirectional propagation of edge states on different domain walls is studied. In addition, we consider a symmetrical double-sided system allowing the separation of the symmetric and antisymmetric modes. Combined edge states protected topologically by pseudospin and pseudospin-valley degree of freedom are demonstrated. Third, we propose an approach to actively control the transmission of the antisymmetric Lamb wave propagating through an infinite line of pillars. Two different situations with bending and compression resonances respectively separated or superimposed are studied. External tensile force and pressure are applied to the pillars, which allows them to couple with the bending and compressive vibrations. The transmission is studied as a function of the amplitude and the relative phase of the external sources
30
Bates, Colin Robert. "Macroalgae as microhabitat : seaweed traits and wave action as predictors of invertebrate epifaunal diversity." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/31214.
Full textAbstract:
In many coastal environments, anthropogenic stressors yield changes in seaweed biodiversity. Here, I describe three studies addressing how such floristic changes might affect provision of habitat by seaweeds for small mobile invertebrate epifauna. In chapter 2, I used observational and manipulative (transplant) experiments to test how changes in seaweed biodiversity influenced biodiversity of associated invertebrates. I found that invertebrate epifaunal richness and abundance were not affected by changes in seaweed biodiversity. Invertebrate assemblage structure was, in most cases, not influenced by changes in seaweed composition; only when algal assemblages were composed of monocultures of species with 'foliose' morphologies did I observe a change in invertebrate assemblage structure. Correlations between algal functional composition and invertebrate assemblage structure were observed, but not between algal species composition and invertebrate assemblage structure. These results suggest that changes in seaweed biodiversity will have implications for invertebrate epifauna only under specific scenarios of algal change. In Chapter 3, I tested the performance of host taxonomic relatedness and functional (i.e. morphological) group affiliation as predictors of associated invertebrate epifauna. Neither general framework performed well; invertebrate assemblages found on congeneric host species were as similar as those found on hosts classified in different kingdoms, and taxon richness and abundance of invertebrates varied substantially within seaweed functional groups. Species identity was identified as a key predictor of the performance of seaweeds as hosts for invertebrate epifauna. In chapter 4, I examined the context dependence of these host identity effects by testing how host morphological complexity and maximum wave velocity interacted to determine local invertebrate diversity. Three types of host species were identified: (a) morphologically `simple' thalli that were minimally utilized as habitat under any of the tested wave regimes, (b) thalli that were coarsely branched and were utilized by invertebrates under relatively benign wave conditions but became less utilized under higher wave action, and (c) 'complex' algal hosts that supported diverse invertebrate assemblages under all tested wave conditions. Together, these studies support the view that invertebrates that use seaweeds as habitat are host-generalists, and therefore consequences for invertebrates of changes in seaweed biodiversity are likely to be minimal.Science, Faculty of
Botany, Department of
Graduate
31
Jämte, Jan. "Antirasismens många ansikten." Doctoral thesis, Umeå universitet, Statsvetenskapliga institutionen, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-81637.
Full textAbstract:
This thesis contributes to the knowledge and understanding of the anti-racist movement in Sweden by describing its development from the early 1930s to the mid-2000s. It pays special attention to mapping and analyzing the ideas that have motivated anti-racist activities and their importance for mobilizing support and movement activity. Using the theoretical toolbox of the framing perspective, the strengths, weaknesses, possibilities and limitations of different anti-racist frames are discussed, as are the consequences of different types of intra-movement frame disputes and frame contests with external actors. By tracing and describing the historical development of the movement and different types of anti-racist frames, I create a typology of different anti-racist actors - what I call pragmatic, radical and moderate anti-racists. The activities of these types of actors are described throughout the long and winding history of the movement. In the thesis, the movement’s history is divided into four waves of protest. The movement’s roots stretch back to the 1930s and the struggle against Fascism and Nazism. It continues during the 1960s and onwards with the anti-apartheid movement, the 1980s mass mobilizations against domestic racist groups and the intensified struggles of the last decades against racist extremism, right-wing populism and various aspects of structural racism. Based on the typology, three cases are selected for further scrutiny. Pragmatic anti-racism is studied through the activities of Stoppa rasismen (Stop racism) in the 1980s, radical anti-racism through Antifascistisk aktion (Antifascist action, also known as AFA) during the 1990s and moderate anti-racism through Samling mot rasism och diskriminering (Gathering against racism and discrimination) at the turn of the millennium. By gaining access to extensive empirical material I have been able to follow each case from its first steps to its downfall. The material has been gathered from a variety of sources using different qualitative techniques. I have conducted semi-structured interviews with activists and analyzed protocols, pamphlets, journals, internal bulletins, mails, posters, speeches, web pages that have been disbanded, pictures, films and books. The analysis shows that the different types of actors face different challenges, and have different strengths and weaknesses when it comes to mobilizing consensus and fostering participation. However, the three actors have also faced common challenges when trying to mobilize against racism given the national context, the self-image of Sweden as a tolerant, open and egalitarian country and the dominant views of racism, which taken together has turned racism into a serious but fairly marginal problem. The analysis also shows the effects of frame disputes and frame contests with regard to diagnostic, prognostic and motivational aspects of framing. At times the dividing lines have led to a broadening of the movement and its work, creating a wide mobilization potential and a strong multitudinous movement. During other periods the differences have contributed to long and profound conflicts that have drained the organizations and activists of time, resources and energy. Instead of focusing on combating their opponents, the anti-racist groups have been engulfed in internal strife, which has severely fragmented, divided and weakened the movement and hindered mobilization – contributing to turning the movement into a dispersed “milieu” by the mid-2000s. The thesis concludes with a chapter discussing how the empirical applicability of the framing perspective can be improved.
32
Sahin, Hatice Bahar. "Drosophila fragile X mental retardation protein and WAVE/SCAR complex interaction, its role in synapse growth and actin modifying pathways." Strasbourg, 2009. http://www.theses.fr/2009STRA6260.
Full textAbstract:
Le syndrome de l’X Fragile est la cause héréditaire la plus commune des retards mentaux qui touche environ 1 sur 4000 garçons et 1 sur 8000 femmes. Les patients ont en moyenne un IQ inférieur à 75, en raison de défauts de transmission et de plasticité neuronale. Ce syndrome est causé par la perte de fonction de la protéine « Fragile X Mental Retardation Protein » (FMRP) via des mécanismes mal connus. Comprendre le rôle de FMRP dans la plasticité neuronale est très important pour traiter cette maladies. Cependant, étant donnée la difficulté d’étudier la protéine chez les humains pour des raisons éthiques, la maladie a été explorée en plusieurs aspects sur des modèles animaux simples, tels que Drosophila melanogaster. Ceci permet d’utiliser des approches génétiques, de biologie cellulaire et moléculaire et électrophysiologiques. La jonction neuromusculaire de la drosophile (JNM) représente une structure très accessible et un modèle classique de plasticité neuronale. Les animaux mutants pour la protéine FMRP, connue comme régulatrice de la traduction, ont des JNM très ramifiées par rapport aux animaux sauvages. Ce phénotype ressemble beaucoup aux longues et immatures épines dendritiques des patients atteints du syndrome de l'X fragile. Ainsi, le phénotype basique de la carence en FMRP peut être modélisé avec la JNM de la drosophile. Plusieurs études soulignent le rôle du remodelage du cytosquelette d'actine dans le développement des axones et dans la formation des synapses. Le complexe WAVE est connu pour réguler le complexe actin nucleator Arp2/3 et favorise ainsi le remodelage du cytosquelette. Deux événements cruciaux sont donc nécessaires pour le développement et la modulation de la fonction de JNM: remodelage du cytosquelette d'actine et la synthèse des protéines locales. De plus, les données acquises au laboratoire suggèrent une interférence entre ces deux processus. L’orthologue de FMRP chez la drosophile (dFMR1) representerait donc un pont, en interagissant directement avec le complexe WAVE/SCAR, qui induit le remodelage du cytosquelette d'actine, et avec des ARNm, qui contrôle la traduction locale. A l'intérieur du complexe, la protéine WAVE interagit directement avec HSPC300. Dans ma première année de thèse, j'ai participé à la caractérisation de HSPC300, la plus petite sous-unité du complexe. Nous avons déterminé le rôle de HSPC300 in vivo, caractérisé HSPC300 chez la drosophile et définir son rôle dans la connectivité neuronale. HSPC300 est une protéine de 8 KD hautement enrichie dans le système nerveux, comme observé par un anticorps produit dans la maison. En générant des mutants HSPC300 perte et gain de fonction, nous avons observé que cette petite protéine est essentielle pour la stabilité du complexe WAVE et pour la morphogenèse de JNM. La perte de HSPC300 entraîne des graves défauts des axones et des JNM. Ces défauts sont sauvés en exprimant spécifiquement HSPC300 dans le tissu neural. Ces données impliquent HSPC300 comme un élément indispensable du complexe WAVE, et une protéine cruciale pour le développement du système nerveux (Qurashi et al. 2007). Nous avons précédemment montré que dFMR1 interagit biochimiquement avec CYFIP, un autre membre du complexe WAVE, et on a constaté que les deux protéines affectent la croissance JNM dans des sens opposés. DFMR1 supprime la croissance synaptique alors que CYFIP est nécessaire pour la croissance des synapses. La perte de dFMR1 induit une exagération de la ramification et de la croissance, tandis que la perte de CYFIP donne lieu à des synapses courtes mais extrêmement greffés. En outre, des expériences de dosage ont prouvé que dFMR1 et CYFIP agissent ensemble pour le contrôle de la croissance de JNM et travaillent de façon antagoniste. Durant ma deuxième année, j'ai réalisé un projet en collaboration avec les Pr. Zhang (Chine) et Hassan (VIB, Belgique) et visant à cartographier les régions d’interaction. Nous avons généré des mouches portant une mutation ponctuelle intragénique de dFMR1 obtenu par mutagenèse à l’EMS. Un crible par double hybride montre que des mutations intragéniques spécifiques empêchent FMRP d'interagir avec CYFIP. Nous avons ainsi montré que l’extrémité N-terminale de FMRP est essentielle pour l'interaction avec CYFIP. J'ai analysé le phénotype de JNM en utilisant dix mutants intragéniques dFMR1 et j’ai défini in vivo le domaine requis pour l’interaction FMRP-CYFIP. J'ai montré que les mutants dFMR1 qui maintiennent l'interaction biochimique avec CYFIP, maintiennent aussi l'interaction génétique; par conséquent, la surexpression de CYFIP sauve la surexpression de ces formes de dFMR1 mutantes. Chez les mouches porteuses d'une mutation qui abolit l’interaction biochimique dFMR1-CYFIP, la surexpression de CYFIP ne réprime plus le phénotype de gain de la fonction dFMR1. La co-surexpression crée un phénotype d’une croissance exagérée de JNM, qui n'est pas obtenu par un simple CYFIP ou dFMR1 surexpression. Toutes ces données prouvent in vivo que dFMR1 interagit avec CYFIP par l'intermédiaire de l’extrémité N-terminale de la protéine dFMR1. Leur interaction a un rôle important pour un contrôle précis de la croissance synaptique et pour le remodelage du cytosquelette d'actine. Cette étude est publiée dans le Journal of Neuroscience en Mars 2008 (Reeve et al. 2008). Durant ma troisième année de doctorat, j'ai étudié le rôle de CYFIP dans le remodelage du cytosquelette d'actine chez les photorécepteurs de la drosophile. En utilisant le système binaire UAS/Gal4 nous avons obtenu des mutants conditionnels CYFIP, temps et tissu spécifiques. Nous avons révélé le rôle de CYFIP dans des cellules précises: les cellules photoréceptrices et les cellules pigmentaires. Nous avons également révélé la conséquence directe du défaut de nucléation de l'actine qui est observée dans les jonctions cellule-cellule (Galy et al, in prep). Plusieurs groupes ont suggéré que FMRP a une activité comme répresseur traductionnel. Même si le mode de cette activité est encore un mystère, certains chercheurs ont fourni des preuves montrant que FMRP interagit avec plusieurs composants du complexe RISC. Au cours de ma quatrième année de thèse, j'ai étudié l'interaction FMRP avec RISC en collaboration avec le Pr Bozzetti, en Italie (Specchia et al, in prep). Dans tous les projets auxquels j'ai participé jusqu'à présent, je vise à faire la lumière sur les voies FMRP et WAVE. Nous avions l'intention de déchiffrer les voies contrôlant le remodelage du cytosquelette d'actine et la synthèse des protéines locales dans JNMs chez la mouche. Dans la présente thèse, tous les résultats sont discutés en détailFragile X syndrome is the most common inherited cause of mental retardation affecting approximately 1 in 4000 males and 1 in 7000 females. Average IQ score of the patients is under 75 as a result of neural wiring and synaptic plasticity defects due to loss of functional Fragile X Mental Retardation Protein (FMRP). FMRP is an RNA binding protein and a translational regulator highly abundant in the nervous system. We intend to explore underlying mechanisms of these defects using Drosophila (fruit fly) model organism. Several studies point out the role of actin cytoskeleton remodeling in synapse architecture and function. WAVE (/SCAR) complex stimulates the Arp2/3 complex actin nucleator and thereby promote cytoskeleton remodeling. Current data suggest that the crosstalk between actin cytoskeleton remodeling and local protein synthesis is essential for development and modulation of synapses. During my thesis, I have focused onto this topic and have the tackled three aspects of it: Characterization of the A) WAVE complex and its role in synaptic plasticity, B) the interaction between FMRP and WAVE complex, C) the actin cytoskeleton remodeling during morphogenesis. WAVE protein directly interacts with HSPC300, the smallest subunit of WAVE complex. Using targeted expression we characterize Drosophila HSPC300 and define its role in neural wiring. HSPC300 is highly enriched in the nervous system. Its mutation causes severe axonal/synaptic defects that are rescued by specific HSPC300 expression in the neural tissue. We conclude HSPC300 is an indispensable component of WAVE complex and an essential protein for nervous system development. We have previously shown that FMRP biochemically and genetically interacts with CYFIP, another member of the WAVE complex. To further characterize these interactions FMRP point mutations were generated in collaboration with two different labs. Particular mutants lose CYFIP binding. Using the intragenic mutants we point crucial FMRP residues for CYFIP interaction in vivo. FMRP is a negative regulator of neural growth. Here we describe nature of the FMRP-CYFIP genetic interaction in the context of neuromuscular synapses. We further assess CYFIP role on actin cytoskeleton in neatly organized fly eye and mostly actin-based photoreceptors. Making use of Drosophila genetics we define the spatiotemporal requirement of CYFIP for nervous system development. In all the projects I have been involved so far; I aimed at shedding light on FMRP and WAVE complex interaction. We intend to decipher these proteins and how their interactions regulate actin cytoskeleton remodeling, local protein synthesis and consequently neural connectivity using fly nervous system. I discuss these issues in the presented thesis
33
Beaulieu, Steeve. "Étude et mise au point d'un filtre actif d'harmoniques en vue d'améliorer la qualité de l'alimentation électrique /." Thèse, Chicoutimi : Université du Québec à Chicoutimi, 2007. http://theses.uqac.ca.
Full textAbstract:
Thèse (M.Eng.) -- Université du Québec à Chicoutimi, 2007.La p. de t. porte en outre: Mémoire présenté comme exigence partielle de la maîtrise en ingénierie. CaQCU Bibliogr.: f. [121]-124. Document électronique également accessible en format PDF. CaQCU
34
McWilliam, S. "Response statistics under the action of first and second order wave forces and wind gust loading." Thesis, University of Southampton, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240898.
Full text
35
Wlodarczyk, Tomasz. "STABILITY AND PRESERVATION PROPERTIES OF MULTISYMPLECTIC INTEGRATORS." Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3510.
Full textAbstract:
This dissertation presents results of the study on symplectic and multisymplectic numerical methods for solving linear and nonlinear Hamiltonian wave equations. The emphasis is put on the second order space and time discretizations of the linear wave, the Klein-Gordon and the sine-Gordon equations. For those equations we develop two multisymplectic (MS) integrators and compare their performance to other popular symplectic and non-symplectic numerical methods. Tools used in the linear analysis are related to the Fourier transform and consist of the dispersion relationship and the power spectrum of the numerical solution. Nonlinear analysis, in turn, is closely connected to the temporal evolution of the total energy (Hamiltonian) and can be viewed from the topological perspective as preservation of the phase space structures. Using both linear and nonlinear diagnostics we find qualitative differences between MS and non-MS methods. The first difference can be noted in simulations of the linear wave equation solved for broad spectrum Gaussian initial data. Initial wave profiles of this type immediately split into an oscillatory wave-train with the high modes traveling faster (MS schemes), or slower (non-MS methods), than the analytic group velocity. This result is confirmed by an analysis of the dispersion relationship, which also indicates improved qualitative agreement of the dispersive curves for MS methods over non-MS ones. Moreover, observations of the convergence patterns in the wave profile obtained for the sine-Gordon equation for the initial data corresponding to the double-pole soliton and the temporal evolution of the Hamiltonian functional computed for solutions obtained from different discretizations suggest a change of the geometry of the phase space. Finally, we present some theoretical considerations concerning wave action. Lagrangian formulation of linear partial differential equations (PDEs) with slowly varying solutions is capable of linking the wave action conservation law with the dispersion relationship thus suggesting the possibility to extend this connection to multisymplectic PDEs.Ph.D.
Department of Mathematics
Sciences
Mathematics PhD
36
Antecol, Heather. "Gender differentials in labor market outcomes /." *McMaster only, 1998.
Find full text
37
Gilbert, D. M. "Class, community and collective action : the social development of mining villages in South Wales and Nottinghamshire before 1926." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332968.
Full text
38
Goldberg, Samuel. "Gender, Insanity and Moral Obligation: Widows and the Action for Testamentary Incapacity in Late-Colonial New South Wales." Thesis, Department of History, 2021. https://hdl.handle.net/2123/24915.
Full textAbstract:
The enactment of a Testator’s Family Maintenance Act in 1916 is rightly remembered as a signature achievement of New South Wales’ early feminists, providing protection against the destitution that a cruel will could inflict upon a testator’s family. Yet in the decades before its passage, a challenge to a husband’s testamentary capacity offered an alternative mechanism by which a widow could challenge a will. This thesis explores the stories of the widows who braved the action for testamentary incapacity, in order to recover its social and cultural significance. It identifies the courtroom as a site of dense cultural discourse, in which dominant tropes of gender, insanity and moral obligation structured the court’s consideration of a widow’s claim. It shows that widows played upon these tropes, deploying them in narratives of virtue and transgression to win substantive relief. The action for testamentary capacity thus offered hope for disinherited widows seeking to break the financial shackles posthumously imposed by their husbands. However, in demanding the sublimation of their lived experience to fit dominant cultural narratives, the action excluded women who were unable to perform the necessary identity, perpetuating the same inequality that widows came to court to address.
39
Zouridakis, Georgios. "The introduction of the derivative action into the Greek law on public limited companies as a means of shareholder protection : a comparative analysis of the British, German and Greek law." Thesis, University of Essex, 2016. http://repository.essex.ac.uk/17136/.
Full textAbstract:
Shareholder protection has been a focal point of the Greek legislator's agenda for years. Despite a series of reforms towards the direction of shareholder empowerment, the adequacy of the existing framework remains questionable. The thesis conveys the argument that the remedies for maladministration under Greek company law remain dysfunctional and need to be reformed in order to establish an effective and competitive legal framework for shareholder protection. It is argued that such initiatives are important in order to boost investor confidence and provide an effective monitoring mechanism of corporate governance. In order to assess whether and to what extent the Greek shareholder law attains these objectives, it is examined on a comparative basis with jurisdictions which recently reformed their shareholder law; namely the United Kingdom and Germany. The thesis analyses the imperfections of Greek law. The latter is devoid of a genuine derivative action and the existing functionally equivalent mechanism is unsuitable to overcome the challenges of shareholder litigation. The relevant law is exclusionary and rather biased against individual shareholders. It deters meritorious litigation and does little to ensure that proceedings do not run contrary to the company’s interests. Much of corporate misfeasance escapes the scope and content of the existing provisions and, effectively, corporate wrongdoing is left uncompensated for and undeterred. Furthermore, the broader legal framework cannot compensate for the absence of an appropriate mechanism to enforce directors’ duties and pursue corporate claims via shareholder-initiated litigation. However, the examination of the strategies followed by the UK and Germany provides useful insights for the way forward. The rationale for and the experience from the recently introduced provisions thereto are invaluable in the thesis’ attempt to construct and propose a modern and functioning model of derivative actions for Greece.
40
Boultifat, Chaouki Nacer. "Contrôle acoustique actif du bruit dans une cavité fermée." Thesis, Ecole nationale supérieure Mines-Télécom Atlantique Bretagne Pays de la Loire, 2019. http://www.theses.fr/2019IMTA0134/document.
Full textAbstract:
Cette thèse porte sur le contrôle acoustique actif (ANC) dans une cavité. L’objectif est d’atténuer l’effet d’une onde sonore perturbatrice en des points ou dans un volume. Ceci est réalisé à l’aide d’un contre-bruit généré, par exemple, par un haut-parleur. Cette étude requiert l’utilisation de modèles dynamiques rendant compte de l’évolution des pressions aux points d’intérêt en fonction des bruits exogènes. Ce modèle peut être obtenu par une identification fréquentielle des réponses point-à-point ou en utilisant le modèle physique sous jacent (équation des ondes). Dans ce dernier cas, la recherche d'un modèle de dimension finie est souvent un préalable à l’étude conceptuelle d'un système d’ANC. Les contributions de cette thèse portent donc sur l’élaboration de différents modèles simplifiés paramétrés par la position pour les systèmes acoustiques et sur la conception de lois de commande pour l’ANC. Le premier volet de la thèse est dédié à l’élaboration de différents modèles simplifiés de système de propagation acoustique au sein d’une cavité. Pour cela, les simplifications envisagées peuvent être de nature spatiale autant que fréquentielle. Nous montrons notamment qu'il est possible, sous certaines conditions, d’approximer le système 3D par un système 1D. Ceci a été mis en évidence expérimentalement sur le banc d’essai LS2NBox. Le second volet porte sur la conception de lois de commande. En premier lieu, les stratégies de commandes couramment utilisées pour l’ANC sont comparées. L'effet dela commande multi-objectif H en différents points voisins des points d'atténuation est analysé. La possibilité d’une annulation parfaitedu bruit en un point est aussi discutéeThis thesis deals with active noise control (ANC) in a cavity. The aim is to mitigate the effect of a disturbing sound wave at some points or in a volume. This is achieved using ananti-noise generated, for example, by a loudspeaker. This study requires the use of dynamic models that report changes in pressure at points of interest in response to exogenous noises. Such models can be obtained by frequency identification of point-to-point responses or by using the underlying physical model (wave equation). In the latter case, the search for a low-complexity model (finite dimensional model) is often a prerequisite for the conceptual study of an active control system. The contributions of this thesis concern the development of different simplified models parameterized by the spatial position for acoustic systems, and the design of control laws for noise attenuation. The first part of the thesis is dedicated to the development of various simplified models of acoustic propagation system within a cavity. For that, the simplifications envisaged can be of spatial nature as much as frequential. We show in particular that it is possible, under certain conditions, to approximate the 3D system by a 1D system. This has been demonstrated experimentally on the prototype system, LS2NBox. The second part of the thesis deals with the design of control laws. First, the control strategies commonly used for ANC are compared. The effect of multi-objective H control at different spatial positions close to the attenuation points is analyzed. The possibility of perfect noise cancellation at one point is also discussed
41
Hails, Euan. "Development and delivery of cognitive behavioural therapy training in New South Wales, Australia : project undertaken in the spirit of action research." Thesis, Cardiff University, 2012. http://orca.cf.ac.uk/37090/.
Full textAbstract:
This study set out to investigate the understanding of psychological interventions and their place in practice (psychological mindedness) at an Australian mental health service and whether or not it was possible to train clinicians to introduce cognitive behavioural therapy to practice. The study investigated if, after training, clinicians' self-efficacy and readiness to use learnt skills is increased as they begin to deliver cognitive behavioural therapy (CBT) to patients. To do this a methodological approach was adopted, developed and delivered in the spirit of action research and conducted utilising a practice development model, that employed skills based education and experiential learning methods. A staff scoping survey was conducted to ascertain the psychological mindedness of clinical staff and to gain a picture of the availability of talking therapies across the health service. Following this survey an eight-day CBT training course was developed and delivered. A pre- and post- course questionnaire was applied to gain data on participant’s readiness to use skills and an increase in their self-efficacy pertinent to CBT that they learnt during the course. The results of the scoping survey showed that there was use of talking therapies by clinicians and that these clinicians desired training in CBT. The results of the CBT course questionnaire showed that it is possible to increase clinician’s self-efficacy and readiness to introduce skills to practice post attendance on an eight-day CBT training course. The delivery of focused talking therapy training across a mental health service can over time and with adequate levels of support and supervision, enable the delivery of CBT to service users. Principles of action research, practice development and the use of skills based education and experiential learning methods if implemented and supported actively can increase patient’s access to psychological therapies and train staff in the application of the same.
42
Wang, Yuchen. "Stress Analysis of Seabed Using Finite Difference Modelling." Thesis, Griffith University, 2016. http://hdl.handle.net/10072/366693.
Full textAbstract:
Coastal structures are always facing the threat of damage caused by different wave actions. A better understanding of different seabed behaviours could effectively reduce the damage caused by waves. In this thesis, four different models (u-w-p, u-p, u and w-p) are developed to analyse the different behaviours of seabeds composed of fine granular soil (silt and normally consolidated clay) and coarse granular soil (loose sand, dense sand, and gravel). In relation to the u-w-p model, which is also the most important and comprehensive one used in this study, acceleration, velocity and displacement were considered, with the three important parameters being analysed: pore water pressure, effective stress, and shear stress.
The purpose of this research was to illustrate the general behaviour of various seabeds under wave actions, and to clarify the roles of different seabed soil parameters, then to identify the probability of liquefaction and shear failure for seabed composed of different materials. The research also sought to compare the different behaviour of fine granular soil and coarse granular soil, especially via a detailed description of the behaviour of fine granular soil, and giving a wider picture of seabed response under wave actions, which has not been studied in previous research and could become an important foundation in further analysis of fine grained seabed.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Engineering
Science, Environment, Engineering and Technology
Full Text
43
Leng, Julien. "Controlling flexural waves using subwavelength perfect absorbers : application to Acoustic Black Holes." Thesis, Le Mans, 2019. http://www.theses.fr/2019LEMA1027/document.
Full textAbstract:
Le contrôle des vibrations à basse fréquence adapté aux structures légères est un défi scientifique ettechnologique en raison de contraintes économiques et écologiques de plus en plus strictes. De récentes études enacoustique ont portées sur l’absorption totale d’ondes basses fréquences à l’aide d’absorbeurs parfaits sublongueursd’onde. Ces métamatériaux sont obtenus en exploitant la condition de couplage critique. Unegénéralisation de cette méthode pour le domaine élastodynamique serait d’un grand intérêt pour répondre auxexigences du contrôle des vibrations de structures légères à basse fréquence.Cette thèse vise à adapter le problème d’absorption parfaite des ondes de flexion dans des systèmes 1D et 2D avecdes résonateurs locaux en utilisant la condition de couplage critique. Une étude préliminaire sur des systèmes 1D àgéométries simples sont d’abord proposée. Celle-ci propose une méthode de conception de résonateurs simplespour une absorption efficace des ondes de flexion. Une complexification du système 1D est ensuite considérée avecl’étude du couplage critique de Trou Noir Acoustique (TNA) 1D. Ceci a motivé l’interprétation de l’effet TNA à l’aidedu concept de couplage critique afin de présenter des outils clés à de futures procédures d’optimisation pour ce typede terminaisons. La condition de couplage critique est ensuite étendue aux systèmes 2D. L’absorption parfaite parle premier mode axisymétrique d’un résonateur circulaire inséré dans une plaque mince infinie est analysée. Ladiffusion multiple par une ligne de résonateurs circulaires insérés dans une plaque mince 2D infinie ou semi-infinie,appelée métaplaque, est aussi considérée dans l’optique de se rapprocher d’une application industrielle. A traverscette thèse, des modèles analytiques, des simulations numériques et des expériences sont présentés pour valider lecomportement physique des systèmes présentésThe vibration control adapted to light structures is a scientific and technological challenge due toincreasingly stringent economic and ecological standards. Meanwhile, recent studies in audible acoustics havefocused on broadband wave absorption at low frequencies by means of subwavelength perfect absorbers. Suchmetamaterials can totally absorb the energy of an incident wave. The generalisation of this method for applicationsin elastodynamics could be of great interest for the vibration control of light structures.This thesis aims at adapting the perfect absorption problem for flexural waves in 1D and 2D systems with localresonators using the critical coupling condition. A study of 1D systems with simple geometries is first proposed. Thisprovides methods to design simple resonators for an effective absorption of flexural waves. The 1D systems thenbecome more complex by studying the critical coupling of 1D Acoustic Black Holes (ABH). The ABH effect is theninterpreted using the concept of critical coupling, and key features for future optimisation procedures of ABHs arepresented. The critical coupling condition is then extended to 2D systems. The perfect absorption by the firstaxisymmetric mode of a circular resonator inserted in a thin plate is analysed. Multiple scattering by an array ofcircular resonators inserted in an infinite or semi-infinite 2D thin plate, called metaplate, is also considered to getclose to practical applications. Through this thesis, analytical models, numerical simulations and experiments areshown to validate the physical behaviour of the systems presented
44
Watson, Paul. "Sustainable ‘land use’ Development? : Tension between acting local and thinking global? Case study of public opinion toward Wind Turbines’ in Powys, Wales." Thesis, Umeå universitet, Kulturgeografi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-101523.
Full text
45
Ticha, Lawrence Awa. "Development of amperometric biosensor with cyclopentadienylruthenium (II) thiolato schiff base self-assembled monolayer (SAM) on gold." Thesis, University of the Western Cape, 2007. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_5394_1341319478.
Full textAbstract:
A novel cyclopentadienylruthenium(II) thiolato Schiff base, [Ru(SC6H4NC(H)C6H4OCH2CH2SMe)(&eta5-C2H5]2 was synthesized and deposited as a selfassembled monolayer (SAM) on a gold electrode. Effective electronic communication between the Ru(II) centers and the gold electrode was established by electrostatically cycling the Shiff base-doped gold electrode in 0.1 M NaOH from -200 mV to +600 mV. The SAMmodified gold electrode (Au/SAM) exhibited quasi-reversible electrochemistry. The integrity of this electro-catalytic SAM, with respect to its ability to block and electro-catalyze certain Faradaic processes, was interrogated using Cyclic and Osteryoung Square Wave voltammetric experiments. The formal potential, E0', varied with pH to give a slope of about - 34 mV pH-1. The surface concentration, &Gamma
, of the ruthenium redox centers was found to be 1.591 x 10-11 mol cm-2. By electrostatically doping the Au/SAM/Horseradish peroxidase at an applied potential of +700 mV vs Ag/AgCl, a biosensor was produced for the amperometric analysis of hydrogen peroxide, cumene hydroperoxide and tert-butylhydroperoxide. The electrocatalytic-type biosensors displayed typical Michaelis-Menten kinetics with their limits of detection of 6.45 &mu
M, 6.92 &mu
M and 7.01 &mu
M for hydrogen peroxide, cumene hydroperoxide and tert-butylhydroperoxide respectively.
46
West, Natasha. "Nanocomposite immunosensor for anti-transglutaminase antibody." Thesis, University of the Western Cape, 2009. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_6426_1298354109.
Full textAbstract:
Coeliac disease (CD) is a gluten intolerance condition that results in the flattening of the villi, which line the bowel. It is the most common cause of malabsorption of food nutrients. This inability to absorb sufficient levels of nutrients causes many of the common symptoms experienced by CD patients. Some of the symptoms, which lead to an increase in mortality rate, include chronic diarrhea, fatigue, iron-deficient anemia and osteoporosis. People with CD have higher than normal levels of certain antibodies in their blood. Thus, the concentration of anti-transglutaminase antibody (anti-tTG) in human sera is an important analytical marker for the diagnosis of CD. An immunosensor is a type of biosensor that has an antigen or antibody fragment as its biological recognition component. The specificity of the molecular recognition of antigens by antibodies to form a stable complex is the basis of immunosensor technology. In this work, overoxidized polypyrrole (OvoxPpy) was electrosynthesized as a noval sensor platform on a glassy carbon electrode (GCE). The OvoxPpy was then doped with gold-nanoparticles (GNP) by electrodeposition using cyclic voltammetry to form GNP|OvoxPpy||GCE electrode system. Morphology and size of the GNP|OvoxPpy||GCE nanocomposite were determined using scanning electron microscopy. The electrochemical immunosensor for anti-tTG antibodies was prepared by immobilizing transglutaminase antigen (tTG-antigen) onto the GNP|OvoxPpy||GCE by drop coating and allowed to incubate for 2 hrs. The electrochemical characterization of the nanocomposite platform and immunosensor were studied by voltammetry and electrochemical impedance spectroscopy (EIS)...
47
De, Beer Edmund Johannes. "Die vergoeding vir arbeid in Suid-Afrika : 'n teologies-etiese studie / E.J. de Beer." Thesis, North-West University, 2004. http://hdl.handle.net/10394/691.
Full textAbstract:
On the basis of descriptive and prescriptive ethics and by means of literature study and exegesis
of the Scriptures, this study poses an answer to the question: "How should factors that define
labour compensation in South Africa since 1994 be judged according to theological ethics?"
Since the subsistence farming of the seventeenth century in South Africa labour compensation
has changed to a mainly capitalistic system with money as the most important compensation to
labourers for services rendered. Since the seventeenth century a period of unfolding and
development of careers has taken place mainly as a result of the influence of colonists from
Europe. Gradual development taking place in the economic field has made subsequent factors in
lieu of labour compensation more relevant for labourers. Various factors with regard to
compensation of labour after 1994 - when the first fully-fledged democratic voting took place
in South Africa - defines that it must be seen against the developmental background before
1994.
In this study thirteen factors that have an influence on compensation since 1994, will be
identified. Some factors tend to lean towards underpayment and others to overpayment. Interior
factors relating to insufficient payment are unemployment, child labour, HIV/Aids and
gambling. Foreign factors relative to insufficient payment are illegal immigration and cheap
imports. Relevant to this, there are also factors resulting in higher remuneration of labourers.
Labour laws with regard to affirmative action and minimum wages have a positive influence on
payment for labourers. Illegal conduct of labourers gives rise to theft, robbery and corruption.
Positive reactions are also in place with regard to remuneration of labourers. In view of this,
over-pay, strikes and emigration play an important role.
The factors that influence payment since 1994 are being judged according to the Scriptures,
pertaining labour and remuneration. God created mankind serving as inhabitants and workers of
the earth. He also decreed that mankind will live from the fruit of his labour. This decree forms
the basis by which labourers receive remuneration for their efforts. Through fellowship man
shows that he is sewing God and fellow-country men and does not labour only for his own
advantage. The fall of man has far-reaching influences on mankind, his labours, place of labour
and the consequent remuneration be receives for services rendered. One cannot fatalistically
accept the influence of the fall of mankind. The recreation of mankind, started by Jesus Christ
also affects the area of labour. This study demonstrates how remuneration for labour does not
comply to Bible principles. Guidance will be given to how, especially believers, be they
employers or employees, portray God's image through their conduct. Believers should execute
their labours in such a way, that they are worthy of decent remuneration. Christian employers
ought to be reasonable when paying employees, create and protect job opportunities and where
possible, employ more labourers. Maximum opportunity should be granted by the ruling
authority in order that as many people possible have the opportunity to labour without being
exploited.Thesis (Ph.D. (Ethics))--North-West University, Potchefstroom Campus, 2005.
48
Maiko, Khumo Gwendoline. "The Isolation and Electrochemical Studies of Flavanoids from Galenia africana and Elytropapus rhinocerotis from the North Western Cape." Thesis, University of the Western Cape, 2010. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_5427_1305881229.
Full textAbstract:
In this study two medicinal plant species, namely Galenia africana and Elytropapus rhinocerotis, the former belonging to the family Aizoceae and the latter belonging to the family Asteraceae, have been investigated and different compounds isolated and characterized. Both species are important plants used in traditional medicine in Africa and particularly in South Africa. Flavanoids are secondary metabolites found in plants. They have a protective function against UV radiation and have a defence against invading illnesses due to their important antioxidant activity. Much of the food we eat and some beverages we drink contain flavonoids. The aim of this study was to investigate the electrochemistry of flavanoids isolated from these species.
49
Huang, Tianli. "Multi-modal propagation through finite elements applied for the control of smart structures." Phd thesis, Ecole Centrale de Lyon, 2012. http://tel.archives-ouvertes.fr/tel-00946214.
Full textAbstract:
Le sujet de thèse concerne l'analyse de la propagation des ondes dans les structures complexes et leurs exploitations pour le contrôle semiactif et le contrôle de santé de structures intelligentes. Les structures composites munies de patches piézoélectriques sont la cible principale des investigations. Les patches piézoélectriques sont disposés avec une périodicité. Des travaux précédents ont montré l'intérêt de ce type de configuration pour l'amortissement actif de modes de structures en basses fréquences. L'objectif principal de cette thèse est l'extension de ces constatations dans une bande de fréquences plus large : basses et moyennes fréquences. La maîtrise des paramètres de propagation et de diffusion des ondes est la finalité recherchée. Dans ce cadre, les travaux proposés se baseront sur une technique particulière développée au sein de l'équipe Dynamique des Systèmes et des Structures: la technique WFE (Wave Finite Element), Ondes par éléments finis. Cette approche, construite à l'aide d'un modèle éléments finis d'une cellule représentative de l'essentiel des paramètres de propagation et de diffusion des ondes dans les structures. Elle a été validée sur des cas simples de structures, principalement isotrope monodimensionnel. La modélisation dans ce cas des sandwichs plaques composites munies de couches piézoélectriques sera opérée. Des simulations numériques poussées seront effectuées afin de cerner le cadre d'application de la WFE pour ce type de structures. Des optimisations pourront être réalisées avec ces outils numériques afin d'obtenir des paramètres géométriques et électriques optimaux dans la conception des structures intelligentes. Les travaux de cette thèse sont intégrés dans le projet CALIOP en collaborant avec le laboratoire de Mécanique Appliquée R.Chaléat de l'Institut FEMTOSTet G.W. Woodruff School of Mechanical Engineering de Georgia Institute of Technology.
50
Willemse, Chandre Monique. "Nanocomposite-graphene based platform for heavy metal detection." Thesis, University of the Western Cape, 2010. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_8123_1323852117.
Full textAbstract:
This study reports the synthesis of graphene by oxidizing graphite to graphite oxide using H2SO4 and KMnO4 and reducing graphene oxide to graphene by using NaBH4. Graphene was then characterized using FT-IR, TEM, AFM, XRD, Raman spectroscopy and solid state NMR. Nafion-Graphene in combination with a mercury film electrode, bismuth film electrode and antimony film electrode was used as a sensing platform for trace metal analysis in 0.1 M acetate buffer (pH 4.6) at 120 s deposition time, using square-wave anodic stripping voltammetry (SWASV). Detection limits were calculated using 3Ïblank/slope. For practical applications recovery studies was done by spiking test samples with known concentrations of metal ions and comparing the results to inductively coupled plasma mass spectrometry (ICPMS). This was then followed by real sample analyses.