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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
141

Inhibition, Synapses, and Spike-Timing: Identification and disruption of pyramidal cell-interneuron interactions in SPW-Rs.

Gilbert, Earl Thomas 25 June 2024 (has links)
The neural circuitry responsible for memory consists of complex components with dynamic interactions. In hippocampal area CA1, interactions between excitatory pyramidal cells and inhibitory interneurons shape ensemble activity which encodes sequential experience. An extremely diverse set of inhibitory interneurons, with variation in gene expression, synaptic targeting, state-dependent activity, and connectivity, contribute substantially to circuit activity, such as theta and sharp wave-ripple oscillations. The precise roles of each interneuron group is not well understood, though characterization of their activity reveals mechanisms underlying hippocampal circuit computation. In this dissertation, I aim to identify and disrupt interactions between pyramidal cells and local interneurons to clarify their role in shaping cell assembly activity. We characterized axo-axonic cell activity in sharp wave-ripples, and compared their control of pyramidal cell activity and ripple events to parvalbumin expressing neurons. We identified pyramidal cell-interneuron interactions during ripples, suggesting they serve as lateral inhibitors between cell assemblies. We additionally developed and implemented a novel neural device to explore the role of cannabinoid disruption of hippocampal oscillations and organization of assemblies in vivo in awake animals. We demonstrate that cannabinoid receptor type 1 within CA1 is responsible for suppression of theta and SPW-Rs. We also found that cannabinoid activation within CA1 circuitry, regardless of muted input from CA3, was sufficient to disrupt sharp wave-ripples, likely through interference of pyramidal cell-interneuron interactions. The work in this dissertation provides insight suggesting that interneuron activity must be studied at the spiking timescale to characterize their control over cell assembly activity. / Doctor of Philosophy / Understanding how the brain creates memory remains one of the greatest questions in the field of neuroscience. Coordinated brain activity serves to build communication on large and small scales, across brain regions and within circuits consisting of small groups of neurons. Precise coordination of activity and communication across neurons and regions is thought to build salient experience, which is achieved through the timing of neuron action potentials, or spikes. Neurons receive thousands of inputs that control their spiking activity. "Go and stop" signals from excitatory and inhibitory interneurons act to conduct synchronized activity, which is required for proper circuit function. Importantly, coordinated spiking across large groups of neurons is responsible for observed "brain waves", or oscillations, which reflect organized activity. In CA1 of the hippocampus, there are >20 subtypes of interneurons that all make distinct contributions to memory function, and the roles of these interneurons have not been fully studied within behaving animals. As engineers develop new tools, new methods become available to study and classify how unique groups of interneurons play a part in circuit activity. Thus, we sought to characterize the role of axo-axonic cells, a specialized interneuron with strong control over spiking activity, in hippocampal oscillations that are responsible for memory encoding and consolidation. We identified a new role for axo-axonic cells in the regulation of pyramidal cell spiking in sharp wave-ripple oscillations. Additionally, we developed a novel neural device that allowed us to investigate the mechanisms that underlie cannabinoids, molecules found in Cannabis sativa, and memory dysfunction. We leveraged the multifunctionality of our T-DOpE probe to focally deliver synthetic cannabinoid into the hippocampus in combination with optical control of circuits, with simultaneous recording of activity. We found that cannabinoids acting within CA1 sufficiently disrupt hippocampal oscillations, likely through hindering pyramidal cell-interneuron interactions. Together, these findings suggest that the spatial and temporal resolution required to study diverse roles of interneurons is high, and experiments designed to explore interneuron activity should especially emphasize fine time-scales.
142

Équations de Hardy-Sobolev sur les variétés Riemanniennes compactes : influence de la géométrie / Hardy-Sobolev equations on the compact Riemannian manifolds : Influence of geometry

Jaber, Hassan 24 June 2014 (has links)
Dans ce Manuscrit, nous étudions l'influence de la géométrie sur les équations de Hardy-Sobolev perturbées ou non sur toute variété Riemannienne compacte sans bord de dimension supérieure ou égale à 3. Plus précisément, dans le cas non perturbé nous démontrons que pour toute dimension de la variété strictement supérieure à, l'existence d'une solution (ou plutôt une condition suffisante d'existence) dépendra de la géométrie locale autour de la singularité. En revanche, dans le cas où la dimension est égale à 3, c'est la géométrie globale (particulièrement, la masse de la fonction de Green) de la variété qui comptera. Dans le cas d'une équation à terme perturbatif sous-critique, nous démontrons que l'existence d'une solution dépendra uniquement de la perturbation pour les grandes dimensions et qu'une interaction entre la géométrie globale de la variété et la perturbation apparaîtra en dimension 3. Enfin, nous établissons une inégalité optimale de Hardy-Sobolev Riemannienne, la variété étant avec ou sans bord, où nous démontrons que la première meilleure constante est celle des inégalités Euclidiennes et est atteinte / In this Manuscript, we investigate the influence of geometry on the Hardy-Sobolev equations on the compact Riemannian manifolds without boundary of dimension greateror equal to 3. More precisely, we prove in the non perturbative case that the existence of solutions depends only on the local geometry around the singularity when the dimension is greater or equal to 4 while it is the global geometry of the manifold when the dimension is equal to 3 that matters. In the presence of a perturbative subcritical term, we prove that the existence of solutions depends only on the perturbation when the dimension is greater or equal to 4 while an interaction between the perturbation and the global geometry appears in dimension 3. Finally, we establish an Optimal Hardy-Sobolev inequality for all compact Riemannian manifolds, with or without boundary, where we prove that the Riemannian sharp constant is the one for the Euclidean inequality and is achieved
143

Dispositifs innovants à pente sous le seuil abrupte : du TEFT au Z²-FET / (Innovative sharp switching devices : from TFET to Z2-FET

Wan, Jing 23 July 2012 (has links)
Tunnel à effet de champ (TFET) et un nouveau composant MOS à rétroaction que nous avons nommé le Z2-FET.Le Z2-FET est envisagé pour la logique faible consommation et pour les applications mémoire compatibles avecles technologies CMOS avancées. Nous avons étudié de manière systématique des TFETs avec différents oxydesde grille, matériaux et structures de canal, fabriqués sur silicium sur isolant totalement déserté (FDSOI). Lesmesures de bruit à basse fréquence (LFN) sur TFETs montrent la prédominance d'un signal aléatoiretélégraphique (RTS), qui révèle sans ambiguïté le mécanisme d’effet tunnel. Un modèle analytique combinantl’effet tunnel et le transport dans le canal a été développé, montrant un bon accord entre les résultatsexpérimentaux et les simulations.Nous avons conçu et démontré un nouveau dispositif (Z2-FET, pour pente sous le seuil verticale et zéroionisation par impact), qui présente une commutation extrêmement abrupte (moins de 1 mV par décade decourant), avec un rapport ION / IOFF >109, un large effet de hystérésis et un potentiel de miniaturisation jusqu'à 20nm. La simulation TCAD a été utilisée pour confirmer que la commutation électrique du Z2-FET fonctionne parl'intermédiaire de rétroaction entre les flux des électrons et trous et leurs barrières d'injection respectives. LeZ2-FET est idéalement adapté pour des applications mémoire à un transistor. La mémoire DRAM basée sur leZ2-FET montre des performances très bonnes, avec des tensions d'alimentation jusqu'à 1,1 V, des temps derétention jusqu'à 5,5 s et des vitesses d'accès atteignant 1 ns. Une mémoire SRAM utilisant un seul Z²-FET estégalement démontrée sans nécessité de rafraichissement de l’information stockée.Notre travail sur le courant GIDL intervenant dans les MOSFETs de type FDSOI a été combiné avec leTFET afin de proposer une nouvelle structure de TFETs optimisés, basée sur l'amplification bipolaire du couranttunnel. Les simulations de nouveau dispostif à injection tunnel amélioré par effet bipolaire (BET-FET) montrentdes résultats prometteurs, avec des ION supérierus à 4mA/��m et des pentes sous le seuil SS inférieures à 60mV/dec sur plus de sept décades de courant, surpassant tous les TFETs silicium rapportés à ce jour.La thèse se conclut par les directions de recherche futures dans le domaine des dispositifs à pente sous leseuil abrupte. / This thesis is dedicated to studying sharp switching devices, including the tunneling field-effect-transistor(TFET) and a new feedback device we have named the Z2-FET, for low power logic and memory applicationscompatible with modern silicon technology. We have extensively investigated TFETs with various gate oxides,channel materials and structures, fabricated on fully-depleted silicon-on-insulator (FD-SOI) substrates.Low-frequency noise (LFN) measurements were performed on TFETs, showing the dominance of randomtelegraphy signal (RTS) noise, which reveals the tunneling mechanism. An analytical TFET model combiningtunneling and channel transport has been developed, showing agreement with the experimental and simulationresults.We also conceived and demonstrated a new device named the Z2-FET (for zero subthreshold swing andzero impact ionization), which exhibits extremely sharp switching with subthreshold swing SS < 1 mV/dec,ION/IOFF current ratio reaching 109, gate-controlled hysteresis and scalability down to 20 nm. The Z2-FEToperates with feedback between carriers flow and their injection barriers. The Z2-FET is used for one-transistordynamic random access memory (DRAM) with supply voltage down to 1.1 V, retention time up to 5.5 s andaccess speed reaching 1 ns. The static RAM (SRAM) application is also demonstrated without the need ofrefreshing stored data.Following our work on gate-induced drain leakage (GIDL) current in short-channel FD-SOI MOSFETs andon TFET operating mechanisms, we propose a new class of optimized TFETs with enhanced ION, based on thebipolar amplification of the tunneling current. Simulations of the bipolar-enhanced tunneling FET (BET-FET),combining the TFET with a heterojunction bipolar transistor, show promising results, with ION > 4×10-3 A/��mand SS < 60 mV/dec over 7 decades of current, outperforming all silicon-compatible TFETs reported to date.The thesis concludes with future research directions in the sharp-switching device arena.
144

企業策略與國家文化對跨國購併之影響 : 以鴻海購併夏普為例 / The Influence of Corporate Strategy and National Culture on Cross-Border M&A

王靖傑, CHING-CHIEH WANG Unknown Date (has links)
跨國購併為企業持續成長的重要策略之一,學者針對此議題亦有諸多探討, 而過去的多數研究皆著重於—企業執行跨國購併後,企業策略與國家文化對於後 續整合的影響。然而,本研究認為文化的影響自企業開啟跨國購併談判以來,便 始終存在。此外,購併談判為跨國購併之起始,其重要性不亞於購併後的整合。 因此,本研究以企業跨國購併歷程為主體,藉此探討跨國購併企業雙方之文化差 異對於整體購併行為之影響。 本研究之目的為探討企業實際購併個案研究,讓企業未來在實際執行購併策 略時,能持續思考國家文化差異之影響,並依據其購併階段之不同,而有相對的 因應方式。 本研究以次級資料作為質性研究依據,藉由廣泛地蒐集資料,撰寫成鴻海購 併夏普之跨國購併個案。透過此篇實際個案研究,發現家文化差異對於企業能否 順利進行購併談判有重大影響,並提出企業依其所屬之購併階段不同,處理相對 應需著重之文化構面,可提高企業跨國購併談判之效率及成功率。 / Cross-border mergers and acquisitions (M&A) are one of the most important strategies for sustainable growth of a company. Many scholars had various discussions on this issue. Most of researches concentrated on how corporate strategy and national culture affect the integration after cross-border M&A. However, this study suggests that cultural impacts have long existed from the very beginning of cross-border M&A negotiations. In addition, M&A negotiation is the start point of cross-border M&A. It is equally important in the integration stage after M&A. Therefore, this study focuses mainly on the process of cross-border M&A in order to explore overall influence on the cross-border M&A due to cultural differences between the enterprises. By analyzing a real M&A case, the purpose of this study is to make enterprise consider the impact of cultural difference when they are having cross-border M&A negotiation. Besides, through this study company can understand what the most important dimension of national culture is while having M&A project. This study is a qualitative research based on extensively searching secondary data of Hon-Hai and Sharp M&A. This case study found that cultural differences between nations affect -whether the enterprise can successfully carry out M&A negotiations. This study also shows that company may generate different strategies corresponding to the difference between national culture dimensions in accordance with different M&A negotiation stage. Doing so may lead to smooth and successful M&A negotiation.
145

Mixing Enhancement Studies on Supersonic Elliptic Sharp Tipped Shallow (ESTS) Lobed Nozzles

Varghese, Albin B M January 2016 (has links) (PDF)
Rapid mixing and spreading of supersonic jets are two important characteristics in supersonic ejectors, noise reduction in jets and fuel mixing in supersonic combustion. It helps in changing the acoustic and thermal signature in supersonic exhaust. The supersonic nozzles in most cases result in compressible mixing layers. The subsonic nozzles form incompressible mixing layers but at high Mach numbers even they form compressible mixing layers. Compressible mixing layers have been found to have much lower mixing and spreading rates than incompressible mixing layer Birch & Eggers (1972). In order to enhance the spreading and mixing of mixing layers from supersonic nozzles various active and passive methods have been deviced. Active methods include fluid injection, fluid lobes and plasma actuation. Passive methods are mostly based on modifying the nozzle geometry such that the fluid expansion is ideal or the shock cell is broken. Many nozzles with exotic shapes have been developed to obtain mixing enhancements in supersonic jets Gutmark et al. (1995). To achieve enhanced mixing an innovative nozzle named as the Elliptic Sharp Tipped Shallow (ESTS) lobed nozzle has been developed in L.H.S.R., I.I.Sc., India Rao & Jagadeesh (2014). This nozzle has a unique geometry involving elliptical lobes and sharp tips. These lobes are generated using a simple manufacturing process from the throat to the exit. This lobed and sharp tipped structure introduces stream wise vortices and azimuthal velocity components which must help in enhanced mixing and spreading. The ESTS lobed nozzle has shown mixing enhancement with 4 lobes. The spreading rate was found to be double of the reference conical nozzle. This thesis is motivated by the need to investigate the flow physics involved in the ESTS lobed nozzle. The effect of varying the number of lobes and the design Mach number of the nozzle on the mixing and spreading characteristics will be further discussed. Visualisation studies have been performed. The schlieren and planar LASER Mie scattering techniques have been used to probe the flow. Instantaneous images were taken at axial planes with the reference conical and ESTS nozzles with three, four, five and six lobes. The nozzles are for design Mach number 2.0 and 2.5. The stagnation chamber pressure was maintained to obtain over expanded, ideally expanded and under expanded flows. LASER scattering was obtained by seeding the flow with water to observe the behaviour of the primary flow. The condensation of moisture due to the cold primary flow mixing with the ambient air was exploited to scatter laser and observe the flow structures in the mixing layer. A comparison of the images of the reference conical nozzle and the ESTS lobed nozzles shows changes in the mixing layers due to the ESTS lobed nozzles. The image of the reference conical nozzle shows a distinct potential core and mixing layers all along the length of the image. For the ESTS lobed nozzles this distinction becomes unclear shortly after the nozzle exit. Thus mixing of the primary flow and ambient air is seen to be enhanced in the case of all the ESTS lobed nozzles. The flow in the case of the ESTS lobed nozzles if found to be highly non axis symmetric. The starting process of the nozzles has been visualised using time resolved schlieren. Image processing was performed on the nozzles to quantify the spread rate. The shock structure of the nozzles has been studied and found to be modified due to the lobed geometry. The level of convolution of the mixing layer due to the lobed structure has been studied using fractal analysis. The four lobed nozzle was found to have the highest spread rate and th most convoluted shear layer. Hence this nozzle was further studied using background oriented schlieren and particle image velocimetry to quantify the flow field. These experimental results have been compared with CFD simulations using the commercial software CFX5. The computations and experiments don’t match accurately but the trends match. This allows for simulations to be used as a good first approximation. The acoustic properties of a jet are dependent on the flow structure behaviour. The ESTS lobes have been found to change the flow structure. Hence the ESTS lobed nozzle was predicted to change the acoustic signature of the flow. The acoustic measurements of the flow were carried out at National Aerospace Laboratories, Bengaluru. The screech of the overexpanded flow was seen to be eliminated and the overall sound levels were found to have been reduced in all cases. Thus the lobed nozzle was found to have acoustic benefits over the reference conical nozzle. Thus the ESTS lobed nozzle has been studied and compared with the conical nozzle using several methods. The changes due to the lobed structure have been studied quantitatively. Future studies would focus on the change in thrust due to the lobed structure. Also new geometries have been proposed inspired by the current design but with possible thrust benefits or manufacturing benefits.
146

Detekce a vizualizace specifických rysů v mračnu bodů / Detection and Vizualization of Features in a Point Cloud

Kratochvíl, Jiří Jaroslav January 2018 (has links)
The point cloud is an unorganized set of points with 3D coordinates (x, y, z) which represents a real object. These point clouds are acquired by the technology called 3D scanning. This scanning technique can be done by various methods, such as LIDAR (Light Detection And Ranging) or by utilizing recently developed 3D scanners. Point clouds can be therefore used in various applications, such as mechanical or reverse engineering, rapid prototyping, biology, nuclear physics or virtual reality. Therefore in this doctoral Ph.D. thesis, I focus on feature detection and visualization in a point cloud. These features represent parts of the object that can be described by the well--known mathematical model (lines, planes, helices etc.). The points on the sharp edges are especialy problematic for commonly used methods. Therefore, I focus on detection of these problematic points. This doctoral Ph.D. thesis presents a new algorithm for precise detection of these problematic points. Visualization of these points is done by a modified curve fitting algoritm with a new weight function that leads to better results. Each of the proposed methods were tested on real data sets and compared with contemporary published methods.
147

Stanovení Q/h charakteristiky přelivů stavidlové komory ČOV Brno-Modřice v podmínkách nedokonalého proudění / Determination of Q/h characteristics of spillways of the sluice chamber of the Brno-Modřice WWTP in conditions of influenced flow

Škrancová, Markéta January 2022 (has links)
The work deal with the measurement, processing and analysis of Q/h characteristics of the sluice chamber in the wastewater treatment plant on a physical hydraulic model in the conditions of influencing the overflow phenomenon by the groundwater level. Based on the achieved results, a measuring system has been projected in the area of the sluice chamber to measure the flow and flow rate of lightened water into the Svratka river. The measurements on the model were performed in the premises of the Laboratory of water Management Research of the Institute of Water Structures of the Faculty of Civil Engineering of Brno University of Technology by the author of this work. The results of the diploma thesis is a flow chart describing the calculation procedure used to determine the immediate flow, on the basis of which a new software of the evaluation unit of the measuring system was realized.
148

Pyroelektrische Materialien: elektrisch induzierte Phasenumwandlungen, thermisch stimulierte Radikalerzeugung

Mehner, Erik 17 October 2018 (has links)
Zur Messung pyrelektrischer Koeffzienten wurde ein Messplatz nach einem erweiterten SHARP-GARN-Verfahren entwickelt und zur Untersuchung von Phasenumwandlungen in Pyroelektrika eingesetzt. Einerseits konnten pyroelektrische Messungen im elektrischen Feld die Pyroelektrizität einer neuen durch elektrisch angetriebene Defektmigration erzeugten Phase in Strontiumtitanat nachweisen. Andererseits gelang es, Ferroelektrizität in der Hochtemperaturphase von Poly(Vinylidenfluorid-Trifluorethylen), mittels phasenreiner Präparation der Hochtemperaturphase unterhalb der CURIEtemperatur und anschließender Polarisierung, nachzuweisen. Ferner ließen sich mittels thermisch angeregter Pyroelektrika Redoxprozesse antreiben, was durch Desinfektion von Escherichia coli Bakterien in wässriger Lösung mittels Lithiumniobat und -tantalat gezeigt wurde. Die Hypothese der Desinfektion durch reaktive Sauerstoffspezies konnte durch spektroskopisch nachgewiesene OH-Radikale - erzeugt mittels thermisch angeregter Bariumtitanatnanopartikel - belegt werden.
149

Temporal Dynamics of Heat Pain Sensations

Hashmi, Javeria Ali 13 August 2010 (has links)
The moment-to-moment fluctuations in pain-evoked sensory and emotional qualities, and how the pain experience differs between sexes are not well understood. Therefore, this thesis sought to 1) characterise the temporal profiles of the most prominent noxious heat-evoked sensations, 2) characterise sex differences in these sensations, 3) evaluate the magnitude of sharp pain quality evoked in hairy and glabrous skin, and 4) determine the role of absolute stimulus temperatures on sex differences in pain adaptation and habituation. A broad-based heat pain model was developed for this study that incorporates a temporally-continuous assessment of multiple sensory and affective pain dimensions, including pain, burning, sharp, stinging, cutting, and annoyance evoked by two types (static, dynamic) of repeated prolonged noxious heat stimuli. The salient hypotheses were: 1) Burning sensations have a different temporal profile compared with sharp and other related qualities, 2) The temporal dynamics of heat pain intensity and annoyance differ between males and females, 3) Sex differences in heat pain are associated with specific pain qualities and specific types of skin, and 4) Moderate-high temperatures induce pain adaptation and habituation in females but not in males. The most prominent findings were 1) sharp, stinging and cutting sensations adapted when stimulus intensity was static, but burning sensations were evoked during static and dynamic stimulus phases, 2) pain and annoyance in women were greater than men during the dynamic phases of the first stimulus but less than men during static stimulus phases and on stimulus repetition, 3) the sex difference in pain adaptation occurred with percept-fixed stimulus intensities and with absolute stimulus temperatures, 4) the sex effects associated with dynamic stimuli occurred in hairy but not glabrous skin. These findings give new insights into the relationships between pain intensity, quality and affect and have strong implications for views on sex differences in pain sensitivity.
150

Temporal Dynamics of Heat Pain Sensations

Hashmi, Javeria Ali 13 August 2010 (has links)
The moment-to-moment fluctuations in pain-evoked sensory and emotional qualities, and how the pain experience differs between sexes are not well understood. Therefore, this thesis sought to 1) characterise the temporal profiles of the most prominent noxious heat-evoked sensations, 2) characterise sex differences in these sensations, 3) evaluate the magnitude of sharp pain quality evoked in hairy and glabrous skin, and 4) determine the role of absolute stimulus temperatures on sex differences in pain adaptation and habituation. A broad-based heat pain model was developed for this study that incorporates a temporally-continuous assessment of multiple sensory and affective pain dimensions, including pain, burning, sharp, stinging, cutting, and annoyance evoked by two types (static, dynamic) of repeated prolonged noxious heat stimuli. The salient hypotheses were: 1) Burning sensations have a different temporal profile compared with sharp and other related qualities, 2) The temporal dynamics of heat pain intensity and annoyance differ between males and females, 3) Sex differences in heat pain are associated with specific pain qualities and specific types of skin, and 4) Moderate-high temperatures induce pain adaptation and habituation in females but not in males. The most prominent findings were 1) sharp, stinging and cutting sensations adapted when stimulus intensity was static, but burning sensations were evoked during static and dynamic stimulus phases, 2) pain and annoyance in women were greater than men during the dynamic phases of the first stimulus but less than men during static stimulus phases and on stimulus repetition, 3) the sex difference in pain adaptation occurred with percept-fixed stimulus intensities and with absolute stimulus temperatures, 4) the sex effects associated with dynamic stimuli occurred in hairy but not glabrous skin. These findings give new insights into the relationships between pain intensity, quality and affect and have strong implications for views on sex differences in pain sensitivity.

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