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The Global ETD Search service is a free service for researchers
to find electronic theses and dissertations. This service is
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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.
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Showing 281 to 287 of 287 (0.045 seconds)Spelling suggestions: "subject:"helical"" "subject:"ahelical""
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Stanovení chyby převodu u čelního ozubení s šikmými zuby / Determination of transmission error at helical gearCzakó, Alexander January 2020 (has links)
This diploma thesis primarily deals with the transmission error issue which is one of the dominant sources of vibration in gear pairs and transmission systems. The vibrations subsequently generate noise which is often subjected to increasingly stricter demands across the industry, including the automotive one. It turns out that reducing the peak-to-peak value of the transmission error has a beneficial effect on the vibro-acoustic properties of gears and gear pairs. This thesis aims to determine the transmission error under static conditions, since a gear pair with a low static transmission error is a good assumption for a low transmission error even under dynamic effects. The resulting values of the transmission error can be influenced already during the design of the gear macro-geometry. It is also suitable to apply micro-geometric adjustments – modifications to the gear teeth. For this reason, the search part of the thesis is dedicated to theoretical knowledge, especially concerning the geometry of gears, modifications of teeth and the overall transmission error and its determination. The transmission error can be determined in several ways, including a technical experiment. However, due to time and financial reasons, this is not always possible, and therefore, the possibility of using numerical simulations is offered. In this thesis, the approach using stress-strain quasi-static contact analysis using the finite element method in Ansys Workbench software is used. The advantage is, among other things, a good comparability of results. The input to the FEM analysis is 3D CAD geometry – in this case, it is specifically a helical gear pair with parallel axes. The model/assembly of this gear pair is created in PTC Creo software fully parametrically, so it is possible to generate arbitrary gear pair configurations by changing the input parameters, which significantly saves time. At the end of this diploma thesis, the stress-strain analysis of various gear configurations is evaluated, with respect to the equivalent stress and contact pressure. Furthermore, the static transmission error – its graphs and peak-to-peak values – is determined from FEM analyses for different gear geometry, including tooth modifications, and for various loading torques. Last but not least, the effects of contact/overlap ratio and centre distance are evaluated.
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Compact Helical Antenna for Smart Implant ApplicationsKarnaushenko, Dmitriy D. 19 October 2017 (has links)
Medical devices have made a big step forward in the past decades. One of the most noticeable medical events of the twenties century was the development of long-lasting, wireless electronic implants such as identification tags, pacemakers and neuronal stimulators. These devices were only made possible after the development of small scale radio frequency electronics. Small radio electronic circuits provided a way to operate in both transmission and reception mode allowing an implant to communicate with an external world from inside a living organism. Bidirectional communication is a vital feature that has been increasingly implemented in similar systems to continuously record biological parameters, to remotely configure the implant, or to wirelessly stimulate internal organs. Further miniaturisation of implantable devices to make the operation of the device more comfortable for the patient requires rethinking of the whole radio system concept making it both power efficient and of high performance. Nowadays, high data throughput, large bandwidth, and long term operation requires new radio systems to operate at UHF (ultra-high frequency) bands as this is the most suitable for implantable applications. For instance, the MICS (Medical Implant Communication System) band was introduced for the communication with implantable devices. However, this band could only enable communication at low data rates. This was acceptable for the transmission of telemetry data such as heart beat rate, respiratory and temperature with sub Mbps rates. Novel developments such as neuronal and prosthetic implants require significantly higher data rates more than 10 Mbps that can be achieved with large bandwidth communicating systems operating at higher frequencies in a GHz range. Higher operating frequency would also resolve a strong issue of MICS devices, namely the scale of implants defined by dimensions of antennas used at this band. Operation at 2.4 GHz ISM band was recognized to be the most adequate as it has a moderate absorption in the human body providing a compromise between an antenna/implant scale and a total power efficiency of the communicating system.
This thesis addresses a key challenge of implantable radio communicating systems namely an efficient and small scale antenna design which allows a high yield fabrication in a microelectronic fashion. It was demonstrated that a helical antenna design allows the designer to precisely tune the operating frequency, input impedance, and bandwidth by changing the geometry of a self-assembled 3D structure defined by an initial 2D planar layout. Novel stimuli responsive materials were synthesized, and the rolled-up technology was explored for fabrication of 5.5-mm-long helical antenna arrays operating in ISM bands at 5.8 and 2.4 GHz. Characterization and various applications of the fabricated antennas are successfully demonstrated in the thesis.
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Design and Experimentation of Darrieus Vertical Axis Wind TurbinesGonzalez Campos, Jose Alberto 07 September 2020 (has links)
No description available.
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Low Temperature Waste Energy Harvesting by Shape Memory Alloy ActuatorHegana, Ashenafi B. 04 October 2016 (has links)
No description available.
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Unbegrenzte Lösungen für Verzahnungsprobleme, von denen Sie nie dachten, dass es sie gibtEigner, Florian 20 June 2024 (has links)
In der Verzahnungsberechnung werden Lösung meist nur optimiert und nicht neu gedacht. In
Hinblick auf neue Fertigungsverfahren, erreicht „Out of the box“-Denken häufig deutliche
Verbesserungen in technischer und ökonomischer Sicht. Die Software next|gear ermöglicht derart
disruptives Vorgehen.
Um einen ganzheitlichen Ansatz in der Verzahnungsentwicklung zu erreichen, wurde ein
hyperbolisches Grundkonzept entwickelt, das die meisten der bekannten konstant übersetzenden
Getriebetypen beschreiben kann. Neben der freien Wahl von zwei Achsen und Zähnezahlen,
einschließlich negativer Zahlen bei Innenverzahnungen, gibt es für die Berechnung der
kinematischen Auslegung drei weitere kontinuierliche Parameter, die die äußere Form des
Zahnrades beschreiben. Diese Berechnungsgrundlage entfaltet das meiste Potential im
Zusammenhang mit den Freiheiten, die junge Fertigungsverfahren mit Kunststoff z.B. im
Spritzgussverfahren erlaubt. Hier sind die Fertigungsrestriktionen in der Regel andere als bei
spanabhebenden Verfahren.
Nichtdestotrotz könne auch sämtliche konventionelle Fertigungsverfahren mit dem
Berechnungskonzept, basierend auf der Konjugation von Oberflächenpunkten, abgebildet werden.
Mit dem Ansatz, einen durchgängigen Berechnungsprozess für alle einbezogenen
Verzahnungsarten zu beschreiben, wird aufgezeigt, welche Herausforderungen in der
Geometrieberechnung gelöst werden konnten. Dies wird am Beispiel eines Planetengetriebes mit
innenverzahnter Schraubradverzahnung gezeigt, das inzwischen in Serie für die
Automobilindustrie hergestellt wird. / In gear calculation, solutions are usually only optimised and not rethought. With regard to new
manufacturing processes, 'out of the box' thinking often achieves significant improvements from a
technical and economic perspective. The next|gear software enables such a disruptive approach.
In order to achieve a holistic approach to gear development, a hyperbolic basic concept was
developed that can describe most of the known constant-ratio gear types. In addition to the free
choice of two axes and numbers of teeth, including negative numbers for internal gears, there are
three further continuous parameters for calculating the kinematic design, which describe the
external shape of the gear. This calculation basis unfolds the greatest potential in connection with
the freedom that young manufacturing processes with plastic, e.g. injection moulding, allow. The
manufacturing restrictions here are generally different to those for machining processes.
Nevertheless, all conventional manufacturing processes can also be modelled with the calculation
concept based on the conjugation of surface points.
The approach of describing a consistent calculation process for all types of gearing involved shows
which challenges could be solved in geometry calculation. This is demonstrated using the example
of a planetary gearbox with internal helical gearing, which is now produced in series for the
automotive industry.
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トカマクプラズマにおけるプラズマ回転の動的形成過程上杉, 喜彦, 高村, 秀一, 大野, 哲靖, 叶, 民友 03 1900 (has links)
科学研究費補助金 研究種目:基盤研究(B)(2) 課題番号:11480113 研究代表者:上杉 喜彦 研究期間:1999-2001年度
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Study of the pathophysiological role of nitric oxide on the amyloid-induced toxicity attending to the biochemical modifications and cellular damagesGuix Ràfols, Francesc Xavier 22 January 2009 (has links)
Aquesta tesi demostra que el peroxinitrit produït com a conseqüència del pèptid beta-amiloide (A) contribueix l'augment de la relació A42/A40 que ocorre a la malaltia d'Alzheimer. L'A42 contribueix a l'aparició de la malaltia degut a la seva major toxicitat (quan es compara amb l'A40) que resulta d'una gran estabilitat i capacitat agregativa. A més el peroxinitrit incrementa la toxicitat d'aquest degut a què potencia la seva agregació en forma d'oligomers altament tòxics. De fet els oligomers formats de nitro-A42 presenten una major toxicitat que aquells formats de A42 . En conjunt aquest resultats senyalen l'important paper que l'A42 té en la malaltia d'Alzheimer. Per altra banda, des de la identificació dels agregats d'A i la subseqüent formació dels cabdells neurofibrilars (NFT) com a els dos trets distintius de la malaltia, un gran esforç s'ha dedicat a establir els mecanismes moleculars que uneixen ambdós processos. Aquesta tesi demostra que el peroxinitrit format a partir de l'agregació de d'Ai la conseqüent nitrotirosinació de proteïnes, potencia l'agregació de la proteïna tau en forma de fibres. D'aquesta forma, la nitrotirosinació de la proteïna triosafosfat isomerasa (TPI) podria ser el vincle entre la toxicitat derivada del agregats d'Ai la patologia derivada de la proteïna tau. Per tant, la nitrotirosinació de la TPI podria explicar la progressió temporal que ocorre als cervells de pacients amb la malaltia d'Alzheimer des de la toxicitat induïda per l'Ai l'aparició dels NFT. Els resultats presentats en aquesta tesi podrien obrir nous aspectes en la recerca de la malaltia d'Alzheimer així com en altres malalties que cursin amb estrès oxidatiu i plegament erroni de proteïnes. / This thesis demonstrates that amyloid ß-peptide (Aß)-induced peroxynitrite contributes to the switch of the Aβ42/Aβ40 ratio that occurs in Alzheimer's disease (AD). Since Aβ42 is more toxic due to its higher aggregation and stability, it contributes to the trigger of the disease. In addition the aggregation of Aβ42 in form of the highly toxic oligomers is incremented by the presence of peroxynitrite. Moreover, these nitro-Aß42 oligomers are more toxic than those non-nitrated. All these results support the important role of peroxynitrite in AD etiology. Furthermore, since the identification of Aß accumulation and the subsequent formation of neurofibrillary tangles (NFT) as the two defining pathological hallmarks of AD, a fair amount of research on AD has been driven by the need to find the molecular mechanism linking Aß and NFT. This thesis shows the Aß-induced peroxynitrite, and the consequent nitrotyrosination of proteins, promotes tau fibrillization. Thus triosephosphate isomerase (TPI) nitrotyrosination could be the link between Aß-induced toxicity and tau pathology. Therefore, TPI nitrotyrosination may explain the temporal progression from Aß toxicity to NFT formation in AD brain. The work presented in this thesis could open a novel angle in the research of the pathophysiology of AD and could also have an impact to the research in other neurodegenerative diseases involving oxidative stress and protein misfolding.
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