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Nisar, Zeeshan. „Self-supervised learning in the presence of limited labelled data for digital histopathology“. Electronic Thesis or Diss., Strasbourg, 2024. http://www.theses.fr/2024STRAD016.
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Un défi majeur dans l'application de l'apprentissage profond à l'histopathologie réside dans la variation des colorations, à la fois inter et intra-coloration. Les modèles d'apprentissage profond entraînés sur une seule coloration (ou domaine) échouent souvent sur d'autres, même pour la même tâche (par exemple, la segmentation des glomérules rénaux). L'annotation de chaque coloration est coûteuse et chronophage, ce qui pousse les chercheurs à explorer des méthodes de transfert de coloration basées sur l'adaptation de domaine. Celles-ci visent à réaliser une segmentation multi-coloration en utilisant des annotations d'une seule coloration, mais sont limitées par l'introduction d'un décalage de domaine, réduisant ainsi les performances. La détection et la quantification de ce décalage sont essentielles. Cette thèse se concentre sur des méthodes non supervisées pour développer une métrique de détection du décalage et propose une approche de transfert de coloration pour le minimiser. Bien que ces algorithmes réduisent le besoin d'annotations, ils peuvent être limités pour certains tissus. Cette thèse propose donc une amélioration via l'auto-supervisionA key challenge in applying deep learning to histopathology is the variation in stainings, both inter and intra-stain. Deep learning models trained on one stain (or domain) often fail on others, even for the same task (e.g., kidney glomeruli segmentation). Labelling each stain is expensive and time-consuming, prompting researchers to explore domain adaptation based stain-transfer methods. These aim to perform multi-stain segmentation using labels from only one stain but are limited by the introduction of domain shift, reducing performance. Detecting and quantifying this domain shift is important. This thesis focuses on unsupervised methods to develop a metric for detecting domain shift and proposes a novel stain-transfer approach to minimise it. While multi-stain algorithms reduce the need for labels in target stains, they may struggle with tissue types lacking source-stain labels. To address this, the thesis focuses to improve multi-stain segmentation with less reliance on labelled data using self-supervision. While this thesis focused on kidney glomeruli segmentation, the proposed methods are designed to be applicable to other histopathology tasks and domains, including medical imaging and computer vision
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Sun, Xiaowei. „Interaction of green tea or black tea polyphenols with protein in the presence or absence of other small ligands“. Miami University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=miami1556296109059913.
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3
Duck, Graham Ian. „Distributed Bragg grating sensing, strain transfer mechanics and experiments“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ58592.pdf.
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Dillard, Joshua Ryan. „Demographics and Transfer of Escherichia coli Within Bos taurus Populations“. DigitalCommons@CalPoly, 2015. https://digitalcommons.calpoly.edu/theses/1484.
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In the United States, symptoms caused by pathogenic strains of Escherichia coli are on the rise. A major source of these pathogenic strains is the E. coli in the digestive tract of cattle. The purpose of this project was to determine if E. coli are transferred between individuals of the same species and if interspecies transmission is possible. Proximity of cattle was also studied as a contributing factor to the transfer of E. coli. To accomplish this goal, E. coli isolates from cattle and cohabitating ground squirrels were compared through a new method of bacterial strain typing called pyroprinting. Bulls from the Cal Poly Bull Test were sampled every summer from May to September when around 200 bulls from ranches across California are housed together to be tested and eventually auctioned off. The impact of cattle origin (ranch, city) and habitation (pen) on E.coli isolate strain type were evaluated via pyroprinting . The cattle were studied to see if transfer was related to proximity of cohabitation. Since the complete population of intestinal E. coli could not be sampled, transfer could not be directly seen. The probability of sharing E. coli in each time point was used to infer transfer. There was an increase in the probability of sharing E. coli from the May sample date to the September date, indicating that some form of transfer was occurring. There was an even greater increase in the probability of sharing E. coli when the bulls were housed in close proximity. Lastly, ground squirrels cohabitating in the area were found to house some of the same strains as the cattle. This makes transfer between squirrels and cattle a possibility. Overall, this paper shows that the intestinal E. coli composition of bulls may be readily altered by the introduction of new bulls into a population.
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Zutavern, Zachary Scott. „Fiber optic strain gauge calibration and dynamic flexibility transfer function identification in magnetic bearings“. Thesis, Texas A&M University, 2003. http://hdl.handle.net/1969.1/152.
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Historical attempts to measure forces in magnetic bearings have been unsuccessful as a result of relatively high uncertainties. Recent advances in the strain-gauge technology have provided a new method for measuring magnetic bearing forces. Fiber optic strain gauges are roughly 100 times more sensitive than conventional strain gauges and are not affected by electro-magnetic interference. At the Texas A&M Turbomachinery Laboratory, installing the fiber-optic strain gauges in magnetic bearings has produced force measurements with low uncertainties. Dynamic flexibility transfer functions exhibiting noticeable gyroscopic coupling have been identified and compared with results of a finite element model. The comparison has verified the effectiveness of using magnetic bearings as calibrated exciters in rotordynamic testing. Many applications including opportunities for testing unexplained rotordynamic phenomena are now feasible.
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Caruthers, Elena Joy Caruthers. „Investigating Lower Limb Muscle Function during the Sit to Stand Transfer and Stair Climbing“. The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1498569178798838.
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7
Nowak, Stephanie Beth. „Understanding Time-Variant Stress-Strain in Turkey: A Numerical Modeling Approach“. Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/26072.
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Over the past century, a series of large (> 6.5) magnitude earthquakes have struck along the North Anatolian Fault Zone (NAFZ) in Turkey in a roughly East to West progression. The progression of this earthquake sequence began in 1939 with the Ms 8.0 earthquake near the town of Erzincan and continued westward, with two of the most recent ruptures occurring near the Sea of Marmara in 1999. The sequential nature of ruptures along this fault zone implies that there is a connection between the location of the previous rupture and that of the future rupture zones. This study focuses on understanding how previous rupture events and tectonic influences affect the stress regime of the NAFZ and how these stress changes affect the probability of future rupture along any unbroken segments of the fault zone using a two dimensional finite element modeling program.
In this study, stress changes due to an earthquake are estimated using the slip history of the event, estimations of rock and fault properties along the fault zone (elastic parameters), and the far-field tectonic influence due to plate motions. Stress changes are not measured directly. The stress regime is then used to calculate the probability of rupture along another segment of the fault zone.
This study found that when improper estimates of rock properties are utilized, the stress changes may be under- or over- estimated by as much as 350% or more. Because these calculated stress changes are used in probability calculations, the estimates of probability can be off by as much as 20%. A two dimensional model was built to reflect the interpreted geophysical and geological variations in elastic parameters and the 1939 through 1999 rupture sequence was modeled. The far-field tectonic influence due to plate motions contributed between 1 and 4 bars of stress to the unbroken segments of the fault zone while earthquake events transferred up to 50 bars of stress to the adjacent portions of the fault zone.
The 1999 rupture events near Izmit and Düzce have increased the probability of rupture during the next ten years along faults in the Marmara Sea to 38% while decreasing the probability of rupture along the faults near the city of Bursa by ~6%. Large amounts of strain accumulation are interpreted along faults in the Marmara Sea, further compounding the case for a large rupture event occurring in that area in the future.Ph. D.
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Intiang, Jittakant. „Use of triple beam resonant gauges in torque measurement transfer standard“. Thesis, Brunel University, 2010. http://bura.brunel.ac.uk/handle/2438/4500.
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A new torque transfer standard using metallic TBTF resonant sensor was developed to overcome the overload capability problem which occurs with conventional metallic resistance strain gauges. Previous research work, however, has shown that the first prototype of the metallic TBTF resonant sensor was not suitable for use in a torque transfer standard due to its size and subsequent sensitivity to parasitic lateral forces. To maximize the benefits from this sensor, particularly overload capability and long-term stability, in the high accuracy torque measurement application area, there is a need to develop significantly smaller devices. The aim of this thesis is to research through FEA modelling and experimental characterisation the key performance parameters required to produce a miniaturised metallic TBTF resonant sensor that provides better performance when applied in a torque measurement system. For high accuracy any torque transducer using these sensors ought to have low sensitivity to parasitic influences such as bending moments and lateral forces, which can only be achieved with reduced size. The problems with the existing design, key design issues, possible configuration and packaging solutions of the metallic TBTF resonant sensor that could be used for achieving a higher accuracy torque transfer standard are considered. Two designs of miniaturised metallic TBTF resonant sensors, SL20 and SL12, are considered and experimentally investigated. The lateral forces are reduced by 52% for SL20 design and by 80% for SL12 design when compared to the original SL40 design. A torque transducer using the SL20 design was calibrated falling into the Torque Transfer Standard class of accuracy 1 category, uncertainty 0.8%. A torque transducer using the SL12 design was made and calibration showed a class of accuracy 0.5 category, uncertainty 0.2%. The results from this research indicate that the SL12 design is suitable for use in a torque transfer standard. The SL12 design is optimal and the smallest size possible based on the overload capability design criteria requiring the tine cross sectional area to remain constant.
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Ruchi, Sangeetika. „Computational Modeling of Laser Therapy of Port-Wine Stains- Based on Reduced Scattering Method“. University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1428070493.
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Sears, Nicholas C. „Investigations into the Quasi-Static and Dynamic Properties of Flexible Hybrid Electronic Material Systems“. The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1525278328687427.
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Zhao, Weixin. „Development of a portable optical strain sensor with applications to diagnostic testing of prestressed concrete“. Diss., Kansas State University, 2011. http://hdl.handle.net/2097/19764.
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Doctor of PhilosophyDepartment of Mechanical and Nuclear Engineering
B. Terry Beck
The current experimental method to determine the transfer length in prestressed concrete members consists of measuring concrete surface strains before and after de-tensioning with a mechanical strain gage. The method is prone to significant human errors and inaccuracies. In addition, since it is a time-consuming and tedious process, transfer lengths are seldom if ever measured on a production basis. A rapid, non-contact method for determining transfer lengths in prestressed concrete members has been developed. The new method utilizes laser-speckle patterns that are generated and digitally recorded at various points along the prestressed concrete member. User-friendly software incorporating robust and fast digital image processing algorithms was developed by the author to extract the surface strain information from the captured speckle patterns. Based on the laser speckle measurement technique, four (4) successively improved generations of designs have been made. A prototype was fabricated for each design either on an optical breadboard for concept validation, or in a portable self-contained unit for field testing. For each design, improvements were made based on the knowledge learned through the testing of the previous version prototype. The most recent generation prototype, incorporating a unique modular design concept and self-calibration function, has several preferable features. These include flexible adjustment of the gauge length, easy expansion to two-axis strain measurement, robustness and higher accuracy. Extensive testing has been conducted in the laboratory environment for validation of the sensor’s capability in concrete surface strain measurement. The experimental results from the laboratory testing have shown that the measurement precision of this new laser speckle strain measurement technique can easily achieve 20 microstrain. Comparison of the new sensor measurement results with those obtained using traditional strain gauges (Whittemore gauge and the electrical resistance strain gauge) showed excellent agreement. Furthermore, the laser speckle strain sensor was applied to transfer length measurement of typical prestressed concrete beams for both short term and long term monitoring. The measurement of transfer length by the sensor was unprecedented since it appears that it was the first time that laser speckle technique was applied to prestressed concrete inspection, and particularly for use in transfer length measurement. In the subsequent field application of the laser speckle strain sensor in a CXT railroad cross-tie plant, the technique reached 50 microstrain resolution, comparable to what could be obtained using mechanical gauge technology. It was also demonstrated that the technique was able to withstand extremely harsh manufacturing environments, making possible transfer length measurement on a production basis for the first time.
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Stein, Alexander [Verfasser]. „Fourier-Transform-Spektroskopie an zweiatomigen Molekülen gebildet aus Alkali- und/oder Erdalkaliatomen / Alexander Stein“. Hannover : Technische Informationsbibliothek (TIB), 2016. http://d-nb.info/1170428770/34.
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Karlsson, Alexander, und Eric Marcus. „Evaluation of Strain and Temperature Measurements with Fiber Bragg Grating for Loss Verification and Heat Transfer of Ball Bearings“. Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-86149.
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Volvo Cars is in a change of producing only electric and hybrid cars by 2025.Subcomponent testing is a crucial part to ensure the quality of the individual buildingblocks in an electric machine. Any way of making these tests more reliable and less timeconsuming is of great interest at Volvo. Force and temperature on bearings are especiallyhard to measure accurately, because of their placement and dynamic behavior. Accurateand reliable measurements is also a vital part in creating realistic Computer-AidedEngineering (CAE) models for simulation purposes. Simulations on bearings could lead tobetter bearing choices and accelerate the design process. This could increase bearing lifeand increase the Electrical Vehicle (EV) range due to minimized friction losses. FiberBragg Grating (FBG) sensors is a technology that has some key advantages overconventional sensors. They are immune to EMI, smaller in size, can have multiple sensorsin one fiber and can measure multiple physical quantities at the same time. Volvo Cars isinterested in investigating whether this sensor technology could be a candidate forreplacing some of the current measurement setup configurations.The project was divided into three parts, validating sensor equipment, find method forinstallation and measurement on a bearing and development of a CAE model for bearinglosses and heat transfer. To validate the sensor equipment a Measurement SystemAnalysis (MSA) was performed on two FBG fibers, one FBG isolated from strain fortemperature measurement and one FBG array with multiple sensing points. From theMSA it could be seen that the FBG temperature sensor had a total uncertainty of 3.4 °CThe FBG array had a strain uncertainty of 1.04 μ𝜀 and a temperature uncertainty of 0.4 °C.The uncertainty of both the FBG array and the FBG temperature sensor is highlydependent on the calibration of the sensitivity constant. The force measurement on thebearing was done with a concept based on the wavelength difference, produced by strain,between two FBG sensors. The concept was tested in a dynamic component rig where anaxial force could be applied, and the wavelength difference measured. The temperatureon the outer ring of the bearing was measured using an FBG isolated from strain. The testresults were promising, but since the FBG is sensitive to temperature and strain theincreased temperature difference between the two fibers affected the results. Thecalibration method needs to be compensated for the increased temperature differencebetween the fibers which is generated when the rotational speed is increased, and thiscould not be done with a single temperature measurement. The two developed CAEmodels was both constructed in MATLAB and showed similar behavior with experimentaltests done by others. To validate the models, physical test for heat transfer and bearinglosses should be performed.
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Koop, Julie L. „A new strain of Wolbachia in the harlequin beetle riding pseudoscorpion male killing, reproductive compensation and horizontal gene transfer /“. abstract, 2008. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1460764.
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Harold, Douglas A. „An Evaluation of Optical Fiber Strain Sensing for Engineering Applications“. Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/41239.
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A fatigue test has been performed on 7075-T651 aluminum specimens which were bonded with polyimide coated optical fibers with discrete Bragg gratings. These fibers were bonded with AE-10 strain gage adhesive. The results indicate that lower strain amplitudes do not produce cause for concern, but that larger strain amplitudes (on the order of 3500 μ) may cause some sensors to become unreliable.
The strain response of acrylate coated optical fiber strain sensors bonded to aluminum specimens with AE-10 and M-Bond 200 strain gage adhesives was investigated with both axial and cantilever beam tests. These results were compared to both the strain response of conventional strain gages and to model predictions. The results indicate that only about 82.6% of the strain in the specimen was transferred through the glue line and fiber coating into the fiber. Thus, multiplying by a strain transfer factor of approximately 1.21 was sufficient to correct the optical fiber strain output. This effect was found to be independent of the adhesive used and independent of the three-dimensional profile of the glue line used to attach the fiber. Finally, this effect did not depend on whether the fiber had a polyimide or an acrylate coating.
Further investigation was conducted on the feasibility of using optical fiber strain sensors for monitoring subcritical damage (such as matrix cracks) in fiber reinforced composite materials. These results indicate that an array of optical fibers which monitor the strain profile on both sides of a composite panel may be sufficient for these purposesMaster of Science
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Demchak, Tony Eugene. „Reform, foreign technology, and leadership in the Russian Imperial and Soviet navies, 1881–1941“. Diss., Kansas State University, 2016. http://hdl.handle.net/2097/32720.
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Doctor of PhilosophyHistory
Michael Krysko
David R. Stone
This dissertation examines the shifting patterns of naval reform and the implementation of foreign technology in the Russian Empire and Soviet Union from Alexander III’s ascension to the Imperial throne in 1881 up to the outset of Operation Barbarossa in 1941. During this period, neither the Russian Imperial Fleet nor the Red Navy had a coherent, overall strategic plan. Instead, the expansion and modernization of the fleet was left largely to the whims of the ruler or his chosen representative. The Russian Imperial period, prior to the Russo-Japanese War, was characterized by the overbearing influence of General Admiral Grand Duke Alexei Alexandrovich, who haphazardly directed acquisition efforts and systematically opposed efforts to deal with the potential threat that Japan posed. The Russo-Japanese War and subsequent downfall of the Grand Duke forced Emperor Nicholas II to assert his own opinions, which vacillated between a coastal defense navy and a powerful battleship-centered navy superior to the one at the bottom of the Pacific Ocean. In the Soviet era, the dominant trend was benign neglect, as the Red Navy enjoyed relative autonomy for most of the 1920s, even as the Kronstadt Rebellion of 1921 ended the Red Navy’s independence from the Red Army. M. V. Frunze, the People’s Commissar of the Army of Navy for eighteen months in 1925 and 1926, shifted the navy from the vaguely Mahanian theoretical traditions of the past to a modern, proletarian vision of a navy devoted to joint actions with the army and a fleet composed mainly of submarines and light surface vessels. As in the Imperial period, these were general guidelines rather than an all-encompassing policy. The pattern of benign neglect was shattered only in 1935, when Stalin unilaterally imposed his own designs for a mighty offensive fleet on the Soviet military, a plan that was only interrupted by the outbreak of World War II.
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Heaton-Adegbile, Philip. „In-vitro assessment of load transfer and strain distribution across the cement-bone and bone-implant interfaces in artificially replaced acetabulum“. Thesis, University of Portsmouth, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.424079.
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Aydemir, Evsen Ozlem. „Investigation of strain related to displacement transfer and along-strike variation using 3-D seismic interpretation, physical modelling and computer-graphics visualization“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0004/MQ28173.pdf.
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Vice, Garrett S. „Structural controls of the Astor Pass-Terraced Hills geothermal system in a region of strain transfer in the western Great Basin, northwestern Nevada“. abstract and full text PDF (UNR users only), 2008. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1456425.
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Elbaz, Anas. „Sources laser compatibles silicium à base de Ge et GeSn à bande interdite directe“. Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS077/document.
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La photonique silicium connait un essor très important, porté notamment par la réalisation de câbles optiques actifs permettant de transférer optiquement des données à haut débit dans des environnements de type “High performance computing” ou “data center”. L'intégration de cette source laser est un enjeu très important pour la photonique silicium. Actuellement, ces sources sont obtenues avec des semi-conducteurs de type III-V sur substrats GaAs ou InP. Leur intégration dans une filière silicium est délicate et surtout ne permet pas de tirer pleinement parti de l'environnement de fabrication CMOS de la microélectronique.L'intégration d'une source optique monolithique représente donc un enjeu considérable. Les éléments de la colonne IV (Si, Ge) sont des semi-conducteurs à bande interdite indirecte, avec une faible efficacité de recombinaison radiative, et ne sont donc pas a priori de bons candidats. Un changement de paradigme est cependant en cours avec la récente démonstration qu'il était possible de manipuler la structure de bande des semi-conducteurs à base de germanium pour les rendre à bande interdite directe, i.e. les transformer en émetteurs efficaces. Cette ingénierie peut être réalisée soit en utilisant des tenseurs externes comme le nitrure de silicium soit en réalisant des alliages avec de l'étain (GeSn), ou en combinant les deux. Cette thèse porte donc sur l'étude de ces semi-conducteurs à bande interdite directe, avec pour objectif de faire la démonstration d'un laser avec ce nouveau type de matériauxSilicon photonics is experiencing a very important development. The laser source integration is a very important issue in silicon photonics. Currently, these sources are obtained with type III-V semiconductors on GaAs or InP substrates. Their integration in a silicon industry is delicate and above all does not allow to take full advantage of a CMOS environment.The integration of a monolithically optical source represents an important challenge. The elements of column IV (Si, Ge) are indirect bandgap semiconductors, with low radiative recombination efficiency, and therefore are not good candidates. However, a paradigm shift is underway with the recent demonstration that it was possible to manipulate the band structure of germanium-based semiconductors to direct bandgap, i.e. transform them into efficient transmitters. This engineering can be achieved either by using external tensors such as silicon nitride or by making alloys with tin (GeSn), or by combining both. This thesis deals with the study of these direct bandgap semiconductors. The goal will be to demonstrate a laser with this new type of materials
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Champiré, Florian. „Étude expérimentale du comportement hydro-mécanique de la terre crue compactée pour la construction“. Thesis, Lyon, 2017. http://www.theses.fr/2017LYSET007/document.
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Le matériau terre peut apporter une réponse face aux problèmes que les constructions modernes rencontrent en termes d’enjeux sociétaux, économiques et écologiques. Cependant, les difficultés à comprendre et à prédire son comportement représente un obstacle au développement de cette technique dans les pays développés. Cette thèse s’insère dans un projet de recherche appelé « Primaterre » et financé par l’Agence Nationale de la Recherche française (ANR). Il vise à apporter les connaissances scientifiques nécessaires afin de pallier ce manque et aider à établir des règlementations adaptées. Ce travail s’intéresse plus particulièrement à l’impact de l’eau sur le comportement mécanique de la matrice fine du matériau, qui a un impact essentiel sur le comportement du matériau dans son ensemble. Cette matrice est constituée de sables, de limons, et d’argiles, et ce sur trois types de terres prélevées sur d’anciennes constructions en pisé. Afin de réaliser des échantillons les plus identiques et homogènes possible, un moule a tout d’abord été conçu, ce qui a permis de travailler avec des échantillons cylindriques de 3,5cm de diamètre et 7cm de hauteur. Une cellule triaxiale a été utilisée et, la seconde étape a été de concevoir les dispositifs permettant la mesure des déformations axiales et radiales, le conditionnement à température contrôlée et l’imposition d’un flux d’air humide variable de part et d’autre de l’échantillon. Différents types d’essais ont alors pu être réalisés : des essais triaxiaux à différent taux d’humidité relative ainsi que des essais de gonflement. Les paramètres mécaniques obtenus ont pu être analysés à la lumière des caractéristiques matériaux mesurées en parallèle. Enfin, l’analyse des essais de gonflement a été menée à bien à l’aide d’un modèle numérique, et ce afin de pouvoir évaluer des paramètres caractéristiques plus complexes. Ce travail de thèse se conclut par une étude supplémentaire, visant à évaluer l’impact du changement de taille d’échantillon sur les paramètres mécaniques mesurés précédemment. Ces essais ont été effectués sur des échantillons approximativement deux fois plus grands, et grâce à un dispositif expérimental plus simple, utilisant la mesure par corrélation d’imagesEarthen buildings can provide an answer to face difficulties in modern constructions in both terms of sociology, economics as well as ecology. However, the difficulty to understand and to predict their behavior prevent the spreading of this technique in developed countries. This PhD is part of a research program called “Primaterre” and founded by the French National Agency for Research. It aims at providing the necessary scientific knowledge to overcome this lack and at helping the creation of appropriate standards. This work is more precisely focusing on the impact of water on the mechanical behavior of the fine proportion of the material, including sand, silt and clay, and on three different earths coming from existing rammed earth constructions. In order to be able to produce samples as identical and homogeneous as possible, a mold has first been designed, which enable to manufacture cylindrical samples with diameter of 3.5cm and height of 7cm. A triaxial cell was used and, the second step was to design different devices allowing the measurement of axial and radial deformations, the conditioning at constant temperature, and the command of a variable moist air flux at both sides of the sample. Different types of tests have thus been realized : triaxial tests at different relative humidity, as well as swelling tests. The mechanical parameters thus obtained have been analyzed in comparison with material characteristics measured in parallel. Finally, results of swelling tests have been analysed using numerical modelling, in order to assess more complex material characteristics. This thesis work ends with an additional study, aiming at evaluating the impact of scale change on the mechanical parameters previously measured. Tests have been conducted on sample approximatively twice larger, and thanks to a simpler experimental device using measurement through image correlation
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Nejedlý, Pavel. „Návrh a pevnostní kontrola senzoru pro měření teplot a sil při válcování za tepla“. Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2009. http://www.nusl.cz/ntk/nusl-228581.
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In the process of hot rolling is roll surface thermo-mechanically stressed. To define lifetime of roll or to increase it by change of thermal mode, temperatures and forces acting on this roll need to be known. For this purpose should be used sensors, that are placed near by surface of roll. Aim of the first part of diploma thesis is to debug 2D computing model (MKP) to achieve the match of temperature graphs with experimentally measured values, which was recorded by temperature sensors in real process of rolling. In the second part the same temperature boundary conditions are applied on 3D model, which is used to solve mechanical strength check of the temperature sensor. The last part of thesis is design and verification of mechanical strength of the designed force sensor. The used boundary conditions were acquired in Laboratory of heat transfer and flow. The computing system ANSYS 11 is used to design a model of geometry and numerical calculation. This diploma thesis will be used as donating solution for the granted project, which started in this year with Laboratory of heat transfer and flow partnership.
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Leo, Riccardo. „The axial response of offshore piles in sand from large scale tests“. Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017.
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This thesis focuses on deep foundations used in offshore environment, in particular for offshore wind turbines. Piles are necessary when the bearing capacity of the shallow soil layers is not enough to ensure stability. Piles can work on both axial and lateral response. In the thesis only axially loaded piles will be considered. The analysis of the axial behavior of piles should be considered in terms of ultimate capacity as well as the load transfer mechanism between the pile and the soil.
The technical aim of this thesis concerns the understanding of the load transfer curves, their extrapolation and the exploration of load distribution along the pile during a given load. To achieve this, a thorough study of literature on current design methods is carried out and two instrumented piles will be analysed in order to understand how the load is distributed along the pile shaft and how experimental load transfer curves can be extrapolated.
The more general aim of this work is to optimize design procedures and try to reduce the cost related piles and their installation in offshore environment, since it is quite known to be higher than onshore fields, as it will be explained in the first chapter of this thesis.
A geotechnical software IGtH Pile developed by the Institute of geotechnical Engineering (IGtH), Leibniz Universität Hannover will be used in the evaluation of the ultimate capacity and the results will be compared with a Matlab code developed at the IWES research institute.
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Magnin, Jean-Pierre. „Isolement d'une souche Hfr de la bactérie photosynthétique Rhodobacter capsulatus et cartographie du chromosome“. Grenoble 1, 1987. http://www.theses.fr/1987GRE10151.
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Ghrib, Abdelhamid. „Ingénierie de contrainte dans des cavités germanium : vers une application de laser intégré sur silicium“. Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112357/document.
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Le germanium dopé n et contraint en tension est un candidat potentiel pour démontrer un laser sur silicium compatible avec un environnement CMOS. Dans ce travail de thèse, j’ai d’abord développé un formalisme qui permet de calculer le gain optique en fonction de la déformation en tension, du dopage n et de l’injection des porteurs. Une technique de transfert de déformation via le dépôt de couche contrainte de SiN a été optimisée. J’ai réalisé plusieurs types de cavités germanium contraintes sous forme de guides d’onde et de microdisques. Le transfert de déformation a été optimisé par sous-gravure et par une méthode de bi-encapsulation qui a permis d’aboutir à une déformation biaxiale homogène et élevée de l’ordre de 1.5%. L’évaluation des déformations a été confrontée à des simulations par éléments finis, photoluminescence et spectroscopie Raman. L’étude expérimentale et théorique des guides d’onde a montré l’avantage de la direction <100> par rapport à la direction <110> permettant une injection plus efficace de porteurs en centre de zone. L’étude expérimentale des microdisques a permis d’observer des modes de galerie avec un facteur de qualité Q = 1540 à λ = 1940 nm. D’autre part, j’ai mis en évidence par photoluminescence la présence d’un fort dopage de 4×10¹⁹ cm⁻³ dans des couches germanium sur silicium épitaxiées par épitaxie par jets moléculaires utilisant une technique de co-dopage. Une modélisation du gain modal a permis de mettre en exergue l’effet du gradient de déformation dans le volume de la cavité. L’élargissement homogène a été introduit dans la modélisation du gain optique afin de prendre en compte l’impact d’un dopage élevéTensile strained and n-doped germanium is a potential candidate to demonstrate a laser on silicon in a CMOS-compatible environment. In this thesis, I developed a formalism to calculate the optical gain as a function of tensile strain, n-doping and carrier injection. A tensile strain transfer technique via strained SiN layer deposition has been optimized. I realized several types of strained germanium cavities. Tensile strain transfer was optimized by under-etching and a bi-encapsulation technique which allowed to achieve a high and uniform biaxial strain up to 1.5%. The evaluation of strain level was faced with finite elements modeling, photoluminescence and Raman spectroscopy. The experimental and theoretical study of the waveguides showed the advantage of the <100> direction as compared with the <110> direction for more efficient carrier injection at zone center. The experimental study of microdisks allowed us to observe gallery modes with quality factor up to Q = 1540 at λ= 1940 nm. On the other hand, photoluminescence enhancement has shown the presence of a heavy doping of 4×10¹⁹ cm⁻³ in germanium on silicon layers grown by molecular beam epitaxy and using a co-doping technique. Modeling the modal gain helped to emphasize the effect of the strain gradient in the cavity volume. The homogeneous broadening was introduced in the optical gain modeling to take into account the impact of a high doping
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Nguyen, Tran. „Optical measurement of shape and deformation fields on challenging surfaces“. Thesis, Loughborough University, 2012. https://dspace.lboro.ac.uk/2134/10551.
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A multiple-sensor optical shape measurement system (SMS) based on the principle of white-light fringe projection has been developed and commercialised by Loughborough University and Phase Vision Ltd for over 10 years. The use of the temporal phase unwrapping technique allows precise and dense shape measurements of complex surfaces; and the photogrammetry-based calibration technique offers the ability to calibrate multiple sensors simultaneously in order to achieve 360° measurement coverage. Nevertheless, to enhance the applicability of the SMS in industrial environments, further developments are needed (i) to improve the calibration speed for quicker deployment, (ii) to broaden the application range from shape measurement to deformation field measurement, and (iii) to tackle practically-challenging surfaces of which specular components may disrupt the acquired data and result in spurious measurements. The calibration process typically requires manual positioning of an artefact (i.e., reference object) at many locations within the view of the sensors. This is not only timeconsuming but also complicated for an operator with average knowledge of metrology. This thesis introduces an automated artefact positioning system which enables automatic and optimised distribution of the artefacts, automatic prediction of their whereabouts to increase the artefact detection speed and robustness, and thereby greater overall calibration performance. This thesis also describes a novel technique that integrates the digital image correlation (DIC) technique into the present fringe projection SMS for the purpose of simultaneous shape and deformation field measurement. This combined technique offers three key advantages: (a) the ability to deal with geometrical discontinuities which are commonly present on mechanical surfaces and currently challenging to most deformation measurement methods, (b) the ability to measure 3D displacement fields with a basic single-camera single-projector SMS with no additional hardware components, and (c) the simple implementation on a multiple-sensor hardware platform to achieve complete coverage of large-scale and complex samples, with the resulting displacement fields automatically lying in a single global coordinate system. A displacement measurement accuracy of ≃ 1/12,000 of the measurement volume, which is comparable to that of an industry-standard DIC system, has been achieved. The applications of this novel technique to several structural tests of aircraft wing panels on-site at the research centre of Airbus UK in Filton are also presented. Mechanical components with shiny surface finish and complex geometry may introduce another challenge to present fringe projection techniques. In certain circumstances, multiple reflections of the projected fringes on an object surface may cause ambiguity in the phase estimation process and result in incorrect coordinate measurements. This thesis presents a new technique which adopts a Fourier domain ranging (FDR) method to correctly identifying multiple phase signals and enables unambiguous triangulation for a measured coordinate. Experiments of the new FDR technique on various types of surfaces have shown promising results as compared to the traditional phase unwrapping techniques.
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Pillet, Guillaume. „Diffusion thermique de nanocarbones au voisinage d'une surface de polymère thermoplastique“. Thesis, Toulouse 3, 2019. http://www.theses.fr/2019TOU30247.
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Les applications intégrant les nanotubes de carbone augmentent rapidement maintenant que leur bio-toxicité a été évaluée comme limitée. Une fois intégrés dans une matrice polymère, il est possible d'ajuster les propriétés mécaniques et électriques de celle-ci. Dans cette thèse, nous avons étudié la formation et la diffusion de films minces de nanotubes de carbones multi-parois (MWCNT) à la surface d'un polymère thermoplastique haute performance, le poly éther éther cétone (PEEK) possédant un point de fusion élevé (342 ° C). La synthèse des films composites conducteurs électriques comportent différentes étapes de préparation (dispersion dans des liquides, création d'interface en jouant sur les miscibilités). L'optimisation des paramètres de recuit a permis d'avoir des mesures électriques et optiques exploitables. Nous avons analysé en détail la diffusion du polymère dans le film de nanotubes et étudié la dynamique du front de diffusion à l'aide de la microscopie électronique. Un modèle simple pour la conductivité électrique permet expliquer quantitativement les observations expérimentales. La corrélation entre la conductivité électrique et la transmittance optique d'une couche composite donnée, permet d'étudier la diffusion en fonction de la durée de recuit. Les propriétés piézo-électriques des films composites minces fabriqués ne sont que partiellement réversibles en raison du transfert limité des contraintes mécaniques au réseau de nanotubes de carbone. En contrôlant l'imprégnation des agglomérats de nanotubes par le polymère, il est possible de contrôler les propriétés électriques de la surface, ce qui peut avoir des applications pour la réparation de surfaces composites et la restauration de leurs propriétés électriques ou mécaniques. La spectroscopie Raman et la microscopie électronique à transmission ont été utilisées pour la caractérisation structurelle. Le travail présenté est définitivement multidisciplinaire couvrant la synthèse, la caractérisation structurelle et mesures de transport électronique pour comprendre la formation de surface composites conductrices électriqueThe use of carbon nanotubes is growing fast since their limited bio-toxicity has been assessed. When embedded in a polymeric matrix, one can tailor the mechanical and electrical properties. In this thesis, we studied the formation and diffusion of multiwall carbon nanotube (MWCNT) thin films at the surface of a high performance thermoplastic polymer, poly-ether-ether-ketone (PEEK) with a high temperature melting point (342 °C). The synthesis and characterization of the electrically conductive composite films consists of different preparation steps (dispersion in liquids, creation of interface by playing on the miscibilities) and the optimization of the annealing parameters followed by electrical and optical measurements. We analyzed in detail the diffusion of the polymer into the nanotube film and studied the diffusion front using electron microscopy. A simple model of the electrical conductivity can explain quantitatively the experimental observations. Correlating the electrical conductivity and optical transmittance of a given composite layer allows studying the diffusion as a function annealing time. Piezo-electrical properties of the fabricated thin composite film are only partially reversible due to limited transfer of mechanical stress to the carbon nanotube network. By controlling the impregnation of the agglomerated nanotubes by the polymer, it is possible to control the electrical properties of the surface which may have applications for the repair of composite surfaces and the restoration of electrical or mechanical surface properties. Raman spectroscopy and transmission electron microscopy have been used for the structural characterization. The presented work is definitively multidisciplinary covering synthesis, structural characterization and electronic transport measurements to understand the formation of electrically conducting surface composites
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Yoshida, Yukihiro. „Effet élastocalorique dans le caoutchouc naturel et le terpolymère : Mécanismes responsables de la variation de température et bilan énergétique sous déformation“. Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI070.
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Les effets électrocaloriques, qui se traduisent par une variation de température induite par une variation d’entropie ont été étudiés comme alternative aux systèmes de réfrigération utilisant un cycle de compression/détente. Le travail de thèse se focalise sur l’étude de l’effet élastocalorique dans le caoutchouc naturel et le terpolymère (P(VDF-TrFE-CTFE). En premier lieu, l’effet élastocalorique dans le caoutchouc naturel qui compte parmi les meilleurs candidats, a été évalué pour des cycles de déformation réalisés avec différentes valeurs d’allongement. Une variation de température de 4 °C a pu être observée. Il est usuel d’utiliser la relation déformation/contrainte en fonction de la variation de température pour évaluer l’effet élastocalorique. Il a été démontré que cette méthode ne peut pas être utilisée dans le cas du caoutchouc naturel et qu’elle doit être remplacée par la mesure de la variation de l’énergie mécanique en fonction de la température. Et dans ce cas, une variation linéaire entre ces deux dernières grandeurs a été observée. En réalisant un bilan d’énergie pendant l’essai, non seulement, le rendement énergétique a pu être évalué mais il a été aussi possible de prendre en compte l’effet Mullins et la cristallisation induite par la déformation pour le caoutchouc naturel. Dans un second temps, l’effet élastocalorique a été étudié sur le terpolymère (P(VDF-TrFE-CTFE), ce qui a permis de montrer qu’il était possible d’obtenir une variation de température de 2.1 °C sous réserver de pré-déformer le terpolymère à plus de 1050 % avant. Par comparaison avec d’autres matériaux présentant une bonne conversion élastocalorique, le fort potentiel de ce matériau a pu être mis en évidence. Enfin, il a été mis en évidence que la plus grande partie de l’énergie mécanique était bien convertie en énergie thermiqueCaloric effects (CEs), which are the phenomena that temperature variation is caused by entropy change, have been investigated for the novel system which might be able to replace conventional vapor compression refrigeration system. In the present thesis, the elastocaloric effect (ElCE) of natural rubber (NR) and terpolymer, poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) (P(VDF-TrFE-CTFE)), was focused. First of all, NR, which is an excellent candidate material for ElCE, was evaluated in cyclic deformation with different strain levels. It was found that NR exhibits temperature variation of around 4.0 °C. In general, the relation between stress/strain versus temperature variation is used to evaluate ElCE. The unsuitability of such evaluation method for NR was demonstrated. The evaluation method for ElCE which uses energy balance was then proposed. A linear relation between the temperature variation caused by ElCE and the applied mechanical energy by deformation was experimentally found. This fact verifies the suitability of the proposed method. Using the energy balance, besides, not only the conversion efficiency but also the influences of the Mullins effect and the strain-induced crystallization on the ElCE of NR were discussed. ElCE of P(VDF-TrFE-CTFE) was also evaluated in order to find out the potential of polymer. It was found that present terpolymer which is not one of the elastomers can also exhibit a large temperature variation, 2.1 °C, caused by ElCE if a large pre-stretch such as more than 1050 % is applied in advance. By comparison with other materials for ElCE, it was demonstrated that P(VDF-TrFE-CTFE) can be a high potential material for ElCE. It was also shown that P(VDF-TrFE-CTFE) converts most of the applied mechanical energy into the heat energy
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Xie, Zhong Jian. „Effet élastocalorique dans le caoutchouc naturel“. Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI025/document.
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Les effets caloriques représentent la capacité d’un matériau à voir son entropie varier sous l’effet d’une sollicitation externe et peuvent être utilisés pour des systèmes de refroidissement à l'état solide en remplacement (ou complément) des dispositifs traditionnels à base de fluides frigorifiques. Dans cette thèse, nous avons cherché à étudier l'effet élastocalorique du caoutchouc naturel. Après une présentation des différents matériaux caloriques et du caoutchouc naturel, le chapitre 2 détaille la caractérisation élastocalorique du caoutchouc naturel, et les résultats sont interprétés à partir de la notion de cristallisation induite par la déformation. Le changement de température adiabatique élastocalorique et la variation d’entropie associée atteignent 9K et 50kJ.m-3.K-1, ce qui est très important comparé aux autres matériaux caloriques. L’effet élastocalorique étant maximum pour une déformation voisine de 4,5, une pré-déformation peut être appliquée pour éviter la zone moindre activité élastocalorique. La mesure directe de l’effet élastocalorique est ensuite comparée à une méthode indirecte déduite du facteur de Clapeyron, et les divergences sont discutées. Dans le chapitre 3, la contrainte et la température élastocalorique sont simulées par un modèle de Flory modifié sur la base de la cristallisation. Il est possible de prédire le comportement contrainte-déformation à différentes températures, ainsi que les variations de température élastocaloriques à température ambiante. Dans le chapitre 4, les effets de la fatigue sur l’effet élastocalorique du caoutchouc naturel sont ensuite étudiés. La résistance à la fatigue pour de grandes amplitudes de déformation est très faible (< 800 cycles). Trois régimes de déformation intermédiaire sont ensuite testés : 0-3, 2-5, et 4-7, et permet d’établir que le régime 2-5 est le plus performant (jusqu’à 100 000 cycles). Dans le dernier chapitre, un modèle de système régénératif de refroidissement à base de matériaux caloriques est développé afin d’établir des lignes directrices pour le choix des matériaux élastocaloriquesIn this thesis, we aimed to study the eC effect of natural rubber (NR) and to prove its potential to act as an eC material primarily. The method for improving the eC effect efficiency and fatigue life of NR were also proposed. The eC effect of NR is characterized directly, and interpretation based on the theory of strain-induced crystallization/crystallite (SIC) is proposed. The eC adiabatic temperature change and isothermal entropy change of NR can be up to 9 K and 50 kJ.m-3.K-1 (56 J.kg-1.K-1), which are larger than most of caloric materials. Two coefficients, eC strain coefficient and eC stress coefficient , are defined for evaluating the eC performance at different strains, where is the specific entropy, is the engineering strain, is the temperature and is the stretching stress. It’s found that both coefficients are maximum for a strain around 4.5, indicating that the highest eC performance occurred at middle strain, which is attributed to the occurrence of SIC. To improve the eC performance, it is proposed to apply a pre-strain, so that the low strain regime where eC performance is low can be skipped. Moreover, the large needed deformation can be reduced by the pre-strain and thus the possibility of a compact cooling system designed based on NR is improved. The fatigue property of eC effect of NR is then investigated. The fatigue life at large deformation strain amplitudes (strain of 1-6) is about 800 cycles for the tested NR, which is too short to be used for a cooling system. Decreasing strain amplitude is necessary to extend fatigue life up to requirement of a cooling device. For the same small strain amplitude of 3, the fatigue property is compared at amorphous strain regime (strain of 0-3), onset strain of melting (strain of 2-5) and high strain of SIC (strain of 4-7). It’s found that a larger eC temperature change and a better fatigue property can be obtained at two SIC strain regimes (strain of 2-5 and 4-7) than amorphous strain regime. Especially, the fatigue property at the onset strain of melting (strain of 2-5) is better than that at high strain of SIC (strain of 4-7). A high-cycle fatigue was applied at the strain of 2-5 (most promising strain regime) up to 1.7×105 cycles. It was observed that there is no crack of the sample, as well as a degradation degree of 12% of the eC temperature change. Furthermore, the eC stress coefficient (4.4 K/MPa) at onset strain of melting is larger than that at high strain of SIC (1.6 K/MPa). As a result, the middle strain regime (onset strain regime of melting) can get a higher eC performance, larger temperature change, and better fatigue life, which should be chosen for eC cooling system
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Wouts, Jérémy. „Étude et modélisation du comportement en compression du bois sous sollicitations d'impacts“. Thesis, Valenciennes, 2017. http://www.theses.fr/2017VALE0025.
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Le bois est un matériau cellulaire naturel et excellent absorbeur d’énergie. Employé au sein de structures du type limiteur d’impact, il subit de nombreux phénomènes lors d’un cas de chute. Une large campagne expérimentale est réalisée afin d’analyser les réponses en compression du hêtre et de l’épicéa, en fonction de la direction de sollicitation, de la vitesse de déformation pour la plage [0.001-600] s−1 et de deux types de restrictions latérales qualifiées d’extrêmes. La direction longitudinale se révèle la plus sensible à la vitesse ainsi qu’au type de restrictions latérales et les conséquences sur la capacité d’absorption d’énergie du bois sont alors significatives. Par ailleurs, les protocoles développés ont vocation à être déclinés pour un large panel d’essences aux propriétés mécaniques variées. Un modèle matériau élastoplastique, isotrope transverse et sensible à la vitesse de déformation est élaboré à l’aide des techniques multi-échelles et de la micromécanique. Les propriétés élastiques macroscopiques sont estimées à l’aide du schéma d’homogénéisation de Mori-Tanaka à partir de données issues de la microstructure. Un critère de type Gurson étendu reposant sur l’approche micromécanique de l’endommagement ductile est employé pour retranscrire le comportement non linéaire, la densification et le caractère compressible du bois. Des paramètres de dégradation découplés du critère sont appliqués selon la direction longitudinale. La modélisation proposée repose sur une description simplifiée du bois et les résultats numériques associés illustrent la bonne capacité du modèle à reproduire les différentes réponses observées lors d’un cas de chuteWood is a natural cellular material, which is widely and advantageously used as shock absorber for the transport of radioactive materials. Accident situations are evaluated based on the 9 m drop test, which allows us to observe the complex crushing behavior of wood. A compressive experimental study is conducted on spruce and beech wood species over a large range of strain rates (from 0.001 to 600 s−1) to investigate the effect of the loading direction and of two extreme lateral confinements. The longitudinal direction is the most sensitive to the effect of strain rate and of lateral confinements which have significant consequences on the energy absorption. Besides, the experimental investigation can be adapted to various wood species with very different mechanical properties. A strain rate dependent elastoplastic model with transversal isotropy is developed using multi-scale and micromechanics techniques. The elastic macroscopic properties of wood are estimated with a Mori-Tanaka scheme and information extracted from the microstructure. The Gurson type criterion based on the micromechanical approach of the ductile damage is used in order to describe the non linear behavior of wood, its densification regime and its compressibility as well. Additionally, uncoupled degradation parameters are applied to reproduce the failure mechanisms involved in the longitudinal response. A simplified description of wood is used within the modeling and the numerical results exhibit the good ability of the model to reproduce the various wood responses during an accident situation
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Tran, Thu Huong. „Comportement homogénéisé des matériaux composites : prise en compte de la taille des éléments microstructuraux et des gradients de la déformation“. Phd thesis, Université Paris-Est, 2013. http://tel.archives-ouvertes.fr/tel-01038058.
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L'objectif principal du travail réalisé au cours de la thèse consistera à proposer une démarche théorique rigoureuse visant à intégrer les éléments microstructuraux et les gradients de déformation dans une approche micromécanique. La thèse comportera deux volets : - Dans une première partie, on s'attachera à établir un cadre théorique rigoureux permettant d'intégrer les effets du gradient de la déformation et les longueurs caractéristiques de la microstructure sur le comportement effectif des matériaux composites - L'approche par développement asymptotique conduit à la résolution d'une succession problèmes d'élasticité tridimensionnelle posée sur une cellule élémentaire du milieu périodique. La résolution de ces problèmes d'élasticité, et par conséquent la détermination des propriétés effectives du composite, nécessite la mise en œuvre d'une méthode de résolution numérique. Dans cette seconde partie du travail, il s'agira de proposer une méthode de résolution basée sur la transformée de Fourier rapide (Méthode FFT)
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Haspot, Victor. „Exploitation d’hétérostructures d’oxydes intégrant La₂⁄₃Sr₁⁄₃MnO₃ pour des applications spin-orbitroniques et magnoniques“. Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASP079.
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Les dispositifs spintroniques classiques utilisent l'interaction d'échange entre les spins des électrons de conduction et les moments magnétiques locaux dans les matériaux magnétiques pour créer des courants polarisés en spin, ou pour manipuler l’aimantation par transfert de spin à partir de courants polarisés en spin. Une nouvelle direction de la spintronique - appelée aussi spin-orbitronique - exploite le couplage spin-orbite dans les matériaux non magnétiques au lieu de l'interaction d'échange dans les matériaux magnétiques dans le but de générer, détecter ou exploiter des courants polarisés en spin. Une autre voie - la magnonique - explore quant à elle le potentiel des ondes de spin pour transporter et traiter des informations dans des nanostructures magnétiques. Pour une large gamme d'applications dans ces deux domaines, des matériaux avec des très faibles valeurs d'amortissement magnétique sont nécessaires. Dans cette thèse, nous avons d'abord exploré le potentiel du matériau demi-métallique La₂⁄₃Sr₁⁄₃MnO₃ (LSMO) pour obtenir de très faible valeur d’amortissement magnétique. Nous avons étudié notamment l'effet de la contrainte et de la température sur les processus de relaxations magnétiques des couches minces LSMO. Par la suite, les films LSMO ont été utilisés comme injecteurs de spin dans des hétérostructures d’oxydes dans une perspective spin-orbitronique. Aussi, nous avons étudié l'opportunité de contrôler l'interconversion spin-charge en ajoutant un matériau ferroélectrique, BiFeO₃ (BFO) en exploitant les effets d'interfaces. Enfin, nous avons exploré le potentiel des bicouches LSMO / BFO dans le but de réaliser des cristaux magnoniques reprogrammablesClassical spintronic devices use the exchange interaction between conduction electron spins and local spins in magnetic materials to create spin-polarized currents, or to manipulate nanomagnets by spin transfer from spin-polarized currents. A novel direction of spintronics –called spin-orbitronics - exploits the spin-orbit coupling in nonmagnetic materials instead of the exchange interaction in magnetic materials to generate, detect or exploit spin-polarized currents. Another one –magnonics- explores the potential of spin waves to carry and process information in magnetic nanostructures. For a broad range of applications in both fields, materials with ultralow magnetic damping values are required. In this thesis we first explored the potential of the half metallic material La₂⁄₃Sr₁⁄₃MnO₃ (LSMO) to obtain very low damping. We studied the effect of strain and temperature on the damping of LSMO thin films. Subsequently, LSMO films were used as spin-current injectors in spin-orbitronic heterostructures. In those we also studied the opportunity to control the spin-charge interconversion by adding a ferroelectric material, BiFeO₃ (BFO) by exploiting the interface effects. Finally, we explored the potential of LSMO/BFO bilayers for reprogrammable magnonic crystals
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Antoine, Pierre-Cornélius. „Etude des dalles sur sols renforcés au moyen d'inclusions rigides ou non“. Doctoral thesis, Universite Libre de Bruxelles, 2010. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209997.
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Soft soil reinforcement by inclusion is a growing technique caracterized by a pile grid and a granular embankment introduced between the reinforced soil and the structure. Unlike traditionnal methods, the load is partially transferred to the pile heads by arching in the embankment. The application area of this research focuses on the shallow foundations case, in which the thickness of the embankment is small. The litterature review shows that only a few studies were dedicated to that case, and that fundamental questions remains concerning the load transfer in the embankment. Chosen method for this research consists in two-dimensionnal physical modelling, analysis of the conducted simulations, and development of an analytical model in order to predict the load transfer to the piles by arching in the embankment. The results of this PhD thesis provide original elements of evidence of the load transfer in the studied system, proposes an analytical model based on block division of the granular embankment by shear bands - which is in good agreement with experimental data - and lead to a better understanding of arching in soils.Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished
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Edwards, Ylva. „Influence of waxes on bitumen and asphalt concrete mixture performance“. Doctoral thesis, KTH, Väg- och banteknik, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-553.
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This doctoral thesis consists of a literature review, presented in two papers, and another six papers describing experimental studies of the influence of different kinds of wax and polyphosporic acid on bitumen and asphalt concrete mixture properties. The literature review should give an extensive description of the field of knowledge concerning wax in bitumen. Effects of wax in crude oil, bitumen and asphalt concrete as well as test methods for studying these effects are described. Theories behind possible mechanisms are also discussed, and commercial wax as additive to bitumen for different purposes included. The experimental parts comprise laboratory studies involving totally five 160/220 penetration base bitumens from different sources, two isolated bitumen waxes, five commercial waxes and one polyphosphoric acid. Asphalt concrete slabs, containing base or modified bitumen were prepared and tested. Binder properties were evaluated using different types of laboratory equipment, such as dynamic shear rheometer (DSR), bending beam rheometer (BBR), differential scanning calorimeter (DSC), force ductilometer, as well as equipment for determining conventional parameters like penetration, softening point, viscosity, and Fraass breaking point. Fourier Transform Infrared (FTIR) spectroscopy and Thin Layer Chromatography (TLC-FID) were used for chemical characterization. The binders were aged by means of the rolling thin film oven test (RTFOT) and pressure ageing vessel (PAV) in combination. Asphalt concrete properties were evaluated at low temperatures using the tensile strain restrained specimen test (TSRST) and creep test at -25°C. Dynamic creep testing was performed at 40°C, as well as complex modulus tests between 0 and 20°C. Binder test results indicated that the magnitude and type of effect on bitumen rheology depend on the bitumen itself, type of crystallizing fraction in the bitumen and/or type and amount of additive used. Bitumen composition was found to be of decisive importance. Adding polyethylene wax or polyphosphoric acid, especially to a non-waxy 160/220 penetration grade bitumen, showed no or positive effects on the rheological behaviour at low temperatures (decrease in stiffness) as well as medium and high temperatures (increase in complex modulus and decrease in phase angle). However, the corresponding positive effects could not be shown in dynamic creep testing (at 40°C) of asphalt concrete mixtures containing these modified binders. Adding FT-paraffin decreased the physical hardening index for all bitumens. Also polyethylene wax and montan wax showed this effect for some bitumens. Slack wax showed a large increasing effect on physical hardening, and polyphosphoric acid none or a minor negative effect. No correlation between physical hardening index (PHI) and wax content by DSC was found in this study, involving both natural bitumen wax and commercial wax. Addition of the commercial waxes used showed no or marginally positive influence on bitumen ageing properties for the bitumens and test conditions used. Comparing asphalt mixture test results to the corresponding binder test results, the effects on asphalt mixtures from adding commercial wax or polyphosphoric acid were less evident. Significant binder physical hardening by BBR could not be confirmed by TSRST.QC 20101006
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Yang, Chou-Chuan, und 楊洲權. „Applying Wavelet Transfor technology to the examination of pharmaceutical bottles stain“. Thesis, 2011. http://ndltd.ncl.edu.tw/handle/42781185602705547044.
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碩士國立臺灣大學
工業工程學研究所
99
In today’s world, the trend to seek superior quality and utmost profit has become an absolute priority.To increase production quantity while decreasing costs and labors becomes one single most important challenge in the field of product productions. The ability to provide stable quality in raw materials helps to maintain consistent quality in final products. This can greatly reduce complex or unnecessary testing procedures, hence, simplifying the production process as a whole. This thesis provides an example of such, targeting specifically at the bottling production of the pharmaceutical industry. A consumer perceives the first impression and confidence rating of a pharmaceutical product mainly from the bottling or packaging. Even though the bottling appearance does not actually affect the quality of a drug, any impurity or stain in the packaging can drastically impair a consumer’s confidence in the quality of the medicine. This is the reason why the bottling industry for pharmaceutical companies includes the evaluation for visible stain and impurity as one of their main testing procedures. Wavelet Transform is an excellent technique for signal analysis. It offers technologies to determine specified signal, to evaluate low entropy, to form multiresolution analysis, to extract from correlation analysis, and it providesextensive wavelet bases. All of which makes Wavelet Transform exceptional in signal De-noise. This thesis proposes a method applying Wavelet Transform to the testing of pharmaceutical bottles. Wavelet Transform gives advantages to the De-noise of bottle surface resolution. 2D Wavelet Transform can De-noise signal resolutions from coarse to smooth without damaging the original resolutions, while compressing the resolution. Furthermore,using the singular points function from 1D Wavelet Transform can replace the traditional pattern matching function and its threshold limitation. Such method can detect stain from the coarseness on the bottle surfacemuch more in-depth. Using the LabVIEW software from National Instruments,this thesis presents an integrated software program includingall of the Wavelet Transform functions mentioned above. The proposed program offers an innovativestrategy for the testing and analysis of bottle surface stain. It elevates the functionality and effectiveness of the bottle stain examination used by the current pharmaceutical industry.
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Dadpay, Chakameh. „Theoretical and experimental analysis of strain transfer rate in coated Fiber Bragg Grating strain sensors“. Thesis, 2008. http://spectrum.library.concordia.ca/975967/1/MR45285.pdf.
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Fiber Bragg Grating (FBG) sensors have seen significant development in recent years, especially in the aerospace industry for structural health monitoring due to their versatility and measurement capability. Improvement in sensor's reliability and accuracy, however, continue to be two parameters critical to the eventual implementation of this technology in high value targets and can be enhanced by the effect of both mechanical and optical characteristics of the fiber. This thesis presents an evaluation of the strain transfer capability of different coated FBG strain sensors (i.e. Gold, Polyamide and Acrylic) bonded to metallic host structures. A theoretical relationship for the strain transfer rate from the host structure to the fiber core has been developed. This relationship considers the strain transfer loss through the layers of the system based on their material properties and their geometry. In addition, a simulated analysis using finite element modeling has been developed. Parametric analysis of both the analytical and simulation models revealed the impact of coating material selection, coating thickness selection, and bonding condition on the strain transfer loss. Results illustrate that metallic fiber coatings (i.e. Gold) are more suitable for improved strain transfer than their polymeric counterparts. Additionally a set of experiments were conducted using Acrylic coated FBG sensor bonded to an Aluminium sample to validate the results from theory and the simulation. The strain on the FBG sensor was measured and compared with a calibrated strain gauge mounted on the host structure to characterize the strain transfer loss. The experimental results were compared with the results for the same configuration of the sensor and its host structure, from the theory and simulation and were found to be in good agreement.
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Chen, Po-Wen, und 陳博文. „Flexible Carbon Nanotube Networks based Piezoresistive Strain Sensors made by Transfer Printing Method“. Thesis, 2019. http://ndltd.ncl.edu.tw/handle/z8gf4y.
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38
Gu, Shao-Cheng, und 顧少騁. „Stair Climbing Biped Robot Using Stair-slope Transform Approach Based on Three-Mass with Angular Momentum Model“. Thesis, 2014. http://ndltd.ncl.edu.tw/handle/83125002586961557945.
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碩士國立臺灣大學
電機工程學研究所
102
The approaches of biped walking robots have been proposed to overcome several situations, such as walking on uneven terrains, circumventing obstacles, collision avoidance, push recover, striding across obstacles, climbing stairway. In order to maintain balance, the stability of biped robots is crucial and fundamental. The zero moment point (ZMP) theory has been proposed for determining whether robots fall down or not. If ZMP exceed the scope of the polygon of the feet, the biped robots will fall down. Some simplified models have been proposed based on ZMP. Linear inverted pendulum model (LIPM), one-mass model, uses the limited dynamic parameters, concentrating total mass and angular momentum on one point. To reduce the model error of LIPM caused by mass, three-mass model and multiple masses inverted pendulum model (MMIPM) are developed. Apart from these, to reduce the error caused by moment of inertia, there is an improved model replace the point mass by a flywheel to explicitly represent embodiment of the centroid moment of inertia. To further improve the accuracy of model, we propose a new model that combine three-mass and angular momentum, named three-mass with angular momentum model. The proposed model not only take trunk''s rotation into account and also consider the effect of the rotational inertia of two legs. There are many research effects in the past for biped robot climbing stairs, virtual slope method for planning walking trajectory has been proposed based on one-mass model. However, using one-mass model does not considerate the rotation of the trunk. With the proposed model, it gains the freedom of using trunk rotation to reduce the moment of the support leg when climbing stairs. Moreover, due to the difficulty in verifying the correction of the virtual slope method with any models more complex than one-mass models. The virtual slope method cannot be directly used with proposed model. Therefore, this paper propose a new method named Stair-slope Transform Approach to solve this problem. The validation of this model and the method is confirmed from the simulations and experiments.
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Xin, Hao. „Toward roll-to-roll transfer of large-scale graphene for flexible electronics fabrication“. Thesis, 2013. http://hdl.handle.net/2152/28500.
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Graphene is a promising material for flexible electronics due to its extraordinary electrical, mechanical, and optical properties. One of the biggest challenges today is to transfer large-scale graphene sheet to flexible substrates with minimal quality degradation. In this thesis, a bilayer polymer support for graphene transfer is proposed. Liquid PDMS (polydimethylsiloxane) is first coated on graphene to conform to its surface morphology. A flexible plastic substrate is then pressed on PDMS as a durable support. After PDMS is cured, electrochemical delamination is used to separate graphene from the copper foil. Due to the extremely low work of adhesion between graphene and PDMS, the graphene film on PDMS can be further transferred onto silicon wafer or other flexible substrates by simple adhesion. An added benefit of the PDMS layer is its strain isolation effect, which could protect graphene-based devices from breaking under external loads applied on the flexible substrate. The strain isolation effect of PDMS is verified with an analytical model and finite element analysis. The design of a prototype roll-to-roll graphene transfer machine is also presented.text
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Alhassan, Ali Faya. „Transfer pricing in the Saudi Arabia oil and gas sector“. Thesis, 2012. http://hdl.handle.net/1959.13/936356.
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Research Doctorate - Doctor of Philosophy (PhD)This study examines transfer pricing behaviour for the purpose of shifting profits between national tax jurisdictions with different rates of profit tax in the context of the Saudi oil and gas sector as well as that of several other countries (i.e., Australia, Canada, Czech Republic, France, Korea, Japan, Kuwait, Norway, Poland, Sweden, UK and US). The methodology of the Bartelsman and Beetsma (2003) is proposed as the basis for testing the hypothesis. The results of this study show that the Bartelsman and Beetsma (2003) model when applied to the Saudi Arabia oil and gas sector does not detect transfer pricing behaviour for the purpose of shifting profit. However, the Bartelsman and Beetsma (2003) model when applied to other countries such as Japan, Korea, Norway, Poland, and the United Kingdom does show results that suggests the presence of transfer pricing behaviour for the purpose of shifting profits.
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Chih-ChaoHsu und 許智超. „Study on carbon nanonets applications in strain sensors and flexible FETS by nano-transfer printing method“. Thesis, 2012. http://ndltd.ncl.edu.tw/handle/19498530022680970620.
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博士國立成功大學
系統及船舶機電工程學系碩博士班
100
Nano-transfer printing (nTP) is increasingly used for micro-fabrication of nano-scale materials onto flexible plastic substrates. This thesis reports a novel nTP process (called as “polymer tape bonding”) for single-walled carbon nanonets (SWCNNs) for use in strain sensors and flexible field effect transistors. Traditional SWCNNs grown on silicon substrate by alcohol catalytic chemical vapour deposition (ACCVD) can serve as strain sensing elements in strain sensors and nano electromechanical system (NEMS) sensors, but ACCVD is not well suited to the task. To improve SWCNN fabrication, this paper deposits a Parylene-C thin film on SWCNNs for transfer-printing onto flexible plastic substrates with polyimide tape. Quantification of the fabricated SWCNN strain sensing ability (gauge factor) is performed by comparing two specimens with different pattern features and substrates. Gauge factor is measured by tensile testing. SWCNN density variations relative to the observed gauge factors are discussed. Results show SWCNN gauge factors range from 1.46 to 8.22 depending on the substrate and pattern width. It is further observed that the gauge factor of the presented SWCNN thin film increases when the width of the SWCNN decreases to the low micro-dimensions, i.e. below 40m, indicating a significant scaling factor. Also, the presented nTP method is used to fabricate the SWCNN flexible top-gated field effect transistor on PEN and polyimide base with standard integrated circuit (IC) compatible processes. Finally, electric characteristics of the flexible SWCNN top-gate thin film transistors are measured by the I-V measurement, the SWCNN TFT achieved the averaged mobility of 53.89cm2/Vs with applied Vds=0.1V as a p-type FET, and the mobility is ranged from 30.10 to 96.85cm2/Vs. and the on-to-off ratio of the current devices is approximately 100.
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Chen, Hsiang-Yun. „Energy Transfer Dynamics and Dopant Luminescence in Mn-Doped CdS/ZnS Core/Shell Nanocrystals“. Thesis, 2012. http://hdl.handle.net/1969.1/148167.
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Mn-doped II-VI semiconductor nanocrystals exhibit bright dopant photoluminescence that has potential usefulness for light emitting devices, temperature sensing, and biological imaging. The bright luminescence comes from the 4T1→6A1 transition of the Mn2+ d electrons after the exciton-dopant energy transfer, which reroutes the exciton relaxation through trapping processes. The driving force of the energy transfer is the strong exchange coupling between the exciton and Mn2+ due to the confinement of exciton in the nanocrystal. The exciton-Mn spatial overlap affecting the exchange coupling strength is an important parameter that varies the energy transfer rate and the quantum yield of Mn luminescence. In this dissertation, this correlation is studied in radial doping location-controlled Mn-doped CdS/ZnS nanocrystals. Energy transfer rate was found decreasing when increasing the doping radius in the nanocrystals at the same core size and shell thickness and when increasing the size of the nanocrystals at a fixed doping radius.
In addition to the exciton-Mn energy transfer discussed above, two consecutive exciton-Mn energy transfers can also occur if multiple excitons are generated before the relaxation of Mn (lifetime ~10^-4 - 10^-2 s). The consecutive exciton-Mn energy transfer can further excite the Mn2+ d electrons high in conduction band and results in the quenching of Mn luminescence. The highly excited electrons show higher photocatalytic efficiency than the electrons in undoped nanocrystals.
Finally, the effect of local lattice strain on the local vibrational frequency and local thermal expansion was observed via the temperature-dependent Mn luminescence spectral linewidth and peak position in Mn-doped CdS/ZnS nanocrystals. The local lattice strain on the Mn2+ ions is varied using the large core/shell lattice mismatch (~7%) that creates a gradient of lattice strain at various radial locations. When doping the Mn2+ closer to the core/shell interface, the stronger lattice strain softens the vibrational frequency coupled to the 4T1→6A1 transition of Mn2+ (Mn luminescence) by ~50%. In addition, the lattice strain also increases the anharmonicity, resulting in larger local thermal expansion observed from the nearly an order larger thermal shift of the Mn luminescence compared to the Mn-doped ZnS nanocrystals without the core/shell lattice mismatch.
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Sung, Ting-Yu, und 宋庭宇. „Design of Flexible and Stretchable High Sensitive Strain Sensors using Carbon Nanotube Forests via Novel Transfer Technique“. Thesis, 2013. http://ndltd.ncl.edu.tw/handle/41360732837475140675.
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碩士國立臺灣大學
機械工程學研究所
101
In this study, we use the way of coating with thin iron film on silicon substrates to grow carbon nanotubes, and carbon nanotubes will only grow on substrates which have coated with thin iron film. Therefore, we first design the mask pattern with a spiral of different width and length, and use photolithography to produce silicon substrates of different spiral pattern. Then we coat with the iron film on silicon substrates and lift off. Finally, we can grow spiral carbon nanotube forests by chemical deposition method. By using the photolithography to grow carbon nanotubes, we can grow narrower width and longer length of carbon nanotube forests in smaller area and can improve the height consistency of the overall carbon nanotubes. We use PDMS as the material to transfer carbon nanotubes, and also use a new technique to transfer spiral carbon nanotubes. Because of the flexibility and high stretchability of PDMS, the composites of PDMS and carbon nanotubes can produce high stretchable and flexible strain sensors. The experimental results show that the strain of the designed sensors can up to 25% and the sensitivity of repeated stretching of our sensors are better than other sensors which is flexible and high stretchable in other literatures. On the other hand, the width and length of spiral carbon nanotubes will influence the sensitivity of the sensor. The wider the width of spiral, the better the sensitivity of sensor. Also, the cutting length of the composites of PDMS and carbon nanotubes must be greater than 13mm, and therefore the sensor sensitivity will be stabilized. In our strain sensors, the alignment direction of carbon nanotubes and the direction of strain axis are perpendicular so that the sensors have excellent repeatability. The linearity of strain and resistance change can be determined by R-square value. The R-square values of our sensors are close to 1, which represents the resistance change of sensor is nearly linear. When growing carbon nanotube forests coated with metal particles is transferred by PDMS, they can produce sensors with metal particles. The sensitivity of these kinds of sensors is better than the original sensors. Metal particles in sensors can effectively improve the sensor hysteresis and response time, but they will also reduce the maximum strain of sensors.
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Bouse, Scott. „Investigation of Transfer Function Analysis as a Means to Predict Strain on Rat Tibiae from Ankle Torque Waveforms“. 2009. http://hdl.handle.net/1969.1/ETD-TAMU-2009-12-7226.
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Electrical Muscle Stimulation (EMS) is used as a countermeasure in animal
disuse studies that seek to determine which forms of exercise are most effective in
mitigating the effects of disuse atrophy on bone and muscle. Although EMS has been
used for many years in our lab and others, few researchers have been able to quantify the
levels of strain on rat tibiae during EMS and far fewer have investigated the causal
relationship between torque produced at the ankle and strain on the tibia. This thesis
sought to investigate the relationship between ankle torque and tibial strain by using a
combination of techniques, namely: (1) the addition of rosette strain gages, (2) improved
synchronization between ankle torque and tibial strain recordings, and (3) spectral
analysis between torque and strain waveforms.
In previous work, few methods existed to align torque and strain recordings
temporally, as those data were recorded on separate computers and synchronizing events
were not captured. Attempting to create a torque-strain crossplot with unsynchronized
data does not always yield valid results, so a method of reliably synchronizing those data
is required. This thesis developed methods to capture simultaneous (synchronizing)
events in both torque and strain recordings and then used those captured events to
synchronize data between two computers. Following that synchronization, stiffness
calculations were run on torque-strain crossplots to determine linear-model relationships
between torque and strain for each method of synchronization. The results from those
regressions were then used to determine if one or more synchronization techniques are
superior to others, in terms of repeatability or precision. The results of these analyses have shown that using portions of the curves can dramatically increase computing speed
while providing high levels of repeatability in synchronization measures.
After synchronization techniques had been investigated, 3-element rosette data
were used to calculate the principal strains on the surface of the tibiae, and the percentage
of principal strains that are accounted for in the axial direction. Since the strain
environment changes along the axis of the bone, the principal strain data were plotted
versus the distance from proximal epiphysis to rosette gage, and statistical analysis was
presented.
After rosette data were analyzed, the torque and strain data pairs were fed into a
signal processing suite for the purpose of transfer function calculation. Using the
synchronization methods outlined above, two means of synchronization were compared
in the transfer function program. Results for these analyses demonstrated that transfer
functions are slightly dependent on synchronization methods, but that calculated gains do
not differ between synchronization techniques.
The specific shapes of the transfer functions highlight the relative
attenuation/amplification of frequencies in torque and strain signals. Specifically, a range
of frequencies, commonly called a band, between 24 and 32Hz is attenuated by the soft
tissues and mechanical linkages in the lower leg of rats. This finding gives researchers
looking to increase or decrease modeling stimulus to bone a new piece of information
about the relative efficiency of EMS exercise. For example, EMS performed at 24-25Hz
might produce less strain in the tibia than EMS at 22-23Hz, despite the 22-23Hz
stimulation producing marginally less torque.
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Zhou, Songsheng. „New Solutions of Half-Space Contact Problems Using Potential Theory, Surface Elasticity and Strain Gradient Elasticity“. Thesis, 2011. http://hdl.handle.net/1969.1/ETD-TAMU-2011-12-10675.
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Size-dependent material responses observed at fine length scales are receiving growing attention due to the need in the modeling of very small sized mechanical structures. The conventional continuum theories do not suffice for accurate descriptions of the exact material behaviors in the fine-scale regime due to the lack of inherent material lengths. A number of new theories/models have been propounded so far to interpret such novel phenomena. In this dissertation a few enriched-continuum theories - the adhesive contact mechanics, surface elasticity and strain gradient elasticity - are employed to study the mechanical behaviors of a semi-infinite solid induced by the boundary forces.
A unified treatment of axisymmetric adhesive contact problems is developed using the harmonic functions. The generalized solution applies to the adhesive contact problems involving an axisymmetric rigid punch of arbitrary shape and an adhesive interaction force distribution of any profile, and it links existing solutions/models for axisymmetric non-adhesive and adhesive contact problems like the Hertz solution, Sneddon's solution, the JKR model, the DMT model and the M-D model.
The generalized Boussinesq and Flamant problems are examined in the context of the surface elasticity of Gurtin and Murdoch (1975, 1978), which treats the surface as a negligibly thin membrane with material properties differing from those of the bulk. Analytical solution is derived based on integral transforms and use of potential functions. The newly derived solution applies to the problems of an elastic half-space (half-plane as well) subjected to prescribed surface tractions with consideration of surface effects. The newly derived results exhibit substantial deviations from the classical predictions near the loading points and converge to the classical ones at a distance far away from those points. The size-dependency of material responses is clearly demonstrated and material hardening effects are predicted.
The half-space contact problems are also studied using the simplified strain gradient elasticity theory which incorporates material microstructural effects. The solution is obtained by taking advantage of the displacement functions of Mindlin (1964) and integral transforms. Significant discrepancy between the current and the classical solutions is seen to exist in the immediate vicinity of the loading area. The discontinuity and singularity exist in classical solution are removed, and the stress and displacement components change smoothly through the solid body.
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Spassov, Sashko G. [Verfasser]. „Investigation of scrapie associated prion protein PrP27-30 and strain differentiation of transmissible spongiform encephalopathy by Fourier transform infrared spectroscopy techniques / vorgelegt von Sashko Georgiev Spassov“. 2006. http://d-nb.info/980867703/34.
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47
Zhao, Ruogang. „The Development and Application of Tools to Study the Multiscale Biomechanics of the Aortic Valve“. Thesis, 2012. http://hdl.handle.net/1807/33866.
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Calcific aortic valve disease (CAVD) is one of the most common causes of cardiovascular disease in North America. Mechanical factors have been closely linked to the pathogenesis of CAVD and may contribute to the disease by actively regulating the mechanobiology of valve interstitial cells (VICs). Mechanical forces affect VIC function through interactions between the VIC and the extracellular matrix (ECM). Studies have shown that the transfer of mechanical stimulus during cell-ECM interaction depends on the local material properties at hierarchical length scales encompassing tissue, cell and cytoskeleton.
In this thesis, biomechanical tools were developed and applied to investigate hierarchical cell-ECM interactions, using VICs and valve tissue as a model system. Four topics of critical importance to understanding VIC-ECM interactions were studied: focal biomechanical material properties of aortic valve tissue; viscoelastic properties of VICs; transduction of mechanical deformation from the ECM to the cytoskeletal network; and the impact of altered cell-ECM interactions on VIC survival.
To measure focal valve tissue properties, a micropipette aspiration (MA) method was implemented and validated. It was found that nonlinear elastic properties of the top layer of a multilayered biomaterial can be estimated by MA by using a pipette with a diameter smaller than the top layer thickness. Using this approach, it was shown that the effective stiffness of the fibrosa layer is greater than that of the ventricularis layer in intact aortic valve leaflets (p<0.01). To characterize the viscoelastic properties of VICs, an inverse FE method of single cell MA was developed and compared with the analytical half-space model. It was found that inherent differences in the half-space and FE models of single cell MA yield different cell viscoelastic material parameters. However, under particular experimental conditions, the parameters estimated by the half-space model are statistically indistinguishable from those predicted by the FE model. To study strain transduction from the ECM to cytoskeleton, an improved texture correlation algorithm and a uniaxial tension release device were developed. It was found that substrate strain fully transfers to the cytoskeletal network via focal adhesions in live VICs under large strain tension release. To study the effects of cell-ECM interactions on VIC survival, two mechanical stimulus systems that can simulate the separate effects of cell contraction and cell monolayer detachment were developed. It was found that cell sheet detachment and disrupted cell-ECM signaling is likely responsible for the apoptosis of VICs grown in culture on thin collagen matrices, leading to calcification.
The studies presented in this thesis refine existing biomechanical tools and provide new experimental and analytical tools with which to study cell-ECM interactions. Their application resulted in an improved understanding of hierarchical valve biomechanics, mechanotransduction, and mechanobiology.