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Caractérisation de la chiralité optique dans des systèmes plasmoniques / Characterization of optical chirality effects in plasmonic systemsPham, Kim Anh Aline 06 November 2018 (has links)
L'objectif de ce projet de thèse est de mettre en évidence des phénomènes de chiralité optique induits dans des systèmes plasmoniques. La manipulation des différents degrés de liberté de la lumière est mise en évidence par le biais de techniques expérimentales complémentaires basées sur la tomographie en polarisation, la microscopie à fuites radiatives et la microscopie en champ proche optique (SNOM). D'une part, nous rapportons une méthode de caractérisation non-invasive afin de révéler la présence conjointe de chiralité planaire et volumique au sein de métasurfaces plasmoniques. Pour décrire cette chiralité mixte, une généralisation du modèle de Kuhn est développée. D'autre part, nous démontrons deux dispositifs plasmoniques exploitant le couplage spin-orbite optique pour contrôler les moments angulaires de spin et orbitaux de la lumière. En particulier, le mécanisme réciproque de l'effet spin Hall optique est démontré à l'aide de nano-ouvertures en forme de T: la trajectoire des plasmons de surface est adressée dans le moment angulaire de spin des photons. Cette fonctionnalité est ensuite mise en œuvre dans une expérience de brouillage d'interférence. La génération de vortex plasmoniques est également réalisée par le biais de cavités spirales, dont la chiralité conditionne l'intensité et le moment angulaire orbital des vortex. Enfin, une preuve de concept sur la mesure de la densité locale d’états optique, façonnée par un environnement chiral, est démontrée à l'aide d'une sonde SNOM classique et quantique. Ce travail permet de connecter les grandeurs de densité et de flux de chiralité aux interactions lumière-matière. L'étude de la chiralité dans le contexte de la plasmonique ouvre des perspectives prometteuses dans la nano-manipulation optique, la séparation de molécules chirales et le contrôle de sources quantiques. / In this thesis, we aim at demonstrating chiral optical effects in plasmonic systems. The manipulation of the different degrees of freedom of light is evidenced by complementary experimental approaches based on polarisation tomography, leakage radiation microscopy and scanning near-field optical microscopy (SNOM). On one hand, we report on a non-invasive method to reveal the coexistence of surface and bulk chirality in plasmonic metasurfaces. Specifically, we extend the model of Kuhn to describe this chirality mixture. On the other hand, we demonstrate two plasmonic devices which rely on the optical spin-orbit coupling to control the spin and the orbital angular momentum of light. In particular, the reciprocal mechanism of the spin-Hall effect of light is shown using T-shaped nano-apertures: the trajectory of surface plasmons can be encoded in the spin of the photons. This which-path marker is then implemented in an interference erazer experiment. Plasmonic vortex generation is also reported in spiral cavities. The spiral chirality rules the intensity as well as the angular orbital momentum of the singular fields. Finally, as a proof of concept, we demonstrate using a conventional and quantum SNOM probe that the local density of optical states can be structured by a chiral environment. We also connect the density and flux chirality to light-matter interactions. Studying chirality in the context of plasmonics opens promising prospects in the optical nano-manipulation, chiral molecules discrimination and the control of quantum sources.
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Estimation du mouvement fort en champ proche / Estimation of Near-Fault Strong Ground-MotionFayjaloun, Rosemary 25 October 2018 (has links)
Les données accumulées sur les mouvements du sol apportent des connaissances très importantes sur les processus de rupture des séismes, les caractéristiques du milieu de propagation, la relation entre le mouvement du sol et les dommages des structures... Cependant, les séismes de faible et moyenne amplitude étant plus fréquents que les grands événements sismiques, les bases de données de mouvements de sol utilisées dans le développement de modèles de prédiction du mouvement du sol ne contiennent pas beaucoup de données de forts séismes. Le point le plus critique concerne les stations proches de la rupture de la faille, pour lesquelles les bases de données restent mal échantillonnées. Les pays à sismicité modérée ou élevée pour lesquels des failles majeures peuvent se briser à proximité de ses grandes villes, sont donc confrontés à un risque sismique majeur, mais le manque d’enregistrements du mouvement ne permet pas une bonne prédiction des mouvements fort du sol. Il est donc nécessaire de simuler le mouvement fort en champ proche. Cette thèse est divisée en 2 parties. La partie 1 se concentre sur une meilleure compréhension de la rupture sismique et de son rapport avec le mouvement du sol proche de la faille. Les mécanismes de génération des valeurs de pics du mouvement du sol sont étudiés pour des ruptures homogènes et hétérogènes. Une analyse quantitative de sensibilité du mouvement du sol aux paramètres cinématiques de la rupture est présentée, pour des sites au voisinage de la rupture ainsi qu’en champ lointain. Un second chapitre est consacré à un effet de source majeur en champ proche: l’effet de directivité. Ce phénomène se produit lorsque la rupture se propage vers un site, avec une vitesse de rupture proche de la vitesse de l'onde de cisaillement Vs; les ondes se propageant vers le sites interfèrent de manière constructive et génèrent une onde de grande amplitude appelée pulse. Les caractéristiques de ce pulse, notamment sa durée, représentent des paramètres d’intérêt pour le génie parasismique. Une équation simple est présentée pour relier la durée du pulse à la configuration géométrique de la rupture et du site d'intérêt et aux paramètres de la source. La partie 2 est consacrée à une meilleure estimation de l’aléa sismique au Liban en simulant le mouvement fort pour des sites proches de la faille principale: la faille de Yammouneh. Le Liban est situé dans un environnement tectonique actif où le risque sismique est considéré comme modéré à élevé. Historiquement, des tremblements de terre destructifs se sont produits dans le passé, le dernier remontant à 1202. Cependant, en raison de la sismicité de grande ampleur actuellement peu fréquente, aucun mouvement fort n'a jamais été enregistré au Liban à ce jour. La faille de Yammouneh est une grande faille en décrochement traversant le Liban du Nord au Sud, situant toutes les villes et infrastructures à moins de 25km de la faille. Une tomographie de la structure de la croûte du Liban, en termes de vitesse des ondes de cisaillement Vs, est réalisée en utilisant le bruit ambiant. À notre connaissance, il s’agit de la première étude de la tomographie Vs 3D au Liban. Par la suite, une approche hybride est utilisée pour simuler le mouvement du sol en champ proche sur une large bande de fréquences (0.1-10Hz). Aux basses fréquences (≤1Hz), des ruptures potentielles de M7 sont simulées (comme définie dans les chapitres précédents), et les fonctions sources obtenues sont convoluées aux fonctions de Green calculées pour le modèle de propagation des ondes issu de la tomographie Vs afin d’estimer le mouvement du sol à proximité de la faille. Le mouvement du sol est complété par un contenu haute fréquence (jusqu’à 10 Hz), en utilisant un modèle stochastique calibré par des enregistrements en champ proche, et en tenant compte de la phase impulsive due à la directivité de la rupture. / Accumulated data of strong ground motions have been providing us very important knowledge about rupture processes of earthquakes, propagation-path, site-amplification effects on ground motion, the relation between ground motion and damage... However, most of the ground motion databases used in the development of ground motion prediction models are primarily comprised of accelerograms produced by small and moderate earthquakes. Hence, as magnitude increases, the sets of ground motions become sparse. Ground motion databases are poorly sampled for short source-to-site distance ranges (‘Near-fault’ ranges). However, the strongest ground shaking generally occurs close to earthquake fault rupture. Countries of moderate to high seismicity for which major faults can break in the vicinity of its major cities are facing a major seismic risk, but the lack of earthquake recordings makes it difficult to predict ground motion. Strong motion simulations may then be used instead. One of the current challenges for seismologists is the development of reliable methods for simulating near-fault ground motion taking into account the lack of knowledge about the characteristics of a potential rupture. This thesis is divided into 2 parts. Part 1 focuses on better understanding the seismic rupture process and its relation with the near-fault ground motion. The mechanisms of peak ground motion generating are investigated for homogeneous as well as for heterogeneous ruptures. A quantitative sensitivity analysis of the ground motion to the source kinematic parameters is presented, for sites located in the vicinity of the fault rupture, as well as far from the rupture. A second chapter is dedicated to a major near-fault source effect: the directivity effect. This phenomenon happens when the rupture propagates towards a site of interest, with a rupture speed close to the shear-wave speed (Vs); the waves propagating towards the site adds up constructively and generates a large amplitude wave called the pulse. The features of this pulse are of interest for the earthquake engineering community. In this chapter, a simple equation is presented that relates the period of the pulse to the geometric configuration of the rupture and the site of interest, and to the source parameters.Part 2 is dedicated to better estimate the seismic hazard in Lebanon by simulating the strong ground motion at sites near the main fault (the Yammouneh fault). Lebanon is located in an active tectonic environment where the seismic hazard is considered moderate to high. Historically, destructive earthquakes occurred in the past, the last one dates back to 1202. However, strong motion has never been recorded in Lebanon till now due to the presently infrequent large-magnitude seismicity, and therefore facing an alarming note of potential new ruptures. The Yammouneh fault is a large strike-slip fault crossing Lebanon, making all its regions located within 25km away from the fault. At first, the crustal structure tomography of Lebanon, in terms of Vs, is performed using the ambient noise, in order to characterise the wave propagation from the rupture to the ground surface. To our knowledge, this is the first study of the 3D Vs tomography in Lebanon. Afterwards, a hybrid approach is presented to simulate broadband near-fault ground motion . At low-frequencies (≤1Hz), potential ruptures of M7 are simulated (as defined in the previous chapters), and the generated slip rate functions are convolved with the Green’s functions computed for the propagation medium defined by the Vs tomography. The ground-motion is complemented by a high-frequency content (up to 10Hz), using a stochastic model calibrated by near-fault recordings and accounting for the presence of the directivity pulse. The computed peak ground acceleration is compared to the design acceleration in Lebanon.
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A Secure Anti-Counterfeiting System using Near Field Communication, Public Key Cryptography, Blockchain, and Bayesian GamesAlzahrani, Naif Saeed 16 July 2019 (has links)
Counterfeit products, especially in the pharmaceutical sector, have plagued the international community for decades. To combat this problem, many anti-counterfeiting approaches have been proposed. They use either Radio Frequency Identification (RFID) or Near Field Communication (NFC) physical tags affixed to the products. Current anti-counterfeiting approaches detect two counterfeiting attacks: (1) modifications to a product's tag details, such as changing the expiration date; and (2) cloning of a genuine product's details to reuse on counterfeit products. In addition, these anti-counterfeiting approaches track-and-trace the physical locations of products as the products flow through supply chains.
Existing approaches suffer from two main drawbacks. They cannot detect tag reapplication attacks, wherein a counterfeiter removes a legitimate tag from a genuine product and reapplies it to a counterfeit or expired product. Second, most existing approaches typically rely on a central server to authenticate products. This is not scalable and creates tremendous processing burden on the server, since significant volumes of products flood through the supply chain's nodes. In addition, centralized supply chains require substantial data storage to store authentication records for all products. Moreover, as with centralized systems, traditional supply chains inherently have the problem of a single-point of failure.
The thesis of this dissertation is that a robust, scalable, counterfeiting-resistant supply chain that addresses the above drawbacks and can be simultaneously achieved by (i) using a combination of NFC tags on products and a distributed ledger such as blockchain for reapplication-proof, decentralized, and transparent product authentication (ii) a novel game-theoretical consensus protocol for enforcing true decentralization, and enhancing the protocol's security and performance.
In this dissertation, we first propose a new Tag Reapplication Detection (TRD) system to detect reapplication attacks using low-cost NFC tags and public key cryptography. To detect reapplication attacks, TRD tracks the number of times a tag has been read in the supply chain using a 'central' authentication server. Second, leveraging the blockchain technology, we propose the Block-Supply Chain, a transformation of TRD into a decentralized supply chain. In this chain, each node maintains a blockchain (distributed public ledger) per product. This blockchain comprises chained blocks, where each is an authentication event. The Block-Supply Chain can detect tag reapplication attacks and can replace the centralized supply chain design, thus overcoming the centralization issues.
One of the fundamental characteristics of blockchain technology is the consensus protocol. Consensus protocols ensure that all nodes in the blockchain network agree on the validity of a block to be included in the public ledger. The first and most popular of the existing consensus protocols is Proof of Work (PoW). However, PoW requires massive computational effort, resulting in high energy and computing resources consumption. Alternatively, Byzantine Fault Tolerance (BFT) protocols, such as Tendermint, were adapted in blockchain technology to be efficient and easy to implement. Nevertheless, not all of BFT protocols guarantee true decentralization, and they are mostly based on fixed-validators. BFT fixed-validators protocols typically rely on fixed, static validators responsible for validating all newly proposed blocks. This opens the door for adversaries to launch several attacks on these validators, such as Distributed Denial of Service (DDoS) and Eclipse attacks. In contrast, a truly decentralized protocol ensures that variable sets of anonymous validators execute the blocks' validations. Building on this observation, we propose the TrueBFT, a truly decentralized BFT-based consensus protocol that does not require PoW and randomly employs a different set of validators on each block's proposal. TrueBFT is designed for permissioned blockchains (in such blockchains, the participants who can transact on the blockchain are limited, and each participant is required to have permission to join the system). Our simulations show that TrueBFT offers remarkable performance with a satisfactory level of security compared to the state-of-the-art protocol Tendermint.
Another issue with current consensus protocols, particularly the BFT, is that the majority of them do not take the number of employed validators into consideration. The number of validators in a blockchain network influences its security and performance substantially. In response, we integrate a game theoretical model into TrueBFT that analyzes the risk likelihood of each proposer (i.e., the node that creates and proposes the new block). Consequently, each time a new block is proposed, the 'number of validators' becomes proportional to the risk likelihood block's proposer. Additionally, the game model reinforces the honest behavior of the validators by rewarding honest validators and punishing dishonest ones.
Together, TRD, Block-Supply Chain, and the game-theoretical TrueBFT consensus protocol enable robust, scalable, decentralized anti-counterfeiting supply chain that is resistant to tag reapplication attacks, as well as attacks to consensus protocols such as DDoS and Eclipse attacks.
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Improving Treatment Dose Accuracy in Radiation TherapyWong, Tony Po Yin, tony.wong@swedish.org January 2007 (has links)
The thesis aims to improve treatment dose accuracy in brachytherapy using a high dose rate (HDR) Ir-192 stepping source and in external beam therapy using intensity modulated radiation therapy (IMRT). For HDR brachytherapy, this has been achieved by investigating dose errors in the near field and the transit dose of the HDR brachytherapy stepping source. For IMRT, this study investigates the volume effect of detectors in the dosimetry of small fields, and the clinical implementation and dosimetric verification of a 6MV photon beam for IMRT. For the study of dose errors in the near field of an HDR brachytherapy stepping source, the dose rate at point P at 0.25 cm in water from the transverse bisector of a straight catheter was calculated with Monte Carlo code MCNP 4.A. The Monte Carlo (MC) results were used to compare with the results calculated with the Nucletron Brachytherapy Planning System (BPS) formalism. Using the MC calculated radial dose function and anisotropy function with the BPS formalism, 1% dose calculation accuracy can be achieved even in the near field with negligible extra demand on computation time. A video method was used to analyse the entrance, exit and the inter-dwell transit speed of the HDR stepping source for different path lengths and step sizes ranging from 2.5 mm to 995 mm. The transit speeds were found to be ranging from 54 to 467 mm/s. The results also show that the manufacturer has attempted to compensate for the effects of inter-dwell transit dose by reducing the actual dwell time of the source. A well-type chamber was used to determine the transit doses. Most of the measured dose differences between stationary and stationary plus inter-dwell source movement were within 2%. The small-field dosimetry study investigates the effect of detector size in the dosimetry of small fields and steep dose gradients with a particular emphasis on IMRT measurements. Due to the finite size of the detector, local discrepancies of more than 10 % are found between calculated cross profiles of intensity modulated beams and intensity modulated profiles measured with film. A method to correct for the spatial response of finite sized detectors and to obtain the
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Localization effects in ternary nitride semiconductorsLiuolia, Vytautas January 2012 (has links)
InGaN based blue and near-ultraviolet light emitting diodes and laser diodes have been successfully commercialized for many applications such as general lighting, display backlighting and high density optical storage devices. Despite having a comparably high defect density, these devices are known for their efficient operation, which is attributed to localization in potential fluctuations preventing carriers from reaching the centers of nonradiative recombination. Nitride research is currently headed towards improving deep ultraviolet AlGaN and green InGaN emitters with higher Al and In molar fractions. The efficiency of these devices trails behind the blue counterparts as the carrier localization does not seem to aid in supressing nonradiative losses. In addition, the operation of ternary nitride heterostructure based devices is further complicated by the presence of large built-in electric fields. Although the problem can be ameliorated by growing structures in nonpolar or semipolar directions, the step from research to production still awaits. In this thesis, carrier dynamics and localization effects have been studied in three different nitride ternary compounds: AlGaN epitaxial layers and quantum wells with high Al content, nonpolar m-plane InGaN/GaN quantum wells and lattice matched AlInN/GaN heterostructures. The experimental methods of this work mainly consist of spectroscopy techniques such as time-resolved photoluminescence and differential transmission pump-probe measurements as well as spatial photoluminescence mapping by means of scanning near-field microscopy. The comparison of luminescence and differential transmission measurements has allowed estimating the localization depth in AlGaN quantum wells. Additionally, it has been demonstrated that the polarization degree of luminescence from m-InGaN quantum wells decreases as carriers diffuse to localization centers.What is more, dual-scale localization potential has been evidenced by near-field measurements in both AlGaN and m-InGaN. Larger scale potential fluctuation have been observed directly and the depth of nanoscopic localization has been estimated theoretically from the recorded linewidth of the near-field spectra. Lastly, efficient carrier transport has been observed through AlInN layer despite large alloy inhomogeneities evidenced by broad luminescence spectra and the huge Stokes shift. Inhomogeneous luminescence from the underlying GaN layer has been linked to the fluctuations of the built-in electric field at the AlInN/GaN interface. / <p>QC 20121101</p>
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Fabrication Of Nanostructured Samples For The Investigation Of Near Field Radiation TransferArtvin, Zafer 01 September 2012 (has links) (PDF)
Radiative heat transfer in nanostructures with sub-wavelength dimensions can exceed that predicted by Planck' / s blackbody distribution. This increased effect is due to the tunneling of infrared radiation between nanogaps, and can allow the eventual development of nano-thermo-photo-voltaic (Nano-TPV) cells for energy generation from low temperature heat sources. Although near field radiation effects have been discussed for many years, experimental verification of these effects is very limited so far. In this study, silica coated silicon wafer sample chips have been manufactured by using MEMS fabrication methods for testing the near field radiation effects. A variety of samples with 1× / 1, 2× / 2 and 5× / 5 mm2 area, and with 25 nm, 50 nm, 100 nm and 200 nm (nano-gap) separations have been prepared. 3D structures with vacuum gaps have been obtained by bonding of the silica coated wafers. The samples have been tested in an experimental setup by a collaborative group at Ö / zyegin University, Istanbul. An increase in the net radiation heat transfer with decreasing nano-gap size has been reported by the Ö / zyegin group who used these samples in a parallel study. The thesis outlines the micro-fabrication techniques used for the sample preparation. Also, the manufacturing problems we have faced during this research program are discussed.
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Oxidative Dissolution of Spent Fuel and Release of Nuclides from a Copper/Iron Canister : Model Developments and ApplicationsLiu, Longcheng January 2001 (has links)
Three models have been developed and applied in the performance assessment of a final repository. They are based on accepted theories and experimental results for known and possible mechanisms that may dominate in the oxidative dissolution of spent fuel and the release of nuclides from a canister. Assuming that the canister is breached at an early stage after disposal, the three models describe three sub-systems in the near field of the repository, in which the governing processes and mechanisms are quite different. In the model for the oxidative dissolution of the fuel matrix, a set of kinetic descriptions is provided that describes the oxidative dissolution of the fuel matrix and the release of the embedded nuclides. In particular, the effect of autocatalytic reduction of hexavalent uranium by dissolved H2, using UO2 (s) on the fuel pellets as a catalyst, is taken into account. The simulation results suggest that most of the radiolytic oxidants will be consumed by the oxidation of the fuel matrix, and that much less will be depleted by dissolved ferrous iron. Most of the radiolytically produced hexavalent uranium will be reduced by the autocatalytic reaction with H2 on the fuel surface. It will reprecipitate as UO2 (s) on the fuel surface, and thus very little net oxidation of the fuel will take place. In the reactive transport model, the interactions of multiple processes within a defective canister are described, in which numerous redox reactions take place as multiple species diffuse. The effect of corrosion of the cast iron insert of the canister and the reduction of dissolved hexavalent uranium by ferrous iron sorbed onto iron corrosion products and by dissolved H2 are particularly included. Scoping calculations suggest that corrosion of the iron insert will occur primarily under anaerobic conditions. The escaping oxidants from the fuel rods will migrate toward the iron insert. Much of these oxidants will, however, be consumed by ferrous iron that comes from the corrosion of iron. The nonscavenged hexavalent uranium will be reduced by ferrous iron sorbed onto the iron corrosion products and by dissolved hydrogen. In the transport resistance network model, the transport of reactive actinides in the near field is simulated. The model describes the transport resistance in terms of coupled resistors by a coarse compartmentalisation of the repository, based on the concept that various ligands first come into the canister and then diffuse out to the surroundings in the form of nuclide complexes. The simulation results suggest that carbonate accelerates the oxidative dissolution of the fuel matrix by stabilizing uranyl ions, and that phosphate and silicate tend to limit the dissolution by the formation of insoluble secondary phases. The three models provide powerful tools to evaluate "what if" situations and alternative scenarios involving various interpretations of the repository system. They can be used to predict the rate of release of actinides from the fuel, to test alternative hypotheses and to study the response of the system to various parameters and conditions imposed upon it. / QC 20100521
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Connecting the human body - Models, Connections and CompetitionKariyannavar, Kiran January 2012 (has links)
Capacitive communication using human body as a electrical channel has attracted much attention in the area of personal area networks (PANs) since its introduction by Zimmerman in 1995. The reason being that the personal information and communication appliances are becoming an integral part of our daily lives. The advancement in technology is also helping a great deal in making them interesting,useful and very much affordable. If we interconnect these body-based devices with capacitive communication approach in a manner appropriate to the power, size, cost and functionality, it lessens the burden of supporting a communication channel by existing wired and wireless technologies. More than that, using body as physical communication channel for a PAN device compared to traditional radio transmission seems to have a lot of inherent advantages in terms of power and security etc. But still a lot of feasibility and reliability issues have to be addressed before it is ready for prime time. This promising technology is recently sub-classified into body area networks (BAN) and is currently under discussion in the IEEE 802.15.6 Task Group for addressing the technical requirements to unleash its full potential for BANs. This could play a part in Ericsson's envision of 50 billion connections by 2020. This thesis work is part of the main project to investigate the models, interface and derive requirements on the analog-front-end (AFE) required for the system. Also to suggest a first order model of the AFE that suits this communication system.In this thesis work the human body is modeled along with interfaces and transceiver to reflect the true condition of the system functioning. Various requirements like sensitivity, dynamic range, noise figure and signal-to-noise ratio (SNR) requirements are derived based on the system model. An AFE model based on discrete components is simulated, which was later used for proof of concept. Also a first order AFE model is developed based on the requirements derived. The AFE model is simulated under the assumed interference and noise conditions. The first order requirements for the submodules of the AFE are also derived. Future work and challenges are discussed.
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Mechanical properties of PVDF/MWCNT fibers prepared by flat/cylindrical near-field electrospinningKe, Chien-An 04 September 2012 (has links)
This study presents near-field electrospinning (NFES) on flat and hollow cylindrical process to fabricate permanent piezoelectricity of polyvinylidene fluoride (PVDF)/ multi-walled carbon nanotube (MWCNT) piezoelectric nanofibers. Then the mechanical properties of fibers were measured. PVDF is a potential piezoelectric polymer material combining desirable mechanical, thermal, electrical properties with excellent chemical resistance. The existing researches mostly focused on piezoelectric thin film process. However, the research of characteristic about piezoelectric fiber is little. The methods of measurement of the mechanical properties (Young¡¦s modulus, hardness, and tensile strength¡Belongation) of the electrospun PVDF/MWCN composite nanofiber were carried out by using nano-indention test (MTS Nanoindenter Windows XP System) and tensile test (Microforce Testing System). By setting electric field (1¡Ñ107 V/m), rotating velocity (900 rpm) of the hollow cylindrical glass tube on a motion X-Y stage (2 mm/sec) and PVDF solution concentration (16 wt%), and MWCNT (0.03 wt%), in-situ electric poling, mechanical stretching and morphology of PVDF nanofiber were demonstrated. After the experiments of nano-indention test and tensile strength test, it is suggested that the good mechanical properties in NFES on cylindrical process. The results show that the mechanical properties of composite nanofiber are better than the conventional NFES process. The Young¡¦s modulus of 16% PVDF fiber prepared by cylindrical process is 0.89 GPa and hardness is 26.5 MPa. The mechanical properties were increased 56.2% and 49.4% after adding 0.03% of MWCNT, corresponding to 1.39 GPa and 39.6 MPa. The tensile strength was increased 32.7% and elongation at breaking point was increased 35% after adding 0.03% MWCNT.
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Response Of Isolated Structures Under Bi-directional Excitations Of Near-field Ground MotionsOzdemir, Gokhan 01 June 2010 (has links) (PDF)
Simplified methods of analysis described in codes and specifications for
seismically isolated structures are always used either directly in special cases or for
checking the results of nonlinear response history analysis (RHA). Important
predictions for seismically isolated structures by simplified methods are the
maximum displacements and base shears of the isolation system. In this study, the
maximum isolator displacements and base shears determined by nonlinear RHA are
compared with those determined by the equivalent lateral force (ELF) procedure in
order to assess the accuracy of the simplified method in the case of bi-directional
excitations with near-field characteristics. However, although there are currently
many methods for ground motion selection and scaling, little guidance is available
to classify which method is more appropriate than the others in any applications.
Features of this study are that the ground motions used in analysis are selected and
scaled using contemporary concepts and that the ground excitation is considered biv
directional. The variations in response of isolated structures due to application of
ground motions uni-directionally and bi-directionally are also studied by employing
a scaling procedure that is appropriate for the bi-directional analysis. The proposed
new scaling methodology is an amplitude scaling method that is capable of
preserving the horizontal orthogonal components and it is developed especially for
dynamic analysis of isolated structures. Analyses are conducted for two different
symmetric reinforced concrete isolated structure for two different soil conditions in
structural analysis program SAP2000. Effect of asymmetry in superstructure on
isolator displacement is also investigated with further analyses considering 5% mass
eccentricity at each floor level. Furthermore, once the significance of the orthogonal
horizontal component on the response of isolation system is shown, the biaxial
interaction of hysteretic behavior of lead rubber bearings is implemented in
OpenSees by developing a subroutine which was not readily available.
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