<p>The lightweight and good strength of oriented thermoplastic tubes, produced through the ram extrusion process, renders this class of material advantageous from an automotive structural part forming perspective. An analytical model, capable of predicting the forming limits for these materials at elevated temperatures, would avoid the need for difficult and time-consuming tube forming experiments.</p> <p> The uniaxial tensile stress-strain properties of the oriented polypropylene (OPP) tubes along the axial and hoop direction wene determined while methods were developed for obtaining the uniaxial compressive properties of the tube. The uniaxial and biaxial testing of the OPP tubes enabled representation of the experimental plastic work contours for the material at a range of temperatures. The use of the pressure-modified Hill criterion, the concept of plastic work contours in stress space, and the stress strain data from uniaxial testing of the tube allowed accurate prediction of the plastic work contours for the OPP tubes as a function of temperature. The analytical prediction was able to capture the anisotropy, pressure dependency and anisotropic hardening exhibited by the material at elevated temperatures. In addition, the use of a localized necking criterion, which involved the point at which the maximum force along the hoop direction of the tube was reached, allowed the temperature dependent forming limits for the material to be predicted. The forming limits increased with temperature for all of the strain paths considered. In addition, at a given temperature, the forming limits decreased with increasing strain ratio. The limiting strains achieved with axial end feeding were markedly higher than those in which no axial end feeding was used. </p> <p> Good agreement was observed between the predicted forming limits and the results from tube forming tests of the material, along a range of strain paths and at various temperatures.</p> / Thesis / Doctor of Philosophy (PhD)

This thesis work presents a model predictive control (MPC) based trajectory planner forhigh speed lane change and low speed parking scenarios of autonomous four wheel steering(4WS) vehicle. A four wheel steering vehicle has better low speed maneuverabilityand high speed stability compared with normal front wheel steering(FWS) vehicles. TheMPC optimal trajectory planner is formulated in a curvilinear coordinate frame (Frenetframe) minimizing the lateral deviation, heading error and velocity error in a kinematicdouble track model of a four wheel steering vehicle. Using the proposed trajectory planner,simulations show that a four wheel steering vehicle is able to track different type ofpath with lower lateral deviations, less heading error and shorter longitudinal distance. / I detta avhandlingsarbete presenteras en modellbaserad prediktiv kontroll (MPC) -baseradbanplaneringsplan f¨or h¨oghastighetsbanan och l°aghastighetsparametrar f¨or autonomtfyrhjulsdrift (4WS). Ett fyrhjulsdrivna fordon har b¨attre man¨ovrerbarhet med l°ag hastighetoch h¨oghastighetsstabilitet j¨amf¨ort med vanliga fr¨amre hjulstyrningar (FWS). MPC-optimalbanplanerare ¨ar formulerad i en kr¨okt koordinatram (Frenet-ram) som minimerar sidof¨orl¨angningen,kursfel och hastighetsfel i en kinematisk dubbelsp°armodell av ett fyrhjulsstyrda fordon.Med hj¨alp av den f¨oreslagna banaplaneraren visar simuleringar att ett fyrhjulsstyrfordonkan sp°ara olika typer av banor med l¨agre sidof¨orl¨angningar, mindre kursfel ochkortare l¨angsg°aende avst°and.

Airborne Wind Energy is an emerging technology that harnesses the power of the wind by using tethered wings. Among the flying devices are ram-air wings made from coated textiles that utilize dynamic pressure to gain their shape. During flight operation, the textiles are subject to long-term weathering exposure and high aerodynamic loads, leading to degradation processes and the ultimate loss of functional properties. Therefore, a key challenge in the Airborne Wind Energy industry is the improvement of the textile durability of ram-air kites. This thesis contributes to solving this problem by investigating the effects of 200 hours of artificial weathering and 36 weeks of natural weathering on the mechanical properties of selected state-of-the-art kite textiles and the underlying principles of degradation. The tested materials involve two polyamide 6.6 rip-stop weaves coated with polyurethane and silicone, as well as a coated plain weave and a flexible laminate made from high-modulus polyethylene. The results show that all materials are clearly affected by the exposure to weathering, but the implications on the mechanical properties and the rate of degradation vary significantly. The high-modulus polyethylene textiles demonstrate superior tensile properties, but severe coating degradation causes a significant rise in air permeability. Consequently, the high-modulus polyethylene textiles are considered unsuitable for application in ram-air kites, as the high permeability prevents the kite from maintaining sufficiently high pressure. In contrast, the silicone coated polyamide 6.6 textile exhibits superior air permeability after long-term exposure to weathering conditions. FTIR spectroscopy and TGA indicate that the reduced permeability could arise from curing processes in the silicone coating.

The development and evaluation of the design of a Micro-Ram Air Turbine (µRAT), a device being developed to provide power for an autonomous boundary layer measurement system, has been undertaken. The design tools consist of a rotor model and a generator model. The primary focus was on developing and evaluating the generator model for the prediction of generator brake power and output electrical power with and without rectification as a function of shaft speed and electrical load, with only basic manufacturer specifications given as inputs. A series of motored generator evaluation test were conducted at speeds ranging from 9,000 to 25,000 rpm for loads varying between 1 and 3.02 Ohms with output power of up to 80 Watts. Results demonstrated that predicted generated power was at or below 3% error when compared to measured results with about 1% uncertainty. A rotor model was also developed using basic blade element theory. This model neglected induced flow effects and was therefore expected to over predict rotor torque and power. A second rotor model that includes induced flow effects, the open source program X-Rotor, was also used to predict rotor power and for comparison to the blade element rotor model results. Both rotor models were evaluated through wind tunnel validation tests conducted on a turbine generator with two different 3.25 in diameter rotors, rotor-1 (untwisted blades) and rotor-2 (twisted blades). Wind tunnel validation test airspeeds varied between 71-110 mph with electrical loads ranging from 1-20 ohms. Results indicated power predictions to be 50-75% higher for the blade element model and 20-30% for X-Rotor results. The blade element rotor model was modified by applying the Prandtl tip-loss factor to approximately account for the induced flow effects; this addition brought predictions much closer to X-Rotor results. Based on the motor-driven generator test results, it is believed that most of the discrepancy in baseline rotor/generator validation test between predicted and observed power generated is due to inaccuracy in the rotor performance modelling with likely contributors to error being induced flow effects, crude section lift/drag modelling, and aero-elastic deformation. It is concluded that the proposed generator model is sufficient although direct torque measurements may be desired and further development of the µRAT design tools should focus on an improved rotor performance model.

No description available.

Think tanks are identified as policy research institutions that conduct interdisciplinary research on social or policy issues and provide consultation with the government, enterprises and the general public. Civil think tanks place social value prior to profits and uphold research independence. Through producing research content on social issues, civil think tanks make contribution with publications, advocacy, and action promotion. Civil think tanks are facing challenging complexity and obstacles in development due to their independence from governments and universities. To resolve these difficulties, civil think tanks require an innovative business model and a matching management mechanism. This thesis aims to understand the business model performed by civil think tanks and explore a practical management model to support this business. Specific recommendations will be made to the case organization. The case study was performed in collaboration with Youthink Center, one of China’s leading civil think tanks which provides young people with a platform to learn, take advocacy, and action on global frontier issues about sustainable development. A systematic literature review was conducted to elaborate concepts connected to think tanks and understand existing management frameworks. Data regarding this research project was collected through internal and external interviews and documentations.The case-study resulted in an evaluation on the business model of Youthink Center and a proposed management framework in accordance with the business. Key aspects of succeeding in a think tank are to insist on the value proposition of social responsibility and to enhance content creation and influence expansion ability with digital tools. To make this business model operate effectively, think tanks are expected to focus on project management processes, talent gathering, evaluation mechanism, and deeper collaborations on knowledge and technology. Understanding these areas will guide the social think tanks to increase working efficiency and enhance social influence. / Tankesmedjor (think tanks) identifieras som politiska forskningsinstitutioner som bedriver tvärvetenskaplig forskning om sociala eller politiska frågor och erbjuder samråd med regeringen, företag och allmänheten. Civila tankesmedjor lägger socialt värde före vinst och upprätthåller forskningsoberoende. Genom att producera forskningsinnehåll om sociala frågor bidrar civila tankesmedjor med publikationer, förespråkande och handlingsfrämjande. Civila tankesmedjor står inför utmanande komplexitet och hinder i utvecklingen på grund av deras oberoende från regeringar och universitet. För att lösa dessa svårigheter kräver civila tankesmedjor en innovativ affärsmodell och en matchande hanteringsmekanism. Denna uppsats syftar till att förstå den affärsmodell som utförs av civila tankesmedjor och utforska en praktisk ledningsmodell för att stödja denna verksamhet. Specifika rekommendationer kommer att ges till fallorganisationen. Fallstudien utfördes i samarbete med Youthink Center, en av Kinas ledande civila tankesmedjor som ger ungdomar en plattform för att lära sig, ta förtal och agera i globala gränsfrågor om hållbar utveckling. En systematisk litteraturgranskning genomfördes för att utarbeta begrepp kopplade till tankesmedjor och förstå befintliga ledningsramar. Data om detta forskningsprojekt samlades in genom interna och externa intervjuer och dokument. Fallstudien resulterade i en utvärdering av affärsmodellen för Youthink Center och en föreslagen ledningsram i enlighet med verksamheten. Nyckelaspekter för att lyckas med en tankesmedja är att insistera på värdet av socialt ansvar och att förbättra innehållsskapandet och påverka expansionsförmågan med digitala verktyg. För att få denna affärsmodell att fungera effektivt förväntas tankesmedjor att fokusera på projektledningsprocesser, talangsamling, utvärderingsmekanismer och djupare samarbete om kunskap och teknik. Att förstå dessa områden kommer att vägleda de sociala tankesmedjorna för att öka arbetseffektiviteten och förbättra det sociala inflytandet.

Afin de concurrencer les mémoires à accès aléatoire de type DRAM actuellement sur le marché, les mémoires magnétiques ont depuis quelques années fait l'objet de nombreuses études afin de les rendre aussi performantes que possible. Dans ce contexte, les jonctions tunnel magnétiques à double barrière pourraient présenter des avantages significatifs en termes de vitesse de lecture et de consommation électrique. Nous avons en effet fait la démonstration que les structures à double barrière permettent, pour une configuration antiparallèle des aimantations des polariseurs, d'accroître les effets de transfert de spin assurant ainsi des courants d'écriture faibles. Dans la configuration parallèle des polariseurs, le phénomène est inversé et le couple par transfert de spin résultant est considérablement réduit. Cela permettrait de lire l'information plus rapidement en utilisant des tensions du même ordre de grandeurs que celles utilisées pour l'écriture. Nous avons par ailleurs proposé une méthode d'analyse permettant de caractériser les deux barrières tunnel par des mesures électriques en pleine plaque, ce qui facilite le développement des matériaux et atteste des propriétés électriques attendues avant nanofabrication. / Since a few years, magnetic memories have been extensively studied in order to compete with already existing Random Access Memories such as DRAM. In this context, double barrier magnetic tunnel junctions may have significant assets in terms of reading speed and electrical consumption. In fact, we demonstrated that spin transfer torque is enhanced when polarizers magnetizations are antiparallel, thus yielding a decrease of the writing current. On the contrary, when polarizers are parallel, spin transfer torque is drastically shrinked, thus allowing fast reading of the storage layer state at a voltage as large as the writing voltage. Moreover, we proposed an analysis method to characterize both tunnel barriers by full-sheet electrical measurements, leading to considerable gain of time in material developpement.

Les services cloud offrent des coûts réduits, une élasticité et un espace de stockage illimité qui attirent de nombreux utilisateurs. Le partage de fichiers, les plates-formes collaboratives, les plateformes de courrier électroniques, les serveurs de sauvegarde et le stockage de fichiers sont parmi les services qui font du cloud un outil essentiel pour une utilisation quotidienne. Actuellement, la plupart des systèmes d'exploitation proposent des applications de stockage externalisées intégrées, par conception, telles que One Drive et iCloud, en tant que substituts naturels succédant au stockage local. Cependant, de nombreux utilisateurs, même ceux qui sont disposés à utiliser les services susmentionnés, restent réticents à adopter pleinement le stockage et les services sous-traités dans le cloud. Les préoccupations liées à la confidentialité des données augmentent l'incertitude pour les utilisateurs qui conservent des informations sensibles. Il existe de nombreuses violations récurrentes de données à l'échelle mondiale qui ont conduit à la divulgation d'informations sensibles par les utilisateurs. Pour en citer quelques-uns : une violation de Yahoo fin 2014 et annoncé publiquement en Septembre 2016, connue comme la plus grande fuite de données de l'histoire d'Internet, a conduit à la divulgation de plus de 500 millions de comptes utilisateur ; une infraction aux assureurs-maladie, Anthem en février 2015 et Premera BlueCross BlueShield en mars 2015, qui a permis la divulgation de renseignements sur les cartes de crédit, les renseignements bancaires, les numéros de sécurité sociale, pour des millions de clients et d'utilisateurs. Une contre-mesure traditionnelle pour de telles attaques dévastatrices consiste à chiffrer les données des utilisateurs afin que même si une violation de sécurité se produit, les attaquants ne peuvent obtenir aucune information à partir des données. Malheureusement, cette solution empêche la plupart des services du cloud, et en particulier, la réalisation des recherches sur les données externalisées.Les chercheurs se sont donc intéressés à la question suivante : comment effectuer des recherches sur des données chiffrées externalisées tout en préservant une communication, un temps de calcul et un stockage acceptables ? Cette question avait plusieurs solutions, reposant principalement sur des primitives cryptographiques, offrant de nombreuses garanties de sécurité et d'efficacité. Bien que ce problème ait été explicitement identifié pendant plus d'une décennie, de nombreuses dimensions de recherche demeurent non résolues. Dans ce contexte, le but principal de cette thèse est de proposer des constructions pratiques qui sont (1) adaptées aux déploiements dans les applications réelles en vérifiant les exigences d'efficacité nécessaires, mais aussi, (2) en fournissant de bonnes assurances de sécurité. Tout au long de notre recherche, nous avons identifié le chiffrement cherchable (SSE) et la RMA inconsciente (ORAM) comme des deux potentielles et principales primitives cryptographiques candidates aux paramètres des applications réelles. Nous avons identifié plusieurs défis et enjeux inhérents à ces constructions et fourni plusieurs contributions qui améliorent significativement l'état de l'art.Premièrement, nous avons contribué à rendre les schémas SSE plus expressifs en permettant des requêtes booléennes, sémantiques et de sous-chaînes. Cependant, les praticiens doivent faire très attention à préserver l'équilibre entre la fuite d'information et le degré d'expressivité souhaité. Deuxièmement, nous améliorons la bande passante de l'ORAM en introduisant une nouvelle structure récursive de données et une nouvelle procédure d'éviction pour la classe d'ORAM ; nous introduisons également le concept de redimensionnabilibté dans l'ORAM qui est une caractéristique requise pour l'élasticité de stockage dans le cloud. / Cloud services offer reduced costs, elasticity and a promised unlimited managed storage space that attract many end-users. File sharing, collaborative platforms, email platforms, back-up servers and file storage are some of the services that set the cloud as an essential tool for everyday use. Currently, most operating systems offer built-in outsourced cloud storage applications, by design, such as One Drive and iCloud, as natural substitutes succeeding to the local storage. However, many users, even those willing to use the aforementioned cloud services, remain reluctant towards fully adopting cloud outsourced storage and services. Concerns related to data confidentiality rise uncertainty for users maintaining sensitive information. There are many, recurrent, worldwide data breaches that led to the disclosure of users' sensitive information. To name a few: a breach of Yahoo late 2014 and publicly announced on September 2016, known as the largest data breach of Internet history, led to the disclosure of more than 500 million user accounts; a breach of health insurers, Anthem in February 2015 and Premera BlueCross BlueShield in March 2015, that led to the disclosure of credit card information, bank account information, social security numbers, data income and more information for more than millions of customers and users. A traditional countermeasure for such devastating attacks consists of encrypting users' data so that even if a security breach occurs, the attackers cannot get any information from the data. Unfortunately, this solution impedes most of cloud services, and in particular, searching on outsourced data. Researchers therefore got interrested in the fllowing question: how to search on outsourced encrypted data while preserving efficient communication, computation and storage overhead? This question had several solutions, mostly based on cryptographic primitives, offering numerous security and efficiency guarantees. While this problem has been explicitly identified for more than a decade, many research dimensions remain unsolved. The main goal of this thesis is to come up with practical constructions that are (1) suitable for real life deployments verifying necessary efficiency requirements, but also, (2) providing good security insurances. Throughout our reseach investigation, we identified symmetric searchable encryption (SSE) and oblivious RAM (ORAM) as the two potential and main cryptographic primitives' candidate for real life settings. We have recognized several challenges and issues inherent to these constructions and provided a number of contributions that improve upon the state of the art. First, we contributed to make SSE schemes more expressive by enabling Boolean, semantic, and substring queries. Practitioners, however, need to be very careful about the provided balance between the security leakage and the degree of desired expressiveness. Second, we improve ORAM's bandwidth by introducing a novel recursive data structure and a new eviction procedure for the tree-based class of ORAM contructions, but also, we introduce the concept of resizability in ORAM which is a required feature for cloud storage elasticity.

L'objectif principal de mon travail de thèse est de comprendre les processus qui agissent sur la poussière pendant le couplage entre le milieu interstellaire galactique et le milieu intra-amas. Ce processus est d'intérêt particulier dans les phénomènes violents comme les interactions galaxie-galaxie ou le "Ram Pressure Stripping" causé par la chute d'une galaxie vers le centre de l'amas.Initialement, je me suis concentré sur le problème de la destruction de la poussière et le processus de chauffage, en re-visitant les modèles présents en littérature. J'ai particulièrement insisté sur les cas des environnements extrêmes comme le gaz chaud de type coronale (e.g., IGM, ICM, HIM) et les chocs interstellaires générés par les supernovae. Sous ces conditions les petits grains sont détruits rapidement et les gros grains sont chauffés par les collisions avec les électrons énergétiques, en rendent la distribution spectral d'énergie de la poussière très différente de ce qu'on observe dans le milieu interstellaire diffus.Pour tester nos modèles j'ai les appliqués au cas d'une galaxie en interaction, NGC 4438. Les données Herschel de cette galaxie indiquent la présence de la poussière avec une température plus élevée de ce qu'on s'attendait.Avec une analyse à plusieurs longueurs d'onde on montre que cette poussière chaude semble être dans un gaz ionisé et chaud et donc subir à la fois le chauffage collisionnel et la destruction des petits grains.De plus, je me suis focalisé sur l'énigme de longue date à propos de la différence entre les échelles de temps de destruction et formation de la poussière dans la Voie Lactée. Basées sur l'efficacité de destruction de la poussière dans les chocs interstellaires, les estimations précédentes portent à une durée de vie de la poussière plus courte que l'échelle de temps typique de sa formation dans les étoiles AGB. En utilisant un modèle de poussière récent et les dernières estimations pour l'évolution de la poussière, on a réévalué la durée de vie de la poussière dans notre Galaxie. Finalement, j'ai tourné mon attention au phénomène de "Ram Pressure Stripping''. La galaxie ESO 137-001 représente un des meilleurs cas pour étudier cet effet. Sa longue queue H2 intégrée dans une queue de gaz chaud et ionisé soulève des questions sur son possible arrachement de la galaxie ou sa formation en aval dans la queue. Basé sur des récentes simulations numériques, j'ai montré que la formation des molécules de H2 sur la surface des grains dans la queue est un scénario viable. / The main goal of my PhD study is to understand the dust processing that occurs during the mixing between the galactic interstellar medium and the intracluster medium. This process is of particular interest in violent phenomena such as galaxy-galaxy interactions or the "Ram Pressure Stripping'' due to the infalling of a galaxy towards the cluster centre.Initially, I focus my attention to the problem of dust destruction and heating processes, re-visiting the available models in literature. I particularly stress on the cases of extreme environments such as a hot coronal-type gas (e.g., IGM, ICM, HIM) and supernova-generated interstellar shocks. Under these conditions small grains are destroyed on short timescales and large grains are heated by the collisions with fast electrons making the dust spectral energy distribution very different from what observed in the diffuse ISM.In order to test our models I apply them to the case of an interacting galaxy, NGC 4438. Herschel data of this galaxy indicates the presence of dust with a higher-than-expected temperature.With a multi-wavelength analysis on a pixel-by-pixel basis we show that this hot dust seems to be embedded in a hot ionised gas therefore undergoing both collisional heating and small grain destruction.Furthermore, I focus on the long-standing conundrum about the dust destruction and dust formation timescales in the Milky Way. Based on the destruction efficiency in interstellar shocks, previous estimates led to a dust lifetime shorter than the typical timescale for dust formation in AGB stars. Using a recent dust model and an updated dust processing model we re-evaluate the dust lifetime in our Galaxy. Finally, I turn my attention to the phenomenon of "Ram Pressure Stripping''. The galaxy ESO 137-001 represents one of the best cases to study this effect. Its long H2 tail embedded in a hot and ionised tail raises questions about its possible stripping from the galaxy or formation downstream in the tail. Based on recent hydrodynamical numerical simulations, I show that the formation of H2 molecules on the surface of dust grains in the tail is a viable scenario.

Ferroelectricity is very attractive for nonvolatile memories since it allows non-volatility paired with a field driven switching mechanism enabling a very low-power write operation. Non-volatile memories based on ferroelectric lead-zirconium-titanate (PZT) (see fig. la) are available on the market for more than a quarter of a century now [1]. Yet they are limited to niche applications due to the compatibility issues of the ferroelectric material with CMOS processes and the associated limited scalability [2]. The discovery of ferroelectricity in doped hafnium oxide has revived the activities towards a variety of scalable ferroelectric nonvolatile memory devices