• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 9
  • 6
  • 4
  • 2
  • 2
  • 1
  • Tagged with
  • 27
  • 5
  • 4
  • 4
  • 4
  • 4
  • 4
  • 4
  • 3
  • 3
  • 3
  • 3
  • 3
  • 3
  • 2
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Evaluation of Alkali-Silica Reaction (ASR)-Induced Damage Generation and Prolongation in Affected Recycle Concrete

Trottier, Cassandra 24 September 2020 (has links)
Recycled concrete is among the rising eco-friendly construction materials which helps to reduce waste and the need for new natural resources. However, such concrete may present previous deterioration due to, for instance, alkali-silica reaction (ASR), which is an ongoing distress mechanism that may keep being developed in the recycled material. This work aims to evaluate the potential of further distress and crack development (i.e. initiation and propagation) of AAR-affected RCA concrete in recycled mixtures displaying distinct past damage degrees and reactive aggregate types. Therefore, concrete specimens incorporating two highly reactive aggregates (Springhill coarse aggregate and Texas sand) were manufactured in the laboratory and stored in conditions enabling ASR development. The specimens were continuously monitored over time and once they reached marginal (0.05%) and very high (0.30%) expansion levels, they were crushed into RCA particles and re-used to fabricate RCA concrete. The RCA specimens were then placed in the same previous conditions and the “secondary” ASR-induced development monitored over time. Results show that the overall damage in ASR-affected RCA concrete is quite different from affected conventional concrete, especially with regards to the severely damaged RCA particles, where ASR is induced by a reactive coarse aggregate, as the RCA particle itself may present several levels of damage simultaneously caused by past/ongoing ASR and newly formed ASR. Moreover, the influence of the original damage extent in such RCA concrete was captured by the slightly damaged RCA mixture eventually reaching the same damage level as the severely damaged mixture. Furthermore, the original extent of deterioration influence the “secondary” induced expansion and damage of RCA concrete since the higher the original damage level, the higher the cracks numbers and lengths observed in the RCA concrete for the same expansion level whereas wider cracks are generated by RCA having previously been subjected to slight damage thus indicating the difference in the distress mechanism as a function of original extent of damage. In addition, it has been found that distress on RCA containing a reactive sand generates and propagates from the residual mortar (RM) into the new mortar (NM) as opposed to RCA containing a reactive coarse aggregate, being generated and propagated from the original coarse aggregate (i.e. original virgin aggregate – OVA) into the NM. Likewise, RCA containing a reactive sand caused longer and higher number of cracks for the same “secondary” induced expansion than the RCA made of reactive coarse aggregate. Finally, novel qualitative and descriptive models are proposed in this research to explain ASR-induced distress generation and propagation on RCA mixtures made of reactive fine and coarse aggregates.
22

Multiple CubeSat Mission for Auroral Acceleration Region Studies

Castro, Marley Santiago January 2021 (has links)
The Auroral Acceleration Region (AAR) is a key region in understanding the interactionbetween the Magnetosphere and Ionosphere. To understand the physical, spatial, and temporal features of the region, multi-point measurements are required. Distributed small-satellite missions such as constellations of multiple nano satellites (for example multi-unit CubeSats) would enable such type of measurements. The capabilities of such a mission will highly depend on the number of satellites - one reason that makes low-cost platforms like CubeSats a very promising choice. In a previous study, the state-of-the-art of miniaturized payloads for AAR measurements was analyzed and evaluated on the capabilities of different multi-CubeSat configurations equipped with such payloads in addressing different open questions in AAR. This thesis will provide the mission analysis of such a multi-CubeSat mission to the AAR and possible mission design. This includes defining the mission scenario and associated requirements, developing a mathematical description of AAR that allows for specific regions in space to be targeted, an optimisation process for designing orbits targeting these regions, conversion of a satellite formation to appropriate orbits, verifying the scientific performance of this formation and the various costs associated with entering, maintaining, and exiting these orbits.
23

Nyintroduktioner på svenska handelsplatser : Har nyintroduktioner genererat högre avkastning än NASDAQ OMXSPI? / Initial Public Offerings on Swedish marketplaces : Have IPOs created higher returns than NASDAQ OMXSPI?

Karpov, Boris, Klevenstedt, Johan January 2011 (has links)
Denna studie har genomförts i syfte att undersöka huruvida nyintroduktioner generar en överavkastning i förhållande till OMXSPI på svenska handelsplatser under en börsuppgång och en börsnedgång för olika tidsintervall och branscher. Studien har undersökt nyintroduktioner genomförda under tidsperioden Q1 2004 till Q2 2009. Syftet har för avsikt att utmynna i huruvida nyintroduktioner vid svenska handelsplatser är effektiva och om investerare kunnat utnyttja eventuella ineffektiviteter som investeringsstrategier. Undersökningen är en eventstudie baserad på en kvantitativ metod där korrigerade historiska aktiekurser har inhämtats och beräkningar har genomförts med hjälp av två metoder, den genomsnittliga abnormala avkastningen och den genomsnittliga abnormala avkastningen för en buy-and-hold strategi, för att säkerställa en hög validitet i studien. Slutsatsen påvisar att investerare som investerat i nyintroduktioner på AktieTorget under börsuppgången hade kunnat utnyttja den något lägre grad av effektivitet utifrån en buy-andhold strategi på tre månader och erhållit en genomsnittlig signifikant överavkastning gentemot OMXSPI på 32,6 procent. En investerare som valt att investerare i nyintroduktioner utifrån en buy-and-hold period på tre månader på Alternativa Aktiemarknaden under börsnedgången hade i genomsnitt erhållit en signifikant överavkastning på 11,8 procent. För den investeraren som inte tagit hänsyn till när introduktionen genomförts och investerat i nyintroduktioner på AktieTorget utifrån en buy-and-hold period på en månad hade i genomsnitt erhållit en signifikant överavkastning på 18,2 procent.
24

Genealogy of Resilience in the Ontario Looking After Children System

Latour, Laurie-Carol 03 January 2017 (has links)
Resiliency has become common in child welfare parlance in recent decades and producing resilient youth is touted as the panacea to improving notoriously poor outcomes for youth in care, when compared to youth not in the care of the state. The Looking After Children (LAC) system emerged in the U.K out of neoliberal and managerial policies of the 1990s. The LAC system, and its corresponding Assessment and Action Record (AAR), was subsequently imported to Canada and has been heralded to foster resilience in youth in care. The AAR is composed of hundreds of tick box questions posed to young people in care, child welfare workers, and foster parents; these questions are pedagogical and the mined data from the AAR is aggregated to inform child welfare policy. The Looking After Children: A Practitioner’s Guide (Lemay & Ghazal, 2007) instructs workers how to administer the AAR, Second Canadian adaptation (AAR- C2), and it informs workers how to do their job. The notion of resilience in the Practitioner's Guide and the AAR-C2 are based in normative development and day to day experiences (Lemay & Ghazal, 2007). My interest in the LAC system emerges out of my experiences as a child welfare worker and my experience of being a youth in care. I wondered how it was, given the oppressive track record of child welfare in Canada, that the state could initiate a system to produce normal youth. This was a particularly salient question given the massive over- representation of Indigenous youth in foster care. With this critical curiosity as a point of departure I employed a Foucauldian inspired discourse analysis of the Looking After Children: A Practitioner’s Guide (2007, University of Ottawa Press), and three versions of its corresponding Assessment and Action Record, Second Canadian adaptation (AAR- C2) (2006, 2010, 2016, University of Ottawa). My analysis asked the question: How have we come to this ideal of resiliency? What were the contingencies and complex set of practices that enabled this specific notion of resilience to emerge in child welfare? What are the material outcomes of this notion of resilience? My findings suggest that: Youth in care are produced as deviant and outside of normal development, versus the desired resilient youth; youth in care and foster parents are responsibilized to produce resilient outcomes, which can never actually be achieved; the AAR-C2 acts as a surveillance system to enable to production of neoliberal subjects; the LAC system and the AAR-C2 are a method of colonization of Indigenous youth in care. / Graduate
25

Modélisation des réactions de gonflement interne des bétons avec prise en compte des couplages poro-mécaniques et chimiques / Modelling of concrete internal swelling reactions with poro-chemo-mechanical complings

Morenon, Pierre 14 November 2017 (has links)
Les réactions de gonflements internes (RGI) sont des pathologies qui dégradent le béton de certains ouvrages tels que des barrages en étant à l'origine de gonflements. Electricité De France (EDF) doit assurer la sûreté des personnes et des biens situés à l'aval de ses structures. Ce travail a pour but d'améliorer la modélisation des phénomènes physiques liés à ces dégradations notamment l'interaction entre le produit gonflant et le squelette solide. La contrainte intraporeuse générée par la pression du produit peut créer un endommagement. Dans le modèle proposé, la fissuration peut avoir lieu à deux échelles : - Au niveau microscopique c'est le produit gonflant qui comble le volume libre autour du site de réaction avant de mettre en traction le matériau jusqu'à fissuration, ce qui provoque une baisse des caractéristiques du matériau (résistances en traction et en compression, module d'Young). Un critère de plasticité anisotrope et une loi d'écrouissage positif sont proposés pour modéliser ce phénomène. - Au niveau macroscopique, des gradients de gonflements peuvent se développer à l'intérieur d'ouvrages dont les états de contraintes et les conditions d'humidité et de température ne sont pas homogènes. Une fissuration localisée peut alors s'initier. Elle est la source de risques de dislocations des structures pouvant mener à leur ruine, de concentrations de contraintes dans les aciers structuraux, de chemins facilités pour les agents agressifs extérieurs et pour l'eau, composé essentiel au développement rapide de ces pathologies. La prise en compte des couplages hydro-poro-mécaniques est nécessaire à la simulation de ces phénomènes. Cette fissuration est modélisée par un critère plastique de Rankine anisotrope dont l'énergie dissipée par la fissuration est régularisée par la méthode d'Hillerborg. Après avoir présenté ce modèle, il est validé et appliqué à différentes échelles pour des états de contraintes et des conditions environnementales diverses, sur : - des éprouvettes soumises à des contraintes et des blocages multi-axiaux, - des poutres de laboratoire plus ou moins armées subissant des gradients d'humidité importants, - des barrages dans des conditions réelles construits dans les années 1950. Les résultats obtenus avec le modèle permettent de retrouver les déplacements, les contraintes et les résistances de ces structures après vieillissement. Pour les poutres atteintes de réaction alcali-silice, les résultats numériques obtenus montrent notamment une prise en compte réaliste des contraintes induites par la présence d'armatures, ce qui est confirmé par la validation du comportement à rupture. Néanmoins, des difficultés de calage subsistent pour les poutres subissant la réaction sulfatique interne. Elles sont issues des grandes amplitudes d'expansion et des couplages diffusion-fissuration qui rendent spécifique le comportement de ces structures par rapport à des structures subissant des expansions moins importantes. Ce modèle est un outil pour la requalification des ouvrages dans le but d'assurer leur sûreté. Il peut également servir de base de calcul à la simulation de diverses réhabilitations et travaux de confortements. / Internal swelling reactions (ISR) damage the concrete of structures such as dams. Electricité De France (EDF) must ensure the safety of the people and goods located below the dam. This work aims to improve the modeling of the physical phenomena related to these damages, especially the interaction between the swelling product and the solid skeleton. The intraporous stress generated by the product pressure can create cracking, which, in the proposed model, can occur at two scales: - At a microscopic scale, the swelling product fills the gaps around the reaction site, which induces cracking and a decrease of the materials' characteristics (tensile and compression strengths, Young's modulus). Numerically, an anisotropic plastic criteria and a hardening law allow modelling this phenomenon. - At a macroscopic level, swelling gradients can develop inside concrete structures whose stress states and climatic conditions (humidity and temperature) are not homogeneous. A localized cracking can begin. It is a source of structure dislocation risks and stress concentrations in structural reinforcement. It may ease the way in for outside aggressive agents and water, an essential component for these reactions. Hydro-poro-mechanical couplings need to be taken into account when simulating these phenomena. The cracking is modelled by a Rankine plastic criterion whose dissipated energy is regularized by the Hillerborg's method. After presenting the model, several stress states and environmental conditions are applied to the model in order to validate it on: - samples under multi-axial stresses and restraints, - plain and reinforced beams submitted to moisture gradients in laboratory, - 1950s dams in real conditions. The results of the model make it possible to reproduce the displacements, the stresses and residual strength of these structures after aging. For the beams submitted to alkali aggregate reaction, the numerical results show a relevant prediction of the stress induced by reinforcement, confirmed by the failure behaviour. Nevertheless, the model encounters calibration difficulties for beams affected by delayed ettringite formation. They come from large swelling amplitude and diffusion-cracking coupling which are inherent to these structure behaviours. This model is a tool for concrete structure requalification in order to ensure their safety. It can also be a basis for diverse rehabilitations and reinforcement works simulation.
26

Dedolomitization and Alkali-Silica Reactions in Ohio-Sourced Dolostone Aggregates

Smeltz, Jonathan Brett 08 May 2018 (has links)
No description available.
27

Visualizations for simulation-based training : Enhancing the evaluation of missile launch events during after-action reviews of air combat simulation / Visualiseringar för simulatorbaserad utbildning : Förbättring av utvärderingen av robotskott under after-action reviews för luftstridssimulering

ter Vehn, Pontus January 2016 (has links)
This thesis work has been part of an effort to improve the after-action reviews of the air combat simulator training sessions conducted at the Swedish Air Force Combat Simulation Centre (FLSC). Initial studies identified three main needs regarding the evaluation of air-to-air missile shots during beyond-visual-range combat simulation. These needs included an improved detection of where and when in the simulation playback a missile shot took place, a collected view of flight parameters to prevent confusion and cross-referencing between the various displays, as well as the ability to review an aircraft’s flight parameters over time in order to discuss alternative shooting opportunities or maneuvering patterns. To fulfill these three needs, design studies were performed iteratively in collaboration with staff at the FLSC. This work has resulted in a design proposal with a prototype based on the design guidelines and recommendations of the study's participants. The purpose of the visualization is to provide support for instructors and promote the individual learning of pilots. Hopefully, this can ultimately help in answering the question regarding why a missile missed its target. For instructors and air units such aids could mean that operating errors can be more easily identified and also form a basis for discussion during the assessment briefings. / Detta examensarbete har haft som syfte att förbättra utvärderingen av luftstridssimuleringar som bedrivs vid det svenska flygvapnets luftstridssimuleringscentrum, FLSC. Inledande studier identifierade tre huvudsakliga behov för utvärderingen av flygplansburna robotskott avfyrade mot luftmål utom synhåll, på långa avstånd. Dessa behov inkluderar en förbättring när det gäller att upptäcka var och när i en simuleringsuppspelning som ett robotskott har skett, en samlad vy över flygparametrar för att förhindra förvirring och korsreferering mellan olika skärmar, samt möjligheten att utvärdera ett flygplans flygparametrar över tid för att kunna diskutera alternativa avfyrningsmöjligheter eller manövreringsmönster. För att fylla dessa tre behov har iterativa designstudier utförts i samarbete med personalen på FLSC. Detta har resulterat i ett designförslag med en prototyp baserad på de designriktlinjer och -rekommendationer som studiens deltagare delgett. Syftet med visualiseringen är att ge stöd till instruktörer och främja piloters individuella inlärning. Förhoppningsvis kan detta i slutändan bidra till att svara på frågan om varför en robot missade sitt mål. För instruktörer och flygförband kan ett sådant hjälpmedel underlätta identifiering av felmanövreringar och även ligga till grund för värdefulla diskussioner under analysen av genomförda luftsstridsimuleringar.

Page generated in 0.0296 seconds