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  • 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.
1

Étude des mécanismes contrôlant la déformation du magnésium à chaud / A study of the mechanisms controlling the plastic deformation of magnesium at high temperature

Chapuis, Adrien 18 October 2010 (has links)
Le magnésium et ses alliages sont de plus en plus utilisés dans les transports pour leur faible densité (1,7), et on cherche à les utiliser sous la forme corroyée. De structure hexagonale compact, le magnésium est très anisotrope et faiblement ductile à froid. La déformation est contrôlée par l'activation de systèmes de glissement et de maclage, seuls le glissement basal et le maclage de traction sont actifs à froid, alors qu'à chaud sont activés les glissements prismatique et pyramidal <c+a>, et le maclage de compression. Nous avons élaboré des monocristaux de magnésium pur de différentes orientations pour mesurer les contraintes de cission résolues critique (CRSS) des différents systèmes par des essais de compression plane à des températures allant de l'ambiante à 450°C. En parallèle nous avons développé un code de plasticité cristalline pour modéliser la déformation de cristaux contraints, ce programme est basée sur la loi de Schmid et le principe du travail maximum, ce qui permet de prédire les systèmes de déformation activés et la contrainte nécessaire, en fonction des CRSS. Nous avons aussi testé le modèle pour prédire le comportement de l’alliage polycristallin AZ31. / Magnesium and its alloys are increasingly used in the transport industry for their low density (1.7), and ideally could be used after plastic shaping. Due to the hcp structure, magnesium is very anisotropic and exhibits low ductility at room temperature. Strain is controlled by the activation of slip and twinning mechanisms, and only basal slip and tensile twinning operate at RT, whereas at high temperature prismatic and pyramidal <c+a> slip, and compressive twinning are active. Pure magnesium single crystals were produced with different orientations to measure the critical resolved shear stresses (CRSS) of the different deformation mechanisms, by channel-die compression from RT to 450°C. In parallel we developed a crystal plasticity model to simulate the deformation of constrained crystals, this model is based on the Schmid law and the principle of maximum work. The model enables the prediction of activated deformation mechanisms and the stress as a function of the CRSS. We have also used the model to predict the behaviour of a polycrystalline alloy AZ31.
2

A comparison between vector algorithm and CRSS algorithm for indoor localization

Dama, Yousef A.S., Abd-Alhameed, Raed, Hammad, H., Zaid, R., Excell, Peter S. January 2014 (has links)
yes / In this paper a comparison between two indoor localization algorithms using received signal strength is utilized the vector algorithm and the Comparative Received Signal Strength algorithm. The comparison considered the effect of the radio map resolution, the number of access points, and the operating frequency on the accuracy of the localization process. The experiments were carried out using ray tracing software, measured values and MATLAB.
3

Étude des mécanismes contrôlant la déformation du magnésium à chaud

Chapuis, Adrien 18 October 2010 (has links) (PDF)
Le magnésium et ses alliages sont de plus en plus utilisés dans les transports pour leur faible densité (1,7), et on cherche à les utiliser sous la forme corroyée. De structure hexagonale compact, le magnésium est très anisotrope et faiblement ductile à froid. La déformation est contrôlée par l'activation de systèmes de glissement et de maclage, seuls le glissement basal et le maclage de traction sont actifs à froid, alors qu'à chaud sont activés les glissements prismatique et pyramidal , et le maclage de compression. Nous avons élaboré des monocristaux de magnésium pur de différentes orientations pour mesurer les contraintes de cission résolues critique (CRSS) des différents systèmes par des essais de compression plane à des températures allant de l'ambiante à 450°C. En parallèle nous avons développé un code de plasticité cristalline pour modéliser la déformation de cristaux contraints, ce programme est basée sur la loi de Schmid et le principe du travail maximum, ce qui permet de prédire les systèmes de déformation activés et la contrainte nécessaire, en fonction des CRSS. Nous avons aussi testé le modèle pour prédire le comportement de l'alliage polycristallin AZ31.
4

Från sponsorskap till partnerskap / From sponsorship to partnership

Andersson Stridh, Sandra, Karlsson, Johannes January 2016 (has links)
Uppsatsen, Från sponsorskap till Partnerskap, grundar sig i relationen mellan rättshavare och sponsor. Den berör de motiv och faktorer som kan göra ett sponsorskap mer attraktivt, både ur rättshavare och sponsors perspektiv, samt hur man kan öka effekten av relationen.Idrottsrelaterade sponsorinvesteringar har ökat markant i Sverige under senare år. Samtidigt har sponsorskapet blivit allt mer komplext och kommit till en punkt där rättshavare har svårt att möta sponsorns behov. Allt fler företag ställer högre krav på avkastning och efterfrågar också andra värden i sponsorskapet. Transaktionen, pengar mot exponering, som tidigare definierat sponsring har förändrats och är nu inne i ett paradigmskifte. Företag har identifierat andra värden, motiv och potential i sponsorskapet vilket har medfört ett allt mer relationsbaserat fokus där engagemang, förtroende och kommunikation blivit centrala delar för att skapa en starkare attraktionskraft. Denna förändring har också medfört att rättshavarens medvetenhet och förståelse kring företagens sponsormotiv samt effektkrav ställts på prov. Organisatoriska och verktygsmässiga förändringar hos rättshavare krävs för att kunna stärka attraktionskraften gentemot andra rättshavare, idrotter och marknadskanaler, detta genom en övergång från renodlat sponsorskap till en partnerverksamhet.Denna uppsats syftar därför till att undersöka vilka behov företag har av sponsring samt identifiera en struktur för partnerskapet. Uppsatsen syftar även till att skapa en djupare förståelse för företags behov samt vikten av att rättshavare paketerar och profilerar sin verksamhet på ett gynnsamt sätt. Utifrån litteraturen och empirin har vi definierat sponsorskapets fundament vilket också kan appliceras som grunden i ett partnerskap. Uppsatsen tar upp de grundläggande motiv för sponsring samt de parametrar och värden som särskiljer begreppen sponsorskap och partnerskap. En annan central del som har identifierats i denna uppsats, och som stöds både i litteraturen och empirin, är vikten av ett ökat samhällsengagemang. CSR-arbetet (corporate social responsibility) har blivit ett starkt växande verksamhetsområde hos de Allsvenska fotbollsklubbarna och är i många fall direkt avgörande för verksamhetens sponsorintäkter. / Whilst sport sponsorship investments has increased rapidly in Sweden over the past years, it has also reached a point of where the right holders have difficulties to meet the sponsors demand for more articulated outcomes. More and more companies view the sponsorship as more than a mere communication platform of mixed communication activities such as PR, direct on-sales and exposure. Sponsors now start to see the true potential of sponsorship, whereas the relationship could bring more to the company than the sponsorship offer; money in exchange for commercial access. In order to meet this demand the property organizations (in this paper, mostly referred to as the football clubs) have to look for reconstruction of their operations. A turn from the expression “sponsor”, to “partner” can be seen throughout the Swedish football world, though has little actual operational change been set to practice. This paper seeks to examine the new demands set from sponsors as well as identify the true nature of the partnership structure. We believe that with a deeper understanding of sponsor demands the property organizations can create a conceptualized and attractive profile, as well as add structural change into the operations, which could be beneficial for both parties.With help from literature we define sponsorship, which will be viewed as the fundamentals of partnership. Relevant B2B-relationship theories, such as commitment, trust and communication will be applied as cornerstones to a successful partner relationship. The empirical studies, showing that there is a demand for more communicative CSR-activities in the clubs, will be combined with earlier research on the subject of CRSS, cause-related sport sponsorship to highlight the importance of profiling.
5

A Comparison between Vector Algorithm and CRSS Algorithms for Indoor Localization using Received Signal Strength

Obeidat, Huthaifa A.N., Dama, Yousef A.S., Abd-Alhameed, Raed A., Hu, Yim Fun, Qahwaji, Rami S.R., Noras, James M., Jones, Steven M.R. 03 1900 (has links)
no / A comparison is presented between two indoor localization algorithms using received signal strength, namely the vector algorithm and the Comparative Received Signal Strength (CRSS) algorithm. Signal values were obtained using ray tracing software and processed with MATLAB to ascertain the effects on localization accuracy of radio map resolution, number of access points and operating frequency. The vector algorithm outperforms the CRSS algorithm, which suffers from ambiguity, although that can be reduced by using more access points and a higher operating frequency. Ambiguity is worsened by the addition of more reference points. The vector algorithm performance is enhanced by adding more access points and reference points while it degrades with increasing frequency provided that the statistical mean of error increased to about 60 cm for most studied cases. / Unable to contact publisher. Contact webform only works for members - no email addresses. Raed said he would try and get contact details - email 14th March 2016 / The full text is unavailable. The publisher is unable to be contacted.
6

Failure Mechanisms and Texture Evolution of Wrought AZ31B Magnesium at Temperatures Ranging from 25 C to 125 C

Scott, Jonathan Michael 14 March 2012 (has links) (PDF)
Failure mechanisms were studied in wrought AZ31B magnesium alloy under different strain paths and various temperatures. Optical micrographs were used to observe the formation of shear bands and regions of high twin density in samples strained under uniaxial, biaxial and plane strain conditions. Interrupted testing at 4% effective strain increments until failure was used to observe the evolution of the microstructure. Results showed that shear bands with a high percentage of twinned grains appeared early in the samples strained under biaxial or plane strain tension. These bands are similar to the failure region in uniaxial tension specimens. A forming limit diagram for AZ31B was developed from the strain data, showing that plane strain and biaxial tension had very similar limit strains, in contrast to materials like steel or aluminum alloys which typically have greater ductility in biaxial tension compared to plane strain tension. When the experiments are repeated at elevated forming temperatures of 75 C and 125 C there is no observable shear band formation. The forming limit diagrams for each temperature were created and showed a marked increase in biaxial tension formability, compared to plane strain tension. Optical microscopy showed no sign of any compression twins and very few tensile twins in samples strained in biaxial or plane strain tension, up to 12% effective strain. The lack of compression twins at these strain levels shows that the effect of temperature on critical resolved shear stress for < c&plus;a > slip is greater than previously expected.
7

A Comparison between Vector Algorithm and CRSS Algorithms for Indoor Localization using Received Signal Strength

Obeidat, Huthaifa A.N., Dama, Yousif A.S., Abd-Alhameed, Raed, Hu, Yim Fun, Qahwaji, Rami S.R., Noras, James M., Jones, Steven M.R. 09 January 2016 (has links)
No / A comparison is presented between two indoor localization algorithms using received signal strength, namely the vector algorithm and the Comparative Received Signal Strength (CRSS) algorithm. Signal values were obtained using ray tracing software and processed with MATLAB to ascertain the effects on localization accuracy of radio map resolution, number of access points and operating frequency. The vector algorithm outperforms the CRSS algorithm, which suffers from ambiguity, although that can be reduced by using more access points and a higher operating frequency. Ambiguity is worsened by the addition of more reference points. The vector algorithm performance is enhanced by adding more access points and reference points while it degrades with increasing frequency provided that the statistical mean of error increased to about 60 cm for most studied cases. / No full text available. Unable to contact the publisher.
8

Etude expérimentale et simulation numérique des mécanismes de plasticité dans les alliages de zirconium / Experimental study and numerical simulation of the plastic deformation of zirconium single crystals

Lebon, Cyril 16 December 2011 (has links)
Ce travail part du constat d’une part qu'il existe très peu de données expérimentales dans la littérature sur les monocristaux de zirconium et d’autre part qu’aucune loi de comportement monocristalline pour ce matériau n’est déterminée. L'objectif est donc de disposer d'une base de données expérimentale conséquente comme les cissions critiques pour le système prismatique, l'écrouissage, l'activation des systèmes de glissement et les volumes d'activation. Après avoir obtenu ces différents paramètres en utilisant la méthode de corrélation d'images, une approche multiéchelle a été mise en œuvre en s’appuyant d’une part sur la dynamique des dislocations et d’autre part sur des calculs par éléments finis. Une première loi de comportement monocristalline pour le zirconium est proposée et des simulations par éléments finis ont validé cette approche innovante. / There is only few experimental data in the literature on the zirconium single crystals and no constitutive laws for this single crystal material are provided. The goal of this work is then to create an exhaustive experimental database like the Critical Resolved Shear Stress (CRSS) for the prismatic slip, the strain-hardening, the activation of the prismatic glide system and the activation volumes. We determine theses parameters from image correlation method. Then, we develop a new multiscale approach using dislocations dynamics concept and finite element computations. Finally, a first single crystal constitutive law for the zirconium is proposed and a good agreement with the experimental data is obtained.
9

Understanding Information Technology Investment Decision-Making in the Context of Hotel Global Distribution Systems: a Multiple-Case Study

Connolly, Daniel J. 02 December 1999 (has links)
This study investigates what three large, multinational hospitality companies do in practice when evaluating and making IT investment decisions. This study was launched in an attempt to 1) learn more about how multinational hospitality companies evaluate, prioritize, and select IT investments in the context of hotel GDS; 2) call attention to an important and costly topic in hopes of improving current practices; and 3) fill a noticeable literary void so that future researchers on IT and hotel GDS would have a foundation and starting point. The perennial question of any business is "How does an organization add value?" Value can be defined from many different perspectives and may result from tangible and intangible factors. Principal stakeholders include shareholders (investors), customers, and employees. Shareholders typically measure value in terms of economic return on their investment based upon some level of perceived risk. For customers, value is assessed in terms of a price-value relationship; that is, how much they received in terms of product and services for the price they paid. For employees, value is measured by salary and by the intrinsic rewards of the job. Yet, one of the most elusive questions with respect to information technology is "How can value be measured?" Hospitality executives are being pressured daily to invest more in information technology (IT) - especially in the area of hotel global distribution systems (GDS), which have become the cornerstone of a hotel firm's IT infrastructure and portfolio. There are a number of sweeping changes on the horizon impacting hotel GDSs and requiring the development of a well-crafted strategy for global distribution systems. These broad changes include bypass theories to remove airline GDSs and travel agents, the introduction of new and emerging player, and innovative approaches to pricing and promotion. Many of these developments offer promise to hoteliers, but they also threaten their control over their customer relationships and their inventory and add to the complexity and cost of distribution. Selecting the appropriate distribution channels is paramount to success and important if hotel firms are to grow top-line revenue and control overhead; yet the number of choices facing hotel executives is overwhelming. They are also at a loss for measuring value derived from IT. One of the greatest issues plaguing the advancement of technology in the hospitality industry is the difficulty in calculating return on investment. Until recently, most technology investment decisions have been considered using a support or utility mentality that stems from a manufacturing paradigm. Under such thinking, business cases could be built around an application or technology's ability to reduce costs or create labor savings. However, management's attitudes towards technology have been shifting in recent years. The more technologically savvy hospitality companies are looking to IT to build strategic and competitive advantages. These types of investments yield results over time, and seldom in the short-run. This is problematic among owners and investors who demand more immediate results. Moreover, it is difficult to quantify and calculate the tangible benefits of technology when it is used for strategic purposes. Today's financial models are inadequate for estimating the financial benefits for most of the technology projects under consideration today. While the hospitality industry has disciplined models and sufficient history to determine the financial gains or success of opening a new property in a given city, it lacks the same rigorous models and historical data for technology, especially since each technology project is unique. Although this problem is not specific to the hospitality industry, it is particularly problematic since the industry tends to be technologically conservative and unwilling to adopt new technology applications based on the promises of its long-term merits if it cannot quantify the results and calculate a defined payback period. When uncertainty surrounds the investment, when the timing of the cash flows is unpredictable, and when the investment is perceived as risky, owners and investors will most likely channel their investment capital to projects with more certain returns and minimal risk. Thus, under this thinking, technology will always take a back seat to other organizational priorities and initiatives. Efforts must be made to change this thinking and to develop financial models that can accurately predict and capture the financial benefits derived from technology. Given the present predicament and difficulties surrounding the current tools, techniques, and measures, executives are faced with an important choice. They can 1) continue to use the present methods despite their shortcomings, 2) dispense with ROI, cost-benefit, and discounted cash flow analyses altogether for IT projects, or 3) develop new methods, tools, and measures that can accommodate the complexities of IT and quantify the intangibles. This study is a call to action in favor of the latter because the measures determine not only which projects will be accepted but also how their success will be evaluated. Having a rigid evaluation process forces executives to identify a project's potential contribution and align the project's objectives with the firm's strategic goals and objectives. Using the co-alignment principle as its theoretical underpinning, this study employs a multiple-case design to investigate the resource allocation processes used with respect to information technology and global distribution systems. It looks at how three leading, multinational hospitality firms address IT project/investment evaluation and decision-making, the measures they use, and the frustrations they encounter. These frustrations include problems that arise from a hotel firm's fragmented ownership as well as from hotel executives' inability to measure the results of IT through definitive cause-and-effect relationships. The results of the study provide affirmation of the co-alignment principle and document linkages and co-alignment between strategy and IT. Clearly, decisions involving IT and hotel GDSs require multivariate measures, multidimensional perspectives, and multidisciplinary involvement. However, research from the marketing discipline is noticeably absent in this area. This study concludes that because IT plays an important enabling role for marketing initiatives and is redefining the supply chain of a hotel firm, marketing researchers can no longer stand on the sidelines. This study also identifies three important constructs, or classes of variables (context, process, and project), the variables comprising each, and their influences on the evaluation and decision-making processes. These findings add to the understanding of IT evaluation, measurement, and decision-making in the context of hotel GDS. This study clarifies the intangible aspects in hopes that useful measures can be developed in subsequent research to quantify and evaluate these costs and benefits. Finally, this study provides a series of prescriptions or recommendations gleaned from the three companies that were the focus of this study in hopes that they will lead to the development of best practices in the hospitality industry. / Ph. D.

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