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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.
21

Spectral-based tests for periodicities

Wei, Lai 18 March 2008 (has links)
No description available.
22

THE PERCEPTUAL COMPLETION PROCESS: EVIDENCE FROM 8-YEAR-OLDS, 11-YEAR-OLDS, AND ADULTS

Patel, Mohini N. 10 1900 (has links)
<p>Three main theories have been proposed to account for the completion of occluded objects, namely local theories (e.g., Kellman & Shipley, 1991), global theories (e.g., Boselie & Leeuwenberg, 1986), and integrative models of completion (e.g., Sekuler, 1994; van Lier et al., 1994). Here, we investigated age-related changes in the completion of a complex partially occluded object using a prime-matching task. Subjects were shown a prime (global, local, occluded, or no prime) that was followed immediately by two shapes that were judged as being the same or different. In Experiment 1, we tested adults (n = 36/group) at various prime durations (150 - 700 msec) to tap into earlier and later representations of the occluded object. Although the occluded object primed both the global and local shapes at 150 and 500 msec (<em>p</em>s<0.05), only the global shapes were primed at 300 and 700 msec (<em>p</em>s<0.05). Overall, our results are most consistent with integrative models of completion. In Experiment 2, we tested 8-year-olds (n = 20) at a prime duration of 700 msec and 11-year-olds (n = 30/group) at a prime duration of 300 or 700 msec. For 11-year-olds, unlike adults, the occluded object did not significantly prime either the global or local shapes at 300 msec (<em>p</em>>0.50). For both 8- and 11-year-olds, the global, local, and occluded primes did not significantly prime either shape at 700 msec (<em>p</em>s>0.50). Based on the current testing conditions, we found that the perceptual completion process may not be adult-like even at 11 years of age.</p> / Master of Science (MSc)
23

Technicalities of ageing in place : a case study of the integration of residential care services through the use of information technology (IT) in the changing context of care

Ibrahim, Rahimah January 2006 (has links)
Through a case study about the impact of IT adoption in a residential aged care organisation, this thesis examines the increasing pressure for service integration as mainstreamed through reform policies. Specifically, the research investigates the role of IT in facilitating the 1997 aged care reform agenda of 'ageing in place' focusing on the levels of transformation from the policy context to the organisational/management context, and to the context of service provision by care staff. A single embedded case study (Yin, 1993) is used in order to meet the general objective to capture the dynamics of the impact of ageing in place in the three social contexts. The research is informed by social constructionism, a theoretical framework that emphasises the significance and effects of language in shaping social realities (Ainsworth, 2001; Hosking, 1999). The framework, therefore, justifies the qualitative analysis of both written (i.e., policy documents) and spoken (i.e., interviews with staff) texts to address meaning in relation to context. Changing technologies can result in altered societal structures (Betz, 2003) at all levels, from the very complex to the very basic. As such, it is important to understand a few basic premises of technology. First, technology is a human invention to improve the well-being of society (Ayres, 1996). Consequently, technological inventions that improve the quality of life are seen by people as a necessity for modern living. In the case of ageing, modernisation and technological advances effectively resulted in people becoming healthier and living longer (Department of Health and Aged Care [DHAC], 2000). Second, technology is a human means to control nature (Betz, 2003). As such, technological advances can be seen as a modernising process of predicting and regulating the effects of the trends existing in the environment, such as ageing. Ageing in the twenty first century presents a challenge to government's development policies because ageing is depicted as a steady force with a long-term economic impact (Johnson, 1999). Third, a technology becomes powerful when it is sponsored by the market (Betz, 2003; Hughes, 1983). Unless a technology is backed by business, it lacks the influence on a large scale. Fourth, technology is used to enable change. By using IT, governments, business and the community are co-operating through a paradigm similar to the business sector. As a result, the service environment is shifting towards more business-like approaches. To sustain the changes brought by a different paradigm and modes of operation, the rhetoric of technology is employed. Therefore, the purpose of the study is to investigate the use of IT in processes of organisational adaptations to reform, which requires the examination of: a) specific meaning of IT as used in long-term care policies for older people since the last structural reform, b) the rationale behind the introduction of a new IT system into a residential care organisation, and c) the meaning of IT as articulated by care staff who have experienced a change in technology. The first paper represents a rhetorical analysis at the macro or policy level. There is a significant influence of a global political actor in developing proactive strategies on ageing, which results in a new, multi-organisational approach in delivering government-subsidised services, such as residential care. Three key institutional texts were selected to represent international to local policy development since the time ageing became a global concern. Since then, ageing is also viewed as a human rights issue. Using Burke's pentad, an analytic framework to analyse rhetoric in texts (Stillar, 1998), these institutional texts are seen to employ the rhetoric of 'technology for sustainability' to justify changes to policy approaches that seek long-term viability. Technology, in the name of sustainable development ensures support for economic growth, which balances the long-term effects of population ageing. The existence of a global force, such as population ageing, allows the intervening powers of the UN in mainstreaming ageing into development policies. Accordingly, it initiates corresponding actions at national (Australian Commonwealth Government) and state (Queensland Government) levels. IT is a medium of communication, knowledge transfer, and standard practice at these levels of actions. The second paper represents a qualitative analysis at the meso or organisational level. This paper explores the cogent rationale in the introduction of a computer-based, care documentation system in a large residential aged care organisation. Twenty two staff, from every level of the organisation, were interviewed to get an insight into the role of IT in substantive changes to organisational structure and modes of service provision. Responses from staff indicate external and internal influence that pressured the organisation to change. In the bid to sustain the future of aged care, the industry is changing through the introduction of new structure of service delivery. The Aged Care Structural Reform instigated a shift towards sustainable service provision that is consumer-driven, with a fixed cost compliance mechanism and performance criteria that are tied to funding. Facing the requirement for evidence to corroborate funding, a residential care organisation changed its structure of service delivery by introducing a new strategic direction. IT is part of this new strategic direction, planning, and operations of a changed service environment. The third paper represents a qualitative analysis at the micro or individual level to examine the impact of IT at frontline service delivery. This study is also based on interviews with twenty-two staff, across the organisational structure; however, this time the focus is more on staff who are involved in providing direct care to older residents at the organisation. The reason behind this is that IT has always been a management tool which handles management priorities such as financial planning and performance monitoring. The themes arising from the interviews indicate discord at the level of service delivery from the introduction of a new technical system. It also points to the idea that staff generally refer to ethical ideas and future promise of the new system. In summary, these three papers attached to this thesis support the notion that the meaning of technology is socially constructed. First, technology in the aged care sector has particular reference to improving or enhancing the well-being of older people, and in this case, the provision of high quality services that fulfil the needs of older people. Second, IT has an important role in meeting the evidence-based requirement, such as in the use of information in manipulating the use of resources required for the ageing population. Third, the meaning of IT is conceived from the context requiring its use such as the need to use resource efficiently to ensure long-term sustainability, which were emphasised in the last reform. Fourth, IT is used to enable structural changes in organisations to implement generic practices originated from the business sector, requiring the use of strong rhetoric such as balance and future. The limit of this case study is that these dimensions of technology can only be applied to the specific context of aged care and is not generalisable to other political contexts. However, the strength of the study rests on the macro-, meso- and micro-analysis of the meaning of technology. Therefore, future studies should investigate and compare the dimensions of technology in other contexts.
24

Essays on multivariate generalized Birnbaum-Saunders methods

MARCHANT FUENTES, Carolina Ivonne 31 October 2016 (has links)
Submitted by Rafael Santana (rafael.silvasantana@ufpe.br) on 2017-04-26T17:07:37Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Carolina Marchant.pdf: 5792192 bytes, checksum: adbd82c79b286d2fe2470b7955e6a9ed (MD5) / Made available in DSpace on 2017-04-26T17:07:38Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Carolina Marchant.pdf: 5792192 bytes, checksum: adbd82c79b286d2fe2470b7955e6a9ed (MD5) Previous issue date: 2016-10-31 / CAPES; BOLSA DO CHILE. / In the last decades, univariate Birnbaum-Saunders models have received considerable attention in the literature. These models have been widely studied and applied to fatigue, but they have also been applied to other areas of the knowledge. In such areas, it is often necessary to model several variables simultaneously. If these variables are correlated, individual analyses for each variable can lead to erroneous results. Multivariate regression models are a useful tool of the multivariate analysis, which takes into account the correlation between variables. In addition, diagnostic analysis is an important aspect to be considered in the statistical modeling. Furthermore, multivariate quality control charts are powerful and simple visual tools to determine whether a multivariate process is in control or out of control. A multivariate control chart shows how several variables jointly affect a process. First, we propose, derive and characterize multivariate generalized logarithmic Birnbaum-Saunders distributions. Also, we propose new multivariate generalized Birnbaum-Saunders regression models. We use the method of maximum likelihood estimation to estimate their parameters through the expectation-maximization algorithm. We carry out a simulation study to evaluate the performance of the corresponding estimators based on the Monte Carlo method. We validate the proposed models with a regression analysis of real-world multivariate fatigue data. Second, we conduct a diagnostic analysis for multivariate generalized Birnbaum-Saunders regression models. We consider the Mahalanobis distance as a global influence measure to detect multivariate outliers and use it for evaluating the adequacy of the distributional assumption. Moreover, we consider the local influence method and study how a perturbation may impact on the estimation of model parameters. We implement the obtained results in the R software, which are illustrated with real-world multivariate biomaterials data. Third and finally, we develop a robust methodology based on multivariate quality control charts for generalized Birnbaum-Saunders distributions with the Hotelling statistic. We use the parametric bootstrap method to obtain the distribution of this statistic. A Monte Carlo simulation study is conducted to evaluate the proposed methodology, which reports its performance to provide earlier alerts of out-of-control conditions. An illustration with air quality real-world data of Santiago-Chile is provided. This illustration shows that the proposed methodology can be useful for alerting episodes of extreme air pollution. / Nas últimas décadas, o modelo Birnbaum-Saunders univariado recebeu considerável atenção na literatura. Esse modelo tem sido amplamente estudado e aplicado inicialmente à modelagem de fadiga de materiais. Com o passar dos anos surgiram trabalhos com aplicações em outras áreas do conhecimento. Em muitas das aplicações é necessário modelar diversas variáveis simultaneamente incorporando a correlação entre elas. Os modelos de regressão multivariados são uma ferramenta útil de análise multivariada, que leva em conta a correlação entre as variáveis de resposta. A análise de diagnóstico é um aspecto importante a ser considerado no modelo estatístico e verifica as suposições adotadas como também sua sensibilidade. Além disso, os gráficos de controle de qualidade multivariados são ferramentas visuais eficientes e simples para determinar se um processo multivariado está ou não fora de controle. Este gráfico mostra como diversas variáveis afetam conjuntamente um processo. Primeiro, propomos, derivamos e caracterizamos as distribuições Birnbaum-Saunders generalizadas logarítmicas multivariadas. Em seguida, propomos um modelo de regressão Birnbaum-Saunders generalizado multivariado. Métodos para estimação dos parâmetros do modelo, tal como o método de máxima verossimilhança baseado no algoritmo EM, foram desenvolvidos. Estudos de simulação de Monte Carlo foram realizados para avaliar o desempenho dos estimadores propostos. Segundo, realizamos uma análise de diagnóstico para modelos de regressão Birnbaum-Saunders generalizados multivariados. Consideramos a distância de Mahalanobis como medida de influência global de detecção de outliers multivariados utilizando-a para avaliar a adequacidade do modelo. Além disso, desenvolvemos medidas de diagnósticos baseadas em influência local sob alguns esquemas de perturbações. Implementamos a metodologia apresentada no software R, e ilustramos com dados reais multivariados de biomateriais. Terceiro, e finalmente, desenvolvemos uma metodologia robusta baseada em gráficos de controle de qualidade multivariados para a distribuição Birnbaum-Saunders generalizada usando a estatística de Hotelling. Baseado no método bootstrap paramétrico encontramos aproximações da distribuição desta estatística e obtivemos limites de controle para o gráfico proposto. Realizamos um estudo de simulação de Monte Carlo para avaliar a metodologia proposta indicando seu bom desempenho para fornecer alertas precoces de processos fora de controle. Uma ilustração com dados reais de qualidade do ar de Santiago-Chile é fornecida. Essa ilustração mostra que a metodologia proposta pode ser útil para alertar sobre episódios de poluição extrema do ar, evitando efeitos adversos na saúde humana.
25

Climate and sea level variations in the Gulf of Lion : coupling stable and radiogenic isotopes proxies / Variations climatiques et glacio-eustatiques dans le Golfe du Lion : une approche couplée des isotopes stables et radiogéniques

Pasquier, Virgil 17 November 2017 (has links)
De par sa position, le Golfe du Lion est un site idéal pour l’investigation des changements paléo-environnementaux et des processus affectant le dépôt sédimentaire. Les travaux antérieurs ont permis de mettre en évidence les impacts de la variabilité climatique et glacioeustatique sur l’organisation stratigraphique de la marge, mais également sur les exports terrestres de matière organique.L’étude isotopique du carbone organique et de l’azote de la matière organique dans les sédiments du forage PRGL1-4 nous a permis de mettre en évidence de forts exports fluviaux lors des interstades survenus au cours des 200 000 derniers milles ans. La mise en regard de cette découverte avec les enregistrements paléo-climatologiques terrestre et marin disponibles dans la région indique que ces forts exports fluviaux résultent d’une augmentation des précipitations le long de la bordure Nord Méditerranéenne. Grâce à la position dePRGL1-4, nous proposons que ces pluies soient le résultat d’une augmentation du passage de dépressions Nord Atlantique dans le bassin Ouest Méditerranéen.Une caractérisation des isotopes du soufre préservés dans la pyrite sédimentaire a été réalisée. Les résultats obtenus ont permis de mettre en évidence une variation isotopique insoupçonnée, l’une des plus grandes observées de nos jours, dont la cyclicité semble indiquer un fort contrôle climatique. Nous proposons deux mécanismes influençant le fractionnement isotopique: une modulation de l’activité bactérienne par le climat, et/ou (ii) une modulation locale liée la nature des sédiments impliqués dans la formation des pyrites en lien avec les variations eustatiques. / By its position, the Gulf of Lion is an ideal location for investigation of past ecological changes and processes affecting the sedimentary deposition. Previous work has highlighted the impacts of climatic and glacio-eustatic changes on the GoL stratigraphic organization, but also on terrestrial exports of organic matter.This isotopic study based on the organic carbon and nitrogen preserved in PRGL1-4 sediments highlights important rivers runoff during warm periods of the last 200 000 years.Regional intercomparison with terrestrial and marine records indicates that these river exports resulting from an increase of precipitation over the North Mediterranean borderland.Using PRGL1-4 location, out of Mediterranean cyclogenetic area, we suggest that these pluvial events occurred in response to enhance passage of North Atlantic atmospheric perturbation into the Western Mediterranean basin.Pyrite sulfur isotopes investigations over the last 500 kyr have also been done. The stratigraphic variations (up to 76‰) in the isotopic data reported here are among the largest ever observed in pyrite, and are in phase with glacial-interglacial sea level. These results suggest that there exist important but previously overlooked depositional controls on sedimentary sulfur isotope records. Two different mechanisms influencing the isotopic fractionation can explain the observed dataset: a climatic modulation of the bacterial activity, and / or (ii) a local sedimentary modulation involve during early diagenetic formation of pyrite in relation with the eustatic variations.
26

Existence non existence et multiplicité d'ondes stationnaires normalisées pour quelques équations non linéaires elliptiques / Existence, non existence et multiplicité d'ondes stationnaires normalisées pour quelques équations non linéaires elliptiquesExistence, non-existence and multiplicity of normalized standing waves for some nonlinear elliptic equations

Luo, Tingjian 18 December 2013 (has links)
Dans cette thèse, nous étudions l’existence, non existence et multiplicité des ondes stationnairesavec les normes prescrites pour deux types d’équations aux dérivées partiellesnon linéaires elliptiques découlant de différents modèles physiques. La stabilité orbitale desondes stationnaires est également étudiée dans certains cas. Les principales méthodes denos preuves sont des arguments variationnels. Les solutions sont obtenues comme pointscritiques de fonctionnelle associée sur une contrainte.La thèse se compose de sept chapitres. Le Chapitre 1 est l’introduction de la thèse. Dansles Chapitres 2 à 4, nous étudions une classe d’équations de Schrödinger-Poisson-Slaternon linéaires. Nous établissons dans le Chapitre 2 des résultats optimaux non existencede solutions d’énergie minimale ayant une norme L2 prescrite. Dans le Chapitre 3, nousmontrons un résultat d’existence de solutions L2 normalisées, dans une cas où la fonctionnelleassociée n’est pas bornée inférieurement sur la contrainte. Nos solutions sonttrouvées comme des points de selle de la fonctionnelle, mais ils correspondent à des solutionsd’énergée minimale. Nous montrons également que les ondes stationnaires associéessont orbitalement instables. Ici, puisque nos points critiques présumés ne sont pas desminimiseurs globaux, il n’est pas possible d’utiliser de façon systématique les méthodesde compacité par concentration développées par P. L. Lions. Ensuite, dans le Chapitre4, nous montrons que sous les hypothèses du Chapitre 3, il existe une infinité de solutionsayant une norme L2 prescrite. Dans les deux chapitres suivants, nous étudions uneclasse d’équations de Schrödinger quasi-linéaires. Des résultats optimaux non existence desolutions d’énergie minimale sont donnés dans le Chapitre 5. Dans le Chapitre 6, nousprouvons l’existence de deux solutions positives ayant une norme donnée. L’une d’elles,relativement à la contrainte L2, est de type point selle. L’autre est un minimum, soit localou global. Le fait que la fonctionnelle naturelle associée à cette équation n’est pas biendéfinie nécessite l’utilisation d’une méthode de perturbation pour obtenir ces deux pointscritiques. Enfin, au Chapitre 7, nous mentionnons quelques questions que cette thèse asoulevées. / In this thesis, we study the existence, non-existence and multiplicity of standing waves withprescribed norms for two types of nonlinear elliptic partial differential equations arisingfrom various physical models. The orbital stability of the standing waves is also discussedin some cases. The main ingredients of our proofs are variational arguments. The solutionsare found as critical points of an associated functional on a constraint.The thesis consists of seven chapters. Chapter 1 is the Introduction of the thesis.In Chapters 2 to 4, we study a class of nonlinear Schrödinger-Poisson-Slater equations.We establish in Chapter 2 sharp non-existence results of least energy solutions having aprescribed L2-norm. In Chapter 3 we prove an existence result for L2-normalized solutions,in a situation where the associated functional is unbounded from below on the constraint.Our solutions are found as saddle points of the functional but they correspond to leastenergy solutions. We also prove that the associated standing waves are orbitally unstable.Here a key feature is that, since our suspected critical points are not global minimizers, itis not possible to use in a standard way the machinery of compactness by concentrationdeveloped by P. L. Lions. Then, in Chapter 4, we prove that under the assumptions ofChapter 3, there do exist infinitely many solutions having a prescribed L2-norm. In thefollowing two chapters, we investigate a class of quasi-linear Schrödinger equations. Sharpnon-existence results of least energy solutions are given in Chapter 5. In Chapter 6 weprove the existence of two positive solutions having a given norm. One of them, is relativeto the L2-norm constraint, of saddle point type. The other one is a minimum, either localor global. The fact that the natural functional associated with this equation is not welldefined requires the use of a perturbation approach to obtain these two critical points.Finally, in Chapter 7 we mention some questions that this thesis has raised.
27

Systematic Analysis and Comparison of Stress Minimizing Notch Shapes : Obtaining a stress concentration factor of Kt=1 without FEM-Code

Ciomber, Isabelle, Jakel, Roland 08 May 2014 (has links) (PDF)
Als Stand der Technik sind einfache, kreisförmige Verrundungen zur Reduktion von Kerbspannungen an Querschnittsübergängen bekannt, für die aus Tabellenwerken / Diagrammen in der Literatur die Formzahl einfach abgelesen werden kann. Die Effizienz der Spannungsreduktion solcher Lösungen ist jedoch sehr begrenzt. Ziel der Arbeit ist es daher, dem Konstrukteur bzw. Berechnungsingenieur ein Verfahren in die Hand zu geben, mit dem er für Standardquerschnittsübergänge und Standardlastfälle "Nicht-Kreiskerben" ohne teure und zeitaufwendige FEM-Analyse einfach durch Nutzung geeigneter Formzahldiagramme auslegen kann. Dabei sind sogar Formzahlen von nahezu eins möglich, d.h., in der "Kerbe" bleibt praktisch nur noch die Nennspannung übrig. Die Präsentation ist zweitgeteilt: Im ersten Teil werden die Arbeitsmethoden bzw. Softwarefunktionen und verwendeten Softwarewerkzeuge vorgestellt: Dies sind die Programme Creo Parametric als vollparametrisches CAD-Werkzeug und Creo Simulate als p-FEM-Programm der Parametric Technology Coprporation (PTC). Der zweite Teil der Präsentation beschreibt den Gültigkeitsbereich sowie die untersuchten Kerbgeometrien: Die einfache kreisförmige Verrundung als Stand der Technik, die Zwei-Radien-Kerbe, die Baud-Kurve, die Methode der Zugdreiecke nach Claus Mattheck, die elliptische Kerbe sowie die konische Rundung als generalisierte elliptische Kerbe. Es wird kurz eine Bibliothek vorgestellt, mit der solche Kerben einfach ausgelegt werden können, d.h. Ihre exakte Geometrie festgelegt sowie die zugehörige Formzahl αk bestimmt werden kann. / Circular (one-radius) fillets are known as state-of-the-art for reducing notch stresses at cross section transitions. The stress concentration factor Kt of such geometries can be read out from diagrams/tables given in the literature. However, the efficiency of stress reduction of circular notches is very limited. The goal of the work therefor is to present a method for the designer/analyst how to design non-circular notches/fillets just by using suitable Kt-diagrams without time-consuming and expensive FEM analyses. Kt-numbers of nearly one are possible, that means in the "notch" just the nominal stress appears and no stress concentration takes place. The presentation has two parts: Part one describes the working methods and software functions as well as software tools: Creo Parametric as fully-parametric CAD program and Creo Simulate as embedded p-FEM-tool from Parametric Technology Corporation (PTC) have been used. The second part describes the range of validity and the examined notch geometries: The one-radius fillet as state-of-the-art, the two-radii filet, the Baud-curve, the method of tensile triangles from Claus Mattheck, the standard elliptical fillet and the conical round as generalized elliptical fillet. A notch layout library is shortly presented that allows to design such fillets, that means exactly determine the notch geometry and the related stress concentration factor Kt.
28

Left ventricle functional analysis in 2D+t contrast echocardiography within an atlas-based deformable template model framework

Casero Cañas, Ramón January 2008 (has links)
This biomedical engineering thesis explores the opportunities and challenges of 2D+t contrast echocardiography for left ventricle functional analysis, both clinically and within a computer vision atlas-based deformable template model framework. A database was created for the experiments in this thesis, with 21 studies of contrast Dobutamine Stress Echo, in all 4 principal planes. The database includes clinical variables, human expert hand-traced myocardial contours and visual scoring. First the problem is studied from a clinical perspective. Quantification of endocardial global and local function using standard measures shows expected values and agreement with human expert visual scoring, but the results are less reliable for myocardial thickening. Next, the problem of segmenting the endocardium with a computer is posed in a standard landmark and atlas-based deformable template model framework. The underlying assumption is that these models can emulate human experts in terms of integrating previous knowledge about the anatomy and physiology with three sources of information from the image: texture, geometry and kinetics. Probabilistic atlases of contrast echocardiography are computed, while noting from histograms at selected anatomical locations that modelling texture with just mean intensity values may be too naive. Intensity analysis together with the clinical results above suggest that lack of external boundary definition may preclude this imaging technique for appropriate measuring of myocardial thickening, while endocardial boundary definition is appropriate for evaluation of wall motion. Geometry is presented in a Principal Component Analysis (PCA) context, highlighting issues about Gaussianity, the correlation and covariance matrices with respect to physiology, and analysing different measures of dimensionality. A popular extension of deformable models ---Active Appearance Models (AAMs)--- is then studied in depth. Contrary to common wisdom, it is contended that using a PCA texture space instead of a fixed atlas is detrimental to segmentation, and that PCA models are not convenient for texture modelling. To integrate kinetics, a novel spatio-temporal model of cardiac contours is proposed. The new explicit model does not require frame interpolation, and it is compared to previous implicit models in terms of approximation error when the shape vector changes from frame to frame or remains constant throughout the cardiac cycle. Finally, the 2D+t atlas-based deformable model segmentation problem is formulated and solved with a gradient descent approach. Experiments using the similarity transformation suggest that segmentation of the whole cardiac volume outperforms segmentation of individual frames. A relatively new approach ---the inverse compositional algorithm--- is shown to decrease running times of the classic Lucas-Kanade algorithm by a factor of 20 to 25, to values that are within real-time processing reach.
29

Systematic Analysis and Comparison of Stress Minimizing Notch Shapes : Obtaining a stress concentration factor of Kt=1 without FEM-Code

Ciomber, Isabelle, Jakel, Roland 08 May 2014 (has links)
Als Stand der Technik sind einfache, kreisförmige Verrundungen zur Reduktion von Kerbspannungen an Querschnittsübergängen bekannt, für die aus Tabellenwerken / Diagrammen in der Literatur die Formzahl einfach abgelesen werden kann. Die Effizienz der Spannungsreduktion solcher Lösungen ist jedoch sehr begrenzt. Ziel der Arbeit ist es daher, dem Konstrukteur bzw. Berechnungsingenieur ein Verfahren in die Hand zu geben, mit dem er für Standardquerschnittsübergänge und Standardlastfälle "Nicht-Kreiskerben" ohne teure und zeitaufwendige FEM-Analyse einfach durch Nutzung geeigneter Formzahldiagramme auslegen kann. Dabei sind sogar Formzahlen von nahezu eins möglich, d.h., in der "Kerbe" bleibt praktisch nur noch die Nennspannung übrig. Die Präsentation ist zweitgeteilt: Im ersten Teil werden die Arbeitsmethoden bzw. Softwarefunktionen und verwendeten Softwarewerkzeuge vorgestellt: Dies sind die Programme Creo Parametric als vollparametrisches CAD-Werkzeug und Creo Simulate als p-FEM-Programm der Parametric Technology Coprporation (PTC). Der zweite Teil der Präsentation beschreibt den Gültigkeitsbereich sowie die untersuchten Kerbgeometrien: Die einfache kreisförmige Verrundung als Stand der Technik, die Zwei-Radien-Kerbe, die Baud-Kurve, die Methode der Zugdreiecke nach Claus Mattheck, die elliptische Kerbe sowie die konische Rundung als generalisierte elliptische Kerbe. Es wird kurz eine Bibliothek vorgestellt, mit der solche Kerben einfach ausgelegt werden können, d.h. Ihre exakte Geometrie festgelegt sowie die zugehörige Formzahl αk bestimmt werden kann. / Circular (one-radius) fillets are known as state-of-the-art for reducing notch stresses at cross section transitions. The stress concentration factor Kt of such geometries can be read out from diagrams/tables given in the literature. However, the efficiency of stress reduction of circular notches is very limited. The goal of the work therefor is to present a method for the designer/analyst how to design non-circular notches/fillets just by using suitable Kt-diagrams without time-consuming and expensive FEM analyses. Kt-numbers of nearly one are possible, that means in the "notch" just the nominal stress appears and no stress concentration takes place. The presentation has two parts: Part one describes the working methods and software functions as well as software tools: Creo Parametric as fully-parametric CAD program and Creo Simulate as embedded p-FEM-tool from Parametric Technology Corporation (PTC) have been used. The second part describes the range of validity and the examined notch geometries: The one-radius fillet as state-of-the-art, the two-radii filet, the Baud-curve, the method of tensile triangles from Claus Mattheck, the standard elliptical fillet and the conical round as generalized elliptical fillet. A notch layout library is shortly presented that allows to design such fillets, that means exactly determine the notch geometry and the related stress concentration factor Kt.

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