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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.
111

Forecasting Mortality Rates using the Weighted Hyndman-Ullah Method

Ramos, Anthony Kojo January 2021 (has links)
The performance of three methods of mortality modelling and forecasting are compared. These include the basic Lee–Carter and two functional demographic models; the basic Hyndman–Ullah and the weighted Hyndman–Ullah. Using age-specific data from the Human Mortality Database of two developed countries, France and the UK (England&Wales), these methods are compared; through within-sample forecasting for the years 1999-2018. The weighted Hyndman–Ullah method is adjudged superior among the three methods through a comparison of mean forecast errors and qualitative inspection per the dataset of the selected countries. The weighted HU method is then used to conduct a 32–year ahead forecast to the year 2050.
112

New results on the degree of ill-posedness for integration operators with weights

Hofmann, Bernd, von Wolfersdorf, Lothar 16 May 2008 (has links)
We extend our results on the degree of ill-posedness for linear integration opera- tors A with weights mapping in the Hilbert space L^2(0,1), which were published in the journal 'Inverse Problems' in 2005 ([5]). Now we can prove that the degree one also holds for a family of exponential weight functions. In this context, we empha- size that for integration operators with outer weights the use of the operator AA^* is more appropriate for the analysis of eigenvalue problems and the corresponding asymptotics of singular values than the former use of A^*A.
113

Hierarchische Tensordarstellung

Kühn, Stefan 07 November 2012 (has links)
In der vorliegenden Arbeit wird ein neues Tensorformat vorgestellt und eingehend analysiert. Das hierarchische Format verwendet einen binären Baum, um den Tensorraum der Ordnung d mit einer geschachtelten Unterraumstruktur zu versehen. Der Speicheraufwand für diese Darstellung ist von der Größenordnung O(dnr + dr^3), wobei n den Speicheraufwand in den Ansatzräumen kennzeichnet und r ein Rangparameter ist, der durch die Dimensionen der geschachtelten Unterräume bestimmt wird. Das hierarchische Format umfasst verschiedene Standardformate zur Tensordarstellung wie das kanonische oder r-Term-Format und die Unterraum-/Tucker-Darstellung. Die in dieser Arbeit entwickelte zugehörige Arithmetik inklusive mehrerer Approximationsmethoden basiert auf stabilen Methoden der Linearen Algebra, insbesondere die Singulärwertzerlegung und die QR-Zerlegung sind von zentraler Bedeutung. Die rechnerische Komplexität ist hierbei O(dnr^2+dr^4). Die lineare Abhängigkeit von der Ordnung d des Tensorraumes ist hervorzuheben. Für die verschiedenen Approximationsmethoden, deren Effizienz und Effektivität für die Anwendbarkeit des neuen Formates entscheidend sind, werden qualitative und quantitative Fehlerabschätzungen gezeigt. Umfassende numerische Experimente mit einem Fokus auf den Approximationsmethoden bestätigen zum einen die theoretischen Resultate und belegen die Stärken der neuen Tensordarstellung, zeigen aber zum anderen auch weitere, eher überraschende positive Eigenschaften der mit FastHOSVD bezeichneten schnellsten Kürzungsmethode. / In this dissertation we present and a new format for the representation of tensors and analyse its properties. The hierarchical format uses a binary tree in order to define a hierarchical structure of nested subspaces in the tensor space of order d. The strorage requirements are O(dnr+dr^3) where n is determined by the storage requirements in the ansatz spaces and r is a rank parameter determined by the dimensions of the nested subspaces. The hierarchichal representation contains the standard representation like canonical or r-term representation and subspace or Tucker representation. The arithmetical operations that have been developed in this work, including several approximation methods, are based on stable Linear Alebra methods, especially the singular value decomposition (SVD) and the QR decomposition are of importance. The computational complexity is O(dnr^2+dr^4). The linear dependence from the order d of the tensor space is important. The approximation methods are one of the key ingredients for the applicability of the new format and we present qualitative and quantitative error estimates. Numerical experiments approve the theoretical results and show some additional, but unexpected positive aspects of the fastest method called FastHOSVD.
114

Vyhledávání osob ve fotografii / Recognizing Faces within Image

Svoboda, Pavel January 2009 (has links)
The essence of face recognition within the image is generally computer vision, which provides methods and algorithms for the implementation. Some of them are described just in this work. Whole process is split in to three main phases. These are detection, aligning of detected faces and finally its recognition. Algorithms which are used to applied in given issue and which are still in progress from todays view are mentioned in every phase. Implementation is build up on three main algorithms, AdaBoost to obtain the classifier for detection, method of aligning face by principal features and method of Eigenfaces for recognizing. There are theoretically described except already mentioned algorithms neural networks for detection, ASM - Active Shape Models algorithm for aligning and AAM - Active Appearance Model for recognition. In the end there are tables of data retrieved by implemented system, which evaluated the main implementation.
115

Berechnung kinematischer Getriebeabmessungen zur Kalibrierung von Führungsgetrieben durch Messung

Teichgräber, Carsten 24 June 2013 (has links)
Führungsgetriebe die durch Servomotoren angetrieben werden, benötigen für definierte Stellungen des Abtriebsglieds eine programmierte Funktion (elektronische Kurvenscheibe). Diese leitet sich aus dem möglicherweise fehlerbehafteten kinematischen Modell des Getriebes ab (inverse Kinematik). Zur Verbesserung der Genauigkeit der Führungsbewegung wird ein Verfahren zur Justierung der Übertragungsfunktion auf Basis des Newton-Verfahrens unter Nutzung der Singulärwertzerlegung vorgestellt. Dabei werden die realen Getriebeabmessungen anhand einer Messung berechnet und werden anschließend korrigiert zur Anpassung der Übertragungsfunktion verwendet.
116

An Estimation Technique for Spin Echo Electron Paramagnetic Resonance

Golub, Frank 29 August 2013 (has links)
No description available.
117

An Examination into the Statistics of the Singular Vectors for the Multi-User MIMO Wireless Channel

Gunyan, Scott Nathan 13 August 2004 (has links) (PDF)
Many capacity and near-capacity achieving methods in multiple-input-multipleoutput (MIMO) wireless channels make use of the singular value decomposition (SVD) of the channel matrix. For the multi-user case, the SVD of the channel matrix for each user may result in right and left singular vectors that are similar between users. This proposes another descriptive characterization of the multi-user MIMO channel. Closely aligned singular vectors between any two users could reduce the achievable signaling rates of signal processing communication methods as one user would be more difficult to resolve in space-time from another. An examination into how this alignment can be described in realistic MIMO multipath channels using a two ring channel model is presented. The effects of correlation between singular vectors on achievable signaling rates is shown for one existing algorithm that approaches the sum capacity known as block-diagonalization. Analyzed is actual data collected in several indoor and outdoor experiments performed using newly constructed measurement hardware that extends the capabilities of an existing MIMO measurement system.
118

An Efficient Method for Computing Excited State Properties of Extended Molecular Aggregates Based on an Ab-Initio Exciton Model

Morrison, Adrian Franklin January 2017 (has links)
No description available.
119

PROBING ALLOSTERY IN THE EXCHANGE PROTEIN DIRECTLY ACTIVATED BY cAMP (EPAC) USING NMR SPECTROSCOPY

SELVARATNAM, RAJEEVAN January 2013 (has links)
<p>Exchange proteins directly activated by cAMP (EPAC) are guanine nucleotide exchange factors for the small GTPases, Rap1 and Rap2. The central regulatory module of EPAC is a cAMP binding domain (CBD), which in the absence of cAMP provides auto-inhibition of the catalytic guanine nucleotide exchange activity. Binding of the allosteric effector, cAMP, removes the auto-inhibition exerted by the CBD of EPAC. Herein, we investigate through NMR spectroscopy the structural and dynamical basis of auto-inhibition and cAMP-dependent allosteric activation in the CBD of EPAC. Specifically, the work described in this dissertation proposes novel methods that utilize NMR chemical shifts to define the network of residues that mediates long-range intra-molecular signalling, <em>i.e.</em> the chemical shift covariance analysis (CHESCA) and the chemical shift projection analysis (CHESPA). Using CHESCA as explained in Chapter 2, we identified an allosteric network that bridges the sites of cAMP-binding and cAMP-dependent structural changes to those of cAMP-dependent dynamical changes, which are critical for the release of auto-inhibition. The CHESCA results therefore rationalize how cAMP leads to activation through modulation of both structure and dynamics. In order to dissect the determinants of auto-inhibition in the absence of cAMP, several mutations along the signaling pathways identified by CHESCA were implemented and their effect on the auto-inhibitory conformational equilibrium of the apo-CBD was assessed through CHESPA, as outlined in Chapters 3 and 4. Overall, we have shown how CHESCA and CHESPA provide unprecedented insight into the allosteric networks underlying auto-inhibition and cAMP dependent activation in the CBD of EPAC. In addition, the methods employed here to map EPAC allostery are likely to be generally applicable to other systems.</p> / Doctor of Philosophy (PhD)
120

Tools O' the Times : understanding the common proporties of species interaction networks across space

Strydom, Tanya 11 1900 (has links)
Le domaine de l’écologie des réseaux est encore limité dans sa capacité à faire des inférences mondiales à grande échelle. Ce défi est principalement dû à la difficulté d’échantillonnage des interactions sur le terrain, entraînant de nombreuses « lacunes » en ce qui concerne la couverture mondiale des données. Cette thèse adopte une approche « centrée sur les méthodes » de l’écologie des réseaux et se concentre sur l’idée de développer des outils pour aider à combler les lacunes en matière de données en présentant la prédiction comme une alternative accessible à l’échantillonnage sur le terrain et introduit deux « outils » différents qui sont prêts à poser des questions à l’échelle mondiale. Le chapitre 1 présente les outils que nous pouvons utiliser pour faire des prédictions de réseaux et est motivé par l’idée selon laquelle avoir la capacité de prédire les interactions entre les espèces grâce à l’utilisation d’outils de modélisation est impératif pour une compréhension plus globale des réseaux écologiques. Ce chapitre comprend une preuve de concept (dans laquelle nous montrons comment un simple modèle de réseau neuronal est capable de faire des prédictions précises sur les interactions entre espèces), une évaluation des défis et des opportunités associés à l’amélioration des prédictions d’interaction et une feuille de route conceptuelle concernant l’utilisation de modèles prédictifs pour les réseaux écologiques. Les chapitres 2 et 3 sont étroitement liés et se concentrent sur l’utilisation de l’intégration de graphiques pour la prédiction de réseau. Essentiellement, l’intégration de graphes nous permet de transformer un graphe (réseau) en un ensemble de vecteurs, qui capturent une propriété écologique du réseau et nous fournissent une abstraction simple mais puissante d’un réseau d’interaction et servent de moyen de maximiser les informations disponibles. dispo- nibles à partir des réseaux d’interactions d’espèces. Parce que l’intégration de graphes nous permet de « décoder » les informations au sein d’un réseau, elle est conçue comme un outil de prédiction de réseau, en particulier lorsqu’elle est utilisée dans un cadre d’apprentissage par transfert. Elle s’appuie sur l’idée que nous pouvons utiliser les connaissances acquises en résolvant un problème connu. et l’utiliser pour résoudre un problème étroitement lié. Ici, nous avons utilisé le métaweb européen (connu) pour prédire un métaweb pour les espèces canadiennes en fonction de leur parenté phylogénétique. Ce qui rend ce travail particulière- ment passionnant est que malgré le faible nombre d’espèces partagées entre ces deux régions, nous sommes capables de récupérer la plupart (91%) des interactions. Le chapitre 4 approfondit la réflexion sur la complexité des réseaux et les différentes ma- nières que nous pourrions choisir de définir la complexité. Plus spécifiquement, nous remet- tons en question les mesures structurelles plus traditionnelles de la complexité en présentant l’entropie SVD comme une mesure alternative de la complexité. Adopter une approche phy- sique pour définir la complexité nous permet de réfléchir aux informations contenues dans un réseau plutôt qu’à leurs propriétés émergentes. Il est intéressant de noter que l’entropie SVD révèle que les réseaux bipartites sont très complexes et ne sont pas nécessairement conformes à l’idée selon laquelle la complexité engendre la stabilité. Enfin, je présente le package Julia SpatialBoundaries.jl. Ce package permet à l’utili- sateur d’implémenter l’algorithme de wombling spatial pour des données disposées de manière uniforme ou aléatoire dans l’espace. Étant donné que l’algorithme de wombling spatial se concentre à la fois sur le gradient et sur la direction du changement pour un paysage donné, il peut être utilisé à la fois pour détecter les limites au sens traditionnel du terme ainsi que pour examiner de manière plus nuancée la direction des changements. Cette approche pourrait être un moyen bénéfique de réfléchir aux questions liées à la détection des limites des réseaux et à leur relation avec les limites environnementales. / The field of network ecology is still limited in its ability to make large-scale, global inferences. This challenge is primarily driven by the difficulty of sampling interactions in the field, leading to many ‘gaps’ with regards to global coverage of data. This thesis takes a ’methods-centric’ approach to network ecology and focuses on the idea of developing tools to help with filling in the the data gaps by presenting prediction as an accessible alternative to sampling in the field and introduces two different ’tools’ that are primed for asking questions at global scales. Chapter 1 maps out tools we can use to make network predictions and is driven by the idea that having the ability to predict interactions between species through the use of modelling tools is imperative for a more global understanding of ecological networks. This chapter includes a proof-of-concept (where we show how a simple neural network model is able to make accurate predictions about species interactions), an assessment of the challenges and opportunities associated with improving interaction predictions, and providing a conceptual roadmap concerned with the use of predictive models for ecological networks. Chapters 2 and 3 are closely intertwined and are focused on the use of graph embedding for network prediction. Essentially graph embedding allows us to transform a graph (net- work) into a set of vectors, which capture an ecological property of the network and provides us with a simple, yet powerful abstraction of an interaction network and serves as a way to maximise the available information available from species interaction networks. Because graph embedding allows us to ’decode’ the information within a network it is primed as a tool for network prediction, specifically when used in a transfer learning framework, this builds on the idea that we can take the knowledge gained from solving a known problem and using it to solve a closely related problem. Here we used the (known) European metaweb to predict a metaweb for Canadian species based on their phylogenetic relatedness. What makes this work particularly exciting is that despite the low number of species shared between these two regions we are able to recover most (91%) of interactions. Chapter 4 delves into thinking about the complexity of networks and the different ways we might choose to define complexity. More specifically we challenge the more traditional structural measures of complexity by presenting SVD entropy as an alternative measure of complexity. Taking a physical approach to defining complexity allows us to think about the information contained within a network as opposed to their emerging properties. Interest- ingly, SVD entropy reveals that bipartite networks are highly complex and do not necessarily conform to the idea that complexity begets stability. Finally, I present the Julia package SpatialBoundaries.jl. This package allows the user to implement the spatial wombling algorithm for data arranged uniformly or randomly across space. Because the spatial wombling algorithm focuses on both the gradient as well as the direction of change for the given landscape it can be used both for detecting boundaries in the traditional sense as well as a more nuanced look at at the direction of changes. This approach could be a beneficial way with which to think about questions which relate to boundary detection for networks and how these relate to environmental boundaries.

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