Existing microstructure parameters of computed tomography (CT) are able to compute architectural properties of the bone from ex-situ and ex-vivo scans while they are highly affected by the issues of noise and low resolution when applied to clinical in-vivo imaging. A set of improvements of the standard workflow for the quantitative computation of micro-structure from clinical in-vivo scans is proposed in this thesis. Robust methods are proposed (1) for the calibration of density values, (2) the binarization into bone and marrow phase, (3) fuzzy skeletonization and (4) the calibration of the CT volumes in particular for the computation of micro-structural parameters. Furthermore, novel algorithms for the computation of rod-volume fraction with 3D rose diagrams and fractal approaches are proposed and the application of local texture operators to diffusion tensor imaging is proposed. Finally an existing computer program for the application in radiology departments, Structural Insight, was improved and largely extended. In particular the methods of the microstructural calibration, the fractal and the texture operators showed significant improvements of accuracy and precision for the prediction of fracture risk and the quantitative assessment of the progress of Alzheimer's disease, in comparison to existing state-of-the art methods. The methods were tested on artificial and in-vitro data and as well on real-world computed tomography and magnetic resonance imaging (MRI) studies. The proposed novel methods improve the computation of bone characteristics from in-vivo CT and MRI in particular if the methods are combined with each other. In consequence, this allows to assess more information from existing data or to conduct studies with less ray exposure and regarding the MRI method in shorter time than nowadays required.

A framework for assessing the key statistical parameters of complex flows in choosing appropriate turbulence prediction methods on a quantitative basis is developed. These parameters characterise flow/modelling matching conditions quantified in this work. Matching conditions are important in classifying complex turbulent flows in order to frame best practice for model predictions to inform computational aerodynamics design optimisation in the context of virtual test beds. In the incompressible low Reynolds number shear flows considered here, the boundaries of the 'conforming domain' within which turbulence models are valid need to be defined, based on basic mechanisms of turbulence, and the statistical parameters. This has led to a new guideline ‘localness map’ for standard model applications. Since the choice of turbulence model depends on the complexity of the flows considered, it is useful if systematic sets of the parameters indicate the type of flow. They are that of residence time, the degree of spatial non-locality, the straining, and the non-Gaussianity, each of which is appropriately normalised. It can be demonstrated that the quantified map, in particular that of localness for the shear flows, provides a firm foundation for evaluating a wider range of Underlying Flow Regimes, including locating the Underlying Flow Regimes on the generalised localness modeling map as a framework for best practice guidelines. This work produces 7 sets of quantitative localness-structural parameters, which are used as baseline sets for grouping the Underlying Flow Regimes, and hence it opens the possibility of having complete modelling maps for Application Challenges to assess the need for zonal modelling.

A framework for assessing the key statistical parameters of complex flows in choosing appropriate turbulence prediction methods on a quantitative basis is developed. These parameters characterise flow/modelling matching conditions quantified in this work. Matching conditions are important in classifying complex turbulent flows in order to frame best practice for model predictions to inform computational aerodynamics design optimisation in the context of virtual test beds. In the incompressible low Reynolds number shear flows considered here, the boundaries of the 'conforming domain' within which turbulence models are valid need to be defined, based on basic mechanisms of turbulence, and the statistical parameters. This has led to a new guideline ‘localness map’ for standard model applications. Since the choice of turbulence model depends on the complexity of the flows considered, it is useful if systematic sets of the parameters indicate the type of flow. They are that of residence time, the degree of spatial non-locality, the straining, and the non-Gaussianity, each of which is appropriately normalised. It can be demonstrated that the quantified map, in particular that of localness for the shear flows, provides a firm foundation for evaluating a wider range of Underlying Flow Regimes, including locating the Underlying Flow Regimes on the generalised localness modeling map as a framework for best practice guidelines. This work produces 7 sets of quantitative localness-structural parameters, which are used as baseline sets for grouping the Underlying Flow Regimes, and hence it opens the possibility of having complete modelling maps for Application Challenges to assess the need for zonal modelling.

Cette thèse explore l'influence des contraintes et des paramètres structurels sur la sensibilité au vieillissement de la céramique à base de zircone. Il traite d'abord de l'influence des contraintes externes (appliquées) et des contraintes internes (résiduelles). Des contraintes extérieures sont appliquées par des tests de flexion in situ, tandis que des contraintes internes sont obtenues en contrôlant la microstructure des composites d'alumine durcis à la zircone. Le comportement de vieillissement de différents matériaux (3Y-TZP, 4Y-TZP et ZTA) est étudié par diffraction des rayons X (XRD) et spectroscopie Micro-Raman. Le résultat principal est l'influence principale des contraintes résiduelles sur les contraintes appliquées, principalement dans les matériaux de zircone. Il détruit alors l'effet de différents paramètres microstructuraux sur la cinétique du vieillissement. 3Y-TZP échantillons de même composition nominale mais différentes microstructures (caractérisées par leur taille de grain, la teneur en Y2O3 en phase tétragonale et la proportion de phase cubique) sont obtenues en utilisant différents procédés de frittage (frittage en deux étapes ou frittage normal pour différents temps et à différents moments Températures). En utilisant deux modèles semi-empiriques, on peut d'abord quantifier la relation entre la microstructure et les paramètres de traitement, puis la relation entre la cinétique du vieillissement et la microstructure. Enfin, il qualifie différents traitements de surface pour améliorer la résistance au vieillissement de 3Y-TZP. Les échantillons 3Y-TZP sont recuits sur des poudres de différentes compositions (TZ3YE, TZ4YS, 12ceTZP) et leur comportement de vieillissement est comparé. Les résultats montrent qu'une amélioration significative de la résistance au vieillissement peut être atteinte à 134 °C, sans compromettre la ténacité, mais ce gain n'est pas toujours valable à température ambiante ou corporelle. Étant donné que cette thèse traite de nombreux matériaux et des temps de vieillissement très long (jusqu'à plusieurs milliers d'heures), il était essentiel d'accélérer les tests de vieillissement et de réduire le nombre d'échantillons. Ainsi, nous avons mis en place une méthode rapide permettant d'accéder à l'énergie d'activation du vieillissement, avec une réduction de dix fois de la durée des études vieillissantes (présenté en annexe). / This thesis explores the influence of stresses and structural parameters on the sensitivity to ageing of zirconia-based ceramics. It first addresses the influence of both external (applied) stresses and internal (residual) stresses. External stresses are applied by in-situ bending tests, while internal stresses are obtained by controlling the microstructure of zirconia-toughened alumina composites. The ageing behavior of different materials (3Y-TZP, 4Y-TZP and ZTA) is investigated by X-ray diffraction (XRD) and Micro-Raman spectroscopy. The main result is the primary influence of residual stresses over applied stresses, mainly in zirconia materials. It then discriminates the effect of different microstructural parameters on the ageing kinetics. 3Y-TZP samples of same nominal composition but different microstructures (characterized by their grain sizes, content of Y2O3 in tetragonal phase and proportion of cubic phase) are obtained by using different sintering processes (two step sintering or normal sintering for different times and at different temperatures). Using two semi-empirical models, we are first able to quantify the relation between microstructure and processing parameters, and then the relation between ageing kinetics and microstructure. Finally it qualifies different surface treatments to improve the ageing resistance of 3-TZP. 3Y-TZP samples are annealed on powders of different compositions (TZ3YE, TZ4YS, 12ceTZP) and their ageing behavior are compared. The results show that a significant improvement of the ageing resistance can be reached at 134°C, without compromising the toughness, however this gain is not always valid at room or body temperature. Since this thesis deals with many materials and very long ageing times (up to several thousand hours), it was crucial to accelerate ageing tests and reduce the number of samples. Thus we set up a fast method enabling access to the activation energy of ageing, with a tenfold reduction in the duration of the ageing studies (presented in the appendix).

Deutsch: Die vorliegende Arbeit beinhaltet die kombinatorische Synthese sowie biomedizinische Aspekte von neuen, lipophilisierten Nucleosiden (Nucleolipiden) als small molecules. Für die Synthesen wurden sowohl Nucleosid-Metabolite als auch -Antimetabolite lipophilisiert. Als Lipidreste wurden natürlich vorkommende Verbindungen, wie azyklische Terpene und (a)symmetrische Ketone verwendet. Diese wurden am O-2‘,3‘-cis-glycosidischen Rest oder an der N(3)-Position von β-D-Pyrimidinen oder an der N(1)-Position von β-D-Purinen eingeführt. Die Einführung der Reste erfolgte durch Ketalisierung der glyconischen Hydroxylgruppen oder durch direkte Alkylierung sowie durch Dimroth-Umlagerung des Aglycons. Zusätzlich wurden in weiteren Reaktionen ausgewählte Nucleolipide in 2-(Cyanoethyl)phosphoramidit für die automatische DNA-Festphasensynthese von Oligo-nucleotiden umgewandelt. Diese wurden für eine Reihe von Penetrationsversuchen hinsichtlich ihres Einlagerungs-und Penetrationsverhaltens in eine künstliche Lipidmembran untersucht und untereinander verglichen. Die synthetisierten Nucleolipide wurden NMR-spektroskopisch im Hinblick auf die strukturellen Parameter (1) Zuckerpucker (3’T2‘⇌3’T2‘) und (2) die Konformation um die exozyklische C(4‘)-C(5‘)-Bindung (γ+(g)⇌γt⇌γ-(g)) charakterisiert. Außerdem wurden die Nucleolipide hinsichtlich ihrer biologischen Aktivität in in vitro-Tests auf humane, differenzierte THP-1-Makrophagen bezüglich des Immunoeffekts und auf eine Rattengliom- sowie einer humanen Gliom-Zellline bezüglich der Antitumoraktivität getestet. English: The thesis comprises the combinatorial synthesis and biomedicinal aspects of novel lipophilized nucleosides (Nucleolipids) as small molecules. Nucleoside-metabolites, as well as -antimetabolites, were used for the lipophilization. The chemical structure of the lipid residues resembles naturally-occurring compounds, namely acyclic terpenes, and (a)symmetric ketones. They are positioned either at the O-2’,3’-cis-glyconic moiety or at the N(3) of β-D-pyrimidines or N(1) of β-D-purines. The introduction of the lipophilic residues was performed either by ketalization of the glyconic hydroxyls or by direct alkylation as well as by Dimroth rearrangement at the N-alkylated aglycone. Additionally, selected nucleolipids were further converted to 2-(cyanoethyl) phosphoramidites as building blocks for automated solid phase nucleic acid synthesis. The latters were used for the preparation of a series of lipo-oligonucleotides which were studied with respect to their immobilization within artificial lipid bilayers and compared concerning immobilization rate and stability. The resulting nucleolipids were characterized with respect to the structural parameters (1) the sugar pucker (3’T2‘⇌3’T2‘) as well as (2) the conformation around the exocyclic C(4’)-C(5’)-bond (γ+(g)⇌γt⇌γ-(g)) by 1H-NMR-spectroscopy. Moreover, the biological activity of the nucleolipids was tested in-vitro on human, differentiated THP-1-macrophages for the immunoeffect and towards the rat gliom cell line BT4Ca as well as a human gliom (GOS-3) for anticancer activity.

In the present study, a neoclassical general equilibrium model is developed to study the dualistic economic development of a predominantly agrarian economy, Bangladesh. Quantitative analysis is undertaken in order to make assessments of several development strategies within the framework of the model. The linkages between the agricultural (rural) and the manufacturing (urban) sectors via the output and labour markets are incorporated in the model and empirical analysis. In specifying the aggregate relations in the model especially those of the rural sector, the analysis is based on the microeconomic relations of a 'representative peasant household'. The approach is to first estimate the structural parameters of the model (simultaneous system) and then to perform simulation exercises. These simulations permit us to move beyond the restrictions of growth theory, since the direction of influences on different variables and their quantitative dimensions may be assessed. The aim is to determine the differential impact of exogenous investments and related public policy measares on the two sectors, especially on the level of employment, output and wages. Within a disequilibrium growth process which allows for differences in wages in the two sectors, the impact of rural-urban migration of people on the economy of Bangladesh and its policy implications are assessed. The policy simulations suggest that strategies which favour agricultural rather than industrial development have a more positive impact on output, employment, and the reduction of rural-to-urban migration of people. / Thesis / Doctor of Philosophy (PhD)

An innovative approach for characterization of one dimensional Photonic Band Gap structures comprised of metallic inclusions (i.e. subwavelength dipole elements or resonant ring elements) is presented. Through an efficient S- to T-parameters conversion technique, a detailed analysis has been performed to investigate the variation of the dispersion characteristics of 1-D PBG structures as a function of the cell element configuration. Also, for the first time, the angular sensitivity of the structure has been studied in order to obtain the projected band diagrams for both TE and TM polarizations. Polarization sensitivity of the subwavelength cell element is exploited to propose a novel combination of elements which allows achieving PBGs with simultaneous frequency and polarization selectivity. The proposed approach demonstrates that the dispersion characteristic of each orthogonal polarization can be independently adjusted with dipole elements parallel to that same polarization. Generally, the structure has potential applications in orthomode transducer, and generally whenever the polarization of the incoming signal is to be used as a means of separating it from another signal in the same frequency band that is of orthogonal polarization. The current distribution and the resonance behavior of the ring element is studied and the effect of resonance on dispersion characteristics of 1-D PBGs composed of rings is investigated for the first time, for both individual and coupled rings. Interestingly, it is observed that 1-D PBG composed of resonant elements consistently has a bandgap around the resonant frequency of the single layer structure.

An innovative approach for characterization of one dimensional Photonic Band Gap structures comprised of metallic inclusions (i.e. subwavelength dipole elements or resonant ring elements) is presented. Through an efficient S- to T-parameters conversion technique, a detailed analysis has been performed to investigate the variation of the dispersion characteristics of 1-D PBG structures as a function of the cell element configuration. Also, for the first time, the angular sensitivity of the structure has been studied in order to obtain the projected band diagrams for both TE and TM polarizations. Polarization sensitivity of the subwavelength cell element is exploited to propose a novel combination of elements which allows achieving PBGs with simultaneous frequency and polarization selectivity. The proposed approach demonstrates that the dispersion characteristic of each orthogonal polarization can be independently adjusted with dipole elements parallel to that same polarization. Generally, the structure has potential applications in orthomode transducer, and generally whenever the polarization of the incoming signal is to be used as a means of separating it from another signal in the same frequency band that is of orthogonal polarization. The current distribution and the resonance behavior of the ring element is studied and the effect of resonance on dispersion characteristics of 1-D PBGs composed of rings is investigated for the first time, for both individual and coupled rings. Interestingly, it is observed that 1-D PBG composed of resonant elements consistently has a bandgap around the resonant frequency of the single layer structure.

An innovative approach for characterization of one dimensional Photonic Band Gap structures comprised of metallic inclusions (i.e. subwavelength dipole elements or resonant ring elements) is presented. Through an efficient S- to T-parameters conversion technique, a detailed analysis has been performed to investigate the variation of the dispersion characteristics of 1-D PBG structures as a function of the cell element configuration. Also, for the first time, the angular sensitivity of the structure has been studied in order to obtain the projected band diagrams for both TE and TM polarizations. Polarization sensitivity of the subwavelength cell element is exploited to propose a novel combination of elements which allows achieving PBGs with simultaneous frequency and polarization selectivity. The proposed approach demonstrates that the dispersion characteristic of each orthogonal polarization can be independently adjusted with dipole elements parallel to that same polarization. Generally, the structure has potential applications in orthomode transducer, and generally whenever the polarization of the incoming signal is to be used as a means of separating it from another signal in the same frequency band that is of orthogonal polarization. The current distribution and the resonance behavior of the ring element is studied and the effect of resonance on dispersion characteristics of 1-D PBGs composed of rings is investigated for the first time, for both individual and coupled rings. Interestingly, it is observed that 1-D PBG composed of resonant elements consistently has a bandgap around the resonant frequency of the single layer structure.

Nous pouvons trouver des propriétés structurelles similaires dans presque tous les réseaux trophiques (ensemble d’interactions de prédation). L'existence de ces invariants suggère qu’il serait possible, pour chaque réseau trophique, de déterminer des paramètres généraux qui décrivent sa structure. Il serait également possible de faire le cheminement inverse, soit à partir de paramètres généraux, d’obtenir une structure de réseau qui respecte ces invariants. C’est ainsi que fonctionnent les modèles génératifs, qui prédisent une structure à partir de paramètres généraux. Cependant, les modèles génératifs peuvent générer des structures de réseau qui diffèrent des données empiriques, parce qu'ils intègrent différentes hypothèses sur les mécanismes qui façonnent les réseaux trophiques, et donc sur les paramètres généraux qui doivent être utilisés. Dans ce mémoire, j’étudie l'effet de la pondération de la stabilité à l'aide du paramètre sigma (écart-type maximum des forces d’interactions qu’il ne faut pas dépasser si l’on veut que le réseau d’espèces reste stable) sur la distribution des propriétés de réseau obtenues par différents modèles génératifs. En effet, en donnant une plus grande importance aux réseaux dont la structure est a priori stable (potentiellement plus proche de celles retrouvées dans la nature) on pourrait corriger les prédictions des modèles en rapprochant leurs résultats des données empiriques. Le principe de correction fait ici référence à l’utilisation des probabilités par les modèles génératifs : la correction est la modification de ces probabilités en faveur des réseaux stables afin qu’ils soient sur-représentés dans les données générées. Notre hypothèse est donc que la pondération de la stabilité pourrait améliorer les prédictions des modèles génératifs. Les modèles génératifs étudiés ici sont les modèles de cascade, de niche et de hiérarchie emboîtée. Notre principale conclusion est que, de manière contre-intuitive, la pondération de la stabilité n’améliore pas la différence entre les structures de réseaux empiriques et celles des réseaux générés par les mo-dèles. Nos résultats montrent que pour les réseaux étudiés, la plus grande différence entre les réseaux trophiques modélisés par les modèles génératifs et les réseaux empiriques est la nature du modèle et non la correction par la pondération de la stabilité. Cela suggère que ces modèles prédisent la structure à partir d’un nombre de paramètres insuffisants, où de paramètres ne représentant qu’une fraction de la structure du réseau. Le modèle de niche présente la prédiction la plus proche des données empiriques, mais seulement pour les réseaux comptant jusqu'à 20 espèces. Cette étude souligne donc le long chemin qu'il nous reste à parcourir avant de pouvoir représenter les réseaux trophiques de façon réaliste à partir de modèles génératifs simples. / We can find similar structural properties in almost every food web. The existence of these invariants suggests that it could be possible for each food web to determine general parameters. The reverse case also works, i.e. from general parameters, to obtain a network structure. This is how generative models work, they predict a structure from general parameters. However, the network structures obtained from generative models differ from empirical data, because they incorporate different assumptions about the mechanisms that shape food webs and thus the gen-eral parameters used. In this study, I’ll investigate the effect of weighting stability using the sigma parameter (maximum standard deviation of interaction forces that should not be exceeded if the species network is to remain stable). I’m studying its effect on the distribution of network prop-erties obtained by different generative models. Indeed, by giving greater importance to networks whose structure is stable, one could correct the predictions of the models by bringing their results closer to the empirical data. The correction is the modification of these probabilities in favor of stable networks so that they are more easily chosen by the model. Our hypothesis is therefore that weighting stability could improve the predictions of the cascade, niche and nested hierarchy models. Our main conclusion is that stability weighting does not improve the difference between empirical and model-generated network structures. Our results show that for the networks stud-ied, the biggest difference between food webs modeled by generative models and empirical net-works is the nature of the model and not the correction by stability weighting. This suggests that these models predict structure from an insufficient number of parameters or from parameters that represent only a fraction of the network structure. The niche model shows the closest pre-diction to the empirical data, but only for networks with up to 20 species. This study highlights the long way to go before we can realistically represent food webs using generative models.