No description available.

For a thorough investigation of metabolic changes in cases of increased activity or disease, a high-resolution imaging modality would be of high-value. Conventional MR-based metabolite mapping techniques suffer from low spatial resolution and poor sensitivity to low concentrated metabolites. In this work, a novel optimization approach for high-resolution metabolic imaging by means of chemical exchange saturation transfer (CEST) and nuclear Overhauser effect (NOE) will be introduced. The general term of saturation transfer comprises CEST, NOE and magnetization transfer (MT). It describes the transfer of saturated magnetization from low concentrated solute metabolites to bulk water, after frequency selective RF irradiation was applied. The strong enhancement of attenuation effects—observed in a Z-spectrum—can be used to detect changes in metabolite concentrations. The vast complexity of in vivo tissue heavily distorts the baseline in Z-spectra. With a background spin system, modeled from a scout acquisition, saturation pulse amplitudes for each frequency offset were modulated, such that a specific target signal intensity was achieved. Further, a framework for a retrospective look-up correction of magnetic field inhomogeneities and background spin system deviations was developed. The approach of a prospective baseline enhancement (PROBE) was investigated by means of sensitivity and specificity in vitro. It was subsequently translated into a clinical setting at 3 T. A high-resolution mapping of elevated lactate in ischemic regions of acute stroke patients became feasible.

No description available.

Before the 2008 financial crisis, most research in financial mathematics focused on the risk management and the pricing of options without considering effects of counterparties’ default, illiquidity problems, systemic risk and the role of the repurchase agreement (Repo). During the 2008 financial crisis, a frozen Repo market led to a shutdown of short sales in the stock market. Cyclical interdependencies among financial corporations caused that a default of one firm seriously affected other firms and even the whole financial network. In this dissertation, we will consider financial markets which are shaped by financial crisis. This will be done from two distinct perspectives, an investor’s and a regulator’s. From an investor’s perspective, recently models were proposed to compute the total valuation adjustment (XVA) of derivatives without considering a potential crisis in the market. In our research, we include a possible crisis by apply an alternating renewal process to describe a switching between a normal financial status and a financial crisis status. We develop a framework for pricing the XVA of a European claim in this state-dependent framework. We represent the price as a solution to a backward stochastic differential equation and prove the existence and uniqueness of the solution. To study financial networks from a regulator’s perspective, one popular method is the fixed point based approach by L. Eisenberg and T. Noe. However, in practice, there is no accurate record of the interbank liabilities and thus one has to estimate them to use Eisenberg - Noe type models. In our research, we conduct a sensitivity analysis of the Eisenberg - Noe framework, and quantify the effect of the estimation errors to the clearing payments. We show that the effect of the missing specification of interbank connection to clearing payments can be described via directional derivatives that can be represented as solutions of fixed point equations. We also compute the probability of observing clearing payment deviations of a certain magnitude.

L'Analyse de Cycle de Vie (ACV) permet de comptabiliser les émissions de la production à la combustion d'un biocarburant mais elle ne prend pas en compte la dynamique locale de ces émissions, notamment celle des émissions de N2O, principal gaz à effet de serre agricole. Notre objectif fut d'abord d'analyse l'effet du tassement du sol sur les émissions de N2O en combinant expérimentation et modélisation. À l'aide de chambres automatiques sur des parcelles de betterave, nous avons mesuré en 2007-2008 des émissions cumulées de 944-977 g N-N2O ha-1 en sol non tassé et 1,448-1,382 g N-N2O ha-1 en sol tassé. Les émissions plus importantes sur le tassé furent surtout dues aux conditions anoxiques propices à la dénitrification. Nous avons modifié le modèle NOE pour mieux simuler la nitrification et la variation des fractions de N2O sur les produits totaux. Malgré une meilleure prédiction de la nitrification et des flux post-fertilisation, le modèle modifié NOE2 sous-estima les émissions totales. La sévère sous-estimation en été montre que les cycles sec-humides peuvent entraîner de fortes émissions dont le déterminisme n'est ni élucidé ni modélisé. Nous avons ensuite utilisé un modèle d'agro-écosystème (CERES-EGC-NOE2) pour produire les données d'inventaire pour nos ACV locales. L'éthanol de Miscanthus produit en Picardie entraîne potentiellement beaucoup moins d'impacts environnementaux que celui de betterave. Comparés à l'essence, l'éthanol de Miscanthus permettrait une réduction de gaz à effet de serre de 82-85% par MJ, celui de betterave une réduction de 28-42% par MJ en fonction des conditions pédo-climatiques et des pratiques agricoles locales.

The existence of bulk magnetism in matter can be attributed to the magnetic properties of the sub-atomic particles that constitute the former. The fact that the origin of these microscopic magnetic moments cannot be related to the existence of microscopic currents became apparent when this assumption predicted completely featureless bulk magnetic properties in contradiction to the observation of various bulk magnetic properties [1]. This microscopic magnetic moment, independent of other motions, hints at the existence of a hitherto unknown degree of freedom that a particle can possess. This property has come to be known as the "spin" of the particle. The atomic nucleus is comprised of the protons and the neutrons which possess a spin each. The composite object- the atomic nucleus is therefore a tiny magnet itself. In the presence of an external bias like a magnetic field, the nucleus therefore evolves like a magnetic moment and attains a characteristic frequency in its evolution called the Larmor frequency given by, (formula) where η is the magnetogyric ratio of the particle and B is the applied magnetic field. The existence of a natural frequency presents the possibility of a resonance behaviour in the response of the system when probed with a driving field. This is the basic principle of magnetic resonance, which in the context of the atomic nucleus, was discovered independently by Purcell [2] and Bloch [3]. From its conception, the technique and the associated understanding of the involved phenomena have come a long way. In its original form the technique involved the study of the steady-state response of the nuclear magnetic moment to a driving field. This continuous wave NMR had the basic limitation of exciting resonances in a given sample, serially. In due course of time, this technique was replaced by the Fourier transform NMR (FTNMR) [4]. This technique differed from the continuous wave NMR in its study of the transient response of the system in contrast to the steady-state response in the former. The advantage of this method is the parallel observation of all the resonances present in the system ( within the band-width of the excitation). In addition to the bias created by the external field, other internal molecular fields produce additional bias which in turn produce interesting signatures on the spectrum of the system, which are potential carriers of information about the molecular state. The fact that the spins are not isolated from the molecular environment, produces a striking effect on the ideal spectrum of the system. These effects contain in them, the signatures of the molecular local environment and are hence of immense interest to physicists, chemists and biologists.

Es wird eine neue Sequenz von [3,3]-sigmatropen Umlagerungen vorgestellt, die zu 1,2-difunktionalisierten 1,3-Butadienen führt. Dabei werden ausgehend von 3-Butin-1,2-diyl-Derivaten im ersten Umlagerungsschritt 1,2-Butadien-1,4-diyl-Verbindungen erhalten, die anschließend im zweiten Umlagerungsschritt zu den Zielprodukten isomerisieren. Die Anwendungsbreite dieser Synthesemethode wird anhand verschiedener Verbindungsklassen dokumentiert. So gelingt beispielsweise ausgehend von 3-Butinen mit jeweils zwei Imidat-, Thiokohlensäurearylester-, Xantogenat-, Thiocarbamat- sowie Thiobenzoat-Funktionen in 1- und 2-Position die Darstellung der entsprechend 1,2-disubstituierten 1,3-Butadiene, die zwei identische funktionelle Gruppen in Vinylposition tragen. Die geeignete Substitution des Grundgerüstes der 3-Butin-1,2-diyl-Vorläufer zeigt, daß die [3,3]-sigmatropen Isomerisierungen der diastereomeren Edukte stereospezifisch zu den entsprechenden Butadienen führen, die sich bezüglich der Konfiguration der Doppelbindungen unterscheiden. Zur Erklärung dieses Sachverhaltes werden die sterischen Wechselwirkungen diskutiert, die die Konformationen der durchlaufenen Übergangszustände beeinflussen und damit die bevorzugte Bildung bestimmter Konfigurationen der resultierenden Butadiene bedingen. Die Ermittlung der Konfiguration der synthetisierten Diene erfolgt zum einen durch NMR-Spektroskopie, wobei insbesondere die NOE-Differenzspektroskopie ein wertvolles Mittel zur Konfigurationsbestimmung darstellt. Zum anderen werden die unterschiedlichen Reaktivitäten der konfigurationsisomeren Butadiene bei Cycloadditionsreaktionen, speziell Diels-Alder-Reaktionen, zur Aufklärung der Stereochemie der Doppelbindungen genutzt. Gleichzeitig zeigen diese Folgereaktionen exemplarisch das Synthesepotential der Zielprodukte.

Es wird eine neue Sequenz von [3,3]-sigmatropen Umlagerungen vorgestellt, die zu 1,2-difunktionalisierten 1,3-Butadienen führt. Dabei werden ausgehend von 3-Butin-1,2-diyl-Derivaten im ersten Umlagerungsschritt 1,2-Butadien-1,4-diyl-Verbindungen erhalten, die anschließend im zweiten Umlagerungsschritt zu den Zielprodukten isomerisieren. Die Anwendungsbreite dieser Synthesemethode wird anhand verschiedener Verbindungsklassen dokumentiert. So gelingt beispielsweise ausgehend von 3-Butinen mit jeweils zwei Imidat-, Thiokohlensäurearylester-, Xantogenat-, Thiocarbamat- sowie Thiobenzoat-Funktionen in 1- und 2-Position die Darstellung der entsprechend 1,2-disubstituierten 1,3-Butadiene, die zwei identische funktionelle Gruppen in Vinylposition tragen. Die geeignete Substitution des Grundgerüstes der 3-Butin-1,2-diyl-Vorläufer zeigt, daß die [3,3]-sigmatropen Isomerisierungen der diastereomeren Edukte stereospezifisch zu den entsprechenden Butadienen führen, die sich bezüglich der Konfiguration der Doppelbindungen unterscheiden. Zur Erklärung dieses Sachverhaltes werden die sterischen Wechselwirkungen diskutiert, die die Konformationen der durchlaufenen Übergangszustände beeinflussen und damit die bevorzugte Bildung bestimmter Konfigurationen der resultierenden Butadiene bedingen. Die Ermittlung der Konfiguration der synthetisierten Diene erfolgt zum einen durch NMR-Spektroskopie, wobei insbesondere die NOE-Differenzspektroskopie ein wertvolles Mittel zur Konfigurationsbestimmung darstellt. Zum anderen werden die unterschiedlichen Reaktivitäten der konfigurationsisomeren Butadiene bei Cycloadditionsreaktionen, speziell Diels-Alder-Reaktionen, zur Aufklärung der Stereochemie der Doppelbindungen genutzt. Gleichzeitig zeigen diese Folgereaktionen exemplarisch das Synthesepotential der Zielprodukte.

Cette thèse porte sur la caractérisation de structures mécaniques, au travers de leurs paramètres structuraux, à partir d'observations perturbées par des bruits de mesure, supposés additifs blancs gaussiens et centrés. Pour cela, nous proposons d'utiliser des modèles à temps discret à parties linéaire et non-linéaire séparables. La première permet de retrouver les paramètres recherchés tandis que la seconde renseigne sur la non-linéarité présente. Dans le cadre d'une modélisation non-récursive par des séries de Volterra, nous présentons une approche à erreurs-dans-les-variables lorsque les variances des bruits ne sont pas connues ainsi qu'un algorithme adaptatif du type LMS nécessitant la connaissance de la variance du bruit d'entrée. Dans le cadre d'une modélisation par un modèle récursif polynomial, nous proposons deux méthodes à partir d'algorithmes évolutionnaires. La première inclut un protocole d'arrêt tenant compte de la variance du bruit de sortie. Dans la seconde, les fonctions fitness sont fondées sur des fonctions de corrélation dans lesquelles l'influence du bruit est supprimée ou compensée. / This PhD deals with the caracterisation of mechanical structures, by its structural parameters, when only noisy observations disturbed by additive measurement noises, assumed to be zero-mean white and Gaussian, are available. For this purpose, we suggest using discrete-time models with distinct linear and nonlinear parts. The first one allows the structural parameters to be retrieved whereas the second one gives information on the nonlinearity. When dealing with non-recursive Volterra series, we propose an errors-in-variables (EIV) method to jointly estimate the noise variances and the Volterra kernels. We also suggest a modified unbiased LMS algorithm to estimate the model parameters provided that the input-noise variance is known. When dealing with recursive polynomial model, we propose two methods using evolutionary algorithms. The first includes a stop protocol that takes into account the output-noise variance. In the second one, the fitness functions are based on correlation criteria in which the noise influence is removed or compensated.

Cette these etudie les effets de la conversion de la foret tropicale en parcelles agricoles, sur les emissions de n2o par les sols. Ce travail est realise a l’echelle du cycle cultural sur le dispositif experimental de combi (littoral guyanais), a l’aide de mesures in situ et de simulations (modele noe) des flux de n2o. La foret tropicale a ete comparee a des parcelles de foret converties en terres agricoles par la methode ‘chop-and-mulch’. La methode de deforestation ‘chop-and-mulch’ associe coupe mecanique de la vegetation, broyage puis enfouissement des residus forestiers dans le sol. Les terres agricoles etaient soient des parcelles de prairie non paturee soient des parcelles cultivees (maïs fertilise/soja) conduites en semis conventionnel (semis apres travail du sol, sans plante de couverture) ou en semis direct (sans travail du sol, avec plantes de couverture).Les principaux resultats de cette etude sont : le sol de la foret tropicale de combi est un faible emetteur de n2o ; la conversion par la methode ‘chop-and-mulch’ de cette foret en prairie ne conduit pas a une augmentation significative des emissions de n2o entre le 19eme et le 31eme mois suivant la conversion ; la conversion de la foret en parcelles cultivees induit une augmentation significative des emissions de n2o due a la fertilisation et a la modification des parametres edaphiques (densite apparente, temperature, humidite volumique) ; la technique sans travail du sol n’engendre pas de flux de n2o significativement plus eleves que la technique avec travail du sol ; l’introduction du phenomene d’hysterese hydrique dans le modele noe presente un reel potentiel pour l’estimation des emissions de n2o in situ. / This study investigates the effects of the conversion of tropical forest to cultivation on soil n2o emissions. The study was carried out over a complete crop cycle at the experimental site combi (french guianese coast). Nitrous oxide fluxes were obtained in the field and by conducting simulations with the noe model. Undisturbed tropical rainforest was compared to rainforest that had been converted to agricultural land using the ‘chop-and-mulch’ method. The ‘chop-and-mulch’ method is a fire-free method used for vegetation clearing combining the mechanical felling of trees with the mulching of small vegetation. Agricultural land included either mowed grassland or soybean/fertilised maize crop rotation. For croplands the two cultivation practices employed were: conventional seeding (using an offset disc harrow, without cover plants) or direct seeding (no till, with cover plants).The main results of this study are: rainforest soil at combi produced low n2o emissions; rainforest converted to mowed grassland using the 'chop-and-mulch’ method did not lead to a significant increase in n2o emissions between the 19th and 31st months after conversion; the conversion of rainforest to croplands induced a significant increase in soil n2o emissions due to the application of fertiliser and the modification of soil parameters (bulk density, temperature, volumetric moisture); n2o emissions from agricultural practices with no-till were no higher than those produced by conventional agricultural practices using an offset disc harrow; and, the introduction of an hydric hysteresis into the noe model constitutes a promising improvement to estimate in situ n2o emissions.