L’Imagerie par Résonance Magnétique (IRM) est une belle application de la physique et constitue sans aucun doute l’une des techniques les plus performantes d’imagerie médicale. Basée sur le phénomène de la Résonance Magnétique Nucléaire (RMN) du proton contenu dans les molécules d’eau, l’IRM permet d’investiguer en coupes les tissus mous du corps, sur base de contrastes différents. La méthode est non-invasive et n’utilise pas de radiations ionisantes. En plus des données morphologiques, l’IRM permet également d’obtenir des informations fonctionnelles et physiologiques. De nos jours, plus de 10 000 unités IRM existent dans le monde et des millions d’examens sont réalisés chaque année. La technique est en constant développement et le domaine de recherches est multidisciplinaire. Il concerne aussi bien les développements méthodologiques (imagerie rapide, imagerie de diffusion, etc.) que technologiques (imagerie à haut champ, systèmes de gradients à commutation rapide, etc.), le point central des recherches étant l’amélioration de la qualité des images et la diminution du temps d’acquisition. Ceci implique l'optimisation des différentes séquences IRM (séries d'impulsions radiofréquence et de gradients de champ magnétique) tenant compte des contraintes imposées par le matériel, ainsi que le développement et l'optimisation du matériel lui-même. Cette thèse est consacrée au design avancé des séquences d’impulsions et contribue donc à l'optimisation des schémas d’acquisition en IRM. En particulier, le présent travail est focalisé sur la compréhension et l’amélioration d’un certain type de séquences rapides, employant des échos de gradients : les séquences Steady-State Free Precession (SSFP) et plus précisément les séquences dites balanced-SSFP. Dans ce genre de schéma d’acquisition, le système est excité rapidement et périodiquement, conduisant à l’établissement d’un état stationnaire de l’aimantation. La première partie de la thèse est consacrée à une analyse approfondie des propriétés du signal dans une séquence balanced-SSFP, à la fois à l’état stationnaire et à l’état transitoire. Ensuite, de nouveaux schémas d’acquisition sont développés sur base de calculs analytiques et de simulations numériques et sont ensuite testés expérimentalement. D’une part, une manipulation de l’état stationnaire est présentée en vue de supprimer le signal de la graisse sur les images (qui peut être gênant pour le diagnostic de certaines lésions ou maladies). D’autre part, l’application d’une phase de préparation en vue d’obtenir un contraste basé sur le degré de diffusion des molécules d’eau dans les tissus est analysée en détails, afin d’améliorer la qualité d’image produite par des séquences de diffusion existantes. La présente thèse constitue donc un travail de recherches théoriques et expérimentales, allant de la conception de nouveaux schémas d’acquisition à leur expérimentation sur volontaires, en passant par leur implémentation sur un imageur IRM. Ce travail a été réalisé au sein de l’Unité d’IRM – Radiologie de l’Hôpital Erasme, sous la direction de Thierry Metens, Docteur en Sciences et Physicien IRM.

The main objective of this thesis is to investigate the transient response and steady-state performance of a counter-cross flow liquid-to-air membrane energy exchanger (LAMEE). The LAMEE is constructed from several semi-permeable membranes which separate the air and liquid streams. In addition to heat transfer, moisture transfer occurs between the air and liquid streams since the membranes are permeable to water vapor. The LAMEE performance is assessed experimentally and the results are used to verify a numerical model. The verified numerical model is also used to extrapolate the transient and steady-state performance parameters to other test conditions. The transient response of the LAMEE is important since there are times when the LAMEE operates under transient conditions due to daily start-up or changing operating conditions such as flow rates, temperatures or humidities. The transient response of the LAMEE is investigated experimentally and numerically. The number of heat transfer units (NTU), and the ratio of solution and air heat capacity rates (Cr*) are two important parameters that affect the LAMEE performance. The results show that the transient sensible, latent and total effectivenesses increases with time after a step change in the conditions of the inlet liquid desiccant. The experimental and numerical transient effectiveness values and trends are compared for different NTU and Cr* values under summer and winter test conditions and the results show satisfactory agreement. In addition to the transient effectiveness, the time constant of the LAMEE is assessed as an important transient parameter. The time constant represents the time it takes for the LAMEE to reach 63.2% of the steady-state conditions after a step change in inlet conditions. The transient response of the outdoor air temperature and humidity ratio are normalized and used to determine the sensible and latent time constants. It is found that time constant depends on NTU, Cr* and thermal mass capacity of the LAMEE. The experimental and numerical results show that time constant increases as Cr* decreases or NTU increases. Furthermore, the verified numerical model is used to study the effect of outdoor air conditions on the LAMEE time constant. The numerical results reveal that the latent time constant is influenced by outdoor air conditions and the time constant decreases as H* increases, but the sensible time constant is almost constant for various outdoor air conditions. However, the outdoor air conditions affect the transient response of the LAMEE considerably since the total transient response of the LAMEE is closer to the latent transient response for the conditions studied. The steady-state performance of the LAMEE is studied for different NTU and Cr* values under summer test conditions. The experimental data are compared to numerical and analytical results and acceptable agreement is achieved. It is found that the steady-state effectiveness of the LAMEE increases with NTU and Cr*. The maximum total effectiveness reaches 88% for NTU=10 and Cr*=6.3. The verified numerical model is also used to investigate the effect of outdoor air conditions on the steady-state sensible and latent effectiveness of the LAMEE. The sensible effectiveness is significantly influenced by outdoor air conditions variation while the latent effectiveness is only slightly influenced by these variations. The sensible effectiveness decreases as the operating condition factor (H*) increases, but the latent effectiveness increases with H*.

This study aims to investigate the evoked and the induced activity in 40 Hz auditory responses. The 40 Hz activity, also called Pb or P50 or P1 component, has a latency of 50ms and belongs to the category of MLRs (Middle latency responses), which occur right after Auditory Brainstem Responses (ABRs) between 15 and 80ms. Its importance is related to possible clinical applications such as anesthesia, schizophrenia and auditory development. In addition to this, evoked and induced activities at 40 Hz might play an important role in cognitive processing. Trains of right ear rarefaction clicks at the mean rate of 39.1 Hz, intensity of 50dB and duration of 100 were used to elicit the above mentioned activities. Three different sequences have been used: steady state, low jittered and medium jittered. Low jittered sequence has been the main sequence used to study the 40 Hz activity. The advantage of using this sequence is the fact that a deconvolution analysis can be performed and also the fact that it does not differ too much from the standard 40Hz steady-state sequence and this means that a resonance at 40 Hz can still be obtained. Ten healthy subjects (8 males and 2 females; ages ranging from 25 to 47), with no history of audiological or neurological hearing impairment were recorded. Informed consent was signed according to approved IRB protocols. All recordings were done in a sound-proof chamber (Acoustic Systems, Inc.) with subjects lying on a bed comfortably. The subjects were not asked to perform any tasks, but just to passively listen to the acoustical stimuli. Evoked and induced activities were recorded in response to the above mentioned acoustic stimuli. The deconvolution analysis showed that the peak of activity occurs around 152ms. Wavelets analysis has confirmed this observation and has also unveiled and induced activity in the low beta range. This induced activity seems to be strictly related to the evoked activity, as it seems to occur around 390ms, which corresponds to the situation where the 40 Hz evoked activity enters a steady state condition, which lasts until the last acoustic stimulus has been applied. The latter observation is again in accordance with the literature, where it is reported that the 40Hz evoked activity could reflect the initial coactivation of neural assemblies representing specific stimulus features. A change in such stimulus features could be reflected as induced oscillations occurring in the middle beta range (16-22 Hz).

The steady problem of free convective heat transfer from an isothermal inclined elliptic cylinder and its stability is investigated. The cylinder is inclined at an arbitrary angle with the horizontal and immersed in an unbounded, viscous, incompressible fluid. It is assumed that the flow is laminar and two-dimensional and that the Boussinesq approximation is valid. The full steady Navier-Stokes and thermal energy equations are transformed to elliptical co-ordinates and an asymptotic analysis is used to find appropriate far-field conditions. A numerical scheme based on finite differences is then used to obtain numerical solutions. Results are found for small to moderate Grashof and Prandtl numbers, and varying ellipse inclinations and aspect ratios. <br /><br /> A linear stability analysis is performed to determine the critical Grashof number at which the flow loses stability. Comparisons are made with long-time unsteady solutions.

The purpose with this thesis was to examine the cold rolling mill located at Högskolan Dalarna and to stabilize the rolling process, to achieve steady state. Experiments with cold rolling of an aluminium strip have given results for rolling force, friction, reduction, strip tension and strain hardening. Results show that steady state has been found for the experiments with roll force and strain hardening, and not been found for the experiments with friction and reduction. Results show that increased strip tension gives lower roll forces. The roll force equation of Stone shows comparable results with reality for dry contact with reductions up to 30 %, but starts being incomparable with higher reductions. The roll force equation of Stone shows a bit higher roll forces than reality gave, but was comparable within reductions from 13 to 50 %. Experiments have shown that the aluminium strip has gone through strain hardening. Experiments show how the set roll gap did not yield the desired thickness reduction, there for the elastic spring constant for the rolling mill was examined and determined to be 417 N / mm for the specific alloy band. The influence of tension strip for roll force was examined and Results confirm the theory about how the roll force is decreased by increasing tension strip. The work rolls started to slip against the alumina strip as high tension strip; 70 N/mm2, gave low roll force; < 15kN.

The main aim of this paper is to reveal if development and current state of the Turkish Economy are sustainable. Instead of the research tools offered in environmental economics, the holistic approach of ecological economics is used to answer this question. Within that context, the Turkish Economy is assessed within the concept of steady-state economics. Having assessed the data related to the three institutional changes suggested within the concept, this study shows the obstacles and advantages of the Turkish Economy to move towards the steady-state, in other words, sustainability.

The steady problem of free convective heat transfer from an isothermal inclined elliptic cylinder and its stability is investigated. The cylinder is inclined at an arbitrary angle with the horizontal and immersed in an unbounded, viscous, incompressible fluid. It is assumed that the flow is laminar and two-dimensional and that the Boussinesq approximation is valid. The full steady Navier-Stokes and thermal energy equations are transformed to elliptical co-ordinates and an asymptotic analysis is used to find appropriate far-field conditions. A numerical scheme based on finite differences is then used to obtain numerical solutions. Results are found for small to moderate Grashof and Prandtl numbers, and varying ellipse inclinations and aspect ratios. <br /><br /> A linear stability analysis is performed to determine the critical Grashof number at which the flow loses stability. Comparisons are made with long-time unsteady solutions.

This dissertation aims to establish a mathematical model to predict the steady-state (stationary) motion of a nano-particle that is suppressed between two parallel moving objects. The main purpose of this study intends to find an appropriate means to reduce surface damage caused by moving nano-paricle. This study will show that, via the molecular dynamics (MD) analysis, the surface will result in different sizes of damaged layer and surface roughness when a nano-particle moves in a distinct way on it. Therefore, it has a significant value in the applications of high precision polishing and surface cleaning to identify the dominant factors in affecting the motion of nano-particle. The proposed model is to find the steady-state motion by meeting the conditions of force and torque balances on a moving nano-particle. Several hypotheses are suggested to derive the interaction force occurred at the interface between particle and each object. The hypothesis starts from the energy point of view. It is claimed that the potential and kinetic energies of object atoms will increase when nano-particle moves relative to the object. Because of the relative motion, some of the object atoms will be pushed or driven away, depending on the manner of motion. The increment of potential or kinetic energies is assumed to be proportional to the number of pushed or driven atoms. The increase of energy is supplied from the works done by the normal stress and shear stress at the interface of particle. The interaction at the front end of particle is very different from that at the rear end when particle rolls on object surface. There is a pushing action at the front end while a pulling action occurs at the rear end. The magnitudes of both actions are dominated and proportional to the adhesive strength between particle and object. The computer simulations show that the particle motion is mainly affected by the relative adhesive strength among particle and two objects. If the adhesive strength between particle and one object increase, the particle will increase the sliding speed relative to another object. On the other hand, if the adhesive strength between particle and one object is close to that of another object, the particle tends to have significant rolling motion relative to two objects. The suppressed loading between particle and objects has little effect on the qualitative trend of particle motion. The validity of proposed model is evaluated by the molecular dynamics simulation. It indicates that the predicted behaviors of proposed model are consistent with that from the analysis of molecular dynamics simulations.

Power system operation requires accurate monitoring of electrical quantities and a reliable database of the power system. As the power system operation becomes more competitive, the secure operation becomes highly important and the role of state estimation becomes more critical. Recently, due to the development of new technology in high power electronics, new control and monitoring devices are becoming more popular in power systems. It is therefore necessary to investigate their models and integrate them into the existing state estimation applications. This dissertation is dedicated to exploiting the newly appeared controlling and monitoring devices, such as Flexible AC Transmission System (FACTS) devices and (Phasor Measurement Units) PMUs, and developing new algorithms to include them into power system analysis applications. Another goal is to develop a 3D visualization tool to help power system operators gain an in-depth image of the system operation state and to identify limit violations in a quick and intuitive manner. An algorithm of state estimation of a power system with embedded FACTS devices is developed first. This estimator can be used to estimate the system state quantities and Unified Power Flow Controller (UPFC) controller parameters. Furthermore, it can also to be used to determine the required controller setting to maintain a desired power flow through a given line. In the second part of this dissertation, two methods to determine the optimal locations of PMUs are derived. One is numerical and the other one is topological. The numerical method is more effective when there are very few existing measurements while the topology-based method is more applicable for a system, which has lots of measurements forming several observable islands. To guard against unexpected failures of PMUs, the numerical method is extended to account for single PMU loss. In the last part of this dissertation, a 3D graphic user interface for power system analysis is developed. It supports two basic application functions, power flow analysis and state estimation. Different visualization techniques are used to represent different kinds of system information.

<p>The posttranslation modification of histone proteins within the nucleosomes of chromatin plays important roles in the regulation of gene expression in both normal biological and pathobiological processes. These modifications alter local chromatin structure and subsequently alter the expression profile of associated genes. Histone methylation, which was long thought immutable, is one such modification that plays a dual functionality in both activation and repression of gene expression and can be thought of as an information storage mark. With the initial discovery of lysine-specific demethylase 1A (LSD1/KDM1A), an FAD-dependent enzyme that catalyzes the oxidative demethylation of histone H3K4me1/2 and H3K9me1/2 repressing and activating transcription, respectively, the missing counterbalance to dynamic histone methylation was cemented. This discovery further strengthened the link between histone demethylation and transcriptional regulation and the enzyme has since been identified as a target with therapeutic potential.</p><p>Given the significance of KDM1A enzymatic activity, herein we report our efforts to characterize novel binding interactions that dictate the enzymes biological and pathobiological functions. As KDM1A falls into the greater class of flavin-dependent amine oxidases, it contains features that are recurrent within the class, but due to its unique ability to work on histone and non-histone substrates has unprecedented structural elements. Although the active site is expanded compared to the greater amine oxidase superfamily, it is too sterically restricted to encompass the minimal 21-mer peptide substrate footprint of the histone H3 tail. The remainder of the substrate/product is therefore expected to extend along the surface of KDM1A. Using steady-state kinetic analyses, we now show that unmodified histone H3 is a tight-binding, competitive inhibitor of KDM1A demethylation activity with a Ki of 18.9 ± 1.2 nM that is approximately 100-fold higher than the 21-mer peptide product. The relative affinity of dose-response curves is independent of preincubation time suggesting that H3 rapidly reaches equilibrium with KDM1A. Rapid dilution experiments confirmed the increased binding affinity of full-length H3 toward KDM1A was at least partially caused by a slow off-rate with a koff of 0.072 min-1, a half-life (t1/2) of 9.63 min, and residence time (τ) of 13.9 min. Independent affinity capture surface plasmon resonance experiments confirmed the tight-binding nature of the H3/KDM1A interaction revealing a Kd of 9.02 ± 2.27 nM, a kon of 9.26 x 104 ± 1.5 x 104 M-1s-1 and koff of 8.35 x 10-4 ± 3.4 x 105 s-1. Additionally, consistent with H3 being the only histone substrate of KDM1A, no other core histones are inhibitors of demethylation activity. Our data suggests that KDM1A contains a histone H3 secondary specificity recognition element on the enzyme surface and required further characterization.</p><p>In order to characterize this secondary H3 binding site, we turned to the use of cysteine labeling, chemical cross-linking coupled to proteolysis and LC-MS/MS, HDX-MS, and the design of an active, tower domain deletion KDM1A mutant. We now show that the tower domain contributes to the extended binding interface of the KDM1A/H3 interaction. Additionally, we show that the KDM1A tower domain is not required for demethylation activity and that one can functionally uncouple catalytic activity from protein-protein interactions that occur along the KDM1A tower domain interface, a domain unprecedented in the greater amine oxidase family. Furthermore, this towerless mutant will be useful for dissecting molecular contributions to KDM1A function along the tower domain. Our discovery of this secondary binding site within the aforementioned domain points to how pivotal this region is to the control and localization of KDM1A enzymatic activity as it also serves a pivotal role as a protein-protein interaction motif for the nucleation of a multitude of multimeric protein complexes.</p><p>With this in mind, we set out to design a strategy to isolate the core histone demethylase complex from E. coli cellular lysates. With the use of polycistronic vectors that encode both KDM1A and CoREST for coexpression we were able to produce appreciable amounts of chromatographically pure complex. As our CoREST construct in this strategy contains both the ELM2 and SANT2 domain needed for interaction with the HDACs, this core complex will serve as a starting point for future work that will tease apart additional influences on substrate binding and recognition imparted on KDM1A from binding partners. This preparation can therefore be used in a multitude of downstream studies including reconstitution of the core histone demethylase/deactylase complex and in depth kinetic and biophysical analyses and provides an invaluable starting point</p><p>This work provides a foundational understanding of this unprecedented secondary binding site on the surface of the KDM1A tower domain and how it may play an important role in substrate and product recognition. We suspect that this extended interaction interface may control KDM1A localization within specific chromatin loci and allow the enzyme to serve as a docking element for the nucleation of protein complexes or transcriptional machinery. On the other hand, disruption of this point of contact between the KDM1A/H3 binary complex may also facilitate enzyme/product dissociation, thereby tuning the catalytic activity of the demethylase. Additionally, the ability to produce substantial quantities of the core histone demethylase complex is a necessary step in the decoding of the ‘histone code’ hypothesis of KDM1A and its associated complexes. We suspect that the body of this work will prove to be invaluable for future characterization of the enzyme and its role in biology and pathobiology.</p> / Dissertation