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Dissertations / Theses on the topic 'Polarisation'
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GarciÌa, Reyes MariÌa Elena. "Income polarisation." Thesis, University of York, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.420261.
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Bregenzer, Josef Johann. "Integrated polarisation rotators." Thesis, University of Glasgow, 2010. http://theses.gla.ac.uk/1573/.
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The ability to control and manipulate the state of polarisation of optical signals is becoming an increasingly desirable feature in numerous applications including integrated optical circuits, semiconductor optical amplifiers (SOAs) and optical communication systems. This thesis introduces the design, optimisation, fabrication and operation of two novel integrated reciprocal single-section passive polarisation converter devices based upon mode-beating. The converter designs consist of asymmetric profiled waveguides, which were realised in a single reactive ion dry-etch process step. An in-situ custom built sample holder was utilised to place the samples at a predetermined angle to the incoming ions, which resulted in waveguide profiles with sloped sidewalls. This fabrication technique also allowed the incorporation of adiabatic taper sections within the device design. The converter section waveguide profile of the first design consists of two sloped sidewalls. Devices realised on a GaAs/AlGaAs material structure achieved a converted transverse magnetic (TM) polarisation purity of 81.4% at a device length of 30 μm for a transverse electric (TE) polarised input signal at an operating wavelength of λ = 1064 nm. The convention used is that TE refers to light polarised in the plane of the wafer and TM refers to light polarised perpendicular to the plane of the wafer. The total optical loss imposed by this device was evaluated to be 1.72 dB. This design was also used for the monolithic integration of a passive polarisation converter incorporated within a Fabry-Perot semiconductor laser diode on an unstrained GaAs/AlGaAs double quantum well heterostructure material system. A predominantly TM polarised optical output from the converter facet of greater than 80% is demonstrated for a converter length of 20 μm at an emitting wavelength of 867.1 nm. The about 1.4 mm long fabricated device has a current threshold level of 100 mA and a side mode suppression ratio (SMSR) of 25 dB. The second converter design is based on the modification of an already existing stripe waveguide structure. The converter section is defined by applying the above mentioned angled dry-etch process on a certain length of the stripe waveguide. The fabricated asymmetric waveguide core profile consists of a sloped undercut. A TM polarisation purity of 90% at a device length of 55 μm for a TE polarised input signal at an operating wavelength of λ = 1064 nm was achieved at the output. The total optical loss imposed by this device was evaluated to be 0.47 dB.
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Pérez, Linde Angel Joaquin. "Application of cross polarisation techniques to dynamic nuclear polarisation dissolution experiments." Thesis, University of Nottingham, 2010. http://eprints.nottingham.ac.uk/11417/.
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Dynamic Nuclear Polarisation (DNP) was suggested for the first time by Albert Overhauser in early 1950s. In DNP experiments the polarisation from electrons can be transferred to nuclei by irradiation of the electron resonance line. There are several possible mechanisms for polarisation transfer that involve DNP in solid state depending on the width of the electron line in respect to the nuclear Larmor frequency. In this thesis, the efficiency of TEMPO radical (2,2,6,6 tetramethilpiperidine, 1 oxyl) for DNP is demonstrated in combination with nuclear polarisation transfer techniques for dissolution experiments. New cryo-probes were developed for DNP and cross polarisation (CP) for operation temperatures as low as 1.5 K. Two of them were designed for dissolution experiments. Some published sequences of nuclear polarisation transfer were tested at low temperatures and compared. Novel sequences were implemented for efficient CP in organic samples doped with TEMPO to allow for a consecutive dissolution experiment. The combination of DNP with new CP sequences at low temperatures, achieved at least twice the 13C polarisation obtained with DNP and in a substantially shorter time (between 5 to 10 minutes) in samples doped with TEMPO. The polarisation levels obtained in samples of [13C-1] labelled Na acetate in a few minutes was comparable to the polarisation obtained with trityl radicals in a few hours. In addition, another strategy was investigated by using brute force polarisation as a mechanism for achieving large levels of nuclear spin order. The problem presented by this method is the long relaxation time required to obtain the thermal equilibrium polarisation. By doping with lanthanides samples of [13C-1] labelled Na acetate in 1:1 glycerol-water, it was possible to obtain thermal equilibrium for a 13C spin system in less than one hour.
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Böcker, Matthias. "Messung der transversalen L-Polarisation [Lambda-Polarisation] mit dem HERA-B-Detektor." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=971196591.
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Gul-E-Saman. "Surface analysis using polarisation." Thesis, University of York, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.583351.
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Unpolarised light incident on a surface acquires partial polarisation due to the orientation of the dipoles in the scatterer. This thesis focuses on the use of polarised light for diffuse reflectance for surface analysis. Since, the state of polarisation is acquired on interaction with the surface, the polarised light contains information about the surface properties (of the scatterer). A great amount of research has been carried out in computer vision for surface analysis using image analysis techniques. Recently, the trend has been to combine optical techniques with computer vision in order to arrive at better analysis techniques by methods that analyse the intrinsic qualities of the surfaces under study. An overview of the recent work that has been carried out in the field is given in Chapter 2 in context to this thesis. The contributions of this thesis are: 1. the robust computation of polarisation image using M-estimators, the smoothing of phase of polarisation by using directional statistics and using the calculated parameters for effective surface recovery, 2. estimation of the refractive index of a diverse set of surfaces of known and unknown refractive indices and using the estimates for segmentation, 3. estimating the complex refractive index which incorporates the phenomenon of absorption by two methods existing in literature, using a. ellipsometry and b. multiple polarisation measurements while building up on the case of surface analysis being related to its optical properties and 4. carrying out a preliminary study by modifying the geometric factor of the polarimetric bidirectional reflectance distribution function. Experimental evidence has been presented in the thesis for the methods that have been used for a variety of objects with varying geometrical and surface properties. The approach in this thesis has been to adopt simple and adaptable techniques that can be easily employed without the use of sophisticated equipment.
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Thompson, P. G. "Polarisation-tunable plasmonic devices." Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1396243/.
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This research project aims to investigate the phenomenon of extraordinary optical transmission (EOT) in arrays of asymmetric cruciform apertures. The specific area of EOT examined is the dependence of transmission on incident polarisation. The approach to investigating this phenomenon can be divided into three main sections: fabrication, characterisation and simulations. The method of fabrication involved two main processes: fabrication of Au thin films on CaF2 substrates using thermal evaporation, and the milling of cruciform apertures in the thin films using focused in beam (FIB). A 5 nm adhesion layer of Cr was first thermally evaporated onto the CaF2 substrate followed by an Au film, typically of 30 nm thickness. The unit cells have a lattice constant of 2 μm and typical feature sizes of the apertures are between 160 nm and 1675 nm. The transmission and reflection characteristics are examined using Fourier transform infrared spectroscopy (FTIR) for the Mid IR wavelength range. The dependence of the transmission and reflection on polarisation was investigated. It was found that the arrays display two distinct transmission maxima and a point at which transmission is invariant for all polarisations. The transmission peaks occurred in the wavelength range of 2μm to 6 μm. An ensemble of arrays was fabricated to examine the change in wavelength of the transmission peaks and the invariant point as one of the aperture dimensions was varied. It was found that the transmission wavelength and the wavelength of the invariant point could be tuned by altering the dimensions of the cruciform apertures. Simulations for transmission and reflection were carried out in addition to field profile simulations. Together, these confirmed the assumed processes by which the polarisation dependent transmission maxima were generated, i.e. by localised surface plasmons. One of the arrays more closely examined had transmission peaks at 3.9μm and 5.75μm and an invariant point at 4.46μm. For this array simulations were also used to determine the polarisation state of the transmitted wave. The simulations show that arrays of asymmetric apertures change the incident polarisation such that the transmitted wave becomes elliptically polarised with a major axis that is in general different from the polarisation angle of the incident wave. A maximum shift of around 33! was determined using simulations for a wavelength ! = 3.9μm and an incident polarisation of 60! relative to the x axis. Experimental data was obtained that corroborates these findings.
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Watley, Daniel Andrew. "Polarisation mode dispersion compensation." Thesis, University of Cambridge, 2000. https://www.repository.cam.ac.uk/handle/1810/272331.
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Siddiqui, Z. S. "Fast polarisation sampling system for characterisation of polarisation noise in fibre transmission systems." Thesis, University of Essex, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303462.
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Prunet, Simon. "Polarisation du ciel micro-ondes." Phd thesis, Université Paris Sud - Paris XI, 1998. http://tel.archives-ouvertes.fr/tel-00008317.
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La mission ESA Planck offre une opportunité sans précédent de mesurer de manière très précise la polarisation de l'émission Galactique et extragalactique dans le domaine millimétrique et sub-milli\-métrique ; elle devrait notamment permettre de mesurer la polarisation du Fond Cosmique Micro-ondes (FCM). Dans le premier chapitre, nous expliquons brièvement l'intérêt scientifique d'une telle mesure, et revoyons les technologies instrumentales qui la permettent. Dans le second chapitre, nous modélisons les caractéristiques statistiques de l'émission galactique polarisée, en particulier celle des poussières (plus particulièrement importante pour l'instrument haute fréquence -HFI- de Planck). Dans le troisième chapitre, nous présentons une méthode de filtrage multi-fréquence permettant la séparation des différentes composantes astrophysiques de l'émission millimétrique et sub-millimétrique, et permettant de quantifier les erreurs de la mesure des propriétés statistiques (spectre de puissance) de ces différents processus, en particulier le FCM. Dans le quatrième chapitre, nous estimons l'erreur commise sur la mesure des paramètres cosmologiques, conséquence des erreurs estimées au chapitre précédent. Dans un cinquième chapitre, nous estimons la contribution aux anisotropies du FCM de l'effet de lentille gravitationnelle en mouvement, causé par une population d'amas et de groupes de galaxies. Enfin, dans un sixième chapitre, nous présentons un modèle semi-analytique simple de formation de galaxies, où le taux de formation d'étoiles est controlé par la température du milieu intergalactique.
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Campbell, Ewen K. "Atomic polarisation in molecular photodissociation." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:d1fd3e32-62be-4154-880f-431ec6045baa.
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1) species show a preference for the MJ = ±1 sub-levels. For these bands the electronic alignment is very similar to that observed in the dissociation of OCS, indicating a similar mechanism, at least in the exit channel, is responsible for the polarisation in both systems.
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Lin, Jin Tong. "Polarisation effects in fibre lasers." Thesis, University of Southampton, 1990. https://eprints.soton.ac.uk/404646/.
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Single-mode fibre lasers are a new class of active fibre device, which play a remarkable role in optical fibre communications and sensors. They also exhibit a number of new phenomena, one of the most important being polarisation effects. In this thesis, new unexpected fundamental polarisation effects in fibre lasers have been discovered. The phenomena are fluorescence depolarisation, the existence of orthogonal polarisation eigenmodes, and the dependence of the output polarisation on the pump polarisation state. A unified theoretical model, incorporating the electric dipole model for rare-earth ions in a glass matrix, is formulated. The concept of effective pump power is introduced and can be applied to existing laser theory; thus laser performance characteristics such as thresholds, slope efficiencies and the polarisation state of the output can be predicted accurately. The good agreement between theory and experiment enables the derivation of the polarised cross-section ratio. This has been done for Nd3+ and Er3+ ions in silica fibres. From the theoretical analysis the optimum condition for single polarisation operation is deduced. An effective technique for making single-polarisation single-mode (SPSM) fibre lasers has been developed using an integral fibre polariser. The advantages of this technique are low insertion loss, high polarisation extinction ratio and compatibility with existing single-mode fibre components. Laser-diode-pumped SPSM fibres of high performance, both in continuous-wave and Q-switched operations, have been achieved.
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Clegg, James. "Polarisation microscopy of single emitters." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/30775.
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This thesis contains a report on the development of a new type of confocal microscope. The microscope aims to allow the user to be able to determine the three dimensional orientation of single fluorescent emitters. The microscope has at its heart a binary spatial light modulator that allows us to control the excitation electric field in the pupil of the microscope objective. This allows us to exploit the fact that the excitation of, and emission from, a single fluorescent emitter is polarisation and orientation dependent. By changing the field in the excitation pupil we can generate a set of images that when taken together can be analysed to find the emitter orientation. We show that the microscope allows us to resolve the orientation of single fluorescent molecules and nitrogen vacancy centres in nanodiamond. We designed the microscope from scratch using extensive mathematical modelling techniques. We anticipate that these models will be useful to other researchers. One example is that our model of the polarisation distortions introduced during scanning is relevant to any galvanometer-based scanning system. We also developed a full model of a confocal microscope that includes the dipole-like nature of many samples. We use this to calculate, amongst other things, the optical sectioning properties of confocal microscopes. This allows us to validate previous models that ignored polarisation distortions of high numerical aperture lenses and also to make calculations where previous models would have been inadequate, for example in calculating the sectioning strength of sheets of aligned dipoles. As well as developing numerical models, we invented a new method for controlling the polarisation of light using a binary spatial light modulator. This work has applications in materials science, and industrial applications.
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Buchacher, Till. "Polarisation dynamics in ferroelectric materials." Thesis, University of Surrey, 2017. http://epubs.surrey.ac.uk/841383/.
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Ferroelectric materials have established themselves as indispensable in key applications such as piezoelectric transducers and energy storage devices. While the use of ferroelectrics in these fields dates back more than 50 years, little progress has been made to extend applications of ferroelectrics into new fields. To a large extend the observed slow progress is not caused by a lack of potential applications, but to by the inherent complexity associated with a structural phase transition, combined with strong coupling of polarisation, strain and temperature, and the strong modification of the phenomena by material defects. This thesis takes a look at prospective applications in energy storage for pulse power applications, solid state cooling and non-volatile random access memory and identifies key issues that need to be resolved. The thesis delivers time-domain based approaches to determine ferroelectric switching behaviour of bulk materials and thin films down to sub-ns time scales. The approach permitted study of how information written to a ferroelectric memory decays as a result of multiple non-destructive read operations. Furthermore simultaneous direct measurements of temperature and ferroelectric switching established a direct link between the retarded switching phenomenon observed in ferroelectrics and temperature changes brought by the electrocaloric effect. By comparison with analytical models and numerical simulation a large localised temperature change on the scale of individual domains is postulated. It implies a much larger coupling between switching and local temperature than has been previously considered. In extension of the model the frequency dependence of polarisation fatigue under bipolar conditions is explained by the occurrence of large temperature gradients in the material.
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Rong, Weifeng. "Contrôle de polarisation pour la compensation de la dispersion modale de polarisation dans les transmissions optiques." Phd thesis, Télécom ParisTech, 2006. http://pastel.archives-ouvertes.fr/pastel-00001724.
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La dispersion modale de polarisation (PMD) est devenue pour les transmissions optiques haut débit, un des principaux facteurs qui limite la qualité du signal. Au premier ordre, la PMD génère un dédoublement des impulsions alors qu'au deuxième ordre, c'est un élargissement et des distorsions d'impulsions qui se produisent. Plusieurs solutions optiques, pour la compensation de PMD, ont été proposées, toutes utilisent un contrôleur de polarisation. L'objectif de cette thèse est donc l'étude du contrôle de la polarisation rapide et sans fin pour la compensation de PMD. Trois architectures de contrôleur avec deux lames biréfringentes à axe tournant ont été proposées et testées. Ces architectures permettent de transformer continûment les états de polarisation avec seulement deux degrés de liberté. Des simulations et des études expérimentales ont été effectuées, et elles ont démontré la faisabilité des architectures et des algorithmes proposés. Parallèlement, nous nous sommes intéressés à l'évaluation qualitative et quantitative de l'impact de la PMD au deuxième ordre, avec compensation de PMD au premier ordre, en simulant des systèmes de transmission optique à 40Gbit/s. Les résultats ont démontré que les deux composantes de la PMD au deuxième ordre: dépolarisation et dispersion chromatique dépendant de la polarisation, ont des conséquences très différentes sur les pénalités du rapport signal à bruit optique.
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Rong, Weifeng. "Contrôle de polarisation pour la compensation de la dispersion modale de polarisation dans les transmissions optiques /." Paris : École nationale supérieure des télécommunications, 2006. http://catalogue.bnf.fr/ark:/12148/cb402083237.
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Lang, Thiemo. "Étude des effets de polarisation dans des guides d'optique intégrée sur verre : application : convertisseur de polarisation." Grenoble INPG, 1997. http://www.theses.fr/1997INPG0182.
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Nous proposons une etude experimentale approfondie des effets de polarisation dans des guides faits par echange d'ions k#+/na#+ dans le verre. Une meilleure comprehension de ces effets est indispensable a la realisation des circuits d'optique integree performants. Elle nous permettra egalement de proposer de nouveaux composants agissant sur la polarisation. La birefringence des guides confines a ete etudiee d'une facon systematique en fonction des differents parametres de fabrication. Nous avons determine les conditions necessaires a la realisation de guides a faible ou a forte birefringence. Des guides confines monomodes a forte birefringence allant jusqu'a 4. 10#-#4 ont ete obtenus. A cause de l'interaction des champs de contraintes crees pendant l'echange ionique, les coupleurs symetriques et asymetriques ont leurs axes principaux locaux inclines par rapport a la normale au plan de la lame de verre, ce qui limite leur potentiel de realiser des composants a maintien de polarisation. La validite d'un modele theorique decrivant l'inclinaison des quatre modes propres d'un coupleur suivant les axes geometriques ou les axes principaux locaux a ete demontree experimentalement sur des coupleurs de differentes geometries. Une methode simple et originale de redressement des axes principaux des coupleurs a permis la mise au point des composants a maintien de polarisation realises par l'echange d'ions de k#+/na#+. L'inclinaison des axes principaux et l'augmentation de la birefringence d'un guide soumis a l'influence d'un guide voisin a permis la conception de convertisseurs de polarisation passifs bases sur des sections de contraintes asymetriques. Un convertisseur de polarisation a quatre sections alternees presentant un taux de conversion de polarisation de 97%, des pertes de propagation estimees a 0. 3 db/cm et une longueur totale de 16 mm a ete realise. Ces performances sont parmi les meilleures publiees jusqu'a present. A cela s'ajoute la simplicite et la reproductibilite du processus de fabrication.
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Tellechea, Recarte Mónica 1989. "Role of NFAT5 in macrophage polarisation." Doctoral thesis, Universitat Pompeu Fabra, 2017. http://hdl.handle.net/10803/585894.
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Macrophages are exquisite sensors of tissue homeostasis that can rapidly switch between pro- and anti-inflammatory or regulatory modes to respond to perturbations in the microenvironment. This functional plasticity involves a precise orchestration of gene expression patterns whose transcriptional regulators have not been fully characterised. Our project aimed at characterising the contribution of the transcription factor NFAT5 to macrophage functions in different polarisation settings. For that we generated classically and alternatively-polarised WT and NFAT5-deficient macrophages and studied the expression of typical polarisation markers by analysing their mRNA levels by RT-qPCR and also at protein levels by flow cytometry, ELISA and Western Blot. We also checked macrophage functions associated with a pro-inflammatory profile, such as bactericidal capacity and the ability to promote Th1 polarisation over Th2 responses. Finally, we performed in vivo assays to determine the pro-tumoural phenotype of NFAT5-deficient macrophages against syngeneic Lewis lung carcinoma and ID8 ovarian carcinoma cells. Overall, our revealed its predominant role in promoting pro-inflammatory macrophage functions ranging from facilitating Th1 responses to restraining tumour progression.Els macròfags són cèl·lules del sistema immunitari innat que es troben en tots els òrgans. Als teixits, els macròfags actuen per mantenir la homeòstasi canviant ràpidament entre estats inflamatoris i antiinflamatoris per respondre eficientment a les pertorbacions que succeeixen en el seu entorn. Aquesta plasticitat funcional requereix l’expressió coordinada de gens que estan regulats per factors que encara no han estat completament caracteritzats. En aquest treball es volia estudiar la contribució del factor de transcripció NFAT5 com a regulador de les funcions dels macròfags en diferents condicions de polarització. Per això, varem generar macròfags clàssicament activats (M1) i activats de manera alternativa (M2), WT i deficients en NFAT5, i varem analitzar l’expressió de marcadors M1 i M2 a nivell de mRNA i a nivell de proteïna per tècniques de citometria de fluxe, de ELISA i de Western Blot. També es van estudiar funcions inflamatòries dels macròfags, com ara la capacitat per a eliminar bacteris intracel·lulars o la inducció de respostes Th1 en limfòcits T CD4. Finalment es varen dur a terme assajos in vivo amb tumors singènics de pulmó (Lewis lung carcinoma) i el carcinoma d’ovari (ID8) per a determinar si els macròfags deficients en NFAT5 tenen una menor capacitat antitumoral. En resum, els nostres resultats indiquen que NFAT5 contribueix preferentment en la inducció de funcions inflamatòries, com ara la inducció de respostes Th1 i la restricció de la progressió tumoral.
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Laurent, Olivier. "Étude de la polarisation en logique." Phd thesis, Université de la Méditerranée - Aix-Marseille II, 2002. http://tel.archives-ouvertes.fr/tel-00007884.
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Issue des travaux sur la logique linéaire et l'analyse calculatoire de la logique classique, la notion de polarités semble jouer un rôle essentiel dans l'étude actuelle des systèmes logiques. La polarisation est une contrainte qui simplifie les objets tout en conservant une expressivité suffisante d'un point de vue informatique.L'objet de cette thèse est d'étudier et d'exploiter cette nouvelle structure afin en particulier de mettre à jour les relations entre la logique classique et la logique linéaire (LL). L'introduction des polarités dans LL permet de mieux appréhender ce vaste système et de prolonger le développement de différents outils trop complexes en l'absence de cette contrainte. Nous définissons ainsi, pour la logique linéaire polarisée (LLP), des réseaux de preuve intégrant les connecteurs additifs de manière satisfaisante, une sémantique des jeux polarisés qui réconcilie jeux et dualité, une géométrie de l'interaction parallèle et d'autres sémantiques dénotationnelles basées sur des notions connues (espaces de corrélation, catégories de contrôle).
Il est important de montrer que malgré cette contrainte, LLP reste un système suffisamment expressif. Pour cela nous étudions en détail les traductions des différents systèmes de logique classique déterministe connus (LC, lambda-mu calcul, ...) aussi bien en appel par nom qu'en appel par valeur. De surcroît, les traductions obtenues pour ces systèmes sont plus simples que celles vers LL.
Enfin la souplesse de ces traductions nous permet d'analyser plus finement certaines propriétés de la logique classique tout comme LL permet d'analyser la logique intuitionniste. On peut ainsi étudier un équivalent linéaire des CPS-traductions.
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Audet, Daniel. "Spectroscopie de polarisation : isotopes du krypton." Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63319.
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Matthews, Peter Alan. "The polarisation of model radio galaxies." Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303236.
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Camus, Enrique Castro. "Polarisation resolved terahertz time domain spectroscopy." Thesis, University of Oxford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.441048.
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Higdon, Paul D. "Polarisation effects in scanning optical microscopy." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299817.
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O'Neill, Jason Darren. "Brute force polarisation of xenon-129." Thesis, University of Nottingham, 2008. http://eprints.nottingham.ac.uk/13887/.
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In recent years the number of applications using NMR spectroscopy of hyperpolarised noble gases has expanded rapidly. The signal enhancement hyperpolarisation provides has led to its implementation in studies as diverse as materials science and biological imaging. 129Xe in particular, with its easily deformed electron cloud, is proving to be a uniquely sensitive probe for nanoporous structures. At present hyperpolarises gas production is limited to optical pumping (SEOP). In this study we investigate another approach, the brute force technique. At very low temperatures and high magnetic fields the Boltzmann distribution of spins for magnetic nuclei is heavily biased in a single direction. At temperatures below 10 mK and in magnetic fields of 15 T, 129Xe polarisations exceeding 40% are attainable. The utilisation of the brute force technique is hindered by the extraordinarily long relaxation time need for this polarisation to occur. In this study, we give details of our investigations of two relaxation catalysts, oxygen and helium-3. It is shown that paramagnetic molecular oxygen causes rapid relaxation of solid xenon at temperatures as low as 500 mK. We report on the enhanced relaxation, by liquid 3He of xenon films adsorbed on to silica gel and exfoliated graphite substrates. The investigation of this mechanism is extended to other magnetic nuclei and improved rates of relaxation are observed in 13C and 1 H. Details are also given, of how this mechanism of relaxation can be halted by the addition of superfluid 4He. Unique observations in the 129Xe NMR spectra are reported, providing a unique opportunity to study the coupling between individual layers of 129Xe atoms. Finally, a novel mechanism of cooling, by the filtering of energetic atoms through a porous ceramic membrane, is investigated.
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Ward-Thompson, Derek. "A polarisation study of spiral galaxies." Thesis, Durham University, 1987. http://etheses.dur.ac.uk/6654/.
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Optical polarimetry results are presented for four spiral galaxies: NGC 5194 (M51), NGC 1068, NGC 4565 and NGC 4594 (Ml04). M51 and NGC 1068 show spiral polar isation patterns which are interpreted as indicating a spiral magnetic field in each case. NGC 4565 and M104 show polar isations in their dust lanes which are parallel to their galactic planes, and which are interpreted in terms of a magnetic field in the plane of each. It is hypothesised that the observed magnetic fields may be linked to galactic shocks. A discussion of the origin of galactic magnetic fields concludes that there is no evidence which necessitates a primordial magnetic field.
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Mackie, R. A. "Aspects of polarisation in dissociative photoionisation." Thesis, Queen's University Belfast, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.395443.
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Virakul, Phookpat. "Adaptive electrical polarisation mode dispersion compensation." Thesis, University of Nottingham, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438455.
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Ahmed, S. U. "Polarisation coupling in high birefringence fibres." Thesis, King's College London (University of London), 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313837.
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Savory, Sebastian John. "Polarisation mode dispersion in optical fibres." Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621062.
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Qi, Ji. "Development of optical polarisation resolved endoscopy." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/28087.
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Optical polarization is sensitive to morphological, structural and compositional changes of tissue and has attracted much interest as a tool in tissue sensing and characterisation. The fusion of polarisation imaging techniques and medical endoscopy resulting in polarisation resolved endoscopy is one of the most significant steps to translate the technique from an optical laboratory to clinic so as to benefit the whole spectrum of endoscopic investigations and intra-operative guidance in situ during minimally invasive surgery. The work in this thesis focuses on the proof-of-concept studies concerning the development of polarisation resolved endoscopy. In particular, polarised light scattering spectral imaging, 3x3 and 4x4 Mueller polarimetric imaging are successfully integrated to a rigid endoscope with accompanying validation experiments performed. The results have shown that polarisation resolved endoscopy based on light scattering spectroscopy and Mueller polarimetry is feasible to implement and has great potential to become a powerful tool for tissue imaging and characterisation.
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Egger, Hartmut, Udo Kreickemeier, Christoph Moser, and Jens Wrona. "Offshoring and Job Polarisation between Firms." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-211888.
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We set up a general equilibrium model, in which offshoring to a low-wage country can lead to job polarisation in the high-wage country. Job polarisation is the result of a reallocation of labour across firms that differ in productivity and pay wages that are positively linked to their profits by a rent-sharing mechanism. Offshoring involves fixed and task-specific variable costs, and as a consequence it is chosen only by the most productive firms, and only for those tasks with the lowest variable offshoring costs. A reduction in those variable costs increases offshoring at the intensive and at the extensive margin, with domestic employment shifted from the newly offshoring firms in the middle of the productivity distribution to firms at the tails of this distribution, paying either very low or very high wages. We also study how the reallocation of labour across firms affects economy-wide unemployment. Offshoring reduces unemployment when it is confined to high-productivity firms, while this outcome is not guaranteed when offshoring is also chosen by low-productivity firms.
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Klitis, Charalambos. "Polarisation selective integrated silicon photonic devices." Thesis, University of Glasgow, 2018. http://theses.gla.ac.uk/8725/.
Full textAbstract:
The main objective of this thesis was the development of polarisation selective gratings in silicon-on-insulator (SOI) technology. These devices can find numerous applications in the design of highly performing optical filters and, more in general, in all those devices that require on-chip manipulation of the polarisation state. The development of these devices was preceded by the optimisation of several fabrication processes, such as lithography and dry etching, and the re-design of a number of key components such as inverse polymer tapers and metallic heaters for thermal tuning. This activity culminated into a very robust process flow for SOI devices, with repeatable propagation losses in the order of 1 dB/cm, heaters with a very high tuning efficiency of 12 mW per π phase shift and 2dB and 1dB waveguide-to-optical fibre coupling losses for the TE and TM polarised mode, respectively. The grating designs developed in this thesis consisted of periodic holes etched onto the top surface of the silicon optical waveguide. Such geometry overlaps strongly with the TM polarised mode only and does not introduce additional losses to the TE mode. The benefit and the additional functionalities provided by the top grating geometry was assessed on two different polarisation sensitive devices. The first consisted in a microring resonator with integrated gratings for the emission of optical vortex beams, for which the top gratings provided a route to engineer the polarisation state of the emitted beam. The second device was a Bragg grating filter, where the top grating allowed the demonstration of extinction ratio values as high as 60dB by filtering the residual TM mode generated by the strong polarisation scattering.
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CHARES, MARIE-LAURE. "Antennes actives a commutation de polarisation." Rennes 1, 1992. http://www.theses.fr/1992REN10161.
Full textAbstract:
Cette these traite de la conception d'un reseau lineaire et de deux reseaux plans a commutation de polarisation a douze gigahertz. Le principal objectif de cette etude est d'evaluer les possibilites d'integration des circuits integres monolithiques microondes au plus pres de l'element rayonnant. Ce travail comprend la conception des antennes mais egalement d'un commutateur, d'un amplificateur faible bruit et d'un combineur de polarisation sur arseniure de gallium
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Baudot, Rémi. "Programmation logique : non-commutativité et polarisation." Paris 13, 2000. http://www.theses.fr/2000PA132024.
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Dans cette thèse, je m'intéresse aux langages de programmation logique, fondes sur l'isomorphisme de Curry-Howard (programmation - recherche de preuve dans une logique). Afin d'accroitre le pouvoir d'expression de tels langages, je propose de définir un langage de programmation logique base sur la logique non-commutative (nl) de Ruet. Dans ce cadre, j'ai réalisé le prouveur de théorèmes sigma 1 3 qui exploite les propriétés de focalisation et de réversibilité des formules logiques, et possède une implémentation séquentielle des phénomènes d'extraction de formules et de séparation de ressources. Son évolution a donné lieu au langage de programmation noclog décliné en deux versions, basées sur l'alternance des comportements synchrones et asynchrones des connecteurs logiques de nl. Ce travail a permis d'exhiber le pouvoir de représentation spatiale de la logique non-commutative et les limites du focusing, entre autres dans la représentation des décompositions partielles. Me replaçant dans un formalisme commutatif, mes travaux se sont orientés vers l'étude de la logique linéaire polarisée afin d'étudier la nature fondamentale des langages de programmation logique vis-a-vis du paradigme de la focalisation. De ces travaux sont issus une nouvelle division en quatre classes des formules logiques et les deux calculs des séquents llpn et llpp. Ces derniers, éliminant par le fait la frontière entre logique et programmation logique, sont deux langages de programmation polarises. Ces dernières avancées permettent de représenter les phénomènes de décompositions partielles et de représentation du temps logique. On peut ainsi modéliser la sequentialité ou la non-commutativité temporelle grâce à l'utilisation de doubles décalages, contrairement
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Laurent, Olivier. "Etude de la polarisation en logique." Aix-Marseille 2, 2001. https://tel.archives-ouvertes.fr/tel-00007884.
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Deknuydt, Florence. "L'il-17 : polarisation innée et adaptative." Nantes, 2011. http://archive.bu.univ-nantes.fr/pollux/show.action?id=0a95bdaa-9fdf-4d66-bc51-42db3353fd4d.
Full textAbstract:
Ma thèse a porté sur la caractérisation des origines de cellules pouvant produire de l'IL-17 et appelées les Th17. Ces cellules semblent être impliquées aussi bien dans les maladies auto-immunes que dans certaines infections bactériennes. Dans ces différentes pathologies, deux types cellulaires connus comme cellules immunitaires non conventionnelles : les Tregs et les cellules T γδ jouent un rôle primordial. Les premières données obtenues chez la souris suggéraient que ces deux sous populations étaient capables de produire de l'IL-17. J'ai donc employé plusieurs techniques afin de caractériser les cellules immunitaires humaines capables de produire de l'IL-17 et les conditions nécessaires à cette production. Premièrement, j'ai réalisé un travail sur les cellules du sang périphérique en conditions non infectées. Ces travaux m'ont permis de démontrer la capacité des cellules Tregs et particulièrement des cellules MTregs à se polariser en Th17. J'ai mis en évidence que la présence d'IL-1, d'IL-2 et d'un signal TCR permet au MTreg de se polariser en cellules Th17 et que celles-ci perdent leur capacité suppressive ainsi que l'expression de Foxp3. Dans un deuxième temps, je me suis intéressée à cette cytokine dans un contexte pathologique : la Tuberculose. Pour réaliser ce projet, j'ai utilisé un modèle de formation de granulome humain in vitro mis au point par F. Altare et son équipe. J'ai ainsi pu mettre en évidence la présence d 'IL-17 au sein du granulome mycobactérien aussi bien in vitro que sur des coupes histologiques issues de biopsies de patients. De plus, la population la plus apte à se polariser en cellules productrices d'IL-17 au sein du granulome est la population LT γδ. Chez l'homme, il existe deux sous populations de LT γδ : Vδ2- ou Vδ2. Seule la sous population de δ2- semble être capable de produire de l'IL-17 dans le contexte du granulome mycobactérien humain. J'ai aussi pu mettre en évidence que cette production d'IL-17 survient tardivement, dans les stades avancés de granulomes. Enfin il semble exister un lien entre la présence d"IL-17, des cellules δ1 et de la nécrose, puisque ces cellules sont retrouvées uniquement sur les coupes de patients à lésions nécrotiques et que ceci est associé à la présence d'IL-17 au sein de ces mêmes biopsiesDuring my PhD, I characterized the cells producing the pro-inflammatory cytokine: IL-17. These cells seem to be implicated in autoimmune diseases and some bacterial infections. In these pathologies, the immune system plays an important role and particularly two cell subsets: Treg and γδ T cells. During a first period, I investigated these cells in uninfected PBMCs. During this work I demonstrated the capacity of Treg to polarise into Th17. I also demonstrated that Treg could produce IL-17 when they are activated via the TCR combined with IL-1 and IL-2. Moreover when these cells produce IL-17 they loose the expression of Foxp3 and their suppressive capacity. During a second period, I studied this cytokine in a pathologic context: human tuberculosis. To develop this project, I used an in vitro granuloma model developed by F. Altare’s team. During this work, I demonstrated the presence of IL-17 within characteristic structure of human tuberculosis: the granuloma. This cytokine is present in vitro and in sample biopsies of human granuloma. Moreover, within granuloma, γδ T cells have the best capacity to polarise. In Humans, the γδ T cells are composed of two subset: δ1 and δ2. The δ2 cells are mainly found within epithelia, whereas δ1 are mainly circulating. During my study, I could demonstrate that δ1 cells are the only cells to be able to produce IL-17 within human granulomas. This production is only displayed in late stage of granuloma. A relationship seems to exist between IL-17, δ1 and the necrosis present in the middle of granuloma, because these cells are present only in necrotic biopsies thus strongly suggesting a direct role of δ1-induced IL-17 in necrosis induction
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Preece, Michael Alan. "Analysis of cosmic microwave background polarisation." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/analysis-of-cosmic-microwave-background-polarisation(06cf26fc-2604-4955-9980-94457ac8458c).html.
Full textAbstract:
Observations of the Cosmic Microwave Background (CMB) radiation are an extremely important tool for understanding the Universe. The next generation of CMB experiments will attempt to measure the polarisation signal. In particular, the detection of B-mode polarisation, which is mainly generated by gravitational waves from the very early Universe, would provide a strong indicator for the energy level of inflation. However, due to the relative weakness of this signal, and the fact that there exists a much stronger E-mode signal, detecting B-modes polarisation poses several technical challenges. In particular, the standard method of CMB analysis, the pseudo-C_l method, is insufficient for the purposes of analysing B-mode polarisation, because of the difficulties of separating E and B mode polarisation on a cut sky. However, an alternate method, the pure-C_l method, has recently been outlined, which removes the effect of E-B mixing by subtracting out ambiguous modes. In order to test this method, I have written code to implement my own version of the algorithm, as well as the ordinary pseudo-C_l method. I have then used this code to compare the two methods both with and without E-modes, thereby demonstrating that the pure-C_l method does not suffer from issues with E-B mixing. However, I also find that, due to the effects of subtracting out ambiguous modes, the performance of the pure-C_l method is degraded on large scales, by a factor which is dependent on the length of the mask boundary. I have, therefore, investigated this effect. I find that, in general, the issues with this method are limited to only the very largest scales, and they are unlikely to cause significant problems for most masks. However, due to the nature of point source masks, these are particularly susceptible to such effects. Therefore, I have considered this case more carefully. Here, I find that there is indeed a significant effect up to multipoles of l ~ 50, and I have discovered that there is a simple relationship between the additional error caused by a point source mask and the number of sources. Due to the rapidly rising (in l 2 C_l) nature of the point-source power-spectrum, this issue can probably be avoided by only using the point-source mask for high-l measurements and, thus, the effect of point sources on the pure-C_l method will probably be limited. The exception to this, however, is the case where an exceptionally large number of sources must be masked out. In this case, the requirement to apodise the mask in order to implement the method will result in the analysis breaking down. Additionally, I have also looked at several other aspects of B-mode detection. I used various optimal error formulae, in conjunction with my pure-C_l code, to attempt to determine the optimal scan strategy for a given set of parameters, with a particular focus on the QUIJOTE experiment. Ultimately, it was found that this experiment in its original form would only be able to detect values of r of around 0.2, although increasing the number of beams would improve this slightly. Finally, I have outlined a novel null test that is designed to detect systematic errors in CMB experiments using polarisation position angles. I have showed that this method will be able to detect shear-like systematic errors at a level of less than 1%.
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Jaroenjittichai, Phrudth. "Pulsar polarisation as a diagnostic tool." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/pulsar-polarisation-as-a-diagnostic-tool(cbbef2d8-5779-4f5b-a48d-09eec413f247).html.
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The geometry of pulsar beams is one of the intrinsic properties of neutron stars, governing the pulse-profile phenomenon and other aspects of pulsar astron- omy. With a number of pulsars in our dataset, their beam geometry is derived from the polarisation position angle (PPA) using the simple polar cap emission and dipole field model. This includes the rotating vector model (RVM), for which the solutions can hardly be constrained or fail to be consistent because of the lim- itations of the model itself. The inconsistencies in the results suggest that the initial PPAs can be strongly perturbed by additional parameters above the emis- sion altitude, such as the plasma medium or rotational aberration effects, after which their characteristic shape is no longer related to the geometry via the RVM. We investigate further into the effects of wave propagation in the pulsar magne- tosphere, and find an indication that, in most cases, the RVM-calculated PPAs are likely to be altered by plasma effects.In recent years, there have been an increasing number of intermittent and mode-switching pulsars observed to have their radio pulse profiles correlated with the change in pulsar spin frequency (ν ̇) (e.g. Lorimer et al. 2012, Lyne et al. 2010). These two phenomena are understood to be related via the states of plasma in the magnetosphere. As one such pulsar, and also one with known geometry and other astonishing behaviour, PSR B1822–09 is studied in terms of the mode- switching properties, the hollow-cone model and the wave propagation in the magnetosphere. We also study the model for explaining the intermittent pulsars PSRs B1931+24, J1841+0500 and J1832+0029, and find it can be consistently applied for PSRs B1822–09 and B0943+10, and other profile-switching pulsars. However, aspects of the conclusions are limited because of the lack of understand- ing of the connection between the radio flux and the states of plasma. We are also able to use the difference in the PPAs between two states of PSR B0943+10 to predict the change in plasma states and ν ̇, which cannot be measured directly from timing analysis as its switching timescale is too short.
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Boillot, Florence. "Polarisation des taus dans la réaction." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb37603127d.
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Seehoo, Rebecca. "Monocyte/Macrophage Polarisation in Diabetic Complications." Thesis, The University of Sydney, 2015. http://hdl.handle.net/2123/14059.
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Diabetic nephropathy (DN), a complication of diabetes is the leading cause of chronic kidney disease and contributes strongly to the morbidity and mortality of diabetes. Macrophage infiltration into renal tissues is a primary contributing factor to DN onset and progression yet few studies have examined kidney macrophage phenotype in diabetes and DN onset and progression. In this thesis the expression of macrophage phenotype markers was examined in association with kidney disease development in a mouse model of diabetes. Monocyte inflammatory gene expression profile was also examined in people with or without diabetic complications. In diabetic mouse kidney tissue increased expression of pro-inflammatory MCP-1 at 5 weeks preceded that of the anti-inflammatory marker CD163 at 30 weeks of diabetes. These changes occurred prior to altered kidney fibrosis marker expression. Whilst requiring further investigation the presence of increased anti-inflammatory M2 macrophages in kidney prior to damage suggests, at least at this early stage of disease progression, a protective phenotype. In the human study, few differences in monocyte inflammatory gene profiles were observed. This lack of marked change suggests that alterations in function (i.e. infiltration to tissue) occur in response to the circulating diabetic milieu or to tissue damage. Further detailed studies are required to investigate the response of these monocytes to inflammatory stimuli.
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Cherubini, Aurélien. "Utilisation des méthodes de polarisation spontanée et polarisation provoquée pour la détection de CO₂ en milieu poreux carbonaté." Thesis, Bordeaux 3, 2019. http://www.theses.fr/2019BOR30005/document.
Full textAbstract:
Les méthodes géophysiques non intrusives sont requises pour caractériser la zone vadose, les réservoirs d’hydrocarbures, ou les sites de stockages de CO₂. Nous analysons l’impact d’une injection de CO₂ gazeux sur la conductivité électrique et les propriétés électrocinétiques des roches carbonatées partiellement ou totalement saturées grâce aux méthodes de polarisations provoquée et spontanée. Les données sont analysées au regard au regard de mesures effectuées sur une roche chimiquement neutre, vis-à-vis du CO₂, c’est-à-dire , un grès de Fontainebleau. Nous comparons également nos résultats aux données de la littérature. Le coefficient de couplage électrocinétique est un paramètre clé, dont nous allons étudier la dépendance vis-à-vis de la saturation, sujet hautement débattu de nos jours. En utilisant la méthode de polarisation spontanée, nous étudions les relations entre le coefficient de couplage électrocinétique, la pression capillaire ainsi que la perméabilité relative au sein des roches carbonatées. Un système expérimental a été élaboré pour mesurer simultanément la perméabilité relative, l’indice de resistivité et le coefficient de couplage électrocinétique en écoulement diphasique de type eau-gaz, en fonction de la saturation en azote ou en dioxyde de carbone. Les résultats sont comparés à des modèles théoriques basés sur les approches de Brooks et Corey et van Genuchten, dont les exposants nous permettent d’ajuster les données avec les modèles de pression capillaire avec succès. Les échantillons sont saturés avec des saumures de différentes compositions, dont les ions sont mono- ou divalents et pour lesquelles la force ionique est comprise entre 10⁻⁴ et 10⁰ Mol L⁻¹. La valeur absolue du coefficient de couplage électrocinétique augmente lorsque la force ionique de la solution diminue, ce qui a déjà été observé dans les roches gréseuses. Le potentiel zêta a été calculé en utilisant une version modifiée de l’équation d’Helmholtz-Smoluchowski, qui prend en compte les effets liés à la conductivité de surface. Comme pour le coefficient de couplage, la valeur absolue du potentiel zêta chute lorsque la force ionique augmente. Nous nous intéressons également aux effets liés à une injection de CO₂ et à la dissolution de la calcite sur la valeur de ce potentiel zêta. Enfin, nous utilisons la méthode de polarisation provoquée pour déterminer l’influence de conductivité de l’eau porale sur la conductivité électrique complexe, la chargeabilité normalisée ainsi que le temps de relaxation en milieu carbonaté non saturé. Nous montrons que ces paramètres peuvent être considérés comme des paramètres de polarisation de la double couche électrique lorsque la conductivité de l’eau porale est comprise entre 10⁻³ et 10⁰ S m⁻¹Minimally intrusive geophysical methods are required to characterize both the vadose zone of the Earth, hydrocarbon reservoirs and CO₂ sequestration. We investigate the impact of gaseous CO₂ on both electrical conductivity and electrokinetic properties of limestones under saturated and unsaturated conditions, using the spectral induced polarization and the self-potential methods. These data are contrasted with measurements performed on a Fontainebleau sandstone and data from the literature. That said, the dependence of a key parameter, the streaming coupling coefficient, with the saturation remains highly debated. Using the self-potential method, we explore the relationship between the streaming potential coupling coefficient, the capillary pressure curves and the permeability in carbonate rocks characterized by distinct textures. A new core flooding system is used to measure simultaneously both the relative permeability, the resistivity index and the streaming potential coupling coefficient in steady-state two-phase flow conditions as a function of the saturation with CO₂ or N₂. The results are compared with a recently developed theoretical model, which can accommodate either the Brooks and Corey or the van Genuchten models for the capillary pressure curves. Saturation was achieved with monovalent and divalent brines with ionic strength ranging from 1x10⁻³ Mol L⁻¹ to 1x10⁰ Mol L⁻¹. The magnitude of the coupling coefficient increases with decreasing ionic strength similarly to the trend observed for sandstones. The zeta potential has been calculated at full saturation using a modified version of the Helmholtz-Smoluchowski equation that accounts for surface electrical conductivity. Under atmospheric conditions, the magnitude of the zeta potential is decreasing with the increase of the ionic strength. We also investigate the effects of a CO₂ release and the calcite dissolution on the magnitude of the zeta potential. Finally, we use the spectral induced polarization method to determine the pore water conductivity effects on the complex electrical conductivity, the normalized chargeability and the main relaxation time during drainage in a clay free limestone. We also show evidences that these parameters could be considered as polarization parameters of the electrical double layer in the pore water conductivity range 10⁻³ - 10⁰ S m⁻¹
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Ysacco, Cedric. "Préparation et étude de nouveaux dinitroxydes comme agents de polarisation en polarisation dynamique nucléaire (PDN) en phase solide." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4819.
Full textAbstract:
Préparation et étude de nouveaux dinitroxydes comme agents de polarisation en polarisation dynamique nucléaire (PDN) en phase solide. La principale limite de la RMN, en tant qu'outil de détection ou d'imagerie (IRM), est sa faible sensibilité qui résulte principalement de la faible différence d'énergie entre les états de spin nucléaire entre lesquels on observe la résonance. A l'équilibre thermique, la polarisation nucléaire PI (différence de population entre les états de spin) est très faible et le signal RMN, qui lui est proportionnel, sera peu intense. Le but de la Polarisation Dynamique Nucléaire (PDN) est d'augmenter l'intensité de signaux de RMN, en transférant vers des spins nucléaires de la polarisation de spin électronique PS, plus élevée que celle des spins nucléaires (PS/PI = 658 pour 1H). Depuis une quinzaine d'années, la PDN connaît un regain d'intérêt et un champ de développement exceptionnels. Cette renaissance de la PDN est surtout due aux importants travaux de fond du groupe de R. G. Griffin et ceux plus récents du groupe d'Ardenkjaer-Larsen. Ces travaux ont entre autre montré qu'avec des radicaux trityl ou des dinitroxydes, la PDN pouvait permettre d'atteindre de fortes augmentations du rapport signal sur bruit, en RMN en phases solide et liquide. Les propriétés de l'espèce paramagnétique à partir de laquelle se fait le transfert de polarisation spin électronique - spin nucléaire, jouent un rôle primordial dans l'efficacité de ce transfert. Au cours de notre travail, nous avons réalisé les synthèses de cinq nouveaux biradicaux de la famille des dinitroxidesPreparation and study of new dinitroxydes as polarizing agents in dynamic nuclear polarization (DNP) in solid state. Nowadays, nuclear magnetic resonance (NMR) spectroscopy is one of the most important structure elucidation techniques in chemistry and biochemistry, NMR is also the underlying principle of magnetic resonance imaging (MRI). However, the use of NMR to investigate various materials or biological systems is still limited by its inherent low sensitivity. This arises from the relatively small size of the Zeeman interaction of the nuclear spins with an external magnetic field which leads to small Boltzmann polarizations (PI) and weak NMR signals. Dynamic Nuclear Polarization (DNP) is a prominent process to achieve a high non-equilibrium nuclear spin polarization by transferring to nuclear spins the higher electron spin polarization PS (PS/PI = 658 for 1H)) of unpaired electrons, belonging for example to stable free radicals. The past fifteen years has witnessed a renaissance in the use of DNP. This renewed interest is due to the outstanding work of the R. G. Griffin's group and the more recent work of the Ardenkjaer-Larsen's group. These authors have shown, among other, that with the use of trityl radicals or dinitroxides, PDN allowed to reach impressive signal enhancements for solid state and liquid NMR. The characteristics of the paramagnetic species used as polarizing agent play a pivotal role in the efficiency of a DNP process. In the course of our work we have performed the synthesis of five new dinitroxides, and through collaborations we tested their performance as polarizing agents for solid state PDN at 100 K, 9,4 T [263 GHz (RPE), 400 MHz (RMN)]
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Ysacco, Cedric. "Préparation et étude de nouveaux dinitroxydes comme agents de polarisation en polarisation dynamique nucléaire (PDN) en phase solide." Electronic Thesis or Diss., Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4819.
Full textAbstract:
Préparation et étude de nouveaux dinitroxydes comme agents de polarisation en polarisation dynamique nucléaire (PDN) en phase solide. La principale limite de la RMN, en tant qu'outil de détection ou d'imagerie (IRM), est sa faible sensibilité qui résulte principalement de la faible différence d'énergie entre les états de spin nucléaire entre lesquels on observe la résonance. A l'équilibre thermique, la polarisation nucléaire PI (différence de population entre les états de spin) est très faible et le signal RMN, qui lui est proportionnel, sera peu intense. Le but de la Polarisation Dynamique Nucléaire (PDN) est d'augmenter l'intensité de signaux de RMN, en transférant vers des spins nucléaires de la polarisation de spin électronique PS, plus élevée que celle des spins nucléaires (PS/PI = 658 pour 1H). Depuis une quinzaine d'années, la PDN connaît un regain d'intérêt et un champ de développement exceptionnels. Cette renaissance de la PDN est surtout due aux importants travaux de fond du groupe de R. G. Griffin et ceux plus récents du groupe d'Ardenkjaer-Larsen. Ces travaux ont entre autre montré qu'avec des radicaux trityl ou des dinitroxydes, la PDN pouvait permettre d'atteindre de fortes augmentations du rapport signal sur bruit, en RMN en phases solide et liquide. Les propriétés de l'espèce paramagnétique à partir de laquelle se fait le transfert de polarisation spin électronique - spin nucléaire, jouent un rôle primordial dans l'efficacité de ce transfert. Au cours de notre travail, nous avons réalisé les synthèses de cinq nouveaux biradicaux de la famille des dinitroxidesPreparation and study of new dinitroxydes as polarizing agents in dynamic nuclear polarization (DNP) in solid state. Nowadays, nuclear magnetic resonance (NMR) spectroscopy is one of the most important structure elucidation techniques in chemistry and biochemistry, NMR is also the underlying principle of magnetic resonance imaging (MRI). However, the use of NMR to investigate various materials or biological systems is still limited by its inherent low sensitivity. This arises from the relatively small size of the Zeeman interaction of the nuclear spins with an external magnetic field which leads to small Boltzmann polarizations (PI) and weak NMR signals. Dynamic Nuclear Polarization (DNP) is a prominent process to achieve a high non-equilibrium nuclear spin polarization by transferring to nuclear spins the higher electron spin polarization PS (PS/PI = 658 for 1H)) of unpaired electrons, belonging for example to stable free radicals. The past fifteen years has witnessed a renaissance in the use of DNP. This renewed interest is due to the outstanding work of the R. G. Griffin's group and the more recent work of the Ardenkjaer-Larsen's group. These authors have shown, among other, that with the use of trityl radicals or dinitroxides, PDN allowed to reach impressive signal enhancements for solid state and liquid NMR. The characteristics of the paramagnetic species used as polarizing agent play a pivotal role in the efficiency of a DNP process. In the course of our work we have performed the synthesis of five new dinitroxides, and through collaborations we tested their performance as polarizing agents for solid state PDN at 100 K, 9,4 T [263 GHz (RPE), 400 MHz (RMN)]
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Ibrahim, I. "Illumination invariance and shadow compensation on hyperspectral images." Thesis, Cranfield University, 2014. http://dspace.lib.cranfield.ac.uk/handle/1826/8769.
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To obtain intrinsic reflectance of the scene by hyperspectral imaging systems has been a scientific and engineering challenge. Factors such as illumination variations, atmospheric effects and viewing geometries are common artefacts which modulate the way of light reflections from the object into the sensor and that they are needed to be corrected. Some of these factors induce highly scattered and diffuse irradiance which can artificially modify the intrinsic spectral reflectance of the surface, such as that in the shadows. This research is attempted to compensate the shadows in the hyperspectral imagery. In this study, three methods known as the Diffuse Irradiance Compensation (DIC), Linear Regression (LR) and spectro-polarimetry technique (SP) have been proposed to compensate the shadow effect. These methods have various degrees of shadow compensation capabilities, and their pros and cons are elucidated within the context of their classification performances over several data sets recorded within and outside of the laboratory. The spectro-polarimetry (SP) technique has been found to be the most versatile and powerful method for shadow compensation, and it has achieved over 90% of classification accuracy for the scenes with ~30% of shadow areas.
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Flossmann, Florian. "Singularitäten von Phase und Polarisation des Lichts." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=981484360.
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Bouwmans, Géraud. "Microlasers : Dynamique de Couplage et de Polarisation." Phd thesis, Université des Sciences et Technologie de Lille - Lille I, 2001. http://tel.archives-ouvertes.fr/tel-00083926.
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Ce travail s'inscrit dans le cadre général de l'étude des mécanismes de couplage entre oscillateurs. Deux aspects sont abordés qui concernent respectivement le couplage par proximité de deux microlasers au sein d'une même galette et les interactions entre modes de polarisation dans les microlasers YAG présentant de faibles anisotropies.L'étude expérimentale du couplage de deux lasers continus a mis en évidence trois régimes dynamiques différents qui apparaissent successivement à mesure que les fréquences propres des cavités des lasers se rapprochent : i) lasers quasi indépendants, ii) instabilités périodiques et chaotiques et iii) verrouillage de phase des lasers.
Le modèle développé pour rendre compte des caractéristiques du couplage introduit un coefficient de couplage complexe. Il reproduit de façon remarquable l'ensemble des résultats expérimentaux et de plus a permis de proposer une méthode fiable de mesure du coefficient de couplage. Une étude détaillée du recouvrement entre les modes des lasers et le profil non uniforme du gain et de l'indice de réfraction a permis d'établir une expression analytique reproduisant correctement l'évolution des parties réelle et imaginaire du coefficient de couplage en fonction de la distance entre lasers.
La dynamique de polarisation des microlasers YAG, et en particulier des lasers Nd3+,Cr4+:YAG, met en jeu la biréfringence liée aux contraintes locales, l'anisotropie de gain induite par un faisceau de pompe polarisé linéairement et de celle de l'absorbant saturable. Suivant l'importance relative de ces différentes anisotropies, le laser peut émettre dans l'un et/ou l'autre des modes propres de la biréfringence ou avoir une polarisation orientée de façon privilégiée suivant l'un des axes cristallins de l'absorbant.
Les observations expérimentales ont pu être reproduites analytiquement et/ou numériquement à l'aide d'un modèle qui rend compte de l'évolution temporelle des composantes du champ selon les axes propres de la biréfringence ainsi que celle de leur phase relative. L'anisotropie du gain est décrite par deux coefficients d'anisotropie respectivement relatifs à la pompe et au laser. L'anisotropie de l'absorbant saturable est prise en compte grâce à l'introduction d'inversions de populations associées à chacun des axes cristallins.
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Brohée, Dany. "Polarisation des rosettes-E: modèle et instrument." Doctoral thesis, Universite Libre de Bruxelles, 1987. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/213510.
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Dolinska, Aska. "The investigation of quantum polarisation teleportation protocol." View electronic text, 2002. http://eprints.anu.edu.au/documents/disk0/00/00/07/87/index.html.
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Thesis (BSc. (Hons))--Australian National University, 2002.Available via the Australian National University Library Electronic Pre and Post Print Repository. Title from title screen (viewed Mar. 28, 2003). "A thesis submitted for the degree of Bachelor of Science in Physics, The Australian National University" Bibliography: p. 77-80.
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Reppel, Julie-Ann. "Planar laser polarisation spectroscopy imaging in combustion /." Title page, abstract and table of contents only, 2003. http://web4.library.adelaide.edu.au/theses/09PH/09phr4259.pdf.
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Cheng, Li 1973. "Magnetic polarisation of palladium in palladiumiron multilayers." Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=85061.
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This thesis is devoted to the studies of structural and magnetic properties of Pd/Fe multilayers with the principal goal of determining the extent to which the Pd layers are polarised by the Fe atoms and the average moment induced on each Pd atom. Although Pd/Fe multilayers have been the subject of several previous studies, no consensus on the behavior of magnetically polarised Pd has emerged. This work has the novel feature of applying a wide range of characterization techniques on the same sample. These techniques included x-ray diffraction, conversion electron Mossbauer spectroscopy (CEMS), magnetometry and polarised neutron reflectometry. Ag/Fe multilayers were first characterized to confirm the validity of the analysis of the small-angle x-ray reflectivity to obtain layer thicknesses, as well as to determine the temperature dependence of the Fe moment from GEMS data.From the intersection of the results from the complementary measurements on Pd/Fe multilayers, for the first time, an unequivocal understanding of the behavior of magnetically polarised Pd has been achieved. We find, there is a clear excess magnetisation associated with Pd polarisation. At 4.5 K, the Pd in contact with an Fe surface is polarised with an average moment of 0.32 +/- 0.02 muB to a depth of 20 +/- 4 A (9 +/- 2 atomic layers). These results indicate a large exchange splitting of the Pd d-bands for a significant distance from the Fe surface, leaving the spin-up band full, and a moment in the Pd arising from the 0.36 holes in the spin-down band. We also find that the Fe moment at the Pd/Fe interface is slightly enhanced to 2.42 +/- 0.05 muB for about 2.0 +/- 0.3 atomic layers, suggesting that the magnetic properties of Fe is less affected by Pd as compared to the influence of Fe on Pd. Neither the extent of Pd polarisation nor the interface Fe moment agree with values predicted by theoretical calculations (the calculated Pd polarisation depth is 2 atomic layers, and the interface Fe moment is 2.7 muB). The band structure calculations will have to be refined in the light of the results from current study.
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Kluge, Christina. "Regulating human Th17 polarisation by activated macrophages." Thesis, University of Aberdeen, 2012. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=185639.
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Inflammatory diseases such as autoimmune and atopic diseases are a common problem worldwide. Although there have been substantial advances in medical therapies, current treatments are not able to cure these conditions. In order to develop more specific, individually targeted and efficient treatments, a better understanding of the cells, mediators and mechanisms that lead to pathology are necessary. Macrophages and T cells are major players in the human immune system. Despite the abundance of macrophages at inflammatory sites and their secretion of T cell polarising cytokines, their roles as antigen presenting cells has been overlooked until now. This PhD project aimed to determine, firstly, the contribution of differentially activated human macrophages in the regulation of adaptive immune responses in inflammation with the main focus on the pro‐inflammatory T cell subset Th17, secondly, how macrophage functions could be modified to alter T cell polarisation and thirdly, how novel alternative mechanisms using electric fields can alter T cell responses. I demonstrate for the first time that macrophages can efficiently induce T cell polarisation and Th17 differentiation in response to recall and primary antigens and that the specific macrophage activation state is essential to drive Th17 responses. This suggests that macrophages are an important stimulus contributing to pathogenic T cell responses in human inflammatory diseases. Importantly, both memory and naïve T cells gave rise to Th17 cells following culture with antigen‐loaded activated macrophages, where non‐specific effects of mitogenic activation were avoided. Targeting human macrophage signalling pathways through SOCS3, reduced their pro‐inflammatory potential and Th17 polarising ability, pointing to SOCS3 as an effective therapeutic target. As an alternative approach, I demonstrate here that small electric fields of physiological strength strongly influence immune responses and significantly dampen Th17 differentiation. This suggests that EFs have the potential to facilitate healing processes or support conventional therapies for inflammatory diseases. Overall, these data present a strong basis for the development novel treatment possibilities for inflammatory diseases that are distinct from the currently used conventional therapies.