<p>We study the spin polarization and conductance in infinitely long quasi one-dimensionalquantum wires under various conditions in an attempt to reproduce and to explain some of theanomalous conductance features as seen in various experiments. In order to accomplish thistask we create an idealized model of a quantum wire in a split-gate semiconductorheterostructure and we perform self-consistent Hartree-Fock calculations to determine theelectron occupation and spin polarization. Based on those results we calculate the currentthrough the wire as well as the direct and differential conductances. In the frame of theproposed model the results show a high degree of similarity to some of the experimentallyobserved conductance features, particularly the 0.25- and 0.85-plateaus. These results lead usto the conclusion that those conductance anomalies are in fact caused by the electronsspontaneously polarizing due to electron-electron interactions when an applied potentialdrives a current through the wire.</p>

<p>In this Thesis the magnetic and structural properties of thin epitaxial Fe, Co, and Ni films are discussed. Some of the in-situ prepared samples were used to characterize the degree of circular polarization of the newly installed beamline D1011 at MAX-lab. By means of x-ray magnetic circular dichroism (XMCD) and utilizing the associated magneto optic sum rules, the orbital (<i>m</i><i>l</i>) and spin (<i>m</i><i>s</i>) moments are determined directly in <i>m</i><i>B</i>/atom with elemental specificity. The extended x-ray absorption fine structure (EXAFS) measurements yield site specific information on the local crystallographic structure.</p><p>These measurements were performed using the circular x-rays of several beamlines. The influence of the degree of spatial source coherence <i>l</i><i>spat</i> of the x-rays was characterized by means of Fresnel diffractometry. A correlation between enhanced XAS white line intensities and higher values of <i>l</i><i>spat</i> was established for 20 ML Fe, Co, and Ni films on Cu(100).</p><p>The degree of circularly polarized x-rays (<i>P</i><i>c</i>) at beamline D1011 at MAX-lab was characterized by studying Fe films on Cu(100) by means of XMCD. The maximum value of <i>P</i><i>c</i> is experimentally determined to <i>P</i><i>c</i> =0.85.</p><p>The Au/Co/Au trilayer system was studied as a function of Co thickness, temperature, and Au cap thickness. A 10 mono-layer (ML) Co film, with an Au cap of 20 Å, shows a spin reorientation transition (SRT) from an in-plane to an out-of-plane easy direction as the temperature is lowered from 300 K to 200 K. The magnetic properities of these Co films are very different to what is found for bulk samples due to, in particular, the broken symmetry at the interfaces.</p><p>The thickness dependent spin reorientation transition in the Fe/Ag(100) system was characterized by means of XMCD and EXAFS measurements. 3 ML Fe films show an out-of-plane easy direction with an 125% enhanced orbital moment as compared to the 25 ML Fe in-plane film. Simulations of the Fe <i>L</i>-edge EXAFS indicate the bulk Fe bcc structure for film thicknesses of 6-25 ML Fe. For 3 ML Fe strong deviations from this bcc phase is observed.</p><p>Ultrathin Co films deposited on flat and vicinal Cu(111) in the thickness region 1-25 ML were studied by means of XMCD and scanning tunneling microscopy (STM). The vicinal Cu(111) Co deposition leads to the formation of elongated islands preferentially oriented along the step edges. In connection to this particular Co growth mode we observe an increase of both the orbital and the spin moment on the vicinal Cu(111) of about 25% relative to what was observed for Co on flat Cu(111).</p>

Un réseau de Bragg fibré est un tronçon de fibre optique dont le coeur présente une modification périodique et permanente de l’indice de réfraction. Dans sa structure la plus simple, il se comporte, en réflexion, comme un miroir sélectif en longueur d’onde, ne réfléchissant qu’une plage de longueurs d’onde autour de la longueur d’onde de Bragg. Le signal transmis est alors débarrassé des composantes spectrales réfléchies par le réseau de Bragg. Ce composant fibré correspond donc à un filtre optique pour lequel il est important de caractériser les évolutions, en fonction de la longueur d’onde, des réponses en amplitude et en phase. En pratique, les réseaux de Bragg fibrés sont largement utilisés pour la réalisation de différents composants utiles dans le domaine des télécommunications par fibres et des capteurs optiques. De manière générale, il s’avère de plus en plus important de caractériser les propriétés de polarisation induites par la présence de biréfringence des composants optiques ; il en est de même pour les réseaux de Bragg fibrés. En effet, avec l’augmentation des débits de transmission, les communications par fibres optiques sont de moins en moins tolérantes aux effets associés à la polarisation de la lumière. L’utilisation des réseaux de Bragg pour des applications de télécommunications requiert donc de connaître leurs propriétés de polarisation. De même, dans le domaine des capteurs, l’information offerte par l’évolution de ces propriétés en fonction des contraintes extérieures peut être utile pour améliorer les performances et les potentialités des capteurs à réseaux de Bragg. Dans le cadre de cette thèse de doctorat, nous présentons une étude des propriétés spectrales des réseaux de Bragg fibrés en y incluant l’analyse des propriétés de polarisation de la lumière causées par la présence de biréfringence au sein du réseau. Cette étude est menée pour deux catégories de réseaux de Bragg présentant de la biréfringence. Une première catégorie concerne les réseaux inscrits dans des fibres hautement biréfringentes. Pour ces fibres, étant donné les valeurs importantes de biréfringence considérées, ses effets sont directement visibles sur la réponse classique en amplitude. Dans ce cas, nous démontrons qu’il est possible de modéliser complètement les évolutions, en fonction de la longueur d’onde, des paramètres permettant de caractériser les propriétés de polarisation des réseaux de Bragg. Une étude théorique et expérimentale est présentée pour les paramètres de Stokes, le paramètre de PDL (Polarisation Dependent Loss - perte dépendante de la polarisation) et le paramètre de DGD (Differential Group Delay - délai de groupe différentiel). Une seconde étude est menée pour les réseaux de Bragg inscrits dans des fibres standards. Pour ces réseaux, la biréfringence est relativement faible si bien que ses effets sont difficilement perceptibles sur la réponse en amplitude du réseau. Elle n’est donc généralement pas prise en considération lors de l’analyse des propriétés spectrales des réseaux. Nous montrons cependant dans cette thèse de doctorat qu’elle conduit à des valeurs importantes des paramètres de polarisation (paramètres de Stokes, PDL et DGD). Compte tenu des différentes origines possibles de la biréfringence des réseaux, nous exposons deux modèles caractérisant la présence de la biréfringence. Les résultats théoriques obtenus pour ces deux modèles sont alors systématiquement comparés. Nous rapportons finalement des résultats expérimentaux en adéquation avec les résultats théoriques. Pour ces réseaux de Bragg faiblement biréfringents, nous établissons également la relation qui existe entre les paramètres utilisés pour caractériser les propriétés de phase du réseau (courbes de délai et de dispersion) et les paramètres de Stokes et de DGD. En particulier, nous démontrons théoriquement et expérimentalement que les évolutions en fonction de la longueur d’onde de la dispersion chromatique et du DGD ne diffèrent que dans leur valeur absolue, le rapport de ces valeurs étant proportionnel à la biréfringence. En outre, nous discutons la possibilité d’appliquer cette relation à d’autres types de réseaux fibrés et présentons des résultats expérimentaux dans le cas d’un réseau à longs pas. Une application intéressante de la connaissance des paramètres de polarisation des réseaux de Bragg est la détermination de la biréfringence. Nous considérons d’une part le cas d’une biréfringence causée par une contrainte transverse appliquée sur une fibre optique. Nous montrons qu’un réseau de Bragg est utilisable à l’endroit de la contrainte pour obtenir la quantité de biréfringence induite localement. D’autre part, les propriétés de polarisation sont utilisées pour étudier l’évolution de la biréfringence induite lors du processus d’inscription d’une série de réseaux de Bragg de caractéristiques différentes. La reconstruction de la biréfringence de cette série permet alors d’analyser l’impact des paramètres de l’inscription sur la biréfringence photoinduite. Nous proposons finalement une technique originale permettant de réduire les effets de la biréfringence des réseaux. Cette technique est basée sur l’application d’une torsion de la fibre lors de l’inscription, ce qui permet d’introduire du couplage de modes de polarisation au niveau du réseau de Bragg. L’analyse théorique des propriétés spectrales des réseaux menée dans le cas classique est alors adaptée pour tenir compte de l’effet du couplage de modes. Les résultats de simulation obtenus montrent qu’il est en effet possible de réduire la PDL et le DGD de cette manière, ce qui peut s’avérer intéressant dans le cadre d’applications de télécommunications à haut débit.

A key non-destructive technique for analysis, optimization and developing of new functional materials such as sensors, transducers, electro-optical and memory devices is presented. The Thermal-Pulse Tomography (TPT) provides high-resolution three-dimensional images of electric field and polarization distribution in a material. This thermal technique use a pulsed heating by means of focused laser light which is absorbed by opaque electrodes. The diffusion of the heat causes changes in the sample geometry, generating a short-circuit current or change in surface potential, which contains information about the spatial distribution of electric dipoles or space charges. Afterwards, a reconstruction of the internal electric field and polarization distribution in the material is possible via Scale Transformation or Regularization methods. In this way, the TPT was used for the first time to image the inhomogeneous ferroelectric switching in polymer ferroelectric films (candidates to memory devices). The results shows the typical pinning of electric dipoles in the ferroelectric polymer under study and support the previous hypotheses of a ferroelectric reversal at a grain level via nucleation and growth. In order to obtain more information about the impact of the lateral and depth resolution of the thermal techniques, the TPT and its counterpart called Focused Laser Intensity Modulation Method (FLIMM) were implemented in ferroelectric films with grid-shaped electrodes. The results from both techniques, after the data analysis with different regularization and scale methods, are in total agreement. It was also revealed a possible overestimated lateral resolution of the FLIMM and highlights the TPT method as the most efficient and reliable thermal technique. After an improvement in the optics, the Thermal-Pulse Tomography method was implemented in polymer-dispersed liquid crystals (PDLCs) films, which are used in electro-optical applications. The results indicated a possible electrostatic interaction between the COH group in the liquid crystals and the fluorinate atoms of the used ferroelectric matrix. The geometrical parameters of the LC droplets were partially reproduced as they were compared with Scanning Electron Microscopy (SEM) images. For further applications, it is suggested the use of a non-strong-ferroelectric polymer matrix. In an effort to develop new polymerferroelectrets and for optimizing their properties, new multilayer systems were inspected. The results of the TPT method showed the non-uniformity of the internal electric-field distribution in the shaped-macrodipoles and thus suggested the instability of the sample. Further investigation on multilayers ferroelectrets was suggested and the implementation of less conductive polymers layers too. / In dieser Arbeit wird eine zerstörungsfreie Technik zur Analyse, Optimierung, und Entwicklung neuer funktioneller Materialien für Sensoren, Wandler, Speicher und elektrooptische Anwendungen vorgestellt. Die Wärmepuls-Tomographie (engl. Thermal-Pulse Tomography, TPT) liefert dreidimensionale Abbildungen hoher Auflösung von elektrischen Feldern und Polarisationsverteilungen eines Materials. Bei dieser thermischen Methode wird ein fokussierter, gepulster Laserstrahl durch eine undurchsichtige Oberflächenelektrode absorbiert, welche sich dadurch aufheizt. Die einsetzende Wärmediffusion führt – aufgrund der Wärmeausdehnung des Materials – zu Änderungen der Probengeometrie, welche in pyroelektrischen Materialien einen Kurzschlussstrom oder eine Änderung des Oberflächenpotentials zur Folge hat. Diese wiederum enthalten wichtige Informationen über die räumliche Verteilung elektrischer Dipole und Raumladungen im untersuchten Material. Aus dem gemessenen Kurzsschlussstrom kann anschließend das interne elektrische Feld und die Polarisationsverteilung im Material mittels verschiedener Skalentransformations- und Regularisierungsmethoden rekonstruiert werden. Auf diese Weise ermöglichte die TPT-Methode erstmals die Darstellung inhomogener ferroelektrischer Schaltvorgänge in polymeren ferroelektrischen Filmen, welche mögliche Materialien für die Datenspeicherung sind. Die Ergebnisse zeigen eine typische Haftschicht im ferroelektrischen Polymer und unterstützen die Hypothese einer ferroelektrischen Umpolung auf einer der Korngröße äquivalenten Längenskala über Keimbildung und anschließendes Wachstum. Um die Lateral- und Tiefenauflösung zu untersuchen, wurden sowohl die TPT-Methode als auch die äquivalente Methode in der Zeitdomäne (Focused Laser Intensity Modulation Method, FLIMM) auf ferroelektrischen Filme mit Gitterelektroden angewendet. Die Ergebnisse beider Techniken zeigen nach der Datenauswertung mit unterschiedlichen Regularisierungs- und Scale-Methoden eine vollkommene Übereinstimmung. Des Weiteren stellte sich heraus, dass bisherige Untersuchungen der lateralen Auflösung von FLIMM diese möglicherweise überschätzen. Damit behauptet sich TPT als effiziente und verlässliche thermische Methode. Nach einer Optimierung der Optik wurde die TPT-Methode in polymerdispergierten Flüssigkristallen (polymer-dispersed liquid crystals, PDLC), welche in elektrooptischen Anwendungen von Interesse sind, angewendet. Die Ergebnisse deuten auf eine mögliche elektrostatischeWechselwirkung zwischen den COH-Gruppen des Flüssigkristalls und den Fluoratomen der verwendeten ferroelektrischen Matrix hin. Die durch rasterelektronenmikroskopische Aufnahmen (scanning electron microscopy, SEM) gewonnenen geometrischen Parameter der Flüssigkristalltröpfchen konnten mittels TPT reproduziert werden. Für weitere Anwendungen werden schwach ferroelektrische Polymermatrices vorgeschlagen. Im Bestreben neue polymere Ferroelektrete zu entwickeln und deren Eigenschaften zu optimieren, wurden neuartige Mehrschichtsysteme untersucht. Die Ergebnisse aus der TPT-Methode zeigen eine Abweichung der Uniformität der inneren Verteilung des elektrischen Feldes in den geformten Makrodipolen, was auf eine Instabilität der Probe hindeutet. Ebenfalls wurden weitere Untersuchungen an Mehrschicht-Ferroelektreten und die Anwendung von halbleitenden Polymerschichten vorgeschlagen.

The connection between T cell activation, plasma membrane order and actin filament dynamics was the main focus of this study. Laurdan and di-4-ANEPPDHQ, membrane order sensing probes, were shown to report only on lipid packing rather than being influenced by the presence of membrane-inserted peptides justifying their use in membrane order studies. These dyes were used to follow plasma membrane order in live cells at 37°C. Disrupting actin filaments had a disordering effect while stabilizing actin filaments had an ordering effect on the plasma membrane, indicating there is a basal level of ordered domains in resting cells. Lowering PI(4,5)P2 levels decreased the proportion of ordered domains strongly suggesting that the connection of actin filaments to the plasma membrane is responsible for the maintaining the level of ordered membrane domains. Membrane blebs, which are detached from the underlying actin filaments, contained a low fraction of ordered domains. Aggregation of membrane components resulted in a higher proportion of ordered plasma membrane domains and an increase in cell peripheral actin polymerization. This strongly suggests that the attachment of actin filaments to the plasma membrane induces the formation of ordered domains. Limited cholesterol depletion with methyl-beta-cyclodextrin triggered peripheral actin polymerization. Cholesterol depleted cells showed an increase in plasma membrane order as a result of actin filament accumulation underneath the membrane. Moderate cholesterol depletion also induced membrane domain aggregation and activation of T cell signaling events. The T cell receptor (TCR) aggregation caused redistribution of domains resulting in TCR patches of higher order and the bulk membrane correspondingly depleted of ordered domains. This suggests the preexistence of small ordered membrane domains in resting T cells that aggregate upon cell activation. Increased actin polymerization at the TCR aggregation sites showed that actin polymerization is strongly correlated with the changes in the distribution of ordered domains. The distribution of the TCR in resting cells and its colocalization with actin filaments is cell cycle dependent. We conclude that actin filament attachment to the plasma membrane, which is regulated via PI(4,5)P2, plays a crucial role in the formation of ordered domains. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 4: Manuscript.</p>

No description available.

The group theory allows one to study different branches of physics using the same set of commutation relations. It is shown that a formulation of the polarization optics that depends on the representations of the Lorentz group is possible. The set of four Stokes parameters, which is a standard tool of polarization optics, can be used to form a four-vector that is physically unrelated but mathematically equivalent to the space-time four-vector of the special relativity. By using the Stokes parameters, it is also possible to generate four-by-four matrix representations of the ordinary optical filters that are traditionally represented with the two-by-two Jones matrices. These four-by-four matrices are treated as the entities of the Lorentz group. They are like the Lorentz transformations applicable to the four-dimensional polarization space. Besides, optical decoherence process can be formulated within the framework of the SO(3,2) de Sitter group. The connection between the classical and quantum mechanical descriptions of the polarization of light allows the extension of the Stokes parameters to the quantum domain. In this respect, the properties of the polarization of the two-photon system can also be studied within the framework of the Lorentz group.

The aim of this thesis is to analyse migration and socio-economic differentiation in rural and urban spaces: where people move, what the characteristics of migrants are and whether experiences of rural and urban space affect attitudes toward the local living environment and place attachment. The background consists of five themes discussing different aspects of socio-economic differentiation and selective migration, for example polarization and rural gentrification. Integrated in the five themes are summaries of the four papers. The first paper, The divided city? Socio-economic changes in Stockholm metropolitan area, 1970-1994, analyses the income distribution in the Stockholm metropolitan area using residential area statistics regarding income among residents. The results show that polarization and segregation has increased during the study period. The second paper, The attraction of the rural: Characteristics of rural migrants, analyses the socio-economic and demographic characteristics of migrants to the countryside in Sweden using individual register data. The results show that urban areas attract the young, the highly educated and those with high income while rural areas attract older migrants, the self employed and families, but when comparing rural areas, periurban countrysides were more attractive to those with high income and education than more remote areas.  The third paper, Rural gentrification as a migration process: Evidence from Sweden, focuses on rural gentrification as a migration process and is based on an analysis of register data. The results show that rural gentrification in the remote countrysides of Sweden is of marginal importance. In the fourth paper, Place attachment and attitudes among young adults in rural/urban spaces, young adults’ (25-40 years of age) attitudes toward the rural/urban qualities of their local living environment and their place attachments are investigated using a survey. The results show that most people appreciate the environment they live in and they are also attached to this place. However, urban residents with a rural background seem less pleased with and are less attached to their present environment. In conclusion, migration selectivity works to reinforce both patterns of segregation and patterns of ageing. There is indication of both demographic and socio-economic polarization between and within rural and urban areas and this polarization is reinforced by selective migration flows. However, the results also indicate that rural areas are attractive living environments to many, particularly the periurban countryside and that there may be a rural migration potential among urban residents with a rural background.

The abscence of the brazilian artist Tarsila do Amaral (1886–1973) in the general art history is investigated, using the colonial structure as a starting point. In South America she is regarded as one of the greatest artists in modern time, in the rest of the world she is more or less unknown. The conclusion is that the colonial mechanisms are still in progress in our assumed postcolonial world, and has excluded Tarsila do Amaral, and the anthropophagic movement she was a part of, from the art history. The study points out the importance of looking into this neglected artist and the historic event. Not only to add it to the history of art, but also to show how anthropophagy as an artistic strategy created in the 1920’s Brazil is as relevant today as it was then. Three oil paintings of Tarsila do Amaral is used to describe the artistic strategy that solved the problem of beeing shaped as a mirror image to the western world. The paintings A Negra, Abaporu and Antropofagia tells us the story of how the Brazilian people started to see themselves as culturaly independent from Europe. Neither as something opposite nor similiar, but as something between. Anthropophagy is challenging our notion of ”us” and ”them” as well as centre and periphery – and is therefor useful in the writing of art history. Its not only important to make room for Tarsila do Amaral in the history of art – its also urgent to let her contribution be a part of the present art world.

The focus of this thesis is the improvement of acquisition and processing of Mueller matrix polarimetry using a confocal scanning laser ophthalmoscope (CSLO) and the application of Mueller matrix polarimetry to image the retina. Stepper motors were incorporated into a CSLO to semi-automate Mueller matrix polarimetry and were used in retinal image acquisition. Success rates of Fourier transform based edge detection filters, designed to improve the registration of retinal images, were compared. The acquired polarimetry images were used to reassess 2 image quality enhancement techniques, Mueller matrix reconstruction (MMR) and Stokes vector reconstruction (SVR), focusing on the role of auto-contrasting or normalization within the techniques and the degree to which auto-contrasting or normalization is responsible for image quality improvement of the resulting images. Mueller matrix polarimetry was also applied to find the retardance image of a malaria infected retinal blood vessel imaged in a confocal scanning laser microscope (CSLM) to visualize hemozoin within the vessel. Image quality enhancement techniques were also applied and image quality improvement was quantified for this blood vessel. The semi-automation of Mueller matrix polarimetry yielded a significant reduction in experimental acquisition time (80%) and a non-significant reduction in registration time (44%). A larger sample size would give higher power and this result might become significant. The reduction in registration time was most likely due to less movement of the eye, particularly in terms of decreased rotation seen between registered images. Fourier transform edge detection methods increased the success rate of registration from 73.9% to 92.3%. Assessment of the 2 MMR images (max entropy and max signal-to-noise ratio (SNR)) showed that comparison to the best CSLO images (not auto-contrasted) yielded significant average image quality improvements of 158% and 4% when quantified with entropy and SNR, respectively. When compared to best auto-contrasted CSLO images, significant image quality improvements were 11% and 5% for entropy and SNR, respectively. Images constructed from auto-contrasted input images were of significantly higher quality than images reconstructed from original images. Of the 2 other images assessed (modified degree of polarization (DOPM) and the first element of the Stokes vector (S0)), DOPM and S0 yielded significant average image quality improvements quantified by entropy except for the DOPM image of the RNFL. SNR was not improved significantly when either SVR image was compared to the best CSLO images. Compared to the best auto-contrasted CSLO images, neither DOPM nor S0 improved average image quality significantly. This result might change with a larger number of participants. When MMR were applied to images of malaria infected retinal slides, image quality was improved by 19.7% and 15.3% in terms of entropy and SNR, respectively, when compared to the best CSLO image. The DOPM image yielded image quality improvements of 8.6% and -24.3% and the S0 image gave improvements of 9.5% and 9.4% in entropy and SNR, respectively. Although percent increase in image quality was reduced when images were compared to initial auto-contrasted CSLO images, the final image quality was improved when auto-contrasting occurred prior to polarimetry calculations for max SNR and max entropy images. Quantitative values of retardance could not be found due to physical constraints in the CSLM that did not allow for characterization of its polarization properties and vibrational noise. Mueller matrix polarimetry used to find the retardance image of a malaria infected retina sample did yield visualization of hemozoin within the vessel but only qualitatively. In conclusion, improvements in the acquisition and registration of CSLO images were successful in leading to considerably shorter experimentation and processing times. In terms of polarimetric image quality improvement techniques, when compared to the best CSLO image. A large proportion of the improvement was in fact due to partially or completely stretching the pixel values across the dynamic range of the images within the algorithm of each technique. However, in general the image quality was still improved by the Mueller matrix reconstruction techniques using both entropy and SNR to generate the CSLO retinal images and the CSLM imaged malaria infected sample. In the malaria sample, retinal blood vessel visualization was also qualitatively improved. The images yielded from Mueller matrix polarimetry applied to a malaria infected retinal sample localized hemozoin within the blood vessel, but a quantitative image of the phase retardance could not be achieved.