O presente trabalho realiza a investigação de interações hiperfinas em amostras de silício monocristalino através da técnica de Correlação Angular γ-γ Perturbada (CAP), baseada em interações hiperfinas. Para a realização das medidas, utilizou-se núcleos de prova radioativos de 111In -> 111Cd que decaem através da cascata gama 177-245keV com nível intermediário de 245keV (I = 5+/2 , Q = 0.83b, T1/2 = 84.5ns). As amostras foram confeccionadas utilizando vários métodos de inserção de núcleos de prova, possibilitando maior compreensão acerca dos impactos gerados por cada um destes métodos nas medidas CAP. As técnicas de implantação iônica, difusão e evaporação foram cuidadosamente investigadas ressaltando-se suas particularidades. Realizou-se então, um estudo acerca das concentrações de defeitos intrínsecos em função de vários processos de tratamento térmico. Finalmente, foi feita uma análise comparativa para os vários métodos de inserção dos núcleos de prova. Realizou-se, também, medidas CAP em silício monocristalino dopado com fósforo através do processo NTD. A altíssima uniformidade de dopagem associada a este método aliada à inexistência de medidas para este tipo de material ressaltam a relevância dos resultados obtidos. Estes resultados são então comparados com os resultados da literatura para amostras dopadas através de métodos convencionais apresentando-se as respectivas conclusões. / In the present work, a microscopic investigation of hyperfine interactions in single crystal silicon samples was carried out by means of Perturbed Angular γ-γ Correlation technique (PAC), which is based in hyperfine interactions. In order to achieve these measurements, it was used 111In ->111Cd radioactive probe nuclei, which decay through the well known γ cascade 177-245keV with an intermediate level of 245keV (I = 5+/2 , Q = 0.83b , T1/2 = 84.5ns). The samples were prepared using diferent probe nuclei insertion methods, making possible to increase our understanding on the impact generated by each of these techniques in PAC measurements. Ion implantation, difusion and evaporation were carefully investigated giving emphasis on its characteristics and particularities. Then, it was made a study about the concentration of intrinsic defects as function of several annealing processes. Finally, a comparative analysis was made for all these probe nuclei insertion methods. This work also accomplished PAC measurements in single crystal silicon doped with phosphorus by means of NTD method, carried out in a research nuclear reactor. The extremely high doping uniformity allied to the non-existence of previous measurements in these materials emphasize the importance of the results obtained. These results are then compared with literature results for samples doped by conventional methods presenting the respective conclusions.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O estudo de discos magnéticos com a configuração de vórtices magnéticos tem atraído grande interesse científico recentemente. Nessa estrutura os spins formam circuitos fechados no plano e, próximo ao centro do disco, se alinham perpendicularmente ao plano de forma a reduzir a densidade de energia de troca. O grande potencial de aplicação de vórtices magnéticos como, por exemplo, em memórias magnéticas e nanopartículas para o tratamento de câncer, chama a atenção para a investigação das condições de estabilidade e o controle de suas propriedades. Neste trabalho, estudamos a alteração que dois tipos diferentes de anisotropia provocam nas propriedades de vórtices através de medidas de Microscopia de Força Magnética (MFM) e simulações micromagnéticas utilizando o código OOMMF (NIST) que aplica a equação de Landau-Lifshitz-Gilbert para simular a configuração de spin e calcular a energia e a magnetização de microestruturas. A primeira parte do trabalho envolveu o estudo da influência da anisotropia magnetocristalina planar na estabilidade de vórtices magnéticos em discos de Co60Fe40 em relação a discos de permalloy, que possui anisotropia magnetocristalina nula. Os resultados de simulação micromagnética para discos com diâmetros entre 0,5 e 8 m mostraram que a anisotropia favorece o alinhamento dos spins e a divisão da estrutura em domínios, reduzindo a estabilidade do vórtice. Os resultados foram comprovados experimentalmente em medidas de MFM de discos de Co60Fe40 com diâmetros entre 2 e 8 m. Na segunda parte do trabalho foi estudada a influência do fenômeno de exchange bias na dinâmica de vórtices magnéticos. Para isso foram realizadas simulações de discos de Permalloy/Fe50Mn50 com diâmetro de 0,5 m variando o acoplamento magnético entre as camadas. As simulações de curvas de histerese mostraram que o acoplamento aumenta a estabilidade dos vórtices. Nas simulações de relaxação foi observado que devido ao exchange bias o movimento girotrópico do núcleo apresenta uma frequência variável que aumenta com o tempo, o que não acontece na ausência de exchange bias. Já nas simulações em que os discos estão sujeitos a um campo magnético girante foi observado que a velocidade crítica em que a polaridade do vórtice é invertida aumenta com o aumento do acoplamento e com o aumento da frequência do campo. Essa velocidade pode ser escolhida em uma ampla faixa escolhendo os valores do acoplamento magnético e da frequência de oscilação. Portanto é possível controlar a velocidade crítica de inversão da polaridade de vórtices magnéticos através do fenômeno de exchange bias. / The study of magnetic dots with magnetic vortex spin configuration has recently attracted great scientific interest. In this structure, the spins form closed circuits in the plane of the magnetic dot and, near the center, align perpendicularly to the plane in order to reduce exchange energy density. The great potential of applications of magnetic vortices (as for example magnetic memories and nanoparticles for cancer treatment) draws attention for the investigation of the stability conditions for the vortex configuration. In the case of soft ferromagnetic materials in micron and submicron scales, small changes in shape, size and materials anisotropy can modify the energy equilibrium. In this work, we studied the change of vortex proprieties in microsized dots due to two different types of anisotropy using the code OOMMF (NIST) that applies the Landau-Lifshitz-Gilbert equation to simulate the spin configuration and compute the energy and magnetization of microstructures. These results were compared to Magnetic Force Microscopy (MFM) investigations of the magnetic configuration in microsized dots prepared by lithographic process. In the first part, we studied by numerical simulation the influence of planar magnetocrystaline anisotropy in Co60Fe40 disks and compare to permalloy disks, material that shows zero magnetocrystalline anisotropy. The results for disks with diameters between 0.5 and 8 m showed that the anisotropy favors spins alignment and domains division, reducing vortex stability. The results for Co60Fe40 disks with diameters between 2 and 8 m were verify experimentally by MFM measurements. In the second part, we studied the influence of exchange bias in the magnetic vortex dynamics. A series of micromagnetic simulations for Permalloy/Fe50Mn50 disks with 0.5 m of diameter was done varying the magnetic coupling constant between the layers. The hysteresis simulations showed that the vortex stability increases with the coupling constant. In relaxation simulations we observed that the gyrotropic movement has a variable frequency that increases with time, which is not observed when exchange bias is absent. Under a rotating magnetic field, the critical velocity for vortex polarity reversion increases with the coupling constant and frequency. Our results show that the critical velocity can be adjusted in a wide range by selecting the magnetic coupling constant and the oscillating frequency, i.e., it is possible to control the critical velocity for vortex polarity inversion through the exchange bias coupling.

The detection and location of faults on power transmission lines is essential to the protection and maintenance of a power system. Most methods of fault detection and location rely on measurements of electrical quantities provided by current and voltage transformers. These transformers can be expensive and require physical contact with the monitored high voltage equipment. In this work, current transformers were replaced by magnetic field sensing coils. Such coils can be located remotely from substations and switching stations and do not require physical contact with the conductors. Rather than observing each individual conductor, the use of the magnetic field sensors allows the monitoring of the transmission line condition using a collective quantity. This study explores the use of the magnetic field sensors as an alternative measurement device for fault detection and location.

Loggerhead sea turtles nest on either the Atlantic or Gulf coast of Florida. The hatchlings from these nests migrate offshore in opposite directions. The purpose of my study was to determine if Gulf coast hatchlings use magnetic maps, as Atlantic coast hatchlings do, both to locate areas favorable for survival in the Gulf of Mexico and to orient appropriately within surface currents that could transport them into the Atlantic Ocean. To find out, I presented Gulf coast hatchlings with magnetic fields corresponding to different locations inside the Gulf, and within currents leading into (Florida Straits) and within (Gulf Stream) the western portion of the Atlantic Ocean. I conclude that Gulf coast hatchlings (i) use a high resolution magnetic map for navigation within the Gulf of Mexico, (ii) initially remain within the eastern Gulf, but later may (iii) gain entry into currents that transport them into Atlantic waters. / by Maria W. Merrill. / Thesis (M.S.)--Florida Atlantic University, 2010. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2010. Mode of access: World Wide Web.

Today, cancer is the world’s deadliest disease. Despite significant progress to find a cure, especially over the last decade, with immunotherapy rapidly becoming the state of the art, major open questions remain. Each successful therapy is not only limited to a few cancers but also has relatively low specificity to target cancer cells; although cancer cells can indeed be eradicated, many normal cells are sacrificed as collateral damage. To fill this gap, we have developed a class of multiferroic nanostructures known as magnetoelectric nanoparticles (MENs) that can be used to enable externally controlled high-specificity targeted delivery and release of therapeutic drugs on demand. First, the underlying physics of MENs was studied, as it relates to different externally applied sequences of a.c and d.c. magnetic fields to facilitate (i) high-specificity targeting driven by a physical force rather than antibody matching, (ii) a delivery mechanism that enhances cellular uptake (via nanoelectroporation) of therapeutic drugs across the cellular membrane of cancer cells only, and (iii) an externally controlled mechanism that releases the therapeutic drug on-demand. Secondly, the application of MENs as a nuclear magnetic resonance (NMR) nanoprobe was explored. The intrinsically coupled ferromagnetic and ferroelectric phases allowes the nanoparticle to be used as sensitive nanoprobe detectors of biological cells; based on the knowledge that the cellular membrane is an electrically charged medium which creates an ideal environment for MENs to distinguish between cancer and normal cells. Lastly, through in-vivo and in-vitro studies, MENs were used as drug delivery vehicle capable of crossing the blood brain barrier (BBB) and delivering recently discovered MIA690 peptide drug (via nanoelectroporation) to glioblastoma multiforme (GBM) brain cancer cells. Glioblastomas are tumors that arise from astrocytes in the brain; that are highly malignant and reproduces quickly due to their large network of blood vessels. In the following study, we report the binding efficacy of MIA690 to magnetoelecric nanoparticles as well as present an unprecedented targeted and on-demand release to glioblastoma cells through special sequences of a.c. and d.c. magnetic fields. The potential therapeutic and diagnostic impact of MENs for future medicine is beyond the scope of this study, as MENs can be used to treat any type of cancer.

<p>We present an investigation of the magnetic field geometries and inhomogeneous distribution of chemical elements in the atmospheres of peculiar A and B stars. Our study combines high-quality spectroscopic and spectropolarimetric stellar observations with the development and application of novel techniques for theoretical interpretation of the shapes and variability of stellar line profiles. In particular, we extend the method of Doppler imaging to the analysis of spectra in the four Stokes parameters, making it possible to derive detailed and reliable stellar magnetic maps simultaneously with the imaging chemical inhomogeneities.</p><p>The magnetic Doppler imaging is applied to study of magnetic topologies and distributions of chemical elements in the peculiar stars α² CVn and 53 Cam. We found that the magnetic field geometry of 53 Cam is considerably more complex than a low-order multipolar topology, commonly assumed for magnetic A and B stars. Our Doppler imaging analysis also led to a discovery and study of spots of enhanced mercury abundance in the atmosphere of α And, a star where the presence of a global magnetic field is unlikely.</p><p>The ESO 3.6-m telescope is used to collect unique, very high spectral- and time-resolution observations of rapidly oscillating peculiar A (roAp) stars and to reveal line profile variations due to stellar pulsations. We present a detailed characterization of the spectroscopic pulsational behaviour and demonstrate a remarkable diversity of pulsations in different spectral lines. The outstanding variability of the lines of rare-earth elements is used to study propagation of pulsation waves through the stellar atmospheres and identify pulsation modes. This analysis led to a discovery of a non-axisymmetric character of pulsations in roAp stars.</p><p>Our study of chemical stratification in the atmosphere of the roAp star γ Equ provides a compelling evidence for significant variation of the chemical composition with depth. We find a combined effect of extreme chemical anomalies and a growth of pulsation amplitude in the outermost atmospheric layers to be the most likely origin of the high-amplitude pulsational variations of the lines of rare-earth elements.</p><p>Observations of cool magnetic CP stars are obtained with the ESO Very Large Telescope and are used for empirical investigation of the anomalies in the atmospheric temperature structure. We show that the core-wing anomaly of the hydrogen Balmer lines observed in some cool CP stars can be attributed to a hot layer at an intermediate atmospheric depth.</p>

Stellare Magnetfelder spielen eine wichtige Rolle bei der Entstehung und Entwicklung von Sternen. Leider entziehen sie sich aber, aufgrund ihrer großen Entfernung zur Erde, einer direkten Beobachtung. Dies gilt zumindest für derzeitige und in naher Zukunft zur Verfügung stehende Instrumente. Um aber beispielsweise zu verstehen, ob Magnetfelder durch einen Dynamoprozess generiert werden oder Überbleibsel der Sternentstehung sind, ist es zwingend erforderlich, die Oberflächenstruktur und die zeitliche Entwicklung von stellaren Feldern zu untersuchen. Glücklicherweise haben wir mit der Dopplerverschiebung sowie der Polarisation von Licht Mittel zur Verfügung, um indirekt die Magnetfeldtopologie entfernter Sternen zu rekonstruieren, wenn auch nur die schnell rotierender. Die auf den beiden genannten Effekten basierende Rekonstruktionsmethode ist unter dem Namen Zeeman-Doppler Imaging (ZDI) bekannt. Sie stellt eine leistungsfähige Methode dar, um aus rotationsverbreiterten Stokes Profilen schnell rotierender Sterne Oberflächenkartierungen der Temperatur und Magnetfeldverteilung zu erstellen. Durch das ZDI konnten in den vergangenen Jahren die Magnetfeldverteilungen zahlreicher Sterne rekonstruiert werden. Diese Methode stellt allerdings sehr hohe Anforderungen sowohl an die Instrumentierung als auch an die Rechenleistung und ist deshalb häufig mit zahlreichen Annahmen und Näherungen verbunden. Ziel dieser Arbeit war es, Methoden für ein ZDI zu entwickeln, das darauf ausgelegt ist, zeitaufgelöste spektropolarimetrische Daten von aktiven späten Sternen zu invertieren. Es sollte also insbesondere den komplexen und lokalen Magnetfeldstrukturen dieser Sterne Rechnung getragen werden. Um die Orientierung und Stärke solcher Felder zuverlässig rekonstruieren zu können, sollte die Inversion im Stande sein, alle vier Stokes-Komponenten einzubeziehen. Ferner war vorgesehen auf vollständigen polarisierten Strahlungstransportmodellierungen aufzubauen. Dies ermöglicht eine simultane und selbstkonsistente Temperatur- und Magnetfeld-Inversion, die damit dem komplexen Zusammenspiel zwischen Temperatur und Magnetfeld gerecht wird. Schließlich sollte die Anwendung eines neu zu entwickelnden ZDI Programms auf Stokes I und V Beobachtungen von II Pegasi (kurz: II Peg) erste Magnefeldkarten dieses sehr aktiven Sterns liefern. Um den hohen Rechenaufwand, der mit der Inversionsmethode einhergeht, besser bewältigen zu können, wurde zunächst eine schnelle Approximationsmethode für den polarisierten Strahlungstransport entwickelt. Sie basiert auf einer Hauptkomponentenanalyse (PCA) sowie auf künstlichen Neuronalen Netzen. Letztere approximieren den funktionalen Zusammenhang zwischen atmosphärischen Parametern und den zugehörigen lokalen Stokes Profilen. Inverse Probleme sind potentiell schlecht gestellt und erfordern in der Regel eine Regularisierung. Der entwickelte Ansatz verwendet eine lokale Entropie, die auf die Besonderheiten bei der Rekonstruktion lokalisierter Magnetfeder eingeht. Ein weiterer neuartiger Ansatz befasst sich mit der Rauschreduktion polarimetrischer Beobachtungsdaten. Er macht sich die Hauptkomponentenanalyse zu Nutze, um mit Hilfe einer Vielzahl beobachteter Spektrallinien, einzelne Linien mit drastisch vergrößertem Signal-zu-Rausch-Verhältnis wieder zu geben. Diese Methode hat gegenüber anderen Multi-Spektrallinien-Verfahren den Vorteil, nach wie vor eine Inversion auf der Basis einzelner Spektrallinien durchführen zu können. Schließlich wurde das Inversionsprogramm iMap entwickelt, das die zuvor genannten Methoden implementiert. Detaillierte Testrechnungen demonstrieren die Funktionsfähigkeit und Genauigkeit der schnellen Synthese-Methode und weisen einen Zeitgewinn von nahezu drei Größenordnungen gegenüber der konventionellen Strahlungstransportberechnung auf. Desweiteren untersuchen wir den Einfluss der verschiedenen Stokes Komponenten (IV bzw. IVQU) auf die Zuverlässigkeit, ein bekanntes Magnetfeld zu rekonstruieren. Damit belegen wir die Zuverlässigkeit unseres Inversionsprogrammes und zeigen darüber hinaus auch Einschränkungen von Magnetfeldinversionen im allgemeinen auf. Eine erste Inversion von Stokes I und V Profilen von II Peg liefert zum ersten Mal für diesen Stern simultan Temperatur- und Magnetfeldverteilungen. / Stellar magnetic fields, as a crucial component of star formation and evolution, evade direct observation at least with current and near future instruments. However investigating whether magnetic fields are generated by a dynamo process or represent relics from the formation process, or whether they show a behavior similar to the sun or something very different, it is essential to investigate their structure and temporal evolution. Fortunately nature provides us with the possibility to indirectly observe surface topologies on distant stars by means of Doppler shift and polarization of light, though not without its challenges. Based on the mentioned effects, the so called Zeeman-Doppler Imaging technique is a powerful method to retrieve magnetic fields from rapid rotating stars based on measurements of spectropolarimetric observations in terms of Stokes profiles. In recent years, a large number of stellar magnetic field distributions could be reconstructed by Zeeman-Doppler Imaging (ZDI). However, the implementation of this method often relies on many approximations because, as an inversion method, it entails enormous computational requirements. The aim of this thesis is to develop methods for a ZDI, designed to invert time-resolved spectropolarimetric data of active late type stars, and to account for the expected complex and small scale magnetic fields on these stars. In order to reliably reconstruct the detailed field orientation and strength, the inversion method is employed to be able to use of all four Stokes components. Furthermore it is based on fully polarized radiative transfer calculations to account for the intricate interplay between temperature and magnetic field. Finally, the application of a newly developed ZDI code to Stokes I and V observations of II Pegasi (short: II Peg) was supposed to deliver the first magnetic surface maps for this highly active star. To accomplish the high computational burden of a radiative transfer based ZDI, we developed a novel approximation method to speed up the inversion process. It is based on Principal Component Analysis and Artificial Neural Networks. The latter approximate the functional mapping between atmospheric parameters and the corresponding local Stokes profiles. Inverse problems, as we are dealing with, are potentially ill-posed and require a regularization method. We propose a new regularization scheme, which implements a local entropy function that accounts for the peculiarities of the reconstruction of localized magnetic fields. To deal with the relatively large noise that is always present in polarimetric data, we developed a multi-line denoising technique based on Principal Component Analysis. In contrast to other multi-line techniques that extract from a large number of spectral lines a sort of mean profile, this method allows to extract individual spectral lines and thus allows for an inversion on the basis of specific lines. All these methods are incorporated in our newly developed ZDI code iMap, which is based on a conjugated gradient method. An in depth validation of our new synthesis method demonstrates the reliability and accuracy of this approach as well as a gain in computation time by almost three orders of magnitude relative to the conventional radiative transfer calculations. We investigated the influence of the different Stokes components (IV / IVQU) on the ability to reconstruct a known synthetic field configuration. In doing so we validate the capability of our inversion code, and we also assess limitations of magnetic field inversions in general. In a first application to II Peg, a K2 IV subgiant, we derived temperature and magnetic field surface distributions from spectropolarimetric data obtained in 2004 and 2007. It gives for the first time simultaneously the temporal evolution of the surface temperature and magnetic field distribution on II Peg.

Microfabricated solid-state surfaces, also called atom chip', have become a well-established technique to trap and manipulate atoms. This has simplified applications in atom interferometry, quantum information processing, and studies of many-body systems. Magnetic trapping potentials with arbitrary geommetries are generated with atom chip by miniaturized current-carrying conductors integrated on a solid substrate. Atoms can be trapped and cooled to microKelvin and even nanoKelvin temperatures in such microchip trap. However, cold atoms can be significantly perturbed by the chip surface, typically held at room temperature. The magnetic field fluctuations generated by thermal currents in the chip elements may induce spin flips of atoms and result in loss, heating and decoherence. In this thesis, we extend previous work on spin flip rates induced by magnetic noise and consider the more complex geometries that are typically encountered in atom chips: layered structures and metallic wires of finite cross-section. We also discuss a few aspects of atom chips traps built with superconducting structures that have been suggested as a means to suppress magnetic field fluctuations. The thesis describes calculations of spin flip rates based on magnetic Green functions that are computed analytically and numerically. For a chip with a top metallic layer, the magnetic noise depends essentially on the thickness of that layer, as long as the layers below have a much smaller conductivity. Based on this result, scaling laws for loss rates above a thin metallic layer are derived. A good agreement with experiments is obtained in the regime where the atom-surface distance is comparable to the skin depth of metal. Since in the experiments, metallic layers are always etched to separate wires carrying different currents, the impact of the finite lateral wire size on the magnetic noise has been taken into account. The local spectrum of the magnetic field near a metallic microstructure has been investigated numerically with the help of boundary integral equations. The magnetic noise significantly depends on polarizations above flat wires with finite lateral width, in stark contrast to an infinitely wide wire. Correlations between multiple wires are also taken into account. In the last part, superconducting atom chips are considered. Magnetic traps generated by superconducting wires in the Meissner state and the mixed state are studied analytically by a conformal mapping method and also numerically. The properties of the traps created by superconducting wires are investigated and compared to normal conducting wires: they behave qualitatively quite similar and open a route to further trap miniaturization, due to the advantage of low magnetic noise. We discuss critical currents and fields for several geometries. / Mikrotechnologische Oberflächen, sogenannte Atomchips, sind eine etablierte Methode zum Speichern und Manipulieren von Atomen geworden. Das hat Anwendungen in der Atom-Interferometrie, Quanteninformationsverarbeitung und Vielteilchensystemen vereinfacht. Magnetische Fallenpotentiale mit beliebigen Geometrien werden durch Atomchips mit miniaturisierten stromführenden Leiterbahnen auf einer Festkörperunterlage realisiert. Atome können bei Temperaturen im $mu$ K oder sogar nK-Bereich in einer solchen Falle gespeichert und gekühlt werden. Allerdings können kalte Atome signifikant durch die Chip-Oberfläche gestört werden, die sich typischerweise auf Raumtemperatur befindet. Die durch thermische Ströme im Chip erzeugten magnetischen Feldfluktuationen können Spin-Flips der Atome induzieren und Verlust, Erwärmung und Dekohärenz zur Folge haben. In dieser Dissertation erweitern wir frühere Arbeiten über durch magnetisches Rauschen induzierte Spin-Flip-Ratenund betrachten kompliziertere Geometrien, wie sie typischerweise auf einem Atom-Chip anzutreffen sind: Geschichtete Strukturen und metallische Leitungen mit endlichem Querschnitt. Wir diskutieren auch einige Aspekte von Aomchips aus Supraleitenden Strukturen die als Mittel zur Unterdrückung magnetischer Feldfluktuationen vorgeschlagen wurden. Die Arbeit beschreibt analytische und numerische Rechnungen von Spin-Flip Raten auf Grundlage magnetischer Greensfunktionen. Für einen Chip mit einem metallischen Top-Layer hängt das magnetische Rauschen hauptsächlich von der Dicke des Layers ab, solange die unteren Layer eine deutlich kleinere Leitfähigkeit haben. Auf Grundlage dieses Ergebnisses werden Skalengesetze für Verlustraten über einem dünnen metallischen Leiter hergeleitet. Eine gute Übereinstimmung mit Experimenten wird in dem Bereich erreicht, wo der Abstand zwischen Atom und Oberfläche in der Größenordnung der Eindringtiefe des Metalls ist. Da in Experimenten metallische Layer immer geätzt werden, um verschiedene stromleitende Bahnen vonenander zu trennen, wurde der Einfluß eines endlichen Querschnittsauf das magnetische Rauschen berücksichtigt. Das lokale Spektrum des magnetischen Feldes in der Nähe einer metallischen Mikrostruktur wurde mit Hilfe von Randintegralen numerisch untersucht. Das magnetische Rauschen hängt signifikant von der Polarisierung über flachen Leiterbahnen mit endlichem Querschnitt ab, im Unterschied zu einem unendlich breiten Leiter. Es wurden auch Korrelationen zwischen mehreren Leitern berücksichtigt. Im letzten Teil werden supraleitende Atomchips betrachtet. Magnetische Fallen, die von supraleitenden Bahnen im Meissner Zustand und im gemischten Zustand sind werden analytisch durch die Methode der konformen Abbildung und numerisch untersucht. Die Eigenschaften der durch supraleitende Bahnen erzeugten Fallen werden erforscht und mit normal leitenden verglichen: Sie verhalten sich qualitativ sehr ähnlich und öffnen einen Weg zur weiteren Miniaturisierung von Fallen, wegen dem Vorteil von geringem magnetischem Rauschen. Wir diskutieren kritische Ströme und Felder für einige Geometrien.

We present an investigation of the magnetic field geometries and inhomogeneous distribution of chemical elements in the atmospheres of peculiar A and B stars. Our study combines high-quality spectroscopic and spectropolarimetric stellar observations with the development and application of novel techniques for theoretical interpretation of the shapes and variability of stellar line profiles. In particular, we extend the method of Doppler imaging to the analysis of spectra in the four Stokes parameters, making it possible to derive detailed and reliable stellar magnetic maps simultaneously with the imaging chemical inhomogeneities. The magnetic Doppler imaging is applied to study of magnetic topologies and distributions of chemical elements in the peculiar stars α2 CVn and 53 Cam. We found that the magnetic field geometry of 53 Cam is considerably more complex than a low-order multipolar topology, commonly assumed for magnetic A and B stars. Our Doppler imaging analysis also led to a discovery and study of spots of enhanced mercury abundance in the atmosphere of α And, a star where the presence of a global magnetic field is unlikely. The ESO 3.6-m telescope is used to collect unique, very high spectral- and time-resolution observations of rapidly oscillating peculiar A (roAp) stars and to reveal line profile variations due to stellar pulsations. We present a detailed characterization of the spectroscopic pulsational behaviour and demonstrate a remarkable diversity of pulsations in different spectral lines. The outstanding variability of the lines of rare-earth elements is used to study propagation of pulsation waves through the stellar atmospheres and identify pulsation modes. This analysis led to a discovery of a non-axisymmetric character of pulsations in roAp stars. Our study of chemical stratification in the atmosphere of the roAp star γ Equ provides a compelling evidence for significant variation of the chemical composition with depth. We find a combined effect of extreme chemical anomalies and a growth of pulsation amplitude in the outermost atmospheric layers to be the most likely origin of the high-amplitude pulsational variations of the lines of rare-earth elements. Observations of cool magnetic CP stars are obtained with the ESO Very Large Telescope and are used for empirical investigation of the anomalies in the atmospheric temperature structure. We show that the core-wing anomaly of the hydrogen Balmer lines observed in some cool CP stars can be attributed to a hot layer at an intermediate atmospheric depth.

No description available.