[pt] A grande demanda por visualização através de imagens aliada ao caracter não invasivo das medidas de campo magnético motiva o desenvolvimento de ferramentas para o processamento de sinais em biomagnetismo. A técnica de filtragem inversa no domínio da freqüência, utilizada para restauração de imagens óticas, foi aplicada para se obter, a partir do campo magnético medido, uma imagem de sua fonte. Diversas simulações com distribuições de momentos magnéticos foram realizadas para se avaliar a qualidade da recuperação em presença de ruído. A técnica foi também aplicada em medidas experimentais obtidas com um mangnetômetro supercondutor. / [en] The great demand for images and the non-invasive character of the magnetic field measurements encourage the development of tools for signal processing in biomagnetism. The inverse filtering in the frequency domain technique often used in optical image restoration was applied to obtain an image of the source of magnetic field from its measured magnetic signal. Many simulations with two-dimensional magnetic moment distribution were carried out to determine the quality of the recovery in the presence of noise. The algorithm was also used with experimental data from measurement made with a super conducting magnetometer.

The evolution of protoplanetary disks is believed to be driven largely by angular momentum transport resulting from magnetized disk winds and turbulent viscosity. The ionization of the disk that is essential for these processes has been thought to be due to host star coronal X-rays but could also arise from energetic particles produced by coronal flares, or traveling shock waves, and advected by the stellar wind. We have performed test-particle numerical simulations of energetic protons propagating into a realistic T. Tauri stellar wind, including a superposed small-scale magnetostatic turbulence. The isotropic (Kolmogorov power spectrum) turbulent component is synthesized along the individual particle trajectories. We have investigated the energy range [0.1-10] GeV, consistent with expectations from Chandra X-ray observations of large flares on T. Tauri stars and recent indications by the Herschel Space Observatory of a significant contribution of energetic particles to the disk ionization of young stars. In contrast with a previous theoretical study finding a dominance of energetic particles over X-rays in the ionization throughout the disk, we find that the disk ionization is likely dominated by X-rays over much of its area, except within narrow regions where particles are channeled onto the disk by the strongly tangled and turbulent magnetic field. The radial thickness of such regions is 5 stellar radii close to the star and broadens with increasing radial distance. This likely continues out to large distances from the star (10 au or greater), where particles can be copiously advected and diffused by the turbulent wind.

Abstract The Earth’s magnetic field (MF) has been used for navigation for centuries. Man-made metallic structures, such as steel reinforcements in buildings, cause local distortions to the Earth’s magnetic field. Up until the recent decade, these distortions have been mostly considered as a source of error in indoor localization, as they interfere with the compass direction. However, as the distortions are temporally stable and spatially distinctive, they provide a unique magnetic landscape that can be used for constructing a map for indoor localization purposes, as noted by recent research in the field. Most approaches rely on manually collecting the magnetic field map, a process that can be both tedious and error-prone. In this thesis, the map is collected by a robotic platform with minimal sensor equipment. It is shown that a mere magnetometer along with odometric information suffices to construct the map via a simultaneous localization and mapping (SLAM) procedure that builds on the Rao-Blackwellized particle filter as means for recursive Bayesian estimation. Furthermore, the maps are shown to achieve decimeter level localization accuracy that combined with the extremely low-cost hardware requirements makes the presented methods very lucrative for domestic robots. In addition, general auxiliary methods for effective sampling and dealing with uncertainties are presented. Although the methods presented here are devised in mobile robotics context, most of them are also applicable to mobile device-based localization, for example, with little modifications. Magnetic field localization offers a promising alternative to WiFi-based methods for achieving GPS-level localization indoors. This is motivated by the rapidly growing indoor location market. / Tiivistelmä Maan magneettikenttään perustuvat kompassit ovat ohjanneet merenkäyntiä vuosisatojen ajan. Rakennusten metallirakenteet aiheuttavat paikallisia häiriöitä tähän magneettikenttään, minkä vuoksi kompasseja on pidetty epäluotettavina sisätiloissa. Vasta viimeisen vuosikymmenen aikana on huomattu, että koska nämä häiriöt ovat ajallisesti pysyviä ja paikallisesti hyvin erottelevia, niistä voidaan muodostaa jokaiselle rakennukselle yksilöllinen häiriöihin perustuva magneettinen kartta, jota voidaan käyttää sisätiloissa paikantamiseen. Suurin osa tämänhetkisistä magneettikarttojen sovelluksista perustuu kartan käsin keräämiseen, mikä on sekä työlästä että tarjoaa mahdollisuuden inhimillisiin virheisiin. Tämä väitöstutkimus tarttuu ongelmaan laittamalla robotin hoitamaan kartoitustyön ja näyttää, että robotti pystyy itsenäisesti keräämään magneettisen kartan hyödyntäen pelkästään magnetometriä ja renkaiden antamia matkalukemia. Ratkaisu perustuu faktoroituun partikkelisuodattimeen (RBPF), joka approksimoi täsmällistä rekursiivista bayesilaista ratkaisua. Robotin keräämien karttojen tarkkuus mahdollistaa paikannuksen n. 10 senttimetrin tarkkuudella. Vähäisten sensori- ja muiden vaatimusten takia menetelmä soveltuu erityisen hyvin koti- ja parvirobotiikkaan, joissa hinta on usein ratkaiseva tekijä. Tutkimuksessa esitellään lisäksi uusia apumenetelmiä tehokkaaseen näytteistykseen ja epävarmuuden hallintaan. Näiden käyttöala ei rajoitu pelkästään magneettipaikannukseen- ja kartoitukseen. Robotiikan sovellusten lisäksi tutkimusta motivoi voimakkaasti kasvava tarve älylaitteissa toimivalle sisätilapaikannukselle. Tämä avaa uusia mahdollisuuksia paikannukselle ympäristöissä, joissa GPS ei perinteisesti toimi.

As a solution to mid-air haptic actuation with strong and continuous tactile force, Magnetic Rendering is presented as an intuitive haptic display method applying an electromagnet array to produce a magnetic field in mid-air where the force field can be felt as magnetic repulsive force exerted on the hand through the attached magnet discs. The magnetic field is generated by a specifically designed electromagnet array driven by direct current. By attaching small magnet discs on the hand, the tactile sensation can be perceived by the user. This method can provide a strong tactile force on multiple points covering user’s hand and avoid cumbersome attachments with wires, thus it is suitable for a co-located visual and haptic display. In my work, the detailed design of the electromagnet array for haptic rendering purposes is introduced, which is modelled and tested using Finite Element Method simulations. The model is characterized mathematically, and three methods for controlling the magnetic field are applied accordingly: direct control, system identification and adaptive control. The performance of the simulated model is evaluated in terms of magnetic field distribution, force strength, operation distance and force stiffness. The control algorithms are implemented and tested on a 3-by-3 and a 15-by-15 model, respectively. Simulations are performed on a 15-by-15 model to generate a haptic human face, which results in a smooth force field and accurate force exertion on the control points.

De nos jours, la manipulation d’objets à l’aide du champ magnétique se trouve au cœur de nombreuses innovations en nanotechnologies. D’autre part, et du fait de sa capacité d’actionner à très petite échelle, l’utilisation du champ magnétique en biologie et en médecine est en plein essor. En outre, les grandes avancées en matière de fabrication de micro-sources magnétiques ont permis la synthèse d’aimants de tailles micrométriques intégrables dans des microsystèmes microfluidiques comme les laboratoires sur puce, très à la mode à l’heure actuelle. Bien que la séparation de cellules marquées magnétiquement, à l’aide d’un macro-aimant permanent ou d’électroaimant est une tâche aujourd’hui bien maitrisée, le gradient de champ généré par ces sources magnétiques reste insuffisant pour l’isolement de cellules marquées avec une très faible quantité de nanoparticules magnétiques. La réduction de la taille des aimants, évoquée dans cette thèse, constitue une alternative prometteuse, permettant la génération d’énormes gradients de champ magnétique à l’échelle micrométrique. L’objectif de ce travail est donc d’étudier l’attraction de cellules faiblement marquées magnétiquement, sur des réseaux de micro-aimants permanents micro-structurés, dans le but de concevoir un dispositif microfluidique original intégrant des micro-sources magnétiques permanentes, autonomes et passives. / Nowadays, the magnetic field applications at the microscopic scale have been described by an increasing attention as magnetic sources. Moreover, they can be integrated directly in the microchip. Nevertheless, the process of manipulating magnetic micro objects remains a challenge since the generation of magnetic fields and field gradients is strong enough. Previous research has reported the use of microelectromagnets to create magnetic field gradients in order to manipulate biological objects. However, the use of permanent magnetic microstructures permits to avoid Joule heating issues inherent to the electromagnets. In addition, no energy source is required. The aim of this thesis is to study the influence of physico-chemical characteristics of iron oxide nanoparticles on the rate of endocytosis, using an array of micro-magnets. Most probably, the applications of this reserach can be directly related to the gene therapy and can occur in most basic genetic studies. Another part of this work consists of combining microfluidic and magnetic forces in order to develop a cell sorting micro-systems that can be integrated in lab-on-chip or MEMS.

Silicon monoxide maser emission has been detected in many evolved stars in circumstellar envelopes in different vibrationally-excited rotational transitions. It is considered a good tracer to study the dynamics in a region close to the photosphere of the star. We present multi-epoch, total intensity, high-resolution images of 43 GHz, v=1, J=1-0 SiO maser emission toward the Mira variable R Cas. In total we have 23 epochs of data for R Cas at approximate monthly intervals over an optical pulsation phase range of φ = 0.158 to φ = 1.782. These maps show a ring-like distribution of the maser features in a shell, which is assumed to be centred on the star at average radius of 1.6 → 2.3 times the radius of star, R⋆. It is clear from these images that the maser emission is significantly extended around the star. At some epochs a faint outer arc can be seen at about 4 R⋆. The intensity of the emission waxes and wanes during the stellar phase. Some maser features are seen infalling as well as outflowing. We have made initial comparisons of our data with models by Gray et al. (2009). We have investigated the polarization morphology by mapping the linear and circular polarization of SiO masers in the v=1, J=1-0 transition. We found that some of the polarization vectors are either tangential or radial, which indicate a bimodal structure of the linear polarization morphology. Other angles can be seen as well. This is consistent with a radial, stellar-centred magnetic field in the SiO maser shell. We found in some isolated features the fractional linear polarization exceeds 100%. In other features, the polarization angle abruptly flips by 90◦. We found that our data are in the regime that the Zeeman splitting rate g is much greater than the stimulated emission rate R which in turn is greater than the decay rate , which indicates that the solution of Goldreich et al. (1973) can be applied.

Recentemente, uma implementação de um conjunto universal de portas lógicas de um e dois qubits para computação quântica usando estados de spin de pontos quânticos de um único elétron foi proposta. Estes resultados nos motivaram a desenvolver um estudo teórico formal do correspondente modelo de dois spins colocados em um campo magnético externo e acoplados por uma interação mútua de Heisenberg dependente do tempo. Nós então consideramos a assim chamada equação de dois spins, a qual descreve sistemas quânticos de quatro níveis de energia. Uma útil propriedade dessa equação é que o correspondente problema para o caso de campos magnéticos externos paralelos pode ser reduzido ao problema de um único spin em um campo externo efetivo. Isso nos permite gerar uma série de soluções exatas para a equação de dois spins a partir de soluções exatas já conhecidas da equação de um spin. Com base neste fato, nós construímos e apresentamos neste estudo uma lista de novas soluções exatas para a equação de dois spins para diferentes configurações de campos externos e de interação entre as partículas. Utilizando algumas destas soluções obtidas, estudamos a dinâmica da entropia de emaranhamento dos respectivos sistemas considerando diferentes estados de spins inicialmente separáveis. / Recently, an implementation of a universal set of one- and two-qubit logic gates for quantum computing using spin states of single-electron quantum dots was proposed. These results motivated us to develop a formal theoretical study of the corresponding model of two spins placed in an external magnetic field and coupled by a time-dependent mutual interaction of Heisenberg. We then consider the so-called two-spin equation, which describes four-level quantum systems. A useful property of this equation is that the corresponding problem for the case of parallel external magnetic fields can be reduced to the problem of a single spin in an effective external field. This allows us to generate a series of exact solutions for the two-spin equation from the already known exact solutions of the one-spin equation. Based on this fact, we construct and present in this study a list of new exact solutions for the two-spin equation for different configurations of external fields and interaction between particles. Using some of these solutions obtained, we study the dynamics of the entropy of entanglement of the respective systems considering different initially separable spins states.

Over the last two decades, electron tomography, the combination of tomographic methods and transmission electron microscopy (TEM), has considerably contributed to provide new insights into the three-dimensional structure of nanoscale materials. In particular, emerging advances in nanoscience are inevitably linked to developments in quantitative two-dimensional (2D) and three-dimensional (3D) TEM characterization techniques. In many cases, ET is employed to reconstruct the 3D shape (faceting of crystals) and the distribution or the arrangement (assembly) of nanoparticles down to the nanometer and atomic scale. Moreover, it is used to reconstruct the full 3D morphology of complex nanomaterials and composites, which can be evaluated further as a basis for quantitative modelling of physical properties. Beyond these capabilities, ET reveals the 3D chemical composition of nanostructures by combining it with spectroscopic methods, such as, electron energy-loss spectroscopy (EELS) and energy-dispersive X-ray spectroscopy (EDS). In specific cases, ET applied together with electron holography enables reconstructing electrostatic potentials in 3D, for example space-charge related diffusion potentials at pn-junctions in semiconductors. In ferromagnetic materials, this approach also allows for the 3D reconstruction of the internal remanent magnetic induction (B-field).

Supraleitung in Graphit ist kein neues Thema. Dieser Effekt wurde bereits in den 1960er Jahren in Interkalationsverbindungen von Graphit gefunden. Die Supraleitung in reinem Graphit wurde bereits vor etwa 50 Jahren beschrieben. Kürzlich wurden in zweischichtigem Graphen, in dem die Graphenschichten um einen 'magischen' Winkeln um die c Achse verdreht wurden, flache Bänder in der elektronischen Bandstruktur nachgewiesen, welche mit der Entstehung von Supraleitung zusammenhängen. Wir haben die elektrischen Transporteigenschaften in Graphitproben mit unterschiedlichen Elektrodenkonfigurationen untersucht. Wir haben den elektrischen Widerstand von hochgeordnetem natürlichem und synthetischem Graphit mit Elektroden auf der Oberseite der ab Basalebene und auch parallel zur c Achse mit hoher Präzision gemessen und den Einfluss der hochleitenden Stapelfehler untersucht, an denen, eingebettet zwischen den kristallinen Graphitschichten, 2D-Grenzflächen entstehen, die ebenfalls flache Bänder aufweisen. Die Existenz einer gut geordneten rhomboedrischen Graphitphase in allen gemessenen Proben wurde durch Röntgenbeugungsmessungen nachgewiesen. Die Grenzflächen mit der hexagonalen Phase stellen laut theoretischer Vorhersagen einen möglichen Ursprung für die Hochtemperatursupraleitung dar. Die experimentellen Ergebnisse liefern eindeutige Beweise für körnige Supraleitung in diesen Materialien, z. B. einen schrittweisen Temperaturübergang bei ~ 350 K, magnetische Irreversibilität, Zeitabhängigkeit nach einer Feldänderung, die mit dem eingeschlossenen Fluss und Flusskriechen übereinstimmt, und den teilweise abgestoßenen magnetischen Fluss, welcher in Magnetisierungsmessungen beobchtet werden kann. Die Lokalisierung der körnigen Supraleitung an diesen 2D-Grenzflächen verhindert die Beobachtung widerstandsfreier elektrischer Ströme oder eines vollständigen Meißner-Zustands. Der Grund ist, dass die körnige Supraleitung in abgegrenzten Regionen an den Grenzflächen entsteht, welche in eine Multigraphen-Halbleitermatrix eingebettet sind. In dieser Arbeit wird eine detaillierte Untersuchung des Magnetowiderstands in verschiedenen Arten von Graphitproben bei niedrigen und hoch gepulsten Magnetfeldern vorgestellt. / Superconductivity in graphite is not a new topic. Its existence goes back to the 1960s when this effect was found in intercalation compounds of graphite. Superconductivity in pure graphite was reported already around 50 years ago and recently proved in bi-layer graphene, related to 'magic' angles between the graphene layers, twisted around the c axis, with the electronic band structure exhibiting flat bands. We have studied electrical transport properties in graphite samples with different electrode configurations. Measuring with high precision, the electrical resistance of highly ordered natural and synthetic graphite, with electrodes placed on the top of the ab basal plane, and also parallel to the c axis, we investigated the influence of the highly conducting stacking faults, referred as 2D interfaces, embedded between the crystalline regions of graphite, which also exhibit flat bands. The existence of well ordered rhombohedral graphite phase in all measured samples has been proved by x-ray diffraction measurements, suggesting its interfaces with the hexagonal phase as a possible origin of high-temperature superconductivity, predicted by theoretical studies. The results provide clear evidence of granular superconductivity, e.g., a step-like transition in temperature at ~ 350 K, magnetic irreversibility, time dependence after a field change, consistent with trapped flux and flux creep, and the partial magnetic flux expulsion from magnetization measurements. The localization of the granular superconductivity at these 2D interfaces prevents the observation of a zero resistance state or a full Meissner state. The reason is that the superconducting distribution is a mixture of superconducting patches at the interfaces, and they are embedded in a multigraphene semiconducting matrix. A detailed study of the magnetoresistance in different kinds of graphite samples at low and high-pulsed magnetic fields is presented in this work.

High Efficiency Multistage Plasma Thrusters (HEMPTs) are a relatively new form of electric propulsion that show promise for use on a variety of missions and have several advantages over their older EP competitors. One such advantage is their long predicted lifetime and minimal wall erosion due to a unique periodic permanent magnet system. A laboratory HEMPT was built and donated by JPL for testing at Cal Poly. Previous work was done to characterize the performance of this thruster and it was found to exhibit a large plume divergence, resulting in decreased thrust and specific impulse. This thesis explores the design and application of a magnetic shield to modify the thruster’s magnetic field to force more ion current towards the centerline. A previous Cal Poly thesis explored the same concept, and that work is continued and furthered here. The previous thesis tested a shield which increased centerline current but decreased performance. A new shield design which should avoid this performance decrease is studied here. Magnetic modelling of the thruster was performed using COMSOL. This model was verified using guassmeters to measure the field strength at many discrete points within and near the HEMPT, with a focus on the ionization channel and exit plane. A shield design which should significantly reduce the radial field strength at the exit plane without affecting the ionization channel field was modelled and implemented. The HEMPT was tested in a vacuum chamber with and without the shield to characterize any change to performance characteristics. Data were collected using a nude Faraday probe and retarding potential analyzer. The data show a significant increase in centerline current with the application of the shield, but due to RPA malfunction and thruster failure the actual change in performance could not be concluded. The unshielded HEMPT was characterized, however, and was found to produce 12.1 +/- 1.3 mN of thrust with a specific impulse of 1361 +/- 147s. The thruster operated with a total efficiency of 10.63 +/- 3.66%, an efficiency much lower than expected. A large contributor to this low efficiency is likely the use of argon in place of xenon. Its lower mass and higher ionization energy make it a less efficient propellant choice. Further, the thruster is prone to overheating, indicating that significant thermal losses are present in this design.