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Miller, Kenneth Elric. "The star thrust experiment, rotating magnetic field current drive in the field reversed configuration /." Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/9996.
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Peter, Andrew Maxwell. "Paramagnetic spin-up of a field reversed configuration with rotating magnetic field current drive /." Thesis, Connect to this title online; UW restricted, 2003. http://hdl.handle.net/1773/9983.
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Simm, Anthony. "Quantitative interpretation of magnetic field measurements in eddy current defect detection." Thesis, University of Newcastle Upon Tyne, 2013. http://hdl.handle.net/10443/1809.
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For many years, the theoretical and experimental study of eddy current non-destructive evaluation (NDE) has been conducted separately, as most models were not suited to practical industrial applications. The aim of this work is to bridge this gap by investigating the relationship between magnetic fields and defects using both modelling and experimental study and to link these results to quantitative NDE. In this work, 3D FEM numerical simulations are used to predict the response of an eddy current probe being scanned over the area of a defect and understand the underlying change in magnetic field due to the presence of the defect. Experimental investigations are performed to study the feasibility of the proposed magnetic field measurement techniques for defect detection. This experimental work investigates the inspection of both surface and subsurface defects, the use of rectangular (directional) probes and the measurement of complex magnetic field values, as the response in these cases has been found to have a greater correlation with the shape of the defect being studied. As well as the detection of defects, both frequency spectrum and transient information from pulsed eddy current responses are used to reconstruct the profile (depth and width) of a slot shaped defect. The work concludes that the use of magnetic field measurements provides useful information for defect detection and quantification. This will have applications in both industrial and research areas, including visualisation of defects from magnetic field measurements, which can be applied to the monitoring of safety critical components.
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Kurpad, Krishna Nagaraj. "Transmit field pattern control for high field magnetic resonance imaging with integrated RF current sources." Texas A&M University, 2004. http://hdl.handle.net/1969.1/2755.
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The primary design criterion for RF transmit coils for MRI is uniform transverse magnetic (B1) field. Currently, most high frequency transmit coils are designed as periodic, symmetric structures that are resonant at the imaging frequency, as determined by the static magnetic (B0) field strength. These coils are excited by one or more voltage sources. The distribution of currents on the coil elements or rungs is determined by the symmetry of the coil structure. At field strengths of 3T and above, electric properties such as the dielectric constant and conductivity of the load lead to B1 field inhomogeneity due to wavelength effects and perturbation of the coil current distribution from the ideal. The B1 field homogeneity under such conditions may be optimized by adjusting the amplitudes and phases of the currents on the rungs. However, such adjustments require independent control of current amplitudes and phases on each rung of the resonant coil. Due to both the strong coupling among the rungs of a resonant coil and the sensitivity to loading, such independent control would not be possible and B1 homogeneity optimization would involve a time consuming and impractical iterative procedure in the absence of exact knowledge of interactions among coil elements and between the coil and load.
This dissertation is based on the work done towards the design and development of a RF current source that drives high amplitude RF current through an integrated array element. The arrangement is referred to as a current element. Independent control of current amplitude and phase on the current elements is demonstrated. A non-resonant coil structure consisting of current elements is implemented and B1 field pattern control is demonstrated. It is therefore demonstrated that this technology would enable effective B1 field optimization in the presence of lossy dielectric loads at high field strengths.
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Bai, Kun. "Direct field-feedback control for permanent magnet spherical motors." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/50141.
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There are emerging requirements for high accuracy multi-DOF actuators in numerous applications. As one of the novel motors capable of multi-DOF manipulation, permanent magnet spherical motors (PMSMs) that can provide continuous and dexterous motion in one joint have been widely studied for their advantages in structure and energy efficiency. The demands to bring forward the performance of PMSMs for precision applications have motivated this thesis to develop a closed-loop orientation control system with high accuracy and bandwidth. Unlike traditional control methods for PMSMs, which rely on explicit orientation feedback, a new control method (referred to here as direct field-feedback control or in short DFC) directly utilizing the magnetic fields for feedback have been developed in this thesis. Because magnetic field measurements are almost instantaneous and the need for real-time orientation estimation is eliminated in DFC, the system sampling time is greatly reduced. Meanwhile, several field-based methods have been developed for the major components in the DFC system and each component can be processed independently and concurrently with the magnetic field measurements. The parallel computation further improves the system bandwidth and also reduces accumulated error. The DFC system has been experimentally implemented and evaluated. The results show excellent control performances in terms of accuracy and bandwidth. To facilitate the design and analysis of the DFC system, several new algorithms have been developed, which include the modeling and computing of magnetic fields as well as forces and torques, an analysis of bijective relationship between orientation and magnetic fields, and a method for calibration and reconstruction of the rotor magnetic field in 3 dimensional space. These algorithms not only enable the implementation of the DFC system for a PMSM, but also benefit the PMSM studies in design, modeling and field-based sensing. While the immediate outcome of this research is a control system for PMSMs, this new control method can be applied to a broad spectrum of electromagnetic motion systems.
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Laestadius, Andre. "Foundation of Density Functionals in the Presence of Magnetic Field." Doctoral thesis, KTH, Matematik (Avd.), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-145546.
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This thesis contains four articles related to mathematical aspects of Density Functional Theory. In Paper A, the theoretical justification of density methods formulated with current densities is addressed. It is shown that the set of ground-states is determined by the ensemble-representable particle and paramagnetic current density. Furthermore, it is demonstrated that the Schrödinger equation with a magnetic field is not uniquely determined by its ground-state solution. Thus, a wavefunction may be the ground-state of two different Hamiltonians, where the Hamiltonians differ by more than a gauge transformation. This implies that the particle and paramagnetic current density do not determine the potentials of the system and, consequently, no Hohenberg-Kohn theorem exists for Current Density Functional Theory formulated with the paramagnetic current density. On the other hand, by instead using the particle density as data, we show that the scalar potential in the system's Hamiltonian is determined for a fixed magnetic field. This means that the Hohenberg-Kohn theorem continues to hold in the presence of a magnetic field, if the magnetic field has been fixed. Paper B deals with N-representable density functionals that also depend on the paramagnetic current density. Here the Levy-Lieb density functional is generalized to include the paramagnetic current density. It is shown that a wavefunction exists that minimizes the "free" Hamiltonian subject to the constraints that the particle and paramagnetic current density are held fixed. Furthermore, a convex and universal current density functional is introduced and shown to equal the convex envelope of the generalized Levy-Lieb density functional. Since this functional is convex, the problem of finding the particle and paramagnetic current density that minimize the energy is related to a set of Euler-Lagrange equations. In Paper C, an N-representable Kohn-Sham approach is developed that also include the paramagnetic current density. It is demonstrated that a wavefunction exists that minimizes the kinetic energy subject to the constraint that only determinant wavefunctions are considered, as well as that the particle and paramagnetic current density are held fixed. Using this result, it is then shown that the ground-state energy can be obtained by minimizing an energy functional over all determinant wavefunctions that have finite kinetic energy. Moreover, the minimum is achieved and this determinant wavefunction gives the ground-state particle and paramagnetic current density. Lastly, Paper D addresses the issue of a Hohenberg-Kohn variational principle for Current Density Functional Theory formulated with the total current density. Under the assumption that a Hohenberg-Kohn theorem exists formulated with the total current density, it is shown that the map from particle and total current density to the vector potential enters explicitly in the energy functional to be minimized. Thus, no variational principle as that of Hohenberg and Kohn exists for density methods formulated with the total current density.<br><p>QC 20140523</p>
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Guldemir, Hanifi. "Prediction of induction motor line current spectra from design data." Thesis, University of Nottingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287180.
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Zhang, Yanjing. "Electric and magnetic contributions and defect interactions in remote field eddy current techniques." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq22507.pdf.
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Kato, K., T. Noda, H. Shimizu, T. Matsumura, and N. Murayama. "Increase in transient resistance of Bi2223 superconducting bulk by applying external magnetic field." IEEE, 2001. http://hdl.handle.net/2237/6784.
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Hasanyan, Jalil Davresh. "Modeling and Analysis of a Moving Conductive String in a Magnetic Field." Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/87530.
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A wide range of physical systems are modeled as axially moving strings; such examples are belts, tapes, wires and fibers with applied electromagnetic fields. In this study, we propose a model that describes the motion of a current-carrying conductive string in a lateral magnetic field, while it is being pulled axially. This model is a generalization of past studies that have neglected one or more properties featured in our system. It is assumed that the string is moving with a constant velocity between two rings that are a finite distance apart. Directions of the magnetic field and the motion of the string coincide. The problem is first considered in a static setting. Stability critical values of the magnetic field, pulling speed, and current are shown to exist when the uniform motion (along a string line) of the string buckles into spiral forms. In the dynamic setting, conditions for stability of certain solutions are presented and discussed. It is shown that there is a divergence between the critical values in the linear dynamic and static cases. Furthermore, traveling wave solutions are examined for certain cases of our general system. We develop an approximate solution for a nonlinear moving string when a periodic nonstationary current flows through the string. Domains of
parameters are defined when the string falls into a pre-chaotic state, i.e., the frequency of vibrations is doubled.<br>MS
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Sohlström, Hans. "Fibre Optic Magnetic Field Sensors Utilizing Iron Garnet Materials." Doctoral thesis, KTH, Signaler, sensorer och system, 1993. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-48332.
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This thesis deals with the subject of fibre optic magnetic field sensors utilizing iron garnet materials. Such materials exhibit a large Faraday rotation which make them advantageous for application in compact magnetic field sensors. After an introduction, in which fibre optic sensors and optical methods to measure electric current are reviewed, the original research work is summarized. A system for the measurement of the magneto-optic properties of transparent materials is described. Measurement results, showing the influence of temperature, magnetic field direction and sample treatment on the magneto-optical properties of YIG-crystals, are presented. The properties of thin magneto-optical waveguiding films have also been studied using different light coupling methods. Measurement results obtained for holographic grating, prism and edge (end-fire) light coupling to different substituted YIG films are presented. It is shown that the launching method may affect the properties to be measured. The design and performance of several versions of extrinsic guided wave fibre optic magnetic field sensors are then reported. The sensors employ substituted YIG (Yttrium Iron Garnet, Y3Fe5O12) thin film waveguides as sensing elements. Polarization maintaining fibres were used as feed and return to provide two signal channels. The signals were combined in a balanced measurement system, providing insensitivity to both fluctuations in optical power and loss. Sensors have been made both with separate fibres to guide the light to and from the sensing element and with a single fibre for both functions. The two fibre version, although less ”elegant”, is found to have a better performance. This version also makes it possible to determine both the magnitude and sign of the magnetic field. Measurement results indicate a usable measurement range of at least several mT with a noise equivalent magnetic field level of less than 8 nT/root(Hz). The design and performance of multimode fibre optic magnetic field sensors utilizing the Faraday effect in an epitaxially grown thick (YbTbBi)IG film is also described. This type of sensor is found to be linear over a range from 27 mT to less than 270 nT. Sensor prototypes suitable for current monitoring in high voltage transmission lines have also been developed.<br>QC 20111209<br>YIG
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Wong, Lam Chuen. "The spin polarization of current passing through a double level quantum dot under magnetic field /." View abstract or full-text, 2005. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202005%20WONG.
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Grimes, David. "Two methods of modelling electric current systems by analysis of magnetic field data, with particular reference to the quasi-dc magnetic field of the human leg." Thesis, Open University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329113.
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Reidler, Jay S. "Modulation of Pain with Transcranial Direct Current Stimulation and Diffuse Noxious Inhibitory Controls." Thesis, Harvard University, 2014. http://etds.lib.harvard.edu/hms/admin/view/48.
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Background: While pain is essential for physiological functioning, chronic or pathologic pain is responsible for a major burden of disease in society. Novel approaches to treating acute and chronic pain have employed neuromodulatory tools to target the central and peripheral neural structures that mediate pain. Transcranial direct current stimulation (tDCS), for example, is a safe, non-invasive brain stimulation technique that has been shown in preliminary studies to reduce chronic pain when applied to the primary motor cortex. In contrast to this exogenous neuromodulatory approach, diffuse noxious inhibitory controls (DNIC) refers to endogenous pain regulatory mechanisms that decrease pain following introduction of heterotopic noxious stimuli. This thesis explores whether combining these exogenous and endogenous pain modulation approaches synergistically increases the threshold at which pain is perceived.
Methods: We conducted a double-blinded, randomized, placebo-controlled trial with a crossover design to investigate the effects of tDCS and DNIC on pain thresholds in 15 healthy human subjects. Pain thresholds were assessed prior to and following administration of active tDCS, sham tDCS, cold-water-induced DNIC, and combined active tDCS and DNIC. Using magnetic resonance spectroscopy, we examined whether baseline concentrations of brain metabolites such as N-acetylaspartate in pain-related regions of interest were associated with responses to the varying neuromodulatory conditions.
Results: Pain thresholds significantly increased following both active tDCS and the DNIC paradigm. These modulatory approaches appeared to have additive effects when combined. Pain threshold increases after active tDCS were positively correlated with baseline levels of N-acetylaspartate, a marker of good neural function, in the anterior cingulate cortex and negatively correlated with baseline levels of glutamine in the thalamus.
Conclusions: Combining endogenous pain regulatory mechanisms with exogenous stimulation of the motor cortex can more effectively increase pain thresholds in healthy humans. Future studies should examine whether existing pain therapies may be enhanced with noninvasive brain stimulation and activation of DNIC. They should also assess whether brain metabolite levels can be utilized to predict clinical response to therapeutic interventions.
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Ai, Yong-le. "Novel direct field and torque control of six-phase induction machine with special phase current waveform." Thesis, Link to the online version, 2006. http://hdl.handle.net/10019/489.
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Kurth, Fritz. "High Magnetic Field Properties of Fe-pnictide Thin Films." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-189964.
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The recent discovery of high-temperature superconductivity in Fe-based materials triggered worldwide efforts to investigate their fundamental properties. Despite a lot of similarities to cuprates and MgB2, important differences like near isotropic behaviour in contrast to cuprates and the peculiar pairing symmetry of the order parameter (OP) have been reported. The OP symmetry of Fe-based superconductors (FBS) was theoretically predicted to be of so-called s± state prior to various experimental works. Still, most of the experimental results favour the s± scenario; however, definitive evidence has not yet been reported. Although no clear understanding of the superconducting mechanisms yet exists, potential applications such as high-field magnets and Josephson devices have been explored. Indeed, a lot of reports about FBS tapes, wires, and even SQUIDs have been published to this date. In this thesis, the feasibility of high-field magnet applications of FBS is addressed by studying their transport properties, involving doped BaFe2As2 (Ba-122) and LnFeAs(O,F) [Ln=Sm and Nd]. Particularly, it is important to study physical properties in a sample form (i.e. thin films) that is close to the conditions found in applications. However, the realisation of epitaxial FBS thin films is not an easy undertaking. Recent success in growing epitaxial FBS thin films opens a new avenue to delve into transport critical current measurements. The information obtained through this research will be useful for exploring high-field magnet applications. This thesis consists of 7 chapters: Chapter 1 describes the motivation of this study, the basic background of superconductivity, and a brief summary of the thin film growth of FBS. Chapter 2 describes experimental methods employed in this study. Chapter 3 reports on the fabrication of Co-doped Ba-122 thin films on various substrates. Particular emphasis lies on the discovery of fluoride substrates to be beneficial for epitaxy without compromising superconducting properties. It is worth mentioning, that a world record Tc of 28 K for Co-doped Ba-122 thin films is reported here. Chapter 4 describes high-field transport properties (up to dc 35 T) of epitaxial P-doped Ba-122 thin films prepared by MBE. Among the FBS, P-doped Ba-122 shows very high transport critical current densities, although the Tc is lower than for LnFeAs(O,F)[Ln=Sm and Nd]. Additionally, the film is microstructurally clean. These high Jc values are due to a high vortex line energy. Chapter 5 deals with transport properties of epitaxial SmFeAs(O,F) thin films. In the course of this work, a dc 45 T magnet has been used within collaboration with the National High Magnetic Field Laboratory at Tallahassee, FL, USA. SmFeAs(O,F) thin films have been prepared by molecular beam epitaxy (MBE). The investigated film shows a very high transport critical current density (Jc) of over 105 A/cm2 at 45T and 4.2K for both main crystallographic directions, which features favourable for high-field magnet applications. Additionally, by investigating the pinning properties, a dimensional crossover between the superconducting coherence length and the FeAs interlayer distance at 30-40K was observed. Chapter 6 reports on high-field transport properties of NdFeAs(O,F) thin films prepared by MBE. In this case, the transition from Abrikosov to Josephson vortices was observed around 20-30K. Additionally, the angular Jc data were scaled with the anisotropic GinzburgLandau approach. The obtained parameters at given temperature are observed to increase with decreasing temperature, which is different from Co-doped Ba-122. Chapter 7 summarises this work<br>Die kürzliche Entdeckung von Hochtemperatur-Supraleitung in Fe-basierten Materialien löste weltweite Bemühungen aus, deren grundlegende Eigenschaften zu untersuchen. Neben vielen Gemeinsamkeiten mit den Kupraten und MgB2 sind wichtige Unterschiede wie nahezu isotropes Verhalten (im Gegensatz zu den Kupraten) und eine auffällige Paarungssymmetrie des Ordnungsparameters (OP) berichtet worden. Die OP-Symmetrie der Fe-basierten Supraleiter (FBS) wurde theoretisch als s± berechnet, noch bevor experimentelle Versuche unternommen wurden. Derzeit favorisieren experimentelle Ergebnisse das s±-Szenario, dennoch gibt es noch keine definitiven Nachweise. Obwohl noch kein komplettes Verständnis des supraleitenden Mechanismus existiert, wurden schon potentielle Anwendungen wie Josephson-Elemente und Hochfeldmagnete erforscht. In der Tat erschienen zahlreiche Veröffentlichungen über supraleitende Kabel, Bänder und auch SQUIDs. Diese Arbeit befasst sich mit der Durchführbarkeit von Hochfeld-Anwendungen durch die Untersuchung der Transporteigenschaften von FBS, namentlich Ba-122 und LnFeAs(O,F)[Ln=Sm und Nd]. Es ist von großer Wichtigkeit, die physikalischen Eigenschaften in einer Probenform zu untersuchen, die der Form in Anwendungen nahekommt (z.B. Dünnschichten), um dieselben Rahmenbedingungen vorgeben zu können. Es ist jedoch nicht einfach, epitaktische FBS Dünnschichten zu realisieren. Kürzlich gewonnene Erkenntnisse in der Herstellung von epitaktischen FBS-Dünnschichten ermöglichen nun ein tieferes Eindringen in die Transporteigenschaften. Die in diesen Untersuchungen gewonnenen Informationen stellen somit wichtige Argumente in der Diskussion um Hochfeld Anwendungen dar. Diese Arbeit besteht aus sieben Kapiteln: Kapitel 1 beinhaltet die Motivation dieser Arbeit, die Grundlagen der Supraleitung und eine kurze Zusammenstellung der bisherigen Arbeiten zur Dünnschichtherstellung von FBS. Kapitel 2 beschreibt experimentelle Methoden, die im Zuge dieser Arbeit verwendet wurden. Kapitel 3 berichtet von der Herstellung Co-dotierter Ba-122 Dünnschichten (Co-Ba-122) auf verschiedenen Fluoridsubstraten. Dabei wurde Augenmerk darauf gelegt, neben einem verbesserten epitaktischen Wachstum der Dünnschichten die supraleitenden Eigenschaften nicht zu beeinträchtigen. Anzumerken ist, dass in diesem Rahmen Tc-Rekord-Werte von 28 K in Co-Ba-122 erzielt werden konnten. Kapitel 4 beschreibt die Hochfeld-Transporteigenschaften epitaktisch gewachsener P-dotierter Ba-122 Dünnschichten, die durch MBE hergestellt wurden. Unter den FBS zeigt P-dotiertes Ba-122 enorm hohe kritische Transport-Stromdichten, obwohl das Tc niedriger ist als bei LnFeAs(O,F)[Ln=Sm und Nd]. Der Grund dafür konnte in der hohen Flusslinienkern-Energie des P-dotierten Ba-122 ermittelt werden. Kapitel 5 behandelt Transporteigenschaften von epitaktisch gewachsenen SmFeAs(O,F)-Dünnschichten. In diesem Zusammenhang wurde ein dc-45 T-Hochfeldmagnet in Zusammenarbeit mit dem National High Magnetic Field Laboratory in Tallahassee, Florida, USA, genutzt. SmFeAs(O,F)-Dünnschichten wurden mit dem Molekularstrahl-Verfahren (MBE) hergestellt. Die Schichten zeigen sehr hohe kritische Transport-Stromdichten (Jc) von über 105 A/cm2 bei 45 T und 4.2 K für beide kristallographische Hauptrichtungen, parallel zur c-Achse und in der ab-Ebene. Diese Ergebnisse sehen sehr verheißungsvoll für eine Verwendung in Hochfeld-Anwendungen aus. Zusätzlich konnte durch die Untersuchung der Pinning-Eigenschaften ein Dimensionsübergang zwischen supraleitender Kohärenzlänge und FeAs-Ebenenabstand im Bereich 30-40 K beobachtet werden. Kapitel 6 berichtet über die Hochfeld-Transporteigenschaften von NdFeAs(O,F)-Dünnschichten, die mithilfe des MBE-Verfahrens hergestellt wurden. In diesem Falle konnte ein Ubergang von Abrikosov- zu Josephson-Flusslinien im Temperaturbereich 20-30 K beobachtet werden. Zusätzlich konnte die winkelabhängige kritische Stromdichte mit dem anisotropen Ginzburg-Landau-Ansatz skaliert werden. Die erhaltenen Parameter für verschiedene Temperaturen steigen mit fallender Temperatur. Dieses Verhalten ist gegensätzlich zu dem in Co-dotiertem Ba-122 gefundenen. Kapitel 7 gibt eine Zusammenfassung dieser Arbeit
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Jalali, Roya. "Investigating the neurobiological changes associated with cerebellar transcranial direct current stimulation (TDCS) using magnetic resonance imaging (MRI)." Thesis, University of Birmingham, 2017. http://etheses.bham.ac.uk//id/eprint/7661/.
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Anodal cerebellar transcranial direct current stimulation (tDCS) is known to enhance motor learning and it is suggested to hold promise as a therapeutic intervention. However, the neural mechanisms underpinning the effects of cerebellar tDCS are unknown. In addition, it is unclear whether this effect is robust across varying task parameters as if cerebellar tDCS is to be used clinically it must have a consistent effect across a relatively wide range of behaviours. Therefore, I performed four studies to address these questions. In the first three studies, I investigated the neural changes associated with cerebellar tDCS using magnetic resonance spectroscopy (MRS) and resting state functional magnetic resonance imaging (fMRI). My goal was to understand how cerebellar tDCS affected the metabolites within the cerebellum and functional connectivity between the cerebellum and distant brain areas. In addition, I wanted to understand if individual differences in how cerebellar tDCS influenced visuomotor adaptation could be explained by the effect tDCS had on neurobiology. Therefore, healthy participants underwent 3 sessions in which they received concurrent anodal cerebellar tDCS during visuomotor adaptation, MRS and resting state fMRI. I found that in 21% of participants cerebellar tDCS caused enhanced visuomotor adaptation, a decrease in GABA and increase in functional connectivity between the cerebellum and parietal cortex. This work suggests an ‘all-or-nothing’ type effect of cerebellar tDCS. In my final study, I examined the consistency of the cerebellar tDCS effect on visuomotor adaptation across a wide range of task parameters which were systematically varied. Each experiment examined whether cerebellar tDCS had a positive effect on adaptation when a unique feature of the task was altered. I found cerebellar tDCS to have an inconsistent effect on visuomotor adaptation. I conclude that such inconsistencies could be dependent on the amount of participants in each group that are receptive to cerebellar tDCS and suggest that at the very least it warrants substantially large sample size in cerebellar tDCS studies.
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Giersch, Louis Roy Miller. "Experimental investigation of plasma sail propulsion concepts using cascaded arcs and rotating magnetic field current drive /." Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/9958.
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Harle, Thomas. "Radio frequency plasma thrusters : performance evaluation of low magnetic field mode operation through direct thrust measurements." Thesis, University of Surrey, 2015. http://epubs.surrey.ac.uk/807990/.
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This thesis describes an experimental investigation into the performance of a radio frequency plasma thruster (RFPT). This type of thruster does not rely on the use of high voltage ion acceleration grids or beam neutralisers which are typically life limiting elements of an electric thruster. The RFPT excites an atomic or molecular gas into a plasma using an external RF antenna. This plasma is contained by a cylindrical dielectric source tube which is open at one end. An axial magnetic field is applied to the plasma using one or more solenoids or a permanent magnet source. The magnetic field is usually applied such that it is constant throughout the length of the source tube, after which the field diverges. The plasma couples with the imposed magnetic field, generating internal field structures, which can be used to regulate both the power coupling and the rate at which the plasma diffuses out of the source tube. In this study, the thruster performance is measured directly, thus providing missions designers with accurate performance data which can be used to assess applicability of the technology to future missions. A re-configurable lab prototype thruster was constructed and a pendulum type thrust balance was developed in order to make direct measurements of the thrust produced by the Surrey Space Centre (SSC) RFPT. The balance has been developed to allow mounting of the thruster together with the necessary RF and DC electrical feeds as well as the propellant feeds and incorporates sensors which allow measurements to be made in an RF plasma environment. A low magnetic field mode of RFPT operation was investigated in order to assess whether this mode of operation may be able to provide performance increases at reduced imposed magnetic fields (< 20 mT), which could enable the serious consideration of this technology for future flight opportunities. The lowered magnetic fields used here may reduce the risk of interference with spacecraft subsystems and perturbation to the spacecraft orbit, when compared to many of the proposed plasma thrusters which use fields in excess of 40 mT. Direct thrust measurements of an RFPT operating in a low field mode are presented as a function of the propellant flow, RF power and for two source tube lengths. The thrust is shown to peak at a field strength, B_0, which is demonstrated to vary with RF power and propellant flow. The peaks are also shown to correspond generally to peaks in the source plasma density, plasma potential and in some cases to exhaust ion beam current. Ion energy distribution function measurements show that strong beams are not present in thruster configurations which use a 170 mm length source tube but are shown to increase in strength when using a shorter 85 mm length tube. The low field mode is shown to generally provide performance increases over the non-magnetised case by a factor of 4. Low field mode thrust measurements using the shorter 85 mm source tube and matching double saddle antenna revealed enhanced peak performance gains over the 170 mm length case, resulting in an increase of the thrust efficiency by up to a factor of 15. The performance of the RFPT operating in this configuration is shown to produce enhanced or equivalent performance, when compared to similar state of the art configurations but at generally lower imposed magnetic fields. This particular optimisation may make possible a first flight opportunity for the RFPT as weak magnetic fields may be supplied easily by electromagnets. Electromagnets can be easily deactivated or field reversed to avoid interference with spacecraft subsystems and orbital parameters unlike permanent magnets which may be required to generate higher magnetic fields. Operation of the RFPT in the low field mode with an 85~mm source has also revealed new low field mode behaviour compared to the 170 mm case, producing sudden, large reductions in the performance of the thruster for imposed fields beyond B_0 which are shown to correspond to drops in source plasma density, plasma resistance and exhaust beam current.
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Matsumura, T., A. Kimura, H. Shimizu, Y. Yokomizu, and M. Goto. "Fundamental performance of flux-lock type fault current limiter with two air-core coils." IEEE, 2003. http://hdl.handle.net/2237/6786.
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Feredoes, Eva Psychiatry Faculty of Medicine UNSW. "Investigating the neural correlates of higher cognitive functions in humans using transcranial magnetic stimulation and transcranial direct current stimulation." Awarded by:University of New South Wales. Psychiatry, 2005. http://handle.unsw.edu.au/1959.4/23460.
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An important aspect of cognitive neuroscience is to localise specific brain regions involved in cognitive tasks, and to determine the mediating brain processes. There are several investigative approaches towards this, but amongst them, only transcranial magnetic stimulation (TMS) is able to interfere with the brain in such a way as to show the critical involvement of a brain region in a particular behaviour. TMS can be applied in normal subjects during the performance of a cognitive task and the resulting disruption of activity in the targeted brain region leads to an alteration in, or suspension of, behaviour consequent upon that brain activity. More recently, another brain stimulation technique has emerged that may also be able to contribute to the investigation of human cognition. Transcranial direct current stimulation (tDCS) applies a weak direct current to a targeted brain region, modulating cortical excitability and thereby altering the behavioural output. tDCS may be able to provide information that complements TMS and other investigative techniques by modulating behaviour in a way that depends on the role the brain region is carrying out in the task. This thesis describes a series of experiments in which TMS and tDCS were applied to two well-studied cognitive behaviours, working memory (WM) and mental rotation (MR). WM is the temporary retention of information that can be manipulated in order to guide behaviour. The most popular psychological model of WM proposes a multi-modal central executive (CE) that acts upon information stored in dedicated buffers (Baddeley, 1986). The dorsolateral prefrontal cortex (DLPFC) is a strong candidate as a key CE node (D'Esposito & Postle, 2000; Petrides, 2000b; Smith & Jonides, 1997; Stuss & Knight, 2002). MR is a visuo-cognitive process by which an image can be mentally modified into an orientation other than the one in which it is displayed (Corballis & McLaren, 1984). The area centred around the intraparietal sulcus is a brain key region for MR (Alivisatos & Petrides, 1996; Harris et al., 2000; Jordan et al., 2001). The work presented in this thesis examines the roles of the DLPFC and posterior parietal cortex (PPC) in WM and MR, respectively, and also highlights some of the methodological issues that are necessary to consider in order to produce reliable virtual lesions. The studies were carried out in young healthy volunteers, and were approved by the institutional ethics committee. In one study, repetitive TMS (rTMS) was shown to disrupt the manipulation of verbal information held in WM when administered over the right DLPFC, a result which supports a process-based segregation of the human prefrontal cortex for WM. Low- and high-frequency rTMS did not disrupt performance on another popular test of executive processing, n-back, a result which suggests that specific stimulation and task conditions must be met in order to produce virtual lesions, but also questions the critical importance of recruitment of the DLPFC for a running span task. rTMS applied to the right PPC replicated results from a previous TMS investigation, supporting the critical role this region in the rotation of images (Harris & Miniussi, 2003). When the left PPC was stimulated, impairment was produced only for the rotation of inverted stimuli. A role for the left PPC in the rotation of objects-as-a-whole is proposed based on these findings. The use of tDCS in the investigation of WM and MR is amongst the first to be described. Stimulation of the left DLPFC led to decreased performance accuracy on a verbal WM task in a polarity-specific manner. The pattern of results produced supports the role of the DLPFC as a node of a CE. tDCS over the left DLPFC did not modulate n-back task performance, a result which supports the TMS results that the involvement of the left DLPFC is not critical to the successful performance of the n-back task, although methodological issues remain of concern in relation to this conclusion. MR was not affected by tDCS applied to the right PPC and this result is most likely a direct demonstration of the importance of electrode montage. In conclusion, these studies show that rTMS and tDCS can be usefully applied to create virtual cortical lesions or modulate cortical excitability during the performance of cognitive tasks in humans, and can play an important role in investigating cognitive neuropsychological models. More widespread use of these techniques to complement lesion studies and functional neuroimaging is recommended.
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Ichino, Y., R. Honda, M. Miura, et al. "Microstructure and field angle dependence of critical current densities in REBa/sub 2/Cu/sub 3/O/sub y/ thin films prepared by PLD method." IEEE, 2005. http://hdl.handle.net/2237/6777.
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Matsumura, T., H. Shimizu, and Y. Yokomizu. "Design guideline of flux-lock type HTS fault current limiter for power system application." IEEE, 2001. http://hdl.handle.net/2237/6783.
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Vichare, Geeta. "Theoretical modelling of low latitude current system." Thesis, Indian Institute of Geomagnetism, Mumbai, 2001. http://localhost:8080/xmlui/handle/123456789/210.
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Sunwong, Prapaiwan. "Theoretical and experimental considerations of the critical current density of DI-BiSCCO superconducting tapes as a function of magnetic field, field orientation, temperature and strain." Thesis, Durham University, 2013. http://etheses.dur.ac.uk/8455/.
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The critical current density (Jc) of DI-BiSCCO superconducting tapes was measured as a function of magnetic field (B), field orientation (θ), temperature (T) and strain (e) in a 15 T split-pair horizontal superconducting magnet using probes designed and built in-house. Strain was applied to samples using a modified bending beam apparatus with a copper beryllium springboard-shaped sample holder, which is capable of applying uniaxial strains of -1.4% < e < 1.0%. The temperature of the sample was controlled with the use of an inverted insulating cup with a temperature stability of +/-80 mK to +/-200 mK. The vapour-cooled brass critical-current leads (incorporating high-temperature superconducting tapes) were optimised to minimise helium consumption. Optimisation includes consideration of the maximum safe temperature of the current leads and the effects of duty cycle and static helium boil-off. The optimised helium consumption of the leads is a factor of two lower than standard current leads optimised for magnets. Jc(B,T,θ,e) data of the DI-BiSCCO tapes were characterised based on the superconducting-normal-superconducting Josephson junction model where Jc is determined by flux flow along the grain boundaries (or the normal junctions). It was found that grain boundaries in the DI-BiSCCO tapes are thick (several tens of nanometre) and exhibit semiconducting behaviour. The degree of misalignment has been included into the anisotropy analysis of Jc and the correlation between the effective anisotropy and texturing of the sample obtained. Analysis of three different samples (Nb3Sn, YBCO and BiSCCO) is presented where the average local properties of the grain boundaries were extracted from magnetisation and the transport Jc data.
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Bodnar, Stanislav [Verfasser], and Martin [Akademischer Betreuer] Jourdan. "Manipulation of Néel vector in antiferromagnetic Mn2Au by electric current and magnetic field pulses. / Stanislav Bodnar ; Betreuer: Martin Jourdan." Mainz : Universitätsbibliothek der Johannes Gutenberg-Universität Mainz, 2020. http://d-nb.info/1227118910/34.
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Yilmaz, Ayhan Ozan. "Rf Coil System Design For Mri Applications In Inhomogeneous Main Magnetic Field." Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608477/index.pdf.
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In this study, RF coil geometries are designed for MRI applications using inhomogeneous main magnetic fields. The current density distributions that can produce the desired RF magnetic field characteristics are obtained on predefined cubic, cylindrical and planar surfaces and Tikhonov, CGLS, TSVD and Rutisbauer regularization methods are applied to match the desired and generated magnetic fields. The conductor paths, which can produce the current density distribution calculated for each surface selection and regularization technique, are determined using stream functions. The magnetic fields generated by the current distributions are calculated and the error percentages
between the desired and generated magnetic fields are found. Optimum conductor paths that are going to be produced on cubic, cylindrical and planar surfaces and the required regularization method are determined on the basis of error percentages and realizability of the conductor paths.
The optimum conductor path calculated for the planar coil is realized and in the measurement done by LakeShore 3-Channel Gaussmeter, an average error percentage of 11 is obtained between the theoretical and measured magnetic field. The inductance values of the realized RF coil are measured<br>the tuning and matching capacitance values are calculated and the frequency characteristics of the system is tested using Electronic Workbench 5.1. The quality factor value of the tested system is found to be 162.5, which corresponds to a bandwidth of 39,2 KHz at 6,387 MHz (operating frequency of METU MRI system).
The techniques suggested in this study can be used in order to design and realize RF coils on prede¯<br>ned arbitrary surfaces for inhomogeneous main magnetic fields. In addition, a hand held MRI device can be manufactured which uses a low cost permanent magnet to provide a magnetic field and generates
the required RF field with the designed RF coil using the techniques suggested in this study.
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Holmgren, Jens. "Investigation of alternative current measurements in high-voltage applications." Thesis, Linköping University, Department of Science and Technology, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-8149.
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<p>ABB:s MACH2 system uses a number of currents to ignite thyristors for AC/DC-trassfformation and they are measured for control and protection. The measurement methods used today has major drawbacks. Two alternative techniques are investigated, one based on the Hall-Effect (HED) and the other based on Anisotropic Magnetoreistanse (AMR), both techniques sensing the magnetic field produced by currents in a conductor. The HED hawe low sensitivity so some kind of flux concentrators is needed. This adds volume, costs and complexity to the device. The AMR technique is much more sensitive than the HED. Unfortunately AMR are also much more sensitive for high over currents that may damage the devise, and they are not as common on te market. By testing linearity, step response and frequency dependency for some components, my conclusion is that HED components with toroidal flux concentrators utilizing magnetic feedback (Closed Loop, CL) may be used in this particular application. A drawback with CL are that they, when measuring sharp edged step signals, suffer from overshoots at the output that might activate the over current protection.</p>
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Jebari, Nessrine. "Design and Microfabrication of a Biosensor Integrating Magnetofluidic Manipulation and Direct-Field Capacitive Sensing." Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPAST132.
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Les maladies inflammatoires chroniques nécessitent un diagnostic précoce, un pronostic et une prise en charge personnalisée, ce qui peut être réalisé grâce à un suivi non invasif en temps réel de biomarqueurs inflammatoires tels que les cytokines et les protéines de phase aiguë. La sueur, un biofluide accessible et riche en informations, offre un milieu prometteur pour ce type de suivi. Cependant, les biocapteurs actuels pour la sueur sont confrontés à des défis en termes de sensibilité et de spécificité en raison des faibles concentrations de ces biomarqueurs et de la composition complexe de la sueur. Cette thèse présente un nouveau biocapteur combinant la manipulation de nanoparticules magnétiques (NPM) avec la détection capacitive en champ direct (DF-CS). Le biocapteur génère un gradient de champ magnétique contrôlé pour concentrer les immunocomplexes dans une zone de détection capacitive définie, permettant une analyse rapide, quantitative et sans marquage des biomarqueurs. Cette méthode améliore la sensibilité en réduisant les interférences de fond et élimine le besoin d'une fonctionnalisation complexe de la surface. De plus, elle permet la détection de plusieurs analytes, simplifiant la fabrication et améliorant potentiellement la stabilité et la reproductibilité du capteur. Des simulations multiphysiques 3D complètes à l'aide de COMSOL Multiphysics ont été effectuées pour optimiser la conception et les paramètres opérationnels du biosenseur. Ces simulations ont modélisé les interactions entre les champs magnétiques, fluidiques et électriques au sein du dispositif, prédisant une augmentation significative de la sensibilité de la détection capacitive allant jusqu'à 42,48 % à 85 % d'occupation des NPM. Un processus de microfabrication rigoureux en 26 étapes a été développé pour obtenir les structures magnétomicrofluidiques et capacitives. La biocompatibilité a été améliorée grâce à des revêtements de Parylène C et un nouveau protocole de collage à basse température à 45°C a été établi pour les interfaces Parylène C-Parylène C. La caractérisation expérimentale a validé les simulations, confirmant le piégeage magnétique efficace dans la zone de détection. Les mesures de capacitance et d'impédance dans l'air et l'eau déionisée ont démontré la réactivité du capteur aux changements de l'environnement diélectrique. À 200 kHz dans l'eau déionisée, le dispositif R500 a montré une diminution de 17,6 % de la capacitance et de 18,6 % de l'impédance par rapport à l'air, tandis que le dispositif R1000 a présenté des diminutions plus importantes de 25,5 % et 9,5 %, respectivement. Ces résultats démontrent la capacité du capteur à détecter les variations des propriétés diélectriques, une condition essentielle pour la détection des NPM liés aux biomarqueurs dans le biofluide. Les travaux futurs se concentreront sur la fonctionnalisation des NPM avec des anticorps ciblant les biomarqueurs pro-inflammatoires et l'évaluation des performances du capteur dans les échantillons de sueur, notamment la sensibilité, la spécificité et la limite de détection<br>Chronic inflammatory diseases require early diagnosis, prognosis, and personalized management. Real-time, non-invasive monitoring of biomarkers like cytokines and acute-phase proteins in easily accessible biofluids is crucial. Sweat offers a promising medium, but current biosensors face challenges due to low biomarker concentrations and complex sweat composition. This thesis presents a novel biosensor that combines magnetic nanoparticle (MNP) manipulation with direct field capacitive sensing (DF-CS). The biosensor generates a controlled magnetic field gradient to concentrate immunocomplexes in a defined capacitive detection zone, enabling rapid, quantitative, and label-free biomarker analysis. This method enhances sensitivity by reducing background interference and eliminates the need for complex surface functionalization. Additionally, it enables multiplex detection, simplifying fabrication and potentially improving the sensor's stability and reproducibility. Comprehensive 3D multiphysics simulations using COMSOL Multiphysics were conducted to optimize the biosensor's design and operational parameters. These simulations modeled the interactions between magnetic, fluidic, and electric fields within the device, predicting a significant increase in capacitive sensing sensitivity of up to 42.48% at 85% MNP occupancy. A rigorous 26-step microfabrication process was developed to achieve the magnetofluidic and capacitive structures. Biocompatibility was enhanced using Parylene C coatings, and a novel low-temperature bonding protocol at 45°C was established for Parylene C-Parylene C interfaces. Experimental characterization validated the simulations, confirming effective magnetic trapping in the detection zone. Capacitance and impedance measurements in air and deionized water demonstrated the sensor's responsiveness to changes in the dielectric environment. At 200 kHz in deionized water, the R500 device showed a 17.6% decrease in capacitance and an 18.6% increase in impedance compared to air, while the R1000 device exhibited larger increases of 25.5% and 9.5%, respectively. These results demonstrate the sensor's ability to detect variations in dielectric properties, a critical requirement for detecting MNPs bound to biomarkers in biofluids. Future work will focus on functionalizing MNPs with antibodies targeting pro-inflammatory biomarkers and evaluating the sensor's performance in sweat samples, specially in terms of sensitivity, specificity, and limit of detection
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Lommen, Jonathan Lyon Jacob. "Effects of Transcranial Direct-Current Stimulation on Gait Initiation in People with Parkinson’s Disease." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39959.
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Background: Gait initiation is a major issue in Parkinson’s disease (PD). Moreover, the effect of current treatment on motor deficits vary alongside individual differences and disease severity. In some cases, postural instability has been documented as a major side-effect and refractory symptom to dopaminergic medication. Despite these shortcomings, research involving other forms of therapy including deep brain stimulation (DBS) and transcranial magnetic stimulation (TMS), has evidenced the improvement of postural deficits in PD. In this regard, there is a strong rational for the modulation of subcortical brain activity via the application of non-invasive transcranial direct current stimulation (tDCS) to interconnected cortical brain structures. Purpose: Therefore, we sought to determine the effect of tDCS applied to the supplementary motor area (SMA), on gait initiation preparation and performance in PD. Methods: A within subjects repeated measures quasi-experimental design was used to investigate the effects of a 10-minute sham-controlled tDCS intervention. Clinically diagnosed participants (n=12) with idiopathic PD were tested on medication during two sessions that bookended one week. Those who had previously undergone other forms of brain stimulation, had diabetes, severe freezing of gait, or any other neurological or functional limitations that could interfere with gait initiation were excluded from the study. Statistical Analyses/Results: Two-way repeated measures ANOVAs with Bonferroni corrections and a post-hoc analyses when appropriate, revealed a significant reduction in the magnitude of center of pressure (CoP) displacement and velocity in the mediolateral (ML) direction following tDCS. Conclusions: Findings from this study provide insights that may guide scientific research regarding the effects of tDCS on gait initiation among those with PD. Additionally, our work may highlight the importance of ML postural stability for individuals with comorbid and/or pharmacologically induced postural instabilities.
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Yoshida, Yutaka, Yusuke Ichino, Masashi Miura, Yoshiaki Takai, Kaname Matsumoto, and Ataru Ichinose. "High critical current density in high field in Sm/sub 1+x/Ba/sub 2-x/Cu/sub 3/O/sub 6+y/ thin films." IEEE, 2005. http://hdl.handle.net/2237/6776.
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Miura, Masashi, Masakazu Itoh, Yusuke Ichino, et al. "Effect of Sm/Ba substitution on the J/sub c/ in magnetic field of SmBCO thin films by low temperature growth technique." IEEE, 2005. http://hdl.handle.net/2237/6778.
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Chow, Li Sze. "Investigation of direct detection of nerve firing in the human visual system due to axonal field modulation of the magnetic resonance signal." Thesis, University of Sheffield, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425600.
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Bhagurkar, Ashutosh. "Processing of MgB2 bulk superconductor by infiltration and growth." Thesis, Brunel University, 2017. http://bura.brunel.ac.uk/handle/2438/14777.
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Superconductivity in magnesium diboride (MgB2) was discovered in 2001. The relatively high Tc (39 K), high critical current density, long coherence length (∼6 nm), low raw material cost, lower density and relative ease of fabrication make this material an exciting choice for practical applications. Furthermore, lower anisotropy and strongly linked current flow in untextured polycrystalline samples, unlike its HTS counterparts, has enabled the development of different processing routes to fabricate MgB2 in the form of wires, tapes, thin films and bulks. Conventionally, MgB2 is synthesized by in situ sintering, where elemental Mg and B powders are reacted to produce MgB2. Although the superconducting phase can be obtained with relative ease, the resulting sample is generally only around 50% dense, due to formation of large pores inside sintered bulks arising from the volatility of magnesium and 25% volume contraction in MgB2 phase formation. Although the use of high pressure is effective to promote sintering and subsequent densification, the need to use large pressure vessels represents a significant practical limitation for the development of a practical process and of the achievable dimensions in the final MgB2 sample. As a result, the fabrication of high density, bulk MgB2 remains a challenging processing problem. This study explores the “Infiltration and Growth” (IG) technique, an established processing route for fabrication of dense ceramics/ceramic matrix composites, as a potential solution. Boron powders of varying characteristics were infiltrated with Mg(l) to obtain bulk MgB2 samples. The samples were analysed using techniques such as XRD, SEM and hardness to analyse various phases formed during the process. These samples typically contained MgB2 with minor quantities of Mg. Physical properties of superconducting MgB2, such as Tc, Jc and Hc2, were established. Furthermore, the effective current carrying cross-section was estimated from resistivity measurements using Rowel’s analysis. Continuous Mg channels were major defects in IG processed samples and their presence was found to limit long range current flow. These channels are eliminated by incorporating Mg/AlB2/MgB2 powders in the precursor to facilitate in-flux of Mg, leading to a more uniform infiltration process, thereby enabling fabrication of near-net shaped MgB2 bulk superconductors. Such samples showed an almost identical value of trapped magnetic flux at the top and bottom surfaces, suggesting a high degree of uniformity in MgB2. A careful microstructural analysis of a series of samples indicated that MgB2 phase formation in IG process occurred in three distinct stages: (1) Intermediate boride formation (2) Bulk liquid Mg infiltration and (3) MgB2 layer formation. Due to volume expansion involved in stage 1, cracks formed in the β-Boron particles and propagated radially inwards during stage 3. The growing MgB2 particles sintered simultaneously with the formation of grain boundaries during the process. Much enhanced performance of MgB2 was achieved by virtue of C-doping. Increased Jc was attributed to generation of lattice strains and loss of crystallinity in MgB2 as a result of C-doping. Finally, trapped field measurements were performed on homogeneous C-doped MgB2 bulks. The trapped field obtained (4.13 T) in five stacked of bulks is the highest obtained in MgB2 bulks synthesized under ambient pressure conditions.
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Nakanishi, Kunihito. "A study on magnetic fluctuations over the ionospheric E-region driven by the lower atmospheric phenomena." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/215320.
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Vaculík, Vlastimil. "Snímače proudu." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2012. http://www.nusl.cz/ntk/nusl-219715.
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This diploma theisis deals with the theoretical analysis of the known types of current sensors, including for example, current transformers, shunts, and advanced sensors using Hall sensor or Rogowski coil. Subsequently, the rest of the work deals with the issue of current transducers with Hall sensors, without using a ferromagnetic circuit. For optimal currnet measure and overall precision, several possible options are designed and calculated. This includes number of sensing elements and distribution of sensors around the wires. Based on calaculation of magnetic intensity, related 3D charts ale plotted unsing Excel software. These charts illustrate the theoretical calculations of field distribution around conductors for various number of sensor. In the last part, components ale designed for practical implementation and scheme of electrical wiring. According to this scheme there is PCB designed as well. Whole current meter ir practically build and its results are compared with theoretical assumtions that are discussed in conclusion part of this theisis.
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Amadi, Ugwechi. "Transcranial stimulation to enhance cortical plasticity in the healthy and stroke-affected motor system." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:bb27ac6f-a79d-459a-b5a0-e9a209ac7132.
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This thesis investigated transcranial direct current stimulation (tDCS) as applied to the motor system, and its ability to modulate underlying cortical processes and resultant motor behaviours. Functional magnetic resonance imaging (fMRI) and transcranial magnetic stimulation (TMS) were employed to assess the extent to which tDCS induces quantifiable changes in neural structure and function in controls and stroke patients. Modifications in the connectivity of intrinsic functional networks following tDCS application were examined using resting state fMRI. Polarity-specific changes were found: cathodal (inhibitory) tDCS increased the strength of the default mode network and increased functional coupling between major nodes within the motor network. No significant effects were found following anodal (excitatory) tDCS. Although anodal tDCS elicited only subtle changes in resting activity, it is known to produce robust modifications of behaviour. Single and paired-pulse TMS were used to investigate the neurophysiological underpinnings of these changes. Consistent with the theory of homeostatic plasticity, anodal tDCS applied prior to task performance increased GABAA-mediated cortical inhibition and worsened behaviour. The specificity of these changes suggests a central role for the mechanism of surround inhibition. A longitudinal clinical trial in chronic stroke patients was conducted to determine the utility of tDCS as an adjunct in motor rehabilitation. Serial MRI scans revealed that, when combined with motor training, anodal tDCS increased functional activity and grey matter in primarily ipsilesional motor areas. These brain changes were correlated with behavioural improvements in the stroke-affected upper limb. The laterality of connectivity at baseline, as measured by resting state activity and corticospinal tract integrity, was predictive of response to the rehabilitation program, particularly in those stroke patients who received tDCS. Asymmetry favouring the contralesional hemisphere predicted greater behavioural gains. Such results underscore the importance of re-normalisation of structure and functional activity toward the lesioned hemisphere in stroke rehabilitation.
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Rudolph, Matthias [Verfasser], and Dieter [Akademischer Betreuer] Kölle. "Development of an ultra-low field magnetic resonance imaging scanner and DC SQUID based current sensors for the investigation of hyperpolarization techniques / Matthias Rudolph ; Betreuer: Dieter Kölle." Tübingen : Universitätsbibliothek Tübingen, 2018. http://d-nb.info/1168148766/34.
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Zavattoni, Laëtitia. "Conduction phenomena through gas and insulating solids in HVDC gas insulated substations, and consequences on electric field distribution." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENT063/document.
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L'émergence des énergies renouvelables a entraîné le développement de nouvelles technologies pour la distribution de l'énergie sur de longues distances. Ces dernières sont basées sur le transport via de hautes tensions continues (HVDC) pour éviter les pertes capacitives. Ce réseau de distribution est interconnecté via des Postes Sous Enveloppes Métalliques (PSEM), dont l'isolation est composée de gaz sous pression (SF6) et d'isolants solides (résine époxy), qui doivent résister sous HVDC. Dans ces dispositifs, le champ électrique n'est plus déterminé par la permittivité relative des matériaux, mais par leurs résistivités et les phénomènes d'accumulation de charges. Dans le cas d'un isolant solide présentant une interface avec un gaz, des électrons ou des ions vont être susceptibles de se déplacer suivant les lignes de champ électrique et charger la surface de l'isolant solide. Le comportement des propriétés des isolants (solides et gazeux) constitue un enjeu majeur dans le développement de PSEM HVDC, notamment dans la compréhension des mécanismes d'accumulation et relaxation des charges.Dans ce travail de thèse, la caractérisation de l'isolant solide a d'abord été étudiée, basée sur des mesures de courants faibles bruits. Il est ainsi possible de mesurer le courant de fuite dans le volume et sur la surface des échantillons, dans une enceinte sous pression, à haut champ électrique et pour différentes températures. Ces mesures ont mis en évidence que les résistivités de volume et de surface sont fortement impactées par l'augmentation de la température et la teneur en eau des échantillons. Il a également été montré que la résistivité de surface a un comportement non-linéaire en fonction du champ électrique. Un modèle numérique a été développé pour simuler les résultats obtenus, et implémenter les propriétés de surface de l'isolant solide.Les propriétés isolantes du gaz ont également été étudiées pour différentes géométries de champ électrique, dans le but d'estimer la contribution du courant passant à travers le gaz, sur l'accumulation de charge en surface de l'isolant solide. Des courants non négligeables sont mesurés dans le gaz (~pA-nA). Pour déterminer les mécanismes responsables de la présence de tels courants, il a été caractérisé selon plusieurs paramètres (la rugosité de la surface de l'électrode, la nature du matériau, le champ électrique, la température et l'humidité relative). Cela a mis en évidence que les variations de courants dépendent du conditionnement du dispositif, et sont donc fortement influencés par l'humidité relative adsorbée sur les surfaces du dispositif (électrodes et cuves). En présence d'un système sec, de faibles courants sont mesurés (~pA), et augmentent en fonction de la température. A l'inverse, dans le cas d'un système humide, le courant diminue avec l'augmentation de la température. Ces résultats, combinés à l'influence de la rugosité de l'électrode, suggèrent fortement un mécanisme d'injection de charge à la surface de l'électrode, favorisé en présence d'eau adsorbée.Enfin, les résultats obtenus pour les deux isolants solides et gazeux sont utilisés pour élaborer un modèle numérique ayant une forme proche de celle de l'application industrielle, et permettent d'observer la modification de la distribution du champ électrique en présence de la concentration en eau et du gradient de température. Une estimation du courant circulant au travers des isolants est donc possible.En conclusion, ce travail donne les variations des résistivités de volume et de surface dans une résine époxy en fonction de la température et du champ électrique. Il met également en évidence la forte influence de l'humidité relative et de la température sur les mécanismes d'injection de charges qui contribuent au courant mesuré à travers le gaz. Cette caractérisation approfondie permet de développer une simulation qui prédit les variations de la distribution du champ électrique au sein d'un PSEM sous tension continue<br>The emergence of renewable energy leads to a development of new technologies for energy distribution across long distances. The latter will be based on High Voltage Direct Current (HVDC) to avoid capacitance losses. This network is interconnected using Gas Insulated Substation (GIS), which insulation is composed of pressurized gas (SF6) and solid insulators (epoxy resin), which have to withstand HVDC. The electric field is not anymore determined by permittivity of materials, but by resistivities and charge accumulation. In the case of an insulator with an interface with gas, electrons or ions will move across electric field lines and will charge the surface of the solid insulator. The behavior of insulator's properties (gas and solid) constitutes a major challenge for the development of HVDC GIS, to understand the charge relaxation/accumulation mechanisms.In this work, the characterization of solid insulator has first been investigated, based on a low-noise current measurement method. It is thus possible to measure the leakage current through samples and onto their surface, in a pressurized gas, at high electric field and for different temperatures. Those measurements permit to evidence that both volume and surface resistivities are strongly impacted by the increase of temperature and water concentration. It has also been shown that surface resistivity has a non-linear behavior with electric field. A numerical model was developed, to simulate experimental results, showing that the surface properties of the insulator can be implemented.Furthermore, the insulating properties of the gas were also investigated through different electric field geometry (coaxial and uniform), in order to estimate the contribution of current through gas on the charge accumulated on solid insulators. It has been found that a non-negligible current passes through the gas (~pA to nA). To determine the mechanisms responsible for such currents, the latter has been characterized depending on several parameters (electrode surface roughness, material nature, electric field, temperature and relative humidity). It revealed that the variations of currents are strongly impacted by the conditioning of the device and thus by the relative humidity adsorbed on electrodes and enclosure surfaces. In presence of a dry system (dry gas and device) low current were measured (~pA), which increases with temperature. On the contrary, in case of a “wet” system (humid gas and device) the current decreases with increasing temperature. Those results combined with the influence of the electrode roughness, strongly suggest a mechanism of charge injection at the electrode surface, enhanced by water adsorption.Finally, the results obtained for both solid and gaseous insulations are used to develop a numerical model with a shape close to the industrial application, and observe the modification of electric field distribution in presence of water concentration and temperature gradient. An estimation of current flowing through the insulator and gas is thus possible in case of uniform and gradient temperature.In conclusion, this work gives the variations of both volume and surface resistivities in an epoxy resin with temperature and electric field. It also evidences the major influence of relative humidity and temperature on charge injection mechanisms which contribute to the current measured through gas. The extensive characterization performed, enables to develop a simulation which predicts the variations of electric field distribution within an HVDC GIS
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Sudoh, K., Y. Ichino, Y. Yoshida, et al. "Magnetic field dependence of critical current density in Sm/sub 1+x/Ba/sub 2-x/Cu/sub 3/O/sub 6+/spl delta// films prepared by pulsed laser deposition." IEEE, 2003. http://hdl.handle.net/2237/6742.
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Welchko, Brian A. "A high power DC motor controller for an electrical race car using power MOSFETS." Ohio : Ohio University, 1996. http://www.ohiolink.edu/etd/view.cgi?ohiou1239733975.
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NASSERI, SEYED ALI. "Magnetic Domain Wall Motion: Numerical Simulation and Collective Coordinate Modeling." Doctoral thesis, Politecnico di Torino, 2018. http://hdl.handle.net/11583/2710713.
Full textAbstract:
Manipulating magnetic domain walls in nanostructures has been linked with applications in spintronic logic, sensing and storage devices. Recent studies of domain wall motion have focused on perpendicular magnetic anisotropy heterostructures of ultrathin ferromagnets sandwiched between a heavy metal layer and an oxide, in which spin-orbit coupling and broken inversion symmetry can dominate domain wall motion.
Specifically, chiral domain walls are stabilized in these systems due to the Dzyaloshinskii-Moriya interaction, and current-driven domain wall motion is enhanced due to the spin Hall effect. The chirality of the domain walls in such systems may be partially influenced by the application of external in-plane magnetic fields. Such magnetic fields are used in bubble expansion experiments to assess the strength of the Dzyaloshinskii-Moriya interaction. In addition, bombarding the ferromagnetic layer with heavy metal ions can induce local changes in material properties such as magnetic anisotropy which could be used to manipulate local pinning properties.
While computational micromagnetic simulations can help elucidate the behavior of domain walls, their computational cost prohibits extensive studies. As such, assessing the strength of the Dzyaloshinskii-Moriya interaction, extracting material parameters and understanding the behavior of the domain wall to an extent depends on simpler models of domain wall motion based on collective characteristics of the domain wall, and derived from applying model reduction methods to the more complex micromagnetic model.
Several Lagrangian-based collective coordinate models exist to describe domain wall motion, namely the $q-\phi$, $q-\phi-\Delta$, and $q-\phi-\chi$ models. While these models can describe domain wall motion with acceptable accuracy, they fail to replicate results of micromagnetic simulations specially for domain wall motion under the application of in-plane fields in heterostructures of interest. Moreover, recent advances in domain wall motion such as pinning due to irradiation have not been included in these models.
In this work, we will first present the process for developing Lagrangian-based collective coordinate models, culminating in the derivation of a four collective coordinate model for domain wall motion (the $q-\phi-\chi-\Delta$ model). We show how this model can be extended for cases where in-plane magnetic fields are present to correctly account for the physics; this extension involved introducing the canting induced by the in-plane fields in the domains. We also extend these models to describe the dynamics of magnetic bubbles.
In-plane field cases are specifically studied to help identify specific conditions which could help measure properties of the magnetic material. We also compare the equations derived using our Lagrangian-based approach to another reduced model developed through the application of statistical methods to the LLG equation, shedding light on the shortcomings of our approach. The work culminates with a summary of how these models may be made more realistic, through the inclusion of pinning and thermal effects within the model.
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Cimmperman, Piotras. "Plonųjų manganitų sluoksnių tyrimas stipriuose impulsiniuose elektriniuose ir magnetiniuose laukuose." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2006. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2006~D_20061003_100516-61918.
Full textAbstract:
The main aim of this work was to investigate electrical conductivity of La-Ca(Sr)-MnO thin films at high pulsed electric and magnetic fields and to clear up the possibilities to use these materials for high pulsed magnetic field sensor and fault current limiter applications.
The dissertation consists of the preface, six chapters, summary and main conclusions, references, list of publications and abstract (in Lithuanian).
The main objectives of the work, scientific novelty, goals, validation of results, and statements for defense are presented in the preface.
Chapter 1 presents an introduction and review of previous works on electroresistance (ER) and magnetoresistance (MR) phenomena in manganites.
Chapter 2 presents a description of two deposition techniques which were used for preparation of thin manganite films: metal organic chemical vapour deposition (MOCVD) and pulsed laser deposition (PLD).
Measurement equipment and methods are described in Chapter 3. The resistance dependence on voltage was investigated using electric pulses with duration of 5–30 ns and amplitude up to 1000 V in the temperature range of 4.2–300 K. For magnetoresistance measurements a pulsed magnetic field generator, which generates magnetic field pulses of 0.6–2 ms duration with amplitude up to 50 T was used.
Chapter 4 presents an investigation of surface morphology of prepared films and a characterization of their properties at low electric and magnetic fields. The electric and magnetic properties... [to full text]
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Kajimura, Shogo. "Mind wandering regulation by non-invasive brain stimulation." 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225352.
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Frangou, Polytimi. "Inhibitory mechanisms for visual learning in the human brain." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/280767.
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Identifying targets in cluttered scenes is critical for our interactions in complex environments. Our visual system is challenged to both detect elusive targets that we may want to avoid or chase and discriminate between targets that are highly similar. These tasks require our visual system to become an expert at detecting distinctive features that help us differentiate between indistinguishable targets. As the human brain is trained on this type of visual tasks, we observe changes in its function that correspond to improved performance. We use functional brain imaging, to measure learning-dependent modulations of brain activation and investigate the processes that mediate functional brain plasticity. I propose that dissociable brain mechanisms are engaged when detecting targets in clutter vs. discriminating between highly similar targets: for the former, background clutter needs to be suppressed for the target to be recognised, whereas for the latter, neurons are tuned to respond to fine differences. Although GABAergic inhibition is known to suppress redundant neuronal populations and tune neuronal representations, its role in visual learning remains largely unexplored. Here, I propose that GABAergic inhibition plays an important role in visual plasticity through training on these tasks. The purpose of my PhD is to investigate the inhibitory mechanisms that mediate visual perceptual learning; in particular, learning to detect patterns in visual clutter and discriminate between highly similar patterns. I show that BOLD signals as measured by functional Magnetic Resonance Imaging (fMRI) do not differentiate between the two proposed mechanisms. In contrast, Magnetic Resonance Spectroscopy (MRS) provides strong evidence for the distinct involvement of GABAergic inhibition in visual plasticity. Further, my findings show GABA changes during the time-course of learning providing evidence for a distinct role of GABA in learning-dependent plasticity across different brain regions involved in visual learning. Finally, I test the causal link between inhibitory contributions and visual plasticity using a brain stimulation intervention that perturbs the excitation-inhibition balance in the visual cortex and facilitates learning.
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Zidi, Manel. "Utilisation de la Magnéto-Impédance Géante pour la réalisation d'un capteur de courant." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENT096/document.
Full textAbstract:
Le potentiel de la GMI a été exploré pour la réalisation d'un capteur magnétique de mesure du courant électrique. Une partie notable de ce projet a été consacrée à l'investigation de l'électronique de conditionnement du capteur, notamment, l'électronique d'excitation de l'élément sensible et l'électronique de détection de la variation de la tension à ces bornes. Une nouvelle solution d'oscillateur numérique précis, stable et de haute fréquence a été proposée. Un convertisseur tension-courant basé sur la source de Howland a été associé à cet oscillateur. Pour la détection, des technologies innovantes et prometteuses, tel que le détecteur RMS-DC pour les mesures précises, ont été proposées. Un conditionnement électronique permet d'utiliser ce détecteur pour la démodulation des signaux alternatifs. Une approche originale de détecteur d'amplitude sans seuil utilisant un amplificateur limiteur a été développée. Ces technologies ont été intégrées avec succès dans un capteur de courant électrique<br>A GMI current sensor was designed. This study was devoted to the investigation of the electronic conditioning of the sensor. An accurate, stable and high frequency digital oscillator was developed. A voltage-to-current converter based on the Howland source was associated to this oscillator. An innovative and promising technology for precise measurements was proposed: the RMS-DC detector. This detector was conditioned for demodulating AC signals. Also an original approach of an amplitude detector using a limiting amplifier was developed. These technologies have been successfully integrated into a GMI current sensor
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IMPINNA, FABRIZIO. "Electrodynamic Bearings Modeling and Design." Doctoral thesis, Politecnico di Torino, 2010. http://hdl.handle.net/11583/2502012.
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The number of high speed applications is sharply increasing in the last years so that the problem of the choice of the most suitable bearing must be handled. Considering the rotating machines, during the past ten years, high speed turbomolecular pumps have been mass produced showing that the high speed technology is mature.
Since friction, wear, maintenance and lifetime represent the main issues of high speed applications, magnetic bearings, which are a contact free devices, could be considered as a possible solution.
A magnetic bearing is a contact free bearing wherein the load is carried by
magnetic forces. The magnetic field is generated in such a way that it provides necessary stiffness and damping to make the rotor hover safely during operation. Magnetic bearings are characterized by no wear, no maintenance and furthermore they don't require lubrication.
The present work deals with a particular category of magnetic bearing: the
electrodynamic bearings. The most interesting aspect of electrodynamic bearings is that levitation can be obtained by passive means, thus no electronic equipment, such as power electronics or sensors, are necessary. Therefore, electrodynamic suspensions are an advantageous alternative to active magnetic suspensions: they are less complex, less subject to failure, and possibly far lower in cost. On the other hand, the main drawback of
electrodynamic bearings is that a stable levitation is provided only when the speed is above a threshold value, which opens stability issue at low speeds.
Presently, the design of electrodynamic bearings is based on the force-to-angular speed characteristic obtained for a fixed eccentricity. Although this characteristic describes the behaviour of the bearing in quasi-static conditions, it is not suitable for dynamic conditions where the rotor is animated by a nonsynchronous whirl, or even a non periodic motion about the stator axis. A model that could take explicitly into account both the quasi-static and the dynamic conditions is still lacking. Therefore the first objective of the present work is to develop an analytical model of radial
and axial electrodynamic bearings able to describe both quasi-static and dynamic behaviours. In this way not only the static characteristics such as achievable stiffness and force, but also the dynamic performance of a system involving electrodynamic bearings can be evaluated and used as design criteria.
The developed models of radial and axial electrodynamic bearings have been
experimentally validated. Two test rigs, the first based on a radial electrodynamic bearings, the second characterized by the presence of an axial electrodynamic bearing, have been designed and built to this end.
Since the electrodynamic bearings are intrinsically unstable devices, the stability issue is examined in the dissertation. So far, the most common solution to achieve the stability is to add non-rotating damping between the rotor and the stator. It is natural to obtain the stability by adding non-rotating damping between the rotor and the stator. Nevertheless, this strategy is not as easy to apply as it seems, given that the stabilizing device must be contactless, consistently with the electrodynamic bearings issue. Although effective, this solution could imply the installation of a dedicated magnet on the rotor with a consequent increase of the rotor weight and complexity and the rising of some concerns about the mechanical resistance, and a conductor where eddy currents can arise on the statoric part of the system.
In the dissertation a new stabilizing technique for electrodynamic bearings is proposed. Instead of introducing damping between the rotor and the non-rotating part of the bearing, the author propose to introduce an elastic and dissipative element between the statoric part of the bearing and the case of the machine.
The innovative aspect of the proposed solution is that the stabilizing dissipation is introduced into the statoric part of the electrodynamic bearing, which does not rotate. The main advantages of this configuration are: reduced complexity from the constructive point of view since no rotating parts are involved; an easier tuning of the stabilizing system main parameters; an extremely effective contribution to the stability; conventional and low cost devices are suitable for the implementation of the proposed stabilizing system. The wide variety of practical solutions that can
be adopted for the proposed stabilization techniques, such as rubber bushings or squeeze film dampers for example, is an indicative parameter of the true possibility of applying it in industrial applications. The impact of the proposed solution on the rotor stability is investigated, and it is demonstrated that a damping device between the rotor and the statoric part is no longer necessary.
Although electrodynamic bearings are quite complex devices, they are still lacking a clear design procedure, therefore a procedure addressed to optimize the design of electrodynamic bearings for industrial applications could be useful. Since the developed models, able to describe the quasi-static and dynamic behaviours of electrodynamic bearings, have been experimentally validated, they can be assumed as useful tools oriented to the design of these devices. Therefore, at the end of the dissertation, a design procedure based on those models is presented.
The developed models and the proposed stabilizing technique make the electrodynamic bearings ready for the industrial applications.
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Combe, Quentin. "Éjection électromagnétique : modèle et réalisation." Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0107.
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Cette thèse se concentre sur la thématique de l'éjection électromagnétique appliquée dans le cadre de l'industrie du recyclage des métaux. L'objectif de celle-ci est la modélisation et la réalisation d'une architecture de conversion d'énergie permettant la réalisation de cette éjection. Le champ magnétique variable généré est utilisé afin de séparer d'un flux de déchets les matériaux métalliques non ferromagnétique tel que l'aluminium ou le cuivre par le biais d'une force de Laplace engendrée par la conjonction entre le champ magnétique crée et le champ magnétique induit par les courants de Foucault dans les matériaux conducteurs. L'architecture développée se compose de plusieurs éléments: un redresseur, un onduleur et un inducteur. La partie redresseur, à large plage de fonctionnement connectée sur le réseau d'alimentation triphasée permet d'obtenir une tension continu réglable et assure un prélèvement sinusoïdale de courant en phase avec la tension. La partie onduleur, permet de contrôler la puissance transmise, en adaptant l'amplitude et la fréquence du courant traversant la dernière partie du système que forme l'inducteur, responsable de la création du champ magnétique alternatif. Le choix du redresseur s'est porté sur la structure classique du redresseur abaisseur de tension de type Buck en raison de la faible impédance de l'inducteur utilisé. Bien que cette structure permette d'abaisser la tension triphasée, sa plage de fonctionnement peut être facilement augmentée sans l'ajout de composant passif. Le contrôle classique de ce redresseur ne se base que sur ses grandeurs de sorties ce qui peut engendrer des oscillations non contrôlées causées par la mise en résonance du filtre LC d'entrée excité par les harmoniques générés par les commutations des transistors. Nous avons proposé dans cette thèse une nouvelle méthode de contrôle qui traite à la fois de ses grandeurs d'entrée et de sortie et qui permet de contrôler les éventuelles oscillations du filtre LC d'entrée tout en bénéficiant d'une meilleure réponse dynamique lorsque le système est soumis à un échelon de charge. Cette méthode de contrôle se base sur les propriétés de platitude des systèmes différentielles, ainsi elle ne dépend pas du point de fonctionnement et garantit la stabilité large signal du système. Le choix de l'onduleur monophasé s'est porté sur une structure en pont complet permettant l'application de trois niveaux de tension et un large choix de contrôle de l'amplitude, de la forme et de la fréquence du courant traversant l'inducteur. Différents contrôle de ce convertisseur ont été étudiés et comparés. Ceux-ci permettent de faire varier la puissance injectée dans l'inducteur, ont un impact sur le contenu harmonique du courant le traversant et sur les contraintes des différents composants du système. Une modélisation de l'inducteur ainsi qu'une estimation de la valeur du champ magnétique nécessaire à l'éjection est effectuée. Les différentes méthodes proposées sont validées par des résultats de simulations numérique mais également par le biais de tests expérimentaux réalisés sur le système complet<br>This thesis focuses on the subject of electromagnetic ejection applied in the context of the metal recycling industry. The aim of this thesis is the modeling and the development of an architecture of energy conversion allowing the realization of this ejection. The generated variable magnetic field is used to separate non-ferromagnetic metallic materials such as aluminum or copper from a waste stream by means of a Laplace force generated by the conjunction between the magnetic field created and the magnetic field induced by the eddy currents in the conductive materials.The developed architecture is composed of several elements: a rectifier, an inverter and an inductor. The rectifier part with a wide operating range connected to the three-phase grid network allows to obtain an adjustable DC voltage and ensures a sinusoidal current in phase with the voltage. The inverter part allows to control the transferred power, by adjusting the amplitude and frequency of the current flowing through the last part of the system represented by the inductor, responsible for the generation of the variable magnetic field.The rectifier is based on the classical Buck rectifier structure because of the low impedance of the inductor used. Although this structure allows to lower the three-phase grid voltage, its operating range can be easily increased without the addition of passive components. The classical control of this rectifier is based only on its output variables which can lead to uncontrolled oscillations caused by the resonance of the lightly damped input LC filter excited by the harmonics generated by the switching of transistors. In this thesis, we proposed a new control method that deals with both its input and output variables and that allows both to control the oscillations of the input LC filter while obtaining a better dynamic response when the system is subjected to a load step. This control method is based on the flatness properties of differential systems, so it does not depend on the operating point and guarantees the large signal stability of the system.The single-phase inverter is based on a full bridge structure allowing the application of three voltage levels and a wide choice of control of the amplitude, shape and frequency of the current flowing through the inductor. Different controls of this converter have been studied and compared. These allow to vary the power injected in the inductor, have an impact on the harmonic content of the current flowing through it and on the constraints of the different components of the system.A modeling of the inductor as well as an estimation of the value of the magnetic field necessary for the ejection is carried out. The different methods proposed are verified by numerical simulations but also by experimental tests performed on the whole system
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Buchwald, Rajko. "Optoelektrische Magnetfelduntersuchungen an Solarsilizium." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2010. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-39445.
Full textAbstract:
Es werden die Ergebnisse der Untersuchungen von Stromverteilungen an Solarzellen und Solarmaterial durch magnetische, elektrische und optische Messmethoden gezeigt. Die neue magnetfeldtopographische Messmethode CAIC wird hierbei erläutert und deren Stromverteilungen mit Ergebnissen der IR-Durchlichtmikroskopie, der LBIC- und der LIT-Methode verglichen und ausgewertet. Auf Basis der durchgeführten Untersuchungen und der Annahme des Vorhandenseins einer Korngrenzendekoration werden die Stromverlaufsmodelle einer elektrisch aktiven Korngrenze für eine Probe mit pn-Übergang sowie für eine Probe ohne pn-Übergang gezeigt. Anhand von CAIC-Messungen können die Position und die Orientierung leitfähiger und oberflächennaher SiC- und Si<sub>3</sub>N<sub>4</sub>-Ausscheidungen in mc-Silizium ohne pn-Übergang ermittelt werden. Hierfür wird ein Stromverlaufsmodell gezeigt. Weiterhin werden Zellmikrobrüche, Fehler in der Kontaktstruktur und Layoutunterschiede der Kontaktstruktur durch CAIC-Messungen an Solarzellen eindeutig nachgewiesen.
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Nabias, Julie. "Capteur de courant à Magnéto-Impédance Géante (GMI) souple et portatif." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAT013/document.
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La Magnéto-Impédance Géante (GMI pour Giant Magneto-Impedance) présente un certain nombre d’avantages, tels la haute sensibilité, la haute résolution de détection, la large bande passante et la flexibilité de l’élément sensible qui rendent cette technologie très prometteuse pour la réalisation de capteurs de courant flexibles, sans contact, capables de mesurer à la fois les courants continus (DC) et alternatifs (AC).Ce travail de thèse vise à explorer la faisabilité d’un capteur de courant flexible à base de GMI, en portant une attention particulière sur l’impact des paramètres d’influence qui conditionnent largement les solutions de mise en œuvre du capteur.Les effets de la température et des contraintes mécaniques de flexion et de torsion, qui s’appliquent dans un environnement de mesure réel, sont caractérisés en prenant en compte les grandeurs intrinsèques du fil nécessaires à la réalisation d’un capteur industriel. L’impact de la mise en œuvre et du conditionnement électronique vis-à-vis de ces grandeurs d’influence est aussi étudié. Les effets des perturbations magnétiques externes et de l’excentration du conducteur sous test dans la boucle de mesure sont quantifiés et une solution de blindage est proposée. Enfin, le prototype de capteur obtenu à l’issue de ces travaux est présenté, ainsi que ses performances, en dégageant les pistes d’optimisation et d’amélioration<br>The GMI effect displays several advantages, such as high sensitivity, high detection resolution and bandwidth, and mechanical flexibility. These advantages predispose this technology to the implementation of flexible contactless current sensors measuring both DC and AC currents.This thesis work aims at exploring the feasibility of a flexible GMI current sensor. A particular attention to the impact of influence parameters which largely condition the design solutions of the sensor has been paid.The effects of temperature and mechanical constraints such as bending and torsion, which apply in a real measuring environment, are characterized by taking into account the intrinsic features which are necessary to the design of the sensor. The impact of the general measuring configuration and electronics are also studied. The effects of magnetic disturbances and of the position of the current-carrying conductor in the measuring loop are quantified and an adequate shielding method is proposed. Finally, the sensor prototype obtained at the end of this work is described with its performances and the possible optimization and enhancement ways