La tesi s’inicia fent una presentació del comportament dels llits estabilitzats magnèticament i de les seves aplicacions, així com de les limitacions que tenen degut a les pèrdues de les propietats magnètiques en certes condicions.A continuació, es proposa un model matemàtic dels llits fluïditzats estabilitzats magnèticament, basat en la distribució que segueixen les partícules amb les línies del camp. L’estabilització magnètica també s’ha aplicat a llits fluïditzats amb barreges de partícules magnètiques i no magnètiques. S’ha estudiat el comportament d’aquests sistemes, així com la influència de la fracció màssica de material magnètic en el retard en l’aparició del bombolleig. Els resultats obtinguts mostren que l’estabilització magnètica pot aplicar-se no solament a la fluïdització de partícules magnetitzables sinó també a partícules no magnetitzables, si una certa fracció de material magnètic és present en el llit. Es proposen diferents correlacions per al càlcul de la velocitat de transició en funció de les propietats del sistema gas-sòlid i les condicions d’operació.També s’estudia l’efecte del camp magnètic sobre el comportament tèrmic dels llits fluïditzats de partícules magnètiques escalfats amb una superfície calefactora introduïda dins el llit. S’ha determinat la distribució axial i radial de temperatures en el llit. A partir dels resultats experimentals, s’ha desenvolupat un model que permet el càlcul de la conductivitat tèrmica efectiva del llit. A més, mitjançant l’aplicació de l’analogia de Chilton i Colburn a les dades experimentals obtingudes, s’han proposat diferents correlacions per a l’estimació del coeficient de transferència de calor en llits estabilitzats i semi estabilitzats.Finalment, s’ha estudiat experimentalment, mitjançant l’assecament d’aire humit en llits formats per barreges d’alúmina-acer, la transferència de matèria en llits estabilitzats i semi estabilitzats. S’han emprat dos paràmetres, eficiència del llit i factor de eficiència, per comparar el comportament dels diferents tipus de llits. La precisió del model teòric desenvolupat s’ha provat amb els resultats experimentals obtinguts. Els models corresponents als llits fluïditzats clàssics no presenten un bon ajust amb les dades experimentals; ara bé, quan aquests models són modificats tenint en compte l’efecte del camp magnètic, l’ajust amb les dades és molt millor. / First, in this thesis, the behaviour of the magnetically stabilized fluidized bed is presented, as well as its applications; the limitations due to the loss of magnetic properties in certain conditions are also considered.Later, a mathematical model of the magnetically stabilized fluidized bed, based on the arrangement of particles following field lines is proposed. Magnetic stabilization has also been applied to fluidized beds with mixture of magnetisable and non-magnetisable particles. The behaviour of these systems is studied, as well as the influence of the magnetic material mass fraction on the delay of bubbling. The results obtained show that the magnetic stabilization can be applied not only to the fluidization of magnetisable materials but also to non-magnetisable particles, if a certain fraction of magnetisable material is present. Correlations are proposed to calculate the transition velocity as a function of gas-solid properties and operating conditions.Also, the effect of the magnetic field on the thermal behaviour of a fluidized bed of magnetisable particles with an immersed heating surface has been studied. The temperature distribution inside the bed has been determined, both in the radial and axial directions. A model has been developed which allows calculation of the effective thermal conductivity of the bed from experimental data. In addition, by means of the application of the Chilton and Colburn analogy to the experimental data obtained, different correlations for the estimation of the heat transfer coefficient in stabilized and semi-stabilized beds have been proposed.Finally, the mass transfer in magnetically stabilized and semi-stabilized beds has been studied experimentally using the drying of moist air in beds of alumina-steel mixtures. Two parameters, bed efficiency and efficiency factor have been used to compare the behaviour of the different beds. The accuracy of the theoretical model developed has been tested using the results obtained. The models corresponding to the classical fluidized bed do not agree with experimental data; however, when these models are modified to take into account the effect of magnetic stabilization, the accuracy is much better.

Optical spin injection in InAs/GaAs quantum dots (QDs) structures under cryogenic temperature has been investigated in this work using continuous-wave optical orientation spectroscopy. Circularly polarized luminescence from trions in the QDs was used as a measure for the degree of spin polarization of the carriers in the QD ground states. The efficiency of spin conservation of the carriers during the injection process into the QDs and also the influence of the nuclear spins in the QDs were studied both under zero and external magnetic field. It was shown in zero magnetic field that the spin states were less conserved during the injection process for correlated excitons and hot free carriers. While under the external magnetic field, measurements were done in Faraday configuration. Confined electron motion yielding the quantized Landau levels in the InGaAs wetting layer (WL) and lifting of the Landau level spin degeneracy was observed. Also possible spin thermalization in the InGaAs WL during spin injection process was found. Finally, the quench of hyperfine induced spin relaxation by dynamic nuclear polarization (DNP) in the QDs was discovered and believed to be a stronger effect under weak/zero magnetic field.

Effects of a magnetic field on the double-probe technique are studied experimentally by means of symmetric floating computer controlled fast double probes in low and intermediate pressure plasmas. In addition, the effects of the magnetic field on the electron temperature, electron density, and electric field have been investigated. As it is expected, when there is no magnetic field, properties of the discharge plasma are best described by Langmuir theory. Whereas, when there&rsquo / s a magnetic field of sufficient strength Schottky&rsquo / s theory of ambipolar diffusion applies.

The Interplanetary Magnetic Field (IMF) has a controlling effect on the Magnetosphere and Ionosphere. The objective in this work is to investigate the probable effects of IMF on Ionospheric and Geomagnetic response. To fulfill the objective the concept of an event has been created based on the polarity reversals and rate of change of the interplanetary magnetic field components, Bz and By. Superposed Epoch Method (SPE) was employed with the three event definitions, which are based on IMF Bz southward turnings ranging from 6 to 11 nT in order to quantify the effects of IMF By and Bz. For the first event only IMF Bz turnings were taken into account while for the remaining, positive and negative polarity for IMF By were added. Results showed that the increase in the magnitude of IMF Bz turnings increased the drop of F layer critical frequency, f0F2. The drop was almost linear with the increase in magnitude of polarity reversals. Reversals with a positive IMF By has resulted in the continuation of geomagnetic activity more than 4 days, that is to say, the energy, that has penetrated as a consequence of reversal with a positive By polarity, was stored in outer Magnetosphere,whereas, with a negative IMF By the energy was consumed in a small time scale. At the second step of the work, although conclusions about geomagnetic activity could be done, as a consequence of data gaps for f0F2 in addition to having low numbers of events, characterization of f0F2 due to constant IMF By polarity could not be accomplished. Thus, a modeling attempt for the characterization of the response due to polarity reversals of IMF components with the Genetic Programming was carried out. Four models were constructed for different polarity reversal cases and they were used as the components of one general unique model. The model is designed in such a way that given 3 consecutive value of f0F2, IMF By and IMF Bz, the model can forecast one hour ahead value of f0F2. The overall model, GETY-IYON was successful at a normalized error of 7.3%.

Growing needs for precise manipulation in medical surgery, manufacturing automation and structural health monitoring have motivated development of high accuracy, bandwidth and cost-effective sensing systems. Among these is a class of multi-axis electromagnetic devices where embedded magnetic fields can be capitalized for compact position estimation eliminating unwanted friction, stiction and inertia arising from dedicated and separate sensing mechanisms. Using fields for position measurements, however, is a challenging 'inverse problem' since they are often modeled in the 'forward' sense and their inverse solutions are often highly non-linear and non-unique. A general method to design a multisensor system that capitalizes on the existing magnetic field in permanent magnet (PM) actuators is presented. This method takes advantage of the structural field symmetry and meticulous placement of sensors to discretize the motion range of a PM-based device into smaller magnetic field segments, thereby reducing the required characterization domain. Within these localized segments, unique field-position correspondence is induced using field measurements from a network of multiple-axis sensors. A direct mapping approach utilizing trained artificial neural networks to attain multi-DOF positional information from distributed field measurements is employed as an alternative to existing computationally intensive model based methods which are unsuitable for real-time control implementation. Validation and evaluation of this technique are performed through field simulations and experimental investigation on an electromagnetic spherical actuator. An inclinometer was used as a performance comparison and experimental results have corroborated the superior tracking ability of the field-based sensing system. While the immediate application is field-based orientation determination of an electromagnetic actuator, it is expected that the design method can be extended to develop other sensing systems that harnesses other scalar, vector and tensor fields.

There is an increasing interest in nanostructured and nanocomposite surface finishings for automotive and aerospace applications. The widespread applicability of these novel materials is based on their unique mechanical, physical, and chemical properties. An advantageous production method is the electrocodeposition (ECD) process from metal plating baths containing dispersed nanoparticles. By using this technique, a broad range of substrate sizes and shapes can be coated cost-effectively. However, the prediction of the amount as well the distribution of nanoparticles within the metal film fails frequently. There is no complete understanding of the particle incorporation mechanism. The goal of this research was to improve the fundamental understanding of the ECD mechanism. In order to identify the forces affecting the codeposition behavior of nanoparticles in a metal matrix, the effects of a variety of interrelated process parameters on the composite film formation have been investigated systematically. Nanocomposites containing metal and metal oxide nanoparticles in a nickel matrix have been prepared by means of ECD from two different types of nickel plating baths, an acidic sulfamate (pH 4.3) and an alkaline pyrophosphate bath (pH 9.5). The effect of deposition conditions on the ECD process was investigated utilizing two electrode configurations, viz. a parallel plate electrode (PPE) and impinging jet electrode (IJE) and different deposition techniques, viz. direct current (DC) deposition, both pulse plating (PP) and pulse-reverse plating (PRP). The surface charge and sedimentation behavior of the nanoparticles in these electrolytes were characterized by zeta potential and stability measurements. The surface charge, hydrodynamic diameter and colloidal stability of the nanoparticles in the nickel electrolytes were mainly affected by the composition and pH of the bath. The particles tend to form agglomerates in both nickel baths. Smaller agglomerates and an improved colloidal stability occurred in the case of the alkaline bath. Composites with a maximum particle content of either ~3.6 vol-% of 13 nm Al2O3 or ~10.4 vol-% of 21 nm TiO2 were obtained using a parallel plate electrode and DC deposition conditions. Both jet plating as well as pulse plating resulted in a distinct increase of the particle codeposition. A maximum incorporation of ~12 vol-% of 50 nm Al2O3 particles in a nickel matrix was achieved using an unsubmerged IJE system, while PP and PRP resulted in composites with particle contents up to 11 vol-% of 13 nm Al2O3. The particle incorporation increased with the particle content of the electrolyte for all deposition conditions studied. A beneficial effect on the amount of codeposited particles was found with decreasing average current density. The Al2O3 and TiO2 particles were found to be negatively charged in the alkaline pyrophosphate bath, and positively charged in the acidic sulfamate bath. It could be shown that negatively charged particles codeposited preferentially within the nickel matrix. The effect of PP and PRP conditions, e.g. pulse frequency, duty cycle and value of the peak current density, on the ECD of Ni-Al2O3 composites was studied using rectangular current pulses in the order of milliseconds. In general, low duty cycles and high pulse frequencies resulted in an enhanced particle codeposition. Using the unsubmerged IJE system, the effects of jet flow rate, particle loading and current density on the particle incorporation were studied. Referring to the experimental results from the ECD of 50 nm alumina with nickel using an IJE system, a kinetic model was developed. Therefore, the particle flux to the electrode was derived from an analysis of the total force acting on the particle in front of the electrode. The model took into account the convective diffusion of particles to the electrode surface, and the effect of gravitational and buoyancy forces on the particle flux. The gravitational force was found to be important for the ECD of 300 nm particles, but not for 50 nm particles. The effect of an external magnetic field on the ECD of Co or Fe3O4 nanoparticles in a nickel matrix has been studied for different current densities, particle contents of the electrolyte and magnetic flux density. The particle incorporation showed a distinct dependency on the orientation of an externally applied magnetic field. While the particle incorporation increased in a perpendicular field (perpendicular with regard to the electrode surface), it decreased in a parallel orientation. The influence of the magnetic field on the ECD of magnetic nanoparticles with nickel was explained by the interplay of Lorentz force and magnetophoretic force. The structure and the properties of the nickel matrix were significantly altered due to the codeposition of nanoparticles. The pure nickel deposits from the sulfamate bath exhibited a strong <100> texture, and those from the pyrophosphate bath a strong <110> preferred orientation. With increasing plating current density and particle incorporation, a variation in the crystallite size and a loss of texture was observed. High resolution TEM imaging proved a complete embedding of nanoparticles by the nickel matrix without any voids. In the case of both nickel baths, the Vickers microhardness showed a tendency to increase with the amount of particle incorporation. The enhanced hardness of the composite films was associated with modifications in the microstructure of the nickel matrix as well as with the nanoparticle incorporation. The wear resistance as examined by linear abrasion test increased with decreasing current density and due to the particle incorporation. Furthermore, the incorporation of magnetic nanoparticles resulted in a distinct increase of the magnetic hardness of the nickel matrix.

Hemodynamic monitoring is extremely important in the accurate measurement of vital parameters. Current methods are highly invasive or noncontinuous, and require direct access to the patient’s skin. This study intends to explore the modulated magnetic signature of blood method (MMSB) to attain blood flow information. This method uses an applied magnetic field to magnetize the iron in the red blood cells and measures the disturbance to the field with a magnetic sensor [1]. Exploration will be done by experimentally studying in-vitro, as well as simulating in COMSOL the alteration of magnetic fields induced by the flow of a magnetic solution. It was found that the variation in magnetic field is due to a high magnetization of blood during slow flow and low magnetization during rapid flow. The understanding of this phenomenon can be used in order to create a portable, non-invasive, continuous, and accurate sensor to monitor the cardiovascular system.

This work is motivated by the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) experiment. This device uses a helicon antenna to generate a plasma inside a dielectric tube, which is radially confined and directed towards the rocket nozzle by an axial magnetic field. An ion cyclotron heating antenna further heats the ions, and a magnetic nozzle accelerates the plasma along the confining magnetic field as it leaves the rocket, ultimately allowing it to detach from the magnetic field and produce thrust. The experimental research presented here provides insight into the physical mechanisms of power flow in a helicon system by providing an overall system power balance in the form of heat flux measurements, and exploring changes in the heat fluxes in different parts of the system in response to varying operational parameters. An infrared (IR) camera measures the total heat flux into the dielectric tube surface, and axially scanned bolometer and UV photodiode probes measure the radial power loss from particles and radiation. Results from IR camera measurements on three different helicon systems are presented: the VASIMR VX-50 experiment, the VASIMR VX-CR experiment, and the University of Texas at Austin (UT) helicon experiment. These results demonstrate the development of the IR camera diagnostic for use on helicon systems of varying scale and geometry, and show reasonable agreement as to the fraction of input power lost to the dielectric tube walls. On the UT experiment, the results presented account for essentially all of the input power, providing a full system power balance. The data from all three experiments indicate that radial transport of ions to the interior wall is the dominant mechanism of power loss, with UV radiation contributing a small percentage. Additional experiments on the UT helicon explore energy and particle transport to the wall due to capacitive coupling of ions near the antenna. These experiments show clear damage to the dielectric tube surface directly under the antenna, due to physical plasma etching of the surface by bombarding ions that are accelerated into the wall by local electric fields from the antenna. / text

Traditional methods of teaching magnetic induction with lab investigations using a battery, wire and compass are best reserved for demonstration purposes to introduce this particular topic. The modern student who sits in a physics course also lives in a world filled with an increasing number of small portable devices that will eventually be charged wirelessly using some form of magnetic induction. The topic of magnetic induction needs to be placed in the modern context it deserves since the future of transmitting power will eventually be through wireless means. The wireless power transfer kit described in this report is designed to improve student understanding and the application of magnetic induction in an engaging, relevant manner. / text

Diese Dissertation befasst sich mit Beobachtungen von konvektiven Strömungen in der Sonne, und insbesondere mit den Auswirkungen der Rotation auf diese Strömungen auf der Längenskala von Supergranulation und größeren Skalen (>30 Mm). Die Rotation der Sonne verursacht durch die Corioliskraft Wirbelströmungen und bewirkt anisotrope Korrelationen der Geschwindigkeitskomponenten. Man nimmt an, dass diese Korrelationen die Dynamik der Sonne auf großen Längenskalen beeinflussen. Um horizontale Strömungen zu messen, untersuchen wir photosphärische Aufnahmen der Doppler-Geschwindigkeit und der Kontinuumsintensität des ``Helioseismic and Magnetic Imagers'' (HMI) an Bord der Raumsonde ``Solar Dynamics Observatory'' (SDO) mit Hilfe der Methoden Time-Distance-Helioseismologie (TD) und Local Correlation Tracking (LCT) von Granulen. Im Rahmen der Time-Distance-Helioseismologie kann die lokale vertikale Vortizität gemessen werden, indem die Differenz von Wellenlaufzeiten entlang eines geschlossenen Weges ermittelt wird (Laufzeiten gegen den Uhrzeigersinn minus Laufzeiten im Uhrzeigersinn). Die Ergebnisse von TD und LCT stimmen bis zu den höchsten studierten Breitengraden (+/-60°) hervorragend überein, nachdem eine Korrektur für so genannte Center-to-Limb-Effekte angewandt wurde. Nach dem Mitteln in Ost-West-Richtung messen wir abseits des Äquators eine schwache, aber signifikante Korrelation zwischen der horizontalen Komponente der Divergenz und der vertikalen Komponente der Vortizität von supergranularen Strömungen. Ein Vergleich der Messungen mit einem Modell für das Rauschen offenbart, dass die TD-Methode verwendet werden kann, um die vertikale Vortizität von Strömungen auf Längenskalen größer als 15 Mm zu messen. Damit können mit dieser Methode nicht nur Strömungen in Supergranulen, sondern auch in Riesenzellen gemessen werden. Wir stellen außerdem fest, dass das Signal in Messungen der vertikalen Vortizität mit Hilfe von Aufnahmen von SDO/HMI sehr viel leichter detektiert werden kann als mit Hilfe von früheren Aufnahmen. Um den Einfluss der Sonnenrotation auf die Supergranulation im Detail zu studieren, kartieren wir die vertikale Vortizität der Strömungen in der durchschnittlichen Supergranule. Die durchschnittliche Supergranule wird konstruiert, indem Tausende von einzelnen Supergranulen in einem bestimmten Breitengradbereich durch räumliche Verschiebungen zur Deckung gebracht werden. Damit lösen wir zum ersten Mal die vertikale Vortizität in Aus- und Einströmungen räumlich auf. In nördlichen Breiten sind Ausströmungen im Mittel mit einer Zirkulation im Uhrzeigersinn verbunden. Das Signal verschwindet am Äquator und hat in südlichen Breiten das umgekehrte Vorzeichen. Aus- und Einströmungen besitzen eine vertikale Vortizität mit entgegengesetzten Vorzeichen, wie es von Vorhersagen erwartet wird, die sich auf die Corioliskraft stützen. Es wird offenbar, dass der Vortizitätspeak in der durchschnittlichen supergranularen Ausströmung vergleichsweise ausgedehnt und schwach ist (Halbwertsbreite von 13 Mm und Spitzenwert von 4 x 10^{-6}/s im Uhrzeigersinn bei 40° nördlicher Breite), verglichen mit der durchschnittlichen Einströmung (Halbwertsbreite von 8 Mm und Spitzenwert von 8 x 10^{-6}/s gegen den Uhrzeigersinn). Darüberhinaus untersuchen wir mit SDO/HMI-Daten das Magnetfeld in den Einströmungen um die durchschnittliche Supergranule am Äquator herum. Die mittlere Stärke des Magnetfelds stellt sich als richtungsabhängig heraus: In westlicher Richtung (prograd) ist das Netzwerkfeld ungefähr 10% stärker als in östlicher Richtung. Dieses überraschende Ergebnis fügt dem Rätsel um die Supergranulation einen weiteren Aspekt hinzu. Ob ein Zusammenhang mit anderen bekannten Eigenschaften der Supergranulation besteht (beispielsweise zur Superrotation des supergranularen Strömungsmusters oder zu wellenartigen Eigenschaften), ist nicht geklärt.