Several previous studies, including one using early Sanae radar data, have found examples of high speed ionospheric plasma flows on the nightside, mapping to the magnetospheric tail, during periods which were magnetically quiet. These high speed flows were interpreted to be associated with the release of energy from a rapid reconfiguration of tail magnetic field lines due to reconnection. Such events are now known as ‘TRINNIs’ or ‘tail reconnection during IMF northward, non-substorm intervals’. The purpose of this study was to identify further TRINNI events, using SuperDARN data from both hemispheres. In situations where the y-component of the Interplanetary Magnetic Field dominates over the z-component, the directions of both the high speed flows and the underlying convection pattern depend on the direction of the y-component. Some examples of likely TRINNI events for cases where the y-component was positive and negative are presented and discussed. The assumption of a non-substorm interval is justified by magnetometer and GOES satellite data, and the observations are discussed in relation to magnetic reconnection in the magnetotail. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2010.

Magnetic flux continually emerges from the Sun, rising through the solar interior, emerging at the photosphere in the form of sunspots and expanding into the atmosphere. Observations of sunspot rotations have been reported for over a century and are often accompanied by solar eruptions and flaring activity. In this thesis, we present 3D numerical simulations of the emergence of twisted flux tubes from the uppermost layers of the solar interior, examining the rotational movements of sunspots in the photospheric plane. The basic experiment introduces the mechanism and characteristics of sunspot rotation by a clear calculation of rotation angle, vorticity, magnetic helicity and energy, whereby we find an untwisting of the interior portion of the field, accompanied by an injection of twist into the atmospheric field. We extend this model by altering the initial field strength and twist of the sub-photospheric tube. This comparison reveals the rotation angle, helicity and current show a direct dependence on field strength. An increase in field strength increases the rotation angle, the length of fieldlines extending into the atmosphere, and the magnetic energy transported to the atmosphere. The fieldline length is crucial as we predict the twist per unit length equilibrates to a lower value on longer fieldlines, and hence possesses a larger rotation angle. No such direct dependence is found when varying the twist but there is a clear ordering in rotation angle, helicity, and energy, with more highly twisted tubes undergoing larger rotation angles. We believe the final angle of rotation is reached when the system achieves a constant degree of twist along the length of fieldlines. By extrapolating the size of the modelled active region, we find rotation angles and rates comparable with those observed. In addition, we explore sunspot rotation caused by sub-photospheric velocities twisting the footpoints of flux tubes.

The solar corona is a highly conductive plasma which is dominated by the coronal magnetic field. Observations show that important solar phenomena like flares or the heating of the corona are driven by magnetic energy, probably through the process of magnetic reconnection. The release of magnetic energy by reconnection requires that non-ideal processes take place in contradiction to the high conductivity of the corona. One possibility to overcome this problem is to generate strong electrical currents in strongly localised regions. In this thesis we investigate how such localised currents can be formed by slow ideal evolution of topologically simple magnetic fields. To this purpose numerical simulations are carried out using an Eulerian and a Lagrangian MHD relaxation code. We first use a simple example (twisting of a uniform field) to investigate the advantages and disadvantages of both codes and to discover possible limitations for their application. We show that for the problems addressed in this thesis the Lagrangian code is more suited because it can resolve the localised current densities much better than the Eulerian code. We then focus in particular on magnetic fields containing a so-called Hyperbolic Flux Tube (HPT). A recently proposed analytical theory predicts that HFT's are sites where under certain conditions strong current build-up can be expected. We use our code to carry out a systematic parametric study of the dependence of current growth for a typical HFT configuration. We have also developed a completely new version of the analytical theory which is directly based on the set-up of our numerical simulations. We find that the simulations agree with the analytical prediction in a quantitative way but that the analytical theory underestimates the current growth quite substantially, probably by not taking into account the non-linear character of the full problem.

Although the solar corona is one of the most studied areas in solar physics, its activity, such as flares, prominence eruptions and CMEs, is far from understood. Since the solar corona is a low-ß plasma, its structure and dynamics are driven by the magnetic field. The aim of this PhD thesis to study the magnetic field in the solar corona. Unfortunately, high quality direct measurements of the coronal magnetic field are not available and theoretical extrapolation using the observed photospheric magnetic field is required. The thesis is mainly divided in two parts. The first part deals with the comparison between theoretical models of magnetic fields and observed structures in the corona. For any theoretical model, a quantitative method to fit magnetic field lines to observed coronal loops is introduced. This method provides a quantity C that measures how closely a theoretical model can reproduce the observed coronal structures. Using linear force-free field extrapolation, the above field line fitting method is used to study the evolution of an active region. The method is also illustrated when the theoretical magnetic field depends on more than one parameter. The second part of the thesis focuses on the linear force-free field assumption using two different geometric configurations. Firstly a vertical rigid magnetic flux tube is considered. The analytical expression of the magnetic field is obtained as an expansion in terms of Bessel functions. The main properties of this system are discussed and compared with two cylindrically symmetric twist profiles. For the second system, the photosphere is assumed to be an infinite plane. Using translational geometry, the analytical expression of the linear force-free magnetic field that matches a prescribed line of sight magnetic field component is obtained. This solution is compared with the non-linear solution obtained by Roumeliotis (1993).

Orientadores: José Antenor Pomilio, Giancarlo Tosin / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-27T01:27:04Z (GMT). No. of bitstreams: 1 Baader_JohannEduardo_M.pdf: 5709999 bytes, checksum: b70a7b9c4f9062486fb33d399ad88653 (MD5) Previous issue date: 2015 / Resumo: Desde 1997 o Brasil tem acesso à tecnologia de radiação síncrotron com a inauguração do Laboratório Nacional de Luz Síncrotron (LNLS), localizado na cidade de Campinas, SP. Batizada de UVX, a fonte de luz síncrotron brasileira foi um marco no desenvolvimento científico e tecnológico do país, permitindo pesquisas nas mais diversas áreas do conhecimento, como nanotecnologia, biotecnologia, fármacos, agricultura, energias alternativas, dentre outros. Em 2009 o LNLS iniciou o projeto e a construção de uma nova fonte de luz síncrotron brasileira. Nomeada Sirius, está sendo desenvolvida para ser uma das mais avançadas do mundo na geração de luz síncroton. O alto desempenho deste tipo de máquina depende fortemente da qualidade dos campos magnéticos criados pelos inúmeros magnetos que compõem a rede magnética, o que exigem uma técnica de caracterização rápida, acurada e precisa. O Grupo de Magnetos, responsável pelo projeto, construção e caracterização dos magnetos tanto da fonte UVX como da nova fonte, utiliza um sistema de medição conhecido como Técnica de Bobina Girante. Devido às especificações do projeto Sirius, foi necessário o aprimoramento da bancada de caracterização, objetivo este consolidado principalmente através da análise minuciosa das principais fontes de erro do sistema. Um modelo numérico desenvolvido para estudar algumas classes de erros da técnica deu suporte para diversas correções na bancada, o que permitiu alcançar níveis de precisão comparáveis com os sistemas de caracterização de outros laboratórios. Paralelamente, foi construída a bancada de um sistema protótipo de medição magnético, nomeado Técnica de Minibobina Girante, apresentando uma série de vantagens em relação às limitações da bancada oficial. Algumas das melhorias realizadas nesta bancada durante o seu desenvolvimento foram baseadas nos resultados advindos do modelo numérico das fontes de erros / Abstract: Since 1997 Brazil has access to synchrotron radiation technology with the inauguration of the Brazilian Synchrotron Light Source (LNLS), located in Campinas, Brazil. The source of Brazilian synchrotron light known as UVX was a milestone in scientific and technological development of the country, enabling research in several areas of knowledge such as nanotechnology, biotechnology, pharmaceuticals, agriculture, alternative energy etc. In 2009 LNLS initiated the project and the construction of a new source of Brazilian synchrotron light, named Sirius. It is being developed to be one of the most advanced in the world in the generation of synchrotron light. The high performance of this type of machine depends strongly on the quality of the magnetic fields created by magnets that compose the lattice, which demand a fast, accurate and precise characterization technique. The Magnets Group, responsible for the design, construction and characterization of both the magnetic UVX sources as new sources, uses a measuring system known as Rotating Coil System. Due to the specifications of the Sirius design, an improved characterization bench was necessary. This goal was achieved mainly through a careful analysis of the main sources of error in the system. A numerical model to study some classes of errors in the technique provided support for various fixes in the bench, which allowed us to achieve comparable levels of accuracy along with the characteristics of the systems from other laboratories. At the same time, another bench was built as a prototype system for magnetic measurements known as Small Rotating Coil System, presenting a series of advantages over the constraints of the main bench. Some of the improvements made on this bench during its development were based on the results derived from the numerical model of error sources / Mestrado / Energia Eletrica / Mestre em Engenharia Elétrica

Magnetic fields play a key role in a wide variety of phenomena found on the Sun. One such phenomena is the Coronal Mass Ejection (CME) where a large amount of material is ejected from the Sun. CME’s may directly affect the earth, therefore understanding their origin is of key importance for space weather and the near-Earth environment. In this thesis, the nature and evolution of solar magnetic fields is considered through a combination of Magnetic Flux Transport Simulations and Potential Field Source Surface Models. The Magnetic Flux Transport Simulations produce a realistic description of the evolution and distribution of the radial magnetic field at the level of the solar photosphere. This is then applied as a lower boundary condition for the Potential Field Source Surface Models which prescribe a coronal magnetic field. Using these two techniques, the location and variation of coronal null points, a key element in the Magnetic Breakout Model of CMEs, are determined. Results show that the number of coronal null points follow a cyclic variation in phase with the solar cycle. In addition, they preferentially form at lower latitudes as a result of the complex active latitude field. Although a significant number of coronal nulls may exist at any one time (≈ 17), it is shown that only half may satisfy the necessary condition for breakout. From this it is concluded that while the Magnetic Breakout Model of CMEs is an important model in understanding the origin of the CMEs, other processes must occur in order to explain the observed number of CMEs. Finally, the Magnetic Flux Transport Simulations are applied to stellar magnetic fields and in particular to the fast rotating star HD171488. From this speculative study it is shown that the Magnetic Flux Transport Simulations constructed for the Sun may be applied in very different stellar circumstances and that for HD171488 a significantly higher rate of meridional flow (1200-1400 ms⁻¹) is required to match observed magnetic field distributions.

This study examined the short term memory (STM) difference of magnetic resonance imaging (MRI) technologists versus non-MRI technologists. Human and animal studies have indicated that residual magnetic fields have caused changes within the cerebral structure. Research on residual magnetic fields and their effect on STM is still at its infancy. A quasi-experimental design was used to determine if any significant difference existed between the STM of MRI technologists (n = x) and a control population sample (n = x). The STM of both groups was assessed with the use of the Rivermead Behavioural Memory Test-Third Edition. Solicitation of the participants was from a national MRI organization, the American Society of Radiologic Technologists, and community workers within the profession. The control group of participants was solicited through community board postings. Only the New York/New Jersey metro area and the New Hampshire/Maine area participants were used for this study. These participants were of various age ranges, genders, and educational levels. ANOVA and regression analyses were used to analyze the data. The study showed mixed results, indicating no significant STM difference in the overall memory scores of both groups F (1, 80) =3.061, p =..084, but it did show a significant difference in STM when it came to prospective memory, memory of planned events. These findings illustrate a need for further research in this area. Expanding the geographical reach and sample size could clarify the role of MRI on STM. The results of this study suggest that procedures that limit the exposure of the MRI technologists to the residual magnetic fields surrounding MRI machines could yield a reduction in loss of prospective memory.

This thesis aims to develop a calculation method to determine themagnetic field magnitudes in the vicinity of power lines, i.e. bothburied cables and overhead lines. This is done through the numericaluse of Biot Savart's law where the conductors are approximated by aseries of straight segment elements that each contribute to the overallfield strength at the field point. The method is compared to two realcases and to the exact integral solution. Also, a review of some of theresearch material regarding electromagnetic fields from power lines andclaims of adverse health effects due to these fields is conducted.Results show that the numerical error is dependent on the segmentationdegree of the conductors and the mathematical model is inaccurate closeto the conductor. The calculations show slightly higher fieldmagnitudes than the previous survey done by WSP (Williams SalePartnership) far away from the source and slightly lower at the centerconductor. This may be due to the excluded induction in the shieldwires and differences in actual conductor coordinates.

Call number: LD2668 .T4 1966 S562 / Master of Science

Our knowledge of stellar magnetic fields relies almost entirely on circular polarization observations, which has historically limited our understanding of the stellar magnetic field topologies. Recently, it has become possible to obtain phase-resolved high-resolution spectropolarimetric observations in all four Stokes parameters for early-type magnetic stars. Interpretation of such observations with the Magnetic Doppler imaging technique has uncovered a new, previously unknown, level of complexity of surface stellar magnetic fields. This new insight is critical for understanding the origin, evolution and structure of magnetic fields in early-type stars. In this study we observed the magnetic, chemically peculiar Ap stars HD 24712 (DO Eri, HR 1217) and HD 125248 (CS Vir, HR 5355) in all four Stokes parameters with the HARPSpol spectropolarimeter at the ESO 3.6-m telescope. The resulting spectra have high signal-to-noise ratio and superb resolving power, by far surpassing the quality of any existing stellar Stokes parameter observations. We studied variation of the spectrum and magnetic observables of HD 24712 as a function of rotational phase (paper I). In the subsequent magnetic Doppler imaging investigation of this star, we interpreted the phase-resolved Stokes line profile observations (paper II). This analysis showed that HD 24712, unlike more massive Ap stars studied in all four Stokes parameters, has a dominant dipolar field component with a negligible contribution of small-scale magnetic structures. Simultaneously with magnetic mapping we derived surface abundance distributions of Fe, Nd, Na, and Ca. Building upon the technique of Magnetic Doppler imaging, we developed the first three-dimensional abundance inversion code and applied it to reconstruct the abundance distributions of Fe and Ca in three dimensions in the atmosphere of HD 24712 (paper III). We also performed Magnetic Doppler imaging analysis of the spectropolarimetric observations of HD 125248 (paper IV). The reconstructed detailed maps of the surface abundance distribution and magnetic field topology of HD 125248 revealed a magnetic field with significant deviations from the canonical dipolar field geometry, and strong surface abundance inhomogeneities for Cr and several rare earth elements. We assessed our inversion results in the context of magnetic Doppler imaging studies of other magnetic, chemically peculiar Ap stars and latest theoretical research on the evolution and stability of magnetic fields in radiative stellar interiors. Our analysis suggests that old or less massive Ap stars have predominantly dipolar magnetic fields while more massive or younger stars exhibit more complicated field topologies. We also compared our three-dimensional chemical abundance maps of HD 24712 to the predictions of theoretical atomic diffusion calculations in magnetized stellar atmospheres, generally finding a lack of agreement between theory and observations.