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.

Observations of the surface of the Sun reveal multi-scaled, mixed magnetic features that carpet the entire solar surface. Not surprisingly, the global magnetic fields extrapolated from these observations are highly complex. This thesis explores the topology of the Sun's global coronal magnetic fields. The magnetic skeleton of a magnetic field provides us with a way of examining the magnetic field and quantifying its complexity. Using specialised codes to find the magnetic skeletons which were written during the course of this work, we first examine potential field extrapolations of the global solar coronal magnetic field determined from observed synoptic magnetograms from the Heliospheric Magnetic Imager on the Solar Dynamics Observatory. The resolution of the PFSS models is found to be very important for discovering the true nature of the global magnetic skeleton. By increasing the maximum number of harmonics used in the potential field extrapolations and, therefore, the grid resolution, 60 times more null points may be found in the coronal magnetic field. These high resolution fields also have a large global separator network which connects the coronal magnetic field over large distances and involves between 40 % and 60 % of all the null points in the solar atmosphere. This global separator network exists at both solar minimum and solar maximum and has separators that reach high into the solar atmosphere (> 1R☉) even though they connect null points close to the solar surface. These potential field extrapolations are then compared with magnetohydrostatic (MHS) extrapolations of the coronal magnetic field which also provide us with information about the plasma in the corona. With a small component of electric current density in the direction perpendicular to the radial direction, these MHS fields are found to have a plasma beta and pressure typical of the corona. As this small component of electric current density grows, the heliospheric current sheet is warped significantly and the magnetic field, plasma beta and pressure become unphysical. Torsional spine reconnection is also studied local to a single null point. First using a dynamical relaxation of a spiral null point under non-resistive magnetohydrodynamics (MHD) to a MHS equilibrium is form in which a current layer has built up around the spine lines. Then the reconnection under resistive MHD in this current sheet is studied. The current about the spine lines is dissipated and the magnetic energy is mainly converted into heat directly as the field lines untwist about the spine line.

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.

Black hole-neutron star (BH-NS) mergers are promising candidates for the progenitors of short-duration gamma-ray bursts (GRBs). With the right initial conditions, the neutron star becomes tidally disrupted, eventually forming a dense, accreting disk around the black hole. The thermal energy of this black hole-disk system can be extracted via neutrino processes, while the spin energy of the black hole can be extracted via magnetic processes. Either (or even a combination of these) processes could feasibly power a relativistic jet with energy ≥~ 10 49 erg and duration ≤~ 2 s, hence producing a short-duration GRB. In this thesis, we investigate BH-NS mergers with three-dimensional, pseudo-Newtonian simulations. We use the simulation code Charybdis, which uses a dimensionally-split, reconstruct-solve-average scheme (i.e. using Riemann solvers) to solve the Euler equations of hydrodynamics. Although the code is based on a Newtonian framework, it includes pseudo- Newtonian approximations of local gravitational wave effects and the innermost stable circular orbit of the BH, which are both general relativistic phenomena. The code also includes the effects of global neutrino emission, shear viscosity and self-gravity. This thesis comprises two main projects. The first project is a parameter study of the equation of state, which encapsulates the relationship between the pressure of a fluid and its other thermodynamic properties. Although the EOS is well understood at low densities, it is yet to be constrained at supranuclear densities, and so must be treated as a parameter in numerical studies of BH-NS mergers. We present simulations using three existing EOSs, in order to investigate their effect on the merger dynamics. We find that the EOS strongly influences the fate of the NS, the properties of the accretion disk, and the neutrino emission. In the second project, we begin upgrading Charybdis to include magnetic field effects, in order to investigate the magnetic processes described above. We implement existing reconstruction and Riemann solver algorithms for the equations of magnetohydrodynamics, and present 1D tests to compare them. When modelling magnetic fields in more than one dimension, we must also deal with the divergence-free condition, ∇. B = 0. We develop a new constrained transport algorithm to ensure our code maintains this condition, and present 2D tests to confirm its accuracy. This algorithm has many advantages over existing ones, including easier implementation, greater computational efficiency and better parallelisation. Finally, we present preliminary tests that use these algorithms in simulations of BH-NS mergers.

The circumnuclear disc (CND) orbiting the Galaxy's central black hole is a reservoir of material that can ultimately provide energy through accretion, or form stars in the presence of the black hole, as evidenced by the stellar cluster that is presently located at the CND's centre. In this paper, we report the results of a computational study of the dynamics of the CND. The results lead us to question two paradigms that are prevalent in previous research on the Galactic Centre. The first is that the disc's inner cavity is maintained by the interaction of the central stellar cluster's strong winds with the disc's inner rim, and secondly, that the presence of unstable clumps in the disc implies that the CND is a transient feature. Our simulations show that, in the absence of a magnetic field, the interaction of the wind with the inner disc rim actually leads to a filling of the inner cavity within a few orbital time-scales, contrary to previous expectations. However, including the effects of magnetic fields stabilizes the inner disc rim against rapid inward migration. Furthermore, this interaction causes instabilities that continuously create clumps that are individually unstable against tidal shearing. Thus the occurrence of such unstable clumps does not necessarily mean that the disc is itself a transient phenomenon. The next steps in this investigation are to explore the effect of the magnetorotational instability on the disc evolution and to test whether the results presented here persist for longer time-scales than those considered here.

The solar corona is a highly complex and active plasma environment, containing many exotic phenomena such as solar flares, coronal mass ejections, prominences, coronal loops, and bright points. The fundamental element giving coherence to all this apparent diversity is the strong coronal magnetic field, the dominant force shaping the plasma there. In this thesis, I model the 3D magnetic fields of various coronal features using the techniques of magnetic charge topology (MCT) in a potential field. Often the real coronal field has departures from its potential state, but these are so small that the potential field method is accurate enough to pick out the essential information about the structure and evolution of the magnetic field. First I perform a topological analysis of the magnetic breakout model for an eruptive solar flare. Breakout is represented by a topological bifurcation that allows initially enclosed flux from the newly emerging region in my MCT model of a delta sunspot to reconnect out to large distances. I produce bifurcation diagrams showing how this behaviour can be caused by changing the strength or position of the emerging flux source, or the force-free parameter α. I also apply MCT techniques to observational data of a coronal bright point, and compare the results to 3D numerical MHD simulations of the effects of rotating the sources that underlie the bright point. The separatrix surfaces that surround each rotating source are found to correspond to locations of high parallel electric field in the simulations, which is a signature of magnetic reconnection. The large-scale topological structure of the magnetic field is robust to changes in the method of deriving point magnetic sources from the magnetogram. Next, I use a Green’s function expression for the magnetic field to relax the standard topological assumption of a flat photosphere and extend the concept of MCT into a spherical geometry, enabling it to be applied to the entire global coronal magnetic field. I perform a comprehensive study of quadrupolar topologies in this new geometry, producing several detailed bifurcation diagrams. These results are compared to the equivalent study for a flat photosphere. A new topological state is found on the sphere which has no flat photosphere analogue; it is named the dual intersecting state because of its twin separators joining a pair of magnetic null points. The new spherical techniques are then applied to develop a simple six-source topological model of global magnetic field reversal during the solar cycle. The evolution of the large-scale global magnetic field is modelled through one complete eleven-year cycle, beginning at solar minimum. Several distinct topological stages are exhibited: active region flux connecting across the equator to produce transequatorial loops; the dominance of first the leading and then the following polarities of the active regions; the magnetic isolation of the poles; the reversal of the polar field; the new polar field connecting back to the active regions; the polar flux regaining its dominance; and the disappearance of the transequatorial loops.