The propagation and damping of slow magnetoacoustic waves in the solar atmosphere is investigated, with particular emphasis placed on waves with periodicities of five minutes. The basic model of a uniform temperature loop is extended by the addition of an equilibrium temperature gradient allowing study of wave propagation from the transition region to the corona. The inclusion of thermal conduction produces a phase shift between the perturbations in velocity, density and temperature, which for a non-uniform equilibrium temperature varies along the loop and may be observable as a phase shift between intensity and Doppler shift observations. Forward modelling of the simulation results, for both constant and non-constant equilibrium temperature profiles, is undertaken in order to establish the observational consequences for TRACE, SoHO/CDS and Hinode/EIS. Slow waves propagating in a non-uniform equilibrium temperature loop are seen to damp rapidly in the corona, however, as a result of the ionisation balance, the inclusion of damping can actually increase the amplitude of some parts of the oscillation. The ability of several data analysis techniques to identify oscillation signatures are examined. In particular, empirical mode decomposition was found to be a very useful technique for extracting oscillations from a wide range of data sets and is capable of intrinsically determining background trends. Co-spatial and cotemporal TRACE 171 A, CDS and EIS data are analysed for evidence of propagating slow waves. Slow waves with periods of 210 s to 370 s are found with amplitudes of 1.2% to 3.4% in the corona and 2.3% to 6.0% in the transition region.

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Orientador: Antonio Manoel Mansanares. / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin. / Made available in DSpace on 2018-08-12T12:29:07Z (GMT). No. of bitstreams: 1 Guimaraes_AndreOliveira_D.pdf: 2906238 bytes, checksum: a8ad8b4fc0c3d5bbca6671977306a943 (MD5) Previous issue date: 2008 / Resumo: Neste trabalho foram desenvolvidas montagens experimentais baseadas na detecção foto acústica para o estudo de materiais magnetocalóricos, que têm despertado um grande interesse na comunidade científica em virtude de suas possíveis aplicações em sistemas de refrigeração. Utilizando o método de dois feixes, para a configuração fotoacústica ar-amostra-ar, foi possível determinar para a difusividade térmica do Gd, em temperatura ambiente, o valor de (4,5 ± 0,2).10-6 m2/s, por meio da amplitude e da fase do sinal fotoacústico normalizado. Medidas da fase do sinal em varreduras de temperatura permitiram a determinação da difusividade térmica em torno da transição magnética (TC), de forma confiáavel e reprodutiva,a com erros menores que 5%. Com base em princípios envolvidos na fotoacústica, foi desenvolvido um método para medidas do efeito magnetocalórico (EMC). O aquecimento gerado nos materiais em questão pela aplicação de um campo magnético alternado (AC), via efeito magnetocalórico, dá origem a ondas de pressão num gás, que são detectadas por um microfone. Discutiu-se sobre os procedimentos de calibracão envolvidos e a metodologia utilizada para a determinação do efeito. Foram realizadas medidas com amostras de Gd e compostos da família Gd5(Ge1-xSix)4, em pó e em pastilhas. Para um campo aplicado de 20 kOe, os valores máximos do EMC vão de 3 K, para o Gd, a 4,5 K, para os compostos ricos em Si, e se referem a transições magnéticas de segunda ordem. Para amostras com x = 0,5, os valores máximos do EMC estão em torno de 1,7 K, referentes a transições magneto-estruturais de primeira ordem. Para alguns destes compostos e possível observar os dois tipos de transição. Os resultados indicam que a técnica se mostra eficiente, não só para as medidas do efeito em si, mas também para a identificação de fases indesejadas, decorrentes do processo de preparação das amostras. Os erros nas medidas do EMC estão em torno de 15 - 20%, comparáveis aos dos métodos convencionais / Abstract: In this work the photoacoustic technique was used to develop experimental setups to investigate magnetocaloric materials, which have been of great interest due to their applications in refrigeration systems. The value (4,5 ± 0,2).10-6 m2/s was determined, at room temperature, as the thermal di usivity of the Gd, based on the two-beam photoacoustic method, by means of both amplitude and phase of the normalized signal. The thermal diffusivity at temperatures around the magnetic transition (TC) was obtained from the photoacoustic signal phase, in temperature scans, in a reproductible and accurate way, with errors below 5%. A method for measuring the magnetocaloric e ect (MCE), based on the acoustic detection, was developed. The temperature oscillations on such materials, due to the application of an alternating magnetic field, produce acoustic waves which can be detected by a microphone. The details concerning the calibration procedure and the proposed methodology to determine the MCE were discussed, and measurements on Gd and Gd 5(Ge1-xSix)4 compouds were performed in powder and pellet samples. For a 20 kOe applied field, the maximum MCE values, related to magnetic second order transitions, are between 3 K, for the Gd, and 4,5 K, for Si - rich compounds. For the samples with x = 0,5, the maximum MCE values are around 1,7 K, related to magneto-structural first order transitions. It is also possible, for some samples, to observe both first and second order transitions. The obtained results point out this acoustic type detection as an effcient technique to measure the magnetocaloric effect, as well as to detect spurious phases present in some of these compounds. The errors in the MCE measurements are about 15-20%, compared to conventional methods / Doutorado / Física da Matéria Condensada / Doutor em Ciências

The subject of this thesis is the numerical simulation of magneto hydro dynamic waves in the neutral current layer. In the first part, attention is described to the description of basic characteristics and Sun. The next section describes introduction to the theory of MHD equations suitable for solution of wave propagation in a neutral current layer. Then we deal with the numerical simulations of fast magnetoacoustic waves in the neutral current layer. The last section is devoted to the results obtained, their analysis and conclusion.

The topic of the master thesis are the numerical simulations of magnetoacoustic waves in the solar corona in relation to the reconnection of magnetic field. The first part is devoted to the basic description of the Sun, its atmosphere and the processes that occur in it. Other sections are devoted to the description of reconnection of magnetic field and the description of solar flares taking place in the solar corona in relation to the mechanisms of magnetic field reconnection. Then the attention is focused on plasma waves and oscilations. The last section aims to simulate the startup options of the reconnection of magnetic field by oscillations and waves in the Harris current-sheet. Numerical simulations are implemented in FLASH 3.3.