Orientador: Jose Pissolato Filho / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-13T18:17:26Z (GMT). No. of bitstreams: 1 Silva_ValeriaCristiane_M.pdf: 9885573 bytes, checksum: eee5ffee7c0a540498ec7bb5a8436b15 (MD5) Previous issue date: 2009 / Resumo: Este trabalho apresenta a elaboração e a construção de um sensor utilizado na detecçãode intensidade de campo elétrico e consequentemente de descargas atmosféricas. O sensor de diâmetro igual a 10 cm é constituído por uma placa girante composta por quatro aletas, que tem seu movimento de rotação controlado por um mini motor de 12000 rpm, e uma placa fixa, denominada placa de medição, composta por oito aletas que são responsáveis por produzir uma tensão alternada referente ao campo elétrico ao qual o sensor está submetido. Quando o rotor (placa girante) gira sobre o estator (placa de medição), ele expõe a placa de medição ao campo elétrico e isola-o deste campo quando está sobre ele. Dessa forma corta-se o campo elétrico normal estático ou que varia muito lentamente. O medidor de campo elétrico (EFM - do inglês Eletric Field Mill ) cria um campo "variável" que irá induzir uma carga elétrica no estator. A magnitude e polaridade da carga são dependentes da magnitude e polaridade do campo elétrico. A placa de medição gera um sinal da ordem de milivolts, sendo necessário a utilização de amplificadores para torná-lo significante para análise. O sinal amplificado será então digitalizado e enviado à um software para visualização dos dados gerados pelo sensor. Neste trabalho apresenta-se também um estudo sobre origem de cargas nas nuvens, formação de tempestade, assim como formação e classificação dos raios. / Abstract: This paper presents the development and construction of a sensor used to detect intensity of electric field and consequently of lightning. The sensor diameter of 10 cm consists of a plate consisting of four revolving vanes that has its rotation controlled by a small motor to 12000 rpm and a fixed plate, called a measuring board, composed of eight vanes that are responsible for produce a alternating voltage electric field concerning which the sensor is subjected. When the rotor (revolving vanes) turns on the stator (plate measurement), it exposes the plate for measuring the electric field alone, and the field when this is over it. Thus is cut to the normal static electric field or which varies very slowly. The electric field meter (EFM - the English Electric Field Mill) creates a field "variable" that will induce an electric charge in the stator. The magnitude and polarity of the load are dependent on the magnitude and polarity of the electric field. The measurement plate generates a measurement signal of the order of millivolts, requiring the use of amplifiers to make it significant for analysis. The amplified signal is then digitized and sent to a software for visualization of data generated by the sensor. In this work it is also a study of origin of cargoes in the clouds, formation of storm as well as training and classification of rays. / Mestrado / Energia Eletrica / Mestre em Engenharia Elétrica

I develop the first magnetospheric accretion model to take account of the observed complexity of T Tauri magnetic fields, and the influence of stellar coronae. It is now accepted that accretion onto classical T Tauri stars is controlled by the stellar magnetosphere, yet to date the majority of accretion models have assumed that the stellar magnetic field is dipolar. By considering a simple steady state accretion model with both dipolar and complex magnetic fields I find a correlation between mass accretion rate and stellar mass of the form M[dot above] proportional to M[asterisk subscript, alpha superscript], with my results consistent within observed scatter. For any particular stellar mass there can be several orders of magnitude difference in the mass accretion rate, with accretion filling factors of a few percent. I demonstrate that the field geometry has a significant effect in controlling the location and distribution of hot spots, formed on the stellar surface from the high velocity impact of accreting material. I find that hot spots are often at mid to low latitudes, in contrast to what is expected for accretion to dipolar fields, and that particularly for higher mass stars, accreting material is predominantly carried by open field lines. Material accreting onto stars with fields that have a realistic degree of complexity does so with a distribution of in-fall speeds. I have also modelled the rotational modulation of X-ray emission from T Tauri stars assuming that they have isothermal, magnetically confined coronae. By extrapolating from surface magnetograms I find that T Tauri coronae are compact and clumpy, such that rotational modulation arises from X-ray emitting regions being eclipsed as the star rotates. Emitting regions are close to the stellar surface and inhomogeneously distributed about the star. However some regions of the stellar surface, which contain wind bearing open field lines, are dark in X-rays. From simulated X-ray light curves, obtained using stellar parameters from the Chandra Orion Ultradeep Project, I calculate X-ray periods and make comparisons with optically determined rotation periods. I find that X-ray periods are typically equal to, or are half of, the optical periods. Further, I find that X-ray periods are dependent upon the stellar inclination, but that the ratio of X-ray to optical period is independent of stellar mass and radius. I also present some results that show that the largest flares detected on T Tauri stars may occur inside extended magnetic structures arising from the reconnection of open field lines within the disc. I am currently working to establish whether such large field line loops can remain closed for a long enough time to fill with plasma before being torn open by the differential rotation between the star and the disc. Finally I discuss the current limitations of the model and suggest future developments and new avenues of research.