I investigate the self-force acting on static scalar and electric charges in Schwarzschild-de Sitter and Schwarzschild-Anti-de Sitter spacetimes. The self-force occurs when a charged particle's field interacts with the curvature of spacetime so that the particle interacts with its own field. Because the field of a point particle is singular at the location of the particle, it is necessary to decompose the field into a regular part responsible for the self-force and a singular part that does not contribute to the self-force. To do this, I use the mode-sum regularization scheme introduced by Barack and Ori, in which the field is decomposed into a sum over modes, and the singular part is removed from each mode using so-called regularization parameters. I find that the electrostatic self-force in Schwarzschild-de Sitter and Schwarzschild-Anti-de Sitter behaves similarly to Schwarzschild self-force near the black hole, but can deviate strongly at larger distances. This is especially true in Schwarzschild-Anti-de Sitter, where the self-force is seen to increase linearly with distance. I provide an explanation for this behaviour using conformal transformations. A particular feature evident in Schwarzschild-Anti-de Sitter is that the self-force can become negative (attractive) at small distances when the Schwarzschild radius and the cosmological length scale are of a similar order. I find that the scalar self-force in Schwarzschild-de Sitter can not actually be computed, and in Schwarzschild-Anti-de Sitter the asymptotic behaviour is similar to its electrostatic counterpart.

Orientador: Fernando Galembeck / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-27T09:01:49Z (GMT). No. of bitstreams: 1 Balestrin_LiaBeraldodaSilveira_M.pdf: 4255591 bytes, checksum: c4d0f9d5952dc35354bfb9f0d111643b (MD5) Previous issue date: 2015 / Resumo: Quando dois materiais isolantes são atritados, ocorre a triboeletrização de suas superfícies, isto é, a formação de cargas estáticas, distribuídas em padrões fractais. Uma das hipóteses para explicar a eletrização de isolantes é a ocorrência de reações mecanoquímicas seguidas da transferência mútua de massa. Esta dissertação apresenta mapas de potencial elétrico de superfícies atritadas, que também foram examinadas por microscopia eletrônica de varredura (SEI, BEI) e microanálise EDX. Os resultados verificam a hipótese mecanoquímica associada à transferência de fragmentos poliméricos iônicos, sendo as reações iniciadas pela quebra de cadeias seguida da formação de várias espécies de alta energia e produtos de oxidação. Microanálises também detectaram a fixação de N2 nestas superfícies, evidenciando a participação da atmosfera e a formação de triboplasma. As imagens BEI revelam uma distribuição fractal de composição química consistente com a distribuição de fragmentos limitada por difusão, mas superior à dimensão fractal de distribuição de cargas. Esta diferença é atribuída à supressão de cargas devido a microdescargas elétricas desencadeadas por gradientes superiores à rigidez dielétrica do sólido ou do ar. As microdescargas diminuem os gradientes elétricos, mas, ao mesmo tempo, geram novas espécies muito reativas, aumentando a heterogeneidade química das superfícies. Essa dissertação descreve também alguns experimentos acerca da eletrização produzida por simples contato, obtendo-se padrões bem definidos com tempo de contato de 1 h, porém não revelam a transferência de fragmentos poliméricos mutuamente, sugerindo que o cisalhamento desempenhe um papel importante na transferência de fragmentos poliméricos eletrizados. Em um menor grau de aprofundamento, esta dissertação contempla outras consequências de cargas estáticas, como alterações no coeficiente de atrito / Abstract: Triboelectrification occurs when two insulators are rubbed, i.e. static charges are formed on the surface with a fractal distribution pattern. One of the hypotheses raised by the literature indicates that the electrification is accompanied by mutual mass transfer. This dissertation presents electric potential maps of rubbed surfaces, which were also examined by scanning electron microscopy (SEI, BEI) and EDX microanalysis. The results verify the hypothesis that the electrification is due to mechanochemical reactions associated with transfer of charged polymeric fragments. The reaction is initiated by breaking the chains, generating reactive species and oxidation products. Microanalysis also detected N2 fixation on these surfaces, evidencing the contribution of the atmosphere and the formation of triboplasma. The BEI images show a fractal distribution of chemical composition consistent with a fragment distribution limited by diffusion, but higher than the fractal dimension of the charge distribution. This difference is attributed to the suppression of charges due to electrical micro discharge triggered by gradients higher than the dielectric strength of solid or air. The micro discharges decrease electrical gradients, but at the same time, generates very reactive species further increasing the chemical heterogeneity of surfaces. This dissertation also describes some experiments about the electrification produced by single contact, resulting in well-defined patterns with a contact time of 1 h, but do not show the mutual transfer of polymeric fragments, suggesting that the shearing plays an important role in transferring electrified fragments. This work also includes other consequences of static charges, such as changes in the friction coefficient / Mestrado / Físico-Química / Mestra em Química

Ultraprecision single point diamond turning is required to produce parts with sub-nanometer surface roughness and sub-micrometer surface profiles tolerances. These parts have applications in the optics industry, where tight form accuracy is required while achieving high surface finish quality. Generally, parts can be polished to achieve the desired finish, but then the form accuracy can easily be lost in the process rendering the part unusable. Currently, most mid to low spatial frequency surface finish errors are inspected offline. This is done by physically removing the workpiece from the machining fixture and mounting the part in a laser interferometer. This action introduces errors in itself through minute differences in the support conditions of the over constrained part on a machine as compared to the mounting conditions used for part measurement. Once removed, the fixture induced stresses and the part’s internal residual stresses relax and change the shape of the generally thin parts machined in these applications. Thereby, the offline inspection provides an erroneous description of the performance of the machine. This research explores the use of a single, high resolution, capacitance sensor to quickly and qualitatively measure the low to mid spatial frequencies on the workpiece surface, while it is mounted in a fixture on a standard ultraprecision single point diamond turning machine after a standard facing operation. Following initial testing, a strong qualitative correlation exists between the surface profiling on a standard offline system and this online measuring system. Despite environmental effects and the effects of the machine on the measurement system, the capacitive system with some modifications and awareness of its measurement method is a viable option for measuring mid to low spatial frequencies on a workpiece surface mounted on an ultraprecision machine with a resolution of 1nm with an error band of ±5nm with a 20kHz bandwidth. / Thesis / Master of Applied Science (MASc)