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京都大学 / 新制・課程博士 / 博士(理学) / 甲第23705号 / 理博第4795号 / 新制||理||1686(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 嶺重 慎, 准教授 前田 啓一, 准教授 野上 大作 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

To address the growing demand for accurate and reliable wearable technologyin health monitoring and fitness tracking, this report presents a novel stepcounter integrated into a shoe. The goal is to enhance the precision of stepcounting and provide valuable health metrics, such as calorie burning. Theapproach involves a custom-designed circuit board that processes the signalfrom the piezoelectric disks, and an algorithm is developed to accuratelycount steps. The final phase involves constructing a functional prototype forextensive real-world testing. After testing and simulations, the systemdemonstrated a high level of accuracy in step counting. It successfullyprocessed and analyzed step data, providing insightful health metrics thatcould be used for fitness tracking. Lastly, the prototype achieved its goal ofaccurate step counting but also proved to be a significant contribution to thefield of wearable technology. But it could be further improved to have betterdurability and not break. This advancement has the potential to improve thereliability and effectiveness of fitness-tracking devices.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第25120号 / 理博第5027号 / 新制||理||1717(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 上田 佳宏, 准教授 野上 大作, 教授 前田 啓一 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

This thesis focuses on the evolution of zonal flows in self-gravitating accretion discs and their resulting effect on disc stability; it also studies the process of disc gravito-turbulence, with particular emphasis given to the way the turbulent state is able to extract energy from the background flow and sustain itself by means of a feedback. Chapters 1 and 2 provide an overview of systems involving accretion discs and a theoretical introduction to the theory of accretion discs, along with potential methods of angular momentum transport to explain the observed accretion rates. To address the issue of the gravito-turbulence self-sustenance, a compressible non-linear spectral code (dubbed CASPER) was developed from scratch in C; its equations and specifications are laid out in Chapter 3. In Chapter 4 an ideal (no viscosities or cooling) linear stability analysis to non-axisymmetric perturbations is carried out when a zonal flow is present in the flow. This yields two instabilities: a Kelvin-Helmholtz instability (active only if the zonal flow wavelength is sufficiently small) and one driven by self-gravity. A stability analysis of the zonal flow itself is carried out in Chapter 5 by means of an axisymmetric linear analysis, using non-ideal conditions. This considers instability due to both density wave modes (which give rise to overstability) and slow modes (which result in thermal or viscous instability) and, thanks a different perturbation wavelength regime, represents an extension to the classical theory of thermal and viscous instabilities. The slow mode instability is found to be aided by high Prandtl numbers and adiabatic index γ values, while quenched by fast cooling. The overstability is likewise stabilised by fast cooling, and occurs in a non-self-gravitational regime only if γ ≲ 1.305. Lastly, Chapter 6 illustrates the results of the non-linear simulations carried out using the CASPER code. Here the system settles into a state of gravito-turbulence, which appears to be linked to a spontaneously-developing zonal flow. Results show that this zonal flow is driven by the slow mode instability discussed in Chapter 5, and that the presence of zonal flows triggers a non-axisymmetric instability, as seen in Chapter 4. The role of the latter is to constrain the zonal flow amplitude, with the resulting zonal flow disruption providing a generation of shearing waves which permits the self-sustenance of the turbulent state.

Neste trabalho é apresentado um estudo observacional de discos de acresção em Variáveis Cataclísmicas (VCs). São analisadas medidas espectrofotométricas com resolução temporal dos perfis de linhas de emissão. A emissividade em linhas dos sistemas é mapeada utilizando a técnica de tomografia Doppler. Os parâmetros básicos das binárias, tais como período orbital, massas, inclinação orbital, são determinados quando necessário. Um código foi desenvolvido para simular a variabilidade das linhas de emissão em sistemas binários, além da presença de vento. O código foi utilizado para quantificar os parâmetros necessários para um estudo adequado de tomografia do flickering, tais como número de espectros, relação sinal-ruído destes, e frequência e amplitude do flickering em questão. Três sistemas são abordados: V3885 Sgr, RR Pic e V841 Oph. A variabilidade intrínseca de V3885 Sgr é mapeada através da técnica de tomografia do flickering. O flickering foi simulado e verificou-se que a fonte principal de flickering observada em V3885 Sgr não poderia se originar em um disco de acresção Kepleriano, mas sim na face iluminada da estrela secundária. Uma interpretação proposta para este fenômeno seria de um cenário onde o flickering no contínuo UV originado nas regiões centrais do disco ou na mancha quente é reprocessado na face iluminada da secundária. Obtivemos a primeira confirmação, para uma Variável Cataclísmica de curto período (RR Pic), de uma secundária com relação massa/raio distante da sequência principal. No caso de V841 Oph determinamos o período orbital e obtivemos uma razão de massas um pouco inferior a 1. Verificamos a existência de uma região de emissão mais intensa localizada no quadrante oposto ao esperado para a mancha quente, sendo esta região particularmente brilhante em HeI. O disco de acresção de V841 Oph foi verificado como sendo de baixa emissividade em linhas. / An observational study of accretion disks in Cataclysmic Variables (CVs) is presented in this work. Time-resolved spectrophotometric data of the emission line profiles are analyzed. The line emissivity of the systems is mapped using the Doppler tomography technique. The basic orbital parameters of the systems, like the orbital period, mass, orbital inclination, are determined when needed. A code was developed to simulate the emission line profile variability in binary systems, also including the presence of a wind. Such a code was used to quantify the parameters involved in a flickering tomography study, like the number of spectra, signal-to-noise ratio, frequency and amplitude of the flickering. Three systems are analyzed: V3885 Sgr, RR Pic and V841 Oph. The intrinsic variability in V3885 Sgr is mapped using the flickering tomography technique. The flickering was simulated and we have verified that the main flickering source in V3885 Sgr could not be located on the Keplerian accretion disk. The inner face of the secondary star is proposed instead. One interpretation of this phenomenon is a scenery where flickering in the UV continuum from the inner parts of the accretion disk is reprocessed at the illuminated face of the secondary star. The first confirmation of a secondary star with a mass-radius relation far from the main sequence values was obtained for a CV with a short period (RR Pic). In the case of V841 Oph we determined the orbital period and obtained a mass-ratio slightly below 1. We verified the presence of a region of enhanced emission in the quadrant opposite to the one expected for the hot spot. The emission of this region is particularly enhanced in HeI. The V841 Oph accretion disk was verified as being of low emissivity in lines.