No description available.

No description available.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18077号 / 理博第3955号 / 新制||理||1570(附属図書館) / 30935 / 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 川合 光, 准教授 福間 將文, 教授 畑 浩之 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Black hole visualization is a problem of raytracing over curved spacetimes. This paper discusses the physics of light in curved spacetimes, the geometry of black holes, and the appearance of objects as viewed through a relativistic camera (the Penrose-Terrell effect). It then discusses computational issues of how to generate images of black holes with a computer. A method of determining the most efficient series of steps to calculate the value of a mathematical expression is described and used to improve the speed of the program. The details of raytracing over curved spaces not covered by a single chart are described. A method of generating images of several black holes in the same spacetime is discussed. Finally, a series of images generated by these methods is given and interpreted. / text

The detection of a gamma-ray burst (GRB) in the solar neighborhood would have very important implications for GRB phenomenology. The leading theories for cosmological GRBs would not be able to explain such events. The final bursts of evaporating primordial black holes (PBHs), however, would be a natural explanation for local GRBs. We present a novel technique that can constrain the distance to GRBs using detections from widely separated, non-imaging spacecraft. This method can determine the actual distance to the burst if it is local. We applied this method to constrain distances to a sample of 36 short-duration GRBs detected by the Interplanetary Network (IPN) that show observational properties that are expected from PBH evaporations. These bursts have minimum possible distances in the 10(13)-10(18) cm (7-10(5) au) range, which are consistent with the expected PBH energetics and with a possible origin in the solar neighborhood, although none of the bursts can be unambiguously demonstrated to be local. Assuming that these bursts are real PBH events, we estimate lower limits on the PBH burst evaporation rate in the solar neighborhood.

Idiopathic macular hole is a disease of the eye with unknown cause, but a pathology that, over the course of several decades of investigation by clinicians and researchers alike, has become readily treatable with surgical intervention at a very high rate of successful repair. The current study presents a retrospective case series exploring surgical outcomes for treatment of recurrent macular holes. The study additionally provides a window into the past, present, and future of macular holes across all clinical considerations, and importantly performs a supplementary statistical meta analysis of reoperation success rates in the relevant field of published data- the first of its kind. The introductory background of the present study establishes a natural history of idiopathic macular holes in clinical discovery, classification, and management. The study's case series data specifically focuses on the phenomenon of macular hole recurrence, offering surgical outcome measures of patients undergoing primary and secondary repair operations in a single-center, single-surgeon design. The findings of the retrospective series support the hypothesis that macular hole reoperation does achieve successful anatomical closure in a majority of cases. A meta analysis performed on the current field of published clinical research pertaining to recurrent macular holes established cumulative success rates across a variety of surgical conditions. The present study's findings were then compared to the corresponding measures across the landscape of recurrent macular hole literature, to help inform a niche of clinical research that continues to be an area of investigation and discovery. In presenting a cohesive, synthesized narrative of recurrent macular holes, the study provides a foundation wherein ongoing collaborative efforts in the field can continue to build upon a blueprint currently set in place, and work towards finding a cause behind an otherwise idiopathic disease.

The aim of this thesis is to reconsider energy extraction from black hole magnetospheres, and more specifically the Blandford-Znajek (BZ) process from an effective field theory (EFT) perspective. Superradiant instabilities of scalar and vector bound states in the presence of a rotating black hole will be reviewed when the inverse mass of the black hole is much smaller than the Compton wavelength of the bound state particle. Two different matching calculations will be described for the vector bound state case and the overall decay rate will be compared. Force-free electrodynamics will be motivated and discussed in the context of the BZ process. Using a perturbation expansion, the Blandford-Znajek process will be reviewed up to second order in the rotation parameter. The absolute-space/universal-time (3+1) viewpoint will be discussed and applied to the BZ process and an EFT-like description will be discussed when the black hole horizon is parametrically small. Using differential forms, a simplified framework for the BZ process will be introduced in the (3+1) formalism and the field strength F will be simplified in the slow-rotation limit up to first-order in the rotation parameter. Finally, the Blandford-Znajek process will be considered as a superradiant process in the massive vector limit and the total energy flux in this (new) regime will be compared to the known BZ energy flux. / Graduate

Holes with different sizes from microscale to nanoscale were directly fabricated by focused ion beam (FIB) milling in this paper. Maximum aspect ratio of the fabricated holes can be 5:1 for the hole with large size with pure FIB milling, 10:1 for gas assistant etching, and 1:1 for the hole with size below 100 nm. A phenomenon of volume swell at the boundary of the hole was observed. The reason maybe due to the dose dependence of the effective sputter yield in low intensity Gaussian beam tail regions and redeposition. Different materials were used to investigate variation of the aspect ratio. The results show that for some special material, such as Ni-Be, the corresponding aspect ratio can reach 13.8:1 with Cl₂ assistant etching, but only 0.09:1 for Si(100) with single scan of the FIB. / Singapore-MIT Alliance (SMA)

This thesis documents the results of high pressure testing of hole-pattern annular gas seals conducted at the Texas A&M University's Turbomachinery Laboratory. The testing conditions were aimed at determining the test seals sensitivity to pressure ratio, inlet fluid preswirl, rotor speed, and rotor to seal clearance. The rotordynamic coefficients showed only small changes resulting from the different pressure ratios tested. Only the damping terms at the lower frequencies showed some influence. One other notable result from the testing of different pressure ratios is that the seals were tested in a choked flow condition, and there was not a significant change in the seal behavior when the seals transitioned to the choked condition. The inlet fluid preswirl only had a notable effect on the cross-coupled stiffness in the larger clearance tests. These results lead to the conclusion that a swirl brake could have some rotordynamic value, but only if the seals have sufficiently large clearance. Conversely this also means that if hole-pattern seals are being implemented with a small clearance, then a swirl brake would not be an effective way to improve the rotordynamic stability of the system. The only significant effect that the rotor speeds had on the rotordynamic coefficients were that the cross-coupled coefficients increased as the rotor speed increased. This is the expected result because as the rotor speed increases there is a greater shear force on the gas as it passes through the seal resulting in more fluid circumferential velocity, which results in stronger cross-coupled coefficients. The changes in clearance resulted in drastic changes in the magnitude of the coefficients. The smaller clearance yielded much higher coefficients than the larger clearance. All of the rotordynamic coefficients were predicted well by ISOTSEAL. The code was found to do a good job predicting the seal leakage as well. This gives more credence to the coefficients and leakage that ISOTSEAL predicts.

Predictions are presented for a selected compressor using longer hole-pattern seals with L/D ratios from 0.5 to 2.5. Results were obtained for back-to-back and in-line compressors with the seal located at mid-span and at 82% of rotor span respectively, considering different seal lengths, radial seal clearances, as well as constant clearance and convergent-tapered seal geometries. Predictions of the synchronous rotordynamic coefficients and leakage were estimated using a code developed by Kleynhans and Childs with zero preswirl and constant pressure ratio of 0.5. This code does not include moment coefficients; which can affect the results. Results of all configurations show an increase of stiffness and damping coefficients with increasing seal length. In addition, a significant reduction in leakage (approximately 47 percent) as L/D increases is exhibited for constant clearance and convergent-tapered hole-pattern seals. For the back-to-back compressor, the stability analysis predicts that the system is stable for all speeds and L/D ratios. In fact, the rotor cylindrical-bending mode becomes more stable with lengthening the seals, for both constant clearance and convergent-tapered hole-pattern seals. For constant clearance seals (Case A), the synchronous response at mid-span show a critical speed at 8,000 rpm (cylindrical-bending mode) for all L/D ratios, while a reduction of 85 percent in the peak response is exhibited as L/D increases. Case B, in which the radial clearance is increased as L/D increases to have the same leakage as case A, slightly increases the synchronous response of the model compared to case A. For convergent-tapered seals (Case C), the synchronous response at mid-span shows a higher critical speed (9,000 rpm) for all L/D ratios, and a larger reduction (89 percent) in peak response with increasing L/D, compared to Case A. However, the magnitude of the peak response is larger for convergent-tapered seals than that for constant clearance seals, for all L/D ratios. For in-line compressor, the stability analysis predicts two critical speeds at 6,000 (conical mode) and 18,000 rpm (first bending mode) respectively. Both modes are predicted to be stable for all speed and L/D ratios. Synchronous response at the mid-span for Case A shows the peak response at the first critical speed is slightly reduced as L/D increases while the response at the second critical speed is increased for most of the cases. In addition, the second critical speed is reduced from 18,000 to 13,000 rpm, which is not a concern because it remains above the running speed. This was also the trend for convergent-tapered hole-pattern seal. In addition, the increase of radial clearance in Case B slightly increases the amplitude of vibration, compared to Case A.