京都大学 / 新制・課程博士 / 博士(理学) / 甲第25117号 / 理博第5024号 / 新制||理||1716(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 岩室 史英, 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

The thermal efficiency of a gas turbine directly depends on the rotor inlet temperature. The ever increasing demand for more power and advances in the field of engineering enabled this temperature to be pushed higher. But the material strength of the blades and vanes can often impose restrictions on the thermal load it can bear. This is where gas turbine cooling becomes very critical and a better cooling design has the potential to extend the blade life span, enables higher rotor inlet temperatures, conserves compressor bleed air. Among various kinds of cooling involved in gas turbines, film cooling will be the subject of this study. A novel concept for film cooling holes referred to as anti-vortex design proposed in 2007 is explored in this study. Coolant exits through two bifurcated cylindrical holes that branched out on either side of the central hole resulting in a tripod-like arrangement. Coolant from the side holes interacted with the mainstream and produced vortices that countered the main central rotating vortex pairs, weakening it and pushing the coolant jet towards the surface. In order to understand the performance of this anti-vortex tripod film cooling, a flat plate test setup and a low speed subsonic wind tunnel linear cascade were built. Transient heat transfer experiments were carried out in the flat plate test setup using Infrared thermography. Film cooling performance was quantified by measuring adiabatic effectiveness and heat transfer coefficient ratio. In order to gauge the performance, other standard hole geometries were also tested and compared with. Following the results from the flat plate test rig, film cooling performance was also evaluated on the surface of an airfoil. Adiabatic effectiveness was measured at different coolant mass flow rates. The tripod hole consistently provided better cooling compared to the standard cylindrical hole in both the flat plate and cascade experiments. In order to understand the anti-vortex concept which is one of the primary reason behind better performance of the tripod film cooling hole geometry, numerical simulations (CFD) were carried out at steady state using RANS turbulence models. The interaction of the coolant from the side holes with the mainstream forms vortices that tries to suppress the vortex formed by the central hole. This causes the coolant jet from the central to stay close to the surface and increases its coverage. Additionally, the coolant getting distributed into three individual units reduces the exit momentum ratio. Tripod holes were found to be capable of providing better effectiveness even while consuming almost half the coolant used by the standard cylindrical holes. / Ph. D. / The thermal efficiency of a gas turbine directly depends on the rotor inlet temperature. The ever increasing demand for more power and advances in the field of engineering enabled this temperature to be pushed higher. But the material strength of the blades and vanes can often impose restrictions on the thermal load it can bear. This is where gas turbine cooling becomes very critical and a better cooling design has the potential to extend the blade life span, enables higher rotor inlet temperatures, conserves compressor bleed air. Among various kinds of cooling involved in gas turbines, film cooling will be the subject of this study. Its primary function still serves to reduce the heat load on the gas turbine hot gas path components while creating a thin film of cooler fluid, usually bled from compressor at an intermediate stage. A novel concept for film cooling holes referred to as anti-vortex design proposed in 2007 is explored in this study. Coolant exits through two bifurcated cylindrical holes that branched out on either side of the central hole resulting in a tripod-like arrangement. Coolant from the side holes interacted with the mainstream and produced vortices that countered the main central rotating vortex pairs, weakening it and pushing the coolant jet towards the surface. In order to understand the performance of this anti-vortex tripod film cooling, a flat plate test setup and a low speed subsonic wind tunnel linear cascade were built. Transient heat transfer experiments were carried out in the flat plate test setup using Infrared thermography. Film cooling performance was quantified by measuring adiabatic effectiveness and heat transfer coefficient ratio. In order to gauge the performance, other standard hole geometries were also tested and compared with. Following the results from the flat plate test rig, film cooling performance was also evaluated on the surface of an airfoil. Adiabatic effectiveness was measured at different coolant mass flow rates. The tripod hole consistently provided better cooling compared to the standard cylindrical hole in both the flat plate and cascade experiments. In order to understand the anti-vortex concept which is one of the primary reason behind better performance of the tripod film cooling hole geometry, numerical simulations (CFD) were carried out at steady state using RANS turbulence models. The interaction of the coolant from the side holes with the mainstream forms vortices that tries to suppress the vortex formed by the central hole. This causes the coolant jet from the central to stay close to the surface and increases its coverage. Additionally, the coolant getting distributed into three individual units reduces the exit momentum ratio. Tripod holes were found to be capable of providing better effectiveness even while consuming almost half the coolant used by the standard cylindrical holes.

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A polygon mesh, or a 3D mesh, consisting of a collection of vertices, edges, and polygons in three-dimensional space, is the standard way of representing 3D objects. In practice, polygon meshes acquired from the 3D scanning process fail to meet the quality requirements for most practical applications. Mesh defects like holes, duplicate elements, non-manifold elements are introduced during the scanning process, which lowers the quality of the output meshes. In this thesis, we describe a complete mesh-repairing process that fixes all defects within a polygon mesh. This process is divided into two parts: the mesh-cleaning part and the hole-filling part. In the mesh-cleaning part, we describe the ways of repairing different types of mesh defects. In the hole-filling part, we discuss two main hole-filling approaches: the surface-based method and the volumetric. In addition, we present a hybrid algorithm by combining the surface-based approach and the volumetric approach. We compare the meshes created by different hole-filing algorithms and show that the new algorithm is a good alternative to the existing ones. / Thesis (Master, Computing) -- Queen's University, 2013-09-11 23:45:08.591

Purpose: To evaluate the incidence of central hole-induced ring-shaped dysphotopsia after posterior chamber phakic implantable collamer lens (ICL) with central hole (hole ICL) implantation and to investigate the causes of central hole-induced dysphotopsia. MethodsThe clinical study enrolled 29 eyes of 15 consecutive myopic patients implanted with hole ICL. The incidence of ring-shaped dysphotopsia after hole ICL implantation was evaluated. In the experimental simulation study, non-sequential ray tracing was used to construct myopic human eye models with hole ICL and ICL without a central hole (conventional ICL). Simulated retinal images measured in log-scale irradiance were compared between the two ICLs for an extended Lambertian light-emitting disc object 20cm in diameter placed 2m from the corneal vertex. To investigate the causes of hole-induced dysphotopsia, a series of retinal images were simulated using point sources at infinity with well-defined field angles (0 to -20 degrees) and multiple ICL models. ResultsOf 29 eyes, 15 experienced ring-shaped dysphotopsia after hole ICL implantation. The simulation study using an extended Lambertian source showed that hole ICL-evoked ring-shaped dysphotopsia was formed at a retinal field angle of 40 degrees. Component-level analysis using a well-defined off-axis point source from infinity revealed that ring-shaped dysphotopsia was generated by stray light refraction from the inner wall of the hole and the posterior ICL surface. ConclusionHole ICL-evoked ring-shaped dysphotopsia was related to light refraction at the central hole structure. Surgeons are advised to explain to patients the possibility of ring-shaped dysphotopsia after hole ICL implantation.

Variable emission from Sgr A*, the luminous counterpart to the super-massive black hole at the center of our Galaxy, arises from the innermost portions of the accretion flow. Better characterization of the variability is important for constraining models of the low-luminosity accretion mode powering Sgr A*, and could further our ability to use variable emission as a probe of the strong gravitational potential in the vicinity of the 4 x 10(6) M-circle dot black hole. We use the Herschel Spectral and Photometric Imaging Receiver (SPIRE) to monitor Sgr. A* at wavelengths that are difficult or impossible to observe from the ground. We find highly significant variations at 0.25, 0.35, and 0.5 mm, with temporal structure that is highly correlated across these wavelengths. While the variations correspond to < 1% changes in the total intensity in the Herschel beam containing Sgr. A*, comparison to independent, simultaneous observations at 0.85 mm strongly supports the reality of the variations. The lowest point in the light curves, similar to 0.5 Jy below the time-averaged flux density, places a lower bound on the emission of Sgr. A* at 0.25 mm, the first such constraint on the THz portion of the spectral energy distribution. The variability on few hour timescales in the SPIRE light curves is similar to that seen in historical 1.3 mm data, where the longest time series is available, but the distribution of variations in the sub-mm do not show a tail of large-amplitude variations seen at 1.3 mm. Simultaneous X-ray photometry from XMM-Newton shows no significant variation within our observing period, which may explain the lack of very large submillimeter variations in our data if X-ray and submillimeter flares are correlated.

Degree of Master of Science by research only: A dissertation submitted to the faculty of science, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science. Department of Physics Faculty of Science University of the Witwatersrand January 4, 2016 / Quasi-simultaneous observations of a flaring blazar source at multiple frequencies, offer an unprecedented view of the region surrounding a supermassive black hole during a large energy outburst. Blazars are active galaxies that host a super massive black hole releasing large amounts of energy through narrow jets of highly relativistic plasma located along the polar axes. Within these jets, electrons and protons move at relativistic speeds creating interactions that generate radio waves and gamma-rays that travel down the jet towards the observer. Based on the angle of inclination of the source towards the observer ( < 20◦), we can study relativistically boosted emission to peer into regions where high-energy particles (gamma-rays) are thought to be generated. Using high cadence monitoring campaigns, both the slow and fast variations in the source flux can be traced in detail revealing spatial and temporal information about the source state and activity. In this dissertation I studied the physics behind the variable behavior of the bright blazar PKS 1424-418, also known as J1427-4206. PKS 1424-418 is a Southern Hemisphere blazar that recently underwent a number of flaring events detected by FERMI-LAT. The study was specifically concerned with the behavior of PKS 1424-418 during the outburst/flaring events that occurred between 19 October 2012 and 9 October 2013. PKS 1424-418’s daily gamma-ray flux reached an average of 1.4 ± 0.2 x 10−6 ph cm−2 s−1 for E > 100 MeV, triggering radio follow up observations with the Hartebeesthoek Radio Astronomy Observatory 26 m radio telescope at 2.3-GHz, 4.8-GHz, 8.4-GHz and 12.2-GHz frequencies. The objective was to examine the nature of the relationship between the high-energy gamma rays detected by FERMI-LAT and the low-energy radio waves detected by the Hart26m radio telescope. In the study we investigated the relationship between the two energy regimes using Discrete cross-correlation functions to estimate the time-lags between two corresponding frequencies. We also studied the spectral index variation to establish the source behavior over the observing period at multiple epochs. A Lomb-Scargle periodicity search was also performed to investigate whether some periodic modulation was present in the gamma-ray data as it varied quite dramatically on shorter time-scales. Observations in gamma-rays and radio frequencies were done using the All-Sky mode and drift scan technique respectively at the different frequencies. Results indicated the existence of a strong correlation between the gamma-ray and radio data, with the gamma rays leading the radio. With each gamma-ray flaring event the radio spectra indicated some spectral hardening and the possibility of an 86 day gamma-ray period in the shorter term flares was also established in the study. This study however only shows the large scale relationship between time-series over the entire observing period. On smaller scales, each gamma-ray and radio flare is unique and as such requires individual analysis for each respective component. to successfully achieve this, more data is needed to confirm the individual radio flaring periods. Observations at VLBI scales are extremely useful in this kind of work and instrumental in studying the source structure behavior during flaring and will form part of the future work planned for studying blazar source variability.

Essa dissertação consiste de uma revisão dos resultados clássicos sobre a termodinâmica de buracos negros bem como de uma análise crítica das extensões recentes da relação entre a termodinâmica e a dinâmica gravitacional e suas implicações. / This dissertation consists of a revision of the classical results concerning the thermodynamics of black holes as well as a critical analysis of the recent extensions of the relationship between thermodynamics and the gravitational dynamics and its implications.

Philosophiae Doctor - PhD / The continuous increase in energy consumption and decrease in fossil fuels reserves are a primary concern worldwide; especially for South Africa. Therefore, there is an urgent need for alternative energy resources that will be sustainable, and environmentally friendly in order to tackle the ecological degradation generated by the use of fossil fuels. Among many energy ‘niches’, solar energy appears to be one of the most promising and reliable for the African continent because of the constant availability of sun light. Organic conjugated polymers have been identified as suitable materials to ensure proper design and fabrication of flexible, easy to process and cost-effective solar cells. Their tendency to exhibit good semiconducting properties and their capability to absorb photons from the sunlight and convert it into electrical energy are important features that justify their use in organic photovoltaic cells. Many different polymers have been investigated as either electron donating or electron accepting materials. Among them, poly(3-hexylthiophene) is one of the best electron donor materials that have been used in organic photovoltaic cells. It is a good light absorber and its Highest Occupied Molecular Orbital (HOMO) energy level is suitable to allow electron transfer into an appropriate electron acceptor. On the other hand, the molecular ordering found in dendrimers attracted some interest in the field of photovoltaics as this feature can ensure a constant flow of charges. In this work, I hereby report for the first time, the chemical synthesis of a highly crystalline dendritic star copolymer generation 1 poly(propylene thiophenoimine)-co-poly(3-hexylthiophene) (G1PPT-co-P3HT) with high molecular weight and investigate its application as donating material in bulk heterojunction organic photovoltaics.

Thesis (Ph. D.)--Joint Program in Applied Ocean Physics and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering; and the Woods Hole Oceanographic Institution), 2000. / Includes bibliographical references (p. 255-264). / by Jason I. Gobat. / Ph.D.