京都大学 / 新制・課程博士 / 博士(理学) / 甲第24419号 / 理博第4918号 / 新制||理||1702(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 前田 啓一, 講師 LEE Shiu Hang, 教授 太田 耕司 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

Rhythmic collapse and reinflation of tracheal tubes is a form of active ventilation that augments convective gas exchange in multiple orders of insects. The underlying mechanism driving this phenomenon is not known. Among other things, tracheal tube collapse could be caused by either direct impingement of trachea or by a difference of pressure gradients between the intra-tracheal air and the surrounding hemolymph. To determine the relationship between hemolymph pressure and tracheal tube collapse in the ground beetle (Pterostichus commutabulis), we performed direct measurements of hemolymph pressure inside the beetle's prothorax while simultaneously using synchrotron phase contrast imaging to observe morphological changes in the trachea. We observed that a pressure pulse co-occurred with every tube compression observed throughout the body, suggesting that pulses in hemolymph pressure are responsible for tracheal collapse. To assess the effects of the experimental x-ray conditions imposed on the subjects during imaging, hemolymph pressure was also directly measured in the prothorax of beetles less restricted in non-x-ray trials. To compare the pressure patterns in the two experiments, a novel method of identifying and analyzing pressure pulses was developed and applied to the data sets. The comparison provides the first quantitative characterization of a directly measured hemolymph pressure environment, and demonstrates strong similarities in the pressure patterns recorded in both tests. However, pulses occurring during the x-ray experiments exhibited larger average magnitudes. Further video analysis however shows that collapse of the primary tracheal tubes was observed to occur even in the presence of the smallest simultaneously measured pressure pulse (1.01 kPa), suggesting that collapse of the primary tracheal tubes. / Master of Science

No / The impact of rapid climate change on contemporary human populations is of global concern. To contextualize our understanding of human responses to rapid climate change it is necessary to examine the archeological record during past climate transitions. One episode of abrupt climate change has been correlated with societal collapse at the end of the northwestern European Bronze Age. We apply new methods to interrogate archeological and paleoclimate data for this transition in Ireland at a higher level of precision than has previously been possible. We analyze archeological 14C dates to demonstrate dramatic population collapse and present high-precision proxy climate data, analyzed through Bayesian methods, to provide evidence for a rapid climatic transition at ca. 750 calibrated years B.C. Our results demonstrate that this climatic downturn did not initiate population collapse and highlight the nondeterministic nature of human responses to past climate change.

Progressive collapse research aims to characterize and quantify the behavior of different structural systems in events of extreme local damage caused by bombings to improve the performance of targeted structures and to protect occupants. The focus of the research program described herein is the performance of steel gravity frame structures with composite floor systems in column loss scenarios. The goal of the project is to contribute to the development of rational design guidelines for progressive collapse resistance and to assess any potential weaknesses in current design standards. This thesis presents the results of a series of tests performed on a steel frame structure with simple framing connections and a composite floor slab under interior column loss. The specimen was designed and constructed in accordance with typical design practices and was subjected to increasing uniform floor loads after static removal of the central column. No significant structural damage was observed up to a load equivalent to the ultimate gravity design load. Further testing was performed after the deliberate reduction of the capacity of the steel framing connections, ultimately resulting in total collapse of the specimen. / text

Fires in buildings are dangerous in many ways, one big hazard is the risk of building collapse. This is a hazard both to occupants in the building and to the fire service, who might have to enter the building for their firefighting. The consequences of a building collapse can become severe, both in terms of damage to the building and in terms of injuries to people. Despite this, there are few methods to determine how stable a construction is, when exposed to stress from a fire. This thesis has tried to find connections between occurred events where buildings have collapsed, both by a literature study and by looking into some occurred collapses. This has been done by analysing some specific events more deeply, to find out what went wrong in that specific case, and by looking into a broader base of occurred building collapses which has been presented as statistics. Finally contact with personnel from two different fire brigades was taken, to perform a questionnaire and collect information of how they work with the dangers in reality. All of these studies has shown that there are some connections between which buildings collapse more often than others, one example is that small houses collapse more frequently than residential buildings and that roofs is the part of the building which collapses most often. This is confirmed by some of the people from the fire brigades, who thinks it reflects their own experiences regarding building fires. Even though some connections like these can be shown, they can have several explanations as for example, there are many more small houses than residential buildings in Sweden which makes it natural to believe that they collapse more often. Still, some connections are clear and this information can be used to base further studies on and perhaps gain more knowledge to be able to make better judgements on whether a construction is stable or not.

The Deck truss portion of the I-35W Highway Bridge in Minneapolis, Minnesota collapsed on August 1, 2007 while roadwork was underway on the bridge. The entire truss was recovered from the river to study the causes of failure. The National Transportation Safety Board attributes the collapse to inadequate load carrying capacity of the steel gusset plates connecting the main truss members at four specific nodes. Permanent deformations of the members in proximity to these nodes were documented and a surveillance video camera recorded the collapse event in a major section of the structure. The inelastic behavior of the deck truss during the collapse event is studied in this research by performing nonlinear structural analysis on a simplified two-dimensional model. Nonlinear behavior is discretized at specific locations starting with buckling of the critical gusset plates and continuing with yielding in members where the internal forces increased at a higher rate during the post-buckling behavior. The analysis results show the sequence of failure events that lead to the formation of a collapse mechanism in the center span of the deck truss, which is the first to fall into the river. Comparison between the available evidence and the analysis results validate the conclusions drawn in this research. / Master of Science

Sinkhole collapse is a common karst land-use risk around the world. In the Bahamas cover-collapse sinkholes do not exist because soil cover is thin; almost all collapse is due to cave ceiling failure. The most common cave types in the Bahamas are flank margin caves and banana holes. Flank margin caves have three entrance types: dissolution pit, side breach, or ceiling collapse. Both side breach and ceiling collapse are the result of mass erosional forces; pits by focused dissolution. It was previously proposed that slope was a controlling factor in Bahamian cave collapse. This study demonstrated that 7.5 minute topographic maps cannot resolve slopes accurately enough to predict potential collapse locations. Field surveys with 1 m contours allowed for a more concise slope range in which each entrance type preferentially occurred; collapse breaches and pits were common on gentle slopes and side breaches on steep slopes.

Precast concrete multistory buildings are used in an attempt to optimize the available construction space and reduce costs. However, little is known about predicting their capacity in a brittle response mode due to the sudden loss of a critical element that could induce a Progressive Collapse Scenario. Therefore, the National Institute for Standards and Technology (NIST) developed an explicit approach in the design of precast concrete systems that is intended to mitigate a progressive collapse by enhancing the rotational capacity of joints and the robustness of the structural system. A full-scale experiment was conducted to investigate the structural performance of a prototype design under a column-removal scenario. The test assembly frame, consisting of three columns and two beams, was subjected to a displacement controlled vertical force acting at the center to characterize the failure modes and collapse mechanisms. Brittleailures of critical structural elements were observed and significantly impacted the performance.

The development, testing, and use of liquid propellant and hybrid rocket propulsion systems for spacecraft and their launch vehicles routinely involves the use of cryogenic propellants. These propellants provide high energy densities that enable high propulsive efficiency and high engine thrust to vehicle weight ratios. However, use of cryogenic propellants also introduces technical problems not associated with other types of propellants. One of the major technical problems is the phenomenon of propellant tank pressurant and ullage gas collapse. This collapse is mainly caused by heat transfer from most of the ullage gas to tank walls and interfacing propellant, which are both at temperatures well below those of this gas. Pressurant gas is supplied into cryogenic propellant tanks in order to initially pressurize these tanks and then to maintain required pressures as propellant is expelled from these tanks. The cryogenic propellants expelled from the tanks feed rocket engine assemblies, subassemblies, and components at required interface pressures and mass flow rates. The net effect of pressurant and ullage gas collapse is increased total mass and mass flow rate requirements of pressurant gases. For flight vehicles this leads to significant and undesirable weight penalties. For rocket engine component and subassembly ground test facilities this results in high construction and operational cost impacts. Accurate predictions of pressurant gas mass transfer and flow rate requirements are essential to the proper design of systems used to supply these gases to cryogenic propellant tanks. While much work has been done in the past for predicting these gas requirements at low subcritical tank pressures, very little has been done at supercritical tank pressure conditions and there are selected cases where errors of analytical predictions are high. The objectives of this study are to develop a new generalized and improved computer program to determine pressurant gas requirements at both subcritical and supercritical tank pressure conditions, and then evaluate and validate the consistent accuracy of this program over a wide range of conditions by comparison of program results to empirical data.

This thesis presents the results of 67 ABAQUS elasto-plastic Riks ultimate strength analyses of cross-stiffened panels. These panels cover a wide range of typical geometries. Uniaxial compression is applied to the panels, and in some cases combined with lateral pressure. For eight of the panels full-scale experimental results are available, and these verified the accuracy of the ABAQUS results. The 67 ABAQUS results were then compared to the ultimate strength predictions from the computer program ULSAP. In all but 10 cases the ULSAP predicted strength is within 30% of the ABAQUS value, and in all but 4 cases the predicted failure mode also agrees with that of ABAQUS. In one case the ULSAP predicted ultimate strength is 51% below the experimental value, and so this case is studied in detail. The discrepancy is found to be caused by the method which ULSAP uses for panels that experience overall collapse initiated by beam-column-type failure. The beam-column method program ULTBEAM is used to predict the ultimate strength of the 61 panels that ULSAP predicts to fail due to overall collapse of the stiffeners and plating which may or may not be triggered by yielding of the plate-stiffener combination at the midspan (Mode III or III-1). ULTBEAM is found to give more accurate results than ULSAP for Mode III or III-1 failure. Future work is recommended to incorporate ULTBEAM into ULSAP to predict the ultimate strength of panels that fail in Mode III or III-1. / Master of Science