京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第21953号 / 医博第4495号 / 新制||医||1037(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 柳田 素子, 教授 斎藤 通紀, 教授 近藤 玄 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

We present analytic models for the formation and evolution of tidal tails and related structures following single or multiple impulsive disturbances in galaxy collisions. Since the epicyclic approximation is not valid for large radial excursions, we use orbital equations of the form we call p-ellipses (a class of precessing ellipses). These have been shown to provide accurate representations of orbits in logarithmic and power-law halo potentials. In the simplest case of an impulsive collision yielding a purely tidal disturbance the resulting tidal tails have simple structure. Scalings for their maximum lengths and other characteristics as non-linear functions of the tidal amplitude and the exponent of the power-law potentials are described. The analytic model shows that azimuthal caustics (orbit crossing zones of high density also seen in numerical models) are produced generically in these tails at a fixed azimuth relative to the point of closest approach. Long tails, with high-order caustics at their base, and ocular waveforms are also produced at larger amplitudes. The analysis is then extended to non-linear disturbances and multiple encounters, which break the symmetries of purely tidal perturbations. The p-ellipse orbital solutions are similar to those in the linear tidal case. However, as the strength of the non-linear terms is varied the structure of the resulting forms varies from symmetric tails to one-armed plumes. Cases with two or more impulse disturbances are also considered as the simplest analytic models distinguishing between prograde and retrograde encounters. The model shows explicitly how tail growth differs in the two cases. In the prograde case a specific mechanism for the formation of tidal dwarf galaxies at the end of tails is suggested as a consequence of resonance effects in multiple or prolonged encounters. Qualitative comparisons to Arp Atlas systems suggest that the limiting analytic cases are realized in real systems. For example, we identify a few Arp systems which have multiple tidal strands meeting near the base of long tails. These may be swallowtail caustics, where dissipative gas streams are converging and triggering star formation. Ultraviolet and optical images reveal luminous knots of young stars at these 'hinge clump' locations.

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Preeclampsia is an important disease during pregnancy and causes significant maternal and fetal mortality and morbidity. Despite intense research efforts, the etiology and pathogenesis of the disease remain largely unknown. Since placentas from preeclamptic patients are smaller than normal, and cytokine growth factors are suggested to be important in placental growth, the effects of macrophage-colony stimulating factor (M-CSF) on human trophoblast cells were examined. While term trophoblast cells did not respond to M-CSF, those from early trimester and choriocarcinoma cells showed enhanced growth after treatment. In addition, the serum level of M-CSF in hypertensive pregnant women at the second trimester were significantly lower than those of normal pregnant women. These data suggest possible roles of M-CSF in preeclampsia. When M-CSF was administered to pregnant rats on days 8-11, rats had smaller placentas at day 12 and increased fetal resorption rate at day 20. The effects of interleukin-12 (IL-12) was also examined on days 8-11. While placental development was normal at both days 12 and 20, fetuses were significantly smaller at day 20. To remedy the difficulties and dangers associated with obtaining human placentas, I characterized endovascular trophoblast cell behavior in pregnant rats. In normal pregnancy, rat trophoblast cells simulated all features of human endovascular trophoblast behavior including selective invasion into the spiral arteries, retrograde migration, embedding, and secretion of PAS-positive materials as well as IIphysiological changes," In pregnancy terminated with a certain type of spontaneous fetal resorption, defective endovascular trophoblast cell behavior was observed, which was similar to that reported in preeclamptic pregnancy. Finally, the roles of cytoskeleton on trophoblast cell locomotion were investigated in vivo with a cytoskeleton-disrupting agent, cytochalasin B. This treatment impaired trophoblast cell invasion at day 12 and induced smaller fetuses at day 20, suggesting the importance of cytoskeleton in trophoblast movement. In conclusion, the results suggest the importance of the use of appropriate specimens and endpoints in the study of pregnancy, and rats may serve as a suitable animal model for the study of endovascular trophoblast cell behavior with clinical relevance to preeclampsia. / Ph. D.

Bridges and buildings are often supported on deep foundations. These foundations consist of groups of piles coupled together by concrete pile caps. These pile caps, which are often massive and deeply buried, would be expected to provide significant resistance to lateral loads. However, practical procedures for computing the resistance of pile caps to lateral loads have not been developed, and, for this reason, cap resistance is usually ignored. Neglecting cap resistance results in estimates of pile group deflections and bending moments under load that may exceed the actual deflections and bending moments by 100 % or more. Advances could be realized in the design of economical pile-supported foundations, and their behavior more accurately predicted, if the cap resistance can be accurately assessed. This research provides a means of assessing and quantifying many important aspects of pile group and pile cap behavior under lateral loads. The program of work performed in this study includes developing a full-scale field test facility, conducting approximately 30 lateral load tests on pile groups and pile caps, performing laboratory geotechnical tests on natural soils obtained from the site and on imported backfill materials, and performing analytical studies. A detailed literature review was also conducted to assess the current state of practice in the area of laterally loaded pile groups. A method called the "group-equivalent pile" approach (abbreviated GEP) was developed for creating analytical models of pile groups and pile caps that are compatible with established approaches for analyzing single laterally loaded piles. A method for calculating pile cap resistance-deflection curves (p-y curves) was developed during this study, and has been programmed in the spreadsheet called PYCAP. A practical, rational, and systematic procedure was developed for assessing and quantifying the lateral resistance that pile caps provide to pile groups. Comparisons between measured and calculated load-deflection responses indicate that the analytical approach developed in this study is conservative, reasonably accurate, and suitable for use in design. The results of this research are expected to improve the current state of knowledge and practice regarding pile group and pile cap behavior. / Ph. D.

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