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京都大学 / 新制・課程博士 / 博士(医学) / 甲第23774号 / 医博第4820号 / 新制||医||1057(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 伊佐 正, 教授 高橋 淳, 教授 井上 治久 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

<p>In this thesis, we investigate the properties of a model of an anti-phase modulated d-wave superconductor, particularly in the presence of a magnetic field. This so-called model of $\pi$-striped superconductor has been proposed to describe the decoupling between Cu-O planes in $1/8$ doped La$_{2-x}$Ba$_{x}$CuO$_{4}$. The d-wave superconducting order parameter in a $\pi$-striped superconductor oscillates spatially with period 8 and zero average value. Unlike a uniform d-wave superconductor, this model has non-zero density of states at zero energy and exhibits an extended Fermi surface. Within Bogoliubov-de Gennes theory, we study the mixed state of this model and compare it to the case of a uniform d-wave superconductor. We find a periodic structure of the low-energy density of states, with a period that is proportional to $B$, corresponding to Landau levels that are a coherent mixture of particles and holes. These results are also discussed in the context of experiments which observe quantum oscillations in the cuprates.</p> <p>Furthermore, within Bogoliubov-de Gennes theory, a semiclassical approximation is used to study quantum oscillations and to determine the Fermi surface area associated with these oscillations in this model. The Fermi surface is reconstructed via Andreev-Bragg scattering, and the semiclassical motion is along these Fermi surface sections as well as between them via magnetic breakdown. Oscillations periodic in 1/B are found in both the positions and widths of the lowest Landau levels. The area corresponding to these quantum oscillations for intermediate pairing interaction is similar to that reported for experimental measurements in the cuprates. A comparison is made of this theory to data for quantum oscillations in the specific heat measured by Riggs et al.</p> / Doctor of Philosophy (PhD)

The fundamental nature of the flow oscillations which are generated by two opposing planar jets is investigated. Particular attention is given to the underlying mechanism which sustains the oscillations over a wide range of flow parameters. The jet columns are observed to undergo large lateral deflection oscillations once in each direction per cycle, in an asymmetric manner. Extensive characterization of the jet oscillations over a wide range of flow parameters is established, including both the aeroacoustic response, as well as the unique flow features which are synchronized with the oscillations. The impingement region and circulation regions in each quadrant of the flow field are shown to play essential roles in sustaining the oscillations, as the pressurization of the impingement region causes the jets to initially deflect away from the centerline, while the low-pressure regions which form in the circulation zones drive the jet columns back towards, and ultimately across, the centerline. A number of interesting observations are made regarding the oscillation characteristics, including a dependence of the oscillation frequency on the jet aspect ratio, which helps explain much of the discrepancy in the Strouhal numbers reported in the literature to date. Furthermore, the nature of the sound-source field is investigated including the directionality of the various frequency components which are radiated. Unique mitigation strategies of the opposing planar jet oscillations are also explored by attempting to disrupt the circulation regions through the use of splitter plates. The oscillations are weakened considerably as the development and convection of the circulation zones is impeded. Preventing the circulation flow from interacting with the jet exit region drastically increases the effectiveness of the splitter plates, as even short splitter plates are shown to completely eliminate the oscillations. This demonstrates a very effective mitigation strategy of the opposing planar jet oscillator which is ideal for a variety of practical applications. One of the main challenges of the current investigation into the opposing planar jet oscillator is the extent to which the detailed time-varying pressure field can be resolved. Since it is not possible to experimentally detail the time-varying pressure field of the opposing planar jets, a novel PIV-based pressure field mapping technique is developed and benchmarked. A separate apparatus consisting of a planar jet impinging on a v-shaped plate is utilized to benchmark the proposed technique. This technique effectively resolves the features of the time-varying pressure field which are synchronized with the flow oscillations and helps circumvent many of the challenges which existing PIV pressure field mapping techniques face. It also provides a valuable tool for researchers to simultaneously determine the kinematic and dynamic aspects of various flow phenomena in a variety of fields, especially those in the area of aeroacoustics and fluid-structure-interaction. / Thesis / Doctor of Philosophy (PhD)

Fear memories are necessary to initiate anticipatory fear responses when we are confronted with cues that predict an impending threat. However, when a cue no longer predicts threat, an extinction memory is formed that actively inhibits the expression of the fear memory. Failure to acquire, consolidate, or recall extinction memories causes fear memory expression (i.e., fear responding) in the absence of threat, which is a hallmark characteristic of most anxiety-related disorders and post-traumatic stress disorder (PTSD). Of further importance, these disorders occur approximately twice as often in women than men, which is thought to partially rely on sex hormone mediated differences in fear extinction. Moreover, deficits in extinction memory processing can also hinder the success of extinction-based exposure therapy, which is commonly used to treat these disorders. Thus, a better understanding of the factors determining the quality of extinction memories is of utmost importance. The present thesis focuses on three of these factors including the female sex hormone 17β-estradiol (E2), fear extinction timing, and the noradrenergic arousal system. To examine the role of E2 (Manuscript 1; low E2 levels or high E2 levels) and fear extinction timing (Manuscript 2; either immediately or delayed after the initial fear memory formation), we used a special differential fear conditioning procedure that allowed us to separately assess fear memories and extinction memories via peripheral arousal responses (measured via skin conductance responses [SCR]) and, most importantly, via central neurophysiological indicators (measured via electroencephalography [EEG]). Concerning EEG parameters, we were especially interested in neural oscillations (especially in the theta and gamma range). To further advance the understanding of the neurophysiological foundations of both memory systems, we also aimed at disentangling oscillatory and non-oscillatory brain activity (Manuscript 2). Moreover, the crucial role of the noradrenergic arousal system for the quality of extinction memories is highlighted in a review of relevant rodent and human studies (Manuscript 3). By using the described multi-methodological approach, we were able to demonstrate for the first time that peripheral arousal as well as fear-related theta oscillations are sensitive to E2. This was indicated by less fear responding (attenuated peripheral arousal and attenuated theta oscillations) during the recall of fear and extinction memories under high peripheral E2 levels (Manuscript 1). Concerning the role of fear extinction timing, we demonstrate that delayed extinction is advantageous over immediate extinction in reducing peripheral arousal during the recall of the extinction memory (Manuscript 2). Additionally, by disentangling oscillatory and non-oscillatory brain activity, we demonstrate for the first time that oscillatory and non-oscillatory brain activity is sensitive to fear expression. Moreover, by reviewing different rodent and human studies, we highlight the important role of noradrenergic arousal for the recall of extinction memories and, importantly, provide a detailed mechanistic framework of how extinction deficits might be caused after immediate extinction (Manuscript 3). In sum, the present thesis underscores the important role of E2, fear extinction timing, and the noradrenergic system for the recall quality of fear memories and extinction memories in humans.