京都大学 / 新制・課程博士 / 博士(医学) / 甲第23420号 / 医博第4765号 / 新制||医||1053(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 髙橋 良輔, 教授 林 康紀, 教授 福田 和彦 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

With rapid depletion of fossil fuels and increasing environmental concerns, the trend to capture renewable energy, especially through wind energy resources, is increasing. The doubly fed induction generator (DFIG) is the most widely used generator for wind energy conversion because of its various advantages over other types of generators. In a DFIG, the rotor is fed through back to back converters via slip rings. The converters enable the generation control. This control property can be used to support reliable operation of a grid network system. Interarea oscillation has been a major factor in limiting power transfers in interconnected power systems. Poorly damped modes can trigger oscillatory instability, potentially leading to cascading blackouts in such systems. We consider a two-area system where DFIG based wind generation is integrated with conventional synchronous generators. A simple controller is proposed for the DFIG to improve damping of interarca oscillations. To support the proposition, case studies are conducted in Matlab/Simulink. The effectiveness of the proposed controller is then analyzed by eigenvalue analysis and verified with time domain simulation results. The results show that a properly tuned controller can increase the damping of dominant oscillatory mode by nearly 5% while improving the area transfer by about 200 MW of wind power. The results further show that with the proposed control strategy, damping of dominant oscillatory mode increased by more than 10%. / North Dakota State University. Graduate School / North Dakota State University. Department of Electrical and Computer Engineering

La plupart des matériaux étudiés en physique de la matière condensée sont à base de fermions massifs vérifiant les relations de dispersion paraboliques usuelles. Récemment, sont apparus un certain nombre de matériaux dotés de relations de dispersion linéaires : le graphène, système purement bidimensionnel et les isolants topologiques, composés tridimensionnels à base de Bismuth où les fermions de Dirac surfaciques coexistent avec les fermions massifs volumiques. À côté de ces deux grandes familles de matériaux de Dirac, on trouve le composé organique α-(BEDT-TTF)2I3, un système quasi-bidimensionnel du point de vue du transport électronique en raison de sa structure cristalline lamellaire et qui présente une phase de Dirac sous forte pression hydrostatique (P>1,5 GPa). Cette phase de Dirac est singulière puisque ses cônes de Dirac sont inclinés, et donc fortement anisotropes, et qu'ils émergent aux côtés d'une bande de porteurs de charge massifs. Ce travail de thèse porte ainsi sur l'étude, à la fois expérimentale et théorique, des effets des spécificités de la phase de Dirac du α-(BEDT-TTF)2I3 sur son transport électronique en régime quantique. Il examine notamment plusieurs modèles théoriques pour tenter d'interpréter les oscillations quantiques apériodiques mesurées dans le composé organique, ainsi que l'impact de l'inclinaison des cônes de Dirac. Les effets de dopage, surfacique et volumique, sur le α-(BEDT-TTF)2I3 sont également discutés. / The physics of most of the materials studied within condensed matter are based on massive fermions which verify the usual parabolic dispersion relations. Recently, a certain number of materials with linear dispersion relation have appeared: graphene, purely bidimensional and topological insulators, tridimensional compounds based on Bismuth where the surfacic Dirac fermions coexist with bulk massive fermions. Alongside these two families of Dirac materials, there is the organic α-(BEDT-TTF)2I3 compound, a quasi-bidimensional system from an electronic transport point of view because of its lamellar crystalline structure and which exhibits a Dirac phase under high hydrostatic pressure (P>1,5 GPa). This Dirac phase is singular: the Dirac cones are tilted, and highly anisotropic, and they emerge with a massive band. This work is then focus on the study, experimentally and theoretically, of the effects of the α-(BEDT-TTF)2I3 Dirac phase specificities on its electronical transport in quantum regime. It examines particularly several theoretical models to understand the aperiodic quantum oscillations measured in the organic compound, and the impact of Dirac cones tilting. Doping effects, surfacic and in the bulk, on the α-(BEDT-TTF)2I3 are also discussed.

Many living organisms have the ability to execute complex behaviors and cognitive processes that are reliable. In many cases, such tasks are generated in the absence of an ongoing external input that could drive the activity on their underlying neural populations. For instance, writing the word "time" requires a precise sequence of muscle contraction in the hand and wrist. There has to be some patterns of activity in the areas of the brain responsible for this behaviour that are endogenously generated every time an individual performs this action. Whereas the question of how such neural code is transformed in the target motor sequence is a question of its own, their origin is perhaps even more puzzling. Most models of cortical and sub-cortical circuits suggest that many of their neural populations are chaotic. This means that very small amounts of noise, such as an additional action potential in a neuron of a network, can lead to completely different patterns of activity. Reservoir computing is one of the first frameworks that provided an efficient solution for biologically relevant neural networks to learn complex temporal tasks in the presence of chaos. We showed that although reservoirs (i.e. recurrent neural networks) are robust to noise, they are extremely sensitive to some forms of structural perturbations, such as removing one neuron out of thousands. We proposed an alternative to these models, where the source of autonomous activity is no longer originating from the reservoir, but from a set of oscillating networks projecting to the reservoir. In our simulations, we show that this solution produce rich patterns of activity and lead to networks that are both resistant to noise and structural perturbations. The model can learn a wide variety of temporal tasks such as interval timing, motor control, speech production and spatial navigation.

The present thesis investigated memory load and memory decay in auditory working memory. Alpha power as a marker for memory load served as the primary indicator for load and decay fluctuations hypothetically reflecting functional inhibition of irrelevant information. Memory load was induced by presenting auditory signals (syllables and pure-tone sequences) in noise because speech-in-noise has been shown before to increase memory load. The aim of the thesis was to assess with magnetoencephalography whether a-priori temporal expectations for the onset-time of a to-be-remembered stimulus reduces memory load. It was reported previously that top-down modulations such as spatial expectations reduce memory load and improve memory performance. However, this effect has neither been investigated with temporal expectations nor in the auditory domain. The present thesis showed that temporal expectations for a syllable in noise reduced memory load. Reduced alpha power during stimulus maintenance as well as improved performance indicated the decrease in memory load. Alpha power effects emerged from the right cingulo-opercular network, presumably reflecting a reduced need for functional inhibition. Critically, symbolic cues induced temporal expectations. This effect could not be replicated for clear speech. However, more implicit temporal expectations based on the passage of time elicited a similar decrease in alpha power for clear speech reflecting reduced memory load. Memory decay was assessed with variable delay phases in an auditory sensory memory task with pure-tone sequences. Similarly to memory performance, alpha power decreased with longer delay phases. Critically, temporal expectations counteracted memory decay and led to more sustained performance as well as alpha power across different delay phases. These alpha-power effects were localized to frontal and parietal attention networks as well as primary auditory and visual sensory areas. This implies the involvement of different brain regions relevant for encoding and maintenance in auditory memory and questions a parsimonious functional inhibition explanation. A correlation of alpha power and behavioral performance underpinned the importance of alpha power for auditory working memory. Altogether, the results of the present thesis provide evidence for a beneficial effect of a-priori temporal expectations for an auditory signal on working memory. Moreover, alpha dynamics were shown to be a distinct marker for the neural efficiency of managing working memory limitations.

This thesis investigates how the neural system instantiates selective attention to speech in challenging acoustic conditions, such as spectral degradation and the presence of background noise. Four studies using behavioural measures, magneto- and electroencephalography (M/EEG) recordings were conducted in younger (20–30 years) and older participants (60–80 years). The overall results can be summarized as follows. An EEG experiment demonstrated that slow negative potentials reflect participants’ enhanced allocation of attention when they are faced with more degraded acoustics. This basic mechanism of attention allocation was preserved at an older age. A follow-up experiment in younger listeners indicated that attention allocation can be further enhanced in a context of increased task-relevance through monetary incentives. A subsequent study focused on brain oscillatory dynamics in a demanding speech comprehension task. The power of neural alpha oscillations (~10 Hz) reflected a decrease in demands on attention with increasing acoustic detail and critically also with increasing predictiveness of the upcoming speech content. Older listeners’ behavioural responses and alpha power dynamics were stronger affected by acoustic detail compared with younger listeners, indicating that selective attention at an older age is particularly dependent on the sensory input signal. An additional analysis of listeners’ neural phase-locking to the temporal envelopes of attended speech and unattended background speech revealed that younger and older listeners show a similar segregation of attended and unattended speech on a neural level. A dichotic listening experiment in the MEG aimed at investigating how neural alpha oscillations support selective attention to speech. Lateralized alpha power modulations in parietal and auditory cortex regions predicted listeners’ focus of attention (i.e., left vs right). This suggests that alpha oscillations implement an attentional filter mechanism to enhance the signal and to suppress noise. A final behavioural study asked whether acoustic and semantic aspects of task-irrelevant speech determine how much it interferes with attention to task-relevant speech. Results demonstrated that younger and older adults were more distracted when acoustic detail of irrelevant speech was enhanced, whereas predictiveness of irrelevant speech had no effect. All findings of this thesis are integrated in an initial framework for the role of attention for speech comprehension under demanding acoustic conditions.

This paper is concerned with the investigation of the nonlinear eigenvalue problem describing the natural oscillations of a plate with a load that elastically attached to it. We study properties of eigenvalues and eigenfunctions of this eigenvalue problem and prove the existence theorem for eigensolutions. Theoretical results are illustrated by numerical experiments.

Local helioseismology consists of methods which study the propagation of the waves through the solar interior. The properties of the waves encode conditions in the plasma along their propagation trajectories. Local helioseismology allows us to learn about these conditions. The principal method utilised in this thesis is the time-distance local helioseismology. The time-distance method is based on measurements of travel times of the waves, hence it is sensitive especially to plasma flows and sound-speed perturbations, to which we focus. We utilised the inverse modelling, mainly using subtractive optimally localised averaging method with a minimisation of the cross-talk. This method was modified to allow for a simultaneous inversion of vector flows and sound-speed perturbation. This combination makes use of both the difference and the mean point-to-annulus averaging geometries of wave travel times in both the ridge and the phase-speed filtering approaches. The combined inversion provides us with more information about the inverted quantities. Moreover, the user can control the cross-talk and other important mathematical properties of the objects involved. The modified methodology was thoroughly tested. The main results may be summarised in five points. First, for successful inversions of the sound-speed...

Local helioseismology consists of methods which study the propagation of the waves through the solar interior. The properties of the waves encode conditions in the plasma along their propagation trajectories. Local helioseismology allows us to learn about these conditions. The principal method utilised in this thesis is the time-distance local helioseismology. The time-distance method is based on measurements of travel times of the waves, hence it is sensitive especially to plasma flows and sound-speed perturbations, to which we focus. We utilised the inverse modelling, mainly using subtractive optimally localised averaging method with a minimisation of the cross-talk. This method was modified to allow for a simultaneous inversion of vector flows and sound-speed perturbation. This combination makes use of both the difference and the mean point-to-annulus averaging geometries of wave travel times in both the ridge and the phase-speed filtering approaches. The combined inversion provides us with more information about the inverted quantities. Moreover, the user can control the cross-talk and other important mathematical properties of the objects involved. The modified methodology was thoroughly tested. The main results may be summarised in five points. First, for successful inversions of the sound-speed...

Cytoplasmic dynein is a ubiquitous minus-end directed motor protein that is essential for a variety of cellular processes ranging from cargo transport to spindle and chromosome positioning. Specifically, in fission yeast during meiotic prophase, the fused nucleus follows the spindle pole body in oscillatory movements from one cell pole to the other. The three molecular players that are essential to this process are: (i) the motor protein dynein, which powers the movement of the nucleus, (ii) microtubules, which provide the tracts for the movement and (iii) Num1, the anchor protein of dynein at the cortex. Dyneins that are localized to the anchor protein at the cortex and simultaneously bound to the microtubule emanating from the spindle pole body, pull on that microtubule leading to the movement of the nucleus. The spindle pole body, by virtue of its movement establishes a leading and a trailing side. Previous work by Vogel et al. has elucidated the mechanism of these oscillations as that of asymmetric distribution of dynein between the leading and trailing sides. This differential distribution is a result of the load-dependent detachment of dynein preferentially from the trailing microtubules. This self-organization model for dynein, however, requires a continuous redistribution of dynein from the trailing to the leading side. In addition, dyneins need to be bound to the anchor protein to be able to produce force on the microtubules. Anchored dyneins are responsible for many other important processes in the cell such as spindle alignment and orientation, spindle separation and rotation. So we set out to elucidate the mechanism of redistribution of dynein as well as the targeting mechanism of dynein from the cytoplasm to cortical anchoring sites where they can produce pulling force on microtubules. By employing single-molecule observation using highly inclined laminated optical sheet (HILO) microscopy and tracking of fluorescently-tagged dyneins using a custom software, we were able to show that dyneins redistributed in the cytoplasm of fission yeast by simple diffusion. We also observed that dynein bound first to the microtubule and not directly to the anchor protein Num1. In addition, we were able to capture unbinding events of single dyneins from the microtubule to the cytoplasm. Surprisingly, dynein bound to the microtubule exhibited diffusive behaviour. The switch from diffusive to directed movement required to power nuclear oscillations occurred when dynein bound to its cortical anchor Num1. In summary, dynein employs a two-step targeting mechanism from the cytoplasm to the cortical anchoring sites, with the attachment to the microtubule acting as the intermediate step.