Human pluripotent stem cells are increasingly used for cell-based regenerative therapies worldwide, with the use of embryonic and induced pluripotent stem cells as potential treatments for a range of debilitating and chronic conditions. However, with the level of chromosomal aneuploidies the cells may generate in culture, their safety for therapeutic use could be in question. This study aimed to develop sensitive and high-throughput assays for the detection and quantification of human pluripotent stem cell aneuploidies, to assess any changes in their positioning in nuclei, as well as investigate the possible roles of lamins in the accumulation of aneuploidies. Using Droplet Digital PCR™, we optimised the detection of aneuploid cells in a predominantly diploid background. An assay was established for the sensitive detection of up to 1% of mosaicism and was used for the monitoring of low-level chromosome copy number changes across different cell lines, conditions and passages in the human pluripotent stem cells. In addition, fluorescence in-situ hybridisation was used to map genes ALB and AMELX on chromosomes 4 and X, respectively, in karyotype-stable chromosome X aneuploid lymphoblastoid cell lines. Our results demonstrated significant alternations in the gene loci positioning in the chromosome X aneuploid cell lines. Using the same established method, the positioning of ALB and AMELX was monitored, alongside the genomic instability with ddPCR™, in the different human pluripotent stem cell lines, conditions and passage. We demonstrated a highly plastic nuclear organisation in the pluripotent stem cells with many changes occurring within a single passage. Furthermore, these results were not exclusive to a single cell line or condition, regardless of the presence or absence of feeder cells and of passage number, and the flexibility of the chromatin organisation remained throughout the duration of the study. We demonstrated high levels of genomic instability with recurrent gains and losses in the AMELX copy number in the human embryonic stem cells during the course of our study, however no significant changes in their gene loci positioning from these abnormalities were observed. xvi | P a g e Additionally, we observed reduced levels of lamin B2 in the aneuploid lymphoblastoid cell lines and complete loss in some hPSC samples. Our results support recent findings that suggest a link between lamin B2 loss and the formation of chromosome aneuploidies in cell culture. In conclusion, our data demonstrates several key novel findings. Firstly, we have established a sensitive technique for the detection of up to 1% mosaicism, which to our knowledge is the most sensitive assay currently available. Secondly, we showed significant changes in the gene loci positioning between aneuploid and diploid cell lines. Thirdly, utilising our novel ddPCR™ assay, we demonstrated the karyotypical instability of hPCSs with consistent gains and/or loses of gene copy numbers in a short period of time in culture. When studying the effects of different growth conditions, we showed that the karyotypical instability was not exclusive to a single condition or a combination of conditions, and what is more, the karyotypical abnormalities detected were not observed to change the gene positioning of hPSCs significantly, with the genome organisation remaining plastic. Finally, our results support a potential association of lamin B2 loss and karyotypical instability. We conclude that more sensitive and robust techniques need to be readily used by clinicians for the screening of potential therapeutic hPSCs.

This dissertation considers the genesis and dynamics of interfacial instability in vertical laminar gas-liquid flows, using as a model the two-dimensional channel flow of a thin falling film sheared by counter-current gas. The methodology is linear stability theory by means of Orr-Sommerfeld analysis together with direct numerical simulation of the two-phase flow in the case of nonlinear disturbances. The influence of two main flow parameters on the interfacial dynamics, namely the film thickness and pressure drop applied to drive the gas stream, is investigated. To make contact with existing studies in the literature, the effect of various density and viscosity contrasts as well as surface tension is also examined. Energy budget analyses based on the Orr-Sommerfeld theory reveal various coexisting unstable modes (interfacial, shear, internal) in the case of high density contrasts, which results in mode coalescence and mode competition, but only one dynamically relevant unstable interfacial mode for low and intermediate density contrast. Furthermore, high viscosity contrast and increases in surface tension lead to some amount of mode competition for thin film. A study of absolute and convective instability for low density contrast shows that the system is absolutely unstable for all but two narrow regions of the investigated parameter space. These regions are extended at intermediate density contrast and exhibit only small changes with increased viscosity contrast or surface tension. Direct numerical simulations of the system with low density contrast show that linear theory holds up remarkably well upon the onset of large-amplitude waves as well as the existence of weakly nonlinear waves. For high density contrasts corresponding more closely to an air-water-type system, linear stability theory is also successful at determining the most-dominant features in the interfacial wave dynamics at early-to-intermediate times. Nevertheless, the short waves selected by the linear theory undergo secondary instability and the wave train is no longer regular but rather exhibits chaotic motion. Furthermore, linear stability theory also predicts when the direction of travel of the waves changes - from downwards to upwards. The practical implications of this change in terms of loading and flooding is discussed. The change in direction of the wave propagation is represented graphically for each investigated system in terms of a flow map based on the liquid and gas flow rates and the prediction carries over to the nonlinear regime with only a small deviation. Besides the semi-analytical and numerical analyses, experiments with an practically relevant setup and flow system have been carried out to benchmark and validate the models developed in this work.

O objetivo foi investigar a aquisição de habilidades motoras, no modelo do Processo Adaptativo, testando dois ciclos de Instabilidade-Estabilidade-Instabilidade (I-E-I). Duzentos e quarenta homens adultos jovens participaram de dois experimentos realizando uma tarefa seriada de rastreamento. As variáveis dependentes foram as respostas omissas, erradas, corretas e antecipatórias. O Experimento 1 testou o efeito dos Intervalos Inter-Estímulos (IIEs) em uma fase de aquisição num delineamento com seis grupos (300, 400, 500, 600, 700 e 800 ms de IIE); os testes estatísticos indicaram efeito de interação de grupos e blocos em todas as respostas. Com base nesses resultados foi elaborado o experimento principal com a mesma tarefa, num delineamento de três fases (Estabilização, Adaptação I e II) com o intuito de analisar o efeito dos ciclos I-E-I e dos IIEs no desempenho. Foram testados seis grupos nos quais os IIEs eram modificados de uma fase para outra. Os testes estatísticos mostraram efeito de interação entre grupos e blocos para os quatro tipos de resposta. Em seu conjunto, os resultados indicam que a aquisição de habilidades se dá mediante sucessivos ciclos de estabilização-adaptação, que leva ao aumento de complexidade; houve efeito do nível de estabilização alcançado no primeiro ciclo para o segundo ciclo de I-E-I e da magnitude da perturbação; a redundância inicial na estrutura teve efeito no desempenho em respostas funcionais ao longo dos ciclos / The aim of this study was to investigate the acquisition of motor learning as proposed by Adaptive Process model of motor learning by testing two Instability- Stability-Instability cycles (IN-ST-IN). Two hundred and forty young adult men participated in the two experiments in which a serial tracking task was used. The dependent variables were anticipatory, correct, incorrect and omission responses. The first experiment tested the effect of the Inter-Stimuli-Intervals (ISI) in an acquisition phase with a design comprised by six groups (300, 400, 500, 600, 700 e 800 ms of ISI); the MANOVA statistics (6 Groups X 3 Blocks) indicated interaction effect in all responses. Based on these results the main experiment was set up with a design of three phases (Stabilization, Adaptation I and II) with the aim to analyze the effect of the IN-ST-IN cycles and the ISIs on four responses. Six groups were tested in which the ISI were modified in each phase. The MANOVA statistics (6 Groups X 5 Blocks) indicated interaction effect in all responses. In sum, the results indicated that the acquisition process of motor skills takes place in the course of successive stabilization-adaptation cycles that lead to the increase to system\'s complexity; there was observed effect of the first cycle stabilization level on the second cycle; the early redundancy in the structure had effect on the functional responses performance, throughout the cycles

O objetivo foi investigar a aquisição de habilidades motoras, no modelo do Processo Adaptativo, testando dois ciclos de Instabilidade-Estabilidade-Instabilidade (I-E-I). Duzentos e quarenta homens adultos jovens participaram de dois experimentos realizando uma tarefa seriada de rastreamento. As variáveis dependentes foram as respostas omissas, erradas, corretas e antecipatórias. O Experimento 1 testou o efeito dos Intervalos Inter-Estímulos (IIEs) em uma fase de aquisição num delineamento com seis grupos (300, 400, 500, 600, 700 e 800 ms de IIE); os testes estatísticos indicaram efeito de interação de grupos e blocos em todas as respostas. Com base nesses resultados foi elaborado o experimento principal com a mesma tarefa, num delineamento de três fases (Estabilização, Adaptação I e II) com o intuito de analisar o efeito dos ciclos I-E-I e dos IIEs no desempenho. Foram testados seis grupos nos quais os IIEs eram modificados de uma fase para outra. Os testes estatísticos mostraram efeito de interação entre grupos e blocos para os quatro tipos de resposta. Em seu conjunto, os resultados indicam que a aquisição de habilidades se dá mediante sucessivos ciclos de estabilização-adaptação, que leva ao aumento de complexidade; houve efeito do nível de estabilização alcançado no primeiro ciclo para o segundo ciclo de I-E-I e da magnitude da perturbação; a redundância inicial na estrutura teve efeito no desempenho em respostas funcionais ao longo dos ciclos / The aim of this study was to investigate the acquisition of motor learning as proposed by Adaptive Process model of motor learning by testing two Instability- Stability-Instability cycles (IN-ST-IN). Two hundred and forty young adult men participated in the two experiments in which a serial tracking task was used. The dependent variables were anticipatory, correct, incorrect and omission responses. The first experiment tested the effect of the Inter-Stimuli-Intervals (ISI) in an acquisition phase with a design comprised by six groups (300, 400, 500, 600, 700 e 800 ms of ISI); the MANOVA statistics (6 Groups X 3 Blocks) indicated interaction effect in all responses. Based on these results the main experiment was set up with a design of three phases (Stabilization, Adaptation I and II) with the aim to analyze the effect of the IN-ST-IN cycles and the ISIs on four responses. Six groups were tested in which the ISI were modified in each phase. The MANOVA statistics (6 Groups X 5 Blocks) indicated interaction effect in all responses. In sum, the results indicated that the acquisition process of motor skills takes place in the course of successive stabilization-adaptation cycles that lead to the increase to system\'s complexity; there was observed effect of the first cycle stabilization level on the second cycle; the early redundancy in the structure had effect on the functional responses performance, throughout the cycles

A number of models of nature incorporate dimensions beyond our observed four. In this thesis we examine some examples and consequences of classical instabilities that emerge in the higher-dimensional theories of gravity which can describe their low energy phenomenology. <br /><br /> We first investigate a gravitational instability for black strings carrying momentum along an internal direction. We argue that this implies a new type of solution that is nonuniform along the extra dimension and find that there is a boost dependent critical dimension for which they are stable. Our analysis implies the existence of an analogous instability for the five-dimensional black ring. We construct a simple mode of the black ring to aid in applying these results and argue that such rings should exist in any number of space-time dimensions. <br /><br /> Next we consider a recently constructed class of nonsupersummetric solutions of type IIB supergravity which are everywhere smooth and have no horizon. We demonstrate that these solutions are all classically unstable. The instability is a generic feature of horizonless geometries with an ergoregion. We consider the endpoint of this instability and argue that the solutions decay to supersymmetric configurations. We also comment on the implications of the ergoregion instability for Mathur's 'fuzzball' proposal. <br /><br /> Finally, we consider an interesting braneworld cosmology in the Randall-Sundrum scenario constructed using a bulk space-time which corresponds to a charged AdS black hole. In particular, these solutions appear to 'bounce', making a smooth transition from a contracting to an expanding phase. By considering the space-time geometry more carefully, we demonstrate that generically in these solutions the brane will encounter a singularity in the transition region.

A number of models of nature incorporate dimensions beyond our observed four. In this thesis we examine some examples and consequences of classical instabilities that emerge in the higher-dimensional theories of gravity which can describe their low energy phenomenology. <br /><br /> We first investigate a gravitational instability for black strings carrying momentum along an internal direction. We argue that this implies a new type of solution that is nonuniform along the extra dimension and find that there is a boost dependent critical dimension for which they are stable. Our analysis implies the existence of an analogous instability for the five-dimensional black ring. We construct a simple mode of the black ring to aid in applying these results and argue that such rings should exist in any number of space-time dimensions. <br /><br /> Next we consider a recently constructed class of nonsupersummetric solutions of type IIB supergravity which are everywhere smooth and have no horizon. We demonstrate that these solutions are all classically unstable. The instability is a generic feature of horizonless geometries with an ergoregion. We consider the endpoint of this instability and argue that the solutions decay to supersymmetric configurations. We also comment on the implications of the ergoregion instability for Mathur's 'fuzzball' proposal. <br /><br /> Finally, we consider an interesting braneworld cosmology in the Randall-Sundrum scenario constructed using a bulk space-time which corresponds to a charged AdS black hole. In particular, these solutions appear to 'bounce', making a smooth transition from a contracting to an expanding phase. By considering the space-time geometry more carefully, we demonstrate that generically in these solutions the brane will encounter a singularity in the transition region.

There are two coupled primary objectives for this study of buoyancy-driven turbulence. The first objective is to create a new diagnostic for collection of measurements to capture the physics of Rayleigh-Taylor (RT) mixing. The second objective is to use the new diagnostic to specifically elucidate the physics of large Atwood number, ( )( )2 1 2 1 / ρ ρ ρ ρ + − = t A , RT mixing. Both of these objectives have been satisfied through the development of a new hot-wire diagnostic to study buoyancy-driven turbulence in a statistically steady gas channel of helium and air ( 6 . 0 03 . 0 ≤ ≤ t A ). The capability of the diagnostic to simultaneously and instantaneously measure turbulent velocity and density fluctuations allows for a unique investigation into the dynamics of Rayleigh-Taylor mixing layers at large At, through measurements of turbulence and mixing statistics. The new hot-wire diagnostic uses temperature as a fluid marker for helium and air, which is possible due to the Lewis number ~ 1 (Le = ratio of thermal diffusivity to mass diffusivity) for helium and air, and the new diagnostic has been validated in an At = 0.03 mixing layer. The energy density spectrum of v′ ′ ρ , measured experimentally for the first time in RT mixing, is found to closely follow the energy distribution of v′ , up to the Reynolds numbers investigated ( ( ) mix t h gA h υ 6 2 Re 2 / 3 = ~ 1450). Large At experiments, with At = 0.6, have also been achieved for the first time in a miscible RT mixing layer. An asymmetric penetration of the bubbles (rising fluid) and spikes (falling fluid) has been observed, resulting in measured self similar growth parameters αb = 0.060 and αs = 0.088 for the bubbles and spikes, respectively. The first experimental measurements of turbulent velocity and density fluctuations for the large At case, show a strong similarity to lower At behaviors when normalized. However conditional statistics, which separate the bubble (light fluid) and spike (heavy fluid) dynamics, has highlighted differences in v′ ′ ρ and rms v′ in the bubbles and spikes. Larger values of v′ ′ ρ and rms v′ were found in the downward falling spikes, which is consistent with the larger growth rates and momentum of the spikes compared to the bubbles. These conditional statistics are a first in RT driven turbulence.

Richtmyer-Meshkov instability (RMI) occurs when an interface of two fluids with different densities is impulsively accelerated. The main interest in RMI is to understand the growth of perturbations, and numerous theoretical models have been developed and validated against experimental/numerical studies. However, most of the studies assume very simple initial conditions. Recently, more complex RMI has been studied, and this study focuses on two cases: reshocked RMI and multiphase RMI. It is well known that reshock to the species interface causes rapid growth of interface perturbation amplitude. However, the growth rates after reshock are not well understood, and there are no practical theoretical models yet due to its complex interface conditions at reshock. A couple of empirical expressions have been derived from experimental and numerical studies, but these models are limited to certain interface conditions. This study performs parametric numerical studies on various interface conditions, and the empirical models on the reshocked RMI are derived for each case. It is shown that the empirical models can be applied to a wide range of initial conditions by choosing appropriate values of the coefficient. The second part of the study analyzes the flow physics of multiphase RMI. The linear growth model for multiphase RMI is derived, and it is shown that the growth rates depend on two nondimensional parameters: the mass loading of the particles and the Stokes number. The model is compared to the numerical predictions under two types of conditions: a shock wave hitting (1) a perturbed species interface surrounded by particles, and (2) a perturbed particle cloud. In the first type of the problem, the growth rates obtained by the numerical simulations are in agreement with the multiphase RMI growth model when Stokes number is small. However, when the Stokes number is very large, the RMI motion follows the single-phase RMI growth model since the particle do not rapidly respond while the RMI instability grows. The second type of study also shows that the multiphase RMI model is applicable if Stokes number is small. Since the particles themselves characterize the interface, the range of applicable Stokes number is smaller than the first study. If the Stokes number is in the order of one or larger, the interface experiences continuous acceleration and shows the growth profile similar to a Rayleigh-Taylor instability.

This thesis focuses on the propagation of charged particle beams in plasmas, and is divided into two main parts. In the second chapter, a novel theoretical model for underdense electron beam propagation during the nonlinear stage of the resistive Weibel instability (WI) is presented and is used to calculate the stopping time of the beam. The model and supporting simulation results lead to the conclusion that the WI initially enhances beam deceleration but then reduces it when compared to a filamentation-suppressed beam (without WI), so that the overall stopping time of the beam is essentially unaffected by the instability. Using the theoretical model, a criterion is derived that determines when deceleration is no longer enhanced by the instability. We also demonstrate that exotic plasma return current distributions can be obtained within and outside of beam filaments that sharply contrast those observed in collisionless systems. For example, the plasma return current is reversed in selected areas. In the next chapter, a new method for initiating the modulation instability (MI) of a proton beam in a proton driver plasma wakefield accelerator using a short laser pulse preceding the beam is presented. A diffracting laser pulse is used to produce a plasma wave that provides a seeding modulation of the proton bunch with the period equal to that of the plasma wave. Using the envelope description of the proton beam, this method of seeding the MI is analytically compared with the earlier suggested seeding technique that involves an abrupt truncation of the proton bunch. The full kinetic simulation of a realistic proton bunch is used to validate the analytic results. It is further used to demonstrate that a plasma density ramp placed in the early stages of the laser-seeded MI leads to its stabilization, resulting in sustained accelerating electric fields (of order several hundred MV/m) over long propagation distances (100-1000 m). The final chapter describes a harmonic expansion formalism that attempts to explain the post-linear stage of the MI. The formalism is developed first, and then several crippling problems with it are identified. / text

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第19091号 / エネ博第315号 / 新制||エネ||64 / 32042 / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)教授 岸本 泰明, 教授 前川 孝, 教授 中村 祐司 / 学位規則第4条第1項該当