VictorJuiz/thesis huggingface dataset:
An Intrinsic Mechanism of Asymmetric Cell Division and Extrinsic Mechanism of Stem Cell Maintenance Underlies Adult Stem Cell Behaviour
Keywords: Stem Cell
Asymmetry

The interplay between extrinsic and intrinsic processes as they influence a cell’s behaviour is a perennial question in both cellular and developmental biology. In this thesis these two issues are examined in the context of adult stem cells, a somatic stem cell present in the adult murine brain and a germline stem cell present in the adult Drosophila melanogaster ovary. I find that both of these distinct cell types exhibit patterns of non-random chromatid segregation in which the stem cells retain chromosomes carrying the older DNA strands. This unusual behaviour seems to exclusively occur in the context of differentiation, when one cell remains a stem cell and the other goes on to differentiate. Following these studies, the effects of extrinsic processes are tested in adult murine stem cells. It is determined that such cells can only produce neural progeny regardless of their association with foreign environments. These results argue against the phenomenon of stem cell plasticity which is proposed in several other systems and seem to support a primarily intrinsic-centered view of stem cell behaviour. However, the role of adhesion mediating proteins is next studied in such cells to determine their requirement for specific environments. The results of these experiments suggest that adult murine neural stem cells require association with support cells expressing E-Cadherin. Because the loss of such association results in a loss of stem cell number, these data show that intrinsic processes are insufficient to account for all stem cell behaviour. Indeed, based on these data and the results of other studies, it is hypothesized that the extrinsic association of stem cells in these diverse systems determines their polarity and subsequent intrinsic processes that enable these to divide asymmetrically. The implications of this theory are discussed with a view to general biological issues, the proximate mechanisms underlying these phenomena and the ultimate reasons these occur.
Synaptic Transmission in the Leaner Mutant Mouse Calyx of Held/MNTB Synapse
Keywords: Calcium Channels
Leaner Mutant Mouse
Calyx of Held
Synaptic Transmission
Development
Presynaptic
Roscovitine

The effects of alpha1A subunit mutations on presynaptic Ca2+ channel activity and functional development of synaptic properties remain elusive. The calyx of Held/medial nucleus of the trapezoid body synapse is an ideal model for studying the developmental effects of presynaptic voltage-gated Ca2+ channel (VGCC) impairment on synaptic function since simultaneous voltage-clamp recordings can be made directly from the pre- and postsynapse. The alpha1A subunit leaner (tgla/la) mutation induced a profound reduction in synaptic transmission after hearing onset (> postnatal day 12; P12), with relatively preserved relationship between presynaptic Ca2+ current (Pre-ICa) and release and G-protein-mediated inhibition. Some synaptic properties were more reflective of an immature state, while other properties displayed a delay in maturation after P12. Direct presynaptic recordings from P15/16 tgla/la nerve terminals revealed a decrease in the density of Pre-ICa, elevated activation threshold and slowing in the kinetics of VGCCs, all of which contribute to the deficit in transmitter release. Fractional contribution of P/Q-type channels to total Pre-ICa and their role in vesicle release was markedly reduced. N-type Ca2+ channels and close association of VGCCs to release sites was not sufficient to fully compensate for impaired P/Q-type channel function. The extent to which compensatory mechanisms preserve synaptic transmission at tgla/la synapses was further constrained by the developmental narrowing of the action potential waveform. Activation of the cAMP pathway by forskolin or direct modulation of VGCCs by cdk inhibitors rescued deficits in transmitter release at P15/16 tgla/la synapses. The major effect of roscovitine was a slowing of presynaptic VGCC deactivation kinetics accompanied by a leftward shift in the activation curve. Activation of the cAMP pathway or direct modulation of presynaptic VGCCs may serve as two potential pathways to facilitate release and improve neuronal communication at synapses normally compromised by impaired P/Q-type channel function. While significant for the tgla/la mutant, these studies provide an important advancement in our understanding of the crucial developmental and functional roles of P/Q-type Ca2+ channels in driving the maturation of synaptic properties at central synapses. These findings may improve our understanding of the pathophysiology of presynaptic VGCCs and elucidate essential mechanisms underlying the tgla/la phenotype.
The Effect of Ddr1 Deletion on the Expression of Genes Involved in Atherosclerotic Vascular Remodeling and on the Development of Atherosclerotic Calcification
Keywords: collagen receptors
atherosclerosis
vascular smooth muscle cell
calcification

The effect of Ddr1 deletion on the expression of genes involved in atherosclerotic vascular remodeling and on the development of atherosclerotic calcification Pamela J. Ahmad, PhD Institute of Medical Science, 2008 During atherosclerosis, collagen molecules, which are abundant in the healthy vessel, are extensively degraded, re-synthesized or newly synthesized, and remodeled to induce profound changes in VSMCs as they colonize and expand atherosclerotic lesions. The central theme of this thesis was to investigate the effect of genetic deletion of a collagen receptor, DDR1, on VSMC processes during atherosclerosis. In the first study, we demonstrated a role for DDR1 as an important regulator of gene expression in synthetic VSMCs. We have profiled the expression of vascular collagen matrix molecules, MMPs and TIMPs in synthetic VSMCs and we have demonstrated that deletion of Ddr1 is sufficient to accelerate ECM remodeling in synthetic VSMCs, which may influence cell migration during atherosclerosis. Moreover, we have extended our knowledge of DDR1 function in synthetic VSMCs, by demonstrating that DDR1 limits VSMC proliferation in a complex matrix microenvironment representative of the ECM produced in the vessel wall during vascular disease. In the second study, we investigated the role of DDR1 in atherosclerotic calcification, a feature of advanced atherosclerotic disease. Here, we demonstrated that intimal calcification in Ldlr-/- mice fed a high-fat/ high-cholesterol diet may be mediated through the initiation of a chondrogenic transcriptional regulatory program and that deletion of Ddr1 significantly attenuated the frequency and extent of atherosclerotic mineralization in vivo, as well as the ability of vascular smooth muscle cells to calcify in vitro, suggesting an important role for DDR1 in VSMCs as a positive regulator of this pathological process. In our third study, we provided evidence of a biochemical association between MMP-2 and DDR1b in VSMCs, which involves a direct interaction between MMP-2 and the extracellular region of the DDR1 receptor. In addition, we reported an association between endogenous MMP-2 and Stat1 in VSMCs, providing a platform for future research to investigate the functional consequences of these novel interactions.
Development of a Novel Visualization and Measurement Apparatus for the PVT Behaviours of Polymer/Gas Solutions
Keywords: PVT, Volume Swelling
Polymer/Gas Solutions, Surface Tension

The Pressure-Volume-Temperature (PVT) for polymer/gas solutions is an important fundamental property of which accurate data measurement has not been reported until recently. The diffusivity, solubility, and surface tension are critical physical properties of polymer/gas solutions in understanding and controlling polymer processing such as, foaming, blending, and extracting reaction. However, the determination of these properties relies on accurate PVT data as a prerequisite. Due to the difficulties involved in measuring the specific volume while maintaining a sufficiently high pressure and temperature to achieve a single-phase polymer/gas solution, accurate PVT data or volume swelling measurement of polymer/gas solutions is not yet available. In this research, a new methodology was proposed and developed for direct measuring the PVT properties of polymer melts saturated with high-pressure gas at elevated temperatures. The ultimate goal is to develop and construct an apparatus that would provide more accurate fundamental properties through PVT measurement to the foaming industry, which is heavily involved with polymer/gas mixtures.
Droplet Deposition in Solid Ink Printing
Keywords: droplet deposition
solid ink
inkjet printing
droplet generation
pulsed jet
droplet coalescence

Introduced in 1991, solid ink color printing technology is widely used in the office printing, prepress proofing, and wide format color printing markets. Ink droplets are first deposited on a rotating drum and then transferred to paper to reproduce images with high print quality. The objective of this thesis is to develop scientific knowledge of ink droplet deposition, which is needed for precise image buildup on the drum surface. The first problem studied in the thesis is droplet formation from the printhead with varied working voltages and jetting frequencies. Attention is paid to the formation of satellite droplets, the contraction of ligaments and the startup of high frequency jetting. The jetting conditions for obtaining consistent droplet generation with satellites are determined. A theoretical model is developed to predict the lifetime of ligaments. The second problem we studied is the deposition of single droplets on solid surfaces. The surface texture and final shape of deposited droplets are correlated with impact conditions, which include printhead temperature, substrate temperature, distance from printhead to substrate, and the type of substrate surface. An analytical model is developed to evaluate the interaction of oscillation and viscous damping in the droplet during impact. The third problem covered in the thesis is the deposition of multiple ink droplets on the drum surface. Interaction between droplets causes drawback effect, which degrades print quality. We define a parameter to quantify the drawback effect with varied deposition conditions. A simple model is provided to predict conditions for making continuous lines based on the results of two ink droplets deposition. To understand the hydrodynamics in causing drawback effect, a series of experiments using large liquid droplets are carried out. Focus is put on the evolution of spread length and dynamics of contact line. Correlations for maximum and minimum spread lengths are developed, which are used to reveal the cause of drawback effect in the deposition of ink droplets.
Accelerating Successive Approximation Algorithm Via Action Elimination
Keywords: successive approximation, action elimination, heuristic action elimination, action elimination for monotone policy MDPs

This research is an effort to improve the performance of successive approximation algorithm with a prime aim of solving finite states and actions, infinite horizon, stationary, discrete and discounted Markov Decision Processes (MDPs). Successive approximation is a simple and commonly used method to solve MDPs. Successive approximation often appears to be intractable for solving large scale MDPs due to its computational complexity. Action elimination, one of the techniques used to accelerate solving MDPs, reduces the problem size through identifying and eliminating sub-optimal actions. In some cases successive approximation is terminated when all actions but one per state are eliminated. The bounds on value functions are the key element in action elimination. New terms (action gain, action relative gain and action cumulative relative gain) were introduced to construct tighter bounds on the value functions and to propose an improved action elimination algorithm. When span semi-norm is used, we show numerically that the actual convergence of successive approximation is faster than the known theoretical rate. The absence of easy-to-compute bounds on the actual convergence rate motivated the current research to try a heuristic action elimination algorithm. The heuristic utilizes an estimated convergence rate in the span semi-norm to speed up action elimination. The algorithm demonstrated exceptional performance in terms of solution optimality and savings in computational time. Certain types of structured Markov processes are known to have monotone optimal policy. Two special action elimination algorithms are proposed in this research to accelerate successive approximation for these types of MDPs. The first algorithm uses the state space partitioning and prioritize iterate values updating in a way that maximizes temporary elimination of sub-optimal actions based on the policy monotonicity. The second algorithm is an improved version that includes permanent action elimination to improve the performance of the algorithm. The performance of the proposed algorithms are assessed and compared to that of other algorithms. The proposed algorithms demonstrated outstanding performance in terms of number of iterations and omputational time to converge.
Design and Analysis of Micro-electromechanical Resonant Structures
Keywords: Mechanical Engineering
Micro-electromechanical System
Vibration
Nonlinear Oscillation
Axial Force
Orthogonality

Dynamics of a beam-based micro-electromechanical resonator is investigated theoretically and experimentally. The resonant structure comprises a micro-beam and two electrostatic comb-drives, one for exciting the vibration, and the other for detecting the response. Two identical resonators of this type can form a double-ended tuning fork. An analytical linear model of these resonators is developed by assuming the beam to obey the thin beam theory subjected to an axial force. The comb-drives are initially treated as a point mass. The point mass is free to be placed anywhere along the beam span. The exact natural frequencies and mode shapes of vibration are obtained. Further, the mass is considered to have rotary inertia. The influence of the rotary inertia on the natural frequencies and mode shapes of vibration are investigated. Subsequently, the model of a beam with a guided mass is studied to determine the upper limit of the natural frequencies of the resonator. The advantage of this model over the previous ones is in providing detailed insight into the dynamics of the resonator, particularly when the comb-drives are placed at locations other than the mid-point of the beam. It has been shown that the mode shapes of vibration of these resonators are not orthogonal to each other under its classic definition. The orthogonality condition of the mode shapes of the beam-lumped mass system is introduced, and used for studying the forced vibration response. The nonlinear vibration of the system due to stretching is considered for the case of free vibration and the primary resonance. The nonlinear model is used to investigate the effect of damping on the resonator response. The interaction of the electrostatic governing equations and the mechanical model is studied. This model is employed for designing the experiment circuits for testing fabricated resonators. The fabrication processes used are explained, and the design parameters of each resonator are provided. The experimental results are reported, and used to find the axial force and stress of the resonant beams. The model and results of this dissertation can be used in the design of beam-based micromachined resonators for different applications.
3D-tracking of A Priori Unknown Objects in Cluttered Dynamic Environments
Keywords: computer vision
object tracking
real-time
3D

Tracking of an object's full six degree-of-freedom (6-dof) position and orientation (pose) would allow a robotic system to autonomously perform a variety of complex tasks, such as docking from any preferred angle, surveillance of moving subjects, etc. Computer vision has been commonly advocated as an effective tool for 3D (i.e., 6-dof) tracking Objects of Interest (OIs). However, the vast majority of vision-based 6-dof pose trackers reported in the literature require a model of the OI to be provided a priori. Finding/selecting the OI to track is also essential to autonomous operation. A problem that has often been neglected. This Thesis proposes a novel, real-time object-tracking system that solves all of the aforementioned problems. The tracking procedure begins with OI selection. Since what constitutes an OI is application dependent, selection is achieved via a customizable framework of Interest Filters (IFs) that highlight regions of interest within an image. The region of greatest interest becomes the selected OI. Next, an approximate visual 3D model of the selected OI is built on-line by a real-time modeller. Unlike previously proposed techniques, this modeller can build the model of the OI even in the presence of background clutter; an essential task for tracking one object amongst many. Once a model is built, a real-time 6-dof tracker (i.e., the third sub-component) performs the actual 6-dof object tracking via 3D model projection and optical flow. Performing simultaneous modelling and tracking presents several challenges requiring novel solutions. For example, a novel data-reduction scheme based on colour-gradient redundancy is proposed herein that facilitates using colour input images whilst still maintaining real-time performance on current computer hardware. Likewise, a per-pixel occlusion-rejection scheme is proposed which enables tracking in the presence of partial occlusions. Various other techniques have also been developed within the framework of this Thesis in order to achieve real-time efficiency, robustness to lighting variations, ability to cope with high OI speeds, etc. Extensive experiments with both synthetic and real-world motion sequences have demonstrated the ability of the proposed object-tracking system to track a priori unknown objects. The proposed algorithm has also been tested within two target applications: autonomous convoying, and dynamic camera reconfiguration.
Power and Influence: The Effects of Embeddedness on Cooperative Strategic Decision Making
Keywords: Management
Strategy
Organizational Theory
International Relations
Embeddedness View
United Nations

This dissertation investigates whether and why social structure influences cooperative organizational strategic decision making in an international relations context, and in particular, similar voting in the United Nations General Assembly (UNGA). The economic and institutional embeddedness of organizations which are operationalized using network concepts are posited as and found to be influences. Additionally, nested institutional embeddedness is investigated in an inter-organizational setting. Based on a sensitivity analysis, nested organizational embeddedness can potentially have both negative and positive effects. Multiple issues and network methodology combined with an enormous and varied data set offer a wide-range of future research opportunities. More specifically, trade, military alliances, diplomatic visits, and two-mode International Government Organizational (IGO) networks affect voting behaviour in the UNGA due to power and influence relationships that demand or encourage organizational level reciprocity, either as vote buying in backroom bargaining situations or for compliance reasons; maintaining the nation’s good reputation is of importance in international relations. Each type of inter-organizational network involves an interesting theoretical twist that makes it worth researching and while theory testing is the primary objective, outcomes include practical implications for negotiators. Finally, an advantageous data set offers an excellent context for unique and successful testing of embeddedness view concepts in tighter causal relationships compared to other studies that observe performance rather than decision outcomes. Moreover, the methodological approach is a demonstration of how to deal with a multi-faceted econometric challenge.
The Role of Default Correlation in Valuing Credit Dependant Securities
Keywords: Default Correllation
Credit Spreads
Credit Derivatives
Collaterlalized Debt Oligations

In this thesis, I imply a forward-looking systematic factor from CDO market spreads; I show that this factor is a measure of CDO market's expectation of future default correlation, and I empirically show that it is positively related to bond credit spreads. From this, I infer that corporate bond credit spreads are positively related to expected default correlation. The forward-looking factor stems from a CDO valuation model that I propose. The model assumes default can be characterized as a random event that occurs with an uncertain hazard rate that is mixture-Weibull distributed. Calibrating the model to CDO market spreads implies the model parameters. Using two and three mixing densities and data spanning January 2004 to February 2008, I show that the model calibrates to both the North American and European investment grade CDOs with negligible error. The factor I imply from the CDO market quotes is the standard deviation of the implied hazard rate density. I then show that the standard deviation of the implied hazard rate density increases as default correlation increases. This is done by characterizing firms' defaults with stochastic hazard rates that are defined by jump-diffusion processes that are correlated only through the Weiner processes, only through systematic jumps, or both. I use the models to generate CDO model spreads that are used to imply mixture-Weibull hazard rate densities. In addition, I provide evidence that the implied hazard rate density standard deviation has time variation that is independent to that of other common systematic factors. Lastly, I show that bond credit spreads are positively correlated with the standard deviation of the implied hazard rate density, and I conclude that credit spreads are positively related to expected default correlation. I provide evidence that firms' credit spreads are decreasing in firm diversity; that credit spread sensitivity to default correlation is decreasing in firm equity option implied volatility and decreasing in firm diversity; and that the variation in high credit quality bond spreads is predominantly explained by systematic factors whereas the variation in low credit quality bond spreads is explained by systematic and idiosyncratic factors.
The Technological Landscape: Competition and Opportunity
Keywords: Technology
Competition
Agglomeration
Startegy
Knowledge
Innovation

Technological position is a dimension along which organizations can either differentiate from or mimic the behavior of other organizations in the technological landscape. This paper is aimed at providing empirical evidence of the specific ways in which an organization’s technological position choice is impacted by the tension that arises from technological co-location; the information available to the focal firm; and the focal firm’s usage of such information. In this dissertation I examine the factors influencing technological agglomerations in technological positions in the technological landscape. I further examine how the organization’s experience impacts its strategic positioning choice while facing the tradeoff between the expected derivatives of co-location - opportunities and competition. I argue and find that an organization strategically positions itself in the technological landscape based not only on the information it has gathered on its technological environment but also using its own experience and information. Further, my findings show that the organization’s technological positioning choice reflects the tension between opportunity and competition, which questions the notion of isomorphism.