VictorJuiz/thesis huggingface dataset:
Propagation of Shear Waves Generated by a Finite-amplitude Ultrasound Radiation Force in a Viscoelastic Medium
Keywords: elastography
radiation force
harmonic shear waves
modulation frequency

A primary purpose of elasticity imaging, commonly known as elastography, is to extract the viscoelastic properties of a medium (including soft tissue) from the displacement caused by a stress field. Dynamic elastography methods that use the acoustic radiation force of ultrasound have several advantages, such as, non-invasiveness, low cost, and ability to produce a highly localized force field. A method for remotely generating localized low frequency shear waves in soft tissue is investigated, by using the modulated radiation force resulting from two intersecting quasi-CW confocal ultrasound beams of slightly different frequencies. In contrast to most radiation force-based methods previously presented, such shear waves are narrowband rather than broadband. As they propagate within a viscoelastic medium, different frequency-dependent effects will not significantly affect their spectrum, thereby providing a means for measuring the shear attenuation and speed as a function of frequency. Furthermore, to improve the detection signal-to-noise-ratio (SNR), increased acoustic pressure conditions may be needed, causing higher harmonics to be generated due to nonlinear propagation effects. Shear-wave propagation at harmonic modulation frequencies does not appear to have been previously discussed in the elastography literature. The properties of the narrowband shear wave propagation in soft tissue are studied by using the Voigt viscoelastic model and Green’s functions. In particular, the manner in which the characteristics of the viscoelastic medium affect their evolution under both low-amplitude (linear) and high-amplitude (nonlinear) source excitation and conditions that conform to human safety standards. It is shown that an exact solution of the viscoelastic Green’s function is needed to properly represent the propagation in higher-viscosity media, such as soft tissue, at frequencies much beyond a few hundred hertz. Methods for estimating the shear modulus and viscosity in viscoelastic media are developed based on both the fundamental and harmonic shear components.
Architecture Alternatives for Time-interleaved and Input-feedforward Delta-Sigma Modulators
Keywords: Delta-Sigma
Sigma-Delta
oversampling
ADC
data converters
analog-to-digital
Input-Feedforward
Time-Interleaved

This thesis strives to enhance the performance of delta-sigma modulators in two areas: increasing their speed and enabling their operation in a low voltage environment. Parallelism based on time-interleaving can be used to increase the speed of delta-sigma modulators. A novel single-path time-interleaved architecture is derived and analyzed. Finite opamp gain and bandwidth result in a mismatch between the noise transfer functions of the internal quantizers which degrades the performance of the new modulator. Two techniques are presented to mitigate the mismatch problem: a hybrid topology where the first stage uses multiple integrators while the rest of the modulator uses a single path of integrators and a digital calibration method. The input-feedforward technique removes the input-signal component from the internal nodes of delta-sigma modulators. The removal of the signal component reduces the signal swing and distortion requirements for the opamps. These characteristics enable the reliable implementation of delta-sigma modulators in modern CMOS technology. Two implementation issues for modulators with input-feedforward are considered. First, the drawback of the analog adder at the quantizer input is identified and the capacitive input feedforward technique is introduced to eliminate the adder. Second, the double sampled input technique is proposed to remove the critical path generate by the input feedforward path. Novel input-feedforward delta-sigma architecture is proposed. The new digital input feedforward (DIFF) modulator maintains the low swing and low distortion requirements of the input feedforward technique, it eliminates the analog adder at the quantizer input, and it improves the achievable resolution. To demonstrate these advantages, a configurable delta-sigma modulator which can operate as a feedback topology or in DIFF mode is implemented in 0.18μm CMOS technology. Both modulators operate at 20MHz clock with an oversampling ratio of 8. The power consumption in the DIFF mode is 22mW and in feedback mode is 19mW. However, the DIFF mode achieves a peak SNDR of 73.7dB (77.1dB peak SNR) while the feedback mode achieves a peak SNDR of 64.3dB (65.9dB peak SNR). Therefore, the energy required per conversion step for the DIFF architecture (2.2 pJ/step) is less than half of that required by the feedback architecture (5.7 pJ/step).
Spin-c Quantization, Prequantization and Cutting
Keywords: Quantization
Spinors
Symplectic Geometry
Cutting

In this thesis we extend Lerman’s cutting construction to spin-c structures. Every spin-c structure on an even-dimensional Riemannian manifold gives rise to a Dirac operator D+ acting on sections of the associated spinor bundle. The spin-c quantization of a spin-c manifold is defined to be ker(D+)−coker(D+). It is a virtual vector space, and in the presence of a Lie group action, it is a virtual representation. In 2004, Guillemin et al defined signature quantization and showed that it is additive under cutting. We prove that the spin-c quantization of an S^1-manifold is also additive under cutting. Our proof uses the method of localization, i.e., we express the spin-c quantization of a manifold in terms of local data near connected components of the fixed point set. For a symplectic manifold (M,ω), a spin-c prequantization is a spin-c structure together with a connection compatible with ω. We explain how one can cut a spin-c prequantization and show that the choice of a spin-c structure on the complex plane (which is part of the cutting process) must be compatible with the moment level set along which the cutting is performed. Finally, we prove that the spin-c and metaplectic-c groups satisfy a universal property: Every structure that makes the construction of a spinor bundle possible must factor uniquely through a spin-c structure in the Riemannian case, or through a metaplectic-c structure in the symplectic case.
Jamaica's Higher Education Committment under the GATS
Keywords: Jamaica
Caribbean
Education
Higher Education
Education Policy
Higher Education Policy

This research seeks to answer two questions: why did Jamaica include its higher education (HE) sector in its General Agreement on Trade in Services (GATS) ‘Schedule of Commitments’; and, how do the politicians and policy makers view the impact of this decision? For answers, I looked at arguments linking the GATS with national development and with HE. The thesis explores Jamaica’s HE policy strategies, how they are formed, how well, even after the fact, the decision-makers understand the implications of the regulatory framework of the GATS and the loss of control implicit in some of its tenets. This study is anchored in research findings by UNESCO and the World Bank, among others, which show that HE systems serve as the foundation for nations’ social and economic development, in providing the required knowledge and high levels of trained manpower to build their human capital. However, suggestions have been made that inequities in the global trading system constrain small developing countries in implementing policies that serve these objectives. Therefore, the emergence of the GATS as a new regulatory structure for trade in educational services raises concerns about the ability of countries like Jamaica, to promote an HE system likely to meet their needs. iii Twenty senior policy actors within Jamaican society were interviewed to elicit their views on national priorities for HE and, the opportunities or threats to their fulfilment presented by the GATS Commitment. Of particular interest is the growth in cross-border HE services found in Jamaica. The research found that notwithstanding the inequities of the global trading system, Jamaica embraces the concepts of liberalisation and free trade, and its negotiators, in formulating the Commitment, were seized with GATS’ potential for rapidly expanding access to HE. However, the evidence of this research suggests they were ill-prepared to make this decision, and clearly there is need for a better understanding of the role of HE in Jamaica’s development.
Being Young in Old Town: Youth Subjectivities and Associational Life in Bamenda
Keywords: youth
citizenship
associational Life
morality
social adulthood

This study explores the ways in which young people in the neighbourhood of Old Town in Bamenda negotiate the predicament of blocked opportunities and ‘arrested adulthood’ occasioned by the decline in the nation-building project and prolonged socio-economic and moral crisis in Cameroon. I investigate how urban youth in Old Town construct their moral and socio-cultural worlds through involvement in associations. The main finding suggests that faced with growing uncertainty, young people in Bamenda are positioning themselves as important social actors by drawing on local cultural resources such as associations to construct their social worlds that aim to circumvent their exclusion and marginality. In this light, I analyse youth associations as central although not exclusive to negotiating young people’s predicament by focusing on a range of practices through which they seek respectability and claim social adult status. Drawing on the concepts of transition, subjectivities and personhood, I show that young people straddle the worlds of ‘youth’ and social adulthood, statuses that are not only cultural constructions but also the products of differential power relations and social positioning. I contend that the processes of positioning and the production of personhood are largely experienced through involvement in associational life. The study focuses on three associations, namely the Chosen Sisters, the United Sisters and the Ntambag Brothers Association (NBA). Organised on the basis of seniority and gender, I argue that these associations, while negotiating claims to adult status for their members, tend to challenge state-centric notions of citizenship as they simultaneously position themselves as moral actors upon whom society can count on for regeneration. Through a range of social projects, pursued on behalf of and sanctioned by the community, young people in Old Town reaffirm the centrality of interdependence and the situated understanding of social adulthood predicated on the redistribution of one’s success or achievement. This study points to the re-emergent role of associations in negotiating everyday life in the face of crisis. It is a significant contribution towards understanding voluntary and communal associations in general and young people’s modes of transitions into social adulthood.
Development of 8-Hydroxyquinoline Metal Based Organic Light-emitting Diodes
Keywords: Organic Light-Emitting Diodes
8-Hydroxyquinoline Metal

Because of its potential application for flat panel displays, solid-state lighting and 1.5 µm emitter for fiber optical communications, organic light-emitting diodes (OLEDs) have been intensively researched. One of the major problems with current OLED technology relates to inefficient electron injection at the cathode interface, which causes high driving voltage and poor device stability. Making a low resistance cathode contact for electron injection is critical to device performance. This work mainly focuses on cathode interface design and engineering. The Ohmic contact using a structure of C60/LiF/Al has been developed in electron only devices. It is found that application of the C60/LiF/Al contact to Alq based OLEDs leads to a dramatic reduction in driving voltages, a significant improvement in power efficiency, and a much slower aging process. A new cathode structure based on metal-organic-metal (MOM) tri-layer films has been developed. It is found that MOM cathodes reduce reflection by deconstructive optical interference from two metal films. The absolute reflectance from the MOM tri-layer films can be reduced to as low as 7% in the visible light spectrum. In actual working devices, the reflectance can be reduced from ~80% to ~ 20%. MOM cathodes provide a potential low-cost solution for high contrast full-color OLED displays. Low voltage Erq based OLEDs at 1.5 µm emission have been developed. The Erq/Ag cathode interface has been found to be efficient for electron injection. Dramatic improvement in driving voltage and power efficiency has been realized by implementing Bphen and C60 into Erq devices as an electron transport layer. Integration of Erq devices on Si wafers has also been demonstrated.
Autonomic Service Architecture for Next Generation Networks
Keywords: Management
Next Generation Networks

Next generation networks will provide customers with a service mix placing variable demands for resources on the underlying infrastructure, motivating automated telecommunications services management approaches. This thesis proposes the Autonomic Service Architecture (ASA) for automated service delivery over next generation networks. First, we propose an architectural blueprint for ASA. We describe our view of the next generation network infrastructure, which will be application oriented. We elaborate on the layered design of ASA, the virtualization of resources, and the separation between manual and autonomic functions in the service delivery lifecycle. The autonomic functions are delivered by the interaction between Autonomic Resource Brokers (ARBs). The architecture of an ARB is then detailed, with a description of its different components and the message exchanges needed. Next, we discuss a Peer-to-Peer (P2P) naming and mobility management approach for next generation networks using ASA. This P2P approach will help ensure the scalability, robustness, and flexibility that ASA needs to ensure service delivery over next generation networks. The proposed P2P naming and mobility management infrastructure is then detailed, and its performance is evaluated. Finally, we suggest several autonomic resource management algorithms for ASA. The first algorithm is based on the Transportation Model, commonly used in the Operations Research community for cost minimization in delivering a commodity from sources to destinations, adapted to perform allocation of virtual resources. The second algorithm is based on the Assignment Model, commonly used in the Operations Research community for cost minimization in assigning several jobs to several workers, adapted to perform autonomic assignment of dedicated virtual resources. The third algorithm is based on Inventory Control, commonly used in the Operations Research community to analyze inventory systems, placing and receiving orders when needed for a given product, adapted to predict the demand on virtual resources. The fourth algorithm is based on Reinforcement Learning, commonly used in the Machine Learning community by agents to find a control policy that will maximize the observed rewards over their lifetime, adapted to adjust the prices of virtual resources.
Contrasts in Thermal Dffusion and Heat Accumulation Effects in the Fabrication of Waveguides in Glasses using Variable Repetition Rate Femtosecond Laser
Keywords: Femtosecond laser
Waveguide

A variable (0.2 to 5 MHz) repetition rate femtosecond laser was applied to delineate the role of thermal diffusion and heat accumulation effects in forming low-loss optical waveguides in borosilicate glass across a broad range of laser exposure conditions. For the first time, a transition from thermal diffusion-dominated transport at 200-kHz repetition rate to strong heat accumulation at 0.5 to 2 MHz was observed to drive significant variations in waveguide morphology, with rapidly increasing waveguide diameter that accurately followed a simple thermal diffusion model over all exposure variables tested. Amongst these strong thermal trends, a common exposure window of 200-mW average power and ~15-mm/s scan speed was discovered across the range of 200-kHz to 2-MHz repetition rates for minimizing insertion loss despite a 10-fold drop in laser pulse energy. Waveguide morphology and thermal modeling indicate that strong thermal diffusion effects at 200 kHz give way to a weak heat accumulation effect at ~1uJ pulse energy for generating low loss waveguides, while stronger heat accumulation effects above 1-MHz repetition rate offered overall superior guiding. The waveguides were shown to be thermally stable up to 800°C, showing promise for high temperature applications. Using a low numerical aperture (0.4) lens, the effect of spherical aberration was reduced, enabling similar low-loss waveguides over an unprecedented 520-um depth range, opening the door for multi-level, three-dimensional, optical integrated circuits. In contrast to borosilicate glass, waveguides written in pure fused silica under similar conditions showed only little evidence of heat accumulation, yielding morphology similar to waveguides fabricated with low repetition rate (1 kHz) Ti-Sapphire lasers. Despite the absence of heat accumulation in fused silica owing to its large bandgap and high melting point, optimization of the laser wavelength, power, repetition rate, polarization, pulse duration and writing speed resulted in uniform, high-index contrast waveguide structures with low insertion loss. Optimum laser exposure recipes for waveguide formation in borosilicate and fused silica glass were applied to fabricate optical devices such as wavelength-sensitive and insensitive directional couplers for passive optical networks, buried and surface microfluidic and waveguide networks for lab-on-a-chip functionality, and narrowband grating waveguides for sensing.
Photophysics of Conjugated Polymers
Keywords: photophysics
conjugated polymers

Poly (para-phenylenevinylene) (PPV), and its derivatives such as poly [2-methoxy, 5-(2'-ethyl-hexoxy)-1,4-phenylene vinylene] (MEH-PPV), are typical conjugated polymers. In order to implement conjugated polymers into processable electronics technologies, we must first understand their complex photophysical properties as their efficiencies depend on the balance between exciton recombination and charge carrier formation. The inherent complexities of these materials arise from entanglement of the pi-electron system with disorder and nuclear motions of the polymer backbone. This disorder breaks the polymer chain into conformational subunits which can couple, giving rise to a set of delocalized states formed by Coulombic interactions between proximate subunits. Characteristics of PPVs include high quantum yields, non-mirror image absorption and fluorescence line shapes, and large apparent Stokes' shifts. These properties are discussed in the context of the relationships between polymer conformation, electronic structure, coupling, disorder and polymer photophysics. These important influences are often manifest in the dynamics of what happens after photoexcitation. In this work, we present 3-pulse photon echo peak shift (3PEPS) studies of conjugated polymers in both solution and film. To elucidate timescales characteristic of relaxation processes, we have simulated the 3PEPS data simultaneously with absorption and fluorescence, observing a rapid localization of the exciton in the initial ~ 20 fs. Additional contributions to the decay of the peakshift are discussed. We also present transient anisotropy data for PPV polymers and oligomers which is compared to dynamics simulation for isolated chains of PPVs. This work demonstrates the influence of microscopic structure on ultrafast dynamics. We show that relaxation between exciton states can lead to rapid depolarization of the anisotropy, even though the spatial extent of exciton migration may be small. Generally, the connection between conformation and electronic structure is a theme throughout this thesis.
Copyright in the Real World: Making Archival Material Available on the Internet
Keywords: Archival Materials--Digitization
Archivists--Canada
Copyright--Canada
Archives--Canada

The purpose of this study is to investigate the practices of Canadian repositories in making their archival holdings available on the Internet to see whether they are more or less restrictive than copyright law requires. The Internet provides an opportunity to make archival material more widely accessible; however, repositories’ copyright practices in making their holdings available online may affect the extent to which wider access to archival material is actually achieved. The study employed four different sources of evidence, i.e., the website content of 154 Canadian repositories whose websites feature archival material from the repository’s holdings; copyright policy and procedure documents of those repositories; 106 responses to a questionnaire sent to the staff of those repositories; and 22 interviews with repository staff members. In terms of selection for online access, the study found that the repositories studied prefer to select items that are perceived to incur little risk of copyright infringement (because the copyright has expired or because the repository owns the copyright), or items that require few or no resources to investigate copyright status or obtain copyright authorizations. Thus, with regard to selection, repositories were more restrictive than the law required, largely due to lack of resources. Although repositories have no legal or professional obligation to enforce others’ copyright interests, they nonetheless attempt to control further uses of their online holdings through the use of technical measures (e.g., low resolution images, watermarks, etc.) or non-technical measures (e.g., conditions placed on further uses), for reasons not necessarily related to copyright. Overall, the study found that repositories’ practices in making their holding available online were more restrictive than copyright law envisages. While this may be due to factors other than copyright, access to online documentary heritage may be limited as a result.
Opposition, Politicisation and Simplification: Social and Psychological Mechanisms of Elite-led Mobilisation
Keywords: Mobilization
Conflict
Rwanda
Yugoslavia

Drawing on insights from social psychological literature on identity formation, and on social movement and contentious politics literature, this research focuses on elite strategies to gain from or survive a crisis. The research specifically looks at strategies to foster popular support and mobilisation. It explores the use of divisive and ethno-centric discourses and policies aimed at mobilising supporters in times of instability or crisis. More specifically, it studies why some elite mobilising appeals have traction. To do so, the research examines social and psychological mechanisms behind group solidarity. A heightened sense of group solidarity is what leads individuals to think in terms of the group, a necessary step for mobilisation. From there, they can be made to feel appeals for collective action are warranted. Three mechanisms in particular are discussed: opposition, politicisation and simplification. Opposing entails enhancing feelings of attachment by creating a sense of antagonistic relations with another group. Politicising consists in ascribing to group identities a political nature, more conducive to contentious relations. The final strategy is simplification. It amounts to simplifying interpretations of the situation and environment so as to make them more readily internalisable. This framework is applied to contemporary Rwanda and to the lead-up to the wars in Yugoslavia. In the Rwandese case, cultural and historical references were repeatedly used by ruling regimes to foster a Hutu uprising against the Tutsi population. This tactic eventually played a fundamental role in triggering the 1994 genocide. In the former Yugoslavia, Croatian and Serbian elites antagonised group relations by agitating nationalist rhetoric. Though this was a strategy to stay in power or gain support, it also led to the break-up of Yugoslavia and to wars in Slovenia, Croatia and Bosnia-Herzegovina.