A hybrid material design has been developed to improve creep performance in pressurized metallic pipes subjected to high temperatures. Metallic pipes were reinforced with various arrangements of external wires which have substantially greater creep resistance than the pipe material. This research was conducted to explore the field of reinforcement of piping for creep reduction, exploit the creep strength of refractory metals, and investigate structure-property relationships in architectured materials. Two basic wire reinforcement architectures were tested, simple helical windings and braided sleeves. By adjusting the architecture of the reinforcement, apparent tangential (hoop) and longitudinal stresses on the pipe are altered, thereby allowing multiaxial creep strains to be controlled. The utilization of a reinforcement layer in a hybrid layup, where it is not bonded or embedded in a matrix is a relatively unexplored field. Hybridization allows the most desirable properties to be extracted from each component and have them work together in parallel. The use of braided refractory reinforcement is also a particularly novel concept, with refractory materials for reinforcement purposes traditionally being utilized in particle, whisker and discontinuous fibre form. Rather than testing in a uniaxial stress state, the present approach to creep testing pressurized pipes at high temperature remains largely underutilized, and is especially relevant to industry applications where creep takes place in the complex, multiaxial stress state of a pressurized pipe. In a low-temperature reinforcement architecture optimization study of a brass-stainless steel system, designed for ease of fabrication and to negate oxidation issues, pipes were pressurized and creep rupture tested at 400°C. Even in an unoptimized state, braided reinforcement was observed to out-perform a simple iv helical wrap by at least 22%, giving a 10-times life extension without rupture, and a reduction in creep rate in excess of 45-times for reinforcement oriented at a 50°. A simple analytical model from reinforced pressure vessel theory predicts a neutral angle (θN) of 54.7°, at which point the reinforcement is oriented to act proportionally to the applied pressure stresses. An empirical model of effective creep rate with varying reinforcement angle was derived in the present study, and used to find that a braid angle of approximately 54.7±1.5° is optimal to minimize the effective multiaxial creep rate of a hybrid pipe under internal pressure, reducing it to the point of being negligible. The braided reinforcement was observed to be constantly shifting towards the equilibrium point of θN, but only for initial angles below θN. This concept of braid reorientation is generally associated with rapid elastic deformation or static reinforcement of systems at room temperature, and the gradual shift towards θN facilitated by creep deformation has not been reported previously. A relationship for -θ (i.e. creep rate for a given reinforcement angle) was derived, including the reduction in as θ tends to θN. Findings of this optimization study were applied to a high temperature system which served as an acceleration of reformer furnace operating conditions: 253MA pipes were reinforced with tungsten wire and creep rupture tested at 1030-1040°C. Using braided reinforcement oriented at 52.6±1.4° a life extension in excess of 700x was observed, with no signs of bulk deformation after a 309x life extension. These high temperature results were considered in light of the intended industry application, with a balance of life extension, weight reduction and increased operating temperature preferred over outright life extension for the reformer furnace application.

Election boycotts are a common occurrence in unconsolidated democracies, particularly in the developing world, with prominent examples from recent years occurring in Venezuela, Zimbabwe, and Ethiopia. Despite the frequent occurrence of boycotts, there are few studies available in the scholarly literature concerning the effectiveness of electoral boycotts, particularly as a strategy of opposition parties seeking to bring about the end of electoral authoritarian governments. This paper is based in the democratization literature, with a particular focus on the behavior and vulnerabilities of hybrid or electoral authoritarian regimes. Using an original dataset with global coverage including hybrid regimes from 1981 to 2006, this paper uses event-history analysis to determine the efficacy of boycotts in national elections among other risk factors thought to undermine electoral authoritarian regimes as well as the possibilities for subsequent democratization occurring following both contested and boycotted electoral processes.

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No description available.

The use of fibre composites in the design of load carrying aircraft structures has been increasing over the last few decades. At the same time, aluminium alloys are still present in many structural parts, which has led to an increase of the number of hybrid composite-aluminium structures. Often, these materials are joined at their interface by bolted connections. Due to their different response to thermal, mechanical and environmental impact, the composite and the aluminium alloy parts are subject to different design and certification practices and are therefore considered separately.The current methodologies used in the aircraft industry lack well-developed methods to account for the effects of the mismatch of material properties at the interface.One such effect is the thermally induced load which arises at elevated temperature due to the different thermal expansion properties of the constituent materials. With a growing number of hybrid structures, these matters need to be addressed.  The rapid growth of computational power and development of simulation tools in recent years have made it possible to evaluate the material and structural response of hybrid structures without having to entirely rely on complex and expensive testing procedures.However, as the failure process of composite materials is not entirely understood, further research efforts are needed in order to develop reliable material models for the existing simulation tools. The work presented in this dissertation involves modelling and testing of bolted joints in hybrid composite-aluminium structures.The main focus is directed towards understanding the failure behaviour of the composite material under static and fatigue loading, and how to include this behaviour in large scale models of a typical bolted airframe structure in an efficient way. In addition to that, the influence of thermally induced loads on the strength and fatigue life is evaluated in order to establish a design strategy that can be used in the industrial context. The dissertation is divided into two parts. In the first one, the background and the theory are presented while the second one consists of five scientific papers.

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Transition metal clusters are a unique class of chemical substances. Not only do they have well-defined molecular structures, they also exhibit interesting and potentially useful properties that are inherent to metal-metal bonded species. They may be viewed as atom-like building blocks with adjustable properties. Detailed in this dissertation are the efforts to develop synthetic methodologies necessary to bring a cluster system out of the limited sphere of fundamental cluster chemistry and into general synthetic applicability. Specifically, the design and synthesis, structural characterization, and synthetic applications of the cluster complexes of the [Re₆(μ₃-Se)₈]²⁺ core will be discussed. Chapter 1 provides necessary background information of the [Re₆(μ₃-Se)₈]²⁺ core-containing cluster system, the rationales of cluster-supported synthetic and structural chemistry, and the impetus for these endeavors. Chapter 2 details the synthetic applications of stereospecific complexes of the [Re₆(μ₃-Se)₈]²⁺ clusters for the assembly of nanoscopic multicluster arrays using molecular and supramolecular approaches. The synthesis and structural characterization of a triangle-shaped tricluster array and a tetracluster assembly composed of two hydrogen-bonded diclusters are described. Chapters 3 and 4 describe the synthesis of the [Re₆(μ₃-Se)₈]²⁺ core-containing cluster complexes with the water-soluble 1,3,5-triaza-7-phosphaadamantane (PTA) ligand and the chemistry of these cluster-complex ligands for the coordination of a variety of secondary metal ions. In Chapter 5, the supramolecular chemistry of the cluster-PTA complexes with Ag(I) is detailed. The coordination of Ag(I) to a cluster complex with two PTA ligands disposed trans- to each other produces a 2-dimensional, porous solid with nano-sized hydrophobic pores that are potentially useful for storage of hydrocarbons and for occlusion of certain substrates for activation and possible catalysis. Chapter 6 summarizes the efforts to synthesize cluster-polymer hybrid materials by using an initiating cluster complex for the controlled radical polymerization. The synthesis, spectroscopic and structural characterizations of a novel cluster complex with an initiating ligand are described. Preliminary results of its application for the controlled polymerization of methyl methacrylate are detailed. Chapter 7 draws a set of conclusions based on the results presented in Chapters 2-6 and elaborates on some future directions aimed at moving one step forward the cluster-supported synthetic and materials chemistry.

Many emerging applications call for wideband analog-to-digital converters and some require medium-to-high resolution. Incorporating such ADCs allows for shifting as much of the signal processing tasks as possible to the digital domain, where more flexible and programmable circuits are available. However, realizing such ADCs with the existing single stage architectures is very challenging. Therefore, parallel ADC architectures such as time-interleaved structures are used. Unfortunately, such architectures require high-speed high-precision sample-and-hold (S/H) stages that are challenging to implement. In this thesis, a parallel ADC architecture, namely, the frequency-translating hybrid ADC (FTH-ADC) is proposed to increase the conversion speed of the ADCs, which is also suitable for applications requiring medium-to-high resolution ADCs. This architecture addresses the sampling problem by sampling on narrowband baseband subchannels, i.e., sampling is accomplished after splitting the wideband input signals into narrower subbands and frequency-translating them into baseband where identical narrowband baseband S/Hs can be used. Therefore, lower-speed, lower-precision S/Hs are required and single-chip CMOS implementation of the entire ADC is possible. A proof of concept board-level implementation of the FTH-ADC is used to analyze the effects of major analog non-idealities and errors. Error measurement and compensation methods are presented. Using four 8-bit, 100 MHz subband ADCs, four 25 MHz Butterworth filters, two 64-tap FIR reconstruction filters, and four 10-tap FIR compensation filters, a total system with an effective sample rate of 200 MHz is implemented with an effective number of bits of at least 7 bits over the entire 100 MHz input bandwidth. In addition, one path of an 8-GHz, 4-bit, FTH-ADC system, including a highly-linear mixer and a 5th-order, 1 GHz, Butterworth Gm-C filter, is implemented in a 90 nm CMOS technology. Followed by a 4-bit, 4-GHz subband ADC, the blocks consume a total power of 52 mW from a 1.2 V supply, and occupy an area of 0.05 mm2. The mixer-filter has a THD ≤ 5% (26 dB) over its full 1 GHz bandwidth and provides a signal with a voltage swing of 350 mVpp for the subsequent ADC stage.

Besides the traditional face-to-face learning medium, online media are now available for students in various learning environments. The delivery of coursework through online media is on the increase in colleges and universities. However, research on the use of online learning media in beginning collegiate level foundational mathematics courses for non-mathematics and non-science majors is limited. Therefore, the purpose of this study was to investigate, within a foundational mathematics course, connections between media used for instruction in hybrid and online enhanced face-to-face learning environments and students’ media preferences. The online Web Course Tools (WebCT) Vista template used in this study was designed by the researcher and her colleague as a part of the hybrid fellowship project for a two-year college. Applying transactional distance theory and engagement theory, designers carefully analyzed each concept and determined which concepts would be delivered most effectively in each learning medium. This study was quantitative in nature. During Fall 2005, thirty-eight students in the Introduction to Mathematical Modeling course at a community college in the southeast participated in the final study. Students in the hybrid sections comprised the treatment group while students in the online face-to-face section comprised the control group. Throughout the semester, all students were asked to respond to questions on the following instruments: Assignment Feedback, Quiz Feedback, Test Feedback, and Project Feedback. Chi-Square analysis showed that significant differences were found in the majority of items on the Test Feedback instrument related to the linear and quadratic modules. In general, the treatment group preferred online learning at least half of the time and believed online resources provide the basic resources for learning the subject matter. Students’ written responses from the treatment group indicated that both online learner-content interactions, and in-class learner-instructor interactions supplemented the learning of mathematics. The control group preferred predominantly face-to-face learning and believed that learning primarily took place in a physical setting. The findings showed that the proportion of students who completed the course using the hybrid and face-to-face learning environments was not significantly different. Therefore, the data showed the success rate for both learning environments was about the same.