Magnesium alloys are of interest to the automotive industry because of their high specific strength and potential to reduce vehicle weight and fuel consumption. In order to incorporate more magnesium components into automotive structures, efficient welding and joining techniques must be developed. Specifically, a method of making butt-joint welds must be found in order to use sheet magnesium alloys in the form of tailor-welded blanks for structural applications. The existing welding processes each have disadvantages when applied to magnesium alloy sheet. The double-sided arc welding (DSAW) process has been shown to produce high quality welds in aluminum alloy sheet, for tailor-welded blank applications. The DSAW process has not yet been applied to AZ31B magnesium alloy, which has thermo-physical and oxide forming properties similar to those of aluminum alloys. Therefore, this research explores the weldability of AZ31B magnesium alloy, using the DSAW process. Experimental, butt-joint configuration welds were made in 2 mm thick AZ31B-H42 magnesium alloy sheet. Acceptable welds have been produced using welding speeds ranging from 12 mm/s to 100 mm/s and welding powers from 1.6 kW to 8.7 kW. The influence of these parameters on the appearance, geometry, mechanical properties and microstructure of the resulting welds was investigated. Optimal appearance, geometric profile and mechanical properties were obtained at the lowest welding speeds and powers. Under these conditions, mechanical properties of the weld metal were equivalent to those of the fully annealed (0-temper) base metal. However, progressive deterioration in appearance, geometry and mechanical properties occurred at higher welding speeds. The deterioration in mechanical properties was associated with 2 microstructural defects that were observed at higher welding speeds: 1) the formation of larger amounts of Mg17Al12 -phase particles, at the grain boundaries, and 2) the formation of solidification shrinkage micro-porosity at these same inter-granular locations. This research demonstrates that the DSAW process is capable of producing acceptable quality, butt-joint welds in AZ31B magnesium alloy sheet at welding speeds up to 100 mm/s. However, in order to achieve the highest quality welds, low welding power, and, low welding speed, should be used. The highest quality welds were produced at welding speeds of 12 mm/s.

This work describes the design and measurement of a compact bidirectional ultrawideband (UWB) modified equiangular spiral antenna with an integrated feed internally matched to a 50-Ohm microstrip transmission line. A UWB transition from microstrip to double-sided parallel-strip line (DSPSL) soldered to a short (1.14 mm) twin-line transmission line feeds the spiral. The currents on the feed travel in a direction approximately perpendicular to the direction of the currents on the spiral at the points where the feed passes the spiral in close proximity (0.57 mm). Holes were etched from the metal arms of the spiral to reduce the impedance mismatch caused by coupling between the transmission line feed and the spiral. This work also describes a low-loss back-to-back transition from coaxial line to DSPSL, an in-phase connectorized 3 dB DSPSL power divider made using three of those transitions, a 2:1 in-phase DSPSL power divider, a 3:1 in-phase DSPSL power divider, a radial dipole fed by DSPSL, an array of those dipoles utilizing the various power dividers, and a UWB circular monopole antenna fed by DSPSL. Measured and simulated results show good agreement for the designed antennas and circuits.

This study is focused on two-sided assembly line balancing problems of type-I and type-II. This problem is encountered in production environments where a two-sided assembly line is used to produce physically large products. For type-I problems, there is a specified production target for a fixed time interval and the objective is to reach this production capacity with the minimum assembly line length used. On the other hand, type-II problem focuses on reaching the maximum production level using a fixed assembly line and workforce. Two different mathematical models for each problem type are developed to optimally solve the problems. Since the quality of the solutions by mathematical models decreases for large-sized problems due to time and memory limitations, two heuristic approaches are presented for solving large-sized type-I problem. The validity of all formulations is verified with the small-sized literature problems and the performances of the methods introduced are tested with large-sized literature problems.

Word of mouth has been playing an essential role while consumers make their purchase decision since ever, and its diffusion is becoming much faster via the internet nowadays. Surfing the internet gathering information before making the purchase, the so-called ¡uWisdom of Crowds¡vshopping pattern is taking its shape and possibly going to become the main trend in the future. Thus, electronic word of mouth does play an important part during the process of consumers¡¦ decision making, and more and more consumers start to ponder what to believe on the internet. As a result, trust is becoming the key factor if the consumers can take electronic word of mouth into their consideration or not. This research discusses how message sideness appeal and emotion in electronic word of mouth affect consumers¡¦ trust under a positively framed message and a negative framed message. This research adopts experimental method, distributes questionnaire and analyze the data with SPSS12.0. The results present message sideness appeal and emotion have impacts on consumers¡¦ trust. Two-sided appeal can cause higher consumers¡¦ trust than one-sided appeal whether under a positively framed message or a negative framed message. Emotion also plays an important part between message sideness and consumers¡¦ trust during the process of diffusion of electronic word of mouth. The results can not only help the word-of-mouth senders to develop an appropriate writing pattern to make electronic word of mouth more credible and effective, but also provide the business a brand-new point of view and some practical suggestions to develop a new marketing strategy.

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 16, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dissertation advisor: Dr. Murali K. Mantrala. Vita. Includes bibliographical references.

This dissertation comprises three essays analyzing various economic questions relating to open-source software development. The common thread linking these essays is the long-term sustainability of the open-source software development model, which is largely built on unpaid contributions from individual developers scattered across the world. The first essay develops a theoretical analysis of the market for operating systems as two-sided platforms, modeling the effects of competition and compatibility between a proprietary platform developed by a profit-maximizing firm, and an open platform (a public good developed by volunteers). Looking at the impacts on the proprietary platform firm, and application developer firms and users of both platforms, I find that under certain circumstances, a proprietary platform can find it profitable to become compatible with the open platform. However, it is always optimal in terms of social welfare to have compatibility between platforms. The second essay uses a laboratory experiment to examine how these characteristics and levels of motivations that are heterogeneous across individuals interact to result in sustainable, non-zero levels of contribution to open source software. There is a pronounced “leadership effect,” with subjects playing in the first position invariably contributing more frequently than those in the second position, and so on. Heterogeneity preserves the leadership effect, but increases contributions across the board, and eliminates the pattern of declining individual and total group contributions over time frequently observed in public goods experiments. The third essay studies the micro-foundations of open-source software contributions and provides an empirical examination of developer motivations using survey data. If open-source contributions and education are both signals of ability, then their impact on income is likely to be linked. They may be complements if open source contributions reinforce the signal from education by showing that one stands out from the crowd, or they might be substitutes if open-source development replaces expensive education in honing programming skills by offering more immediate feedback. Using an instrumental variables framework to deal with the endogeneity of the education and contribution choices, I find that leading an open-source project and completing college are complementary practices, so that the signaling and reputation-building aspect dominates.

With the adoption of European Commission directives in 2003 related to open data,member States of EU were encouraged to provide citizens access to previously inaccessiblepublic sector data. This published public data could be used, reused and distributed free ofcharge. Following these directives, many municipalities within Sweden and Europe ingeneral created open data portals for publishing public sector data. With such datapublished, expectations of third party innovations were highly envisaged. This thesis adoptsa qualitative research approach to investigate the challenges and proposed solution ofusing open data for third party innovation. The thesis identifies various aspects ofgovernance, architecture and business model that public organizations should take intoconsideration in order to attract third party innovations on open data. Specifically, theresults of this thesis suggest that in order for open data to act as a platform for innovation,there is need for integration of open data policies. This involves developing commonstandards relating to governance, data format, and architecture. Harmonizing thesestandards across municipalities within Sweden and Europe, would provide the muchneededuser based which is necessary to enhance the two-sided nature of innovations onopen data platforms.

Magnesium alloys are of interest to the automotive industry because of their high specific strength and potential to reduce vehicle weight and fuel consumption. In order to incorporate more magnesium components into automotive structures, efficient welding and joining techniques must be developed. Specifically, a method of making butt-joint welds must be found in order to use sheet magnesium alloys in the form of tailor-welded blanks for structural applications. The existing welding processes each have disadvantages when applied to magnesium alloy sheet. The double-sided arc welding (DSAW) process has been shown to produce high quality welds in aluminum alloy sheet, for tailor-welded blank applications. The DSAW process has not yet been applied to AZ31B magnesium alloy, which has thermo-physical and oxide forming properties similar to those of aluminum alloys. Therefore, this research explores the weldability of AZ31B magnesium alloy, using the DSAW process. Experimental, butt-joint configuration welds were made in 2 mm thick AZ31B-H42 magnesium alloy sheet. Acceptable welds have been produced using welding speeds ranging from 12 mm/s to 100 mm/s and welding powers from 1.6 kW to 8.7 kW. The influence of these parameters on the appearance, geometry, mechanical properties and microstructure of the resulting welds was investigated. Optimal appearance, geometric profile and mechanical properties were obtained at the lowest welding speeds and powers. Under these conditions, mechanical properties of the weld metal were equivalent to those of the fully annealed (0-temper) base metal. However, progressive deterioration in appearance, geometry and mechanical properties occurred at higher welding speeds. The deterioration in mechanical properties was associated with 2 microstructural defects that were observed at higher welding speeds: 1) the formation of larger amounts of Mg17Al12 -phase particles, at the grain boundaries, and 2) the formation of solidification shrinkage micro-porosity at these same inter-granular locations. This research demonstrates that the DSAW process is capable of producing acceptable quality, butt-joint welds in AZ31B magnesium alloy sheet at welding speeds up to 100 mm/s. However, in order to achieve the highest quality welds, low welding power, and, low welding speed, should be used. The highest quality welds were produced at welding speeds of 12 mm/s.

Master of Science / Department of Electrical and Computer Engineering / William B. Kuhn / An important concern for high speed circuit designs is that of crosstalk and electromagnetic interference. In PCB board-level designs, crosstalk at microwave frequencies may result from imperfections in shielding of PCB interconnects or more generally transmission lines. Several studies have been done to characterize and improve the isolation between PCB transmission lines for both digital and RF circuits. For example, previous studies in the microwave region have examined the effect that line type, line length, and separation have on crosstalk and suggest that without full shielding, the upper limit of isolation is on the order of 60dB for traditional board-level lines [1]. In order to more fully characterize crosstalk and improve isolation above 60 dB, this thesis studies signal-to-ground-plane separation, considers advanced line types, and examines the effect of 3D shielding. Results are presented from 100MHz to 30GHz for the traditional transmission line structures of microstrip, CPW, differential pair and CPW differential pair. This study shows that with a halving of distance between signal and ground planes, isolation between transmission lines can be reduced by as much as 20dB, making this one of the best ways to improve performance. Advanced methods of shielding are then presented. Direct launch stripline and single-sided CPW improve upon existing crosstalk reduction techniques, while split shielding and ablation of dielectric PCB material are also proposed. The data and additional crosstalk reduction techniques discussed in this thesis serve two purposes. One: with a more complete understanding of the effects that transmission line types and parameters have on crosstalk, engineers can quickly identify potential crosstalk issues and resolve them before manufacturing. Second, this thesis presents the engineer with four new additional techniques that may become available in advanced manufacturing environments. Such techniques can further reduce crosstalk and may allow for isolation values to approach 100 dB at the PC board level.

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