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A new type of fuel cell architecture, the fuel cell ribbon, is presented. The fuel cell ribbon architecture relies on the gas diffusion layer (GDL) to conduct electrical current in-plane to adjacent cells or collector terminals. The potential advantages of the fuel cell ribbon architecture with respect to conventional fuel cell stacks include reduced manufacturing costs, reduced weight, reduced volume, and reduced component cost. The critical component of fuel cell ribbon assemblies, the gas diffusion media, is investigated herein. Analytical models which focus on the electrical loses within the gas diffusion media of the novel architecture are developed. The materials and treatments necessary to fabricate novel gas diffusion media for fuel cell ribbon assemblies are presented. Experimental results for the novel gas diffusion media of are also presented. One dimensional and two dimensional analytical models were developed for the fuel cell ribbon. The models presented in this work focus on the losses associated with the transport of the electrons in fuel cell ribbon assemblies, rather than the complex system of equations that governs the rate of electron production. The 1-D model indicated that the GDL used in ribbon cells must exhibit an in-plane resistance which is approximately an order of magnitude lower than the resistance of gas diffusion media typically used in conventional fuel cells. A 2-D model was developed with which a parametric study of GDL properties and ribbon cell dimensions was performed. The parametric study indicated that ribbon cells of useful size can be constructed using novel diffusion media that offer reduced resistivity, and that the ribbon cells can produce as much as 80-85% of the power density produced in a conventional fuel cell. Novel gas diffusion media for fuel cell ribbons that have the necessary characteristics suggested by the analytical study were developed.. Properties and performance for a commercially available gas diffusion media, ELAT, were measured as a reference for the novel media developed. The increased thickness PAN (ITPN) series diffusion media was constructed of PAN based fibers exhibiting similar resistive properties to the fibers used in ELAT. The ITPN series of materials were woven in a manner which made them approximately twice the thickness of ELAT, effectively reducing their in-plane resistance to half the resistance exhibited by ELAT. The coarsely woven pitch (CWPT) series of materials were constructed in a manner which yielded a similar number of fibers in the plane of the material to ELAT and a similar material thickness to ELAT, but the fibers used were mesophase pitch based fibers which exhibit a resistivity of approximately one-tenth the resistivity of the fibers used to make the ELAT and ITPN materials. The reduction in fiber resistivity led to the CWPT material having an in-plane resistance an order of magnitude lower than ELAT. The widely used ELAT material exhibited an in-plane resistance of 0.39 Ω/sq., a through-plane area specific resistance of 0.007 Ω-cm2, and a Darcy permeability coefficient of 8.1 Darcys. The novel diffusion materials exhibited in-plane resistances in the range of 0.18-0.036 Ω/sq., through-plane area specific resistances in the range of 0.017-0.013 Ω-cm2, and Darcy permeability coefficients in the range of 30-150 Darcys. Experiments were performed to validate the analytical model and to prove the feasibility of fuel cell ribbon concept. When the novel gas diffusers were adhered to a catalyzed membrane and tested in a ribbon test assembly utilizing serpentine flow channels and in-plane current collection, a range of performance was achieved between 0.28-0.4 A/cm2 at a cell output potential of 0.5 V. In contrast, when ELAT was adhered to a catalyzed membrane and tested in the fixture requiring in-plane conduction, a current density of 0.21 A/cm2 was achieved at 0.5 V. Additionally, the 2-D finite element model was used to predict the performance of a ribbon cell based on the cells performance when a conventional method of through-plane conduction was utilized. The agreement between the experimental data and the model predictions was very good for the ELAT and ITPN materials, whereas the predictions for the CWPT materials showed more significant deviation which was likely due to mass transport and contact resistance effects. / Master of Science

The following presents an investigation into questions of spatial direction and continuity. This includes the directing of people via a choreographed sequence of architectural spaces through a site and a building. It further investigates a concept of continuity at various scales. A proposal for an art gallery in downtown Washington DC becomes the vehicle of exploration. The urban scale of this proposal seeks a continuity of relevant existing conditions while also creating opportunities to experience the city as well as the gallery. A serpentine-like continuous band or ribbon becomes the physical element responsible for direction and continuity for the building itself. / Master of Architecture

This essay concerns the temperance movements Blue Ribbon and White Ribbon inNorrbotten, Sweden. Their ideas about alcohol, industrialisation, family, humanity andproductivity. The period examined is 1905-1985, which nearly covers the whole of themovements history. Swedish and international research on the subject reveals temperancemovements had a negative view on the industrial society during the late 19th and early 20thcentury. The perceived problems were alcoholism and predatory capitalism. The family wasvalued highly both in itself and through its importance for the future well-being of the nation.The same results applies to Blue Ribbon and White Ribbon in Norrbotten. In addition greedwas seen as problematic, as well as lost productivity due to alcohol consumption. Humanitywas seen as very important, both within and between countries.

<p>Slice-ribbon conjecture has been proved for some special families of knots. In this thesis, we briefly mention some of these results.</p> / Master of Science (MSc)

Designing self-assembling DNA nanostructures often requires the identification of a route for a scaffolding strand of DNA through the target structure. When the target structure is modeled as a graph, these scaffolding routes correspond to Eulerian circuits subject to turning restrictions imposed by physical constraints on the strands of DNA. Existence of such Eulerian circuits is an NP-hard problem, which can be approached by adapting solutions to a version of the Traveling Salesperson Problem. However, the author and collaborators have demonstrated that even Eulerian circuits obeying these turning restrictions are not necessarily feasible as scaffolding routes by giving examples of nontrivially knotted circuits which cannot be traced by the unknotted scaffolding strand. Often, targets of DNA nanostructure self-assembly are modeled as graphs embedded on surfaces in space. In this case, Eulerian circuits obeying the turning restrictions correspond to A-trails, circuits which turn immediately left or right at each vertex. In any graph embedded on the sphere, all A-trails are unknotted regardless of the embedding of the sphere in space. We show that this does not hold in general for graphs on the torus. However, we show this property does hold for checkerboard-colorable graphs on the torus, that is, those graphs whose faces can be properly 2-colored, and provide a partial converse to this result. As a consequence, we characterize (with one exceptional family) regular triangulations of the torus containing unknotted A-trails. By developing a theory of sums of A-trails, we lift constructions from the torus to arbitrary n-tori, and by generalizing our work on A-trails to smooth circuit decompositions, we construct all torus links and certain sums of torus links from circuit decompositions of rectangular torus grids. Graphs embedded on surfaces are equivalent to ribbon graphs, which are particularly well-suited to modeling DNA nanostructures, as their boundary components correspond to strands of DNA and their twisted ribbons correspond to double-helices. Every ribbon graph has a corresponding delta-matroid, a combinatorial object encoding the structure of the ribbon-graph's spanning quasi-trees (substructures having exactly one boundary component). We show that interlacement with respect to quasi-trees can be generalized to delta-matroids, and use the resulting structure on delta-matroids to provide feasible-set expansions for a family of delta-matroid polynomials, both recovering well-known expansions of this type (such as the spanning-tree expansion of the Tutte polynnomial) as well as providing several previously unknown expansions. Among these are expansions for the transition polynomial, a version of which has been used to study DNA nanostructure self-assembly, and the interlace polynomial, which solves a problem in DNA recombination.

There are three parts in this thesis: In the first part (Chapter 2), we discuss the port excitation (Wave port vs Lumped port) suitable for sub-millimeter wave operations. We realized on printed circuit board a grounded coplanar waveguide (CPWG) and on gallium arsenic (GaAs) a microstrip line. We performed simulation on these structures using high frequency structure simulator (HFSS), and compared the results with measured ones. From the comparison, we found close match for CPWG insertion loss from 10 MHz to 67 GHz using the Wave port. However, for G-S-G lumped port, only matched up to 40 GHz. The wave port not only was more accurate, but also consumed less time in simulation. Consequently, we employed wave port as our simulation excitation for our sub-millimeter wave QFN design. In the second part (Chapter 3), we focused on design of low cost QFN for sub-millimeter wave applications. We fabricated test structures, which include IC pads and transmission lines, wire bonds, QFN leads, and G-S-G structures on printed circuit board. In HFSS simulation, our specially designed ribbon bonds and QFN configuration show return loss less than -20dB and insertion loss less than -0.4 dB up to 60 GHz. Using the same design principles, we strived to improve the performance of a commercially available QFN, which normally operates at 3 to 6 GHz. The extraction method to obtain the high frequency characteristics was introduced first, and the characteristics of a commercially available QFN (with our wire bond configuration) were then obtained. The insertion loss was less than -20 dB and insertion loss less than -0.5 dB up to 20 GHz. In Chapter 5, we discuss the performance discrepancies between the simulated ribbon bond results and that for fabricated wire bonds. In the third part (Chapter 4), we introduced a method to extract the characteristics of a single backside via and investigated the effects of die attachment on the performance of a single and multiple backside via(s). Using silver epoxy and Cu blank layer as die attach methods, we found it was important to provide a broad path (Cu blank layer), as opposed to a restrict path (like silver epoxy) to reduce the inductance of the backside vias. The conclusion and future work are provided in Chapter 5.

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Heidelberg, Univ., Diss., 2007. / Online publiziert: 2008.

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