The main objective of this thesis is to introduce the concept of 'singular chains on topological stacks'. The idea is to functorially associate to a topological stack, a simplicial set which captures its homotopy type. This will allow us to compute the singular homology and cohomology of topological stacks. Noohi and Behrend have given several approaches to this problem, however all of these approaches rely on the choice of an atlas for a topological stack. We shall show that our new approach agrees with the existing approaches but has the advantage of being functorial. Noohi has introduced weak equivalences and brations of topological stacks. In analogy to the singular chains functor for topological spaces, we shall show that the functor Sing preserves the weak equivalences and brations de ned by Noohi under certain ` brancy conditions'. In the second part, we shall push the analogy with the topological singular chains further by considering the adjunction with the geometric realization and the associated counit. We develop a corresponding (but weaker) notion for topological stacks. We shall give a method for computing the homotopy type of a stack which has a groupoid presentation. Finally, we shall compute the homotopy type of certain mapping stacks and develop the totalization of a cosimplicial topological stack. We shall indicate how this (using the approach of Cohen and Jones) gives a method for computing the string topology of a topological stack.

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ITC/USA 2011 Conference Proceedings / The Forty-Seventh Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2011 / Bally's Las Vegas, Las Vegas, Nevada / The increasing of space explorations requires space communication protocols to provide more capabilities, such as dynamic routing, adaptive data transformation and automatic resource allocation. Accordingly, a universal space communication protocol stack should be provided instead of specially designing protocol for given space mission. Considering the requirements and characters of space mission, potential protocols of all layers were compared and analyzed. Simulations were made based on OPNET. And a suggestion for space communication protocol stacks is proposed.

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Abstract The characteristics of PEMFC stacks in different designs and operational conditions are studied and manufactured in this thesis. There are many factors that affect the PEMFC performance. They include the familiar humidity, the torque, the inlet pressure, the geometries of inlet ports and the flow channels in reaction regions, the cell numbers of the stacks, the type of the oxidizer and its flow rate. To understand the performance characteristics of stacks the voltage and current density will be measured as well as the interior temperature of stacks in this research. The membrane exchange assembly (MEA) with Nafion 112, anode Pt 0.4 mg/cm² and cathode Pt 1.0 mg/cm² is used in these experimental works. The experimental results display that increasing the applied torque will reduce the contact resistance between bipolar plate and diffusion layer but increase the difficulty of gas penetrating into the reaction region beneath the bipolar rib. So proper torque is necessary to obtain the best voltage output. The voltage vs. current density also increases as the inlet pressure increases, but its effect will reduce when the inlet pressure increases over 2atm. The geometry and size of inlet port to each cell for a multi-cell stack will influence the voltage output, especially in high current density, so that special attention is needed in designing inlet port. When the air is used as an oxidizer, the fan with a high rotation speed is helpful in an open circuit design. The high air volume flow rate can avoid that the voltage output decays greatly in high current density. Increasing the cell number may cause extra internal resistance due to assembling improperly and reduce the voltage output. So special attention is also needed in assembling. Keyword: Proton Exchange Membrane Fuel Cell Stacks

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In order to serve hundreds of millions of users, contemporary content providers employ tens of thousands of servers to scale their systems. The system software in these environments, however, is struggling to keep up with the increase in demand: contemporary network and storage stacks, as well as related APIs (e.g., BSD socket API) follow a `one-size-fits-all' design, heavily emphasising generality and feature richness at the cost of performance, leaving crucial hardware resources unexploited. Despite considerable prior research in improving I/O performance for conventional stacks, substantial hardware potential still remains unexploited because most of these proposals are fundamentally limited in their scope and effectiveness, as they still have to fit in a general-purpose design. In this dissertation, I argue that specialisation and microarchitectural awareness are necessary in system software design to effectively exploit hardware capabilities, and scale I/O performance. In particular, I argue that trading off generality and compatibility, allows us to radically re-architect the stack emphasising application-specific optimisations and efficient data movement throughout the hardware to improve performance. I first demonstrate that conventional general-purpose stacks fail to effectively utilise contemporary hardware while serving critical Internet workloads, and show why modern microarchitectural properties play a critical role in scaling I/O performance. I then identify core decisions in Operating Systems design that, although they were originally introduced to optimise performance, are now proven redundant or even detrimental. I propose clean-slate, specialised architectures for network and storage stacks designed to exploit modern hardware properties, and application domain-specific knowledge in order to sidestep historical bottlenecks in systems I/O performance, and achieve great scalability. With thorough evaluation of my systems, I illustrate how specialisation and greater microarchitectural awareness could lead to dramatic performance improvements, which could ultimately translate to improved scalability and reduced capital expenditure simultaneously.

There are several disadvantages in conventional unipolar/bipolar plates such as cost expensive, weight heavy and volume large. Therefore, it is difficult in making use conventional unipolar/bipolar plates to portable fuel cells. With a new heterogeneous carbon fiber bipolar plate, pumpless and air-breathing design and in cooperating with a special MEA, portable fuel cell stacks developed in our lab have made portable applications to be possible. The structure of the DMFC stack made with the new carbon fiber bipolar plate is much more simple and weight-light than the other designs. A two-layer 16-Cell DMFC Stack had been designed and made by using the heterogeneous carbon fiber monopolar plates developed in our fuel cell laboratory. With this design, the methanol solution can be directly stored in the anode chamber which can store fuel 17 ml and does not need any auxiliary equipment, so it easy to apply to the portable power source. Not including fuel, total weight of stack is only 50g and the volume is 75 cm3. The 16 cell stack includes two pieces of 117 membrane, 16 anode electrodes loading Pt/Ru 5 mg/cm2 and 16 cathode Pt loading 5 mg/cm2. Each single cell electrode area is about 3.5 cm², so the total electrode area of the 16-cell stack is 56cm2. With methanol concentration 3 M, pumpless, air-breathing, and room temperature, the largest output power density of the fuel cell can reach 10.3 mW/cm², and the total power can reach 578 mW in this stage. The performance of the stack will be further improved in the next stage.

Planar £gPEM Fuel Cell Stacks are designed and fabricated in-house through a deep UV lithography technique, with SU 8 photoresist used as the microstructure mold for the fuel cell flow channel or bipolar plates when micro electroforming. The fuel cell stacks use a new design which means installing the fuel channel into PMMA, by which the fuel supply channel becomes convenient and simplified. The performance of the stack is measured in different inlets, and the effect of the hydrogen inlets is explained. The experimental results are presented in the form of polarization VI curves and PI curves for the different types of inlet. Furthermore, the influence of the inlets is presented and discussed.