The improvement of performance and the maintenance of stability of a portable air-breathing PEMFC are studied in this thesis. The water content within proton exchange membrane affects strongly on the performance and stability of a PEMFC stack, in which water within membrane can form a conduction channel to provide hydrogen ion transferring from anode to cathode. The over-dried condition caused by a long time operation can also be avoided to prevent the membrane from damaging. Thus the proper humidification of a stack is important for a portable air-breathing PEMFC system. The traditional humidifier is too bulky to be suitable for portable fuel cells. A simple humidification system developed in this research is making use of the water stored in the stack bottom and the self-generating heat by chemical reaction to drive the passive humidification system of this stack. The water at the bottom of the tank can be sucked with cotton threads in cathode and a piece of cotton cloth by capillary phenomenon and transfer to the membrane of MEA. The cotton threads humidification in cathode is enough in low and middle current density in this study. It is not enough in high current density due to the large water vapor dissipation in the cathode surface, so a cotton cloth in anode is added to increase the evaporating surface to supply water to membrane. This passive humidification system does not need extra energy, and it only employs the heat generated by the cells. The system follows the simple principle, which is always obeyed in a portable fuel cell system. A 16-cell HFC stack developed in this research adopts carbon fibers as current collectors. Two pieces of 8-cell anodes is placed in the inner sides of the stack, and the 8-cell cathode is located on external sides, which is exposed directly to the ambient air. The 16-cell can connect in series or parallel. The experimental results show that it is helpful to add cotton threads in cathode and cotton cloth in anode to improve the stability of the 16-cell stack during a the long period operation. The 16-cell HFC stack has succeeded in the operation and charging for an IPhone, digital photo frame, and LED light. The experiments have proved that this type of the lightweight humidification system is helpful in the future portable hydrogen fuel cell applications.

The H2/air micro PEMFC stacks were designed and fabricated in-house through MEMS (Micro-Electro-Mechanical System) technology with deep UV lithography manufacturing processes (SU-8 photoresist) and micro electroforming manufacturing processes to construct a novel metallic bipolar plate. The effect of different operating parameters on micro PEMFC stacks performance was experimentally investigated for serpentine flow-field configuration. Experiments were conducted through a serious laboratory experiments with different operating conditions of temperature (25oC, 35 oC and 50 oC), anode backpressures (97kPa, 153kPa, 207kPa) as well as anode humidifier temperature (25oC, 35 oC and 50 oC). Experimental results are presented in the form of polarization VI curves and PI curves under above operating conditions. The influence of the aforementioned parameters was presented and discussed.

The thesis is mainly focused on the investigation of optimal process operation, which is appropriate for new-type stacking package product to achieve the assembly products of two or more packages. By melting solder balls to form the stacking package products, the eventual goals of lightness, thinness and smallness will be accomplished. To increase and stabilize the production yield of stacking package products, different flux, different temperature setting with reflow oven, and different flux dipping method were used. With Taguchi design of experiment, the solder balls combined situations under varied conditions were observed. The best process character of new-type integration assembly products was achieved. The experimental results and mass production data prove that different flux type and temperature setting with reflow oven won¡¦t influence the solder balls connection between two package products. Only the flux dipping method will directly affect solder balls connection between two package products. The abnormal phenomenon is the so-called cold joint in assembly plants. With innovation, silicon gel head is used as a flux adhesive way to achieve the goal of flux transferred. This method can be used in integration process of new-type stacking package products. That will certainly assure that every solder ball on each package product can be helpful for adhesion of flux. The experiments proved that the yield rate of solder balls connection of two package products is 100% after the stacking package products through reflow oven. This proves that using flux with silicon gel head on new-type stacking package products is the best way of process operation. The innovation of this new process has been granted a patent by the Patent office, ROC. Although this is a simple invention, it will bring profit to ASE Co. as well and ensure the leadership of new-type stacking package products in related industries. Keywords: Stack¡BSolder Ball¡BCold Joint¡BSilicon Pad

Proton exchange membrane (PEM) fuel cell possesses the characteristics of microminiaturization and low temperature operation. For this reason, the proton exchange membrane fuel cell is very suitable to serve as power source of portable electronic products. In this paper, a three-dimensional numerical model to evaluate the voltage and the total current density of a PEM fuel cell stack was developed. The polarization curves of the PEM fuel cell stack under three different operating temperatures were investigated. In this study, the micro PEM fuel cell stack contains two single cells. Pure H2 gas stream was supplied as the anode inlet flow and air as the cathode inlet flow under constant pressure at 97 kPa and constant cell temperate (298K¡B308K¡B323K) conditions. Because the cell temperature may affect the chemical reaction rate on the cathode side, we discussed the influences of different temperatures on the cell performance. Solutions were compared with the experimental data. Both the value of power density and the tendency of polarization curve are in good agreement with the experimental data.

Zugl.: Clausthal, Techn. Univ., Diss., 2009

Thesis (Ph.D.)--Indiana University, Dept. of History, 2005. / Source: Dissertation Abstracts International, Volume: 66-06, Section: A, page: 2362. Adviser: James H. Capshew. "Title from dissertation home page (viewed Nov. 28, 2006)."

stack: Minimalist Poetics consists of a portfolio of practice-led research — a volume-length minimalist poem entitled stack — and a critical essay. The poem applies and adapts several minimalist writing strategies, which are evaluated in the critical essay to create a text that is rich in imagery yet indeterminate in meaning. In addition, stack is innovative in its structural approach — through original use of enjambment, footnoting and repetition, lines may be treated as discrete entities and, also, as combinations. A key research question that the practice-led component and the critical essay interrogate is the applicability and development of the poetics of the “New Sentence”, and other formally innovative approaches in the field of minimalist writing. The first part of the critical essay contextualises the creative portfolio in relation to the field of minimalist poetics as a whole. It sets out how stack belongs to a strand of minimalist poetry that evolved out of imagism and objectivism, and whose key practitioners include Robert Grenier, Robert Lax and Aram Saroyan. Subsequently, the thesis outlines the methods that were used to generate the creative portfolio. Effectively these latter sections present a manual for making minimalist poetry. Aside from exploring the written elements of stack, the thesis also examines my practice of conducting what I refer to as ‘minimalist interventions’ (embodied, micro-actions). These interventions, which have taken place in a range of environments, generally function as stimuli for the written aspects of the poem.

Hybrid actuation is an expanding field in which several systems, such as a mechanical, electrical, hydraulic, pneumatic, and/or thermal, among others, are integrated in order to combine certain aspects of each system, and achieve a better and more efficient performance under certain operating conditions. The concept of piezohydraulic actuation takes advantage of the high force capabilities that piezoceramics have and combines it with the operation at high frequencies, in order to achieve the hydraulic actuation of a system under a specified stroke and force. High frequency rectification translates the low stroke of a piezoelectric stack into a desired amount of stroke per unit time. Thus, the low displacement, oscillatory motion of the piezoelectric device (coupled with a high frequency operation) is translated into a unidirectional motion of a hydraulic cylinder. As part of this research, a benchtop piezohydraulic unit has been developed and the concept of piezohydraulic actuation has been demonstrated. The effective bidirectional displacement of a hydraulic cylinder through the actuation of a piezoelectric stack has been achieved. A lumped parameter model is developed in order to simulate the dynamics of the hydraulic system and of the entire piezohydraulic unit. The model did approximate the response of the piezohydraulic unit under a one-sided operation. Time response analysis is performed through the frequency spectrum comparison of the measured and the simulated data. Then a two-stage cycle simulation is used to model the pumping operation of the unit. Discrepancies were obtained between the model and the actual system for the single-ended piezohydraulic unit, nonetheless, a good approximation has been achieved for the pumping operation of the double-ended unit under certain conditions. Furthermore, several factors have been identified that may limit the operation of the piezohydraulic unit. First, the need of high displacement actuators often comes with the requirement of high voltage operation along with high current consumptions. Thus, the amplifier becomes the first limitation to overcome. Second, is the response of the controlled valves. The highest valve operating frequency and their time response will set the limit on the piezohydraulic unit. And finally, once these limitations are overcome, the unit is eventually limited by the dynamics of the fluid and the hydraulic system itself. Attenuation in the frequency response, or the operation near resonance and the possibility of cavitation, are some of the aspects that eventually will limit the operation of the piezohydraulic unit. A custom made, high displacement stack is used along with a custom made switching amplifier. The current system is being limited by the second factor, the solenoid valves. Nonethelss the analysis performed has addresed the relevant issues required for the design and use of another set of controlled valves. Finally, the eventual limitation from the hydraulic system has been determined through the analysis of the fluid dynamics of the system. The analysis does not account for potential cavitation, and future operations at high frequencies should take it into account. / Master of Science

Programmers who want to improve their skills and background in software development rely heavily on developer social platforms such as GitHub and Stack Overflow to enhance their learning. Stack Overflow provides answers to questions they have about languages or library skills they wish to acquire, while contributing to open-source projects hosted on sites like GitHub gives them valuable experience. Students also use these platforms during their education: most will rely heavily on Stack Overflow at some point in their schooling, while many can benefit from contributing to GitHub projects to build their expertise and professional portfolios. We already know from previous research that developers face barriers participating on these platforms, and therefore we may expect that at least some students will experience similar or possibly even bigger barriers. This research describes a semi-structured interview study followed by a survey with university students to explore how they use the GitHub and Stack Overflow platforms. I identified the benefits the students report from using these tools and the barriers they face. I have concluded with some preliminary recommendations on how to reduce the hurdles students may face with these and other developer social platforms, and I have also suggested future work to mitigate these roadblocks. / Graduate

With the explosion of the number of compute nodes, the bottleneck of future computing systems lies in the network architecture connecting the nodes. Addressing the bottleneck requires replacing current backplane-based network topologies. We propose to revolutionize computing electronics by realizing embedded optical waveguides for onboard networking and wireless chip-to-chip links at 200-GHz carrier frequency connecting neighboring boards in a rack. The control of novel rate-adaptive optical and mm-wave transceivers needs tight interlinking with the system software for runtime resource management.