In this study, copper metals were used to fabricate five different flow field plates with various open ratios using MEMS technology. Five samples were prepared for experiments with rib width varying as 150, 200, 300, 450, and 600 £gm at a fixed channel width (300 £gm). The open ratio of flow field plates was varied from 60.0% to 37.9%. Experiments with different operating parameters of anode/cathode pressure drop, cell operating temperature, and gas backpressure were conducted. Furthermore, a simple lumped capacitance model was used to predict the temperature evolution of the fuel cell system. Then, the optimum flow field design and cell operating parameters were finally found. Based on the aforementioned experiments an optimal open ratio ofunity was found like 49.2%. Further, an optimal open ratio in terms of the net power gain factor (= power gain/power consumption) of 38.7% can be obtained for the cases under study. Durability and reliability for copper bipolar plate were examined for long range tests (each run with at least 5 hours duration for consecutive two months). This strongly suggests that copper sheets can be considered as one of possible candidates for flow field material.

Nowadays, Web caching technique has been widely used and become one of the most promising ways to reduce network traffic, server load, and user-experienced latency while users surf the Web. In the context of traditional systems, caching techniques have been extensively studied. However, these techniques are not directly applicable to Web due to larger size of working set and cache storage in proxies. Many studies have presented their approaches to improving the performance of Web caching. Two of most representative approaches are hash routing [25] and directory-base digest [12]. Hash routing provides amapping fromthe URL of object to the location of proxy, which has the cached object, while directory-based digest records the pairs of proxy locations and object URLs for answering the query when local misses occur in any proxy. Hash routing can best utilize storage space by eliminating duplicated objects among proxies,while directory-based digest allows object replicas among proxies to resist proxy failures. These two conventional approaches have complementary tradeoffs. In this thesis, a comprehensive approach to cooperative caching for Web proxies, using a combination of hash routing and directory-based digest, is presented. Our approach tends to subsume these widely used approaches and thus gives a spectrum of trade-off between the overall hit ratio and its associated overhead. Through the simulations using real-life proxy traces, the performance and overhead of our proposed mechanism were evaluated. The experimental results showed that our approach outperforms the previous competitors.

Thèse de doctorat : Sciences économiques : Université Paris-Dauphine : 2009. / bibliogr.p.453-466.

CAMPO (Capital Area Metropolitan Planning Organization) is undergoing a revision of the regional transportation plan for Central Texas. The key goal of the plan is achieving sustainable development through integrating a multimodal transportation system with dense mixed land use. The CAMPO Plan has incorporated the growth management tool of jobs-housing balance to guide future land use development. To improve jobs-housing proximity and encourage compact growth, the concept of an activity center connected by high capacity transit corridors was employed in the plan, targeting the accommodation of 31 percent of the population and 38 percent of employment in Central Texas by 2035 (CAMPO 2035 Plan 2010). At the time when CAMPO was attempting to define appropriate ratios of jobs-housing balance for the activity centers, critical questions arose: what is a good ratio? Further, how should jobs-housing balance be quantified for guiding land use development? And to what extent could jobs-housing ratio be effectively used as an intervention instrument? This report attempts to provide theoretical and empirical evidence of jobs-housing balance and examine the applicability of jobs-housing balance ratio for different planning purpose in local context. Based on a rich literature review, the report removed the "deceptive simple concept" (Cervero 1991, p. 10) of jobs-housing balance on the surface and gathered insights on jobs-housing balance from existing exemplary studies. Absent a single consensus of a good jobs-housing balance ratio, the goal of this report is to present the possible ways of measuring and defining jobs-housing balance in complex urban development. This report analyzed existing jobs-housing balance of the Austin Region, presenting the truth of commute distance and jobs-housing balance ratio. Local municipalities might consider more factors in terms of the application of jobs-housing balance ratio in local context. / text

published_or_final_version / Mathematics / Doctoral / Doctor of Philosophy

No description available.

Objectives: The waist-to-stature ratio (WSR) is newly developed index, proposed to be of greater value as a simple anthropometric indicator, for predicting abdominal obesity and related cardiovascular co-morbidities in adults and children. This study examined age and gender differences in waist-to-stature (WSR) as measure of centripetal fat patterning in a sample of children in Pretoria, South Africa.

No description available.

No description available.

Cutter Soil Mixing (CSM) is a recently developed deep mixing technique that has grown to include the treatment of sandy and silty soils. This study seeks to investigate the influence of (i) sand-silt ratio, (ii) cement content, (iii) water content and (iv) time on the unconfined compressive strength of saturated cement-treated soil specimens. A new test device and method of specimen reconstitution were conceived in order to obtain a saturated mix of soil and cement. A comparison of results show strength increases non-linearly to decreasing total water-cement ratio, and that this trend is largely independent of sand-silt ratio. Furthermore, strength increases non-linearly with time and is independent of sand-silt ratio. Lastly, it is recommended that the strength be correlated with total water-cement ratio rather than cement content, in order to improve data reporting and provide design guidance to engineering practice.