Low temperature fuel cells: Interactions between catalysts and engineering design

For many potential applications of fuel cells, especially road transport, it is highly desirable to use liquid fuels. In this paper it is shown that whether direct fuel cell systems (methanol/air) or indirect, hydrogen reformer to hydrogen are chosen, catalyst performance and cost plays a dominant role in the overall design. Notably, the maximum current densities which can usefully be employed are limited by the conductivity of low cost intercell plates in bipolar designs. Thus to attain respectable volume power densities, thin cell stack designs are essential. Considerations of overall simplicity, cooling and water control together with the need to operate at atmospheric pressure because of the cost, noise and inefficiency of air compressors all favour operating at 100°C or below. Although a number of systems could be constructed with known technology, costs are still too high for all but specialised applications. While useful engineering design work can be done using existing catalysts, present costs are far too high to justify widespread application. The recent discovery in the authors' laboratory of a base metal catalyst for the electrolytic oxidation of methanol together with past workers who have presented data on effective non-platinum air cathodes in acid electrolytes suggest that the quest is worthwhile. Bearing in mind the need to reduce total costs, while some system engineering development is worthwhile to provide solutions to the various physical problems involved, the authors argue that the primary effort on fuel cells should be in the fields of catalysis and electrode structure.     

The roles of cell wall polymers and intracellular components in the thermal softening of cassava roots

Cassava varieties Iapar 19 – Pioneira (short cooking time, domestic vegetable), Taquari (medium-to-long cooking time, domestic vegetable), and Branca de Santa Catarina (long cooking time, industrial vegetable), were selected in order to investigate the cell wall and compositional basis for these textural differences. Pioneira had lower levels of Ca²⁺ and Mg²⁺, and higher levels of phytic acid and monovalent cations than the longer cooking time varieties. Detailed cell wall analysis indicated that the longer cooking Branca cultivar had higher levels of chelator-insoluble pectic polysaccharides. The potential causative roles of these different features were evaluated using vortex-induced cell separation (VICS) studies. Time to achieve the complete VICS of Branca cultivar was reduced to that of Pioneira with externally-supplied chelating agents (CDTA) and Na₂CO₃. Taquari roots did not respond in this way indicating a different biochemical basis for the maintenance of cell adhesion. The results are discussed in relation to the thermal stability of texture in these cassava varieties.     

Spin-Polarised (by CIDEP) Silicon-Containing Radicals

Polarised ESR signals, observed from silicon-centred radicals produced by irradiation of either di-tert butyl peroxide or acetone in the presence of a silicon hydride, are presented and analysed. The novel feature that radical pair mechanism CIDEP can be used to accentuate weak sidebands due to radicals containing rare isotopes (here ²⁹Si) is demonstrated. Adduct radicals formed by reaction with maleic anhydride and vinyltrimethylsilane were also studied. With the former, the adduct produced and observed in early-time experiments remains the same at room temperature and above; in steady-state studies this has been reported not to be so.     

如何扭转电压比较器不被重视的问题

电压比较器在单片机中的出现始于20世纪90年代末.当时,大家认为这项技术仅降低了成本而已.因为,这样的比较器需要的硅器件较少,又能使单片机比较两个模拟电压.于是,认为电压比较器仅仅是一个"1位ADC"的观点始终占据主导地位,并且一直持续到21世纪的头几年. 幸运的是,当8位单片机开始不断涉足更多的混合信号应用时,越来越多具有模拟背景的设计人员开始使用单片机.这些采用混合信号单片机的设计人员非常熟悉电压比较器的灵活性和功能,便着手发掘其潜能.使用片上电压比较器的应用不断涌现,包括传感器输出的模拟信号到数字信号的转换,逻辑门,放大器以及电源转换.     

Cinematic success, aesthetics, and economics: An exploratory recursive model.

Although the reputation of creative artists is based largely on the merit of their work, the latter can sometimes be assessed in several different ways that may not necessarily agree. This lack of evaluative consensus is perhaps most apparent in cinematic success; this can be judged by film critics (initial and final), movie awards (picture, dramatic, visual, technical, and music), and box office performance (including both first weekend and later gross). Previous research not only shows that these success criteria may not always agree, but also that the criteria may have distinct aesthetic and economic antecedents. However, because the success criteria emerge at distinct points across time, a recursive model can be developed that describes the relationships among the criteria as well as their differential dependence on the predictive factors most frequently identified in the literature. The model was constructed using a sample of 1006 English-language, live-action, feature-length narrative films released between 2000 and 2006. The resulting equations indicate the complexity of cinematic success. Nonetheless, overriding this complexity is the fundamental contrast between film as art and film as entertainment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Studies on the Synthesis and Activity of Three Tripalladium Complexes Containing Planaramine Ligands

The present study deals with the synthesis, characterization and activity against human cancer cell lines: A2780, A2780^cisR and A2780^ZD0473R of three tripalladium complexes, MH3, MH4 and MH5, that each have two planaramine ligands bound to the central metal ion. Cellular uptake levels, extent of DNA binding, and nature of interaction with salmon sperm and pBR322 plasmid DNA were determined for each complex. Palladium compounds are much more reactive than their corresponding platinum derivatives, which makes them therapeutically inactive but toxic. However, the results of the present study suggest that significant antitumour activity can be introduced in palladium complexes by lessening their reactivity by the introduction of sterically hindered ligands such as 2‐hydroxypyridine, 3‐hydroxypyridine and 4‐hydroxypyridine. When bound to the central palladium ion, 4‐hydroxypyridine appears to be more activating than 2‐hydroxypyridine and 3‐hydroxypyridine, suggesting that noncovalent interactions, such as hydrogen bonding, may also be key determinants of antitumour activity in addition to the steric effect. While cisplatin binds with DNA to form intrastrand GG adducts that causes local bending of a DNA strand, these planaramine‐derived palladium complexes are expected to bind with DNA and form a number of long‐range interstrand GG adducts that would cause a global change in DNA conformation, provided the tripalladium cations in MH3, MH4 and MH5 persist under physiological conditions.     

Letter Transpositions Within and Across Morphemes.

Three masked-prime naming experiments were conducted to examine the impact of morpheme boundaries on letter transposition confusability effects. In Experiment 1, the priming effects of primes containing letter transpositions within (sunhsine) and transpositions across (susnhine) the constituents of compound words were compared with correctly spelled primes and primes containing letter substitutions in naming correctly spelled targets. Primes containing transpositions within morphemes facilitated naming as much as correctly spelled primes. Primes with transpositions across morphemes did not facilitate naming more than primes with letter substitutions. Experiment 2 replicated Experiment 1 and extended the effects to so-called pseudocompounds (mayhem). Experiment 3 extended the results to agentive derivational morphology (boaster). The results are discussed in the context of visual word recognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Exercise as a treatment for hypertension in low-socioeconomic-status Black children.

Low-socioeconomic-status (SES) Black children have a higher mean blood pressure than most other groups. The antihypertensive effects of a 12-week aerobic exercise program were examined on 11 low-SES Black children, ages 8–12, who had blood pressure above the 95th percentile. A multiple baseline across three groups of children with baseline and exercise conditions was conducted. After the introduction of the exercise program, there were significant decreases in diastolic and systolic blood pressure. Cardiovascular fitness improved concurrently. The results suggest that vigorous exercise can decrease the blood pressure of low-SES hypertensive Black children. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Seismic Vulnerability and Mitigation during Construction of Cable-Stayed Bridges

The implications of earthquake loading during balanced cantilever construction of a cable-stayed bridge are examined. Finite-element models of a cable-stayed bridge were developed and multiple ground motion time history records were used to study the seismic response at the base of the towers for six stages of balanced cantilever construction. Probabilistic seismic hazard relationships were used to relate ground motions to bridge responses. The results show that there can be a high probability of having seismic responses (forces/moments) in a partially completed bridge that exceed, often by a substantial margin, the 10%/50-year design level (0.21% per annum) for the full bridge. The maximum probability of exceedance per annum was found to be 20%. This occurs because during balanced-cantilever construction the structure is in a particularly precarious and vulnerable state. The efficacy of a seismic mitigation strategy based on the use of tie-down cables intended for aerodynamic stability during construction was investigated. This strategy was successful in reducing some of the seismic vulnerabilities so that probabilities of exceedance during construction dropped to below 1% per annum. Although applied to only one cable-stayed bridge, the same approach can be used for construction-stage vulnerability analysis of other long-span bridges.     

Spatial attention and response control in healthy younger and older adults and individuals with Alzheimer's disease: Evidence for disproportionate selection impairments in the simon task.

The authors examined the degree to which aging and Alzheimer's disease (AD) influence the ability to control attention when conflict is presented in terms of incongruent mapping between a stimulus and the appropriate response. In a variant of the Simon task, healthy older adults and older adults with mild or very mild AD showed disproportionately larger reaction time (RT) costs when the stimulus and response were in conflict relative to RT costs of healthy younger adults. Analyses of RT distributions provide support for a 2-process model of the Simon effect in which there is a short-lived transient effect of the irrelevant dimension in younger adults and a more sustained influence across the RT distribution in older adults. An analysis of error rates showed that the older adults with mild and very mild AD made more errors on incongruent trials, suggesting that AD leads to increased likelihood of selecting the prepotent pathway. The findings are discussed in terms of the special nature of the response requirements of the Simon task to better illuminate the attentional decrements in both healthy aging and early stage AD. (PsycINFO Database Record (c) 2010 APA, all rights reserved)