180 research outputs found
Advances in solid polymer electrolyte fuel cell technology with low-platinum-loading electrodes
The Gemini Space program demonstrated the first major application of fuel cell systems. Solid polymer electrolyte fuel cells were used as auxiliary power sources in the spacecraft. There has been considerable progress in this technology since then, particularly with the substitution of Nafion for the polystyrene sulfonate membrane as the electrolyte. Until recently the performance was good only with high platinum loading (4 mg/sq cm) electrodes. Methods are presented to advance the technology by (1) use of low platinum loading (0.35 mg/sq cm) electrodes; (2) optimization of anode/membrane/cathode interfaces by hot pressing; (3) pressurization of reactant gases, which is most important when air is used as cathodic reactant; and (4) adequate humidification of reactant gases to overcome the water management problem. The high performance of the fuel cell with the low loading of platinum appears to be due to the extension of the three dimensional reaction zone by introduction of a proton conductor, Nafion. This was confirmed by cyclic voltammetry
TOWARDS AN UNDERSTANDING OF HOW TUBE INSERTS MITIGATE FOULING IN HEAT EXCHANGERS
A number of studies undertaken by Total have measured the improvement that can be expected when TurbotalTM inserts are installed in heat exchangers. These studies have fully established that TurbotalTM both improve heat transfer coefficient and mitigate fouling. It has been found that fouling levels vary with application. Consequently, economics of installing inserts are difficult to quantify. Gains must be estimated through specific tests. A model that predicts fouling development solves this problem. In this paper first steps towards the understanding of how TurbotalTM limits the fouling rate are described. Authors suggest that the calculation of both pressure drop and heat transfer coefficient in a tube equipped with insert can be used to extend the Ebert & Panchal fouling model to predict the fouling rate in tube equipped with TurbotalTM. This extension of the Ebert-Panchal Model requires adjustment of both the deposition term and the removal term. The deposition term can be adjusted by multiplying by the ratio of plain to enhanced heat transfer coefficients and the removal term can be based on the pressure drop imposed by the insert. This modified model is then compared with operating cases to verify its reliability. Further issues that require consideration are a mechanical effect that gives rise to limiting growth of the fouling deposit, and total suppression of fouling in parts of the exchanger into account
Development of integrated thermionic circuits for high-temperature applications
Integrated thermionic circuits (ITC) capable of extended operation in ambient temperatures up to 500 C are studied. A set of practical design and performance equations is demonstrated. Experimental results are discussed in which both devices and simple circuits were successfully operated in 5000 C environments for extended periods. It is suggested that ITC's may become an important technology for high temperature instrumentation and control systems in geothermal and other high temperature environments
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Fuel cell systems for vehicular applications
The phosphoric acid fuel cell is used as the base line in these evaluations. Two cell sizes (15 and 60 kW) and two fuel options (methanol and propane) are included. Four vehicle types, the city bus, highway bus, delivery van, and general-purpose consumer car are selected for evaluation. Typical drive cycles and economics for these vehicles are compiled, and comparisons are made between the fuel-cell vehicle and current internal-combustion and diesel-engine vehicles. The conclusions of these evaluations are briefly related. Then, the initial results of two aspects of the fuel-cell-powered vehicle evaluation program ongoing at LASL are described. The first part of the program presents the results of detailed computer simulations to illustrate a number of the important system-design considerations in configuring a fuel cell/battery electric vehicle. The next program describes a fuel-cell-powered golf cart currently being used as an engineering test bed. (MCW
Toxoplasma seroprevalence in a rural population in France: detection of a household effect
<p>Abstract</p> <p>Background</p> <p><it>Toxoplasma gondii</it>, the agent of toxoplasmosis, has a complex life cycle. In humans, the parasite may be acquired either through ingestion of contaminated meat or through oocysts present in the environment. The importance of each source of contamination varies locally according to the environment characteristics and to differences concerning human eating habits and the presence of cats; thus, the risk factors may be determined through fine-scale studies. Here, we searched for factors associated with seropositivity in the population of two adjacent villages in Lorraine region, France.</p> <p>Methods</p> <p>All voluntary inhabitants filled out a questionnaire and gave a blood sample. The seroprevalence was estimated globally and according to the inhabitants' ages using a cubic spline regression. A mixed logistic regression model was used to quantify the effect of individual and household factors on the probability of seropositivity.</p> <p>Results</p> <p>Based on serological results from 273 persons, we estimated seroprevalence to be 47% (95% confidence interval: 41 to 53%). That seroprevalence increased with age: the slope was the steepest up to the age of 40 years (OR = 2.48 per 10-year increment, 95% credibility interval: [1.29 to 5.09]), but that increase was not significant afterwards. The probability of seropositivity tended to be higher in men than in women (OR = 2.01, 95% credibility interval: [0.92 to 4.72]) and in subjects eating raw vegetables at least once a week than in the others (OR = 8.4, 95% credibility interval: [0.93 to 72.1]). These effects were close to statistical significance. The multivariable analysis highlighted a significant seroprevalence heterogeneity among households. That seroprevalence varied between 6 and 91% (5<sup>th </sup>and 95<sup>th </sup>percentile of the household seropositivity distribution).</p> <p>Conclusion</p> <p>The major finding is the household effect, with a strong heterogeneity of seroprevalence among households. This effect may be explained by common exposures of household members to local risk factors. Future work will quantify the link between the presence of oocysts in the soil and the seroprevalence of exposed households using a spatial analysis.</p
Chronic Toxoplasma Infection Modifies the Structure and the Risk of Host Behavior
The intracellular parasite Toxoplasma has an indirect life cycle, in which felids are the definitive host. It has been suggested that this parasite developed mechanisms for enhancing its transmission rate to felids by inducing behavioral modifications in the intermediate rodent host. For example, Toxoplasma-infected rodents display a reduction in the innate fear of predator odor. However, animals with Toxoplasma infection acquired in the wild are more often caught in traps, suggesting that there are manipulations of intermediate host behavior beyond those that increase predation by felids. We investigated the behavioral modifications of Toxoplasma-infected mice in environments with exposed versus non-exposed areas, and found that chronically infected mice with brain cysts display a plethora of behavioral alterations. Using principal component analysis, we discovered that most of the behavioral differences observed in cyst-containing animals reflected changes in the microstructure of exploratory behavior and risk/unconditioned fear. We next examined whether these behavioral changes were related to the presence and distribution of parasitic cysts in the brain of chronically infected mice. We found no strong cyst tropism for any particular brain area but found that the distribution of Toxoplasma cysts in the brain of infected animals was not random, and that particular combinations of cyst localizations changed risk/unconditioned fear in the host. These results suggest that brain cysts in animals chronically infected with Toxoplasma alter the fine structure of exploratory behavior and risk/unconditioned fear, which may result in greater capture probability of infected rodents. These data also raise the possibility that selective pressures acted on Toxoplasma to broaden its transmission between intermediate predator hosts, in addition to felid definitive hosts
Padronização de ensaio imunoenzimático para pesquisa de anticorpos das classes IgM e IgG anti-Toxoplasma gondii e comparação com a técnica de imunofluorescência indireta
Development and testing of an implementation strategy for a complex housing intervention: protocol for a mixed methods study
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