Chemical propulsion technology

An overview of NASA's low thrust liquid chemical propulsion program is presented with particular emphasis on thrust system technology in the ten to one thousand pound thrust range. Key technology issues include high performance of cooled low thrust engines; small cryogenic pumps; multiple starts-shutdowns (10) with slow ramps (approximately 10 seconds); thrust variation - 4/1 in flight and 20/1 between flights; long life (100 hours); improved system weight and size; and propellant selection

COMPARISON OF INJECTORS WITH A 200-POUND-THRUST AMMONIA-OXYGEN ENGINE

Injection techniques for 200-pound thrust ammonia- oxygen rocket engin

Effluent characterization from a conical pressurized fluid bed

To obtain useable corrosion and erosion results it was necessary to have data with several levels of particulate matter in the hot gases. One level of particulate loading was as low as possible so that ideally no erosion and only corrosion occurred. A conical fluidized bed was used to obtain some degree of filtration through the top of the bed which would not be highly fluidized. This would minimize the filtration required for the hot gases or conversely the amount of particulate matter in the hot gases after a given level of filtration by cyclones and/or filters. The data obtained during testing characterized the effluent from the bed at different test conditions. A range of bed heights, coal flows, air flows, limestone flows, and pressure are represented. These tests were made to determine the best operating conditions prior to using the bed to determine erosion and corrosion rates of typical turbine blade materials

Technique for predicting high-frequency stability characteristics of gaseous-propellant combustors

A technique for predicting the stability characteristics of a gaseous-propellant rocket combustion system is developed based on a model that assumes coupling between the flow through the injector and the oscillating chamber pressure. The theoretical model uses a lumped parameter approach for the flow elements in the injection system plus wave dynamics in the combustion chamber. The injector flow oscillations are coupled to the chamber pressure oscillations with a delay time. Frequency and decay (or growth) rates are calculated for various combustor design and operating parameters to demonstrate the influence of various parameters on stability. Changes in oxidizer design parameters had a much larger influence on stability than a similar change in fuel parameters. A complete description of the computer program used to make these calculations is given in an appendix

Emissions control for ground power gas turbines

The similarities and differences of emissions reduction technology for aircraft and ground power gas turbines is described. The capability of this technology to reduce ground power emissions to meet existing and proposed emissions standards is presented and discussed. Those areas where the developing aircraft gas turbine technology may have direct application to ground power and those areas where the needed technology may be unique to the ground power mission are pointed out. Emissions reduction technology varying from simple combustor modifications to the use of advanced combustor concepts, such as catalysis, is described and discussed

Muscle transcriptomes of Duroc and Pietrain pig breeds during prenatal formation of skeletal muscle tissue using microarray technology

Mammalian myogenesis is an exclusive prenatal process regulated by the muscle regulatory factor gene family, which itself is regulated by numerous other genes. We developed a microarray consisting of the clones of two muscle-specific cDNA libraries with the addition of 500 genes with known function in myogenesis and energy metabolism. Tissue samples were collected of Duroc and Pietrain prenatal litters of 14 and 21 days of age (complete embryos) and 35, 49, 63, 77, and 91 days of age (longissimus muscle tissue) and RNA was isolated. Microarrays were hybridised with pools of six RNA samples. For each age comparisons between Duroc and Pietrain breeds were made, and transcriptome profile changes in time were made for Duroc pigs. Comparison of Duroc and Pietrain prenatal muscle transcriptome expression profiles revealed differences in myogenesis regulating genes, suggesting differential timing of myogenesis between the two pig breeds. The differential development of the expression of the muscle structural genes strengthens this conclusion. Furthermore, differences in the expression of the energy metabolism genes were found. The results also suggest that the differential fat content between the Duroc and Pietrain pig breeds already starts to develop during early prenatal development. The changes in the muscle transcriptome expression profiles during Duroc prenatal muscle development shows a profile of waves of expression of (i) myoblast proliferation stimulating genes,(ii) followed by myoblast proliferation inhibiting and differentiation stimulating genes during the primary muscle fibre development, which is repeated with lower magnitude during secondary muscle fibre development. Furthermore, expression of energy metabolism genes reaches a nadir when differentiation of myoblasts into myotubes takes place. Microarray expression profiles were validated with five genes showing differential expression in the Duroc ¿ Pietrain comparison, and in the Duroc development in time studies using 18S rRNA for normalisation. The real time PCR confirmed the microarray result

What Do Computer Scientists Tweet? Analyzing the Link-Sharing Practice on Twitter

Twitter communication has permeated every sphere of society. To highlight and share small pieces of information with possibly vast audiences or small circles of the interested has some value in almost any aspect of social life. But what is the value exactly for a scientific field? We perform a comprehensive study of computer scientists using Twitter and their tweeting behavior concerning the sharing of web links. Discerning the domains, hosts and individual web pages being tweeted and the differences between computer scientists and a Twitter sample enables us to look in depth at the Twitter-based information sharing practices of a scientific community. Additionally, we aim at providing a deeper understanding of the role and impact of altmetrics in computer science and give a glance at the publications mentioned on Twitter that are most relevant for the computer science community. Our results show a link sharing culture that concentrates more heavily on public and professional quality information than the Twitter sample does. The results also show a broad variety in linked sources and especially in linked publications with some publications clearly related to community-specific interests of computer scientists, while others with a strong relation to attention mechanisms in social media. This refers to the observation that Twitter is a hybrid form of social media between an information service and a social network service. Overall the computer scientists’ style of usage seems to be more on the information-oriented side and to some degree also on professional usage. Therefore, altmetrics are of considerable use in analyzing computer science

Universal Rights and Wrongs

This paper argues for the important role of customers as a source of competitive advantage and firm growth, an issue which has been largely neglected in the resource-based view of the firm. It conceptualizes Penrose’s (1959) notion of an ‘inside track’ and illustrates how in-depth knowledge about established customers combines with joint problem-solving activities and the rapid assimilation of new and previously unexploited skills and resources. It is suggested that the inside track represents a distinct and perhaps underestimated way of generating rents and securing long-term growth. This also implies that the sources of sustainable competitive advantage in important respects can be sought in idiosyncratic interfirm relationships rather than within the firm itself