602 research outputs found

    High Energy Density Matter for Rocket Propulsion

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    The objective of the High Energy Density Matter (HEDM) program is to identify, develop, and exploit high energy atomic and molecular systems as energetic sources for rocket propulsion applications. It is a high risk, high payoff program that incorporates both basic and applied research, experimental and theoretical efforts, and science and engineering efforts. The HEDM program is co-sponsored by the Air Force Office of Scientific Research (AFOSR) and the Phillips Laboratory (PURKS). It includes both in-house and contracted University/Industry efforts. Technology developed by the HEDM program offers the opportunity for significant breakthroughs in propulsion system capabilities over the current state-of-the-art. One area of great interest is the use of cryogenic solids to increase the density of the propellant and to act as a stable matrix for storage of energetic materials. No cryogenic solid propellant has ever been used in a rocket, and there remain engineering challenges to such a propellant. However, these solids would enable a wide class of highly energetic materials by providing an environment that is at very low temperatures and is a physical barrier to recombination or energy loss reactions. Previous to our experiments only hydrogen atoms had been isolated in solid hydrogen. To date we have succeeded in trapping B, Al, Li, N, and Mg atoms in solid H2. Small molecules, such as B2 and LiB, are also of interest. Current efforts involve the search for new energetic small molecules, increasing free radical concentrations up to 5 mole percent, and scale-up for propulsion testing

    ACTH does not mediate divergent stress responsiveness in rainbow trout

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    Two lines of rainbow trout selected for high (HR) and low (LR) responsiveness to a standardised confinement stressor displayed a sustained divergence in plasma cortisol levels during a 3 h period of confinement (max.: HR: 167 ± 13 ng ml-1; LR: 103 ± 8 ng ml-1; P < 0.001). However, no significant difference in plasma ACTH levels was evident (max: HR: 153 ± 9 pg ml-1; LR: 142 ± 7 pg ml-1). Dexamethasone (DEX) was administered to HR and LR fish to block endogenous adrenocorticotropin (ACTH) release. Administration of a weight-adjusted dose of ACTH to the DEX-blocked fish elevated plasma cortisol levels to a significantly greater extent in HR (233 ± 24 ng ml-1) than LR (122 ± 14 ng ml-1) fish (P < 0.001). Plasma cortisol levels in DEX-blocked HR and LR fish after sham injection were low but also significantly different (HR: 6.7 ± 1 ng ml-1; LR: 2.2 ± 0.2 ng ml-1; P < 0.001). These results indicate that modulation of cortisol responsiveness to stressors in HR and LR fish resides, at least in part, downstream of the hypothalamic-pituitary axis

    The three-spined stickleback as an environmental sentinel: effects of stressors on whole-body physiological indices

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    Indicators of a generalised stress response (changes in cortisol, glucose, RNA:DNA ratio and total protein) when measured in whole-body preparations of individual sticklebacks display significant alterations in response to acute (hours) and chronic (days) disturbances and food withdrawal. In addition, changes in alkali-labile phosphorous, a specific biomarker of exposure to estrogenic contaminants, can be detected in whole-body preparations of estrogen-exposed sticklebacks confirming that the measurement of biomarkers normally assessed in a specific tissue can be equally possible in whole fish

    Lake Michigan lower food web: Long-term observations and \u3ci\u3eDreissena\u3c/i\u3e impact

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    Lake Michigan has a long history of non-indigenous introductions that have caused significant ecological change. Here we present a summary of eight papers that document recent changes and the current state of the lower food web of southern Lake Michigan after the establishment of large dreissenid populations. Results are based on long-term data sets collected by federal and academic research and monitoring programs that place recent changes into a historic context. Dramatic and significant changes in the lower food web, such as the loss of the spring diatom bloom, large declines in phytoplankton productivity, and a decline of Mysis populations, were directly or indirectly attributed to the expansion of Dreissena rostriformis bugensis. Total phosphorus concentrations and loadings also have decreased in the last 20 years. Changes in the Lake Michigan ecosystem induced by D. r. bugensis have produced conditions in the offshore pelagic region that are similar to oligotrophic Lake Superior. The future state of the lower food web in southern Lake Michigan is difficult to predict, mainly because population trends of D.r. bugensis in cold, offshore regions are unknown. Hence, monitoring programs designed to collect long-term, consistent data on the lower food web of Lake Michigan are essential

    Brain monoaminergic activity in rainbow trout selected for high and low stress responsiveness

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    This paper investigates whether two lines of rainbow trout displaying genetically determined variation in stress responsiveness and behavior also show differences in brain monoaminergic activity. In several brain regions, strains of rainbow trout selected for consistently high or low post-stress cortisol levels displayed differences in tissue concentrations of monoamines and/or monoamine metabolites, or in metabolite/monoamine ratios. High-responsive trout reacted to stress by an increase in the concentrations of both serotonin (brain stem), dopamine (brain stem), and norepinephrine (optic tectum, telencephalon), whereas low-responsive fish did not. Brain stem and optic tectum concentrations of monoamine metabolites were also elevated after stress in high responders, but not in low-responsive fish. The simultaneous increase in the concentration of monoamines and their metabolites suggests that both synthesis and metabolism of these transmitters were elevated after stress in high-responsive trout. A divergent pattern was seen in the hypothalamus, where low-responsive fish displayed elevated levels of 5-hydroxyindoleacetic acid (a serotonin metabolite) and 3-methoxy-4-hydroxyphenylglycol (a norepinephrine metabolite). In the telencephalon, both populations had elevated concentrations of these metabolites after stress. These results clearly suggest that selection for stress responsiveness in rainbow trout is also associated with changes in the function of brain monoaminergic systems. The possible functional significance of these observations is discussed with respect to the physiological and behavioral profile of these strains of fish. Literature is reviewed showing that several factors affecting brain monoaminergic activity might be altered by selection for stress responsiveness, or alternatively be under direct influence of circulating glucocorticoids

    The importance of zooplankton‐protozoan trophic couplings in Lake Michigan

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    Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109824/1/lno19913671335.pd

    A revision of Blechnum vulcanicum (Blume) Kuhn and related taxa (Blechnaceae) in Malesia and Oceania

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    The species included in the Blechnum vulcanicum group are all characterised by the presence of unique, minute, surface outgrowths on various aerial parts of a plant; these have previously in error been described as short hairs. However, these so-called ‘hairs’ are distinctive and consist of about 4 to 7 cells in a linear arrangement. The species of Blechnum that have this feature are here recognised as a new Section, Blechnum sect. Pilosa. The species Blechnum vulcanicum (Blume) Kuhn has been widely cited in taxonomic, floristic and ecological studies for Malesia, Australasia and Oceania, but shows much variation across this wide geographic range. The present study rejects this broad view and recognises a total of 14 species in this group. This includes four new species (Blechnum aequabile, B. basipilosum, B. humile and B. megavulcanicum), and three new combinations (Blechnum deltoides, B. feani, and B. tovii)
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