326 research outputs found

    Turboelectric distributed propulsion protection system design trades

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    The NASA N3-X blended-wing body with turboelectric distributed propulsion concept is being studied to achieve N+3 goals such as reduced noise, emissions, and improved energy efficiency. The electrical distribution system is cryogenic in order to maximize its efficiency and increase the power density of all associated components, while the motors, generators, and transmission lines are superconducting. The protection of a superconducting DC network poses unique electrical and thermal challenges due to the low impedance of the superconductor and operation in the superconducting or quenched states. For a given TeDP electrical system architecture with fixed power ratings, conventional and solid-state circuit breakers combined with superconducting fault-current limiters are examined with both voltage and current source control to limit and interrupt the fault current. To estimate the protection system weight and losses, scalable models of cryogenic bidirectional current-source converters, cryogenic bidirectional IGBT solid-state circuit breakers, and resistive-type superconducting fault current limiters are developed to assess how the weight and losses of these components vary as a function of nominal voltage and current and fault current ratings. The scalable models are used to assess the protection system weight for several trade-offs. System studies include the trade-off in fault-current limiting capability of SFCL on CB mass, alongside the fault-current limiting capability of the converter and its impact on CB fault-current interruption ratings and weight

    Initiation of Turbulent Spots in a Laminar Boundary Layer by Rigid Falling Particulates

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    A transitional laminar boundary layer is developed on a 1m wide km long flat plate in a 0.6m deep water channel with a freestream velocity of 15-50 cm/s. A particulate dispenser under computer control ejects individual particles having diameters of 1/3 delta into the free stream. The particulates are introduced with an initial velocity of U(sub infinity) in the direction of the free stream. They have differing specific gravities of 1.03-2.7 which introduces an additional non-dimensional parameter relating the time taken to traverse the boundary layer to the convective time scale. The particulates produce a wake in the upper region of the boundary layer as they sink towards the wall. Visualization data taken over the range 5 x 10(exp 4) less than Re(sub x) less than 5 x 10(exp 5) indicate that turbulent spots are produced by the disturbances due to the wake rather than by the particulates themselves. This suggests that the spot formation process in this case may be inviscid in nature and may not be strongly influenced by the presence of the wall

    Spatial Distribution of Petroleum Hydrocarbons in Sediment Cores from Blind Pass, St. Pete Beach, Florida

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    One hundred and one sediment cores were collected to characterize the spatial distribution of petroleum hydrocarbons within and just outside Blind Pass, St. Pete Beach, Florida. Twenty-five percent of the cores exhibited levels of petroleum hydrocarbons above detection limits of the gas chromatograph/flame ionization detector (GC/FID) (0.01 mg/Kg), but at generally low concentrations. Petroleum hydrocarbon speciation studies of these samples (gas chromatography/mass spectroscopy [GC/MS]) indicate above-detection level (1 μg/Kg) petroleum hydrocarbons are similar to the non-volatile petroleum hydrocarbons found in a Bouchard 155 reference sample collected after the 1993 oil spill in the area, but are in a much degraded and weathered state. Individual petroleum hydrocarbons were, in all but one case, below the threshold effective level (TEL) described in the literature (MacDonald, 1994). The petroleum hydrocarbons were primarily found at 100-300 cm depth in Blind Pass cores. Above-detection level petroleum hydrocarbons were generally found in samples from cores in the center of the channel, near the edges of the shoal, and just outside of Blind Pass. A second mixture of hydrocarbons, primarily phthalates, ketones, and ether, was found at relatively shallow core depths (0-99 cm) in the Mid- and North End Channel cores. These suggest a separate source of contamination, possibly storm water runoff. The fuel fluorescence detector (FFD) probe was investigated for its ability to detect petroleum hydrocarbons in marine sediments. When analyzed with the FFD, all sediments from the cores produced peaks of fluorescence, but none above the background levels of Blind Pass native sediments. All but two samples analyzed by GC/FID were below the detection limits (100 ppm) of the FFD. These samples were found in dark-colored sediments. The combination of the detection limits of the instrument, sediment color, and the degraded nature of the heavier weight petroleum hydrocarbons may have resulted in fluorescence outputs below background levels. These studies demonstrate that the distribution of petroleum hydrocarbons within Blind Pass sediments is generally low and patchy. However, 25% of the cores exhibited levels above detection using GC/FID/MS. These cores could be subjected to individual speciation studies which indicate generally below TEL levels and an association of some, but not all, with the 1993 oil spill in Blind Pass. Appendix A provides photographs and tables for sediment subsamples which exhibited total petroleum hydrocarbon concentrations above detection limits, while Appendix B presents the results from fuel fluorescence detector probe analyses. A discussion of the results of the study in relation to sediment quality guidelines and soil cleanup target level guidance documents is included as Appendix C. Some preliminary results using the above techniques on core samples from the nearby John’s Pass are presented in Appendix D

    Shigella IpaB and IpaD displayed on L. lactis bacterium-like particles induce protective immunity in adult and infant mice

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    Shigella spp. are among the enteric pathogens with the highest attributable incidence of moderate-to-severe diarrhea in children under 5 years of age living in endemic areas. There are no vaccines available to prevent this disease. In this work, we investigated a new Shigella vaccine concept consisting of non-living, self-adjuvanted, Lactococcus lactis bacterium-like particles (BLP) displaying Shigella invasion plasmid antigen (Ipa) B and IpaD and examined its immunogenicity and protective efficacy in adult and newborn/infant mice immunized via the nasal route. Unique advantages of this approach include the potential for broad protection due to the highly conserved structure of the Ipas and the safety and practicality of a probiotic-based mucosal/adjuvant delivery platform. Immunization of adult mice with BLP-IpaB and BLP-IpaD (BLP-IpaB/D) induced high levels of Ipa-specific serum IgG and stool IgA in a dose-dependent manner. Immune responses and protection were enhanced by BLP delivery. Vaccine-induced serum antibodies exhibited opsonophagocytic and cytotoxic neutralizing activity, and IpaB/D IgG titers correlated with increased survival post-challenge. Ipa-specific antibody secreting cells were detected in nasal tissue and lungs, as well as IgG in bronchoalveolar lavage. Bone marrow cells produced IpaB/D-specific antibodies and contributed to protection after adoptive transfer. The BLP-IpaB/D vaccine conferred 90% and 80% protection against S. flexneri and S. sonnei, respectively. Mice immunized with BLP-IpaB/D as newborns also developed IpaB and IpaD serum antibodies; 90% were protected against S. flexneri and 44% against S. sonnei. The BLP-IpaB/D vaccine is a promising candidate for safe, practical and potentially effective immunization of children against shigellosis

    Boynton-Delray Coastal Water Quality Monitoring Program

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    This report discusses a sequence of six cruises in the vicinity of the Boynton-Delray (South Central) treated-wastewater plant outfall plume (26°27\u2743 N, 80°2\u2732 W), the Boynton Inlet (26°32\u2743 N, 80°2\u2730 W), and the Lake Worth Lagoon, Palm Beach County, Florida. The sampling cruises took place on June 5-6, 2007; August 28-29, 2007; October 18-19, 2007; February 14 and 18, 2008; May 19-20, 2008; and July 11-13, 2008. Water was sampled at 18 locations at the surface, middle, and near the seafloor (where there was sufficient depth) for a total of 45 samples; these samples were analyzed for a variety of nutrients and related parameters. The water sampling unit contained a conductivity-temperature-depth (CTD) instrument from which data were obtained at each sampling site. Synchronal ocean current data were measured by a nearby acoustic Doppler current profiler (ADCP) instrument. The inlet measurements were consistently lower in salinity and more acidic (lower in pH) than the coastal ocean and were warmer during the May and, especially, during the February cruises. For most analytes, viz., nitrite+nitrate (N+N), total suspended solids (TSS), chlorophyll-a, silica (Si), and total dissolved nitrogen (TDN), the lagoon concentrations were significantly higher than the coastal ocean; the inlet concentrations appeared to be consistent with lagoon water with partial mixing with the coastal ocean, as expected. Estimates of the nutrient flux to the coastal ocean were computed: approximately 1,500 kg of dissolved nitrogen (N), 2,350 kg of silicate (Si), 33 kg of orthophosphate (P), and 59 kg of ammonium (NH4) per day were delivered to the coastal ocean through the inlet. The outfall boil at South Central outfall (the smallest in volume of the six outfalls in southeast Florida) is only visible under ideal conditions. In the six cruises described in this document, the outfall boil could be found in only one cruise (August 28-29, 2007). Elevated concentrations of nutrients (N+N, P, Si, and P) at the outfall vicinity were measured, and these concentrations decreased rapidly away from the outfall for most analytes, to become undistinguished from the background within 3 km or less. Not finding the boil, however, in five of six cruises meant that the waters with the highest concentrations were probably missed. When the boil was sampled in August 2007, N+N, P, and total dissolved phosphorus (TDP) concentrations at the boil were roughly the same as from the inlet. For other analytes (chlorophyll-a, TSS, Si, and dissolved organic carbon [DOC]), the concentrations at or near the outfall were significantly less than those from the lagoon and inlet on most of the cruises. The coastal ocean appeared to be significantly impacted by the Boynton Inlet and less so from the inlet. A suggestion of a source to the south was seen in some analytes. Measurements from the Gulf Stream Reef area were the lowest in the study, and may provide “background” concentrations for this region. As expected, the coastal ocean was warmer and more stratified in the summer compared to the winter, e.g., whereas no thermocline was noted in the CTD data from February 2007, a strong thermocline was observed in most casts during July 2008. In certain cases (e.g., N+N in June 2007, pH in July 2008), an increase in the concentration (decrease for pH) from north to south implied a source from the south, e.g., the Boca Raton Inlet or Boca Raton outfall

    Malaria vaccine efficacy: the difficulty of detecting and diagnosing malaria

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    New sources of funding have revitalized efforts to control malaria. An effective vaccine would be a tremendous asset in the fight against this devastating disease and increasing financial and scientific resources are being invested to develop one. A few candidates have been tested in Phase I and II clinical trials, and several others are poised to begin trials soon. Some studies have been promising, and others disappointing. It is difficult to compare the results of these clinical trials; even independent trials of the same vaccine give highly discrepant results. One major obstacle in evaluating malaria vaccines is the difficulty of diagnosing clinical malaria. This analysis evaluates the impact of diagnostic error, particularly that introduced by microscopy, on the outcome of efficacy trials of malaria vaccines and make recommendations for improving future trials
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