Fabrication of the V-22 composite AFT fuselage using automated fiber placement

Boeing Helicopters and its subcontractors are working together under an Air Force Wright Research and Development Center (WRDC)-Manufacturing-Technology Large-Composite Primary Structure Fuselage program to develop and demonstrate new manufacturing techniques for producing composite fuselage skin and frame structures. Three sets of aft fuselage skins and frames have been fabricated and assembled, and substantial reductions in fabrication and assembly costs demonstrated

Effects of Tidal Stage and Sun Angles on Intertidal Benthic Microalgal Productivity

Motile benthic diatoms exhibit rhythmic vertical migrations that are influenced by tidal and light cycles. As a consequence of these periodic migrations, corresponding periodicities in benthic microalgal production should occur. Using oxygen microelectrodes, hourly measurements of microalgal production were obtained from subaerially exposed cores collected from low-intertidal muddy sediments in North Inlet estuary, South Carolina, USA Microalgal productivity at low tide was twice that at high tide (mean difference 52 %) and was significantly correlated with diurnal and tidal periodicities (r2 = 0.41; p \u3c 0.0001). Production values ranged from 28.0 to 460.5 µmol O2 mg chl a-1 h-1 and maximum rates were achieved during mid-afternoon low tides. A curvilinear regression equation was constructed to simulate daily and monthly benthic microalgal production based on tidal and light cycles. Comparisons between predictions of the curvilinear equation and published data sets showed a reasonable agreement (r2 = 0.77), suggesting similar phenomena in other estuaries. Current benthic microalgal production models do not account for hourly variability in productivity, leading to potentially large errors when measurements are extrapolated over monthly and annual time scales. Although other physiological and abiotic factors also influence benthic microalgal productivity, much of the short-term variability in production rates may be simply attributed to migratory rhythms within estuarine sediments

Subscale, hydrogen-burning, airframe-integrated-scramjet: Experimental and theoretical evaluation of a water cooled strut airframe-integrated-scramjet: Experimental leading edge

A water-cooled leading-edge design for an engine/airframe integrated scramjet model strut leading edge was evaluated. The cooling design employs a copper cooling tube brazed just downstream of the leading edge of a wedge-shaped strut which is constructed of oxygen-free copper. The survival of the strut leading edge during a series of tests at stagnation point heating rates confirms the practicality of the cooling design. A finite difference thermal model of the strut was also proven valid by the reasonable agreement of calculated and measured values of surface temperature and cooling-water heat transfer

Thermal design and analysis of a hydrogen-burning wind tunnel model of an airframe-integrated scramjet

An aerodynamic model of a hydrogen burning, airframe integrated scramjet engine has been designed, fabricated, and instrumented. This model is to be tested in an electric arc heated wind tunnel at an altitude of 35.39 km (116,094 ft.) but with an inlet Mach number of 6 simulating precompression on an aircraft undersurface. The scramjet model is constructed from oxygen free, high conductivity copper and is a heat sink design except for water cooling in some critical locations. The model is instrumented for pressure, surface temperature, heat transfer rate, and thrust measurements. Calculated flow properties, heat transfer rates, and surface temperature distributions along the various engine components are included for the conditions stated above. For some components, estimates of thermal strain are presented which indicate significant reductions in plastic strain by selective cooling of the model. These results show that the 100 thermal cycle life of the engine was met with minimum distortion while staying within the 2669 N (600 lbf) engine weight limitation and while cooling the engine only in critical locations

Impacts of Seasonality and Nutrients on Microbial Mat Community Structure and Function

To understand the mechanisms responsible for seasonal fluctuations in growth and N2 fixation in intertidal microbial mat communities, we quantified seasonal changes in mat community composition, related these changes to diel and seasonal N2 fixation rates, and evaluated community responses (growth, N2fixation, composition) to long-term (22 d) nutrient addition bioassays. A temperate intertidal cyanobacterial mat community, located in coastal North Carolina, USA, was sampled at monthly intervals for 1 yr (1993-94) to determine changes in community composition. The abundances of major phototrophic groups were quantified based on the relative concentrations of taxaspecific photopigments (chlorophylls and carotenoids). The most abundant phototrophs were cyanobacteria, diatoms, and photosynthetic bacteria. Mat blomass and community composition underwent marked changes on both monthly and seasonal scales and corresponded with seasonal shifts in the diel patterns of N2 fixation. Diatom biomass increased during periods of low N2 fixation. Nutrient (nitrate and phosphate) addition bioassays indicated that both cyanobacterial and diatom growth were N limited. Cyanobacteria were able to circumvent N limitation by N2 fixation. The addition of high concentrations of N (100µM NaNO3) in combination with P (100 µM NaH2P04) resulted in an increase (163%) in the relative abundance of diatoms The addition of P alone more than doubled N2 fixation rates and cyanobacterial abundance increased (+34%) relative to diatoms. However, N and NP additions significantly lowered (by more than 75%) N2 fixation rates. Here we show that manipulative experiments, together with quantitative assessments of community composition based on chemotaxonomic pigments, can provide useful insights into the mechanisms that relate mat community structure and function to environmental constraints, including nutrient limitation and seasonal climatic changes

Fish Kills and Bottom-Water Hypoxia in the Neuse River and Estuary: Reply to Burkholder et al.

Burkholder et al. (1999) authored a comment in Manne Ecology Progress Series (MEPS) that selectively criticizes elements of our findings that appeared earlier in the same journal (Paerl et al. 1998). For the benefit of the readership of MEPS, it would have been useful to have had both their comment and our reply in the same volume. Unfortunately, we were not informed of their comment pnor to its publication

Ecosystem Responses to Internal and Watershed Organic Matter Loading: Consequences for Hypoxia in the Eutrophying Neuse River Estuary, North Carolina, USA

The contrasting impacts of externally supplied (runoff) and internally generated (nutrient stimulated phytoplankton blooms) organic matter on oxygen (02) depletion were examined and evaluated in the eutrophic, salinity-stratified Neuse River Estuary, North Carolina, USA. This nitrogen (N)- limited estuary is experiencing increasing anthropogenic N loading from expanding urban, agricultural and industrial development in its watershed. Resultant algal blooms, which provided organic matter loads capable of causing extensive low 02 (hypoxic) and depleted 02 (anoxic) conditions, have induced widespread mortality of resident fin- and shellfish. Phytoplankton blooms followed periods of elevated N loading, except during extremely high runoff periods (e.g. hurricanes), when high rates of flushing and reduced water residence times did not allow sufficient time for bloom development. During these periods, hypoxia and anoxia were dominated by watershed-derived organic matter loading. Externally vs internally generated organic matter loading scenarios were examined in sequential years (1994 to 1996) to compare the differential impacts of an average discharge year (l0 yr mean hydrological conditions) (1994), N-stimulated summer algal blooms [1995), and a major hurricane (Fran; September 1996). The responses of primary production, hypoxia, and anoxia to these hydrologically contrasting years and resultant organic matter loadings help distinguish watershed from internal forcing of 02 dynamics and fish kills