52,585 research outputs found
Visual attitude orientation and alignment system
Active vehicle optical alignment aid and a passive vehicle three-dimensional alignment target ensure proper orientation and alignment plus control of the closure range and rate between two bodies, one in controlled motion and one at rest
Hypersonic cruise aircraft propulsion integration study, volume 1
A hypersonic cruise transport conceptual design is described. The integration of the subsonic, supersonic, and hypersonic propulsion systems with the aerodynamic design of the airframe is emphasized. An evaluation of various configurations of aircraft and propulsion integration concepts, and selection and refinement of a final design are given. This configuration was used as a baseline to compare two propulsion concepts - one using a fixed geometry dual combustion mode scramjet and the other a variable geometry ramjet engine. Both concepts used turbojet engines for takeoff, landing and acceleration to supersonic speed
Large negotiable certificates of deposit
Certificates of deposit ; Money market
The effect of extreme temperatures on the elastic properties and fracture behavior of graphite/polyimide composites
The influence of elevated and cryogenic temperatures on the elastic moduli and fracture strengths of several C6000/PMR-15 and C6000/NR-15082 laminates was measured. Tests were conducted at -157 C, 24 C, and 316 C (-250 F, 75 F, and 600 F). Both notched and unnotched laminates were tested. The average stress failure criterion was used to predict the fracture strength of quasi-isotropic notched laminates
Study of active cooling for supersonic transports
The potential benefits of using the fuel heat sink of hydrogen fueled supersonic transports for cooling large portions of the aircraft wing and fuselage are examined. The heat transfer would be accomplished by using an intermediate fluid such as an ethylene glycol-water solution. Some of the advantages of the system are: (1) reduced costs by using aluminum in place of titanium, (2) reduced cabin heat loads, and (3) more favorable environmental conditions for the aircraft systems. A liquid hydrogen fueled, Mach 2.7 supersonic transport aircraft design was used for the reference uncooled vehicle. The cooled aircraft designs were analyzed to determine their heat sink capability, the extent and location of feasible cooled surfaces, and the coolant passage size and spacing
Minimum energy, liquid hydrogen supersonic cruise vehicle study
The potential was examined of hydrogen-fueled supersonic vehicles designed for cruise at Mach 2.7 and at Mach 2.2. The aerodynamic, weight, and propulsion characteristics of a previously established design of a LH2 fueled, Mach 2.7 supersonic cruise vehicle (SCV) were critically reviewed and updated. The design of a Mach 2.2 SCV was established on a corresponding basis. These baseline designs were then studied to determine the potential of minimizing energy expenditure in performing their design mission, and to explore the effect of fuel price and noise restriction on their design and operating performance. The baseline designs of LH2 fueled aircraft were than compared with equivalent designs of jet A (conventional hydrocarbon) fueled SCV's. Use of liquid hydrogen for fuel for the subject aircraft provides significant advantages in performance, cost, noise, pollution, sonic boom, and energy utilization
Study of LH2 fueled subsonic passenger transport aircraft
The potential of using liquid hydrogen as fuel in subsonic transport aircraft was investigated to explore an expanded matrix of passenger aircraft sizes. Aircraft capable of carrying 130 passengers 2,780 km (1500 n.mi.); 200 passengers 5,560 km (3000 n.mi.); and 400 passengers on a 9,265 km (5000 n.mi.) radius mission, were designed parametrically. Both liquid hydrogen and conventionally fueled versions were generated for each payload/range in order that comparisons could be made. Aircraft in each mission category were compared on the basis of weight, size, cost, energy utilization, and noise
Aquaculture in Jamaica
Jamaica, with its overfish marine resources, has become a major tilapia producer in Latin America led by a small number of large farms practicing tilapia culture with considerable commercial success. Across the country, however, aquaculture is typically practiced by a large number of small-scale fish farmers who own less than 1.0 ha of land. Production is constrained by lack of credit, finite land space and suitable soil type, but larger existing aquaculturists are expanding further for overseas markets. Inspired by pioneering tilapia fish culture demonstration projects funded by the USAID and the goverment of Jamaica, fish culture production rose from a few hundred kg of Oreochromis niloticus in 1977, to about 5000 t of processed fish mainly red hybrid tilapia, in 2000. Most of this quantity was exported to Europe and North America
Uniform Silicon Isotope Ratios Across the Milky Way Galaxy
We report the relative abundances of the three stable isotopes of silicon,
Si, Si and Si, across the Galaxy using the transition of silicon monoxide. The chosen sources represent a range in
Galactocentric radii () from 0 to 9.8 kpc. The high spectral
resolution and sensitivity afforded by the GBT permit isotope ratios to be
corrected for optical depths. The optical-depth-corrected data indicate that
the secondary-to-primary silicon isotope ratios
and vary much less than predicted on the basis of
other stable isotope ratio gradients across the Galaxy. Indeed, there is no
detectable variation in Si isotope ratios with . This lack of an
isotope ratio gradient stands in stark contrast to the monotonically decreasing
trend with exhibited by published secondary-to-primary oxygen
isotope ratios. These results, when considered in the context of the
expectations for chemical evolution, suggest that the reported oxygen isotope
ratio trends, and perhaps that for carbon as well, require further
investigation. The methods developed in this study for SiO isotopologue ratio
measurements are equally applicable to Galactic oxygen, carbon and nitrogen
isotope ratio measurements, and should prove useful for future observations of
these isotope systems.Comment: 18 pages, 12 figures, 2 tables. Published in The Astrophysical
Journal, Volume 839, Issue
- …