36,342 research outputs found
Barriers to the utilization of synthetic fuels for transportation
The principal types of engines for transportation uses are reviewed and the specifications for conventional fuels are compared with specifications for synthetic fuels. Synfuel processes nearing the commercialization phase are reviewed. The barriers to using synfuels can be classified into four groups: technical, such as the uncertainty that a new engine design can satisfy the desired performance criteria; environmental, such as the risk that the engine emissions cannot meet the applicable environmental standards; economic, including the cost of using a synfuel relative to conventional transportation fuels; and market, involving market penetration by offering new engines, establishing new distribution systems and/or changing user expectations
General aviation approach and landing practices
The characteristics of air traffic patterns at uncontrolled airports and techniques used by a group of general aviation pilots in landing light airplanes are documented. The results of some 1,600 radar tracks taken at four uncontrolled airports and some 600 landings made by 22 pilots in two, four place, single engine light airplanes show that the uncontrolled traffic pattern is highly variable. The altitudes, distances, and piloting procedures utilized may affect the ability for pilots to see-and-avoid in this environment. Most landing approaches were conducted at an airspeed above recommended, resulting in significant floating during flare and touchdowns that were relatively flat and often nose-low
Instabilities leading to vortex lattice formation in rotating Bose-Einstein condensates
We present a comprehensive theoretical study of vortex lattice formation in
atomic Bose-Einstein condensates confined by a rotating elliptical trap. We
consider rotating solutions of the classical hydrodynamic equations, their
response to perturbations, as well as time-dependent simulations. We
discriminate three distinct, experimentally testable, regimes of instability:
{\em ripple}, {\em interbranch}, and {\em catastrophic}. Under
symmetry-breaking perturbations these instabilities lead to lattice formation
even at zero temperature. While our results are consistent with previous
theoretical and experimental results, they shed new light on lattice formation.Comment: 5 pages, 2 figure
Common bearing material has highest fatigue life at moderate temperature
AISI 52100, a high carbon chromium steel, has the longest fatigue life of eight bearing materials tested. Fatigue lives of the other materials ranged from 7 to 78 percent of the fatigue life of AISI 52100 at a temperature of 340 K (150 F)
Flexural fatigue of hollow rolling elements
Hollow cylindrical bars were tested in the rolling-contact fatigue tester to determine the effects of material and outside diameter to inside diameter (OD/ID) ratios of 2.0, 1.6, 1.4, and 1.2 on fatigue failure mode and subsequent failure propagation. The range of applied loads with these OD/ID ratios resulted in maximum tangential tensile stresses ranging from 165 to 655 megapascals (24,000 to 95,000 psi) at the bore surface. Flexural failures of the hollow test bars occurred when this bore stress was 490 megapascals (71,000 psi) or greater with AISI 52100 hollow bars and 338 megapascals (49,000 psi) or greater with AISI M-50 hollow bars. Good correlation was obtained in relating the failures of these hollow bars with flexural failures of drilled balls from previously published full scale bearing tests
Emergent behaviour in a chlorophenol-mineralising three-tiered microbial `food web'
Anaerobic digestion enables the water industry to treat wastewater as a
resource for generating energy and recovering valuable by-products. The
complexity of the anaerobic digestion process has motivated the development of
complex models. However, this complexity makes it intractable to pin-point
stability and emergent behaviour. Here, the widely used Anaerobic Digestion
Model No. 1 (ADM1) has been reduced to its very backbone, a syntrophic
two-tiered microbial food chain and a slightly more complex three-tiered
microbial food web, with their stability analysed as function of the inflowing
substrate concentration and dilution rate. Parameterised for phenol and
chlorophenol degradation, steady-states were always stable and non-oscillatory.
Low input concentrations of chlorophenol were sufficient to maintain
chlorophenol- and phenol-degrading populations but resulted in poor conversion
and a hydrogen flux that was too low to sustain hydrogenotrophic methanogens.
The addition of hydrogen and phenol boosted the populations of all three
organisms, resulting in the counterintuitive phenomena that (i) the phenol
degraders were stimulated by adding hydrogen, even though hydrogen inhibits
phenol degradation, and (ii) the dechlorinators indirectly benefitted from
measures that stimulated their hydrogenotrophic competitors; both phenomena
hint at emergent behaviour.Comment: 19 pages, 8 figure
Development of a high temperature battery
High energy density battery for use on planet Venu
- …