14,030 research outputs found
Application of a cost/performance measurement system on a research aircraft project
The fundamentals of the cost/performance management system used in the procurement of two tilt rotor aircraft for a joint NASA/Army research project are discussed. The contractor's reporting system and the GPO's analyses are examined. The use of this type of reporting system is assessed. Recommendations concerning the use of like systems on future projects are included
The inverse problem for rough controlled differential equations
We provide a necessary and sufficient condition for a rough control driving a
differential equation to be reconstructable, to some order, from observing the
resulting controlled evolution. Physical examples and applications in
stochastic filtering and statistics demonstrate the practical relevance of our
result.Comment: added section on rough path theor
Transversity Distribution Does Not Contribute to Hard Exclusive Electroproduction of Mesons
We show that in hard exclusive electroproduction, ep-->eVp, the leading-twist
hard-scattering coefficient for the production of a transversely polarized
vector meson V vanishes to all orders of perturbation theory. This implies that
this process cannot be used to measure the skewed transversity distribution of
quarks in a hadron. In contrast, a recent calculation obtained a non-zero value
at NLO. We show that this calculation is incorrect because it failed to include
the necessary collinear subtractions. Our method of proof also applies to other
processes whose hard-scattering coefficients are constrained by chirality and
helicity conservation, and thus validates helicity selection rules based on
these symmetries.Comment: 5 pages, 3 figures, ReVTe
Gaseous exhaust emissions from a JT8D-109 turbofan engine at simulated cruise flight conditions
Gaseous emissions from a JT8D-109 turbofan engine were measured in an altitude facility at four simulated cruise flight conditions: Mach 0.8 at altitudes of 9.1, 10, 7, and 12.2 km and Mach 0.9 at 10.7 km. Engine inlet air temperature was held constant at 283 K for all tests. Emissions measurements were made at nominally 6 cm intervals across the horizontal diameter of the engine exhaust nozzle with a single-point traversing gas sample probe. Measured emissions of decreased with increasing altitude from an emission index of 10.4 to one of 8.3, while carbon monoxide increased with increasing altitude from an emission index of 1.6 to one of 4.4. Unburned hydrocarbon emissions were essentially negligible for all flight conditions. Since the engine inlet air temperatures were not correctly simulated, the NOx emission indices were corrected to true altitude conditions by using correlating parameters for changes in combustor inlet temperature, pressure, and temperature rise. The correction was small at the lowest altitude. At the 10.7 and 12.2 km, Mach 0.8 test conditions the correction decreased the measured values by 1 emission index
Measurement of gaseous emissions from a turbofan engine at simulated altitude conditions
Gaseous emission from a TFE 731-2 turbofan engine were measured over a range of fuel-air ratios from idle to full power at simulated from near sea level to 13,200 m. Carbon monoxide and unburned hydrocarbon emissions were highest at idle and lowest at high power settings; oxides of nitrogen exhibited the reverse trend. Carbon monoxide and unburned hydrocarbon levels decreased with increasing altitude. Oxides of nitrogen emissions were successfully correlated by a parametric group of combustor operating variables
Swirl-can combustor performance to near-stoichiometric fuel-air ratio
Emissions and performance characteristics were determined for full-annulus swirl-can modular combustors operated to near stoichiometric fuel air ratios. The purposes of the tests were to obtain stoichiometric data at inlet air temperatures up to 894 K and to determine the effect of module number by investigating 120 and 72 module swirl-can combustors. The maximum average exit temperature obtained with the 120-module swirl-can combustor was 2465 K with a combustion efficiency of 95 percent at an inlet-air temperature of 894 K. The 72-module swirl-can combustor reached a maximum average exit temperature of 2306 K with a combustion efficiency of 92 percent at an inlet air temperature of 894 K. At a constant inlet air temperature, maximum oxides of nitrogen emission index values occurred at a fuel-air ratio of 0.037 for the 72-module design and 0.044 for the 120-module design. The combustor average exit temperature and combustion efficiency were calculated from emissions measurements. The measured emissions included carbon monoxide, unburned hydrocarbons, oxides of nitrogen, and smoke
Charge Density of the Neutron
A model-independent analysis of the infinite-momentum-frame charge density of
partons in the transverse plane is presented for the nucleon. We find that the
neutron parton charge density is negative at the center, so that the square of
the transverse charge radius is positive, in contrast with many expectations.
Additionally, the proton's central u quark charge density is larger than that
of the d quark by about 70 %. The proton (neutron) charge density has a long
range positively (negatively) charged component.Comment: 7 pages, three figures The replacement mainly concerns correcting an
error made in computing the proton up and down quark densities from the
correctly computed proton and neutron charge densities. The proton central u
quark density is now larger than that of the d quar
Self-affine surface morphology of plastically deformed metals
We analyze the surface morphology of metals after plastic deformation over a
range of scales from 10 nm to 2 mm, using a combination of atomic force
microscopy and scanning white-light interferometry. We demonstrate that an
initially smooth surface during deformation develops self-affine roughness over
almost four orders of magnitude in scale. The Hurst exponent of
one-dimensional surface profiles is initially found to decrease with increasing
strain and then stabilizes at . By analyzing their statistical
properties we show that the one-dimensional surface profiles can be
mathematically modelled as graphs of a fractional Brownian motion. Our findings
can be understood in terms of a fractal distribution of plastic strain within
the deformed samples
Stratospheric cruise emission reduction program
A recently implemented NASA effort specifically aimed at reducing cruise oxides of nitrogen from high-altitude aircraft is discussed. The desired emission levels and the combustor technology required to achieve them are discussed. A brief overview of the SCERP operating plan is given. Lean premixed-prevaporized combustion and some of the potential difficulties that are associated with applying this technique to gas turbine combustors are examined. Base technology was developed in several key areas. These fundamental studies are viewed as a requirement for successful implementation of the lean premixed combustion technique
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