145,550 research outputs found
Compatibility analysis for the 1535-1660 MHz band, part 1 Final report, Jan. - Sep. 1969
Electromagnetic compatibility and radio frequency interference of aircraft radio antenna
Color identification testing device
Testing device, which determines ability of a technician to identify color-coded electric wires, is superior to standard color blindness tests. It tests speed of wire selection, detects partial color blindness, allows rapid testing, and may be administered by a color blind person
A definitive heat of vaporization of silicon through benchmark ab initio calculations on SiF_4
In order to resolve a significant uncertainty in the heat of vaporization of
silicon -- a fundamental parameter in gas-phase thermochemistry -- [Si(g)] has been determined from a thermochemical cycle involving
the precisely known experimental heats of formation of SiF_4(g) and F(g) and a
benchmark calculation of the total atomization energy (TAE_0) of SiF_4 using
coupled-cluster methods. Basis sets up to on Si and
on F have been employed, and extrapolations for residual basis
set incompleteness applied. The contributions of inner-shell correlation (-0.08
kcal/mol), scalar relativistic effects (-1.88 kcal/mol), atomic spin-orbit
splitting (-1.97 kcal/mol), and anharmonicity in the zero-point energy (+0.04
kcal/mol) have all been explicitly accounted for. Our benchmark TAE_0=565.89
\pm 0.22 kcal/mol leads to [Si(g)]=107.15 \pm 0.38
kcal/mol ([Si(g)]=108.19 \pm 0.38 kcal/mol): between
the JANAF/CODATA value of 106.5 \pm 1.9 kcal/mol and the revised value proposed
by Grev and Schaefer [J. Chem. Phys. 97, 8389 (1992}], 108.1 \pm 0.5 kcal/mol.
The revision will be relevant for future computational studies on heats of
formation of silicon compounds.Comment: J. Phys. Chem. A, submitted Feb 1, 199
Constraints to the Masses of Brown Dwarf Candidates from the Lithium Test
We present intermediate dispersion (0.7-2.2 \AA ~pix) optical
spectroscopic observations aimed at applying the ``Lithium Test'' to a sample
of ten brown dwarf candidates located in the general field, two in young open
clusters, and two in close binaries. We find evidence for strong Li depletion
in all of them, and thus infer lower mass limits of 0.065~M, depending
only slightly (0.005~M) on the interior models. None of the field
brown dwarf candidates in our sample appears to be a very young (age
~10~yr) substellar object. For one of the faintest proper motion
Pleiades members known (V=20.7) the Li test implies a mass greater than
0.08~M, and therefore it is not a brown dwarf. From our spectra
we estimate spectral types for some objects and present measurements of Halpha
emission strengths and radial velocities. Finally, we compare the positions in
the H-R diagram of our sample of brown dwarf candidates with the theoretical
region where Li is expected to be preserved (Substellar Lithium Region). We
find that certain combinations of temperature calibrations and evolutionary
tracks are consistent with the constraints imposed by the observed Li depletion
in brown dwarf candidates, while others are not.Comment: 20 pp.; 4 figs, available under request; plain LaTeX, ApJ in press,
OACatania-94-00
B747/JT9D flight loads and their effect on engine running clearances and performance deterioration; BCAC NAIL/P and WA JT9D engine diagnostics programs
Flight loads on the 747 propulsion system and resulting JT9D blade to outer airseal running clearances during representative acceptance flight and revenue flight sequences were measured. The resulting rub induced clearance changes, and engine performance changes were then analyzed to validate and refine the JT9D-7A short term performance deterioration model
Expanded study of feasibility of measuring in-flight 747/JT9D loads, performance, clearance, and thermal data
The JT9D jet engine exhibits a TSFC loss of about 1 percent in the initial 50 flight cycles of a new engine. These early losses are caused by seal-wear induced opening of running clearances in the engine gas path. The causes of this seal wear have been identified as flight induced loads which deflect the engine cases and rotors, causing the rotating blades to rub against the seal surfaces, producing permanent clearance changes. The real level of flight loads encountered during airplane acceptance testing and revenue service and the engine's response in the dynamic flight environment were investigated. The feasibility of direct measurement of these flight loads and their effects by concurrent measurement of 747/JT9D propulsion system aerodynamic and inertia loads and the critical engine clearance and performance changes during 747 flight and ground operations was evaluated. A number of technical options were examined in relation to the total estimated program cost to facilitate selection of the most cost effective option. It is concluded that a flight test program meeting the overall objective of determining the levels of aerodynamic and inertia load levels to which the engine is exposed during the initial flight acceptance test and normal flight maneuvers is feasible and desirable. A specific recommended flight test program, based on the evaluation of cost effectiveness, is defined
The nature of operating flight loads and their effect on propulsion system structures
Past diagnostics studies revealed the primary causes of performance deterioration of high by-pass turbofan engines to be flight loads, erosion, and thermal distortion. The various types of airplane loads that are imposed on the engine throughout the lifetime of an airplane are examined. These include flight loads from gusts and maneuvers and ground loads from takeoff, landing, and taxi conditions. Clarification is made in definitions of the airframer's limit and ultimate design loads and the engine manufacturer's operating design loads. Finally, the influence of these loads on the propulsion system structures is discussed
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