2,334 research outputs found
Methane Abundance Variations toward the Massive Protostar NGC 7538 : IRS9
Absorption and emission lines originating from the nu3 C-H stretching
manifold of gas phase CH4 were discovered in the high resolution (R=25,000)
infrared L band spectrum along the line of sight toward NGC 7538 : IRS9. These
observations provide a diagnostic of the complex dynamics and chemistry in a
massive star forming region. The line shapes resemble P Cygni profiles with the
absorption and emission components shifted by ~7 km/s with respect to the
systemic velocity. Similar velocity components were observed in CO at 4.7 um,
but in contrast to CH4, the CO shows deep absorption due to a high velocity
outflow as well as absorption at the systemic velocity due to the cold outer
envelope. It is concluded that the gas phase CH4 abundance varies by an order
of magnitude in this line of sight: it is low in the envelope and the outflow
(X[CH4]<0.4e-6), and at least a factor of 10 larger in the central core. The
discovery of solid CH4 in independent ground and space based data sets shows
that methane is nearly entirely frozen onto grains in the envelope. It thus
appears that CH4 is formed by grain surface reactions, evaporates into the gas
phase in the warm inner regions of protostellar cores and is efficiently
destroyed in shocks related to outflows.Comment: Scheduled for publication in ApJ 615, 01 Nov. 2004. 11 page
Analysis and computer programs to calculate acoustic wave properties of baffled chambers
Analytical methods and four computer programs have been developed for calculating wave motion in closed, baffled chambers with rigid and non-rigid boundaries. Application of these methods to design of injector-face baffles in liquid propellant engines will provide significant insight into effects of baffles on combustion stability
An engineering design study and test program for the Paravulcoon Recovery System Final report, 31 Jul. 1963 - 31 Aug. 1964
High-temperature earth-storable propellant acoustic cavity technology
Design criteria, methods and data, were developed to permit effective design of acoustic cavities for use in regeneratively cooled OME-type engines. This information was developed experimentally from two series of motor firings with high-temperature fuel during which the engine stability was evaluated under various conditions and with various cavity configurations. Supplementary analyses and acoustic model testing were used to aid cavity design and interpretation of results. Results from this program clearly indicate that dynamic stability in regeneratively cooled OME-type engines can be ensured through the use of acoustic cavities. Moreover, multiple modes of instability were successfully suppressed with the cavity
Analysis of the effects of baffles on combustion instability
An analytical model has been developed for predicting the effects of baffles on combustion instability. This model has been developed by coupling an acoustic analysis of the wave motion within baffled chambers with a model for the oscillatory combustion response of a propellant droplet developed by Heidmann. A computer program was developed for numerical solution of the resultant coupled equations. Diagnostic calculations were made to determine the reasons for the improper prediction. These calculations showed that the chosen method of representing the combustion response was a very poor approximation. At the end of the program, attempts were made to minimize this effect but the model still improperly predicts the stability trends. Therefore, it is recommended that additional analysis be done with an improved approximation
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