337 research outputs found
Combustion/particle sizing experiments at the Naval Postgraduate School Combustion Research Laboratory
Particle behavior in combustion processes is an active research area at NPS. Currently, four research efforts are being conducted: (1) There is a long standing need to better understand the soot production and combustion processes in gas turbine combustors, both from a concern for improved engine life and to minimize exhaust particulates. Soot emissions are strongly effected by fuel composition and additives; (2) A more recent need for particle sizing/behavior measurements is in the combustor of a solid fuel ramjet which uses a metallized fuel. High speed motion pictures are being used to study rather large burning particles; (3) In solid propellant rocket motors, metals are used to improve specific impulse and/or to provide damping for combustion pressure oscillations. Particle sizing experiments are being conducted using diode arrays to measure the light intensity as a function of scattering angle; (4) Once a good quality hologram is attained, a need exists for obtaining the particle distributions from hologram in a short period of time. A Quantimet 720 Image Analyzer is being used to reconstruct images
Particle sizing in rocket motor studies utilizing hologram image processing
A technique of obtaining particle size information from holograms of combustion products is described. The holograms are obtained with a pulsed ruby laser through windows in a combustion chamber. The reconstruction is done with a krypton laser with the real image being viewed through a microscope. The particle size information is measured with a Quantimet 720 image processing system which can discriminate various features and perform measurements of the portions of interest in the image. Various problems that arise in the technique are discussed, especially those that are a consequence of the speckle due to the diffuse illumination used in the recording process
A Validation of Mathematical Models for Turbojet Test Cells
Prepared for: Naval Air Propulsion Center Trenton, NJ 09628Previously developed one-dimensional and two-dimensional computer models fox predicting turbojet test cell performance were compared with data obtained from a subscale test cell for the purpose of model validation. Comparisons were made for a variety of configurations and flow rates. A modified one-dimensional mode was found to reasonably predict the variation of augmentation ratio with engine flow; rate, although predicted magnitudes were consistently too small. The model incorporated excess we drag losses and an inaccurate jet spreading para-meter for large engine-augmentor spacings. The two-dimensional model accurately predicted experimental. velocity profiles, but over-predicted pressure variations, except for low engine exit Mach numbers.Naval Air Propulsion Center, Trenton, NJApproved for public release; distribution is unlimited
Uncovering the Active Galactic Nuclei in Low-Ionization Nuclear Emission-Line Regions with Spitzer
The impact of active galactic nuclei on low-ionization nuclear emission-line
regions (LINERs) remains a vigorous field of study. We present preliminary
results from a study of the mid-infrared atomic emission lines of LINERs with
the Spitzer Space Telescope. We assess the ubiquity and properties of AGN in
LINERs using this data. We discuss what powers the mid-infrared emission lines
and conclude that the answer depends unsurprisingly on the emission line
ionization state and, more interestingly, on the infrared luminosity.Comment: To appear in ASP Vol. 373, The Central Engine of Active Galactic
Nuclei, ed. Luis C. Ho and Jian-Min Wang; 4 pages, 2 figure
Osteoporotic Vertebral Fractures: Vertebroplasty and Kyphoplasty
No abstract is available
The BeppoSAX X-ray view of reflection-dominated Seyfert Galaxies
We present new results from BeppoSAX observations of reflection-dominated
Seyfert galaxies, and namely: 1) the Compton-thick Seyfert 2s NGC1068 and
Circinus Galaxy; 2) the Seyfert 1 NGC4051, whose nucleus was observed on May
1998 to have switched off, leaving only a residual reflection component as an
echo of its past activity. Our main focus in this paper is on the soft X-ray
continuum properties and on the X-ray line spectroscopy.Comment: 6 Latex pages, 5 figures, Accepted for publication in Advances in
Space Research, Proceedings of 32nd Sci. Ass. of COSPA
Spitzer Space Telescope Measurements of Dust Reverberation Lags in the Seyfert 1 Galaxy NGC 6418
We present results from a fifteen-month campaign of high-cadence (~ 3 days)
mid-infrared Spitzer and optical (B and V ) monitoring of the Seyfert 1 galaxy
NGC 6418, with the objective of determining the characteristic size of the
dusty torus in this active galactic nucleus (AGN). We find that the 3.6 m
and 4.5 m flux variations lag behind those of the optical continuum by
days and days, respectively. We
report a cross-correlation time lag between the 4.5 m and 3.6 m flux
of days. The lags indicate that the dust emitting at 3.6
m and 4.5 m is located at a distance of approximately 1 light-month
(~ 0.03 pc) from the source of the AGN UV-optical continuum. The reverberation
radii are consistent with the inferred lower limit to the sublimation radius
for pure graphite grains at 1800 K, but smaller by a factor of ~ 2 than the
corresponding lower limit for silicate grains; this is similar to what has been
found for near-infrared (K-band) lags in other AGN. The 3.6 and 4.5 m
reverberation radii fall above the K-band
size-luminosity relationship by factors and ,
respectively, while the 4.5 m reverberation radius is only 27% larger than
the 3.6 m radius. This is broadly consistent with clumpy torus models, in
which individual optically thick clouds emit strongly over a broad wavelength
range.Comment: 13 pages, 9 figure
Supermassive Black Holes in Active Galactic Nuclei. II. Calibration of the M-sigma Relationship for AGNs
We calibrate reverberation-based black hole masses in active galactic nuclei
(AGNs) by using the correlation between black hole mass, M, and bulge/spheroid
stellar velocity dispersion, sigma. We use new measurements of sigma for 6 AGNs
and published velocity dispersions for 10 others, in conjunction with improved
reverberation mapping results, to determine the scaling factor required to
bring reverberation-based black hole masses into agreement with the quiescent
galaxy M-sigma relationship. The scatter in the AGN black hole masses is found
to be less than a factor of 3. The current observational uncertainties preclude
use of the scaling factor to discriminate between broad-line region models.Comment: 16 pages, including 3 figures. Accepted for publication in Ap
Model theory of operator algebras III: Elementary equivalence and II_1 factors
We use continuous model theory to obtain several results concerning
isomorphisms and embeddings between II_1 factors and their ultrapowers. Among
other things, we show that for any II_1 factor M, there are continuum many
nonisomorphic separable II_1 factors that have an ultrapower isomorphic to an
ultrapower of M. We also give a poor man's resolution of the Connes Embedding
Problem: there exists a separable II_1 factor such that all II_1 factors embed
into one of its ultrapowers.Comment: 16 page
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