5,524 research outputs found
Thermodynamic and transport properties of frozen and reacting pH2-oH2 mixtures
Application of experimental state data and spectroscopic term values shows that the thermodynamic and transport properties of reacting pH2-oH2 mixtures are considerably different than those of chemically frozen pH2 at temperatures below 300 R. Calculated H-S data also show that radiation-induced pH2-oH2 equilibration at constant enthalpy produces a temperature drop of at least 28 R, corresponding to an ideal shaft work loss of 15% or more for a turbine operating downstream from the point of conversion. Aside from differences in thermodynamic and transport properties, frozen pH2-oH2 mixtures may differ from pure pH2 on a purely hydrodynamical basis
INTERREGIONAL COMPETITION IN THE U.S. SWINE-PORK INDUSTRY: AN ANALYSIS OF OKLAHOMA'S AND THE SOUTHERN STATES' EXPANSION POTENTIAL
Community/Rural/Urban Development,
Radiometric responsivity determination for Feature Identification and Location Experiment (FILE) flown on space shuttle mission
A procedure was developed to obtain the radiometric (radiance) responsivity of the Feature Identification and Local Experiment (FILE) instrument in preparation for its flight on Space Shuttle Mission 41-G (November 1984). This instrument was designed to obtain Earth feature radiance data in spectral bands centered at 0.65 and 0.85 microns, along with corroborative color and color-infrared photographs, and to collect data to evaluate a technique for in-orbit autonomous classification of the Earth's primary features. The calibration process incorporated both solar radiance measurements and radiative transfer model predictions in estimating expected radiance inputs to the FILE on the Shuttle. The measured data are compared with the model predictions, and the differences observed are discussed. Application of the calibration procedure to the FILE over an 18-month period indicated a constant responsivity characteristic. This report documents the calibration procedure and the associated radiometric measurements and predictions that were part of the instrument preparation for flight
Hierarchical galaxy formation and substructure in the Galaxy's stellar halo
We develop an explicit model for the formation of the stellar halo from
tidally disrupted, accreted dwarf satellites in the cold dark matter (CDM)
framework, focusing on predictions testable with the Sloan Digital Sky Survey
(SDSS) and other wide-field surveys. Subhalo accretion and orbital evolution
are calculated using a semi-analytic approach within the Press-Schechter
formalism. Motivated by our previous work, we assume that low-mass subhalos (v
< 30 km/s) can form significant populations of stars only if they accreted a
substantial fraction of their mass before the epoch of reionization. With this
assumption, the model reproduces the observed velocity function of galactic
satellites in the Local Group, solving the ``dwarf satellite problem'' without
modifying the popular LCDM cosmology. The disrupted satellites yield a stellar
distribution with a total mass and radial density profile consistent with those
observed for the Milky Way stellar halo. Most significantly, the model predicts
the presence of many large-scale, coherent substructures in the outer halo.
These substructures are remnants of individual, tidally disrupted dwarf
satellite galaxies. Substructure is more pronounced at large galactocentric
radii because of the smaller number density of tidal streams and the longer
orbital times. This model provides a natural explanation for the coherent
structures in the outer stellar halo found in the SDSS commissioning data, and
it predicts that many more such structures should be found as the survey covers
more of the sky. The detection (or non-detection) and characterization of such
structures could eventually test variants of the CDM scenario, especially those
that aim to solve the dwarf satellite problem by enhancing satellite
disruption.Comment: 12 pages, 8 figures, Submitted to Ap
Redefining the Missing Satellites Problem
Numerical simulations of Milky-Way size Cold Dark Matter (CDM) halos predict
a steeply rising mass function of small dark matter subhalos and a substructure
count that greatly outnumbers the observed satellites of the Milky Way. Several
proposed explanations exist, but detailed comparison between theory and
observation in terms of the maximum circular velocity (Vmax) of the subhalos is
hampered by the fact that Vmax for satellite halos is poorly constrained. We
present comprehensive mass models for the well-known Milky Way dwarf
satellites, and derive likelihood functions to show that their masses within
0.6 kpc (M_0.6) are strongly constrained by the present data. We show that the
M_0.6 mass function of luminous satellite halos is flat between ~ 10^7 and 10^8
M_\odot. We use the ``Via Lactea'' N-body simulation to show that the M_0.6
mass function of CDM subhalos is steeply rising over this range. We rule out
the hypothesis that the 11 well-known satellites of the Milky Way are hosted by
the 11 most massive subhalos. We show that models where the brightest
satellites correspond to the earliest forming subhalos or the most massive
accreted objects both reproduce the observed mass function. A similar analysis
with the newly-discovered dwarf satellites will further test these scenarios
and provide powerful constraints on the CDM small-scale power spectrum and warm
dark matter models.Comment: 8 pages, 6 figure
Tracing Galaxy Formation with Stellar Halos I: Methods
If the favored hierarchical cosmological model is correct, then the Milky Way
system should have accreted ~100-200 luminous satellite galaxies in the past
\~12 Gyr. We model this process using a hybrid semi-analytic plus N-body
approach which distinguishes explicitly between the evolution of light and dark
matter in accreted satellites. This distinction is essential to our ability to
produce a realistic stellar halo, with mass and density profile much like that
of our own Galaxy, and a surviving satellite population that matches the
observed number counts and structural parameter distributions of the satellite
galaxies of the Milky Way. Our model stellar halos have density profiles which
typically drop off with radius faster than those of the dark matter. They are
assembled from the inside out, with the majority of mass (~80%) coming from the
\~15 most massive accretion events. The satellites that contribute to the
stellar halo have median accretion times of ~9 Gyr in the past, while surviving
satellite systems have median accretion times of ~5 Gyr in the past. This
implies that stars associated with the inner halo should be quite different
chemically from stars in surviving satellites and also from stars in the outer
halo or those liberated in recent disruption events. We briefly discuss the
expected spatial structure and phase space structure for halos formed in this
manner. Searches for this type of structure offer a direct test of whether
cosmology is indeed hierarchical on small scales.Comment: 22 pages, 16 figures, submitted to Ap
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