13,128 research outputs found
A computational study of high-speed microdroplet impact onto a smooth solid surface
Numerical solutions of high-speed microdroplet impact onto a smooth solid
surface are computed, using the interFoam VoF solver of the OpenFOAM CFD
package. Toward the solid surface, the liquid microdroplet is moving with an
impinging gas flow, simulating the situation of ink droplets being deposited
onto substrate with a collimated mist jet in the Optomec Aerosol Jet printing
process. The computed values of maximum spread factor, for the range of
parameters of practical interest to Aerosol Jet printing, were found in very
good agreement with some of the correlation formulas proposed by previous
authors in the literature. Combining formulas selected from different authors
with appropriate modifications yields a maximum spread factor formula that can
be used for first-order evaluations of deposited in droplet size during the
Aerosol Jet technology development. The computational results also illustrate
droplet impact dynamics with lamella shape evolution throughout the spreading,
receding-relaxation, and wetting equilibrium phases, consistent with that
observed and described by many previous authors. This suggests a
scale-invariant nature of the basic droplet impact behavior such that
experiments with larger droplets at the same nondimensional parameter values
may be considered for studying microdroplet impact dynamics. Significant free
surface oscillations can be observed when the droplet viscosity is relatively
low. The border line between periodic free surface oscillations and aperiodic
creeping to capillary equilibrium free surface shape appears at the value of
Ohnesorge number around 0.25. Droplet bouncing after receding is prompted with
large contact angles at solid surface (as consistent with findings reported in
the literature), but can be suppressed by increasing the droplet viscosity
Deficient Reasoning for Dark Matter in Galaxies
Astronomers have been using the measured luminosity to estimate the {\em
luminous mass} of stars, based on empirically established mass-to-light ratio
which seems to be only applicable to a special class of stars---the
main-sequence stars---with still considerable uncertainties. Another basic tool
to determine the mass of a system of stars or galaxies comes from the study of
their motion, as Newton demonstrated with his law of gravitation, which yields
the {\em gravitational mass}. Because the luminous mass can at best only
represent a portion of the gravitational mass, finding the luminous mass to be
different or less than the gravitational mass should not be surprising. Using
such an apparent discrepancy as a compelling evidence for the so-called dark
matter, which has been believed to possess mysterious nonbaryonic properties
and present a dominant amount in galaxies and the universe, seems to be too far
a stretch when seriously examining the facts and uncertainties in the
measurement techniques. In our opinion, a galaxy with star type distribution
varying from its center to edge may have a mass-to-light ratio varying
accordingly. With the thin-disk model computations based on measured rotation
curves, we found that most galaxies have a typical mass density profile that
peaks at the galactic center and decreases rapidly within of the
cut-off radius, and then declines nearly exponentially toward the edge. The
predicted mass density in the Galactic disk is reasonably within the reported
range of that observed in interstellar medium. This leads us to believe that
ordinary baryonic matter can be sufficient for supporting the observed galactic
rotation curves; speculation of large amount of non-baryonic matter may be
based on an ill-conceived discrepancy between gravitational mass and luminous
mass which appears to be unjustified
Optical design for a balloon-borne magnetograph
This report details activities performed in order to accomplish the optical design of a balloon-borne solar vector magnetograph
PROFITABILITY AND RISK OF U.S. AGRICULTURAL BANKS
Study of profitability and risk of agricultural banks is very important in assessing the ability to adequately finance agricultural production and rural development. A recursive system of profitability and risk equations is estimated to compare the performance of agricultural with nonagricultural banks and to identify factors which affect performance. A linear regression model which measures risk-adjusted profitability confirms the results from the recursive system. Results show that agricultural banks perform better than nonagricultural counterparts on average even after controlling for risks and other factors. Further, off-balance-sheet business is found to be negatively related to the risk-adjusted profitability of agricultural banks.Financial Economics,
Nonexistence of reflexive ideals in Iwasawa algebras of Chevalley type
Let be a root system and let \Phi(\Zp) be the standard Chevalley
\Zp-Lie algebra associated to . For any integer , let be
the uniform pro- group corresponding to the powerful Lie algebra p^t
\Phi(\Zp) and suppose that . Then the Iwasawa algebra has
no nontrivial reflexive two-sided ideals. This was previously proved by the
authors for the root system .Comment: Minor changes made, mostly due to helpful comments from the refere
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