26,225 research outputs found
The Star Formation Rate - Dense Gas Relation in the Nuclei of Nearby Galaxies
We investigate the relationship between the star formation rate (SFR) and
dense molecular gas mass in the nuclei of galaxies. To do this, we utilize the
observed 850 micron luminosity as a proxy for the infrared luminosity and SFR,
and correlate this with the observed CO (J=3-2) luminosity. We find tentative
evidence that the LIR-CO (J=3-2) index is similar to the Kennicutt-Schmidt (KS)
index (N ~ 1.5) in the central ~1.7 kpc of galaxies, and flattens to a roughly
linear index when including emission from the entire galaxy. This result may
imply that the volumetric Schmidt relation is the underlying driver behind the
observed SFR-dense gas correlations, and provides tentative confirmation for
recent numerical models. While the data exclude the possibility of a constant
LIR-CO (J=3-2) index for both galaxy nuclei and global measurements at the ~80%
confidence level, the considerable error bars cannot preclude alternative
interpretations.Comment: Accepted at ApJ Letter
A vicinal surface model for epitaxial growth with logarithmic free energy
We study a continuum model for solid films that arises from the modeling of
one-dimensional step flows on a vicinal surface in the
attachment-detachment-limited regime. The resulting nonlinear partial
differential equation, , gives the evolution
for the surface slope as a function of the local height in a monotone
step train. Subject to periodic boundary conditions and positive initial
conditions, we prove the existence, uniqueness and positivity of global strong
solutions to this PDE using two Lyapunov energy functions. The long time
behavior of converging to a constant that only depends on the initial data
is also investigated both analytically and numerically.Comment: 18 pages, 7 figure
A BIO-ECONOMIC DYNAMIC PROGRAMMING ANALYSIS OF THE SEASONAL SUPPLY RESPONSE BY FLORIDA DAIRY PRODUCERS
Seasonal price premiums have been proposed as a means of dampening the highly seasonal patterns of milk production in Florida. A Markov decision bio-economic model of the breeding and replacement decisions was solved via stochastic dynamic programming and used to analyze the potential supply response to seasonal price premiums. The results of the analysis suggest that the seasonal milk supply in Florida is highly price inelastic.Demand and Price Analysis,
Cardinal characteristics and countable Borel equivalence relations
Boykin and Jackson recently introduced a property of countable Borel
equivalence relations called Borel boundedness, which they showed is closely
related to the union problem for hyperfinite equivalence relations. In this
paper, we introduce a family of properties of countable Borel equivalence
relations which correspond to combinatorial cardinal characteristics of the
continuum in the same way that Borel boundedness corresponds to the bounding
number . We analyze some of the basic behavior of these
properties, showing for instance that the property corresponding to the
splitting number coincides with smoothness. We then settle many
of the implication relationships between the properties; these relationships
turn out to be closely related to (but not the same as) the Borel Tukey
ordering on cardinal characteristics
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