9,287 research outputs found
The Global Baroclinic Instability in Accretion Disks. II: Local Linear Analysis
This paper contains a local linear stability analysis for accretion disks
under the influence of a global radial entropy gradient beta = - d log T / d
log r for constant surface density. Numerical simulations suggested the
existence of an instability in two- and three-dimensional models of the solar
nebula. The present paper tries to clarify, quantify, and explain such a global
baroclinic instability for two-dimensional flat accretion disk models. As a
result linear theory predicts a transient linear instability that will amplify
perturbations only for a limited time or up to a certain finite amplification.
This can be understood as a result of the growth time of the instability being
longer than the shear time which destroys the modes which are able to grow. So
only non-linear effects can lead to a relevant amplification. Nevertheless, a
lower limit on the entropy gradient ~beta = 0.22 for the transient linear
instability is derived, which can be tested in future non-linear simulations.
This would help to explain the observed instability in numerical simulations as
an ultimate result of the transient linear instability, i.e. the Global
Baroclinic Instability.Comment: 35 pages, 11 figures; ApJ in pres
Issues for further study
The topics covered include the following: a lunar outpost map, lunar resource utilization, asteroid resource utilization, space energy utilization, and space 'real estate' utilization
Complexity and growth for polygonal billiards
We establish a relationship between the word complexity and the number of
generalized diagonals for a polygonal billiard. We conclude that in the
rational case the complexity function has cubic upper and lower bounds. In the
tiling case the complexity has cubic asymptotic growth.Comment: 12 pages, 4 figure
Recurrence in generic staircases
The straight-line flow on almost every staircase and on almost every square
tiled staircase is recurrent. For almost every square tiled staircase the set
of periodic orbits is dense in the phase space
Surface properties of ocean fronts
Background information on oceanic fronts is presented and the results of several models which were developed to study the dynamics of oceanic fronts and their effects on various surface properties are described. The details of the four numerical models used in these studies are given in separate appendices which contain all of the physical equations, program documentation and running instructions for the models
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