17,364 research outputs found
The evolution of Giant Molecular Filaments
In recent years there has been a growing interest in studying giant molecular
filaments (GMFs), which are extremely elongated (> 100pc in length) giant
molecular clouds (GMCs). They are often seen as inter-arm features in external
spiral galaxies, but have been tentatively associated with spiral arms when
viewed in the Milky Way. In this paper, we study the time evolution of GMFs in
a high-resolution section of a spiral galaxy simulation, and their link with
spiral arm GMCs and star formation, over a period of 11Myrs. The GMFs generally
survive the inter-arm passage, although they are subject to a number of
processes (e.g. star formation, stellar feedback and differential rotation)
which can break the giant filamentary structure into smaller sections. The GMFs
are not gravitationally bound clouds as a whole, but are, to some extent,
confined by external pressure. Once they reach the spiral arms, the GMFs tend
to evolve into more substructured spiral arm GMCs, suggesting that GMFs may be
precursors to arm GMCs. Here, they become incorporated into the more complex
and almost continuum molecular medium that makes up the gaseous spiral arm.
Instead of retaining a clear filamentary shape, their shapes are distorted both
by their climb up the spiral potential and their interaction with the gas
within the spiral arm. The GMFs do tend to become aligned with the spiral arms
just before they enter them (when they reach the minimum of the spiral
potential), which could account for the observations of GMFs in the Milky Way.Comment: 15 pages, 11 figures, MNRAS accepte
A generalization of the S-function method applied to a Duffing-Van der Pol forced oscillator
In [1,2] we have developed a method (we call it the S-function method) that
is successful in treating certain classes of rational second order ordinary
differential equations (rational 2ODEs) that are particularly `resistant' to
canonical Lie methods and to Darbouxian approaches. In this present paper, we
generalize the S-function method making it capable of dealing with a class of
elementary 2ODEs presenting elementary functions. Then, we apply this method to
a Duffing-Van der Pol forced oscillator, obtaining an entire class of first
integrals
Solving 1ODEs with functions
Here we present a new approach to deal with first order ordinary differential
equations (1ODEs), presenting functions. This method is an alternative to the
one we have presented in [1]. In [2], we have establish the theoretical
background to deal, in the extended Prelle-Singer approach context, with
systems of 1ODEs. In this present paper, we will apply these results in order
to produce a method that is more efficient in a great number of cases.
Directly, the solving of 1ODEs is applicable to any problem presenting
parameters to which the rate of change is related to the parameter itself.
Apart from that, the solving of 1ODEs can be a part of larger mathematical
processes vital to dealing with many problems.Comment: 31 page
Explaining Jupiter's magnetic field and equatorial jet dynamics
Spacecraft data reveal a very Earth-like Jovian magnetic field. This is
surprising since numerical simulations have shown that the vastly different
interiors of terrestrial and gas planets can strongly affect the internal
dynamo process. Here we present the first numerical dynamo that manages to
match the structure and strength of the observed magnetic field by embracing
the newest models for Jupiter's interior. Simulated dynamo action primarily
occurs in the deep high electrical conductivity region while zonal flows are
dynamically constrained to a strong equatorial jet in the outer envelope of low
conductivity. Our model reproduces the structure and strength of the observed
global magnetic field and predicts that secondary dynamo action associated to
the equatorial jet produces banded magnetic features likely observable by the
Juno mission. Secular variation in our model scales to about 2000 nT per year
and should also be observable during the one year nominal mission duration.Comment: 7 pages, 4 figures, accepted for publication in Geophysical Research
Letter
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