8,161 research outputs found
Dynamics of the giant planets of the solar system in the gaseous proto-planetary disk and relationship to the current orbital architecture
We study the orbital evolution of the 4 giant planets of our solar system in
a gas disk. Our investigation extends the previous works by Masset and
Snellgrove (2001) and Morbidelli and Crida (2007, MC07), which focussed on the
dynamics of the Jupiter-Saturn system. The only systems that we found to reach
a steady state are those in which the planets are locked in a quadruple mean
motion resonance (i.e. each planet is in resonance with its neighbor). In total
we found 6 such configurations. For the gas disk parameters found in MC07,
these configurations are characterized by a negligible migration rate. After
the disappearance of the gas, and in absence of planetesimals, only two of
these six configurations (the least compact ones) are stable for a time of
hundreds of millions of years or more. The others become unstable on a
timescale of a few My. Our preliminary simulations show that, when a
planetesimal disk is added beyond the orbit of the outermost planet, the
planets can evolve from the most stable of these configurations to their
current orbits in a fashion qualitatively similar to that described in Tsiganis
et al. (2005).Comment: The Astronomical Journal (17/07/2007) in pres
Transient growth in stable collisionless plasma
The first kinetic study of transient growth for a collisionless homogeneous
Maxwellian plasma in a uniform magnetic field is presented. A system which is
linearly stable may display transient growth if the linear operator describing
its evolution is non-normal, so that its eigenvectors are non-orthogonal. In
order to include plasma kinetic effects a Landau fluid model is employed. The
linear operator of the model is shown to be non-normal and the results suggest
that the nonnormality of a collisionless plasma is intrinsically related to its
kinetic nature, with the transient growth being more accentuated for smaller
scales and higher plasma beta. The results based on linear spectral theory have
been confirmed with nonlinear simulations.Comment: accepted as a Letter in Physics of Plasma
Solar wind turbulent spectrum at plasma kinetic scales
The description of the turbulent spectrum of magnetic fluctuations in the
solar wind in the kinetic range of scales is not yet completely established.
Here, we perform a statistical study of 100 spectra measured by the STAFF
instrument on the Cluster mission, which allows to resolve turbulent
fluctuations from ion scales down to a fraction of electron scales, i.e. from
km to m. We show that for
(that corresponds approximately to the frequency in the spacecraft frame Hz), all the observed spectra can be described by a general law
, where is
the wave-vector component normal to the background magnetic field and
the electron Larmor radius. This exponential tail found in the solar wind seems
compatible with the Landau damping of magnetic fluctuations onto electrons.Comment: published in APJ, 15 of November 2012 (with reduced "Discussion"
section
Gravitational Clustering: A Simple, Robust and Adaptive Approach for Distributed Networks
Distributed signal processing for wireless sensor networks enables that
different devices cooperate to solve different signal processing tasks. A
crucial first step is to answer the question: who observes what? Recently,
several distributed algorithms have been proposed, which frame the
signal/object labelling problem in terms of cluster analysis after extracting
source-specific features, however, the number of clusters is assumed to be
known. We propose a new method called Gravitational Clustering (GC) to
adaptively estimate the time-varying number of clusters based on a set of
feature vectors. The key idea is to exploit the physical principle of
gravitational force between mass units: streaming-in feature vectors are
considered as mass units of fixed position in the feature space, around which
mobile mass units are injected at each time instant. The cluster enumeration
exploits the fact that the highest attraction on the mobile mass units is
exerted by regions with a high density of feature vectors, i.e., gravitational
clusters. By sharing estimates among neighboring nodes via a
diffusion-adaptation scheme, cooperative and distributed cluster enumeration is
achieved. Numerical experiments concerning robustness against outliers,
convergence and computational complexity are conducted. The application in a
distributed cooperative multi-view camera network illustrates the applicability
to real-world problems.Comment: 12 pages, 9 figure
On the cosmic convergence mechanism of the massless dilaton
The converging mechanism discussed in [Damour & Nordtvedt, Physical Review
Letters,70,15] for scalar-tensor theories has been applied to dilaton-like
theories in several subsequent papers. In the present communication, we show
that an unfortunate assumption in those studies led to a scalar-field equation
unsuitable for the study of the dilaton field. The corrected scalar-field
equation turns to change the numerical outcome of those studies in general, but
even sometimes their qualitative aftermath. Therefore, the present result call
for new investigations of the subject. On the other hand, our result shows that
the string-inspired theory presented in [Minazzoli & Hees, Physical Review
D,88,4] is naturally solution to the problem of the effective constancy of the
fundamental coupling constants at late cosmic times, while it requires less
fine-tuning than other massless dilaton or usual stalar-tensor theories.Comment: 4 pages -- accepted for publication in Physics Letters
Constructing the secular architecture of the solar system I: The giant planets
Using numerical simulations, we show that smooth migration of the giant
planets through a planetesimal disk leads to an orbital architecture that is
inconsistent with the current one: the resulting eccentricities and
inclinations of their orbits are too small. The crossing of mutual mean motion
resonances by the planets would excite their orbital eccentricities but not
their orbital inclinations. Moreover, the amplitudes of the eigenmodes
characterising the current secular evolution of the eccentricities of Jupiter
and Saturn would not be reproduced correctly; only one eigenmode is excited by
resonance-crossing. We show that, at the very least, encounters between Saturn
and one of the ice giants (Uranus or Neptune) need to have occurred, in order
to reproduce the current secular properties of the giant planets, in particular
the amplitude of the two strongest eigenmodes in the eccentricities of Jupiter
and Saturn.Comment: Astronomy & Astrophysics (2009) in pres
Review: A Coherent and Comprehensive Model of the Evolution of the Outer Solar System
Since the discovery of the first extra-solar planets, we are confronted with
the puzzling diversity of planetary systems. Processes like planet radial
migration in gas-disks and planetary orbital instabilities, often invoked to
explain the exotic orbits of the extra-solar planets, at first sight do not
seem to have played a role in our system. In reality, though, there are several
aspects in the structure of our Solar System that cannot be explained in the
classic scenario of in-situ formation and smooth evolution of the giant
planets. This paper describes a new view of the evolution of the outer Solar
System that emerges from the so-called 'Nice model' and its recent extensions.
The story provided by this model describes a very "dynamical" Solar System,
with giant planets affected by both radial migrations and a temporary orbital
instability. Thus, the diversity between our system and those found so far
around other stars does not seem to be due to different processes that operated
here and elsewhere, but rather stems from the strong sensitivity of chaotic
evolutions to small differences in the initial and environmental conditions.Comment: in press in CR Physique de l'Academie des Science
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