4,446 research outputs found
Thermo-kinetic approach of single-particles and clusters involving anomalous diffusion under viscoelastic response
We present a thermo-kinetic description of anomalous diffusion of
single-particles and clusters in a viscoelastic medium in terms of a
non-Markovian diffusion equation involving memory functions. The scaling
behaviour of these functions is analyzed by considering hydrodynamics and
cluster-size space random walk arguments. We explain experimental results on
diffusion of Brownian particles in the cytoskeleton, in cluster-cluster
aggregation and in a suspension of micelles.Comment: To be published in the Journal of Physical Chemistry
Wave modes excited by photospheric p-modes and mode conversion in a multi-loop system
Context. Waves are ubiquitous in the solar corona and there are indications
that they are excited by photospheric p-modes. However, it is unclear how
p-modes in coronal loops are converted to sausage modes and transverse (kink)
modes, which are observed in the corona. Aims. We aim to investigate how those
wave modes are excited in the lower corona by photospheric acoustic waves.
Methods. We built 3D magnetohydrostatic loop systems with multiple inclinations
spanning from the photosphere to the lower corona. We then simulated these
atmospheres with the MANCHA code, in which we perturb the equilibrium with a
p-mode driver at the bottom of the domain. By splitting the velocity
perturbation into components longitudinal, normal, and azimuthal to the
magnetic flux surfaces we can study wave behavior. Results. In vertical flux
tubes, we find that deformed fast sausage surface waves and slow sausage body
waves are excited. In inclined flux tubes fast kink surface waves, slow sausage
body waves, and either a fast sausage surface wave or a plane wave are excited.
In addition, we calculate a wave conversion factor (0 C 1) from
acoustic to magnetic wave behavior by taking the ratio of the mean magnetic
energy flux to the sum of the mean magnetic and acoustic energy flux and
compare it to a commonly used theoretical conversion factor. We find that
between magnetic field inclinations of 10 to 30 those two
methods lie within 40%. For smaller inclinations the absolute deviation is
smaller than 0.1.Comment: 14 pages, 14 figure
Discrete variational integrators and optimal control theory
A geometric derivation of numerical integrators for optimal control problems
is proposed. It is based in the classical technique of generating functions
adapted to the special features of optimal control problems.Comment: 17 page
High frequency waves in the corona due to null points
This work aims to understand the behavior of non-linear waves in the vicinity
of a coronal null point. In previous works we have showed that high frequency
waves are generated in such magnetic configuration. This paper studies those
waves in detail in order to provide a plausible explanation of their
generation. We demonstrate that slow magneto-acoustic shock waves generated in
the chromosphere propagate through the null point and produce a train of
secondary shocks that escape along the field lines. A particular combination of
the shock wave speeds generates waves at a frequency of 80 mHz. We speculate
that this frequency may be sensitive to the atmospheric parameters in the
corona and therefore can be used to probe the structure of this solar layer
Tulczyjew's triples and lagrangian submanifolds in classical field theories
In this paper the notion of Tulczyjew's triples in classical mechanics is
extended to classical field theories, using the so-called multisymplectic
formalism, and a convenient notion of lagrangian submanifold in multisymplectic
geometry. Accordingly, the dynamical equations are interpreted as the local
equations defining these lagrangian submanifolds.Comment: 29 page
Geometric numerical integration of nonholonomic systems and optimal control problems
A geometric derivation of numerical integrators for nonholonomic systems and
optimal control problems is obtained. It is based in the classical technique of
generating functions adapted to the special features of nonholonomic systems
and optimal control problems.Comment: 6 pages, 1 figure. Submitted to IFAC Workshop on Lagrangian and
Hamiltonian Methods for Nonlinear Control, Sevilla 200
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