14,193 research outputs found
Hypercyclic operators on countably dimensional spaces
According to Grivaux, the group of invertible linear operators on a
separable infinite dimensional Banach space acts transitively on the set
of countable dense linearly independent subsets of . As a
consequence, each is an orbit of a hypercyclic operator on
. Furthermore, every countably dimensional normed space supports a
hypercyclic operator.
We show that for a separable infinite dimensional Fr\'echet space ,
acts transitively on if and only if possesses a
continuous norm. We also prove that every countably dimensional metrizable
locally convex space supports a hypercyclic operator
Excitation of acoustic waves by vortices in the quiet Sun
Five-minutes oscillations is one of the basic properties of solar convection.
Observations show mixture of a large number of acoustic wave fronts propagating
from their sources. We investigate the process of acoustic waves excitation
from the point of view of individual events, by using realistic 3D radiative
hydrodynamic simulation of the quiet Sun. The results show that the excitation
events are related to dynamics vortex tubes (or swirls) in the intergranular
lanes. These whirlpool-like flows are characterized by very strong horizontal
velocities (7 - 11 km/s) and downflows (~ 7 km/s), and are accompanied by
strong decreases of the temperature, density and pressure at the surface and in
a ~ 0.5-1 Mm deep layer below the surface. High-speed whirlpool flows can
attract and capture other vortices. According to our simulation results, the
processes of the vortex interaction, such as vortex annihilation, can cause the
excitation of acoustic waves.Comment: 10 pages, 5 figure, submitted to ApJ
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