24 research outputs found
Frame Theory for Signal Processing in Psychoacoustics
This review chapter aims to strengthen the link between frame theory and
signal processing tasks in psychoacoustics. On the one side, the basic concepts
of frame theory are presented and some proofs are provided to explain those
concepts in some detail. The goal is to reveal to hearing scientists how this
mathematical theory could be relevant for their research. In particular, we
focus on frame theory in a filter bank approach, which is probably the most
relevant view-point for audio signal processing. On the other side, basic
psychoacoustic concepts are presented to stimulate mathematicians to apply
their knowledge in this field
Gravitational Collapse and Disk Formation in Magnetized Cores
We discuss the effects of the magnetic field observed in molecular clouds on
the process of star formation, concentrating on the phase of gravitational
collapse of low-mass dense cores, cradles of sunlike stars. We summarize recent
analytic work and numerical simulations showing that a substantial level of
magnetic field diffusion at high densities has to occur in order to form
rotationally supported disks. Furthermore, newly formed accretion disks are
threaded by the magnetic field dragged from the parent core during the
gravitational collapse. These disks are expected to rotate with a sub-Keplerian
speed because they are partially supported by magnetic tension against the
gravity of the central star. We discuss how sub-Keplerian rotation makes it
difficult to eject disk winds and accelerates the process of planet migration.
Moreover, magnetic fields modify the Toomre criterion for gravitational
instability via two opposing effects: magnetic tension and pressure increase
the disk local stability, but sub-Keplerian rotation makes the disk more
unstable. In general, magnetized disks are more stable than their nonmagnetic
counterparts; thus, they can be more massive and less prone to the formation of
giant planets by gravitational instability.Comment: Chapter 16 in "Magnetic Fields in Diffuse Media", Springer-Verlag,
eds. de Gouveia Dal Pino, E., Lazarian, A., Melioli,