7,999 research outputs found
Fluid Models for Kinetic Effects on Coherent Nonlinear Alfven Waves. II. Numerical Solutions
The influence of various kinetic effects (e.g. Landau damping, diffusive and
collisional dissipation, and finite Larmor radius terms) on the nonlinear
evolution of finite amplitude Alfvenic wave trains in a finite-beta environment
is systematically investigated using a novel, kinetic nonlinear Schrodinger
(KNLS) equation. The dynamics of Alfven waves is sensitive to the sense of
polarization as well as the angle of propagation with respect to the ambient
magnetic field. Numerical solution for the case with Landau damping reveals the
formation of dissipative structures, which are quasi-stationary, S-polarized
directional (and rotational) discontinuities which self-organize from parallel
propagating, linearly polarized waves. Parallel propagating circularly
polarized packets evolve to a few circularly polarized Alfven harmonics on
large scales. Stationary arc-polarized rotational discontinuities form from
obliquely propagating waves. Collisional dissipation, even if weak, introduces
enhanced wave damping when beta is very close to unity. Cyclotron motion
effects on resonant particle interactions introduce cyclotron resonance into
the nonlinear Alfven wave dynamics.Comment: 38 pages (including 23 figures and 1 table
Fast Zonal Field Dynamo in Collisionless Kinetic Alfven Wave Turbulence
The possibility of fast dynamo action by collisionless kinetic Alfven Wave
turbulence is demonstrated. The irreversibility necessary to lock in the
generated field is provided by electron Landau damping, so the induced electric
field does not vanish with resistivity. Mechanisms for self-regulation of the
system and the relation of these results to the theory of alpha quenching are
discussed. The dynamo-generated fields have symmetry like to that of zonal
flows, and thus are termed zonal fields
Influence of zonal flows on unstable drift modes in ETG turbulence
The linear instability of the electron temperature gradient (ETG) driven
modes in the presence of zonal flows is investigated. Random and deterministic
- like profiles of the zonal flow are considered. It is shown that the
presence of shearing by zonal flows can stabilize the linear instability of ETG
drift modes
Collateral and Debt Maturity Choice. A Signaling Model
This paper derives optimal loan policies under asymmetric information where banks offer loan contracts of long and short duration, backed or unbacked with collateral. The main novelty of the paper is that it analyzes a setting in which high quality firms use collateral as a complementary device along with debt maturity to signal their superiority. The least-cost signaling equilibrium depends on the relative costs of the signaling devices, the difference in firm quality and the proportion of good firms in the market. Model simulations suggest a non-monotonic relationship between firm quality and debt maturity, in which high quality firms have both long-term secured debt and short-term secured or non-secured debt.
Coherent Structure of Zonal Flow and Onset of Turbulent Transport
Excitation of the turbulence in the range of drift wave frequency and zonal flow in magnetized plasmas is analyzed. Nonlinear stabilization effect on zonal flow drive is introduced, and the steady state solution is obtained. The condition for the onset of turbulent transport is obtained and partition ratio of fluctuation energy into turbulence and zonal flows is derived. The turbulent transport coefficient, which includes the effect of zonal flow, is also obtained. Analytic result and direct numerical simulation show a good agreemen
The population of SNe/SNRs in the starburst galaxy Arp 220. A self-consistent analysis of 20 years of VLBI monitoring
The nearby ultra-luminous infrared galaxy (ULIRG) Arp 220 is an excellent
laboratory for studies of extreme astrophysical environments. For 20 years,
Very Long Baseline Interferometry (VLBI) has been used to monitor a population
of compact sources thought to be supernovae (SNe), supernova remnants (SNRs)
and possibly active galactic nuclei (AGNs). Using new and archival VLBI data
spanning 20 years, we obtain 23 high-resolution radio images of Arp 220 at
wavelengths from 18 cm to 2 cm. From model-fitting to the images we obtain
estimates of flux densities and sizes of all detected sources. We detect radio
continuum emission from 97 compact sources and present flux densities and sizes
for all analysed observation epochs. We find evidence for a LD-relation within
Arp 220, with larger sources being less luminous. We find a compact source LF
with , similar to SNRs in normal
galaxies. Based on simulations we argue that there are many relatively large
and weak sources below our detection threshold. The observations can be
explained by a mixed population of SNe and SNRs, where the former expand in a
dense circumstellar medium (CSM) and the latter interact with the surrounding
interstellar medium (ISM). Nine sources are likely luminous, type IIn SNe. This
number of luminous SNe correspond to few percent of the total number of SNe in
Arp 220 which is consistent with a total SN-rate of 4 yr as inferred
from the total radio emission given a normal stellar initial mass function
(IMF). Based on the fitted luminosity function, we argue that emission from all
compact sources, also below our detection threshold, make up at most 20\% of
the total radio emission at GHz frequencies.Comment: Accepted for publication in Astronomy and Astrophysic
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