183 research outputs found
Derivation of Instrument Requirements for Polarimetry using Mg, Fe, and Mn lines between 250 and 290 nm
Judge et al. (2021) recently argued that a region of the solar spectrum in
the near-UV between about 250 and 290 nm is optimal for studying magnetism in
the solar chromosphere due to an abundance of Mg II, Fe II, and Fe I lines that
sample various heights in the solar atmosphere. In this paper we derive
requirements for spectropolarimetric instruments to observe these lines. We
derive a relationship between the desired sensitivity to magnetic field and the
signal-to-noise of the measurement from the weak-field approximation of the
Zeeman effect. We find that many lines will exhibit observable polarization
signals for both longitudinal and transverse magnetic field with reasonable
amplitudes
Lyapunov spectra of billiards with cylindrical scatterers: comparison with many-particle systems
The dynamics of a system consisting of many spherical hard particles can be
described as a single point particle moving in a high-dimensional space with
fixed hypercylindrical scatterers with specific orientations and positions. In
this paper, the similarities in the Lyapunov exponents are investigated between
systems of many particles and high-dimensional billiards with cylindrical
scatterers which have isotropically distributed orientations and homogeneously
distributed positions. The dynamics of the isotropic billiard are calculated
using a Monte-Carlo simulation, and a reorthogonalization process is used to
find the Lyapunov exponents. The results are compared to numerical results for
systems of many hard particles as well as the analytical results for the
high-dimensional Lorentz gas. The smallest three-quarters of the positive
exponents behave more like the exponents of hard-disk systems than the
exponents of the Lorentz gas. This similarity shows that the hard-disk systems
may be approximated by a spatially homogeneous and isotropic system of
scatterers for a calculation of the smaller Lyapunov exponents, apart from the
exponent associated with localization. The method of the partial stretching
factor is used to calculate these exponents analytically, with results that
compare well with simulation results of hard disks and hard spheres.Comment: Submitted to PR
Dynamic fibrils in H-alpha and C IV
Aim: To study the interaction of the solar chromosphere with the transition
region, in particular active-region jets in the transition region and their
relation to chromospheric fibrils. Methods: We carefully align image sequences
taken simultaneously in C IV with the Transition Region and Coronal Explorer
and in H-alpha with the Swedish 1-m Solar Telescope. We examine the temporal
evolution of "dynamic fibrils", i.e., individual short-lived active-region
chromospheric jet-like features in H-alpha. Results: All dynamic fibrils appear
as absorption features in H-alpha that progress from the blue to the red wing
through the line, and often show recurrent behavior. Some of them, but not all,
appear also as bright features in C IV which develop at or just beyond the apex
of the H-alpha darkening. They tend to best resemble the H-alpha fibril at +700
mA half a minute earlier. Conclusions: Dynamic chromospheric fibrils observed
in H-alpha regularly correspond to transition-region jets observed in the
ultraviolet. This correspondence suggests that some plasma associated with
dynamic fibrils is heated to transition-region temperatures.Comment: 8 pages, 8 figure
The Lyapunov spectrum of the many-dimensional dilute random Lorentz gas
For a better understanding of the chaotic behavior of systems of many moving
particles it is useful to look at other systems with many degrees of freedom.
An interesting example is the high-dimensional Lorentz gas, which, just like a
system of moving hard spheres, may be interpreted as a dynamical system
consisting of a point particle in a high-dimensional phase space, moving among
fixed scatterers. In this paper, we calculate the full spectrum of Lyapunov
exponents for the dilute random Lorentz gas in an arbitrary number of
dimensions. We find that the spectrum becomes flatter with increasing
dimensionality. Furthermore, for fixed collision frequency the separation
between the largest Lyapunov exponent and the second largest one increases
logarithmically with dimensionality, whereas the separations between Lyapunov
exponents of given indices not involving the largest one, go to fixed limits.Comment: 8 pages, revtex, 6 figures, submitted to Physical Review
- …