434 research outputs found
On the choice of parameters in solar structure inversion
The observed solar p-mode frequencies provide a powerful diagnostic of the
internal structure of the Sun and permit us to test in considerable detail the
physics used in the theory of stellar structure. Amongst the most commonly used
techniques for inverting such helioseismic data are two implementations of the
optimally localized averages (OLA) method, namely the Subtractive Optimally
Localized Averages (SOLA) and Multiplicative Optimally Localized Averages
(MOLA). Both are controlled by a number of parameters, the proper choice of
which is very important for a reliable inference of the solar internal
structure. Here we make a detailed analysis of the influence of each parameter
on the solution and indicate how to arrive at an optimal set of parameters for
a given data set.Comment: 14 pages, 15 figures. Accepted for publication on MNRA
On The Determination of MDI High-Degree Mode Frequencies
The characteristic of the solar acoustic spectrum is such that mode lifetimes
get shorter and spatial leaks get closer in frequency as the degree of a mode
increases for a given order. A direct consequence of this property is that
individual p-modes are only resolved at low and intermediate degrees, and that
at high degrees, individual modes blend into ridges. Once modes have blended
into ridges, the power distribution of the ridge defines the ridge central
frequency and it will mask the true underlying mode frequency. An accurate
model of the amplitude of the peaks that contribute to the ridge power
distribution is needed to recover the underlying mode frequency from fitting
the ridge.
We present the results of fitting high degree power ridges (up to l = 900)
computed from several two to three-month-long time-series of full-disk
observations taken with the Michelson Doppler Imager (MDI) on-board the Solar
and Heliospheric Observatory between 1996 and 1999.
We also present a detailed discussion of the modeling of the ridge power
distribution, and the contribution of the various observational and
instrumental effects on the spatial leakage, in the context of the MDI
instrument. We have constructed a physically motivated model (rather than some
ad hoc correction scheme) resulting in a methodology that can produce an
unbiased determination of high-degree modes, once the instrumental
characteristics are well understood.
Finally, we present changes in high degree mode parameters with epoch and
thus solar activity level and discuss their significance.Comment: 59 pages, 38 figures -- High-resolution version at
http://www-sgk.harvard.edu:1080/~sylvain/preprints/ -- Manuscript submitted
to Ap
1D generalized statistics gas: A gauge theory approach
A field theory with generalized statistics in one space dimension is
introduced. The statistics enters the scene through the coupling of the matter
fields to a statistical gauge field, as it happens in the Chern-Simons theory
in two dimensions. We study the particle-hole excitations and show that the
long wave length physics of this model describes a gas obeying the Haldane
generalized exclusion statistics. The statistical interaction is found to
provide a way to describe the low-T critical properties of one-dimensional
non-Fermi liquids.Comment: 8 pages, revte
The Sub-Surface Structure of a Large Sample of Active Regions
We employ ring-diagram analysis to study the sub-surface thermal structure of
active regions. We present results using a large number of active regions over
the course of Solar Cycle 23. We present both traditional inversions of
ring-diagram frequency differences, with a total sample size of 264, and a
statistical study using Principal Component Analysis. We confirm earlier
results on smaller samples that sound speed and adiabatic index are changed
below regions of strong magnetic field. We find that sound speed is decreased
in the region between approximately r=0.99R_sun and r=0.995R_sun (depths of 3Mm
to 7Mm), and increased in the region between r=0.97R_sun and r=0.985R_sun
(depths of 11Mm to 21Mm). The adiabatic index is enhanced in the same deeper
layers that sound-speed enhancement is seen. A weak decrease in adiabatic index
is seen in the shallower layers in many active regions. We find that the
magnitudes of these perturbations depend on the strength of the surface
magnetic field, but we find a great deal of scatter in this relation, implying
other factors may be relevant.Comment: 16 pages, 11 figures, accepted for publication in Solar Physic
Generating functional analysis of complex formation and dissociation in large protein interaction networks
We analyze large systems of interacting proteins, using techniques from the
non-equilibrium statistical mechanics of disordered many-particle systems.
Apart from protein production and removal, the most relevant microscopic
processes in the proteome are complex formation and dissociation, and the
microscopic degrees of freedom are the evolving concentrations of unbound
proteins (in multiple post-translational states) and of protein complexes. Here
we only include dimer-complexes, for mathematical simplicity, and we draw the
network that describes which proteins are reaction partners from an ensemble of
random graphs with an arbitrary degree distribution. We show how generating
functional analysis methods can be used successfully to derive closed equations
for dynamical order parameters, representing an exact macroscopic description
of the complex formation and dissociation dynamics in the infinite system
limit. We end this paper with a discussion of the possible routes towards
solving the nontrivial order parameter equations, either exactly (in specific
limits) or approximately.Comment: 14 pages, to be published in Proc of IW-SMI-2009 in Kyoto (Journal of
Phys Conference Series
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