20,205 research outputs found
Standing sausage modes in coronal loops with plasma flow
Magnetohydrodynamic waves are important for diagnosing the physical
parameters of coronal plasmas. Field-aligned flows appear frequently in coronal
loops.We examine the effects of transverse density and plasma flow structuring
on standing sausage modes trapped in coronal loops, and examine their
observational implications. We model coronal loops as straight cold cylinders
with plasma flow embedded in a static corona. An eigen-value problem governing
propagating sausage waves is formulated, its solutions used to construct
standing modes. Two transverse profiles are distinguished, one being the
generalized Epstein distribution (profile E) and the other (N) proposed
recently in Nakariakov et al.(2012). A parameter study is performed on the
dependence of the maximum period and cutoff length-to-radius
ratio in the trapped regime on the density parameters
( and profile steepness ) and flow parameters (magnitude
and profile steepness ). For either profile, introducing a flow
reduces relative to the static case. depends
sensitively on for profile N but is insensitive to for profile E. By
far the most important effect a flow introduces is to reduce the capability for
loops to trap standing sausage modes: may be
substantially reduced in the case with flow relative to the static one. If the
density distribution can be described by profile N, then measuring the sausage
mode period can help deduce the density profile steepness. However, this
practice is not feasible if profile E better describes the density
distribution. Furthermore, even field-aligned flows with magnitudes
substantially smaller than the ambient Alfv\'en speed can make coronal loops
considerably less likely to support trapped standing sausage modes.Comment: 11 pages, 9 figures, to appear in Astronomy & Astrophysic
Role of quark-interchange processes in evolution of mesonic matter
We divide the cross section for a meson-meson reaction into three parts. The
first part is for the quark-interchange process, the second for quark-antiquark
annihilation processes and the third for resonant processes. Master rate
equations are established to yield time dependence of fugacities of pions,
rhos, kaons and vetor kaons. The equations include cross sections for inelastic
scattering of pions, rhos, kaons and vector kaons. Cross sections for
quark-interchange-induced reactions, that were obtained in a potential model,
are parametrized for convenient use. The number densities of pion and rho (kaon
and vector kaon) are altered by quark-interchange processes in equal magnitudes
but opposite signs. The master rate equations combined with the hydrodynamic
equations for longitudinal and transverse expansion are solved with many sets
of initial meson fugacities. Quark-interchange processes are shown to be
important in the contribution of the inelastic meson-meson scattering to
evolution of mesonic matter.Comment: 28 pages, 1 figure, 8 table
Phase transitions in a holographic s+p model with backreaction
In a previous paper (arXiv:1309.2204, JHEP 1311 (2013) 087), we present a
holographic s+p superconductor model with a scalar triplet charged under an
SU(2) gauge field in the bulk. We also study the competition and coexistence of
the s-wave and p-wave orders in the probe limit. In this work we continue to
study the model by considering the full back-reaction The model shows a rich
phase structure and various condensate behaviors such as the "n-type" and
"u-type" ones, which are also known as reentrant phase transitions in condensed
matter physics. The phase transitions to the p-wave phase or s+p coexisting
phase become first order in strong back-reaction cases. In these first order
phase transitions, the free energy curve always forms a swallow tail shape, in
which the unstable s+p solution can also play an important role. The phase
diagrams of this model are given in terms of the dimension of the scalar order
and the temperature in the cases of eight different values of the back reaction
parameter, which show that the region for the s+p coexisting phase is enlarged
with a small or medium back reaction parameter, but is reduced in the strong
back-reaction cases.Comment: 15 pages(two-column), 9 figure
- …