3,564 research outputs found
Non-Thermal Emission from Relativistic Electrons in Clusters of Galaxies: A Merger Shock Acceleration Model
We have investigated evolution of non-thermal emission from relativistic
electrons accelerated at around the shock fronts during merger of clusters of
galaxies. We estimate synchrotron radio emission and inverse Compton scattering
of cosmic microwave background photons from extreme ultraviolet (EUV) to hard
X-ray range. The hard X-ray emission is most luminous in the later stage of
merger. Both hard X-ray and radio emissions are luminous only while signatures
of merging events are clearly seen in thermal intracluster medium (ICM). On the
other hand, EUV radiation is still luminous after the system has relaxed.
Propagation of shock waves and bulk-flow motion of ICM play crucial roles to
extend radio halos. In the contracting phase, radio halos are located at the
hot region of ICM, or between two substructures. In the expanding phase, on the
other hand, radio halos are located between two ICM hot regions and shows
rather diffuse distribution.Comment: 19 pages, 5 figures, accepted for publication in Ap
Large deformation of spherical vesicle studied by perturbation theory and Surface evolver
With tangent angle perturbation approach the axial symmetry deformation of a
spherical vesicle in large under the pressure changes is studied by the
elasticity theory of Helfrich spontaneous curvature model.Three main results in
axial symmetry shape: biconcave shape, peanut shape, and one type of myelin are
obtained. These axial symmetry morphology deformations are in agreement with
those observed in lipsome experiments by dark-field light microscopy [Hotani,
J. Mol. Biol. 178, (1984) 113] and in the red blood cell with two thin
filaments (myelin) observed in living state (see, Bessis, Living Blood Cells
and Their Ultrastructure, Springer-Verlag, 1973). Furthermore, the biconcave
shape and peanut shape can be simulated with the help of a powerful software,
Surface Evolver [Brakke, Exp. Math. 1, 141 (1992) 141], in which the
spontaneous curvature can be easy taken into account.Comment: 16 pages, 6 EPS figures and 2 PS figure
Fermi acceleration at fast shock in a solar flare and impulsive loop-top hard X-ray source
We propose that non-thermal electrons are efficiently accelerated by
first-order Fermi process at the fast shock, as a natural consequence of the
new magnetohydrodynamic picture of the flaring region revealed with Yohkoh. An
oblique fast shock is naturally formed below the reconnection site, and boosts
the acceleration to significantly decrease the injection energy. The slow
shocks attached to the reconnection X-point heat the plasma up to 10--20 MK,
exceeding the injection energy. The combination of the oblique shock
configuration and the pre-heating by the slow shock allows bulk electron
acceleration from the thermal pool. The accelerated electrons are trapped
between the two slow shocks due to the magnetic mirror downstream of the fast
shock, thus explaining the impulsive loop-top hard X-ray source discovered with
Yohkoh. Acceleration time scale is ~ 0.3--0.6 s, which is consistent with the
time scale of impulsive bursts. When these electrons stream away from the
region enclosed by the fast shock and the slow shocks, they are released toward
the footpoints and may form the simultaneous double-source hard X-ray structure
at the footpoints of the reconnected field lines.Comment: 13 pages, 3 postscript figures, used AASTeX macros; accepted in
Astrophysical Journal Letter
On the peak in the far-infrared conductivity of strongly anisotropic cuprates
We investigate the far-infrared and submillimeter-wave conductivity of
electron-doped La_(2-x)Ce_xCuO_4 tilted 1 degree off from the ab-plane. The
effective conductivity measured for this tilt angle reveals an intensive peak
at finite frequency (\nu ~ 50 cm{-1}) due to a mixing of the in-plane and
out-of-plane responses. The peak disappears for the pure in-plane response and
transforms to the Drude-like contribution. Comparative analysis of the mixed
and the in-plane contributions allows to extract the c-axis conductivity which
shows a Josephson plasma resonance at 11.7 cm{-1} in the superconducting state.Comment: 4 pages, 4 figures include
Evidence for a Nodeless Gap from the Superfluid Density of Optimally Doped Pr_{1.855}Ce_{0.145}CuO_{4-y} Films
We present measurements of the ab-plane magnetic penetration depth,
\lambda(T), in five optimally doped Pr_{1.855}Ce_{0.145}CuO_{4-y} films for 1.6
K \leq T \leq T_c \sim 24 K. Low resistivities, high superfluid densities
n_s(T)\propto \lambda^{-2}(T), high T_c's, and small transition widths are
reproducible and indicative of excellent film quality. For all five films,
\lambda^{-2}(T)/\lambda^{-2}(0) at low T is well fitted by an exponential
temperature dependence with a gap, \Delta_{min}, of 0.85 k_B T_c. This behavior
is consistent with a nodeless gap and is incompatible with d-wave
superconductivity.Comment: 5 pages, 4 figures, reorganized for clarit
Effect of Compton Scattering on the Electron Beam Dynamics at the ATF Damping Ring
Compton scattering provides one of the most promising scheme to obtain
polarized positrons for the next generation of -- colliders.
Moreover it is an attractive method to produce monochromatic high energy
polarized gammas for nuclear applications and X-rays for compact light sources.
In this framework a four-mirror Fabry-P\'erot cavity has been installed at the
Accelerator Test Facility (ATF - KEK, Tsukuba, Japan) and is used to produce an
intense flux of polarized gamma rays by Compton scattering
\cite{ipac-mightylaser}. For electrons at the ATF energy (1.28 GeV) Compton
scattering may result in a shorter lifetime due to the limited bucket
acceptance. We have implemented the effect of Compton scattering on a 2D
tracking code with a Monte-Carlo method. This code has been used to study the
longitudinal dynamics of the electron beam at the ATF damping ring, in
particular the evolution of the energy spread and the bunch length under
Compton scattering. The results obtained are presented and discussed. Possible
methods to observe the effect of Compton scattering on the ATF beam are
proposed
Approximation of the Schwinger--Dyson and the Bethe--Salpeter Equations and Chiral Symmetry of QCD
The Bethe--Salpeter equation for the pion in chiral symmetric models is
studied with a special care to consistency with low-energy relations. We
propose a reduction of the rainbow Schwinger--Dyson and the ladder
Bethe--Salpeter equations with a dressed gluon propagator. We prove that the
reduction preserves the Ward--Takahashi identity for the axial-vector current
and the PCAC relation.Comment: 10 pages, LaTe
Evidence for a quantum phase transition in the electron-doped cuprate Pr2-xCexCuO4+d from Hall and resistivity measurements
The doping and temperature dependence of the Hall coefficient, RH, and
ab-plane resistivity in the normal state down to 350mK is reported for oriented
films of the electron-doped high-Tc superconductor Pr2-xCexCuO4+d. The doping
dependence of b (r=r0+AT^b) and R_sub_H (at 350 mK) suggest a quantum phase
transition at a critical doping near x=0.165.Comment: 11 pages 4 figures Phys. Rev. Lett. 92, 167001 (2004
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