14,306 research outputs found
Site-selective Cu NMR study of the vortex cores of TlBaCuO
We report site-selective Cu NMR studies of the vortex core states of
an overdoped TlBaCuO with = 85 K. We observed
a relatively high density of low-energy quasi-particle excitations at the
vortex cores in a magnetic field of 7.4847 T along the c axis, in contrast to
YBaCuO.Comment: 5 pages, 6 figures, submitted to J. Phys. Chem. Solids (QuB2006,
Tokai
Recombination kinetics of a dense electron-hole plasma in strontium titanate
We investigated the nanosecond-scale time decay of the blue-green light
emitted by nominally pure SrTiO following the absorption of an intense
picosecond laser pulse generating a high density of electron-hole pairs. Two
independent components are identified in the fluorescence signal that show a
different dynamics with varying excitation intensity, and which can be
respectively modeled as a bimolecular and unimolecolar process. An
interpretation of the observed recombination kinetics in terms of interacting
electron and hole polarons is proposed
On the equation of motion of compact binaries in Post-Newtonian approximation
A third post-Newtonian (3 PN) equation of motion for two spherical compact
stars in a harmonic coordinate has been derived based on the surface integral
approach and the strong field point particle limit. The strong field point
particle limit enables us to incorporate a notion of a self-gravitating regular
star into general relativity. The resulting 3 PN equation of motion is Lorentz
invariant, unambiguous, and conserves an energy of the binary orbital motion.Comment: 7 pages, no figure. Proceedings of the 5th Amaldi Conference on
Gravitational Waves, Pisa, Italy, 6-11 July 200
Transitions to improved confinement regimes induced by changes in heating in zero-dimensional models for tokamak plasmas
It is shown that rapid substantial changes in heating rate can induce
transitions to improved energy confinement regimes in zero-dimensional models
for tokamak plasma phenomenology. We examine for the first time the effect of
step changes in heating rate in the models of E-J.Kim and P.H.Diamond,
Phys.Rev.Lett. 90, 185006 (2003) and M.A.Malkov and P.H.Diamond, Phys.Plasmas
16, 012504 (2009) which nonlinearly couple the evolving temperature gradient,
micro-turbulence and a mesoscale flow; and in the extension of H.Zhu,
S.C.Chapman and R.O.Dendy, Phys.Plasmas 20, 042302 (2013), which couples to a
second mesoscale flow component. The temperature gradient rises, as does the
confinement time defined by analogy with the fusion context, while
micro-turbulence is suppressed. This outcome is robust against variation of
heating rise time and against introduction of an additional variable into the
model. It is also demonstrated that oscillating changes in heating rate can
drive the level of micro-turbulence through a period-doubling path to chaos,
where the amplitude of the oscillatory component of the heating rate is the
control parameter.Comment: 8 pages, 14 figure
Scaling Laws in High-Energy Inverse Compton Scattering. II. Effect of Bulk Motions
We study the inverse Compton scattering of the CMB photons off high-energy
nonthermal electrons. We extend the formalism obtained by the previous paper to
the case where the electrons have non-zero bulk motions with respect to the CMB
frame. Assuming the power-law electron distribution, we find the same scaling
law for the probability distribution function P_{1,K}(s) as P_{1}(s) which
corresponds to the zero bulk motions, where the peak height and peak position
depend only on the power-index parameter. We solved the rate equation
analytically. It is found that the spectral intensity function also has the
same scaling law. The effect of the bulk motions to the spectral intensity
function is found to be small. The present study will be applicable to the
analysis of the X-ray and gamma-ray emission models from various astrophysical
objects with non-zero bulk motions such as radio galaxies and astrophysical
jets.Comment: 10 pages, 3 figures, accepted version by Physical Review
Constraints on Cold Dark Matter in the Gamma-ray Halo of NGC 253
A gamma-ray halo in a nearby starburst galaxy NGC 253 was found by the
CANGAROO-II Imaging Atmospheric Cherenkov Telescope (IACT). By fitting the
energy spectrum with expected curves from Cold Dark Matter (CDM) annihilations,
we constrain the CDM-annihilation rate in the halo of NGC 253. Upper limits for
the CDM density were obtained in the wide mass range between 0.5 and 50 TeV.
Although these limits are higher than the expected values, it is complementary
important to the other experimental techniques, especially considering the
energy coverage. We also investigate the next astronomical targets to improve
these limits.Comment: 13 pages, 5 figures, aastex.cls, natbib.sty, To appear in ApJ v596n1,
Oct. 10, 200
Turbulence characteristics of the B\"{o}dewadt layer in a large enclosed rotor-stator system
A three-dimensional (3D) direct numerical simulation is combined with a
laboratory study to describe the turbulent flow in an enclosed annular
rotor-stator cavity characterized by a large aspect ratio G=(b-a)/h=18.32 and a
small radius ratio a/b=0.152, where a and b are the inner and outer radii of
the rotating disk and h is the interdisk spacing. The rotation rate Omega under
consideration is equivalent to the rotational Reynolds number Re=Omegab2/nu=9.5
x 104, where nu is the kinematic viscosity of the fluid. This corresponds to a
value at which an experiment carried out at the laboratory has shown that the
stator boundary layer is turbulent, whereas the rotor boundary layer is still
laminar. Comparisons of the 3D computed solution with velocity measurements
have given good agreement for the mean and turbulent fields. The results
enhance evidence of weak turbulence at this Reynolds number, by comparing the
turbulence properties with available data in the literature. An approximately
self-similar boundary layer behavior is observed along the stator side. The
reduction of the structural parameter a1 under the typical value 0.15 and the
variation in the wall-normal direction of the different characteristic angles
show that this boundary layer is three-dimensional. A quadrant analysis of
conditionally averaged velocities is performed to identify the contributions of
different events (ejections and sweeps) on the Reynolds shear stress producing
vortical structures. The asymmetries observed in the conditionally averaged
quadrant analysis are dominated by Reynolds stress-producing events in this
B\"{o}dewadt layer. Moreover, case 1 vortices (with a positive wall induced
velocity) are found to be the major source of generation of special strong
events, in agreement with the conclusions of Lygren and Andersson.Comment: 16 page
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