677 research outputs found
Calculation of the Self-energy of Open Quantum Systems
We propose an easy method of calculating the self-energy of semi-infinite
leads attached to a mesoscopic system.Comment: 6 pages, 2 figures, published in J. Phys. Soc. Jp
Large orbital magnetic moments in carbon nanotubes generated by resonant transport
The nonequilibrium Green's function method is used to study the ballistic
transport in metallic carbon nanotubes when a current is injected from the
electrodes with finite bias voltages. We reveal, both analytically and
numerically, that large loop currents circulating around the tube are induced,
which come from a quantum mechanical interference and are much larger than the
current along the tube axis when the injected electron is resonant with a
time-reversed pair of degenerate states, which are, in fact, inherent in the
zigzag and chiral nanotubes. This results in large orbital magnetic moments,
making the nanotube a molecular solenoid.Comment: 5 pages, 4 figures; typos correcte
A note on a local ergodic theorem for an infinite tower of coverings
This is a note on a local ergodic theorem for a symmetric exclusion process
defined on an infinite tower of coverings, which is associated with a finitely
generated residually finite amenable group.Comment: Final version to appear in Springer Proceedings in Mathematics and
Statistic
Bayesian Approach to Find a Long-Term Trend in Erratic Polarization Variations Observed in Blazars
We developed a method to separate a long-term trend from observed temporal
variations of polarization in blazars using a Bayesian approach. The temporal
variation of the polarization vector is apparently erratic in most blazars,
while several objects occasionally exhibited systematic variations, for
example, an increase of the polarization degree associated with a flare of the
total flux. We assume that the observed polarization vector is a superposition
of distinct two components, a long-term trend and a short-term variation
component responsible for short flares. Our Bayesian model estimates the
long-term trend which satisfies the condition that the total flux correlates
with the polarized flux of the short-term component. We demonstrate that
assumed long-term polarization components are successfully separated by the
Bayesian model for artificial data. We applied this method to photopolarimetric
data of OJ 287, S5 0716+714, and S2 0109+224. Simple and systematic long-term
trends were obtained in OJ 287 and S2 0109+224, while no such a trend was
identified in S5 0716+714. We propose that the apparently erratic variations of
polarization in OJ 287 and S2 0109+224 are due to the presence of the long-term
polarization component. The behavior of polarization in S5 0716+714 during our
observation period implies the presence of a number of polarization components
having a quite short time-scale of variations.Comment: 12 pages, 7 figures, accepted for publication in PAS
Resonant-state expansion of the Green's function of open quantum systems
Our series of recent work on the transmission coefficient of open quantum
systems in one dimension will be reviewed. The transmission coefficient is
equivalent to the conductance of a quantum dot connected to leads of quantum
wires. We will show that the transmission coefficient is given by a sum over
all discrete eigenstates without a background integral. An apparent
"background" is in fact not a background but generated by tails of various
resonance peaks. By using the expression, we will show that the Fano asymmetry
of a resonance peak is caused by the interference between various discrete
eigenstates. In particular, an unstable resonance can strongly skew the peak of
a nearby resonance.Comment: 7 pages, 7 figures. Submitted to International Journal of Theoretical
Physics as an article in the Proceedings for PHHQP 2010
(http://www.math.zju.edu.cn/wjd/
Multiwavelength observation from radio through very-high-energy Gamma-ray of OJ 287 during the 12-year cycle flare in 2007
We performed simultaneous multiwavelength observations of OJ 287 with the
Nobeyama Millimeter Array for radio, the KANATA telescope and the KVA telescope
for optical, the Suzaku satellite for X-ray and the MAGIC telescope for very
high energy (VHE) gamma-ray in 2007. The observations were conducted for a
quiescent state in April and in a flaring state in November-December. We
clearly observed increase of fluxes from radio to X-ray bands during the
flaring state while MAGIC could not detect significant VHE gamma-ray emission
from the source. We could derive an upper limit (95% confidence level) of 1.7%
of the Crab Nebula flux above 150 GeV from about 41.2 hours of the MAGIC
observation. A simple SSC model suggests that the observed flaring activity
could be caused by evolutions in the distribution of the electron population
rather than changes of the magnetic field strength or Doppler beaming factor in
the jet.Comment: Contribution to the 31st ICRC, Lodz, Poland, July 200
Photopolarimetric Monitoring of Blazars in the Optical and Near-Infrared Bands with the Kanata Telescope. I. Correlations between Flux, Color, and Polarization
We report on the correlation between the flux, color and polarization
variations on time scales of days--months in blazars, and discuss their
universal aspects. We performed monitoring of 42 blazars in the optical and
near-infrared bands from 2008 to 2010 using TRISPEC attached to the "Kanata"
1.5-m telescope. We found that 28 blazars exhibited "bluer-when-brighter"
trends in their whole or a part of time-series data sets. This corresponds to
88% of objects that were observed for >10 days. Thus, our observation
unambiguously confirmed that the "bluer-when-brighter" trend is common in the
emission from blazar jets. This trend was apparently generated by a variation
component with a constant and relatively blue color and an underlying red
component. Prominent short-term flares on time scales of days--weeks tended to
exhibit a spectral hysteresis; their rising phases were bluer than their decay
phases around the flare maxima. In contrast to the strong flux--color
correlation, the correlation of the flux and polarization degree was relatively
weak; only 10 objects showed significant positive correlations. Rotations of
polarization were detected only in three objects: PKS 1510-089, 3C 454.3, and
PKS 1749+096, and possibly in S5 0716+714. We also investigated the dependence
of the degree of variability on the luminosity and the synchrotron peak
frequency, \nu_peak. As a result, we found that lower luminosity and higher
\nu_peak objects had smaller variations in their amplitudes both in the flux,
color, and polarization degree. Our observation suggests the presence of
several distinct emitting sources, which have different variation time-scales,
colors, and polarizations. We propose that the energy injection by, for
example, internal shocks in relativistic shells is a major factor for blazar
variations on time scales of both days and months.Comment: 39 pages, accepted for publication in PAS
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