907 research outputs found
Nonequilibrium relaxation analysis of a quasi-one-dimensional frustrated XY model for charge-density waves in ring-shaped crystals
We propose a model for charge density waves in ring shaped crystals, which
depicts frustration between intra- and inter-chain couplings coming from
cylindrical bending. It is then mapped to a three dimensional uniformly
frustrated XY model with one dimensional anisotropy in connectivity. The
nonequilibrium relaxation dynamics is investigated by Monte Carlo simulations
to find a phase transition which is quite different from that of usual whisker
crystal. We also find that the low temperature state is a three dimensional
phase vortex lattice with a two dimensional phase coherence in a cylindrical
shell and the system shows power law relaxation in the ordered phase.Comment: 6 pages, 6 epsfiles, revised versio
Comparison of transient horizontal magnetic fields in a plage region and in the quiet Sun
Properties of transient horizontal magnetic fields (THMFs) in both plage and
quiet Sun regions are obtained and compared. Spectro-polarimetric observations
with the Solar Optical Telescope (SOT) on the Hinode satellite were carried out
with a cadence of about 30 seconds for both plage and quiet regions located
near disk center. We select THMFs that have net linear polarization (LP) higher
than 0.22%, and an area larger than or equal to 3 pixels, and compare their
occurrence rates and distribution of magnetic field azimuth. We obtain
probability density functions (PDFs) of magnetic field strength and inclination
for both regions.The occurrence rate in the plage region is the same as for the
quiet Sun. The vertical magnetic flux in the plage region is ~8 times larger
than in the quiet Sun. There is essentially no preferred orientation for the
THMFs in either region. However, THMFs in the plage region with higher LP have
a preferred direction consistent with that of the plage-region's large-scale
vertical field pattern. PDFs show that there is no difference in the
distribution of field strength of horizontal fields between the quiet Sun and
the plage regions when we avoid the persistent large vertical flux
concentrations for the plage region. The similarity of the PDFs and of the
occurrence rates in plage and quiet regions suggests that a local dynamo
process due to the granular motion may generate THMFs all over the sun. The
preferred orientation for higher LP in the plage indicates that the THMFs are
somewhat influenced by the larger-scale magnetic field pattern of the plage.Comment: 11 pages, 7 figures, A&A accepte
Quenching of phase coherence in quasi-one dimensional ring crystals
The comparison of the single-particle (SP) dynamics between the whisker and
ring NbSe crystals provides new insight into the phase transition
properties in quasi-one-dimensional charge density wave (CDW) systems.Comment: 9 pages, 4 figure
Direct observation of high-speed plasma outflows produced by magnetic reconnection in solar impulsive events
Spectroscopic observations of a solar limb flare recorded by SUMER on SOHO
reveal, for the first time, hot fast magnetic reconnection outflows in the
corona. As the reconnection site rises across the SUMER spectrometer slit,
significant blue- and red-shift signatures are observed in sequence in the Fe
XIX line, reflecting upflows and downflows of hot plasma jets, respectively.
With the projection effect corrected, the measured outflow speed is between
900-3500 km/s, consistent with theoretical predictions of the Alfvenic outflows
in magnetic reconnection region in solar impulsive events. Based on theoretic
models, the magnetic field strength near the reconnection region is estimated
to be 19-37 Gauss.Comment: 5 pages, 6 color figures, 1 animation onlin
Is the Polar Region Different from the Quiet Region of the Sun?
Observations of the polar region of the Sun are critically important for
understanding the solar dynamo and the acceleration of solar wind. We carried
out precise magnetic observations on both the North polar region and the quiet
Sun at the East limb with the Spectro-Polarimeter of the Solar Optical
Telescope aboard Hinode to characterize the polar region with respect to the
quiet Sun. The average area and the total magnetic flux of the kG magnetic
concentrations in the polar region appear to be larger than those of the quiet
Sun. The magnetic field vectors classified as vertical in the quiet Sun have
symmetric histograms around zero in the strengths, showing balanced positive
and negative flux, while the histogram in the North polar region is clearly
asymmetric, showing a predominance of the negative polarity. The total magnetic
flux of the polar region is larger than that of the quiet Sun. In contrast, the
histogram of the horizontal magnetic fields is exactly the same between the
polar region and the quiet Sun. This is consistent with the idea that a local
dynamo process is responsible for the horizontal magnetic fields. A
high-resolution potential field extrapolation shows that the majority of
magnetic field lines from the kG-patches in the polar region are open with a
fanning-out structure very low in the atmosphere, while in the quiet Sun,
almost all the field lines are closed.Comment: Accepted for publication in AP
Setup for shot noise measurements in carbon nanotubes
We have constructed a noise measurement setup for high impedance carbon
nanotube samples. Our setup, working in the frequency range of 600 - 900 MHz,
takes advantage of the fact that the shot noise power is reasonably large for
high impedance sources so that relatively large, fixed non-matching conditions
can be tolerated.Comment: 2 pages, 2 figures, published on AIP conference proceedings 200
A Hot Microflare Observed With RHESSI and Hinode
RHESSI and Hinode observations of a GOES B-class flare are combined to
investigate the origin of 15 MK plasma. The absence of any detectable hard
X-ray emission coupled with weak blueshifted emission lines (indicating upward
velocities averaging only 14 km/s) suggests that this was a result of direct
heating in the corona, as opposed to nonthermal electron precipitation causing
chromospheric evaporation. These findings are in agreement with a recent
hydrodynamical simulation of microflare plasmas which found that higher
temperatures can be attained when less energy is used to accelerate electrons
out of the thermal distribution. In addition, unusual redshifts in the 2 MK Fe
XV line (indicating downward velocities of 14 km/s) were observed cospatial
with one of the flare ribbons during the event. Downflows of such high
temperature plasma are not predicted by any common flare model.Comment: 6 pages, 4 figures, ApJL (Accepted
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