33,981 research outputs found
Logarithmic temperature dependence of conductivity at half-integer filling factors: Evidence for interaction between composite fermions
We have studied the temperature dependence of diagonal conductivity in
high-mobility two-dimensional samples at filling factors and 3/2 at
low temperatures. We observe a logarithmic dependence on temperature, from our
lowest temperature of 13 mK up to 400 mK. We attribute the logarithmic
correction to the effects of interaction between composite fermions, analogous
to the Altshuler-Aronov type correction for electrons at zero magnetic field.
The paper is accepted for publication in Physical Review B, Rapid
Communications.Comment: uses revtex macro
Low-Altitude Reconnection Inflow-Outflow Observations during a 2010 November 3 Solar Eruption
For a solar flare occurring on 2010 November 3, we present observations using
several SDO/AIA extreme-ultraviolet (EUV) passbands of an erupting flux rope
followed by inflows sweeping into a current sheet region. The inflows are soon
followed by outflows appearing to originate from near the termination point of
the inflowing motion - an observation in line with standard magnetic
reconnection models. We measure average inflow plane-of-sky speeds to range
from ~150-690 km/s with the initial, high-temperature inflows being the
fastest. Using the inflow speeds and a range of Alfven speeds, we estimate the
Alfvenic Mach number which appears to decrease with time. We also provide
inflow and outflow times with respect to RHESSI count rates and find that the
fast, high-temperature inflows occur simultaneously with a peak in the RHESSI
thermal lightcurve. Five candidate inflow-outflow pairs are identified with no
more than a minute delay between detections. The inflow speeds of these pairs
are measured to be 10^2 km/s with outflow speeds ranging from 10^2-10^3 km/s -
indicating acceleration during the reconnection process. The fastest of these
outflows are in the form of apparently traveling density enhancements along the
legs of the loops rather than the loop apexes themselves. These flows could
either be accelerated plasma, shocks, or waves prompted by reconnection. The
measurements presented here show an order of magnitude difference between the
retraction speeds of the loops and the speed of the density enhancements within
the loops - presumably exiting the reconnection site.Comment: 31 pages, 13 figures, 1 table, Accepted to ApJ (expected publication
~July 2012
Geometry and topology of two kinds of extreme Reissner-Nordstrm-anti-de Sitter black holes
Different geometrical and topological properties have been shown for two
kinds of extreme Reissner-Nordstrm-anti-de Sitter black holes. The
relationship between the geometrical properties and the intrinsic
thermodynamical properties has been made explicit.Comment: Latex, 12 pages, 4 figure
Twist, Writhe & Helicity in the inner penumbra of a sunspot
The aim of this work is the determination of the twist, writhe, and self
magnetic helicity of penumbral filaments located in an inner Sunspot penumbra.
To this extent, we inverted data taken with the spectropolarimeter (SP) aboard
Hinode with the SIR (Stokes Inversion based on Response function) code. For the
construction of a 3D geometrical model we applied a genetic algorithm
minimizing the divergence of the magnetic field vector and the net
magnetohydrodynamic force, consequently a force-free solution would be reached
if possible. We estimated two proxies to the magnetic helicity frequently used
in literature: the force-free parameter and the current helicity term. We show
that both proxies are only qualitative indicators of the local twist as the
magnetic field in the area under study significantly departures from a
force-free configuration. The local twist shows significant values only at the
borders of bright penumbral filaments with opposite signs on each side. These
locations are precisely correlated to large electric currents. The average
twist (and writhe) of penumbral structures is very small. The spines (dark
filaments in the background) show a nearly zero writhe. The writhe per unit
length of the intraspines diminishes with increasing length of the tube axes.
Thus, the axes of tubes related to intraspines are less wrung when the tubes
are more horizontal. As the writhe of the spines is very small, we can conclude
that the writhe reaches only significant values when the tube includes the
border of a intraspine.Comment: 7 pages, 4 figures; Astrophysical Journal, in pres
Composite-fermion crystallites in quantum dots
The correlations in the ground state of interacting electrons in a
two-dimensional quantum dot in a high magnetic field are known to undergo a
qualitative change from liquid-like to crystal-like as the total angular
momentum becomes large. We show that the composite-fermion theory provides an
excellent account of the states in both regimes. The quantum mechanical
formation of composite fermions with a large number of attached vortices
automatically generates omposite fermion crystallites in finite quantum dots.Comment: 5 pages, 3 figure
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