7,032 research outputs found
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
Phase diagram of the one-dimensional Holstein model of spinless fermions
The one-dimensional Holstein model of spinless fermions interacting with
dispersionless phonons is studied using a new variant of the density matrix
renormalisation group. By examining various low-energy excitations of finite
chains, the metal-insulator phase boundary is determined precisely and agrees
with the predictions of strong coupling theory in the anti-adiabatic regime and
is consistent with renormalisation group arguments in the adiabatic regime. The
Luttinger liquid parameters, determined by finite-size scaling, are consistent
with a Kosterlitz-Thouless transition.Comment: Minor changes. 4 pages, 4 figures. To appear in Physical Review
Letters 80 (1998) 560
Reconnection Outflows and Current Sheet Observed with Hinode/XRT in the 2008 April 9 "Cartwheel CME" Flare
Supra-arcade downflows (SADs) have been observed with Yohkoh/SXT (soft X-rays
(SXR)), TRACE (extreme ultra-violet (EUV)), SoHO/LASCO (white light),
SoHO/SUMER (EUV spectra), and Hinode/XRT (SXR). Characteristics such as low
emissivity and trajectories which slow as they reach the top of the arcade are
consistent with post-reconnection magnetic flux tubes retracting from a
reconnection site high in the corona until they reach a lower-energy magnetic
configuration. Viewed from a perpendicular angle, SADs should appear as
shrinking loops rather than downflowing voids. We present XRT observations of
supra-arcade downflowing loops (SADLs) following a coronal mass ejection (CME)
on 2008 April 9 and show that their speeds and decelerations are consistent
with those determined for SADs. We also present evidence for a possible current
sheet observed during this flare that extends between the flare arcade and the
CME. Additionally, we show a correlation between reconnection outflows observed
with XRT and outgoing flows observed with LASCO.Comment: 32 pages, 23 figures, Accepted for publication by the Astrophysical
Journal (Oct. 2010
Observations of the structure and evolution of solar flares with a soft X-ray telescope
Soft X ray flare events were observed with the S-056 X-ray telescope that was part of the ATM complement of instruments aboard SKYLAB. Analyses of these data are reported. The observations are summarized and a detailed discussion of the X-ray flare structures is presented. The data indicated that soft X-ray emitted by a flare come primarily from an intense well-defined core surrounded by a region of fainter, more diffuse emission. An analysis of flare evolution indicates evidence for preliminary heating and energy release prior to the main phase of the flare. Core features are found to be remarkably stable and retain their shape throughout a flare. Most changes in the overall configuration seem to be result of the appearance, disappearance or change in brightness of individual features, rather than the restructuring or reorientation of these features. Brief comparisons with several theories are presented
Cosmic ray moderation of the thermal instability
We apply the Hermite-Bieler theorem in the analysis of the effect of cosmic rays on the thermal stability of an initially uniform, static background. The cosmic rays were treated in a fluid approximation and the diffusion coefficient was assumed to be constant in time and space. The inclusion of cosmic rays does not alter the criterion for the thermal stability of a medium subjected to isobaric perturbations. It does alter the criteria for the stability of a medium perturbed by small amplitude sound waves. In the limit of a high background cosmic ray pressure to thermal pressure ratio, the instability in response to high frequency sound waves is suppressed
Entanglement Sharing and Decoherence in the Spin-Bath
The monogamous nature of entanglement has been illustrated by the derivation
of entanglement sharing inequalities - bounds on the amount of entanglement
that can be shared amongst the various parts of a multipartite system.
Motivated by recent studies of decoherence, we demonstrate an interesting
manifestation of this phenomena that arises in system-environment models where
there exists interactions between the modes or subsystems of the environment.
We investigate this phenomena in the spin-bath environment, constructing an
entanglement sharing inequality bounding the entanglement between a central
spin and the environment in terms of the pairwise entanglement between
individual bath spins. The relation of this result to decoherence will be
illustrated using simplified system-bath models of decoherence.Comment: 5 pages, 1 figure v2: 6 pages 2 figures, additional example and
reference
Hamiltonian formulation of nonlinear travelling Whistler waves
International audienceA Hamiltonian formulation of nonlinear, parallel propagating, travelling whistler waves is developed. The complete system of equations reduces to two coupled differential equations for the transverse electron speed and a phase variable representing the difference in the phases of the transverse complex velocities of the protons and the electrons. Two integrals of the equations are obtained. The Hamiltonian integral H, is used to classify the trajectories in the phase plane, where and w=u2 are the canonical coordinates. Periodic, oscilliton solitary wave and compacton solutions are obtained, depending on the value of the Hamiltonian integral H and the Alfvén Mach number M of the travelling wave. The second integral of the equations of motion gives the position x in the travelling wave frame as an elliptic integral. The dependence of the spatial period, L, of the compacton and periodic solutions on the Hamiltonian integral H and the Alfvén Mach number M is given in terms of complete elliptic integrals of the first and second kind. A solitary wave solution, with an embedded rotational discontinuity is obtained in which the transverse Reynolds stresses of the electrons are balanced by equal and opposite transverse stresses due to the protons. The individual electron and proton phase variables and are determined in terms of and . An alternative Hamiltonian formulation in which is the new independent variable replacing x is used to write the travelling wave solutions parametrically in terms of
A current driven instability in parallel, relativistic shocks
Recently, Bell has reanalysed the problem of wave excitation by cosmic rays
propagating in the pre-cursor region of a supernova remnant shock front. He
pointed out a strong, non-resonant, current-driven instability that had been
overlooked in the kinetic treatments, and suggested that it is responsible for
substantial amplification of the ambient magnetic field. Magnetic field
amplification is also an important issue in the problem of the formation and
structure of relativistic shock fronts, particularly in relation to models of
gamma-ray bursts. We have therefore generalised the linear analysis to apply to
this case, assuming a relativistic background plasma and a monoenergetic,
unidirectional incoming proton beam. We find essentially the same non-resonant
instability noticed by Bell, and show that also under GRB conditions, it grows
much faster than the resonant waves. We quantify the extent to which thermal
effects in the background plasma limit the maximum growth rate.Comment: 8 pages, 1 figur
Upper Critical Field in a Spin-Charge Separated Superconductor
It is demonstrated that the spatial decay of the pair propagator in a
Luttinger liquid with spin charge separation contains a logarithmic correction
relative to the free fermi gas result in a finite interval between the spin and
charge thermal lengths. It is argued that similar effects can be expected in
higher dimensional systems with spin charge separation and that the temperature
dependence of the upper critical field curve is a probe of this
effect.Comment: 3 pages, postscript file (compressed and uuencoded
Thyrotropin and growth promoting immunoglobulin (TGI) of FRTL-5 cells have no growth stimulating activity on human thyroid epithelial cell cultures
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