4,789 research outputs found
Coronal Mass Ejections Associated with Slow Long Duration Flares
It is well known that there is temporal relationship between coronal mass
ejections (CMEs) and associated flares. The duration of the acceleration phase
is related to the duration of the rise phase of a flare. We investigate CMEs
associated with slow long duration events (LDEs), i.e. flares with the long
rising phase. We determined the relationships between flares and CMEs and
analyzed the CME kinematics in detail. The parameters of the flares (GOES flux,
duration of the rising phase) show strong correlations with the CME parameters
(velocity, acceleration during main acceleration phase and duration of the CME
acceleration phase). These correlations confirm the strong relation between
slow LDEs and CMEs. We also analyzed the relation between the parameters of the
CMEs, i.e. a velocity, an acceleration during the main acceleration phase, a
duration of the acceleration phase, and a height of a CME at the end of the
acceleration phase. The CMEs associated with the slow LDEs are characterized by
high velocity during the propagation phase, with the median equal 1423 km/s. In
half of the analyzed cases, the main acceleration was low (a<300 m/s^2), which
suggests that the high velocity is caused by the prolongated acceleration phase
(the median for the duration of the acceleration phase is equal 90 minutes).
The CMEs were accelerated up to several solar radii (with the median 7 Rsun),
which is much higher than in typical impulsive CMEs. Therefore, slow LDEs may
potentially precede extremely strong geomagnetic storms. The analysis of slow
LDEs and associated CMEs may give important information for developing more
accurate space weather forecasts, especially for extreme events.Comment: Solar Physics, accepte
Scaling of impact fragmentation near the critical point
We investigated two-dimensional brittle fragmentation with a flat impact
experimentally, focusing on the low impact energy region near the
fragmentation-critical point. We found that the universality class of
fragmentation transition disagreed with that of percolation. However, the
weighted mean mass of the fragments could be scaled using the pseudo-control
parameter multiplicity. The data for highly fragmented samples included a
cumulative fragment mass distribution that clearly obeyed a power-law. The
exponent of this power-law was 0.5 and it was independent of sample size. The
fragment mass distributions in this regime seemed to collapse into a unified
scaling function using weighted mean fragment mass scaling. We also examined
the behavior of higher order moments of the fragment mass distributions, and
obtained multi-scaling exponents that agreed with those of the simple biased
cascade model.Comment: 6 pages, 6 figure
Complete Supersymmetric Quantum Mechanics of Magnetic Monopoles in N=4 SYM Theory
We find the most general low energy dynamics of 1/2 BPS monopoles in the N=4
supersymmetric Yang-Mills theories (SYM) when all six adjoint Higgs expectation
values are turned on. When only one Higgs is turned on, the Lagrangian is
purely kinetic. When all six are turned on, however, this moduli space dynamics
is augmented by five independent potential terms, each in the form of half the
squared norm of a Killing vector field on the moduli space. A generic
stationary configuration of the monopoles can be interpreted as stable non BPS
dyons, previously found as non-planar string webs connecting D3-branes. The
supersymmetric extension is also found explicitly, and gives the complete
quantum mechanics of monopoles in N=4 SYM theory. We explore its supersymmetry
algebra.Comment: Errors in the SUSY algebra corrected. The version to appear in PR
Word Processors with Line-Wrap: Cascading, Self-Organized Criticality, Random Walks, Diffusion, Predictability
We examine the line-wrap feature of text processors and show that adding
characters to previously formatted lines leads to the cascading of words to
subsequent lines and forms a state of self-organized criticality. We show the
connection to one-dimensional random walks and diffusion problems, and we
examine the predictability of catastrophic cascades.Comment: 6 pages, LaTeX with RevTeX package, 4 postscript figures appende
Avalanche Merging and Continuous Flow in a Sandpile Model
A dynamical transition separating intermittent and continuous flow is
observed in a sandpile model, with scaling functions relating the transport
behaviors between both regimes. The width of the active zone diverges with
system size in the avalanche regime but becomes very narrow for continuous
flow. The change of the mean slope, Delta z, on increasing the driving rate, r,
obeys Delta z ~ r^{1/theta}. It has nontrivial scaling behavior in the
continuous flow phase with an exponent theta given, paradoxically, only in
terms of exponents characterizing the avalanches theta = (1+z-D)/(3-D).Comment: Explanations added; relation to other model
Diffusion-Reorganized Aggregates: Attractors in Diffusion Processes?
A process based on particle evaporation, diffusion and redeposition is
applied iteratively to a two-dimensional object of arbitrary shape. The
evolution spontaneously transforms the object morphology, converging to
branched structures. Independently of initial geometry, the structures found
after long time present fractal geometry with a fractal dimension around 1.75.
The final morphology, which constantly evolves in time, can be considered as
the dynamic attractor of this evaporation-diffusion-redeposition operator. The
ensemble of these fractal shapes can be considered to be the {\em dynamical
equilibrium} geometry of a diffusion controlled self-transformation process.Comment: 4 pages, 5 figure
Supertubes in Matrix model and DBI action
We show the equivalence between the supertube solutions with an arbitrary
cross section in two different actions, the DBI action for the D2-brane and the
matrix model action for the D0-branes. More precisely, the equivalence between
the supertubes in the D2-brane picture and the D0-brane picture is shown in the
boundary state formalism which is valid for all order in \alpha'. This is an
application of the method using the infinitely many D0-branes and
anti-D0-branes which was used to show other equivalence relations between two
seemingly different D-brane systems, including the D-brane realization of the
ADHM construction of instanton. We also apply this method to the superfunnel
type solutions successfully.Comment: 24 pages, references added, version to appear in JHE
Condensation of Tubular D2-branes in Magnetic Field Background
It is known that in the Minkowski vacuum a bunch of IIA superstrings with
D0-branes can be blown-up to a supersymmetric tubular D2-brane, which is
supported against collapse by the angular momentum generated by crossed
electric and magnetic Born-Infeld (BI) fields. In this paper we show how the
multiple, smaller tubes with relative angular momentum could condense to a
single, larger tube to stabilize the system. Such a phenomena could also be
shown in the systems under the Melvin magnetic tube or uniform magnetic field
background. However, depending on the magnitude of field strength, a tube in
the uniform magnetic field background may split into multiple, smaller tubes
with relative angular momentum to stabilize the system.Comment: Latex 10 pages, mention the dynamical joining of the tubes, modify
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