8,067 research outputs found
Co- and counter-helicity interaction between two adjacent laboratory prominences
The interaction between two side-by-side solar prominence-like plasmas has been studied using a four-electrode magnetized plasma source that can impose a wide variety of surface boundary conditions. When the source is arranged to create two prominences with the same helicity (co-helicity), it is observed that helicity transfer from one prominence to the other causes the receiving prominence to erupt sooner and faster than the transmitting prominence. When the source is arranged to create two prominences with opposite helicity (counter-helicity), it is observed that upon merging, prominences wrap around each other to form closely spaced, writhing turns of plasma. This is followed by appearance of a distinct bright region in the middle and order of magnitude higher emission of soft x rays. The four-electrode device has also been used to change the angle of the neutral line and so form more pronounced S-shapes
Pitch-angle diffusion coefficients from resonant interactions with electrostatic electron cyclotron harmonic waves in planetary magnetospheres
Pitch-angle diffusion coefficients have been calculated for resonant
interaction with electrostatic electron cyclotron harmonic (ECH) waves in
the magnetospheres of Earth, Jupiter, Saturn, Uranus and Neptune.
Calculations have been performed at two radial distances of each planet. It
is found that observed wave electric field amplitudes in the magnetospheres
of Earth and Jupiter are sufficient to put electrons on strong diffusion in
the energy range of less than 100 eV. However, for Saturn, Uranus and
Neptune,
the observed ECH wave amplitude are insufficient to put electrons on strong
diffusion at any radial distance
Observational Evidence of Sausage-Pinch Instability in Solar Corona by SDO/AIA
We present the first observational evidence of the evolution of sausage-pinch
instability in Active Region 11295 during a prominence eruption using data
recorded on 12 September 2011 by the Atmospheric Imaging Assembly (AIA) onboard
the Solar Dynamics Observatory (SDO). We have identified a magnetic flux tube
visible in AIA 304 \AA\ that shows curvatures on its surface with variable
cross-sections as well as enhanced brightness. These curvatures evolved and
thereafter smoothed out within a time-scale of a minute. The curved locations
on the flux tube exhibit a radial outward enhancement of the surface of about
1-2 Mm (factor of 2 larger than the original thickness of the flux tube) from
the equilibrium position. AIA 193 \AA\ snapshots also show the formation of
bright knots and narrow regions inbetween at the four locations as that of 304
\AA\ along the flux tube where plasma emission is larger compared to the
background. The formation of bright knots over an entire flux tube as well as
the narrow regions in < 60 s may be the morphological signature of the sausage
instability. We also find the flows of the confined plasma in these bright
knots along the field lines, which indicates the dynamicity of the flux tube
that probably causes the dominance of the longitudinal field component over
short temporal scales. The observed longitudinal motion of the plasma frozen in
the magnetic field lines further vanishes the formed curvatures and plasma
confinements as well as growth of instability to stablize the flux tube.Comment: 12 pages, 5 figure
Nehari manifold approach for fractional Kirchhoff problems with extremal value of the parameter
In this work we study the following nonlocal problem
\begin{equation*}
\left\{
\begin{aligned}
M(\|u\|^2_X)(-\Delta)^s u&= \lambda {f(x)}|u|^{\gamma-2}u+{g(x)}|u|^{p-2}u
&&\mbox{in}\ \ \Omega,
u&=0 &&\mbox{on}\ \ \mathbb R^N\setminus \Omega,
\end{aligned}
\right.
\end{equation*}
where is open and bounded with smooth boundary,
with
and . The exponents satisfy
(when ) and (when ). The parameter
involved in the problem is real and positive. The problem under
consideration has nonlocal behaviour due to the presence of nonlocal fractional
Laplacian operator as well as the nonlocal Kirchhoff term , where
. The weight functions are continuous, is positive while is allowed to
change sign. In this paper an extremal value of the parameter, a threshold to
apply Nehari manifold method, is characterized variationally for both
degenerate and non-degenerate Kirchhoff cases to show an existence of at least
two positive solutions even when crosses the extremal parameter value
by executing fine analysis based on fibering maps and Nehari manifold
Adaptive mufti-objective particle swarm optimization algorithm
In this article we describe a novel Particle Swarm Optimization (PSO) approach to Multi-objective Optimization (MOO) called Adaptive Multi-objective Particle Swarm Optimization (AMOPSO). AMOPSO algorithm's novelty lies in its adaptive nature, that is attained by incorporating inertia and the acceleration coefficient as control variables with usual optimization variables, and evolving these through the swarming procedure. A new diversity parameter has been used to ensure sufficient diversity amongst the solutions of the non dominated front. AMOPSO has been compared with some recently developed multi-objective PSO techniques and evolutionary algorithms for nine function optimization problems, using different performance measures
Laboratory simulations of astrophysical jets and solar coronal loops: new results
An experimental program underway at Caltech has produced plasmas where the shape is neither fixed by the vacuum chamber nor fixed by an external coil set, but instead is determined by self-organization. The plasma dynamics is highly reproducible and so can be studied in considerable detail even though the morphology of the plasma is both complex and time-dependent. A surprising result has been the observation that self-collimating MHD-driven plasma jets are ubiquitous and play a fundamental role in the self-organization. The jets can be considered lab-scale simulations of astrophysical jets and in addition are intimately related to solar coronal loops. The jets are driven by the combination of the axial component of the J×B force and the axial pressure gradient resulting from the non-uniform pinch force associated with the flared axial current density. Behavior is consistent with a model showing that collimation results from axial non-uniformity of the jet velocity. In particular, flow stagnation in the jet frame compresses frozen-in azimuthal magnetic flux, squeezes together toroidal magnetic field lines, thereby amplifying the embedded toroidal magnetic field, enhancing the pinch force, and hence causing collimation of the jet
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