27,460 research outputs found
Simulating coronal condensation dynamics in 3D
We present numerical simulations in 3D settings where coronal rain phenomena
take place in a magnetic configuration of a quadrupolar arcade system. Our
simulation is a magnetohydrodynamic simulation including anisotropic thermal
conduction, optically thin radiative losses, and parametrised heating as main
thermodynamical features to construct a realistic arcade configuration from
chromospheric to coronal heights. The plasma evaporation from chromospheric and
transition region heights eventually causes localised runaway condensation
events and we witness the formation of plasma blobs due to thermal instability,
that evolve dynamically in the heated arcade part and move gradually downwards
due to interchange type dynamics. Unlike earlier 2.5D simulations, in this case
there is no large scale prominence formation observed, but a continuous coronal
rain develops which shows clear indications of Rayleigh-Taylor or interchange
instability, that causes the denser plasma located above the transition region
to fall down, as the system moves towards a more stable state. Linear stability
analysis is used in the non-linear regime for gaining insight and giving a
prediction of the system's evolution. After the plasma blobs descend through
interchange, they follow the magnetic field topology more closely in the lower
coronal regions, where they are guided by the magnetic dips.Comment: 47 pages, 59 figure
Optical properties of TlNi2Se2: Observation of pseudogap formation
The quasi-two-dimensional nickel chalcogenides is a newly
discovered superconductor. We have performed optical spectroscopy study on
single crystals over a broad frequency range at various
temperatures. The overall optical reflectance spectra are similar to those
observed in its isostructure . Both the suppression in
and the peaklike feature in suggest the progressive
formation of a pseudogap feature in the midinfrared range with decreasing
temperatures, which might be originated from the dynamic local fluctuation of
charge-density-wave (CDW) instability. We propose that the CDW instability in
is driven by the saddle points mechanism, due to the existence of
van Hove singularity very close to the Fermi energy.Comment: 5 pages, 4 figure
Concurrent bandits and cognitive radio networks
We consider the problem of multiple users targeting the arms of a single
multi-armed stochastic bandit. The motivation for this problem comes from
cognitive radio networks, where selfish users need to coexist without any side
communication between them, implicit cooperation or common control. Even the
number of users may be unknown and can vary as users join or leave the network.
We propose an algorithm that combines an -greedy learning rule with a
collision avoidance mechanism. We analyze its regret with respect to the
system-wide optimum and show that sub-linear regret can be obtained in this
setting. Experiments show dramatic improvement compared to other algorithms for
this setting
Testing of a novel web browser interface for the Chinese market
This paper compares the perspicacity, appropriateness and preference of web browser icons from leading software providers with those of a culture-specific design. This online study was conducted in Taiwan and involved 103 participants, who were given three sets of web browser icons to review, namely Microsoft Internet Explorer, Macintosh Safari, and culturally specific icons created using the Culture-Centred Design methodology. The findings of the study show that all three sets have generally high recognition rates, but that some icon functions (e.g. Go/Visit and Favourite) in all three sets have poor recognition rates and are considered inappropriate
Prescribed pattern transformation in swelling gel tubes by elastic instability
We present a study on swelling-induced circumferential buckling of tubular
shaped gels. Inhomogeneous stress develops as gel swells under mechanical
constraints, which gives rise to spontaneous buckling instability without
external force. Full control over the post-buckling pattern is experimentally
demonstrated. A simple analytical model is developed using elastic energy to
predict stability and post-buckling patterns upon swelling. Analysis reveals
that height to diameter ratio is the most critical design parameter to
determine buckling pattern, which agrees well with experimental and numerical
results.Comment: 32 pages, 7 figure
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