521 research outputs found
Pulse-beam heating of deep atmospheric layers triggering their oscillations and upwards moving shocks that can modulate the reconnection in solar flares
We study processes occurring after a sudden heating of the chromosphere at
the flare arcade footpoints which is assumed to be caused by particle beams.
For the numerical simulations we adopt a 2-D magnetohydrodynamic (MHD) model,
in which we solve a full set of the time-dependent MHD equations by means of
the FLASH code, using the Adaptive Mesh Refinement (AMR) method. In the initial
state we consider a model of the solar atmosphere with densities according to
the VAL-C model and the magnetic field arcade having the X-point structure
above, where the magnetic reconnection is assumed. We found that the sudden
pulse-beam heating of the chromosphere at the flare arcade footpoints generates
magnetohydrodynamic shocks, one propagating upwards and the second one
propagating downwards in the solar atmosphere. The downward moving shock is
reflected at deep and dense atmospheric layers and triggers oscillations of
these layers. These oscillations generate the upwards moving
magnetohydrodynamic waves that can influence the above located magnetic
reconnection in a quasi-periodic way. Because these processes require a sudden
heating in very localized regions in the chromosphere therefore they can be
also associated with seismic waves
Radio fiber bursts and fast magnetoacoustic wave trains
We present a model for dm-fiber bursts that is based on assuming fast sausage
magnetoacoustic wave trains that propagate along a dense vertical filament or
current sheet. Eight groups of dm-fiber bursts that were observed during solar
flares were selected and analyzed by the wavelet analysis method. To model
these fiber bursts we built a semi-empirical model. We also did
magnetohydrodynamic simulations of a propagation of the magnetoacoustic wave
train in a vertical and gravitationally stratified current sheet. In the
wavelet spectra of the fiber bursts computed at different radio frequencies we
found the wavelet tadpoles, whose head maxima have the same frequency drift as
the drift of fiber bursts. It indicates that the drift of these fiber bursts
can be explained by the propagating fast sausage magnetoacoustic wave train.
Using new semi-empirical and magnetohydrodynamic models with a simple radio
emission model we generated the artificial radio spectra of the fiber bursts,
which are similar to the observed ones.Comment: 7 pages, 10 figure
H dissociation over Au-nanowires and the fractional conductance quantum
The dissociation of H molecules on stretched Au nanowires and its effect
on the nanowire conductance are analyzed using a combination of Density
Functional (DFT) total energy calculations and non-equilibrium Keldish-Green
function methods. Our DFT simulations reproduce the characteristic formation of
Au monoatomic chains with a conductance close to % the conductance quantum . These stretched Au nanowires are shown to be better catalysts for
H dissociation than Au surfaces. This is confirmed by the nanowire
conductance evidence: while not affected practically by molecular hydrogen,
atomic hydrogen induces the appearance of fractional conductances () as observed experimentally.Comment: 4 pages, 3 figure
The Role of CAD in Enterprise Integration Process
This article deals with the problem of the mutual influence between software systems used in enterprise environment and enterprise integration processes. The position of CAD data and CAx systems in the integrated environment of manufacturing enterprises is clarified. As a consequence, the key role of CAx systems used in those companies is emphasized. It is noted that the integration of CAD data is nowadays only on a secondary level, via primarily integrated PDM systems. This limitation is a reason why we are developing a unified communication model focused on product-oriented data. Our approach is based on Internet technologies, so we believe that is independent enough. The proposed system of communication is based on a simple request-replay dialogue. The structure of this model is open and extensible, but we assume supervision supported by an Internet portal
BART 2001–2004: An intelligent robotic observatory
BART is a robotic observatory located at the Astronomical Institute in Ondrejov, Czech Republic. It is a relatively low-cost (25 cm + two wide-field lenses) device developed for rapid follow-ups of GRBs. Since 2001 when it started
to observe, it has done several such observations. Meanwhile, photometric monitoring tasks are performed, using an intelligent selection algorithm. Not only the
telescope is automatic, the entire observatory does not require human presence: system prepares the schedule, observes, registers the images and stores them into
database without human intervention: human assistance is reduced to maintenance and weather checking. BART is a primary developing platform for RTS2, the robotic
telescope operation software, which allows for unattended observation as well as control of the entire observatory
Macropolyhedral boron-containing cluster chemistry: two-electron variations in intercluster bonding intimacy. Contrasting structures of 19-vertex [(eta(5)-C5Me5)HIrB18H19(PHPh2)] and [(eta(5) -C5Me5)IrB18H18(PH2Ph)]
Fused double-cluster [(5-C5Me5)IrB18H18(PH2Ph)]8, from syn-[(5-C5Me5)IrB18H20] 1 and PH2Ph, retains the three-atoms-in-common cluster fusion intimacy of 1, in contrast to [(5-C5Me5)HIrB18H19(PHPh2)]6, from PHPh2 with 1, which exhibits an opening to a two atoms-in-common cluster fusion intimacy. Compound 8 forms via spontaneous dihydrogen loss from its precursor [(5-C5Me5)HIrB18H19(PH2Ph)]7, which has two-atoms-in-common cluster-fusion intimacy and is structurally analogous to 6
A New Perspective on Clustered Planarity as a Combinatorial Embedding Problem
The clustered planarity problem (c-planarity) asks whether a hierarchically
clustered graph admits a planar drawing such that the clusters can be nicely
represented by regions. We introduce the cd-tree data structure and give a new
characterization of c-planarity. It leads to efficient algorithms for
c-planarity testing in the following cases. (i) Every cluster and every
co-cluster (complement of a cluster) has at most two connected components. (ii)
Every cluster has at most five outgoing edges.
Moreover, the cd-tree reveals interesting connections between c-planarity and
planarity with constraints on the order of edges around vertices. On one hand,
this gives rise to a bunch of new open problems related to c-planarity, on the
other hand it provides a new perspective on previous results.Comment: 17 pages, 2 figure
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