2,658 research outputs found
Collisions, magnetization, and transport coefficients in the lower solar atmosphere
The lower solar atmosphere is an intrinsically multi-component and
collisional environment with electron and proton collision frequencies in the
range Hz, which may be considerably higher than the
gyro-frequencies for both species. We aim to provide a reliable quantitative
set of data for collision frequencies, magnetization, viscosity, and thermal
conductivity for the most important species in the lower solar atmosphere.
Having such data at hand is essential for any modeling that is aimed at
describing realistic properties of the considered environment.
We describe the altitude dependence of the parameters and the different
physics of collisions between charged species, and between charged and neutrals
species. Regions of dominance of each type of collisions are clearly
identified. We determine the layers within which either electrons or ions or
both are unmagnetized. Protons are shown to be un-magnetized in the lower
atmosphere in a layer that is at least 1000 km thick even for a kilo-Gauss
magnetic field that decreases exponentially with altitude. In these layers the
dynamics of charged species cannot be affected by the magnetic field, and this
fact is used in our modeling. Viscosity and thermal conductivity coefficients
are calculated for layers where ions are unmagnetized. We compare viscosity and
friction and determine the regions of dominance of each of the phenomena.
We provide the most reliable quantitative values for most important
parameters in the lower solar atmosphere to be used in analytical modeling and
numerical simulations of various phenomena such as waves, transport and
magnetization of particles, and the triggering mechanism of coronal mass
ejections.Comment: To appear in Astron. Astrophy
On quantum plasma: a plea for a common sense
The quantum plasma theory has flourished in the past few years without much
regard to the physical validity of the formulation or its connection to any
real physical system. It is argued here that there is a very limited physical
ground for the application of such a theory.Comment: EPL, to be published 201
Adaptive Tuning of Feedback Gain in Time-Delayed Feedback Control
We demonstrate that time-delayed feedback control can be improved by
adaptively tuning the feedback gain. This adaptive controller is applied to the
stabilization of an unstable fixed point and an unstable periodic orbit
embedded in a chaotic attractor. The adaptation algorithm is constructed using
the speed-gradient method of control theory. Our computer simulations show that
the adaptation algorithm can find an appropriate value of the feedback gain for
single and multiple delays. Furthermore, we show that our method is robust to
noise and different initial conditions.Comment: 7 pages, 6 figure
The Magellanic Stream and the density of coronal gas in the Galactic halo
The properties of the Magellanic Stream constrain the density of coronal gas
in the distant Galactic halo. We show that motion through ambient gas can
strongly heat Stream clouds, driving mass loss and causing evaporation. If the
ambient gas density is too high, then evaporation occurs on unreasonably short
timescales. Since heating dominates drag, tidal stripping appears to be
responsible for producing the Stream. Requiring the survival of the cloud MS IV
for 500 Myr sets an upper limit on the halo gas density n_H< 10^{-5} cm^{-3} at
50 kpc, roughly a factor of 10 lower than that estimated from the drag model of
Moore & Davis (1994). Implications for models of the evolution of gas in galaxy
halos are discussed.Comment: 4 pages, 1 figure, in press, ApJ
The role of farmed fish in the diets of the resource-poor in Egypt.
The Egyptian aquaculture industry provides more than 100,000 full-time or part-time jobs and produces the country’s least-expensive farmed animal protein. Thus, aquaculture plays an important role in both sustaining livelihoods and improving the diet quality and nutritional health of Egyptians, including a significant proportion of the 25.5% who are resource-poor. Recognizing this dual role, WorldFish has promoted sustainable growth in Egyptian aquaculture for more than 20 years. Through its work, WorldFish has identified a lack of quality data about fish consumption preferences and practices. Eager to fill this knowledge gap, WorldFish partnered with the Environment and Development Group (EDG) to study consumption of fish, red meat and poultry among the resource-poor in Egypt. This study aimed to characterize current consumer preferences for and consumption patterns of animal-source foods, comparing red meat, poultry and fish. The resulting data is meant to contribute to a better understanding of what drives demand for fish among the resource-poor in Egypt, allowing value chain actors to more successfully market their products to this segment of the population
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Electron capture by Ne2+ ions from atomic hydrogen
Using a merged-beam technique, the absolute, total electron-capture cross section has been measured for collisions of Ne2+ ions with hydrogen (deuterium) atoms at collision energies between 139 and 1490 eV/u. These data are compared to three other published measurements, two of which differ from one another by a factor greater than two. Early quantal rate coefficient calculations for Ne2+ ions with hydrogen at eV/u energies predict a cross section many orders of magnitude below the previously measured cross section at 40 eV/u. A possible explanation is given for the discrepancy between theory and experiment
Theoretical study of the formation of C<sub>18</sub>H and C<sub>18</sub>H<sub>2</sub> molecules by low energy irradiation with atomic and molecular hydrogen
Translocation of single-stranded DNA through single-walled carbon nanotubes
We report the fabrication of devices in which one single-walled carbon nanotube spans a barrier between two fluid reservoirs, enabling direct electrical measurement of ion transport through the tube. A fraction of the tubes pass anomalously high ionic currents. Electrophoretic transport of small single-stranded DNA oligomers through these tubes is marked by large transient increases in ion current and was confirmed by polymerase chain reaction analysis. Each current pulse contains about 10 7 charges, an enormous amplification of the translocated charge. Carbon nanotubes simplify the construction of nanopores, permit new types of electrical measurements, and may open avenues for control of DNA translocation.published_or_final_versio
Comparative study on the implementation of the ECHR at the national level
A Comparative analysis of the application of the European Convention on Human Rights in the national legal framework of several contracting states to the Conventio
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