2,490 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
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
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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
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
Protein disulfide isomerase A1 regulates breast cancer cell immunorecognition in a manner dependent on redox state
Oxidoreductase protein disulphide isomerases (PDI) are involved in the regulation of a variety of biological processes including the modulation of endoplasmic reticulum (ER) stress, unfolded protein response (UPR), ER‑mitochondria communication and the balance between pro‑survival and pro‑death pathways. In the current study the role of the PDIA1 family member in breast carcinogenesis was investigated by measuring ROS generation, mitochondrial membrane disruption, ATP production and HLA‑G protein levels on the surface of the cellular membrane in the presence or absence of PDIA1. The results showed that this enzyme exerted pro‑apoptotic effects in estrogen receptor (ERα)‑positive breast cancer MCF‑7 and pro‑survival in triple negative breast cancer (TNBC) MDA‑MB‑231 cells. ATP generation was upregulated in PDIA1‑silenced MCF‑7 cells and downregulated in PDIA1‑silenced MDA‑MB‑231 cells in a manner dependent on the cellular redox status. Furthermore, MCF‑7 and MDA‑MB‑231 cells in the presence of PDIA1 expressed higher surface levels of the non‑classical human leukocyte antigen (HLA‑G) under oxidative stress conditions. Evaluation of the METABRIC datasets showed that low PDIA1 and high HLA‑G mRNA expression levels correlated with longer survival in both ERα‑positive and ERα‑negative stage 2 breast cancer patients. In addition, analysis of the PDIA1 vs. the HLA‑G mRNA ratio in the subgroup of the living stage 2 breast cancer patients exhibiting low PDIA1 and high HLA‑G mRNA levels revealed that the longer the survival time of the ratio was high PDIA1 and low HLA‑G mRNA and occurred predominantly in ERα‑positive breast cancer patients whereas in the same subgroup of the ERα‑negative breast cancer mainly this ratio was low PDIA1 and high HLA‑G mRNA. Taken together these results provide evidence supporting the view that PDIA1 is linked to several hallmarks of breast cancer pathways including the process of antigen processing and presentation and tumor immunorecognition
Atomic Configuration of Nitrogen Doped Single-Walled Carbon Nanotubes
Having access to the chemical environment at the atomic level of a dopant in
a nanostructure is crucial for the understanding of its properties. We have
performed atomically-resolved electron energy-loss spectroscopy to detect
individual nitrogen dopants in single-walled carbon nanotubes and compared with
first principles calculations. We demonstrate that nitrogen doping occurs as
single atoms in different bonding configurations: graphitic-like and
pyrrolic-like substitutional nitrogen neighbouring local lattice distortion
such as Stone-Thrower-Wales defects. The stability under the electron beam of
these nanotubes has been studied in two extreme cases of nitrogen incorporation
content and configuration. These findings provide key information for the
applications of these nanostructures.Comment: 25 pages, 13 figure
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Differentiating the role of lithium and oxygen in retaining deuterium on lithiated graphite plasma-facing components
Laboratory experiments have been used to investigate the fundamental interactions responsible for deuterium retention in lithiated graphite. Oxygen was found to be present and play a key role in experiments that simulated NSTX lithium conditioning, where the atomic surface concentration can increase to >40% when deuterium retention chemistry is observed. Quantum-classical molecular dynamic simulations elucidated this oxygen-deuterium effect and showed that oxygen retains significantly more deuterium than lithium in a simulated matrix with 20% lithium, 20% oxygen, and 60% carbon. Simulations further show that deuterium retention is even higher when lithium is removed from the matrix. Experiments artificially increased the oxygen content in graphite to approximately 16% and then bombarded with deuterium. XPS showed depletion of the oxygen and no enhanced deuterium retention, thus demonstrating that lithium is essential in retaining the oxygen that thereby retains deuterium
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