15,526 research outputs found
Some unexplored features of the nonlinear compressive magnetoacoustic Alfvenic waves
The theory of nonlinear magnetoacoustic wave in the past has strictly been
focused on purely compressive features of the mode. We show that a complete set
of nonlinear equations necessarily includes both compressional and shear
components of the magnetic field. These two turn out to be described by exactly
the same nonlinear equations, which make the use of such a complete full set of
equations far less complicated than expected. Present results should
considerably enrich the theory of these waves by opening up new frontiers of
investigation and providing some completely new types of nonlinear solutions.Comment: Phys. Scripta, to be publishe
Response to Comment of Shukla and Akbari-Moghanjoughi
Shukla and Akbari-Moghanjoughi have {\it corrected} their Comment (see their
version 1 on `arXiv:1207.7029v1) to EPL on our work [1] after receiving our
Response from the Editors of EPL. We have a pleasant duty at hand to present
our second Response to their second version of the Comment. It is hoped that
this response adds strength to our plea {\it for a common sense} [1] on quantum
description of plasmas.Comment: Submitted to EP
Degradation of Phosphorene in Air: Understanding at Atomic Level
Phosphorene is a promising two dimensional (2D) material with a direct band
gap, high carrier mobility, and anisotropic electronic properties.
Phosphorene-based electronic devices, however, are found to degrade upon
exposure to air. In this paper, we provide an atomic level understanding of
stability of phosphorene in terms of its interaction with O2 and H2O. The
results based on density functional theory together with first principles
molecular dynamics calculations show that O2 could spontaneously dissociate on
phosphorene at room temperature. H2O will not strongly interact with pristine
phosphorene, however, an exothermic reaction could occur if phosphorene is
first oxidized. The pathway of oxidation first followed by exothermic reaction
with water is the most likely route for the chemical degradation of the
phosphorene-based devices in air
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
Stress buildup in the Himalaya
The seismic cycle on a major fault involves long periods of elastic strain and stress accumulation, driven by aseismic ductile deformation at depth, ultimately released by sudden fault slip events. Coseismic slip distributions are generally heterogeneous with most of the energy being released in the rupture of asperities. Since, on the long term, the fault's walls generally do not accumulate any significant permanent deformation, interseismic deformation might be heterogeneous, revealing zones of focused stress buildup. The pattern of current deformation along the Himalayan arc, which is known to produce recurring devastating earthquakes, and where several seismic gaps have long been recognized, might accordingly show significant lateral variations, providing a possible explanation for the uneven microseismic activity along the Himalayan arc. By contrast, the geodetic measurements show a rather uniform pattern of interseismic strain, oriented consistently with long-term geological deformation, as indicated from stretching lineation. We show that the geodetic data and seismicity distribution are reconciled from a model in which microseismicity is interpreted as driven by stress buildup increase in the interseismic period. The uneven seismicity pattern is shown to reflect the impact of the topography on the stress field, indicating low deviatoric stresses (<35 MPa) and a low friction (<0.3) on the Main Himalayan Thrust. Arc-normal thrusting along the Himalayan front and east-west extension in southern Tibet are quantitatively reconciled by the model
Geochemistry of K/T boundaries in India and contributions of Deccan volcanism
Three possible Cretaceous/Tertiary (K/T) boundary sections in the Indian subcontinent were studied for their geochemical and fossil characteristics. These include two marine sections of Meghalaya and Zanskar and one continental section of Nagpur. The Um Sohryngkew river section of Meghalaya shows a high iridium, osmium, iron, cobalt, nickel and chromium concentration in a 1.5 cm thick limonitic layer about 30 cm below the planktonic Cretaceous-Palaeocene boundary identified by the characteristic fossils. The Bottaccione and Contessa sections at Gubbio were also analyzed for these elements. The geochemical pattern at the boundary at the Um Sohryngkew river and Gubbio sections are similar but the peak concentrations and the enrichment factors are different. The biological boundary is not as sharp as the geochemical boundary and the extinction appears to be a prolonged process. The Zanskar section shows, in general, similar concentration of the siderophile, lithophile and rare earth elements but no evidence of enrichment of siderophiles has so far been observed. The Takli section is a shallow inter-trappean deposit within the Deccan province, sandwiched between flow 1 and flow 2. The geochemical stratigraphy of the inter-trappeans is presented. The various horizons of ash, clay and marl show concentration of Fe and Co, generally lower than the adjacent basalts. Two horizons of slight enrichment of iridium are found within the ash layers, one near the contact of flow 1 and other near the contact of flow 2, where iridium occurs at 170 and 260 pg/g. These levels are lower by a factor of 30 compared to Ir concentration in the K/T boundary in Meghalaya section. If the enhanced level of some elements in a few horizons of the ash layer are considered as volcanic contribution by some fractionation processes than the only elements for which it occurs are REE, Ir and possibly Cr
X-ray emission from O-type stars : DH Cep and HD 97434
We present X-ray emission characteristics of the massive O-type stars DH Cep
and HD 97434 using archival XMM-Newton observations. There is no convincing
evidence for short term variability in the X-ray intensity during the
observations. However, the analysis of their spectra reveals X-ray structure
being consistent with two-temperature plasma model. The hydrogen column
densities derived from X-ray spectra of DH Cep and HD 97434 are in agreement
with the reddening measurements for their corresponding host clusters NGC 7380
and Trumpler 18, indicating that the absorption by stellar wind is negligible.
The X-ray emission from these hot stars is interpreted in terms of the standard
instability-driven wind shock model.Comment: 13 pages ; 2 figures; 2 tables (Accepted for publication in New
Astronomy
Ion thermal effects in oscillating multi-ion plasma sheath theory
The effects of ion temperature are discussed in a two-ion electron plasma and
for a model applicable to the oscillating sheath theory that has recently been
much in the focus of researchers. The differences between the fluid and kinetic
models have been pointed out, as well as the differences between the
approximative kinetic description (which involves the expansion of the plasma
dispersion function), and the exact kinetic description. It is shown that the
approximative kinetic description, first, can not describe the additional
acoustic mode which naturally exists in the plasma with an additional ion
population with a finite temperature, and, second, it yields an inaccurate
Landau damping of the bulk ion acoustic mode. The reasons for these two
failures are described. In addition to this, a fluid model is presented that is
capable of capturing both of these features that are missing in the
approximative kinetic description, i.e., two (fast and slow) ion acoustic
modes, and the corresponding Landau damping of both modes
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