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