11,111 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
Hall instability of solar flux tubes
The magnetic network which consists of vertical flux tubes located in
intergranular lanes is dominated by Hall drift in the photosphere-lower
chromosphere region (). In the internetwork regions, Hall drift
dominates above in the photosphere and below in the
chromosphere. Although Hall drift does not cause any dissipation in the ambient
plasma, it can destabilise the flux tubes and magnetic elements in the presence
of azimuthal shear flow. The physical mechanism of this instability is quite
simple: the shear flow twists the radial magnetic field and generates azimuthal
field; torsional oscillations of the azimuthal field in turn generates the
radial field completing feedback loop. The maximum growth rate of Hall
instability is proportional to the absolute value of the shear gradient and is
dependent on the ambient diffusivity. The diffusivity also determines the most
unstable wavelength which is smaller for weaker fields.
We apply the result of local stability analysis to the network and
internetwork magnetic elements and show that the maximum growth rate for
kilogauss field occurs around and decreases with increasing altitude.
However, for a field, the maximum growth rate remains almost constant
in the entire photosphere-lower chromosphere except in a small region of lower
photosphere. For shear flow gradient , the Hall growth time
is 10 minute near the footpoint. Therefore, network fields are likely to be
unstable in the photosphere, whereas internetwork fields could be unstable in
the entire photosphere-chromosphere. Thus the Hall instability can play an
important role in generating low frequency turbulence which can heat the
chromosphere.Comment: 8 page, 4 figure
Recommended from our members
Galactic R Coronae Borealis Stars: The C-2 Swan Bands, The Carbon Problem, And The C-12/C-13 Ratio
Observed spectra of R Coronae Borealis (RCB) and hydrogen-deficient carbon (HdC) stars are analyzed by synthesizing the C-2 Swan bands (1, 0), (0, 0), and (0, 1) using our detailed line list and the Uppsala model atmospheres. The (0, 1) and (0, 0) C-2 bands are used to derive the C-12 abundance, and the (1, 0) (CC)-C-12-C-13 band to determine the C-12/C-13 ratios. The carbon abundance derived from the C-2 Swan bands is about the same for the adopted models constructed with different carbon abundances over the range 8.5 (C/He = 0.1%) to 10.5 (C/He = 10%). Carbon abundances derived from C I lines are about a factor of four lower than the carbon abundance of the adopted model atmosphere over the same C/He interval, as reported by Asplund et al., who dubbed the mismatch between adopted and derived C abundance as the "carbon problem." In principle, the carbon abundances obtained from C-2 Swan bands and that assumed for the model atmosphere can be equated for a particular choice of C/He that varies from star to star. Then, the carbon problem for C-2 bands is eliminated. However, such C/He ratios are in general less than those of the extreme helium stars, the seemingly natural relatives to the RCB and HdC stars. A more likely solution to the C-2 carbon problem may lie in a modification of the model atmosphere's temperature structure. The derived carbon abundances and the C-12/C-13 ratios are discussed in light of the double degenerate and the final flash scenarios.Robert A. Welch Foundation of Houston, TX F-634McDonald Observator
Economic potential of forest resources of Nepal
Nepal's forest resources underpin the livelihoods of rural people in important ways. During the country's 'planned development' over the past 50 years, the government, donors and policy makers have viewed these resources as a key vehicle for ushering in economic growth and for meeting basic needs. They underscore the potential value of forest
resources for achieving conservation and socio-economic objectives. To what extent have economic incentives been generated to effectively harness these resources to meet the
said objectives is an open question. To address this question, this paper reviews briefly and broadly the economic potential of the country's forest resources in terms of forest goods and services. Estimates of economic potential of timber and non-timber forest products and environmental services have been assessed. A number of recommendations for realizing the potential for achieving development and poverty reduction objectives is provided
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
- …