1,319 research outputs found
Solar activity forecast with a dynamo model
Although systematic measurements of the solar polar magnetic field exist only
from mid 1970s, other proxies can be used to infer the polar field at earlier
times. The observational data indicate a strong correlation between the polar
field at a sunspot minimum and the strength of the next cycle, although the
strength of the cycle is not correlated well with the polar field produced at
its end. This suggests that the Babcock Leighton mechanism of poloidal field
generation from decaying sunspots involves randomness, whereas the other
aspects of the dynamo process must be reasonably ordered and deterministic.
Only if the magnetic diffusivity within the convection zone is assumed to be
high, we can explain the correlation between the polar field at a minimum and
the next cycle. We give several independent arguments that the diffusivity must
be of this order. In a dynamo model with diffusivity like this, the poloidal
field generated at the mid latitudes is advected toward the poles by the
meridional circulation and simultaneously diffuses towards the tachocline,
where the toroidal field for the next cycle is produced. To model actual solar
cycles with a dynamo model having such high diffusivity, we have to feed the
observational data of the poloidal field at the minimum into the theoretical
model. We develop a method of doing this in a systematic way. Our model
predicts that cycle 24 will be a very weak cycle. Hemispheric asymmetry of
solar activity is also calculated with our model and compared with
observational data.Comment: 17 pages, 18 figures, submitted to MNRA
Elasticity of DNA and the effect of Dendrimer Binding
Negatively charged DNA can be compacted by positively charged dendrimers and
the degree of compaction is a delicate balance between the strength of the
electrostatic interaction and the elasticity of DNA. We report various elastic
properties of short double stranded DNA (dsDNA) and the effect of dendrimer
binding using fully atomistic molecular dynamics and numerical simulations. In
equilibrium at room temperature, the contour length distribution P(L) and
end-to-end distance distribution P(R) are nearly Gaussian, the former gives an
estimate of the stretch modulus {\gamma}_1 of dsDNA in quantitative agreement
with the literature value. The bend angle distribution P({\theta}) of the dsDNA
also has a Gaussian form and allows to extract a persistence length, L_p of 43
nm. When the dsDNA is compacted by positively charged dendrimer, the stretch
modulus stays invariant but the effective bending rigidity estimated from the
end-to-end distance distribution decreases dramatically due to backbone charge
neutralization of dsDNA by dendrimer. We support our observations with
numerical solutions of the worm-like-chain (WLC) model as well as using
non-equilibrium dsDNA stretching simulations. These results are helpful in
understanding the dsDNA elasticity at short length scales as well as how the
elasticity is modulated when dsDNA binds to a charged object such as a
dendrimer or protein.Comment: 21 pages, 5 figure
The Waldmeier Effect in Sunspot Cycles
We discuss two aspects of the Waldmeier Effect, namely (1) the rise times of
sunspot cycles are anti-correlated to their strengths (WE1) and (2) the rates
of rise of the cycles are correlated to their strengths (WE2). From analysis of
four different data sets we conclude that both WE1 and WE2 exist in all the
data sets. We study these effects theoretically by introducing suitable
stochastic fluctuations in our regular solar dynamo model.Comment: Magnetic Coupling between the Interior and Atmosphere of the Sun;
Astrophysics and Space Science Proceeding
Reply to comments of Dikpati et al
We present here our response to Dikpati et al.'s criticism of our recent
solar dynamo model.Comment: 8 pages, 2 figure
Tungsten Heavy Alloys with Two phase Matrix
WNiCo alloys subjected to a two-stage or cyclic heat treatment develop a unique microstructure wherein apart from tungsten grains and matrix phase, fine tungsten precipitates are distributed in the matrix. This is unlike conventional heavy alloys such as WNiFe and WNiFeCo where the matrix is single phase without any secondary microstructural features. The purpose of developing a two-phase matrix is to realise superior mechanical properties compared to conventional alloys, especially strength with comparable or superior elongation and impact toughness. This advantage has rendered WNiCo alloys (with two-phase matrix) suitable candidates for advanced kinetic energy penetrators. The present study focusses on processing 92W-5Ni-3Co alloy using cyclic heat treatment and optimisation of parameters involved in cyclic heat treatment as well as subsequent vacuum heat treatment. Any refinement in processing parameters will help in improving the mechanical properties given the fact that processing parameters, microstructural features and mechanical properties are strongly interdependent in the case of tungsten heavy alloys
Survey of incidence of various surface defects in goat and sheep skin in Madras
23,429 goat skins and 37,026 sheep skins were examined to find out the incidence of various surface defects in them. 33.44 percent of goat
skins and 14.6 per cent of sheep skins were found to be affected in quality. Major defects common to both goat and sheep skins were
abscess, fire-mark and psoroptosis. In addition to the above common defects demodecosis and sheep pox appreciably deteriorated the quality of
goat and sheep skins respectively. Seasonal variation in the incidence of the major defects were also studied
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