628 research outputs found
Lower mass limit of an evolving interstellar cloud and chemistry in an evolving oscillatory cloud
Simultaneous solution of the equation of motion, equation of state and energy equation including heating and cooling processes for interstellar medium gives for a collapsing cloud a lower mass limit which is significantly smaller than the Jeans mass for the same initial density. The clouds with higher mass than this limiting mass collapse whereas clouds with smaller than critical mass pass through a maximum central density giving apparently similar clouds (i.e., same Av, size and central density) at two different phases of its evolution (i.e., with different life time). Preliminary results of chemistry in such an evolving oscillatory cloud show significant difference in abundances of some of the molecules in two physically similar clouds with different life times. The problems of depletion and short life time of evolving clouds appear to be less severe in such an oscillatory cloud
On non-LTE H<SUB>2</SUB><SUP>+</SUP> as missing solar opacity
A careful examination has revealed that use of incomplete reaction processes and incorrect rates have led Krishna Swamy and Stecher to overestimate the H2+ opacity by a factor of 104 at λ = 2000 Å. H2+ is not a significant source of opacity in the solar atmosphere
On the Correlation Between CO Absorption and Far-Ultraviolet Non-Linear Extinction Toward Galactic OB Stars
A sample of 59 sight lines to reddened Galactic OB stars was examined for
correlations of the strength of the CO Fourth Positive (A - X) absorption band
system with the ultraviolet interstellar extinction curve parameters. We used
archival high-dispersion NEWSIPS IUE spectra to measure the CO absorption for
comparison to parametric fits of the extinction curves from the literature. A
strong correlation with the non-linear far-UV curvature term was found with
greater absorption, normalized to E(B-V), being associated with more curvature.
A weaker trend with the linear extinction term was also found. Mechanisms for
enhancing CO in dust environments exhibiting high non-linear curvature are
discussed.Comment: 10 pages, including 6 figures. LaTeX2e (emulateapj5.sty). To appear
in ApJ, Sep 20, 200
Diffusion with rearranging traps
A model for diffusion on a cubic lattice with a random distribution of traps
is developed. The traps are redistributed at certain time intervals. Such
models are useful for describing systems showing dynamic disorder, such as
ion-conducting polymers. In the present model the traps are infinite, unlike an
earlier version with finite traps, this model has a percolation threshold. For
the infinite trap version a simple analytical calculation is possible and the
results agree qualitatively with simulation.Comment: Latex, five figure
Percolation in Models of Thin Film Depositions
We have studied the percolation behaviour of deposits for different
(2+1)-dimensional models of surface layer formation. The mixed model of
deposition was used, where particles were deposited selectively according to
the random (RD) and ballistic (BD) deposition rules. In the mixed one-component
models with deposition of only conducting particles, the mean height of the
percolation layer (measured in monolayers) grows continuously from 0.89832 for
the pure RD model to 2.605 for the pure RD model, but the percolation
transition belong to the same universality class, as in the 2- dimensional
random percolation problem. In two- component models with deposition of
conducting and isolating particles, the percolation layer height approaches
infinity as concentration of the isolating particles becomes higher than some
critical value. The crossover from 2d to 3d percolation was observed with
increase of the percolation layer height.Comment: 4 pages, 5 figure
How the geometry makes the criticality in two - component spreading phenomena?
We study numerically a two-component A-B spreading model (SMK model) for
concave and convex radial growth of 2d-geometries. The seed is chosen to be an
occupied circle line, and growth spreads inside the circle (concave geometry)
or outside the circle (convex geometry). On the basis of generalised
diffusion-annihilation equation for domain evolution, we derive the mean field
relations describing quite well the results of numerical investigations. We
conclude that the intrinsic universality of the SMK does not depend on the
geometry and the dependence of criticality versus the curvature observed in
numerical experiments is only an apparent effect. We discuss the dependence of
the apparent critical exponent upon the spreading geometry and
initial conditions.Comment: Uses iopart.cls, 11 pages with 8 postscript figures embedde
Molecular Analysis of Disease-Responsive Genes Revealing the Resistance Potential Against Fusarium Wilt (Fusarium udum Butler) Dependent on Genotype Variability in the Leguminous Crop Pigeonpea
Fusarium wilt (FW), caused by Fusarium udum Butler (FU), is among the
challenging factors in the production of pigeonpea. Therefore, exploring a superior
pigeonpea genotype from landraces or local cultivars through the selection of
innate resistance to FW using different biological and molecular approaches, and
validating its resistance response, could be an alternative to sustainable crop
improvement. Five distinct pigeonpea genotypes, with resistant (ICP2894) and
susceptible (ICP2376) controls, were selected on the basis of the incidence percentage
of FW, from three different states of India. Among them, the cultivar Richa,
which displayed low incidence of FW (10.0%) during the genotype evaluation,
was further examined for its innate resistance to FW. Molecular characterization
of antioxidant (AO) enzyme [APX and SOD] and pathogenesis-related (PR) protein
[CHS and b-1, 3-glucanase] families were performed. The obtained results of
reverse transcription-polymerase chain reaction-based expression study and in silico
analysis showed a higher level of induction of PR and AO genes, and the
strong interaction of their putative proteins with fungal cellobiohydrolase-c protein
established their antifungal activity, conferring early plant defense responses to FU in Richa. Our study demonstrated a strong and combinatorial approach
involving biological assay, molecular experiments, and in silico analysis to identify
a superior pigeonpea genotype that was resistant to FW across a major
biogeographic region
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