708 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
Guaiacol as a new reagent for the spectrophotometric determination of uranium
Guiacol, i.e. o-hydroxyanisole, gives a distinct color reaction with U(VI)
suitable for spectrophotometric determination of the metal. The complex formed in the reaction has an
absorption maximum at 352 nm. Optimum pH for the color development ranges from 6.5 to 8.5. The molar
absorptivity and Sandell's sensitivity of the method were found to be 3.75×103
l.mol-1.cm-1 and 0.063 μg.cm-2, respectively. Many anions and
cations do not interfere up to 100 ppm. The method has been made very specific by selective
extraction of U(VI) with TBP from a mixture of different cations and anions in the presence of 60%
NH4NO3 as salting out agent followed by developing the color in the non-aqueous
phase by adding quaiacol in methanol at pH 6.5 to 8.5 An amount as low as 30 μg of uranium (VI)
per 10 ml of the solution could be satisfactorily determined with an RSD of ±2.0%. The method
was applied to rock samples after U(VI) had been extracted from a sample solution into 25% TBP in
hexane. Results obtained by the new method compare very well with those of conventional fluorimetric
and radiometric assays. The features of the method include excellent precision, rapidity, good
selectivity, and ease of performance
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
Molecular and Physiological Alterations in Chickpea under Elevated CO2 Concentrations
The present study reports profiling of the elevated carbon
dioxide (CO2) concentration responsive global transcriptome
in chickpea, along with a combinatorial approach for
exploring interlinks between physiological and transcriptional
changes, important for the climate change scenario.
Various physiological parameters were recorded in two
chickpea cultivars (JG 11 and KAK 2) grown in open top
chambers under ambient [380 parts per million (ppm)]
and two stressed/elevated CO2 concentrations (550 and
700 ppm), at different stages of plant growth. The elevated
CO2 concentrations altered shoot and root length, nodulation
(number of nodules), total chlorophyll content and nitrogen
balance index, significantly. RNA-Seq from 12 tissues
representing vegetative and reproductive growth stages of
both cultivars under ambient and elevated CO2 concentrations
identified 18,644 differentially expressed genes including
9,687 transcription factors (TF). The differential regulations
in genes, gene networks and quantitative real-time
polymerase chain reaction (qRT-PCR) -derived expression
dynamics of stress-responsive TFs were observed in both
cultivars studied. A total of 138 pathways, mainly involved
in sugar/starch metabolism, chlorophyll and secondary
metabolites biosynthesis, deciphered the crosstalk operating
behind the responses of chickpea to elevated CO2
concentration
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
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