285 research outputs found
Oxidation studies. I. Oxidation of primary alcohols by peroxydisulfate
Results on the oxidation of primary alcohols (methanol, ethanol, n-propanol, n-butanol and isobutanol) by peroxydisulfate in aqueous solution in the temperature range 50°-80°, under uncatalysed, Ag+ catalysed and deaerated conditions are presented. Oxygen was found to have a retarding effect on the rate of peroxydisulfate disappearance, -RS2O3−, and the inhibition period was a maximum in the case of ethanol and isobutanol. Both under uncatalysed and Ag+ catalysed conditions -RS2O3− varied with [S2O8-]3/2 for all the alcohols; -RS2O3− was independent of alcohol concentration for all the alcohols except for methanol and ethanol where a one-half order with respect to [alcohol] was observed. In the Ag+ catalysed oxidation -RS2O3− varied as [Ag+]½ with all the alcohols. The effect of [H+], ionic strength, temperature, initially added product of the reaction on the rate are discussed and the stoichiometries of the reactions determined. In the light of the observed results, reaction mechanisms are postulated with SO4•− as the reactive species formed by thermal decomposition of S2O8− under uncatalysed conditions and by the interaction of Ag+ and S2O8- under Ag+ catalysed conditions. The existence of Ag++ in catalysed reactions is postulated. The values of rate constants, frequency factors, energies of activation entropies of activation, etc., were evaluated
Vortex behavior near a spin vacancy in 2D XY-magnets
The dynamical behavior of anisotropic two dimensional Heisenberg models is
still a matter of controversy. The existence of a central peak at all
temperatures and a rich structure of magnon peaks are not yet understood. It
seems that the central peaks are related, in some way, to structures like
vortices. In order to contribute to the discussion of the dynamical behavior of
the model we use Monte Carlo and spin dynamics simulations as well analytical
calculations to study the behavior of vortices in the presence of nonmagnetic
impurities. Our simulations show that vortices are attracted and trapped by the
impurities. Using this result we show that if we suppose that vortices are not
very much disturbed by the presence of the impurities, then they work as an
attractive potential to the vortices explaining the observed behavior in our
simulations.Comment: 4 pages, 6 figure
Monte Carlo study of the critical temperature for the planar rotator model with nonmagnetic impurities
We performed Monte Carlo simulations to calculate the
Berezinskii-Kosterlitz-Thouless (BKT) temperature for the
two-dimensional planar rotator model in the presence of nonmagnetic impurity
concentration . As expected, our calculation shows that the BKT
temperature decreases as the spin vacancies increase. There is a critical
dilution at which . The effective interaction
between a vortex-antivortex pair and a static nonmagnetic impurity is studied
analytically. A simple phenomenological argument based on the pair-impurity
interaction is proposed to justify the simulations.Comment: 5 pages, 5 figures, Revetex fil
Marine fisheries of the south-west coast of India during 2008
The south-west region comprising the states of
Kerala, Karnataka and Goa with a coastline of
994 km and 7.83 lakh fishermen population, had
been the most productive and the largest contributor
to the country’s total marine fish landings. Marine
fish production in this region during the year 2008
has been estimated as 11.11 lakh t, contributing
about 34.5% to the all India landing
Discommensurational and Inhomogeneous States Induced by a Strong Magnetic Field in Low-Dimensional Antiferromagnets
Anisotropic antiferromagnetic systems of dimensionality greater than one in
an external field are shown to exhibit a complicated array of ground states
depending on the spin structure of the surface. The simplest structure that
exhibits these effects is the spin ladder with the surface being the ladder
end, which can be either compensated or non-compensated spins. The structure
with the compensated end has a surface spin flop phase, the non-compensated end
has a discommensurational phase, and the transition to these phases can be
either first or second order with a tricritical point.Comment: 10 page
Estimated marine fish landings (in tonnes)in India during 2002 and 2003
Estimated marine fishing landing in India during 2002 and 2003 is 2.59 and 2.58 millon tonnes respectively. Gear wise landing were also estimated during this period
Morphology of supported polymer electrolyte ultra-thin films: a numerical study
Morphology of polymer electrolytes membranes (PEM), e.g., Nafion, inside PEM
fuel cell catalyst layers has significant impact on the electrochemical
activity and transport phenomena that determine cell performance. In those
regions, Nafion can be found as an ultra-thin film, coating the catalyst and
the catalyst support surfaces. The impact of the hydrophilic/hydrophobic
character of these surfaces on the structural formation of the films has not
been sufficiently explored yet. Here, we report about Molecular Dynamics
simulation investigation of the substrate effects on the ionomer ultra-thin
film morphology at different hydration levels. We use a mean-field-like model
we introduced in previous publications for the interaction of the hydrated
Nafion ionomer with a substrate, characterized by a tunable degree of
hydrophilicity. We show that the affinity of the substrate with water plays a
crucial role in the molecular rearrangement of the ionomer film, resulting in
completely different morphologies. Detailed structural description in different
regions of the film shows evidences of strongly heterogeneous behavior. A
qualitative discussion of the implications of our observations on the PEMFC
catalyst layer performance is finally proposed
Overview of marine fisheries in India during 2007
Fisheries sector in India plays an important role
in the country’s economy and it supports the livelihood
of millions of people. India is having 8,129 km of
coastal length with 2.02 million sq. km of Exclusive
Economic Zone (upto 200 m depth) and 0.452 million
sq. km of continental shelf area
Heavy Quark Solitons: Strangeness and Symmetry Breaking
We discuss the generalization of the Callan-Klebanov model to the case of
heavy quark baryons. The light flavor group is considered to be and the
limit of heavy spin symmetry is taken. The presence of the Wess-Zumino-Witten
term permits the neat development of a picture , at the collective level, of a
light diquark bound to a ``heavy" quark with decoupled spin degree of freedom.
The consequences of symmetry breaking are discussed in detail. We point
out that the mass splittings of the heavy baryons essentially measure
the ``low energy" physics once more and that the comparison with experiment is
satisfactory.Comment: 17 pages, RevTEX. Minor typos corrected and new references adde
Oscillating Solitons Pinned to a Nonmagnetic Impurity in Layered Antiferromagnets
We argue that an oscillatory motion of impurity-pinned solitons may occur in
layered antiferromagnetic compounds. The characteristic frequencies of these
modes, that may be detected by resonance or inelastic neutron scattering, are
estimated analytically and depend on the soliton sizes and types .Comment: 11 pages, 1 figur
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