21,643 research outputs found
Agriculture as a source of fuel prospects and impacts, 2007 to 2017
Resource /Energy Economics and Policy,
EVALUATING THE IMPACTS OF AN INCREASE IN FUEL-ETHANOL DEMAND ON AGRICULTURE AND THE ECONOMY
Fuel ethanol demand is projected to increase because of proposed ban on methyl tertiary butyl ether (MTBE) in gasoline, renewable fuels standard, and the revised eight-hour ozone standards. In this paper, several scenarios of increased fuel ethanol demand and its effects on crop and feed prices, farm income and state finances under current tax-subsidy structure, are analyzed using a multi-sector econometric model AGMOD.Resource /Energy Economics and Policy,
Stability of Naked Singularity arising in gravitational collapse of Type I matter fields
Considering gravitational collapse of Type I matter fields, we prove that,
given an arbitrary - mass function and a -
function (through the corresponding - metric function
), there exist infinitely many choices of energy distribution
function such that the `true' initial data () leads
the collapse to the formation of naked singularity. We further prove that the
occurrence of such a naked singularity is stable with respect to small changes
in the initial data. We remark that though the initial data leading to both
black hole and naked singularity form a "big" subset of the true initial data
set, their occurrence is not generic. The terms `stability' and `genericity'
are appropriately defined following the theory of dynamical systems. The
particular case of radial pressure has been illustrated in details
to get clear picture of how naked singularity is formed and how, it is stable
with respect to initial data.Comment: 16 pages, no figure, Latex, submitted to Praman
Tropical rainforest bird community structure in relation to altitude, tree species composition, and null models in the Western Ghats, India
Studies of species distributions on elevational gradients are essential to
understand principles of community organisation as well as to conserve species
in montane regions. This study examined the patterns of species richness,
abundance, composition, range sizes, and distribution of rainforest birds at 14
sites along an elevational gradient (500-1400 m) in the Kalakad-Mundanthurai
Tiger Reserve (KMTR) of the Western Ghats, India. In contrast to theoretical
expectation, resident bird species richness did not change significantly with
elevation although the species composition changed substantially (<10%
similarity) between the lowest and highest elevation sites. Constancy in
species richness was possibly due to relative constancy in productivity and
lack of elevational trends in vegetation structure. Elevational range size of
birds, expected to increase with elevation according to Rapoport's rule, was
found to show a contrasting inverse U-shaped pattern because species with
narrow elevational distributions, including endemics, occurred at both ends of
the gradient (below 800 m and above 1,200 m). Bird species composition also did
not vary randomly along the gradient as assessed using a hierarchy of null
models of community assembly, from completely unconstrained models to ones with
species richness and range-size distribution restrictions. Instead, bird
community composition was significantly correlated with elevation and tree
species composition of sites, indicating the influence of deterministic factors
on bird community structure. Conservation of low- and high-elevation areas and
maintenance of tree species composition against habitat alteration are
important for bird conservation in the southern Western Ghats rainforests.Comment: 36 pages, 5 figures, two tables (including one in the appendix)
Submitted to the Journal of the Bombay Natural History Society (JBNHS
Genericity aspects in gravitational collapse to black holes and naked singularities
We investigate here the genericity and stability aspects for naked
singularities and black holes that arise as the final states for a complete
gravitational collapse of a spherical massive matter cloud. The form of the
matter considered is a general Type I matter field, which includes most of the
physically reasonable matter fields such as dust, perfect fluids and such other
physically interesting forms of matter widely used in gravitation theory. We
first study here in some detail the effects of small pressure perturbations in
an otherwise pressure-free collapse scenario, and examine how a collapse
evolution that was going to the black hole endstate would be modified and go to
a naked singularity, once small pressures are introduced in the initial data.
This allows us to understand the distribution of black holes and naked
singularities in the initial data space. Collapse is examined in terms of the
evolutions allowed by Einstein equations, under suitable physical conditions
and as evolving from a regular initial data. We then show that both black holes
and naked singularities are generic outcomes of a complete collapse, when
genericity is defined in a suitable sense in an appropriate space.Comment: 24 pages, 6 figures, some changes in text and figures to match the
version accepted for publication by IJMP
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