1,943 research outputs found
Vacuum Fluctuations of Energy Density can lead to the observed Cosmological Constant
The energy density associated with Planck length is while the energy density associated with the Hubble length is
where . The observed value of the dark
energy density is quite different from {\it either} of these and is close to
the geometric mean of the two: .
It is argued that classical gravity is actually a probe of the vacuum {\it
fluctuations} of energy density, rather than the energy density itself. While
the globally defined ground state, being an eigenstate of Hamiltonian, will not
have any fluctuations, the ground state energy in the finite region of space
bounded by the cosmic horizon will exhibit fluctuations . When used as a source of gravity, this should
lead to a spacetime with a horizon size . This bootstrapping condition
leads naturally to an effective dark energy density which is precisely the observed value. The model
requires, either (i) a stochastic fluctuations of vacuum energy which is
correlated over about a Hubble time or (ii) a semi- anthropic interpretation.
The implications are discussed.Comment: r pages; revtex; comments welcom
Why do we observe a small but non zero cosmological constant ?
The current observations seem to suggest that the universe has a positive
cosmological constant of the order of while the most natural value for
the cosmological constant will be where
is the Planck length. This reduction of the cosmological constant from
to may be interpreted as due to the ability of
quantum micro structure of spacetime to readjust itself and absorb bulk vacuum
energy densities. Being a quantum mechanical process, such a cancellation
cannot be exact and the residual quantum fluctuations appear as the ``small''
cosmological constant. I describe the features of a toy model for the spacetime
micro structure which could allow for the bulk vacuum energy densities to be
canceled leaving behind a small residual value of the the correct magnitude.
Some other models (like the ones based on canonical ensemble for the four
volume or quantum fluctuations of the horizon size) lead to an insignificantly
small value of with showing that obtaining the
correct order of magnitude for the residual fluctuations in the cosmological
constant is a nontrivial task, becaue of the existence of the small
dimensionless number .Comment: couple of references added; matches with published versio
A note on entropic force and brane cosmology
Recently Verlinde proposed that gravity is an entropic force caused by
information changes when a material body moves away from the holographic
screen. In this note we apply this argument to brane cosmology, and show that
the cosmological equation can be derived from this holographic scenario.Comment: 5 pages, no figures;references adde
Studies on the inheritance of leaf blast resistance in rice
Studies on the inheritance of leaf blast resistance in seven differential varieties of rice tested against two Indian isolates of the international races IA-11 add ID-1 of Pyricularia oryzae Cav. under standardized experimental conditions revealed the presence of three dominant genes, one each in Zenith. Tetep and Ginga conferring resistance to IA-11 and two, one each in Zenith and Tetep, to the race ID-1. The genes of Zenith were independent of those of Tetep. C.l. 5309 possessed inhibitory genes inhibiting the resistance of Zenith but not of Telep. Mode of segregation of resistance o Norin 20 to the race IA-11 was found to be anamolous. Studies on the crosses among susecptible varieties showed the existence of dominant genes conferring susceptibility, two each in P.I. 180061 and Yakeiko. This is a new feature of the present studies and its utility in evolving homozygous recessive resistant varieties have been pointed out
Studies on forecasting outbreaks of blast disease of rice. I. Influence of meteorological factors on blast incidence at Cuttack
This article does not have an abstract
The relation between loss in viability and seed-borne micro-flora in rice
This article does not have an abstract
Fusarium sp. parasitic on Epipyrops, a lepidopterous parasite of the sugarcane Pyrilla
This article does not have an abstract
Towards an Optimal Reconstruction of Baryon Oscillations
The Baryon Acoustic Oscillations (BAO) in the large-scale structure of the
universe leave a distinct peak in the two-point correlation function of the
matter distribution. That acoustic peak is smeared and shifted by bulk flows
and non-linear evolution. However, it has been shown that it is still possible
to sharpen the peak and remove its shift by undoing the effects of the bulk
flows. We propose an improvement to the standard acoustic peak reconstruction.
Contrary to the standard approach, the new scheme has no free parameters,
treats the large-scale modes consistently, and uses optimal filters to extract
the BAO information. At redshift of zero, the reconstructed linear matter power
spectrum leads to a markedly improved sharpening of the reconstructed acoustic
peak compared to standard reconstruction.Comment: 20 pages, 5 figures; footnote adde
Concept of temperature in multi-horizon spacetimes: Analysis of Schwarzschild-De Sitter metric
In case of spacetimes with single horizon, there exist several
well-established procedures for relating the surface gravity of the horizon to
a thermodynamic temperature. Such procedures, however, cannot be extended in a
straightforward manner when a spacetime has multiple horizons. In particular,
it is not clear whether there exists a notion of global temperature
characterizing the multi-horizon spacetimes. We examine the conditions under
which a global temperature can exist for a spacetime with two horizons using
the example of Schwarzschild-De Sitter (SDS) spacetime. We systematically
extend different procedures (like the expectation value of stress tensor,
response of particle detectors, periodicity in the Euclidean time etc.) for
identifying a temperature in the case of spacetimes with single horizon to the
SDS spacetime. This analysis is facilitated by using a global coordinate chart
which covers the entire SDS manifold. We find that all the procedures lead to a
consistent picture characterized by the following features: (a) In general, SDS
spacetime behaves like a non-equilibrium system characterized by two
temperatures. (b) It is not possible to associate a global temperature with SDS
spacetime except when the ratio of the two surface gravities is rational (c)
Even when the ratio of the two surface gravities is rational, the thermal
nature depends on the coordinate chart used. There exists a global coordinate
chart in which there is global equilibrium temperature while there exist other
charts in which SDS behaves as though it has two different temperatures. The
coordinate dependence of the thermal nature is reminiscent of the flat
spacetime in Minkowski and Rindler coordinate charts. The implications are
discussed.Comment: 12 page
Relation between the age of rice plant and its susceptibility to Helminthosporium and blast diseases
The susceptibility of rice plants of different ages to Helminthosporium disease was studied by conducting artificial infection tests on three different dates during the season. Three varieties, 2 susceptible and a resistant were included in the study. It was found that the susceptibility increased with age of plants and the relative susceptibility of varieties, as compared between plants of the same age remained the same at any time during the season. Inoculations carried out in September produced the maximum infection. Susceptibility to Blast disease at different ages was studied in 2 field experiments. It was found that younger plants were most susceptible and the resistance increased as the plants grew older. Only the post-planting age of the plants had an effect on their susceptibility
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