401 research outputs found
The CWKB particle production and classical condensate in de Sitter spacetime
The complex time WKB approximation is an effective tool in studying particle
production in curved spacetime. We use it in this work to understand the
formation of classical condensate in expanding de Sitter spacetime. The CWKB
leads to the emergence of thermal spectrum that depends crucially on horizons
(as in de Sitter spacetime) or observer dependent horizons (as in Rindler
spacetime). A connection is sought between the horizon and the formation of
classical condensate. We concentrate on de Sitter spacetime and study the
cosmological perturbation of mode with various values of . We find
that for a minimally coupled free scalar field for , the one-mode
occupation number grows more than unity soon after the physical wavelength of
the mode crosses the Hubble radius and soon after diverges as , where . The results substantiates the previous works in this
direction. We also find the correct oscillation and behaviour of at
small from a single expression using CWKB approximation for various values
of . We also discuss decoherence in relation to the formation of
classical condensate. We also find that the squeezed state formalism and CWKB
method give identical results.Comment: 19 pages, revtex, 5 figure
A new regime of anomalous penetration of relativistically strong laser radiation into an overdense plasma
It is shown that penetration of relativistically intense laser light into an
overdense plasma, accessible by self-induced transparency, occurs over a finite
length only. The penetration length depends crucially on the overdense plasma
parameter and increases with increasing incident intensity after exceeding the
threshold for self-induced transparency. Exact analytical solutions describing
the plasma-field distributions are presented.Comment: 6 pages, 2 figures in 2 separate eps files; submitted to JETP Letter
Traits associated with the escape strategy are responsible for flash flooding tolerance of rice during the emergence and seedling stages
To identify the adaptive traits responsible for flooding tolerance during the initial growth stages of rice, dry seeds of 53 contrasting genotypes were sown in soil and watered normally (control) or submerged with 10 cm of water for 17 days. Subsequently, the plants were kept under normal rice cultivation conditions for a further 7 days. Cluster analysis showed that 53 genotypes were divided into three groups based on emergence date, percentage of plants reaching the water’s surface, maximum coleoptile length, shoot elongation rate during submergence and increases in shoot dry weight after de-submergence. Twelve genotypes were placed in cluster 1 and characterized by fast emergence, rapid coleoptile elongation, and vigorous shoot growth under control and submergence conditions. The genotypes in cluster 1 attained also a higher increase in shoot dry weight at different time of submergence and de-submergence than the genotypes in clusters 2 and 3. A significant correlation was observed between the increase in shoot dry weight and traits related with fast and vigorous shoot elongation and coleoptile. In conclusion, flooding tolerance during initial growth stages were mainly due to major submergence avoidance or escape mechanisms, and crop establishment of direct-seeded rice in flood-prone areas is accomplished by harnessing reserves for fast shoot elongation
Higher Curvature Corrections to Primordial Fluctuations in Slow-roll Inflation
We study higher curvature corrections to the scalar spectral index, the
tensor spectral index, the tensor-to-scalar ratio, and the polarization of
gravitational waves. We find that the higher curvature corrections can not be
negligible in the dynamics of the scalar field, although they are energetically
negligible. Indeed, it turns out that the tensor-to-scalar ratio could be
enhanced and the tensor spectral index could be blue due to the Gauss-Bonnet
term. We estimate the degree of circular polarization of gravitational waves
generated during the slow-roll inflation. We argue that the circular
polarization can be observable with the help both of the Gauss-Bonnet and
parity violating terms. We also present several examples to reveal
observational implications of higher curvature corrections for chaotic
inflationary models.Comment: 12 pages, 4 figure
Electromagnetic energy penetration in the self-induced transparency regime of relativistic laser-plasma interactions
Two scenarios for the penetration of relativistically intense laser radiation
into an overdense plasma, accessible by self-induced transparency, are
presented. For supercritical densities less than 1.5 times the critical one,
penetration of laser energy occurs by soliton-like structures moving into the
plasma. At higher background densities laser light penetrates over a finite
length only, that increases with the incident intensity. In this regime
plasma-field structures represent alternating electron layers separated by
about half a wavelength by depleted regions.Comment: 9 pages, 4 figures, submitted for publication to PR
Exact results on the dynamics of multi-component Bose-Einstein condensate
We study the time-evolution of the two dimensional multi-component
Bose-Einstein condensate in an external harmonic trap with arbitrary
time-dependent frequency. We show analytically that the time-evolution of the
total mean-square radius of the wave-packet is determined in terms of the same
solvable equation as in the case of a single-component condensate. The dynamics
of the total mean-square radius is also the same for the rotating as well as
the non-rotating multi-component condensate. We determine the criteria for the
collapse of the condensate at a finite time. Generalizing our previous work on
a single-component condensate, we show explosion-implosion duality in the
multi-component condensate.Comment: Two-column 6 pages, RevTeX, no figures(v1); Added an important
reference, version to appear in Physical Review A (v2
Slow relaxation in the two dimensional electron plasma under the strong magnetic field
We study slow relaxation processes in the point vortex model for the
two-dimensional pure electron plasma under the strong magnetic field. By
numerical simulations, it is shown that, from an initial state, the system
undergoes the fast relaxation to a quasi-stationary state, and then goes
through the slow relaxation to reach a final state. From analysis of simulation
data, we find (i) the time scale of the slow relaxation increases linearly to
the number of electrons if it is measured by the unit of the bulk rotation
time, (ii) during the slow relaxation process, each electron undergoes an
superdiffusive motion, and (iii) the superdiffusive motion can be regarded as
the Levy flight, whose step size distribution is of the power law. The time
scale that each electron diffuses over the system size turns out to be much
shorter than that of the slow relaxation, which suggests that the correlation
among the superdiffusive trajectories is important in the slow relaxation
process.Comment: 11pages, 19 figures. Submitted to J. Phys. Soc. Jp
Quantum Brownian Motion in a Bath of Parametric Oscillators: A model for system-field interactions
The quantum Brownian motion paradigm provides a unified framework where one
can see the interconnection of some basic quantum statistical processes like
decoherence, dissipation, particle creation, noise and fluctuation. We treat
the case where the Brownian particle is coupled linearly to a bath of time
dependent quadratic oscillators. While the bath mimics a scalar field, the
motion of the Brownian particle modeled by a single oscillator could be used to
depict the behavior of a particle detector, a quantum field mode or the scale
factor of the universe. An important result of this paper is the derivation of
the influence functional encompassing the noise and dissipation kernels in
terms of the Bogolubov coefficients. This method enables one to trace the
source of statistical processes like decoherence and dissipation to vacuum
fluctuations and particle creation, and in turn impart a statistical mechanical
interpretation of quantum field processes. With this result we discuss the
statistical mechanical origin of quantum noise and thermal radiance from black
holes and from uniformly- accelerated observers in Minkowski space as well as
from the de Sitter universe discovered by Hawking, Unruh and Gibbons-Hawking.
We also derive the exact evolution operator and master equation for the reduced
density matrix of the system interacting with a parametric oscillator bath in
an initial squeezed thermal state. These results are useful for decoherence and
backreaction studies for systems and processes of interest in semiclassical
cosmology and gravity. Our model and results are also expected to be useful for
related problems in quantum optics. %\pacs
{05.40.+j,03.65.Sq,98.80.Cq,97.60.Lf}Comment: 42 pages, Latex, umdpp93-210 (submitted to Physical Review D, 3
December 1993
Dietary Factors Modulate Helicobacter-associated Gastric Cancer in Rodent Models
Since its discovery in 1982, the global importance of Helicobacter pylori–induced disease, particularly in developing countries, remains high. The use of rodent models, particularly mice, and the unanticipated usefulness of the gerbil to study H. pylori pathogenesis have been used extensively to study the interactions of the host, the pathogen, and the environmental conditions influencing the outcome of persistent H. pylori infection. Dietary factors in humans are increasingly recognized as being important factors in modulating progression and severity of H. pylori–induced gastric cancer. Studies using rodent models to verify and help explain mechanisms whereby various dietary ingredients impact disease outcome should continue to be extremely productive.National Institutes of Health (U.S.) (P01CA028842)National Institutes of Health (U.S.) (P01CA026731)National Institutes of Health (U.S.) (P30ES002109
Social Waves in Giant Honeybees Repel Hornets
Giant honeybees (Apis dorsata) nest in the open and have evolved a plethora of defence behaviors. Against predatory wasps, including hornets, they display highly coordinated Mexican wave-like cascades termed ‘shimmering’. Shimmering starts at distinct spots on the nest surface and then spreads across the nest within a split second whereby hundreds of individual bees flip their abdomens upwards. However, so far it is not known whether prey and predator interact and if shimmering has anti-predatory significance. This article reports on the complex spatial and temporal patterns of interaction between Giant honeybee and hornet exemplified in 450 filmed episodes of two A. dorsata colonies and hornets (Vespa sp.). Detailed frame-by-frame analysis showed that shimmering elicits an avoidance response from the hornets showing a strong temporal correlation with the time course of shimmering. In turn, the strength and the rate of the bees' shimmering are modulated by the hornets' flight speed and proximity. The findings suggest that shimmering creates a ‘shelter zone’ of around 50 cm that prevents predatory wasps from foraging bees directly from the nest surface. Thus shimmering appears to be a key defence strategy that supports the Giant honeybees' open-nesting life-style
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