333 research outputs found
Effect of the Generalized Uncertainty Principle on Post-Inflation Preheating
We examine effects of the Generalized Uncertainty Principle, predicted by
various theories of quantum gravity to replace the Heisenberg's uncertainty
principle near the Planck scale, on post inflation preheating in cosmology, and
show that it can predict either an increase or a decrease in parametric
resonance and a corresponding change in particle production. Possible
implications are considered.Comment: v1: 9 pages, revtex4, no figures, accepted for publication in JCAP;
v2: one reference added and various cosmetic (but no physics) changes to
match published versio
Impact of environmental factors on efficiency of rice production in Bangladesh
This study uses environment variables in Data Envelopment Analysis (DEA) and examines the influence of environmental factors on efficiency of rice production in Bangladesh.Data was collected from Bangladesh Bureau of Statistics (BBS) and Bangladesh Meteorology Department Efficiency with and without environmental factors of three type of rice production (AUS, AMAN and BORO) are measured using data envelopment analysis.Efficiency of rice production which measured without environmental factors is explained by the environmental factors (Rainfall, Temperature and Humidity) using Tobit regression to weigh up the impact of these factors on rice production.Efficiency of BORO production with environmental factors is almost similar to the efficiency of production without environmental factors. Production efficiency of AUS and AMAN employing environmental factors is higher than that of without environmental factors. Humidity has a positive and significant effect on all types of rice production.Temperature has a negative impact on production efficiency, implying that global warming could be a cause for a decrease in efficiency of rice production.Rainfall has a positive impact only on BORO production
Coverage Analysis of mmWave and THz-Enabled Aerial and Terrestrial Heterogeneous Networks
Heterogeneous networks (HetNets) are becoming a promising solution for future wireless systems to satisfy the high data rate requirements. This paper introduces a stochastic geometry framework for the analysis of the downlink coverage probability in a multi-tier HetNet consisting of a macro-base station (MBS) operating at sub-6 GHz, millimeter wave (mmWave)-enabled unmanned aerial vehicles (UAVs) operating at 28 GHz, and small BSs operating both at mmWave and THz frequencies. The analytical expressions for the coverage probability for each tier have been derived in the paper. Monte Carlo simulations are then performed to validate the analytical expressions. The effectiveness of the HetNet is analyzed on various performance metrics including association and coverage probabilities for different network parameters. We show that the mmWave and THz-enabled cells provide significant improvement in the achievable data rates because of their high available bandwidths, however, they have a degrading effect on the coverage probability due to their high propagation losses
Aquaculture for income and nutrition: Final report
The United States Agency for International Development-Aquaculture for Income and Nutrition (USAID-AIN) project, implemented by WorldFish, emphasized technology development for improved fish strains, and capacity building in hatcheries and nurseries for wider dissemination and uptake among small- and medium-scale household and commercial producers. Improving nutritional benefits from household aquaculture investment was also an important activity of the project. Specifically, AIN aimed to increase aquaculture production by developing hatcheries and nurseries, disseminating improved fish and shrimp seed, enhancing farm management skills of smallholder farmers, promoting new technologies to expand commercial aquaculture, developing backward and forward market linkages, supporting policy reform and building capacity of the public and private sectors, which resulted in increased productivity and revenue for farmers. This report also highlights the major achievements of the AIN project between 2011 and 2016
Path integral duality and Planck scale corrections to the primordial spectrum in exponential inflation
The enormous red-shifting of the modes during the inflationary epoch suggests
that physics at the Planck scale may modify the standard, nearly,
scale-invariant, primordial, density perturbation spectrum. Under the principle
of path-integral duality, the space-time behaves as though it has a minimal
length (which we shall assume to be of the order of the Planck
length), a feature that is expected to arise when the quantum gravitational
effects on the matter fields have been taken into account. Using the method of
path integral duality, in this work, we evaluate the Planck scale corrections
to the spectrum of density perturbations in the case of exponential inflation.
We find that the amplitude of the corrections is of the order of , where and denote the inflationary
and the Planck energy scales, respectively. We also find that the corrections
turn out to be completely independent of scale. We briefly discuss the
implications of our result, and also comment on how it compares with an earlier
result.Comment: 12 pages, 1 figure, RevTex4 forma
Big Crunch Avoidance in k = 1 Semi-Classical Loop Quantum Cosmology
It is well known that a closed universe with a minimally coupled massive
scalar field always collapses to a singularity unless the initial conditions
are extremely fine tuned. We show that the corrections to the equations of
motion for the massive scalar field, given by loop quantum gravity in high
curvature regime, always lead to a bounce independently of the initial
conditions. In contrast to the previous works in loop quantum cosmology, we
note that the singularity can be avoided even at the semi-classical level of
effective dynamical equations with non-perturbative quantum gravity
modifications, without using a discrete quantum evolution.Comment: Minor changes, To appear in Physical Review
Averaging Robertson-Walker Cosmologies
The cosmological backreaction arises when one directly averages the Einstein
equations to recover an effective Robertson-Walker cosmology, rather than
assuming a background a priori. While usually discussed in the context of dark
energy, strictly speaking any cosmological model should be recovered from such
a procedure. We apply the Buchert averaging formalism to linear
Robertson-Walker universes containing matter, radiation and dark energy and
evaluate numerically the discrepancies between the assumed and the averaged
behaviour, finding the largest deviations for an Einstein-de Sitter universe,
increasing rapidly with Hubble rate to a 0.01% effect for h=0.701. For the LCDM
concordance model, the backreaction is of the order of Omega_eff~4x10^-6, with
those for dark energy models being within a factor of two or three. The impacts
at recombination are of the order of 10^-8 and those in deep radiation
domination asymptote to a constant value. While the effective equations of
state of the backreactions in Einstein-de Sitter, concordance and quintessence
models are generally dust-like, a backreaction with an equation of state
w_eff<-1/3 can be found for strongly phantom models.Comment: 18 pages, 11 figures, ReVTeX. Updated to version accepted by JCA
Inverse cascade in decaying 3D magnetohydrodynamic turbulence
We perform direct numerical simulations of three-dimensional freely decaying
magnetohydrodynamic (MHD) turbulence. For helical magnetic fields an inverse
cascade effect is observed in which power is transfered from smaller scales to
larger scales. The magnetic field reaches a scaling regime with self-similar
evolution, and power law behavior at high wavenumbers. We also find power law
decay in the magnetic and kinematic energies, and power law growth in the
characteristic length scale of the magnetic field.Comment: 6 pages, 5 figures, minor changes to match published versio
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