13,186 research outputs found
Quintessence with Hybrid Potential
I present the numerical solution of equations of the evolution of a universe
containing background fluids (radiation, dark matter and baryonic matter), plus
a scalar matter field with a hybrid potential that is a combination of
exponential potential and power-law potential. The plot of the evolution of
density parameters is compatible with our universe; and today's values of
density parameters of dark energy, dark matter, baryonic matter, and Hubble
parameter, and the age and size of our universe, found from this model, are
very close to (and some times the same as) measured values.Comment: 10 pages, 4 figures include
Study of the antibacterial activity of total extract and Petroleum ether, chloroform, ethyl acetate and aqueous fractions of aerial parts of heliotropium bacciferum against staphylococcus aureus, Bacillus cereus, Pseudomonas aeruginosa, E.coli, Salmonella enteritidis
Heliotropium bacciferum is One of the plants belonging to the family Boraginaceae , which is Restricted distribution in the south of Iran. It is used for Hypotension, fever, stomach ulcers in traditional medicine. In this study, the antibacterial effects of extracts and fractions of chloroform, ethyl acetate and aqueous, aerial parts of Heliotropium bacciferum Forssk was evaluated against five bacterial strains. The methanol extract were prepared using the percolation method. Fractions of chloroform, Petroleum ether, ethyl acetate, methanol and aqueous respectively by Liquid - Liquid fractionation of the total extract were prepared. The antibacterial activity against two Gram positive bacteria, three Gram negative bacterial using Minimum inhibitory concentration in microplate and well plate method. Results showed that H. bacciferum extracts exhibited a significant activity against strains Staphylococcus aureus, Bacillus cereus,Pseudomonas aeruginosa, E.coli, Salmonella enteritidis. MIC and well plate is between 7.6-125 μg/ml. The results of this study indicate that extracts of the plant H.bacciferum has a antimicrobial effect against strains are listed And among the extracts, aqueous part is that most antibacterial effect of the other fraction and then methanolic extract has the greatest effect
Quintessence Ghost Dark Energy Model
A so called "ghost dark energy" was recently proposed to explain the present
acceleration of the universe expansion. The energy density of ghost dark
energy, which originates from Veneziano ghost of QCD, is proportional to the
Hubble parameter, , where is a constant which is
related to the QCD mass scale. In this paper, we establish the correspondence
between ghost dark energy and quintessence scalar field energy density. This
connection allows us to reconstruct the potential and the dynamics of the
quintessence scalar field according to the evolution of ghost energy density.Comment: 8 pages, 7 figures, version to appear in Europhys. Let
The Cognitive Compressive Sensing Problem
In the Cognitive Compressive Sensing (CCS) problem, a Cognitive Receiver (CR)
seeks to optimize the reward obtained by sensing an underlying dimensional
random vector, by collecting at most arbitrary projections of it. The
components of the latent vector represent sub-channels states, that change
dynamically from "busy" to "idle" and vice versa, as a Markov chain that is
biased towards producing sparse vectors. To identify the optimal strategy we
formulate the Multi-Armed Bandit Compressive Sensing (MAB-CS) problem,
generalizing the popular Cognitive Spectrum Sensing model, in which the CR can
sense out of the sub-channels, as well as the typical static setting of
Compressive Sensing, in which the CR observes linear combinations of the
dimensional sparse vector. The CR opportunistic choice of the sensing
matrix should balance the desire of revealing the state of as many dimensions
of the latent vector as possible, while not exceeding the limits beyond which
the vector support is no longer uniquely identifiable.Comment: 8 pages, 2 figure
The effect of the stochasticity of photoionization on 3D streamer simulations
Positive streamer discharges require a source of free electrons ahead of them
for their growth. In air, these electrons are typically provided by
photoionization. Here we investigate how stochastic fluctuations due to the
discreteness of ionizing photons affect positive streamers in air. We simulate
positive streamers between two planar electrodes with a 3D plasma fluid model,
using both a stochastic and a continuum method for photoionization. With
stochastic photoionization, fluctuations are visible in the streamer's
direction, maximal electric field, velocity, and electron density. The
streamers do not branch, and we find good agreement between the averaged
stochastic results and the results with continuum photoionization. The
streamers stay roughly axisymmetric, and we show that results obtained with an
axisymmetric model indeed agree well with the 3D results. However, we find that
positive streamers are sensitive to the amount of photoionization. When the
amount of photoionization is doubled, there is even better agreement between
the stochastic and continuum results, but with half the amount of
photoionization, stochastic fluctuations become more important and streamer
branching starts to occur
Graded Betti numbers of powers of ideals
Using the concept of vector partition functions, we investigate the
asymptotic behavior of graded Betti numbers of powers of homogeneous ideals in
a polynomial ring over a field. Our main results state that if the polynomial
ring is equipped with a positive \ZZ-grading, then the Betti numbers of
powers of ideals are encoded by finitely many polynomials.
More precisely, in the case of \ZZ-grading, \ZZ^2 can be splitted into a
finite number of regions such that each region corresponds to a polynomial that
depending to the degree , \dim_k \left(\tor_i^S(I^t, k)_{\mu}
\right) is equal to one of these polynomials in . This refines, in a
graded situation, the result of Kodiyalam on Betti numbers of powers of ideals.
Our main statement treats the case of a power products of homogeneous ideals
in a \ZZ^d-graded algebra, for a positive grading.Comment: 20 page
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