269 research outputs found
Consistency of Gravity with the Cosmological Observations in Palatini Formalism
In this work we study the dynamics of universe in
modified gravity with Palatini formalism. We use data from recent observations
as Supernova Type Ia (SNIa) Gold sample and Supernova Legacy Survey (SNLS)
data, size of baryonic acoustic peak from Sloan Digital Sky Survey (SDSS), the
position of the acoustic peak from the CMB observations and large scale
structure formation (LSS) from the 2dFGRS survey to put constraint on the
parameters of the model. To check the consistency of this action, we compare
the age of old cosmological objects with the age of universe. In the combined
analysis with the all the observations, we find the parameters of model as
and
.Comment: 12 pages, 7 figure
Uncertainty in the Fluctuations of the Price of Stocks
We report on a study of the Tehran Price Index (TEPIX) from 2001 to 2006 as
an emerging market that has been affected by several political crises during
the recent years, and analyze the non-Gaussian probability density function
(PDF) of the log returns of the stocks' prices. We show that while the average
of the index did not fall very much over the time period of the study, its
day-to-day fluctuations strongly increased due to the crises. Using an approach
based on multiplicative processes with a detrending procedure, we study the
scale-dependence of the non-Gaussian PDFs, and show that the temporal
dependence of their tails indicates a gradual and systematic increase in the
probability of the appearance of large increments in the returns on approaching
distinct critical time scales over which the TEPIX has exhibited maximum
uncertainty.Comment: 5 pages, 5 figures. Accepted to appear in IJMP
Power-law Parameterized Quintessence Model
We introduce a power-law parameterized quintessence model for the dark energy
which accelerate universe at the low redshifts while behaves as an ordinary
matter for the early universe. We construct a unique scalar potential for this
parameterized quintessence model. As the observational test, the Supernova Type
Ia (SNIa) Gold sample data, size of baryonic acoustic peak from Sloan Digital
Sky Survey (SDSS), the position of the acoustic peak from the CMB observations
and structure formation from the 2dFGRS survey are used to constrain the
parameters of the quintessence model. The best fit parameters indicates that
the equation of state of this model at the present time is less than one
which violates the energy condition in General Relativity. Finally
we compare the age of old objects with age of universe in this model.Comment: 11 pages, 17 figures, submitted to Phys. Rev.
Quantitative features of multifractal subtleties in time series
Based on the Multifractal Detrended Fluctuation Analysis (MFDFA) and on the
Wavelet Transform Modulus Maxima (WTMM) methods we investigate the origin of
multifractality in the time series. Series fluctuating according to a qGaussian
distribution, both uncorrelated and correlated in time, are used. For the
uncorrelated series at the border (q=5/3) between the Gaussian and the Levy
basins of attraction asymptotically we find a phase-like transition between
monofractal and bifractal characteristics. This indicates that these may solely
be the specific nonlinear temporal correlations that organize the series into a
genuine multifractal hierarchy. For analyzing various features of
multifractality due to such correlations, we use the model series generated
from the binomial cascade as well as empirical series. Then, within the
temporal ranges of well developed power-law correlations we find a fast
convergence in all multifractal measures. Besides of its practical significance
this fact may reflect another manifestation of a conjectured q-generalized
Central Limit Theorem
Long range correlation in cosmic microwave background radiation
We investigate the statistical anisotropy and Gaussianity of temperature
fluctuations of Cosmic Microwave Background radiation (CMB) data from {\it
Wilkinson Microwave Anisotropy Probe} survey, using the multifractal detrended
fluctuation analysis, rescaled range and scaled windowed variance methods. The
multifractal detrended fluctuation analysis shows that CMB fluctuations has a
long range correlation function with a multifractal behavior. By comparing the
shuffled and surrogate series of CMB data, we conclude that the multifractality
nature of temperature fluctuation of CMB is mainly due to the long-range
correlations and the map is consistent with a Gaussian distribution.Comment: 10 pages, 7 figures, V2: Added comments, references and major
correction
Long-range correlation and multifractality in Bach's Inventions pitches
We show that it can be considered some of Bach pitches series as a stochastic
process with scaling behavior. Using multifractal deterend fluctuation analysis
(MF-DFA) method, frequency series of Bach pitches have been analyzed. In this
view we find same second moment exponents (after double profiling) in ranges
(1.7-1.8) in his works. Comparing MF-DFA results of original series to those
for shuffled and surrogate series we can distinguish multifractality due to
long-range correlations and a broad probability density function. Finally we
determine the scaling exponents and singularity spectrum. We conclude fat tail
has more effect in its multifractality nature than long-range correlations.Comment: 18 page, 6 figures, to appear in JSTA
Mona Lisa, the stochastic view and fractality in color space
A painting consists of objects which are arranged in specific ways. The art
of painting is drawing the objects, which can be considered as known trends, in
an expressive manner. Detrended methods are suitable for characterizing the
artistic works of the painter by eliminating trends. It means that we study the
paintings, regardless of its apparent purpose, as a stochastic process. We
apply multifractal detrended fluctuation analysis to characterize the
statistical properties of Mona Lisa, as an instance, to exhibit the fractality
of the painting. Our results show that Mona Lisa is long range correlated and
almost behaves similar in various scales.Comment: 16 pages, 5 figures, to appear in Int. J. Mod. Phys.
The Nucleotide Exchange Factor Ric-8A is a Chaperone for the Conformationally Dynamic Nucleotide-Free State of G Alpha I1
Heterotrimeric G protein alpha subunits are activated upon exchange of GDP for GTP at the nucleotide binding site of G alpha, catalyzed by guanine nucleotide exchange factors (GEFs). In addition to transmembrane G protein-coupled receptors (GPCRs), which act on G protein heterotrimers, members of the family cytosolic proteins typified by mammalian Ric-8A are GEFs for Gi/q/12/13-class G alpha subunits. Ric-8A binds to G alpha.GDP, resulting in the release of GDP. The Ric-8A complex with nucleotide-free G alpha i1 is stable, but dissociates upon binding of GTP to G alpha i1. To gain insight into the mechanism of Ric-8A-catalyzed GDP release from G alpha i1, experiments were conducted to characterize the physical state of nucleotide-free G alpha i1 (hereafter referred to as G alpha i1[]) in solution, both as a monomeric species, and in the complex with Ric-8A. We found that Ric-8A-bound, nucleotide-free G alpha i1 is more accessible to trypsinolysis than G alpha i1.GDP, but less so than G alpha i1[] alone. The TROSY-HSQC spectrum of [N-15]G alpha i1[] bound to Ric-8A shows considerable loss of peak intensity relative to that of [N-15]G alpha i1.GDP. Hydrogen-deuterium exchange in G alpha i1[] bound to Ric-8A is 1.5-fold more extensive than in G alpha i1.GDP. Differential scanning calorimetry shows that both Ric-8A and G alpha i1.GDP undergo cooperative, irreversible unfolding transitions at 47 degrees and 52 degrees, respectively, while nucleotide-free G alpha i1 shows a broad, weak transition near 35 degrees. The unfolding transition for Ric-8A: G alpha i1[] is complex, with a broad transition that peaks at 50 degrees, suggesting that both Ric-8A and G alpha i1[] are stabilized within the complex, relative to their respective free states. The C-terminus of G alpha i1 is shown to be a critical binding element for Ric-8A, as is also the case for GPCRs, suggesting that the two types of GEF might promote nucleotide exchange by similar mechanisms, by acting as chaperones for the unstable and dynamic nucleotide-free state of G alpha
Interacting Ghost Dark Energy in Non-Flat Universe
A new dark energy model called "ghost dark energy" was recently suggested to
explain the observed accelerating expansion of the universe. This model
originates from the Veneziano ghost of QCD. The dark energy density is
proportional to Hubble parameter, , where is a
constant of order and is
QCD mass scale. In this paper, we extend the ghost dark energy model to the
universe with spatial curvature in the presence of interaction between dark
matter and dark energy. We study cosmological implications of this model in
detail. In the absence of interaction the equation of state parameter of ghost
dark energy is always and mimics a cosmological constant in the
late time, while it is possible to have provided the interaction is
taken into account. When , all previous results of ghost dark energy in
flat universe are recovered. To check the observational consistency, we use
Supernova type Ia (SNIa) Gold sample, shift parameter of Cosmic Microwave
Background radiation (CMB) and the Baryonic Acoustic Oscillation peak from
Sloan Digital Sky Survey (SDSS). The best fit values of free parameter at
confidence interval are: ,
and . Consequently
the total energy density of universe at present time in this model at 68% level
equates to .Comment: 19 pages, 9 figures. V2: Added comments, observational consequences,
references, figures and major corrections. Accepted for publication in
General Relativity and Gravitatio
Exact Analysis of Level-Crossing Statistics for (d+1)-Dimensional Fluctuating Surfaces
We carry out an exact analysis of the average frequency
in the direction of positive-slope crossing of a given level
such that, , of growing surfaces in spatial
dimension . Here, is the surface height at time , and
is its mean value. We analyze the problem when the surface growth
dynamics is governed by the Kardar-Parisi-Zhang (KPZ) equation without surface
tension, in the time regime prior to appearance of cusp singularities (sharp
valleys), as well as in the random deposition (RD) model. The total number
of such level-crossings with positive slope in all the directions is then
shown to scale with time as for both the KPZ equation and the RD
model.Comment: 22 pages, 3 figure
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