1,550 research outputs found
Observational Constraints on the Generalized Chaplygin Gas
In this paper we study a quintessence cosmological model in which the dark
energy component is considered to be the Generalized Chaplygin Gas and the
curvature of the three-geometry is taken into account. Two parameters
characterize this sort of fluid, the and the parameters. We use
different astronomical data for restricting these parameters. It is shown that
the constraint agrees enough well with the astronomical
observations.Comment: Accepted by IJMPD; 18 pages; 10 Figure
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Insights into Pathophysiology from Medication-induced Tremor
Background: Medication-induced tremor (MIT) is common in clinical practice and there are many medications/drugs that can cause or exacerbate tremors. MIT typically occurs by enhancement of physiological tremor (EPT), but not all drugs cause tremor in this way. In this manuscript, we review how some common examples of MIT have informed us about the pathophysiology of tremor.
Methods: We performed a PubMed literature search for published articles dealing with MIT and attempted to identify articles that especially dealt with the medication’s mechanism of inducing tremor.
Results: There is a paucity of literature that deals with the mechanisms of MIT, with most manuscripts only describing the frequency and clinical settings where MIT is observed. That being said, MIT emanates from multiple mechanisms depending on the drug and it often takes an individualized approach to manage MIT in a given patient.
Discussion: MIT has provided some insight into the mechanisms of tremors we see in clinical practice. The exact mechanism of MIT is unknown for most medications that cause tremor, but it is assumed that in most cases physiological tremor is influenced by these medications. Some medications (epinephrine) that cause EPT likely lead to tremor by peripheral mechanisms in the muscle (β-adrenergic agonists), but others may influence the central component (amitriptyline). Other drugs can cause tremor, presumably by blockade of dopamine receptors in the basal ganglia (dopamine-blocking agents), by secondary effects such as causing hyperthyroidism (amiodarone), or by other mechanisms. We will attempt to discuss what is known and unknown about the pathophysiology of the most common MITs
Cosmological constraints combining H(z), CMB shift and SNIa observational data
Recently H(z) data obtained from differential ages of galaxies have been
proposed as a new geometrical probe of dark energy. In this paper we use those
data, combined with other background tests (CMB shift and SNIa data), to
constrain a set of general relativistic dark energy models together with some
other models motivated by extra dimensions. Our analysis rests mostly on
Bayesian statistics, and we conclude that LCDM is at least substantially
favoured, and that braneworld models are less favoured than general
relativistic ones.Comment: 17 pages, 11 figures; improved discussion, new figures, updated to
match published versio
Uniting cosmological epochs through the twister solution in cosmology with non-minimal coupling
We investigate dynamics of a flat FRW cosmological model with a barotropic
matter and a non-minimally coupled scalar field (both canonical and phantom).
In our approach we do not assume any specific form of a potential function for
the scalar field and we are looking for generic scenarios of evolution. We show
that dynamics of universe can be reduced to a 3-dimensional dynamical system.
We have found the set of fixed points and established their character. These
critical points represent all important epochs in evolution of the universe :
(a) a finite scale factor singularity, (b) an inflation (rapid-roll and
slow-roll), (c) a radiation domination, (d) a matter domination and (e) a
quintessence era. We have shown that the inflation, the radiation and matter
domination epochs are transient ones and last for a finite amount of time. The
existence of the radiation domination epoch is purely the effect of a
non-minimal coupling constant. We show the existence of a twister type solution
wandering between all these critical points.Comment: 22 pages, 5 figs; (v2.) 27 pages, 12 figs, JCAP in pres
Testing the viability of the interacting holographic dark energy model by using combined observational constraints
Using the data coming from the new 182 Gold type Ia supernova samples, the
shift parameter of the Cosmic Microwave Background given by the three-year
Wilkinson Microwave Anisotropy Probe observations, and the baryon acoustic
oscillation measurement from the Sloan Digital Sky Survey, and lookback
time measurements, we have performed a statistical joint analysis of the
interacting holographic dark energy model. Consistent parameter estimations
show us that the interacting holographic dark energy model is a viable
candidate to explain the observed acceleration of our universe.Comment: 15 pages, 9 figures, accepted for publication in JCA
Reconstructing the properties of dark energy from recent observations
We explore the properties of dark energy from recent observational data,
including the Gold Sne Ia, the baryonic acoustic oscillation peak from SDSS,
the CMB shift parameter from WMAP3, the X-ray gas mass fraction in cluster and
the Hubble parameter versus redshift. The model with curvature
and two parameterized dark energy models are studied. For the
model, we find that the flat universe is consistent with observations at the
confidence level and a closed universe is slightly favored by these
data. For two parameterized dark energy models, with the prior given on the
present matter density, , with ,
and , our result seems to suggest that the
trend of dependence for an evolving dark energy from a
combination of the observational data sets is model-dependent.Comment: 16 pages, 15 figures, To appear in JCA
Density growth in Kantowski-Sachs cosmologies with cosmological constant
In this work the growth of density perturbations in Kantowski-Sachs
cosmologies with a positive cosmological constant is studied, using the 1+3 and
1+1+2 covariant formalisms. For each wave number we obtain a closed system for
scalars formed from quantities that are zero on the background and hence are
gauge-invariant. The solutions to this system are then analyzed both
analytically and numerically. In particular the effects of anisotropy and the
behaviour close to a bounce in the cosmic scale factor are considered. We find
that typically the density gradient in the bouncing directions experiences a
local maximum at or slightly after the bounce.Comment: 33 pages, 17 picture
First Measurement of the Transverse Spin Asymmetries of the Deuteron in Semi-Inclusive Deep Inelastic Scattering
First measurements of the Collins and Sivers asymmetries of charged hadrons
produced in deep-inelastic scattering of muons on a transversely polarized
6-LiD target are presented. The data were taken in 2002 with the COMPASS
spectrometer using the muon beam of the CERN SPS at 160 GeV/c. The Collins
asymmetry turns out to be compatible with zero, as does the measured Sivers
asymmetry within the present statistical errors.Comment: 6 pages, 2 figure
First Measurement of Chiral Dynamics in \pi^- \gamma -> \pi^- \pi^- \pi^+
The COMPASS collaboration at CERN has investigated the \pi^- \gamma -> \pi^-
\pi^- \pi^+ reaction at center-of-momentum energy below five pion masses,
sqrt(s) < 5 m(\pi), embedded in the Primakoff reaction of 190 GeV pions
impinging on a lead target. Exchange of quasi-real photons is selected by
isolating the sharp Coulomb peak observed at smallest momentum transfers, t' <
0.001 (GeV/c)^2. Using partial-wave analysis techniques, the scattering
intensity of Coulomb production described in terms of chiral dynamics and its
dependence on the 3\pi-invariant mass m(3\pi) = sqrt(s) were extracted. The
absolute cross section was determined in seven bins of with an
overall precision of 20%. At leading order, the result is found to be in good
agreement with the prediction of chiral perturbation theory over the whole
energy range investigated.Comment: 10 pages, 5 figure
Spin Structure of the Proton from Polarized Inclusive Deep-Inelastic Muon-Proton Scattering
We have measured the spin-dependent structure function in inclusive
deep-inelastic scattering of polarized muons off polarized protons, in the
kinematic range and . A
next-to-leading order QCD analysis is used to evolve the measured
to a fixed . The first moment of at is .
This result is below the prediction of the Ellis-Jaffe sum rule by more than
two standard deviations. The singlet axial charge is found to be . In the Adler-Bardeen factorization scheme, is
required to bring in agreement with the Quark-Parton Model. A
combined analysis of all available proton and deuteron data confirms the
Bjorken sum rule.Comment: 33 pages, 22 figures, uses ReVTex and smc.sty. submitted to Physical
Review
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