551 research outputs found
Cosmological Constraints on f(R) Acceleration Models
Models which accelerate the expansion of the universe through the addition of
a function of the Ricci scalar f(R) leave a characteristic signature in the
large-scale structure of the universe at the Compton wavelength scale of the
extra scalar degree of freedom. We search for such a signature in current
cosmological data sets: the WMAP cosmic microwave background (CMB) power
spectrum, SNLS supernovae distance measures, the SDSS luminous red galaxy power
spectrum, and galaxy-CMB angular correlations. Due to theoretical uncertainties
in the nonlinear evolution of f(R) models, the galaxy power spectrum
conservatively yields only weak constraints on the models despite the strong
predicted signature in the linear matter power spectrum. Currently the tightest
constraints involve the modification to the integrated Sachs-Wolfe effect from
growth of gravitational potentials during the acceleration epoch. This effect
is manifest for large Compton wavelengths in enhanced low multipole power in
the CMB and anti-correlation between the CMB and tracers of the potential. They
place a bound on the Compton wavelength of the field be less than of order the
Hubble scale.Comment: 8 pages, 7 figure
Clustering of Photometric Luminous Red Galaxies II: Cosmological Implications from the Baryon Acoustic Scale
A new determination of the sound horizon scale in angular coordinates is
presented. It makes use of ~ 0.6 x 10^6 Luminous Red Galaxies, selected from
the Sloan Digital Sky Survey imaging data, with photometric redshifts. The
analysis covers a redshift interval that goes from z=0.5 to z=0.6. We find
evidence of the Baryon Acoustic Oscillations (BAO) signal at the ~ 2.3 sigma
confidence level, with a value of theta_{BAO} (z=0.55) = (3.90 \pm 0.38)
degrees, including systematic errors. To our understanding, this is the first
direct measurement of the angular BAO scale in the galaxy distribution, and it
is in agreement with previous BAO measurements. We also show how radial
determinations of the BAO scale can break the degeneracy in the measurement of
cosmological parameters when they are combined with BAO angular measurements.
The result is also in good agreement with the WMAP7 best-fit cosmology. We
obtain a value of w_0 = -1.03 \pm 0.16 for the equation of state parameter of
the dark energy, Omega_M = 0.26 \pm 0.04 for the matter density, when the other
parameters are fixed. We have also tested the sensitivity of current BAO
measurements to a time varying dark energy equation of state, finding w_a =
0.06 \pm 0.22 if we fix all the other parameters to the WMAP7 best-fit
cosmology.Comment: 7 pages, 7 figures, Accepted for publication to MNRA
Clustering of photometric luminous red galaxies I : Growth of Structure and Baryon Acoustic Feature
The possibility of measuring redshift space (RSD) distortions using
photometric data have been recently highlighted. This effect complements and
significantly alters the detectability of baryon acoustic oscillations (BAO) in
photometric surveys. In this paper we present measurements of the angular
correlation function of luminous red galaxies (LRGs) in the photometric catalog
of the final data release (DR7) of the Sloan Digital Sky Survey II (SDSS). The
sample compromise ~ 1.5 x 10^6 LRGs distributed in 0.45 < z < 0.65, with a
characteristic photometric error of ~ 0.05. Our measured correlation centered
at z=0.55 is in very good agreement with predictions from standard LCDM in a
broad range of angular scales, . We find that the
growth of structure can indeed be robustly measured, with errors matching
expectations. The velocity growth rate is recovered as when no prior is imposed on the growth factor and the background geometry
follows a LCDM model with WMAP7+SNIa priors. This is compatible with the
corresponding General Relativity (GR) prediction for our
fiducial cosmology. If we adopt a parametrization such that , with in GR, and combine our
measurement with the corresponding ones from spectroscopic LRGs at lower
redshifts we obtain . In addition we find evidence for
the presence of the baryon acoustic feature matching the amplitude, location
and shape of LCDM predictions. The photometric BAO feature is detected with 98
% confidence level at z=0.55.Comment: 16 pages, 19 figures, minor changes to text to match accepted version
by MNRA
Terminological challenges in the translation of science documentaries: a case-study
This article aims to describe some of the main terminological problems audiovisual translators have to face when dealing with the translation of science documentaries, specifically in the English-Catalan combination. The first section of the article presents some theoretical concepts which underlie this research and which are taken, for the most part, from Cabré's Communicative Theory of Terminology. Then, specific terminological problems audiovisual translators have to solve are described using the data provided by a corpus of four science documentaries lasting approximately 50 minutes each. These challenges include identifying a term, understanding a term, finding the right equivalent, dealing with the absence of an adequate equivalent, solving denominative variations, choosing between in vivo and in vitro terminology, and overcoming mistranscriptions
Oxygen minimum zones in the tropical Pacific across CMIP5 models: mean state differences and climate change trends
We analyse simulations of the Pacific Ocean oxygen minimum zones (OMZs) from 11 Earth system model contributions to the Coupled Model Intercomparison Project Phase 5, focusing on the mean state and climate change projections. The simulations tend to overestimate the volume of the OMZs, especially in the tropics and Southern Hemisphere. Compared to observations, five models introduce incorrect meridional asymmetries in the distribution of oxygen including larger southern OMZ and weaker northern OMZ, due to interhemispheric biases in intermediate water mass ventilation. Seven models show too deep an extent of the tropical hypoxia compared to observations, stemming from a deficient equatorial ventilation in the upper ocean, combined with too large a biologically driven downward flux of particulate organic carbon at depth, caused by particle export from the euphotic layer that is too high and remineralization in the upper ocean that is too weak.
At interannual timescales, the dynamics of oxygen in the eastern tropical Pacific OMZ is dominated by biological consumption and linked to natural variability in the Walker circulation. However, under the climate change scenario RCP8.5, all simulations yield small and discrepant changes in oxygen concentration at mid depths in the tropical Pacific by the end of the 21st century due to an almost perfect compensation between warming-related decrease in oxygen saturation and decrease in biological oxygen utilization. Climate change projections are at odds with recent observations that show decreasing oxygen levels at mid depths in the tropical Pacific.
Out of the OMZs, all the CMIP5 models predict a decrease of oxygen over most of the surface and deep ocean at low latitudes and over all depths at high latitudes due to an overall slow-down of ventilation and increased temperature
Two classes of nonlocal Evolution Equations related by a shared Traveling Wave Problem
We consider reaction-diffusion equations and Korteweg-de Vries-Burgers (KdVB)
equations, i.e. scalar conservation laws with diffusive-dispersive
regularization. We review the existence of traveling wave solutions for these
two classes of evolution equations. For classical equations the traveling wave
problem (TWP) for a local KdVB equation can be identified with the TWP for a
reaction-diffusion equation. In this article we study this relationship for
these two classes of evolution equations with nonlocal diffusion/dispersion.
This connection is especially useful, if the TW equation is not studied
directly, but the existence of a TWS is proven using one of the evolution
equations instead. Finally, we present three models from fluid dynamics and
discuss the TWP via its link to associated reaction-diffusion equations
Vesicles of double hydrophilic pullulan and poly(acrylamide) block copolymers : a combination of synthetic- and bio-derived blocks
The formation of vesicular structures with average diameters from 200 to 300 nm consisting of double hydrophilic diblock copolymers pullulan-b-poly(N,N-dimethylacrylamide) (Pull-b-PDMA) and pullulan-b-poly(N-ethylacrylamide) (Pull-b-PEA) in aqueous solution is described. Bio-derived pullulan was depolymerized and functionalized with alkyne endgroups. Furthermore, azide end functionalized acrylamide blocks PDMA and PEA were synthesized via RAFT polymerization. Individual blocks were conjugated via copper catalyzed azide alkyne cycloaddition (CuAAC) to afford defined double hydrophilic block copolymers. Aqueous solutions of the synthesized block copolymers showed formation of completely hydrophilic vesicles that were observed via various techniques including dynamic light scattering (DLS), static light scattering (SLS), laser scanning confocal microscopy (LSCM), and cryogenic scanning electron microscopy (SEM)
A note on the convergence of parametrised non-resonant invariant manifolds
Truncated Taylor series representations of invariant manifolds are abundant
in numerical computations. We present an aposteriori method to compute the
convergence radii and error estimates of analytic parametrisations of
non-resonant local invariant manifolds of a saddle of an analytic vector field,
from such a truncated series. This enables us to obtain local enclosures, as
well as existence results, for the invariant manifolds
Synthesis, coordination study, and catalytic Pauson−Khand reactions of QuinoxP*(CO)4‑μ-alkyne dicobalt complexes
The coordination of the P-stereogenic and sterically demanding bisphosphine QuinoxP* to μ-alkyne dicobalt hexacarbonyl complexes was studied experimentally and computationally. Whereas the coordination occurred exclusively in a chelating fashion, the diastereoselectivity was highly substrate dependent. However, it could be explained from the computed structure and energies of the different coordination modes. The fluxional behavior of these complexes was also studied computationally. Their performance as catalysts for the Pauson−Khand reaction was explored, and outstanding reactivity was observed. Although the asymmetric induction was low to moderate, the stereochemical outcome could be mechanistically rationalized. This report provides promising results in terms of reactivity and mechanistic understanding for further developments of highly active chiral catalysts for intermolecular Pauson−Khand reactions
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