The universe seen at different scales

A large-scale smoothed-out model of the universe ignores small-scale inhomogeneities, but the averaged effects of those inhomogeneities may alter both observational and dynamical relations at the larger scale. This article discusses these effects, and comments briefly on the relation to gravitational entropy.Comment: 17 pages; matches published version in Phys. Lett. A (Einstein special issue

Lagrangian description of fluid flow with pressure in relativistic cosmology

The Lagrangian description of fluid flow in relativistic cosmology is extended to the case of flow accelerated by pressure. In the description, the entropy and the vorticity are obtained exactly for the barotropic equation of state. In order to determine the metric, the Einstein equation is solved perturbatively, when metric fluctuations are small but entropy inhomogeneities are large. Thus, the present formalism is applicable to the case when the inhomogeneities are small in the large scale but locally nonlinear.Comment: 11 pages (RevTeX); accepted for publication in Phys. Rev.

Back Reaction And Local Cosmological Expansion Rate

We calculate the back reaction of cosmological perturbations on a general relativistic variable which measures the local expansion rate of the Universe. Specifically, we consider a cosmological model in which matter is described by a single field. We analyze back reaction both in a matter dominated Universe and in a phase of scalar field-driven chaotic inflation. In both cases, we find that the leading infrared terms contributing to the back reaction vanish when the local expansion rate is measured at a fixed value of the matter field which is used as a clock, whereas they do not appear to vanish if the expansion rate is evaluated at a fixed value of the background time. We discuss possible implications for more realistic models with a more complicated matter sector.Comment: 7 pages, No figure

Soft-bottom fishes and spatial protection: findings from a temperate marine protected area

Numerous studies over the last decades have focused on marine protected areas (MPAs) and their effects on fish communities. However, there is a knowledge gap regarding how species that live associated with soft-substrates (e.g., sand, mud) respond to spatial protection. We analyzed abundance, biomass and total lengths of the soft-bottom fishes in a multiple-use MPA in the north-eastern Atlantic, the Luiz Saldanha Marine Park (Portugal), during and after the implementation of its management plan. Data were collected by experimental fishing in areas with three different levels of protection, during the implementation period and for three years after full implementation of the MPA. Univariate analysis detected significant biomass increases between the two periods. Fish assemblages were mainly structured by depth and substrate, followed by protection level. Community composition analyses revealed significant differences between protection levels and between the two periods. Species exhibited a broad variation in their response to protection, and we hypothesize that factors such as species habitat preferences, body size and late maturity might be underlying determinants. Overall, this study provides some evidence of protection effectiveness in soft-bottom fish communities, supported by the significant increase in biomass in the protected areas and the positive trends of some species.project LIFE-BIOMARES [LIFE06 NAT/P/000192]; project BUFFER (ERA-Net BiodivERsA); company SECIL-Companhia Geral de Cal e Cimento S.A.; FCT-Foundation for Science and Technology [CCMAR/Multi/04326/2013, SFRH/BD/80771/2011]; Foundation for Science and Technology [SFRH/BD/80771/2011]; 2012 Sesimbra Scientific Priz

Dark Energy from structure: a status report

The effective evolution of an inhomogeneous universe model in any theory of gravitation may be described in terms of spatially averaged variables. In Einstein's theory, restricting attention to scalar variables, this evolution can be modeled by solutions of a set of Friedmann equations for an effective volume scale factor, with matter and backreaction source terms. The latter can be represented by an effective scalar field (`morphon field') modeling Dark Energy. The present work provides an overview over the Dark Energy debate in connection with the impact of inhomogeneities, and formulates strategies for a comprehensive quantitative evaluation of backreaction effects both in theoretical and observational cosmology. We recall the basic steps of a description of backreaction effects in relativistic cosmology that lead to refurnishing the standard cosmological equations, but also lay down a number of challenges and unresolved issues in connection with their observational interpretation. The present status of this subject is intermediate: we have a good qualitative understanding of backreaction effects pointing to a global instability of the standard model of cosmology; exact solutions and perturbative results modeling this instability lie in the right sector to explain Dark Energy from inhomogeneities. It is fair to say that, even if backreaction effects turn out to be less important than anticipated by some researchers, the concordance high-precision cosmology, the architecture of current N-body simulations, as well as standard perturbative approaches may all fall short in correctly describing the Late Universe.Comment: Invited Review for a special Gen. Rel. Grav. issue on Dark Energy, 59 pages, 2 figures; matches published versio

Newtonian Cosmology in Lagrangian Formulation: Foundations and Perturbation Theory

The ``Newtonian'' theory of spatially unbounded, self--gravitating, pressureless continua in Lagrangian form is reconsidered. Following a review of the pertinent kinematics, we present alternative formulations of the Lagrangian evolution equations and establish conditions for the equivalence of the Lagrangian and Eulerian representations. We then distinguish open models based on Euclidean space $\R^3$ from closed models based (without loss of generality) on a flat torus \T^3. Using a simple averaging method we show that the spatially averaged variables of an inhomogeneous toroidal model form a spatially homogeneous ``background'' model and that the averages of open models, if they exist at all, in general do not obey the dynamical laws of homogeneous models. We then specialize to those inhomogeneous toroidal models whose (unique) backgrounds have a Hubble flow, and derive Lagrangian evolution equations which govern the (conformally rescaled) displacement of the inhomogeneous flow with respect to its homogeneous background. Finally, we set up an iteration scheme and prove that the resulting equations have unique solutions at any order for given initial data, while for open models there exist infinitely many different solutions for given data.Comment: submitted to G.R.G., TeX 30 pages; AEI preprint 01

Statistics of gravitational lenses in the clumpy Universe

We evaluate the effect of small scale inhomogeneities on large scale observations within the statistics of gravitationally lensed quasars. At this aim, we consider a cosmological model whose large scale properties (dynamics, matter distribution) are the same as in Friedmann-Lemaitre models, but whose matter distribution is locally inhomogeneous. We use the well known Dyer-Roder distances to allow a simple analytical expression of the optical depth, and pay particular attention on the different role played by the different notions of distances (filled beam angular diameter distance and Dyer-Roder distances) when calculating this quantity, following the prescription from Ehlers & Schneider for a coherent formalism. We find that the expected number of gravitationally lensed quasars is a decreasing function of the clumpiness parameter.Comment: 11 pages, 9 figures. MNRAS, in pres

Measurement of functional microcirculatory geometry and velocity distributions using automated image analysis

This study describes a new method for analyzing microcirculatory videos. It introduces algorithms for quantitative assessment of vessel length, diameter, the functional microcirculatory density distribution and red blood-cell (RBC) velocity in individual vessels as well as its distribution. The technique was validated and compared to commercial software. The method was applied to the sublingual microcirculation in a healthy volunteer and in a patient during cardiac surgery. Analysis time was reduced from hours to minutes compared to previous methods requiring manual vessel identification. Vessel diameter was detected with high accuracy (>80%, d > 3 pixels). Capillary length was estimated within 5 pixels accuracy. Velocity estimation was very accurate (>95%) in the range [2.5, 1,000] pixels/s. RBC velocity was reduced by 70% during the first 10 s of cardiac luxation. The present method has been shown to be fast and accurate and provides increased insight into the functional properties of the microcirculation

Psychometric evaluation of the Cohen-Mansfield Agitation Inventory in an acute general hospital setting

YesObjectives The Cohen-Mansfield Agitation Inventory (CMAI; (Cohen-Mansfield and Kerin, 1986)) is a well-known tool for assessing agitated behaviours in people with dementia who reside in long-term care. No studies have evaluated the psychometric qualities and factor structure of the CMAI in acute general hospitals, a setting where people with demand may become agitated. Method Longitudinal study investigating pain, agitation and behavioural problems in 230 people with dementia admitted to acute general hospitals in 2011–2012. Cohen-Mansfield Agitation Inventory was completed as part of a battery of assessments including PAINAD to measure pain. Results A nine-item two-factor model of aggressive and nonaggressive behaviours proved to be the best-fitting measurement model in this sample, (χ2 = 96.3, df = 26, p<0.001; BIC [Bayesian Information Criterion] = 4593.06, CFI [Comparative Fit Index] = 0.884, TLI [Tucker Lewis Index] = 0.839, RMSEA [Root Mean Square Error of the Approximation] = 0.108). Although similar to the original factor structure, the new model resulted in the elimination of item 13 (screaming). Validity was confirmed with the shortened CMAI showing similar associations with pain as the original version of the CMAI, in particular the link between aggressive behaviours and pain. Conclusion The factor structure of the CMAI was broadly consistent with the original solution although a large number of items were removed. Scales reflecting physical and verbal aggression were combined to form an Aggressive factor, and physical and verbal nonaggressive behaviours were combined to form the Nonaggressive factor. A shorter, more concise version of the CMAI was developed for use in acute general hospital settings. Copyright © 2017 John Wiley & Sons, Ltd.Alzheimer's Society and the BUPA Foundation. Grant Number: 13