Late time failure of Friedmann equation

It is widely believed that the assumption of homogeneity is a good zero{\it th} order approximation for the expansion of our Universe. We analyze the correction due to subhorizon inhomogeneous gravitational fields. While at early times this contribution (which may act as a negative pressure component) is perturbatively subdominant, we show that the perturbative series is likely to diverge at redshift of order 1, due to the growth of perturbations. So, the homogeneous Friedmann equation can not be trusted at late times. We suggest that the puzzling observations of a present acceleration of the Universe, may just be due to the unjustified use of the Friedmann equation and not to the presence of a Dark Energy component. This would completely solve the coincidence problem.Comment: 7 pages, 2 figures. Replaced version contains new sections with discussions and an explicit computation. Some parts rewritten and references added.Submitted to PR

Is there a link between treatments with exogenous corticosteroids and dog behaviour problems?

Possible side effects of exogenous corticosteroids have been described in both humans and laboratory animals, with recent studies highlighting this issue in dogs. In this paper the behaviour of 345 dogs drawn from the caseload of a behaviour clinic based in the north of Italy between February 2012 and November 2014 were analysed. Possible relationships between dogs that received treatment with corticosteroids versus dogs that received treatment with drugs other than corticosteroids and positive or negative affective states, aggression towards people, other behaviour problems apart from aggression, occurrence of severe bites, and prescription of psychoactive drugs were initially assessed using a Pearson's chi-squared test. Regression analysis was then performed in order to evaluate the best predictors of the investigated items. The goal of this retrospective survey was to investigate possible relationships between the affective states associated with the behavioural complaint of dogs and their previous history of treatment with corticosteroids. Results showed that a history of corticosteroid treatment was a significant predictor of a range of behaviour problems associated with negative affective state, but this result may be confounded by age-related effects

Empowering formative assessment using embedded Web Widgets in Wikis

The article can be viewed at: http://opensym.org/wsos2013/proceedings/p0901-notari.pdfIn this article we describe how we developed and how we use a tool for teachers enhancing inter-group collaboration of learners using wikis in project-based learning settings with over 100 participants, where different groups of students develop similar projects and each project has an own wiki page. To achieve our goal we extended typical wiki functionality by using web widgets, mini applications embedded anywhere in the wiki environment using the iframe tag. Two different evaluation widgets (rating widget and 'working progress' widget) are placed on each of the project pages. The project groups use the 'working progress' widget to declare the amount of work done. The teacher and the rest of the learning community use the 'rating' widget to rate the ongoing project work. A so called 'meta widget' showing a summary of the results of the 'rating' and 'working progress' widget can be displayed on the start page of the learning community or if a project is divided in different milestones, on the page describing the goals and timeline for the milestone. Evaluation widgets and meta widget, which easily can be embedded by the teacher potentially all over the wiki pages, enhances visibility of quality and termination degree of a project and enhance so the self, the tutor and the peer review opportunities in such large scale project based learning settings. The created evaluation widgets and meta widgets have been embedded in the wiki of a three months curriculum. The evaluation of utility and usability of the widgets is ongoing. The educational value of rating and reflecting about the working progress of a given task is discussed

Effect of inhomogeneities on the expansion rate of the Universe

While the expansion rate of a homogeneous isotropic Universe is simply proportional to the square-root of the energy density, the expansion rate of an inhomogeneous Universe also depends on the nature of the density inhomogeneities. In this paper we calculate to second order in perturbation variables the expansion rate of an inhomogeneous Universe and demonstrate corrections to the evolution of the expansion rate. While we find that the mean correction is small, the variance of the correction on the scale of the Hubble radius is sensitive to the physical significance of the unknown spectrum of density perturbations beyond the Hubble radius.Comment: 19 pages, 2 figures Version 2 includes some changes in numerical factors and corrected typos. It is the version accepted for publication in Physical review

AC losses reduction in Hairpin Windings produced via Additive Manufacturing

One of the key challenges of hairpin windings is the reduction of their high losses at high-frequency operations. Hairpin layouts comprising conductors with variable cross sections have proven good loss performance in previous studies. However, they come at the cost of significant manufacturing complications. The aim of this work is to design hairpin layouts featuring reduced losses compared to classical configurations, exploiting the flexibility enabled by additive manufacturing. In this context, the choice of a proper material with relatively high conductivity and low ecological impact plays an important role. Hence, this article first presents an overview of materials that can be used for the winding additive manufacturing, aiming to select the most suitable one for the application at hand. Then, the loss performance is evaluated and compared against classical copper hairpins. The results demonstrate that opportunely selected alloys featuring asymmetric configurations can compete against classical hairpin windings. © 20XX IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other worksThis paper reflects only the author's view. JU is not responsible for any use that may be made of the information it contains

Light Propagation and Large-Scale Inhomogeneities

We consider the effect on the propagation of light of inhomogeneities with sizes of order 10 Mpc or larger. The Universe is approximated through a variation of the Swiss-cheese model. The spherical inhomogeneities are void-like, with central underdensities surrounded by compensating overdense shells. We study the propagation of light in this background, assuming that the source and the observer occupy random positions, so that each beam travels through several inhomogeneities at random angles. The distribution of luminosity distances for sources with the same redshift is asymmetric, with a peak at a value larger than the average one. The width of the distribution and the location of the maximum increase with increasing redshift and length scale of the inhomogeneities. We compute the induced dispersion and bias on cosmological parameters derived from the supernova data. They are too small to explain the perceived acceleration without dark energy, even when the length scale of the inhomogeneities is comparable to the horizon distance. Moreover, the dispersion and bias induced by gravitational lensing at the scales of galaxies or clusters of galaxies are larger by at least an order of magnitude.Comment: 27 pages, 9 figures, revised version to appear in JCAP, analytical estimate included, typos correcte

"Swiss-Cheese" Inhomogeneous Cosmology & the Dark Energy Problem

We study an exact swiss-cheese model of the Universe, where inhomogeneous LTB patches are embedded in a flat FLRW background, in order to see how observations of distant sources are affected. We find negligible integrated effect, suppressed by (L/R_{H})^3 (where L is the size of one patch, and R_{H} is the Hubble radius), both perturbatively and non-perturbatively. We disentangle this effect from the Doppler term (which is much larger and has been used recently \cite{BMN} to try to fit the SN curve without dark energy) by making contact with cosmological perturbation theory.Comment: 35 pages, 6 figure

Consommations de substances en Suisse : analyse des tendances à partir des enquêtes HBSC, ESS et CoRolAR. Partie 1 : les substances illégales

Sur mandat de l’Office fédéral de la santé publique (OFSP), la fondation Addiction Suisse et l’Institut universitaire de médecine sociale et préventive du CHUV (IUMSP) ont mis en commun les données existantes sur la consommation de substances légales (alcool et tabac) et illégales (cannabis, cocaïne, héroïne) issues d’enquêtes en population générale afin de mesurer des tendances de consommation. Trois études représentatives de la population suisse en termes de poids démographique des cantons, de la pyramide des âges et de l’importance relative des sexes, s’intéressent à la consommation de substances telles que l'alcool, le tabac, le cannabis, la cocaïne et l’héroïne. La première, mise en oeuvre depuis 1986, est l’étude internationale Health Behaviour in School-aged Children (HBSC), menée auprès des élèves âgés de 11 à 15 ans. La seconde, l'Enquête suisse sur la santé (ESS), existe depuis 1992 et s’adresse à la population générale suisse âgée de 15 ans et plus. La troisième enquête, Continuous Rolling Survey of Addictive Behaviours and Related Risks (CoRolAR), est une enquête téléphonique permanente, réalisée entre 2011 et 2016 auprès de la population suisse. Elle s’intéresse spécifiquement à l'évolution des comportements face aux addictions. A partir d’un modèle statistique robuste et d’une revue non exhaustive de la littérature, ce rapport propose une représentation et une interprétation des tendances de consommation du cannabis, de la cocaïne et de l’héroïne en Suisse de 1992 à 2016, en les différenciant selon le sexe, l’âge, et la cohorte de naissance