The potential energy landscape of a model glass former: thermodynamics, anharmonicities, and finite size effects

It is possible to formulate the thermodynamics of a glass forming system in terms of the properties of inherent structures, which correspond to the minima of the potential energy and build up the potential energy landscape in the high-dimensional configuration space. In this work we quantitatively apply this general approach to a simulated model glass-forming system. We systematically vary the system size between N=20 and N=160. This analysis enables us to determine for which temperature range the properties of the glass former are governed by the regions of the configuration space, close to the inherent structures. Furthermore, we obtain detailed information about the nature of anharmonic contributions. Moreover, we can explain the presence of finite size effects in terms of specific properties of the energy landscape. Finally, determination of the total number of inherent structures for very small systems enables us to estimate the Kauzmann temperature

TESS asteroseismology of the known red-giant host stars HD 212771 and HD 203949

International audienc

Nonperturbative renormalization group approach to frustrated magnets

This article is devoted to the study of the critical properties of classical XY and Heisenberg frustrated magnets in three dimensions. We first analyze the experimental and numerical situations. We show that the unusual behaviors encountered in these systems, typically nonuniversal scaling, are hardly compatible with the hypothesis of a second order phase transition. We then review the various perturbative and early nonperturbative approaches used to investigate these systems. We argue that none of them provides a completely satisfactory description of the three-dimensional critical behavior. We then recall the principles of the nonperturbative approach - the effective average action method - that we have used to investigate the physics of frustrated magnets. First, we recall the treatment of the unfrustrated - O(N) - case with this method. This allows to introduce its technical aspects. Then, we show how this method unables to clarify most of the problems encountered in the previous theoretical descriptions of frustrated magnets. Firstly, we get an explanation of the long-standing mismatch between different perturbative approaches which consists in a nonperturbative mechanism of annihilation of fixed points between two and three dimensions. Secondly, we get a coherent picture of the physics of frustrated magnets in qualitative and (semi-) quantitative agreement with the numerical and experimental results. The central feature that emerges from our approach is the existence of scaling behaviors without fixed or pseudo-fixed point and that relies on a slowing-down of the renormalization group flow in a whole region in the coupling constants space. This phenomenon allows to explain the occurence of generic weak first order behaviors and to understand the absence of universality in the critical behavior of frustrated magnets.Comment: 58 pages, 15 PS figure

The walking behaviour of pedestrian social groups and its impact on crowd dynamics

Human crowd motion is mainly driven by self-organized processes based on local interactions among pedestrians. While most studies of crowd behavior consider only interactions among isolated individuals, it turns out that up to 70% of people in a crowd are actually moving in groups, such as friends, couples, or families walking together. These groups constitute medium-scale aggregated structures and their impact on crowd dynamics is still largely unknown. In this work, we analyze the motion of approximately 1500 pedestrian groups under natural condition, and show that social interactions among group members generate typical group walking patterns that influence crowd dynamics. At low density, group members tend to walk side by side, forming a line perpendicular to the walking direction. As the density increases, however, the linear walking formation is bent forward, turning it into a V-like pattern. These spatial patterns can be well described by a model based on social communication between group members. We show that the V-like walking pattern facilitates social interactions within the group, but reduces the flow because of its "non-aerodynamic" shape. Therefore, when crowd density increases, the group organization results from a trade-off between walking faster and facilitating social exchange. These insights demonstrate that crowd dynamics is not only determined by physical constraints induced by other pedestrians and the environment, but also significantly by communicative, social interactions among individuals.Comment: 18 pages; 6 figures; Accepted for publication in PLoS ON

How Humans Differ from Other Animals in Their Levels of Morphological Variation

Animal species come in many shapes and sizes, as do the individuals and populations that make up each species. To us, humans might seem to show particularly high levels of morphological variation, but perhaps this perception is simply based on enhanced recognition of individual conspecifics relative to individual heterospecifics. We here more objectively ask how humans compare to other animals in terms of body size variation. We quantitatively compare levels of variation in body length (height) and mass within and among 99 human populations and 848 animal populations (210 species). We find that humans show low levels of within-population body height variation in comparison to body length variation in other animals. Humans do not, however, show distinctive levels of within-population body mass variation, nor of among-population body height or mass variation. These results are consistent with the idea that natural and sexual selection have reduced human height variation within populations, while maintaining it among populations. We therefore hypothesize that humans have evolved on a rugged adaptive landscape with strong selection for body height optima that differ among locations

‘You can’t show impact with a new pair of shoes’: negotiating disadvantage through Pupil Premium

The Pupil Premium policy was introduced in 2010 by the UK coalition government to tackle the attainment gap disproportionately affecting children from low-income families. Semi-structured interviews and policy documents are examined for the way the policy has been enacted in a single comprehensive secondary school in England. In 2014, this school had a lower population of Pupil Premium pupils (18%) compared to (29%) nationally and (25%) countywide. Despite this, the study provides evidence that the Pupil Premium has become invested within and gives rise to, a number of neoliberal techniques, technologies and practices. The study bridges insights from Mitchell Dean’s ‘analytics of government’ and Ball et al.’s work on policy enactment to provide an in-depth, grounded analysis of the way the policy plays out within this school’s context. It argues that the combination of national accountability measures used to show impact for Pupil Premium, and the school’s ongoing struggle to raise overall attainment, leads school leaders and staff members to rethink the concept of disadvantage for their school population. This results in disadvantage being reconceptualised to fit a matrix of moral/pastoral obligations and efficiency/economic competitiveness, in which the tensions between these two orientations are uncomfortable and unresolved

Does student loan debt deter higher education participation? New evidence from England

Research among prospective UK undergraduates in 2002 found that some students, especially from low social classes, were deterred from applying to university because of fear of debt. This paper investigates whether this is still the case today in England despite the changing higher education landscape since 2002. The paper describes findings from a 2015 survey of prospective undergraduates and compares them with those from the 2002 study. We find that students’ attitudes to taking on student loan debt are more favorable in 2015 than in 2002. Debt averse attitudes remain much stronger among lower-class students than among upper-class students, and more so than in 2002. However, lower-class students did not have stronger debt averse attitudes than middle-class students. Debt averse attitudes seem more likely to deter planned higher education participation among lower-class students in 2015 than in 2002

The Honey Bee Epigenomes: Differential Methylation of Brain DNA in Queens and Workers

Using genome-wide methylation profiles in honey bee queen and worker brains to understand how contrasting organismal outputs are generated from the same genotype