Gender homophily from spatial behavior in a primary school: a sociometric study

We investigate gender homophily in the spatial proximity of children (6 to 12 years old) in a French primary school, using time-resolved data on face-to-face proximity recorded by means of wearable sensors. For strong ties, i.e., for pairs of children who interact more than a defined threshold, we find statistical evidence of gender preference that increases with grade. For weak ties, conversely, gender homophily is negatively correlated with grade for girls, and positively correlated with grade for boys. This different evolution with grade of weak and strong ties exposes a contrasted picture of gender homophily

An elasto-visco-plastic model for immortal foams or emulsions

A variety of complex fluids consist in soft, round objects (foams, emulsions, assemblies of copolymer micelles or of multilamellar vesicles -- also known as onions). Their dense packing induces a slight deviation from their prefered circular or spherical shape. As a frustrated assembly of interacting bodies, such a material evolves from one conformation to another through a succession of discrete, topological events driven by finite external forces. As a result, the material exhibits a finite yield threshold. The individual objects usually evolve spontaneously (colloidal diffusion, object coalescence, molecular diffusion), and the material properties under low or vanishing stress may alter with time, a phenomenon known as aging. We neglect such effects to address the simpler behaviour of (uncommon) immortal fluids: we construct a minimal, fully tensorial, rheological model, equivalent to the (scalar) Bingham model. Importantly, the model consistently describes the ability of such soft materials to deform substantially in the elastic regime (be it compressible or not) before they undergo (incompressible) plastic creep -- or viscous flow under even higher stresses.Comment: 69 pages, 29 figure

Parameter estimators of random intersection graphs with thinned communities

This paper studies a statistical network model generated by a large number of randomly sized overlapping communities, where any pair of nodes sharing a community is linked with probability $q$ via the community. In the special case with $q=1$ the model reduces to a random intersection graph which is known to generate high levels of transitivity also in the sparse context. The parameter $q$ adds a degree of freedom and leads to a parsimonious and analytically tractable network model with tunable density, transitivity, and degree fluctuations. We prove that the parameters of this model can be consistently estimated in the large and sparse limiting regime using moment estimators based on partially observed densities of links, 2-stars, and triangles.Comment: 15 page

Genetic variability of muscle biological characteristics of young Limousin bulls

Genetic parameters of 4 muscle biological characteristics (protein to DNA ratio (Pro/DNA), lactate dehydrogenase (LDH) activity, isocitrate dehydrogenase (ICDH) activity and the proportion of type I myosin heavy chains (MHC I)), in the Semitendinosus and the Longissimus thoracis, were estimated simultaneously with average daily gain (ADG), 480-d final weight (FW), carcass lean and fat contents (CL% and CF% respectively) in a sample of young Limousin bulls tested in station. The data came from 144 animals, the progeny of 15 sires. Sire and residual variances and covariances were estimated u using an expectation maximization restricted maximum likelihood (EM-REML) procedure applied to a multitrait mixed model. Heritability coefficients of production traits, ADG, FW, CL% and CF%, were 0.19, 0.49, 0.39 and 0.43, respectively, while heritability coefficients of muscle characteristics, Pro/DNA, LDH, ICDH and MHC I, were 0.11, 0.26, 1.03 and 0.35 respectively, in the Semitendinosus muscle and 0.29, 0.31, 0.28 and 0.41, respectively, in the Longissimus thoracis muscle. In both muscles, the oxidative activity of the ICDH appeared to be genetically associated with the proportion of type I myosin heavy chains and opposed to the glycolytic activity of the LDH. The LDH activity was clearly associated with higher muscle-to-fat ratio, while the opposite relationship was observed between that ratio and the ICDH activity or the MHC I proportion.Les paramètres génétiques de 4 caractéristiques biologiques - le rapport protéines /ADN (Pro/DNA), les activités de la lactate déshydrogénase (LDH) et de l’isocitrate déshydrogénase (ICDH) et la proportion en chaînes lourdes de myosine lente (MHC I) - des muscles Semitendinosus et Longissimus thoracis, et ceux du gain moyen quotidien (ADG), du poids vif finaL à 480 j (FW) et des teneurs de la carcasse en muscles et en dépôts adipeux (CL% and CF% respectivement), ont été estimés simultanément à partir d’un échantillon de taurillons Limousins contrôlés en station. Le fichier comprenait 144 veaux issus de 15 pères testés sur descendance. Les variances et covariances paternelles et résiduelles ont été estimées par la méthode du maximum de vraisemblance restreinte, avec l’algorithme d’espérance-maximisation, appliquée à un modèle mixte multicaractère (EM-REML). Les coefficients d’héritabilité des variables de production, ADG, FW, CL% et CF%, s’élevaient respectivement à 0,19, 0,49, 0,39 et 0,43, tandis que les coefficients d’héritabilité des caractéristiques musculaires, Pro/DNA, LDH, ICDH et MHC I, valaient respectivement 0,11, 0,26, 1,03 et 0,35 dans le muscle Semitendinosus et 0,29, 0,31, 0,28 et 0,41 dans le muscle Longissimus thoracis. Dans les 2 muscles, l’activité oxidative de l’ICDH était génétiquement associée à la proportion de myosine lente et opposée à l’activité glycolytique du LDH. Cette activité du LDH était positivement corrélée avec le rapport muscles / dépôts adipeux, alors qu’une relation inverse était observée avec l’activité de l’ICDH et la proportion de MHC I

A study of the static yield stress in a binary Lennard-Jones glass

The stress-strain relations and the yield behavior of model glass (a 80:20 binary Lennard-Jones mixture) is studied by means of MD simulations. First, a thorough analysis of the static yield stress is presented via simulations under imposed stress. Furthermore, using steady shear simulations, the effect of physical aging, shear rate and temperature on the stress-strain relation is investigated. In particular, we find that the stress at the yield point (the ``peak''-value of the stress-strain curve) exhibits a logarithmic dependence both on the imposed shear rate and on the ``age'' of the system in qualitative agreement with experiments on amorphous polymers and on metallic glasses. In addition to the very observation of the yield stress which is an important feature seen in experiments on complex systems like pastes, dense colloidal suspensions and foams, further links between our model and soft glassy materials are found. An example are hysteresis loops in the system response to a varying imposed stress. Finally, we measure the static yield stress for our model and study its dependence on temperature. We find that for temperatures far below the mode coupling critical temperature of the model ($Tc = 0.435$), \sigmay decreases slowly upon heating followed by a stronger decrease as \Tc is approached. We discuss the reliability of results on the static yield stress and give a criterion for its validity in terms of the time scales relevant to the problem.Comment: 14 pages, 18 figure

Simulation of the Microwave Emission of Multi-layered Snowpacks Using the Dense Media Radiative Transfer Theory: the DMRT-ML Model

DMRT-ML is a physically based numerical model designed to compute the thermal microwave emission of a given snowpack. Its main application is the simulation of brightness temperatures at frequencies in the range 1-200 GHz similar to those acquired routinely by spacebased microwave radiometers. The model is based on the Dense Media Radiative Transfer (DMRT) theory for the computation of the snow scattering and extinction coefficients and on the Discrete Ordinate Method (DISORT) to numerically solve the radiative transfer equation. The snowpack is modeled as a stack of multiple horizontal snow layers and an optional underlying interface representing the soil or the bottom ice. The model handles both dry and wet snow conditions. Such a general design allows the model to account for a wide range of snow conditions. Hitherto, the model has been used to simulate the thermal emission of the deep firn on ice sheets, shallow snowpacks overlying soil in Arctic and Alpine regions, and overlying ice on the large icesheet margins and glaciers. DMRT-ML has thus been validated in three very different conditions: Antarctica, Barnes Ice Cap (Canada) and Canadian tundra. It has been recently used in conjunction with inverse methods to retrieve snow grain size from remote sensing data. The model is written in Fortran90 and available to the snow remote sensing community as an open-source software. A convenient user interface is provided in Python

Identification of Movement Strategies during the Sit-to-Walk Movement in Patients with Knee Osteoarthritis

Patients with osteoarthritis (OA) of the knee commonly alter their movement to compensate for deficiencies. This study presents a new numerical procedure for classifying sit-to-walk (STW) movement strategies. Ten control and twelve OA participants performed the STW task in a motion capture laboratory. A full body biomechanical model was used. Participants were instructed to sit in a comfortable self-selected position on a stool height adjusted to 100% of their knee height and then stand and pick up an object from a table in front of them. Three matrices were constructed defining the progression of the torso, feet and hands in the sagittal plane along with a fourth expressing the location of the hands relative to the knees. Hierarchical clustering (HC) was used to identify different strategies. Trials were also classified as to whether the left (L) and right (R) extremities used a matching strategy (bilateral) or not (asymmetrical). Fisher’s exact test was used to compare this between groups. Clustering of the torso matrix dichotomised the trials in two major clusters; subjects leaning forward (LF) or not. The feet and hands matrices revealed sliding the foot backward (FB) and moving an arm forward (AF) strategies respectively. Trials not belonging in the AF cluster were submitted to the last HC of the fourth matrix exposing three additional strategies, the arm pushing through chair (PC), arm pushing through knee (PK) and arm not used (NA). The control participants used the LF+FBR+PK combination most frequently whereas the OA participants used the AFR+PCL. OA patients used significantly more asymmetrical arm strategies, p=0.034. The results demonstrated that control and OA participants favour different STW strategies. The OA patients asymmetrical arm behaviour possibly indicates compensating for weakness of the affected leg. These strategy definitions may be useful to assess post-operative outcomes and rehabilitation progress