Flow of temporal network properties under local aggregation and time shuffling: a tool for characterizing, comparing and classifying temporal networks

Although many tools have been developed and employed to characterize temporal networks, the issue of how to compare them remains largely open. It depends indeed on what features are considered as relevant, and on the way the differences in these features are quantified. In this paper, we propose to characterize temporal networks through their behaviour under general transformations that are local in time: (i) a local time shuffling, which destroys correlations at time scales smaller than a given scale $b$, while preserving large time scales, and (ii) a local temporal aggregation on time windows of length $n$. By varying $b$ and $n$, we obtain a flow of temporal networks, and flows of observable values, which encode the phenomenology of the temporal network on multiple time scales. We use a symbolic approach to summarize these flows into labels (strings of characters) describing their trends. These labels can then be used to compare temporal networks, validate models, or identify groups of networks with similar labels. Our procedure can be applied to any temporal network and with an arbitrary set of observables, and we illustrate it on an ensemble of data sets describing face-to-face interactions in various contexts, including both empirical and synthetic data

From temporal network data to the dynamics of social relationships

Networks are well-established representations of social systems, and temporal networks are widely used to study their dynamics. Temporal network data often consist in a succession of static networks over consecutive time windows whose length, however, is arbitrary, not necessarily corresponding to any intrinsic timescale of the system. Moreover, the resulting view of social network evolution is unsatisfactory: short time windows contain little information, whereas aggregating over large time windows blurs the dynamics. Going from a temporal network to a meaningful evolving representation of a social network therefore remains a challenge. Here we introduce a framework to that purpose: transforming temporal network data into an evolving weighted network where the weights of the links between individuals are updated at every interaction. Most importantly, this transformation takes into account the interdependence of social relationships due to the finite attention capacities of individuals: each interaction between two individuals not only reinforces their mutual relationship but also weakens their relationships with others. We study a concrete example of such a transformation and apply it to several data sets of social interactions. Using temporal contact data collected in schools, we show how our framework highlights specificities in their structure and temporal organization. We then introduce a synthetic perturbation into a data set of interactions in a group of baboons to show that it is possible to detect a perturbation in a social group on a wide range of timescales and parameters. Our framework brings new perspectives to the analysis of temporal social networks

PHASE CHANGE UNDER STATIC ELECTRICAL FIELD; IN THE CASE OF LIPIDS

International audiencePhase change in biological tissues may be affected by electrical and magnetic disturbances. Freezing under static electric field of water, aqueous solution and pork meat has been investigated by the authors, showing the ability of this process to refine ice crystals in frozen matrices. SEF affects the supercooling, which is usually reduced with SEF. SEF also triggers the nucleation. The use of radiofrequencies and microwaves has also been used recently by researchers to promote refined ice crystallization in food systems. A focus is proposed on recent experiments done on solidification of a vegetable fat mix (Vegetaline ® – France) under static electric field (SEF). Results showed that SEF affects the supercooling and the phase change temperature of the fat mix indicating a possible impact on the crystalline structure of the solidified fat

Ohmic heating applied to the baking process: experimental and numerical approaches

International audienceThis work aims at studying the feasibility of ohmic heating (OH) technology applied to the baking process. The method includes proofing (fermentation) and baking and leads to the production of crustless sandwich bread without the need of cutting the crust away, in a shorter time and with theoretically lower energy costs than conventional baking. An ohmic cell was made to study the electrical conductivity (EC) of bread dough under different experimental conditions. The results showed that the EC increased linearly with the temperature, except during the starch gelatinization stage (60 – 76 °C) because of the bounding of water. The EC decreased with the porosity of the dough when fermented by yeasts, and drastically decreased with the reduction of salt content in the dough, showing the need to control the product formulation. An ohmic baking oven monitored by a PLC was developed to perform both proofing and baking in the same apparatus. The results showed that using OH to quickly reach the optimal temperature of yeast activity (35 °C) significantly reduced the lag phase and shortened the total proofing time. A numerical model was developed and validated by experimental results, taking into account heat and water (vapour and liquid water) transfers. The results confirmed the importance of temperature gradients between the surface of the electrodes and the core of the product, first observed by the underbaked aspect of the bread loaf on its sides. Different baking scenarios and their impacts on temperature and water content gradients were modelled

Congélation de produits alimentaires : amélioration de la cristallisation par applications de micro-ondes

National audienceLa qualité d'un produit congelé est liée à la cristallisation ; en règle générale, plus la taille des cristaux de glace est petite, meilleure sera la qualité du produit. Un procédé innovant a été évalué dans le cadre du projet européen (FREEZEWAVE). Une assistance micro-ondes (2450 MHz) a été utilisée pour perturber le changement d'état de l'eau. Sur un prototype de laboratoire, les expériences ont confirmé que, quels que soient le mode d'application des micro-ondes et les paramètres du procédé, on observe une réduction de la taille des cristaux. Cet impact positif a été obtenu sur diverses matrices alimentaires, dont des pommes de terre. Un modèle de prédiction a par ailleurs permis de qualifier ces cinétiques. Deux concepts sont avancés pour expliquer ces effets bénéfiques. Abstract FREEZEWAVE project (SUSFOOD ERA-net project 2015-2018

Acute and two-week effects of Neotame, Stevia Rebaudioside M and sucrose-sweetened biscuits on postprandial appetite and endocrine response in adults with overweight/obesity – a randomised crossover trial from the SWEET Consortium.

BackgroundSweeteners and sweetness enhancers (S&SE) are used to replace energy yielding sugars and maintain sweet taste in a wide range of products, but controversy exists about their effects on appetite and endocrine responses in reduced or no added sugar solid foods. The aim of the current study was to evaluate the acute (1 day) and repeated (two-week daily) ingestive effects of 2 S&SE vs. sucrose formulations of biscuit with fruit filling on appetite and endocrine responses in adults with overweight and obesity.MethodsIn a randomised crossover trial, 53 healthy adults (33 female, 20 male) with overweight/obesity in England and France consumed biscuits with fruit filling containing 1) sucrose, or reformulated with either 2) Stevia Rebaudioside M (StRebM) or 3) Neotame daily during three, two-week intervention periods with a two-week washout. The primary outcome was composite appetite score defined as [desire to eat + hunger + (100 - fullness) + prospective consumption]/4.FindingsEach formulation elicited a similar reduction in appetite sensations (3-h postprandial net iAUC). Postprandial insulin (2-h iAUC) was lower after Neotame (95% CI (0.093, 0.166); p InterpretationIn conclusion, biscuits reformulated to replace sugar using StRebM or Neotame showed no differences in appetite or endocrine responses, acutely or after a two-week exposure, but can reduce postprandial insulin and glucose response in adults with overweight or obesity.FundingThe present study was funded by the Horizon 2020 program: Sweeteners and sweetness enhancers: Impact on health, obesity, safety and sustainability (acronym: SWEET, grant no: 774293)

Contribution a l'etude des transferts thermiques couples a haute temperature et a haute pression

SIGLEINIST T 73557 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Innovative baking and refrigeration processes for a sustainable food industry

International audienc

Multi-scale Strategy for Sugar and Salt Reduction in Sweet Products

International audienc