HAL-Ecole des Ponts ParisTech
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Revising clustering and small-worldness in brain networks
No full textAs more connectome data become available, the question of how to best analyse the structure of biological neural networks becomes increasingly pertinent. In brain networks, knowing that two areas are connected is often not sufficient, as the directionality and weight of the connection affect the dynamics in crucial ways. Still, the methods commonly used to estimate network properties, such as clustering and small-worldness, usually disregard features encoded in the directionality and strength of network connections. To address this issue, we propose using fully-weighted and directed clustering measures that provide higher sensitivity to non-random structural features. Using artificial networks, we demonstrate the problems with methods routinely used in the field and how fully-weighted and directed methods can alleviate them. Specifically, we highlight their robustness to noise and their ability to address thresholding issues, particularly in inferred networks. We further apply our method to the connectomes of different species and uncover regularities and correlations between neuronal structures and functions that cannot be detected with traditional clustering metrics. Finally, we extend the notion of small-worldness in brain networks to account for weights and directionality and show that some connectomes can no longer be considered ``small-world''. Overall, our study makes a case for a combined use of fully-weighted and directed measures to deal with the variability of brain networks and suggests the presence of complex patterns in neural connectivity that can only be revealed using such methods
A two-parameter deformation of the quasi-shuffle\\ and new bases of quasi-symmetric functions
No full text14 pagesWe define a two-parameter deformation of the quasi-shuffle by means of the formal group law associated with the exponential generating function of the homogeneous Eulerian polynomials, and construct bases of and \WQSym whose product rule is given by this operation
The impacts of combining incentives on carpooling for commuting in the Paris region
No full textInternational audienceCarpooling is one solution to help reduce the negative externalities of solo driving. The aim of this study is to analyze the effect of incentives on solo drivers’ intention to carpool. A questionnaire survey was carried out among 1,329 participants, including 590 (38.39%) residents of the Paris metropolitan area who use a car to get to work. Modal choice estimates were modeled using multinomial logit and binomial logit econometric models for car drivers only. First, we analyzed the effect of non-financial incentives, such as nudges and trust in others during the carpooling trip. Second, we analyzed the effect of the combination of nudges with employer subsidies for sustainable mobility on the intention to carpool as a driver or passenger for the home-to-work (or home-to-school) commute. The results show that people aged 18–49, employees, and those with higher levels of education are more receptive to behavioral interventions such as nudges. Applying nudges in isolation is more effective at encouraging carpooling for commuting than combining nudges with employers’ subsidies for sustainable mobility
Reaching out to socially distant trainees. Experimental evidence from variations on the standard farmer trainer system
No full textInternational audienceThe farmer trainer (FT) model has gained momentum as a cost-effective alternative to traditional agricultural extension systems. However, there may be friction in the transmission of information, whereby farmers closer to the FT may benefit more than socially distant farmers. This study explores whether variations on the standard FT model facilitate the diffusion of information outside the FT’s pre-existing social network. On top of a standard FT training, a sub-sample of voluntary FTs in rural Uganda was randomly assigned to receive (i) vouchers for accessing professional extension agents, (ii) a signpost advertising the trainer services or (iii) further training aimed at tailoring the training to the specific needs of the trainees. The results show that the FTs assigned these treatment variations trained more farmers, a larger proportion of whom belonged to the FT’s own close circle. The FTs who received vouchers were the only ones to reach out to more socially distant farmers and were also those who organized the most training sessions. We show that these effects are independent of any FT prominence in the village. Nevertheless, further evidence suggests exercising caution regarding the presence of friction in the transmission of knowledge, since knowledge and technology adoption appear to increase only among farmers closely connected to the FT
Chemical Modification of Commercial Fabrics by Photoinduced Grafting Tannic Acid to Produce Antioxidant and Antibacterial Textiles
No full textInternational audienceThe goal of this study was to provide antioxidant and antibacterial properties to different types of fabrics via tannic acid (TA) covalent grafting. To that extent, TA was first methacrylated using glycidylmethacrylate. TA derivatives were characterized using infrared spectroscopy and 1H NMR to assess the degree of acrylation. Antioxidant and antibacterial properties of TA were preserved after chemical modification. The coating process was studied using infrared spectroscopy (IR), weight gain, and radical scavenging activity (RSA) measurements. To covalently bond TA to raw polypropylene (PP) and PP coated with chitosan, photoinduced grafting was performed. The process was optimized and resulted in fabrics with enough tannic acid to provide strong antioxidant activity, with RSA ranging at 95%. The antibacterial activity was assessed against E. coli and S. aureus, the main strains responsible for nosocomial infections. Results revealed a substantial reduction of bacterial contamination for PP samples coated with chitosan, with stronger activity against E. coli, attributed to hydrophobic repellence. This study highlights the benefits of using tannic acid to obtain antioxidant and antibacterial fabrics
Modelling the climate in Titan’s lake regions
No full textInternational audienceTitan interestingly has many similarities with the Earth. It has a thick atmosphere, made mostly of dinitrogen, and a surface pressure of 1.5 bar. It also hosts a hydrological cycle similar to the water cycle on Earth, but based on methane. We then observe similar landscapes and weather processes as on Earth: clouds, rain, rivers, lakes, seas (Hayes, 2016, Ann Rev EPS; Turtle et al., 2018, GRL)… Although we gathered many observations of Titan with the Cassini-Huygens mission, the conditions at its surface are still mostly a mystery. How strong are the winds? What are the variations of the surface methane humidity? How frequent are clouds? What is their distribution in size? How frequent is rain? The NASA Dragonfly mission will have many meteorological sensors to probe the weather on Titan in the mid 2030s (Barnes et al., 2021, PSJ). Nevertheless, we need to have sounded expectations of the surface conditions, lower troposphere properties and relevant processes to prepare the drone and its instruments
Calibrating and validating the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) urban cooling model: case studies in France and the United States
No full textInternational audienceUnderstanding the cooling service provided by vegetation in cities is important to inform urban policy and planning. However, the performance of decision-support tools estimating heat mitigation for urban greening strategies has not been evaluated systematically. Here, we further develop a calibration algorithm and evaluate the performance of the urban cooling model developed within the open-source InVEST (Integrated Valuation of Ecosystem Services and Tradeoffs) software. The urban cooling model estimates air temperature reduction due to vegetation based on four predictors, shade, evapotranspiration, albedo, and building density, and was designed for data-rich and data-scarce situations. We apply the calibration algorithm and evaluate the model in two case studies (Paris, France, and Minneapolis–St Paul, USA) by examining the spatial correlation between InVEST predictions and reference temperature data at a 1 km horizontal resolution. In both case studies, model performance was high for nighttime air temperatures, which are an important indicator of human wellbeing. After calibration, we found medium performance for surface temperatures during daytime but low performance for daytime air temperatures in both case studies, which may be due to model and data limitations. We illustrate the model adequacy for urban planning by testing its ability to simulate a green infrastructure scenario in the Paris case study. The predicted air temperature change compared well to that of an alternative physics-based model (r2=0.55 and r2=0.85 for daytime and nighttime air temperatures, respectively). Finally, we discuss opportunities and challenges for the use of such parsimonious decision-support tools, highlighting their importance to mainstream ecosystem services information for urban planning
Micromechanical Estimates Compared to FE-Based Methods for Modelling the Behaviour of Micro-Cracked Viscoelastic Materials
No full textInternational audienceThe purpose of this study is to investigate the effective behaviour of a micro-cracked material whose matrix bulk and shear moduli are ruled by a linear viscoelastic Burgers model. The analysis includes a detailed study of randomly oriented and distributed cracks displaying an overall isotropic behaviour, as well as aligned cracks resulting in a transversely isotropic medium. Effective material properties are approximated with the assumption that the homogenized equivalent medium exhibits the characteristics of a Burgers model, leading to the identification of short-term and long-term homogenized modules in the Laplace–Carson space through simplified formulations. The crucial advantage of this analytical technique consists in avoiding calculations of the inverse Laplace–Carson transform. The micromechanical estimates are validated through comparisons with FE numerical simulations on 3D microstructures generated with zero-thickness void cracks of disc shape. Intersections between randomly oriented cracks are accounted for, thereby highlighting a potential percolation phenomenon. The effects of micro-cracks on the material’s behaviour are then studied with the aim of providing high-performance creep models for macrostructure calculations at a moderate computation cost through the application of analytical homogenization techniques
