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3D Fabrication of Artificial Cell Microenvironments for Mechanobiology
No full textInternational audienceArtificial scaffolds are indispensable tools in unraveling the complexity of mechanobiology under controlled conditions. Recent breakthroughs in microfabrication techniques for biological applications have revolutionized the field, enabling welldefined features that span from the subcellular to the multicellular scale. These methods particularly allow for unprecedented control of cell stimulation. This review will showcase research that combines such scaffolds with various stimulation techniques: mechanical stimulation, actuation by magnetic or electric fields, chemical stimulation, or manipulation by light. Additionally, it will introduce passive scaffolds that are actuated by the cells themselves. These systems help to understand forces applied by the cells to their environment and pave the way toward dynamic biohybrid, cell-based systems
Mode Competition Phenomena and Impact of the Initial Conditions in Nonlinear Vibrations Leading to Railway Curve Squeal
No full textInternational audienceCurve squeal is a highly disturbing tonal noise produced by railway vehicles on tight curves, primarily attributed to lateral sliding at the wheel-rail interface. An essential step to estimate curve squeal noise levels is to determine the nonlinear self-sustained vibrations, for which time integration is a commonly used method. However, although it is known that the initial conditions affect the solutions obtained with time integration, their impact on the limit cycles is often overlooked. This study investigates this aspect for a curve squeal model based on falling friction and a modal reduction of the wheel and provides some insights on the mode competition phenomena and the nature of the final limit cycles obtained. The paper first details the curve squeal model, stability analysis, as well as the initial condition derivation, and then discusses the time integration and limit cycle results in both time and frequency domains. The results reveal two primary families of limit cycles that can be obtained for both types of initial conditions. The cases where stationary vibrations result in a quasi-periodic regime converge to a unique limit cycle which displays three fundamental frequencies corresponding to specific wheel modes, plus harmonic interactions among them
Clustered Archimax copulas
No full textInternational audienceWhen modeling multivariate phenomena, properly capturing the joint extremal behavior is often one of the many concerns. Archimax copulas appear as successful candidates in case of asymptotic dependence. In this paper, the class of Archimax copulas is extended via their stochastic representation to a clustered construction. These clustered Archimax copulas are characterized by a partition of the random variables into groups linked by a radial copula; each cluster is Archimax and therefore defined by its own Archimedean generator and stable tail dependence function. The proposed extension allows for both asymptotic dependence and independence between the clusters, a property which is sought, for example, in applications in environmental sciences and finance. The model also inherits from the ability of Archimax copulas to capture dependence between variables at pre-extreme levels. The asymptotic behavior of the model is established, leading to a rich class of stable tail dependence functions.</div
Progressive querying on knowledge graphs
No full textInternational audienceThe exact evaluation of queries over knowledge graphs encoded as RDF data has been extensively studied. However, in a wide array of applications, RDF queries do not even terminate, due to performance reasons. Notably, queries on public SPARQL endpoints are oftentimes timed out without returning any results.To address this, we propose a novel solution to the problem of progressive query answering and introduce the PING system that implements it on top of SPARK. In our approach, graph query answering leverages a hierarchical structure, which facilitates effective data partitioning, thus allowing us to reduce the sizes of intermediate results and return progressive answers. Moreover, it allows the RDF query evaluation algorithms to directly locate and access the different hierarchy levels required for query answering. Navigating through the hierarchy levels allows expanding or shrinking query results at different granularities. The extensive experimental study on real-world graph datasets, with varied query workloads, shows PING's effectiveness and efficiency, on both exact and progressive query answering, and its superiority to the most relevant baselines
Kinetically constrained models
No full text125 pages, 17 figuresThis is a preprint of the following work: Ivailo Hartarsky, Cristina Toninelli. Kinetically constrained models. Springer Nature Switzerland, 53, 2025, SpringerBriefs in Mathematical Physics. It is the version of the author’s manuscript prior to acceptance forpublication and has not undergone editorial and/or peer review on behalf of the Publisher (where applicable).The final authenticated version is available online at: http://dx.doi.org/10.1007/978-3-031-93115-4International audienceThe goal of this book is to provide an introduction to the mathematical theory of Kinetically constrained models developed in the last twenty years, intended for both mathematicians and physicists
Hide Exposures by Removing Mastermind’s External Sources on Social Network (Student Abstract)
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Node Regression on Latent Position Random Graphs via Local Averaging
No full textInternational audienceNode regression consists in predicting the value of a graph label at a node, given observations at the other nodes. To gain some insight into the performance of various estimators for this task, we perform a theoretical study in a context where the graph is random. Specifically, we assume that the graph is generated by a Latent Position Model, where each node of the graph has a latent position, and the probability that two nodes are connected depend on the distance between the latent positions of the two nodes. In this context, we begin by studying the simplest possible estimator for graph regression, which consists in averaging the value of the label at all neighboring nodes. We show that in Latent Position Models this estimator tends to a Nadaraya Watson estimator in the latent space, and that its rate of convergence is in fact the same. One issue with this standard estimator is that it averages over a region consisting of all neighbors of a node, and that depending on the graph model this may be too much or too little. An alternative consists in first estimating the true distances between the latent positions, then injecting these estimated distances into a classical Nadaraya Watson estimator. This enables averaging in regions either smaller or larger than the typical graph neighborhood. We show that this method can achieve standard nonparametric rates in certain instances even when the graph neighborhood is too large or too small
Flow dynamics, heat and mass transfer of laminar, round twin-jet impinging a uniformly heated flat plate
No full textInternational audienceThe aim of this study is to describe the flow as well as the heat and mass transfer of twin laminar jet impinging a flat catalytic sample. The Navier–Stokes and energy equations are solved by numerical simulations. When the flow reaches a steady state, a passive scalar transport equation is added to account for mass transfer on the impinging plate. The computed flows for a range of Reynolds number (3.3–100), jet-to-jet distance (2. 4 − 6.2) and two temperature gradients between the sample and the jet injection (0 and 300 K), are analyzed. The jet-to-jet interactions are specially described in the case where a fountain flow resulting from the wall-jets colliding is observed. Described interactions are classified in a topological diagram according to the Reynolds number and the normalized jet spacing for the isothermal case as well as in the presence of temperature gradient. The heat and mass transfer description is further conditioned on the flow characteristics as identified by the topological diagram. It is observed that the average Nusselt number on the sample is the lowest when the fountain flow is blocked by the impinging jet shear layer interaction. Mass transfer on the sample is then described by the ratio of the mass flux orthogonal and parallel to the injection line within the boundary layer on the sample. The ratio is lower than 1 when the flow is blocked. This study points out the importance of the presence of a fountain flow on heat and mass transfer quantities in the flow surrounding the catalytic sample
Uncertainty analysis of thiele-small parameter variations in electroacoustic active absorbers due to temperature effects
No full textInternational audienceActive noise control techniques using electroacoustic absorbers are based on a loudspeaker system in which the acoustic impedance can be adjusted to match a desired target value. These techniques rely on the Thiele-Small parameters of the loudspeaker as part of the control law. Therefore, uncertainty in these parameters introduces uncertainty into the control itself. Due to the nature of the materials used in the construction of the membrane, their mechanical properties can be affected by environmental factors such as temperature and humidity. This work proposes an uncertainty analysis of the Thiele-Small parameters of electroacoustic absorbers due to temperature variation. The acoustic impedance of an electroacoustic absorber is measured using an impedance tube over a temperature range of -10◦C to +50◦C. A one-degree-of-freedom analytical model with corrections for low and high frequencies is used to identify the Thiele-Small parameters. These parameters are evaluated both for average values along temperature variations and by employing Bayesian inference to quantify uncertainty and to obtain probability distribution functions for each parameter concerning temperature variation. This uncertainty quantification allows for the implementation of more robust control strategies that account for variations in the parameters along with the controlled variable
Comparison of Environmental Impacts of AC, DC and Mixed Distribution Networks
No full textInternational audienceThe electrification growth has led to an increasing number of DC devices, such as PV panels and electric vehicle chargers. This revives the option of a DC distribution network, or rather mixed AC-DC network. The comparison between such alternatives needs to take into account the environmental impacts associated with the manufacture of specific power electronics devices. This article proposes a comparison of the fabrication impacts and losses of three technical choices for low-voltage electrical grids: DC, AC and mixed AC/DC. A case study is chosen based on typical mixed consumer-width distributed energy sources. Simulations are performed over 20-year period for each of the three architectures. This study finds that a mixed topology can be a promising alternative to traditional AC grids, as it reduces converter impacts, especially for short cable lengths. However, the optimal architecture for a given system can vary depending on factors such as nominal power, cable length, and consumption profile. To explore this variability, a detailed sensitivity analysis is performed