HAL-Polytechnique
Not a member yet
51406 research outputs found
Sort by
Building without income mixing: Public housing quotas in France
No full textWe study the effects of the SRU law introduced in France in December 2000 to support scattered development of public housing in cities and favor social mixity. This law imposes 20% of public dwellings to all medium and large municipalities of large-enough cities, with fees for those not abiding by the law. Using exhaustive fiscal data, we evaluate the effects of the law over the 1996-2008 period using a difference-in-differences approach at the municipality and neighborhood levels. We find that the law stimulated public housing construction in treated municipalities, but only slightly increased the presence of low-income households. Indeed, new public dwellings enter categories to which medium-income are eligible and most additional occupants are not poor. Within municipalities, the policy decreased public housing segregation but it barely decreased low-income segregation. This comes from local authorities increasing over time the presence of public dwellings in neighborhoods away from existing public housing but in places concentrating low-income households
Residual stress control in large format polylactic acid additive manufacturing via fast thermomechanical simulation and in-operando imaging techniques
No full textInternational audiencePolymer-based Large Format Additive Manufacturing (LFAM) is an extrusion-based technology utilizing a robotic arm-mounted nozzle to deposit large-diameter polymer beads from heated polymer pellets. However, technical challenges arise due to slower cooling rates and heat accumulation, significant deformation that should be accounted for updating the nozzle path, as well as the development of residual stresses from thermo-chemical shrinkage leading to debonding. To overcome these challenges, the study proposes to combine recent and fast thermal and mechanical approaches. This computationally efficient digital twin of the process is validated experimentally on a thin-wall structure using polylactic acid as a feedstock material. To do so, anisotropic material properties are characterized, and in-operando temperature and displacement field measurements are performed using an infrared thermal camera and backward Digital Image Correlation techniques. Numerical results are in satisfying agreement with experimental data. The validated digital twin is then utilized to characterize the effect of process parameters on the number of layers above the glass transition temperature, the formation of residual stresses and the position offset between the top surface of the structure and the nozzle. This paper presents a fast numerical tool to better design fabrication conditions and improve the quality and fabricability of LFAM-produced parts
Terrestrial Very-Long-Baseline Atom Interferometry: summary of the second workshop
No full textInternational audienceThis summary of the second Terrestrial Very-Long-Baseline Atom Interferometry (TVLBAI) Workshop provides a comprehensive overview of our meeting held in London in April 2024 (Second Terrestrial Very-Long-Baseline Atom Interferometry Workshop, Imperial College, April 2024), building on the initial discussions during the inaugural workshop held at CERN in March 2023 (First Terrestrial Very-Long-Baseline Atom Interferometry Workshop, CERN, March 2023). Like the summary of the first workshop (Abend et al. in AVS Quantum Sci. 6:024701, 2024), this document records a critical milestone for the international atom interferometry community. It documents our concerted efforts to evaluate progress, address emerging challenges, and refine strategic directions for future large-scale atom interferometry projects. Our commitment to collaboration is manifested by the integration of diverse expertise and the coordination of international resources, all aimed at advancing the frontiers of atom interferometry physics and technology, as set out in a Memorandum of Understanding signed by over 50 institutions (Memorandum of Understanding for the Terrestrial Very Long Baseline Atom Interferometer Study)
Metal Foil Detectors assembly for the beam and background monitoring in the LHCb experiment
No full textInternational audienceAfter an upgrade in 2019--2021, the LHCb experiment is taking data in Run 3 (2022--2026) with an instantaneous luminosity of proton-proton collisions of cms. This article presents the Radiation Monitoring System (RMS-R3) for controlling the beam and background conditions at LHCb. It runs continuously during the detector's operation, and independently of the main LHCb data acquisition. Its design is based on robust and radiation-hard Metal Foil Detector technology. The RMS-R3 monitors the instantaneous luminosity and its evolution. The analysis of the RMS-R3 Run 3 data demonstrates its linear response with a high reproducibility in a five-decade dynamic range of luminosity over a long period of operation
Shearmetry in fluids by using size-controlled anisotropic LaPO 4 :Eu 3+ nanorods as polarized luminescent probes
No full textInternational audienceOrientation analysis of colloidally dispersed nanorods (NRs) provides a powerful means to measure local shear stress in fluids. Lanthanide-doped crystalline NRs, with their polarized luminescence properties, offer a promising platform for such shearmetry applications, as their emission spectra reflect the degree of collective orientation induced by shear. However, precise control over the morphology of the NRs is essential for ensuring reliable measurements, particularly in complex and dynamic flow environment. Herein, we present size-controlled synthesis of Eu-doped LaPO 4 NRs and their application in shearmetry within a microfluidic channel designed to generate curved streamlines. By analyzing 2D shear maps obtained using NRs of varied sizes, we quantitatively evaluate the impact of NR size on the shearmetry performance. Size-control of the NRs was achieved by adding a surfactant during hydrothermal synthesis. The collective orientation of NRs, induced by flow shear, was determined by analyzing the polarized Eu 3+ emission spectra. We reveal that NRs of smaller aspect ratio (AR) and length respond more rapidly to shear variations, yielding symmetric and accurate shear stress profiles even in complex, dynamic flows. Additionally, smaller NRs extend the measurable shear stress range up to 0~15000 mPa, covering values typical of biofluidic systems and microfluidic devices. These results provide a novel framework for advanced fluidic analysis highlighting the critical role of the nanoprobe morphology
Algorithme Self-Consistent Field pour la méthode Hartree-Fock restreinte à couche ouverte (ROHF)
No full textInternational audienceIn this chapter, we propose a simple geometrical derivation of the restricted open-shell Hartree-Fock (ROHF) equations in the density matrix and molecular orbitals formalism. We then introduce a new, parameter-free, basic fixed-point method to solve these equations, that, in contrast with existing self consistent field (SCF) schemes, is not based on the introduction of a non-physical, parameter-dependent, composite Hamiltonian. We also extend the Optimal Damping Algorithm to the ROHF framework. We finally present numerical results on challenging systems (complexes with transition metals) demonstrating the performance of the new algorithms we propose
Scaffold with Stochastic Gradients: New Analysis with Linear Speed-Up
No full textThis paper proposes a novel analysis for the Scaffold algorithm, a popular method for dealing with data heterogeneity in federated learning. While its convergence in deterministic settings-where local control variates mitigate client drift-is well established, the impact of stochastic gradient updates on its performance is less understood. To address this problem, we first show that its global parameters and control variates define a Markov chain that converges to a stationary distribution in the Wasserstein distance. Leveraging this result, we prove that Scaffold achieves linear speed-up in the number of clients up to higher-order terms in the step size. Nevertheless, our analysis reveals that Scaffold retains a higher-order bias, similar to FedAvg, that does not decrease as the number of clients increases. This highlights opportunities for developing improved stochastic federated learning algorithms
A Novel Approach to Guidance and Control of USVs Combining Flatness-Based and Model-Free Controllers
No full textInternational audienceThis work presents a new approach to the guidance and control of marine craft by combining Flatness-Based and Model-Free controllers. Its goal is to develop a general regulator for Unmanned Surface Vehicles (USV). To do so, the well-known USV maneuvering model is simplified and proven to be flat. A flatness-based controller is derived for the simplified USV model and the loop is closed via an intelligent proportional derivative (iPD) regulator derived from model-free control. We thus associate the well-documented natural robustness of flatness-based control and adaptivity of iPDs. The controller is applied in simulation to two surface vessels, one meeting the simplifying hypotheses, the other one being a generic USV of the literature, and is shown to stabilize both systems even in the presence of unmodeled environmental disturbances
Hot electrons and cold holes: operation, efficiency and design of a two-temperature hot-carrier solar cell
No full textInternational audienceHot-carrier solar cells (HCSCs) offer potential for enhancing the energy-conversion efficiency of photovoltaic devices up to 86%. However, most HCSC models to date assume that electrons and holes have the same temperature, while many reports in III-V materials indicate that electrons can be much hotter than their counterparts. We present here a detailed balance HCSC model that includes different temperatures for electrons and holes. We focus on the impact of the temperature imbalance on the voltage of such a HCSC, and on its power-conversion efficiency. Surprisingly, a temperature imbalance at a fixed effective temperature leads to a slight power-conversion efficiency increase, up to 1-2 percentage points, primarily due to an increase in fill factor and possibly of opencircuit voltage. Yet, we show that the knowledge of the effective temperature alone is sufficient to design a satisfying HCSC
Matrix CUSUM statistic, July 23 -August 22, 2012
No full textStructural changes occur in dynamic networks quite frequently and its detection is an important question in many situations such as fraud detection or cybersecurity. Real-life networks are often incompletely observed due to individual non-response or network size. In the present paper we consider the problem of change-point detection at a temporal sequence of partially observed networks. The goal is to test whether there is a change in the network parameters. Our approach is based on the Matrix CUSUM test statistic and allows growing size of networks. We show that the proposed test is minimax optimal and robust to missing links. We also demonstrate the good behavior of our approach in practice through simulation study and a real-data application