Archive ouverte de Centrale Lyon
Not a member yet
32420 research outputs found
Sort by
In situ effect of printing parameters on microstructural anisotropy of bioink based hydrogel during micro-extrusion bioprinting process for tissue engineered substitute.
No full textThe study introduces a mechanically driven, temperature‑controlled bioprinter that permits rigorous control of nozzle geometry and extrusion speed, enabling in‑situ synchrotron SAXS/WAXS analysis of hydrogel filaments during deposition. Two tubular nozzles (radii 0.400 mm and 0.125 mm, length 12.7 mm) were tested while extruding an alginate‑gelatine–cellulose‑nanocrystal bio‑ink at 24 °C. Scattered intensity images were collected at q = 5 × 10⁻³ Å⁻¹ along the filament, and azimuthal profiles were used to compute apparent Herman’s orientation factors, aiming to map shear‑induced macromolecular alignment. However, the X‑ray beam was mistakenly focused on the downstream D5 detector, producing an effective footprint of ~500 µm—larger than the hydrogel diameter—so measurements extended 300 µm beyond the sample and averaged signals from core and periphery. This spatial blurring suppressed local anisotropy, precluded deconvolution, and rendered the orientation maps unusable. A 50 µm beam, centred on the sample, is required for meaningful resolution. Despite this limitation, the work constitutes the first attempt to probe nozzle‑driven orientation effects during bioprinting in real time, highlighting both the promise of coupled mechanical extrusion and synchrotron scattering, and the critical need for precise beam alignment in microscale flow studies
A Collaborative Vocabulary Notebook as a Complementary Tool to Language Courses at the University Level
No full textInternational audienceWhile essential to second language learning, vocabulary learning is a complex and time-consuming task. It rarely takes place explicitly in classrooms and, consequently, learners are often expected to carry out this activity autonomously. Many tools targeting vocabulary learning exist, but they are frequently conceptualized as stand alone products, leaving little room for integration within institutional curricula and collaboration between learners. In this paper, we present a shared vocabulary notebook tool to enhance vocabulary learning in and outside the classroom. This tool was designed according to an iterative and participatory process to integrate both learners’ and teachers’ needs. In 2024, we conducted a 6-week study in 4 classes of French L2 learners at Carnegie Mellon University. We explored both learners’ and teachers’ uses and perceptions of the tool. We cross-checked interaction traces to qualitative outputs (i.e., focus groups carried out with the learners and interviews involving participating teachers). We present results regarding the integration of the tool in teaching and learning practices, the expectations and apprehensions linked to the collaborative and social dimensions, and the limitations of a stand-alone vocabulary notebook tool. Our findings have broader implications for the community as regards the design of tools to support vocabulary learning
The influence of vehicles on smoke propagation in transversely ventilated tunnels
No full textInternational audienceWe present an experimental study to assess the influence of realistic traffic conditions on the ventilation required to confine the smoke produced by a tunnel fire. The experiments are performed on a reducedscale tunnel, with hot smoke modeled by a buoyant helium-air release. The tunnel is ventilated by two extraction vents placed on both sides of the source to confine the smoke, and a longitudinal flow is induced by a longitudinal pressure gradient. The traffic condition is simulated by arranging cubic blocks, representing vehicles, of two different sizes inside the tunnel. For each block size and various tunnel configurations (different damper geometries and positions, and the presence or absence of vertical barriers downstream of the vents), experiments are performed with and without longitudinal flow. The presence of vehicles can lead to outcomes that differ from the well-established results in the literature obtained in their absence, i.e., in an empty tunnel. Specifically, the performance of rectangular dampers becomes equivalent to that of squared-centered dampers unless vertical barriers are used. Furthermore, when barriers are employed, the geometry and position of the dampers become irrelevant to ventilation efficiency. Obstacles primarily affect ventilation efficiency when they interact with the buoyant smoke and change its stratification regime.</div
A memristive neural decoder for cryogenic fault-tolerant quantum error correction
No full textInternational audienceAbstract Neural decoders for quantum error correction rely on neural networks to classify syndromes extracted from error correction codes and find appropriate recovery operators to protect logical information against errors. Its ability to adapt to hardware noise and long-term drifts make neural decoders promising candidates for inclusion in a fault-tolerant quantum architecture. However, given their limited scalability, it is prudent that small-scale (local) neural decoders are treated as first stages of multi-stage decoding schemes for fault-tolerant quantum computers with millions of qubits. In this case, minimizing the decoding time to match the stabilization measurements frequency and a tight co-integration with the QPUs is highly desired. Cryogenic realizations of neural decoders can not only improve the performance of higher stage decoders, but they can minimize communication delays, and alleviate wiring bottlenecks. In this work, we design and analyze a neural decoder based on an in-memory computation (IMC) architecture, where crossbar arrays of resistive memory devices are employed to both store the synaptic weights of the neural decoder and perform analog matrix–vector multiplications. In simulations supported by experimental measurements, we investigate the impact of TiO x -based memristive devices’ non-idealities on decoding fidelity. We develop hardware-aware re-training methods to mitigate the fidelity loss, restoring the ideal decoder’s pseudo-threshold for the distance-3 surface code. This work provides a pathway to scalable, fast, and low-power cryogenic IMC hardware for integrated fault-tolerant quantum error correction
Reinforcement Learning-Assisted Ferroelectric Domain Wall Design Using a Machine Learning Phase-Field Surrogate
No full textInternational audiencePrecise manipulation of ferroelectric domain walls (DWs) has garnered increasing interest for applications in DW memory devices. Although recent advancements in scanning probe microscopy-based automated experiments have improved tip control efficiency, achieving real-time optimization of the tip trajectory to configure arbitrary domain structures remains challenging. In this study, we introduce a reinforcement learning (RL) framework for autonomous DW manipulation, leveraging a 3-D machine learning phase-field surrogate model to accelerate environment dynamics. The RL agent is trained to optimize the tip trajectory, enabling it to achieve target DW configurations within both single-goal and goal-augmented RL frameworks while effectively generalizing across a range of target structures. This framework offers a promising approach for facilitating the realtime design of 2-D ferroelectric DWs.</div
A Multi-Scale Comparison of Heat Stress Metrics in Lyon using meteorological, reanalysis and remote sensing datasets
No full textInternational audienceHeat extremes significantly impact human health, causing heat stroke, reduced productivity, and heat-related mortality. In Europe, the increasing frequency of intense heat waves results from a combination of natural climate variability and anthropogenic climate change. Urbanization exacerbates these extremes through the urban heat island (UHI) effect, intensifying warming in cities and their surroundings. Since the 2000s, France has experienced severe heat waves leading to substantial loss of life, with Lyon experiencing a significant mortality increase after Paris, as reported by the EM-DAT database.Heat stress exhibits high spatiotemporal variability influenced by morphological and climatic conditions. While heat stress classifications based on climate and urban development provide a general overview of population impacts, they lack the detailed resolution needed to understand intra-urban temperature intensification.This study investigates the complex dynamics of heat stress at a micro-scale by analyzing three heat stress indices over the Lyon region from 2000 to 2022 during summer (June-August): 1) a temperature-based heat index, 2) the Universal Thermal Climate Index (UTCI), and 3) UHI intensity. A comparative spatiotemporal analysis was conducted across these datasets.Maximum and minimum air temperature and relative humidity data were obtained from Météo-France's ground observation network. Hourly data were converted to daily values for heat stress index (HSI) calculation. High-resolution (0.25° x 0.25°) daily UTCI data were extracted from the ERA5 reanalysis dataset. Landsat 5, 7, and 8 satellite images covering Lyon were acquired and processed using a single-channel method, including radiometric and geometric corrections, and NDVI-based emissivity corrections, to derive land surface temperature (LST). Image fusion techniques were applied to combine the multi-temporal satellite data into a single dataset.Cubic interpolation was used to standardize the temporal resolution of the LST, ground observation, and reanalysis data and to address data gaps. The HSI was calculated using Steadman’s index, using daily air temperature and relative humidity. Spatial and temporal analysis of surface temperatures was performed over urban and rural areas of Lyon to calculate UHI intensity. Using the HSI derived from direct temperature data as a benchmark, bias correction, root mean square error, and correlation analyses were conducted to validate the UTCI and UHI. Spatial mapping of the derived HSI was performed using QGIS, and temporal analysis was conducted to compare seasonal, annual, and decadal HSI patterns.Results revealed significant discrepancies between air temperature-based and thermal data-derived metrics, particularly in urbanized areas where land surface characteristics and anthropogenic activities enhance heat retention. Urban areas exhibited significantly higher temperatures and increased heat stress compared to rural areas due to the UHI effect. Remote sensing data provided more localized and detailed information on heat stress than traditional temperature-based indices. Despite some disparities, the datasets complemented each other by enabling necessary spatial and temporal adjustments. This research highlights the need for multi-dimensional approaches to heat stress assessment, integrating both meteorological and remotely sensed data. These findings have crucial implications for urban planning and climate adaptation strategies in Lyon and other European cities facing increasing heat stress risks.
Koszul-Tate resolutions and decorated trees
No full text44 pagesGiven a commutative algebra , a proper ideal , and a resolution of by projective -modules, we construct an explicit Koszul-Tate resolution. We call it the arborescent Koszul-Tate resolution since it is indexed by decorated trees. When the -module resolution has finite length, only finitely many operations are needed in our constructions -- this is to be compared with the classical Tate algorithm, which requires infinitely many such computations if is not a complete intersection. As a by-product of our construction, the initial projective -module resolution becomes equipped with an explicit -algebra
Resistance to Oxidation and Tribological Behavior of MoS2 Nanoparticles in Severe Environmental Conditions
No full textInternational audienceAbstract This study investigates the oxidation resistance and tribological performance of MoS 2 nanoparticles under severe environmental conditions. Friction tests were conducted in dry and strictly controlled environments using a reciprocating pin-on-flat tribometer installed in a controlled environment chamber. This system was connected via a transfer chamber to an XPS spectrometer, enabling post-mortem analysis of the rubbed surfaces without air exposure. The friction tests were performed under pressures ranging from 10 −9 to 200 mbar (simulating ambient air) and at two temperatures (25 and 100 °C). The results show that the nanoparticles maintain excellent tribological performance and good chemical stability from ultrahigh vacuum up to 200 mbar of oxygen at 25 °C, and up to 1 mbar of oxygen at 100 °C. The increase in the friction coefficient observed under certain experimental conditions is attributed to particle oxidation
ECL5/CATANA: Transition from Non-Synchronous Vibration to Rotating Stall at transonic speed
No full textInternational audienceNon-Synchronous Vibration (NSV), flutter or rotating stall can cause severe blade vibrations and limit the operating range of compressors and fans. To enhance the understanding of these phenomena, this paper investigates the corresponding mechanisms in modern composite Ultra-High-Bypass-Ratio (UHBR) fans based on the ECL5/CATANA test campaign. Extensive steady and unsteady instrumentation such as Stereo-PIV, fast-response pressure probes and rotor strain gauges are used to derive aerodynamic and structural characteristics of the rotor at throttled operating conditions. The study focuses on the analysis of the transition region from transonic to subsonic speeds where two distinct phenomena are observed. At transonic design speed, rotating stall is encountered, while NSV is observed at 90 % speed. At the intermediate 95 % speedline a peculiar behavior involving a single stalled blade was observed. The results emphasize that rotating stall and NSV exhibit different wave characteristics: Rotating stall comprises lower wave numbers and higher propagation speeds around 78 % rotor speed, while small scale disturbances propagate at 57 % rotor speed and lock in with blade eigenmodes, causing NSV. Both phenomena are observed in a narrow range of operation, and even simultaneously at specific conditions. The presented results contribute to the understanding of different types of operating range limiting phenomena in modern UHBR fans and serve as a basis for the validation of numerical simulations
