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SmartDetector: a valid and affordable AI-based markerless motion capture system for psychological experiments
No full textInternational audienceIn this paper, we evaluate the validity of SmartDetector—a markerless motion capture device based on artificial intelligence—by comparing it to a conventional optoelectronic motion capture system (i.e., Qualisys) in the context of stimuli construction for psychological experiments. To this end, simultaneous motion capture recordings were performed using both the conventional system and the SmartDetector, enabling the creation of 2D kinematic data and the generation of two versions of point-light displays. Three perceptual experiments were then conducted to facilitate comparisons between the two systems: a recognition task, a detection task, and a discrimination task. Bayesian analysis was employed to test the null hypotheses regarding the stimuli generated by SmartDetector versus those produced by the conventional motion capture system. The results suggest that participants achieved comparable performance across both types of stimuli depending on the task with reduced processing time and lower costs for SmartDetector. These findings appear to validate SmartDetector as a reliable and accessible alternative for creating point-light displays, reducing processing time and costs, thus reinforcing its potential for widespread adoption by professionals in the field
Quantification of intracellular mechanical fields in invasive cancer cells using digital volume correlation, confocal microscopy, and finite element method
No full textInternational audienceCell invasion process, which appears in the progression of tumours, such as glioblastoma, is highly dependent on cellular mobility. Cellular movement results from the interaction of chemical, biological and mechanical factors both inside and outside the invasive cancer cell. To identify and understand the relationship between these factors, it is necessary to quantify and visualise the extra- and intracellular kinematic fields during cell movement. This study proposes a new methodology for the experimental measurement of full kinematic fields inside cancer cells and the use of a digital twin simulation of the cell to obtain the stress and force fields. Confocal microscopy, Digital Volume Correlation (DVC) and Finite Element Method (FEM) are used in this methodology. To demonstrate the efficiency of this approach, highly invasive glioblastoma cells have been used as a model
Hydrodynamic effects of ship passage in confined channels: A multi-parameter study
No full textInternational audienceThis study investigates the impact of inland navigation on inland. Two methods were used: experimental campaigns in the towing tank of the Pprime Institute and numerical simulations with the CFD software StarCCM+. These approaches allowed detailed analysis of the hydrodynamic effects caused by ship passage in confined channels. The experiments reproduced various navigation scenarios using adjustable banks. Flow velocities and surface elevations were measured with Stereo-PIV and stereo-refraction techniques. A numerical model was also developed using the SST k–ω turbulence model and mesh refinement near the free surface. It was validated against the experimental data. Four key parameters were studied: ship speed, initial water depth, channel width, and bank slope. Each had a strong influence on flow characteristics. Extreme conditions (high speed, shallow depth, narrow channels, and sloped banks) produced amplified effects. These included deeper surface depressions, stronger return currents, larger waves, more turbulent wakes, and sharper velocity gradients, especially near banks. This study highlights the need to control navigation conditions to protect riverbanks
Primary Experimental Feedback on a Co-manipulated Robotic System for Assisted Cervical Surgery
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Experimental and theoretical study of metal combustion in oxygen flows
No full textThe effects of oxygen flow speed and pressure on the iron and mild steel combustion are investigated experimentally and theoretically. The studied specimens are vertical cylindrical rods subjected to an axial oxygen flow and ignited at the upper end by laser irradiation. Three main stages of the combustion process have been identified experimentally: (1) Induction period, during which the rod is heated until an intensive metal oxidation begins at its upper end; (2) Static combustion, during which a laminar liquid "cap" slowly grows on the upper rod end; and, after the liquid cap detachment from the sample, (3) Dynamic combustion, which is characterized by a rapid metal consumption and turbulent liquid motions. An analytical description of these stages is given. In particular, a model of the dynamic combustion is constructed based on the turbulent oxygen transport through the liquid metal-oxide flow. This model yields a simple expression for the fraction of metal burned in the process, and allows one to calculate the normal propagation speed of the solid metal--liquid interface as a function of the oxygen flow speed and pressure. A comparison of the theory with the experimental results is made
Dislocation evolution and redistribution during stress relaxation in single crystal AD730TM after prior plastic strain at 700 °C
No full textInternational audienceUnderstanding dislocation evolution during viscoplastic deformation is essential to accurately predict high-temperature superalloy behavior. While creep and monotonic deformation are well studied, the evolution of the dislocation substructures during stress relaxation, particularly following prior plastic straining, remains unclear. This study investigates a single crystal γ/γ' AD730TM superalloy deformed at 700 °C, focusing on dislocation evolution and redistribution. Transmission electron microscopy reveals that stacking faults formed during plastic straining progressively disappear during relaxation, suggesting thermally activated mechanisms such as dislocation re-association and recovery. After re-association, perfect dislocations spread into the matrix, forming a homogeneous dislocation network. These microstructural evolutions are believed to underlie the macroscopic stress relaxation behavior, which exhibits two regimes in the Norton diagram: an initial high-stress exponent regime linked to rapid dislocation rearrangement, followed by a low-stress exponent regime associated with broader dislocation activity
Balancing power output and efficiency in thermophotovoltaics through spectral shaping of selective emitters
No full textInternational audienceThermophotovoltaic (TPV) systems propose a promising method of converting heat into electricity, with the thermal emitter playing a pivotal role. However, optimizing its emission spectrum poses a significant challenge, with sub-bandgap losses and thermalization from high-energy photon absorption contributing to this complexity. Although the absorption of high-energy photons is beneficial for increasing the system’s power output by providing additional energy, it simultaneously diminishes the system’s efficiency. This study addresses these challenges by exploring the optimization of the emission spectrum of selective thermal emitters in TPV systems. Our objective is to reach a balance between maximizing electrical power output, which favors a broadband spectrum, and maximizing efficiency, which requires a narrowband spectrum. To achieve this, numerical optimization methods are coupled with the Shockley-Queisser limit to find an optimal compromise between these opposing criteria. Ultimately, this optimization endeavor aims to enhance the overall performance of TPV systems. Here, we present the results of calculations predicting the spectral shapes of ideal selective emitters for TPVsystems with emitter temperatures ranging from 300◦C to 2000◦C and photovoltaic cell bandgap energies from 0.17 eV to 1.1 eV. For a configuration with an emitter at 900◦C coupled to a 0.25 eV bandgap cell under the assumption of perfect coupling (view factor of 1), the ideal emission spectrum was found to have emissivity of unity between 0.25 eV and 0.62 eV and zero elsewhere. Accounting for this ideal emission spectrum, the results show an efficiency of 41.5% and an output power density of 2.59 W∕cm2
Transient thermo-elasto-hydrodynamic study of herringbone-grooved mechanical face seal during start-up stage
No full textInternational audienceA comprehensive numerical solution is developed for the transient thermo-elasto-hydrodynamic (TEHD) characteristics of mechanical face seals. Transient lubrication features of the fluid film, transient thermal deformation features of the seal rings, dynamic behavior, and rough faces contacting are coupled.The finite volume method is utilized for the fluid film solution, and the Duhamel's principle contributes to calculation of the time-varying solid properties. An overall flowchart for the numerical solution is established, with an approach of Parallel Dual Time Steps (PDTS approach) proposed and utilized for the explicit time solver. Both of the efficiency and accuracy of the PDTS approach are evaluated by comparing with the reference. An outer-herringbone-grooved face seal in a start-up stage is studied. The simultaneously existing physical effects of the face expansion and the seal ring movement are successfully simulated with the proposed method. Neglecting viscosity-temperature effect and convergent gap forming could underestimate the load-carrying capacity of the fluid film; smaller contacting force but larger maximum contacting pressure are found comparing with the THD and HD results; performance keeps varying at steady speed due to thermal lag effect. The proposed numerical solution could be impactful for mechanism analyzing of the undesirable running of mechanical face seals related to the transient TEHD effects.</p
Flame morphology boundaries and fundamental combustion properties in unobstructed channels
No full textWe investigated the effect of fundamental combustion properties (FCP) on the 3D morphology and dynamics of flames and shocks during acceleration and transition to detonation in unobstructed channels. To achieve this, an extensive experimental campaign was conducted using a two-directional schlieren setup. The effect of selected FCP was assessed by evaluating nine different mixtures of hydrogen, methane, and hydrogen/methane blends, using oxygen with and without dilution by nitrogen, helium, or argon. The experimental results revealed two characteristic flame evolution behaviors during flame acceleration (FA), depending on the mixtures: i) a symmetric flame inversion (tulip flame) during the early stages of FA, followed by a short, symmetric flame in the later stages, with the formation of a precursor wave located relatively far from the flame, and ii) an asymmetric, wrinkled flame during the early stages, which develops into a large flame with the tip inclined toward a corner of the channel, accompanied by the formation of multiple precursor waves ahead of the flame in the later stages of FA. For a more robust statistical analysis, a morphology database was compiled from literature sources reporting similar flame morphologies to those observed in our experiments. This database was analyzed using the Feature Elimination Technique in conjunction with the Logistic Regression Model, which enabled the identification of FCP boundaries between the observed flame morphologies. The analysis showed that the pairs of properties most influencing flame morphology are the expansion ratio and the ratio of the laminar flame speed to the sound speed in the combustion products, i.e., (σ, σs L /c b ), as well as the latter ratio with the heat capacity ratio, i.e., (σs L /c b , γ). Additionally, this methodology helped to identify experimental conditions where little or no data is available in the literature, such as for mixtures with Lewis numbers smaller than unity, which are expected to be affected by thermodiffusive instabilities. These boundaries can, therefore, serve as guidelines for selecting experimental conditions that develop specific flame and shock morphologies and dynamics
Towards the Quantification of the Interfacial Toughness Through Buckle Propagation in Controlled Thickness Gradient
No full textWe present a novel approach for evaluating interfacial toughness in thin film–substrate systems by analyzing the propagation of straight-sided buckles in films with a well-controlled thickness gradient. Experimentally, buckles initiate in thicker regions under compressive stress and arrest consistently as the thickness decreases, where the available elastic energy is no longer sufficient to drive further delamination. This arrest mechanism is reproduced through finite element simulations incorporating a cohesive zone model. Analysis of the mode-mixity angle indicates predominantly mode-I fracture at the buckle front and mode-II fracture at the lateral edges, promoting buckle propagation toward thinner regions of the gradient. Finally, we show that the film–substrate interfacial toughness can be quantified numerically by using the critical arrest thickness of the buckle as an energetic criterion