École Centrale de Lyon

A study of the energetics of solids leads to the conclusion that the equation of state for all classes of solids in compression can be expressed in terms of a universal function. The form of this universal function is determined by sealing experimental compression data for measured isotherms of a wide variety of solids. The equation of state is thus known (in the absence of phase transitions), if zero-pressure volume and isothermal compression and its pressure derivative are known. The discovery described by the authors has two immediate consequences: first, despite the well known differences in the microscopic energetics of the various classes of solids, there is a single equation of state for all classes in compression; and second, a new method is provided for analysing measured isotherms and extrapolating high-pressure data from low-pressure (e.g. acoustic) data.

Space-time correlation measurements in the roughly isotropic turbulence behind a regular grid spanning a uniform airstream give the simplest Eulerian time correlation if we choose for the upstream probe signal a time delay which just ‘cancels’ the mean flow displacement. The correlation coefficient of turbulent velocities passed through matched narrow-band niters shows a strong dependence on nominal filter frequency (∼ wave-number at these small turbulence levels). With plausible scaling of the time separations, a scaling dependent on both wave-number and time, it is possible to effect a good collapse of the correlation functions corresponding to wave-numbers from 0·5 cm −1 , the location of the peak in the three-dimensional spectrum, to 10 cm −1 , about half the Kolmogorov wave-number. The spectrally local time-scaling factor is a ‘parallel’ combination of the times characterizing (i) gross strain distortion by larger eddies, (ii) wrinkling distortion by smaller eddies, (iii) convection by larger eddies and (iv) gross rotation by larger eddies.

Particle image velocimetry (PIV) measurements are made in a highly turbulent swirling flow. In this flow, we observe a coexistence of turbulent fluctuations and an unsteady swirling motion. The proper orthogonal decomposition (POD) is used to separate these two contributions to the total energy. POD is combined with two new vortex identification functions, Γ1 and Γ2. These functions identify the locations of the centre and boundary of the vortex on the basis of the velocity field. The POD computed for the measured velocity fields shows that two spatial modes are responsible for most of the fluctuations observed in the vicinity of the location of the mean vortex centre. These two modes are also responsible for the large-scale coherence of the fluctuations. The POD computed from the Γ2 scalar field shows that the displacement and deformation of the large-scale vortex are correlated to these modes. We suggest the use of such a method to separate pseudo-fluctuations due to the unsteady nature of the large-scale vortices from fluctuations due to small-scale turbulence.

Local binary pattern (LBP) is a nonparametric descriptor, which efficiently summarizes the local structures of images. In recent years, it has aroused increasing interest in many areas of image processing and computer vision and has shown its effectiveness in a number of applications, in particular for facial image analysis, including tasks as diverse as face detection, face recognition, facial expression analysis, and demographic classification. This paper presents a comprehensive survey of LBP methodology, including several more recent variations. As a typical application of the LBP approach, LBP-based facial image analysis is extensively reviewed, while its successful extensions, which deal with various tasks of facial image analysis, are also highlighted.

Knowledge about the human skin mechanical properties is essential in several domains, particularly for dermatology, cosmetic or to detect some cutaneous pathology. This study proposes a new method to determine the human skin mechanical properties in vivo using the indentation test. Usually, the skin mechanical parameters obtained with this method are influenced by the mechanical properties of the subcutaneous layers, like muscles. In this study, different mechanical models were used to evaluate the effect of the subcutaneous layers on the measurements and to extract the skin elastic properties from the global mechanical response. The obtained results demonstrate that it is necessary to take into account the effect of the subcutaneous layers to correctly estimate the skin Young's modulus. Moreover, the results illustrate that the variation of the measured Young's modulus at low penetration depth cannot be correctly described with usual one-layer mechanical models. Thus a two-layer elastic model was proposed, which highly improved the measurement of the skin mechanical properties.

In order to establish a sagittal plane curve reference table for standing subjects examined laterally, we determined an easily reproducible standard posture. A sample of 100 healthy subjects from 20 to 29 years of age, was chosen (43 women, 57 men). The reciprocal angulations of each vertebral body in relation to the others were fed into a digitalizer and studied by computer. The study particularly concerns maximum kyphosis, maximum lordosis, sacral base slopes, and the tilt of intermediate vertebral bodies. The dispersion of the results is remarkably wide and, within the extreme values, the distribution is irregular. Individual correlations of these values are often dispersed, but spinal morphotypology. For considerable lengths, average values cannot be used as norms, given the wide span of values. Only the extreme limits are useful for the appreciation of curves as excessive, insufficient, or inverted.

We have studied the atomistic origins of the ultralow friction coefficient of a molybdenum disulphide (${\mathrm{MoS}}_{2}$) coating in ultrahigh vacuum conditions. A friction coefficient in the ${10}^{\mathrm{\ensuremath{-}}3}$ range is associated with friction-induced orientation of ``easy shear'' basal planes of the ${\mathrm{MoS}}_{2}$ crystal structure parallel to the sliding direction. In addition to this basal plane orientation, an orientation disorder around the c axis is observed, indicating that frictional anisotropy during intercrystallite slip could be at the origin of the vanishing of the friction force. Experimental HRTEM lattice fringe imaging of ${\mathrm{MoS}}_{2}$ wear particles clearly show the existence of characteristic Moir\'e patterns. We have simulated TEM lattice fringe images of a [0001] ${\mathrm{MoS}}_{2}$ crystal and produced rotational Moir\'e patterns by superimposing two such images. A qualitative agreement between experimental and simulated Moir\'e patterns is demonstrated, which gives credence that ultralow friction of ${\mathrm{MoS}}_{2}$ in high vacuum can be attributed to a superlubric situation, by frictional anisotropy of sulphur-rich basal planes during intercrystallite slip.

Various titania samples of industrial origin (Degussa and Tioxide) have been characterized by electrical photoconductance measurements and tested as photocatalysts in various liquid media (either pure organic liquids or aqueous solutions) as a function of their structure (anatase versus rutile). Anatase was constantly found more active than rutile, whatever the reaction chosen (mild oxidation of pure cyclohexane and 2-propanol; total degradation of phenol and nitrophenol isomers in water). In identical conditions, Degussa was found more active, but the intrinsic activity, expressed in moles converted per hour and per square meter of active surface, was found slightly higher for anatase Tioxide. The higher activity of anatase with respect to that of rutile could be explained by the interpretation of the photoconductance measurements, which evidence the higher aptitude of anatase (i) to photoadsorb oxygen, in O2- and O- forms; (ii) to photodesorb it; and (iii) to have a lower relative electron−hole recombination rate. The origin of the differences in the photocatalytic behavior of titania leading to mild oxidation in pure liquid organic phase and total oxidative degradation in aqueous medium is also analyzed.

Interest in multimodal optimization function is expanding rapidly since real-world optimization problems often require the location of multiple optima in the search space. In this context, fitness sharing has been used widely to maintain population diversity and permit the investigation of manly peaks in the feasible domain. This paper reviews various strategies of sharing and proposes new recombination schemes to improve its efficiency. Some empirical results are presented for high and a limited number of fitness function evaluations. Finally, the study compares the sharing method with other niching techniques.

The paper describes studies of the turbulence of the liquid in a bubbly, grid-generated turbulent flow field. Laser-Doppler and hot-film anemometry are used for the experimental investigation. It is found that the turbulent kinetic energy increases strongly with the void fraction α. Roughly speaking, there exist two distinct regimes: the first one corresponds to low value of α, where hydrodynamic interactions between bubbles are negligible, and the second one to higher values, for which, owing to their mutual interactions, the bubbles transfer a greater amount of kinetic energy to the liquid. The Reynolds stress tensor shows that the quasi-isotropy is not altered. At low enough values of α, the difference between the turbulent kinetic energy in the liquid phase and the energy associated with the grid-generated turbulence proves to be approximately equal to the intensity of the pseudo-turbulence, defined as the fluctuating energy that would be induced by the motion of the bubbles under non-turbulent conditions. The one-dimensional spectra exhibit a large range of high frequencies associated with the wakes of the bubbles and the classical $-\frac{5}{3}$ power law is progressively replaced by a $-\frac{8}{3}$ dependence.

This review summarizes recent advances in the area of tribology based on the outcome of a Lorentz Center workshop surveying various physical, chemical and mechanical phenomena across scales. Among the main themes discussed were those of rough surface representations, the breakdown of continuum theories at the nano- and microscales, as well as multiscale and multiphysics aspects for analytical and computational models relevant to applications spanning a variety of sectors, from automotive to biotribology and nanotechnology. Significant effort is still required to account for complementary nonlinear effects of plasticity, adhesion, friction, wear, lubrication and surface chemistry in tribological models. For each topic, we propose some research directions.

By 2050, about one third of the French population will be over 65. Our laboratory's current research focuses on the monitoring of elderly people at home, to detect a loss of autonomy as early as possible. Our aim is to quantify criteria such as the international activities of daily living (ADL) or the French Autonomie Gerontologie Groupes Iso-Ressources (AGGIR) scales, by automatically classifying the different ADL performed by the subject during the day. A Health Smart Home is used for this. Our Health Smart Home includes, in a real flat, infrared presence sensors (location), door contacts (to control the use of some facilities), temperature and hygrometry sensor in the bathroom, and microphones (sound classification and speech recognition). A wearable kinematic sensor also informs postural transitions (using pattern recognition) and walk periods (frequency analysis). This data collected from the various sensors are then used to classify each temporal frame into one of the ADL that was previously acquired (seven activities: hygiene, toilet use, eating, resting, sleeping, communication, and dressing/undressing). This is done using support vector machines. We performed a 1-h experimentation with 13 young and healthy subjects to determine the models of the different activities, and then we tested the classification algorithm (cross validation) with real data.

Environmental pollution is escalating due to rapid global development that often prioritizes human needs over planetary health. Despite global efforts to mitigate legacy pollutants, the continuous introduction of new substances remains a major threat to both people and the planet. In response, global initiatives are focusing on risk assessment and regulation of emerging contaminants, as demonstrated by the ongoing efforts to establish the UN's Intergovernmental Science-Policy Panel on Chemicals, Waste, and Pollution Prevention. This review identifies the sources and impacts of emerging contaminants on planetary health, emphasizing the importance of adopting a One Health approach. Strategies for monitoring and addressing these pollutants are discussed, underscoring the need for robust and socially equitable environmental policies at both regional and international levels. Urgent actions are needed to transition toward sustainable pollution management practices to safeguard our planet for future generations.

Abstract Oxidation of ammonia to nitrite by bacteria and archaea is responsible for global emissions of nitrous oxide directly and indirectly through provision of nitrite and, after further oxidation, nitrate to denitrifiers. Their contributions to increasing N 2 O emissions are greatest in terrestrial environments, due to the dramatic and continuing increases in use of ammonia‐based fertilizers, which have been driven by requirement for increased food production, but which also provide a source of energy for ammonia oxidizers (AO), leading to an imbalance in the terrestrial nitrogen cycle. Direct N 2 O production by AO results from several metabolic processes, sometimes combined with abiotic reactions. Physiological characteristics, including mechanisms for N 2 O production, vary within and between ammonia‐oxidizing archaea (AOA) and bacteria (AOB) and comammox bacteria and N 2 O yield of AOB is higher than in the other two groups. There is also strong evidence for niche differentiation between AOA and AOB with respect to environmental conditions in natural and engineered environments. In particular, AOA are favored by low soil pH and AOA and AOB are, respectively, favored by low rates of ammonium supply, equivalent to application of slow‐release fertilizer, or high rates of supply, equivalent to addition of high concentrations of inorganic ammonium or urea. These differences between AOA and AOB provide the potential for better fertilization strategies that could both increase fertilizer use efficiency and reduce N 2 O emissions from agricultural soils. This article reviews research on the biochemistry, physiology and ecology of AO and discusses the consequences for AO communities subjected to different agricultural practices and the ways in which this knowledge, coupled with improved methods for characterizing communities, might lead to improved fertilizer use efficiency and mitigation of N 2 O emissions.

This review concerns recent progress in primary atomization modeling. The numerical approaches based on direct simulation are described first. Although direct numerical simulation (DNS) offers the potential to study the physical processes during primary atomization in detail, thereby supplementing experimental diagnostics, it also introduces severe numerical challenges. We outline these challenges and the numerical methods to address them, highlighting some recent efforts in performing detailed simulation of the primary atomization process. The second part is devoted to phenomenological models of primary atomization. Because earlier conventional models of breakup are well reported in the available literature, we highlight only two recent developments: (a) stochastic simulation of the liquid jet depletion in the framework of fragmentation under scaling symmetry and (b) primary atomization in terms of Reynolds-averaged Navier-Stokes (RANS) mixing with a strong variation of density.

Studies of Vickers hardness of magnesium oxide are presented in the literature for three purposes. They give information about relations between hardness and brittleness, (plasticity and toughness behavior); they show the anisotropical effect of the structure of the material and they are a tool to study the chemomechanical effects (Rebinder effects). Generally, the Vickers hardness is evaluated by measurements of the diagonals of residual indentation. Equipment was built which gives a record of the applied depression depth (h) as a function of the carried load P (in the range 10−1 N to 10+1 N). Investigation of the curves P(h) during loading and unloading and microscopical observations of residual indentation show that phenomena are complex. The contact is elastoplastic. The roles played by the plasticity and elasticity are discussed. The physical meaning of Vickers hardness, determined by use of residual indentation measurements, is analyzed.

This book summarizes the most recent theoretical, computational and experimental results dealing with homogeneous turbulence dynamics. A large class of flows is covered: flows governed by anisotropic production mechanisms (e.g. shear flows) and flows without production but dominated by waves (e.g. homogeneous rotating or stratified turbulence). Compressible turbulent flows are also considered. In each case, main trends are illustrated using computational and experimental results, while both linear and nonlinear theories and closures are discussed. Details about linear theories (e.g. Rapid Distortion Theory and variants) and nonlinear closures (e.g. EDQNM) are provided in dedicated chapters, following a fully unified approach. The emphasis is on homogeneous flows, including several interactions (rotation, stratification, shear, shock waves, acoustic waves, and more) which are pertinent to many application fields – from aerospace engineering to astrophysics and earth sciences.

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Abstract High and low rates of ammonium supply are believed to favour ammonia-oxidising bacteria (AOB) and archaea (AOA), respectively. Although their contrasting affinities for ammonium are suggested to account for these differences, the influence of ammonia concentration on AOA and AOB has not been tested under environmental conditions. In addition, while both AOB and AOA contribute to nitrous oxide (N2O) emissions from soil, N2O yields (N2O–N produced per NO2 −–N generated from ammonia oxidation) of AOA are lower, suggesting lower emissions when AOA dominate ammonia oxidation. This study tested the hypothesis that ammonium supplied continuously at low rates is preferentially oxidised by AOA, with lower N2O yield than expected for AOB-dominated processes. Soil microcosms were supplied with water, urea or a slow release, urea-based fertiliser and 1-octyne (inhibiting only AOB) was applied to distinguish AOA and AOB activity and associated N2O production. Low ammonium supply, from mineralisation of organic matter, or of the fertiliser, led to growth, ammonia oxidation and N2O production by AOA only, with low N2O yield. High ammonium supply, from free urea within the fertiliser or after urea addition, led to growth of both groups, but AOB-dominated ammonia oxidation was associated with twofold greater N2O yield than that dominated by AOA. This study therefore demonstrates growth of both AOA and AOB at high ammonium concentration, confirms AOA dominance during low ammonium supply and suggests that slow release or organic fertilisers potentially mitigate N2O emissions through differences in niche specialisation and N2O production mechanisms in AOA and AOB.

This paper presents a comparative study of three predictive current control schemes for permanent-magnet synchronous machine (PMSM) drives. The first control scheme predicts the future evolution of the currents for each possible configuration of the inverter legs. Then, the switching state which minimizes a given cost function is selected and applied during the next sampling time. The second control scheme uses a modulator to apply two configurations of the inverter legs during a computation period. Among these configurations, one leads to null voltages. The duration of the other configuration is calculated in order to minimize the distance between the obtained state vector and the desired one. The third control scheme uses a model of the PMSM in order to predict the stator voltages which allows us to reach the desired currents after one modulation period. An algebraic method is presented to compute the duty cycle of each leg of the inverter in a direct manner. These control schemes are detailed and tested using the same switching frequency on the same test bench (1.6-kW PMSM drive). A simulation study is performed in order to compare sensitivity to parameters of each control scheme. Experiments confirm the simulation results.