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MITIGATION OF NON-SYNCHRONOUS VIBRATION WITH GEOMETRIC MISTUNING: EXPERIMENTAL INVESTIGATION OF LEADING-EDGE MODIFICATION ON THE OPEN TEST CASE ECL5
No full textThe mitigation of Non-Synchronous Vibration (NSV) is essential to extend the operational range of fans and compressors in aircraft engines. Near the stability limit at part-speed conditions, increased tip blockage enables circumferential convection of aerodynamic disturbances, leading to coupled blade vibrations known as lock-in. Previous studies have shown that local variations in blade geometry influence the propagation of these disturbances. In particular, asymmetric tip clearance affects their speed and intensity, potentially altering the dominant flow wave numbers and the corresponding structural nodal diameters involved in lock-in.In earlier work, non-uniform tip clearance was found to significantly influence disturbance formation, though it did not provide sufficient NSV suppression. To enhance the local aerodynamic effect, this study investigates geometric modifications of the blade leading edge.A numerical investigation using unsteady RANS simulations is conducted on the open test case geometry ECL5 to assess the influence of leading-edge modifications on disturbance propagation. The study also examines variations in the mistuning pattern, defined by the circumferential distribution of cut blades. Selected geometrically mistuned configurations were experimentally tested at Centrale Lyon. This paper presents both numerical and experimental results, providing a detailed characterization of the effects of geometric modifications on local aerodynamics and fluid-structure interactions relevant to NSV behavior
Wet Chemical Etching of GaAs Nanowires for Quantum Confinement
No full textInternational audienceThe quantum confinement in III−V semiconductors displays important applications such as lasers or single-photon sources. III−V nanowires (NWs) are ideal candidates for the integration of direct bandgap material on silicon. However, to reach quantum confinement, small diameters are needed. In this work, we perform wet chemical etching of NWs to reduce their diameter. In contrast to plasma irradiation and hightemperature techniques, this approach is more energy-efficient and causes less physical damage. With accurate control of the etching rate in an acidic solution, we obtained NW diameters as small as 20 nm. A 60 nm-thick AlGaAs shell was regrown on the NWs after the etching, and STEM images showed a fully crystalline interface of the core and the shell. Finally, photoluminescence measurements reveal a blueshift of ∼20 meV due to reduced diameters. This study demonstrates the potential of a top-down approach via wet chemical etching to tune the III−V NW morphology
Planar pulsating traveling wave solutions of non-cooperative Fisher--KPP systems in space-time periodic media
No full textInternational audienceNon-cooperative Fisher-KPP systems with space-time periodic coefficients are motivated for instance by models for structured populations evolving in periodic environments. This paper is concerned with entire solutions describing the invasion of open space by a persistent population at constant speed. These solutions are important in the understanding of long-time behaviors for the Cauchy problem. Adapting methods developed for scalar equations satisfying the comparison principle as well as methods developed for systems with homogeneous coefficients, we prove, in each spatial direction, the existence of a critical speed such that: there exists no almost planar generalized transition waves with a smaller speed; if the direction is rational, each rational speed not smaller than the critical speed is the speed of a planar pulsating traveling wave with time and transverse space periodicity; if the coefficients are homogeneous in space, each speed not smaller than the critical speed is the speed of a planar pulsating traveling wave with time periodicity
A Hilbert--Mumford criterion for generalised Monge--Ampère equations
No full textWe give a new numerical criterion in the spirit of GIT for existence of solutions to inverse Hessian equations, including in particular the J-equation. Our criterion is formulated in terms of stability of pairs in the sense of Paul. To that end, we build on previous work of the author with Dervan, and generalise a result of Zhang, proving isometry between generalised Chow line bundles and mixed Deligne pairings
Locally -categorical theories and locally Roelcke precompact groups
No full textInternational audienceIt is well-known that Polish Roelcke precompact groups are the groups that can be represented as automorphism groups of -categorical structures in continuous logic and that there is a precise correspondence between properties of the group and properties of the structure. The goal of this paper is to extend this correspondence to the classes of locally Roelcke precompact groups and locally -categorical structures, the latter of which we define here. We characterise locally Roelcke precompact groups in terms of their isometric actions. We define locally -categorical theories and structures, prove an appropriate version of the Ryll-Nardzewski theorem, and identify the Polish locally Roelcke precompact groups as the automorphism groups of such structures. In all locally -categorical structures, there is a definable metric, which we call localising, and which captures the coarse geometric structure of the corresponding automorphism group. We show that two locally -categorical structures are bi-interpretable if and only if their automorphism groups are isomorphic. Finally, we show that (the unit ball of) a Banach space is -categorical if and only if the corresponding affine space is locally -categorical (as a metric space)
Optical sensor characterization for rapid detection of nitrogen phosphorus and potassium concentrations in soil
No full textInternational audienceAccurate and timely monitoring of soil nutrient concentrations, particularlynitrogen (N), phosphorus (P), and potassium (K), is crucial for optimizing agriculturalproductivity and minimizing environmental impact. In this study, we present thecharacterization of an optical sensor designed for the rapid and non-destructiveassessment of N, P, and K levels in soil samples. The sensor employs Visible-NearInfrared (VIS–NIR) spectroscopy to analyse the spectral signatures of soil samplesand extract quantitative information regarding nutrient concentrations. A total of30 experimental samples classified into six distinct categories, comprising varioussoil-fertilizer mixtures, were prepared to calibrate the sensor's performance. Thesesamples were made from four primary constituents: black soil (sourced from a farmin the Auvergne-Rhone-Alpes region of France), NPK (6:3:12) fertilizer, ammoniumnitrate, and urea. The six categories were grouped into two sets: sample type 1consisted of pure samples, while sample types 2 through 6 were mixtures of soiland fertilizer. The mixed samples were prepared with nutrient concentrations higherthan those typically found in agricultural soils to enable controlled calibration ofsensor performance. The pure sample, specifically Sample10, consisting of humussoil without fertilizer amendment, was included as a reference to approximatereal-soil conditions. Laboratory experiments involved illuminating the sampleswith specific wavelengths of light and measuring the intensity of reflected lightwithin a controlled environment. Calibration curves and equations specific to eachmacronutrient were developed through regression analysis using data collected fromthe experiments. Performance evaluation metrics, including Root Mean Square Error(RMSE), Coefficient of Determination (R2), Predicted Residual Error Sum of Squares(PRESS), and Standard Error (s), were employed to assess model accuracy. Resultsdemonstrated satisfactory performance across all sample types, with average R2,RMSE, PRESS, and s values of 0.7835 V, 0.0097 V, 0.0003 V, and 0.0003 V, respectively.Statistical analyses further validated the sensor, indicating average standard errorsof 0.003 V for repeatability and 0.001 V for reproducibility, along with a sensitivity of7% and a linearity of R2 = 0.8. These findings validate the effectiveness of the opticalsensor in accurately quantifying soil macronutrient concentrations
Measuring mechanical fields in tribology: physical quantities, methods, and insights
No full textContact interfaces are inherently heterogeneous across various length scales. Capturing the interface behaviour therefore requires not only macroscopic force and displacement measurements, but also local measurements along the interface. Such a refined view of the interface offers a unique opportunity to identify the elementary mechanisms that take place along the contact. It also provides highly constraining data to validate or falsify models. In this Chapter, we give an overview of the interface-related mechanical quantities whose spatial distribution can be experimentally measured. For each quantity, we describe the principal measurement techniques, illustrate their applications through examples and highlight some of the tribological insights that were obtained thanks to those local measurements. The accessible quantities include contact area, slip, gap, forces/stresses, stiffness and strains. We distinguish direct interfacial measurements and bulk measurements, based on methods spanning direct imaging, molecular probes, particle tracking velocimetry, digital image correlation, fluorescent liquids, interferences, Raman spectroscopy, ultrasound, X-ray computed tomography, photoelasticimetry and various local sensors. This overview aims to serve as a guide for selecting the appropriate techniques and interpreting local measurements in tribological contacts.</div
Conjecture de Kakeya et algèbres de von Neumann de réseaux de rang supérieur
No full textIf the non-commutative L p space of SLn(Z) has the completely bounded approximation property for some non-trivial value of p, then some form of the Kakeya conjecture holds in dimension d, for all d ≤ n+12 . The proof relies on a spherical analogue of the following question in Euclidean harmonic analysis, that we raise and investigate: does a radially symmetric Fourier multiplier that is bounded on Lp(R d ) for some p ̸ = 2 necessarily have a continuous symbol? We leave the question open, but we prove that the primitive of such function is smooth in the sense of Zygmund, give some necessary conditions for Lp-boundedness in terms of Besov spaces and Littlewood-Paley decomposition for the symbol, and observe that a negative answer implies some form of the Kakeya conjecture in dimension d. We then provide spherical forms of these results, which, when combined with a refinement of Lafforgue's rank 0 reduction, leads to the claimed result.</div
Numerical modeling of dust particle motion in a corona discharge-based ionic wind cleaning system for solar panels
No full textInternational audienceThis study explores innovative solutions to reduce efficiency losses in solar panels caused by dust accumulation, using corona discharge as a mitigation method. Ions produced by the positive or negative corona discharge transfer momentum to neutral air molecules through collisions, resulting in an airflow (ionic wind) that can help to eliminate dust accumulation. The cleaning system whose operation is numerically modeled consists of a corona blower device that moves along the panel, conveying the dust in a linear direction and providing a non-contact cleaning method. Dust particles are affected by different forces, such as Coulomb force, gravitational force, aerodynamic drag force, and van der Waals adhesion. Poisson's equation, the continuity equation for charged particles and the Navier-Stokes equations are solved to evaluate the Coulomb and drag force. Emphasis is placed on understanding how forces affect particle trajectories, and which forces are most relevant to the operation of the cleaning system