Balancing Biases and Preserving Privacy on Balanced Faces in the Wild

Demographic biases exist in current models used for facial recognition (FR). Our Balanced Faces in the Wild (BFW) dataset is a proxy to measure bias across ethnicity and gender subgroups, allowing one to characterize FR performances per subgroup. We show that results are non-optimal when a single score threshold determines whether sample pairs are genuine or imposters. Furthermore, within subgroups, performance often varies significantly from the global average. Thus, specific error rates only hold for populations matching the validation data. We mitigate the imbalanced performances using a novel domain adaptation learning scheme on the facial features extracted from state-of-the-art neural networks, boosting the average performance. The proposed method also preserves identity information while removing demographic knowledge. The removal of demographic knowledge prevents potential biases from being injected into decision-making and protects privacy since demographic information is no longer available. We explore the proposed method and show that subgroup classifiers can no longer learn from the features projected using our domain adaptation scheme. For source code and data, see https://github.com/visionjo/facerec-bias-bfw.Comment: arXiv admin note: text overlap with arXiv:2102.0894

On Universal Halos and the Radial Orbit Instability

The radial orbit instability drives dark matter halos toward a universal structure. This conclusion, first noted by Huss, Jain, and Steinmetz, is explored in detail through a series of numerical experiments involving the collapse of an isolated halo into the non-linear regime. The role played by the radial orbit instability in generating the density profile, shape, and orbit structure is carefully analyzed and, in all cases, the instability leads to universality independent of initial conditions. New insights into the underlying physics of the radial orbit instability are presented.Comment: 31 pages, 11 figures, submitted to the Astrophysical Journa

Elaboration of Ti3SiC2 deposits on glass by aerosol deposition method: influence of some parameters on microstructure and electrical properties

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Elaboration de matériaux poreux géopolymères à porosité multi-échelle et contrôlée

Ce travail est basé sur l élaboration, la caractérisation, et le contrôle de la porosité d un matériau poreux à matrice géopolymérique, synthétisé à partir du mélange de métakaolin, d une solution de silicate alcaline, d hydroxyde alcalin, et de fumée de silice comme agent porogène. Ce mélange donne lieu à une mousse avec production continue de dihydrogène in-situ au sein d un gel visqueux évolutif. Le contrôle de la porosité à cette valeur élevée de pH est régi par un équilibre entre des cinétiques de réactions de polycondensation (consolidation) et de production de gaz. L influence des différents paramètres est testée par la caractérisation du réseau poreux obtenu. La conductivité thermique d échantillons homogènes est mesurée par fluxmètre et par fil chaud. Ces valeurs sont discutées à partir de l analyse de la microstructure et des différents modèles analytiques issus de la littérature. Une démarche numérique inverse est utilisée pour retrouver la valeur de conductivité thermique du squelette solide s du matériau. En effet il est difficile d obtenir un matériau pseudo-dense pour une même composition. Un calcul par éléments finis, avec une méthode d homogénéisation, est appliqué sur des Volumes Elémentaires Représentatifs construits à partir des données expérimentales. La valeur de s est alors évaluée entre 0,98 et 1,12 W.m-1.K-1. Les mousses ont des taux de porosité compris entre 65 et 85% et des valeurs de conductivités thermiques comprises entre 0,12 et 0,35 W.m-1.K-1, ce qui en fait un matériau isolant.This work is focused on the preparation, the characterization, and the control of the porosity in geopolymer foams, synthesized from the mixing of metakaolin, a alkali silicate solution, alkali hydroxide, and silica fume as the pore forming agent. This mixture results in a foam in which hydrogen gas is produced continuously in an evolutive viscous gel. The control of porosity, in consideration of the very high value of pH, requires the establishment of an equilibrium between the kinetics of polycondensation reactions (hardening) and the kinetics of gassing. The influence of different parameters is studied through the characterization of the obtained porous network. The thermal conductivity of the homogeneous samples is measured with a fluxmeter and also with a hot wire method. The values obtained are then discussed in relation to the microstructure and relevant analytical models of the literature. An inverse numerical approach is used to find the thermal conductivity value of the skeleton of the foam s. In fact, it is difficult to prepare a material with a low pore volume fraction from the same composition. A finite element calculation, coupled with a homogenization method, is applied on Representative Volume Elements constructed in relation with the experimental data. The value of s is then calculated between 0.98 and 1.12 W.m-1.K-1. The foams have pore volume fractions values between 65 and 85% corresponding to thermal conductivity values between 0.12 and 0.35 W.m-1.K-1, yielding a good material for thermal insulation.LIMOGES-BU Sciences (870852109) / SudocSudocFranceF

Potassium geopolymer foams made with silica fume pore forming agent for thermal insulation

International audiencePorous potassium based geopolymers with a mutli-scale porosity were synthesized. Silica fume is introduced as an additive to the geopolymer formulation. The free silicon contained inside this silica fume is oxidized in alkaline solution, releasing molecular hydrogen which generates the porosity. Previous work has shown how the porosity can be controlled with temperature, repeated temperature cycles and the mass introduced. Using this protocol, homogeneous foams were made and then studied with scanning electron microscopy. In particular the foam expansion has been followed with time in relation to the microstructure. The thermal conductivity values of the foams were evaluated using a fluxmeter method. The effective thermal conductivities are comprised between 0.12 and 0.35 W m−1 K−1 for apparent densities ranging from 0.40 to 0.85 g cm−3. The corresponding calculated pore volume fractions are in the range of 65–85%. The interest of this material is that it combines the advantages of low bulk density and insulating properties with the characteristics of a geopolymer skeleton. Literature reports a very good fire and acid/base resistance, a low cost of production and the possibility of recycling industrial waste in the form of silica fume

Porosity control of cold consolidated geomaterial foam: Temperature effect

International audiencePorous K-geopolymers with mutli-scale porosity were synthetized, based on the production of molecular hydrogen due to the oxidation of free silicon associated with polycondensation reactions. The various drying steps at low temperatures influencing the foams morphology were evaluated in function of parameters like mass effect, mold dimensions and drying cycles. The results obtained evidenced the possibility to perform reproducible foams with a control of their porosity. These foams are in agreement with the environmental demand with their recycling properties and their low cost of production due to the cheap materials used and the low temperature of synthesis. Some other advantages like their fire resistance, acid/base resistance, their good mechanical properties and their good thermal conductivity is a good point for future applications. As an example a homogeneous foam with a pore size of 1.5 mm at 50 °C (9 days for an achieved drying but consolidated before) can be prepared. Moreover the porosity can be controlled with various temperature cycles decreasing the time of synthesis. From the cycles tested (70–55 °C and 70–23 °C), some homogeneous samples were obtained with pores sizes varying from 0.5 to 1.5 mm. Then the work was extended to larger surfaces exchange, what evidences the importance of drying and mass effects upon the porosity as well as the mechanical properties of the mold used during synthesis

Analytical and numerical identification of the skeleton thermal conductivity of a geopolymer foam using a multi-scale analysis

International audienceThis work focuses on the identification of the thermal conductivity of potassium geopolymer foams by experimental and numerical/analytical approaches. The porous foams, synthesized by a direct foaming process, display pore volume fractions ranging between 65% and 85% with thermal conductivities from 0.35 to 0.12 W m-1 K-1 respectively. A quantitative characterization of the pore volume fractions has been made by image analysis, taking into account the multi-scale aspect of these foams. Motivated by the character of the microstructure, an inverse multi-scale analytical method was applied to find the value of the thermal conductivity of the skeleton λs. In fact, due to the range of pore volume fractions, standard analytical relations describing thermal conductivity were found to be of limited use. In order to take into account the local aspects of the microstructure and to treat the actual pore volume fractions, an inverse numerical approach, based on a finite element calculation coupled with a homogenization method, was used. As a result, the multi-scale analytical approach evaluates the value of λs between 0.95 and 1.19 W m-1 K-1. Numerical results, taking faithfully into account local parameters of the pore network, give λs values within the range 1.09-1.12 W m-1 K-1. The numerical values of λs are in agreement with values obtained in the literature

Fabrication of dense and adherent ceramic coatings by powder deposition without sintering

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Elaboration of lead-free Na0.5Bi0.5TiO3–BaTiO3 (NBT-BT) thick films by aerosol deposition method (ADM)

International audienceThick and dense ceramic films of lead-free 0.94 Na 0.5 Bi 0.5 TiO 3 – 0.06 BaTiO 3 (NBT-BT) composition were elaborated by aerosol deposition method (ADM) at room temperature. A powder of suitable grain size was elaborated by solid state reaction. Using this powder, two samples were elaborated by ADM respectively on glass and metallic substrates, in order to check for microstructure and electrical properties. This process allowed obtaining a thick film (3.2 µm) with dense microstructure. Measurement of electrical properties revealed a lossy dielectric behavior indicating interfacial phenomena at the electrode – film interface. The measurement of the ferroelectric hysteresis cycle does not show any characteristics of a ferroelectric behavior, but corresponds well to the one of a lossy non-linear dielectric. The absence of ferroelectricity is probably due to the low grain size of the obtained thick film (130 nm). Further experiments are in progress in order to try to obtain ferroelectric properties