Fourier-based schemes with modified Green operator for computing the electrical response of heterogeneous media with accurate local fields

A modified Green operator is proposed as an improvement of Fourier-based numerical schemes commonly used for computing the electrical or thermal response of heterogeneous media. Contrary to other methods, the number of iterations necessary to achieve convergence tends to a finite value when the contrast of properties between the phases becomes infinite. Furthermore, it is shown that the method produces much more accurate local fields inside highly-conducting and quasi-insulating phases, as well as in the vicinity of the phases interfaces. These good properties stem from the discretization of Green's function, which is consistent with the pixel grid while retaining the local nature of the operator that acts on the polarization field. Finally, a fast implementation of the "direct scheme" of Moulinec et al. (1994) that allows for parcimonious memory use is proposed.Comment: v2: `postprint' document (a few remaining typos in the published version herein corrected in red; results unchanged

Analyse morphologique et modélisation pour l'optimisation structurelle d'électrodes

This work, which combines image analysis, Fourier methods and morphological models, focuses on the prediction and optimization of the transport properties of fuel cell materials in the classical framework of the homogenization of random media. The materials under study are critical layers found in fuel cells.These devices produce clean electrical energy (and water) from chemical fuel oxidation.The materials studied here are novel types of fuel cells that combine several preexisting architectures. Their performance is determined by the ionic and electronic conductivity, on the one hand, and by permeability and specific surfaces exchange between the solid and porous phases. For materials with highly-contrasted properties (pores and solid, isolating and conducting media), the effective properties strongly depend on the spatial arrangement (morphology) of the various phases.Fuel cell layers are first described and modeled using 2D scanning electron microscopy images and image analysis.Microstructures are characterized by morphological descriptors and realistic random 3D media, based on Boolean and Gaussian fields, are developed to represent the materials. The latter are parametrized by simple geometrical characteristics including volume fractions and covariances.They are visually and quantitatively validated using morphological data.Second, the transport properties are predicted numerically using Fourier methods. In conductivity, a modified algorithm is proposed to suppress the Gibbs artifacts. For permeability, the scheme of Wiegman (2007) is used.The permeability of ideal Boolean models is computed and compared with various analytical estimates.The Berryman-Milton bound, previously known for the Boolean model of spheres, is computed for a Boolean model of flat cylinders, using an analytical expression for cylinder covariogramm. The ionic and electronic conductivity of anode layers, and their permeability are predicted using previously developed models. The permeability, which strongly depends on the morphology, is computed for various values of the models' parameters, including the specific surface area between solid and phases.Several virtual materials with improved properties are proposed.Ce travail, qui associe analyse d'image, modélisation morphologique et calculs par transformées de Fourier, s'inscrit dans la thématique classique de l'homogénéisation de milieux hétérogènes, et dans le cadre notoirement problématique de l'optimisation multifonctionnelle de matériaux multiphasiques. Les matériaux qui font l'objet de cette thèse, collecteur de courant et anode, sont des éléments critiques des piles à combustibles (PAC). Ce dispositif convertit une énergie chimique en électricité grâce à l'oxydation d'un combustible, et ne rejette que de l'eau. Les PAC développées dans le cadre du projet européen Evolve sont d'un type nouveau, combinant des architectures préexistantes. Leur performance est déterminée par la conductivité ionique et électronique d'une part, par la perméabilité et les surfaces d'échange entre phases solides et pores d'autre part. Dans le cas d'un contraste de propriétés infini entre les phases (pores et solide, milieux isolant et conducteur), les propriétés effectives dépendent fortement de la répartition spatiale (morphologie) des phases en présence. On s'intéresse, dans un premier temps, à la segmentation, à la description et à la modélisation 3D de couches de piles à combustible, à partir d'images 2D acquises en microscopie électronique à balayage. Les microstructures sont segmentées puis caractérisées par des descripteurs morphologiques. On développe des modèles de milieux aléatoires 3D multiphasiques représentatifs des milieux réels. Ceux-ci reposent sur des modèles Booléens et de Gaussiennes seuillées et sont paramétrés par des caractéristiques géométriques simples du matériau (fractions volumiques, covariances, échelles caractéristiques). Ils sont validés visuellement et quantitativement, à l'aide de données morphologiques. Dans un second temps, on s'intéresse à la prédiction des propriétés de transport, à l'aide d'outils numériques par transformées de Fourier. Un algorithme amélioré, qui s'affranchit de l'effet de Gibbs est proposé en conductivité et la méthode de Wiegman (2007) est utilisée en perméabilité. La perméabilité de milieux booléens idéaux est calculée puis comparée à divers estimateurs analytiques. La borne de Berryman-Milton, connue précédemment dans le cadre du milieu Booléen de sphères, est calculée analytiquement pour un milieu Booléen de cylindres à l'aide d'une formule exacte pour le covariogramme de cylindres. Les propriétés de conductivité ionique et électronique de l'anode, et sa perméabilité, sont ensuite prédites à l'aide des modèles de milieux aléatoires précédemment développés et validés. La perméabilité, particulièrement sensible à la morphologie, est calculée pour divers paramètres du modèle, dont les surfaces spécifiques entre phases solides et pores. Plusieurs matériaux virtuels aux propriétés améliorées sont proposés

Morphological modeling of three-phase microstructures of anode layers using SEM images

International audienceA general method is proposed to model 3D microstructures representative of three-phase anode layers used in fuel cells. The models are based on SEM images of cells with varying morphologies. The materials are first characterized using three morphological measurements: (cross-)covariances, granulometry and linear erosion. They are measured on segmented SEM images, for each of the three phases. Second, a generic model for three-phase materials is proposed. The model is based on two independent underlying random sets which are otherwise arbitrary. The validity of this model is verified using the cross-covariance functions of the various phases. In a third step, several types of Boolean random sets and plurigaussian models are considered for the unknown underlying random sets. Overall, good agreement is found between the SEM images and three-phase models based on plurigaussian random sets, for all morphological measurements considered in the present work: covariances, granulometry and linear erosion. The spatial distribution and shapes of the phases produced by the plurigaussian model are visually very close to the real material. Furthermore, the proposed models require no numerical optimization and are straightforward to generate using the covariance functions measured on the SEM images

Stokes flow through a Boolean model of spheres: Representative volume element

International audienceThe Stokes flow is numerically computed in porous media based on 3D Boolean random sets of spheres. Two configurations are investigated in which the fluid flows inside the spheres or in the complementary set of the spheres. Full-field computations are carried out using the Fourier method of Wiegmann (2007). The latter is applied to large system sizes representative of the microstructure. The overall permeability of the two models as well as the representative volume element are estimated as a function of the pore volume fraction. We give numerical estimates for the asymptotic behavior of the permeability in the dilute limit for the solid phase, and close to the percolation threshold of the pores. FFT maps of the velocity field are presented, for increasing values of the pore volume fraction. The patterns of the local velocity field is analyzed using various morphological criteria. The tortuosity of the streamlines is found to be much higher than the geometrical tortuosity, for both models. The histograms of the velocity field are computed at increasing pore volume fraction. The covariance of orientation is used to characterize the spatial correlation of the velocity field

Structural and Morphological Study of PbS:ZnO Nanowires Films Deposited Using Thermal Evaporation Method

We obtained ZnO Nanowires films deposited on two types of substrate (Si (100) and glass) with 12 wt % PbS as dopant by simple thermal evaporation technique. High Resolution Transmission Electron Microscopy (HRTEM) and Energy-dispersive X-ray spectroscopy(EDX) images have confirmed the formation of ZnO Nanowires (NWs). EDX technique was used to investigate the elements content (standard analysis and mapping modes). Morphology and thickness of the films were investigated from surface and cross section of the films via Scanning Electron Microscopy (SEM) images. The Raman, photoluminescence (PL) and X-ray Diffraction (XRD) have confirmed the hexagonal phase structure of the ZnO Nanowires, which appeared to be very fine and their diameters were less than 40 nm and their lengths were of several micrometers using SEM and HRTEM. The effect of PbS as dopant on the growth of ZnO Nanowires as well as on the morphology for two substrates was investigated and compared. These Nanowires films could be applied in several fields. Mapping -EDX has confirmed the stoichiometry of prepared films. Finally, the structure (phase) was verified by different characterization techniques. The optoelectronic application of Nanostructures film will be study later

The Accuracy Of The Annual Financial Report Data: An Empirical Analysis Of GCC Firms

Company’s might try to enhance the picture of their income numbers (looks better than it should be) in the eyes of the reader of their annual financial reports.  These information could be used by investors and accounting researchers who their decisions depend on the information provided in financial reports.  When companies engage in income enhancement, investment decisions may be adversely affected.  The objective of this paper is to examine income numbers in a sample of the Gulf Cooperation Council (GCC) firms (UAE, Qatar, Oman, Saudi Arabia, Kuwait and, Bahrain) to determine if the frequency of the second digits conforms to the expected distribution.  The results indicate that the null hypothesis could be rejected, suggesting the annual financial data may not be as accurate as expected.  In other words, income enhancement at the second digit exists. We also discussed accounting standards that have been used by these companies.     &nbsp

Impact of opioid-free analgesia on pain severity and patient satisfaction after discharge from surgery: multispecialty, prospective cohort study in 25 countries

Background: Balancing opioid stewardship and the need for adequate analgesia following discharge after surgery is challenging. This study aimed to compare the outcomes for patients discharged with opioid versus opioid-free analgesia after common surgical procedures.Methods: This international, multicentre, prospective cohort study collected data from patients undergoing common acute and elective general surgical, urological, gynaecological, and orthopaedic procedures. The primary outcomes were patient-reported time in severe pain measured on a numerical analogue scale from 0 to 100% and patient-reported satisfaction with pain relief during the first week following discharge. Data were collected by in-hospital chart review and patient telephone interview 1 week after discharge.Results: The study recruited 4273 patients from 144 centres in 25 countries; 1311 patients (30.7%) were prescribed opioid analgesia at discharge. Patients reported being in severe pain for 10 (i.q.r. 1-30)% of the first week after discharge and rated satisfaction with analgesia as 90 (i.q.r. 80-100) of 100. After adjustment for confounders, opioid analgesia on discharge was independently associated with increased pain severity (risk ratio 1.52, 95% c.i. 1.31 to 1.76; P < 0.001) and re-presentation to healthcare providers owing to side-effects of medication (OR 2.38, 95% c.i. 1.36 to 4.17; P = 0.004), but not with satisfaction with analgesia (beta coefficient 0.92, 95% c.i. -1.52 to 3.36; P = 0.468) compared with opioid-free analgesia. Although opioid prescribing varied greatly between high-income and low- and middle-income countries, patient-reported outcomes did not.Conclusion: Opioid analgesia prescription on surgical discharge is associated with a higher risk of re-presentation owing to side-effects of medication and increased patient-reported pain, but not with changes in patient-reported satisfaction. Opioid-free discharge analgesia should be adopted routinely

Global burden and strength of evidence for 88 risk factors in 204 countries and 811 subnational locations, 1990–2021: a systematic analysis for the Global Burden of Disease Study 2021

Background: Understanding the health consequences associated with exposure to risk factors is necessary to inform public health policy and practice. To systematically quantify the contributions of risk factor exposures to specific health outcomes, the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2021 aims to provide comprehensive estimates of exposure levels, relative health risks, and attributable burden of disease for 88 risk factors in 204 countries and territories and 811 subnational locations, from 1990 to 2021. Methods: The GBD 2021 risk factor analysis used data from 54 561 total distinct sources to produce epidemiological estimates for 88 risk factors and their associated health outcomes for a total of 631 risk–outcome pairs. Pairs were included on the basis of data-driven determination of a risk–outcome association. Age-sex-location-year-specific estimates were generated at global, regional, and national levels. Our approach followed the comparative risk assessment framework predicated on a causal web of hierarchically organised, potentially combinative, modifiable risks. Relative risks (RRs) of a given outcome occurring as a function of risk factor exposure were estimated separately for each risk–outcome pair, and summary exposure values (SEVs), representing risk-weighted exposure prevalence, and theoretical minimum risk exposure levels (TMRELs) were estimated for each risk factor. These estimates were used to calculate the population attributable fraction (PAF; ie, the proportional change in health risk that would occur if exposure to a risk factor were reduced to the TMREL). The product of PAFs and disease burden associated with a given outcome, measured in disability-adjusted life-years (DALYs), yielded measures of attributable burden (ie, the proportion of total disease burden attributable to a particular risk factor or combination of risk factors). Adjustments for mediation were applied to account for relationships involving risk factors that act indirectly on outcomes via intermediate risks. Attributable burden estimates were stratified by Socio-demographic Index (SDI) quintile and presented as counts, age-standardised rates, and rankings. To complement estimates of RR and attributable burden, newly developed burden of proof risk function (BPRF) methods were applied to yield supplementary, conservative interpretations of risk–outcome associations based on the consistency of underlying evidence, accounting for unexplained heterogeneity between input data from different studies. Estimates reported represent the mean value across 500 draws from the estimate's distribution, with 95% uncertainty intervals (UIs) calculated as the 2·5th and 97·5th percentile values across the draws. Findings: Among the specific risk factors analysed for this study, particulate matter air pollution was the leading contributor to the global disease burden in 2021, contributing 8·0% (95% UI 6·7–9·4) of total DALYs, followed by high systolic blood pressure (SBP; 7·8% [6·4–9·2]), smoking (5·7% [4·7–6·8]), low birthweight and short gestation (5·6% [4·8–6·3]), and high fasting plasma glucose (FPG; 5·4% [4·8–6·0]). For younger demographics (ie, those aged 0–4 years and 5–14 years), risks such as low birthweight and short gestation and unsafe water, sanitation, and handwashing (WaSH) were among the leading risk factors, while for older age groups, metabolic risks such as high SBP, high body-mass index (BMI), high FPG, and high LDL cholesterol had a greater impact. From 2000 to 2021, there was an observable shift in global health challenges, marked by a decline in the number of all-age DALYs broadly attributable to behavioural risks (decrease of 20·7% [13·9–27·7]) and environmental and occupational risks (decrease of 22·0% [15·5–28·8]), coupled with a 49·4% (42·3–56·9) increase in DALYs attributable to metabolic risks, all reflecting ageing populations and changing lifestyles on a global scale. Age-standardised global DALY rates attributable to high BMI and high FPG rose considerably (15·7% [9·9–21·7] for high BMI and 7·9% [3·3–12·9] for high FPG) over this period, with exposure to these risks increasing annually at rates of 1·8% (1·6–1·9) for high BMI and 1·3% (1·1–1·5) for high FPG. By contrast, the global risk-attributable burden and exposure to many other risk factors declined, notably for risks such as child growth failure and unsafe water source, with age-standardised attributable DALYs decreasing by 71·5% (64·4–78·8) for child growth failure and 66·3% (60·2–72·0) for unsafe water source. We separated risk factors into three groups according to trajectory over time: those with a decreasing attributable burden, due largely to declining risk exposure (eg, diet high in trans-fat and household air pollution) but also to proportionally smaller child and youth populations (eg, child and maternal malnutrition); those for which the burden increased moderately in spite of declining risk exposure, due largely to population ageing (eg, smoking); and those for which the burden increased considerably due to both increasing risk exposure and population ageing (eg, ambient particulate matter air pollution, high BMI, high FPG, and high SBP). Interpretation: Substantial progress has been made in reducing the global disease burden attributable to a range of risk factors, particularly those related to maternal and child health, WaSH, and household air pollution. Maintaining efforts to minimise the impact of these risk factors, especially in low SDI locations, is necessary to sustain progress. Successes in moderating the smoking-related burden by reducing risk exposure highlight the need to advance policies that reduce exposure to other leading risk factors such as ambient particulate matter air pollution and high SBP. Troubling increases in high FPG, high BMI, and other risk factors related to obesity and metabolic syndrome indicate an urgent need to identify and implement interventions

Morphological analysis and modelling for structural optimization of electrodes

Ce travail, qui associe analyse d'image, modélisation morphologique et calculs par transformées de Fourier, s'inscrit dans la thématique classique de l'homogénéisation de milieux hétérogènes, et dans le cadre notoirement problématique de l'optimisation multifonctionnelle de matériaux multiphasiques. Les matériaux qui font l'objet de cette thèse, collecteur de courant et anode, sont des éléments critiques des piles à combustibles (PAC). Ce dispositif convertit une énergie chimique en électricité grâce à l'oxydation d'un combustible, et ne rejette que de l'eau. Les PAC développées dans le cadre du projet européen Evolve sont d'un type nouveau, combinant des architectures préexistantes. Leur performance est déterminée par la conductivité ionique et électronique d'une part, par la perméabilité et les surfaces d'échange entre phases solides et pores d'autre part. Dans le cas d'un contraste de propriétés infini entre les phases (pores et solide, milieux isolant et conducteur), les propriétés effectives dépendent fortement de la répartition spatiale (morphologie) des phases en présence. On s'intéresse, dans un premier temps, à la segmentation, à la description et à la modélisation 3D de couches de piles à combustible, à partir d'images 2D acquises en microscopie électronique à balayage. Les microstructures sont segmentées puis caractérisées par des descripteurs morphologiques. On développe des modèles de milieux aléatoires 3D multiphasiques représentatifs des milieux réels. Ceux-ci reposent sur des modèles Booléens et de Gaussiennes seuillées et sont paramétrés par des caractéristiques géométriques simples du matériau (fractions volumiques, covariances, échelles caractéristiques). Ils sont validés visuellement et quantitativement, à l'aide de données morphologiques. Dans un second temps, on s'intéresse à la prédiction des propriétés de transport, à l'aide d'outils numériques par transformées de Fourier. Un algorithme amélioré, qui s'affranchit de l'effet de Gibbs est proposé en conductivité et la méthode de Wiegman (2007) est utilisée en perméabilité. La perméabilité de milieux booléens idéaux est calculée puis comparée à divers estimateurs analytiques. La borne de Berryman-Milton, connue précédemment dans le cadre du milieu Booléen de sphères, est calculée analytiquement pour un milieu Booléen de cylindres à l'aide d'une formule exacte pour le covariogramme de cylindres. Les propriétés de conductivité ionique et électronique de l'anode, et sa perméabilité, sont ensuite prédites à l'aide des modèles de milieux aléatoires précédemment développés et validés. La perméabilité, particulièrement sensible à la morphologie, est calculée pour divers paramètres du modèle, dont les surfaces spécifiques entre phases solides et pores. Plusieurs matériaux virtuels aux propriétés améliorées sont proposés.This work, which combines image analysis, Fourier methods and morphological models, focuses on the prediction and optimization of the transport properties of fuel cell materials in the classical framework of the homogenization of random media. The materials under study are critical layers found in fuel cells.These devices produce clean electrical energy (and water) from chemical fuel oxidation.The materials studied here are novel types of fuel cells that combine several preexisting architectures. Their performance is determined by the ionic and electronic conductivity, on the one hand, and by permeability and specific surfaces exchange between the solid and porous phases. For materials with highly-contrasted properties (pores and solid, isolating and conducting media), the effective properties strongly depend on the spatial arrangement (morphology) of the various phases.Fuel cell layers are first described and modeled using 2D scanning electron microscopy images and image analysis.Microstructures are characterized by morphological descriptors and realistic random 3D media, based on Boolean and Gaussian fields, are developed to represent the materials. The latter are parametrized by simple geometrical characteristics including volume fractions and covariances.They are visually and quantitatively validated using morphological data.Second, the transport properties are predicted numerically using Fourier methods. In conductivity, a modified algorithm is proposed to suppress the Gibbs artifacts. For permeability, the scheme of Wiegman (2007) is used.The permeability of ideal Boolean models is computed and compared with various analytical estimates.The Berryman-Milton bound, previously known for the Boolean model of spheres, is computed for a Boolean model of flat cylinders, using an analytical expression for cylinder covariogramm. The ionic and electronic conductivity of anode layers, and their permeability are predicted using previously developed models. The permeability, which strongly depends on the morphology, is computed for various values of the models' parameters, including the specific surface area between solid and phases.Several virtual materials with improved properties are proposed