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International audience; The hygrothermal behavior of a bio-based multilayered wall has been studied by numerical simulations. The key point of these research investigations was to properly describe the hygrothermal transfers occurring inside the studied wall solution. In previous work, the case of the wall subjected to a given real climate (Wroughton HIVE demonstrator, UK, Feb 2018) has been investigated. The present work, focused on the moisture regulation capacity of the wall, considers an improved kinetics model of sorption, different layer configurations, one additional climate (Bordeaux, FR, Apr 2008) and the effect of indoor cyclic loads. Compared to the classical approach, the local kinetics approach results in prediction of stronger and steeper hygric dynamics with larger relative humidity variations at small time scales. The study of the different wall configurations allows to determine the best one in terms of moisture damping: the vapor control membrane is advantageously removed provided the OSB3 12 mm layer is replaced by an OSB4 18 mm layer. Moreover, the simulations show that the Moisture Buffer Value characteristic of each material layer is not a sufficient criterion to evaluate hygric performance of the wall; strong hygric interactions occur with the layer's permeability independently of its sorption capacity. Finally, water content hysteresis phenomena are studied and it appears that under usual operating conditions, they can be ignored by adjusting the layers' permeabilities for adequate fits on the Moisture Buffer Value tests.

International audience; This modeling study investigates the effects of the initial conditions on a bio-based multi-layered wall by hygrothermal simulations. Such a study cannot be found in the relevant literature. In a first step, the work consists in numerically generating different climate histories for the studied wall, using two different real climates: a winter and a spring climate. Then, the wall preloaded with these two different climate histories and therefore different hygric and thermal initial conditions is subjected to several cycle of 18 days of the spring climate. This study highlights the significant effects of the initial conditions on the subsequent simulations: strong differences are predicted about relative humidity and water content. Many cycles of 18 days of the spring climate have to be applied to obtain a hygric convergence of the two simulations, i.e., to erase the wall hygric history. The analytic analysis of the results leads to define characteristic times of hygric dependency of about 35–40 days. It appears that the hygric predictions of the simulations become independent of the initial conditions after about three times these characteristic times, i.e., about 3.5 months. Comparatively, the thermal history takes only a few days to be erased. © 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

In 2019, 135 million people in 55 countries were in food crises or worse, and 2 billion people did not have regular access to safe, nutritious and sufficient food. COVID-19 (coronavirus) has exacerbated these hardships and may result in an additional 121 million people facing acute food insecurity by the end of 2020. Further, since the beginning of the pandemic, an estimated 1.6 billion learners in 199 countries worldwide were affected by school closures, with nearly 370 million children not receiving a school meal in 150 countries. The paper presents the evidence on the potential negative short-term and long-term effects of school meal scheme disruption during Covid-19 globally. It shows how vulnerable the children participating in these schemes are, how coping and mitigation measures are often only short-term solutions, and how prioritizing school re-opening is critical. For instance, it highlights how girls are at greater risk of not being in school or of being taken out of school early, which may lead to poor nutrition and health for themselves and their children. However, well-designed school feeding programmes have been shown to enable catch-up from early growth failure and other negative shocks. As such, once schools re-open, school meal schemes can help address the deprivation that children have experienced during the closures and provide an incentive for parents to send and keep their children, especially girls, in school.

International audience; The classical models describing hygric transport inside building materials seem unsuitable for bio-based materials. Based on the assumption of an instantaneous local equilibrium between relative humidity and water content evolving according to the sorption isotherms, they predict much shorter stabilisation times than those obtained experimentally. A new approach is presented here: it frees from the local instantaneous equilibrium by introducing local kinetics to describe the transformation of water from the vapour state to the absorbed liquid state and vice versa. In the framework of the European IsoBio project, a multilayered wall mainly made of bio-based materials was developed. The different layers were characterised in terms of sorption, vapour permeabilities and thermal conductivities. The sorption measurements performed on representative samples allowed determination of the local kinetic constants. The hygrothermal behaviour of the test wall was then studied in an instrumented demonstrator (Hive, Wroughton, UK). The recorded measurements were compared with simulations based on the instantaneous local equilibrium model (TMC code) and on the local kinetics of sorption model (TMCKIN code). TMC very significantly underestimated the dynamics of the local relative humidity variations whereas TMCKIN succeeded in predicting these dynamics and produced results close to measurements.

COVID-19 triggered mass innovation that grew flexible learning modalities and pathways that can be built upon in future sector plans to make education systems more resilient. These tools must be paired with investments in the people expected to use them and strengthened data systems. To ensure plans are rooted in ever-pressurised budgets, Education Ministers will increasingly need to turn to economic analysis. Expansion of partnerships will be necessary to secure greater and more innovative forms of finance but also affordable digital learning solutions. If these opportunities are seized alongside the disruption wrought by the pandemic, they can equalize opportunities and accelerate progress.

Some countries are starting to reopen schools as others develop plans to do so following widespread and extended closures due to COVID-19 (coronavirus). Using data from two surveys and 164 countries, this research brief describes the educational strategies countries are putting into place, or plan to, in order to mitigate learning impacts of extended school closures, particularly for the most vulnerable children. In addition, it highlights emerging good practices.

This research brief is one of a series that explores the impact of COVID-19 (coronavirus) on education. It focuses on the potential parental role in learning and its association with foundational reading and numeracy skills. COVID-19 is depriving many children of learning opportunities at school. The availability of child-oriented books and engagement of parents can play an important role for continued learning at home, especially where there is no access to technology. All policy decisions and implementation on continuing education remotely should also be cognizant of the need to ensure parents’ capability to help their child learn, to prevent exacerbating further global learning inequities to the detriment of the most vulnerable.

International audience; A bio-based multilayered wall has been developed in the framework of the European ISOBIO project. A key point was to be able to perform proper simulations of the hygrothermal transfers occurring through the wall local predictions are of first importance to characterize the behavior of the wall and thereafter its ability to ensure comfortable hygrothermal conditions inside buildings. A previous study proved that the conventional assumption of an instantaneous equilibrium between local relative humidity and water content according to the sorption isotherm is not relevant for bio-based porous materials, where in practice slow sorption kinetics occur. In the present study, an improved expression of the local kinetics is proposed and validated by sorption experiments. Then, Moisture Buffer Value tests are performed (Nordtest project's protocol). The simulations are adjusted to these measurements by using the inverse method in order to refine the knowledge of some critical parameters. Depending on the studied materials, the local kinetics constants are between 0.15 and 14 day-1/(kg.m-3). Finally, the ISOBIO wall is studied in a bi-climate room under a wide range of operating conditions. Simulations carried out with the conventional approach (TMC) and the local kinetics approach (TMCKIN) are compared to measurements this clearly shows that the latter is able to predict well the relative humidity dynamics while the former underestimates it by a factor up to 66%. These results highlight the relevance of the new expression of the local kinetics and its ability to describe well the local hygric dynamics is certainly an achievement.

The classic models describing the hygric mass transfers inside porous materials seem unsuitable in the case of bio-based materials. They are based on the assumption of instantaneous local equilibrium between relative humidity and water content (Kunzel in Simultaneous heat and moisture transport in building components—one- and two-dimensional calculation using simple parameters, Fraunhofer IRB Verlag, Stuttgart, 1995). These two parameters evolve according to the diffusive fluxes following the sorption isotherms. This study shows that it leads to predicting much shorter times of stabilization than those experimentally obtained. A new approach is presented here; it is free from the local instantaneous equilibrium introducing a local kinetics to describe the transformation of water from vapor state to liquid state and vice versa. The local kinetics of sorption is coupled with the well-known hysteresis phenomenon. It is adjusted from bibliographic data (Collet et al. in Energy Build 62:294–303, 2013) giving mass evolution of three hemp concretes under adsorption/desorption conditions. 1D cylindrical simulations allow an excellent fitting on the experiments. Finally, a semiempirical model is proposed, allowing to determine the kinetics parameters more easily.

International audience; A bio-based multi-layered reference wall has been developed within the framework of the European ISOBIO project. One of the key points of this project was to be able to perform proper simulations of the hygrothermal transfers occurring inside such walls. Previous published investigations, also performed in the framework of this project, have demonstrated that the classic assumption of instantaneous equilibrium between local relative humidity and water content according to the sorption isotherm is not relevant for bio-based porous materials, where, in practice, a rather slow kinetics of sorption occurs. The theoretical background developed in this previous study is used here to determine the kinetic constants of the bio-based construction materials and to perform 1D hygrothermal simulations. The kinetics constants are determined thanks to a 1D cylindrical tool based on the local kinetics approach, validated against several experiments of sorption. Then, heat and hygric transfers recorded on a demonstrator building (The HIVE, Wroughton, UK) are analyzed and are simulated using two modeling tools: TMC based on the Künzel approach and TMCKIN based on the local kinetic approach. From the simulations, the local kinetics improves the small timescale RH dynamics. The comparison with measurements performed in the demonstrator confirms the relevance of the local kinetics approach.

This study addresses the modeling of the denebulization (i.e., the removal of droplets) of warm fogs (T ≥ 0°C) by hygroscopic salt microparticles from the initial seeding at the top of the fog layer to the fall of the rain droplets on the ground. Two main phenomena can occur: condensation of water vapor on salted droplets and the concomitant evaporation of fog droplets, and coalescence between the salted droplets and the fog droplets. Three salts have been investigated: NaCl, CaCl2, and KCl. Based on the conservation equations, the modeling approach (1D) considers the hygroscopicity of the salts through the water activity in the aqueous solution and the coalescence induced by gravity and turbulence. From this study, NaCl is the most efficient salt in the tested operating conditions. Actually, this result can be explained by the strong hygroscopicity of this salt in very dilute solutions. From the calculations, 15 kg of NaCl particles of 6.7-μm diameter can dissipate a typical fog layer of 40 m in height within less than 17 min over 0.25 km2. According to the calculations, a fog layer of 100 m in height can be denebulized within 45 min. The contribution of the coalescence induced by gravity and by turbulence seems to have a negligible effect on the final horizontal visibility, the condensation/evaporation phenomena being preponderant for these operating conditions.

International audience; The aim of the present study is to better understand the mechanisms involved during silicon deposition from silane, SiH4, into agglomerates of sub-micrometer-size particles treated by fluidized bed (FB)CVD. Two models of silicon deposition into agglomerates assumed either stable, or in permanent formation/desegregation, are developed. In the first case, classical equations of diffusion/reaction in a porous medium are solved, whereas in the second case, the multifluid Eulerian code, MFIX, is used. By comparison with experimental energy dispersive X-ray (EDX) data, modeling results show that the limiting step is not gaseous diffusion into the agglomerates. Very high local deposition rates near the silane entrance probably explain theirformation. These results allow us to propose original deposition conditions involving much lower local deposition rates, which should limit agglomeration due to CVD.

There are some major advantages to be gained in processing micronic europium doped yttrium oxide Y2O3 particles for phosphor applications using spray pyrolysis. To better understand the influence of the operating conditions and also why hollow particles are formed, a complete one-dimensional modeling of the pure evaporation then evaporation/precipitation steps of micronic water/Y(NO3)3 droplets has been performed. Among the main results, it appears that no concentration gradient exists inside droplets during the pure evaporation stage and that the evaporation/precipitation stage, occurring in less than 10−3 s, leads to compact particles theoretically formed of a coherent porous medium of Y(NO3)3·5H2O. But the analysis of phenomena occurring during the thermolysis step between 95 and 300°C has revealed that a partial liquefaction of the hydrated yttrium nitrate occurs with concomitant release of gas. As a consequence, a crust of lightly hydrated yttrium nitrate probably appears, followed by particle inflation and leading to the formation of broken hollow particles. © 2007 American Institute of Chemical Engineers AIChE J, 2008

The purpose of the study is the modeling of the denebulization of fogs by micronic hygroscopic particles from the initial seeding to the fall of the rain droplets on the ground. The microparticles generated by flares are made of hygroscopic salts. Three stages occur: first, the condensation of water vapor on solid particles, this is the deliquescent stage which is very fast and can be ignored by the model, then the stage of condensation of water vapor on liquid salted particles / evaporation of fog droplets and finally the coalescence stage when the liquid salted particles diameter become large enough. Three different salts have been tested: NaCl, CaCl2 and KCl. The 1-D modeling approach studied considers the conservation equations (salt mass, water mass, salted droplets number density, fog droplets number density), the hygroscopicity of the salts through the water activity in the aqueous solution and the coalescence induced by gravity. The model reveals that NaCl is the most efficient salt because of its stronger hygroscopicity at high dilution rates although CaCl2 is the more hygroscopic at low dilution rates. A cloud of NaCl particles of 9 μm diameter initially generated over a height of about 7 m with a number density of 12 cm−3 allows to completely dissipates a typical fog layer of 40 m within less than 13 mn. This means that 10 kg of NaCl particles could be able to clear such a fog over 13.25 ha. The model shows that a layer of 100 m can be cleared within 29 mn. From the calculations, the contribution of the coalescence to the denebulization process is less than 1%, phenomena of condensation / evaporation are preponderant for these operating conditions.

This work deals with the integration of off-preform and in-preform physico-chemical phenomena involved in isothermal isobaric CVI for processing of ceramic-matrix composites (CMC). A global modeling approach featuring coupled reactor fluid mechanics and porous medium gas transport has been developed. The coupling between transport and reaction phenomena inside and outside the preform is rather strong, both physically and numerically. In a model case study of SiC infiltration from methyltrichlorosilane in a fibrous preform, the impact of the free medium on densification is proved, quantified and discussed, especially through flow rate and reactor diameter variations. Important counter-effects of the reactive preform on the surrounding gas-phase composition are shown; also, the effect of true experimental parameters is investigated. The total densification time is affected by the gas flow rate and the density field evolution relies both on the flow rate and the reactor diameter. Such an approach brings new guidelines for the optimization of perform.

An elastomeric material was investigated with a bubble inflation rheometer, and its mechanical behavior was modeled as a rubber-like solid. Classical strain energy functions were considered and the hyper-elastic constants were calculated by a direct identification procedure from simple uniaxial and equibiaxial extension test data, and the results are compared against those obtained by an inverse method from bubble inflation test data. The latter amounted to minimizing a cost function and matching the measured response to a finite element analysis solution, which depended on the unknown material parameters. The optimization employed the Levenberg-Marquardt algorithm and Abaqus software to compute the cost function and its gradients. The constants so obtained were further used in finite dement analysis, and the numerical results were compared with experiments. This study showed that the inverse method, used to estimate the material parameters, is a good alternative to the direct identification, especially since the latter often requires homogeneous strain state, which is very difficult to obtain.

The biaxial rheological behavior of materials such as elastomers or polymers can be obtained using a bubble-inflation-technique. A circular membrane is clamped at the rim and expanded under gas pressure. The inflation of the circular membrane is recorded using a CCD video camera and the blowing pressure by a pressure sensor. Then, from elongation and curvature radius measurements at the pole of the bubble, one can deduce equibiaxial stress-strain data. This study describes the optimization of a bubble-inflation rheometer. The most sensitive point of the technique is the estimation of the elongation at the bubble pole, deduced from video camera measurements. A direct measurement of the bubble thickness was performed using a magnetic probe in order to validate rheometer results. Such a validation has evidently never been carried out before. Results of quasi-static equibiaxial characterization of elastomers are presented and analyzed.

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The analysis aims to make a diagnosis of the entire education sector in order to highlight its strengths and weaknesses and to identify more efficient strategies for its improvement. The report, recommends actions even if sometimes the distance between diagnosis and recommendations is low. This study follows the diagnosis of the education sector and is structured as follows: i) the changing context of education sector (school-age population growth and by geographical areas, economic growth), ii) the financing and sector costs (Share of government resources allocated to education, arbitration intra-sectoral spending current education, household expenditure), iii) the enrollment and its disparities (By place of residence, level of life, gender in the allocation of resources), iv) the quality of learning (acquisition level of students, factors in the quality of learning), v) the issue of teaching (teacher salaries, allocation of teaching staff), vi) low efficiency in the use of resources, vii) the social and economic impacts of education, viii) structures of school.

Bismuth oxide thin films are of great interest due to their significant band gap, high refractive index, and dielectric permittivity, as well as marked photoconductivity and photoluminescence.[1] These properties make Bi2O3 films well suited for many applications such as microelectronics,[2] sensor technology,[3] optical coatings,[4] and ceramic glass manufacturing.[5] In this work, we report the synthesis of Bi2O3 films on alumina particles using fluidized bed (FB) CVD under atmospheric pressure. Bismuth triphenyl (Bi(Ph)3) was used as a metal-organic (MO) CVD precursor.

International audience; Using the multifluid Eulerian code MFIX, the silicon Fluidized Bed Chemical Vapor Deposition process from silane (SiH4) has been modelled under transient conditions. In order to constitute an experimental database, a preliminary experimental study has been performed using a bed of Geldart's group B particles. After a detailed analysis and comparison of the kinetic models available in the literature, four of them have been implemented in the MFIX code and two hydrodynamic models have been tested. 3-D simulations have shown that a strong interaction exists between the bed hydrodynamics, heat and reactive mass transfers and that Si deposition from silane mainly occurs in the dense zones of the bed whereas the unsaturated species silylene (SiH2) forms in bubbles and slugs and leads to Si deposition mainly at their periphery; its contribution to deposition can be locally as high as that of SiH4. The average contribution of SiH2 to deposition increases with the inlet concentration of silane and can reach 30%. The kinetic models derived from the law of Furusawa et al. and from the data compiled by Buss et al. and the hydrodynamic model based on the true granular energy equation and the Princeton solid phase stress model have revealed to be the most appropriate ones for the conditions tested.

Computational fluid dynamic (CFD) models must be thoroughly validated before they can be used with confidence for designing fluidized bed reactors. In this study, validation data were collected from a fluidized bed of (Geldart's group B) alumina particles operated at different gas velocities involving two fluidization hydrodynamic regimes (bubbling and slugging). The bed expansion, height of bed fluctuations and frequency of fluctuations were measured from videos of the fluidized bed. The Eulerian–Eulerian two fluid model MFIX was used to simulate the experiments. Two different models for the particle stresses—Schaeffer [Syamlal, M., Rogers, W., O’Brien, T.J., 1993. MFIX documentation: theory guide. Technical Report DOE/METC-94/1004 (DE9400087), Morgantown Energy Technology Centre, Morgantown, West Virginia (can be downloaded from Multiphase Flow with Interphase eXchanges (MFIX) website 〈 http://www.mfix.org 〉 ); Schaeffer, D.G., 1987. Instability in the evolution equations describing incompressible granular flow. Journal of Differential Equations 66, 61–74.] and Princeton [Srivastava, A., Sundaresan, S., 2003. Analysis of a frictional–kinetic model for gas–particle flow. Powder Technology 129(1–3), 72–85.] models—and different values of the restitution coefficient and internal angle of friction were evaluated. 3-D simulations are required for getting quantitative and qualitative agreement with experimental data. The results from the Princeton model are in better agreement with data than that from the Schaeffer model. Both free slip and Johnson–Jackson boundary conditions give nearly identical results. An increase in coefficient of restitution ( e ) from 0.8 to 1 leads to larger bed expansions and lower heights of fluctuations in the bubbling regime, whereas it leads to unchanged bed expansion and to a massive reduction in the height of fluctuations in the slugging regime. The angle of internal friction ( φ ) in the range 10 – 40 ∘ does not affect the bed expansion, but its reduction significantly reduces the height of fluctuations.

International audience; Titanium oxide (TiO2) submicron powders have been treated by Chemical Vapor Deposition (CVD) in a vibro-fluidized bed in order to deposit silicon layers of nanometer scale on each individual grain from silane (SiH4). Experimental results show that for the conditions tested, the original granular structure of the powders is preserved for 90% of the initial bed weight while the remaining 10% consists of agglomerates in millimetre range found near the distributor of the reactor. A comparison between experimental and modelling results using the MFIX code shows that for Geldart's Group B alumina particles (Al2O3), the model represents both the bed hydrodynamics and silane conversion rates quite well. The future objective is to extend the simulation capability to cohesive submicron powders in order to achieve better predictability of the phenomena governing ultrafine particles.

International audience; There are a number of some major advantages to be gained in processing micronic europium-doped yttrium oxide Y2O3 particles for phosphor applications using spray pyrolysis. In order to maximise production rates, it is tempting to use relatively dense sprays, but then coalescence occurs increasing final particle diameters, which must be prevented. Moreover, the influence of the operating conditions on the process behaviour is poorly understood. A complete one-dimensional model of the evaporation stage of micronic water/Y(NO3)3 droplets considering only the evaporation process and then both evaporation and gravity-induced coalescence phenomena has been established. Calculations of pure evaporation have shown that the amounts of evaporated water and droplet compositions depend only on the local temperature and not on the thermal history of the spray. Coupled calculations have shown that, in comparison with evaporation, coalescence plays a minor role on droplet diameter, but non-negligible as the increase of the final mean droplet diameter due to coalescence reaches up to 10% at low flow rates in the operating conditions tested. Injecting a preheated air flow directly into the nebuliser is a promising method to minimise coalescence effects: optimal operating conditions for which coalescence is completely insignificant were obtained by simulation.

International audience; The Computational Fluid Dynamics code MFIX was used for transient simulations of siliconFluidizedBed Chemical Vapor Deposition (FBCVD) from silane (SiH4) on coarse alumina powders. FBCVD experiments were first performed to obtain a reference database for modelling. Experimental thermal profiles existing along the bed were considered in the model. 3D simulations provide better results than 2D ones and predict silane conversion rate with a mean deviation of 9% compared to experimental values. The model can predict the temporal and spatial evolutions of local void fractions, gas and particle velocities, species gas fractions and silicon deposition rate. We aim at mid term to model FBCVD treatments of submicronic powders in a vibrated reactor since we have performed experiments proving the efficacy of the process to treat submicronic particles.

International audience; The control of pyrocarbon (pyC) chemical vapor infiltration (CVI) is a key issue in the processing of high-performance C/C composites with applications in aerospace parts and braking technology. For years, the precise investigation of deposition kinetics and pyC nanometerscale anisotropy has been rehearsed in chemical vapor deposition (CVD) and several variants of CVI with various pore sizes, and using mostly propane, propylene, and methane as source precursors. A literature survey and the analysis of recent experimental data have helped to understand better the role of gas-phase intermediate species in the various nanotextural transitions; a coherent modeling frame, which is suitable for propane, propylene, and methane—the latter having a neatly lower reactivity—has been set up and tested against experimental results from independent teams. The relation between nanotexture and processing conditions is then explained.

Proc. EuroCVD12 conference, Sitges/Barcelona, Spain, 1999; International audience; An integrated modelling approach of Chemical Vapour Infiltration of a fibrous preform by methyltrichlorosilane, featuring coupled reactor fluid mechanics and porous medium gas transport has been developed. The coupling between transport/reaction phenomena inside and outside the preform is rather strong, both physically and numerically. An important counter-effect of the reactive preform on the surrounding gas-phase composition is evidenced; also, an appreciable dissymmetry of the densification rate inside the preform, even with negligible convective transport inside it. Such an approach brings new informations for understanding the physico-chemical phenomena of CVI and new guidelines for preform densification optimisation.

International audience; It can be extremely useful to know biaxial properties of materials like elastomers used for mechanical applications or thermoplastics for the simulation of injection stretch/blow moulding or thermoforming processes. The biaxial stress-strain data of such materials can be obtained using a bubble-inflation-technique. A circular membrane is clamped at the rim and inflated by a pressure applied to one of its side. The inflation of the circular membrane is recorded using a CCD video camera and the blowing pressure by a pressure sensor. This technique was applied to the determination of an elastomer rheological behaviour, and will be adapted for thermoplastics (including a heating device). First, an experimental setup was carried out, using a thickness measurement magnetic probe, in order to validate rheometer results. Circonferential biaxial Cauchy stress-elongation curve of the elastomer studied was compared with the uniaxial stress-elongation curve.