Investigation expérimentale et modélisation numérique du procédé de traitement thermique superficiel par laser avec différents modèles de balayage

RÉSUMÉ: Le traitement thermique de surface par laser représente une des solutions les plus innovantes dans l'industrie moderne grâce à ses nombreux avantages. Les recherches concernant ce procédé n'ont pas encore révélé toutes ses spécificités et ses subtilités. Cela limite fortement les possibilités d'exploiter adéquatement ses avantages et d'optimiser ses performances. L'objectif de ce projet consiste à investiguer aussi bien expérimentalement que numériquement le procédé de traitement thermique de surface par laser dans le but de développer une stratégie d'optimisation prédictive de ses performances dans le cas de l'utilisation de différents modèles de balayage de la source laser. Cette stratégie permet de conduire à des modèles prédictifs simples, précis et robustes des performances du procédé. Pour atteindre cet objectif, une méthodologie en trois phases est adoptée. La première consiste à conduire une investigation expérimentale pour analyser les effets des modèles de balayage considérés sur les caractéristiques du profile de dureté. L'expérimentation est conduite selon d es plans d'expériences structurés appliqués à des plaques en acier AISI 4340 en utilisant une source laser Nd:Yag de 3 kW. L'analyse des résultats expérimentaux est réalisée à l'aide de techniques statistiques éprouvées. La deuxième phase consiste à développer et à valider expérimentalement un modèle numérique 3D en utilisant la méthode des éléments finis afin de réduire les coûts de l'expérimentation et simuler le comportement du procédé sous des conditions difficiles à réaliser expérimentalement. Les résultats des simulations ont révélé que les modèles 3D permettent de fournir une prédiction cohérente ainsi qu'une analyse qualitative et quantitative du comportement du procédé. Cette analyse a permis d'identifier les variables et les conditions les plus pertinentes à considérer dans une modélisation prédictive. Finalement, la troisième phase consiste à exploiter les avantages qu'offrent les réseaux de neurones artificiels dans le développement de la stratégie d'optimisation prédictive proposée. Des modèles directs et inverses du procédé ont constitués les ingrédients de base de cette stratégie. Une base de données intégrant les données provenant de l'expérimentation et les données issues des simulations numériques est utilisée pour l'apprentissage et pour la validation des modèles. De nombreux critères statistiques sont utilisés pour évaluer les performances des modèles aussi bien en termes xiv de précision que de robustesse. Les résultats obtenus montrent que cette stratégie conduit à des modèles prédictifs précis et robustes. -- Mot(s) clé(s) en français : Traitement thermique de surface par laser, Acier AISI 4340, Analyse thermique, Modèles de balayage, Profil de dureté, Planification d'expériences, ANOVA, Modélisation numérique 3D, Modèle prédictif, Réseaux de neurones artificiels. -- ABSTRACT: Laser surface hardening represents one of the innovative solutions in modern industry thanks to its several advantages. Research has not yet revealed all its details and subtleties, which severely limits the possibility of optimizing its performance and adequately exploiting its advantages. The objective of this project is to investigate experimentally and numerically the laser surface transformation hardening process in order to develop an integrated performance optimization strategy when using different scanning patterns. To achieve this goal, a three-phase methodology is adopted. The first phase consists in performing an experimental investigation to evaluate the effects of the hardening modes and parameters on the hardness profile characteristics. The experimentations are conducted according to structured experimental designs applied to AISI 4340 steel plates using a 3 kW Nd:Yag laser source. The experimental data analysis is carried out using improved statistical tools. The second phase consists of developing and experimentally validating a 3D finite element method based numerical model in order to reduce the cost of experimentation and to simulate the process behaviour under conditions that are difficult to perform experimentally. Simulation results revel that the 3D models provide a consistent prediction as well as a qualitative and quantitative analysis of the process performances. This analysis is used to identify the most relevant variables and conditions to consider in the predictive modeling and the optimisation approach. Finally, the third step consists in exploring the advantages of artificial neural networks to develop an effective predictive optimization strategy. The proposed direct and inverse process models are based on a mixture of data collected from experimental investigations and 3D numerical simulations. A combination of statistical tools and learning procedures are used to improve the modeling procedure. The results shown that this strategy can lead to accurate and consistent predictive models. -- Mot(s) clé(s) en anglais : Laser Surface hardening, AISI 4340 Steel, Thermal Analysis, Hardness Profile, Scanning Patterns, Design of Experiments, ANOVA, Predictive Modeling, 3D Numerical Model, Artificial Neuron Networks

Assessment of Lead, Copper and Cadmium Tolerance by Four Vegetable Species

Heavy metal pollution in agriculture soils has serious negative effects on human health and has become an important issue both in developed and developing countries. This study was conducted in ElOurdanine region (Monastir, Tunisia) and performed at four different sites using treated wastewater for irrigation. The aim is to detect the ability of accumulation of some heavy metals by four vegetable crops: peas (leguminosae), carrot (Apiaceae), lettuce (Asteraceae) and spinach (Chenopodiaceae) grown in contaminated soil. Total of 4 soils samples from the four experimental sites were collected and analyzed before and after vegetables cultivation. The quantitative content of Cadmium (Cd), copper (Cu) and lead (Pb) in the four species revealed differential abilities of accumulation. Significant differences were recorded. The comparison of the four species together showed that lettuce and spinach are the most accumulators of heavy metals, an average concentrations above than 7.50 mg.kg-1 DM were recorded, while the pea pods were characterized by the lower concentrations (<0.5 mg.kg-1 DM for Cd), carrot expressed a moderate accumulation with an average of four sites not exceeding 3 mg.kg-1 DM for Cd. The lower accumulators (pea and carrot) would be most suitable for cultivation on contaminated soils while both spinach and lettuce appear to be high accumulators of Cd and Pb that are considered a higher risk to human health than Cu

Morphological and Molecular Identification of Seedborne Fungi in Squash (Cucurbita maxima, Cucurbita moschata).

Squash is one of the most important crops of tropical and temperate regions, and it can be affected by several fungal pathogens. Most of these pathogens infect the seeds, which become an efficient vehicle to disperse seedborne pathogens over long distances, with consequent severe crop losses. The main objective of this study was the identification of the principal seedborne fungi in seeds extracted from 66 samples of asymptomatic and symptomatic squash fruit (Cucurbita maxima, Cucurbita moschata) collected in two countries, Tunisia and Italy. The symptoms of fruit decay were identified and classified according to lesion size. Following the blotter test, 14 fungal species were detected from the seeds. Seedborne fungi were identified in all fruit samples tested, including asymptomatic fruit. The most frequent fungi from Tunisian seeds were Alternaria alternata (25.1%), followed by Stagonosporopsis cucurbitacearum (24.6%), Fusarium solani (16.6%), Rhizopus stolonifer (13.3%), F. fujikuroi (7.8%), Albifimbria verrucaria (3.3%), and Stemphylium vesicarium (2.3%). For the fruits from Italy, the most frequently identified fungal species in seed samples were Alternaria alternata (40.0%), followed by F. fujikuroi (20.8%), Stemphylium vesicarium (3.0%), and Curvularia spicifera (2.1%). Morphological identification was confirmed by molecular diagnosis using the available species-specific primers. Furthermore, specific primers were designed to identify Albifimbria verrucaria, Paramyrothecium roridum, and Stemphylium vesicarium. Application of seed-health testing methods, including such conventional and molecular diagnostic tools, will help to improve seed quality and crop yields

The expected number of olympic medals: a case study of team Portugal at Tokyo 2020

The 2020 Summer Olympic Games reached to an end in Tokyo, Japan. Even though all the hiccups, constraints, and challenges imposed by the COVID-19 pandemic, the Games were successfully held in August 2021. For the first time in history, Team Portugal won four medals (one gold, one silver, and two bronzes). In 2018 the Portuguese Olympic Committee signed a contract with the Portuguese Institute of Sport and Youth (i.e., Portuguese government) listing the deliverables of the mission Tokyo 2020 against a funding scheme of 18.5 million euros (Contrato n.º 33-A/2018; Contrato -Programa de Desenvolvimento Desportivo n.º CP/1/DDF/2018). The document sets, among other goals and deliverables, that no less than two medals would be won at Tokyo 2020 (section IV.1. of the contract). On the road to Tokyo, Portugal got more than two medallists at World Championships in several Olympic sports. Indeed, there were six to eight potential medallists at the 2020 Olympic Games (O Jogo, 2021). There is evidence that just one-third to one-fourth of the Olympic athletes are able to excel and outperform at the Olympic Games. In the sport of competitive swimming, just 29.82% of all male Olympians and 53.84% of the finalists at Rio 2016 improved their entry times (Barbosa, 2016a). On average, only 30% of the swimmers were able to improve their entry time at the 2012 and 2016 Olympic Games (Barbosa, 2016b). At Rio 2016, Team Portugal was expected to win two medals out of nine potential medallists, i.e., almost 25% of effectiveness (Garcia, 2016). Thus, one can wonder if the Portuguese Olympic Committee was sensible, assuming that two athletes would reach the podium spot out of six to eight potential medallists. Also, it begs the question if the four medals won were an outstanding achievement, deemed as a substantial improvement of the Portuguese sports system or, if alternatively, the Portuguese Olympic Committee underestimated the number of medals that the country could win.info:eu-repo/semantics/publishedVersio

Salt effect on physiological, biochemical and anatomical structures of two Origanum majorana varieties (Tunisian and Canadian)

In this study, we evaluated the salt concentration effect on plant growth, mineral composition, antioxidant responses and anatomical structure of two varieties of Origanum majorana after exposure to NaCl treatment. Our results show an inclusive behaviour of the two varieties, since the majority of sodium was exported and accumulated in their aerial parts. The Canadian variety (CV) appeared relatively more tolerant to salt than the Tunisian one (TV). Transversal section of leaves showed a thickening of dorsal and ventral cuticle, more importantly in CV than in TV, in the presence and in absence of salt. This was accompanied by an increase in the length of palisade cells, and the width of spongy collenchyma lacuna. The stem had a subquadrangular shape in TV and quadrangular in the Canadian variety. At mature stage, the stem pit was reabsorbed in the TV and replaced by a large cavity, whereas it remained unchanged in CV. The relative salt tolerance of the CV was related to: (1) a good selectivity in favour of K+: (2) a strong peroxidase activity and (3) an increase in the lengthening of palisade cell accompanied with an increase of lacunae in spongy parenchyma in CV.Key words: Origanum majorana, salinity, growth, mineral nutrition, leaves, stems, anatomical, antioxidant

Effect of growth stages on phenolics content and antioxidant activities of shoots in sweet marjoram (Origanum majorana L.) varieties under salt stress

We investigated the contributions of salinity and development stage on total polyphenols, flavonoids,  condensed tannins contents, phenolic content, 1,1-diphenyl-2-picrylhydrazyl (DPPH) and superoxide  scavenging activities at three phenolic stages: early vegetative stage (EVS), late or prefloral vegetative (LVS) stage and flowering stage (FS). The total phenolic, flavonoids and condensed tannins contents were more  important in the presence and absence of salt at prefloral or building stage than at EVS and FS. In addition, salt stress increased total polyphenol and individual phenolic contents in shoots of Origanum majorana. This  increase was more important in LVS than in EVS and FS. Moreover, the antiradical activity of the shoots (DPPH) decreased with the addition of NaCl. In fact, LVS extracts showed the highest antioxidant properties.  Furthermore, at LVS, marjoram grown at 75 mM showed a higher antiradical ability against DPPH radical and antioxidant activity, compared to EVS and LVS. Data reported here revealed the variation of phenolic  compound contents at different stages of growth of O. majorana, and the possible role of these changes in the response of the plant to salt was also discussed.Key words: Antiradical activity, Origanum majorana, early vegetative stage (EVS), late or prefloral vegetative (LVS) stage and flowering stage (FS), phenolic content

Improved recovery of antioxidant compounds from refined pumpkin peel extract: a mixture design method approach

This study employed the mixture design method to determine optimal solvent combinations, aiming to obtain refined extracts from squash peels with enhanced antioxidant properties. We optimized extraction solvents, focusing on recovering the total phenolic compounds (TPC) and increased antioxidant properties using a second-order polynomial equation through the response surface methodology (RSM). Six solvents (MeOH, Hexane, DCM, EtOAc, BuOH, and water) were assessed for their effects on TPC and antioxidant activity in preliminary experiments. The refined extracts underwent a HPLC analysis for a phenolic composition determination and were further evaluated for their antibacterial activity and cytotoxicity. The results revealed a rich phenolic content in the refined extract from peels of Bejaoui landrace, primarily catechin (8.06 mg/g dry extract (DE)), followed by epicatechin and kaempferol (5 mg/g DE). Antibacterial tests against Enterococcus faecalis, Pseudomonas aeruginosa, Salmonella typhimurium, and Staphylococcus aureus showed significant antimicrobial activities, especially for Karkoubi and batati landraces, where the growth inhibitions were 99%, 96%, 97%, and 80% and 94%, 89%, 98%, and 96% for the respective bacteria. The peel extracts exhibited a negligible cytotoxicity on the RAW264.7 cell line, even at high concentrations. Our findings emphasize the potential antioxidant and antibacterial properties of peel extracts due to diverse phenolic compounds, suggesting the potential use of squash peels in the food and nutraceuticals industries as sources of natural antimicrobial agents.This study was supported by the Tunisian Ministry of Higher Education and Scientific Research and was funded under the scope of the Project PulpIng-H2020-PRIMA 2019—Section 2—Multi-topic 2019. To the Foundation for Science and Technology (FCT, Portugal) for financial support by national funds FCT/MCTES (PIDDAC) to CIMO (UIDB/00690/2020 and UIDP/00690/2020) and SusTEC (LA/P/0007/2020); to FCT for the contract of L. Barros (CEEC Institutional); to the General Secretariat for Research and Technology of the Ministry of Development and Investments under the PRIMA Program. PRIMA is an Art.185 initiative supported and co-funded under Horizon 2020, the European Union’s Program for Research and Plants 2022, 11, 800 16 of 18 Innovation (Prima2019-08).info:eu-repo/semantics/publishedVersio

Effect of reduced tillage under various mulch types on soil fertility and yield of an organic pepper crop

The effects of mulching on soil characteristics and plant development for pepper crops conducted in organic farming were studied in the Sahel coast of Tunisia. The types of mulching used for tests are straw mulching, compost mulching, and plastic mulching which were compared with bare soil without mulching (control). The soil characteristics under these different mulching systems were evaluated by soil physical and biological parameters such as penetration resistance at 0-60 cm layer, microbial biomass, organic matter, and water content at 0-20 cm layer. Measurements were performed every week for 50 days. The obtained results showed that compost mulching led to a better growth rate and improved the structural and water state of cultivated soil by decreasing its resistance to penetration and increasing its organic matter content. It can be concluded that the "Beldi" organic pepper crop under conservation tillage and compost mulching has presented the best combination thus leading to motivating results such as the positive effects of soil physical properties and microbial biomass on the final crop yield