Développement d’un revêtement glaciophobe permettant de réduire l’adhérence et l’accumulation de la glace sur les structures portuaires en acier

L’accumulation de la glace dans les pays nordiques est un problème sévère qui engendre de sérieuses conséquences dans divers domaines particulièrement les infrastructures portuaires fluviales ou marines. Dans ces environnements, marqués par la présence d’humidité relative très élevée et par la présence de sels dans les zones marines, les épisodes de givrage consécutifs mènent à la détérioration par la corrosion. La lutte contre ces effets néfastes a suscité le développement de plusieurs types de revêtements de protection comme solution passive parmi lesquels les revêtements à base d’époxy. Ces derniers ont prouvé leur potentiel anticorrosif, une excellente durabilité et une résistance mécanique supérieure. Toutefois, la recherche d’un revêtement d’époxy intrinsèquement glaciophobe a conduit à reconsidérer les stratégies antigivrantes existantes et exclure la superhydrophobicité. Parmi les restantes, celle intégrant l’utilisation de matériaux à faible module d’élasticité et hydrophobe à base de silicone pour la réduction de la contrainte d’adhérence de la glace a été retenue. Ainsi, en couplant l’effet des polymères de silicone et des époxy en des matrices dites époxy-silicone, un revêtement glaciophobe a été formulé en deux étapes. D’abord, une étude paramétrique a été conduite lors de la sélection de la matrice de polymère. Puis, le revêtement glaciophobe a été formulé par l’utilisation d’additifs à base d’organosilane modifiant dans le volume la chimie de la matrice. En comparant les propriétés mécaniques des matrices avec la contrainte d’adhérence de la glace, aucune corrélation apparente avec le module d’élasticité des thermodurcissables n’a été observée. Cependant, en se basant sur un agent de cure particulier et en variant l’énergie de rupture, il a été observé que la contrainte d’adhérence de la glace varie positivement avec cette dernière. Il s’agit d’une formule hydrophobe non texturée contournant les insuffisances des surfaces superhydrophobes sujettes au givrage par condensation dans les cavités de surface. Le revêtement développé offre une diminution de l’adhérence de la glace avec un facteur de réduction de 11 comparé avec l’acier soit 94 kPa en régime statique (push-off), et 48 kPa en régime dynamique (par centrifuge). Selon, les tests d’accumulation de givre, réalisés pour la simulation en environnement à humidité très élevée, l’accumulation est inéluctable. Cependant, la genèse des cristaux de glace y est différente aidant ainsi à minimiser la contrainte de retrait de la glace. En plus, le potentiel antigivre de ce revêtement a démontré une baisse de la température de nucléation de la glace jusqu’à -21°C. D’autre part, des essais de mesure de l’adhérence mécanique du revêtement développé au substrat en acier ont montré une bonne adhérence à ce dernier. La résistance aux intempéries a été vérifiée grâce au vieillissement accéléré avec une bonne résistance aux rayonnements UV. La réduction de l’absorptivité à l’eau suggère également la présence d’une barrière anticorrosive. Enfin, la bonne résistance à l’abrasion témoigne que le revêtement pourrait être utilisé comme une bonne solution pour la réduction de l’adhérence de la glace au niveau des zones portuaires. Ice accumulation on infrastructure in the northern countries represent a severe problem that leads to disastrous consequences in various fields, especially fluvial and marine harbor infrastructures. In these environments, characterized by the presence of very high relative humidity and salts, consecutive episodes of icing may lead to the deterioration of the infrastructure by corrosion. Fighting against these harmful effects has prompted a wave of several strategies, including many types of protective coatings as a passive solution, among which are epoxy-based coatings. Those ones have proven their anti-corrosive potential, excellent durability, and outstanding mechanical resistance. However, the search for an intrinsically icephobic coating with good performance in such an environment has led to consideration of existing strategies excluding superhydrophobicity. Hence, among these, the chosen one is aiming at the use of silicone-based hydrophobic materials with low modulus of elasticity for the reduction of ice adhesion strength. Thus, by coupling the effects of silicone polymers and epoxies in so-called epoxy-silicone matrices, an icephobic coating was formulated in two steps. First, a parametric study was conducted during the selection of the polymeric matrix. Then, the icephobic coating was formulated by bulk chemical modification using organosilane-based additives. Also, by comparing the mechanical properties of the matrices with the adhesion strength of the ice, no apparent correlation with the Young elastic modulus of the thermosets was reported. However, based on a particular curing agent and varying the fracture energy, the adhesion strength of the ice was found to vary positively. On one hand, this hydrophobic, non-textured formula overcomes the shortcomings of superhydrophobic surfaces prone to frosting by condensation in surface cavities. The coating developed offers an ice adhesion reduction with a factor of 11 for steel, i.e. 94 kPa in static conditions (push-off) and 48 kPa in dynamic conditions (by centrifugal removal). According to light and heavy frost accumulation tests carried out for the simulation of a very high humidity environment, the accumulation is inevitable. However, the genesis of ice crystals is different which helped to minimize the ice detachment strength. Finally, the anti-icing potential of this coating demonstrated a drop in the nucleation temperature of the ice down to -21°C. On the other hand, the mechanical adhesion tests of the developed coating on the steel substrate showed good adhesion to the substrate. Weather resistance has been verified through accelerated aging with good UV resistance. In addition, the reduction in water absorptivity also suggests the presence of an anticorrosive barrier. These aspects, coupled with the good abrasion resistance, testifies that the coating could be used as a good candidate for the reduction of ice adhesion on harbor structures

Développement d’un modèle de procédé pour analyser la performance d’un four horizontal de cuisson d’anodes

La production des anodes de carbone utilisées dans les cuves d’électrolyse pour la réduction de l’alumine est très complexe et énergivore. Leur cuisson a lieu dans des fours spécialisés dont le fonctionnement nécessite beaucoup d’attention afin d’en améliorer la performance. C’est dans cette optique que s’inscrit le présent projet de recherche rendu compte tout au long de ce mémoire. Cependant, l’évaluation des coûts de travaux pour la recherche de moyens d’amélioration a orienté cette étude vers la modélisation mathématique du procédé comme outil de travail. Ce projet fait partie des travaux réalisés dans le cadre des activités de la Chaire de recherche UQAC-AAI sur le carbone. Le modèle de procédé développé au cours de cette étude nous a permis d’évaluer les effets de plusieurs paramètres qui interviennent dans le fonctionnement des fours. Ceux-ci jouent un rôle important dans la qualité des anodes de carbone parce que la cuisson est la dernière étape où les propriétés des anodes sont fixées. Le modèle est basé sur la solution des équations des bilans de masse et d’énergie dans les différentes parties du four. L’écoulement des gaz a été considéré bidirectionnel, une simplification qui est réaliste, mais qui a aussi permis d’éviter la solution complexe des équations de la quantité de mouvement. L’approche simplifiée utilisée dans ce modèle a réduit le temps de calcul tout en permettant la représentation de tous les phénomènes importants du procédé de cuisson des anodes. L’intérêt fut porté vers les paramètres énergétiques de cuisson des anodes que représentent la quantité de carburant injectée et la quantité de matières volatiles contenus dans les anodes. L’impact de certains paramètres de caractéristiques géométriques et physiques des fours de cuissons a été également évalué. Les résultats obtenus ont été consolidés par les travaux antérieurs sur d’autres fours en général. Ainsi, cette analyse a été enrichissante car elle a permis de prévoir l’effet que certains paramètres pourraient engendrer sur la cuisson des anodes. De même, à l’issu de cette étude, il est plus aisé de prédire le comportement d’un four de cuisson en fonctionnement sous des contraintes de productions différentes. Elle a toutefois permis d’approfondir nos connaissances du point de vue énergétiques et de mieux comprendre le procédé de cuisson des anodes de carbones dans les fours. The production of carbon anodes used in electrolysis cells for the reduction of alumina is highly complex and energy-intensive. These carbon anodes are baked in specialized furnaces, which require a great deal of attention in order to improve their performance. It is with this principle in mind that this research project has been carried out in this master’s thesis. The assessment, based on the cost, of work required for the improvement of the furnace operation has oriented this project towards the mathematical modeling of the process as a working tool. This master’s project is part of the work carried out within the framework of the activities of the UQAC-AAI research chair on carbon. The process model developed during this study allowed the evaluation of the effects of several parameters entailed in the operation of baking furnaces. These play an important role in the quality of baked carbon anodes because baking is the last step where the anode properties are fixed. The model is based on the solution of the mass and heat balance equations in different parts of the furnace. The gas flow was considered two dimensional, a simplification that is realistic and also one that allowed avoiding the complex solution of momentum equations. The simplified approach used in this model helped reduce the computation time while allowing the representation of all important phenomena of the anode baking process. The focus was kept on the energy parameters of anode baking, which are represented by the quantity of fuel injected and the amount of volatile matter contained in the anodes. The impact of some parameters of geometrical and physical characteristics of the baking furnaces was also evaluated. The results obtained have been corroborated by previous works on other horizontal furnaces in general. This analysis was worthwhile because it allowed predicting the effect that certain parameters could have on the baking of anodes. Also, with the model developed, it is now possible to predict the behavior of a baking furnace in operation under constraints of different production scenarios. This work has enriched our knowledge from the point of view of energy use as well as in terms of a better understanding of the anode baking process in these furnaces

Spatial and temporal variation of malaria entomological parameters at the onset of a hydro-agricultural development in central Côte d'Ivoire

A deeper understanding of the ecology and small-scale heterogeneity of malaria transmission is essential for the design of effective prevention, control and elimination interventions. The spatial and temporal distribution of malaria vectors was investigated in five villages in close proximity to a hydro-agricultural system in Côte d'Ivoire over the course of construction and the early phase of irrigated rice farming.; The study was carried out in five villages (Raffierkro, N'Douakro, Ahougui, Kpokahankro, Koffikro) near Bouaké, central Côte d'Ivoire, between early 2007 and late 2009. In each village, mosquitoes were collected by human landing catches and identified morphologically at genus and species level, and entomological parameters were determined. Plasmodium infection was assessed by dissection and an enzyme-linked immunosorbent assay.; A total of 19,404 mosquitoes belonging to the genus Anopheles were sampled during 328 human-night catches. Before the construction of the hydro-agricultural system, comparable densities of Anopheles gambiae were observed in all villages. In subsequent years, densities in Raffierkro and Ahougui were significantly higher than the other villages [Kruskal-Wallis (KW) test = 31.13, p > 0.001]. The density of Anopheles funestus in the five villages was comparable in the early stage of the project, while a high density was reported in Koffikro at the end (KW test = 11.91, p = 0.018). Transmission of Plasmodium falciparum is perennial in the study area. Over the course of the study, high entomological inoculation rates (EIRs) were found: 219-328 infectious bites per person per year with An. gambiae. For An. funestus considerably lower EIRs were observed (5.7-39.4). Changing patterns of An. gambiae were not correlated with malaria transmission.; In this study setting, located in the bioclimatic transition zone of Côte d'Ivoire, rice cultivation was not observed to increase malaria transmission. The entomological parameters recorded until the onset of rice-growing activities in a hydro-agricultural system presented considerable heterogeneity both in space and time; a strong increase of Anopheles mosquitoes was observed in two of the five villages located in close proximity to the dam and irrigated rice fields. Malaria still is a main public health problem in all villages that require adequate control measures

Efficacy of ICON® Maxx in the laboratory and against insecticide-resistant Anopheles gambiae in central Côte d'Ivoire

ABSTRACT: BACKGROUND: Long-lasting treatment kits, designed to transform untreated nets into long-lasting insecticidal nets (LLINs), may facilitate high coverage with LLINs where non-treated nets are in place. In this study, the efficacy of ICON(R) Maxx (Syngenta) was evaluated under laboratory conditions and in an experimental hut trial in central Cote d'Ivoire, where Anopheles gambiae s.s. are resistant to pyrethroid insecticides. METHODS: In the laboratory, polyester and polyethylene net samples were treated with ICON(R) Maxx, washed up to 20 times and their efficacy determined in World Health Organization (WHO) cone assays against a susceptible laboratory An. gambiae s.s. colony. Over a 12-month period, the polyester nets were evaluated in a hut trial to determine mosquito deterrence, induced exophily, blood-feeding inhibition and mortality. RESULTS: In the laboratory, ICON(R) Maxx-treated polyethylene nets showed higher efficacy against pyrethroid-susceptible mosquitoes than polyester nets. After 20 washings, insecticidal efficacy in bioassays was 59.4% knockdown (KD) and 22.3% mortality for polyethylene, and 55.3% KD and 17.9% mortality for polyester nets. In experimental huts, treated nets showed strong deterrence, induced exophily and an over three-fold reduction in blood-fed mosquitoes. More than half (61.8%) of the mosquitoes entering the huts with treated nets were found dead the next morning despite high levels of KD resistance. After washing the treated nets, KD and mortality rates were close to or exceeded predefined WHO thresholds in cone bioassays. CONCLUSION: In contrast to previous laboratory investigation, ICON(R) Maxx-treated nets showed only moderate KD and mortality rates. However, under semi-field conditions, in an area where mosquitoes are resistant to pyrethroids, ICON(R) Maxx showed high deterrence, induced exophily and provided a significant reduction in blood-feeding rates; features that are likely to have a positive impact in reducing malaria transmission. The WHO cone test may not always be a good proxy for predicting product performance under field condition

ETUDE DU COMPORTEMENT AU REPOS ET DES PREFERENCES TROPHIQUES DE ANOPHELES GAMBIAE DANS LA VILLE D’ADZOPE, COTE D’IVOIRE

An entomological follow up, carried out by house resting collection and outdoor resting collections was achieved from June 2006 to September 2008 in Adzope, a town located in South-west Côte d’Ivoire, in the forest zone. This study aimed at identifying the origin of the An. gambiae females bloodmeals. In total, 539 mosquitoes were collected, 390 house resting mosquitoes and 149 outdoor resting ones. The mosquitoes collected in the two environments belong to 3 genera: Anopheles (92.5 %), Culex (7.2 %) and Mansonia(0.2 %). An. gambiae was the only anopheles species collected. The study of its resting behavior reveals the existence in Adzope of two populations: endophilic and exophilic. The origin of 60 bloodmeals of this species was identified by the PCR-heteroduplex. In houses, the bloodmeals were collected on humans (97%) and goats (3%). In outdoor shelters, the collection was made on humans (87.5%), birds (3%) and cows (1.5%). The bloodmeals from unknown origins were 1.5%. Actually, the poultry was the host preference for animal-feeding females. An. gambiae presents a high anthropophilic rate and therefore a threat for Adzope population

Surveys of Arboviruses Vectors in Four Cities Stretching Along a Railway Transect of Burkina Faso: Risk Transmission and Insecticide Susceptibility Status of Potential Vectors

Background: A severe outbreak of dengue occurred in Burkina Faso in 2016, with the most cases reported in Ouagadougou, that highlights the necessity to implement vector surveillance system. This study aims to estimate the risk of arboviruses transmission and the insecticide susceptibility status of potential vectors in four sites in Burkina Faso.Methods: From June to September 2016, house-to-house cross sectional entomological surveys were performed in four cities stretching along a southwest-to-northeast railway transect. The household surveys analyzed the presence of Aedes spp. larvae in containers holding water and the World Health Organization (WHO) larval abundance indices were estimated. WHO tube assays was used to evaluate the insecticide susceptibility within Aedes populations from these localities.Results: A total of 31,378 mosquitoes' larvae were collected from 1,330 containers holding water. Aedes spp. was the most abundant (95.19%) followed by Culex spp. (4.75%). Aedes aegypti a key vector of arboviruses (ARBOV) in West Africa was the major Aedes species found (98.60%). The relative larval indices, house index, container and Breteau indexes were high, up to 70, 35, and 10, respectively. Aedes aegypti tended to breed mainly in discarded tires and terracotta jars. Except in Banfora the western city, Ae. aegypti populations were resistant to deltamethrin 0.05% in the other localities with low mortality rate under 20% in Ouagadougou whereas they were fully susceptible to malathion 5% whatever the site. Intermediate resistance was observed in the four sites with mortality rates varying between 78 and 94% with bendiocarb 0.1%.Conclusions: This study provided basic information on entomological indices that can help to monitor the risks of ARBOV epidemics in the main cities along the railway in Burkina Faso. In these cities, all larval indices exceeded the risk level of ARBOV outbreak. Aedes aegypti the main species collected was resistant to deltamethrin 0.05% and bendiocarb 0.1% whereas they were fully susceptible to malathion 5%. The monitoring of insecticide resistance is also important to be integrated to the vector surveillance system in Burkina Faso

Step by step progress to achieve an icephobic silicone‐epoxy hybrid coating: Tailoring matrix composition and additives

This study details the fabrication of an icephobic coating for steel produced using a silicone–epoxy hybrid resin; the coating has good mechanical properties and weathering resistance for outdoor applications. Silicone–epoxy hybrid resins and amino‐functional silane‐curing agents were selected for investigation and applied to steel samples. Wettability, ice adhesion strength, and the mechanical and weathering resistance properties of the developed coatings were assessed using a drop‐shape analyzer, Fourier transform infrared, X‐ray photoelectron spectroscopy, as well as push‐off, tensile, and QUV tests. The possible correlation between ice adhesion strength and Young modulus was also investigated. The best‐performing matrix in terms of mechanical properties and weathering resistance had its surface energy characteristics altered—via two fluorinated silicone additives at various concentrations—to lower ice adhesion strength. For the steel substrates, the optimized additive‐altered surface showed a lower ice adhesion strength (decreasing from 362 to 94 kPa) with an adhesion reduction factor of 10.6. The fabricated coatings can serve as a protective layer for marine harbor infrastructures

Spatial Assessment of Contact Between Humans and Anopheles and Aedes Mosquitoes in a Medium-Sized African Urban Setting, Using Salivary Antibody-Based Biomarkers

International audienceBACKGROUND: Anarchic and poorly controlled urbanization led to an increased risk of mosquito-borne diseases (MBD) in many African cities. Here, we evaluate the spatial heterogeneity of human exposure to malaria and arboviral disease vectors in an urban area of northern Senegal, using antibody-based biomarkers of exposure to Anopheles and Aedes mosquito bites.METHODS: A cross-sectional study was undertaken during the rainy season of 2014 in 4 neighborhoods of Saint-Louis, a city in northern Senegal. Among children aged 6-59 months in each neighborhood, the dried blood spot technique was used to evaluate immunoglobulin G (IgG) responses to both gSG6-P1 (Anopheles) and Nterm-34-kDa (Aedes) salivary peptides as validated biomarkers of respective mosquito bite exposure.RESULTS: IgG response levels to gSG6-P1 and Nterm-34-kDa salivary peptides varied significantly between the 4 neighborhoods (P < .0001). The level of exposure to Aedes bites also varied according to household access to sanitation services (P = .027), whereas that of exposure to Anopheles bites varied according to insecticide-treated bed net use (P = .006). In addition, spatial clusters of high contact between humans and mosquitoes were identified inside 3 neighborhoods.CONCLUSIONS: Antibody-based biomarkers of exposure to Anopheles and Aedes mosquito bites could be helpful tools for evaluating the heterogeneity of exposure to malaria and arboviral disease vectors by national control program

Pattern of antibody responses to Plasmodium falciparum antigens in individuals differentially exposed to Anopheles bites

International audienceBackground : In malaria-endemic areas, human populations are frequently exposed to immunomodulatory salivary components injected during mosquito blood feeding. The consequences on pathogen-specific immune responses are not well known. This study evaluated and compared the humoral responses specific to merozoite stage vaccine candidates of Plasmodium falciparum, in children differentially exposed to Anopheles bites in a natural setting.Methods : The cross-sectional study was carried out in Bouaké (Côte d’Ivoire) where entomological data and blood samples from children (0–14 years) were collected in two sites with similar malaria prevalence. Antibody (IgG, IgG1, IgG3) responses to PfAMA1 and PfMSP1 were evaluated by ELISA. Univariate and multivariate analysis were performed to assess the relationship between the immune responses to P. falciparum antigens and exposure to Anopheles bites in the total cohort and in each site, separately. The individual level of exposure to Anopheles bites was evaluated by quantifying specific IgG response to the Anopheles gSG6-P1 salivary peptide, which represents a proxy of Anophelesexposure.Results : The anti-Plasmodium humoral responses were different according to the level of exposure of children, with those highly exposed to Anopheles presenting significantly lower antibody responses to PfMSP1 in total popula-tion (IgG and IgG3) and in Petessou village (IgG, IgG1, IgG3). No significant difference was seen for PfAMA1 antigen between children differently exposed to Anopheles. In Dar-es-Salam, a neighbourhood where a high Culex density was reported, children presented very low antibody levels specific to both antigens, and no difference according to the exposure to Anopheles bites was found.Conclusion : These findings may suggest that immunomodulatory components of Anopheles saliva, in addition to other factors, may participate to the modulation of the humoral response specific to Plasmodium merozoite stage antigens. This epidemiological observation may form a starting point for additional work to decipher the role of mos-quito saliva on the modulation of the anti-Plasmodium acquired immunity and clinical protection in combining both field and ex vivo immunological studies