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The study of the collision behavior of solid objects has received a significant amount of research in various fields such as industrial applications of powders and grains, impacts of proppants and between proppant and rocks during hydraulic fracturing, and the study of debris flows and avalanches and the interactions of landslide materials with protective barriers. This problem has predominantly been studied through the coefficient of restitution (COR), which is computed from the dropping and rebound paths of particles; its value corresponds to 1 for perfectly elastic impacts and 0 for perfectly plastic impacts (i.e., at the collision there is no rebound of the particle). Often, the colliding particles (or particle–block systems) are not perfectly clean, and there is debris (or dust) on their surfaces, forming a coating, which is a highly possible scenario in the debris flows of natural particles and fragments; however, the topic of the influence of natural coatings on the surfaces of particles on the collision behavior of particle–block systems has been largely overlooked. Thus, the present study attempts to provide preliminary results with respect to the influence of natural coating on the surfaces of sand grains in the COR values of grain–block systems using a stiff granitic block as an analogue wall. Montmorillonite powder, which belongs to the smectite clay group, was used and a sample preparation method was standardized to provide a specific amount of clay coating on the surfaces of the sand grains. The results from the study showed a significant influence of the smectite coating in the COR values of the grain–block systems, which was predominantly attributed to the dissipation of energy at the collision moment because of the compression of the soft coating of microparticles. Additionally, the method of analysis for calculating the COR values based on one and two high-speed cameras was explored, as the impacts of natural grains involve deviations from the vertical, which influences the rebound paths. Thus, a sensitivity analysis was performed investigating the differences in the COR values in two-dimensional and three-dimensional analysis of the impact tests. [ABSTRACT FROM AUTHOR]

Pine pitch canker (PPC) is a major threat to pine forests worldwide because of the extensive tree deaths, reduced growth, and degradation of timber quality caused by it. Furthermore, the aggressive fungus responsible for this disease (Fusarium circinatum) can also infect pine seeds, causing damping-off in young seedlings. This study proposes an approach based on coating treatments consisting of natural products to ensure seed protection. Seeds from two pine species (the most sensitive to this disease, Pinus radiata D. Don, and a more resistant one, Pinus sylvestris L.) were coated with single and binary mixtures of low and medium molecular weight chitosan and/or ethanolic-propolis extract. The germination rate, pre- and post-emergence mortality, total phenolic content, and radical scavenging activity were assessed. All treatments, and especially the one based on chitosan oligomers, had a beneficial impact on P. sylvestris seedlings, significantly enhancing survival rates and displaying a positive influence on the total phenolic content and on the seedlings' radical scavenging activity. Conversely, non-significant negative effects on germination percentages were observed in the case of P. radiata seeds. The proposed treatments show promise for the protection of P. sylvestris seedlings against PPC. [ABSTRACT FROM AUTHOR]