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In the present study, we used computational fluid dynamics to analyze the sag caused by spray painting, considering the change in paint shape due to flow. We focused on the paint adhering to the target surface because this behavior has not been previously examined. The particle method was adopted for the calculation because it enabled a stable analysis of the paint droplets and the complex uneven surface of the paint film. A high-speed camera and image analysis were used to capture the spray painting and identify the parameter values. Using the developed model, we analyzed the change in the film thickness distribution for painting on a flat plate in the vertical direction. It was confirmed that the numerical and experimental data correlated for two conditions of the target distance. In addition, we proposed a new index, Degree of Sagging (DSG), to evaluate the amount of sag based on the physical properties of the paint rheology and the geometry of the target. In the painting tests on flat plates with different angles, a strong positive correlation of 0.95 was observed between the sum of the calculated DSG values and the measured paint flow distance due to sag. In the painting tests on L-shaped surfaces, the predicted sag appearance by DSG agreed with the measured results at 14 of the 15 measurement points under all conditions. Overall, a computational model was developed for field implementation that could predict painting thickness distribution and sag occurrence. Note to Practitioners—The present work is motivated by the problem that teaching painting robots in a painting site is particularly time consuming. To address this problem, off-line programming methods have been proposed to computationally predict paint quality and film thickness and determine the painting route. Conventional approaches have approximated the paint deposition model with a function, which determines the paint thickness distribution, or simulated this model with high accuracy by considering electrostatic forces and wind velocity fields using computational fluid dynamics (CFD) modeling methods. However, two major problems exist in the field implementation of these studies: The first problem is the inability to predict defects, including sagging, that may occur after painting. In the conventional approach, the behavior of the paint after it adheres to the target is outside the scope of the calculation. The second problem is the high computational resource cost of CFD simulation, which renders its application to robotic painting challenging. In painting sites, the painting thickness must be accurately predicted and routed in a short period of time. In this paper, we present a method for analyzing film thickness distributions by considering time series changes of flow and propose a function-based model for predicting sagging based on the simulation results. The model for sag prediction was shown to be computationally inexpensive enough to be implemented in the field. The results of several painting experiments with a real robot confirmed the validity of the predictions made by this method. Our method could be implemented in the near future as a prediction system for off-line evaluation of painting routes, which could significantly reduce teaching cost. Since the target in this paper was a flat plate, it is necessary to conduct evaluation tests using various target shapes and painting conditions. Also, integration with the painting route optimization method has not yet been achieved, which is a topic that will be addressed in the future.

Recently, mechanochemical multifunction cavitation (MC-MFC) was developed to improve the corrosion resistance of the magnesium surface. MFC is a technology that combines water jet peening and ultrasound cavitation. MC-MFC is a technology that adds phosphoric acid to water. It can improve the corrosion resistance by forming a phosphate film on the Mg surface. Conventional anodic oxidation, plating, and chemical vapor deposition can improve corrosion resistance by forming a film on the Mg surface, but it is difficult to improve characteristics such as compressive residual stress on the surface. MFC-treated surfaces have previously imparted various properties such as imparting compressive residual stress necessary to improve the fatigue strength to Al alloys and Cr-Mo steels. In this study, the effect of film formed on MC-MFC processed surface on compressive residual stress was investigated.

The chemically synthesized endoperoxide compound N-89 and its derivative N-251 were shown to have potent antimalarial activity. We previously demonstrated that N-89 and N-251 potently inhibited the RNA replication of hepatitis C virus (HCV), which belongs to the Flaviviridaefamily. Since antimalarial and anti-HCV mechanisms have not been clarified, we were interested whether N-89 and N-251 possessed the activity against viruses other than HCV. In this study, we examined the effects of N-89 and N-251 on other flaviviruses (dengue virus and Japanese encephalitis virus) and hepatitis viruses (hepatitis B virus and hepatitis E virus). Our findings revealed that N-89 and N-251 moderately inhibited the RNA replication of Japanese encephalitis virus and hepatitis E virus, although we could not detect those anti-dengue virus activities. We also observed that N-89 and N-251 moderately inhibited the replication of hepatitis B virus at the step after viral translation. These results suggest the possibility that N-89 and N-251 act on some common host factor(s) that are necessary for viral replications, rather than the possibility that N-89 and N-251 directly act on the viral proteins except for HCV. We describe a new type of antiviral reagents, N-89 and N-251, which are applicable to multiple different viruses.