The vibration of the handles of a vertical disc stump grinder causes significant damage to people who operate the machine for a long time. First, we tested the vibration of the handle of a vertical disc stump grinder. Second, we evaluated the allowable years of operating the vertical disc stump grinder according to the assessment standard ISO 5349 for human exposure to hand-transmitted vibration by the International Organization for Standardization. Third, we established a finite element model of the stump grinder based on the experience model of the engine and the power spectrum of the cutting force of the grinder. Finally, we proposed an optimization scheme for the vertical disc stump grinder according to the finite element model. The experimental results indicate that the output weighted acceleration of the existing handle of the vertical disc stump grinder is 47.89 m/s 2 and the allowable years for operating the grinder are less than one. The simulation results indicate that the finite element model of the vertical disc stump grinder is useful for analyzing the vibration of the handle. The output weighted acceleration of the existing handle of the vertical disc stump grinder is 8.87 m/s 2 after optimization, with the allowable years of operation increased to 3 years. Thus, the optimization scheme is feasible.

The impact of high-risk behaviors on the spread of COVID-19 infection among young people is an important problem to address. This study analyzed the association between cooperativeness and high-risk behaviors. We conducted a cross-sectional study among fourth-year medical students at Tokyo Medical and Dental University. The students were asked about cooperative attitude in a hypothetical situation of performing a task together with an unfamiliar classmate, who did not cooperate to complete the task previously. The response items were as follows: “cooperate”, “don’t want to cooperate and do it alone (non-cooperative)”, and “don’t want to cooperate and let the partner do it alone (punishment)”. Eating out and vaccine hesitancy were also treated as high-risk behaviors. Poisson regression was used to investigate the association between cooperative attitude and each high-risk behavior, adjusted for demographics. Of the 98 students, 23 (23.5%), 44 (44.9%), and 31 (31.6%) students chose “noncooperative”, “cooperative”, and “punishment”, respectively. Cooperative-type students exhibited 2.77-fold (PR: 2.77, 95% CI: 1.03–7.46), and punishment-type students exhibited 3.16-fold greater risk of eating or drinking out (PR: 3.16, 95% CI: 1.14–8.75) compared with those of the noncooperative type. Among medical students, the “cooperative” type and “punishment” type comprised the high-risk group for eating out during the pandemic.

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Obstacle-crossing performance is an important criterion for evaluating the power chassis of forestry machinery. In this paper, a new six-swing-arm wheel-legged chassis (SWC&F) is designed according to the characteristics of forest terrain, using herringbone legs to control the ride comfort and stability of the chassis in the process of crossing obstacles. First, the kinematic model of the SWC&F is established, the coordinate analytical expression of each wheel centre position is derived, and the swing angle range of each wheel leg of the chassis is calculated according to the installation position of the hydraulic cylinder. Next, the control model of the system is constructed, and the obstacle-crossing performance of the SWC&F is analyzed by ADAMS/Simulink co-simulation using the PID control method and conventional control method, respectively. The results show that the maximum obstacle crossing height of the SWC&F can reach 411.1 mm, and the chassis with PID control system has good dynamic response characteristics and smooth motion, which meets the requirements of forest chassis obstacle crossing design. The study can provide the foundation for the practical laws of the physical prototype of the forest vehicle chassis.

With the aim of reducing the vibration and maximum stress of a cogged V-belt and determining the appropriate cogged V-belt for the vertical disc stump grinder (RG25HD), this paper analyses the relationship between, on the one hand, the horizontal displacement of the vibration and node stress and, on the other, the tooth profile and belt speed. In addition, the pattern of the vibration and node stress of the cogged V-belt is investigated using various tooth profiles and belt speeds. Our approach uses a rigid/flexible coupling simulation of belt power transmission based on a finite element flexible body method and employs Recurdyn multi-body dynamics software. After the simulation, we obtain the stress distribution of the belt, the lateral displacement curve and the node stress curve. Our results indicate that cog shape affects belt stress and vibration. When selecting or designing a cogged V-belt, a belt with trapezoidal cogs is preferable. Regarding the effect of belt speed, the trapezoidal cogged V-belt’s lateral vibrating displacement and maximal stress increase with an increase in belt speed. Therefore, when the stump grinder is in operation, its revolving speed should be maintained at a low rate to reduce vibration and prolong the belt’s life.