Alendronate (Alen)-modified hydroxyapatite (HAp) nanoparticles with multilayers of poly(allylamine) (PAA) and alginate (ALG) were fabricated for bone-specific dual delivery of drug and mineral. Negatively charged HAp nanoparticles were coated with three layers of PAA and ALG using a layer-by-layer (LbL) method and then conjugated with Alen at the outmost layer of the LbL-coated HAp nanoparticles via carbodiimide chemistry. Alenmodified HAp nanoparticles had a spherical morphology and an average size of 61.5 nm. The superior adsorption property of the Alen-modified HAp nanoparticles was quantitatively confirmed using tricalcium phosphate disks as a bone model, compared to HAp nanoparticles. Cell culture assays revealed a higher proliferation rate and alkaline phosphatase activity of osteoblasts treated with the Alen-modified HAp nanoparticles.
The effects of the slope of the ground and the obstacle conditions on the lateral overturning/backward rollover of a tractor with an implement were analyzed through dynamic simulation. The tractor and implement’s 3D simulation model was constructed. As for simulation conditions, four heights and three shapes were set for obstacles, and eight slopes were set for the ground to be traveled by the implemented tractor. Under each condition, the critical speed at which the tractor begins to overturn and roll over was derived, and factors that caused the overturn and rollover were analyzed. As a result of instability types, backward rollover happens when the ground slope is low and lateral overturning happens at a specific slope or higher regardless of the obstacle conditions. In the case of the tractor and implement under study, the tendency changed at a slope of 25°. As the obstacle height increased, overturning and rollover safety decreased. In the case of the obstacle shape, safety was lowest for the rectangular obstacle and highest for the right-side triangular obstacle. The driving safety of the tractor with the implement was lower than that of the tractor with no implement. This appears to be mainly due to the change in the position of the center of gravity caused by the attached implement. The critical speed of the tractor with the implement was 3.26 times lower than that of the tractor with no implement on average. It is judged that the safety of the implemented tractor can be identified by using this study.
This study analyzed the lateral overturning and backward rollover characteristics of a multi-purpose agricultural machine recently developed in South Korea. Free body diagrams for theoretical analysis and a three-dimensional model for dynamic simulation were created by reflecting the actual dimensions and material properties of the multi-purpose agricultural machine. The simulation model was verified using the minimum turning radius and angle of static falling down sidelong derived through the certified performance test. The lateral overturning and backward rollover characteristics of the multi-purpose agricultural machine were analyzed using a verified simulation model and theoretical equations derived through literature review. In the lateral overturning analysis, the critical traveling speed at which lateral overturning occurs was derived according to the inner steering angle of the front wheels under steady-state turning conditions. In the backward rollover analysis, the critical angular velocity and theoretical traveling speed of the main body at which backward rollover occurs were derived according to lifting angle of the front wheels. There was no significant difference between the theoretical analysis and simulation results at 5% significance level, and we derived the appropriate traveling speed conditions of the multi-purpose agricultural machine that do not cause lateral overturning and backward rollover.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.