Cholesterol oxidase, a bio-catalyst that can catabolize cholesterol, has proven applications in medicine. Here, a support material was used to enhance the characteristics of the enzyme. Magnetite (Fe3O4) is widely used as an enzyme support; however, the interaction between the enzyme and the support should be capped with another material, such as chitosan biopolymerbased material. In this study, chitosan-magnetite materials were synthesized by mixing both compounds and activating with glutaraldehyde. The materials were then characterized by Fourier Transform Infrared (FTIR) Spectroscopy. The enzyme kinetic parameters were studied by following the cholesterol oxidation reaction using high-performance liquid chromatography (HPLC) and comparing the results between the free and the immobilized enzyme. The substrate concentration was 2.5 mg/mL. The effect of enzyme concentration was tested using different concentrations of enzyme (0.5, 1, and 2 mg/mL) to determine the best operating conditions. The best conditions for the oxidation reaction were immobilized enzyme at a 2 mg/mL concentration. Enzyme immobilization significantly decreased the optimum substrate concentration to 0.1 mg/mL.

The yaw motion stability and course-keeping ability of ships are important factors with regard to collision danger, particularly for ships operating in narrow channels, crowded routes, or port areas. Yaw motion may become unstable due to external forces, such as wind. To investigate yaw stability and course-keeping ability, this study developed a nonlinear dynamic system of a three-degree-of-freedom mathematical model to determine steady state equilibrium. Yaw motion behavior was then analyzed using the eigenvalue characteristic of the obtained equilibrium points. The numerical results for an Indonesian ro-ro ferry showed that the rudder angle required to maintain the ship's course tended to increase as wind velocity increased. In beam wind, the necessary rudder angle was larger than the maximum possible rudder angle when the wind velocity was 24 m/s or more. The ship could be controlled by the rudder during operation, but its yaw motion tended to be unstable in following wind. The stable oscillation of yaw motion occurs when the wind velocity is higher than 11 m/s, and the range of heading and rudder angles increases as wind velocity increases.