Monitoring and assessing aquatic ecosystems using the behavior of organisms is essential for sustainable ecosystem management. Oligochaetes, which inhabit various freshwater ecosystems, are frequently used to evaluate the environmental conditions of freshwater ecosystems. Tubifex tubifex (Müller, 1774) (Oligochaeta, Tubificidae) is tolerant to organic pollution and has been used to evaluate the toxicity of toxicants, including heavy metals. We studied the behavioral responses of T. tubifex to three different copper concentrations (0.1, 0.5, and 1.0 mg L-1). The specimens were exposed to copper in an observation cage containing 150 mL of dechlorinated water. Movement behavior (diameter, speed, acceleration, meander, and turning rate) was continuously observed for two hours before and after the copper treatments. After the treatments, the diameter shrank and showed rapid twisting movement under all the copper conditions. The turning rate had a positive correlation with meander and acceleration both before and after treatment at all three concentrations, whereas speed and meander had a negative correlation. Length and turning rate also showed a negative correlation. The correlation coefficient between speed and acceleration in the highest copper concentration changed from positive before treatment (r=0.64) to negative (r= - 0.52) after treatment. Our results present the possibility of using behavioral parameters to detect copper contamination in freshwater ecosystems.

The aim of this study was to investigate dry matter productivity and nitrate nitrogen content in the growth stages of barnyard millet (Echinochloa esculenta) cultivated for feed, which was treated with different nitrogen fertilization levels. An early variety of barnyard millet (cv. Shirohie) was used for the test, and the different treatments with nitrogen fertilizer were as follows: 50% (N-40 kg/ha, T1), 100% (N-80 kg/ha, reference amount, T2), 150% (N-120 kg/ha, T3), 200% (N- 160 kg/ha, T4), 250% (N-200 kg/ha, T5), and 300% (N-240 kg/ha, T6). Sowing was done on May 13, 2021 and plants were harvested for four stage; vegetative stage, elongation stage, heading stage, and milk stage. The length of the millet increased significantly as the amount of nitrogen fertilization increased during the harvest period (p<0.05), but the difference was insignificant during the milk stage (p>0.05). Moreover, barnyard millet dry matter yield increased significantly as the levels of nitrogen fertilization increased (p<0.05), but there was no significant difference in dry matter yield among nitrogen fertilization levels during the heading stage (p>0.05). Chlorophyll also was significantly higher in T5 (250%) at all harvesting times, whereas nitrate nitrogen content was highest at the vegetative stage, gradually decreased as growth progressed, and lowest at the milk stage. Finally, as the nitrogen fertilization levels increased, the nitrate nitrogen content was significantly higher in all treatment groups (p<0.05). Therefore, our results suggest that the most appropriate nitrogen fertilizer levels is between 150%–200%, considering the dry matter yield, feed ingredients and nitrate nitrogen content in barnyard millet for feed.

Electroanalytical study for the rotating cylinder electrode in molten LiCl-KCl eutectic salt (58– 42mol%) containing MgCl2 (0.1wt%) at 600°C is conducted. The researches of rotating cylinder electrode have been widely conducted for the century. The advantage of the electrode is that it can mitigate the unintended natural convection by providing a controlled diffusion boundary layer thickness. However, the experimental data for the high temperature molten salts is barely existed. The study adopts the electrochemical techniques such as cyclic voltammetry for the static cell and linear sweep voltammetry for the dynamic cell to calculate the diffusion coefficient. The peak current density and limiting current density are measured according to the scan rate. In order to evaluate the mass transfer under hydrodynamic flow condition, the revolution speeds of cylindrical electrode are varied from 10 rpm to 500 rpm which are corresponded to the Reynolds number of 4 and 185 respectively. The flow regime covers from the laminar to semi-turbulent regime (transient) as the critical Reynolds number Recrit is 200. The limiting current density shows a linear trend with the revolution speed and agrees well with the existing mass transfer correlations. For the extended flow regime, a new mass transfer correlation is suggested as the relation of non-dimensional numbers (Sh = aRebScc) based on the dimensionless analysis.

As the decommissioning of nuclear power plants increases, there is an increasing interest in the amounts of radioactive waste. Especially, the radiation dose limit for packaging of radioactive wastes shall not exceed 2 mSv·h−1 and 0.1 mSv·h−1 on contact and at 2 m, respectively in South Korea. The DEMplus provides various environmental geometry and all properties such as materials, absorptions, and reflections and the estimation of the radiation dose rates is based on the radiation interactions of the designed 3D geometry model. With the consideration of the radiation dose rate by using DEMplus and its strategy of packaging plan, the radiation shielding was optimized and estimated in this paper. The modular shielded containers (MSC) with shielding inserted were used for radioactive wastes that require shielded packaging. In order to verify the accuracy of the estimated radiation dose rate by using DEMplus, the estimated results were compared with those obtained using MicroShield. The trends of the estimated radiation dose rates using DEMplus and the estimation of MicroShield were similar to each other. The results of this study demonstrated the feasibility of using DEMplus as a means of estimating the radiation dose limit in packaging plan of the radioactive waste.

In thermal cutting process, gas flow injected from the nozzle has a significant effect on the cutting materials. The gas flow is difficult to observe gases are transparent, therefore, in this study, Schlieren method was adopted to visualize the gas flow inside the kerf. The kerf shape was inserted between two slices of transparent glass in order to imitate the real cutting environment. In order to get the flow characteristics, a high speed camera was equipped and the image processing was applied to compare the before and after injection images. As a result, the method for visualizing gas flow was successfully developed and also expected to be applied to the analysis of purging gas in various welding environments.

This study deals with replacement analysis of deteriorated equipment for improving productivity of production system. Frequent breakdown of the deteriorated equipment causes a situation that reduces productivity such as low product quality, process delay, and repair cost. However, the replacement of new equipment will be required a high initial investment cost, so it is important to analysis the economic feasibility. Therefore, we analyze the effect of the production system due to the aging effect of the equipment and the feasibility of equipment replacement based on the economic analysis. The process flow, working time, logistics movement, etc. are analyzed in order to build the simulation modeling for a ship and land switchboard production system. Using numerical examples, the economic feasibility analysis of equipment replacement through replacement of existing deteriorated equipment and additional arrangement of new facilities is performed.

With the development of maritime ICT, the introduction of e-navigation and the MASS (maritime autonomous surface ship), the types and scope of maritime communication networks are expanding, and the need for digital AtoN services is increasing. However, due to problems such as the aging of fishing crews, coastal backlight, weather conditions, and inexperience with regard to the use of advanced navigation equipment on board, the visual and electronic perception of AtoN is degraded, and it is difficult to ensure safe ship navigation. In this study, in response to the introduction of the MASS, a plan for the development of an active customized virtual digital AtoN service system in consideration of ship operating conditions and geographic conditions is proposed. The proposed service system may facilitate electronic identification of AtoN and contribute to preventing marine accidents by ensuring the safe navigation of ships.