• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.2
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• pp.93-103
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• 2023

Warships widely spread numerous chaffs using a blast, which form chaff clouds that create false radar cross-sections to deceive enemy radars. In this study, we established a numerical framework based on a one-way coupling of computational fluid dynamics and discrete element method to simulate the spatiotemporal distribution of chaff clouds for warships in the air. Using the framework, we investigated the effects of wind, initial chaff cartridge angle, and blast pressure on the distribution of chaff clouds. We observed three phases for the chaff cloud diffusion: radial diffusion by the explosion, omnidirectional diffusion by turbulence and collision, and gravity-induced diffusion by the difference in the fall speed. The wind moved the average position of the chaff clouds, and the diffusion due to drag force did not occur. The direction of radial diffusion by the explosion depended on the initial angle of the cartridge, and a more vertical angle led to a wider distribution of the chaffs. As the blast pressure increased, the chaff clouds spread out more widely, but the distribution difference in the direction of gravity was not significant.

• Clean Technology
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• v.29 no.2
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• pp.95-101
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• 2023

An experiment was conducted to produce vaterite-type precipitated calcium carbonate from waste oyster shells in order to use them as recyclable resources. Calcined oyster shells containing calcium oxide as their main component were prepared at a temperature of 800℃ for 24 h. The oyster shells were dissolved in nitric acid or hydrochloric acid solution to make 0.1 M calcium nitrate or calcium chloride aqueous solution, and a carbonation reaction was performed using a 0.1 M sodium carbonate aqueous solution under various experimental conditions, which included varying the amount of aspatic acid additive, the amount of NH₄OH added, the reaction time, the reaction temperature, the stirring speed, and the type of dissolved acid. The XRD, SEM, and size distributions were analyzed and the vaterite content was calculated. Spherical precipitated calcium carbonate with a vaterite content of 95.9% was synthesized by adding 0.1 mol aspatic acid/1 mol CaO and 2 cm³ of NH₄OH, and reacting for 1 h at 25℃ while stirring at 600 rpm. The average particle diameter was found to be 12.11 ㎛. Calcium carbonate contatining high vaterite is used as high value added calcium carbonate for medical, food, inke additiver, etc.

• Journal of Marine Life Science
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• v.1 no.1
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• pp.25-30
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• 2016

We investigated the possibility of a bio-monitoring system for detecting hypoxic water in coastal area using shell valve movements of Pacific oyster (Crassostrea gigas), which showed most aquaculture production in Korea, with Hall element sensor. In filtrating water to confirm shell valve movement (SVM) under normal condition, it showed spikes which mean a relatively fast closing condition after opened condition of average 5~12 mm, and then the SVM showed back to opening condition slower than closing speed SVM numbers during light period were similar to that of dark period (p<0.05). When dissolved oxygen (DO) concentration was reduced from 7 mg l^-1 to 3 mg l^-1, SVM numbers were increasing with decreasing of DO, and showed abnormality SVMs as compare with normal condition. Moreover, in the condition of 2 mg l^-1, Distance between light and left shell showed gradually decreased, and then we could not detected SVMs due to closed condition. Thus, if we quickly detect abnormal environmental variations as hypoxia water using bio-monitoring of SVM, it may be contribute to increased productivity by dramatically reducing damages in aquaculture.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.21 no.1
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• pp.182-192
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• 2022

Motorcycle accidents are increasing at an average annual rate of 10.01%, and fatalities are also increasing by 2.64%. Enforcement cameras are installed to enforce safe driving of more-than or equal-to four-wheeled vehicles on the road. Even though the main purpose of this enforcement camera is to disencourage the speed violation of all types of vehicle, one cannot expect complete enforcement by these cameras. In particular, enforcement of the motorcycle should rely on on-site activities through the input of on-site personnel. Recently, to discourage the illegal acts of motorcycling, the National Police Agency introduced the 'National Police Agency SMART National Report'. However, it is necessary to prepare an appropriate practical plan to maximize the effect of enforcement requiring continuous manpower management. This study proposed four types of rider certification IDs for delivery motorcycles. These IDs are institutional devices to manage delivery motorcycle riders. In addition, a experiment on enforcement was conducted using those license ID systems for delivery motorcycles. This experiment confirmed through the image-processing program (D-MESO) if one of the systems was possible to implement for enforcement on the delivery motorcycle rider's license.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.16 no.5
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• pp.217-222
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• 2023

The purpose of this paper was to synthesize a polymer organic hard mask that simplifies the manufacturing process, reduces process time significantly, and thereby lowers manufacturing costs. The results of measuring residual metals through vapor refining showed that 9-Naphthalen-1-ylcarbazole(9-NC) measured 101.75ppb in the 4th zone, 2-Naphthol (2-NA) measured 306.98ppb in the 5th zone, and 9-Fluorenone(9-F) measured between 129.05ppb across the 4th and 5th zones. After passing through a filtration system, the synthesized organic hard mask measured residual metals in the range of 9 to 7ppb. Additionally, the thermal analysis indicated a decrease of 2.78%, a molecular weight of 942, carbon content of 89.74%, and a yield of 72.4%. The etching rate was measured at an average of 18.22Å/s, and the coating thickness deviation was averaged at 1.19. For particle sizes below 0.2㎛ in the organic hard mask, no particles were observed. By varying the coating speed at 1,000, 1,500, and 1,800rpm and measuring the resulting coating thickness, the shrinkage rate ranged from 17.9% to 20.8%. The coating results demonstrated excellent adhesion to SiON, and it was evident that the organic hard mask was uniformly applied.

• Korean Journal of Agricultural Science
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• v.50 no.3
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• pp.383-394
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• 2023

In Korea, the U.S. Tier-4 Final emission standards have been applied to agricultural machinery since 2015. This study was conducted to analyze the emission characteristics of agricultural tractors during plow tillage operations using PEMS (portable emissions measurement systems). The tractor working speed was set as M2 (5.95 km/h) and M3 (7.60 km/h), which was the most used gear stage during plow tillage operation. An engine idling test was conducted before the plow tillage operation was conducted because the level of emissions differed depending on the temperature of the engine (cold and hot states). The estimated level of emissions for the regular area (660 m²), which was the typical area of cultivation, was based on an implement width of 2.15 m and distance from the work area of 2.2 m. As a result, average emission of CO (carbon monoxide), THC (total hydrocarbons), NOx (nitric oxides), and PM (particulate matter) were approximately 6.17×10-2, 3.36×10^-4, 2.01×10^-4, and 6.85×10^-6 g/s, respectively. Based on the regular area, the total emission of CO, THC, NOx, and PM was 2.62, 3.76×10^-2, 1.63, and 2.59×10^-4 g, respectively. The results of total emission during plow tillage were compared to Tier 4 emission regulation limits. Tier 4 emission regulation limits means maximum value of the emission per consumption power (g/kWh), calculated as ratio of the emission and consumption power. Therefore, the total emission was converted to the emission per power using the rated power of the tractor. The emission per power was found to be satisfied below Tier 4 emission regulation limits for each emission gas. It is necessary to measure data by applying various test modes in the future and utilize them to calculate emission because the emission depends on various variables such as measurement environment and test mode.

• Korean Journal of Agricultural and Forest Meteorology
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• v.26 no.1
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• pp.53-62
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• 2024

In this study, we built a model to estimate frost occurrence in South Korea using single-input deep learning and multi-input deep learning. Meteorological factors used as learning data included minimum temperature, wind speed, relative humidity, cloud cover, and precipitation. As a result of statistical analysis for each factor on days when frost occurred and days when frost did not occur, significant differences were found. When evaluating the frost occurrence models based on single-input deep learning and multi-input deep learning model, the model using both GRU and MLP was highest accuracy at 0.8774 on average. As a result, it was found that frost occurrence model adopting multi-input deep learning improved performance more than using MLP, LSTM, GRU respectively.

• Journal of the Korean Society of Radiology
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• v.83 no.6
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• pp.1259-1272
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• 2022

Purpose As part of ongoing efforts to improve the current e-learning center, a survey was conducted regarding user experience and satisfaction to identify areas of improvement. Materials and Methods Radiologists (n = 454/617) and radiology residents (n = 163/617) of the Korean Society of Radiology were asked to answer a survey via email. The questionnaire asked for basic user information as well as user experiences relating to the e-learning center, such as workplace, frequency of use, overall satisfaction levels, reasons for satisfaction or dissatisfaction, and other suggestions for improvement. Results Annual members and all members of the e-learning center reported above average satisfaction levels of 67% and 42%, respectively. Approximately 30% of respondents viewed e-learning center lectures more than 5 times a month, with residents having a particularly high usage frequency. There was a high demand for additional lectures covering more diverse specialties (e-learning for annual members only: n = 28/97, e-learning for all members: n = 72/166), a smoother and more convenient searching platform/interface (n = 37/97 and n = 58/166, respectively), and regular content updates. In addition, many of the members suggested the addition of user-friendly functions such as playback speed control, a way to save viewing history, as well as requests for improved system stability. Conclusion Based on survey results, the educational committee plans to continue its efforts to improve the e-learning center by increasing the quality and quantity of available lectures, and increasing technical support to improve the stability and convenience of the e-learning digital system.

• Journal of Astronomy and Space Sciences
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• v.25 no.2
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• pp.157-166
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• 2008

We have investigated a statistical relationship between sawtooth oscillations and geomagnetic storms during 2000-2004. First of all we selected a total of 154 geomagnetic storms based on the Dst index, and distinguished between different drivers such as Coronal Mass Ejection (CME) and Co-rotating Interaction Region (CIR). Also, we identified a total of 48 sawtooth oscillation events based on geosynchronous energetic particle data for the same 2000-2004 period. We found that out of the 154 storms identified, 47 storms indicated the presence of sawtooth oscillations. Also, all but one sawtooth event identified occurred during a geomagnetic storm interval. It was also found that sawtooth oscillation events occur more frequently for storms driven by CME $({\sim}62%)$ than for storms driven by CIR $({\sim}30%)$. In addition, sawtooth oscillations occurred mainly $({\sim}82%)$ in the main phase of storms for CME-driven storms while they occurred mostly $({\sim}78%)$ during the storm recovery phase for CIR-driven storms. Next we have examined the average characteristics of the Bz component of IMF, and solar wind speed, which were the main components for driving geomagnetic storm. We found that for most of the sawtooth events, the IMF Bz corresponds to -15 to 0 nT and the solar wind speed was in the range of $400{\sim}700km/s$. We found that there was a weak tendency that the number of teeth for a given sawtooth event interval was proportional to the southward IMF Bz magnitude.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.58 no.4
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• pp.416-423
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• 2013

Germination is controlled by internal factors of seeds and external factors such as water, temperature and light. We investigated the relationship between germination characteristics of four waxy rice cultivars and patterns of water uptake, antioxidant enzymes and free soluble sugars during early imbibition. Seed viabilities by tetrazolium test of four different rice cultivars were higher than 95% and germination rates of the hulled rice seeds were on 95% average. However, germination rate of intact rice among four cultivars showed a big difference depending on temperature. Water uptake of hulled and intact rice seeds during imbibition reached a stationary phase at around 30% moisture content. Although rates of water uptake were faster in hulled rice and high temperature than intact rice and low temperature condition, difference of those among cultivars was greater under low temperature than high temperature. The time required for rice seeds to uptake 30% water was negatively correlated with percentage of germination, germination energy, germination speed and mean germination time. Guaiacol peroxidase activity at 24h of imbibition was correlated with germination energy and germination speed but not percentage of germination. Catalase activity, soluble protein and maltose concentration at 24h of imbibition were not correlated with characteristics of germination. These results suggest that a time required for rice seeds to uptake 30% of water significantly correlated with germination and guaiacol peroxidase activity during early imbibition plays an important role in initiation of germination.