• Korean Journal of Materials Research
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• v.34 no.2
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• pp.111-115
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• 2024

Silicon carbide (SiC) has emerged as a promising material for next-generation power semiconductor materials, due to its high thermal conductivity and high critical electric field (~3 MV/cm) with a wide bandgap of 3.3 eV. This permits SiC devices to operate at lower on-resistance and higher breakdown voltage. However, to improve device performance, advanced research is still needed to reduce point defects in the SiC epitaxial layer. This work investigated the electrical characteristics and defect properties using DLTS analysis. Four deep level defects generated by the implantation process and during epitaxial layer growth were detected. Trap parameters such as energy level, capture-cross section, trap density were obtained from an Arrhenius plot. To investigate the impact of defects on the device, a 2D TCAD simulation was conducted using the same device structure, and the extracted defect parameters were added to confirm electrical characteristics. The degradation of device performance such as an increase in on-resistance by adding trap parameters was confirmed.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.36 no.2
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• pp.61-69
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• 2024

Wave conditions are crucial for offshore wind farm design, particularly in determining structural loads and layout. However, there is limited wave hindcasting research for the Wangdeungdo Island area, a potential offshore wind site. This study used the MIKE21 model for a year-long wave hindcast around Wangdeungdo in 2021. Validation showed high reproducibility for significant wave heights with RMSE values of 0.177 and 0.225 and Pearson correlations of 0.971 and 0.970 at Sangwangdeungdo and Buan buoys. Subsequent analysis of the wave characteristics near Wangdeungdo indicated significant seasonal variations and differences in maximum significant wave heights across locations, which are expected to significantly impact the design loads for offshore wind structures.

• Development and Reproduction
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• v.27 no.3
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• pp.101-115
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• 2023

Environmental factors impact oyster growth, condition, and gonadal development, which is linked to gamete characteristics observed through histology. The reproductive cycle of bivalves is related to energy storage and utilization. Therefore, in this study, the year-round growth change and gonadal development of oysters were observed using histological analysis, and the biochemical composition changes were confirmed. The oysters used in this study are being nurtured in Gadeok-do, and 40 oysters were randomly sampled monthly from March 2021 to February 2022. Result of histological analysis of gonads, oysters were showed early development from December to February, late development from March and April, mature and ripe from May to July, spawned from August to October, and spent from November to December. Condition index values of oysters decreased in summer and autumn and increased again when entered the spent after spawning. The protein content of oysters was high in May, the maturity period, and the lipid content decreased during the spawning period. In addition, EPA and DHA, the major fatty acids of oysters, were low during the spawning period and high during the maturation period. As a result, this study suggested a close relationship between changes in oyster growth, biochemical composition, and the reproductive cycle.

• Elastomers and Composites
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• v.59 no.2
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• pp.51-63
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• 2024

Polypropylene (PP) is a commodity plastic that is widely used owing to its cost-effectiveness, lightweight nature, easy processability, and outstanding chemical and thermomechanical characteristics. However, the imperative to address energy and environmental crises has spurred global initiatives toward a circular economy, necessitating sustainable alternatives to traditional fossil-fuel-derived plastics. In this study, we conducted a series of comparative investigations of bio-based polypropylene (bio-PP) blends with current PP of the same and different grades. An extrusion-based processing methodology was employed for the bio-PP composites. Talc was used as an active filler for the preparation of the composites. A comparative analysis with the current petroleum-based PP indicated that the thermal properties and tensile characteristics of the bio-PP blends and composites remained largely unaltered, signifying the feasibility of bio-PP as a potential substitute for the current PP. To achieve a higher Young's modulus, elongation at break (EAB), and melt flow index (MFI), we prepared different composites of PP of different grades and bio-PP with varying talc contents. Interestingly, at higher biomass contents, the composites exhibited higher MFI and EAB values with comparable Young's moduli. Notably, the impact strengths of the composites with various biomass and talc contents remained unaltered. In-depth investigations through surface analysis confirmed the uniform dispersion of talc within the composite matrix. Furthermore, the moldability of the bio-PP composites was substantiated by comprehensive rheological property assessments encompassing shear rate and shear viscosity. Thus, from these outcomes, the fabricated bio-PP-based composites could be an alternative to petroleum-based PP composites for sustainable automobile applications.

• Journal of Internet Computing and Services
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• v.25 no.2
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• pp.79-92
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• 2024

ChatGPT, as a representative chatbot leveraging generative artificial intelligence technology, is used valuable not only in scientific and technological domains but also across diverse sectors such as society, economy, industry, and culture. This study conducts an explorative analysis of user sentiments and needs for ChatGPT by examining global social media discourse on Reddit. We collected 10,796 comments on Reddit from December 2022 to August 2023 and then employed keyword analysis, sentiment analysis, and need-mining-based topic modeling to derive insights. The analysis reveals several key findings. The most frequently mentioned term in ChatGPT-related comments is "time," indicative of users' emphasis on prompt responses, time efficiency, and enhanced productivity. Users express sentiments of trust and anticipation in ChatGPT, yet simultaneously articulate concerns and frustrations regarding its societal impact, including fears and anger. In addition, the topic modeling analysis identifies 14 topics, shedding light on potential user needs. Notably, users exhibit a keen interest in the educational applications of ChatGPT and its societal implications. Moreover, our investigation uncovers various user-driven topics related to ChatGPT, encompassing language models, jobs, information retrieval, healthcare applications, services, gaming, regulations, energy, and ethical concerns. In conclusion, this analysis provides insights into user perspectives, emphasizing the significance of understanding and addressing user needs. The identified application directions offer valuable guidance for enhancing existing products and services or planning the development of new service platforms.

• Korean Journal of Community Nutrition
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• v.4 no.2
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• pp.207-218
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• 1999

The increased number of elderly in Korea presents great challenges for community nutrition programs. Strategies to enhance elderly nutrition are needed, as well as dietary advice that are reality-based and tailored to the need of the elderly. The purpose of this study was to evaluate the overall effectiveness of an elderly nutrition improvement program(ENIP), by assessing changes in nutrition knowledge, attitudes, and behavior after program completion. ENIP was conducted in Suwon for 4 months in 1998 at 5 centers for the elderly. The program provided individual nutrition counseling and brief biweekly group education sessions. To stimulate participation and motivation, the elderly in two centers were served free milk packs(200ml) three time a week during the program(milk＋education group), and the elderly in 3 other centers were served yoghurt on the program day(education group). Altogether, 102 subjects finished the program(milk＋education group 67 ; education group 35). Data about nutrition knowledge, dietary attitudes, diet records(24 hour recall) and dietary habit was collected before(baseline) and after the program(follow-up). The Drop-out rate for the milk＋education group(2.9%) was significantly lower than that for the education group(30.0%)(p<.001). The Nutrition Knowledge fo females milk＋education group increased significantly after the program, but no significant differences were observed in other groups. Over 60% of all the elderly showed positive responses to the healthy eating attitudes. Energy, protein, vitamin A, riboflavin, Calcium and Potassium intakes improved in the male milk＋education group. The Vitamin C intake improved in the male education group. Energy and vitamin A intakes improved in the female milk＋education group and energy, vitamin A, thiamin, riboflavin, niacin, Ca nad P in the female education group. A stepwise multiple regression analysis was performed to examine the effects of food intake changes on overall nutrient quality. For all elderly, the fish intake explained 12.6% of the variance, followed by candy intake and vegetable intake(model $R^2$=19.6%). Dietary habits such as meal time regularity and salty food reduction were markedly improved in both groups. Sixty-one percent of the milk＋education subjects stated their participation was voluntary and active, while 51% of education subjects did. Sixty four percent of the subjects stated their interest on diet increased remarkably through program participation. Considering the results, it is conjectured that ENIP had a great impact on nutrient intake, dietary attitudes and habits. Milk supplement showed no direct effects on elderly nutrition improvement, but it encouraged the program by reducing drop-out rates and inducing voluntary participation. Therefore milk supplement could enhance the community nutrition education program. Moreover it is strongly suggested that the ENIP be expanded to other communities.

• Journal of the Korean Solar Energy Society
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• v.31 no.3
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• pp.8-16
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• 2011

The objective of this study is to analyze the characteristic of thermal environment in the summer season by conducting the field observation of temperature, relative humidity, and globe temperature in some parts of the city. Observation point was divided to a densely populated area, a residential area, a green area, a waterfront green area and a suburban district by the distribution ratio of green area. In this study, the correlation between maximum temperature and globe temperature, study on index for intensity of the tropical night and the temperature distribution characteristic of measurement points by the distribution ratio of green area were analyzed. The results of this study are as follows. (1) The difference between temperature and globe temperature by the distribution ratio of green area is confirmed. The difference of nighttime is more clearly that of daytime. (2) The average temperature and globe temperature of the densely populated area($29.2^{\circ}C$, $33.7^{\circ}C$) are higher than that of the waterfront green area($27.9^{\circ}C$, $32.0^{\circ}C$) by $1.3^{\circ}C$ and $1.7^{\circ}C$, respectively. (3) The number of tropical nights has different days of tropical nights by the distribution ratio of green area of 17days for the Daegu weather station, 14days for adensely populated area, 14days for a residential area, 6days for a green area, 2days for a waterfront green area, and 2days for a suburban district. (4) The results of the slope of trend line for the effects of the temperature on globe temperature change and the intercept for the size of the impact of radiant energy gained around by the analysis of the correlation between the maximum temperature and globe temperature can be utilized objective evaluation index of the each point's artificial effects.

• Korean Chemical Engineering Research
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• v.55 no.4
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• pp.456-466
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• 2017

This work investigated the particle morphology change to difference in milling media in a metal based composite fabrication process using a stirred ball mill with ball behavior of DEM simulation. A simulation of the three dimensional motion of grinding media in the stirred ball mill for the research of grinding mechanism to clarify the force, kinetic energy, and medium velocity of grinding media were calculated. In addition, the rotational speed of the stirred ball mill was changed to the experimental conditions for the composite fabrication, and change of the input energy was also calculated while changing the ball material, the flow velocity, and the friction coefficient under the same conditions. As the rotating speed of the stirred ball mill increased, the impact energy between the grinding media to media, media to wall, and media and the stirrer increased quantitatively. Also, we could clearly analyze the change of the particle morphology under the same experimental conditions, and it was found that the ball behavior greatly influences in the particle morphology changes.

• Tunnel and Underground Space
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• v.25 no.2
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• pp.168-185
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• 2015

The thermal-hydrological-mechanical (T-H-M) behavior of rock mass surrounding a large-scale high-temperature cavern thermal energy storage (CTES) at a shallow depth has been investigated, and the effects of hydrological conditions such as water table and rock permeability on the behavior have been examined. The liquid saturation of ground water around a storage cavern may have a small impact on the overall heat transfer and mechanical behavior of surrounding rock mass for a relatively low rock permeability of $10^{-17}m^2$. In terms of the distributions of temperature, stress and displacement of the surrounding rock mass, the results expected from the simulation with the cavern below the water table were almost identical to that obtained from the simulation with the cavern in the unsaturated zone. The heat transfer in the rock mass with reasonable permeability ${\leq}10^{-15}m^2$ was dominated by the conduction. In the simulation with rock permeability of $10^{-12}m^2$, however, the convective heat transfer by ground-water was dominant, accompanying the upward heat flow to near-ground surface. The temperature and pressure around a storage cavern showed different distributions according to the rock permeability, as a result of the complex coupled processes such as the heat transfer by multi-phase flow and the evaporation of ground-water.

• Journal of the Korean earth science society
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• v.43 no.2
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• pp.265-282
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• 2022

This study analyzes the impact of long-range transport of biomass burning emissions from northeastern China on the concentration of particulate matter of diameter less than 10 ㎛ (PM₁₀) in Korea using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). Korea was impacted by anthropogenic emissions from eastern China, dust storms from northern China and Mongolia, and biomass burning emissions from northeast China between April 4-and 7, 2020. The contributions of long-range PM₁₀ transport were calculated by separating biomass burning emissions from mixed air pollutants with anthropogenic emissions and dust storms using the zeroing-out method. Further, the radiation energy budget over land and sea around the Korean Peninsula was analyzed according to the distribution of biomass burning emissions. Based on the WRF-Chem simulation during April 5-6, 2020, the contribution of long-range transport of biomass burning emissions was calculated as 60% of the daily PM₁₀ average in Korea. The net heat flux around the Korean Peninsula was in a negative phase due to the influence of the large-scale biomass burning emissions. However, the contribution of biomass burning emissions was analyzed to be <45% during April 7-8, 2020, when the anthropogenic emissions from eastern China were added to biomass burning emissions, and PM₁₀ concentration increased compared with the concentration recorded during April 5-6, 2020 in Korea. Furthermore, the net heat flux around the Korean Peninsula increased to a positive phase with the decreasing influence of biomass burning emissions.