• The Journal of the Korea institute of electronic communication sciences
• /
• v.17 no.4
• /
• pp.595-606
• /
• 2022

Korea has the characteristics of traditional power system such as large-scale power generation and large-scale power transmission systems, including 20 GW large-scale power generation complexes in several regions with unit generator capacity exceeding 1.4 GW, 2-3 ultra-high-voltage transmission lines that transport power from large-scale power generation complexes, and 6 ultra-high-voltage transmission lines that transport power from non-metropolitan areas to the metropolitan area. Due to the characteristics of the power system, the penetration level for renewable energy is low, but due to frequency stability issue, some generators are reducing the output of generators. In the future, the issue of maintaining the stability of the power system is expected to emerge as the most important issue in accordance with the policy of expanding renewable energy. When non-inertial inverter-based renewable energy, such as solar and wind power, surges rapidly, the means to improve the power system stability in an independent system is to install a natural inertial resource synchronous condenser (SC) and a virtual inertial resource BESS in the system. In this study, we analyzed the effect of renewable energy on power system stability and the BESS effect to maintain the minimum frequency through a power system simulation. It was confirmed that the BESS effect according to the power generation constraint capacity reached a maximum of 122.81 %.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.35 no.5
• /
• pp.299-308
• /
• 2022

This study was conducted to predict the tendency for heat exchange and boil-off gas (BOG) in a liquefied hydrogen tank under sloshing excitation. First, athe fluid domain excited by sloshing was modeled using a multiphase-thermal flow domain in which liquid hydrogen and hydrogen gas are in the saturated state. Both the the volume of fluid (VOF) and Eulerian-based multi-phase flow methods were applied to validate the accuracy of the pressure prediction. Second, it was indirectly shown that the fluid velocity prediction could be accurate by comparing the free surface and impact pressure from the computational fluid dynamics with those from the experimental results. Thereafter, the heat ingress from the external convective heat flux was reflected on the outer surfaces of the hydrogen tank. Eulerian-based multiphase-heat flow analysis was performed for a two-dimensional Type-C cylindrical hydrogen tank under rotational sloshing motion, and an inflation technique was applied to transform the fluid domain into a computational grid model. The heat exchange and heat flux in the hydrogen liquid-gas mixture were calculated throughout the analysis,, whereas the mass transfer and vaporization models were excluded to account for the pure heat exchange between the liquid and gas in the saturated state. In addition, forced convective heat transfer by sloshing on the inner wall of the tank was not reflected so that the heat exchange in the multiphase flow of liquid and gas could only be considered. Finally, the effect of sloshing on the amount of heat exchange between liquid and gas hydrogen was discussed. Considering the heat ingress into liquid hydrogen according to the presence/absence of a sloshing excitation, the amount of heat flux and BOG were discussed for each filling ratio.

• Membrane Journal
• /
• v.33 no.4
• /
• pp.191-200
• /
• 2023

Polyethersulfone (PES) is a widely employed membrane material for water and industrial purification applications owing to its hydrophilicity and ease of phase separation. However, PES membranes and filters prepared using the nonsolvent induced phase separation method often encounter significant flux decline due to pore clogging and cake layer formation on the dense membrane surfaces. Our investigation revealed that tight microfiltration or loose ultrafiltration membranes can be subject to physical fouling due to the formation of a dense skin layer on the bottom side caused by water intrusion to the gap between the shrank membrane and the substrate. To investigate the effect of the bottom surface porosity on membrane fouling, two membranes with the same selective layers but different sub-layer structures were prepared using single and double layer casting methods, respectively. The double layered PES membrane with highly porous bottom surface showed high flux and physical fouling tolerance compared to the pristine single layer membrane. This study highlights the importance of physical optimization of the membrane structure to prevent membrane fouling.

• Journal of Life Science
• /
• v.33 no.9
• /
• pp.754-765
• /
• 2023

Exosomes are a type of extracellular vesicle containing proteins and messenger and microRNAs; they are secreted by all cell types. Once released, exosomes are selectively taken up by other cells adjacent or at a distance, releasing their contents and reprogramming the target cells. Since exosomes are natural vesicles produced by cells as small sizes, it is generally accepted that exosomes have a non-toxic nature and non-immunogenic behaviors. Recently, exosomes have elicited scientific attention as drug delivery vehicles to the central nervous system. The central nervous system has a blood-brain barrier that makes it difficult for drugs to penetrate. Thus, the blood-brain barrier has been a major obstacle to the development of drugs for treating neurodegenerative diseases. However, accumulating evidence suggests that exosomes can cross the blood-brain barrier primarily through transcytosis. Consequently, exosomes are expected to become a new delivery vehicle that can cross the blood-brain barrier and deliver drugs into the brain parenchyma. In addition, since different types of exosomes are secreted depending on the cell type and disease state, exosomes can also be utilized as biomarkers for the diagnosis of diseases in the central nervous system. In this review, we summarized recent research trends on exosomes, including clinical trials as biomarkers and treatment options for diseases in the central nervous system.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2020.06a
• /
• pp.106-106
• /
• 2020

물 이용 측면에서 유출해석은 강수, 증발산, 침투, 유출 등 물 순환의 핵심이다. 또 기상자료는 증발산량을 산정하는데 꼭 필요하다. 그러나 해외 수자원 사업에서 기상자료가 없어 곤란을 겪는 경우가 많다. 여기서, NASA POWER에서 전지구 0.5° 격자로 제공하는 위성기반의 일 기상자료를 이용한 증발산량과, 지상의 기상자료를 이용한 증발산량을, 각각 일 유출 모형에 적용한 결과를 비교하였다. 유역면적 4,134 ㎢인 대청댐 유역에 1984년부터 2001년까지 일별 유입량을 모의하고 관측 유입량과 비교하고, R², RMSE, NSE 등으로 평가하였다. 지상의 기상관측소는 위도 36.21°, 경도 127.34°인 대전 관측소를, 위성자료는 대전 지점과 동일한 위치의 경위도의 기상자료를 적용하였고, 일 증발산량은 Penman-Monteith 방법으로, 일 유출량은 ONE 모형에 의해 모의하였다. 강수량을 대청댐 유역 면적강수량을 적용한 경우, 지상 기상자료를 적용하여 유입량을 모의한 결과는 연평균하여 연 유입량 668.1 mm, 일 최대 82.9 mm, 유출률 56.1%(관측은 연 강수량 1,191.3 mm, 연 유입량 668.3 mm, 일 최대 87.0 mm, 유출률 56.1%)로 나타났고, R² 0.805, RMSE 2.425, NSE 0.802였고, 위성 기상자료를 적용하여 유입량을 모의한 결과는 연평균하여 연 유입량 668.4 mm, 일 최대 83.7 mm, 유출률 57.8%로 나타났고, R² 0.803, RMSE 2.431, NSE 0.801였다. 또한, 강수량을 위성 제공의 강수량을 적용한 경우, 지상 기상자료를 적용하여 유입량을 모의한 결과는 연평균하여 연 유입량 718.0 mm, 일 최대 97.7 mm, 유출률 56.7%(관측은 연 강수량 1,265.3 mm, 유출률 52.8%)로 나타났고, R² 0.582, RMSE 3.524, NSE 0.581였고, 위성 기상자료를 적용하여 유입량을 모의한 결과는 연평균하여 연 유입량 741.5 mm, 일 최대 99.0 mm, 유출률 58.6%로 나타났고, R² 0.578, RMSE 3.541, NSE 0.577였다. 결과적으로 위성 기상자료를 이용하여 증발산량을 산정하여 일 유출해석에 적용한 결과는 지상 기상자료를 이용한 경우와 거의 같은 값을 나타내, NASA POWER가 제공한 기상자료의 활용성은 매우 높게 나타났다. 그러나 위성 제공 강수량의 활용은 R², RMSE, NSE 등의 지표가 낮게 나타나, 신중하게 검토되어야 할 것으로 평가하였다.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.43 no.1
• /
• pp.21-32
• /
• 2023

Interrill erosion dominates in forest areas, and the erosion rate in surface-disturbed areas is significantly increased by the development and expansion of rill. In this study, soil erosion experiments using simulated rainfall and inflow were performed to understand the development and the micromorphological changes of rill on steep slopes. The characteristic factors of the micromorphology, such as the rill cross section, rill volume, rill density, rill order, and rill sharpness, were analyzed according to steepness and location (upper or lower) of slope. The head-cut of the simultaneous incised rills by rainfall simulation moved rapidly upslope, and the randomly developed rills expanded deeply and widely with their connection. The rill cross section evolved to downslope gradually increased. The rill volume occupied about 78 % of the sediment volume, confirming that the contribution of the sediment from the rill erosion is greater than that of the interrill erosion. Although the rate of increase in rill order slowed as the slope increased, the total length and density of the rill generally increased. As the slope increased from 15° to 20°, the bed incision of rills became larger than the sidewall expansion, and the rill sharpness increased by 1.6 times. The runoff coefficient on the lower slope decreased by 12.3 % than that on the upper slope. It was evaluated that the subsoil exposures and formation changes by the rill expansion increased the infiltration rate. Although the sediment accompanying the rills generally increased with slope increase, it was directly influenced by the hydraulic velocity of enhanced rill with the local convergence and expansion in the process of the rill evolution.

• Proceedings of the Korea Contents Association Conference
• /
• 2006.11a
• /
• pp.145-148
• /
• 2006

This study aimed at preventing women from suffering from health problems and stress due to excessive lookism and encouraging them to participate in sports activities to form desirable body image and eventually to live a healthy and sound life. To achieve this goal, this study formed a population with members of sports centers located in Seoul and Daejeon areas as of 2006 and made a sample of 450 participants in physical exercise at a sports center through stratified cluster random sampling and that of 450 non-participants through a survey with mothers and sisters of those students from elementary and secondary schools within the areas for sampling the participants' group, thereby analyzing the data on a total of 900 persons. A questionnaire was used as a tool to collect data; a reliability test presented weight-, health-, and figure-related factors as a=.807, a=.819, and a=.784, respectively. This study used such statistical analysis methods as t-test, One-way ANOVA, and the Analysis of Covariance to analyze data. This study produced the following conclusions through these research methods and procedure. Pticipation in physical exercise has a positive effect on body image. Pticipation in physical exercise at a sports center show higher satisfaction with body image than non-participats.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
• /
• v.4 no.2
• /
• pp.117-131
• /
• 2006

A coupled T-H-M(Thermo-Hydro-Mechanical) analysis was carried out for KENTEX (KAERI Engineering-scale T-H-M Experiment for Engineered Barrier System), which is a facility for validating the coupled T-H-M behavior in the engineered barrier system of the Korean reference HLW(high-level waste) disposal system. The changes of temperature, water saturation, and stress were estimated based on the coupled T-H-M analysis, and the influence of the types of mechanical constitutive material laws was investigated by using elastic model, poroelastic model, and poroelastic-plastic model. The analysis was done using ABAQUS, which is a commercial finite element code for general purposes. From the analysis, it was observed that the temperature in the bentonite increased sharply for a couple of days after heating the heater and then slowly increased to a constant value. The temperatures at all locations were nearly at a steady state after about 37.5 days. In the steady state, the temperature was maintained at $90^{\circ}C$ at the interface between the heater and the bentonite and at about $70^{\circ}C$ at the interface between the bentonite and the confining cylinder. The variation of the water saturation with time in bentonite was almost same independent of the material laws used in the coupled T-H-M processes. By comparing the saturation change of T-H-M and that of H-M(Hydro-Mechanical) processes using elastic and poroelastic material mod31 respectively, it was found that the degree of saturation near the heater from T-H-M calculation was higher than that from the coupled H-M calculation mainly because of the thermal flux, which seemed to speed up the saturation. The stresses in three cases with different material laws were increased with time. By comparing the stress change in H-M calculation using poroelasetic and poroelasetic-plastic model, it was possible to conclude that the influence of saturation on the stress change is higher than the influence of temperature. It is, therefore, recommended to use a material law, which can model the elastic-plastic behavior of buffer, since the coupled T-H-M processes in buffer is affected by the variation of void ratio, thermal expansion, as well as swelling pressure.

• Restorative Dentistry and Endodontics
• /
• v.32 no.3
• /
• pp.208-221
• /
• 2007

The fracture toughness test is believed as a clinically relevant method for assessing the fracture resistance of the dentinal restoratives. The objectives of this study were to measure the fracture toughness $(K_{1C})$ and microtensile bond strength of dentin-resin composite interface and compare their relationship for their use in evaluation of the integrity of the dentin-resin bond. A minimum of six short-rod specimens for fracture toughness test and fifteen specimens for microtensile bond strength test was fabricated for each group of materials used. After all specimens storing for 24 hours in distilled water at $37^{\circ}C$, they were tensile-loaded with an EZ tester universal testing machin. Statistical analysis was performed using ANOVA and Tukey's test at the 95% confidence level, Pearson's coefficient was used to verify the correlation between the mean of fracture toughness and microtensile bond strength. FE-SEM was employed on fractured surface to describe the crack propagation. Fracture toughness value of Clearfil SE Bond (SE) was the highest, followed by Adper Single Bond 2 (SB), OptiBond Solo (OB), ONE-STEP PLUS (0S), ScotchBond Multi-purpose (SM) and there was significant difference between SE and other 4 groups (p < 0.05). There were, however, no significant difference among SB, OB, OS, SM (p > 0.05). Microtensile bond strength of SE was the highest, followed by SB, OB, SM, OS and OS only showed significant lower value (p < 0.05). There was no correlation between fracture toughness and microtensile bond strength values. FE-SEM examination revealed that dentin bonding agent showed different film thickness and different failure pattern according to the film thickness. From the limited results of this study, it was noted that there was statistically no correlation between K1C and ${\mu}TBS$. We can conclude that for obtaining the reliability of bond strength test of dentin bonding agent, we must pay more attention to the test procedure and its profound scrutiny.

• Journal of agriculture & life science
• /
• v.46 no.6
• /
• pp.117-126
• /
• 2012

This study carried out on the manufacturing of pidan. The production of pidan can be one of solutions for over-produced eggs and stable egg price. For the alkali-pickling solution for manufacturing of Pidan, the tested concentration of NaOH and NaCl were respectively as 3, 5, 7% and 5, 10, 15, 20%, and examined every 2 days for 14days. According to the results, pH value of alkali-pickling solution was increased by the increment of NaOH concentration and the pickling period, and was decreased by the increment of NaCl concentration. The pH value of egg yolk was increased by the increment of NaOH concentration, but it was not significantly different by the NaCl concentration. By the increment of NaOH and NaCl concentrations, the alkali infiltration in egg yolk and egg white was accelerated. Furthermore, the weight change of the eggs in the alkali-solution has no effects on manufacturing of Pidan. Liquefied albumen showed significant differences by NaOH concentration rather than that of NaCl. There was no liquefied albumen for 14days at 3% of NaOH, but it was found between 11-12days at 5% and 8-10days at 7%, respectively. The pH values of egg white when it was liquefied albumen were between 11.8 and 12.0. Pidan was made by heat treatment after 6-7days dipped in the solution at the concentration of 7%, about 10days at 5%, and 12-14days at 3% of NaOH, respectively. Although, the period of manufacturing of Pidan was saved by the increment of NaOH concentration, liquefied albumen was accelerated and the food preference was decreased by ammonia odor. Therefore, the suitable concentration of NaOH is between 3 and 5%, and that of NaCl is between 5 and 10% due to the effect of salinity by the soaking period. Through this study, optimal pickling solution and dipping time for manufacturing of Pidan was figured out, and also find out that it can save a time about 15days for manufacturing of Pidan.