• Korean Journal of Materials Research
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• v.9 no.6
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• pp.577-582
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• 1999

In order to make the electroconductive $Si_3N_4$-TiN composities, the Si-Ti(N) compacts were nitrided at $1450^{\circ}C$ for 20hours, and then they were post-sintered by a gas-pressure-sintering technique at 1TEX>$1950^{\circ}C$ for 3.5 hours. As starting powders, commercial si powder of about $10\mu\textrm{m}$, two types of Ti powders of 100 and 325 mesh, and fine-sized TiN of $2.5\mu\textrm{m}$ powders were used. In the $Si_3N_4$-TiN sintered bodies used Ti powders, the relative density and fracture strength and electrical conductivity are low due to the existence of large amounts of coarse pores. However, in the $Si_3N_4$-TiN composite used TiN powder, the fracture toughness, fracture strength and electrical resistivity were $5.0MPa{\cdot}m^{1/2}$, 624MPa and $1400{\omega}cm$, respectively. The dispersion of TiN particles in the composite inhibited the growth of $Si_3N_4$ in the shape of rod and made strong strain field contrasts at the $Si_3N_4$-TiNinterfaces. It was recognized that microstructural control is required to improve the electrical conductivity and mechanical properties of $Si_3N_4$-TiN composites by dispersing TiN particles homogeneously.

• Applied Chemistry for Engineering
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• v.31 no.2
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• pp.153-163
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• 2020

Compared to gaeous hydrogen, liquid hydrogen has approximately 1/800 volume, 800 times higher volumetric energy density at the same pressure, and the advantage of lower explosion risk and easier transportation than gaseous hydrogen. However, hydrogen liquefaction requires larger scale facility investment than simple compression storage method. Therefore, the research on energy-saving hydrogen liquefaction processes is highly necessary. In this study, helium/neon (mole ratio 80 : 20) refrigeration cycle was investigated as the main refrigeration process for hydrogen liquefaction. Process simulation for less energy consumption were carried out using PRO/II with PROVISION V10.2 of AVEVA. For hydrogen liquefaction, energy consumption was compared in three cases: Using a helium/neon refrigerant cycle, a SMR+helium/neon refrigerant cycle, and a C3-MR+helium/neon refrigerant cycle. As a result, the total power consumptions of compressors required to liquefy 1 kg of hydrogen are 16.3, 7.03 and 6.64 kWh, respectively. Therefore, it can be deduced that energy usage is greatly reduced in the hydrogen liquefaction process when the pre-cooling is performed using the SMR process or the C3MR process, which have already been commercialized, rather than using only the helium/neon refrigeration cycle for the hydrogen liquefaction process.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.4
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• pp.718-725
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• 2017

A liquid storage tank is one of the most important structures in industrial complexes dealing with chemicals, and its structural damage due to an earthquake may cause a disastrous event such as the leakage of hazardous materials, fire, and explosion. It is thus essential to assess the seismic fragility of liquid storage tanks and prepare for seismic events in advance. When a liquid storage tank is oscillated by a seismic load, the hydrodynamic pressure caused by the liquid-structure interaction increases the stress and causes structural damage to the tank. Meanwhile, the seismic fragility of the structure can be estimated by considering the various sources of uncertainty and calculating the failure probabilities in a given limiting state. To accurately evaluate the seismic fragility of liquid storage tanks, a sophisticated finite element analysis is required during their reliability analysis. Therefore, in this study, FERUM-ABAQUS, a recently-developed computational platform integrated with commercial finite element and reliability analysis software packages, is introduced to perform the finite element reliability analysis and calculate the failure probability of a liquid storage tank subjected to a seismic load. FERUM-ABAUS allows for automatic data exchange between these two software packages and for the efficient seismic fragility assessment of a structure. Using this computational platform, the seismic fragility curve of a liquid storage tank is successfully obtained.

• Journal of the Korean Applied Science and Technology
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• v.34 no.4
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• pp.866-873
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• 2017

Exhaust regulations of automobile are being reinforced increasingly as environmental problems issues came to the fore by industrial development. However, it is known that the exhaust emission is not only influenced by the system of automobile but also the fuel properties. In particular, high-performance engines have required high-performance fuels with high lubricity as CRDI engines(diesel engine) have been developed and commercialized. This paper have examined that the fuel property variations affect a major parts and an exhaust gas of automobile. It was confirmed that the high pressure pump, the injector and the DPF(diesel particulate filter) were damaged and fuel efficiency was get worse due to use the fuel of lacking lubricity property($651{\mu}m$/quality standard: less in $400{\mu}m$). In addition, through an iron component was detected in the broken DPF, it was estimated that the breakage of the DPF was caused by the excessive exhaust of the particulate matter due to the iron component of the fuel.

• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.71-71
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• 2018

Sea pollution accidents have been occurred due to the increase of marine ship traffic. Oil spill from the hull hole induced by tanker collision results in the huge sea pollution. Proper and prompt reaction on such oil spill disaster is needed to minimize the damage. Thru-hull emergency wood plug is typically used to manually close small holes, while it is required to develop some mechanical devices for closing large holes in the hull due to huge fluid pressure. Accurate estimation of oil discharge and velocity from such holes are important to develop proper device to control hull hole damage. High resolution CFD modeling investigation on the configurations of hull hole of 7.5 m initial depth and 30 cm diameter, which was observed in the oil spill accident of the Hebei Sprit off the west coast of Korea in 2007, has been carried out to compute the oil spill velocity distribution in terms of flow depth. Friction loss due to the viscous flow and the discharge coefficient of crude oil with specific gravity SG = 0.85 and viscosity of $4-12cP(mPa{\cdot}s)$ at the temperature of $20^{\circ}C-100^{\circ}C$ are presented in terms of Reynolds number based on the results of high-resolution CFD modeling.

• Food Science and Preservation
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• v.25 no.1
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• pp.155-163
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• 2018

The present study was carried out to investigate the physicochemical properties of hot water extracts of red ginseng powder prepared by two-stage hot air drying method using steamed ginseng and steaming liquid for 2.5 h under high-temperature and high-pressure autoclave condition. The total polyphenols, total flavonoids, total sugar, acid polysaccharides and crude saponin in hot water extracts from red ginseng powder were analyzed and determined, and the flavor components of ginseng were measured using color difference meter and an electronic tongue. The total polyphenol, total flavonoid, total polysaccharide, and acid polysaccharide of the red ginseng hot water extract obtained by autoclaving (ARG) were 9.06 mg GAE/g, 3.38 mg NE/g, 35.22 g/100 g, and 10.90 g/100 g, respectively. The final contents of the total polyphenols, total flavonoids, crude saponin were higher than those determined using other red ginseng methods; the time required for steamed red ginseng production reduced. The total ginsenoside content of ginseng including Rb1 was 10.69 mg/g, which is the lowest ARG. The processing conditions affected the conversion to ginsenosides unique to red ginseng. Red ginseng and steaming liquid obtained from the autoclave are expected to be in need for non-food materials and products as well as foods by improving the flavor components through conversion of red ginseng components into low molecular weight.

• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.6
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• pp.659-677
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• 2022

Hydrogen is emerging as a next-generation energy source and development and supply of FCEV (hydrogen fuel cell electric vehicle) is expected to occur rapidly. Accordingly, measures to respond to hydrogen car accidents are required and researches on the safety of hydrogen cars are being actively conducted. In this study, In this study, we developed a hydrogen car accident scenarios suitable for domestic conditions for the safety evaluation of hydrogen car in road tunnels through analysis of existing experiments and research data and analyzed and presented the hazard distance according to the accident results of the hydrogen car accident scenarios. The accident results according to the hydrogen car accident scenario were classified into minor accidents, general fires, jet flames and explosions. The probability of occurrence of each accident results are predicted to be 93.06%, 1.83%, 2.25%, and 2.31%. In the case of applying the hydrogen tank specifications of FCEV developed in Korea, the hazard distance for explosion pressure (based on 16.5 kPa) is about 17.6 m, about 6 m for jet fire, up to 35 m for fireball in road tunnel with a standard cross section (72 m²).

• Journal of Aerospace System Engineering
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• v.15 no.5
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• pp.98-105
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• 2021

This study presented the results of the static load tests conducted to verify the structural robustness of the composite oxidant tank for a space launch vehicle. First, we introduced the test equipment used in the static load test of the composite oxidant tank, and then described the test requirements that the composite oxidant tank must satisfy. In addition, we presented a test set-up diagram consisting of the static load test fixture, hydraulic pressure, control equipment, and data acquisition equipment, and the load profile of the static load test of the composite oxidant tank consisting of shear, equivalent compression, bending, and combination tests. As a result of load control, we verified the reliability of this test by showing the errors between the input load and the feedback load in each channel according to the increase of the test load, and the feedback error between the channel A and channel B of load cell in each load actuator. As a result of the static load test, the load of the actuator was properly controlled within the allowable error range in each test, and we found that the test specimen did not cause damage or buckling that causes significant structural defects in the required load.

• Journal of the Korea Convergence Society
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• v.12 no.5
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• pp.345-354
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• 2021

This study was conducted to identify the factors affecting the quality of life of the elderly according to economic activity. The subjects of this study were 5,991 elderly aged 65 years or older among subjects of the 7th National Health and Nutrition Survey. The variables of this study consisted of demographic characteristics, physical and psychological factors, data analysis was performed using the complex sample analysis of the IBM SPSS 25.0 program. As a result of this study, the factors that influenced the quality of life of the elderly in economic activity were gender, age, outpatient use frequency, arthritis, activity restrictions, subjective health, and stress, and their explanatory power was 34.2% (p<.001). The factors that influenced the quality of life of the elderly without economic activity were sex, age, number of hospitalizations, high blood pressure, arthritis, hearing impairment, masticatory discomfort, activity restriction, subjective health and stress, and their explanatory power was 35.5% (p<.001). The results of this study can provide basic data on the factors affecting the quality of life according to economic activities in the intervention of the elderly's quality of life. Intervention is required to improve the quality of life for the elderly according to economic activity.

• Annals of Pediatric Endocrinology and Metabolism
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• v.23 no.4
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• pp.196-203
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• 2018

Purpose: The hemoglobin glycation index (HGI) represents the degree of nonenzymatic glycation and has been positively associated with cardiometabolic risk factors (CMRFs) and cardiovascular disease in adults. This study aimed to investigate the association between HGI, components of metabolic syndrome (MS), and alanine aminotransferase (ALT) in a pediatric nondiabetic population. Methods: Data from 3,885 subjects aged 10-18 years from the Korea National Health and Nutrition Examination Survey (2011-2016) were included. HGI was defined as subtraction of predicted glycated hemoglobin ($HbA1_c$) from measured $HbA1_c$. Participants were divided into 3 groups according to HGI tertile. Components of MS (abdominal obesity, fasting glucose, triglycerides, high-density lipoprotein cholesterol, and blood pressure), and proportion of MS, CMRF clustering (${\geq}2$ of MS components), and elevated ALT were compared among the groups. Results: Body mass index (BMI) z-score, obesity, total cholesterol, ALT, abdominal obesity, elevated triglycerides, and CMRF clustering showed increasing HGI trends from lower-to-higher tertiles. Multiple logistic regression analysis showed the upper HGI tertile was associated with elevated triglycerides (odds ratio, 1.65; 95% confidence interval, 1.18-2.30). Multiple linear regression analysis showed HGI level was significantly associated with BMI z-score, $HbA1_c$, triglycerides, and ALT. When stratified by sex, age group, and BMI category, overweight/obese subjects showed linear HGI trends for presence of CMRF clustering and ALT elevation. Conclusion: HGI was associated with CMRFs in a Korean pediatric population. High HGI might be an independent risk factor for CMRF clustering and ALT elevation in overweight/obese youth. Further studies are required to establish the clinical relevance of HGI for cardiometabolic health in youth.