• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.5
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• pp.688-696
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• 2016

This paper evaluates the effect of hot weather conditions on the fresh concrete characteristics of 80-MPa high-strength concrete. The slump flow, packing ability, setting time, hydration heat, and compressive strength were evaluated under exterior temperatures of $20^{\circ}C$, $30^{\circ}C$, and $40^{\circ}C$. The slump flow, arrival speed of 500 mm, and their changes with the elapsed time were found to bring the occurrence of rapid slump loss forward by about 30 minutes when increasing the temperature by $10^{\circ}C$ from $20^{\circ}C$. The initial and final setting times of the concrete at $20^{\circ}C$ were 7 hours and 12 hours, which were reduced by 1 hour and 3 hours at $30^{\circ}C$ and by 2 hours and 5 hours at $40^{\circ}C$, respectively. The hydration heat characteristics at $20^{\circ}C$ and $30^{\circ}C$ were similar in terms of the highest temperature of the concrete casting depth and the time when the maximum temperature occurred. However, at $40^{\circ}C$, the maximum temperature occurred about 4 hours earlier, and the highest temperature per the concrete casting depth increased by about $12^{\circ}C$. Therefore, it is concluded that the characteristics can vary according to the exterior temperature. Thus, quality assurance should consider workability, temperature cracks due to hydration heat, the properties of strength development, and other characteristics.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.22 no.3
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• pp.57-68
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• 2017

Continuous monitoring of spatial and temporal changes in key marine environmental parameters such as SST (sea surface temperature) near IORS (Ieodo Ocean Research Station) is demanded to investigate the ocean ecosystem, climate change, and sea-air interaction processes. In this study, we aimed to develop the system for continuously measuring SST using a TIR (thermal infrared) sensor mounted at the IORS. New SST algorithm is developed to provide SST of better quality that includes automatic atmospheric correction and emissivity calculation for different oceanic conditions. Then, the TIR-based SST products were validated against in-situ water temperature measurements during May 17-26, 2015 and July 15-18, 2015 at the IORS, yielding the accuracy of 0.72-0.85 R-square, and $0.37-0.90^{\circ}C$ RMSE. This TIR-based SST observing system can be installed easily at similar Ocean Research Stations such as Sinan Gageocho and Ongjin Socheongcho, which provide a vision to be utilized as calibration site for SST remotely sensed from satellites to be launched in future.

• Korean Chemical Engineering Research
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• v.57 no.6
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• pp.790-803
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• 2019

The dioctyl terephthalic acid (DOTP) process produces plastic plasticizers by esterification of terephthalic acid with powder in the form of octanol. In this study, the dust explosion characteristics of terephthalic acid directly injected into the manhole in the form of powder in the presence of flammable solvent or vapor in the reactor of this process were investigated. Dust particle size and particle size distribution dust characteristics were investigated, and pyrolysis characteristics of dust were investigated to estimate fire and explosion characteristics and ignition temperature. Also, the minimum ignition energy experiment was performed to evaluate the explosion sensitivity. As a result, the average particle size of terephthalic acid powder was $143.433{\mu}m$. From the thermal analysis carried out under these particle size and particle size distribution conditions, the ignition temperature of the dust was about $253^{\circ}C$. The lower explosive limit (LEL) of the terephthalic acid was determined to be $50g/m^3$. The minimum ignition energy (MIE) for explosion sensitivity is (10 < MIE < 300) mJ, and the estimated minimum ignition energy (Es) based on the ignition probability is 210 mJ. The maximum explosion pressure ($P_{max}$) and the maximum explosion pressure rise rate $({\frac{dP}{dt}})_{max}$ of terephthalic acid dust were 7.1 bar and 511 bar/s, respectively. The dust explosion index (Kst) was 139 mbar/s, corresponding to the dust explosion grade St 1.

• Smart Media Journal
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• v.8 no.3
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• pp.23-30
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• 2019

With the popularization of the Internet and smartphone uses, people in the modern era are living in a multi-channel environment in which they access the information system freely through various methods and media. In the process of utilizing such services, users must authenticate themselves, the typical of which is ID & password authentication. It is considered the most convenient method as it can be authenticated only through the keyboard after remembering its own credentials. On the other hand, modern web services only allow passwords to be set with high complexity by different combinations. Passwords consisting of these complex strings also increase proportionally, since the more services users want to use, the more user authentication information they need to remember is recommended periodically to prevent personal information leakage. It is difficult for the blind, the disabled, or the elderly to remember the authentication information of users with such high entropy values and to use it through keyboard input. Therefore, this paper proposes a user authentication method using Google Assistant, MFCC and DTW algorithms and speaker authentication to provide the handicapped users with an easy user authentication method in the login process.

• Journal of the Korean Geotechnical Society
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• v.37 no.8
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• pp.51-58
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• 2021

South Korea, as the 10th country to join the Artemis program led by NASA, is actively supporting various researches related to the lunar exploration. In particular, the utilization of water as a resource in the Moon has been focused since it was discovered that ice exists at the lunar pole as a form of frozen soil. Information on the thermal conductivity of lunar regolith can be used to estimate the existence for ice water extraction by thermal mining. In this study, the vacuum pressure effect on thermal conductivity of KLS-1 was investigated with a DTVC (Dusty Thermal Vacuum Chamber). The reliability of KLS-1 was reconfirmed through comparison with thermal conductivity of known standard lunar regolith simulants such as JSC-1A. An empirical equation to assess thermal conductivity considering dry unit weight and vacuum pressure was proposed. The results from this study can be implemented to simulate lunar cryogenic environment using the DTVC.

• Journal of The Korean Society of Agricultural Engineers
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• v.64 no.6
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• pp.65-75
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• 2022

Livestock industry in Korea has been growing rapidly and has reached 23 trillion Korean won in 2021. This study focuses on broiler, which is one of the largest sectors in livestock industry. As the effects of climate change get more serious, primary industry such as livestock industry is fragile to climate change since it directly interacts with nature. Therefore, maintaining suitable rearing environment is important. One of the most frequently used ventilation type for controlling the rearing environment of broiler house, tunnel ventilation, causes frequent air velocity fluctuation which makes maintaining the rearing environment important. By measuring the air temperature, relative humidity and air velocity in various points inside the broiler house, the internal thermal environment uniformity was analyzed according to length, width and zone. The experimental house was found to have dead zone with high air temperature, relative humidity and low air velocity near the end of the inlet and at the end of the broiler house. By using heat stress index to analyze quantitatively, zone with highest heat stress index was found to increase by 7.55% compared to the lowest zone. As a result, to maintain uniform rearing environment inside the broiler house, different factors must be measured and analyzed and used to operate the environmental control facilities.

• Journal of Conservation Science
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• v.37 no.6
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• pp.648-658
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• 2021

In this study, we aimed to analyze the chemical changes that occur in Korean paper in an accelerated deterioration environment of 105℃. We selected the Korean paper produced with different types of cooking agents (plant lye, Na₂CO₃) and during different manufacturing seasons (winter, summer). The degree of deterioration of the Korean paper was confirmed by measuring the brightness, yellowness, and pH level, and the degree of change in each vibrational region of cellulose as deterioration progressed through infrared (FT-IR) spectroscopy. The FT-IR analysis showed that, as deterioration progressed, the absorbance of the amorphous region in cellulose decreased, whereas the absorbance of the crystalline region slightly increased. X-Ray diffraction (XRD) analysis and Raman spectroscopy were performed to verify the changes in the crystalline and amorphous regions in cellulose indicated by the FT-IR results. Furthermore, the crystallinity index (CI) was calculated; it showed a slight increase after deterioration; therefore, CI was confirmed to follow the same trend as that observed for absorbance in the FT-IR results. In addition, as a result of Raman spectroscopic analysis, the degree of decomposition of the amorphous region in the cellulose under the manufacturing conditions was confirmed by the fluorescence measured after the deterioration.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.29 no.1
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• pp.1-7
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• 2023

Chlorine dioxide (ClO₂) is widely used for post-harvest sterilization treatment. However, there are limitations in the retail application of ClO₂ due to difficulties in handling, expensive facilities, and safety concerns. Therefore, it is necessary to develop a ClO₂ technology that can be easily applied and continuously released for a long period. In this study, a series of ClO₂ self-releasing sachets were developed. First, poly(ether-block-amide) (PEBAX) and polyethylene-glycol (PEG) composite films containing different ratios of citric acid (CA) were prepared using the solution casting method. The as-prepared PEBAX/PEG-CA composite films were evaluated using FT-IR, DSC, and TGA to confirm chemical structure and thermal properties. Subsequently, PEBAX/PEG-CA composite films were designed in the form of a sachet and NaClO₂ powder was transferred into the sachet to achieve a ClO₂ self-releasing system. The ClO₂-releasing behavior of the sachet was investigated by measuring the release amount of the gas using UV-vis. The release amount of ClO₂ increased with increasing CA contents owing to the existence of higher protons (trigger) in the polymer matrix. Further, ClO₂ gas was released for a longer time. Therefore, the as-prepared smart sachet can be tuned according to applications and packaging sizes to serve an optimal sterilization effect.

• Journal of the Korea Institute of Construction Safety
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• v.6 no.1
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• pp.12-18
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• 2024

High-rise, large-scale, and diversification of buildings are possible, and the reduction of concrete cross-sections reduces the weight of the structure, thereby increasing or decreasing the height of the floor, securing a large number of floors at the same height, securing a large effective space, and reducing the amount of materials, rebar, and concrete used for designating the foundation floor. In terms of site construction and quality, a low water binder ratio can reduce the occurrence of dry shrinkage and minimize bleeding on the concrete surface. It has the advantage of securing self-fulfilling properties by improving fluidity by using high-performance sensitizers, making it easier to construct the site, and shortening the mold removal period by expressing early strength of concrete. In particular, with the rapid development of concrete-related construction technology in recent years, the application of ultra-high-strength concrete with a design standard strength of 100 MPa or higher is expanding in high-rise buildings. However, although high-rise buildings with more than 120 stories have recently been ordered or scheduled in Korea, the research results of developing ultra-high-strength concrete with more than 130 MPa class considering field applicability and testing and evaluating the actual applicability in the field are insufficient. In this study, in order to confirm the applicability of ultra-high-strength concrete in the field, a preliminary experiment for the member of a reduced simulation was conducted to find the optimal mixing ratio studied through various indoor basic experiments. After that, 130 MPa-class ultra-high-strength concrete was produced in a ready-mixed concrete factory in a mock member similar to the life size, and the flow characteristics, strength characteristics, and hydration heat of concrete were experimentally studied through on-site pump pressing.

• Journal of the Microelectronics and Packaging Society
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• v.25 no.2
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• pp.25-30
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• 2018

Sn-Pb solder has been used in automotive electronics for decades. However, recently, due to the environmental and health concerns, some international environmental organizations such as the end-of-life vehicle (ELV) enacted legislation banning of the Pb usage in automotive electronics. For this reason, many studies to develop and promote Pb-free soldering have been significantly reported. Meanwhile, because of flexibility and lightweight, flexible printed circuit boards (FPCBs) have been increasingly used in automotive electronics for lightweight to improve fuel efficiency and space utilization. Although the properties of lead-free solders for automotive electronics have been widely studied, there is a lack of research on the reliability performance of the lead-free solder joint on FPCB under user conditions. This study reported the properties of solder joints between Pb-free solders such as Sn3.0Ag0.5Cu, Sn0.7Cu and Sn0.5Cu0.01Al (Si), and various FPCBs finished with organic solderability preservative (OSP) and electroless nickel immersion gold (ENIG). To evaluate on joint properties and reliabilities with different solder compositions and surface-finishing materials, pull strength test, thermal shock test, and bending cycle test were performed and analyzed. After the bending cycle test of solder joint on OSP-finishing, the fractures were occurred in solder and the lifetime of Sn3.0Ag0.5Cu solder joint was the longest.