• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.1
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• pp.41-50
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• 2021

In this study, the flow path width (Gap Size), which is the flow path of fluid, was selected differently among various factors that determine the Ccontrol Force of MR damper, and the change of Control Force was confirmed accordingly. For this purpose, two MR dampers with a Gap Size of 1.0mm and 1.5mm were fabricated, respectively, and dynamic load experiments were conducted according to changes in applied current and vibration conditions The experimental results showed that the minimum Control Force was 3.2 times higher than 1.5mm in the case of 1.0mm Gap Size, and the maximum Control Force was 2.3 times higher than 1.5mm in the case of 1.0mm Gap Size. In addition, the increased width of the Control Force according to applied current was 34N for Gap Size 1.0mm, and 12.7N for Gap Size 1.5mm. As the gap Size increased, the overall Control Force and the increase in the Control Force by the applied current decreased. Next, the dynamic range, which is a performance evaluation index of the semi-active Control device, was 2.3 on average under 1.0mm condition and 2.8 on average under 1.5mm condition, confirming the possibility of utilization as a semi-active Control device.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.2
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• pp.345-353
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• 2021

This study examined the level of resilience and forgiveness, which are important factors of the future competencies of university students. First, a liberal arts course based on mindfulness theory, "Future Society and understanding of the human mind," was developed with expert validity. This class was opened as a liberal arts class. A test of resilience test and forgiveness scale were conducted before and after the class to determine if there was any change in the level of resilience and forgiveness of university students. There were 18 students in the experimental group and 21 general students in the control group attending S University in Seoul. In both groups, a structured resilience test and forgiveness scale were conducted before and after the experiment. SPSS 20.0 program was used for data processing, and the effectiveness was analyzed using a t-test, paired t-test, and cohen d score for the effect size. The group that showed an effect was verified by confirming the effect size to determine if it was meaningful. The analysis revealed a significant difference in the total resilience score and the sub-factors in positivity and control ability.

• Journal of Internet Computing and Services
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• v.21 no.6
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• pp.41-50
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• 2020

The consequences of wearing high heels can be different according to the heel height, gait speed, shoe design, heel base area, and shoe size. This study aimed to focus on the knee extension and flexion range of motion (ROM) during gait, which were challenged by wearing five different shoe heel types and two different self-selected gait speeds (comfortable and fast) as experimental conditions. Measurement standards of knee extension and flexion ROM were individually calibrated at the time of heel strike, mid-stance, toe-off, and stance phase based on the 2-minute video recordings of each gait condition. Seven healthy young women (20.7 ± 0.8 years) participated and they were asked to walk on a treadmill wearing the five given shoes at a self-selected comfortable speed (average of 2.4 ± 0.3 km/h) and a fast speed (average of 5.1 ± 0.2 km/h) in a random order. All of the shoes were in size 23.5 cm. Three of the given shoes were 9.0 cm in height, the other two were flat shoes and sneakers. A motion capture software (Kinovea 0.8.27) was used to measure the kinematic data; changes in the knee angles during each gait. During fast speed gait, the knee extension angles at heel strike and mid-stance were significantly decreased in all of the 3 high heels (p<0.05). The results revealed that fast gait speed causes knee flexion angle to significantly increase at toe-off in all five types of shoes. However, there was a significant difference in both the knee flexion and extension angles when the gait in stiletto heels and flat shoes were compared in fast gait condition (p<0.05). This showed that walking fast in high heels leads to abnormal knee ROM and thus can cause damages to the knee joints. The findings in this preliminary study can be a basis for future studies on the kinematic changes in the lower extremity during gait and for the analysis of causes and preventive methods for musculoskeletal injuries related to wearing high heels.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.1
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• pp.51-58
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• 2021

In this paper, a multi-scale finite element (FE) modeling methodology for three-dimensional (3D) needle-punched (NP) C/SiC with a complex microstructure is presented. The variations of the material properties induced by the needle-punching process and complex geometrical features could pose challenges when estimating the material behavior. For considering these features of composites, a 3D microscopic FE approach is introduced based on micro-CT technology to produce a 3D high fidelity FE model. The image processing techniques of micro-CT are utilized to generate discrete-gray images and reconstruct the high fidelity model. Furthermore, a subcell modeling technique is developed for the 3D NP C/SiC based on the high fidelity FE model to expand to the macro-scale structural problem. A numerical homogenization approach under periodic boundary conditions (PBCs) is employed to estimate the equivalent behavior of the high fidelity model and effective properties of subcell components, considering geometry continuity effects. For verification, proposed models compare excellently with experimental results for the mechanical behavior of tensile, shear, and bending under static loading conditions.

• Clean Technology
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• v.27 no.1
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• pp.39-46
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• 2021

A road structure washing vehicle equipped with a 4 HP, 80 LPM ultrafine bubble generator was used to clean a tunnel wall and the surface of the surrounding structure, consisting of concrete and tiles, in a heavy traffic area around an apartment complex in the city. Ultrafine bubbles were generated by supplying air at 2 to 3 LPM and using a specially designed nozzle, whereas fine bubbles made by an impeller in a gas-liquid mixing self-priming pump were produced with an average diameter of 165.4 nm and 6.81 × 107 particles mL-1. Using a high pressure washer gun that can perform high-pressure cleaning at 150 bar and 30 LPM, ultrafine bubbles were used to wash dust adsorbed on the surface of the road structures. The experimental analysis was divided into before and after washing. The samples were analyzed by applying ISO 8502-3 to measure surface contamination of dust adsorbed on the surface. Using the transparent tape attached to the surface, the removal rate was calculated by measuring the weight of the dust, and the number of particles was calculated using the gravimetric method and the software, ImageJ. The results of the experiment showed that the number of dust particles adsorbed on the tile wall surface before and after washing were 3,063 ± 218 particles mL-1 and 20 ± 5 particles mL-1, respectively, with weights of 580 ± 82 mg and 13 ± 4 mg. Particles on the surface of the concrete structure before and after washing were 8,105 ± 1,738 particles mL-1 and 39 ± 6 particles mL-1, respectively, with weights of 1,448 ± 190 mg and 118 ± 32 mg.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.5
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• pp.9-16
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• 2020

A CFRP sheet has been applied as a structural reinforcement in the field, and various studies are conducted to evaluate the effect of CFRP sheets on reinforced concrete. Although many experiments were performed from previous studies, there are still limitations to analyze structural behaviors with various parameters in experiments directly. This study shows the FEA on structural behaviors of RC beams reinforced with CFRP sheets using ABAQUS software. To simulate debonding failure of CFRP sheets which is a major failure mode of RC beam with CFRP sheets, a cohesive element was applied between the bottom surface of RC beam and CFRP sheets. Both quasi-static method and 2-D symmetric FE model technique were performed to solve nonlinear problems. Results obtained from the FE models show good agreements with experimental results. It was found that reinforcement level of CFRP sheets is closely related to structural behavior of reinforced concrete including maximum strength, initial stiffness and deflection at failure. Also, as over-reinforcement of CFRP sheets could give rise to the brittle failure of RCstructure using CFRP sheets, an appropriate measure should be required when installing CFRP sheets in the structure.

• Journal of radiological science and technology
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• v.44 no.6
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• pp.671-677
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• 2021

Interest in the everyday hazards of radon has recently increased as such, this study attempted to examine the dangers of radon in spilled groundwater by comparing the radon concentrations of the drained groundwater and tap water used in recirculating systems in Incheon Subway restrooms. At five stations of Incheon Subway Line 1 and three stations of Line 2, drained groundwater is recirculated and used in restrooms for toilet flushing. Stations restroom tap water for hand washing that used as a control and the measured values of each were compared. With the cooperation of Incheon Transportation Corporation, samples of spilled groundwater and tap water were collected sealed to prevent contact with the air, and a DURRIDGE RAD7 was used as the experimental equipment. The collected samples were subjected to radial equilibration for approximately 3.5 h, at which the radon concentration reached its maximum, and then calculated as 10 measurements using the RAD7 underwater radon measurement mode. In all eight stations, the radon concentration in tap water was lower than the recommended amount. However, in an average of 7 out of the eight stations, the radon concentration in the effluent groundwater was 100 times higher than that in tap water. Since high radon concentrations in groundwater runoff can be harmful to humans, and there is no accurate standard for radon concentrations in domestic water, it is necessary to continuously monitor radon in water and prepare a guidance of recommended values.

• Journal of the Korean earth science society
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• v.42 no.6
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• pp.623-631
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• 2021

The increased transport of marine hazardous and noxious substances (HNS) has resulted in frequent HNS spill accidents domestically and internationally. There are about 6,000 species of HNS internationally, and most of them have toxic properties. When an accidental HNS spill occurs, it can destroys the marine ecosystem and can damage life and property due to explosion and fire. Constructing a spectral library of HNS according to wavelength and developing a detection algorithm would help prepare for accidents. In this study, a ground HNS spill experiment was conducted in France. The toluene spectrum was determined through hyperspectral sensor measurements. HNS present in the hyperspectral images were detected by applying the spectral mixture algorithm. Preprocessing principal component analysis (PCA) removed noise and performed dimensional compression. The endmember spectra of toluene and seawater were extracted through the N-FINDR technique. By calculating the abundance fraction of toluene and seawater based on the spectrum, the detection accuracy of HNS in all pixels was presented as a probability. The probability was compared with radiance images at a wavelength of 418.15 nm to select abundance fractions with maximum detection accuracy. The accuracy exceeded 99% at a ratio of approximately 42%. Response to marine spills of HNS are presently impeded by the restricted access to the site because of high risk of exposure to toxic compounds. The present experimental and detection results could help estimate the area of contamination with HNS based on hyperspectral remote sensing.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.20 no.6
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• pp.147-161
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• 2021

The purpose of this study was to investigate the psychological state and driving safety of drivers driving around the truck platoon driving. Using the driving simulator, the experimental environment was constructed with the situation of changing lanes to the platoon and driving within the platoon. We tried to qualitatively and quantitatively analyze the driver's psychological state and driving safety through simulation driving experiments. As a result, in the case of the older driver group, there were many cases where they judged themselves to be driving safely, even though they were driving dangerously in the actual lane change to the platoon or driving within the platoon. In particular, this group showed that the narrower the distance between vehicles, the greater the misrecognition. The results of this study are expected to be useful in deriving the optimum interval when the interval between platooning of trucks needs to be temporarily extended.

• Journal of the Korean Applied Science and Technology
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• v.38 no.6
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• pp.1524-1532
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• 2021

In this study, Gomchwi (Ligularia fischen) derived from Taebaek-si, Gangwon-do was extracted with 70% ethanol (LFE) and antioxidant activity was measured. The following experimental techniques were used to evaluate the antioxidant efficacy of LFE. Total phenolic contents, ABTS/DPPH radical scavenging analysis, cell viability assay, NO assay, and quantitative real-time PCR technique. The content of polyphenol and flavonoid was each 113.97±0.37 mg GAE/g or 29.22±2.06 mg QE/g in LFE. DPPH radical scavenging activity was measured to be 25 ㎍/㎖ 11.26±0.95%, 50 ㎍/㎖ 17.12±0.63%, 100 ㎍/㎖ 29.54±0.36%, 250 ㎍/㎖ 68.31±0.28%, 500 ㎍/㎖ 75.12±0.05%, and 1000 ㎍/㎖ 75.75±1.57%. In addition, ABTS radical scavenging activity was identified as LFE 25 ㎍/㎖ 13.75±0.21%, 50 ㎍/㎖ 26.71±0.20%, 100 ㎍/㎖ 56.92±0.22%, 250 ㎍/㎖ 91.30±0.12%, 500 ㎍/㎖ 93.40±0.02, and 1000 ㎍/㎖ 93.19±0.04%. There was no significant cytotoxicity of LFE. NO production was significantly decreased to LFE 50 ㎍/㎖ 79.40±2.64%, 100 ㎍/㎖ 55.01±5.36%, and 200 ㎍/㎖ 30.93±3.11%. Also, the NOS2 gene expression was significantly reduced to LFE 50 ㎍/㎖ 0.94±0.11, 100 ㎍/㎖ 0.59±0.05, and 200 ㎍/㎖ 0.32±0.04. This result objectively confirmed the antioxidant effect of Gomchwi. We will continue to conduct in-depth research. Therefore, it is believed that the possibility of using Gomchwi as a cosmetic and functional food material can be established.