• Tunnel and Underground Space
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• v.33 no.6
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• pp.519-533
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• 2023

In this study, the linear cutting tests of pick cutters were carried out on a granitic rock with the average compressive strength over 100 MPa. From the tests, the correlation between the cutter acting force and the temperature measured by infrared thermal imaging camera during rock cutting was analyzed. In every experimental condition, the maximum temperature was measured at the rock surface where the chipping occurred, and the temperature generated in the rock was closely correlated with the cutter acting force. On the other hand, the temperature of a pick cutter increased up to only 36℃ above the ambient temperature, and the correlation with the cutter force was not obvious. This can be attributed to the short cutting distance under laboratory conditions and the high thermal conductivity of the tungsten carbide inserts. However, the relatively high temperature of the tungsten carbide inserts was found to be maintained. Therefore, it is recommended that a reinforcement between the insert and the head of a pick cutter or the quality improvement of silvering brazing in the production of a cutter is necessary to maintain the high cutting performance of a pick cutter.

• Journal of Korea Water Resources Association
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• v.56 no.spc1
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• pp.1059-1069
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• 2023

Dam-break flow occurs when an elevated dam suddenly collapses, resulting in the catastrophic release of rapid and uncontrolled impounded water. This study compares laminar and turbulent closure models for simulating three-dimensional dam-break flows using OpenFOAM. The Reynolds-Averaged Navier-Stokes (RANS) model, specifically the k-ε model, is employed to capture turbulent dissipation. Two scenarios are evaluated based on a laboratory experiment and a modified multi-layered block obstacle scenario. Both models effectively represent dam-break flows, with the turbulent closure model reducing oscillations. However, excessive dissipation in turbulent models can underestimate water surface profiles. Improving numerical schemes and grid resolution enhances flow recreation, particularly near structures and during turbulence. Model stability is more significantly influenced by numerical schemes and grid refinement than the use of turbulence closure. The k-ε model's reliance on time-averaging processes poses challenges in representing dam-break profiles with pronounced discontinuities and unsteadiness. While simulating turbulence models requires extensive computational efforts, the performance improvement compared to laminar models is marginal. To achieve better representation, more advanced turbulence models like Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS) are recommended, necessitating small spatial and time scales. This research provides insights into the applicability of different modeling approaches for simulating dam-break flows, emphasizing the importance of accurate representation near structures and during turbulence.

• Journal of Sensor Science and Technology
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• v.33 no.1
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• pp.34-39
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• 2024

Energy harvesting technology that converts the wasted energy resources into electrical energy is emerging as a semipermanent power source for self-powered electronics and wireless low-power sensor systems. Among the various energy conversion techniques, flexible piezoelectric energy harvesters (f-PEHs), using materials with piezoelectric effects, have attracted significant interest because they can harvest a small mechanical energy into electrical signals without constraints of time and space in various environments. In this study, we used a flexible piezoelectric composite film fabricated by dispersing BaHf_xTi_(1-x)O₃ (x = 0, 0.01, 0.05, 0.1) piezoelectric powders inside a polymeric matrix to facilitate f-PEHs. The fabricated f-PEH with optimal Hf contents (x = 0.05) generated a maximum output voltage of 0.95 V and current signal of 130 nA with stable electrical/mechanical disabilities under periodically bending deformations. In addition, we demonstrated a cantilever-type f-PEH and investigated its potential as a sensor by characterizing the output performance under mechanical vibrations at various frequencies. This study provides the breakthrough for realizing self-powered energy harvesting and sensing systems by adopting the lead-free piezoelectric composites under vibrational environments.

• Journal of Yeungnam Medical Science
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• v.40 no.4
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• pp.388-393
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• 2023

Background: Differentiating between bacterial and nonbacterial colitis remains a challenge. We aimed to evaluate the value of serum procalcitonin (PCT) and C-reactive protein (CRP) in differentiating between bacterial and nonbacterial colitis. Methods: Adult patients with three or more episodes of watery diarrhea and colitis symptoms within 14 days of a hospital visit were eligible for this study. The patients' stool pathogen polymerase chain reaction (PCR) testing results, serum PCT levels, and serum CRP levels were analyzed retrospectively. Patients were divided into bacterial and nonbacterial colitis groups according to their PCR. The laboratory data were compared between the two groups. The area under the receiver operating characteristic curve (AUC) was used to evaluate diagnostic accuracy. Results: In total, 636 patients were included; 186 in the bacterial colitis group and 450 in the nonbacterial colitis group. In the bacterial colitis group, Clostridium perfringens was the commonest pathogen (n=70), followed by Clostridium difficile toxin B (n=60). The AUC for PCT and CRP was 0.557 and 0.567, respectively, indicating poor discrimination. The sensitivity and specificity for diagnosing bacterial colitis were 54.8% and 52.6% for PCT, and 52.2% and 54.2% for CRP, respectively. Combining PCT and CRP measurements did not increase the discrimination performance (AUC, 0.522; 95% confidence interval, 0.474-0.571). Conclusion: Neither PCT nor CRP helped discriminate bacterial colitis from nonbacterial colitis.

• Journal of the Korean Recycled Construction Resources Institute
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• v.12 no.2
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• pp.188-195
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• 2024

Recently, the use of recycled aggregates from construction waste has been introduced as a solution for environmental problems and aggregate shortage. In spite of the various methods to promote recycling of recycled aggregate, the use of recycled aggregate as the structural aggregate has been limited because the quality of recycled aggregate(especially recycled fine aggregate) has been considered lower than that of natural aggregate. In this work, recycled fine aggregate was immersed for an hour in acrylic resin solutions of various concentrations to improve its quality, the appropriate immersion concentration was selected by measuring the absorption capacity and skeletal density of the recycled fine aggregate, and mortar specimens were prepared to evaluate the mechanical performance in order to propose a applicable treatment process to promote the use of recycled fine aggregate. According to the experimental results, as the acrylic resin concentration increased, the absorption capacity and skeletal density of the recycled fine aggregate decreased. The absorption capacity was lowest at acrylic resin concentrations around 6 to 8 %. However, among mortar specimens made of recycled fine aggregate immersed in acrylic resin solution, the compressive strength was the highest at 4 % acrylic resin concentration, suggesting that the use of higher concentration acrylic resin solution can actually lower the compressive strength of mortar.

• Journal of the Korean Society of Radiology
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• v.82 no.1
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• pp.116-127
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• 2021

Purpose To evaluate the feasibility of texture analysis of gray-scale ultrasound (US) images for staging of hepatic fibrosis. Materials and Methods Altogether, 167 patients who had undergone routine US and laboratory tests for a fibrosis-4 (FIB-4) index were included. Texture parameters were measured using a dedicated in-house software. Regions of interest were placed in five different segments (3, 5, 6, 7, 8) for each patient. The FIB-4 index was used as the reference standard for hepatic fibrosis grade. Comparisons of the texture parameters between different fibrosis groups were performed with the Student's t-test or Mann-Whitney U-test. Diagnostic performance was evaluated by receiver operating curve analysis. Results The study population comprised of patients with no fibrosis (FIB-4 < 1.45, n = 50), mild fibrosis (1.45 ≤ FIB-4 ≤ 2.35, n = 37), moderate fibrosis (2.35 < FIB-4 ≤ 3.25, n = 27), and severe fibrosis (FIB-4 > 3.25, n = 53). Skewness in hepatic segment 5 showed a difference between patients with no fibrosis and mild fibrosis (0.2392 ± 0.3361, 0.4134 ± 0.3004, respectively, p = 0.0109). The area under the curve of skewness for discriminating patients with no fibrosis from those with mild fibrosis was 0.660 (95% confidence interval, 0.551-0.758), with an estimated accuracy, sensitivity, specificity of 64%, 87%, 48%, respectively. Conclusion A significant difference was observed regarding skewness in segment 5 between patients with no fibrosis and patients with mild fibrosis.

• Korean Journal of Radiology
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• v.24 no.5
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• pp.465-475
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• 2023

Objective: To evaluate the feasibility of ultrasound shear wave elastography (SWE) for predicting hepatic fibrosis and native liver outcomes in patients with biliary atresia. Materials and Methods: This prospective study included 33 consecutive patients with biliary atresia (median age, 8 weeks [interquartile range, 6-10 weeks]; male:female ratio, 15:18) from Severance Children's Hospital between May 2019 and February 2022. Preoperative (within 1 week from surgery) and immediate postoperative (on postoperative days [PODs] 3, 5, and 7) ultrasonographic findings were obtained and analyzed, including the SWE of the liver and spleen. Hepatic fibrosis, according to the METAVIR score at the time of Kasai portoenterostomy and native liver outcomes during postsurgical follow-up, were compared and correlated with imaging and laboratory findings. Poor outcomes were defined as intractable cholangitis or liver transplantation. The diagnostic performance of SWE in predicting METAVIR F3-F4 and poor hepatic outcomes was analyzed using receiver operating characteristic (ROC) analyses. Results: All patients were analyzed without exclusion. Perioperative advanced hepatic fibrosis (F3-F4) was associated with older age and higher preoperative direct bilirubin and SWE values in the liver and spleen. Preoperative liver SWE showed a ROC area of 0.806 and 63.6% (7/11) sensitivity and 86.4% (19/22) specificity at a cutoff of 17.5 kPa for diagnosing F3-F4. The poor outcome group included five patients with intractable cholangitis and three undergoing liver transplantation who showed high postoperative liver SWE values. Liver SWE on PODs 3-7 showed ROC areas of 0.783-0.891 for predicting poor outcomes, and a cutoff value of 10.3 kPa for SWE on POD 3 had 100% (8/8) sensitivity and 73.9% (17/23) specificity. Conclusion: Preoperative liver SWE can predict advanced hepatic fibrosis, and immediate postoperative liver SWE can predict poor native liver outcomes in patients with biliary atresia.

• The Journal of the Convergence on Culture Technology
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• v.10 no.3
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• pp.833-838
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• 2024

The urban railway sleeper floating track(STEDEF) is a structure that structurally separates the sleepers and the concrete bed using sleeper boots and resilience pads to reduce vibration transmitted to the concrete bed. Recently, the resilience pads of sleeper floating tracks that have been in use for more than 20 years are deteriorating. Accordingly, in order to evaluate the performance of the resilience pad, a static spring stiffness test is being performed after extracting the resilience pad. This evaluation technique is performed after replacing the resilience pad in use. However, the track natural frequency can change depending on the resilience pad spring stiffness and the uplift and subsidence of the concrete bed. In this study, modal testing technique was used to evaluate the track natural frequency. For this purpose, the sleeper boots material, resilience pad spring stiffness, and track natural frequency according to concrete bed uplift and subsidence were measured using modal tests at a laboratory scale. It was analyzed that the natural frequency of the sleeper floating track was directly affected by changes in the spring stiffness of the resilience pad. In addition, the change in natural frequency due to the uplift and subsidence of the concrete bed was also found to be large. Therefore, it is believed that the modal test technique presented in this study can be used to evaluate the resilience pad deterioration and voided sleepers.

• Journal of Space Technology and Applications
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• v.4 no.2
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• pp.121-136
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• 2024

Korea Pathfinder Lunar Orbiter (KPLO), launched in August 2022, is successfully carrying out its mission. Korea's lunar lander and rover programs are expected to proceed in the future. To successfully carry out the mission after the lunar lander has landed on the surface, the performance of the equipment to be mounted should be checked in a laboratory environment similar to the Moon. Scientists and engineers of several countries, including the United States and China, use lunar soil simulant which is developed to resemble lunar soil for simulating the surface of the lunar landing site. Several lunar probe landing sites are being discussed in Korea, and lunar soil simulants such as Korea Hanyang Lunar Simulant-1 (KOHLS-1), Korea Aerospace University Mechanical Lunar Simulants (KAUMLS), and Korea Lunar Simulant-1 (KLS-1), which are similar to the characteristics of lunar mare soil, have been developed. However, those simulants are not useful if the landing site is chosen as a highland area. In this study, we introduce the process of developing KIGAM-L1, a lunar highland soil simulant similar to the chemical composition of the Apollo 16 lunar soil sample and the particle size distribution of lunar soil sample 60500-1, in case the lunar lander lands at highland area.

• Journal of Korean society of Dental Hygiene
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• v.24 no.4
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• pp.301-309
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• 2024

Objectives: This study aimed to measure the awareness and needs for intellectual property (IP) education among university students majoring in health-related fields to inform the development of future IP education curricula. Methods: The study was conducted through an online survey from January 5 to 26, 2024, targeting students from the health-related departments (Department of Physical Therapy, Health Administration, Clinical Laboratory Science, and Dental Hygiene) at Dankook University located in Cheonan City, Chungcheongnam-do. Results: A total of 151 students participated in the survey. Among the respondents, 84.8% were women, and the largest groups of respondents were from the Health Administration and Dental Hygiene departments, each accounting for 32.5%. Only 13.9% of the respondents had taken courses related to IP, and 22.5% had related activity experience. The overall average importance score of IP education was 3.88 (±0.80), and the overall average need score was 3.78 (±0.80). An Importance-Performance Analysis (IPA) Matrix analysis revealed that 13 topics fell into the first quadrant (high importance, high need), one topic into the second quadrant (low importance, high need), 18 topics into the third quadrant (low importance, low need), and four topics into the fourth quadrant (high importance, low need). The educational topics identified as first quadrant include 'Securing patent rights', 'Requirements for patent registration', 'Effects and contents of patent rights', 'Patent infringement and remedies', and 'Effects and contents of copyrights'. Conclusions: Future IP education programs should develop innovative educational content and methods that consider both the importance and needs to increase students' interest and engagement.