• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.5
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• pp.8-14
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• 2021

Post-tensioned prestressed concrete members experience immediate prestress losses as well as time-dependent prestress losses such as creep, dry shrinkage and relaxation. In addition, the stress of the upper and lower parts of the member changes due to the change in dead load due to the replacement of the upper slab and/or pavement. Such changes in fiber stress may affect the safety of the member, and it is necessary to adjust the prestressing force. Therefore, in this study, a screw type of re-tensioning post-tension kit is proposed, and it is verified that the safety against load and the stability against strain are satisfied through the load transfer test specified in EAD160004 and KCI-PS101.

• Tribology and Lubricants
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• v.35 no.1
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• pp.65-70
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• 2019

Self-loosening of bolts owing to external forces occurs in several machines that are clamped by bolts and nuts. This study focuses on the self-loosening of the aiming bolt of the head lamp in a vehicle. It is important to prevent the aiming bolt from self-loosening as it has a decisive effect on the angle of the head lamp. A nut clamped with a bolt, known as a retainer, is made of plastic and has a partial screw thread. In addition, a transverse load has a considerable impact on the self-loosening of a bolt. We concentrate on the self-loosening of a bolt by a transverse load. The aim of this study is to define the limits of the external force that loosen the bolt. Based on the above conditions, we derive a theoretical equation and develop a numerical analysis program that can calculate the limiting forces for self-loosening. To verify the developed program, we design a test device that can measure the self-loosening by applying sliding forces to the aiming bolt. Using this method, we can draw the following conclusions. First, the developed testing device is suitable to prove the theory for calculating the self-loosening force. Second, the equation confirms the relationship of bolt self-loosening between resistance torque and shear force. Finally, the equation obtains the minimum value of the resistance torque required to decrease the change in the angle of the head lamp, thereby improving the possibility of increasing the stability of the head lamp.

• The Korean Journal of Food And Nutrition
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• v.32 no.4
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• pp.335-341
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• 2019

Beta-carotene is the most prominent member of the group of carotenoids, natural colorants that occur in the human diet. Beta-carotene is also an effective source of vitamin A in both conventional foods and vitamin supplements, and it's generally safe. In this study, we explored the beta-carotene contents in agricultural products widely and specifically grown in Korea. The beta-carotene contents were ranging from 223 to $27,908{\mu}g/100g$ in leaves, and 0 to $7,588{\mu}g/100g$ in vegetables. In leaves and vegetables, the amount of beta-carotene was the highest in green tea powder ($27,908{\mu}g/100g$), followed by pepper ($7,588{\mu}g/100g$). In fruits, the beta-carotene content was found to range from $0{\mu}g/1,011g$ to maximum of $293.66{\mu}g/100g$(plumcot). However, there beta-carotene was not detected in strawberry. In the case of cereals and specialty crops, the beta-carotene contents were $326{\mu}g/100g$ for non-glutinous rice, $313{\mu}g/100g$ for glutinous rice, $57{\mu}g/100g$ for amaranth and $15{\mu}g/100g$ for pine nut, respectively. However, the beta-carotene content was not detected in other samples. This study revealed the presence of beta-carotene content in agricultural products specifically grown in Korea for nutritional information and food composition database.

• Tribology and Lubricants
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• v.35 no.2
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• pp.114-122
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• 2019

High-speed rotating machinery requires low cost and reliable bearing elements with low friction, stable rotordynamic characteristics, and a simple design. This study experimentally evaluates the effects of bearing-support elements on the vibrational characteristics of a small-sized, high-speed permanent magnetic motor. A series of coast down tests from 100 krpm characterize the vibrational behaviors, rotor displacement, and housing acceleration of motors supported by ball bearings, ball bearings with a metal mesh damper, and gas foil bearings, respectively. Two eddy-current sensors installed in the horizontal and vertical directions measure the displacement of the rotor at its front nut, and a 3-axis accelerometer attached to the motor housing measures the housing acceleration. The test results reveal that synchronous (1X) vibration components most significantly affect the rotor displacement and housing acceleration, independent of the bearing-support elements. The motor supported by the deep-groove ball bearings results in the largest rotor vibrations increasing with speed; this is due to the absence of a damping mechanism. Additionally, the metal mesh damper effectively reduces the rotor displacement, housing acceleration, and sound-pressure level in the high-speed region (i.e., above 40 krpm), thus implying its substantial damping performance when installed on the outer race of the ball bearing. Lastly, the gas foil bearing supported motor yields the smallest rotor displacement, housing acceleration, and lowest sound-pressure level because of its hydrodynamic airborne operation, which does not require rolling elements that may cause mechanical friction and vibrations.

• Proceedings of the Plant Resources Society of Korea Conference
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• 2019.10a
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• pp.20-20
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• 2019

Sedge family is second largest family in the Korean flora with more than 240 taxa, following Aster family (about 300 taxa). Although high species diversity, a very limited number of taxa has been utilized for ethnobotanical usages. In the study, previous researches on Cyperaceae ethnobotanical information are documented and analyzed for future research directions on the taxa. A total number of seven taxa has been used for medicinal, food, and material purposes: Carex boottiana Hook. & Arn., Cyperus amuricus Maxim., Cyperus esculentus L., Cyperus exaltatus Retz., Cyperus rotundus L., Eleocharis kuroguwai Ohwi, and Bolboschoenus maritimus (L.) Palla. Underground parts such as tubers are used with medicinal purpose, and aboveground portions such as leaves and stems provide materials for various tools and foods for people and animals. They are all native to Korea, except C. esculentus, which is introduced from Mediterranean areas for anti-erosion materials. The ethnobotanical value of C. esculentus has been well recognized from ancient times, for example, starch grains in USA (excavations at the Mashantucket Pequot Reservation) and Tiger nut milk (Horchata de chufa in Spain). Among material sources, C. exaltatus has a long history in the Korean peninsula from Three Kingdoms of Korea (57 BC~668 AD). C. rotundus is distributed widely in Asia, Africa, Europe, and America, and utilized for medicines, food, and materials. In addition, Eleocharis kuroguwai is only one taxon utilized for ethnobotanical uses among fifteen Eleocharis Korean native species. The number of species with ethnobotanical uses is small in sedge family, but the family has long been utilized accompanying long human history. Cyperus papyrus L., the source of papyrus paper (Egypt in the Nile Delta), is also a member of sedge family. Sedge family has contributed to human societies in various aspects but, the cultural, botanical, ecological values of family members have been underestimated.

• Korean Journal of Community Nutrition
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• v.25 no.6
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• pp.512-519
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• 2020

Objectives: A cross-sectional study was conducted to investigate the associations between food groups and hearing loss. Methods: Data of 1,312 individuals were used from the Korea National Health and Nutrition Examination Survey 2013. Hearing loss was determined with a pure tone average (PTA) of greater than 25 dB in either ear. The PTA was measured as the average hearing threshold at speech frequencies of 0.5, 1, 2, and 4 kHz. The dietary intake was examined with a food frequency questionnaire with 112 food items. The food items were classified into 25 food groups. A weighted logistic regression was used to investigate the association. Results: Individuals in the highest tertile of vegetables and nuts food groups were less likely to have hearing loss than those in the lowest tertile [Odds Ratio (OR) = 0.58 (95% Confidence interval (CI) 0.38-0.91), P = 0.019; OR = 0.59 (95% CI 0.39-0.90), P = 0.020, respectively], after adjusting for confounding variables of age, sex, body mass index, drinking, smoking, diabetes, hypertension, and physical activity. Conclusions: In this cross-sectional study, we observed that high intake of vegetables and nuts food groups revealed significant inverse associations with hearing loss, after adjusting for confounding variables among 1,312 participants.

• Journal of the Korean Society of Industry Convergence
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• v.25 no.2_1
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• pp.177-184
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• 2022

The automatic defect sorting function of machinery parts is being introduced to the automation of the manufacturing process. In the final stage of automation of the manufacturing process, it is necessary to apply computer vision rather than human visual judgment to determine whether there is a defect. In this paper, we introduce a deep learning method to improve the classification performance of typical mechanical parts, such as welding parts, galvanized round plugs, and electro galvanized nuts, based on the results of experiments. In the case of poor welding, the method to further increase the depth of layer of the basic deep learning model was effective, and in the case of a circular plug, the surrounding data outside the defective target area affected it, so it could be solved through an appropriate pre-processing technique. Finally, in the case of a nut plated with zinc, since it receives data from multiple cameras due to its three-dimensional structure, it is greatly affected by lighting and has a problem in that it also affects the background image. To solve this problem, methods such as two-dimensional connectivity were applied in the object segmentation preprocessing process. Although the experiments suggested that the proposed methods are effective, most of the provided good/defective images data sets are relatively small, which may cause a learning balance problem of the deep learning model, so we plan to secure more data in the future.

• Journal of Korean Society of Water and Wastewater
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• v.36 no.5
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• pp.261-273
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• 2022

In this study, we collect water control valves that have had accidents due to existing cracks, etc. are collected, and propose investigation items for strengthening the valve structural safety evaluation through a series of analyzes from valve specifications to physicochemical properties are proposed. The results of this study are as follows. First, there was a large variation in the thickness of the body or flange of the valves to be investigated, which is considered to be very important factor, because it may affect the safety of the valve body against internal pressure and the flange connected with the bolt nut. Second, 60% of the valves under investigation had many voids in the valve body and flange, etc. and the decrease in thickness due to corrosion was relatively large on the inner surface in contact with water rather than the outer surface. It is judged that the investigation of depth included voids is very important factor. Third, all valves to be investigated are made of gray cast iron foam, and therefore it is judged that there is no major problem in chemical composition. It is judged that the chemical composition should be investigated. Fourth, as a physical investigation item, the analysis of metal morphology structure seems to be a very important factor for nodular cast iron from rather than a gray cast iron foam water valve with a flake structure. As it was found to be 46.7~68.8% of the standard recommended by KS, it could have a direct effect on damage such as cracks, and therefore it is judged that the evaluation of tensile strength is very important in evaluating the safety of the valve.

• The Korean Journal of Food And Nutrition
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• v.36 no.4
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• pp.309-320
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• 2023

This study examined the determinants of healthy food purchases before and after COVID-19 in Korea. Binomial and multinomial logistic regression models were applied to Korea Rural Economic Institute's Food Consumer Behavior Survey data from 2019 to 2021. The analysis revealed a significant decrease in the non-intake of healthy food in 2021 compared to 2019, suggesting the impact of COVID-19 on healthy food consumption. Consumption patterns also changed, with a decrease in direct purchases and an increase in gift-based purchases. Several variables showed significant effects on healthy food intake. Single-person households exhibited a higher probability of eating healthy food after COVID-19. The group perceiving themselves as healthy had a lower likelihood of consuming healthy food pre-COVID-19, but this changed after the pandemic. Online food purchases, eco-friendly food purchases, and nut consumption showed a gradual decrease in the probability of non-intake over time. Gender and age also influenced healthy food intake. The probability of eating healthy food increased in the older age group compared to the younger group, and the probability increased significantly after COVID-19. The probability of buying gifts was significantly higher in those in their 60s, indicating that the path to obtaining healthy food differed by age.

• Composites Research
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• v.36 no.4
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• pp.259-263
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• 2023

This study investigated the open hole tensile (OHT) properties of carbon fiber/epoxy composites and compared them to bolt joint tensile (BJT) properties. The net nominal modulus and strength (1376 MPa) were found to be higher than the gross nominal strength (1041 MPa), likely due to increasing hole size. The OHT and BJT specimens exhibited similar stiffness, as expected without bolt rotation causing secondary bending. OHT specimens experienced a sharp drop in stress indicating unstable crack propagation, delamination, and catastrophic failure. BJT specimens failed through shear out on the bolt side and bearing failure on the nut side, involving fiber kinking, matrix splitting, and delamination, resulting in lower strength compared to OHT specimens. The strength retention of carbon fiber/epoxy composites with open holes was 66%. Delamination initiation at the hole's edge caused a reduction in the stress concentration factor. Filling the hole with a bolt suppressed this relieving mechanism, leading to lower strength in BJT specimens compared to OHT specimens. Bolt joint efficiency was calculated as 15%. The reduction in strength in bolted joints was attributed to fiber-matrix splitting and delamination, aligning with Hart Smith's bolted joint efficiency diagram. These findings contribute to materials selection and structural reliability estimation for carbon fiber/epoxy composites. They highlight the behavior of open hole and bolt joint configurations under tensile loading, providing valuable insights for engineering applications.