• Electrical & Electronic Materials
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• v.8 no.5
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• pp.633-639
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• 1995

Dropouts in magnetic media are a primary quality deficiency which is detrimental to magnetic signal quality and thus the major impediment to error-free recording, especially in high density digital recorders. The specific form of defects and causes found to be responsible for signal dropouts occurring in magnetic tape were studied. Dropout occurred when the RF signal falls to low level due to the various types of surface defects. However, the fall in the level of the RF signal in gravure roll coated tapes was most often caused by foreign particles adhering to the magnetic tape. It was also shown from the present study that scattered particles trapped under the tape surface or put on the top can lift it as it crosses the head, creating a spherical tent shaped defect and causing a temporary signal drop. Dropout producing substances were identified through optical and microchemical analyses. The results were correlated with measured electrical signal losses combined with analytical microscopy to clarify source identification of defects.

• Nuclear Engineering and Technology
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• v.51 no.1
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• pp.31-44
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• 2019

This study simulated a control rod assembly (CRA), which is a part of reactor shutdown systems, in immersed and fluid flow conditions. The CRA was inserted into the reactor core within a predetermined time limit under normal and abnormal operating conditions, and the CRA (which consists of complex geometric shapes) drop behavior is numerically modeled for simulation. A full-scale prototype CRA drop test is established under room temperature and water-fluid conditions for verification and validation. This paper describes the details of the numerical modeling and analysis results of the several conditions. Results from the developed numerical simulation code are compared with the test results to verify the numerical model and developed computer code. The developed code is in very good agreement with the test results and this numerical analysis model and method may replace the experimental and CFD method to predict the drop behavior of CRA.

• Bulletin of the Korean Chemical Society
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• v.4 no.5
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• pp.203-208
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• 1983

A thermal decomposition of trichloroethylene was studied in the temperature range of 440-$460^{\circ}C$ by using the conventional static system. In order to investigate the pressure dependence of reaction and to eliminate free radical process, propylene was used as the bath gas. The pressure range investigated was 10∼900 Torr. The decomposition was the unimolecular dehydrochlorination and the reaction products were hydrogen chloride and dichloroacetylene. Results were interpreted in terms of the Ric-Ramsperger-Kassel-Marcus (RRKM) unimolecular rate theory and the Arrhenius parameters were determined from fall-off behaviors. The Arrhenius parameters are found to be log $A=13.8{\pm}0.2sec^{-1}$ and E = $56.6{\pm}0.7$ kcal/mole, respectively.

• Journal of Engineering Education Research
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• v.26 no.1
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• pp.12-19
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• 2023

With the introduction of the accreditation of engineering programs in Korea, universities affiliated with the programs have opened introductory engineering design courses for first- or second-year students. Since these courses mainly aim at cultivating problem-solving skills through team projects, this type of classes has opened as face-to-face classes. However, from the beginning of 2020, online teaching was recommended or forced on universities due to the COVID-19 pandemic. Thus, effective design of online courses on introductory engineering design was inevitable during the period. In this paper, we introduce a case study of the course in the Department of Computer Science at S University in Fall 2021. Through concrete suggestions on project areas, selection of team members considering grade levels and interest, several systems for prevention of free riding, and carefully designed open-book exams, the course resulted in both high achievements and high satisfaction.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.11a
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• pp.14-15
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• 2021

Even though the Al. form system, which was developed to replace the Euro-form, has been used as the slab lower formwork for almost all concrete structures based on the light weight and high conversion rate, the low-noise Drop method has been developed and used in order to overcome the limitations of the Al. Form system such as noise pollution and safety accidents caused by free fall during the demolding. However, as the low-noise drop method is still insufficient, Safety Full Drop Al. Form method is expected to be in the spotlight in the construction market based on its excellent advantages compared to the developed methods. In addition, we plan to conduct research to further contribute to securing the quality of the overall structure through continuous improvement and supplementation by introducing an automation system to the very construction method.

• Journal of the Korean Society of Marine Environment & Safety
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• v.17 no.4
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• pp.331-337
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• 2011

We described for the production of cloud-free satellite sea surface temperature(SST) data around Northeast Asian using NOAA AVHRR(Advanced Very High Resolution Radiometer) SST data during 1990-2005. As a result of Markov model, it was found that the value of Markov coefficient in the strong current region such as Kuroshio region showed smaller than that in the weak current. The variations of average SST and regional difference of seasonal day-to-day SST in spring and fall were larger than those in summer and winter. In particular, the distribution of the regional difference appeared large in the vicinity of continental in spring and fall. The difference of seasonal day-to-day SST was also small in Kuroshio region and southern part of East Sea due to the heat advection by warm currents.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.18 no.4
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• pp.383-389
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• 2006

In three dimensional wave field, a direct numerical simulation model, which is able to handle free-fall and slope-fall of a waterdrop due to overtopping, is proposed to evaluate the overtopping rate on the coastal structures like an absorbing revetment. A comparison between the numerical model and existing experimental results for overtopping rate was made to validate the proposed numerical model's accuracy, and showed fairly good agreement between them. It is confirmed in numerical and hydraulic(existing) model test that the overtopping quantity on a absorbing revetment becomes larger with an increase in Ursell number. Also, the overtopping rate estimated by 3-D numerical model is compared with it obtained by 2-D numerical model.

• Journal of Biosystems Engineering
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• v.41 no.1
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• pp.21-33
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• 2016

Purpose: In order to ensure that vegetable seedlings (with a soil block around their roots) are planted in an upright orientation after metering in a vegetable transplanter, they need to be dropped freely from a certain height. The walk-behind hand-tractor-powered machines do not have sufficient space to drop the seedlings from that height. In the present work, a hopper-type planting device was developed for the walk-behind hand-tractor-powered vegetable transplanter to ensure that the soil block seedlings are planted in an upright orientation. Methods: Various dimensionless terms were developed based on the dimensional analysis approach, and their effect on the planting of soil block seedlings in an upright orientation (planting efficiency) was studied. The optimum design dimensions of the hopper-type planting device were identified by the Taguchi method of optimization. Results: The ratio of the height of free fall to the sliding distance of the seedling on the surface of the hopper had the highest influence on planting efficiency. The planting efficiency was highest for plants with a height $15{\pm}2cm$. The plant handling Froude number, in interaction with the design of the hopper-type planting device, also significantly affected the planting efficiency. Of the hopper design factors, the length of the slide of the seedlings on the surface of the hopper was most important, and induced sufficient velocity and rotation to cause the seedling to fall in an upright orientation. An evaluation of the performance of the planting device under actual field conditions revealed that the planting efficiency of the developed planting device was more than 97.5%. Conclusions: As the seedlings were fed to the metering device manually, an increase in planting rate increased missed plantings. The planting device can be adopted for any vegetable transplanter in which the seedlings are allowed to drop freely from the metering device.

• Archives of Craniofacial Surgery
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• v.20 no.4
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• pp.228-232
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• 2019

Background: The epidemiology of nasal fractures varies according to factors such as the era and area of the study, as well as the age of the patient. We compared the characteristics and causes of pediatric nasal fractures. Methods: A total of 2,321 patients with nasal fractures from 2010 to 2017 were examined. The patients were divided into age groups using the Korean school system of age classification. The causes of injury were divided into five groups: violence, fall or slip down, sports, road traffic accidents, and others. Fractures were classified using the Stranc and Robertson standard: vector of force and plane of fracture. Results: Violence was the most common cause of nasal fracture in patients older than 12 years. Violence was a significantly less frequent cause among patients younger than 12 years old than among adolescent and adult patients. Nasal fractures due to violence were not observed in patients younger than 10 years. Plane 2 and lateral force fractures were the most common; however, in patients younger than 12 years, frontal force fractures were significantly more frequent than were lateral force fractures. Conclusion: As children may simply be injured due to a fall or slip down, it is important for the parents and guardians to ensure their safety. As they become older, children should abstain from violence and be monitored. It is therefore very important to ensure that the environment is free of violence in order to prevent such injuries.

• Korean Journal of Soil Science and Fertilizer
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• v.35 no.6
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• pp.327-334
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• 2002

Method of besoil analysis were difficult to be applied universally since the use and the source material of bedsoils are diverse from country to country. Korean Standard Methods for Bedsoil Analysis was developed to measure the particle and bulk density. Fifty-three samples for horticultural bedsoil and nine samples for paddy rice bedsoil in the current market were collected. Particle density was measured by electrical pyconometer with He gas, and bulk density by the sandbox method, free fall method, plunger compaction method, free fall and plunger method, and sample weight compaction method. While the use of glass pycnometer which measures particle density to fill blank space with water was inappropriate due to floating organic and calcined inorganic materials in the water, the electrical pycnometer with gas type was suitable considering speed and accuracy. For bulk density, the sandbox method recommended as European Standard Method was more reasonable in principle than other methods. However, this method requires expensive apparatus and intricate process. Plunger compaction method was proposed as standard method, since it had higher consistence with the sandbox method than other methods, as well as an advantage of easy and prompt measurement. Particle density of bedsoil ranged $1.48{\sim}2.67Mg\;m^{-3}$(mean $1.93Mg\;m^{-3}$) for horticultural bedsoil and $2.33{\sim}2.67Mg\;m^{-3}$ (mean $2.43Mg\;m^{-3}$) for paddy rice bedsoil by the electrical pycnometer with He gas. Bulk density of bedsoil ranged $0.11{\sim}0.40Mg\;m^{-3}$ (mean $0.22Mg\;m^{-3}$) for horticultural bedsoil and $0.84{\sim}1.26Mg\;m^{-3}$(mean $1.01Mg\;m^{-3}$) for paddy rice bedsoil by plunger compaction method.