• KEPCO Journal on Electric Power and Energy
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• v.6 no.4
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• pp.393-397
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• 2020

Shunt reactor, a facility for reactive power compensation, is switched several times a day depending on the load pattern. When the circuitbreaker opens the shunt reactor over-voltage is generated by several factors which degrade the insulating performance of internal parts of the circuit-breaker and cause severe voltage stress on the equipment in the power system. Transient phenomenon occurring during the switching of shunt reactor are available in laboratories that verify the performance of the circuit-breaker by simulating the power system. However, it is difficult to measure the transient phenomenon that occurs during actual operation in actual power system due to many limitations. Therefore, this paper deals with the modeling using EMTP to analyze the reignition and current chopping which causes more severe transient recovery voltage in the small inductive current breaking in actual power systems. In addition, this paper analyzes the main phenomenon that cause circuit-breaker failure in opening shunt reactor using EMTP model.

• Journal of the Korea Convergence Society
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• v.12 no.11
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• pp.487-499
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• 2021

This study identifies factors related to suicidal ideation such as demographics, health behaviors and subjective perceptions of high school students. This study analysis using the chi-square test and multiple logistic regression to find out the factors related to suicidal ideation using the 2020 youth online health pattern survey of 25,987 Korean high school students. Sociodemographic factors that affected suicidal ideation in these subjects included grade, gender, and housing type. The health behavior characteristics were experiences with drinking, smoking, sex, and drug misuse. Finally, the subjective perception characteristics included health status, happiness status, loneliness, stress level, and depression. Therefore, it is expected that will be used as basic data for strategies to prevent suicide among high school students in Korea in the covid-19 environment.

• Korean Journal of Community Nutrition
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• v.7 no.5
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• pp.675-685
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• 2002

A study was performed to develop as a screening tool, the Simple Evaluation Questionnaire for screening Overweight Dietary Patterns in people in their 20's. We used the data from the 20 to 29 year old subjects who participated in the three surveys: the health behavior survey, the dietary habit survey and the food intake survey - as part of the National Health and Nutrition Survey of 1998. The 1,493 adults were classified into two body fatness groups, that of normal (including the underweight) , and the overweight (including the obese) on the basis of their relative body weight (RBW). When comparing general variables between the two groups, significant differences (11 variables) were found in gender, sadness/depression state, stress level, age, number of diseases, age when overweightedness started, maximum body weight, sleep length, presently a smoker, everyday smoking habits, number of alcoholic drinks in the past month, and the number of alcoholic drinks when dunk, as well as snacking frequency and fatty food consumption. There were significant differences between the two groups in the three variables of daily soup/kuk, pan fried fish/meat/poultry and cooked fish paste/ham/dried squid in terms of cooked food intake, and 11 variables of food size, cooked rice, stews, vegetables and kimchi at breakfast, panfried foods and beverage/teas at lunch, cooked rice and stews (liquid) at dinner, cooked fish paste/ham/dried squid at snacks and cooked fishpaste/ham/dried squid at snack between lunch and dinner. In terms of raw food intake, we observed significant differences (8 variables) in daily food intake and grains, grains/vegetables/fishes (shellfish) at breakfast, meat at lunch and milt at snack after dinner. After developing questions with indicators and analyzing the indicators by logistic regression analysis using 34 variables, including these 33, plus eating-out frequency, we chose 10 questions for the simple evaluation of dietary patterns for the overweight category, in order to give each one point each. Among them we assigned an additional point to one question and two points to another question. The average scores of the overweight and normal groups, as shown by the questionnaire developed, were 5.97 $\pm$ 2.36 and 7.36 $\pm$ 2.21, respectively. A score of seven points was selected as the cut-off point. We examined the sensitivity, specificity and positive predictive value of the questionnaire to the results of 49.3%,75.4% and 68.8%, respectively. The total score categorized as an overweight dietary pattern was 30.2%.

• Journal of Korean Tunnelling and Underground Space Association
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• v.4 no.4
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• pp.277-286
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• 2002

Most of the problems in dealing with the tunnel construction are the uncertainties and complexities of the stress conditions and rock strengths in ahead of the tunnel excavation. The limitations on the investigation technology, inaccessibility of borehole test in mountain area and public hatred also restrict our knowledge on the geologic conditions on the mountainous tunneling area. Nevertheless an extensive and superior geophysical exploration data is possibly acquired deep within the mountain area, with up to the tunnel locations in the case of alternative design or turn-key base projects. An appealing claim in the use of artificial neural networks (ANN) is that they give a more trustworthy results on our data based on identifying relevant input variables such as a little geotechnical information and biological learning principles. In this study, error back-propagation algorithm that is one of the teaching techniques of ANN is applied to presupposition on Rock Mass Ratings (RMR) for unknown tunnel area. In order to verify the applicability of this model, a 4km railway tunnel's field data are verified and used as input parameters for the prediction of RMR, with the learned pattern by error back propagation logics. ANN is one of basic methods in solving the geotechnical uncertainties and helpful in solving the problems with data consistency, but needs some modification on the technical problems and we hope our study to be developed in the future design work.

• School Mathematics
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• v.11 no.1
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• pp.17-37
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• 2009

Concept and model of multiplication is not single. Concepts of multiplication can be classified into three cases: repeated addition, times idea, pairs set. Models of multiplication can be classified into four cases: measurement, rectangular pattern, combinatorial problem, number line. Among diverse cases of multiplication's concept and model, which case does elementary mathematics education lay stress on? This question is a controvertible didactical point. In this thesis, (1) mathematical and didactical analysis of multiplication's concept and model is performed, (2) a concrete program of teaching multiplication which is based on times idea is contrived, (3) With this new program, the teaching experiment is performed and its result is analyzed. Through this study, I obtained the following results and suggestions. First, the degree of testee's understanding of times idea is not high. Secondly, a sort of test problem which asks the testee to find times value is more easy than the one to find multiplicative resulting value. Thirdly, combinatorial problem can be handled as an application of multiplication. Fourthly, the degree of testee's understanding of repeated addition is high. In conclusion, I observe the fact that this new program which is based on times idea could be a alternative program of teaching multiplication which could complement the traditional method.

• Knowledge Management Research
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• v.23 no.3
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• pp.259-284
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• 2022

In order to help the understanding of web novel users, this study was intended to quantitatively verify the user's behavioral types according to the characteristics of web novels. For this purpose, the direction of the study proceeded as follows. First, the motives of web novel users were investigated by referring to the motives of other digital content users. In addition, specific behavioral types of users were also collected. As a result, the motivation for using web novels was found to be 'interpersonal relationships and information acquisition with others', 'leisure activities', and 'escape from reality/relieve tension'. After that, the groups were classified as to whether there was a difference between groups according to the motives of use. As a result, the 'hobbies' type, a group with a particularly high motivation for using leisure activities, the 'stress relief' type, a group with very high escapism and tension relief characteristics, and a group with high interpersonal relationships and information acquisition with others The 'communication' type was classified as a 'multipurpose' type with high overall motivation characteristics. Then, in order to find out the specific characteristics between the types, personas were constructed based on the different behavior type data. Through this, the theoretical contribution of this study is meaningful in that it revealed the motives of web novel users. As a practical contribution, the persona was formed by combining the users' motives and behavioral patterns and visualized to be close to the actual representative users. These results are expected to help improve the web novel service by providing useful indicators for actual writers, platform managers, and users.

• Korea journal of population studies
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• v.33 no.1
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• pp.133-160
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• 2010

This study aims to analyze marital satisfaction over the family life course and to find its determinants in Korea and Japan. The data for this study came from nationwide representative sample surveys on family in these two countries including 5,308 Korean and 4,920 Japanese men and women living with their spouses. In order to see the cultural difference and similarity in marital relations, the effects of education, income, employment, marriage gradients (normative patterns between the spouses), family stress, and quality of conjugal interactions on Korean and Japanese couples' marital satisfaction were examined. It was found that the marital satisfaction showed a U-shape pattern for both Korean and Japanese couples. In both countries husbands tend to have higher marital satisfaction than wives over the entire life course. The most important determinants of Korean and Japanese couples' marital satisfaction are good qualities of conjugal interactions including deep trust and concerns for spouse and sex life satisfaction. For Korean couples good conjugal interactions is better predictor of marital satisfaction than sex life, while for Japanese couples sex life is more important determinant of marital satisfaction.

• Journal of the Korea Concrete Institute
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• v.21 no.4
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• pp.489-499
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• 2009

It is quite difficult to predict the flexural strength of post-tensioned members with unbonded tendons (unbonded posttensioned members, UPT members) because of debonding behavior between concrete and prestressing tendons, which is different from that with bonded tendons. Despite many previous researches, our understanding on the flexural strength of UPT members is still insufficient, and thus, national codes use different methods to calculate the strength, which quite often give very different results. Therefore, this paper reviews various existing methods, and aims at proposing an improved rational strength model for UPT flexural members having better accuracy. Additionally, a database containing a large number of test data on UPT flexural members has been established and used for verification of the proposed flexural strength model. The analysis results show that the proposed method provides much better accuracy than many existing methods including the rigid-body model that utilizes the assumption of concentrated deformation and plastic hinge length, and that it also gives proper consideration on the effects of primary parameters such as reinforcement ratio, loading pattern, concrete strength, etc. Especially, the proposed method also well predicts the ultimate stress of unbonded tendons of over-reinforced members, which are often possible in construction fields, and high strength concrete members.

• Korean Journal of Agricultural Science
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• v.23 no.1
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• pp.25-38
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• 1996

To investigate the stability problem of irrigation-drainage channel excavation slope on soft ground, analyzed the behavior of the soft ground with excavation slope by the limit equilibrium method and the finite element method, and compared with field tests. The results of this study were summarized as follows; 1. When rapid drawdown the water level, the crack was occurred by the effect of the excess pore water pressure, and the pore water pressure was decreased slowly. 2. As the width of excavation was larger, the crack width was larger. And, excavated depth was deeper, the progressive failure was appeared. 3. When the soft ground excavation was small-scale, the minimum safety factor was more effected by cohesion(1.0, 1.5, 2.0, 2.5, 3.0) than excavated slope inclination(1:l, 1:1.5, 1:2). 4. As excavation was progressed, the settlement occurred on the top-slope due to plastic domain, and heaving was occurred at the bottom of excavation. 5. The maximum shear stress was appeared greatly as the base part of slope went down. Because of the increase of the maximum shear stress, tension area occurred and local failure possibility was increased. 6. As the excavation depth was increased, the maximum shear strain was appeared greatly at the base of slope and distribution pattern was concentrated beneath the middle of slope.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.2
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• pp.171-182
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• 2007

For minimizing the effect on the focus of civil traffic and environment conditions related to the excavation at the traffic jamming points, an underground station tunnel was planned with 35.5 m in length and bigger area than $200\;m^2$ in sedimentary rock mass. It faced the case that the overburden was just under 13 m. Not based on a pattern design but on the case histories of similar projects and arching effect, the design of large section tunnel under shallow overburden was investigated on three design subjects which are shape effect on the section area, application method of support pressure, and supporting and tunnel safety. According to the mechanical effect from section shape, a basic design and a preliminary design was obtained, and then supporting method of large section was planned by the supporting of NATM and a pipe roof method for subsidence prevention and mechanical stability. From the comparative study between both designs, it was found that the basic design was suitable and acceptable for the steel alignment of tunnel lining, safety and the design parameter restricted by the limit considered as partition of the excavation facilities. Through the analysis result of preliminary design showing the mechanical stability without stress concentration in tunnel arch level, it also was induced that shape effect of the large section area and yielding load obtained from deformation zone in the surrounding rock mass of tunnel have to be considered as major topics for the further development of design technique on the large section tunnel.