• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.2
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• pp.121-131
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• 2007

Recently, the probability of rock joints being exposed to free faces is getting higher for the scale of rock mass structures gets larger. Also, the frequency of occurring dynamic events such as earthquakes and blasting has been increasing. Thus, the shear behavior of rock joints under different conditions needs to be investigated. In this study, a series of direct shear tests were carried out under various conditions to examine the velocity-dependent shear behavior of saw-cut rock joints. Two types of direct shear test were carried out. The first was to examine the velocity-dependent shear behavior of saw-cut rock joints at seven different shear velocities, each with three different normal stresses. The second was to examine the shear behavior of saw-cut rock joints when three different instantaneous shear velocities changed. As a result, the coefficient of friction was affected by normal stress. The breakpoint velocity, the point when the change of shear velocity starts to affect the frictional behavior, became lower as normal stress increased. Also, as the shear velocity became lower, the degree of stress-drop on stick-slip behavior became larger. As a result of examining the changes of friction coefficient, velocity weakening (decrease of friction coefficient) was observed. The decrement of friction coefficient due to the changes of shear velocity under slow shear velocity was larger than that under fast shear velocity.

• Journal of the Korean Applied Science and Technology
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• v.37 no.1
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• pp.83-90
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• 2020

Plate heat exchangers(PHE) have been commercialized since the 1920s. Since then, although the basic concept of PHEs has changed little, its design and construction have progressed significantly to accommodate higher temperatures, higher pressures, and large heat exchanging capacities. The development trend of PHEs is consistent with heat plate developments with better thermal efficiency, lower pressure drop, and good flow distribution. The purpose of this paper is to introduce the main development processes of a plate cooler for medium-speed engine lubricant oil cooling in vessels which is in line with the development trend of PHEs and to provide its thermal performance data that were found out during experimental tests. The plate cooler in this study cannot measure the wall temperatures directly due to its structural characteristics, so the heat transfer coefficients were calculated using the modified Wilson Plot method. The water-to-water tests were first conducted experimentally to figure out the characteristics of heat transfer coefficients and pressure drops on the water side and then the water-to-oil tests followed to obtain the heat transfer coefficients on the oil side. The test results showed that heat transfer coefficients and pressure drops on both water and oil side increased with flow rates, and it was also found that all the development targets of the plate cooler in this study were achieved successfully.

• Tunnel and Underground Space
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• v.27 no.4
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• pp.217-229
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• 2017

This study focuses on the improvement of the working environment in domestic collieries where temperature is increasing due to heat of the earth that is caused by the long-term mining. In order to improve the working environment of the mine, a ventilation evaluation was carried out for Hwasoon Mining Industry. In order to increase the ventilation efficiency of the mine, numerical analysis of the effect on temperature was carried out by using climsim, a temperature prediction program. The analysis shows that A coal mine needs $6,152m^3/min$ for in-flow ventilation rate but the total input air flowrate is $4,710m^3/min$, $1,442m^3/min$ of in-flow ventilation rate shortage. The 93 m hypothetical ventilation shaft from -395 ML to -488 ML could result about $3^{\circ}C$ temperature drop in the coal mine of -488 ML far. As a result of predicting the $CO_2$ concentration at -523 ML development using artificial neural network, the emission of $CO_2$ increased as the amount of coal and coal bed thickness increased. The factors that have the greatest effect on the amount of $CO_2$ emissions were coal layer thickness and coal mining. And, as the air quantity increases, it has a great effect on the decrease of carbon dioxide concentration.

• Anxiety and mood
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• v.10 no.1
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• pp.11-16
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• 2014

Objective : Despite the high prevalence and clinical importance of panic disorder, studies on the clinical characteristics and course of panic disorder are relatively rare. This study is a multi-center, and retrospective study to examine the clinical characteristics and course of Korean panic disorder patients who visit university hospital. Methods : The study subjects were panic disorder patients who had visited the psychiatric outpatient clinics of 8 university hospitals in South Korea from January to December in 2008. Finally, 238 panic patients were included in this study. Their medical charts were retrospectively reviewed and reassessed by experienced psychiatrists to examine their clinical characteristics, demographic data and clinical course in repose to pharmacotherapy. Results : Among the 238 patients (121 males vs. 117 females), the mean age of disease onset was $41.3{\pm}12.7$ years and female patients showed 5 years older age of disease onset, compared with male patients. The mean score of PSR scale was $4.5{\pm}1.0$ at the first visit, reflecting a 'marked' level of severity of illness and impairment in functioning. Only 110 patients (46.4%) completed the whole follow up visits, whereas 128 patients (53.6%) dropped out during the treatment. After $17.7{\pm}0.5$ months of mean follow up period, the mean score of PSR scale at the last visit was reduced into $2.1{\pm}0.9$, reflecting a 'residual' severity of illness and impairment in functioning. The cumulative recovery rate was 62.1% in the completer group, whereas that of the drop-out group was 47.7%. Conclusions : The mean age of disease onset in Korean panic disorder patients who had visited university hospital was about 10 years older than that of Western panic disorder patients in previous studies, and the Korean panic disorder patients who had visited university hospital showed a relatively higher cumulative recovery rate. These differences might result from an ethnic difference in clinical characteristics and course in response to pharmacotherapy of panic disorder.

• Journal of Korean Society of Environmental Engineers
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• v.37 no.1
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• pp.23-33
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• 2015

This study was carried out for the purpose of minimizing the area of rapid flow inside the water tank. And the shape of incurrent canal was improved, and then the characteristics of fluid flow occurring inside the water tank was analyzed by using the Computational Fluid Dynamics (CFD) simulation method. better multiple hoe screw nozzle incurrent canal was used instead of conventional drop current canal used for the water tank. And according to the results of analyzing the characteristics of fluid flow, in case a screw blade was installed inside the nozzle, fluid flow was sprayed wide. And wide fluid flow was shown inside the cylindrical water tank too. Besides, a tracer simulation was carried out, in case of installing 1 and 2 multiple hoe screw nozzle incurrent canals at the cubic water tank. As a result, MODAL, MODAL index value was close to 1, in case of installing 2 canals. Therefore, it was possible to obtain the results of being close to the characteristics of plug flow.

• Journal of the Korean Institute of Landscape Architecture
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• v.38 no.1
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• pp.107-118
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• 2010

Palaces of a country can be representative aggregate of the culture and arts of the country. Palaces were used not only as a living place to protect kings and royal families and to live cultural lives, but also a political place to govern the country. Kings in Choseon founded the country on the Sung Confucianism, their philosophical background. They built Bangji and Wondo as constant reminders of their philosophy. Bangji is the most apparent characteristic in the palace gardens of the Choseon Dynasty. Finding out the original form of Jidang, restoring the original and passing it on to future generations can be passing on the spiritual culture of our ancestors. This study is done to find out or locate well preserved Jidang, transformed Jidang and lost Jidang in Changdeokgung, which is the best conserved palace of Choseon. This study is composed of Jidang which has been kept in its original state, transformed Jidang, locating lost Jidang and Jidnang which has been unearthed. The total number of Donggwoldo's Jidangs is 17; those that are kept in their original state, 4; transformed Jidangs, 5; Jidangs that were lost and have been located, 8; and newly appeared Jidangs, 2. From the results, opinions on restoration are presented. This study can be a small drop in the thin stream of tradition passing onto future generations in this world where knowledge and information are transported momentarily and the classification of culture and border is mixed, yielding vagueness.

• Journal of the Korean Ceramic Society
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• v.40 no.9
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• pp.874-880
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• 2003

The effect of h-BN content on microstructure, mechanical properties, and machinability of AlN-BN based machinable ceramics were investigated. The relative density of sintered compact decreased with increasing h-BN content. The four-point flexural strength also decreased from 238 MPa of monolith up to 182 MPa by the addition of 30 vol％ h-BN. Both low Young's modulus and residual tensile stress, formed by the thermal expansion coefficient difference between AIN and h-BN, might cause the strength drop in AlN-BN composite. The crack deflection, and pull-out phenomena increased by the plate-like h-BN. However, the fracture toughness decreased with h-BN content. The second phases, consisted of YAG and ${\gamma}$-Al$_2$O$_3$, were formed by the reaction between Al$_2$O$_3$ and Y$_2$O$_3$. During end-milling process, feed and thrust forces measured for AlN-(10～30) vol％ BN composites decreased with increasing h-BN particles, showing excellent machinability. Also, irrespective of h-BN content, relatively good surfaces with roughness less than 0.5 m (Ra) could be achieved within short lapping time.

• Journal of Industrial Convergence
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• v.19 no.1
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• pp.117-127
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• 2021

The purpose of this study was to identify the relationship between social support, academic self-efficacy, and learning agility on intention of academic dropout among nursing students. Data collection was conducted online surveys from November 9 to 27, 2020. The 363 students were conveniently sampled from the school of nursing in K-do in Korea. The contents of the self-reported questionnaire included social support, academic self-efficacy, learning agility, intention of academic dropout. As a result, The score of each variables were like this: social support 4.32, academic self-efficacy 3.66, learning agility 3.40, intention of academic dropout 2.08. The factors that affecting intention of academic dropout among nursing students are academic self-efficacy, learning agility, satisfaction on major, perceived mental health status, grade in score and grade, which explained 30.4% of the variances. Therefore in order to lower the intention of dropping out of nursing students, it is considered that the development of programs considering individual characteristics and systematic support are necessary.

• Journal of Convergence for Information Technology
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• v.11 no.2
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• pp.138-145
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• 2021

The purpose of this study was to investigate the mediating effects of academic procrastination behavior on the relationship between academic stress and dropout intention. The research questions are First, does the academic stress of college students influence the intention to drop out? Second, does academic procrastination behavior the relationship between academic stress and dropout intention? A survey was conducted on 218 college students about academic stress, dropout intention, and academic procrastination behavior. Correlation analysis was conducted to find out the relationship between academic stress, dropout, and academic procrastination behavior, and Multiple regression analysis was performed to determine the moderating effect of academic procrastination behavior. The mediating effect was verified using Baron and Kenny's procedure, and the significance was verified by Sobel verification. The results are as follows: First, academic stress, dropout intention, and academic delay behavior showed significant positive correlations.. Second, Academic stress showed 15% of explanatory power as an influential factor on dropout intention, and 5% of explanatory power was an influential factor on academic procrastination behavior. Third, the through mediation analysis, there was partial mediated effects of academic procrastination behavior between academic stress and dropout intention. Our findings suggest that to improve the dropout intention among college students, educators should carefully design and develop an education program

• Korean Journal of Applied Biomechanics
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• v.33 no.3
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• pp.110-117
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• 2023

Objective: The purpose of this study was to find out kinematic and kinetic differences the lower extremity joint according to the landing type during vertical jump movement after jump landing, and to present an efficient landing method to reduce the incidence of injury in youth players. Method: Total of 24 Youth players under Korean Sport and Olympic Committee, who used either heel contact landing (HCG) or toe contact landing (TCG) participated in this study (HCG (12): CG height: 168.7 ± 9.7 cm, weight: 60.9 ± 11.6 kg, age: 14.1 ± 0.9 yrs., career: 4.3 ± 2.9 yrs., TCG height: 174.8 ± 4.9 cm, weight: 66.9 ± 9.9 kg, age 13.9 ± 0.8 yrs., career: 4.7 ± 2.0 yrs.). Participants were asked to perform jump landing consecutively followed by vertical jump. A 3-dimensional motion analysis with 19 infrared cameras and 2 force plates was performed in this study. To find out the significance between two landing styles independent t-test was performed and significance level was set at .05. Results: HCG showed a significantly higher dorsi flexion, extension and flexion angle at ankle, knee and hip joints, respectively compared with those of TCG (p<.05). Also, HCG revealed reduced RoM at ankle joint while it showed increased RoM at knee joint compared to TCG (p<.05). In addition, HGC showed greater peak force, a loading rate, and impulse than those of TCG (p<.05). Finally, greater planta flexion moment was revealed in TCG compared to HCG at ankle joint. For the knee joint HCG showed extension and flexion moment in E1 and E2, respectively, while TCG showed opposite results. Conclusion: Compared to toe contact landing, the heel contact landing is not expected to have an advantage in terms of absorbing and dispersing the impact of contact with the ground to the joint. If these movements continuously used, performance may deteriorate, including injuries, so it is believed that education on safe landing methods is needed for young athletes whose musculoskeletal growth is not fully mature.