• Restorative Dentistry and Endodontics
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• 제19권1호
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• pp.45-63
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• 1994

128 freshly extracted human molars were used to study the interaction between dentinal smear layer removal with various agents, and the shear bond strength of a light cured glass ionomer cement to dentin. It was proposed that the removal of smear layers using acidic cleaners followed by incorporation of Fe mordant with dentin could enhanced the infiltration of monomer component in light curing glass ionomer cement and resulted in a high bond strength. For the first treatment process for removal of smear layers on the surfaces of dentin, 50 % citric acid, 10% maleic acid and 10 % phosphoric acid were used, and for the second treatment process, 15% ferric chloride, 6.8% ferric oxalate or 30% potassium oxalate were used. Distilled water was used as a control. After double sequential treatment on dentin, a light curing glass ionomer cement was bonded to dentin. After being immersed in water at 31'C for 24 hours, shear bond strengths were measured Instron testing machine(Model No.4202, USA). Surface changes were also observed using SEM (Hitachi, S-2300, Japan) after treatment process with each agents. The following conclusions were drawn : 1. Dentin surface cleaned with maleic acid and treated with ferric oxalate showed the highest bond strength with light curing glass ionomer cement. 2. Bond strengths of glass ionomer cement to dentin treated with maleic acid or citric acid were the highest, and that treated with phosphoric acid showed the lowest. 3. The effect of ferric oxalate on shear bond strength to dentin was always higher than that of ferric chloride. 4. The smear layers were clearly removed and the orifices of dentinal tubules were opened widely by the citric acid, maleic acid and phosphoric acid. 5. The orifices of dentinal tubules opened after using the first solution were closed with the treatment of ferric chloride. 6. The precipitate like crystals were formed on dentin surfaces and tubules, but a significant decrease in bond strength of glass ionomer cement to dentin surface treated with potassium oxalate.

• 농촌계획
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• 제26권4호
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• pp.117-129
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• 2020

The purpose of this study is to verify the effect of the authentic leadership of social enterprise leaders on the happiness and job crafting of employees, the mediation effect of job crafting in the authentic leadership of the leader and the happiness of the employees, and the coordination effect by the Grit of the employees. For verification, the relationship between authentic leadership and job crafting, happiness and grit and seven research theories were established. In addition, 47 questionnaires were drawn through prior research on happiness, authentic leadership, job crafting, and grit, and five executives and workers of social enterprises in Chungcheongbuk-do(Province) were surveyed on a five-point Likert scale. The collected survey data were conducted through the SPSS and AMOS for basic statistical analysis. The Macro Process of the bootstrap method was used to verify the mediation effects, the regulated effects. This study has conducted exploratory and confirmatory factor analysis, correlation analysis, structural model analysis through the survey results and the analysis results verify the hypothesizes. The study found that authentic leadership affects the happiness and job crafting of employees, and that job crafting affects the happiness of employees, and the relationship between authentic leaders and employees affects job crafting. It has also been shown that the Grit of its employees affects their job crafting and happiness and also has a mediation effect on job crafting and happiness. In the policy environment of the changing rural development project, the social economy establishment plan for the virtuous circle of resources in the region should be considered, and education programs should be introduced to improve the authentic leadership of the leaders.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.106-109
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• 2005

Springback is a common phenomenon in sheet metal forming, caused by the elastic recovery of the internal stresses after removal of the tooling. Recently, advanced high strength steels (AHSS) such as TRIP and DP are finding acceptance in the automotive industry because their superior strength to weight ratio can lead to improved fuel efficiency and assessed crashworthiness of vehicles. The major troubles of the automotive structural members stamped with high strength steel sheets are the tendency of the large amount of springback due to the high yield strength and the tensile strength. The amount of springback is mainly influenced by the type of the yield function and anisotropic model induced by rolling. The discrepancy of the deep drawn product comparing the data of from the product design induced by springback must be compensated at the tool design stage in order to guarantee its function and assembly with other parts. The methodology of compensation of the low shape accuracy induced by large amount of springback is developed by the expert engineer in the industry. Recently, the numerical analysis is introduced in order to predict the amount of springback and to improve the shape accuracy prior to tryout stage of press working. In this paper, the tendency of springback is evaluated with respect to the blank material. The stamping process is analyzed fur the front side member formed with AHSS sheets such as TRIP60 and DP60. The analysis procedure fully covers the binderwrap, stamping, trimming and springback process with the commercial elasto-plastic finite element code LS-DYNA3D.

• Journal of Preventive Medicine and Public Health
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• 제35권4호
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• pp.305-312
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• 2002

Objectives : The reproductive history of women has been suggested to have a possible influence on the risk of osteoporotic fractures. The purpose of this study was to assess the association between reproductive history and hip fractures in the elderly women. Methods : The study subjects were drawn from women members of the Korean Elderly Pharmacoepidemiologic Cohort (KEPEC), aged 65 years or over, whose reproductive histories were available, and who were beneficiaries of the Korea Medical Insurance Corporation (KMIC) in 1993 and lived in Busan city, Korea. The information on reproductive histories, and possible confounders, were collected from mailed questionnaires. Potential hip fracture cases were collected from the claims data obtained between 1993 and 1998, with a hospital survey conducted to confirm the final diagnoses. Rate ratios and their 95% confidence intervals, were calculated using a Cox's proportional hazard model. Results : Following up 5,215 women for 6 years, 51 cases were confirmed with hip fractures. When adjusted for age, weight and physical activity, the rate ratio of hip fractures in women who had given birth three or more times was 0.56 (95% CI: 0.25-1.25), compared with those who had given birth two or less times. When adjusted for age, number of births, weight and physical activity, the rate ratio in women who first gave birth when younger than 22 years was 0.60 (95% CI: 0.34-1.08) compared with those who had giving birth at 22 years or older. Conclusions : According to these findings, an early age when first giving birth might decrease the risk of hip fractures in elderly Korean women.

• Korean Journal of Geomatics
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• 제2권1호
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• pp.47-55
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• 2002

Remote sensing is the science and art of obtaining information about an object, area or phenomenon through the analysis of data acquired by a device that is not in contact with the object, area, or phenomenon under investigation./sup 1)/ EOC (Electro -Optical Camera) sensor loaded on the KOMPSAT-1 (Korea Multi- Purpose Satellite-1) performs the earth remote sensing operation. EOC can get high-resolution images of ground distance 6.6m during photographing; it is possible to get a tilt image by tilting satellite body up to 45 degrees at maximum. Accordingly, the device developed in this study enables to obtain images by photographing one pair of tilt image for the same point from two different planes. KOMPSAT-1 aims to obtain a Korean map with a scale of 1:25,000 with high resolution. The KOMPSAT-1 developed automated feature extraction system based on stereo satellite image. It overcomes the limitations of sensor and difficulties associated with preprocessing quite effectively. In case of using 6, 7 and 9 ground control points, which are evenly spread in image, with 95% of reliability for horizontal and vertical position, 3-dimensional positioning was available with accuracy of 6.0752m and 9.8274m. Therefore, less than l0m of design accuracy in KOMPSAT-1 was achieved. Also the ground position error of ortho-image, with reliability of 95%, is 17.568m. And elevation error showing 36.82m was enhanced. The reason why elevation accuracy was not good compared with the positioning accuracy used stereo image was analyzed as a problem of image matching system. Ortho-image system is advantageous if accurate altitude and production of digital elevation model are desired. The Korean map drawn on a scale of 1: 25,000 by using the new technique of KOMPSAT-1 EOC image adopted in the present study produces accurate result compared to existing mapping techniques involving high costs with less efficiency.

• Current Research on Agriculture and Life Sciences
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• 제5권
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• pp.134-142
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• 1987

The purpose of this study is to establish more rational and practical planning theory for amusementpark. It analyze and considerate the fluctuation of the people who come and use a Tong-Ch'on amusementpark. The results drawn from this research work are as follows ; There are considerable correlation between use fluctuation and some factors. The factors are season (spring, summer, autumn) as a time, temperature, cloud amount, duration of sunshine, weather (rainy day) as a climate and date (weekday, holiday) as a social system. The important variables are temperature, cloud amount, duration of sunshine and date (week day, holiday) to estimate the user of amusementpark. I can reduce the following two types of regression models. 1.${\log}_eY1=6.9114+0.1135TEM+0.00002_eSUM-0.4068WI+0.4316W3$ ($R^2=0.94$) 2. ${\log}_eY2=7.2069+0.1177TEM-0.0990CLO+0.488W3$ ($R^2=0.95$) Y ; Number of User TEM ; Temperature CLO ; Amount of cloud SUN ; Duration of Sunshine WI ; Weekday W3 ; Holiday Those model is inorder to estimate the user for management of Tong-Ch'on amusementpark and use on the computation of facility size for reconstruction. Besides the amusementpark, city park and outdoor recreation area could estimate of user throuth this method. But, I am not sure about the regression models because I didn't apply the regression models to the other amusementpark, city park or outdoor recreation area. Therefore, I think that this problem needs to study in the future.

• Steel and Composite Structures
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• 제36권1호
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• pp.47-62
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• 2020

In this study, free vibration behavior of trapezoidal sandwich plates with porous core and two graphene platelets (GPLs) reinforced nanocomposite outer layers are presented. The distribution of pores and GPLs are supposed to be functionally graded (FG) along the thickness of core and nanocomposite layers, respectively. The effective Young's modulus of the GPL-reinforced (GPLR) nanocomposite layers is determined using the modified Halpin-Tsai micromechanics model, while the Poisson's ratio and density are computed by the rule of mixtures. The FSDT plate theory is utilized to establish governing partial differential equations and boundary conditions (B.C.s) for trapezoidal plate. The governing equations together with related B.C.s are discretized using a mapping- generalized differential quadrature (GDQ) method in the spatial domain. Then natural frequencies of the trapezoidal sandwich plates are obtained by GDQ method. Validity of current study is evaluated by comparing its numerical results with those available in the literature. A special attention is drawn to the role of GPLs weight fraction, GPLs patterns of two faces through the thickness, porosity coefficient and distribution of porosity on natural frequencies characteristics. New results show the importance of this permeates on vibrational characteristics of porous/GPLR nanocomposite plates. Finally, the influences of B.C.s and dimension as well as the plate geometry such as face to core thickness ratio on the vibration behaviors of the trapezoidal plates are discussed.

• 한국BIM학회 논문집
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• 제9권3호
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• pp.41-53
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• 2019

As a central part in smart construction, BIM has been rapidly spread in construction industry at large. However, the level of applying BIM in construction stage is still relatively lower than that in design stage due to unclear application method, inadequate design BIM model, technical faults of BIM itself, etc. Under these circumstances, public owners inevitably need to adjust the scope and pace in BIM application considering their internal support and capabilities of contractors. This study aims to suggest major BIM-applicable tasks during construction stage in the process of establishing gradual long-term and short-term introduction strategy for public apartment housing projects. Those major tasks were identified with the combination of the importance of tasks and the future benefits of BIM using IPA method. To do so, the degrees of contribution to achieving objectives in construction, current task execution, and communication requirement were investigated by internal site managers. On the other hand, the expected benefits and current level of using BIM were assessed by BIM experts. Among operational tasks by phases, design review, construction plan review, making as-built drawing, etc. were categorized as major tasks. In addition, progress control, regular meeting, master schedule development, work inspection, on-site quality check, etc. were also drawn as major tasks by management areas. The results of this study will provide the useful reference for owners concerned about the introduction of new technologies.

• 한국산학기술학회논문지
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• 제20권2호
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• pp.655-661
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• 2019

본 연구는 차량용 리어 디퓨저의 시작 위치에 따른 주행 성능 변화를 분석하고자 하였다. 이를 위해 CATIA 3D 설계 프로그램을 이용하여 상용 SUV 차량을 참고하여 차량을 모델링하고 뒤 타이어를 기준으로 300, 400, 500 mm 떨어진 위치부터 리어 디퓨저가 시작되도록 설계했다. 그리고 유동 해석 프로그램인 Fluent를 이용해 차량 주행속도가 60km/h, 100km/h, 140km/h 일 경우를 조건으로 하여 유동해석 후 양력과 항력의 변화를 분석하고 공기의 유선 변화를 확인했다. 해석 결과, 리어 디퓨저는 시작 위치에 상관없이 디퓨저가 없는 경우에 비해 양력과 항력을 감소시켰다. 이는 리어 디퓨저가 있을 경우 공기가 차량 하면부를 지나 후면부로 빠져나올 때 발생하는 박리 현상을 억제하여 와류 현상을 감소시키기 때문이다. 또한 본 연구에서는 SP 400의 조건일 때 양력이 가장 작았고 양력 감소 효과도 가장 좋았기 때문에 주행 중 타이어의 접지력을 최대로 확보할 수 있어서 이 경우를 최적의 조건으로 결정하였다.

• Human Ecology Research
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• 제57권1호
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• pp.127-142
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• 2019

This study investigates factors that impact dating relationship stability(DRS) among college students by applying two key concepts from the Interdependence Theory suggested by Kelly & Thibaut (1978; Thibaut & Kelly, 1959), the comparison level(CL) and comparison level for alternatives($CL_{alt}$). This study also examined mediating effects of commitment on the relationship between CL and DRS and $CL_{alt}$ and DRS. The research used a survey data set drawn from 327 college students currently involved in a dating relationship. The collected data set was then analyzed using SPSS software ver. 23.0 and AMOS software ver. 25.0, to produce the descriptive statistics, Pearson's correlations, and path analysis with bootstrapping. First, both CL and $CL_{alt}$ had a significant direct impact on DRS. In terms of effect size, CL's effect size was comparatively larger than $CL{_{alt}}'s$. The mediating effects from the commitment were evidenced. In the model, the commitment partially mediated the relationships between CL and DRS, and $CL_{alt}$ and DRS. The findings suggest that commitment still plays a key role in dating relationships among college students who currently have a romantic partner. The findings of this study show the possibilities in applying the concepts and theory of interdependence to explain current dating relationships among young adults.