• Journal of Korean society of Dental Hygiene
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• v.10 no.4
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• pp.595-605
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• 2010

Objectives : A precedent research has documented that occupational stress is closely associated with increased the risk of fatigue and decreased in job satisfaction. This study was conducted in an effort to assess the relationship of occupational stress to self-perceived fatigue and job satisfaction by using job strain model. Methods : The number of respondents was 122 dental hygienist who work in dental clinic and period of the investigation was July 2009 through september 2009. A structured questionnaire was employed to evaluate the participants' sociodemographics, job-related factors, health-related behaviors, occupational stress, job satisfaction and self-perceived fatigue. Occupational stress and self-perceived fatigue were assessed using the Korean Occupational Stress Scale-Short form (KOSS-SF) and the Multidimensional Fatigue Scale (MFS), respectively. Results : In job strain model, the ratio of Q2(High Strain Job) group that more susceptible to disease by stress than other group was 16% and the proportion of high fatigue group(Q3, Q4 group) and low job satisfaction group(Q3, Q4 group) was 48%, 45% respectively. In logistic regression analyses, a High Strain Job group was associated with higher odds of react factor(fatigue, job satisfaction) and the odds was down by 3.3%~7.5% after adjustment for age, smoking, alcohol drinking, regular exercise. So the effective strategy for fatigue, job satisfaction reduction for dental hygienist requires additional program focusing on innovated work environment that provide a enough leisure time and exercise program considering the personality traits. Conclusions : The results of this study suggest that occupational stress is a determinant predictor of self perceived fatigue and job satisfaction. Thus, a stress management program for the reduction of occupational stress, and the promotion of dental hygienist impact assessment health and quality of life is strongly recommended.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.214-224
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• 1990

A "two-fluid" model using thermal eddy diffusivity concept and Lumley's drag reduction theory, is proposed to analyze heat transfer of the turbulent dilute gas-particle flow in a vertical pipe with constant wall heat flux. The thermal eddy diffusivity is derived to be a function of the ratio of the heat capacity-density products .rho. over bar $C_{p}$ of the gaseous phase and the particulate phase and also of the ratio of thermal relaxation time scale to that of turbulence. The Lumley's theory dictates the variation of the viscous sublayer thickness depending on the particle loading ratio Z and the relative particle size $d_{p}$/D. At low loading ratio, the size of viscous sublayer thickness is important for suspension heat transfer, while at higher loading, the effect of the ratio .rho. $_{p}$ over bar $C_{p}$$_{p}$/ .rho. $_{f}$ over bar $C_{p}$$_{f}$ is dominant. The major cause of decrease in the suspension Nusselt number at lower loading ratio is found to be due to the increase of the viscous sublayer thickness caused by the suppression of turbulence near the wall by the presence of solid particles. Predicted Nusselt numbers using the present model are in satisfactory agreements with available experimental data both in pipe entrance and the fully developed regions.

• Composites Research
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• v.14 no.3
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• pp.1-9
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• 2001

A new non-destructive fatigue prediction model of the composite laminates is developed. The natural frequencies of fatigue-damaged laminates under extensional loading are related to the fatigue life of the laminates by establishing the equivalent flexural stiffness reduction as a function of the elastic properties of sublaminates. The flexural stiffness is derived by relating the 90-ply elastic modulus reduction, and using the laminate plate theory to the degraded elastic modulus and the intact elastic modulus of other laminates. The natural frequency reduction model, in which the dominant fatigue mode can be identified from the sensitivity scale factors of sublaminate elastic properties, provides natural frequency vs. fatigue cycle curves for the composite laminates. Vibration tests were also conducted on $[{90}_2/0_2]_s$ carbon/epoxy laminates to verify the natural frequency reduction model. Correlations between the predictions of the model and experimental results are good.

• Industrial Engineering and Management Systems
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• v.13 no.4
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• pp.454-462
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• 2014

Retention of possible churning customer is one of the most important issues in customer relationship management, so companies try to predict churn customers using their large-scale high-dimensional data. This study focuses on dealing with large data sets by reducing the dimensionality. By using six different dimension reduction methods-Principal Component Analysis (PCA), factor analysis (FA), locally linear embedding (LLE), local tangent space alignment (LTSA), locally preserving projections (LPP), and deep auto-encoder-our experiments apply each dimension reduction method to the training data, build a classification model using the mapped data and then measure the performance using hit rate to compare the dimension reduction methods. In the result, PCA shows good performance despite its simplicity, and the deep auto-encoder gives the best overall performance. These results can be explained by the characteristics of the churn prediction data that is highly correlated and overlapped over the classes. We also proposed a simple out-of-sample extension method for the nonlinear dimension reduction methods, LLE and LTSA, utilizing the characteristic of the data.

• Structural Engineering and Mechanics
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• v.61 no.3
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• pp.419-426
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• 2017

Recently, the transportation of dangerous explosive goods is increasing, which makes vehicle blasting accidents a potential threat for the safety of bridge structures. In addition, blasting accidents happen more easily when earthquake occurs. Excessive dynamic response of bridges under extreme loads may cause local member damage, serviceability issues, or even failure of the whole structure. In this paper, a new explosion-proof and aseismic system is proposed including cable support damping bearing and steel-fiber reinforced concrete based on the existing researches. Then, considering one 40m-span simply supported concrete T-bridge as the prototype, through scale model test and numerical simulation, the dynamic response of the bridge under three conditions including only earthquake, only blast load and the combination of the two extreme loads is obtained and the applicability of this explosion-proof and aseismic system is explored. Results of the study show that this explosion-proof and aseismic system has good adaptability to seism and blast load at different level. The reducing vibration isolation efficiency of cable support damping bearing is pretty high. Increasing cables does not affect the good shock-absorption performance of the original bearing. The new system is good at shock absorption and displacement limitation. It works well in reducing the vertical dynamic response of beam body, and could limit the relative displacement between main girder and capping beam in different orientation so as to solve the problem of beam falling. The study also shows that the enhancement of steel fibers in concrete could significantly improve the blast resistance of main beam. Results of this paper can be used in the process of antiknock design, and provide strong theoretical basis for comprehensive protection and support of girder bridges.

• Structural Engineering and Mechanics
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• v.52 no.5
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• pp.875-887
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• 2014

The aim of the shaking table experiment is to verify the isolation effect of a storage liquid tank with multiple friction pendulum bearings. A 1:20 scale model of a real storage liquid tank that is widely used in the petroleum industry was examined by the shaking table test to compare its anchored base and isolated base. The seismic response of the tank was assessed by employing the time history input. The base acceleration, wave height and tank wall stress were used to evaluate the isolation effect. Finally, the influences of the bearing performance that characterizes the isolated tank, such as the friction force and residual displacement, were discussed.

• Journal of Navigation and Port Research
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• v.37 no.2
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• pp.195-201
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• 2013

Recently according to increase of enlarged scale ports in conformity with increase in over size vessels and container handling service, pollutants generated from ports are increasing. In advanced countries, reduction in carbon dioxide emission assigned to them has been implemented according to the Climate Change Convention and Kyoto Protocol from 2008 to 2012 in order to lessen carbon dioxide emission. Henceforth increase in discussion on the measure of constructing Green Port and low-carbon port is expected in our nation's field of port as well, it is considered that the effort in reduction with regard to undesirable output which causes environmental problem of analysis target during measuring effectiveness. Therefore, in this study, effectiveness was estimated through directional technology distance function considering undesirable output differently from effectiveness analysis of existing container terminal, and then performed comparative analysis with the result analyzed with BCC output-oriented model. As the result of analysis, in 2007 DMU3 and DMU5, and in 2010 DMU2 and DMU4 appeared to be efficient terminals in BCC output oriented model, and in directional technology distance function model, DMU1, DMU3 in 2007, DMU3, DMU5 in 2008, DMU7 in 2009, and DMU2, DMU5 in 2010 appeared to be efficient terminals.

• Journal of Ocean Engineering and Technology
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• v.32 no.1
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• pp.9-20
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• 2018

The present study deals with the conceptual design of a motion reduction device for a floating wave-offshore wind hybrid power generation platform. A damping plate attached to the bottom of a column of a large semi-submersible is introduced to reduce the motion of the platform. Performance analyses on various shapes and configurations of damping plates were performed using the potential flow solver, and the appropriate configuration and size of the damping plate were selected based on the numerical results. In order to see the effect of viscous damping, a small scale model test was performed in a 2D wave flume. The performances of five different damping plates were measured and discussed based on the results of free decay tests and regular wave tests.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.36 no.2
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• pp.54-59
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• 2004

The methods for the minimization of fresh water consumption, waste water generation and water contamination have been greatly investigated and developed for last ten years. Recently, the rising cost of waste water treatment and the more strict environmental regulation lead to the higher demand of more efficient and systematic methods for process water management. The water reuse technology, which not only reduce the process water needs but also minimize waste water generation within the process, could be one of most efficient way for current demand. In this study, the practical way for reduction of water pollution and optimal reuse or recycle of process water in a newsprint mill was investigated by using a simulation model. The result of computer simulation showed that the COD level of approach system could be reduced by 50% after the stock concentration at the 2nd disc filter was increased upto 30%. The application of WRDF(Wrinkled Rotary Drum Filter) to the newsprint mill was carried out with pilot scale. The process water treated by WRDF had enough cleanliness to substitute the forming fabric shower water with the PDF water, which could result in the 30% reduction in fresh water consumption.

• Structural Engineering and Mechanics
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• v.38 no.2
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• pp.141-156
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• 2011

A cable stayed bridge under construction has low structural damping and is not as stable as the completed bridge. Control countermeasures, such as the installation of energy dissipating devices, are thus required. In this study, the general procedure and key issues on adopting an active control device, the active mass damper (AMD), for vibration control of cable stayed bridges under construction were studied. Taking a typical cable stayed bridge as the prototype structure; a lab-scale test structure was designed and fabricated firstly. A baseline FEM model was then setup and updated according to the modal parameters measured from vibration test on the structure. A numerical study to simulate the bridge-AMD control system was conducted and an efficient LQG-based controller was designed. Based on that, an experimental implementation of AMD control of the transverse vibration of the bridge model was performed. The results from numerical simulation and experimental study verified that the AMD-based active control was feasible and efficient for reducing dynamic responses of a complex structural system. Moreover, the discussion made in this study clarified some critical problems which should be addressed for the practical implementation of AMD control on real cable-stayed bridges.