• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.6
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• pp.1309-1320
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• 2015

This study made an attempt to analyse the relationship between operation environment and fleet size per route which represents the level of service for inner-city bus service. Regression analysis method has been adopted as main analysis tool and 98 routes of bus operation status in Ulsan city as of 2013 has also been selected for analysis target. Correlation analysis was performed to identify the relationship between dependent and independent variables. There are three types of model for whole sample, type operation, and bus route operation system. These are the results of the current study. 1. The model developed for whole sample of 98 routes is as follows. Y(Fleet Size)=$-4.532+0.00002877*X_1$(Revenue). This model shows that it is necessary to have more than 140 passengers per day to increase fleet size of each bus route in Ulsan. 2. Models developed by type of operation (which are standard, express, and middle sized) are shown below. Stand Bus : Y(Fleet Size)=$-10.954+0.00004283*X_1$(Revenue). It is identified that more than 153 passengers need to use standard bus to increase fleet size per each standard bus, Middle Sized Bus : Y(Fleet Size)=-0.859+0.00001438*X1(Revenue). For middle sized bus, at least 52 daily passengers are needed to increase number of bus in each route. 3. Models developed for each route operation systems are as belows. Joint Operation Group : Y(Fleet Size)=$-4.786+0.00003028*X_1$(Revenue). Individual Operation Group : Y(Fleet Size)=$-2.339+0.00002030*X_1$(Revenue). These model provide similar result which 140 people is the minimum number of passenger to raise the number of vehicles in each route. This result shows that the route operation systems does not affect the raise number of cars significantly.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.2
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• pp.187-194
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• 2012

The strength of particle-reinforced metal matrix composites is, in general, known to be increased by the geometrically necessary dislocations punched around a particle that form during cooling after consolidation because of coefficient of thermal expansion (CTE) mismatch between the particle and the matrix. An additional strength increase may also be observed, since another type of geometrically necessary dislocation can be formed during extensive deformation as a result of the strain gradient plasticity due to the elastic-plastic mismatch between the particle and the matrix. In this paper, the magnitudes of these two types of dislocations are calculated based on the dislocation plasticity. The dislocations are then converted to the respective strengths and allocated hierarchically to the matrix around the particle in the axisymmetric finite-element unit cell model. The proposed method is shown to be very effective by performing finite-element strength analysis of $SiC_p$/Al2124-T4 composites that included ductile failure in the matrix and particlematrix decohesion. The predicted results for different particle sizes and volume fractions show that the length scale effect of the particle size obviously affects the strength and failure behavior of the particle-reinforced metal matrix composites.

• The Journal of the Convergence on Culture Technology
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• v.8 no.6
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• pp.655-660
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• 2022

This paper analyzes the problem of the economic order quantity (lot size) of a retailer in a two-stage supply chain consisting of a supplier, a retailer(distributor), and a customer. In this two-stage supply chain, the supplier permits the retailer to defer payment for a certain fixed period of time for the purchase cost to be paid by the retailer as a price differentiation strategy with his competitor. In addition, in the case of customer goods such as food and grain, it is common to see that end-customer demand is generally depend on the level of inventory displayed by the retailer. From this perspective, this paper analyzes the inventory problem of retailers under the assumption that the supplier may allow a certain period to suspend payments for the purchase of goods and the end customer demand is a function of the retailer's inventory level increasing with size. In this regard, we need to analyze how much the length of the grace period for product purchase costs affect the retailer's lot-sizing policy. Therefore, we formulate the retailer's annual net profit and analyze the effect of the length of credit period on the retailer's inventory policy numerically.

• Steel and Composite Structures
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• v.36 no.2
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• pp.143-161
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• 2020

In nanosized structures as the surface area to the bulk volume ratio increases the classical continuum mechanics approaches fails to investigate the mechanical behavior of such structures. In perforated nanobeam structures, more decrease in the bulk volume is obtained due to perforation process thus nonclassical continuum approaches should be employed for reliable investigation of the mechanical behavior these structures. This article introduces an analytical methodology to investigate the size dependent, surface energy, and perforation impacts on the nonclassical bending behavior of regularly squared cutout nanobeam structures for the first time. To do this, geometrical model for both bulk and surface characteristics is developed for regularly squared perforated nanobeams. Based on the proposed geometrical model, the nonclassical Gurtin-Murdoch surface elasticity model is adopted and modified to incorporate the surface energy effects in perforated nanobeams. To investigate the effect of shear deformation associated with cutout process, both Euler-Bernoulli and Timoshenko beams theories are developed. Mathematical model for perforated nanobeam structure including surface energy effects are derived in comprehensive procedure and nonclassical boundary conditions are presented. Closed forms for the nonclassical bending and rotational displacements are derived for both theories considering all classical and nonclassical kinematics and kinetics boundary conditions. Additionally, both uniformly distributed and concentrated loads are considered. The developed methodology is verified and compared with the available results and an excellent agreement is noticed. Both classical and nonclassical bending profiles for both thin and thick perforated nanobeams are investigated. Numerical results are obtained to illustrate effects of beam filling ratio, the number of hole rows through the cross section, surface material characteristics, beam slenderness ratio as well as the boundary and loading conditions on the non-classical bending behavior of perforated nanobeams in the presence of surface effects. It is found that, the surface residual stress has more significant effect on the bending deflection compared with the corresponding effect of the surface elasticity, Es. The obtained results are supportive for the design, analysis and manufacturing of perforated nanobeams.

• The Journal of Information Systems
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• v.26 no.2
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• pp.63-83
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• 2017

Purpose: In Korea, market size of social commerce has been increased steadily and highly, but profits of social commerce companies have been decreased because of excessive marketing cost. To overcome this stagnant market environment, new marketing strategy that could attract customers and make customers continue to use social commerce is required instead of cost consuming marketing strategy. The purpose of this study is to investigate the relationship among characteristics of social commerce - that is, economic value and information quality - usefulness, enjoyment, satisfaction and repurchase intention by applying motivation theory to the area of social commerce. Design/Methodology/Approach: Previous researches have been studied by applying Expectation-Confirmation Model (ECM), Theory of Planned Behavior (TPB), Technology Acceptance Model (TAM) and Stimulus-Organism-Response (S-O-R) Model, although there are many studies related with customer acceptance model in the field of e-commerce. However, there is not so many studies in applying motivation theory. So this study adopts new approach to examine why customers use social commerce based on motivation theory. Thus, this study adopts economic value and information quality as antecedents, and then customers will perceive extrinsic and intrinsic motivation; usefulness is extrinsic and enjoyment is intrinsic, and adopts satisfaction and repurchase intention as a dependent variable. The data of questionnaire were collected from customers who have experience to buy something in social commerce. 228 questionnaires as data unit of individual level were collected using random sampling. Findings: This study proved empirically that the relationship between antecedents and motivation factors has a positive influence, and motivation factors also have a positive influence on repurchase intention through satisfaction. This study provides the managers an insight that social commerce companies should pay more attention to improve customer satisfaction in order to increase higher performance in repurchase intention of social commerce.

• Health Policy and Management
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• v.24 no.1
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• pp.35-46
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• 2014

Background: This paper describes the relationship and effect of health examination on personal medical cost by identifying the difference of the cost for medical care in physician visit between the population without and with health examination. Methods: After classifying into three cohorts in which, independent variables were designed according to the Andersen's behavioral model, the association of personal medical cost for medical care and prescription drugs which is dependent variable was analyzed by t-test and Mann-Whitney test for description and gamma regression model for inference. Results: In personal average medical cost, the population with health examination paid significantly more than without health examination, 11.6% more in cohort 2008, 26.6% more in cohort 2009, and 48.0% more in combined cohort. The odds ratio on medical expenditure of outpatients with health examination was 1.067, 1.126, 1.398 significantly in cohort 2008, 2009, and combined cohort respectively, comparing to the group without health examination. In independent variables, that is female, the elderly, never married, non-working, non-metropolitan, the higher family income, the smaller family size, people with disability, the people with chronic disease, and people with health examination have significantly being paid more tendency showing positive association with medical cost. Conclusion: This result showed that medical expenditure in physician visit has been increased after taking a health examination. Therefore reasonable limitation of getting preventive medical service is suggested to avoid medical shopping around and reduce being repeated health examination by unifying control to find out easily the clinical results from various medical facilities.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.12
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• pp.1831-1843
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• 2001

In this study, convective boiling tests were conducted for enhanced tube bundles. The surface geometry consists of pores and connecting gaps. Tubes with three different pore sizes (d$_{p}$ = 0.20, 0.23 and 0.27 mm) were tested using R-123 and R-l34a for the following range: 8 kg/m$^2$s G 26 kg/m$^2$s, 10 kW/m$^2$ q0 40 kW/m$^2$and 0.1 $\chi$ 0.9. The convective boiling heat transfer coefficients were strongly dependent on heat flux with negligible dependency on mass flux or quality. For the present enhanced geometry (pores and gaps), the convective effect was apparent. The gaps of the present tubes may have served routes for the passage of two-phase mixtures, and enhanced the boiling heat transfer. The convective effect was more pronounced at a higher saturation temperature. More bubbles will be generated at a higher saturation temperature, which will lead to enhanced convective contribution. The pore size where the maximum heat transfer coefficient was obtained was larger for R-l34a (d$_{p}$ = 0.27 mm) compared with that for R-123 (d$_{p}$ = 0.23 mm). This trend was consistent with the previous pool boiling results. For the enhanced tube bundles, the convective effect was more pronounced for R-134a than for R-123. This trend was reversed for the smooth tube bundle. Possible reasoning is provided based on the bubble behavior on the tube wall. Both the modified Chen and the asymptotic model predicted the present data reasonably well. The RMSEs were 14.3% for the modified Chen model and 12.7% for the asymptotic model.model.

• The Journal of Information Systems
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• v.21 no.1
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• pp.1-17
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• 2012

Common Method Bias(CMB) may cause the potential inflation of correlations between measures assessed via the same method. The problem of CMB has been well known in behavioral sciences because the survey method with self-reporting is vulnerable to CMB. Thus, the discussion on CMB is still ongoing in the MIS research in US. However, in Korea, the MIS research has never paid attention on the CMB problem. The purpose of this study is to examine the CMB problem in the Korean MIS research. To evaluate the effect of CMB, empirical studies on Technology Acceptance Model(TAM) are selected because (1) TAM is one of the MIS research areas studied intensively, (2) TAM is a theoretical model well supported by the existing empirical studies so that the result of this study would have a great ripple effect when the CMB problem turned out to be serious, (3) CMB is domain-specific. 47 TAM samples (out of 45 studies) from three Korean Journals were selected and the relevant data were collected such as correlation matrixes and the measures of the dependent variable. To find and evaluate the size of CMB, two analytic methods (Marker-Variable Technique and Method-Method Pair Technique) are employed. The result showed that there exists CMB in the Korean studies but the problem is not so serious to distort the empirical testing, compared with that of US studies. However, considering that CMB can contaminate the testing results, Korean MIS researchers should explicitly deal with the problem in designing empirical studies and collecting data.

• Tribology and Lubricants
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• v.31 no.6
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• pp.302-307
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• 2015

The use of turbocharger in internal combustion engines has increased as it is a key components for improving system efficiency without increasing engine size. Because of increasing demand, many studies have evaluated rotordynamic performance so as to increase rotation speed. This paper presents a linear and nonlinear analysis model for a turbocharger rotor supported by a floating ring bearing. We constructed rotor model by using the finite element method and approximated bearings as being infinitely short. In the linear model, we considered fluid film force as stiffness and damping element. In nonlinear analysis, calculation of the fluid film force involved solving the time dependent Reynolds equation. We verified the developed model by comparing the results to those of previous research. The analysis results show that there are four unstable modes, which are rigid body modes combining ring and rotor motion. As the rotating speed increases, the logarithmic decrement shows that certain unstable modes goes into the stable area or the stable mode goes into the unstable area. These unstable modes appear as sub-synchronous vibrations in nonlinear analysis. In nonlinear analysis frequency jump phenomenon demonstrated in several experimental studies appears. The analysis results also showed that frequency jump phenomenon occurs when the vibration mode changes and the sequence of unstable mode matches the linear analysis result. However, the natural frequency predicted using linear analysis differs from those obtained using nonlinear analysis.

• Information Systems Review
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• v.22 no.1
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• pp.73-89
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• 2020

This study started to identify the "Forward-looking" of the technology appraisal model introduced to diversify financing methods of SMEs and improve financial accessibility. The multivariate regression analysis was performed by setting the business performance(growth, profitability, and stability) of technology financing companies as dependent variables, technology appraisal items as independent variables, number of employees, age of the company, asset and the Korea Standard of Industry Classification related to firm size and industry characteristics as control variables. As a result of the analysis, the technology appraisal items did not explain the profitability of the company significantly and had a limited explanatory power on growth potential. However, in terms of stability, we confirmed that R&D capacity is a significant variable explaining the debt ratio of technology financing companies. Therefore, it is concluded that the 'Forward-looking' reflection on the growth and profitability of the company should be strengthened in the future adjustment of the technology appraisal model and the development of the technology appraisal model for investment.