• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.3
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• pp.213-223
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• 2015

The helicopter initial design model was established by using the latest weight estimation equations based on the Tishchenko's methodology through the study existing initial design tools. The sequential decomposition method is used to reduce analysis time in the sizing. Empirical parameters of the weight estimation equation were also extracted from numerical and regression analysis for a helicopter database. Design input and output values were compared with the RISPECT design tool. Finally, comparison of the re-design resulting for several existing helicopters was presented and showed the good agreement within less than 5% in the weight estimation and main rotor sizing. Established initial design model was proved to be effectively used as initial design tool.

• Journal of the Korean Geotechnical Society
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• v.33 no.12
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• pp.59-73
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• 2017

Numerical analysis using 3D finite element program (PLAXIS 3D) evaluated the interaction of soil - pile structure under dynamic surface loading. The dynamic p-y curve of the 1-g shaking table experiment by numerical analysis was calculated, and the parametric studies were presented by considering the pile-soil condition, the pile tip condition, and the loading condition. The frequency of 1.4 Hz is almost equal to the natural frequency of the pile - soil system. The p and y values of resonance phenomenon are significantly different from the results of other frequencies. The results can be summarized by a third order polynomial function representing the trend line in the p-y curve. In the case of a single pile, the shape of the dominant curve was found to be an ellipse by mathematical proof. The elliptic equation can be used for the dynamic design or analysis of soil-pile system.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.38 no.4
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• pp.307-315
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• 1989

In this paper, we have analyzed the temperature variation trend of a slab on between the process of reheating furnace and the termination of roughing mill process during hot rolling process. 1) cooling by radiation and convection current in the air, 2) plastic deformation heat, 3) cooling by descaling water, 4) cooling by contact with rolling rolls and/or transmitting rolls. For the analysis, the factors have been adopted as the problems of the rolling process to be solved such that we have established an application technique in relation to the determination of boundary conditions on the slab surface. We have presented a procedure for an analysis of the cooling phenomenon treated as a problem of two-dimensional transient heat flow using finite difference equation and suggested techniques of implementing sequentialized rolling tasks in correlation with the procedure. From the result of simulation, it is shown that the difference between calculation value and measurement value is within the range of the industrial measurement error. Also, it is proved that the assumptions, conditions, and properties used in the computer simulation is appropriate by showing that the pattern of a drop in temperature at each rolling event is in accord with real circumstances.

• Journal of Digital Convergence
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• v.10 no.4
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• pp.107-118
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• 2012

Smart TV is expected to take the center stage of the recent "smartization" trend in IT and consumer electronics as it performs a hub for various smart IT devices, such as smart phone, smart pad, PC, etc. It is distinct from traditional TVs or even IPTVs in the sense that it provides immersive and interactive experiences via apps downloaded through TV app store. Smart TV could serve as a new intermediary device between other smart devices and the Internet. While it started experiencing a rapid growth, little research has been conducted to understand this emerging technology in terms of its user acceptance and adoption by users. The current research attempts to fill the gap in the field by examining factors and processes for this new technology to be adopted by users. This paper draws on theories of IT acceptance and use, such as the "Unified Theory of Acceptance and Use of Technology", to investigate factors affecting "intention to use" of smart TV. The proposed research model is analyzed using the structural equation modeling approach. Findings show that such factors as innovativeness, switching cost, switching benefit, service interface, and user interface affect users' intention to use smart TV, through effort expectation, performance expectation, and social influence. Theoretical and managerial implications are discussed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.12 s.255
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• pp.1203-1210
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• 2006

The filmwise condensation heat transfer coefficients of R-134a on the horizontal copper and stainless steel tubes were measured and analyzed. The outside diameter of the tubes was 15.88 mm, and the tube thickness ranged from 0.89 to 1.65 mm. The polished stainless steel tube had an RMS surface roughness($R_q$) of 0.37 $\mu$m, and commercial stainless steel tubes had an surface roughness($R_q$) of 1.855 $\mu$m. The tests were conducted at the saturation temperatures of 20 and $30^{\circ}C$, and the liquid wall subcoolings from 0.4 to $2.1^{\circ}C$. The measured condensation heat transfer coefficients were significantly lower than the predicted data by the Nusselt analysis. This trend in the stainless steel tube was explained by the effects of thermal resistance of tube material and surface roughness. Based on the experimental data with respect to wall thickness and surface roughness, it was suggested that the existing correlation on external condensation should be modified by considering material and surface roughness factors. The revised correlation was developed by introducing the effects of wall thickness and surface roughness into the Nusselt equation. The average deviation of the revised correlation was 13.0 %.

• Journal of Digital Convergence
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• v.11 no.11
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• pp.251-256
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• 2013

In the past, customers utilize a secondhand book market as a major counter for their purchasing used books. With expansion of internet and IT devices, many customers would like to buy their used books in an on-line secondhand book store which has more price competitiveness and ease. Nowadays a new concept off-line secondhand book market which has the advantages of both on-line and off-line is a growing trend instead of existing secondhand book markets in the economic recession. In this study, we established customer service satisfaction for 'Aladin store', which is the advanced concept off-line secondhand book store, with the most typical service quality test technique SERVQUAL. First, we selected appropriate service quality factor for the advanced concept off-line secondhand book market such as Aladin store. After that, we analyzed which factors are influencing repurchase intentions, through customer survey. The conclusion provides the secondhand book store's service quality improvement and strategy toward customer satisfaction including the existing used book stores.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.1
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• pp.104-111
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• 2017

This research focuses on simulation and visualization of flow field characteristics inside a centrifugal pump. The 3D numerical analysis was carried out by using a numerical CFD tool, addressing a Reynolds Average Navier-Stock code with a standard k-${\varepsilon}$ two-equation turbulence model. The simulation accounts for friction head loss due to rough walls at suction, impeller, discharge areas and volumetric head loss at impeller wear ring. A comparison of performance curves between simulation and experimentation is included, and it reveals a same trend of those results with a small difference of maximum 5 %. At best efficiency point, velocity vectors are smooth but it changes significantly under off-design point, a strong recirculation appears at the outlet of impeller passages near tongue area. A relatively uniform preassure distribution was observed around the impeller in despite of the tongue. Within the volute, because of its geometry, spiral vortexes formed, proving that the flow field in this region was relatively turbulent and unsteady.

• The Journal of Information Systems
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• v.29 no.2
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• pp.95-110
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• 2020

Purpose This paper attempts to explain the recent expanding trend in Mobile Grocery Shopping(MGS). More specifically, the authors have applied the Post Acceptance Model(PAM) in order to examine the conceptual structure among the four constructs of 'Expectation Confirmation', 'Perceived Usefulness', 'User Satisfaction', and 'Continuance Intention to Use' in Mobile Grocery Shopping. Design/methodology/approach Through a survey agency, data were collected from a sample of 312 consumers who had the previous experience in Mobile Grocery Shopping. The Structural Equation Modeling(SEM) analysis was conducted with the survey data using AMOS 22.0. Subsequently, 8,200 real customer data from an open market site were collected in order to find out their revisit and repurchase behavior. Findings This study supported the causal relationships of Expectation Confirmation → Perceived Usefulness, Expectation Confirmation → User Satisfaction, Perceived Usefulness → User Satisfaction, and User Satisfaction → Continuance Intention to Use, but did not support the direct effect of Perceived Usefulness on the Continuance Intention to Use Mobile Grocery Shopping. This implies that consumers with any experience in Mobile Grocery Shopping would not consider repurchase, unless they are satisfied with the experience even though they perceive its usefulness. Also, Expectation Confirmation has much larger effect on User Satisfaction than Perceived Usefulness. In addition, the real customer data showed that the revisit and the repurchase rate of mobile grocery shoppers were higher than those of online grocery shoppers, although the rates of adding to shopping carts, coupon downloads, and adding to favorites are similar.

• Journal of Nutrition and Health
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• v.32 no.8
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• pp.957-966
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• 1999

Underreporting of dietary intake is common and might distort analysis and interpretation of dietary surveys. This study was designed to investigate the degree of underreporting and characterastics of under-reporting group in Korean college female students. Dietary survey of 1-day 24-hour recall method was conducted on 379 college students in Seoul and Chonan areas. Physical activity and life style were aquired from questionnnaires. Underreporting was defined as energy intake(EI) lower than 0.9BMR(based metabolic rate), since EI<0.98BMR is statistically judged as bias in 1-day 24 hour recall. BMR was calculated from Schofield's equation. Proportion of underreporting was 18.7% and it's not so different from one of American or European women. Intake of nutrients except vitamin A by underreporting group was lower than other groups(p<0.001). Proportions of subjects with nutrient intake level less than 75% of Korean RDA were more than 80% in protein, Ca, Fe, vitamin A, riboflavin, niacin, zinc as well as energy. Dietary quality of underreporting group was also worse than other groups. Proportion of subjects less than 3 food groups among 5 food group was higher in underreporting group. The number of foods eaten by underreporting group were also less than those of other groups. BMI and body weight were the largest in underreporting group(p<0.05) and the trial of weight reduction was shown higher trend(p<0.01). Different in PAC and other characteristics between underreporting group and other group were not significant. Not only dietary quantity but also dietary quality were worse in the underreporting group. Furthermore underreporting in college female students seemed to be affected by body weight and concern for weight reduction.

• Korea journal of population studies
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• v.8 no.2
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• pp.79-92
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• 1985

Fertility has been declined since 1966 (see Table 1). This fertility reduction was duely caused by age at first marriage, induced abortion and contraceptive practice which has been largely increased in recent years. Although tbe proximate determinant such as induced abortion, age at marriage and breastfeeding can and do have an effect on fertility, the principal cause of the reduction in fertility in Korea during the fertility transition can be supported by correlation between level of fertility and contraceptive prevalence (See Fig. 4). Taking a regression equation between fertility (TER. Y) and prevalence level (X), the total fertility rate in 1984 was estimated as 1.9 and 2.1 based on lenear and expotential function shown as follow; $Y_1$=5.709-0.0549 X and $Y_2$_______80________ 1+e2.433+0.017X ($R^2$=O. 93) ($R^2$=0. 96) Where $Y_1$ and $Y_2$ denote total fertility rates obtained through two equations respectivelly. The peak of contraceptive prevalence was assumdd as 80 percent which is almost upper limit in human society. On the other hand, an observed value of 1984 fertility level obtained from five month period shows 2.1 which is coincident with logistic fitting after the adjustment of response error assumed around 10 to 20 percent, At any rate, fertility of Korean women will have been reached replacement level (2.1) by 1985.Thus policy for family planning program must be reviewed toward the direction of integrated approach particularly with MCH program inasmuch as fertility in Korea has already shown population replacement level that require more good quality of service in family planning and their There must be an advanced level of fertility in Korea because wide use of contraception and induced life abortion and age at marriage will effect modern fertility which shows up and down trend between 2.1 and 1.5 in general.