• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.7
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• pp.696-708
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• 1992

In this study, we have several objectives. First, In spite of a fixed bandwidth waste of reservation channel, we maximize the efficiency of transmission channel by the multiple access algorithm that performs channel reservation and data transmission independently, eliminating the frame structure of transmission channel and reserving it by the slot unit . Second, In order to improve the entire system performance, we accommodate the variation of traffic at each earth station more effectively, and accomplish the stable delay characteristics and the equlity of service #or users. For this purpose, we design the satellite channel that consists of reservation channel and transmission channel which are logically separate and operate Independently. We also design a demand assignment multiple access algorithm based on the satellite channel structure.

• Environmental Engineering Research
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• v.19 no.3
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• pp.197-203
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• 2014

This study estimated spatial and seasonal variation of water quality to understand characteristics of Nakdong river basin, Korea. All together 11 parameters (discharge, water temperature, dissolved oxygen, 5-day biochemical oxygen demand, chemical oxygen demand, pH, suspended solids, electrical conductivity, total nitrogen, total phosphorus, and total organic carbon) at 22 different sites for the period of 2003-2011 were analyzed using multivariate statistical techniques (cluster analysis, principal component analysis and factor analysis). Hierarchical cluster analysis grouped whole river basin into three zones, i.e., relatively less polluted (LP), medium polluted (MP) and highly polluted (HP) based on similarity of water quality characteristics. The results of factor analysis/principal component analysis explained up to 83.0%, 81.7% and 82.7% of total variance in water quality data of LP, MP, and HP zones, respectively. The rotated components of PCA obtained from factor analysis indicate that the parameters responsible for water quality variations were mainly related to discharge and total pollution loads (non-point pollution source) in LP, MP and HP areas; organic and nutrient pollution in LP and HP zones; and temperature, DO and TN in LP zone. This study demonstrates the usefulness of multivariate statistical techniques for analysis and interpretation of multi-parameter, multi-location and multi-year data sets.

• Asia-Pacific Journal of Business
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• v.13 no.3
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• pp.281-291
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• 2022

Purpose - We study whether the bullwhip effect is prevalent among Korean firms and how the characteristics of it differ from the ones in other countries. Design/methodology/approach - We obtained quarterly financial and operational information on KOSPI-listed firms in manufacturing, wholesale, and retail industries from 2013 to 2019. We explore the variation of the bullwhip effect across firms and validate hypotheses. Findings - First, we find that for the KOSPI-listed firms, the bullwhip effect is more prevalent compared with the production smoothing. We provide additional findings by using sub-samples of manufacturing firms, wholesaling and retailing firms, big-sized firms, small- and medium-sized firms, domestic-sales intensive firms, and export intensive firms. Second, we show that in general, the bullwhip effect of Korean firms increases with the days in inventory or the demand seasonality ratio. However, the persistence of demand shock does not affect the bullwhip effect of Korean firms. Research implications or Originality - We compare our results with those in other studies that use information on the U.S. and Chinese firms. Our findings show that factors explaining the bullwhip effect across Korean firms have similarities and differences compared with firms in the U.S. and Chinese firms.

• Environmental and Resource Economics Review
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• v.18 no.3
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• pp.495-521
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• 2009

This paper measures welfare losses from beef consumption reduction, which might be resulted from psychological anxiety about potential outbreak of BSE (commonly known as "bad cow dieses") risks after announcement of resuming US-beef imports in April of 2008. Unlike the previous literature of utilizing the contingent valuation method or experimental market approach, this study estimated quality-differentiated consumer demand functions using the information of self-reported beef consumption quantity, individually constructed price indices of beef, and subjective perception of BSE risks. The empirical results based on a survey sample of 360 residents in Jeon Ju city were consistent with the anticipation from economic theory, in terms of coefficients of own prices, substitute prices and income variables. The announcement of resuming US-beef imports did not make significant differences in the sign and sizes of the main economic variables. However, the subjective perception variable about BSE risks had negative significant impacts on beef demand functions after the announcement but not significant before the announcement. The welfare losses in a form of equivalent variation (EV) corresponding to the increases in concerns about BSE risks were measured to be about 30 thousand won per household.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.6
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• pp.663-669
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• 2005

The aim of this study was to investigate the ozone decay pattern for the effective application of ozone in drinking water treatment. In order to measure the ozone decomposition in water, ozone measuring instrument was developed with flow injection analysis (FIA) method. From the result of continuous residual ozone concentration in water, it was confirmed that the ozone decay pattern was divided with instantaneous ozone demand(I.D) and pseudo first-order rate($k_c$) phases, which were influenced by the variation of ozone dose. The empirical model obtained from I.D and $k_c$ values enabled us to predict the residual ozone concentration according to the reaction time, showing the high correlation between model and experimental values. The concentration of OH radical and $R__{ct}$ could be indirectly measured by OH radical probe compound. In both I.D and $k_c$ phases, the production pattern of OH radical could be observed, which was also affected by the variation of ozone dose. Finally, it was confirmed that the ozone consumption rate was varied according to the each drinking water treatment process and seasoning. Therefore, the optimum position and dosage of ozone have to be selected by considering various factors.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.2
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• pp.713-720
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• 2013

The objectives of this study are to identify whether the small area variation also exists in the oriental medicine and, if it exists, what causes, to expand our boundary of research interests on the small area variation observed at the western medicine toward the oriental medicine as one of the fundamental research foundations and to provide any fundamental findings from this study results to the healthcare politicians to promote consumer's rational behaviors for the use of healthcare. This study analyzed the health insurance claim data (2010, 2011) which were the patients of western medicine and the outpatients of the oriental medicine with the top 10 most frequent diseases and looked into the variation of healthcare utilization among the areas after grouping resident area into an 86-area category. The study result shows that the small area variation was also observed at the part of the oriental medicine in which the characteristics of patients critically affect the healthcare expenditure per visit day rather than those of providers and the characteristics of both patients and providers equally affect the healthcare expenditure per patient. Therefore, this study suggests that government set up healthcare policies on the standardization of oriental medicine to prevent its over-utilization and unmet need, enforcing the roles of oriental medicine in the markets, enhancing the appropriate health care utilization, and expanding provision and sharing the health care information to reduce unnecessary health care utilization.

• The Transactions of the Korea Information Processing Society
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• v.3 no.7
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• pp.1669-1679
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• 1996

In this paper, we address the problem of how to replace huffers in multimedia database systems with time-varying skewed data access. The access pattern in the multimedia database system to support audio-on-demand and video-on-demand services is generally skewed with a few popular objects. In addition the access pattem of the skewed objects has a time-varying property. In such situations, our analysis indicates that conventional LRU(least Recently Used) and LFU(Least Frequently Used) schemes for buffer replacement algorithm(ABRN:Adaptive Buffer Replacement using Neural suited. We propose a new buffer replacement algorithm(ABRN:Adaptive Buffer Replacement using Neural Networks)using a neural network for multimedia database systems with time-varying skewed data access. The major role of our neural network classifies multimedia objects into two classes:a hot set frequently accessed with great popularity and a cold set randomly accessed with low populsrity. For the classification, the inter-arrival time values of sample objects are employed to train the neural network.Our algorithm partitions buffers into two regions to combine the best roperties of LRU and LFU.One region, which contains the 핫셋 objects, is managed by LFU replacement and the other region , which contains the cold set objects , is managed by LRUreplacement.We performed simulation experiments in an actual environment with time-varying skewed data accsee to compare our algorithm to LRU, LFU, and LRU-k which is a variation of LRU. Simulation resuults indicate that our proposed algorthm provides better performance as compared to the other algorithms. Good performance of the neural network-based replacement scheme means that this new approach can be also suited as an alternative to the existing page replacement and prefetching algorithms in virtual memory systems.

• Earthquakes and Structures
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• v.7 no.4
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• pp.485-510
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• 2014

In performance-based seismic design procedures Peak Ground Acceleration (PGA) and pseudo-Spectral acceleration ($S_a$) are commonly used to predict the response of structures to earthquake. Recently, research has been carried out to evaluate the predictive capability of these standard Intensity Measures (IMs) with respect to different types of structures and Engineering Demand Parameter (EDP) commonly used to measure damage. Efforts have been also spent to propose alternative IMs that are able to improve the results of the response predictions. However, most of these IMs are not usually employed in probabilistic seismic demand analyses because of the lack of reliable Ground Motion Prediction Equations (GMPEs). In order to define seismic hazard and thus to calculate demand hazard curves it is essential, in fact, to establish a GMPE for the earthquake intensity. In the light of this need, new GMPEs are proposed here for the elastic input energy spectra, energy-based intensity measures that have been shown to be good predictors of both structural and non-structural damage for many types of structures. The proposed GMPEs are developed using mixed-effects models by empirical regressions on a large number of strong-motions selected from the NGA database. Parametric analyses are carried out to show the effect of some properties variation, such as fault mechanism, type of soil, earthquake magnitude and distance, on the considered IMs. Results of comparisons between the proposed GMPEs and other from the literature are finally shown.

• Journal of Korean Society of Transportation
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• v.28 no.1
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• pp.115-124
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• 2010

VDF(volume-delay function) is one of the most important factor to improve the reliability of traffic demand estimation because it is for estimation of link travel time based on the traffic volume variation. Because VDF of link except for freeway is applied as the parameter of BPR(bureau of public road) of U.S., it causes to deteriorate the accuracy of traffic demand estimation. The purpose of this paper is to establish new parameter of VDF based on the real-surveyed traffic data in order to improve the problem of the existing VDF. We suggest the reclassification of road hierarchy, the approach of traffic survey, the estimating method of VDF parameter, and the improvements of new VDF application. The new VDF allows us to estimate more realistic traffic situation in parts of demand, travel time and path between origin-destination.

• The Journal of Fisheries Business Administration
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• v.34 no.2
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• pp.131-139
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• 2003

The products of the quality certificated fisheries which are protected from environmental pollution, decomposition are hygienically safe and convenient for food. However, consumers have not yet understood the recognition of the system of quality certfication so far because of lack of demand on the quality certification fisheries. Above all, to put the system of the quality QC in place sucessfully, to understand the variation of consumer's inclination efficiently, the empirical study must be carried out by both consumer's take part in the market of the quality certificated fisheries products and how much the amount of consumption is in this market. The purpose of this study, under the preconditions where these have limited fisheries items in consumer's inclination survey, is to analyze the demand of QC though the Double Hurdle Model. Explanatory variables included were household characteristics such as housewives' age and education, her job, household income as well as their health perceptions and food purchase behaviors. Survey from 530 household was collected in Pusan City in 2003, of 502 were actually used for empirical analysis. The Double-hurdle framework proved to a better representation of the factors influencing the separate decision participation and consumption levels. According to the results of this study, whether or not, participating In the market of quality certicipating in the market of qualify certificated fisheries products is affected by how much experience and confidence these have got. housewives' having a job or not. Furthermore, the amount of consumption is mostly affected income. This value is attributed to the safety of QC fisheries products in comparison with regular fisheries. Findings suggest that the consumers put substantially high monetary value on safe food, such as high quality fisheries products. Therefore, first of all, legal and institutional systems should be clearly and strictly identified for the QC products.