• Journal of the Korean Geographical Society
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• v.40 no.2 s.107
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• pp.187-201
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• 2005

With the trend of urban polynucleation, the issue of detecting economic clusters or urban employment centers has been considered as crucial. However, the prior researches had some limitations in detecting economic clusters in the empirical analysis: i.e. inherent inefficiency of density-based clustering methods, difficulty in detecting linear types of spatial clusters and lacks of consideration of economic significance. The purpose of this paper is to propose the clustering method with the procedure of testing statistical and economic significance named as VCEC (Variable Clumping method for Economic Clusters) and to apply it to a case analysis of Erie County, New York, in order to test its validity. By applying a search radius and a total employment as an economic threshold, 'the both statistically and economically significant clusters' were detected in the Erie County, and proved to be efficient.

• Environmental Analysis Health and Toxicology
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• v.4 no.1_2
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• pp.55-65
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• 1989

Nevertheless the serious environmental pollution in Korea has been discussed in concern with health effect, the significant effect are not determined easily. Toxicological method has been used to establish safe levels of exposure for environmental pollutants to have threshold health effect below which significant effects are unlikely to occur. However the conventional method cannot to establish safe levels of exposure for non-threshold pollutants have been used to express comprehensive pollution degree, not in detailed toxic effects. Acceptable exposure or risk levels are decides by policymakers who consider descriptions and estimates of risks together with social and economic benefits. This paper focuses on the concept development of risk assessment and describes some risks of environmental pollution based on the surveyed date in Korea. The current concepts of risk assessment in policy descisions can be explored and areas for possible improvement, given current scientific knowledge are identified. The experience of foreign countries can provide a realistic basis for evaluating the existing data of environmental pollutants. To improve the environmental quality, risk regulation should be managed as soon as possible in Korea.

• Research in Plant Disease
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• v.14 no.2
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• pp.117-121
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• 2008

To determine the economic threshold level of Meloidogyne incognita on cucumber in greenhouse conditions, cucumber seedlings(Cucumis sativa L. cv. 'Super Manchon') grafted on 'Jangsushintozoa'(Cucurbita maxima x Cu. moschata) were planted in wooden boxes($30{\times}40{\times}15cm,\;L{\times}W{\times}D$) under a plastic house in August 01 and harvested from Sep. 01-Oct. 30, 2006. The initial nematode population densities(Pi) in the wooden boxes were adjusted to 0, 10, 30, 100, 300, and 600 second-stage juveniles(J2)/100 $cm^3$ soil. The relationship of total fruit yield to Pi level could be adequately described by a linear regression equation, $Y=0.82-0.04{\cdot}Log_{10}$(Pi+1). Initial nematode densities(Pi) before planting in excess of 5 J2/1,000 $cm^3$ soil caused in total yields loss that is equivalent to the costs of granular nematicide application; Pi level in excess of 25 J2/1,000 $cm^3$ soil caused in total yields loss that exceed the costs for application of fumigants at current control costs. We propose two different management strategies depending on nematode densities, (i) application of non-fumigant granular nematicides for M. incognita Pi level of 5 J2/1,000 $cm^3$ soil and (ii) fumigant treatment with Pi level over 25 J2/1,000 $cm^3$ soil. Soil samples to determine population density of Meloidogyne spp. for advisory purposes should be taken several months before planting time, which allows a period of time enough for implementing management procedures.

• Korean journal of applied entomology
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• v.50 no.4
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• pp.289-293
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• 2011

This study was conducted to develop economic injury level (EIL) of onion thrips, Thrips tabaci, on welsh onion (Allium fistulosum L. var) in the early transplanting stage. The changes of welsh onion biomass, yield loss, and T. tabaci density were investigated according to the inoculation periods of T. tabaci. In the early transplanting stage of welsh onion, the yield loss (%) increased with increasing inoculation periods: 17.0, 53.3, 38.4, and 80.8% yield loss in 5, 10, 15, and 20 d inoculation periods, respectively. The relationship between Cumulative Insect Days (CID) of T. tabaci and yield loss (%) of welsh onion was well described by a nonlinear logistic equation. Using the estimated equation, EIL of T. tabaci on welsh onion was estimated to 30 CID per plant based on the yield loss 12% (an empirical gain threshold 5% + marketable rate 93% of welsh onion). ET was calculated to 24 CID, which corresponds to 80% of EIL. Until a more defined EIL-model is developed, the present results should be useful for T. tabaci management in early growth stage of welsh onion. The effect of T. tabaci attack on the yield of welsh onion in late growing season (120 days after transplanting) was also examined. The yield of welsh onion increased at a low population density of T. tabaci and decreased at higher densities, showing a typical over-compensatory response.

• The Korean Journal of Pesticide Science
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• v.18 no.3
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• pp.196-201
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• 2014

This study was conducted to develop economic injury level (EIL) of sweet potato whitefly, Bemisia tabaci, on oriental melon. In greenhouse, seedlings of oriental melon were transplanted at June 8, 2010 and we inoculated adult B. tabaci with the density of 0, 1, 5, 10, or 20 per ten leaves at July 14. Adult of B. tabaci increased approximately twenty five-fold at 60 days after inoculation in the plot of 20 adults per ten leaves. The damages on leaves and fruits by B. tabaci were started to appear at 20 days after inoculation, and the damage rates of leaves or fruits were 28.5 or 31.5 percent at 60 days after inoculation, respectively, in the plot of inoculation with 20 adults per ten leaves. The yield of oriental melon was reduced as the inoculation density of B. tabaci increased, and the relationship between inoculation density of B. tabaci and the rate of damaged fruit could be described by a linear regression Y = 0.961x + 0.0562 ($R^2$ = 0.976). Based on the relationship, the economic injury level was 5.1 adults of B. tabaci per leaf and the control threshold estimated by 80% level of economic injury level was 4.1 adults per leaf for control of sweet potato whitefly.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.10a
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• pp.40-44
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• 2002

선박 설계시 최적화에 있어 종래에는 Random search Parametric study, Hook&Jeeves Method등이 사용되어져 왔으나 1960년대 Genetic algorithm이 소개되고 꾸준히 발전함과 함께 선박 설계에서도 Genetic algorithm이 사용되기 시작하였다. 본 논문에서는 이러한 Genetic algorithm 중 Simple Genetic algorithm(SGA), Micro Genetic algorithm(MGA), Threshold Genetic algorithm(TGA), Hybrid Genetic algorithm(HGA)을 선박 설계에 적용하여 그 성능을 비교 검토해 보았다. MGA는 계산 부담을 줄이기 위해 작은 개체로 효율적인 탐색을 하며, TGA는 local optimum에서 쉽게 벗어나게 할 수 있는 특징이 있다. HGA는 Hook&Jeeves Method를 Genetic algorithm과 병합되어 있다. 이를 바탕으로 본 논문에서 망간단괴 수송선의 경제성을 평가한다. 평가 방법은 연간 300만톤을 생산한다고 가정하여 연간 운송 용적을 동호제약으로 해서 최적화를 한 뒤, 이를 이용하여 몇가지 Case로 나누어서 초기 자본, 연간 비용, 20년간 총 비용을 계산하여 가장 경제적인 선박을 선택한다.

• THE INTERNATIONAL COMMERCE & LAW REVIEW
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• v.40
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• pp.33-63
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• 2008

This study introduces the adoption of the logistics industry by the Korean government as a threshold of overcoming economic difficulties. The core contents of the National Logistics Plans (2001-2020) which contain the basic principles of the logistics policies of the Korean government and its aim to be an 'Excellent Nation of Logistics' is introduced. The economic effect of the logistics policies implemented between 2001 and 2005, (the period of the first Medium-term Logistics Plan according to the National Logistics Plans (2001-2020) set up by the Korean government at the end of 2000) is estimated through input-output analysis. The input-output analysis result is as follows: the total output effect is 8,856 billion won of which indirect output effect is 3,982.9 billion won; indirect output effect comes mainly from real estate and business services, non-metal products, metal products, electrical and electronics products, finance and insurance, wholesale and retail, petroleum and coal; the total amount of value-added effect is 3,376 billion won and total import effect is 726 billion won. Employment effect including self-employed and unpaid family supporters with paid laborers is 79,203.7 people of which paid laborers comprise 67,547.7 people.

• Journal of the Economic Geographical Society of Korea
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• v.12 no.4
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• pp.540-556
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• 2009

The hub and spoke network is a critical network-based infrastructure that is widely applied in current transportation and telecommunications systems, including Internets, air transportation networks and highway systems. This main idea of hub location models is to construct a network system which achieves the economy of scale of flows. The main purpose of this study is to introduce new hub location problems that take into account network reliability. Two standard models based on assignment schemes are proposed, and a minimum threshold model is provided as an extension in terms of hub network design. The reliability and interaction potentials of 15 nodes in the U.S. are used to examine model behaviors. According to the type of models and reliability, hubs, and minimum threshold levels, relationships among the flow economy of scale, network costs, and network resiliency are analyzed.

• Journal of Korea Port Economic Association
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• v.34 no.4
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• pp.181-190
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• 2018

The goal of this study is empirically to investigate the asymmetric relationship between two variables using the dry cargo freight rates and raw material price data from January 2012 to May 2018. First, we estimate the asymmetry of macroeconomic indicators of commodity prices by using a two - step threshold cointegration test. Second, the asymmetric relation test of the trade balance of existing commodity price changes is tested by bypassing to the high frequency dry cargo freight rate index. As a result of the estimation, in contrast to the existing linear analysis, each boundary value for the lower limit and the upper limit has different asymmetry. This implies that the period of fluctuation of the sudden residual that causes irregular rate of return fluctuations does not establish a long term equilibrium relationship between the raw material price and the dry cargo freight rate. Therefore, in order to consider the sudden price change in the analysis, it is necessary to include the band of inaction that controls the irregular volatility, which is consistent with the asymmetry hypothesis.

• Research in Plant Disease
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• v.14 no.1
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• pp.21-25
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• 2008

This study was conducted to decide disease incidence level of rice leaf blast required for reasonable fungicide application in paddy field. We induced the disease development by inoculating rice blast pathogens on rice seedlings (Jinmibyeo) in the greenhouse and transplanting the infected seedlings in the field two weeks after rice plants were transplanted. We scored the disease incidence, grouped and marked according to degree of percentage of diseased leaf area at maximum stage of disease development. The percent diseased leaf area (PDLA) had negative correlations with panicle number per hill, ripened grain (%), and total yield; their correlation coefficients (r), $-0.97^{**}$, $-1.00^{**}$ and $-0.96^{**}$, respectively. However, it had positive correlations with spikelets per panicle and thousand grain weight; their correlation coefficients (r), $0.98^{**}$ and $0.98^{**}$, respectively. Gain threshold (GT) calculated based on control cost and market price was estimated to be 8.35. Economic injury level (EIL) obtained based on GT and coefficient of damage of regression equation between disease incidence and the different yield components; panicle number per hill, spikelets per panical, ripened grain(%), thousand grain weight and yield were 41.8, 9.7, 19.1, 291.1 and 3.4%, respectively. Economic threshold (ET) for yield was 2.7% ($3.4%(EIL){\times}0.8$) on PDLA. These results suggest that application of fungicide is necessary when two under leaves are almost covered with lesions or contained more than twenty large lesions under leaves at maximum tillering stage.