• 한국경영과학회지
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• 제3권1호
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• pp.31-46
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• 1978

Consider a time interval during which the demand for trips is fixed (e.g. the rush hour period). The traveller has a choice between various public modes, whose travel times and fares are fixed, and the automobile mode, for which travel time and cost depend on the volume of traffic flow on those roads, which are subject to congestion. We consider the equilibrium in terms of a representative travellerm, who choses for any trip the mode and route with the least combined money and time cost. When several (parallel) model or routes are chosen, then the combined cost of money and time must be equal among these. Our problem is first, to find the optimal flows of cars and of public mode carriers on the various links of their networks and second the optimal fares for trips by the variousmodes. The object is to minimize the total operating costs of the carriers and car plus the total time costs to travellers. The optimal fares are related to, but not identical with the dual variables of the underlying Nonlinear Program. They are equal to these dual variables only in the case, when congestion tolls on trips or on the use of specific roads are collected from automobile users. When such tolls are not collected, they must be passed on as subsidies to travellers using competing modes. The optimal fares of public modes are then reduced by the amounts of these subsidies. Note that subsidies are not a flat payment to public carriers, but are calculated on the basis of tickets sold. Fares and subsidies depend in general on tile period considered. They will be higher during periods of higher demand. When the assumption of fixed trip demand is relaxed, this tare system is no longer best, but only second best since too much traffic will, in general, be generated. The Free Rider Theorem states the following : Suppose road tolls can be charged, so that a best pricing system for public modes is posssible. Then there may exist free rides on some routes and modes, but never on a complete round trip.

• 한국초지조사료학회지
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• 제40권1호
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• pp.66-72
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• 2020

본 연구는 사일리지용 옥수수(whole crop maize: WCM)의 메타자료를 통해 적정 파종 및 수확시기에 대한 탐색을 생육도일(Growing degree days, ℃; GDD)을 이용하여 검토하였다. WCM의 원자료(1982~2012년)는 학위논문, 학회지 및 연구보고서로부터 실험별 연도, 품종, 지역, 파종시기 및 수확시기 등 생육정보가 포함된 3,152점이었다. 수집한 자료 중 파종시기 및 수확시기와 관련된 자료는 데이터입력, 자료선별 및 오류자료수정 과정을 거쳐 최종데이터세트(파종시기 29점, 수확시기 92점; 총 121점)를 구성하였고 최적점 설정, 메타분석, 2차모형 구축을 통하여 적정 파종 및 수확시기의 허용 범위를 고려한 기간과 GDD를 제시하였다. WCM의 적정 파종 및 수확기간은 각각 4월 14일~5월 3일 및 8월 15일~9월 4일이었으며 이 때 GDD는 23.7~99.6℃ 및 1,328.7~1,602.1℃였다. 이상에서 GDD는 WCM의 적정 파종 및 수확시기의 판단기준으로 사용 가능할 것으로 사료된다

• 과학교육연구지
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• 제33권1호
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• pp.69-76
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• 2009

이 연구의 목적은 확률 논리와 조합 논리가 형성되지 않은 학생들에게 논리 지도를 위한 최적의 시기를 찾고자 하는 것이다. 초등학교 4, 5, 6학년 학생 430명을 대상으로 논리의 형성정도를 사전에 검사하였다. 검사도구는 GALT를 참고하여 개발하였고, 이는 과학 교육 전문가에게 타당도를 검증 받았다. 처리 프로그램은 두 가지 논리가 모두 형성되지 않은 각 학년 20명의 학생을 대상으로 수행하였다. 이는 바둑돌과 카드를 반복적으로 수행하는 검사도구이다. 4주 뒤 사후검사에서 확률논리와 조합논리의 발달정도를 알아보는 검사를 다시 수행하였고 그 변화는 확인되었다. 확률논리의 경우 4, 5, 6학년에서 형성율이 각각 15%, 25%, 40% 증가하였고, 평균도 .15, .30, .50 증가하였다. T-검증에 의한 의미있는 결과는 6학년 중에서 얻어졌다. 그러나 과도기 학생 비율(21.7%)를 제외하면 형성 학생의 비율은 5.0%로 여전히 저조하였고, 다수의 학생(73.3%)은 미형성 상태를 유지하였다. 조합논리의 경우 4, 5, 6학년에서 형성율이 각각 20%, 25%, 63.2% 증가하였고, 평균도 .20, .25, .63 증가하였다. T-검증에 의한 의미있는 결과는 역시 6학년 중에서 얻어졌다. 그러나 처치 후 논리 형성 학생으로의 전이는 없었으며, 과도기 학생의 비율만 35% 증가하였다. 위의 연구결과, 확률논리와 조합논리가 형성되지 않은 학생들은 학습을 통한 향상은 이루어 졌지만, 인지발달과 같은 질적인 변화는 이루어지지 않았다. 이 연구로 인하여 확률논리와 조합논리의 학습 효과가 큰 6학년 학생들의 인지수준 개선을 위한 여러 분야에서의 더 활발한 연구가 이루어지길 기대한다.

• 환경영향평가
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• 제20권6호
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• pp.879-890
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• 2011

The GOSAT (Greenhouse gases Observing SATellite) data provide new opportunities the most regionally complete and up-to-date assessment of $CO_2$. However, in practice, GOSAT records often suffer from missing data values mainly due to unfavorable meteorological condition in specific time periods of data acquisition. The aim of this research was to identify optimal spatial interpolation techniques to ensure the continuity of $CO_2$ from samples taken in the North East Asia. The accuracy among ordinary kriging (OK), universal kriging (UK) and simple kriging (SK) was compared based on the combined consideration of $R^2$ values, Root Mean Square Error (RMSE), Mean Error (ME) for variogram models. Cross validation for 1312 random sampling points indicate that the (UK) kriging is the best geostatistical method for spatial predictions of $CO_2$ in the East Asia region. The results from this study can be useful for selecting optimal kriging algorithm to produce $CO_2$ map of various landscapes. Also, data users may benefit from a statistical approach that would allow them to better understand the uncertainty and limitations of the GOSAT sample data.

• 대한의용생체공학회:의공학회지
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• 제33권1호
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• pp.1-7
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• 2012

Hemorrhagic shock is a common cause of death in emergency rooms. Early diagnosis of hemorrhagic shock makes it possible for physicians to treat patients successfully. Therefore, the purpose of this study was to select an optimal survival prediction model using physiological parameters for the two analyzed periods: two and five minutes before and after the bleeding end. We obtained heart rates, mean arterial pressures, respiration rates and temperatures from 45 rats. These physiological parameters were used for the training and testing data sets of survival prediction models using an artificial neural network (ANN) and support vector machine (SVM). We applied a 5-fold cross validation method to avoid over-fitting and to select the optimal survival prediction model. In conclusion, SVM model showed slightly better accuracy than ANN model for survival prediction during the entire analysis period.

• 방송공학회논문지
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• 제15권6호
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• pp.845-852
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• 2010

클라이언트로부터의 요구메시지의 통계를 바탕으로 하여 방송 서버는 데이터 아이템에 대하여 최적의 컷오프 포인트를 이용하여 핫 아이템과 콜드 아이템으로 나눈다. 핫 아이템은 주기적으로 방송되는데 이 때, 방송 주기는 아이템들의 인기도, 즉 요구확률에 따라 정해진다. 핫 아이템이 방송되지 않은 빈 슬롯에는 적절한 콜드 아이템을 골라 방송하게 되는데, 이 때 대기시간과 대기 중인 요구 메시지의 수 등을 고려하여 콜드 아이템을 정한다. 최적의 컷오프 포인트를 해석적으로 구하기 위하여 평균 응답시간을 컷오프 포인트의 함수로 나타나도록 계산하였다. 요청 도착율과 아이템의 인기도를 변화하면서 수행한 시뮬레이션을 통하여 본 논문에서 제안한 방법이 기존의 방법들보다 더욱 우수한 성능을 나타냄을 보였다.

• 한국농공학회지
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• 제40권2호
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• pp.59-68
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• 1998

This study was conducted to derive optimal design floods by generalized gamma distribution model of the annual maximum series at eight watersheds along Geum, Yeongsan and Seomjin river systems. Design floods obtained by different methods for evaluation of parameters and for plotting positions in the generalized gamma distribution model were compared by the relative mean errors and graphical fit along with 95% confidence limits plotted on gamma probability paper. The results were analyzed and summarized as follows. 1. Basic statistics and parameters were calculated by the generalized gamma distribution model using different methods for parameters. 2. Design floods according to the return periods were obtained by different methods for evaluation of parameters and for plotting positions in the generalized gamma distribution model. 3. It was found that design floods derived by sundry averages method for parameters and Cunnane method for plotting position in the generalized gamma distribution are much closer to those of the observed data in comparison with those obtained by the other methods for parameters and for plotting positions from the viewpoint of relative mean errors. 4. Reliability of design floods derived by sundry averages method in the generalized gamma distribution was acknowledged within 95% confidence interval.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제55권11호
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• pp.520-526
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• 2006

Corona interferences, such as radio noise, audible noise and television noise, need to be taken into account in the design of HVDC transmission line conductor configuration. Therefore the line designer requires data from which to estimate the corona performance of any set of conductors. To get a sufficiently complete set of design data, it is necessary to examine the corona test of a large number of conductor geometries. This paper presents the results of corona cage test among three types of candidate conductors. It is quite clear from test results that the conductor geometries play an important role in establishing the magnitude of corona noise. Corona noise data from corona cage test are expressed as a statistical distribution of results obtained over long periods of time and various weather conditions. Therefore we can determine an environmentally-friendly conductor bundle for HVDC overhead transmission line. Based on this finding results, various simulations about HVDC line configurations, such as pole space and pole height, will be conducted. And then finally an optimal configuration for HVDC transmission line will be decided.

• 한국환경과학회지
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• 제22권10호
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• pp.1353-1361
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• 2013

The objectives of this paper are the characterization of the pretreatment of wastewater by microfiltration (MF) membranes for river maintenance and water recycling. This is done by investigation of the proper coagulation conditions, such as the types and doses of coagulants, mixing conditions (velocity gradients and mixing periods), pH, etc., using jar tests. The effluent water from a pore control fiber (PCF) filter located after the secondary clarifier at Kang-byeon Sewage Treatment Plant (K-STP) was used in these experiments. Two established coagulants, aluminum sulfate (Alum) and poly aluminum chloride (PAC), which are commonly used in sewage treatment plants to treat drinking water, were used in this research. The results indicate that the optimal coagulation velocity gradients (G) and agitation period (T) for both Alum and PAC were 200-250 $s^{-1}$ and 5 min respectively, but the coagulation efficiencies for both Alum and PAC were lower at low values of G and T. For a 60 min filtration period on the MF, the flux efficiencies ($J/J_0$ (%)) at the K-STP effluent that were coagulated by PAC and Alum were 92.9 % and 79.9 %, respectively, under the same coagulation conditions. It is concluded that an enhanced membrane process is possible by effective filtration of effluent at the K-STP using the coagulation-membrane separation process.

• Agribusiness and Information Management
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• 제11권1호
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• pp.10-26
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• 2019

This study is exploratory research on a relationship between changes in cultivated area of major crops and farm income by regions. We investigated level of income, volatility of income, and migration of suitable region by climate changes as factors influencing changes in cultivated area. Research processes are as follows. First, we classify the regions where cultivated areas are expanded or reduced through the trends of cultivated area by region and crop during recent 10 years. Second, we compare the changes in income related factors between groups during the same periods. Finally, the results from portfolio analysis show changes in stable income-based optimal crops. From these procedures, we found that the changes in cultivated area are not simply explained by income-related factors. In cases of vegetables, however, we also found that high volatility of income could contribute to reduce cultivated area of the crops. The results from portfolio analysis are not always consistent in all of cases. This means that crop selection can be decided by other factors than stable income.