• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.5
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• pp.723-730
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• 2016

Solar cells in a PV module are connected in series and parallel to produce a higher voltage and current. The PV module has performance characteristics depending on solar radiation and temperature. In addition, the PV system causes power loss by special situations, including the shadows of the surrounding environment, such as nearby buildings and trees. In other words, an increase in power loss and a decrease in life cycle can occur because of the partial shadow and hot-spot effect. Therefore, this paper proposes the optimal configuration algorithm of a bypass diode to improve the output of a PV module and one of a PV array to minimize the loss of the PV array. In addition, this paper presents a model of a PV module and PV array based on the PSIM S/W. The simulation results confirmed that the proposed optimal configuration algorithms are useful tools for improving the performance of PV system.

• Journal of Navigation and Port Research
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• v.37 no.6
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• pp.699-707
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• 2013

With the increase in the trade volume between countries, the market of freight forwarders industry has been gradually growing. However, not only in Korea, with the number of global freight forwarders increasing, global competition has been increasingly fierce, and domestic freight forwarders are facing enormous challenges, therefore, the relevant policy sectors have carried out a series of supportive policies, while academics have conducted various researches. But most of them have focused on the current situation or the business model, and they could not get feedback on government support policies from enterprises. Using the AHP analysis, this study decided the priority of the government's ongoing supporting policies, compared the cognitive differences among of the companies of 3 different sizes, which was further verified using t-test. Then we compared the government support policies with the actual expectations of the companies to see if they matched on the basis of the previous results of this study, in order to help to strengthen the competitiveness of our freight forwarding industry.

• Journal of the Korean Institute of Gas
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• v.24 no.1
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• pp.17-22
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• 2020

Light Naphtha is distillated from crude oil unit and separated into the methane, ethylene and propylene by boiling point difference in sequence. This separation is conducted using a series of binary-like columns. This separation method is known that the energy consumed in the reboiler is used to separate the heaviest components and most of this energy is discarded as vapor condensation in the overhead cooler. In this study, the first two columns of the separation process are replaced with the Petlyuk column. A structural design was exercised by the stage computation with ideal tray efficiency in equilibrium condition. Compared with the performance of a conventional system of 3-column model, The design outcome shows that the procedure is simple and efficient because the composition of the liquid component in the column tray was designed to be similar to the equilibrium distillation curve. The performance of the new process indicates that an energy saving of 12.1% is obtained and the cost savings of 44 million won per day based on gross domestic product is reduced under same total number of trays and the initial investment cost is saved.

• Korean Journal of Soil Science and Fertilizer
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• v.35 no.6
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• pp.344-351
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• 2002

Chemical speciation and transport of heavy metals in soil environment could be controlled by humic acid. In order to understand the mechanism on competitive adsorption of Cd and Cu on the surface of humic acid extracted from peat, the charge development of humic acid were investigate through a batch adsorption experiment with a series of different background electrolytes levels. The competitive adsorption of Cd and Cu to the humic acid were estimated according to the model using the proton binding constant obtained from the above batch test. The affinity of Cu to the carboxyl group on the humic acid was higher than that of Cd, but the affinity to the phenolic group was lower than to the carboxyl group. It seems that the amount of adsorbed Cd and Cu could be estimated using the proton binding constant obtained from a solution with single background ion. However, it is difficult to interpret the competitive adsorption of Cd and Cu with the constant for single background ion.

• Journal of Korean Society of Transportation
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• v.22 no.6
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• pp.159-173
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• 2004

Using a generalized translog multiproduct cost function model, this paper examines economies of scale and scope in the vertically-integrated Korean railway industry. The paper then conceptualizes that the Korea National Railroad (KNR) produces four outputs (passenger-kilometers, ton-kilometers of freight, average length of passenger trips, and average length of freight haul) using three input factors(labor, fuel and maintenance, and rolling stock and capital). Using time series data collected from the KNR's annual records for the years from 1977 to 2002, the simultaneous equation system consisting of a cost function and two input share equatins is estimated with the Zellner's iterative seemingly unrelated regression. The findings show that the cost function corresponding to a non-Cobb-Douglas, non-homothetic, and non-homogeneous production technology adequately represents the KNR's cost structure. On the other hand, the Korean railway industry experiences sizeable overall scale economies, which result from substantial product-specific scale economies associated with passenger-kilometers and freight ton-kilometers and from scope economies associated with their joint production. In addition, the magnitude of economies of scope is influenced largely by the ratio of passenger trips, and has increased over time as the former has increased while the latter has decreased.

• Journal of The Korean Society of Grassland and Forage Science
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• v.32 no.1
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• pp.75-84
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• 2012

Mechanized operation model and mechanical cultivation technology for winter barley, rye, Italian ryegrass and sudan grass wrap silage production system at the paddy field for cropping system was developed. Also, a series of experiment were performed and lots of data were collected and analyzed to develope mechanical technology, coverage area, and optimum size of the farm (break-even point) for wrap silage production system. The coverage area for winter barley or rye wrap-silage production system is determined around 61.9, 73.4, 77.5, 88.2 ha in the case of drill seeding and different ripening species by tractor power 50, 75, 100, 130 ps, respectably. The break-even point of the farming size is analyzed as 20 ha and its production cost is estimated around 367, 383, 430, 443 won/TDN-kg in the case of winter barley wrap-silage by tractor power 50, 75, 100, 130 ps, respectably. The break-even point of the farming size is analyzed as coverage area and its production cost is estimated around 237, 215 won/TDN-kg in the case of winter barley wrap silage and sudan grass by the tractor power 50, 100 ps, respectably.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.25 no.1
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• pp.6-11
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• 1989

Some distinctive defects in the conventional stow net were examined and presented in the previous report of this series. To find out the more effective gear by correcting the defects, the authors carried out another experiment by using a newly designed gear. 1. Special features of the newly designed gear are: (1) stretched width of front end on top, bottom and side panel are decreased 20%, on the other hand, the frank of the panels are increased 10% compared with the conventional gear. Front end of top and bottom panels are bias cutten up to 20% of the length of panels. (2) Length of the head rope and ground rope are shortened 6% by changing of the shape of the top and bottom panels. (3) Lacing lines are attached to four longitudinal seaming lines with suitable hanging ratio. (4) Stretched height of the shearing device were shortened 17%, and the buoyancy on top of the device were increased 20%. (5) Length of the biforked pendants were arranged to be shorter on top-most and bottom-most ones, and loner on middle ones. 2. The observed result can be expressed as (1) Wrinkles in the front end of top panels are removed and fringe line of panels become smooth. (2) Opening height of mouth is observed 3% higher than that of the conventional gear. (3) Opening width is 1.5 to 1.6 times wider than that of the conventional gear. (4) Hydrodynamic resistance is decreased 10%-17%.

• Journal of KIISE:Software and Applications
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• v.26 no.11
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• pp.1261-1269
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• 1999

다층 퍼셉트론은 다양한 응용 분야에 성공적으로 적용되고 있는 대표적인 신경회로망 모델이다. 그러나 다층 퍼셉트론의 학습에서 나타나는 플라토에 기인한 느린 학습 속도와 지역 극소는 실제 응용문제에 적용함에 있어서 가장 큰 문제로 지적되어왔다. 이 문제를 해결하기 위해 여러 가지 다양한 학습알고리즘들이 개발되어 왔으나, 계산의 비효율성으로 인해 실제 문제에는 적용하기 힘든 예가 많은 등, 현재까지 만족할 만한 해결책은 제시되지 못하고 있다. 본 논문에서는 다층퍼셉트론의 베이시스 함수로 사용되는 시그모이드 함수를 보다 일반화된 형태로 정의하여 사용함으로써 학습에 있어서의 플라토를 완화하고, 지역극소에 빠지는 것을 줄이는 접근방법을 소개한다. 본 방법은 기존의 변형된 가중치 수정식을 사용한 학습 속도 향상의 방법들과는 다른 접근 방법을 택함으로써 기존의 방법들과 함께 사용하는 것이 가능하다는 특징을 갖고 있다. 제안하는 방법의 성능을 확인하기 위하여 간단한 패턴 인식 문제들에의 적용 실험 및 기존의 학습 속도 향상 방법을 함께 사용하여 시계열 예측 문제에 적용한 실험을 수행하였고, 그 결과로부터 제안안 방법의 효율성을 확인할 수 있었다. Abstract A multilayer perceptron is the most well-known neural network model which has been successfully applied to various fields of application. Its slow learning caused by plateau and local minima of gradient descent learning, however, have been pointed as the biggest problems in its practical use. To solve such a problem, a number of researches on learning algorithms have been conducted, but it can be said that none of satisfying solutions have been presented so far because the problems such as computational inefficiency have still been existed in these algorithms. In this paper, we propose a new learning approach to minimize the effect of plateau and reduce the possibility of getting trapped in local minima by generalizing the sigmoidal function which is used as the basis function of a multilayer perceptron. Adapting a new approach that differs from the conventional methods with revised updating equation, the proposed method can be used together with the existing methods to improve the learning performance. We conducted some experiments to test the proposed method on simple problems of pattern recognition and a problem of time series prediction, compared our results with the results of the existing methods, and confirmed that the proposed method is efficient enough to apply to the real problems.

• Journal of the Korean Institute of Gas
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• v.7 no.4 s.21
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• pp.44-52
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• 2003

In this work dynamic heat transfer in a CPFS (cable penetration fire stop) system built in the firewall of nuclear power plants is three-dimensionally investigated to develop a test-simulator that can be used to verify effectiveness of the sealant. Dynamic heat transfer in the fire stop system is formulated in a parabolic PDE (partial differential equation) subjected to a set of initial and boundary conditions. First, the PDE model is divided into two parts; one corresponding to heat transfer in the axial direction and the other corresponding to heat transfer on the vertical planes. The first PDE is converted to a series of ODEs (ordinary differential equations) at finite discrete axial points for applying the numerical method of SOR (successive over-relaxation) to the problem. The ODEs are solved by using an ODE solver In such manner, the axial heat flux can be calculated at least at the finite discrete points. After that, all the planes are separated into finite elements, where the time and spatial functions are assumed to be of orthogonal collocation state at each element. The initial condition of each finite element can be obtained from the above solution. The heat fluxes on the vertical planes are calculated by the Galerkin FEM (finite element method). The CPFS system was modeled, simulated, and analyzed here. The simulation results were illustrated in three-dimensional graphics. Through simulation, it was shown clearly that the temperature distribution was influenced very much by the number, position, and temperature of the cable stream, and that dynamic heat transfer through the cable stream was one of the most dominant factors, and that the feature of heat conduction could be understood as an unsteady-state process.

• Journal of Korean Society of Forest Science
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• v.73 no.1
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• pp.70-75
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• 1986

The secular trend and seasonal variation of chestnut prices have been analyzed, and the production and price for the next two decades (1985-2004) have been forecasted by the derived equation model. The results of the study can be summarized as follows; 1) The chestnut prices went up at the rate of 10.95% per annum during 1965-1972, but, due to excessive supply of chestnuts, went down at the rate of 7.25% during 1973-1984. 2) In a year, the prices were lowest at the harvesting season, especially on October, and highest on July. Such a seasonal fluctuations of chestnut prices tend to be even with the passage of time, but the range of fluctuation is still wide. 3) It was forecasted under certain premises that the annual chestnut production will be increased by 99,000 tons in 1992, but the amount will fall rapidly to about 23,000 tons in 2004. The prices will be similar to the present level or have slightly upward Tendency until 1992, but this will be rapidly raised thereafter.