• 전기학회논문지
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• 제64권2호
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• pp.232-239
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• 2015

Faced with unbalanced grid operation mode, the high voltage direct current (HVDC) based on voltage source converter (VSC) can be properly controlled by a dual current control scheme. For the modular multilevel converter (MMC) controlling the AC side current is able to limit the arm current which flows along the IGBT of submodule (SM) to rated current. However the limitation of the arm current results in leaving the control range of active power at MMC confined to below the rated capacity. As a result, limiting the arm current causes the problem that the DC side voltage of the HVDC can not be controlled to the reference value since MMC HVDC adjusts the DC side voltage through the active power. In this paper, we propose the algorithm adjusting the active powers of both MMCs to resolve the problem. The back-to-back MMC HVDC applying the algorithm is modeled by PSCAD/EMTDC to verify the algorithm.

• 한국항해항만학회지
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• 제30권2호
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• pp.137-143
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• 2006

The optimum grillage design belongs to nonlinear constrained optimization problem. The determination of beam scantlings for the grillage structure is a very crucial matter out of whole structural design process. The performance of optimization methods, based on penalty functions, is highly problem-dependent and many methods require additional tuning of some variables. This additional tuning is the influences of penalty coefficient, which depend strongly on the degree of constraint violation. Moreover, Binary-coded Genetic Algorithm (BGA) meets certain difficulties when dealing with continuous and/or discrete search spaces with large dimensions. With the above reasons, Real-coded Micro-Genetic Algorithm ($R{\mu}GA$) is proposed to find the optimum beam scantlings of the grillage structure without handling any of penalty functions. $R{\mu}GA$ can help in avoiding the premature convergence and search for global solution-spaces, because of its wide spread applicability, global perspective and inherent parallelism. Direct stiffness method is used as a numerical tool for the grillage analysis. In optimization study to find minimum weight, sensitivity study is carried out with varying beam configurations. From the simulation results, it has been concluded that the proposed $R{\mu}GA$ is an effective optimization tool for solving continuous and/or discrete nonlinear real-world optimization problems.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.564-564
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• 2012

Graphene has been emerged as a fascinating material for future nanoelectronic applications due to its extraordinally electronic properties. However, their zero-bandgap semimetallic nature is a major problem for applications in high performance field-effect transistors (FETs). Graphene nanoribbons (GNRs) with narrow widths (${\geq}10nm$) exhibit semiconducting behavior, which can be used to overcome this problem. In previous reports, GNRs were produced by several approaches, such as electron beam lithography patterning, chemically derived GNRs, longitudinal unzipping of carbon nanotubes, and inorganic nanowire template. Using these methods, however, the width distribution of GNRs was a quiet broad and substantial defects were inevitably occurred. Here, we report a novel approach for fabricating width-tailored GNRs by focused ion beam-assisted chemical vapor deposition (FIB-CVD). Width-tailored phenanthrene ($C_{14}H_{10}$) templates for direct growth of GNRs were prepared on $SiO_2$/Si substrate by FIB-CVD. The GNRs on the templates were synthesized at $900-1,050^{\circ}C$ with introducing $CH_4$ $(20sccm)/H_2$ (10 sccm) mixture gas for 10-300 min. Structural characterizations of the GNRs were carried out using Raman spectroscopy, scanning electron microscopy, and atomic force microscopy.

• Journal of Power Electronics
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• 제19권1호
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• pp.119-133
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• 2019

Although the dual modulation wave method can solve the low-frequency neutral point potential (NPP) fluctuation problem for three-level neutral point clamped converters, it also increases the switching frequency and limits the zero-sequence voltage. That makes it harmful when dealing with the NPP drift problem if the converter suffers from a long dead time or asymmetric loads. By introducing two degrees of freedom (2-DOF), an NPP control based on a search optimization method can demonstrate its ability to cope with the above mentioned two types of NPP problems. However, the amount of calculations for obtaining an optimal 2-DOF is so large that the method cannot be applied to certain industrial applications with an inexpensive digital signal processor. In this paper, a novel optimal 2-DOF-based NPP control is proposed. The relationships between the NPP and the 2-DOF are analyzed and a method for directly determining the optimal 2-DOF is also discussed. Using a direct calculation method, the amount of calculations is significantly reduced. In addition, the proposed method is able to maintain the strongest control ability for the two types of NPP problems. Finally, some experimental results are given to confirm the validity and feasibility of the proposed method.

• 수산경영론집
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• 제23권2호
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• pp.101-128
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• 1992

How to distribute fisheries catches from producer to consumer is very important for everybody joined fisheries marketing channels (FMC), because most people are influenced their revenue and expenditure through marketing channels. Many institutions in Korea after 1960's have tried to develop the rationalization of FMC, but they have not gotten the satisfactory results in general in spite of a lot fruits. Comparing with general manufacturing industry, the fisheries industry has some specializations in the marketing channels. It makes them unique structure included wholesale market system similiar to fresh (perishable) food market with expertised technology. Wholesale market collects, distributes the fisheries catches and evaluates in by auction or bidding without consideration of producer's opinion. It is very necessary institution to make a decision to equatible price for fresh food and to play an important role for marketing effectiveness with minimum total transation and with massed reserve among institutions. But it has two weak points to increase the marketing cost and to make products bad fresh (perishable). Therefore, both Producer and consumer want to find the direct channels not to pass through wholesale market and to get more profit. I wanted to explain what problems of traditional FMC are and why the direct channel is necessary as follows in this paper. Chapter II : The types and specialization of FMC Chapter III : The structure and problem of fisheries wholesale market channel Chapter IV Marketing cost of FMC and direct channel I suggested when the direct channel in FMC is designed, new planner must carry out marketing functions which are performanced by wholesaler, middle man and the joined members of auction at wholesale market. In view of consumption area, these functions are : (1) the finding of production partner to make a business ; (2) communication of information ; (3) collecting ; (4) distribution ; (5) selecting and grading ; (6) evaluating ; (7) financing and payment ; (8) organization, in view of consumption area. The government must support also the group or individual of new direct channels to succeed it with (1) furnishing of market information (2) supplying of land and facility (3) financing (4) feed-back of dierct channels totally (5) making an opportunity of communication between producer and consumer. I want to emphasize again wholesale market is necessary and important institution for equatible price of fresh food in spite of the its weak points. At the same time. the direct channels are necessary to reduce the marketing cost and to keep better fresh food.

• 한국염색가공학회지
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• 제21권5호
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• pp.51-57
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• 2009

Since heavy metal pollution is a significant global environmental problem and very dangerous to human health, the improved methods for detecting heavy metals are required recently. Colorimetric chemosensors are now considered as one of the most effective analytical method used in the environment monitoring. New direct dyes having the function of colorimetric chemosensors were synthesized. When metal ions such as $Al^{3+}$, $Ca^{2+}$, $Cd^{2+}$, $Cr^{3+}$, $Cu^{2+}$, $Fe^{2+}$, $Fe^{3+}$, $Hg^{2+}$, $Li^+$, $Mg^{2+}$, $Na^+$, $Ni^{2+}$, $Pb^{2+}$ and $Zn^{2+}$ were added each solution of new direct dyes, the color of solution was changed and can be easily detected with naked eyes without expensive experimental equipment such as atomic absorption spectrometer (AAS) or inductively coupled plasma?mass spectrometer (ICP-MS). The new benzidine analogues were diazotized and reacted with couplers such as H-acid, J-acid, Chromotropic acid, Nevill-winther acid and gamma acid to synthesize new direct dyes. The structures of the new direct dyes were confirmed by high resolution mass spectrometer (FAB ionization) and evaluated with UV-Vis spectroscopy. The UV-VIS spectroscopy was measured for the dye solutions by adding various concentrations of metal ions. It was observed that the absorbance in UV-Vis spectra was changed as the heavy metal ions were added.

• 한국물환경학회지
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• 제25권5호
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• pp.785-791
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• 2009

Using artificial rainfall simulator, the soil loss, which is deemed as the most cause of muddy water problem among Non-point source (NPS) pollutant, was studied by the analysis of direct runoff, groundwater discharge, and soil water storage properties concerned with rainfall intensity, slope of area, and land cover. The direct runoff showed increasing tendency in both straw covered and bared soil as slope increases from 5% to 20%. The direct runoff volume from straw covered surface were much lower than bared surface. The infiltration capacity of straw covered surface increased, because the surface sealing by fine material of soil surface didn't occur due to the straw covering. Under the same rainfall intensity and slope condition, 2.4~8.2 times of sediment yield were occurred from bared surface more than straw covered surface. The volume of infiltration increased due to straw cover and the direct runoff flow decreased with decrease of tractive force in surface. To understand the relationship of the rate of direct runoff, groundwater discharge, and soil water storage by the rainfall intensity, slope, and land cover, the statistical test was performed. It shows good relationship between most of factors, except between the rate of groundwater storage and rainfall intensity.

• 한국측량학회지
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• 제30권2호
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• pp.181-188
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• 2012

최근 항공측량분야에서 항측용 디지털카메라와 라이다 및 GPS/INS와 같은 센서들을 이용해 다양한 공간정보를 획득하고 있다. 또한 GPS/INS와 항측용 디지털카메라의 연계를 통한 Direct Georeferencing 기술이 널리 활용되고 있다. 하지만 여러 센서의 결합에 따른 센서검정(Sensor Calibration)을 실시해야 하는 문제점이 따른다. 특히, 통합센서의 Boresight Calibration은 GPS/INS 항공삼각측량 및 Direct-georeferencing을 사용하는 작업절차에서 중요한 요소이다. 이를 해결하기 위해 본 연구에서는 항공기용 센서의 검정을 위한 국가차원의 테스트베드를 세종시 부지에 설치하고 항공영상의 항공삼각측량에 의해 함께 사용되는 GPS와 INS 센서결합에 따른 정확한 검정을 수행하여 시스템 변수의 정의, 시스템적인 에러를 평가하고 Direct Georeferencing에 필요한 외부표정요소 직접결정을 위한 효율적인 방법의 조사와 통합된 센서의 정확도 평가를 수행하였다.

• 대한치과보철학회지
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• 제41권2호
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• pp.160-168
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• 2003

Statement of problem : Direct denture reline resins tend to discolor during service in the oral environment by intrinsic and extrinsic factor. Purpose : This study was designed to evaluate the color stability of direct denture reline resins. Material and methods : Mild Rebaron(GC Corp., Japan), Meta Base M(Sun medical Co., Japan), Mild Rebaron LC(GC Corp., Japan) and as a control group, Vertex SC(Dentimex Zeist, Holland) were chosen for this study. Ten specimens of each direct denture reline resins were fabricated. Treatment methods designed for this study were the coffee staining test(7days) and the accelerated aging test(100hours). The color changes before and after treatment were measured by Tristimulous colorimeter(Yasuda seiki seisakusho, Ltd. Japan) and analyzed. Results All the direct denture reline resins subjected to the coffee staining test and the accelerated aging test showed noticible difference in color change. After coffee staining test, Meta Base M showed the highest color change followed by Vertex SC. Mild Rebaron LC and Mild Rebaron. There were no statistical differences between Meta Base M and Vertex SC and between Mild Rebaron LC and Mild Rebaron(p>0.05). After accelerated aging test. Mild Rebaron LC showed the highest color change followed by Vertex SC, Meta Base M and Mild Rebaron. There were no statistical differences only between Mild Rebaron and Mata Base M(p>0.05) but among the others, there were statistical differences(p<0.05). Conclusion : Within the limitation of this study, all the direct denture reline resins subjected to the extrinsic and intrinsic factors showed noticible difference in color change, and there were differences among manufacturers.

• Applied Biological Chemistry
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• 제27권
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• pp.68-79
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• 1984

An increased population and rapidly expanding industrial development have led to enormous amounts of various domestic and industrial wastes. The proper disposal of ever-increasing wastes is a growing global problem. Land treatment is one of the rational approaches that are environmentally safe and economically practical. It has long been practised in many sites. Recycling of industrial wastes on agricultural land can provide better possible means for maintaining environmental quality and utilizing waste-resources. Even though industrial wastes are beneficial as soil amendment and fertilizer, they have some limitation on land application because of wide variability as well as physicochemical problem in their composition. A direct application of solid and liquid wastes on land is being practised in Korea and some experimental results are presented. The direct application of fermentation waste on rice resulted in a 6 percent yield increase. Another organic residue from glutamic acid fermentation is widely used not only as a direct application as a liquid fertilizer but also for a raw material of organic compound fertilizer. These wastes are much promising as sources of plant nutrients, since they have large amounts of nutrients, especially nitrogen with few toxic metals. On the other hand, fertilizers developed from inorganic industrial wastes include calcium silicate, calcium sulfate and ammonium sulfate. The calcium silicate fertilizer simply produced from slag, by-product of iron and steel manufacturing plant is one of the most successful example of the conversion of wastes to fertilizer and slag production capacity totals to over three million MT/year. About 200,000 MT of calcium silicate fertilizer is currently applied in the paddy rice every year. Calcium sulfate, a waste from the wet phosphoric acid process is to some extent used as a filler of compound fertilizers but quite large quantites are directly applied for the reclamation of tidal flat.