• 오토저널
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• 제10권6호
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• pp.72-84
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• 1988

Engine performance is one of the main objectives specified at the beginning of a new engine design project. The cycle simulation for SI engine is based on the zero-dimensional gas exchange model and a heat release expression by Viebe. This program also requires minimum input data and takes only a short time to run. Heat transfer from cylinder transfer formula. The flow coefficient (effective area) is calculated from valve lift using the standard flow coefficient curve and engine friction is calculated from the Millington and Hartles' engine friction formula. The chemical species considered in burned gas are 6 species CO, CO, H$_{2}$, H$_{2}$O, $O_{2}$, N$_{2}$ and the cylinder pressure, homogeneous cylinder temperature, gas composition and burned fraction are calculated at each crank angle through the cycle. To check the validity and accuracy, experimental study was done with 3 engines for measuring cylinder pressure, indicated mean effective pressure, brake mean effective pressure and air flow rate, etc. Despite its simple assumptions, cycle simulation showes excellent breathing and performance correlation when compared with data of tested engines, and have been proved useful in engine design.

• Journal of Power Electronics
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• 제16권6호
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• pp.2350-2358
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• 2016

The one cycle control (OCC) scheme for active power filters (APFs) has shown excellent harmonic suppression and implementation simplicity. However, its real world application is limited because the non-ideal supply voltage for APFs can influence its performance so that the source currents are still distorted after compensation. This paper proposes a modified one cycle control (MOCC) scheme to improve the performance of three-phase shunt APFs under non-ideal supply voltage conditions. In this paper a detailed mathematical derivation has been presented and the key control law of the MOCC has been developed for adaption to the non-ideal supply voltages, following the control philosophy of simplicity. A relatively simple sequence filter is introduced to extract the harmonic components of supply voltages. The modified scheme can be easily implemented. The proposed control strategy has excellent performance and a 5kVA APF hardware platform has been implemented to validate the feasibility and performance of the proposed strategy.

• 대한산업공학회지
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• 제28권4호
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• pp.415-424
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• 2002

Semiconductor manufacturing has been emerged as a highly competitive but profitable business. Accordingly it becomes very important for semiconductor manufacturing companies to meet customer demands at the right time, in order to keep the leading edge in the world market. However, due-date oriented production is very difficult task because of the complex job flows with highly resource conflicts in fabrication shop called FAB. Due to its cyclic manufacturing feature of products, to be completed, a semiconductor product is processed repeatedly as many times as the number of the product manufacturing cycles in FAB, and FAB processes of individual manufacturing cycles are composed with similar but not identical unit processes. In this paper, we propose a production scheduling and control scheme that is designed specifically for semiconductor scheduling environment (FAB). The proposed scheme consists of three modules: simulation module, cycle due-date estimation module, and dispatching module. The fundamental idea of the scheduler is to introduce the due-date for each cycle of job, with which the complex job flows in FAB can be controlled through a simple scheduling rule such as the minimum slack rule, such that the customer due-dates are maximally satisfied. Through detailed simulation, the performance of a cycle due-date based scheduler has been verified.

• International Journal of Contents
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• 제4권4호
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• pp.1-6
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• 2008

In this paper, we propose improved loop splitting method for maximizing parallelism of single loops with non-constant dependence distances. By using the iteration and distance for the source of the first dependence, and by our defined theorems, we present generalized and optimal algorithms for single loops with non-uniform dependences (MPSL). By the extension of the MPSL method, we also apply to exploit parallelism from nested loops with simple subscripts, based on cycle shrinking and loop interchanging method. The algorithms generalize how to transform general single loops with non-uniform dependences as well as nested loops with simple subscripts into parallel loops.

• KDI Journal of Economic Policy
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• 제31권2호
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• pp.47-85
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• 2009

본 연구는 1970년 이후 우리나라 거시경제변수들의 경기변동과 관련된 특징들을 포괄적으로 분석하는 것을 목적으로 한다. 본 연구에서는 우리나라의 각종 거시경제 변수들이 어떠한 특성을 보여 왔는지에 대해 실증분석하였다. 실증분석에서는 크게 국내 경제의 순환적 변동을 어떻게 식별할 것인지, 주요 경제변수들이 전체 경기순환과정에서 어떠한 패턴으로 변동하고 있는지, 그리고 경기변동과정의 안정성에 대한 변화 여부 등의 이슈를 다루었다. 분석 결과, 1970년 이후 우리나라 거시경제의 안정성은 외환위기 기간을 제외하고는 개선되었으며, 특히 2000년 이후부터는 경제내의 부문 간에 상호보완적인 관계가 나타나면서 전체적인 경기변동성이 감소하였던 것으로 나타나고 있다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2004년도 가을 학술발표회 논문집
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• pp.150-156
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• 2004

Though the concept of Life-Cycle Cost (LCC) itself is not new, its effectiveness for planning, design, rehabilitation and maintenance/management of civil infrastructures is becoming increasingly recognized. For the decision problems as in the case of the LCC of plant facilities, equipments, bridge decks, pavements, etc., the Life-Cycle Cost Analysis (LCCA) is relatively simple, and thus its practical implementation is rather straightforward. However, when it comes to major infrastructures such as bridge, tunnels, underground facilities, etc., the LCCA problem becomes extremely complex because lack of cost data associated with various direct and indirect losses, and the absence of uncertainty data available for the assessment as well. As a result, the LCC studies have been largely limited only to those relatively simple LCCA problems of planning or conceptual design for making decisions. Accordingly, in the recent years, the researchers have pursued extensive studies on the LCC effectiveness mostly related to LCC models and frameworks for civil infrastructures. Moreover, recently the demand on the practical application of LCC effective decisions in design and maintenance is rapidly growing unprecedently in civil engineering practice. Indirction cost is very important on LCC formulation. But that is very difficult and complicate the estimation every LCC. The objective of this paper is to suggest efficient regression model for the estimation of indirect cost approach to the practical application of LCC for the design and rehabilitation of civil. infrastructures considering traffic, traffic network, detour condition, and workzone condition. In this paper, it performed the sensitivity analysis and correlation analysis of parameter for development of regression model of inflection cost.

• 대한기계학회논문집B
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• 제33권6호
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• pp.403-410
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• 2009

This paper proposes a new approach to find the optimum ratios between sizes of the heat exchangers of the heat recovery steam generator (HRSG) system with limited size to maximize the efficiency of the steam turbine (bottom) cycle of combined cycle power plants (CCPP), but without performing the bottom cycle analysis. This could be achieved by minimizing the unavailable exergy (the sum of the destroyed and the lost exergies) resulted from the heat transfer process of the HRSG system. The present approach is relatively simple and straightforward because the process of the trial-and-error method, typical in performing the bottom cycle analysis for the system optimization, could be avoided. To demonstrate the usefulness of the present method, a single-stage HRSG system was chosen and the optimum evaporation temperature was obtained corresponding to the condition of the maximum useful work. The results show that the optimum evaporation temperature based on the present exergy analysis appears similar to that based on the bottom cycle analysis. Also shown is the dependency of size (NTU) ratios between the heat exchangers on the inlet gas temperature, which is another important factor in determining the optimum condition once overall size of the heat recovery steam generator is given. The present approach turned out to be a useful tool for optimization of the singlestage HRSG systems and can easily be extended to multi-stage systems.

• International Journal of Automotive Technology
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• 제2권1호
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• pp.1-7
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• 2001

This paper presents further investigation into the effect of over-expansion cycle in a spark-ignition engine. On the basis of the results obtained in previous studies, several combinations of late-closing (LC) of intake valve and expansion ratio were tested using a single-cylinder production engine. A large volume of intake capacity was inserted into the intake manifold to simulate multi-cylinder engines. With the large capacity volume, LC can decrease the pumping loss and then increase the mechanical efficiency. Increasing the expansion ratio from 11 to 23.9 with LC application can produce about 13% improvement of thermal efficiency which was suggested to be caused by the increased cycle efficiency. The decrease of compression ratio from 11 to 5.5 gives little effect on the thermal efficiency if the expansion ratio could be kept constant. Thus, the expansion ratio is revealed to be a determining factor for cycle efficiency, while compression ratio is no more important, which suggests the usefulness of controlling the intake charge with intake valve closure timing. These were successfully explained by simple thermodynamic calculation and thus the mechanism could be verified by the estimation.

• Reproductive and Developmental Biology
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• 제33권3호
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• pp.147-152
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• 2009

Lysophosphatidic acid (LPA), a simple phospholipid-derived mediator implicated in diverse biological actions, acts through the specific G-protein coupled receptors, LPA receptor (LPAR) $1{\sim}5$. Our previous study showed that LPAR3 is expressed in the uterine endometrium in a cell type- and stage-specific manner and LPA via LPAR3 increases PTGS2 expression in the uterine endometrium during the period of implantation. Although LPAR3 is considered to be predominant LPA receptor in the uterine endometrium, other LPA receptors might playa role to mediate LPA functions in the uterine endometrium during pregnancy. Among LPARs, we investigated expression of LPAR1 during the estrous cycle and pregnancy in this study. Uterine endometrial tissue samples were collected from day (D) 12 and D15 of the estrous cycle and from D12, D15, D30, D60, D90 and D114 of pregnancy. Northern blot analysis determined that LPAR1 mRNA was constitutively expressed in the uterine endometrial tissues during the estrous cycle and pregnancy of all stages. Analysis by immunoblotting revealed that LPAR1 proteins were present in the porcine uterine endometrium during the estrous cycle and pregnancy. Immunohistochemical experiments demonstrated that LP AR1 protein was localized to endometrial epithelium and stromal cell, specifically to nuclei of these cell types. Results in this study show that LPAR1 is constitutively expressed in the uterine endometrium during the estrous cycle and pregnancy. These results suggest that LPA via LPAR1 may playa role in the uterine endometrial function throughout pregnancy in pigs.

• Nuclear Engineering and Technology
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• 제41권6호
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• pp.785-796
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• 2009

A KALIMER-600 concept which is a type of sodium-cooled fast reactor, has been developed at KAERI. It uses sodium as a primary coolant and is a pool-type reactor to enhance safety. Also, a supercritical carbon dioxide ($CO_2$) Brayton cycle is considered as an alternative to an energy conversion system to eliminate the sodium water reaction and to improve efficiency. In this study, a simplified model for analyzing the thermodynamic performance of the KALIMER-600 coupled with a supercritical $CO_2$ Brayton cycle was developed. To develop the analysis model, a commercial modular modeling system (MMS) was adopted as a base engine, which was developed by nHance Technology in USA. It has a convenient graphical user interface and many component modules to model the plant. A new user library for thermodynamic properties of sodium and supercritical $CO_2$ was developed and attached to the MMS. In addition, some component modules in the MMS were modified to be appropriate for analysis of the KALIMER-600 coupled with the supercritical $CO_2$ cycle. Then, a simplified performance analysis code was developed by modeling the KALIMER-600 plant with the modified MMS. After evaluating the developed code with each component data and a steady state of the plant, a simple power reduction and recovery event was evaluated. The results showed an achievable capability for a performance analysis code. The developed code will be used to develop the operational strategy and some control logics for the operation of the KALIMER-600 with a supercritical $CO_2$ Brayton cycle after further studies of analyzing various operational events.