• 한국자동차공학회논문집
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• 제15권6호
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• pp.128-136
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• 2007

It is well known that two representative methods satisfy EURO-IV regulation from EURO-III. The first method is to achieve the regulation through the reduction of NOx in an engine by utilizing relatively high EGR rate and the elimination of subsequently increased PM by DPF. However, it results in the deterioration of fuel economy due to relatively high EGR rate. The second is to use the high combustion strategy to reduce PM emission by high oxidation rate and trap the high NOx emissions with DeNOx catalysts such as Urea-SCR. While it has good fuel economy relative to the first method mentioned above, its infrastructure is demanded. In this paper, the number distribution of nano PM has been evaluated by Electrical Low Pressure Impactor(ELPI) and CPC in case of Urea-SCR system in second method. From the results, the particle number was increased slightly in proportion to the amount of urea injection on Fine Particle Region, whether AOC is used or not. Especially, in case of different urea injection pressure, the trends of increasing was distinguished from low and high injection pressure. As low injection pressure, the particle number was increased largely in accordance with the amount of injected urea solution on Fine Particle Region. But Nano Particle Region was not. The other side, in case of high pressure, increasing rate of particle number was larger than low pressure injection on Nano Particle Region. From the results, the reason of particle number increase due to urea injection is supposed that new products are composited from HCNO, sulfate, NH3 on urea decomposition process.

• 품질경영학회지
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• 제31권4호
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• pp.81-94
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• 2003

6 시그마는 세계 초우량 기업들뿐만 아니라 한국의 우수한 기업들에 의해서 이미 도입되고 추진되고 있다. 6 시그마는 제품 및 서비스의 품질뿐만 아니라 판매와 구매, 그리고 회계 등 경영의 모든 프로세스에 총체적으로 접근하는 경영혁신활동이다. 6 시그마는 고객의 관점에서 품질문제를 과학적으로 접근하여 품질로 인한 대규모의 손실비용을 제거함으로서 경영이익 극대화를 추구한다. 본 연구에서는 6 시그마의 중추적 역할을 하고 있는 블랙벨트를 통해 6 시그마 성공의 핵심요인을 실증적으로 도출함으로써 6 시그마가 한국기업에 정착되기 위한 방향을 제시하고자 한다. 6 시그마를 도입하여 추진하고 있는 국내 기업들을 대상으로 6 시그마 성공의 핵심 요인을 분석한 결과, 최고경영층의 리더십과 6 시그마 활동에 대한 보상 및 인센티브가 가장 중요한 요인이라고 분석되었다. 그리고 블랙벨트의 관점에서 공정유형과 추진단계별로 6 시그마 핵심요인간에 차이가 있는 것으로 나타나 유의한 연구결과가 도출되었다.

• Journal of Power Electronics
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• 제16권4호
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• pp.1513-1525
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• 2016

Rapid and accurate phase synchronization is critical for the reliable control of grid-tied inverters. However, the commonly used software phase-locked loop methods do not always satisfy the need for high-speed and accurate phase synchronization under severe grid imbalance conditions. To address this problem, this study develops a novel open-loop phase locking scheme based on a synchronous reference frame. The proposed scheme is characterized by remarkable response speed, high accuracy, and easy implementation. It comprises three functional cascaded blocks: fast orthogonal signal generation block, fast fundamental-frequency positive sequence component construction block, and fast phase calculation block. The developed virtual orthogonal signal generation method in the first block, which is characterized by noise immunity and high accuracy, can effectively avoid approximation errors and noise amplification in a wide range of sampling frequencies. In the second block, which is the foundation for achieving fast phase synchronization within 3 ms, the fundamental-frequency positive sequence components of unsymmetrical grid voltages can be achieved with the developed orthogonal signal construction strategy and the symmetrical component method. The real-time grid phase can be consequently obtained in the third block, which is free from self-tuning closed-loop control and thus improves the dynamic performance of the proposed scheme. The proposed scheme is adaptive to severe unsymmetrical grid voltages with sudden changes in magnitude, phase, and/or frequency. Moreover, this scheme is able to eliminate phase errors induced by harmonics and random noise. The validity and utility of the proposed scheme are verified by the experimental results.

• 방사성폐기물학회지
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• 제3권2호
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• pp.135-148
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• 2005

방사성 폐기물의 지층 처분장 건설 및 운영을 위한 개념 선정 단계에서는 폐기물 운반 및 거치뿐 아니라, 처분장의 건설/운영/폐쇄 기간 동안 지하 처분장의 작업 환경 및 위생, 안전, 그리고 처분장내의 수분 제거와 같은 향후 처분장의 환경을 위해 처분장 환기시스템에 대한 고려가 향후 처분장의 환경을 위해 반드시 필요하다. 본 논문은 동굴처분 방식의 중-저준위 처분장 및 지하 심부에 위치하게 될 고준위 처분장에 대한 환기시스템 개념설계 기준 및 요구사항에 대한 내용이다. 방사성폐기물 처분장의 환기 시스템에서 가장 주된 기본 설계 개념은 처분장 건설과 폐기물저장을 위한 작업활동을 위해 각각 독립적이고 분리된 환기시스템을 적용하여야 한다는 것이다. 본 논문에서는 방사성폐기물 처분장의 환기시스템의 설계과정에 대해 기술하고 환기회로 모델링 방법, 자연 환기, 환기 모니터링 시스템과 실시간 환기 시뮬레이션, 화재 시뮬레이션 및 비상 방재 시스템에 관한 사항도 논의하였다

• 한국멀티미디어학회논문지
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• 제10권4호
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• pp.421-431
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• 2007

이동 통신 기술의 급격한 발전으로, 이동 컴퓨팅 환경에서 데이터 서비스에 대한 수요가 점차 증가하고 있다. 이동 컴퓨팅 환경에서의 여러 단점을 극복하고자 캐쉬가 등장하게 되었다. 이동 호스트 내에 캐쉬가 존재하면, 통신 대역폭의 절약 및 질의에 대한 빠른 응답을 가져올 수 있지만, 이동 호스트가 서버 데이터와의 캐쉬 일관성(consistency)을 유지시켜야 한다는 문제가 생기게 된다. 본 논문에서는 기존의 기법들이 가지는 문제점들을 보완하기 위해 데이터의 주기성을 고려한 캐쉬 일관성 유지 기법을 제안한다. 제안한 기법은 데이터를 주기적, 비주기적 데이터로 분류하고 주기적 데이터에 만료시간을 삽입한다. 또한 무효화 메시지를 저장해서 단절 후에 선별적으로 캐쉬 데이터가 나누어질 수 있도록 해서, 캐쉬 내의 데이터가 접속 단절 후에 일방적으로 버려지는 것을 막을 수 있게 된다. 이렇게 함으로서 서버와 이동 호스트간의 통신에 사용하는 전체 대역폭의 낭비와 서버접속에 필요한 이동 호스트의 전력의 낭비를 줄일 수 있다. 마지막으로 기존의 기법과의 실험을 통해서 제안한 기법의 효율성을 알아보고자 한다.

• International Journal of Fluid Machinery and Systems
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• 제8권4호
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• pp.283-293
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• 2015

The effect of the inlet swirling flow in a hydraulic turbine draft tube is a very complex phenomenon, which has been extensively investigated both theoretically and experimentally. In fact, the finding of the optimal flow distribution at the draft tube inlet in order to get the best performance has remained a challenge. Thus, attempting to answer this question, it was assumed that through an automatic optimization process a Genetic Algorithm would be able to manage a parameterized inlet velocity profile in order to achieve the best flow field for a particular draft tube. As a result of the optimization process, it was possible to obtain different draft-tube flow structures generated by the automatic manipulation of parameterized inlet velocity profiles. Thus, this work develops a qualitative and quantitative analysis of these new draft tube flow field structures provoked by the redesigned inlet velocity profiles. The comparisons among the different flow fields obtained clearly illustrate the importance of the flow uniformity at the end of the conduit. Another important aspect has been the elimination of the re-circulating flow area which used to promote an adverse pressure gradient in the cone, deteriorating the pressure recovery effect. Thanks to the evolutionary optimization strategy, it has been possible to demonstrate that the optimized inlet velocity profile can suppress or mitigate, at least numerically, the undesirable draft tube flow characteristics. Finally, since there is only a single swirl number for which the objective function has been minimized, the energy loss factor might be slightly affected by the flow rate if the same relation of the axial-tangential velocity components is maintained, which makes it possible to scale the inlet velocity field to different operating points.

• Journal of Power Electronics
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• 제16권3호
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• pp.1110-1121
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• 2016

The mathematical model of a three phase PWM converter under the stationary αβ reference frame is deduced and constructed based on a Proportional-Resonant (PR) regulator, which can replace trigonometric function calculation, Park transformation, real-time detection of a Phase Locked Loop and feed-forward decoupling with the proposed accurate calculation of the inductance voltage vector. To avoid the parallel resonance of the LCL topology, the active damping method of the proportional capacitor-current feedback is employed. As to current vector error elimination, an optimized PR controller of the inner current loop is proposed with the zero-pole matching (ZPM) and cancellation method to configure the regulator. The impacts on system's characteristics and stability margin caused by the PR controller and control parameter variations in the inner-current loop are analyzed, and the correlations among active damping feedback coefficient, sampling and transport delay, and system robustness have been established. An equivalent model of the inner current loop is studied via the pole-zero locus along with the pole placement method and frequency response characteristics. Then, the parameter values of the control system are chosen according to their decisive roles and performance indicators. Finally, simulation and experimental results obtained while adopting the proposed method illustrated its feasibility and effectiveness, and the inner current loop achieved zero static error tracking with a good dynamic response and steady-state performance.

• 한국기록관리학회지
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• 제16권2호
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• pp.29-55
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• 2016

전자정부 추진 이래 공공기관은 전자문서시스템이나 업무관리시스템을 통하여 문서를 생산하고 있으며, 대부분의 공문서가 개발사 의존적 독자포맷인 hwp로 저장되고 관리되고 있다. 이러한 독자포맷은 특정 소프트웨어에 의해서만 내용 확인이 가능하므로 해당 소프트웨어의 구매는 불가피하다. 라이선스를 구매하였다 할지라도 과거 또는 향후 버전에 대한 지원 여부가 불확실하므로 장기보존 대책이 요구된다. 기관 간 문서 유통 시 독자포맷과 XML 기반의 유통 규격 간 변환 과정에서 서식 누락, 대응 규격 부재로 인해 변환 실패나 원문서 변형을 초래하기도 한다. 본 연구는 개방형 문서 포맷(ODF)을 소개하고 공공영역에서의 문서 생산, 유통, 관리, 활용과 보존에 ODF 도입 시 예상되는 영향을 검토하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.9-10
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• 2010

Since the discovery of graphene by mechanical exfoliation from graphite[1], various fabrication methods are available today such as chemical exfoliation, epitaxial graphene on SiC substrates, etc. In view of industrialization, the mechanical exfoliation method may not be an option. Epitaxial graphene on SiC substrates, in this respect, is by far more practical because the method consists of conventional thermal treatments familiar to semiconductor industry. Still, the use of the SiC substrate itself, and hence the incompatibility with the Si technology, lessens the importance of this technology in its future industrialization. In this context, we have tackled the problem of forming graphene on Si substrates (GOS). Our strategy is to form an ultrathin (~80 nm) SiC layer on top of a Si substrate, and to graphitize the top SiC layers by a vacuum annealing. We have actually succeeded in forming the GOS structure [2,3,4]. Raman-scattering microscopy indicates presence of few-layer graphene (FLG) formed on our annealed SiC/Si heterostructure, with the G ($1580\;cm^{-1}$) and the G'($2700\;cm^{-1}$) bands, both related to ideal graphene, clearly observed. Presence of the D ($1350\;cm^{-1}$) band indicates presence of defects in our GOS films, whose elimination remains as a challenge in the future. To obtain qualified graphene films on Si substrate, formation of qualified SiC films is crucial in the first place, and is achieved by tuning the growth parameters into a process window[5]. With a potential for forming graphene films on large-scale Si wafers, GOS is a powerful candidate as a key technology in bringing graphene into silicon technology.

• 대한건축학회논문집:계획계
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• 제34권5호
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• pp.3-10
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• 2018

The purpose of this study is to estimate the attractiveness value according to the preference level on architectural aesthetic. This research starts from the concept that aesthetic is phenomenon and from the viewpoint of 'attraction value' which affects goods. Interactive internet surveys were conducted for 500 citizens of Seoul metropolitan city who are potential users of the Nodle Islet Cultural Center. Based on the scenarios and questionnaires with fuzzy models, we have examined the evaluation of architectural aesthetic and monetary willing-to-payment, and estimated the economic value by preference level of architectural aesthetic through linear regression analysis. The main results of the study are as follows: First, the economic value of the Nodle Islet Cultural Center was estimated at ?15,683.43/person. Residents of Seoul metropolitan city were willing to accept the increase in the above-mentioned amount of the facility fares when their preferred works (average 86.81 points) were constructed. (P <0/05) Second, it is confirmed that the economic value increases dramatically as the preference level of architectural aesthetic increases. Third, it is presumed that the infinite valuation of architectural aesthetic and the problem of free riding coexist in the estimation of economic valuation of architectural aesthetic for public buildings. Fourth, by mixing the fuzzy logic with contingent valuation method, starting point bias and no response biases that happened in contingent valuation could be disappeared. bias elimination must be considered seriously because another bias could be happened in full process of the research. The results of this study will serve as a basis for spreading architectural aesthetic value-oriented research from the vague and obscure aesthetic-centered discussion on the existing architectural aesthetic. In addition, it will be an opportunity to draw institutional application and utilization strategy of architectural aesthetic through architectural aesthetic value research.