Numerical analysis of NOx reduction for compact design in marine urea-SCR system

Cheolyong Choi,Yonmo Sung,Gyung Min Choi,Duck Jool Kim 대한조선학회 2015 International Journal of Naval Architecture and Oc Vol.7 No.6

In order to design a compact urea selective catalytic reduction system, numerical simulation was conducted by computational fluid dynamics tool. A swirl type static mixer and a mixing chamber were considered as mixing units in the system. It had great influence on flow characteristics and urea decomposition into ammonia. The mixer caused flow recirculation and high level of turbulence intensity, and the chamber increased residence time of ureawater-solution injected. Because of those effects, reaction rates of urea decomposition were enhanced in the region. When those mixing units were combined, it showed the maximum because the recirculation zone was significantly developed. NH3 conversion was maximized in the zone due to widely distributed turbulence intensity and high value of uniformity index. It caused improvement of NOx reduction efficiency of the system. It was possible to reduce 55% length of the chamber and connecting pipe without decrease of NOx reduction efficiency.

Dickey-Fuller Test for an Extended MA Model

Cheolyong Park,Jeongcheol Ha,Tae Yoon Kim,Sun-Young Hwang,Heesoo Lee 계명대학교 자연과학연구소 2019 Quantitative Bio-Science Vol.38 No.1

The AR(1) model Xt=ρXt-1+ϵt with iid error ϵt has been used extensively for the inference of the stochastic process Xt where its key parameter ρ plays an essential role. In particular, the Dickey-Fuller test (DF test) has been extensively used for testing random walk model (or ρ=1) in the literatures. However, it is well known that the DF test is subject to serious size distortion when errors are correlated. This study proposes the use of an extended MA(∞) model Xt=∑<SUP>∞</SUP>(i=0) bi ϵt-i for a more precise inference of Xt by the DF test. We develop and investigate a new persistency parameter b∞=limj→∞ bj from the extended MA(∞) model. It is shown that the DF test serves well for testing the MA(∞) model with the new persistency parameter b∞. Our approach critically addresses the size distortion issues in the literatures.

Time Series Model Identification in the Frame of Random Walk Model

Cheolyong Park,Seul Gee Kim,JinCheol Park,Jeongcheol Ha,Tae Yoon Kim 계명대학교 자연과학연구소 2018 Quantitative Bio-Science Vol.37 No.1

In principle, any stochastic process can be expressed in the frame of the random walk model (RWM) because it equals to the sum of its regular increments (or errors), with its initial value equal to 0. Using this intrinsic versatility of the RWM, we herein demonstrate that the RWM can serve as a useful frame for identifying the underlying time series models. This is done by reparametrization of the RWM based on the “linear dependency of error”. Our approach is applied to various time series models (e.g., stationary processes, trend stationary process (TSP), mixture model, asymmetric difference, fractional Brownian motion and symmetric α-stable self-similar stationary increment process). As an empirical application of our approach, we discuss the well-known RWM vs. TSP controversy over macroeconomic time series.

A Rejoinder to “Dickey-Fuller Test for an Extended MA Model”

Cheolyong Park,Jeongcheol Ha,Tae Yoon Kim,Sun-Young Hwang,Heesoo Lee 계명대학교 자연과학연구소 2019 Quantitative Bio-Science Vol.38 No.1

3차원 광메모리를 이용한 인증 기법

박철용(CheolYong Park),류재철(JaeCheol Ryou) 한국정보보호학회 2016 정보보호학회논문지 Vol.26 No.6

최근 사용자 인증에 대한 요구가 증가하면서 패스워드, 그래픽인증, 토큰, 생체인식, 복합 인증 등 다양한 인증 기법이 사용되고 있다. 특히 편의성으로 인해 패스워드, 그래픽, 생체 인증 등 2차원적 요소(2차원 평면)의 데이터를 정보로 이용하고 2차원 모양의 특징 정보를 저장하여 인증에 적용되는데 저장되는 정보는 2차원 정보로 기록 저장된다. 이러한 인증 데이터는 정보를 기록하고 갱신함에 있어 추가적인 데이터 기록을 요구하는 문제가 있다. 또한 2차원 메모리는 저장 데이터의 양이 증가할수록 저장 데이터를 인증 데이터와 비교하는 시간이 증가하여 인증 절차 수행에 소요되는 시간이 증가하는 단점도 있다. 이러한 인증 데이터를 메모리에 저장 및 인증하는 기술에 있어 신속하게 인증 절차를 수행하는 것은 중요한 요소가 되었다. 본 논문에서는 메모리를 사용한 인증 데이터의 기록 및 인증에 있어 기존 방식의 단점을 보완하고자 3차원 광메모리를 이용하여 데이터의 기록시 기록요소를 다양하게 변경하여 서로 다른 저장 데이터를 다중 기록하는 방식을 구성함으로써 고밀도 기록이 가능하게 하고, 데이터의 기록 및 복원시 병렬처리가 가능한 방식을 적용하여 신속한 데이터의 기록 및 복원이 가능한 기법을 제안한다. 또한 인증 데이터 갱신시 기존에 기록된 저장 데이터를 조합하여 조합한 데이터를 인증에 이용함으로써 매번 추가적인 데이터 기록을 요구하는 문제를 해결하고자 한다. 제안한 인증 방식은 3차원 광메모리에 데이터를 기록 저장 후, 복원시 기록 조건에 상응하는 조건을 만족해야만 데이터가 복원되는 방식을 적용한 인증 기법을 제안하고 이를 시험을 통해 인증 기법으로 적용 가능함을 확인하였다. Recently the need for user authentication with increasing, there are a variety of mechanisms, such as password, graphic authentication, token, biometrics and multiple authentication. in particular, the data of the 2-dimensional(2D) factors such as password, graphic authentication, biometrics is used because of the convenience. The stored information is problematic in that additional data recording needs to be performed whenever authentication data is updated. Furthermore, this storage method is problematic in that the time it takes to perform authentication increases because the time it takes to compare storage data with authentication data increases in proportion to an increase in the amount of the storage data. Accordingly, authentication through the rapid comparison of storage data with authentication data is a very important factor in data recording and authentication technology using memory. Using the three-dimensional(3D) optical memory by variously changing the recoding elements during recoding of data constitutes the way that multiple recoding different data storage. This enables high-density recoding in this way, and by applying the possible parallel processing at the time of recording and restoring method, provided that it is possible to quickly record and restore the data. In addition, each time to solve problems that require additional data recorded by a combination of the stored data record in the old data using a combination of the authentication. The proposed mechanism is proposed an authentication method using scheme after the recoding data in 3D optical memory to apply the conditions corresponding to the recoding condition when restoring the recorded data and through the experiment it was confirmed possible application as an authentication mechanism.

스포츠 경쟁력 지수로서 페이지랭크 기반 방법론 사용에 대한 소고

박철용(Cheolyong Park) 한국데이터정보과학회 2021 한국데이터정보과학회지 Vol.32 No.6

최근에 스포츠 경쟁력을 객관적으로 판단하는 방법으로 페이지랭크 (PageRank) 방법이 사용되기 시작하였다. 원래 페이지랭크가 웹사이트의 연결 네트워크 정보를 이용하여 특정 웹사이트의 중요도를 평가하는 것에 착안하여, 특정 운동 경기의 승패 관계를 연결 네트워크로 파악하여 페이지랭크를 해당 운동 경기의 경쟁력 지수로 사용하고자 하는 시도이다. 페이지랭크는 경쟁력이 높은 상대에게 얻은 승리를 경쟁력이 낮은 상대에게 얻은 승리보다 더 높이 평가하는 구조이기 때문에 단순 승패만 따지는 방법보다 경쟁력을 판단하기 더 합리적인 방법으로 여겨진 것이다. 페이지랭크는 연결여부만 고려하기 때문에 가중페이지랭크 (weighted PageRank)로 발전하였고, 학술지 평가에서는 SJR (Scimago Journal Rank)와 아이겐팩터 (Eigenfactor)로 발전하게 되었다. 이 논문에서는 이 방법에서 사용된 공식을 중심으로 각 항목들이 스포츠 경쟁력 관점에서 어떤 의미를 가지는지 살펴본다. 마지막으로 2018년 중학교와 고등학교의 배드민턴 단체 경기 자료에 이 방법들을 적용하고 그 결과를 비교한다. Recently PageRank has started being used as an objective method of measuring a sports competency. This is based on the observation that PageRank measures a website’s importance in a network of websites’ connection and thus can be applied to sports by considering win-loss results of the sports as a network. PageRank can be considered a more reasonable method than simple win-loss counts because PageRank gives more weights to a win over higher rankers than to lower rankers. Since PageRank just considers whether two websites are connected or not, it is evolved into weighted PageRank, and further into SJR (Scimago Journal Rank) and Eigenfactor as journal citation indices. In this article, we will review the formulas of these methods to understand the meaning of each term from the perspective of a sports competency index. Finally we will apply these methods to badminton team match data of middle and high schools in 2018 and then compare the results.

Numerical analysis of NO_x reduction for compact design in marine urea-SCR system

Choi, Cheolyong,Sung, Yonmo,Choi, Gyung Min,Kim, Duck Jool The Society of Naval Architects of Korea 2015 International Journal of Naval Architecture and Oc Vol.7 No.6

In order to design a compact urea selective catalytic reduction system, numerical simulation was conducted by computational fluid dynamics tool. A swirl type static mixer and a mixing chamber were considered as mixing units in the system. It had great influence on flow characteristics and urea decomposition into ammonia. The mixer caused flow recirculation and high level of turbulence intensity, and the chamber increased residence time of urea-water-solution injected. Because of those effects, reaction rates of urea decomposition were enhanced in the region. When those mixing units were combined, it showed the maximum because the recirculation zone was significantly developed. $NH_3$ conversion was maximized in the zone due to widely distributed turbulence intensity and high value of uniformity index. It caused improvement of $NO_x$ reduction efficiency of the system. It was possible to reduce 55% length of the chamber and connecting pipe without decrease of $NO_x$ reduction efficiency.

용존유기물질의 페놀계 성분에 의한 과황산 활성화

김철용 ( Cheolyong Kim ),안준영 ( Jun-young Ahn ),조수빈 ( Soobin Cho ),황인성 ( Inseong Hwang ) 한국물환경학회(구 한국수질보전학회) 2019 한국물환경학회·대한상하수도학회 공동 춘계학술발표회 Vol.2019 No.-

A Rao-Robson Chi-Square Test for Multivariate Normality Based on the Mahalanobis Distances

Park, Cheolyong The Korean Statistical Society 2000 Communications for statistical applications and me Vol.7 No.2

Many tests for multivariate normality are based on the spherical coordinates of the scaled residuals of multivariate observations. Moore and Stubblebine's (1981) Pearson chi-square test is based on the radii of the scaled residuals, or equivalently the sample Mahalanobis distances of the observations from the sample mean vector. The chi-square statistic does not have a limiting chi-square distribution since the unknown parameters are estimated from ungrouped data. We will derive a simple closed form of the Rao-Robson chi-square test statistic and provide a self-contained proof that it has a limiting chi-square distribution. We then provide an illustrative example of application to a real data with a simulation study to show the accuracy in finite sample of the limiting distribution.

변이 기반 다시점 영상의 인식 깊이감 조절

조철용(Cheolyong Jo),김만배(Manbae Kim),엄기문(Gi-Mun Um),허남호(Namho Hur),김진웅(Jinwoong Kim) 한국방송·미디어공학회 2008 방송공학회논문지 Vol.13 No.6