• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• 제4권2호
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• pp.95-102
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• 2000

Methane combustion over perovskite-type oxides prepared using the malic acid method was investigated. To enhance the catalytic activity, the perovskite oxides were modified by the substitution of metal into their A or B site. In addition, the reaction conditions, such as the temperature, space velocity, and partial pressure of the methane were varied to understand their effect on the catalytic performance. With the LaCoO3-type catalyst, the partial substitution of Sr or Ba into site A enhanced the catalytic activity in the methane combustion. With the LaBO3(B=Co, Fe, Mn, Cu)-type catalyst, the catalytic activities were exhibited in the order of Co>Fe Mn>Cu. Futhermore, the partial substitution of Co into site B enhanced the catalytic activity, whereas an excess amount of Co decreased the activity. The surface area and catalytic activity of the perovskite catalysts prepared using the malic acid method showed higher values than those prepared using the solid reaction method. The catalytic activity was enhanced with decreased methane concentration and with a decrease in the space velocity.

• Journal of Ecology and Environment
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• 제30권2호
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• pp.171-177
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• 2007

Korean rivers and their surrounding environments have been used excessively for rice production in the past and more recently for construction of urban areas to accomodate the rapidly increasing population. Affected Korean rivers experience dramatic fluctuations in their water levels and have faster currents compared with those in other countries. In order to restore more natural conditions in rivers experiencing such conditions, we employed a partial restoration method, which is designed to achieve physical and biological stability simultaneously. Concrete blocks were introduced to increase the river's physical stability during floods, and terra cottem, a soil enhancer, was used to reduce water loss due to intense heat. These interventions increased the river's ability to hold water and thereby promoted plant growth. This restoration method increased vegetation coverage and species diversity in treated areas, and changed the species composition in treated areas to more closely approximate that of the control site. These results suggest that this method is effective in restoring damaged habitats to more natural conditions.

• 한국전기전자재료학회논문지
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• 제19권2호
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• pp.162-168
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• 2006

Recently, diagnosis techniques have been investigated to detect a Partial Discharge associated with a dielectric material defect in a high voltage electrical apparatus, However, the properties of detection technique of Partial Discharge aren't completely understood because the physical process of Partial Discharge. Therefore, this paper analyzes the process on surface discharge of polymer insulator using wavelet transform. Wavelet transform provides a direct quantitative measure of spectral content in the time~frequency domain. As it is important to develop a non-contact method for detecting the kaolin contamination degree, this research analyzes the electromagnetic waves emitted from Partial Discharge using wavelet transform. This result experimentally shows the process of Partial Discharge as a two-dimensional distribution in the time-frequency domain. Feature extraction parameter namely, maximum and average of wavelet coefficients values, wavelet coefficients value at the point of $95\%$ in a histogram and number of maximum wavelet coefficient have used electromagnetic wave signals as input signals in the preprocessing process of neural networks in order to identify kaolin contamination rates. As result, root sum square error was produced by the test with a learning of neural networks obtained 0.00828.

• 한국안전학회지
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• 제24권2호
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• pp.30-36
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• 2009

This paper aims at the precursor analysis and DB development of electrical fires based on thermal and current signals for partial disconnection and poor contact on electric wires through experiments and simulations. Also, DB system required for developing the precursor DB with these data was studied and designed. Firstly, in case of partial disconnection, characteristics were derived and analyzed by experiment and electrical-thermal finite element method(Flux 3D) on the model wires which consist of VCTF and IV electric wires. Based on the characteristics, About 351 partial disconnection precursor patterns were generated by the thermal analysis for electric wire according to deterioration time under normal state and 200% overload state of rated current. Secondly, in order to develop poor contact precursor patterns, temperature value and the current signal were considered. In simulating the poor contact situation on connector area of MCCB, connection torque was changed. Through the experimental analysis, about 251 poor contact precursor patterns were generated. Finally, Using thermal precursor patterns obtained by partial disconnection and poor contact, electrical fire thermal precursor DB was developed.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1996년도 추계학술대회논문집; 한국과학기술회관, 8 Nov. 1996
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• pp.275-281
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• 1996

In order to examine the validity of an asymptotic solution obtained from the method of multiple scales, we investigate a third-order subharmonic resonance response of a bar constrained by a nonlinear spring to a harmonic excitation. The motion of the bar is governed by a linear partial differential equation with a nonlinear boundary condition. The nonlinear boundary value problem is solved by using the finite difference method. The numerical solution is compared with the asymptotic solution.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2004년도 ICCAS
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• pp.110-115
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• 2004

The hybrid fault diagnosis method based on a combination of the signed digraph (SDG) and the partial least-squares (PLS) has the advantage of improving the diagnosis resolution, accuracy and reliability, compared to those of previous qualitative methods, and of enhancing the ability to diagnose multiple fault. In this study, the method is applied for the multiple fault diagnosis of the Tennessee Eastman challenge process, which is a realistic industrial process for evaluating process contol and monitoring methods. The process is decomposed using the local qualitative relationships of each measured variable. Dynamic PLS (DPLS) model is built to estimate each measured variable, which is then compared with the estimated value in order to diagnose the fault. Through case studies of 15 single faults and 44 double faults, the proposed method demonstrated a good diagnosis capability compared with previous statistical methods.

• 수산해양기술연구
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• 제25권4호
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• pp.209-213
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• 1989

이상으로부터 부분 캐비테이션이 발생하는 익형에 대하여 지금까지 사용된 경계층 제어법과는 달리 전자력 가속에 의하여 익형의 전연 부근에서 흐름을 가속시킨 결과 경계층의 억제에 의해 부분 캐비테이션의 두께 및 길이가 다소 감소하였음을 알 수 있었다. 앞으로의 연구는 캐비테이션의 종류 및 조건들에 맞는 최적의 유동속도 가속장치 설계가 이루어 져야 할 것으로 생각된다.

• 정보처리학회논문지:컴퓨터 및 통신 시스템
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• 제6권9호
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• pp.397-406
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• 2017

클라우드 환경에서의 대용량 암호화 데이터 서비스를 위하여 기존의 암호화 알고리즘을 사용할 경우 데이터 암호화에 많은 시간 소요의 문제점이 대두된다. 이러한 단점을 보완하기 위해 일반적으로 부분 암호화 방법을 사용한다. 그러나 기존의 부분 암호화 방법은 암호화되지 않은 잔존 영역으로 인해 암호화된 데이터를 유추할 수 있다는 단점이 존재한다. 본 논문에서는 이러한 단점을 해결하기 위해 암호화 속도를 높이면서 보안을 준수하는 부분 암호화 방법을 제안한다. 제안하는 방법은 헤더 생성, 부분 암호화, 블록 셔플의 과정으로 구성된다. 1단계 헤더 생성 과정에서는 알고리즘에 필요한 헤더 데이터를 생성하고 2단계 부분 암호화 과정에서는 LEA (Lightweight Encryption Algorithm)를 이용하여 데이터의 일부분을 암호화하고 암호화하지 않은 부분의 데이터와 암호화 과정 중에 생성된 블록을 XOR하여 모든 데이터를 변형시키며, 3단계 블록 셔플 과정에서는 헤더에 저장한 셔플 데이터를 이용하여 블록을 섞어 데이터를 알아볼 수 없는 형태로 바꾸어 암호화를 수행한다. 제안하는 방법을 모바일 디바이스에 적용하여 구현한 결과 암호화한 데이터는 알아볼 수 없는 형태로 모두 바뀌어 데이터를 유추할 수 없었고, 암호 키 없이는 데이터를 복원할 수 없었다. 제안하는 방법은 블록 경량 암호화 알고리즘인 LEA에 비해 암호화 속도가 약 273% 정도 향상되어 대용량 데이터를 암호화하는데 있어 빠른 처리가 가능함을 확인하였다.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제25권4호
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• pp.173-195
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• 2021

A new implicit discontinuous Galerkin spectral element method (DGSEM) based on the first order hyperbolic system(FOHS) is presented for solving elliptic type partial different equations, such as the Poisson problems. By utilizing the idea of hyperbolic formulation of Nishikawa[1], the original Poisson equation was reformulated in the first-order hyperbolic system. Such hyperbolic system is solved implicitly by the collocation type DGSEM. The steady state solution in pseudo-time, which is the solution of the original Poisson problem, was obtained by the implicit solution of the global linear system. The optimal polynomial orders of 𝒪(𝒽^𝑝+1)) are obtained for both the solution and gradient variables from the test cases in 1D and 2D regular grids. Spectral accuracy of the solution and gradient variables are confirmed from all test cases of using the uniform grids in 2D.

• 융합보안논문지
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• 제5권3호
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• pp.93-97
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• 2005

MacCormack 방법은 hyperbolic 편미분 방정식의 근을 구하는데 많이 쓰이는 방법으로 그 정확도가 2차 오더가 된다. 하지만 이 방법으로 편미분방정식을 풀 경우 불연속인 점에서는 엔트로피를 만족하지 않는 경우가 있어 우리는 임의의 항을 첨가하여 근을 구해야한다. 이 임의의 항을 첨가하지 않고 직접 방정식으로부터 구하는 방법을 생각하는데 있어서 기존의 MacCormack 방법에 새 central scheme의 개념을 이용하면 전형적인 MacCormack 방법의 정확도와 장점을 보존할 수 있다. 이 새로운 방법을 이용하여 1D Burgers' 방정식과 1D Euler gas dynamic 방정식에 활용하여 그 결과를 살펴본다.