• 정보처리학회논문지B
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• 제10B권5호
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• pp.521-526
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• 2003

본 논문에서는 영역의 경계를 추출하기 위해 영상의 밝기 정보와 곡선전개 방식을 이용한 기하 활성 모델을 제안한다. 영역의 경계를 추출하는 문제를 추출한 영역의 평균 밝기 값과 전개중인 폐곡선 영역의 밝기 값의 차론 최소화시키는 것으로 설정한다. 최적의 해를 구하는 방법으로 레벨세트 이론을 적용한 곡선전개 방법을 이용한다. 이 방식은 일반적인 활성 모델에 비해 초기 곡선 설정에 제약이 없고 동시에 여러 영역의 경계 추출이 가능하다. 제안 모델은 에지 정보가 충분치 못한 영상의 경우에도 일반적인 에지 기반 방식에 비해 추출 결과가 양호하였다. 비등방성 확산 필터를 사용하여 영상을 전처리 함으로써 보다 나은 추출이 수행되었다. CT나 MRI 영상을 이용하여 모델의 성능을 확인하였다.

• 한국지능시스템학회논문지
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• 제17권5호
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• pp.679-683
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• 2007

Vapnik의 통계적 학습이론은 분류, 회귀, 그리고 군집화를 위하여 SVM(support vector machine), SVR(support vector regression), 그리고 SVC(support vector clustering)의 3가지 학습 알고리즘을 포함한다. 이들 중에서 SVC는 가우시안 커널함수에 기반한 지지벡터를 이용하여 비교적 우수한 군집화 결과를 제공하고 있다. 하지만 SVM, SVR과 마찬가지로 SVC도 커널모수와 정규화상수에 대한 최적결정이 요구된다 하지만 대부분의 분석작업에서 사용자의 주관적 경험에 의존하거나 격자탐색과 같이 많은 컴퓨팅 시간을 요구하는 전략에 의존하고 있다. 본 논문에서는 SVC에서 사용되는 커널모수와 정규화상수의 효율적인 결정을 위하여 차분진화를 이용한 DESVC(differential evolution based SVC)를 제안한다 UCI Machine Learning repository의 학습데이터와 시뮬레이션 데이터 집합들을 이용한 실험을 통하여 기존의 기계학습 알고리즘과의 성능평가를 수행한다.

• 한국재료학회지
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• 제32권10호
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• pp.408-413
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• 2022

The oxygen evolution reaction (OER) is very sluggish compared to the hydrogen evolution reaction (HER). Considering this difference is essential when designing and developing a cost-effective and facile synthesis method for a catalyst that can effectively perform OER activity. The material should possess a high surface area and more active sites. Considering these points, in this work we successfully synthesized sheets of cobalt phosphate hydrate (CP) and sulphurated cobalt phosphate hydrate (CPS) material, using simple successive ionic layered adsorption and reaction (SILAR) methods followed by sulfurization. The CP and CPS electrodes exhibited overpotentials of 279 mV with a Tafel slope of 212 mV dec^-1 and 381 mV with a Tafel slope of 212 mV dec^-1, respectively. The superior performance after sulfurization is attributed to the intrinsic activity of the deposited well-aligned nanosheet structures, which provided a substantial number of electrochemically active surface sites, speeded electron transfer, and at the same time improved the diffusion of the electrolyte.

• Korean Chemical Engineering Research
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• 제61권4호
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• pp.627-634
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• 2023

Graphitic carbon nitride (g-C₃N₄) has attracted considerable attention since its discovery for its catalysis of water splitting to hydrogen and oxygen under visible light irradiation. However, pristine g-C₃N₄ confers only low photocatalytic efficiency and requires surface cocatalysts to reach moderate activity due to a lack of accessible surface active sites. Inspired by the high specific surface area and superior electron transfer of graphene, we developed a strongly coupled binary structure of graphene and g-C₃N₄ aerogel with 3D porous skeleton. The as-prepared 3D structure photocatalysts achieve a high surface area that favors efficient photogenerated charge separation and transfer, enhances the light-harvesting efficiency, and significantly improves the photocatalytic hydrogen evolution rate as well. The photocatalyst performance is observed to be optimized at the ratio 3:7 (g-C₃N₄:GO), leading to photocatalytic H₂ evolution of 16125.1 mmol. g^-1. h^-1 under visible light irradiation, more than 161 times higher than the rate achieved by bulk g-C₃N₄.

• 전자공학회논문지C
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• 제35C권12호
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• pp.85-98
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• 1998

본 논문은 특정 응용에 적합한 퍼지 제어기의 최적 설계 파라메터 (퍼지 규칙과 소속 함수)를 찾는데 역전파 학습 과정과 유전 알고리즘을 결합한 Lamarckian 상호적응 기법을 이용한 뉴로-퍼지 제어기의 새로운 설계 방법을 제안한다. 설계 파라메타들은 진화에 의한 전역적 탐색을 통해 높은 포함값과 유용한 퍼지 규칙들을 갖는 규칙 베이스와 작은 근사화 오차와 좋은 제어 성능을 갖는 소속 함수들을 얻도록 제어기간 파라메타 조절을 수행하며, 학습에 의한 국부적 탐색을 통해 각 퍼지 제어기가 원하는 제어 결과를 나타내도록 제어기내 파라메타 조절을 수행한다. 제안한 상호적응 설계 방법은 유전 알고리즘의 모든 세대에서 역전파 학습이 이루어지므로 보다 좋은 근사화 능력을 나타나고, 사용한 무게 중심 비퍼지화기가 정확한 비퍼지화값을 계산하므로 보다 좋은 제어 성능을 가지며, 퍼지 규칙 베이스와 소속 함수들의 최적화 탐색 과정이 입출력 공간의 같은 퍼지 분할 상에서 통합된 적응 함수에 의하여 동시에 수행되므로 탐색을 위한 작업 공간이 아주 작아지는 장점이 있다. 시뮬레이션 결과는 Lamarckian 상호 적응에 의해 얻어진 FLC가 퍼지 규칙수, 근사화 능력, 제어 성능등 모든 면에서 다른 방법에 의해 얻어진 FLC보다 가장 우수함을 보여준다.

• Computers and Concrete
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• 제22권1호
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• pp.53-62
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• 2018

Cracking of concrete cover induced by reinforcement corrosion is a critical issue for life-cycle design and maintenance of reinforced concrete structures. However, the critical degree of corrosion, based on when the concrete surface cracks, is usually hard to predict accurately due to the heterogeneity inherent in concrete. To investigate the influence of concrete heterogeneity, a modified rigid-body-spring model, which could generate concrete sections with randomly distributed coarse aggregates, has been developed to study the corrosion-induced cracking process of the concrete cover and the corresponding critical degree of corrosion. In this model, concrete is assumed to be a three-phase composite composed of coarse aggregate, mortar and an interfacial transition zone (ITZ), and the uniform corrosion of a steel bar is simulated by applying uniform radial displacement. Once the relationship between radial displacement and degree of corrosion is derived, the critical degree of corrosion can be obtained. The mesoscale model demonstrated its validity as it predicted the critical degree of corrosion and cracking patterns in good agreement with analytical solutions and experimental results. The model demonstrates how the random distribution of coarse aggregate results in a variation of critical degrees of corrosion, which follows a normal distribution. A parametric study was conducted, which indicates that both the mean and variation of critical degree of corrosion increased with the increase of concrete cover thickness, coarse aggregates volume fraction and decrease of coarse aggregate size. In addition, as tensile strength of concrete increased, the average critical degree of corrosion increased while its variation almost remained unchanged.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 추계종합학술대회 논문집(1)
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• pp.441-444
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• 2000

This paper covers the performance testing for layer 3 Ethernet switch based on various methodologies by which we can measure essential metrics such as throughput, latency, frame loss rate, and back to back frames. In the first place, layer 2 and layer 3 switch evolution is introduced followed by description of IP packet switching in layer 3 switch. And then, the above test metrics and test methodologies are illustrated as well. At last, we conduct the performance testing for layer 3 switch in case of transmitting packets of 64, 128, 256, 512, 1024, 1280, and 1518 byte size and analyze then results.

• 한국통신학회:학술대회논문집
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• 한국통신학회 1991년도 추계종합학술발표회논문집
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• pp.150-154
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• 1991

As subsriber's requirements for high quality of telecom service are increased, a telecommunication network becomes complex and huge, and its management becomes an essential and an important factor in the evolution of telecommunication networks. In this paper, we focus on the network performance management and discuss the strategy of near real-time performance evaluation and control in Korea Telecome (KT) networks.

• ETRI Journal
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• 제37권6호
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• pp.1065-1076
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• 2015

Network densification is regarded as the dominant driver for wireless evolution into the era of 5G. However, in this context, interference-limited dense small cell deployments are facing technical challenges in mobility management. The recently announced results from an LTE field test conducted in a dense urban area show a handover failure (HOF) rate of over 21%. A major cause of HOFs is the transmission failure of handover command (HO CMD) messages. In this paper, we propose two enhancements to HO performance in LTE networks - radio link failure-proactive HO, which helps with the reliable transmission of HO CMD messages while the user equipment is under a poor radio link condition, and Early Handover Preparation with Ping-Pong Avoidance (EHOPPPA) HO, which assures reliable transmission of HO CMD under a good radio link condition. We analyze the HO performance of EHOPPPA HO theoretically, and perform simulations to compare the performance of the proposed schemes with that of standard LTE HO. We show that they can decrease the HOF rate to nearly zero through an analysis, and based on the simulation results, by over 70%, without increasing the ping-pong probability.

• 한국전기전자재료학회논문지
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• 제21권5호
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• pp.447-452
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• 2008

We synthesized nano-sized $La_{1-x}Sr_xCoO_3$ ($x=0.1{\sim}0.4$) cathode catalyst for the zinc air secondary batteries by citrate method, And we measured the cathode's electrochemical characteristics according to content of strontium compose the cathode catalyst. We controlled the pH of precursor solution by 10 in the process of manufacturing the precursor, We heat treated the prepared precursor at various calcination temperature ($500{\sim}900^{\circ}C$), and examined the optimum calcinations temperature by XRD analysis and electrochemical evaluation. We examined the ORR (oxygen reduction reaction) and OER (oxygen evolution reaction) performance of the prepared $La_{1-x}Sr_xCoO_3$ catalyst powder. When we consider ORR and OER performance simultaneously, $La_{0.7}Sr_{0.3}CoO_3$ catalyst has shown the best performance because of its lowest voltage deference between charge and discharge.