• Proceedings of the Korean Society of Propulsion Engineers Conference
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• v.y2005m4
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• pp.23-26
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• 2005

The method of decreasing the ecological risk for the LRE(Liquid Rocket Engine) test is developed, working on the cryogenic oxidizer and the high-boiling fuel(Kerosene). This Method is based on the study that contains a technical solution method and an accident occurrence range for decreasing of accident probability and damage. This paper contains schematic on the all risk circumstance bring to accident, block-diagram for an accident growth process in case of the propellant leakage, evaluation method of safety distance from test stand to residential area. It will be used to alternative method for the risk reduction of complex technical systems.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.7
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• pp.730-735
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• 2004

This paper describes what brings about DC offset and the impact or the DC offset on the performance or direct-conversion mobile receiver in WCDMA system. The performance degradation of $E_{b}/N_{o}$ due to the DC offset is presented through simulation result. Direct-conversion RF Transceiver which has the function of DC offset control is implemented and then applied to the WCDMA test-bed for the performance evaluation. The receiver performance degradation of $E_{c}/I_{o}$ is evaluated and analyzed by varying DC offset value. The practical test showed the minimum requirement of DC offset value to meet system performance.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.7
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• pp.634-641
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• 2009

In this work, the behavior of vibratory hub loads induced due to the uncertainties of composite material properties for each of the participating rotor blades is investigated. The random material properties of composites available from the existing experimental data are processed by using the Monte-Carlo simulation technique to obtain the stochastic distribution of sectional stiffnesses of composite blades. The coefficients of variation (standard deviation divided by the mean) obtained from the sectional stiffness constants are used as an input to the comprehensive aeroelastic analysis code that can evaluate the hub loads of a rotor system. It is found that the uncertainty effects of composite material properties inevitably bring a dissimilarity to the rotor system. The influence of hub vibration response with respect to the individual stiffness (flatwise bending, chordwise bending and torsion) changes is also identified.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.6
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• pp.557-563
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• 2010

This paper addresses the issue of adaptive global optimization using Kriging metamodel known as EGO(Efficient Global Optimization). The algorithm adaptively chooses where to generate subsequent samples based on an explicit trade-off between reduction of global uncertainty and exploration of the region of the interest. A strategy that saves the computational cost by using expectations derived from probabilistic nature of approximate model is proposed. At every iteration, a candidate test point that seems to be feasible/inactive or has little possibility to improve for minimum is identified and excluded from updating approximate models. By doing that the computational cost is saved without loss of accuracy.

• Journal of Power System Engineering
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• v.4 no.2
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• pp.40-45
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• 2000

Some engineering materials are often known to have considerable spatial variation in their resisting strength and other properties. The objective of this study is to investigate the averaging effect and the applicability of extremal statistic for the statistical size effect. In the present study, it is assumed that the material property is a stationary random process in space. The theoretical autocorrelation function of the material strength are discussed for several correlation lengths. And, in order to investigate the statistical size effect, the material properties was simulated by using the non-Gaussian random process method. The material properties were plotted on the Weibull probability papers. The main results are summarized as follows: The autocorrelation function of the material properties are almost independent of the averaging length. The variance decreases with increasing the averaging length. As correlation length is smaller, the slope is larger. And also, it was found that Weibull statistics based on the weakest-link model could not explain the spatial variation of material properties with respect to the size effect satisfactory.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.5
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• pp.959-966
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• 2020

With the growing importance of the fishery industry and the rapid growth of the aquaculture industry, research on smart farms through ICT convergence in the aquaculture field is in progress. To enable monitoring of the growing environment at the farm site, an underwater drone drive unit, an image collection device, an integrated controller for posture stabilization, and a remote control device capable of controlling and controlling drones through real-time underwater images were proposed, and design, development, and tests were conducted. By utilizing underwater drones, it is possible to replace the supply and demand of manpower and high-cost work in the aquaculture industry, and to manage fish farms in a stable manner by reducing the probability of farming deaths.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.94-94
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• 2011

배관 구조물에서는 내부 미세 균열에서부터 국부 좌굴, 볼트 풀림, 피로 균열 등과 같이 다양한 형태의 손상이 복합적으로 발생 가능하다. 이러한 복합 손상은 배관 구조물의 누수, 누유 등의 사고를 야기할 수 있다. 하지만 기존의 단일 스케일 계측 시스템으로부터 복합 손상에 의한 실시간 누수를 진단하기는 매우 어렵다. 본 연구 단계에서는 누수를 야기하는 복합 손상을 효율적으로 진단하기 위하여 선행 연구에서 제안된 압전센서를 이용한 자가 계측 회로 기반의 다중 스케일 계측 시스템을 구조물의 복합 손상 진단에 적용하였다. 자가 계측 회로 기반 다중 스케일 계측 시스템은 크게 두 가지 형태의 신호를 계측한다. 첫 번째 스케일은 임피던스 계측으로부터 특정 주파수 대역폭에 대한 구조 응답을 계측하며, 두 번째 스케일은 유도 초음파 계측으로부터 단일 중심 주파수에 해당하는 구조물의 응답을 계측한다. 복합 손상을 손상 유형별로 분류하기 위하여 E/M 임피던스(Electro-mechanical impedance)및 유도 초음파(Guided wave) 계측으로부터 추출한 특성을 이용하여 2차원 손상지수를 계산하고 이를 지도학습 기반 패턴인식 기법(Supervised learning based pattern recognition) 중 확률론적 신경망 기법(Probabilistic Neural Network, PNN)에 적용한다. 제안된 기법의 적용성 검토를 위하여 파이프 구조물에 인위적으로 다중 손상을 생성시켜 시험을 수행하였다. 본 연구에서 제안된 기법이 실제 배관 구조물에 성공적으로 적용된다면 손상 부재의 거동 및 구조물 성능의 손상에 대한 영향을 효율적으로 진단하고 평가함으로써 배관 구조물의 효과적인 유지관리가 가능할 것으로 예상된다.

• Journal of Labour Economics
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• v.27 no.1
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• pp.55-76
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• 2004

The objective of this study is to investigate why the applicants for entrance to the science and engineering college are shrinking. We focus on the social situation of the science and engineering college graduates, more concretely, focus on the job stability, social position and the compensation in comparison with the non-science and engineering college graduate. We find that the science and engineering college graduates have the higher rate of separation from his job, the fewer opportunity of improving the social situation and the lower compensation throughout his life from the first job in comparison with the non-science and engineering college graduates. However, this study can not identify why the science and engineering college graduates receive the socially unkind treatment.

• Journal of The Korean Association of Information Education
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• v.20 no.2
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• pp.197-206
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• 2016

A fill-in-the-blank with choices are widely used in classrooms in order to check whether students' understand what is being taught. Although there have been proposed many algorithms for generating this type of questions, most of them focus on preparing sentences with blanks rather than generating multiple choices. In this paper, we propose a novel algorithm for generating multiple choices, given a sentence with a blank. Because the algorithm is based on a statistical language model, we can generate relatively unbiased result and adjust the level of difficulty with ease. The experimental results show that our approach automatically produces similar multiple-choices to those of the exam writers.

• 한국HCI학회:학술대회논문집
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• 2007.02b
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• pp.575-581
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• 2007

웹사이트를 어떻게 디자인했을 때 지식을 보다 효율적으로 전달할 수 있는가에 많은 관심이 쏠리고 있다. 최근의 몇몇 커뮤니케이션 연구들은 인터넷의 독특한 정보 전달 구조인 하이퍼텍스트 구조가 정보 전달에 있어서 핵심적인 영향을 끼치고 있으며, 따라서 하이퍼텍스트를 어떤 방식으로 구조화하는지에 따라 지식의 전달 내용도 바뀔 수 있다고 주장하고 있다. 이 연구는 이러한 학자들의 의견과 궤를 같이 하여, 이용자의 사전 지식의 차이에 따라 비선형적 웹사이트 구조가 구조적인 지식과 선언적인 지식을 전달하는 데, 어떠한 차이점을 가지는지를 시험적으로 검증한 예비 조사적 연구이다. 관련된 기존 문헌 연구를 통해, 사전 지식이 높은 이용자는 선형 구조보다는 비선형 웹 구조를 통해서 구조적인 지식을 습득하는 데, 유리할 것이고 사전 지식이 낮은 이용자는 선형 구조보다는 비선형 웹구조를 통해서 학습할 때, 선언적인 지식을 습득할 확률이 높을 것이라고 예상되었다. 이를 소규모 집단 실험으로 검증한 결과, 통계적으로 유의한 수준은 아니었지만 비선형적 웹구조는 구조적인 지식을 증가시키는 경향성이 발견되었다. 또한 사전 지식이 높은 이용자 역시 비선형 구조에서 높은 구조적 지식을 습득하는 경향성이 있었다. 그러나 선언적인 지식의 경우에는 웹 구조의 영향이 크게 상관이 없는 것으로 나타났다.