• 한국안전학회지
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• 제27권3호
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• pp.57-62
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• 2012

The purpose of this paper is to find dangerous factors of a water purifier when water leaks due to inappropriate use and analyze the patterns of damaged parts in order to provide data for the examination of the cause of the problem. If the water purifier is inspected and managed by a non-specialist, when the FLC(Float Level Controller) at the top is inclined, water leakage may occur to the water purifier. The leaked water flows onto the cables and hoses and enters the thermostat terminal, heater, PCB, power supply connection connector, etc., becoming a dangerous factor that may cause a system failure, fire, etc. Due to the water that entered the input terminal, low noise and white smoke were generated at first. However, the flame gradually propagated due to the continuous inflow of moisture. It was found that when moisture reached the PCB, a carbonized conductive path was formed at the varistor terminal, input terminal, semiconductor device terminal, etc., and the flame became larger, which might result in a fire. From the metal microscope analysis of a damaged condenser terminal, it was found that the amorphous structure unique to copper cable disappeared, and voids, boundary surface and disorderly fine particles occurred. Also, in the case of the connector into which moisture penetrated, fusion and deformation occurred at the cable connection clips. The result of analysis of the power supply cable connector using a thermal image camera showed that most of the heat was generated from the cable connection clips and the temperature at the connection center was normal.

• 한국화재소방학회논문지
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• 제23권4호
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• pp.120-129
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• 2009

건축물 화재에서는 발화물과 주변 가연물이 소실하기 때문에 화재현장 조사만으로 출화원인을 규명하기 어렵다. 따라서 본 연구는 현장조사와 화재실험을 통해 화재의 원인과 확대과정을 추정하는 방법에 관하여 고찰하였다. 본 연구에서는 화재원인 불명으로 판단된 공동주택의 화재사례를 대상으로 현장의 잔존물에서 출화장소와 초기연소물을 추정하고, 출화물로 추정된 가연물을 대상으로 연소실험을 실행하여 출화원인 등을 추정하였다. 화재실험에서는 가연물의 종류 및 배치 등을 출화이전의 상태로 재현하고 출화조건을 가정하여 반복적으로 실행하여 연소 후의 상황과 화재현장의 잔존물을 비교함으로써 출화원인 및 초기 화재확대과정을 규명하였다.

• 정보보호학회논문지
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• 제9권2호
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• pp.83-92
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• 1999

암호를 사용함으로써 정보를 위.변조나 노출 위협으로부터 보호할 수 있지만, 암호의 잘못된 사용은 몇 가지 문제점을 발생시킬 수 있다. 만약 키가 손상되면 암호의 적법한 소유자조차도 암호문을 해독할 수 없으며, 범죄 등의 목적에 암호가 사용되었을 경우, 수사 기관이 수사에 어려움을 겪을 수 있다. 이러한 문제점을 해결하기 위해 키 또는 메시지를 복구할 수 있도록 키를 신뢰기관에 위탁하는 키 위탁(key escrow) 방식이 제안되었다. 키 위탁은 유사시 키 복구를 보장하면서 동시에 사용자의 사생활을 침해해서는 안된다. 본 논문에서는 키 위탁 시스템이 가져야할 요구사항을 도출하고, EIGamal 암호 시스템에 기반한 새로운 키 위탁 방식을 제안한다. 제안 방식은 도청기한의 제한, 키의 복구에 관련된 부정 방지와 이에 대한 사용자의 shadow 공개키 생성 방지 등의 속성을 갖는 새로운 키위탁 방식이다. Cryptography techniques can prevent eavesdroppers from maliciously intercepting or modifying sensitive information. however misuses of encryption may cause other problems First if the encryption key is lost or damaged even an authorized access to the original data will be denied. Second criminals can prevent authorized law enforcement officers from examining the necessary information by using the strong encrypted data can provide solutions for the situations. In this paper we propose a new key escrow system based on the ElGamal cryptosystem. Our system provide time-bound eavesdropping under court authorized permission protect from trustee's cheating and prevent user's shadow public key generation.

• Journal of Radiation Protection and Research
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• 제45권4호
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• pp.163-170
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• 2020

Background: Gut microflora contributes to the nutritional metabolism of the host and to strengthen its immune system. However, if the intestinal barrier function of the living body is destroyed by radiation exposure, the intestinal bacteria harm the health of the host and cause sepsis. Therefore, this study aims to trace short-term radiation-induced changes in the mouse gut microflora-dominant bacterial genus, and analyze the degree of intestinal epithelial damage. Materials and Methods: Mice were irradiated with 0, 2, 4, 8 Gy X-rays, and the gut microflora and intestinal epithelial changes were analyzed 72 hours later. Five representative genera of Actinobacteria, Firmicutes, and Bacteroidetes were analyzed in fecal samples, and the intestine was pathologically analyzed by Hematoxylin-Eosin and Alcian blue staining. In addition, DNA fragmentation was evaluated by the TdT-mediated dUTP nick-end labeling (TUNEL) assay. Results and Discussion: The small intestine showed shortened villi and reduced number of goblet cells upon 8 Gy irradiation. The large intestine epithelium showed no significant morphological changes, but the number of goblet cells were reduced in a radiation dose-dependent manner. Moreover, the small intestinal epithelium of 8 Gy-irradiated mice showed significant DNA damaged, whereas the large intestine epithelium was damaged in a dose-dependent manner. Overall, the large intestine epithelium showed less recovery potential upon radiation exposure than the small intestinal epithelium. Analysis of the intestinal flora revealed fluctuations in lactic acid bacteria excretion after irradiation regardless of the morphological changes of intestinal epithelium. Altogether, it became clear that radiation exposure could cause an immediate change of their excretion. Conclusion: This study revealed changes in the intestinal epithelium and intestinal microbiota that may pave the way for the identification of novel biomarkers of radiation-induced gastrointestinal disorders and develop new therapeutic strategies to treat patients with acute radiation syndrome.

• 한국자동차공학회논문집
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• 제14권6호
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• pp.95-103
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• 2006

Wheel treads of E.M.U. are usually under a heavy thermal load by brake frictional heat between wheel and brake shoe and damaged by repeated thermal and mechanical loads. To examine the cause of wheel tread damage of E.M.U.'s in service running, a systematic approach has been used. This study is composed of three parts. Frictional heat analysis was conducted in the first part by finite element method. Two kinds of brake shoes in service were considered. In the second part, experimental study was carried out on a brake dynamometer. Temperatures were measured for the two brake shoes. And experimental study in service running E.M.U.'s was performed. Wheel and brake shoe temperatures were measured by using thermocouples and temperature indicating strips. Finally metallurgical characteristics were examined by a SEM/EDS and the cause of the wheel damage was analyzed. It seems that aggregated ferrous component is a main cause of the wheel tread damage.

• 한국기계가공학회지
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• 제19권4호
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• pp.1-8
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• 2020

Mechanical components that support structures in aerospace and power generation industries require high-strength materials. Particularly, in the aerospace industry, aluminum alloys, titanium alloys, and composite materials are increasingly used due to their high maneuverability and durability to withstand low temperature extreme environments; however, ultra-high-strength steel is still used in key components under heavy loads such as landing gears. In this paper, the fault cause analysis and troubleshooting of aircraft parts made of ultra-high-strength steel (300M) broken during normal operation are described. To identify the cause of the defect, a temporary inspection of the same aircraft was performed, and material testing, non-destructive inspection, microstructure examination, and fracture area inspection of the damaged parts were performed. Fracture analysis results showed that a crack in the shape of a branch developed from the tool mark in the direction of the intergranular strain. Based on the results, the cause of fracture was confirmed to be stress corrosion.

• 한국화재소방학회논문지
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• 제18권4호
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• pp.72-77
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• 2004

본 연구에서는 외부화염에 의한 비닐코드의 손상에 따른 단락 진행과정, 외형 및 표면 구조,조성 변화 등 단락 특성을 연구하였다. 초고속이미지시스템(HSIS)을 이용하여 단락과정을 분석한 결과, 열적피로에 의해 피복이 소실되면서 전선 도체가 닿아 수회에 걸쳐 단락이 발생하였으며. 실체현미경과 SEM을 이용하여 외형과 표면구조를 분석한 결과, 전원 측 전선은 두 가닥 모두에 용융흔이 형성되었으며 V자형의 흠을 나타냈다. 부하 측 전선의 용융흔은 전원 측 보다 큼을 알 수 있었다. EDX에 의한 조성분석 결과. 전원 측에서는 Cu와 O가 검출되었으며 부하 측에서는 Cu와 O 이외에 피복재료인 Cl과 Ca를 검출할 수 있었다. 이와 같은 실험과 분석결과를 바탕으로 전기화재의 원인을 규명하는데 많은 도움이 될 것으로 기대한다.

• Corrosion Science and Technology
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• 제8권4호
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• pp.153-156
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• 2009

The water cooling system for VFD (Variable Frequency Drive) of a fossil fuel power plant was reported to be shut down due to a water leak at the metal connection of the heat-sink to the hoses. In order to identify the cause of the failure, the system was visually inspected, and corrosion products were analyzed with SEM equipped with EDX. The failure was observed repeatedly at the nipples of certain location, suggesting galvanic corrosion. In a U-shaped heat sink with two nipples, for inlet and outlet, only one nipple was corrosively damaged at the tip, while the other was not. Most of the corrosion products were observed at the sound nipple and in the filter, identified as $Cu(OH)_2$. Some other corrosion products, composed of mostly $Cu_2O$, were found at the corrosively attacked nipple. A fair amount of Cl was also detected on the surface of the damaged nipple. It was concluded that galvanic corrosion was occurred due to a current leakage over the whole system, and the damage was accelerated by the accumulated chlorine ions in the cooling water.

• 통합자연과학논문집
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• 제13권1호
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• pp.34-40
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• 2020

This study aims to create a model for predicting the number of extinguishment manpower to put out forest fires by taking into account the climate, the situation, and the extent of the damage at the time of the forest fires. Past research has been approached to determine the cause of the forest fire or to predict the occurrence of a forest fire. How to deal with forest fires is also a very important part of how to deal with them, so predicting the number of extinguishment manpower is important. Therefore predicting the number of extinguishment manpower that have been put into the forest fire is something that can be presented as a new perspective. This study presents a model for predicting the number of extinguishment manpower inputs considering the scale of the damage with forest fire on a scale bigger than 0.1 ha as data based on the forest fire annual report(Korea Forest Service; KFS) from 2015 to 2018 using the moderated multiple regression analysis. As a result, weather factors and extinguished time considering the damage show that affect forest fire extinguishment manpower.

• 한국해양공학회지
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• 제22권3호
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• pp.47-57
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• 2008

Many accidents occur on the oceans. Accidents involving ships can cause enormous damage. When an accident occurs, the cost of environmental restoration can bankrupt even a top-ranked international company. The potential damages resulting from ship accidents have resulted in many international agreements such as MARPOL, SOLAS, ISM Code, etc. The viability of damaged ships has become more and more important. A damaged ship's viability and cargo safety can be improved by a safety assessment design procedure. We consider th￡ shipbuilding industry's distributed characteristics to define a safety assessment system with software engineering-based requirements analysis. We used a distributed network-based simulation method (HLA - High level architecture), because of ease of reuse and expansion of existing components to other situations, and because it is a military standard. HLA is the standard for distributed network-based simulation in many countries including the United States, Canada, Israel, and Korea. The paper describes research to develop a prototype of a network-based safety assessment simulation system by software engineering based analysis.