• 한국철도학회논문집
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• 제18권3호
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• pp.186-193
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• 2015

본 연구에서는 차세대 고속열차의 신뢰성 성장률 분석에 대한 연구를 수행하였다. 차세대 고속열차의 신뢰성 평가를 효과적으로 수행하기 위해서 6개의 서브시스템으로 분류를 하였으며, 이에 대한 기능블록선도와 신뢰성블록선도를 도출하였다. 또한 안정화 시험 중에 수행된 시험결과를 바탕으로 고장정보분석을 수행하였다. 그리고 Duane 모델에 기반한 신뢰성 성장률 분석을 차세대 고속열차의 실험 결과에 적용하였다. 본 연구를 통해서 지속적인 차량의 유지 보수 활동이 신뢰성 성장에 영향을 미치고 있음을 확인하였다.

• 경영과학
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• 제30권1호
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• pp.91-102
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• 2013

This study has an aim to analyze the effects of ADS on conjunctivitis patients among the residents of Seoul, Korea, between 2005 and 2008. For this purpose, the number of medical services provided to conjunctivitis patients on the days of windblown dust storms and the days without any windblown dust storms were analyzed by conducting paired t-test. The interactive effects of the ADS density and the accuracy of ADS forecast on the fluctuation of conjunctivitis cases were also investigated. The results showed that, even with an accurate forecast issued 24 hours prior to the event, the average number of medical services provided for conjunctivitis was higher on the index days than the comparison days. On the other hand, in cases of failure to provide an accurate forecast 24 hours prior to the ADS event, the number of conjunctivitis attacks reported was statistically significantly higher on the index days for 3~5 days after the occurrence of a dust storm in relation to the comparison days. We also found that the rate of increase in asthma treatments on the index days with low level of $PM_{10}$ concentration rather than high $PM_{10}$ level was more significant for all lag days. This study provides evidence that ADS events are significantly associated with conjunctivitis symptoms and the failure to forecast ADS events with low $PM_{10}$ level might aggravate conjunctivitis disease.

• 공학논문집
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• 제7권1호
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• pp.53-60
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• 2005

Community Wireless Networks define the next generation wireless services. Multimedia usages for financial services over community Wireless LAN (WLAN) based mesh networks require link stability. Several new services are being proposed for multimedia over WLANs. Portable Internet Services are implemented by several wireless carriers to proliferate their customer base. However, these services are still expensive and require a central telecom/wireless carrier whose monopoly and preference defines the availability of new services. Our research project identifies the usage of these critical services in public places over the financial services backbone architecture to provide efficient easy-to-use and economical services to their customers and merchants without being dependent on the central wireless carrier. The user connects to the network using his regular WLAN NIC using the Mesh Router/Bridge interconnectivity and obtains the needed multimedia and financial services from the ATM-AP Gateway, In our proposed scenario, the ATN AP-MR use AODV protocol and MR-MC is based on 802.11g/a/b IEEE standard. We use multi path routing protocols for reducing the congestion over a particular route. We demonstrate the results of our simulations and test-bed outcome to evaluate link failure rate and oversubscription factors to eliminate network congestion and non-availability of the critical financial services.

• Computers and Concrete
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• 제18권2호
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• pp.267-278
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• 2016

In order to observe the internal damage of concrete in real time, we introduced acoustic emission nondestructive detecting technology into a series of fracture tests; the test results revealed the whole process that concrete undergoes when it sustains damage that leads to failure, according to the change rules of the acoustic emission parameters. The results showed that both the initiation and unstable loads can be accurately determined using the abrupt change of the acoustic emission rate curves and the turning point of the acoustic emission parameters' accumulative curves. The whole process, from damage to failure, includes five phases, beginning with damage, such as cracking, a stable crack growth process, a critical unstable stage, and unstable propagation. The brittle fracture characteristics of concrete change when steel bars are joined, because the steel bars and the concrete structure bond, which causes an increase in the acoustic emission signals within the fracture process of the reinforced concrete. The unstable propagation stage is also extended. Our research results provide a valid methodology and technical explanations, which can help researchers to monitor the cracking process of concrete structures, in real time, during actual projects.

• 한국농공학회지
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• 제39권2호
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• pp.9-18
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• 1997

Abstract This paper presents a heuristic method for optimal design of water distribution system with multiple sources and potential links. In multiple source pipe network, supply rate at each source node affects the total cost of the system because supply rates are not uniquely determined. The Linear Minimum Cost Flow (LMCF) model may be used to a large scale pipe network with multiple sources to determine supply rate at each source node. In this study the heuristic method based on the LMCF is suggested to determine supply rate at each source node and then to optimize the given layout. The heuristic method in turn perturbs links in the longest path of the network to obtain the supply rates which make the optimal design of the pipe network. Once the best tree network is obtained, the frequency count of reconnecting links by considering link failure is in turn applied to form loop to enhance the reliability of the best tree network. A sample pipe network is employed to test the proposed method. The results show that the proposed method can yield a lower cost design than the LMCF alone and that the proposed method can be efficiently used to design irrigation systems or rural water distribution systems.

• 수산해양기술연구
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• 제50권2호
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• pp.162-168
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• 2014

The friction and wear characteristics of the rubber matrix composites filled with nano sized silica particles were investigated at ambient temperature by pin-on-disc friction test. The volume fraction of silica particles was 19%. The cumulative wear volume and wear rate of these materials on counterpart roughness were determined experimentally. The major failure mechanisms were lapping layers, deformation of matrix, ploughing, debonding of particles, fracture of particles and microcracking by scanning electric microscopy photograph of the tested surface. The cumulative wear volume showed a tendency to increase with increase of sliding distance. The wear rate of these composites tested indicated low value as increasing the sliding distance.

• 비파괴검사학회지
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• 제22권6호
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• pp.609-620
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• 2002

It is well known that during tensile testing, a part of the mechanical work done on the specimen is transformed into heat energy. However, the ultimate temperature rise and the rate of temperature rise is related to the nature of the material, conditions of the test and also to the deformation behaviour of the material during loading. The recent advances in infrared sensors and image/data processing techniques enable observation and quantitative analysis of the heat energy dissipated during such tensile tests. In this study, infrared imaging technique has been used to characterise the tensile deformation in AISI type 316 nuclear grade stainless steel. Apart from identifying the different stages during tensile deformation, the technique provided an accurate full-field temperature image by which the point and time of strain localization could be identified. The technique makes it possible to visualise the region of deformation and failure and also predict the exact region of fracture in advance. The effect of thermal gradients on plastic flow in the case of interrupted straining revealed that the interruption of strain and restraining at a lower strain rate not only delays the growth of the temperature gradient, but the temperature rise per unit strain decreases. The technique is a potential NDE tool that can be used for on-line detection of thermal gradients developed during extrusion and metal forming process which can be used for ensuring uniform distribution of plastic strain.

• 핵의학기술
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• 제15권2호
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• pp.99-103
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• 2011

Brain Perfusion SPECT (Diamox)는 아세타졸아미드를 사용하여 혈관예비능을 평가하는데 아주 유용한 검사이다. 1day-protocol method는 영상의 질이 뛰어나고 한 번에 두 가지 영상을 얻을 수 있는 이점이 있어, 검사실과 내원 환자에 모두 유리하다. 하지만 긴 검사시간으로 인해 다른 검사보다 재검사율이 높은 문제점을 가지고 있다. 이에 시행한 환자의 성별, 나이, 상병, 머리고정기구 사용 여부에 따른 재검사율을 파악하여 검사의 최적화를 도모하고자 하였다. 2010년 3월부터 2011년 2월까지 시행한 환자 676명(남:359명, 여:317명)을 대상으로 하였으며, 머리의 움직임을 유발하는 요인을 성별, 연령, 상병의 종류, 머리고정기구 적용여부로 나누어 검사결과에 기여하는 여부와 정도를, 카이제곱 검정기법과 이분형 로지스틱 회귀분석기법을 사용하여 검증하였다. 남성이 3.4%, 여성이 1.5%로 남성이 여성보다 실패율이 높았으며, 70대가 1.0%로 가장 높은 실패율을 보였다. 카이제곱 검정결과 p-value는 0.001미만으로 통계적으로 유의한 차이가 있는 것으로 나타났다. 이분형 로지스틱 회귀분석결과에서는 성별, 상병(CI), 머리고정기구 사용이 통계적으로 유의한 수준에서 영향을 끼치는 요인으로 평가 되었다. 각각의 Wald value는 3.3, 3.7, 9.3으로 머리고정기구의 사용이 가장 큰 영향을 주는 것으로 나타났다. 연구결과를 통해 연령을 제외한 성별과 상병 그리고 머리고정기구 사용이 검사수행결과에 통계적으로 유의한 수준의 영향력을 가지는 요인들임을 알게 되었으며. 그 중 머리고정기구 사용은 검사수행결과에 끼치는 영향이 가장 큰 요인임을 알 수 있었다. 검사의 시행에 있어서 머리고정기구를 필수적으로 사용한다면 Brain Perfusion SPECT(Diamox)검사의 재검사율을 크게 낮출 수 있을 것으로 기대된다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.1434-1441
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• 2005

For anchored system applications, each ground anchor is tested after installation and prior to being put into service to loads that exceed the design. This load testing methodology, combined with specific acceptance criteria, is used to verify that the ground anchor can carry the design load without excessive deformations and that the assumed load transfer mechanisms have been properly developed behind the assumed critical failure surface. After acceptance, the ground anchor is stressed to a specified load and the load is locked-off. The two types of load tests conducted during the research program included performance test and creep test which were carried out in accordance with testing procedures by AASHTO(AASHTO 1990) and FHWA(Weatherby 1998) at Samsung-Dong 00 Site. Form the measurements, ultimate load and creep rate of anchors are proposed for straight shaft pressured grouted anchors in waste landfill. The load distribution on the grout was obtained from the measured strain data at each fraction of the ultimate load during the load tests.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.916-923
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• 2005

In this study, to observe aging effect of undrained shear behavior for Nak-Dong River sand, undrained static and cyclic triaxial tests were performed with changing relative density ($D_r$), consolidation stress ratio($K_c$) and consolidation time. As a result of the test, the modulus of elasticity to all samples estimated within elastic zone by the micro strain of about 0.05% in case of static shear behavior increased with the lapse of consolidation time significantly, so aging effect was shown largely. Also strength of phase transformation point(S_{PT}$) and strength of critical stress ratio point($S_{CSR}$) increased with the lapse of consolidation time. Undrained cyclic shear strength($R_f$) obtained from the failure strain 5% increased in proportion to relative density($D_r$) and initial static shear stress($q_{st}$), $R_f$ of consolidated sample for 1,000 minutes increased about 10.6% compared to that for 10 minutes at the loose sand, and $R_f$ increased about 7.0% at the medium sand. In situ application range of $R_f$ to the magnitude of earthquake for Nak-Dong River sand was proposed by using a increasing rate of $R_f$ as being aging effect shown from this test result.