• 품질경영학회지
• /
• 제25권2호
• /
• pp.1-14
• /
• 1997

This paper considers maximum likelihood (ML) estimation of lifetime distribution under stress bounded ramp tests in which the stress is increased linearly from used condition stress to the stress u, pp.r bound. The following assumptions are used: exponential lifetime distribution under a constant stress, an inverse power law relationship between stress and mean of exponential lifetime distribution, and a cumulative exposure model for the effect of changing stress. Likelihood equations for the parameters involved in the model and asymptotic distribution of the estimators are obtained, and a numerical example is given.

• Investigative Magnetic Resonance Imaging
• /
• 제2권1호
• /
• pp.14-30
• /
• 1998

망간은 체내 필수원소의 하나이며 주로 간과 뇌의 기저핵게 축적되며 간을 통하여 배설된다. 망간은 체내 대사가 매우 빠르기 때문에 직업적 망간 폭로를 측정하는데 어려움이 있다. 특히 용접공과 같이 망간 폭로가 간헐적이거나 불규칙한 경우에는 혈중 및 요중 망간과 같은 기존 생체폭로지표로는 장기간에 걸친 폭로량을 정확하게 반영하기 힘들다. 뇌자기공명영상이 대두됨에 따랄 뇌내에 축적된 망간을 영상으로 확인하는 것이 가능하게 되었다. 초기에는 만성간부전 및 장기간에 걸친 정맥영양주입환자 등에서 뇌기저부의 고신호간도 소견이 보고되었다. 망간은 상자성 물질로 뇌자기공명영상에서 T1 이완시간을 단축시켜 T1 강조영상에서 고신호강도를 나타난다. 망간축적에 따른 고신호강도는 주로 담창구, 흑질, 피간 및 뇌하수체 등에서 나타난다. 저자들은 최근까지 국내 및 국외에서 직업적 및 비직업적으로 망간에 폭로된 사람에서 보고된 뇌자기공명영상소견을 수집하여 분석하였다. 우선 T1강조영상에서 관찰되는 고신호 강도와 연령, 성별, 직업적 망간 폭로 및 신경학적 이상 유무간의 관계를 분석하였다. 생물학적 폭로지표와 고신호강도간의 관계도 분석하였다. 고신호강도와 뇌내 망간축적, 신경세포손상 및 신경학적 이상간의 관계에 대한 문헌들을 분석하였다. T1강조영상에서 나타나는 고신호강도는 뇌내 망간축적 정도를 반영한다. 이러한 관계를 이용하여 신호강도를 분석하므로써 뇌내 망간축적 정도를 추정할수 있다. 뇌내 망간축적은 기저핵의 신경세포손상을 초래한다. 그러나 신경학적 이상은 비교적 단기간에 걸친 망간 축적과는 무관하게 보인다. 이는 신경학적 이상소견은 마간의 누적축적량과 관련되어 있기 때문인것으로 추정된다. 뇌자기 공명영사에서 관찰되는 고신호강도 소견은 표적 장기의 망간적 축적량을 반영하는데는 충분하지 못한 것으로 보인다. 따라서이러한 놔자기공명영상의 특성 및 비용-효과적인 측면을 고려할 대 망간폭로집안에서의 망간폭로정도를 추정하기 위하여 놔자기공명영상을 사용하는 것은 바람직하지 않다고 보인다. 그러나 망간과 관련된 건강장해가 의심되는 파킨슨증 환자에서 망간폭로를 확인 및 추정하는 데에는 매우 유용하게 활용할 수 있다.

• Journal of Radiation Protection and Research
• /
• 제45권2호
• /
• pp.81-87
• /
• 2020

Background: Kori unit #1 is permanently shut down after a 40-year lifetime. The Nuclear Safety and Security Commission recommends establishing initial decommissioning plans for all nuclear and radwaste treatment facilities. Therefore, the Korea Atomic Energy Research Institute (KAERI) must establish an initial and final decommissioning plan for radwaste-treatment facilities. Radiation safety assessment, which constitutes one chapter of the decommissioning plan, is important for establishing a decommissioning schedule, a strategy, and cost. It is also a critical issue for the government and public to understand. Materials and Methods: This study provides a method for assessing external radiation dose to workers during decommissioning. An external dose is calculated following each exposure scenario, decommissioning strategy, and working schedule. In this study, exposure dose is evaluated using the deterministic method. Physical characterization of the facility is obtained by both direct measurement and analysis of the drawings, and radiological characterization is analyzed using the annual report of KAERI, which measures the ambient dose every month. Results and Discussion: External doses are calculated at each stage of a decommissioning strategy and found to increase with each successive stage. The maximum external dose was evaluated to be 397.06 man-mSv when working in liquid-waste storage. To satisfy the regulations, working period and manpower must be managed. In this study, average and cumulative exposure doses were calculated for three cases, and the average exposure dose was found to be about 17 mSv/yr in all the cases. Conclusion: For the three cases presented, the average exposure dose is well below the annual maximum effective dose restriction imposed by the international and domestic regulations. Working period and manpower greatly affect the cost and entire decommissioning plan; hence, the chosen option must take account of these factors with due consideration of worker safety.

• 한국방사선학회논문지
• /
• 제15권6호
• /
• pp.803-811
• /
• 2021

본 연구에서는 공정 시뮬레이션 기술을 적용하여 조사유기응력부식균열 시험 작업자의 피폭량 평가를 하였다. 상용 공정 시뮬레이션 코드인 DELMIA Version 5를 사용하여 조사유기응력부식균열 분석 시험 설비, 핫셀 및 작업자를 작성하고 조사유기응력부식균열 시험 공정을 구현하였으며, 사용자 코딩을 통해 선량이 분포된 공간을 지나는 작업자의 누적 피폭량을 평가할 수 있도록 하였다. 작업자 모사를 위해 시험 공정별로 인체의 근골격계를 모방하여 약 200 개 이상의 자유도를 가지는 휴먼 마니킨 자세를 작성하였다. 작업자 피폭량 계산을 위하여 휴먼 마니킨 작업의 하위정보에 접근하여 자세 별 좌표, 시작 시간 및 유지 시간을 추출하였으며, 공간 선량 값과 자세 유지 시간을 곱하여 누적 피폭량을 계산하였다. 피폭량 평가를 위한 공간 선량은 MCNP6 Version 1.0을 사용하여 핫셀 내·외부 공간 선량을 계산하였으며, 계산된 공간 선량은 공정 시뮬레이션 도메인에 입력하였다. 공정 시뮬레이션을 이용한 피폭량 평가 결과와 전형적인 피폭량 평가 결과를 비교 분석한 결과, 상시 출입구역 내 일상 시험 작업에 대한 연간 피폭량은 각각 0.388 mSv/year 및 1.334 mSv/year로서 공정 시뮬레이션을 이용한 피폭량 평가 결과가 전형적인 방법의 피폭량 평가 결과 대비 70 % 낮게 예측되었다. 공간 선량 높은 구역에서 수행되는 특수작업에 대해서도 공정 시뮬레이션을 이용한 피폭량 평가를 수행하였으며, 피폭량이 높은 작업을 쉽게 선별할 수 있었고, 해당 작업의 휴먼 마니킨 자세와 공간 선량 가시화를 통해 직관적으로 작업 개선안을 도출할 수 있었다.

• Asian Pacific Journal of Cancer Prevention
• /
• 제16권10호
• /
• pp.4339-4345
• /
• 2015

Occupational exposure to wood dust is one cause of nasopharyngeal cancer (NPC); however, assessing this exposure remains problematic. Therefore, the objective of this study was to develop a semi-quantitative exposure assessment method and then utilize it to evaluate the association between occupational exposure to wood dust and the development of NPC. In addition, variations in risk by histology were examined. A case-control study was conducted with 327 newly diagnosed cases of NPC at the National Cancer Institute and regional cancer centers in Thailand with 1:1 controls matched for age, gender and geographical residence. Occupational information was obtained through personal interviews. The potential probability, frequency and intensity of exposure to wood dust were assessed on a job-by-job basis by experienced experts. Analysis was performed by conditional logistic regression and presented in odds ratio (ORs) estimates and 95% confidence intervals (CI). Overall, a non significant relationship between occupational wood dust exposure and NPC risk for all subjects was observed (ORs=1.61, 95%CI 0.99-2.59); however, the risk became significant when analyses focused on types 2 and 3 of NPC (ORs=1.62, 95%CI 1.03-2.74). The significant association was stronger for those exposed to wood dust for > 10 year (ORs=2.26, 95%CI 1.10-4.63), for those with first-time exposure at age > 25 year (ORs=2.07, 95%CI 1.08-3.94), and for those who had a high cumulative exposure (ORs=2.17, 95%CI 1.03-4.58) when compared with those considered unexposed. In conclusion, wood dust is likely to be associated with an increased risk of type 2 or 3 NPC in the Thai population. The results of this study show that semi-quantitative exposure assessment is suitable for occupational exposure assessment in a case control study and complements the information from self-reporting.

• Current Photovoltaic Research
• /
• 제6권3호
• /
• pp.81-85
• /
• 2018

The photovoltaic modules installed in the actual field are affected by various external environments and the electrical performance output value is generally lowered compared to initial output value. The most of photovoltaic modules consists of low iron glass, encapsulant (EVA), back sheet, frame and junction box assembly based on the solar cells. In this paper, the characteristics of encapsulant which is an important constituent material of photovoltaic module were verified by maximum power determination, electro luminescence images, yellowness index measurement, and gel content measurement after ultraviolet (UV) irradiation exposure. The most commonly installed 72 cells crystalline photovoltaic modules were tested after various UV exposure of 0, 15, 30, and $60kWh/m^2$ and compared with the reference module. After UV exposure of $15kWh/m^2$, which is the current international test condition, a small amount of change was observed in yellowness index and electroluminescence, while a gell content rapidly increased. At a cumulative dose of $60kWh/m^2$, which will be a new international test condition in the near future, however, the yellowness index increased sharply and showed the greatest output power drop.

• 한국환경과학회지
• /
• 제25권8호
• /
• pp.1107-1114
• /
• 2016

This research, sponsored by the Korean Ministry of Environment in 2014, was the first epidemiological study in Korea that investigated the health impact assessment of radon exposure. Its purpose was to construct a model that calculated the annual mean cumulative radon exposure concentrations, so that reliable conclusions could be drawn from environment-control group research. Radon causes chronic lung cancer. Therefore, the long-term measurement of radon exposure concentration, over one year, is needed in order to develop a health impact assessment for radon. Hence, based on the seasonal correction model suggested by Pinel et al.(1995), a predictive model of annual mean radon concentration was developed using the year-long seasonal measurement data from the National Institute of Environmental Research, the Korea Institute of Nuclear Safety, the Hanyang University Outdoor Radon Concentration Observatory, and the results from a 3-month (one season) survey, which is the official test method for radon measurement designated by the Korean Ministry of Environment. In addition, a model for evaluating the effective annual dose for radon was developed, using dosimetric methods. The model took into account the predictive model for annual mean radon concentrations and the activity characteristics of the residents.

• Asian Pacific Journal of Cancer Prevention
• /
• 제14권5호
• /
• pp.2783-2787
• /
• 2013

To assess the risk of cancer incidence after medical radiation exposure for coronary artery disease (CAD), a retrospective cohort study was conducted based on Taiwan's National Health Insurance Research Database (NHIRD). Patients with CAD were identified according to the International Classification of Diseases code, 9th Revision, Clinical Modification (ICD-9-CM), and their records of medical radiation procedures were collected from 1997 to 2010. A total of 18,697 subjects with radiation exposure from cardiac imaging or therapeutic procedures for CAD were enrolled, and 19,109 subjects receiving cardiac diagnostic procedures without radiation were adopted as the control group. The distributions of age and gender were similar between the two populations. Cancer risks were evaluated by age-adjusted incidence rate ratio (aIRR) and association with cumulative exposure were further evaluated with relative risks by Poisson regression analysis. A total of 954 and 885 subjects with various types of cancers in both cohorts after following up for over 10 years were found, with incidences of 409.8 and 388.0 per 100,000 person-years, respectively. The risk of breast cancer (aIRR=1.85, 95% confidence interval: 1.14-3.00) was significantly elevated in the exposed female subjects, but no significant cancer risk was found in the exposed males. In addition, cancer risks of the breast and lung were increased with the exposure level. The study suggests that radiation exposure from cardiac imaging or therapeutic procedures for CAD may be associated with the increased risk of breast and lung cancers in CAD patients.

• Journal of Radiation Protection and Research
• /
• 제47권2호
• /
• pp.86-92
• /
• 2022

Background: The present study investigated the radiation dose distribution of balloon kyphoplasty (BKP) among surgeons and medical staff, and this is the first research to observe such exposure in Japan. Materials and Methods: The study subjects were an orthopedic surgeon (n = 1) and surgical staff (n = 9) who intervened in BKP surgery performed at the National Hospital Organization Disaster Medical Center (Tokyo, Japan) between March 2019 and October 2019. Only disposable protective gloves (0.022 mmPb equivalent thickness or less) and trunk protectors were used, and no protective glasses or thyroid drapes were used. Results and Discussion: The surgery time per vertebral body was 36.2 minutes, and the fluoroscopic time was 6.8 minutes. The average exposure dose per vertebral body was 1.46 mSv for the finger (70 ㎛ dose equivalent), 0.24 mSv for the lens of the eye (3 mm dose equivalent), 0.11 mSv for the neck (10 mm dose equivalent), and 0.03 mSv for the chest (10 mm dose equivalent) under the protective suit.The estimated cumulative radiation exposure dose of 23 cases of BKP was calculated to be 50.37 mSv for the fingers, 8.27 mSv for the lens, 3.91 mSv for the neck, and 1.15 mSv for the chest. Conclusion: It is important to know the exposure dose of orthopedic surgeons, implement measures for exposure reduction, and verify the safety of daily use of radiation during surgery and examination.

• 농촌의학ㆍ지역보건
• /
• 제29권2호
• /
• pp.265-285
• /
• 2004

이 연구는 농약의 노출에 의해 중추신경 증상이 발생할 수 있으며, 장기간의 농약노출로 인해 중추신경계 영향이 있을 것이라는 가설을 검정하기 위해 농약 누적노출을 추정하였으며, 농약 노출 관련 요인에 따라 신경독성증상 호소의 차이를 보았다. 연구결과는 다음과 같다. 지난 1년 동안 농약살포시간은 과수농민 69.6시간, 밭농민 41.1시간, 축산농업인 25.8시간으로 통계적으로 유의한 차이가 있었으며, 누적노출지수는 과수농민 119.5g, 밭농민 63.9g, 축산농업인 23.7g으로 통계적으로 유의한 차이가 있었다(p<0.01). 누적노출지수에 의해 분류하면, 과수농민은 고노출군, 밭농민은 중간노출군. 축산농민은 저노출군에 해당하였다. 과거 농약중독 경험률은 과수농민 40.7%, 밭농민 35.1%, 축산농민 23.8%로 통계적으로 유의한 차이가 있었으며 (p<0.001), 지난 3개월 동안 농약중독 증상 경험률은 과수농민 67.2%, 밭농민 55.3%, 축산농민 20.5% 순으로 통계 적으로 유의한 차이가 있었다(p<0.001). 신경독성 자각증상의 총점과 6개 이상 증상을 호소하는 경우는 대조군 및 축산농민에 비해 밭농민 및 과수농민에서 유의하게 증가하였다(p<0.001). 연령, 교육수준, 성, 흡연, 음주를 보정한 상태에서도 6개 이상 신경독성 증상 발생의 교차 비는 비노출군에 비해 과수농민이 3.08(95% CI 1.50-6.30)배, 누적노출지수가 75% 이상 높은 군이 2.75(958% CI 1.12-6.78) 배, 과거 농약중독 경험이 있는 경우 1.97(95% CI 1.21-3.20)배, 현재 농약중독증상을 경험한 경우 정상군에 비해 경도 중독군 3.03(95% CI 1.47-6.22)배, 중등도 중독군이 6.34(95% CI 3.03-13.25)배 높게 나타났다. 이상의 결과로 볼 때, 신경독성증상의 발생에 일관되게 농약노출과 관련된 요인이 유의하게 나타나고, 농약노출이 높은 것으로 평가된 과수농민에서 중추신경계 증상 호소가 유의하게 녹게 나타나 만성 농약노출에 의해 중추신경계 영향이 발생할 가능성이 제기된다.