• Journal of the Korean Data and Information Science Society
• /
• 제25권5호
• /
• pp.1117-1125
• /
• 2014

In a longitudinal study, subjects can experience same type of events repeatedly. Also, there may exist intermittent dropouts resulting in repeated observation gaps during which no recurrent events are observed. Furthermore, when such observation gaps have incomplete forms caused by the unknown termination times of observation gaps, ordinary approaches result in biased estimates. In this study, we investigate the effect of ignoring observation gaps and propose methods to overcome this problem. For estimating the distribution of unknown termination times, an interval-censored mechanism is applied and two cases are considered. Simulation studies are carried out to evaluate the performance of the proposed method. Conviction data of young drivers with several suspensions are analyzed to illustrate the suggested approach.

• 대기
• /
• 제33권5호
• /
• pp.441-456
• /
• 2023

The mobile observation method, in which a meteorological drone observes while ascending, can observe the vertical profile of wind at 1 m-interval. In addition, since continuous flights are possible at time intervals of less than 30 minutes, high-resolution observation data can be obtained both spatially and temporally. In this study, we verify the accuracy of mobile observation data from meteorological drone (drone) and fill the spatio-temporal observation gaps in the lower atmosphere. To verify the accuracy of mobile observation data observed by drone, it was compared with rawinsonde observation data. The correlation coefficients between two equipment for a wind speed and direction were 0.89 and 0.91, and the root mean square errors were 0.7 m s^-1 and 20.93°. Therefore, it was judged that the drone was suitable for observing vertical profile of the wind using mobile observation method. In addition, we attempted to resolve the observation gaps in the lower atmosphere. First, the vertical observation gaps of the wind profiler between the ground and the 150 m altitude could be resolved by wind observation data using the drone. Secondly, the temporal observation gaps between 3-hour interval in the rawinsonde was resolved through a drone observation case conducted in Taean-gun, Chungcheongnam-do on October 13, 2022. In this case, the drone mobile observation data every 30-minute intervals could observe the low-level jet more detail than the rawinsonde observation data. These results show that the mobile observation data of the drone can be used to fill the spatio-temporal observation gaps in the lower atmosphere.

• 응용통계연구
• /
• 제25권4호
• /
• pp.621-632
• /
• 2012

Recurrent event data can be easily found in longitudinal studies such as clinical trials, reliability fields, and the social sciences; however, there are a few observations that disappear temporarily in sight during the follow-up and then suddenly reappear without notice like the Young Traffic Offenders Program(YTOP) data collected by Farmer et al. (2000). In this article we focused on inference for a cumulative mean function of the recurrent event data with these incomplete observation gaps. Defining a corresponding risk set would be easily accomplished if we know the exact intervals where the observation gaps occur. However, when they are incomplete (if their starting times are known but their terminating times are unknown) we need to estimate a distribution function for the terminating times of the observation gaps. To accomplish this, we treated them as interval-censored and then estimated their distribution using the EM algorithm proposed by Turnbull (1976). We proposed a nonparametric estimator for the cumulative mean function and also a nonparametric test to compare the cumulative mean functions of two groups. Through simulation we investigated the finite-sample performance of the proposed estimator and proposed test. Finally, we applied the proposed methods to YTOP data.

• Communications for Statistical Applications and Methods
• /
• 제20권4호
• /
• pp.283-290
• /
• 2013

Subjects can experience two types of recurrent events in a longitudinal study. In addition, there may exist intermittent dropouts that results in repeated observation gaps during which no recurrent events are observed. Therefore, theses periods are regarded as non-risk status. In this paper, we consider a special case where information on the observation gap is incomplete, that is, the termination time of observation gap is not available while the starting time is known. For a statistical inference, incomplete termination time is incorporated in terms of interval-censored data and estimated with two approaches. A shared frailty effect is also employed for the association between two recurrent events. An EM algorithm is applied to recover unknown termination times as well as frailty effect. We apply the suggested method to young drivers' convictions data with several suspensions.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2000년도 춘계학술대회논문집B
• /
• pp.795-800
• /
• 2000

A CCFL(Counter Current Flow Limit) test have been performed in narrow annular gaps with large diameter, because it has been confirmed that the CCFL phenomena affected the critical power in hemispherical narrow gap geometries from the SONATA(Simulation Of Naturally Arrested Thermal Attack)-IV (In-Vessel)/VISU(Visualization)-II experiments. The objectives of the CCFL experiments are to investigate the small gap sizes(1, 2mm) effect on CCFL under the large diameter condition and to confirm the findings of the VISU-II study that global dryout in hemispherical narrow gaps was induced by the CCFL. The test section was made of acrylic resin to allow visual observation on the two-phase flow behaviors inside annular gaps. It was observed from visualization that a part of water supplied was accumulated in the upper plenum and a significant increase in the differential pressure across the gap was occurred, which was the definition of the CCFL occurrence in this experimental study. From the experimental results in annular gap with large diameter it can be known that an increase in the differential pressure was not big at small air flow-rates. When the CCFL was occurred, the differential pressure across gaps was increased significantly and a water accumulated in the upper plenum. The occurrence of CCFL was correlated using the Wallis parameter.

• Journal of the Korean Data and Information Science Society
• /
• 제25권2호
• /
• pp.327-336
• /
• 2014

재발 사건 자료란 연구대상이 같은 종류의 사건을 반복적으로 경험할 때 발생하는 자료이다. 이러한 재발 사건은 사회과학, 자연과학, 공학, 의약학 등 다양한 분야에서 나타날 수 있다. 재발 사건자료를 분석할 때 연구자의 관심에 따라 사건 발생시간이나 사건 발생간의 소요시간을 이용하여 분석할 수 있다. 이 논문에서는 사건 발생시점간의 소요시간을 이용하여 불완전한 관측을 가진 재발 사건자료를 분석하고자 한다. 이 자료의 특징은 일부 관측대상들이 일정기간 동안 연구에서 제외되는 관측틈을 갖는다는 것이다. 이 때 관측틈은 불완전한 형태로 나타나게 되는데 그 이유는 관측틈의 시작시점은 알고 있지만 종료시점은 알 수 없기 때문이다. 이러한 미지의 종료시점을 추정하기 위해서 구간 중도 절단 방법이 적용된다. 따라서 종료시점이 추정된 후 프레일티를 포함한 회귀모형을 적용하여 공변량이 사건 재발에 미치는 영향을 알아볼 수 있다. 또한 제안한 방법을 실제자료에 적용하여 관측틈을 고려한 경우와 고려하지 않은 경우를 비교하고자 한다.

• Journal of Ecology and Environment
• /
• 제47권4호
• /
• pp.228-240
• /
• 2023

Growing complexity in ecosystem structure and functions, under impacts of climate and land-use changes, requires interdisciplinary understandings of processes and the whole-system, and accurate estimates of the changing functions. In the last three decades, observation networks for biodiversity, ecosystems, and ecosystem functions under climate change, have been developed by interested scientists, research institutions and universities. In this paper we will review (1) the development and on-going activities of those observation networks, (2) some outcomes from forest carbon cycle studies at our super-site "Takayama site" in Japan, and (3) a few ideas how we connect in-situ and satellite observations as well as fill observation gaps in the Asia-Oceania region. There have been many intensive research and networking efforts to promote investigations for ecosystem change and functions (e.g., Long-Term Ecological Research Network), measurements of greenhouse gas, heat, and water fluxes (flux network), and biodiversity from genetic to ecosystem level (Biodiversity Observation Network). Combining those in-situ field research data with modeling analysis and satellite remote sensing allows the research communities to up-scale spatially from local to global, and temporally from the past to future. These observation networks oftern use different methodologies and target different scientific disciplines. However growing needs for comprehensive observations to understand the response of biodiversity and ecosystem functions to climate and societal changes at local, national, regional, and global scales are providing opportunities and expectations to network these networks. Among the challenges to produce and share integrated knowledge on climate, ecosystem functions and biodiversity, filling scale-gaps in space and time among the phenomena is crucial. To showcase such efforts, interdisciplinary research at 'Takayama super-site' was reviewed by focusing on studies on forest carbon cycle and phenology. A key approach to respond to multidisciplinary questions is to integrate in-situ field research, ecosystem modeling, and satellite remote sensing by developing cross-scale methodologies at long-term observation field sites called "super-sites". The research approach at 'Takayama site' in Japan showcases this response to the needs of multidisciplinary questions and further development of terrestrial ecosystem research to address environmental change issues from local to national, regional and global scales.

• 대한원격탐사학회지
• /
• 제35권5_1호
• /
• pp.727-736
• /
• 2019

본 연구에서는 여러 장의 무인항공기 영상을 사용하여 대상지역에 대한 포인트 클라우드를 생성하고, 데이터 세트 간 발생하는 이격과 중복점을 제거하는 방안에 대한 연구를 수행하였다. 이를 위해 사진 측량 기반의 IBA(Incremental Bundle Adjustment)기법을 적용하여 무인기의 위치/자세를 보정하고 스테레오 페어를 구성했다. 각각의 스테레오 영상으로부터 에피폴라 영상을 생성하고 MDR(Multi-Dimensional Relaxation) 정합 기법을 적용하여 포인트 클라우드를 생성하였다. 다음으로 스테레오 영상 간 관측 벡터에 기반한 포인트 클라우드 등록을 통해 서로 다른 스테레오 페어로부터 생성된 포인트 클라우드 간 이격을 제거하였다. 마지막으로 점유격자(Occupancy grid) 기반 통합 알고리즘을 적용하여 중복점이 제거된 하나의 포인트 클라우드를 생성하였다. 실험은 무인항공기에서 취득된 연직 촬영 영상을 사용하였으며, 실험을 통해 서로 다른 스테레오 페어로부터 생성된 포인트 클라우드 간 이격 및 중복점 제거가 가능함을 확인하였다.

• Journal of Forest and Environmental Science
• /
• 제37권1호
• /
• pp.62-68
• /
• 2021

Despite numerous efforts on reducing road-kill worldwide, the collisions have been occurring continuously. Many factors are affecting road-kill occurrences and the effect is various by species. We investigated Hydropotes inermis argyropus road-kill characteristics on the national highway. We examined 9,099 H. i. argyropus road-kill points with distance to the gaps on road (interchange and intersection) and distance to six natural land-cover types as explanatory variables. We also examined the number of road-kill occurrences according to temporal variation using chi-square test with 9,658 events. In general, H. i. argyropus road-kill location tended to occur close to the gaps on road, agricultural lands and forests. The average distance from road-kill to the gap was 694.7 m and 78.6% of the collisions were occurred within 1 km from the gaps. In addition, Kruskal-Wallis test showed the distance between road-kill points and each land cover and the gaps was significantly different. The temporal analyses showed that the differences of the H. i. argyropus road-kill frequency are significant in both month and season. Our results implies H. i. argyropus road-kill location tended to occur close to the gaps on road, agricultural lands and forests in general, especially during May and June, according to their seasonal behavior. Thus, we suggest there is a need of concentrated management on the roads with specific characteristics for both wildlife and human safety.

• Safety and Health at Work
• /
• 제5권4호
• /
• pp.169-174
• /
• 2014

We have been examining the issue of healthcare workers' exposure to antineoplastic drugs for nearly a decade and have observed that there appears to be more publications on the subject matter originating from Europe than from North America. The concern is that findings from Europe may not be generalizable to North America because of differences in handling practices, regulatory requirements, and training. Our objective was to perform a literature review to confirm our observation and, in turn, identify gaps in knowledge that warrants addressing in North America. Using select keywords, we searched for publications in PubMed and Web of Science. All papers were initially classified according to the originating continent and then categorized into one or more subject categories (analytical methods, biological monitoring, occupational exposure, surface contamination, and probability of risk/exposure). Our review identified 16 papers originating from North America and 55 papers from Europe with surface contamination being the subject matter most often studied overall. Based on our results, we are of the opinion that North American researchers need to further conduct dermal and/or urinary drug contamination studies as well as assess the exposure risk faced by healthcare workers who handle antineoplastic drugs. Trends in exposure levels should also be explored.