• ETRI Journal
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• 제31권4호
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• pp.466-468
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• 2009

In this letter, we propose a one-way ranging algorithm that is based on wireless synchronization with measured timestamps and clock frequency offsets. In our proposed algorithm, an active mobile node initiates a ranging procedure by transmitting a ranging frame, and the anchor nodes report their timestamps for the received ranging frame to a reference anchor node. The synchronization of a pair of nodes is provided with instantaneous time information, and the corresponding difference of distances can be calculated.

• 제어로봇시스템학회논문지
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• 제19권2호
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• pp.125-130
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• 2013

Compared to OWR (One-Way Ranging) method that requires precise network time synchronization, TWR (Two-Way Ranging) method has advantages in building an indoor WPAN (Wireless Personal Area Network) location system with lower cost. However, clock offsets of nodes in WPAN system should be eliminated or compensated to improve location accuracy of the TWR method. Because conventional clock offset elimination methods requires multiple TWR transactions to reduce clock offset, they produce network traffic burden instead. This paper presents a clock offset estimation method that can reduce clock offset error with a single TWR transaction. After relative clock offsets of sensor nodes are estimated, clock offsets of mobile tags are estimated using a single TWR communication. Simulation results show that location accuracy of the proposed method is almost similar to the conventional clock offset elimination method, while its network traffic is about a half of the conventional method.

• 아동학회지
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• 제8권1호
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• pp.65-82
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• 1987

The purpose of the present research was to study mothers' perceptions about their children' cognitive abilities and the relations between such perceptions and the children's cognitive level. The subjects of this study were 60 children (mean age: 6 years 1 month: age range = 5;8 to 6;7) and their mothers. Each child responded to 18 tasks drawn from the Kodae-Binet IQ test. Subsequently, the mothers were asked 4 questions: an estimate of her child's success or failure on the tasks, a rating of the certainty of her judgment, an estimate of the age of mastery on each task both for her owr child and children in general. The data of the present study were analyzed with the 3-way ANOVA (sex x birth order x mother's education level), t-test, and Pearson correlation coefficient. Significant differences were found in (1) mothers' accuracy of their children's cognitive abilities according to children's birth order, (2) mothers' accuracy, overestimation, and certainty according to the level of difficulty of each task, and (3) mothers' estimate of age at mastery according to the level of each task. Furthermore, there were positive correlations between accurate predictions by the mother and correct answers by the child and between overestimations by the mother and correct answers by the child.

• 대한임베디드공학회논문지
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• 제5권4호
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• pp.234-242
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• 2010

Two-way ranging methods such as TWR and SDS-TWR have been considered for many ranging systems because these methods are useful in the absence of synchronization. To estimate the location of a mobile node, complicated ranging procedures consisting of ranging frames between an anchor node and the mobile node are performed. Supporting multiple mobile nodes such as a few hundreds or thousands and several anchor nodes, the ranging procedures have the fatal disadvantage of processing delay and inefficient traffic bandwidth. On the other hand, the one-way ranging method is simple and fast, but susceptible to network synchronization. In this paper, we propose a method to modify asynchronous ranging equations to establish exact frequency or frequency offset, a method to estimate frequencies or frequency offsets, and a method to establish post-facto synchronization with anchor nodes. The synchronization for a node pair is adapted using instantaneous time information and corresponding difference of distances can be determined. We evaluate the performance of TWR, SDS-TWR and proposed ranging algorithms.

• 로봇학회논문지
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• 제12권3호
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• pp.350-355
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• 2017

UWB (Ultra Wide Band) refers to a system with a bandwidth of over 500 MHz or a bandwidth of 20% of the center frequency. It is robust against channel fading and has a wide signal bandwidth. Using the IR-UWB based ranging system, it is possible to obtain decimeter-level ranging accuracy. Furthermore, IR-UWB system enables acquisition over glass or cement with high resolution. In recent years, IR-UWB-based ranging chipsets have become cheap and popular, and it has become possible to implement positioning systems of several tens of centimeters. The system can be configured as one-way ranging (OWR) positioning system for fast ranging and TWR (two-way ranging) positioning system for cheap and robust ranging. On the other hand, the ranging based positioning system has a limitation on the number of terminals for localization because it takes time to perform a communication procedure to perform ranging. To overcome this problem, code multiplexing and channel multiplexing are performed. However, errors occur in measurement due to interference between channels and code, multipath, and so on. The measurement filtering is used to reduce the measurement error, but more fundamentally, techniques for removing these measurements should be studied. First, the TWR based positioning was analyzed from a stochastic point of view and the effects of outlier measurements were summarized. The positioning algorithm for analytically identifying and removing single outlier is summarized and extended to three dimensions. Through the simulation, we have verified the algorithm to detect and remove single outliers.

• 한국방사성폐기물학회:학술대회논문집
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• 한국방사성폐기물학회 2003년도 가을 학술논문집
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• pp.609-613
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• 2003

사용후핵연료 및 방사성물질을 저장하기 위한 저장시스템은 사용후핵연료를 저장하는 동안 안전성 문제를 야기하지 않도록 격납을 설계하고 평가하여야 하며, 격납 평가는 ANSI Nl4.5 또는 ISO 12807에서 규정하고 있는 절차에 따른 허용 누설률을 계산하여 평가할 수 있다. 따라서, ISO 12807에서 규정한 평가방법에 따라 PWR 사용후핵연료 24 다발을 저장하였을 경우와 금속전환체 24다발을 저장하였을 경우에 대한 허용 누설률을 평가하였다. OWR 사용후핵연료 24다발을 저장하였을 경우 허용 누설률은 $1.38{\times}10_{-10}m_3/s$로, 금속전환체 24다발을 저장하였을 경우 $4.46{\times}10_{-10}m_3/s$로 평가되었다. 따라서, 사용후핵연료를 저장하였을 경우보다 금속전환체를 저장하였을 경우 격납 조건이 수월해 짐을 알 수 있었다.

• Journal of Gastric Cancer
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• 제8권4호
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• pp.225-231
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• 2008

목적: 위 점막하 종양(gastric submucosal tumor, gastric SMT)은 최근 건강검진의 보편화로 증가하는 추세에 있다. 이에 반해 악성도에 따라 예후가 달라지고, 방사선 검사나 내시경 조직검사로 다른 종양과의 감별이 어려워 아직도 치료 방침을 결정하는데 어려움이 있다. 이에 저자들은 위 점막하 종양 환자에서 임상병리학적 특성을 분석하고, 이에 따른 복강경 수술과 개복술의 결과를 각각 비교 분석하였다. 위 점막하종양의 복강경 절제술의 학습곡선 의미를 도출하여, 위 점막하종양의 적절한 치료방법을 제시하고자 한다. 대상 및 방법: 2003년 4월부터 2008년 8월까지 본원에서 위점막하종양으로 개복 위절제술을 받은 25명과 복강경 위절제술을 시행 받은 78명의 환자들을 대상으로 하였으며, 수술 후 임상경과 및 병리학적 특징에 대하여 전향적인 자료 수집 후 후향적으로 결과를 비교 분석하였다. 결과: 환자의 평균 연령은 53.7세(22~80세)였으며 남녀비는 각각 44명, 59명으로 1 : 1.34였다. 대부분 무증상으로 내원하였으며, 주로 쐐기형 위절제술을 시행 받았다. 종양의 평균 장경은 4.33 cm (1.2~17.0 cm)였고, 주로 위상부에 위치하였으며, 평균 수술 시간은 117.3분(35~255분)이었다. 평균 출혈량은 113.9 ml (0~1,000 ml), 평균 수술 후 재원기간은 8.0일(1~69일)이었다. 술 전 내시경적 절제술이 실패하여 수술이 의뢰된 환자가 5명 있었다. 수술 후 합병증은 13명(12.6%)에서 발생하였고, 수술과 관련된 사망은 없었다. 위 점막하종양의 대부분은 간질유래성증양으로 58명(56.3%)이며, 이중 현재까지 크기가 5 cm 이상이고 복강경 위절제술을 시행한 2명이 재발되었다. 복강경 수술 군과 개복 수술 군에 따라 수술 시간 및 출혈량, 합병증에는 차이가 없었지만, 두 군 간에 환자의 증상(P<0.001), 종양의 크기 (P<0.001), 수술방법 중 쐐기형 절제술 시행(P=0.037), 술 후 연식섭취 시간(P<0.001), 술 후 퇴원 일(P=0.002)에는 차이가 있었다. 위 점막하종양의 복강경 위절제술은 26예 이상의 수술 경험이 필요하고, 이러한 학습 곡선을 극복함으로써 수술 시간, 출혈량을 줄일 수 있다. 결론: 5 cm 미만의 위 점막하종양에서는 복강경적 치료방법이 개복술보다 안전하고, 효과적인 치료방법으로 생각되며, 다양한 형태의 위 점막하종양을 복강경적 절제술로 시행 할 경우에는 학습 곡선을 먼저 극복하기 위해 노력하는 것이 권장된다.