• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.640-644
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• 2003

There are many difficulties to get the scattered field generated by obstacle which has arbitrary shape or irregular surface impedance by using analytic solution or numerical methods. In this study, we propose experimental method of acoustic scattering holography that can predict the far-field scattered field based on nearfield measurements. In particular we can get the scattered fields of each wave-number components of incident fields. We express the relationship of wave-number components between incident fields and scattered fields using scattering matrix which is transfer matrix of wave-number components. Lastly, we prove the relation between wave-number components of incident and scattered field by experiments. The errors which are caused by measurements and decomposition methods are also analyzed.

• 한국측량학회지
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• 제36권6호
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• pp.621-628
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• 2018

GPS (Global Positioning System)를 이용하여 위치를 결정하기 위해서는 4개 이상의 가시위성이 있어야 한다. 하지만 도심지역과 같은 환경에서는 이러한 조건을 만족하기 어려운 경우도 있다. 특히, 가시위성이 3개뿐인 경우 외부로부터 위치결정에 필요한 시계오차정보를 활용하는 측위기법이 대안으로 사용되기도 한다. 본 연구에서는 먼저 수신기 시계오차특성을 분석한 후 시계오차의 보간에 적합한 방법으로 LSC (Least-Squares Collocation)을 제안하였다. 실험을 위해 국내 상시관측소와 상시관측소 근처에 설치된 수신기로부터 수신된 GPS 데이터를 이용하였다. DGPS (Differential GPS)기법을 통해 먼저 시계오차를 계산했으며 효율적인 보간을 위해 구간을 나눈 후 보간하는 방법을 적용하였다. 시계오차의 계산이 불가능한 epoch에 대해 LSC 보간법을 적용함으로써 시계오차를 계산하였다. 실험결과를 분석하기 위해 원래 데이터로부터 계산된 시계오차와 보간된 시계오차와의 차이인 잔차를 계산하였다. 계산결과 잔차의 평균은 0.24m 그리고 표준편차는 0.49m로 충분한 정확도의 확보가 가능한 것으로 판단된다.

• 한국학교보건학회지
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• 제1권1호
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• pp.103-113
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• 1988

The analysis of the visual impairment and refractive errors among 4,004 school children in Seoul in 1986 with ancilliary questionnaire on various socio-environmental and visual factors was conducted. The number of the student with subnormal vision (0.7 or less) was 1,552 (38,8 %), and the rate of subnormal vision was increased with the higher grading of the school classes. Rate of myopes among the 1,552 students vision 0.7 or less consists of 52 % in primary school, 83.5 % in middle school, and 94 % in high school, and they were increased with the higher grading of the school class. The acutest increase of rates were observed at the stages of 2nd year class of male, and 1st year class of female at the middle school. Among the glasses-wearer of myopic students of vision 0.5 or less, the rate of adequately corrected cases was 42.5 %, whereas the overcorrected in 6.8 %, and undercorrected in 49.3 %. The main reasons of glasses negligence among the non-possessor of glasses with the vision of 0.5 or less were indicated in prominence of numbers of' "no complaints without glasses" (42 %). "unawareness of visual disturbance" (20%), "annoyance with wearing glasses" (13.4%), and "no permission from parents" (11.5 %) rather than the "economical reasons". The amblyopic components were estimated 126 cases (3.2%) in combination of refractive errors. According to the analysis of ancilliary questionnaire, the-conclusion with the statistical significance was that the myopization of the children's eyes appeared susceptible with a number of socio-environmental factors including the eating habits, length of T.V. watching period and distance, reading distance and type of illumination during near work, and school achievement. The possibility of prevention in some extents of progress of the myopia following the improvement of the relevant environmental factors in younger stage of children would be considered as deducible one.

• Journal of Periodontal and Implant Science
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• 제30권3호
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• pp.699-707
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• 2000

The purpose of this study was to analyze the statistical errors of articles in the Journal of Korean Academy of Periodontology from 1973 to 1999. Of the 662 articles examined, 263 were included which analyzed the data. They were classified into 2 groups with time lapse; group 1: 1973∼1989, group 2: 1990∼1999. Authors made checklists for analyzing the data and detecting the errors and analyzed them with professional statistician. The results were as follows: 1. Of 263 atricles which applied statistical method, 40(19.3%) was in group 1, 223(49.0%) in group2. 2. In the number of statistical method applied, 170(64.6%) were analyzed with 1 statistical method, 73(27.8%) with 2 methods, 18(6.8%) with 3 methods, and 2(0.8%) with 4 methods 3. The number of statistical methods applied was 14, and they were applied in order of 119 of ANOVA, 72 of Student t-test, 63 of Paired t-test, 36 of CORRELATION, and 21 of Mann- Whitney U test. 4. In 87(33.1%) of 263 articles and in 18 error items, statistical errors were found out. In group I, 9 items (55%) of error were found out, and were in order of 5 of Student t-test instead of Paired t-test, and 4 of unnecessary statistical analysis. In group II, 16 items (29.1%) of error were found out, and were in order of 22 of Student t-test instead of Paired t-test, 7 of no multiple comparison test after ANOVA, 6 of Student t-test instead of ANOVA, 6 of unnecessary statistical analysis, and 5 of ANOVA instead of Paired t-test. In conclusion, the results noted that statistical analyses were increased, but statistical errors were decreased with time. But authors suggest that researchers should refer to standard statistical texts and seek advice from professional statisticians to avoid the statistical errors.

• Nuclear Engineering and Technology
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• 제44권1호
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• pp.61-70
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• 2012

In this study, a simple post-reconstruction dual-energy computed tomography (CT) method is proposed. A dual-energy CT algorithm for monochromatic x-rays was adopted and applied to the dual-energy CT of polychromatic x-rays by assigning a representative mono-energy. The accuracy of algorithm implementation was tested with mathematical phantoms. To test the sensitivity of this algorithm to the inaccuracy of representative energy value in energy values, a simulation study was performed with mathematical phantom. To represent a polychromatic x-ray energy spectrum with a single-energy, mean energy and equivalent energy were used, and the results were compared. The feasibility of the proposed method was experimentally tested with two different micro-CTs and a test phantom made of polymethyl methacrylate (PMMA), water, and graphite. The dual-energy calculations were carried out with CT images of all possible energy pairs among 40, 50, 60, 70, and 80 kVp. The effective atomic number and the electron density values obtained from the proposed method were compared with theoretical values. The results showed that, except the errors in the effective atomic number of graphite, most of the errors were less than 10 % for both CT scanners, and for the combination of 60 kVp and 70 kVp, errors less than 6.0 % could be achieved with a Polaris 90 CT. The proposed method shows simplicity of calibration, demonstrating its practicality and feasibility for use with a general polychromatic CT.

• Archives of Plastic Surgery
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• 제49권1호
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• pp.121-126
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• 2022

Background Although they may not replace standard training methods that use surgical microscopes, smartphones equipped with high-resolution screens and high-definition cameras are an attractive alternative for practicing microsurgical skills. They are ubiquitous, simple to operate, and inexpensive. This study compared anastomoses of chicken femoral vessels using a smartphone camera versus a standard operative microscope. Methods Forty anastomoses of non-living chicken femoral vessels were divided into four groups. A resident and an experienced microsurgeon performed anastomoses of femoral chicken vessels with 8-0 and 10-0 sutures, using a smartphone camera and a surgical microscope. The time to complete the anastomosis and the number of anastomosis errors were compared using the Mann-Whitney U test. Results The time taken to perform an anastomosis by the experienced microsurgeon was significantly longer when using the smartphone (median: 32.5 minutes vs. 20 minutes, P<0.001). The resident completed the anastomoses with both types of equipment without a significant difference in the operative times. When using a smartphone, the operation times were not significantly different between the resident and the experienced microsurgeon (P=0.238). The resident showed non-significant differences in operation time and the number of errors when using a smartphone or an operative microscope (P=1.000 and P=0.065, respectively). Conclusions Microsurgical practice with non-living chicken femoral vessels can be performed with a smartphone, though it can take longer than with an operative microscope for experienced microsurgeons. The resident may also experience frustration and tend to make more anastomosis errors when using a smartphone versus an operative microscope.

• Smart Structures and Systems
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• 제15권3호
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• pp.717-733
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• 2015

Modal parameters of a structure are commonly used quantities for system identification and damage detection. With a limited number of studies on the statistics assessment of modal parameters, this paper presents procedures to properly account for the uncertainties present in the process of extracting modal parameters. Particularly, this paper focuses on how to deal with the measurement error in an ambient vibration test and the modeling error resulting from a modal parameter extraction process. A bootstrap approach is adopted, when an ensemble of a limited number of noised time-history response recordings is available. To estimate the modeling error associated with the extraction process, a model prediction expansion approach is adopted where the modeling error is considered as an "adjustment" to the prediction obtained from the extraction process. The proposed procedures can be further incorporated into the probabilistic analysis of applications where the modal parameters are used. This study considers the effects of the measurement and modeling errors and can provide guidance in allocating resources to improve the estimation accuracy of the modal data. As an illustration, the proposed procedures are applied to extract the modal data of a damaged beam, and the extracted modal data are used to detect potential damage locations using a damage detection method. It is shown that the variability in the modal parameters can be considered to be quite low due to the measurement and modeling errors; however, this low variability has a significant impact on the damage detection results for the studied beam.

• 한국축산식품학회지
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• 제21권2호
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• pp.163-168
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• 2001

This study was conducted to analyze the errors occurred between standard plate count(SPC) and Bactometer, Malthus, Bactoscan and to investigate correlation coefficient(r) between SPC and each equipments for the purpose of making new calibration curve. Correlation coefficients of three different types of equipments to SPC value were 0.71, 0.81, 0.84 respectively(n=287) and that of three types of equipments were 0.71∼0.82 relatively low. In raw milk, correlation coefficients of three types of equipments of SPC were in the range of 0.67∼0.73 below 3.0${\times}10^4$(CUF/ml) of bacterial number, and those between the three types of equipments were 0.68∼0.72. Between 3.0${\times}10^4$∼5.0${\times}10^5$(CFU/ml) of bacterial number, correlation coefficients of the three different types of equipments were 0.71∼0.81. and those between the three different types of equipments were 0.64∼0.77. Over 5.0${\times}10^5$(CFU/ml), correlation coefficient of the three types equipments were 0.66∼0.83 and those between them were 0.70∼0.85 respectively. The error of the three different types equipments to SPC value was significantly high, 37∼53% of them was under 50% of error range, and in case of raw milk less than 3.0${\times}10^4$ of bacterial number, 44∼67% of them showed over 100% of error.

• 한국측량학회지
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• 제5권2호
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• pp.37-46
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• 1987

단사진을 이용한 측량은 교통, 산업, 산림, 범죄수사 및 일상생활에서 많은 활용면이 있으므로 본 논문에서는 이와같은 단사진 측량방법중 공간후방교회법(Space Resection)을 이용하는 방법과 2차원 사영변환을 이용하는 방법으로 나누어 해석기법을 제시하였다. 또한 측량용 비측량용 사진기를 사용한 단사진의 정확도를 비교분석 하였으며, 정확도를 향상시킬 수 있는 최적의 상태를 알기 위하여 기준점 수 및 배치형태를 변화시키면서 좌표 및 길이의 오차에 대하여 분석하였다. 그 결과 초점거리가 긴 측량용사진기 Wild P31이나 중형사진기 ASAHI PENTAX 6$\times$7의 경우 기준점 수 및 배치형태가 오차에 미치는 영향이 작았으나 초점거리가 짧은 비측량용 사진기 NIKON FM2는 기준점수 및 배치형태가 오차에 미치는 영향이 컸다. 따라서 이러한 단점을 극복하고 오차가 수렴하기 위해서는 최소한 기준점수 6점 이상을 측량대상 지역에 고루 분포시키고 또한 측량대상물을 촬영축에 직각방향으로 배치하여야 한다는 것을 알 수 있었다.

• Journal of Positioning, Navigation, and Timing
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• 제12권4호
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• pp.423-430
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• 2023

One recent notable method for real-time elimination of ionospheric errors in geodetic applications is the Predicted Global Ionosphere Map (PGIM). This study analyzes the level of accuracy achievable when applying the PGIM provided by the Center for Orbit Determination of Europe (CODE) to the Korean Peninsula region. First, an examination of the types and lead times of PGIMs provided by the International GNSS Service (IGS) Analysis Center revealed that CODE's two-day prediction model, C2PG, is available approximately eight hours before midnight. This suggests higher real-time usability compared to the one-day prediction model, C1PG. When evaluating the accuracy of PGIM by assuming the final output of the Global Ionosphere Map (GIM) as a reference, it was found that on days with low solar activity, the error is within ~2 TECU, and on days with high solar activity, the error reaches ~3 TECU. A comparison of the errors introduced when using PGIM and three solar activity indices-Kp index, F10.7, and sunspot number-revealed that F10.7 exhibits a relatively high correlation coefficient compared to Kp-index and sunspot number, confirming the effectiveness of the prediction model.