• 응용통계연구
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• 제33권4호
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• pp.439-449
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• 2020

메타 분석은 여러 연구 결과들을 종합시켜주는 분석 방법 중 하나이다. 이 때 수집되는 연구 문헌들은 소규모 연구인 경우 통계적으로 유의한 결과를 보이는 연구가 출간될 확률이 높기 때문에, 선택 편향의 특수한 경우인 출판 편향이 종종 발생한다. 선택 편향을 보정하는 방법에는 조건부 가능도와 가중 추정 방정식이 있는데 이 방법들은 실제 얻기 힘든 정확한 선택 확률 모형을 필요로한다. 반면 쌍별 유사가능도 접근법은 선택 확률 모형을 정확히 알 수 없는 경우에도 선택 편향을 보정할 수 있는 방법으로 제안되었다. 본 논문은 메타분석에서 쌍별 유사가능도 접근법의 성능과 문제점을 수치적으로 연구한다.

• 영어어문교육
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• 제16권1호
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• pp.123-142
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• 2009

The present study used multi-faceted Rasch measurement to explore the characteristics and bias patterns of non-native raters when they scored L2 writing tasks. Three raters scored 254 writing tasks written by Korean university students on two topics adapted from the TOEFL Test of Written English (TWE). The written products were assessed using a five-category rating scale (Content, Organization, Language in Use, Grammar, and Mechanics). The raters only showed a difference in severity with regard to rating categories but not in task types. Overall, the raters scored Grammar most harshly and Organization most leniently. The results also indicated several bias patterns of ratings with regard to the rating categories and task types. In rater-task bias interactions, each rater showed recurring bias patterns in their rating between two writing tasks. Analysis of rater-category bias interaction showed that the three raters revealed biased patterns across all the rating categories though they were relatively consistent in their rating. The study has implications for the importance of rater training and task selection in L2 writing assessment.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 추계학술대회 논문집
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• pp.461-463
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• 1999

In this paper, we have systematically investigated the variation of electrical characteristics with back-gate bias of n-channel SOI MOSFET\\`s. When positive bias is applied back-gate surface is inverted and back channel current is increased. When negative bias is applied back-gate surface is accumulated but it does not affect to the electrical characteristics.

• Journal of Astronomy and Space Sciences
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• 제27권4호
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• pp.367-375
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• 2010

In this study, we compared the precipitable water vapor (PWV) data derived from the radiosonde observation data at Sokcho Observatory and the PWV data at Sokcho Global Positioning System (GPS) Observatory provided by Korea Astronomy and Space Science Institute, from 0000 UTC, June 1, 2007 to 1200 UTC, May 31, 2009, and analyzed the radiosonde bias between the day and the night. In the scatter diagram of the daytime and nighttime radiosonde PWV data and the GPS PWV data, dry bias was found in the daytime radiosonde observation as known in the previous study. In addition, for all the rainfall events, the tendency that the wet bias of the radiosonde PWV increased as the GPS PWV decreased and the dry bias of the radiosonde PWV increased as the GPS PWV increased was significantly less distinctive in nighttime than in daytime. The quantitative analysis of the bias and error of the radiosonde PWV data showed that the mean bias decreased in the second year, regardless of nighttime or daytime rainfall, and the non-rainfall root mean square error (RMSE) was similar to that of the previous studies, while the rainfall RMSE was larger to a certain extent.

• 한국안광학회지
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• 제9권2호
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• pp.291-299
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• 2004

ECR-PECVD 방법을 이용하여 ECR power, $CH_4/H_2$ 가스 혼합비와 유량, 증착시간을 고정 시켜놓고 기판 bias 전압을 변화 시켜가면서 유리 기판위에 DLC 박막을 제작하였다. Raman, FTIR 및 UV/Vis 스펙트럼을 측정하여 기판 bias 진압에 따른 이용 충돌이 박막의 특성 변화에 미치는 영향을 조사하였다. FTIR 분석결과로부터 기판 bias 전압을 증가시킬수록 이용충돌 현상이 두드러져 탄소와 결합하고 있던 수소원자들의 탈수소화 현상을 확인할 수 있었고, 박막의 두께는 bias 전압을 증가시킬수록 감소되었다. 그리고 Raman 스펙트럼으로부터 Gaussian curve fitting을 통하여 sp3/sp2의 결합수에 비례하는 D/G피크의 면적 강도비(ID/IG)는 기판 bias 전압을 증가시킬수록 증가하였다. 그리고 광 투과율은 증착시간을 길게 할수록, 기판 bias 전압을 크게할수록 감소하였으나, 박막의 밀도가 증가하고 더 매끄러운 DLC 박막이 형성되었다. 이 결과로부터 DLC 박막은 기판 bias 전압의 크기를 증가시킬수록 특성이 더 향상됨을 알 수 있었다.

• 한국진공학회지
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• 제9권4호
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• pp.328-334
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• 2000

ECR-PECVD 방법을 이용하여 ECR power, $CH_4/H_2$ 가스 혼합비와 유량, 증착시간을 고정시켜놓고 기판 bias 전압을 변화 시켜가면서 DLC 박막을 제작하였고, 제작된 박막의 두께, Raman과 FTIR 스펙트럼 그리고 미소경도 등을 측정 및 분석하여 기판 bias전압에 따른 이온충돌이 박막의 특성 변화에 미치는 영향을 조사하였다. FTIR 분석 결과로부터 기판 bias 전압을 증가시킬수록 이온충돌 현상이 두드러져 탄소와 결합하고 있던 수소원자들의 탈수소화 현상을 확인할 수 있었고, 박막의 두께는 bias 전압을 증가시킬수록 감소되었다. 그리고 Raman 스펙트럼으로부터 Gaussian curve fitting을 통하여 $sp^3$/$sp^2$의 결합수에 비례하는 D와 G peak의 면적 강도비(ID/IG)는 기판 bias 전압을 증가시킬수록 증가하였고, 또한 경도도 증가하였다. 이 결과로부터 본 연구에서 제작된 수소를 함유한 비정질 탄소 박막은 기판 bias 전압의 크기를 증가시킬수록 DLC 특성이 더 향상됨을 알 수 있었다.

• Journal of Astronomy and Space Sciences
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• 제29권3호
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• pp.295-303
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• 2012

In this study, we compared the precipitable water vapor (PWV) data derived from the radiosonde observation data at Sokcho Observatory and the PWV data at Sokcho Global Positioning System (GPS) Observatory provided by Korea Astronomy and Space Science Institute, for the years of 2006, 2008, 2010, and analyzed the radiosonde seasonal, diurnal bias according to radiosonde sensor types. In the scatter diagram of the daytime and nighttime radiosonde PWV data and the GPS PWV data, dry bias was found in the daytime radiosonde observation as known in the previous study. Overall, the tendency that the wet bias of the radiosonde PWV increased as the GPS PWV decreased and the dry bias of the radiosonde PWV increased as the GPS PWV increased. The quantitative analysis of the bias and error of the radiosonde PWV data showed that the mean bias decreased in the nighttime except for 2006 winter, and in comparison for summer, RS92-SGP sensor showed the highest quality.

• 제어로봇시스템학회논문지
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• 제13권12호
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• pp.1243-1251
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• 2007

In this paper a study on the simplified observability analysis of GPS/INS is introduced. Errors for the position, velocity, attitude, gyro and accelerometer biases, and lever arm between GPS antenna and inertial sensors are considered in the observablity analysis. From the error dynamics model in which relatively small terms are neglected, simple observability conditions are obtained such that the observability of GPS/INS is determined by the test on the attutude, gyro bias, and lever arm. Unobservable errors for the position, velocity, and accelerometer bias are determined by those for the attitude, gyro bias, and lever arm. The simplified observability conditions are applied to a constant speed horizontal motion. It is shown that there are seven unobservable modes for the motion including the vertical component of gyro bias. The analytic observability analysis results are confirmed with a covariance simulation.

• Journal of Preventive Medicine and Public Health
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• 제55권5호
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• pp.424-427
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• 2022

A retrospective record-linkage study (RLS) based on medical records containing drug prescription histories involves immortal time bias (ITB). Thus, it is necessary to control for this bias in the research planning and analysis stages. Furthermore, a summary of a meta-analysis including RLSs that did not control for ITB showed that specific drugs had a preventive effect on the occurrence of the disease. Previous meta-analytic results of three systematic reviews evaluating the association between statin intake and gastric cancer risk showed that the summary hazard ratio (sHR) of the RLSs was lower than 1 and was statistically significant. We should consider the possibility of ITB in the sHR of RLSs and interpret the results carefully.

• 한국표면공학회지
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• 제29권2호
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• pp.93-99
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• 1996

In this work BN thin films were deposited on Si substrate by R. F. sputtering method at $200^{\circ}C$ and in Ar + $N_2$ mixed gas atmosphere. In order to investigate the effect of ion bombardment on substrate for c-BN bonding, substrate bias voltage was applied. The optimum substrate bias voltage for c-BN bonding was determined by FTIR analysis on specimens which were deposited with various bias voltages. Then BN thin film was deposited with this optimum condition and its phase, morphology, chemical composition, and refractive index were compared with those of BN film which was deposited without bias voltage. FTIR results showed that BN films deposited with substrate bias voltage were composed of mixed phases of c-BN and h-BN, while those deposited without bias voltage were h-BN only. When pure Ar gas was used for sputtering gas, BN films were delaminated easily from substrate in air, while when 10% $N_2$ gas was added to the sputtering gas, although c-BN specific infrared peak was reduced, delamination did not occur. GXRD and TEM results showed that BN films were amorphous phases regardless of substrate bias voltage, and AES results showed that the chemical compositions of B/N were about 1.7~1.8. The refractive index of BN film deposited with bias voltage was higher than that without bias voltage. The reason is believed to be the existence of c-BN bonding in BN film and the higher density of film that deposited with the substrate bias voltage.