• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2009년도 춘계학술대회 논문집
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• pp.1027-1028
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• 2009

• Journal of Mechanical Science and Technology
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• 제19권6호
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• pp.1253-1267
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• 2005

Misalignment can be an important problem in the integration of GPS/INS. Observability analysis of the alignment errors in the integration of low-grade inertial sensors and multi-antenna GPS is presented in this paper. A control-theoretic approach is adopted to study the observability of time-varying error dynamics models. The relationship between vehicle motions and the observability of the errors in the lever arm and relative attitude between GPS antenna array and IMU is given. It is shown that alignment errors can be made observable through maneuvering. The change of acceleration makes the components of the relative attitude error that are orthogonal to the direction of the acceleration change observable. The change of angular velocity makes the components of the lever arm error that are orthogonal to the direction of the angular velocity observable. The motion of constant angular velocity has no influence on the estimation of the lever arm.

• Journal of the Korean Data and Information Science Society
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• 제10권1호
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• pp.193-198
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• 1999

The estimation of parameters in regression models with multiplicative errors is usually based on the gamma or log-normal likelihoods. Under reciprocal misspecification, we compare the small sample efficiencies of two sets of estimators via a Monte Carlo study. We further consider the case where the errors are a random sample from a Weibull distribution. We compute the asymptotic relative efficiency of quasi-likelihood estimators on the original scale to least squares estimators on the log-transformed scale and perform a Monte Carlo study to compare the small sample performances of quasi-likelihood and least squares estimators.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2001년도 춘계학술대회 논문집(한국공작기계학회)
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• pp.9-14
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• 2001

A new model utilizing a transfer function is introduced in the present paper for analizing motion errors of hydrostatic tables. Relationship between film reaction force in a single hydrostatic pad and form error of a guide rail is derived at various spacial frequencies by finite element analysis, and it is expressed as a transfer function. This transfer function clarifies so called averaging effect of the oil film quantitively. For example, it is found that the amplitide of the film reaction force is reduced as the spacial frequency increases or relative width of the pocket is reduced. Motion errors of a multiple pad table is estimated from transfer function, geometric relationship between each pads and form errors of a guide rail, which is named as Transfer Function Method. Calculated motion errors by TFM show good agreement with motion errors calculated by Multi Pad Method, which is considered entire table as an analysis object. From the results, it is confirmed that the proposed TFM is very effective to analyze the motion errors of hydrostatic tables.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2005년도 추계학술대회 논문집
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• pp.418-423
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• 2005

In designing underground structure such as tunnels, estimating geotechnical characteristics of the ground is one of the most important and difficult tasks. In this paper, a methodology that can identify geotechnical parameters using only field-measured relative convergence displacements is presented. By using only relative convergence measurement data, inevitable errors in absolute convergence estimation can be avoided and in turn the parameter estimation process can be simplified. The methodology utilizes sensitivity relationship between static displacement measurements and geotechnical parameters. The feasibility and applicability of the proposed methodology is verified via a 3-d numerical example of a tunnel structure.

• 한국대기환경학회지
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• 제22권3호
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• pp.271-285
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• 2006

A two-dimensional photochemical transport model (2D PTM) is simulated to describe the transport and chemical reaction of ozone related to aerosols in the troposphere and stratosphere. The vertical profiles and total amounts of ozone, which are advected by both residual Eulerian circulation and the adiabatic circulation under certain circumstance, have been compared with the observation data such as ozonesondes, Brewer spectrometer, the Upper Atmosphere Research Satellite (UARS), and the Total Ozone Mapping Spectrophotometer (TOMS). As a result, we find that the observed distribution of ozone Is adequately reproduced in the model at middle and high latitude in the Northern Hemisphere as well as at Phang ($36^{\circ}\;02'N,\;129^{\circ}\;23'E$) in South Korea. In particular, the 2D PTM is well simulated in the ozone decrease due to the Pinatubo volcanic eruption in 1991. However, ozone mixing ratio are more underestimated than those of UARS and ozonesondes, because are very sensitive to the latitude of transport across the tropopause associated with both Rummukainen errors and off-line model. Relative mean bias errors and relative root mean square errors of ozone calculations using the 2D PTM are shown within${\pm}10%$, respectively.

• 한국정밀공학회지
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• 제18권4호
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• pp.97-103
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• 2001

Accuracy of a machined part is determined by the relative motion between the cutting tool and the workpiece. One of the important factors which affects the relative motion is the geometric errors of a machine tool. In this study, firstly, geometric errors are measured by laser interferometer, and the positioning error of each control point selected uniformly on the control surface CAD model can be estimated from th oirm shaping model and geometric error data base. Where a form shaping function is derived from the link of homogeneous transformation matrix. Secondly, control points are shifted to the estimated amount of positioning errors. A new control surface is modeled with NURBS(Non Uniform Rational B-Spline) surface approximation to the shifted control points. By generating tool paths to the redesigned control surface, we reduce the machining error quite.

• 대한기계학회논문집A
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• 제20권5호
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• pp.1508-1515
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• 1996

The method of utilizing sensitivity linkages for the analysis of mechanical errors are proposed. As sources of the mechanical error, tolerances in the link length and clearances in thejoints are considered. It is demonstrated that the problem of calculating mechanical errors of a 4-bar mechanism can be transformed into a problem of conventeional velocity analysis of a sensitivity linkage. As a result of the present study, it is found and proved that the mechanical error of the output angle in the 4-Bar mechaism is represented as a simple harmonic function with respect to the relative position of the pin on the clearance circle. Also the vector representing the mechanical error of a coupler point makes, in general, an ellipse as the relative angle varies on the clearance circle. With these results we can better identify the characteristic of the mechanical errors in linkages.

• 응용통계연구
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• 제16권1호
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• pp.1-14
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• 2003

본 연구에서는 현행 경제활동인구조사 체계에 근거하여 대영역 내의 시군구 단위 행정자치구역들에 대한 실업통계들을 생산할 수 있는 소지역 추정법이 제안된다. 고려된 소지역 추정량들은 합성 추정량, 복합추정량과 같은 설계기반 간접 추정량들이며 이러한 추정량들에 대한 평균제곱오차 추정식이 경제활동인구조사 체계 하에서 산정되어 시군구 단위 소지역 추정값들에 대한 정확도의 측도로써 활용된다. 2000년 12월 충북지역의 경제활동인구조사 자료로부터 이 지역 내의 10개 시군구 단위 행정자치구역들에 대한 실업자 총계 및 잭나이프 평균제곱오차가 본 연구에서 제시된 추정절차에 의해 추정된다. 시군구 단위 실업자 총계 추정값들의 신뢰성은 이들 추정값들의 상대편향(Relative Bias)과 상대오차제곱근(Relative Root Mean Square Error)에 의해 평가된다. 현행 한국 경제활동인구조사체계 하에서 복합추정량이 다른 추정량들에 비해 매우 안정적임을 밝힌다.

• 한국안광학회지
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• 제12권3호
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• pp.1-5
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• 2007

본 연구는 한국안광학회지 11권 2호 p. 121-129(2006)년에 게재된 [경기도 일부지역의 성별, 연령별 굴절이상 분포에 관한 연구] 논문의 후속 연구로서, 기존 논문에서는 굴절이상안에서 일반적으로 나타나는 경도근시와 원시 그리고 난시의 연령별 분포를 보았으며, 당해 연구에서는 그에 따른 굴절력의 변화와 굴절이상의 상대 위험도를 평가하였다. 연구결과 굴절력은 40세전후로 굴절력의 변화가 생겨 약 46세부터는 급격히 굴절력이 감소함으로써 50대에 이르러 (+)굴절력으로 변하는 것을 볼 수 있었다. 근시의 상대위험도는 젊은 연령대에서 Odds 값이 증가하나 46세 이후로는 오히려 Odds 값이 감소하는 것으로 나타났다. 이와 반대로 원시의 경우는 나이가 들수록 그 위험도가 떨어지다가 36세부터 그 위험도가 0.24(95% CI: 0.07-0.88)로 증가할 수 있는 것으로 나타났다. 즉 노안이 진행되는 연령이 40세 이전으로 좀 더 빨라질 수 있다는 결과가 나왔다.