• Journal of the Optical Society of Korea
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• 제16권3호
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• pp.228-235
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• 2012

It is very important to analyze effectively the tolerance of an optical system with high resolution as the projection lens of photolithography or as the objective lens of a microscope. We would like to find an effective assembly structure and compensators to correct aberrations through global wavefront sensitivity analysis using Zernike polynomial expansion from the field and pupil coordinates rather than from only pupil coordinates. In this paper, we introduce global wavefront coefficients by small perturbations of the optical system, and analyze the optical performance with these coefficients. From this analysis, it is possible to see how we can enlarge the tolerance through the proper assembly structure and compensators.

• 한국위성정보통신학회논문지
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• 제1권2호
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• pp.32-37
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• 2006

한국전자통신연구원은 2008년 말에 발사될 예정인 통신해양위성에 탑재될 Ka대역 안테나서브시스템을 개발하고 있다. Ka대역 통신용 안테나 서브시스템은 위성체의 동,서 판넬에 각각 하나씩 구성되어 있다. 이를 추진하기 위하여 한국전자통신연구원은 현제 대한항공(주)과 공동으로 통신위성 안테나 서브시스템을 설계하고 있다. 본 논문은 이득 변화 등과 같은 안테나 서브시스템 성능 규격을 검증하기 위하여 Ka 대역 반사판 포인팅 에러분석에 대하여 기술한다. 수행된 분석은 열변형에 의한 반사판 표면 변형 데이터 이며 이를 Ticra로 빔패턴의 변화를 확인하였다.

• Journal of Positioning, Navigation, and Timing
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• 제8권3호
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• pp.95-105
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• 2019

A method that applies space-time adaptive signal processing (STAP) algorithm based on an array antenna consisting of multiple antenna elements has been known to be effective to remove wide-band jamming signals in GPS receivers. However, the occurrence of phase distortion in navigation signals has been a problem when navigation signals, from which jamming signals are removed using STAP, are supplied to global positioning system (GPS) receivers. This paper verified the navigation performance degradation as a result of phase distortion. To mitigate this phenomenon, this paper proposes a mode switching scheme, in which a bypass mode is adopted to make the best use of the tracking performance of receivers without performing signal processing when jamming signals are not present or weak, and a STAP mode is employed when jamming signals exceed the threshold value. In this paper, the mode switching scheme is proposed for two environments: when receivers are stationary, and when receivers are moving. This paper confirmed that the performance of position error improved because phase distortion could be excluded due to STAP if the bypass mode was adopted under a condition where the jamming signal power level was below the threshold value in an environment where receivers were stationary. However, this paper also observed that the navigation failed due to the instability of tracking performance of receivers due to phase distortion that occurred at the switching time, although the number of switching could be reduced dramatically by proposing a dual threshold scheme of on- and off-thresholds that switched a mode due to the array antenna characteristics of varying gains according to the jamming signal incident direction in an environment where receivers were moving. The analysis results verified that running the STAP algorithm at all times is more efficient than the mode switching, in terms of maintaining stable navigation and ensuring position error performance, to remove jamming signals in an environment where receivers were moving.

• 한국컴퓨터정보학회논문지
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• 제20권3호
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• pp.57-67
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• 2015

본 논문에서는 적외선 영상에서 탐지된 표적의 픽셀정보를 이용하여 실제 환경에서의 표적의 위치를 추정하는 geolocation 기법에 대하여 제안한다. 제안하는 기법은 지대지 전장 환경에서 공중 정찰을 통한 적대 표적의 위치를 파악하는 시스템에 적용이 가능하다. 적대 표적의 geolocation에 영향을 주는 요소는, 시스템의 광학적 왜곡, 지형적 왜곡, 정찰 모듈의 GPS(Global Positioning System) 및 IMU(Inertial Measurement Unit) 왜곡을 들 수 있다. 본 논문에서는 광학적 왜곡과 지형적 왜곡에 적응적인 geolocation 을 위하여 광학 정보의 다항식 최적화와 지구 곡률을 고려한 시선거리 계산 기법을 적용하였으며, 3차원 모의 환경에서 실험한 결과 시스템 요구사항 내에서 geolocation의 정확도를 만족함을 확인하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.834-839
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• 2007

This paper investigates the distortion of magnetic field of a brushless DC (BLDC) motor due to deformed rubber magnet. Global or local deformation of rubber magnet in the BLDC motor is mathematically modeled by using the Fourier series. Distorted magnetic field is calculated by using the finite element method, and unbalanced magnetic force are calculated by using the Maxwell stress tensor. The first harmonic deformation in the global deformation of rubber magnet generates the first harmonic driving frequency of the unbalanced magnetic force, and the rest harmonic deformations of rubber magnet except the harmonic deformation with multiple of common divisor of pole and slot introduces the driving frequencies with multiple of slot number ${\pm}1$ to the unbalanced magnetic force. However, the harmonic deformation with multiple of common divisor of pole and slot does not generate unbalanced magnetic force due to the rotational symmetry. When the rubber magnet is locally deformed, the unbalanced magnetic force has the first harmonic driving frequency and the driving frequencies with multiples of slot number ${\pm}1$.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제18권2호
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• pp.181-192
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• 2014

In this paper, we propose a robust real-time myocardial border tracking algorithm for echocardiography. Commonly, after an initial contour of LV border is traced at one or two frame from the entire cardiac cycle, LV contour tracking is performed over the remaining frames. Among a variety of tracking techniques, optical flow method is the most widely used for motion estimation of moving objects. However, when echocardiography data is heavily corrupted in some local regions, the errors bring the tracking point out of the endocardial border, resulting in distorted LV contours. This shape distortion often occurs in practice since the data acquisition is affected by ultrasound artifacts, dropout or shadowing phenomena of cardiac walls. The proposed method deals with this shape distortion problem and reflects the motion realistic LV shape by applying global deformation modeled as affine transform partitively to the contour. We partition the tracking points on the contour into a few groups and determine each affine transform governing the motion of the partitioned contour points. To compute the coefficients of each affine transform, we use the least squares method with equality constraints that are given by the relationship between the coefficients and a few contour points showing good tracking results. Many real experiments show that the proposed method supports better performance than existing methods.

• Structural Engineering and Mechanics
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• 제21권3호
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• pp.275-293
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• 2005

When a thin-walled multicell box girder is subjected to an eccentric load, the distortion becomes an important global response in addition to flexure and torsion. The three global responses appear in a combined form when a conventional shell element is used thus it is not an easy task to examine the three global responses separately. This study is to propose an analysis method using conventional shell element in which the three global responses can be separately decomposed. The force decomposition method which was designed for a single-cell box girder by Nakai and Yoo is expanded herein to multicell box girders. The eccentric load is decomposed in the expanded method into flexural, torsional, and multimode distortional forces by using the force equilibrium. From the force decomposition, the combined global responses of multicell box girders can be resolved into separate responses and the distortional response which is of primary concern herein can be obtained separately. It is shown from a series of extensive comparative studies using three box girder bridge models that the expanded method produces accurate decomposed results. Noting that the separate consideration of individual global response is of paramount importance for optimized multicell box girder design, it can be said that the proposed expanded method is extremely useful for practicing engineers.

• 한국전자파학회:학술대회논문집
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• 한국전자파학회 2005년도 종합학술발표회 논문집 Vol.15 No.1
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• pp.111-114
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• 2005

The isolation performance of the S-band single-pole single-throw (SPST) monolithic microwave integrated circuit (MMIC) switch with two different RF-interconnection approaches, microstrip and grounded coplanar waveguide (GCPW) lines, are investigated. On-to-off isolation is improved by 5.8 dB with the GCPW design compared with the microstrip design and additional improvement of 6.9dB is obtained with the coplanar wire-bond interconnection (CWBI) at 3.4 GHz. The measured insertion loss and third-order inter-modulation distortion (IMD3) are less than 2.43 dB over 2.5 CHz $\sim$ 4 GHz and greater than 64 dBc.

• International Journal of CAD/CAM
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• 제6권1호
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• pp.89-97
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• 2006

This paper presents a novel approach for non-iterative surface smoothing with feature preservation on arbitrary meshes. Laplacian operator is performed in a global way over the mesh. The surface smoothing is formulated as a quadratic optimization problem, which is easily solved by a sparse linear system. The cost function to be optimized penalizes deviations from the global Laplacian operator while maintaining the overall shape of the original mesh. The features of the original mesh can be preserved by adding feature constraints and barycenter constraints in the system. Our approach is simple and fast, and does not cause surface shrinkage and distortion. Many experimental results are presented to show the applicability and flexibility of the approach.

• International Journal of Advanced Culture Technology
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• 제10권3호
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• pp.272-280
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• 2022

During last few years, pandemic of COVID-19 has been a global issue. Under the COVID-19, global events have been restricted or canceled to secure public hygiene and safety. Since one of the largest global events is Olympic Games, we selected recent Olympic Games as our case of analysis. Tokyo Olympic Games (TOG) was held in 2021, but it encountered a millennium disaster, the pandemic of COVID-19. In such a special period, it is of great significance to explore the emotional tendency of global views before and TOG via artificial intelligence. This paper vastly collects the TOG comment data of mainstream websites in South Korea, China, and the United States by implementing crawler program for sentiment analysis (SA). And we use a variety of sentiment analysis models to compare the accuracy of the experimental results, to obtain more reliable SA results. In addition, in the prediction results, to reduce the distortion of opinion by a minority, we introduce an algorithm called "Removing Biased Minority Opinions (RBMO)" and provide how to apply this method to the interpretation domain. Through our method, more authoritative SA results were obtained, which in turn provided a basis for predicting the sentiment tendency of countries around the world in TOG during the COVID-19 epidemic.