• Proceedings of the Korean Society of Computer Information Conference
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• 2011.01a
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• pp.85-88
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• 2011

Fuzzy C-Means (FCM) 알고리듬은 가장 널리 사용되는 군집화 알고리듬 중 하나로 다양한 응용 분야에서 사용되고 있다. 하지만 FCM은 여러 가지 문제점을 가지고 있으며 초기 원형 설정이 그 중 하나이다. FCM은 국부 최적해에 수렴하므로 초기 원형 설정에 따라 클러스터링 결과가 달라진다. 이 논문에서는 이러한 FCM의 초기 원형 설정 문제를 개선하기 위하여 커널밀도 추정 (kernel density estimation) 기법을 활용하는 방법을 제안한다. 제안한 방법에서는 먼저 커널 밀도 추정을 수행한 후 밀도가 높은 지역에 클러스터의 초기 원형을 설정하고 원형이 설정된 영역의 밀도를 감소시키는 과정을 반복함으로써 효율적으로 초기 원형을 설정할 수 있다. 제안된 방법이 일반적으로 사용되는 무작위 초기화 방법에 비해 효율적이라는 사실은 실험결과를 통해 확인할 수 있다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.8
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• pp.1659-1664
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• 2011

Fuzzy C-Means (FCM) is one of the most widely used clustering algorithms and has been used in many applications successfully. However, FCM has some shortcomings and initial prototype selection is one of them. As FCM is only guaranteed to converge on a local optimum, different initial prototype results in different clustering. Therefore, much care should be given to the selection of initial prototype. In this paper, a new initialization method for FCM using kernel density estimation (KDE) is proposed to resolve the initialization problem. KDE can be used to estimate non-parametric data distribution and is useful in estimating local density. After KDE, in the proposed method, one initial point is placed at the most dense region and the density of that region is reduced. By iterating the process, initial prototype can be obtained. The initial prototype such obtained showed better result than the randomly selected one commonly used in FCM, which was demonstrated by experimental results.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.4
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• pp.512-519
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• 2012

This paper proposes a 3-D pose (positions and orientations) estimation system based on the recognition of circular ring patterns. To deal with monocular vision-based pose estimation problem, we specially design a circular ring pattern that has a simplicity merit in view of object recognition. A pose estimation procedure is described in detail, which utilizes the geometric transformation of a circular ring pattern in 2-D perspective projection space. The proposed method is evaluated through the analysis of accuracy and precision with respect to 3-D pose estimation of a quadrotor-type vehicle in 3-D space.

• The Korean Journal of Applied Statistics
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• v.24 no.3
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• pp.547-557
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• 2011

In this paper we developed a statistical model for traffic volume data which collected from a spot of specific local state road. One peculiar property of daily traffic data is that it has bimodal shape which have two peaks on times of both going to office and coming back to home. So, various mixture models of circular distribution are suggested for bimodal traffic data and EM algorithms are applied to estimate the parameters of the suggested models. To compare the accuracy of the suggested models, classical regressions with dummy variables are also considered. The suggested models for traffic volumn data can be effectively used to estimate missing values due to measuring instrument disorder.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.48 no.5
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• pp.13-24
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• 2011

This paper deals with a 3D-pose (orientation and position) estimation problem of a circular object in 3D-space. Circular features can be found with many objects in real world, and provide crucial cues in vision-based object recognition and location. In general, as a circular feature in 3D space is perspectively projected when imaged by a camera, it is difficult to recover fully three-dimensional orientation and position parameters from the projected curve information. This paper therefore proposes a 3D pose estimation method of a circular feature using a coplanar point. We first interpret a circular feature with a coplanar point in both the projective space and 3D space. A procedure for estimating 3D orientation/position parameters is then described. The proposed method is verified by a numerical example, and evaluated by a series of experiments for analyzing accuracy and sensitivity.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.4
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• pp.643-650
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• 2020

The phased array antenna has an advantage enabling rapid beam aim without the mechanical rotation of the antenna, because it arranges multiple elements in a linear or planer (grid or circular) and electronically controls the phase for each element. The planar array antenna is generally used a grid array and a circular array, and the circular form has the higher resolution comparing to the grid form due to the its structural characteristics. However, a concentric circular array (CCA) or a concentric ring array (CRA) with multiple circular arrays which each has different radius is used in the limited area, because the entire radius should be increased for the circular array with a number of elements. In this paper, we introduce the angle-of-arrival (AOA) estimator for an adaptive beamforming satellite system based on CRA and provide the simulation results for performance evaluation. In addition, simulation results are compared and analyzed to the case for the circular array antenna.

• Journal of Advanced Navigation Technology
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• v.10 no.4
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• pp.385-393
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• 2006

In this paper, we proposed a location estimation algorithm considering an extension of searching area in 2.45GHz band RTLS and analyzed its performance in terms of an average estimation error distance. The extendable searching area was assumed to be square of $300m{\times}300m$ and 2 dimensions. The arrangement shape of available readers was considered circle, rectangle, and shrinkage rectangle for extendable searching area. Also, we assumed that propagation path was LOS (Line-Of-Sight) environment, and analyzed the estimation error performance as a function of the number of received sub-blink considering an arrangement shape of available readers in searching area. From the results, compared with rectangle shape, circle shape showed the higher estimation accuracy. Also, we confirmed that the proposed location estimation algorithm provided high estimation accuracy in the shrinkage rectangle shape that was suitable for extension of searching area.

• Journal of Plant Biology
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• v.37 no.2
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• pp.183-193
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• 1994

인삼(Panax ginseng C.A. Meyer)의 뇌두 캘러스로부터 분리한 원형질체와 배양된 원형질체의 미세구조 변화와 원형질막 표면을 투과 및 주사전자현미경으로 조사하였다. 분리 직후의 원형질체에서는 캘러스세포에서보다 작은 액포들이 많이 형성되어 있었다. 또한 활면소포체의 수가 증가하였으며 이들은 원형질막과 평행으로 배열하였다. 활면소포체는 가끔 세포질을 둘러싸서 세포질분리체(cytosegresome)를 형성하였고, 이 구조는 세포질을 분해시킨 후 액포로 변화하기도 하였다. 배양된 원형질체에서는 분리 직후의 원형질체와 비교하여 조면소포체, 딕티오좀, 리보좀, 미토콘드리아, proplastid 및 액포 등의 수가 현저하게 증가하였다. 딕티오좀으로부터 많은 소낭들이 형성되었고 이들은 세포질 전반에 걸쳐 존재하였다. 때로는 소낭들이 원형질막 바깥으로 돌출되어 돌기를 형성하기도 하였다. 배양된 원형질체의 표면에는 섬유소로 구성되어 있을 것으로 추정되는 섬유상 구조들이 형성되어 있었다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.2
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• pp.395-400
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• 2008

This paper relates to the performance analysis of DoA estimation algorithm in 2-dimensional circular array antenna for the receiving of GPS signal which is used for the performance improvement by elimination of jammer signal. By performing the spatial filtering after the DoA estimation in array antenna, the quality of receiving signal can improve by the nulling of jammer signal from the undesired direction and the forming of beam from the desired direction. In this paper, the MUSIC and MinNorm algorithm used for DoA estimation were applied after fixing the angle and power of jammer signal in 4 element and 7 element circular array antenna. In order to performance analysis, the estimation result and estimation error were computed by computer simulation. As a result, the MUSIC and MinNorm were fairly good in azimuth and elevation angle estimation of DoA in case of good signal to noise ratio and the MUSIC has better performance compared to MinNorm in case of poor signal to noise ratio.

• Journal of the Korean Data and Information Science Society
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• v.21 no.2
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• pp.241-250
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• 2010

Over the past few decades, several studies have been made on the modeling of circular data. But these studies focused mainly on the symmetrical cases including von Mises distribution. Recently, many studies with skew-normal distribution have been conducted in the linear case. In this paper, we dealt the problem of fitting of non-symmetrical circular data with wrapped skew-normal distribution which can be derived by using the principle of wrapping. Wrapped skew-normal distribution is very flexible to asymmetical data as well as to symmetrical data. Multi-modal data are also fitted by using the mixture of wrapped skew-normal distributions. To estimate the parameters of mixture, we suggested the EM algorithm. Finally we verified the accuracy of the suggested algorithm through simulation studies. Application with real data is also considered.