• Journal of Positioning, Navigation, and Timing
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• 제6권3호
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• pp.105-116
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• 2017

Several wireless localization algorithms are evaluated for the IR-UWB-based indoor location with the assumption that the ranging measurements contain the channelwise Non-Calibration Error (NCE). The localization algorithms can be divided into the Model-free Localization (MfL) methods and Model-based Kalman Filtering (MbKF). The algorithms covered in this paper include Iterative Least Squares (ILS), Direct Solution (DS), Difference of Squared Ranging Measurements (DSRM), and ILS-Common (ILS-C) methods for the MfL methods, and Extended Kalman Filter (EKF), EKF-Each Channel (EKF-EC), EKF-C, Cubature Kalman Filter (CKF), and CKF-C for the MbKF. Experimental results show that the DSRM method has better accuracy than the other MfL methods. Also, it demands smallest computation time. On the other hand, the EKF-C and CKF-C require some more computation time than the DSRM method. The accuracy of the EKF-C and CKF-C is, however, best among the 9 methods. When comparing the EKF-C and CKF-C, the CKF-C can be easily used. Finally, it is concluded that the CKF-C can be widely used because of its ease of use as well as it accuracy.

• Coupled systems mechanics
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• 제7권5호
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• pp.583-610
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• 2018

This paper discusses the issues associated with modeling frictional contact between solid bodies undergoing large deformations. The most common model for friction on contact interfaces in solid mechanics is the Coulomb friction model, in which two distinct responses are possible: stick and slip. Handling the transition between these two phases computationally has been a source of algorithmic instability, lack of convergence and non-unique solutions, particularly in the presence of large deformations. Most computational models for frictional contact have used penalty or updated Lagrangian approaches to enforce frictional contact conditions. These two approaches, however, present some computational challenges due to conditioning issues in penalty-type implementations and the iterative nature of the updated Lagrangian formulation, which, particularly in large simulations, may lead to relatively slow convergence. Alternatively, a plasticity-inspired implementation of frictional contact has been shown to handle the stick-slip conditions in a local, algorithmically efficient manner that substantially reduces computational cost and successfully avoids the issues of instability and lack of convergence often reported with other methods (Laursen and Simo 1993). The formulation of this approach, however, has been limited to the small deformations realm, a fact that severely limited its application to contact problems where large deformations are expected. In this paper, we present an algorithmically consistent formulation of this method that preserves its key advantages, while extending its application to the realm of large-deformation contact problems. We show that the method produces results similar to the augmented Lagrangian formulation at a reduced computational cost.

• 한국멀티미디어학회논문지
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• 제7권3호
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• pp.319-326
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• 2004

본 논문에서는 물체의 경계선을 고려한 칼라 영상 분할 방법을 제안한다. 제안 방법은 먼저 원영상을 벡터 양자화한 후 양자화된 영상의 인덱스 맵을 이용하여 초기 영역을 설정하였다. 그 후 HSI컬러 공간을 이용한 영역 병합에서 물체의 경계선을 고려하기 위해 경계선 제한 성분을 적용하여 영역들을 병합하였다. 또한 RGB 컬러 공간을 이용하여 HSI 컬러 공간에서 병합되지 않은 영역들을 병합하였다. 그리 고 영역병합 알고리즘을 통해 반복적인 처리를 감소시킴으로써 처리 시간을 줄였다. 실험 결과에서는 다양한 영상에 대해 주요 영역들의 분할 결과 및 처리소요시간에서 우수한 성능을 보였다.

• 방사성폐기물학회지
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• 제10권4호
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• pp.237-246
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• 2012

본 연구에서는 콜로이드와 핵종의 복합이동에 관한 수치모델을 개발하였다. 콜로이드와 핵종의 반응-이동 지배방정식을 풀기 위하여 Operator Splitting Method 중 Strang의 분리 SNI 방식을 수치해석 방법으로 채택하였고 이는 MATLAB을 이용하여 코드화 되었다. 개발된 수치모델은 용질의 이동 및 분산만을 고려한 해석해를 통한 검증과정에서 피어슨 상관계수의 제곱값($r^2$)이 0.99 이상으로 나타나 모델의 정확성이 입증되었다.

• Journal of Positioning, Navigation, and Timing
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• 제5권1호
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• pp.1-9
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• 2016

Range-based wireless localization system must measure accurate range between a mobile node (MN) and reference nodes. However, non-line-of-sight (NLOS) error caused by the spatial structures disturbs the localization system obtaining the accurate range measurements. Localization methods using the range measurements including NLOS error yield large localization error. But filter-based localization methods can provide comparatively accurate location solution. Motivated by the accuracy of the filter-based localization method, a filter residual-based NLOS error estimation method is presented in this paper. Range measurement-based residual contains NLOS error. By considering this factor with NLOS error properties, NLOS error is mitigated. Also a process noise covariance matrix tuning method is presented to reduce the time-delay estimation error caused by the single dynamic model-based filter when the speed or moving direction of a MN changes, that is the used dynamic model is not fit the current dynamic of a MN. The presented methods are evaluated by simulation allowing direct comparison between different localization methods. The simulation results show that the presented filter is more accurate than the iterative least squares- and extended Kalman filter-based localization methods.

• Structural Engineering and Mechanics
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• 제11권1호
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• pp.71-87
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• 2001

A frequency domain response analysis is presented for building frames passively controlled by viscoelastic dampers, under harmonic ground excitation. Three different models are used to represent the linear dynamic force-deformation characteristics of viscoelastic dampers namely, Kelvin model, Linear hysteretic model and Maxwell model. The frequency domain solution is obtained by (i) an iterative pseudo-force method, which uses undamped mode shapes and frequencies of the system, (ii) an approximate modal strain energy method, which uses an equivalent modal damping of the system in each mode of vibration, and (iii) an exact method which uses complex frequency response function of the system. The responses obtained by three different methods are compared for different combinations of viscoelastic dampers giving rise to both classically and non-classically damped cases. In addition, the effect of the modelling of viscoelastic dampers on the response is investigated for a certain frequency range of interest. The results of the study are useful in appropriate modelling of viscoelastic dampers and in understanding the implication of using modal analysis procedure for building frames which are passively controlled by viscoelastic dampers against base excitation.

• 한국통신학회논문지
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• 제18권8호
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• pp.1226-1237
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• 1993

제한된 주파수 대역폭을 이용하여 신호를 전송하기 위해서는 여러종류의 특성을 갖는 필터들이 필요하다. 이 논문에서는 이러한 필터들을 효율적으로 설계하기위한 두가지 방식을 제시하였다. 특히 fractionally-spaced(FS) 구조가 사용될때 더욱 효율적으로 필터를 설계할 수 있다. FS 구조의 특성을 최소자승 오차 방식과 결합하여, 출력오차에 영향을 주지않고, 적절한 주파수 특성을 갖는 SF 필터 설계 방식을 제시하였다. 예로, noise 신호들을 적절히 이용하면, 한개의 SF 필터가, QAM 복조에 필요한 phase splitter, 수신 필터 그리고 등화기 기능까지 갖도록 설계할 수 있다. 두번째로 임의의 주파수 특성이 요구되는 필터의 설계 방식을 제시하였다. weighting factor를 이용한 최소자숭법을 iterative하게 사용하여 최적설계를 얻는다. 이를위해 weighting factor를 효율적으로 update하기 위한 새로운 알고리듬을 이용하였다. 마지막으로, 더욱 복잡한 조건을 갖는 필터를, 이 두가지 방식을 같이 이용하여, 효율적으로 설계할 수 있는것을 보였다.

• 한국조사연구학회:학술대회논문집
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• 한국조사연구학회 2002년도 춘계학술대회 발표논문집
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• pp.8-34
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• 2002

이 연구의 주된 목적은 외국의 교육 및 심리검사를 번안하여 사용하는 경우, 번안된 검사와 原 검사간의 평형성 (equivalence)을 경험적으로 측정하기 위하여 차별문항기능기법을 응용하는 것이다. 즉, 평형성이라는 것은 타당한 그룹비교를 위한 하나의 전제조건으로서 이런 평형성이 확립되지 않은 채 번안된 검사들의 무분별한 사용은 바람직하지 않다. 서로 다른 접근법을 가지고 있는 두 개의 차별문항기능기법, 로지스틱 판별분석과 SIBTEST가 상호보완적인 목적으로 이용되었고, 최선의 대응변수를 모색하려는 시도로서 다변량 대응기법과 순환적인 정화기법이 사용되었다. 5개의 하위척도를 가진 외향성 척도 중 3개의 척도에서는 적은 수의 차별기능문항을 발견하였으나, 나머지 2개의 척도에서는 반 이상의 문항에서 차별기능을 추출하였다 마지막으로, 대응변수의 선택에 대한 문제들이 논의되고 있다.

• Advances in materials Research
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• 제8권4호
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• pp.337-359
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• 2019

Shape Memory Polymer Composites (SMPC) have gained popularity over the last few decades due to its flexible shape memory behaviour over wide range of strains and temperatures. In this paper, non-linear bending analysis has been carried out for SMPC beam under the application of uniformly distributed transverse load (UDL). Simplified C⁰ continuity Finite Element Method (FEM) based on Higher Order Shear Deformation Theory (HSDT) has been adopted for flexural analysis of SMPC. The numerical solutions are obtained by iterative Newton Raphson method. Material properties of SMPC with Shape Memory Polymer (SMP) as matrix and carbon fibre as reinforcements, have been calculated by theory of volume averaging. Effect of temperature on SMPC has been evaluated for numerous parameters for instance number of layers, aspect ratio, boundary conditions, volume fraction of carbon fiber and laminate stacking orientation. Moreover, deflection profile over unit length and behavior of stresses across thickness are also presented to elaborate the effect of glass transition temperature (T_g). Present study provides detailed explanation on effect of different parameters on the bending of SMPC beam for large strain over a broad span of temperature from 273-373K, which encompasses glass transition region of SMPC.

• Journal of Radiation Protection and Research
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• 제45권1호
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• pp.35-44
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• 2020

Background: Cadmium zinc telluride (CZT) is a promising material because of a high detection efficiency, good energy resolution, and operability at room temperature. However, the cost of CZT dramatically increases as its size increases. In this study, to achieve a large effective volume with relatively low cost, an array structure comprised of individual virtual Frisch-grid CZT detectors was proposed. Materials and Methods: The prototype consisted of 2 × 2 CZTs, a holder, anode and cathode printed circuit boards (PCBs), and an application-specific integrated circuit (ASIC). CZTs were used and the non-contacting shielding electrode method was applied for virtual Frisch-grid effect. An ASIC was used, and the holder and the PCBs were fabricated. In the current system, because the CZTs formed a common cathode, a total of 5 channels were assigned for data processing. Results and Discussion: An experiment using ¹³⁷Cs at room temperature was conducted for 10 minutes. Energy and timing information was acquired and the depth of interaction was calculated by the timing difference between the signals of both electrodes. Based on obtained three-dimensional position information, the energy correction was carried out, and as a result the energy spectra showed the improvements. In addition, a Compton image was reconstructed using the iterative method. Conclusion: The virtual Frisch-grid CZT detector based on the array structure was developed and the energy spectra and the Compton image were successfully acquired.