• The Journal of the Korea institute of electronic communication sciences
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• 제15권1호
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• pp.79-84
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• 2020

Wireless power transfer is more convenient than wired power transfer, but has a shorter transfer distance and lower efficiency. In addition, it is difficult to charge multiple devices simultaneously. In this paper, we propose a method of magnetic beam forming by using multiple transmitters in order to increase transfer distance and improve efficiency of wireless power transfer. To do this, the relationship between the transmitter coil current and magnetic field at the center of receiver coil is modelled, and calculate the optimal transmitter coil current using the characteristics of the pseudoinverse. Finally, the validity of the proposed method is verified by simulation.

• Korean Journal of Optics and Photonics
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• 제5권2호
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• pp.298-303
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• 1994

Microlens arrays are fabricated by melting "islands" of thick photoresist on a glass substrate. Microlenses with diameters $25\mu\textrm{m}$, $50\mu\textrm{m}$, $100\mu\textrm{m}$are made. Their surface profiles are obtained by a scanning electron microscope and a mechanical surface profilometer. The wavefront of the microlenses is measured by phase-shifting techniques using a Mach-Zehnder-like configuration. Thereby wavefront errors, focal lengths. point spread functions are obtained. The microlens with the diameter of $100\mu\textrm{m}$ has focal length of $164\mu\textrm{m}$ and spot diameter is less than $5\mu\textrm{m}$..

• The Korean Journal of Applied Statistics
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• 제28권1호
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• pp.49-60
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• 2015

Various kinds of ordination methods such as correspondence analysis and canonical correspondence analysis are used in community ecology to visualize relationships among species, sites, and environmental variables. Ter Braak (1986), Jackson and Somers (1991), Parmer (1993), compared the ordination methods using eigenvalue and distance graph. However, these methods did not show the relationship between population and biplot because they are only based on surveyed data. In this paper, a method that measures the extent to show population information to biplot was introduced to compare ordination methods objectively.

• The Journal of the Acoustical Society of Korea
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• 제14권4호
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• pp.96-99
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• 1995

Under signal range mismatch, the LCMV beamformer has the performance degradation to cancel a desired signal. Using the eigenstructure properties of the array covariance matrix, we investigate the cause of this problem. From this investigation, a robust beamformer to source range mismatch is presented. The proposed beamformer has the maximum output signal-to-noise ration (SNR). When a desired signal is in a far field, the weight vector of the proposed beamformer is not biased.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 한국퍼지및지능시스템학회 2004년도 추계학술대회 학술발표 논문집 제14권 제2호
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• pp.81-84
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• 2004

본 논문에서는 1대의 CCD카메라로 주행 중 차선과 선행차량을 인식하고 선행차량까지의 거리를 실시간으로 계측하는 알고리즘을 제시하였다. 도로와 카메라간의 기하구조를 분석하여 사영행렬을 추출하였고, 주행 중 차간 거리를 실시간으로 계측하는데 이용하였다. 또한 차선 인식을 위해서 Hough Transform을 적용하여 처리시간을 단축하였다. 도로상의 장애물은 인식된 주행차선 내로 한정하였고 도로 영상에서 수평에지성분을 구한 후 히스토그램 투영을 적용하여 장애물을 검출하였다. 거리가 점차 멀어질수록 계측오차가 증가함을 볼 수 있었으나 기존의 방법에 비하여 주행 중에 운전자가 장애물을 판단하여 제동을 취할 수 있는 정도의 유효한 오차특성을 보였다.

• Journal of the Korean Regional Science Association
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• 제33권1호
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• pp.29-41
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• 2017

This study proposes an integrated accessibility measurement algorithm, which is applied to the Seoul Metropolitan public transportation system consisting of bus and subway networks, and analyzes the result. We construct a public transportation network graph linking bus-subway networks and take the time distance as the link weight in the graph. We develop a time-distance algorithm to measure the time distance between each pair of transit stations based on the T-card transaction database. The average travel time between nodes has been computed via the shortest-path algorithm applied to the time-distance matrix, which is obtained from the average speed of each transit route in the T-card transaction database. Here the walking time between nodes is also taken into account if walking is involved. The integrated time-distance accessibility of each node in the Seoul Metropolitan public transportation system has been computed from the T-card data of 2013. We make a comparison between the results and those of the bus system and of the subway system, and analyze the spatial patterns. This study is the first attempt to measure the integrated time-distance accessibility for the Seoul Metropolitan public transportation system consisting of 16,277 nodes with 600 bus routes and 16 subway lines.

• The Journal of the Acoustical Society of Korea
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• 제43권4호
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• pp.369-382
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• 2024

To suppress the reverberation in the active sonar system, the non-negative matrix factorization-based reverberation suppression methods have been researched recently. An estimation loss function, which makes the multiplication of basis matrices same as the input signals, has to be considered to design the non-negative matrix factorization methods, but the conventional method simply chooses the Kullback-Leibler divergence asthe lossfunction without any considerations. In this paper, we examined that the Kullback-Leibler divergence is the best lossfunction or there isthe other loss function enhancing the performance. First, we derived a modified reverberation suppression algorithm using the generalized beta-divergence function, which includes the Kullback-Leibler divergence. Then, we performed Monte-Carlo simulations using synthesized reverberation for the modified reverberation suppression method. The results showed that the Kullback-Leibler divergence function (β = 1) has good performances in the high signal-to-reverberation environments, but the intermediate function (β = 1.25) between Kullback-Leibler divergence and Euclidean distance has better performance in the low signal-to-reverberation environments.

• The Journal of the Acoustical Society of Korea
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• 제39권2호
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• pp.120-130
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• 2020

This paper solves the problem in underdetermined convolutive mixture by improving the disadvantages of the multichannel nonnegative matrix factorization technique widely used in blind source separation. In conventional researches based on Spatial Covariance Matrix (SCM), each element composed of values such as power gain of single channel and correlation tends to degrade the quality of the separated sources due to high variance. In this paper, level and frequency normalization is performed to effectively cluster the estimated sources. Therefore, we propose a novel SCM and an effective distance function for cluster pairs. In this paper, the proposed SCM is used for the initialization of the spatial model and used for hierarchical agglomerative clustering in the bottom-up approach. The proposed algorithm was experimented using the 'Signal Separation Evaluation Campaign 2008 development dataset'. As a result, the improvement in most of the performance indicators was confirmed by utilizing the 'Blind Source Separation Eval toolbox', an objective source separation quality verification tool, and especially the performance superiority of the typical SDR of 1 dB to 3.5 dB was verified.

• Journal of Korean Society of Transportation
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• 제26권1호
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• pp.203-213
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• 2008

U-Turn offers convenience to drivers. U-Turn increases efficiency of traffic flow. But Standard of U-Turn is not clear. It caused many problems of traffic flow and traffic safety. This study estimate length between U-Turn location with front intersection based on stopping sight distance and left-turn vehicle's queue length. Variables are used traffic volume and operation speed. This study Analysis of U-Turn vehicle's behaviors and classification of conflict form by investigation. U-Turn length estimating based on relationship analysis between conflict with U-Turn length. Variables are used lane changing angles and operation speed. This study estimates length between U-Turn location with back intersection based on gap acceptance theory. Variables are used traffic volume, operation speed and lane changing angles. So, U-Turn location and length estimated considering traffic flow and traffic safety.

• The Korean Journal of Applied Statistics
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• 제24권2호
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• pp.373-381
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• 2011

This paper discusses how to get the sums of squares due to treatment factors when Type I Analysis is used by projections for the analysis of data under the assumption of a two-way ANOVA model. The suggested method does not need to calculate the residual sums of squares for the calculation of sums of squares. There-fore, the calculation is easier and faster than classical ANOVA methods. It also discusses how eigenvectors and eigenvalues of the projection matrices can be used to get the calculation of sums of squares. An example is given to illustrate the calculation procedure by projections for unbalanced data.