• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.555-556
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• 2014

In this paper, topology optimization of two-dimensional acoustic lenses is presented by using the phase field method. The objective of the optimization is to maximize the acoustic pressure at a specified domain inside the acoustic domain for a given frequency, and the constraint is imposed on the amount of the material of the acoustic lens. Topology optimization of two-dimensional acoustic lenses are obtained as the steady state of the phase transition described by the Allen-Cahn equation. The Helmholtz equation modeling the wave propagation is solved by using a finite element method. The effectiveness of the proposed method is verified by applying it for several two-dimensional acoustic lens system design problems.

• Journal of the Korean Society of Visualization
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• v.9 no.2
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• pp.48-53
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• 2011

The shape of nozzle cross-section plays an important role in stabilizing electrospray jet. The angle of contact line is governed based on the famous Young-Laplace equation. Compared to a round nozzle that has a constant curvature along the orifice, the square nozzle has four square corner edges and four straight edges that hold the meniscus in a different manner and is of interest in this study. By utilizing both square and round capillary nozzle, we examine the effect of nozzle shape in electrohydrodynamic jetting. The ejections were recorded with a high speed camera and analyzed to examine the jetting repeatability based on dynamic movement of meniscus. The result suggests that if the corner edges are not sharp, then its effect on repeatability is also limited.

• Proceedings of the Korean Information Science Society Conference
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• 2006.10d
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• pp.302-305
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• 2006

In this paper, we have proposed a novel method using quantization of wavelet coefficients for secret data communication. First, speech signal is partitioned into small time frames and the frames are transformed into frequency domain using a WT(Wavelet Transform). We quantize the wavelet coefficients and embedded secret data into the quantized wavelet coefficients. The destination regard quantization errors of received speech as seceret dat. As most speech watermark techniques have a trade off between noise robustness and speech quality, our method also have. However we solve the problem with a partial quantization and a noise level dependent threshold. In additional, we improve the speech quality with de-noising method using wavelet transform. Since the signal is processed in the wavelet domain, we can easily adapt the de-noising method based on wavelet transform. Simulation results in the various noisy environments show that the proposed method is reliable for secret communication.

• Proceedings of the Korean Information Science Society Conference
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• 2001.10c
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• pp.70-72
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• 2001

분산 시스템의 규모가 점점 커지고 이기종 환경이 증가함에 따른 시스템 관리가 더욱 어려워지고 있다. 물리적으로 원거리에 위치한 자원들의 상태를 감독하고 시스템 운용을 위해 많은 인력과 시간을 낭비하는 문제점 또한 대두되고 있다. 이러한 분산 시스템의 부수적인 문제를 해결하기 위한 분산 시스템 관리의 효율적인 운영을 위해서 각 분산 시스템의 일관된 성능 데이터 관리 방안이 필요하다. 이기종의 시스템들을 관리할 경우 각 시스템들의 성능 데이터들이 상이한 형식을 가지고 있기 때문에 플랫폼에 독립적이지가 못하다. 그러므로 시스템의 성능을 나타내는 데이터를 정형적인 형식을 정해서 표면, 관리하는 것이 필요하다. 본 논문에서는 XML과 XML 스키마를 사용해서 이질적인 시스템간의 성능 데이터에 대한 일관된 형식을 제공하고 플랫폼에 독립적인 관리 방안을 제안한다.

• Archives of Pharmacal Research
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• v.26 no.12
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• pp.1014-1017
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• 2003

Two new phenylpropanoid glycosides, 1-$\beta$-D-glucopyranosyl-2,6-dimethoxy-4-propenylphenol (1) and 1-[$\beta$-D-glucopyranosyl-(1$\rightarrow6)-\beta$-D-glucopyranosyl]-2,6-dimethoxy-4-propenylphenol (2) were isolated from the stem bark of Acanthopanax trifoliatus along with four known compounds (3∼6). Their structures were established on the basis of spectral and chemical evidences.

• Archives of Pharmacal Research
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• v.28 no.2
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• pp.164-168
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• 2005

The EtOAc extract of Youngia koidzumiana significantly inhibited the diacylglycerol acyltransferase (DGAT) from rat liver microsomes. Bioactivity-guided fractionation led to the isolation of nine compounds, the structures of which were established using physicochemical and spectral data. Of the isolated compounds, oleanolic acid (2), methyl ursolate (7) and corosolic aicd (8) inhibited DGAT, with $IC_{50}$ values of 31.7, 26.4, and $44.3{\mu}M$, respectively. However, sesquit-erpenoids showed only weak inhibitory effects toward DGAT.

• Korean Journal of Computational Design and Engineering
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• v.3 no.4
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• pp.274-282
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• 1998

A feature is a local shape of a product directly related to the manufacturing process. The feature plays a role of the bridge connecting CAD and CAM. In the process planning for he CAM, information on manufacturing is required. To get the a manufacturing information from CAD dat, we need to recognize features. Once features are recognized, they are used as an input for the process planning. In this paper, we thoroughly investigate the composite features, which are generated by interacting simple features. The simple features in the composite feature usually have precedence relation in terms of process sequence. Based on the reason for the precedence relation, we classify the composite features for the process planning. In addition to the precedence relation, approach direction is used as an input for the process planning. In the process planning, the number of set-up orientations are minimized whole process sequence for the features are generated. We propose a process planning algorithm based on the topological sort and breadth-first search of graphs. The algorithn is verified using sample products.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.4
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• pp.30-39
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• 1998

Currently, LAMA(Local Automatic Message Accounting) is a billing mechanism which is being used for billing process, in which billing dat is written on MT(Magnetic Tape), collected at each regional billing center and then processed once a month. However, in order to prepare further development of telecommunication network and future new services, computerization of billing process and new daily billing processing system are urgently needed. Therefore Korea Telecom had developed a CAMA (Centralized Automatic Message Accounting) system for M10CN switch. In the CAMA system, billing data generated in switches is transfered on-line using approproate protocols and various transmission media and immediately processed. The CAMA system for M10CN switch consists of three parts such as ED (Extraction Device), TD(Transmission Device) and HC(Host Collector). The system also has redundancy to maintain continuance and confidence of system operation.

• Proceedings of the KIPE Conference
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• 2019.11a
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• pp.124-125
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• 2019

This paper proposes a novel control method to minimize conduction losses of dual active bridge (DAB) converters for on-board chargers of electric vehicles (EVs). In the control method, two variables are regulated, which are the phase-shift angle between the primary and secondary full bridges and the switching frequency. From time-domain analysis, an optimal phase-shift angle is derived to achieve the minimum RMS value of the transformer current. The proposed method was implemented for a 3.6-kW SiC-based prototype to validate its effectiveness. A high efficiency over 97.3% has been achieved for a wide output voltage range.

• The Korean Journal of Applied Statistics
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• v.18 no.3
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• pp.661-671
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• 2005

The aim of this study is to propose a clustering method, called tree-structured clustering, by recursively partitioning continuous multivariate dat a based on overall $R^2$ criterion with a practical node-splitting decision rule. The clustering method produces easily interpretable clustering rules of tree types with the variable selection function. In numerical examples (Fisher's iris data and a Telecom case), we note several differences between tree-structured clustering and K-means clustering.