• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.24 no.8B
• /
• pp.1567-1576
• /
• 1999

In this paper, we propose new methods to detect a scene cut and a dissolve region in compressed MPEG video sequences. The scene cut detection method uses edge images obtained using DCT AC coefficients and the dissolve detection method utilizes the macroblock type information of the MPEG stream. The proposed scene cut detection method is insensitive to brightness and can detect scene changes more precisely than the methods using DC coefficients since AC edge images can express original images more exactly than DC edge images do. The proposed dissolve detection method using the number of intra macroblocks(MBs) computationally efficient since it does not require the decoding process. Experimental results show that the proposed methods perform better in detection scene changes than conventional other methods.

• Proceedings of the KIPE Conference
• /
• 2020.08a
• /
• pp.355-356
• /
• 2020

본 논문에서는 PFC와 LLC공진형 컨버터로 구성되는 단상 AC/DC 정류기 시스템에서 발생하는 출력전압 120Hz 리플 저감에 관한 전향보상 제어기법을 제안한다. 제안하는 방법은 입/출력 전력 차이를 이용하여 DC-link의 전압 리플을 계산하고, 선형화된 LLC공진형 컨버터의 주파수 이득 곡선을 기반으로 120Hz에 대한 리플 성분을 전향 보상하여 저감 시키는 방법이며, 시뮬레이션을 이용하여 타당성을 검증하였다.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.31 no.3B
• /
• pp.293-303
• /
• 2011

An efficient diagonalized approximate factorization algorithm (DAF) is developed for the solution of three-dimensional incompressible viscous flows. The pressure-based, artificial compressibility (AC) method is used for calculating steady incompressible Navier-Stokes equations. The AC form of the governing equations is discretized in space using a second-order-accurate finite volume method. The present DAF method is applied to derive a second-order accurate splitting of the discrete system of equations. The primary objective of this study is to investigate the computational efficiency of the present DAF method. The solutions of the DAF method are evaluated relative to those of well-known four-stage Runge-Kutta (RK4) method for fully developed and developing laminar flows in curved square ducts and a laminar flow in a cavity. While converged solutions obtained by DAF and RK4 methods on the same computational meshes are essentially identical because of employing the same discrete schemes in space, both algorithms shows significant discrepancy in the computing efficiency. The results reveal that the DAF method requires substantially at least two times less computational time than RK4 to solve all applied flow fields. The increase in computational efficiency of the DAF methods is achieved with no increase in computational resources and coding complexity.

• Proceedings of the KIEE Conference
• /
• 1997.07c
• /
• pp.1133-1136
• /
• 1997

This study established AC-DC system model including DC Link, and then BC Link equation was derived from the model. The equation was included into the calculational algorithm of AC system and solved using fast decoupled method. To minimize the line loss of AC-DC system, optimum theory was applied to the equations.

• Proceedings of the KIEE Conference
• /
• 1997.11a
• /
• pp.432-434
• /
• 1997

In order to find the steady-state operating condition of HVDC system interacting with AC power system, the load flow calculation of AC/HVDC system is performed. For the calculation, each generating unit is modeled by an equivalent voltage source and coupled impedance. The rectifier station is modeled by a controlled DC voltage source. EMTP simulation of the AC/HVDC system is also performed to verify the result of the load flow calculation.

• The Transactions of the Korean Institute of Electrical Engineers B
• /
• v.50 no.1
• /
• pp.10-14
• /
• 2001

The superconducting transmission cable is one of interesting part in power application using high temperature superconducting wire. One important parameter in HTS cable design is transport current sharing because it is related with current transmission capacity and loss. In this paper, we calculate self inductances of each layer and mutual inductances between two layers from magnetic field energy, and current sharing of each layer for 4-layer cable using the electric circuit model which contain inductance and resistance (by joint and AC loss). Also, transport current losses which are calculated by monoblock model and Norris equation are compared. As a results, outer layer has always larger transport current than inner layer, and current capacity of each layer is largely influenced by resistance per unit cable length. As a conclusion, for high current uniformity and low AC loss, we have to decrease inductances themselves or those differences.

• Proceedings of the Korean Information Science Society Conference
• /
• 2005.07a
• /
• pp.463-465
• /
• 2005

본 논문에서는 802.l1e MAC의 EDCA 모드를 기반으로 한 무선랜 환경에서 realtime data인 voice traffic의 QoS를 향상하기 위한 방안을 연구하였다. 동적으로 채널의 상태를 보고, 네트워크 상태를 예측하여 채널 경쟁에 참여할지를 결정하는 방안으로, 경쟁이 치열할 때 voice traffic에 차별화된 가중치를 더 줄 수 있어 전반적인 voice traffic의 성능 향상에 기여한다. 본 연구에서 SU(slot utilization)을 계산하여 PT(Probability of Transmission)을 구할 때, 기존의 DCC 알고리즘을 그대로 802.11e에 적용하게 되면 4개의 AC에 똑같은 알고리즘이 적용되어 802.11e의 핵심인 차별화된 QoS를 지원하는데 무리가 있다. 기존 DCC 알고리즘에서 재시도 회수만 고려해 구하는 것을 802.11e 구조에 맞추어 4개의 AC별로 차별화하여 전송확률(PT)를 구할 수 있게 하였다. 뿐만 아니라, 재시도 회수를 고려하여 재시도 회수가 않은 packet에는 PT값이 높게 나을 수 있게 하고, 최대 가능한 재시도 회수에 도달할 때에는 상위 AC 영역의 값이 나오게 하여 AC의 upgrade가 되는 효과를 가져오게 하였다. 이 때 각 AC의 lower bound와 upper bound를 정하고, 이 때 802.11e의 최대 재시도 회수 parameter와의 상관관계를 정의하여 하위 AC가 상위 AC의 영역을 침범하지 못하도록 정의하고 있다. 추가적으로 SU의 값을 구할 때에도 현재의 SU값 대신 누적된 평균 SU값을 사용해 PT값을 구하여, utilization, latency, Packet loss등 전반적인 부분의 성능개선을 확인할 수 있다.

• Journal of Korea Society of Industrial Information Systems
• /
• v.24 no.2
• /
• pp.57-63
• /
• 2019

In order to facilitate the supply of gradually increasing power demand, it is also necessary to increase the number of power cables for power transmission as well as generation facilities. However, the expansion of electric power cables for supplying power to most urban areas requires a space for installation of additional cables, and the space for installing cables in domestic downtown areas is insufficient at present. The superconducting power cable, which can transmit more power with the same size, has emerged as an alternative to overcome the insufficient cable installation space. However, superconducting power cables, which have the advantage of large power transmission, have some losses in the AC (Alternating Current) system. Therefore, the design and analysis of AC losses are essential to introduce superconducting power cables in AC power transmission systems. In this paper, we analyze the AC loss of various superconducting power cables and consider the actual superconducting power cables and their application to the system. Although there is a theoretical calculation method of AC loss for single superconducting wire, it is not easy to calculate AC loss of superconducting power cable with large number. Therefore, the authors intend to analyze various kinds of superconducting power cable AC loss by using electromagnetic finite element analysis considering E-J (Electric field-Current density) characteristics of superconductivity. The analysis of the AC loss characteristics of the superconducting power cable will be an important factor in the design and development of the superconducting power cable to be applied to the actual system.

• Applied Chemistry for Engineering
• /
• v.5 no.4
• /
• pp.657-661
• /
• 1994

A method to analyse the concentration of mixture (AC/urea) and the concentration of urea or AC alone was developed. In this study, the decomposition of AC solution to ammonium bicarbonate was suppressed by using of 15% w/v ammonia as a solvent and the error of equilibrium point was maintained less than 1 %. Strong peaks at $1600cm^{-1}$ for urea and at $1405cm^{-1}$ for AC, corresponding to the N-H bending and symmetric carboxylate ion stretch were used to construct calibration graph and equations for the measurement of concentration. The errors of calculated concentration were ${\pm}0.1%$ w/v for AC and ${\pm}0.3%$ w/v for urea.

• Journal of the Institute of Electronics Engineers of Korea SP
• /
• v.45 no.6
• /
• pp.88-94
• /
• 2008

A DCT-based energy-ratio measure for autofocus in digital camera is proposed in this paper. This measure, namely AC2DC1 and AC5DC1, determines the sharpness of an image using a ratio between AC and DC energy in the DCT domain. This method is derived from energy analysis of DCT coefficients. Autofocus score calculation method is used to assess the performance of the proposed measure and to compare it with other measures. Experimental results under various conditions verify the robustness of the proposed focus measure for the Gaussian as well as impulsive noises.