• 대한기계학회논문집B
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• 제27권6호
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• pp.766-772
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• 2003

The pseudospectral method for stability analysis was used to find the most influential disturbance mode for transition of plane channel flows and Blasius flow at their critical Reynolds numbers. A number of various oblique disturbance waves were investigated for their pseudospectra and resolvent norm contours in each flow, and an exhaustive search method was employed to find the disturbing waves to which the flows become most unstable. In plane Poiseuille flow an oblique disturbance with a wavelength of 3.59h (where h is the half channel width) at an angle $28.7^{\circ}$ was found to be the most influential for the flow transition to turbulence, and in plane Couette flow it is an oblique wave with a wavelength of 3.49h at an angle of $19.4^{\circ}$. But in Blasius flow it was found that the most influential mode is a normal wave with a wavelength of $3.44{\delta}_{999}$. These results imply that the most influential disturbance mode is closely related to the fundamental acoustic wave with a certain shear sheltering in the respective flow geometry.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1999년도 추계학술대회 논문집 - 한국공작기계학회
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• pp.464-469
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• 1999

Recently, the need for designing multi-stage gear drive has been increased as the hear drives are used more in the applications with high-speed and small volume. The design of multi-stage gear drives includes not only dimensional design but also configuration design of various machine elements. Until now, however, the researches on the design of gear drives are mainly focused on the single-stage gear drives and the design practices for multi-stage gear drives, especially in configuration design activity, mainly depend on the experiences and 'sense' of the designer by trial and error. We propose a design algorithm to automate the dimension design and the configuration design of multi-stage gear drives. The design process consists of four steps. The number of stage should be determined in the first step. In second step, the gear ratios of each reduction stage are determined using random search, and the ratios are basic input for the dimension design of gears, which is performed by the exhaustive search in third step. The designs of gears are guaranteed by the pitting resistance and bending strength rating practices by AGMA rating formulas. In configuration design, the positions of gears are determined to minimize the volume of gearbox using simulated annealing algorithm. The effectiveness of the algorithm is assured by the design example of a 4-stage gear drive.

• 한국항행학회논문지
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• 제16권5호
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• pp.871-878
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• 2012

64-비트 블록 암호 LBlock은 무선 센서 네트워크 환경과 같이 제한된 환경에 적합하도록 설계된 경량 블록 암호이다. 본 논문에서는 LBlock에 대한 차분 오류 공격을 제안한다. 랜덤 니블 오류 주입 가정에 기반을 둔 이 공격은 평균 5개의 랜덤 니블 오류와 $2^{25}$의 전수조사를 이용하여, LBlock의 비밀키를 복구한다. 이는 일반적인 수 초 내에 가능함을 의미한다. 본 논문의 공격 결과는 기제안된 LBlock에 대한 차분 오류 공격 결과보다 더 효율적이다.

• Preventive Nutrition and Food Science
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• 제20권2호
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• pp.133-136
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• 2015

Freshwater softshell turtle (Trionyx sinensis) extract has been used traditionally as a tonic soup, and to recover from physical fatigue. To support these claims, the forelimb grip strength of mice was measured after feeding a soft-shell turtle extract for 7 days. The T. sinensis extract significantly increased the grip strength to $1.25{\pm}0.07N$ (P<0.01), which is 16.8% higher than the force on day 0. After exercising, the blood glucose levels in extract-fed mice were 202% higher and urea levels were 73% lower, which were both significantly different than the levels observed after control treatment. Lactate dehydrogenase was significantly higher by 314%, and glutathione peroxidase increased by 165%. In addition, the obesity markers, serum triglyceride and cholesterol, decreased to 62% and 49%, respectively, after mice were fed the extract. These data show that the T. sinensis extract provided more energy for forelimb exercise, prevented protein catabolism and muscle fatigue, and decreased the oxidative stress caused by an exhaustive workout.

• 방송공학회논문지
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• 제16권2호
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• pp.247-257
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• 2011

본 논문에서는 장면의 밝기에 적합한 셔터 속도를 가진 두 장의 LDR (low dynamic range) 영상을 취득하여 HDR (high dynamic range) 영상을 고속으로 생성하는 효율적인 기법을 제안한다. 즉, 장면의 밝기에 최적인 HDR 영상을 취득하기 위해 본 논문에서는 오직 두 장의 초기 입력 LDR 영상을 이용하여 장면의 밝기에 대한 노출 곡선을 초기 추정한 후, 장면의 밝기 변화에 따른 최적의 셔터 속도를 시간 변화에 따라 지속적으로 추정하는 기법을 제안한다. 성능 평가를 위해 기존의 고화질 HDR 기법으로 생성한 영상과 제안된 방법으로 취득된 영상간의 유사도를 PSNR (peak signal to noise ratio)로 비교하였으며, 모든 두 장의 조합을 탐색하지 않고도 최적에 근사하는 두 개의 셔터 속도를 얻을 수 있음을 보인다.

• 한국정보처리학회논문지
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• 제7권2S호
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• pp.701-710
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• 2000

This paper presents a new method for an efficient coding of very low bit-rate color video based on adaptive wavelet transform. Our approach reveals that the coding process works more efficiently if the quantized wavelet coefficients are preprocessed by a mechanism exploiting the redundancies in the wavelet subband structure. Thus, we focuses optimized activity of coding part, and exhaustive overlapped block motion compensation is utilized to ensure coherency in motion compensated error frames, and raised cosine window is applied. The horizontal and vertical components of motion vectors are encoded separately using adaptive arithmetic coding while significant wavelet coefficients are encoded in bit-plane order using adaptive arithmetic coding. On average the proposed codec exceeds H.263 and ZTE in peak signal-to-noise ratio by as much as 2.07 and 1.38dB at 28 kbits, respectively. Fore entire sequence coding, 3DWCVC method is superior to H.263 and ZTE by 0.35 and 0.71dB on average, respectively.

• Journal of Information Processing Systems
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• 제12권4호
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• pp.754-764
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• 2016

The exhaustive list of sparsification methods for a digital image suffers from achieving an adequate number of zero and near-zero coefficients. The method proposed in this paper, which is known as the Discrete Rajan Transform Sparsification, overcomes this inadequacy. An attempt has been made to compare the simulation results for benchmark images by various popular, existing techniques and analyzing from different aspects. With the help of Discrete Rajan Transform algorithm, both lossless and lossy sparse representations are obtained. We divided an image into $8{\times}8-sized$ blocks and applied the Discrete Rajan Transform algorithm to it to get a more sparsified spectrum. The image was reconstructed from the transformed output of the Discrete Rajan Transform algorithm with an acceptable peak signal-to-noise ratio. The performance of the Discrete Rajan Transform in providing sparsity was compared with the results provided by the Discrete Fourier Transform, Discrete Cosine Transform, and the Discrete Wavelet Transform by means of the Degree of Sparsity. The simulation results proved that the Discrete Rajan Transform provides better sparsification when compared to other methods.

• 한국통신학회논문지
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• 제40권8호
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• pp.1485-1491
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• 2015

본 논문에서는 상향링크 Massive multiple-input multiple-output 시스템 상황에서의 파일럿 할당 알고리즘을 소개한다. 기존에 제안된 파일럿 할당 알고리즘은 최적 알고리즘에 비해 성능 열화가 크기 때문에, 본 논문에서는 Pre-determined Interference 기법과 Pre-determined Desired-term 기법을 이용한 알고리즘을 제안한다. 제안하는 기법은 최적 알고리즘에 비해 복잡도가 낮음과 동시에 성능 열화가 작다. 실험 결과를 통해 제안하는 기법의 성능을 확인한다.

• 한국통신학회논문지
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• 제37권8A호
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• pp.601-611
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• 2012

본 논문에서는, 다중 안테나 다중 사용자가 존재하는 3-cell 간섭 Broadcast 채널 (IFBC: interference broadcast channel) 에서 얻을 수 있는 공간 다중화 이득 (spatial multiplexing gain)에 대해서 소개한다. 이러한 공간 다중화 이득을 최대화하면서 총 수율을 높이기 위하여, 우리는 간섭 정렬 기법 (IA: interference alignment)에 스케쥴링 기법을 더한 방법을 제안하며, 이는 IFBC 환경에서 TDMA 기법보다 높은 수율 성능을 보인다. 최적의 스케쥴링 방법은 다중 사용자 이득을 이용하여 총 수율을 최대화하는 전수 조사 알고리즘을 이용한다. 또한, 전수 조사의 계산 복잡도가 매우 높기 때문에, 이를 효과적으로 줄이는 coordinated ascent 방법을 이용한 부최적 스케쥴링 방법도 제안 한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권9호
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• pp.3751-3770
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• 2015

Many sorts of image processing software facilitate image editing and also generate a great number of doctored images. Forensic technology emerges to detect the unintentional or malicious image operations. Most of forensic methods focus on the detection of single operations. However, a series of operations may be used to sequentially manipulate an image, which makes the operation detection problem complex. Forensic investigators always want to know as much exhaustive information about a suspicious image's entire processing history as possible. The detection of the operation chain, consisting of a series of operations, is a significant and challenging problem in the research field of forensics. In this paper, based on the histogram distribution uniformity of a manipulated image, we propose an operation chain detection scheme to identify histogram equalization (HE) followed by the dither-like operation (DLO). Two histogram features and a local spatial feature are utilized to further determine which DLO may have been applied. Both theoretical analysis and experimental results verify the effectiveness of our proposed scheme for both global and local scenarios.