• Interaction and multiscale mechanics
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• 제4권4호
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• pp.291-311
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• 2011

To simulate the self excited torsional vibrations of rotating drill strings (DSs) in vertical bore-holes, the nonlinear wave models of homogeneous and sectional torsional pendulums are formulated. The stated problem is shown to be of singularly perturbed type because the coefficient appearing before the second derivative of the constitutive nonlinear differential equation is small. The diapasons ${\omega}_b\leq{\omega}\leq{\omega}_l$ of angular velocity ${\omega}$ of the DS rotation are found, where the torsional auto-oscillations (of limit cycles) of the DS bit are generated. The variation of the limit cycle states, i.e. birth (${\omega}={\omega}_b$), evolution (${\omega}_b<{\omega}<{\omega}_l$) and loss (${\omega}={\omega}_l$), with the increase in angular velocity ${\omega}$ is analyzed. It is observed that firstly, at birth state of bifurcation of the limit cycle, the auto-oscillation generated proceeds in the regime of fast and slow motions (multiscale motion) with very small amplitude and it has a relaxation mode with nearly discontinuous angular velocities of elastic twisting. The vibration amplitude increases as ${\omega}$ increases, and then it decreases as ${\omega}$ approaches ${\omega}_l$. Sectional drill strings are also considered, and the conditions of the solution at the point of the upper and lower section joints are deduced. Besides, the peculiarities of the auto-oscillations of the sectional DSs are discussed.

• International journal of advanced smart convergence
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• 제6권2호
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• pp.65-71
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• 2017

Fingerprints are increasingly used for user authentication in small devices such as mobile phones. Therefore, it is important for Fingerprint authentication systems in personal devices to protect the user's fingerprint information while performing efficiently with a lightweight matching algorithm. In this paper, we propose a new method to extract strong minutiae with unique numbers from fingerprint images. Strong minutiae are at all times obtained from fingerprint images, and can be useful for secure and rapid fingerprint authentication. The binary information of strong minutiae of a fingerprint can be transformed securely and can create cancelable fingerprint templates. Also the bit-strings of strong minutiae decrease computing time necessary for the matching procedure between two fingerprints due to the simplicity of bitwise operations. First, we enroll several fingerprints images of a finger. From these images we select a reference fingerprint and put a number on each minutia. Following this procedure, we search for mated-minutiae between the reference fingerprint and other fingerprints one by one. Finally we derive unique numbers of strong minutiae of the finger. In the experiment with the FVC2004 fingerprint database, we show that using the proposed method, strong minutiae can be extracted successfully.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.324-329
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• 2005

Dynamic Encoding Algorithm for Searches (DEAS) which is known as a fast and reliable non-gradient optimization method, was proposed [1]. DEAS reaches local or global optimum with binary strings (or binary matrices for multi-dimensional problem) by iterating the two operations; bisectional search (BSS) and unidirectional search (UDS). BSS increases binary strings by one digit (i.e., 0 or 1), while UDS performs increment or decrement of binary strings in the BSS' result direction with no change of string length. Because the interval of UDS exponentially decreases with increment of bit string length (BSL), DEAS is difficult to escape from local optimum when DEAS falls into local optimum. Therefore, this paper proposes hopping UDS (HUDS) which performs UDS by hopping as many as BSL in the final point of UDS process. HUDS helps to escape from local optimum and enhances a probability searching global optimization. The excellent performance of HUDS will be validated through the well-known benchmark functions.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2012년도 한국컴퓨터종합학술대회논문집 Vol.39 No.1(A)
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• pp.385-387
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• 2012

Succinct 표현은 n개의 이산 객체를 정수 값으로 표현하는 대신 이진화하여 표현하는 방법으로 o(n) bit만을 사용하는 공간 효율적인 방법이다. Succinct 표현을 위한 1차원 비트스트링은 이산 객체의 저장 위치에 접근하기 위해서 rank와 select 함수를 필요로 하며, 다양한 연구들에 의해 현재 rank와 select 함수는 o(n) 비트를 사용하여 O(1) 시간에 수행되고, 실용적인 구현이 가능하다. 또한, 2차원 비트 스트링에 대한 연구도 진행되어, 현재 O($n^2$) bit를 사용하여 O(logn) 시간에 rank를, O($log^2n$) 시간에 select를 수행할 수 있다. 본 논문에서는 2차원 비트스트링 상에서의 rank 및 select 함수를 새롭게 정의하고 o($n^2$) 비트만을 사용하여 O(logn) 시간에 rank 질의를, 그리고 O($log^2n$)시간에 select 질의를 수행할 수 있는 방법을 제안한다.

• 한국컴퓨터정보학회논문지
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• 제14권3호
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• pp.75-82
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• 2009

영상의 비교는 PSNR을 이용하는 것이 일반적이다. PSNR이 35이상일 경우 육안으로 품질 차이를 구분하기 어렵다고 판단한다. 2006년 Lee 등은 원본 이미지 대신 원본 이미지의 MSB 비트열을 공개함으로써 소유권을 증명할 수 있는 프로토콜을 제안하면서, 두 이미지의 MSB 비트열의 유사도를 측정하기 위한 새로운 함수를 사용하였다. 이때의 유사도는 품질을 측정하기 위한 PSNR과는 그 의미가 조금 다른 측면이 있다. 즉, 원본 이미지로부터 생성된 대상 이미지가 현저히 떨어질 경우, PSNR은 매우 낮은 값을 보이지만 품질이 떨어지더라도 유사도 측면에서 본다면 두 영상의 상관관계는 매우 높게 나와야 할 것이다. 본 논문에서는 Lee 등이 제안한 MSB 비교 함수를 수정한 후, ICOR함수를 제안하였으며, 이 함수를 이용하여 두 이미지의 상관관계 판단에 적용할 수 있는지 분석하였다.

• 전기전자학회논문지
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• 제11권1호통권20호
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• pp.38-45
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• 2007

A new 8-bit single-slope ADC using analog RAMP generator with digitally controllable dynamic range has been proposed and simulated for column level or per-pixel CMOS image sensor application. The conversion gain of ADC can he controlled easily by using frequency divider with digitally controllable diviber ratio, coarse/fine RAMP with class-AB op-amp, resistor strings, decoder, comparator, and etc. The chip area and power consumption can be decreased by simplified analog circuits and passive components. Proposed frequency divider has been implemented and verified with 0.65um, 2-poly, 2-metal standard CMOS process. And the functional verification has been simulated and accomplished in a 0.35$\mu$m standard CMOS process.

• 정보보호학회논문지
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• 제14권6호
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• pp.111-123
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• 2004

해쉬 함수란 임의의 길이의 비트 열을 입력으로 하여 고정된 길이의 비트 열을 출력하는 함수이다. 셀룰러 오토마타는 유한상태머신으로서 인접한 셀과의 결합 논리로 의사난수를 효과적으로 생성할 수 있는 특성을 가지고 있다. 신상욱 등$^{[1]}$ 과 Mihaljevic 등$^{[7]}$ 은 하드웨어 구현에 효율적인 셀룰러 오토마타에 기반한 해쉬 함수를 제안하였다. 본 논문에서는 [1]과 [7]에서 제안된 셀룰러 오토마타 기반 해쉬 함수에 대한 충돌 쌍을 각각 0.46875와 0.5의 확률로 찾을 수 있음을 보인다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 F
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• pp.2742-2744
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• 1999

In this paper, an auto-tuning method for fuzzy logic controller based on the genetic algorithm is presented. In the proposed method, normalization parameters and membership function parameters of fuzzy controller are translated into binary bit-strings, which are processed by the genetic algorithm in order to be optimized for the well-chosen objective function (i.e. fitness function). To examine the validity of the proposed method. a genetic algorithm based fuzzy controller for an indirect vector control of induction motors is simulated and experiment is carried out. The simulation and experimental results show a significant enhancement in shortening development time and improving system performance over a traditional manually tuned fuzzy logic controller.

• ETRI Journal
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• 제42권3호
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• pp.446-458
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• 2020

In this study, an efficient scheme for hiding data directly in partially encrypted versions of high efficiency video coding (HEVC) videos is proposed. The content owner uses stream cipher to selectively encrypt some HEVC-CABAC bin strings in a format-compliant manner. Then, the data hider embeds the secret message into the encrypted HEVC videos using the specific coefficient modification technique. Consequently, it can be used in third-party computing environments (more generally, cloud computing). For security and privacy purposes, service providers cannot access the visual content of the host video. As the coefficient is only slightly modified, the quality of the decrypted video is satisfactory. The encrypted and marked bitstreams meet the requirements of format compatibility, and have the same bit rate. At the receiving end, data extraction can be performed in the encrypted domain or decrypted domain that can be adapted to different application scenarios. Several standard video sequences with different resolutions and contents have been used for experimental evaluation.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 B
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• pp.509-511
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• 1998

Design of fuzzy logic controllers encounters difficulties in the selection of optimized membership function and fuzzy rule base, which is traditionally achieved by tedious trial-and-error process. In this paper We proposed a new method to generate fuzzy logic controllers throught genetic algorithm(GA). The controller design space is coded in base-7 strings chromosomes, where each bit gene matches the 7 discrete fuzzy value. The developed approach is subsequently applied to the design of proportional plus integral type fuzzy controller for a do-servo motor control system. It was presented in discrete fuzzy linguistic value, and used a membership function with Gaussian curve. The performance of this control system is demonstrated higher than that of a conventional PID controller and fuzzy logic controller(FLC).