• Wind and Structures
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• 제30권2호
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• pp.181-198
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• 2020

In the traditional buffeting response analysis method, the spanwise incomplete correlation of buffeting forces is always assumed to be same as that of the incident wind turbulence and the action of the signature turbulence is ignored. In this paper, three typical bridge decks usually adopted in the real bridge engineering, a single flat box deck, a central slotted box deck and a two-separated paralleled box deck, were employed as the investigated objects. The wind induced pressure on these bridge decks were measured via a series of wind tunnel pressure tests of the sectional models. The influences of the wind speed in the tests, the angle of attack, the turbulence intensity and the characteristic distance were taken into account and discussed. The spanwise root coherence of buffeting forces was also compared with that of the incidence turbulence. The signature turbulence effect on the spanwise root coherence function was decomposed and explained by a new empirical method with a double-variable model. Finally, the formula of a sum of rational fractions that accounted for the signature turbulence effect was proposed in order to fit the results of the spanwise root coherence function. The results show that, the spanwise root coherence of the drag force agrees with that of incidence turbulence in some range of the reduced frequency but disagree in the mostly reduced frequency. The spanwise root coherence of the lift force and the torsional moment is much larger than that of the incidence turbulence. The influences of the wind speed and the angle of attack are slight, and they can be ignored in the wind tunnel test. The spanwise coherence function often involves several narrow peaks due to the signature turbulence effect in the high reduced frequency zone. The spanwise coherence function is related to the spanwise separation distance and the spanwise integral length scales, and the signature turbulence effect is related to the deck-width-related reduced frequency.

• 한국군사과학기술학회지
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• 제9권2호
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• pp.11-19
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• 2006

The underwater electromagnetic signatures of a naval ship are mainly generated from three sources which are the permanent and induced magnetic field in the ship's hull and other ferrous components, the cathodic current electromagnetic field established by the Impressed Current Cathodic Protection(ICCP) system or the Sacrificial Anode and the stray electromagnetic fields generated by onboard equipment. These signatures can be minimized by certain design methods or installation of signature reduction equipment. In this paper, we represented the characteristic of the underwater electromagnetic signature and the signature reduction techniques for a naval ship. Also, we measured the electromagnetic field changes emitted from the real ship using the Electric and Magnetic field Measurement System(EMMS). We found that the underwater electromagnetic signature for a naval ship can be used as input or trigger signal in a surveillance system and an influence mine.

• 한국멀티미디어학회논문지
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• 제7권12호
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• pp.1639-1649
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• 2004

In this paper, a method for detection of forged signatures based on spectral analysis of directional gradient density function and a weighted fuzzy classifier is proposed. The well defined outline of an incoming signature image is extracted in a preprocessing stage which includes noise reduction, automatic thresholding, image restoration and erosion process. The directional gradient density function derived from extracted signature outline is highly related to the overall shape of signature image, and thus its frequency spectrum is used as a feature set. With this spectral feature set, having a property to be invariant in size, shift, and rotation, a weighted fuzzy classifier is evaluated for the verification of freehand and random forgeries. Experiments show that less than 5% averaged error rate can be achieved on a database of 500 signature samples.

• ETRI Journal
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• 제32권6호
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• pp.871-880
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• 2010

Many applications dealing with image management need a technique for removing duplicate images or for grouping related (near-duplicate) images in a database. This paper proposes a concentric circle-based image signature which makes it possible to detect near-duplicates rapidly and accurately. An image is partitioned by radius and angle levels from the center of the image. Feature values are calculated using the average or variation between the partitioned sub-regions. The feature values distributed in sequence are formed into an image signature by hash generation. The hashing facilitates storage space reduction and fast matching. The performance was evaluated through discriminability and robustness tests. Using these tests, the particularity among the different images and the invariability among the modified images are verified, respectively. In addition, we also measured the discriminability and robustness by the distribution analysis of the hashed bits. The proposed method is robust to various modifications, as shown by its average detection rate of 98.99%. The experimental results showed that the proposed method is suitable for near-duplicate detection in large databases.

• 한국산업정보학회논문지
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• 제23권2호
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• pp.19-28
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• 2018

본 연구에서는 함정 신호해석 연구에 필요한 해양기상환경 자료의 표본추출에 관한 연구를 수행하였다. 이를 위해 한국 기상청으로부터 품질검사가 완료된 최신의 해양 기상자료를 수집하고, 측정 자료의 가용 구간을 설정하여 이상치를 제거하였다. 품질검사와 이상치를 제거한 자료는 함정 신호의 확률론적 해석을 위해 지정학적 위협과 부이의 유효면적을 고려하여 단순임의추출법을 통해 축소되었다. 이후 표본의 크기는 모집단의 크기와 신뢰수준 95%를 고려하여 100, 200 그리고 400개로 설정하였으며, 상관관계가 높은 수온과 기온을 기준으로 하는 2차원 층화추출법으로 최종표본을 추출하였다. 추출 표본은 제곱오차의 합과 신뢰구간을 추정하고 이를 비교하여 함정의 확률론적 신호해석을 위해 필요한 해양기상조건의 크기를 제시하였다.

• 한국추진공학회지
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• 제23권5호
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• pp.27-35
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• 2019

스텔스 기술은 레이더 및 적외선 시커와 같은 탐지기로부터의 탐지를 피하는 기술이다. 특히 IR 미사일은 항공기 자체의 열을 감지하기 때문에 적외선 신호에 의한 탐지는 더욱 위협적이며 적외선 스텔스 기술은 항공기 및 UCAV(Unmanned Combat Aerial Vehicle)의 생존을 보장하는데 필수적이다. 본 연구에서는 UCAV 노즐 설계에 따른 공력 및 적외선 스텔스 성능 분석이 수행되었다. 수치해석 결과에 따르면 Double S형 노즐은 엔진의 고온부를 차폐할 수 있기 때문에 적외선 신호를 줄이는 데 효과적이다. 또한, Double S형 노즐에서 회전부 위치가 뒤쪽에 위치할수록 적외선 신호가 감소함을 확인하였다.

• 전자공학회논문지B
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• 제31B권6호
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• pp.1-9
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• 1994

Astorage structure using signatures is proposed to evaluate efficently queries including conditions of nested attributes in the nested relational databases This method stores a subrelation signature into the storage structure for a nested tuple with its subrelation pointer. During query processing steps, the subrelation signatures are matched first with the nested predicates in the query. When the match operation completes with success then physical retrieval of the subrelation occurrs resulting in reduction of disk 1/Os.

• 한국지능시스템학회논문지
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• 제23권6호
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• pp.539-544
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• 2013

본 논문에서는 다항식 기반 RBFNNs를 이용하여 3차원 얼굴인식 알고리즘을 설계하고 인식률을 산출하는 방법을 제시한다. 2차원 얼굴인식의 경우 얼굴 포즈, 조명 등과 같은 외부 환경에 의해 인식률이 저하된다. 이러한 단점을 보완하기 위해 3차원 영상을 획득하여 얼굴인식을 수행한다. 얼굴인식을 수행하기 전에 3D스캐너를 통해 얻은 얼굴영상의 포즈 보상을 실시하고 얼굴의 형상을 정면으로 향하게 한다. 그리고 Point Signature 기법을 이용하여 얼굴의 깊이 값을 추출하게 된다. 추출된 데이터는 고차원 데이터로서 학습 및 인식을 수행함에 있어 문제가 생길 수 있기 때문에 PCA알고리즘을 수행하여 차원을 축소한 데이터를 사용한다. 효율적인 학습을 위해 최적화 알고리즘을 통해 파라미터 최적화를 수행하며 PSO, DE, GA 알고리즘을 사용하여 인식 성능을 확인한다.

• 한국산학기술학회논문지
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• 제18권12호
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• pp.793-798
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• 2017

현대의 함정에서는 추진 기관에서 생성된 고온의 폐기가스와 가열된 폐기관의 금속표면온도를 저감하기 위해 적외선 신호저감 장치(Infra-red Signature Suppression system, IRSS)를 설치하고 있다. 국내 함정에 탑재된 일반적인 IRSS는 이덕터, 믹싱튜브 그리고 디퓨져로 구성되며, 이 중 디퓨져는 금속표면에 내기 외기의 압력차에 의한 공기 막을 생성시켜 온도를 저감시키는 역할을 한다. 본 연구에서는 국외 선진 기술사에서 설계한 IRSS의 디퓨져 형상을 분석하여 설계 변수를 선정하였으며, 분석 조건을 줄이면서 설계 변수의 특성을 효과적으로 파악 할 수 있는 다구치 실험계획법을 통해 IRSS 디퓨져의 성능에 영향을 미치는 설계 변수의 특성을 검토하였다. 디퓨져의 성능분석에는 선행 연구에서 정립한 열 유동해석 기술을 활용하였다. IRSS의 성능평가에는 함정 적외선 신호의 세기와 직접적으로 관련되는 디퓨져 출구에서의 폐기가스 온도와 금속표면온도의 면적평균 값을 기준으로 하였으며, 폐기가스의 온도는 디퓨져 출구의 직경 변화에 크게 영향을 받고, 디퓨져 금속표면의 온도는 디퓨져 링의 개수 변화에 크게 영향 받음을 확인하였다.

• ETRI Journal
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• 제41권6호
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• pp.863-872
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• 2019

Elliptic curve cryptography is a relatively lightweight public-key cryptography method for key generation and digital signature verification. Some lightweight curves (eg, Curve25519 and Curve Ed448) have been adopted by upcoming Transport Layer Security 1.3 (TLS 1.3) to replace the standardized NIST curves. However, the efficient implementation of Curve Ed448 on Internet of Things (IoT) devices remains underexplored. This study is focused on the optimization of the Curve Ed448 implementation on low-end IoT processors (ie, 8-bit AVR and 16-bit MSP processors). In particular, the three-level and two-level subtractive Karatsuba algorithms are adopted for multi-precision multiplication on AVR and MSP processors, respectively, and two-level Karatsuba routines are employed for multi-precision squaring. For modular reduction and finite field inversion, fast reduction and Fermat-based inversion operations are used to mitigate side-channel vulnerabilities. The scalar multiplication operation using the Montgomery ladder algorithm requires only 103 and 73 M clock cycles on AVR and MSP processors.