• 새물리
• /
• 제68권11호
• /
• pp.1275-1280
• /
• 2018

We demonstrated transmission direct phase-measuring deflectometry (DPMD) with a specular phase object having discontinuous surfaces by using two displays and a two-dimensional array detector for display and by recording the distorted fringe patterns. Three-dimensional (3D) information was obtained by calculating the height map directly from the phase information. We developed a mathematical model of the phase-height relationship in transmission DPMD. Unlike normal transmission deflectometry, this method supports height measurement directly from the phase. Compared with other 3D measurement techniques such as interferometry, this method has the advantages of being inexpensive and easy to implement.

• Current Optics and Photonics
• /
• 제7권6호
• /
• pp.655-664
• /
• 2023

Ghost imaging (GI) technology is developing rapidly, but there are inevitably some limitations such as the influence of atmospheric turbulence. In this paper, we study a ghost imaging system in atmospheric turbulence and use a gamma-gamma (GG) model to simulate the medium to strong range of turbulence distribution. With a compressed sensing (CS) algorithm and generative adversarial network (GAN), the image can be restored well. We analyze the performance of correlation imaging, the influence of atmospheric turbulence and the restoration algorithm's effects. The restored image's peak signal-to-noise ratio (PSNR) and structural similarity index map (SSIM) increased to 21.9 dB and 0.67 dB, respectively. This proves that deep learning (DL) methods can restore a distorted image well, and it has specific significance for computational imaging in noisy and fuzzy environments.

• Current Optics and Photonics
• /
• 제8권2호
• /
• pp.183-191
• /
• 2024

High-resolution retinal imaging based on adaptive optics (AO) is important for early diagnosis related to retinal diseases. However, in practical applications, closed-loop AO correction takes a relatively long time, and traditional open-loop correction methods have low accuracy in correction, leading to unsatisfactory imaging results. In this paper, a SH-U-net-based open-loop AO wavefront correction method is presented for a retinal AO imaging system. The SH-U-net builds a mathematical model of the entire AO system through data training, and the Root mean square (RMS) of the distorted wavefront is 0.08λ after correction in the simulation. Furthermore, it has been validated in experiments. The method improves the accuracy of wavefront correction and shortens the correction time.

• 한국방재학회 논문집
• /
• 제10권1호
• /
• pp.111-117
• /
• 2010

수중구조물에 의한 파랑의 변형을 예측하기 위해 3차원 수치모형을 도입하여 수치모형 실험을 수행하였다. 본 수치모형은 Navier-Stokes 방정식을 유한차분법을 이용하여 계산하는 동수압 모형으로서, 난류의 해석을 위해서 상대적으로 큰 에디(eddy)만을 고려하는 SANS(Spatially Averaged Navier-Stokes) 방정식의 해를 구하는 LES(large-eddy-simulation) 기반의 수치모형이다. 엇갈림 격자체계에서 유한차분법을 사용하여 지배방정식을 해석하는 모형으로서 수치기법으로 Two-step projection 기법을 사용하여 SANS 방정식을 계산하였으며, Bi-CGSTAB 기법을 이용하여 Poisson 방정식의 해를 구하고 압력장을 계산하였다. 또한, 자유수면의 추적을 위하여 2차 정확도의 VOF(volume-of-fluid) 기법을 사용하였다. 먼저 선형파를 일정 수심상에서 조파시켜 해석해와 비교한 후 수중구조물이 설치된 지형에 적용하여 파랑의 변형을 수치모의하여 수리모형 실험결과와 비교 및 분석하였다.

• 정보보호학회논문지
• /
• 제29권6호
• /
• pp.1383-1392
• /
• 2019

적대적 공격은 기계학습 분류 모델의 오분류를 유도하는 적대적 데이터를 생성하는 공격으로, 실생활에 적용된 분류 모델에 혼란을 야기하여 심각한 피해를 발생시킬 수 있다. 이러한 적대적 공격 중 블랙박스 방식의 공격은, 대상 모델과 유사한 대체 모델을 학습시켜 대체 모델을 이용해 적대적 데이터를 생성하는 공격 방식이다. 이 때 사용되는 야코비 행렬 기반의 데이터 어그멘테이션 기법은 합성되는 데이터의 왜곡이 심해진다는 단점이 있다. 본 논문은 기존의 데이터 어그멘테이션 방식에 존재하는 단점을 보완하기 위해 감쇠 요소를 추가한 데이터 어그멘테이션을 사용하여 대체 모델을 학습시키고, 이를 이용해 적대적 데이터를 생성하는 방안을 제안한다. 실험을 통해, 기존의 연구 결과보다 공격 성공률이 최대 8.5% 가량 높음을 입증하였다.

• 한국수산과학회지
• /
• 제42권2호
• /
• pp.165-170
• /
• 2009

Recently, wide spread distribution of the giant jellyfish, Nemopilema nomurai, has occurred in the East China Sea. This increased distribution has caused serious problems in inshore and offshore fisheries in Korea and Japan. As a result, it is necessary to evaluate the damage caused to the fisheries by jellyfish. Accordingly, several hydroacoustic studies have been conducted to estimate the target strength (TS) of the giant jellyfish. However, the effects of fluctuation in the acoustic scattering characteristics on swimming patterns have not yet been elucidated. Therefore, in this study, we theoretically estimated the effects of changes in the acoustic scattering pattern on the swimming behavior of jellyfish using the Distorted Wave Born Approximation (DWBA) model. The results confirmed that acoustic scattering of jellyfish results in a significant change in their swimming pattern. Specifically, our theoretical estimation indicated that the TS of giant jellyfish (d=40 cm) fluctuated until 8.5 dB at 38 kHz, 13.8 dB at 70 kHz, and 15.1 dB at 120 kHz based on changes in their swimming patterns.

• 한국컴퓨터정보학회논문지
• /
• 제9권3호
• /
• pp.121-125
• /
• 2004

대부분의 수기 숫자 인식 시스템에서는 자모 형태를 이용한 특징 점 추출과, 형태소 적 분석기법을 많이 사용하였다. 본 연구에서는 체인코드를 사용하고, 생성된 체인코드를 미분하여 최소 값이 되는 미분코드를 만들었다. 이 미분코드는 대부분의 수기 숫자에 적용해 본 결과 숫자 변별력이 매우 뛰어남을 알 수 있었다. 처리 순서는 몇 개의 수기숫자를 전 처리하고, 체인코드와 미분코드를 생성 한 후, HMM 인식 네트워크를 사용하여 숫자 인식하였다. 처리 결과 96.1%의 수기숫자를 인식하였으며, 매우 심하게 왜곡된 숫자는 인식하지 못하였다.

• 한국근적외분광분석학회:학술대회논문집
• /
• 한국근적외분광분석학회 2001년도 NIR-2001
• /
• pp.1287-1287
• /
• 2001

The structure of water molecules in the pure liquid state has been subjected to extensive research for several decades. Questions still remain unanswered, however, and no single model has been found capable of explaining all the anomalies of water. In the present study near-infrared spectra of water in the temperature region 6-$80^{\circ}C$ have been analysed by use of principal component analysis (PCA) and two-dimensional correlation spectroscopy in order to study the dynamic behaviour of the water band centred at 1440 nm, which is due to the combination of symmetric and antisymmetric O-H stretching modes. It has been found that the wavelengths 1412 and 1491 nm account for more than 99% of the spectral variation, representing two major water species with weaker and stronger hydrogen bonds, respectively. A third species located at 1438 nm, whose concentration was relatively constant as a function of temperature, is also indicated. A somewhat distorted two-state structural model for water is suggested.

• 한국정밀공학회지
• /
• 제28권7호
• /
• pp.789-795
• /
• 2011

In elliptical vibration cutting (EVC), cutting performance is largely affected by the shape of an elliptical path of the cutting tool. In this study, two parallel piezoelectric actuators were used to make an elliptical vibration cutting device. When harmonic voltages of $90^{\circ}$ out-of-phase are supplied to the EVC device, creation of an ideal elliptical trajectory whose major and minor axes are parallel to the cutting and thrust directions is anticipated from a kinematic analysis of the EVC device, however, the paths we experimentally observed showed significant distortions in its shape ranging from skew to excessive elongation of the major axis of the ellipse. To compensate distortions, an analytical model describing the elliptical path of the cutting tool was developed and verified with experimental results, and based on the analytical model, the distorted elliptical paths created at 100 Hz, 1 kHz, and 16 kHz were corrected for skew and elongation.

• Journal of Power Electronics
• /
• 제13권5호
• /
• pp.884-895
• /
• 2013

In this paper, the Fourier-based PLL (Phase-locked Loop) is introduced with a new structure, capable of selective harmonic detection in single and three-phase systems. The application of the FB-PLL to harmonic detection is discussed and a new model applicable to three-phase systems is introduced. An analysis of the convergence of the FB-PLL based on a linear model is presented. Simulation and experimental results are included for performance analysis and to support the theoretical development. The decomposition of an input signal in its harmonic components using the Fourier theory is based on previous knowledge of the signal fundamental frequency, which cannot be easily implemented with input signals with varying frequencies or subjected to phase-angle jumps. In this scenario, the main contribution of this paper is the association of a phase-locked loop system, with a harmonic decomposition and reconstruction method, based on the well-established Fourier theory, to allow for the tracking of the fundamental component and desired harmonics from distorted input signals with a varying frequency, amplitude and phase-angle. The application of the proposed technique in three-phase systems is supported by results obtained under unbalanced and voltage sag conditions.