• Nuclear Engineering and Technology
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• 제52권10호
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• pp.2250-2261
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• 2020

Accurate localization of radioactive materials is crucial in homeland security and radiological emergencies. Coded-aperture gamma camera is an interesting solution for such applications and can be developed into portable real-time imaging devices. However, traditional reconstruction methods cannot effectively deal with signal-independent noise, thereby hindering low-noise real-time imaging. In this study, a novel reconstruction method with excellent noise-suppression capability based on a multi-layer perceptron (MLP) is proposed. A coded-aperture gamma camera based on pixel detector and coded-aperture mask was constructed, and the process of radioactive source imaging was simulated. Results showed that the MLP method performs better in noise suppression than the traditional correlation analysis method. When the Co-57 source with an activity of 1 MBq was at 289 different positions within the field of view which correspond to 289 different pixels in the reconstructed image, the average contrast-to-noise ratio (CNR) obtained by the MLP method was 21.82, whereas that obtained by the correlation analysis method was 5.85. The variance in CNR of the MLP method is larger than that of correlation analysis, which means the MLP method has some instability in certain conditions.

• Journal of electromagnetic engineering and science
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• 제6권2호
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• pp.130-134
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• 2006

This paper presents the reduction characteristics of penetrated electromagnetic fields through a narrow slot in a planar conducting screen of infinite extent. When a plane wave is excited to the narrow slot, the aperture electric field is controlled by the parallel wire or parallel plate connected on the slot. The magnitude of penetrated electromagnetic fields through a narrow slot is controlled by electric field distributions on the slot. An integral equation for the aperture electric field on narrow slots is derived and solved by applying Galerkin's method of moments. The results show that the magnitude of the penetrated electromagnetic field can be effectively reduced by installing the parallel wire or parallel plate on the slot.

• Journal of the Optical Society of Korea
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• 제20권4호
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• pp.500-509
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• 2016

Integrating spheres play a central role in the radiometric calibration of remote sensors. With the development of the wide field of view (FOV) remote sensors, aperture diameters of remote sensors are becoming larger and larger. To satisfy the radiometric calibration requirements of full FOV and full aperture, an 8000mm diameter large aperture integrating sphere uniform source with a variable exit port was designed and manufactured. This integrating sphere will be used for pre-launch test and radiometric calibration of remote satellites. In this paper, optical theories were used to design the output spectral radiance. The LightTools software based on ray-tracing simulation method was used to determine the best combination and distribution of inner light sources. A spectral experiment was made to verify the spectral radiance design. To reduce the influence of longtime power-on, a new characteristic measurement method was developed to obtain the radiation characteristic of the integrating sphere, which could greatly improve the measuring efficiency. This method could also be applied to measure other large aperture uniform sources. The obtained results indicate that the spatial uniformity is 98.35%, and the angular uniformity at center position is 98.78%.

• 전자공학회논문지A
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• 제32A권12호
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• pp.36-47
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• 1995

The main purpose of this paper is to determine a new focal point and field distribution due to the shape deformation of reflector antenna by numerical method such as geometrical optics and the aperture field method. It is shown the 4 types deformations to be added into original shape of parabola antenna and offset antenna: linear, quadratic, cubic and hybrid distortion. These results can be applied to deformed reflector antenna in order to fit a focal point and radiation pattern.

• 대한기계학회논문집
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• 제16권9호
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• pp.1654-1668
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• 1992

본 연구에서는 경험적으로 측정점 사이의 간격과 구경의 크기를 정하는 방법 에 대하여 살펴보았다.이에 반하여 둘러싸기 오차(wraparound error)는 이산화된 파수 성분 데이타의 처리 과정에서 발생하게 되는데, 이를 줄이기 위한 방법의 일환으 로 본 논문에서는 제로패딩(zero padding)방법을 도입하였다. 또한 둘러싸기 오차 (wraparound error)의 크기를 정량화하여 신뢰할 수 있는 예측결과의 범위를 살펴보았 다.

• 대한기계학회논문집
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• 제19권4호
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• pp.950-967
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• 1995

Acoustic holography makes it possible to reconstruct the acoustic field based on the measurement of the pressure distribution on the hologram surface. Because of the merit that one can obtain an entire three-dimensional wave field from the data recorded on a two-dimensional surface, the holographic method has been widely studied. Being an experimental method, holography has an unavoidable error which is generate by sampling in space and frequency domain and finite aperture size. Its magnitude is dependent on the space and frequency domain and finite aperture size. Its magnitude is dependent on the shape of hologram surface, acoustic holography may be classified into four types of holography : rectangular type planeholography, circular type plane holography, cylindrical holography and spherical holography. In this paper, four types of holography are studied by modal summation method. Numerical simulation is performed using a monopole source with varying parameters to find out effects to the estimation error in each holography. Experiments of circular type plane holography and cylindrical holography explain strong relation between the shape of hologram surface and the acoustic field.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2000년도 춘계종합학술대회
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• pp.101-104
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• 2000

본 논문에서는 외부에 존재하는 전자파원으로부터 공동 구조의 벽면에 존재하는 개구를 통해 공동내부로 침투되는 전계의 크기를 모멘트법으로 계산하였다. 모멘트법으로 계산한 결과와 다른 수치해석 방법을 사용한 결과와 비교하였고 해석 결과는 비교치와 잘 일치하고 있음을 확인하고 있다. 또 한 개구를 통한 전자계 침투는 공동과 개구의 구조에 의존하는 특정 주파수에서 최대치를 나타내고 있음을 확인하고 있다.

• Current Optics and Photonics
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• 제2권4호
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• pp.361-367
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• 2018

Ultrafast deep-ultraviolet (DUV) pulse generation from the subwavelength aperture of a plasmonic waveguide was investigated. The plasmonic nanofocusing of near-infrared (NIR) pulses was exploited to enhance DUV photoemission of surface third harmonic generation (STHG) at the amorphous $SiO_2$ dielectric. The generated DUV pulses which are successfully made from a nano-aperture using 10 fs NIR pulses have a spectral bandwidth of 13 nm at a carrier wavelength of 266 nm. This method is applicable for tip-based ultrafast UV laser spectroscopy of nanostructures or biomolecules

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 추계학술대회 논문집
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• pp.643-648
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• 2011

This paper deals with the ESM(equivalent source method) with the continuation of acoustic near-field for NAH(near-field acoustic holography) to overcome the finite measurement aperture effect and reconstruct the normal velocity on an arbitrarily shaped structure surface. The continuation method is an extension of the measured sound field into a region outside and is based on the Green's function relating acoustic quantities on the two conformal surfaces. This algorithm is not limited to planar surfaces and can be applied to arbitrarily shaped surfaces. The ESM is an alternative approach of BEM-based NAH for the reconstruction on a general structure. In ESM the acoustic field is represented by a set of point sources located over a surface that is close to the structure surface. The simulation results of this study shows that the reconstruction error of particle velocity on the source surface is 11% and 16% for planar and cylindrical sources separately.

• 한국지반공학회논문집
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• 제16권1호
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• pp.221-226
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• 2000

단일 균열시스템에서 간극 크기에 따른 상대투과도의 변화 특성을 측정하기 위해 본 연구에서는Hele-Shaw평판 형태의 유리 평판을 제작하여 실험을 수행하였다. 평판의 재질은 유동 양상 관찰을 위해 유리를 사용하였고, 간극 크기는 실제 현장에서 관측되는 30에서 $120\mum$ 사이의 범위에서 7가지 경우를 설정하여 정상유동법에 의한 실험을 수행하였다. 또한 실험 측정결과에 대한 보다 정확한 포화도 계산 및 분석의 편의를 위해 디지털 영상 편집법 (digital image process technique)을 이용한 해석모델을 개발ㆍ이용하였으며, 균열에서의 2상 유체유동 양상에 직접적인 영향을 미치는 간극크기와 매질의 표면 특성을 나타내는 임계포화도를 이용하여 단일 균열에 대한상대투과도 실험관계식을 도출하였다.