• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2018.05a
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• pp.73-75
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• 2018

항만시설 및 배후지를 파랑으로부터 방호하는 기능을 가지는 외곽시설 중 항내 정온을 유지하여 하역효율을 높이고, 항내 항행 및 정박 중인 선박의 안전을 확보하고, 항내시설을 보전하기 위하여 설치하는 것으로는 방파제가 있으며, 배치형태로는 항의 외곽에 설치되는 경우와 연안으로 이격되어 설치되는 경우가 있다. 연안으로 이격되어 설치되는 이안제는 필연적으로 방파제 양단으로 회절파랑이 발생하게 되며 이안제 좌 우측으로 각각 분기되어 진행하는 파랑은 회절에 의해 방파제 배후 안쪽으로 휘어져 위상간 간섭을 일으키며 중첩되면서 전파된다. 지형적인 여건으로 진행방향이 같아지게 되고 항 입구부로 향한다면 파랑의 에너지 중첩에 의한 영향이 항내로 나타날 수 있다. 본 연구에서는 항 입구부에 이안제가 설치되는 경우, 이안제 길이에 따라 발생하는 좌 우측 회절 파랑의 위상차가 항내 파고에 미치는 영향을 수치실험을 통해 검토하였다. 이로부터 항내에서의 파고는 이안제의 길이에 따른 좌 우측 회절 파랑의 위상차에 의한 중첩의 영향으로 증폭 혹은 상쇄되어 나타남을 확인하였다.

• Korean Journal of Materials Research
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• v.6 no.8
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• pp.796-800
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• 1996

질소가스 분위기 중에서 Cu30V70 및 Fe30Cr70 혼합분말을 기계적 합금화 (MA)처리한 결과, 두 합금계에서 비정질화가 관찰되었다. 결정질에서 비정질상으로의 구조변화 과정을 Xtjs 회절 및 중성자 회절법에 의해 관찰되었다. 결정질에서 비정질상으로의 구조변화 과정을 X선 회절 및 중성자 회절법에 의해 관찰하였다. 그 결과, 이 합금계에서의 비정질화는 각 결정구조에서 전형적으로 존재하는 8면체 unit가 선택적으로 붕괴되어 4면체 unit로 변화되어 가는 과정임을 알 수 있었다. 또한, 중성자회절 결과로부터 질소원자는 금속원자로 이루어진 4면체의 중심에 위치하고 있음을 알 수 있었다.

• Korean Journal of Optics and Photonics
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• v.3 no.3
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• pp.155-160
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• 1992

1)iscussed in this paper are the effects of phase modulation on the line spread functions (LSF) and MTFs of ;I binocular objective system. The binocular objective lens is made in Korea. It has rotationally symmetric aberrations. The LSFs and MTFs are measured experimentally. The phase modulation is carried out by applying phase retardation n on the aperture. The area where the phase is not retarded presents a double annular type. The OTF curves of phase modulated aperture are compared with that of unmodulated aperture. The comparison shows that there is the aberration compensation effect in aberration loaded system. Therefore the performance of many optical system can be improved without any loss of light energy by properly modulating the phase on the aperture.

• Korean Journal of Optics and Photonics
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• v.3 no.3
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• pp.148-154
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• 1992

With nonhardening fixer, dichromated bleacher and alcohol drying, the diffraction efficiency of over 71o/c has been achie'{ed for holographic phase gratings in silver halide emulsion. The swollen emulsion of Agfa 8E75 HD film is identified by scanning electron microscope (SEM) after chemical processing. Dichromated bleacher and rapid dehydration using alcohol drying make a strong modulation so that diffraction efficiency is. increased over 20%. The principal characteristic parameters in coupled wave theory are investigated and new modified parameter values are presented by computer simulation. Controlling the emulsion thickness has an important role as a potential source for high diffraction efficiency.ciency.

• Korean Journal of Optics and Photonics
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• v.7 no.3
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• pp.207-212
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• 1996

We propose an extended additional layer method (EALM) of calculating the coupling coefficient of arbitrary shaped diffraction gratings. In EALM, to determine the unperturbed field distribtution, a grating region is replaced by a new uniform layer whose dielectric constant is the average value of the dielectric constant of a grating region in both longitudinal and transverse directions. Using this method, we calculate the coupling coefficient for a five-layer distributed feedback structure device with trapezoidal and triangular gratings. The validity of this method is established by comparing the results calculated by partitioning the grating region up to five uniform layers.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.5
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• pp.23-31
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• 1989

The electromagnetic diffraction problem for the incidence of E-polarized planewave on both interfaces of an arbitrary-angled dielectrc wedge is solved in conjunction with the edge condition near the tip of dielectric wedge in the static limit. The diffraction coefficients obtained by the tip of the wedge, the diffraction coefficients presented in this paper approach more closely to the exact pattem of a perfectly conducting wedge as the relative dielectric constants of the dielectric wedge increase.

• Korean Journal of Optics and Photonics
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• v.15 no.4
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• pp.313-320
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• 2004

We present a null testing method fer aspheric surfaces, utilizing a phase-shifting diffraction grating interferometer along with a binary amplitude computer generated hologram (CGH). The binary amplitude CGH is designed to compensate for the wavefront between a point source and the aspheric surface under test. The fringe visibility of the grating interferometer is controlled easily by selecting suitable grating diffraction orders for the measurement and reference wavefronts or by optimizing the groove shape of the grating used. The binary amplitude CGH is designed by numerical analysis of ray tracing and fabricated using e-beam lithography for autostigmatic testing. Experimental results of a large-scale aspheric mirror surface are discussed to verify the measurement performance of the proposed diffraction grating interferometer.

• Applied Microscopy
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• v.35 no.4
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• pp.1-9
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• 2005

In this paper it is reported that a comprehensive study of the crystal structure of the fine size S-phase ($Al_2CuMg$) precipitate in Al-Cu-Mg alloy by electron diffraction experiments. The experiments involve taking the selected area diffraction pattern for a S-phase particle, simulations of the pattern based on the kinematical diffraction theory and quantitative data collection from the zone axis diffraction patterns for the comparison with calculated diffraction intensity using both the kinematical and the dynamical diffraction theory. As a result, a good fitting model of the S-phase structure turns out to be the model reported early by X-ray methods (Perlitz & Westgren, 1943), not the new model determined by HRTEM methods (Radmilovic et al., 1999).

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.8
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• pp.48-56
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• 2000

Effects of the correlated random fluctuation in each grating half-period have been studied by an effective index transfer matrix method in quarter wavelength shifted DFB lasers. As the correlation coefficient changes from 0 to -1, single mode stability and wavelength accuracy are less degraded by the reduced error in the grating period. This fact shows that holographic grating fabrication is better than electron-beam lithography in discrete device fabrication provided that the magnitude of the random fluctuation is the same.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.16 no.10
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• pp.934-940
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• 1991

A modified quantizing method is introduced to teach single layer learning algorithm, which is implemented optically. The proposed optical system consists of input masks, holographic diffraction grating. LCD and CCD camera. The 2 dimensional interconnections between input neurons and output neurons are realized using holographic phase grating, which is fabricated for equal intensity distribution of diffraction orders. The two gray levels of LCD act as binary weights for each interconnection. The weights are compensated according to the learning algorithm in which the amount of weights to be compensated is determined by comparing the output patterns with target patterns. The learning process is iterated until the predetermined conditions are satisfied. Optical experiments are performed for two learning rates, 0.5 and 0.9 and the experimental results show that the proposed system is useful for optical neural networks.