• Title/Summary/Keyword: Bragg reflection

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Preparation of Polystyrene Thin Films Containing Bragg Structure and Investigation of Their Photonic Characteristics (Bragg 구조를 갖는 Polystyrene 박막필름의 제조방법과그들의 광학적 특성 조사)

  • Cho, Sungdong
    • Journal of Integrative Natural Science
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    • v.3 no.3
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    • pp.138-142
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    • 2010
  • Polystyrene thin films containing Bragg structures have been successfully obtained by the removal of DBR porous silicon films from the DBR structured porous silicon/polystyrene composite film in HF/$H_2O$ mixture solution and by replicating the nano-structures of porous silicon containing Bragg structure. Polystyrene thin films containing Bragg structures displayed unique optical reflection resonances in optical reflection spectrum. This optical reflection band was resulted from the interference of reflection wavelength at Bragg structure of polystyrene thin films. The wavelength of reflection resonances could be modified by the change of Bragg structure of the master. Polystyrene thin films containing Bragg structures were flexible and maintained their optical characteristics upon bending. The Polystyrene thin films replicate the photonic features and the nanostructure of the master.

BRAGG RESONANT REFLECTION OF OBLIQUELY INCIDENT WATER WAVES

  • Cho, Yong-Sik
    • Water Engineering Research
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    • v.1 no.1
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    • pp.75-81
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    • 2000
  • The bragg reflection of obliquely incident monochromatic water waves propagating over a sinusoidally varying topography is theoretically investigated in this study. The eigenfunction expansion method is first employed to calculate reflection coefficients of water waves due to depth changes. A reasonable agreement is observed. Obtained reflection coefficients of normally incident waves are compared with laboratory measurements. Reflection coefficients of obliquely incident waves are then calculated. The wavenumber providing the Bragg reflection agrees well with analytical predictions.

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Bragg Reflection of Obliquely Incident Waves (비스듬히 입사하는 파랑의 Bragg반사)

  • Jo, Yong-Sik;An, Yeong-Chang
    • Journal of Korea Water Resources Association
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    • v.35 no.1
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    • pp.91-96
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    • 2002
  • The present research describes the Bragg reflection of obliquely incident waves propagating over sinusoidally varying topographies. A numerical model based on the boundary element method is employed. Wave numbers providing Bragg reflection are calculated and compared to theoretical predictions. The reflection coefficients obtained from this model are also compared with those of the eigenfunction expansion method. A very good agreement is observed.

Bragg Reflection on a Sloping Beach (경사지형에서의 Bragg반사)

  • Lee, Jong-In;Jo, Yong-Sik;Lee, Jeong-Gyu
    • Journal of Korea Water Resources Association
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    • v.32 no.4
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    • pp.447-455
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    • 1999
  • In this study, the Bragg resonant of cnoidal waves propagating over a sinusoidally varying topography lying on a uniformly sloping beach is investigated. The governing equations derived from the Boussinesq equations are numerically integrated. The effects of fast varying terms and nonlinearity in reflection coefficients are also examined. Variation of reflection coefficient for different sloping beaches is studied. It is found that reflection coefficients are not strongly dependent on slopes of beaches.

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Study for the Bragg Detuning Effects on the Transmission Holograms and the Reflection Holograms (투과형 홀로그램과 반사형 홀로그램에서의 Bragg detuning 현상에 대한 연구)

  • Kwon, Yun-Young;Kim, Kun-Yul;Park, Joo-Youn
    • Transactions of the Society of Information Storage Systems
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    • v.2 no.3
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    • pp.189-195
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    • 2006
  • Bragg detuning effect if, one of the serious problems if the photopolymer is used for the recording material of holography memories. And the critical reasons of that are known as the bulk refractive index change and shrinkage of recording material. However, the trials for analyzing the effect are mainly on the K-sphere and biased on the transmission hologram. So, we approached Bragg detuning effect numerically and applied the method to the transmission holograms and the reflection holograms all together. We simulated it with MATLAB. As a result, the bulk refractive index change causes+Bragg detuning effect on the transmission holograms and the reflection holograms. But the shrinkage leads to+Bragg detuning effect on the transmission hologram and-Bragg detuning effect on the reflective hologram. Compared to experimental result, the bulk refractive index change(${\fallingdotseq}4{\times}10^{-4}$) and the ratio of shrinkage to the thickness of the material(${\fallingdotseq}1.67{\times}10^{-3}$) could be matched with Bragg detuning effect on the transmission hologram and the reflection hologram.

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Investigation of surface-piercing fixed structures with different shapes for Bragg reflection of water waves

  • Ding, Wei-Wei;Zou, Zao-Jian;Wu, Jing-Ping;Huang, Bai-Gang
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.11 no.2
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    • pp.819-827
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    • 2019
  • Bragg reflection of water waves by three kinds of surface-piercing fixed structures with rectangular, cosinoidal and triangular shapes is studied. Boundary element method is used to analyze the wave scattering by these structures based on the linear wave theory. Results of reflection and transmission coefficients are validated by comparing with those available in literature. These structures with proper configurations are proved to be effective in attenuating waves by using Bragg reflection, and the triangular structures are found to be the best choices among the structures with same width and same area. Systematic calculations are then carried out for the triangular structures by varying the number, the draft, the width, the gap and the combination of width and gap of the structures to analyze their influences on the characteristics of Bragg reflection. The results are of reference values for design of the structures to attenuate waves based on the Bragg reflection.

Bragg Reflection of Long Waves Generated by Short Wave Groups on a Sloping Beach (경사지형에서 파군에 의해 생성된 장파의 Bragg 반사)

  • Jung, Jae-Sang;Cho, Yong-Sik
    • Journal of Korea Water Resources Association
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    • v.36 no.3 s.134
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    • pp.413-422
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    • 2003
  • Numerical analysis for the Bragg reflection due to sinusoidally varying seabeds tying on a sloping beach was performed by using a couple of ordinary differential equations derived from the Boussinesq equations. Incident waves were wane groups generated by two short waves with slightly different phases. Effects of the slope of a seabed to the reflection were investigated in detail. It is shown that the reflection of long waves enhanced by increasing the slope of a seabed. This phenomenon caused by increase of wave amplitude due to increase of nonlinearity and shoaling.

Spatial Modulation of Nonlinear Waves due to Bragg Reflection (Bragg 반사에 의한 비선형파의 공간적 파형변조해석)

  • Choi, Ka-Ram;Koo, Weon-Cheol
    • Journal of Ocean Engineering and Technology
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    • v.24 no.6
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    • pp.34-40
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    • 2010
  • Bragg reflection of nonlinear waves is simulated by a 2D fully nonlinear numerical wave tank (NWT). The developed NWT was based on the Boundary Element Method (BEM) with potential theory and the mixed Eulerian-Lagrangian (MEL) time marching scheme with Runge-Kutta 4th-order time integration. A spatial variation of wave elevations and their Fourier amplitudes of each component are compared to investigate the effect of sea bottom ripples and their relative heights. The incident waves over an undulated sea bottom are partially reflected and changed to partial standing waves due to Bragg reflection. The present results are verified with linear calculations and experimental data. It is found that the 1st-order wave component is mainly affected by Bragg reflection and its spatial modulation is significant in front of the bottom ripples.

Analysis of Bragg Reflection using Two-Dimensional Boundary Element Method (2차원 경계요소법을 이용한 Bragg반사 해석)

  • Kim, Yeong-Taek;Jo, Yong-Sik;Lee, Jeong-Gyu
    • Journal of Korea Water Resources Association
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    • v.33 no.6
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    • pp.805-814
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    • 2000
  • A numerical model based on the boundary element method is employed to describe diffraction of monochromatic water waves due to varying topographies. The model is firstly verified by comparing obtained reflection and transmission coefficients of waves over a trench to those of the eigenfunction expansion method. The model is then used to investigate the Bragg reflection of waves over sinusoidally varying topographies. Calculated reflection coefficients are compared to available laboratory measurements and semi-theoretical results. A reasonably good agreement is observed.served.

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Analysis of Bragg Reflection of Waves due to Rectangular Impermeable Submerged Breakwaters with Two-Dimensional Finite Element Method (2차원 유한요소법을 이용한 불투과성 사각형 수중방파제의 Bragg 반사 해석)

  • Cho, Yong-Sik;Jeong, Woo-Chang
    • Journal of Korea Water Resources Association
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    • v.36 no.3 s.134
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    • pp.447-454
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    • 2003
  • The Bragg reflection of monochromatic waves propagating over a rectangular-typed impermeable submerged breakwaters is numerically investigated by using the finite element method. The reflection coefficients calculated from the present model are compared with those of laboratory measurements and the eigenfunction expansion method. A good agreement is observed. The finite element model is also applied to calculate reflection coefficients according to variations of length and width of submerged breakwater.