• Title/Summary/Keyword: domain wall velocity

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Characteristic of $LiNbO_3$ Domain Inversion and Fabrication of Electrooptic Device Application using Domain Reversal ($LiNbO_3$ 기판의 도메인 반전 특성과 이를 이용한 기능성 광변조기의 제작)

  • Jeong, W.J.;Kim, W.K.;Yang, W.S.;Lee, H.M.;Kwon, S.W.;Song, M.K.;Lee, H.Y.
    • Journal of the Institute of Electronics Engineers of Korea SD
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    • v.44 no.3 s.357
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    • pp.20-25
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    • 2007
  • The periodic domain-inversion in the selective areas of $Ti:LiNbO_3$ Mach-Zender waveguides was performed and band-pass modulators and single sideband (SSB) modulators were fabricated by using domain-reversal. The domain wall velocity was precisely controlled by real-time analysis of a poling-induced response current under an applied voltage. The domain wall velocity was significantly affected by the crystal orientation of the domain wall propagation which influenced the final domain geometry. In a certain case, the decomposition of $LiNbO_3$ crystal was observed, for example, under the condition of too fast domain wall propagation. The fabricated band-pass modulator with a periodic domain-inversion structure showed the maximum modulation efficiency at 30.3 GHz with 5.1 GHz 3dB-bandwidth, and SSB modulator was measured to show 33 dB USB suppression over LSB at 5.8 GHz RF.

Characteristics of Lifted Flames in Nonpremixed Turbulent Confined Jets (제한공간에서 비예혼합 난류제트 화염의 부상특성)

  • Cha, Min-Suk;Chung, Suk-Ho
    • Journal of the Korean Society of Combustion
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    • v.1 no.1
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    • pp.41-49
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    • 1996
  • Effects of ambient geometry on the liftoff characteristics are experimentally studied for nonpremixed turbulent jet flames. To clarify the inconsistency of the nozzle diameter effect on the liftoff height, the ambiences of finite and infinite domains are studied. For nonpremixed turbulent jet issuing from a straight nozzle to infinite domain, flame liftoff height increases linearly with nozzle exit mean velocity and is independent of nozzle diameter. With the circular plate installed on the upstream of nozzle exit, flame liftoff height is lower with plate at jet exit than without, but flame liftoff characteristics are similar to the case of infinite domain. For the confined jet having axisymmetric wall boundary, the ratio of the liftoff height and nozzle diameter is proportional to the nozzle exit mean velocity demonstrating the effect of the nozzle diameter on the liftoff height. The liftoff height increases with decreasing outer axisymmetric wall diameter. At blowout conditions, the blowout velocity decreases with decreasing outer axisymmetric wall diameter and liftoff heights at blowout are approximately 50 times of nozzle diameter.

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A Modelling of magnetization reversal characteristics in magneto-optic memory system (광자기 기억장치에서의 자화반전 특성 모델링)

  • 한은실;이광형;조순철
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.19 no.10
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    • pp.1849-1860
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    • 1994
  • Domain wall dynamics in thin film of amorphous Rare Earth-Transistion Metal alloys were investigated using numerical integration of the Landau-Lifshitz-Gilbert equation. The thin film was divided into a two-dimensional square lattice ($30\times30$) of dipoles. Nearest-neighbor exchange interaction magnetic anisotropy, applied magnetic field, and demagnetiing field of interacting anisotropy, applied magnetic field, and demagnetizing field of interacting dipoles were considered. It was assumed that the film had perfect uniaxial anisotropy in the perpendicular direction and the magnetization reversal existed in the film. The time of domain wall creation and the thickness of the wall were investigated. Also the motion of domain walls under an applied field was considered. Simulation results showed that the time of domain wall creation was decreased significantly and the average velocity of domain wall was increased somewhat when the demagnetizing field was considered.

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Monitoring Method for Pipe Thinning using Accelerometers (가속도계를 이용한 배관 감육 감시 방법)

  • Choi, Young-Chul;Park, Jin-Ho;Yoon, Doo-Byung;Sohn, Chang-Ho;Hwang, Il-Soon
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2006.11a
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    • pp.156-162
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    • 2006
  • Pipe thinning is one of the major issues for the structural fracture of pipes of nuclear power plants. Therefore a method to inspect a large area of piping systems quickly and accurately is needed. In this paper, we proposed the method for monitoring pipe thinning. Our basic idea come from that a group velocity of impact wave is different as wall thickness. If the group velocity is measured, wall thickness can be estimated. To obtain the group velocity, time-frequency analysis is used. This is because an arrival time difference can be measured easily in time-frequency domain rather than time domain. To test the performance of this technique, experiments have been performed for a plate and U type pipe. Results show that the proposed technique is quite powerful in the monitoring pipe thinning.

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Monitoring Pipe Thinning Using Time-frequency Analysis (시간-주파수 기법을 이용한 배관 감육 감시 방법)

  • Sohn, Chang-Ho;Park, Jin-Ho;Yoon, Doo-Byung;Chong, Ui-Pil;Choi, Young-Chul
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.16 no.12 s.117
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    • pp.1224-1230
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    • 2006
  • Pipe thinning is one of the major issues for the structural fracture of pipes of nuclear power plants. Therefore a method to inspect a large area of piping systems quickly and accurately is needed. In this paper, we proposed the method for monitoring pipe thinning. Our basic idea come from that a group velocity of impact wave is different as wall thickness. If the group velocity is measured, wall thickness can be estimated. To obtain the group velocity, time -frequency analysis is used. This is because an arrival time difference can be measured easily in time-frequency domain rather than time domain. To test the performance of this technique, experiments have been performed for a plate and U type pipe. Results show that the proposed technique is quite powerful in the monitoring pipe thinning.

Dynamics of Transverse Magnetic Domain Walls in Rectangular-shape Thin-film Nanowires Studied by Micromagnetic Simulations

  • Lee, Jun-Young;Choi, Sang-Kook;Kim, Sang-Koog
    • Journal of Magnetics
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    • v.11 no.2
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    • pp.74-76
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    • 2006
  • Dynamic behaviors of transverse domain walls (TDWs) in rectangular shaped thin-film magnetic nanowires with different widths under applied magnetic fields less than the Walker field were studied by micromagnetic simulations. It was found that the velocity of stable TDWs in the viscous region increases from 147 to 419 m/s and their mass decreases from $6.24{\times}10^{-23}\;to\;2.70{\times}10^{-23}kg$ with increasing strength of the applied magnetic field ranging from 5 to 20 Oe for the nanowire with a dimension of 10 nm in thickness and $5{\mu}m$ in length, and 50 nm in width. With increasing the width of nanowires from 50 to 125 nm at a specific field strength of 5 Oe, the TDW's velocity also increases from 147 to 246 m/s and its mass decreases from $6.24{\times}10^{-23}\;to\;5.91{\times}10^{-23}kg$.

Hydrodynamic forces on blocks and vertical wall on a step bottom

  • Mondal, Ramnarayan;Alam, Md. Mahbub
    • Wind and Structures
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    • v.30 no.5
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    • pp.485-497
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    • 2020
  • A study, using potential water wave theory, is conducted on the oblique water wave motion over two fixed submerged rectangular blocks (breakwaters) placed over a finite step bottom. We have considered infinite and semi-infinite fluid domains. In both domains, the Fourier expansion method is employed to obtain the velocity potentials explicitly in terms of the infinite Fourier series. The unknown coefficients appearing in the velocity potentials are determined by the eigenfunction expansion matching method at the interfaces. The derived velocity potentials are used to compute the hydrodynamic horizontal and vertical forces acting on the submerged blocks for different values of block thickness, gap spacing between the two blocks, and submergence depth of the upper block from the mean free surface. In addition, the wave load on the vertical wall is computed in the case of the semi-infinite fluid domain for different values of blocks width and the incident wave angle. It is observed that the amplitudes of hydrodynamic forces are negligible for larger values of the wavenumber. Furthermore, the upper block experiences a higher hydrodynamic force than the lower block, regardless of the gap spacing, submergence depth, and block thickness.

LARGE EDDY SIMULATION OF TURBULENT CHANNEL FLOW USING ALGEBRAIC WALL MODEL

  • MALLIK, MUHAMMAD SAIFUL ISLAM;UDDIN, MD. ASHRAF
    • Journal of the Korean Society for Industrial and Applied Mathematics
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    • v.20 no.1
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    • pp.37-50
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    • 2016
  • A large eddy simulation (LES) of a turbulent channel flow is performed by using the third order low-storage Runge-Kutta method in time and second order finite difference formulation in space with staggered grid at a Reynolds number, $Re_{\tau}=590$ based on the channel half width, ${\delta}$ and wall shear velocity, $u_{\tau}$. To reduce the calculation cost of LES, algebraic wall model (AWM) is applied to approximate the near-wall region. The computation is performed in a domain of $2{\pi}{\delta}{\times}2{\delta}{\times}{\pi}{\delta}$ with $32{\times}20{\times}32$ grid points. Standard Smagorinsky model is used for subgrid-scale (SGS) modeling. Essential turbulence statistics of the flow field are computed and compared with Direct Numerical Simulation (DNS) data and LES data using no wall model. Agreements as well as discrepancies are discussed. The flow structures in the computed flow field have also been discussed and compared with LES data using no wall model.

Analytical Study on Hydroelastic Vibration of Stiffened Plate for a Rectangular Tank (사각형 탱크 보강판의 유체구조 연성진동에 대한 이론적 인구)

  • Kim, K.S.;Kim, D.W.;Lee, Y.B.;Choi, B.H.;Choi, S.H.;Kim, Y.S.
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2005.11b
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    • pp.65-68
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    • 2005
  • In this paper, a theoretical study is carried out on the hydroelastic vibration of a rectangular tank wall. It is assumed that the tank wall is clamped along the plate edges. The fluid velocity potential is used for the simulation of fluid domain and to obtain the added mass due to wall vibration. In addition, the vibration characteristics of stiffened wall of the rectangular tank are investigated. Assumed mode method is utilized to the stiffened plate model and hydrodynamic force is obtained by the proposed approach. The coupled natural frequencies are obtained from the relationship between kinetic energies of a wall including fluid and the potential energy of the wall. The theoretical result is compared with the three-dimensional finite element method and then added mass effect is discussed due to tank length and potential mode.

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