• 한국해양공학회지
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• 제28권4호
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• pp.338-344
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• 2014

The purpose of this study was to evaluate the dispersion degree of particles using a nanoindentation test for titanium oxide nanoparticles/epoxy resin nanocomposites. Thus, the effects of the particle size and weight fraction, dispersion agent, and position of the sample on the modulus and degree of particle dispersion in the nanocomposites were investigated. As a result, the dispersion degree of large particles was found to be better than that of smaller particles in composites. It could be found that the aggregation or agglomeration of small particles with large surface energy occurred more easily in nanocomposites because of the large specific surface area. The moduli of the upper side of the film-shaped sample obtained from a nanoindentation test were low scattering, while the values for the bottom side were high scattering. Thus, the dispersion situation of the nanoparticles on the upper side of film-shaped samples could be considered to be better than that for the bottom side. This could be concluded due to the non-uniform nanoparticle dispersion in the same sample. The modulus obtained from nanoindentation test increased slightly with the content of nanoparticles and increased with the indented depth for the same sample. The latter is presumably due to the increase in the accumulated particles facing the indenter with the indented depth. The nanoindentation test was found to be a useful method to evaluate the dispersion status of nanoparticles in nanocomposites.

• Journal of information and communication convergence engineering
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• 제5권2호
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• pp.164-170
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• 2007

In this paper, the new method alternating with the method for forming the symmetrical distribution of power and local dispersion in high bit-rate WDM system with optical phase conjugator (OPC) is proposed. The proposed method is carried by finding out the optimal values of OPC position offset and fiber dispersion offset. It is assumed to be that NRZ-formatted 24-channels of 40 Gbps are simultaneously propagated in WDM system with non zero - dispersion shifted fiber (NZ-DSF) of 1,000 km. It is confirmed that the compensation extents of overall WDM channels are more improved by applying the induced optimal values into WDM system than those in WDM system with the conventional mid-span spectral inversion (MSSI) technique, and the searching procedure of the optimal values makes little difference of performance if the optimal value of one parameter related with another parameter. And, it is confirmed that the flexible design of WDM system with OPC is possible by effectiviely using by these optimal values. Thus, it is expected that the proposed method alternate with the forming method of the symmetrical distributions of power and local dispersion.

• 한국전자파학회논문지
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• 제29권3호
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• pp.225-232
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• 2018

본 논문은 H(2,4) 기법을 기반으로 한 저분산 유한차분 시간영역법(Finite-Difference Time-Domain: FDTD)을 이용하여 상수 도전율과 비유전율을 갖는 유전체의 광대역 전자기 특성을 정확하게 해석하는 방법을 제안했다. 수치분산오차를 최소화하기 위해서 제안한 FDTD 기법에서 이용하는 세 개의 변수의 최적값을 계산하였다. 잘 알려진 정확한 FDTD 기법들과 제안한 FDTD 방법으로 2차원 원형 유전체 실린더의 광대역 산란 문제를 계산하였고, 그 결과를 이론값과 비교하여 제안한 방법의 우수성을 검증하였다.

• 한국소음진동공학회논문집
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• 제25권8호
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• pp.575-582
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• 2015

This paper deals with the dispersion relation of the waves sustained in a cylindrical shell submerged in the fluid. The waveguide finite method and the boundary element method are used to predict the dispersion characteristic of the cylindrical shell. The dispersion diagram of the cylinder is estimated from the eigenvalue problem and the forced vibration response. It follows that the water-loading leads to the decrease of the cut-on frequencies and the phase speeds of the bending waves. On the contrary, the longitudinal waves and the torsional waves are hardly affected by the fluid, and therefore the order of the cut-on frequencies of the waves is changed. The acoustic dispersion diagram is also estimated from the forced acoustic response to identify the characteristics of the wave radiated to the fluid. It follows that the acoustic waves on and near the surface of the cylinder are the same as those in the structure. But at the far field the acoustic waves caused by subsonic waves e.g., the bending waves disappear as the increase of the distance. Conclusively, the characteristics of waves in cylindrical shells are significantly affected by water-loading in terms of the cut-on frequency, the wave speed, the order of the cut-on and radiation.

• 한국전기전자재료학회논문지
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• 제24권8호
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• pp.682-685
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• 2011

An engine oil sensor based on multiwall carbon nanotubes was fabricated with screen printing method. Since carbon nanotubes are generally intertwined, dispersion of the carbon nanotubes in the binding agent (ethyl cellulose, a-terpineol, frit) is a key factor for large yield of engine oil sensor. By conventional dispersion method, a hand-mill method, the maximum yield was 80% at most. However, we used the hand ultrasonic, in order to increase the yield of the sensors. As a results, our engine oil sensor fabricated by the screen printing method shows excellent yield rate of 97%, when we dispersed a paste by the hand ultrasonic method.

• Korean Journal of Hydrosciences
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• 제5권
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• pp.85-97
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• 1994

A hybrid finite difference method for the longitudinal dispersion equation, which is based on combining the Holly-Preissmann scheme with fifth-degree Hermite interpolating polynomial and the generalized Crank-Nicholson scheme, is described and comparatively evaluated with other characteristics-based numerical methods. Longitudinal dispersion of an instantaneously-loaded pollutant source is simulated, and computational results are compared with the exact solution. The present method is free from wiggles regardless of the Courant number, and exactly reproduces the location of the peak concentration. Overall accuracy of the computation increases for smaller value of the weighting factor, $\theta$of the model. Larger values of $\theta$ overestimates the peak concentration. Smaller Courant number yields better accuracy, in general, but the sensitivity is very low, especially when the value of $\theta$ is small. From comparisons with the hybrid method using cubic interpolating polynomial and with splitoperator methods, the present method shows the best performance in reproducing the exact solution as the advection becomes more dominant.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1986년도 한국자동제어학술회의논문집; 한국과학기술대학, 충남; 17-18 Oct. 1986
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• pp.65-67
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• 1986

The model simplification method of the linear time invariant continuous system is proposed. Using the energy dispersion method the dynamic modes with dominent energy contribution are selected, and the poles of the denomenater are retained. And there is investigated how the dynamic modes affected the system characteristic. The parameters of the numerator are determined by time moment matching method. This method is that the algorithm is simple and also the simplified model found is always stable if the original system is stable, and through examples we assured that this method leads to good results in both transient and steady state responses.

• Structural Engineering and Mechanics
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• 제55권2호
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• pp.335-348
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• 2015

The influence of the interface imperfect bonding on the flexural wave dispersion in the bilayered hollow circular cylinder is studied with utilizing three-dimensional linear theory of elastodynamics. The shear-spring type model is used for describing the imperfect bonding on the interface between the layers and the degree of the imperfectness is estimated through the dimensionless shear-spring parameters which enter the mentioned model. The method for finding the analytical expressions for the sought values and dispersion equation are discussed and detailed. Numerical results on the lowest first and second modes are presented and analyzed. These results are obtained for various values of the shear-spring parameters. According to these results, in particular, it is established that as a results of the imperfection of the bonding between the layers the new branches of the dispersion related the first fundamental mode arise and the character of the dispersion curve related to the second mode becomes more complicated.

• Current Optics and Photonics
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• 제7권4호
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• pp.443-448
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• 2023

The ±1-order Kelly sidebands with dispersion-dependent spacing of mode-locking fiber lasers are investigated for frequency-tunable terahertz signal generation. The principle of dispersion dependence of Kelly sidebands is analyzed. A new method, which is a dispersion-management mechanism introduced into the fiber-laser cavity, is proposed to generate Kelly sidebands with widely tunable wavelength spacing. A spacing tuning range of up to 28.46 nm of the ±1-order Kelly sidebands is obtained in simulation. Using the data of the optical spectrum with dispersion-dependent Kelly sidebands, the frequency spectrum of generated terahertz signals is calculated. Consequently, the signal frequency can be changed from 0.09 to 2.27 THz.

• 한국해안해양공학회지
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• 제3권4호
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• pp.197-208
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• 1991

좌표변환된 깊이방향 평균 X-Y 수치모형을 수립하여 하구에서 염도확산을 분석하였다. 조간대의 수치적 모의, 잔차류, 폐경계조건 등이 검토되었으며, 특히 지배방정식 중 확산항의 처리에 시간분할방법(fractional step method)을 이용하여 수치해의 안정성 및 간편성을 도모하였다. 개발된 모형을 금강하구에 실제 적용하여 유속장과 염도장을 만족스럽게 재현시켰으며 유속장에 따른 확산계수산정에 대해서도 연구하였다.