• Korean Journal of Optics and Photonics
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• v.15 no.2
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• pp.104-108
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• 2004

A simple dispersion measurement technique has been demonstrated by using a self-seeding laser oscillation of a Fabry-Perot laser through a closed loop. The optical pulses of different wavelengths emitted from the Fabry-Perot laser travel down an optical fiber and the group velocity difference between the pulses due to the chromatic dispersion of the optical fiber is measured through the self-seeding laser oscillation process. The dispersion parameter of the optical fiber is calculated from the measured group velocity difference. The performance of the proposed technique has been confirmed experimentally and the accuracy of dispersion parameter measurement was comparable to that of commercial instruments with expensive equipment and components. The repeatability of the proposed method was better than 0.5%.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.9
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• pp.5585-5593
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• 2014

This study tested the hypothesis that the significance of the heterogeneous dispersion parameter in safety performance function (SPF) used to estimate the expected crashes is affected by the endogenous heterogeneous prior distributions, and analyzed the impacts of the mis-specified dispersion parameter on the evaluation results for traffic safety countermeasures. In particular, this study simulated the Poisson means based on the heterogeneous dispersion parameters and estimated the SPFs using both the negative binomial (NB) model and the heterogeneous negative binomial (HNB) model for analyzing the impacts of the model mis-specification on the mean and dispersion functions in SPF. In addition, this study analyzed the characteristics of errors in the crash reduction factors (CRFs) obtained when the two models are used to estimate the posterior means and variances, which are essentially estimated through the estimated hyper-parameters in the heterogeneous prior distributions. The simulation study results showed that a mis-estimation on the heterogeneous dispersion parameters through the NB model does not affect the coefficient of the mean functions, but the variances of the prior distribution are seriously mis-estimated when the NB model is used to develop SPFs without considering the heterogeneity in dispersion. Consequently, when the NB model is used erroneously to estimate the prior distributions with heterogeneous dispersion parameters, the mis-estimated posterior mean can produce large errors in CRFs up to 120%.

• Proceedings of the IEEK Conference
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• 2001.10a
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• pp.353-356
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• 2001

The relation between the flocculation and dispersion of metal oxide powders and the properties of solvents, such as dielectric constant and solubility parameter, was investigated for TiO$_2$, $Al_2$O$_3$and Fe$_2$O$_3$particles. The particle size and median diameter of these metal oxides were measured in many organic solvents, from which the effect of solvents on the flocculation and dispersion of metal oxide powders was considered. The metal oxide powders of TiO$_2$, $Al_2$O$_3$and Fe$_2$O$_3$tend to disperse in a solvent of higher polarity, whereas they are apt to flocculate in a solvent of low dielectric constant, because the Hamaker constant between the particles becomes larger in such a solvent. There we, however, some solvents that do not obey these tendencies. It is possible to evaluate the flocculation and dispersion of these metal oxide powders in many solvents by using numeral balances of Hansen’s three-dimensional solubility parameter (f$_{d}$, f$_{p}$ and f$_{h}$). There exists a solvent giving the optimal dispersion for each metal oxide, and the optimal dispersion point of f$_{d}$, f$_{p}$ and f$_{h}$ is determined by the combination of various metal oxide powders and solvents.nts.nts.nts.

• Composites Research
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• v.35 no.1
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• pp.18-22
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• 2022

Dispersion is one of the most important factors in the manufacture of composite materials. In the manufacture of composite materials, solvents are used to better disperse the reinforcement, nano-filler in the matrix. Since dispersion is affected with solvents, it is necessary to study which solvent is adopted to get good dispersion. In this study, the dispersion behavior and solubility of graphene oxide(GO) were examined under various solvents (DMF, NMP, ethylene glycol, Acetone, DI water) to identify dispersion. As a result of UV-Vis spectroscopy absorbance measurement, it was found that DMF and ethylene glycol had the best dispersibility, whereas DI water showed the lowest dispersibility. In addition, as a result of visually observing the dispersion according to the surface tension and time, it was found that the dispersibility was excellent in the order of DI water, ethylene glycol, NMP, DMF, and acetone, which was consistent with the Hansen solubility parameter value.

• Journal of Korea Society of Digital Industry and Information Management
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• v.11 no.1
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• pp.79-88
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• 2015

In this paper, it is investigated that the limitation due to the asymmetry of optical power and chromatic dispersion with respect to optical phase conjugator (OPC) for compensating optical signal distortion in WDM system is overcomed by using OPC position offset and optimal dispersion coefficients of fiber sections, which depend on OPC position offset. It is confirmed that overall WDM channels are efficiently compensated by applying the optimal parameter values obtained from the proposed method into 24 channels ${\times}40$ Gbps WDM system with non zero - dispersion shifted fiber (NZ-DSF) of 1, 000 km, such as power penalties of inter-channel are reduce to almost 3.5 dB from the infinite value. It is also confirmed that the flexible design of WDM system with OPC is possible by using the optimal parameters, in which OPC is placed at ${\pm}15km$ from 500 km for efficiently compensating overall channels. Thus, the methods proposed in this research will be expected to alternate with the method of making a symmetrical distribution of power and local dispersion in real optical link which generates a serious problem if it was not made but it is the condition in the case of applying the OPC into multi-channels WDM system.

• Advances in nano research
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• v.6 no.3
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• pp.201-217
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• 2018

In the present research, wave propagation characteristics of a rotating FG nanobeam undergoing rotation is studied based on nonlocal strain gradient theory. Material properties of nanobeam are assumed to change gradually across the thickness of nanobeam according to Mori-Tanaka distribution model. The governing partial differential equations are derived for the rotating FG nanobeam by applying the Hamilton's principle in the framework of Euler-Bernoulli beam model. An analytical solution is applied to obtain wave frequencies, phase velocities and escape frequencies. It is observed that wave dispersion characteristics of rotating FG nanobeams are extremely influenced by angular velocity, wave number, nonlocal parameter, length scale parameter, temperature change and material graduation.

• Structural Engineering and Mechanics
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• v.59 no.6
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• pp.951-972
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• 2016

The purpose of this study is to illustrate the propagation of the shear waves (SH-waves) in a prestressed hetrogeneous orthotropic media overlying a pre-stressed anisotropic porous half-space with self weight. It is considered that the compressive initial stress, mass density and moduli of rigidity of the upper layer are space dependent. The proposed model is solved to obtain the different dispersion relations for the SH-wave in the elastic-porous medium of different properties. The effects of compressive and tensile stresses along with the heterogeneity, porosity, Biot's gravity parameter on the dispersion of SH-wave are shown numerically. The wave analysis further indicates that the technical parameters of upper and lower half-space affect the wave velocity significantly. The results may be useful to understand the nature of seismic wave propagation in geophysical applications and in the field of earthquake and material science engineering.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.6
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• pp.15-20
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• 1998

The linewidth enhancement factor $\alpha$ and fiber dispersion of 1.55 ${\mu}{\textrm}{m}$ strained multi-quantum well laser diodes are measured using small signal power modulation transfer function in a dispersive fiber. The measured fiber dispersion values are between 16.766 and 16.786ps/nm/km and these are the expected values from standard single mode fiber. To measure the $\alpha$ parameter in the actual operational range of the laser diodes, the dependence of $\alpha$ on laser output power is measured. The $\alpha$ parameter increases linearly as the power of the laser diode increases. This result can explain the non-linear gain effect on the $\alpha$ parameter more accurately than any other measurements.

• Journal of Advanced Navigation Technology
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• v.12 no.3
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• pp.201-207
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• 2008

Design rule of optical transmission link consisted of dispersion management (DM) controlling accumulated dispersion in total fiber length by precompensation and postcompensation, and optical phase conjugator (OPC) positioned at mid-way are proposed. DM schemes investigated in this paper are 2 types depending on the position of precompensation and postcompensation; bi-end type and concentration type. It is confirmed that effective residual dispersion ranges, as a design parameter of optical link, of transmission section from transmitter to OPC and transmission section from OPC to receiver are independence on the positions of dispersion compensating fiber (DCF) accomplishing precompensation and postcompensation, if both DCF position is symmetry with respect to OPC.

• Proceedings of the Korean Statistical Society Conference
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• 2003.05a
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• pp.109-114
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• 2003

The concept of dispersion is intrinsic to the theory and practice of statistics. A formulation of the concept of dispersion can be obtained by comparing the probability of intervals centered about a location parameter, which is peakedness ordering introduced first by Birnbaum (1948). We consider statistical inference concerning peakedness ordering between two arbitrary distributions. We propose nonparametric maximum likelihood estimator of two distributions under peakedness ordering and a likelihood ratio test for equality of dispersion in the sense of peakedness ordering.