• Journal of computational fluids engineering
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• v.3 no.1
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• pp.63-72
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• 1998

The numerical simulations of flowfield and pollutant dispersion over two-dimensional hills of various shapes are described. The Reynolds-averaged Wavier-Stokes equations and concentration diffusion equation based on the gradient diffusion theory have been applied to the atmospheric shear flow over the bell-shaped hills which are basic components of the complex terrain. The flow characteristics such as velocity profiles of the geophysical boundary layer, speed-up phenomena, mean pollutant concentration profiles are compared with experimental data to validate the present numerical procedure and it has been found that the present numerical results agree well with experiments and other numerical data. It has been also found that the distributions of ground level concentration are strongly influenced by the source location and height.

• Proceedings of the Optical Society of Korea Conference
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• 2006.02a
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• pp.87-88
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• 2006

Bragg fibers, consisting of a low index core (including air) surrounded by a series of periodic layers of alternate high and low refractive index materials, each being higher than that of the core, form a 1D photonic bandgap (PBG). In view of the multitude of individual physical parameters that characterize a Bragg fiber, they offer a wide choice of parametric avenues to tailor their propagation characteristics. Owing to their unique PBG guidance mechanism, Bragg fibers indeed exhibit unusual dispersion characteristics that are otherwise nearly impossible to achieve in conventional silica fibers. Solid core Bragg fibers, amenable to fabrication by the highly mature MCVD technology, could be designed to realize broadband supercontinuum light. This talk would review our recent works on modeling of propagation characteristics, dispersion tailoring in them for applications as metro as well as dispersion compensating fibers and also as supercontinuum light generators.

• Journal of Mechanical Science and Technology
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• v.20 no.12
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• pp.2147-2158
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• 2006

The continuous wavelet transform (CWT) has a frequency-adaptive time-frequency tiling property, which makes it popular for the analysis of dispersive elastic wave signals. However, because the time-frequency tiling of CWT is not signal-dependent, it still has some limitations in the analysis of elastic waves with spectral components that are dispersed rapidly in time. The objective of this paper is to introduce an advanced time-frequency analysis method, called the dispersion-based continuous wavelet transform (D-CWT) whose time-frequency tiling is adaptively varied according to the dispersion relation of the waves to be analyzed. In the D-CWT method, time-frequency tiling can have frequency-adaptive characteristics like CWT and adaptively rotate in the time-frequency plane depending on the local wave dispersion. Therefore, D-CWT provides higher time-frequency localization than the conventional CWT. In this work, D-CWT method is applied to the analysis of dispersive elastic waves measured in waveguide experiments and an efficient procedure to extract information on the dispersion relation hidden in a wave signal is presented. In addition, the ridge property of the present transform is investigated theoretically to show its effectiveness in analyzing highly time-varying signals. Numerical simulations and experimental results are presented to show the effectiveness of the present method.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.9
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• pp.805-811
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• 2014

In this investigation, we constructed and demonstrated a simple Yb-doped fiber laser, of which longitudinal modes are mode-locked without any additional devices to compensate the dispersion caused by optical components. Non-linear polarization rotation (NPR) was adopted for the mode-locking mechanism and a polarization controller (PC) was used for a kind of spectral filters to restrict the bandwidth for mode-locking. As the result, the laser was successfully operated as mode-locked with the repetition rate of 42.2 MHz and the spectrum was broadened up to approximately 16 nm at 1033 nm center wavelength when the laser was mode-locked. In this paper, the operation of the developed Yb-doped mode-locked laser is explained with the concept of Lyot filter realized by a PC, which enables mode-locking under normal dispersion. In the industrial applications, this laser can be used as a seed laser of the high power lasers for optical manufacturing.

• Journal of the Korean Society of Marine Environment & Safety
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• v.5 no.1
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• pp.9-18
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• 1999

To predict the oil spill dispersion phenomena in the ocean, the oil spill response model, which can be used for strategic purpose on the oil spill site, based on Lagrangian particle-tracking method was formulated and applied to the neighboring area with Pusan port where the oil spill incident occurred when the tanker ship No.1 Youil struck on a small rock near the Namhyungjeto on September 21, 1995. The real-time tidal currents to be required as input data of the oil spill model were obtained by the two-dimensional hydrodynamic model and the tide prediction model. Evaluation of tidal currents using observation data was successful. For wind data, other input data of oil spill model, observed data on the spot were used. To verify the oil spill model, the oil spill modelling results were compared with the field data obtained from the spill site. Compared the modelling results with the observation data, there exist some discrepancies but the general pattern of modelling results was similar to that of field observation. The modelling results on 7 days after spill occurred showed that the 40% of spilled oil is in floating, 36% in evaporated, 23% at shore, and 1% in out of boundary, respectively. According to the evaluation of weighting curves of effective components to the dispersion of oil, the winds make a 37% of contribution to the dispersion of oil, turbulent diffusion 39.5%, and tidal currents 23.5%, respectively. Provided the more accurate wind data are supported, more favorable results might be obtained.

• Natural Product Sciences
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• v.27 no.1
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• pp.36-44
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• 2021

The essential oils from the aerial parts (leaves and flowers) of Spiraea hypericifolia L. (Rosaceae), collected in Northern Kazakhstan, were obtained by distillation in two dispersion media (distilled water and 15% NaCl solution). The chemical composition of the essential oils was evaluated by GC-MS for the first time. The yield of the essential oil was 0.04% (in fresh growth conditions) and 0.02% (in dry growth conditions) respectively regardless of which dispersion media (H2O or 15% NaCl solution) was used at the isolation of essential oil. The main compounds were aliphatic hydrocarbons (alkanes) (40.6-53.2%), aldehydes (8.4-17.4%), diterpenoids (9.1-16.7%) and ketones (6.2-8.7%). Content of monoterpenoids was depended on dispersion media (2.2-3.6% where H2O was dispersion media and 8.4-8.5% where 15% NaCl solution was dispersion media). n-Heneicosane (17.4-34.1%) and n-tricosane (14.3-19.5%) were the main constituents of the essential oil of S. hypericifolia. There were many insects from different classes in S. hypericifolia at flowering. Important components such as α-methylene-γ-butyrolactone (0.8-2.8%), benzyl cyanide (0.7-1.1%), β-damascenone (1.2-2.9%), (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene (1.8-2.7%), β-ionone (0.5-1.8%) and others were detected in small amounts.

• Journal of Powder Materials
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• v.16 no.3
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• pp.209-216
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• 2009

A composite of rapidly solidified Al-6061 alloy powder with graphite particle reinforcements was prepared by ball milling and subsequent hot extrusion. The microstructure and mechanical properties of these composites were investigated as a function of milling time. With increasing milling time, the gas atomized initially and spherical powders became elongated with a maximum aspect ratio after milling for 30 h. Then, refinement and spheroidization were achieved by further milling to 70 h with a homogeneous and fine dispersion of graphite particles forming between the matrix alloy layers. The best compression and wear properties were obtained in the powder milled for 70 h, associated with the increased fine and homogeneous distribution of graphite particles in the aluminum alloy matrix.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.5
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• pp.1785-1795
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• 2013

Most of the previous models for analysis of shallow water flow assumed the uniform velocity distributions over the flow depth so that they produced incorrect velocity prediction at meandering part due to the ignorance of secondary current. In this study, the vertical velocity profiles in longitudinal and transverse direction were decomposed as the mean and variation components, which resulted in additional dispersion stresses terms in momentum equations. The proposed model were applied at the channels with $30^{\circ}$, $90^{\circ}$, $270^{\circ}$ bends, and shallow water flow in curved channel was analyzed using dispersion stresses. The dispersion stresses acted as a sink or source in the momentum equations, which caused the transverse convection of momentum to shift from the inner bank to the outer bank.

• The Journal of the Acoustical Society of Korea
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• v.22 no.1
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• pp.61-68
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• 2003

The guided wave has been widely employed to characterize thin plates and layered media. The dispersion curves of phase and group velocities are essential for the quantitative application of guided waves. In the present work, a fully automated system for the measurement of backward radiation of LLW has been developed. The specimen moves in two dimensional plane as well as in angular rotation. The signals of backward radiation of LLW were measured from an elastic plate in which specific modes of Lamb wave were strongly generated. Phase velocity of the corresponding modes was determined from the incident angle. The generated Lamb waves propagated forward and backward with the leakage of energy into water. Backward radiated LLW was detected by the same transducer and its frequency components were analyzed to extract the related information to the dispersion curves. The dispersion curves of phase velocity were measured by varying the incident angle. Moving the specimen in the linear direction of LLW propagation, group velocity was determined by measuring the transit time shift in the ultrasonic waveform.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.78-78
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• 2015

Metamaterials, artificially structured nanomaterials, have enabled unprecedented phenomena such as invisibility cloaking and negative refraction. Especially, hyperbolic metamaterials also known as indefinite metamaterials have unique dispersion relation where the principal components of its permittivity tensors are not all with the same signs and magnitudes. Such extraordinary dispersion relation results in hyperbolic dispersion relations which lead to a number of interesting phenomena, such as super-resolution effect which transfers evanescent waves to propagating waves at its interface with normal materials and, the propagation of electromagnetic waves with very large wavevectors comparing they are evanescent waves and thus decay quickly in natural materials. In this abstract, I will focus discussing our efforts in achieving the unique optical property overcoming diffraction limit to achieve several extraordinary metamaterials and metadevices demonstration. First, I will present super-resolution imaging device called "hyperlens", which is the first experimental demonstration of near- to far-field imaging at visible light with resolution beyond the diffraction limit in two lateral dimensions. Second, I will show another unique application of metamaterials for miniaturizing optical cavity, a key component to make lasers, into the nanoscale for the first time. It shows the cavity array which successfully captured light in 20nm dimension and show very high figure of merit experimentally. Last, I will discuss the future direction of the hyperbolic metamaterial and outlook for the practical applications. I believe our efforts in sub-wavelength metamaterials having such extraordinary optical properties will lead to further advanced nanophotonics and nanooptics research.