• Proceedings of the KSRS Conference
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• 2002.10a
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• pp.12-16
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• 2002

The clear sky radiative forcings of aerosols were evaluated over East Asia. We first investigated optical characteristics of aerosol using sky radiation measurements. An algorithm of Nakajima et al. (1996) is used for retrieving aerosol parameters such as optical thickness, ${\AA}$ngstr$\"{O}$m exponent, single scattering albedo, and size distribution from sky-radiation measurements, which then can be used for examining spatial and temporal variations of aerosol. Obtaining aerosol radiative forcing at TOA and surface, a radiative transfer model is used with inputs of obtained aerosol parameters and GMS-5 satellite-based cloud optical properties. Results show that there is a good agreement of simulated downwelling radiative flux at the surface with observation within 10 W m$^{-2}$ rms errors under the clear sky condition. However, a relatively large difference up to 40 W m$^{-2}$ rms error is found under the cloudy sky condition. The computed aerosol radiative forcing at the surface shows downward flux changes ranging from -100 to -170 W m$^{-2}$ per unit aerosol optical thickness at 0.7 $\mu$m. The different values of aerosol radiative forcing among the stations is mainly due to the differences in single scattering albedo ($\omega$$_{0.7}$) and asymmetric parameter (g$_1$) related to the geographical and seasonal variations.

• Journal of information and communication convergence engineering
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• v.8 no.5
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• pp.581-585
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• 2010

A grid was sandwiched between two cascaded imaging plates. Using a fan-beam X-ray tube and a single exposure scheme, the two imaging plates, respectively, recorded grid-less and grid type information of the object. Referring to the mathematical model of the Grid-less and grid technique, it was explained that the collected components whereas that of imaging plates with grid was of high together with large scattered components whereas that of imaging plate with grid was of low and suppressed scattered components. Based on this assumption and using a Gaussian convolution kernel representing the effect of scattering, the related data of the imaging plates were simulated by computer. These observed data were then employed in the developed post-processing estimation and restoration (kalman-filter) algorithms and accordingly, the quality of the resultant image was effectively improved.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.1016-1019
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• 2002

This paper deals with a fundamental and classical scattering problem by a finite strip. For the analysis of scattered acoustic field, a “single” integral equation is derived. Firstly, the complexity by considering the effect of the mean flow is alleviated by the introduction of Prandtl-Glauert coordinate and the new dependent variable. Secondly, the difficulty of solving the resultant strongly-coupled integral equations which always appear in this kind of 3-part mixed boundary value problem is solved by observing some good properties of the functions in complex domain and manipulating the equations and variables for the use of those properties. The solution can be obtained asymptotically in terms of gamma function and Whittaker function. One aim of this study is the improvement of methodology for the research using integral equations. The other is the basic understanding of scattering by a finite strip related to the linear cascade model of rotating fan blades.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.49.3-50
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• 2016

Two major radiative transfer (RT) techniques have been developted to model late-type galaxies: approximate RT and Monte Carlo (MC) RT. In the approximate RT, first proposed by Kylafis & Bahcall, only two terms of unscattered (direct) and single-scattered intensities are computed and higher-order multiple scattering components are approximated, saving computing time and cost compared to MC RT. However, the approximate RT can yield errors in regions where multiple scattering effect is significant. In order to examine how significant the errors of the approximate RT are, we compare results of the approximate RT with those of SKIRT, a state-of-the-art MC RT code, which is basically free from the approximation errors by fully incorporating all the multiple scattered intensities. In this study, we present quantitative errors in the approximate RT for late type galaxy models with various optical depths and inclination angles. We report that the approximate RT is not reliable if the central face-on optical depth is intermediate or high (${\tau}_V$ > 3).

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1999.04a
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• pp.35-40
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• 1999

In order to know the characteristics of attenuation of coda wave in the Kyungsang Sedimentary Basin quality factor for coda wave or coda Q is estimated from the earthquake data recorded in the KIGAM microearthquake network. The single scattering model for coda wave generation is adopted in estimating coda Q. Coda Q appears to be largely dependent on the normalized time(a) which is the ratio of elapsed time to S-wave travel time. In the present study coda Q(Qc) is estimated in the range of a=1.5-3.Q and expressed in terms of frequency(f). The deduced function in the range of 1 to 25 Hz is Qc=36.8283 f1.15095 to represent the strong dependence of coda Q on frequency. It is found that the difference of Qc between U-D N-S and E-W components is negligible, This face supports the back-scattering theory that coda were originates from scattered waves by randomly distributed heterogeneities in the crust. On the other hand it is observed that the coda Q increases with depth.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.6
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• pp.467-474
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• 2005

The expanded multi-Gaussian beam model has recently been developed that can calculate the radiation beam field from a single, rectangular transducer with great computational efficiency. In this study, this model is adopted to calculate the radiation beam field for a phased array transducer with various time delays to achieve steering and/or focusing. The calculation beam fields are compared to those obtained by well known Rayleigh-Sommerfeld integral that provides the exact solution in order to explore the validity of the expanded multi-Gaussian beam model And then, this study proposes a complete ultrasonic measurement model including the expanded beam model, far-field scattering model and system efficiency, Using the proposed model, phased array ultrasonic testing signals for a flat-bottomed hole with/without focusing were performed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.5
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• pp.541-548
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• 2013

This paper presents a vector network analysis system for 2-port scattering parameters of microwave devices using some basic microwave instruments/devices such as signal generators, vector voltmeter, directional couplers and frequency mixers. The analytical model and implementation method for scattering parameter measurements - which can replace the vector network analyzers - are presented. The performance of the implemented system is evaluated through 1- and 2-port scattering parameter measurements, respectively. The vector volt signals which determine the scattering parameters are detected in two distinct methods depending on the frequency band of interests; a direct-detection method with a single signal generator and vector voltmeter for relatively low band and a heterodyne method to frequency down-mix associated with an additional signal source as well as frequency mixers for high band are used, respectively. Using these two methods, scattering parameters of UHF and X bands are evaluated and their performances are verified through a comercial vector network analyzer.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.6 no.3
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• pp.80-90
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• 1995

The scattering parameters of a microstrip single line, a right-angle bend and a coupled line are calculated using the multiport network model for the frequency range from 1 to 18 GHz. The single line is analyzed using the planar waveguide model. The right-angle bend is broken into two rectangular segments, and each segment is analyzed in a similar fashion as the single line. Impedance matrices corresponding to the two segments are combined by the segmentation method. In the analysis of elec- tromagnetic coupling of the coupled line, a new method is employed resulting in much less computation time than those previous methods involving Green's functions. A good agreement between the numerical results for the three structures and those from SuperCompact reveals the usefulness of the multiport network medel in analyzing complicated mirostrip single and coupled line discontinuities.

• Journal of Information Processing Systems
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• v.13 no.4
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• pp.677-688
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• 2017

In order to solve the undetected probability of multiple targets in ultra-wideband (UWB) through-the-wall radar imaging (TWRI), a time-delay and amplitude modified back projection (BP) algorithm is proposed. The refraction point is found by Fermat's principle in the presence of a wall, and the time-delay is correctly compensated. On this basis, transmission loss of the electromagnetic wave, the absorption loss of the refraction wave, and the diffusion loss of the spherical wave are analyzed in detail. Amplitude compensation is deduced and tested on a model with a single-layer wall. The simulating results by finite difference time domain (FDTD) show that it is effective in increasing the scattering intensity of the targets behind the wall. Compensation for the diffusion loss in the spherical wave also plays a main role. Additionally, the two-layer wall model is simulated. Then, the calculating time and the imaging quality are compared between a single-layer wall model and a two-layer wall model. The results illustrate the performance of the time-delay and amplitude-modified BP algorithm with multiple targets and multiple-layer walls of UWB TWRI.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.21-21
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• 2011

A series of Quasi-Elastic Neutron Scattering (QENS) experiments helps us to understand the single-particle (hydrogen atom) dynamics of a globular protein and its hydration water and strong coupling between them. We also performed Molecular Dynamics (MD) simulations on a realistic model of the hydrated hen-egg Lysozyme powder having two proteins in the periodic box. We found the existence of a Fragile-to-Strong dynamic Crossover (FSC) phenomenon in hydration water around a protein occurring at TL=$225{\pm}5K$ by analyzing Intermediate Scattering Function (ISF). On lowering of the temperature toward FSC, the structure of hydration water makes a transition from predominantly the High Density Liquid (HDL) form, a more fluid state, to predominantly the Low Density Liquid (LDL) form, a less fluid state, derived from the existence of a liquid?liquid critical point at an elevated pressure. We showed experimentally and confirmed theoretically that this sudden switch in the mobility of the hydration water around a protein triggers the dynamic transition (so-called glass transition) of the protein, at a temperature TD=220 K. Mean Square Displacement (MSD) is the important factor to show that the FSC is the key to the strong coupling between a protein and its hydration water by suggesting TL${\fallingdotseq}$TD. MD simulations with TIP4P force field for water were performed to understand hydration level dependency of the FSC temperature. We added water molecules to increase hydration level of the protein hydration water, from 0.30, 0.45, 0.60 and 1.00 (1.00 is the bulk water). These confirm the existence of the FSC and the hydration level dependence of the FSC temperature: FSC temperature is decreased upon increasing hydration level. We compared the hydration water around Lysozyme, B-DNA and RNA. Similarity among those suggests that the FSC and this coupling be universal for globular proteins, biopolymers.