• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.1
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• pp.304-308
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• 2004

The $Cd_{1-x}Zn_xS$ thin films were grown on the Si(100) wafers by a hot wall epitaxy method(HWE). The source and substrate temperature are $600^{\circ}C\;and\;440^{\circ}C$ respectively. The crystalline structure of epilayers was investigated by double crystal X-ray diffraction(DCXD). Hall effect on the sample was measured by the van der Pauw method and studied on the carrier density and mobility dependence on temperature. In order to explore the applicability as a photoconductive cell, we measured the sensitivity($\gamma$), the ratio of photocurrent to darkcurrent(pc/dc), maximum allowable power dissipation(MAPD), spectral response and response time. The results indicated that the photoconductive characteristic were the best for the $Cd_{0.53}Zn_{0.47}S$ samples annealed in Cu vapor compare with in Cd, Se, air and vacuum vapour. Then we obtained the sensitivity of 0.99, the value of pc/dc of $1.65{\times}10^7$, the MAPD of 338mW, and the rise and decay time of 9.7ms and 9.3ms, respectively

• Current Optics and Photonics
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• 제5권2호
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• pp.141-146
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• 2021

We have evaluated the suppression effect of atmospheric-turbulence-induced optical scintillation in terrestrial free-space optical (FSO) communication systems using a gain-saturated erbium-doped fiber amplifier (EDFA). The variation of EDFA output signal power has been measured with different amounts of gain saturation and modulation indices of the optical input signal. From the measured results, we have found that the peak-to-peak power variation was decreased drastically below 2 kHz of modulation frequency, in both 3-dB and 6-dB gain compression cases. Then, the power spectral density (PSD) of optical scintillation has been calculated with Butterworth-type transfer function. In the calculation, different levels of atmospheric-turbulence-induced optical scintillation have been taken into account with different values of the Butterworth cut-off frequency. Finally, the suppression effect of optical scintillation has been estimated with the measured frequency response of the EDFA and the calculated PSD of the optical scintillation. From our estimated results, the atmospheric-turbulence-induced optical scintillation could be suppressed efficiently, as long as the EDFA were operated in a deeply gain-saturated region.

• Journal of Korean Association for Spatial Structures
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• 제19권2호
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• pp.101-108
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• 2019

In this paper, the characteristic of intrinsic mode function(IMF) and its orthogonalization of ensemble empirical mode decomposition(EEMD), which is often used in the analysis of the non-linear or non-stationary signal, has been studied. In the decomposition process, the orthogonal IMF of EEMD was obtained by applying the Gram-Schmidt(G-S) orthogonalization method, and was compared with the IMF of orthogonal EMD(OEMD). Two signals for comparison analysis are adopted as the analytical test function and El Centro seismic wave. These target signals were compared by calculating the index of orthogonality(IO) and the spectral energy of the IMF. As a result of the analysis, an IMF with a high IO was obtained by GSO method, and the orthogonal EEMD using white noise was decomposed into orthogonal IMF with energy closer to the original signal than conventional OEMD.

• Journal of Powder Materials
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• 제27권6호
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• pp.477-483
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• 2020

Metal-organic frameworks (MOFs) are of significant interest because of their high porosity, which facilitates their utilization in gas storage and catalysis. To enhance their current properties in these applications, it is necessary to elucidate the interactions between molecules in a confined environment that differ from those in bulk conditions. Herein, we study the confined molecular interaction by investigating the solvent-dependent photophysical properties of two different-sized molecules inside MOF-5. Ruthenium tris-bipyridine (Rubpy) and coumarin 153 (C153) are encapsulated in MOF-5. Rubpy with MOF-5 (Rubpy@MOF) is prepared by building MOF-5 around it, resulting in limited space for solvent molecules in the pores. The smaller C153 is encapsulated in the preformed MOF-5 (C153@MOF) by simply soaking the MOF in a concentrated C153 solution. C153@MOF permits more space for solvent molecules in the pore. Their characteristic absorption and emission spectra are examined to elucidate the confined molecular interactions. Rubpy@MOF and C153@MOF exhibit different spectral shifts compared to the guest molecules under bulk conditions. This discrepancy is attributed to the different micro-environments inside the pores, derived from confined host-guest interactions in the interplay of solvent molecules.

• Journal of Positioning, Navigation, and Timing
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• 제9권4호
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• pp.293-304
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• 2020

In this paper, various modulation techniques, including the legacy Global Navigation Satellite System (GNSS) signal modulation techniques, are introduced and the spectral characteristics and correlation characteristics of signals with various modulation techniques are analyzed based on numerical simulation. With the development of various GNSS services, the limited frequency band has become increasingly saturated, and issues of interoperability and compatibility have emerged in the new GNSS design. Since the efficient allocation of frequency resources is closely related to spectrum design, modulation techniques are one of the important signal design parameters of new signal design. Signal modulation techniques are closely related to various figure of merits (FoMs) as well as spectrum characteristic, and in some cases there is a complicated trade-off between FoMs. Thus, the FoMs associated with modulation technology should be analyzed and the best signal candidates should be chosen carefully via the trade-off analysis for FoMs. In this paper, we define the modulation technique based on Phase Shift Keying (PSK), Binary Offset Carrier (BOC) and Continuous Phase Modulation (CPM) for the design of KPS signals, and the FoMs of signals in terms of spectrum and correlation function are evaluated. Signals with various modulation techniques are implemented through a numerical simulation, and the relevant FoMs are analyzed.

• Journal of the Korea Institute of Military Science and Technology
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• 제25권1호
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• pp.1-8
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• 2022

Electronic equipment mounted on military vehicles is exposed to external shocks and vibrations. This causes problems in tactical operation and also causes cost loss in equipment maintenance. Therefore, to optimize the test standards for military vehicles with vibration, dynamic characteristics should be analyzed and standardized through actual driving tests. In this paper, the internal structure of 2.5tons military vehicle is designed in the form of a drawer and lathe, and the dynamic characteristics are identified by experiment, and the design is proposed.

• Nuclear Engineering and Technology
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• 제54권7호
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• pp.2635-2649
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• 2022

CEFR is a small core-size sodium-cooled fast reactor (SFR) using high enrichment fuel with stainless-steel reflectors, which brings a significant challenge to the deterministic methodologies due to the strong spectral effect. The neutronic simulation of the start-up experiments conducted at the CEFR have been performed with a deterministic code system RAST-F, which is based on the two-step approach that couples a multi-group cross-section generation Monte-Carlo (MC) code and a multi-group nodal diffusion solver. The RAST-F results were compared against the measurement data. Moreover, the characteristic of neutron spectrum in the fuel rings, and adjacent reflectors was evaluated using different models for generation of accurate nuclear libraries. The numerical solution of RAST-F system was verified against the full core MC solution MCS at all control rods fully inserted and withdrawn states. A good agreement between RAST-F and MCS solutions was observed with less than 120 pcm discrepancies and 1.2% root-mean-square error in terms of k_eff and power distribution, respectively. Meanwhile, the RAST-F result agreed well with the experimental values within two-sigma of experimental uncertainty. The good agreement of these results indicating that RAST-F can be used to neutronic steady-state simulations for small core-size SFR, which was challenged to deterministic code system.

• Journal of Sensor Science and Technology
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• 제31권5호
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• pp.353-359
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• 2022

This study investigated via computational analysis the application utility of series-cascaded ring resonators based on silicon-on-insulator (SOI) slot optical waveguides in integrated optical biochemical sensors. The radii of the two rings in the series-cascaded ring resonators were 59.4 ㎛ and 77.6 ㎛ respectively, and the coupling distance was 0.5 ㎛. The series-cascaded ring resonators were computationally analyzed using FIMMProp and PICWave numerical software. The free spectral range (FSR), full width at half maximum (FWHM), sensitivity, and quality-factor (Q-factor) of the series-cascaded ring resonators were 12.2 nm, 0.134 nm, 4100 nm/RIU, and 11580, respectively, and the measurement range was calculated to be slightly smaller than 3×10^-3 RIU. Although the measurement range was smaller than that of the single ring resonator, upon considering other characteristic parameters, the series-cascaded ring resonators are found to be more effective as integrated sensors than single ring resonators.

• Wind and Structures
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• 제34권1호
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• pp.137-149
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• 2022

In this paper, the fluctuating lift and drag forces on 5:1 rectangular cylinders with two different geometric scales in three turbulent flow-fields are investigated. The study is particularly focused on understanding the influence of the ratio of turbulence integral length scale to structure characteristic dimension (the length scale ratio). The results show that both fluctuating lift and drag forces are influenced by the length scale ratio. For the model with the larger length scale ratio, the corresponding fluctuating force coefficient is larger, while the spanwise correlation is weaker. However, the degree of influence of the length scale ratio on the two fluctuating forces are different. Compared to the fluctuating drag, the fluctuating lift is more sensitive to the variation of the length scale ratio. It is also found through spectral analysis that for the fluctuating lift, the change of length scale ratio mainly leads to the variation in the low frequency part of the loading, while the fluctuating drag generally follows the quasi-steady theory in the low frequency, and the slope of the drag spectrum at high frequencies changes with the length scale ratio. Then based on the experimental data, two empirical formulas considering the influence of length scale ratio are proposed for determining the lift and drag aerodynamic admittances of a 5:1 rectangular cylinder. Furthermore, a simple relationship is established to correlate the turbulence parameter with the fluctuating force coefficient, which could be used to predict the fluctuating force on a 5:1 rectangular cylinder under different parameter conditions.

• Structural Engineering and Mechanics
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• 제82권5호
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• pp.651-665
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• 2022

While the lateral confinement provided by an FRP jacket to a concrete column is passive in nature, confinement is activated when the concrete expands due to additional compression stresses or significant shear deformations. This characteristic of FRP jacketing theoretically leads to similar initial stiffness properties of FRP retrofitted buildings as the buildings without retrofit. In the current study, to validate this theoretical assumption, the initial stiffness characteristics, and thus, the potential seismic demands were investigated through forced vibration tests on two identical full-scale substandard reinforced concrete buildings with or without FRP retrofit. Power spectral density functions obtained using the acceleration response data captured through forced vibration tests were used to estimate the modal characteristics of these buildings. The test results clearly showed that the natural frequencies and the mode shapes of the buildings are quite similar. Since the seismic demand is controlled by the fundamental vibration modes, it is confirmed using vibration-based full-scale tests that the seismic demands of RC buildings remain unchanged after CFRP jacketing of columns. Furthermore, the damping characteristics were also found similar for both structures.