• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.12
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• pp.1049-1055
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• 2018

This paper proposes the Signal Quality Indicator (SQI) to certify the wired communication channels connected between sub-systems embedded in guided flight systems. The communication signals can be distorted due to the poor interconnections of wired channels, the interference from the signals passing through the adjacent routed channels, and additive white Gaussian noises. As the ways to find out the condition of the communication channels, we present the Hamming distance based SQI (H-SQI) and the Euclidean distance based SQI (E-SQI). Two SQIs are compared in terms of the SQI resolution performance and the required number of hardware resources for implementations. The E-SQI requires the 10 times FPGA resources and an additional analog-digital converter over the H-SQI in spite of its outstanding SQI resolution performance. Moreover, the H-SQI could have the enough SQI resolution performance to find out the channel condition by increasing the oversampling rate, so the H-SQI is the more adequate than the E-SQI for the SQI of the guided flight systems.

• JSTS:Journal of Semiconductor Technology and Science
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• v.16 no.2
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• pp.159-165
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• 2016

Recently, active efforts are being made for future Si CMOS technology by various researches on emerging devices and materials. Capability of low power consumption becomes increasingly important criterion for advanced logic devices in extending the Si CMOS. In this work, a junctionless field-effect transistor (JLFET) with ultra-thin poly-Si (UTP) channel is designed aiming the sub-10-nm technology for low-power (LP) applications. A comparative study by device simulations has been performed for the devices with crystalline and polycrystalline Si channels, respectively, in order to demonstrate that the difference in their performances becomes smaller and eventually disappears as the 10-nm regime is reached. The UTP JLFET would be one of the strongest candidates for advanced logic technology, with various virtues of high-speed operation, low power consumption, and low-thermal-budget process integration.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.6
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• pp.669-676
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• 2008

The adaptive resource optimization problem in multi-input multi-output orthogonal frequency division multiple access (MIMO-OFDMA) systems is addressed. This paper, adaptive modulation and coding(AMC) and power control algorithms is proposed with SFC(Space-Frequency Coding), which aims to maximize the system capacity based on the CQI(Channel Quality Information). Firstly, power level is decided to each sub-channels with received feedback signal to noise ratio(SNR). In the second step, sub-carriers are allocated according to modulation type. Simulation results show that the proposed algorithm achieves a better performance than conventional algorithm in terms of capacity.

• Korean Journal of Optics and Photonics
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• v.15 no.4
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• pp.343-348
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• 2004

We report the design and basic operating characteristics of an radio frequency excited waveguide $CO_2$ laser. Four picecs of waveguide channels are placed in one laser cavity to increase a power per unit length with the form of a 2 ${\times}$ 2 matrix. Four independent optical outputs are measured from the front of output coupler, and these beams are combined to a Gaussian mode beam far from the output coupler. A 12 W output power has been obtained with $CO_2$ : $N_2$ : He : Xe = 1 : 1 : 3 : 0.2 of the gas mixture and 200 W of radio frequency.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.292-295
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• 2008

In a SCWR (SuperCritical pressure Water cooled Reactor), the coolant temperature initially at below the pseudo-critical temperature at the bottom of a reactor core increases as the coolant flows upward through the sub-channels of the fuel assemblies, and it finally becomes higher than the pseudo-critical temperature when it leaves the reactor core. At certain conditions, heat transfer deterioration occurs near the pseudo-critical temperature and it may cause a drastic rise of the fuel surface temperature resulting a fuel failure. Therefore, an accurate estimation of the heat transfer coefficient is very important for the thermal-hydraulic design of a reactor core. An experiment on heat transfer to the vertically upward flowing $CO_2$ at a supercritical pressure in a circular tube were performed at KAERI. The internal diameter of the test section is 6.32 mm, which corresponds to the hydraulic diameter of a sub-channel in the conceptional design proposed by KAERI. The test range of the mass flux is 285 to 1200 kg/m$^2$s and the maximum heat flux is 170 kW/m$^2$. The inlet pressure is maintained at 8.12 MPa, which is 1.1 times the critical pressure. A new correlation, which covers both the normal and deterioration heat transfer regimes was proposed and compared with the estimations by exiting correlations.

• 한국전산유체공학회:학술대회논문집
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• 2006.05a
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• pp.395-397
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• 2006

Air interlacing serves to protect the yarn against damage, strengthens inter-filament compactness or cohesion, and ensures fabric consistency. The air interlacing nozzle is used to introduce intermittent nips to a filament yarn so as to improve its performance in textile processing. The effect of various interlacing nozzle geometries on the interlacing process was studied. The geometries of interlacing nozzles with single or multiple air inlets located across the width of yarn channels are investigated. The basis case is the yarn channel, with a perpendicular main air inlet in the middle. Other cases have main air inlets, slightly inclined double sub air inlets, The yarn channel cross sectional shapes are either semicircular or rectangular shapes. The compressed impinging jet from the main air inlet hole hits the opposing bottom wall of the yarn channel, is divided into two branches, joins with the compressed air coming out from sub air inlet at the bottom and creates two free jets at both ends of the yarn channel. The compressed air movement in the cross-section consists of two opposing directional vortices. The CFD-FASTRAN flow parallel solver was used to perform steady simulations of impinging jet flow inside of the interlace nozzles. The vortical structure and the flow pattern such as pressure contour, particle traces, velocity vector plots inside of interlace nozzle geometry are discussed in this pater.

• International Journal of Aeronautical and Space Sciences
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• v.9 no.1
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• pp.66-75
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• 2008

In this work, we explore the feasibility of roll-pitch-yaw integrated autopilots for high angle-of-attack missiles. An investigation of the aerodynamic characteristics of a surface-to-air missile is presented, which reveals the strong effects of cross coupling between the longitudinal and lateral dynamics. Robust control techniques based on $H_{\infty}$ synthesis are employed to design roll-pitch-yaw integrated autopilots. The performance of the proposed roll-pitch-yaw integrated controller is tested in high-fidelity nonlinear five-degree-of-freedom simulations accounting for kinematic cross-coupling effects between the lateral and longitudinal channels. Against nonlinearity and cross-coupling effects of the missile dynamics, the integrated controller demonstrates superior performance when compared with the controller designed in a decoupled manner.

• Bulletin of the Korean Chemical Society
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• v.34 no.5
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• pp.1481-1486
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• 2013

Bifunctional Fe-SBA-15-$SO_3H$ mesoporous materials with different Si/Fe molar ratios (3, 5, and 7) have been synthesized via a simple direct hydrothermal method and characterized by XRD, $N_2$-adsorption/desorption, TG/DTG and FT-IR techniques, and used as solid acid catalysts in the esterification of lactic acid with methanol. XRD and $N_2$ sorption characterizations show successful iron doping within the mesoporous channels of SBA-15-$SO_3H$. The FT-IR and TG/DTG characterizations also reveal the presence of iron. With the incorporation of Fe ions into the SBA-15-$SO_3H$, the acid sites substantially increased because of the self-separated acidity of the hydrolysis of $Fe^{3+}$ solutions. However, in the Si/Fe = 3 molar ratio, the catalytic conversion decreased which is caused by the reduced cooperation effect between the acid pairs due to the weakened hydrogen bonds and collapse of the pore structure. This further suggests that the mesoporous structure decreases with the decrease in Si/Fe ratio.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.8B
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• pp.757-763
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• 2006

In this paper, a novel multiple access scheme using SMA(Split and Merge Algorithm) is proposed to reduce the accessdelay of wireless MAC protocols. The key idea of the SMA is to dynamically split and merge the contending terminals depending on their traffic loads for effective control of access to the channels. The SMA divides the collided terminals into several sub-groups if a collision occurs and merges the idle terminals of the split sub-groups into their original group. The merge algorithm can be used to resolve collision and split operation can be used to dynamic group management. The simulation results indicate that our algorithm may provide a higher throughput and a lower collision rate than the existing algorithms, especially under heavy traffic loads.

• Current Optics and Photonics
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• v.5 no.4
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• pp.421-430
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• 2021

The multifocal multiphoton microscopy (MMM) enables high-speed imaging by the concurrent scanning and detection of multiple foci generated by lenslet array or diffractive optical element. The MMM system mainly suffers from crosstalk generated by scattered emission photons that form ghost images among adjacent channels. The ghost image which is a duplicate of the image acquired in sub-images significantly degrades overall image quality. To eliminate the ghost image, the photon reassignment method was established using maximum likelihood estimation. However, this post-processing method generally takes a longer time than image acquisition. In this regard, we propose a novel strategy for rapid noise reduction in the MMM system based upon Monte-Carlo (MC) simulation. Ballistic signal, scattering signal, and scattering noise of each channel are quantified in terms of photon distribution launched in tissue model based on MC simulation. From the analysis of photon distribution, we successfully eliminated the ghost images in the MMM sub-images. If the priori MC simulation under a certain optical condition is established at once, our simple, but robust post-processing technique will continuously provide the noise-reduced images, while significantly reducing the computational cost.