• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.5
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• pp.368-375
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• 2018

In the present study, aerodynamic load analysis for a floating off-shore wind turbine was conducted to examine the effect of periodic platform motion in the direction of 6-DOF on rotor aerodynamic performance. Blade-element momentum method(BEM) was used for a numerical simulation, the unsteady airload effects due to the flow separation and the shed wake were considered by adopting a dynamic stall model based on the indicial response method. Rotor induced downwash was estimated using the momentum theory, coupled with empirical corrections for the turbulent wake states. The periodic platform motions including the translational motion in the heave, sway and surge directions and the rotational motion in the roll, pitch and yaw directions were considered, and each platform motion was applied as a sinusoidal function. For the numerical simulation, NREL 5MW reference wind turbine was used as the target wind turbine. The results showed that among the translation modes, the surge motion has the largest influence on changing the rotor airloads, while the effect of pitch motion is predominant for the rotations.

• Journal of computational fluids engineering
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• v.20 no.3
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• pp.94-103
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• 2015

The turbulent flow characteristics in the channel flow are investigated using large eddy simulation(LES) of FDS code, built in NIST(USA), in which the near-wall flow is solved by Werner-Wengle wall function. The periodic flow condition is applied in streamwise direction to get the fully developed turbulent flow and symmetric condition is applied in lateral direction. The height of the channel is H=1m, and the length of the channel is 6H, and the lateral length is H. The total grid is $32{\times}32{\times}32$ and $y^+$ is kept above 11 to fulfill the near-wall flow requirement. The Smagorinsky model is used to solve the sub-grid scale stress. Smagorinsky constant $C_s$ is 0.2(default in FDS). Three cases of Reynolds number(10,700, 26,000, 49,000.), based on the channel height, are analyzed. The simulated results are compared with direct numerical simulation(DNS) and particle image velocimetry(PIV) experimental data. The linear low-Re eddy viscosity model of Launder & Sharma and non-linear low-Re eddy viscosity model of Abe-Jang-Leschziner are utilized to compare the results with LES of FDS. Reynolds normal stresses, Reynolds shear stresses, turbulent kinetic energys and mean velocity flows are well compared with DNS and PIV data.

• Progress in Medical Physics
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• v.27 no.2
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• pp.55-63
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• 2016

We studied the method to gain a clear LSF using a thick aluminum sheet and to acquire the spatial resolution value with a high accuracy for a low spatial resolution imaging modality. In this study, aluminum sheets with thicknesses varying from 0.3 mm to 1.2 mm were tested to derive a modulation transfer function (MTF) for the oversampling and non-oversampling methods. The results were evaluated to verify the feasibility of the use of thick sheets for periodic quality assurance. Oversampling was more accurate than non-oversampling, and an aluminum sheet with a correction factor less than 2 at the cut-off frequency, which was less than 0.8 mm in this case, was confirmed to be suitable for MTF measurements. Therefore, MTF derivation from a thick aluminum sheet with thickness correction is plausible for a medical imaging modality.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.8
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• pp.629-637
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• 2013

Chaos communication systems have the characteristics such as non-periodic, wide-band, non-predictability of signals and easy implementation. There have been many studies about chaos communication systems because of these advantages. But, chaos communication systems have low BER(Bit Error Rate) compare to general digital communication system. Existing researches on chaos communication systems only analyze BER performance according to various chaos maps. There are no studies on analysis of BER performance according to PDF(Probability Density Function) of chaos maps. In this paper, we analyze the BER performance according to changing parameter, equation, and initial values of chaos map's PDF. In addition, we propose new chaos map to improve BER performance. Simulation results show that BER performance of CDSK(Correlation Delay Shift Keying) is changed when PDF of chaos map changed. And the proposed chaos map has a better BER performance compare to previous chaos maps such as Tent map, Logistic map, and Henon map.

• Journal of Digital Convergence
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• v.18 no.3
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• pp.195-205
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• 2020

The purpose of this study was to investigate the effects of early cognitive training and tailored telephone coaching program for ischemic stroke. Among 28 participants, assigned into the experimental(n=15) and control group(n=13). Only the experimental group was received a 4-week cognitive training and 11 session of tailored telephone coaching. The effect ot the program was evaluated four times(baseline, 4weeks, 8weeks, 12months) using the tool on Depression, Mini Mental State Examination(MMSE), Neuropsychological battery, Activities of Daily Living(ADL). The repeated measures ANOVA showed that the experimental group showed improvement in MMSE, verbal memory and executive function compared to the control group. Especially, the improvement of executive function which is related to ADL was a remarkable result. This suggests that early intervention is very important for recovery cognitive function and independent daliy life after stroke, and periodic telephone coaching should be done together for mid-to long term effects.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.43 no.3
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• pp.95-100
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• 2020

Machines and facilities are physically or chemically degenerated by continuous usage. One of the results of this degeneration is the process mean shift. The representative type of the degeneration is wear of tool or machine. According to the increasing wear level, non-conforming products cost and quality loss cost are increasing simultaneously. Therefore a periodic preventive resetting the process is necessary. The total cost consists of three items: adjustment cost (or replacement cost), non-conforming cost due to product out of upper or lower limit specification, and quality loss cost due to difference from the process target value and the product characteristic value among the conforming products. In this case, the problem of determining the adjustment period or wear limit that minimizes the total cost is called the 'process mean shift' problem. It is assumed that both specifications are set and the wear level can be observed directly. In this study, we propose a new model integrating the quality loss cost, process variance, and production volume, which has been conducted in different fields in previous studies. In particular, for the change in production volume according to the increasing in wear level, we propose a generalized production quantity function g(w). This function can be applied to most processes and we fitted the g(w) to the model. The objective equation of this model is the total cost per unit wear, and the determining variables are the wear limit and initial process setting position that minimize the objective equation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.30 no.4
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• pp.261-269
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• 2019

This study investigates a method of designing pixel-type frequency selective surfaces(FSS) with flexibility while considering factors, such as polarization and incident angle. Among the various methods used to solve the discrete space problem when designing a pixel-type FSS, the binary particle swarm optimization(BPSO) algorithm is one of the most applicable techniques to determine the periodic structure pattern of an FSS. Therefore, a method of efficiently designing FSS with roll-off band pass characteristics using an improved BPSO algorithm is proposed. To solve the convergence problem in the fitness function design to induce particles in the desired solution, FSS with desired roll-off wave characteristics can be easily obtained by applying a fitness function using "slope" as an input parameter.

• Journal of the Korea Convergence Society
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• v.9 no.11
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• pp.465-477
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• 2018

The purpose of this study is to analyze the effect of three - week high altitude ski training on the myocardial performance of cross - country skiers and to provide basic data for the future improvement of cross - country skiers'. The subjects were 6 cross - country skiing male college athletes. To investigate the effects of periodic and high altitude training on cross - country skiers, a general linear model ANOVA with repeated measure And analyzed using the Paired Samples t-test. In high altitude ski training for 3 weeks, the body composition did not change but the isokinetic muscular function of the shoulder joint, hip joint, knee joint, and ankle joint was decreased. Therefore, further study is needed if it is considered that continuous strength training should be performed during the ski training period such as SP period.

• Journal of Yeungnam Medical Science
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• v.40 no.2
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• pp.146-155
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• 2023

Background: Despite the recent increasing trend in the prevalence of type 2 diabetes among older individuals, the relationship between diabetic retinopathy (DR) and chronic kidney disease (CKD) in these patients remains unclear. This study investigated the severity of renal dysfunction according to the degree of DR in older patients with type 2 diabetes. Methods: A total of 116 patients with diabetes and CKD stage ≥3 who visited both the nephrology and ophthalmology outpatient departments between July 2021 and January 2022 were screened. There were 53 patients in the no DR group, 20 in the nonproliferative DR (NPDR) group, and 43 in the proliferative DR (PDR) group. Results: DR severity was related to the deterioration of renal function. The proportion of patients with advanced CKD significantly increased with DR severity (p for trend <0.001). In the multivariate regression model adjusted for age of ≥80 years, male sex, poorly controlled diabetes, macroalbuminuria, insulin use, diabetes duration of ≥10 years, cerebrovascular accident, hypertension, hyperlipidemia, and cardiovascular disease history, the odds ratio compared with the no DR group was approximately 4.6 for the NPDR group and approximately 11.8 for the PDR group, which were both statistically significant (p=0.025 and p<0.001, respectively). Conclusion: DR severity in older patients with diabetes may be associated with deterioration of renal function and high prevalence of advanced CKD. Therefore, periodic examination for DR in older patients with diabetes is important for predicting renal function deterioration and CKD progression.

• Journal of Digital Convergence
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• v.16 no.6
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• pp.407-416
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• 2018

The purpose of this study is to evaluate elite high school kayaker's iso-kinetic muscle function and provide physical training advices. Biodex system IV, Biodex stabilizer system, Inbody 3.0 and CNP-5403 are used to investigate 11 kayaker's muscle function(peak torque, average power and work fatigue), dynamic balance, body compositions, and flexibility. S4, S5, S8, S10, S11 are needed to train shoulder muscle strength and power. S5, S6, S10, S11 are needed to strengthen shoulder muscle endurance. S5, S7, S8, S10, S11 are needed to train knee muscle strength and power. S1, S4, S5, S10 are needed to strengthen knee muscle endurance. S3, S10, S11 are needed to train wrist muscle endurance. Based on these results we should establish an muscle function enhancing program with periodic inspection for elite kayakers. And standardized training program should be sublated.