• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.12B
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• pp.1483-1490
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• 2009

Orthogonal frequency division multiplexing (OFDM) has been investigated as an enabling technology for future wireless communications such as ad hoc, mesh and sensor networks. However, prior works on bit-loading lack consideration of the constraints on energy and computing facility in sensor networks. In this paper, we suggest an adaptive bit allocation algorithm for a frequency selective fading channel environment which exploits channel state information obtained through a feedback channel. The proposed algorithm significantly reduces computational complexity and satisfies the power budget. Also, its throughput is comparable to the optimum solution. Simulation results support the claim stated.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.10
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• pp.1128-1135
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• 2010

The relay based cellular system has been introduced to provide the service to satisfy the user requirement. The main reasons of using relay station are to expand a service coverage and to increase a system throughput with satisfying the service requirement level. This paper proposes a new resource allocation algorithm which supports the users' throughput fairness and service coverage in the Fixed Relay Based Cellular system with OFDMA. The performance of proposed algorithm is compared with the performances of proportional fairness(PF) algorithm. The simulation result shows that the proposed algorithm increases the number of active users in the service coverage while paying small amount of throughput loss.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.1
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• pp.45-55
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• 2018

Concerns are emerging in marine industry on the additional fatigue damages induced by hydroelasticity, and large container carriers, among others, are considered to be susceptible to this hydroelastic response due to its large size, deck openings and high speed. This study focuses on the fatigue damage estimation of 9,400TEU container carrier based on the full scale measurement data via long-base strain gage installed on the ship. Some correlation analyses have been also done to check whether there was significant torsional response during the voyage. Direct cycle counting method was used to derive stress histogram and the long-term fatigue damage was estimated based upon that analyzed data. It turned out that the fatigue damage of this particular ship during the measurement period increased by more than 60% due to the hydroelastic response of the hull, and main contribution is considered to come from vertical bending mode.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.2
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• pp.46-52
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• 2009

In this paper, the timing estimator based on the principle of the best linear unbiased estimator (BLUE) is proposed in OFDMA uplink systems. The proposed timing estimator exploits the phase information of the differential correlation between adjacent subcarriers. The differential correlation can extract the information about timing offset and mitigate the distortion of the signal caused by the frequency selectivity of channel. Compared with conventional methods, the proposed estimator shows more accurate capability in estimation. In addition, the estimator is hardly affected by the distortion caused by the frequency selectivity of channel. Simulation results confirm that the proposed estimator shows a small error mean and a relatively small error variance. In addition, the performance of the estimator is evaluated by means of SNR loss. It is shown by simulations that the SNR loss of the proposed estimator by estimation errors is less than 0.4 dB for the SNR values between 0 and 20 dB. This might indicate that the proposed estimator is suitable for the timing synchronization of multiple users in OFDMA uplink systems.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.10
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• pp.720-727
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• 2019

Resonating thermal lags of solid fuel with heat transfer oscillations generated by boundary layer oscillation is the primary mechanism of the occurrence of the LFI (Low Frequency Combustion Instability) in hybrid rocket combustion. This study was experimentally attempted to confirm that how the boundary layer was perturbed and led to the LFI. Special attention was also made on oxidizer swirl injection to investigate the contribution to combustion stabilization. Also the overall behavior of fluctuating boundary layer flow and the occurrence of the LFI was monitored as swirl intensity increased. Fluctuating boundary layer was successfully monitored by the captured image and POD (Proper Orthogonal Decomposition) analysis. In the results, oscillating boundary layer became stabilized as the swirl intensity increases. And the coupling strength between high frequency p', q' diminished and periodical amplification of RI (Rayleigh Index) with similar frequency band of thermal lag was also decreased. Thus, results confirmed that oscillating axial boundary layer triggered by periodic coupling of high frequency p', q' is the primary mechanism to excite thermal resonance with thermal lag characteristics of solid fuel.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.3
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• pp.147-155
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• 2022

The accumulated ice and snow during the operation of aircraft and railway vehicles can degrade aerodynamic performance or damage the major components of vehicles. Therefore, it is crucial to predict the temporal growth of ice for operational safety. Numerical simulation of ice is widely used owing to the fact that it is economically cheaper and free from similarity problems compared to experimental methods. However, numerical simulation of ice generally divides the analysis into multi-step and assumes the quasi-steady assumption that considers every time step as steady state. Although this method enables efficient analysis, it has a disadvantage in that it cannot track continuous ice evolution. The purpose of this study is to construct a surrogate model that can predict the temporal evolution of ice shape using reduced-order modeling. Reduced-order modeling technique was validated for various ice shape generated under 100 different icing conditions, and the effect of the number of training data and the icing conditions on the prediction error of model was analyzed.

• The Journal of Korean Society for Radiation Therapy
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• v.25 no.2
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• pp.123-129
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• 2013

Purpose: The way check the movement of the fiducial marker insertion in the treatment of patients with prostate cancer. However the existing methods of fiducial marker verification process difficult to identify the specific location of the marker behind the femur and pelvic bone. So to study the evaluation of maker match with using kilo voltage (KV) X-ray by On-board imager to both oblique verification method. Materials and Methods: Five patients were selected for rectal ballooning and inserted fiducial marker. Compare the position of the fiducial marker of reference plan 2D/2D Anterior/Posterior verification method and 2D/2D both oblique verification method. So to measurement the shift score of X, Y, Z (axis) and measure exposure dose given to patients and compare matching time. Results: 2 dimensional OBI KV X-ray imaging using two-dimensional matching image are orthogonal, so locating fiducial marker matching clear and useful DRR (digital reconstruction radiography) OBI souce angle ($45^{\circ}/315^{\circ}$) matching most useful. 2D/2D both oblique verification method was able to see clearly marker behind the pelvic bone. Also matching time can be reduced accordingly. According to the method of each matching results for each patient in each treatment fraction, X, Y, and Z axis the Mean $value{\pm}SD$ (standard deviation) is X axis (AP/LAT: $0.4{\pm}1.67$, OBLIQUE: $0.4{\pm}1.82$) mm, Y axis (AP/LAT: $0.7{\pm}1.73$, OBLIQUE: $0.2{\pm}1.77$) mm, Z axis (AP/LAT: $0.8{\pm}1.94$, OBLIQUE:$1.5{\pm}2.8$) mm. In addition, the KV X-ray source dose radiation exposure given to the patient taking average when AP/LAT matching is (0.1/2.1) cGY, when $315^{\circ}/45^{\circ}$ matching is (0.27/0.26) cGY. Conclusion: In conclusion for inserted fiducial marker of prostate cancer patients 2D/2D both oblique matching method is more accurate verification than 2D/2D AP/LAT matching method. Also the matching time less than the 2D/2D AP/LAT matching method. Taken as the amount of radiation exposure to patients less than was possible. Suggest would improve the treatment quality of care patients more useful to establish a protocol such as case.