• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.2
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• pp.273-279
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• 2007

I evaluate the BER performance of OFDM systems in frequency selective Doppler time variant fading channels, considering the pilot patterns for channel estimation. The performance of the systems is degraded due to channel estimation error. For the reduction of performance degradation in acceptable level, the optimum distance of pilot symbols in pilot pattern is 5 subcarriers in frequency domain and 6 OFDM block in time domain.

• Proceedings of the KIEE Conference
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• 1999.07b
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• pp.991-993
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• 1999

This study proposed a new algorithm to assess autonomic function activity using Time-Frequency Representation(TFR). TFR is a way of describing the time-valiant energy of a signal. A discrete Wigner representation that is capable of filtering out any cross terms occuring in the Wigner-Ville Distribution(WVD) is used for time-variant energy distribution of heart rate variability(HRV) signals. And the marginal condition are evaluated to estimate power spectrum of HRV signals. The proposed algorithm showed that estimated power spectrum of HRV signals well describe the autonomic nerve system function and also showed the dynamics of autonomic nervous system response.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.542-547
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• 2003

A network based intrusion detection system(N-IDS), can detect intruders coming in through packets in real time environment. The ability of capture of packet is the most important factor when we evaluate the performance of the system. The time delay between the time handling one packet capture and next one is variant become of packet handling mechanism. So for N-IDS can not settle this problem because most systems use a single processor. In this thesis, we solve the problem of irregular tine delay with a file socket and multi-thread processing. We designed and implement, the Crasto system. By an accurate observation, the performance testing shows that the Crasto reduces the capture delay time to 1/5 comparing to the existing single process N-IDS, and maintain delay time regularly.

• Computers and Concrete
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• v.15 no.4
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• pp.643-671
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• 2015

Chloride induced reinforcement corrosion is widely accepted to be the most frequent mechanism causing premature degradation of reinforced concrete members, whose economic and social consequences are growing up continuously. Prevention of these phenomena has a great importance in structural design, and modern Codes and Standards impose prescriptions concerning design details and concrete mix proportion for structures exposed to different external aggressive conditions, grouped in environmental classes. This paper focuses on reinforced concrete column section load carrying capacity degradation over time due to chloride induced steel pitting corrosion. The structural element is considered to be exposed to marine environment and the effects of corrosion are described by the time degradation of the axial-bending interaction diagram. Because chlorides ingress and consequent pitting corrosion propagation are both time-dependent mechanisms, the study adopts a time-variant predictive approach to evaluate residual strength of corroded reinforced concrete columns at different lifetimes. Corrosion initiation and propagation process is modelled by taking into account all the parameters, such as external environmental conditions, concrete mix proportion, concrete cover and so on, which influence the time evolution of the corrosion phenomenon and its effects on the residual strength of reinforced concrete columns sections.

• Journal of Korean language education
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• v.29 no.2
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• pp.181-208
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• 2018

The aim of this study is to design a Real-time video Korean curriculum. Curriculum using real-time video, which is a variant of distance learning, teaches Korean to students studying in distant places through real-time video communication program. This is expected to supplement the lack of interaction in existing video classes and enable online simultaneous interaction, while increasing learning opportunities for Korean language students living in distance places. To find out the needs of the subjects for the curriculum design, this study conducted a one-on-one interview with 9 female married immigrants who are enrolled in the Cyber University which is opening a curriculum later. According to the survey, the students answered that they have a high intention of attending classes if the lack of interaction in existing distance classes are supplemented. Therefore, we could confirm the demand of a curriculum consisting of an overall real-time video education and multilateral individual connection. Also, we found out that there is a demand in performance rather than comprehension and a high demand for detailed feedback from the teacher. The result shows that the curriculum needs to establish performance-oriented contents to progress to an advanced level Korean Language, and include a study plain comprising of real-time interaction.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.45 no.3
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• pp.40-48
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• 2022

An automated material handling system (AMHS) has been emerging as an important factor in the semiconductor wafer manufacturing industry. In general, an automated guided vehicle (AGV) in the Fab's AMHS travels hundreds of miles on guided paths to transport a lot through hundreds of operations. The AMHS aims to transfer wafers while ensuring a short delivery time and high operational reliability. Many linear and analytic approaches have evaluated and improved the performance of the AMHS under a deterministic environment. However, the analytic approaches cannot consider a non-linear, non-convex, and black-box performance measurement of the AMHS owing to the AMHS's complexity and uncertainty. Unexpected vehicle congestion increases the delivery time and deteriorates the Fab's production efficiency. In this study, we propose a Q-Learning based dynamic routing algorithm considering vehicle congestion to reduce the delivery time. The proposed algorithm captures time-variant vehicle traffic and decreases vehicle congestion. Through simulation experiments, we confirm that the proposed algorithm finds an efficient path for the vehicles compared to benchmark algorithms with a reduced mean and decreased standard deviation of the delivery time in the Fab's AMHS.

• The Journal of the Acoustical Society of Korea
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• v.33 no.1
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• pp.48-53
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• 2014

The underwater acoustic communication (UAC) is characterized by doubly spread channel. It is included in the time-variant doppler shift and delay-time spreads due to multiple paths. To compensate such distorted signals, various techniques including time-reversal processing, spatial diversity, phase estimator, and equalizer are being applied. In this paper, a spatial filter based on the beamforming is proposed as a method to mitigate such inter-symbol interferences that are generated in time-varying multipath channels. The proposed technique realizes coherent communications by steering the direction of the desired signals and improves the performance of UAC by increasing the signal-to-interference plus noise ratio using the array gain.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.6B
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• pp.601-609
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• 2002

In multi-path wireless channels with time-variant delay profile, a mobile station measures the received signal strength and report it to network which performs network control function such as handover. In order to improve the maximum ratio combining (MRC) gain, it also should search the strongest signal paths and measure their time offsets fast and exactly. This paper proposes some methods of fast and exactly measuring the multi-path signal strength and time offset. Since the W-CDMA system adopts antenna diversity technique for the next generation high speed packet access (HSDPA) service, we derive the optimum design parameter values for the proposed methods through computer simulations under the HSDPA conditions o( low speed of mobile, of no power control, and of multi-path wireless environment with transmit and receive antenna diversity. Finally, we prove the validity of the proposed methods by showing the improvement of the bit error rate (BER) performance.

• Journal of the Korean Dietetic Association
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• v.5 no.2
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• pp.182-193
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• 1999

The purpose of this research is to analysis the general job of 76 dietitian on common management of school food service in Kyoung-buk area. In this research we asked them some general aspects, and made use of three variants(job performing time, the degree of major recognition, and the degree of difficulty) each question after classifying their jobs into 13 standard jobs. Statistical data analysis was completed using SPSS package program. The results of this survey showed the following : 1. The types of common management are as in the following : of the whole 76, 37 on the rotative trip to one single school, 8 to two schools, 1 to three schools, 28 on the trip to one single school plus central food production and 1 on the trip to two schools plus central food production. 2. The average job performing time in his or her school is 2813 minutes(8.52 hours) per week. 3. The factor of the evaluation and study of school foodservice has the highest level in every variant, but there were no standard job which needed the high-level difficulty and the longer job performing time as it needed the low degree of major recognition.

• Wind and Structures
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• v.32 no.2
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• pp.89-104
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• 2021

Non-synoptic winds generated by tornadoes, downbursts or gust fronts exhibit significant non-stationarity and can cause significant wind load effect on flexible structures such as long-span bridges. However, conventional assumptions on stationarity used to evaluate the structural wind-induced vibration are inadequate. In this paper, an efficient frequency domain scheme based on fast CQC method, which can predict non-stationary buffeting random responses of long-span bridges, is presented, and then this approach is applied to evaluate the buffeting response of a long-span suspension bridge located in a complex mountainous wind environment as an example. In this study, the data-driven method based on one available measured wind speed sample is firstly presented to establish non-stationary wind models, including time-varying mean wind speed, time-varying intensity envelope function and uniformly modulated fluctuating spectrum. Then, a linear time-variant (LTV) system based on the proposed scheme can be generally applied to calculate the non-stationary buffeting responses. The effectiveness and accuracy of the proposed scheme are verified through Monte Carlo time domain simulation implemented in ANSYS platform. Also, the transient effect nature of the bridge responses is further illustrated by comparison of the non-stationary, quasistationary and steady-state cases. Finally, buffeting response analysis with traditional stationary treatment (10 min constant mean plus stationary wind fluctuation) is performed to illustrate the importance of the non-stationary characteristics embedded in original wind speed samples.