• Aerospace Engineering and Technology
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• v.9 no.1
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• pp.98-105
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• 2010

Fast Fourier Transform is the fast implementation of Discrete Fourier Transform, which deletes periodic operation of DFT. According to the definition, radix-2 FFT can be implemented byre cursive call which divides the input signal points into 2 signal points. Because of its time-consuming stack-copy operation, this recursive method is very slow. To overcome this drawback, butterfly operation with signal rearrangement was devised. Based on the ideas of signal rearrangement and butterfly operation, this paper applies the signal rearrangement method to the Radix-3 FFT and checks the validity of this method.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.44 no.2
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• pp.115-123
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• 2021

A lot of sensor and control signals is generated by an industrial controller and related internet-of-things in discrete manufacturing system. The acquired signals are such records indicating whether several process operations have been correctly conducted or not in the system, therefore they are usually composed of binary numbers. For example, once a certain sensor turns on, the corresponding value is changed from 0 to 1, and it means the process is finished the previous operation and ready to conduct next operation. If an actuator starts to move, the corresponding value is changed from 0 to 1 and it indicates the corresponding operation is been conducting. Because traditional fault detection approaches are generally conducted with analog sensor signals and the signals show stationary during normal operation states, it is not simple to identify whether the manufacturing process works properly via conventional fault detection methods. However, digital control signals collected from a programmable logic controller continuously vary during normal process operation in order to show inherent sequence information which indicates the conducting operation tasks. Therefore, in this research, it is proposed to a recurrent neural network-based fault detection approach for considering sequential patterns in normal states of the manufacturing process. Using the constructed long short-term memory based fault detection, it is possible to predict the next control signals and detect faulty states by compared the predicted and real control signals in real-time. We validated and verified the proposed fault detection methods using digital control signals which are collected from a laser marking process, and the method provide good detection performance only using binary values.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.7
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• pp.1001-1007
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• 2014

This paper proposes a method to reduce operation time using discrete cosine transform and to improve image quality by the DC gain correction. Conventional filtered back projection (FBP) filtering in the frequency domain using Fourier transform, but the filtering process uses complex number operations. To simplify the filtering process, we propose a filtering process using discrete cosine transform. In addition, the image quality of reconstructed images are improved by correcting DC gain of sinograms. To correct the DC gain, we propose to find an optimum DC weight is defined as the ratio of sinogram DC and optimum DC. Experimental results show that the proposed method gets better performance than the conventional method for phantom and clinical CT images.

• Journal of Chest Surgery
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• v.21 no.4
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• pp.727-733
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• 1988

Two cases of the discrete membranous subaortic stenosis were experienced at the Department of Thoracic & Cardiovascular Surgery, National Medical Center, Seoul, Korea. Case I was 31 years old male with a history of aortic valve replacement[Ionescu-Shiley, 19mm] at the other hospital in 1980. Heart failure was noticed 6 years later. On cardiac catheterization, pressure gradient between left ventricle 4 aorta was 104 mmHg, but subvalvular aortic stenosis was not detected by preoperative 2-D echo <% left ventriculogram. Above case revealed stenoinsufficiency of the prosthetic valve. Under the diagnosis of the prosthetic valve failure, re-do aortic valve replacement[Bjork-Shiley, 23 mm] was done. During operation, the discrete membranous subaortic stenosis was incidentally found, and it was completely resected. So we thought that above discrete membranous subaortic stenosis was not detected at first operation, and it was progressed during 6 years, and accelerated the degeneration of the prosthetic valve. Case II was 20 years old female. Her complaints were exertional dyspnea, angina, syncope, which were aggravated since 5 years ago. 2-D echo <% left ventriculogram revealed the discrete membranous subaortic stenosis. Pressure gradient was 20 mmHg, but her symptoms were serious. Associated cardiac anomaly was the persistent left superior vena cava without connection with right superior vena cava. Complete excision of the membranous tissue was done. Post-operative pressure gradient between left ventricle & aorta was absent, and her complaints were nearly subsided. Both cases were type I according to the Newfeld classification of the discrete subvalvular aortic stenosis, and complete excision of the membranous tissue was done without myotomy or mymectomy. And short-term follow-up results[Case I:2 years, Case II: 1 ~ years] were good except soft systolic murmur[grade II/VI] at the aortic area in both cases.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.3
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• pp.363-368
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• 2008

In this paper, the Resistive Companion Form(RCF) analysis method is applied to analyze small signal stability of power systems including thyristor controlled FACTS equipments such as SVC. The eigenvalue sensitivity analysis algorithm in discrete systems based on the RCF analysis method is presented and applied to the power system including SVC. As a result of simulation, the RCF analysis method is proved very effective to precisely calculate the variations of eigenvalues or newly generated unstable oscillation modes after periodic switching operations of SVC. Also the eigenvalue sensitivity analysis method based on the RCF analysis method enabled to precisely calculate eigenvalue sensitivity coefficients of controller parameters about the dominant oscillation mode after periodic switching operations in discrete systems. These simulation results are different from those of the conventional continuous system analysis method such as the state space equation and proved that the RCF analysis method is very effective to analyze the discrete power systems including periodically operated switching equipments such as SVC.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.33 no.4
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• pp.58-68
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• 2010

Particle Swarm Optimization (PSO) which has been well known to solve continuous problems can be applied to discrete combinatorial problems. Several DPSO (Discrete Particle Swarm Optimization) algorithms have been proposed to solve discrete problems such as traveling salesman, vehicle routing, and flow shop scheduling problems. They are different in representation of position and velocity vectors, operation mechanisms for updating vectors. In this paper, the performance of 5 DPSOs is analyzed by applying to traditional Traveling Salesman Problems. The experiment shows that DPSOs are comparable or superior to a genetic algorithm (GA). Also, hybrid PSO combined with local optimization (i.e., 2-OPT) provides much improved solutions. Since DPSO requires more computation time compared with GA, however, the performance of hybrid DPSO is not better than hybrid GA.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.8
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• pp.647-661
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• 2017

This paper presents a robust method for autonomously landing on small bodies. Autonomous landing is accomplished by generating and following reference position and attitude profiles. The position and attitude tracking controllers are based on discrete sliding mode control, which explicitly treats the discrete and impulsive natures of thruster operation. Vision-based inertial navigation is used for autonomous navigation for landing. Numerical simulation is carried out to evaluate the performance of the proposed method in a realistic situation with environmental uncertainties.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.3
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• pp.184-191
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• 2018

Orthogonal frequency division multiplexing(OFDM) is a multicarrier modulation(MCM) system that enables high-speed communications using multiple carriers and has advantages of power and spectral efficiency. Therefore, this study aims to complement the existing shortcomings and to design an efficient MCM system. The proposed system uses the inverse discrete wavelet transform(IDWT) operation instead of the inverse fast Fourier transform(IFFT) operation. The bit error rate(BER), spectral efficiency, and peak-to-average power ratio(PAPR) performance were compared with the conventional OFDM system through the OFDM system design based on wavelet transform. Our results showed that the conventional OFDM and Wavelet-OFDM exhibited the same BER performance, and that the Wavelet-OFDM using the discrete Meyer wavelet had the same spectral efficiency as the conventional OFDM. In addition, all systems of Wavelet-OFDM based on various wavelets confirm a PAPR performance lower than that of conventional OFDM.

• Nuclear Engineering and Technology
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• v.21 no.3
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• pp.223-230
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• 1989

This paper describes dynamic simulation of the spent fuel storage system which is described by statistical discrete event models. It visualizes flow and queue of system over time, assesses the operational performance of the system acitivies and establishes the system components and streams. It gives information on system organization and operation policy with reference to the design. System was tested and analyzed over a number of critical parameters to establish the optimal system. Workforce schedule and resources with long processing time dominate process. A combination of two workforce shifts a day and two cooling pits gives the optimal solution of storage system. Discrete system simulation is an useful tool to get information on optimal design and operation of the storage system.

• Journal of the Korean Data and Information Science Society
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• v.22 no.4
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• pp.811-817
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• 2011

We shall introduce a general probability mass function which includes several discrete probability mass functions. Especially, when the random variable X is Poisson, binomial, and negative binomial random variables as some special cases of the introduced distribution, the maximum likelihood estimator (MLE) and the uniformly minimum variance unbiased estimator (UMVUE) of the probability P(X ${\leq}$ t) are considered. And the efficiencies of the MLE and the UMVUE of the reliability ar compared each other.