• The Korean Journal of Applied Statistics
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• v.34 no.1
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• pp.25-38
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• 2021

Recently the need for network surveillance to detect abnormal behavior within dynamic social networks has increased. We consider a dynamic version of the degree corrected stochastic block model (DCSBM) to simulate dynamic social networks and to monitor for a significant structural change in these networks. To apply a control charting procedure to network surveillance, in-control model parameters must be estimated from the Phase I data, that is from historical data. In network surveillance, however, there are many situations where sufficient relevant historical data are unavailable. In this paper we propose a self-starting Shewhart control charting procedure for detecting change in the dynamic networks. This procedure can be a very useful option when we have only a few initial samples for parameter estimation. Simulation results show that the proposed procedure has good in-control performance even when the number of initial samples is very small.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2015.10a
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• pp.190-193
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• 2015

The current sea route sign system based on an electronic marine chart only has a data manufacture specification for uses at ECDIS. Therefore, it has a limitation in expressing various sea route data and falls short of productivity as it is frozen to prevent being changed for a long time. Also, it cannot satisfy requirements from high tech such as lattice structure data and time series information. Currently, although it builds each independent operation system based S-57, it has been found that it is the most important requirement from consumers that the entire monitoring system can mutually interwork by standardizing and uniting formats of all protocols. In addition, current status information and alarm system is using AIS, TRS, WCDMA telecommunication and processing all the data after saving it into each different server. Lighthouse lantern which currently has used was utilized to do a performance test of a developed system. All of created data was trasmitted through the RS-232, It is clear that the data was received by a situation monitoring system. In addition, when the data was transmitted after saving in a database, same data was ordinarily received. In this thesis, we will implemented the status information and alarm system of Marine transportation facilities which is a sea route sign system based on S-63 electronic marine chart, S/W, after uniting each different protocol and making combined system.

• Journal of Korean Society of Environmental Engineers
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• v.32 no.3
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• pp.234-240
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• 2010

The effectiveness of adding powdered zeolite and granular activated carbon (GAC) before starvation into biological reactor for recovering its performances was investigated. Two types of carrier addition in Sequencing Batch Reactor (SBR) system for non-saline and saline wastewater were evaluated after starvation periods. During the experiment, settleablity (SVI), floc size, fractal dimension, $COD_{Mn}$, T-N, T-P removal efficiencies and recovery time were monitored. When the wastewater feeding was resumed after starvation period for 5days, the SVI increased at the beginning of resumption and then decreased with time in both types. And the larger the floc size and fractal dimension of floc, the more increased removal efficiency for $COD_{Mn}$, T-N and T-P was also. Its performance recovery was strongly correlated with floc size and fractal dimension of activated sludge. After resuming the wastewater feeding, the SVI, floc size, fractal dimension, $COD_{Mn}$, T-N, T-P removal efficiency of SBR with carrier improved and reached its initial value faster compared to those of SBR without carrier.

• 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 Internet Computing and Services
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• v.19 no.3
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• pp.49-56
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• 2018

Euclidean distance (ED) between error distribution and Dirac delta function has been used as an efficient performance criterion in impulsive noise environmentsdue to the outlier-cutting effect of Gaussian kernel for error signal. The gradient of ED for its minimization has two components; $A_k$ for kernel function of error pairs and the other $B_k$ for kernel function of errors. In this paper, it is analyzed that the first component is to govern gathering close together error samples, and the other one $B_k$ is to conduct error-sample concentration on zero. Based upon this analysis, it is proposed to normalize $A_k$ and $B_k$ with power of inputs which are modified by kernelled error pairs or errors for the purpose of reinforcing their roles of narrowing error-gap and drawing error samples to zero. Through comparison of fluctuation of steady state MSE and value of minimum MSE in the results of simulation of multipath equalization under impulsive noise, their roles and efficiency of the proposed normalization method are verified.

• Korean Chemical Engineering Research
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• v.49 no.4
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• pp.423-431
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• 2011

Recentincreasing awareness of the environmental damage caused by the $CO_2$ emission of fossil fuelsstimulated the interest in alternative and renewable sources of energy. Fuel cell is a representative example of hydrogen energy utilization. In this study, Molten Carbonate Fuel Cell system is simulated by using $Aspen^{TM}$. Stack model is consisted of equilibrium reaction equations using $ACM^{TM}$(Aspen Custom Modeler). Balance of process of fuel cell system is developed in Aspen $Plus^{TM}$ and simulated at steady-state. Analysis of performance of the system is carried out by using sensitivity analysis tool with main operating parameters such as current density, S/C ratio, and fuel utilization and recycle ratio.In Aspen $Dynamics^{TM}$, dynamics of MCFC system is simulated with PID control loops. From the simulation, we proposed operation range which generated maximum power and efficiency in MCFC power plant.

• Journal of Aerospace System Engineering
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• v.12 no.2
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• pp.7-14
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• 2018

In this study, a new check valve was studied to improve the load pressure of a brake system with a small piezoelectric-hydraulic pump. During the pressurization process, the steady-state pressure at the load is affected by the ratio of the cross-sectional area of the check valve the chamber pressure and load pressure. Since the flow path cover of the check valve is made wider than the cross-sectional area of the output flow to prevent backflow, a method of reducing the area ratio is proposed for a higher load pressure by mounting an additional mass to a thin plate spring type check valve. To identify the effect of mounting an additional mass to the existing check valve on the load pressure, a simple brake system with a small piezoelectric-hydraulic pump was modeled using a commercial code AMESim. The AMESim modeling was verified by comparing the simulation results with the experimental results of the pump the existing check valve. The additional mass was added to the verified AMESim modeling and higher load pressure was able to be obtained through simulation. The 35% performance improvement in load pressure identified by carrying out pressurization test of the brake system after adopting the new check valve the small piezoelectric-hydraulic pump.

• Korean Journal of Remote Sensing
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• v.37 no.2
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• pp.359-365
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• 2021

GEO-KOMPSAT-2A (GK2A) AMI (Advanced Meteorological Imager) Best Detector Select (BDS) map is pre-determined and uploaded before the satellite launch. After the launch, there is some possibility of a detector performance change driven by an abrupt temperature variation and thus the status of BDS map needs to be evaluated and updated if necessary. To investigate performance of entire elements of the detectors, AMI BDS analyses were conducted based on a technical note provided from the AMI vendor (L3HARRIS). The concept of the BDS analysis is to investigate the stability of signals from detectors while they are staring at targets (deep space and internal calibration target). For this purpose, Long Time Series (LTS) and Output Voltage vs. Bias Voltage (V-V) methods are used. The LTS for 30 secs and the V-V for two secs are spanned respectively for looking at the targets to compute noise components of detectors. To get the necessary data sets, these activities were conducted during the In-Orbit Test (IOT) period since a normal operation of AMI is stopped and special mission plans are commanded. With collected data sets during the GK2A IOT, AMI BDS map was intensively examined. It was found that about 1% of entire detector elements, which were evaluated at the ground test, showed characteristic changes and those degraded elements are replaced by alternative best ones. The stripping effects on AMI raw images due to the BDS problem were clearly removed when the new BDS map was applied.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.20 no.6
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• pp.27-32
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• 2020

This paper compare the adaptive equalization performance according to the values of adaptive step variation speed for adapting in VS-CCA (Variable Stepsize-Compact Constellation Algorithm) based on nonlinear function function of error signal. The VS-CCA algorithm compacts the 16-QAM nonconstant modulus signal into the 4 groups of 4-QAM constant modulus signal constellation in quadature plane, then the error signal is generated using the constant modulus of transmitted signal statistics. The adaptive equalizer coefficient were updated in order to achieve the minimum cost function by varying step based on the nonlinear function of error signal. In this time, the instantaneous adaptive step is determined according to the value of step variation speed of nonlinear function and the different equalization performance were obtained according to the step variation speed value. The equalizer internal index and external index which represents the robustness of external noise were used for the performance comparison index. As a result of computer simulation, it was confirmed that the value of variation speed less than 1.0 give more superior in every performance index compared to the greater than 1.0 in steady state.

• Journal of Biomedical Engineering Research
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• v.18 no.4
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• pp.429-438
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• 1997

Mechanical valve is one of the most widely used implantable artificial organs of which the reliability is so important that its failure means the death of patient. Therefore early noninvasive detection is essentially required, though mechanical valve failure with thrombosis is the most common. The objective of this paper is to detect the thrombosis formation by spectral analysis and neural network. Using microphone and amplifier, we measured the sound from the mechanical valve which is attached to the pneumatic ventricular assist device. The sound was sampled by A/D converter(DaqBook 100) and the periodogram is the main algorithm for obtaining spectrum. We made the thrombosis models using pellethane and silicon and they are thrombosis model on the valvular disk, around the sewing ring and fibrous tissue growth across the orifice of valve. The performance of the measurment system was tested firstly using 1 KHz sinusoidal wave. The measurement system detected well 1KHz spectrum as expected. The spectrum of normal and 5 kinds of thrombotic valve were obtained and primary and secondary peak appeared in each spectrum waveform. We find that the secondary peak changes according to the thrombosis model. So to distinguish the secondary peak of normal and thrombotic valve quantatively, 3 layer back propagation neural network, which contains 7, 000 input node, 20 hidden layer and 1 output was employed The trained neural network can distinguish normal and valve with more than 90% probability. As a conclusion, the noninvasive monitoring of implanted mechanical valve is possible by analysing the acoustical spectrum using neural network algorithm and this method will be applied to the performance evaluation of other implantable artificial organs.