• Journal of the Korean Data and Information Science Society
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• v.24 no.6
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• pp.1113-1125
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• 2013

Corporate bankruptcy prediction has been an important topic in the accounting and finance field for a long time. Several data mining techniques have been used for bankruptcy prediction. However, there are many limits for application to real classification problem with a single model. This study proposes ensemble SVM (support vector machine) model which assembles different SVM models with each different kernel functions. Our ensemble model is made and evaluated by v-fold cross-validation approach. The k top performing models are recruited into the ensemble. The classification is then carried out using the majority voting opinion of the ensemble. In this paper, we investigate the performance of ensemble SVM classifier in terms of accuracy, error rate, sensitivity, specificity, ROC curve, and AUC to compare with single SVM classifiers based on financial ratios dataset and simulation dataset. The results confirmed the advantages of our method: It is robust while providing good performance.

• Journal of IKEEE
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• v.19 no.1
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• pp.101-109
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• 2015

As the number of smartphone users grows, number of applications and the expected overall functionality in a smartphone grow simultaneously. With ever-so increasing expectations comes intense competition to squeeze in myriads of functions in a limited space that is only getting 'slimmer' by the year. In order to achieve this, companies often decrease the size of components in smartphones - battery connectors in particular. While they may fit, smaller battery connectors have their disadvantages due to the heat generated by the high current flow in the circuits. In collaborating with Korea's leading battery connector manufacturers, this research presents current issues and design concepts that should be considered when engineers design power connectors based on their electrical and thermal analysis.

• Convergence Security Journal
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• v.7 no.3
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• pp.109-120
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• 2007

VoIP service provides various functions that PSTN phone service hasn't been able to provide. Since it also has superiority in service charge, the number of user is increasing these days. When we think of the other side in cost aspect, the spam caller can also send his/her commercial message over phone line using more economic way. This paper presents the characteristics that should be considered to detect the spam call using greylisting method. We have explored static and dynamic characteristics in VoIP calls, and analyzed the relation among them. Especially, we have surveyed the authentication and charging method of Korean VoIP service provider. We have analyzed each charging method using our spam call simulation result, and derived the charging method that can be favored by spam caller. The contribution of the work is in analysis result of static aspect for SPIT Level calculation in greylisting method.

• Earthquakes and Structures
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• v.11 no.6
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• pp.1077-1099
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• 2016

One of the main shortcomings in the current passive base isolation system is lack of adaptability. The recent research and development of a novel adaptive seismic isolator based on magnetorheological elastomer (MRE) material has created an opportunity to add adaptability to base isolation systems for civil structures. The new MRE based base isolator is able to significantly alter its shear modulus or lateral stiffness with the applied magnetic field or electric current, which makes it a competitive candidate to develop an adaptive base isolation system. This paper aims at exploring suitable control algorithms for such adaptive base isolation system by developing a close-loop semi-active control system for a building structure equipped with MRE base isolators. The MRE base isolator is simulated by a numerical model derived from experimental characterization based on the Bouc-Wen Model, which is able to describe the force-displacement response of the device accurately. The parameters of Bouc-Wen Model such as the stiffness and the damping coefficients are described as functions of the applied current. The state-space model is built by analyzing the dynamic property of the structure embedded with MRE base isolators. A Lyapunov-based controller is designed to adaptively vary the current applied to MRE base isolator to suppress the quake-induced vibrations. The proposed control method is applied to a widely used benchmark base-isolated structure by numerical simulation. The performance of the adaptive base isolation system was evaluated through comparison with optimal passive base isolation system and a passive base isolation system with optimized base shear. It is concluded that the adaptive base isolation system with proposed Lyapunov-based semi-active control surpasses the performance of other two passive systems in protecting the civil structures under seismic events.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.8
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• pp.921-927
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• 2012

Reliability-based design optimization (RBDO) can be used to determine the reliability of a system by means of probabilistic design criteria, i.e., the possibility of failure considering stochastic features of design variables and input parameters. To assure these criteria, various reliability analysis methods have been developed. Most of these methods assume that distribution functions are continuous. However, in real problems, because real data is often discrete in form, it is important to estimate the distributions for discrete information during reliability analysis. In this study, we employ the Akaike information criterion (AIC) method for reliability analysis to determine the best estimated distribution for discrete information and we suggest an RBDO method using AIC. Mathematical and engineering examples are illustrated to verify the proposed method.

• Journal of Advanced Navigation Technology
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• v.3 no.1
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• pp.20-31
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• 1999

In this paper, we have chosen KimPo International Airport as an area for estimating the flutter interference, in order to analyze the flutter interference. The field test at 25 points around KimPo International Airport and the simulation have been performed for estimating the flutter interference. We consider the received power of a direct wave, the height of an antenna, the ERP of a transmitting point, transmit frequency, and the reflection coefficients of an airplane, the transmit/receive point coordinates as estimation functions for the flutter. From the results, we have found that the flutter interference from flights is very serious around the route of flight circumference, and often occurs when the height of an airplane is low, range from 40 to 240 m. Besides, the degree of the flutter interference can be changed according to the distance between an airplane and a transmitting point, elevation angle, and the reflection coefficients of an airplane.

• Journal of Korea Multimedia Society
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• v.7 no.1
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• pp.44-53
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• 2004

This paper aims at presenting high quality at low resolution apply by a new antialiasing method for voxelized implicit surfaces. Implicit surfaces create a unique type of 3D-modeling. Some use of implicit surfaces are scientific and medical visualization, animation, medical simulation and interactive modeling. One of previous antialiasing methods for implicit surfaces presented by raytracing or texture mapping is making use of a stochastic sampling. But this method requires more calculation time and costs which is caused by complicated and difficult implicit functions. In the meanwhile, voxelized implicit surfaces generally use high resolution for good quality images but it costs to generate. In order to this problem, this paper suggests a shifted double Z-buffer which is very simple, more efficient and easy. Tn addition, there are applied box-filter and tent-filter to the double Z-buffer antialiasing method for better images. For results this method generate high quality image and it is easy to apply to various filters and is able to extend to multi Z-buffer.

• Journal of Advanced Navigation Technology
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• v.13 no.6
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• pp.901-906
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• 2009

This paper proposes a call admission control(CAC) method for wireless networks, which is based on the upper bound of a possibility distribution of handoff calls dropping rates. The possibility distribution is estimated in a fuzzy inference and a learning algorithm in neural network. The learning algorithm is considered for tuning the membership functions(then parts)of fuzzy rules for the inference. The fuzzy inference method is based on a weighted average of fuzzy sets. The proposed method can avoid estimating excessively large handoff calls dropping rates, and makes possibile self-compensation in real time for the case where the estimated values are smaller than real values. So this method makes secure CAC, thereby guaranteeing the allowed CDR. From simulation studies we show that the estimation performance for the upper bound of call dropping rate is good, and then handoff call dropping rates in CAC are able to be sustained below user's desired value.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.4
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• pp.744-751
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• 2006

Even many kinds of Internet-based services have been generated due to the great development of the Internet. PSTN still exists in the center of the national infrastructure network and the transit exchanges will be maintained the core roles in PSTN for many years in the future. These transit exchanges often suffer from unexpected overload situation because they have to process Intelligent Network calls and mobile calls additionally as well as POTS (Plain Old Telephone Service). In this paper, we suggest an efficient overload control algorithm for the distributed transit switching system under the various types of call services. We also show that this algorithm can be implemented easily cooperating with the network management control functions. The simulation technique is used to show that the proposed algorithm effectively controls calls and maintains safely the call processor's load under the various kinds of overload situations.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.1
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• pp.18-27
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• 2004

In this paper, we presents an analytical simulation procedure for evaluation in baseband digital modulated signals distortions in the present of RF power amplifier(SSPA) nonlinear behavior and backoff operations of OFDM wireless transmission system. we obtained the optimum nonlinear transfer function of designed SSPA with the SiGe HBT bias currents of OFDM multi-channel wireless transmission system and compared this transfer function to SSPA nonlinear modeling functions mathematically, we finds optimum bias conditions of designed SSPA. With the derived nonlinear modeling function of SSPA, We analysed the PSD characteristics of in-band and out-band output powers of SSPA EVM measurement results of distorted constellation signals with the input power levels of SSPA. The results of paper can be applied to find the SSPA linearly with optimum bias currents and determine the SSPA input backoff bias for AGC control circuits of SSPA.