• The Korean Journal of Applied Statistics
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• v.21 no.6
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• pp.923-932
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• 2008

We are likely to face complex multivariate data which can be characterized by having a non-trivial correlation structure. For instance, omitted covariates may simultaneously affect more than one count in clustered data; hence, the modeling of the correlation structure is important for the efficiency of the estimator and the computation of correct standard errors, i.e., valid inference. A standard way to insert dependence among counts is to assume that they share some common unobservable variables. For this assumption, we fitted correlated random effect models considering multilevel model. Estimation was carried out by adopting the semiparametric approach through a finite mixture EM algorithm without parametric assumptions upon the random coefficients distribution.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.3
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• pp.421-426
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• 2002

Hybrid cascade multilevel PWM inverter has advantages of hybrid structure which enhances the better utilization of power semiconductor switches, that is, both hi호 power-low frequency switch, GTO and low power-high frequency switch, IGBT can be used in the same circuit. In this paper, a static var compensator using hybrid cascade 5-level PWM inverter is presented for high voltage/high power applications. The proposed system is modelled by circuit DQ transformation, and thus an equivalent circuit is obtained which reveals the important characteristics of the system and lead to the related equations. Finally, circuit structure and characteristics is presented and the validity of the characteristics analysis is shown through PSIM simulation.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 1994.04a
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• pp.715-725
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• 1994

The objective of this research is to develop a cost model for integrated CAD system. A computerized system realizing this model then is used to aid designers. The first area is to propose a conceptual framework of a multilevel cost model. The methodology of constructing the model is discussed. Then suggestion of an object oriented programming technique for implementing the model is presented. Complicate estimation procedure can be systematically handled by this technique. Interval analysis to deal with the uncertainty of information and decision during design process is used. An experimentation algorithm for calculating the cost distribution is proposed to overcome the shortcoming of interval analysis. Major focus of this research is on net shape manufacturing processes including die casting, injection molding, and metal forming.

• Journal of Preventive Medicine and Public Health
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• v.35 no.1
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• pp.76-82
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• 2002

Objective : To investigate the relationships of occupational class, educational level and deprivation with mortality in Korea Methods : This study used existing South Korean national data on occupation, educational level, and deprivation and death. Mortality was investigated using registered death data from 1993 to 1997 obtained from the Korean National Statistics Office (NSO) with denominators drawn from the 1995 Census. Statistical analysis consisted of poisson regression modeling and multilevel analysis. Results : The lower occupational class (manual workers) group had a higher mortality rate than the higher occupational class (non-manual workers) group Educational level, and deprivation were both inversely related withand mortality. Occupation was strongly associated with education. Area-based deprivation indicators and individual indices for social class made an independent contribution to the mortality risk. Conclusions : The findings of this study suggests that the relationships of occupational class, educational level and deprivation with mortality appears to be stronger in Korea than in European countries.

• Journal of the Optical Society of Korea
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• v.13 no.3
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• pp.386-391
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• 2009

PSPICE circuit parameters of the blue laser diodes grown on wurtzite AlGaInN multiple quantum well structures were extracted directly from the three level rate equations. The relevant optical gain parameters were separately calculated from the self-consistent multiband Hamiltonian. The resulting equivalent circuit model for a blue laser diode was schematically presented, and its modulation characteristics, including the pulse response and the frequency response, have been demonstrated by using a conventional PSPICE.

• Current Optics and Photonics
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• v.8 no.3
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• pp.239-245
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• 2024

This paper proposes single logarithmic amplification (single-LA) and deep learning (DL)-based fixed-threshold on-off keying (OOK) detection for free-space optical (FSO) communication. Multilevel LAs (MLAs) can be used to mitigate intensity fluctuations in the received OOK signal by their nonlinear gain characteristics; however, it is ineffective in the case of high scintillation, owing to degradation of the OOK signal's extinction ratio. Therefore, a DL technique is applied to realize effective scintillation compensation in single-LA applications. Fully connected (FC) networks and fully connected neural networks (FCNN), which have nonlinear modeling characteristics, are deployed in this work. The performance of the proposed method is evaluated through simulations under various scintillation effects. Simulation results show that the proposed method outperforms the conventional adaptive-threshold-decision, single-LA-based, MLA-based, FC-based, and FCNN-based OOK detection techniques.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.3
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• pp.17-23
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• 2020

This paper proposes a simulation model using an equivalent circuit for the development of an MMC system. The MMC has been chosen as the most suitable topology for high voltage power transmission, such as a voltage-type HVDC, and it has dozens to hundreds of sub-modules in the form of a half-bridge or full-bridge connected in series. A simulation study is essential for the development of an MMC algorithm. On the other hand, it is virtually impossible to construct and implement MMC simulation models, including hundreds or thousands of switching devices. Therefore, this paper presents an MMC equivalent model, which is easily expandable and implemented by modeling the dynamic characteristics. The voltage and current equation of the equivalent circuit was calculated using the direction of the arm current and switching signal. The model was implemented on Matlab/Simulink. In this paper, to show the validity of the model developed using Matlab/Simulink, the simulation results of a five-level MMC using the real switching element and the proposed equivalent model are shown. The validity of the proposed model was verified by showing that the current and voltage waveform in the two models match each other.

• Journal of Cadastre & Land InformatiX
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• v.48 no.2
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• pp.197-211
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• 2018

We conducted this research to examine how well regional housing prices are suited to use as an alternative to conventional census-based regional deprivation indices in health and medical geography studies. To examine the relative performance of mean regional housing prices compared to conventional census-based regional deprivation indices, we compared several multilevel logistic regression models, where the first level was individuals and the second was health districts in the Seoul Metropolitan Area (SMA) in Korea, for the sake of adjusting the regional clustering tendency of unknown factors. In these models, we predicted two dichotomous variables that represented individuals' after-lunch tooth brushing behavior and use of dental floss by individual characteristics and regional indices. Then, we compared the relative predictive performance of the models using the Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC). The results from the estimations showed that mean regional housing prices and census-based deprivation indices were correlated with the two types of dental health behavior in a statistical sense. The results also revealed that the model with mean regional housing prices showed smaller AIC and BIC compared with other models with conventional census-based deprivation indices. These results imply that it is possible for housing prices summarized using aerial units to be used as an alternative to conventional census-based deprivation indices when the census variables employed cannot properly reflect the characteristics of the aerial units.

• Journal of Electrical Engineering and Technology
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• v.9 no.5
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• pp.1471-1481
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• 2014

This paper presents the new power dissipation model of individual switching device in a high-level modular multilevel converter (MMC), which can be mostly used in voltage sourced converter (VSC) based high-voltage direct current (HVDC) system and flexible AC transmission system (FACTS). Also, the voltage balancing method based on sorting algorithm is newly proposed to advance the MMC functionalities by effectively adjusting switching variations of the sub-module (SM). The proposed power dissipation model does not fully calculate the average power dissipation for numerous switching devices in an arm module. Instead, it estimates the power dissipation of every switching element based on the inherent operational principle of SM in MMC. In other words, the power dissipation is computed in every single switching event by using the polynomial curve fitting model with minimum computational efforts and high accuracy, which are required to manage the large number of SMs. After estimating the value of power dissipation, the thermal condition of every switching element is considered in the case of external disturbance. Then, the arm modeling for high-level MMC and its control scheme is implemented with the electromagnetic transient simulation program. Finally, the case study for applying to the MMC based HVDC system is carried out to select the appropriate insulated-gate bipolar transistor (IGBT) module in a steady-state, as well as to estimate the proper thermal condition of every switching element in a transient state.

• The Journal of the Acoustical Society of Korea
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• v.20 no.2
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• pp.35-43
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• 2001

Many speech recognition systems have used pronunciation lexicon with possible multiple phonetic transcriptions for each word. The pronunciation lexicon is of often manually created. This process requires a lot of time and efforts, and furthermore, it is very difficult to maintain consistency of lexicon. To handle these problems, we present a model based on morphophon-ological analysis for automatically generating Korean pronunciation variants. By analyzing phonological variations frequently found in spoken Korean, we have derived about 700 phonemic contexts that would trigger the multilevel application of the corresponding phonological process, which consists of phonemic and allophonic rules. In generating pronunciation variants, morphological analysis is preceded to handle variations of phonological words. According to the morphological category, a set of tables reflecting phonemic context is looked up to generate pronunciation variants. Our experiments show that the proposed model produces mostly correct pronunciation variants of phonological words. Then we estimated how useful the pronunciation lexicon and training phonetic transcription using this proposed systems.