• The Transactions of the Korean Institute of Electrical Engineers A
• /
• v.50 no.2
• /
• pp.90-95
• /
• 2001

Electric arc furnaces (EAFs) has a process to cause the degradation of the electric power quality such as voltage flicker. In order to adequately understand and analyze the effects on the power system from these loads, obtaining an accurate representation of the characteristics of the loads is crucial. In this paper, a mixed chaotic EAF model to represent the low frequency and high frequency variations of the arc current respectively has been proposed. The Lorenz system may contribute to the low frequency components of arc current and the logistic equation may contribute to the high frequency components, and the proposed mixed model will be a combination of both Lorenz and logistic model. The concept of chaotic parameters, such as chaotic resistance, inductance of admittance has been also proposed for the characterization of arc furnace operation and the highly nonlinear physical processes. The power quality indices are calculated from the simulated waveforms and compared with the actual power quality indices statistics in order to illustrate the model's capabilities.

• Tribology and Lubricants
• /
• v.16 no.2
• /
• pp.106-113
• /
• 2000

Effects of surface roughness on bearing performances are investigated numerically in this study, especially for the parallel thrust bearing. Although mating surfaces are parallel and separated by thin fluid film, the pressure distribution is formed due to asperities. Model surface is generated numerically with given autocorrelation function and some surface profile parameters. Then the average Reynolds equation is applied to predict the effects of surface roughness between hydrodynamic and mixed lubrication regimes. In this equation, flow factors are defined as correction terms to smooth out high frequency surface roughness. The correlation length is proposed to get the minimum load for the parallel thrust bearing for various sliding conditions.

• Korean Journal of Medicinal Crop Science
• /
• v.18 no.1
• /
• pp.15-21
• /
• 2010

This study was conducted to investigate the effects of Lycii fructus and Astragalus membranaceus mixed extracts on immunomodulators and prevention in a streptozotocin-induced diabetes rat model. A total of 28 male rats were divided into four dietary groups and fed a commercial diet (A), commercial diet plus induced diabetes by a streptozotocin (STZ) injection (B), induced diabetes by STZ plus medicinal crop extracts(I&$H^{(R)}$) diet (C), and medicinal crop extracts (I&$H^{(R)}$) diet (D). Immunoblotting analyses revealed cytokine expression, and ELISA analyses revealed immunoglobulin E and nitric oxide production. As a results, the tumor necrosis factor-$\alpha$ (TNF-$\alpha$) and inducible nitric oxide synthase (iNOS) as a inflammatory cytokine were decreased. Interleukin-6 (IL-6) and signal transducer and activation of transcription 3 (STAT3) cytokine related in diabetes expression through JAK/STAT3 pathway were also decreased. Furthermore, immunoglobulin E and nitric oxide production were decreased in the serum and lens, respectively. These results suggest that Lycii fructus and Astragalus membranaceus mixed extracts provide positive effects on immunomodulators and prevention in diabetes and eye disease complications.

• Journal of the Korean Data and Information Science Society
• /
• v.23 no.4
• /
• pp.739-748
• /
• 2012

In this paper we propose a mixed effects least squares support vector machine (LS-SVM) for the censored data which are observed from different groups. We use weights by which the randomly right censoring is taken into account in the nonlinear regression. The weights are formed with Kaplan-Meier estimates of censoring distribution. In the proposed model a random effects term representing inter-group variation is included. Furthermore generalized cross validation function is proposed for the selection of the optimal values of hyper-parameters. Experimental results are then presented which indicate the performance of the proposed LS-SVM by comparing with a standard LS-SVM for the censored data.

• Journal of the Korean Data and Information Science Society
• /
• v.27 no.2
• /
• pp.531-538
• /
• 2016

In this paper we deal with the small area estimation for the case that the response variables take binary values. The mixed effects models have been extensively studied for the small area estimation, which treats the spatial effects as random effects. However, when the spatial information of each area is given specifically as coordinates it is popular to use the geographically weighted logistic regression to incorporate the spatial information by assuming that the regression parameters vary spatially across areas. In this paper, relaxing the linearity assumption and propose a geographically weighted kernel logistic regression for estimating small area proportions by using basic principle of kernel machine. Numerical studies have been carried out to compare the performance of proposed method with other methods in estimating small area proportion.

• The Korean Journal of Applied Statistics
• /
• v.28 no.2
• /
• pp.211-219
• /
• 2015

Generalized linear mixed models are used to analyze longitudinal categorical data. Random effects specify the serial dependence of repeated outcomes in these models; however, the estimation of a random effects covariance matrix is challenging because of many parameters in the matrix and the estimated covariance matrix should satisfy positive definiteness. Several approaches to model the random effects covariance matrix are proposed to overcome these restrictions: modified Cholesky decomposition, moving average Cholesky decomposition, and partial autocorrelation approaches. We review several approaches and present potential future work.

• The Korean Journal of Applied Statistics
• /
• v.29 no.2
• /
• pp.291-299
• /
• 2016

This paper discusses how to establish estimable functions when there are fixed and random effects in design models. It proves that estimable functions of mixed models are not related to random effects. A fitting constants method is used to obtain sums of squares due to random effects and Hartley's synthesis is used to calculate coefficients of variance components. To test about the fixed effects the degrees of freedom associated with divisor are determined by means of the Satterthwaite approximation.

• Environmental and Resource Economics Review
• /
• v.16 no.4
• /
• pp.803-832
• /
• 2007

Electricity and heat load profiles by use types on an hourly basis at the least are essential for assessing economic viability of new cogeneration and CES projects and for optimally operating existing cogeneration and CES facilities. We adopt a multilevel model to specify heat load profiles so as to utilize in a flexible manner the panel nature of our data on weather and heating/cooling use. Converting the multilevel model to the linear mixed-effects model, we estimate the model by panel FGLS. The estimated load profile model for each distinct use type accounts for the effects of temperature, humidity, each hour over the year, each day of the week, each type of legal holidays, and heating/cooling area on energy use. To save space, we feature in detail the heating profile of the household.

• Proceedings of KOSOMES biannual meeting
• /
• 2001.10a
• /
• pp.137-144
• /
• 2001

A Plankton ecosystem model was developed to investigate effects of hydrodynamic processes including advection and diffusion on size-structured phytoplankton dynamics in the mesohaline zone of the York River estuarine system, Virginia, USA. The model included 12 state variables representing the distribution of carbon and nutrients in the surface mixed layer. Groupings of autotrophs and heterotrophs were based on cell site and ecological hierarchy Forcing functions included incident radiation, temperature, wind stress, mean How and tide which includes advective transport and turbulent mixing. The ecosystem model was developed in FORTRAN using differential equations that were solved using the 4th order Runge-Kutta technique. The model showed that microphytoplankton blooms during winter-spring resulted from a combination of vertical advection and diffusion of phytoplankton cells rather than in-situ production in the lower York River estuary.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.58 no.3
• /
• pp.241-250
• /
• 2022

This paper describes the design of H-infinity controller for robust control of a DC motor system. The suggested controller can ensure robustness against disturbance and model uncertainty by minimizing H-infinity norm of the transfer function from exogenous input to performance output and applying the small gain theorem. In particular, the controller was designed to reduce the effects of disturbance and model uncertainty simultaneously by formalizing these problems as a mixed sensitivity problem. The validity of the proposed controller was demonstrated by computer simulations and real experiments. Moreover, the effectiveness of the proposed controller was confirmed by comparing its performance with PI controller, which was tested under the same experimental condition as the H-infinity controller.