• Communications for Statistical Applications and Methods
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• 제19권1호
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• pp.135-145
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• 2012

It is well known that the maximum likelihood estimator(MLE) in normal mixture models with unequal variances does not fall in the interior of the parameter space. Recently, a doubly smoothed maximum likelihood estimator(DS-MLE) (Seo and Lindsay, 2010) was proposed as a general alternative to the ordinary maximum likelihood estimator. Although this method gives a natural modification to the ordinary MLE, its computation is cumbersome due to intractable integrations. In this paper, we derive an EM algorithm for the DS-MLE under normal mixture models and propose a fast computational tool using a local quadratic approximation. The accuracy and speed of the proposed method is then presented via some numerical studies.

• Communications for Statistical Applications and Methods
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• 제24권3호
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• pp.271-290
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• 2017

We study a bivariate response regression model with arbitrary marginal distributions and joint distributions using Frank and Clayton's families of copulas. The proposed model is used for fitting dependent bivariate data with explanatory variables using the log-odd log-logistic Weibull distribution. We consider likelihood inferential procedures based on constrained parameters. For different parameter settings and sample sizes, various simulation studies are performed and compared to the performance of the bivariate odd-log-logistic-Weibull regression model. Sensitivity analysis methods (such as local and total influence) are investigated under three perturbation schemes. The methodology is illustrated in a study to assess changes on schoolchildren's oral health-related quality of life (OHRQoL) in a follow-up exam after three years and to evaluate the impact of caries incidence on the OHRQoL of adolescents.

• Communications for Statistical Applications and Methods
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• 제27권1호
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• pp.97-108
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• 2020

This paper compares several methods for estimating parameters of normal inverse Gaussian distribution. Ordinary maximum likelihood estimation and the method of moment estimation often do not work properly due to restrictions on parameters. We examine the performance of adjusted estimation methods along with the ordinary maximum likelihood estimation and the method of moment estimation by simulation and real data application. We also see the effect of the initial value in estimation methods. The simulation results show that the ordinary maximum likelihood estimator is significantly affected by the initial value; in addition, the adjusted estimators have smaller root mean square error than ordinary estimators as well as less impact on the initial value. With real datasets, we obtain similar results to what we see in simulation studies. Based on the results of simulation and real data application, we suggest using adjusted maximum likelihood estimates with adjusted method of moment estimates as initial values to estimate the parameters of normal inverse Gaussian distribution.

• Communications for Statistical Applications and Methods
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• 제27권1호
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• pp.37-46
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• 2020

Recurrent event data frequently occur in clinical studies, demography, engineering reliability and so on (Cook and Lawless, The Statistical Analysis of Recurrent Events, Springer, 2007). Sometimes, two or more different but related type of recurrent events may occur simultaneously. In this study, our interest is to estimate the covariate effect on bivariate recurrent event times with zero inflations. Such zero inflation can be related with susceptibility. In the context of bivariate recurrent event data, furthermore, such susceptibilities may be different according to the type of event. We propose a joint model including both two intensity functions and two cure rate functions. Bivariate frailty effects are adopted to model the correlation between recurrent events. Parameter estimates are obtained by maximizing the likelihood derived under a piecewise constant hazard assumption. According to simulation results, the proposed method brings unbiased estimates while the model ignoring cure rate models gives underestimated covariate effects and overestimated variance estimates. We apply the proposed method to a set of bivariate recurrent infection data in a study of child patients with leukemia.

• Journal of Chest Surgery
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• 제17권1호
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• pp.59-66
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• 1984

After open heart surgery, the patient must be carefully observed and adequately managed for his survival. This report reviewed 10 cases of ventricular septal defect and 12 mitral valvular diseases as hemodynamics early after open heart surgery. For postoperative 24 hours, clinical status was evaluated for left atrial pressure, central venous pressure,DP[LAP-CVP], peak systolic pressure, heart rate, urine amount, and other clinical findings. Especially, on postoperative fourth hour, cardiac output was most decreased, when the changes of monitoring were compared with two groups with or without using cardiotonics. Finally, we concluded as followings; 1.Postoperatively, variation of CVP was noted in VSD, but mitral valvular disease was more variable change of LAP. 2.DP was 1.3\ulcorner.4 cmH2O in VSD, and 6.4\ulcorner.2 cmH2O in mitral valvular disease. 3.Parameter using cardiotonic was CVP in VSD, and LAP in mitral valvular disease.

• 한국염색가공학회지
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• 제6권2호
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• pp.40-46
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• 1994

In order to study the properties of cochineal color, variation of uv, visible spectra by pH, dyeing properties on the silk in several dyeing conditions and thermodynamic parameter were investigated. Cochineal colors had an unusual to pH, especially had instability in alkali condition. An increase in the dyeing temperature and in time resulted in an increase in the dye content of silk fibers. Concentration of cochineal color in the silk fiber was related to pH and the maximum exhaustion of cochineal colors showed at about pH 3. The value of apparent diffusion coefficients and standard affinities of dyeing increased with the increase of dyeing temperature. The standard heats of dyeing(ΔH°), variation of entropy(ΔS°) and activation energy(E/sub act/) were caculated to be -1.72kcal/mo1, -3.77cal/mo1ㆍdeg and 1.26kcal/mo1, respectively. Silk fabrics were dyed bright red by tin chloride, reddish purple by copper sulfate, and bluish gray by iron sulfate, respectively. Lightfastness of silk fabrics mordanted by metal ion was weak.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 추계 학술발표회
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• pp.1151-1155
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• 2010

Frost depth is one of important factors to design roadway structure, and it can be estimated with numerical simulation on thermal distribution through subgrade soils. Thermal conductivity is a key parameter for accurate prediction on thermal distribution, but there are few studies on thermal conductivity of subgrade soils in Korea. Thermal conductivity can be affected by several factors such as dry density, moisture content, and saturation degree based on previous researches. Two empirical equations to estimate thermal conductivity are applied to access the accuracy of these equations with experimental data. Results indicate that the equation can be used to estimate thermal conductivity with proper quartz fraction.

• Journal of Astronomy and Space Sciences
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• 제23권4호
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• pp.405-414
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• 2006

Satellite formation flying has become a critical issue in the aerospace engineering because it is considered as an enabling technology for many space missions. Thus, many nonlinear control theories have been developed for the tracking problem of satellite formation flying, which include full-nonlinear dynamics, external disturbances and parameter uncertainty. In this study, nonlinear adaptive control law is developed using an adaptive backstepping technique to solve the relative position tracking problem of the satellite formation flying in the presence of mass uncertainty and the bounded external disturbance. Simulation studies are included to demonstrate the proposed controller performance. The proposed controller is shown to guarantee the system stability against the external bounded disturbances in the presence of mass uncertainty.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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• pp.507-512
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• 2002

Prestressed concrete I-girders were used in the bridge applications in the early 1950s. During the last four decades, the most widely used girder length of bridges have been below 30 meters. The main objective of this study is to develope the alternative section for widely spaced girder of 30 meters span bridge. Girder spacing, the number of strands and compressive strength of concrete are major parameters for widely spaced girders. The optimal girder spacing is determined through the parameter studies of design using widely spaced girders. 30m span bridges of widely girder spacing must use high-strength concrete. Although the basic unit cost of concrete is higher for high-strength concrete, it may be partially or even fully offset by reduced quantities of concrete as result of the smaller number of girders used. High-strength concrete girders have more prestressing strands per girder, but the total number of strands for all of the girders is less than that required for the larger number of normal-strength concrete girders. It could design PSC-I Birdge with widely spaced girder owing to high-strength concrete.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1994년도 하계학술대회 논문집 A
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• pp.472-474
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• 1994

A new integral variable structure system without the reaching phase problems is presented for the prescribed control of the BLDDSM under load variation and parameter uncertainties. The control technique can yields the complete robustness of initially prescribed output dynamics in the sliding surface against the modeling errors. The comparative simulation and experiment studies of the BLDDSM position control are carried out in comparison with two previous algorithms.