• Title/Summary/Keyword: Positive definiteness

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Vector decomposition of the evolution equations of the conformation tensor of Maxwellian fluids

  • Cho, Kwang-Soo
    • Korea-Australia Rheology Journal
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    • v.21 no.2
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    • pp.143-146
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    • 2009
  • Breakthrough of high Weisenberg number problem is related with keeping the positive definiteness of the conformation tensor in numerical procedures. In this paper, we suggest a simple method to preserve the positive definiteness by use of vector decomposition of the conformation tensor which does not require eigenvalue problem. We also derive the constitutive equation of tensor-logarithmic transform in simpler way than that of Fattal and Kupferman and discuss the comparison between the vector decomposition and tensor-logarithmic transformation.

Factors Affecting on Organizational Commitment of Hospital Nurses (병원근무 간호사의 직장애착도와 관련요인)

  • JeKal, Bon-Sun;Lee, Sung-Hee
    • Journal of Korean Academy of Nursing Administration
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    • v.13 no.1
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    • pp.65-73
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    • 2007
  • Purpose: This study was carried out to find out the factors affecting on organizational commitment of hospital nurses. Method: The questionnaire-based research was done with 989 hospital nurses between January and March, 2004. Results: Variables such as job satisfaction, met expectations, compensation and welfare status of hospital, work involvement, positive affectivity had significant positive direct effect on organizational commitment in order of size, however, vertical conflict and job opportunity had negative direct effect in order of size. It was found that the following variables, listed in order of size, had significant total effects on organizational commitment: job satisfaction, met expectations, vertical conflict, compensation and welfare status of hospital, positive affectivity, work involvement, job opportunity, job autonomy, work definiteness, division justice, stability of employment, expectations before entering a hospital. Conclusion: It is recommended that programs for job satisfaction promotion, met expectations promotion, adequate compensation and welfare of hospital, work definiteness and work autonomy, solving conflict, positive affectivity promotion should be implemented to increase organizational commitment of hospital nurses.

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Factors Affecting on Organizational Commitment of Military Hospital Nursing Officers (군병원 간호장교의 조직애착에 영향을 미치는 요인)

  • Kim, Eun-Hee;Kam, Sin;Lee, Kyung-Eun;Han, Chang-Hyun;Park, Ki-Soo
    • Health Policy and Management
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    • v.11 no.4
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    • pp.109-128
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    • 2001
  • This study was conducted to investigate the factors affecting on organizational commitment of military hospital nursing officers. For the purpose of this study, the self-administerd questionnaire survey was done with 440 military hospital nursing officers during february, 2001. The major results of the study were summarized as follows: By path analysis using LISREL 7.0, variables such as met expectations, work involvement, pay, work definiteness, positive affectivity, family support, peer support, promotion opportunity, expectations before entering a military hospital had significant positive effect on Job satisfaction in order of size, however, vertical conflict and horizontal conflict had significant negative effect in order of size. Variables such as job satisfaction, met expectations, promotion opportunity, positive affectivity, pay had significant positive direct effect on organizational commitment in order of size, however, job routinization, job opportunity had significant negative direct effect in order of size. It was found that the following variables, listed m order of size, had significant total effects on organizational commitment: job satisfaction, met expectations, positive affectivity, promotion opportunity, pay, vertical conflict, job routinization, family support, work involvement, work definiteness, job opportunity. In considering above findings, the program or plan for job satisfaction promotion, met expectations, fair promotion opportunity, adequate pay, work definiteness, solving conflict, positive affectivity promotion would be implemented to increase organizational commitment of military hospital nursing officers.

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Bayesian Modeling of Random Effects Covariance Matrix for Generalized Linear Mixed Models

  • Lee, Keunbaik
    • Communications for Statistical Applications and Methods
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    • v.20 no.3
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    • pp.235-240
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    • 2013
  • Generalized linear mixed models(GLMMs) are frequently used for the analysis of longitudinal categorical data when the subject-specific effects is of interest. In GLMMs, the structure of the random effects covariance matrix is important for the estimation of fixed effects and to explain subject and time variations. The estimation of the matrix is not simple because of the high dimension and the positive definiteness; subsequently, we practically use the simple structure of the covariance matrix such as AR(1). However, this strong assumption can result in biased estimates of the fixed effects. In this paper, we introduce Bayesian modeling approaches for the random effects covariance matrix using a modified Cholesky decomposition. The modified Cholesky decomposition approach has been used to explain a heterogenous random effects covariance matrix and the subsequent estimated covariance matrix will be positive definite. We analyze metabolic syndrome data from a Korean Genomic Epidemiology Study using these methods.

A NEW CRITERION FOR MOMENT INFINITELY DIVISIBLE WEIGHTED SHIFTS

  • Hong T. T. Trinh
    • Communications of the Korean Mathematical Society
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    • v.39 no.2
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    • pp.437-460
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    • 2024
  • In this paper we present the weighted shift operators having the property of moment infinite divisibility. We first review the monotone theory and conditional positive definiteness. Next, we study the infinite divisibility of sequences. A sequence of real numbers γ is said to be infinitely divisible if for any p > 0, the sequence γp = {γpn}n=0 is positive definite. For sequences α = {αn}n=0 of positive real numbers, we consider the weighted shift operators Wα. It is also known that Wα is moment infinitely divisible if and only if the sequences {γn}n=0 and {γn+1}n=0 of Wα are infinitely divisible. Here γ is the moment sequence associated with α. We use conditional positive definiteness to establish a new criterion for moment infinite divisibility of Wα, which only requires infinite divisibility of the sequence {γn}n=0. Finally, we consider some examples and properties of weighted shift operators having the property of (k, 0)-CPD; that is, the moment matrix Mγ(n, k) is CPD for any n ≥ 0.

Bayesian baseline-category logit random effects models for longitudinal nominal data

  • Kim, Jiyeong;Lee, Keunbaik
    • Communications for Statistical Applications and Methods
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    • v.27 no.2
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    • pp.201-210
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    • 2020
  • Baseline-category logit random effects models have been used to analyze longitudinal nominal data. The models account for subject-specific variations using random effects. However, the random effects covariance matrix in the models needs to explain subject-specific variations as well as serial correlations for nominal outcomes. In order to satisfy them, the covariance matrix must be heterogeneous and high-dimensional. However, it is difficult to estimate the random effects covariance matrix due to its high dimensionality and positive-definiteness. In this paper, we exploit the modified Cholesky decomposition to estimate the high-dimensional heterogeneous random effects covariance matrix. Bayesian methodology is proposed to estimate parameters of interest. The proposed methods are illustrated with real data from the McKinney Homeless Research Project.

Integral Sliding Mode Control for Robot Manipulators (로봇 매니퓰레이터를 위한 적분 슬라이딩 모드 제어)

  • Yoo, Dong-Sang
    • Journal of Institute of Control, Robotics and Systems
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    • v.14 no.12
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    • pp.1266-1269
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    • 2008
  • We propose an integral sliding mode control for robot manipulators guaranteeing that sliding motion exists starting from an initial time. Also, we prove the asymptotic stability for robot manipulators using three important properties in the robot dynamics: skew-symmetry, positive-definiteness, and boundedness of robot parameter matrices. From illustrative examples, we show that the proposed method effectively controls for robot manipulators.

A Comparison of Sliding Mode and Integral Sliding Mode Controls for Robot Manipulators (로봇 매니퓰레이터를 위한 슬라이딩 모드와 적분 슬라이딩 모드 제어의 비교)

  • Yoo, Dong-Sang
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.58 no.1
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    • pp.168-172
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    • 2009
  • We compare an integral sliding mode control with a typical sliding mode control for robot manipulators through two primitive tasks: set-point regulation and trajectory tracking control. To prove the asymptotic stability of two methods for robot manipulators, we introduce three important properties in the robot dynamics: skew-symmetry, positive-definiteness, and boundedness of robot parameter matrices and we present one unified control structure using a parametric velocity vector. From illustrative examples, we show that two methods effectively control for robot manipulators.

Autoregressive Cholesky Factor Modeling for Marginalized Random Effects Models

  • Lee, Keunbaik;Sung, Sunah
    • Communications for Statistical Applications and Methods
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    • v.21 no.2
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    • pp.169-181
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    • 2014
  • Marginalized random effects models (MREM) are commonly used to analyze longitudinal categorical data when the population-averaged effects is of interest. In these models, random effects are used to explain both subject and time variations. The estimation of the random effects covariance matrix is not simple in MREM because of the high dimension and the positive definiteness. A relatively simple structure for the correlation is assumed such as a homogeneous AR(1) structure; however, it is too strong of an assumption. In consequence, the estimates of the fixed effects can be biased. To avoid this problem, we introduce one approach to explain a heterogenous random effects covariance matrix using a modified Cholesky decomposition. The approach results in parameters that can be easily modeled without concern that the resulting estimator will not be positive definite. The interpretation of the parameters is sensible. We analyze metabolic syndrome data from a Korean Genomic Epidemiology Study using this method.

Poisson linear mixed models with ARMA random effects covariance matrix

  • Choi, Jiin;Lee, Keunbaik
    • Journal of the Korean Data and Information Science Society
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    • v.28 no.4
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    • pp.927-936
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    • 2017
  • To analyze longitudinal count data, Poisson linear mixed models are commonly used. In the models the random effects covariance matrix explains both within-subject variation and serial correlation of repeated count outcomes. When the random effects covariance matrix is assumed to be misspecified, the estimates of covariates effects can be biased. Therefore, we propose reasonable and flexible structures of the covariance matrix using autoregressive and moving average Cholesky decomposition (ARMACD). The ARMACD factors the covariance matrix into generalized autoregressive parameters (GARPs), generalized moving average parameters (GMAPs) and innovation variances (IVs). Positive IVs guarantee the positive-definiteness of the covariance matrix. In this paper, we use the ARMACD to model the random effects covariance matrix in Poisson loglinear mixed models. We analyze epileptic seizure data using our proposed model.