• Advances in nano research
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• v.16 no.5
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• pp.445-458
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• 2024

The objective of this paper is to present free vibration and static stability analyses of rotating composite beams reinforced with carbon nanotubes (CNTs) under uniform thermal loads. Beam structural equations and CNT-reinforced composite (CNTRC) beam formulations are derived based on Timoshenko beam theory (TBT). The temperature-dependent properties of the beam material, such as the elastic modulus, shear modulus, and material density, are assumed to vary over the thickness according to the rule of mixture. The beam material is modeled as a mixture of single-walled carbon nanotubes (SWCNTs) in an isotropic matrix. The SWCNTs are aligned and distributed in the isotropic matrix with different patterns of reinforcement, namely the UD (uniform), FG-O, FG-V, FG- Λ and FG-X distributions, where FG-V and FG- Λ are asymmetric patterns. Numerical examples are presented to illustrate the effects of several essential parameters, including the rotational speed, hub radius, effective material properties, slenderness ratio, boundary conditions, thermal force, and moments due to temperature variation. To the best of the authors' knowledge, this study represents the first attempt at the finite element modeling of rotating CNTRC Timoshenko beams under a thermal environment. The results are presented in tables and figures for both symmetric and asymmetric distribution patterns, and can be used as benchmarks for further validation.

• Structural Engineering and Mechanics
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• v.6 no.7
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• pp.817-826
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• 1998

A finite element model based on the incremental endochronic theory for flexible pavement materials was developed in this study. Three grid systems with eight-node cubic isoparametric elements, and different loading steps were used to perform the calculations for a specimen of circular cylinder. The uniaxial stress experimental results on an asphalt mixture at $60^{\circ}C$ in SHRP conducted by University of California at Berkeley were used to check the ability of the derived numerical model. Then, the numerical results showed isotropic response and deviatoric response on the specimen in a three dimensional manner, which provided a better understanding for a deformed flexible material under the specified loading conditions.

• Tribology and Lubricants
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• v.28 no.1
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• pp.7-11
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• 2012

In this paper, the results of finite element(FE) analysis of chemical mechanical polishing(CMP) process using 2-dimensional elements were discussed. The objective of this study is to find the generation mechanism of microscratches on a wafer surface during the process. Especially, a FE model with a particle inside pad pore was considered to observe how such a contact situation could contribute to microscratch generation. The results of the finite element simulations revealed that during CMP process the pad-particle mixture could be formed and this would be a major factor leading to microscratch generation.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 1993.10a
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• pp.118-118
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• 1993

We consider a discrete event dynamic system called periodic job shop, where an identical mixture of items called minimal part set(MPS) is repetitively produced in the same processing order and the primary performance measure is the cycle time. The precedence relationships among events(starts of operations) are represented by a directed graph with rocurront otructure. When each operation starts as soon as all its preceding operations complete(called earliest starting), the occurrences of events are modeled in a linear system using a special algebra called minimax algebra. By investigating the eigenvalues and the eigenvectors, we develop conditions on the directed graph for which a stable steady state or a finite eigenvector exists. We demonstrate that each finite eigenvector, characterized as a finite linear combination of a class of eigenvalue, is the minimum among all the feasible schedules and an identical schedule pattern repeats every MPS. We develop an efficient algorithm to find a schedule among such schedules that minimizes a secondary performance measure related to work-in-process inventory. As a by-product of the linear system approach, we also propose a way of characterizing stable steady states of a class of discrete event dynamic systems.

• International Journal of Aeronautical and Space Sciences
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• v.11 no.2
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• pp.59-68
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• 2010

The aim of this work is to analyze high temperature flows around an axisymmetric blunt body taking into account chemical and vibrational non-equilibrium state for air mixture species. For this purpose, a finite volume methodology is employed to determine the supersonic flow parameters around the axisymmetric blunt body. This allows the capture of a shock wave before a blunt body placed in supersonic free stream. The numerical technique uses the flux vector splitting method of Van Leer. Here, adequate time stepping parameters, along with Courant, Friedrich, Lewis coefficient and mesh size level are selected to ensure numerical convergence, sought with an order of $10^{-8}$.

• Transactions of the Society of Information Storage Systems
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• v.7 no.2
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• pp.60-64
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• 2011

Chemical mechanical planarization is one of the core processes in fabrication of semiconductors, which are increasingly used for information storage devices like solid state drives. For higher data capacity in storage devices, CMP process is required to show ultimate precision and accuracy. In this work, 2-dimensional finite element models were developed to investigate the effects of the slurry particle impact on microscratch generation and the phenomena generated at pad-particle-wafer contact interface. The results revealed that no plastic deformation and corresponding material removal could be generated by simple impact of slurry particles under real CMP conditions. From the results of finite element simulations, it could be concluded that the pad-particle mixture formed in CMP process would be one of major factors leading to microscratch generation.

• Korean Journal of Metals and Materials
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• v.47 no.9
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• pp.567-572
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• 2009

The densification behaviors of mixtures of copper and steel powders during cold die compaction were investigated. We proposed the pressure-dependent yield function based on the rule of the mixtures of each yield function of a critical relative density type. The constitutive equations were implemented into a finite element program (DEFORM2D) to analyze the densification and deformation behavior of powder mixtures, and the simulated results are in good agreement with the experimental results in reference studies.

• Clinical and Experimental Pediatrics
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• v.48 no.11
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• pp.1179-1186
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• 2005

Purpose : A universal standard of the birth weight for gestational age cannot be made since girth weight distribution varies with race and other sociodemographic factors. This report aims to establish the birth weight distribution curve by gestational age, specific for Korean live births. Methods : We used the national birth certificate data of all live births in Korea from January 2001 to December 2003; for live births with gestational ages 24 weeks to 44 weeks(n=1,509,763), we obtained mean birth weigh, standard deviation and 10th, 25th, 50th, 75th and 90th percentile values for each gestational age group by one week increment. Then, we investigated the birth weight distribution of each gestational age group by the normal Gaussian model. To establish final standard values of Korean birth weight distribution by gestational age, we used the finite mixture model to eliminate erroneous birth slights for respective gestational ages. Results : For gestational ages 28 weeks 32 weeks, birth weight distribution showed a biologically implausible skewed tail or bimodal distribution. Following correction of the erroneous distribution by using the finite mixture model, the constructed curve of birth weight distribution was compared to those of other studies. The Korean birth weight percentile values were generally lower than those for Norwegians and North Americans, particularly after 37 weeks of gestation. The Korean curve was similar to that of Lubchenco both 50th and 90th percentiles, but generally the Korean curve had higher 10th percentile values. Conclusion : This birth weight distribution curve by gestational age is based on the most recent and the national population data compared to previous studies in Korea. We hope that for Korean infants, this curve will help clinicians in defining and managing the large for gestational age infants and also for infants with intrauterine growth retardation.

• The Korean Journal of Applied Statistics
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• v.32 no.2
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• pp.199-211
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• 2019

This paper is concerned with issues in the finite mixture of regression modeling as well as the simultaneous selection of the number of mixing components and relevant predictors. We propose a penalized likelihood method for both mixture components and regression coefficients that enable the simultaneous identification of significant variables and the determination of important mixture components in mixture of regression models. To avoid over-fitting and bias problems, we applied smoothly clipped absolute deviation (SCAD) penalties on the logarithm of component probabilities suggested by Huang et al. (Statistical Sinica, 27, 147-169, 2013) as well as several well-known penalty functions for coefficients in regression models. Simulation studies reveal that our method is satisfactory with well-known penalties such as SCAD, MCP, and adaptive lasso.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.10
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• pp.1435-1450
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• 2004

The investigation, which includes the material homogenization and the calculation of local stress concentration of long-fibrous composites in a microscopic level, has been performed to analyze the behavior of fiber-reinforced composites by using finite element method. In order to carry out this study, the finite element models of composites have been generated by the idealized arrays as square and hexagonal-packed type. In the FE analysis, the boundary conditions of micromechanical finite element method(MFEM) have been defined and verified by comparing with the results from multi-cells, and the effective material properties of composites composed of graphite/epoxy have been also evaluated by rules of mixture. For acquiring the relation between the global and local behaviors of composites, the magnifications of strain, stress, and interfacial stress of composites subjected to a longitudinal and transverse loading respectively have been calculated. And the magnifications have been proposed as the stress concentration in the microscopic level at composite material.