• Advances in nano research
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• v.13 no.4
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• pp.393-406
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• 2022

In the present article, functionally graded small-scaled plates based on modified strain gradient theory (MSGT) are studied for analyzing the nonlinear bending and post-buckling responses. Von-Karman's assumptions are applied to incorporate geometric nonlinearity and the first-order shear deformation theory is used to model the plates. Modified strain gradient theory includes three length scale parameters and is reduced to the modified couple stress theory (MCST) and the classical theory (CT) if two or all three length scale parameters become zero, respectively. The Ritz method with Legendre polynomials are used to approximate the unknown displacement fields. The solution is found by the minimization of the total potential energy and the well-known Newton-Raphson technique is used to solve the nonlinear system of equations. In addition, numerical results for the functionally graded small-scaled plates are obtained and the effects of different boundary conditions, material gradient index, thickness to length scale parameter and length to thickness ratio of the plates on nonlinear bending and post-buckling responses are investigated and discussed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.1
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• pp.436-444
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• 2013

This article presents the dynamic response of nano-scale plates using the nonlocal continuum theory and higher-order shear deformation theory. The nonlocal elasticity of Eringen has ability to capture the small scale effects and the higher-order shear deformation theory has ability to capture the quadratic variation of shear strain and consequently shear stress through the plate thickness. The solutions of transient dynamic analysis of nano-scale plate are presented using these theories to illustrate the effect of nonlocal theory on dynamic response of the nano-scale plates. The relations between nonlocal and local theories are discussed by numerical results. Also, the effects of nonlocal parameters, aspect ratio, side-to-thickness ratio, size of nano-scale plate and time step on dynamic response are investigated and discussed. The amplitude and cycle increase when nonlocal parameter increase. In order to validate the present solutions, the reference solutions are used and discussed. The theoretical development as well as numerical solutions presented herein should serve as reference for nonlocal theories as applied to the transient dynamic analysis of nano-scale structures.

• Journal of Distribution Science
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• v.14 no.3
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• pp.39-44
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• 2016

Purpose - The purpose of this research is to investigate whether Korea's economic growth can be explained by the endogenous growth theory. Specifically, we test whether R&D expenditure has a positive and significant effect on the economic growth. Research design, data, and methodology - We hypothesize that R&D expenditure has a positive effect on the economic growth after adding control variables in the growth equation. Korean annual data from 1963 to 2011 from Science and Technology Annual of the Ministry of Education, Science and Technology, the Bank of Korea, etc. are used. We estimate the growth equation by GMM in addition to OLS. Results - We found that R&D expenditure has a positive and significant effect on the economic growth after adding the ratio of investment to GDP, the ratio of FDI to GDP, the ratio of government expenditure to GDP, inflation and the ratio of trade openness to GDP as control variables in the growth equation. Conclusions - Our results show that Korea's rapid economic growth for the past five decades can be explained by the R&D-based endogenous economic growth theory. Our results suggest that the policy attention of the Korean government be paid to R&D promotion.

• Earthquakes and Structures
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• v.16 no.3
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• pp.359-368
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• 2019

This paper focuses on the study of dynamic analysis of thick plates resting on Winkler foundation. The governing equation is derived from Mindlin's theory. This study is a parametric analysis of the reflections of the thickness / span ratio, the aspect ratio and the boundary conditions on the earthquake excitations are studied. In the analysis, finite element method is used for spatial integration and the Newmark-${\beta}$ method is used for the time integration. While using finite element method, a new element is used. This element is 17-noded and it's formulation is derived from using higher order displacement shape functions. C++ program is used for the analyses. Graphs are presented to help engineers in the design of thick plates subjected to earthquake excitations. It is concluded that the 17-noded finite element is used in the earthquake analysis of thick plates. It is shown that the changes in the aspect ratio are more effective than the changes in the aspect ratio. The center displacements of the reinforced concrete thick clamped plates for b/a=1, and t/a=0.2, and for b/a=2, and t/a=0.2, reached their absolute maximum values of 0.00244 mm at 3.48 s, and of 0.00444 mm at 3.48 s, respectively.

• Journal of the Korean Geotechnical Society
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• v.25 no.6
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• pp.89-99
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• 2009

In order to clarify the relation between the physical properties and the strength parameters of compaction materials and to develop a method for evaluating the strength parameters required for design from the physical indices including void ratio and dry density, compaction test, one-dimensional compression test, and exhausted-drained triaxial compression test were carried out with decomposed granite soils. The test results showed that the specimens became over-consolidated by compaction and the increase of the strength parameters of the specimens by the increase of the compaction energy could be verified quantitatively. A method for the evaluation of strength parameters from the void ratio of soil after compaction using preconsolidation theory which evaluates over-consolidation of materials was developed and its engineering applicability was tested for verification.

• Steel and Composite Structures
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• v.21 no.1
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• pp.1-36
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• 2016

In the present study, the nonlinear magneto-electro-mechanical free vibration behavior of rectangular double-bonded sandwich microbeams based on the modified strain gradient theory (MSGT) is investigated. It is noted that the top and bottom sandwich microbeams are considered with boron nitride nanotube reinforced composite face sheets (BNNTRC-SB) with electrical properties and carbon nanotube reinforced composite face sheets (CNTRC-SB) with magnetic fields, respectively, and also the homogenous core is used for both sandwich beams. The connections of every sandwich beam with its surrounding medium and also between them have been carried out by considering Pasternak foundations. To take size effect into account, the MSGT is introduced into the classical Timoshenko beam theory (CT) to develop a size-dependent beam model containing three additional material length scale parameters. For the CNTRC and BNNTRC face sheets of sandwich microbeams, uniform distribution (UD) and functionally graded (FG) distribution patterns of CNTs or BNNTs in four cases FG-X, FG-O, FG-A, and FG-V are employed. It is assumed that the material properties of face sheets for both sandwich beams are varied in the thickness direction and estimated through the extended rule of mixture. On the basis of the Hamilton's principle, the size-dependent nonlinear governing differential equations of motion and associated boundary conditions are derived and then discretized by using generalized differential quadrature method (GDQM). A detailed parametric study is presented to indicate the influences of electric and magnetic fields, slenderness ratio, thickness ratio of both sandwich microbeams, thickness ratio of every sandwich microbeam, dimensionless three material length scale parameters, Winkler spring modulus and various distribution types of face sheets on the first two natural frequencies of double-bonded sandwich microbeams. Furthermore, a comparison between the various beam models on the basis of the CT, modified couple stress theory (MCST), and MSGT is performed. It is illustrated that the thickness ratio of sandwich microbeams plays an important role in the vibrational behavior of the double-bonded sandwich microstructures. Meanwhile, it is concluded that by increasing H/lm, the values of first two natural frequencies tend to decrease for all amounts of the Winkler spring modulus.

• Journal of Preventive Medicine and Public Health
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• v.42 no.2
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• pp.143-150
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• 2009

Objectives : South Korea has experienced unprecedented ups and downs in the sex ratio at birth(SRB), which has been a unique phenomenon in the last two decades. However, little is known about socioeconomic factors that influence the SRB. Employing the diffusion theory by Rogers, this study was undertaken to examine the trends in social variations in the SRB from 1981 to 2004 in Korea. Methods : The data was taken from Vital Birth Statistics for the period from 1981-2004. We computed the annual male proportion of live births according to the parental education(university, middle/high school, primary) and occupation(non-manual, manual, others). Logistic regression analysis was employed to estimate the odds ratios of male birth according to social position for the equidistant three time periods(1981-1984, 1991-1994, and 2001-2004). Results : An increased SRB was detected among parents with higher social position before the mid 1980s. Since then, however, a greater SRB was found for the less educated and manual jobholders. The inverse social gradient for the SRB was most prominent in early 1990s, but the gap has narrowed since the late 1990s. The mother's socioeconomic position could be a sensitive indicator of the social variations in the sex ratio at birth. Conclusions : Changes in the relationship of parental social position with the SRB were detected during the 1980-2004 in Korea. This Korean experience may well be explained by diffusion theory, suggesting there have been socioeconomic differences in the adoption and spread of sex-detection technology.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.214-224
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• 1990

A "two-fluid" model using thermal eddy diffusivity concept and Lumley's drag reduction theory, is proposed to analyze heat transfer of the turbulent dilute gas-particle flow in a vertical pipe with constant wall heat flux. The thermal eddy diffusivity is derived to be a function of the ratio of the heat capacity-density products .rho. over bar $C_{p}$ of the gaseous phase and the particulate phase and also of the ratio of thermal relaxation time scale to that of turbulence. The Lumley's theory dictates the variation of the viscous sublayer thickness depending on the particle loading ratio Z and the relative particle size $d_{p}$/D. At low loading ratio, the size of viscous sublayer thickness is important for suspension heat transfer, while at higher loading, the effect of the ratio .rho. $_{p}$ over bar $C_{p}$$_{p}$/ .rho. $_{f}$ over bar $C_{p}$$_{f}$ is dominant. The major cause of decrease in the suspension Nusselt number at lower loading ratio is found to be due to the increase of the viscous sublayer thickness caused by the suppression of turbulence near the wall by the presence of solid particles. Predicted Nusselt numbers using the present model are in satisfactory agreements with available experimental data both in pipe entrance and the fully developed regions.

• Journal of the Korean Data and Information Science Society
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• v.3 no.1
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• pp.79-90
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• 1992

We consider hazard ratio as a descriptive measure to compare the hazard experience of a treatment group with that of a control group with censored survival data. In this paper, we propose a kernel estimator of hazard ratio. The uniform consistency and asymptotic normality of a kernel estimator are proved by using counting process approach via martingale theory and stochastic integrals.

• Archives of Pharmacal Research
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• v.5 no.2
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• pp.53-60
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• 1982

The mixing of salicylic acid and wheat starch powders was studied using a V-type mixer. After the optimum operating conditions of the mixer were examined, the mixing characteristics relating to dilution ratio, particle size of active ingradient and addition ratio of lubricants were investigated. The coefficient of variation was expressed by a power law relating to the dilution ratio and the particle size of active ingredient. Furthermore, the comparison of results with the theoretically estimated value of mixing index suggested that the mixing of cohesive pharmacceutical powders is a complex stochastic process and cannot be explained fully by a simple theory based on a complete random mixing.