• Advances in nano research
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• 제5권4호
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• pp.313-336
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• 2017

This article investigates vibration behavior of magneto-electro-elastic functionally graded (MEE-FG) nanobeams embedded in two-parameter elastic foundation using a third-order parabolic shear deformation beam theory. Material properties of MEE-FG nanobeam are supposed to be variable throughout the thickness based on power-law model. Based on Eringen's nonlocal elasticity theory which captures the small size effects and using the Hamilton's principle, the nonlocal governing equations of motions are derived and then solved analytically. Then the influences of elastic foundation, magnetic potential, external electric voltage, nonlocal parameter, power-law index and slenderness ratio on the frequencies of the embedded MEE-FG nanobeams are studied.

• Earthquakes and Structures
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• 제26권4호
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• pp.299-309
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• 2024

The present paper develops application of third-order shear deformation theory (TSDT) and modified couple stress theory (MCST) to size-dependent bending analysis of a functionally graded cylindrical micro-shell. The radial and axial displacement components are described based on TSDT for more accurate analysis. The effect of small scales is accounted based on MCST. The principle of virtual work is used for derivation of bending governing equations. The solution is presented for a simply-supported boundary condition to account the influence of various important parameters such as micro length scale parameter, in-homogeneous index and some dimensionless geometric parameters such as length to radius and length to thickness ratios on the bending results. A comparative analysis is presented to examine the effect of order of employed shear deformation theory on the axial and radial displacements.

• Journal of Preventive Medicine and Public Health
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• 제53권5호
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• pp.371-380
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• 2020

Objectives: This study investigated the effects of socio-demographic factors on the decreasing trend in the sex ratio at birth from 1997 to 2017 in Korea. Methods: Data from 10 349 602 live births registered with Statistics Korea from 1997 to 2017 were analyzed. The secondary sex ratio (SSR), defined as the ratio of male to female live births, during the study period (1997-1999 [phase I], 2000-2002 [phase II], 2003-2005 [phase III], 2006-2008 [phase IV], 2009-2011 [phase V], 2012-2014 [phase VI], and 2015-2017 [phase VII]) was calculated according to selected socio-demographic factors, such as parental age, education, occupation, and birth order. Logistic regression models were used to estimate odds ratios (ORs) and 95% confidence intervals for a male birth after adjusting for potential confounders. Results: The SSR gradually decreased from 1.10 (in 1998-2000 and 2002) to 1.05 (in 2013-2016). While a decreasing trend in the SSR was not noted among first births, male-biased sex ratios were prominent among third and higher-order births, for which the highest SSR was 1.46 in 1998. Higher birth order was significantly associated with an excess of male births in phases I-VI (≥third vs. first, OR range, 1.03 to 1.35). Advanced maternal age was significantly associated with an excess of female births in phases II, III, and V (≥40 vs. 20-24 years, OR range, 0.92 to 0.95). Conclusions: This study demonstrated that advanced maternal age and reduction of the artificially-biased SSR among third and higher-order births may partially explain the decreasing trend in the SSR from 1997 to 2017 in Korea.

• 멤브레인
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• 제9권4호
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• pp.209-214
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• 1999

본 연구의 목적은 냉연공장 폐수재이용을 위해 3단 역삼투시스템 사용시 각단에서의 투과특성을 조사하는 것이다 판틀형 모듈 7개를 사용하여 회수율이 75% 가 되도록 3단 (배열 : 4+2+1) 으로 구성하여 장기간에 걸친 pilot test를 통해 막오염 진행에 따른 각 단에서의 유량 및 수질변화를 조사하였다 실험결과 각 단 모듈 1개당 평균 투과수량은 운전초기에는 1단, 2단, 3단의 순서로 많았으나 운전시간이 경과하며 막오염이 진행됨에 따라 1단은 감소하는 반면 2단은 거의 변화가 없고 3단의 투과수량은 증가하였다 즉 막오염은 주로 1단에서 발생하며 점차 2단. 3단으로 진행되는 것을 확인할수 있었다. 한편 투과수 수질은 예상한 것과 같이 1단이 가장 우수하였고 다음으로는 2단, 3단의 순서였으며 막오염에 영향을 받지않았다.

• 대한화학회지
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• 제40권8호
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• pp.579-584
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• 1996

폴리엔의 HOMO-LUMO gap, 정적 및 동적인 3차 편극율을 시간의존 Hartree Fock 반경험적 PM3, AM1, MODO, MINDO/3 방법을 이용하여 구하였다. $C_2H_4$로부터 $C_{32}H_{34}$까지 모든 계산이 수행되었다. HOMO-LUMO gap은 MINDO/3>MNDO>PM3>AM1 순서로 증가하였으며, THG, DC-EFIDHG, IDRI, OKE효과는 AM1>MNDO>PM3 순서로 증가하였다. 다양한 3차 효과는 THG>DC-EFISHG>IDRI>OKE순서로 증가함을 보여주고 있다.

• Journal of applied mathematics & informatics
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• 제31권3_4호
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• pp.399-416
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• 2013

The semilocal convergence of a third order iterative method used for solving nonlinear operator equations in Banach spaces is established by using recurrence relations under the assumption that the second Fr´echet derivative of the involved operator satisfies the ${\omega}$-continuity condition given by $||F^{\prime\prime}(x)-F^{\prime\prime}(y)||{\leq}{\omega}(||x-y||)$, $x,y{\in}{\Omega}$, where, ${\omega}(x)$ is a nondecreasing continuous real function for x > 0, such that ${\omega}(0){\geq}0$. This condition is milder than the usual Lipschitz/H$\ddot{o}$lder continuity condition on $F^{\prime\prime}$. A family of recurrence relations based on two constants depending on the involved operator is derived. An existence-uniqueness theorem is established to show that the R-order convergence of the method is (2+$p$), where $p{\in}(0,1]$. A priori error bounds for the method are also derived. Two numerical examples are worked out to demonstrate the efficacy of our approach and comparisons are elucidated with a known result.

• Journal of applied mathematics & informatics
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• 제26권5_6호
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• pp.1057-1069
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• 2008

We consider singularly perturbed Boundary Value Problems (BVPs) for third and fourth order Ordinary Differential Equations(ODEs) of convection-diffusion type with discontinuous source term and a small positive parameter multiplying the highest derivative. Because of the type of Boundary Conditions(BCs) imposed on these equations these problems can be transformed into weakly coupled systems. In this system, the first equation does not have the small parameter but the second contains it. In this paper a computational method named as 'An asymptotic finite element method' for solving these systems is presented. In this method we first find an zero order asymptotic approximation to the solution and then the system is decoupled by replacing the first component of the solution by this approximation in the second equation. Then the second equation is independently solved by a fitted mesh Finite Element Method (FEM). Numerical experiments support our theoritical results.

• 대한지리학회지
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• 제46권2호
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• pp.115-133
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• 2011

야마다의 산지차수구분법은 상향식으로 정의할 수 있는데, 이는 저차수 산지들이 모여 점차 차상위차수 산지를 이룸과 동시에 산지의 영역과 규모가 확대되기 때문이다. 하지만 산지를 총체적으로 이해하고 각종 산지 정보를 체계적으로 관리하기 위해서는, 특정 규모의 산지를 이루는데 기여한 차하위차수 산지만을 강조하는 야마다의 산지구분법에는 한계가 있다. 왜냐하면 상위차수 산지내에는 차하위차수 산지뿐만 아니라 독립된 차차하위, 차차차하위 산지도 포함되어 있기 때문이다. 이와 같은 문제점을 해결하기 위해 본 연구에서 제시된 산지분류법은 기본적으로 하향식이다. 여기서 하향식이란 최고위차수 산지를 구성하는 차하위차수 산지, 다시 이를 구성하는 차차하위차수 산지로 산지를 세분해나가 최종적으로 2차수 산지를 구성하고 있는 1차수 산지까지 분류해 나가는 것을 의미한다. 본 연구에서는 야마다 산지차수구분법을 근간으로 특정 산체를 구성하고 있는 모든 산지 요소를 체계적으로 분류하고 구분된 산지에 대한 새로운 명명법을 제시함으로써 산지정보의 종합적 체계적 관리를 위한 데이터베이스의 근간을 마련했다.

• 한국수학교육학회지시리즈A:수학교육
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• 제23권2호
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• pp.75-78
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• 1985

• Kyungpook Mathematical Journal
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• 제22권2호
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• pp.285-288
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• 1982