• Communications of the Korean Mathematical Society
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• v.23 no.3
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• pp.371-376
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• 2008

In this paper, it is shown that if f satisfies the following functional inequality (0.1) $${\parallel}\sum\limits_{i,j=1}^3\;f{(xi,yj)}{\parallel}{\leq}{\parallel}f(x_1+x_2+x_3,\;y_1+y_2+y_3){\parallel}$$ then f is a bi-additive mapping. We moreover prove that if f satisfies the following functional inequality (0.2) $${\parallel}2\sum\limits_{j=1}^3\;f{(x_j,\;z)}+2\sum\limits_{j=1}^3\;f{(x_j,\;w)-f(\sum\limits_{j=1}^3\;xj,\;z-w)}{\parallel}{\leq}f(\sum\limits_{j=1}^3\;xj,\;z+w){\parallel}$$ then f is an additive-quadratic mapping.

• Communications of the Korean Mathematical Society
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• v.21 no.4
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• pp.665-673
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• 2006

In a recent paper, Domokos and $Kolumb\'{a}}n$ [2] gave an interesting interpretation of variational inequalities (VI) and vector variational inequalities (VVI) in Banach space settings in terms of variational inequalities with operator solutions (in short, OVVI). Inspired by their work, in a former paper [4], we proposed the scheme of generalized vector variational inequality with operator solutions (in short, GOVVI) which extends (OVVI) into a multivalued case. In this note, we further develop the previous work [4]. A more general pseudomonotone operator is treated. We present a result on the existence of solutions of (GVVI) under the weak pseudomonotonicity introduced in Yu and Yao [8] within the framework of (GOVVI) by exploiting some techniques on (GOVVI) or (GVVI) in [4].

• Bulletin of the Korean Mathematical Society
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• v.32 no.2
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• pp.153-162
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• 1995

Ky Fan's minimax inequality is an important tool in nonlinear functional analysis and its applications, e.g. game theory and economic theory. Since Fan gave his minimax inequality in [2], various extensions of this interesting result have been obtained (see [4,11] and the references therein). Using Fan's minimax inequality, Ha [6] obtained a non-compact version of Sion's minimax theorem in topological vector spaces, and next Geraghty-Lin [3], Granas-Liu [4], Shih-Tan [11], Simons [12], Lin-Quan [10], Park-Bae-Kang [17], Bae-Kim-Tan [1] further generalize Fan's minimax theorem in more general settings. In [9], using the concept of submaximum, Komiya proved a topological minimax theorem which also generalized Sion's minimax theorem and another minimax theorem of Ha in [5] without using linear structures. And next Lin-Quan [10] further generalizes his result to two function versions and non-compact topological settings.

• Journal of the Korean Home Economics Association
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• v.49 no.8
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• pp.37-46
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• 2011

Using the 1987-2008 quarterly aggregated data of the Household Income and Expenditure Survey, this study investigated the factors influencing household saving rate. The independent variables in the AR regression model were the GDP growth rate, shares of the total household expenditure allocated to tax & social insurance, and education, the variables reflecting the conditions of the asset market including interest rate, stock market index, and real estate price index, and the variables representing the social economic conditions including the index of aging and income inequality. Among the independent variables interest rate, stock market index, and income inequality were found to be significantly associated with the household saving rate. These results suggested that the redistribution and financial market policies favorable to savers may be effective for raising the household saving rate.

• Korean Journal of Mathematics
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• v.16 no.4
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• pp.527-535
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• 2008

Let $I{\in}C^{1,1}$ be a strongly indefinite functional defined on a Hilbert space H. We investigate the number of the critical points of I when I satisfies one pair of Torus-Sphere variational linking inequality. We show that I has at least two critical points when I satisfies one pair of Torus-Sphere variational linking inequality with $(P.S.)^*_c$ condition. We prove this result by use of the limit relative category and critical point theory on the manifold with boundary.

• The Pure and Applied Mathematics
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• v.11 no.2
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• pp.155-166
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• 2004

In this paper, we introduce new monotone concepts for set-valued mappings, called generalized C(x)-L-pseudomonotonicity and weakly C(x)-L-pseudomonotonicity. And we obtain generalized Minty-type lemma and the existence of solutions to vector variational inequality problems for weakly C(x)-L-pseudomonotone set-valued mappings, which generalizes and extends some results of Konnov & Yao [11], Yu & Yao [20], and others Chen & Yang [6], Lai & Yao [12], Lee, Kim, Lee & Cho [16] and Lin, Yang & Yao [18].

• The Pure and Applied Mathematics
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• v.15 no.4
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• pp.387-392
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• 2008

In this note, an alternative proof and extensions are provided for the following conclusions in [6, Theorem 1 and Theorem 3]: The functions $\frac1{x^2}-\frac{e^{-x}}{(1-e^{-x})^2}\;and\;\frac1{t}-\frac1{e^t-1}$ are decreasing in (0, ${\infty}$) and the function $\frac{t}{e^{at}-e^{(a-1)t}}$ for a $a{\in}\mathbb{R}\;and\;t\;{\in}\;(0,\;{\infty})$ is logarithmically concave.

• Communications of Mathematical Education
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• v.8
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• pp.273-278
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• 1999

In this paper, we consider the existence of solutions to the variational-type inequalities for single-valued mappings and set-valued mappings on reflexive Banach spaces using Fan's section theorem.

• Korean Journal of Social Welfare Studies
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• v.40 no.1
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• pp.87-114
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• 2009

Most previous studies on income inequality have limitations in reflecting recent changes and heterogeneity in women's working patterns and their family structure by regarding them as a homogeneous group. This study aims to investigate the trends of income inequality among women during the past 9 years since 1997 and to examine what is the most influential factor on these changes. The results show that the overall trend of income inequality among women is decreasing due to the income decrease of the middle class women and the income increase of the lower class. Among various factors, education, age, and marital status are key factors affecting inequality changes during this period. This study has the following policy implications: first, it is necessary to implement the child care services for the divorced and separated women, who are more likely to fall in poverty. Second, the increase of the basic pension benefits is needed particularly for the poor old women, who is more likely live longer in a desperate status.

• Journal of Korea Technology Innovation Society
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• v.12 no.3
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• pp.457-470
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• 2009

This paper applies a income mobility method to technology inequality using conditional human capital stock and shows their empirical results during the 1980 to 2000. There are several interesting empirical results coming out this analysis. Among the results, the paper turns out that world technology inequality mobility measurement is significantly higher for rapid formation of human capital stock countries than for slow formation of human capital stock countries. This paper, therefore, suggests that technology policy need to focus on improving the public education structure to recover the rate of return to human capital investment and to speed up technology development and deployment in Korea.