• Kyungpook Mathematical Journal
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• 제47권4호
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• pp.595-600
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• 2007

In this paper we consider weighted arithmetic and geometric means of several positive definite operators proposed by Sagae and Tanabe and we establish a reverse inequality of the arithmetic and geometric means via Specht ratio and the Thompson metric on the convex cone of positive definite operators.

• 호남수학학술지
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• 제40권3호
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• pp.529-538
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• 2018

The purpose of the present paper is to establish connections between various subclasses of analytic univalent functions by applying certain convolution operator involving Poisson distribution series. To be more precise,we investigate such connections with the classes of analytic univalent functions with positive coefficients in the open unit disk.

• 대한수학회지
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• 제60권5호
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• pp.999-1021
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• 2023

Using the results in the paper [12], we give an estimate for the first positive and negative Dirac eigenvalue on a 7-dimensional Sasakian spin manifold. The limiting case of this estimate can be attained if the manifold under consideration admits a Sasakian Killing spinor. By imposing the eta-Einstein condition on Sasakian manifolds of higher dimensions 2m + 1 ≥ 9, we derive some new Dirac eigenvalue inequalities that improve the recent results in [12, 13].

• East Asian mathematical journal
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• 제17권1호
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• pp.71-85
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• 2001

The strong convergences of solutions to a nonlinear Volterra equation are studied in Banach space. As an application, a nonlinear heat flow in a homogeneous bar of unit length of a material with memory is investigated.

• 충청수학회지
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• 제12권1호
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• pp.125-131
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• 1999

We obtain some sufficient conditions for oscillation of the neutral difference equation with positive and negative coefficients $${\Delta}(x_n-cx_{n-m})+px_{n-k}-qx_{n-l}=0$$, where ${\Delta}$ denotes the forward difference operator, m, k, l, are nonnegative integers, and $c{\in}[0,1),p,q{\in}\mathbb{R}^+$.

• Kyungpook Mathematical Journal
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• 제54권3호
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• pp.365-374
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• 2014

In this paper, we introduce a new subclass of meromorphic functions defined in the punctured unit disc. We derive inclusion relationships, radius problem and some other interesting properties of this class are investigated.

• 한국수학교육학회지시리즈B:순수및응용수학
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• 제26권3호
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• pp.189-197
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• 2019

In this paper we obtain some new inequalities for the weighted chaotically geometric mean of two positive operators on a complex Hilbert space.

• 대한수학회논문집
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• 제32권3호
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• pp.661-676
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• 2017

Let T be a bounded linear operator acting on a complex Hilbert space ${\mathfrak{H}}$. In this paper we introduce the class, denoted ${\mathcal{Q}}(A(k),m)$, of operators satisfying $T^{m{\ast}}(T^{\ast}{\mid}T{\mid}^{2k}T)^{1/(k+1)}T^m{\geq}T^{{\ast}m}{\mid}T{\mid}^2T^m$, where m is a positive integer and k is a positive real number and we prove basic structural properties of these operators. Using these results, we prove that if P is the Riesz idempotent for isolated point ${\lambda}$ of the spectrum of $T{\in}{\mathcal{Q}}(A(k),m)$, then P is self-adjoint, and we give a necessary and sufficient condition for $T{\otimes}S$ to be in ${\mathcal{Q}}(A(k),m)$ when T and S are both non-zero operators. Moreover, we characterize the quasinilpotent part $H_0(T-{\lambda})$ of class A(k) operator.

• 융합경영연구
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• 제9권5호
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• pp.15-25
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• 2021

Purpose: In the Korean railway infrastructure process, contractors and operators are involved at a later stage, which results in significant inefficiency. This study examines the benefits of early stakeholder involvement in Korean railway infrastructure projects and provides practical guidelines. Design, data and methodology: Literatures and foreign cases are analyzed. Building on the new product development model, we derive propositions explaining the relationship between early stakeholder involvement and the performance of Korean railway infrastructure project. Results: Major propositions include that early involvement of contractor has a positive effect on the project performance by shortening the infrastructure construction period and that early involvement of railway operator has a positive effect on the project performance by improving the effectiveness of railway infrastructure. Four requirements for the success of early stakeholder involvement are addressed. Conclusions: This study suggests that early stakeholder involvement shortens the construction period and improves railway infrastructure effectiveness. Academic contribution is to present the framework on railway infrastructure projects as holistic interactions among stakeholders. Practical contribution is to provide railway policy makers and other business practitioners with policy guidelines to improve railway infrastructure project process and to recommend an open access to relevant data.

• Kyungpook Mathematical Journal
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• 제49권1호
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• pp.167-181
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• 2009

Based on Ricatti equation $XA^{-1}X=B$ for two (positive invertible) operators A and B which has the geometric mean $A{\sharp}B$ as its solution, we consider a cubic equation $X(A{\sharp}B)^{-1}X(A{\sharp}B)^{-1}X=C$ for A, B and C. The solution X = $(A{\sharp}B){\sharp}_{\frac{1}{3}}C$ is a candidate of the geometric mean of the three operators. However, this solution is not invariant under permutation unlike the geometric mean of two operators. To supply the lack of the property, we adopt a limiting process due to Ando-Li-Mathias. We define reasonable geometric means of k operators for all integers $k{\geq}2$ by induction. For three positive operators, in particular, we define the weighted geometric mean as an extension of that of two operators.