• Bulletin of the Korean Mathematical Society
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• v.38 no.2
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• pp.379-387
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• 2001

In this paper, we study the value distribution of meromorphic functions and prove the following theorem: Let f(z) be a transcendental meromorphic function. If f and f'have the same zeros, then f'(z) takes any non-zero value b infinitely many times.

• Korean Journal of Mathematics
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• v.4 no.2
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• pp.83-88
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• 1996

In 1994 Z.Liang constructed an iterative method for the solution of nonlinear equations involving m-accretive operators in uniformly smooth Banach spaces. In this paper we apply the slight variants of Liang's iterative methods and generalize the results of Z.Liang. Moreover our proof is more simple than Liang's proof.

• Proceedings of the Korean Ceranic Society Conference
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• 2000.10a
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• pp.190.2-190
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• 2000

• The Pure and Applied Mathematics
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• v.6 no.2
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• pp.87-93
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• 1999

A holomorphic function f on D = {z : │z│ ＜ 1} is called uniformly locally univalent if there exists a positive constant $\rho$ such that f is univalent in every hyperbolic disk of hyperbolic radius $\rho$. We establish a characterization of uniformly locally univalent functions and investigate uniform local univalence of holomorphic universal covering projections.

• Journal of the Chungcheong Mathematical Society
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• v.1 no.1
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• pp.19-26
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• 1988

In this paper, we calculate the precise estimation of range of a Gateaux differentiable operator, and apply to the existence of a periodic solution of the second order nonlinear differential equation $$z^{{\prime}{\prime}}+Az^{\prime}+G(z)=e(t)=e(t+2{\pi})$$.

• Journal of the Chungcheong Mathematical Society
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• v.16 no.2
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• pp.31-41
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• 2003

In this paper, we will show that the bounds for coefficients of harmonic, orientation-preserving, univalent mappings f defined on ${\Delta}$ = {z : |z| > 1} with $f({\Delta})={\Delta}$ are sharp by finding extremal functions.

• Bulletin of the Korean Mathematical Society
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• v.23 no.2
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• pp.161-166
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• 1986

Through the paper, we consider functions f analytic in the unit disk D={z:vertical bar z vertical bar <1} normalized by f(0)=0 and f'(0)=1. Following Rogosinski [5], we let T denote the class of all typically-real functions f which preserve half-plane in the following sense.

• Journal of the Korean Solar Energy Society
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• v.23 no.4
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• pp.29-35
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• 2003

We studied the water splitting into $H_2$ and $O_2$ using two different semiconductor photo catalysts and redox mediator, mimicking the Z-scheme mechanism of the photosynthesis, $H_2$ evolution took place on a Pt-$SrTiO_2$ (Cr-Ta doped) photocatalyst using $I^-$ electron donor under the visible light irradiation. The Pt-$WO_3$ photocatalyst showed an excellent activity of the $O_2$ evolution using $IO_3^-$ electron acceptor under visible light. $H_2$ and $O_2$ gases evolved in the stoichiometric ratio($H_2/O_2$=2) under visible light using a mixture of the Pt-$WO_3$ and Pt-$SrTiO_3$ (Cr-Ta doped) suspended in NaI aqueous solution. We proposed a two-step photo-excitation mechanism using redox mediator under the visible irradiation.

• YAKHAK HOEJI
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• v.44 no.2
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• pp.155-161
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• 2000

New cephalosporin antibiotics , 3-[(4-carboxy-5-ethylthioisothiazol-3-yl)oxymethyl]-7-[(1H-tetra-zol-1-yl)acetamido]-3-cephem-4-carboxylic acid 2, 3-[(4-carboxy-5-ethylthioisothiazol-3-yl) oxymethyl]-7-[(2-aminothiazol-4-yl)acetamido]-3-cephem-4-carboxylic acid 3, 3-[(4-carb oxy-5-ethylthioisothiazol-3-yl)-oxymethyl]-7-[5-(ethylthio-3-hydroxyisothiazol-4-yl)carboxamido]-3-cephem-4-carboxylic acid 4, 3-[(4-car-boxy-5-ethylthioisothiazo1-3-yl)oxymethy1]-7-[(Z)-2-(fur-2-yl)-2-(methoxyimino)acetamido]-3-cephem-4-carboxylic acid 5, 7-[(Z)-2-(2-aminothiazol-4-yl)-2-[(alkoxyimino)acetamido]-3-[(4-carboxy-5-ethylthioisothiazol-3-yl)oxymethyl]-3-cephem-4-carboxylic acid 6-8 were synthesized. Antibacterial activities and structure-activity relationships of these new cephalosporin derivatives were examined. Among them, 7-[(Z)-2-(2-aminothiazol-4-yl)-2-(1-carboxy-1-methylethoxyimino)acetamido]-3-[(4-carboxy-5-ethylthylth-ioisothiazol-3-yl)oxymethyl]-3-cephem-4-carboxylic acid 7 exhibited good antibacterial activities compared to cefotaxime and ceftriaxone.

• Journal of the Korean Geotechnical Society
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• v.17 no.6
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• pp.193-205
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• 2001

In this study the behavior of pile groups is investigated experimentally. Special attention is given to the load transfer characteristics of pile groups and to the evaluation of the group effects under vertical and horizontal loadings. In the laboratory experiments, vertical and lateral loadings were imposed on model piles in sand. Model piles made of PVC embedded in Joomoonjin sand were used in this study. Pile arrangements($2\times2,\; 3\times3$) and pile spacings(2.5D, 5.OD, 7.5D) were considered. Load-transfer curves(t-z, q-z and p-y curves), load-deflection curves and group interaction factors were obtained from the experimental results. The group interaction factors under both vertical and horizontal loadings were proposed for the cases of $2\times2\; and\; 3\times3$ pile groups with varying ratios of pile spacings. p-multipliers in this study were found for the individual piles in $2\times2\; and\; 3\times3$ pile groups.