Nak Eun Cho

Prof. Nak Eun Cho

Pukyong National Unitversity

Research Focus & Metrics

Academic Career Length

27Years (2000-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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12 February 2004 in Journal of Mathematical Analysis and Applications
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NCNak Eun Cho
Nak Eun Cho
OKOh Sang Kwon
Oh Sang Kwon
Hari Mohan SrivastavaHari Mohan Srivastava
Hari Mohan Srivastava

5 October 2019 in Mathematica Slovaca
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VKVirendra Kumar
Virendra Kumar
NCNak Eun Cho
Nak Eun Cho
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Hari Mohan SrivastavaHari Mohan Srivastava
Hari Mohan Srivastava
Let $\begin{array}{} \mathcal{S}^*_B \end{array}$ be the class of normalized starlike functions associated with a function related to the Bell numbers. By establishing bounds on some coefficient functionals for the family of functions with positive real part, we derive for functions in the class $\begin{array}{} \mathcal{S}^*_B \end{array}$ several sharp coefficient bounds on the first six coefficients and also further sharp bounds on the corresponding Hankel determinants. Bounds on the first three consecutive higher-order Schwarzian derivatives for functions in the class $\begin{array}{} \mathcal{S}^*_B \end{array}$ are investigated.

29 January 2019 in Bulletin of the Australian Mathematical Society
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NCNak Eun Cho
Nak Eun Cho
BKBogumiła Kowalczyk
Bogumiła Kowalczyk
ALAdam Lecko
Adam Lecko
We apply the Schwarz lemma to find general formulas for the third coefficient of Carathéodory functions dependent on a parameter in the closed unit polydisk. Next we find sharp estimates of the Hankel determinant $H_{2,2}$ and Zalcman functional $J_{2,3}$ over the class ${\mathcal{C}}{\mathcal{V}}$ of analytic functions $f$ normalised such that $\text{Re}\{(1-z^{2})f^{\prime }(z)\}>0$ for $z\in \mathbb{D}:=\{z\in \mathbb{C}:|z|<1\}$ , that is, the subclass of the class of functions convex in the direction of the imaginary axis.

9 January 2020 in Revista de la Real Academia de Ciencias Exactas, Fisicas y Naturales. Serie A. Matematicas
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NCNak Eun Cho
Nak Eun Cho
BKBogumiła Kowalczyk
Bogumiła Kowalczyk
OKOh Sang Kwon
Oh Sang Kwon
ALAdam Lecko
Adam Lecko
YSYoung Jae Sim
Young Jae Sim
For analytic functionsfin the unit disk $${\mathbb {D}}$$D normalized by $$f(0)=0$$f(0)=0 and $$f'(0)=1$$f′(0)=1 satisfying in $${\mathbb {D}}$$D respectively the conditions $${{\,\mathrm{Re}\,}}\{ (1-z)f'(z) \}> 0,\ {{\,\mathrm{Re}\,}}\{ (1-z^2)f'(z) \}> 0,\ {{\,\mathrm{Re}\,}}\{ (1-z+z^2)f'(z) \}> 0,\ {{\,\mathrm{Re}\,}}\{ (1-z)^2f'(z) \} > 0,$$Re{(1-z)f′(z)}>0,Re{(1-z2)f′(z)}>0,Re{(1-z+z2)f′(z)}>0,Re{(1-z)2f′(z)}>0, the sharp upper bound of the third logarithmic coefficient in case when $$f''(0)$$f′′(0) is real was computed.

16 April 2013 in Journal of Inequalities and Applications
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SKShanmugam Sivaprasad Kumar
Shanmugam Sivaprasad Kumar
VKVirendra Kumar
Virendra Kumar
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NCNak Eun Cho
Nak Eun Cho
Let − 1 ≤ B < A ≤ 1 . The condition on β is determined so that 1 + β z p ′ ( z ) / p k ( z ) ≺ ( 1 + A z ) / ( 1 + B z ) ( − 1 < k ≤ 3 ) implies p ( z ) ≺ 1 + z . Similarly, the condition on β is determined so that 1 + β z p ′ ( z ) / p n ( z ) or p ( z ) + β z p ′ ( z ) / p n ( z ) ≺ 1 + z ( n = 0 , 1 , 2 ) implies p ( z ) ≺ ( 1 + A z ) / ( 1 + B z ) or 1 + z . In addition to that, the condition on β is derived so that p ( z ) ≺ ( 1 + A z ) / ( 1 + B z ) when p ( z ) + β z p ′ ( z ) / p ( z ) ≺ 1 + z . A few more problems of the similar flavor are also considered. MSC:30C80, 30C45.

10 May 2019 in Mathematics
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LSLei Shi
Lei Shi
IAIzaz Ali
Izaz Ali
Muhammad ArifMuhammad Arif
Muhammad Arif
NCNak Eun Cho
Nak Eun Cho
SHShehzad Hussain
Shehzad Hussain
HKHassan Khan
Hassan Khan
In the present article, we consider certain subfamilies of analytic functions connected with the cardioid domain in the region of the unit disk. The purpose of this article is to investigate the estimates of the third Hankel determinant for these families. Further, the same bounds have been investigated for two-fold and three-fold symmetric functions.