scholarly journals A new general idea for starlike and convex functions

2016 ◽  
Vol 47 (4) ◽  
pp. 445-454 ◽  
Author(s):  
Shigeyoshi Owa ◽  
Srivastava Hari Mohan ◽  
Toshio Hayami ◽  
Kazuo Kuroki

Let $\mathcal{A}$ be the class of functions $f(z)$ which are analytic in the open unit disk $\mathbb{U}$ with $f(0)=0$ and $f'(0)=1$. For the class $\mathcal{A}$, a new general class $\mathcal{A}_{k}$ is defined. With this general class $\mathcal{A}_{k}$, two interesting classes $\mathcal{S}_{k}^{\ast}(\alpha)$ and $\mathcal{K}_{k}(\alpha)$ concerning classes of starlike of order $\alpha$ in $\mathbb{U}$ and convex of order $\alpha$ in $\mathbb{U}$ are considered.

Filomat ◽  
2016 ◽  
Vol 30 (7) ◽  
pp. 1911-1917 ◽  
Author(s):  
Nak Cho ◽  
Hyo Lee ◽  
Rekha Srivastava

In the present paper, we obtain some characterizations for a certain generalized Bessel function of the first kind to be in the subclasses SpT(?,?), UCT(?,?), PT(?) and CPT(?) of normalized analytic functions in the open unit disk U. Furthermore, we consider an integral operator related to the generalized Bessel Function which we have characterized here.


2020 ◽  
Vol 44 (4) ◽  
pp. 533-538
Author(s):  
PARDEEP KAUR ◽  
SUKHWINDER SINGH BILLING

Let ℋαϕ(β) denote the class of functions f, analytic in the open unit disk ???? which satisfy the condition ( ( ) ) zf-′(z-)- zf-′′(z-) ℜ (1 − α) + α 1 + ′ > β, z ∈ ????, ϕ(z ) f (z ) where α, β are pre-assigned real numbers and ϕ(z) is a starlike function. The special cases of the class ℋαϕ(β) have been studied in literature by different authors. In 2007, Singh et al. [?] studied the class ℋαz(β) and they established that functions in ℋαz(β) are univalent for all real numbers α, β satisfying the condition α ≤ β < 1 and the result is sharp in the sense that constant β cannot be replaced by a real number smaller than α. Singh et al. [?] in 2005, proved that for 0 < α < 1 functions in class ℋαz(α) are univalent. In 1975, Al-Amiri and Reade [?] showed that functions in class ℋαz(0) are univalent for all α ≤ 0 and also for α = 1 in ????. In the present paper, we prove that members of the class ℋαϕ(β) are close-to-convex and hence univalent for real numbers α, β and for a starlike function ϕ satisfying the condition β + α − 1 < αℜ( ) zϕ′(z) ϕ(z)≤ β < 1.


2021 ◽  
Vol 2021 ◽  
pp. 1-7
Author(s):  
Davood Alimohammadi ◽  
Ebrahim Analouei Adegani ◽  
Teodor Bulboacă ◽  
Nak Eun Cho

It is well-known that the logarithmic coefficients play an important role in the development of the theory of univalent functions. If S denotes the class of functions f z = z + ∑ n = 2 ∞ a n z n analytic and univalent in the open unit disk U , then the logarithmic coefficients γ n f of the function f ∈ S are defined by log f z / z = 2 ∑ n = 1 ∞ γ n f z n . In the current paper, the bounds for the logarithmic coefficients γ n for some well-known classes like C 1 + α z for α ∈ 0 , 1 and C V hpl 1 / 2 were estimated. Further, conjectures for the logarithmic coefficients γ n for functions f belonging to these classes are stated. For example, it is forecasted that if the function f ∈ C 1 + α z , then the logarithmic coefficients of f satisfy the inequalities γ n ≤ α / 2 n n + 1 , n ∈ ℕ . Equality is attained for the function L α , n , that is, log L α , n z / z = 2 ∑ n = 1 ∞ γ n L α , n z n = α / n n + 1 z n + ⋯ , z ∈ U .


Author(s):  
Young Jae Sim ◽  
Oh Sang Kwon

For real numbersαandβsuch that0≤α<1<β, we denote by𝒦α,βthe class of normalized analytic functions which satisfy the following two sided-inequality:α<ℜ1+zf′′z/f′z<β  z∈𝕌,where𝕌denotes the open unit disk. We find some relationships involving functions in the class𝒦(α,β). And we estimate the bounds of coefficients and solve the Fekete-Szegö problem for functions in this class. Furthermore, we investigate the bounds of initial coefficients of inverse functions or biunivalent functions.


2014 ◽  
Vol 2014 ◽  
pp. 1-4
Author(s):  
Edmond Aliaga ◽  
Nikola Tuneski

The class𝒰(λ,μ)of normalized analytic functions that satisfy|(z/f(z))1+μ·f′(z)−1|<λfor allzin the open unit disk is studied and sufficient conditions for anα-convex function to be in𝒰(λ,μ)are given.


2003 ◽  
Vol 2003 (41) ◽  
pp. 2603-2608 ◽  
Author(s):  
Dinggong Yang ◽  
Shigeyoshi Owa

A subclass𝒞p(λ,μ)(p∈ℕ, 0<λ<1, −λ≦μ<1)ofp-valently convex functions in the open unit disk𝕌is introduced. The object of the present paper is to discuss some interesting properties of functions belonging to the class𝒞p(λ,μ).


Filomat ◽  
2017 ◽  
Vol 31 (2) ◽  
pp. 227-245 ◽  
Author(s):  
Najla Alarifi ◽  
Rosihan Ali ◽  
V. Ravichandran

Let f be a normalized analytic function in the open unit disk of the complex plane satisfying zf'(z)/f(z) is subordinate to a given analytic function ?. A sharp bound is obtained for the second Hankel determinant of the kth-root transform z[f(zk)/zk]1/k. Best bounds for the Hankel determinant are also derived for the kth-root transform of several other classes, which include the class of ?-convex functions and ?-logarithmically convex functions. These bounds are expressed in terms of the coefficients of the given function ?, and thus connect with earlier known results for particular choices of ?.


Author(s):  
Abbas Kareem Wanas

In this paper, by making use the second kind Chebyshev polynomials, we introduce and study a certain class of bi-starlike and bi-convex functions with respect to symmetrical points defined in the open unit disk. We find upper bounds for the second and third coefficients of functions belong to this class.


2012 ◽  
Vol 62 (1) ◽  
Author(s):  
Jin-Lin Liu

AbstractFor analytic functions f(z) in the open unit disk U and convex functions g(z) in U, Nunokawa et al. [NUNOKAWA, M.—OWA, S.—NISHIWAKI, J.—KUROKI, K.—HAYAMI, T: Differential subordination and argumental property, Comput. Math. Appl. 56 (2008), 2733–2736] have proved one theorem which is a generalization of the result [POMMERENKE, CH.: On close-toconvex analytic functions, Trans. Amer. Math. Soc. 114 (1965), 176–186]. The object of the present paper is to generalize the theorem due to Nunokawa et al..


Filomat ◽  
2013 ◽  
Vol 27 (7) ◽  
pp. 1351-1356 ◽  
Author(s):  
Qing-Hua Xu ◽  
Lv. Chun-Bo ◽  
Nan-Chen Luo ◽  
H.M. Srivastava

In the present paper, the authors derive several sharp estimates for the Taylor-Maclaurin coefficients of functions in a certain general class S?(A, B) of spirallike functions in the open unit disk U, which is defined here by using the principle of differential subordination The results presented here would generalize those given in the earlier work of R. J. Libera.


Sign in / Sign up

Export Citation Format

Share Document