Abstract and Applied Analysis

Volume 2012 (2012), Article ID 140924, 10 pages

doi:10.1155/2012/140924

Research Article

Univalence Conditions Related to a General Integral Operator

Nicoleta Breaz¹ and Virgil Pescar²

¹Department of Mathematics, Faculty of Science, “1 Decembrie 1918” University of Alba Iulia, Nicolae Iorga Street No. 11-13, 510009 Alba Iulia, Romania

²Department of Mathematics, Faculty of Mathematics and Computer Science, Transilvania University of Braşov, 500091 Braşov, Romania

Received 28 June 2012; Revised 29 October 2012; Accepted 31 October 2012

Academic Editor: Naseer Shahzad

Copyright © 2012 Nicoleta Breaz and Virgil Pescar. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

We consider a general integral operator based on two types of analytic functions, namely, regular functions and, respectively, functions having a positive real part. Some univalence conditions for this integral operator are obtained.

1. Introduction

Let be the class of functions of the form

which are analytic in the open unit disk, and normalized by . Also, let denote the subclass of consisting of univalent functions, in the open unit disk. We denote by , the class of functions which are analytic in , , for all and , the so-called Caratheodory functions.

In [1], Pescar introduced and studied the following integral operator:

where are complex numbers, , , .

In this paper, we generalize this integral operator, by considering the general integral operator defined as follows:

where , are complex numbers, , , , .

Remarks. This integral operator extends many other integral operators from related works on this field as those given by Srivastava, Mocanu, Owa, Pescar, Orhan, Breaz, and others. Using this new operator and the related univalence conditions that are going to be proved here, one can study some other already known operators in a unified perspective. Thus, for different particular cases of the parameters , , , our integral operator is shown to be an extension of the following integral operators.

(i)For , the integral operator is the operator from (1.2), introduced by Pescar in [1].(ii)For , , , the integral operator was studied in [2], by Miller and Mocanu.(iii)For , , the integral operator was studied in [3], by Pescar and Breaz.(iv)For , , , and , the integral operator was studied in [4], by Breaz et al. and also in [5], by Srivastava et al.(v)For , , , we get the integral operator defined by D. Breaz and N. Breaz, in the paper [6].(vi)For , , , and , the operator was studied by Breaz et al., in the paper [7].

More precisely, if we are interested to study various properties of two or more different operators reminded above (and other similar operators which are not mentioned here), we can do this in an integrated manner by simply allowing the parameters involved in the definition, to be more general and consequently by studying only one operator, having the form (1.3). In this paper, we will study some univalence criteria for this new operator.

The following known results will be used in order to prove our results.

Lemma 1.1 (see [8]). Let be a complex number, and . If

for all , then for any complex number , ,

Lemma 1.2 (see [9]). Let be a regular function in the open disk with , fixed. If has in one zero with multiplicity , then

the equality for () can hold only if

where is constant.

Lemma 1.3 (see [10]). For each ,

Lemma 1.4 (see [11]). If is regular in and , then

Also, for the statement of our main results, we need to define the following classes:

2. Main Results

Theorem 2.1. Let be complex numbers, , positive real numbers, , , and the functions , , .

If

then the general integral operator , defined by (1.3), is in the class .

Proof. We consider the regular function

After some calculus, we have

for all .

Since , by applying Lemma 1.2 for , we get

Also since , from Lemma 1.2, we have

If we put these last two inequalities in (2.3), together with the inequality from the hypothesis, we get

Now we take into account the fact that

thus obtaining

Further from Lemma 1.1, for , it is obvious that .

Corollary 2.2. Let , be complex numbers, , positive real numbers, , , . If

then the function

is in the class .

Proof. In Theorem 2.1, we take .

Corollary 2.3. Let , be complex numbers, , positive real numbers and , . If

then the function

belongs to the class .

Proof. In Theorem 2.1, we take .

Theorem 2.4. Let be complex numbers, , , and the functions , , , with

If

then the general integral operator belongs to the class .

Proof. Let consider again the regular function:

After some calculus, we have

Since and , for all , from Lemma 1.2, we obtain

Using these last two inequalities, the inequality from the hypothesis, and the fact that

from (2.16) we get

for all .

Hence, by Lemma 1.1, we have that .

Corollary 2.5. Let be complex numbers, , and , , , with

If

then the integral operator defined by

is in the class .

Proof. In Theorem 2.4, we take .

Corollary 2.6. Let be complex numbers, , , and , with

If

then the integral operator defined by

is in the class .

Proof. We put in Theorem 2.4, .

Theorem 2.7. Let be complex numbers, , and , . If

then the general integral operator .

Proof. We consider the same regular function as in the proof of the previous theorems, and after some calculus we get

for all .

Since , from Lemma 1.3, we get

, , and since , from Lemma 1.4, we get

, .

Now if we use (2.28) and (2.29) in (2.27), we obtain

for all .

We consider two cases.

(1) If , we have

and further if we use this inequality together with the inequality from the hypothesis, from (2.30), we get

for all , and with Lemma 1.1 the proof is complete.

(2) If , we obtain

and further if we put this last inequality in (2.30) we get

for all .

Now by applying first the inequality condition from the hypothesis and then Lemma 1.1 for , the proof is complete.

Corollary 2.8. Let be complex numbers, , and . If

then the integral operator

is in the class .

Proof. In Theorem 2.7, we take .

Corollary 2.9. Let be complex numbers, , and . If

then the integral operator

is in the class .

Proof. In Theorem 2.7 we take .

Acknowledgment

The authors wish to thank the reviewers for their constructive comments which helped them to improve the quality of the paper.

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