4.1.1. Problem background, state of the art ….. plays an important/vital role in …..
….. is an important issue for …..
….. is extensively/widely used in …..
….. is a very effective method for …..
In the last few years there has been a growing interest in …..
Quite recently, considerable attention has been paid to …..
….. have/has been gaining importance in recent years …..
….. have/has been utilized in many applications such as …..