Ref1

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwjK-8SSm4DVAhWML48KHeSpC6EQFggoMAA&url=http%3A%2F%2Fwww.ifrj.upm.edu.my%2F20%2520(02)%25202013%2F6%2520IFRJ%252020%2520(02)%25202013%2520Rabeta%2520(343).pdf&usg=AFQjCNHvCj7Au8nGcnyw_xl3HX_3xK8DEg