dai and all other friends in Singapore and back home for being there for me both at good as well as hard times. In addition, I would also like to acknowledge NTU and Advanced Remanufacturing and Technology Center (ARTC) for supporting my PhD work and A*STAR SINGA for providing me the scholarship. Last but not least, I express my heartfelt thanks to my parents, sister and family for their ceaseless blessing, love and support.