Iranian Journal of Engineering Education Vol.8 No.30 Summer 2006 ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ Proprietor: The Academy of Sciences of IR Iran, Department of Engineering Science Executive Manager: Prof. Mahmood Yaghoubi Editor-in-Chief: Prof. Parviz Davami Editorial Board: Prof. Ali Kaveh Iran University of Science and Technology Prof. Morteza Sohrabi Amirkabir University of Technology Prof. Mohmoud Yaghoubi University of Shiraz Prof. Hassan Zohoor Sharif University of Technology Prof. Mehdi Bahadori Nejad Sharif University of Technology Prof. Parviz Davami Sharif University of Technology Prof. Mohamad Reza Eslami Amirkabir University of Technology Prof. Parviz Jabbehdar Maralani University of Tehran Editorial Advisory Board: Prof. Mehdi Sabaghian, USA Prof. Majid Sadegh Azar, Iran Prof. Jalal Shaygan, Iran Prof. Mehdi Sohrabi, Iran Prof. Mostafa Sohrabpour, Iran Prof. Saeed Sohrabpour, Iran Prof. Mohammad Soltaniyeh, Iran Prof. Mahmoud Tabyani, Iran Prof. Jafar Tofighi, Iran Prof. Abolhassan Vafaei, Iran Prof. Mehrdad Abedi, Iran Prof. Hooshang Afshari, Iran Prof. Goodarz Ahmadi, USA Prof. Mohammad Reza Aref, Iran Prof. Gholamhossein Daneshi, Iran Prof. Farhad Golestani Fard, Iran Prof. Iraj Goodarznia, Iran Prof. Ali Haerian, Iran Prof. Jalal Hejazi Dehghani, Iran Prof. Tahereh Khaghazchi, Iran Prof. Esmaeel Khoshravan, Iran Executive Director: Mr. Mohammad Mehdi Ghafari Coordinator: Ms. Behnaz Darabi Text- Editor: Ms. Foroozandeh Saadatmand Cover Designer: Ms. Mahboobeh Asgharpour Page Layout: Ms. Yeganeh Khodami Mailing Address: The Academy of Sciences of IR Iran, Office of Iranian Journal of Engineering Education, No. 17 Shahmoradi Alley Darband Ave. Tajrish, Tehran 19717 Iran. Po. Box: 19735-167 Tel/Fax: + 98 21 22719005 Email: ijee78@ias.ac.ir ISSN: 1607-2316