Mehraboon Irani, Principal and Head - Private Client Group Business at Nirmal Bang Securities says that Nifty has bottomed out for some time after rally from 4500. He advises investors to buy good quality stocks at Nifty's 4500, 4400 & 4600 levels and Infosys and other IT stocks on every sharp fall. BHEL stocks also represent a good long term opportunity, he added.