Lenovo unveiled a lighter, quicker ThinkPad notebook computer on Monday to appeal to customers who like the convenience of tablets and smartphones. The ThinkPad X1 Carbon will go on sale later this month, the Chinese computer maker said. Lenovo Group acquired the ThinkPad brand with IBM Corp.'s personal computer unit in 2005. Lenovo passed Dell Inc. last year to become the second-largest PC manufacturer after Hewlett-Packard Co.