Researchers said Monday they had moved a step closer to curing the common cold by creating an image of the doorway used by the cold virus to infect human cells.They used a technique known as X-ray crystallography to make an atomic map of the receptor, a kind of chemical doorway, that the virus uses to infect cells.Reporting in the Proceedings of the National Academy of Sciences, the two teams of researchers said their finding could possibly lead to a treatment for the common cold, which is currently incurable.