NORWALK - A Westport biologist has been awarded the Nobel Prize for medicine just days after succumbing to pancreatic cancer. The Nobel Committee does not usually award the prize posthumously, but its members say they did not know Dr. Ralph Steinman had died until they made the announcement this morning. However, they confirmed the prize would stand. "It is very sad that our dad won't be here to see what dendritic cells do next," Steinman's son, Adam Steinman, said of his father's research. "But it would have been his greatest wish to see the incredible honor of this Nobel Prize." Steinman's work included immune system research and the discovery of cells used in cancer treatments. His family accepted the award on his behalf at Rockefeller University in Manhattan.