The flag of the state of Arizona flies at half-staff outside University Medical Center in Tucson, Ariz., on Jan. 8. Chris Morrison/AP hide caption

itoggle caption Chris Morrison/AP

Natasha Smahlei, a model, works at the Caitlin Raymond International Registry exhibit in October during the New England Business Expo at the DCU Center in Worcester, Mass. Paul Kapteyn/Courtesy of www.telegram.com hide caption

itoggle caption Paul Kapteyn/Courtesy of www.telegram.com

Natasha Smahlei, a model, works at the Caitlin Raymond International Registry exhibit in October during the New England Business Expo at the DCU Center in Worcester, Mass. Paul Kapteyn/Courtesy of www.telegram.com hide caption

itoggle caption Paul Kapteyn/Courtesy of www.telegram.com

In Oxford, England, people are 16 times more likely to get a particular kind of hip replacement than residents of London. Wikimedia Commons hide caption

itoggle caption Wikimedia Commons

Most gases used in anesthesiology eventually end up in the atmosphere where they trap heat even more effectively than carbon dioxide. iStockphoto.com hide caption

itoggle caption iStockphoto.com

A CT scan of the brain shows the cerebellum, a small portion of each temporal lobe, and the sinuses. Andrew Ciscel via Wikimedia Commons hide caption

itoggle caption Andrew Ciscel via Wikimedia Commons