Ramp Inner Boundry (IMAGE) University of California - Santa Barbara Caption The center of this tube is described by a curve that forms the boundary of a mathematical surface (gray) describing the sheet. Credit Courtesy PRL Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.