In a method and apparatus for identifying features of multidimensional image data in hypermedia systems a multidimensional image, secondary image map and object index associate a program action with each object defined in an image. The energy-conducting pipe is a hollow stainless steel pipe which is passivation treated and can accommodate a filler thereinside. An ECU serves as a status detection unit to detect factors which affect the exhaust gas purifying performance of the catalyst unit, and serves as a control unit which controls the electric field applied by the electrodes, on the basis of the detected operating conditions. The method of making the optical component includes providing a preform having a content of OH-groups in the amount of about 0. Defined within those edges are engagement surfaces 30 that detachably retain the tube 14. The pockets preferably are oriented so that a cord passing through the cord lock will run along a path that is not parallel to the sidewalls but is at an angle of about 10\xb0.