A valve that includes an expandable valve body defining a lumen and a longitudinally moveable obstructer retained within the lumen of the valve body between the proximal and distal ends of the valve when the valve is in an expanded configuration. The present invention further relates to a process for the preparation of bosentan and its pharmaceutically acceptable salts. This invention further provides the above-described vectors, wherein the gene encodes an inducer of apoptosis. Also disclosed are a system and technique for simultaneously presenting multiple, s content object data streams on the user interface in a manner which encourages multidimensional browsing using traditional navigation commands. The micronized barium sulfate of the invention is particularly suitable for use as an additive or filler for adhesives, colorants, rubber articles andor cosmetics. In the present invention, pipestages are clocked only when a valid instruction needs to advance in order to conserve power and to minimize stalling.