<a href=" http://www.espaitaronja.com/lipitor-5mg-tablet-ezee.pdf ">atorvastatin 80 mg in acute coronary syndrome definition</a> The two opposing waves (emitted and reflected) interfere with one another creating a standing wave. Certain parts of the wave called nodes don't move. And when the standing wave is parallel with gravity some portions of it have a constant downward pressure and other portions have a constant upward pressure -- the nodes however have very little (virtually zero) pressure. さんの一首