To cancel the lower-frequency portions of the noise, noise-cancelling headphones use active noise control. They incorporate a microphone that measures ambient sound, generate a waveform that is the exact negative of the ambient sound, and mix it with any audio signal the listener desires.
Esophageal hiatus. In human anatomy, the esophageal hiatus is an opening in the diaphragm through which the esophagus and the vagus nerve pass. It is located in the right crus, one of the two tendinous structures that connect the diaphragm to the spine. Fibers of the right crus cross one another below the hiatus.
The hiatus is an opening in the diaphragm -- the muscular wall separating the chest cavity from the abdomen. Normally, the esophagus (food pipe) goes through the hiatus and attaches to the stomach. In a hiatal hernia (also called hiatus hernia) the stomach bulges up into the chest through that opening. There are two main types of hiatal hernias: sliding and paraesophageal (next to the esophagus).