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.
An esophageal ulcer refers to an ulceration (erosion or sore) of the esophagus, the flexible tube connecting the mouth to the stomach. Esophageal Ulcers are typically lumped together with gastric (stomach) and duodenal (part of the small intestine) ulcers under the umbrella term peptic ulcers.