Trachea act as a resonator to amplify sound. In some birds, the tracheal rings are complete, and may even be ossified. In amphibians, the trachea is normally extremely short, and leads directly into the lungs, without clear primary bronchi. A longer trachea is, however, found in some long-necked salamanders, and in caecilians. While there are irregular cartilagenous nodules on the amphibian trachea, these do not form the rings found in amniotes. The only vertebrates to have lungs, but no trachea, are the lungfish and the "Polypterus", in which the lungs arise directly from the pharynx. The word "trachea" is used to
Human-body model Human-body model The human-body model (HBM) is the most commonly used model for characterizing the susceptibility of an electronic device to damage from electrostatic discharge (ESD). The model is a simulation of the discharge which might occur when a human touches an electronic device. The HBM definition most widely used is the test model defined in the United States military standard, MIL-STD-883, Method 3015.9, Electrostatic Discharge Sensitivity Classification. This method establishes a simplified equivalent electrical circuit and the necessary test procedures required to model an HBM ESD event. An internationally widely used standard is JEDEC standard JS-001. HBM is used