Empty stomachs contract, causing both hunger pangs and the secretion of chemical messages that travel to the brain to serve as a signal to initiate feeding behavior. this is an example of

This is an example of a physiological mechanism.  A physiological mechanism is an automatic  mechanism that governs our body using our bodily organs to stay alive and  functioning. Other examples of physiological mechanisms include those we use  for sleeping and regulate body temperature.

characterization of nanoparticles is a critical step in nanomaterial production as it provides information of dimension, morphology, surface charge, distribution and degree of surface functionalization.