In nuclear and particle physics, the concept of a cross section is used to express the likelihood of interaction between particles. When particles are thrown against a foil made of a certain substance, the cross section is a hypothetical area measure around the target particles (usually its atoms) that represents a surface. If a particle of the beam crosses this surface, there will be some kind of interaction.
The bandoneón is a type of concertina particularly popular in Argentina and Uruguay. It plays an essential role in the orquesta tipica, the tango orchestra. The bandoneón, called bandonion by its German inventor, Heinrich Band (1821–1860), was originally intended as an instrument for religious music and the popular music of the day, in contrast to its predecessor, the German concertina (or Konzertina), considered to be a folk instrument by some modern authors.