In the diagram, each peak is at a tissue boundary. Waves reflect from tissue boundary - the first peak shows the thickness of body fat. The other peaks show reflections at different depths/distances.

It doesn't matter where you measure it, as long as it is the same point on each wave (look for where the pattern repeats). You should also be able to count the number of waves in a diagram.

Like any substance, neutron stars have an equation of state, or more precisely a phase diagram ... as compressed waves, had a maximum of c/√3 in strongly interacting QCD matter, where c is ...

Quanta behave very differently to macroscopic matter: particles can behave like waves, and waves behave as though they are particles. A network of quantum satellites that communicate with ground ...