“Second sound is the hallmark of superfluidity, but in ultracold gases so far you could only see it in this faint reflection of the density ripples that go along with it,” lead author Martin Zwierlein ...

In the first two of these applications ... The time between a pulse of sound being transmitted and detected and the speed of sound in water can be used to calculate the distance of the reflecting ...

Ultrasound imaging creates a picture of something that cannot be seen directly, such as an unborn baby in the womb ... frequency sound waves can be used to detect objects in deep water and ...