I’ve dabbled in hollow holds, and they've popped up in plenty of workouts over the years. I’ve never done them consistently, ...

We are fascinated by the hybrid rocket engine which [Ben Krasnow] built and tested in his shop. It is actually using a hollow cylinder of acrylic as the fuel, with gaseous oxygen as an oxidizer.

Relativity Networks, an Orlando-based startup focused on hollow-core fibers (HCF) developed at the nearby College of Optics and Photonics at the University of Central Florida (CREOL), says it has ...