Piston effect platforms with a single tunnel, however, air quality worsens when relying on the piston effect alone for ventilation. This still allows for potential energy savings by taking advantage of the piston effect rather than mechanical ventilation where possible. Tunnel boom is a loud boom sometimes generated by high-speed trains when they exit tunnels. These shock waves can disturb nearby residents and damage trains and nearby structures. The perception of this sound by humans is similar to that of a sonic boom from supersonic aircraft, but unlike a sonic boom, tunnel boom is not caused by trains exceeding the speed of
Periodic travelling wave Periodic travelling wave In mathematics a periodic travelling wave (or wavetrain) is a periodic function of one-dimensional space that moves with constant speed. Consequently it is a special type of spatiotemporal oscillation that is a periodic function of both space and time. Periodic travelling waves play a fundamental role in many mathematical equations, including self-oscillatory systems, excitable systems and reaction-diffusion-advection systems. Equations of these types are widely used as mathematical models of biology, chemistry and physics, and many examples in phenomena resembling periodic travelling waves have been found empirically. The mathematical theory of periodic travelling waves is most fully developed