Propagation of pulses
The propagation of pulsed wave fields in a homogeneous medium or in a homogeneous line with known dispersion law and damping can be regarded from the ray, wave, and energy points of view. The review describes the most significant theoretical results on one-dimensional pulse propagation, using all three approaches. Greatest attention is paid to the principal part of a high-frequency pulse, the part governed by frequencies closest to the pulse carrier frequency. Paradoxes pertaining to superluminal and negative ``group velocities'' are resolved, and questions connected with amplification or attenuation of waves in wave beams and active media are discussed.