Quasi-Stationary and Transient Patterns in Jets
  Apparent evolution of relativistic flows as traced by radio emission results
from a combination of several factors related to propagation of relativistic
blobs or shocks, velocity, density and pressure stratification of the
underlying flow, plasma instability and (possibly also) phase and time travel
effect. This combination can create an intricate and chaotic patterns of the
observed morphological changes in radio emission, which complicates the
analysis and interpretation of kinematic and physical properties of the jet
plasma. Recent studies have indicated that slow and quasi-stationary patterns
in jets are most likely formed by plasma instabilities while faster,
superluminally moving patterns are related to highly relativistic plasma
condensations produced by the nuclear flares. Some of the stationary patterns
may also be related to recollimation shocks or locations where strong
non-thermal continuum is produced in jets. Similarities and differences of the
AGN and XRB jets in this respect are reviewed.
