  Herbig-Haro (HH) jets are commonly thought of as homogeneous beams of plasma
traveling at hypersonic velocities. Structure within jet beams is often
attributed to periodic or ``pulsed'' variations of conditions at the jet
source. Simulations based on this scenario result in knots extending across the
jet diameter. Observations and recent high energy density laboratory
experiments shed new light on structures below this scale and indicate they may
be important for understanding the fundamentals of jet dynamics. In this paper
we offer an alternative to ``pulsed'' models of protostellar jets. Using direct
numerical simulations we explore the possibility that jets are chains of
sub-radial clumps propagating through a moving inter-clump medium. Our models
explore an idealization of this scenario by injecting small ($r<r_{jet}$),
dense ($\rho>\rho_{jet}$) spheres embedded in an otherwise smooth inter-clump
jet flow. The spheres are initialized with velocities differing from the jet
velocity by $\sim15$%. We find the consequences of shifting from homogeneous to
heterogeneous flows are significant as clumps interact with each other and with
the inter-clump medium in a variety of ways. Structures which mimic what is
expected from pulsed-jet models can form, as can previously unseen
``sub-radial'' behaviors including backward facing bow shocks and off-axis
working surfaces. While these small-scale structures have not been seen before
in simulation studies, they are found in high resolution jet observations. We
discuss implications of our simulations for the interpretation of protostellar
jets with regard to characterization of knots by a ``lifetime'' or ``velocity
history'' approach as well as linking observed structures with central engines
which produce the jets.
