  We present Particle-in-Cell simulation results of relativistic shear flows
for hybrid positron-electron-ion plasmas and compare to those for pure e+e- and
pure e-ion plasmas. Among the three types of relativistic shear flows, we find
that only hybrid shear flow is able to energize the electrons to form a
high-energy spectral peak plus a hard power-law tail. Such electron spectra are
needed to model the observational properties of gamma-ray bursts.
