  We observed 20 Palomar-Green (PG) quasars at low redshift ($z<0.5$) with
total flux density > 1 mJy, including 4 radio-loud quasars (RLQs) and 16
radio-quiet quasars (RQQs), using the Very Long Baseline Array (VLBA) at 5 GHz.
Ten RQQs are clearly detected in the VLBA images, and a compact radio core is
identified in eight of them, indicating the prevalence of active galactic
nucleus (AGN)-related radio emission in this flux-density-limited RQQ sample.
The RQQs and RLQs in our sample have a division at $\sim$30~mJy. The radio
emission from RQQs appears to be the result of a combination of star formation
and AGN-associated activities. All RQQs in our sample have a 5 GHz flux density
ratio of Very Large Array (VLA) A-array to D-array $f_{\rm c} = S_{\rm A}^{\rm
VLA}/S_{\rm D}^{\rm VLA}$ above 0.2. The RQQs with $f_a$ (VLBA and VLA flux
density ratio $S^{\rm VLBA}/S_{\rm A}^{\rm VLA}) > 0.2$ versus $f_a < 0.2$ show
significant differences in morphology, compactness and total flux density.
$f_{\rm a}$ of RQQs is systematically lower than that of RLQs, probably due to
the extended jets or relic jets of RQQs on 10s to 100s parsecs which are
resolved out in VLBA images. Future larger samples, especially with the
addition of milli-arcsec resolution radio images of RQQs with total flux
densities below 1 mJy, can test the conclusions of this paper and contributes
to the understanding of the radio emission mechanism of RQQs, and the dichotomy
and physical connection between RQQs and RLQs.
