  By using thermal and Lorentz force, the vortex motion is successfully
manipulated in the mixed state of underdoped La$_{2 - x}$Sr$_{x}$CuO$_{4}$
single crystals and optimally doped YBa$_{2}$Cu$_{3}$O$_{7 - \delta}$ thin
films. A conclusion is drawn that the strong Nernst signal above $T_{c}$ is
induced by vortex motion. In the normal state, in order to reduce the
dissipative contribution from the quasiparticle scattering and enhance the
signal due to the possible vortex motion, a new measurement configuration is
proposed. It is found that the in-plane Nernst signal ($H$ $| | $ $c$) can be
measurable up to a high temperature in the pseudogap region, while the
Abrikosov flux flow dissipation can only be measured up to $T_{c}$. This may
point to different vortices below and above $T_{c}$ if we attribute the strong
Nernst signal in the pseudogap region to the vortex motion. Below $T_{c}$ the
dissipation is induced by the motion of the Abrikosov vortices. Above $T_{c}$
the dissipation may be caused by the motion of the spontaneously generated
unbinded vortex-antivortex pairs.
