Pattern formations in electroconvection by colored noise

We report noise-induced threshold shifts in ac-driven electroconvection (EC) in nematic liquid crystals (NLCs). It has been known that noise plays a role in stabilization (f
_c
> f
_c
^*
) or destabilization (f
_c
<; f
_c
^*
) effects on EC depending on its cutoff frequencies f
_c
; therefore, these effects monotonically increase (f
_c
> f
_c
^*
) or decrease (f
_c
<; f
_c
^*
) the EC threshold V
_c
. However, we have found an interesting threshold shift not showing the monotonic behavior for around a characteristic f
_c
^*
; this “reversed bell-shaped behavior” implies “inverse stochastic resonance (ISR)”. We also were able to observe traveling waves (TWs) in the noise-induced phenomena; basically, TWs are one of the typical EC, which have been well understood in the so-called weak electrolyte model showing a Hopf bifurcation. Considering the characteristic of colored noise (i.e., intensity V
_N
and cutoff frequency f
_c
), ISR and TW are presented and discussed.