DETECTION OF CRITICAL MODE CONVECTION IN THE PRESENCE OF A THERMAL-GRADIENT USING CHEMICAL WAVES AS A PASSIVE INDICATOR

The detection of the lowest critical modes, gamma1(1) and gamma0(1), f or thermal convection in a vertical tube is reported. Their visualizat ion was through the distortion they caused to chemical waves propagati ng in a manganese-catalyzed Belousov-Zhabotinsky medium. A time depend ent temperature gradient was allowed to develop in the system and the dynamical behavior of spontaneously occurring trigger waves was record ed as magnetic resonance images. The work also illustrates the potenti al of magnetic resonance imaging to provide information on the tempera ture dependence of the propagation velocity of trigger waves and of th e frequency of pacemaker activity.