Theoretical results and discussion

The ejqjerimental scenario can be partly imderstood with the SM [24, 111, 112]. One finds that the general shape of the measured ZZ instability limit in the q-s plane, shown in 

In technical terms it is the opposite sign of the coefficient q of Eq. 39 which is responsible for the different behaviour 

The mean flow also has the effect of transforming the Eckhaus instability on the large q side into a SV instability. This effect becomes noticeable only in the upper part as the ZZ line is approached because at smaller e the ratio Syls is very small, see the broken line in Fig. 13.8 a. In fact the SV instability then turns around and joins the ZZ line smoothly. This effect indicates that the SV instability may become relevant and could be a clue to the observations quoted above [29, 37, 108]. 

From the curve CR in Fig. 13.8b we see that at larger e a short wavelength instability comes into play, i.e. a roll system with a different wave-vector, particular in different orientation, starts growing. This may saturate the often-observed rectangular patterns or, for a non-symmetric superposition, lead to the sometimes-observed oblique modulated structures [17, 105]. In order to examine this possibility one would have to test the stability of such patterns by a suitable Galerkin procedure, which was done for normal rolls. However, since there are other possibilities, in particular turbulent states, this approach is not exhaustive and has to be complemented by simulations of the dynamics. 

9 Recently most material parameters of Merck Phase V have been measured, see note added at the end. The material parameters of 152 have either been measured directly or fitted to EHC measurements [49]. 

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