\[sec\_reinter\].

These results are supported by figs. \[plot\_3\] and \[plot\_3b\] which show the influence of an increased density $\rho$ for fixed values of $\mu$ on the evacuation times.

![Density-dependence of the evacuation time in the ordered and disordered regime for $\mu=0.9$.[]{data-label="plot_3"}](\DIR/fig7.eps){width="0.9\columnwidth"}

![Relative time difference of the evacuation times for $\mu=0$ and $\mu=0.9$ in the three regimes.[]{data-label="plot_3b"}](\DIR/fig8.eps){width="0.9\columnwidth"}

In the disordered regime even the influence of the large value $\mu =0.9$ is only visible for higher densities ($\rho>0.1$). The cooperative regime shows a similar behaviour. In contrast, in the ordered regime even for very small densities $\rho$ the influence of the high value $\mu=0.9$ is very strong (fig. \[plot\_3\]). This is supported by fig. \[plot\_3b\], where the relative time differences for the two values $\mu=0$ and $\mu=0.9$ for all three regimes are shown. Here the very strong increase of the relative time difference in the ordered regime after a very small density of $\rho=0.003$ is remarkable. After this increase the relative time difference remains almost constant.

Reinterpretation of the ordered phase {#sec_reinter}
-------------------------------------

The introduction of the friction parameter $\mu$ allows an improved interpretation of the ordered regime, i.e. the case of strong coupling ($k_S>3$) to the static field $S$ and weak 