Mirror shear effects

Fig. 1.13. The shear-thinning viscosity is significantly reduced at the beginning when the droplet collides with its mirror image. Subsequently, it rises during the expansion of the rim and drops again when the rim contracts. The effective viscosity which leads to the same droplet collision complex diameter is the same as the mean droplet viscosity of the shear-thinning case at the moment shortly after the collision. This implies the fact that relatively small region of high shear rates and reduced viscosity at the beginning of the collision is more important than the mean viscosity during the collision. The reason for this phenomenon can be seen in Fig. 1.14 and is explained as follows ...

The sample is sheared in the narrow gap and exerts a torque on the cylinder s. Light reflected from the mirror v measures the amount of twist of the torsion wire at C. Guard rings g and g are fixed and serve to reduce end effects. 

Even though cube comers largely eliminate the effect of tilt, lateral displacements produce a shear that has a similar effect on the interferogram. In practice, it is easier to meet the tolerance on lateral displacements than on tilts, so that retroreflectors have a definite experimental advantage over plane mirrors for a given drive. Steel [3] has suggested a combination of a movable cube comer and stationary plane mirrors that introduces neither shear nor tilt. An interferometer based on this principle, shown... 

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