Q statistics and disequilibrium in dynamic speckle measures

HÉCTOR RABAL; LUCIANO ZUNINO; OSVALDO A. ROSSO; NELLY CAP

Maceió

Conferencia; XVIII Conference on Nonequilibrium Statistical Mechanics and Nonlinear Physics (MEDYFINOL 2014); 2014

Laser light scattered by rough surfaces shows a granular appearance named speckle. When the optical properties of the surface evolve in time the granularity seems to boil and it is named dynamic speckle. Scattered light in free propagation can be registered by CCD cameras. The registered image is a simultaneous realization of a high number of samples of essentially the same phenomenon (but for negligible differences in sensitivity). Then, the dynamics of the phenomenon can be searched for by statistical analysis of the registered images. The phenomenon has found applications in many fields, such as the monitoring of the drying state of polymers, blood clotting, seeds analysis, cancer diagnosis, perfusion and many others. Many heuristic tools have been proposed to that end. We have explored several of them using q statistics generalizations and found that the free parameter q choice provides some advantages. We show some examples of these improvements. The drying process of paint and other polymers leads to a final static state. If this state is considered as equilibrium, a distance D between non equilibrium drying states and the final one can be defined based on the histogram of the images. Entropy, starting with a low value in the initial states, increases to that final maximal state. Then, entropy is created to its final value with an instantaneous rate I that depends on the distance D. This dependence of the rate as a function of the distance to equilibrium is characteristic of the drying process and can be used to follow its evolution. We show some results in paint and epoxy drying and blood clotting. Instead of free propagation, an image forming experimental set up permits the simultaneous observation of regions with different dynamics. These images can be segmented according to local dynamics features. Most of the tools employed so far to measure the dynamics employ intensity based tools. These measures of activity may be prone to artifacts due to detector non linearity. So, algorithms that are robust under such defect are of considerable interest. A measure that only requires monotonic response of the detector is permutation entropy. We employed several versions of this algorithm including a weighted one to test paint drying under illumination non uniformity. We used images of a coin covered with fresh paint in such way that no part of its topography could be perceived in the dynamic laser images. A stack of these images was processed with permutation entropy in several q statistics variants and found that the underlying topographic details could be perceived even under non uniform illumination. Experimental results are shown.