This paper presents the experimental results on the formation, dynamics and evolution towards chaos of complex space charge structures that emerge in front of a positively biased electrode immersed in a quiescent plasma. In certain experimental conditions, we managed to obtain the so-called multiple double layers (MDLs) with non-concentric configuration. Our experiments show that the interactions between each MDL's constituent entities are held responsible for the complex dynamics and eventually for its transition to chaos through cascades of spatio-temporal sub-harmonic bifurcations. Further, we build a theoretical model based on the fractal approximation (scale relativity theory) in order to reproduce the experimental results (plasma self-structuring and scenario of evolution to chaos). Comparing the experimental results with the theoretical ones, we observe a good correlation between them.

We report experimental results showing that a discharge plasma, which self-structures as concentric multiple double layers, is capable of evolving towards chaos through a cascade of spatio-temporal sub-harmonic bifurcations when the applied constraint (in the form of voltage applied on a supplementary electrode immersed in the plasma) is gradually increased. By considering that the plasma particles (electrons, ions and neutrals) move on fractal curves, a theoretical model able to explain both the plasma self-structuring and the scenario of evolution to chaos is constructed. The experimental results were found to be in good agreement with those obtained from the theoretical model.

This study highlights the benefits of optimizing the decolorization of bromocresol green (a colorant/pH indicator widely used in the industry, whose degradation produces toxic byproducts) by adsorption on active carbon. A set of experiments were planned and performed based on the design of experiments methodology for the following parameters: the colorant concentration (0.009-0.045 g/L), the amount of adsorbent (0.5-3 g/L), and the contact time (60-240 min). Modeling and optimization strategies were employed to determine the working conditions leading to efficiency maximization. Using the response surface methodology, the optimum values of the primary process parameters were established. In addition, a modified bacterial foraging optimization algorithm was applied as an alternative optimizer in combination with artificial neural networks in order to determine multiple combinations of parameters that can lead to maximum process efficiency. Different solutions were obtained with the considered strategies, and the maximum efficiency obtained was >99%. The study emphasizes that adsorption on active carbon is an effective method for bromocresol green decolorization in wastewater that can be further improved using advanced optimization methods.

Natural rubber, as well as natural reinforced rubber, with different carbon nanotubes concentrations, 10 and 20 mm, thick, have been structurally, chemically, and thermally investigated. Scanning electron microscopy techniques, as well as X-ray energy dispersive analysis, Raman, and thermal conductivity analysis, were used in characterizing materials in order to establish a connection among the CNT concentration, homogeneity of reinforcing elements within the natural rubber, and their thermal conductivity characteristics. The theoretical approach reveals the dependence between the thermal conductivity and reinforcing elements. The final result confirms the increase of the effective thermal conductivity with the concentration of CNT.