Today, tissue regeneration is one of the greatest challenges in the field of medicine, since it represents hope after accidents or illnesses. Tissue engineering is the science based on improving or restoring tissues and organs. In this work, five formulations of chitosan/poly(vinyl alcohol)/graphene oxide (CS/PVA/GO) nanocomposites were studied for the development of biodegradable films with potential biomedical applications. The characterization of the films consisted of Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The antibacterial activity was evaluated in vitro against Gram-positive bacteria Bacillus cereus and Staphylococcus aureus and Gram-negative Salmonella spp. and Escherichia coli, by contact of the film above inoculum bacterial in Müeller–Hinton agar. On the other hand, in vivo tests in which the material implanted in the subcutaneous tissue of Wistar rats demonstrated that the formulation CS/PVA/GO (14.25:85:0.75) was the best antibacterial film with adequate degradation in vivo. All together, these results indicate the potential of the films using nanocomposites of CS/PVA/GO in tissue engineering and cell regeneration.
This work reviews the state-of-the-art of the main soot modeling approaches used in turbulent diffusion flames. Accordingly, after a short introduction about the subject addressed here, the main soot formation mechanisms are described next. This description provides the basis for the discussions about the different soot modeling techniques employed nowadays for soot predictions. Since combustion and radiation models have a significant impact on soot predictions, as a consequence of the strong coupling between chemistry, turbulence and soot formation, a general overview about these models is also provided. For the sake of clarity, the main soot formation models reviewed in this work are classified as semi-empirical soot precursor models and detailed ones. Both advantages and disadvantages of the referred soot modeling approaches are properly discussed. In the last part of this review, comparative results obtained using some of the main soot models currently available are presented along with a discussion about the prospects for soot modeling in turbulent flames. Finally, some conclusions and references are provided.Overall, based on the literature reviewed, it is concluded that there is yet a long path to be followed before understanding first and having then a soot model able to properly describe the formation of this critical pollutant for a variety of situations of industrial interest.
Tens or even hundreds of chemical species are produced in the nascent stages of hydrocarbon-based fuels combustion that eventually lead to the formation of soot particles and aggregates. In such context, the study of sootrelated chemical species formation and its associated physical-chemical phenomena are of great importance to delve into how in combustion processes the formation of this critical pollutant is carried out. In this work thus, accounting for an ethylene/air laminar diffusion flame previously experimentally characterized employing a Gülder burner configuration, both soot precursors and soot formation are analyzed. Computational mesh independence is addressed here by refining grid elements in such a way that element sizes in the reaction zone are of about 30µm, thus capturing species and temperature gradients in such regions. The NBP (Narayanaswamy, Blanquart and Pitsch Stanford University mech) chemical kinetic mechanism featuring 149 chemical species and 1651 reactions is used for describing gas phase chemistry. Radiation effects are addressed using the discrete ordinates method (DOM) and computing the associated absorption coefficient from a WSGG model. Two soot formation models, an acetylene-based semiempirical and a statistical PAH-based method of moments (MOM), are employed in the soot-related numerical simulations carried out. Temperature profiles predicted using the MOM soot formation model are in fair agreement with the experimental results (peak temperature discrepancies of about 3%). Along the flame centerline and near the burner surface, predicted soot volume fractions match as well the corresponding experimental trends. In the radial direction however, both models lack of precision for describing the soot peak values and their physical location. From the species molar fractions results discussed here, it is observed that one and two aromatic ring groups are the most abundant PAH, so these PAH might be sufficient for soot nucleation purposes. The numerical models and methodologies developed in this work will be used in future for predicting soot formation in turbulent diffusion flames.
This study seeks to determine whether the Fruta del Norte project affected the main economic and social indicators of the Yantzaza canton, where the large-scale mining project is located. To do so, the analysis centers on key economic variables (such as business productivity and employment) and development variables (such as health and school enrollment). The specific methodology used is a synthetic control model, which enables the generation of a counterfactual for the treated canton. The findings suggest that Fruta del Norte had a positive impact on local economic activity in Yantzaza. The local economic dynamism spurred by Fruta del Norte had positive effects on local formal employment; however, increases in the rates of school dropout and adolescent pregnancy were observed.
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