Gelation Time of Hexamethylenetetramine Polymer Gels Used in Water Shutoff Treatment

Among the methods available to reduce water production, injecting a gelling system composed of a polymer and a crosslinker has been widely used. In this work, a hydrogel was prepared by crosslinking of an aqueous solution containing hexamethylenetetramine (HMTA) as crosslinker, hydrochloric acid (HCl) as an activator, and the co-polymer of 2-acrylamido-2methyl-propanesulfonic-acid sodium salt (AMPS) and acrylamide (PAMPS). In order to indicate the effective factors on the gelation time and also to develop the quadratic mathematical models, central composite design (CCD) was applied. Therefore, the main purpose was to establish functional relationship between the three factors (polymer concentration, HMTA, and hydrochloric acid) and a response (gelation time) by using a statistical technique. In order to determine the optimum value of these factors for maximum gelation time, a simultaneous optimization was also applied. The results of the analysis of variance (ANOVA) of the developed model illustrated that the fitted model was significant in a 99% confidence limit. The results showed that hydrochloric acid was identified as the main factor effecting the gelation time and there was also an interaction between HMTA and hydrochloric acid. Finally, a mechanism for the reaction between PAMPS and HMTA were presented

Multi-cation perovskites prevent carrier reflection from grain surfaces

© 2020, The Author(s), under exclusive licence to Springer Nature Limited. The composition of perovskite has been optimized combinatorially such that it often contains six components (AxByC1−x−yPbXzY3−z) in state-of-art perovskite solar cells. Questions remain regarding the precise role of each component, and the lack of a mechanistic explanation limits the practical exploration of the large and growing chemical space. Here, aided by transient photoluminescence microscopy, we find that, in perovskite single crystals, carrier diffusivity is in fact independent of composition. In polycrystalline thin films, the different compositions play a crucial role in carrier diffusion. We report that methylammonium (MA)-based films show a high carrier diffusivity of 0.047 cm2 s−1, while MA-free mixed caesium-formamidinium (CsFA) films exhibit an order of magnitude lower diffusivity. Elemental composition studies show that CsFA grains display a graded composition. This curtails electron diffusion in these films, as seen in both vertical carrier transport and surface potential studies. Incorporation of MA leads to a uniform grain core-to-edge composition, giving rise to a diffusivity of 0.034 cm2 s−1 in CsMAFA films. A model that invokes competing crystallization processes allows us to account for this finding, and suggests further strategies to achieve homogeneous crystallization for the benefit of perovskite optoelectronics

Stilbopinae, a new subfamily for the Iranian fauna

Systematic study of Ichneumonidae was carried out during 2009 to 2012 in Sari region and suburb.In this study Malaise trap, Window trap, Yellow Pan trap, Light trap and Sweeping trap were used for collecting. Stilbops vetula (Gravenhorst, 1829) from Stilbopinae subfamily is reported for the first time from Iran

Effect of the Type of Restorative Material on Bonding Efficacy and Microleakage of a Self-Etching Adhesive System

Background: Prompt L-Pop is a self-etching dentin adhesive, which is recommended to use with both compomers and composite resins. The aims of this investigation were to determine and compare the microleakage, shear bond strength, and shear push out strength of composite and compomer to dentin with application of Prompt L-Pop as adhesive system. Methods: After application of Prompt L-Pop on the occlusal dentinal surfaces of 24 intact molar teeth, the specimens were divided into two groups (n=12). Composite resin(Filtec Z250) and compomer (F2000) were used to dentinal surfaces of group 1 and 2 respectively, using a plastic mold. Twenty-four truncated cavities were prepared in 24 horizontal occlusal coronal dentinal wafer. After application of Prompt L-Pop, the specimens divided into two groups (n=12), and the cavities in group 1 and 2 were filled with composite and compomer respectively. After application of Prompt-L-Pop on the surfaces of 20 class V cavities, the cavities were randomly divided into two groups (n=10), and were restored with composite resin and compomer respectively. The bond strength values and microleakage scores of groups were evaluated. Results: Compomer material revealed more but not statistically significant different means (SD) of shear bond strengths (Mpa) and shear push out strength (MPa). There were no significant differences in enamel and also dentinal microleakage scores, between two groups (p>0.05). Conclusion: Improving bonding efficacy and microleakage result of compomer in this study, would be because Prompt LPop is a water based material and therefore chemically more compatible with hydrophilic restorative materials, such as compomers. Keywords: Restorative material, Bond strength, Microleakage, self-etching adhesive system, Composite, Compomer

Hybrid Learning Using Genetic Algorithms and Decision Trees for Pattern Classification

This paper introduces a hybrid learning methodology that integrates genetic algorithms (GAs) and decision tree learning (ID3) in order to evolve optimal subsets of discriminatory features for robust pattern classification. A GA is used to search the space of all possible subsets of a large set of candidate discrimination features. For a given feature subset, ID3 is invoked to produce a decision tree. The classification performance of the decision tree on unseen data is used as a measure of fitness for the given feature set, which, in turn, is used by the GA to evolve better feature sets. This GA-ID3 process iterates until a feature subset is found with satisfactory classification performance. Experimental results are presented which illustrate the feasibility of our approach on difficult problems involving recognizing visual concepts in satellite and facial image data. The results also show improved classification performance and reduced description complexity when compared against sta..