Performance Evaluation of Two High‐Shear Impellers in an Unbaffled Stirred Tank

High‐shear impellers (HSIs) are mixers used in industrial stirred tanks to incorporate powders into liquids and break down particle agglomerates. A detailed numerical study of two commercial ring‐style HSIs of laboratory scale was carried out and their performance was compared with the Rushton turbine (RT). It was found that power and pumping numbers or their ratio cannot be simply connected for properly selecting an impeller in applications where highly localized viscous dissipation is desirable. The ratio of the average viscous dissipation in the impeller swept volume to the mean in the entire volume at two constant values of power input turned out to be lower for HSIs compared to that evaluated for RT. However, at higher power input, the dimensionless average viscous dissipation in the blade swept volume was found to be similar for the HSI of two rings and the RT, corroborating the high local viscous dissipation of this HSI when operated at higher speeds.     

A simple model for the semicontinuous heterophase polymerization: Ethyl methacrylate as a case example

A simple but comprehensive model considering homogeneous and micellar nucleation, coagulation, entry of radicals to particles and to micelles and radicals' exit from particles, is presented. The model is validated, in a starved semicontinuous heterophase polymerization of ethyl methacrylate, at three monomer addition rates. The model accurately describes the overall and instantaneous conversion, the average particle density and diameter, and the number and weight average molar masses evolutions over time. It is found that even though the average number of radicals is much smaller than 0.5, the system is not 0-1. An empirical function was used to describe the gel effect. The homogeneous nucleation was the prevailing mechanism for particle formation and large exit rates of radicals were observed. POLYM. ENG. SCI., 60: 223–232, 2019. © 2019 Society of Plastics Engineers     

Review of the environmental policy instruments in the standardization of H2 for the decarbonization of Mexico

The objective of this work is to review the environmental and ecological policy instruments that Mexican legislation for existence of an Official Mexican Hydrogen Standard according to the premises motivates decarbonization. There is a worldwide interest in hydrogen (H₂) and its incorporation into legal systems. In Mexico there are large legal gaps that question the legality of H₂, because it is not recognized in a federal law and is only considered in technical standards of voluntary application. Also, Mexico has forest, agricultural, and livestock waste that, if properly used, can cover the energy demand of communities. The main findings of this study refer to the fact that, according to international standards for the management of H₂ and taking into account the regulatory limitations in Mexico, it is possible to promote, an Official Mexican Standard exclusively aimed at establishing the minimum requirements for the design, construction, operation and maintenance of H₂ storage, considering the areas of the opportunity offered by foreign experiences, according to the Mexican context. It is concluded that the parameters of legality exist in the instruments of environmental policy, to support the existence of an Official Mexican Standard of H₂.     

User encoding for clustering in very sparse recommender systems tasks

Multimedia Tools and Applications - Recommender Systems are a very useful tool which let companies and service providers focus in the preferences of their customers, helping them to avoid an...     

Development and in vivo response of hydroxyapatite/whitlockite from chicken bones as bone substitute using a chitosan membrane for guided bone regeneration

Biomaterials that meet the requirements to stimulate bone tissue formation play a vital role in orthopedics and dentistry. In this work, chitosan and a biphasic, non-cytotoxic material hydroxyapatite/whitlockite were obtained from natural sources, which are available as organic waste. The osteogenic activity was assessed using a rabbit model animal with a chitosan barrier membrane in combination with a bone-filling graft substitute composed of hydroxyapatite/whitlockite. FT-IR results showed the typical absorption bands of the chitosan and hydroxyapatite. Moreover, the X-ray diffraction pattern revealed a typical hexagonal phase of hydroxyapatite and rhombohedral structures related to whitlockite. Masson's trichrome stain showed an early formation of extracellular matrix mineralized, in accord with the surface morphology of a cortical mature bond observed by Scanning Electron Microscopy. The immunocytochemistry results showed a significant increase of positive immunoreactive cells to osteonectin in the treated defects in comparison with the control defects 6 and 8 weeks postoperatively. Overall, the results confirm that the use of this low-cost and versatile biomaterial as a barrier membrane and a bone substitute graft are useful for bone tissue engineering.     

Real‐time monitoring by proton relaxometry of radical polymerization reactions of acrylamide in aqueous solution

The potential of time‐domain nuclear magnetic resonance (TD‐NMR) for the real‐time monitoring of solution radical polymerizations is demonstrated. A model system composed of a redox‐pair initiator system, acrylamide as monomer and water as solvent was investigated. A second‐generation continuous wave free precession technique was employed to measure the longitudinal relaxation time constant (T₁) of the samples throughout the polymerization reactions. This parameter was shown to be sensitive to the reactant feed free‐radical enhancement of the water molecule relaxation time, making it a good probe to monitor monomer conversion in real time in an automated, non‐destructive fashion. It was found that the T₁ value was better than the transverse relaxation time constant (T₂) for describing the evolution of the polymerization reactions, due to its greater sensitivity to paramagnetic effects. The TD‐NMR signal variation observed was linked to the formation, propagation and termination steps of the radical polymerization kinetics scheme. These first results may contribute to the application of real‐time monitoring of radical polymerization reactions employing low‐cost and robust TD‐NMR spectrometers. © 2018 Society of Chemical Industry     

Dry Fractionation of Cupuassu (Theobroma grandiflorum) Fat: Physical–Chemical Properties and Polymorphic Behavior

Physical chemical properties of cupuassu fat were modified by dry fractionation. Stearin and olein fractions were obtained at 29, 26, and 24 °C. Polymorphic behavior of unfractionated cupuassu fat (UCF) and its fractions were studied in situ by small-angle (SAXS) and wide-angle (WAXS) X-ray scattering using synchrotron light. Polymorphic transitions were followed in real time tempering samples with a thermal cycle. For UCF, the main polymorphic form crystallized under selected conditions was the β’₂. α and β’₁-forms appeared in trace amounts. β₂-form was obtained after storage at 25 °C for 3 months. Stearins obtained at 26 (S-26) and 24 °C (S-24) showed a similar polymorphic behavior. However, S-26 with improved physical properties might be more suitable for chocolate production or as a trans-fat alternative than UCF. Stearin fraction obtained at 29 °C (S-29) had a complex polymorphic behavior. The α-form was the first polymorphic form detected followed by β’₂-form. There was a polymorphic transition from α to β’₁-form but no transition between β’-forms. They were independent to each other showing fractionation in two different solid solutions. Increased contents of the triacylglycerols (TAG) SOA and SOB together with lower contents of SOO compared to UCF led to co-crystallization because there was no complete compatibility among all TAG present in S-29. β₁-form crystallized after storage forming crystals with a double-layer arrangement and a characteristic morphology. This form could be useful for accelerating crystallization process in melted liquid systems.     

Influence of carboxymethylation on the gelling capacity,rheological properties,and antioxidant activity of feruloylated arabinoxylans from different sources

Feruloylated arabinoxylans (FAX) are gelling polysaccharides presenting antioxidant activity (AC) and potential application as delivery systems. The influence of carboxymethylation on the gelling capacity, rheological properties, and AC of FAX from wheat flour (FAX1) and maize distillers grains (FAX2) was analyzed. The degree of substitution of carboxymethyl groups was 0.27 and 1.77 for carboxymethylated FAX1 (CFAX1) and FAX2 (CFAX2), which presented a change in M _n from 446 to 362 kDa and from 120 to 180 kDa, and a loss in FA content from 1.05 to traces and from 10.13 to 0.12, respectively, after carboxymethylation. G′ value at the end of rheological tests for FAX1 (71 Pa) and FAX2 (726 Pa) was higher than the corresponding G″ value. In contrast, G″ value for CFAX1 (0.35 Pa) and CFAX2 (0.03 Pa) was higher than the respective G′ value, indicating that they do no form gels. The AC increased in CFAX1 in relation to FAX1 from 4.49 to 8.30 mmol Trolox equivalent antioxidant capacity (TEAC) kg⁻¹, respectively, while it decreased in CFAX2 with regard to FAX2 from 11.31 to 9.43 mmol TEAC kg⁻¹, respectively. Carboxymethylation could be a path to design FAX derivatives offering alternative potential applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48325.     

Validation of scientific topic models using graph analysis and corpus metadata

Probabilistic topic modeling algorithms like Latent Dirichlet Allocation (LDA) have become powerful tools for the analysis of large collections of documents (such as papers, projects, or funding applications) in science, technology an innovation (STI) policy design and monitoring. However, selecting an appropriate and stable topic model for a specific application (by adjusting the hyperparameters of the algorithm) is not a trivial problem. Common validation metrics like coherence or perplexity, which are focused on the quality of topics, are not a good fit in applications where the quality of the document similarity relations inferred from the topic model is especially relevant. Relying on graph analysis techniques, the aim of our work is to state a new methodology for the selection of hyperparameters which is specifically oriented to optimize the similarity metrics emanating from the topic model. In order to do this, we propose two graph metrics: the first measures the variability of the similarity graphs that result from different runs of the algorithm for a fixed value of the hyperparameters, while the second metric measures the alignment between the graph derived from the LDA model and another obtained using metadata available for the corresponding corpus. Through experiments on various corpora related to STI, it is shown that the proposed metrics provide relevant indicators to select the number of topics and build persistent topic models that are consistent with the metadata. Their use, which can be extended to other topic models beyond LDA, could facilitate the systematic adoption of this kind of techniques in STI policy analysis and design.