Influence of Specific Surface Area of Aluminium Powder on the reactivity of aluminium/ammonium perchlorate composition

Aluminium/ammonium perchlorate (40/60 wt.%) is a pyrotechnic composition widely used as an igniter charge for small calibre rocket motors. Five different types of aluminium powders with specific surface area varying from 0.52 m²/g to 6.00 m²/g have been studied to evaluate the influence of specific surface area on the ignition characteristics of the charge. While the peak pressure varies from 35.5 ksc to 54.5 ksc (0.30 g in 48.0 cm³ vol.), the corresponding time to P_max varies from 11.2 ms to 1.6 ms showing higher reactivity of the mix with increase in aluminium surface area. This order of reactivity agrees with the order of reactivity determined from the DTG curves of the metal oxidation by comparing the peak height to half width ratio. However, the total gas generated by all the charges is approximately the same and the difference in peak pressure is caused by the difference in the rate of reaction and after about 30 ms all the compositions exhibit the same order of temperature and pressure. The charge has got an ignition temperature of about 640 K and the ignition is preceded by the exothermic decomposition of ammonium perchlorate. The activation energy varies from 92.2 kJ/mol to 127.6 kJ/mol and the corresponding pre-exponential factor from 9.7 × 10⁶ min⁻¹ to 7.1 × 10⁹ min⁻¹ and they exhibit the kinetic compensation effect with an isokinetic temperature of 647 K.     

Green Nanosilver as Reinforcing Eco-Friendly Additive to Epoxy Coating for Augmented Anticorrosive and Antimicrobial Behavior

Epoxy resin GY250 representing diglycidyl ethers of bisphenol-A (DGEBA) was reinforced with 1, 3 and 5wt % of surface functionalized silver nanoparticles (F-AgNPs) which were synthesized using Couroupita guianensis leaves extract with a view of augmenting the corrosion control property of the epoxy resin and also imparting antimicrobial activity to epoxy coatings on mild steel. Corrosion resistance of the coatings was evaluated by EIS, potentiodynamic polarization studies and cross scratch tests. AFM, SEM, HRTEM and EDX were utilized to investigate the surface topography, morphology and elemental composition of the coatings on MS specimens. Results showed that the corrosion resistance, hardness and T_g of the DGEBA/F-AgNPs coatings increased at 1wt % of F- AgNPs. The DGEBA/F-AgNPs coatings also offered manifold antimicrobial protection to the MS surfaces by inhibiting the growth of biofilm forming bacteria like P. aeruginosa, B. subtilis, the most common human pathogen E. coli and the most virulent human pathogenic yeast C. albicans.     

Mangiferin Inhibits Apoptosis in Doxorubicin-Induced Vascular Endothelial Cells via the Nrf2 Signaling Pathway

Doxorubicin increases endothelial permeability, hence increasing cardiomyocytes’ exposure to doxorubicin (DOX) and exposing myocytes to more immediate damage. Reactive oxygen species are major effector molecules of doxorubicin’s activity. Mangiferin (MGN) is a xanthone derivative that consists of C-glucosylxanthone with additional antioxidant properties. This particular study assessed the effects of MGN on DOX-induced cytotoxicity in human umbilical vein endothelial cells’ (HUVECs’) signaling networks. Mechanistically, MGN dramatically elevated Nrf2 expression at both the messenger RNA and protein levels through the upregulation of the PI3K/AKT pathway, leading to an increase in Nrf2-downstream genes. Cell apoptosis was assessed with a caspase-3 activity assay, transferase-mediated dUTP-fluorescein nick end labeling (TUNEL) staining was performed to assess DNA fragmentation, and protein expression was determined by Western blot analysis. DOX markedly increased the generation of reactive oxygen species, PARP, caspase-3, and TUNEL-positive cell numbers, but reduced the expression of Bcl-2 and antioxidants’ intracellular concentrations. These were effectively antagonized with MGN (20 μM), which led to HUVECs being protected against DOX-induced apoptosis, partly through the PI3K/AKT-mediated NRF2/HO-1 signaling pathway, which could theoretically protect the vessels from severe DOX toxicity.     

Agricultural proteins as multifunctional additives in ZnO-free synthetic isoprene rubber vulcanizates

Corn zein and wheat gliadin protein are compounded into synthetic cis-1,4-polyisoprene rubber (IR) and sulfur-cured in a zinc oxide (ZnO)-free system. The curing kinetics and mechanical and morphological properties are compared to a ZnO-activated or carbon black (CB)-reinforced cure system. The proteins provide reversion resistance and reinforcement to IR at filler loadings as low as 1 part per hundred rubber (phr). The zein-IR composites exhibit higher moduli, better filler–matrix adhesion, and less filler agglomeration/migration than gliadin-IR because zein is more chemically compatible with IR. The gliadin-IR composites have a lower percent set and hysteresis, indicating the formation of an elastic restoring gliadin network. Optimal properties are achieved at 2-phr gliadin and 4-phr zein. At gliadin loading >2 phr and zein loading >4 phr, the protein domain size increases and mechanical properties deteriorate. At equal filler loading, property improvements over CB-IR are observed for one or both proteins. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48141.     

Crystal slip modeling of small strain yield behavior in textured copper tubing

A self-consistent polycrystalline model developed by Kr?ner, and Budiansky and Wu (KBW) was used to model small strain (2 and 8 × 10_-6) biaxial yield behavior in textured copper tubing. The results were compared to simulations using the Bishop-Hill model and a lower bound (LB) model which neglected strain compatibility. It was found that the Bishop-Hill model poorly represents texture effects whereas the KBW and LB models give accurate predictions of biaxial yield surfaces at these strain levels. A linear latent hardening law was used with both the KBW and LB model. Varying the latent hardening ratio an order of magnitude had little effect on the yield surface. Introducing the odd 1 coefficients of the generalized spherical harmonic expansion was also found to have negligible effect on the predicted yield loci. Formerly Graduate Student of Mechanical Engineering at Brigham Young University Formerly Graduate Student of Materials Science and Engineering at the University of Florida     

Forcing biological sciences into architectural design:On conceptual confusions in the field of biomimetic architecture

Certain confusion may be observed in the field of biomimetic architecture,as it emerges at the crossroad of two disciplinary domains:architectural design and bi...     

A Feature Selection Strategy to Optimize Retinal Vasculature Segmentation

Diabetic retinopathy (DR) is a complication of diabetes mellitus that appears in the retina. Clinitians use retina images to detect DR pathological signs related to the occlusion of tiny blood vessels. Such occlusion brings a degenerative cycle between the breaking off and the new generation of thinner and weaker blood vessels. This research aims to develop a suitable retinal vasculature segmentation method for improving retinal screening procedures by means of computer-aided diagnosis systems. The blood vessel segmentation methodology relies on an effective feature selection based on Sequential Forward Selection, using the error rate of a decision tree classifier in the evaluation function. Subsequently, the classification process is performed by three alternative approaches: artificial neural networks, decision trees and support vector machines. The proposed methodology is validated on three publicly accessible datasets and a private one provided by Hospital Sant Joan of Reus. In all cases we obtain an average accuracy above 96% with a sensitivity of 72% in the blood vessel segmentation process. Compared with the state-of-the-art, our approach achieves the same performance as other methods that need more computational power. Our method significantly reduces the number of features used in the segmentation process from 20 to 5 dimensions. The implementation of the three classifiers confirmed that the five selected features have a good effectiveness, independently of the classification algorithm.     

Regulating Li-Ion Transport through Ultrathin Molecular Membrane to Enable High-Performance All-Solid-State–Battery

Solid-state lithium metal batteries with garnet-type electrolyte provide several advantages over conventional lithium-ion batteries, especially for safety and energy density. However, a few grand challenges such as the propagation of Li dendrites, poor interfacial contact between the solid electrolyte and the electrodes, and formation of lithium carbonate during ambient exposure over the solid-state electrolyte prevent the viability of such batteries. Herein, an ultrathin sub-nanometer porous carbon nanomembrane (CNM) is employed on the surface of solid-state electrolyte (SSE) that increases the adhesion of SSE with electrodes, prevents lithium carbonate formation over the surface, regulates the flow of Li-ions, and blocks any electronic leakage. The sub-nanometer scale pores in CNM allow rapid permeation of Li-ions across the electrode–electrolyte interface without the presence of any liquid medium. Additionally, CNM suppresses the propagation of Li dendrites by over sevenfold up to a current density of 0.7 mA cm⁻² and enables the cycling of all-solid-state batteries at low stack pressure of 2 MPa using LiFePO₄ cathode and Li metal anode. The CNM provides chemical stability to the solid electrolyte for over 4 weeks of ambient exposure with less than a 4% increase in surface impurities.     

Effect of External Stress on the Behavior of Oxide Scales on 9Cr-1Mo Steel

Tensile specimens of 9Cr-1Mo steel weresubjected to oxidation in air at a temperature of 973 Kfor periods of 25, 47, 70, 97, 120, and 140 hr. Theintegrity of the oxide scale was examined by an in-situ technique which involved the recording of theacoustic-emission activity associated with the breakingof the scale. Specimens were also subjected to oxidationfor the same times after subjecting them to an external stress of 40 MPa. The applicationof the external stress was found to alter the integrityof the scale. Spalling of the scale occurred to a lesserextent when external stress was applied due to partial release of growth stresses becauseof the elongation of the specimen. The scale buckledbefore spalling when no external stress was applied. Onthe other hand, the scale developed wedge-type cracks before spalling when subjected toexternal stress during oxidation. Postoxidationexamination of the stressed specimen revealedsubstantial segregation of silicon and chromium at thegrain boundaries (oxide ridges). The specimens, which wereoxidized without external stress, revealed a reductionin the concentration of chromium on the surface. Thisbehavior was attributed to enhanced spalling in the case of the latter specimen compared to theformer.