Effect of Tempering on the Oxidation Behaviour of a Roll-Grade High-Speed Steel During Thermal Cycling

Oxidation of Metals - The oxidation characteristics of a roll-grade high-speed steel with different tempering heat treatments were studied under thermal cycling conditions at 650 °C...     

Partial hydrogenation of propyne over copper-based catalysts and comparison with nickel-based analogues

The partial hydrogenation of propyne was studied over copper-based catalysts derived from Cu–Al hydrotalcite and malachite precursors and compared with supported systems (Cu/Al₂O₃ and Cu/SiO₂). The as-synthesized samples and the materials derived from calcination and reduction were characterized by XRF, XRD, TGA, TEM, N₂ adsorption, H₂-TPR, XPS, and N₂O pulse chemisorption. Catalytic tests were carried out in a continuous flow-reactor at ambient pressure and 423–523 K using H₂:C₃H₄ ratios of 1–12 and were complemented by operando DRIFTS experiments. The propyne conversion and propene selectivity correlated with the copper dispersion, which varied with the type of precursor or support and the calcination and reduction temperatures. The highest exposed copper surface was attained on hydrotalcite-derived catalysts, which displayed C₃H₆ selectivity up to 80% at full C₃H₄ conversion and stable performance in long-run tests at T ? 473 K. Both activated Cu–Al hydrotalcites (this work) and Ni–Al hydrotalcites [S. Abelló, D. Verboekend, B. Bridier, J. Pérez-Ramírez, J. Catal. 259 (2008) 85] exhibited a relatively high alkene selectivity under optimal operation conditions, but they present a markedly distinctive catalytic behavior with respect to temperature and hydrogen-to-alkyne ratio. The product distribution was assigned through Density Functional Theory (DFT) simulations to the different stability of subsurface phases (carbides, hydrides) and the energies and barriers for the competing reaction mechanisms. The behavior of Cu in partial alkyne hydrogenation resembles that of Au nanoparticles, while Ni is closer to Pd.     

Improvements in star photometry for aerosol characterizations

This work addresses the applicability of the Astronomical Langley method to retrieve accurate calibration constants for a star photometer at a high mountain site. For this application, this method provides more accurate and reliable calibration constants than the classical Langley method. The Astronomical Langley method has been also tested in an urban environment using one year of star photometer measurements in the city of Granada (37.16°N, 3.60°W, 680 m a.s.l.). Under low and stable aerosol load conditions the calibration constants obtained are close to those retrieved at altitude. Finally, an analysis of the applicability of the one-star and classical two-star methods to retrieve aerosol optical depth (δ_A(λ)) at night is performed. For the one-star method the estimated errors in δ_A(λ) are close to 0.02 for λ<800 nm and 0.01 for λ>800 nm. For the two-star method the uncertainties are larger than those obtained by the one-star method, and thus can lead to unreliable values of the δ_A(λ). As a concluding remark, we consider that the one-star method is more appropriate, especially in an urban environment.     

Phytochemical Composition and in Vitro Analysis of Nopal (O. Ficus-Indica) Cladodes at Different Stages of Maturity

This study aimed to determine the phytochemical profile and nutraceutical properties of nopal cladodes (Opuntia ficus-indica) at different stages of maturity. Medium-age cladodes showed the highest total saponins, phytosterols, and indigestible fiber, as well as the highest in vitro antioxidant capacity and digestive enzymes inhibitory activity. Furthermore, these cladodes presented the highest content of p-hydroxybenzoic acid, p-coumaric acid, rutin, narcissin, nicotiflorin, β-sitosterol, and sitosteryl-3-β-glucopyranoside, as well as several amino acids, organic acids, and fatty acids. Whereas young cladodes contained the highest concentration of condensed and hydrolyzable tannins. These results demonstrated that maturity affects the nutritional and nutraceutical properties of nopal cladodes.     

Transformation During Aging of Niobium-Rich Carbides in Cast Heat-Resistant Alloys

Metallurgical and Materials Transactions A - The changes occurring in two heat-resistant alloys while aged at 750&nbsp;°C for different periods of time were studied. Aging promoted...     

Integrating affective learning into intelligent tutoring systems

Affectivity has influence in learning face-to-face environments and improves some aspects in students, such as motivation. For that reason, it is important to integrate affectivity elements into virtual environments. We propose a conceptual model that suggests which elements of tutor, student and dialogue should be integrated and implemented into learning systems. We design an ontology guided by methontology, and apply a mathematical evaluation (OntoQA) to determine the richness of the proposed model. The mathematical evaluation states that the proposed model has relationship richness and horizontal nature. We developed a software application implementing the conceptual model in order to prove its effectivity to generate students’ motivation. The findings suggest that the implemented affective learning ontology impacts positively the motivation in students with low academic performance, in female students and in engineering students.     

An integrated approach to Deacon chemistry on RuO2-based catalysts

Rationally designed RuO₂-based Deacon catalysts can contribute to massive energy saving compared to the current electrolysis process in chemically recycling HCl to produce molecular chlorine. Here, we report on our integrated approach between state-of-the-art experiments and calculations. The aim is to understand industrial Deacon catalyst in its realistic surface state and to derive mechanistic insights into this sustainable reaction. We show that the practically relevant RuO₂/SnO₂ consists of two major RuO₂ morphologies, namely 2–4 nm-sized particles and 1–3-ML-thick epitaxial RuO₂ films attached to the SnO₂ support particles. A large fraction of the small nanoparticles expose {1 1 0} and {1 0 1} facets, whereas the film grows with the same orientations, due to the preferential surface orientation of the rutile-type support. Steady-state Deacon kinetics indicate a medium-to-strong positive effect of the partial pressures of reactants and deep inhibition by both water and chlorine products. Temporal Analysis of Products and in situ Prompt Gamma Activation Analysis strongly suggest a Langmuir–Hinshelwood mechanism and that adsorbed Cl poisons the surface. Under relevant operation conditions, the reactivity is proportional to the coverage of a specific atomic oxygen species. On the extensively chlorinated surface that can be described as surface oxy-chloride, oxygen activation is the rate-determining step. DFT-based micro-kinetic modeling reproduced all experimental observations and additionally suggested that the reaction is structure sensitive. Out of the investigated models, the 2 ML RuO₂ film-covered SnO₂ gives rise to significantly higher reactivity than the (1 0 1) surface, whereas the 1 ML film seems to be inactive.     

Linkages in tubulin-colchicine functions: the role of the ring C (C') oxygens and ring B in the controls

Linkages between structural components of colchicine (COL) and its biphenyl analogues (allocolchicine, ALLO, and its analogues) in the binding to tubulin and its functional consequences were scrutinized. Three ring ALLO analogues with the carbomethoxyl in position 4' of ring C' replaced by a carbomethyl (KAC) and methoxy (MAC) groups were synthesized. The binding properties and consequences of binding (microtubule inhibition, abnormal polymerization, and induction of GTPase activity) were compared within the series of three ring and two ring compounds, as well as between pairs consisting of a two ring and a three ring compound with identical groups in position 4'. Binding measurements showed that the binding of KAC to the COL binding site proceeded with similar chemical characteristics as that of its two ring analogue (TKB), but with the kinetic characteristics of ALLO. The binding constant of KAC was found to be 1.9 x 10(6) M-1 and that of MAC was 4.6 x 10(5) M-1. The binding strength of the three ring analogues in descending order was KAC > ALLO > MAC, with increments similar to the biphenyl compounds, TKB > TCB > TMB. The difference in binding affinities between the pairs of three ring and two ring molecules was invariant (delta delta G degree = -1.3 +/- 0.2 kcal/mol-1), showing that in all cases ring B makes only an entropic contribution by suppressing free rotation about the biaryl bond. In the case of microtubule inhibition, all three ring compounds inhibited strongly with similar potencies, even though the spread in inhibition strength between the corresponding two ring molecules was > 3.3 kcal mol-1 of free energy. This difference was interpreted in terms of the ability of the various molecules to maintain tubulin in the proper conformation for binding in abnormal geometry to the growth end of a microtubule. This ability attains a maximal plateau value for three ring compounds, independently of the oxygen-containing group in ring C' (or C) and is maintained for the methyl ketone whether in a two or three ring compound. The induction of the GTPase activity was found to follow in general the binding affinity, with the exception that molecules that contained a methyl ketone were stronger GTPase inducers than expected from their alignment according to binding affinity. The finding that the binding of tropolone methyl ether (ring C of COL) induced a GTPase activity shows that ring C contains the ability to induce both substoichiometric microtubule inhibition and GTPase activity. Rings A and B act only as anchors in the binding, with ring A making an energetic contribution, while the effect of ring B is only entropic. It was concluded that both microtubule assembly inhibition and induction of GTPase activity were modulated by the same postbinding conformational change in tubulin. The difference between the strengths of these activities induced by ligands reflects the difference between a narrow allosteric effect between two well-defined sites in the case of GTPase activity and a broad effect aimed at the multiple sites involved in the incorporation of a tubulin protomer into the microtubule structure. Thus, there seems to be a loose thermodynamic linkage between binding and GTPase activity, while there is none between binding and microtubule inhibition, the two phenomena being linked only kinetically.     

Biodegradation of 2,4,6-trichlorophenol in a packed-bed biofilm reactor equipped with an internal net draft tube riser for aeration and liquid circulation

For the aerobic biodegradation of the fungicide and defoliant 2,4,6-trichlorophenol (2,4,6-TCP), a bench-scale packed-bed bioreactor equipped with a net draft tube riser for liquid circulation and oxygenation (PB-ALR) was constructed. To obtain a high packed-bed volume relative to the whole bioreactor volume, a high A(D)/A(R) ratio was used. Reactor's downcomer was packed with a porous support of volcanic stone fragments. PB-ALR hydrodynamics and oxygen mass transfer behavior was evaluated and compared to the observed behavior of the unpacked reactor operating as an internal airlift reactor (ALR). Overall gas holdup values epsilon(G), and zonal oxygen mass transfer coefficients determined at various airflow rates in the PB-ALR, were higher than those obtained with the ALR. When comparing mixing time values obtained in both cases, a slight increment in mixing time was observed when reactor was operated as a PB-ALR. By using a mixed microbial community, the biofilm reactor was used to evaluate the aerobic biodegradation of 2,4,6-TCP. Three bacterial strains identified as Burkholderia sp., Burkholderia kururiensis and Stenotrophomonas sp. constituted the microbial consortium able to cometabolically degrade the 2,4,6-TCP, using phenol as primary substrate. This consortium removed 100% of phenol and near 99% of 2,4,6-TCP. Mineralization and dehalogenation of 2,4,6-TCP was evidenced by high COD removal efficiencies ( approximately 95%), and by the stoichiometric release of chloride ions from the halogenated compound ( approximately 80%). Finally, it was observed that the microbial consortium was also capable to metabolize 2,4,6-TCP without phenol as primary substrate, with high removal efficiencies (near 100% for 2,4,6-TCP, 92% for COD and 88% for chloride ions).