Assessment of viscoelastic crack bridging toughening in refractory materials

Viscoelastic bridges can be formed in refractory ceramics while cooling from high temperatures. Such bridges can shield crack tips, thus reducing the effective crack tip stress intensity factors leading to higher resistance to creep and thermal shock. The extent to which the crack tip stress intensity is reduced can be estimated from fracture mechanics models that include experimental measurement of crack bridging and microstructural parameters. In this paper a novel approach is proposed for the assessment of the effective crack bridging toughening from combining destructive and non-destructive test methods. Fracture toughness values were determined applying chevron notched specimen technique and surface damage of the specimen was monitored by image analysis. Different cordierite–mullite compositions characterized by different microstructure morphologies and crack propagation behaviour were investigated. A brief discussion about the correlation between thermo-mechanical properties, microstructure, crack propagation behaviour and thermal shock resistance is presented. Moreover, an empirical model able to determine the presence and effectiveness of the viscoelastic crack bridging ligaments acting in the microstructure under thermal shock conditions and their degradation with increasing thermal shock cycles from parameters measured at room temperature is presented.     

Adaptation of the musical composition method for solving constrained optimization problems

Many real-world problems may be expressed as nonlinear constrained optimization problems (CNOP). For this kind of problems, the set of constraints specifies the feasible solution space. In the last decades, several algorithms have been proposed and developed for tackling CNOP. In this paper, we present an extension of the “Musical Composition Method” (MMC) for solving constrained optimization problems. MMC was proposed by Mora et al. (Artif Intell Rev 1–15, doi:10.1007/s10462-011-9309-8, 2012a). The MMC is based on a social creativity system used to compose music. We evaluated and analyzed the performance of MMC on 12 CNOP benchmark cases. The experimental results demonstrate that MMC significantly improves the global performances of the other tested metaheuristics on some benchmark functions.     

Comparison of composition and antioxidant capacity of some cereals and pseudocereals

Polyphenols, phenolic acids, fibres and antioxidant capacity were determined in water, acetone and methanol extracts of buckwheat, rice, soybean, quinoa and 3 amaranth cultivars. Their antioxidant activities were comparatively assessed by total radical‐trapping antioxidative potential (TRAP), ferric ion‐reducing antioxidant power (FRAP), cupric‐reducing antioxidant capacity (CUPRAC) and nitric oxide (NO^?) assays, which comprised of contributions from polyphenols and phenolic acids (especially from the most abundant ferulic acid). The correlation coefficients between polyphenols and antioxidant activities of cereal and pseudocereal methanol extracts with FRAP, NO^?, CUPRAC and TRAP were 0.99, 0.97, 0.96 and 0.77, respectively. The weakest correlation was with dietary fibres, an average one exhibited with tannins and marked correlation was shown with the phenolics. All the applied methods have shown that pseudocereals have higher antioxidant activity than some cereals (rice and buckwheat) and can be successfully replaced by cereals in case of allergy.     

Enzymatic Polymerization of Phosphonate Nucleosides

5′‐O‐Phosphonomethyl‐2′‐deoxyadenosine (PMdA) proved to be a good substrate of the Therminator polymerase. In this article, we investigated whether the A, C, T and U analogues of this phosphonate nucleoside (PMdN) series can function as substrates of natural DNA polymerases. PMdT and PMdU could only be polymerized enzymatically to a limited extent. Nevertheless, PMdA and PMdC could be incorporated into a DNA duplex with complete chain elongation by all the DNA polymerases tested. A mixed sequence of four nucleotides containing modified C, T and A residues could be obtained with the Vent(exo^?) and Therminator polymerases. The kinetic values for the incorporation of PMdA by Vent(exo^?) polymerase were determined; a reduced K_M value was found for the incorporation of PMdA compared to the natural substrate. Future polymerase directed evolution studies will allow us to select an enzyme with a heightened capacity to process these modified DNA building blocks into modified strands.     

Redox stable Ni-YSZ anode support in solid oxide fuel cell stack configuration

State-of-the-art nickel-based SOFC anode-supported cells are highly sensitive to reoxidation of the metal phase at the temperature of utilization. This work presents results on redox stable nickel-YSZ (yttria-stabilized zirconia) anode-supported cells, for both smaller and larger scale cells. A 55 cm² cell was mounted in a SOFC stack repeat element and tested over 40 full redox cycles. Performances and electrochemical impedance results of the repeat element are compared to the smaller sized cells of similar anode support structure.     

Influence of Ni on martensitic phase transformations in NiTi shape memory alloys

High-precision data on phase transformation temperatures in NiTi, including numerical expressions for the effect of Ni on M_S, M_F, A_S, A_F and T₀, are obtained, and the reasons for the large experimental scatter observed in previous studies are discussed. Clear experimental evidence is provided confirming the predictions of Tang et al. 1999 [19] regarding deviations from a linear relation between the thermodynamic equilibrium temperature and Ni concentration. In addition to affecting the phase transition temperatures, increasing Ni contents are found to decrease the width of thermal hysteresis and the heat of transformation. These findings are rationalized on the basis of the crystallographic data of Prokoshkin et al. 2004 [68] and the theory of Ball and James [25]. The results show that it is important to document carefully the details of the arc-melting procedure used to make shape memory alloys and that, if the effects of processing are properly accounted for, precise values for the Ni concentration of the NiTi matrix can be obtained.