Effective elastic properties and residual stresses in directionally solidified eutectic Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/YAG/ZrO<Subscript>2</Subscript> ceramics estimated by finite element analysis

Effective elastic properties and residual stresses were assessed in directionally solidified ternary eutectic ceramic, Al₂O₃/YAG/ZrO₂, by finite element analyses. A 3D finite element model was generated from a CT scan, representative of the microstructure and with a similar volume fraction. Effective elastic properties were calculated by numerical homogenisation. They highlight a quasi-isotropic behaviour of the ternary eutectic ceramics. Despite the difficulties to measure the strain, the dispersion observed in the results and the limited reliability of the materials properties, the results constitute a step towards a better understanding of the material behaviour. Thermal residual stresses induced by the manufacturing were also evaluated. Tensile residual stresses in yttria-stabilised zirconia and compressive residual stresses in YAG and alumina were highlighted. This evaluation also shed light on the influence of the phase morphology in the microstructure. Indeed, the computed spatial distribution of the residual stresses showed that they are different from one position to another due to the variation in phase morphology and also to material properties variability. Therefore, it is important when numerically assessing the thermomechanical properties to take into account the microstructure morphology as well as the variability of material properties.     

Combinatorial auctions for exchanging resources over a grid network

In grid systems, users compete for different types of resources such that they may execute their applications. Traditional grid systems are formed of organisations that join together for the purpose of collaborative projects. Resources of each of the participating organisation are pooled such that members of individual organisations may access the shared infrastructure. In general, each participant is both a provider and a consumer of resources. Whilst such systems address large organisations, in this paper we address democratic grid systems to satisfy needs of small organisations and even individuals, where on-demand grids may be formed by drawing idling resources available on the Internet. Whilst traditional grid systems resort to allocations that satisfy system specific objectives such as maximization of the resource utilisation, market mechanisms try to obtain allocations that are efficient economically. Economic mechanisms permit to achieve equilibrium between supply and demand and furthermore provide incentives for providers. Combinatorial auction has been argued as an effective mechanism to address the problem of resource allocation within grid systems. Auctions within which multiple types of resources in varying quantities may be traded eliminate the exposure problem by addressing co-allocation. In this paper, we describe a combinatorial exchange where multiple providers and multiple consumers may participate. We describe the winner determination problem that incorporates the time dimension, i.e. resource bundles may be requested for different time ranges, and describe a set of heuristics that have been designed to be fast. We show that these achieve a high level of efficiency as compared to exact solutions. The second part focusses on the pricing problem. The objective is to compute prices that represent the state of the market and bring trustworthy feedback to participants. Drawing on the approach taken by Kwasnica et al. (Manage Sci 51(3):419–434, 2005), we propose a pricing model that computes per-item pricing. Per-item pricing allows users to deduce the price of bundles that they require by linear summation. Furthermore, we propose a model that computes prices as a function of time, thus permitting users, in particular consumers to adjust their demand trading off price and time of execution.     

Local microstructural modification in dynamically consolidated metal powders

Powders of 4330V steel, aluminum-6 pct silicon, and copper have been dynamically consolidated under well-characterized conditions using shock waves. Different regions in the final microstructures correlate well with the shock conditions during compaction, demonstrating the importance of the shock history in determining the final microstructure. Martensite is observed to form locally at powder particle surfaces in compacts of 4330V steel, and interparticle melting and rapid re-solidification are observed in compacts of aluminum-6 pct silicon. Microprobe analyses of locally melted regions in the aluminum alloy indicate a homogeneous distribution of 6 pct silicon, well above the maximum equilibrium solid solubility. Comparison with the structure of “splat caps,” found in the starting powder, suggests that locally melted regions experience a cooling rate comparable to that obtained in splat quenching. The extent of martensite formation and local melting are in good agreement with current models for energy deposition at powder particle surfaces during consolidation. The general implications of the analysis and observations are discussed.     

Max–min fair survivable networks

In this paper, we discuss applications of max–min fairness (MMF) in survivable networks. We focus on two specific applications intended to face failure situations and provide several computational results for each of them. The first application, called simple robust routing, generalizes the multipath routing in order to achieve acceptable levels of traffic demand satisfaction in case of single link failures while avoiding classical rerouting procedures. Such a method can be seen as a special case of dedicated resource recovery schemes. The second application is concerned with two shared resource restoration strategies and the corresponding problems of computing the MMF minimum traffic demand satisfaction ratio vectors associated with the set of single link failures. We consider the local rerouting and end-to-end rerouting without stub-release strategies. Computational results for realistic network instances provide a comparison of different routing and rerouting strategies in terms of traffic satisfaction rate. The question of estimating the bandwidth overhead, which can be required by the “simple robust routing scheme” in comparison with the classical restoration schemes, is also studied and answers based on computational results are provided. This work is in continuation of our earlier works on MMF (Nace et al., IEEE Trans Netw 14:1272–1281, 2006; Nace et al., Comput Oper Res 35:557–573, 2008).     

Cationic polymerization of high-molecular-weight phthalaldehyde-butanal copolymer

Low ceiling temperature polyaldehydes are of interest for transient materials because the temperature of depolymerization can be at or below room temperature. There is interest in expanding the number of aldehydes which can be copolymerized so as to change the vapor pressure and other properties of the depolymerized products. Although fast depolymerization has been achieved with polyaldehydes, the rate of monomer evaporation after depolymerization can be controlled by incorporating lower molecular weight monomers into the polymer. High vapor pressure aliphatic aldehydes have been copolymerized with low vapor pressure and high reactivity phthalaldehyde to create stable, high molecular weight polymers with high vapor pressure. A method for measuring the depolymerization time by quartz crystal microbalance has been developed. The copolymer of phthalaldehyde and butanal improves the evaporation time for the polymer by a factor of 11. The onset of thermal decomposition of the copolymer was increased from 107 °C for the phthalaldehyde homopolymer to 141 °C for the copolymer. The tensile strength of the copolymer was 0.8–1.6 GPa. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46921.     

Operating characteristics of aqueous magnetite electrochemical capacitors

Operating characteristics, including capacitance, leakage current, operating potential range, cycling stability and open-circuit self-discharge behaviours, of the magnetite (Fe₃O₄) supercapacitor, containing 10 wt % carbon black as conductive additive, in aqueous electrolytes of Na₂SO₃, KOH and Na₂SO₄ were investigated. Although the capacitance of the oxide was found to depend heavily on electrolyte composition, the self-discharge mechanism in these electrolytes appeared to be the same. Reduction in the dissolved oxygen content (DOC) of the electrolyte reduced the leakage current and profoundly improved the cycling stability. In particular, Na₂SO_3(aq) gives the highest capacitance, nearly 30 F (g-Fe₃O₄)^–1 or 80 F cm^–2 of actual surface area, with an operation range of 1.1 V based on a leakage current less than 0.1 mA F^–1, and the electrode showed no deterioration after 10⁴ cycles under a DOC < 0.1 ppm.     

X-ray photoelectron spectroscopic study of the ability to monofunctionalize polymer surfaces by low energy atomic bombardment

Low energy atomic bombardment is designed to limit the potentially reactive species to the atoms which are present in a radiofrequency (r.f.) plasma discharge. This might give the ability to monofunctionalize surfaces for specific applications such as biocompatibility. Bombardment of polystyrene and poly(trans)isoprene with nitrogen atoms does not result in the incorporation of any heteroatoms at the polymer surface. Other attempts were made on poly(acrylic acid) and poly(methyl methacrylate) without any results, even though the samples had been activated by argon ion bombardment; the thermalized atoms seem to have insufficient energy to functionalize these polymers. In contrast, ion bombardment performed with low energy nitrogen ions (500–1500eV) is able to incorporate a majority of amine functions. © 1998 Society of Chemical Industry.     

Study of an implicit scheme for integrating Maxwell's equations

We study theoretically and numerically an implicit scheme for solving Maxwell's equations. Space discretization is obtained by the finite element method, while Newmark's scheme provides the time discretization.