Ba(Ti1−xSnx)O3 (x=0.13) Dielectric Ceramics Prepared by Coprecipitation

Fine-grain BaTi_0.87Sn_0.13O₃ (BTS₁₃) powder was synthesized from an oxalate precursor and used to prepare sintered ferroelectric BTS₁₃ ceramics. The evolution of the morphology and structure of a BTS₁₃ precipitate precursor as a function of temperature was analyzed. We compare the sintering behavior as well as the dielectric properties of the BTS₁₃ ceramics obtained using uniaxial and cold isostatic pressing.     

Robust design via simulation experiments: a modified dual response surface approach

The existing procedures for robust design, devised for physical experiments, may be too limiting when the system can be simulated by a computer model. In this paper we introduce a modification of the dual response surface modelling, which incorporates the option of stochastically simulating some of the noise factors when their probabilistic behaviour is known. Our method generalizes both the crossed and the combined array approaches and finds a natural application to integrated parameter and tolerance design. The method appears suitable for designing complex measurement systems and in this paper is applied to the design of a high‐precision optical profilometer. Copyright © 2008 John Wiley & Sons, Ltd.     

Porcine pancreatic lipase immobilized on polysiloxane–polyvinyl alcohol hybrid matrix: catalytic properties and feasibility to mediate synthesis of surfactants and biodiesel

Polysiloxane–polyvinyl alcohol hybrid matrix was prepared by a sol–gel technique and its capacity to bind porcine pancreatic lipase investigated. The loading of 250 units g^?1 support was shown to be effective, resulting in an immobilized lipase with high catalytic activity. Both free and immobilized lipases were characterized by determining the activity profile as a function of pH, temperature, substrate concentration and thermal stability. Application of the immobilized lipase in non‐conventional biocatalysis for the synthesis of surfactants and biodiesel was also analyzed. Production of sugar fatty acid esters was found to be dependent on the carbohydrate and the highest molar conversion (50% in 3–4 h of reaction) was achieved for substrates containing fructose and lauric or oleic acids. Biodiesel synthesis from babassu oil and ethanol, propanol or butanol was feasible and regardless of the kind of alcohols, results revealed that the immobilized PPL could efficiently convert triglycerides to fatty acid alkyl esters attaining yields varying from 75 to 95%. Copyright © 2007 Society of Chemical Industry     

CFD simulations of hydrogen combustion in a simplified EPR containment with CFX and REACFLOW

The prediction of over-pressures and temperatures that are generated by hydrogen explosions in case of a severe nuclear accident is a crucial stage of the safety analysis of the containment. The investigation presented in this paper is a continuation of the numerical studies of validation and benchmarking that were carried out in the European co-sponsored project HYCOM. In the present work, numerical simulations of hydrogen deflagrations within a simplified, real-scale European Pressure Reactor (EPR) containment have been performed with two CFD codes, CFX4 and REACFLOW. The analysis has been focused not only on overpressure peaks and pressure oscillations, but also on pressure differences between the two sides of the same wall of internal compartments. Different geometrical configurations have been considered in term of presence of vents between internal compartments and in term of vents number, size and position. Single and multiple ignition points have also been taken into account. The paper describes the main results of the investigation and it is a demonstration of how CFD modelling can provide significant indications for real-scale safety applications within the limits of uncertainty of the accident scenarios.     

Sub-critical fouling in a membrane bioreactor for municipal wastewater treatment: experimental investigation and mathematical modelling

Fouling is a major limitation for the application of membrane bioreactors (MBRs) in municipal wastewater treatment; the critical flux concept represents a valid tool for process optimisation in planning fouling control strategies. The paper presents the results obtained on a large pilot MBR equipped with a plate-and-frame ultrafiltration membrane. The experimental assessment of flux criticality was carried out by flux-stepping tests showing the positive impact of liquid temperature on the value of the critical threshold. The reliability of short-term tests was then verified over a long period by determining the time of sustainability, t(sust), of six different sub-critical fluxes ranging between 17 and 30Lm(-2)h(-1). An exponential fitting was observed in terms of fouling rate both before and after t(sust), though fouling after t(sust) is likely to be ascribed not only to cake formation. Finally, a new mathematical formulation was proposed according to the local flux approach to model the sub-critical TMP transients. The model involves both bound and free forms of EPS and, once experimentally calibrated, it provided a fair prediction of the TMP jump.     

A multi-agent architecture for plug and produce on an industrial assembly platform

Modern manufacturing companies face increased pressures to adapt to shorter product life cycles and the need to reconfigure more frequently their production systems to offer new product variants. This paper proposes a new multi-agent architecture utilising “plug and produce” principles for configuration and reconfiguration of production systems with minimum human intervention. A new decision-making approach for system reconfiguration based on tasks re-allocation is presented using goal driven methods. The application of the proposed architecture is described with a number of architectural views and its deployment is illustrated using a validation scenario implemented on an industrial assembly platform. The proposed methodology provides an innovative application of a multi-agent control environment and architecture with the objective of significantly reducing the time for deployment and ramp-up of small footprint assembly systems.     

Implicit Hierarchical Quad‐Dominant Meshes

We present a method for producing quad‐dominant subdivided meshes, which supports both adaptive refinement and adaptive coarsening. A hierarchical structure is stored implicitly in a standard half‐edge data structure, while allowing us to efficiently navigate through the different level of subdivision. Subdivided meshes contain a majority of quad elements and a moderate amount of triangles and pentagons in the regions of transition across different levels of detail. Topological LOD editing is controlled with local conforming operators, which support both mesh refinement and mesh coarsening. We show two possible applications of this method: we define an adaptive subdivision surface scheme that is topologically and geometrically consistent with the Catmull–Clark subdivision; and we present a remeshing method that produces semi‐regular adaptive meshes.