The effect of glucose on the formation of the nanocrystalline transition alumina phases

Series of alumina powders were synthesized starting from sodium aluminate solution prepared from Bayer liquor. The neutralisation of sodium aluminate solution was performed with the use of sulphuric acid. The influence of glucose as a non-surfactant additive on the structure of alumina powders at moderate pH was investigated. The results show that the properties of the powders are influenced by the initial pH value of the solution, as well as the duration of the neutralisation step. High pHs lead to the formation of powders with heterogeneous structure with bayerite as a dominant phase, which during calcinations converts to η-alumina with high surface area. Addition of glucose to the starting aluminate solution leads to the formation of nanocrystalline boehmite with estimated average crystallite size less than 3 nm and high surface area (above 300 m²/g). After calcinations, boehmite transforms to γ-alumina. The results have shown that during the heat treatment, structural transformations proceeded simultaneously with the significant changes in the textural properties of the obtained mesoporous γ- and η-alumina powders.     

Characterization of the tool/fabric and fabric/fabric friction for woven-fabric composites during the thermostamping process

The dynamic coefficients of friction for Twintex® commingled glass-polypropylene balanced plain-weave and unbalanced twill-weave fabrics at the tool/fabric and fabric/fabric interfaces during the composite thermostamping process are characterized. The effects of fabric velocity and pressure on the coefficients of friction under conditions similar to those during the thermostamping process are studied. A phenomenological friction model accounting for pressure and velocity dependence is developed based on the experimental results and implemented into the commercial finite element codes ABAQUS/Explicit and LS-DYNA via user-defined subroutines. The mechanical behavior of the fabric is modeled using a mesoscopic approach. The friction subroutines are validated with a finite element model of the experimental friction test. The forming of a hemispherical dome is simulated using ABAQUS and LS-DYNA. Punch forces and yarn stresses are compared between variable friction and constant friction models, and the simulation results justify the necessity for a variable friction model to accurately predict part quality.     

Synthesis and Characterization of a Composite Zeolite–Metglas Carbon Dioxide Sensor

The synthesis of a faujasite–Metglas composite material that can be used in gas‐sensing applications is presented. A continuous faujasite film was synthesized on a Metglas magnetoelastic strip using the secondary growth method. The ability of the new composite to remotely sense carbon dioxide in a nitrogen atmosphere at room temperature over a wide range of concentrations is demonstrated by monitoring the changes in the resonance frequency of the strip. The novel sensor combines the electromagnetic properties of the magnetoelastic material with the adsorption properties of the faujasite crystals. Experiments performed over a period of a few months showed that the composite sensor remained fully operational, thus indicating its long‐term stability. Furthermore, the present work demonstrates that a zeolite–Metglas composite can be used as a sensor of an analyte in a mixture as long as it adsorbs selectively larger amounts of the particular analyte than other compounds present in the mixture.     

Vivid: A framework for heterogeneous problem solving

We introduce Vivid, a domain-independent framework for mechanized heterogeneous reasoning that combines diagrammatic and symbolic representation and inference. The framework is presented in the form of a family of denotational proof languages (DPLs). We present novel formal structures, called named system states, that are specifically designed for modeling potentially underdetermined diagrams. These structures allow us to deal with incomplete information, a pervasive feature of heterogeneous problem solving. We introduce a notion of attribute interpretations that enables us to interpret first-order relational signatures into named system states, and develop a formal semantic framework based on 3-valued logic. We extend the assumption-base semantics of DPLs to accommodate diagrammatic reasoning by introducing general inference mechanisms for the valid extraction of information from diagrams, and for the incorporation of sentential information into diagrams. A rigorous big-step operational semantics is given, on the basis of which we prove that the framework is sound. We present examples of particular instances of Vivid in order to solve a series of problems, and discuss related work.     

Hertzian-Crack Suppression in Ceramics with Elastic-Modulus-Graded Surfaces

Hertzian (spherical) indentation experiments were carried out in a graded alumina-glass composite whose Young's modulus increased with depth beneath the indented surface. An in situ processing method involving impregnation of a dense, fine-grained alumina by an aluminosilicate glass was employed to fabricate such a composite. With this technique, a monotonic, unidirectional variation in Young's modulus of as much as 50% was introduced over a distance of approximately 2 mm, while keeping the coefficient of thermal expansion and the Poisson ratio for the glass and the alumina nearly the same. The macroscopically graded, elastic composite so produced with nearly full density has essentially no macroscopic, long-range residual stresses following processing. The unidirectional variation in Young's modulus under the indenter is shown to fully suppress the formation of Hertzian cone cracks. Without these elastic-modulus gradients, cone-crack formation was observed in bulk glass and alumina. Finite-element analyses of spherical indentation on elastically graded substrates were also performed to develop a quantitative understanding of the experimental trends. It is reasoned that the present innovations, involving functionally graded surfaces and their in situ processing, provide new possibilities for enhancing certain contact-damage resistance characteristics in various ceramic materials for a broad range of engineering applications. Furthermore, this contact-damage-resistance phenomenon in functionally graded ceramics is elastic in nature, and is, therefore, likely to be immune to mechanical fatigue within the elastic limit.     

Electrolytic flotation of pyrite

Electrolytic flotation, a rather unconventional flotation technique used in effluent treatment, was investigated on pyrite; the process was enhanced by xanthate and also a cationic collector. This was then compared with classical floatability experiments. Zeta-potential measurements, under similar pulp conditions, were carried out to explain the process mechanism. The mineral flotation behavior in the presence of common modifiers was also examined during electrolytic flotation. The latter produces fine gas bubbles, has favorable hydrodynamic conditions and assists in flocculation of particles prior to flotation, as shown.     

Advanced QoS provisioning in IP networks: the European premium IP projects

This article describes the current evolution of QoS architectures, mechanisms, and protocols in the Internet, as it is ongoing in the framework of the European Union funded research projects on premium IP networks. A short review of the proposed standard approaches to QoS (e.g., differentiated services, integrated services, and label switching technologies) is given. Then we focus on the state-of-the-art architectures, mainly based on DiffServ concepts. Several issues arise when trying to implement these architectures in the real world: QoS aspects, network monitoring of the offered QoS, and end-user control of received QoS. The article then discusses the existing results and the current direction of European research and development in these areas.     

Pretwisted beam subjected to thermal loads: A gradient thermoelastic analogue

It is well known from the classical torsion theory that the cross section of a prismatic beam subjected to end torsional moments will rotate and warp in the longitudinal direction. Rotation is depicted through the angle of twist per unit length and depends in general on the position along the length of the beam, while the warping function addresses the longitudinal distortion of the unrotated cross sections. In the present study, we consider a prismatic beam that possesses an initial twist which is constant along its length. A thermal field is present along the beam and its ends are loaded with axial forces and torsional moments. The governing equilibrium equations and the corresponding boundary conditions were obtained using an energy variational statement. A one-dimensional gradient thermoelastic analogue is developed. The advantageous aspect of the present study is that the additional (and peculiar) boundary conditions required by the gradient elasticity theory and the related microstructural lengths, analogous to micromechanical lengths, emerge in a natural way from the geometrical characteristics of the beam cross section and the material properties. We have examined various examples with different cross sections and loads to demonstrate the applicability of the model to the design of special yarns useful in smart textiles and thermally activated microdrilling actuators.     

Insight into the Greek electric sector and energy planning with mature technologies and fuel diversification

The numerous available options for the development of the Greek electric sector in combination with the various techno-economic and political constraints make energy planning rather complex. Furthermore, as full auctioning of CO₂ allowances shall be the rule from 2013 onwards for the electric sector following free allocation, even more uncertainties emerge. This work aims at investigating the main characteristics of the Greek electric system taking into consideration the various allowance allocation schemes, evaluates fundamental energy scenarios and ultimately performs energy planning. The reliability of the algorithm utilised is assessed by predicting successfully key figure energy results for years 2004–2008. Main parameter under investigation in the study is the cost of CO₂ emissions allowances, while expansion scenarios are evaluated according to a newly developed set of indices standing for feasibility, environmental performance, cost effectiveness and energy safety. Many expansion scenarios examined were proved unrealistic as led to extremely high utilization of imported fuels for electricity production, while others proved inefficient on environmental or economic basis. Finally, it was proved that if a “conservative” energy planning is adopted, emissions reduction in 2020 can reach 6.3% over 2005.     

The effect of heat treatment on the corrosion behaviour of 319 aluminium alloy

The effect of various heat treatments on the corrosion behaviour of 319 T1 cast aluminium alloy was investigated. From this alloy, specimens were heat treated in T5, T6 and two steps solution heat treatment T6 conditions and afterwards were subjected to electrochemical corrosion in a 0.1 M NaCl solution (pH = 12). From the above treatments, T5 heat treatment did not improve the corrosion resistance of the as‐received alloy in contrast to T6 heat treatment which improved the corrosion resistance of the same alloy. However, two steps solutionizing T6 treatment showed the best corrosion resistance of the aluminium alloy.