Meso-scale structures of bidisperse mixtures of particles fluidized by a gas

Flow characteristics of bidisperse mixtures of particles fluidized by a gas predicted by the mixture based kinetic theory of [Garzó et al., 2007a] and [Garzó et al., 2007b] and the species based kinetic theory model of Iddir and Arastoopour (2005) are compared. Simulations were carried out in two- and three-dimensional periodic domains. Direct comparison of the meso-scale gas-particle flow structures, and the domain-averaged slip velocities and meso-scale stresses reveals that both mixture and species based kinetic theory models manifest similar predictions for all the size ratios examined in this study. A detailed analysis is presented in which we demonstrate when the species based theory of Iddir and Arastoopour (2005) will reduce to a mathematical form similar to the mixture framework of [Garzó et al., 2007a] and [Garzó et al., 2007b] . We also find that the flow characteristics obtained for bidisperse mixtures are very similar to those obtained for monodisperse systems having the same Sauter mean diameter for the cases examined; however, the domain-averaged properties of monodisperse and bidisperse gas-particle flows do demonstrate quantitative differences. The use of filtered two-fluid models that average over meso-scale flow structures has already been described in the literature; it is clear from the present study that such filtered models are needed for coarse-grid simulations of polydisperse systems as well.     

Structural and luminescence properties of pure and Al-doped ZnO nanopowders

Pure and Al doped zinc oxide nanopowders have been synthesized by sol-gel route. This is a simple and inexpensive method permitting to obtain a very small grain size powders. Zinc acetate dehydrate was first dissolved in a mixture of 2-methoxyethanol and mono-ethanolamine (MEA) solution, were used as a solvent and stabilizer respectively and doped with a quantity of aluminum nitrate, varying from 0 to 10 mol%. The obtained gel is then calcinated in air at 500 °C. The samples are characterized by XRD, SEM and photoluminescence (PL) studies. The XRD results indicate that pure and Al-doped ZnO powders are solid solutions crystallizing in pure würtzite structure, and consisted of a mixture of nanoparticles with grain size between 23 and 36 nm. The grain size decreases strongly with increasing Al concentration and reaches its lowest value at 5 mol% Al. The PL spectra show that the most important establishment is that the powders show luminescence peaks from green to ultraviolet light, and thus can be used to manufacture transmitters using these emissions. The peaks connected to the blue luminescence are the most intense, and they are generated by transitions involving (Zn_i). The SEM images show a formation of pebbles with sizes decreasing with Al concentration and a morphology evaluating, qualitatively, from pebbles without cavities to highly porous ones.     

A new look at the measurement of cementitious paste setting by Vicat test

The Vicat test is a standard test for measuring the setting times of cement paste and mortar. The physical background of the test is based on the resistance of a paste to dynamic penetration by a rod with a certain weight and shape (shear strain). The information obtained (initial and final set time) is very useful to compare cement setting properties. This study shows that it is possible to obtain more fundamental information about the setting property kinetics with only one modification of the testing procedure.The apparent mass of the static full immersed needle is measured.Due to the deformation of the cement paste at rest, the needle apparent mass varies with time. We show that the variation of the stress mobilized at the plate surface is related to the increase of yield stress during the setting period. The results of these experiments are discussed and compared with the traditional Vicat test for cement paste.     

Using X-ray microtomography to evaluate cavity formation in a superplastic magnesium alloy processed by equal-channel angular pressing

The magnesium AZ31 alloy exhibits excellent superplastic properties after processing by equal-channel angular pressing (ECAP) and testing in tension at a temperature of 623 K. Experiments show that there is an increase in the elongations to failure with increasing numbers of passes in ECAP. X-ray microtomography was used to obtain detailed information on the morphologies of cavities developed during superplastic flow and the results were analyzed in terms of the different possible cavity growth mechanisms. The results show that superplastic elongations are attained in this alloy because the finer grain structure introduced by ECAP is associated with lower flow stresses in tensile testing at elevated temperatures and this leads to a reduction in the rate of growth of internal cavities.     

An efficient design of CORDIC in Quantum-dot cellular automata technology

Power dissipation of future-integrated systems, consisting of a numberless of devices, is a challenge that cannot be easily solved by classical technologies. Quantum-dot Cellular Automata (QCA) is a Field-Coupled Nanotechnology (FCN) and a potential alternative to traditional CMOS technologies. It offers various features like extremely low-power dissipation, very high operating frequency and nanoscale feature size. This study presents a novel design of CORDIC circuit based on QCA technology. The proposed circuit is based on several proposed QCA sub-modules as adder and Flip-Flop. To design and verify the proposed architecture, QCADesigner tool is employed and power consumption is estimated using QCAPro software. The proposed QCA CORDIC achieves about 69% reduction in power and area compared to previous existing designs. The outcome of this work can open up a new window of opportunity for the design of the CORDIC module and can be used in low-power signal and image processing systems.     

Volatile compounds and compositional quality of virgin olive oil from Oueslati variety: Influence of geographical origin

Headspace solid-phase microextraction (HS-SPME) was applied to the analysis of volatile compounds of virgin olive oils from Oueslati variety cultivated in different geographical areas. Thus, olives at the same stage of maturation were harvested from seven regions in the Centre and the South of the country for oil extraction and analysis. Twenty-seven compounds were characterised by GC-FID and GC–MS. Compounds belonging mainly to alcohols, esters, aldehydes, ketones and hydrocarbons chemical classes characterised the volatile profiles. Significant differences in the proportion of volatiles from oils of different geographical origins were detected. The results suggest that, besides genetic factors, environmental conditions influence volatile formation.     

Search-based detection of model level changes

Software models, defined as code abstractions, are iteratively refined, restructured, and evolved due to many reasons such as reflecting changes in requirements or modifying a design to enhance existing features. For understanding the evolution of a model a-posteriori, change detection approaches have been proposed for models. The majority of existing approaches are successful to detect atomic changes. However, composite changes, such as refactorings, are difficult to detect due to several possible combinations of atomic changes or eventually hidden changes in intermediate model versions that may be no longer available. Moreover, a multitude of refactoring sequences may be used to describe the same model evolution. In this paper, we propose a multi-objective approach to detect model changes as a sequence of refactorings. Our approach takes as input an exhaustive list of possible types of model refactoring operations, the initial model, and the revised model, and generates as output a list of refactoring applications representing a good compromise between the following two objectives (i) maximize the similarity between the expected revised model and the generated model after applying the refactoring sequence on the initial model, and (ii) minimize the number of atomic changes used to describe the evolution. In fact, minimizing the number of atomic changes can important since it is maybe easier for a designer to understand and analyze a sequence of refactorings (composite model changes) rather than an equivalent large list of atomic changes (Weissgerber and Diehl 2006). Due to the huge number of possible refactoring sequences, a metaheuristic search method is used to explore the space of possible solutions. To this end, we use the non-dominated sorting genetic algorithm (NSGA-II) to find the best trade-off between our two objectives. The paper reports on the results of an empirical study of our multi-objective model changes detection technique as applied on various versions of real-world models taken from open source projects and one industrial project. We compared our approach to the simple deterministic greedy algorithm, multi-objective particle swarm optimization (MOPSO), an existing mono-objective changes detection approach, and two model changes detection tools not based on computational search. The statistical test results provide evidence to support the claim that our proposal enables the generation of changes detection solutions with correctness higher than 85 %, in average, using a variety of real-world scenarios.     

Experimental and fuzzy modelling analysis on dynamic cutting force in micro milling

Prediction of cutting forces is very important for the design of cutting tools and for process planning. This paper presents a fuzzy modelling method of cutting forces based on subtractive clustering. The subtractive clustering combined with the least-square algorithm identifies the fuzzy prediction model directly from the information obtained from the sensors. In the micro-milling experimental case study, four sets of cutting force data are used to generate the learning systems. The systems are tested against each other to choose the best model. The obtained results prove that the proposed solution has the capability to model the cutting force in spite of uncertainties in the micromilling process.     

Design of a Fixed‐Order RST Controller for Interval Systems: Application to the Control of Piezoelectric Actuators

This paper presents a technique for designing a robust polynomial RST controller for parametric uncertain systems. The uncertain parameters are assumed to be bounded by intervals. The computation of the controller is addressed by introducing the interval arithmetic. The controller synthesis is formulated as a set inversion problem that can be solved using the SIVIA algorithm. The proposed method is afterwards applied to design a robust controller for a piezoelectric microactuator. The experimental results show the efficiency of the proposed method. Finally, a fine stability analysis is performed to analytically prove the robustness of the designed controller.     

Synthesis and characterization of composite Hg-polyaniline powder material

A simple synthesis method is proposed to obtain a composite powder material constituted by polyaniline powder containing mercury droplets closely linked into PANI matrix. ¹⁹⁹Hg solid state NMR spectroscopy indicates that incorporated mercury is in a metallic form and proves a redox reaction between polyaniline (leucoemeraldine form) and an aqueous solution of Hg(I). This composite powder material has been studied by voltammetry with a cavity microelectrode (CME). This electrode appears suitable for characterizing such a material. CME containing Hg-polyaniline (Hg-PANI) powder has been used as an electrochemical microsensor for lead trace analysis by anodic stripping voltammetry of water without electrolyte addition.