Grain-Boundary and Grain Electrical Resistances in CoxFe3−xO4

The complex impedance analysis technique was used to separate the grain-boundary and grain impedances of ferrites of the system Co_xFe_3−xO₄. All the samples, for x = 0.886, 0.960, 0.980, 0.995, 0.999, 1.005, 1.011, 1.021, 1.041, and 1.126, were fabricated by the traditional routine under the same conditions of preparation and sintering. The variations of both grain-boundary and grain resistances with temperature were evaluated in the frequency range 100 Hz < f < 40 MHz. The values of the activation energies for both conduction processes were determined from the Arrhenius plots, and the variations of these activation energies and of the resistances at 20° and 150°C were drawn as a function of x. A sharp change in these quantities was observed at the stoichiometric composition (x = 1). Explanations and suggestions for the observed behaviors have been made.     

Parallel OLAP query processing in database clusters with data replication

We consider the problem of improving the performance of OLAP applications in a database cluster (DBC), which is a low cost and effective parallel solution for query processing. Current DBC solutions for OLAP query processing provide for intra-query parallelism only, at the cost of full replication of the database. In this paper, we propose more efficient distributed database design alternatives which combine physical/virtual partitioning with partial replication. We also propose a new load balancing strategy that takes advantage of an adaptive virtual partitioning to redistribute the load to the replicas. Our experimental validation is based on the implementation of our solution on the SmaQSS DBC middleware prototype. Our experimental results using the TPC-H benchmark and a 32-node cluster show very good speedup.     

Model and procedure for performance and availability-wise parallel warehouses

Consider data warehouses as large data repositories queried for analysis and data mining in a variety of application contexts. A query over such data may take a large amount of time to be processed in a regular PC. Consider partitioning the data into a set of PCs (nodes), with either a parallel database server or any database server at each node and an engine-independent middleware. Nodes and network may even not be fully dedicated to the data warehouse. In such a scenario, care must be taken for handling processing heterogeneity and availability, so we study and propose efficient solutions for this. We concentrate on three main contributions: a performance-wise index, measuring relative performance; a replication-degree; a flexible chunk-wise organization with on-demand processing. These contributions extend the previous work on de-clustering and replication and are generic in the sense that they can be applied in very different contexts and with different data partitioning approaches. We evaluate their merits with a prototype implementation of the system.     

Investigating polypropylene–green coconut fiber composites in the molten and solid states through various techniques

A series of polypropylene (PP)–green coconut fiber (GCF) composites were prepared by melt mixing and their properties studied in the molten state using an advanced nonlinear harmonic testing technique, and in the solid state using standard mechanical testing and scanning electron microscopy (SEM). The effect of fiber loading as well as the role of maleated polypropylene as compatibilizing agent was investigated. PP–GCF composites are heterogeneous materials that, in the molten state, are found to exhibit essentially a nonlinear viscoelastic character, in contrast with the pure PP, which has a linear viscoelastic region up to 50–60% strain. Complex modulus increases with GCF content but in such a manner that the observed reinforcement is at best of hydrodynamic origin, without any specific chemical interaction occurring between the polymer matrix and the fibers. The addition of maleated polypropylene improves the wetting of fibers by the molten polymer but the effect is so small that specific chemical reactions could hardly be considered as occurring. Flexural modulus data confirm the reinforcing effects of the fiber and an improvement is noted when some maleated polypropylene is used, with an optimum level of around 1% (or the PP content). SEM microphotographs clearly show that maleated polypropylene imparts a better wetting of GC fibers by PP, but chemical interactions are unlikely to occur between the polymer and GCF. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1922–1936, 2006     

Solubility, density and viscosity of a mixture of R-600a and polyol ester oil

Experimental data on solubility, liquid phase density and viscosity of a mixture of R-600a and a POE ISO 7 lubricant oil are presented. A specially designed experimental facility for simultaneous measurements of the physical properties was used in the experiments at temperatures ranging from 10 to 60 °C. The VLE data were correlated with the Heil–Prausnitz and Flory–Huggins activity models and the Peng–Robinson equation of state (EoS). Liquid density was correlated with the Peng–Robinson EoS and with a first-order Redlich–Kister expansion for the excess molar volume. Liquid viscosity was correlated with an excess-property approach based on the classical Eyring liquid viscosity model. Satisfactory agreement was obtained between models and experiments; maximum root mean square (RMS) deviations of models used in the VLE, density and viscosity predictions were 1.1% (VLE EoS), 0.2% (Redlich–Kister) and 3.0% (Grunberg–Nissan), respectively.     

Copolymerization of Styrene onto Polyethersulfone Films Induced By Gamma Ray Irradiation

Summary Radiation-induced grafting of styrene into polyethersulfone (PES) films were investigated by simultaneous method in solution using gamma-ray from a radio nuclide ⁶⁰Co source. The starting materials were prepared via casting method of the polymeric solution. The grafted membranes have side chains of polystyrene which may be sulfonated to become proton conductive to be used as polymer electrolyte membrane in fuel cell. The localized energy of high intensity gamma-ray induced breaking of chemical bonds leads to free radical formation, a reactive species having a single unpaired electron. The radical start a conventional polymerization sequence comparable with that obtained with a chemical catalyst acting as initiator. The effects of grafting conditions include monomer concentration, irradiation total dose, dose rate and addition of cross linking agent, were studied by means of the techniques of structure analysis, morphology, thermal degradation and crystallinity. The degree of grafting (DOG) was analyzed by percentage of the weight increase. As a result, the reaction always follows the same pattern: DOG increases rapidly initially whilst propagation is the main reaction, then more slowly as termination becomes more frequent.     

A study of the air-side heat transfer and pressure drop characteristics of tube-fin ‘no-frost’ evaporators

A study is presented on the influence of the air flow rate and surface geometry on the thermal-hydraulic performance of commercial tube-fin ‘no-frost’ evaporators. A specially constructed wind-tunnel calorimeter was used in the experiments from which data on the overall thermal conductance, pressure drop, Colburn j-factor and Darcy friction factor, f, were extracted. Eight different evaporator samples with distinct geometric characteristics, such as number of tube rows, number of fins and fin pitch were tested. Semi-empirical correlations for j and f are proposed in terms of the air-side Reynolds number and the finning factor. A discussion is presented on the performance of the evaporators with respect to specific criteria such as the pumping power as a function of heat transfer capacity and the volume of material in each evaporator.     

Advances in genomics for the improvement of quality in coffee

Coffee is an important crop that provides a livelihood to millions of people living in developing countries. Production of genotypes with improved coffee quality attributes is a primary target of coffee genetic improvement programmes. Advances in genomics are providing new tools for analysis of coffee quality at the molecular level. The recent report of a genomic sequence for robusta coffee, Coffea canephora, is a major development. However, a reference genome sequence for the genetically more complex arabica coffee (C. arabica) will also be required to fully define the molecular determinants controlling quality in coffee produced from this high quality coffee species. Genes responsible for control of the levels of the major biochemical components in the coffee bean that are known to be important in determining coffee quality can now be identified by association analysis. However, the narrow genetic base of arabica coffee suggests that genomics analysis of the wild relatives of coffee (Coffea spp.) may be required to find the phenotypic diversity required for effective association genetic analysis. The genomic resources available for the study of coffee quality are described and the potential for the application of next generation sequencing and association genetic analysis to advance coffee quality research are explored. © 2016 Society of Chemical Industry     

Grape by‐product extracts against microbial proliferation and lipid oxidation: a review

The wine industry is responsible for the production of million tons of waste, such as grape skin, stalk, sludge and seeds, which can be considered inexpensive sources of phenolic compound owing to incomplete extraction during wine production. Phenolic compounds, also called polyphenols, comprise the most abundant bioactive compounds in grape and are recognized by their antioxidant and antimicrobial potential. Because of their functional properties, extracts obtained from grape wastes, which are rich in phenolic compounds, can be employed in the development of many products, ranging from medical to food applications, decreasing the growth of spoilage and pathogenic microorganisms and inhibiting lipid oxidation. These characteristics are motivating the research for alternative sources of natural antioxidant and antimicrobial agents, aimed at decreasing the use of artificial additives, which have been associated with some toxic effects. This article provides a review of the use of grape by‐product extracts and their bioactive compounds as natural antioxidant and antimicrobial agents in food products. © 2016 Society of Chemical Industry