Hindered and compression settling: parameter measurement and modelling.

The Vesilind settling velocity function forms the basis of flux theory used both in state point analysis (for design and capacity rating) and one-dimensional dynamic models (for dynamic process modelling). This paper proposes new methods to address known shortcomings of these methods, based on an extensive set of batch settling tests conducted at different scales. The experimental method to determine the Vesilind parameters from a series of bench scale settling tests is reviewed. It is confirmed that settling cylinders must be slowly stirred in order to represent settling performance of full scale plants for the whole range of solids concentrations. Two new methods to extract the Vesilind parameters from settling test series are proposed and tested against the traditional manual method. Finally, the same data set is used to propose an extension to one-dimensional (1-D) dynamic settler models to account for compression settling. Using the modified empirical function, the model is able to describe the batch settling interface independently of the number of layers.     

Assessing heterogeneity in meta-analysis: Q statistic or I2 index?

In meta-analysis, the usual way of assessing whether a set of single studies is homogeneous is by means of the Q test. However, the Q test only informs meta-analysts about the presence versus the absence of heterogeneity, but it does not report on the extent of such heterogeneity. Recently, the I2 index has been proposed to quantify the degree of heterogeneity in a meta-analysis. In this article, the performances of the Q test and the confidence interval around the I2 index are compared by means of a Monte Carlo simulation. The results show the utility of the I2 index as a complement to the Q test, although it has the same problems of power with a small number of studies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Electrooxidation of Aqueous p-Methoxyphenol on Lead Oxide Electrodes

Oxidation of p-methoxyphenol (pmp) in aqueous solution on bismuth-doped lead oxide was studied, and the effects of the initial pmp concentration, applied potential and hydrodynamic conditions upon the oxidation rate were identified. Under all conditions studied, the concentration decay of pmp during electrooxidation follows first—order reaction kinetics. Through analysis of rotating ring-disc currents, the faradaic efficiencies for oxidation at various concentrations of pmp in solution were determined. Using u.v.—vis. and H¹RMN spectroscopy for solution analysis, it is shown that partial oxidation of pmp occurs in chloride-free aqueous solutions. The principal products were p-benzoquinone and maleic acid, with low production of CO₂ up to 1000 C dm^–3 charge. Mineralization to CO₂ was considerably improved upon addition of chloride ions to the solution. In situ FTIR spectra of the electrode surface during electrolysis indicated that the presence of chloride ions enhances the mineralization of pmp by reaction of benzoquinone with anodically generated hypochlorite.     

Chlorophenols identification in water using an electronic nose and ANNs (artificial neural networks) classification.

Electronic artificial noses are being developed as systems for the automated detection and classification of odours, vapors and gases. In the food industry, such devices are used as aids for quality control or process-monitoring tools. An electronic nose (EN) is generally composed of a chemical sensing system and a pattern recognition system (e.g. artificial neural network). An EN based on a non-specific conducting polymer array was used to monitor chlorophenols in water samples. Operational parameters for the EN were optimized by a Plackett-Burman factorial design. The experimental parameters studied were: sample volume, platen temperature, sample equilibration time, loop fill time, sample pressurization time and injection time. Optimal experimental conditions were applied to chlorophenols determination and differentiation in ultrapure water samples spiked with the EPA listed chlorophenols. Data analysis was carried out using principal component analysis (PCA) and artificial neural networks (ANNs) to predict the chlorophenols presence in water samples. The obtained results showed that it was possible to differentiate the five chlorophenol groups: monochlorophenol, dichlorophenol, trichlorophenol, tetrachlorophenol and pentachlorophenol. Differentiation of chlorophenol groups was based on Mahalanobis distance between the formed clusters. This Mahalanobis distance is designated by the Quality Factor, a value >2 for this quality factor means a good differentiation between the clusters.     

The role of metal–ceramic interfaces on the high temperature mechanical response of nanostructured nickel–yttria tetragonal zirconia polycrystals (Ni–YTZP)

High temperature creep of a metal–ceramic composite consisted of yttria tetragonal zirconia polycrystals (YTZP) with a certain amount of nickel grains (Ni–YTZP, 2.5% vol.) has been studied. The average grain size of YTZP grains was 0.20 μm, whereas that of the Ni grains was 50–70 nm. This work reports the mechanical response under creep of such composite materials. It is found that the activation energy for creep is significantly higher than that reported in similar systems with much larger nickel grains. This fact has been explained in terms of the chemical nature of the metal–ceramic interfaces.     

Some practical aspects of fitting and testing the Zipf-Mandelbrot model

Summary The standardization of distribution fitting procedures is recommended also in informetrics. We examined the possibility of that standardization when fitting the Zipf-Mandelbrot (ZM) distribution. After propositions of possible steps of standardization, we stress the unique role of maximum likelihood estimates concerning the chi-square goodness-of-fit tests. We touch upon the possible correlation between the parameters of the ZM distribution. A numerical example demonstrates the method and the results.     

Chemical composition of new copper alloys for machining and its effect on their susceptibility to corrosion cracking

Zinc‐containing copper alloys, the so‐called α + β brasses, are commonly used in contact with potable water. These materials are alloyed with lead to improve machinability. In wrought special brass alloys, reducing the content of this alloying element or replacing it with alternative alloying additions may give rise to a new type of machinable copper alloys which differ from the original alloys by their contents of other modifier elements such as Si (or possibly, Mg, Bi, and P). These alloys have a very low content of lead required for the break‐up of chips during machining. Even though these types of brass exhibit a very good machinability, the effects of their chemical composition on the resistance of the alloy to corrosion cracking have not yet been given sufficient attention. This paper aims to present an assessment of three new types of machinable copper alloys regarding their susceptibility to stress corrosion cracking, in comparison to that of the lead‐alloyed variety, in 0.05 M NaCl, NaNO₂, and Na₂SO₄ solutions. The slow strain rate test has been used for this purpose, and its results were correlated with metallographic evaluation of the number and depth of the cracks observed on the test specimen surfaces on completion of the test.     

Operator splitting and upwinding for the Navier-Stokes equations

We present an operator splitting scheme for the unsteady Navier-Stokes equations for incompressible viscous fluid flow. Like other operator splitting methods applied to these equations, the difficulties associated with the nonlinearity and the incompressibility condition are decoupled. At each time step we obtain two subproblems of Stokes type and a linear one of elliptic type. The linear problem gives us uncoupled scalar problems of transport type; then, we may take advantage of well known upwind techniques for such kind of problems in order to handle large Reynolds numbers flow with coarse meshes. To show the efficiency of the scheme we report numerical results up to Reynolds numbers Re=4000 obtained with very coarse meshes.