Mathematical modeling and computer simulation of the rotating impeller particle flotation process: Part II. Particle agglomeration and flotation

Effective removal of unwanted particles from a molten metal alloy by flotation relies on purging a gas into the melt through a rotating impeller. This device is commonly known as a rotary degasser. Unwanted particles in the melt attach to the rising gas bubbles and rise to the slag layer where they are removed from the metal bulk. In addition, the turbulence created by the rotating impeller causes the randomly distributed solid particles to agglomerate into relatively large clusters. These clusters float up or settle down due to the difference between their density and that of the melt. A mathematical model has been developed to describe the particle dynamics and particle agglomeration that occur during the rotary degassing of aluminum melts. While previous investigations addressed particle collisions in low intensity turbulent fields where the size of the colliding particles is smaller than the Kolmogorov length scale, this model is more encompassing as it considers both low intensity and high intensity turbulence. Consequently, this model is more representative of a typical industrial rotary degassing operation.     

GrAFCI+ A fast generator-based algorithm for mining frequent closed itemsets

Knowledge and Information Systems - Mining itemsets for association rule generation is a fundamental data mining task originally stemming from the traditional market basket analysis problem....     

Scheduling Independent Multiprocessor Tasks

We study the problem of scheduling a set of n independent multiprocessor tasks with prespecified processor allocations on a fixed number of processors. We propose a linear time algorithm that finds a schedule of minimum makespan in the preemptive model, and a linear time approximation algorithm that finds a schedule of makespan within a factor of (1+\eps) of optimal in the non-preemptive model. We extend our results by obtaining a polynomial time approximation scheme for the parallel processors variant of the multiprocessor task model.     

Characterization of the kinetic and mechanistic differences between free-surface and bulk grain growth in WC-Co materials

The rate of grain growth at different high temperatures in the bulk and at the free surface of a WC-Co substrate was measured. The microstructure, phase evolution, and elemental composition at the free surface were characterized at various stages of the grain-growth process and compared to equivalent characteristics of the bulk. A dramatic difference in the rate of grain growth between the free surface and the bulk of the material was observed. Grains in the free surface grew at a much faster rate than those in the bulk. Since this fast rate of growth was found to coincide with the vaporization of the binder phase from the free surface, it is suggested that this increase in the rate of growth is related to a change in the growth mechanism from an interfacial reaction limited growth in the bulk to a surface diffusion rate limited growth at the free surface. The contact points between grains provide bridges for atomic transport from high free-energy regions (small grains) to low free-energy regions (large grains); hence, the contiguity of the material has a strong influence on the rate of growth.     

Structural,morphological and electrical properties of Cr2O3 nanoparticles

Chromium oxide (Cr₂O₃) nanoparticles have been prepared by chemical precipitation followed by calcination at high temperatures. The influence of calcination temperature on the particle size, microstructure, surface area and morphology was examined by X-ray diffraction, Fourier transform infrared, N₂ adsorption–desorption isotherms, transmission electron microscopy and thermal analysis techniques. The results indicate the formation of a nanosized single Cr₂O₃ phase. The particles possess high specific surface area and mesoporous structure, and their sizes increase with increasing the calcinations temperature. DC conductivity was measured in the temperatures range of 170–475 K. For the high temperature region, the conduction was found to be due to small polaron hopping of holes. While for the low temperatures region, the conduction was attributed to variable range hopping mechanism of holes. The temperature dependence of the AC conductivity and dielectric constant was investigated in the same temperature range at four test frequencies. In addition, the impedance spectra of these nanoparticles were investigated only at temperatures above 350 K.     

Circulating plasma levels of nucleosomes in patients with systemic lupus erythematosus: correlation with serum antinucleosome antibody titers and absence of clear association with disease activity

OBJECTIVE: To assess nucleosome plasma levels in patients with systemic lupus erythematosus (SLE) and to study the correlations with serum antinucleosome, anti-double-stranded DNA (anti-dsDNA), and antihistone antibody activities, as well as with disease activity (by the SLE Disease Activity Index [SLEDAI]). METHODS: In a cross-sectional study, we assessed 58 SLE patients for their plasma nucleosome levels. Plasma nucleosome levels as well as serum antinucleosome, anti-double-stranded DNA, and antihistone antibody activities were assessed by enzyme-linked immunosorbent assay. SLE activity was evaluated using the SLEDAI: RESULTS: The mean (+/-SD) plasma nucleosome concentration in SLE patients was 52 +/- 159 ng/ml (range 5-1,180), and was significantly higher than that of the controls (16 +/- 8.8 ng/ml, range 8-52; P = 0.03). Thirteen of the 58 lupus patients had levels over the range of normal (defined as the control mean + 3 SD, or 42 ng/ml). An inverse correlation was found between nucleosome plasma levels and serum antinucleosome antibody activity in the entire group of SLE patients, those with active disease, and those with inactive disease, respectively. No correlation was found between the SLEDAI and nucleosome plasma concentrations. CONCLUSION: Nucleosome plasma levels may be normal or increased in SLE, and found in patients with active or inactive SLE. Longitudinal studies are needed to further establish whether high levels of circulating nucleosomes may predict the occurrence of an SLE flare.     

Microstructure investigation and thermal stability of 99.1% aluminum processed by equal channel angular extrusion

Microstructure evolution of 99.1% aluminum after equal-channel angular extrusion (ECAE) and subsequent heat-treatment was investigated. After deformation the samples were annealed at different temperatures. The deformed and annealed states were characterized by Transmission Electron Microscopy (TEM), X-ray diffraction (XRD), and microhardness tests. It was shown that the observed microstructure changes during subsequent annealing have to be associated with recovery and cells formation. The initial stages of recovery were investigated using weak-beam technique. The microstructure obtained after annealing for 1 h at 100 °C consists of some arrangements of the dislocations into sub-grain boundaries within the wide preexisting grains. Annealing at 300 °C led to the appearance of a duplex microstructure consisting of bands of slightly coarsened grains associated with refined grains. No growth of dislocation cells was observed up to 400 °C. In XRD measurements, the lattice parameter increase with subsequent heating. This indicates a continuous grain growth during annealing. This is due to the important increase of coherency length, D observed parallel to a substantial decrease of rms-strain, ε.     

Cyanine dyes as corrosion inhibitors. I. Electrochemical corrosion behaviour of copper metal treated with hydroxystyryl cyanine dye

The effect of 2-(o-hydroxystyryl) pyridinium-1-ethyl iodide cyanine dye on the corrosion behaviour of copper metal in nitric acid solution has been studied. Weight loss measurements, galvanostatic polarization curves, open-circuit potential variation of copper electrode with time and the cathodic protective current values indicate that styryl cyanine dye gives an anticorrosive character. The inhibition effect is more pronounced in the case of copper metal coated by dye thin film than that obtained by its addition to the corrosion medium.     

Distribution Line Carrier Sensitivity Analysis Using Bus Impedance Matrix

In a previous paper[1] we described the use of a bus impedance matrix approach for determining the signal strength of distribution line carrier signals. The technique used bus impedance matrices to calculate transimpedances which are the ratios of the voltage at any point on the line to the current injected at any point on the line. In the current paper we apply sensitivity analysis to this bus impedance approach and show how simply new transimpedances can be obtained from the original values when changes in the distribution line are made.