Particle–bubble interaction and attachment in flotation

Flotation is an important unit operation in the minerals industry, among others. Current state-of-the-art flotation modelling combines computational fluid dynamics (CFD) with user-defined algorithms based on the “induction time” concept to describe selective bubble–particle attachment and separation of hydrophobic and hydrophilic particles.We have undertaken experimental studies permitting direct observation of particle–bubble interaction and attachment at the microscale to provide empirical data for comparison with new theoretical predictions.Observations were made on a model system in which 150 μm glass particles were dropped onto a captive 1.3 mm air bubble formed in water within a glass cell. The interactions were recorded on high-speed digital video, permitting direct estimation of relevant parameters such as the approach velocity, and the duration of particle sliding over the bubble surface. A new experimental configuration has allowed the particle path toward, around, and away from the bubble to be totally unimpeded.Particle trajectories show a significant deviation at separations much larger than their own diameter; such deviations are due to the hydrodynamics. Comparisons with theoretical predictions indicate that the bubble surface exhibited mobility intermediate between “full slip” and “no slip”. Theoretical predictions for an immobile bubble surface were practically symmetrical about the bubble's equator, while asymmetry was apparent in the theoretical predictions for a mobile bubble surface. However, the strongest asymmetries were seen in the observed particle trajectories and speeds.Particles dropping more centrally were seen to slide over the surface of the bubble. In several cases the sliding particle ‘jumped in’ toward the bubble, which is interpreted as the precise moment of attachment. This provides for a direct estimate of the threshold duration to achieve attachment, i.e. “induction time”. Among the events observed were rotation of the particle upon jumping in, and particle jump-in below the bubble's equator. Explanations are proposed in terms of particle properties and flow phenomena.     

Effects of trypsin‐hydrolyzed wheat gluten peptide on wheat flour dough

BACKGROUND: Gluten peptide was prepared by trypsin hydrolysis and characterized by high‐performance liquid chromatographic analysis. The effects on non‐frozen and frozen doughs of trypsin‐hydrolyzed gluten peptide (THGP) and its combination with ascorbic acid or KBrO₃ were investigated. RESULTS: Molecular analysis of THGP showed a decrease in the high‐molecular‐weight and an increase in the low‐molecular‐weight sodium dodecyl sulfate‐soluble fractions, compared with those of control wheat gluten. The addition of 8% THGP decreased the mixing time and tolerance of the dough, both with and without ascorbic acid or KBrO₃. However, the maximum resistance and extensibility of the rested dough containing 8% THGP, with and without ascorbic acid or KBrO₃, were not significantly different from those of the control dough. The addition of 8% THGP significantly increased the loaf volume of bread baked from non‐frozen dough when combined with 60 ppm ascorbic acid or 30 ppm KBrO₃, but it had a significant effect both with and without ascorbic acid or KBrO₃ on frozen‐dough bread. A large difference in volume was observed between breads made with and without THGP at the oven‐spring, rather than at proofing. CONCLUSION: The addition of 8% THGP increased the loaf volume of bread made from freeze‐damaged dough and this effect increased when THGP was combined with 60 ppm ascorbic acid. Copyright © 2008 Society of Chemical Industry     

Vasoactive intestinal peptide stimulation of human trabecular meshwork cell growth

PURPOSE: To demonstrate that vasoactive intestinal peptide (VIP), a 28-amino acid neuropeptide, is a growth factor of human trabecular meshwork (TM) cells in culture and in a corneoscleral explant organ culture treated with laser trabeculoplasty (LTP). METHODS: Proliferating human TM cells in cell cultures were incubated with VIP for 20 hours, followed by total cell number determination, using a Coulter counter. The percentage of proliferating TM cells was assessed, using an antibody against the proliferating cell nuclear antigen (PCNA). To test the growth effect of VIP on TM cells in situ, corneoscleral explants in organ cultures were first treated with argon LTP to initiate TM-cell proliferation and then were exposed to VIP for 48 hours. The mitotic TM cells were demonstrated immunocytochemically, using anti-PCNA in paraffin sections of the explants; and the total number of TM cells was determined after paraffin sections were counterstained by hematoxylin. RESULTS: Vasoactive intestinal peptide dose-dependently stimulated the proliferation of TM cells in cell culture. Treatment with 5 x 10(-10) M VIP resulted in a maximal increase of 40% in cell number. The effect of VIP was blocked by a VIP antagonist. The number of PCNA-stained TM cells and the total cell number in the TM in LTP-treated corneoscleral explants were increased by VIP. CONCLUSIONS: Exogenously applied VIP stimulated the proliferation of human TM cells in subconfluent cultures and in LTP-treated corneoscleral explants. In that LTP has been shown to increase the number of TM cells in situ, the growth stimulatory effect of VIP may help enhance this therapy.     

Study on corrosion characteristics and stress corrosion cracking of the weldment for HT-60 steel in synthetic seawater

The contents of this paper include the evaluation of corrosion characteristics and the behaviour of stress corrosion cracking (SCC) for the weldment and post weld heat treatment (PWHT) specimen and parent of HT-60 steel using a slow strain rate test (SSRT) in synthetic seawater. Corrosion characteristics were obtained from the polarization curves by potentiostat, and SCC phenomena were evaluated through the parameters such as reduction of area and time to failure by comparing the experimental results in corrosive environment with those obtained in air. Corrosion rate of the weldment was the fastest, followed by parent and PWHT specimen. SCC phenomena between the weldment of HT-60 steel and synthetic seawater were shown. Besides, SCC was dependent upon the pulling speed greatly. Maximum severity of SCC was obtained at a speed of 10⁻⁶ mm/min, whereas SCC could not be seen almost at 10⁻⁴ mm/min. The resistance to SCC for PWHT specimen was improved considerably compared that of the weldment at 10⁻⁶ mm/min. In case of SCC failure, it was verified from SEM examination that brittle mode and lots of pits could be seen at the fractured region near the surface of the specimen.     

Reliability analysis and comparison of several structures

In this study, we consider the redundant structure with the function of swithover processing which is assumed to cause the increase of the failure rate of the system. A single component system and a simple redundant system are compared in terms of the four reliability measures such as the reliability function, the MTBF, the failure rate and the mean residual life (MRL). We find the relations of the MTBF, the failure rate, and the MRL between two systems. We also consider a quad configuration system and a parallel string configuration system and evaluate the four reliability measures for two systems. As a numerical example, the total system down of an ATM switching system is considered.     

Response of a high-strength flexible laminate to dynamic tension

The dynamic stress–strain behaviour of the Spectra Shield^® LCR (laminated composite roll) is determined from tests using a tensile split Hopkinson bar, and the experimental results indicate that it is highly strain rate sensitive. The failure strain decreases initially with strain rate up to a critical value, and rises thereafter, while the failure stress increases with strain rate to a similar value of strain rate, after which it decreases. The nature of failure of filaments is observed to change with strain rate, first becoming increasingly brittle and then returning to more ductile modes once the critical strain rate is exceeded. The increase in failure strain and stress are accounted for in terms of strain rate hardening. An explanation of the reduction in failure stress beyond the critical strain rate is proposed with respect to increasing viscoelastic hysteresis and reduction in the time available for filament alignment.     

Measuring the particle size of a known distribution using the focused beam reflectance measurement technique

The accuracy of the focused beam reflectance measurement (FBRM) probe, which measures a chord length distribution, from Mettler-Toledo Lasentec^® has been explored. A particle video microscope (PVM) probe, which provides in situ digital images, was used as a direct visual method to test the reliability of the FBRM results. These probes can provide in situ particle characterization at high pressures. The FBRM has been used to study emulsions and ice and clathrate hydrate formation. The ability of the FBRM to accurately characterize unimodal and bimodal distributions of particles and droplets and to measure agglomeration events was investigated. It was found that while the FBRM can successfully identify system changes, certain inaccuracies exist in the chord length distributions. Particularly, the FBRM was found to oversize unimodal distributions of glass beads, but undersize droplets in an emulsion and was unable to measure full agglomerate sizes. The onset of ice and hydrate nucleation and growth were successfully detected by the FBRM, but quantitative analysis of the particle and agglomerate sizes required simultaneous PVM measurements to be performed.     

Enhancing adhesion by ion beam-induced atomic mixing at the interface between copper film and polyimide substrate

Ion beam mixing was used to improve the adhesion between deposited Cu film (400 Å) and polyimide (PI) substrate. Ar⁺ ion with the energy levels between 180 and 200 keV, and the dose between 10¹⁴ to 4 × 10¹⁶ ions/cm² were used. The surface analyses were carried out by Rutherford Backscattering Spectroscopy (SEM). RBS analysis, using 2 MeV He⁺ ions, showed mixing of Cu and FI and the mixing depended on the Ar⁺ energy and dose. The X-ray study showed a very broad halo for deposited Cu film but the (111) peak appeared after the Ar⁺ implantation and the peak increased with Ar⁺ ion dose. Optical micrographs showed that Cu film formed circular bubbles after many thermal cycles when adhesion was poor and fracture cracks when adhesion was good.     

Interleaved concatenated coding for the turbulent atmosphericdirect detection optical communication channel

The performance of two concatenated coding systems using a K =3, R=1/2 convolutional inner code and a Reed-Solomon (RS) (15, 9) or (15, 7) outer code was measured over a 5.76-km-long atmospheric direct detection optical communication channel. Inner code interleaving of 100 μs combined with outer code interleaving of 240 bits (60 RS symbols) was found to be sufficient to obtain a decoded BER of less than 10^-6 under conditions of moderate channel turbulence and an average of 6-10 detected photons per channel bit