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Foam drainage on thick porous substrate

Armstrong T., Smith H., Arjmandi-Tash O., Cook J., Trybala A., Starov V.

Physicochemical Problems of Mineral Processing

2018

Vol. 54, iss. 1

193--202

The use of foam-based applications as a method of drug delivery represents a recent and promising area of research. The interaction of foam and porous substrates have been recently theoretically described using a mathematical model, which combines the equation of foam drainage with that of imbibition of liquid into the porous substrate. Below the drainage of foam placed on chalk experimentally investigated to verify the theory prediction. The surfactants sodium dodecyl sulfate (SDS) and Triton X-100 were used to form a foam. The initial liquid volume fractions of the foam were found to be ranging in between 14.12 and 16.46%. The porosity and permeability of the chalk substrate were experimentally obtained at 59.1% and 3.122·10-11 m2 respectively. The height of foam deposited onto the thick porous substrate (chalk) was 2.5 cm and 6 cm. The imbibition into the chalk, the height of foam, and the bubble size within the foam were monitored. The latter enabled the kinetics of the drainage/imbibition to be determined and compared with the predictions according to the theoretical model. The rate of decrease in foam height was initially high and decreased over time as predicted by the theoretical model. All the foam displayed an initial rapid imbibition through the porous substrate, which is again in the agreement with the theory predictions. It was found that solutions with lower surfactant concentrations could penetrate deeper into the chalk. The imbibition front was observed to be uniform: evenly distributed liquid throughout the cross-section of the porous substrate.

Variable Stars in M13. II. The Red Variables and the Globular Cluster Period-Luminosity Relation

Osborn W., Layden A., Kopacki G., Smith H., Anderson M., Kelly A., McBride K., Pritzl B.

Acta Astronomica

2017

Vol. 67, No. 2

131--158

New CCD observations have been combined with archival data to investigate the nature of the red variables in the globular cluster M13. Mean magnitudes, colors and variation ranges on the UBVIC system have been determined for the 17 cataloged red variables. 15 of the stars are irregular or semi-regular variables that lie at the top of the red giant branch in the color-magnitude diagram. Two stars are not, including one with a well-defined period and a light curve shape indicating it is an ellipsoidal or eclipsing variable. All stars redder than (V-IC)0=1.38 mag vary, with the amplitudes being larger with increased stellar luminosity and with bluer filter passband. Searches of the data for periodicities yielded typical variability cycle times ranging from 30 d up to 92 d for the most luminous star. Several stars have evidence of multiple periods. The stars' period-luminosity diagram compared to those from microlensing survey data shows that most M13 red variables are overtone pulsators. Comparison with the diagrams for other globular clusters shows a correlation between red variable luminosity and cluster metallicity.