A conceptual design of spacers with hairy structures for membrane processes

The development of membrane technology requires spacers that can significantly enhance the mass-transfer rate while avoiding a severe pressure drop across the membrane module. A potential solution to this challenge is to introduce some flexible and dynamic structures into the spacer mesh. The current work was motivated to explore a conceptual design of spacers with hairy structures. The hairy structures were simulated using highly flexible nylon fibers that were fixed on a well-designed framework. The effects of fiber asymmetry and spacing on the vibrations were discussed in terms of the observations via a high speed camera. A variety of spacer prototypes were employed in a forward osmosis process to examine the performance of the hairy structures. The experimental results indicate that fiber vibrations could have a great impact on the mass transfer in the vicinity of the membrane surface and enhance the filtration flux (up to ~20%). This fundamental study not only provides insight into the mechanisms underlying the complex fiber-flow interactions but also charts the direction for future hairy spacer design

Operator theory and function theory in Drury-Arveson space and its quotients

The Drury-Arveson space $H^2_d$, also known as symmetric Fock space or the $d$-shift space, is a Hilbert function space that has a natural $d$-tuple of operators acting on it, which gives it the structure of a Hilbert module. This survey aims to introduce the Drury-Arveson space, to give a panoramic view of the main operator theoretic and function theoretic aspects of this space, and to describe the universal role that it plays in multivariable operator theory and in Pick interpolation theory.Comment: Final version (to appear in Handbook of Operator Theory); 42 page

Evidence-based Kernels: Fundamental Units of Behavioral Influence

This paper describes evidence-based kernels, fundamental units of behavioral influence that appear to underlie effective prevention and treatment for children, adults, and families. A kernel is a behavior–influence procedure shown through experimental analysis to affect a specific behavior and that is indivisible in the sense that removing any of its components would render it inert. Existing evidence shows that a variety of kernels can influence behavior in context, and some evidence suggests that frequent use or sufficient use of some kernels may produce longer lasting behavioral shifts. The analysis of kernels could contribute to an empirically based theory of behavioral influence, augment existing prevention or treatment efforts, facilitate the dissemination of effective prevention and treatment practices, clarify the active ingredients in existing interventions, and contribute to efficiently developing interventions that are more effective. Kernels involve one or more of the following mechanisms of behavior influence: reinforcement, altering antecedents, changing verbal relational responding, or changing physiological states directly. The paper describes 52 of these kernels, and details practical, theoretical, and research implications, including calling for a national database of kernels that influence human behavior

Impact of a biofouling layer on the vapor pressure driving force and performance of a membrane distillation process

The heat and mass transfer resistances of fouling layers can cause a significant flux decline in a membrane distillation (MD) process. In addition, the hydrophilicity and microporous nature of a fouling layer can affect the driving force and correspondingly the flux in MD via curvature effects on the vapor pressure as described by the Kelvin equation. This study explores the effect of the hydrophilicity of the sludge on the particle size, vapor pressure and pore-size distribution (PSD) in the biofouling layer and on the permeation flux in cross-flow MD. Two sets of hydrophilic sludge cultures were selected via the Microbial-Adhesion-to-Hydrocarbon method. Cross-flow MD experiments conducted with these two sludges displayed a 60% reduction in the flux relative to using a Milli-Q water feed. However, there was no significant difference in the fluxes for the two sludges. Characterization of the pore-size distribution of the two sludges using evapoporometry, a novel technique based on the vapor-pressure depression caused by small pores, indicated a vapor-pressure depression of 31% and 21% for the more- and less-hydrophilic sludges, respectively. However the effect of the 10% difference in vapor-pressure depression, when combined with the effect of the biofouling layer on the heat- and mass-transfer resistances, could not be detected within the experimental error in this study. Nevertheless, a major conclusion is that the vapor-pressure depression caused by a biofouling layer, or other foulants, could cause a significant reduction in the driving force for MD. © 2013 Elsevier B.V