3,791 research outputs found
Exclusion zone phenomena in water -- a critical review of experimental findings and theories
The existence of the exclusion zone (EZ), a layer of water in which plastic
microspheres are repelled from hydrophilic surfaces, has now been independently
demonstrated by several groups. A better understanding of the mechanisms which
generate EZs would help with understanding the possible importance of EZs in
biology and in engineering applications such as filtration and microfluidics.
Here we review the experimental evidence for EZ phenomena in water and the
major theories that have been proposed. We review experimental results from
birefringence, neutron radiography, nuclear magnetic resonance, and other
studies. Pollack and others have theorized that water in the EZ exists has a
different structure than bulk water, and that this accounts for the EZ. We
present several alternative explanations for EZs and argue that Schurr's theory
based on diffusiophoresis presents a compelling alternative explanation for the
core EZ phenomenon. Among other things, Schurr's theory makes predictions about
the growth of the EZ with time which have been confirmed by Florea et al. and
others. We also touch on several possible confounding factors that make
experimentation on EZs difficult, such as charged surface groups, dissolved
solutes, and adsorbed nanobubbles.Comment: 14 pg
Magnetism of Covalently Functionalized Carbon Nanotubes
We investigate the electronic structure of carbon nanotubes functionalized by
adsorbates anchored with single C-C covalent bonds. We find that, despite the
particular adsorbate, a spin moment with a universal value of 1.0 per
molecule is induced at low coverage. Therefore, we propose a mechanism of
bonding-induced magnetism at the carbon surface. The adsorption of a single
molecule creates a dispersionless defect state at the Fermi energy, which is
mainly localized in the carbon wall and presents a small contribution from the
adsorbate. This universal spin moment is fairly independent of the coverage as
long as all the molecules occupy the same graphenic sublattice. The magnetic
coupling between adsorbates is also studied and reveals a key dependence on the
graphenic sublattice adsorption site.Comment: final version, improved discussion about calculations and defect
concentratio
The longitudinal thickness of air-shower fronts
Linsely (1983) has proposed a technique for the detection and analysis of air showers at large distances from the shower axis based on a measurement of the shower front thickness and the assumption that this thickness is closely related to the core distance. Some of the problems involved with realizing such a technique were investigated, and some related observations are reported. The practical problems of how consistent the measurements of the shower front would be, how one would use the measurement, and how the rate of triggered events would depend on the minimum pulse width required are studied
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