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A Design Path for Hierarchical Self-Assembly of Patchy Colloids
Patchy colloids are promising candidates for building blocks in directed
self-assembly. To be successful the surface patterns need to both be simple
enough to be synthesized, while feature-rich enough to cause the colloids to
self-assemble into desired structures. Achieving this is a challenge for
traditional synthesis methods. Recently it has been suggested that the surface
pattern themselves can be made to self-assemble. In this paper we show that a
wide range of functional structures can be made to self-assemble using this
approach. More generally we present a design path for hierarchical targeted
self-assembly of patchy colloids. At the level of the surface structure, we use
a predictive method utilizing universality of patterns of stripes and spots,
coupled with stoichiometric constraints, to cause highly specific and
functional patterns to self-assemble on spherical surfaces. We use a
minimalistic model of an alkanethiol on gold as a model system and demonstrate
that, even with limited control over the interaction between surface
constituents, we can obtain patterns that causes the colloids themselves to
self-assemble into various complex geometric structures. We demonstrate how
variations of the same design path cause in-silico self-assembly of strings,
membranes, cubic and spherical aggregates, as well as various crystalline
patterns.Comment: 8 pages, 5 figure
Secondary and compound concentrators for parabolic dish solar thermal power systems
A secondary optical element may be added to a parabolic dish solar concentrator to increase the geometric concentration ratio attainable at a given intercept factor. This secondary may be a Fresnel lens or a mirror, such as a compound elliptic concentrator or a hyperbolic trumpet. At a fixed intercept factor, higher overall geometric concentration may be obtainable with a long focal length primary and a suitable secondary matched to it. Use of a secondary to increase the geometric concentration ratio is more likely to e worthwhile if the receiver temperature is high and if errors in the primary are large. Folding the optical path with a secondary may reduce cost by locating the receiver and power conversion equipment closer to the ground and by eliminating the heavy structure needed to support this equipment at the primary focus. Promising folded-path configurations include the Ritchey-Chretien and perhaps some three element geometries. Folding the optical path may be most useful in systems that provide process heat
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