The smectic order of wrinkles

A thin elastic sheet lying on a soft substrate develops wrinkled patterns when subject to an external forcing or as a result of geometric incompatibility. Thin sheet elasticity and substrate response equip such wrinkles with a global preferred wrinkle spacing length and with resistance to wrinkle curvature. These features are responsible for the liquid crystalline smectic-like behaviour of such systems at intermediate length scales. This insight allows better understanding of the wrinkling patterns seen in such systems, with which we explain pattern breaking into domains, the properties of domain walls and wrinkle undulation. We compare our predictions with numerical simulations and with experimental observations

Effects of Trophic Skewing of Species Richness on Ecosystem Functioning in a Diverse Marine Community

Widespread overharvesting of top consumers of the world’s ecosystems has “skewed” food webs, in terms of biomass and species richness, towards a generally greater domination at lower trophic levels. This skewing is exacerbated in locations where exotic species are predominantly low-trophic level consumers such as benthic macrophytes, detritivores, and filter feeders. However, in some systems where numerous exotic predators have been added, sometimes purposefully as in many freshwater systems, food webs are skewed in the opposite direction toward consumer dominance. Little is known about how such modifications to food web topology, e.g., changes in the ratio of predator to prey species richness, affect ecosystem functioning. We experimentally measured the effects of trophic skew on production in an estuarine food web by manipulating ratios of species richness across three trophic levels in experimental mesocosms. After 24 days, increasing macroalgal richness promoted both plant biomass and grazer abundance, although the positive effect on plant biomass disappeared in the presence of grazers. The strongest trophic cascade on the experimentally stocked macroalgae emerged in communities with a greater ratio of prey to predator richness (bottom-rich food webs), while stronger cascades on the accumulation of naturally colonizing algae (primarily microalgae with some early successional macroalgae that recruited and grew in the mesocosms) generally emerged in communities with greater predator to prey richness (the more top-rich food webs). These results suggest that trophic skewing of species richness and overall changes in food web topology can influence marine community structure and food web dynamics in complex ways, emphasizing the need for multitrophic approaches to understand the consequences of marine extinctions and invasions

Interfacial curvature in graft and diblock copolymers and implications for long-range order in cylindrical morphologies

Microstructures of block copolymers in the strong segregation limit are characterized by well-defined interfaces separating the different block materials into domains on a nanometer scale. In this paper, we address the effects of architectural and conformational asymmetry of the blocks on the interfacial curvature characteristics and on the degree of long-range order in the cylindrical morphologies. Experimental (TEM and SAXS) curvature data from polyisoprene−polystyrene (I2S) simple graft block copolymers and from polyisoprene−poly(tert-butyl methacrylate) (PtBMA) linear, conformationally asymmetric diblock copolymers are presented and compared to data from polyisoprene−polystyrene linear diblock copolymers. The experimental data are elucidated by a simple curvature free energy model which accounts for core-space-filling without explicitly specifying the shape of the microdomain. This model allows the prediction of preferred interfacial curvature characteristics as a function of molecular architecture. Good agreement is obtained between the theoretically calculated mean and Gaussian curvatures and the experimentally measured values. A key finding is that the degree of frustration, as measured by the difference between the free energy of the preferred curvature of a given block copolymer and that of the nearest accessible space-filling structure (such as the cylindrical structure), is correlated with the degree of long-range order