Top-down control inhibits spatial self-organization of a patterned landscape

Regular, self-organized spatial patterns in primary producers have been described in a wide range of ecosystems and are predicted to affect community production and resilience. Although consumers are abundant in most systems, the effect of trophic interactions on pattern formation in primary producers remains unstudied. We studied the effects of top-down control by herbivores on a self-organized landscape of regularly spaced, diatom-covered hummocks alternating with water-filled hollows on an intertidal mudflat in The Netherlands. Spatial patterns developed during spring but were followed by a rapid collapse in summer, leading to a flat landscape with low diatom densities and little variation in sediment bed level. This dramatic decline co-occurred with a gradual increase of benthic herbivores. A manipulative field experiment, where benthic herbivores were removed from the sediment, revealed that both diatom growth and hummock formation were inhibited by the activity of benthic herbivores. Our study provides clear evidence of top-down control of spatial self-organized patterns by benthic herbivores within a biological-geomorphic landscape.     

PET-modified red mud as catalysts for oxidative desulfurization reactions

This work describes the synthesis of catalysts based on red mud/polyethylene terephthalate(PET) composites and their subsequent heat treatment under N2 atmosphere.The materials were characterized by scanning electron microscopy(SEM),temperature programmed reduction(TPR),Fourier transform infrared spectroscopy(FT–IR),X-ray diffraction(XRD),thermogravimetric(TG) analysis and N2adsorption/desorption.The catalysts were evaluated in the oxidative desulfurization reaction of dibenzothiophene(DBT) in a biphasic system.The results indicated that the PET impregnation on red mud increased the affinity of the catalyst with the nonpolar phase(fuel),in which the contaminant was dissolved,allowing a higher conversion(up to 80%) and selectivity to the corresponding dibenzothiophene sulfone.The sulfone compound is more polar than DBT and diffused into the polar solvent as indicated by the data obtained via gas chromatography–mass spectrometry(GC–MS).     

The face of the city is its information

What is it in the externally represented face of the city that makes it recognizable and imaginable? What makes some urban elements and artifacts more legible and better remembered than others? Or put more generally: What makes an object an external representation and what makes it better perceived and/or remembered? Our answer to all these questions is “the information they embody and convey”. Some elements, including those that compose the face of the city, are quantitatively and qualitatively more informative than others and are therefore more legible and better perceived and remembered, quantitatively, in terms of Shannon's theory of information (The Mathematical Theory of Communication, University of Illinois Press, Urbana, IL, 1949), and qualitatively in terms of Haken's (Information and Self-organization: a Macroscopic Approach to Complex Systems, Springer, Heidelberg, 1988/2000) notion of semantic information. In this paper, we elaborate on this point of view in three steps: In the first, we introduce Shannonian information and show how it can be used to define the amount of information externally represented in different urban elements. In the second, we show how this is related to processes of grouping and categorization that give meaning to the face of the city and thus form its semantic information. In the third, we discuss implications for cognition in general and for cognitive mapping in particular.