Santa Fe Institute

About: Santa Fe Institute is a nonprofit organization based out in Santa Fe, New Mexico, United States. It is known for research contribution in the topics: Population & Context (language use). The organization has 558 authors who have published 4558 publications receiving 396015 citations. The organization is also known as: SFI.

Transparent and Catalytic Carbon Nanotube Films

Abstract: We report on the synthesis of thin, transparent, and highly catalytic carbon nanotube films. Nanotubes catalyze the reduction of triiodide, a reaction that is important for the dye-sensitized solar cell, with a charge-transfer resistance as measured by electrochemical impedance spectroscopy that decreases with increasing film thickness. Moreover, the catalytic activity can be significantly enhanced by exposing the nanotubes to ozone in order to introduce defects. Ozone-treated, defective nanotube films could serve as catalytic, transparent, and conducting electrodes for the dye-sensitized solar cell. Other possible applications include batteries, fuel cells, and electroanalytical devices.

Network structure and robustness of marine food webs

Abstract: Previous studies suggest that food-web theory has yet to account for major differences in food-web properties of marine versus other types of ecosystems. We examined this issue by ana- lyzing the network structure of food webs for the Northeast US Shelf, a Caribbean reef, and Benguela, off South Africa. The values of connectance (links per species 2 ), link density (links per spe- cies), mean chain length, and fractions of intermediate, omnivorous, and cannibalistic taxa of these marine webs are somewhat high but still within the ranges observed in other webs. We further com- pared the marine webs by using the empirically corroborated 'niche model' that accounts for observed variation in diversity (taxon number) and complexity (connectance). Our results substanti- ate previously reported results for estuarine, fresh-water, and terrestrial datasets, which suggests that food webs from different types of ecosystems with variable diversity and complexity share fun- damental structural and ordering characteristics. Analyses of potential secondary extinctions result- ing from species loss show that the structural robustness of marine food webs is also consistent with trends from other food webs. As expected, given their relatively high connectance, marine food webs appear fairly robust to loss of most-connected taxa as well as random taxa. Still, the short average path length between marine taxa (1.6 links) suggests that effects from perturbations, such as over- fishing, can be transmitted more widely throughout marine ecosystems than previously appreciated.

Critical phenomena in atmospheric precipitation

Abstract: Critical phenomena occur near continuous phase transitions. As a tuning parameter crosses its critical value, an order parameter increases as a power law. At criticality, order-parameter fluctuations diverge and their spatial correlation decays as a power law1. In systems where the tuning parameter and order parameter are coupled, the critical point can become an attractor, and self-organized criticality (SOC) results2,3. Here we argue, using satellite data, that a critical value of water vapour (the tuning parameter) marks a non-equilibrium continuous phase transition to a regime of strong atmospheric convection and precipitation (the order parameter)—with correlated regions on scales of tens to hundreds of kilometres. Despite the complexity of atmospheric dynamics, we find that important observables conform to the simple functional forms predicted by the theory of critical phenomena. In meteorology the term 'quasi-equilibrium' refers to a balance between slow large-scale driving processes and rapid release of buoyancy by moist convection4. Our study indicates that the attractive quasi-equilibrium state, postulated long before SOC (ref. 5), is the critical point of a continuous phase transition and is thus an instance of SOC.

Scaling and power-laws in ecological systems.

Abstract: Scaling relationships (where body size features as the independent variable) and power-law distributions are commonly reported in ecological systems. In this review we analyze scaling relationships related to energy acquisition and transformation and power-laws related to fluctuations in numbers. Our aim is to show how individual level attributes can help to explain and predict patterns at the level of populations that can propagate at upper levels of organization. We review similar relationships also appearing in the analysis of aquatic ecosystems (i.e. the biomass spectra) in the context of ecological invariant relationships (i.e. independent of size) such as the 'energetic equivalence rule' and the 'linear biomass hypothesis'. We also discuss some power-law distributions emerging in the analysis of numbers and fluctuations in ecological attributes as they point to regularities that are yet to be integrated with traditional scaling relationships and which we foresee as an exciting area of future research.