A two-dimensional (2D) porous layer can make an ideal membrane for separation of chemical mixtures because its infinitesimal thickness promises ultimate permeation. Graphene--with great mechanical strength, chemical stability, and inherent impermeability--offers a unique 2D system with which to realize this membrane and study the mass transport, if perforated precisely. We report highly efficient mass transfer across physically perforated double-layer graphene, having up to a few million pores with narrowly distributed diameters between less than 10 nanometers and 1 micrometer. The measured transport rates are in agreement with predictions of 2D transport theories. Attributed to its atomic thicknesses, these porous graphene membranes show permeances of gas, liquid, and water vapor far in excess of those shown by finite-thickness membranes, highlighting the ultimate permeation these 2D membranes can provide.

Most of the terrestrial net primary production enters the decomposer system as dead organic matter, and the subsequent recycling of C and nutrients are key processes for the functioning of ecosystems and the delivery of ecosystem goods and services. Although climatic and substrate quality controls are reasonably well understood, the functional role of biodiversity for biogeochemical cycles remains elusive. Here we ask how altering litter species diversity affects species-specific decomposition rates and whether large litter-feeding soil animals control the litter diversity-function relationship in a temperate forest ecosystem. We found that decomposition of a given litter species changed greatly in the presence of litters from other cooccurring species despite unaltered climatic conditions and litter chemistry. Most importantly, soil fauna determined the magnitude and direction of litter diversity effects. Our data show that litter species richness and soil fauna interactively determine rates of decomposition in a temperate forest, suggesting a combination of bottom-up and top-down controls of litter diversity effects on ecosystem C and nutrient cycling. These results provide evidence that, in ecosystems supporting a well developed soil macrofauna community, animal activity plays a fundamental role for altered decomposition in response to changing litter diversity, which in turn has important implications for biogeochemical cycles and the long-term functioning of ecosystems with ongoing biodiversity loss.biodiversity ͉ soil fauna ͉ temperate forest ecosystem P lants interact with ecosystem C and nutrient turnover in various ways (1, 2), but the importance of plant species diversity for these processes is not well understood. Living plant diversity can influence decomposition and nutrient dynamics through changes in microclimatic conditions (1, 3), complementary nutrient use (4, 5), and rhizosphere processes. In addition, the amount and quality of plant litter input have a strong impact on C and nutrient cycling (6-8). This litter effect depends on the relative contribution of different species and their characteristic litter traits to the overall community litter pool. There is clear evidence suggesting that observed rates of community litter mass loss and nutrient mineralization may deviate substantially from those expected from single-litter-species decomposition of component species because of nonadditive interactions among litter species (3, 9-13).We lack a mechanistic understanding of litter species interactions, and the variable results, ranging from clearly negative to strongly positive litter mixing effects, on decomposition are difficult to explain (11-13). Recent theory, and the rare attempts to perform experimental tests of specific mechanisms, have concentrated on bottom-up controls of distinct litter chemistries through nutrient translocation among litter species, or inhibiting compounds, and the results have been conflicting (10-16). Besides potential bottom-up control on litter species interaction...

No abstract

Energy systems are regularly subject to major disruptions affecting economic activities, operation of infrastructure and the society as a whole. Resilience assessment comprises the pre-event oriented classical risk assessment as a central element, but it goes beyond that because it also includes and evaluates post-event strategies to improve the functioning of the system during its future operation. First, an overview of resilience definitions used across various scientific disciplines is presented, followed by an in-depth analysis of resilience assessment and quantification for energy systems. The relevant literature is classified by approach and according to four key functions of resilience: resist, restabilize, rebuild, and reconfigure. Findings show that irrespective of the research field, a resilient system always operates with an aim to minimize the potential consequences resulting from a disruptive event and to efficiently recover from a potential system performance loss.