Has land use pushed terrestrial biodiversity beyond the planetary boundary? A global assessment

Land use and related pressures have reduced local terrestrial biodiversity, but it is unclear how the magnitude of change relates to the recently proposed planetary boundary (“safe limit”). We estimate that land use and related pressures have already reduced local biodiversity intactness—the average proportion of natural biodiversity remaining in local ecosystems—beyond its recently proposed planetary boundary across 58.1% of the world’s land surface, where 71.4% of the human population live. Biodiversity intactness within most biomes (especially grassland biomes), most biodiversity hotspots, and even some wilderness areas is inferred to be beyond the boundary. Such widespread transgression of safe limits suggests that biodiversity loss, if unchecked, will undermine efforts toward long-term sustainable development

Modeling Guidelines and a Benchmark for Power System Simulation Studies of Three-Phase Single-Stage Photovoltaic Systems

This paper presents modeling guidelines and a benchmark system for power system simulation studies of grid-connected, three-phase, single-stage Photovoltaic (PV) systems that employ a voltage-sourced converter (VSC) as the power processor. The objective of this work is to introduce the main components, operation/protection modes, and control layers/schemes of medium- and high-power PV systems, to assist power engineers in developing circuit-based simulation models for impact assessment studies, analysis, and identification of potential issues with respect to the grid integration of PV systems. Parameter selection, control tuning, and design guidelines are also briefly discussed. The usefulness of the benchmark system is demonstrated through a fairly comprehensive set of test cases, conducted in the PSCAD/EMTDC software environment. However, the models and techniques presented in this paper are independent of any specific circuit simulation software package. Also, they may not fully conform to the methods exercised by all manufacturers, due to the proprietary nature of the industry

Influence of initial micro-crack damage on strength and micro-cracking behavior of an intrusive crystalline rock

Rocks inherently contain some micro-cracks. The existence of initial micro-cracks introduces weakness to the rock specimen and hence affects the strength and deformation behavior of rocks. This paper numerically investigates the influence of initial micro-crack damage on the strength and deformation behavior and the associated micro-cracking process of a crystalline rock using a previously-calibrated grain-based model (GBM), which is implemented in two-dimensional Particle Flow Code (PFC2D). The initial micro-crack damage is generated by loading/unloading of the model numerically, and a damage parameter is defined to quantify the degree of initial micro-crack damage. After the initial micro-crack damage is generated, compressive loading tests under different confining pressures are conducted. The simulation results reveal that the initial micro-crack damage has a significant influence on the simulated stress–strain curve, rock strength, elastic modulus, and total number of generated micro-cracks. In general, as the initial micro-crack damage increases in the numerical model, the simulated rock strength and elastic modulus gradually decrease. However, the decrease in rock property (strength and elastic modulus) will become significant only after sufficiently high initial micro-crack damage in the model is reached. The elastic modulus to UCS ratio (E/UCS) is not significantly affected by the initial micro-crack damage. Overall, the initial micro-crack damage weakens the model. The simulation results are in good agreement with previous laboratory tests results. The PFC2D-GBM approach in this study can be used to capture the strength and deformation behavior of damaged rocks, which are induced from initially-generated micro-cracks, e.g., rock drilling and coring, cyclic loading, and thermal loading.MOE (Min. of Education, S’pore