A Dissipative-Particle-Dynamics Model for Simulating Dynamics of Charged Colloid

A mesoscopic colloid model is developed in which a spherical colloid is represented by many interacting sites on its surface. The hydrodynamic interactions with thermal fluctuations are taken accounts in full using Dissipative Particle Dynamics, and the electrostatic interactions are simulated using Particle-Particle-Particle Mesh method. This new model is applied to investigate the electrophoretic mobility of a charged colloid under an external electric field, and the influence of salt concentration and colloid charge are systematically studied. The simulation results show good agreement with predictions from the electrokinetic theory.Comment: 17 pages, 8 figures, submitted to the proceedings of High Performance Computing in Science & Engineering '1

Robust evidence for reversal in the aerosol effective climate forcing trend

Anthropogenic aerosols exert a cooling influence that offsets part of the greenhouse gas warming. Due to their short tropospheric lifetime of only up to several days, the aerosol forcing responds quickly to emissions. Here we present and discuss the evolution of the aerosol forcing since 2000. There are multiple lines of evidence that allow to robustly conclude that the anthropogenic aerosol effective radiative forcing – both aerosol-radiation and aerosol-cloud interactions – has become globally less negative, i.e. that the trend in aerosol effective radiative forcing changed sign from negative to positive. Bottom-up inventories show that anthropogenic primary aerosol and aerosol precursor emissions declined in most regions of the world; observations related to aerosol burden show declining trends, in particular of the fine-mode particles that make up most of the anthropogenic aerosols; satellite retrievals of cloud droplet numbers show trends consistent in sign, as do observations of top-of-atmosphere radiation. Climate model results, including a revised set that is constrained by observations of the ocean heat content evolution show a consistent sign and magnitude for a positive forcing relative to 2000 due to reduced aerosol effects. This reduction leads to an acceleration of the forcing of climate change, i.e. an increase in forcing by 0.1 to 0.3 W m-2, up to 12 % of the total climate forcing in 2019 compared to 1750 according to IPCC

The magic of the pentangle: Dynamic symmetry from Merlin to Penrose

AbstractMerlin the Magician instructs his charges Arthur and Kay in the secrets of dynamic symmetry, the logarithmic spiral, the golden fraction, -rectangle, and -triangle, Fibonacci numbers and the pentangle. The pentangle is central to the late fourteenth-century “Sur Gawain and the Green Knight”, to medieval sign theory as well as to recent research in quasi-periodic alloy crystals

Symmetry and modularity

AbstractMany complex structures may be generated from simple modules with the aid of an algorithm or generating rule. The properties of space generally impose restrictions on the shape of the module. As examples we consider tilings of the euclidean plane and of the sphere, lattices and lattice complexes, Dirichlet Domains and space-filling, and the decomposition and recombining of some polyhedra into space fillers