Ludwig: A parallel Lattice-Boltzmann code for complex fluids

This paper describes `Ludwig', a versatile code for the simulation of Lattice-Boltzmann (LB) models in 3-D on cubic lattices. In fact `Ludwig' is not a single code, but a set of codes that share certain common routines, such as I/O and communications. If `Ludwig' is used as intended, a variety of complex fluid models with different equilibrium free energies are simple to code, so that the user may concentrate on the physics of the problem, rather than on parallel computing issues. Thus far, `Ludwig''s main application has been to symmetric binary fluid mixtures. We first explain the philosophy and structure of `Ludwig' which is argued to be a very effective way of developing large codes for academic consortia. Next we elaborate on some parallel implementation issues such as parallel I/O, and the use of MPI to achieve full portability and good efficiency on both MPP and SMP systems. Finally, we describe how to implement generic solid boundaries, and look in detail at the particular case of a symmetric binary fluid mixture near a solid wall. We present a novel scheme for the thermodynamically consistent simulation of wetting phenomena, in the presence of static and moving solid boundaries, and check its performance.Comment: Submitted to Computer Physics Communication

Species‐habitat networks reveal conservation implications that other community analyses do not detect

Grassland restoration is an important conservation intervention supporting declining insect pollinators in threatened calcareous grassland landscapes. While the success of restoration is often quantified using simple measures of diversity or similarity to target communities, these measures do not capture all fundamental aspects of community reconstruction. Here, we develop species–habitat networks that aim to define habitat-level foraging dependencies of pollinators across restored grassland landscapes and compare their value to these more conventional measures of community restoration. We assessed this across Salisbury Plain (UK), which represents the largest area of chalk grassland in northwestern Europe, encompassing six distinct management types aimed at the restoration and maintenance of species-rich calcareous grassland. Sites that were previously disturbed or reverting from arable agriculture were comparable with those of ancient grasslands in terms of pollinator abundance and species richness. However, intensively managed grasslands exhibited notably lower values across nearly all measured indicators, including flower and pollinator richness and abundance, than ancient grasslands, with unmanaged grasslands following closely behind. This underscores the need for caution with both long-term neglect and highly intensive management. Applying our species–habitat network approach, we found that pollinator communities in grasslands recovering from past military disturbance showed stronger modular associations with those in ancient grasslands than areas recovering from intensive agriculture. This highlights the importance of habitat history in shaping restoration trajectories. We propose that species–habitat networks should be part of the standard analytical toolkit assessing the effectiveness of restoration at landscape scale, particularly for mobile species such as insects