Domain decomposition with Robin boundary conditions across a phase interface

Domain decompositions are typically pursued in order to split up large elliptic boundary-value problems into a set of smaller problems that can each be solved separately, with the solution to the larger problem obtained through iterative application of inter-domain boundary conditions. Here we review a related problem that arises in the study of unsteady advection-diffusion with two solvent phases. A boundary iteration scheme is devised and tested within the context of an idealised Poisson problem. The method is then used in the simulation of capillary chromatography and the results compared to an available analytical solution

The interaction of helical tip and root vortices in a wind turbine wake

Analysis of the helical vortices measured behind a model wind turbine in a water channel are reported. Phase-locked measurements using planar particle image ve- locimetry are taken behind a Glauert rotor to investigate the evolution and breakdown of the helical vortex structures. Existing linear stability theory predicts helical vortex filaments to be susceptible to three unstable modes. The current work presents tip and root vortex evolution in the wake for varying tip speed ratio and shows a breaking of the helical symmetry and merging of the vortices due to mutual inductance between the vortical filaments. The merging of the vortices is shown to be steady with rotor phase, however, small-scale non-periodic meander of the vortex positions is also ob- served. The generation of the helical wake is demonstrated to be closely coupled with the blade aerodynamics, strongly influencing the vortex properties which are shown to agree with theoretical predictions of the circulation shed into the wake by the blades. The mutual inductance of the helices is shown to occur at the same non-dimensional wake distance

Mutual inductance of two helical vortices

The pairing of helical tip vortices in the wake of a two-bladed rotor is investigated experimentally. Time-resolved particle image velocimetry measurements provide a clear temporal and spatial evolution of the vortical structures, highlighting the transition to instability and the effect of tip speed ratio and helical spacing. The temporal growth rate of the vortex system instabilities were measured and are shown to be dependent on helical spacing. The evolution of filaments and their growth rates support the argument that the mutual inductance mode is the driving mechanism behind the transition to an unstable wake. The measurements are in agreement with maximum growth rates predicted by linear stability analyses of single- and double-helix arrangements. In addition, the wake topology due to varying rotor load through tip speed ratio variation is shown to play an important role in the initial symmetry breaking that drives the wake transition

On the Use of Matrix-Free Shift-Invert Strategies For Global Flow Instability Analysis

A novel time-stepping shift-invert algorithm for linear stability analysis of laminar flows in complex geometries is presented. This method, based on a Krylov subspace iteration, enables the solution of complex non-symmetric eigenvalue problems in a matrix-free framework. Validations and comparisons to the classical exponential method have been performed in three different cases: (i) stenotic flow, (ii) backward-facing step and (iii) lid-driven swirling flow. Results show that this new approach speeds up the required Krylov subspace iterations and has the capability of converging to specific parts of the global spectrum. It is shown that, although the exponential method remains the method of choice if leading eigenvalues are sought, the performance of the present method could be dramatically improved with the use of a preconditioner. In addition, as opposed to other methods, this strategy can be directly applied to any time-stepper, regardless of the temporal or spatial discretization of the latter

The global distribution of Bacillus anthracis and associated anthrax risk to humans, livestock and wildlife.

Bacillus anthracis is a spore-forming, Gram-positive bacterium responsible for anthrax, an acute infection that most significantly affects grazing livestock and wild ungulates, but also poses a threat to human health. The geographic extent of B. anthracis is poorly understood, despite multi-decade research on anthrax epizootic and epidemic dynamics; many countries have limited or inadequate surveillance systems, even within known endemic regions. Here, we compile a global occurrence dataset of human, livestock and wildlife anthrax outbreaks. With these records, we use boosted regression trees to produce a map of the global distribution of B. anthracis as a proxy for anthrax risk. We estimate that 1.83 billion people (95% credible interval (CI): 0.59-4.16 billion) live within regions of anthrax risk, but most of that population faces little occupational exposure. More informatively, a global total of 63.8 million poor livestock keepers (95% CI: 17.5-168.6 million) and 1.1 billion livestock (95% CI: 0.4-2.3 billion) live within vulnerable regions. Human and livestock vulnerability are both concentrated in rural rainfed systems throughout arid and temperate land across Eurasia, Africa and North America. We conclude by mapping where anthrax risk could disrupt sensitive conservation efforts for wild ungulates that coincide with anthrax-prone landscapes

Historical Distribution and Molecular Diversity of Bacillus anthracis, Kazakhstan

This study provides useful baseline data for guiding future disease control programs

Persistent anthrax as a major driver of wildlife mortality in a tropical rainforest

Anthrax is a globally important animal disease and zoonosis. Despite this, our current knowledge of anthrax ecology is largely limited to arid ecosystems, where outbreaks are most commonly reported. Here we show that the dynamics of an anthrax-causing agent, Bacillus cereus biovar anthracis, in a tropical rainforest have severe consequences for local wildlife communities. Using data and samples collected over three decades, we show that rainforest anthrax is a persistent and widespread cause of death for a broad range of mammalian hosts. We predict that this pathogen will accelerate the decline and possibly result in the extirpation of local chimpanzee (Pan troglodytes verus) populations. We present the epidemiology of a cryptic pathogen and show that its presence has important implications for conservation

A new family of covalent inhibitors block nucleotide binding to the active site of pyruvate kinase

PYK (pyruvate kinase) plays a central role in the metabolism of many organisms and cell types, but the elucidation of the details of its function in a systems biology context has been hampered by the lack of specific high-affinity small-molecule inhibitors. High-throughput screening has been used to identify a family of saccharin derivatives which inhibit LmPYK (Leishmania mexicana PYK) activity in a time- (and dose-) dependent manner, a characteristic of irreversible inhibition. The crystal structure of DBS {4-[(1,1-dioxo-1,2-benzothiazol-3-yl)sulfanyl]benzoic acid} complexed with LmPYK shows that the saccharin moiety reacts with an active-site lysine residue (Lys335), forming a covalent bond and sterically hindering the binding of ADP/ATP. Mutation of the lysine residue to an arginine residue eliminated the effect of the inhibitor molecule, providing confirmation of the proposed inhibitor mechanism. This lysine residue is conserved in the active sites of the four human PYK isoenzymes, which were also found to be irreversibly inhibited by DBS. X-ray structures of PYK isoforms show structural differences at the DBS-binding pocket, and this covalent inhibitor of PYK provides a chemical scaffold for the design of new families of potentially isoform-specific irreversible inhibitors