On the development and analysis of coupled surface-subsurface models of catchments. Part 3. Analytical solutions and scaling laws

The objective of this three-part work is the formulation and rigorous analysis of a number of reduced mathematical models that are nevertheless capable of describing the hydrology at the scale of a river basin (i.e. catchment). Coupled effects of surface and subsurface flows are considered. In this third part, we focus on the development of analytical solutions and scaling laws for a benchmark catchment model that models the river flow (runoff) generated during a single rainfall. We demonstrate that for catchments characterised by a shallow impenetrable bedrock, the shallow-water approximation allows a reduction of the governing formulation to a coupled system of one-dimensional time-dependent equations for the surface and subsurface flows. Asymptotic analysis is used to derive semi-analytical solutions of the model. We provide simple asymptotic scaling laws describing the peak flow formation. These scaling laws can be used as an analytical benchmark for assessing the validity of other physical, conceptual, or statistical models of catchments

On the development and analysis of coupled surface-subsurface models of catchments. Part 2. A three-dimensional benchmark model and its properties

The objective of this three-part work is the formulation and rigorous analysis of a number of reduced mathematical models that are nevertheless capable of describing the hydrology at the scale of a river basin (i.e. catchment). Coupled effects of surface and subsurface flows are considered. In this second part, we construct a benchmark catchment scenario and investigate the effects of parameters within their typical ranges. Previous research on coupled surface-subsurface models have focused on numerical simulations of site-specific catchments; here our focus is broader and emphasises the study of general solutions to the mathematical models, and their dependencies on dimensionless parameters. This study provides a foundation based on the examination of a geometrically simple three-dimensional benchmark scenario. We develop a nondimensional coupled surface-subsurface model, and extract the key dimensionless parameters. We then apply asymptotic methods in order to discuss some potential simplifications, including the reduction of the geometry to a two-dimensional form, where the principal groundwater and overland flows occur in the hillslope direction. Numerical solutions demonstrate the effects of model parameters and provide guidance on the validity of the dimensional reductions

On the development and analysis of coupled surface-subsurface models of catchments. Part 1. Parameter estimation and sensitivity analysis of catchment properties

The objective of this three-part work is the formulation and rigorous analysis of a number of reduced mathematical models that are nevertheless capable of describing the hydrology at the scale of a river basin (i.e. catchment). Coupled effects of surface and subsurface flows are considered. In this first part, we identify and analyse the key physical parameters that appear in governing formulations used within hydrodynamic rainfall-runoff models. Such parameters include those related to the catchment dimensions, topography, soil and rock properties, rainfall intensities, Manning's coefficients, and river channel dimensions. Despite the abundance of research that has produced data sets describing properties of specific river basins, there have been few studies that have investigated the ensemble of typical scaling of key physical properties; these are needed in order to perform a proper dimensional analysis of rainfall-runoff models. Therefore, in this work, we perform an extensive analysis of the parameters; our results form a benchmark and provide guidance to practitioners of the typical parameter sizes and interdependencies. Crucially, the analysis is presented in a fashion that can be reproduced and extended by other researchers, and wherever possible, uses publicly available data sets for catchments in the United Kingdom

The ventilation of buildings and other mitigating measures for COVID-19: a focus on wintertime.

The year 2020 has seen the emergence of a global pandemic as a result of the disease COVID-19. This report reviews knowledge of the transmission of COVID-19 indoors, examines the evidence for mitigating measures, and considers the implications for wintertime with a focus on ventilation.This work was undertaken as a contribution to the Rapid Assistance in Modelling the Pandemic (RAMP) initiative, coordinated by the Royal Society

Through history to growth dynamics: deciphering the evolution of spatial networks

Many ramified, network-like patterns in nature, such as river networks or blood vessels, form as a result of unstable growth of moving boundaries in an external diffusive field. Here, we pose the inverse problem for the network growth—can the growth dynamics be inferred from the analysis of the final pattern? We show that by evolving the network backward in time one can not only reconstruct the growth rules but also get an insight into the conditions under which branch splitting occurs. Determining the growth rules from a single snapshot in time is particularly important for growth processes so slow that they cannot be directly observed, such as growth of river networks and deltas or cave passages. We apply this approach to analyze the growth of a real river network in Vermont, USA. We determine its growth rule and argue that branch splitting events are triggered by an increase in the tip growth velocity.ISSN:2045-232

Understanding the Screening Process of New Molecules

Globally there is a huge market for herbicides. Syngenta and its competitors spend large amounts of money in trying to develop new herbicides which are highly effective (kills the plants that the farmer wants to get rid of), selective (does not harm the crops that the farmer is trying to protect), safe (not harmful to humans or the environment) and cheap to produce. Every year Syngenta chemists develop around one thousand new compounds that could be used as herbicides. Accurately evaluating the efficacy, selectivity, safety and ease of production of each one of these compounds would be extremely expensive. Initially synthesizing compounds even in tiny quantities requires a lot of work. Different compounds will then require different levels of dosage, may target certain species of plants better than others, may work more effectively in conjugation with different solvents etc. A huge amount of time and money could be spent optimizing the application of a particular compound, which then turns out to be very poor compared to existing herbicide products on the market. In order to attempt to select only the best performing compounds in a cost effective way, Syngenta use a screening cascade. This process begins by testing all of the candidate compounds in laboratory experiments, referred to as assays, to see if they can (e.g.) target a particular enzyme, or penetrate a leaf. These lab experiments only require a tiny quantity of each compound to be synthesized. Compounds which perform poorly in these first experiments are discarded from the trial. We call this the first screen. Compounds which pass this first round are then passed to a second round in which a small amount of the compound is applied to several small pots containing a few different species of plant. Compounds which perform poorly in this second experiment are discarded from the trial process. We call this the second screen. In subsequent screens larger quantities of the compounds are used in the experiments, which makes them a lot more expensive. By using more compounds the candidate herbicides can be tested on a larger range or species, at different dosages, in conjunction with various different conditions, and with less sampling error. As the screening process progresses, the screens become steadily more rigorous and consequently more expensive. At the same time the number of compounds remaining in the trial goes down. Finally a small number of compounds are taken to the final level, called the field trial. In this trial the compounds are applied outdoors in the way they would be used if they were eventually developed into a commercial product