Detection of contaminant plumes released from landfills: Numerical versus analytical solutions

Contaminant leaks released from landfills are a threat to groundwater quality. The groundwater monitoring systems installed in the vicinity of such facilities are vital. In this study the detection probability of a contaminant plume released from a landfill has been investigated by means of both a simulation and an analytical model for both homogeneous and heterogeneous aquifer conditions. Since the detection probability is a sensitive quantity, we first compare the two methods for homogeneous aquifer conditions to assess the errors that are encountered by performing simulations. The analysis shows that the simulation model yields the detection probabilities of a contaminant plume at a given monitoring well quite well in the homogeneous case. For heterogeneous aquifers we apply the approximated analytical model based on macro-dispersivities. Here we find that this model is insufficient in monitoring system design, since the obtained analytical values of the detection probabilities at a given monitoring well differ significantly from those computed by simulation.Delft Institute of Applied MathematicsElectrical Engineering, Mathematics and Computer Scienc

Fabrication of ‘finger-geometry’ silicon solar cells by electrochemical anodisation

Cells made from crystalline silicon dominate the market for photovoltaics, but improvements in cost-effectiveness are still necessary for uptake to increase. In this paper, we investigate the fabrication of a cell structure which has the potential to be compatible with cheap low-purity silicon substrates. In our cell design the charge-collecting p–n junction protrudes into the substrate like fingers, thus significantly reducing the required carrier diffusion length compared to a front planar junction cell. The macroporous structure is created by electrochemical anodisation of an n-type silicon substrate in an HF and H2O2 (aqueous) electrolyte. The pores are loaded with a boron-containing glass which is then annealed to diffuse the dopant into the silicon substrate forming a volume junction. The anodisation conditions have been optimised using intentionally contaminated single-crystal silicon as a model system. We characterise the junction formed by electron beam induced current and current–voltage measurements. The anodisation study is extended to n-type multicrystalline silicon and it is found that the orientation of the grains strongly influences the geometry of the pores formed. The potential for using this cell structure for low-cost photovoltaics is discussed and potential problems are highlighted

The urgent need for robust coral disease diagnostics

Coral disease has emerged over recent decades as a significant threat to coral reef ecosystems, with declines in coral cover and diversity of Caribbean reefs providing an example of the potential impacts of disease at regional scales. If similar trends are to be mitigated or avoided on reefs worldwide, a deeper understanding of the factors underlying the origin and spread of coral diseases and the steps that can be taken to prevent, control, or reduce their impacts is required. In recent years, an increased focus on coral microbiology and the application of classic culture techniques and emerging molecular technologies has revealed several coral pathogens that could serve as targets for novel coral disease diagnostic tools. The ability to detect and quantify microbial agents identified as indicators of coral disease will aid in the elucidation of disease causation and facilitate coral disease detection and diagnosis, pathogen monitoring in individuals and ecosystems, and identification of pathogen sources, vectors, and reservoirs. This information will advance the field of coral disease research and contribute knowledge necessary for effective coral reef management. This paper establishes the need for sensitive and specific molecular-based coral pathogen detection, outlines the emerging technologies that could serve as the basis of a new generation of coral disease diagnostic assays, and addresses the unique challenges inherent to the application of these techniques to environmentally derived coral samples