Tracing back the source of contamination

From the time a contaminant is detected in an observation well, the question of where and when the contaminant was introduced in the aquifer needs an answer. Many techniques have been proposed to answer this question, but virtually all of them assume that the aquifer and its dynamics are perfectly known. This work discusses a new approach for the simultaneous identification of the contaminant source location and the spatial variability of hydraulic conductivity in an aquifer which has been validated on synthetic and laboratory experiments and which is in the process of being validated on a real aquifer

Applying NMR Relaxation Methods to the Study of Liquids in Porous Media

The work presented within this thesis focusses on the development of NMR relaxation techniques to unambiguously characterise the adsorption behaviour of liquids imbibed within catalytic materials. Principally, this study is centred on γ-alumina, which is used industrially as both a catalyst and a catalyst support. Ratios of fixed field T1 and T2 values were compared with fast field cycling (FFC-) NMR measurements. For each technique the relative advantages and disadvantages were explored, and methodologies allowing a robust implementation of these techniques to study the adsorption were presented. Fixed field measurements of T1,B/T1,pore and e_surf=-T2/T1 were used to compare the relative interaction strength for a range of liquids imbibed within γ-alumina. A strong correlation between the adsorbate polarity and the T1,B/T1,pore ratio of rigid molecules showed the sensitivity of high field NMR to surface adsorption processes. However when flexible molecules were studied the presence of internal motions distorted the trends in the relaxation behaviour, making both the T1,B/T1,pore and e_surf measurements unsuitable. FFC-NMR was explored as an alternative to fixed field NMR. This allowed the measurement of relaxation behaviour over a range of low field strengths. The FFC-NMR data showed a clear ordering of the solid-liquid interaction strengths, which was more consistent with the predicted physical chemistry of the system than the order given by a fixed field analysis. For methanol and acetone imbibed within γ-alumina multicomponent relaxation behaviour was observed. The origin of this was shown to be functionality specific adsorption behaviour, and the presence of a stable reaction intermediate respectively. These observations led to a more granular understanding of the adsorption. A formal modelling approach was then applied to the FFC-NMR data in order to extract quantitative correlation times that described the dynamics of each adsorbate at the catalyst surface. The sensitivity of FFC-NMR to coadsorption was further studied through the use of binary liquid mixtures. A model for the interpretation of the relaxation behaviour of each component in the binary mixture was proposed and used to demonstrate the liquid structuring and micro-phase separation that occurred during adsorption.EPSRC grant EP/M507350/

Dynamical Systems

Complex systems are pervasive in many areas of science integrated in our daily lives. Examples include financial markets, highway transportation networks, telecommunication networks, world and country economies, social networks, immunological systems, living organisms, computational systems and electrical and mechanical structures. Complex systems are often composed of a large number of interconnected and interacting entities, exhibiting much richer global scale dynamics than the properties and behavior of individual entities. Complex systems are studied in many areas of natural sciences, social sciences, engineering and mathematical sciences. This special issue therefore intends to contribute towards the dissemination of the multifaceted concepts in accepted use by the scientific community. We hope readers enjoy this pertinent selection of papers which represents relevant examples of the state of the art in present day research. [...