Status of the TOUGH-FLAC simulator and recent applications related to coupled fluid flow and crustal deformations

This paper presents recent advancement in and applications of TOUGH-FLAC, a simulator for multiphase fluid flow and geomechanics. The TOUGH-FLAC simulator links the TOUGH family multiphase fluid and heat transport codes with the commercial FLAC^3D geomechanical simulator. The most significant new TOUGH-FLAC development in the past few years is a revised architecture, enabling a more rigorous and tight coupling procedure with improved computational efficiency. The applications presented in this paper are related to modeling of crustal deformations caused by deep underground fluid movements and pressure changes as a result of both industrial activities (the In Salah CO₂ Storage Project and the Geysers Geothermal Field) and natural events (the 1960s Matsushiro Earthquake Swarm). Finally, the paper provides some perspectives on the future of TOUGH-FLAC in light of its applicability to practical problems and the need for high-performance computing capabilities for field-scale problems, such as industrial-scale CO₂ storage and enhanced geothermal systems. It is concluded that despite some limitations to fully adapting a commercial code such as FLAC^3D for some specialized research and computational needs, TOUGH-FLAC is likely to remain a pragmatic simulation approach, with an increasing number of users in both academia and industry.     

Synthesis and characterisation of fluorescent pyrene‐end‐capped polylactide fibres

Fluorescent markers are critical for tracking the position and movement of molecules both in vivo and in vitro. Conventionally, synthetic dyes are non‐covalently added to polymers for fluorescent tracking, but often diffuse away. Here we demonstrate, for the first time, a facile method for the synthesis of fluorescent poly(lactic acid) nano‐/microfibres for biomedical applications using solution spin blowing. Pyrene‐end‐capped poly(l ‐lactide) (PLLA) derivatives were synthesised using the ring‐opening polymerisation of l ‐lactide and they were characterised using spectroscopic and thermal analyses. Submicrometre‐sized fluorescent fibres were produced from these PLLA derivatives using solution blow spinning techniques generating polymer blends and core–shell fibres. Such system could be further exploited to incorporate electrically conductive carbon allotropes via the pyrene aromaticity, producing fluorescent and electrically active fibres for in vitro monitoring and electrical stimulation. © 2018 Society of Chemical Industry     

Linked multicontinuum and crack tensor approach for modeling of coupled geomechanics, fluid flow and transport in fractured rock

In this paper, we present a linked multicontinuum and crack tensor approach for modeling of coupled geomechanics, fluid flow, and solute transport in fractured rock. We used the crack tensor approach to calculate effective block-scale properties, including anisotropic permeability and elastic tensors, as well as multicontinuum properties relevant to fracture-matrix interactions and matrix diffusion. In the modeling, we considered stress dependent properties, through stress-induced changes in fracture apertures, to update permeability and elastic tensors. We evaluated the effectiveness and accuracy of our multicon-tinuum approach by comparing our modeling results with that of three independent discrete fracture network (DFN) models. In two of the three alternative DFN models, solute transport was simulated by particle tracking, an approach very different from the standard solute transport used in our multicon-tinuum modeling. We compared the results for flow and solute transport through a 20 m × 20 m model domain of fractured rock, including detailed comparison of total flow rate, its distribution, and solute breakthrough curves. In our modeling, we divided the 20 m × 20 m model domain into regular blocks, or continuum elements. We selected a model discretization of 40 × 40 elements (having a side length of 0.5 m) that resulted in a fluid-flow rate equivalent to that of the DFN models. Our simulation results were in reasonably good agreement with the alternative DFN models, for both advective dominated transport (under high hydraulic gradient) and matrix-diffusion retarded transport (under low hydraulic gradient). However, we found pronounced numerical dispersion when using larger grid blocks, a problem that could be remediated by the use of a finer numerical grid resolution, while maintaining a larger grid for evaluation of equivalent properties, i.e. a property grid overlapping the numerical grid. Finally, we encountered some difficulties in using our approach when element sizes were so small that only one or a few fractures intersect an element-this is an area of possible improvement that will be pursued in future research.     

Chemical sputtering of deuterated carbon surfaces at various surface temperatures

The chemical sputtering of deuterated amorphous carbon (a-C:D) surfaces irradiated by 1-50 eV deuterium atoms at surface temperatures between 300 and 1000 K was studied using classical molecular dynamics. A quasi-stationary state was reached by cumulative bombardment for each energy and temperature. Results were compared with available experimental data and previous modeling results and the applicability of molecular dynamics for thermally generated processes was discussed. An attempt is made to correct the absence of the thermally stimulated desorption/degassing of hydrogen from the MD simulations, which evolve at the longer time scales.     

An investigation of governance frameworks for public projects in Norway and the UK

This paper describes four case studies which formed a key part of an investigation into public investment project governance frameworks in Norway and the UK. The studies looked at how the embedded governance principles worked out in practice, how they affected PM, and how consistent their effects were with their aims. Conclusion is made about the actual effects of the frameworks, and various areas for improvement or further study are highlighted.     

A conceptual optimisation strategy for radiography in a digital environment

Using a completely digital environment for the entire imaging process leads to new possibilities for optimisation of radiography since many restrictions of screen/film systems, such as the small dynamic range and the lack of possibilities for image processing, do not apply any longer. However, at the same time these new possibilities lead to a more complicated optimisation process, since more freedom is given to alter parameters. This paper focuses on describing an optimisation strategy that concentrates on taking advantage of the conceptual differences between digital systems and screen/film systems. The strategy can be summarised as: (a) always include the anatomical background during the optimisation, (b) perform all comparisons at a constant effective dose and (c) separate the image display stage from the image collection stage. A three-step process is proposed where the optimal setting of the technique parameters is determined at first, followed by an optimisation of the image processing. In the final step the optimal dose level-given the optimal settings of the image collection and image display stages-is determined.     

An optimisation strategy in a digital environment applied to neonatal chest imaging

The aim of this study was to find the optimum tube voltage for neonatal chest imaging in computed radiography. The study was designed to take full advantage of the benefits of digital imaging, for example, by comparing the tube voltages at constant effective dose. A phantom study using a living rabbit was first conducted. Images were collected at tube voltages ranging from 40 to 90 kV(p). The reproduction of four structures (central vessels, peripheral vessels, carina and thoracic vertebrae) was rated by 10 radiologists. The reproduction of both central and peripheral vessels was relatively independent of tube voltage. The carina was better reproduced at higher tube voltages whereas the opposite was true for the thoracic vertebrae. Based on the higher importance of the reproduction of the carina it was decided that 90 kV(p) was the optimal tube voltage. To validate the result from the phantom study, a follow-up study was conducted in which images of neonates collected at the tube voltage regularly used at Sahlgrenska University Hospital (70 kV(p)) were compared with images collected at the tube voltage proposed by the phantom study. The follow-up study confirmed the results from the phantom study that the reproduction of the carina was better at 90 than at 70 kV(p). In conclusion, for neonatal chest imaging-given the same effective dose-90 kVp gives better reproduction of important structures than the regularly used 70 kV(p).     

Two-dimensional simulations of bulk heterojunction solar cell characteristics

We present a two-dimensional model of a bulk heterojunction solar cell in which we include the effects of optical interference, exciton diffusion, charge separation via the formation of polaron pairs, and charge transport in two separate interpenetrating phases. Our model shows that the current is increased by an order of magnitude with a full optical model compared to assuming that absorbed photons have a Lambertian profile, and depends much more strongly on applied bias when dissociation via polaron pairs is considered. We find a power efficiency at solar intensities of 1-3% depending on the morphology, and show that the fill factor decreases from 40% at low intensities to 20% at solar intensities because of the increase in the open circuit voltage and decreases much more rapidly at higher intensities due to the decrease in the power efficiency.     

Investigating the effects of reduced size on the properties of ferroelectrics

A series of experiments has been undertaken to understand more about the fundamental origin of the thickness-induced permittivity collapse often observed in conventional thin film ferroelectric heterostructures. The various experiments are discussed, highlighting the eventual need to examine permittivity collapse in thin film single crystal material. It has been seen that dielectric collapse is not a direct consequence of reduced size, and neither is it a consequence of unavoidable physics associated with the ferroelectric-electrode boundary. Research on three-dimensional shape-constrained ferroelectrics, emphasizing self-assembled structures based on nanoporous alumina templates and on FIB-milled single crystals, is also presented, and appears to represent an exciting area for ongoing research.