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  • Conference paper
    Heuberger CF, Staffell I, Shah N, Mac Dowell Net al., 2016,

    Levelised Value of Electricity - A Systemic Approach to Technology Valuation

    , 26th European Symposium on Computer Aided Process Engineering - ESCAPE 26
  • Conference paper
    Jacobs CT, Piggott MD, Kramer SC, Funke SWet al., 2016,

    On the validity of tidal turbine array configurations obtained from steady-state adjoint optimisation

    , VII European Congress on Computational Methods in Applied Sciences and Engineering, Publisher: ECCOMAS Proceedia, Pages: 8247-8261

    Extracting the optimal amount of power from an array of tidal turbines requires an intricate understanding of tidal dynamics and the effects of turbine placement on the local and regional scale flow. Numerical models have contributed significantly towards this understanding, and more recently, adjoint-based modelling has been employed to optimise the positioning of the turbines in an array in an automated way and improve on simple man-made configurations (e.g. structured grids of turbines) [1]. Adjoint-based optimisation of high-resolution and ideally 3D transient models is generally a very computationally expensive problem. Multiple approaches are therefore used in practice to obtain feasible runtimes: using high viscosity values to obtain a steady-state solution, or a sequence of steady-state solutions for "time-varying" setups; limiting the number of adjoint computations; or reformulating the problem to allow for coarser mesh resolution to make it feasible for resources assessment (e.g. [2] , [3]). However, such compromises may affect the reliability of the modelled turbines, their wakes and interactions, and thus bring into question the validity of the computed optimal turbine positions. This work considers a suite of idealised simulations of flow past tidal turbine arrays in a two-dimensional channel. It compares four regular array configurations, detailed by Divett et al. [4] , with the configuration found through adjoint optimisation in a steady-state, high-viscosity setup. The optimised configuration produces considerably more power than the other configurations (approximately 40% more than the best man-made configuration). The same configurations are then used to produce a suite of transient simulations that do not use constant high-viscosity, and instead use large eddy simulation (LES) to parameterise the resulting turbulent structures. All simulations are performed using OpenTidalFarm [1]. It is shown that the 'low background viscosity'/LES simu

  • Journal article
    Hylton N, Hinrichsen TF, Vaquero-Stainer AR, Yoshida M, Pusch A, Hopkinson M, Hess O, Phillips CC, Ekins-Daukes NJet al., 2016,

    Photoluminescence upconversion at GaAs/InGaP2 interfaces driven by a sequential two-photon absorption mechanism

    , Physical Review B, Vol: 93, ISSN: 2469-9950

    This paper reports on the results of an investigation into the nature of photoluminescence upconversion at GaAs/InGaP2 interfaces. Using a dual-beam excitation experiment, we demonstrate that the upconversion in our sample proceeds via a sequential two-photon optical absorption mechanism. Measurements of photoluminescence and upconversion photoluminescence revealed evidence of the spatial localization of carriers in the InGaP2 material, arising from partial ordering of the InGaP2. We also observed the excitation of a two-dimensional electron gas at the GaAs/InGaP2 heterojunction that manifests as a high-energy shoulder in the GaAs photoluminescence spectrum. Furthermore, the results of upconversion photoluminescence excitation spectroscopy demonstrate that the photon energy onset of upconversion luminescence coincides with the energy of the two-dimensional electron gas at the GaAs/InGaP2 interface, suggesting that charge accumulation at the interface can play a crucial role in the upconversion process.

  • Journal article
    Gambhir A, Sandwell P, Nelson J, 2016,

    The future costs of OPV - A bottom-up model of material and manufacturing costs with uncertainty analysis

    , Solar Energy Materials and Solar Cells, Vol: 156, Pages: 49-58, ISSN: 0927-0248

    Organic photovoltaic (OPV) technology has the potential to provide cheap solar electricity, given advances in low-cost production and module efficiency and lifetime. However, several uncertainties remain in terms of the future costs of OPV modules, which depend on future material and manufacturing costs, as well as key performance characteristics. This assessment takes an engineering-based approach to assessing the potential future cost of each component of OPV modules, as well as the future scale of OPV production plants and associated scale economies, using stochastic analysis to account for uncertainty. The analysis suggests that OPV module costs could fall within a (interquartile) range of US$0.23–0.34/Wp, with a median cost estimate of US$0.28/Wp in the near-term, with future costs most sensitive to manufacturing scale, cell efficiency and module fill factor. This compares to a projected range of module costs for more established PV technologies (crystalline silicon, cadmium telluride and copper indium gallium selenide) of US$0.35–0.6/Wp by 2020. In levelised cost of electricity terms, OPV could compete with the established technologies in both roof- and ground-mounted systems if it can achieve a 10-year lifetime.

  • Journal article
    Dong J, Wu X, Chen Y, Brandon N, Li X, Yang J, Yu J, Zhang W, Hu Y, Yu W, Wang J, Liang S, Hu J, Hou H, Liu B, Yang Cet al., 2016,

    A study on Pb2+/Pb electrodes for soluble lead redox flow cells prepared with methanesulfonic acid and recycled lead

    , Journal of Applied Electrochemistry, Vol: 46, Pages: 861-868, ISSN: 1572-8838

    Electrodeposition and electrodissolution reactionsof the Pb2?/Pb electrode were studied on a glassy carbonrotating disk electrode in aqueous solutions of CH3SO3H andPb(CH3SO3)2. The electrolytic parameters, kinematic viscosityand ionic conductivity, were determined with variousconcentrations of CH3SO3H and Pb(CH3SO3)2. The diffusioncoefficient of Pb2? in this electrolyte prepared with CH3SO3Hwas determined by the Levich Equation. Both the concentrationsof CH3SO3H and Pb(CH3SO3)2 were found responsiblefor the equilibrium potential shifts and exchange currentdensity variations. The electrochemical processes at the Pb2?/Pb electrode were identified as being under mixed ohmicdiffusioncontrol. The electrolyte conductivity and the ionicactivity of Pb2? were recognized as important parameters fordesigning the soluble lead redox flow cells. During constantcurrent charge–discharge measurement, the specific capacityof the Pb2?/Pb electrode was about 253 mAh g-1Pb, about98 % of the theoretical value. The impurity elements Fe, Ba,Al, and Zn in the Pb2? electrolytes prepared with recycledlead exhibited insignificant influences on the Pb2?/Pb reactions.It is reasonable to believe that the recycled lead can beapplied in soluble lead redox flow batteries, and the cost maybe further reduced with recycled lead because expensiveimpurity-control processes seemed to be avoidable.

  • Journal article
    Sikarwar VS, Zhao M, Clough P, Yao J, Zhong X, Memon MZ, Shah N, Anthony EJ, Fennell PSet al., 2016,

    An overview of advances in biomass gasification

    , Energy and Environmental Science, Vol: 9, Pages: 2939-2977, ISSN: 1754-5692

    Biomass gasification is a widely used thermochemical process for obtaining products with more value and potential applications than the raw material itself. Cutting-edge, innovative and economical gasification techniques with high efficiencies are a prerequisite for the development of this technology. This paper delivers an assessment on the fundamentals such as feedstock types, the impact of different operating parameters, tar formation and cracking, and modelling approaches for biomass gasification. Furthermore, the authors comparatively discuss various conventional mechanisms for gasification as well as recent advances in biomass gasification. Unique gasifiers along with multi-generation strategies are discussed as a means to promote this technology into alternative applications, which require higher flexibility and greater efficiency. A strategy to improve the feasibility and sustainability of biomass gasification is via technological advancement and the minimization of socio-environmental effects. This paper sheds light on diverse areas of biomass gasification as a potentially sustainable and environmentally friendly technology.

  • Conference paper
    N Daina, J W Polak, 2016,

    Hazard based modelling of electric vehicles charging patterns

    , 2016 IEEE Transportation Electrification Conference and Expo, Asia-Pacific (ITEC Asia-Pacific), Publisher: IEEE, Pages: 479-484
  • Conference paper
    Mumford J, DeVos Y, Liu Y, Mestagh S, Waigmann Eet al., 2016,

    EFSA guidelines on environmental risk assessment of GM animals, including insects

    , GMOs in Integrated Plant Production, Publisher: IOBC, Pages: 39-46, ISSN: 0253-1100

    Future applications for the marketing of genetically modified organisms (GMOs) in the EU may include food/feed products derived from genetically modified (GM) animals, and the release of GM animals, including insects, into the environment. Efforts towards the development of GM insects to control insect vectors of human diseases and manage agricultural pests have progressed substantially with various GM insect × trait combinations in the development pipeline. As a proactive measure, the scientific GMO Panel of the European Food Safety Authority (EFSA) has developed guidelines on: (1) the risk assessment of food/feed derived from GM animals including animal health and welfare aspects; and (2) the environmental risk assessment (ERA) of living GM animals, including insects, released into the environment for commercial purposes. The latter assists applicants in the preparation and presentation of their applications by describing the elements and data requirements for a structured ERA of GM insects consistent with the current Directive 2001/18/EC. A dedicated Working Group (WG) was involved in the elaboration of the ERA guidelines on GM insects, which underwent a public consultation before their finalisation. Relevant comments received were considered by the WG. The WG also took into account the external scientific report on GM insects commissioned by EFSA (Benedict et al., 2010). This report provided background information by mapping relevant fields of expertise and identified essential elements to be considered when performing an ERA of GM insects. Content and stakeholder involvement for the EFSA guidelines are presented.

  • Journal article
    Tainio M, de Nazelle AJ, Götschi T, Kahlmeier S, Rojas-Rueda D, Nieuwenhuijsen MJ, de Sá TH, Kelly P, Woodcock Jet al., 2016,

    Can air pollution negate the health benefits of cycling and walking?

    , Preventive Medicine, Vol: 87, Pages: 233-236, ISSN: 1096-0260

    Active travel (cycling, walking) is beneficial for the health due to increased physical activity (PA). However, active travel may increase the intake of air pollution, leading to negative health consequences. We examined the risk–benefit balance between active travel related PA and exposure to air pollution across a range of air pollution and PA scenarios.The health effects of active travel and air pollution were estimated through changes in all-cause mortality for different levels of active travel and air pollution. Air pollution exposure was estimated through changes in background concentrations of fine particulate matter (PM2.5), ranging from 5 to 200 μg/m3. For active travel exposure, we estimated cycling and walking from 0 up to 16 h per day, respectively. These refer to long-term average levels of active travel and PM2.5 exposure.For the global average urban background PM2.5 concentration (22 μg/m3) benefits of PA by far outweigh risks from air pollution even under the most extreme levels of active travel. In areas with PM2.5 concentrations of 100 μg/m3, harms would exceed benefits after 1 h 30 min of cycling per day or more than 10 h of walking per day. If the counterfactual was driving, rather than staying at home, the benefits of PA would exceed harms from air pollution up to 3 h 30 min of cycling per day. The results were sensitive to dose–response function (DRF) assumptions for PM2.5 and PA.PA benefits of active travel outweighed the harm caused by air pollution in all but the most extreme air pollution concentrations.

  • Journal article
    Huang X, Restuccia F, Gramola M, Rein Get al., 2016,

    Experimental study of the formation and collapse of an overhang in the lateral spread of smouldering peat fires

    , Combustion and Flame, Vol: 168, Pages: 393-402, ISSN: 0010-2180

    Smouldering combustion is the driving phenomenon of wildfires in peatlands, and is responsible for large amounts of carbon emissions and haze episodes world wide. Compared to flaming fires, smouldering is slow, low-temperature, flameless, and most persistent, yet it is poorly understood. Peat, as a typical organic soil, is a porous and charring natural fuel, thus prone to smouldering. The spread of smouldering peat fire is a multidimensional phenomenon, including two main components: in-depth vertical and surface lateral spread. In this study, we investigate the lateral spread of peat fire under various moisture and wind conditions. Visual and infrared cameras as well as a thermocouple array are used to measure the temperature profile and the spread rate. For the first time the overhang, where smouldering spreads fastest beneath the free surface, is observed in the laboratory, which helps understand the interaction between oxygen supply and heat losses. The periodic formation and collapse of overhangs is observed. The overhang thickness is found to increase with moisture and wind speed, while the spread rate decreases with moisture and increases with wind speed. A simple theoretical analysis is proposed and shows that the formation of overhang is caused by the spread rate difference between the top and lower peat layers as well as the competition between oxygen supply and heat losses.

  • Journal article
    Hallett TB, Anderson S-J, Asante CA, Bartlett N, Bendaud V, Bhatt S, Burgert CR, Cuadros DF, Dzangare J, Fecht D, Gething PW, Ghys PD, Guwani JM, Heard NJ, Kalipeni E, Kandala N-B, Kim AA, Kwao ID, Larmarange J, Manda SOM, Moise IK, Montana LS, Mwai DN, Mwalili S, Shortridge A, Tanser F, Wanyeki I, Zulu Let al., 2016,

    Evaluation of geospatial methods to generate subnational HIV prevalence estimates for local level planning

    , AIDS, Vol: 30, Pages: 1467-1474, ISSN: 0269-9370

    Objective: There is evidence of substantial subnational variation in the HIV epidemic. However, robust spatial HIV data are often only available at high levels of geographic aggregation and not at the finer resolution needed for decision making. Therefore, spatial analysis methods that leverage available data to provide local estimates of HIV prevalence may be useful. Such methods exist but have not been formally compared when applied to HIV.Design/methods: Six candidate methods – including those used by the Joint United Nations Programme on HIV/AIDS to generate maps and a Bayesian geostatistical approach applied to other diseases – were used to generate maps and subnational estimates of HIV prevalence across three countries using cluster level data from household surveys. Two approaches were used to assess the accuracy of predictions: internal validation, whereby a proportion of input data is held back (test dataset) to challenge predictions; and comparison with location-specific data from household surveys in earlier years.Results: Each of the methods can generate usefully accurate predictions of prevalence at unsampled locations, with the magnitude of the error in predictions similar across approaches. However, the Bayesian geostatistical approach consistently gave marginally the strongest statistical performance across countries and validation procedures.Conclusions: Available methods may be able to furnish estimates of HIV prevalence at finer spatial scales than the data currently allow. The subnational variation revealed can be integrated into planning to ensure responsiveness to the spatial features of the epidemic. The Bayesian geostatistical approach is a promising strategy for integrating HIV data to generate robust local estimates.

  • Journal article
    Chen Z, Wang X, Atkinson A, Brandon Net al., 2016,

    Spherical indentation of porous ceramics: cracking and toughness

    , Journal of the European Ceramic Society, Vol: 36, Pages: 3473-3480, ISSN: 0955-2219

    A combined experimental-numerical approach is used to characterise the fracture of a porous bulk ceramic material (La0.6Sr0.4Co0.2Fe0.8O3) with porosities of 5-45%, undergoing spherical indentation. The Gurson model was used in FEM to describe the densification of the porous material. Indentation-induced radial cracks were observed, when the applied nominal contact pressure exceeded threshold values, with no Hertzian ring-cone cracks found. FEM analysis indicated that the cracks propagated mainly during unloading, driven by the tensile hoop stress generated near the contact circle. The stress intensity at the crack tip was estimated using an approximate analysis of the FEM stress field to derive toughness values that were consistent with values determined by conventional methods, provided that the crack length is sufficiently large compared with the contact radius and can be measured accurately. The absence of ring-cone cracks in the elastic field during loading is due to the material’s high modulus-to-hardness ratio and the small indenter radius as predicted by established theory.

  • Journal article
    Wu B, Ibrahim KA, Brandon NP, 2016,

    Electrical conductivity and porosity in stainless steel 316L scaffolds for electrochemical devices fabricated using selective laser sintering

    , Materials and Design, Vol: 109, Pages: 51-59, ISSN: 1873-4197

    Battery electrode microstructures must be porous, to provide a large active surface area to facilitate fast charge transfer kinetics. In this work, we describe how a novel porous electrode scaffold, made from stainless steel 316L powder can be fabricated using selective laser sintering by proper selection of process parameters. Porosity, electrical conductivity and optical microscopy measurements were used to investigate the properties of fabricated samples. Our results show that a laser energy density between 1.50–2.00 J/mm2 leads to a partial laser sintering mechanism where the powder particles are partially fused together, resulting in the fabrication of electrode scaffolds with 10% or higher porosity. The sample fabricated using 2.00 J/mm2 energy density (60 W–1200 mm/s) exhibited a good electrical conductivity of 1.80 × 106 S/m with 15.61% of porosity. Moreover, we have observed the porosity changes across height for the sample fabricated at 60 W and 600 mm/s, 5.70% from base and increasing to 7.12% and 9.89% for each 2.5 mm height towards the top surface offering graded properties ideal for electrochemical devices, due to the changing thermal boundary conditions. These highly porous electrode scaffolds can be used as an electrode in electrochemical devices, potentially improving energy density and life cycle.

  • Journal article
    Blaker JJ, Anthony DB, Tang G, Shamsuddin SR, Kalinka G, Weinrich M, Abdolvand A, Shaffer MSP, Bismarck Aet al., 2016,

    Property and shape modulation of carbon fibers using lasers

    , ACS Applied Materials & Interfaces, Vol: 8, Pages: 16351-16358, ISSN: 1944-8244

    An exciting challenge is to create unduloid-reinforcing fibers with tailored dimensions to produce synthetic composites with improved toughness and increased ductility. Continuous carbon fibers, the state-of-the-art reinforcement for structural composites, were modified via controlled laser irradiation to result in expanded outwardly tapered regions, as well as fibers with Q-tip (cotton-bud) end shapes. A pulsed laser treatment was used to introduce damage at the single carbon fiber level, creating expanded regions at predetermined points along the lengths of continuous carbon fibers, whilst maintaining much of their stiffness. The range of produced shapes was quantified and correlated to single fiber tensile properties. Mapped Raman spectroscopy was used to elucidate the local compositional and structural changes. Irradiation conditions were adjusted to create a swollen weakened region, such that fiber failure occurred in the laser treated region producing two fiber ends with outwardly tapered ends. Upon loading the tapered fibers allow for viscoelastic energy dissipation during fiber pull-out by enhanced friction as the fibers plough through a matrix. In these tapered fibers, diameters were locally increased up to 53%, forming outward taper angles of up to 1.8°. The tensile strength and strain to failure of the modified fibers were significantly reduced, by 75% and 55%, respectively, ensuring localization of the break in the expanded region; however, the fiber stiffness was only reduced by 17%. Using harsher irradiation conditions, carbon fibers were completely cut, resulting in cotton-bud fiber end shapes. Single fiber pull-out tests performed using these fibers revealed a 6.75 fold increase in work of pull-out compared to pristine carbon fibers. Controlled laser irradiation is a route to modify the shape of continuous carbon fibers along their lengths, as well as to cut them into controlled lengths leaving tapered or cotton-bud shapes.

  • Journal article
    Ruenraromgsak P, Chen S, Hu S, Melbourne J, Sweeney S, Thorley AJ, Skepper JN, Shaffer MSP, Tetley TD, Porter AEet al., 2016,

    Translocation of functionalized multi-walled carbon nanotubes across human pulmonary alveolar epithelium: dominant role of epithelial type 1 cells

    , ACS Nano, Vol: 10, Pages: 5070-5085, ISSN: 1936-0851

    Uptake and translocation of short functionalized multi-walled carbon nanotubes (short-fMWCNTs) through the pulmonary respiratory epithelial barrier depend on physicochemical property and cell type. Two monoculture models, immortalized human alveolar epithelial type 1 (TT1) cells and primary human alveolar epithelial type 2 cells (AT2), which constitute the alveolar epithelial barrier, were employed to investigate the uptake and transport of 300 and 700 nm in length, poly(4-vinylpyridine)-functionalized, multi-walled carbon nanotubes (p(4VP)-MWCNTs) using quantitative imaging and spectroscopy techniques. The p(4VP)-MWCNT exhibited no toxicity on TT1 and AT2 cells, but significantly decreased barrier integrity (*p < 0.01). Uptake of p(4VP)-MWCNTs was observed in 70% of TT1 cells, correlating with compromised barrier integrity and basolateral p(4VP)-MWCNT translocation. There was a small but significantly greater uptake of 300 nm p(4VP)-MWCNTs than 700 nm p(4VP)-MWCNTs by TT1 cells. Up to 3% of both the 300 and 700 nm p(4VP)-MWCNTs reach the basal chamber; this relatively low amount arose because the supporting transwell membrane minimized the amount of p(4VP)-MWCNT translocating to the basal chamber, seen trapped between the basolateral cell membrane and the membrane. Only 8% of AT2 cells internalized p(4VP)-MWCNT, accounting for 17% of applied p(4VP)-MWCNT), with transient effects on barrier function, which initially fell then returned to normal; there was no MWCNT basolateral translocation. The transport rate was MWCNT length modulated. The comparatively lower p(4VP)-MWCNT uptake by AT2 cells is proposed to reflect a primary barrier effect of type 2 cell secretions and the functional differences between the type 1 and type 2 alveolar epithelial cells.

  • Journal article
    Sukhodolov T, Rozanov E, Ball WT, Bais A, Tourpali K, Shapiro AI, Telford P, Smyshlyaev S, Fomin B, Sander R, Bossay S, Bekki S, Marchand M, Chipperfield MP, Dhomse S, Haigh JD, Peter T, Schmutz Wet al., 2016,

    Evaluation of simulated photolysis rates and their response to solar irradiance variability

    , JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, Vol: 121, Pages: 6066-6084, ISSN: 2169-897X

    The state of the stratospheric ozone layer and the temperature structure of the atmosphere are largely controlled by the solar spectral irradiance (SSI) through its influence on heating and photolysis rates. This study focuses on the uncertainties in the photolysis rate response to solar irradiance variability related to the choice of SSI data set and to the performance of the photolysis codes used in global chemistry-climate models. To estimate the impact of SSI uncertainties, we compared several photolysis rates calculated with the radiative transfer model libRadtran, using SSI calculated with two models and observed during the Solar Radiation and Climate Experiment (SORCE) satellite mission. The importance of the calculated differences in the photolysis rate response for ozone and temperature changes has been estimated using 1-D a radiative-convective-photochemical model. We demonstrate that the main photolysis reactions, responsible for the solar signal in the stratosphere, are highly sensitive to the spectral distribution of SSI variations. Accordingly, the ozone changes and related ozone-temperature feedback are shown to depend substantially on the SSI data set being used, which highlights the necessity of obtaining accurate SSI variations. To evaluate the performance of photolysis codes, we compared the results of eight, widely used, photolysis codes against two reference schemes. We show that, in most cases, absolute values of the photolysis rates and their response to applied SSI changes agree within 30%. However, larger errors may appear in specific atmospheric regions because of differences, for instance, in the treatment of Rayleigh scattering, quantum yields, or absorption cross sections.

  • Journal article
    Aitken ARA, Roberts JL, van Ommen TD, Young DA, Golledge NR, Greenbaum JS, Blankenship DD, Siegert MJet al., 2016,

    Repeated large-scale retreat and advance of Totten Glacier indicated by inland bed erosion

    , Nature, Vol: 533, Pages: 385-389, ISSN: 0028-0836
  • Journal article
    Menke R, Abraham E, Parpas P, Stoianov Iet al., 2016,

    Demonstrating demand response from water distribution system through pump scheduling

    , Applied Energy, Vol: 170, Pages: 377-387, ISSN: 0306-2619

    Significant changes in the power generation mix are posing new challenges for the balancing systems of the grid. Many of these challenges are in the secondary electricity grid regulation services and could be met through demand response (DR) services. We explore the opportunities for a water distribution system (WDS) to provide balancing services with demand response through pump scheduling and evaluate the associated benefits. Using a benchmark network and demand response mechanisms available in the UK, these benefits are assessed in terms of reduced green house gas (GHG) emissions from the grid due to the displacement of more polluting power sources and additional revenues for water utilities. The optimal pump scheduling problem is formulated as a mixed-integer optimisation problem and solved using a branch and bound algorithm. This new formulation finds the optimal level of power capacity to commit to the provision of demand response for a range of reserve energy provision and frequency response schemes offered in the UK. For the first time we show that DR from WDS can offer financial benefits to WDS operators while providing response energy to the grid with less greenhouse gas emissions than competing reserve energy technologies. Using a Monte Carlo simulation based on data from 2014, we demonstrate that the cost of providing the storage energy is less than the financial compensation available for the equivalent energy supply. The GHG emissions from the demand response provision from a WDS are also shown to be smaller than those of contemporary competing technologies such as open cycle gas turbines. The demand response services considered vary in their response time and duration as well as commitment requirements. The financial viability of a demand response service committed continuously is shown to be strongly dependent on the utilisation of the pumps and the electricity tariffs used by water utilities. Through the analysis of range of water demand scenarios a

  • Journal article
    Liberti E, Menzel R, Shaffer MS, McComb DWet al., 2016,

    Probing the size dependence on the optical modes of anatase nanoplatelets using STEM-EELS

    , Nanoscale, Vol: 8, Pages: 9727-9735, ISSN: 2040-3372

    Anatase titania nanoplatelets with predominantly exposed {001} facets have been reported to have enhanced catalytic properties in comparison with bulk anatase. To understand their unusual behaviour, it is essential to fully characterize their electronic and optical properties at the nanometer scale. One way of assessing these fundamental properties is to study the dielectric function. Valence electron energy-loss spectroscopy (EELS) performed using a scanning transmission electron microscope (STEM) is the only analytical method that can probe the complex dielectric function with both high energy (<100 meV) and high spatial (<1 nm) resolution. By correlating experimental STEM-EELS data with simulations based on semi-classical dielectric theory, the dielectric response of thin (<5 nm) anatase nanoplatelets was found to be largely dominated by characteristic (optical) surface modes, which are linked to surface plasmon modes of anatase. For platelets less than 10 nm thick, the frequency of these optical modes varies according to their thickness. This unique optical behaviour prompts the enhancement of light absorption in the ultraviolet regime. Finally, the effect of finite size on the dielectric signal is gradually lost by stacking consistently two or more platelets in a specific crystal orientation, and eventually suppressed for large stacks of platelets.

  • Journal article
    Siegert MJ, Ross N, Li J, Schroeder DM, Rippin D, Ashmore D, Bingham R, Gogineni Pet al., 2016,

    Subglacial controls on the flow of Institute Ice Stream, West Antarctica

    , Annals of Glaciology, Vol: 57, Pages: 19-24, ISSN: 1727-5644

    The Institute Ice Stream (IIS) rests on a reverse-sloping bed, extending >150 km upstream into the ~1.8 km deep Robin Subglacial Basin, placing it at the threshold of marine ice-sheet instability. Understanding IIS vulnerability has focused on the effect of grounding-line melting, which is forecast to increase significantly this century. Changes to ice-flow dynamics are also important to IIS stability, yet little is known about them. Here we reveal the trunk of the IIS occurs downstream of the intersection of three discrete subglacial features; a large ‘active’ subglacial lake, a newly-discovered sharp transition to a zone of weak basal sediments, and a major tectonic rift. The border of IIS trunk flow is confined by the sediment on one side, and by a transition between basal melting and freezing at the border with the Bungenstock Ice Rise. By showing how basal sediment and water dictate present-day flow of IIS, we reveal that ice-sheet stability here is dependent on this unusual arrangement.

  • Journal article
    O'Keeffe J, Buytaert W, Mijic A, Brozovic N, Sinha Ret al., 2016,

    The use of semi-structured interviews for the characterisation of farmer irrigation practices

    , Hydrology and Earth System Sciences, Vol: 20, Pages: 1911-1924, ISSN: 1607-7938

    Generating information on the behaviours, characteristics and drivers of users, as well on the resource itself, is vital in developing sustainable and realistic water security options. In this paper we present a methodology for collecting qualitative and quantitative data on water use practices through semi-structured interviews. This approach facilitates the collection of detailed information on actors' decisions in a convenient and cost-effective manner. The interview is organised around a topic guide, which helps lead the conversation in a standardised way while allowing sufficient opportunity to identify relevant issues previously unknown to the researcher. In addition, semi-structured interviews can be used to obtain certain types of quantitative data. While not as accurate as direct measurements, it can provide useful information on local practices and farmers' insights. We present an application of the methodology on two districts in the State of Uttar Pradesh in North India. By means of 100 farmer interviews, information was collected on various aspects of irrigation practices, including irrigation water volumes, irrigation cost, water source and their spatial variability. A statistical analysis of the information, along with some data visualisation is also presented, which highlights a significant variation in irrigation practices both within and between the districts. Our application shows that semi-structured interviews are an effective and efficient method of collecting both qualitative and quantitative information for the assessment of drivers, behaviours and their outcomes in a data scarce region. The collection of this type of data could significantly improve insight on water resources, leading to more realistic management options and increased water security in the future.

  • Journal article
    Bradley AV, Duarte Rosa IM, Pontius Jr RG, Ahmed SE, Araujo MB, Brandão Jr A, Câmara G, Carnerio TGS, Hartley A, Smith MJ, Ewers RMet al., 2016,

    SimiVal, a Multi-Criteria Map Comparison Tool for Land-Change Model Projections

    , Environmental Modelling and Software, Vol: 82, Pages: 229-240, ISSN: 1873-6726

    The multiple uses of land-cover models have led to validation with choice metrics or an adhoc choice of the validation metrics available. To address this, we have identified the majordimensions of land-cover maps that ought to be evaluated and devised a SimilarityValidation (SimiVal) tool. SimiVal uses a linear regression to test a modelled projectionagainst benchmark cases of, perfect, observed and systematic-bias, calculated by rescalingthe metrics from a random case relative to the observed, perfect case. The most informativeregression coefficients, p-value and slope, are plot on a ternary graph of ‘similarity space’whose extremes are the three benchmark cases. This plot provides a rigorous similarityassessment against these extremes and other projections. SimiVal is tested on projectionsof two deliberately contrasting land-cover models to show the similarity between intra- andinter-model parameterisations. Predictive and exploratory models can benefit from the tool.

  • Journal article
    Lu X, Gray C, Brown LE, Ledger ME, Milner AM, Mondragón RJ, Woodward G, Ma Aet al., 2016,

    Drought rewires the cores of food webs

    , Nature Climate Change, Vol: 6, Pages: 875-878, ISSN: 1758-678X

    Droughts are intensifying across the globe with potentially devastating implications for freshwater ecosystems. We used new network science approaches to investigate drought impacts on stream food webs and explored potential consequences for web robustness to future perturbations. The substructure of the webs was characterized by a core of richly connected species surrounded by poorly connected peripheral species. Although drought caused the partial collapse of the food webs, the loss of the most extinction-prone peripheral species triggered a substantial rewiring of interactions within the networks’ cores. These shifts in species interactions in the core conserved the underlying core/periphery substructure and stability of the drought-impacted webs. When we subsequently perturbed the webs by simulating species loss in silico, the rewired drought webs were as robust as the larger, undisturbed webs. Our research unearths previously unknown compensatory dynamics arising from within the core that could underpin food web stability in the face of environmental perturbations.

  • Journal article
    Stocker BD, Prentice IC, Cornell SE, Davies-Barnard T, Finzi AC, Franklin O, Janssens I, Larmola T, Manzoni S, Näsholm T, Raven JA, Rebel KT, Reed S, Vicca S, Wiltshire A, Zaehle Set al., 2016,

    Terrestrial nitrogen cycling in Earth system models revisited.

    , New Phytologist, Vol: 210, Pages: 1165-1168, ISSN: 1469-8137
  • Journal article
    Sunyer MA, Luchner J, Onof C, Madsen H, Arnbjerg-Nielsen Ket al., 2016,

    Assessing the importance of spatio-temporal RCM resolution when estimating sub-daily extreme precipitation under current and future climate conditions

    , International Journal of Climatology, Vol: 37, Pages: 688-705, ISSN: 1097-0088

    The increase in extreme precipitation is likely to be one of the most significant impacts of climate change in cities due to increased pluvial flood risk. Hence, reliable information on changes in sub-daily extreme precipitation is needed for robust adaptation strategies. This study explores extreme precipitation over Denmark generated by the regional climate model (RCM) HIRHAM-ECEARTH at different spatial resolutions (8, 12, 25 and 50 km), three RCM from the RiskChange project at 8 km resolution and three RCMs from ENSEMBLES at 25 km resolution at temporal aggregations from 1 to 48 h. The performance of the RCM simulations in current climate as well as projected changes for 2081–2100 is evaluated for non-central moments of order 1–3 and for the 2- and 10-year events. The comparison of the RCM simulations and observations shows that the higher spatial resolution simulations (8 and 12 km) are more consistent across all temporal aggregations in the representation of high-order moments and extreme precipitation. The biases in the spatial pattern of extreme precipitation change across temporal and spatial resolution. The hourly extreme value distributions of the HIRHAM-ECEARTH simulations are more skewed than the observational dataset, which leads to an overestimation by the higher spatial resolution simulations. Nevertheless, in general, under current conditions RCM simulations at high spatial resolution represent extreme events and high-order moments better. The changes projected by the RCM simulations depend on the global climate model (GCM)–RCM combination, spatial resolution and temporal aggregation. The simulations disagree on the magnitude and spatial pattern of the changes. However, there is an agreement on higher changes for lower temporal aggregation and higher spatial resolution. Overall, the results from this study show the influence of the spatial resolution on the precipitation outputs from RCMs. The bia

  • Journal article
    Sandwell P, Chan NLA, Foster S, Nagpal D, Emmott CJM, Candelise C, Buckle SJ, Ekins-Daukes N, Gambhir A, Nelson Jet al., 2016,

    Off-grid solar photovoltaic systems for rural electrification and emissions mitigation in India

    , Solar Energy Materials and Solar Cells, Vol: 156, Pages: 147-156, ISSN: 0927-0248

    Over one billion people lack access to electricity and many of them in rural areas far from existing infrastructure. Off-grid systems can provide an alternative to extending the grid network and using renewable energy, for example solar photovoltaics (PV) and battery storage, can mitigate greenhouse gas emissions from electricity that would otherwise come from fossil fuel sources. This paper presents a model capable of comparing several mature and emerging PV technologies for rural electrification with diesel generation and grid extension for locations in India in terms of both the levelised cost and lifecycle emissions intensity of electricity. The levelised cost of used electricity, ranging from $0.46–1.20/kWh, and greenhouse gas emissions are highly dependent on the PV technology chosen, with battery storage contributing significantly to both metrics. The conditions under which PV and storage becomes more favourable than grid extension are calculated and hybrid systems of PV, storage and diesel generation are evaluated. Analysis of expected price evolutions suggest that the most cost-effective hybrid systems will be dominated by PV generation around 2018.

  • Journal article
    Blanga R, Berman M, Biton M, Tariq F, Yufit V, Gladkich A, Greenbaum SG, Brandon N, Golodnitsky Det al., 2016,

    Peculiarities of ion transport in confined-in-ceramics concentrated polymer electrolytes

    , Electrochimica Acta, Vol: 208, Pages: 71-79, ISSN: 1873-3859

    Polyethylene-oxide/lithium-aluminate films were deposited by electrophoretic deposition. Films impregnated with lithium iodide formed highly concentrated polymer-in-ceramic solid electrolytes. Solid-state NMR, FIB-SEM tomography with modelling, and EIS studies showed that only a few percent of the interfacial lithium in the sample is capable of inducing a fast ion-migration path in the system. We suggest that despite suppressed crystallinity of PEO confined in ceramics the ion transport in the polymer medium impedes the total conductivity of the composite electrolyte at near-ambient temperatures. After melting of the polymer and its complexes, the interfacial conduction through perpendicular LiAlO2/LiI grain boundaries becomes feasible. This, together with ion transport via molten, confined polymer electrolyte is followed by the increase of the overall conductivity of the composite system.

  • Journal article
    Hey J, Malloy AC, Martinez-Botas R, Lamperth Met al., 2016,

    Online Monitoring of Electromagnetic Losses in an Electric Motor Indirectly Through Temperature Measurement

    , IEEE TRANSACTIONS ON ENERGY CONVERSION, Vol: 31, Pages: 1347-1355, ISSN: 0885-8969
  • Journal article
    Doblin MA, van Sebille E, 2016,

    Drift in ocean currents impacts intergenerational microbial exposure to temperature

    , Proceedings of the National Academy of Sciences of the United States of America, Vol: 113, Pages: 5700-5705, ISSN: 1091-6490

    Microbes are the foundation of marine ecosystems [Falkowski PG, Fenchel T, Delong EF (2008) Science 320(5879):1034-1039]. Until now, the analytical framework for understanding the implications of ocean warming on microbes has not considered thermal exposure during transport in dynamic seascapes, implying that our current view of change for these critical organisms may be inaccurate. Here we show that upper-ocean microbes experience along-trajectory temperature variability up to 10 °C greater than seasonal fluctuations estimated in a static frame, and that this variability depends strongly on location. These findings demonstrate that drift in ocean currents can increase the thermal exposure of microbes and suggests that microbial populations with broad thermal tolerance will survive transport to distant regions of the ocean and invade new habitats. Our findings also suggest that advection has the capacity to influence microbial community assemblies, such that regions with strong currents and large thermal fluctuations select for communities with greatest plasticity and evolvability, and communities with narrow thermal performance are found where ocean currents are weak or along-trajectory temperature variation is low. Given that fluctuating environments select for individual plasticity in microbial lineages, and that physiological plasticity of ancestors can predict the magnitude of evolutionary responses of subsequent generations to environmental change [Schaum CE, Collins S (2014) Proc Biol Soc 281(1793):20141486], our findings suggest that microbial populations in the sub-Antarctic (∼40°S), North Pacific, and North Atlantic will have the most capacity to adapt to contemporary ocean warming.

  • Journal article
    Jamil Z, Ruiz-Trejo E, Boldrin P, Brandon NPet al., 2016,

    Anode fabrication for solid oxide fuel cells: Electroless and electrodeposition of nickel and silver into doped ceria scaffolds

    , International Journal of Hydrogen Energy, Vol: 41, Pages: 9627-9637, ISSN: 1879-3487

    A novel fabrication method using electroless and electrodeposited Ni/Ag/GDC for SOFC anodes is presented. First a porous Ce0.9Gd0.1O2−x (GDC) scaffold was deposited on a YSZ electrolyte by screen printing and sintering. The scaffold was then metallized with silver using Tollens' reaction, followed by electrodeposition of nickel from a Watt's bath. The electrodes (Ni/Ag/GDC) were tested in both symmetrical and fuel cell configurations. The microstructures of the Ni/Ag/GDC anodes were analyzed using scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX). Nano-particles of Ni formed in the porous GDC scaffold provided triple phase boundaries (TPB). The electronic conductivity of the Ni/Ag/GDC (3.5/24.7/71.8 vol%) electrode was good even at relatively low Ni volume fractions. The electrochemical performance was examined in different concentrations of humidified hydrogen (3% H2O) and over a range of temperatures (600–750 °C). The total area specific resistance (ASR) of the anode at 750 °C in humidified 97 vol% H2 was 1.12 Ω cm2, with low-frequency polarization (R_l) as the largest contributor. The electrodes were successfully integrated into a fuel cell and operated in both H2 and syngas.

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