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Journal articleBoon M, Bijeljic B, Niu B, et al., 2016,
Observations of 3-D transverse dispersion and dilution in natural consolidated rock by X-ray tomography
, Advances in Water Resources, Vol: 96, Pages: 266-281, ISSN: 0309-1708Recent studies have demonstrated the importance of transverse dispersion for dilution and mixing of solutes but most observations have remained limited to two-dimensional sand-box models. We present a new core-flood test to characterize solute transport in 3-D natural-rock media. A device consisting of three annular regions was used for fluid injection into a cylindrical rock core. Pure water was injected into the center and outer region and a NaI solution into the middle region. Steady state transverse dispersion of NaI was visualized with an X-ray medical CT-scanner for a range of Peclét numbers. Three methods were used to calculate Dt: (1) fitting an analytical solution, (2) analyzing the second-central moment, and (3) analyzing the dilution index and reactor ratio. Transverse dispersion decreased with distance due to flow focusing. Furthermore, Dt in the power-law regime showed sub-linear behavior. Overall, the reactor ratios were high confirming the homogeneity of Berea sandstone.
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Journal articleJaligot R, Wilson DC, Cheeseman CR, et al., 2016,
Applying value chain analysis to informal sector recycling: A case study of the Zabaleen
, Resources, Conservation and Recycling, Vol: 114, Pages: 80-91, ISSN: 0921-3449A methodology has been developed to apply value chain analysis (VCA) to the informal recycling sector, and demonstrated using the Zabaleen in Cairo, Egypt as a case study. The VCA methodology provides a ‘toolkit’ comprising four stages. The first involves mapping the value chain and has been demonstrated using the recycling of polyethylene terephthalate (PET) bottles as the particular example. Stage 2 tabulates the value added at each step in the value chain; this has been demonstrated for different types of plastics as well as other recycled fractions. Stage 3 identifies and then applies a set of indicators for the development of the informal sector recycling value chain in order to address technical and socio-economic challenges. The indicators proposed are in three categories: connections in the value chain, waste valorisation and the enabling environment. Stage 4 involves developing a system dynamic map that shows connections between the indicators, and the stocks and flow variables in the value chain. In particular, it identifies the most highly connected indicators on which to focus interventions, as these are likely to have the greatest impact on the overall system. For the Zabaleen, these are improving the quality of waste inputs into the value chain through source segregation, optimising access to waste and upgrading recycling activities through access to finance and technical knowledge.
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Journal articleGray CL, Hill SLL, Newbold T, et al., 2016,
Local biodiversity is higher inside than outside terrestrial protected areas worldwide
, Nature Communications, Vol: 7, Pages: 1-7, ISSN: 2041-1723Protected areas are widely considered essential for biodiversity conservation. However, few global studies have demonstrated that protection benefits a broad range of species. Here, using a new global biodiversity database with unprecedented geographic and taxonomic coverage, we compare four biodiversity measures at sites sampled in multiple land uses inside and outside protected areas. Globally, species richness is 10.6% higher and abundance 14.5% higher in samples taken inside protected areas compared with samples taken outside, but neither rarefaction-based richness nor endemicity differ significantly. Importantly, we show that the positive effects of protection are mostly attributable to differences in land use between protected and unprotected sites. Nonetheless, even within some human-dominated land uses, species richness and abundance are higher in protected sites. Our results reinforce the global importance of protected areas but suggest that protection does not consistently benefit species with small ranges or increase the variety of ecological niches.
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Journal articleOmoruyi U, Page S, Hallett J, et al., 2016,
Homogeneous Catalyzed Reactions of Levulinic Acid: To γ-Valerolactone and Beyond
, Chemsuschem, Vol: 9, Pages: 2037-2047, ISSN: 1864-564XPlatform chemicals derived from lignocellulosic plant biomass are viewed as a sustainable replacement for crude oil-based feedstocks. Levulinic acid (LA) is one such biomass-derived chemical that has been widely studied for further catalytic transformation to γ-valerolactone (GVL), an important ‘green’ fuel additive, solvent, and fine chemical intermediate. Although the transformation of LA to GVL can be achieved using heterogeneous catalysis, homogeneous catalytic systems that operate under milder reactions, give higher selectivities and can be recycled continuously are attracting considerable attention. A range of new homogeneous catalysts have now been demonstrated to efficiently convert LA to GVL and to transform LA directly to other value-added chemicals such as 1,4-pentanediol (1,4-PDO) and 2-methyltetrahydrofuran (2-MTHF). This Minireview covers recent advances in the area of homogeneous catalysis for the conversion of levulinic acid and levulinic ester derivatives to GVL and chemicals beyond GVL.
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Journal articleAlhajaj A, Mac Dowell N, Shah N, 2016,
A techno-economic analysis of post-combustion CO2 capture and compression applied to a combined cycle gas turbine: Part II. Identifying the cost-optimal control and design variables
, International Journal of Greenhouse Gas Control, Vol: 52, Pages: 331-343, ISSN: 1750-5836A detailed optimization-orientated model of monoethanolamine-based CO2 capture plant and compression train in which all the technical and economic assumptions are defined and/or optimized was developed and used to simultaneously determine the cost optimal control and design variables including feed fraction ratio at different degrees of capture (DOC), which represents the amount of CO2 removed, for plant designs that partially bypass the CO2 capture process so as to achieve low to moderate reductions of CO2, but at lower overall cost. The effects of varying carbon prices on the levelized cost of CO2 capture and compression were also studied. The capture bypass option was observed to be the cost optimal choice for lower than 60% overall DOC. Carbon prices were observed to have a clear impact on the cost optimal DOC, with the cost-optimal DOC shifting from 70%–80% to 85%–90% at carbon prices of $4/tCO2to $23/tCO2 respectively. The study highlighted that if a suitably high carbon price does not materialize through a market mechanism, appropriate policies need to be put in place to achieve decarbonisation targets.
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Conference paperFu H, Cao K, Xu R, et al., 2016,
Footstep energy harvesting using heel strike-induced airflow for human activity sensing
, 13th IEEE International Conference on Wearable and Implantable Body Sensor Networks (BSN), Publisher: IEEE, Pages: 124-129, ISSN: 2376-8886Body sensor networks are increasingly popular in healthcare, sports, military and security. However, the power supply from conventional batteries is a key bottleneck for the development of body condition monitoring. Energy harvesting from human motion to power wearable or implantable devices is a promising alternative. This paper presents an airflow energy harvester to harness human motion energy from footsteps. An air bladder-turbine energy harvester is designed to convert the footstep motion into electrical energy. The bladders are embedded in shoes to induce airflow from foot-strikes. The turbine is employed to generate electrical energy from airflow. The design parameters of the turbine rotor, including the blade number and the inner diameter of the blades (the diameter of the turbine shaft), were optimized using the computational fluid dynamics (CFD) method. A prototype was developed and tested with footsteps from a 65 kg person. The peak output power of the harvester was first measured for different resistive loads and showed a maximum value of 90.6 mW with a 30.4 Ω load. The harvested energy was then regulated and stored in a power management circuit. 14.8 mJ was stored in the circuit from 165 footsteps, which means 90 μJ was obtained per footstep. The regulated energy was finally used to fully power a fitness tracker which consists of a pedometer and a Bluetooth module. 7.38 mJ was consumed by the tracker per Bluetooth configuration and data transmission. The tracker operated normally with the harvester working continuously.
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Journal articleJordan T, Bamber J, Williams C, et al., 2016,
An ice sheet wide framework for radar-inference of englacial attenuation and basal reflection with application to Greenland
, Cryosphere, Vol: 10, Pages: 1547-1570, ISSN: 1994-0424Radar inference of the bulk properties of glacierbeds, most notably identifying basal melting, is, in general,derived from the basal reflection coefficient. On the scale ofan ice sheet, unambiguous determination of basal reflectionis primarily limited by uncertainty in the englacial attenuationof the radio wave, which is an Arrhenius function oftemperature. Existing bed-returned power algorithms for derivingattenuation assume that the attenuation rate is regionallyconstant, which is not feasible at an ice-sheet-wide scale.Here we introduce a new semi-empirical framework for derivingenglacial attenuation, and, to demonstrate its efficacy,we apply it to the Greenland Ice Sheet. A central featureis the use of a prior Arrhenius temperature model to estimatethe spatial variation in englacial attenuation as a firstguess input for the radar algorithm. We demonstrate regionsof solution convergence for two input temperature fields andfor independently analysed field campaigns. The coverageachieved is a trade-off with uncertainty and we propose thatthe algorithm can be “tuned” for discrimination of basal melt(attenuation loss uncertainty ∼ 5 dB). This is supported byour physically realistic (∼ 20 dB) range for the basal reflectioncoefficient. Finally, we show that the attenuation solutioncan be used to predict the temperature bias of thermomechanicalice sheet models and is in agreement with known modeltemperature biases at the Dye 3 ice core.
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Journal articlede Hoogh K, Gulliver J, van Donkelaar A, et al., 2016,
Development of West-European PM2.5 and NO2 land use regression models incorporating satellite-derived and chemical transport modelling data
, ENVIRONMENTAL RESEARCH, Vol: 151, Pages: 1-10, ISSN: 0013-9351 -
Journal articleBrant HL, Ewers RM, Vythilingam I, et al., 2016,
Vertical stratification of adult mosquitoes (Diptera: Culicidae) within a tropical rainforest in Sabah, Malaysia
, Malaria Journal, Vol: 15, ISSN: 1475-2875BackgroundMalaria cases caused by Plasmodium knowlesi, a simian parasite naturally found in long-tailed and pig-tailed macaques, are increasing rapidly in Sabah, Malaysia. One hypothesis is that this increase is associated with changes in land use. A study was carried out to identify the anopheline vectors present in different forest types and to observe the human landing behaviour of mosquitoes. MethodsMosquito collections were carried out using human landing catches at ground and canopy levels in the Tawau Division of Sabah. Collections were conducted along an anthropogenic disturbance gradient (primary forest, lightly logged virgin jungle reserve and salvage logged forest) between 18:00-22:00h. ResultsAnopheles balabacensis, a vector of P. knowlesi, was the predominant species in all collection areas, accounting for 70% of the total catch, with a peak landing time of 18:30-20:00h. Anopheles balabacensis had a preference for landing on humans at ground level compared to the canopy (p<0.0001). A greater abundance of mosquitoes were landing in the logged forest compared to the primary forest (p<0.0001). There was no difference between mosquito abundance in the logged forest and lightly logged forest (p=0.554). A higher evening temperature (p<0.0001) and rainfall (p<0.0001) significantly decreased mosquito abundance during collection nights. ConclusionsThis study demonstrates the potential ability of An. balabacensis to transmit P. knowlesi between canopy-dwelling simian hosts and ground-dwelling humans, and that forest disturbance increases the abundance of this disease vector. These results, in combination with regional patterns of land use change, may partly explain the rapid rise in P. knowlesi cases in Sabah. This study provides essential data on anthropophily for the principal vector of P. knowlesi which is important for the planning of vector control strategies.
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Journal articleLe Quéré C, Buitenhuis ET, Moriarty R, et al., 2016,
Role of zooplankton dynamics for Southern Ocean phytoplankton biomass and global biogeochemical cycles
, Biogeosciences, Vol: 13, Pages: 4111-4133, ISSN: 1726-4170Global ocean biogeochemistry models currently employed in climate change projections use highly simplified representations of pelagic food webs. These food webs do not necessarily include critical pathways by which ecosystems interact with ocean biogeochemistry and climate. Here we present a global biogeochemical model which incorporates ecosystem dynamics based on the representation of ten plankton functional types (PFTs): six types of phytoplankton, three types of zooplankton, and heterotrophic procaryotes. We improved the representation of zooplankton dynamics in our model through (a) the explicit inclusion of large, slow-growing macrozooplankton (e.g. krill), and (b) the introduction of trophic cascades among the three zooplankton types. We use the model to quantitatively assess the relative roles of iron vs. grazing in determining phytoplankton biomass in the Southern Ocean high-nutrient low-chlorophyll (HNLC) region during summer. When model simulations do not include macrozooplankton grazing explicitly, they systematically overestimate Southern Ocean chlorophyll biomass during the summer, even when there is no iron deposition from dust. When model simulations include a slow-growing macrozooplankton and trophic cascades among three zooplankton types, the high-chlorophyll summer bias in the Southern Ocean HNLC region largely disappears. Our model results suggest that the observed low phytoplankton biomass in the Southern Ocean during summer is primarily explained by the dynamics of the Southern Ocean zooplankton community, despite iron limitation of phytoplankton community growth rates. This result has implications for the representation of global biogeochemical cycles in models as zooplankton faecal pellets sink rapidly and partly control the carbon export to the intermediate and deep ocean.
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Journal articleClancy ARJ, White E, Tay HH, et al., 2016,
Systematic Comparison of Conventional and Reductive Single-walled Carbon Nanotube Purifications
, Carbon, Vol: 108, Pages: 423-432, ISSN: 0008-6223As-synthesised single-walled carbon nanotubes (SWCNTs) are often contaminated withamorphous carbon and residual catalyst particles. These contaminants have a detrimental effecton the effective mechanical and electronic properties, limiting their performance in manyapplications. A comparative series of SWCNT purifications including acid treatments, gasphase purifications and recently-developed reductive purifications have been conducted usinga single commercial SWCNT type (Tuball™). Each of the purification procedures was selectedfor its potential scalability to bulk quantities and evaluated for the extent of impurity removal,SWCNT damage, and overall yield. Raman spectra confirmed that reductive purification usingsodium naphthalide gave the lowest D/G ratio, suggesting that the sp2carbon framework wasmost effectively preserved, while removing a large percentage of the metal impurities.Conversely, nitric acid treatment was most effective at removing catalytic impurities, but thesp2carbon framework was most heavily damaged in the process. The development of scalable,one pot, reductive separations provides a useful new approach to SWCNT purification.
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Journal articleFunke SW, Kramer SC, Piggott MD,
Design optimisation and resource assessment for tidal-stream renewable energy farms using a new continuous turbine approach
, Renewable Energy, ISSN: 1879-0682This paper presents a new approach for optimising the design of tidal stream turbine farms. In this approach, the turbine farm is represented by a turbine density function that specifies the number of turbines per unit area and an associated continuous locally-enhanced bottom friction field. The farm design question is formulated as a mathematical optimisation problem constrained by the shallow water equations and solved with efficient, gradient-based optimisation methods. The resulting method is accurate, computationally efficient, allows complex installation constraints, and supports different goal quantities such as to maximise power or profit. The outputs of the optimisation are the optimal number of turbines, their location within the farm, the overall farm profit, the farm's power extraction, and the installation cost.We demonstrate the capabilities of the method on a validated numerical model of the Pentland Firth, Scotland. We optimise the design of four tidal farms simultaneously, as well as individually, and study how farms in close proximity may impact upon one another.
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Journal articleNewbold T, Hudson LN, Arnell AP, et al., 2016,
Has land use pushed terrestrial biodiversity beyond the planetary boundary? A global assessment
, Science, Vol: 353, Pages: 288-291, ISSN: 0036-8075Land use and related pressures have reduced local terrestrial biodiversity, but it is unclear how the magnitude of change relates to the recently proposed planetary boundary (‘safe limit’). We estimate that land use and related pressures have already reduced local biodiversity intactness – the average proportion of natural biodiversity remaining in local ecosystems – beyond its recently-proposed planetary boundary across 58.1% of the world’s land surface, where 71.4% of the human population live. Biodiversity intactness within most biomes (especially grassland biomes), most biodiversity hotspots, and even some wilderness areas, is inferred to be beyond the boundary. Such widespread transgression of safe limits suggests that biodiversity loss, if unchecked, will undermine efforts towards long-term sustainable development.
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Journal articleSandwell P, Duggan G, Nelson J, et al., 2016,
The environmental impact of lightweight HCPV modules: efficient design and effective deployment
, Progress in Photovoltaics, Vol: 24, Pages: 1458-1472, ISSN: 1099-159XWe present a life cycle analysis of a lightweight design of high concentration photovoltaic module. The materials and processes used in construction are considered to assess the total environmental impact of the module construction in terms of the cumulative energy demand and embodied greenhouse gas emissions, which were found to be 355.3MJ and 27.9 kgCO2eq respectively. We consider six potential deployment locations and the system energy payback times are calculated to be 0.22–0.33 years whilst the greenhouse gas payback times are 0.29–0.88 years. The emission intensities over the life- times of the systems are found to be 6.5–9.8 g CO2eq/kWh, lower than those of other HCPV, PV and CSP technologies in similar locations.
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ReportFew SPM, Schmidt O, Gambhir A, 2016,
Electrical energy storage for mitigating climate change
, Publisher: Grantham Institute, Imperial College London, 20 -
Journal articleKossieris P, Makropoulos C, Onof C, et al., 2016,
A rainfall disaggregation scheme for sub-hourly time scales: coupling a Bartlett-Lewis based model with adjusting procedures
, Journal of Hydrology, Vol: 556, Pages: 980-992, ISSN: 0022-1694Many hydrological applications, such as flood studies, require the use of long rainfall data at fine time scales varying from daily down to 1 min time step. However, in the real world there is limited availability of data at sub-hourly scales. To cope with this issue, stochastic disaggregation techniques are typically employed to produce possible, statistically consistent, rainfall events that aggregate up to the field data collected at coarser scales. A methodology for the stochastic disaggregation of rainfall at fine time scales was recently introduced, combining the Bartlett-Lewis process to generate rainfall events along with adjusting procedures to modify the lower-level variables (i.e., hourly) so as to be consistent with the higher-level one (i.e., daily). In the present paper, we extend the aforementioned scheme, initially designed and tested for the disaggregation of daily rainfall into hourly depths, for any sub-hourly time scale. In addition, we take advantage of the recent developments in Poisson-cluster processes incorporating in the methodology a Bartlett-Lewis model variant that introduces dependence between cell intensity and duration in order to capture the variability of rainfall at sub-hourly time scales. The disaggregation scheme is implemented in an R package, named HyetosMinute, to support disaggregation from daily down to 1-min time scale. The applicability of the methodology was assessed on a 5-min rainfall records collected in Bochum, Germany, comparing the performance of the above mentioned model variant against the original Bartlett-Lewis process (non-random with 5 parameters). The analysis shows that the disaggregation process reproduces adequately the most important statistical characteristics of rainfall at wide range of time scales, while the introduction of the model with dependent intensity-duration results in a better performance in terms of skewness, rainfall extremes and dry proportions.
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Journal articleWearn OR, Carbone C, Rowcliffe JM, et al., 2016,
Grain-dependent responses of mammalian diversity to land use and the implications for conservation set-aside
, Ecological Applications, Vol: 26, Pages: 1409-1420, ISSN: 1939-5582Diversity responses to land-use change are poorly understood at local scales, hindering our ability to make forecasts and management recommendations at scales which are of practical relevance. A key barrier in this has been the underappreciation of grain-dependent diversity responses and the role that β-diversity (variation in community composition across space) plays in this. Decisions about the most effective spatial arrangement of conservation set-aside, for example high conservation value areas, have also neglected β-diversity, despite its role in determining the complementarity of sites. We examined local-scale mammalian species richness and β-diversity across old-growth forest, logged forest, and oil palm plantations in Borneo, using intensive camera- and live-trapping. For the first time, we were able to investigate diversity responses, as well as β-diversity, at multiple spatial grains, and across the whole terrestrial mammal community (large and small mammals); β-diversity was quantified by comparing observed β-diversity with that obtained under a null model, in order to control for sampling effects, and we refer to this as the β-diversity signal. Community responses to land use were grain dependent, with large mammals showing reduced richness in logged forest compared to old-growth forest at the grain of individual sampling points, but no change at the overall land-use level. Responses varied with species group, however, with small mammals increasing in richness at all grains in logged forest compared to old-growth forest. Both species groups were significantly depauperate in oil palm. Large mammal communities in old-growth forest became more heterogeneous at coarser spatial grains and small mammal communities became more homogeneous, while this pattern was reversed in logged forest. Both groups, however, showed a significant β-diversity signal at the finest grain in logged forest, likely due to logging-induced envir
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Reportvan Sebille E, Spathi C, Gilbert A, 2016,
The ocean plastic pollution challenge: towards solutions in the UK
, Publisher: Grantham Institute, Imperial College London, 19 -
Journal articleBrindley HE, Bantges RJ, 2016,
The spectral signature of recent climate change
, Current Climate Change Reports, Vol: 2, Pages: 112-126, ISSN: 2198-6061Spectrally resolved measurements of the Earth’s reflected shortwave (RSW) and outgoing longwave radiation (OLR) at the top of the atmosphere intrinsically contain the imprints of a multitude of climate relevant parameters. Here, we review the progress made in directly using such observations to diagnose and attribute change within the Earth system over the past four decades. We show how changes associated with perturbations such as increasing greenhouse gases are expected to be manifested across the spectrum and illustrate the enhanced discriminatory power that spectral resolution provides over broadband radiation measurements. Advances in formal detection and attribution techniques and in the design of climate model evaluation exercises employing spectrally resolved data are highlighted. We illustrate how spectral observations have been used to provide insight into key climate feedback processes and quantify multi-year variability but also indicate potential barriers to further progress. Suggestions for future research priorities in this area are provided.
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Journal articleTerrer C, Vicca S, Hungate BA, et al., 2016,
Mycorrhizal association as a primary control of the CO2 fertilization effect
, Science, Vol: 353, Pages: 72-74, ISSN: 1095-9203Plants buffer increasing atmospheric CO2 concentrations through enhanced growth, but the question whether nitrogen availability constrains the magnitude of this ecosystem service remains unresolved. Synthesizing experiments from around the world, we show that CO2 fertilization is best explained by a simple interaction between nitrogen availability and mycorrhizal association. Plant species that associate with ectomycorrhizal fungi show a strong biomass increase (30 ± 3%, P<0.001) in response to elevated CO2 regardless of nitrogen availability, whereas low nitrogen availability limits CO2 fertilization (0 ± 5%, P=0.946) in plants that associate with arbuscular mycorrhizal fungi. The incorporation of mycorrhizae in global carbon cycle models is feasible, and crucial if we are to accurately project ecosystem responses and feedbacks to climate change.
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Journal articleHunt I, Zhao Y, Patel Y, et al., 2016,
Surface cooling causes accelerated degradation compared to tab cooling for lithium-Ion pouch cells
, Journal of the Electrochemical Society, Vol: 163, Pages: A1846-A1852, ISSN: 0013-4651One of the biggest causes of degradation in lithium-ion batteries is elevated temperature. In this study we explored the effects ofcell surface cooling and cell tab cooling, reproducing two typical cooling systems that are used in real-world battery packs. For newcells using slow-rate standardized testing, very little difference in capacity was seen. However, at higher rates, discharging the cellin just 10 minutes, surface cooling led to a loss of useable capacity of 9.2% compared to 1.2% for cell tab cooling. After cyclingthe cells for 1,000 times, surface cooling resulted in a rate of loss of useable capacity under load three times higher than cell tabcooling. We show that this is due to thermal gradients being perpendicular to the layers for surface cooling leading to higher localcurrents and faster degradation, but in-plane with the layers for tab cooling leading to more homogenous behavior. Understandinghow thermal management systems interact with the operation of batteries is therefore critical in extending their performance. Forautomotive applications where 80% capacity is considered end-of-life, using tab cooling rather than surface cooling would thereforebe equivalent to extending the lifetime of a pack by 3 times, or reducing the lifetime cost by 66%.
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Journal articleKramer SC, Piggott MD, 2016,
A correction to the enhanced bottom drag parameterisation of tidal turbines
, Renewable Energy, Vol: 92, Pages: 385-396, ISSN: 0960-1481Hydrodynamic modelling is an important tool for the development of tidal stream energy projects. Many hydrodynamic models incorporate the effect of tidal turbines through an enhanced bottom drag. In this paper we show that although for coarse grid resolutions (kilometre scale) the resulting force exerted on the flow agrees well with the theoretical value, the force starts decreasing with decreasing grid sizes when these become smaller than the length scale of the wake recovery. This is because the assumption that the upstream velocity can be approximated by the local model velocity, is no longer valid. Using linear momentum actuator disc theory however, we derive a relationship between these two velocities and formulate a correction to the enhanced bottom drag formulation that consistently applies a force that remains close to the theoretical value, for all grid sizes down to the turbine scale. In addition, a better understanding of the relation between the model, upstream, and actual turbine velocity, as predicted by actuator disc theory, leads to an improved estimate of the usefully extractable energy. We show how the corrections can be applied (demonstrated here for the models MIKE 21 and Fluidity) by a simple modification of the drag coefficient.
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Journal articleBraun LM, Rodriguez DA, Cole-Hunter T, et al., 2016,
Short-term planning and policy interventions to promote cycling in urban centers: Findings from a commute mode choice analysis in Barcelona, Spain
, Transportation Research Part A: Policy and Practice, Vol: 89, Pages: 164-183, ISSN: 0965-8564Background: Cycling for transportation has become an increasingly important component of strategies to address public health, climate change, and air quality concerns in urban centers. Within this context, planners and policy makers would benefit from an improved understanding of available interventions and their relative effectiveness for cycling promotion. We examined predictors of bicycle commuting that are relevant to planning and policy intervention, particularly those amenable to short- and medium-term action. Methods: We estimated a travel mode choice model using data from a survey of 765 commuters who live and work within the municipality of Barcelona. We considered how the decision to commute by bicycle was associated with cycling infrastructure, bike share availability, travel demand incentives, and other environmental attributes (e.g., public transport availability). Self-reported and objective (GIS-based) measures were compared. Point elasticities and marginal effects were calculated to assess the relative explanatory power of the independent variables considered. Results: While both self-reported and objective measures of access to cycling infrastructure were associated with bicycle commuting, self-reported measures had stronger associations. Bicycle commuting had positive associations with access to bike share stations but inverse associations with access to public transport stops. Point elasticities suggested that bicycle commuting has a mild negative correlation with public transport availability (-0.136), bike share availability is more important at the work location (0.077) than at home (0.034), and bicycle lane presence has a relatively small association with bicycle commuting (0.039). Marginal effects suggested that provision of an employer-based incentive not to commute by private vehicle would be associated with an 11.3% decrease in the probability of commuting by bicycle, likely reflecting the typical emphasis of such incentives on public tran
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Journal articleAdams T, Mac Dowell N, 2016,
Off-design point modelling of a 420 MW CCGT power plant integrated with an amine-based post-combustion CO2 capture and compression process
, Applied Energy, Vol: 178, Pages: 681-702, ISSN: 1872-9118The use of natural gas for power generation is becoming increasingly important in many regions in the world. Given that the combined cycle gas turbine (CCGT) power stations are lower in capital cost and carbon intensity than their coal-fired counterparts, natural gas fired power stations are considered a vital part of the transition to a low carbon economy. However, CCGTs are not themselves “low carbon” and in order to reach a carbon intensity of less than 50 kgCO2/MWh, it will be necessary to decarbonise them via CCS, with post-combustion CCS currently regarded as being a promising technology for this application. In this study, we present a detailed model of a 420 MW triple-pressure reheat CCGT and evaluate its technical and economic performance under full and part load conditions. We evaluate the technical performance of our CCGT model by comparison to an equivalent model implemented in Thermoflow THERMOFLEX and observe agreement of power output and efficiency to within 4.1% and the temperature profile within the HRSG within 2.9%. We further integrate the CCGT with a dynamic model of an amine based CCS process, and observe a reduction in the base plant efficiency from 51.84% at full-load and 50.23% at 60% load by 8.64% points at full-load and 7.93% points at 60% load. A core conclusion of this paper is that CCGT power plants equipped with post-combustion CCS technologies are well suited to dynamic operation, as might be required in an energy system characterised by high penetrations of intermittent renewable power generation.
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Journal articleCarter E, Archer-Nicholls S, Ni K, et al., 2016,
Seasonal and Diurnal Air Pollution from Residential Cooking and Space Heating in the Eastern Tibetan Plateau.
, Environmental Science & Technology, Vol: 50, Pages: 8353-8361, ISSN: 1520-5851Residential combustion of solid fuel is a major source of air pollution. In regions where space heating and cooking occur at the same time and using the same stoves and fuels, evaluating air-pollution patterns for household-energy-use scenarios with and without heating is essential to energy intervention design and estimation of its population health impacts as well as the development of residential emission inventories and air-quality models. We measured continuous and 48 h integrated indoor PM2.5 concentrations over 221 and 203 household-days and outdoor PM2.5 concentrations on a subset of those days (in summer and winter, respectively) in 204 households in the eastern Tibetan Plateau that burned biomass in traditional stoves and open fires. Using continuous indoor PM2.5 concentrations, we estimated mean daily hours of combustion activity, which increased from 5.4 h per day (95% CI: 5.0, 5.8) in summer to 8.9 h per day (95% CI: 8.1, 9.7) in winter, and effective air-exchange rates, which decreased from 18 ± 9 h(-1) in summer to 15 ± 7 h(-1) in winter. Indoor geometric-mean 48 h PM2.5 concentrations were over two times higher in winter (252 μg/m(3); 95% CI: 215, 295) than in summer (101 μg/m(3); 95%: 91, 112), whereas outdoor PM2.5 levels had little seasonal variability.
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Journal articleZhao L, Moore J, O'Gorman EJ, et al., 2016,
Weighting and indirect effects identify keystone species in food webs
, Ecology Letters, Vol: 19, Pages: 1032-1040, ISSN: 1461-0248Species extinctions are accelerating globally, yet the mechanisms that maintain local biodiversity remain poorly understood. The extinction of species that feed on or are fed on by many others (i.e. ‘hubs’) has traditionally been thought to cause the greatest threat of further biodiversity loss. Very little attention has been paid to the strength of those feeding links (i.e. link weight) and the prevalence of indirect interactions. Here, we used a dynamical model based on empirical energy budget data to assess changes in ecosystem stability after simulating the loss of species according to various extinction scenarios. Link weight and/or indirect effects had stronger effects on food-web stability than the simple removal of ‘hubs’, demonstrating that both quantitative fluxes and species dissipating their effects across many links should be of great concern in biodiversity conservation, and the potential for ‘hubs’ to act as keystone species may have been exaggerated to date.
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Journal articleCosta DD, da Silva Pereira TA, Fragoso CR, et al., 2016,
Understanding drought dynamics during dry season in Eastern Northeast Brazil
, Frontiers in Earth Science, Vol: 4, ISSN: 2296-6463Eastern Northeast Brazil (ENEB) generally experiences a high variability in precipitation in the dry season, with amplitudes that can overcome 500mm. The understanding of this variability can help in mitigating the socio-economic issues related to the planning and management of water resources this region, which is highly vulnerable to drought. This work aims to assess spatio-temporal variability of precipitation during the dry season and investigate the relationships between climate phenomena and drought events in the ENEB, using univariate (Spearman correlation) and multivariate statistical techniques, such as Principal Component Analysis, Cluster Analysis, and Maximum Covariance Analysis. The results indicate that the variability of precipitation in the dry season can be explained mainly (62%) by local physical conditions and climate conditions have a secondary contribution. Further analysis of the larger anomalous events suggests that the state of Atlantic and Pacific oceans can govern the occurrence of those events, and the conditions of Atlantic Ocean can be considered a potential modulator of anomalous phenomena of precipitation in ENEB.
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Journal articleCooper MA, Michaelides K, Siegert MJ, et al., 2016,
Paleofluvial landscape inheritance for Jakobshavn Isbræ catchment, Greenland
, Geophysical Research Letters, Vol: 43, Pages: 6350-6357, ISSN: 1944-8007Subglacial topography exerts strong controls on glacier dynamics, influencing the orientation and velocity of ice flow, as well as modulating the distribution of basal waters and sediment. Bed geometry can also provide a long-term record of geomorphic processes, allowing insight into landscape evolution, the origin of which may predate ice sheet inception. Here we present evidence from ice-penetrating radar data for a large dendritic drainage network, radiating inland from Jakobshavn Isbræ, Greenland's largest outlet glacier. The size of the drainage basin is ∼450,000 km2 and accounts for about 20% of the total land area of Greenland. Topographic and basin morphometric analyses of an isostatically uplifted (ice-free) bedrock topography suggests that this catchment predates ice sheet initiation and has likely been instrumental in controlling the location and form of the Jakobshavn ice stream, and ice flow from the deep interior to the margin, now and over several glacial cycles.
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Journal articleBantges RJ, Brindley HE, Chen XH, et al., 2016,
On the detection of robust multi-decadal changes in the Earth’s Outgoing Longwave Radiation spectrum
, Journal of Climate, Vol: 29, Pages: 4939-4947, ISSN: 1520-0442Differences between Earth’s global mean all-sky outgoing longwave radiation spectrum as observed in 1970 [Interferometric Infrared Spectrometer (IRIS)], 1997 [Interferometric Monitor for Greenhouse Gases (IMG)], and 2012 [Infrared Atmospheric Sounding Instrument (IASI)] are presented. These differences are evaluated to determine whether these are robust signals of multidecadal radiative forcing and hence whether there is the potential for evaluating feedback-type responses. IASI–IRIS differences range from +2 K in the atmospheric window (800–1000 cm−1) to −5.5 K in the 1304 cm−1 CH4 band center. Corresponding IASI–IMG differences are much smaller, at 0.2 and −0.8 K, respectively. More noticeably, IASI–IRIS differences show a distinct step change across the 1042 cm−1 O3 band that is not seen in IASI–IMG comparisons. This step change is a consequence of a difference in behavior when moving from colder to warmer scenes in the IRIS data compared to IASI and IMG. Matched simulations for the relevant periods using ERA reanalyses mimic the spectral behavior shown by IASI and IMG rather than by IRIS. These findings suggest that uncertainties in the spectral response of IRIS preclude the use of these data for quantitative assessments of forcing and feedback processes.
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Journal articleGarcia Trenco A, White E, Shaffer M, et al., 2016,
A one-step Cu/ZnO Quasi-Homogeneous Catalyst for DME Production from Syn-gas
, Catalysis Science & Technology, Vol: 6, Pages: 4389-4397, ISSN: 2044-4753A simple one-pot synthetic method allows the preparation of hybrid catalysts, based on colloidal Cu/ZnO nanoparticles(NPs), used for the liquid phase synthesis of DME from syngas. The method obviates the high temperature calcinations andpre-reduction treatments typically associated with such catalysts. The hybrid catalysts are applied under typicalindustrially relevant conditions. The nature of the hybrid catalysts, the influence of the acid component, mass ratiobetween components, and Cu/Zn composition are assessed. The best catalysts comprise a colloidal mixture of Cu/ZnONPs, as the methanol synthesis component, and -Al2O3, as the methanol dehydration component. These catalysts showhigh DME selectivity (65-70 %C). Interestingly, the activity (relative to Cu content) is up to three times higher than that forthe reference hybrid catalyst based on the commercial Cu/ZnO/Al2O3 methanol synthesis catalyst. The hybrid catalysts arestable for at least 20 h time-on-stream, not showing any significant sintering of the Cu0phase. Post-catalysis,TEM/EDXshows that the hybrid catalysts consist of Cu0and ZnO NPs with an average size of 5-7 nm with -Al2O3 particles in closeproximity.
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