University of Leeds
  • Leeds, W.Yorkshire, United Kingdom
Recent publications
Large Amplitude Oscillatory Extension (LAOE) experiments were used to analyze the influence of rolling speed on the non-linear viscoelasticity of the dough sheets with different water additions (34%, 38%), and then the correlations between LAOE parameters with noodle quality were investigated. The E′M and E′L values were ten times higher than the η′eM and η′eL values, and the dough sheet along the sheeting direction exhibited higher E′L, E′M, η′eL, η′eM, and S values than that perpendicular to the sheeting direction at the same rolling speed, water addition, frequency and strain amplitude. The E′L, E′M, η′eL, η′eM, and S values decreased as the rolling speed increased, and this phenomenon was more pronounced for the dough sheet with 34% water addition than that with 38% water addition. The elastic modulus and fracture stress of dry noodles, and hardness and tensile force of cooked noodles had highly linear correlations with LAOE parameters (E′L, E′M, η′eL, and η′eM) when the water addition was the same.
Learning-oriented behaviour is important for risk identification and safety management, especially in high-risk industries. Yet, its effect in relation to employee safety citizenship behaviour (SCB) has not been systematically investigated. This study aims at: (a) examining the impact of safety learning behaviour on SCB; (b) examining the relationship between job risk assessment, safety training and safety learning; and (c) examining the mediating effect of safety learning on the relationship between job risk assessment, safety training and SCB. Data were collected from a sample of 316 employees of six large-scale gold mining companies in Ghana, and analysed using the partial least squares-structural equation analysis. The results showed positive significant associations between safety learning and employee-safety voice and safety stewardship behaviours. Job risk assessment, safety training and safety learning were also associated positively with each other. The results showed further that safety learning mediates the relationship between safety training and employee safety voice and safety stewardship behaviours. Our findings provide implications for theory and practice as it points out the critical influence of learning-oriented supervisors behaviour for promoting future-directed workplace safety.
Hypothesis Dynamics of polymer-coated silica composite nanoparticles (CPs) during bubble coarsening is highly dominated by the behaviour of the polymer layer, while in-situ particle aggregation would lead to accelerated bubble coalescence. Experiments CPs-stabilized foams were prepared in 0.1 M and 0.55 M Na2SO4 solution, referring to the 0.1 M and 0.55 M foam/bubble respectively. The 0.1 M to 0.55 M transition foam was also prepared. High resolution Cryo-SEM was originally used to investigate the CPs behaviour at the bubble-stabilizing interface during bubble coarsening and accelerated coalescence. Findings The 0.1 M bubble-stabilizing interface buckles in uniaxial compression due to coarsening, with the CPs being observed to desorb from the interface. While the CPs were visualized to rearrange into crumpled particle multi-layers surrounding the shrinking 0.55 M bubbles, due to the adhesion between interpenetrating polymer chains and the unique lubrication effect of the PVP layers. The 0.1 M to 0.55 M transition foaming behaviour was also studied. Cracks and voids were observed at interfaces surrounding the transition bubbles driven by in-situ particle aggregation, resulting in accelerated bubble coalescence during the transition process.
This study explored whether British and Malaysian drivers differ in their use of explicit (turn signals) and implicit (e.g., vehicle position, speed) communicative cues when judging the intention of other road users. Participants viewed videoclips of car drivers and motorcyclists who either continued straight or turned into a junction. The clips terminated immediately prior to any manoeuvre being made and participants were asked to judge whether or not the vehicle would turn. Explicit signals (turn indicators) were manipulated such that valid signals were made 50% of the time. Although both groups of drivers were more accurate on validly signalled trials, British drivers were more affected by signal validity, performing particularly poorly on invalid trials. British drivers were better at judging intentions of cars than motorcycles, whereas Malaysians performed better for motorcycles than cars on invalid trials. We conclude that British drivers heavily rely on explicit signals when judging intention whereas Malaysian drivers are more attuned to implicit signals. Familiarity with vehicle type may also impact performance, especially where cues are ambiguous. Implications for driving abroad and autonomous vehicles are discussed.
A series of novel N-benzoylthiourea-pyrrolidine carboxylic acid derivatives bearing an imidazole moiety has been prepared and their various biological activities are evaluated. The ability of forming intermolecular hydrogen-bonds of these molecules was pursued in the search of the best antimicrobial activity. The synthesized compounds were tested to search whether they had an enzyme inhibitory potency against AChE and BChE, which are the main targets for Alzheimer's disease. The prepared compounds were also screened for antituberculosis activity against M. tuberculosis H37Rv strain and the antibacterial activity against E. coli, A. baumannii, S. aureus, B. subtilis, A. hydrophila, bacteria. In addition, their antifungal activities are also evaluated against C. tropicalis, C. albicans, C. glabrata strains.
Sustainable consumption is a growing niche with an increasing number of initiatives aimed at lowering domestic environmental consumption footprints. Third-party assured product eco-labelling has emerged as a key governance mechanism to promote sustainable consumption. However, does the purchasing of eco-labelled products really support a transition towards more sustainable consumption? In this paper, we explore eco-labelling through the lens of the rebound literature. While theorizing of the rebound effect originated in energy economics and has long been centred on eco-efficiency, we extend its rationale to products that are associated with a price premium in return for added environmental quality attributes. Reporting on two inter-related studies into the link between purchasing of environmentally friendly products and different types of environmental resource consumption, we find that eco-labelled products flourish in more affluent economies that are characterized by higher levels of overall resource consumption; and that willingness to consume environmentally friendly products is positively related to higher individual carbon, water and material footprints. Hence, we argue that eco-labelling in its current form is inextricably linked to higher – rather than lower – levels of resource consumption. Consequently, the governance mechanism that underpins eco-labelling is associated with an indirect behavioural consumer rebound effect.
It is often assumed that a small proportion of a given vehicle fleet produces a disproportionate amount of air pollution emissions. If true, policy actions to target the highly polluting section of the fleet could lead to significant improvements in air quality. In this paper, high-emitter vehicle subsets are defined and their contributions to the total fleet emission are assessed. A new approach, using enrichment factor in cumulative Pareto analysis is proposed for detecting high emitter vehicle subsets within the vehicle fleet. A large dataset (over 94,000 remote-sensing measurements) from five UK-based EDAR (emission detecting and reporting system) field campaigns for the years 2016–17 is used as the test data. In addition to discussions about the high emitter screening criteria, the data analysis procedure and future issues of implementation are discussed. The results show different high emitter trends dependent on the pollutant investigated, and the vehicle type investigated. For example, the analysis indicates that 23 % and 51 % of petrol and diesel cars were responsible for 80 % of NO emissions within that subset of the fleet, respectively. Overall, the contributions of vehicles that account for 80 % of total fleet emissions usually reduce with EURO class improvement, with the subset fleet emissions becoming more homogenous. The high emitter constituent was more noticeable for pollutant PM compared with the other gaseous pollutants, and it was also more prominent for petrol cars when compared to diesel ones.
Many crop species play host to a diverse range of soil-borne symbionts ranging from parasitic, such as potato cyst nematodes (PCN), to mutualistic, including arbuscular mycorrhizal fungi (AMF). Each of these organisms may establish symbiosis with the host prior to the arrival of another which may impact the fitness of all parties involved. We simulated a range of arrival time scenarios for both AMF and PCN and determined their consequences on potato host plants and subsequent symbionts to reflect the likely complexity of symbioses that occur in the field. Simulations were focussed on the first few weeks of plant growth to identify the importance of symbiont interactions during early plant development. Our data indicate that the order in which symbionts are introduced to crop roots is not only important for their own success, but also for that of the host and its additional symbionts. The presence of AMF increased the PCN population on the host, with earlier introduction of AMF increasing the magnitude of the effect. However, presence of AMF also increased the potato's tolerance to PCN, ameliorating the negative effects of the increased PCN burden. This tolerance was stronger the earlier the AMF were introduced and was sustained even when AMF were introduced after PCN. Overall, we show that the initial few weeks of crop emergence and growth may reflect a window of opportunity where the prosperity of the crop and its tolerance of parasites can potentially be influenced by coordinating application of AMF propagules. Additionally, these timings impact the success of below-ground plant parasites that can persist and impact crops for several years.
This study proposes and tests a framework relating to the effect of entrepreneurial bricolage on international opportunity recognition (IOR) and the influence of the latter on export intensity. Survey data from 193 export-oriented entrepreneurial firms operating in Ghana indicates that entrepreneurial bricolage has an inverted U-shaped relationship with IOR – and that IOR has a positive effect on export intensity. A further analysis reveals that explorative learning enhances the inverted U-shaped relationship between bricolage and IOR, while exploitative learning improves the IOR–export intensity relationship. Our findings present important implications for international entrepreneurship research and the management of export-oriented entrepreneurial firms in developing economies.
Conventional protection schemes have essentially been developed for power systems dominated by synchronous generators. High penetration of power-electronic interfaced renewable energy sources (PEIRESs) can adversely impact the reliability of protection systems, thereby increasing the risk of widespread disturbances. This paper proposes a robust wide-area backup protection (WABP) scheme against asymmetrical faults for transmission systems with high penetration of renewables. The scheme exploits the full potential of available synchrophasors without placing any rigid constraints on PMU locations. To this end, the faulted line and a few appropriately selected PEIRESs are replaced by equivalent current sources using the Substitution Theorem. The remaining PEIRESs are substituted by their equivalent impedances accounting for their response to a fault, considering the control strategies and overcurrent limits of these PEIRESs. This results in a linear system of equations whose solution readily indicates the faulted line on account of the weighted sum of squared residuals (WSSR) concept. To add to the security of the proposed scheme, the fault distance on the pinpointed line is also calculated and checked to ensure it lies within the acceptable range. A total of more than 80,000 simulations conducted on the IEEE 39-bus test system verify that the proposed scheme performs properly irrespective of the numbers/locations of PEIRESs and their control strategies.
Carbon deposition is an inevitable phenomenon in regenerative cooling systems using endothermic hydrocarbon fuels (EHFs), which seriously affects heat transfer performance and even clogs cooling channels. In this study, a framework of 2D dynamic coking study is established by coupling simultaneously a detailed pyrolysis model with the MC-II coking model. Two types of coke, i.e., catalytic coke and pyrolytic coke, are considered, and the coking process is simulated via dynamic mesh techniques. The flow and heat transfer characteristics, and heat sink before and after the carbon deposition under typical working conditions are compared and discussed in detail. The results reveal that the secondary cracking reactions promote the concentration of the coking precursors, and the coking simulation results agree well with the experiment. The maximum fluid flow velocity and maximum solid temperature are increased after the coking formation due to the reduction of the cross section area and the poor thermal conductivity of the deposited coke. As the coke deposits, the total heat sink per temperature rise and pressure drop both deteriorate. However, the maximum conversion of n-decane is almost unchanged, which can be well explained by the local DamkÖhler (Da) number.
Whole-body vibrations provide important proprioceptive feedback for the control of human locomotion. However, these vibrations are also reported to have a detrimental effect on several existing musculoskeletal disorders. Studies have to date reported on the limits of these centre-of-mass (CoM) vibrations mainly for the level walk. However, their impact remains unquantified for other walking situations such as ramp ascent and descent (A/D). Orthotic devices have also been reported as improving limb mobility, but their contribution to whole-body vertical dynamics has not yet been investigated in ramp walking studies. This study presents methods for evaluating normal limits of CoM-vibrations on a ramp, with and without the effect of an ankle–foot orthosis (AFO). Experiments are performed on a force plate and CoM-vibrations data is recorded as a function of impact forces for both normal and AFO walking conditions. These CoM-vibrations are then modelled using a regression technique and analysed in the frequency domain. The normal limits of CoM-vibrations are quantified as limb compliance properties and stability margins for both A/D. A comparison between normal and AFO walking conditions identified significant variations (Friedman-test, p < 0.05) in lower limb compliance dynamics and stability margins. Results also showed the significant impact of AFO adjustments on musculoskeletal dynamics. This preliminary study defines the normal limits of impact forces and their efficiency associated with the wearing of an AFO. Clinically, these outcomes are important in evaluating the deleterious effects of impact forces in patients and on the effectiveness of measures taken to overcome impact forces using assistive devices.
Sweet sorghum (SS) is an agricultural crop that is produced commercially in Nigeria. The crop has a high biowaste energy in its stalk, which is an attractive source of bioenergy in rural areas where it is produced. The residue–to-produce ratio (RPR) of the crop is 1.25 kg of biowaste for 1 kg of SS produced. The solid residue that results from the crop can be subjected to gasification to produce combustible gases: carbon monoxide (CO), hydrocarbon gases (total hydrocarbons) and hydrogen. The combustible gases can be piped into a burner for heat or into a Compression Ignition (CI) engine for electricity generation. This will enhance energy security as well as energy equity in rural areas in Nigeria and sub-saharan African countries where the crop is also produced. This research was aimed at optimising the gasification of SS stalk residue to maximise the yield of combustible gases from the first stage of the process. The restricted ventilation cone calorimeter method was used to gasify SS stalks on a laboratory scale. The test was carried out at air flow rates per exposed flat surface area of 9, 11.2, 12.9, 14.3, 15.5, 16.3, and 19.2 g/s·m² respectively, which controls the gasification rate or power output. The speciation of the gases that evolved from the gasification of the biomass samples was carried out by an FTIR that was calibrated for 60 species. Current uses of biomass residues in open fire heating generates toxic fine particulate emissions and this work aimed to show that this was not a greater problem with gasification. A dynamic electrical mobility particle spectrometer (DMS500) was used to measure the particulate size distribution and concentration, as an efficient gasifier should not be generating major yields of soot, which would be a problem for a downstream reciprocating engine. The optimum equivalence ratio (Ф) for the best energy transfer to the gaseous products was 2.1, which was similar to previous work on pine using this equipment where the optimum equivalence ratio was 2.8. The hot gases efficiency at the optimum Ф was 81%, which compares well to that of 78% for pine.
This chapter reviews the range of transport policy responses to the COVID-19 pandemic. The primary focus is on responses in England but comparative perspectives are provided with the devolved administration in Scotland where divergence is becoming increasingly evident. In July 2021, with just under one-half of the population having received two vaccine doses, social distancing restrictions have largely been lifted. Continued high levels of infection are influencing a slow return to work, with ongoing implications for the viability of public transport. The chapter reflects on the policy interventions to date and looks ahead to the key challenges for the months and years ahead. In particular, the chapter focusses on public transport. While huge amounts of public funding have been used to support public transport; it seems inevitable that there will need to be a readjustment in patterns of supply given the changing nature of work and business travel.
This paper presents a novel ankle rehabilitation exoskeleton with two rotational degrees of freedom, which is suitable for dynamical rehabilitation for patients with neurological impairments. Its stiffness performance is assessed in consideration that the interaction between the footplate and the ground may deflect the mechanism away from the desired/predefined motion patterns. The novel design employs a universal-prismatic-universal (U-P-U) joint link, whose constraint type changes between a couple and a line vector during manipulation of the exoskeleton. To conduct a stiffness analysis of such a mechanism with a type-variable constraint – for the first time – a modified screw-based method (SBM) is proposed. Comparisons with the results obtained from finite element analysis verified that, the modified SBM provides reliable estimates of the exoskeleton's stiffness within the complete workspace (covering the constraint-type transition configurations). The stiffness of the exoskeleton is further evaluated by acquiring the minimum/maximum stiffness values, after computing the distribution of the most crucial linear and angular stiffness parameters within the workspace. Moreover, the influence of the architectural parameters on the stiffness properties is considered for further design optimization.
Quantifying soil structural dynamics and aggregate turnover is important in understanding soil organic carbon (SOC) stocks, particularly over decadal and larger time scales. Until now it has remained unclear clear how soil aggregate size and its associated carbon respond to both long-term soil fertility and climate change. Here, we explore changes in soil structure and aggregate organic C (OC) stocks under different fertilization practices by combining field chronosequence SOC measurements with dynamic and process modeling in a long-term wheat-maize field experiment on the North China Plain. The fertilization practices comprise no fertilization (CK), chemical fertilization (NPK), and combined manure and NPK treatments (MNPK). The experimental measurements included the mass of OC stocks in different soil aggregate size classes. We used this information to calibrate parameters of the Carbon, Aggregation, and Structure Turnover (CAST) model and to predict future changes in aggregate structure and the resulting OC stocks using the RCP2.6 scenarios that were defined by the outputs of five future climate models from IPCC projection. With trends towards a wetter climate and increasing soil moisture under the RCP2.6 scenarios for the region, soil OC stocks will increase in all three treatments, with the strongest increase under MNPK due to exogenous C inputs. The CAST model output further suggests that changes in microaggregate (250–53 μm) OC stocks in the NPK and MNPK treatments accounted for 78.6 % and 75.3 % of the calculated change in total SOC stocks between the early and late 21st century. In conclusion, our combined data and modeling approach describes changes in soil aggregate C, identifies the primary soil aggregate size class of microaggregates involved in C sequestration in an agricultural soil, and predicts the role of Fluvaquent soils on the North China Plain as a future C sink.
Academic and industrial literature highlight the importance of airport-driven development (ADD) for the 21st Century. Several different types of ADD concepts have been defined, such as aerotropolis and airport city, but there are often substantial differences between authors about definitions. Such differences can potentially create confusion when ADD concepts are used by airport planners in their planning documents (e.g., master plans) and the marketing materials (e.g., brochures and airport websites). Given that large amounts of investment can often depend upon the marketing of a particular ADD concept, such confusion is highly problematic for the air transport industry. However, previous research has not explicitly addressed this issue. To help fill this research gap, the current paper has four different purposes, to: (1) compare definitions of the airport-driven development concepts in the academic literature, (2) compare definitions with real-life examples given by researchers; (3) compare academic definitions and examples with industry usage, as found on airport websites and in airport planning documents; and (4) investigate aspects of the transferability of the ADD concepts (from one region to another and from the academic literature to the industry and vice-versa). Using information from airport websites and master plans, it was found that the terms aerotropolis and airport city are used interchangeably by researchers but not by the industry. However, the use of terms by the industry depends heavily upon the (continental) location of airports, with the analysis presented in the paper distinguishing between airports in North America, Latin America, South and East Asia, Europe and the Middle East. Such analysis enables conclusions to be made about the transferability of ADD concepts, originating in the Global North, to the Global South.
High pressure and high temperature (HPHT) conditions in geothermal wells have necessitated the need to develop thermally stable geothermal drilling mud systems to combat potential drilling complications. This is because mud fluids degrade under HPHT conditions due to high temperature effects. This study therefore aims to establish the optimum concentration of a cationic surfactant that would successfully modify the surface of silica nanoparticles and thereafter, evaluate the performance of modified nano silica as a rheological and filtration property enhancer in water-based muds (WBMs). The surface of silica nanoparticle was successfully modified by adding Hexadecyltrimethylammonium bromide (CTAB) to silica solution. Different mud formulations containing modified nano silica with varying zeta potential values, SNP3 -S2, SNP3 -S4, SNP3 -S5, SNP3 -S6, and SNP3 -S7 with -17.7 mV, 20 mV, 28.2 mV, 35.4 mV, and 37.1 mV respectively were investigated. Results showed that modified nano silica with the highest absolute value of zeta potential enhanced drilling mud rheology as temperature increased from 149°C to 232 °C. The optimal amount of CTAB was found to be between 1.0 and 2.0 wt.%. Filtration loss was reduced by 11.4, 17.6, and 29.5% on average for mud samples SNP3-S5, SNP3-S6, and SNP3-S7, respectively, at all temperatures. Mud cake thickness was reduced by 19.9, 11.6, and 28.7% on average by mud samples SNP3-S5, SNP3-S6, and SNP3-S7 respectively at all temperatures.
Energy networks are the systems of pipes and wires by which different energy vectors are transported from where they are produced to where they are needed. As such, these networks are central to facilitating countries’ moves away from a reliance on fossil fuels to a system based around the efficient use of renewable and other low carbon forms of energy. In this review we highlight the challenges facing energy networks from this transition in a sample of key high income countries. We identify the technical and other innovations being implemented to meet these challenges and describe some of the new policy and regulatory developments that are incentivising the required changes. We then review evidence from the literature about the benefits of moving to a more integrated approach based on the concept of a Multi-Vector Energy Network (MVEN). Under this approach the different networks are planned and operated together to achieve greater functionality and performance than simply the sum of the individual networks. We find that most studies identify a range of benefits from an MVEN approach, but that these findings are based on model simulations. Further work is therefore needed to verify whether the benefits can be realised in practice and to identify how any risks can be mitigated.
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33,958 members
Krzysztof J Kubiak
  • School of Mechanical Engineering
Samit Chakrabarty
  • School of Biomedical Sciences; Chakrabarty group
Martin Zebracki
  • Citizenship and Belonging Group
Woodhouse Lane, LS2 9JT, Leeds, W.Yorkshire, United Kingdom
Head of institution
Professor Simone Buitendijk
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