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Implementing bridge model updating for operation and maintenance purposes: examination based on UK practitioners’ views
No full textThere has been a vision of creating bridge digital twins as virtual simulation models of bridge assets to facilitate remote management. Bridge model updating is one digital twin technology which can enable the continuous updating of the structural model as new monitoring data is collected. This paper examines why there is currently little industry uptake of monitoring, modelling and model updating for the operation and maintenance of bridges despite over two decades of research in these fields. The study analyses the findings from a series of semi-structured industry interviews with expert bridge professionals in the U.K. and from an extensive literature survey of bridge model updating studies to examine the disconnects between research and practice and the practical issues of implementing bridge model updating. In particular, the study found that localised damage resulting in local reduction in structural stiffness, a key assumption made in the majority of research, is subject to question by practitioners as many common types of bridge damage may not induce noticeable change in structural stiffness that existing model updating techniques would identify. Key recommendations for future research are proposed to drive adoption of bridge monitoring, modelling and model updating and thus realise their industrial value
The initiation of void growth during stripping of Li electrodes in solid electrolyte cells
No full textWe analyse the initiation of void growth in the Li electrode during the stripping phase of an Li-ion cell with a solid (ceramic) electrolyte. We first show that standard Butler-Volmer kinetics fails to predict the observed void formation. This motivated us to recognise that void initiation/growth involves power-law creep of the Li electrode that is linked to the motion of dislocations. We show, via thermodynamic considerations, that dislocations significantly affect the interface kinetics and use variational principles to develop a modified form of Butler-Volmer kinetics for the interface flux that is associated with a deforming Li electrode. Numerical solutions are presented for the coupled flux of Li+ in a single-ion conductor solid electrolyte and the associated creep deformation of the Li electrode for an imposed stripping current. This involves solution of a Laplace equation for flux in the electrolyte and the nonlinear Stokes flow equations for a power-law creeping solid in the electrode. These two domains are coupled together via the modified Butler-Volmer relation. The calculations predict that an increasing stack pressure needs to be exerted with increasing cell current to avoid the initiation of void growth and are in excellent quantitative agreement with measurements for an Li/LLZO/Li cell
Band-limited double-phase method for enhancing image sharpness in complex modulated computer-generated holograms
No full textHerein, we propose a band-limited double-phase method to improve the quality of reconstructed images encoded by double-phase holograms (DPHs) derived from complex-amplitude light waves. Although the quality of images produced by DPHs was improved compared to that of conventional holographic images, it still suffered from degradation because of the spatial shifting noise generated during the conversion from complex-amplitude holograms to phase-only holograms. The proposed method overcomes this shortcoming by defining a band-limiting function according to the spatial distribution of DPHs in the frequency domain to remove the specific spatial frequency components severely affected by the spatial shifting of DPHs. The sharpness of images reconstructed from band-limited DPHs with appropriate optical filtering showed an improvement of 36.84% in simulations and 51.67% in experiments evaluated by 10-90% intensity variation
Re-framing the threat of global warming: an empirical causal loop diagram of climate change, food insecurity and societal collapse
No full textThere is increasing concern that climate change poses an existential risk to humanity. Understanding these worst-case scenarios is essential for good risk management. However, our knowledge of the causal pathways through which climate change could cause societal collapse is underdeveloped. This paper aims to identify and structure an empirical evidence base of the climate change, food insecurity and societal collapse pathway. We first review the societal collapse and existential risk literature and define a set of determinants of societal collapse. We develop an original methodology, using these determinants as societal collapse proxies, to identify an empirical evidence base of climate change, food insecurity and societal collapse in contemporary society and then structure it using a novel-format causal loop diagram (CLD) defined at global scale and national granularity. The resulting evidence base varies in temporal and spatial distribution of study and in the type of data-driven methods used. The resulting CLD documents the spread of the evidence base, using line thickness and colour to depict density and type of data-driven method respectively. It enables exploration of how the effects of climate change may undermine agricultural systems and disrupt food supply, which can lead to economic shocks, socio-political instability as well as starvation, migration and conflict. Suggestions are made for future work that could build on this paper to further develop our qualitative understanding of, and quantitative complex systems modelling capabilities for analysing, the causal pathways between climate change and societal collapse
Structural, electronic, and optical properties of two-dimensional hafnium monoxide nanosheets
No full textUltrathin two-dimensional transition metal oxides are highly desirable as promising materials for energy storage, gas sensors, photonic and electronic devices. In this work, we studied the structural stability, electronic structure and optical properties of two-dimensional hafnium monoxide with hexagonal and tetragonal lattice by the first principles calculations. Phonon dispersion reveals the lattice dynamic stability of hexagonal structures. Results of band structure showed that both hexagonal and tetragonal HfO nanosheets had highly anisotropic metallic behavior. The optical properties showed strong light absorption and anisotropy
MPM simulation of solitary wave run-up on permeable boundaries
No full textWaves attenuate rapidly as they propagate through porous media due to significant energy dissipation. The ability of permeable armour layers to absorb wave energy is therefore of great interest to the researchers and engineers tasked with the construction of structures that defend vulnerable coastlines from the wave attack. The goal of this research is to determine the effectiveness of vertical and sloped permeable barriers in minimising the wave run-up. Traditional methods for ascertaining the efficacy of protective barriers have used small-scale physical models. However, these are expensive and have been shown to suffer from the scaling problems, therefore numerical methods are gaining popularity. This paper investigates the effect of modifying the mean grain size of a permeable barrier on the run-up response to a solitary wave, using the Material Point Method (MPM), which is capable of handling large deformation problems within a Lagrangian framework, with a background mesh facilitating the solution of the governing equations and allowing for simple imposition of the boundary conditions. A double-point MPM is adopted, with two sets of material points representing the solid and liquid phases respectively, to accurately model situations where the fluid moves through the solid skeleton, such as in the case of wave run-up on porous structures. The multi-phase version of the MPM package Anura3D (www.anura3d.com) is used in the study, with a focus on the influence of changing the mean grain size of composition particles of a porous structure on solitary wave run-ups, on both vertical and sloped permeable boundaries. It has been shown that with an increase in the mean grain size, and therefore the permeability, the overall wave run-up height can be significantly reduced. The proposed study could contribute to a better understanding on the wave run-up reduction on porous structures, and provide useful design guidelines to the coastal defences
Dirac surface plasmons in photoexcited bismuth telluride nanowires: Optical pump-terahertz probe spectroscopy
No full textCollective excitation of Dirac plasmons in graphene and topological insulators has opened new possibilities of tunable plasmonic materials ranging from THz to mid-infrared regions. Using time resolved Optical Pump-Terahertz Probe (OPTP) spectroscopy, we demonstrate the presence of plasmonic oscillations in bismuth telluride nanowires (Bi2Te3 NWs) after photoexcitation using an 800 nm pump pulse. In the frequency domain, the differential conductivity (Δσ = σpump on - σpump off) spectrum shows a Lorentzian response where the resonance frequency (ωp), attributed to surface plasmon oscillations, shifts with photogenerated carrier density (n) as. This dependence establishes the absorption of THz radiation by the Dirac surface plasmon oscillations of the charge carriers in the Topological Surface States (TSS) of Bi2Te3 NWs. Moreover, we obtain a modulation depth, tunable by pump fluence, of ∼40% over the spectral range of 0.5 to 2.5 THz. In addition, the time evolution of Δσ(t) represents a long relaxation channel lasting for more than 50 ps. We model the decay dynamics of Δσ(t) using coupled second order rate equations, highlighting the contributions from surface recombination as well as from trap mediated relaxation channels of the photoinjected carriers. This journal i
Light Rechargeable Lithium-ion Batteries Using V2O5 Cathodes
No full textSolar energy is one of the most actively pursued renewable energy sources, but like many other sustainable energy sources, its intermittent character means solar cells have to be connected to an energy storage system to balance production and demand. To improve the efficiency of this energy conversion and storage process, photo-batteries have recently been proposed where one of the battery electrodes is made from a photo-active material that can directly be charged by light without using solar cells. Here, we present photo-rechargeable lithium-ion batteries (Photo-LIBs) using photocathodes based on vanadium pentoxide nanofibers mixed with P3HT and rGO additives. These photocathodes support the photo-charge separation and transportation process needed to recharge. The proposed Photo-LIBs show capacity enhancements of more than 57% under illumination and can be charged to ~ 2.82 V using light and achieve conversion efficiencies of ~ 2.6% for 455 nm illumination and ~ 0.22% for 1 sun illumination
Research on product-service systems: topic landscape and future trends
No full textPurpose: The paper attempts to address the following research questions (RQs): RQ1: What are the main research topics within PSS research? RQ2: What are future trends for PSS research? Design/methodology/approach: Twenty years of research (1999–2018) on product-service systems (PSS) produced a significant amount of scientific literature on the topic. As the PSS field is relatively new and fragmented across different disciplines, a review of the prior and relevant literature is important in order to provide the necessary framework for understanding current developments and future perspectives. This paper aims to review and organize research contributions regarding PSS. A machine-learning algorithm, namely Latent Dirichlet Allocation, has been applied to the whole literature corpus on PSS in order to understand its structure. Findings: The adopted approach resulted in the definition of eight distinct and representative topics able to deal adequately with the multidisciplinarity of the PSS. Furthermore, a systematic review of the literature is proposed to summarize the state-of-the-art and limitations in the identified PSS research topics. Based on this critical analysis, major gaps and future research challenges are presented and discussed. Originality/value: On the basis of the results of the topic landscape, the paper presents some potential research opportunities on PSSs. In particular, challenges, transversal to the eight research topics and related to recent technology trends and digital transformation, have been discussed
On the selection of charging facility locations for EV-based ride-hailing services: A computational case study
No full textThe uptake of Electric Vehicles (EVs) is rapidly changing the landscape of urban mobility services. Transportation Network Companies (TNCs) have been following this trend by increasing the number of EVs in their fleets. Recently, major TNCs have explored the prospect of establishing privately owned charging facilities that will enable faster and more economic charging. Given the scale and complexity of TNC operations, such decisions need to consider both the requirements of TNCs and local planning regulations. Therefore, an optimisation approach is presented to model the placement of CSs with the objective of minimising the empty time travelled to the nearest CS for recharging as well as the installation cost. An agent based simulation model has been set in the area of Chicago to derive the recharging spots of the TNC vehicles, and in turn derive the charging demand. A mathematical formulation for the resulting optimisation problem is provided alongside a genetic algorithm that can produce solutions for large problem instances. Our results refer to a representative set of the total data for Chicago and indicate that nearly 180 CSs need to be installed to handle the demand of a TNC fleet of 3000 vehicles