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Uncertainty quantification for data-driven turbulence modelling with Mondrian forests
No full textData-driven turbulence modelling approaches are gaining increasing interest from the CFD community. Such approaches generally aim to improve the modelled Reynolds stresses by leveraging data from high fidelity turbulence resolving simulations. However, the introduction of a machine learning (ML) model introduces a new source of uncertainty, the ML model itself. Quantification of this uncertainty is essential since the predictive capability of a data-driven model diminishes when predicting physics not seen during training. In this work, we explore the suitability of Mondrian forests (MF's) for data-driven turbulence modelling. MF's are claimed to possess many of the advantages of the commonly used random forest (RF) machine learning algorithm, whilst offering principled uncertainty estimates. An example test case is constructed, with a turbulence anisotropy constant derived from high fidelity turbulence resolving simulations. A number of flows at several Reynolds numbers are used for training and testing. MF predictions are found to be superior to those obtained from a linear and non-linear eddy viscosity model. Shapley values, borrowed from game theory, are used to interpret the MF predictions. Predictive uncertainty is found to be large in regions where the training data is not representative. Additionally, the MF predictive uncertainty is found to exhibit stronger correlation with predictive errors compared to an a priori statistical distance measure, which indicates it is a better measure of prediction confidence. The MF predictive uncertainty is also found to be better calibrated and less computationally costly than the uncertainty estimated from applying jackknifing to random forest predictions. Finally, Mondrian forests are used to predict the Reynolds discrepancies in a convergent-divergent channel, which are subsequently propagated through a modified CFD solver. The resulting flowfield predictions are in close agreement with the high fidelity data. A procedure for sampling the Mondrian forests' uncertainties is introduced. Propagating these samples enables quantification of the uncertainty in quantities of interest such as velocity or a drag coefficient, due to the uncertainty in the Mondrian forests' predictions. This work suggests that uncertainty quantification can be incorporated into existing data-driven turbulence modelling frameworks by replacing random forests with Mondrian forests. This would also open up the possibility of online learning, whereby new training data could be added without having to retrain the Mondrian forests
Electrochemical and structural evolution of structured V<inf>2</inf>O<inf>5</inf> microspheres during Li-ion intercalation
No full textWith the development of stable alkali metal anodes, V2O5 is gaining traction as a cathode material due to its high theoretical capacity and the ability to intercalate Li, Na and K ions. Herein, we report a method for synthesizing structured orthorhombic V2O5 microspheres and investigate Li intercalation/de-intercalation into this material. For industry adoption, the electrochemical behavior of V2O5 as well as structural and phase transformation attributing to Li intercalation reaction must be further investigated. Our synthesized V2O5 microspheres consisted of small primary particles that were strongly joined together and exhibited good cycle stability and rate capability, triggered by reversible volume change and rapid Li ion diffusion. In addition, the reversibility of phase transformation (α, ε, δ, γ and ω-LixV2O5) and valence state evolution (5+, 4+, and 3.5+ ) during intercalation/de-intercalation were studied via in-situ X-ray powder diffraction and X-ray absorption near edge structure analyses
The relationship between nested patterns and the ripple effect in complex supply networks
No full textSupply networks (SNs) play a vital role in fuelling trade and economic growth. Due to their interconnectedness, firm-level disruptions can cause perturbations to ripple through SNs, magnifying initial impact. Contemporary research on ripple effects focussed on understanding various structural features of SNs to predict and control disruption propagation. Our work adds to this body of knowledge by analysing an intriguing topological property that emerges in SNs: ‘nestedness’, which is defined as a pattern of organisation where products that are supplied by specialist suppliers are a subset of products that are supplied by generalist suppliers. In other words, generalists are also specialists. While previous research examined the emergence of nestedness and its possible reasons, its relationship to SN resilience remained unknown. Here, we develop a cascade model by bringing together the product-supplier-buyer structure; which provides us with fine-grained information on SN dependencies. We simulate disruptions in nested and non-nested organisations of the global automotive SN, and find that nested organisations are significantly more robust to random disruptions but vulnerable to hub disruptions under cascade conditions. However, nested structures are not as resilient; as they do not benefit from a response strategy where buyers seek alternative suppliers; because alternative suppliers do not exist. On the other hand, randomly connected SNs are vulnerable to cascades but can allow network reconfiguration
Giant photoluminescence enhancement in MoSe<inf>2</inf>monolayers treated with oleic acid ligands
No full textThe inherently low photoluminescence (PL) yields in the as prepared transition metal dichalcogenide (TMD) monolayers are broadly accepted to be the result of atomic vacancies (i.e., defects) and uncontrolled doping, which give rise to non-radiative exciton decay pathways. To date, a number of chemical passivation schemes have been successfully developed to improve PL in sulphur based TMDs i.e., molybdenum disulphide (MoS2) and tungsten disulphide (WS2) monolayers. Studies on solution based chemical passivation schemes for improving PL yields in selenium (Se) based TMDs are however lacking in comparison. Here, we demonstrate that treatment with oleic acid (OA) provides a simple wet chemical passivation method for monolayer MoSe2, enhancing PL yields by an average of 58-fold, while also improving spectral uniformity across the material and reducing the emission linewidth. Excitation intensity dependent PL reveals trap-free PL dynamics dominated by neutral exciton recombination. Time-resolved PL (TRPL) studies reveal significantly increased PL lifetimes, with pump intensity dependent TRPL measurements also confirming trap free PL dynamics in OA treated MoSe2. Field effect transistors show reduced charge trap density and improved on-off ratios after treatment with OA. These results indicate defect passivation by OA, which we hypothesise as ligands passivating chalcogen defects through oleate coordination to Mo dangling bonds. Importantly, this work combined with our previous study on OA treated WS2, verifies OA treatment as a simple solution-based chemical passivation protocol for improving PL yields and electronic characteristics in both selenide and sulphide TMDs-a property that has not been reported previously for other solution-based passivation schemes. This journal i
Landscapes of cellular phenotypic diversity in breast cancer xenografts and their impact on drug response
No full textThe heterogeneity of breast cancer plays a major role in drug response and resistance and has been extensively characterized at the genomic level. Here, a single-cell breast cancer mass cytometry (BCMC) panel is optimized to identify cell phenotypes and their oncogenic signalling states in a biobank of patient-derived tumour xenograft (PDTX) models representing the diversity of human breast cancer. The BCMC panel identifies 13 cellular phenotypes (11 human and 2 murine), associated with both breast cancer subtypes and specific genomic features. Pre-treatment cellular phenotypic composition is a determinant of response to anticancer therapies. Single-cell profiling also reveals drug-induced cellular phenotypic dynamics, unravelling previously unnoticed intra-tumour response diversity. The comprehensive view of the landscapes of cellular phenotypic heterogeneity in PDTXs uncovered by the BCMC panel, which is mirrored in primary human tumours, has profound implications for understanding and predicting therapy response and resistance
Electrochemical fabrication of TiO<inf>2</inf> micro-flowers for an efficient intracellular delivery using nanosecond light pulse
No full textIntroduction of foreign cargo into the targeted living cell with high transfection efficiency and high cell viability is an important mean for many biological and biomedical research purpose. Here, we have demonstrated a newly developed Titanium oxide micro-flower structure (TMS) for intracellular delivery. The TMS were formed on titanium (Ti) substrate using an electrochemical anodization process. The TMS consists of branches of titanium dioxide (TiO2) nanotubes, which play an important role in efficient cargo delivery. Due to nanosecond pulse laser exposure, Ti substrate heat-up, generating cavitation bubbles. These bubbles can rapidly grow, coalesce, and collapse to induce explosion resulting in very strong fluid flow through the TiO2 nanotubes and disrupt the cell plasma membrane promoting the delivery of biomolecules into cells. Using this platform, we successfully deliver dyes with 93% efficiency and nearly 98% cell viability into HCT cells, and this technique is potentially applicable for cellular therapy and diagnostics
Investigation of the dispersion of multi-layer graphene nanoplatelets in cement composites using different superplasticiser treatments
No full textThe emergence of nanomaterials research over the past decades, allows the construction sector to turn the cement-based structures into fully digitised, cognitive assets with additional functionalities and improved durability and sustainability performance. Multi-layer graphene nanoplatelets (GNPs) is one such nanomaterial that could be used in cementitious structures. However, the homogenous dispersion of commercially available GNPs has been found to be a key challenge in the literature. This study aimed to develop a practical dispersion protocol to promote the use of GNPs in cementitious systems. Four different commonly used superplasticisers were tested, including a lignosulphonate, a naphthalene-based and two polycarboxylates, along with sonication. The GNPs were characterised using Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA) and X-Ray Diffraction analysis (XRD). The effect of the different superplasticisers on the GNPs dispersion in water was tested with zeta-potential, while UV–Vis spectroscopy was used to examine the effect of the superplasticiser dosage. This was followed by rheology testing that assessed the impact of the superplasticisers on dispersing the GNPs in cement paste. It was found that dispersion of GNPs in water with sonication is not sufficient and a chemical treatment is also needed. The polycarboxylates that work by a steric hindrance mechanism, by physically separating the GNPs and cement particles, were found to be more effective compared to the plasticisers that work by electrostatic repulsion. This research provides a practical dispersion protocol for GNPs in cementitious systems to promote more advanced construction materials
A Fibre-optic Strain Measurement System to Monitor the Impact of Tunnelling on Nearby Heritage Masonry Buildings
No full textFibre-optic sensing technologies provide the opportunity to measure detailed structural response in real time over long durations. This paper describes a first-of-its-kind application of Fibre Bragg Grating (FBG) measurement to monitor the impact of tunnelling works on two Grade-I listed buildings in London, UK. After describing the principles behind the strain sensing technology, laboratory tests are discussed. These tests are used to calibrate strain sensors and validate the newly developed temperature compensation technique. The arrangement of sensors and their installation on the buildings is then presented. Fibre-optic temperature and strain measurements from the ensuing three-year monitoring period are compared with other independent measurements. It is demonstrated that the system enabled direct real-time monitoring of both the short- and long-term impact of tunnelling on the historic assets in a reliable manner
What is design for social sustainability? A systematic literature review for designers of product-service systems
No full textSocial sustainability is concerned with the wellbeing and flourishing of societies now and in the future. Despite its importance, it has been largely overlooked compared with environmental and economic dimensions of sustainability. Additionally, although there is a longstanding history of design being used to tackle social and sustainability problems, the concept of design for social sustainability is not well-understood. In light of this, the current study aims to conceptually develop design for social sustainability. It specifically focuses on how this concept can be developed for the design of product-service systems. A systematic literature review of social design and sustainable design literature is conducted to synthesise fragmented knowledge on design for social sustainability. A total of 69 articles are analysed with respect to terminology, context, methods, focus and key themes. In doing so, it helps to summarise current knowledge and identify several promising areas for further research. In particular, it calls for additional contextual and place-based perspectives; development of appropriate metrics, methods and tools; and research on the linkages between design for social sustainability and existing sustainable design approaches and methods. This article contributes to knowledge in three ways: (1) it integrates disparate knowledge on design for social sustainability within the domain of product-service systems, (2) it defines design for social sustainability and makes progress toward operationalising the concept by identifying its key dimensions, and (3) it identifies current gaps in the literature and highlights areas for further research. This study is important for designers of product-service systems because it sheds a light on what is desirable and achievable
Variety of Ordered Patterns in Donor-Acceptor Polymer Semiconductor Films Crystallized from Solution
No full textA huge challenge is to control the nucleation of crystallites/aggregates in the solution during polymer film formation to generate desired structures. In this work, we investigate crystallization of P(NDI2OD-T2), a donor-acceptor polymer semiconductor, with controlled solution flow along the contact line between the drying film and solution through a seesaw-like pivoting of samples during polymer drying. By controlling the pivoting frequency/amplitude, various types of line patterns can be observed: (I) an array of fishbone-like stripes oriented in the film-growth direction; (II) the pinning-depinning of contact line (PDCL)-mechanism-defined patterned wires along the contact line; and (III) periodic twined crystalline line pattern oriented in the direction of the contact line. The rich variety of pattern formation observed is attributed to the distinctiveness of the donor-acceptor conjugated polymer structure. The result measured from thin-film transistors made of the generated films/structures showed that the charge mobility of P(NDI2OD-T2) does not change much with the film morphology, which supports recent controversy over the charge-transportation mechanism of some donor-acceptor polymer semiconductors