922017 research outputs found
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Nanoparticle transport within non-Newtonian fluid flow in porous media
No full textControl over dispersion of nanoparticles in polymer solutions through porous media is important for subsurface applications such as soil remediation and enhanced oil recovery. Dispersion is affected by the spatial heterogeneity of porous media, the non-Newtonian behavior of polymer solutions, and the Brownian motion of nanoparticles. Here, we use the Euler-Lagrangian method to simulate the flow of nanoparticles and inelastic non-Newtonian fluids (described by Meter model) in a range of porous media samples and injection rates. In one case, we use a fine mesh of more than 3 million mesh points to model nanoparticles transport in a sandstone sample. The results show that the velocity distribution of nanoparticles in the porous medium is non-Gaussian, which leads to the non-Fickian behaviour of nanoparticles dispersion. Due to pore space confinement, the longtime mean square displacement of nanoparticles depends nonlinearly on time. Additionally the gradient of shear stress in the pore-space of the porous medium dictates the transport behaviour of nanoparticles in the porous medium. Furthermore, the Brownian motion of nanoparticles increases the dispersion of nanoparticles along the longitudinal and transverse direction
Combining Topic Modeling with Grounded Theory: Case Studies of Project Collaboration
No full textThis paper proposes an Artificial Intelligence (AI) Grounded Theory for management studies. We argue that this novel and rigorous approach that embeds topic modelling will lead to the latent knowledge to be found. We illustrate this abductive method using 51 case studies of collaborative innovation published by Project Management Institute (PMI). Initial results are presented and discussed that include 40 topics, 6 categories, 4 of which are core categories, and two new theories of project collaboration
Extracellular volume fraction improves risk-stratification for ventricular arrhythmias and sudden death in non-ischemic cardiomyopathy.
No full textObjectivesTo evaluate whether CMR-based parametric mapping and strain analysis can improve the risk-stratification for ventricular arrhythmias (VA) and sudden death (SD) in non-ischemic cardiomyopathy (NICM). Methods and resultsSecondary analysis of a prospective single-centre-registry (NCT02326324), including 703 consecutive NICM patients, 618 with extracellular volume (ECV) available. The combined primary endpoint included appropriate implantable cardioverter defibrillator therapies, sustained ventricular tachycardia, resuscitated cardiac arrest and SD. During a median follow-up of 21 months, 14 patients (2%) experienced the primary endpoint. Native T1 was not associated with the primary endpoint. Left ventricular global longitudinal strain lost its significant association after adjustment for left ventricular ejection fraction (LVEF). Among patients with ECV available, 11 (2%) reached the primary endpoint. Mean ECV was significantly associated with the primary endpoint and the best cut-off was 30%. ECV≥30% was the strongest independent predictor of the primary endpoint (HR 14.1, p=0.01) after adjustment for LGE and LVEF. ECV≥30% discriminated the arrhythmic risk among LGE+ cases and among those with LVEF≤35%. A simple clinical risk-stratification model, based on LGE, LVEF≤35% and ECV≥30%, achieved an excellent predictive ability (Harrell’s C 0.82) and reclassified the risk of 32% of the study population as compared to LVEF≤35% alone. Conclusions Comprehensive CMR evaluation in NICM showed that ECV was the only parameter with an independent and strong predictive value for VA/SD, on top of LGE and LVEF. A risk-stratification model based on LGE, LVEF≤35% and ECV≥30% achieved an excellent predictive ability for VA/SD
Latent class trajectory modelling: impact of changes in model specification
No full textLatent class trajectory models (LCTMs) are often used to identify subgroups of patients that are clinically meaningful in terms of longitudinal exposure and out¬come, e.g. drug response patterns. These models are increasingly applied in medicine and epidemiology. However, in many published studies, it is not clear whether the chosen models, where subgroups of patients are identified, represent real heterogeneity in the population, or whether any associations with clinically meaningful characteristics are accidental. In particular, we note an apparent over-reliance on lowest AIC or BIC values. While these are objective measures of goodness of fit, that can help identify the optimal number of subgroups, they are not sufficient on their own to fully evaluate a given trajectory model. Here we demonstrate how longitudinal latent class models can substantially change by making small modification in model specification, and the potential impact of this on the relationship to clinical outcomes. We show that the predicted trajectory patterns and outcome probabilities differ when pre-specified cubic versus linear shapes are tested on the same data. However, both could be interpreted to be the “correct” model. We emphasise that LCTMs, as all unsupervised approaches, are hypotheses generating, and should not be directly implemented in clinical practice without significant testing and validation
Billing Models for Peer-to-Peer Electricity Trading Markets with Imperfect Bid-Offer Fulfillment
No full textThis paper proposes four new billing models for peerto-peer electricity trading markets that take into account electricity volume deviations of market participants from their bids and volumes. These billing models incorporate different cost sharing mechanisms so that (i) the costs incurred due to these deviations are minimal for consumers and prosumers and (ii) include non peer-to-peer participants as well. The former is achieved by designing cost sharing mechanisms which split the cost socially, while the latter is achieved by introducing a mid market that clears all the available supply from the P2P market. Through simulations of a small-scale community, we have demonstrated the effectiveness of our billing models in significantly increasing prosumers’ rewards and reducing consumers’ bills.<br/
A five-spin supramolecule for simulating quantum decoherence of Bell states
No full textWe report a supramolecule that contains five spins of two different types, and with, crucially, two different and predictable interaction energies between the spins. The supramolecule is characterised and the interaction energies demonstrated by EPR spectroscopy. Based on the measured parameters we propose experiments that would allow this designed supramolecule to be used to simulate quantum decoherence in maximally entangled Bell states that could be used in quantum teleportation
Investigation of the Electronic Structure and Luminescence Spectra of Uranium-(IV), -(V) and -(VI) Complexes Using Multi-configurational Methods
No full textInterpreting electronic spectra of uranium-containing compounds is an important component of fundamental chemistry as well as in the assessment of waste streams in the nuclear fuel cycle. Here we employ multiconfigurational calculations with CASSCF or DMRGSCF methods on exemplar uranium molecules [UVIO2Cl4]2-, [UV(TRENTIPS)(N)]- and [UIVCl5(THF)]-, featuring an array of geometries and oxidation states, to determine their effectiveness in predicting electronic spectra, compared to literature calculations and experimental data. For [UVIO2Cl4]2-, DMRGSCF alone shows poor agreement with experiment, which can be improved by adding corrections for dynamic correlation with MC-PDFT to give results of similar quality to TD-DFT. However, for [UV(TRENTIPS)(N)]- the addition of dynamical correlation via MC-PDFT or CASPT2 made no improvements over CASSCF, suggesting that perhaps other factors such as solvation effects could be more important in this case. Finally, for [UIVCl5(THF)]-, dynamical correlation included via MS-CASPT2 on top of CASSCF calculations is crucial to obtain a quantitatively correct spectrum; here, MC-PDFT fails to even qualitatively describe the spectrum, highlighting the shortcomings of single-state methods in cases of near-degeneracy
Ageing in Place over time::The making and unmaking of home
No full text‘Ageing in place’ is a key component of UK policy, aimed at supporting older people to remain living in their own homes and communities for as long as possible. Although wide-ranging, the scholarly literature in this field has not sufficiently examined the interconnections between ageing in place and the changing experience of ‘home’ over time. This paper addresses this gap in a novel way by bringing together qualitative secondary analysis of longitudinal data with critical literature on ‘home’ and Mason’s (2018) cutting-edge theories of ‘affinities’ to understand the multi-dimensionality of home in relation to ageing in place. The paper makes significant methodological, empirical, and theoretical contributions to the field of scholarship on home, by demonstrating how homes are made and unmade over time. Discussions of home emerged organically in the longitudinal data that focused on people’s travel and transport use, allowing our qualitative secondary analysis approach to look anew at how experiences of home are dynamically shaped by people’s potent connections inside and outside the dwelling. Presenting an empirical analysis of four case studies, the paper suggests that future discussions in the field of ageing in place should pay closer attention to the factors which shape experiences of the un/making of home over time, such as how deteriorating physical and mental health can shape how people experience their dwelling and neighbourhood as well as their relationships across these settings.<br/
Finite element modelling of hot compression testing of titanium alloys
No full textThis paper presents experimental results and finite element analysis of hot upsetting of titanium alloys Ti64 and Ti407 using a dilatometer in loading mode. All samples showed barrelling, as a consequence of an inhomogeneous temperature distribution and friction. The FE analysis is a full thermomechanical model of the test calibrated using multiple thermocouples. At each nominal temperature and strain-rate, the true flow stress-strain response is inferred using the difference between the initially assumed constitutive response input to the FE analysis, 𝜎𝜎=𝑓𝑓(𝑇𝑇,𝜀𝜀˙,𝜀𝜀), and the predicted response of the model. The analysis applies new procedures for: (i) modelling the thermal gradient; (ii) finding the flow stress correction due to the inhomogeneity, using literature data as the input to the FE analysis; (iii) smoothing the constitutive data, fitting empirical 𝜎𝜎=𝑓𝑓(𝑇𝑇,𝜀𝜀˙) surfaces at multiple discrete strains. The extracted true constitutive data confirms the moderate strain-softening behaviour in Ti64 alloy, and the FE model predicts the distribution of local deformation conditions, for application in interpretation of microstructure and texture evolution. This highlights the difference between nominal and actual test conditions, showing that the discrepancy varies systematically with test conditions, with the central strain and strain-rate being magnified significantly, by factors of order 2–3
Peer-to-Peer, Community Self-Consumption, and Transactive Energy: A Systematic Literature Review of Local Energy Market Models
No full textPeer-to-peer, community or collective self-consumption, and transactive energy markets offer new models for trading energy locally. Over the past five years, there has been significant growth in the amount of academic literature examining how these local energy markets might function. This systematic literature review of 139 peer-reviewed journal articles examines the market designs used in these energy trading models. A modified version of the Business Ecosystem Architecture Modelling framework is used to extract market model information from the literature, and to identify differences and similarities between the models. This paper examines how peer-to-peer, community self-consumption and transactive energy markets are described in current literature. It explores the similarities and differences between these markets in terms of participation, governance structure, topology, and design. This paper systematises peer-to-peer, community self-consumption and transactive energy market designs, identifying six archetypes. Finally, it identifies five evidence gaps which require future research before these markets could be widely adopted. These evidence gaps are the lack of: consideration of physical constraints; a holistic approach to market design and operation; consideration about how these market designs will scale; consideration of information security; and, consideration of market participant privacy