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Computational modelling of water-fuelled Hall Effect Thrusters
No full textThis paper presents a Particle-In-Cell code designed for the simulation of water-fuelled
Hall Efect Thrusters, including two diferent propellants: water vapour and oxygen
(the latter being intended for water electrolysis propulsion with oxygen supplied
through the anode and hydrogen through the cathode). The reactive model is struc‑
tured in two stages, encompassing not only the initial reactions of water vapour
and oxygen molecules (1st stage) but also the reactions of the diatomic and mono‑
atomic products resulting from them (2nd stage). Specifcally, the model accounts
for 45 reactions in the case of water vapour and 18 reactions in the case of oxygen,
including the most relevant excitation events for each species. The Particle-In-Cell
code uses a combination of a 0-dimensional model with a 2-dimensional model.
The 0-dimensional model provides initial neutral and electron densities, as well
as the most signifcant reactions, to facilitate the convergence of the 2-dimensional
model without the computational burden of starting a simulation from scratch. The
0-dimensional model reveals that the reactions considered within the 2nd stage are
crucial for the plasma species composition of the discharge. The oxygen plasmas
consist mainly of O+ and O+
2 ions in a similar proportion, while double and negative
ions do not play a signifcant role. Neutrals (O2 and O) also show similar distributions,
depending on the thruster’s operating conditions. Water vapour plasmas are domi‑
nated by OH+, H2O+, H+, and O+ ions, with other species such as H+
2 , O++, and nega‑
tive ions being negligible. The neutral population is predominantly composed of mon‑
oatomic H particles. The 0-dimensional model also demonstrates that all ionisation
fractions of the species follow an exponentially increasing trend with the electron tem‑
perature. Finally, the 2-dimensional model provides additional insight into the plasma
evolution, electron temperature, power losses coming from the reactive model
and equilibrium points of the system
Portable molecular diagnostic platform for rapid point-of-care detection of mpox and other diseases
No full textThe World Health Organization’s designation of mpox as a public health emergency of international concern in August 2024 underscores the urgent need for effective diagnostic solutions to combat this escalating threat. The rapid global spread of clade II mpox, coupled with the sustained human-to-human transmission of the more virulent clade I mpox in the Democratic Republic of Congo, highlights a critical gap in point-of-care diagnostics for this emergent disease. In response, we developed Dragonfly, a portable molecular diagnostic platform for point-of-care use that integrates power-free nucleic acid extraction (<5 minutes) with lyophilised colourimetric LAMP chemistry. The platform demonstrated an analytical limit-of-detection of 100 genome copies per reaction for monkeypox virus, effectively distinguishing it from other orthopoxviruses, herpes simplex virus, and varicella-zoster virus. Clinical validation on 164 samples, including 51 mpox-positive cases, yielded 96.1% sensitivity and 100% specificity for orthopoxviruses, and 94.1% sensitivity and 100% specificity for monkeypox virus. Here, we present a rapid, accessible, and robust point-of-care diagnostic solution for mpox, suitable for both low- and high-resource settings, addressing the global resurgence of orthopoxviruses in the context of declining smallpox immunity
IT-enabled organisational transformation and green employment growth in microfirms
No full textIn this paper, we explore whether IT-enabled organisational transformation (ITOT) moderates the relationship between eco-innovation and the growth performance of microfirms. Our framework conceptualises ITOT in microfirms as a multistage process that includes: (i) setting a digitalisation strategy, (ii) adopting advanced information systems technology (IST) artefacts and (iii) developing in-house digital resources and capabilities. The analysis of a sample of 5015 microfirms from 39 countries indicates that eco-innovations boost firm growth when coupled with (i) a formalised digitalisation strategy, (ii) adoption of advanced IST artefacts (e.g., digital technologies that characterise Industry 4.0) and (iii) digital resources and capabilities in microfirms. These findings contribute to the growing digitalisation literature by highlighting the essential role that ITOT processes play in enabling sustainability-led growth pathways for microfirms. The paper advocates for the viability and performance benefits of a twin digital and ecological transformation and showcases the potential of ITOT for an economically successful net-zero transition that embraces microfirms
Numerical study of a parabolic-trough CPV-T collector with spectral-splitting liquid filters
No full textConventional flat-plate photovoltaic-thermal (PV-T) collectors generate electricity and heat simultaneously; however, the outlet temperature of the latter is typically below 60 °C, limiting their widespread application. The use of optical concentration can enable higher-temperature heat to be generated, but this can also lead to a rise in the operating temperature of the PV cells in the collector and, in turn, to a deterioration in their electrical performance. To overcome this challenge, an optical spectral-splitting filter that absorbs the infrared and transmits the visible portion of the solar spectrum can be used, such that wavelengths below the bandgap are sent to the cells for electricity generation, while those above it are sent to a thermally decoupled absorber for the generation of heat at a temperature that is considerably higher than that of the cells. In this study, a triangular primary PV-T channel, wherein the primary heat transfer fluid (water) flows, is integrated into a parabolic trough concentrator of geometrical concentration ratio ~10, while a secondary liquid filter (water, AgSiO2-eg or Therminol-66) is introduced for spectral splitting. Optical, electrical and thermal-fluid (sub-)models are developed and coupled to study the performance of this collector. Each sub-model is individually checked against results taken from the literature with maximum deviations under 10%. Subsequently, the optical and electrical models are coupled with a 3-D thermal-fluid CFD model (using COMSOL Multiphysics 6.1) to predict the electrical and thermal performance of the collector. Results show that when water is used as the optical filter, the maximum overall thermal (filter channel plus primary channel) and electrical efficiencies of the collector reach ~45% and 15%, respectively. A comparison between water, AgSiO2-eg and Therminol-66 reveals that AgSiO2-eg improves the thermal efficiency of the filter channel by ~25% (absolute) compared to Therminol-66 and water, however, this improvement — which arises from the thermal performance of the filter — comes at an expense of a ~5% electrical efficiency loss
Inconsistences in prescribing epinephrine autoinjectors
No full textA key strategy in supporting patients at risk of anaphylaxis is the provision of self-administered epinephrine (“self-epi”). However, there seems to be a lower threshold for prescribing self-epi in food allergy than for venom. Self-epi is often recommended to someone where the risk of food-anaphylaxis is relatively low (under 5%) yet a similar level of risk in a venom-allergic patient is considered not to justify self-epi. We can only speculate as to the reasons for this: it may be harder to avoid food allergens (which can be hidden and undisclosed) compared to a bee or wasp, and the effort needed to avoid food allergens is greater. Evidence suggests that self-epi does not reduce rates of hospitalization or fatal anaphylaxis. Therefore, the rationale for self-epi should be based on supporting patients and empowering them to lead a more normal life. Surprisingly, studies suggest that self-epi has an adverse impact on quality-of-life, perhaps because it creates a perception that those with self-epi are more at risk of a life-threatening reaction. We must be cognizant of the fact that when the risk of anaphylaxis is relatively low, the prescription of self-epi can be associated with harms as well as potential benefits
Online graph topology learning via time-vertex adaptive filters: from theory to cardiac fibrillation
No full textGraph Signal Processing (GSP) provides a powerful framework for analysing complex, interconnected systems by modelling data as signals on graphs. While recent advances have enabled graph topology learning from observed signals, existing methods often struggle with time-varying systems and real-time applications. To address this gap, we introduce AdaCGP, a sparsity-aware adaptive algorithm for dynamic graph topology estimation from multivariate time series. AdaCGP estimates the Graph Shift Operator (GSO) through recursive update formulae designed to address sparsity, shift-invariance, and bias. Through comprehensive simulations, we demonstrate that AdaCGP consistently outperforms multiple baselines across diverse graph topologies, achieving improvements exceeding 83\% in GSO estimation compared to state-of-the-art methods while maintaining favourable computational scaling properties. Our variable splitting approach enables reliable identification of causal connections with near-zero false alarm rates and minimal missed edges. Applied to cardiac fibrillation recordings, AdaCGP tracks dynamic changes in propagation patterns more effectively than established methods like Granger causality, capturing temporal variations in graph topology that static approaches miss. The algorithm successfully identifies stability characteristics in conduction patterns that may maintain arrhythmias, demonstrating potential for clinical applications in diagnosis and treatment of complex biomedical systems
Impact of doping on sodium self-diffusion in Na2Ti3O7
No full textThere is intensive research by the community to improve materials for energy storage applications beyond lithium-ion batteries. The use of sodium as the charge carrier has benefits and can revolutionize the field. The wide use of sodium-ion batteries is partially hindered by the slow diffusion of sodium ions in the anode. Here we use density functional calculations to investigate the diffusion properties of sodium ions in Na2Ti3O7. We introduce trivalent (aluminium (Al), gallium (Ga), and scandium (Sc)) and tetravelant (silicon (Si), germanium (Ge), and tin (Sn)) substitutional dopants to calculate their impact on the Na self-diffusion process. Considering a potential migration pathway, sodium atoms migrate via the vacancy mechanism with an energy barrier of 0.69 eV in undoped Na2Ti3O7. This is substantially reduced by 0.3 eV when an Al substitutes for a titanium atom in the pathway of migration
Exploring the linkage between mechanical behaviour and particlescale interaction of kaolinite
No full textThe response of clay to mechanical compression is highly dependent on its stress history. Generally, normally consolidated clays exhibit a relatively soft response, while over-consolidated clays exhibit a much stiffer response upon reloading. In the literature this difference has been qualitatively attributed to differences in clay microstructure. This paper uses coarse-grained molecular dynamics simulations to propose that an additional contribution comes from the non-linear, non-monotonic relationship between the inter-particle forces and the separation distances. At large separation distances, clay particles
interact via repulsive non-contact forces when the particles initially become close enough to interact. The strength of the mutual repulsion increases with decreasing separation until a maximum repulsive interaction energy, termed an energy barrier, is reached. Once this energy barrier is overcome, the particle interactions become attractive so that the particles effectively become bonded to each other. This paper uses a new approach to interaction models for particle-scale simulation to show that the compressive forces experienced by particles under engineering stress levels are sufficient to push particle pairs into this
attractive force regime; and that, upon subsequent unloading, these particles remain bonded to each other. The difference in macro-scale compressibility between normally
consolidated and over-consolidated clays can be explained, at least in part, by this attraction and by particles irreversibly bonding togethe
Varying effects of risk factors on economic losses from fishing vessel accidents: a Bayesian random-parameter quantile regression with heterogeneity in means
No full textUnderstanding the determinants of economic loss in fishing vessel accidents is crucial for maritime risk assessment and policy development. This study proposes a Bayesian Random-Parameter Quantile Regression with Heterogeneity in Means (BRPQRHM) framework, and compares it with the Bayesian fixed-parameter regression (BFPR), Bayesian fixed-parameter quantile regression (BFPQR), and Bayesian random-parameter quantile regression (BRPQR) to investigate the varying and heterogeneous effects of vessel, environment, and accident-related factors on economic loss. The proposed approach addresses key limitations of conventional models by offering three major advantages by enabling a richer characterization of covariate effects across quantiles, improving robustness to outliers in heavy-tailed and skewed data, and accounting for unobserved heterogeneity through random parameters influenced by covariates. Using a dataset of fishing vessel accidents in Ningbo waters, the results demonstrate substantial variations in covariate effects across quantiles and highlight the superiority of quantile regression in modeling the skewed and heavy-tailed distribution of economic losses. The BRPQR and BRPQRHM models significantly improve model fit at higher quantiles and reveal that the effects of variables such as human errors and crew qualifications are probabilistic rather than fixed. In particular, the BRPQRHM model at the 98% quantile captures complex interactions between crew effects and contextual factors, including vessel width, visibility, and accident type. These findings underscore the importance of accounting for the unobserved heterogeneity and provide novel insights into the risk factors associated with severe fishing vessel accidents