UK APAP R-matrix electron-impact excitation cross-sections for modelling laboratory and astrophysical plasma

Systematic R-matrix calculations of electron-impact excitation for ions of astrophysical interest have been performed since 2007 for many iso-electronic sequences as part of the UK Atomic Process for Astrophysical Plasma (APAP) network. Rate coefficients for Maxwellian electron distributions have been provided and used extensively in the literature and many databases for astrophysics. Here, we provide averaged collision strengths to be used to model plasma where electrons are non-Maxwellian, which often occurs in laboratory and astrophysical plasma. We also provide many new Maxwellian-averaged collision strengths, which include important corrections to the published values. Recently, we made available the H- and He-like collision strengths. Here, we provide data for ions of the Li-, Be-, B-, C-, N-, O-, Ne-, Na-, and Mg-like sequences

Scotland’s Assets for Epidemic Preparedness : Workshop at the University of Strathclyde

MOSAEC (Mobilising Scotland's Assets in equitable ways for Epidemic Control) seeks to develop interdisciplinary research ideas and teams that will ensure we are better prepared for future epidemics. The focus of this workshop was on Scotland’s assets and how these can be used to improve epidemic preparedness and reduce inequalities. A series of presentations provided context for the diverse assets employed in epidemic response with discussions around previous use of assets, opportunities to employ other assets and the steps needed to operationalise key assets

Absolute rate coefficients for dielectronic recombination of sodium-like iron ions : experiment and theory

Absolute dielectronic recombination (DR) rate coefficients for sodium-like Fe15+ forming magnesium-like Fe14+ have been measured using the electron–ion merged-beams technique at the heavy ion storage ring Main Cooler Storage Ring, Lanzhou. The measured DR rate coefficients in the energy range from 0 to 90 eV cover all of the DR resonances due to 3s → 3p and 3s → 3d (Δn = 0) transitions and part of the DR resonances from 3s → 4ℓ (Δn = 1) core excitation. The experimental results are compared with theoretical calculations by using three independent state-of-the-art perturbative techniques: a multiconfiguration Breit–Pauli method using the AUTOSTRUCTURE code, a relativistic configuration interaction method using the Flexible Atomic Code and a multiconfiguration Dirac–Fock method using the Jena Atomic Calculator codes. Our theoretical results show excellent agreement with the experimental data in the energy range of 0–40 eV. However, in the energy range of 40–90 eV, a discrepancy is observed between the experiment and theory. Furthermore, temperature-dependent plasma recombination rate coefficients are derived from the measured DR rate coefficients over the temperature range of 103–108 K and are compared with previously available results in the literature. Within the temperature ranges relevant to photoionized plasmas and collisionally ionized plasmas, our results show good agreement with the experimental result from S. Schippers et al. (2010), as well as with the theoretical data of M. F. Gu (2004) and Z. Altun et al.; however, the earlier theoretical data from M. Arnaud & J. Raymond and P. Mazzotta et al., which are based on LS-coupling calculations, significantly underestimate the plasma rate coefficients in the low-temperature range. The present results provide a benchmark data set for astrophysical modeling

Comparing the chatter characteristic in milling of Ti6Al4V alloy with and without laser assistance

Laser-assisted machining (LAM) is a promising technique to enhance the machinability of difficult-to-cut materials. However, many challenges remain for its practical engineering application, despite extensive research on the material removal mechanism in LAM. One key challenge is to elucidate how the laser affects the machining dynamics (e.g. cutting forces and chatter characteristics) and machined qualities in realistic machining scenarios. Therefore, this study aims to investigate the relationship between chatter characteristics and laser assistance in milling processes. Two sets of milling experiments with different depths of cut were conducted on wedge-shaped Ti6Al4V alloys with and without laser assistance. The milling forces were measured and analyzed using Short-time Fourier transforms and Wavelet transforms to detect chatter in frequency and time-frequency domains. Moreover, four indicators (i.e., standard deviation, Kurtosis, fuzzy entropy, envelope entropy) were extracted to monitor the milling conditions. The results showed that dry milling experienced a transition from stable machining to slight chatter at an axial depth of cut (ADOC) of 1.75 µm and then to severe chatter at ADOC=4.63 µm under the same cutting parameters, while LAM only exhibited slight chatter at ADOC=4.00 µm, demonstrating the specific effect of laser assistance on suppressing chatter. This was further confirmed by the observed surface morphology and roughness

Enhanced interfacial thermal transport in diamond nanothread reinforced polymer nanocomposites : insights from atomistic simulations and density functional theory

Diamond nanothreads (DNTs), a novel class of nanomaterials that outperform traditional carbon-based nanomaterials, are exceptional reinforcers for advanced polymer composites and hold great promise in various applications of composites. In this atomistic simulation study, the novelty lies in the comprehensive exploration of DNT–polymer interfacial thermal conductance and the identification of methyl functionalization as a superior strategy, with clear implications for designing advanced thermal management composites. It is found that DNTs, derived from surface modifications (i.e. hydrogenation and functionalization) of carbon nanotubes (CNTs) with a chirality of (3, 0), demonstrate significantly enhanced interfacial thermal conductance in nanocomposite systems compared to unmodified CNTs. In particular, the incorporation of DNT_C-CH3 achieves the highest interfacial thermal conductance of 0.115 GW m−2 K−1, signifying a 140% improvement over CNTs. Through analyzing the phonon density of states (PDOS) of different reinforcements and a paraffin wax matrix, it is revealed that the low-frequency (0–70 THz) phonons dominate the interfacial thermal conductance due to their more significant contribution compared to the high-frequency (70–120 THz) phonons. Among all interfacial material combinations, DNT_C-CH3/paraffin wax exhibits the best matching in terms of the PDOS overlap, the PDOS peak intensity and the PDOS peak position in the low-frequency regime, which facilitates the most effective phonon transport across the interface and thereby leads to significant enhancement in interfacial thermal conductance. Furthermore, density functional theory (DFT) calculations uncover the optimal molecular electrostatic potential distribution and the highest binding energy of DNT_C-CH3/paraffin wax molecular structures, indicating excellent interfacial compatibility and strong adhesion between the reinforcement and the matrix material, which plays an important role in enhancing the interfacial thermal conductance. The findings of this study not only deepen the understanding of the physical mechanisms governing interfacial thermal conductance but also highlight the great potential of DNT reinforced composites in advanced thermal management applications

Energy aware computer vision algorithm deployment on heterogeneous architectures

Computer vision algorithms, specifically convolutional neural networks (CNNs) and feature extraction algorithms, have become increasingly pervasive in many vision tasks. As algorithm complexity grows, it raises computational and memory requirements, which poses a challenge to embedded vision systems with limited resources. Heterogeneous architectures have recently gained momentum as a new path forward for energy efficiency and faster computation, as they allow for the effective utilisation of various processing units, such as Central Processing Unit (CPU), Graphics Processing Unit (GPU), and Field Programmable Gate Array (FPGA), which are tightly integrated into a single platform to enhance system performance. However, partitioning algorithms over each accelerator requires careful consideration of hardware limitations and scheduling. We propose two low-high power heterogeneous systems and a method of partitioning CNNs and a feature extraction algorithm (SIFT) onto the hardware. We benchmark feature detection and image classification algorithms on heterogeneous systems and their discrete accelerator counterparts. We demonstrate that both systems outperform FPGA/GPU-only accelerators. Experimental results show that for the SIFT algorithm, there is 18% runtime improvement over the GPU. In the case of MobilenetV2 and ResNet18 networks, the high power system achieves 17.75%/5.55% runtime and 6.25%/2.08% energy improvements respectively, against their discrete counterparts. The low-power system achieves 6.32%/16.21% runtime and 7.32%/3.27% energy savings. The results show that effective partitioning and scheduling of imaging algorithms on heterogeneous systems is a step towards better efficiency over traditional FPGA/GPU-only accelerators

Hit where it hurts : city vulnerability during wartime

Success in center-seeking rebellions requires rebels to oust the incumbent government. Yet not all center-seeking rebels attack the capital and those that do often take a circuitous route. We build from existing literature to integrate theories of rebel strength with a broader understanding of both the strategic and symbolic value of territory. Building a new dataset of location value and employing novel empirical techniques, we demonstrate that as a location’s value increases relative to the capital city for a group, the rebels become less likely to move against the capital as they can build offensive strength, fortify their defensive position, and appease local constituents in their current geographic domain. Relative strength conditions these strategies, as stronger groups tend to take a more straight-line approach to the capital, middling groups advance in zig-zag patterns, and the weakest groups move in spiral formations to maximize their defensive and symbolic positions. positions. We find that these patterns hold across a wide range of population thresholds. Several case studies help illustrate the mechanisms central to these dynamics. By combining considerations of both rebel strength and territorial value, this paper brings several strands of literature on civil war geography into conversation and broadens our understanding of the conflict process

Synergistic effect between oxygen vacancy and Brønsted acid sites boosting efficient hydrogenolysis of esters to alkanes

Fundamental knowledge of the active site requirements for the activation of C−O bonds on heterogeneous catalysts is essential for the design of efficient hydrodeoxygenation catalysts. Pt−WOx (x < 3) catalysts have shown activity and selectivity for the C−O bond breaking of various biomass-derived oxygenates. Yet, the nature of the active sites and the structure−performance relationship have not been well understood because of the intimate coupling of multiple sites. Here, we construct a hybrid catalyst with integrated defective tungsten oxide (e.g., WO2.72) and Pt/C to investigate the role of multiple sites (e.g., metal sites, Bro̷nsted acid, and oxygen vacancy) that are active toward the hydrogenolysis of esters to alkanes in Pt−WOx catalysts. Experimental and theoretical results suggest that oxygen vacancies derived from the defective tungsten oxide (WOx) supply coordinatively unsaturated sites to adsorb and activate the oxygen atom of the carbonyl group of esters, while Pt metal provides an active hydrogen atom for this process. More importantly, it is found that the hydroxyl derived from W−OH in WOx, as a typical Bro̷nsted acid site, can contribute to the adsorption and activation of the C−O bond of esters. The synergistic effect of oxygen vacancies and Bro̷nsted acid sites results in a remarkably efficient acyl C−O bond cleavage of esters, which boosts the hydrodeoxygenation of esters under mild conditions (T ≤ 200 °C). These insights into the structure−performance relationships offer rational methods for designing efficient catalysts for low-temperature hydrodeoxygenation of biomass-derived esters

The mobilities of visual artists : the case of South Africa

Creative industries and talent have traditionally clustered in a handful of global cities. Yet, recent developments, including digital technologies and the COVID-19 pandemic are reshaping these spatial dynamics. Drawing on 30 interviews, this paper considers the mobilities of visual artists in South Africa and whether they need to locate in the established centres to realise their ambitions. It explores how these entrepreneurs choose a ‘home base’ for their operations and how they mobilise three forms of mobility: 1) temporary mobility, which entails physically attending exhibitions and residencies, 2) mediated mobility, which involves working with intermediaries to create a presence in key markets remotely, and 3) virtual mobility, which harnesses the internet and social media to promote and sell products in local, national and global markets. The paper argues that although surviving in the marketplace is difficult, being permanently located in big cities, like Cape Town or Johannesburg, is not essential. It contributes to existing conceptualisations of mobilities by considering how they are practised and negotiated by individuals, with different circumstances, who operate within specific and challenging contexts. The paper demonstrates that there is no single approach for visual artists who instead flexibly adjust three key dimensions of mobility (time, space and modes of interaction) to overcome barriers and accommodate their needs and preferences. It also advances our understanding of creative labour, including the locational choices of creative workers and the strategies they use to overcome the challenges associated with global competition and the do-it-yourself (D.I.Y.) model

Numerical investigation of premixed hydrogen combustion in dual-fuel marine engines at high load

Zero-emission fuels are expected to drive the maritime sector decarbonisation, with hydrogen emerging as a long-term solution. This study aims to investigate by using CFD modelling a hydrogen fuelled marine dual-fuel engine to identify operating settings ranges for different hydrogen energy fractions (HEF), as well as parametrically optimise the diesel fuel injection timing and temperature at inlet valve closing (IVC). A large marine four-stroke engine with nominal power of 10.5 MW at 500 rev/m is considered, assuming operation at 90 % load and hydrogen injection in the cylinders intake ports. CFD models are developed for several operating scenarios in both diesel and dual-fuel modes. The models are validated against measured data for the engine diesel mode and literature data for a hydrogen-fuelled light-duty engine. A convergence study is conducted to select the grid compromising between computational effort and accuracy. Parametric runs for 20 %, 40 % and 60 % HEF with different IVC temperature and diesel start of injection are modelled to quantify the engine performance, emissions, and combustion characteristics. A single parameter optimisation is conducted to determine the most effective pilot diesel injection timings. The results reveal the IVC temperature range for stable hydrogen combustion to avoid incomplete combustion at low IVC temperature and knocking above 360 K. The proposed settings lead to higher peak heat release rate and in-cylinder pressure compared to the diesel mode without exceeding the permissible in-cylinder pressure rise limits for 60 % HEF. However, NOx emissions increase to 12.9 g/kWh in the dual-fuel mode. The optimal start of injection (SOI) for the diesel fuel, in the case of 60 % HEF, is found 8 °CA BTDC resulting in an indicated thermal efficiency of 43.2 % and stable combustion. Advancing SOI beyond the optimal value results in incomplete combustion. This is the first study on hydrogen use in large marine four-stroke engines providing insights for the engine design and operation, and as such it contributes to the maritime industry decarbonisation efforts