A tractable inhomogeneous closure theory for flow over mean topography

The quasi-diagonal direct interaction approximation (QDIA) is shown to be a computationally tractable closure theory for inhomogeneous two-dimensional turbulent flow over mean (single-realization) topography. In this paper numerical results for the QDIA are compared to direct numerical simulation (DNS) at moderate Reynolds number for two cases with quite different topographic and mean field amplitudes. The QDIA is found to be in excellent agreement with DNS for cases where the small-scale topographic amplitude is significant. For cases where the small-scale topography is weak, the QDIA closely reproduces the evolving mean field and large-scale energy containing transients but under represents the amplitudes of the small-scale transients in a similar way to the homogeneous DIA. We discuss the prospects of ameliorating the small-scale deficiencies using a regularization of the interaction coefficients

Systematic derivation of a surface polarization model for planar perovskite solar cells

Increasing evidence suggests that the presence of mobile ions in perovskite solar cells can cause a current-voltage curve hysteresis. Steady state and transient current-voltage characteristics of a planar metal halide CH$_3$NH$_3$PbI$_3$ perovskite solar cell are analysed with a drift-diffusion model that accounts for both charge transport and ion vacancy motion. The high ion vacancy density within the perovskite layer gives rise to narrow Debye layers (typical width $\sim$2nm), adjacent to the interfaces with the transport layers, over which large drops in the electric potential occur and in which significant charge is stored. Large disparities between (I) the width of the Debye layers and that of the perovskite layer ($\sim$600nm) and (II) the ion vacancy density and the charge carrier densities motivate an asymptotic approach to solving the model, while the stiffness of the equations renders standard solution methods unreliable. We derive a simplified surface polarisation model in which the slow ion dynamic are replaced by interfacial (nonlinear) capacitances at the perovskite interfaces. Favourable comparison is made between the results of the asymptotic approach and numerical solutions for a realistic cell over a wide range of operating conditions of practical interest.Comment: 32 pages, 7 figure

Phenothiazinium photosensitisers XI. Improved toluidine blue photoantimicrobials.

The phenothiazinium derivative toluidine blue O (TBO) is widely employed as a photoantimicrobial agent in clinical trialling, particularly in dentistry. However, its activity against a range of pathogenic microbial species is not significantly different to that of the standard photoantimicrobial methylene blue. In the current study, derivatives of TBO with varying hydrocarbon substitution in chromophore position 2 were synthesised via the established anilinethiosulphonic route, using the mild oxidant silver(II) carbonate to allow substituent preservation. The resulting series of analogues demonstrated the expected increases in visible absorption wavelength and lipophilicity with increasing hydrocarbon content, as well as decreased aggregation for derivatives with bulkier substituents, and all produced singlet oxygen on illumination in vitro. Screening against a range of bacterial and fungal pathogens relevant to infection control showed remarkable increases in activity relative to the parent compound, particularly against the clinically important Gram-negative bacterium Pseudomonas aeruginosa. In addition, in order to demonstrate clinical relevance, the photoactivities of the new derivatives against microbial targets were compared to conventional antibacterial and antifungal drugs, as well as biocides commonly used for local disinfection. Activity here was also generally greater than that of the conventional agents used for comparison, considerably so relative to the local disinfectant agents

Negative impact of the first COVID-19 lockdown upon health-related behaviours and psychological wellbeing in people living with severe and complex obesity in the UK

BACKGROUND: Coronavirus disease 2019 (COVID-19) has led to unprecedented changes in the way we live, particularly for people at higher risk of severe illness from COVID-19. People with pre-existing health conditions have been markedly impacted and, in some instances, left unsupported due to reduced provision of routine healthcare services. People living with obesity (PLWO) are identified as at higher risk of severe illness from COVID-19 infection. Currently, there is a paucity of evidence about the impact of the first COVID-19 lockdown on PLWO, including those accessing weight management and bariatric surgery services (WMS). METHODS: 543 adults (16–80 years) with obesity (BMI ≥ 30 kg/m2) were recruited between 14th May and 9th July 2020 through social media advertisements, professional and patient obesity organisations and WMS. Participants completed an online survey regarding the impact of the first COVID-19 lockdown upon, mental health, well-being, health-related behaviours, risk mitigating behaviours, access to WMS and weight stigma. FINDINGS: During the first COVID-19 lockdown, the majority of PLWO reported deterioration of their mental health and health-related behaviours such as diet, physical activity (PA) and sleep. With 55% reporting an unhealthier diet, 61% reduced PA and 80% worsening of their sleep. Higher depression and lower wellbeing scores were found to associate with the greatest adverse impact upon health-related behaviours. PLWO who were attending WMS prior to the first lockdown reported a greater deterioration of their diet, with nearly 50% reporting worsening of their diet and PA worsening compared to PLWO who were not attending WMS. Most participants took two or more risk mitigating actions (73%). PLWO attending WMS reported reduced access (44%) with insufficient information (49%) from their clinical service providers. The majority of participants reported no change in perceived weight stigma. INTERPRETATION: This study shows the detrimental impact of the first COVID-19 lockdown on PLWO in relation to health-related behaviours, mental health and access to WMS. Our findings show that PLWO with poor mental health and those attending WMS were most adversely impacted and highlights the need for greater mental health support and continued provision of support from WMS for PLWO during future lockdowns. FUNDING: This research was funded through National Institute for Health Research University College London Hospitals Biomedical Research Centre funding

Observations and dynamical implications of active normal faulting in South Peru

SUMMARY Orogenic plateaus can exist in a delicate balance in which the buoyancy forces due to gravity acting on the high topography and thick crust of the plateau interior are balanced by the compressional forces acting across their forelands. Any shortening or extension within a plateau can indicate a perturbation to this force balance. In this study, we present new observations of the kinematics, morphology and slip rates of active normal faults in the South Peruvian Altiplano obtained from field studies, high-resolution DEMs, Quaternary dating and remote sensing. We then investigate the implications of this faulting for the forces acting on the Andes. We find that the mountains are extending ∼NNE–SSW to ∼NE–SW along a normal fault system that cuts obliquely across the Altiplano plateau, which in many places reactivates Miocene-age reverse faults. Radiocarbon dating of offset late Quaternary moraines and alluvial fan surfaces indicates horizontal extension rates across the fault system of between 1 and 4 mm yr–1—equivalent to an extensional strain rate in the range of 0.5–2 × 10−8 1 yr–1 averaged across the plateau. We suggest the rate and pattern of extension implies there has been a change in the forces exerted between the foreland and the Andes mountains. A reduction in the average shear stresses on the sub-Andean foreland detachment of ≲4 MPa (20–25 per cent of the total force) can account for the rate of extension. These results show that, within a mountain belt, the pattern of faulting is sensitive to small spatial and temporal variations in the strength of faults along their margins.Denman Baynes Senior Studentship, Clare College Cambridge Arup Santander Mobility Grant (University of Cambridge

Integro-differential closure equations for inhomogeneous turbulence

We present numerical and computational techniques to solve systems of integro-differential closure equations for inhomogeneous two-dimensional turbulent flow. The closure equations, representing the first tractable closure theory for inhomogeneous flow over mean (single realization) topography, are based on a quasi-diagonal direct interaction approximation derived via renormalization techniques. The equations are computationally challenging due to the potentially long time history integrals. In order to reduce the computational cost we have implemented a formal restart procedure for the two and three point cumulant terms. The restart procedure is shown to be in good agreement with the closure without restarts and results are compared to direct numerical simulation of the barotropic vorticity equation

Modelling solvent consumption from SEI layer growth in lithium-ion batteries

Predicting lithium-ion battery (LIB) lifetime is one of the most important challenges holding back the electrification of vehicles, aviation, and the grid. The continuous growth of the solid-electrolyte interface (SEI) is widely accepted as the dominant degradation mechanism for LIBs. SEI growth consumes cyclable lithium and leads to capacity fade and power fade via several pathways. However, SEI growth also consumes electrolyte solvent and may lead to electrolyte dry-out, which has only been modelled in a few papers. These papers showed that the electrolyte dry-out induced a positive feedback loop between loss of active material (LAM) and SEI growth due to the increased interfacial current density, which resulted in capacity drop. This work, however, shows a negative feedback loop between LAM and SEI growth due to the reduced solvent concentration (in our case, EC), which slows down SEI growth. We also show that adding extra electrolyte into LIBs at the beginning of life can greatly improve their service life. This study provides new insights into the degradation of LIBs and a tool for cell developers to design longer lasting batteries