Density-dependent electron scattering in photoexcited GaAs in strongly diffusive regime

Mics Z, D'Angio A, Jensen SA, Bonn M, Turchinovich D. Density-dependent electron scattering in photoexcited GaAs in strongly diffusive regime. Applied Physics Letters. 2013;102(23).In a series of systematic optical pump–terahertz probe experiments, we study the density-dependent electron scattering rate in photoexcited GaAs in the regime of strong carrier diffusion. The terahertz frequency-resolved transient sheet conductivity spectra are perfectly described by the Drude model, directly yielding the electron scattering rates. A diffusion model is applied to determine the spatial extent of the photoexcited electron-hole gas at each moment after photoexcitation, yielding the time-dependent electron density, and hence the density-dependent electron scattering time. We find that the electron scattering time decreases from 320 to 60 fs, as the electron density changes from 1015 to 1019 cm−3

High-temperature ceramic matrix composites using microwave enhanced chemical vapor infiltration

To deliver the next generation of aerospace propulsion systems, major modifications to the materials used and their manufacture are required. High-temperature ceramic fibre reinforced ceramic matrix composites (HT-CMCs), specifically SiCf/SiC, have been identified as potential candidates to operate in the hostile aero-thermo-chemical environments experienced in service without compromising structural integrity, whilst keeping mass at a premium. Presently a lack of notably higher temperature properties and durability compared to Ni-super alloys, combined with high manufacturing costs, is preventing widespread utilisation of these composites. Current advanced manufacturing techniques are able to produce these HT-CMCs, which are starting to come into service but all of these techniques introduce compromising features, such as a residual silicon phase, thermal stresses or micro cracking in the matrix microstructure. One of these advanced methods, chemical vapour infiltration (CVI), is an effective manufacturing route capable of creating near fully dense components with an extremely refined microstructure with little or no preform degradation and minimal residual stresses. CVI’s challenges, however, are three fold; i) processing uses isothermal heating rates so batch production times are typically 2 – 3 months; ii) premature pore closure results in a need for repeated machining stages to re-open the closed channels, which reduces process efficiency to between 5-10%; iii) as a consequence of the previous two points, associated costs are very high and the product expensive. Microwave energy (MCVI) has been proposed as a potential solution to heat the SiC fibre preform for CVI; it produces a favourable inverse temperature profile, meaning the temperature is hottest at the centre of the component in contrast to conventional CVI. This inverse profile initiates densification at the centre of the sample, thus avoiding surface porosity closure. It is expected that the use of a microwave-enhanced CVI processing routes could yield near fully dense products in as little as 72 – 96 hours. This poster presents an update on the forming and characterising of the SiC matrix inside the SiC fabric preform (the latter made of Tyranno ZMI, UBE industries) using the MCVI technique. Kinetics, composition, densification profile, morphology and mechanism of growth of the SiC matrix have all been observed and analysed using a suite of characterisation techniques to see the effect of changing the processing variables. Transmission electron microscopy (TEM) and high resolution scanning electron microscopy (SEM) have been used to observe the degree of crystallinity of the resulting SiC and more specifically the grain growth mechanism and thus the resulting morphology. Wave dispersive spectroscopy (WDS) and Raman has been used to determine the (consistently near stoichiometric) Si to C ratio with an accuracy of ±2% due to a small contribution from traces of oxygen present, the results corroborating the data obtained using the TEM. Raman identified the deposit as ß-SiC and, after further analysis, a number of common polytopes were found including 3C, 6H/15R and 4H. Presented results suggest MCVI is a viable method of producing SiC composites that are potentially suitable for the next generation of aerospace material, though a better understanding of the extent to which full densification can be achieved is still required

An immune-based biomarker signature is associated with mortality in COVID-19 patients

Immune and inflammatory responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) contribute to disease severity of coronavirus disease 2019 (COVID-19). However, the utility of specific immune-based biomarkers to predict clinical outcome remains elusive. Here, we analyzed levels of 66 soluble biomarkers in 175 Italian patients with COVID-19 ranging from mild/moderate to critical severity and assessed type I IFN–, type II IFN–, and NF-κB–dependent whole-blood transcriptional signatures. A broad inflammatory signature was observed, implicating activation of various immune and nonhematopoietic cell subsets. Discordance between IFN-α2a protein and IFNA2 transcript levels in blood suggests that type I IFNs during COVID-19 may be primarily produced by tissue-resident cells. Multivariable analysis of patients’ first samples revealed 12 biomarkers (CCL2, IL-15, soluble ST2 [sST2], NGAL, sTNFRSF1A, ferritin, IL-6, S100A9, MMP-9, IL-2, sVEGFR1, IL-10) that when increased were independently associated with mortality. Multivariate analyses of longitudinal biomarker trajectories identified 8 of the aforementioned biomarkers (IL-15, IL-2, NGAL, CCL2, MMP-9, sTNFRSF1A, sST2, IL-10) and 2 additional biomarkers (lactoferrin, CXCL9) that were substantially associated with mortality when increased, while IL-1α was associated with mortality when decreased. Among these, sST2, sTNFRSF1A, IL-10, and IL-15 were consistently higher throughout the hospitalization in patients who died versus those who recovered, suggesting that these biomarkers may provide an early warning of eventual disease outcome

Inborn errors of type I IFN immunity in patients with life-threatening COVID-19.

Clinical outcome upon infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) ranges from silent infection to lethal coronavirus disease 2019 (COVID-19). We have found an enrichment in rare variants predicted to be loss-of-function (LOF) at the 13 human loci known to govern Toll-like receptor 3 (TLR3)- and interferon regulatory factor 7 (IRF7)-dependent type I interferon (IFN) immunity to influenza virus in 659 patients with life-threatening COVID-19 pneumonia relative to 534 subjects with asymptomatic or benign infection. By testing these and other rare variants at these 13 loci, we experimentally defined LOF variants underlying autosomal-recessive or autosomal-dominant deficiencies in 23 patients (3.5%) 17 to 77 years of age. We show that human fibroblasts with mutations affecting this circuit are vulnerable to SARS-CoV-2. Inborn errors of TLR3- and IRF7-dependent type I IFN immunity can underlie life-threatening COVID-19 pneumonia in patients with no prior severe infection

The risk of COVID-19 death is much greater and age dependent with type I IFN autoantibodies

International audienceSignificance There is growing evidence that preexisting autoantibodies neutralizing type I interferons (IFNs) are strong determinants of life-threatening COVID-19 pneumonia. It is important to estimate their quantitative impact on COVID-19 mortality upon SARS-CoV-2 infection, by age and sex, as both the prevalence of these autoantibodies and the risk of COVID-19 death increase with age and are higher in men. Using an unvaccinated sample of 1,261 deceased patients and 34,159 individuals from the general population, we found that autoantibodies against type I IFNs strongly increased the SARS-CoV-2 infection fatality rate at all ages, in both men and women. Autoantibodies against type I IFNs are strong and common predictors of life-threatening COVID-19. Testing for these autoantibodies should be considered in the general population

The risk of COVID-19 death is much greater and age dependent with type I IFN autoantibodies

International audienceSignificance There is growing evidence that preexisting autoantibodies neutralizing type I interferons (IFNs) are strong determinants of life-threatening COVID-19 pneumonia. It is important to estimate their quantitative impact on COVID-19 mortality upon SARS-CoV-2 infection, by age and sex, as both the prevalence of these autoantibodies and the risk of COVID-19 death increase with age and are higher in men. Using an unvaccinated sample of 1,261 deceased patients and 34,159 individuals from the general population, we found that autoantibodies against type I IFNs strongly increased the SARS-CoV-2 infection fatality rate at all ages, in both men and women. Autoantibodies against type I IFNs are strong and common predictors of life-threatening COVID-19. Testing for these autoantibodies should be considered in the general population