Inferring HIV-1 transmission networks and sources of epidemic spread in Africa with deep-sequence phylogenetic analysis

To prevent new infections with human immunodeficiency virus type 1 (HIV-1) in sub-Saharan Africa, UNAIDS recommends targeting interventions to populations that are at high risk of acquiring and passing on the virus. Yet it is often unclear who and where these ‘source’ populations are. Here we demonstrate how viral deep-sequencing can be used to reconstruct HIV-1 transmission networks and to infer the direction of transmission in these networks. We are able to deep-sequence virus from a large population-based sample of infected individuals in Rakai District, Uganda, reconstruct partial transmission networks, and infer the direction of transmission within them at an estimated error rate of 16.3% [8.8–28.3%]. With this error rate, deep-sequence phylogenetics cannot be used against individuals in legal contexts, but is sufficiently low for population-level inferences into the sources of epidemic spread. The technique presents new opportunities for characterizing source populations and for targeting of HIV-1 prevention interventions in Africa

Effect of Precipitation Control on Strength and Impact Toughness in Advanced Pressure Vessel Steel

This paper reports the effect of increase in vanadium (V) content on changes in precipitation reaction and on mechanical properties in SA1017 grade 23 steel (2.25Cr-1.5W-VNbTi) for application to pressure vessels in advanced nuclear reactors. Increase in V content prohibits formation of coarse M23C6 carbide and allows only fine MX carbo-nitrides precipitation in this steel during tempering. Calculation based on Ashby-Orowan equation suggests that increase in yield strength is mainly attributed to precipitation hardening of fine MX carbo-nitrides and it shows a good agreement with experimental results. Meanwhile, step-cooling heat treatment causing temper embrittlement decreases Charpy impact toughness of steels at sub-zero temperatures, but higher V-alloyed steel shows higher toughness. Because interfaces between MX carbo-nitrides and the matrix act as strong trap sites of segregating P, its segregation toward prior austenite grain boundaries is decreased. Therefore, alloy design of V content for SA1017 grade 23 improves strength without degradation of impact toughness and temper embrittlement. (C) The Minerals, Metals & Materials Society and ASM International 201911Nsciescopu

Superledge model for interphase precipitation during austenite-to-ferrite transformation

A model for interphase precipitation has been developed based on the ledge mechanism of austenite-to-ferrite transformation. Carbide precipitation is considered on the migrating ferrite/austenite interface as an interaction of transformation and precipitation kinetics. The derived equations describe sheet spacing and particle spacing of interphase-precipitated carbides as well as the overall interface velocity which are related to the nucleation rates of carbides and ferrite ledges, respectively. The microstructure characteristics of interphase precipitation are predicted as a function of transformation temperature and steel composition and replicate trends observed experimentally