Aproximación al control de la microestructura de dos aceros microaleados con contenido medio de carbono en condiciones de conformado en caliente

El objetivo principal de este trabajo es estudiar el comportamiento a fluencia de dos aceros microaleados de contenido medio de carbono, en condiciones de conformado en caliente analizando su evolución microstructural a través de la dependencia del tamaño de grano recristalizado (Drec) con el parámetro de Zener-Hollomon, Z. Se observó que esta dependencia muestra un comportamiento bimodal asociado a la transición entre la recristalización dinámica cíclica y de pico simple. También, se ha observado que la variación del Drec normalizado por el vector de Burgers (b) con la tensión de estado estable sss a su vez normalizada por el modulo de cizalladura (m) exhibe el mismo comportamiento bimodal arriba mencionado. Debido a la complejidad de los dos aceros estudiados, el tamaño de grano recristalizado no se ajusta a la ecuación universal de Derby. Para explicar este comportamiento cabe pensar en el efecto de los precipitados y de la microestructura inicial sobre el tamaño de grano recristalizado. The main aim of the present investigation was to study the flow behaviour of two medium carbon microalloyed steels under hot forming conditions, and to analyse their microstructural evolution. The dependence of recrystallized grain size (Drec) on the Zener-Hollomon parameter Z shows a bimodal behaviour with transition from single to cyclic dynamic recrystallization. We also observed that the variation of Drec normalized by the Burgers vector (b) with the steady state stress sss normalized by shear modulus (m) shows the same bimodal behaviour cited above. The Derby’s universal equation reported in the literature for recrystallized grain sizes was not followed; it seems that the presence of fine precipitated particles has a clear effect on this disagreementPeer ReviewedPostprint (published version

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century

Contribution a l'etude du comportement du monocristal en grandes deformtions plastiques

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 83297 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Aproximación al control de la microestructura de dos aceros microaleados con contenido medio de carbono en condiciones de conformado en caliente

El objetivo principal de este trabajo es estudiar el comportamiento a fluencia de dos aceros microaleados de contenido medio de carbono, en condiciones de conformado en caliente analizando su evolución microstructural a través de la dependencia del tamaño de grano recristalizado (Drec) con el parámetro de Zener-Hollomon, Z. Se observó que esta dependencia muestra un comportamiento bimodal asociado a la transición entre la recristalización dinámica cíclica y de pico simple. También, se ha observado que la variación del Drec normalizado por el vector de Burgers (b) con la tensión de estado estable sss a su vez normalizada por el modulo de cizalladura (m) exhibe el mismo comportamiento bimodal arriba mencionado. Debido a la complejidad de los dos aceros estudiados, el tamaño de grano recristalizado no se ajusta a la ecuación universal de Derby. Para explicar este comportamiento cabe pensar en el efecto de los precipitados y de la microestructura inicial sobre el tamaño de grano recristalizado. The main aim of the present investigation was to study the flow behaviour of two medium carbon microalloyed steels under hot forming conditions, and to analyse their microstructural evolution. The dependence of recrystallized grain size (Drec) on the Zener-Hollomon parameter Z shows a bimodal behaviour with transition from single to cyclic dynamic recrystallization. We also observed that the variation of Drec normalized by the Burgers vector (b) with the steady state stress sss normalized by shear modulus (m) shows the same bimodal behaviour cited above. The Derby’s universal equation reported in the literature for recrystallized grain sizes was not followed; it seems that the presence of fine precipitated particles has a clear effect on this disagreementPeer Reviewe