HYTEC results of the MoMas reactive transport benchmark

International audienceA specific benchmark has been developed by the french research group MoMas in order to improve numerical solution methods applied by reactive transport models, i.e. codes which couple hydrodynamic flow and mass transport in porous media with geochemical reactions. The HYTEC model has been applied to this benchmark exercise and this paper summarizes some of the principal results. HYTEC is a general-purpose code, applied by industrials and research groups to a wide variety of domains, including soil pollution, nuclear waste storage, cement degradation, water purification systems, storage of CO2 and valorization of stabilized wastes. The code has been applied to the benchmark test-cases without any specific modification. Apart from the benchmark imposed output, additional information is provided to highlight the behavior of HYTEC specifically and the simulation results in particular

Operator splitting-based reactive transport models in strong feedback of porosity change: the contribution of analytical solutions for accuracy validation and estimator improvement

Journal of Contaminant Hydrology, Special issue : Frontiers in Reactive Transport: Microbial Dynamics nad Redox Zonation in the Subsurface Edited by T.D. Scheibe and C.I. SteefelInternational audienceReactive transport is a highly non-linear problem requiring the most efficient algorithms to rapidly reach an accurate solution. The non-linearities are increased and the resolution is even more demanding and CPU-intensive when considering feedback of dissolution or precipitation reactions on hydrodynamic flow and transport, commonly referred to as the variable porosity case. This is particularly true near clogging, which leads to very stiff systems and therefore small time-steps. The operator-splitting approach often cited is a widely use method to solve these problems: it consists in solving sequentially the transport then the chemistry part of the problem. Operator-splitting appears to be an accurate approach, provided that the solution is iteratively improved at each time-step. The paper details analytical solutions and test-cases for this class of problems. They demonstrate that iterative improvement is then compulsory. They also helped develop an improved estimator/corrector method which allows to reach convergence faster and to reduce stiffness. The efficiency improvement is significant as illustrated by an example of carbonation of a cement paste, a well-known problem that leads to complete clogging of the interface layer

Present state and future modeling of geochemistry in hydrogeological systems

International audienceA first step towards understanding and controlling the fate and dissemination of radioactive waste is to create a concise and comprehensive theoretical framework for the rather non-linear processes involved — hence, the need for geochemical models. Two classes of geochemical models are commonly used, i.e., static and hydrodynamic models. In contrast to static models, hydrodynamic models combine geochemical reactions with hydrogeological processes such as ground-water flow, diffusion and dispersion. In this review, we examine the present state of geochemical models in terms of included processes, thermodynamic databases, missing phenomena, numerical behavior and performance. It is shown that over the past decade, significant progress has been made with respect to modeling of geochemistry in hydrodynamic systems: this is illustrated by describing several applications. Finally, we focus on the perspectives of geochemical modeling in the assessment of the safety of nuclear waste disposal

Aggregated End-to-end Visibility and its Application on Rapid and Automatic Outage Triage in Monitoring Microservices

In a microservice architecture, a user request can go through a large number of servers owned by several different teams before a response is returned. The request can fail due to failure in any of the servers. Troubleshooting an outage that affects the end user experience in microservice architecture can involve multiple teams and can take a substantial amount of time. This disclosure describes techniques to rapidly locate the root cause entity of a customer-facing failure to node(s) deep within the infrastructure of the service. Per the techniques, end user product teams mark requests with metadata known as critical user interactions (CUI). The metadata is propagated along with the request. Performance metrics are gathered from servers that the requests go through. The performance metric is keyed by CUI, server node, and peer node for every adjacent pair of nodes. These piecemeal metrics keyed by CUI together offer end-to-end visibility for a set of requests grouped by the CUI of the end product, enabling the rapid and automatic triage of an outage to an interior server without requiring domain expertise on the product or the server

Benchmarking of Dairy Processors’ Associations : actors and their activities in The Netherlands, Zambia and South Africa

This report describes a study of dairy processors’ associations in three countries. As the dairy sectors in these countries are at different stages of development, the challenges these associations face are very different indeed, and so are their functions and structures. Learnings from these cases are drawn for the situation in Kenya

Impact of fodder management on dairy farm performance in Kenya

This study assesses the impact of adoption of fodder conservation and feed rationing interventions on economic performance and nitrogen use efficiency (NUE) of dairy farms in central Kenya. A comparison was done between groups of farms in these intervention categories and with control farms that had no interventions. The results show that fodder conservation increased daily milk yield by 3 litres per lactating cow, while feed rationing in addition to fodder conservation gave an additional 3 litres milk per lactating cow per day in comparison to fodder conservation alone. We recommend farmers to adopt fodder conservation measures in combination with ration formulation in order to increase their profitability. Ration formulation advisory programs should include follow up visits to enable farm managers better understand formulation concepts, and potentially benefit from the effects of manure utilisation and soil mining for better estimates of NUE

Intercomparison of reactive transport models applied to UO2 oxidative dissolution and uranium migration

International audienceOxidative dissolution of uranium dioxide (UO2) and the subsequent migration of uranium in a subsurface environment and an underground waste disposal have been simulated with reactive transport models. In these systems, hydrogeological and chemical processes are closely entangledand their interdependency has been analyzed in detail, notably with respect to redox reactions, kinetics of mineralogical evolution and hydrodynamic migration of species of interest. Different codes, where among CASTEM, CHEMTRAP and HYTEC, have been used as an intercomparison and verification exercise. Although the agreement between codes is satisfactory, it is shown that the discretization method of the transport equation (i.e. finite elements (FE) versus mixed-hybrid FE and finite differences) and the sequential coupling scheme may lead to systematic discrepancies

Increase in venous thromboembolism in SARS-CoV-2 infected lung tissue:proteome analysis of lung parenchyma, isolated endothelium, and thrombi

Aims: COVID-19 pneumonia is characterized by an increased rate of deep venous thrombosis and pulmonary embolism. To better understand the pathophysiology behind thrombosis in COVID-19, we performed proteomics analysis on SARS-CoV-2 infected lung tissue. Methods: Liquid chromatography mass spectrometry was performed on SARS-CoV-2 infected postmortem lung tissue samples. Five protein profiling analyses were performed: whole slide lung parenchyma analysis, followed by analysis of isolated thrombi and endothelium, both stratified by disease (COVID-19 versus influenza) and thrombus morphology (embolism versus in situ). Influenza autopsy cases with pulmonary thrombi were used as controls. Results: Compared to influenza controls, both analyses of COVID-19 whole-tissue and isolated endothelium showed upregulation of proteins and pathways related to liver metabolism including urea cycle activation, with arginase being among the top upregulated proteins in COVID-19 lung tissue. Analysis of isolated COVID-19 thrombi showed significant downregulation of pathways related to platelet activation compared to influenza thrombi. Analysis of isolated thrombi based on histomorphology shows that in situ thrombi have significant upregulation of coronavirus pathogenesis proteins. Conclusions: The decrease in platelet activation pathways in severe COVID-19 thrombi suggests a relative increase in venous thromboembolism, as thrombi from venous origin tend to contain fewer platelets than arterial thrombi. Based on histomorphology, in situ thrombi show upregulation of various proteins related to SARS-CoV-2 pathogenesis compared to thromboemboli, which may indicate increased in situ pulmonary thrombosis in COVID-19. Therefore, this study supports the increase of venous thromboembolism without undercutting the involvement of in situ thrombosis in severe COVID-19.</p

Infection of zebrafish embryos with live fluorescent Streptococcus pneumoniae as a real-time pneumococcal meningitis model

Background: Streptococcus pneumoniae is one of the most important causes of bacterial meningitis, an infection where unfavourable outcome is driven by bacterial and host-derived toxins. In this study, we developed and characterized a pneumococcal meningitis model in zebrafish embryos that allows for real-time investigation of early host-microbe interaction. Methods: Zebrafish embryos were infected in the caudal vein or hindbrain ventricle with green fluorescent wild-type S. pneumoniae D39 or a pneumolysin-deficient mutant. The kdrl:mCherry transgenic zebrafish line was used to visualize the blood vessels, whereas phagocytic cells were visualized by staining with far red anti-L-plastin or in mpx:GFP/mpeg1:mCherry zebrafish, that have green fluorescent neutrophils and red fluorescent macrophages. Imaging was performed by fluorescence confocal and time-lapse microscopy. Results: After infection by caudal vein, we saw focal clogging of the pneumococci in the blood vessels and migration of bacteria through the blood-brain barrier into the subarachnoid space and brain tissue. Infection with pneumolysin-deficient S. pneumoniae in the hindbrain ventricle showed attenuated growth and migration through the brain as compared to the wild-type strain. Time-lapse and confocal imaging revealed that the initial innate immune response to S. pneumoniae in the subarachnoid space mainly consisted of neutrophils and that pneumolysin-mediated cytolytic activity caused a marked reduction of phagocytes. Conclusions: This new meningitis model permits detailed analysis and visualization of host-microbe interaction in pneumococcal meningitis in real time and is a very promising tool to further our insights in the pathogenesis of pneumococcal meningitis