Measurements and scaling of buoyancy-induced flows in ventilated tunnels

We investigate the ventilation conditions required to control the propagation of smoke, produced by a tunnel fire, in the presence of two inertial forcings: a transverse extraction system and a longitudinal flow. For that purpose, we performed a series of experiments in a reduced-scale tunnel, using a mixture of air and helium to simulate the release of hot smoke during a fire. Experiments were designed to focus on the ventilation flows that allow the buoyant release to be confined between two adjacent extraction vents. Different source conditions, in terms of density and velocity of the buoyant release, were analysed along with different vent configurations. Experiments allowed us to quantify the increase of the extraction velocity needed to confine the buoyant smoke, overcoming the effect of an imposed longitudinal velocity. Vents with a rectangular shape, and spanning over the whole tunnel width, provide the best performance. Finally, we studied the stratification conditions of the flow, individuating four regimes. Interestingly, when the stratification conditions fade out, as both the longitudinal flow and vertical extraction flows increase, the flow dynamics becomes almost independent of the forcing induced by the presence of buoyant smoke, which eventually acts as a passive scalar transported by the flow

Experimental and Numerical Investigations of the Wind Pressure Coefficient at a Tunnel Portal

The effect of the external wind on a road tunnel is the subject of the investigations reported here. Reduced-scale models of various geometrical configurations of a tunnel portal were investigated through wind tunnel experiments combined with numerical simulations. The study aimed at evaluating the mean wind pressure coefficient at the portal. In addition to the incident wind direction, it is shown that the pressure coefficient depends largely on the tunnel geometry and the presence of surrounding buildings. Similar conclusions could be drawn from the numerical investigations. The standard k-ε model used here led to satisfactory predictions of the pressure coefficients

Wind-induced pressure at a tunnel portal

International audienc

Constraining landslide timing in a data-scarce context: from recent to very old processes in the tropical environment of the North Tanganyika-Kivu Rift region

peer reviewedUnderstanding when landslides occur and how they evolve is fundamental to grasp the dynamics of the landscapes and anticipate the dangers they can offer up. However, knowledge on the timing of the landslides remains overlooked in large parts of the world. This is particularly the case in low-capacity regions, where infrastructures are weak or absent and data scarcity is the norm. The tropics stand out as such regions, despite being affected by high and increasing landslide impacts. There, persistent cloud cover, rapid natural vegetation regeneration, cultivation practices and high weathering rates further challenge the harvest of timing information. Based on a synthesis of our recent work, we present new findings on the characterisation of the timing of the landslides in the North Tanganyika-Kivu Rift region, a tropical environment with very low capacity and high population density. Our aim is also to highlight the methodological approaches and research strategies that we adopt to investigate such slope processes in a large region lacking baseline studies. From an inventory of more than 9000 landslides with various timing accuracy (from daily to thousands of years), we identify causes and triggers of the slope instabilities in a context of important human-induced landscape changes. This is achieved through a holistic approach that combines field work, satellite remote sensing, historical photograph processing and geomorphic marker understanding. The role of the needs of the local stakeholders in the setting up of the research strategy is also highlighted, and research perspectives are discussed. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature

Global temporal changes in the proportion of children with advanced disease at the start of combination antiretroviral therapy in an era of changing criteria for treatment initiation

Introduction: The CD4 cell count and percent at initiation of combination antiretroviral therapy (cART) are measures of advanced HIV disease and thus are important indicators of programme performance for children living with HIV. In particular, World Health Organization (WHO) 2017 guidelines on advanced HIV disease noted that >80% of children aged <5 years started cART with WHO Stage 3 or 4 disease or severe immune suppression. We compared temporal trends in CD4 measures at cART start in children from low-, middle- and high-income countries, and examined the effect of WHO treatment initiation guidelines on reducing the proportion of children initiating cART with advanced disease. Methods: We included children aged <16 years from the International Epidemiology Databases to Evaluate acquired immunodeficiency syndrome (AIDS) (IeDEA) Collaboration (Caribbean, Central and South America, Asia-Pacific, and West, Central, East and Southern Africa), the Collaboration of Observational HIV Epidemiological Research in Europe (COHERE), the North American Pediatric HIV/AIDS Cohort Study (PHACS) and International Maternal Pediatric Adolescent AIDS Clinical Trials (IMPAACT) 219C study. Severe immunodeficiency was defined using WHO guidelines. We used generalized weighted additive mixed effect models to analyse temporal trends in CD4 measurements and piecewise regression to examine the impact of 2006 and 2010 WHO cART initiation guidelines. Results: We included 52,153 children from fourteen low-, eight lower middle-, five upper middle- and five high-income countries. From 2004 to 2013, the estimated percentage of children starting cART with severe immunodeficiency declined from 70% to 42% (low-income), 67% to 64% (lower middle-income) and 61% to 43% (upper middle-income countries). In high-income countries, severe immunodeficiency at cART initiation declined from 45% (1996) to 14% (2012). There were annual decreases in the percentage of children with severe immunodeficiency at cART initiation after the WHO guidelines revisions in 2006 (low-, lower middle- and upper middle-income countries) and 2010 (all countries). Conclusions: By 2013, less than half of children initiating cART had severe immunodeficiency worldwide. WHO treatment initiation guidelines have contributed to reducing the proportion of children and adolescents starting cART with advanced disease. However, considerable global inequity remains, in 2013, >40% of children in low- and middle-income countries started cART with severe immunodeficiency compared to <20% in high-income countries