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A series of measurements taken with two instrumented track bicycles in a velodrome are presented. The bicycle wheel speed, cadence, roll angle, steering angle, power, and airspeed are recorded. The experimentally-measured values are compared to existing theoretical models of roll and steering angles. The accuracy of the roll angle calculations is dependent on the fidelity of the modelled cyclist path and decreases for higher riding speeds. Experimental measurements of the steering angle show a reasonable agreement to theoretical calculations, albeit with reduced steering angles on the bends at higher speeds. There is also seen an increasing steering angle oscillation within each pedal cycle with increasing bicycle velocity which may influence a cyclist’s rolling resistance and the aerodynamic flow around the bicycle’s front end. Observations are made of changes in the flow field ahead of the bicycle due to the presence of other riders on the track, showing an effective tailwind of up to 0.7 m/s. The measured power shows a decrease at the bend entry due to the changing roll angle. Data presented in this paper provides new insights and can help to provide a validation of values used in existing track cycling analytic models.

Methane, a potent greenhouse gas, is a significant contributor to global warming, with future increases in its abundance potentially leading to an increase of more than 1 ∘ C by 2050 beyond other greenhouse gases if left unaddressed. To remain within the crucial target of limiting global warming to 1.5 ∘ C, it is imperative to evaluate the potential of methane removal techniques. This study presents a scoping analysis of different catalytic technologies (thermal, photochemical and electrochemical) and materials to evaluate potential limitations and energy requirements. An analysis of mass transport and reaction rates is conducted for atmospheric methane conversion system configurations. For the vast majority of catalytic technologies, the reaction rates limit the conversion which motivates future efforts for catalyst development. An analysis of energy requirements for atmospheric methane conversion shows minimum energy configurations for various catalytic technologies within classic tube or parallel plate architectures that have analogs to ventilation and industrial fins. Methane concentrations ranging from 2 ppm (ambient) to 1000 ppm (sources, such as wetlands, fossil-fuel extraction sites, landfills etc) are examined. The study finds that electrocatalysis offers the most energy efficient approach (∼0.2 GJ tonne −1 CO 2 e) for new installations in turbulent ducts, with a total energy intensity < 1 GJ tonne −1 CO 2 e. Photocatalytic methane removal catalysts are moderately more energy intensive (∼2 GJ tonne −1 CO 2 e), but could derive much of their energy input from ‘free’ solar energy sources. Thermal systems are shown to be excessively energy intensive ( > 100 GJ tonne −1 ), while combining photovoltaics with electrochemical catalysts (∼1 GJ tonne −1 CO 2 e) have comparable energy intensity to photocatalytic methane removal catalysts.

Conversations about climate engineering are difficult to have in many spaces. While public debate deserves exploration, we focus on the difficulties scientific discussions around climate engineering face. For inspiration on how to improve this contested space we turn specifically to the history of controversial medical research. Some ways to move forward might consist of establishing an oversight mechanism, defining boundaries and introducing a specialised review system.

A Man with Shortness of Breath and ProteinuriaA 20-year-old man was admitted with hemoptysis and hypoxemia. CT of the chest revealed pulmonary emboli; urinalysis showed proteinuria and hematuria. Diagnostic tests were performed.

Non-technical summaryThis paper reviews efforts to meet the climate goals of the Paris Agreement: to limit global warming to well below 2°C and ideally to 1.5°C above pre-industrial levels. The paper shows how the likelihood of breaching these thresholds presents the need for additional measures, in mitigation and intervention. Three climate actions are discussed: emissions reduction, greenhouse gas removal, and solar radiation modification. These actions differ in timescale and current state of knowledge. Progress must intensify if they are to aid in securing a safe and stable climate for future generations.Technical summaryCurrent assessments of global greenhouse gas emissions suggest the Paris Agreement temperature thresholds of 1.5°C and 2°C warming above pre-industrial levels could be breached. The impacts on humans and ecosystems could be severe. Global trends suggest a prolonged reliance on fossil fuels. Additional measures to limit global warming are therefore needed. Here, we review three climate actions: emissions reduction, greenhouse gas removal (GGR), and solar radiation modification (SRM). Emissions reduction requires shifting energy production away from fossil fuels (the primary contribution of anthropogenic greenhouse gas emissions), reducing energy use in key sectors, and optimising land management. GGR efforts must scale sustainably in the near term. The scale-up of novel methods is constrained by economic and technological challenges and, in some cases, limited knowledge. SRM has received growing attention, given the immediate impacts of global warming and the protracted timescales of emissions reduction and GGR. Robust research and governance frameworks are needed to assess the risks posed by SRM, alongside the risks of forgoing SRM. These three actions could enable society to fulfil the Paris Agreement, limiting global warming and its impacts while atmospheric greenhouse gas concentrations are reduced to sustainable levels.Social media summaryThe progress of climate mitigation and intervention towards securing a sustainable future in a safe and stable climate.

ObjectivesTo help people make decisions about the most effective mitigation measures against SARS-CoV-2 transmission in different scenarios, the likelihoods of transmission by different routes need to be quantified to some degree (however uncertain). These likelihoods need to be communicated in an appropriate way to illustrate the relative importance of different routes in different scenarios, the likely effectiveness of different mitigation measures along those routes, and the level of uncertainty in those estimates. In this study, a pragmatic expert elicitation was undertaken to supply the underlying quantitative values to produce such a communication tool.ParticipantsTwenty-seven individual experts from five countries and many scientific disciplines provided estimates.Outcome measuresEstimates of transmission parameters, assessments of the quality of the evidence, references to relevant literature, rationales for their estimates and sources of uncertainty.Results and conclusionThe participants’ responses showed that there is still considerable disagreement among experts about the relative importance of different transmission pathways and the effectiveness of different mitigation measures due to a lack of empirical evidence. Despite these disagreements, when pooled, the majority views on each parameter formed an internally consistent set of estimates (for example, that transmission was more likely indoors than outdoors, and at closer range), which formed the basis of a visualisation to help individuals and organisations understand the factors that influence transmission and the potential benefits of different mitigation measures.

We report on an experimental and theoretical study of the transient flows which develop as a naturally ventilated room adjusts from one temperature to another. We focus on a room heated from below by a uniform heat source, with both high- and low-level ventilation openings. Depending on the initial temperature of the room relative to (i) the final equilibrium temperature and (ii) the exterior temperature, three different modes of ventilation may develop. First, if the room temperature lies between the exterior and the equilibrium temperature, the interior remains well-mixed and gradually heats up to the equilibrium temperature. Secondly, if the room is initially warmer than the equilibrium temperature, then a thermal stratification develops in which the upper layer of originally hot air is displaced upwards by a lower layer of relatively cool inflowing air. At the interface, some mixing occurs owing to the effects of penetrative convection. Thirdly, if the room is initially cooler than the exterior, then on opening the vents, the original air is displaced downwards and a layer of ambient air deepens from above. As this lower layer drains, it is eventually heated to the ambient temperature, and is then able to mix into the overlying layer of external air, and the room becomes well-mixed. For each case, we present new laboratory experiments and compare these with some new quantitative models of the transient flows. We conclude by considering the implications of our work for natural ventilation of large auditoria.

Harry Rutter and colleagues reflect on the challenges of conveying uncertain estimates for viral transmission in a complex system

The year 2020 has seen the emergence of a global pandemic as a result of the disease COVID-19. This report reviews knowledge of the transmission of COVID-19 indoors, examines the evidence for mitigating measures, and considers the implications for wintertime with a focus on ventilation.