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To study the physics of small-scale properties of homogeneous isotropic turbulence at increasingly high Reynolds numbers, direct numerical simulation results have been obtained for forced isotropic turbulence at Taylor-scale Reynolds number $R_\lambda =2500$ on a $32\,768^3$ three-dimensional periodic domain using a GPU pseudo-spectral code on a 1.1 exaflop GPU supercomputer (Frontier). These simulations employ the multi-resolution independent simulation (MRIS) technique (Yeung & Ravikumar 2020, Phys. Rev. Fluids, vol. 5, 110517) where ensemble averaging is performed over multiple short segments initiated from velocity fields at modest resolution, and subsequently taken to higher resolution in both space and time. Reynolds numbers are increased by reducing the viscosity with the large-scale forcing parameters unchanged. Although MRIS segments at the highest resolution for each Reynolds number last for only a few Kolmogorov time scales, small-scale physics in the dissipation range is well captured – for instance, in the probability density functions and higher moments of the dissipation rate and enstrophy density, which appear to show monotonic trends persisting well beyond the Reynolds number range in prior works in the literature. Attainment of range of length and time scales consistent with classical scaling also reinforces the potential utility of the present high-resolution data for studies of short-time-scale turbulence physics at high Reynolds numbers where full-length simulations spanning many large-eddy time scales are still not accessible. A single snapshot of the $32\,768^3$ data is publicly available for further analyses via the Johns Hopkins Turbulence Database.
Humanity’s impact on the planet is undeniable. Fairly and effectively addressing environmental problems begins with understanding their causes and impacts. Is over-population the main driver of environmental degradation? Poverty? Capitalism? Poor governance? Imperialism? Patriarchy? Clearly these are not technical questions, but political ones.
Updated to cover new debates, data, and policy, and expanded to include chapters on colonialism, race and gender, and the impacts of energy and resource extraction, this book introduces students to diverse perspectives and helps them develop an informed understanding of why environmental problems occur.
How the international community should act is deeply contested. Guiding students through the potential responses, including multilateral diplomacy, transnational voluntary action, innovative financial mechanisms, problem displacement, consumer-focused campaigns, and resistance, this book explains the different forms of political action, their limitations and injustices.
Online resources include lecture slides, a test bank for instructors, updated weblinks to videos, and suggested readings for students.
The study of the shape of droplets on surfaces is an important problem in the physics of fluids and has applications in multiple industries, from agrichemical spraying to microfluidic devices. Motivated by these real-world applications, computational predictions for droplet shapes on complex substrates – rough and chemically heterogeneous surfaces – are desired. Grid-based discretisations in axisymmetric coordinates form the basis of well-established numerical solution methods in this area, but when the problem is not axisymmetric, the shape of the contact line and the distribution of the contact angle around it are unknown. Recently, particle methods, such as pairwise-force smoothed particle hydrodynamics (PF-SPH), have been used to conveniently forego explicit enforcement of the contact angle. The pairwise-force model, however, is far from mature, and there is no consensus in the literature on the choice of pairwise-force profile. We propose a new pair of polynomial force profiles with a simple motivation and validate the PF-SPH model in both static and dynamic tests. We demonstrate its capabilities by computing droplet shapes on a physically structured surface, a surface with a hydrophilic stripe and a virtual wheat leaf with both micro-scale roughness and variable wettability. We anticipate that this model can be extended to dynamic scenarios, such as droplet spreading or impaction, in the future.
Building on the book’s assessment of the incentives of cities to protect the environment, the chapter outlines an agenda for cities to meet the challenges presented by climate change. The chapter starts by charting an agenda for cities to adapt to the impacts of planetary climate change, because cities have the greatest incentives and levers to address this aspect of the climate challenge. Then the chapter identifies plausible contributions that cities can make to societal decarbonization. The federal government has been, at best, an inconsistent partner in decarbonizing the economy. Climate regulation in major cities provides a means of ensuring that the societal decarbonization project continues to advance, regardless of who is in power federally. The chapter emphasizes the need for higher levels of government to better support municipal efforts to tackle climate change and suggests ways for lawmakers at higher levels of government, in particular the federal level, to do so if they are interested in environmental protection.
Wall-based active and passive flow control for drag reduction in low-Reynolds-number (${\textit{Re}}$) turbulent flows can lead to three typical phenomena: (i) attenuation or (ii) amplification of the near-wall cycle, and (iii) generation of spanwise rollers. The present study conducts direct numerical simulations of a low ${\textit{Re}}$ turbulent channel flow and demonstrates that each flow response can be generated with a wall transpiration at two sets of spatial scales, termed streak and roller scales. The effect of the transpiration is controlled by its relative phase to the background flow, which can be parametrised by the wall pressure. Streak scales (i) attenuate the near-wall cycle if transpiration and wall pressure are approximately in-phase or (ii) amplify it otherwise, and (iii) roller scales energise spanwise rollers when transpiration and wall pressure are out-of-phase. Conditions for establishing these robust phase relations are derived from the analytical solution to the pressure Poisson equation and rely on splitting the pressure into its fast, slow and Stokes component. The importance of each condition depends on the relative magnitude of the pressure components, which is significantly altered by the transpiration. The analogy in flow response suggests that transpiration with the two scale families and their phase relations to the wall pressure represent fundamental building blocks for flows over tailored surfaces including riblets, porous and permeable walls.
A discrete Markov model is proposed to study the interscale dynamics of high Reynolds number wall turbulence. The amplitude modulation of the small turbulent scales due to the interaction with large turbulent scales is investigated for three experimental turbulent boundary layers. Through an appropriate discretisation of the turbulence signals, recently proved universal thermodynamic bounds for discrete-state stochastic systems are shown to apply to continuous-state systems like turbulence, regardless of the distance from the wall and the Reynolds number. Adopting Schnakenberg’s network theory for stochastic processes, we provide evidence for a direct proportionality relation between the mean cycle affinity-based entropy production rate (a stochastic thermodynamic quantity) and a mean entropy production rate associated with the net large-to-small-scale turbulent kinetic energy production. Finally, new insights into the relative arrangement (lag/lead) between large and small scales are provided.
The Spence Shale of Utah and Idaho preserves a diverse soft-bodied biota from the Cambrian. While the fauna is dominated by arthropods and echinoderms, soft-bodied animals belonging to other groups are known. Here we document Tentalus spencensis gen. et sp. nov. from the High Creek locality of the Spence Shale. The fossil has a crown of short stubby tentacles and appears to have been attached to the sediment through a stalk. The morphology of Tentalus suggests that it is a dinomischiid or deuterostome; however, it cannot be attributed to any of the known species, based on the short and conical tentacles surrounding an oral region, and polyp-like oblong columnar trunk terminating in a stalk, that do not resemble any described species.
The moulting of birds creates different trailing-edge gaps in their wings, which inspires the handling of damaged wings in micro-air vehicles. The effects of the moult gap on aerodynamic performance are investigated by employing a bird-inspired flapping wing model. The aerodynamic performance is evaluated by numerically solving the Navier–Stokes equations for incompressible flows. Moult-gapped wings with different gap widths and positions are compared with the original intact wing in terms of aerodynamic forces and vortex structures. It is found that the decrease in the average lift is slower than that expected from the classical aerodynamic model. The moult gap results in three-dimensional gap vortices, which interact with leading-edge vortices and tip vortices. The interaction generates a pair of parallelly arranged vortex loops on each wing. The downwash momentum associated with this pair of vortex loops is enhanced by the gap vortices. The gap-vortices-enhanced downwash compensates for the loss in the lifting surface, increasing the aerodynamic force per unit area. A composite actuator disk model is proposed based on the vortex loops. The proposed model accounts for not only the finite-span wing effects but also the vortex compensation effects, while the previous quasi-steady model only accounts for the finite-span wing effects.
This chapter outlines a framework for understanding what drives city governments in the early twenty-first century to engage in environmental protection efforts in the absence of mandates or generous subsidies from higher levels of government. The chapter begins by emphasizing is the central preoccupation at the local level with promoting economic growth, partly to fund the services that local governments provide, such as police and firefighting. The chapter distinguishes between two archetypal categories of environmental problems: local public goods problems, such as the need to collect solid waste or inadequate green space, that local residents benefit from addressing; and global public goods problems, such as planetary warming, that people throughout the world benefit from addressing. Local elites may push from “the top” for measures, such as building parks and collecting garbage, that simultaneously will improve the local environment and promote economic growth by making their cities more attractive to existing and new residents. In addition, community groups may push from “the bottom” for measures to improve the local as well as the global environment, such as limiting planetary warming. However, U.S. local governments are likely to resist imposing costs on local actors to address global environmental problems, such as limiting climate change, because of localities’ nested position as relatively small entities within a large federation competing for businesses and residents. Left to their own devices, local governments are more likely to undertake measures that will yield local benefits, such as improvements in the health of local residents and the beautification of the local environment. For cities to contribute meaningfully to addressing the global task of limiting planetary warming, local activists will need to mobilize over a sustained period to maintain the pressure on local officials who are sensitive to the need to cultivate local economic prosperity.
New York City’s policy efforts in the first two decades of the twenty-first century emphasize the potential for local governments to materially improve their local environments. During the mayoralty of Michael Bloomberg (2002-2013), the city government sought from the top to remake the city’s physical environment to appeal to postindustrial elites to promote local economic development. Under Mayor Bill de Blasio (2014-2021), the administration explicitly prioritized equity alongside economic growth and this commitment was reflected in environmental policy in a focus on investing in community parks. Under both mayors, environmental policy came from community groups, as well as city leaders. For example, across the two administrations, prominent environmental justice advocates prompted the city to adopt measures to address longstanding inequities in the allocation of responsibility for solid waste management, although the injustices persisted at the end of the de Blasio administration. Overall, the history of New York City’s efforts to address problems such as lack of greenspace, contaminated lands, and solid waste management underscores that change can come from the top and the bottom, but that there are legal, fiscal and other constraints on the ability of cities to address even paradigmatically local environmental problems.
Humanity’s impact on the planet is undeniable. Fairly and effectively addressing environmental problems begins with understanding their causes and impacts. Is over-population the main driver of environmental degradation? Poverty? Capitalism? Poor governance? Imperialism? Patriarchy? Clearly these are not technical questions, but political ones.
Updated to cover new debates, data, and policy, and expanded to include chapters on colonialism, race and gender, and the impacts of energy and resource extraction, this book introduces students to diverse perspectives and helps them develop an informed understanding of why environmental problems occur.
How the international community should act is deeply contested. Guiding students through the potential responses, including multilateral diplomacy, transnational voluntary action, innovative financial mechanisms, problem displacement, consumer-focused campaigns, and resistance, this book explains the different forms of political action, their limitations and injustices.
Online resources include lecture slides, a test bank for instructors, updated weblinks to videos, and suggested readings for students.
Many of the contemporary discussions of the potential for cities to address climate change overlook the historical efforts of cities to protect their residents from environmental harms. In the nineteenth and early twentieth centuries, before the emergence of the administrative state at the state and federal levels, local governments were often the first level of government to provide many Americans with environmental protection. Supplying safe drinking water was an early priority for expanding cities. With water more readily available, city governments then built sewage systems. They also built parks, established systems for collecting solid waste, and attempted to address air pollution from the combustion of coal. The historical efforts of cities, well documented by historians, emphasize that city governments can positively contribute to protecting the environment. However, these efforts also offers cautionary lessons about the limitations of relying on local governments to address large-scale problems, and help to explain the substantial federalization of environmental law in the latter twentieth century. Federalization diminished the ability of cities to innovate in the environmental field but cities still have considerable legal authority to pursue environmental policies to address contemporary challenges.
Humanity’s impact on the planet is undeniable. Fairly and effectively addressing environmental problems begins with understanding their causes and impacts. Is over-population the main driver of environmental degradation? Poverty? Capitalism? Poor governance? Imperialism? Patriarchy? Clearly these are not technical questions, but political ones.
Updated to cover new debates, data, and policy, and expanded to include chapters on colonialism, race and gender, and the impacts of energy and resource extraction, this book introduces students to diverse perspectives and helps them develop an informed understanding of why environmental problems occur.
How the international community should act is deeply contested. Guiding students through the potential responses, including multilateral diplomacy, transnational voluntary action, innovative financial mechanisms, problem displacement, consumer-focused campaigns, and resistance, this book explains the different forms of political action, their limitations and injustices.
Online resources include lecture slides, a test bank for instructors, updated weblinks to videos, and suggested readings for students.
Humanity’s impact on the planet is undeniable. Fairly and effectively addressing environmental problems begins with understanding their causes and impacts. Is over-population the main driver of environmental degradation? Poverty? Capitalism? Poor governance? Imperialism? Patriarchy? Clearly these are not technical questions, but political ones.
Updated to cover new debates, data, and policy, and expanded to include chapters on colonialism, race and gender, and the impacts of energy and resource extraction, this book introduces students to diverse perspectives and helps them develop an informed understanding of why environmental problems occur.
How the international community should act is deeply contested. Guiding students through the potential responses, including multilateral diplomacy, transnational voluntary action, innovative financial mechanisms, problem displacement, consumer-focused campaigns, and resistance, this book explains the different forms of political action, their limitations and injustices.
Online resources include lecture slides, a test bank for instructors, updated weblinks to videos, and suggested readings for students.
Humanity’s impact on the planet is undeniable. Fairly and effectively addressing environmental problems begins with understanding their causes and impacts. Is over-population the main driver of environmental degradation? Poverty? Capitalism? Poor governance? Imperialism? Patriarchy? Clearly these are not technical questions, but political ones.
Updated to cover new debates, data, and policy, and expanded to include chapters on colonialism, race and gender, and the impacts of energy and resource extraction, this book introduces students to diverse perspectives and helps them develop an informed understanding of why environmental problems occur.
How the international community should act is deeply contested. Guiding students through the potential responses, including multilateral diplomacy, transnational voluntary action, innovative financial mechanisms, problem displacement, consumer-focused campaigns, and resistance, this book explains the different forms of political action, their limitations and injustices.
Online resources include lecture slides, a test bank for instructors, updated weblinks to videos, and suggested readings for students.