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179459 results in Earth and Environmental Sciences

Page 144 of 8973

  • Theory of soft active equilibrium wetting

  • Ghansham Rajendrasingh Chandel, Siddhartha Das
  • Journal:
    Journal of Fluid Mechanics / Volume 1019 / 25 September 2025
    Published online by Cambridge University Press:
    18 September 2025, A39
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  • We must address active matter in the context of soft boundaries to bridge the gap between our understanding of active matter and the dynamics of biological systems (represented as active matter) under natural conditions. However, the physics of such active drops (matter) in contact with a soft and deformable surface has remained elusive. In this paper, we attempt to fill this gap and develop a theory for soft, active wetting. Our theory, which accounts for the various free energies for passive substrate and active drops as well as the active stresses, provides an equilibrium description of (active) particle orientation inside the drop and an equilibrium shape of the drop–soft-solid system. We obtain an analytical equation relating the activity to the internal pressure of an active drop. The equilibrium calculation further yields an ordered state of the polarisation field inside the drop. As compared to the non-active drops, the active drops with extensile activity press more into the soft surface, while the active drops with contractile activity either rise out of the soft surface (for smaller magnitude of negative activity) or make the soft surface bulge (for larger magnitude of negative activity). Finally, the three-phase contact line undergoes a rotation that depends on the strength of activity. These findings shed light on the manner in which the active stresses interact with surface tension and elasticity at the fundamental level.

  • 7 - Multilateral Diplomacy

  • from Part II - Responding to Global Environmental Problems
  • Hayley Stevenson, Universidad Torcuato Di Tella, Buenos Aires
  • Book:
    Global Environmental Politics
    Published online:
    04 September 2025
    Print publication:
    18 September 2025, pp 112-139

  • Summary

    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.

  • 2 - The Tragedy of the Commons

  • from Part I - Why Do Environmental Problems Occur?
  • Hayley Stevenson, Universidad Torcuato Di Tella, Buenos Aires
  • Book:
    Global Environmental Politics
    Published online:
    04 September 2025
    Print publication:
    18 September 2025, pp 19-33

  • Summary

    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.

  • Reimagining urban science for global sustainability: Five strategic research areas

  • Xuemei Bai, Giles B. Sioen, Şiir Kilkiş, Timon McPhearson, Zeenat Niazi, Jago Dodson, Tri Atmaja, Kensuke Fukushi, Niki Frantzeskaki, Harini Nagendra, Wanyu Shih, Thomas Elmqvist, Tischa Muñoz-Erickson, Xiangzheng Deng, Burak Güneralp, Shuaib Lwasa, Noboru Zama
  • Journal:
    Global Sustainability / Volume 8 / 2025
    Published online by Cambridge University Press:
    18 September 2025, e38
    • Article
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  • Non-technical summary

    Cities, as complex systems, are faced with increasingly diverse and connected challenges across social, economic, environmental, and health domains. To help cities address these challenges, the Future Earth Urban Knowledge-Action Network developed a cross-disciplinary urban research agenda through expert elicitations and extensive consultation. Five research themes to guide urban sustainability research were identified including: (1) advancing urban sustainability transformations, (2) ensuring equity, (3) boosting innovation in low to lower-middle income countries, (4) managing complexity and systemic risks, and (5) navigating environmental change. Advancing this agenda will require collaboration across disciplines and geographies, transdisciplinary coproduction, and enhanced support to urban science.

    Technical Abstract

    Cities and urban regions are at the forefront of transformations toward global sustainability. As urbanization accelerates, there is increasing demand for cities to play multiple, complex and synthetic roles across social and environmental domains within and beyond their boundaries, for example driving economic development while mitigating and adapting to global environmental changes. To help cities in meeting this challenge, urban science, a rapidly growing field that includes inter- and transdisciplinary research, needs to expand and evolve, with clear priorities. Combining expert elicitation and community consultation, the Future Earth Urban Knowledge-Action Network developed a strategic research agenda for urban science for the next decade. The urban science research agenda describes five critical research themes for scientific advances: (1) accelerate urban sustainability transformations, (2) ensure equity and inclusivity, (3) amplify innovation from the low to lower-middle income countries, (4) negotiate complexity and systemic risks, and (5) navigate environmental change. Under each research theme, we review the state of the art, identify remaining gaps, and outline key research questions needing to be addressed to advance science toward urban transformations. Interconnections across, and enabling conditions to advance, these priority research themes are discussed.

    Social media summary

    Globally co-designed urban research agenda reveals pressing priorities for sustainability and resilience.

  • Nonlinear flapping and symmetry-breaking bifurcation modulation of a piezoelectric metamaterial beam in viscous flow

  • Shuai Liu, Jiawei Mao, Hao Liu, Penglin Gao, Yegao Qu
  • Journal:
    Journal of Fluid Mechanics / Volume 1019 / 25 September 2025
    Published online by Cambridge University Press:
    18 September 2025, A2

  • In this paper we propose a novel control strategy for modulating nonlinear flapping and symmetry-breaking (S-B) bifurcations of a piezoelectric metamaterial beam behind a circular cylinder subjected to viscous flow. The beam incorporates distributed piezoelectric meta-cells connected via unidirectional circuits to enable self-sensing and adaptive control. A strongly coupled nonlinear fluid-structure-electro-control model within an arbitrary Lagrangian–Eulerian framework is developed for predicting the flapping dynamics of the large deformable piezoelectric metamaterial beam. The system exhibits multiple flow-induced modes, including limit-cycle oscillations, subharmonic responses and S-B deflections. These dynamic regimes arise from nonlinear bifurcations of the system, namely the period-doubling and spontaneous S-B bifurcations. Flapping control and wake topology transition of the system is achieved by suppressing the periodic-doubling bifurcation based on the vibration rebound effect through a self-sensing and adaptive-actuation mechanism of the beam. Floquet stability analysis confirms the effectiveness of control in delaying instability onset and suppressing chaotic transitions. Symmetry modulation of the beam is achieved via the localised perturbations induced from the piezoelectric meta-cells, which reshape the stability of the system. The transition from S-B mode to symmetry-recovery mode reflects a shift from a flow-separation-dominated to vibration-dominated vortex shedding pattern. This symmetry transition reorganises the energy exchange pathways between the flow and the beam. Quantitative analyses of the wake recovery and the energy harvesting efficiency confirm enhanced flow energy conversion under control. These results establish a framework for bifurcation control of slender structures in viscous flow, providing potential applications for underwater energy harvesting and flexible propulsion in unsteady environments.

  • Symmetry groups and invariant solutions of plane Poiseuille flow

  • Pratik P. Aghor, John F. Gibson
  • Journal:
    Journal of Fluid Mechanics / Volume 1019 / 25 September 2025
    Published online by Cambridge University Press:
    18 September 2025, A36

  • Equilibrium, travelling-wave and periodic-orbit solutions of the Navier–Stokes equations provide a promising avenue for investigating the structure, dynamics and statistics of transitional flows. Many such invariant solutions have been computed for wall-bounded shear flows, including plane Couette, plane Poiseuille and pipe flow. However, the organisation of invariant solutions is not well understood. In this paper we focus on the role of symmetries in the organisation and computation of invariant solutions of plane Poiseuille flow. We show that enforcing symmetries while computing invariant solutions increases the efficiency of the numerical methods, and that redundancies between search spaces can be eliminated by consideration of equivalence relations between symmetry subgroups. We determine all symmetry subgroups of plane Poiseuille flow in a doubly periodic domain up to translations by half the periodic lengths and classify the subgroups into equivalence classes, each of which represents a physically distinct set of symmetries and an associated set of physically distinct invariant solutions. We calculate fifteen new travelling waves of plane Poiseuille flow in seven distinct symmetry groups and discuss their relevance to the dynamics of transitional turbulence. We present a few examples of subgroups with fractional shifts other than half the periodic lengths and one travelling-wave solution whose symmetry involves shifts by one third of the periodic lengths. We conclude with a discussion and some open questions about the role of symmetry in the behaviour of shear flows.

  • Optimal body force for heat transfer in turbulent vertical heated pipe flow

  • Shijun Chu, Elena Marensi, Ashley P. Willis
  • Journal:
    Journal of Fluid Mechanics / Volume 1019 / 25 September 2025
    Published online by Cambridge University Press:
    18 September 2025, A21

  • The vertical heated pipe is widely used in thermal engineering applications, as buoyancy can help drive a flow, but several flow regimes are possible: shear-driven turbulence, laminarised flow and convective turbulence. Steady velocity fields that maximise heat transfer have previously been calculated for heated pipe flow, but were calculated independently of buoyancy forces, and hence independently of the flow regime and time-dependent dynamics of the flow. In this work, a variational method is applied to find an optimal body force of limited magnitude $A_0$ that maximises heat transfer for the vertical arrangement, with the velocity field constrained by the full governing equations. In our calculations, mostly at Reynolds number ${\textit{Re}}=3000$, it is found that streamwise-independent rolls remain optimal, as in previous steady optimisations, but that the optimal number of rolls and their radial position is dependent on the flow regime. Surprisingly, while it is generally assumed that turbulence enhances heat transfer, for the strongly forced case, time dependence typically leads to a reduction. Beyond offering potential improvement through the targeting of the roll configuration for this application, wider implications are that optimisations under the steady flow assumption may overestimate improvements in heat transfer, and that strategies that simply aim to induce turbulence may not necessarily be efficient in enhancing heat transfer either. Including time dependence and the full governing equations in the optimisation is challenging but offers further enhancement and improved reliability in prediction.

  • 4 - Decarbonization Efforts in NYC

  • Katrina M. Wyman, New York University, Danielle Spiegel-Feld, New York University
  • Book:
    Local Greens
    Published online:
    11 October 2025
    Print publication:
    18 September 2025, pp 55-71

  • Summary

    In the early twenty-first century, New York and other cities established targets to reduce their greenhouse gas emissions to help limit global climate change. Limiting these emissions is not an obvious task for local governments: no city’s efforts will materially affect planetary temperatures, and curtailing these emissions imposes costs on local actors mainly for the benefit of the world as a whole. Between 2007, when the city set its first GHG reduction target, and 2019, the city’s emission reduction efforts were consistent with the preoccupation of local elites with economic growth. The city did not impose costly requirements on local actors to reduce their emissions, and the city did not achieve significant emission reductions. However, in 2019, the city government passed a local law that establishes declining caps on greenhouse gas emissions from buildings, and portends real costs on private actors – including the owners of residential real estate – if the city enforces the law. This 2019 law emerged from the efforts of city insiders, and local progressive interest groups motivated by environmental, social justice and labor concerns in the first Trump presidency. The history of the city’s efforts to reduce greenhouse gas emissions illustrates the precarious politics of local decarbonization efforts.

  • 12 - Problem Displacement

  • from Part II - Responding to Global Environmental Problems
  • Hayley Stevenson, Universidad Torcuato Di Tella, Buenos Aires
  • Book:
    Global Environmental Politics
    Published online:
    04 September 2025
    Print publication:
    18 September 2025, pp 253-279

  • Summary

    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.

  • 11 - Individualising Responsibility

  • from Part II - Responding to Global Environmental Problems
  • Hayley Stevenson, Universidad Torcuato Di Tella, Buenos Aires
  • Book:
    Global Environmental Politics
    Published online:
    04 September 2025
    Print publication:
    18 September 2025, pp 226-252

  • Summary

    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.

  • 1 - Global Politics and the Environment

  • Hayley Stevenson, Universidad Torcuato Di Tella, Buenos Aires
  • Book:
    Global Environmental Politics
    Published online:
    04 September 2025
    Print publication:
    18 September 2025, pp 1-16

  • Summary

    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.

  • 14 - Appraising Global Environmental Governance

  • from Part II - Responding to Global Environmental Problems
  • Hayley Stevenson, Universidad Torcuato Di Tella, Buenos Aires
  • Book:
    Global Environmental Politics
    Published online:
    04 September 2025
    Print publication:
    18 September 2025, pp 312-323

  • Summary

    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.

  • Morphological diversity of the cetacean mandibular symphysis coincides with novel modes of aquatic feeding

  • Rebecca J. Strauch, Jacob S. Berv, Danielle Fraser, Nicholas D. Pyenson, Carlos Mauricio Peredo
  • Journal:
    Paleobiology / Volume 52 / Issue 1 / February 2026
    Published online by Cambridge University Press:
    17 September 2025, pp. 145-154
    • Article
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  • In whales, extreme modifications to the ancestral mammalian feeding apparatus facilitate novel modes of aquatic feeding. These modifications manifest in morphological diversity across a suite of characters, including the mandibular symphysis. Cetaceans span a range of symphyseal morphologies, with one lineage (crown mysticetes) evolving a highly mobile condition unique among mammals. Here, we use phylogenetic comparative methods to examine the evolution of symphyseal fusion and elongation across 206 extant and fossil cetacean taxa. Ancestral state reconstructions corroborate observations from the fossil record that suggest the ancestral condition for Cetacea was a fused, moderately elongated symphysis. Shifts in symphyseal morphology coincided with ocean restructuring and diversification of feeding modes. Evolutionary rates peaked in the middle–late Eocene and at the Eocene/Oligocene boundary as whales evolved shorter, unfused symphyses. During the Eocene, ankylosed mandibles became less common with the appearance of increasingly pelagic whales. Mysticetes evolved decoupled, highly mobile mandibles near the Eocene/Oligocene boundary. Several odontocete lineages underwent a trait reversal and converged on fully fused, elongated mandibles in the Miocene. Analyses evaluating the influence of ecological variables indicate strong correlations in feeding strategy, dentition, and prey type. The loss of prey-processing behavior and changes to masticatory loading regimes may explain concurrent trends in symphyseal morphology and tooth simplification. We suggest that the functional and morphological diversity of the symphysis in whales is a consequence of aquatic feeding imposing different mechanical constraints than those associated with feeding on land.

Page 144 of 8973