5,139 research outputs found
Dynamics of heavy and buoyant underwater pendulums
The humble pendulum is often invoked as the archetype of a simple, gravity
driven, oscillator. Under ideal circumstances, the oscillation frequency of the
pendulum is independent of its mass and swing amplitude. However, in most
real-world situations, the dynamics of pendulums is not quite so simple,
particularly with additional interactions between the pendulum and a
surrounding fluid. Here we extend the realm of pendulum studies to include
large amplitude oscillations of heavy and buoyant pendulums in a fluid. We
performed experiments with massive and hollow cylindrical pendulums in water,
and constructed a simple model that takes the buoyancy, added mass, fluid
(nonlinear) drag, and bearing friction into account. To first order, the model
predicts the oscillation frequencies, peak decelerations and damping rate well.
An interesting effect of the nonlinear drag captured well by the model is that
for heavy pendulums, the damping time shows a non-monotonic dependence on
pendulum mass, reaching a minimum when the pendulum mass density is nearly
twice that of the fluid. Small deviations from the model's predictions are
seen, particularly in the second and subsequent maxima of oscillations. Using
Time- Resolved Particle Image Velocimetry (TR-PIV), we reveal that these
deviations likely arise due to the disturbed flow created by the pendulum at
earlier times. The mean wake velocity obtained from PIV is used to model an
extra drag term due to incoming wake flow. The revised model significantly
improves the predictions for the second and subsequent oscillations.Comment: 15 pages, 8 figures, J. Fluid Mech. (in press
Transnational Climate Change Governance and the Global South
Alongside intergovernmental climate change negotiations, a groundswell of
climate actions by cities, regions, businesses, investors, and civil society
groups has emerged. These transnational actors seek to address mitigation and
adaptation to climate change; independently, with each other and with
governments and international organizations. Many have welcomed transnational
climate initiatives as a crucial addition to the formal climate regime,
contributing to a growing momentum to act on climate change. However, critics
have raised concerns about whether transnational actors are genuinely
interested in mitigation and adaptation, or whether they are they are
representing business-as-usual as clean and green. Moreover, are transnational
climate initiatives appropriately targeted to address needs of both developed
and developing countries; do they exacerbate imbalances in global climate
governance between the global North and South? This paper explores the
multifaceted relation between developing countries and transnational climate
governance. It discusses developing country engagement on the basis of their
political support for transnational initiatives, their leadership of, and
participation in transnational climate initiatives, and the implementation and
performance of such initiatives from the perspective of the global South
Effective and geographically balanced? An output-based assessment of non-state climate actions
At COP21 in Paris, governments reiterated the importance of ‘non-Party’ contributions, placing big bets that the efforts of cities, regions, investors, companies, and other social groups will help keep average global warming limited to well under 2°C. However, there is little systematic knowledge concerning the performance of non-state and subnational efforts. We established a database of 52 climate actions launched at the 2014 UN Climate Summit in New York to assess output performance – that is, the production of relevant outputs – to understand whether they are likely to deliver social and environmental impacts. Moreover, we assess to which extent climate actions are implemented across developed and developing countries. We find that climate actions are starting to deliver, and output performance after one year is higher than one might expect from previous experiences with similar actions. However, differences exist between action areas: resilience actions have yet to produce specific outputs, whereas energy and industry actions perform above average. Furthermore, imbalances between developing and developed countries persist. While many actions target low-income and lower-middle-income economies, the implementation gap in these countries remains greater. More efforts are necessary to mobilize and implement actions that benefit the world’s most vulnerable people
Strengthening non-state climate action: a progress assessment of commitments launched at the 2014 UN Climate Summit
This report provides the first progress assessment of climate actions launched at the 2014 UN Climate Summit in New York. It considers the distribution and performance of climate actions along multiple dimensions that are relevant to both mitigation and adaptation. While it is too early for a conclusive assessment of the effectiveness of climate actions, this study makes a first and indispensable step toward such an assessment. Initial findings are encouraging. One year after their launch, most climate actions have performed well in terms of producing outputs, putting them on track to implementing their commitments in the coming years. The research for this project is underpinned by the Global Aggregator for Climate Actions (GAFCA), a database developed between January and September 2015 by a research team at the German Development Institute/Deutsches Institut für Entwicklungspolitik (DIE) and the London School of Economics and Political Science (LSE). GAFCA includes data on organizational characteristics, geography of implementation and output performance of climate actions. It creates the foundation for a long-term systematic examination of climate actions that can inform more effective efforts to strengthen such actions. Our analysis is focused on three broad questions: Have organizers of the 2014 UN Climate Summit engaged a wide range of non-state and sub-national actions that set targets relevant to both mitigation and adaptation? Do climate actions align with the interests of both developing and developed countries, and do they achieve an appropriate balance in implementation in the global North and South? Have climate actions started to deliver on their commitments one year since they were launched at the 2014 UN Climate Summit? (Output performance
Settling behaviour of thin curved particles in quiescent fluid and turbulence
The motion of thin curved falling particles is ubiquitous in both nature and
industry but is not yet widely examined. Here, we describe an experimental
study on the dynamics of thin cylindrical shells resembling broken bottle
fragments settling through quiescent fluid and homogeneous anisotropic
turbulence. The particles have Archimedes numbers based on the mean descent
velocity . Turbulence
reaching a Reynolds number of is generated in a water
tank using random jet arrays mounted in a co-planar configuration. After the
flow becomes statistically stationary, a particle is released and its
three-dimensional motion is recorded using two orthogonally positioned
high-speed cameras. We propose a simple pendulum model that accurately captures
the velocity fluctuations of the particles in still fluid and find that
differences in the falling style might be explained by a better alignment of
the particle incidence angle with its velocity direction. By comparing the
trajectories under background turbulence with the quiescent fluid cases, we
measure a decrease in the mean descent velocity in turbulence for the
conditions tested. We also study the secondary motion of the particles and
identify descent events that are unique to turbulence such as 'long gliding'
and 'rapid rotation' events. Lastly, we show an increase in the radial
dispersion of the particles under background turbulence and correlate the
timescale of descent events with the local settling velocity.Comment: 25 pages, 18 figures, 5 movie
Beyond national climate action : the impact of region, city, and business commitments on global greenhouse gas emissions
This article quantifies the net aggregate impact in 2030 of commitments by individual non-state and subnational actors (e.g. regions, cities and businesses, collectively referred to as ‘NSAs’) to reduce greenhouse gas (GHG) emissions. The analysis was conducted for NSAs operating within ten major emitting economies that together accounted for roughly two-thirds of global GHG emissions in 2016. Our assessment includes 79 regions (e.g. subnational states and provinces), approximately 6,000 cities, and nearly 1,600 companies with a net emissions coverage of 8.1 GtCO2e/year, or a quarter of the ten economies’ total GHG emissions in 2016. The analysis reflects a proposed methodology to aggregate commitments from different subnational (i.e. regional and city government) and non-state (i.e. business) actors, accounting for overlaps. If individual commitments by NSAs in the ten high-emitting economies studied are fully implemented and do not change the pace of action elsewhere, projected GHG emissions in 2030 for the ten economies would be 1.2–2.0 GtCO2e/year or 3.8%–5.5% lower compared to scenario projections for current national policies (31.6–36.8 GtCO2e/year). On a country level, we find that the full implementation of these individual commitments alone could result in the European Union and Japan overachieving their nationally determined contributions (NDCs), while India could further overachieve its unconditional NDC target. In the United States, where the national government has rolled back climate policies, NSAs could become a potential driving force for climate action. Key policy insights Full implementation of reported and quantifiable individual commitments by regions, cities and businesses (NSAs) in ten major economies could reduce emissions by 3.8%–5.5% in 2030 below current national policies scenario projections. National governments’ mitigation targets could be more ambitious if they would take NSA commitments into account. With full implementation of such action, the European Union and Japan would overachieve their NDC targets. For the United States such action could help meeting its original 2025 NDC target in spite of rollbacks in national climate policies. The full universe of NSA climate action expands far beyond the subset of commitments analysed in this study; NSAs could become a strong driving force for enhanced action towards the Paris climate goals.</p
Photodissociation of water in crystalline ice: a molecular dynamics study
Ultraviolet irradiation of ice is of great interest for understanding the
chemistry in both atmospheric and astrophysical environments. In interstellar
space, photodissociation of H2O molecules can be a driving force behind the
chemistry on icy dust grains in dense, cold molecular clouds even though the
flux of UV photons is extremely low. The mechanisms of such photoinduced
processes are poorly understood, however. In this work the photodissociation
dynamics of a water molecule in crystalline ice at 10 K is studied
computationally using classical molecular dynamics. Photodissociation in the
first bilayer leads mainly to H atoms desorbing (65%), while in the third
bilayer trapping of H and OH dominates (51%). The kinetic energy distribution
of the desorbing H atoms is much broader than that for the corresponding
gas-phase photodissociation. The H atoms on average move 11 Angstroms before
becoming trapped, while OH radicals typically move 2 Angstroms. In accordance
with experiments a blueshift of the absorption spectrum is obtained relative to
gas-phase water.Comment: 23 pages, 5 figure
The many faces of small B cell lymphomas with plasmacytic differentiation and the contribution of MYD88 testing
Plasmacytic differentiation may occur in almost all small B cell lymphomas (SBLs), although it varies from being uniformly present (as in lymphoplasmacytic lymphoma (LPL)) to very uncommon (as in mantle cell lymphomas (MCLs)). The discovery of MYD88 L265P mutations in the vast majority of LPLs has had a major impact on the study of these lymphomas. Review of the cases contributed to the 2014 European Association for Haematopathology/Society for Hematopathology slide workshop illustrated how mutational testing has helped refine the diagnostic criteria for LPL, emphasizing the importance of identifying a clonal monotonous lymphoplasmacytic population and highlighting how LPL can still be diagnosed with extensive nodal architectural effacement, very subtle plasmacytic differentiation, follicular colonization, or uncommon phenotypes such as CD5 or CD10 expression. MYD88 L265P mutations were found in 11/11 LPL cases versus only 2 of 28 other SBLs included in its differential diagnosis. Mutational testing also helped to exclude other cases that would have been considered LPL in the past. The workshop also highlighted how plasmacytic differentiation can occur in chronic lymphocytic leukemia/small lymphocytic lymphoma, follicular lymphoma, SOX11 negative MCL, and particularly in marginal zone lymphomas, all of which can cause diagnostic confusion with LPL. The cases also highlighted the difficulty in distinguishing lymphomas with marked plasmacytic differentiation from plasma cell neoplasms. Some SBLs with plasmacytic differentiation can be associated with amyloid, other immunoglobulin deposition, or crystal-storing histiocytosis, which may obscure the underlying neoplasm. Finally, although generally indolent, LPL may transform, with the workshop cases suggesting a role for TP53 abnormalities
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