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Open accessJournal ArticleDOI: 10.1063/5.0030535

Transition paths of marine debris and the stability of the garbage patches.

02 Mar 2021-Chaos (AIP Publishing.)-Vol. 31, Iss: 3, pp 033101-033101
Abstract: We used transition path theory (TPT) to infer “reactive” pathways of floating marine debris trajectories. The TPT analysis was applied on a pollution-aware time-homogeneous Markov chain model constructed from trajectories produced by satellite-tracked undrogued buoys from the National Oceanic and Atmospheric Administration's Global Drifter Program. The latter involved coping with the openness of the system in physical space, which further required an adaptation of the standard TPT setting. Directly connecting pollution sources along coastlines with garbage patches of varied strengths, the unveiled reactive pollution routes represent alternative targets for ocean cleanup efforts. Among our specific findings we highlight: constraining a highly probable pollution source for the Great Pacific garbage patch; characterizing the weakness of the Indian Ocean gyre as a trap for plastic waste; and unveiling a tendency of the subtropical gyres to export garbage toward the coastlines rather than to other gyres in the event of anomalously intense winds.

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Topics: Great Pacific garbage patch (61%), Marine debris (59%), Indian Ocean Gyre (57%) ... read more

6 results found

Open accessJournal ArticleDOI: 10.1140/EPJS/S11734-021-00191-0
Luzie Helfmann1, Luzie Helfmann2, Luzie Helfmann3, Jobst Heitzig1  +5 moreInstitutions (4)
Abstract: Agent-based models are a natural choice for modeling complex social systems. In such models simple stochastic interaction rules for a large population of individuals on the microscopic scale can lead to emergent dynamics on the macroscopic scale, for instance a sudden shift of majority opinion or behavior. Here we are introducing a methodology for studying noise-induced tipping between relevant subsets of the agent state space representing characteristic configurations. Due to a large number of interacting individuals, agent-based models are high-dimensional, though usually a lower-dimensional structure of the emerging collective behaviour exists. We therefore apply Diffusion Maps, a non-linear dimension reduction technique, to reveal the intrinsic low-dimensional structure. We characterize the tipping behaviour by means of Transition Path Theory, which helps gaining a statistical understanding of the tipping paths such as their distribution, flux and rate. By systematically studying two agent-based models that exhibit a multitude of tipping pathways and cascading effects, we illustrate the practicability of our approach.

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3 Citations

Open accessJournal ArticleDOI: 10.1175/MWR-D-21-0024.1
Abstract: Nonlinear atmospheric dynamics produce rare events that are hard to predict and attribute due to many interacting degrees of freedom. Sudden stratospheric warming event is a model example. Approximately once every other year, the winter polar vortex in the boreal stratosphere rapidly breaks down, inducing a shift in midlatitude surface weather patterns persisting for up to 2-3 months. In principle, lengthy numerical simulations can be used to predict and understand these rare transitions. For complex models, however, the cost of the direct numerical simulation approach is often prohibitive. We describe an alternative approach which only requires relatively short-duration computer simulations of the system. The methodology is illustrated by applying it to a prototype model of an SSW event developed by Holton and Mass (1976) and driven with stochastic forcing. While highly idealized, the model captures the essential nonlinear dynamics of SSWs and exhibits the key forecasting challenge: the dramatic separation in timescales between the dynamics of a single event and the return time between successive events. We compute optimal forecasts of sudden warming events and quantify the limits of predictability. Statistical analysis relates these optimal forecasts to a small number of interpretable physical variables. Remarkably, we are able to estimate these quantities using a data set of simulations much shorter than the timescale of the warming event. This methodology is designed to take full advantage of the high-dimensional data from models and observations, and can be employed to find detailed predictors of many complex rare events arising in climate dynamics.

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1 Citations

Open accessJournal ArticleDOI: 10.1063/5.0057409
23 Sep 2021-Chaos
Abstract: In the past few decades, boreal summers have been characterized by an increasing number of extreme weather events in the Northern Hemisphere extratropics, including persistent heat waves, droughts and heavy rainfall events with significant social, economic, and environmental impacts. Many of these events have been associated with the presence of anomalous large-scale atmospheric circulation patterns, in particular, persistent blocking situations, i.e., nearly stationary spatial patterns of air pressure. To contribute to a better understanding of the emergence and dynamical properties of such situations, we construct complex networks representing the atmospheric circulation based on Lagrangian trajectory data of passive tracers advected within the atmospheric flow. For these Lagrangian flow networks, we study the spatial patterns of selected node properties prior to, during, and after different atmospheric blocking events in Northern Hemisphere summer. We highlight the specific network characteristics associated with the sequence of strong blocking episodes over Europe during summer 2010 as an illustrative example. Our results demonstrate the ability of the node degree, entropy, and harmonic closeness centrality based on outgoing links to trace important spatiotemporal characteristics of atmospheric blocking events. In particular, all three measures capture the effective separation of the stationary pressure cell forming the blocking high from the normal westerly flow and the deviation of the main atmospheric currents around it. Our results suggest the utility of further exploiting the Lagrangian flow network approach to atmospheric circulation in future targeted diagnostic and prognostic studies.

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Open accessJournal ArticleDOI: 10.3390/JMSE9111289
Abstract: This Communication reports on the increases in the sizes of garbage patches, and their environmental implications, outlining the dimensions of what is a growing problem connected with the “plastisphere”. The paper presents some data on the distribution of garbage patches in the world’s oceans and makes some predictions on future growth, which is partly associated with the future increases in worldwide plastics production. The findings demonstrate that the size of the main garbage patches is increasing, posing a threat to the environment and marine life. The paper urges for better plastic waste management to prevent it from reaching the oceans, along with concerted actions in respect of plastic collection and cleaning up the oceans, which may include new technological solutions.

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Topics: Garbage (60%)

Open accessPosted Content
Abstract: Rare events play a crucial role in many physics, chemistry, and biology phenomena, when they change the structure of the system, for instance in the case of multistability, or when they have a huge impact. Rare event algorithms have been devised to simulate them efficiently, avoiding the computation of long periods of typical fluctuations. We consider here the family of splitting or cloning algorithms, which are versatile and specifically suited for far-from-equilibrium dynamics. To be efficient, these algorithms need to use a smart score function during the selection stage. Committor functions are the optimal score functions. In this work we propose a new approach, based on the analogue Markov chain, for a data-based learning of approximate committor functions. We demonstrate that such learned committor functions are extremely efficient score functions when used with the Adaptive Multilevel Splitting algorithm. We illustrate our approach for a gradient dynamics in a three-well potential, and for the Charney-DeVore model, which is a paradigmatic toy model of multistability for atmospheric dynamics. For these two dynamics, we show that having observed a few transitions is enough to have a very efficient data-based score function for the rare event algorithm. This new approach is promising for use for complex dynamics: the rare events can be simulated with a minimal prior knowledge and the results are much more precise than those obtained with a user-designed score function.

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Topics: Rare events (56%), Complex dynamics (53%), Markov chain (52%) ... read more


53 results found

Journal ArticleDOI: 10.1137/0201010
Abstract: The value of depth-first search or “backtracking” as a technique for solving problems is illustrated by two examples. An improved version of an algorithm for finding the strongly connected componen...

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Topics: Depth-first search (67%), Strongly connected component (61%), Backtracking (58%) ... read more

5,156 Citations

Journal ArticleDOI: 10.1126/SCIENCE.1260352
Jenna Jambeck1, Roland Geyer2, Chris Wilcox3, Theodore R. Siegler4  +4 moreInstitutions (7)
13 Feb 2015-Science
Abstract: Plastic debris in the marine environment is widely documented, but the quantity of plastic entering the ocean from waste generated on land is unknown. By linking worldwide data on solid waste, population density, and economic status, we estimated the mass of land-based plastic waste entering the ocean. We calculate that 275 million metric tons (MT) of plastic waste was generated in 192 coastal countries in 2010, with 4.8 to 12.7 million MT entering the ocean. Population size and the quality of waste management systems largely determine which countries contribute the greatest mass of uncaptured waste available to become plastic marine debris. Without waste management infrastructure improvements, the cumulative quantity of plastic waste available to enter the ocean from land is predicted to increase by an order of magnitude by 2025.

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Topics: Municipal solid waste (59%), Marine debris (58%), Plastic pollution (58%) ... read more

4,410 Citations

Open accessJournal ArticleDOI: 10.1073/PNAS.1314705111
Abstract: There is a rising concern regarding the accumulation of floating plastic debris in the open ocean. However, the magnitude and the fate of this pollution are still open questions. Using data from the Malaspina 2010 circumnavigation, regional surveys, and previously published reports, we show a worldwide distribution of plastic on the surface of the open ocean, mostly accumulating in the convergence zones of each of the five subtropical gyres with comparable density. However, the global load of plastic on the open ocean surface was estimated to be on the order of tens of thousands of tons, far less than expected. Our observations of the size distribution of floating plastic debris point at important size-selective sinks removing millimeter-sized fragments of floating plastic on a large scale. This sink may involve a combination of fast nano-fragmentation of the microplastic into particles of microns or smaller, their transference to the ocean interior by food webs and ballasting processes, and processes yet to be discovered. Resolving the fate of the missing plastic debris is of fundamental importance to determine the nature and significance of the impacts of plastic pollution in the ocean.

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Topics: Marine debris (60%), Plastic pollution (59%), Great Pacific garbage patch (55%) ... read more

1,469 Citations

Journal ArticleDOI: 10.1039/TF9383400029
Abstract: According to our present notions, the theory of reaction rates involves three steps. First, one should know the behaviour of all molecules present in the system during the reaction, how they will move, and which products they will yield when colliding with definite velocities, etc. Practically, this amounts in most cases to the construction of the energy surface for the reacting system. Professor Eyring told us about the results which can be obtained by the application of quantum mechanics to molecular systems for this part of the theory. The second step in the theory I would call the statistical part. It endeavours to solve the problem of the rate of elementary reactions. Assuming only the material on the left side of a chemical equation to be present in a vessel, and the molecules of these to have the Maxwell-Boltzman energy and velocity distribution, one wants to know how many molecules corresponding to the right side of the equation will be formed in unit time. The elementary properties of the molecules are supposed to be known in this second step and one wants to express the reaction rate of elementary reactions in terms of these. The present paper will be devoted entirely to this second step. The third step is the consideration of the co-operation of the various elementary reactions, which may occur beside and must occur after each other in order to complete a real reaction. In especially favourable cases there is only one important chain of reactions leading to the final products and this has one link which is so much slower than all the others, that it is made responsible for the observed rate. The others are then assumed to be so much faster that one has practically equilibrium between the two sides of their chemical equations.

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Topics: Elementary reaction (55%)

711 Citations

Open accessJournal ArticleDOI: 10.1073/PNAS.0905466106
Abstract: Characterizing the equilibrium ensemble of folding pathways, including their relative probability, is one of the major challenges in protein folding theory today. Although this information is in principle accessible via all-atom molecular dynamics simulations, it is difficult to compute in practice because protein folding is a rare event and the affordable simulation length is typically not sufficient to observe an appreciable number of folding events, unless very simplified protein models are used. Here we present an approach that allows for the reconstruction of the full ensemble of folding pathways from simulations that are much shorter than the folding time. This approach can be applied to all-atom protein simulations in explicit solvent. It does not use a predefined reaction coordinate but is based on partitioning the state space into small conformational states and constructing a Markov model between them. A theory is presented that allows for the extraction of the full ensemble of transition pathways from the unfolded to the folded configurations. The approach is applied to the folding of a PinWW domain in explicit solvent where the folding time is two orders of magnitude larger than the length of individual simulations. The results are in good agreement with kinetic experimental data and give detailed insights about the nature of the folding process which is shown to be surprisingly complex and parallel. The analysis reveals the existence of misfolded trap states outside the network of efficient folding intermediates that significantly reduce the folding speed.

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686 Citations

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