The Experts below are selected from a list of 68985 Experts worldwide ranked by ideXlab platform
Max Rietkerk - One of the best experts on this subject based on the ideXlab platform.
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the Dynamic Regime concept for ecosystem management and restoration
2004Co-Authors: Audrey L Mayer, Max RietkerkAbstract:Abstract Because the response of ecosystem patterns and processes to disturbance is rarely linear, the Dynamic Regime concept offers a more realistic construct than linear models for understanding ecosystems. Dynamic Regimes, and shifts between them, have been reported for a diversity of ecosystem types (e.g., terrestrial, marine, aquatic) at a variety of scales (e.g., from small lakes to the global climate). Ecosystem Regimes that are obvious at one scale may not be at another. Regimes are maintained by internal relationships and feedbacks between species, and these internal Dynamics can interact with large-scale external forces (such as global weather patterns) and trigger shifts to alternative Regimes. The Dynamic Regime concept is commonly used in ecosystem management, restoration, and sustainability efforts, in what are known as “state-and-transition,” “threshold,” or “alternative stable state” models. Here we review the application of this concept to ecosystem management and restoration, and discuss...
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The Dynamic Regime Concept for Ecosystem Management and Restoration
2004Co-Authors: Audrey L Mayer, Max RietkerkAbstract:Abstract Because the response of ecosystem patterns and processes to disturbance is rarely linear, the Dynamic Regime concept offers a more realistic construct than linear models for understanding ecosystems. Dynamic Regimes, and shifts between them, have been reported for a diversity of ecosystem types (e.g., terrestrial, marine, aquatic) at a variety of scales (e.g., from small lakes to the global climate). Ecosystem Regimes that are obvious at one scale may not be at another. Regimes are maintained by internal relationships and feedbacks between species, and these internal Dynamics can interact with large-scale external forces (such as global weather patterns) and trigger shifts to alternative Regimes. The Dynamic Regime concept is commonly used in ecosystem management, restoration, and sustainability efforts, in what are known as “state-and-transition,” “threshold,” or “alternative stable state” models. Here we review the application of this concept to ecosystem management and restoration, and discuss...
Audrey L Mayer - One of the best experts on this subject based on the ideXlab platform.
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Fisher Information and Dynamic Regime changes in ecological systems
2005Co-Authors: Audrey L Mayer, Christopher W. Pawlowski, Heriberto CabezasAbstract:Abstract Ecosystems often exhibit transitions between multiple Dynamic Regimes (or steady states), such as the conversion of oligotrophic to eutrophic conditions and associated aquatic ecological communities, due to natural (or increasingly) anthropogenic disturbances. As ecosystems experience perturbations of varying regularity and intensity, they may either remain within the state space neighborhood of the current Regime or “flip” into the neighborhood of a Regime with different characteristics. An increasingly integral aspect of many ecological, economic, and social decisions is their impact on the sustainability of particular Dynamic Regimes of ecosystems. Sustainability entails a human preference for one particular Regime versus another, and the persistence of that Regime with regard to the human and natural perturbations exacted on the system. Information theory has significantly advanced our ability to quantify the organizational complexity inherent in systems despite imperfect observations or ‘signals’ from the source system. Fisher Information is one of several measures developed under the theme of estimation theory. Fisher Information can be described in three ways: as a measure of the degree to which a parameter (or state of a system) can be estimated; as a measure of the relative amount of information that exists between different states of a system; as a measure of the disorder or chaos of a system. Fisher Information may be a useful measure to identify the degree to which a system is at risk of “flipping” into a different Dynamic Regime. We developed a Fisher Information index for Dynamic systems in a periodic steady state and applied it to a simple, two species Lotka–Volterra predator–prey model. Changes in the carrying capacity (size) of the system resulted in different stable steady states establishing themselves, each with a characteristic Fisher Information. By repeatedly calculating Fisher Information over time, transitions or “flips” between steady states were identified with changes in Fisher Information. We then examined data collected from four ecological systems (of increasingly large spatial and temporal scale) that have demonstrated Regime transitions: the Bering Strait/Pacific Ocean food web; the western Africa savanna; the Florida (USA) pine–oak system; the global climate system. These datasets are noisy and reflect several to many cycles that are out of phase, which complicates the identification of both Dynamic Regimes and transitions. If transition phases between Regimes can be detected early enough, human activity suspected of contributing to Regime changes can be altered (or continued if the resultant steady state is desirable, such as in ecosystem restoration efforts).
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the Dynamic Regime concept for ecosystem management and restoration
2004Co-Authors: Audrey L Mayer, Max RietkerkAbstract:Abstract Because the response of ecosystem patterns and processes to disturbance is rarely linear, the Dynamic Regime concept offers a more realistic construct than linear models for understanding ecosystems. Dynamic Regimes, and shifts between them, have been reported for a diversity of ecosystem types (e.g., terrestrial, marine, aquatic) at a variety of scales (e.g., from small lakes to the global climate). Ecosystem Regimes that are obvious at one scale may not be at another. Regimes are maintained by internal relationships and feedbacks between species, and these internal Dynamics can interact with large-scale external forces (such as global weather patterns) and trigger shifts to alternative Regimes. The Dynamic Regime concept is commonly used in ecosystem management, restoration, and sustainability efforts, in what are known as “state-and-transition,” “threshold,” or “alternative stable state” models. Here we review the application of this concept to ecosystem management and restoration, and discuss...
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The Dynamic Regime Concept for Ecosystem Management and Restoration
2004Co-Authors: Audrey L Mayer, Max RietkerkAbstract:Abstract Because the response of ecosystem patterns and processes to disturbance is rarely linear, the Dynamic Regime concept offers a more realistic construct than linear models for understanding ecosystems. Dynamic Regimes, and shifts between them, have been reported for a diversity of ecosystem types (e.g., terrestrial, marine, aquatic) at a variety of scales (e.g., from small lakes to the global climate). Ecosystem Regimes that are obvious at one scale may not be at another. Regimes are maintained by internal relationships and feedbacks between species, and these internal Dynamics can interact with large-scale external forces (such as global weather patterns) and trigger shifts to alternative Regimes. The Dynamic Regime concept is commonly used in ecosystem management, restoration, and sustainability efforts, in what are known as “state-and-transition,” “threshold,” or “alternative stable state” models. Here we review the application of this concept to ecosystem management and restoration, and discuss...
M A Meyers - One of the best experts on this subject based on the ideXlab platform.
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adiabatic shear localization in the crmnfeconi high entropy alloy
2018Co-Authors: Shiteng Zhao, Bingfeng Wang, Senhat M Alotaibi, Yong Liu, M A MeyersAbstract:Abstract The mechanical behavior of the single phase (fcc) CrMnFeCoNi high-entropy alloy (HEA) is examined in the Dynamic Regime. A series of experiments by Dynamic-loading hat-shaped specimens using stopper rings to control the displacement are performed, and the alloy resists adiabatic shear-band formation up to a very large imposed shear strain of ∼7. It is proposed that the combination of the excellent strain-hardening ability and moderate thermal-softening effect retard shear localization. Recrystallized ultrafine-grained grains (diameters of 100–300 nm) with twins are revealed inside the shear band. Their formation is explained by the rotational Dynamic recrystallization mechanism. The stability of the structure at high strain rates strongly suggests a high ballistic resistance for this class of alloys.
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high velocity deformation of al 0 3 cocrfeni high entropy alloy remarkable resistance to shear failure
2017Co-Authors: Shiteng Zhao, H Diao, P K Liaw, M A MeyersAbstract:The mechanical behavior of a single phase (fcc) Al0.3CoCrFeNi high-entropy alloy (HEA) was studied in the low and high strain-rate Regimes. The combination of multiple strengthening mechanisms such as solid solution hardening, forest dislocation hardening, as well as mechanical twinning leads to a high work hardening rate, which is significantly larger than that for Al and is retained in the Dynamic Regime. The resistance to shear localization was studied by Dynamically-loading hat-shaped specimens to induce forced shear localization. However, no adiabatic shear band could be observed. It is therefore proposed that the excellent strain hardening ability gives rise to remarkable resistance to shear localization, which makes this material an excellent candidate for penetration protection applications such as armors.
Axel Lubk - One of the best experts on this subject based on the ideXlab platform.
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spectral field mapping in plasmonic nanostructures with nanometer resolution
2018Co-Authors: Jonas Krehl, Giulio Guzzinati, Johannes Schultz, Pavel Potapov, Darius Pohl, Jerome Martin, Johan Verbeeck, Andreas Fery, B Buchner, Axel LubkAbstract:Plasmonic nanostructures and -devices are rapidly transforming light manipulation technology by allowing to modify and enhance optical fields on sub-wavelength scales. Advances in this field rely heavily on the development of new characterization methods for the fundamental nanoscale interactions. However, the direct and quantitative mapping of transient electric and magnetic fields characterizing the plasmonic coupling has been proven elusive to date. Here we demonstrate how to directly measure the inelastic momentum transfer of surface plasmon modes via the energy-loss filtered deflection of a focused electron beam in a transmission electron microscope. By scanning the beam over the sample we obtain a spatially and spectrally resolved deflection map and we further show how this deflection is related quantitatively to the spectral component of the induced electric and magnetic fields pertaining to the mode. In some regards this technique is an extension to the established differential phase contrast into the Dynamic Regime. Characterizing plasmonic coupling has proven elusive. Here, the authors obtain a spectrally resolved deflection map related to a focused electron beam, which has excited a surface plasmon resonance, and relate this deflection to the spectral component of the induced electric and magnetic fields pertaining to the mode.
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spectral field mapping in plasmonic nanostructures with nanometer resolution
2018Co-Authors: Jonas Krehl, Giulio Guzzinati, Johannes Schultz, Pavel Potapov, Darius Pohl, Jerome Martin, Johan Verbeeck, Andreas Fery, B Buchner, Axel LubkAbstract:Plasmonic nanostructures and devices are rapidly transforming light manipulation technology by allowing to confine and enhance optical fields on sub-wavelength length scales. Advances in this field heavily rely on the development of nanoscale characterization methods yielding insight into the fundamental interaction between light and surface plasmonic resonances. Notwithstanding, the direct imaging of transient fields permitting a direct mapping of plasmonic coupling, e.g., in terms of field enhancement, has been proven elusive to date. Here, we fill that gap by directly measuring the deflection of a focused electron beam, which has excited a surface plasmon resonance, in a transmission electron microscope equipped with an energy filter. By scanning the beam over the sample we obtain a spectrally resolved deflection map and we show that this deflection may be related to induced electric and magnetic fields in a quantitative manner. This method resembles the widespread differential phase contrast techniques employed to measure static electric and magnetic fields and extends them to the Dynamic Regime.
Ioan Pop - One of the best experts on this subject based on the ideXlab platform.
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two phase flow in porous media Dynamic capillarity and heterogeneous media
2016Co-Authors: Van Cj Hans Duijn, Xiulei Cao, Ioan PopAbstract:We investigate a two-phase porous media flow model, in which Dynamic effects are taken into account in phase pressure difference. We consider a one-dimensional heterogeneous case, with two adjacent homogeneous blocks separated by an interface. The absolute permeability is assumed constant, but different in each block. This may lead to the entrapment of the non-wetting phase (say, oil) when flowing from the coarse material into the fine material. We derive the interface conditions coupling the models in each homogeneous block. In doing so, the interface is approximated by a thin porous layer, and its thickness is then passed to zero. Such results have been obtained earlier for standard models, based on equilibrium relationship between the capillary pressure and the saturation. Then, oil is trapped until its saturation on the coarse material side of the interface exceeds an entry value. In the non-equilibrium case, the situation is different. Due to the Dynamic effects, oil may still flow into the fine material even after the saturation drops under the entry point, and this flow may continue for a certain amount of time that is proportional to the non-equilibrium effects. This suggests that operating in a Dynamic Regime reduces the account of oil trapped at interfaces, leading to an enhanced oil recovery. Finally, we present some numerical results supporting the theoretical findings.
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two phase flow in porous media Dynamic capillarity and heterogeneous media
2015Co-Authors: Van Cj Hans Duijn, Xiulei Cao, Ioan PopAbstract:We investigate a two-phase porous media flow model, in which Dynamic effects are taken into account in phase pressure difference. We consider a one-dimensional heterogeneous case, with two adjacent homogeneous blocks separated by an interface. The absolute permeability is assumed constant, but different in each block. This may lead to the entrapment of the nonwetting phase (say, oil) when flowing from the coarse material into the fine material. We derive the interface conditions coupling the models in each homogeneous block. In doing so, the interface is approximated by a thin porous layer, and its thickness is then passed to zero. Such results have been obtained earlier for standard models, based on equilibrium relationship between the capillary pressure and the saturation. Then, oil is trapped until its saturation on the coarse material side of the interface, exceeds an entry value. In the non-equilibrium case, the situation is different. Due to the Dynamic effects, oil may still flow into the fine material even after the saturation drops under the entry point, and this flow may continue for a certain amount of time that is proportional to the non-equilibrium effects. This suggests that operating in a Dynamic Regime reduces the account of oil trapped at interfaces, leading to an enhanced oil recovery. Finally, we present some numerical results supporting the theoretical findings. Keywords: Dynamic capillary pressure · immiscible flow · heterogeneity · trapping
