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Keith Beven - One of the best experts on this subject based on the ideXlab platform.
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Validation and Equifinality
Simulation Foundations Methods and Applications, 2019Co-Authors: Keith BevenAbstract:In this chapter, the concept of Equifinality of model representations is discussed, from a background of model applications in the environmental sciences. Equifinality in this context is used to indicate that there may be many different model structures, parameter sets and auxiliary conditions that might appear to give equivalent output predictions or acceptable fits to any observation data available for use in model calibration. This does not imply that the resulting ensemble of models will give similar predictions when used to predict the future under some changed conditions. As new information becomes available to allow model validation, this can be used to constrain the ensemble of models within a Bayesian updating framework, although epistemic sources of uncertainty can make it difficult to define appropriate likelihood measures. It seems likely that the Equifinality concept will persist into the future in the form of ensembles of (stochastic) model runs being used to estimate prediction uncertainties. However, more research is needed into the limitations of model structures, information content of data sets subject to epistemic uncertainties and means of evaluating and validating models in the inexact sciences.
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comment on Equifinality of formal dream and informal glue bayesian approaches in hydrologic modeling by jasper a vrugt cajo j f ter braak hoshin v gupta and bruce a robinson
Stochastic Environmental Research and Risk Assessment, 2009Co-Authors: Keith BevenAbstract:Comment on “Equifinality of formal (DREAM) and informal (GLUE) Bayesian approaches in hydrologic modeling?” by Jasper A. Vrugt, Cajo J. F. ter Braak, Hoshin V. Gupta and Bruce A. Robinson
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Comment on “Equifinality of formal (DREAM) and informal (GLUE) Bayesian approaches in hydrologic modeling?” by Jasper A. Vrugt, Cajo J. F. ter Braak, Hoshin V. Gupta and Bruce A. Robinson
Stochastic Environmental Research and Risk Assessment, 2008Co-Authors: Keith BevenAbstract:Comment on “Equifinality of formal (DREAM) and informal (GLUE) Bayesian approaches in hydrologic modeling?” by Jasper A. Vrugt, Cajo J. F. ter Braak, Hoshin V. Gupta and Bruce A. Robinson
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A manifesto for the Equifinality thesis
Journal of Hydrology, 2005Co-Authors: Keith BevenAbstract:This essay discusses some of the issues involved in the identification and predictions of hydrological models given some calibration data. The reasons for the incompleteness of traditional calibration methods are discussed. The argument is made that the potential for multiple acceptable models as representations of hydrological and other environmental systems (the Equifinality thesis) should be given more serious consideration than hitherto. It proposes some techniques for an extended GLUE methodology to make it more rigorous and outlines some of the research issues still to be resolved.
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towards an alternative blueprint for a physically based digitally simulated hydrologic response modelling system
Hydrological Processes, 2002Co-Authors: Keith BevenAbstract:A critique of the Freeze and Harlan blueprint for a distributed physically based hydrological model leads to the conclusion that it will be abandoned. An alternative blueprint as a modelling methodology is proposed that explicitly recognises the potential for Equifinality in scale-dependent model representations. An inductive rather than deductive definition of physically-based is proposed that reflects the important role of observables in constraining the feasible models.
Ulrich Salzmann - One of the best experts on this subject based on the ideXlab platform.
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el nino southern oscillation pliocene climate and Equifinality
Philosophical Transactions of the Royal Society A, 2009Co-Authors: Sarah G Bonham, Alan M. Haywood, Daniel J. Lunt, Mathew Collins, Ulrich SalzmannAbstract:It has been suggested that, during the Pliocene ( ca 5–1.8 Ma), an El Nino state existed as a permanent rather than an intermittent feature; that is, the tropical Pacific Ocean was characterized by a much weaker east–west gradient than today. One line of inquiry used to investigate this idea relates modern El Nino teleconnections to Pliocene proxy data by comparing regional differences in precipitation and surface temperature with climate patterns associated with present-day El Nino events, assuming that agreement between Pliocene data and observations of modern El Nino events supports this interpretation. Here, we examine this assumption by comparing outputs from a suite of Mid-Pliocene climate simulations carried out with the UK Met Office climate model. Regional patterns of climate change associated with changes in model boundary conditions are compared with observed El Nino–Southern Oscillation teleconnection patterns. Our results indicate that many of the proposed ‘permanent El Nino’ surface temperature and precipitation patterns are observable in Mid-Pliocene climate simulations even when they display variability in tropical Pacific sea surface temperatures (SSTs) or when forced with a modern east–west SST gradient. Our experiments highlight the possibility that the same outcome may be achieved through different initial conditions (Equifinality); an important consideration for reconstructed patterns of regional Mid-Pliocene climate.
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El Niño–Southern Oscillation, Pliocene climate and Equifinality
Philosophical transactions. Series A Mathematical physical and engineering sciences, 2008Co-Authors: Sarah G Bonham, Alan M. Haywood, Daniel J. Lunt, Mathew Collins, Ulrich SalzmannAbstract:It has been suggested that, during the Pliocene ( ca 5–1.8 Ma), an El Nino state existed as a permanent rather than an intermittent feature; that is, the tropical Pacific Ocean was characterized by a much weaker east–west gradient than today. One line of inquiry used to investigate this idea relates modern El Nino teleconnections to Pliocene proxy data by comparing regional differences in precipitation and surface temperature with climate patterns associated with present-day El Nino events, assuming that agreement between Pliocene data and observations of modern El Nino events supports this interpretation. Here, we examine this assumption by comparing outputs from a suite of Mid-Pliocene climate simulations carried out with the UK Met Office climate model. Regional patterns of climate change associated with changes in model boundary conditions are compared with observed El Nino–Southern Oscillation teleconnection patterns. Our results indicate that many of the proposed ‘permanent El Nino’ surface temperature and precipitation patterns are observable in Mid-Pliocene climate simulations even when they display variability in tropical Pacific sea surface temperatures (SSTs) or when forced with a modern east–west SST gradient. Our experiments highlight the possibility that the same outcome may be achieved through different initial conditions (Equifinality); an important consideration for reconstructed patterns of regional Mid-Pliocene climate.
Philippe Archambault - One of the best experts on this subject based on the ideXlab platform.
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Absence of Equifinality of hand position in a double-step unloading task
Experimental Brain Research, 2010Co-Authors: Nahid Norouzi-gheidari, Philippe ArchambaultAbstract:Equifinality, during arm reaching movements, relates to the capacity of the neuromuscular system to attain the same final position in the presence or absence of transient perturbations. There have been several controversies regarding Equifinality in the literature. A brief elastic perturbation, applied during a fast arm movement or just before its initiation, typically does not affect final arm position. On the other hand, several experiments have shown that velocity-dependent perturbations, such as Coriolis force or negative damping, while transient in nature, have a significant effect on final arm position when compared to unperturbed movements. In this study, an unloading paradigm was used to study the role of reflexes with respect to Equifinality. The effects on final arm position of suddenly decreasing a static load maintained by fourteen subjects were analyzed. Subjects maintained an initial load produced by a double-joint manipulandum moving in the horizontal plane. The load was suddenly decreased, either in one or in two successive steps with different time intervals, resulting in a rapid reflex-mediated change in arm position. Unloading led to short-latency changes in the activity of shoulder and elbow muscles and significant variations in tonic activity. It was found that the final hand position was shorter for double- versus single-step unloading if the time between two successive changes in load was greater than 100 ms. With a shorter time interval, the final hand positions were the same. This difference in final hand positions was inversely proportional to the hand velocity at the time of the second change in load. Further, agonist/antagonist co-activation increased in double-step unloading. Thus, the change in both the load and the movement velocity may influence the magnitude of the unloading reflex. This may be indicative of a dependence of stretch reflexes on velocity. Perturbation may cause a reflex-mediated increase in joint stiffness, which could explain why Equifinality is not preserved after some perturbations, such as velocity-dependant external forces.
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Absence of Equifinality of hand position in a double-step unloading task
Experimental Brain Research, 2010Co-Authors: Nahid Norouzi-gheidari, Philippe ArchambaultAbstract:Equifinality, during arm reaching movements, relates to the capacity of the neuromuscular system to attain the same final position in the presence or absence of transient perturbations. There have been several controversies regarding Equifinality in the literature. A brief elastic perturbation, applied during a fast arm movement or just before its initiation, typically does not affect final arm position. On the other hand, several experiments have shown that velocity-dependent perturbations, such as Coriolis force or negative damping, while transient in nature, have a significant effect on final arm position when compared to unperturbed movements. In this study, an unloading paradigm was used to study the role of reflexes with respect to Equifinality. The effects on final arm position of suddenly decreasing a static load maintained by fourteen subjects were analyzed. Subjects maintained an initial load produced by a double-joint manipulandum moving in the horizontal plane. The load was suddenly decreased, either in one or in two successive steps with different time intervals, resulting in a rapid reflex-mediated change in arm position. Unloading led to short-latency changes in the activity of shoulder and elbow muscles and significant variations in tonic activity. It was found that the final hand position was shorter for double- versus single-step unloading if the time between two successive changes in load was greater than 100 ms. With a shorter time interval, the final hand positions were the same. This difference in final hand positions was inversely proportional to the hand velocity at the time of the second change in load. Further, agonist/antagonist co-activation increased in double-step unloading. Thus, the change in both the load and the movement velocity may influence the magnitude of the unloading reflex. This may be indicative of a dependence of stretch reflexes on velocity. Perturbation may cause a reflex-mediated increase in joint stiffness, which could explain why Equifinality is not preserved after some perturbations, such as velocity-dependant external forces.
Sarah G Bonham - One of the best experts on this subject based on the ideXlab platform.
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el nino southern oscillation pliocene climate and Equifinality
Philosophical Transactions of the Royal Society A, 2009Co-Authors: Sarah G Bonham, Alan M. Haywood, Daniel J. Lunt, Mathew Collins, Ulrich SalzmannAbstract:It has been suggested that, during the Pliocene ( ca 5–1.8 Ma), an El Nino state existed as a permanent rather than an intermittent feature; that is, the tropical Pacific Ocean was characterized by a much weaker east–west gradient than today. One line of inquiry used to investigate this idea relates modern El Nino teleconnections to Pliocene proxy data by comparing regional differences in precipitation and surface temperature with climate patterns associated with present-day El Nino events, assuming that agreement between Pliocene data and observations of modern El Nino events supports this interpretation. Here, we examine this assumption by comparing outputs from a suite of Mid-Pliocene climate simulations carried out with the UK Met Office climate model. Regional patterns of climate change associated with changes in model boundary conditions are compared with observed El Nino–Southern Oscillation teleconnection patterns. Our results indicate that many of the proposed ‘permanent El Nino’ surface temperature and precipitation patterns are observable in Mid-Pliocene climate simulations even when they display variability in tropical Pacific sea surface temperatures (SSTs) or when forced with a modern east–west SST gradient. Our experiments highlight the possibility that the same outcome may be achieved through different initial conditions (Equifinality); an important consideration for reconstructed patterns of regional Mid-Pliocene climate.
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El Niño–Southern Oscillation, Pliocene climate and Equifinality
Philosophical transactions. Series A Mathematical physical and engineering sciences, 2008Co-Authors: Sarah G Bonham, Alan M. Haywood, Daniel J. Lunt, Mathew Collins, Ulrich SalzmannAbstract:It has been suggested that, during the Pliocene ( ca 5–1.8 Ma), an El Nino state existed as a permanent rather than an intermittent feature; that is, the tropical Pacific Ocean was characterized by a much weaker east–west gradient than today. One line of inquiry used to investigate this idea relates modern El Nino teleconnections to Pliocene proxy data by comparing regional differences in precipitation and surface temperature with climate patterns associated with present-day El Nino events, assuming that agreement between Pliocene data and observations of modern El Nino events supports this interpretation. Here, we examine this assumption by comparing outputs from a suite of Mid-Pliocene climate simulations carried out with the UK Met Office climate model. Regional patterns of climate change associated with changes in model boundary conditions are compared with observed El Nino–Southern Oscillation teleconnection patterns. Our results indicate that many of the proposed ‘permanent El Nino’ surface temperature and precipitation patterns are observable in Mid-Pliocene climate simulations even when they display variability in tropical Pacific sea surface temperatures (SSTs) or when forced with a modern east–west SST gradient. Our experiments highlight the possibility that the same outcome may be achieved through different initial conditions (Equifinality); an important consideration for reconstructed patterns of regional Mid-Pliocene climate.
Nahid Norouzi-gheidari - One of the best experts on this subject based on the ideXlab platform.
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Absence of Equifinality of hand position in a double-step unloading task
Experimental Brain Research, 2010Co-Authors: Nahid Norouzi-gheidari, Philippe ArchambaultAbstract:Equifinality, during arm reaching movements, relates to the capacity of the neuromuscular system to attain the same final position in the presence or absence of transient perturbations. There have been several controversies regarding Equifinality in the literature. A brief elastic perturbation, applied during a fast arm movement or just before its initiation, typically does not affect final arm position. On the other hand, several experiments have shown that velocity-dependent perturbations, such as Coriolis force or negative damping, while transient in nature, have a significant effect on final arm position when compared to unperturbed movements. In this study, an unloading paradigm was used to study the role of reflexes with respect to Equifinality. The effects on final arm position of suddenly decreasing a static load maintained by fourteen subjects were analyzed. Subjects maintained an initial load produced by a double-joint manipulandum moving in the horizontal plane. The load was suddenly decreased, either in one or in two successive steps with different time intervals, resulting in a rapid reflex-mediated change in arm position. Unloading led to short-latency changes in the activity of shoulder and elbow muscles and significant variations in tonic activity. It was found that the final hand position was shorter for double- versus single-step unloading if the time between two successive changes in load was greater than 100 ms. With a shorter time interval, the final hand positions were the same. This difference in final hand positions was inversely proportional to the hand velocity at the time of the second change in load. Further, agonist/antagonist co-activation increased in double-step unloading. Thus, the change in both the load and the movement velocity may influence the magnitude of the unloading reflex. This may be indicative of a dependence of stretch reflexes on velocity. Perturbation may cause a reflex-mediated increase in joint stiffness, which could explain why Equifinality is not preserved after some perturbations, such as velocity-dependant external forces.
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Absence of Equifinality of hand position in a double-step unloading task
Experimental Brain Research, 2010Co-Authors: Nahid Norouzi-gheidari, Philippe ArchambaultAbstract:Equifinality, during arm reaching movements, relates to the capacity of the neuromuscular system to attain the same final position in the presence or absence of transient perturbations. There have been several controversies regarding Equifinality in the literature. A brief elastic perturbation, applied during a fast arm movement or just before its initiation, typically does not affect final arm position. On the other hand, several experiments have shown that velocity-dependent perturbations, such as Coriolis force or negative damping, while transient in nature, have a significant effect on final arm position when compared to unperturbed movements. In this study, an unloading paradigm was used to study the role of reflexes with respect to Equifinality. The effects on final arm position of suddenly decreasing a static load maintained by fourteen subjects were analyzed. Subjects maintained an initial load produced by a double-joint manipulandum moving in the horizontal plane. The load was suddenly decreased, either in one or in two successive steps with different time intervals, resulting in a rapid reflex-mediated change in arm position. Unloading led to short-latency changes in the activity of shoulder and elbow muscles and significant variations in tonic activity. It was found that the final hand position was shorter for double- versus single-step unloading if the time between two successive changes in load was greater than 100 ms. With a shorter time interval, the final hand positions were the same. This difference in final hand positions was inversely proportional to the hand velocity at the time of the second change in load. Further, agonist/antagonist co-activation increased in double-step unloading. Thus, the change in both the load and the movement velocity may influence the magnitude of the unloading reflex. This may be indicative of a dependence of stretch reflexes on velocity. Perturbation may cause a reflex-mediated increase in joint stiffness, which could explain why Equifinality is not preserved after some perturbations, such as velocity-dependant external forces.