34 research outputs found
Quantifying Eulerian Eddy Leakiness in an Idealized Model
An idealized eddyâresolving ocean basin, closely resembling the North Pacific Ocean, is simulated using MITgcm. We identify rotationally coherent Lagrangian vortices (RCLVs) and sea surface height (SSH) eddies based on the Lagrangian and Eulerian framework, respectively. General statistical results show that RCLVs have a much smaller coherent core than SSH eddies with the ratio of radius is about 0.5. RCLVs are often enclosed by SSH anomaly contours, but SSH eddy identification method fails to detect more than half of RCLVs. Based on their locations, two types of eddies are classified into three categories: overlapping RCLVs and SSH eddies, nonoverlapping SSH eddies, and nonoverlapping RCLVs. Using Lagrangian particles, we examine the processes of leakage and intrusion around SSH eddies. For overlapping SSH eddies, over the lifetime, the material coherent core only accounts for about 25% and about 50% of initial water leak from eddy interior. The remaining 25% of water can still remain inside the boundary, but only in the form of filaments outside the coherent core. For nonoverlapping SSH eddies, more water leakage (about 60%) occurs at a faster rate. Guided by the number and radius of SSH eddies, fixed circles and moving circles are randomly selected to diagnose the material flux around these circles. We find that the leakage and intrusion trends of moving circles are quite similar to that of nonoverlapping SSH eddies, suggesting that the material coherence properties of nonoverlapping SSH eddies are not significantly different from random pieces of ocean with the same size
Quantifying Eulerian Eddy Leakiness in an Idealized Model
An idealized eddyâresolving ocean basin, closely resembling the North Pacific Ocean, is simulated using MITgcm. We identify rotationally coherent Lagrangian vortices (RCLVs) and sea surface height (SSH) eddies based on the Lagrangian and Eulerian framework, respectively. General statistical results show that RCLVs have a much smaller coherent core than SSH eddies with the ratio of radius is about 0.5. RCLVs are often enclosed by SSH anomaly contours, but SSH eddy identification method fails to detect more than half of RCLVs. Based on their locations, two types of eddies are classified into three categories: overlapping RCLVs and SSH eddies, nonoverlapping SSH eddies, and nonoverlapping RCLVs. Using Lagrangian particles, we examine the processes of leakage and intrusion around SSH eddies. For overlapping SSH eddies, over the lifetime, the material coherent core only accounts for about 25% and about 50% of initial water leak from eddy interior. The remaining 25% of water can still remain inside the boundary, but only in the form of filaments outside the coherent core. For nonoverlapping SSH eddies, more water leakage (about 60%) occurs at a faster rate. Guided by the number and radius of SSH eddies, fixed circles and moving circles are randomly selected to diagnose the material flux around these circles. We find that the leakage and intrusion trends of moving circles are quite similar to that of nonoverlapping SSH eddies, suggesting that the material coherence properties of nonoverlapping SSH eddies are not significantly different from random pieces of ocean with the same size
Diagnostics of coherent eddy transport in the South China Sea based on satellite observations
The large discrepancy between Eulerian and Lagrangian work motivates us to examine the leakage of Eulerian eddies and quantify the contribution of coherent eddy transport in the South China Sea (SCS). In this study, Lagrangian particles with a resolution of 1/32° are advected by surface geostrophic currents derived from satellite observations spanning 23 years, and two types of methods are employed to identify sea surface height (SSH) eddies and Lagrangian coherent structures. SSH eddies are proven to be highly leaky during their lifetimes, with more than 80% of the original water leaking out of the eddy interior. As a result of zonal and meridional eddy propagation, the leaked water exhibits a spatial pattern of asymmetry relative to the eddy center. The degree of eddy leakage is found to be independent of several eddy parameters including the nonlinearity parameter U/c, which has been commonly used to assess eddy coherency. Finally, the Lagrangian coherent structures in the SCS are diagnosed and the associated coherent eddy diffusivity is calculated. It is found that coherent eddies contribute to less than 5% of the total eddy material transport in both zonal and meridional directions. These findings suggest that previous studies based on the Eulerian framework significantly overestimate the contribution of coherent eddy transport in the SCS
Agent-Aware Training for Agent-Agnostic Action Advising in Deep Reinforcement Learning
Action advising endeavors to leverage supplementary guidance from expert
teachers to alleviate the issue of sampling inefficiency in Deep Reinforcement
Learning (DRL). Previous agent-specific action advising methods are hindered by
imperfections in the agent itself, while agent-agnostic approaches exhibit
limited adaptability to the learning agent. In this study, we propose a novel
framework called Agent-Aware trAining yet Agent-Agnostic Action Advising (A7)
to strike a balance between the two. The underlying concept of A7 revolves
around utilizing the similarity of state features as an indicator for
soliciting advice. However, unlike prior methodologies, the measurement of
state feature similarity is performed by neither the error-prone learning agent
nor the agent-agnostic advisor. Instead, we employ a proxy model to extract
state features that are both discriminative (adaptive to the agent) and
generally applicable (robust to agent noise). Furthermore, we utilize behavior
cloning to train a model for reusing advice and introduce an intrinsic reward
for the advised samples to incentivize the utilization of expert guidance.
Experiments are conducted on the GridWorld, LunarLander, and six prominent
scenarios from Atari games. The results demonstrate that A7 significantly
accelerates the learning process and surpasses existing methods (both
agent-specific and agent-agnostic) by a substantial margin. Our code will be
made publicly available
Is Centralized Training with Decentralized Execution Framework Centralized Enough for MARL?
Centralized Training with Decentralized Execution (CTDE) has recently emerged
as a popular framework for cooperative Multi-Agent Reinforcement Learning
(MARL), where agents can use additional global state information to guide
training in a centralized way and make their own decisions only based on
decentralized local policies. Despite the encouraging results achieved, CTDE
makes an independence assumption on agent policies, which limits agents to
adopt global cooperative information from each other during centralized
training. Therefore, we argue that existing CTDE methods cannot fully utilize
global information for training, leading to an inefficient joint-policy
exploration and even suboptimal results. In this paper, we introduce a novel
Centralized Advising and Decentralized Pruning (CADP) framework for multi-agent
reinforcement learning, that not only enables an efficacious message exchange
among agents during training but also guarantees the independent policies for
execution. Firstly, CADP endows agents the explicit communication channel to
seek and take advices from different agents for more centralized training. To
further ensure the decentralized execution, we propose a smooth model pruning
mechanism to progressively constraint the agent communication into a closed one
without degradation in agent cooperation capability. Empirical evaluations on
StarCraft II micromanagement and Google Research Football benchmarks
demonstrate that the proposed framework achieves superior performance compared
with the state-of-the-art counterparts. Our code will be made publicly
available
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The dependence of upper ocean gyres on wind and buoyancy forcing
A series of numerical simulations with different forcing conditions are carried out, to investigate the roles played by buoyancy and wind forcing on the upper ocean gyres, and to contrast the laminar and eddying regimes. Model experiments show that the buoyancy-driven eastward geostrophic flow tends to suppress the formation of the wind-driven subpolar gyre, but the northward eddy heat transport can homogenize the subpolar water and reduce the meridional temperature gradient by about two-third, thus counteracting the buoyancy effect and saving the subpolar gyre. For the subtropical gyre, its transport is enhanced by eddy mixing, and the role of buoyancy forcing is very sensitive to the choice of diapycnal diffusivity. Our results suggest that eddy effects must be considered in the dynamics of the subpolar gyre, and vertical diffusivity should be selected carefully in simulating the basin-wide circulations
Contrastive Identity-Aware Learning for Multi-Agent Value Decomposition
Value Decomposition (VD) aims to deduce the contributions of agents for
decentralized policies in the presence of only global rewards, and has recently
emerged as a powerful credit assignment paradigm for tackling cooperative
Multi-Agent Reinforcement Learning (MARL) problems. One of the main challenges
in VD is to promote diverse behaviors among agents, while existing methods
directly encourage the diversity of learned agent networks with various
strategies. However, we argue that these dedicated designs for agent networks
are still limited by the indistinguishable VD network, leading to homogeneous
agent behaviors and thus downgrading the cooperation capability. In this paper,
we propose a novel Contrastive Identity-Aware learning (CIA) method, explicitly
boosting the credit-level distinguishability of the VD network to break the
bottleneck of multi-agent diversity. Specifically, our approach leverages
contrastive learning to maximize the mutual information between the temporal
credits and identity representations of different agents, encouraging the full
expressiveness of credit assignment and further the emergence of
individualities. The algorithm implementation of the proposed CIA module is
simple yet effective that can be readily incorporated into various VD
architectures. Experiments on the SMAC benchmarks and across different VD
backbones demonstrate that the proposed method yields results superior to the
state-of-the-art counterparts. Our code is available at
https://github.com/liushunyu/CIA
Diagnostics of Coherent Eddy Transport in the South China Sea Based on Satellite Observations
The large discrepancy between Eulerian and Lagrangian work motivates us to examine the leakage of Eulerian eddies and quantify the contribution of coherent eddy transport in the South China Sea (SCS). In this study, Lagrangian particles with a resolution of 1/32° are advected by surface geostrophic currents derived from satellite observations spanning 23 years, and two types of methods are employed to identify sea surface height (SSH) eddies and Lagrangian coherent structures. SSH eddies are proven to be highly leaky during their lifetimes, with more than 80% of the original water leaking out of the eddy interior. As a result of zonal and meridional eddy propagation, the leaked water exhibits a spatial pattern of asymmetry relative to the eddy center. The degree of eddy leakage is found to be independent of several eddy parameters including the nonlinearity parameter U/c, which has been commonly used to assess eddy coherency. Finally, the Lagrangian coherent structures in the SCS are diagnosed and the associated coherent eddy diffusivity is calculated. It is found that coherent eddies contribute to less than 5% of the total eddy material transport in both zonal and meridional directions. These findings suggest that previous studies based on the Eulerian framework significantly overestimate the contribution of coherent eddy transport in the SCS
Characteristics of Mesoscale Eddies in the Vicinity of the Kuroshio: Statistics from Satellite Altimeter Observations and OFES Model Data
Mesoscale eddies propagate westward in the northwestern Pacific Ocean and interact with the Kuroshio in the vicinity of the western boundary of the ocean. However, the processes affecting the eddy properties and the detailed structure of the eddies when they encounter the Kuroshio remain unclear. In this study, we analyze the statistics of the eddy properties around the Kuroshio using 25 years of satellite altimeter data and the eddy-resolving OFES model product. The spatial compositions of the eddies in the northwestern Pacific show that, as the eddies propagate westward, their radius and amplitude decrease sharply when they approach the Kuroshio region. The radius, amplitude, and kinetic energy of the eddies reaching the Kuroshio region decay much faster during their lifespan compared with the eddies in the interior of the Pacific Ocean. Furthermore, the three-dimensional structure of the eddies obtained from the OFES model data shows that the maximum temperature anomalies in the cyclonic and anticyclonic eddies occur at ~300 m, and the maximum depth reduces as a result of the interaction between the eddies and the main Kuroshio current
The relationship between body mass index and clinical efficacy of knee arthroplasty in patients with knee osteoarthritis
Background: Increase body mass index (BMI) is often accompanied by metabolic diseases such as diabetes, which will increase the uncertainty of total knee arthroplasty (TKA) efficacy and the risk of postoperative complications. The present study was to study the relationship between increase BMI and clinical efficacy of knee arthroplasty in patients with knee osteoarthritis. Methods: A total of 97 patients (36 males and 61 females) with knee osteoarthritis (KOA) who underwent TKA surgery were selected. According to the preoperative body mass index (BMI), the patients were divided into a normal group (n=42), overweight group (n=35), and obese group (n=20). All patients received TKA after admission. Seven days after surgery, the American Knee Society (AKS) and the Hospital for Special Surgery (HSS) scales were used to evaluate the recovery of knee function. The recovery was poor if the scores of AKS and HSS were less than 70. Results: Seven days after TKA, the scores of AKS and HSS in different BMI groups were significantly different, and decreased with the increase of BMI (P<0.05). Age, increased BMI, diabetes, preoperative range of motion (ROM), intraoperative blood loss, postoperative C-reactive protein (CRP), postoperative posterior slope angle (PSA), postoperative infection, and postoperative deep vein thrombosis (DVT) of lower extremities were related to AKS score <70 (P<0.05). Diabetes, preoperative ROM, intraoperative blood loss, postoperative CRP, postoperative PSA, and postoperative infection were related to HSS score <70 (P<0.05). Increased BMI, diabetes, postoperative CRP, postoperative infection, and postoperative DVT were independent risk factors for AKS score <70 (HR =3.458, 1.152, 2.960, 1.023, 3.589, P<0.05). Increased BMI, diabetes, postoperative CRP, and postoperative infection were independent risk factors for HSS score <70 (HR =6.891, 1.263, 1.967, 1.235, P<1.235). The area under the curve (AUC) (95% CI) of BMI in diagnosing AKS <70 was 0.740 (0.641-0.839). The AUC (95% CI) of BMI in diagnosing HSS <70 was 0.809 (0.723-0.894). Conclusions: The increase of BMI is an independent risk factor for the poor recovery of knee function after TKA in with KOA