Exploring the Benefits of Teams in Multiagent Learning

For problems requiring cooperation, many multiagent systems implement solutions among either individual agents or across an entire population towards a common goal. Multiagent teams are primarily studied when in conflict; however, organizational psychology (OP) highlights the benefits of teams among human populations for learning how to coordinate and cooperate. In this paper, we propose a new model of multiagent teams for reinforcement learning (RL) agents inspired by OP and early work on teams in artificial intelligence. We validate our model using complex social dilemmas that are popular in recent multiagent RL and find that agents divided into teams develop cooperative pro-social policies despite incentives to not cooperate. Furthermore, agents are better able to coordinate and learn emergent roles within their teams and achieve higher rewards compared to when the interests of all agents are aligned.Comment: 10 pages, 6 figures, Published at IJCAI 2022. arXiv admin note: text overlap with arXiv:2204.0747

Towards a Better Understanding of Learning with Multiagent Teams

While it has long been recognized that a team of individual learning agents can be greater than the sum of its parts, recent work has shown that larger teams are not necessarily more effective than smaller ones. In this paper, we study why and under which conditions certain team structures promote effective learning for a population of individual learning agents. We show that, depending on the environment, some team structures help agents learn to specialize into specific roles, resulting in more favorable global results. However, large teams create credit assignment challenges that reduce coordination, leading to large teams performing poorly compared to smaller ones. We support our conclusions with both theoretical analysis and empirical results.Comment: 15 pages, 11 figures, published at the International Joint Conference on Artificial Intelligence (IJCAI) in 202

Expansion of the Multi-Link Frontier™ Coronary Bifurcation Stent: Micro-Computed Tomographic Assessment in Human Autopsy and Porcine Heart Samples

BACKGROUND: Treatment of coronary bifurcation lesions remains challenging, beyond the introduction of drug eluting stents. Dedicated stent systems are available to improve the technical approach to the treatment of these lesions. However dedicated stent systems have so far not reduced the incidence of stent restenosis. The aim of this study was to assess the expansion of the Multi-Link (ML) Frontier™ stent in human and porcine coronary arteries to provide the cardiologist with useful in-vitro information for stent implantation and selection. METHODOLOGY/PRINCIPAL FINDINGS: Nine ML Frontier™ stents were implanted in seven human autopsy heart samples with known coronary artery disease and five ML Frontier™ stents were implanted in five porcine hearts. Proximal, distal and side branch diameters (PD, DD, SBD, respectively), corresponding opening areas (PA, DA, SBA) and the mean stent length (L) were assessed by micro-computed tomography (micro-CT). PD and PA were significantly smaller in human autopsy heart samples than in porcine heart samples (3.54±0.47 mm vs. 4.04±0.22 mm, p = 0.048; 10.00±2.42 mm(2) vs. 12.84±1.38 mm(2), p = 0.034, respectively) and than those given by the manufacturer (3.54±0.47 mm vs. 4.03 mm, p = 0.014). L was smaller in human autopsy heart samples than in porcine heart samples, although data did not reach significance (16.66±1.30 mm vs. 17.30±0.51 mm, p = 0.32), and significantly smaller than that given by the manufacturer (16.66±1.30 mm vs. 18 mm, p = 0.015). CONCLUSIONS/SIGNIFICANCE: Micro-CT is a feasible tool for exact surveying of dedicated stent systems and could make a contribution to the development of these devices. The proximal diameter and proximal area of the stent system were considerably smaller in human autopsy heart samples than in porcine heart samples and than those given by the manufacturer. Special consideration should be given to the stent deployment procedure (and to the follow-up) of dedicated stent systems, considering final intravascular ultrasound or optical coherence tomography to visualize (and if necessary optimize) stent expansion

Identification of Novel Genetic Loci Associated with Thyroid Peroxidase Antibodies and Clinical Thyroid Disease

Peer reviewe

Instantaneous Degradation of Nerve Agent Simulants using Zirconium-based Metal-organic Polyhedra

Metal-organic polyhedra (MOPs) are discrete molecules made of metal ions/clusters and organic ligands, and their crystal packing leads to the generation of intrinsic and extrinsic porosity. Due to their structural versatility, porosity, and nanoscale size, MOPs are considered an attractive platform for catalysis. In this study, we report for the first time the use of three zirconium(IV)-based MOPs for the degradation of trace concentrations of the nerve agent simulant, dimethyl 4-nitrophenyl phosphate (DMNP). All three MOPs degraded DMNP instantaneously, with half-lives ranging from t1/2 = 17 to 130 s. The catalytic activity of MOPs is thought to be due to (1) their periodic packing resulting in long-range order that creates extrinsic porosity, allowing DMNP to diffuse in and interact with the pore surface and Lewis acids (Zr(IV) centers) of MOPs, and (2) the lability of Zr-Cp (Cp = cyclopentadienyl) bond, allowing Cp ligands to rearrange and make space for DMNP to interact with the Zr(IV). The catalytic activity of MOPs is not deteriorated by increasing the concentration of the nerve agent simulant nor in consecutive catalytic experiments, highlighting their robustness as catalysts. Our study showcases the promise of MOPs as one of the fastest active catalysts for the instantaneous degradation of nerve agents

A 1500 year record of coastal sediment accumulation preserved in beach deposits at Keppel Bay, Queensland, Australia

The coastal plain formed by a series of relict beach ridges on the margin of Keppel Bay, central Queensland, Australia, preserves a detailed record of coastal sediment accumulation. Importantly, this record spans the historical period and extends back to early Holocene times, well before European settlement. The relict and modern beach ridges comprise fine sand that was originally deposited in Keppel Bay during flood discharge events of the Fitzroy River. This sediment was then reworked onto the shoreline by the prevailing tide, wave and wind-generated currents. Optically stimulated luminescence (OSL) ages of the ridges reveal a long-term positive coastal sediment budget in Keppel Bay and show that during approximately the last 1500 years, sets of beach ridges were emplaced in rapid episodes, up to a few decades long. The OSL ages of the ridges suggests there is a 500-200 yr periodicity to these phases of rapid sediment accumulation. Our preliminary interpretation of these data is that this pattern of formation relates to the recurrence interval of high magnitude flood discharge events of the Fitzroy River and there has been a general decline in the rate at which sediment has accumulated on the Keppel Bay coast during the last 1500 years. This reduction may reflect a long-term decline in major rainfall events in the Fitzroy River catchment. The trace element composition of ridges deposited during the last 100 yrs indicates there has been a greater contribution from areas of basaltic soils within the catchment. This trace-element record reveals the impact on river and coastal sediment composition brought on by changes in catchment land use

Impact of Platinum Primary Particle Loading on Fuel Cell Performance: Insights from Catalyst/Ionomer Ink Interactions.

A variety of electrochemical energy conversion technologies, including fuel cells, rely on solution-processing techniques (via inks) to form their catalyst layers (CLs). The CLs are heterogeneous structures, often with uneven ion-conducting polymer (ionomer) coverage and underutilized catalysts. Various platinum-supported-on-carbon colloidal catalyst particles are used, but little is known about how or why changing the primary particle loading (PPL, or the weight fraction of platinum of the carbon-platinum catalyst particles) impacts performance. By investigating the CL gas-transport resistance and zeta (ζ)-potentials of the corresponding inks as a function of PPL, a direct correlation between the CL high current density performance and ink ζ-potential is observed. This correlation stems from likely changes in ionomer distributions and catalyst-particle agglomeration as a function of PPL, as revealed by pH, ζ-potential, and impedance measurements. These findings are critical to unraveling the ionomer distribution heterogeneity in ink-based CLs and enabling enhanced Pt utilization and improved device performance for fuel cells and related electrochemical devices

The CO2CRC Otway shallow CO2 controlled release experiment: Preparation or Phase 2

CO2CRC and its partners are undertaking a feasibility study for a planned CO2 controlled release and monitoring experiment on a shallow fault at the CO2CRC Otway Research Facility. In this project we plan to image, using a diverse range of geophysical and geochemical CO2 monitoring techniques, the migration of CO2 up a fault from a controlled release point at approximately 30 m depth. This paper describes the results of site characterisation and modelling work undertaken to date. It also includes a description of the activities planned that will enable for a more detailed characterization of the fault and proposed injection interval. Together these results will enable an assessment as to whether the planned injection experiment is feasible and how it can be optimally designed