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18 results on '"Stern, Alon"'

1. A Negotiating Strategy for a Hybrid Goal Function in Multilateral Negotiation

Author

Stern, Alon, Kraus, Sarit, and Sarne, David

Subjects
Computer Science - Multiagent Systems
Abstract

In various multi-agent negotiation settings, a negotiator's utility depends, either partially or fully, on the sum of negotiators' utilities (i.e., social welfare). While the need for effective negotiating-agent designs that take into account social welfare has been acknowledged in recent work, and even established as a category in automated negotiating agent competitions, very few designs have been proposed to date. In this paper, we present the design principles and results of an extensive evaluation of agent HerbT+, a negotiating agent aiming to maximize a linear tradeoff between individual and social welfare. Our evaluation framework relies on the automated negotiating agents competition (ANAC) and includes a thorough comparison of performance with the top 15 agents submitted between 2015-2018 based on negotiations involving 63 agents submitted to these competitions. We find that, except for a few minor exceptions, when social-welfare plays a substantial role in the agent's goal function, our agent outperforms all other tested designs.

Published
2022

3. On the representation of capsizing in iceberg models

Author

Wagner, Till J. W., Stern, Alon A., Dell, Rebecca W., and Eisenman, Ian

Subjects
Physics - Atmospheric and Oceanic Physics
Abstract

Although iceberg models have been used for decades, they have received far more widespread attention in recent years, in part due to efforts to explicitly represent icebergs in climate models. This calls for increased scrutiny of all aspects of typical iceberg models. An important component of iceberg models is the representation of iceberg capsizing, or rolling. Rolling occurs spontaneously when the ratio of iceberg width to height falls below a critical threshold. Here we examine previously proposed representations of this threshold, and we find that there have been crucial errors in the representation of rolling in many modeling studies to date. We correct these errors and identify an accurate model representation of iceberg rolling. Next, we assess how iceberg rolling influences simulation results in a hierarchy of models. Rolling is found to substantially prolong the lifespan of individual icebergs and allow them to drift farther offshore, although it is found to have relatively small impacts on the large-scale freshwater distribution in comprehensive model simulations. The results suggest that accurate representations of iceberg rolling may be of particular importance for operational forecast models of iceberg drift, as well as for regional changes in high-resolution climate model simulations., Comment: 12 pages, 7 figures

Published
2017
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4. On the representation of capsizing in iceberg models

Author

Wagner, Till JW, Stern, Alon A, Dell, Rebecca W, and Eisenman, Ian

Subjects
Climate Action, Icebergs, Capsizing, Meltwater, Stability, Modelling, Oceanography, Maritime Engineering
Abstract

Although iceberg models have been used for decades, they have received far more widespread attention in recent years, due in part to efforts to explicitly represent icebergs in climate models. This calls for increased scrutiny of all aspects of typical iceberg models. An important component of iceberg models is the representation of iceberg capsizing, or rolling. Rolling occurs spontaneously when the ratio of iceberg width to height falls below a critical threshold. Here we examine previously proposed representations of this threshold, and we find that there have been crucial flaws in the representation of rolling in many modeling studies to date. We correct these errors and identify an accurate model representation of iceberg rolling. Next, we assess how iceberg rolling influences simulation results in a hierarchy of models. Rolling is found to substantially prolong the lifespan of individual icebergs and allow them to drift farther offshore. However, rolling occurs only after large icebergs have lost most of their initial volume, and it thus has a relatively small impact on the large-scale freshwater distribution in comprehensive model simulations. The results suggest that accurate representations of iceberg rolling may be of particular importance for operational forecast models of iceberg drift, as well as for regional changes in high-resolution climate model simulations.

Published
2017

6. Journey of an Arctic Ice Island

Author

Crawford, Anna J., Wadhams, Peter, Wagner, Till J.W., Stern, Alon, Abrahamsen, E. Povl, Church, Ian, Bates, Richard, and Nicholls, Keith W.

Published
2016

11. Wind-driven upwelling around grounded tabular icebergs

Author

Stern, Alon, Johnson, Eric, Wagner, Till, Holland, David, Wadhams, Peter, Bates, C. Richard, Abrahamsen, Povl, Nicholls, Keith, Crawford, Anna, Gagnon, Jonathan, Tremblay, Jean-Eric, University of St Andrews. Earth and Environmental Sciences, University of St Andrews. Centre for Ancient Environmental Studies, University of St Andrews. Marine Alliance for Science & Technology Scotland, University of St Andrews. Scottish Oceans Institute, University of St Andrews. St Andrews Sustainability Institute, and University of St Andrews. School of Geography & Sustainable Development

Subjects
GC, Upwelling, Ekman, NDAS, GC Oceanography, Iceberg
Abstract

Funding was provided by NSF Polar Programs - Grant Number: ARC-1304137. Temperature and salinity data collected around grounded tabular icebergs in Baffin Bay in 2011, 2012 and 2013 indicate wind-induced upwelling at certain locations around the icebergs. These data suggest that along one side of the iceberg, wind forcing leads to Ekman transport away from the iceberg, which causes upwelling of the cool saline water from below. The upwelling water mixes with the water in the thermocline, causing the mixed layer to become cooler and more saline. Along the opposite side of the iceberg, the surface Ekman transport moves towards the iceberg, which causes a sharpening of the thermocline as warm fresh water is trapped near the surface. This results in higher mixed layer temperatures and lower mixed layer salinities on this side of the iceberg. Based on these in situ measurements, we hypothesize that the asymmetries in water properties around the iceberg, caused by the opposing effects of upwelling and sharpening of the thermocline, lead to differential deterioration around the iceberg. Analysis of satellite imagery around iceberg PII-B-1 over a six month monitoring period reveals differential decay around the iceberg, in agreement with this mechanism. Publisher PDF

Published
2015

12. Wind-driven upwelling around grounded tabular icebergs

Author

Stern, Alon A., Johnson, Eric, Holland, David M., Wagner, Till J.W., Wadhams, Peter, Bates, Richard, Abrahamsen, E. Povl, Nicholls, Keith W., Crawford, Anna, Gagnon, Jonathan, and Tremblay, Jean-Eric

Abstract

Temperature and salinity data collected around grounded tabular icebergs in Baffin Bay in 2011, 2012, and 2013 indicate wind-induced upwelling at certain locations around the icebergs. These data suggest that along one side of the iceberg, wind forcing leads to Ekman transport away from the iceberg, which causes upwelling of the cool saline water from below. The upwelling water mixes with the water above the thermocline, causing the mixed layer to become cooler and more saline. Along the opposite side of the iceberg, the surface Ekman transport moves towards the iceberg, which causes a sharpening of the thermocline as warm fresh water is trapped near the surface. This results in higher mixed layer temperatures and lower mixed layer salinities on this side of the iceberg. Based on these in situ measurements, we hypothesize that the asymmetries in water properties around the iceberg, caused by the opposing effects of upwelling and sharpening of the thermocline, lead to differential deterioration around the iceberg. Analysis of satellite imagery around iceberg PII-B-1 reveals differential decay around the iceberg, in agreement with this mechanism.

Published
2015

14. Wind‐driven upwelling around grounded tabular icebergs

Author

Stern, Alon A., primary, Johnson, Eric, additional, Holland, David M., additional, Wagner, Till J.W., additional, Wadhams, Peter, additional, Bates, Richard, additional, Abrahamsen, E. Povl, additional, Nicholls, Keith W., additional, Crawford, Anna, additional, Gagnon, Jonathan, additional, and Tremblay, Jean‐Eric, additional

Published
2015
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16. The 'footloose' mechanism: iceberg decay from hydrostatic stresses

Author

Wagner, Till J.W., Wadhams, Peter, Bates, Richard, Elosegui, Pedro, Stern, Alon, Vella, Dominic, Abrahamsen, E. Povl, Crawford, Anna, Nicholls, Keith W., Wagner, Till J.W., Wadhams, Peter, Bates, Richard, Elosegui, Pedro, Stern, Alon, Vella, Dominic, Abrahamsen, E. Povl, Crawford, Anna, and Nicholls, Keith W.

Abstract

We study a mechanism of iceberg breakup that may act together with the recognized melt and wave-induced decay processes. Our proposal is based on observations from a recent field experiment on a large ice island in Baffin Bay, East Canada. We observed that successive collapses of the overburden from above an unsupported wavecut at the iceberg waterline created a submerged foot fringing the berg. The buoyancy stresses induced by such a foot may be sufficient to cause moderate-sized bergs to break off from the main berg. A mathematical model is developed to test the feasibility of this mechanism. The results suggest that once the foot reaches a critical length, the induced stresses are sufficient to cause calving. The theoretically predicted maximum stable foot length compares well to the data collected in situ. Further, the model provides analytical expressions for the previously observed “rampart-moat” iceberg surface profiles.

Published
2014

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