Game Theoretical Interactions of Moving Agents

Game theory has been one of the most successful quantitative concepts to describe social interactions, their strategical aspects, and outcomes. Among the payoff matrix quantifying the result of a social interaction, the interaction conditions have been varied, such as the number of repeated interactions, the number of interaction partners, the possibility to punish defective behavior etc. While an extension to spatial interactions has been considered early on such as in the "game of life", recent studies have focussed on effects of the structure of social interaction networks. However, the possibility of individuals to move and, thereby, evade areas with a high level of defection, and to seek areas with a high level of cooperation, has not been fully explored so far. This contribution presents a model combining game theoretical interactions with success-driven motion in space, and studies the consequences that this may have for the degree of cooperation and the spatio-temporal dynamics in the population. It is demonstrated that the combination of game theoretical interactions with motion gives rise to many self-organized behavioral patterns on an aggregate level, which can explain a variety of empirically observed social behaviors

A precise measurement of the magnetic field in the corona of the black hole binary V404 Cygni

Observations of binary stars containing an accreting black hole or neutron star often show x-ray emission extending to high energies (>10 kilo­–electron volts), which is ascribed to an accretion disk corona of energetic particles akin to those seen in the solar corona. Despite their ubiquity, the physical conditions in accretion disk coronae remain poorly constrained. Using simultaneous infrared, optical, x-ray, and radio observations of the Galactic black hole system V404 Cygni, showing a rapid synchrotron cooling event in its 2015 outburst, we present a precise 461 ± 12 gauss magnetic field measurement in the corona. This measurement is substantially lower than previous estimates for such systems, providing constraints on physical models of accretion physics in black hole and neutron star binary systems. This article has a correction. Please see: http://science.sciencemag.org/content/360/6386/eaat927

Erratum for the Report “A precise measurement of the magnetic field in the corona of the black hole binary V404 Cygni”

In the Report “A precise measurement of the magnetic field in the corona of the black hole binary V404 Cygni,” a calculation error led to values of the magnetic field that were about 14 times too high. The mathematical expressions given in the Report were correct, but the code used to calculate the numerical values included an extraneous factor, which led to incorrect results. The magnetic fields calculated from the observations at different wavelengths were all scaled by the same factor, so after this is removed they remain consistent with each other. The corrected value of the magnetic field is lower than previously calculated, making the field in V404 Cygni even more unlike those estimated for other systems. However, the lower magnetic field is no longer consistent with the value predicted from the equipartition model. The text, materials and methods, Table S1, and Figure S3 have been updated to reflect the corrected magnetic field values and to state that the system was not in equipartition. No other results or conclusions of the study were affected. The authors thank J. Malzac (Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse) for alerting them to this error

Sea-ice thickness and mass at Ice Station Belgica, Bellingshausen Sea, Antarctica

Ice Station Belgica was commenced in late winter 2007 in the Bellingshausen Sea as part of Sea Ice Mass Balance in Antarctica (SIMBA), an IPY 2007 cruise on the research vessel N.B. Palmer. A primary objective was to build on the work of previous Antarctic drift station experiments to geophysically characterize sea ice in terms of thickness, surface and ice bottom morphology, and ultimately area-unitized mass. A 24 day drift station was established at approximately 70°S and 93°W in mixed first-year and multi-year ice with three geophysical study sites selected on a 5 km2 floe. A comprehensive time series assessment of elevation-surveyed transects ranging from 100 m to 300 m in length included snow surface elevation, snow depth, electromagnetic (EM) profiling, and direct drilling for ice draft and ice freeboard. Additional work included a snow surface morphology characterization of a 100 m x 300 m area between the primary time series EM transects. Correlation of EM ice thicknesses with collocated drilled ice thickness yielded equations for the correction of EM underestimation of thick deformed ice, particularly at pressure ridges. Mean ice thickness from corrected EM was compared to isostatic ice thickness calculated from surface elevation, snow depth, ice freeboard and respective snow, slush, ice, and sea water densities. Results were consistent, with mean ice thicknesses for multi-year ice of 2.35 m, 2.34 m, and 2.41 m, with similar variance, for corrected EM, drilling, and buoyancy methods respectively. Additionally, a mean ice thickness of 2.31 m was calculated from ASPeCt observations of the ice field associated with the floe, using the method incorporating mean sail heights and fractional coverage of surface deformities or ridging. Temporal series assessment of ice freeboard indicated a slightly negative mean ice freeboard (<0.04 m), with clear evidence of new snow-ice formation from the freezing of slush. The three distinct snow and ice regions assessed on the Belgica floe had mean corrected EM ice thickness of 0.52 +/- 0.04 m (+/- 1 std. deviation), 0.92 +/- 0.17 m, and 2.35 +/- 1.37 m, and mean snow depths of 0.08 +/- 0.03 m, 0.36 +/- 0.09 m, and 0.68 +/- 0.31 m respectively. Each ice type represented a sizable fraction of the floe's total area (similar to 20%, 40%, and 40% respectively from visual estimates) reflecting a complex dynamic and thermodynamic history of formation, as well as the difficulty in characterizing even a single floe by a single class or mean value for thickness and snow depth. Implications of these results are discussed with regards to the resolution of satellite-based altimetry and snow depth products and efforts to generate and validate satellite sea ice and snow thickness products

The role of the atmospheric circulation in the record minimum extent of open water in the Ross Sea in the 2003 austral summer

The contribution of the atmospheric circulation to a record minimum extent of open water in the polar Ross Sea (RS) region in the 2003 austral summer is examined. Two major findings are reached in this study. The first is that the origins of this anomaly are more complex than previously thought, with an anomalous atmospheric circulation contributing at least as much to the lack of open water as damming of sea ice by a large iceberg known as C-19. Only in the western RS, where C-19 lay, is damming found to restrict open water in the spring of 2002 (October-December), but even here the coldest spring in the last 15 years extended the sea-ice formation season. Elsewhere in the RS the divergent northward ice drift that normally occurs widely reversed to southward in early spring and was then followed by negligible ice motion. The most anomalous springtime ice drift occurred in the central and eastern RS rather than near C-19 and was mirrored in the weakest southerly winds on record in central areas. The unusual southward ice drift in early spring 2002 caused widespread convergence and compaction of the normally thin and undeformed first-year ice along and north of the central and eastern Ross Ice Shelf (RIS). Compacted ice with few leads would have been slow to melt in the warmest summer (January-February) months. Direct observations also indicate that sea surface temperatures (SSTs) rapidly fell to freezing in the central and western RS in February 2003 supporting new ice formation. All the available data indicate these were due to the cold spring and the extensive, compact ice cover in the late spring of 2002 and in January 2003 preventing most of the incoming solar radiation from reaching the ocean. The second finding is that sea ice in the summer of 2003 would have been very extensive even if C-19 had not occurred. This is based on comparisons with other years of extensive summer ice, notably one when no large iceberg occurred. Ice motion and atmospheric circulation patterns in this case resembled those in the spring of 2002 and the summer of 2003. Evidence that the anomalous atmospheric circulation in the RS in the spring of 2002 was typical of El Niño events is also discussed

Sources and fluxes of dissolved iron in the Bellingshausen Sea (West Antarctica): The importance of sea ice, icebergs and the continental margin

This study was conducted to estimate the potential for natural iron fertilization in the Bellingshausen Sea, a remote region in the Pacific sector of the Southern Ocean. Seawater samples were collected during early austral spring 2007 near the continental margin, in the wake of an iceberg and near Peter I Island in order to identify and quantify Fe sources to the upper ocean. We concomitantly collected sea ice cores for Fe analysis during a time series sampling program on an ice floe. Looking at the upper 200m, our seawater data together with other published data suggest a large-scale exponential meridional decrease of DFe concentrations with increasing distance from the coastline noticeable up to 1400km to the north into the ACC. From this DFe gradient we estimated DFe fluxes into the upper mixed layer of the Bellingshausen Sea using a simple one-dimensional horizontal and vertical diffusion/advection model. We also estimated the melting input from sea ice and icebergs. DFe fluxes were compared for three biogeochemical provinces: ice covered continental shelf, marginal ice zone near the continental margin, and the open ocean. Fe in sea ice decreased with time enabling us to estimate a melt flux of 0.3μmol/m2/d DFe. We found that going from the continental shelf to the open ocean the dominant Fe fluxes gradually change from horizontal advection on the continental shelf (54% of a total DFe flux of 7.6±5.0μmol/m2/d) via sea ice melt in the pack ice near the continental margin (56% of a total DFe flux of 0.55±0.18μmol/m2/d) to vertical advection (58% of a total DFe flux of 0.038±0.027μmol/m2/d) in the ice free open ocean. A significant DFe flux of 0.6μmol/m2/d was estimated for iceberg melting, but this flux took place below the upper mixed layer and was not taken into further account. Fueling the high horizontal flux on the continental shelf is likely benthic diffusion and sediment resuspension. This is indicated by enhanced total dissolvable Fe (TD-Fe) and dissolved Fe (DFe) in the upper 200m close to Peter I Island, and near the seafloor at the other stations. Also mid-depth TD-Fe increases near the continental margin were observed.Comparison of estimates of biogenic Fe fixation (based on estimates for Southern Ocean carbon fixation) with the fluxes computed here, indicates an excess of new DFe input on the continental shelf and increasing Fe limitation going from the continental margin towards the open ocean.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Spring phytoplankton onset after the ice break-up and sea-ice signature (Adélie Land, East Antarctica)

The phytoplankton onset following the spring ice break-up in Adélie Land, East Antarctica, was studied along a short transect, from 400 m off the continent to 5 km offshore, during the austral summer of 2002. Eight days after the ice break-up, some large colonial and solitary diatom cells, known to be associated with land-fast ice and present in downward fluxes, were unable to adapt in ice-free waters, while some other solitary and short-colony forming taxa (e.g., Fragilariopsis curta, F. cylindrus) did develop. Pelagic species were becoming more abundant offshore, replacing the typical sympagic (ice-associated) taxa. Archaeomonad cysts, usually associated with sea ice, were recorded in the surface waters nearshore. Rough weather restricted the data set, but we were able to confirm that some microalgae may be reliable sea-ice indicators and that seeding by sea ice only concerns a few taxa in this coastal area of East Antarctica. Keywords: Ice break-up; phytoplankton; sea-ice signature; East Antarctica (Published: 10 January 2011) Citation: Polar Research 2011, 30, 5910, doi: 10.3402/polar.v30i0.591

The role of polynyas on the atmospheric budget of methane

info:eu-repo/semantics/inPres