Evolution and Walrasian Behavior in Market Games

We revisit the question of price formation in general equilibrium theory. We explore whether evolutionary forces lead to Walrasian equilibrium in the context of a market game, introduced by Shubik (1972). Market games have Pareto inferior (strict) Nash equilibria, in which some, and possibly all, markets are closed. We introduce a strong version of evolutionary stable strategies (SESS) for finite populations. Our concept requires stability against multiple, simultaneous mutations. We show that the introduction of a small number of ``trading mutants'' is sufficient for Pareto improving trade to be generated. Provided that agents lack market power, Nash equilibria corresponding to approximate Walrasian equilibria constitute the only approximate SESS.

Upper Bounds for the Hausdorff Dimension of Weierstrass Curves

We produce an upper bound for the Hausdorff dimension of the graph of a Weierstrass-type function. Whilst strictly weaker than existing results, it has the advantage of being directly computable from the theory of hyperbolic iterated function systems (IFS)

Preparing business students for workplace reality: using global virtual teams in logistics and SCM education

Purpose: This paper presents and examines the use and effects of global virtual teams as a tool in the logistics and supply chain management classroom to prepare students in a simulation environment for the demands of their future careers in the profession. Design/methodology/approach: Literature of logistics and supply chain management education is combined with streams from management learning literature. The way the tool of global virtual teams was applied is explained, followed by an analysis of quantitative and qualitative participant response data. From the data analysis the effects of individual factors in the design and application of the global virtual team are isolated and recommendations are extracted for future use of the tool. Findings: The paper finds that the application of global virtual teams helped participating students to develop the management skills required for a career in logistics and supply chain management. Although students perceived the international nature and the lose frame provided by the tool as challenges, most learning effects were caused by these challenges. The paper also shows that the set up by the involved educators is crucial for the learning effect in particular towards similar weights of the assessments and the number of group members from each geographical area. Research limitations/implications: The paper does not examine all potentially amendable factors but focusses on those that were seen as relevant and practically achievable under the available resources to ensure the tool can be easily scaled up by adding further institutions and participants. Originality/value: The paper is the first application of global virtual teams in logistics and supply chain management education. It provides the theoretical foundations and rationale for its application and is relevant to educators by giving them access to this tool for improvement of their students’ career preparedness

On representations of Gal(Q‾/Q)\mathrm{Gal}(\overline{\mathbb{Q}}/\mathbb{Q}), GT^\widehat{GT} and Aut(F^2)\mathrm{Aut}(\hat{F}_2)

By work of Belyi, the absolute Galois group $G_{\mathbb{Q}}=\mathrm{Gal}(\overline{\mathbb{Q}}/\mathbb{Q})$ of the field $\mathbb{Q}$ of rational numbers can be embedded into $A=\mathrm{Aut}(\widehat{F_2})$, the automorphism group of the free profinite group $\widehat{F_2}$ on two generators. The image of $G_{\mathbb{Q}}$ lies inside $\widehat{GT}$, the Grothendieck-Teichm\"uller group. While it is known that every abelian representation of $G_{\mathbb{Q}}$ can be extended to $\widehat{GT}$, Lochak and Schneps put forward the challenge of constructing irreducible non-abelian representations of $\widehat{GT}$. We do this virtually, namely by showing that a rich class of arithmetically defined representations of $G_{\mathbb{Q}}$ can be extended to finite index subgroups of $\widehat{GT}$. This is achieved, in fact, by extending these representations all the way to finite index subgroups of $A=\mathrm{Aut}(\widehat{F_2})$. We do this by developing a profinite version of the work of Grunewald and Lubotzky, which provided a rich collection of representations for the discrete group $\mathrm{Aut}(F_d)$.Comment: 19 pages; some typos were fixe

Pulsar Nulling and Vacuum Radio Emission from Axion Clouds

Non-relativistic axions can be efficiently produced in in the polar caps of pulsars, resulting in the formation of a dense cloud of gravitationally bound axions. Here, we investigate the interplay between such an axion cloud and the electrodynamics in the pulsar magnetosphere, focusing specifically on the dynamics in the polar caps, where the impact of the axion cloud is expected to be most pronounced. For sufficiently light axions $m_a \lesssim 10^{-7}$ eV, we show that the axion cloud can occasionally screen the local electric field responsible for particle acceleration and pair production, inducing a periodic nulling of the pulsar's intrinsic radio emission. At larger axion masses, the small-scale fluctuations in the axion field tend to suppress the back-reaction of the axion on the electrodynamics; however, we point out that the incoherent oscillations of the axion in short-lived regions of vacuum near the neutron star surface can produce a narrow radio line, which provides a complementary source of radio emission to the plasma-resonant emission processes identified in previous work. While this work focuses on the leading order correction to pair production in the magnetosphere, we speculate that there can exist dramatic deviations in the electrodynamics of these systems when the axion back-reaction becomes non-linear.Comment: v1: 6 pages, 1 figure, Supplementary Material (7 pages

Deep cover bleeder entry performance and support loading: A case study

Several questions have emerged in relation to deep cover bleeder entry performance and support loading: how well do current modeling procedures calculate the rear abutment extent and loading? Does an improved understanding of the rear abutment extent warrant a change in standing support in bleeder entries? To help answer these questions and to determine the current utilization of standing support in bleeder entries, four bleeder entries at varying distances from the startup room were instrumented, observed, and numerically modeled. This paper details observations made by NIOSH researchers in the bleeder entries of a deep cover longwall panel—specifically data collected from instrumented pumpable cribs, observations of the conditions of the entries, and numerical modeling of the bleeder entries during longwall extraction. The primary focus was on the extent and magnitude of the abutment loading expe- rienced by the standing support. As expected, the instrumentation of the standing supports showed very little loading relative to the capacity of the standing supports—less than 23 Mg load and 2.54 cm conver- gence. The Flac3D program was used to evaluate these four bleeder entries using previously defined mod- eling and input parameter estimation procedures. The results indicated only a minor increase in load during the extraction of the longwall panel. The model showed a much greater increase in stress due to the development of the gateroad and bleeder entries, with about 80% of the increase associated with development and 20% with longwall extraction. The Flac3D model showed very good correlation between expected gateroad loading during panel extraction and that expected based on previous studies. The results of this study showed that the rear abutment stress experienced by this bleeder entry design was minimal. The farther away from the startup room, the lower the applied load and smaller the con- vergence in the entry if all else is held constant. Finally, the numerical modeling method used in this study was capable of replicating the expected and measured results near seam

Effects of a Hazing-Light System on Migration and Collision Avoidance of Eiders at an Artificial Oil-Production Island, Arctic Alaska

During migration, Common and King Eiders (Somateria mollissima and S. spectabilis) cross the Beaufort and Chukchi Seas of Arctic Alaska. Because they may become attracted to lights, eiders are susceptible to collision with structures, including offshore oil facilities. We used ornithological radar in 2001 – 04 to characterize the behavior of eiders migrating past Northstar Island, an oil-production island near Prudhoe Bay, Alaska, and to assess the effects of a hazing-light system on migrating eiders. “Eider” radar targets exhibited pulsed, irregular periods of movement; movement rates were higher when sea ice was present, without precipitation, and during tailwinds and crosswinds but were not affected by lights. Velocities (ground speeds) were higher when ice was present and with strong tailwinds. They were lower at night when the lights were on, but higher during the day when the lights were on. Radar targets exhibited little variation in flight behavior as they passed the island; the proportion of non-directional behavior was larger when ice was present, with tailwinds, with weak winds, and near the full moon when it was not visible. Lights had no effect on flight behavior. Birds tended to exhibit more course changes as they approached the island, greater angular changes when they changed course, and larger net increases in passing distance as a result of those course changes when the lights were on; however, none of these differences were statistically significant. Overall, the hazing lights at Northstar did not disrupt the birds’ migratory movements but resulted in increased avoidance of the island.En période de migration, l’eider à duvet et l’eider à tête grise (Somateria mollissima et S. spectabilis) survolent la mer de Beaufort et la mer des Tchouktches dans l’Alaska de l’Arctique. Comme ils sont attirés par les lumières, les eiders risquent d’entrer en collision avec des structures, y compris les installations pétrolières au large. De 2001 à 2004, nous avons utilisé un radar ornithologique pour caractériser le comportement des eiders qui migrent au-delà de l’île Northstar, une île de production pétrolière près de Prudhoe Bay, en Alaska, et pour évaluer les effets d’un système d’éclairage de dispersion sur les eiders en migration. Les « eiders » ciblés par le radar présentaient des périodes de mouvement pulsées et irrégulières; les taux de mouvement étaient plus importants en présence de glace marine, en l’absence de précipitation et en présence de vent arrière et de vent latéral, mais n’étaient pas touchés par les lumières. Les vélocités (vitesses au sol) étaient plus élevées en présence de glace et de forts vents arrière. Elles étaient plus basses la nuit lorsque les lumières étaient allumées, mais plus élevées le jour lorsque les lumières étaient allumées. Nous avons observé peu de variation quant au comportement de vol des cibles atteintes par le radar pendant qu’elles survolaient l’île; la proportion de comportements de vol non directionnels était plus importante en présence de glace, de vent arrière, de vent faible et lorsque la pleine lune n’était pas visible. Les lumières n’ont pas eu d’impact sur le comportement de vol. Lorsque les lumières étaient allumées, les oiseaux avaient tendance à changer de direction plus souvent durant leur vol à l’approche de l’île et à effectuer de plus grandes variations angulaires lorsqu’ils changeaient de direction, puis présentaient une nette augmentation de la distance de passage à la suite de ces changements de direction. Toutefois, aucune de ces différences n’était statistiquement importante. En général, les lumières de dispersion de l’île Northstar n’ont pas nui aux mouvements migratoires des oiseaux, mais ces derniers ont davantage évité de voler près de l’île