Bridge trisections in rational surfaces

We study smooth isotopy classes of complex curves in complex surfaces from the perspective of the theory of bridge trisections, with a special focus on curves in $\mathbb{CP}^2$ and $\mathbb{CP}^1\times\mathbb{CP}^1$. We are especially interested in bridge trisections and trisections that are as simple as possible, which we call "efficient". We show that any curve in $\mathbb{CP}^2$ or $\mathbb{CP}^1\times\mathbb{CP}^1$ admits an efficient bridge trisection. Because bridge trisections and trisections are nicely related via branched covering operations, we are able to give many examples of complex surfaces that admit efficient trisections. Among these are hypersurfaces in $\mathbb{CP}^3$, the elliptic surfaces $E(n)$, the Horikawa surfaces $H(n)$, and complete intersections of hypersurfaces in $\mathbb{CP}^N$. As a corollary, we observe that, in many cases, manifolds that are homeomorphic but not diffeomorphic have the same trisection genus, which is consistent with the conjecture that trisection genus is additive under connected sum. We give many trisection diagrams to illustrate our examples.Comment: 46 pages, 28 color figure

Social Reciprocity

We conduct a survey and find that 47% of respondents state they would sanction free riders in a team production scenario even though the respondent was not personally affected and no direct benefits could be expected to follow an intervention. To understand this phenomenon, we define social reciprocity as the act of demonstrating ones disapproval, at some personal cost, for the violation of a widely-held norm (for example, don’t free ride). Social reciprocity differs from reciprocity because social reciprocators punish all norm violators, regardless of group affiliation or whether or not the punisher bears the costs. Social reciprocity also differs from altruism because, while the latter is an outcome-oriented act benefiting someone else, the former is a triggered response not conditioned on future outcomes. To test the robustness of our survey results, we run a public goods experiment that allows players to punish each other. The experiment confirms the existence of social reciprocity and additionally demonstrates that more socially efficient outcomes arise when reciprocity can be expressed socially. Further we find that most subjects who punish do so to discipline transgressors and helping others is largely a positive externality. Finally, to provide some theoretical foundations for social reciprocity, we show that generalized punishment norms survive in one of the two stable equilibria of an evolutionary public goods game with selection drift.reciprocity, norm, experiment, public good, learning, evolution

No Switchbacks: Rethinking Aspiration-Based Dynamics in the Ultimatum Game

The stylized facts of ultimatum bargaining in the experimental lab are that offers tend to be near an equal split of the surplus and low, near perfect offers are routinely rejected. Bimmore et al (1995) use aspiration-based evolutionary dynamics to model the evolution of fair play in a binary choice version of this game, and show that incredible threats to reject low offers persist in equilibrium. We focus on two possible extensions of this analysis: (1) the model makes assumptions about agent motivations (aspiration levels) and the structure of the game (binary strategy space) that have not yet been tested experimentally, and (2) the standard dynamic is based on the problematic assumption that unhappy games who switch strategies may end up using the same strategy that was just rejected. To examine the implications of not allowing agents to “switch back” to their original strategy, we develop a “no switchback dynamic” and run a new, binary choice, experiment with induced aspirations. We find that the resulting dynamic predicts the evolution of play better than the standard dynamic and that aspirations are a significant motivator for our participants.ultimatum game, learning, aspirations, switchbacks, replicator dynamics

Eliminating the Flaws in New England's Reserve Markets

New England’s wholesale electricity market has been in operation, since May 1, 1999. When the market began it was understood that the rules were not perfect (Cramton and Wilson 1998). However, it was decided that it was better to start the market with imperfect rules, rather than postpone the market for an indefinite period. After several months of operation, we now have a sense of the extent market imperfections have resulted in observed problems. Here we study the three reserve markets—ten-minute spinning reserve (TMSR), ten-minute non-spinning reserve (TMNSR), and thirty-minute operating reserve (TMOR); we also discuss the closely related operable capability (OpCap) market. The paper covers the first four months of operation from May 1 to August 31, 1999. It is based on the market rules and their implementation by the ISO, and the market data during this period, including bidding, operating, and settlement information. Since that data are confidential, we have presented only aggregate information in the tables and figures that follow. Although this paper will cover only the reserves markets, we have studied the data from the energy, AGC, and capacity markets as well. Since all of the NEPOOL markets are interrelated, one cannot hope to understand one market without having an understanding of the others.Auctions, Electricity Auctions, Multiple Item Auctions

Why Punish: Social Reciprocity and the Enforcement of Prosocial Norms

Recently economists have become interested in why people who face social dilemmas in the experimental lab use the seemingly incredible threat of punishment to deter free riding. Three theories have evolved to explain punishment. We survey each theory and se behavioral data from surveys and experiments to show that the theory called social reciprocity in which people punish norm violators indiscriminately explains punishment best. We also show that social reciprocity can evolve in a population of free riders and contributors if the initial conditions are favorable.social dilemma, public good, punishment, reciprocity, norm, evolutionary game theory, experiment

The Impact of the UK New Deal for Lone Parents on Benefit Receipt

This paper evaluates the UK New Deal for Lone Parents (NDLP) program, which aims to return lone parents to work. Using rich administrative data on benefit receipt histories and a "selection on observed variables" identification strategy, we find that the program modestly reduces benefit receipt among participants. Methodologically, we highlight the importance of flexibly conditioning on benefit histories, as well as taking account of complex sample designs when applying matching methods. We find that survey measures of attitudes add information beyond that contained in the benefit histories and that incorporating the insights of the recent literature on dynamic treatment effects matters even when not formally applying the related methods. Finally, we explain why our results differ substantially from those of the official evaluation of NDLP, which found very large impacts on benefit exits.program evaluation, active labor market policy, matching, lone parents, New Deal

Social Reciprocity

We define social reciprocity as the act of demonstrating one's disapproval, at some personal cost, for the violation of widely-held norms (e.g., don't free ride). Social reciprocity differs from standard notions of reciprocity because social reciprocators intervene whenever a norm is violated and do not condition intervention on potential future payoffs, revenge, or altruism. Instead, we posit that social reciprocity is a triggered normative reponse. Our experiment confirms the existence of social reciprocity and demonstrates that more socially efficient outcomes arise when reciprocity can be expressed socially. Too provide theoretical foundations for social reciprocity, we show that generalized punishment norms survive in one of the two stable equilibria of an evolutionary game with selection drift.reciprocity, norm, experiment, public good, learning, evolution