Critical behavior in an evolutionary Ultimatum Game

Experimental studies have shown the ubiquity of altruistic behavior in human societies. The social structure is a fundamental ingredient to understand the degree of altruism displayed by the members of a society, in contrast to individual-based features, like for example age or gender, which have been shown not to be relevant to determine the level of altruistic behavior. We explore an evolutionary model aiming to delve how altruistic behavior is affected by social structure. We investigate the dynamics of interacting individuals playing the Ultimatum Game with their neighbors given by a social network of interaction. We show that a population self-organizes in a critical state where the degree of altruism depends on the topology characterizing the social structure. In general, individuals offering large shares but in turn accepting large shares, are removed from the population. In heterogeneous social networks, individuals offering intermediate shares are strongly selected in contrast to random homogeneous networks where a broad range of offers, below a critical one, is similarly present in the population.Comment: 13 pages, 7 figure

From Ultimatum to Nash Bargaining: Theory and Experimental Evidence

commitment;imperfect observability;ultimatum bargaining games;Nash bargaining game;experiments

The Nova Rate in M94 (NGC 4736)

A multi-epoch H$\alpha$ survey of the early-type spiral galaxy M94 (NGC 4736) has been completed as part of a program to establish the galaxy's nova rate. A total of four nova candidates were discovered in seven epochs of observation during the period from 2005 to 2007. After making corrections for temporal coverage and spatial completeness, a global nova rate of 5.0$^{+1.8}_{-1.4}$ yr$^{-1}$ was determined. This rate corresponds to a specific-luminosity nova rate of 1.4 $\pm$ 0.5 novae per year per 10$^{10} L_{\odot,K}$ when the $K$ luminosity is determined from the $B-K$ color, or 1.5 $\pm$ 0.4 novae per year per 10$^{10} L_{\odot,K}$ when the $K$ luminosity is derived from the Two Micron All Sky Survey. These values are slightly lower than that of other galaxies with measured nova rates, which typically lie in the range of $2-3$ novae per year per 10$^{10} L_{\odot}$ in the $K$ band.Comment: Accepted for publication in the Astrophysical Journal; 18 pages, 4 figures. The revised version includes a few stylistic changes and cleans up some typo

Community projects: an experimental analysis of a fair implementation process

We define and experimentally test a public provision mechanism that meets three basic ethical requirements and allows community members to influence, via monetary bids, which of several projects is implemented. For each project, participants are assigned personal values, which can be positive or negative. We provide either public or private information about personal values. This produces two distinct public provision games, which are experimentally implemented and analyzed for various projects. In spite of the complex experimental task, participants do not rely on bidding their own personal values as an obvious simple heuristic whose general acceptance would result in fair and efficient outcomes. Rather, they rely on strategic underbidding. Although underbidding is affected by projects’ characteristics, the provision mechanism mostly leads to the implementation of the most efficient project

Scope and significance of non-uniform classification practices in breast cancer with non-inflammatory skin involvement: a clinicopathologic study and an international survey

Background: The study evaluates the scope of non-uniform classification practices concerning breast carcinomas with non-inflammatory skin involvement. Patients and methods: We compared the clinical course of patients with histologically proven non-inflammatory skin involvement: 119 (65.4%) with clinically obvious ‘classical' skin changes (Group A) and 63 (34.6%) with no or only discreet changes (Group B). A questionnaire was circulated to pathology departments in 24 countries to assess the practice concerning the placement of skin- involved breast carcinomas in the TNM classification. Results: Patients in Group B showed a significantly better disease specific survival (P = 0.0002). Eighty-six respondents (70.5%) of the survey preferred the ‘histological view' and classified tumors with only histological proven skin involvement as T4b/stage IIIB. The opposing classification principle (‘clinical view'), which dictates that T4b breast cancer is a clinical diagnosis and the classical signs must be present, was supported by 31 respondents (25.4%). Conclusions: A large number of breast cancer patients with non-inflammatory skin involvement are only histologically proven and show, compared with cases exhibiting the classical clinical signs, significant differences in clinical course and prognosis. In general, both subsets were aggregated in one T category/stage (T4b/IIIB). This results in a considerable distortion of the reported statistical dat

Incomplete Punishment Networks in Public Goods Games: Experimental Evidence

Abundant evidence suggests that high levels of contributions to public goods can be sustained through self-governed monitoring and sanctioning. This experimental study investigates the effectiveness of decentralized sanctioning institutions in alternative punishment networks. Our results show that the structure of punishment network significantly affects allocations to the public good. In addition, we observe that network configurations are more important than punishment capacities for the levels of public good provision, imposed sanctions and economic efficiency. Lastly, we show that targeted revenge is a major driver of anti-social punishment