Direct observation of a Fermi liquid-like normal state in an iron-pnictide superconductor

There are two prerequisites for understanding high-temperature (high-T$_c$) superconductivity: identifying the pairing interaction and a correct description of the normal state from which superconductivity emerges. The nature of the normal state of iron-pnictide superconductors, and the role played by correlations arising from partially screened interactions, are still under debate. Here we show that the normal state of carefully annealed electron-doped BaFe$_{2-x}$Co$_{x}$As$_2$ at low temperatures has all the hallmark properties of a local Fermi liquid, with a more incoherent state emerging at elevated temperatures, an identification made possible using bulk-sensitive optical spectroscopy with high frequency and temperature resolution. The frequency dependent scattering rate extracted from the optical conductivity deviates from the expected scaling $M_{2}(\omega,T)\propto(\hbar\omega)^{2}+(p\pi k_{B}T)^{2}$ with $p\approx$ 1.47 rather than $p$ = 2, indicative of the presence of residual elastic resonant scattering. Excellent agreement between the experimental results and theoretical modeling allows us to extract the characteristic Fermi liquid scale $T_{0}\approx$ 1700 K. Our results show that the electron-doped iron-pnictides should be regarded as weakly correlated Fermi liquids with a weak mass enhancement resulting from residual electron-electron scattering from thermally excited quasi-particles.Comment: 6+9pages, 3+9 figures To be published in Scientific Report

Using Multi-Agent Simulation to Explore the Contribution of Facilitation to GSS Transition

Significant prior research has shown that facilitation is a critical part of GSS transition. This study examines an under-researched aspect of facilitation—its contributions to self-sustained GSS use among group members. Integrating insights from Adaptive Structuration Theory, experimental economics, and the Collaboration Engineering literature, we formalize interactions of group members in GSS transition as strategic interactions in a minimum-effort coordination game. The contributions of facilitation are interpreted as coordination mechanisms to help group members achieve and maintain an agreement on GSS use by reducing uncertainties in the coordination game. We implement the conjectured coordination mechanisms in a multi-agent simulator. The simulator offers insights into the separate and combined effects of common facilitation practices during the lifecycle of GSS transition. These insights can help the Collaboration Engineering community to identify and package the facilitation routines that are critical for group members to achieve self-sustained GSS use and understand how facilitation routines should be adapted to different stages of GSS transition lifecycle. Moreover, they indicate the value of the multi-agent approach in uncovering new insights and representing the issue of GSS transition with a new view

Growth Matters: Identifying Best Practices in Growing Civic Collaborations.

The recently introduced Health Children and Families Act represents a potential $15B investment in promoting community health by legislating the implementation of the Nurse-Family Partnerships (NFP) program in all 50 states. Although legislation does not mandate the implementation strategy, civic collaboration has been found to be uniquely successful. To fully leverage the value of civic collaboration, this study aims to identify and formalize one important aspect of collaborative activity the growth process during the initial stages of collaboration. By comparing field observations from several community health programs, we have identified the features of civic collaborations most associated with favorable program outcomes. Specifically, successful collaborations have started with small initial groups, proceeded to engage in high quality planning processes, and have slowly included new members. Using a coordination game model from experimental economics, we formalize strategic behaviors in civic collaboration as a minimum-effort coordination game with Pareto ranked equilibria. Three best practices (small initial group, planning, and growth) observed from the field are interpreted as interventions in coordination failures within the game. This coordination game framework is incorporated into an agent-based model. A series of experiments in the agent-based model offer an in-depth understanding of the separate and combined effects of the three best practices and how their contributions change over the lifecycle of a civic collaboration program. Findings from this study not only inform the program implementation of Healthy Children and Families Act, but also help stakeholders in other civic collaboration programs to understand and adopt the best practices and achieve optimal outcomes.Ph.D.InformationUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/55673/1/erikwj_1.pd

Influence of feed ration size on somatic and muscle growth in landlocked dwarf and farmed Atlantic salmon Salmo salar

We examined the possible adaptation of the dwarf Bleke population of Atlantic salmon Salmo salar from Lake Byglandsfjord in southern Norway to limited food resources. The growth performance and muscle development in juvenile Bleke and farmed S. salar under satiated or restricted (50%) feeding were examined for 10 months, starting 3 weeks after first‐feeding stage. Four‐thousand fish were divided into four replicated groups and random samples of 16–40 fish per group were measured six times during the experiment. The two strains showed no significant difference in mean body mass when fed restricted ration, but the individual variation was considerably higher in the farmed fish. Both Bleke and farmed S. salar grew significantly faster when fed to satiation, but the farmed S. salar showed much higher gain in mass and were three times heavier (201.5 g v. 66.7 g) and possessed twice as many fast muscle fibres (179682 v. 84779) compared with landlocked S. salar after 10 months. Farmed fish fed full ration displayed both hypertrophic and hyperplasic muscle growth, while the increased growth in Bleke S. salar was entirely associated with a larger fibre diameter. The landlocked Bleke strain has apparently adapted to low food availability by minimising the metabolic costs of maintenance and growth through reduced dominance hierarchies and by an increase in average muscle fibre diameter relative to the ancestral condition.PostprintPeer reviewe

Understanding the Influence of Power and Perspective-Taking on Collaborative Decision-Making

Public engagement in collaborative natural resource management necessitates perspective taking, shared understanding, and collaboration. There is currently little understanding about how to reliably generate perspective-taking and collaboration, particularly in situations involving the unequal distribution of resources. Here we examine how using a computer-mediated scenario to simulate resource gain and loss influenced individual perspective-taking and behavior. Participants (n=180) were randomly assigned to each condition: high resources, low resources, lose resources, gain resources. Multilevel analysis revealed that losing resources decreased perspective-taking and collaboration. We discuss the theoretical and practical implications of this research for public engagement in environmental decisions

Follow the slash(dot): Effect of feedback on new members in an online community

ABSTRACT Many virtual communities involve ongoing discussions, with large numbers of users and established, if implicit rules for participation. As new users enter communities like this, both they and existing members benefit when new users learn the standards for participation. Slashdot is a news and discussion site that has developed a system of distributed moderation to provide feedback about the value of posts on their site. This study examines three explanations for how new users learn to participate in a digital community: learning transfer from previous experiences, observation of other members, and feedback from other members. We find that new user behavior is affected by a combination of their viewing behavior, the moderation feedback they receive, and replies to their comments

A Basin Redox Transect at the Dawn of Animal Life

Multiple eukaryotic clades make their first appearance in the fossil record between ~810 and 715 Ma. Molecular clock studies suggest that the origin of animal multicellularity may have been part of this broader eukaryotic radiation. Animals require oxygen to fuel their metabolism, and low oxygen levels have been hypothesized to account for the temporal lag between metazoan origins and the Cambrian radiation of large, ecologically diverse animals. Here, paleoredox conditions were investigated in the Fifteenmile Group, Ogilvie Mountains, Yukon, Canada, which hosts an 811 Ma ash horizon and spans the temporal window that captures the inferred origin and early evolution of animals. Iron-based redox proxies, redox-sensitive trace elements, organic carbon percentages and pyrite sulfur isotopes were analyzed in seven stratigraphic sections along two parallel basin transects. These data suggest that for this basin, oxygenated shelf waters overlay generally anoxic deeper waters. The anoxic water column was dominantly ferruginous, but brief periods of euxinia likely occurred. These oscillations coincide with changes in total organic carbon, suggesting euxinia was primarily driven by increased organic carbon loading. Overall, these data are consistent with proposed quantitative constraints on Proterozoic atmospheric oxygen being greater than 1% of modern levels, but less than present levels. Comparing these oxygen levels against the likely oxygen requirements of the earliest animals, both theoretical considerations and the ecology of modern oxygen-deficient settings suggest that the inferred oxygen levels in the mixed layer would not have been prohibitive to the presence of sponges, eumetazoans or bilaterians. Thus the evolution of the earliest animals was probably not limited by the low absolute oxygen levels that may have characterized Neoproterozoic oceans, although these inferred levels would constrain animals to very small sizes and low metabolic rates.Earth and Planetary SciencesOrganismic and Evolutionary Biolog

Intending the Unintended: The Act of Building Agent-based Models as a Regular Source of Knowledge Generation

Poverty is a complex issue that is rarely conducive to analysis in laboratory or field experiments. Effective interventions that aim to decrease or eliminate poverty require an understanding of the intricate web of associated social issues. The need for this increased comprehension necessitates the use of alternative robust means of analysis: one such being agent-based modelling. The strengths of agent-based modelling to disaggregate complex social behaviours and understand them are well known. However, while people have explored how the modelling process can prove to be fruitful, the usually unintended insight gained and the knowledge engendered during the model design process goes largely unnoticed. In this paper, we aspire to show precisely how the model building process is critical in leading to unintended knowledge generation for modellers by drawing from three US based examples where agent-based modelling was used to aid research into the effects of interventions that address poverty and human development through programs and issues facing low-income families. With these examples, we illustrate some of the means to harness new knowledge generated. In our discussion, we also highlight the advantageous nature of agent-based model design as an independent source of knowledge generation

Understanding leadership in a world of shared problems: advancing network governance in large landscape conservation

Conservation of large landscapes requires three interconnected types of leadership: collaborative leadership, in which network members share leadership functions at different points in time; distributive leadership, in which network processes provide local opportunities for members to act proactively for the benefit of the network; and architectural leadership, in which the structure of the network is intentionally designed to allow network processes to occur. In network governance, each leadership approach is necessary to achieve sustained, successful outcomes. We discuss each of these approaches to leadership and offer specific practices for leaders of networks, including: shaping the network's identity and vision, attracting members, instilling leadership skills in members, and advancing common interests. These practices are then illustrated in case studies