Assortative Mixing Equilibria in Social Network Games

It is known that individuals in social networks tend to exhibit homophily (a.k.a. assortative mixing) in their social ties, which implies that they prefer bonding with others of their own kind. But what are the reasons for this phenomenon? Is it that such relations are more convenient and easier to maintain? Or are there also some more tangible benefits to be gained from this collective behaviour? The current work takes a game-theoretic perspective on this phenomenon, and studies the conditions under which different assortative mixing strategies lead to equilibrium in an evolving social network. We focus on a biased preferential attachment model where the strategy of each group (e.g., political or social minority) determines the level of bias of its members toward other group members and non-members. Our first result is that if the utility function that the group attempts to maximize is the degree centrality of the group, interpreted as the sum of degrees of the group members in the network, then the only strategy achieving Nash equilibrium is a perfect homophily, which implies that cooperation with other groups is harmful to this utility function. A second, and perhaps more surprising, result is that if a reward for inter-group cooperation is added to the utility function (e.g., externally enforced by an authority as a regulation), then there are only two possible equilibria, namely, perfect homophily or perfect heterophily, and it is possible to characterize their feasibility spaces. Interestingly, these results hold regardless of the minority-majority ratio in the population. We believe that these results, as well as the game-theoretic perspective presented herein, may contribute to a better understanding of the forces that shape the groups and communities of our society

Calculations of radar backscattering coefficient of vegetation-covered soils

A model for simulating the measured backscattering coefficient of vegetation-covered soil surfaces includes both coherent and incoherent components of the backscattered radar pulses from a rough sil surface. The effect of vegetation canopy scattering is also incorporated into the model by making the radar pulse subject to two-way attenuation and volume scattering when it passes through the vegetation layer. Model results agree well with the measured angular distributions of the radar backscattering coefficient for HH polarization at the 1.6 GHz and 4.75 GHz frequencies over grass-covered fields. It was found that the coherent scattering component is very important at angles near nadir, while the vegetation volume scattering is dominant at incident angles 30 degrees

Dissolved oxygen measurements in the Machipongo River system near Willis Wharf, Virginia

Most aquatic organisms require· oxygen to survive and consequently, the dissolved oxygen (DO) content of the water is one of the most important measures of water quality. Sources of oxygen are the atmosphere and photosynthesis. Oxygen is consumed by plants and animals during respiration and by microorganisms that decompose organic matter. The more sources and sinks of oxygen, the more difficult it is to understand and predict the oxygen dynamics of a river system. Grossly polluted systems turn out to be quite simple, because the pollutant source dominates. Natural, unimpacted systems often show a balance between a number of sources and sinks and therefore are much more complex. The rivers of the Eastern Shore of Virginia typify this latter case. The Machipongo River, including its tributary Parting Creek, drains mostly agricultural land and forest. The river has extensive fringe marshes and tidal flats which are exposed at low water. A large mechanized clam processing facility located at Willis Wharf, Virginia also discharged wastewaters to Parting Creek. The organic loadings in these wastewaters have varied over time as processing techniques and production levels changed. Mathematical models are very useful tools that allow water quality managers to predict the environmental response to various actions, such as an increase in pollutant loads when a new facility begins discharging wastewaters or a decrease in pollutant loads when treatment levels are increased. Models can be only as good as the field data upon which they are based. When a system is complex, the data set must be comprehensive, and often extensive in time, so that there is sufficient information to allow the effects of all major factors to be determined. For the Machipongo River, such a field effort would be very expensive. Consequently, studies have been more limited in scope and designed to examine one factor only, namely the effects of the clam processing wastewaters. In the spring of 1989, a field study was undertaken to see if water quality differed between Parting Creek, which received the clam wastes, and the Machipongo River, which had no comparable wastewater loading. In the fall of 1990, another study was conducted to see whether conditions had changed in response to waste load reductions at the clam processing plant. Subsequently, the clam processing plant was closed, so the waste loading to Parting Creek was eliminated. This report describes the data collected during the spring of 1992, when there was no discharge from the plant. At a later date, these data will be compared with those from prior years to determine what, if any, change in water quality has resulted from the elimination of this point source of organic wastes

Public goods and decay in networks

We propose a simple behavioral model to analyze situations where (1) a group of agents repeatedly plays a public goods game within a network structure and (2) each agent only observes the past behavior of her neighbors, but is affected by the decisions of the whole group. The model assumes that agents are imperfect conditional cooperators, that they infer unobserved contributions assuming imperfect conditional cooperation by others, and that they have some degree of bounded rationality. We show that our model approximates quite accurately regularities derived from public goods game experiments

Letters from Your Northern Neighbors Who Are Now Satisfied and Prosperous Lower Rio Grande Valley Farmers [brochure]

Brochure published by Oliver-Jackson Investment Company featuring Letters from Your Northern Neighbors Who Are Now Satisfied and Prosperous Lower Rio Grande Valley Farmers.https://scholarworks.utrgv.edu/lrgv/1026/thumbnail.jp

A Post Establishment Analysis of Various Thinning Decisions for Black Walnut Plantations

In the Central Hardwood Region, the quantity and quality of hardwood timber critically depend on forest management decisions made by landowners. We fill a key gap in hardwood management by building a spatially explicit thinning model for black walnut to guide the first pre-commercial thin under user defined planting density, pre-establishment seedling survival and post establishment crop tree choices. We fmd that growth and yield of individual trees is influenced by multiple synergistic choices made during the pre-establishment and postestablishment phase. Later, we link our model with the Forest Vegetation Simulator (FVS) to project stand attributes under the impact of future thinning and harvest decisions. \Ve demonstrate a framework that could guide investments in hardwoods on private lands based on sound scientific evidence and tools that pinpoint forest management options over the plantation life cycle

Network Creation Games: Think Global - Act Local

We investigate a non-cooperative game-theoretic model for the formation of communication networks by selfish agents. Each agent aims for a central position at minimum cost for creating edges. In particular, the general model (Fabrikant et al., PODC'03) became popular for studying the structure of the Internet or social networks. Despite its significance, locality in this game was first studied only recently (Bil\`o et al., SPAA'14), where a worst case locality model was presented, which came with a high efficiency loss in terms of quality of equilibria. Our main contribution is a new and more optimistic view on locality: agents are limited in their knowledge and actions to their local view ranges, but can probe different strategies and finally choose the best. We study the influence of our locality notion on the hardness of computing best responses, convergence to equilibria, and quality of equilibria. Moreover, we compare the strength of local versus non-local strategy-changes. Our results address the gap between the original model and the worst case locality variant. On the bright side, our efficiency results are in line with observations from the original model, yet we have a non-constant lower bound on the price of anarchy.Comment: An extended abstract of this paper has been accepted for publication in the proceedings of the 40th International Conference on Mathematical Foundations on Computer Scienc

Playing with networks : How economists explain

Peer reviewe

TugaTAC Broker: A Fuzzy Logic Adaptive Reasoning Agent for Energy Trading

Smart Grid technologies are changing the way energy is generated, distributed and consumed. With the increasing spread of renewable power sources, new market strategies are needed to guarantee a more sustainable participation and less dependency of bulk generation. In PowerTAC (Power Trading Agent Competition), different software agents compete in a simulated energy market, impersonating broker companies to create and manage attractive tariffs for customers while aiming to profit. In this paper, we present TugaTAC Broker, a PowerTAC agent that uses a fuzzy logic mechanism to compose tariffs based on its customers portfolio. Fuzzy sets allow adaptive configurations for brokers in different scenarios. To validate and compare the performance of TugaTAC, we have run a local version of the PowerTAC competition. The experiments comprise TugaTAC competing against other simple agents and a more realistic configuration, with instances of the winners of previous editions of the competition. Preliminary results show a promising dynamic: our approach was able to manage imbalances and win the competition in the simple case, but need refinements to compete with more sophisticated market. (c) Springer International Publishing Switzerland 2016

Selfish Network Creation with Non-Uniform Edge Cost

Network creation games investigate complex networks from a game-theoretic point of view. Based on the original model by Fabrikant et al. [PODC'03] many variants have been introduced. However, almost all versions have the drawback that edges are treated uniformly, i.e. every edge has the same cost and that this common parameter heavily influences the outcomes and the analysis of these games. We propose and analyze simple and natural parameter-free network creation games with non-uniform edge cost. Our models are inspired by social networks where the cost of forming a link is proportional to the popularity of the targeted node. Besides results on the complexity of computing a best response and on various properties of the sequential versions, we show that the most general version of our model has constant Price of Anarchy. To the best of our knowledge, this is the first proof of a constant Price of Anarchy for any network creation game.Comment: To appear at SAGT'1