Homogeneous Agents Research Articles

Emergent Star Networks with Ex Ante Homogeneous Agents

The acquisition and dispersion of information, a critical aspect of economic decisions, can occur through a network of agents (Jackson, 2009). Empirical and theoretical findings suggest that an efficient information dispersion network takes the form of a star: small numbers of agents gather information and distribute it to a large group. Despite these findings, controlled tests of this theory failed to find evidence of the emergence of such networks with an exception of Goeree et al (2008), which reports frequent star network formation with ex ante heterogeneous agents and perfect information. Empirical evidence suggests that these conditions may not always be feasible in natural environments (Feick and Price, 1987; Conley and Udry, 2010). Complement to earlier experimental research, we study institutional conditions under which star networks emerge in the presence of ex ante homogeneous agents. We find that investment limits and the right-of-first-refusal, both of which regularly coexist with star networks in natural environments, have a surprisingly strong ability to promote the formation of star networks with ex ante homogeneous agents. Using a cluster analysis, we trace the large positive effects of these institutions to the impact they have on individual's behavioral rules. In particular, we find that these institutions encourage individual rationality as well as positive habits, which then lead to the frequent and stable emergence of star networks. Our results may have important implications for environments characterized by ex ante homogeneous agents, e.g., those found in technology, marketing and agricultural sectors.

Chrysanthemum-like Co3O4 architectures: Hydrothermal synthesis and lithium storage performances

Three-dimensional chrysanthemum-like Co3O4 was prepared via a facile hydrothermal route without any template, and a subsequent calcination process. With a controlled concentration of the homogeneous precipitation agent, urea, a chrysanthemum-like precursor was hydrothermally obtained at 120°C for 20h, and the morphology was kept for Co3O4 after a subsequent calcination at 300°C for 2h. Co3O4 chrysanthemum-like architectures are assemblies of nanorods radiating from a common centre, and the nanorods consisted of interconnected nanoparticles with the size of about 30nm. When tested as an anode material of Li-ion batteries, chrysanthemum-like Co3O4 presented a discharge capacity of ∼450mAh/g after 50 discharge/charge cycles.

Asset Pricing with Heterogeneous Investment Horizons

We consider an analytically tractable asset pricing model describing the trading activity in a stylized market with two assets. Traders are boundedly rational expected utility maximizers with different beliefs about future prices and different investment horizons. In particular, we analyze the effects of the latter source of heterogeneity on the dynamics of price. We find that in the case with homogeneous agents, longer investment horizons lead to more stable dynamics. This is not true, however, in the case of a mixed population of traders, when the increase of heterogeneity in the investment horizons can introduce instability in the system. Furthermore, the role of heterogeneity turns out to be different for different trading behaviors and its effect on the aggregate dynamics depends on the whole ecology of agents' beliefs.

Testing a Forgotten Aspect of Akerlof's Gift Exchange Hypothesis: Relational Contracts with Individual and Uniform Wages

Empirical work on Akerlof's theory of gift exchange in labor markets has concentrated on the fair wage-effort hypothesis. In fact, however, the theory also contains a social component that stipulates that homogenous agents that are employed for the same wage level will exert more effort, resulting in higher rents and higher market efficiency, than agents that receive different wages. We present the first test of this component, which we call the fair uniform-wage hypothesis. In our laboratory experiment, we establish the existence of a significant efficiency premium of uniform wages. However, it is not the consequence of a stronger level of reciprocity by agents, but of the retrenchment of sanctioning options on the side of principals with uniform wages. Hence, implementing limitations to contractual freedom can have efficiency-enhancing effects.

A Dynamic Model of Search and Intermediation

This paper develops a dynamic model of an economy with search frictions in which homogeneous agents choose between specializing as producers or as merchants, and can change occupation at any time. Merchants operate alongside a decentralized search market and provide immediacy in trade in return for a price. Agents who discover the location of a merchant have the option of returning to the merchant in future periods, paying the merchant’s price and avoiding search. We characterize equilibria in symmetric strategies with one-period memory, and derive conditions under which merchants and their clients form a repeated relationship. We also investigate the prospect of an endogenous emergence of an institution of intermediation when the status quo ante is an economy with no merchants.

Optimal Mechanisms for Heterogeneous Multi-Cell Aquifers

Standard economic models of groundwater management impose restrictive assumptions regarding perfect transmissivity (i.e., the aquifer behaves as a bathtub), no external effects of groundwater stocks, observability of individual extraction rates, and/or homogeneous agents. In this article, we derive regulatory mechanisms for inducing the socially optimal extraction path in Markov perfect equilibrium for aquifers in which these assumptions do not hold. In spite of the complexity of the underlying system, we identify an interesting case in which a simple linear mechanism achieves the social optimum. To illustrate potential problems that can arise by erroneously imposing simplifying assumptions, we conduct a simulation based on data from the Indian state of Andhra Pradesh.

Functional, Overlapping, Competing Jurisdictions Among Fractionalized Agents: Medieval Spain

Most economists doubt the operability of functional, overlapping, competing jurisdictions (FOCJ) among large groups of homogenous agents; few could be found that would hold that FOCJ would work among large groups of socially distant agents. Yet, it is under precisely those circumstances that FOCJ would offer the most benefit, allowing socially distant agents to use their own legal courts, judged according to their own law, to minimize confrontations with other groups. This paper argues that FOCJ can be used to facilitate exchange and foster quality institutions and cordially relations among large groups of socially distant agents. Medieval Spain, where Christians, Jews and Muslims resided in close proximity from approximately 711-1492 is used to provide evidence of such a system in practice.

Filtered Social Learning

Knowledge sharing is economically important but also typically incomplete: we “filter” our communication. This paper analyzes the consequences of filtering. In the model, homogeneous agents share knowledge with their peers whenever the private benefits exceed communication costs. The welfare implications of this transmission mechanism hinge on whether units of knowledge complement, substitute for, or are independent of each other. Both substitutability and complementarity generate externalities; cheaper communication eliminates externalities in the former case but not necessarily in the latter. Complementary basic skills such as numeracy catalyze technology adoption, and adoption may be path dependent even when payoffs are certain and independent across agents.

Graph-Theoretic Analysis and Synthesis of Relative Sensing Networks

This work provides a general framework for the analysis and synthesis of a class of relative sensing networks (RSNs) in the context of its <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> performance. We consider RSNs with homogeneous and heterogeneous agent dynamics. In both cases, explicit graph theoretic expressions and bounds for the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> performance are derived. The <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> performance turns out to be a function of the number of edges in the graph, whereas the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> performance is structure dependent and related to the spectral radius of the graph Laplacian. The analysis results are then used to develop synthesis methods for RSNs. An optimal topology is designed using the Kruskal's Algorithm for <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> performance, and a semi-definite program for the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> performance of uncertain RSNs.

Evolution of Strategies With Different Representation Schemes in a Spatial Iterated Prisoner's Dilemma Game

The iterated prisoner's dilemma (IPD) game has been frequently used to examine the evolution of cooperative behavior among agents in the field of evolutionary computation. It has been demonstrated that various factors are related to the evolution of cooperative behavior. One well-known factor is spatial relations among agents. The IPD game is often played in a 2-D grid world. Such a spatial IPD game has a neighborhood structure, which is used to choose opponents for the IPD game and parents for genetic operations. Another important factor is the choice of a representation scheme to encode the strategy of each agent. Different representation schemes often lead to different results. Whereas the choice of a representation scheme is known to be important, a mixture of different representation schemes has not been examined for the spatial IPD game in the literature. That is, a population of homogeneous agents with the same representation scheme has been usually assumed in the literature. In this paper, we introduce the use of different representation schemes in a single population to the spatial IPD game in order to examine the evolution of cooperative behavior under more general assumptions. With the use of different representation schemes, we can examine the evolution of cooperative behavior in various settings such as partial interaction through the IPD game, partial interaction through crossover, full interaction through the IPD game and crossover, and no interaction between different subpopulations of agents.

Optimal Mechanisms for Heterogeneous Multi-Cell Aquifers

Standard economic models of groundwater management impose restrictive assumptions regarding perfect transmissivity (i.e., the aquifer behaves as a bathtub), no external effects of groundwater stocks, observability of individual extraction rates, and/or homogenous agents. In this article, we derive regulatory mechanisms for inducing the socially optimal extraction path in Markov perfect equilibrium for aquifers in which these assumptions do not hold. In spite of the complexity of the underlying system, we identify an interesting case in which a simple linear mechanism achieves the social optimum. To illustrate potential problems that can arise by erroneously imposing simplifying assumptions, we conduct a simulation based on data from the Indian state of Andhra Pradesh.

The Role of Belief in the Emergence of Social Conventions in Artificial Social System

The emergence of social conventions in multi-agent systems has been analyzed mainly by considering a group of homogeneous autonomous agents that can reach a global agreement using locally available information. We use novel viewpoint to consider that the process through which agents coordinate their behaviors to reduce conflict is also the process agents use to evaluate trust relations with their neighbors during local interactions. In this paper, we propose using the belief update rule called Instances of Satisfying and Dissatisfying (ISD) to study the evolution of agents' beliefs during local interactions. We also define an action selection rule called “highest cumulative belief” (HCB) to coordinate their behavior to reduce conflicts among agents in MAS (multi-agent systems). We find that the HCB can cause a group of agents to achieve the emergence of social conventions. Furthermore, we discover that if a group of agents can achieve the emergence of social conventions through ISD and HCB rules in an artificial social system, after a number of iterations this group of agents can enter the harmony state wherein each agent fully believes its neighbors.

Weaving the social fabric

PurposeThe purpose of this paper is to investigate the performance of cultural algorithms (CAs) over a complete range of optimization problem complexities, from fixed to chaotic and specifically observing whether there is a given homogeneous agent topology within a culture which can dominate across all complexities.Design/methodology/approachIn order to apply the CA overall complexity classes it was necessary to generalize on its co‐evolutionary nature to keep the variation in the population across all complexities. First, previous CA approaches were reviewed. Based on this the existing implementation was extended to produce a more general one that could be applied across all complexity classes. As a result a new version of the cultural algorithms toolkit, CAT 2.0, was produced, which supported a variety of co‐evolutionary features at both the knowledge and population levels. The system was applied to the solution of a 150 randomly generated problems ranging from simple to chaotic complexity classes.FindingsNo homogeneous social fabric tested was dominant over all categories of problem complexity; as the complexity of problems increased so did the complexity of the social fabric that was need to deal with it efficiently. A social fabric that was good for fixed problems might be less adequate for periodic problems, and chaotic ones.Originality/valueThe paper presents experimental evidence that social structure of a cultural system can be related to the frequency and complexity type of the problems that presented to a cultural system.

In vivo evaluation of a novel albumin-binding prodrug of doxorubicin in an orthotopic mouse model of prostate cancer (LNCaP)

PSA, which is overexpressed in prostate carcinoma, represents a molecular target for selectively releasing an anticancer agent from a prodrug formulation. In this study, we report on the in vivo antitumor efficacy of an efficacious albumin-binding prodrug of doxorubicin (PSA9) that incorporates p-aminobenzyloxycarbonyl (PABC) as a self-immolative spacer in addition to the heptapeptide, Arg-Ser-Ser-Tyr-Tyr-Ser-Leu, which serves as a substrate for PSA. The prodrug is cleaved very efficiently by PSA releasing H-Ser-Leu-PABC-doxorubicin and subsequently doxorubicin in PSA-positive cell lysates and prostate tumor homogenates as the final cleavage product. PSA9 at 3 × 6 mg kg(-1) doxorubicin equivalents (intravenous) was compared with conventional doxorubicin at equitoxic doses (at 3 × 3 mg kg(-1); intravenous) in an orthotopic mouse model of prostate cancer using LNCaP lentiviral luciferase-neomycin cells transduced with luciferase. Whereas doxorubicin did not show any efficacy against the primary tumor or metastases, the prodrug reduced the primary tumor by 30-50% and circulating PSA levels, and in addition, showed a pronounced reduction in lung and bone metastases by ∼77% and ∼96%, respectively, and a positive trend regarding the activity against liver and lymph-node metastases compared with control and doxorubicin-treated animals. The incorporation of PABC as a self-immolative spacer together with a PSA substrate demonstrates superior antitumor effects over doxorubicin attributed to an efficient cleavage by PSA releasing doxorubicin as the final active agent in prostate tumor homogenates. Using this approach for developing effective prodrugs against prostate cancer, is worthy of further preclinical optimization.

Cooperative control of multi-agent dynamical systems in target-enclosing operations using cyclic pursuit strategy

This article is concerned with formation stability analysis of distributed cooperative control for target-enclosing operations by multiple homogeneous dynamic agents. To this end, we first present an on-line path generator design method based on a cyclic pursuit scheme. Then, we provide Lyapunov and asymptotic stability conditions which should hold for the above path generation laws. These conditions are derived based on a simple stability analysis method for linear systems with a generalised frequency variable. The formation control scheme combined with a cyclic pursuit based distributed on-line path generator satisfying the derived stability conditions guarantees the required global convergence property with theoretical rigour. Furthermore, in order to show its distinctive features clearly, we present how to analyse a global formation stability for multi-agent systems, where each agent is modelled as a class of second-order systems and is locally stabilised by a proportional-derivative (PD) controller. Some simulation examples illustrate the distinctive features of the proposed method and the achievement of a desired pursuit pattern.

On the hidden hazards of adaptive behavior

Abstract Adaptive behavior has been observed in almost all aspects of real-world. One of the main advantages of acting adaptively is its stabilizing effect on dynamic equilibrium, associated with which are three favorable features: (a) non-destabilizing characteristics, (b) low-speed effectiveness and (c) the convexity of the stabilization regime in terms of the adaptive parameter. It is shown either in theory or by counter-examples that these advantages may not be preserved if the adaptive mechanism is applied to multi-dimensional processes. The necessary and sufficient conditions for the relevant phenomena are provided for two-dimensional dynamic processes with application to duopolistic dynamics. Our findings not only help to clarify hidden misconceptions and prevent potential abuse of adaptive mechanisms, but also illustrate the possible pitfalls arising from generalizing well-known characteristics of low dimensional and/or homogeneous agent models to high-dimensional and heterogenous agent models.

Collusion in homogeneous and heterogeneous tournaments

In tournaments, only the relative performance of agents is important. Therefore, the agents have an incentive to collude by jointly deviating to low effort levels. Previous papers on collusion have proposed to make the tournament asymmetric to prevent agents from colluding. However, by allowing side payments between the agents and focusing on implicit enforcement of collusion, the current study demonstrates that this is not true. Often, the principal prefers to hire homogeneous agents to make collusions less stable.

Peer Effects and Endogenous Network Formation

This paper presents a model of endogenous network formation in the presence of peer effects for a general class of payoff functions with local complementarities in effort levels and positive local externalities. Links are one-sided and agents move simultaneously. I find that equilibrium networks display - other than the complete and the empty network - a core-periphery structure, which is commonly observed in empirical studies. Ex-ante homogenous agents may obtain very different ex-post outcomes, depending on the network that arises in equilibrium. The mulitiplicity of equilibria serves as an explanation for large differences in behaviour across otherwise identical groups. These findings are applicable to a wide range of social and economic phenomena.

Labor Supply, Biased Technological Change and Economic Growth

We consider a model of factor saving innovations and study the effects of exogenous changes in labor supply. In a biased innovations setting, as economies accumulate capital, labor becomes relatively scarce and expensive. As a consequence, incentives for labor saving and capital using innovations appear. By the same token, exogenous changes in labor supply affect factor prices. In general, a reduction in labor supply decreases current output and generates incentives for labor saving innovations. Therefore, the effect that a change in the supply of labor has on factor prices is mitigated and, depending on the initial conditions, it may be contrasted by the effect of the technological bias. Finally, the movements of the factor prices affect the saving decisions and consequently the dynamics of economic growth. We explore the consequences of an exogenous decrease in labor supply in two different settings: a homogenous agents model with infinite horizon and an overlapping generations model. Se utiliza un modelo de innovaciones sesgadas para estudiar los efectos de cambios exogenos en la oferta laboral. En un contexto de innovaciones sesgadas, a medida que las economias acumulan capital, el trabajo se hace relativamente mas escaso y mas caro, por este motivo, hay incentivos para adoptar tecnologias ahorradoras de trabajo. Del mismo modo un cambio en la oferta laboral afecta la abundancia de factores y sus precios relativos. En general, una reduccion de la oferta laboral, hace que el trabajo sea mas caro y genera incentivos para cambio tecnologico ahorrador de trabajo. Asi, el efecto inicial que tiene el cambio en la oferta laboral sobre los precios de los factores es mitigado por el cambio tecnologico. Finalmente, los movimientos en la remuneracion a los factores afectan las decisiones de ahorro y, por lo tanto, la dinamica del crecimiento. En este trabajo se exploran las consecuencias de una reduccion de la oferta laboral en dos contextos teoricos diferentes: un modelo de agentes homogeneos y horizonte infinito y un modelo de generaciones traslapadas.

Interorganizational Information Exchange and Efficiency: Organizational Performance in Emergency Environments

Achieving efficiency in coordinated action in rapidly changing environments has challenged both researchers and practitioners. Emergency events require both rapid response and effective coordination among participating organizations. We created a simulated operations environment using agent-based modeling to test the efficiency of six different organizational designs that varied the exercise of authority, degree of uncertainty, and access to information. Efficiency is measured in terms of response time, identifying time as the most valuable resource in emergency response. Our findings show that, contrary to dominant organizational patterns of hierarchical authority that limit communication among members via strict reporting rules, any communication among members increases the efficiency of organizations operating in uncertain environments. We further found that a smaller component of highly interconnected, self adapting agents emerges over time to support the organization's adaptation in changing conditions. In uncertain environments, heterogeneous agents prove more efficient in sharing information that guides coordination than homogeneous agents.