Agent Modeling in Stochastic Repeated Games

There are many situations in which two or more agents (e.g., human or computer decision makers) interact with each other repeatedly in settings that can be modeled as repeated games. In such situations, there is evidence that agents sometimes deviate greatly from what conventional game theory would predict. There are several reasons why this might happen, one of which is the focus of this dissertation: sometimes an agent's preferences may involve not only its own payoff (as specified in the payoff matrix), but also the payoffs of the other agent(s). In such situations, it is important to be able to understand what an agent's preferences really are, and how those preferences may affect the agent's behavior. This dissertation studies how the notion of Social Value Orientation (SVO), a construct in social psychology to model and measure a person's social preference, can be used to improve our understanding of the behavior of computer agents. Most of the work involves the life game, a repeated game in which the stage game is chosen stochastically at each iteration. The work includes the following results: * Using a combination of the SVO theory and evolutionary game theory, we studied how an agent's SVO affects its behavior in Iterated Prisoner's Dilemma (IPD). Our analysis provides a way to predict outcomes of agents playing IPD given their SVO values. * In the life game, we developed a way to build a model of agent's SVO based on observations of its behavior. Experimental results demonstrate that the modeling technique works well. * We performed experiments showing that the measured social preferences of computer agents have significant correlation with that of their human designers. The experimental results also show that knowing the SVO of an agent's human designer can be used to improve the performance of other agents that interact with the given agent. * A limitation of the SVO model is that it only looks at agents' preferences in one-shot games. This is inadequate for repeated games, in which an agent's actions may depend on both its SVO and whatever predictions it makes of the other agent's behavior. We have developed an extension of the SVO construct called the behavioral signature, a model of how an agent's behavior over time will be affected by both its own SVO and the other agent's SVO. The experimental results show that the behavioral signature is an effective way to generalize SVO to situations where agents interact repeatedly

The Life Game: Cognitive Strategies for Repeated Stochastic Games

Abstract—Standard models in bio-evolutionary game theory involve repetitions of a single stage game (e.g., the Prisoner’s Dilemma or the Stag Hunt); but it is clear that repeatedly playing the same stage game is not an accurate model of most individuals’ lives. Rather, individuals ’ interactions with others correspond to many different kinds of stage games. In this work, we concentrate on discovering behavioral strate-gies that are successful for the life game, in which the stage game is chosen stochastically at each iteration. We present a cognitive agent model based on Social Value Orientation (SVO) theory. We provide extensive evaluations of our model’s performance, both against standard agents from the game theory literature and against a large set of life-game agents written by students in two different countries. Our empirical results suggest that for life-game strategies to be successful in environments with such agents, it is important (i) to be unforgiving with respect to trust behavior and (ii) to use adaptive, fine-grained opponent models of the other agents. Keywords-repeated games, non-zero-sum games, stochastic games, social value orientation I

Coercive Nuclear Campaigns in the 21st Century: Understanding Adversary Incentives and Options for Nuclear Escalation

FY 2012-2013. Project Leads: Lieber, Keir A. and Press, Daryl G.The project leads will examine why and how regional powers armed with nuclear weapons may employ them coercively during a conventional war. More specifically, a set of research questions will provide insight on the paths of nuclear escalation, weak state strategies of coercive escalation, and the type of targets regional powers may strike to pursue escalatory strategies.NAApproved for public release; distribution is unlimited

Computational chemistry for graphene-based energy applications: progress and challenges

YesResearch in graphene-based energy materials is a rapidly growing area. Many graphene-based energy applications involve interfacial processes. To enable advances in the design of these energy materials, such that their operation, economy, efficiency and durability is at least comparable with fossil-fuel based alternatives, connections between the molecular-scale structure and function of these interfaces are needed. While it is experimentally challenging to resolve this interfacial structure, molecular simulation and computational chemistry can help bridge these gaps. In this Review, we summarise recent progress in the application of computational chemistry to graphene-based materials for fuel cells, batteries, photovoltaics and supercapacitors. We also outline both the bright prospects and emerging challenges these techniques face for application to graphene-based energy materials in future.vesk

Global, regional, and national life expectancy, all-cause mortality, and cause-specific mortality for 249 causes of death, 1980-2015 : a systematic analysis for the Global Burden of Disease Study 2015

Background Improving survival and extending the longevity of life for all populations requires timely, robust evidence on local mortality levels and trends. The Global Burden of Disease 2015 Study (GBD 2015) provides a comprehensive assessment of all-cause and cause-specific mortality for 249 causes in 195 countries and territories from 1980 to 2015. These results informed an in-depth investigation of observed and expected mortality patterns based on sociodemographic measures. Methods We estimated all-cause mortality by age, sex, geography, and year using an improved analytical approach originally developed for GBD 2013 and GBD 2010. Improvements included refinements to the estimation of child and adult mortality and corresponding uncertainty, parameter selection for under-5 mortality synthesis by spatiotemporal Gaussian process regression, and sibling history data processing. We also expanded the database of vital registration, survey, and census data to 14 294 geography-year datapoints. For GBD 2015, eight causes, including Ebola virus disease, were added to the previous GBD cause list for mortality. We used six modelling approaches to assess cause-specific mortality, with the Cause of Death Ensemble Model (CODEm) generating estimates for most causes. We used a series of novel analyses to systematically quantify the drivers of trends in mortality across geographies. First, we assessed observed and expected levels and trends of cause-specific mortality as they relate to the Socio-demographic Index (SDI), a summary indicator derived from measures of income per capita, educational attainment, and fertility. Second, we examined factors affecting total mortality patterns through a series of counterfactual scenarios, testing the magnitude by which population growth, population age structures, and epidemiological changes contributed to shifts in mortality. Finally, we attributed changes in life expectancy to changes in cause of death. We documented each step of the GBD 2015 estimation processes, as well as data sources, in accordance with Guidelines for Accurate and Transparent Health Estimates Reporting (GATHER). Findings Globally, life expectancy from birth increased from 61.7 years (95% uncertainty interval 61.4-61.9) in 1980 to 71.8 years (71.5-72.2) in 2015. Several countries in sub-Saharan Africa had very large gains in life expectancy from 2005 to 2015, rebounding from an era of exceedingly high loss of life due to HIV/AIDS. At the same time, many geographies saw life expectancy stagnate or decline, particularly for men and in countries with rising mortality from war or interpersonal violence. From 2005 to 2015, male life expectancy in Syria dropped by 11.3 years (3.7-17.4), to 62.6 years (56.5-70.2). Total deaths increased by 4.1% (2.6-5.6) from 2005 to 2015, rising to 55.8 million (54.9 million to 56.6 million) in 2015, but age-standardised death rates fell by 17.0% (15.8-18.1) during this time, underscoring changes in population growth and shifts in global age structures. The result was similar for non-communicable diseases (NCDs), with total deaths from these causes increasing by 14.1% (12.6-16.0) to 39.8 million (39.2 million to 40.5 million) in 2015, whereas age-standardised rates decreased by 13.1% (11.9-14.3). Globally, this mortality pattern emerged for several NCDs, including several types of cancer, ischaemic heart disease, cirrhosis, and Alzheimer's disease and other dementias. By contrast, both total deaths and age-standardised death rates due to communicable, maternal, neonatal, and nutritional conditions significantly declined from 2005 to 2015, gains largely attributable to decreases in mortality rates due to HIV/AIDS (42.1%, 39.1-44.6), malaria (43.1%, 34.7-51.8), neonatal preterm birth complications (29.8%, 24.8-34.9), and maternal disorders (29.1%, 19.3-37.1). Progress was slower for several causes, such as lower respiratory infections and nutritional deficiencies, whereas deaths increased for others, including dengue and drug use disorders. Age-standardised death rates due to injuries significantly declined from 2005 to 2015, yet interpersonal violence and war claimed increasingly more lives in some regions, particularly in the Middle East. In 2015, rotaviral enteritis (rotavirus) was the leading cause of under-5 deaths due to diarrhoea (146 000 deaths, 118 000-183 000) and pneumococcal pneumonia was the leading cause of under-5 deaths due to lower respiratory infections (393 000 deaths, 228 000-532 000), although pathogen-specific mortality varied by region. Globally, the effects of population growth, ageing, and changes in age-standardised death rates substantially differed by cause. Our analyses on the expected associations between cause-specific mortality and SDI show the regular shifts in cause of death composition and population age structure with rising SDI. Country patterns of premature mortality (measured as years of life lost [YLLs]) and how they differ from the level expected on the basis of SDI alone revealed distinct but highly heterogeneous patterns by region and country or territory. Ischaemic heart disease, stroke, and diabetes were among the leading causes of YLLs in most regions, but in many cases, intraregional results sharply diverged for ratios of observed and expected YLLs based on SDI. Communicable, maternal, neonatal, and nutritional diseases caused the most YLLs throughout sub-Saharan Africa, with observed YLLs far exceeding expected YLLs for countries in which malaria or HIV/AIDS remained the leading causes of early death. Interpretation At the global scale, age-specific mortality has steadily improved over the past 35 years; this pattern of general progress continued in the past decade. Progress has been faster in most countries than expected on the basis of development measured by the SDI. Against this background of progress, some countries have seen falls in life expectancy, and age-standardised death rates for some causes are increasing. Despite progress in reducing age-standardised death rates, population growth and ageing mean that the number of deaths from most non-communicable causes are increasing in most countries, putting increased demands on health systems. Copyright (C) The Author(s). Published by Elsevier Ltd.Peer reviewe

Offering differentiated services for peer-to-peer streaming

In traditional overlay multicast network, all peers are treated as equal regardless of their importance and contribution to the network. In this thesis, we consider that each user may have a different cost function depending on his privilege, delay to source, available bandwidth, and the like. We propose a fully distributed and scalable protocol to construct an overlay tree to minimize the overall cost of the users. It uses aggregation to account for the total cost of one's descendants, and reduces tree cost by a continuous improvement process. Through simulation, we show that our protocol converges reasonably quickly. When compared with other schemes, our resultant overlay tree offers differentiated services to users by appropriately taking into account individual user's cost functions. Moreover, it is shown that the bandwidth efficiency of our system can be adjusted easily by tuning a system parameter

Scalable Island Multicast for Peer-to-Peer Streaming

Despite the fact that global multicast is still not possible in today's Internet, many local networks are already multicast-capable (the so-called multicast “islands”). However, most application-layer multicast (ALM) protocols for streaming have not taken advantage of the underlying IP multicast capability. As IP multicast is more efficient, it would be beneficial if ALM can take advantage of such capability in building overlay trees. In this paper, we propose a fully distributed protocol called scalable island multicast (SIM), which effectively integrates IP multicast and ALM. Hosts in SIM first form an overlay tree using a scalable protocol. They then detect IP multicast islands and employ IP multicast whenever possible. We study the key issues in the design, including overlay tree construction, island management, and system resilience. Through simulations on Internet-like topologies, we show that SIM achieves lower end-to-end delay, lower link stress, and lower resource usage than traditional ALM protocols