Normal functions for algebraically trivial cycles are algebraic for arithmetic reasons

For families of smooth complex projective varieties we show that normal functions arising from algebraically trivial cycle classes are algebraic, and defined over the field of definition of the family. In particular, the zero loci of those functions are algebraic and defined over such a field of definition. This proves a conjecture of Charles.Comment: New title. 15 page

Ethnic Innovation and U.S. Multinational Firm Activity

This paper studies the impact that immigrant innovators have on the global activities of U.S. firms by analyzing detailed data on patent applications and on the operations of the foreign affiliates of U.S. multinational firms. The results indicate that increases in the share of a firm’s innovation performed by inventors of a particular ethnicity are associated with increases in the share of that firm’s affiliate activity in their native countries. Ethnic innovators also appear to facilitate the disintegration of innovative activity across borders and to allow U.S. multinationals to form new affiliates abroad without the support of local joint venture partners. Thus, this paper points out that immigration can enhance the competitiveness of multinational firms

Toward Secure Trust and Reputation Systems for Electronic Marketplaces

In electronic marketplaces, buying and selling agents may be used to represent buyers and sellers respectively. When these marketplaces are large, repeated transactions between traders may be rare. This makes it difficult for buying agents to judge the reliability of selling agents, discouraging participation in the market. A variety of trust and reputation systems have been proposed to help traders to find trustworthy partners. Unfortunately, as our investigations reveal, there are a number of common vulnerabilities present in such models---security problems that may be exploited by `attackers' to cheat without detection/repercussions. Inspired by these findings, we set out to develop a model of trust with more robust security properties than existing proposals. Our Trunits model represents a fundamental re-conception of the notion of trust. Instead of viewing trust as a measure of predictability, Trunits considers trust to be a quality that one possesses. Trust is represented using abstract trust units, or `trunits', in much the same way that money represents quantities of value. Trunits flow in the course of transactions (again, similar to money); a trader's trunit balance determines if he is trustworthy for a given transaction. Faithful execution of a transaction results in a larger trunit balance, permitting the trader to engage in more transactions in the future---a built-in economic incentive for honesty. We present two mechanisms (sets of rules that govern the operation of the marketplace) based on this model: Basic Trunits, and an extension known as Commodity Trunits, in which trunits may be bought and sold. Seeking to precisely characterize the protection provided to market participants by our models, we develop a framework for security analysis of trust and reputation systems. Inspired by work in cryptography, our framework allows security guarantees to be developed for trust/reputation models--provable claims of the degree of protection provided, and the conditions under which such protection holds. We focus in particular on characterizing buyer security: the properties that must hold for buyers to feel secure from cheating sellers. Beyond developing security guarantees, this framework is an important research tool, helping to highlight limitations and deficiencies in models so that they may be targeted for future investigation. Application of this framework to Basic Trunits and Commodity Trunits reveals that both are able to deliver provable security to buyers

Supplying Stalemates: The Strategic Logic of Arms Transfers to Violent Non-State Actors

State sponsorship of Violent Non-State Actors (VNSAs) has been shown to prolong intra-state conflicts and increase the probability that intra-state conflicts escalate into inter-state wars. The detrimental effect that state sponsorship of VNSAs has to global peace and security warrants a thorough examination. Previous academic studies have examined the logic underpinning state sponsorship but the study of the varying levels of support to different VNSAs states provide has not been fully explored. This study adds to the existing literature by not only demonstrating the strategic logic of sponsorship, but at what magnitude states will aid VNSAs under differing circumstances. State sponsorship takes many forms including financial assistance and the provision of safe havens, but this study will focus on arms transfers. Through the examination of three case studies, I determine that the primary determining factor is the ex-ante probability that the VNSA will be able to perpetuate the conflict. Significant to this study is the finding that VNSAs that are facing elimination may become the most dangerous in terms of weaponry capabilities in a surprisingly short amount of time as state sponsors provide more lethal armaments in an attempt to prolong the conflict.Master of Art

Addressing the Issues of Coalitions and Collusion in Multiagent Systems

In the field of multiagent systems, trust and reputation systems are intended to assist agents in finding trustworthy partners with whom to interact. Earlier work of ours identified in theory a number of security vulnerabilities in trust and reputation systems, weaknesses that might be exploited by malicious agents to bypass the protections offered by such systems. In this work, we begin by developing the TREET testbed, a simulation platform that allows for extensive evaluation and flexible experimentation with trust and reputation technologies. We use this testbed to experimentally validate the practicality and gravity of attacks against vulnerabilities. Of particular interest are attacks that are collusive in nature: groups of agents (coalitions) working together to improve their expected rewards. But the issue of coalitions is not unique to trust and reputation; rather, it cuts across a range of fields in multiagent systems and beyond. In some scenarios, coalitions may be unwanted or forbidden; in others they may be benign or even desirable. In this document, we propose a method for detecting coalitions and identifying coalition members, a capability that is likely to be valuable in many of the diverse fields where coalitions may be of interest. Our method makes use of clustering in benefit space (a high-dimensional space reflecting how agents benefit others in the system) in order to identify groups of agents who benefit similar sets of agents. A statistical technique is then used to identify which clusters contain coalitions. Experimentation using the TREET platform verifies the effectiveness of this approach. A series of enhancements to our method are also introduced, which improve the accuracy and robustness of the algorithm. To demonstrate how this broadly-applicable tool can be used to address domain-specific problems, we focus again on trust and reputation systems. We show how, by incorporating our work into one such system (the existing Beta Reputation System), we can provide resistance to collusion. We conclude with a detailed discussion of the value of our work for a wide range of environments, including a variety of multiagent systems and real-world settings