No description available.

The thesis contributes to the study of the relationship between competition and incentives, when asymmetric information is taken into account. Our main focus is the analysis of loan relationships. The first two chapters analyze the relationship between borrowers' financial constraints and endogenous fluctuations. We try to provide a potential departure from the traditional corporate finance theories by showing that the characteristics of firms' capital structure (i.e. their debt-to-equity ratio) can be affected by macroeconomic conditions. We construct a dynamic economy with asymmetric information in the credit market. The features of optimal securities issued at equilibrium are influenced by macroeconomic conditions. As a by-product, the debt-to-equity ratio in the overall economy will evolve according to the dynamics of aggregate variables. The remaining of the thesis develops a theoretical analysis of credit relationships where multiple financiers compete over the loan contracts they are offering to entrepreneurs-borrowers. To this extent, Chapter 3 proposes a unified framework to analyze the so-called literature on competing mechanisms and provides new results in terms of characterizing the equilibria of multi-principal multi-agent games. In the specific context of common agency games, we show that the introduction of a separability requirement on agent's preferences with respect to the contract offers she receives from principals is a sufficient condition to retrieve the Revelation Principle. Importantly, no restriction on principals' preferences is introduced. Chapter 4 investigates credit market relationships when competing lenders are explicitly considered. A reformulation of the traditional credit channel of Monetary Policy is then suggested. When lenders are strategically competing on their credit contract offers, positive-profit equilibria typically arise. Our analysis considers both the exclusive case and the non-exclusive one and it argues that monetary factors may affect the real sector mainly by modifying the structure of markets. The last chapter discusses the welfare implications of contractual externalities that arise in the presence of multiple financiers. We consider a scenario where a Social Planner is subject to the same informational constraints faced by principals in a simple model of the credit market. We identify conditions that sustain constrained-efficiency of market equilibria.

Underwater operation and sampling has been replaced by ROV (Remotely Operated Vehicle) and underwater manipulator gradually, which can avoid divers to face the dangers due to the environmental pressure and low temperature. When ROV to carry out the mission, the operator sees the undersea environment and the target with the information feedback from the sensors. Recently, we developed a general purpose controller for controlling underwater robotic systems. We plan to install the manipulator on the ROV with the same general purpose controller. One of the concerns in desgining is: the ROV generally mantains neutral buoyant in seawater. When adding or removing any components, the arrangement of balast weight needs to done again to keep the balance of the system. Moreover, the center of gravity will be changed such that dynamics of the ROV will be different when collaborating with the underwater manipulator. To resolve these problems, we review the design and hope to reduce the size and weight of each component.The new design also introduces the use of a junction box. The junction box keeps all the circuits, power converters and motor control card. It allows the reconfiguration of power and commands pathway much easier. To reduces of the size of the housings, the gear transmission set is moved out of the housing. According to the positioning accuray requirement of each axis, a DC servomotor or a DC motor is installed. Underwater manipulators do not require agile motion. Therefore we use a gear-worm set as the transmission between links to increase torque. The motion control is implemented with a Jacobian to calculate the increment joint angles for joint coordinate control. Human-interface was developed with Borland C++ Builder and OpenGL to let the operator to simulate and control of the manipulator with an input of a 3D joystick.

none

none

The aggregate power of all resources on the Internet is enormous. The Internet can be viewed as a massive virtual organization that holds tremendous amounts of information and resources with different ownerships. However, little is known about how to run this organization efficiently. This dissertation studies the problems of distributed task and resource allocation among self-interested agents in virtual organizations. The developed solutions are not allocation mechanisms that can be imposed by a centralized designer, but decentralized interaction mechanisms that provide incentives to self-interested agents to behave cooperatively. These mechanisms also take computational tractability into consideration due to the inherent complexity of distributed task and resource allocation problems. Targeted allocation mechanisms can achieve global task allocation efficiency in a virtual organization and establish stable resource-sharing communities based on agents’ own decisions about whether or not to behave cooperatively. This high level goal requires solving the following problems: synthetic task allocation, decentralized coalition formation and automated multiparty negotiation. For synthetic task allocation, in which each task needs to be accomplished by a virtual team composed of self-interested agents from different real organizations, my approach is to formalize the synthetic task allocation problem as an algorithmic mechanism design optimization problem. I have developed two approximation mechanisms that I prove are incentive compatible for a synthetic task allocation problem. This dissertation also develops a decentralized coalition formation mechanism, which is based on explicit negotiation among self-interested agents. Each agent makes its own decisions about whether or not to join a candidate coalition. The resulting coalitions are stable in the core in terms of coalition rationality. I have applied this mechanism to form resource sharing coalitions in computational grids and buyer coalitions in electronic markets. The developed negotiation mechanism in the decentralized coalition formation mechanism realizes automated multilateral negotiation among self-interested agents who have symmetric authority (i.e., no mediator exists and agents are peers). In combination, the decentralized allocation mechanisms presented in this dissertation lay a foundation for realizing automated resource management in open and scalable virtual organizations.

This dissertation consists of three essays on microeconomics. The first essay considers matching markets, markets where buyers and sellers and concerned about who they interact with. It proposes a model to analyze these markets akin to the standard supply and demand framework. The second essay considers mechanism design, the problem of designing rules to make collective decisions in the presence of private information. It proposes the concept of strategyproofness in the large, which is that an agent without too fine information has negligible gains from misreporting her type in a large market. It argues that, for all practical purposes, this concept correctly separates mechanisms where behavior akin to price-taking is observed, and those where participants rampantly manipulate their stated preferences. A Theorem is proven that gives a precise sense in which strategyproofness in the large is not a very restrictive property. The third essay considers the evolutionary origins of the endowment effect bias, where the willingness to pay for a good is smaller than the willingness to accept. It gives evidence that this bias is not present in a modern hunter-gatherer population, questioning standard evolutionary accounts. It shows that cultural shocks in a subpopulation did give rise to the bias. / Economics

<p>\abstract</p><p>{\em Mechanism design} studies optimization problems taking into accounts of the selfish agents. {\em Network externality} is the effect a consumer receives from other consumers of the same good. This effect can be negative or positive. We first consider several mechanism design problems under the network externality assumption. The externality model used in this dissertation is more general than the widely used cardinality based model. In particular the network we consider in this dissertation is a graph, which is not necessarily complete. Our goal is to design {\em truthful} mechanisms to maximize the seller's revenue. Our main results under the network externality utility model are several optimal or near optimal mechanisms for {\em digital goods auctions}. To do so we invent several novel approximation schemes as well as applying results from the {\em approximation algorithm} literature. In particular when the agents exhibit negative network externality, we first model the problem as a two staged {\em pricing game}. We then show that the pricing game is an exact {\em potential game} which always admits a pure {\em Nash Equilibrium}. We then study the {\em best} and {\em worst} Nash Equilibrium in this game in terms of the revenue. We show two positive results. For the best Nash Equilibrium we show a $2$-approximation to the maximum revenue on bipartite graphs. For the worst Nash Equilibrium we use the notion of a {\em $\delta$-relaxed} equilibrium. In the sense that the prices for the same type of agents are within $\delta$ factor of each other. We accompany our positive results with matching hardness results. On the other hand, when the agents exhibit positive network externality, we take the {\em Myersonian} approach. We first give a complete characterization for all the truthful mechanisms. Using this characterization we present a truthful mechanism which achieves the optimal expected revenue among all the truthful mechanisms when the prior distributions of the agents are {\em independent} and {\em regular}. We also show near optimal mechanisms when the prior distributions are possibly {\em correlated}. </p><p>{\em Prior-free} auctions can approximate meaningful benchmarks for</p><p>non-identical bidders only when sufficient qualitative information</p><p>about the bidder asymmetry is publicly known.</p><p>We consider digital goods auctions where there is a {\em</p><p>total ordering} of the bidders that is known to the seller,</p><p>where earlier bidders are in some sense thought to have higher</p><p>valuations. </p><p>We define</p><p>an appropriate revenue benchmark: the maximum revenue that can be</p><p>obtained from a bid vector using prices that are nonincreasing in the</p><p>bidder ordering and bounded above by the second-highest bid. </p><p>This {\em monotone-price benchmark} is always as large as the well-known</p><p>fixed-price benchmark, so designing prior-free auctions with</p><p>good approximation guarantees is only harder. </p><p>By design, an auction that approximates the monotone-price benchmark</p><p>satisfies a very strong guarantee: it is, in particular, simultaneously</p><p>near-optimal for </p><p>essentially every {\em Bayesian} environment in which bidders'</p><p>valuation distributions have nonincreasing monopoly prices, or in</p><p>which the distribution of each bidder stochastically dominates that</p><p>of the next. Even when there is no distribution over bidders'</p><p>valuations, such an auction still provides a quantifiable</p><p>input-by-input performance guarantee. We design a simple $O(1)$-competitive prior-free</p><p>auction for digital goods with ordered bidders.</p> / Dissertation

Compliant mechanisms (CMs) take advantage of the deformation of their flexible members to transfer motion, force, or energy, offering attractive advantages in terms of manufacturing and performance over traditional rigid-body mechanisms (RBMs). This dissertation aims to advance the topology optimization (TO) technique (1) to design CMs that are more effective in performing their functions while being sufficiently strong to resist yield or fatigue failure; and (2) to design CMs from the perspective of mechanisms rather than that of structures, particularly with the insight into the concepts of joints, actuations, and functions of mechanisms. The existing TO frameworks generally result in CMs that are much like load-bearing structures, limiting the applications of CMs. These CMs (1) do not have joints, (2) are actuated by a translational force, and (3) can only do simple work such as amplifying motion or gripping. Three TO frameworks for the synthesis of CMs are proposed in this dissertation and they are summarized below. First, a framework was developed for the design of efficient and strong CMs. The widely used stiffness-flexibility criterion for CM design with TO results in lumped CMs that are intrinsically efficient in transferring motion, force, or energy but are prone to high localized stress and thus weak to resist yield or fatigue failure. Indeed, distributed CMs may have a better stress distribution than lumped CMs but have the weakness of being less efficient in motion, force, or energy transfer than lumped CMs. Based on this observation, the proposed framework rendered the concept of hybrid systems, hybrid CMs in this case. Further, the hybridization was achieved by a proposed super flexure hinge element and a design criterion called input stroke criterion in addition to the traditional stiffness-flexibility criterion. Both theoretical exploration and CM design examples are presented to show the effectiveness of the proposed approach. The proposed framework has two main contributions to the field of CMs: (1) a new design philosophy, i.e., hybrid CMs through TO techniques and (2) a new design criterion—input stroke. Second, a systematic framework was developed for the integrated design of CMs and actuators for the motion generation task. Both rotary actuators and bending actuators were considered. The approach can simultaneously synthesize the optimal structural topology and actuator placement for the desired position, orientation, and shape of the target link in the system while satisfying the constraints such as buckling constraint, yield stress constraint and valid connectivity constraint. A geometrically nonlinear finite element analysis was performed for CMs driven by a bending actuator and CMs driven by a rotary actuator. Novel parameterization schemes were developed to represent the placements of both types of actuators. A new valid connectivity scheme was also developed to check whether a design has valid connectivity among regions of interest based on the concept of directed graphs. Three design examples were constructed and a compliant finger was designed and fabricated. The results demonstrated that the proposed approach is able to simultaneously determine the structure of a CM and the optimal locations of actuators, either a bending actuator or a rotary actuator, to guide a flexible link into desired configurations. Third, the concept of a module view of mechanisms was proposed to represent RBMs and CMs in a general way, particularly using five basic modules: compliant link, rigid link, pin joint, compliant joint, and rigid joint; this concept was further developed for the unified synthesis of the two types of mechanisms, and the synthesis approach was thus coined as module optimization technique—a generalization of TO. Based on the hinge element in the finite element approach developed at TU Delft (Netherlands in early 1970), a beam-hinge model was proposed to describe the connection among modules, which result in a finite element model for both RBMs and CMs. Then, the concept of TO was borrowed to module optimization, particularly to determine the “stay” or “leave” of modules that mesh a design domain. The salient merits with the hinge element include (1) a natural way to describe various types of connections between two elements or modules and (2) a provision of the possibility to specify the rotational input and output motion as a design problem. Several examples were constructed to demonstrate that one may obtain a RBM, or a partially CM, or a fully CM for a given mechanical task using the module optimization approach.

abstract: This dissertation presents three essays in economics. Firstly, I study the problem of allocating an indivisible good between two agents under incomplete information. I provide a characterization of mechanisms that maximize the sum of the expected utilities of the agents among all feasible strategy-proof mechanisms: Any optimal mechanism must be a convex combination of two fixed price mechanisms and two option mechanisms. Secondly, I study the problem of allocating a non-excludable public good between two agents under incomplete information. An equal-cost sharing mechanism which maximizes the sum of the expected utilities of the agents among all feasible strategy-proof mechanisms is proved to be optimal. Under the equal-cost sharing mechanism, when the built cost is low, the public good is provided whenever one of the agents is willing to fund it at half cost; when the cost is high, the public good is provided only if both agents are willing to fund it. Thirdly, I analyze the problem of matching two heterogeneous populations. If the payoff from a match exhibits complementarities, it is well known that absent any friction positive assortative matching is optimal. Coarse matching refers to a situation in which the populations into a finite number of classes, then randomly matched within these classes. The focus of this essay is the performance of coarse matching schemes with a finite number of classes. The main results of this essay are the following ones. First, assuming a multiplicative match payoff function, I derive a lower bound on the performance of n-class coarse matching under mild conditions on the distributions of agents' characteristics. Second, I prove that this result generalizes to a large class of match payoff functions. Third, I show that these results are applicable to a broad class of applications, including a monopoly pricing problem with incomplete information, as well as to a cost-sharing problem with incomplete information. In these problems, standard models predict that optimal contracts sort types completely. The third result implies that a monopolist can capture a large fraction of the second-best profits by offering pooling contracts with a small number of qualities. / Dissertation/Thesis / Ph.D. Economics 2011