Contractibility and Contractible Approximations of Soft Global Constraints

We study contractibility and its approximation for two very general classes of soft global constraints. We introduce a general formulation of decomposition-based soft constraints and provide a sufficient condition for contractibility and an approach to approximation. For edit-based soft constraints, we establish that the tightest contractible approximation cannot be expressed in edit-based terms, in general

Agency Theory: Methodology, Analysis

Designing a contract is often more of an economic than a legal problem. A good contract protects parties against opportunistic behavior while providing motivation to cooperate. This is where economics and, especially contract theory, may prove helpful by enhancing our understanding of incentive issues. The purpose of this book is to provide specific tools which will help to write better contracts in real world environments. Concentrating on moral hazard literature, this book derives a tentative checklist for drafting contracts. As an economic contribution to a field traditionally considered an art rather than a science, this treatment also gives much attention to methodological issues

Tethered Motion Planning for a Rappelling Robot

The Jet Propulsion Laboratory and Caltech developed the Axel rover to investigate and demonstrate the potential for tethered extreme terrain mobility, such as allowing access to science targets on the steep crater walls of other planets. Tether management is a key issue for Axel and other rappelling rovers. Avoiding tether entanglement constrains the robot's valid motions to the set of outgoing and returning path pairs that are homotopic to each other. In the case of a robot on a steep slope, a motion planner must additionally ensure that this ascent-descent path pair is feasible, based on the climbing forces provided by the tether. This feasibility check relies on the taut tether configuration, which is the shortest path in the homotopy class of the ascent-descent path pair. This dissertation presents a novel algorithm for tethered motion planning in extreme terrains, produced by combining shortest-homotopic-path algorithms from the topology and computational geometry communities with traditional graph search methods. The resulting tethered motion planning algorithm searches for this shortest path, checks for feasibility, and then generates waypoints for an ascent-descent path pair in the same homotopy class. I demonstrate the implementation of this algorithm on a Martian crater data set such as might be seen for a typical mission. By searching only for the shortest path, and ordering that search according to a heuristic, this algorithm proceeds more efficiently than previous tethered path-planning algorithms for extreme terrain. Frictional tether-terrain interaction may cause dangerously intermittent and unstable tether obstacles, which can be categorized based on their stability. Force-balance equations from the rope physics literature provide a set of tether and terrain conditions for static equilibrium, which can be used to determine if a given tether configuration will stick to a given surface based on tether tension. By estimating the tension of Axel's tether when driving, I divide potential tether tension obstacles into the following categories: acting as obstacles, acting as non-obstacles, and hazardous intermittent obstacles where it is uncertain whether the tether would slip or stick under normal driving tension variance. This dissertation describes how to modify the obstacle map as the categorization of obstacles fluctuates, and how to alter a motion plan around the dangerous tether friction obstacles. Together, these algorithms and methods form a framework for tethered motion planning on extreme terrain.</p

Exploring Japanese learners' perception, production, and beliefs concerning spoken English contractions

This mixed-methods study examined the beliefs and performance of 10 adult Japanese speakers of English regarding the phenomenon of contraction in spoken English. Over the course of three months, a collective case study approach involving listening tasks and semi-structured interviews was employed to investigate the topic from multiple dimensions, both qualitatively and quantitatively. In addition to the creation of individual portraits of these English learners by exploring their unique learning histories, and their oral/aural performance, similar performance data collected from four native English speakers were used to further contextualize the Japanese participants’ results. Analysis revealed distinct tendencies regarding contraction production and perception ability as they relate, for instance, to contraction type and the ratio of contraction. The research also uncovered common themes regarding general and individual-specific contraction-related beliefs. These findings can serve as a touchstone for researchers and educators concerned with the English oral/aural development of Japanese learners, specifically with regard to contraction-related issues affecting them

TOPOLOGICAL STRUCTURE OF SPATIALLY-DISTRIBUTED NETWORK CODED INFORMATION

In this paper we generalize work using topological methods for testing wireless/sensor network coverage to the problem of covering a geographically-distributed wireless network with linear network coded data. We define the coverage complex, a new type of simplicial complex built on the nodes of the network which captures properties of the data coverage, and use tools from algebraic topology, persistent homology, and matroid theory to study it. The coverage complex shares properties with the Rips complex, however it also suffers from a more diverse variety of potential failures. We extend the standard coverage criteria to account for some of these situations using persistent homology, multi-sheeted localized covers of the space, and Mayer-Vietoris sequences. We also investigate the combinatorial properties of the coverage complex, determining the correspondence between it and the lattice of linear subspaces of a vector space. Finally we present algorithms for computing coverage complexes, present a software package designed to compute and experiment with coverage complexes, and provide a summary of ongoing and future work

Essays on CEO compensation.

This thesis analyzes CEO compensation contracts in a principal-agent framework with moral hazard. It focuses on two issues: the form and the timing of performance-based pay. On the one hand, if CEOs are assumed to be mean-variance maximizers, I show that it is suboptimal to provide incentives with contracts which are convex in performance. This is because these contracts make the variance of pay an increasing function of the CEO's effort, which is inefficient. Sticks are more efficient than carrots, although the latter may be used in case the agent is protected by limited liability. On the other hand, if CEOs are assumed to be not only risk averse but also prudent, convex contracts and rewards may be optimal, since they protect against downside risk. A calibration of a HARA-lognormal model shows that CEO preferences which minimize the suboptimality of the typically observed contracts (relative to the optimal contract) feature decreasing absolute risk aversion, as well as low and decreasing relative risk aversion. However, when CEO pay is contingent on a lognormally distributed stock price, it is hard to rationalize the use of convex contracts for incentive provision. The thesis then examines the optimal evaluation and payment date, when the CEO's actions materialize with a lag. Information asymmetries are progressively resolved: the precision of signals that shareholders receive regarding the final outcome is increasing with time. However, the accumulation of exogenous shocks make deferred compensation noisy. The optimal timing of CEO pay, which minimizes the extent of the mispricing at the payment date, is derived. Opportunities for two types of managerial short-termism are then introduced. To ensure that the manager does not engage in short-termist and inefficient behavior, it is often optimal to reduce the power of incentives, and to postpone the evaluation and payment date