We studied the migration of nonmagnetic, submicrometer polystyrene beads submerged in a magnetic fluid in the presence of nonuniform magnetic fields as a potential method for size-based separation of submicrometer, nonmagnetic species. Since the polystyrene beads are much larger than the magnetic fluid nanoparticles, the magnetic fluid was treated as a one-component continuum with respect to the beads. We found that the polystyrene beads will migrate in the direction of decreasing magnetic fields and will focus over a region where the magnetic field or its gradient vanishes, as predicted by our model. The concentration profiles predicted by our model, which has no adjustable or fitted parameters, agree reasonably well with the experimental data both qualitatively and quantitatively. / Singapore-MIT Alliance (SMA)

This paper analyzes the link between equity-based compensation and created incentives by (1) deriving a measure of incentives suitable for both linear and non-linear compensation contracts, (2) analyzing the effect of risk on incentives, and (3) clarifying the role of the agent's private trading decisions in incentive creation. With option-based compensation contracts, the average pay-forperformance sensitivity is not an adequate measure of ex-ante incentives. Pay-for-performance covaries negatively with marginal utility and hence overstates the created incentives. Second, more noise in the performance measure implies that the manager is less certain about the effect of effort on performance, which in turn makes her less willing to exert effort. Finally, the private trading decisions by the manager have first-order effects on incentives. By reducing her holdings of the market asset, the manager achieves an effect similar to "indexing" the stock or option grant, making explicit indexation of the contract redundant.

This paper shows that, provided circuits contain no zero-delay loops, a tight relationship, full abstraction, exists between a natural event-based operational semantics for circuits and a natural denotational semantics for circuits based on causal functions on value timelines. The paper also discusses what goes wrong if zero-delay loops are allowed, and illustrates the application of this semantic relationship to modeling questions.

In model-based recognition, ad hoc techniques are used to decide if a match of data to model is correct. Generally an empirically determined threshold is placed on the fraction of model features that must be matched. We rigorously derive conditions under which to accept a match, relating the probability of a random match to the fraction of model features accounted for, as a function of the number of model features, number of image features and the sensor noise. We analyze some existing recognition systems and show that our method yields results comparable with experimental data.

This thesis describes two programs for generating tests for digital circuits that exploit several kinds of expert knowledge not used by previous approaches. First, many test generation problems can be solved efficiently using operation relations, a novel representation of circuit behavior that connects internal component operations with directly executable circuit operations. Operation relations can be computed efficiently by searching traces of simulated circuit behavior. Second, experts write test programs rather than test vectors because programs are more readable and compact. Test programs can be constructed automatically by merging program fragments using expert-supplied goal-refinement rules and domain-independent planning techniques.

This thesis explores ways to augment a model-based diagnostic program with a learning component, so that it speeds up as it solves problems. Several learning components are proposed, each exploiting a different kind of similarity between diagnostic examples. Through analysis and experiments, we explore the effect each learning component has on the performance of a model-based diagnostic program. We also analyze more abstractly the performance effects of Explanation-Based Generalization, a technology that is used in several of the proposed learning components.

This thesis addresses the problem of recognizing solid objects in the three-dimensional world, using two-dimensional shape information extracted from a single image. Objects can be partly occluded and can occur in cluttered scenes. A model based approach is taken, where stored models are matched to an image. The matching problem is separated into two stages, which employ different representations of objects. The first stage uses the smallest possible number of local features to find transformations from a model to an image. This minimizes the amount of search required in recognition. The second stage uses the entire edge contour of an object to verify each transformation. This reduces the chance of finding false matches.

We present a new method for rendering novel images of flexible 3D objects from a small number of example images in correspondence. The strength of the method is the ability to synthesize images whose viewing position is significantly far away from the viewing cone of the example images ("view extrapolation"), yet without ever modeling the 3D structure of the scene. The method relies on synthesizing a chain of "trilinear tensors" that governs the warping function from the example images to the novel image, together with a multi-dimensional interpolation function that synthesizes the non-rigid motions of the viewed object from the virtual camera position. We show that two closely spaced example images alone are sufficient in practice to synthesize a significant viewing cone, thus demonstrating the ability of representing an object by a relatively small number of model images --- for the purpose of cheap and fast viewers that can run on standard hardware.

Thesis (Ph. D.)--Lehigh University, 2004. / Includes bibliographical references (p. 93-101). Also available on the Internet.

This dissertation addresses different kinds of Mandarin multi-verb constructions (MVCs), seeking to solve a long-standing problem in Chinese linguistics: namely, how to account for a plethora of constructions, including a subset called serial verb constructions. In most previous studies, only a limited number of MVCs have been examined by any one researcher. By contrast, this dissertation aims to provide a unified account of all types of Mandarin MVCs. I argue such a goal can be achieved through a usage-based cognitive approach. By proposing that MVCs display varying degrees of event integration, my analysis can differentiate meaningfully among distinct kinds of MVCs. Based on the form-meaning pairing criterion, I argue that MVCs of different types can be localized along portions of a continuum of event integration. This study mines the Lancaster Corpus of Mandarin Chinese for MVCs. The corpus results show there is lexical restrictedness as measured by verb type/token ratios in certain MVCs. The continuum of type/token ratios is argued to correlate with the continuum of event integration of MVCs, with lower ratios correlating with higher degrees of event integration and with higher ratios correlating with lower degrees of event integration. The corpus data indicate there is a strong interaction between lexical items and construction types. Certain verbs are easily attracted to a particular construction or even a particular verb position. Also, the corpus results reflect an asymmetry in MVCs in that verbs in one position may be more restricted. The position-specific patterns of type/token frequency largely reveal the event structures underlying particular MVCs. Generally, the verb position having a higher type/token ratio represents a core phase. The corpus results show the mutual attraction of verbs and constructions, the strong tendency to use MVCs for encoding unitary albeit complex events, and the link between lexical restrictedness and event integration as evidenced by the large variety of types of MVCs in Mandarin. The findings support a usage-based model where constructions are understood to be conventionalized units, and fixed idiomatic expressions are considered to be as important to the expressive inventory of the language as are open or fully productive syntactic structures.