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Recent Submissions

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    Speech acts and pragmatics in sentence generation
    (University of Waterloo, 1992-09) Shelley, Cameron
    A fundamental advance in recent theories about natural language pragmatics involves the realization that people use language not just to describe propositions, but also to perform actions. This idea can be taken as a given starting point for investigating the questions: how are linguistic actions, or speech acts, performed and understood? How far can descriptions, as locutions, be used as speech acts What role does inference play in the performance and understanding of speech acts? Many previous theories of speech acts have taken speech acts to be independent and primitive units of communication, implicit in, but separate from, description and inference. In this thesis, I argue for an alternative model of speech acts. I propose that speech acts can be explained by a combination of description and inference, without the requirement of separate conventions. This explanation relies instead on an account of explicit linguistic units, including clausal moods and performative verbs, in addition to the inferential mechanism provided by Gricean conversational implicature. In addition to outlining a model for the description and comparison of speech acts, I present a small sentence generator that partially implements the model, and discuss how it can be enhanced in future. Also, I illustrate the relevance of this model for a current computational theory of syntactic style. My model of speech acts suggests how this computational stylistic theory can be extended into the areas of semantic style and lexical style.
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    Solving partial constraint satisfaction problems using local search and abstraction
    (University of Waterloo, 1992-09) Yang, Qiang; Fong, Philip W. L.
    Partial constraint satisfaction problems (PCSPs) were proposed by Freuder and Wallace to address some of the representational difficulties with traditional constraint satisfaction techniques. However, the reasoning method of their proposal was limited to traditional backtracking based algorithms. In this paper, we extend the PCSP model by associating it with a local search algorithm, which has found great successes in solving many large scale problems in the past. Furthermore, we extend the combined model to incorporate abstract problem solving, and show that the extended model has not only the advantages of both PCSP and local search, but also a number of new features useful for scheduling applications. We demonstrate the feasibility of our approach by an application to a university course scheduling domain.
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    Highly parallel sparse triangular solution
    (University of Waterloo, 1992-10) Alvarado, Fernando L.; Pothen, Alex; Schreiber, Robert
    In this paper we survey a recent approach for solving sparse triangular systems of equations on highly parallel computers. This approach employs a partitioned representation of the inverse of the triangular matrix so that the solution can be computed by matrix-vector multiplication. The number of factors in the partitioned inverse is proportional to the number of general communication steps (router steps on a CM-2) required in a highly parallel algorithm. We describe partitioning algorithms that minimize the number of factors in the partitioned inverse over all symmetric permutations of the triangular matrix such that the permuted matrix continues to be triangular. For a Cholesky factor we describe an O(n) time and space algorithm to solve the partitioning problem above, where n is the order of the matrix. Our computational results on a CM-2 demonstrate the potential superiority of the partitioned inverse approach over the conventional substitution algorithm for highly parallel sparse triangular solution. Finally we describe current and future extensions of these results.
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    Characterization of virus-like particles from the BEVS platform with a special focus on gradient ultracentrifugation
    (University of Waterloo, 2026-08-28) Cheng, Nicholas
    Coronaviruses continue to be an evolving threat, and Severe Acute Respiratory Syndrome (SARS) Virus-Like-Particles (VLPs) may be suitable as vaccine candidates. Early indications were that a SARS-VLP could be generated based on a universal betacoronavirus sequence using only Spike, Envelope and Membrane structural proteins. This process involved the generation of VLPs through the insect cell-baculovirus expression vector system (IC-BEVS), followed by semi-purification via gradient ultracentrifugation and subsequent fractionation. Collected fractions were analyzed by bicinchonic acid assay, flow virometry, immunoblotting, and multi-angle dynamic light scattering. Particle concentration, size, DNA content, and surface protein composition was determined for semi-purified samples. This study provides a clearer understanding of biological dynamics in VLP generation workflows, by comparing HIV-VLPs, SARS-VLPs, baculovirus, and other co-produced particles. It was expected that significant concentrations of particles would not be observed in uninfected Sf9 cell culture supernatant samples, baculovirus alone would be observed in non-VLP producing samples, and VLPs would be observed in addition to baculovirus in VLP major structural protein producing samples. MADLS was used to assess the size and concentration of all particles produced and semi-purified, since all samples would be treated identically prior to measurement. It can be concluded that though both types of VLPs possess similarly-derived envelopes, their behavior is highly dependent on structural protein composition. In terms of particle diameter, VLPs were expected to range between 50 nm and 250 nm, and baculovirus at 250 nm and greater. Post semi-purification, it was noted that some particles in the expected size range of baculovirus and VLP were detected in all samples, between fractions of densities 1.05 to 1.21 g/mL. Further analysis elucidated that uninfected samples had significantly lower measurement accuracy and a larger range of mean concentrations and sizes for those particles, which indicates a lack of reliability. Particles in the expected size range for VLPs found in non-VLP producing baculovirus samples were far more consistent, and determined to be real particles between densities 1.07 to 1.17 g/mL. These may be extracellular vesicles produced by insect cells under stress of infection, which have been documented in literature. Particles in the expected size range for baculovirus for this sample were also found in this density range. In VLP producing samples, particles were found that were consistent with expected size ranges for VLPs and baculovirus in the density ranges of 1.07 to 1.17 g/mL. Data from multiple orthogonal methods confirmed that the fraction containing the highest concentration of non-fluorescent HIV-VLPs, SARS-VLPs, and baculovirus was that with a density of 1.13 g/mL. Fluorescent HIV-VLPs by contrast, appeared less dense and had a maximum concentration at a density of 1.10 g/mL. In examining MADLS as a method of better characterizing the SARS-VLP, significant knowledge about the IC-BEVS was obtained which will assist in further developing this system and associated downstream purification processes.
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    The stability of the partitioned inverse approach to parallel sparse triangular
    (University of Waterloo, 1992-10) Pothen, Alex; Higham, Nicholas J.
    Several authors have recently considered a parallel method for solving sparse triangular systems with many right-hand sides. The method employs a partition into sparse factors of the product form of the inverse of the coefficient matrix. It is shown here that the method can be unstable, stability is guaranteed if a certain scalar that depends on the matrix and the partition is small, and that this scalar is small when the matrix is well-conditioned. Moreover, when the partition is chosen so that the factors have the same sparsity structure as the coefficient matrix, the backward error matrix can be taken to be sparse.