Showing papers by "University of Waterloo published in 1987"

An Introduction to Splines for Use in Computer Graphics and Geometric Modeling

Abstract: 1 Introduction 2 Preliminaries 3 Hermite and Cubic Spline Interpolation 4 A Simple Approximation Technique - Uniform Cubic B-splines 5 Splines in a More General Setting 6 The One-Sided Basis 7 Divided Differences 8 General B-splines 9 B-spline Properties 10 Bezier Curves 11. Knot Insertion 12 The Oslo Algorithm 13 Parametric vs. Geometric Continuity 14 Uniformly-Shaped Beta-spline Surfaces 15 Geometric Continuity, Reparametrization, and the Chain Rule 16 Continuously-Shaped Beta-splines 17 An Explicity Formulation for Cubic Beta-splines 18 Discretely-Shaped Beta-splines 19 B-spline Representations for Beta-splines 20 Rendering and Evaluation 21 Selected Applications

Negative binomial and mixed Poisson regression

Abstract: A number of methods have been proposed for dealing with extra-Poisson variation when doing regression analysis of count data. This paper studies negative-binomial regression models and examines efficiency and robustness properties of inference procedures based on them. The methods are compared with quasilikelihood methods. Plusieurs methodes ont ete proposees en vue de traiter le probleme de la variation extra-poissonnienne dans une analyse de regression pour donnees de denombrement. Cet article a pour objet l'etude de modeles de regression binomiale negative et se penche sur les proprietes d'efficacite et de robustesse des methodes inferentielles decoulant des modeles. Ces dernieres sont comparees aux methodes de quasi-vraisemblancce.

Constraints on human arm movement trajectories.

Abstract: AUSTKA< T The underlying pirn-esses in movement organization and control were studied by varying the conditions under which arm movements were made. The three-dimensional movement trajectories of the following conditions were contrasted: pointing to a target with the index linger versus grasping a disk the same size as the target, grasping a fragile object versus a soil resilient object, and grasping a disk either to throw into a large box or place into a light litting well. Results showed that the arm trajectories, as represented by the resultant velocity profile of the wrist, varied considerably in their shape with the main factor being when peak velocity was reached as a function of the total duration of the movement. It appeared that when task demands required greater precision, the main deceleration phase of the trajectory was increased in duration. These results do not support a movement production mechanism that has access to an abstract representation of a base velocity profile and that creates trajectories by a simple scaling procedure in the temporal domain. Rather, the results support a view of movement production as relatively specific to the past experience of the performer and the constraints of the task. Ix's processus a la base du controlc el de ('organisation du mouvement out etc etudies en variant les conditions sous lesquelles les mouvements du bras etaient executes. Les trajectoires de mouvemenl tridimcnsionncl des conditions suivantes etaient niises en contraste: pointer une cible avee l'index versus saisir un disque de la meme taille que la cible; saisir un objet fragile versus un object elastique. mou; ct, saisir un disque suit pour le lancer dans une grnnde boitc soit le placer dans un puits bien ajustc. Les resultats indiquent que les trajectoires du bras, lelles que represenlees par le prolil de velocite resultant du poignel, varicnt considerablement dans leur forme avec le facteur principal apparaissant au moment ou 1c pic de velocite etait atteinl en tant que function de la duiee tolale du mouvement. Lorsque la tache requiert line plus grande precision la phase de deceleration principale dc la trajecloire augmente en duree. Cos resultats n'appuient pas un mccanisme dc production du mouvemenl ayant acccs a line representation abslraitc d'un prolil dc velocite dc base et creant des trajectoires par un procedc d'echelonncment simple dans le domaine temporcl. Cos resultats supported! plulol I \"idee d'unc production de mouvement coiiunc relativement specilique ii lexperience passcc du …

The role of free radicals in senescence and wounding.

Abstract: Reactions involving free radicals are an inherent feature of plant senescence and appear to contribute to a process of oxidative deterioration that leads ultimately to cell death. Radical species derived from molecular oxygen are the primary mediators of this oxidative damage, but non-radical excited states of oxygen, specifically singlet oxygen, may also be involved. Several lines of evidence suggest that degradation of lipids in senescing membranes and the ensuing release of free fatty acids initiate oxidative deterioration by providing substrate for lipoxygenase. In some tissues, lipoxygenase activity increases with advancing senescence in a pattern that is consistent with its putative role in promoting oxidative damage. However, there are important exceptions to this which may be explained by the fact that the timing and extent of peroxidative reactions initiated by lipoxygenase are likely to be determined more by the availability of substrate for the enzyme than by changes in its activity. There are both membranous and cytosolic forms of lipoxygenase in senescing tissues, and peroxidation of membrane lipids appears to be initiated by the membranous enzyme once the appropriate fatty acid substrates, linoleic acid and linolenic acid, become available. Since lipid peroxidation is known to form alkoxy and peroxy radicals as well as singlet oxygen, these reactions in membrane bilayers are probably a major source of activated oxygen species in senescing tissues. Further-more, there are indications that activated oxygen from the lipoxygenase reaction can become substrate for the cytosolic form of the enzyme which, in turn, may raise the titre of activated oxygen during senescence. Additional possible sources of increased free radical production in senescing tissues include peroxidase, which shows greatly increased activity with advancing age, leakage of electrons from electron transport systems to oxygen, in particular from the photosynthetic electron transport system, and decompartmentalization of iron, which would facilitate formation of the highly reactive hydroxyl radical from the less reactive superoxide anion. A variety of macromolecules can be damaged by activated oxygen. Unsaturated fatty acids are especially prone to attack, and this implies that membranes are primary targets of free radical damage. The manifestations of this damage in senescing tissues range from altered membrane fluidity and phase properties to leakiness that can be attributed to a destabilized and highly perturbed membrane bilayer. There is also a progressive breakdown of cellular protein with advancing senescence. Free radicals can inactivate proteins by reacting with specific amino acid residues, and a number of in zitro studies have indicated that such alteration renders the proteins more prone to hydrolysis by proteases. Thus, although there is no direct evidence linking enhanced proteolysis during senescence to free radical damage, there is reason to believe that this may be a contributing factor. Wounding of certain plant tissues also initiates a series of reactions that revolve around the breakdown of membrane lipids and their peroxidation. Indeed, as in the case of senescence, membrane deterioration follokving wounding appears to be facilitated by a self-perpetuating wave of free radical production emanating from peroxidation within the lipid bilayer. There is also recent evidence for activation of an O2- -producing NADPH oxidase in plant tissues following fungal infection that may be analogous to the well-characterized O2- -generating NADPH oxidase associated with the plasma membrane of polymorphonuclear leukocytes. This raises the interesting possibility that plants and animals share a common defence response to invading organisms. Contents Summary 317 I. Introduction 318 II. Species of activated oxygen 319 III. Sites of activated oxygen production 319 IV. Free radical production during senescence 323 V. Targets of free radical damage in senescing tissues 330 VI. The role of free radicals in seed ageing 336 VII. The role of free radicals in wounding 337 VIII. Concluding remarks 338 Acknowledgement 338 References 338.

Projected gradient methods for linearly constrained problems

Abstract: The aim of this paper is to study the convergence properties of the gradient projection method and to apply these results to algorithms for linearly constrained problems. The main convergence result is obtained by defining a projected gradient, and proving that the gradient projection method forces the sequence of projected gradients to zero. A consequence of this result is that if the gradient projection method converges to a nondegenerate point of a linearly constrained problem, then the active and binding constraints are identified in a finite number of iterations. As an application of our theory, we develop quadratic programming algorithms that iteratively explore a subspace defined by the active constraints. These algorithms are able to drop and add many constraints from the active set, and can either compute an accurate minimizer by a direct method, or an approximate minimizer by an iterative method of the conjugate gradient type. Thus, these algorithms are attractive for large scale problems. We show that it is possible to develop a finite terminating quadratic programming algorithm without non-degeneracy assumptions.

Frank's family of bivariate distributions

Abstract: SUMMARY This paper examines the properties of a new class of bivariate distributions whose members are stochastically ordered and likelihood ratio dependent The proposed class can be used to construct bivariate families of distributions whose marginals are arbitrary and which include the Frechet bounds as well as the distribution corresponding to independent variables Three nonparametric estimators of the association parameter are suggested and Monte Carlo experiments are used to compare their small-sample behaviour to that of the maximum likelihood estimate

A new determination of the ground state interatomic potential for He2

Abstract: A simple accurate potential of the HFD-B form, which appears to be the best characterization of the He-He interaction constructed to date, is presented. It has been fitted to low temperature second virial coefficient data and recent accurate room temperature viscosity data, while at the same time pinning the repulsive wall to the value calculated by Ceperley and Partridge at 1 Bohr. It possesses a well depth of 10·948 K, considerably deeper than many of the recent empirical or ab initio potentials. It reproduces, within experimental error, such dilute gas properties as second virial coefficients, viscosities and thermal conductivities over a wide temperature range. It also predicts, within experimental error, such microscopic properties as differential cross sections, high energy integral cross sections and backward glory oscillations in the integral cross sections. Finally, it accounts for nuclear magnetic relaxation in 3He and supports a weakly bound state in the 4He interaction.

Regression Methods for Poisson Process Data

Abstract: This article is directed toward situations where individuals can experience repeated events, and data on an individual consist of the number and occurrence times of events, along with concomitant variables. Methods of regression analysis are presented, based on Poisson process and proportional intensity assumptions. These include parametric and semi-parametric approaches to model fitting, model assessment, and the treatment of random effects. In addition, insight is gained as to the central role of Poisson and mixed Poisson regression analysis of counts in these methods, and as to the effects of unobserved heterogeneity on semi-parametric analyses. The methods in the article are based on the proportional intensity Poisson process model, for which an individual with given fixed covariate vector x has repeated events occur according to a nonhomogeneous Poisson process with intensity function λx(t) = λ0(t)exp(x′β). Estimation of β and the baseline intensity λ0(t) are considered when λ0(t) is specifi...

Travel, tourism, and hospitality research: A handbook for managers and researchers

Abstract: Partial table of contents: A MANAGERIAL PERSPECTIVE. A Perspective on the Purpose and Nature of Tourism Research Methods (C. Gunn). FUNDAMENTALS OF TRAVEL AND TOURISM RESEARCH. Scaling and Attitude Measurement in Travel and Tourism Research (G. McDougall & H. Munro). NATIONAL, REGIONAL, AND MUNICIPAL PERSPECTIVES. Research in National Tourist Organizations (G. Taylor). SOME DISCIPLINARY PERSPECTIVES. The Political Dimensions of Tourism (L. Richter). AN INDUSTRY SECTOR PERSPECTIVE. Research Needs of Travel Retailers and Wholesalers (E. Wohlmuth). ASSESSING THE IMPACTS OF TOURISM. Event Tourism: Evaluating the Impacts (D. Getz). DATA COLLECTION METHODS OF PARTICULAR RELEVANCE. En Route Surveys (F. Hurst). SPECIAL MARKETING APPLICATIONS. Estimating the Potential of International Markets (D. Wynegar). Index.

Theorist: A Logical Reasoning System for Defaults and Diagnosis

Abstract: We provide an introduction to Theorist, a logic programming system that uses a uniform deductive reasoning mechanism to construct explanations of observations in terms of facts and hypotheses. Observations, facts, and possible hypotheses are each sets of logical formulas that represent, respectively, a set of observations on a partial domain, a set of facts for which the domain is a model, and a set of tentative hypotheses which may be required to provide a consistent explanation of the observations.

Three-dimensional movement trajectories in Fitts' task: Implications for control

Abstract: According to Fitts (1954), movement time (MT) is a function of the combined effects of movement amplitude and target width (index of difficulty). Aiming movements with the same index of difficulty ...

Control Volume Finite-Element Method for Heat Transfer and Fluid Flow Using Colocated Variables— 1. Computational Procedure

Abstract: A novel computational procedure for the prediction of incompressible fluid flow using primitive variables is presented. The formulation retains the geometric flexibility of the finite-element method and derives the governing discrete algebraic equations by using a conservation balance applied to discrete control volumes distributed throughout the domain. A novel method of closure, to relate the control volume surface values to the nodal point values, is introduced whereby a local discrete analog to the governing differential equation is formed at the control volume Surfaces. From this discrete equation analog the control surface values are determined in terms of the nodal values that represent the discrete problem unknowns. The manner in which this discrete equation is formed, solved, and used permits resolution of two longstanding problems in computational fluid dynamics, namely accurate convection modeling and preclusion of pressure field decoupling. A new and general boundary condition specifi...

Airlift reactors: characteristics, applications and design considerations

Abstract: Bioreactors of the airlift type are a promising design for aerobic fermentations. The basic knowledge required for understanding and predicting the performance of these reactors is only now beginning to emerge. In this review we present our observations and those of other investigators in an attempt to build up a coherent picture of airlift devices. All the major aspects—mixing and hydrodynamics, mass and heat transfer—in these reactors are considered. Comparisons between bubble columns and airlift systems are made where analogies, similarities and/or differences between them provide insight into airlift systems. Throughout, the areas of particular concern and those in need of further research in this field are mentioned. Extensive work on all forms of airlift reactors, particularly in non-Newtonian media—homogeneous and suspensions—remains to be done. Current knowledge does not permit airlift reactor design with a high degree of confidence. However, the technical feasibility of all types of fermentations...

An experimental comparison of RGB, YIQ, LAB, HSV, and opponent color models

Abstract: The increasing availability of affordable color raster graphics displays has made it important to develop a better understanding of how color can be used effectively in an interactive environment. Most contemporary graphics displays offer a choice of some 16 million colors; the user's problem is to find the right color.Folklore has it that the RGB color space arising naturally from color display hardware is user-hostile and that other color models such as the HSV scheme are preferable. Until now there has been virtually no experimental evidence addressing this point.We describe a color matching experiment in which subjects used one of two tablet-based input techniques, interfaced through one of five color models, to interactively match target colors displayed on a CRT.The data collected show small but significant differences between models in the ability of subjects to match the five target colors used in this experiment. Subjects using the RGB color model matched quickly but inaccurately compared with those using the other models. The largest speed difference occurred during the early convergence phase of matching. Users of the HSV color model were the slowest in this experiment, both during the convergence phase and in total time to match, but were relatively accurate. There was less variation in performance during the second refinement phase of a match than during the convergence phase.Two-dimensional use of the tablet resulted in faster but less accurate performance than did strictly one-dimensional usage.Significant learning occurred for users of the Opponent, YIQ, LAB, and HSV color models, and not for users of the RGB color model.

Data compression using dynamic Markov modelling

Abstract: A method of dynamically constructing Markov chain models that describe the characteristics of binary messages is developed. Such models can be used to predict future message characters and can therefore be used as a basis for data compression. To this end, the Markov modelling technique is combined with Guazzo's arithmetic coding scheme to produce a powerful method of data compression. The method has the advantage of being adaptive: messages may be encoded or decoded with just a single pass through the data. Experimental results reported here indicate that the Markov modelling approach generally achieves much better data compression than that observed with competing methods on typical computer data.

Natural Attenuation of Aromatic Hydrocarbons in a Shallow Sand Aquifer

Abstract: Inadvertent release of petroleum products such as gasoline into the subsurface can initiate ground water contamination, particularly by the toxic, water-soluble and mobile gasoline components: benzene, toluene and xylenes (BTX). This study was undertaken to examine the processes controlling the rate of movement and the persistence of dissolved BTX in ground water in a shallow, unconfined sand aquifer. Water containing about 7.6 mg/ L total BTX was introduced below the water table and the migration of contaminants through a sandy aquifer was monitored using a dense sampling network. BTX components migrated slightly slower than the ground water due to sorptive retardation. Essentially all the injected mass of BTX was lost within 434 days due to biodegradation. Rates of mass loss were similar for all monoaromatics; benzene was the only component to persist beyond 270 days. Laboratory biodegradation experiments produced similar rates, even when the initial BTX concentration varied. A dominant control over BTX biodegradation was the availability of dissolved oxygen. BTX persisted at the field site in layers low in dissolved oxygen. Decreasing mass loss rates over time observed in the field experiment are not likely due to first-order deeradation rates, but rather to the persistence of small fractions of BTX mass in anoxic layers.

Model studies of polychlorinated dibenzo-p-dioxin formation during municipal refuse incineration.

Abstract: Toxic chlorinated dibenzo-p-dioxins are known to be formed in incinerators that burn municipal refuse. These compounds were synthesized by surface-catalyzed reactions on fly ash particulates taken from incinerators. Dioxins were produced catalytically from chlorinated phenol precursors, from non-chlorinated compounds that were chemically dissimilar to dioxins, and from reaction of phenol with inorganic chlorides. The relative amounts of dioxins formed from [13C6]pentachlorophenol with different fly ashes that had been cleaned of all organic compounds corresponded well with those amounts originally found on the samples as received from the incinerators. The optimum temperature range for the formation of dioxins from pentachlorophenol was 250 degrees to 350 degrees C.

Synthesizing Statistical Knowledge from Incomplete Mixed-Mode Data

Abstract: The difficulties in analyzing and clustering (synthesizing) multivariate data of the mixed type (discrete and continuous) are largely due to: 1) nonuniform scaling in different coordinates, 2) the lack of order in nominal data, and 3) the lack of a suitable similarity measure. This paper presents a new approach which bypasses these difficulties and can acquire statistical knowledge from incomplete mixed-mode data. The proposed method adopts an event-covering approach which covers a subset of statistically relevant outcomes in the outcome space of variable-pairs. And once the covered event patterns are acquired, subsequent analysis tasks such as probabilistic inference, cluster analysis, and detection of event patterns for each cluster based on the incomplete probability scheme can be performed. There are four phases in our method: 1) the discretization of the continuous components based on a maximum entropy criterion so that the data can be treated as n-tuples of discrete-valued features; 2) the estimation of the missing values using our newly developed inference procedure; 3) the initial formation of clusters by analyzing the nearest-neighbor distance on subsets of selected samples; and 4) the reclassification of the n-tuples into more reliable clusters based on the detected interdependence relationships. For performance evaluation, experiments have been conducted using both simulated and real life data.

Analyzing the structure of argumentative discourse

Abstract: Consider a discourse situation where the speaker tries to convince the hearer of a particular point of view The first task for the hearer is to understand what it is the speaker wants him to believe--to analyze the structure of the argument being presented, before judging credibility and eventually respondingThis paper describes a model for the analysis of arguments that includes:• a theory of expected coherent structure which is used to limit analysis to the reconstruction of particular transmission forms;• a theory of linguistic clues which assigns a functional interpretation to special words and phrases used by the speaker to indicate the structure of the argument;• a theory of evidence relationships which includes the demand for pragmatic analysis to accommodate beliefs not currently heldThe implications of this particular design for dialogue analysis in general are thus:• structure is an important feature to extract in a representation to control the processing;• linguistic constructions can be assigned useful interpretations;• pragmatic analysis is crucial in cases where the participants differ in beliefs

The Poisson-Inverse Gaussian distribution as an alternative to the negative binomial

Abstract: The basic distributional properties and estimation techniques of the Poisson-Inverse Gaussian (P-IG) distribution are reviewed. Its use both as a mixed and compound claim frequency model are also discussed, as well as a review of the aggregate claims distribution when the P-IG is the claim frequency component. The many properties which are analogous to those of the negative binomial are emphasized, and the superior fit to automobile claim frequency data is demonstrated. The P-IG merits consideration as a model for claim frequency data due to its good fit to data, physical justification, and its abundance of convenient mathematical properties.

The feeding and energetics of stream-resident trout in winter*

Abstract: The feeding of brook and brown trout in a temperate Canadian stream was studied over two winters. Stomach analyses indicate that feeding continues throughout the winter. Both species had similar diets. Despite continuous feeding, condition factors declined significantly in early winter and remained low until the spring, suggesting an early-winter depletion of lipid reserves. Energy (calorific) intake was similar in winter to that found in late summer or spring and therefore was not the cause of low winter condition. The derived energy from feeding was insufficient to offset the costs of maintenance metabolism in the early winter period, for both immature and recently spawned fish. It is suggested that stream-dwelling trout suffer a metabolic deficit during acclimation to rapidly declining water temperatures in November/December. Such a phenomenon has important physiological implications for overwinter survival.

Influence of event anticipation on postural actions accompanying voluntary movement.

Abstract: The central organization of anticipatory postural adjustments was investigated by examining the influence of preparatory set on the temporal relationship between postural and arm (focal) muscle activation. Surface EMG was recorded from the right tibialis anterior, lateral gastrocnemius, anterior deltoid and posterior deltoid muscles when pushing or pulling on a stiff handle. Preparatory set was manipulated by informing the subject of the upcoming direction of responding with a 80, 50 or 20% certainty. This created high, neutral and low levels of preparatory set, respectively. All six subjects showed activation of postural muscles in advance of focal muscles for both push and pull responses. However, only three subjects showed the expected effect of preparatory set on reaction time performance, i.e., an increase of reaction time with decreasing response probability. For these three subjects, the time between the activation of postural and focal muscles was the same for the high and neutral levels of preparatory set, but increased with a low level of preparatory set. The increased postural-focal latency for the low preparatory set condition was due to a longer delay for the activation of the focal muscles but not the postural muscles. This finding suggests that anticipatory postural adjustments and the activation of focal muscles are triggered by separate motor commands.