Showing papers by "University of Waterloo published in 1989"

Functional Equations in Several Variables: With Applications to Mathematics, Information Theory and to the Natural and Social Sciences

Abstract: Preface Further information 1. Axiomatic motivation of vector addition 2. Cauchy's equation: Hamel basis 3. Three further Cauchy equations: an application to information theory 4. Generalizations of Cauchy's equations to several multiplace vector and matrix functions: an application to geometric objects 5. Cauchy's equations for complex functions: applications to harmonic analysis and to information measures 6. Conditional Cauchy equations: an application to geometry and a characterization of the Heaviside functions 7. Addundancy, extensions, quasi-extensions and extensions almost everywhere: applications to harmonic analysis and to rational decision making 8. D'Alembert's functional equation: an application to noneuclidean mechanics 9. Images of sets and functional equations: applications to relativity theory and to additive functions bounded on particular sets 10. Some applications of functional equations in functional analysis, in the geometry of Banach spaces and in valauation theory 11. Characterizations of inner product spaces: an application to gas dynamics 12. Some related equations and systems of equations: applications to combinatorics and Markov processes 13. Equations for trigonometric and similar functions 14. A class of equations generalizing d'Alembert and Cauchy Pexider-type equations 15. A further generalization of Pexider's equation: a uniqueness theorem: an application to mean values 16. More about conditional Cauchy equations: applications to additive number theoretical functions and to coding theory 17. Mean values, mediality and self-distributivity 18. Generalized mediality: connection to webs and nomograms 19. Further composite equations: an application to averaging theory 20. Homogeneity and some generalizations: applications to economics 21. Historical notes Notations and symbols Hints to selected 'exercises and further results' Bibliography Author index Subject index.

Designs for Computer Experiments

Abstract: A computer experiment generates observations by running a computer model at inputs x and recording the output (response) Y. Prediction of the response Y to an untried input is treated by modeling the systematic departure of Y from a linear model as a realization of a stochastic process. For given data (selected inputs and the computed responses), best linear prediction is used. The design problem is to select the inputs to predict efficiently. The issues of choice of stochastic-process model and computation of efficient designs are addressed, and applications are made to some chemical kinetics problems.

Sorption nonideality during organic contaminant transport in porous media

Abstract: In modeling subsurface contaminant transport, sorption is often simplified by assuming instantaneous equilibrium, isotherm linearity, and sorption‐desorption singularity. Data exhibiting behavior that deviates from that predicted by this simple model have been reported, challenging the validity of these assumptions. This nonideal sorptive behavior has been attributed to several different factors, including kinetic sorption reactions, diffusive mass transfer resistances, isotherm nonlinearity, and sorption‐desorption nonsingularity. These factors are examined and their relative impact on contaminant transport is evaluated. For hydrophobic organic compounds, physical nonequilibrium (i.e., rate‐limited mass‐transfer in aggregated or layered systems) and intraorganic matter diffusion (rate‐limited diffusion within the sorbent organic matter matrix) are probably the predominant factors causing nonideality. The relative importance of these factors is scale‐dependent. For smaller scale systems, mass‐transfer lim...

Constraint propagation algorithms for temporal reasoning: a revised report

Abstract: This paper revises and expands upon a paper presented by two of the present authors at AAAI 1986 [Vilain & Kautz 1986]. As with the original, this revised document considers computational aspects of interval-based and point-based temporal representations. Computing the consequences of temporal assertions is shown to be computationally intractable in the interval-based representation, but not in the point-based one. However, a fragment of the interval language can be expressed using the point language and benefits from the tractability of the latter. The present paper departs from the original primarily in correcting claims made there about the point algebra, and in presenting some closely related results of van Beek [1989].

Numerical Evaluation of Multivariate Contingent Claims

Abstract: We develop a numerical approximation method for valuing multivariate contingent claims. The approach is based on an n-dimensional extension of the lattice binomial method. Closed-form solutions for the jump probabilities and the jump amplitudes are obtained. The accuracy of the method is illustrated in the case of European options when there are three underlying assets. Article published by Oxford University Press on behalf of the Society for Financial Studies in its journal, The Review of Financial Studies.

Tests for Detecting Overdispersion in Poisson Regression Models

Abstract: Poisson regression models are widely used in analyzing count data. This article develops tests for detecting extra-Poisson variation in such situations. The tests can be obtained as score tests against arbitrary mixed Poisson alternatives and are generalizations of tests of Fisher (1950) and Collings and Margolin (1985). Accurate approximations for computing significance levels are given, and the power of the tests against negative binomial alternatives is compared with those of the Pearson and deviance statistics. One way to test for extra-Poisson variation is to fit models that parametrically incorporate and then test for the absence of such variation within the models; for example, negative binomial models can be used in this way (Cameron and Trivedi 1986; Lawless 1987a). The tests in this article require only the Poisson model to be fitted. Two test statistics are developed that are motivated partly by a desire to have good distributional approximations for computing significance levels. Simu...

A new approach to text searching

Abstract: We introduce a family of simple and fast algorithms for solving the classical string matching problem, string matching with don't care symbols and complement symbols, and multiple patterns. In addition we solve the same problems allowing up to k mismatches. Among the features of these algorithms are that they are real time algorithms, they don't need to buffer the input, and they are suitable to be implemented in hardware.

Inference Based on Retrospective Ascertainment: An Analysis of the Data on Transfusion-Related AIDS

Abstract: In some epidemiologic studies, identification of individuals for study is dependent on the occurrence of some event. Once an individual is identified, the time of a previous event, termed an initiating event, is determined retrospectively. This article considers problems of estimation when initiating events occur as a nonhomogeneous Poisson process, and the time s from the initiating event to the final event has pdf f(s) independent of the time of the initiating event. A simple form for the likelihood function is obtained and methods of parametric and nonparametric estimation are developed and considered. In particular, the model is related to a Poisson process in the plane, and for the parametric case simple algorithms are developed for parameter estimation. Regression models are also considered as well as various generalizations of the basic problem. Parallel to the theoretical development, data on patients diagnosed with acquired immune deficiency syndrome (AIDS) are considered and a detailed ...

Oxygen isotope exchange between sulphate and water during bacterial reduction of sulphate

Abstract: The bacterial reduction of sulphate is accompanied by oxygen isotope exchange reactions. The mechanisms were not investigated in detail but it is suggested that the formation of sulphate-enzyme complexes as intermediary reaction products are facilitating the exchange of 18 O between water and sulphate. Under the experimental conditions the observed fractionation factor is close to 25‰ at 30°C and approaches 27‰ at 17°C. Extrapolated values from a field study indicate a difference of ∼ 29‰ at ∼ 5°C.

A gray-level threshold selection method based on maximum entropy principle

Abstract: A description is given of a gray-level threshold selection method for image segmentation that is based on the maximum entropy principle. The optimal threshold value is determined by maximizing the a posteriori entropy subject to certain inequality constraints which are derived by means of spectral measures characterizing uniformity and the shape of the regions in the image. For this purpose, the authors use both the gray-level distribution and the spatial information of an image. The effectiveness of the method is demonstrated by its performance on some real-world images. An extension of this method to chromatic images is provided. >

Updating derived relations: detecting irrelevant and autonomously computable updates

Abstract: Consider a database containing not only base relations but also stored derived relations (also called materialized or concrete views). When a base relation is updated, it may also be necessary to update some of the derived relations. This paper gives sufficient and necessary conditions for detecting when an update of a base relation cannot affect a derived relation (an irrelevant update), and for detecting when a derived relation can be correctly updated using no data other than the derived relation itself and the given update operation (an autonomously computable update). The class of derived relations considered is restricted to those defined by PSJ-expressions, that is, any relational algebra expressions constructed from an arbitrary number of project, select and join operations (but containing no self-joins). The class of update operations consists of insertions, deletions, and modifications, where the set of tuples to be deleted or modified is specified by a selection condition on attributes of the relation being updated.

Hydraulic Conductivity Measurements in the Unsaturated Zone Using Improved Well Analyses

Abstract: The flow of ponded water into and through the unsaturated zone depends on both the saturated and unsaturated components of the hydraulic conductivity. Recent studies indicate that the ratio of the saturated (Kfs) to the unsaturated (φm) components (Kfs/φm=α*) of flow lies within prescribed bounds for most field soils, i.e., 1m−1≤α*≤ 100 m−1. In addition, the fact that the calculation of Kfs and φm is not strongly dependent on the choice of α*, suggests that a site estimation of α* leads to reasonable “best estimates” of Kfs and φm when using the constant head well permeameter technique. As a consequence, measurement of the steady flow rate using only one ponded head may be all that is necessary for many practical applications. Multiple head measurements or independent measurements of α* or φm can be used, however, to give more accurate estimates of Kfs if required.

Diffusive contaminant transport in natural clay: a field example and implications for clay-lined waste disposal sites

Abstract: Vertical core samples were obtained from an impervious, unweathered, water-saturated clay deposit beneath a 5-year-old hazardous waste landfill at a site in southwestern Ontario. Sections of the cores were analyzed for chloride and volatile organic compounds. Waste-derived chloride was detected in the clay to a maximum depth of 83 cm below the bottom of the landfill. The most mobile organic compounds were found only to a depth of /approximately/ 15 cm. The downward transport of these chemical species into the clay was the result of simple Fickian diffusion. This study has implications for low-permeability clay liners used at waste disposal sites. For liners of typical thickness (/approximately/ 1 m), simple diffusion can cause breakthrough of mobile contaminants in approximately 5 years; the diffusive flux of contaminants out of such liners can be large.

Sociability and Social Withdrawal in Childhood: Stability and Outcomes

Abstract: The stability and long-term correlates of both social withdrawal and sociability were investigated in a longitudinal study of normal children in kindergarten through the fifth grade. Both observational and peer assessment indices of withdrawal and sociability were considered; furthermore, a distinction was made between observed active versus passive solitude. Of particular interest was whether social withdrawal in early childhood was predictive of subsequent internalizing problems, as assessed by self-reports of social competence, overall self-worth, loneliness, and depression as well as teacher ratings of shy/anxious behavior, in later childhood. Results indicated a modest degree of stability for observed social withdrawal but not for observed sociability, nor for active or passive forms of solitude. Somewhat higher stability correlations were obtained for peer assessments of both sociability and withdrawal. In terms of predictive outcomes, significant relations were found between early social withdrawal in kindergarten and Grade 2 and subsequent internalizing problems in Grades 4 and 5, although the pattern of results was mixed. These data suggest that social withdrawal in early childhood may be predictive of risk for internalizing difficulties in later childhood.

Visibility of targets: Model for calculation:

Abstract: The introduction of the visibility level as a criterion for the obtainable visual information necessitates a metric to allow its quantification. On the basis of adrian's, aulhorn's and blackwell's data a method has been developed to compute the luminance difference thresholds increment L (photometric luminance) of visual targets of variable size and positive and negative contrast. Another parameter relevant to increment l is the observation time to cope with practical viewing conditions in which fixation was found to be restricted to 0.1 to 0.2 s. The effect of age on the threshold contrast and that of disability glare has been incorporated. The numerical description allows the determination of the visibility level (vl) of objects in the visual field. A practical example of how to obtain vl is presented.

A dynamical systems approach to Bianchi cosmologies: Orthogonal models of class A

Abstract: The authors write the Einstein field equations for the orthogonal class B Bianchi cosmologies as an autonomous DE in terms of expansion-normalized dimensionless variables. The theory of dynamical systems is then used to give a qualitative description of the evolution of the models. Comparisons are made with other work on this problem.

Operation Everest II: adaptations in human skeletal muscle.

Abstract: Adaptations in skeletal muscle in response to progressive hypobaria were investigated in eight male subjects [maximal O2 uptake = 51.2 +/- 3.0 (SE) ml.kg-1.min-1] over 40 days of progressive decompression to the stimulated altitude of the summit of Mt. Everest. Samples of the vastus lateralis muscle extracted before decompression (SL-1), at 380 and 282 Torr, and on return to sea level (SL-2) indicated that maximal activities of enzymes representative of the citric acid cycle, beta-oxidation, glycogenolysis, glycolysis, glucose phosphorylation, and high-energy phosphate transfer were unchanged (P greater than 0.05) at 380 and 282 Torr over initial SL-1 values. After exposure to 282 Torr, however, representing an additional period of approximately 7 days, reductions (P less than 0.05) were noted in succinic dehydrogenase (21%), citrate synthetase (37%), and hexokinase (53%) between SL-2 and 380 Torr. No changes were found in the other enzymes. Capillarization as measured by the number of capillaries per cross-sectional area (CC/FA) was increased (P less than 0.05) in both type I (0.94 +/- 0.8 vs. 1.16 +/- 0.05) and type II (0.84 +/- 0.07 vs. 1.05 +/- 0.08) fibers between SL-1 and SL-2. This increase was mediated by a reduction in fiber area. No changes were found in fiber-type distribution (type I vs. type II). These findings do not support the hypothesis, at least in humans, that, at the level of the muscle cell, extreme hypobaric hypoxia elicits adaptations directed toward maximizing oxidative function.

Experiments in quadratic 0-1 programming

Abstract: We present computational experience with a cutting plane algorithm for 0–1 quadratic programming without constraints. Our approach is based on a reduction of this problem to a max-cut problem in a graph and on a partial linear description of the cut polytope.