Showing papers by "University of Waterloo published in 1980"

The Belief in a Just World

Abstract: The “belief in a just world” refers to those more or less articulated assumptions which underlie the way people orient themselves to their environment. These assumptions have a functional component which is tied to the image of a manageable and predictable world. These are central to the ability to engage in long-term goal-directed activity. In order to plan, work for, and obtain things they want, and avoid those which are frightening or painful, people must assume that there are manageable procedures which are effective in producing the desired end states (Erikson, 1950; Merton, 1957).

Exact spatially homogeneous cosmologies

Abstract: We consider perfect fluid spatially homogeneous cosmological models. Starting with a new exact solution of Blanchi type VIII, we study generalizations which lead to new classes of exact solutions. These new solutions are discussed and classified in several ways. In the original type VIII solution, the ratio of matter shear to expansion is constant, and we present a theorem which delimits those space-times for which this condition holds.

Algebraic and topological aspects of feedback stabilization

Abstract: In this paper we give essentially complete results concerning various algebraic and topological aspects of feedback stabilization. In particular, we give necessary and sufficient conditions for a given transfer function matrix to have a right-coprime or a left-coprime factorization, and exhibit a large class of transfer function matrices that have both. We give the most general set of feedback stability criteria available to date, and derive a characterization of all compensators that stabilize a given plant. We define what is meant by "proper" and "strictly proper" in an abstract setting and show that (i) every strictly proper plant can be stabilized by a proper compensator, and (ii) every compensator that stabilizes a strictly proper plant must be proper. We then define a topology for unstable plants and compensators, and show that it is the weakest topology in which feedback stability is a robust property.

Quadratic knapsack problems

Abstract: The quadratic knapsack (QK) model naturally arises in a variety of problems in operations research, statistics and combinatorics. Some “upper planes” for the QK problem are derived, and their different uses in a branch-and-bound scheme for solving such a problem are discussed. Some theoretical results concerning the class of all upper planes, as well as extensive computational experience, are reported.

J integral applications for short fatigue cracks at notches

Abstract: Elastic and elastic-plastic fracture mechanics solutions are modified to predict the behaviour of short cracks. An effective crack length, l 0 is introduced into the solutions for both the linear elastic stress intensity factor and the J integral. Crack growth results for short cracks, in both elastic and plastic strain fields of unnotched specimens, when interpreted in terms of the modified solutions, show excellent agreement with elastic long crack data. The modified J integral solutions are extended to plastically strained notches, and the solutions obtained are tested in the correlation of data for growth of sort cracks near notches of varying severity with data for long crack under elastic loading. Although constant stress amplitude tests of these notches gave crack growth rate versus crack length curves which varied from monotonically increasing for blunt notches, to an initial decrease followed by an increase of sharp notches, all the data fell within the long crack data when correlated by the J integral solutions. Conversely, these solutions can be used to predict elastic and inelastic short crack growth curves for notches of various severities.

Applicability of coupled‐pair theories to quasidegenerate electronic states: A model study

Abstract: The coupled-pair many-electron theory, its linear approximation, and various other approximate coupled-pair approaches based on the orthogonally spin-adapted coupled-pair theory are applied to simple model systems in which the degree of quasidegeneracy can be continuously varied over a wide range. The four-electron models studied are three ab initio minimum basis set models involving four hydrogen atoms in various spatial arrangements as well as the semiempirical Pariser–Parr–Pople π-electron model of cis-butadiene. The results are compared with the exact full configuration interaction results as well as with those obtained with other approximate limited configuration interaction approaches and Davidson's formula estimate, and the effect of quasidegeneracy on various approaches is discussed. We also examine the difference between the correlation energies obtained with the coupled-pair many-electron theory and its linear version and discuss the source of these differences and of the breakdown of the latter approximation in the case of very strong quasidegeneracies.

Decomposition techniques for large-scale systems with nonadditive interactions: Stability and stabilizability

Abstract: In this paper, we study decomposition techniques for nonlinear large-scale systems, which have the feature that the interactions between the various subsystems are nonadditive. Using the technique of decomposing a graph into its strongly connected components, we first rewrite the system differential equations into a hierarchical form, by renumbering and aggregating the original state variables, if necessary. In this hierarchical form, each subsystem interacts only with "lower" subsystems but not with "higher" subsystems. Once the system equations have been rearranged in this hierarchical form, we show that the overall system is uniformly asymptotically stable (respectively exponentially stable, globally exponentially stable) if and only if each of the subsystems is uniformly asymtotically stable (respectively exponentially stable, globally exponentially stable). The main technique used to do this is the converse Lyapunov theory. We then turn to problems of stabilizability, and show that, once the system equations have been arranged in hierarchical form, the overall system can be stabilized by a decentralized control law if and only if each of the subsystems can be stabilized. Several examples are presented to illustrate the various theorems.

Two Single Machine Sequencing Problems Involving Controllable Job Processing Times

Abstract: This paper presents simple methods for solving two single machine sequencing problems when job processing times are themselves decision variables having their own associated linearly varying costs. These are the problems of minimizing the total processing cost plus either the average flow cost or the maximum tardiness cost. The paper treats only problems with zero ready times and no precedence constraints.

On the stabilization of nonlinear systems using state detection

Abstract: In this paper, we study the problem of stabilizing a nonlinear control system by means of a feedback control law, in cases where the entire state of the system is not available for measurement. The proposed method of stabilization consists of three parts: 1) determine a stabilizing control law based on state feedback, assuming the state vector x(t) can be measured; 2) construct a state detection mechanism, which generates a vector z(t) such that z(t)-x(t)\rightarrow 0 as t\rightarrow \infty and 3) apply the previously determined control law to z(t) . This scheme is well established for linear time-invariant systems, and its global convergence has previously been studied in the case of nonlinear systems. Hence, the contribution of this paper is in showing that such a scheme works in the absence of any linearity assumptions, and in studying both local asymptotic stability and global asymptotic stability.

Biomechanics of vegetative channel linings

Abstract: A method to determine and apply the biomechanical properties of vegetative channel linings is presented. The method is used to evaluate the stiffness of vegetation commonly used to protect earth channels from erosion. Using the vegetation stiffness and stem length, the deflected height of the channel lining is predicted to yield a relative roughness under given flow conditions. The relative roughness is used to calculate a value of the Darcy-Weisbach friction factor or Manning's n. A method to design a vegatated channel is included.

The Freshwater Zooplankton of Sri Lanka, with a Discussion of Tropical Freshwater Zooplankton Composition

Abstract: Based on the study of over 500 zooplankton samples collected in Sri Lanka (Ceylon) during 1965–1974, the species composition from different habitats is analysed. The zooplankton assemblage is typically tropical with relatively few species of Cladocera and Copepoda. The Rotifera include a large number of species of the genus Brachionus. The limnetic zooplankton resembles the pond zooplankton closely in that all the eurytopic species found in the different types of habitats, including ponds, also occur in the limnetic zooplankton. The large Cladocera belonging to the genus Daphnia are very rare. In general, large zooplankters are absent. The size composition of the zooplankton has a smaller range than in temperate regions. This is due to the absence of large-sized zooplankton species. The reasons for the differences in species variety and size composition between zooplankton of temperate and tropical regions is perhaps due to a number of factors. These include the effects of high and uniform temperatures, food availability and predation by fish and invertebrates.

The Effects of Perceived Activity Choice upon Frequency of Exercise Behavior

Abstract: The purpose of this study was to investigate the effect of perceived activity choice upon the frequency of exercise behavior of adult women. Thirty-six recent enrollees in a private health club were recruited for involvement in a new exercise program. At an initial organizational meeting, subjects ranked their preferences for different activities and completed a number of self-report inventories. Subjects were paired on the basis of their activity preferences so as to establish two matched groups of subjects. One member of each pair was then randomly assigned to a choice condition while the other was assigned to a no choice control condition. Perceived choice was manipulated at the time of an individual's next visit to the club, with subjects in the choice group being led to believe that their initial activity selections were the basis for their programs whereas subjects in the control group were informed that they had been assigned a standardized exercise program by the club's instructresses. The overall attendance of the choice group was better than that of the control group. Across both groups there was a significant decline in attendance over the 6-week period but the decrement was significantly greater in the control group. At the conclusion of the 6-week period, subjects in the choice condition expressed a greater intention to continue exercising at the club than did subjects in the control condition.

Inference in the Generalized Gamma and Log Gamma Distributions

Abstract: This paper is concerned with the problem of obtaining confidence intervals or tests of significance for the parameters or other characteristics of the generalized gamma distribution. Procedures are given whereby confidence intervals for the parameters, quantiles or the reliability (survivor) function of the distribution can be obtained, when the generalized gamma index parameter is known. Their application in studying robustness and model-dependence in lifetime distributions is also discussed.

Redundancy in Data Structures: Improving Software Fault Tolerance

Abstract: The increasing cost of computer system failure has stimulated interest in improving software reliability. One way to do this is by adding redundant structural data to data structures. Such redundancy can be used to detect and correct (structural) errors in instances of a data structure. The intuitive approach of this paper, which makes heavy use of examples, is complemented by the more formal development of the companion paper, "Redundancy in Data Structures: Some Theoretical Results."

Searching for Nonsolar Planets

Abstract: The use of infrared techniques to search for nonsolar planets is examined and compared with other possible methods. Long focus astrometry, spectroscopic radial velocity measurements and spaceborne apodization all use visible light and need further refinement to be practical. Infrared offers an advantage of about 10 to the 5th over visible light as regards the ratio of power received from star and planet. Long baseline infrared interferometry from earth orbit could place an interferometric null on the star to enhance planetary radiation and a spinning interferometer would modulate planetary emission to permit synchronous detection; such an interferometer is illustrated. The limit to sensitivity would be set by thermal radiation to the detector and the infrared component of zodiacal light.

Unitary Group Approach to the Many-Electron Correlation Problem via Graphical Methods of Spin Algebras

Abstract: The various existing approaches for the evaluation of matrix elements of unitary group generators and their products with respect to the basis of electronic Gelfand states or the corresponding Yamanouchi-Kotani states are interrelated, and their desirable features combined, yielding a direct algorithm for the evaluation of matrix elements of products of two generators and, consequently, a simple and efficient algorithm for the calculation of two-electron matrix elements of spin-independent Hamiltonians needed in the unitary group configuration interaction (shell model) approach. Moreover, this algorithm is compatible with the efficient generation and representation scheme for electronic Gelfand states based on the distinct row table concept. Diagrammatic techniques based on the time-independent Wick theorem and graphical methods of spin algebras are used to derive the required factors for both one and two-generator (or electron) matrix elements for three different phase conventions and several possible simplifications in the evaluation of the two-electron part of the Hamiltonian matrix are outlined.

In vitro simulation of senescence-related membrane damage by ozone-induced lipid peroxidation

Abstract: Recent evidence indicates that as cells deteriorate, increasing proportions of the membrane lipids become crystalline (gel phase) at physiological temperature. Microsomal as well as chloroplast membranes from ageing bean (Phaseolus vulgaris) cotyledon and leaf tissue acquire regions of gel-phase lipid as senescence advances1–5. Gel-phase lipid has also been detected in microsomal membranes from aged batch cultures of green algae (Scenedesmus quadricauda)6, microsomal membranes from regressing corpus luteum of rat7 and plasma membranes of chick intestinal cells infected with an intracellular coccidial parasite8. These observations suggest that the presence of gel-phase lipid in membranes at physiological temperature may be a generalised feature of cell deterioration whether it is attributable to natural ageing or to some kind of infection. Moreover, the resulting mixture of liquid-crystalline-(fluid) and gel-phase lipid in the bilayer is likely tb render the membranes leaky9,10, and could thus readily account for the loss of cellular compartmentalisation that accompanies tissue senescence. The present study reports that phase changes occurring naturally during senescence of bean cotyledons1,2 can be simulated by exposing isolated membranes from young cotyledon tissue to ozone, a treatment that induces lipid peroxidation11. This finding has considerable bearing on previous observations which implicate atmospheric ozone as a source of crop damage by reason of its ability to induce premature plant senescence12, and lipid peroxidation as a major cause of membrane deterioration in ageing systems13,14.

Fighting back is not the way: suicide and the women of Kaliai

Abstract: A case study of the suicide of a young Kaliai girl in northwest New Britain, Papua New Guinea introduces a discussion of suicide as an expression of power by otherwise powerless people, and a consideration of the validity of using the legal terms suicide and homicide in a cross-cultural context. Data on different forms of self-killing practiced by Kaliai women support the argument that these terms are inadequate and inappropriate when applied to people who do not share European legal and cultural traditions. [suicide, women, political behavior, comparative legal systems, Melanesia]

The Species and Size Composition of Tropical Freshwater Zooplankton with Special Reference to the Oriental Region (South East Asia)

Abstract: A contrast between temperate and tropical Cladocera, Copepoda and Rotifera zooplankton fauna shows a markedly different size composition and species diversity. There are fewer species, and these are generally smaller in the tropics than in either the North or South Temperate Zones. Larger species of the genera Daphnia and Simocephalus are relatively rare in the tropics, while members of Eurycerus and Saycia are absent. Members of the families Holopedidae, Leptodoridae and Polyphemidae increase in abundance toward the temperate regions. Two small cyclopoid copepods are common in tropical zooplankton, while many of the common larger species of other regions are absent or very rare. The chief rotifer components are Keratella tropica and species of Brachionus.