Showing papers by "University of Waterloo published in 1973"

Matching, euler tours and the chinese postman

Abstract: The solution of the Chinese postman problem using matching theory is given. The convex hull of integer solutions is described as a linear programming polyhedron. This polyhedron is used to show that a good algorithm gives an optimum solution. The algorithm is a specialization of the more generalb-matching blossom algorithm. Algorithms for finding Euler tours and related problems are also discussed.

Gas production during refuse decomposition

Abstract: Gas production in sanitary landfills is a subject of much concern because of the potential hazards of CH4 combustion and of groundwater contamination by CO2. This study investigated the pattern of sanitary landfill gas production and the factors which affect it. A basis for study was prepared by examining factors which influence gas production in soil and sewage sludge digesters. The factors studied included moisture content, temperature, pH, alkalinity, Eh, and nutrition. It was then undertaken to determine whether or not this information was applicable to the landfill. A pattern for landfill gas production was proposed based on the assumption that an anaerobic environment would be achieved and maintained after refuse placement. Four phases were identified: I. Aerobic; II. Anaerobic Non-Methanogenic; III. Anaerobic Methanogenic Unsteady; and IV. Anaerobic Methanogenic Steady. The duration of these phase and the relative amounts of gases produced within each phase were studied. An investigation of information available on factors affecting gas production in sanitary landfills also was made. It was found that, in general, the principles developed from the study of gas production in other media were applicable to the landfill environment. It was found that gas production increases with increased moisture content but that conditions of high infiltration are often conducive to reduction in gas production apparently caused by modifications to the microbial environment. There appears to exist a typical pattern of temperature variation within the landfill with a peak temperature being reached during the initial phase of aerobic decomposition. The magnitude of this peak is related to the refuse temperature at placement. Subsequent temperatures are lower and tend to fluctuate with season. Optimum temperatures for gas production are in the range of from 30°C to 35°C, however, landfill temperatures are often lower than this. Optimum levels of pH and alkalinity exist which maximize gas production rates. The types and amounts of gas produced are influenced by refuse composition. A scheme was proposed to illustrate how the various factors influence landfill gas production and how these may interact. Those factors over which some control may be exerted during landfill design and operation were identified.

Sugar and Slaves: The Rise of the Planter Class in the English West Indies, 1624-1713

Abstract: First published by UNC Press in 1972, Sugar and Slaves presents a vivid portrait of English life in the Caribbean more than three centuries ago. Using a host of contemporary primary sources, Richard Dunn traces the development of plantation slave society in the region. He examines sugar production techniques, the vicious character of the slave trade, the problems of adapting English ways to the tropics, and the appalling mortality rates for both blacks and whites that made these colonies the richest, but in human terms the least successful, in English America.

Level-crossing problems for random processes

Abstract: In a variety of practical problems involving random processes, it is necessary to have statistical information on their level-crossing properties. This paper presents a survey of known results on certain aspects of this problem and provides a basis for further study in the area. The goal has been to give a broad view of the problems considered in the literature and a brief indication of the techniques used in their solution. Much material of a more or less historical nature has been included since, to the authors' knowledge, no other survey of this nature exists.

Flexible roughness in open channels

Abstract: The logarithmic flow formula for open channels is valid for flow over a roughness cover made up of flexible plastic strips. The deflection of such roughness is an important parameter as the deflection directly influences the relative roughness. Dimensionless parameters which relate the amount of bending to the stiffness of the roughness and the boundary shear are defined. Three regimes of boundary behavior are observed for flexible plastic roughness, leading to two resistance functions. The flexible plastic roughness is produced by affixing thin plastic strips of various thickness to the bed of a flume. The flow of water over flexible plastic strips simulates flow over a vegetative channel lining.

Listening for mispronunciations: A measure of what we hear during speech

Abstract: Ss heard a passage from Lewis Carroll’s Through the Looking Glass and were asked to indicate, as quickly as possible, whenever they heard a mispronunciation. Mispronunciations were produced by changing one consonant sound in a three-syllable word by one, two, or four distinctive features (e.g., busily to “pizily,” “visily,” or “sizily”). Mispronunciations involving a single feature change were seldom detected, while two and four feature changes were readily detected. The syllable in which a mispronunciation occurred did not affect the probability of detecting a mispronunciation. However, reaction times to mispronounced words were at least a third of a second slower when they occurred in the-first syllable of the word. The results were taken to support the notion that words are identified by their distinctive features.

Oxygen transfer into mycelial pellets

Abstract: The oxygen uptake rate in mycelial pellets of Aspergillus niger was studied experimentally and theoretically. The specific rate of respiration of mycelial pellets was found to decrease significantly with increasing pellet size. The distribution of respiratory activity in the mycelial pellets was evaluated and the specific rate of respiration of disrupted mycelia showed adaptation to the concentration of oxygen in the medium. The decrease of the specific rate of respiration of the mycelial pellets could be estimated according to diameter, mycelial density, oxygen diffusivity, and adaptation to the concentration of oxygen. Good agreement was found between the theoretical analysis and the experimental data.

Mechanism of Surface Charging of High-Voltage Insulators in Vacuum

Abstract: In vacuum, the surface of insulators becomes electrically charged when subjected to high-voltage stresses. The charging mechanism is described. A model simulating the charging shows that the surface charge densities are proportional to the applied voltage and depend on the secondary electron emission of the dielectric surface. It is also time dependent. Surface charges are shown to explain many results obtained in studies of insulator surface breakdown.

Normal likelihoods and their relation to large sample theory of estimation

Abstract: Normal likelihoods are shown to be associated with asymptotic normal distributions of large sample theory. An examination of the likelihood function can indicate when standard large sample theory of estimation can be applied and when it may be inaccurate and misleading to do so. Transformations that improve the accuracy and so extend the domain of application of asymptotic methods can sometimes be suggested by their effect on the likelihood function. An examination of the likelihood function can therefore prove useful in the usual application of the frequency theory approach to estimation.

Self‐diffusion and viscosity of some liquids as a function of temperature

Abstract: Self-diffusion coefficients of 15 liquids have been measured as a function of temperature between their melting and boiling points. The systems investigated were the benzenes, C6H5X where X = H, F, Cl, Br, and I, n-paraffins, CnHn + 2 where n = 7, 9, 10, 12, 14, 16, and 18, acetone, acetic acid and water. The pulsed nmr technique was employed for the diffusion measurements. In addition, the viscosities of the halogenated benzenes have been measured between 20°C and their melting points. The diffusion results obtained in this study have been found in excellent agreement with the best values available for benzene (Collings and Mills, 1970) and water (Longworth, 1960). The relation between the apparent molecular diameter d (d = 2.24(η VD/RT)1/2) and the critical volume as suggested by Dullien (1972) has been extended to include the temperature dependence of d. It is also shown that the temperature dependence of d is similar for all liquids studied here with respect to the reduced temperature. The increase of d for Tr < 0.46 shows the invalidity of the Stokes-Einstein relation for this temperature range (Tr = T/Tc). A normalized plot of d has been found very useful in checking the consistency of viscosity and self-diffusion data. The relations proposed in this work can be used to predict self-diffusion coefficients and viscosities over the normal liquid range.

The formation of particles in freshwater leachates of dead leaves1

Abstract: Leaves of similar morphology and condition release a similar quantity of soluble organic material. However, the quantity of material that precipitates, the rate of precipitation and the size of particles that result depend on leaf species and water chemistry. A microbial componcnt and an abiotic component are apparent in the precipitates; the latter bears a similarity to particulate material from scawatcr and soils. It is now well established that allochthonous organic matter is important in the productivity of streams ( Hynes 1970; Fisher and Likens 1972; Cummins 1973). Previous work in this laboratory has been concerned with the fate of the autumnal leaves that fall into water. Our earlier experiments were with leaves that had been leached to constant weight before being used, and this represented a considerable loss of material ( Kaushik and Hynes 1971). In 1968, therefore, we began a study of the leachate, with particular reference to the finding that organic particles are formed when bubbles are passed through seawater (Riley 1963, 1970). These seawater particles are variable in size and shape, but they are described as being usually either semitransparent flakes or globular aggregations with mean diameters of 25-50 p. It has been suggested that they are formed by adsorption of organic matter onto the surfaces of the bubbles, which then burst and leave them in the water, We felt that similar particles might also be formed by turbulence such as occurs in streams. Saunders ( 1969) had already tried to form particles by passing bubbles through lake water, but with little success, and had concluded that the mechanism does not appear to be important in freshwater. There are, however, several reports of micropar’ This investigation was supported by an opcrating grant from the National Research Council of Canada. ticulate organic detritus in both lotic and lentic freshwater habitats (Egglishaw 1964; Pfistcr et al. 1969). Nykvist ( 1963 and earlier papers) has studied the release of soluble materials from dead leaves and has mentioned the formation of “clots” in the solutions, although he did not investigate them further. Also, when McConnell (1968) studied the effects of water extracts from oak leaves on the growth of Xenopus larvae, he concluded that the larvae fed on particles that had probably been formed from the solutions by microbial action, Soil scientists have long been aware of the complexing of dissolved organic matter with metals, which may at times result in the formation of particles. Schnitzer and Poapst (1967) have stated that heavy summer rains may bring concentrations of organic matter into the soil solution as high as several thousand parts per million. Some of this material enters streams, the amount depending on the concavity or convexity of the drainage slope and the permeability of the soil ( Freeze 1972)) and these factors probably also influence the quantities and the sizes of any accompanying particles. Fisher and Likens (1972) have recently shown that a large proportion of the organic matter that comes in from an undisturbed watershed is actually in solution. The fate then of the dissolved material, both from the soil and leached from leaves, and the probability that at least some of it becomes particulate and may form food for fine particle feeders such as Simuliidae LIMNOLOGY AND OCEANOGRAPHY 968 NOVEMBER 1973, V. 18(6) FARTICJLE FORMATION IN FRESHWATER 969 Table 1. Composition of standard water in mg liter-l

Retention characteristics of motor short-term memory cues.

Abstract: The retention characteristics of several cues thought to underlie movement reproduction ability were examined and the results were discussed in terms of two models of motor short-term memory (Laabs, 1973; Pepper & Herman, 1970). Trace decay was indexed by constant error and not variable error. It appeared that the movement cues studied all had access to the central processing capacity in that forgetting did not occur until rehearsal was blocked by the introduction of a secondary task. However, there was some evidence to indicate that different cues are centrally represented in varying degrees of exactness. In this respect reliance on active movement cues and location cues produced better reproduction than passive movement and distance cues, respectively. The existence of an adaptation level established from the range of movement utilized was supported, and short movements were more dependent on central processing capacity than were long movements.

Life histories of Nemouridae and Leuctridae in Southern Ontario (Plecoptera)

Abstract: The life-histories of seven species of Nemouridae and two of Leuctridae have been investigated in Southern Ontario. Eleven sampling stations were chosen to illustrate the range of temperature conditions found in local streams.