Showing papers by "University of Waterloo published in 1982"

Contributions to the Theory of Logic Programming

Abstract: Hom clauses of first-order predicate logic can be regarded as a high-level programming language when SLD-resolution, a special-purpose resolution theorem prover, is used as interpreter. Consequently, the semantics of Hom clauses can be studied both by model-theoretic and fixpoint methods (in the sense of Scott). This possibility is exploited here by identifying the least (greatest) fixpoint with a least (greatest) model. Successful termination of SLD-resolution is characterized by least fupoints. A semantic characterization of finite failure of SLD-resolution is given, which coincides with the greatest fixpoint only for a special case of clauses. It is shown that nondeterministic flowchart schemata of bounded nondeterminacy are modeled by this special case; the connection between finite failure and greatest fixpoint is then used to give a semantic characterization of termination, blocking, and nontermination of such flowchart schemata.

Axonal guidance during development of the great cerebral commissures: Descriptive and experimental studies, in vivo, on the role of preformed glial pathways

Abstract: Do structures exist within the embryonic central nervous system that guide axons across the midline during development of the great cerebral commissures (corpus callosum, anterior commissure)? With the use of serial section and reconstructive computer graphic techniques we have found that during normal ontogeny of the mouse forebrain and before the arrival of the pioneer fibers of the corpus callosum at the midline, a population of primitive glial cells migrates medially (through the fused walls of the dorsal septum) from the ependymal zones of each hemisphere. At the midline, and well rostral to the lamina terminalis, these cells unite to form a bridgelike structure or "sling" suspended below the longitudinal cerebral fissure. The first callosal axons grow along the surface of this cellular bridge as they travel toward the contralateral side of the brain. The "sling" disappears neonatally. The fibers of the anterior commissure grow within the lamina terminalis along a different type of preformed glial structure. Movement of these axons occurs through an aligned system of glial processes separated by wide extracellular spaces. Do these transient glial tissues actually provide guidance cues to the commissural axons? Analyses of three situations in which the glial "sling" is genetically or surgically impaired or nonexistent indicate that this structure does, indeed, play an essential role in the development of the corpus callosum. We have analyzed (1) the embryonic stages of a congenitally acallosal mouse mutant (strain BALB/cCF), (2) several pouch stages of a primitive acallosal marsupial, Didelphys virginiana (opossum), and (3) animals in which the "sling" had been lesioned surgically through the uterine wall in the normal embryo (strain C57BL/6J). In the acallosal mouse mutant fusion of the septal midline is delayed by about 72 hours and the "sling" does not form. Although the would-be callosal axons approach the midline on schedule, they do not cross. Instead, the callosal fibers whirl into a pair of large neuromas adjacent to the longitudinal fissure. Similarly, in the opossum, fusion of the medial septal walls and formation of the glial "sling" are also lacking. However, in this species, instead of traveling dorsally, the "callosal" axons turn ventrally and pass contralaterally by way of the anterior commissure pathway. Surgical disunion of the glial "sling" also resulted in acallosal individuals. The callosal pathology in these affected animals mimicked exactly that of the genetically lesioned mutant. Our observations suggest that many different types of oriented glial tissues exist within the embryonic neural anlage. We propose that such tissues have the ability to influence the directionality of axonal movements and, thereby, play a crucial role in establishing orderly fiber projections within the developing central nervous system.

Matrix Triangularization By Systolic Arrays

Abstract: Given an n x p matrix X with p < n, matrix triangularization, or triangularization in short, is to determine an n x n nonsingular matrix Al such that MX = [ R 0 where R is p x p upper triangular, and furthermore to compute the entries in R. By triangularization, many matrix problems are reduced to the simpler problem of solving triangular- linear systems (see for example, Stewart). When X is a square matrix, triangularization is the major step in almost all direct methods for solving general linear systems. When M is restricted to be an orthogonal matrix Q, triangularization is also the key step in computing least squares solutions by the QR decomposition, and in computing eigenvalues by the QR algorithm. Triangularization is computationally expensive, however. Algorithms for performing it typically require n3 operations on general n x n matrices. As a result, triangularization has become a bottleneck in some real-time applications.11 This paper sketches unified concepts of using systolic arrays to perform real-time triangularization for both general and band matrices. (Examples and general discussions of systolic architectures can be found in other papers.6.7) Under the same framework systolic triangularization arrays arc derived for the solution of linear systems with pivoting and for least squares computations. More detailed descriptions of the suggested systolic arrays will appear in the final version of the paper.© (1982) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The Assessment of Social Intimacy

Abstract: Research exploring the psychological importance of closeness with others has been hampered by the absence of a reliable and valid measure of this variable. The development of the Miller Social Intimacy Scale (MSIS), a 17-item measure of the maximum level of intimacy currently experienced, is presented. Evidence for internal consistency and test-retest reliability as well as for convergent, discriminant and construct validity is discussed in the context of the need for further scientific exploration of this important phenomenon.

Algebraic design techniques for reliable stabilization

Abstract: In this paper we study two problems in feedback stabilization. The first is the simultaneous stabilization problem, which can be stated as follows. Given plants G_{0}, G_{1},..., G_{l} , does there exist a single compensator C that stabilizes all of them? The second is that of stabilization by a stable compensator, or more generally, a "least unstable" compensator. Given a plant G , we would like to know whether or not there exists a stable compensator C that stabilizes G ; if not, what is the smallest number of right half-place poles (counted according to their McMillan degree) that any stabilizing compensator must have? We show that the two problems are equivalent in the following sense. The problem of simultaneously stabilizing l + 1 plants can be reduced to the problem of simultaneously stabilizing l plants using a stable compensator, which in turn can be stated as the following purely algebraic problem. Given 2l matrices A_{1}, ..., A_{l}, B_{1}, ..., B_{l} , where A_{i}, B_{i} are right-coprime for all i , does there exist a matrix M such that A_{i} + MB_{i} , is unimodular for all i? Conversely, the problem of simultaneously stabilizing l plants using a stable compensator can be formulated as one of simultaneously stabilizing l + 1 plants. The problem of determining whether or not there exists an M such that A + BM is unimodular, given a right-coprime pair ( A, B ), turns out to be a special case of a question concerning a matrix division algorithm in a proper Euclidean domain. We give an answer to this question, and we believe this result might be of some independent interest. We show that, given two n \times m plants G_{0} and G_{1} we can generically stabilize them simultaneously provided either n or m is greater than one. In contrast, simultaneous stabilizability, of two single-input-single-output plants, g 0 and g 1 , is not generic.

The flash pyrolysis of aspen-poplar wood

Abstract: A continuous fluidized bed bench scale flash pyrolysis unit operating at atmospheric pressure and feed rates of about 15 g/h has been successfully designed and operated. A unique solids feeder capable of delivering constant low rates of biomass has also been developed. Extensive pyrolysis tests with hybrid aspen-popular sawdust (105–250 μm) have been carried out to investigate the effects of temperature, particle size, pyrolysis atmosphere and wood pretreatment on yields of tar, organic liquids, gases and char. At optimum pyrolysis conditions high tar yields of up to 65% of the dry wood weight fed are possible at residence times of less than one second. On a concu et employe avec succes, a l'echelle du laboratoire, une unite de pyrolyse-eclair a lit fluidise continu; le dispositif fonctionnait a la pression atmospherique et a des debits d'alimentation d'environ 15 g/h. On a aussi mis au point un dispositif unique d'alimentation en matieres solides, capable d'assurer de faibles debits constants de biomasse. On a fait des experiences poussees de pyrolyse sur des sciures d'hybrides de peuplier-faux tremble (105—250 μm), dans le but d'etudier les effets de la temperature, de la granulometrie des particules, de l'atmosphere de la pyrolyse et d'un traitement prealable du bois sur les rendements en goudron, liquides organiques, gaz et matieres carbonisees. Il est possible, dans les conditions optimales de pyrolyse, d'obtenir des rendements eleves en goudron, qui peuvent atteindre 65% du bois sec d'alimentation en poids pour des temps de sejour de moins d'une seconde.

Modeling and measurement of minority-carrier lifetime versus doping in diffused layers of n + -p silicon diodes

Abstract: The results of minority-carrier lifetime measurements in heavily phosphorus-doped n+diffused layers of p-n junction diodes using a spectral response technique are reported in this paper. Exact modeling of current-flow equations, modified to include bandgap reduction due to high carrier concentration and Auger recombination, is used to compute the dependence of diffused-layer photocurrent J pth on the incident light energy and intensity. The photocurrent in the diffused layer is also obtained by subtracting the theoretical value of the space charge and uniformly doped p-region component from the experimentally measured photocurrent of the diode at each wavelength. Note that all calculated values based on light intensity include computed transmittance/reflectance through the oxide layer at each wavelength. The comparison of the values of J pth with J pexp , using nonlinear least square techniques, then directly gives the lifetime profile in the diffused layer. A simple expression is given for lifetime as a function of doping which may be used in modeling and prediction of device performance. Using this experimental technique it was found that the lifetime in the diffused layer is an order of magnitude less than that corresponding to uniformly doped bulk-silicon values and is very much process dependent; its value being 3.72 × 10-11s for surface concentration of 3.0 × 1020cm-3and increases to 2.9 × 10-8s at doping concentration of 1.0 × 1017cm-3.

Extended Reading of Continuous Text on Television Screens

Abstract: Thirty-two subjects read continuous text for 2 h. Half read from a television screen (video condition) and half read from a book. Subjects experienced little nausea or headache in either condition....

Elemental fingerprints of isotopic contamination of hebridean Palaeocene mantle-derived magmas by archaean sial

Abstract: One of the major puzzles presented by the geochemistry of the Palaeocene plateau lavas of Skye and Mull (N.W. Scotland) is that, although a very strong case can be made that the magmas are variably isotopically contaminated by Archaean Lewisian continental crust, little evidence has been gleaned to date from their major- and trace-element compositions to illuminate this hypothetical process. The combined results of published Sr-, Nd- and Pb-isotope studies of these lavas allow the basalts and hawaiites to be divided into three broad groups: essentially uncontaminated; contaminated with granulite-facies Archaean crust; contaminated with amphibolite-facies Archaean crust. Members of each group show distinctive chondrite-normalised incompatible-element patterns. The processes which gave rise to isotopic contamination of these lavas also affected the abundances and ratios of Ba, Rb, Th, K, Sr and light REE in the magmas, whilst having negligible effects on their abundances and ratios of Nb, Ta, P, Zr, Hf, Ti, Y and middle-heavy REE. Because such a wide range of elements were affected by the contamination process, it is postulated that the contaminant was a silicate melt of one or more distinctive crustal rock types, rather than an aqueous or similar fluid causing selective elemental movements from wall rocks into the magmas. As previous experimental and isotopic studies have shown that the Skye and Mull basic magmas were not constrained by cotectic equilibria at the time when they interacted with sial, the compositions of the contaminated lavas have been modelled in terms of simple magma-crust mixtures. Very close approximations to both the abundances and ratios of incompatible elements in the two groups of contaminated basalts may be obtained by adding 15% to 20% of Lewisian leucogneisses to uncontaminated Palaeocene basalt. Nevertheless, major-element constraints suggest that the maximum amount of granitic contaminant which has been added to these magmas lies between 5% and 10%. These estimates may be reconciled by postulating that the contaminants were large-fraction cotectic partial melts of Lewisian leucogneisses, leaving plagioclase residua. A corollary of this hypothesis is that it is necessary to postulate that the “magma chambers” where the sialic contamination occurred were, in fact, dykes or (more probably) sills. The very large surface-to-volume ratios of such magmas bodies would permit the systematic stripping, by partial melting, of the most-easily-fusible leucogneisses and pegmatites from the Lewisian crust, whilst failing to melt its major rock types. A present-day analogue to this situation may be the extensive sill-like magma bodies detected by geophysical methods within the continental crust beneath the Rio Grande Rift, southwestern U.S.A.

Bad Data Rejection Properties of Weighted Least Absolute Value Techniques Applied to Static State Estimation

Abstract: A new method for obtaining an estimate of the state of a power system using weighted least absolute value (WLAV) techniques is presented. This paper shows how the WLAV estimator simultaneously detects and rejects bad data while obtaining an accurate estimate of the state. The test results presented show that the WLAV estimates, obtained with or without bad data present, are comparable to the estimates obtained by a weighted least squares (WLS) estimator using only good data.

Measurement of Electron Transport System (ETS) activity in soil.

Abstract: Electron transport system (ETS) activity was measured in amended and nonamended soil by measuring the reduction of 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyl tetrazolium chloride (INT) to iodonitrotetrazolium formazan (INT-formazan), which can be easily extracted with methanol without interference from other compounds found in soil. A high correlation between ETS activity and oxygen consumption was observed. This technique allows rapid quantitative measurements of microbial ETS activity in soil.

The Complexity of Fault Detection Problems for Combinational Logic Circuits

Abstract: In this correspondence we analyze the computational complexity of fault detection problems for combinational circuits and propose an approach to design for testability. Although major fault detection problems have been known to be in general NP-complete, they were proven for rather complex circuits. In this correspondence we show that these are still NP-complete even for monotone circuits, and thus for unate circuits. We show that for k-level (k ≥ 3) monotone/unate circuits these problems are still NP-complete, but that these are solvable in polynomial time for 2-level monotone/unate circuits. A class of circuits for which these fault detection problems are solvable in polynomial time is presented. Ripple-carry adders, decoder circuits, linear circuits, etc., belong to this class. A design approach is also presented in which an arbitrary given circuit is changed to such an easily testable circuit by inserting a few additional test-points.

A numerical simulation of the D.C. continuous casting process including nucleate boiling heat transfer

Abstract: The steady-state thermal problem associated with the direct-chill continuous casting of A6063 aluminum cylindrical ingots is solved using the numerical finite element technique. Excellent correlation is demonstrated between the numerical model and experimental data from ingots cast at two different speeds. By application of the model, effective heat transfer coefficients are calculated as a function of vertical position on the outside surface of the ingot. It is shown that direct application of these coefficients to the modeling of different casting situations will produce substantial errors in the region in which heat transfer is by nucleate boiling. Using theories of nucleate boiling with forced convection and film cooling, a method is developed to calculate the external boundary conditions in the submold region of the ingot, thus making it possible for the first time to define explicitly all of the thermal boundary conditions associated with this casting configuration. These theories are incorporated into the numerical model, and a subsequent simulation shows excellent agreement with experimental data from a third ingot.

Contaminant Migration in Saturated Unconsolidated Geologic Deposits

Abstract: This paper presents a brief review of the theory of solute migration through porous, nonindurated geologic deposits and examines the laboratory and field evidence upon which transport concepts are currently based. Existing predictive models are considered in relation to the recognized transport processes, including molecular diffusion, mechanical dispersion, and some types of chemical interactions.

Large order perturbation theory in the context of atomic and molecular physics—interdisciplinary aspects

Abstract: The paper is introduced by a description of the role of divergent series in mathematics and their particular use in quantum mechanics. It is emphasized that there is a formal similarity between divergent series in nonrelativistic quantum mechanics and those series occurring in quantum field theory. It is indicated that studies of divergent series in nonrelativistic quantum mechanics can be helpful in the verification of suminability techniques in quantum field theory. The general problems of the application of perturbation theory to the study of the hydrogen atom in external fields are discussed. It is shown how the problem of the continuous spectrum can be bypassed. Further it is shown that algebraic techniques are very useful for a transparent formulation of perturbation theory. The theory is applied to the study of the hydrogen atom in a magnetic field and in an electric field and also to the study of the hydrogen molecule ion. The results for the hydrogen atom in a magnetic field and the hydrogen molecule ion are discussed in detail and the large order behavior of perturbation terms is compared with analytic formulas. Finally the questions of the summability for the series corresponding to the quartic anharmonic oscillator and the hydrogen atom in a magnetic field are discussed. It is seen that large order perturbation theory can be built into a continued fraction representation of a divergent perturbation series. Numerical results are presented for the two perturbation series mentioned above.

Vesicular-Arbuscular Mycorrhizae of Southern Ontario Ferns and Fern-Allies

Abstract: Thirty-nine species and varieties of common Pteridophytes of southern Ontario were surveyed for the presence of VAM. The sporophytes of the three Equisetum spp. and the two Lycopodium spp. examined...