Showing papers by "University of Toronto published in 1987"

Concurrency Control and Recovery in Database Systems

Abstract: This book is an introduction to the design and implementation of concurrency control and recovery mechanisms for transaction management in centralized and distributed database systems. Concurrency control and recovery have become increasingly important as businesses rely more and more heavily on their on-line data processing activities. For high performance, the system must maximize concurrency by multiprogramming transactions. But this can lead to interference between queries and updates, which concurrency control mechanisms must avoid. In addition, a satisfactory recovery system is necessary to ensure that inevitable transaction and database system failures do not corrupt the database.

Supervisory control of a class of discrete event processes

Abstract: This paper studies the control of a class of discrete event processes, i.e. processes that are discrete, asynchronous and possibly nondeter-ministic. The controlled process is described as the generator of a formal language, while the controller, or supervisor, is constructed from the grammar of a specified target language that incorporates the desired closed-loop system behavior. The existence problem for a supervisor is reduced to finding the largest controllable language contained in a given legal language. Two examples are provided.

Complexity of finding embeddings in a k -tree

Abstract: A k-tree is a graph that can be reduced to the k-complete graph by a sequence of removals of a degree k vertex with completely connected neighbors. We address the problem of determining whether a graph is a partial graph of a k-tree. This problem is motivated by the existence of polynomial time algorithms for many combinatorial problems on graphs when the graph is constrained to be a partial k-tree for fixed k. These algorithms have practical applications in areas such as reliability, concurrent broadcasting and evaluation of queries in a relational database system. We determine the complexity status of two problems related to finding the smallest number k such that a given graph is a partial k-tree. First, the corresponding decision problem is NP-complete. Second, for a fixed (predetermined) value of k, we present an algorithm with polynomially bounded (but exponential in k) worst case time complexity. Previously, this problem had only been solved for $k = 1,2,3$.

Beta 1-6 branching of Asn-linked oligosaccharides is directly associated with metastasis

Abstract: Neoplastic transformation has been associated with a variety of structural changes in cell surface carbohydrates, most notably increased sialylation and beta 1-6-linked branching of complex-type asparagine (Asn)-linked oligosaccharides (that is, -GlcNAc beta 1-6Man alpha 1-6Man beta 1-). However, little is known about the relevant glycoproteins or how these transformation-related changes in oligosaccharide biosynthesis may affect the malignant phenotype. Here it is reported that a cell surface glycoprotein, gp 130, is a major target of increased beta 1-6-linked branching and that the expression of these oligosaccharide structures is directly related to the metastatic potential of the cells. Glycosylation mutants of a metastatic tumor cell line were selected that are deficient in both beta 1-6 GlcNAc transferase V activity and metastatic potential in situ. Moreover, induction of increased beta 1-6 branching in clones of a nonmetastatic murine mammary carcinoma correlated strongly with acquisition of metastatic potential. The results indicate that increased beta 1-6-linked branching of complex-type oligosaccharides on gp 130 may be an important feature of tumor progression related to increased metastatic potential.

The Evolution of Multiple Memory Systems

Abstract: The existence of multiple memory systems has been proposed in a number of areas, including cognitive psychology, neuropsychology, and the study of animal learning and memory. We examine whether the existence of such multiple systems seems likely on evolutionary grounds. Multiple systems adapted to serve seemingly similar functions, which differ in important ways, are a common evolutionary outcome. The evolution of multiple memory systems requires memory systems to be specialized to such a degree that the functional problems each system handles cannot be handled by another system. We define this condition as functional incompatibility and show that it occurs for a number of the distinctions that have been proposed between memory systems. The distinction between memory for song and memory for spatial locations in birds, and between incremental habit formation and memory for unique episodes in humans and other primates provide examples. Not all memory systems are highly specialized in function, however, and the conditions under which memory systems could evolve to serve a wide range of functions are also discussed. Memory is a function that permits animals and people to acquire, retain, and retrieve many different kinds of information. It allows them to take advantage of previous experience to help solve the multitude of problems with which their environment confronts them, such as how to recognize the familiar, predict events, return to particular places, and assess the consequences of behavior Recently the question has arisen as to whether the

Dopamine receptors and the dopamine hypothesis of schizophrenia.

Abstract: The discovery of neuroleptic drugs in 1952 provided a new strategy for seeking a biological basis of schizophrenia. This entailed a search for a primary site of neuroleptic action. The Parkinsonian effects caused by neuroleptics suggested that dopamine transmission may be disrupted by these drugs. In 1963 it was proposed that neuroleptics blocked "monoamine receptors" or impeded the release of monoamine metabolites. The neuroleptic concentration in plasma water or cerebrospinal fluid was of the order of 2 nM for haloperidol in clinical therapy. A systematic research was made between 1963 and 1974 for a primary site of neuroleptic action which would be sensitive to 2 nM haloperidol and stereoselective for (+)-butaclamol. Direct evidence that neuroleptics selectively blocked dopamine receptors occurred in 1974 with the finding that nanomolar concentrations of these drugs stereoselectively inhibited the binding of [3H]-dopamine or [3H]-haloperidol. These binding sites, now termed D2 dopamine receptors (which inhibit adenylate cyclase), are blocked by neuroleptics in direct relation to the antipsychotic potencies of the neuroleptics. No such correlation exists for D1 receptors (which stimulate adenylate cyclase). Based on the fact that dopamine-mimetic drugs elicited hallucinations, and that neuroleptics caused rigidity, Van Rossum in 1966 had suggested a hypothesis that dopamine pathways may be overactive in schizophrenia. The D2-selective blockade by all neuroleptics (except the monoamine-depleting reserpine) provided strong support for the dopamine hypothesis. Further support now comes from postmortem data and in vivo positron tomographic data, both of which indicate that the density of D2 receptors are elevated in the schizophrenic brain. The postmortem data indicate a bimodal pattern with half the schizophrenics having striatal D2 densities of 14 pmol/g (control is 13 pmol/g) and the other half having 26 pmol/g. Current positron tomographic data indicate D2 densities of 14 pmol/g in control subjects, but values of 34 pmol/g in drug-naive schizophrenics. Future tests of the dopamine hypothesis of schizophrenia may entail an examination of the amino acid composition and genes for D2 receptors in schizophrenic tissue, an examination of the ability of the D2 receptor to become phosphorylated and to desensitize into the low-affinity state, and an examination of the interaction of D2 receptors with D1 receptors or other neurotransmitters.

Age differences in recall and recognition

Abstract: An experiment is reported in which young and elderly adults performed cued-recall and recognition tests while carrying out a choice reaction-time task. An analysis of covariance, with recognition performance as the covariate, showed a reliable age decrement in recall. It was therefore concluded that older people perform more poorly on recall tasks than they do on recognition tasks. Performance on the secondary (reaction time) task showed that recall was associated with greater resource "costs" than was recognition and that this effect was amplified by increasing age. The results are in line with the suggestion that recall requires more processing resources than does recognition and that such resources are depleted as people grow older. The literature on age differences in human memory includes a large number of studies comparing the performance of young and old adults on tests of recall and recognition memory. The results of these studies have consistently shown an age decrement in recall performance (see Botwinick, 1978; Burke &

On the supermal controllable sublanguage of a given language

Abstract: The concept of controllable language has been shown to play a basic role in the existence theory of supervisory controls for discrete event processes. In this paper the supremal controllable sublanguage S of a given language L is characterized as the largest fixpoint of a monotone operator $\Omega $. In the case where the languages involved are regular it is shown that the fixpoint S can be computed as the limit of the (finite) sequence $\{ {K_j } \}$ given by $K_{j + 1} = \Omega (K_j )$, $K_0 = L$. An effective computational algorithm is developed, and three examples are provided for illustration.

Trust between humans and machines, and the design of decision aids

Abstract: A problem in the design of decision aids is how to design them so that decision makers will trust them and therefore use them appropriately. This problem is approached in this paper by taking models of trust between humans as a starting point, and extending these to the human-machine relationship. A definition and model of human-machine trust are proposed, and the dynamics of trust between humans and machines are examined. Based upon this analysis, recommendations are made for calibrating users' trust in decision aids.

Generalized Additive Models: Some Applications

Abstract: Generalized additive models have the form η(x) = α + σ fj (x j ), where η might be the regression function in a multiple regression or the logistic transformation of the posterior probability Pr(y = 1 | x) in a logistic regression. In fact, these models generalize the whole family of generalized linear models η(x) = β′x, where η(x) = g(μ(x)) is some transformation of the regression function. We use the local scoring algorithm to estimate the functions fj (xj ) nonparametrically, using a scatterplot smoother as a building block. We demonstrate the models in two different analyses: a nonparametric analysis of covariance and a logistic regression. The procedure can be used as a diagnostic tool for identifying parametric transformations of the covariates in a standard linear analysis. A variety of inferential tools have been developed to aid the analyst in assessing the relevance and significance of the estimated functions: these include confidence curves, degrees of freedom estimates, and approximat...

Gene for von Recklinghausen neurofibromatosis is in the pericentromeric region of chromosome 17

Abstract: Linkage analysis of 15 Utah kindreds demonstrated that a gene responsible for von Recklinghausen neurofibromatosis (NF) is located near the centromere on chromosome 17. The families also gave no evidence for heterogeneity, indicating that a significant proportion of NF cases are due to mutations at a single locus. Further genetic analysis can now refine this localization and may lead to the eventual identification and cloning of the defective gene responsible for this disorder.

The statistics of cosmic background radiation fluctuations

Abstract: Calculs des fonctions de correlations du rayonnement et des spectres de puissance angulaire pour des anisotropies de fond de microondes, attendues dans des univers avec une matiere sombre froide dominante (Ω=1)

Local Likelihood Estimation

Abstract: A scatterplot smoother is applied to data of the form {(x 1, y 1), (x 2, y 2, …, (xn, yn )} and uses local fitting to estimate the dependence of Y on X. A simple example is the running lines smoother, which fits a least squares line to the y values falling in a window around each x value. The value of the estimated function at x is given by the value of the least squares line at x. A smoother generalizes the least squares line, which assumes that the dependence of Y on X is linear. In this article, we extend the idea of local fitting to likelihood-based regression models. One such application is to the class of generalized linear models (Nelder and Wedderburn 1972). We enlarge this class by replacing the covariate form β0 + xβ1 with an unspecified smooth function s(x). This function is estimated from the data by a technique we call local likelihood estimation. The method consists of maximum likelihood estimation for β0 and β1, applied in a window around each x value. Multiple covariates are incor...

Hard examples for resolution

Abstract: Exponential lower bounds are proved for the length-of-resolution refutations of sets of disjunctions constructed from expander graphs, using the method of Tseitin. Since these sets of clauses encode biconditionals, they have short (polynomial-length) refutations in a standard axiomatic formulation of propositional calculus.

Phenomenological theory of optical second- and third-harmonic generation from cubic centrosymmetric crystals

Abstract: We present a macroscopic theory for anisotropic second- and third-harmonic generation obtained in reflection from the surface and bulk of cubic centrosymmetric single crystals. The theory is based on possible electric dipole, electric quadrupole, and magnetic dipole sources. Completely general expressions for the harmonic fields are obtained for (100), (111), and (110) faces independent of the details of the surface response but consistent with crystal symmetry. The results obtained agree with all existing experimental data obtained by various groups during the past few years. The possibility of separating out surface and bulk responses is considered using symmetry, polarization, or geometry arguments and it is concluded that for second-harmonic generation this cannot be done in general without additional information. Third-harmonic generation, barring any strong resonantly enhanced surface electric dipole effects, is essentially a bulk probe.

Clonal Analysis Using Recombinant DNA Probes from the X-Chromosome

Abstract: It has been demonstrated that restriction fragment length polymorphisms of X-chromosome genes can be used in conjunction with methylation patterns to determine the clonal composition of human tumors. In this report, we show that several X-chromosome probes can be used for such analyses. In particular, probes derived from the hypoxanthine phosphoribosyltransferase gene and the phosphoglycerate kinase gene could be used for clonal analysis in over 50% of American females. The X-inactivation patterns observed with these probes were found to accurately reflect clonality in more than 95% of 92 tumors tested.

Diagnosis and treatment of normal eating.

Abstract: The shift in societal preference toward a thin physique has led to an increasing prevalence of dieting such that "normal" eating for North American women is now characterized by dieting. In this article, we explore similarities between such normal dieters and individuals with an eating disorder and question whether a continuity exists between normal and abnormal eating behavior. The regulation of intake among normal dieter and patient populations is compared and is explained by the boundary model of consumption, which leads to the conclusion that in neither group is eating technically disordered, although it does depart from appropriate physiological norms. We conclude that many normal eaters (i.e., dieters or restrained eaters) display characteristics of eating-disorder pathologies and should be treated accordingly. Such treatment involves changing both the patient and the environment, especially societal attitudes toward body weight and shape. The current societal preference for a thin physique has spawned a corresponding societal preoccupation with dieting and weight loss. The extent of this preoccupation is such that it may now be accurate to regard dieting and its attendant diet mentality as normative, both descriptively and prescriptively. In short, it is now "normal" for individuals in our society to express concern about their weight and to engage in fitful attempts to change it. A normal lifestyle now requires periodic exercise; normal eating now requires periodic dieting. Why is a thin physique prized, especially among women? Answers to this question typically refer to historical variation in the sort of physique that is most highly valued. In former times, endomorphy was preferred, as is evidenced by the inevitably referenced Rubenesque nude. Nowadays, women are induced to strive toward a condition of ruddy-cheeked emaciation. Describing this historical shift does not account for it, of course, and the explanations usually tendered are both easy to produce and difficult to prove. Their validity aside, these explanations tend to fall into three classes: The first class focuses on the aesthetics of physique, with thin women seen as more beautiful and, consequently, of greater sexual allure; the second class emphasizes the implicit personality correlates of various physiques, with thinness connoting power, health, and other contemporary values; and the third class infers behaviors from the physique itself, with thinness reflecting the sort of self-control that is presumably required to achieve and maintain slender

5-year Results of a Prospective Study of Percutaneous Transluminal Angioplasty

Abstract: This paper presents the results of a prospective study of percutaneous transluminal angioplasty (PTA) for the treatment of patients with peripheral arterial occlusive disease and identifies the variables that are predictive of long-term success. The variables believed to be important prognostically were recorded for 984 consecutive PTAs performed between July 1978 and July 1986. Success or failure was defined using a combination of clinical and objective vascular laboratory criteria. The overall long-term success was estimated by the Kaplan-Meier method and differences between curves of success rate versus time for each variable were determined by the Wilcoxon and log-rank statistics. The combination of variables associated with success were determined by the Cox proportional hazards regression model. For all cases, the initial success rate was 88.6 +/- 1.0% and at 5 years was 48.2 +/- 2.3%. The following variables, when considered individually, were associated with success (p less than 0.05): indication for PTA, site of PTA, severity of lesion, runoff, number of sites dilated, diabetes, and the occurrence of a complication. From the Cox model, by using a stepwise multiple regression procedure, the following combination of variables were found to be predictive of success (p less than 0.05): (1) indication (claudication vs. salvage), (2) site (common iliac vs. other), (3) severity of lesion (stenosis vs. occlusion), and (4) runoff (good vs. poor). For all combinations of these four significant variables, curves of the success rate versus time were calculated. In conclusion, this study has identified the combination of four variables that together predict if PTA is likely to be successful in the management of a patient with peripheral arterial occlusive disease.

The Formation and Extent of the Solar System Comet Cloud

Abstract: The formation of the solar system comet cloud and its subsequent evolution over an interval equal to the age of the solar system are simulated. Assuming that the comets formed in the outer planetary region, it is shown that the formation of the current comet cloud was driven mainly by an interaction between planetary perturbations and torquing due to Galactic tides. An inner edge to the cloud is found at about 3000 AU, the radius where the timescales for the two processes are comparable. Results suggest that the flux of comets into the inner solar system during a comet shower initiated by the close passage of a passing star may be up to 20 times higher than the steady state rate. 23 references.

Semantic Interpretation and the Resolution of Ambiguity

Abstract: Preface 1. Introduction 2. Semantic interpretation 3. The Absity semantic interpreter 4. Lexical disambiguation 5. Polaroid words 6. Structural disambiguation 7. The semantic enquiry desk 8. Conclusion 9. Speculations, partially baked ideas, and exercises for the reader References Index of names Index of subjects.

New Green-function formalism for surface optics

Abstract: A new Green-function formalism is developed for calculating fields generated by sources in the presence of a multilayer geometry. The approach is to formulate the problem immediately in terms of s- and p-polarized waves generated, so that the calculation of the effect of interfaces proceeds by the introduction of Fresnel reflection and transmission coefficients and parallels the simple physical picture of light progressing through the structure.

Modular feedback logic for discrete event systems

Abstract: We examine a modular approach to the synthesis of state feedback controls for the problem of maintaining a predicate on the state set of a discrete dynamic system invariant. Dynamical systems are modeled by automata together with a mechanism for enabling and disabling a subset of state transitions. The basic problem of interest is to ensure by appropriate control action that a given predicate on the state set of the process remains invariantly true whenever it is initially satisfied. Assuming the predicate can be decomposed into the conjunction or disjunction of component predicates, we determine conditions under which it is possible to synthesize the appropriate control in a modular fashion.

Human brain dopamine receptors in children and aging adults.

Abstract: Since spontaneous oral dyskinesias are more prevalent in the elderly, and since these movements may be controlled by the balance of brain dopamine D1 and D2 dopamine receptors, we measured the densities of these receptors in 247 postmortem brain striata. In childhood, the densities of D1 and D2 dopamine receptors in the brain striatum rise and fall together. After age 20 years, D1 receptors disappear at 3.2% per decade while D2 receptors disappear at about 2.2% per decade. Overall, therefore, the D1/D2 ratio falls with age. Since perioral motion in rats is dominated by a high D1/D2 ratio, the observed decline in the human D1/D2 ratio with age suggests that the perioral control mechanisms for humans and rats may be different.

The role of consciousness in priming effects on categorization: Assimilation versus contrast as a function of awareness of the priming task.

Abstract: Consciousness of a priming event at the time information about the event is retrieved from memory is argued to make a qualitative difference as to the consequences of the prime for subsequent social judgments. Two experiments are reported that provide evidence bearing on this hypothesis. Experiment 1 demonstrated that whether or not subjects can recall any of the priming stimuli presented in a first task dramatically influences which of two evaluatively dissimilar primed constructs they subsequently use in their categorizations of a target description. Subjects who could recall one or more primes showed contrast effects with regard to the more accessible construct, whereas subjects who could not recall any primes showed assimilation effects. Experiment 2 showed that interruption of the priming task resulted in assimilation effects for both the recall and the no-recall subjects. Together, these findings suggest that the function of consciousness of the priming events is to enable subjects to process subseq...

Found ations of assumption-based truth maintenance systems: preliminary report

Abstract: In this paper we (1) define the concept of a Clause Management System (CMS) -- a generalization of de Kleer's ATMS, (2) motivate such systems in terms of efficiency of search and abductive reasoning, and (3) characterize the computation affected by a CMS in terms of the concept of prime implicants.

Multiple memory systems and consciousness.

Abstract: This Introduction to the Special Issue on Human Memory discusses some of the recent and current developments in the study of human memory from the neuropsychological perspective. A problem of considerable current interest, that of multiple memory systems, is a problem in classification. Much of the evidence for it is derived from clinical and experimental observations of dissociations between performances in memory tasks. The distinction between short-term and long-term memory is considered as an example of classification by dissociation. Current conceptualizations of multiple long-term memory systems are reviewed from the vantage point that distinguishes among three major kinds of memory--episodic, semantic, and procedural. These systems are briefly described and compared, and current views concerning the relation between them are discussed. The role of consciousness in memory is raised against the backdrop of the suggestion that it may be necessary to differentiate among several kinds of consciousness.