Showing papers by "University of Waterloo published in 1998"
TL;DR: This paper introduces the reader to a response surface methodology that is especially good at modeling the nonlinear, multimodal functions that often occur in engineering and shows how these approximating functions can be used to construct an efficient global optimization algorithm with a credible stopping rule.
Abstract: In many engineering optimization problems, the number of function evaluations is severely limited by time or cost. These problems pose a special challenge to the field of global optimization, since existing methods often require more function evaluations than can be comfortably afforded. One way to address this challenge is to fit response surfaces to data collected by evaluating the objective and constraint functions at a few points. These surfaces can then be used for visualization, tradeoff analysis, and optimization. In this paper, we introduce the reader to a response surface methodology that is especially good at modeling the nonlinear, multimodal functions that often occur in engineering. We then show how these approximating functions can be used to construct an efficient global optimization algorithm with a credible stopping rule. The key to using response surfaces for global optimization lies in balancing the need to exploit the approximating surface (by sampling where it is minimized) with the need to improve the approximation (by sampling where prediction error may be high). Striking this balance requires solving certain auxiliary problems which have previously been considered intractable, but we show how these computational obstacles can be overcome.
6,914 citations
TL;DR: It is argued that the simplest explanation for the observed biological activity of plant growth promoting rhizobacteria relates to the relative amounts of 1-aminocyclopropane-1-carboxylate deaminase and 1-amino-2-car boxylate oxidase in the system under consideration.
1,390 citations
TL;DR: A relatively simple control scheme for regulation of upright posture that provides almost instantaneous corrective response and reduces the operating demands on the CNS is proposed.
Abstract: Winter, David A., Aftab E. Patla, Francois Prince, Milad Ishac, and Krystyna Gielo-Perczak. Stiffness control of balance in quiet standing. J. Neurophysiol. 80: 1211–1221, 1998. Our goal was to pro...
1,389 citations
TL;DR: A future challenge is to elucidate how UV-B-exposed plants balance damage, repair, acclimation and adaptation responses in a photobiologically dynamic environment.
968 citations
TL;DR: A model is proposed for the movement of the apoplastic path will be less used and the hydraulic water across roots and it is shown how the complex, ‘com- resistance’ will be high.
Abstract: uptake of water. On the contrary, at low rates of transpiration such as during the night or during stress conOn the basis of recent results with young primary ditions (drought, high salinity, nutrient deprivation), maize roots, a model is proposed for the movement of the apoplastic path will be less used and the hydraulic water across roots. It is shown how the complex, ‘com- resistance will be high. The role of water channels posite anatomical structure’ of roots results in a ‘com- (aquaporins) in the transcellular path is in the fine posite transport’ of both water and solutes. Parallel adjustment of water flow or in the regulation of uptake apoplastic, symplastic and transcellular pathways play in older, suberized parts of plant roots lacking a suban important role during the passage of water across stantial apoplastic component. The composite transthe different tissues. These are arranged in series port model explains how plants are designed to within the root cylinder (epidermis, exodermis, central optimize water uptake according to demands from the cortex, endodermis, pericycle stelar parenchyma, and shoot and how external factors may influence water tracheary elements). The contribution of these struc- passage across roots. tures to the root’s overall radial hydraulic resistance is examined. It is shown that as soon as early metaxy- Key words: Composite transport model, endodermis, exolem vessels mature, the axial (longitudinal) hydraulic dermis, hydraulic conductivity, reflection coefficient, root, resistance within the xylem is usually not rate-limiting. water, water channels. According to the model, there is a rapid exchange of water between parallel radial pathways because, in contrast to solutes such as nutrient ions, water per- Introduction meates cell membranes readily. The roles of apoplastic One of the essential functions of roots is to supply the barriers (Casparian bands and suberin lamellae) in the shoot with water from the soil. The process of water root’s endo- and exodermis are discussed. The model
883 citations
TL;DR: A Bayesian approach for finding classification and regression tree (CART) models by having the prior induce a posterior distribution that will guide the stochastic search toward more promising CART models.
Abstract: In this article we put forward a Bayesian approach for finding classification and regression tree (CART) models. The two basic components of this approach consist of prior specification and stochastic search. The basic idea is to have the prior induce a posterior distribution that will guide the stochastic search toward more promising CART models. As the search proceeds, such models can then be selected with a variety of criteria, such as posterior probability, marginal likelihood, residual sum of squares or misclassification rates. Examples are used to illustrate the potential superiority of this approach over alternative methods.
749 citations
TL;DR: Some recent reports suggest that preferred footedness may serve as a more accurate predictor of functional laterality, especially in the left-handed population, and the present study sought to test this claim by selectively recruiting individuals with 'crossed' lateral preferences.
647 citations
TL;DR: The results suggest that cumulative loading of the low back is important etiologically and highlight the need for better information on the response of spinal tissues to cumulative loading.
606 citations
TL;DR: It is shown that there are substantial optical changes in the human lens with increasing age and during accommodation, since both the magnitude and the sign of the spherical aberration change with age and stretching.
593 citations
TL;DR: The results suggested that STC has limited capacity and that it requires central processing mechanisms, and suggested that no memory for T1 was formed in STM when STC was not engaged.
582 citations
TL;DR: In this article, the authors explored the use of multiple isotopic tracers to evaluate the processes involved in nitrate attenuation in ground water and found that reduced sulfur and carbon are electron donors for nitrate reduction.
Abstract: This study explores the use of multiple isotopic tracers to evaluate the processes involved in nitrate attenuation in ground water. δ15N and δ18O are used to provide information about the role of denitrification on nitrate attenuation, and δ34S, δ18O, and δ13C are used to evaluate the role of reduced sulfur and carbon as electron donors for nitrate reduction. The focus of this study is a zone of significant NO3−1 attenuation occurring in a sand aquifer impacted by septic system contamination. The NO3−1 pattern, the ground water flow system, and changes in other chemical parameters suggest that the NO3−1 depletion is caused by denitrification. This is supported by the nitrate δ15N and δ18O data which both show significant isotopic enrichment as NO3−1 depletion proceeds along the flow path. The increase of sulfate and dissolved inorganic carbon observed in the zone of nitrate attenuation suggests that reduced sulfur in addition to carbon is also involved in denitrification. This is supported by a trend toward depleted sulfate δ34S and δ18O values in the zone of sulfate increase, which reflects the input of sulfate formed by the oxidation of biogenic pyrite present in the aquifer sediments. The trend toward depleted δ13 values in the zone of increasing dissolved inorganic carbon reflects the input of organic carbon into this carbon pool. Chemical mass balance indicates that carbon is the dominant electron donor; however, this study demonstrates the effectiveness of using multiple isotopic tracers for providing insight into the processes affecting nitrate attenuation in ground water.
Posted Content•
TL;DR: In this article, it was shown that the exponential quantum speed-up obtained for partial functions (i.e., problems involving a promise on the input) by Deutsch and Jozsa and by Simon cannot be obtained for any total function, and that there is a classical deterministic algorithm that computes some total Boolean function f with bounded-error using T black-box queries.
Abstract: We examine the number T of queries that a quantum network requires to compute several Boolean functions on {0,1}^N in the black-box model. We show that, in the black-box model, the exponential quantum speed-up obtained for partial functions (i.e. problems involving a promise on the input) by Deutsch and Jozsa and by Simon cannot be obtained for any total function: if a quantum algorithm computes some total Boolean function f with bounded-error using T black-box queries then there is a classical deterministic algorithm that computes f exactly with O(T^6) queries.
We also give asymptotically tight characterizations of T for all symmetric f in the exact, zero-error, and bounded-error settings. Finally, we give new precise bounds for AND, OR, and PARITY. Our results are a quantum extension of the so-called polynomial method, which has been successfully applied in classical complexity theory, and also a quantum extension of results by Nisan about a polynomial relationship between randomized and deterministic decision tree complexity.
TL;DR: These results provide comparative benchmarks for researchers and clinicians working with different groups of older adults and indicate balance confidence is amenable to change and able to distinguish between elders at various levels of functional mobility.
Abstract: Background. Balance confidence is an important indicator of functional mobility and independence in older adults. Preliminary psychometric evidence for the Activities-specific Balance Confidence (ABC) Scale is promising, with a series of four studies adding information on the discriminative and evaluative properties of this tool. Methods. The original validation sample was reinterviewed one year later. In the second study, the ABC was administered to 475 older adults ranging from home care clients to highly functioning individuals in community exercise programs. The third study compared 31 residents of retirement homes given a 10-week balance control exercise program and fall education with 32 residents who received only fall education. The fourth study examined balance confidence preoperatively and postoperatively for 27 patients undergoing hip or knee replacement. Results. ABC scores remained stable over 12 months in higher functioning elders, but deteriorated in retirement home residents over 26 weeks. Ten weeks of balance training significantly improved balance confidence, as did hip or knee replacement with standard physical therapy. ABC scores lower than 50 indicated a low level of physical functioning characteristic of home care clients. ABC scores above 50 and lower than 80 indicated a moderate level of functioning characteristic of elders in retirement homes and persons with chronic health conditions. ABC scores above 80 are indicative of highly functioning, usually physically active older adults, and are achievable through exercise and rehabilitative therapies.
TL;DR: The bacterial plant growth-promoting effect in the presence of nickel was probably not attributable to the reduction of nickel uptake by seedlings, and may reflect the ability of the bacterium to lower the level of stress ethylene induced by the nickel.
Abstract: A plant growth-promoting bacterium, Kluyvera ascorbataSUD165, that contained high levels of heavy metals was isolated from soil collected near Sudbury, Ontario, Canada. The bacterium was resistant to the toxic effects of Ni2+, Pb2+, Zn2+, and CrO4−, produced a siderophore(s), and displayed 1-aminocyclopropane-1-carboxylic acid deaminase activity. Canola seeds inoculated with this bacterium and then grown under gnotobiotic conditions in the presence of high concentrations of nickel chloride were partially protected against nickel toxicity. In addition, protection by the bacterium against nickel toxicity was evident in pot experiments with canola and tomato seeds. The presence of K. ascorbata SUD165 had no measurable influence on the amount of nickel accumulated per milligram (dry weight) of either roots or shoots of canola plants. Therefore, the bacterial plant growth-promoting effect in the presence of nickel was probably not attributable to the reduction of nickel uptake by seedlings. Rather, it may reflect the ability of the bacterium to lower the level of stress ethylene induced by the nickel.
Book•
05 Jan 1998TL;DR: 1. Cryptography.- 1. Early History.; 2. The Idea of Public Key Cryptography.; 3. The RSA Cryptosystem.; 4. Diffie-Hellman and the Digital Signature Algorithm; 5. Secret Sharing, Coin Flipping, and Time Spent on Homework.; 6. Passwords, Signatures, and Ciphers; 7. Randomized Algorithms and Complexity Classes.
Abstract: 1. Cryptography.- 1. Early History.- 2. The Idea of Public Key Cryptography.- 3. The RSA Cryptosystem.- 4. Diffie-Hellman and the Digital Signature Algorithm.- 5. Secret Sharing, Coin Flipping, and Time Spent on Homework.- 6. Passwords, Signatures, and Ciphers.- 7. Practical Cryptosystems and Useful Impractical Ones.- Exercises.- 2. Complexity of Computations.- 1. The Big-O Notation.- Exercises.- 2. Length of Numbers.- Exercises.- 3. Time Estimates.- Exercises.- 4. P, NP, and NP-Completeness.- Exercises.- 5. Promise Problems.- 6. Randomized Algorithms and Complexity Classes.- Exercises.- 7. Some Other Complexity Classes.- Exercises.- 3. Algebra.- 1. Fields.- Exercises.- 2. Finite Fields.- Exercises.- 3. The Euclidean Algorithm for Polynomials.- Exercises.- 4. Polynomial Rings.- Exercises.- 5. Grobner Bases.- Exercises.- 4. Hidden Monomial Cryptosystems.- 1. The Imai-Matsumoto System.- Exercises.- 2. Patarin's Little Dragon.- Exercises.- 3. Systems That Might Be More Secure.- Exercises.- 5. Combinatorial-Algebraic Cryptosystems.- 1. History.- 2. Irrelevance of Brassard's Theorem.- Exercises.- 3. Concrete Combinatorial-Algebraic Systems.- Exercises.- 4. The Basic Computational Algebra Problem.- Exercises.- 5. Cryptographic Version of Ideal Membership.- 6. Linear Algebra Attacks.- 7. Designing a Secure System.- 6. Elliptic and Hyperelliptic Cryptosystems.- 1. Elliptic Curves.- Exercises.- 2. Elliptic Curve Cryptosystems.- Exercises.- 3. Elliptic Curve Analogues of Classical Number Theory Problems.- Exercises.- 4. Cultural Background: Conjectures on Elliptic Curves and Surprising Relations with Other Problems.- 5. Hyperelliptic Curves.- Exercises.- 6. Hyperelliptic Cryptosystems.- Exercises.- 1. Basic Definitions and Properties.- 2. Polynomial and Rational Functions.- 3. Zeros and Poles.- 4. Divisors.- 5. Representing Semi-Reduced Divisors.- 6. Reduced Divisors.- 7. Adding Reduced Divisors.- Exercises.- Answers to Exercises.
TL;DR: The use of granular iron for in situ degradation of dissolved chlorinated organic compounds is rapidly gaining acceptance as a cost-effective technology for ground water remediation as discussed by the authors, and the first field demonstration of the technology is of particular importance since it provides the longest available record of performance (five years).
Abstract: The use of granular iron for in situ degradation of dissolved chlorinated organic compounds is rapidly gaining acceptance as a cost-effective technology for ground water remediation. This paper describes the first field demonstration of the technology, and is of particular importance since it provides the longest available record of performance (five years). A mixture of 22% granular iron and 78% sand was installed as a permeable “wall” across the path of a contaminant plume at Canadian Forces Base, Borden, Ontario. The major contaminants were trichloroethene (TCE, 268 mg/L) and tetrachloroethene (PCE, 58 mg/L). Approximately 90% of the TCE and 86% of the PCE were removed by reductive dechlorination within the wall, with no measurable decrease in performance over the five year duration of the test. Though about 1% of the influent TCE and PCE appeared as dichloroethene isomers as a consequence of the dechlorination of TCE and PCE, these also degraded within the iron-sand mixture. Performance of the field installation was reasonably consistent with the results of laboratory column studies conducted to simulate the field behavior. However, if a more reactive iron material, or a higher percentage of iron had been used, complete removal of the chlorinated compounds might have been achieved. Changes in water chemistry indicated that calcium carbonate was precipitating within the reactive material; however, the trace amount of precipitate detected in core samples collected four years after installation of the wall suggest that the observed performance should persist for at least another five years. The study provides strong evidence that in situ use of granular iron could provide a long-term, low-maintenance cost solution for many ground water contamination problems.
TL;DR: The Process Risk Model was applied to model the human health risk associated with Escherichia coli O157:H7 in ground beef hamburgers and predicted a probability of Hemolytic Uremic Syndrome, which is likely high for all hamburger meals, but may be reasonable for the home-prepared hamburger described by this model.
TL;DR: The psychology of elicitation and the currently available methods are briefly reviewed, but the primary discussion is on the distinction between 'general' elicitation methods for a class of problems and 'application-specific' methods which are useful only once.
Abstract: Summary. Elicitation of expert opinion is becoming increasingly important in the elicitation of prior distributions. In this paper, the psychology of elicitation and the currently available methods are briefly reviewed, but the primary discussion is on the distinction between 'general' elicitation methods for a class of problems and 'application-specific' methods which are useful only once. Examples of both types of elicitation are given, along with a discussion about general versus application-specific methods, and predictive versus structural elicitation.
TL;DR: The authors outlines antecedents of involvement and mediating roles of developmental processes leading to participants' behavioral loyalty (i.e., involvement → psychological commitment → resistance) in order to predict participants' behavior loyalty.
Abstract: This paper outlines antecedents of involvement and mediating roles of developmental processes leading to participants' behavioral loyalty (i.e., involvement → psychological commitment → resistance ...
TL;DR: In this article, the authors describe the solution of an optimal power flow (OPF) problem in rectangular form by an interior-point method (IPM) for nonlinear programming.
Abstract: The paper describes the solution of an optimal power flow (OPF) problem in rectangular form by an interior-point method (IPM) for nonlinear programming. Some OPF variants when formulated in rectangular form have quadratic objective and quadratic constraints. Such quadratic features allow for ease of matrix setup, and inexpensive incorporation of higher-order information in a predictor-corrector procedure that generally improves IPM performance. The mathematical development of the IPM in the paper is based on a general nonlinear programming problem. Issues in implementation to solve the rectangular OPF are discussed. Computational tests apply the IPM to both the rectangular and polar OPF versions. Test results show that both algorithms perform extremely well.
TL;DR: Some specific exercises are described that have been shown to challenge muscle and enhance performance but that are performed in such a way as to minimize loading of the spine to reduce the risk of injury exacerbation.
Abstract: Despite the wide variety of exercises that are prescribed for the low back, the scientific foundation to justify their choice is not as complete as one may think, or expect. Thus, the clinician must often call upon "clinical opinion" when selecting exercise. Given that low back tissues may need stressing to enhance their health but too much loading can be detrimental, choosing the optimal exercise requires judgment based on clinical experience and scientific evidence. To assist in developing better exercise programs, this review documents some recent biomechanical evidence from my laboratory and from laboratories of other researchers that has been reported in various publications in an attempt to update clinicians on issues of low back exercise. Among the issues examined are mechanisms of injury; the relative importance of "strength" (ie, maximum force a muscle can produce during a single exertion to create joint torque), "flexibility," and "endurance"; and training to enhance stability. Finally, some specific exercises are described that have been shown to challenge muscle and enhance performance but that are performed in such a way as to minimize loading of the spine to reduce the risk of injury exacerbation. These exercises form a basic program for rehabilitation and maintenance of low back health.
TL;DR: Compared to the other groups, social phobia was associated with greater concern about mistakes (CM), doubts about actions (DA), and parental criticism (PC) on one measure and more socially prescribed perfectionism (SP) on the other measure and the remaining dimensions of perfectionism failed to differentiate among groups.
01 Jan 1998
TL;DR: In this article, the authors discuss the effect of negative stereotyping on academic performance of women and minorities in the academic domain. But, the very existence of the pattern is alarming and the ill effects and the existence of stereotype threat cannot be ruled out.
Abstract: Publisher Summary It is now a known fact that groups that have been subjected to constant negative stereotyping based on their academic proficiency and ability, tend to perform poorly in the academic spheres. Women subjected to this kind of negative stereotyping also show negative trends in performance, though in a slightly different pattern. However, the very existence of the pattern is alarming. Though it can be argued that there has been considerable improvement in these conditions in the recent years, the ill effects and the very existence of “stereotype threat” cannot be ruled out. This kind of threat, if strong enough, along with decreasing academic performance, can also pose serious threats to an individual's social interaction patterns as well as overall intellectual performance. Understanding the stereotype threat model can help in undermining the performance patterns in women and minorities. This chapter elaborates on the various aspects of stereotype threat so as to understand how exactly people's performances are affected by this condition. It also highlights intervention plans and methods to reduce the threat.
TL;DR: The results showed a progressive slowing from the young to the elderly to the PD subjects and there does not appear to be a relationship between the PD subject's steady-state velocity and their age, number of years diagnosed,number of hours off medication, or the rating on the Hoehn and Yahr scale.
TL;DR: Rhodococcus sp.
Abstract: The psychrotroph Rhodococcus sp. strain Q15 was examined for its ability to degrade individual n-alkanes and diesel fuel at low temperatures, and its alkane catabolic pathway was investigated by biochemical and genetic techniques. At 0 and 5°C, Q15 mineralized the short-chain alkanes dodecane and hexadecane to a greater extent than that observed for the long-chain alkanes octacosane and dotriacontane. Q15 utilized a broad range of aliphatics (C10 to C21 alkanes, branched alkanes, and a substituted cyclohexane) present in diesel fuel at 5°C. Mineralization of hexadecane at 5°C was significantly greater in both hydrocarbon-contaminated and pristine soil microcosms seeded with Q15 cells than in uninoculated control soil microcosms. The detection of hexadecane and dodecane metabolic intermediates (1-hexadecanol and 2-hexadecanol and 1-dodecanol and 2-dodecanone, respectively) by solid-phase microextraction–gas chromatography-mass spectrometry and the utilization of potential metabolic intermediates indicated that Q15 oxidizes alkanes by both the terminal oxidation pathway and the subterminal oxidation pathway. Genetic characterization by PCR and nucleotide sequence analysis indicated that Q15 possesses an aliphatic aldehyde dehydrogenase gene highly homologous to the Rhodococcus erythropolis thcA gene. Rhodococcus sp. strain Q15 possessed two large plasmids of approximately 90 and 115 kb (shown to mediate Cd resistance) which were not required for alkane mineralization, although the 90-kb plasmid enhanced mineralization of some alkanes and growth on diesel oil at both 5 and 25°C.
TL;DR: It is shown that the DSSPP is computationally intractable and traditional shortest path algorithms cannot guarantee an optimal solution and a heuristic algorithm based on the k-shortest path algorithm is subsequently proposed to solve the problem.
Abstract: The dynamic and stochastic shortest path problem (DSSPP) is defined as finding the expected shortest path in a traffic network where the link travel times are modeled as a continuous-time stochastic process. The objective of this paper is to examine the properties of the problem and to identify a technique that can be used to solve the DSSPP given information that will be available in networks with Intelligent Transportation System (ITS) capabilities. The paper first identifies a set of relationships between the mean and variance of the travel time of a given path and the mean and variance of the dynamic and stochastic link travel times on these networks. Based on these relationships it is shown that the DSSPP is computationally intractable and traditional shortest path algorithms cannot guarantee an optimal solution. A heuristic algorithm based on the k-shortest path algorithm is subsequently proposed to solve the problem. Lastly, the trade-off between solution quality and computational efficiency of the proposed algorithm is demonstrated on a realistic network from Edmonton, Alberta.
TL;DR: The results indicate that the accident involvement rates of 16-19 year old drivers are higher than those of 20-24 and 25-59 year olds in all situations that were examined, but that they were disproportionately high on weekends, at nighttime and with passengers.
TL;DR: Southern hybridization experiments suggest that there is a single copy of the ACC deaminase gene in Enterobacter cloacae strains UW4 and CAL2 and that there may be several different types of ACC deaminationase genes in different microbes.
Abstract: We have recently proposed that one way that plant growth-promoting rhizobacteria (PGPR) stimulate plant growth is through the activity of the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminas...
TL;DR: Evidence of previously active and severe disease, as manifested by the prior use of medications and by radiologic changes as well as an elevated ESR at presentation, are prognostic indicators for death.
Abstract: Objective
To investigate prognostic factors associated with mortality in patients with psoriatic arthritis (PsA).
Methods
Patients followed up at the Toronto PsA Clinic between 1978 and 1994 were included. Patients were reviewed at initial clinic entry and at 6-month intervals using a standard protocol. Data on deaths were collected in a prospective manner, and death certificates were used to identify the primary and antecedent cause(s) of death. All death information was recorded in the clinic's computerized database. Only factors that represented standard clinical measures of isease activity and progression were studied. The relationship between potential prognostic factors recorded at the time of the first clinic visit and the mortality rate was determined using the Cox relative risk regression model.
Results
There were 428 patients (234 men and 194 women), of whom 68% were known to be alive on September 1, 1994, 20% were lost to followup but assumed to be alive, and 12% had died. Multivariate analysis revealed that an erythrocyte sedimentation rate (ESR) > 15 mm/hour, medications used prior to initial clinic visit, radiologic damage, and the absence of nail lesions were associated with an increased overall mortality rate. There is some suggestion that prior medication use was least important for deaths associated with the circulatory system, while radiologic damage was particularly important for such deaths. A marked sex-associated effect was noted among deaths caused by injuries/poisoning, since 6 of the deaths occurred in men and only 1 was in a woman.
Conclusion
Patients with PsA are at an increased risk of death compared with the general population. Evidence of previously active and severe disease, as manifested by the prior use of medications and by radiologic changes as well as an elevated ESR at presentation, are prognostic indicators for death. The presence of nail lesions appears to be a protective factor that has the most clinical importance in the context of previously active and severe disease.
TL;DR: MCT3 appears to be the major MCT isoform responsible for efflux of glycolytically derived lactic acid from white skeletal muscle, and the significance of the two isoforms may be related to their regulation rather than their intrinsic properties.