Showing papers by "University of Waterloo published in 1995"
TL;DR: The inverted pendulum model permitted us to understand the separate roles of the two mechanisms during these critical unbalancing and rebalancing periods and confirmed the critical importance of the hip abductors/adductors in balance during all phases of standing and walking.
2,940 citations
TL;DR: The greater item responsiveness of the ABC scale makes it more suitable to detect loss of balancing confidence in more highly functioning seniors, and greater situation-specificity of items may also assist clinicians in targeting appropriate interventions.
Abstract: BACKGROUND: This study provides a replication of the Falls Efficacy Scale (FES) and a head-to-head comparison with the Activities-specific Balance Confidence (ABC) Scale designed to include a wider continuum of activity difficulty and more detailed item descriptors. METHODS: Items for the newly developed 16-item ABC Scale were generated by 15 clinicians and 12 elderly outpatients. Psychometric testing involved 60 community seniors (aged 65-95) self-classified as either high or low in mobility confidence according to their perceived need for a walking aid and personal assistance to ambulate outdoors. RESULTS: Both the FES and ABC scales were found to be internally consistent and demonstrated good test-retest reliability, convergent and criterion validity. Scalogram analyses indicated a stronger cumulative scale in the case of the ABC and skewness in the distribution of FES scores. While both scales were able to discriminate between the two mobility groups, the ABC scale was a more efficient discriminator and yielded a wider range of responses. CONCLUSIONS: The present study provided additional psychometric support for the FES. However, the greater item responsiveness of the ABC scale makes it more suitable to detect loss of balancing confidence in more highly functioning seniors. Greater situation-specificity of items may also assist clinicians in targeting appropriate interventions. Language: en
2,443 citations
TL;DR: The relative benefit of an active treatment over a control is usually expressed as the relative risk, the Relative risk reduction, or the odds ratio, but for clinical decision making, it is more meaningful to use the measure "number needed to treat."
Abstract: The relative benefit of an active treatment over a control is usually expressed as the relative risk, the relative risk reduction, or the odds ratio. These measures are used extensively in both clinical and epidemiological investigations. For clinical decision making, however, it is more meaningful to use the measure "number needed to treat." This measure is calculated on the inverse of the absolute risk reduction. It has the advantage that it conveys both statistical and clinical significance to the doctor. Furthermore, it can be used to extrapolate published findings to a patient at an arbitrary specified baseline risk when the relative risk reduction associated with treatment is constant for all levels of risk.
1,660 citations
TL;DR: In this review the physiological changes to host cells, the causes of the phenomenon of metabolic load, and several strategies to avoid some of the problems associated with metabolic load are elaborated and discussed.
603 citations
TL;DR: In this paper, a 3D inverse dynamics model of the lower limbs and power profiles were derived using a dot product of the angular velocities and joint moments resolved in a global reference system.
500 citations
TL;DR: The key idea is to use point estimates based on Poisson models and to develop robust variance estimates that are valid more generally and illustrated on reliability and warranty data.
Abstract: Nelson discussed a method of estimating the cumulative mean function for identically distributed processes of recurrent events. We show that a similar approach can be used with more general models, including regression, The key idea is to use point estimates based on Poisson models and to develop robust variance estimates that are valid more generally. The methods are illustrated on reliability and warranty data.
458 citations
TL;DR: In this paper, two within-subject policy-capturing studies support the notion that media choice research has focused on attempts to determine what theory best explains people's choices of communication media.
Abstract: Recent media choice research has focused on attempts to determine what theory best explains people's choices of communication media. Two within-subject policy-capturing studies support the notion t...
418 citations
TL;DR: This article found that children who were poor emotion regulators exhibited more wary and anxious behaviors during free play and other episodes, and were rated as having more internalizing problems than those who were good emotion regulators and the average group.
Abstract: It was proposed that the interaction between the constructs of emotion regulation and social interaction would predict social adaptation in preschoolers. Ninety-six 4-year-olds were observed in quartets of unfamiliar same-sex peers. Based on parent temperament ratings and observed free play behaviors, 68 children from the original sample were classified as: low social interaction, good emotion regulators; low social interaction, poor emotion regulators; high social interaction, good emotion regulators; high social interaction, poor emotion regulators; or average. The results indicated that the low social interaction children who were poor regulators displayed more wary and anxious behaviors during free play and other episodes, and were rated as having more internalizing problems than both the low social interaction children who were good regulators and the average group. The high social interaction children who were poor regulators were rated as having more externalizing problems than either the high social interaction children who were good regulators or the average group. Thus, it seems as if emotion dysregulation is associated with psychological maladaptation, but that this association is tempered by the degree to which children engage in social interaction.
400 citations
TL;DR: In this paper, the authors proposed a new premium principle, where risk loadings are imposed by a proportional decrease in the hazard rates, which is scale invariant and additive for layers.
Abstract: This paper proposes a new premium principle, where risk loadings are imposed by a proportional decrease in the hazard rates. This premium principle is scale invariant and additive for layers. It is shown that this principle will generate stop-loss contracts as optimal reinsurance arrangements in a competitive market when the reinsurer is less risk-averse than the direct insurer. Finally, increased limits factors are calculated based on this principle.
351 citations
TL;DR: This article found that people encountering deviants who violate a stereotype try to maintain the stereotype by subtyping the deviants, and they use the deviant's additional attributes to justify sub-typing them.
Abstract: People encountering deviants who violate a stereotype try to maintain the stereotype by subtyping the deviants. They use the deviants' additional attributes to justify subtyping them. Participants read about counterstereotypic targets. Participants who were given no additional information about targets, and so had no grounds for subtyping them, did generalize from them and changed their stereotypes. However, participants who were told that targets had an additional, neutral attribute appeared to use it as grounds for subtyping them; their stereotypes remained unchanged. Participants came to view the neutral attributes as atypical of the stereotype and as associated with deviance, that is, as good reasons for subtyping the deviant. Neutral attributes blocked generalization from truly counterstereotypic targets but not from overly stereotypic ones, suggesting that their effect was due to participants' attempts to explain away individuals who strongly challenge their stereotypes.
314 citations
TL;DR: It is pointed out that, in the case of helium, calculations of virial coefficients and transport properties based on an accurate state-of-theart ab initio potential are now sufficiently accurate that the traditional practices can be usefully reversed.
Abstract: For helium, the accuracy of calculated transport properties and virial coefficients based on an accurate ab initio potential now exceeds that of the best measurements. The ab initio results should be used to calibrate measuring apparatus.
TL;DR: In this paper, the authors argue that human consciousness has no survival value and that in order to understand the origins and function of consciousness, we should examine the behavioural and neural precursors to consciousness in nonhumans.
Abstract: The commentary argues (1) that we cannot be sure that human consciousness has survival value and (2) that in order to understand the origins and, perhaps, the function of consciousness, we should examine the behavioural and neural precursors to consciousness in nonhumans. An example is given of research on the role of context in decisions regarding fleeing from probable predators in the Mongolian gerbil.
TL;DR: The authors examined childhood social withdrawal and aggression as predictive of adolescent maladaption, comparing and contrasting social and emotional outcomes associated with aggression and social withdrawal, and also focused on childhood social competence as a predictor of adolescent adaptation.
Abstract: We examined childhood social withdrawal and aggression as predictive of adolescent maladaption, comparing and contrasting social and emotional outcomes associated with aggression and social withdrawal. We also focused on childhood social competence as a predictor of adolescent adaptation. The sample comprised 60 children for whom a complete data set was available at both ages 7 and 14 years. The predictors were aggregated measures of social withdrawal, aggression, and social competence derived from three sources—behavioral observations, peer assessments, and teacher ratings. The outcomes focused primarily on markers of internalizing and externalizing problems. The results indicated that childhood social withdrawal uniquely and significantly contributed to the prediction of adolescent loneliness, felt insecurity, and negative self-regard. Aggression predicted adolescent delinquent activity; social competence predicted felt security in the peer group and substance use in adolescence.
TL;DR: A model and a procedure for determining traffic assignment and optimizing signal timings in saturated road networks and taking account of drivers' route choice behavior in response to signal split changes is presented.
Abstract: This article presents a model and a procedure for determining traffic assignment and optimizing signal timings in saturated road networks. Both queuing and congestion are explicitly taken into account in predicting equilibrium flows and setting signal split parameters for a fixed pattern of origin-to-destination trip demand. The model is formulated as a bilevel programming problem. The lower-level problem represents a network equilibrium model involving queuing explicitly on saturated links, which predicts how drivers will react to any given signal control pattern. The upper-level problem is to determine signal splits to optimize a system objective function, taking account of drivers' route choice behavior in response to signal split changes. Sensitivity analysis is implemented for the queuing network equilibrium problem to obtain the derivatives of equilibrium link flows and equilibrium queuing delays with respect to signal splits. The derivative information is then used to develop a gradient descent algorithm to solve the proposed bilevel traffic signal control problem. A numerical example is included to demonstrate the potential application of the assignment model and signal optimization procedure.
TL;DR: Differences among children in frontal asymmetry were a function of power in the left frontal region, and these EEG/behavior findings suggest that resting frontal asymmetric may be a marker for certain temperamental dispositions.
Abstract: The pattern of frontal activation as measured by the ongoing electroencephalogram (EEG) may be a marker for individual differences in infant and adult disposition to respond with either positive or negative affect. We studied 48 4-year-old children who were first observed in same-sex quartets during free-play sessions, while making speeches, and during a ticket-sorting task. Social and interactive behaviors were coded from these sessions. Each child was subsequently seen 2 weeks later when EEG was recorded while the child attended to a visual stimulus. The pattern of EEG activation computed from the session was significantly related to the child's behavior in the quartet session. Children who displayed social competence (high degree of social initiations and positive affect) exhibited greater relative left frontal activation, while children who displayed social withdrawal (isolated, onlooking, and unoccupied behavior) during the play session exhibited greater relative right frontal activation. Differences among children in frontal asymmetry were a function of power in the left frontal region. These EEG/behavior findings suggest that resting frontal asymmetry may be a marker for certain temperamental dispositions.
TL;DR: Whether the same estimates of individual muscle and L4/L5 lumbar joint compressive forces result from an optimization compared to an electromyography (EMG) assisted approach for solving the inderminate moment equilibrium equations in the same anatomical model is determined.
TL;DR: In this article, the authors examine the role of cross-border shopping in the context of tourism between Canada and the United States and the implications that this has for the role shopping as a generator of tourism.
TL;DR: In foods that are frozen only for preservation, AFPs may inhibit recrystallization during freezing, storage, transport and thawing, thus preserving food texture by reducing cellular damage and also minimizing the loss of nutrients by reducing drip.
TL;DR: In this paper, the dimensionless flow resistance in the corners of capillary tubes was applied to the imbibition of a slug of a wetting fluid introduced in a 300-and a 500-μm square capillary tube.
TL;DR: In this paper, a new alternative septic-system design is presented utilizing reactive porous media barriers for passive in situ attenuation of NO3−, which consists of solid organic carbon (sawdust) which promotes NO3- attenuation by heterotrophic denitrification.
Abstract: A new alternative septic-system design is presented utilizing reactive porous media barriers for passive in situ attenuation of NO3−. The reactive material consists of solid organic carbon (sawdust) which promotes NO3- attenuation by heterotrophic denitrification. Four field trials are discussed demonstrating two barrier configurations: as a horizontal layer positioned in the vadose zone below a conventional septic-system infiltration bed and as a vertical wall intercepting a horizontally flowing downgradient plume. During one year of operation both barrier configurations have been successful in substantial attenuation (60 to 100%) of input NO3- levels of up to 125 mg/1 as N. The horizontal layer configuration can be readily installed during the construction of new infiltration beds, whereas the vertical wall configuration may be more appropriate for retrofitting existing septic systems where NO3- contamination has already occurred. The layer configuration allows the flexibility of constructing the barrier in the vadose zone by using coarse silt or fine sand matrix material that has the ability to remain tension-saturated, and thus anaerobic, even when positioned above the water table.
Advantages of the barrier system are that it is simple to construct, no surface structures or additional plumbing are necessary, and treatment is passive requiring no energy consumption and little or no maintenance. Mass balance calculations and preliminary results suggest that conveniently sized barriers have the potential to last for decades without replenishment of the reactive material.
TL;DR: In this article, a new class of black hole solutions for the dilaton with regular horizons and singularity only at the origin is presented. But their asymptotic behavior is neither asymptonically flat nor (anti-)de Sitter.
TL;DR: Data from three previous studies that included VA measurements taken with logMAR charts from subjects with normal, healthy eyes were collated and additional data from 42 subjects were added, showing VA levels far superior to the data from the standard references of Pitts (1982) and Weale.
Abstract: There are many useful longitudinal and cross-sectional epidemiological studies of how visual acuity (VA) deteriorates with age. However, few studies have evaluated age-related VA changes in normal, healthy eyes. Data from three previous studies that included VA measurements taken with logMAR charts from subjects with normal, healthy eyes were collated and additional data from 42 subjects were added. This provided VA results from 223 subjects (age range 18 to 80 years). Mean logMAR VA improved from -0.13 (Snellen equivalent 6/4.5) in 18- to 24-year-olds to -0.16 (Snellen 6/4(-1)) in 25- to 29-year-olds and then gradually became worse with age to a mean value of -0.02 (Snellen 6/6+1) for subjects over 75 years of age. The inadequacy of 6/6 as a norm value of VA is illustrated. The data show VA levels far superior to the data from the standard references of Pitts (1982) and Weale. (1975, 82) We suggest that this is because we used logMAR charts (providing nontruncated data), the subject's optimal refractive correction (rather than habitual) and strict exclusion criteria ensuring that only subjects with normal, healthy eyes were recruited for the studies.
TL;DR: In this paper, a quadratic functional equation was used to characterize inner product spaces and several other functional equations were also used for inner product space characterization, including funtional equations.
Abstract: Quadratic functional equation was used to characterize inner product spaces. Several other functional equations were also used to characterize inner product spaces. In this paper we solve five funtional equations (1), (2), (3), (4), and (5) connected to quadratic functional equation and inner product spaces.
TL;DR: A new information theoretic discretization method optimized for supervised learning is proposed and described that seeks to maximize the mutual dependence as measured by the interdependence redundancy between the discrete intervals and the class labels, and can automatically determine the most preferred number of intervals for an inductive learning application.
Abstract: Inductive learning systems can be effectively used to acquire classification knowledge from examples. Many existing symbolic learning algorithms can be applied in domains with continuous attributes when integrated with a discretization algorithm to transform the continuous attributes into ordered discrete ones. In this paper, a new information theoretic discretization method optimized for supervised learning is proposed and described. This approach seeks to maximize the mutual dependence as measured by the interdependence redundancy between the discrete intervals and the class labels, and can automatically determine the most preferred number of intervals for an inductive learning application. The method has been tested in a number of inductive learning examples to show that the class-dependent discretizer can significantly improve the classification performance of many existing learning algorithms in domains containing numeric attributes. >
TL;DR: In this article, a solid phase microextraction (SPME) method coupled with GC-MS, GC-NPD and GC-FID has been developed for the analysis of 22 nitrogen-containing herbicides in water.
TL;DR: It is proved that SCS does not have a polynomial time linear approximation algorithm, unless {\bf P} = {\bf NP", and a new method for analyzing the average-case performance of algorithms for sequences, based on Kolmogorov complexity is introduced.
Abstract: The problems of finding shortest common supersequences (SCS) and longest common subsequences (LCS) are two well-known {\bf NP}-hard problems that have applications in many areas including computational molecular biology, data compression, robot motion planning and scheduling, text editing, etc. A lot of fruitless effort has been spent in searching for good approximation algorithms for these problems. In this paper, we show that these problems are inherently hard to approximate in the worst case. In particular, we prove that (i) SCS does not have a polynomial time linear approximation algorithm, unless {\bf P} = {\bf NP}; (ii) There exists a constant $\delta > 0$ such that, if SCS has a polynomial time approximation algorithm with ratio $\log^{\delta} n$, where $n$ is the number of input sequences, then {\bf NP} is contained in {\bf DTIME}$(2^{\polylog n})$; (iii) There exists a constant $\delta > 0$ such that, if LCS has a polynomial time approximation algorithm with performance ratio $n^{\delta}$, then {\bf P} = {\bf NP}. The proofs utilize the recent results of Arora et al. [Proc. 23rd IEEE Symposium on Foundations of Computer Science, 1992, pp. 14-23] on the complexity of approximation problems.
In the second part of the paper, we introduce a new method for analyzing the average-case performance of algorithms for sequences, based on Kolmogorov complexity. Despite the above nonapproximability results, we show that near optimal solutions for both SCS and LCS can be found on the average. More precisely, consider a fixed alphabet $\Sigma$ and suppose that the input sequences are generated randomly according to the uniform probability distribution and are of the same length $n$. Moreover, assume that the number of input sequences is polynomial in $n$. Then, there are simple greedy algorithms which approximate SCS and LCS with expected additive errors $O(n^{0.707})$ and $O(n^{\frac{1}{2}+\epsilon})$ for any $\epsilon > 0$, respectively.
Incidentally, our analyses also provide tight upper and lower bounds on the expected LCS and SCS lengths for a set of random sequences, solving a generalization of another well-known open question on the expected LCS length for two random sequences [K. Alexander, The rate of convergence of the mean length of the longest common subsequence, 1992, manuscript],[V. Chvatal and D. Sankoff, J. Appl. Probab., 12 (1975), pp. 306-315], [D. Sankoff and J. Kruskall, eds., Time Warps, String Edits, and Macromolecules: The Theory and Practice of Sequence Comparison, Addison-Wesley, Reading, MA, 1983].
TL;DR: Research demonstrating age differences in learning to use a computer is reviewed and the effects of attitudes, anxiety, and cognitive abilities on computer use, as well as research on training novices to use computers are explored.
Abstract: Given the aging of the workforce and the general population, it is important to determine how best to train older adults to use computers. Generally, research has shown that training takes significantly more time for older adults compared with younger learners, and that older adults commit more errors in post-training evaluations. This paper reviews research demonstrating age differences in learning to use a computer. We also explore the effects of attitudes, anxiety, and cognitive abilities on computer use, as well as research on training novices to use computers. Finally, we discuss designing the human-computer interface for the advantage of older users.
01 Jun 1995
TL;DR: In this paper, the authors give a proof of Euler's discovery and then give analogous evaluations with proof for corresponding alternating sums for the harmonic sum of the form (1+{1 \over 2+\dots+{ 1 \over n})^2 \, (n+1)^{-m).
Abstract: In response to a letter from Goldbach, Euler considered sums of the form $$\sh(s,t):=\sum\limits_{n=1}^\infty (1+{1 \over 2^s}+\dots+{1 \over (n-1)^s}) \, n^{-t},$$ where $s$ and $t$ are positive integers. As Euler discovered by a process of extrapolation (from $s+t \le 13$), $\sh(s,t)$ can be evaluated in terms of Riemann $\zeta$-functions when $s+t$ is odd. We provide rigorous proof of Euler's discovery and then give analogous evaluations with proof for corresponding alternating sums. Relatedly we give a formula for the harmonic sum $$\sum\limits_{n=1}^\infty (1+{1 \over 2}+\dots+{1 \over n})^2 \, (n+1)^{-m}.$$ This evaluation involves $\zeta$-functions and $\sh(2,m).$
TL;DR: This article found that Neotropical migrants consistently increased in number and abundance as forest size increased, and that the number of houses surrounding a forest severely under-mined its suitability for Neotropic migrants.
Abstract: Many bird species are in local or regional decline because of habitat loss or degradation. We at- tempted to disentangle the effects of residential development from the effects of forest size on forest-bird com- munities, with particular emphasis on Neotropical migrant species. Two variables were examined for their in- fluence on avian diversity and abundance:forest size and the number of houses outside a forest within 100 m of the edge. We found that Neotropical migrants consistently increased in number and abundance as forest size increased. Of greater interest, we found that the number of houses surrounding a forest severely under- mined its suitability for Neotropical migrants. Neotropical migrants consistently decreased in diversity and abundance as the level of adjacent development increased, regardless of forest size. The effects of development were striking: 4-ha woodlots without any nearby houses had on average a richer, more abundant Neotropical community than did 25-ha urban woodiots. No predictable pattern of change concerning development or for- est size was observed for short-distance migrants or permanent residents. Current planning regulations gener- ally permit housing right up to forest edges. This practice may prevent protection of ecological features within the forest. Threshold distances for housing developments around forests need to be determined to prevent or minimize adverse effects on features and functions within the forests. Efectos del desarrollo urbano sobre los bosques habitados por aves neotropicales migratorias Resumen: Numerosas especies de aves han disminuido a nivel local o regional debido a la p4rdida del hdbi- tat y a la degradaci6n del ambiente. Intentamos separar los efectos del desarroUo residencial de los efectos del tama~o del bosque sobre las comunidades de aves, poniendo particular dnfasis en las especies neotropicales migratorias. Se examinaron dos variables para determinar su influencia en la diversidad y abundancia de las aves: el tama~o del bosque y el numero de casas fuera del bosque a menos de 100 m del borde. Encontra- mosque las aves neotropicales migratorias incrementaron consistentemente en nftmero yen abundancia, en ia medida en que el tamar~o del bosque se increment6. De mayor interes aftn, encontramos que el namero de casas que rodean al bosque disminuy6 severamente su grado de adecuaci6n para ser usado por los mi- grantes neotropicales. Las aves neotropicales migratorias decrecieron consistentemente en diversidad yen abundancia, a medida que el nivel de desaroUo de las dreas adyacentes se increment6, independientemente del tama~o del bosque. Los impactos del desarroUo fueron sorprendentes: 4-ha de un rodal sin ninguna casa en las cercanias tuvo en promedio una comunidad de aves neotropicales mds rica y abundante queen un rodal de 25-ha un drea urbana. No se observ6n ingan patr6n de cambio predecible en relaci6n al desarrollo o ai tama~o del bosque para aves migratorias de corta distancia o residentes permanentes. Las regulacions actuales de planificaci6n, permtten en general la urbanizaci6n hasta el borde mismo del bosque. Esta prtic- tica puede ser insuficiente para proteger las caracteristicas ecol6gicas dentro del bosque. Se necesita determi- nar las distancias umbrales que debe guardar el desarroUo urbano alrededor de los bosques, para prevenir o minimizar los impactos adversos sobre las caracteristicas y las funciones dentro dei bosque.
TL;DR: It is concluded that at least part of the acceleration of whole body VO2 kinetics with endurance training is a rapid phenomenon, occurring before changes in VO2 peak and/or muscle oxidative potential.
Abstract: The rates of increase in O2 uptake (VO2) after step changes in work rate from 25 W to 60% of pretraining peak VO2 (VO2 peak) were measured at various times during an endurance training program (2 h/day at 60% pretraining VO2 peak). Seven untrained males [23 +/- 1 (SE) yr] performed a series of repeated step changes in work rate before training (PRE) and after 4 days (4D), 9 days (9D), and 30 days (30D) of training. VO2 kinetic responses were determined from breath-by-breath data averaged across four repetitions and analyzed using a two-component exponential model. Mean response time (time taken to reach 63% of steady-state VO2) was faster (P < 0.01) than PRE (38.1 +/- 2.6 s) at both 4D (34.9 +/- 2.4 s) and 9D (32.5 +/- 1.8 s) and was faster (P < 0.01) at 30D than at all other times (28.3 +/- 1.0 s). Blood lactate concentrations (after 6 min of cycling) were also lower at 4D and 9D than PRE (P < 0.01) and were lower at 30D than at all other times (P < 0.01). VO2 peak was unchanged from PRE (3.52 +/- 0.20 l/min) at 8D (3.55 +/- 0.20 l/min) but was increased (P < 0.01) at 30D (3.89 +/- 0.18 l/min). Muscle oxidative capacity (maximal citrate synthase activity) was not significantly increased until 30D (P < 0.01). It is concluded that at least part of the acceleration of whole body VO2 kinetics with endurance training is a rapid phenomenon, occurring before changes in VO2 peak and/or muscle oxidative potential.