Showing papers by "University of Victoria published in 2002"

Reproduction numbers and sub-threshold endemic equilibria for compartmental models of disease transmission

Abstract: A precise definition of the basic reproduction number, Ro, is presented for a general compartmental disease transmission model based on a system of ordinary dierential equations. It is shown that, if Ro 1, then it is unstable. Thus,Ro is a threshold parameter for the model. An analysis of the local centre manifold yields a simple criterion for the existence and stability of super- and sub-threshold endemic equilibria for Ro near one. This criterion, together with the definition of Ro, is illustrated by treatment, multigroup, staged progression, multistrain and vectorhost models and can be applied to more complex models. The results are significant for disease control.

Nonlocal Continuum Field Theories

Abstract: 1. Motion and Deformation.- 2. Stress.- 3. Constitutive Axioms.- 4. Nonlocal Electromagnetic Theory.- 5. Constitutive Equations of Memory-Dependent Nonlocal Electromagnetic Elastic Solids.- 6. Nonlocal Linear Elasticity.- 7. Nonlocal Fluid Dynamics.- 8. Nonlocal Linear Electromagnetic Theory.- 9. Memory-Dependent Nonlocal Thermoelastic Solids.- 10. Memory-Dependent Nonlocal Fluids.- 11. Memory-Dependent Nonlocal Electromagnetic Elastic Solids.- 12. Memory-Dependent Nonlocal Electromagnetic Thermofluids.- 13. Nonlocal Microcontinua.- 14. Memory-Dependent Nonlocal Micropolar Electromagnetic Elastic Solids.- 15. Nonlocal Continuum Theory of Liquid Crystals.

Statistical Analysis in Climate Research

Abstract: 1. Introduction Part I. Fundamentals: 2. Probability theory 3. Distributions of climate variables 4. Concepts in statistical inference 5. Estimation Part II. Confirmation and Analysis: 6. The statistical test of a hypothesis 7. Analysis of atmospheric circulation problems Part III. Fitting Statistical Models: 8. Regression 9. Analysis of variance Part IV. Time Series: 10. Time series and stochastic processes 11. Parameters of univariate and bivariate time series 12. Estimating covariance functions and spectra Part V. Eigen Techniques: 13. Empirical orthogonal functions 14. Canonical correlation analysis 15. POP analysis 16. Complex eigentechniques Part VI. Other Topics: 17. Specific statistical concepts in climate research 18. Forecast quality evaluation Part VII. Appendices.

Toward a Theory of Entrepreneurial Cognition: Rethinking the People Side of Entrepreneurship Research:

Abstract: The failure of past “entrepreneurial personality”—based research to clearly distinguish the unique contributions to the entrepreneurial process of entrepreneurs as people, has created a vacuum with...

Confocal microwave imaging for breast cancer detection: localization of tumors in three dimensions

Abstract: The physical basis for breast tumor detection with microwave imaging is the contrast in dielectric properties of normal and malignant breast tissues. Confocal microwave imaging involves illuminating the breast with an ultra-wideband pulse from a number of antenna locations, then synthetically focusing reflections from the breast. The detection of malignant tumors is achieved by the coherent addition of returns from these strongly scattering objects. In this paper, we demonstrate the feasibility of detecting and localizing small (<1 cm) tumors in three dimensions with numerical models of two system configurations involving synthetic cylindrical and planar antenna arrays. Image formation algorithms are developed to enhance tumor responses and reduce early- and late-time clutter. The early-time clutter consists of the incident pulse and reflections from the skin, while the late-time clutter is primarily due to the heterogeneity of breast tissue. Successful detection of 6-mm-diameter spherical tumors is achieved with both planar and cylindrical systems, and similar performance measures are obtained. The influences of the synthetic array size and position relative to the tumor are also explored.

The role of the thermohaline circulation in abrupt climate change

Abstract: The possibility of a reduced Atlantic thermohaline circulation in response to increases in greenhouse-gas concentrations has been demonstrated in a number of simulations with general circulation models of the coupled ocean-atmosphere system. But it remains difficult to assess the likelihood of future changes in the thermohaline circulation, mainly owing to poorly constrained model parameterizations and uncertainties in the response of the climate system to greenhouse warming. Analyses of past abrupt climate changes help to solve these problems. Data and models both suggest that abrupt climate change during the last glaciation originated through changes in the Atlantic thermohaline circulation in response to small changes in the hydrological cycle. Atmospheric and oceanic responses to these changes were then transmitted globally through a number of feedbacks. The palaeoclimate data and the model results also indicate that the stability of the thermohaline circulation depends on the mean climate state.

Institutional effects of interorganizational collaboration: The emergence of proto-institutions

Abstract: We argue that collaboration can act as a source of change in institutional fields through the generation of “proto-institutions”: new practices, rules, and technologies that transcend a particular collaborative relationship and may become new institutions if they diffuse sufficiently. A four-year study of the collaborative activities of a small nongovernmental organization in Palestine suggests that collaborations that are both highly embedded and have highly involved partners are the most likely to generate proto-institutions.

The BABAR detector

Abstract: BABAR, the detector for the SLAC PEP-II asymmetric e+e- B Factory operating at the upsilon 4S resonance, was designed to allow comprehensive studies of CP-violation in B-meson decays. Charged particle tracks are measured in a multi-layer silicon vertex tracker surrounded by a cylindrical wire drift chamber. Electromagentic showers from electrons and photons are detected in an array of CsI crystals located just inside the solenoidal coil of a superconducting magnet. Muons and neutral hadrons are identified by arrays of resistive plate chambers inserted into gaps in the steel flux return of the magnet. Charged hadrons are identified by dE/dx measurements in the tracking detectors and in a ring-imaging Cherenkov detector surrounding the drift chamber. The trigger, data acquisition and data-monitoring systems, VME- and network-based, are controlled by custom-designed online software. Details of the layout and performance of the detector components and their associated electronics and software are presented.

Carbohydrates in fish nutrition: effects on growth, glucose metabolism and hepatic enzymes

Abstract: The utilisation of dietary carbohydrates and their effects on fish metabolism are reviewed. Details on how dietary carbohydrates affect growth, feed utilisation and deposition of nutrients are discussed. Variations in plasma glucose concentrations emphasizing results from glucose tolerance tests, and the impact of adaptation diets are interpreted in the context of secondary carbohydrate metabolism. Our focus then shifts to selected aspects of hormonal regulation of carbohydrate metabolism and dietary carbohydrates and their variable effects on glycogen and glucose turnover. We analyse the interaction of carbohydrates with other nutrients, especially protein and protein sparing, and de novo synthesis of lipids, and finish by discussing the correlation of dietary carbohydrates with fish health.

Variability in Reaction Time Performance of Younger and Older Adults

Abstract: Age differences in three basic types of variability were examined: variability between persons (diversity), variability within persons across tasks (dispersion), and variability within persons across time (inconsistency). Measures of variability were based on latency performance from four measures of reaction time (RT) performed by a total of 99 younger adults (ages 17--36 years) and 763 older adults (ages 54--94 years). Results indicated that all three types of variability were greater in older compared with younger participants even when group differences in speed were statistically controlled. Quantile-quantile plots showed age and task differences in the shape of the inconsistency distributions. Measures of within-person variability (dispersion and inconsistency) were positively correlated. Individual differences in RT inconsistency correlated negatively with level of performance on measures of perceptual speed, working memory, episodic memory, and crystallized abilities. Partial set correlation analyses indicated that inconsistency predicted cognitive performance independent of level of performance. The results indicate that variability of performance is an important indicator of cognitive functioning and aging.

Extending the theory of planned behavior: Predicting the use of public transportation

Abstract: An expanded version of the theory of planned behavior (TPB) was used to predict and explain public transportation use. A pre-post design was used to examine changes in university students’ bus ridership after the implementation of a universal bus pass (U-pass) program. Bus ridership significantly increased after the U-pass was implemented, and associated changes in attitudes and beliefs about transportation modes were found. In both phases, students’ public transportation use was well predicted by the original TPB. However, 2 additional constructs—a descriptive norm, and the interaction between intention and perceived behavioral control—significantly improved prediction in both phases of the study. These constructs might be useful additions to the original TPB, at least in this behavioral domain.

Enhancing breast tumor detection with near-field imaging

Abstract: This article outlines the main features of active, passive, and hybrid systems under investigation for breast cancer detection. Our main focus is on active microwave systems, in particular microwave tomography and confocal microwave imaging.

An inverted continental Moho and serpentinization of the forearc mantle

Abstract: Volatiles that are transported by subducting lithospheric plates to depths greater than 100 km are thought to induce partial melting in the overlying mantle wedge, resulting in arc magmatism and the addition of significant quantities of material to the overlying lithosphere. Asthenospheric flow and upwelling within the wedge produce increased lithospheric temperatures in this back-arc region, but the forearc mantle (in the corner of the wedge) is thought to be significantly cooler. Here we explore the structure of the mantle wedge in the southern Cascadia subduction zone using scattered teleseismic waves recorded on a dense portable array of broadband seismometers. We find very low shear-wave velocities in the cold forearc mantle indicated by the exceptional occurrence of an 'inverted' continental Moho, which reverts to normal polarity seaward of the Cascade arc. This observation provides compelling evidence for a highly hydrated and serpentinized forearc region, consistent with thermal and petrological models of the forearc mantle wedge. This serpentinized material is thought to have low strength and may therefore control the down-dip rupture limit of great thrust earthquakes, as well as the nature of large-scale flow in the mantle wedge.

Inter-organizational collaboration and the dynamics of institutional fields

Abstract: While many aspects of the collaborative process have been discussed in the management literature, the connection between collaboration and the dynamics of institutional fields has remained largely unconsidered. Yet, collaboration is an important arena for inter–organizational interaction and, therefore, a potentially important context for the process of structuration upon which institutional fields depend. In this paper, we argue that institutionalization and collaboration are interdependent; institutional fields provide the rules and resources upon which collaboration is constructed, while collaboration provides a context for the ongoing processes of structuration that sustain the institutional fields of the participants.

Earth system models of intermediate complexity: closing the gap in the spectrum of climate system models

Abstract: We propose a new perspective on the hierarchy of climate models which goes beyond the ''classical'' climate modeling pyramid that is restricted mainly to atmospheric processes, Most notably, we introduce a new indicator, called ''integration'', which characterizes the number of interacting components of the climate system being explicitly described in a model. The location of several model types, from conceptual to comprehensive, is presented in a new spectrum of climate system models. In particular. the location of the Earth system Models of Intermediate Complexity (EMICs) in this spectrum is discussed in some detail and examples are given, which indicate that there is currently a broad range of EMICs in use. In some EMICs, the number of processes and/or the detail of description is reduced for the sake of simulating the feedbacks between as many components of the climate system as feasible. Others, with a lesser degree of interaction, or ''integration'', are used for long-term ensemble simulations to study specific aspects of climate variability. EMICs appear to be closer to comprehensive coupled models of atmospheric and oceanic circulation (CGCMs) than to ''conceptual'' or ''box'' models. We advocate that EMICs be considered as complementary to CGCMs and conceptual models, because we believe that there is an advantage of having a spectrum of climate system models which are designed to tackle specific aspects of climate and which together provide the proper tool for climate system modeling.

Listener Responses as a Collaborative Process: The Role of Gaze

Abstract: The authors examined precisely when and how listeners insert their responses into a speaker's narrative. A collaborative theory would predict a relationship between the speaker's acts and the listener's responses, and the authors proposed that speaker gaze coordinated this collaboration. The listener typically looks more at the speaker than the reverse, but at key points while speaking the speaker seeks a response by looking at the listener, creating a brief period of mutual gaze called here a gaze window. The listener was very likely to respond with “mhm,” a nod, or other reaction during this period, after which the speaker quickly looked away and continued speaking. This model was tested with 9 dyads in which 1 person was telling a close-call story to the other. The results confirmed the model for each dyad, demonstrating both collaboration in dialogue at the microlevel and a high degree of integration and coordination of audible and visible acts, in this case, speech and gaze.

The Role of Internal Tides in Mixing the Deep Ocean

Abstract: Internal wave theory is used to examine the generation, radiation, and energy dissipation of internal tides in the deep ocean. Estimates of vertical energy flux based on a previously developed model are adjusted to account for the influence of finite depth, varying stratification, and two-dimensional topography. Specific estimates of energy flux are made for midocean ridge topography. Weakly nonlinear theory is applied to the wave generation at idealized topography to examine finite amplitude corrections to the linear theory. Most internal tide energy is generated at low modes associated with spatial scales from roughly 20 to 100 km. The Richardson number of the radiated internal tide typically exceeds unity for these motions, and so direct shear instability of the generated waves is not the dominant energy transfer mechanism. It also seems that wave–wave interactions are ineffective at transferring energy from the large wavelengths that dominate the energy flux. Instead, it appears that most of ...

Are Entrepreneurial Cognitions Universal? Assessing Entrepreneurial Cognitions across Cultures:

Abstract: In this study we examine three research questions concerned with entrepreneurial cognition and culture: (1) Do entrepreneurs have cognitions distinct from those of other business people? (2) To wha...

Burden and Well-Being Among Caregivers: Examining the Distinction

Abstract: Purpose: This study assessed overall quality of life of caregivers, using a path model in which burden was conceptualized as distinct from well-being. Design and Methods: Data were drawn from a representative sample of caregivers to dementia and nondementia care receivers in British Columbia, Canada ( N � 243). The model used was based on a previously proposed stress/appraisal path model and used multiple regression path estimates. Primary stressors were care receiver cognitive status, physical function, and behavioral problems; the primary appraisal variable was hours of caregiving during the previous week. Mediators were perceived social support, frequency of getting a break, and hours of formal service use; secondary appraisal was subjective burden. The outcome measure was generalized well-being. Results: Well-being was directly affected by four variables: perceived social support, burden, self-esteem, and hours of informal care. Burden was affected directly by behavioral problems, frequency of getting a break, self-esteem, and informal hours of care and was not affected by perceived social support. Discussion: The finding that perceived social support is strongly related to well-being but unrelated to burden reinforces the conceptual distinctiveness of the latter two concepts. This suggests that quality of life of caregivers could be improved even with burden in their lives and that the overwhelming focus in caregiving research on burden should be supplemented with an emphasis on quality of life.

Structural Basis of Gating by the Outer Membrane Transporter FecA

Abstract: Siderophore-mediated acquisition systems facilitate iron uptake. We present the crystallographic structure of the integral outer membrane receptor FecA from Escherichia coli with and without ferric citrate at 2.5 and 2.0 angstrom resolution. FecA is composed of three distinct domains: the barrel, plug, and NH2-terminal extension. Binding of ferric citrate triggers a conformational change of the extracellular loops that close the external pocket of FecA. Ligand-induced allosteric transitions are propagated through the outer membrane by the plug domain, signaling the occupancy of the receptor in the periplasm. These data establish the structural basis of gating for receptors dependent on the cytoplasmic membrane protein TonB. By compiling available data for this family of receptors, we propose a mechanism for the energy-dependent transport of siderophores.

A picture is worth a thousand lies: Using false photographs to create false childhood memories

Abstract: Because image-enhancing technology is readily available, people are frequently exposed to doctored images. However, in prior research on how adults can be led to report false childhood memories, subjects have typically been exposed to personalized and detailed narratives describing false events. Instead, we exposed 20 subjects to a false childhood event via a fake photograph and imagery instructions. Over three interviews, subjects thought about a photograph showing them on a hot air balloon ride and tried to recall the event by using guided-imagery exercises. Fifty percent of the subjects created complete or partial false memories. The results bear on ways in which false memories can be created and also have practical implications for those involved in clinical and legal settings.

Formation of Giant Planets by Fragmentation of Protoplanetary Disks

Abstract: The evolution of gravitationally unstable protoplanetary gaseous disks has been studied with the use of three-dimensional smoothed particle hydrodynamics simulations with unprecedented resolution. We have considered disks with initial masses and temperature profiles consistent with those inferred for the protosolar nebula and for other protoplanetary disks. We show that long-lasting, self-gravitating protoplanets arise after a few disk orbital periods if cooling is efficient enough to maintain the temperature close to 50 K. The resulting bodies have masses and orbital eccentricities similar to those of detected extrasolar planets.

Schema Theory and Knowledge-Based Processes in Second Language Reading Comprehension: A Need for Alternative Perspectives

Abstract: Despite major theoretical developments in second language (L2) reading comprehension over the last two decades, many attempts at explaining the role of knowledge in comprehension are still made almost exclusively in the context of schema theory. I first review and critically analyze the major assumptions underlying schema theory. Then, I consider an alternative perspective, a construction-integration model of text comprehension, and discuss how this perspective, when applied to L2 reading comprehension, offers a fundamentally different and more comprehensive account of the role of knowledge and knowledge-based processes that L2 researchers had previously tried to explain within schema-theoretic principles.

Adaptive synthesis and design of resonator filters with source/load-multiresonator coupling

Abstract: The paper presents a universal and comprehensive synthesis technique of coupled resonator filters with source/load-multiresonator coupling. The approach is based on repeated analyses of a circuit with the desired topology; no similarity transformation is needed. Restrictions imposed by the implementation on the coupling coefficients such as signs and orders of magnitudes are straightforwardly handled within this technique. The technique is then used to synthesize and design filters with full or almost full coupling matrices by selecting, among the infinite number of solutions, the matrix that corresponds to the actual implementation. In such cases, analytical techniques and those based on similarity transformations cannot be used since they provide no mechanism to constrain individual coupling coefficients in order to discriminate between two full coupling matrices, which are both solutions to the synthesis problem. Using the technique described in this paper, a filter designer can extract the coupling matrix of a filter of arbitrary order and topology while enforcing relevant constraints. There is no need to master all the different existing similarity-transformation-based techniques and the topologies to which they are applicable. For the first time, detailed investigations of parasitic coupling effects, for either compensation or utilization, are made possible. The method is applied to the synthesis of a variety of filters, some of which are then designed and built and their response measured.