title: Vibration Analysis of Human Knee Joint in Healthy and Osteoarthritic Knees

title: Vibration Analysis of Healthy and Osteoarthritic Knees

contributor:
MacGregor, John
Chemical Engineering

subject:
vibration
analysis
knee
osteoarthritis
knee joint

abstract: The goal of this thesis is to investigate the possibility of using vibration analysis to detect and assess a very common joint disease known as osteoarthritis (OA). For this purpose, patients with various levels of OA, healthy to severe OA, were recruited and MRI and vibration recordings were made on both knees. MRI images were analyzed by a radiologist and different symptoms related to osteoarthritis in the knee were scored for each observation. Vibration signals of the patients' knees were recorded using 5 accelerometers placed at different locations of the knee. This thesis divides into two major sections; the first section deals with design of an apparatus (a function specific brace and the electronic hardware) for acquiring and recording vibration data from a patient's knee. The second section deals with the analysis of the recorded data using a combination of signal processing techniques (Fourier and wavelet transforms) and multivariate statistical methods (principal component (PCA) and partial least square (PLS)). The brace designed and built for the purpose of this research has several unique properties not found in commercial knee braces. It provides a robust and secure base for attachment of the sensors to the knee and shows very good adaptation to the dynamics of the knee during motion. In the analysis section we show that combining signal processing and multivariate statistical techniques (such as PCA and PLS) provides strong tools for analysis of the data. The result of our analysis shows that there is a strong correlation between vibration analysis and some of the symptoms of osteoarthritis such as cartilage degeneration and formation of osteophytes. We conclude that vibration signals of the knee joint (crepitus) during flexion/extension cycle of the knee, when it is under stress, can be a good indicator of the general severity of OA in patients.

abstract: Thesis

abstract: Master of Science (MS)


title: Dynamic Behaviour of Solids in a Single Screw Extruder: Aspects of Heat Transfer

contributor:
Thompson, M. R.
Chemical Engineering

subject:
screw
extruder
heat
heat transfer
behaviour
solids

abstract: Effective heat transfer through a bed of particulate solid largely affects the production rate and the process stability in an extrusion process. Most classical models in single screw extrusion treat the solids bed as a continuum behaving as an elastic plug or fluid while neglecting the discrete nature of the particles and the presences of the fluid. The heat transfer within the solids bed in these models is calculated based on thermophysical properties of the bulk system without consideration for the presence of the interstitial fluid. From a practical point of view, experimental measurements of solids bed heat transfer within a rotating screw, particularly cross channel, as the bed moves down the length of the solids conveying zone are impossible to perform. A new device was designed to model the radial compressive stresses and shear stresses on a solids bed of plastics, similar to the environment within the screw channel of a single screw extruder. This device enables the user to visualize the nature of the solids bed under different experimental conditions through a transparent wall. Also, the device provides ways to explore the heat transfer in a solids bed under different conditions by embedded thermocouples on the top or through the front wall of the containing chamber. The results reported in this study have shown that the discrete nature of the solid bed has a strong affect on the heat transfer within the bed. The rate of heat transfer within the different beds of polymer did not appear dominated by the thermophysical properties of the materials. Rather, the evidence supports that conduction through the pseudo-static interstitial fluid (i.e. air) dominated the rate at which a polymer bed heats up; a finding similarly found for the sintering of powdered metals and ceramics in the literature. This finding would imply that differences in melting rates found in extruders are not related to the heat transfer in the solids bed; however, this statement only holds true so long as the granules making up the bed remain static (i.e. plug-like) and do not circulate within the screw channel. Quite interestingly, pellet circulation within the solid bed was observed in LLDPE over a range of test conditions. This pellet circulation resulted in enhanced heat transfer within the bed of LLDPE (a raise of 10°C) compared to PS and PP. PP exhibited pellet circulation but only over a small window of operation. Different ways to improve heat transfer within solid bed were subsequently tested in this project, such as starve feed, forced convection and spherical particle. From this work, improved understanding of heat transfer in the solids conveying zone of a single screw extruder was gained.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: Initiation and Termination of a Hybrid Atom Transfer Radical Polymerization System

title: Initiation and Termination of a Hybrid ATRP System

contributor:
Zhu, Shiping
Faucher, Santiago
Chemical Engineering

subject:
termination
hybrid
initiation
atom
polymerization
hybrid atom transfer
radical

abstract: Atom transfer radical polymerization (ATRP) is a controlled/living polymerization process used to synthesize polymers with controlled molecular weight and narrow polymer distributions. Control of these key parameters allows for the fabrication of well-defined macromolecular structures, a necessary tool for the synthesis of advanced materials. Since its discovery in 1995, ATRP has received considerable interest and widespread adoption from the academic community. Unfortunately, it faces several complex challenges which have hindered its full scale commercialization, mainly its high catalyst loadings to obtain fast reaction kinetics. One of the premises of this research project was to augment the slow reaction rates of ATRP while using extremely low catalyst concentrations. A hybrid ATRP system was employed which encompassed the fast reaction kinetics associated with conventional free radical processes, with the attractive control features of ATRP. When high free radical initiator concentrations in the range of 0.1 M to 0.2 M were used in concert with ATRP, fast reaction rates were realized, while maintaining a polymerization with living characteristics. Conversions of 81% (0.117M) and 91% (0.234M) were achieved within 2 hours as compared to typical ATRPs where achieving such conversions would take up to 24 hours. For those same free radical initiator loadings (0.117M and 0.234M) the reaction demonstrated living characteristics with molecular weight growing in a linear fashion with respect to increasing monomer conversion. Despite the high free radical initiator concentration, the polymer distribution remained relatively narrow, not exceeding a polydispersity of 1.30. Chain extension experiments from a synthesized macroinitiator were successful which demonstrated the living characteristics of the hybrid ATRP process. The aforementioned polymerizations were conducted with various copper concentrations. Catalyst concentrations as low as 16 ppm (0.234mM) were found to be effective, i.e. one catalyst mediated the growth of over 100 polymer chains, and thus saving post polymerization purification. Moreover, the expensive ligand cost could be cut dramatically through a nearly 100 time reduction in the ligand concentration for these polymerizations. A hybrid ATRP system was used as a unique method to determine termination rate coefficients of MMA at 70°C as a function of both conversion and chain length. A three dimensional composite map was developed to elucidate the coupling effects of both conversion and chain length on the termination rate coefficient over a total range of data which can be used for modelling systems of this nature.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: The Influence of Paper Surface Chemistry on Bacteriophage Activity

contributor:
Pelton, R. H.
Filipe, C.
Chemical Engineering

subject: paper chemistry bacteriophage activity influence

abstract: Bacteriophages are promising biosensing systems in bioactive paper application due to their specific detection of bacteria. Different chemicals including wet strength resins were used to improve paper properties. This work investigated the influence of wet strength resins (PAE and PVAm) on bacteriophage activity, and proposed another method of using Poly NIP AM microgel to separate bacteriophage from paper surface. Compared with filter paper, the cationic polymer PAE and PVAm treated paper exhibited high phage binding efficiency but low phage activity due to the electrostatic interaction. PVAm had strong phage adsorption and almost completely deactivated the phage particle. Streptavidin was coupled to PolyNIPAM microgel in the presence of EDC, and T4 bacteriophage genetically modified with biotin was immobilized to microgel particle which resulted in a 10-fold improvement in attachment when compared with T4 wild-type phage. The microgel-phage coupling efficiency was very low, there were more than 10^6 micro gel particle for every active phage. And micro gel supported phages were deactivated after coating on the PAE/PVAm treated paper.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: Synthesis and Characterization of Environment-Responsive Membranes for Bioseparations

contributor:
Filipe, C.
Ghosh, R.
Chemical Engineering

subject: synthesis characterization environment responsive membrane bioseparation

abstract: Environment-responsive membranes were created by modification of a commerical polyvinylidene fluoride (PVDF) membrane support with a thermo-responsive hydrogel composed of poly N-vinyllactams cross-linked with bisacrylamide. The modified membranes were then characterized by their percentage mass gains as well as by their valve effect in response to changes in salt concentration. One set of membranes, with a large valve effect, was selected for highest retention of intermediately sized proteins was examined for ultrafiltration-based protein separation applications. A batch separation protocol featuring pulsed sample injection technique (PSIT) was then used to sieve single proteins and to fractionate a synthetic binary protein mixture and a synthetic ternary protein mixture with some success, demonstrating the potential of these environment-responsive membranes for use in multi-component separations. A second set of membranes, with a small valve effect, was selected for its ability to alter between hydrophobic and hydrophilic states under different environmental conditions and its potential in hydrophobic interaction membrane chromatography (HIMC) applications was successfully demonstrated by comparing against a benchmark membrane that is used successfully for HIMC applications in prior literature.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: Reference Management for Steady-State Transitions Under Constrained Model Predictive Control

contributor:
Swartz, Christopher
Chemical Engineering

subject:
reference
management
steady-state
predictive control
constrain
model
transition

abstract: There are increasing economic incentives within the chemical process industry towards demand driven operation with product diversification, requiring flexible operation in responsive plants. In continuous processes, this is realized through steady-state transitions but requires consideration of process dynamics arising from operation that is inherently transient in nature. The steady-state economic optimum is typically defined at the intersection of constraints, and requires multivariable control with optimal constraint handling capabilities. Thus, constrained model predictive control is well-suited to realize the profit potential at the economic optimum. In this thesis, feasible and optimal steady-state transitions are achieved using reference management with consideration of the closed-loop dynamics of constrained model predictive control. The supervisory control scheme is used to determine the optimal setpoint trajectory which is subsequently tracked by regulatory control, incorporating feedback for the rejection of high frequency disturbances and eliminating steady-state offset in the presence of model mismatch. The separation of economic and control objectives enables the lower level to be tuned for stability and the upper level to be tuned for performance. The mathematical formulation results in a multi-level optimization problem with an economic objective function at the upper level, and a series of control performance objective functions arising from constrained model predictive control at the lower levels. The solution strategy proposed converts the multi-level optimization problem into a single-level optimization problem using the Karush-Kuhn-Tucker conditions, and solves the resulting complementarity conditions using an interior point approach. Alternative objective formulations are investigated based on maximizing profit during transient operation. The first formulation is typically based on a quadratic objective function minimizing the transition time, indirectly improving economic operation by reducing the amount of off-specification product produced. The second formulation is based on the explicit consideration of economics. The profit calculated during transient operation is based on the difference between the revenue generated by the production of acceptable product within specified univariate product quality bands, and the operational costs of raw materials and utilities. The resulting linear objective function is further extended to incorporate control performance considerations to improve conditioning for gradient based optimization. The proposed methodology is applied to a single-input single-output linear system, demonstrating the potential benefits of simultaneous rather than sequential optimization in terms of computational efficiency and solution reliability. Alternative objective function and constraint formulations are investigated, and the effect on the optimal solution assessed. In particular, the possibility of indeterminacy is shown and handled using hierarchical optimization. The methodology is also demonstrated on additional examples including non-minimum phase systems and multi-input multi-output linear systems. Application to a multi-input multi-output nonlinear system corresponding to styrene polymerization using the proposed methodology is detailed. The set of differential and algebraic equations defining the process is discretized using orthogonal collocation on finite elements. The optimal operation during grade transitions based on explicit consideration of economics is determined, and additional improvements realized by manipulating the production rate. Finally, reference management with online re-optimization is investigated for a single-input single-output linear system based on a bias update, and the improvement in closed-loop performance assessed for output disturbances and model mismatch. The methodology is also demonstrated on a multi-input multi-output system based on a linear model when applied to the nonlinear process. The proposed methodology developed for steady-state transitions may also be applied to batch operation, startups and shutdowns. Future extensions include analysis of closed-loop stability due to the incorporation of feedback within the cascade control scheme, and the explicit consideration of uncertainty.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: Performance Analysis of LP-MPC Cascade Control Systems

contributor:
Swartz, C. L. E.
Chemical Engineering

subject: performance analysis LP-MPC cascade system

abstract: Model Predictive Control (MPC) algorithms are widely applied in the chemical process industry. The main advantage of these controllers over others is their ability to provide multivariable control of the process subject to specified constraints. The presence of degrees of freedom in the plant provide an opportunity for the introduction of an optimization level (Real-Time Optimization (RTO) level), to determine optimal set points and target values for controlled variables and manipulated variables respectively, and the constraints the plant should follow to provide maximum profit. Industrial MPC controllers typically include an upper level steady-state optimizer, which usually comprises a linear programming (LP) or quadratic programming (QP) problem. This local optimizer may serve either as an integrating level between the low frequency nonlinear steady-state RTO and regulatory level, or as an independent optimizer with an economic objective function. Many researchers have reported success of LP-MPC cascade control system implementations (Sorensen and Cutler, 1998; Verne et al., 1999). However, despite its apparent success, poor LP-MPC cascade system performance and possible instability have also been reported. In particular, Shah et al. (2002) show that in the presence of a steady-state LP optimizer, the set-points could have a large variation relative to the controlled variable variation; thus the LP could degrade the MPC performance by sending highly variable set-points to the controller. Kozub (2002) indicates that in a control system with an LP steady-state optimizer, an LP instability problem may arise under certain conditions. These observations motivated research which aims to investigate the effect of the various factors on the stability and performance of the two-level LP-MPC cascade control system. Such factors include plant/model mismatch, the frequency of LP implementation, the LP objective function, constraints and type of disturbances. Since the optimization can be executed at different frequencies, two most common scenarios are considered: (i) when the LP is implemented at steady-state only and (ii) when the LP is implemented at every MPC iteration. Initially, steady-state LP optimization only is considered and it is shown that the set-points may fail to converge to constant values in the absence of external disturbances under certain conditions. Then, the effects of optimization frequency and control structure on the closed-loop properties of the LP-MPC control system are investigated. Results of a number of case studies are shown, and root causes for observed behavior discussed. As a part of the regulatory level analysis, the calculation of the closed-loop equilibrium of a process controlled by constrained MPC is studied. This problem arises in process design and operations, and is often applied within an optimization framework. It is shown that the effect of the control system on the resulting steady-state must be explicitly accounted for, and that in the general case, the use of a steady-state process model only is not sufficient for this calculation to be correctly executed. Two solution strategies, sequential and simultaneous, are presented and evaluated. The effect of high frequency noise-like disturbances on the two-level control system behavior is analyzed. The analysis which verified by case studies, showed that the LP may have an effect of amplifying the system noise through the bias term which is used for the model update. Such amplification may result in high variation of the LP set points provided to the MPC, thereby degrading the overall performance of the two-level system.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: Wet Granulation in a Twin Screw Extruder

contributor:
Thompson, Michael
Chemical Engineering

subject:
granulation
twin screw
screw
extruder

abstract: This thesis covers a systematic examination of wet granulation in a twin screw extruder. Granulation of the excipient, (alpha)-lactose monohydrate, was done with the aid of PVP in an aqueous solution which acted as a binding agent. The influences on agglomeration by the following processing parameters were studied: screw elements design, screw rotational speed, binding solution concentration, and binder addition method. Qualitative efforts had also been made in modeling the process to gain valuable insight into how the elements affected agglomeration and granule rupture. A commercial software package PFC^2D, based on the Discrete Element Method (DEM), was used to simulate the dynamic behavior of the screw elements in the barrel. Within the optimal range of 7.5 -10wt% binder concentration, all the screw profiles were studied for their capacity to produce desirable granules suited to solid oral dosage form production. By increasing the rotational speed from 30 RPM to 80 RPM, the granules size of the conveying, discharging and chopping elements decreased whereas this operating parameter had little effect on granule size within kneading blocks. The nominal particle size produced by a screw element increased from 300(mu)m to 1mm when dispersive mixing was its dominant purpose (i.e. the kneading block), thereby meeting our criteria for a suitable granule in tab letting. Similar size development of the granules was not found with the other conveying or distributive mixing elements. In regards to particle shape, the kneading blocks produced elongated shape granules while other elements tested in this study produced smaller, more spherical agglomerates. Either shape was found effective in tabletting. Wet granulation was not feasible with more extreme concentrations of the aqueous binder (i.e. 5 wt% or 12 wt%) in this project, and the hand pre-blend method was the only approach found suitable for metering this additive into the system while maintaining steady feeding rates and output.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: A Study of the Influence of Heterogeneous Nucleation on the Foamability of a Polymer Clay Nanocomposite

subject:
heterogenous nucleation
nucleation
heterogenous
foamability
polymer
polymer clay
nanocomposite

abstract: Polymer composites are fast becoming a material in the manufacturing of automotive interior and exterior parts such as facias and dashboard components. Production of rigid structural foams are ideal because they reduce the overall weight as well as reduce the amount of material used to manufacture the part. Polymer-clay nanocomposites are a classification of materials containing a blend of polymer and a small weight percentage of nanoclay. These materials are currently of interest to automotive part manufacturers because they are known to deliver improved mechanical properties and increase foamability of a polymer. The current study investigates the changes in material properties and the foamability of a thermoplastic polyolefin (TPO)-clay nanocomposite as the degree of intercalation was varied. The TPO-clay nanocomposite was produced by melt blending TPO, nanoclay and maleic anhydride grafted polypropylene (MAHgPP) in a co-rotating twin screw extruder. The material was subjected to a multi-pass process to vary the degree of intercalation. Degree of intercalation was tracked by rheology, XRD and TEM micrographs. Part density, cell density and flexural modulus measurements were performed on foamed and non-foamed injection molded bars to observe changes in the foamability of the material. Material was also processed without clay and analyzed in the same manner. Through TEM and XRD analysis it was found that the degree of intercalation and delamination was varied with increasing number of passes. Rheological measurements showed that the TPO-clay nanocomposite underwent (beta)-scission and intercalation simultaneously. The changes in intercalation had a positive effect on the foamability of the TPO-clay nanocomposite. As well, the TPO-clay nanocomposite experienced an increase in flexural properties for both unfoamed and foamed parts compared to the TPO-PPgMAH blend; TPO-clay nanocomposite experienced a 44% and 23% increase in the flexural modulus for unfoamed and foamed parts respectively. Data also showed that there was a limit to the number of times the TPO-clay nanocomposite can be recycled before the foamability of the material begins to decrease, which was attributed to material degradation.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: Bad Weather Effect Removal in Images and Videos

contributor:
Kirubarajan, Thia
Electrical and Computer Engineering

subject:
Weather Removal
Image Processing

abstract:
Commonly experienced bad weather conditions like fog, snow and rain generate pixel intensity changes in images and videos taken in outdoor environment and impair the performance of algorithms in outdoor vision systems. Hence, the impact of bad weather conditions need to be processed to improve the performance of outdoor vision systems.

This thesis focuses on three most common weather conditions: fog, snow and rain. Their physical properties are first analyzed. Based on their properties, traditional methods are introduced individually to remove these weather conditions' effect on images or videos. For fog removal, the scattering model is used to describe the fog scene in images and estimate the clear scene radiance from single input images. In this thesis two scenario are discussed, one with videos and the other with single images. The removal of snow and rain in videos is easier than in single images. In videos, temporal and chromatic properties of snow and rain can be used to remove their impact. While in single images, traditional methods with edge preserving filters were discussed.

However, there are multiple limitations of traditional methods that are based on physical properties of bad weather conditions. Each of them can only deal with one specific weather condition at a time. In real application scenarios, it is difficult for vision systems to recognize different weather conditions and choose corresponding methods to remove them. Therefore, machine learning methods have advantages compared with traditional methods. In this thesis, Generative Adversarial Network (GAN) is used to remove the effect of these weather conditions. GAN performs the image to image translation instead of analyzing the physical properties of different weather conditions. It gets impressive results to deal with different weather conditions.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: Interaction of Supercritical Carbon Dioxide with Quaternary-Ammonium Organoclays in the Processing of Thermoplastic Elastomer Nanocomposites

subject:
carbon dioxide
ammonium
organoclays
thermoplastic
elastomer
nanocomposites
quaternary ammonium

abstract: Organically modified montmorillonite has been extensively used as nanofiller in studies of polymer layered silicate nanocomposites, promising materials for today's automotive industry because the nano-materials reduce the overall weight of vehicle. However, industrial applications have not followed suit primarily due to cost/performance issues. Supercritical carbon dioxide is promising as an aid in the production of a fully exfoliated polymer layered silicate nanocomposite but has not been fundamentally studied in this regard at present. As the first stage in studies of using supercritical carbon dioxide for aiding the production of thermoplastic elastomer nanocomposites, this thesis investigates the influence of this unique supercritical fluid on the microstructure and surface chemistry of five organically modified clays. Four alkyl-based quaternary ammonium surfactants with different number and length of chains attached and one aromatic quaternary ammonium surfactant were chosen to vary the degree of C02-philicity exhibited by the organoclay. In a high pressure batch vessel, the different organoclays were suspended in the supercritical solvent at temperatures of 50°C and 200°C and pressures of 7.6 MPa and 9.7 MPa for a fixed time and then removed after depressurization at 0.2 MPa/s or 4.8 MPa/s. The structures of these treated clays were characterized by XRD, TEM, DSC, TGA, FT -IR, and SEM, and their chemical properties were analyzed by various methods including atomic absorption spectroscopy, and contact angle measurement. The potential role of water to favor the interaction between scC02 and an organoclay was also investigated. Solute-solvent interactions plasticized the organic modifier while suspended in the supercritical fluid, which resulted in greater chain mobility and further cation exchange. The results indicate that surfactants exhibiting a paraffin-type conformation within the galleries of the clay were most likely to experience significant basal expansion, provided the tilt angle was not already close to being perpendicular to the silicate surface. For those organoclays demonstrating basal expansion, it was noted that the resulting particle size was increased due to enhanced porosity. Water proved useful in clay expansion in certain cases and primarily while operating conditions allowed the co-solvent to remain adsorbed to the clay surface.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: DO THE BENEFITS OF RETRIEVAL PRACTICE REMAIN UNDER STRESS?

contributor:
Kim, Joseph
Psychology

abstract: Stress is a ubiquitous experience in the student population. This is concerning, as stress impairs memory functioning. Since memory functioning largely determines academic success, stress prevents students from fulfilling their academic potential. But this impairing effect of stress may not always emerge. Recent research has shown that stress does not impair memory performance if students learn information by practicing retrieval. This has been coined as an inoculation effect. Though surprising, this may simply result from automatizing the retrieval process. This study sought to replicate this finding using ecologically valid materials and test whether the inoculation effect occurred with multiple-choice questions (MCQs). Participants learnt a passage by either restudying it or by practicing retrieval. They returned two days later and completed the Trier Social Stress Test or a control version. They then freely recalled the passage and completed the MCQs. Although the results are preliminary, the trends in the data indicate that stress had no effect on free recall performance or MCQ performance when information was learnt by practicing retrieval. This result is discussed along with this study’s limitations. Post hoc analyses are also discussed with future research directions. Altogether, this study adds to a longstanding literature reporting negative effects of stress on cognition and adds to a new literature that investigates ways to nullify effects of stress on memory performance.

abstract: Thesis

abstract: Master of Science (MSc)


title: Neural Mechanisms of Motor Cortical Representation Modulation

contributor:
Nelson, Aimee
Kinesiology

subject:
Neural Mapping
mapping
motor cortex mapping
motor representations

abstract: TMS can be used to generate representational maps by delivering pulses at throughout a grid, centered over the most sensitive spot to elicit a resulting MEP called the motor hotspot. The areas of these maps are modulated by muscle contraction and have been shown to increase in area with increasing contraction intensity. Both intracortical inhibition (SICI), and intracortical facilitation (ICF) are paired pulse paradigms in which contraction causes a reduction in magnitude. The present study aimed to categorize changes in the above circuits and representational maps as well as expose a possible relationship between both metrics in the context of graded contraction. To study these questions 15 healthy, right-handed volunteers participated in a study measuring SICI, ICF and cortical maps under conditions of REST, 10, 20 and 30% of MVC of the right FDI muscle. SICI and ICF showed significant reduction between REST and no differences amongst contraction levels. However, SICI displayed a graded reduction through contraction levels when analyzed on a trial-by-trial basis sorted by actual contraction level. Cortical representational area increased from REST to all contraction states and between 10 and 30% MVC confirming the graded growth observed in previous studies. Further, analysis shows that SICI, ICF and area all exhibited the majority of their modulation within the first 10% of contraction. Both SICI and ICF were not significantly correlated to the growth in representational area. This may be in part due to participants’ variability in the level of contraction sustained during measures, which also made it unfeasible to conduct a correlation of trial-by-trial data between map area and circuit magnitudes. We present evidence to corroborate previous findings for the effects of contraction on intracortical circuits and representational area during graded contraction as well as contribute to the methodology of such investigations concerning the control of varied contraction.

abstract: Thesis

abstract: Master of Science (MSc)


title: Wireless Sensor Systems for In-Vivo Applications

contributor:
Deen, M. J.
Electrical and Computer Engineering

subject:
wireless
sensor
system
in vivo

abstract: Rapid developments in microelectronics technology have allowed for phenomenal achievements in biomedical engineering. In the past few decades, an enormous amount of researches were done in the field of medical implantable microelectronic systems. The prevalence of research in this particular field have led to the design of novel systems for in-vivo applications, for example, using microelectronic systems to replace catheterization in clinical studies of urinary incontinence. In this thesis research, we study two types of wireless modules towards our goal of wireless systems for in-vivo applications. The first system, a 2.4 GHz wireless pressure sensor system, is designed as a pressure sensing module to operate as a part of a pill imaging device published in [32]. This pressure module samples pressure data and passes them to the pill imaging capsule via a serial-port-interface (SPI). The 2.4 GHz wireless pressure system has an overall system dimension of 75.0 x 20.5 x 17.5 mm3 with a current consumption of 5 mA when operating from a 3 V supply. The pressure sensitivity of this system is observed as 1.14 cmH20/LSB (least significant bit). The second system, 125kHz RFID (radio-frequency identification) dual sensor system, is designed to explore the possibility of powering the device and transmitting data using the RFID technology. The 125kHz RFID dual sensor system has an overall system dimension of 30.0 x 15.0 x 15.0 mm3 with a current consumption of 1.5 mA while operating at 3 V. The pressure sensitivity of this system is observed as 2.93 cmH20/LSB and the temperature sensitivity is observed as 0.069 °C/LSB. And, the detections of rapid pressure changes in both systems are successful. The work performed in this thesis research has provided a cost-effective method of designing medical implantable systems using off-the-shelf components as compared to full-custom designs. In this research, it is also observed that power consumption is a major issue in medical implantable systems. Finally, the possibility of transmitting data and powering such systems using RFID technology has been verified.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: Multivariable Model-Based Predictive Control for Injection Molding

contributor:
Hrymak, A. N.
Chemical Engineering

subject:
multivariable
model
predictive control
predict
control
injection molding
injection
mold

abstract: The rigorous quality criterion and intricate shapes of plastic injection molded parts require molders to improve process control systems in order to keep their competitive status in the market. In recent research, various advanced control algorithms are employed to develop in-line process controllers. In modem controllers design, in-mold process variables play a very important role in connecting machine variables and quality variables. Model-based predictive control (MPC) is used to investigate the controllability of cavity pressure and cavity temperature within a cycle or cycle-to-cycle. The objective of the present work is to demonstrate a procedure to develop MPC controllers based on simulation results. Moldflow® was used to simulate the injection molding process for a thin-wall cell phone cover. Cavity pressure profiles and part surface temperature profiles were extracted to develop the dynamic model for controller design. Thermal analysis for the cooling stage was investigated by ANSYS® FEM software. Mold surface temperature profiles were used for controller design. Dynamic matrix control, a type of MPC control, was developed by using Matlab® MPC Toolbox. A single-input/single-output MPC controller was developed to control cavity pressure in filling stage by manipulating injection flow rate. Simulation studies were then used to develop a MPC controller to implement a closed-loop control. The controller performed very well to control the pressure profile to trace the set-point, even with melt temperature or mold temperature change. Two MPC controllers were developed to control cavity surface cycle average temperature by manipulating coolant flow rate and coolant temperature. Both controllers show good controllability for cycle average temperature control. A two-input/two-output DMC controller was implemented to control cavity pressure and part surface temperature in the packing stage. Packing pressure and mold temperature were manipulated to trace the controlled profile set-points in each sampling time. Results shows that the controller was able to meet the set-point very well, for an unmeasured disturbance, based on a closed-loop test. All the controllers were developed based on simulation results, which will have some differences with real production data. Therefore, the model parameter and controller tuning parameter should be validated and modified if needed before real-time application.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: Path Planning and Sensor Management for Multisensor Airborne Surveillance

subject:
Radar tracking
Sensor management
Path planning
Optimization

abstract:
As a result of recent technological advances in modernized sensor sets and sensor platforms, sensor management combined with sensor platform path planning are studied to conduct intelligence, surveillance and reconnaissance (ISR) operations in novel ways.
This thesis addresses the path planning and sensor management for aerial vehicles to cover areas of interest (AOIs), scan objects of interest (OOIs) and/or track multiple detected targets in surveillance missions.
The problems in this thesis, which include 1) the spatio-temporal coordination of sensor platforms to observe AOIs or OOIs, 2) the optimal sensor geometry and path planning for localization and tracking of targets in a mobile three-dimensional (3D) space, and 3) the scheduling of sensors working in different (i.e., active and passive) modes combined with path planning to track targets in the presence of jammers, emerge from real-world demands and scenarios.

The platform path planning combined with sensor management is formulated as optimization problems with problem-dependent performance evaluation metrics and constraints.
Firstly,
to cover disjoint AOIs over an extended time horizon using multiple aerial vehicles for persistent surveillance,
a joint multi-period coverage path planning and temporal scheduling, which allows revisiting in a single-period path, is formulated as a combinatorial optimization with novel objective functions.
Secondly,
to use a group of unmanned aerial vehicles (UAVs) cooperatively carrying out search-and-track (SAT) in a mobile 3D space with a number of targets,
a joint path planning and scanning (JPPS) is formulated based on the predictive information gathered from the search space.
The optimal 3D sensor geometry for target localization is also analyzed with the objective to minimize the estimation uncertainty under constraints on sensor altitude, sensor-to-sensor and sensor-to-target distances for active or passive sensors.
At last,
to accurately track targets in the presence of jammers broadcasting wide-band noise by taking advantage of the platform path planning and the jammer's information captured by passive sensors,
a joint path planning and active-passive scheduling (JPPAPS) strategy is developed based on the predicted tracking performance at the future time steps in a 3D contested environment.
The constraints on platform kinematic, flyable area and sensing capacity are included in these optimization problems.

For these multisensor path planning and decision making, solution techniques based on the genetic algorithm are developed with specific chromosome representations and custom genetic operators using either the non-dominated sorting multiobjective optimization (MOO) architecture or the weighted-sum MOO architecture.
Simulation results illustrate the performance and advantage of the proposed strategies and methods in real-world surveillance scenarios.

abstract: Thesis

abstract: Doctor of Philosophy (PhD)


title: Characterizing the Response of TAC- and CAR-Engineered T cells Following Antigenic Stimulation

contributor:
Bramson, Jonathan
Biochemistry and Biomedical Sciences

subject:
immunology
t cells
immunotherapy
gene therapy
cancer
genetic engineering
immuno-oncology
chimeric antigen receptors

abstract:
T lymphocytes engineered with chimeric antigen receptors (CARs) have shown remarkable
success in the treatment of leukemias. Conventional CARs seek to recapitulate TCR and
costimulatory signals through fusion of T cell signaling elements into a single receptor. The
robust anti-tumor activity of CAR T cells is often accompanied by debilitating toxicities due to
excessive T cell activation and cytokine production following infusion. Our lab has generated a
novel chimeric receptor termed T cell antigen coupler (TAC), which is designed to engage native T cell signaling domains for cellular activation. In a murine xenograft model, we previously found that TAC T cells mediated rapid tumour regression in the absence of toxicities. Comparatively, CAR T cells elicited significant lethal toxicities to the mice due to reactivity against an unspecific antigen that resulted in excessive proliferation and cytokine production in vivo. Here, we report that TAC and CAR T cells have fundamentally different biology, both at rest, and during activation. TAC T cells were more sensitive to the context of stimulation compared to CAR T cells. Whereas TAC T cells can discriminate between antigen bound to a bead, or antigen present on a cell, CAR T cells do not make the same distinction and responds equally well to both. Compared to several different CAR constructs, TAC T cells are less prone to tonic signaling and T cell differentiation in the absence of antigen. These findings support that TAC T cells may pose a safety benefit as a cancer immunotherapy, due to its distinct biology from CAR T cells that enables them to require more stringent contexts for activation.

abstract: Thesis

abstract: Master of Science (MSc)

abstract:
Cytotoxic T cells are also known as “resident killer” cells of the immune system, as they can
seek and eliminate diseased or infected tissue, including cancer cells. However, cancer cells can evade elimination by T cells over time. Genetic engineering of T cells allows us to re-arm T cells against cancer cells. T cells isolated from a patient are genetically modified to recognize cancer cells specifically. So far, these modified T cells have been successful against several leukemias. However, the side effects of this treatment can be substantial and life-threatening, due to the massive reaction of the T cells against the cancer cells following infusion. We explore the biology of two different types of engineered T cells to better understand the interaction between T cell and tumour cell. Our results aim towards mitigating the side effects of T cell treatment, while investigating how we can improve its effectiveness for the future.


title: Elastocapillary interactions between liquids and thin solid films under tension

contributor:
Dalnoki-Veress, Kari
Physics and Astronomy

subject:
Soft Matter
Surface tension
Elasticity
Elastocapillarity
Wetting
Pattern formation

abstract: PhD Thesis

abstract:
In this thesis, experiments are described which study the elastocapillary interactions between liquids and taut solid films. The research employs contact angle measurements to elucidate how capillary forces deform compliant solid structures, but also to attain fundamental insight into the energy of interfaces involving amorphous solids.

The majority of the work focuses on how capillary deformations of compliant elastic membranes introduce modifications to descriptions of common wetting phenomena. Particular focus is given to studying partial wetting in the presence of compliant membranes in various geometries: droplet on a free-standing membrane, droplet capped by a membrane but sessile on a rigid substrate, and droplet pressed between two free-standing membranes. The mechanical tension in these membranes is found to play an equivalent role as the interfacial tensions. As such, the mechanical tension is incorporated into Young-Dupre's law (capped droplet on a rigid substrate) or Neumann's triangle (droplet on free-standing membrane), leading to departures from the classical wetting descriptions. In addition, one study is conducted investigating how viscous dewetting is affected by the liquid film being capped by an elastic film. The results of this study show that the dewetting rate and rim morphology are dictated by the elastic tension.

Another important aspect of the work is demonstrating the utility of anisotropic membrane tension for liquid patterning. A biaxial tension is shown to produce droplets and dewetting holes which are elongated along the high tension direction. The compliant membrane geometry can also be designed to produce droplets and holes with square morphology.

In the final project, the surface energy of strained glassy and elastomeric solids is studied. Glassy solids are shown to have strain-dependent surface energies, which implies that surface energy (energy per unit area) and surface stress (force per unit length) are not equivalent for this class of materials by virtue of the Shuttleworth equation. On the other hand, this study provides strong evidence that surface energy and surface stress are equivalent for elastomeric interfaces.

abstract: Thesis

abstract: Doctor of Philosophy (PhD)


title: Does the school setting matter? Examining associations between school and classroom settings and health behaviours among students in Ontario

contributor:
Georgiades, Katholiki
Health Sciences

subject:
school climate
adolescents
physical activity
cannabis

abstract:
BACKGROUND: Low rates of physical activity and high rates of cannabis use among adolescents are concerning given the health outcomes associated with these health behaviours. Although individual-level characteristics are strongly associated with physical activity and cannabis use, research also suggests that the school setting may influence these health behaviours.
PURPOSE: To: 1) Determine the extent to which students’ cannabis use and physical activity vary across school and classroom settings, 2) Identify characteristics of the school setting that are associated with cannabis use and physical activity among students in grades 6-12 in Ontario.
METHODS: This study used data from the School Mental Health Surveys, a cross-sectional school-based survey of 31,124 students, 3,373 teachers, and 206 principals from 248 schools across Ontario. Multilevel modelling was used to explore school and class effects while controlling for student compositional effects.
RESULTS: About 5% of the variability in student physical activity and 14% of the variability in student cannabis use was attributable to between school and classroom differences. Students’ perception of school climate was positively associated with physical activity, and negatively associated with cannabis use.
CONCLUSIONS: Findings highlight the potential influence of the school and classroom environment on students’ physical activity and cannabis use.  School and classroom contexts may be important environments for targeted interventions, policies and programs.

abstract: Thesis

abstract: Master of Public Health (MPH)

abstract: Despite the known benefits of physical activity and harms associated with cannabis use, physical activity rates are low while cannabis use is high among Canadian youth. Previous research has highlighted the potential for the school environment to influence students’ health behaviours. The current study examined the extent to which   physical activity and cannabis use varied across school and classroom settings and identified characteristics of the school environment that were associated with these health behaviours. There was significant between school and classroom variability in levels of physical activity and cannabis use. School climate was positively associated with physical activity, and negatively associated with cannabis use. Identifying modifiable characteristics of the school environment that are associated with students’ health behaviours can inform development of interventions, policies, and programs to increase physical activity and reduce cannabis use.


title: Sub-Wavelength Microwave Radar Imaging for Detection of Breast Cancer Tumors

contributor:
Nikolova, Natalia
Bakr, Mohamed
Electrical and Computer Engineering

subject:
microwave
radar
breast cancer
cancer
tumour
detect

abstract: Ultra-wideband microwave imaging, with its advantages of absence of breast compression, nonionizing and noninvasive properties, is a complementary method to X-ray mammography for breast cancer detection that is safe and reasonably inexpensive. The motivation for employing microwave imaging techniques for detecting early-stage breast cancer stems from published research results showing the strong contrast in the dielectric properties at microwave frequencies between normal breast tissue and malignant lesion. This thesis contributes to development of novel techniques for the detection of early-stage breast cancer tumors well below a centimeter with specificity and high degree of accuracy, i.e., with minimum false negatives/positives. In our proposed approach, a modified Shannon entropy criterion (SEC) is formulated for determining when the time-reversed wave focuses back to the source target in the presence of an inhomogeneous lossy medium. It is demonstrated through two examples, the time-reversal mirror and cavity, that the SEC is found to be more robust than the inverse varimax norm. TR has been shown to be superior to other simple delay-based focusing techniques and here we have extended the TR algorithm by making it more robust in localizing small tumors. The importance of this finding becomes evident as the SEC allows for the detection of tumors that are sub-wavelength in size. Our novel sub-wavelength ultra-wide band (UWB) microwave radar imaging technique exploits the principle of phase-shifting mask (PSM) from optical lithography and is implemented using a time-reversal (TR) algorithm based on the transmission-line matrix (TLM) method. We incorporate the SEC in a TR algorithm to achieve a robust imaging algorithm exploiting the measurements acquired by our phase-shifting mask (PSM) experimental set-up. Unlike the FDTD TR algorithm by Kosmas et al., which excites one of the 23 antenna elements, we propose a different system where all antennas are stimulated simultaneously with their excitation based on the PSM principle. A 0.5-mm diameter tumor was detected and located using a 200-ps UWB pulse in a realistic inhomogeneous two dimensional breast model. The breast model was derived from magnetic resonance imaging data and simulated using the TLM method. The effect of the dielectric contrast and proximity of tumor to the antenna receivers are examined. A TLM-based TR algorithm employing two types of time reversal mirrors (TRMs) is proposed to improve the accuracy of localizing the sub-wavelength tumors. The final part of the thesis examines the feasibility and the design of a narrowbeam UWB antenna for microwave breast cancer detection focusing on the antenna feed structure and the printed TEM horn antenna. A feed structure of an UWB antenna for microwave radar imaging is designed. The UWB antennas are fundamental components of the UWB radar imaging hardware. The performance of the antenna is crucial for the resolution and the reliability of the whole imaging system. A TEM horn antenna is studied and suggestions are made regarding the hardware implementations of the experimental setup. We conclude by suggesting future work toward hardware and practical implementation of UWB microwave radar imaging with high resolution.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: Induction of Genomic Instability During Transformation of Human Cells with SV40 Large T Antigen

contributor:
Bacchetti, Silvia
Biology

subject:
genome
instability
human
cell
SV40
antigen
transform
SV40 large T antigen

abstract: Human cells transformed by SV40 large T antigen achieve an extended lifespan and continue to grow and divide past the normal growth limit. This extended lifespan often ends at crisis when the cells die through fatal cell division. A few cells will survive this crisis and continue to proliferate indefinitely and are therefore considered immortal. Transformation of cells by SV40 large T antigen is associated with the induction of genomic instability at early times. This instability may contribute to a cells surviving crisis and becoming immortal through the chance disruption of genes involved in cell proliferation and regulation of cell death. Genetic instability is also observed in human tumours and the mechanisms by which it occurs both in tumour cells and SV40 transformed cells may be similar. In order to investigate these mechanisms, human and rodent cells were transfected with wild type and mutant forms of SV40 large T antigen and analyzed cytogenetically. The results of this study demonstrate that the amino terminal 147 amino acids of SV40 large T antigen are sufficient for the induction of genomic instability and at least three regions within this amino terminal fragment are necessary. One between amino acids 17 and 27. A second being the retinoblastoma protein binding site, and the third between amino acids 130 and 147. Finally, binding of T antigen to p53 appears to not be required for the induction of genomic instability, but may be necessary for the survival of aberrant cells. There is an apparent correspondence between the ability of T antigen mutants to induce genomic instability, and their abilities to induce cellular DNA synthesis and to transform and immortalize cells.

abstract: Thesis

abstract: Master of Science (MS)


title: Study of Spatial and Temporal Filtering Techniques and Their Applications in Fiber Optic Communication Systems

contributor:
Kumar, Shiva
Xu, Changqing
Electrical and Computer Engineering

subject:
spatial filter
temporal filter
time
space
filter
fiber optic
communication

abstract:
This thesis studies spatial and temporal filtering techniques and their applications in fiber optic communication systems. Differential mode delay (DMD) in multimode fibers (MMFs) and multipath interference (MPI) are two major impairments in fiber optic communication systems. DMD lends to inter symbol interference in MMF communication systems which seriously limit the bit rate-distance product of the system. MPI leads to interference pattern at the output of a single mode fiber link which increases the bit error rate of the system. In this thesis, we propose a method which uses spatial filtering technique in a 4F system to reduce DMD and MPI effects. Typically, higher order modes have higher spatial frequency components and therefore, they are spatially separated from the lower mode after Fourier transform. By optimizing the bandwidth of a spatial filter, unwanted higher order modes can be suppressed. Therefore, DMD and MPI effects in fiber optic communication systems can be reduced at the cost of losing some fraction of the signal power.
In this thesis, we also propose a new application of temporal filtering technique. A time lens is a phase modulator which introduces a quadratic phase factor in time domain. Combined with single mode fibers, a time lens can be used to perform Fourier transform in time domain. A tunable optical filter can be implemented using a modified temporal 4F system which is analogy with the spatial 4F system. The merit of this method is that no additional signal processing is needed to reverse the bit sequence at the output of the 4F system and that the channels to be demultiplexed at a node can be dynamically reconfigured.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: A MCU-Controlled Photovoltaic System with Maximum Power Point Tracker

contributor:
Szabados, Barna
Electrical and Computer Engineering

subject:
photovoltaic system
power point
tracker
mcu-control

abstract: Given the growing concern over climate change, air pollution, rising energy prices, and the uncertain reliability of conventional fuel sources, solar power has become more popular in a variety of applications. Solar power is free, safe, abundant, renewable, and has few negative impacts on the environment. The photovoltaic array is substantially influenced with unpredictable environmental conditions (sun illumination and array temperature), which in turn, results in nonlinear Voltage-Current (or Power-Voltage, Power-Current) characteristics. These characteristics make it difficult to estimate the maximum power operating point. To extract the maximum power available from photovoltaic (PV) arrays on a continuous basis, a device called the Maximum Power Point Tracker (MPPT) is needed to continuously deliver the highest possible power to the load given unpredictable variations in environmental conditions. The PV system used in our experiment has a maximum 300W capability. Two sets of PV arrays are used in parallel to demonstrate the scalability of the system; each branch consists of three series-connected PV modules that are individually rated at 50W. Two DC-DC buck-type converters are implemented. A 24V battery bank is used as a power storage unit and is also connected to the load. An MC-based 56F8013 and its demonstration board from Freescale are employed to implement different MPPT control schemes, with multiple-PWM channels. The design can therefore adequately handle two main independent switches for each power converter. Several MPPT control algorithms are validated and comparatively analyzed in both indoor and outdoor experiments in real time. A new control strategy (called Adaptive Hill-Climbing) is proposed as a modified version of the conventional Hill-Climbing method using an optimally adaptive power window. Other methods including dp/dv method and IncCond method are also implemented in the PV system. The experimental investigation is conducted using these control topologies to seek continuously varying Maximum Power Point (MPP) from solar arrays. The experimental results show that the new proposed control method strongly outperforms the other methods. This thesis shows that the proposed MPPT can increase the power generated by PV arrays by up to at least 30% more than a PV system without an MPPT. The proposed MPPT system is adaptive to environmental disturbances; it is flexible and can be expanded to an N-parallel PV system.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: LEMoNet: Low Energy Wireless Sensor Network Design for Data Center Monitoring

contributor:
Zheng, Rong Jr
Computing and Software

subject:
Data center monitoring
Wireless sensor networks
Bluetooth low energy

abstract: Today’s data centers (DCs) consume up to 3% of the energy produced worldwide, much of which is wasted due to over-cooling and underutilization of IT equipment. This wastage in part stems from the lack of real-time visibility of fine-grained thermal distribution in DCs. Wireless sensing is an ideal candidate for DC monitoring as it is cost-effective, facility-friendly, and can be easily re-purposed. In this thesis, we develop LEMoNet, a novel low-energy wireless sensor network design for monitoring co-location DCs. It employs a two-tier network architecture and a multi-mode data exchange protocol to balance the trade-offs between low power consumption and high data reliability. We have evaluated the performance of LEMoNet by deploying custom-designed sensor and gateway nodes in a SHARCNET DC at A.N. Bourns Science Building. We show experimentally that LEMoNet achieves an average data yield of over 98%. Under normal operations with one temperature and one humidity reading every thirty seconds, the battery lifetime of LEMoNet sensor nodes is projected to be 14.9 years on a single lithium coin battery.

abstract: Thesis

abstract: Master of Science (MSc)


title: Xin as a novel regulator of mitochondrial morphology and bioenergetics in skeletal muscle

contributor:
Hawke, Thomas
Medical Sciences

abstract: Xin is a striated muscle specific, cytoskeletal adaptor protein that our lab has recently localized to the mitochondria and peri-mitochondrial regions of skeletal muscle. Further, we have identified mild mitochondrial structural and functional impairments in the skeletal muscle of Xin-/- mice. The objective of this study was to investigate the physiological effects of Xin deficiency in combination with the metabolic stress of a high fat diet, as well as the impact on skeletal muscle mitochondrial structure and function. Wild-type (WT) and Xin knockout (Xin-/-) mice were fed a high-fat diet (HFD- 60%kcal fat) for 8 weeks. HFD-fed Xin-/- mice did not gain greater body or fat mass relative to WT mice. However, Xin-/- mice had increased fasted blood glucose levels (Xin-/-: 15.81.042, WT: 10.70.652; p<0.05) and reduced glucose tolerance (AUC Xin-/-: 51.41.7, WT: 31.13.1; p<0.05) after 8 weeks of HFD feeding. Electron microscopy analysis revealed an ~1.5-fold (46.4%7.5; p<0.05) increase in intermyofibrillar mitochondrial content and a ~2.8-fold (186.3%9.6; p<0.05) increase in size, associated with mitochondrial swelling, streaming and loss of cristae. Complex I and complex II supported respiration were also impaired when corrected to mitochondrial content (complex I: JO2 Xin-/-: 130.722.3, WT: 210.238.8; p<0.05; complex II: JO2 Xin-/-: 124.413.9, WT: 175.620.9; p<0.05). We observed no changes to the protein content of either the autophagic proteins p62 or LC3, or the mitochondrial fission proteins Drp1 or Fis1 or fusion proteins Mfn1 or Mfn2. Overall, Xin-/- mice exhibited abnormal muscle mitochondrial morphology, decreased mitochondrial respiration and dysregulated glucose handling, independent of changes in body weight.  Future studies are needed to identify Xin-specific binding partners and determine if Xin may be an unidentified contributor to mitochondrial myopathy and the development of metabolic disorders.

abstract: Thesis

abstract: Master of Science (MSc)


title: EXAMINING THE EFFECT OF EXERCISE BREAKS INTENSITY ON ATTENTION AND LEARNING IN A UNIVERSITY SETTING

contributor:
HEISZ, JENNIFER
Kinesiology

subject: Cognition, Exercise, Learning, Memory, Attention

abstract: During a university lecture, students’ attention typically declines as the lecture progresses. Lapses in attention can interfere with learning and memory for the presented material to negatively impact a student’s overall academic performance. Prior research has shown that incorporating five-minute high-intensity exercise breaks during a university lecture improved student attention and comprehension compared to a computer break or no break. Although promising, high-intensity exercises may not be suitable for a university classroom. To improve feasibility for implementation, the current study aimed to determine whether reducing the intensity of the exercise breaks could still yield similar cognitive benefits. One hundred participants watched a 50-minute online lecture with no breaks (control; n = 25) or while intermittently taking exercise breaks of high (n = 26), medium (n = 26) or low intensity (n = 23). Attention was measured throughout the lecture and comprehension was measured after learning. The groups did not significantly differ on their ability to pay attention (Time 1: X2(2) = 3.61, p = .31; Time 2: X2(2) = 3.20, p = .36) or comprehend (F(1,93) = . 26, p = .6) the lecture material. However, when controlling for significant group differences in academic performance outside of the study (F(3, 113) = 3.52, p = .02) and baseline comprehension performance during the study, small positive improvements were observed on comprehension following an exercise break of all intensities (Cohen’s d < .67 and >.08), but with the largest effect size seen for high intensity exercise breaks towards the end of the lecture. These positive trends point to the benefit exercise breaks on learning in a university setting and establish the foundation for further research.

abstract: Thesis

abstract: Master of Science (MSc)


title: The effects of moderate intensity aerobic exercise on general and state anxiety in young adults

contributor:
Heisz, Jennifer
Kinesiology

subject:
anxiety
aerobic exercise

abstract: Anxiety disorders are highly debilitating mental illnesses. They are characterized by heightened worry, physiological arousal, and avoidance behaviours that manifest as psychological, physiological, and behavioral disturbances. Critically, a large proportion of the population suffers from elevated anxiety symptoms. Physical exercise has been proposed as a potential treatment for managing anxiety symptoms. The present study examined the effect of moderate intensity aerobic exercise training on both general and state anxiety symptoms in young adults. We hypothesized that general anxiety would be significantly lower after nine weeks of aerobic exercise training compared to no exercise training. We also hypothesized that a single bout of exercise would reduce state anxiety, and this reduction would be augmented with training. Fifty-five inactive participants (47 females, 85%) age 18 to 24 (M ± SD = 19.29 ± 1.37 years) were randomized into one of two groups: 1) exercise group, or 2) non-exercise control group. The exercise group completed three moderate intensity continuous aerobic exercise sessions per week for nine weeks, whereas the control group were asked to remain inactive. General anxiety was measured before and after the intervention using the Beck Anxiety Inventory, while state anxiety was measured twice a week using the short-form of the state scale of Spielberger State-Trait Anxiety Inventory. There was a significant interaction between group and baseline anxiety severity (p = .041) when controlling for aerobic fitness. Further exploration of this interaction revealed that the effect of aerobic exercise on post-intervention general anxiety was moderated by baseline anxiety severity [B = -9.84, p = .041, CI = -19.23 to -0.44]. Only the exercise subgroup with functionally-relevant baseline anxiety had lower post-intervention anxiety than the control group [B = -10.66, p = .0033, CI = -17.60 to -3.73]. Furthermore, an acute bout of exercise reduced state anxiety relative to the control group, but the effect did not emerge until weeks 4 to 6 of training (p < .001). Neither anxiety outcome was associated with changes in aerobic fitness, suggesting that some other aspect of the exercise program may have caused the benefits on anxiety. Collectively, these findings point to regular aerobic exercise as an effective tool for young adults to manage anxiety.

abstract: Thesis

abstract: Master of Science (MSc)


title: MODELING OF THE DYNAMIC TRANSFORMATION ABOVE THE AE3 TEMPERATURE

contributor:
Zurob, Hatem
Materials Science and Engineering

subject: dynamic transformation

abstract: The dynamic precipitation of ferrite during austenite deformation above the Ae3 temperature, was first reported by Yada et al. in the 1980s. These observations were later confirmed for a wide range of steel compositions and processing conditions. The aim of this work is to clarify the mechanism by which ferrite formation takes place above the Ae3 temperature. To that end, a simple model for ferrite growth as a result of the movement of disconnections under applied stress is established. This motion, opposed by the back stress, increases the Gibbs energy as a result of deformation of ferrite above Ae3. Preliminary calculation suggests that the dynamic transformation is possible near the Ae3 temperature for large stress. The results are discussed in terms of experiments using a deformation dilatometer.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: THE CONSTRUCTION OF MODERN TIMEKEEPING IN THE ANGLO-AMERICAN WORLD, 1876-1913

contributor:
Heathorn, Stephen
History

subject:
History of Science
Timekeeping
Standard Time
Time Zones
Transnational History
Canada
Britain
United States
Astronomy
International Relations
Diplomacy
Nineteenth Century

abstract: This dissertation asks why the system of time measurement set up towards the end of the nineteenth century took the form that it did. The answer is partially dependant on the advent of new technologies such as railways, steamships, and telegraphs. However, instead of focusing on a teleological story of technological progress, this dissertation derives its answer by examining the social, political, and cultural context of the individuals involved. The dissertation uses the 1884 International Meridian Conference as a case study to suggest that time reform was driven by professional context more than by technological imperatives or national interest. Astronomers and engineers came to the conference with very different visions for modern timekeeping. Using a constructivist lens, this dissertation examines the decision-laden process by which temporal knowledge was constructed. Questions about the very nature of accurate time was at the heart of the debate: was time a public good, a commodity, or a specialized tool? The answers to these questions depended heavily on one’s profession, and as a result the conference, directed by astronomers who preferred time as a specialized tool, rejected standard time as a broad reformation of civil timekeeping for the public. The process of construction continued after the conference as well, as the universality of standard time became wrapped up with the heightened accuracy required by specialized astronomical time. Entrepreneurs latched on to this, selling accurate time as a desirable symbol of modernity, while at the same time large numbers of people continued to use older timekeeping methods that were more convenient. New timekeeping methods did not sweep aside the old, leaving timekeeping a more complex, rather than a simplified, process. The standard time system which emerged from this complexity was far from inevitable, and in fact remained largely incomplete.

abstract: Thesis

abstract: Doctor of Philosophy (PhD)

abstract: This dissertation asks why the system of time measurement set up towards the end of the nineteenth century took the form that it did. While partially dependent on new technologies such as railways and telegraphs, timekeeping was shaped more directly by the cultural context of the individuals involved. The dissertation uses the 1884 International Meridian Conference as a case study to suggest that time reform was driven by professional norms more than by national interest or changes in technology. Astronomers and engineers came to the conference with very different visions for modern timekeeping. Indeed, questions about the very nature of accurate time was at the heart of the debate: was time a public good, a commodity, or a specialized tool? The answers to these questions depended heavily on one’s profession, and as a result the standard time system that emerged was far from inevitable, and in fact remained incomplete.


title: Ligand Interactions at the Active Site of Aspartate Transcarbamoylase from Escherichia Coli

contributor:
Chan, W. W. -C.
Biochemistry

subject:
ligand
active site
aspartate
transcarbamoylase
escherichia coli
e coli

abstract:
The carbamoyl region of the active site of aspartate transcarbamoylase from Escherichia coli was probed using an enzyme assay in which the two substrates were varied near their respective K_m 's. The inhibitors tested, some synthesized and some commercially available, were chosen to satisfy the structural requirements for binding to either the dicarboxylate or phosphate region with a substituent capable of extending into the carbamoyl region. However, the dicarboxylate based inhibitors were found to bind in an abnormal manner (unlike L-aspartate or succinate on which they were based). The carbamoyl region was found to contain a positively charged side-chain and preliminary results indicate that tetrahedral groups are not preferred over trigonal moieties. It is suggested that electrostatic stabilization of the negative charge which develops in the transition state may be a major factor in promoting catalysis. The identity of this charged group in the carbamoyl region is postulated to be His134 based on available X-ray diffraction data. The binding subsites of the active site of this enzyme were also found to be oriented in essentially the same plane. These results will greatly aid in the design of future mechanism-based
inhibitors to this enzyme that may have therapeutic value (at this time the mammalian enzyme is thought to have a similar catalytic mechanism).

abstract: Thesis

abstract: Master of Science (MS)


title: Molecular Cloning of a Chinese Hamster Mitochondrial Protein Related to the Chaperonin Family of Proteins

contributor:
Gupta, R. S.
Biochemistry

subject:
molecule
clone
chinese hamster
mitochondria
protein
chaperonin
family

abstract: The complete cDNA sequence of a mitochondrial protein from Chinese hamster ovary cells has been determined. This protein, designated P1, was originally identified in cells resistant to the microtubule inhibitor podophyllotoxin (Gupta, 1981). The mutant cell line contained an alteration of the P1 protein that gave rise to a new, more acidic protein, designated M1 (Gupta et al., 1982). The P1 protein was determined to be microtubule-related based on the cross-resistance pattern of the mutants to other microtubule inhibitors, and corelease with tubulin under conditions which cause microtubule depolymerization (Gupta et al., 1982). Subcellular fractionation studies localized this protein to the matrix of the mitochondria (Gupta and Austin, 1987). Antibodies raised against P1 were used to isolate a cDNA clone from human cells (Jindal et al.,1989). The human cDNA clone was used as a probe to screen for clones of the P1 protein in bacteriophage (lambda)gt10/(lambda)gt11 cDNA libraries prepared from CHO cells. The P1 cDNA encodes a protein of 573 amino acids with a relative molecular mass of 60,983 daltons. The first 26 amino acids meet the requirements of a mitochondrial matrix targeting sequence. The mature protein is 547 residues in length with a relative molecular mass of 57,949 daltons. The deduced amino acid sequence shows 97% identity to the the human P1 protein. More interestingly, the amino acid sequence shows extensive homology (42 to 55% identical residues and an additional 15 to 20% conservative replacements) to the chaperonin class of molecular chaperones. This class of proteins includes the hsp60 protein of yeast, the groEL protein of Escherichia coli, the ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit binding protein of plant chloroplasts, and the 62-65-kDa major antigenic protein of mycobacteria and Coxiella burnetii. The homology of P1 with the above proteins begins after the putative mitochondrial presequence and extends to the c-terminal end. Several regions throughout the protein sequence are highly conserved and are proposed to be functional domains of the protein. Also highly conserved is a Gly-Gly-Met repeating motif at the carboxy-terminus. The function of this sequence is undetermined, as yet. A dendrogram was constructed from the sequence homology data. It suggested that mitochondrial P1 evolved from purple bacteria which is the endosymbiont which gave rise to mitochondria. The chaperonin class of proteins have been shown to assist in the assembly of oligomeric protein structures. It is suggested that the P1 protein may play a similar role in mammalian cells. The high degree of homology between P1 and the 65-kDa mycobacterial antigen also suggests that P1 may be involved in certain autoimmune diseases.

abstract: Thesis

abstract: Master of Science (MS)


title: Sequential Scalar Quantization of Two Dimensional Vectors in Polar and Cartesian Coordinates

contributor:
Dumitrescu, Sorina
Electrical and Computer Engineering

subject:
Data Compression
Sequential Scalar Quantization

abstract:
This thesis addresses the design of quantizers for two-dimensional vectors, where the scalar components are quantized sequentially. Specifically, design algorithms for unrestricted polar quantizers (UPQ) and successively refinable UPQs (SRUPQ) for vectors in polar coordinates are proposed. Additionally, algorithms for the design of sequential scalar quantizers (SSQ) for  vectors with correlated components in Cartesian coordinates are devised. Both the entropy-constrained (EC) and fixed-rate (FR) cases are investigated.

The proposed UPQ and SRUPQ design algorithms are developed for continuous bivariate sources with circularly symmetric densities. They are globally optimal for the class of
UPQs/SRUPQs with magnitude thresholds confined to a finite set. The time complexity for the UPQ design is $O(K^2 + KP_{max})$ in the EC case, respectively $O(KN^2)$ in the FR case,
where  $K$ is the size of the set from which the magnitude thresholds are selected, $P_{max}$ is an upper bound for the number of phase levels corresponding to a magnitude bin, and $N$ is the total number of quantization bins. The time complexity of the SRUPQ design is $O(K^3P_{max})$ in the EC case, respectively $O(K^2N^{'2}P_{max})$ in the FR case, where $N'$ denotes the ratio between the number of bins of the fine UPQ and the coarse UPQ.

The SSQ design is considered for finite-alphabet correlated sources. The proposed algorithms are globally optimal for the class of SSQs with convex cells, i.e, where each quantizer cell is the intersection of the source alphabet with an interval of the real line. The time complexity for both EC and FR cases amounts to $O(K_1^2K_2^2)$, where $K_1$ and $K_2$ are the respective sizes of the two source alphabets. It is also proved that, by applying the proposed SSQ algorithms to finite, uniform discretizations of correlated sources with continuous joint probability density function, the performance approaches that of the optimal SSQs  with convex cells for the original sources as the accuracy of the discretization increases.

The proposed algorithms generally rely on solving the minimum-weight path (MWP) problem in the EC case, respectively the length-constrained MWP problem or a related problem in the FR case, in a weighted directed acyclic graph (WDAG) specific to each problem. Additional computations are needed in order to evaluate the edge weights in this WDAG. In particular, in the EC-SRUPQ case, this additional work includes solving the MWP  problem between multiple node pairs in some other WDAG. In the EC-SSQ (respectively, FR-SSQ) case, the additional computations consist of solving the MWP (respectively, length-constrained MWP) problem for a series of other WDAGs.

abstract: Dissertation

abstract: Doctor of Philosophy (PhD)


title: ROLE OF BMI1 IN PROMOTING BREAST CANCER TUMORIGENESIS THROUGH ATTENUATING THE DNA DAMAGE RESPONSE PATHWAY

contributor:
Tang, Damu
Medical Sciences

subject:
Breast Cancer
BMI1
ATM
c-Myc

abstract: Breast cancer (BC) is a complex disease with over 25,000 new diagnoses made in Canadian women every year.  The disease can be caused by inactivation of the ataxia telangiectasia mutated (ATM) pathway, a major anti-tumor mechanism that protects against the abnormal cell division and growth that occurs in breast cancer, but how the pathway is inactivated has yet to be completely elucidated.  BMI1 is an established oncogene that is overexpressed in BC and is associated with poor disease prognosis. BMI1 is a component of the polycomb repressive complex 1 (PRC1) that acts to repress transcription of the ARF/INK4A locus encoding two important tumor suppressor genes. We have recently shown a novel property of BMI1 in attenuation of ATM function independent of this locus. We thus hypothesize a role of BMI1 in promoting BC formation through inhibiting oncogene-induced ATM activation, allowing cancer-promoting genes to induce abnormal cellular growth. To examine this hypothesis, we transiently expressed oncogene c-Myc with or without BMI1 co-expression. As expected, ectopic c-Myc expression upregulated γH2AX, a demonstrated target of ATM; concurrent BMI1 expression reduced the γH2AX levels. Similar observations were also obtained using a BMI1 mutant deficient in promoting PRC1-mediated repression of the ARF/INK4A locus. These observations support the concept that BMI1 contributes to ATM inactivation during BC tumorigenesis through mechanisms independent of PRC1. To further examine this concept, we investigated the association of γH2AX and BMI1 in vivo. In MCF7 cell-produced xenograft tumors, the presence of γH2AX nuclear foci was clearly observed, indicative of ATM activation during BC tumorigenesis. In xenografts generated by MCF7 cells stably expressing BMI1, a trend of reduction in γH2AX nuclear foci was observed. To further model BMI1’s pathological relevance in c-Myc induced BC under a more physiological setting, we are developing transgenic mouse models (GEM) with breast-specific c-Myc expression with or without a breast-specific BMI1 knockout. The goal of these experiments is to recapitulate the above in vitro and in vivo observations. The expectation, should it be achieved, will significantly strengthen the connection between BMI1 and ATM during breast cancer tumorigenesis.

abstract: Thesis

abstract: Master of Science (MSc)

abstract: Breast cancer (BC) is a complex disease with over 25,000 new diagnoses made in Canadian women every year.  Normally there are anti-tumor mechanisms in place to protect against the abnormal cell division and growth that is associated with breast cancer. We propose a novel function of protein BMI1 to explain how breast cancer cells override these protective pathways. BMI1 is known to contribute to BC through inhibiting production of key tumor suppressing proteins and has recently been shown to decrease activity of the ataxia telangiectasia mutated (ATM)- mediated tumor inhibiting pathway.  We propose a novel role of BMI1 in promoting breast tumor formation through inhibiting the ATM-mediated anti-tumor barrier, allowing cancer-promoting genes (oncogenes) to induce abnormal cellular growth.  BMI1 was shown to be able to reduce oncogene induced ATM activity, in an action independent of established mechanisms.  Additionally in MCF7 BC tumors, the presence of BMI resulted in a trend of reduction in ATM activity.  Continued work to develop a transgenic mouse model with a breast specific BMI1 knockout will help further our understanding of BMI1’s role in BC tumorigenesis.


title: Restriction Enzyme Polymorphisms in the Region of the Small Heat Shock Genes in Drosophila

subject:
drosophila
polymorphism
enzyme
genes
heat shock
restriction

abstract: A survey of restriction enzyme polymorphisms was performed with fifteen iso-female lines of D. melanogaster amd eighteen single representaives of other Drosophila species. Three enzymes: Bam H1, Eco R1, and Pst 1 were used to probe the genetic structure of the region containing the genes Hsp 22, Hsp 23, Hsp 26, and Hsp 27. The results for within D. melanogaster show that all variation in the DNA sequence is limited to the non-coding region. The restriction patterns confirm the hypothesis that the hsp 22-27 genes are a result of tandem duplications. The values for Nei's estimate of sequence diversity (delta) are 0.034 between populations of D. melanogaster, 0.113 between sibling species, and 0.123 between nonsibling species. These estimates were compared to values obtained for protein and enzyme variation. DNA sequence divergence between nonsibling species versus nonsibling species show less differentiation than protein and enzyme divergence. The restriction enzyme phenotype was used to generate phylogenies which is in approximate agreement with previously reported phylogenies. Molecular drive and selectionist hypotheses of differential rates of evolution during cladogenesis and anagenesis are discussed.

abstract: Thesis

abstract: Master of Science (MS)


title: The Mechanism of Fibrosis Induced by Biomaterials

contributor:
Jones, K.
Chemical Engineering

subject: fibrosis biomaterial

abstract: Biomaterials are used in many different areas. Often, after implantation, severe host reactions occur which cause the malfunction or failure of the device. In our study, we wanted to investigate the mechanism of biomaterial-induced fibrosis. We focused on three areas: i) the relationship between inflammation and fibrosis after implantation, ii) the role that the SMAD3 gene plays, and iii) how MRL mice react to biomaterials. After implantation, acute inflammation occurs immediately. In pathological fibrosis, it has traditionally been believed that the inflammation is linked to the downstream fibrosis, though this theory has been challenged recently. In our project, we did not observe a direct relationship between intentionally induced inflammation and biomaterial-induced fibrosis. We did observe the dependency of the host reaction on the type of implanted biomaterial. The SMAD3 gene is tightly linked to the pro-fibrotic cytokine TGF-(beta). The SMAD3 protein mediates the TGF-(beta) pathway intracellularly. It was found in pulmonary fibrosis, SMAD3 knockout (KO) mice had lower production of collagen. In our project, we did not observe a difference in cellular behaviour on the surface of the implanted biomaterial between wild-type (WT) and SMAD3 KO mice. We did observe a difference in the production of TGF-(beta)1. This could be a clue that biomaterial-induced fibrosis has more than one mechanism/pathway that is not dependent on TGF-(beta). In our last project, we studied MRL mice that showed potential in scarless wound healing. We observed a higher production of MMP-2, MMP-9 and TGF-(beta)1. Histologically, however, we did not see a difference in cellular behaviour between MRL and C57BL/6 mice. Our results open up the possibilities of different mechanisms and pathways in biomaterial-induced fibrosis. Future studies of cytokines and specific cells could help us further understand the process of encapsulation of the implanted biomaterials.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: A Comparative Study of Machine Learning Algorithms

contributor:
Deza, Antoine
Franek, Frantisek
Computing and Software

subject:
Machine Learning
Comparative Study
Data Science
University Admissions
Software Engineering
Computer Science
K-Nearest Neighbours
Decision Tree
Random Forest
Gradient Tree Boosting
Logistic Regression
Naive Bayes
Support Vector Machine
Neural Network

abstract: The selection of machine learning algorithm used to solve a problem is an important choice. This paper outlines research measuring three performance metrics for eight different algorithms on a prediction task involving under- graduate admissions data. The algorithms that were tested are k-nearest neighbours, decision trees, random forests, gradient tree boosting, logistic regression, naive bayes, support vector machines, and artificial neural net- works. These algorithms were compared in terms of accuracy, training time, and execution time.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: Chronic use effects, or just the effects of using chronic? Examining the roles of lifetime and current severity of cannabis use in neurocognitive performance and ADHD symptoms.

contributor:
MacKillop, James
Psychology

subject:
cannabis
cannabis use disorder
age of first use
cognition
neuropsychology
ADHD

abstract: Cannabis use is becoming increasingly prevalent in Canada and the United States, where legality and public perception have recently shifted to be more permissive of recreational use. Despite established negative health consequences associated with persistent use, there remains considerable debate in the scientific community surrounding the potentially harmful effects of cannabis use on human cognition. Evidence exists that heavy cannabis use predicts diminished performance within several neurocognitive domains and also predicts greater risk of having ADHD. Further evidence suggests that earlier age of first cannabis use strengthens these associations, however the findings in these literatures are mixed and in need of further delineation. This thesis sought to examine continuous associations among current cannabis use severity, age of first use, neuropsychological performance, and ADHD symptomatology. Two studies using large samples of community adults were conducted. Study 1 analyzed data from the Human Connectome Project, and examined performance on a battery of neuropsychological measures among young adults, and found recent use to be the strongest predictor of differences in episodic memory and processing speed, and CUD predicted lower fluid intelligence. Lifetime exposure to cannabis was not associated with any outcome measures. Study 2 examined similar associations in a sample of adults representative of the Hamilton community, and also included self-reported symptoms of ADHD. Study 2 found current cannabis use severity to be predictive of more impulsive reward preferences, and also of both hyperactive-impulsive and inattentive symptoms of ADHD. Both studies found a lack of support for the role of age of first cannabis use in differential cognitive performance, and also failed to find associations between cannabis involvement and several cognitive domains such as working memory, behavioural inhibition, executive function, and psychomotor dexterity. These findings challenge some of the current literature, and highlight the necessity of further investigation to better understand interrelationships among cannabis use, cognition, and ADHD.

abstract: Thesis

abstract: Master of Science (MSc)

abstract: It is unclear to what extent cannabis use effects mental functions such as memory, attention, and intelligence. The goal of this research was to investigate how recent and early-life cannabis use is related to these cognitive functions and real-life problems with attention and impulse control as seen in ADHD. Two studies were performed to investigate these relationships, and together found recent cannabis use rather than lifetime use to be predictive of performance on select cognitive abilities and ADHD symptoms. Age of first cannabis use and lifetime use were not associated with differences in cognition, suggesting that cannabis use in adolescence may not necessarily cause lasting detrimental changes. Rather, people who have symptoms of ADHD may be more likely to use cannabis earlier and in more problematic ways.


title: The impact of repetition on memory: Fluency as a cue for encoding and retrieval

contributor:
Milliken, Bruce
Psychology

subject: memory, fluency, repetition, false recognition

abstract: There has long been interest in the effect of repetition on memory amongst cognitive psychologists. A major area of research has examined how repetition at study improves encoding and subsequent memory performance. Another focus in the literature has been on manipulating fluency at retrieval to influence feelings of familiarity, with item repetition at test inducing a classic false recognition effect. Examination of these disparate areas of research hints that similar mechanisms may be operational in producing effects of repetition at study and repetition at test. Work from the false recognition literature suggests that items are more likely to be classified as “old” if they are made to be fluent at test. In other words, fluency may be used as a cue to indicate that information is already known. This fluency attribution process may also influence encoding: if increased fluency signals that information is known, then there may be no need to encode that information. The empirical goal of this thesis was first to better understand the impact of repetition on encoding, and then to better understand the role of fluency when both learning and retrieving information. This thesis documents some of the first examples of a counter-intuitive repetition decrement effect, in which items seen a single time are better remembered than items seen twice in succession. Evidence connecting this repetition decrement effect to effects of false recognition is presented, with the suggestion of a common process leading to these two memory effects. More important, this thesis demonstrates the impact of fluency at both encoding and retrieval, and can allow for better understanding of how human cognition operates on a daily basis.

abstract: Dissertation

abstract: Doctor of Philosophy (PhD)


title: Perturbative Failure Near Horizons: the Rindler Example

contributor:
Burgess, Cliff
Physics and Astronomy

subject: Quantum, Field, Theory, Horizons, Perturbation, Gravity

abstract:
Quantum field theory (QFT) in curved spacetime treats a gravitational field as a classical background upon which quantum corrections may be computed. When couplings are assumed to be small, it is traditionally believed that perturbation theory yields trustworthy predictions about interacting quantum fields in such settings — this work asserts that this is not always the case.
It is argued that perturbative predictions about evolution for very long times near a horizon are subject to problems of secular growth — ie. powers of small couplings come systematically together with growing functions of time. Such growth signals a breakdown of na ̈ıve perturbative calculations of late-time behaviour, regardless of how small ambient curvatures might be. Evidence is built that such breakdowns should be generic for gravitational fields, particularly those containing horizons. This work makes use of the Rindler horizon in flat Minkowski space to demonstrate an explicit example of such perturbative breakdown. A loop correction involving an IR/UV interplay is shown to result in a two-point correlation function which exhibits secular growth. This result is shown to parallel a breakdown occurring in finite temperature QFT, where problems of secular growth are known to occur. The problematic correction is then resummed, allowing for trustworthy late-time inferences. We conclude by discussing how this calculation may be relevant for predictions near black hole horizons.

abstract: Thesis

abstract: Master of Science (MSc)

abstract: Perturbation theory is an approximation technique widely used in the study of quantum field theory (QFT). In this work it is argued that the predictions of per- turbation theory can fail when used on a QFT living in a spacetime that contains an event horizon. This work focuses on perturbative breakdowns that occur after long lengths of time have passed, providing an explicit example in the simplest possible spacetime with an event horizon: Rindler space. It is argued that this breakdown may occur in more complicated settings.